Systems and methods for an evaporative emission system and a fuel system having a single delta pressure sensor

Abstract

Methods and systems are provided for including a single pressure sensor in an evaporative emissions system and a fuel system. In one example, a method may include: measuring a differential pressure between the evaporative emissions system and the fuel system using a differential pressure sensor coupled by a fuel tank isolation valve disposed between a fuel vapor storage canister of the evaporative emissions system and a fuel tank of the fuel system. The differential pressure measured by the differential pressure sensor may be used to check each of the fuel tank isolation valve, the fuel system, and the evaporative emissions system for degradation.

Description

Technical Field

[0001] This specification generally relates to methods and systems for a non-integrated refueling canister only system.

[0002] Background of the Invention / Summary of the Invention

[0003] A vehicle fuel system may include an evaporative emissions system designed to reduce the release of fuel vapors to the atmosphere. For example, vaporized hydrocarbons (HC) from a fuel tank may be stored in a fuel vapor storage canister filled with an adsorbent that adsorbs and stores the vapors. Subsequently, when the engine is in operation, the fuel vapors may be purged from the evaporative emissions system into the engine intake manifold for use as fuel. In some examples, the evaporative emissions system may be configured to store refueling vapors, running loss vapors, and diurnal vapors. However, in other examples, the evaporative emissions system and the fuel system may be configured as a non-integrated refueling canister only system (NIRCOS). In such a system, during a refueling event, the fuel tank is sealed and fuel vapors are directed only to the fuel vapor storage canister. For example, due to limited engine run time, a plug-in hybrid electric vehicle (PHEV) may include a NIRCOS. If the fuel tank vents, long periods of electric mode driving (where the engine is off and the vehicle is propelled by torque from an electric motor) can cause the fuel vapor storage canister to become overloaded and discharge fuel vapors to the atmosphere.

[0004] To isolate the fuel tank from the fuel vapor storage canister, a NIRCOS may include a fuel tank isolation valve (FTIV) between the fuel tank and the fuel vapor storage canister. For example, the FTIV may be a solenoid valve controlled by a pulse width modulation signal. The FTIV may be at least partially opened to regulate fuel tank pressure during an engine on state and to prepare the fuel tank for refueling (e.g., during an engine off state). Typically, a pressure sensor is coupled to the fuel system (such as a fuel tank pressure transducer coupled to the fuel tank) to measure fuel tank pressure. The fuel vapor storage canister side of the FTIV may include an additional pressure sensor to monitor degradation of the evaporative emissions system.

[0005] However, the inventors have recognized here that including two pressure sensors in the NIRCOS can increase the cost of the system and lead to multiple points of degradation, as each sensor can degrade independently. By eliminating one of the sensors, the cost and complexity can be reduced. However, including only the fuel tank pressure sensor (and eliminating the fuel vapor storage canister side pressure sensor) would require opening the FTIV to test for degradation on the fuel vapor storage canister side of the evaporative emissions system, which would not only allow refueling vapor to load into the fuel vapor storage canister. In another example, eliminating the fuel tank pressure sensor would result in a lack of knowledge of the fuel tank pressure, which could degrade fuel tank pressure control during engine operation and fuel tank depressurization during refueling events.

[0006] Here, the inventors have recognized that a single delta pressure sensor can be connected across the FTIV, thereby reducing the cost / complexity of the NIRCOS and the total cost of the vehicle while still enabling the detection of degradation in both the evaporative emissions system and the fuel system.

[0007] In one example, the above problem can be solved by a method that includes: differentiating degradation between each of a sealed fuel tank, an evaporative emissions system, and the FTIV based on a differential pressure measured by a delta pressure sensor coupled across a fuel tank isolation valve (FTIV), the FTIV being positioned between the sealed fuel tank and the evaporative emissions system. In this way, a single delta pressure sensor can be used to identify degradation in the evaporative emissions system, the fuel system, and / or the FTIV.

[0008] As an example, a first pressure port of the Δ pressure sensor may be fluidly coupled to a pipe located between the FTIV and the sealed fuel tank, and a second pressure port of the Δ pressure sensor may be fluidly coupled to a pipe located between the FTIV and a fuel vapor storage charcoal canister of the evaporative emissions system. In the absence of a restricting component (such as a valve) between the sealed fuel tank and the first pressure port and / or between the fuel vapor storage charcoal canister and the second pressure port, the differential pressure measured by the Δ pressure sensor indicates the relative pressure (or vacuum) of the evaporative emissions system and the relative pressure (or vacuum) of the sealed fuel tank. For example, the relative pressure (or vacuum) of the evaporative emissions system is relative to the pressure of the sealed fuel tank, and the relative pressure (or vacuum) of the sealed fuel tank is relative to the pressure of the evaporative emissions system. In this way, changes in the differential pressure measured by the Δ pressure sensor can be used to detect evaporative emissions system degradation during, for example, a charcoal canister side engine shut-off test, and the relative pressure (or vacuum) of the sealed fuel tank can be used to detect and distinguish fuel system and FTIV degradation, such as when the fuel tank is not fully sealed. In cases where only one Δ pressure sensor is included for both the evaporative emissions system and the fuel system, vehicle cost, complexity, and the number of degradation points can be reduced.

[0009] It should be understood that the above summary is provided to introduce a series of concepts in a simplified form, which are further described in the detailed description. This does not mean identifying the key or essential features of the claimed subject matter, the scope of which is uniquely defined by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. Brief Description of the Drawings

[0010] Figure 1 An exemplary vehicle system is schematically shown.

[0011] Figure 2 A schematic illustration showing a fuel system and an evaporative emissions system coupled to an engine system is shown.

[0012] Figure 3 A high-level flowchart showing an exemplary method for diagnosing components of a fuel system and an evaporative emissions system using the output of a Δ pressure sensor coupled across a fuel tank isolation valve (FTIV) is shown.

[0013] Figure 4 An exemplary method for determining whether there is degradation in the FTIV or the fuel tank side of the FTIV based on Δ pressure sensor measurement results is shown.

[0014] Figure 5Illustrates an exemplary method for performing a diagnostic test on the fuel vapor storage canister side using the measurement results of a Δ - pressure sensor.

[0015] Figure 6 Illustrates an exemplary method for evaluating the purge path of an evaporative emission system using the output from a Δ - pressure sensor.

[0016] Figure 7 Illustrates an exemplary method for evaluating the vent path of an evaporative emission system using the output from a Δ - pressure sensor.

[0017] Figure 8 Illustrates an exemplary method for regulating the fuel tank pressure based on the output from a Δ - pressure sensor during engine operation and refueling events.

[0018] Figure 9 Is a predictive exemplary timeline for determining whether there is degradation on the fuel tank side of the FTIV or the FTIV using the output from a single Δ - pressure sensor coupled across the FTIV.

[0019] Figure 10 Is a predictive exemplary timeline for performing a diagnostic test on the fuel vapor storage canister side of the FTIV using the output from a single Δ - pressure sensor coupled across the FTIV.

[0020] Figure 11 Is a predictive exemplary timeline for determining whether there is a purge path blockage in the evaporative emission system based on the output from a single Δ - pressure sensor.

[0021] Figure 12 Is a predictive exemplary timeline for determining whether there is a vent path blockage in the evaporative emission system based on the output from a single Δ - pressure sensor.

[0022] Figure 13 Is a predictive exemplary timeline for regulating the pressure on the fuel tank side of the FTIV based on the measurement results of a Δ - pressure sensor coupled across the FTIV.

[0023] Figure 14 Is a predictive exemplary timeline for depressurizing the fuel tank for a refueling event using the output from a Δ - pressure sensor. Detailed Description

[0024] The following description relates to systems and methods for using a single differential pressure (dP) sensor to measure pressure in a fuel system and an evaporative emission system (such as Figure 2 the fuel system and evaporative emission system shown). The fuel system and evaporative emission system may be included in a vehicle system (such as Figure 1in the vehicle system shown. For example, the fuel system and the evaporative emission system can be a non-integrated only refueling emission charcoal canister system (NIRCOS) included in a plug-in hybrid electric vehicle (PHEV), where the fuel tank of the fuel system is sealed and isolated from the fuel vapor storage charcoal canister of the evaporative emission system by a fuel tank isolation valve (FTIV). Figure 3 shows an advanced flowchart for identifying deterioration of the fuel system and the evaporative emission system based on the output of a dP sensor and according to whether the vehicle's engine is on or off. More specifically, deterioration of the FTIV and the fuel tank side of the FTIV can be detected according to the Figure 4 exemplary method, and an example of the exemplary method is shown in the Figure 9 timeline; deterioration of the fuel vapor storage charcoal canister side of the FTIV can be detected according to the Figure 5 exemplary method, and an example of the exemplary method is shown in the Figure 10 timeline. In addition, clogging of the fuel vapor storage charcoal canister side of the FTIV can be checked according to the Figure 6 and Figure 7 exemplary methods, and the exemplary methods are also shown in the Figure 11 and Figure 12 exemplary timelines. The pressure in the fuel tank can be regulated using the output from the dP sensor, for example, according to the Figure 8 exemplary method, to maintain the pressure in the fuel tank below a threshold pressure and to depressurize the tank during a refueling event. Figure 13 shows an exemplary timeline for depressurizing the fuel tank while the engine is running, and Figure 14 shows an exemplary timeline for depressurizing the fuel tank for a refueling event while the engine is off.

[0025] As used herein, the term "vacuum" refers to a negative pressure relative to a reference pressure (such as atmospheric pressure), and the term "pressure" can refer to both negative and positive pressures relative to a reference pressure.

[0026] Figure 1 shows an exemplary vehicle system 100. The vehicle system 100 includes a fuel combustion engine 110 and a motor 120. As a non-limiting example, the engine 110 includes an internal combustion engine, and the motor 120 includes an electric motor. The motor 120 can be configured to utilize or consume a different energy source than the engine 110. For example, the engine 110 can consume liquid fuel (e.g., gasoline) to produce an engine output, while the motor 120 can consume electrical energy to produce a motor output. Thus, a vehicle having the propulsion system 100 can be referred to as a hybrid electric vehicle (HEV).

[0027] Vehicle system 100 can utilize a variety of different operating modes depending on the operating conditions encountered by the vehicle propulsion system. Some of these modes can enable the engine 110 to be maintained in an off state (e.g., set to a deactivated state), where fuel combustion at the engine is stopped. For example, under selected operating conditions, the motor 120 can propel the vehicle via the drive wheels 130, as indicated by arrow 122, while the engine 110 is deactivated.

[0028] During other operating conditions, the engine 110 can be set to a deactivated state (as described above), and the motor 120 can be operated to charge the energy storage device 150. For example, the motor 120 can receive wheel torque from the drive wheels 130, as indicated by arrow 122, and can convert the vehicle's kinetic energy into electrical energy to be stored at the energy storage device 150, as indicated by arrow 124. This operation can be referred to as vehicle regenerative braking. Thus, in some examples, the motor 120 can act as a generator. However, in other examples, alternatively, the generator 160 can receive wheel torque from the drive wheels 130 and can convert the kinetic energy of the wheels into electrical energy to be stored at the energy storage device 150, as indicated by arrow 162. As another example, during a start operation, the motor 120 can use the energy stored at the energy storage device 150 to crank-start the engine 110, as indicated by arrow 186.

[0029] During still some other operating conditions, the engine 110 can operate by burning fuel received from the fuel system 140, as indicated by arrow 142. For example, the engine 110 can operate to propel the vehicle via the drive wheels 130, as indicated by arrow 112, while the motor 120 is deactivated. During other operating conditions, both the engine 110 and the motor 120 can each operate to propel the vehicle via the drive wheels 130, as indicated by arrows 112 and 122, respectively. The configuration where both the engine and the motor can selectively propel the vehicle can be referred to as a parallel-type vehicle propulsion system. It should be noted that in some examples, the motor 120 can propel the vehicle via a first set of drive wheels, and the engine 110 can propel the vehicle via a second set of drive wheels.

[0030] In other examples, the vehicle system 100 may be configured as a series-type vehicle propulsion system, where the engine does not directly propel the drive wheels. Instead, the engine 110 may be operable to provide power to the motor 120, which in turn may propel the vehicle via the drive wheels 130, as indicated by arrow 122. For example, during selected operating conditions, the engine 110 may drive the generator 160, as indicated by arrow 116, and the generator 160 may in turn supply electrical energy to one or more of the motor 120 (as indicated by arrow 114) or the energy storage device 150 (as indicated by arrow 162). As another example, the engine 110 may be operable to drive the motor 120, which in turn may act as a generator to convert the engine output into electrical energy. The electrical energy may be stored in the energy storage device 150 for later use by the motor, for example.

[0031] The fuel system 140 may include one or more fuel storage tanks 144 for storing fuel on the vehicle. For example, the fuel tank 144 may store one or more liquid fuels, including (but not limited to) gasoline, diesel, and alcohol fuels. In some examples, the fuel may be stored on the vehicle as a mixture of two or more different fuels. For example, the fuel tank 144 may be configured to store a mixture of gasoline and ethanol (such as E10, E85, etc.) or a mixture of gasoline and methanol (such as M10, M85, etc.), where these fuels or fuel mixtures may be delivered to the engine 110, as indicated by arrow 142. Still other suitable fuels or fuel mixtures may be supplied to the engine 110, where the fuel or fuel mixture may be combusted to produce an engine output (e.g., torque). The engine output may be used to propel the vehicle (as indicated by arrow 112) or recharge the energy storage device 150 via the motor 120 or the generator 160.

[0032] In some examples, the energy storage device 150 may be configured to store electrical energy, which may be supplied to other electrical loads (other than the motor) residing on the vehicle, including cabin heating and air conditioning systems, engine starting systems, headlights, cabin audio and video systems, etc. As a non-limiting example, the energy storage device 150 may include one or more storage batteries and / or capacitors.

[0033] The control system 190 may communicate with one or more of the engine 110, the motor 120, the fuel system 140, the energy storage device 150, and the generator 160. The control system 190 may receive sensed feedback information from one or more of the engine 110, the motor 120, the fuel system 140, the energy storage device 150, and the generator 160. The control system 190 may send command signals to one or more of the engine 110, the motor 120, the fuel system 140, the energy storage device 150, and the generator 160 in response to this sensed feedback.

[0034] The control system 190 can receive an indication of a driver request output for the vehicle propulsion system from the vehicle driver 102. For example, the control system 190 can receive sensing feedback regarding the position of the pedal 192 from the pedal position sensor 194. The pedal 192 can schematically be a brake pedal and / or an accelerator pedal that can be depressed by the vehicle driver 102. Additionally, in some examples, the control system 190 can communicate with a remote engine start receiver 195 (or transceiver) that receives a wireless signal 106 from a key fob 104 having a remote start button 105. In other examples (not shown), remote engine start can be initiated via a cellular phone or a smartphone-based system, where the user's phone sends data to a server and the server communicates with the vehicle to start the engine.

[0035] The energy storage device 150 can periodically receive electrical energy from a power source 180 residing external to the vehicle (e.g., an external fixed power grid that is not part of the vehicle), as indicated by arrow 184. As a non-limiting example, the vehicle system 100 can be configured as a plug-in HEV, where electrical energy can be supplied from the power source 180 to the energy storage device 150 via an electrical power transfer cable 182. During an operation of recharging the energy storage device 150 from the power source 180, the electrical transfer cable 182 can electrically couple the energy storage device 150 and the power source 180. When the vehicle propulsion system operates to propel the vehicle, the electrical transfer cable 182 can be disconnected between the power source 180 and the energy storage device 150. The control system 190 can identify and / or control the amount of electrical energy stored at the energy storage device, and the amount of the electrical energy can be referred to as a state of charge (SOC).

[0036] In other examples, the electrical power transfer cable 182 can be omitted, where electrical energy can be wirelessly received from the power source 180 at the energy storage device 150. For example, the energy storage device 150 can receive electrical energy from the power source 180 via one or more of electromagnetic induction, radio waves, and electromagnetic resonance. Thus, it should be understood that any suitable means can be used to recharge the energy storage device 150 from a power source that does not form part of the vehicle. In this way, the motor 120 can propel the vehicle by utilizing an energy source other than the fuel utilized by the engine 110.

[0037] In some other examples, the vehicle system 100 may include one or more solar cells 108 operative to convert incident solar radiation into electrical energy. The solar cells 108 are electrically coupled to the solar battery 30 via a charge controller 32. The solar cells 108 and the charge controller 32 are operative to supply current for charging the solar battery 30. In this example, the solar battery 30 is housed within and electrically coupled to the energy storage device 150, but in other configurations, the solar battery 30 may be electrically coupled to the energy storage device 150 while being separately housed. Thus, the solar battery 30 may be configured to provide charge to or receive charge from the energy storage device 150 according to engine operating conditions, state of charge, and one or more battery requirements. In some other configurations, the solar battery 30 may be physically and electrically isolated from the energy storage device 150. In some examples, the solar battery 30 may be configured to independently supply charge directly to vehicle actuators and devices. In some other examples, the charge controller 32 may be used to supply charge directly to vehicle actuators and devices without first storing the charge in the solar battery 30.

[0038] The solar cells 108 may be mounted on any convenient outer surface of the vehicle, such as the roof, hood, trunk, etc. However, additionally or alternatively, the solar cells 108 may be mounted on the interior of the vehicle, such as on the instrument panel or other passenger compartment surfaces adjacent to windows or interior light bulbs. Generally, the solar cells are operative to convert the solar radiation incident thereon into electrical energy. In some embodiments, the solar cells 108 may include a series of photovoltaic cells formed of an amorphous semiconductor material (such as silicon). Additionally, the individual photovoltaic cells may be interconnected to provide a constant flow of electrical energy to a common output cable 188 that electrically couples the solar cells 108 to the charge controller 32 and the solar battery 30. In this manner, the solar cells 108 may generate electrical energy to propel the vehicle or power one or more additional vehicle actuators or devices, and the motor 120 may propel the vehicle by utilizing an energy source other than the fuel utilized by the engine 110.

[0039] The fuel system 140 can periodically receive fuel from a fuel source residing outside the vehicle. As a non-limiting example, the vehicle system 100 can refuel by receiving fuel via the fuel dispensing device 170, as indicated by arrow 172. In some examples, the fuel tank 144 can be configured to store the fuel received from the fuel dispensing device 170 until the fuel is supplied to the engine 110 for combustion. The control system 190 can receive an indication of the level of fuel stored in the fuel tank 144 via a fuel level sensor. The level of fuel stored in the fuel tank 144 (e.g., as identified by the fuel level sensor) can be communicated to the vehicle driver, for example, via a fuel gauge or indication in the vehicle instrument panel (e.g., message center) 196.

[0040] The vehicle system 100 can also include an ambient temperature / humidity sensor 198, and roll stability control sensors, such as one or more lateral and / or longitudinal and / or yaw rate sensors 199. The vehicle instrument panel 196 can include one or more indicator lights, and / or a text-based display where messages are shown to the driver. The vehicle instrument panel 196 can also include various input devices for receiving driver input, such as buttons, touchscreens, voice input / recognition, etc. For example, the vehicle instrument panel 196 can include a refueling button 197, which can be manually actuated or pressed by the vehicle driver to initiate refueling. For example, as described in more detail below, in response to the vehicle driver actuating the refueling button 197, the fuel tank (e.g., fuel tank 144) in the vehicle can be depressurized so that refueling can be performed.

[0041] The control system 190 can use various suitable communication technologies to communicatively couple to other vehicles or infrastructure. For example, the control system 190 can be communicatively coupled to other vehicles or infrastructure via a wireless network 131, which can include Wi-Fi, Bluetooth, a cellular service, a wireless data transfer protocol, etc. The control system 190 can broadcast (and receive) information regarding vehicle data, vehicle diagnostics, traffic conditions, vehicle location information, vehicle operating procedures, etc. via vehicle-to-vehicle (V2V), vehicle-to-infrastructure-to-vehicle (V2I2V), and / or vehicle-to-infrastructure (V2I or V2X) technologies. The information exchanged between vehicles can be transmitted directly between vehicles, or can be transmitted multi-hop. In some examples, longer range communication (e.g., WiMax) can be used in combination with V2V or V2I2V to extend the coverage area for several miles. In still some other examples, the vehicle control system 190 can be communicatively coupled to other vehicles or infrastructure via the wireless network 131 and the Internet (e.g., cloud).

[0042] The vehicle system 100 may further include an on-vehicle navigation system 132 with which a vehicle driver can interact, such as a Global Positioning System (GPS). The navigation system 132 may include one or more position sensors for helping to estimate vehicle speed, vehicle altitude, vehicle orientation / position, etc. This information may also be used to infer engine operating parameters, such as local air pressure. As discussed above, the control system 190 may further be configured to receive information via the Internet or other communication networks. Information received from the GPS may be cross-referenced with information obtainable via the Internet to determine local weather conditions, local vehicle regulations, etc.

[0043] Figure 2 A schematic illustration showing the vehicle system 206 is presented. It can be understood that the vehicle system 206 may include the same vehicle system as the Figure 1 depicted vehicle system 100. The vehicle system 206 may obtain propulsion force from the engine system 208 and / or an on-vehicle energy storage device, such as Figure 1 the energy storage device 150 shown. An energy conversion device, such as a generator (e.g., Figure 1 the generator 160), may be operable to absorb energy from vehicle movement and / or engine operation and convert the absorbed energy into an energy form suitable for storage by the energy storage device.

[0044] The engine system 208 may include an engine 210 having a plurality of cylinders 230. The engine 210 may be, for example, Figure 1 the engine 110 shown. The engine 210 may include an engine intake system 223 and an engine exhaust system 225. The engine intake system 223 may include an intake throttle valve 262 that is fluidly coupled to the engine intake manifold 244 via an intake passage 242. Air may be directed to the intake throttle valve 262 after passing through an air filter 252, which is coupled to the intake passage 242 upstream of the intake throttle valve 262. The engine exhaust system 225 includes an exhaust manifold 248 that leads to an exhaust passage 235 that directs exhaust to the atmosphere. The engine exhaust system 225 may include an emission control device 270 mounted in a close-coupled position. The emission control device may include one or more of the following: a three-way catalytic converter, a lean NOx trap, a particulate filter (e.g., a diesel particulate filter or a gasoline particulate filter), an oxidation catalyst, etc. It should be understood that the engine may include other components, such as various valves and sensors, as further elaborated herein. In some embodiments in which the engine system 208 is a supercharged engine system, the engine system may further include a supercharging device, such as a turbocharger (not shown).

[0045] The engine system 208 is coupled to a fuel system 218 and an evaporative emissions system 219. The fuel system 218 includes a fuel tank 220 coupled to a fuel pump 234 that supplies fuel to an engine 210 of a propulsion vehicle system 206. The evaporative emissions system 219 includes a fuel vapor storage canister 222. During a fuel tank refueling event, fuel can be pumped into the vehicle from an external source through a refueling port 284, and fuel vapor can be directed to the fuel vapor storage canister 222, as further described below. When in a closed position, a fuel door 286 can prevent access to the refueling port 284. The fuel door 286 can typically be locked in the closed position such that the fuel door 286 cannot be opened. The fuel door 286 can be unlocked in response to determining that the fuel tank 220 is depressurized during a fuel tank refueling event, as will be described with respect to Figure 8 as described. When unlocked, the fuel door 286 can be opened to enable access to the refueling port 284. The fuel tank 220 can hold a variety of fuel mixtures, including fuels having an alcohol concentration range, such as various gasoline-ethanol mixtures, including E10, E85, gasoline, etc., and combinations thereof. A fuel level sensor 282 located in the fuel tank 220 can provide an indication of the fuel level (“fuel level input”) to a controller 12 of a control system 290 (which can be, for example, Figure 1 the control system 190). As depicted, the fuel level sensor 282 can include a float connected to a variable resistor. Alternatively, other types of fuel level sensors can be used.

[0046] The fuel pump 234 is configured to deliver pressurized fuel to a fuel injector (such as an exemplary fuel injector 266) of the engine 210. Although only a single fuel injector 266 is shown, additional fuel injectors can be provided for each cylinder. It should be understood that the fuel system 218 can be a returnless fuel system, a return fuel system, or various other types of fuel systems. Vapor generated in the fuel tank 220 can be directed via a conduit 231 to the fuel vapor storage canister 222 for storage before being purged to an engine intake system 223. Thus, the fuel system 218 can be in fluid communication with the evaporative emissions system 219.

[0047] The fuel vapor storage canister 222 is filled with a suitable adsorbent 280 for temporarily trapping fuel vapors (including vaporized hydrocarbons) generated during fuel tank refueling operations. In one example, the adsorbent 280 is activated carbon (e.g., carbon). Although a single fuel vapor storage canister 222 is shown, it should be understood that the fuel system 218 and the evaporative emission system 219 may include any number of fuel vapor storage canisters. When purge conditions are met, such as when the fuel vapor storage canister is saturated, the vapors stored in the fuel vapor storage canister 222 can be purged to the engine intake system 223 via the purge line 228 by opening the canister purge valve (CPV) 212, which can be a normally closed valve. In one example, the canister purge valve 212 can be a solenoid valve, where the opening or closing of the valve is effected via actuation of the canister purge solenoid.

[0048] The fuel vapor storage canister 222 may include a buffer zone 222a (or buffer region), and each of the fuel vapor storage canister and the buffer zone includes an adsorbent. For example, the buffer zone 222a is shown filled with adsorbent 280a. As shown, the volume of the buffer zone 222a may be less than the volume of the fuel vapor storage canister 222 (e.g., is a portion thereof). The adsorbent 280a in the buffer zone 222a may be the same as or different from the adsorbent 280 in the fuel vapor storage canister (e.g., both may include carbon). The buffer zone 222a may be positioned within the fuel vapor storage canister 222 such that during fuel vapor storage canister loading, fuel tank vapors are first adsorbed within the buffer zone and then, when the buffer zone is saturated, additional fuel tank vapors are adsorbed in the fuel vapor storage canister. In contrast, during fuel vapor storage canister purging, fuel vapors are first desorbed from the fuel vapor storage canister (e.g., to a threshold amount), and then from the buffer zone. In other words, the loading and unloading of the buffer zone is not coincident with the loading and unloading of the fuel vapor storage canister. Accordingly, the role of the fuel vapor storage canister buffer zone is to attenuate any fuel vapor spikes flowing from the fuel tank to the fuel vapor storage canister, thereby reducing the likelihood of any fuel vapor spikes entering the engine.

[0049] The fuel vapor storage canister 222 includes a vent passage 227 for delivering gas from the fuel vapor storage canister 222 to the atmosphere when storing fuel vapor from the fuel tank 220. The vent passage 227 can also allow fresh air to be drawn into the fuel vapor storage canister 222 when purging the stored fuel vapor to the engine intake 223 via the purge line 228 and the canister purge valve 212. Although this example shows the vent passage 227 in communication with fresh, non-heated air, various modifications can also be used. In some examples, an air filter can be coupled to the vent passage 227. The vent passage 227 can include a canister vent valve (CVV) 214 to regulate the flow of air and vapor between the fuel vapor storage canister 222 and the atmosphere. When a vent valve is included, the vent valve can be a normally open valve such that air that has been stripped of fuel vapor after passing through the fuel vapor storage canister can be pushed out to the atmosphere (e.g., during refueling with the engine off). Similarly, during a purge operation (e.g., during regeneration of the fuel vapor storage canister and with the engine running), the fuel vapor storage canister vent valve can be opened to allow a fresh air stream to strip the fuel vapor stored in the fuel vapor storage canister. In one example, the canister vent valve 214 can be a solenoid valve, where the opening or closing of the valve is effected via actuation of the canister vent solenoid. Specifically, the canister vent valve 214 can be a normally open valve that closes when the canister vent passage solenoid is actuated.

[0050] The evaporative emission system 219 can also include a hybrid fuel vapor storage canister 211. Hydrocarbons desorbed from the fuel vapor storage canister 222 (hereinafter also referred to as the “main fuel vapor storage canister”) can be adsorbed within the hybrid fuel vapor storage canister. The hybrid fuel vapor storage canister 211 can include an adsorbent material 280b that is different from the adsorbent material included in the main fuel vapor storage canister 222. Alternatively, the adsorbent material in the hybrid fuel vapor storage canister 211 can be the same as the adsorbent material included in the main fuel vapor storage canister 222 (e.g., the adsorbent 280 can be the same as the adsorbent material 280b).

[0051] A hydrocarbon (HC) sensor 213 can be present in the evaporative emission system 219 to indicate the hydrocarbon concentration in the vent passage 227. As shown, the hydrocarbon sensor 213 is positioned between the main fuel vapor storage canister 222 and the hybrid fuel vapor storage canister 211. The probe (e.g., the sensing element) of the hydrocarbon sensor 213 is exposed to the fluid flow in the vent passage 227 and senses the hydrocarbon concentration of the fluid flow. In one example, the hydrocarbon sensor 213 can be used by the control system 290 to determine breakthrough of hydrocarbon vapor from the main fuel vapor storage canister 222.

[0052] One or more temperature sensors 215 may be coupled to and / or disposed within the fuel vapor storage canister 222. When the adsorbent in the fuel vapor storage canister adsorbs fuel vapor, heat (heat of adsorption) is generated. Similarly, when the adsorbent in the fuel vapor storage canister adsorbs fuel vapor, heat is consumed. In this manner, the adsorption and desorption of fuel vapor by the fuel vapor storage canister can be monitored and estimated based on temperature changes within the fuel vapor storage canister. Additionally, one or more canister heating elements 216 may be coupled to and / or disposed within the fuel vapor storage canister 222. The canister heating element 216 can be used to selectively heat the fuel vapor storage canister (and the adsorbent contained therein) prior to performing a purge operation, for example, to enhance the desorption of fuel vapor. As described above, heating the fuel vapor storage canister can be particularly beneficial for purging heavy hydrocarbon fractions (e.g., higher molecular weight hydrocarbons). The canister heating element 216 can include an electrical heating element, such as an electrically heatable conductive metal, ceramic, or carbon element. In some embodiments, the canister heating element 216 can include a microwave energy source, or can include a fuel vapor storage canister jacket coupled to a hot air source or a hot water source. The canister heating element 216 can be coupled to one or more heat exchangers that can facilitate the transfer of heat (e.g., from hot exhaust) to the fuel vapor storage canister 222. The canister heating element 216 can be configured to heat the air within the fuel vapor storage canister 222 and / or directly heat the adsorbent located within the fuel vapor storage canister 222. In some embodiments, the canister heating element 216 can be included in a heater compartment coupled to the interior or exterior of the fuel vapor storage canister 222. In some embodiments, the fuel vapor storage canister 222 can be coupled to one or more cooling circuits and / or cooling fans. In this manner, the fuel vapor storage canister 222 can be selectively cooled to enhance the adsorption of fuel vapor (e.g., prior to a refueling event). In some examples, the canister heating element 216 can include one or more Peltier elements that can be configured to selectively heat or cool the fuel vapor storage canister 222.

[0053] Since the vehicle is driven by the engine system 208 during some conditions and by the energy storage device under other conditions, the hybrid vehicle system 206 may have reduced engine operation time. While the reduced engine operation time reduces carbon emissions from the vehicle, they can also result in insufficient purge of fuel vapors from the evaporative emissions system 219. Additionally, due to the reduced engine operation time, the consumption of fuel can be slow. For example, without any refueling events, the fuel contained in the fuel tank 220 can last for a relatively long duration (e.g., months to a year). If the fuel tank 220 is vented regularly, such as via the conduit 231 to the evaporative emissions system 219, the fuel in the fuel tank 220 can age and lose its volatility, such as by the escape of lower molecular weight hydrocarbons (e.g., light fractions) to the fuel vapor storage charcoal canister. As a result, the fuel vapor storage charcoal canister 222 can become overloaded, and when the aged fuel is used for combustion in the engine, engine performance can deteriorate. For example, the reduction in fuel volatility can result in long and polluting starts.

[0054] To address this issue, a fuel tank isolation valve (FTIV) 236 can be included in the conduit 231 such that the fuel tank 220 is connected to the charcoal canister 222 via the valve. In some examples, the FTIV can also be a tank pressure control (TPC) valve. When closed, the FTIV 236 can isolate the fuel tank 220 from the evaporative emissions system 219 and the atmosphere. Thus, the fuel tank 220 can be constructed of a suitable material (e.g., steel) to withstand pressure variations, such as a pressure of 5 pounds per square inch or a vacuum (relative to atmospheric pressure). The FTIV 236 can be a normally closed valve to prevent the diversion of diurnal vapors or "operational loss" vapors from the fuel tank 220 to the charcoal canister 222. During a refueling operation, the FTIV 236 can be temporarily opened to divert fuel vapors from the fuel tank 220 to the fuel vapor storage charcoal canister 222, as described below with respect to Figure 8 that which is described. Additionally, when the fuel tank pressure is above a threshold (e.g., above the mechanical pressure limit of the fuel tank), the FTIV 236 can also be temporarily opened such that fuel vapors can be released to the fuel vapor storage charcoal canister and the fuel tank pressure can be maintained below the threshold, as also described with respect to Figure 8 that which is described. Further still, the FTIV 236 can be opened at a predetermined duty cycle in order to detect FTIV degradation and / or degradation in the fuel system 218 (e.g., on the fuel tank side of the FTIV), as described below with respect to Figure 4 that which is described. In some examples, a vacuum pump 238 can be included in the vent duct 227 to evacuate the evaporative emissions system and facilitate detection, as elaborated below.

[0055] A differential (e.g., difference) pressure sensor (e.g., dP sensor) 221 may be coupled across the FTIV 236 to the fuel system 218 and the evaporative emissions system 219. In one example, the dP sensor 221 is the only pressure sensor included in the fuel system 218 and the evaporative emissions system 219, and does not include an absolute pressure sensor. A first conduit 231a may fluidly couple a first pressure port of the dP sensor 221 to the conduit 231 on the fuel tank side of the FTIV, and a second conduit 231b may fluidly couple a second pressure port of the dP sensor 221 to the conduit 231 on the fuel vapor storage canister side of the FTIV. The dP sensor 221 may be, for example, a media isolated pressure sensor. A pressure sensitive diaphragm (such as a stainless steel diaphragm, a titanium diaphragm, or a nickel alloy diaphragm) may be included within the dP sensor 221 between the first pressure port and the second pressure port to separate the two media (e.g., fuel vapor at the first pressure port and fresh air at the second pressure port). The dP sensor 221 may generate a voltage proportional to the differential pressure (e.g., pressure difference) between the first pressure port (corresponding to the pressure of the fuel system 218 (and the fuel tank 220)) and the second pressure port (corresponding to the pressure of the evaporative emissions system 219 (e.g., the pressure on the fuel vapor storage canister side of the FTIV 236)). When the FTIV 236 is open, the pressure at the first pressure port of the dP sensor 221 is the same as the pressure at the second pressure port. In the absence of a pressure difference, the dP sensor 221 may output a small voltage (e.g., 0.45 - 1.0V) equivalent to a pressure difference of 0 inches H2O. When the FTIV 236 is closed, the pressure at the first port may be determined relative to the pressure at the second port (and vice versa). As an example, when the CVV 214 is open and the CPV 212 is closed, the fuel vapor storage canister side (also referred to herein as the canister side) may be at atmospheric pressure, and thus, the dP sensor 221 may provide an indication of the fuel tank 220 pressure relative to atmospheric pressure. As another example, during a purge of the fuel vapor storage canister 222 when the CVV 214 is open and the CPV 212 is open, the vacuum from the engine intake manifold 244 may reduce the pressure on the canister side of the FTIV 236, and this pressure reduction may be indicated by the dP sensor 221 relative to the pressure of the fuel tank 220 (e.g., the pressure on the fuel tank side of the FTIV 236). In still some other examples, the control system 290 may diagnose components of the fuel system and the evaporative emissions system based on the differential pressure measured by the dP sensor 221, as described below with reference to Figures 3 to 7 as described.

[0056] One or more temperature sensors 217 may also be coupled to the fuel system 218 for providing an estimate of the fuel system temperature. In one example, the fuel system temperature is the fuel tank temperature, where the temperature sensor 217 is a fuel tank temperature sensor coupled to the fuel tank 220. Although the illustrated example shows the temperature sensor 217 directly coupled to the fuel tank 220, in an alternative embodiment, the temperature sensor may be coupled between the fuel tank 220 and the FTIV 236.

[0057] Fuel vapors released from the fuel vapor storage canister 222 during, for example, a purge operation may be directed via a purge line 228 into the engine intake manifold 244. The flow of the vapor along the purge line 228 may be regulated by a canister purge valve 212 coupled between the fuel vapor storage canister and the engine intake passage. The mass and rate of the vapor released by the CPV 212 may be determined by the duty cycle of an associated canister purge valve solenoid (not shown). Thus, the duty cycle of the canister purge valve solenoid may be determined by the controller 12 in response to engine operating conditions such as engine speed-load conditions, air-fuel ratio, fuel vapor storage canister loading, etc. By commanding the canister purge valve closed, the controller may isolate the evaporative emissions system 219 from the engine intake passage. An optional canister check valve (not shown) may be included in the purge line 228 to prevent intake manifold pressure from causing the gas to flow in the opposite direction of the purge flow. Thus, the check valve can be beneficial if the canister purge valve control is not accurately timed or if the canister purge valve itself may be forced open due to high intake manifold pressure. An estimate of the manifold absolute pressure (MAP) or manifold vacuum (ManVac) may be obtained by the controller 12 from a MAP sensor 240 coupled to the engine intake manifold 244. Alternatively, the MAP may be inferred from alternative engine operating conditions such as the mass air flow (MAF), which is measured by a MAF sensor (not shown) coupled to the intake manifold.

[0058] The fuel system 218 and the evaporative emission system 219 can be operated by the controller 12 in multiple modes by selectively adjusting various valves and solenoids. For example, the fuel system and the evaporative emission system can operate in a fuel vapor storage mode (e.g., when the engine is not running), in which the controller 12 can keep the CVV 214 open while keeping the CPV 212 and the FTIV 236 closed. In this way, fuel vapor can be prevented from flowing from the fuel tank 220 to the fuel vapor storage canister 222 and from the fuel vapor storage canister 222 to the engine intake manifold 244. As another example, the fuel system and the evaporative emission system can operate in a refueling mode (e.g., when the vehicle driver requests refueling of the fuel tank), in which the controller 12 can open the FTIV 236 while keeping the CVV 214 open and keeping the CPV 212 closed to depressurize the fuel tank and then enable fuel to be added thereto. In this way, the FTIV 236 can remain open during the refueling operation to allow refueling vapor to be stored in the fuel vapor storage canister. After refueling is completed, the FTIV 236 can be closed. As yet another example, the fuel system and the evaporative emission system can operate in a canister purge mode (e.g., after the light-off temperature of the emission control device has been reached and the engine is running), in which the controller 12 can open the CPV 212 while keeping the CVV 214 open and keeping the FTIV 236 closed. The vacuum generated by the engine intake manifold 244 can be used to draw fresh air through the vent passage 227 and through the fuel vapor storage canister 222 to purge the stored fuel vapor into the engine intake manifold 244. In this mode, the fuel vapor purged from the canister is burned in the engine. The purge can continue until the amount of fuel vapor in the canister is below a threshold.

[0059] During the purge, the known vapor amount / concentration can be used to determine the fuel vapor stored in the fuel vapor storage canister, and then during a later part of the purge operation (when the fuel vapor storage canister is sufficiently purged or empty), the known vapor amount / concentration can be used to estimate the load state of the fuel vapor storage canister. For example, one or more oxygen sensors (not shown) can be coupled to the fuel vapor storage canister 222 (e.g., downstream of the fuel vapor storage canister) or located in the engine intake passage and / or the engine exhaust passage to provide an estimate of the fuel vapor storage canister load (i.e., the amount of fuel vapor stored in the fuel vapor storage canister). Based on the fuel vapor storage canister load and further based on engine operating conditions (such as engine speed-load conditions), the purge flow rate can be determined.

[0060] The control system 290 is shown receiving information from a plurality of sensors 16, various examples of which are described herein, and sending control signals to a plurality of actuators 81, various examples of which are also described herein. As an example, the sensors 16 can include: an exhaust gas sensor 226 located upstream of the emission control device 270, a temperature sensor 232 coupled to the exhaust passage 235, a MAP sensor 240, a temperature sensor 217, a hydrocarbon sensor 213, a dP sensor 221, and a pressure sensor 229 located downstream of the emission control device 270. Other sensors (such as additional pressure, temperature, air-fuel ratio, and composition sensors) can be coupled to various locations in the vehicle system 206. As another example, the actuators 81 can include a fuel injector 266, an FTIV 236, a CPV 212, a CVV 214, a fuel pump 234, a vacuum pump 238, and an intake throttle valve 262.

[0061] The control system 290 can further receive information about the position of the vehicle from an on-board global positioning system (GPS). The information received from the GPS can include vehicle speed, vehicle altitude, vehicle location, etc. This information can be used to infer engine operating parameters, such as local air pressure (e.g., atmospheric pressure). The control system 290 can further be configured to receive information via the Internet or other communication networks. The information received from the GPS can be cross-referenced with information available via the Internet to determine local weather conditions, local vehicle regulations, etc. The control system 290 can use the Internet to obtain updated software modules, which can be stored in a non-transitory memory.

[0062] The controller 12 of the control system 290 can be configured as a conventional microcomputer, including a microprocessor unit, input / output ports, read-only memory, random access memory, keep-alive memory, a controller area network (CAN) bus, etc. The controller 12 can be configured as a powertrain control module (PCM). The controller can switch between a sleep mode and a wake-up mode to obtain additional energy efficiency. The controller can receive input data from various sensors, process the input data, and trigger the actuators in response to the processed input data, based on instructions or code programmed therein corresponding to one or more routines, examples of which are referenced Figures 3 to 8 are described.

[0063] As mentioned above, to reduce vehicle cost, a single Δ pressure sensor (e.g., dP sensor 221) can be included for measuring the fuel system (e.g., Figure 2 the fuel system 218) and the evaporative emission system (e.g., Figure 2The relative pressure of the evaporative emission system 219). More specifically, the dP sensor can be coupled across a fuel tank isolation valve (e.g., Figure 2 the FTIV 236), which isolates the fuel system from the evaporative emission system when closed. The output of the dP sensor (i.e., the pressure difference between the fuel tank side and the canister side of the FTIV) can be used, for example, according to Figures 3 to 8 an exemplary method to detect FTIV degradation, detect fuel tank side degradation, detect canister side degradation and blockage, regulate fuel tank pressure during engine operation (e.g., when the engine is on), and depressurize the fuel tank for a refueling event.

[0064] First, turning to Figure 3 , a high-level flowchart of an exemplary method 300 for diagnosing components of an evaporative emission system and a fuel system based on the output of a dP sensor is provided. As will be described below and elaborated further with respect to Figures 4 to 7 , different components of the fuel system and the evaporative emission system can be diagnosed depending on whether the engine is on or off. Thus, the Figures 3 to 7 methods will be described together, although it should be understood that the Figures 3 to 7 methods can also be performed independently of each other. The instructions for implementing method 300 and the remaining methods included herein can be executed by a controller (e.g., Figure 2 the controller 12) based on instructions stored in the controller's memory and in conjunction with signals received from sensors of the engine, such as the sensors described above with reference to Figures 1 to 2 (e.g., Figure 2 the dP sensor 221). The controller can employ actuators of the engine system (e.g., Figure 2 the FTIV 236 and the vacuum pump 238) to adjust engine operation according to the methods described below. For example, Figure 3 method 300 includes performing a “passive” diagnosis of the FTIV and the fuel tank side of the FTIV using only the output of the dP sensor without additional adjustment of the actuators of the fuel system and the evaporative emission system. Thus, portions of method 300 can be performed each time the engine is turned off and the controller receives the output from the dP sensor.

[0065] Method 300 begins at 302 and includes evaluating operating parameters. The operating parameters can include, for example, vehicle state, engine state, evaporative emission system state, and fuel system state. The vehicle state can refer to whether the vehicle is on or off, which can be determined based on, for example, the position of the ignition switch. The engine state can refer to whether the engine is on or off, and if the engine is on, the engine state can further refer to engine operating parameters such as engine speed, engine load, etc. If the engine is stationary (e.g., engine speed is zero) and no combustion occurs in the engine cylinders (e.g., no fuel is supplied to the engine cylinders), then the engine is likely off. The evaporative emission system state can refer to the operating mode of the evaporative emission system (such as the fuel vapor storage mode, refueling mode, and canister purge mode, as described above with respect to Figure 2 ), and / or the states of various actuators of the evaporative emission system (such as the canister vent valve (e.g., Figure 2 's CVV 214) and the canister purge valve (e.g., Figure 2 's CPV 212)). The fuel system state can refer to whether the fuel system is sealed with the FTIV closed. Additionally, the differential pressure between the evaporative emission system and the fuel system can be measured by a dP sensor. For example, when the CVV remains open, thus connecting the evaporative emission system to the atmosphere, the pressure in the evaporative emission system can equal atmospheric pressure. Therefore, the fuel tank pressure can be determined relative to atmospheric pressure based on the output from the dP sensor.

[0066] At 304, it is determined whether the engine is off. For example, when the vehicle is on and operating in an electric mode where only torque from an electric motor (e.g., Figure 1 's motor 120) is used to propel the vehicle, the engine can be off. In another example, when the vehicle is off (e.g., the vehicle's ignition switch is in the off position), but the controller may be operating in a wake-up mode to, for example, perform diagnostic routines, transmit data, etc., the engine can be off.

[0067] If the engine is not off, method 300 proceeds to 306 and includes checking the canister side for blockages on the purge side. Blockages (e.g., obstructions) in the purge path or vent path of the evaporative emission system can degrade the performance of the evaporative emission system, such as when a purge event is requested. Therefore, when the engine is running, the purge path and vent path can be evaluated for blockages to ensure optimal purging, as will be described with respect to Figures 6 to 7 After 306, method 300 ends.

[0068] Conversely, if the engine is off at 304, method 300 proceeds to 308 and includes maintaining the FTIV closed. Maintaining the FTIV closed prevents fuel vapor from flowing from the fuel tank to the evaporative emission system, such as to the fuel vapor storage charcoal canister. Additionally, maintaining the FTIV closed isolates the fuel tank side (also referred to herein as the tank side) from the charcoal canister side of the FTIV and seals the fuel tank. This can create a pressure differential between the sealed fuel tank and the charcoal canister side, which is in communication with the atmosphere (e.g., through a ventilation line (such as Figure 2 ventilation duct 227) and an open charcoal canister ventilation valve).

[0069] At 310, it is determined whether the dP sensor pressure measurement is greater than a first threshold or less than a second threshold, where these thresholds are non-zero. As mentioned above, with the charcoal canister side in communication with the atmosphere, the dP sensor reading indicates the relative pressure of the fuel tank with respect to atmospheric pressure. Due to the volatility of the fuel, the fuel tank pressure is not expected to be equal to atmospheric pressure. Additionally, the pressure inside the fuel tank varies with temperature. For example, when the temperature increases and more fuel evaporates, the fuel tank pressure increases. As another example, when the temperature decreases and the fuel vapor condenses, the fuel tank pressure can decrease, creating a vacuum inside the fuel tank (e.g., a negative pressure with respect to atmospheric pressure). Thus, the tank side pressure can fluctuate with diurnal temperature variations. If the FTIV is open, fluidly coupling the first pressure port of the dP sensor and the second pressure port of the dP sensor, the dP sensor will indicate a zero differential pressure (e.g., no pressure differential). Additionally, if there is degradation on the tank side of the FTIV such that the fuel tank is coupled to the atmosphere (e.g., the fuel tank is not fully sealed), the dP sensor will read a relative pressure of zero or close to zero. Thus, the first threshold can correspond to a threshold amount of non-zero positive pressure with respect to atmospheric pressure (e.g., a positive pass threshold), above which indicates no degradation on the tank side of the FTIV or on the FTIV itself. Similarly, the second threshold can correspond to a threshold amount of non-zero negative pressure (e.g., a vacuum) with respect to atmospheric pressure (e.g., a negative pass threshold), below which indicates no degradation on the tank side of the FTIV or on the FTIV itself. In one non-limiting example, the first threshold is a differential pressure of 3 inches H2O, and the second threshold is a differential pressure of -3 inches H2O (e.g., a 3-inch H2O vacuum on the tank side with respect to the charcoal canister side).

[0070] If the differential pressure measurement result output by the dP sensor is greater than a first threshold or less than a second threshold (e.g., the relative pressure on the tank side compared to the canister side is not between the first threshold and the second threshold), then method 300 proceeds to 312 and includes indicating that no tank side deterioration and no FTIV deterioration are detected. In a case where the differential pressure measurement result output by the dP sensor indicates that the fuel tank pressure is not approximately equal to the canister side pressure (e.g., atmospheric pressure), it can be assumed that the fuel tank is sufficiently sealed from both the evaporative emission system and the atmosphere. Indicating that no tank side deterioration and no FTIV deterioration are detected may also include storing the indication at the controller (e.g., in the controller's memory).

[0071] At 314, method 300 includes performing a canister side engine off diagnosis, as will be referenced Figure 5 described. The canister side of the FTIV can be diagnosed conclusively only when deterioration of the tank side and the FTIV are ruled out. For example, if the FTIV has deteriorated and is stuck in the open position, the dP sensor may measure a differential pressure that is substantially equal to zero, which can lead to an incorrect indication of deterioration of the canister side of the FTIV. After 314, method 300 ends.

[0072] Conversely, if the differential pressure reading output by the dP sensor at 310 is not greater than the first threshold or less than the second threshold (e.g., the pressure difference between the tank side and the canister side is between the first threshold and the second threshold), then method 300 proceeds to 316 and includes determining whether there is tank side deterioration or FTIV deterioration, as will be described below with respect to Figure 4 described. After 316, method 300 ends.

[0073] Continuing to Figure 4 , an exemplary method 400 for detecting deterioration of the fuel tank side of the FTIV and the FTIV itself and differentiating between the two is shown. Method 400 can be performed when the engine is off, for example, as part of method 300 of Figure 3 (e.g., at 316). Figure 3 's method 300 includes a "passive" check of the fuel system and the FTIV, while method 400 includes actively changing the fuel system and evaporative emission system pressures, as described below.

[0074] Method 400 starts at 402 and includes closing the CVV of the evaporative emission system and actuating the vacuum pump of the evaporative emission system (e.g., Figure 2 's vacuum pump 238). By actuating the CVV to a closed position (and maintaining the canister purge valve of the evaporative emission system and the FTIV closed), the canister side of the FTIV can be sealed. For example, the vacuum pump can evacuate the evaporative emission system to a predetermined vacuum level.

[0075] At 404, it is determined whether the dP sensor detects canister side vacuum. With the FTIV closed, the pressure on the canister side can decrease while the pressure on the canister side can remain constant, resulting in an increase in the differential pressure measured by the dP sensor. Specifically, the dP sensor measurement result can indicate a canister side vacuum relative to the tank side. Thus, detecting a canister side vacuum can mean that the differential pressure measured by the dP sensor is greater than or equal to a threshold value, where the threshold value corresponds to a non-zero differential pressure indicating that the canister side is under vacuum relative to the fuel tank side. In some examples, the threshold value can be set based on a predetermined amount of vacuum applied by the vacuum pump, where the threshold value increases as the predetermined amount of vacuum increases. For example, the controller can input the predetermined amount of vacuum applied by the vacuum pump into a look-up table or equation and output the corresponding threshold value. In other examples, the threshold value can be a constant predetermined value that is independent of the amount of vacuum applied by the vacuum pump.

[0076] If the FTIV, such as when the FTIV is stuck in the open position (e.g., stuck and not fully closed due to degradation), the differential pressure measured by the dP sensor can be zero or close to zero. Thus, if the dP sensor does not detect a canister side vacuum (e.g., the differential pressure measured by the dP sensor is less than the threshold value), method 400 proceeds to 406 and includes indicating FTIV degradation. For example, in the case where the FTIV degrades and is stuck in at least a partially open position, the pressure at the first pressure port of the dP sensor (which is connected to the tank side of the FTIV) and the pressure at the second pressure port (which is connected to the canister side of the FTIV) can be the same, resulting in a zero differential pressure. Indicating FTIV degradation can include setting a diagnostic trouble code (DTC) at the controller and can also include illuminating a malfunction indicator lamp (MIL) to alert the vehicle driver to service the vehicle. Additionally, fuel vapor storage canister purge can be adjusted in response to an indication of FTIV degradation. For example, during purge, the vacuum drawn on the fuel vapor storage canister can be transmitted through the degraded and at least partially open FTIV to the fuel tank, resulting in additional fuel vapor being drawn through the open FTIV into the fuel vapor storage canister and ultimately into the engine intake. In the case of purging two fuel vapor sources (e.g., fuel vapor desorbed from the fuel vapor storage canister and fuel vapor from the fuel tank), the purge flow rate can be reduced to prevent engine stall. For example, the CPV can be adjusted to an open position that is further closed compared to when FTIV degradation is not indicated to reduce the purge flow rate.

[0077] At 408, method 400 includes deactivating the vacuum pump and opening the CVV. In this way, the evaporative emission system can rebalance to atmospheric pressure. By returning the evaporative emission system and the fuel system (through the degraded FTIV) to atmospheric pressure, less fuel can be evaporated compared to keeping the evaporative emission system and the fuel system under vacuum. After 408, method 400 ends.

[0078] However, if the dP sensor does not detect a canister-side vacuum at 404 (e.g., the differential pressure is greater than or equal to a threshold), which indicates that the canister side and the tank side are isolated from each other through a fully closed FTIV, then method 400 proceeds to 410 and includes opening and closing the FTIV at a predetermined duty cycle until the tank-side relative pressure has decreased by a threshold amount. Each time the FTIV is opened, the evaporative emission system will vacuum the fuel system, thereby creating a reduced differential pressure after each opening of the FTIV (e.g., the tank-side pressure becomes more similar to the canister-side pressure). In addition, each time the FTIV is opened, the dP sensor will read a differential pressure of zero or close to zero because, with the FTIV open, the pressure at the first pressure port of the dP sensor can be approximately equal to the pressure at the second pressure port of the dP sensor. Therefore, the differential pressure can be evaluated when the FTIV is closed. The threshold amount can be a non-zero differential pressure amount and can be determined based on the starting differential pressure before opening and closing the FTIV at a certain duty cycle. For example, the controller can input the starting differential pressure into a look-up table or an equation and output the threshold amount.

[0079] Once the tank-side relative pressure has decreased by the threshold amount, then at 412, method 400 includes maintaining the FTIV closed to isolate the tank side of the FTIV from the canister side of the FTIV. At 414, method 400 includes deactivating the vacuum pump and opening the CVV. In this way, the canister side can rebalance to atmospheric pressure while the tank side will remain under vacuum. By connecting the canister side of the FTIV to the atmosphere, any degradation in the canister side that could prevent the canister side from maintaining a vacuum will not affect the dP sensor reading.

[0080] At 416, method 400 includes determining a bleed-up threshold based on the relative tank-side pressure after the canister side is balanced to the atmosphere. With the tank side under vacuum and the canister side at atmospheric pressure, the pressure at the first pressure port of the dP sensor (which is connected to the tank side of the FTIV) is less than the pressure at the second pressure port (which is connected to the canister side of the FTIV). When the dP sensor reading remains substantially constant (e.g., the rate of change of the differential pressure increases or decreases approximately to zero), it can be determined that the canister side is balanced to atmospheric pressure. The bleed-up threshold can refer to an increase in the tank-side pressure (e.g., a decrease in the vacuum) that can occur over a certain duration, and above which it can be inferred that the fuel tank side of the FTIV does not maintain a vacuum, such as when air from the atmosphere is introduced into the fuel tank through an orifice or disconnection. Thus, the bleed-up threshold can be set for a predetermined amount of increase in the tank-side pressure starting from the initial differential pressure (corresponding to the differential pressure after the canister side is balanced to the atmosphere). Alternatively, a threshold rate of pressure bleed can be determined, which can be a non-zero rate corresponding to the rate of increase in the tank-side pressure (e.g., loss of vacuum) in the case where the fuel tank side of the FTIV is not fully sealed.

[0081] At 418, method 400 includes monitoring the differential pressure over the duration. The duration can be a predetermined duration, such as 30 seconds. With the canister side connected to the atmosphere, the canister-side pressure is not expected to change significantly. Thus, the change in the differential pressure measured by the dP sensor can be attributed to the change in the tank-side pressure, and the tank-side pressure relative to atmospheric pressure can be inferred based on the differential pressure measurement. In an illustrative example, if the differential pressure measured by the dP sensor is -10 inches H2O, then it can be inferred that the tank-side pressure is -10 inches H2O relative to atmospheric pressure.

[0082] At 420, it is determined whether the tank-side relative pressure is less than the bleed-up threshold after the duration has elapsed. If the tank-side relative pressure remains less than the bleed-up threshold (or if the rate of pressure bleed is less than the threshold rate), then method 400 proceeds to 422 and includes indicating that no tank-side deterioration and no FTIV deterioration are detected. Additionally, the result of the test can be stored at the controller, such as stored in the memory of the controller.

[0083] At 426, method 400 includes performing a canister-side engine-off diagnosis, as described with respect to Figure 5 what is described. In the case where it is determined that the FTIV nominally functions (e.g., is not deteriorated), the dP sensor readings can be used to detect canister-side deterioration without potential FTIV deterioration confounding their interpretation. After 426, method 400 ends.

[0084] Conversely, if the relative canister-side pressure at 420 is greater than or equal to the venting threshold (or the rate of pressure venting is greater than or equal to the threshold rate), then method 400 proceeds to 424 and includes indicating canister-side deterioration. As mentioned above, in the case where the relative canister-side pressure reaches the venting threshold within the duration, it can be inferred that the fuel canister side of the FTIV is not fully sealed, such that air from the atmosphere enters the canister side through, for example, an orifice, thereby increasing the canister-side pressure. Indicating canister-side deterioration can include setting a corresponding DTC at the controller and can also include illuminating the MIL to alert the vehicle driver to service the vehicle. Then the method can proceed to 426 because as long as deterioration of the FTIV is not indicated, the canister side can still be checked for deterioration even if the canister side has deteriorated. Additionally, during the day-night cycle, the FTIV can remain open in response to an indication of canister-side deterioration. For example, an increase in fuel tank temperature due to day-night temperature and sun loading can increase fuel evaporation, thereby increasing the fuel tank pressure. In the presence of canister-side deterioration, the increased pressure can cause fuel vapor to escape to the atmosphere to relieve the pressure. By keeping the FTIV open, a smaller pressure can accumulate in the fuel tank and at least a portion of the fuel vapor will be directed to the fuel vapor storage canister rather than the atmosphere, thereby reducing vehicle emissions.

[0085] Next, turning to Figure 5 , an exemplary method 500 for diagnosing a canister-side engine-off test is shown. Since deterioration of the fuel vapor storage canister side of the FTIV can result in undesired evaporative emissions, checking the canister side for deterioration can help ensure that vehicle emissions remain within emission requirements. In some examples, method 500 can be executed as part of method 300 of Figure 3 (e.g., at 314) or as part of method 400 of Figure 4 (e.g., at 426). However, in other examples, method 500 of Figure 5 can be executed whenever the conditions for the canister-side engine-off diagnostic test are met, as will be described below.

[0086] Method 500 begins at 502 and includes evaluating operating parameters. The operating parameters can include, for example, vehicle status, engine status, evaporative emission system status, and fuel system status. Vehicle status can refer to whether the vehicle is on or off, which can be determined based on, for example, the position of the ignition switch. Engine status can refer to whether the engine is on (e.g., the engine has a non-zero speed and combustion is occurring in the engine cylinders) or off (e.g., the engine speed is zero and no combustion is occurring in the engine cylinders). Evaporative emission system status can refer to the operating mode of the evaporative emission system (such as fuel vapor storage mode, refueling mode, and canister purge mode, as described above with respect to Figure 2As described, the status of various actuators of the evaporative emission system, and / or whether any deterioration in the evaporative emission system is indicated. The fuel system status may refer to whether the fuel system is sealed with the FTIV closed, and / or whether any deterioration in the fuel system is indicated. Additionally, the differential pressure between the evaporative emission system and the fuel system may be measured by a dP sensor.

[0087] At 504, it is determined whether the conditions for the canister-side engine-off diagnostic test are met. The entry conditions for the canister-side engine-off diagnostic test may include: the engine is off and there is no indication of FTIV deterioration. The conditions may also include: no other canister-side deterioration is indicated, such as an electrical short, vacuum pump deterioration, and / or deterioration of the CVV (such as the CVV being stuck in the open position). In some examples, the conditions may also include: the FTIV has been evaluated recently (e.g., within a first predetermined duration) according to, for example, Figure 3 and / or Figure 4 the exemplary method, and a second predetermined duration has elapsed since the start of the previous canister-side engine-off diagnostic test.

[0088] If the conditions for the canister-side engine-off diagnostic test are not met, method 500 proceeds to 506 and includes maintaining the current operating parameters. Maintaining the current operating parameters may include not changing the control of the evaporative emission system actuators (such as the CVV, CPV, and vacuum pump). For example, if the CVV is currently open, it will not be commanded to close and will remain open. After 506, method 500 ends.

[0089] If the conditions for the canister-side engine-off diagnostic test are met, method 500 proceeds to 508 and includes maintaining the FTIV and CPV closed and closing the CVV. For example, the FTIV will not be actuated to open. With the FTIV closed, the dP sensor outputs the pressure difference between the canister side of the fuel vapor storage of the FTIV and the fuel tank side of the FTIV. Additionally, the CPV will not be actuated to open, thereby isolating the evaporative emission system from the engine's intake manifold. Further, with the CVV commanded to close, the evaporative emission system will be sealed off from the atmosphere. Thus, the evaporative emission system will be sealed off from the fuel system, the engine, and the atmosphere.

[0090] At 510, method 500 includes actuating a vacuum pump until the relative pressure on the canister side has decreased by a threshold amount. For example, the pressure at a first pressure port of a dP sensor coupled to the fuel system may be higher than the pressure at a second pressure port of the dP sensor coupled to the evaporative emissions system. As the vacuum pump evacuates the evaporative emissions system, the pressure differential between the first pressure port and the second pressure port may increase. Thus, the threshold amount may correspond to a predetermined vacuum target (e.g., -10 inches H2O) to be applied to the canister side starting from an initial differential pressure. In an illustrative example, if the initial relative pressure is 5 inches H2O (e.g., the pressure on the tank side is 5 inches H2O higher than the pressure on the canister side) and the predetermined vacuum target is -10 inches H2O, then the vacuum pump may be actuated until the dP sensor reads a relative pressure of 15 inches H2O (which means the canister side pressure has decreased by 10 inches H2O relative to the tank side pressure).

[0091] At 512, method 500 includes deactivating the vacuum pump. In the event that a target vacuum amount has been reached within the canister side, the vacuum pump may be deactivated in order to maintain the canister side at the target vacuum.

[0092] At 514, method 500 includes determining a bleed threshold based on the canister side relative pressure. The bleed threshold may refer to an increase in the canister side relative pressure (e.g., a decrease in relative vacuum) that may occur over a certain duration, at or above which it can be inferred that the fuel vapor storage canister side of the FTIV does not hold a vacuum, such as in a situation where air from the atmosphere is introduced into the evaporative emissions system through an orifice or disconnection. Thus, the bleed threshold may be set for a predetermined amount of increase in the canister side relative pressure starting from an initial differential pressure (e.g., the differential pressure when the vacuum pump is deactivated). Alternatively, a threshold rate of pressure bleed may be determined, which may be a non-zero rate corresponding to the rate of increase in the canister side pressure (e.g., vacuum loss) of the FTIV indicating that the canister side of the FTIV is not fully sealed. Elaborating on the above illustrative example, if the dP sensor reads a differential pressure of 15 inches H2O when the vacuum pump is deactivated, then for a canister side relative pressure of -15 inches H2O, the canister side pressure is 15 inches H2O less than the tank side pressure. The bleed threshold may be set to a differential pressure of 13 inches H2O corresponding to a canister side relative pressure of -13 inches H2O, which means the amount by which the canister side relative pressure may increase is less than 2 inches H2O in order to remain below the threshold.

[0093] At 516, method 500 includes monitoring the differential pressure over the duration. The duration may be a predetermined duration, such as 30 seconds. Although the tank side pressure may fluctuate, such as due to diurnal temperature, the tank side pressure is not expected to change significantly during the duration. Thus, changes in the differential pressure measured by the dP sensor may be attributed to changes in the canister side pressure.

[0094] At 518, it is determined whether the canister-side relative pressure is less than a bleed threshold. If the canister-side relative pressure is not less than the bleed threshold (or if the rate of pressure bleed is not less than a threshold rate), then method 500 proceeds to 520 and includes indicating canister-side deterioration. For example, the canister side may not be sealed such that air enters from the atmosphere through an orifice, a valve stuck in an open position (e.g., a canister vent valve (CVV) or a canister purge valve (CPV)), or a disconnect. Indicating canister-side deterioration may include setting a corresponding diagnostic trouble code (DTC) at the controller and may also include illuminating the malfunction indicator lamp (MIL) to alert the vehicle driver to service the vehicle. Additionally, in some examples, canister purging may be prohibited. For example, if the fuel vapor storage canister is purged when there is an orifice in the evaporative emissions system, unmetered air may enter through the orifice, resulting in a lean engine operation. Thus, purging may be prohibited until the vehicle is repaired and the DTC is cleared. Further, a tank-side diagnostic test (such as method 400 according to Figure 4 may not be performed when canister-side deterioration is indicated. For example, canister-side deterioration may confound the tank-side diagnostic test.

[0095] If at 518 the canister-side relative pressure is less than the bleed threshold after the duration (or if the rate of pressure bleed is less than the threshold rate), then method 500 proceeds to 522 and includes indicating that no canister-side deterioration is detected. Additionally, the result of the test may be stored at the controller, such as in the controller's memory. Then, the controller may, for example, schedule a subsequent canister-side engine-off diagnosis and / or update the purge schedule.

[0096] At 524, method 500 includes opening the CVV. The CVV may be opened to connect the evaporative emissions system to the atmosphere when the canister-side engine-off diagnostic test is complete. With the evaporative emissions system connected to the atmosphere, the differential pressure (dP) sensor reading may correspond to the pressure of the fuel tank relative to the atmosphere, which may facilitate fuel tank pressure control, as described with respect to Figure 8 After 524, method 500 ends.

[0097] The above-described canister-side engine-off diagnostic test can be used to detect deterioration that prevents the evaporative emissions system from sealing completely, such as due to an orifice, a valve stuck in an open position, etc. However, the canister-side engine-off diagnostic test does not detect blockages in the evaporative emissions system that may degrade the operation of the fuel vapor storage canister purge operation. In one example, if the purge line connecting the fuel vapor storage canister to the engine intake (e.g., Figure 2If there is a blockage in the purge line 228), then fuel vapor may not be purged into the engine intake manifold (or, if flow is restricted, the purge flow rate may be reduced). In another example, if there is a blockage in the vent line connecting the fuel vapor storage canister to the atmosphere, then during purge, fresh air may not be drawn across the fuel vapor storage canister, which can result in incomplete fuel vapor storage canister cleaning.

[0098] Then proceed to Figure 6 , an exemplary method 600 for detecting a blockage in a purge path of an evaporative emissions system is provided. The purge path may include, for example, a purge line and a CPV. Figure 6 The method 600 can be performed using vacuum from the intake manifold when the engine is on, as will be described below. For example, the method 600 can be performed as part of the method 300 (e.g., at 306) in response to the engine being on. However, in other examples, the method 600 can be performed whenever conditions for evaluating the purge path are met, as will be described below. Figure 3 The method 600 starts at 602 and includes evaluating operating parameters. The operating parameters can include, for example, vehicle state, engine state, evaporative emissions system state, and fuel system state. The vehicle state can refer to whether the vehicle is on or off, which can be determined based on, for example, the position of the ignition switch. The engine state can refer to whether the engine is on (e.g., the engine has a non - zero speed and combustion is occurring in the engine cylinders) or off (e.g., the engine speed is zero and no combustion is occurring in the engine cylinders), and if the engine is on, the engine state can further refer to engine operating parameters such as engine speed, engine load, manifold absolute pressure (MAP), etc. The evaporative emissions system state can refer to the operating mode of the evaporative emissions system (such as the fuel vapor storage mode, refueling mode, and canister purge mode, as described above with respect to Figure 6 , the states of various actuators of the evaporative emissions system, and / or whether any deterioration in the evaporative emissions system is indicated. The fuel system state can refer to whether the fuel system is sealed with the FTIV closed and / or whether any deterioration in the fuel system is indicated. Additionally, the differential pressure between the evaporative emissions system and the fuel system can be measured by a dP sensor.

[0099] At 604, it is determined whether conditions for evaluating the purge path are met. The conditions for evaluating the purge path can include, for example, the engine being on and no indication of FTIV deterioration. The conditions can also include an indication of no canister - side deterioration, such as described above with respect to Figure 2

[0100] At 604, it is determined whether conditions for evaluating the purge path are met. The conditions for evaluating the purge path can include, for example, the engine being on and no indication of FTIV deterioration. The conditions can also include an indication of no canister - side deterioration, such as described above with respect to Figure 5The described deteriorations, electrical short circuits, vacuum pump deterioration, deterioration of the CVV (such as the CVV being stuck in the open position), and / or deterioration of the CPV (such as the CPV being stuck in the closed position). Evaluating the conditions of the purge path may also include that the MAP is less than a threshold pressure, where the threshold pressure refers to the amount of vacuum in the intake manifold sufficient for evaluating the purge path.

[0101] If the conditions for evaluating the purge path are not met, method 600 proceeds to 606 and includes maintaining the operating parameters. Maintaining the operating parameters may include not changing the control of the evaporative emission system actuators (such as the CVV and CPV). For example, if the CVV is currently open, it will not be commanded to close and will remain open. After 606, method 600 ends.

[0102] If the conditions for evaluating the purge path are met, method 600 proceeds to 608 and includes closing the CVV and opening the CPV. With the CPV open, the intake manifold can evacuate the evaporative emission system. Additionally, with the CVV closed, air may not be drawn across the fuel vapor storage canister, which can reduce the amount of fuel vapor desorbed from the adsorbent within the fuel vapor storage canister and purged to the intake manifold.

[0103] At 610, it is determined whether the canister side relative vacuum is greater than or equal to a threshold. The canister side relative vacuum can be determined based on the dP sensor measurement results. For example, the pressure at the first pressure port of the dP sensor connected to the fuel system may be higher than the pressure at the second pressure port of the dP sensor connected to the evaporative emission system. When the intake manifold evacuates the evaporative emission system, the pressure difference between the first pressure port and the second pressure port can increase. Although the tank side pressure may fluctuate, such as due to day-night temperature, the tank side pressure is not expected to change significantly during the purge path evaluation. Therefore, the change in the differential pressure measured by the dP sensor can be attributed to the change in the canister side pressure. As an exemplary example, if the dP sensor measures a differential pressure of 10 inches H2O, which indicates that the tank side pressure is 10 inches H2O higher than the canister side pressure, then the canister side relative vacuum (e.g., negative pressure) is 10 inches H2O. The threshold can be a non-zero pressure value, which can be determined based on the starting differential pressure (e.g., the differential pressure value just before closing the CVV and opening the CPV at 608) and the minimum amount of vacuum that the canister side would reach in the absence of a purge path blockage. Therefore, the threshold can be further determined based on the MAP. For example, the controller can input the starting differential pressure and the MAP into a look-up table or equation and output the threshold. Determining whether the canister side relative vacuum is greater than or equal to the threshold may also include: determining whether the canister side relative vacuum reaches or exceeds the threshold within a predetermined duration.

[0104] If the canister-side relative vacuum is greater than or equal to a threshold (e.g., the canister-side relative pressure is less than), method 600 proceeds to 612 and includes indicating that no purge path blockage is detected. For example, in the case where there is no blockage in the purge path (such as no obstruction in the purge line and the CPV is fully open), the vacuum drawn by the intake manifold successfully evacuates the evaporative emission system to at least the threshold vacuum amount within a predetermined duration. Indicating that no purge path blockage is detected may include, for example, storing the result in the memory of the controller.

[0105] If the canister-side relative vacuum is not greater than or equal to the threshold (e.g., the canister-side relative pressure is greater than the threshold), method 600 proceeds to 614 and includes indicating that a purge path blockage is detected. A purge path blockage (such as a degraded CPV that is not fully open, or an obstruction in the purge line) may, for example, prevent the intake manifold from evacuating the evaporative emission system or may reduce the rate at which the evaporative emission system is evacuated. Indicating a purge path blockage may include setting a corresponding DTC at the controller and may also include illuminating the MIL to alert the vehicle driver to service the vehicle. Additionally, canister purging may be prohibited until the vehicle is repaired and the DTC is cleared.

[0106] At 616, method 600 includes opening the CVV and closing the CPV. By opening the CVV, the evaporative emission system can be connected to the atmosphere. Additionally, by closing the CPV, the evaporative emission system is isolated from the intake manifold. Thus, the evaporative emission system can rebalance to atmospheric pressure. After 616, method 600 ends.

[0107] Proceed to Figure 7 , an exemplary method 700 for detecting a blockage in the vent path of an evaporative emission system is provided. The vent path may include, for example, a vent duct and the CVV, and an air filter (if included). Similar to Figure 6 method 600, Figure 7 method 700 can be performed using the vacuum from the intake manifold when the engine is on. For example, method 700 can be performed as part of Figure 3 method 300 (e.g., at 306) in response to the engine being turned on. However, in other examples, method 700 can be performed whenever the conditions for evaluating the vent path are met, as will be described below. Figure 7 as follows.

[0108] Method 700 begins at 702 and includes evaluating operating parameters. The operating parameters can include, for example, vehicle state, engine state, evaporative emission system state, and fuel system state. The vehicle state can refer to whether the vehicle is on or off, which can be determined based on, for example, the position of the ignition switch. The engine state can refer to whether the engine is on (e.g., the engine has a non-zero speed and combustion is occurring in the engine cylinders) or off (e.g., the engine speed is zero and no combustion is occurring in the engine cylinders), and if the engine is on, the engine state can further refer to engine operating parameters such as engine speed, engine load, MAP, etc. The evaporative emission system state can refer to the operating mode of the evaporative emission system (such as the fuel vapor storage mode, refueling mode, and canister purge mode, as described above with respect to Figure 2 ), the state of the various actuators of the evaporative emission system, and / or whether any deterioration in the evaporative emission system is indicated. The fuel system state can refer to whether the fuel system is sealed with the FTIV closed and / or whether any deterioration in the fuel system is indicated. Additionally, the differential pressure between the evaporative emission system and the fuel system can be measured by a dP sensor.

[0109] At 704, it is determined whether the conditions for evaluating the ventilation path are met. The conditions for evaluating the ventilation path can include, for example, the engine being on and no indication of FTIV deterioration. The conditions can also include an indication of no canister side deterioration, such as the deterioration, electrical short circuit, vacuum pump deterioration, CVV deterioration (such as the CVV being stuck in the open position), CPV deterioration (such as the CPV being stuck in the closed position), and / or cleaning path blockage described above with respect to Figure 5 . The conditions for evaluating the ventilation path can further include the MAP being less than a threshold pressure, where the threshold pressure refers to the amount of vacuum in the intake manifold sufficient for evaluating the ventilation path.

[0110] If the conditions for evaluating the ventilation path are not met, method 700 proceeds to 706 and includes maintaining the operating parameters. Maintaining the operating parameters can include not changing the control of the evaporative emission system actuators (such as the CVV and CPV). For example, if the CPV is currently closed, then it will not be commanded to open and will remain closed. After 706, method 700 ends.

[0111] If the conditions for evaluating the ventilation path are met, method 700 proceeds to 708 and includes opening the CPV while maintaining the CVV open. With the CPV open, the intake manifold can draw a vacuum on the evaporative emissions system. Additionally, with the CVV open, fresh air can be drawn through the ventilation passage and across the fuel vapor storage canister, resulting in a smaller canister-side vacuum compared to the amount of canister-side vacuum that could be generated with the CVV closed. Thus, a limited amount of vacuum can accumulate in the evaporative emissions system, which can be less than the amount of vacuum before the evaporative emissions system reaches pressure equilibrium and the amount of vacuum in the intake manifold remains substantially constant. However, if the ventilation path is blocked, fresh air may not be drawn into the evaporative emissions system, and the vacuum can continue to accumulate, as will be described below.

[0112] At 710, method 700 includes monitoring an increase in canister-side relative vacuum. The canister-side relative vacuum can be determined based on dP sensor measurements. For example, the pressure at a first pressure port of the dP sensor coupled to the fuel system can be higher than the pressure at a second pressure port of the dP sensor coupled to the evaporative emissions system. With the FTIV closed, when the intake manifold draws a vacuum on the evaporative emissions system, the pressure difference between the first pressure port and the second pressure port can increase. Although the tank-side pressure can fluctuate, such as due to diurnal temperature, the tank-side pressure is not expected to change significantly during the ventilation path evaluation. Thus, the change in the differential pressure measured by the dP sensor can be attributed to a change in the canister-side pressure. As an illustrative example, if the dP sensor measures a differential pressure of 10 inches H2O, which indicates that the tank-side pressure is 10 inches H2O higher than the canister-side pressure, then the canister-side relative vacuum (e.g., negative pressure) is 10 inches H2O. If a subsequent dP sensor output corresponds to a differential pressure of 12 inches H2O, then the canister-side relative vacuum has increased by 2 inches H2O. If a subsequent dP sensor output corresponds to a differential pressure of 10 inches H2O, then the canister-side relative vacuum has not increased or decreased (e.g., remained stable). For example, monitoring an increase in canister-side relative vacuum can include comparing a current canister-side relative vacuum measurement to an initial canister-side relative vacuum measurement (such as the canister-side relative vacuum just before opening the CPV) (e.g., at 708).

[0113] At 712, method 700 includes determining whether the canister-side relative vacuum continues to increase after a threshold duration. The threshold duration can be a non-zero duration that represents the maximum amount of time expected for the evaporative emissions system to reach pressure equilibrium when the ventilation path is not blocked (e.g., there is no blockage and the CVV is fully open).

[0114] If the canister-side relative vacuum does not continue to increase after a threshold duration has elapsed (e.g., the canister-side relative vacuum reaches a maximum value before the threshold duration and remains substantially constant), method 700 proceeds to 714 and includes indicating that a vent path blockage is not detected. For example, in the case of no vent path blockage (such as no obstruction in the vent duct and the CVV being fully open), the vacuum drawn by the intake manifold can evacuate the evaporative emission system to a limited steady vacuum level within a predetermined duration. Indicating that a vent path blockage is not detected can include, for example, storing the result in the memory of the controller.

[0115] If the canister-side relative vacuum continues to increase after a threshold duration has elapsed, method 700 proceeds to 716 and includes indicating that a vent path blockage is detected. For example, the CVV may deteriorate and become stuck in at least a partially closed position, there may be an obstruction in the vent duct, or, if an air filter is included, for example, the air filter may be clogged. Such a blockage can prevent the evaporative emission system from reaching pressure equilibrium because, in the absence of air (or insufficient air) flowing through the vent duct to maintain pressure, the intake manifold can continue to evacuate the evaporative emission system. Indicating a vent path blockage can include setting a corresponding DTC at the controller and can also include illuminating the MIL to alert the vehicle driver to service the vehicle. Further, canister purging can be prohibited until the vehicle is repaired and the DTC is cleared. Additionally, the CPV can be opened during refueling to prevent premature closing of the fueling nozzle. For example, during refueling, refueling vapor can create pressure in the fuel tank, which can be vented to the evaporative emission system through the open FTIV. However, in the case of a blocked vent path, the evaporative emission system may not be in communication with the atmosphere, resulting in increased pressure in the evaporative emission system and the fuel system, which may prematurely close the fueling nozzle. Thus, by opening the CPV, the evaporative emission system and the fuel system can be in communication with the engine. If the vehicle's emission control device is warm (e.g., above its light-off temperature), the engine can be rotated without fueling (e.g., using a starter motor or an electric motor) to direct the refueling vapor towards the emission control device when refueling with the CPV open. If the emission control device is cold (e.g., the temperature of the emission control device is less than its light-off temperature), spark can be provided while the engine is rotating to combust the refueling vapor. As an example, if the vehicle is an autonomous HEV and a refueling event is known a priori to be requested (e.g., within a certain duration), the controller can proactively start the engine to heat the emission control device to its light-off temperature before arriving at the gas station.

[0116] At 718, method 718 includes closing the CPV. With the CPV closed, the evaporative emission system will be isolated from the engine intake passage, and the intake manifold will no longer vacuum the evaporative emission system. After 718, method 700 ends.

[0117] In one example, Figures 3 to 7 the methods may together include: differentiating degradation between each of a sealed fuel tank, an evaporative emission system, and the FTIV based on a differential pressure measured by a dP sensor coupled across the FTIV, the FTIV being positioned between the sealed fuel tank and a fuel vapor storage canister of the evaporative emission system. For example, when the engine is off and the FTIV is closed, in response to a differential pressure between a first higher threshold and a second lower threshold, the method may include: differentiating degradation between the sealed fuel tank and the FTIV rather than with the evaporative emission system. Differentiating degradation between the sealed fuel tank and the FTIV may include: actuating a vacuum pump of the evaporative emission system to evacuate the evaporative emission system, and indicating degradation of the FTIV and non - degradation of the sealed fuel tank in response to the differential pressure remaining between the first higher threshold and the second lower threshold. For example, indicating degradation of the FTIV may include setting a corresponding DTC at the controller. In response to the differential pressure not remaining between the first higher threshold and the second lower threshold after actuating the vacuum pump, a vacuum may be applied to the sealed fuel tank by opening and closing the FTIV until the relative pressure of the sealed fuel determined based on the differential pressure measured by the dP sensor when the FTIV is closed decreases by a first threshold amount. Then the relative pressure of the sealed fuel tank is monitored using the dP sensor, and indicating degradation of the sealed fuel tank and non - degradation of the FTIV in response to the relative pressure of the sealed fuel tank reaching or exceeding a third threshold within a first predetermined duration. Indicating degradation of the sealed fuel tank may include setting a corresponding DTC at the controller. Additionally, differentiating degradation between each of the sealed fuel tank, the evaporative emission system, and the FTIV may include: closing the canister vent valve to isolate the evaporative emission system from the atmosphere; actuating the vacuum pump until the relative pressure of the evaporative emission system determined based on the differential pressure measured by the dP sensor decreases by a second threshold amount; and indicating degradation of the evaporative emission system and non - degradation of the FTIV or degradation of the sealed fuel tank in response to the relative pressure of the evaporative emission system reaching or exceeding a fourth threshold within a second predetermined duration. Indicating degradation of the evaporative emission system may include setting a corresponding DTC at the controller.

[0118] In another example, Figures 3 to 7The method may include: determining a deterioration of the FTIV and, in response thereto, setting a first DTC and not determining a deterioration of the fuel tank side of the FTIV or the fuel vapor storage canister side of the FTIV; determining a deterioration of the fuel tank side of the FTIV (which may not be a deterioration of the FTIV), and in response thereto, setting a second DTC; and determining a deterioration of the fuel vapor storage canister side of the FTIV (which may not be a deterioration of the FTIV or the fuel tank side of the FTIV), and in response thereto, setting a third DTC. In some examples, determining a deterioration of the fuel vapor storage canister side of the FTIV may occur simultaneously with or during a deterioration of the fuel tank side of the FTIV. As illustrated herein by way of example, a method of operating and performing actions in response to determining a deterioration may include: operating (e.g., operating while the vehicle is in motion and optionally while the engine is combusting fuel) in the presence of a deterioration of the FTIV, the fuel tank side of the FTIV, and / or the fuel vapor storage side of the FTIV, and operating in the absence of a deterioration of the FTIV, the fuel tank side of the FTIV, and / or the fuel vapor storage side of the FTIV.

[0119] In yet another example, Figures 3 to 7 the method may include: determining the presence or absence of a blockage in a purge path of the evaporative emission system and determining the presence or absence of a blockage in a vent path of the evaporative emission system. In some examples, determining the presence or absence of a blockage in the purge path occurs when there is no blockage in the vent path, and determining the presence or absence of a blockage in the vent path occurs when there is no blockage in the purge path. Additionally, instructions stored in a memory may include: when the engine is running, sending a signal to open a canister purge valve, sending a signal to close a canister vent valve, and determining the presence or absence of a blockage in the purge path based on an output of a dP sensor. In another example, instructions stored on a memory may include: when the engine is running, sending a signal to open a canister purge valve and determining the presence or absence of a blockage in the vent path based on an output of a dP sensor.

[0120] Next, Figure 8 illustrates an exemplary method 800 for regulating fuel tank pressure based on an output of a single dP sensor (e.g., Figure 2 the dP sensor 221) that is coupled across an FTIV (e.g., Figure 2 the FTIV 236) that isolates a fuel system (e.g., the fuel tank side of the FTIV) from an evaporative emission system (e.g., the fuel vapor storage canister side of the FTIV). A fuel tank (such as Figure 2The fuel tank 220) can be a sealed fuel tank of NICROS as part of, for example, a hybrid vehicle system. In this way, the vehicle's engine is actuated less frequently, such that the vehicle is propelled more often by torque from an electric motor (e.g., operating in an all-electric mode) rather than by torque from the engine. Additionally, when a refueling event is requested, if the fuel tank is pressurized relative to atmospheric pressure, the fuel tank can be made to communicate with the evaporative emissions system such that fuel vapor is directed to a fuel vapor storage charcoal canister (e.g., Figure 2 the fuel vapor storage charcoal canister 222) in order to prevent fuel mist from being ejected from the fuel system when the fuel port (e.g., Figure 2 the fuel port 286) is opened.

[0121] Method 800 begins at 802 and includes evaluating operating parameters. The operating parameters can include, for example, vehicle state, engine state, evaporative emissions system state, and fuel system state. The vehicle state can refer to whether the vehicle is on or off, which can be determined based on, for example, the position of the ignition switch. The engine state can refer to whether the engine is on or off, and if the engine is on, the engine state can further refer to engine operating parameters such as engine speed, engine load, MAP, etc. The engine may be off if it is stationary (e.g., engine speed is zero) and no combustion occurs within the engine cylinders (e.g., no fuel is supplied to the engine cylinders). The evaporative emissions system state can refer to the operating mode of the evaporative emissions system (such as fuel vapor storage mode, refueling mode, and charcoal canister purge mode, as described above with respect to Figure 2 ), and / or the states of various actuators of the evaporative emissions system (such as the charcoal canister vent valve (e.g., Figure 2 the CVV 214) and the charcoal canister purge valve (e.g., Figure 2 the CPV 212)). The fuel system state can refer to, for example, whether the fuel system is sealed with the FTIV closed, and the fuel level in the fuel tank. Additionally, the differential pressure between the evaporative emissions system and the fuel system can be measured by a dP sensor. For example, with the CVV held open such that the evaporative emissions system is connected to the atmosphere, the pressure of the evaporative emissions system can equal atmospheric pressure. Thus, the fuel tank pressure can be determined relative to atmospheric pressure based on the output from the dP sensor.

[0122] At 804, it is determined whether the engine is off (e.g., stationary and no combustion occurring). For example, when the vehicle is on and operating in a mode where only torque from an electric motor (e.g., Figure 1When propelling the vehicle in electric mode using the torque of the motor 120), the engine can be turned off. In another example, when the vehicle is off (e.g., the vehicle's ignition switch is in the off position), but the controller may be operating in a wake-up mode to perform tasks such as diagnostic routines, transmit data, etc., the engine can be turned off.

[0123] If the engine is not off (e.g., the engine is on, such as for combustion, speed is above zero), then method 800 proceeds to 806 and includes determining whether the tank-side relative pressure is less than a first threshold. The first threshold can be a non-zero pressure value above which the fuel tank pressure can reach the mechanical limit of the fuel tank. Thus, to prevent fuel tank deterioration, the fuel tank can be reduced to a pressure less than the threshold. Additionally, by maintaining the pressure of the fuel tank at a pressure less than the first threshold, the fuel tank depressurization during a refueling event can be accelerated, as will be further described below. The tank-side relative pressure (e.g., the relative pressure of the fuel tank) can be determined using a dP sensor, where the dP sensor outputs a signal corresponding to the pressure difference between the fuel system and the evaporative emissions system (e.g., the pressure of the fuel tank relative to the pressure of the evaporative emissions system). In the case where the FTIV remains normally closed and the CVV remains normally open, thus connecting the evaporative emissions system to the atmosphere, the dP sensor reading can correspond to the tank-side pressure relative to atmospheric pressure. Thus, the first threshold can refer to a predetermined threshold relative pressure above atmospheric pressure.

[0124] If the tank-side relative pressure is less than the first threshold, then method 800 proceeds to 822 and includes maintaining the operating parameters. Maintaining the operating parameters can include not changing the control of the fuel system and evaporative emissions system actuators (such as the CVV, FTIV, and CPV). For example, in the case where the tank-side relative pressure is less than the first threshold, the fuel tank can be within its nominal operating pressure range, and the fuel tank may not be in communication with the evaporative emissions system. Thus, for example, the FTIV may not be actuated to open and will remain closed. After 822, method 800 ends.

[0125] If the tank-side relative pressure is not less than the first threshold (e.g., the tank-side relative pressure is greater than or equal to the first threshold), then method 800 proceeds to 808 and includes opening the CPV and adjusting the first threshold based on new dP sensor measurements. By opening the CPV and keeping the CVV open, the vacuum from the engine's intake manifold due to natural engine aspiration can be directed to the fuel vapor storage charcoal canister (e.g., Figure 2 the fuel vapor storage charcoal canister 222), thereby sucking fresh air from the atmosphere through the ventilation duct in the evaporative emissions system (e.g., Figure 2The vent passage 227) and passes through the fuel storage vapor canister. By drawing fresh air across the fuel vapor storage canister, the stored fuel vapor can be desorbed and directed to the engine intake passage. Additionally, when the CPV is open and the intake manifold is evacuating the evaporative emission system, the canister side will no longer be at atmospheric pressure, resulting in a change in the dP sensor measurement. For example, as the canister side pressure drops below atmospheric pressure, the pressure differential between the canister side of the FTIV and the fuel tank side of the FTIV can increase. Accordingly, the first threshold can be increased by a corresponding amount. As an illustrative example, if the threshold is 10 inches H2O when the canister side is at atmospheric pressure and the dP sensor reading increases from 15 inches H2O before the CPV is opened to 23 inches H2O after the CPV is opened, i.e., an 8-inch H2O differential pressure increase, then the threshold can be increased to 18 inches H2O. In this manner, the first threshold can remain constant relative to the canister side pressure. The condition that the tank side pressure is greater than or equal to the first threshold is a first example of a fuel tank depressurization condition, which refers to the condition of the fuel tank that makes it necessary to ventilate the fuel tank to reduce the pressure (e.g., depressurize the fuel tank), such as the pressure of the fuel tank.

[0126] In some examples, additionally or alternatively, the first threshold can be adjusted based on MAP, which can be measured by a MAP sensor (e.g., Figure 2 the MAP sensor 240). For example, changes in MAP can affect the canister side pressure. Accordingly, the controller can adjust the first threshold based on MAP, e.g., where the first threshold increases as MAP decreases (e.g., the pressure differential between the canister side and the tank side can increase as the manifold vacuum increases).

[0127] At 810, method 800 includes opening and closing the FTIV in a pulsating manner. Each time the FTIV is opened, the evaporative emission system will evacuate the fuel system, resulting in a reduced differential pressure after each opening of the FTIV (e.g., the tank side pressure becomes more similar to the canister side pressure). In this manner, the fuel tank pressure can be relieved. When the CPV is open, fuel vapor from the fuel tank can be purged to the engine intake passage for combustion instead of being stored in the fuel vapor storage canister (since the fuel vapor storage canister can be configured to store fuel vapor only during a fuel tank refueling event). In some examples, when the CPV is open, a compensation factor can be determined to adjust the fuel command to correct for the ingestion of fuel vapor, thereby maintaining the desired air-fuel ratio (AFR). For this example, the fuel vapor concentration can be determined based on the output from an oxygen sensor, a hydrocarbon sensor, or any sensor that can give an indication of the fuel vapor concentration. In some examples, opening and closing the FTIV in a pulsating manner can include: opening and closing the FTIV at a predetermined duty cycle.

[0128] Each time the FTIV is opened, the dP sensor will measure a differential pressure that is zero or close to zero because, with the FTIV open, the pressure at the first pressure port of the dP sensor can be substantially equal to the pressure at the second pressure port of the dP sensor. Thus, at 812, method 800 includes measuring the tank-side relative pressure with the FTIV closed. For example, when the FTIV is opened and closed during pulsation, each time the FTIV is closed, the differential pressure measurement output by the dP sensor can be used to determine the tank-side pressure relative to the canister-side pressure. Similarly, the differential pressure measurement output by the dP sensor when the FTIV is open is not available for determining the relative tank-side pressure. Additionally, in some examples, the pulsation rate (or pulsation duty cycle) can be adjusted based on the differential pressure measured with the FTIV closed (e.g., according to a predetermined duty cycle). Adjusting the FTIV pulsation can include adjusting the duration of each pulse and / or the interval between successive pulses. For example, the controller can input the fuel tank relative pressure (determined from the differential pressure) and a first threshold into a look-up table, algorithm, or equation and output a corresponding pulsation rate (or pulsation duty cycle). As one example, the FTIV pulsation rate can decrease as the fuel tank relative pressure approaches the first threshold.

[0129] At 814, it is determined whether the tank-side relative pressure is less than the first threshold (adjusted as at 808). As described above, the tank-side relative pressure can be measured by the dP sensor coupled across the FTIV with the FTIV closed. If the tank-side relative pressure is not less than the first threshold, which means there is still too much pressure on the tank side to relieve (and the fuel tank depressurization condition still exists), then method 800 returns to 810 and includes opening and closing the FTIV in a pulsating manner. Conversely, if the tank-side relative pressure is less than the first threshold, then method 800 proceeds to 816 and includes closing the FTIV (or maintaining it closed). In the case where the tank-side relative pressure is less than the first threshold, the fuel tank can still be within its nominal operating pressure range (and the fuel tank depressurization condition no longer exists). By closing the FTIV, the fuel system will be isolated from the evaporative emissions system again, interrupting ventilation of the fuel tank.

[0130] At 818, method 800 includes closing the CPV. With the CPV closed, the evaporative emissions system will be isolated from the intake manifold, and the evaporative emissions system will no longer be evacuated. The evaporative emissions system can rebalance to atmospheric pressure through the ventilation passage and the open CVV. After 818, method 800 ends.

[0131] Returning to 804, alternatively, if the engine is off, then method 800 proceeds to 820 and includes determining whether a fuel tank refueling event is requested. The refueling event can be requested by the vehicle driver such as by depressing a refueling button on the vehicle's dashboard (e.g., Figure 1is requested by the refueling button 197). Accordingly, the controller can receive a request for a refueling event from the vehicle driver via the refueling button.

[0132] If a refueling event is not requested, method 800 proceeds to 822 and includes maintaining the operating parameters. For example, the fuel tank will not be depressurized for a refueling event. Accordingly, the FTIV will not be actuated open and will remain closed. After 822, method 800 ends.

[0133] If a refueling event is requested, method 800 proceeds to 824 and includes determining whether the tank side is pressurized. For example, a dP sensor can be used to measure the tank side pressure relative to the canister side pressure. With the canister side open to the atmosphere via the open CVV, the dP sensor measurement can indicate the tank side pressure relative to atmospheric pressure. If the dP sensor measurement indicates that the tank side pressure is greater than the canister side pressure (e.g., atmospheric pressure), it can be determined that the tank side is pressurized. As another example, if the tank side relative pressure is greater than or equal to a second threshold, it can be determined that the tank side is pressurized, where the second threshold can be less than the first threshold. The second threshold can refer to a second (smaller) non-zero predetermined threshold relative pressure above atmospheric pressure such that if the tank side relative pressure is greater than or equal to the second threshold, the tank side is pressurized relative to atmospheric pressure. The tank side pressure being greater than or equal to the second threshold in the case of a requested refueling event is a second example of a fuel tank depressurization condition.

[0134] If the tank side is pressurized (e.g., the tank side relative pressure is greater than or equal to the second threshold), method 800 proceeds to 826 and includes opening and closing the FTIV in a pulsating manner. The FTIV can be opened and closed in a pulsating manner as described at 810, for example to vent (e.g., depressurize) the fuel tank. Each time the FTIV is opened, fuel vapor can flow from the fuel tank to the fuel vapor storage canister (e.g., via conduit 231, as Figure 2 shown), where at the fuel vapor storage canister, the fuel vapor can be adsorbed by an adsorbent in the fuel vapor storage canister. Additionally, as the fuel vapor flows from the fuel tank to the fuel vapor storage canister through the open FTIV, the tank side pressure decreases.

[0135] At 828, method 800 includes measuring the tank side relative pressure when the FTIV is closed, as described above at 812. For example, when the FTIV is opened and closed during a pulse, the differential pressure measurement of the dP sensor can be used to determine the tank side pressure relative to the canister side pressure each time the FTIV is closed. Additionally, the tank side relative pressure measured when the FTIV is closed (as opposed to when the FTIV is open) can be used to adjust the pulse, as also described above. The method can then return to 824 to determine if the tank side is pressurized. Once the tank side is not pressurized (e.g., the tank side relative pressure is less than a second threshold, as measured when the FTIV is closed), method 800 proceeds to 830.

[0136] In the case where the fuel tank is depressurized at 830 (e.g., depressurization conditions are not present), method 800 includes commanding (or maintaining) the FTIV to be open. By opening the FTIV and maintaining it open, refueling vapors can be directed to the fuel vapor storage canister. Additionally, the CPV can remain closed throughout the depressurization and refueling process to prevent fuel vapors from flowing to the intake manifold.

[0137] At 832, method 800 includes unlocking the fuel filler door to allow refueling. For example, the fuel filler door can remain locked and closed prior to the fuel tank being depressurized to prevent access to the refueling port (e.g., Figure 2 refueling port 284), thus prohibiting refueling until the fuel tank has been depressurized. With the fuel filler door unlocked, the vehicle driver can open the fuel filler door and access the refueling port to refill the fuel tank. The FTIV can remain open throughout the refueling operation to allow refueling vapors (such as fuel vapors displaced by liquid fuel) to be vented to the fuel vapor storage canister.

[0138] At 834, it is determined whether the refueling event is complete. In one example, when the vehicle driver has closed the fuel filler door (which can be indicated to the controller by a sensor, for example), the refueling event can be determined to be complete. If the refueling event is not complete, such as if the fuel filler door remains open, method 800 proceeds to 836 and includes continuing the refueling operation. In this way, the fuel filler door will not be locked and the FTIV will remain open. If the refueling event is complete, method 800 proceeds to 838 and includes locking the fuel filler door. In this way, additional fuel tank refills can be prohibited until a subsequent refueling event is requested.

[0139] At 840, method 800 includes closing the FTIV. With the FTIV closed, the fuel system can be isolated from the evaporative emission system again. Closing the FTIV seals the fuel tank, preventing additional fuel vapors from flowing to the fuel vapor storage canister. After 840, method 800 ends.

[0140] Thus, in one example, Figure 8Method 800 may include: determining a decompression condition of a fuel tank included in an engine system and coupled to an evaporative emission system via an FTIV, and in response thereto, communicating the fuel tank with the evaporative emission system by opening and closing the FTIV in a pulsating manner; and determining when the decompression condition no longer exists, and in response thereto, interrupting the pulsation. In some examples, ventilating the fuel tank occurs when the decompression condition exists, and interrupting the pulsation occurs when the decompression condition does not exist. As a first example, the decompression condition is determined when the engine is on and in response to the relative pressure of the fuel tank being greater than or equal to a first higher threshold pressure (such as measured by a dP sensor across the FTIV when the FTIV is closed rather than when the FTIV is open). In the first example, interrupting the pulsation includes maintaining the FTIV closed. As a second example, the decompression condition is determined when the engine is off, in response to the relative pressure of the fuel tank being greater than or equal to a second lower threshold pressure, and further in response to receiving a request for a refueling event. In the second example, interrupting the pulsation includes maintaining the FTIV open.

[0141] Additionally, instructions stored in a memory may include: determining a decompression condition based on a dP sensor across the FTIV when the FTIV is closed (and independent of the dP sensor measurement when the FTIV is open), and in response, performing at least one of the following: opening and closing the FTIV in a pulsating manner via instructions for sending a signal to the FTIV, and opening a CPV via instructions for sending a different signal to the CPV of the evaporative emission system. In some examples, the method may include: determining whether to perform one or more of the actions of sending a signal to the FTIV and opening the CPV based on a determination of whether the engine is on or off and a determination of whether a fuel tank refueling event is requested.

[0142] As illustrated by way of example herein, a method of operating and performing actions in response to a determination of a fuel tank decompression condition may include: operating under that condition (e.g., operating while the vehicle is in motion and the engine is combusting or while the vehicle and / or engine is stationary), determining whether that condition exists (such as based on the output of a dP sensor being greater than a threshold), and performing an action in response thereto; and operating when that condition does not exist, determining that the condition does not exist, and performing a different action in response thereto. For example, in response to a fuel tank decompression condition existing, the fuel tank may be ventilated by opening and closing the FTIV in a pulsating manner, where the pulsation is adjusted based on the output of the dP sensor; and in response to a fuel tank decompression not existing, the FTIV may be maintained closed. In another example, in response to a transition from a fuel tank decompression condition existing to a fuel tank decompression not existing, and further in response to a request for a fuel tank refueling event, the FTIV may be maintained open and the fuel port may be unlocked to enable access to the fuel tank.

[0143] Next, Figure 9 an exemplary timeline 900 is shown for determining whether a fuel tank isolation valve (e.g., Figure 2 FTIV 236) in an engine system or the fuel tank side of the FTIV is degraded. For example, a controller (e.g., Figure 2 controller 12) can, for example, according to Figure 3 an exemplary method, utilize the output from a Δ pressure sensor (such as Figure 2 dP sensor 221) coupled across the FTIV to "passively" diagnose the FTIV and the tank side of the FTIV. As described with respect to Figure 2 , when closed, the FTIV isolates the fuel system including the fuel tank from the evaporative emissions system including the fuel vapor storage canister. A first pressure port of the dP sensor is coupled to the tank side of the FTIV, while a second pressure port of the dP sensor is coupled to the canister side of the FTIV. The signal output by the dP sensor corresponds to the pressure difference between the first pressure port and the second pressure port (e.g., between the tank side and the canister side of the FTIV when closed). Thus, the controller can interpret the dP sensor measurements to determine whether to perform an active diagnostic test (such as Figure 4 an exemplary method) to determine whether there is degradation of the FTIV or the tank side.

[0144] The dP sensor measurements (e.g., differential pressure measured by the dP sensor) are shown in graph 902; the position of the canister purge valve (e.g., Figure 2 CPV 212) of the evaporative emissions system is shown in graph 904; the position of the FTIV is shown in graph 906; the position of the canister vent valve (e.g., Figure 2 CVV 214) of the evaporative emissions system is shown in graph 908; the activation state of the vacuum pump (e.g., Figure 2 vacuum pump 238) of the evaporative emissions system is shown in graph 910; an indication of FTIV degradation is shown in graph 912; and an indication of tank side degradation is shown in graph 914. For all of the above graphs, the horizontal axis represents time, where time increases from left to right along the horizontal axis. The vertical axis represents each of the marked parameters. For graph 902, the dP sensor differential pressure measurements increase upward along the vertical axis. As indicated, a positive value (e.g., a value above the horizontal axis) indicates that the tank side pressure (P 箱 ) is greater than the canister side pressure (P 炭罐) and negative values (e.g., values below the horizontal axis) indicate that the pressure on the tank side is less than the pressure on the canister side. For graphs 904, 906, and 908, the vertical axis represents whether each valve (respectively, CPV, FTIV, and CVV) is open or closed, where in this example, the marked closed position is fully closed and the marked open position is fully open. For graph 910, the vertical axis represents whether the vacuum pump is on (activated) or off (deactivated). For graphs 912 and 914, the vertical axes respectively represent whether deterioration of the FTIV or the tank side is indicated ("yes" or "no"). Additionally, dash 916a indicates the positive-pass threshold for "passive" diagnosis of the FTIV and the tank side, dash 916b indicates the negative-pass threshold for "passive" diagnosis of the FTIV and the tank side, dash 918 indicates the tank side vacuum threshold, and dash 920 indicates the tank side relative pressure bleed threshold.

[0145] Throughout Figure 9 In the exemplary timeline 900, the engine is off (e.g., stationary, with no combustion occurring within the engine cylinders). Before time t1, the differential pressure (graph 902) between the tank side and the canister side of the FTIV is greater than the positive-pass threshold (dash 916a), which indicates that the pressure on the tank side is greater than the pressure on the canister side. When the differential pressure is above the positive-pass threshold, the controller can determine that the fuel tank is isolated from the atmosphere. For example, when the FTIV is closed (graph 906) and the CVV is open (graph 908), the tank side of the FTIV is isolated from the canister side of the FTIV, and the canister side is connected to the atmosphere through the open CVV (and is thus at atmospheric pressure). Additionally, since the pressure on the tank side is not equal to atmospheric pressure, it can be inferred that the tank side is not deteriorated and is not connected to the atmosphere through, for example, a break or an orifice. Therefore, before time t1, the "passive" diagnosis indicates that no deterioration of the FTIV and the tank side is detected.

[0146] At time t1, the dP sensor measurement result (graph 902) becomes lower than the positive flow threshold (dash line 916a). In the case where the canister side pressure approaches the fuel tank side pressure, the "passive" diagnosis can no longer confirm that the fuel tank side of the FTIV and the FTIV are not deteriorated. Therefore, at time t2, the CVV is commanded to close (graph 908) and the vacuum pump is activated (graph 910), while the CPV remains closed (graph 904). With both the CVV and the CPV closed, the vacuum pump evacuates the canister side of the FTIV to the target vacuum level. As shown in graph 902, as the canister side pressure decreases, the differential pressure increases because the difference between the fuel tank side pressure and the canister side pressure increases. The fact that the differential pressure increases when the canister side is being evacuated indicates that the FTIV is closed, as commanded (graph 906). Therefore, the indication of FTIV deterioration remains off (graph 912). However, if, for example, the FTIV deteriorates and gets stuck in the open position, the differential pressure can remain substantially equal to zero, as shown by the dashed segment 902a. Therefore, if the differential pressure remains between the positive flow threshold and the negative flow threshold when the canister side is being evacuated, it indicates FTIV deterioration (dashed segment 912a).

[0147] Once the canister side reaches the target vacuum level, at time t3, the FTIV is opened and closed at a predetermined duty cycle until the fuel tank side relative pressure decreases by a threshold amount. For example, when the dP sensor measurement result is at or below the fuel tank side evacuation threshold (dash line 918), the fuel tank side relative pressure may have decreased by the threshold amount, where the fuel tank side evacuation threshold refers to the threshold amount by which the pressure on the fuel tank side decreases. Each time the FTIV is opened, the canister side will evacuate the fuel tank side, thereby creating a reduced differential pressure after each opening of the FTIV (e.g., the fuel tank side pressure becomes more similar to the canister side pressure). Additionally, each time the FTIV is opened, the dP sensor reads a differential pressure of zero or close to zero because when the FTIV is open, the pressure at the first pressure port of the dP sensor can be approximately equal to the pressure at the second pressure port of the dP sensor. Therefore, the differential pressure can be evaluated when the FTIV is closed.

[0148] At time t4, in response to the differential pressure (graph 902) decreasing below the fuel tank side evacuation threshold (dash line 918), the FTIV is kept closed (graph 906), the vacuum pump is deactivated (graph 910), and the CVV is opened (graph 908). With the vacuum pump closed and the CVV open, the canister side of the FTIV is connected to the atmosphere, while the fuel tank side of the FTIV remains sealed and under vacuum. The canister side pressure increases above the fuel tank side pressure, so the differential pressure drops below the horizontal axis, as shown in graph 902.

[0149] Once the canister side has re - balanced to atmospheric pressure and the dP sensor measurements are stable, at time t5, a tank - side pressure relief threshold (dash line 920) is set based on the current dP sensor measurements and the allowable increase in the relative pressure on the tank side of the sealed fuel system. With the canister side connected to the atmosphere, the canister - side pressure remains stable. Thus, the change in differential pressure can be attributed to the change in tank - side pressure. For example, the tank - side pressure relief is monitored for a certain duration, which ends at time t7. As shown in graph 902, the differential pressure (and thus the relative tank - side pressure) remains below the tank - side pressure relief threshold (dash line 920), which indicates that the fuel - tank side of the FTIV remains under vacuum. Thus, no tank - side deterioration is indicated (graph 914). Conversely, if the differential pressure (e.g., the relative tank - side pressure) exceeds the tank - side pressure relief threshold before the duration has elapsed at time t7, such as shown by dash - segment 902b reaching the tank - side pressure relief threshold at time t6, then tank - side deterioration may be indicated, as shown by dash - segment 914b.

[0150] Next, Figure 10 An exemplary timeline 1000 is shown for determining whether the fuel - vapor storage canister side of a fuel - tank isolation valve (e.g., Figure 2 the FTIV 236) in an engine system is deteriorated via a canister - side engine - off test. For example, a controller (e.g., Figure 2 the controller 12) can use the output from a Δ - pressure sensor (such as Figure 5 the dP sensor 221) coupled across the FTIV, according to an exemplary method such as Figure 2 to determine whether there is deterioration (e.g., disconnections, orifices, etc.) in the canister side that could result in undesired evaporative emissions. As described with respect to Figure 2 when closed, the FTIV isolates the fuel system including the fuel tank from the evaporative - emission system including the fuel - vapor storage canister (e.g., Figure 2 the fuel - vapor storage canister 222). The first pressure port of the dP sensor is coupled to the tank side of the FTIV, while the second pressure port of the dP sensor is coupled to the canister side of the FTIV. The signal output by the dP sensor corresponds to the pressure difference between the first and second pressure ports (e.g., between the tank side and the canister side of the FTIV when closed). Thus, the controller can use the dP sensor measurements to determine whether the canister side can maintain a vacuum, as will be described below.

[0151] The dP sensor measurements (e.g., the differential pressure measured by the dP sensor) are shown in graph 1002; the canister purge valve of the evaporative - emission system (e.g., Figure 2the position of the CPV 212); the position of the FTIV is shown in graph 1006; the position of the canister purge valve of the evaporative emission system (e.g., Figure 2 the CVV 214) is shown in graph 1008; the activation state of the vacuum pump of the evaporative emission system (e.g., Figure 2 the vacuum pump 238) is shown in graph 1010; and an indication of canister side deterioration is shown in graph 1012. For all of the above graphs, the horizontal axis represents time, where time increases from left to right along the horizontal axis. The vertical axis represents each of the marked parameters. For graph 1002, the dP sensor differential pressure measurement results increase upward along the vertical axis. As indicated, positive values (e.g., values above the horizontal axis) indicate that the tank side pressure (P 箱 ) is greater than the canister side pressure (P 炭罐 ), while negative values (e.g., values below the horizontal axis) indicate that the tank side pressure is less than the canister side pressure. For graphs 1004, 1006, and 1008, the vertical axis represents whether each valve (respectively, the CPV, FTIV, and CVV) is open or closed. For graph 1010, the vertical axis represents whether the vacuum pump is on (activated) or off (deactivated). For graph 1012, the vertical axis represents whether deterioration of the canister side of the FTIV is indicated ("yes" or "no"). Additionally, dash line 1014 indicates the canister side evacuation (e.g., vacuum) threshold, and dash line 1016 indicates the canister side relative pressure bleed threshold.

[0152] Throughout Figure 10 the exemplary timeline 1000, the engine is off (e.g., stationary, no combustion occurs within the engine cylinders). In Figure 10 the example, prior to time t1, the canister side pressure is greater than the tank side pressure because the differential pressure measurement results are below the horizontal axis (graph 1002).

[0153] At time t1, the conditions for performing the canister side engine off test are met, as described with respect to Figure 5 , such as no indication of FTIV deterioration. Accordingly, the CVV is closed (graph 1008), thereby isolating the canister side from the atmosphere while maintaining the CPV (graph 1004) and FTIV (graph 1006) closed. Accordingly, at time t1, the canister side of the FTIV (e.g., the evaporative emission system) is sealed. Also at time t1, the vacuum pump is activated (graph 1010) in order to reduce the canister side relative pressure by a threshold amount, which can be met when the dP sensor measurement results reach the canister side evacuation threshold (dash line 1014). Since the tank side pressure is not expected to change significantly during the canister side engine off diagnostic test, any change in the dP sensor measurement results (graph 1002) can be attributed to a change in the canister side relative pressure.

[0154] Between time t1 and time t2, with the vacuum pump activated and the sealed evaporative emission system being evacuated, the canister side pressure decreases. First, the differential pressure decreases as the canister side pressure approaches the (lower) tank side pressure, and then, once the canister side pressure decreases below the tank side pressure (e.g., crosses the horizontal axis), the differential pressure decreases again as the relative vacuum on the canister side increases.

[0155] At time t2, the differential pressure (graph 1002) reaches the canister side evacuation threshold (dash line 1014), which indicates that the canister side pressure has decreased by a threshold amount. Accordingly, the vacuum pump is deactivated (graph 1010), and the canister side pressure relief threshold (dash line 1016) is set based on the current dP sensor measurement and the allowable increase in the relative pressure on the canister side of the sealed evaporative emission system. The controller can interpret a positive differential pressure measurement (graph 1002) as a negative canister side pressure (e.g., vacuum) relative to the tank side pressure. Thus, a decrease in the differential pressure can be interpreted as an increase in the relative pressure on the canister side. With the tank side pressure being substantially constant, changes in the differential pressure can be attributed to changes in the canister side pressure. The canister side pressure relief can be monitored for a certain duration, e.g., which ends at time t4.

[0156] As shown by the differential pressure measurement (graph 1002) remaining above the canister side pressure relief threshold (dash line 1016), the relative pressure on the canister side is less than the canister side pressure relief threshold, which indicates that the canister side of the FTIV remains under vacuum. Accordingly, canister side deterioration is not indicated (graph 1012). Conversely, if the relative pressure on the canister side exceeds the canister side pressure relief threshold before the duration has elapsed at time t4, such as indicated by dash segment 1002a reaching the canister side pressure relief threshold at time t3, canister side deterioration can be indicated, as shown by dash segment 1012a.

[0157] At time t4, the CVV is opened (graph 1008), thereby connecting the evaporative emission system to the atmosphere. Accordingly, the canister side re - balances to atmospheric pressure. As the amount of vacuum on the canister side decreases and the canister side pressure approaches the tank side pressure, the dP sensor measurement (graph 1002) decreases. Then, when the canister side pressure exceeds the tank side pressure, the differential pressure measurement drops below the horizontal axis. For example, the differential pressure measurement can return to approximately the starting differential pressure measurement (e.g., the differential pressure before the canister side engine - off diagnostic test at time t1).

[0158] However, the canister side engine - off test may not detect a blockage present in the evaporative emission system. Accordingly, the controller can use the vacuum generated by natural engine aspiration to perform an engine - on test to evaluate for an evaporative emission system blockage, as described with respect to Figures 6 to 7 as described.

[0159] For example, Figure 11 FIG. 1100 shows a timeline for evaluating an evaporative emission system (e.g., Figure 2 the evaporative emission system 219) that couples the evaporative emission system to a purge path of an engine intake manifold, the purge path including a purge line (e.g., Figure 2 the purge line 228) and a canister-side purge valve (e.g., Figure 2 the CPV 212) disposed within the purge line. A controller (e.g., Figure 2 the controller 12) may detect a blockage in the purge path using the output from a differential pressure sensor (such as Figure 6 the dP sensor 221) coupled across the FTIV, according to, for example, Figure 2 an exemplary method. As described with respect to Figure 2 FIG. 17, when closed, the FTIV isolates a fuel system including a fuel tank from an evaporative emission system including a fuel vapor storage canister (e.g., Figure 2 the fuel vapor storage canister 222). A first pressure port of the dP sensor is coupled to the tank side of the FTIV, while a second pressure port of the dP sensor is coupled to the canister side of the FTIV. A signal output by the dP sensor corresponds to the pressure difference between the first pressure port and the second pressure port (e.g., between the tank side and the canister side of the FTIV when closed). Thus, the controller may use the dP sensor measurements to determine that a blockage exists in the purge path that may degrade the purge from the fuel vapor storage canister to the intake manifold.

[0160] The dP sensor measurements (e.g., the differential pressure measured by the dP sensor) are shown in graph 1102; the position of the CPV is shown in graph 1104; the position of the FTIV is shown in graph 1106; the position of the canister vent valve (e.g., Figure 2 the CVV 214) of the evaporative emission system is shown in graph 1108; and an indication of a blockage in the purge path is shown in graph 1110. For all of the above graphs, the horizontal axis represents time, where time increases from left to right along the horizontal axis. The vertical axis represents each of the labeled parameters. For graph 1102, the dP sensor differential pressure measurements increase upward along the vertical axis. As indicated, positive values (e.g., values above the horizontal axis) indicate that the tank side pressure (P 箱 ) is greater than the canister side pressure (P 炭罐 ), while negative values (e.g., values below the horizontal axis) indicate that the tank side pressure is less than the canister side pressure. For graphs 1104, 1106, and 1108, the vertical axis represents whether each valve (respectively, the CPV, the FTIV, and the CVV) is open or closed. For graph 1110, the vertical axis represents whether a blockage in the purge path is detected ("yes" or "no"). Additionally, a dash line 1112 indicates a canister side relative vacuum threshold.

[0161] Throughout Figure 11 exemplary timeline 1100, the engine is on, the engine speed is above zero and combustion is occurring within the engine cylinders. Additionally, the engine is operating under natural aspiration, thereby generating a manifold air pressure (MAP) that is less than atmospheric pressure (e.g., manifold vacuum). Prior to time t1, the CPV is closed (graph 1104), thereby isolating the evaporative emission system from the engine intake manifold; and the FTIV is closed (graph 1106), thereby isolating the charcoal canister side of the FTIV from the fuel tank side of the FTIV. Additionally, the CVV is open (graph 1108), thereby connecting the charcoal canister side to the atmosphere. Thus, the charcoal canister side is at atmospheric pressure. As shown in graph 1102, prior to time t1, the dP sensor measurement (graph 1102) indicates that the tank side pressure is greater than the charcoal canister side pressure. Thus, the fuel tank pressure is above atmospheric pressure.

[0162] At time t1, the conditions for evaluating the purge path are met, such as those described with respect to Figure 6 such as an indication of no FTIV degradation. Thus, the CPV is commanded to open (graph 1104), thereby connecting the charcoal canister side to the intake manifold; while the CVV is commanded to close (graph 1108), thereby isolating the charcoal canister side from the atmosphere. Thus, the intake manifold evacuates the evaporative emission system, and fresh air is not drawn into the evaporative emission system through the vent passage and the CVV. Also at time t1, a charcoal canister side relative vacuum threshold (dash 1112) is set based on the differential pressure measurement just prior to closing the CVV and opening the CPV and the minimum vacuum level that the charcoal canister side would reach in the absence of a purge path blockage, and the charcoal canister side relative vacuum threshold can be further based on the MAP.

[0163] After time t1, the charcoal canister side relative vacuum is monitored. The charcoal canister side relative vacuum can be determined based on the dP sensor measurement (graph 1102). For example, when the intake manifold evacuates the evaporative emission system, the pressure difference between the charcoal canister side and the fuel tank side of the FTIV can increase. Although the tank side pressure can fluctuate, such as due to diurnal temperature, the tank side pressure is not expected to change significantly during the purge path evaluation. Thus, the change in the differential pressure measured by the dP sensor can be attributed to the change in the charcoal canister side pressure, and the controller can interpret the increase in the differential pressure as an increase in the charcoal canister side relative vacuum (e.g., a decrease in the charcoal canister side relative pressure).

[0164] At time t2, the canister side relative vacuum reaches the canister side relative vacuum threshold (dash 1112), as the dP sensor measurement (graph 1102) reaches the canister side relative vacuum threshold. Accordingly, the intake manifold can sufficiently evacuate the evaporative emission system and does not indicate a purge path blockage (graph 1110). When the purge path assessment is complete, the CPV is commanded closed (graph 1104) to isolate the evaporative emission system from the intake manifold, and the CVV is commanded open (graph 1108) to connect the evaporative emission system to the atmosphere. The canister side pressure rebalances to atmospheric pressure, as shown by the dP sensor measurement (graph 1102) decreasing as the canister side vacuum decreases. For example, the differential pressure measurement may return to approximately the starting differential pressure measurement (e.g., the differential pressure prior to the purge path assessment at time t1).

[0165] Conversely, if the purge path is blocked, the intake manifold may not sufficiently evacuate the canister side to reach the canister side relative vacuum threshold (dash 1112) within the threshold duration. For example, as shown by dash segment 1102a, the differential pressure (and thus, the canister side relative vacuum) may remain below the canister side relative vacuum threshold. The controller may continue to monitor the canister side relative vacuum until the threshold duration elapses at time t3, at which point a purge path blockage is indicated (dash segment 1110a). While continuing to monitor the canister side relative vacuum prior to time t3, the CPV will remain open (dash segment 1104a) and the CVV will remain closed (dash segment 1108a).

[0166] Figure 12 An exemplary timeline 1200 is shown for evaluating a vent path that connects an evaporative emission system (e.g., Figure 2 the evaporative emission system 219) to the atmosphere, the vent path including a vent duct (e.g., Figure 2 the vent duct 227) and a canister side vent valve (e.g., Figure 2 the CVV 214) disposed within the vent duct. For example, a controller (e.g., Figure 2 the controller 12) may detect a blockage in the vent path using the output from a Δ pressure sensor (such as Figure 7 the dP sensor 221) coupled across the FTIV according to, for example, Figure 2 an exemplary method. As described with respect to Figure 2 when closed, the FTIV isolates the fuel system including the fuel tank from the evaporative emission system including the fuel vapor storage canister (e.g., Figure 2isolated from the fuel vapor storage canister 222). The first pressure port of the dP sensor is coupled to the tank side of the FTIV, and the second pressure port of the dP sensor is coupled to the canister side of the FTIV. The signal output by the dP sensor corresponds to the pressure difference at the first and second pressure ports (e.g., between the tank side and the canister side of the FTIV when closed). Thus, the controller can use the dP sensor measurement results to determine if there is a blockage in the ventilation path that could cause deterioration of the fuel vapor storage during canister purge to the intake manifold and during refueling events.

[0167] The dP sensor measurement results (e.g., the differential pressure measured by the dP sensor) are shown in graph 1202; the position of the canister purge valve of the evaporative emission system (e.g., Figure 2 the CPV 212) is shown in graph 1204; the position of the FTIV is shown in graph 1206; the position of the CVV is shown in graph 1208; and an indication of a blockage in the ventilation path is shown in graph 1210. For all of the above graphs, the horizontal axis represents time, where time increases from left to right along the horizontal axis. The vertical axis represents each of the labeled parameters. For graph 1202, the dP sensor differential pressure measurement results increase upward along the vertical axis. As noted, positive values (e.g., values above the horizontal axis) indicate that the tank side pressure (P 箱 ) is greater than the canister side pressure (P 炭罐 ), while negative values (e.g., values below the horizontal axis) indicate that the tank side pressure is less than the canister side pressure. For graphs 1204, 1206, and 1208, the vertical axis represents whether each valve (the CPV, FTIV, and CVV respectively) is open or closed. For graph 1210, the vertical axis represents whether a blockage in the ventilation path is detected ("yes" or "no").

[0168] Throughout Figure 12 the exemplary timeline 1200, the engine is on, the engine speed is above zero and combustion is occurring within the engine cylinders. Additionally, the engine is operating naturally aspirated, resulting in a manifold air pressure (MAP) less than atmospheric pressure (e.g., manifold vacuum). Before time t1, the CPV is closed (graph 1204), isolating the evaporative emission system from the engine intake manifold; and the FTIV is closed (graph 1206), isolating the canister side of the FTIV from the fuel tank side of the FTIV. Additionally, the CVV is open (graph 1208), coupling the canister side to the atmosphere. Thus, the canister side is at atmospheric pressure. As shown in graph 1202, before time t1, the dP sensor measurement results (graph 1202) indicate that the tank side pressure is greater than the canister side pressure. Thus, the fuel tank pressure is above atmospheric pressure.

[0169] At time t1, conditions for evaluating the ventilation path are met, such as relative to Figure 7 as described, such as an indication of no FTIV degradation. Accordingly, the CPV is commanded to open (graph 1204), thereby connecting the canister side to the intake manifold; while maintaining the CVV open (graph 1208). Accordingly, the intake manifold evacuates the evaporative emission system, and fresh air is drawn into the evaporative emission system through the ventilation duct and the open CVV.

[0170] Starting at time t1, the relative vacuum on the canister side is monitored. The relative vacuum on the canister side can be determined based on the dP sensor measurement results (graph 1202). For example, when the intake manifold evacuates the evaporative emission system, the pressure difference between the canister side of the FTIV and the tank side of the FTIV can increase. Although the tank side pressure can fluctuate, such as due to diurnal temperature, the tank side pressure is not expected to change significantly during the ventilation path evaluation. Accordingly, the change in the differential pressure measured by the dP sensor can be attributed to the change in the canister side pressure, and the controller can interpret the increase in the differential pressure as an increase in the relative vacuum on the canister side (e.g., a decrease in the relative pressure on the canister side). However, due to the open CVV and the fresh air entering the evaporative emission system through the ventilation path, a limited amount of vacuum can accumulate in the evaporative emission system, which can be less than the amount of vacuum before the evaporative emission system reaches pressure equilibrium and the amount of vacuum in the intake manifold remains substantially constant. However, if the ventilation path is blocked, fresh air may not be drawn into the evaporative emission system, and the vacuum can continue to accumulate. Accordingly, the controller monitors the relative vacuum on the canister side for a threshold duration.

[0171] At time t2, the threshold duration has elapsed. The relative vacuum on the canister side remains constant, as shown by the dP sensor measurement results (curve 1202) remaining stable at time t2 and between time t2 and time t3. Accordingly, the ventilation path is unobstructed, such that there is sufficient air flow through the ventilation path to displace the air and vapor purged into the intake manifold, and no blockage of the ventilation path is indicated (graph 1210). In the case where the ventilation path evaluation is complete, at time t3, the CPV is commanded to close (curve 1204) to isolate the evaporative emission system from the intake manifold. The canister side pressure rebalances to atmospheric pressure, as shown by the dP sensor measurement results (graph 1202) decreasing as the canister side vacuum decreases. For example, the differential pressure measurement results can return to approximately the starting differential pressure measurement results (e.g., the differential pressure before the ventilation path evaluation at time t1).

[0172] Conversely, if the ventilation path is blocked, the relative vacuum on the canister side can continue to increase when the intake manifold evacuates the canister side and air is not drawn through the ventilation path. For example, as shown by dash segment 1202a, after the threshold duration has elapsed at time t2, the differential pressure (and thus, the relative vacuum on the canister side) can remain below the canister side relative vacuum threshold. Thus, at time t3, a blocked ventilation path is indicated (dash segment 1210a). Additionally, in the presence of a blocked ventilation path, commanding the opening of the CVV at time t3 may not connect the evaporative emission system to the atmosphere. In Figure 12 the example of, the canister side remains under vacuum and does not rebalance to atmospheric pressure (dash segment 1202a). However, with the CPV closed, the manifold vacuum does not continue to evacuate the evaporative emission system, and thus, the canister side relative vacuum can remain substantially constant.

[0173] As described herein, a single Δ pressure sensor can be used not only to diagnose components of the evaporative emission system and the fuel system, but also for fuel tank pressure control. Now turning to Figure 13 , an exemplary timeline 1300 for controlling the pressure in a fuel tank during engine operation is shown. For example, a controller (e.g., Figure 2 controller 12) can, for example, in accordance with Figure 8 the exemplary method, in response to a depressurization condition, utilize the output from a Δ pressure sensor (such as Figure 2 dP sensor 221) coupled across a fuel tank isolation valve to depressurize the fuel tank. The fuel tank can be, for example, a sealed fuel tank included in a PHEV, such as part of a NIRCOS. As described with respect to Figure 2 , when closed, the FTIV isolates the fuel system including the fuel tank from the evaporative emission system including a fuel vapor storage canister, which can be a "refuel only" fuel vapor storage canister. The first pressure port of the dP sensor is coupled to the tank side of the FTIV, while the second pressure port of the dP sensor is coupled to the canister side of the FTIV. The signal output by the dP sensor corresponds to the pressure difference at the first and second pressure ports (e.g., between the tank side and the canister side of the FTIV when closed). Thus, the controller can use the dP sensor measurements to determine whether to depressurize the fuel tank.

[0174] The dP sensor measurements (e.g., the differential pressure measured by the dP sensor) are shown in graph 1302; the canister purge valve of the evaporative emission system is shown in graph 1304 (e.g., Figure 2the position of the CPV 212); and the position of the FTIV is shown in plot 1306. For all of the above plots, the horizontal axis represents time, where time increases from left to right along the horizontal axis. The vertical axis represents each of the marked parameters. For plot 1302, the dP sensor differential pressure measurement results increase upward along the vertical axis. As indicated, positive values (e.g., values above the horizontal axis) indicate that the tank side pressure (P 箱 ) is greater than the canister side pressure (P 炭罐 ), while negative values (e.g., values below the horizontal axis) indicate that the tank side pressure is less than the canister side pressure. For plots 1304 and 1306, the vertical axis represents whether each valve (respectively, the CPV and the FTIV) is open or closed. Additionally, the tank side relative pressure threshold is indicated by dash line 1308.

[0175] Throughout Figure 13 the exemplary timeline 1300, the engine is on, the engine speed is above zero and combustion is occurring within the engine cylinders. Additionally, the engine is operating by natural aspiration, thereby generating a manifold air pressure (MAP) that is less than atmospheric pressure (e.g., a manifold vacuum). Prior to time t1, the CPV is closed (plot 1304), thereby isolating the evaporative emission system from the engine intake manifold; and the FTIV is closed (plot 1306), thereby isolating the canister side of the FTIV from the fuel tank side of the FTIV. Additionally, the canister vent valve of the evaporative emission system (e.g., Figure 2 the CVV 214) remains open (not shown) throughout the timeline 1300, thereby coupling the canister side to the atmosphere. Thus, the canister side is at atmospheric pressure, and the dP sensor measurement results (plot 1302) indicate the tank side pressure relative to atmospheric pressure.

[0176] As shown in plot 1302, prior to time t1, the dP sensor measurement results indicate that the tank side pressure is greater than the canister side pressure. Thus, the fuel tank pressure is above atmospheric pressure. Additionally, the tank side relative pressure is greater than the tank side relative pressure threshold (dash line 1308), which indicates that the fuel tank may be approaching the mechanical pressure threshold above which fuel tank deterioration can occur. Thus, at time t1, the CPV is commanded to open (plot 1304) such that the fuel tank pressure can be relieved.

[0177] After opening the CPV at time t1, the dP sensor measurement (graph 1302) increases as the intake manifold evacuates the charcoal canister side of the FTIV, reducing the relative pressure on the charcoal canister side. Consequently, the difference between the tank side pressure and the charcoal canister side pressure increases. Since the charcoal canister side pressure (which is the reference pressure for the tank side relative pressure) changes, the tank side relative pressure threshold (dash 1308) increases at time t2 to reflect the change in differential pressure. For example, after the CPV is opened, once the dP sensor measurement stabilizes, the controller can adjust the tank side relative pressure threshold.

[0178] With the adjusted tank side relative pressure threshold set, between time t2 and time t3, the FTIV is opened and closed in a pulsating manner, such as at a predetermined duty cycle, until the differential pressure (and thus, the tank side relative pressure) is less than the tank side relative pressure threshold. For example, each time the FTIV is opened, the charcoal canister side will evacuate the tank side, resulting in a reduced differential pressure after each opening of the FTIV (e.g., the tank side pressure becomes more similar to the charcoal canister side pressure). Additionally, each time the FTIV is opened, the dP sensor reads a differential pressure of zero or close to zero because when the FTIV is open, the pressure at the first pressure port of the dP sensor can be approximately equal to the pressure at the second pressure port of the dP sensor. Therefore, the differential pressure can be evaluated when the FTIV is closed.

[0179] At time t3, the dP sensor measurement (graph 1302) is less than the tank side relative pressure threshold (dash 1308), indicating that the fuel tank has been sufficiently depressurized. Accordingly, the FTIV is maintained closed (graph 1306), and the CPV is commanded to close (graph 1304), isolating the evaporative emission system from the intake manifold. With the CPV closed and the CVV remaining open (not shown), the charcoal canister side re - balances to atmospheric pressure, as indicated by the decrease in differential pressure (curve 1302). Additionally, with the intake manifold no longer evacuating the charcoal canister side, the tank side relative pressure threshold (dash 1308) returns to the starting value, which is the charcoal canister side pressure threshold relative to atmospheric pressure. As shown in graph 1302, after the charcoal canister side re - balances to atmospheric pressure, the dP sensor measurement is below the tank side relative pressure threshold and remains relatively stable.

[0180] Next, Figure 14 An exemplary timeline 1400 for depressurizing a fuel tank for a refueling event (e.g., a second example of depressurization conditions) is shown. For example, a controller (e.g., Figure 2 controller 12) can, for example, according to Figure 8 an exemplary method, utilize a Δ - pressure sensor coupled across a fuel tank isolation valve (such as Figure 2The output of the dP sensor 221) is used to depressurize the fuel tank. The fuel tank can be, for example, a sealed fuel tank included in a PHEV. As described with respect to Figure 2 When closed, the FTIV isolates the fuel system including the fuel tank from the evaporative emission system including the fuel vapor storage canister (e.g., Figure 2 the fuel vapor storage canister 222), which can be a "refueling-only" fuel vapor storage canister. The first pressure port of the dP sensor is coupled to the tank side of the FTIV, and the second pressure port of the dP sensor is coupled to the canister side of the FTIV. The signal output by the dP sensor corresponds to the pressure difference between the first pressure port and the second pressure port (e.g., between the tank side and the canister side of the FTIV when closed). Thus, the controller can use the dP sensor measurement results during a refueling event to determine whether to depressurize the fuel tank.

[0181] The dP sensor measurement results (e.g., the differential pressure measured by the dP sensor) are shown in graph 1402; the indication of a refueling request is shown in graph 1404; the position of the FTIV is shown in graph 1406; and the status of the fuel port is shown in graph 1408. For all of the above graphs, the horizontal axis represents time, where time increases from left to right along the horizontal axis. The vertical axis represents each of the marked parameters. For graph 1402, the dP sensor differential pressure measurement results increase upward along the vertical axis. As indicated, a positive value (e.g., a value above the horizontal axis) indicates that the tank side pressure (P 箱 ) is greater than the canister side pressure (P 炭罐 ), while a negative value (e.g., a value below the horizontal axis) indicates that the tank side pressure is less than the canister side pressure. For graph 1404, the vertical axis represents whether a refueling event ("yes" or "no") has been requested, such as by the vehicle driver pressing a refueling button (e.g., Figure 1 the refueling button 197) on the instrument panel. For graph 1406, the vertical axis represents whether the FTIV is open or closed. For graph 1408, the vertical axis represents whether the fuel port is locked (which prevents opening the fuel tank and refueling) or unlocked (which enables opening the fuel tank and refueling).

[0182] Throughout Figure 14 the exemplary timeline 1400, the engine is off, the engine is stationary and no combustion occurs within the engine cylinders. Although not shown, it should still be understood that throughout timeline 1400, the canister purge valve (e.g., Figure 2 the CPV 212) remains closed, isolating the evaporative emission system from the engine intake manifold; and the canister vent valve (e.g., Figure 2 the CVV 214) remains open, coupling the evaporative emission system to the atmosphere.

[0183] Prior to time t1, the FTIV is closed (graph 1406), isolating the canister side of the FTIV from the fuel tank side of the FTIV; and no refueling event is requested (graph 1404). The fuel port (e.g., Figure 2 the fuel port 286) remains locked, preventing access to the refueling port of the fuel tank (e.g., Figure 2 the refueling port 284). With the canister side connected to the atmosphere through the open CVV, the dP sensor measurement (graph 1402) indicates the tank side pressure relative to atmospheric pressure. As shown in graph 1402, the tank side pressure is greater than the canister side pressure and, thus, greater than atmospheric pressure.

[0184] At time t1, a refueling event is requested (graph 1404), such as by the vehicle operator. Since the tank side pressure is greater than atmospheric pressure (e.g., greater than a threshold differential pressure above atmospheric pressure), the fuel port remains locked (graph 1408). To relieve the tank side pressure, starting at time t2, the fuel tank is vented by opening and closing the FTIV in a pulsating manner, such as at a predetermined duty cycle (graph 1406). Each time the FTIV is opened, fuel vapor is directed from the fuel tank to the fuel vapor storage canister, causing a reduced differential pressure (e.g., the tank side pressure becomes more similar to the canister side pressure) after each opening of the FTIV. The fuel vapor is adsorbed by the adsorbent within the fuel vapor canister, and clean air (e.g., fuel vapor - free) exits through the open vent into the atmosphere, maintaining the canister side at atmospheric pressure. Additionally, each time the FTIV is opened, the dP sensor reads a differential pressure of zero or close to zero because when the FTIV is open, the pressure at the first pressure port of the dP sensor is approximately equal to the pressure at the second pressure port of the dP sensor. Thus, the differential pressure can be evaluated when the FTIV is closed.

[0185] At time t3, the fuel tank is fully depressurized such that when the FTIV is closed, the dP sensor measurement (graph 1402) shows a differential pressure of zero. In response to the tank side pressure being equal to the canister side pressure (e.g., atmospheric pressure), at time t4, the FTIV is commanded to open (graph 1406) and the fuel port is unlocked (graph 1408). Thus, the vehicle driver can access the refueling port and refill the fuel tank. When fuel is added to the fuel tank, the refueling vapor is directed through the open FTIV to the fuel vapor storage canister, where the refueling vapor is adsorbed by the adsorbent, and clean air is directed from the evaporative emission system through the open vent to the atmosphere.

[0186] At time t5, the refueling event is complete and, as a result, the refueling event is no longer requested (graph 1404). Accordingly, the FTIV is commanded to close (graph 1406), thereby isolating the tank side of the FTIV from the canister side of the FTIV. As a result, fuel vapor will no longer flow from the fuel tank to the fuel vapor storage canister. Additionally, the fuel fill port is locked (graph 1408), thereby preventing access to the refueling port until a subsequent refueling event is requested.

[0187] In this manner, a single Δ pressure sensor is used in the NIRCOS system to determine the differential pressure across the FTIV that isolates the fuel tank of the fuel system from the fuel vapor storage canister of the evaporative emissions system. Specifically, the differential pressure can be measured when the FTIV is closed. The differential pressure can be used to determine the relative pressure or vacuum on the fuel tank side (e.g., of the fuel system) of the FTIV and the relative pressure or vacuum on the fuel vapor storage canister side (e.g., of the evaporative emissions system) of the FTIV. Additionally, the relative pressures measured by the Δ pressure sensor can be used for evaporative emissions system and fuel system diagnostic testing. The technical effect of a single Δ pressure sensor coupled across the fuel tank isolation valve disposed between the fuel vapor storage canister of the evaporative emissions system and the fuel tank of the fuel system is that the differential pressure measured by the Δ pressure sensor can be used to inspect each of the fuel tank isolation valve, the fuel system, and the evaporative emissions system for degradation. Additionally, the relative pressure of the fuel system can be used for fuel tank pressure control, such as by venting the fuel tank in response to the presence of a fuel tank depressurization condition. By opening and closing the FTIV in a pulsating manner during venting and measuring the differential pressure only when the FTIV is closed, feedback regarding the relative pressure on the fuel tank side of the FTIV can be maintained, thereby enabling controlled and effective fuel tank depressurization. The technical effect of measuring the differential pressure of the evaporative emissions system when the fuel tank isolation valve disposed between the fuel vapor storage canister of the evaporative emissions system and the fuel tank of the fuel system is closed rather than when the fuel tank isolation valve is open, using a single Δ pressure sensor coupled across the fuel tank isolation valve, is that the relative fuel tank pressure can be determined based on the measured differential pressure. Accordingly, a single Δ pressure sensor can replace two pressure sensors (one coupled to the fuel system and one coupled to the evaporative emissions system), thereby reducing vehicle cost.

[0188] As a first example, a method includes: differentiating degradation between each of a sealed fuel tank, an evaporative emissions system, and the FTIV based on a differential pressure measured by a differential pressure sensor coupled by a cross fuel tank isolation valve (FTIV), the FTIV being positioned between the sealed fuel tank and the evaporative emissions system. In the previous example, additionally or alternatively, a first pressure port of the differential pressure sensor is fluidly coupled between the FTIV and the sealed fuel tank, and wherein a second pressure port of the differential pressure sensor is fluidly coupled between the FTIV and a fuel vapor storage charcoal canister of the evaporative emissions system. In any or all of the foregoing examples, additionally or alternatively, no limiting components are coupled between the sealed fuel tank and the FTIV, and / or no limiting components are coupled between the fuel vapor storage charcoal canister and the FTIV. In any or all of the foregoing examples, additionally or alternatively, no limiting components are coupled between the first pressure port of the differential pressure sensor and the sealed fuel tank, and / or no limiting components are coupled between the second pressure port of the differential pressure sensor and the fuel vapor storage charcoal canister. In any or all of the foregoing examples, additionally or alternatively, differentiating degradation between each of the sealed fuel tank, the evaporative emissions system, and the FTIV further includes: setting a corresponding diagnostic code in a controller based on the differentiation, and further includes: differentiating degradation between the sealed fuel tank and the FTIV rather than the evaporative emissions system when the differential pressure is between a positive pass threshold and a negative pass threshold with the FTIV closed and the evaporative emissions system in communication with the atmosphere. In any or all of the foregoing examples, additionally or alternatively, differentiating degradation between the sealed fuel tank and the FTIV rather than the evaporative emissions system further includes: actuating a vacuum pump of the evaporative emissions system to evacuate the evaporative emissions system to a target vacuum amount; indicating degradation of the FTIV rather than the sealed fuel tank in response to the differential pressure remaining between the positive pass threshold and the negative pass threshold; and performing a fuel tank pressure relief test in response to the differential pressure increasing above the positive pass threshold. In any or all of the foregoing examples, additionally or alternatively, the fuel tank pressure relief test includes: commanding the FTIV to open and close at a predetermined duty cycle; measuring the differential pressure when the FTIV is closed; maintaining the FTIV closed in response to the differential pressure decreasing by a threshold amount; monitoring a relative pressure of the sealed fuel tank for a certain duration; and indicating degradation of the sealed fuel tank in response to the relative pressure of the sealed fuel tank reaching or exceeding a threshold pressure within a threshold duration.In any or all of the foregoing examples, additionally or alternatively, the relative pressure of the sealed fuel tank is the pressure of the sealed fuel tank relative to the pressure of the evaporative emissions system, and wherein the pressure of the sealed fuel tank relative to the pressure of the evaporative emissions system is determined based on the differential pressure measured by the differential pressure sensor coupled across the FTIV. In any or all of the foregoing examples, additionally or alternatively, differentiating degradation between each of the sealed fuel tank, the evaporative emissions system, and the FTIV further includes: closing the canister vent valve to isolate the evaporative emissions system from the atmosphere; actuating a vacuum pump of the evaporative emissions system until the relative pressure of the evaporative emissions system has decreased by a threshold amount; determining a bleed threshold based on the relative pressure of the evaporative emissions system; monitoring the relative pressure of the evaporative emissions system for a certain duration; and in response to the relative pressure of the evaporative emissions system reaching or exceeding the bleed threshold within a threshold duration, indicating degradation of the evaporative emissions system rather than degradation of the FTIV or degradation of the sealed fuel tank. In any or all of the foregoing examples, additionally or alternatively, the relative pressure of the evaporative emissions system is the pressure of the evaporative emissions system relative to the pressure of the sealed fuel tank, and wherein the pressure of the evaporative emissions system relative to the pressure of the sealed fuel tank is determined based on the differential pressure measured by the differential pressure sensor coupled across the FTIV.

[0189] As a second example, a method for an engine includes: indicating deterioration of a fuel tank isolation valve (FTIV) in response to a differential pressure measured as zero by a Δ pressure sensor coupled across the FTIV that is closed and has its fuel vapor storage canister side evacuated while the fuel tank is coupled to the fuel vapor storage canister; indicating deterioration of the fuel tank side of the FTIV in response to a relative pressure on the fuel tank side increasing above a first threshold during a fuel tank pressure relief test; and indicating deterioration of the fuel vapor storage canister side of the FTIV in response to a relative pressure on the fuel vapor storage canister side increasing above a second threshold during a canister side engine off test. In the previous example, additionally or alternatively, the fuel tank pressure relief test includes: evacuating the fuel vapor storage canister side of the FTIV while the FTIV is closed; opening and closing the FTIV at a predetermined duty cycle to evacuate the fuel tank side of the FTIV by the fuel vapor storage canister side of the FTIV; keeping the FTIV closed while coupling the canister side of the FTIV to the atmosphere; and monitoring the relative pressure on the fuel tank side of the FTIV for a certain duration. In any or all of the foregoing examples, additionally or alternatively, the relative pressure on the fuel tank side of the FTIV is measured by the Δ pressure sensor and is the pressure of the fuel tank side relative to the fuel vapor storage canister of the FTIV. In any or all of the foregoing examples, additionally or alternatively, the canister side engine off test includes: isolating the fuel vapor storage canister side of the FTIV from the atmosphere and the intake manifold of the engine; evacuating the fuel vapor storage canister side of the FTIV while the FTIV is closed until the relative pressure on the fuel vapor storage canister side of the FTIV has decreased by a threshold amount; and monitoring the relative pressure on the fuel vapor storage canister side of the FTIV for a certain duration. In any or all of the foregoing examples, additionally or alternatively, the relative pressure on the fuel vapor storage canister side of the FTIV is measured by the Δ pressure sensor and is the pressure of the fuel vapor storage canister side of the FTIV relative to the pressure on the fuel tank side of the FTIV.

[0190] As a third example, a system for a vehicle includes: an engine system including an engine configured to propel the vehicle by burning air and fuel; a fuel system including a fuel tank for storing the fuel; an evaporative emissions system fluidly connected to the fuel system via a pipe and fluidly connected to an intake passage of the engine via a purge line, the pipe including a fuel tank isolation valve (FTIV), the evaporative emissions system including a fuel vapor storage canister; a canister vent valve positioned in a vent passage of the evaporative emissions system; a canister purge valve positioned in the purge line; a Δ pressure sensor coupled across the FTIV, the Δ pressure sensor including a first pressure port fluidly connected to the pipe between the fuel tank and the FTIV and a second pressure port fluidly connected to the pipe between the fuel vapor storage canister and the FTIV; and a controller storing instructions in a non-transitory memory, which when executed cause the controller to: determine a differential pressure across the FTIV based on a voltage signal output by the Δ pressure sensor; determine at least one of a fuel system relative pressure and a fuel system relative vacuum based on the differential pressure across the FTIV; determine at least one of an evaporative emissions system relative pressure and an evaporative emissions system relative vacuum based on the differential pressure across the FTIV; and, when the engine is off, evaluate at least one of the FTIV and the fuel system for degradation based on the differential pressure across the FTIV. In the previous example, additionally or alternatively, the evaporative emissions system further includes a vacuum pump, and evaluating at least one of the FTIV and the fuel system for degradation includes: closing the canister vent valve, maintaining the canister purge valve closed, and actuating the vacuum pump in response to a differential pressure between a positive flow threshold and a negative flow threshold when the FTIV is closed; indicating FTIV degradation in response to the differential pressure remaining between the positive flow threshold and the negative flow threshold; indicating no FTIV degradation and opening and closing the FTIV at a predetermined duty cycle in response to the differential pressure increasing above the positive flow threshold or decreasing below the negative flow threshold; maintaining the FTIV closed once the fuel system relative pressure has decreased by a first threshold amount, the fuel system relative pressure being measured when the FTIV is closed; monitoring the fuel system relative pressure for a first threshold duration; indicating fuel system degradation in response to the fuel system relative pressure reaching or exceeding a fuel system relative pressure threshold; and indicating no fuel system degradation in response to the fuel system relative pressure remaining below the fuel system relative pressure threshold.In any or all of the foregoing examples, additionally or alternatively, the controller stores additional instructions in a non-transitory memory that, when executed, cause the controller to: in response to an indication of no FTIV degradation, when the engine is off, evaluate the evaporative emission system for degradation by commanding the canister purge valve to close, maintaining the canister vent valve and the FTIV closed, evacuating the evaporative emission system with the vacuum pump until the relative pressure of the evaporative emission system has decreased by a second threshold amount, and monitoring the relative pressure of the evaporative emission system for a second threshold duration; indicate evaporative emission system degradation in response to the relative pressure of the evaporative emission system reaching or exceeding an evaporative emission system relative pressure threshold; and indicate no evaporative emission system degradation in response to the relative pressure of the evaporative emission system remaining below the evaporative emission system relative pressure threshold. In any or all of the foregoing examples, additionally or alternatively, the controller stores additional instructions in a non-transitory memory that, when executed, cause the controller to: when the engine is on, evaluate the purge path including the purge line and the canister purge valve for blockage by commanding the canister vent valve to close, maintaining the FTIV closed, and commanding the canister purge valve to open to draw a vacuum on the evaporative emission system from the engine's intake manifold; indicate purge path blockage in response to the relative vacuum of the evaporative emission system remaining below an evaporative emission system relative vacuum threshold; and indicate no purge path blockage in response to the relative vacuum of the evaporative emission system reaching or exceeding the evaporative emission system relative vacuum threshold. In any or all of the foregoing examples, additionally or alternatively, the controller stores additional instructions in a non-transitory memory that, when executed, cause the controller to: when the engine is on, evaluate the vent path including the vent passage and the canister vent valve for blockage by commanding the canister vent valve to close, maintaining the FTIV closed, and commanding the canister purge valve to open to draw a vacuum on the evaporative emission system from the engine's intake manifold; indicate vent path blockage in response to the relative vacuum of the evaporative emission system continuing to increase after a third threshold duration has elapsed; and indicate no vent path blockage in response to the relative vacuum of the evaporative emission system stabilizing before the third threshold duration has elapsed.

[0191] In another representation, a method includes: when the engine is off, diagnosing degradation of at least one of a fuel tank, an evaporative emission system coupled to the fuel tank via a pipe, and a fuel tank isolation valve (FTIV) based on an output of a Δ - pressure sensor coupled across the FTIV, the FTIV being disposed within the pipe; and when the engine is on, checking for blockage in at least one of a purge path and a vent path of the evaporative emission system based on the output of the Δ - pressure sensor. As a first example, diagnosing degradation of at least one of the fuel tank, the evaporative emission system, and the fuel tank isolation valve includes: the Δ - pressure sensor measuring a pressure difference between the evaporative emission system and the fuel system while the evaporative emission system is being evacuated and the FTIV remains closed, the pressure difference being less than a threshold. As a second example, checking for blockage in at least one of the purge path and the vent path includes: opening a canister purge valve of the evaporative emission system to evacuate the evaporative emission system through an intake manifold of the engine.

[0192] It should be noted that the exemplary control and estimation routines included herein can be used with various engine and / or vehicle system configurations. The control methods and routines disclosed herein can be stored as executable instructions in a non - transitory memory and can be executed by a control system including a controller in conjunction with various sensors, actuators, and other engine hardware. The specific routines described herein can represent one or more of any number of processing strategies (such as event - driven, intermittent - driven, multi - tasking, multi - threading, etc.). Thus, the various actions, operations, and / or functions shown can be executed in the order shown, executed in parallel, or in some cases, omitted. Similarly, the processing order is not necessarily required to achieve the features and advantages of the exemplary embodiments described herein, but is provided for ease of illustration and description. One or more of the actions, operations, and / or functions shown can be repeatedly executed according to the particular strategy used. Additionally, the actions, operations, and / or functions described can be graphically represented as code to be programmed into the non - transitory memory of a computer - readable storage medium for an engine control system, where the described actions are implemented by executing the instructions in a system including various engine hardware components in conjunction with an electronic controller.

[0193] It should be understood that the configurations and routines disclosed herein are exemplary in nature and these specific embodiments should not be considered to have a limiting meaning since many variations are possible. For example, the above techniques can be applied to V - type 6 - cylinder, inline 4 - cylinder, inline 6 - cylinder, V - type 12 - cylinder, opposed 4 - cylinder, and other engine types. The subject matter of the present disclosure includes all novel and non - obvious combinations and sub - combinations of the various systems and configurations and other features, functions, and / or characteristics disclosed herein.

[0194] The following claims particularly point out certain combinations and sub - combinations that are considered novel and non - obvious. These claims may refer to "a" element or "a first" element or their equivalents. Such claims should be understood to include the combination of one or more such elements, neither requiring nor precluding two or more such elements. Other combinations and sub - combinations of the disclosed features, functions, elements, and / or characteristics may be claimed by modifying these claims or by presenting new claims in this application or related applications. Such claims are also considered to be included within the subject matter of this disclosure, whether broader, narrower, the same, or different in scope compared to the original claims.

[0195] According to the present invention, there is provided a method having: differentiating degradation between each of a sealed fuel tank, an evaporative emission system, and the FTIV based on a differential pressure measured by a differential pressure sensor coupled by a cross - fuel - tank isolation valve (FTIV), the FTIV being positioned between the sealed fuel tank and the evaporative emission system.

[0196] According to one embodiment, a first pressure port of the differential pressure sensor is fluidly coupled between the FTIV and the sealed fuel tank, and wherein a second pressure port of the differential pressure sensor is fluidly coupled between the FTIV and a fuel vapor storage canister of the evaporative emission system.

[0197] According to one embodiment, unrestricted components are coupled between the sealed fuel tank and the FTIV, and / or unrestricted components are coupled between the fuel vapor storage canister and the FTIV.

[0198] According to one embodiment, unrestricted components are coupled between the first pressure port of the differential pressure sensor and the sealed fuel tank, and / or unrestricted components are coupled between the second pressure port of the differential pressure sensor and the fuel vapor storage canister.

[0199] According to one embodiment, differentiating degradation between each of the sealed fuel tank, the evaporative emission system, and the FTIV further includes: setting a corresponding diagnostic code in a controller based on the differentiation, and further includes: differentiating degradation between the sealed fuel tank and the FTIV rather than the evaporative emission system when the differential pressure is between a positive - pass threshold and a negative - pass threshold with the FTIV closed and the evaporative emission system in communication with the atmosphere.

[0200] According to one embodiment, differentiating degradation between the sealed fuel tank and the FTIV rather than the evaporative emissions system further includes: actuating a vacuum pump of the evaporative emissions system to evacuate the evaporative emissions system to a target vacuum amount; indicating degradation of the FTIV rather than the sealed fuel tank in response to the differential pressure remaining between the positive-pass threshold and the negative-pass threshold; and performing a fuel tank pressure relief test in response to the differential pressure increasing above the positive-pass threshold.

[0201] According to one embodiment, the fuel tank pressure relief test includes: commanding the FTIV to open and close at a predetermined duty cycle; measuring the differential pressure while the FTIV is closed; maintaining the FTIV closed in response to the differential pressure decreasing by a threshold amount; monitoring the relative pressure of the sealed fuel tank for a certain duration; and indicating degradation of the sealed fuel tank in response to the relative pressure of the sealed fuel tank reaching or exceeding a threshold pressure within the threshold duration.

[0202] According to one embodiment, the relative pressure of the sealed fuel tank is the pressure of the sealed fuel tank relative to the pressure of the evaporative emissions system, and wherein the pressure of the sealed fuel tank relative to the pressure of the evaporative emissions system is determined based on the differential pressure measured by the Δ pressure sensor coupled across the FTIV.

[0203] According to one embodiment, differentiating degradation between each of the sealed fuel tank, the evaporative emissions system, and the FTIV further includes: closing a canister vent valve to isolate the evaporative emissions system from the atmosphere; actuating a vacuum pump of the evaporative emissions system until the relative pressure of the evaporative emissions system decreases by a threshold amount; determining a relief threshold based on the relative pressure of the evaporative emissions system; monitoring the relative pressure of the evaporative emissions system for a certain duration; and indicating degradation of the evaporative emissions system rather than the FTIV or the sealed fuel tank in response to the relative pressure of the evaporative emissions system reaching or exceeding the relief threshold within the threshold duration.

[0204] According to one embodiment, the relative pressure of the evaporative emissions system is the pressure of the evaporative emissions system relative to the pressure of the sealed fuel tank, and wherein the pressure of the evaporative emissions system relative to the pressure of the sealed fuel tank is determined based on the differential pressure measured by the Δ pressure sensor coupled across the FTIV.

[0205] According to the present invention, there is provided a method for an engine, which has: indicating deterioration of the fuel tank isolation valve (FTIV) in response to a differential pressure measured to be zero when the FTIV is closed and the fuel vapor storage canister side of the FTIV is evacuated, across the FTIV coupled between a fuel tank and a fuel vapor storage canister; indicating deterioration of the fuel tank side of the FTIV in response to a relative pressure on the fuel tank side increasing above a first threshold during a fuel tank pressure relief test; and indicating deterioration of the fuel vapor storage canister side of the FTIV in response to a relative pressure on the fuel vapor storage canister side increasing above a second threshold during an engine-off test on the canister side.

[0206] According to one embodiment, the fuel tank pressure relief test includes: evacuating the fuel vapor storage canister side of the FTIV when the FTIV is closed; opening and closing the FTIV at a predetermined duty cycle to evacuate the fuel tank side of the FTIV by the fuel vapor storage canister side of the FTIV; keeping the FTIV closed while coupling the canister side of the FTIV to the atmosphere; and monitoring the relative pressure on the fuel tank side of the FTIV for a certain duration.

[0207] According to one embodiment, the relative pressure on the fuel tank side of the FTIV is measured by the differential pressure sensor and is the pressure of the fuel tank side relative to the fuel vapor storage canister of the FTIV.

[0208] According to one embodiment, the engine-off test on the canister side includes: isolating the fuel vapor storage canister side of the FTIV from the atmosphere and the intake manifold of the engine; evacuating the fuel vapor storage canister side of the FTIV when the FTIV is closed until the relative pressure on the fuel vapor storage canister side of the FTIV has decreased by a threshold amount; and monitoring the relative pressure on the fuel vapor storage canister side of the FTIV for a certain duration.

[0209] According to one embodiment, the relative pressure on the fuel vapor storage canister side of the FTIV is measured by the differential pressure sensor and is the pressure of the fuel vapor storage canister side of the FTIV relative to the pressure on the fuel tank side of the FTIV.

[0210] According to the present invention, there is provided a system for a vehicle having: an engine system including an engine configured to propel the vehicle by combusting air and fuel; a fuel system including a fuel tank for storing the fuel; an evaporative emission system fluidly connected to the fuel system via a pipe and fluidly connected to an intake passage of the engine via a purge line, the pipe including a fuel tank isolation valve (FTIV), the evaporative emission system including a fuel vapor storage canister; a canister vent valve positioned in a vent passage of the evaporative emission system; a canister purge valve positioned in the purge line; a Δ pressure sensor coupled across the FTIV, the Δ pressure sensor including a first pressure port fluidly connected to the pipe between the fuel tank and the FTIV and a second pressure port fluidly connected to the pipe between the fuel vapor storage canister and the FTIV; and a controller storing instructions in a non-transitory memory, which when executed cause the controller to: determine a differential pressure across the FTIV based on a voltage signal output by the Δ pressure sensor; determine at least one of a fuel system relative pressure and a fuel system relative vacuum based on the differential pressure across the FTIV; determine at least one of an evaporative emission system relative pressure and an evaporative emission system relative vacuum based on the differential pressure across the FTIV; and when the engine is off, evaluate at least one of the FTIV and the fuel system for degradation based on the differential pressure across the FTIV.

[0211] According to one embodiment, the evaporative emission system further includes a vacuum pump, and evaluating at least one of the FTIV and the fuel system for degradation includes: closing the canister vent valve, maintaining the canister purge valve closed, and actuating the vacuum pump in response to a differential pressure between a positive flow threshold and a negative flow threshold when the FTIV is closed; indicating FTIV degradation in response to the differential pressure remaining between the positive flow threshold and the negative flow threshold; indicating no FTIV degradation and opening and closing the FTIV at a predetermined duty cycle in response to the differential pressure increasing above the positive flow threshold or decreasing below the negative flow threshold; maintaining the FTIV closed once the fuel system relative pressure has decreased by a first threshold amount, the fuel system relative pressure being measured when the FTIV is closed; monitoring the fuel system relative pressure for a first threshold duration; indicating fuel system degradation in response to the fuel system relative pressure reaching or exceeding a fuel system relative pressure threshold; and indicating no fuel system degradation in response to the fuel system relative pressure remaining below the fuel system relative pressure threshold.

[0212] According to one embodiment, the controller stores additional instructions in a non-transitory memory, which when executed cause the controller to: in response to an indication of no FTIV deterioration, when the engine is off, evaluate the evaporative emission system for deterioration by commanding the canister vent valve to close, maintaining the canister purge valve and the FTIV closed, evacuating the evaporative emission system using the vacuum pump until the relative pressure of the evaporative emission system has decreased by a second threshold amount, and monitoring the relative pressure of the evaporative emission system for a second threshold duration; indicate evaporative emission system deterioration in response to the relative pressure of the evaporative emission system reaching or exceeding an evaporative emission system relative pressure threshold; and indicate no evaporative emission system deterioration in response to the relative pressure of the evaporative emission system remaining below the evaporative emission system relative pressure threshold.

[0213] According to one embodiment, the controller stores additional instructions in a non-transitory memory, which when executed cause the controller to: when the engine is on, evaluate the purge path including the purge line and the canister purge valve for blockage by commanding the canister vent valve to close, maintaining the FTIV closed, and commanding the canister purge valve to open to draw a vacuum on the evaporative emission system from the intake manifold of the engine; indicate purge path blockage in response to the relative vacuum of the evaporative emission system remaining below an evaporative emission system relative vacuum threshold; and indicate no purge path blockage in response to the relative vacuum of the evaporative emission system reaching or exceeding the evaporative emission system relative vacuum threshold.

[0214] According to one embodiment, the controller stores additional instructions in a non-transitory memory, which when executed cause the controller to: when the engine is on, evaluate the vent path including the vent passage and the canister vent valve for blockage by commanding the canister vent valve to close, maintaining the FTIV closed, and commanding the canister purge valve to open to draw a vacuum on the evaporative emission system from the intake manifold of the engine; indicate vent path blockage in response to the relative vacuum of the evaporative emission system continuing to increase after a third threshold duration has elapsed; and indicate no vent path blockage in response to the relative vacuum of the evaporative emission system stabilizing before the third threshold duration has elapsed.

Claims

1. A method for a vehicle, comprising: Distinguishing deterioration between each of a sealed fuel tank, an evaporative emission system, and the FTIV (Fuel Tank Isolation Valve) based on a differential pressure measured by a differential pressure sensor coupled across the FTIV, the FTIV being positioned between the sealed fuel tank and the evaporative emission system; Wherein distinguishing deterioration between each of the sealed fuel tank, the evaporative emission system, and the FTIV further comprises: when the differential pressure is between a positive pass threshold and a negative pass threshold with the FTIV closed and the evaporative emission system in communication with the atmosphere, distinguishing deterioration between the sealed fuel tank and the FTIV rather than the evaporative emission system.

2. The method according to claim 1, wherein a first pressure port of the differential pressure sensor is fluidly coupled between the FTIV and the sealed fuel tank, and wherein a second pressure port of the differential pressure sensor is fluidly coupled between the FTIV and a fuel vapor storage canister of the evaporative emission system.

3. The method according to claim 2, wherein no restrictive component is coupled between the sealed fuel tank and the FTIV, and / or no restrictive component is coupled between the fuel vapor storage canister and the FTIV.

4. The method according to claim 2, wherein no restrictive component is coupled between the first pressure port of the differential pressure sensor and the sealed fuel tank, and / or no restrictive component is coupled between the second pressure port of the differential pressure sensor and the fuel vapor storage canister.

5. The method according to claim 1, wherein differentiating degradation between each of the sealed fuel tank, the evaporative emission system, and the FTIV further comprises: Setting a corresponding diagnostic code in a controller based on the distinction.

6. The method according to claim 5, wherein distinguishing deterioration between the sealed fuel tank and the FTIV rather than the evaporative emission system further comprises: Actuating a vacuum pump of the evaporative emission system to evacuate the evaporative emission system to a target vacuum amount; Indicating deterioration of the FTIV rather than the sealed fuel tank in response to the differential pressure remaining between the positive pass threshold and the negative pass threshold; and Performing a fuel tank pressure relief test in response to the differential pressure increasing above the positive pass threshold.

7. The method according to claim 6, wherein the fuel tank pressure relief test comprises: Commanding the FTIV to open and close at a predetermined duty cycle; Measuring the differential pressure when the FTIV is closed; Maintaining the FTIV closed in response to the differential pressure decreasing by a threshold amount; Monitoring the relative pressure of the sealed fuel tank for a certain duration; And Indicating deterioration of the sealed fuel tank in response to the relative pressure of the sealed fuel tank reaching or exceeding a threshold pressure within a threshold duration.

8. The method according to claim 7, wherein the relative pressure of the sealed fuel tank is the pressure of the sealed fuel tank relative to the pressure of the evaporative emission system, and wherein the pressure of the sealed fuel tank relative to the pressure of the evaporative emission system is determined based on the differential pressure measured by the differential pressure sensor coupled across the FTIV.

9. The method according to claim 1, wherein differentiating degradation between each of the sealed fuel tank, the evaporative emission system, and the FTIV further comprises: Closing the canister purge valve to isolate the evaporative emission system from the atmosphere; Actuating a vacuum pump of the evaporative emission system until a relative pressure of the evaporative emission system has decreased by a threshold amount; Determining a bleed threshold based on the relative pressure of the evaporative emission system; Monitoring the relative pressure of the evaporative emission system for a certain duration; And In response to the relative pressure of the evaporative emission system reaching or exceeding the bleed threshold within a threshold duration, indicating degradation of the evaporative emission system rather than degradation of the FTIV or degradation of the sealed fuel tank.

10. The method according to claim 9, wherein the relative pressure of the evaporative emission system is the pressure of the evaporative emission system relative to the pressure of the sealed fuel tank, and wherein the pressure of the evaporative emission system relative to the pressure of the sealed fuel tank is determined based on the differential pressure measured by the differential pressure sensor coupled across the FTIV.

11. A system for a vehicle, comprising: An engine system including an engine configured to propel the vehicle by combusting air and fuel; A fuel system including a fuel tank for storing the fuel; An evaporative emission system fluidly communicating with the fuel system via a pipe and fluidly communicating with an intake passage of the engine via a purge line, the pipe including a fuel tank isolation valve, i.e., FTIV, and the evaporative emission system including a fuel vapor storage canister; A canister purge valve positioned in a vent passage of the evaporative emission system; A canister purge valve positioned in the purge line; A differential pressure sensor coupled across the FTIV, the differential pressure sensor including a first pressure port fluidly coupled to the pipe between the fuel tank and the FTIV and a second pressure port fluidly coupled to the pipe between the fuel vapor storage canister and the FTIV; And A controller storing instructions in a non-transitory memory, which when executed, cause the controller to: Determine a differential pressure across the FTIV based on a voltage signal output by the differential pressure sensor; Determine at least one of a fuel system relative pressure and a fuel system relative vacuum based on the differential pressure across the FTIV; Determine at least one of an evaporative emission system relative pressure and an evaporative emission system relative vacuum based on the differential pressure across the FTIV; And When the engine is off, evaluate at least one of the FTIV and the fuel system for degradation based on the differential pressure across the FTIV. Differentiate degradation between each of the fuel tank, the evaporative emission system, and the FTIV, the degradation including: differentiating degradation between the fuel tank and the FTIV rather than the evaporative emission system when the differential pressure is between a positive flow threshold and a negative flow threshold with the FTIV closed and the evaporative emission system in communication with the atmosphere.

12. The system of claim 11, wherein the evaporative emission system further includes a vacuum pump, and wherein evaluating at least one of the FTIV and the fuel system for degradation includes: Closing the canister vent valve, maintaining the canister purge valve closed, and actuating the vacuum pump in response to a differential pressure between a positive flow threshold and a negative flow threshold with the FTIV closed; Indicating FTIV degradation in response to the differential pressure remaining between the positive flow threshold and the negative flow threshold; Indicating no FTIV degradation and opening and closing the FTIV at a predetermined duty cycle in response to the differential pressure increasing above the positive flow threshold or decreasing below the negative flow threshold; Maintaining the FTIV closed once the relative pressure of the fuel system has decreased by a first threshold amount, the relative pressure of the fuel system being measured with the FTIV closed; Monitoring the relative pressure of the fuel system for a first threshold duration; Indicating fuel system degradation in response to the relative pressure of the fuel system reaching or exceeding a fuel system relative pressure threshold; and Indicating no fuel system degradation in response to the relative pressure of the fuel system remaining below the fuel system relative pressure threshold.

13. The system of claim 12, wherein the controller stores additional instructions in a non-transitory memory, which when executed, cause the controller to: In response to an indication of no FTIV degradation, When the engine is off, evaluate the evaporative emission system for degradation by commanding the canister vent valve closed, maintaining the canister purge valve and the FTIV closed, evacuating the evaporative emission system with the vacuum pump until the relative pressure of the evaporative emission system has decreased by a second threshold amount, and monitoring the relative pressure of the evaporative emission system for a second threshold duration; Indicating evaporative emission system degradation in response to the relative pressure of the evaporative emission system reaching or exceeding an evaporative emission system relative pressure threshold; and Indicating no evaporative emission system degradation in response to the relative pressure of the evaporative emission system remaining below the evaporative emission system relative pressure threshold.

14. The system of claim 13, wherein the controller stores additional instructions in a non-transitory memory, which when executed, cause the controller to: When the engine is on, evaluate the purge path including the purge line and the canister purge valve for blockage by commanding the canister vent valve closed, maintaining the FTIV closed, and commanding the canister purge valve open to draw a vacuum on the evaporative emission system from the intake manifold of the engine. Indicating a clog in the purge path in response to the evaporative emission system relative vacuum remaining below the evaporative emission system relative vacuum threshold; and Indicating no clog in the purge path in response to the evaporative emission system relative vacuum reaching or exceeding the evaporative emission system relative vacuum threshold.

15. The system of claim 13, wherein the controller stores additional instructions in a non-transitory memory that, when executed, cause the controller to: When the engine is on, evaluate the vent path including the vent passage and the canister vent valve for clogging by commanding the canister vent valve closed, maintaining the FTIV closed, and commanding the canister purge valve open to draw a vacuum on the evaporative emission system from the engine's intake manifold; Indicating a clog in the vent path in response to the evaporative emission system relative vacuum continuing to increase after a third threshold duration has elapsed; and Indicating no clog in the vent path in response to the evaporative emission system relative vacuum stabilizing before the third threshold duration has elapsed.

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