Method and system for a fuel system

Abstract

Methods and systems for fuel systems are provided. In one example, a fuel system includes a plurality of canisters having a fuel tank isolation valve (FTIV) configured to control a fluid connection between each of the plurality of canisters and a fuel tank. The FTIV is actuated based on one or more of a fuel tank pressure and a load of each of the plurality of canisters.

Description

Technical Field

[0001] The present description generally relates to methods and systems for a fuel system including multiple vapor canisters. Background Art

[0002] A vehicle emissions control system may be configured to store vapors from fuel tank refueling and daytime engine operation in a vapor canister. This configuration is known as onboard fuel recovery and includes a canister sized to adsorb vapors during refueling, running losses, hot soaks, and vehicle shut downs. The stored vapors may be purged during subsequent engine operating conditions. The stored vapors may be directed to the engine intake for combustion, which may affect fuel economy.

[0003] Heavy-duty vehicles may include an off-board recovery vehicle emission control system. An off-board recovery system may not capture vapors during refueling, which may allow its canister to be smaller in size than an on-board configuration. However, to reduce emissions, a heavy-duty vehicle may include an on-board recovery vehicle emission control system.

[0004] Heavy-duty vehicles may include relatively large fuel tanks compared to passenger vehicles. A single large canister in a heavy-duty vehicle may present limitations during refueling, which may cause the refueling pump to shut down prematurely. Therefore, a series canister arrangement may only gradually reach a certain fuel tank size. A parallel canister arrangement in a heavy-duty vehicle may be susceptible to releasing vapors during prolonged vehicle shut-off events with high daytime temperatures due to the vapors loading more canisters through the canister. Therefore, a canister sizing and arrangement for on-board vapor recovery in a heavy-duty vehicle is needed. Summary of the invention

[0005] In one example, the above problems can be solved by a fuel system including a fuel tank, a first canister, a second canister, a third canister, and a first fuel tank isolation valve (FTIV), the FTIV configured to fluidly couple the fuel tank to the first canister vent line, the second canister vent line, and the third canister vent line. In this way, system complexity can be reduced while reducing decompression time and unintentional venting to the atmosphere.

[0006] It should be understood that the above summary is provided to introduce a series of concepts further described in the detailed description in a simplified form. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is uniquely defined by the claims following the detailed description. Furthermore, the claimed subject matter is not limited to embodiments that address any disadvantages mentioned above or in any part of this disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The advantages described herein will be more fully understood by reading the examples of embodiments herein referred to as detailed description either alone or with reference to the accompanying drawings, in which:

[0008] Figure 1 A schematic diagram of an engine included in a hybrid vehicle is shown.

[0009] Figure 2 An example of an engine including multiple canisters is shown.

[0010] Figure 3 A first embodiment of a fuel system including a plurality of canisters is shown.

[0011] Figure 4 A second embodiment of a fuel system including multiple canisters is shown.

[0012] Figure 5 A method for depressurizing a fuel tank of a fuel system based on loading of a plurality of canisters is presented.

[0013] Figure 6 A method for back-purging one or more of a plurality of canisters based on a fuel tank pressure is presented.

[0014] Figure 7 Shows that in the implementation Figure 5 The method changes when the condition of the fuel system changes. DETAILED DESCRIPTION

[0015] The following description relates to systems and methods for managing fuel tank pressure and canister loading of a fuel system. Figure 1 A schematic diagram of an engine included in a hybrid vehicle is shown. Figure 2 A prior art example of an engine including a single canister is shown. Figure 3 A first embodiment of a fuel system including a plurality of canisters is shown. Figure 4 A second embodiment of a fuel system including multiple canisters is shown. Figure 5 A method for depressurizing a fuel tank of a fuel system based on loading of a plurality of canisters is presented. Figure 6 A method for back-purging one or more of a plurality of canisters based on a fuel tank pressure is presented. Figure 7 Shows that in the implementation Figure 5 The method changes when the condition of the fuel system changes.

[0016] Figures 1 to 4An example configuration with relative positioning of various components is shown. In at least one example, if it is shown as directly contacting each other or directly connected, such elements can be referred to as direct contact or direct connection, respectively. Similarly, in at least one example, the elements shown as adjacent or adjacent to each other can be adjacent or adjacent to each other, respectively. As an example, components that are coplanarly contacted with each other can be referred to as coplanar contact. As another example, in at least one example, elements that are positioned apart from each other with only space between them and no other components can be referred to as such. As another example, elements that are shown as above / below each other, on both sides opposite to each other, or on the left / right side of each other can be referred to as such relative to each other. In addition, as shown in the accompanying drawings, in at least one example, the topmost element or the vertex of the element can be referred to as the "top" of the component, and the bottommost element or the bottommost point of the element can be referred to as the "bottom" of the component. As used herein, top / bottom, upper / lower, above / below can be relative to the vertical axis of the accompanying drawings, and are used to describe the positioning of the elements of the accompanying drawings relative to each other. Thus, in one example, the element shown as being above other elements is located directly above the other elements. As yet another example, the shapes of elements depicted within the drawings may be referred to as having these shapes (e.g., such as being round, straight, planar, curved, rounded, chamfered, angled, etc.). Additionally, in at least one example, elements shown as intersecting one another may be referred to as intersecting elements or intersecting one another. Further, in one example, elements shown as being within another element or shown as being outside another element may be referred to as such. It should be understood that one or more components referred to as being "substantially similar and / or identical" may differ from one another according to manufacturing tolerances (e.g., within a deviation of 1% to 5%).

[0017] Figure 1 An example vehicle propulsion system 100 is shown. The vehicle propulsion 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 may consume a liquid fuel (e.g., gasoline) to produce an engine output, while the motor 120 may consume electrical energy to produce a motor output. Therefore, a vehicle having the propulsion system 100 may be referred to as a hybrid electric vehicle (HEV).

[0018] The vehicle propulsion system 100 may utilize a variety of different operating modes depending on the operating conditions encountered by the vehicle propulsion system. Some of these modes may enable the engine 110 to be maintained in an off state (i.e., set to a deactivated state) in which fuel combustion at the engine is stopped. For example, under selected operating conditions, the motor 120 may propel the vehicle via the drive wheels 130 as indicated by arrow 122, while the engine 110 is deactivated.

[0019] During other operating conditions, engine 110 may be set to an inactive state (as described above), while motor 120 may be operated to charge energy storage device 150. For example, motor 120 may receive wheel torque from drive wheel 130, as indicated by arrow 122, wherein the motor may convert kinetic energy of the vehicle into electrical energy for storage at energy storage device 150, as indicated by arrow 124. Thus, in some examples, motor 120 may provide generator functionality. However, in other examples, generator 160 may alternatively receive wheel torque from drive wheel 130, wherein the generator may convert kinetic energy of the vehicle into electrical energy for storage at energy storage device 150, as indicated by arrow 162.

[0020] During still other operating conditions, as indicated by arrow 142, the engine 110 may be operated by combusting fuel received from the fuel system 140. For example, when the motor 120 is deactivated, the engine 110 may be operated to propel the vehicle via the drive wheels 130 as indicated by arrow 112. During other operating conditions, both the engine 110 and the motor 120 may each be operated to propel the vehicle via the drive wheels 130 as indicated by arrows 112 and 122, respectively. A configuration in which both the engine and the motor may selectively propel the vehicle may be referred to as a parallel-type vehicle propulsion system. It should be noted that in some examples, the motor 120 may propel the vehicle via a first set of drive wheels, and the engine 110 may propel the vehicle via a second set of drive wheels.

[0021] In other examples, the vehicle propulsion system 100 may be configured as a series-type vehicle propulsion system, whereby the engine does not directly propel the drive wheels. Instead, the engine 110 may be operated to power 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, which in turn may supply electrical energy to one or more of the following: 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 operated to drive the motor 120, which in turn may provide a generator function to convert the engine output into electrical energy, where the electrical energy may be stored at the energy storage device 150 for subsequent use by the motor.

[0022] 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 blend of two or more different fuels. For example, the fuel tank 144 may be configured to store a blend of gasoline and ethanol (e.g., E10, E85, etc.) or a blend of gasoline and methanol (e.g., M10, M85, etc.), whereby these fuels or fuel blends may be delivered to the engine 110, as indicated by arrow 142. Some other suitable fuels or fuel blends may be supplied to the engine 110, where they may be burned at the engine to produce an engine output. The engine output may be used to propel the vehicle as indicated by arrow 112, or the energy storage device 150 may be recharged via the motor 120 or the generator 160.

[0023] In some examples, energy storage device 150 may be configured to store electrical energy that may be supplied to other electrical loads resident on the vehicle (in addition to the motor), including cabin heating and air conditioning systems, engine starting systems, headlight systems, cabin audio and video systems, etc. As non-limiting examples, energy storage device 150 may include one or more batteries and / or capacitors.

[0024] 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 sensory 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. In addition, the control system 190 may send control 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 sensory feedback. The control system 190 may receive an indication of an operator-requested output of the vehicle propulsion system from the vehicle operator 102. For example, the control system 190 may receive sensory feedback from a pedal position sensor 194 in communication with a pedal 192. The pedal 192 may schematically refer to a deceleration pedal and / or an accelerator pedal. Additionally, in some examples, the control system 190 may 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), a remote engine start may be initiated via a cell phone or smartphone-based system where the user's cell phone sends data to a server and the server communicates with the vehicle to start the engine.

[0025] As indicated by arrow 184, energy storage device 150 may periodically receive electrical energy from a power source 180 that resides external to the vehicle (e.g., not part of the vehicle). As a non-limiting example, vehicle propulsion system 100 may be configured as a plug-in hybrid electric vehicle (PHEV), whereby electrical energy may be supplied to energy storage device 150 from power source 180 via power transmission cable 182. During operation to recharge energy storage device 150 from power source 180, power transmission cable 182 may electrically couple energy storage device 150 and power source 180. When the vehicle propulsion system is operating to propel the vehicle, power transmission cable 182 may be disconnected between power source 180 and energy storage device 150. Control system 190 may identify and / or control the amount of electrical energy stored at the energy storage device, which amount of electrical energy may be referred to as a state of charge (SOC).

[0026] In other examples, power transmission cable 182 may be omitted, where power may be received wirelessly at energy storage device 150 from power source 180. For example, energy storage device 150 may receive power from power source 180 via one or more of electromagnetic induction, radio waves, and electromagnetic resonance. Thus, it should be understood that any suitable method may be used to recharge energy storage device 150 from a power source that is not part of the vehicle. In this way, motor 120 may propel the vehicle by utilizing an energy source different from the fuel utilized by engine 110.

[0027] Fuel system 140 may periodically receive fuel from a fuel source residing outside the vehicle. As a non-limiting example, vehicle propulsion system 100 may be refueled by receiving fuel via fuel dispensing device 170, as indicated by arrow 172. In some examples, fuel tank 144 may be configured to store fuel received from fuel dispensing device 170 until the fuel is supplied to engine 110 for combustion. In some examples, control system 190 may receive an indication of a fuel level stored at fuel tank 144 via a fuel level sensor. The fuel level stored at fuel tank 144 (e.g., as identified by the fuel level sensor) may be communicated to a vehicle operator, for example, via a fuel gauge or an indication in a vehicle instrument panel 196.

[0028] The vehicle propulsion system 100 may also include an ambient temperature / humidity sensor 198 and stability control sensors, such as lateral and / or longitudinal and / or yaw rate sensors 199. The vehicle dashboard 196 may include indicator lights and / or a text-based display in which messages are displayed to the operator. The vehicle dashboard 196 may also include various input portions for receiving operator input, such as buttons, a touch screen, voice input / recognition, etc. For example, the vehicle dashboard 196 may include a refueling button 197 that may be automatically actuated or pressed by the vehicle operator to initiate refueling. For example, in response to the vehicle operator actuating the refueling button 197, a fuel tank in the vehicle may be depressurized so that refueling may be performed.

[0029] In some examples, vehicle propulsion system 100 may include one or more onboard cameras 135. For example, onboard cameras 135 may communicate photographic and / or video images to control system 190. In some examples, for example, onboard cameras may be utilized to record images within a predetermined radius of the vehicle.

[0030] The vehicle system 100 may also include an onboard navigation system 132 (e.g., a global positioning system) with which the vehicle operator can interact. The navigation system 132 may include one or more position sensors for assisting in estimating vehicle speed, vehicle altitude, vehicle position / location, etc. This information may be used to infer engine operating parameters, such as local atmospheric pressure. As described above, the control system 190 may also be configured to receive information via the Internet or other communication networks. Information received from the GPS may be cross-referenced with information available via the Internet to determine local weather conditions, etc. In some examples, the vehicle system 100 may include laser, radar, sonar, acoustic sensors 133 that may enable the collection of vehicle position, traffic information, etc., via the vehicle.

[0031] The vehicle system 100 can communicate wirelessly with the wireless network 131. The control system 190 can communicate with the wireless network 131 via a modem, a router, a radio signal, etc. Data about the status of various vehicle systems can be transmitted between the control system 190 and the wireless network. Additionally or alternatively, the wireless network 131 can transmit the status of other vehicles to the control system 190.

[0032] Figure 2A schematic diagram of a prior art example of a vehicle system 206 is shown. The vehicle system 206 includes an engine system 208 coupled to an evaporative emission control system 251 and a fuel system 218. The evaporative emission control system 251 (also referred to as the evaporative emission system 251) includes a first canister 222 and a second canister 201 that can be used to capture and store fuel vapors. Although only two canisters are shown, the evaporative emission control system 251 may include three or more canisters. In some examples, the vehicle system 206 may be a hybrid electric vehicle system, such as Figure 1 The vehicle propulsion system 100. Therefore, the engine 210 may be similar to Figure 1 The engine 110, and Figure 2 The control system 214 can be connected with Figure 1 The control system 190 is the same.

[0033] The engine system 208 may include an engine 210 having a plurality of cylinders 230. The engine 210 includes an engine intake 223 and an engine exhaust 225. The engine intake 223 includes a throttle 262 fluidly coupled to an intake manifold 244. Fresh intake air enters the intake passage 242 and flows through an air filter 253. The air filter 253 located in the intake passage 242 may clean the intake air before the intake air is directed to the intake manifold 244. The cleaned intake air leaving the air filter 253 may flow through a throttle 262 (also referred to as an intake throttle 262) via the intake passage 242 into the intake manifold 244. Therefore, the intake throttle 262, when fully opened, may achieve a higher level of fluid communication between the intake manifold 244 and the intake passage 242 downstream of the air filter 253. The amount of intake air provided to the intake manifold 244 may be controlled via a throttle 262 based on engine conditions. The engine exhaust port 225 includes an exhaust manifold 248 leading to an exhaust passage 235 that directs exhaust gas to the atmosphere. The engine exhaust port 225 may include one or more emission control devices 270 that may be mounted in a close coupled position in the exhaust port. The one or more emission control devices may include a three-way catalyst, a lean NO x Traps, diesel particulate filters, oxidation catalysts, etc. It will be appreciated that other components may be included in the engine, such as various valves and sensors.

[0034] Each cylinder 230 can be served by one or more valves. In the present example, each cylinder 30 includes a corresponding intake valve 264 and an exhaust valve (not shown). Each intake valve 264 can be maintained in a desired position via a corresponding spring. The engine system 208 also includes one or more camshafts 268 for operating the intake valve 262. In the depicted example, the intake camshaft 268 is coupled to the intake valve 264 and can be actuated to operate the intake valve 264. In some embodiments, where the intake valves of multiple cylinders 230 are coupled to a common camshaft, the intake camshaft 268 can be actuated to operate all intake valves of all coupled cylinders.

[0035] The intake valve 264 can be actuated between an open position that allows intake air to enter the corresponding cylinder and a closed position that substantially blocks intake air from the cylinder. An intake camshaft 268 can be included in the intake valve actuation system 269. The intake camshaft 268 includes an intake cam 267 having a cam lobe profile for opening the intake valve 264 within a defined intake duration. The lobe profile can affect the cam lift height, cam duration, and / or cam timing. A controller (such as controller 212) may be able to switch the intake valve duration by longitudinally moving the intake cam lobe 268 and switching between cam profiles.

[0036] It should be understood that the intake camshaft and / or the exhaust camshaft may be coupled to the cylinder subgroup, and there may be multiple intake camshafts and / or exhaust camshafts. The intake valve actuation system 269 may also include push rods, rocker arms, tappets, etc. Therefore, the intake valve actuation system may include multiple electromechanical actuators. Such devices and features may control the actuation of the intake valve 264 by converting the rotational motion of the cam into the translational motion of the valve. As previously discussed, the valve may also be actuated via additional cam lobe profiles on the camshaft, wherein the cam lobe profiles between different valves may provide a variable cam lift height, cam duration, and / or cam timing. However, if desired, an alternative camshaft (overhead and / or pushrod) arrangement may be used. In addition, in some examples, the cylinders 230 may each have more than one exhaust valve. In other examples, the intake valves 264 of one or more cylinders may be actuated by a common camshaft. Further, in some examples, some of the intake valves 264 may be actuated by their own independent camshafts or other devices.

[0037] The engine system 208 may include a variable valve timing system, such as a variable cam timing (VCT) system 260. Thus, the VCT system 260 may be operably and communicatively coupled to an intake valve actuation system 269. The VCT system 260 may include an intake camshaft phaser 265 coupled to a common intake camshaft 268 to vary intake valve timing. The VCT system 260 may be configured to advance or retard valve timing by advancing or retarding cam timing, and may be controlled by the controller 212. In some embodiments, valve timing, such as intake valve closing (IVC), may be varied by a continuously variable valve lift (CVVL) device.

[0038] The valve / cam control devices and systems described above may be hydraulically driven, electrically actuated, or a combination thereof. In one example, the position of the camshaft may be changed via cam phase adjustment by an electrical actuator (e.g., an electrically actuated cam phaser) having a fidelity exceeding that of most hydraulically operated cam phasers. Signal lines may send control signals to the VCT system 260 and may receive cam timing and / or cam selection measurements from the VCT system. Thus, the valve actuation system described above may enable closing of the intake valve to block fluid flow therethrough when desired.

[0039] although Figure 2 Although not shown, vehicle system 206 may also include an exhaust gas recirculation (EGR) system to direct a desired portion of the exhaust gas from exhaust passage 235 to intake manifold 244 via an EGR passage. Controller 212 may vary the amount of EGR provided by adjusting an EGR valve in the EGR passage. By directing exhaust gas into engine 210, the amount of oxygen available for combustion is reduced, thereby reducing the combustion flame temperature and reducing, for example, NO x formation.

[0040] Fuel system 218 may include a fuel tank 220 coupled to a fuel pump system 221. Fuel pump system 221 may include one or more pumps for pressurizing the fuel delivered to the injectors (such as exemplary injectors 266) of engine 210. Although only a single injector 266 is shown, additional injectors are provided for each cylinder. It should be understood that fuel system 218 may be a returnless fuel system, a return fuel system, or various other types of fuel systems. Fuel tank 220 may store a variety of fuel blends, including fuels with a range of alcohol percentages or amounts, such as various gasoline-ethanol blends, including E10, E85, gasoline, etc., and combinations thereof. A fuel level sensor 234 located in fuel tank 220 may provide an indication of fuel level ("fuel level input") to controller 212. As depicted, fuel level sensor 234 may include a float connected to a variable resistor. Alternatively, other types of fuel level sensors may be used.

[0041] The vapor generated in the fuel system 218 may be directed to the evaporative emission control system 251 via a vapor recovery line 231, which includes a first fuel vapor filter canister 222 and a second fuel filter canister 201. The first fuel vapor filter canister 222 may also be referred to as the first filter canister 222, and the second fuel vapor filter canister 201 may be referred to as the second filter canister 201 in this article. The fuel vapor stored in the first filter canister 222 and the second filter canister 201 may be extracted to the engine intake 223 later. The vapor recovery line 231 may be connected to the fuel tank 220 via one or more conduits, and may include one or more valves for isolating the fuel tank during certain conditions. For example, the vapor recovery line 231 may be connected to the fuel tank 220 via one or more of the conduits 271, 273 and 275, or a combination thereof.

[0042] Additionally, in some examples, one or more fuel tank vent valves are located in conduits 271, 273, or 275. Among other functions, the fuel tank vent valves may allow the fuel vapor canister of the emission control system to be maintained at a low pressure or vacuum without increasing the fuel evaporation rate of the fuel tank (which would otherwise occur if the fuel tank pressure were reduced). For example, conduit 271 may include a graded vent valve (GVV) 287, conduit 273 may include a fill limit vent valve (FLVV) 285, and conduit 275 may include a graded vent valve (GVV) 283. Additionally, in some examples, recovery line 231 may be coupled to a fuel fill system 219 (or refueling system 219). In some examples, the refueling system may include a fuel tank cap 205 for sealing the refueling system from the atmosphere. The refueling system 219 is coupled to the fuel tank 220 via a fuel fill pipe or neck 211.

[0043] In addition, the fuel supply system 219 may include a fuel supply lock 245. In some embodiments, the fuel supply lock 245 may be a fuel tank cap locking mechanism. The fuel tank cap locking mechanism may be configured to automatically lock the fuel tank cap in a closed position so that the fuel tank cap cannot be opened. For example, when the pressure or vacuum in the fuel tank is greater than a threshold value, the fuel tank cap 205 may remain locked via the fuel supply lock 245. In response to a fuel supply request, such as a request initiated by the vehicle driver, the fuel tank may be decompressed, and the fuel tank cap may be unlocked after the pressure or vacuum in the fuel tank drops below a threshold value. The fuel tank cap locking mechanism may be a clutch that prevents the removal of the fuel tank cap when engaged. The clutch may be electrically locked, for example, by a solenoid, or may be mechanically locked, for example, by a pressure diaphragm.

[0044] In some embodiments, refuel lock 245 may be a refuel pipe valve located at the mouth of fuel fill pipe 211. In such embodiments, refuel lock 245 may not prevent removal of fuel tank cap 205. Rather, refuel lock 245 may prevent a refuel pump from being inserted into fuel fill pipe 211. The refuel pipe valve may be electrically locked, such as by a solenoid, or mechanically locked, such as by a pressure diaphragm.

[0045] In some embodiments, refuel lock 245 may be a refuel door lock, such as a clutch that locks a refuel door located in a body panel of the vehicle. The refuel door lock may be electrically locked, such as by a solenoid, or mechanically locked, such as by a pressure diaphragm.

[0046] In embodiments where an electrical mechanism is used to lock refuel lock 245, for example, when the fuel tank pressure drops below a pressure threshold, refuel lock 245 may be unlocked by a command from controller 212. In embodiments where a mechanical mechanism is used to lock refuel lock 245, for example, when the fuel tank pressure drops to atmospheric pressure, refuel lock 245 may be unlocked via a pressure gradient.

[0047] The evaporative emission control system 251 may include one or more emission control devices, such as one or more fuel vapor canisters filled with a suitable adsorbent. The canister is configured to temporarily capture fuel vapors (including evaporated hydrocarbons) during fuel tank filling operations and "running losses" (i.e., fuel that evaporates during vehicle operation). In one example, the adsorbent used is activated carbon. The evaporative emission system 251 may also include a canister vent path or vent line 227 that vents gases from the canister 222 to the atmosphere when storing or capturing fuel vapors from the fuel system 218.

[0048] Purge line 227 may allow fresh air to be drawn into canister 222 while stored fuel vapor is being purged from first canister 222 and second canister 201 to engine intake 223 via purge line 228 and canister purge valve 261 (also referred to as purge valve 261). For example, purge valve 261 may be normally closed but may be opened during certain conditions such that vacuum from engine intake manifold 244 is provided to fuel vapor canister 222 for purging.

[0049] FTIV 252 may be located between fuel tank 220, first canister 222, and second canister 201 within conduit 278. FTIV 252 may be a normally closed valve that, when open, allows fuel vapor to be exhausted from fuel tank 220 to only first canister 222 via conduit 278, to only second canister 201 via conduit 279, or both. Fuel vapor may be stored within first canister 222 and second canister 201, and air stripped of fuel vapor may then be exhausted to the atmosphere via exhaust line 227. At a later time when purge conditions exist, fuel vapor stored in first canister 222 and second canister 201 may be purged along purge line 228 to engine intake 223 via canister purge valve 261. Thus, FTIV 252 may isolate and seal fuel tank 220 from evaporative emission system 251 when closed. It should be noted that some vehicle systems may not include FTIV 252.

[0050] Fuel system 218 may be operated in a variety of modes by selectively adjusting various valves and solenoids by controller 212. For example, fuel system 218 may be operated in a fuel vapor storage mode (e.g., during a fuel tank refueling operation and the engine is not running), wherein controller 212 may open FTIV 252 while closing canister purge valve (CPV) 261 to direct refueling vapors directly into the first and second canisters while preventing fuel vapors from being directed into the intake manifold.

[0051] As another example, the fuel system may be operated in a refueling mode (e.g., when a vehicle operator requests a fuel tank refueling), where controller 212 may open FTIV 252 while maintaining CPV 261 closed to depressurize the fuel tank before allowing fuel to be added to the fuel tank. Thus, FTIV 252 may remain open during the refueling operation to allow refueling vapors to be stored in the canister. After refueling is complete, the FTIV may be closed.

[0052] As yet another example, the fuel system may be operated in a canister purge mode (e.g., when the emission control device light-off temperature has been reached and the engine is running), where controller 212 may open CPV 261 while closing FTIV 252. In this context, vacuum generated by the intake manifold of the operating engine may be used to draw fresh air through exhaust line 227 and through first canister 222 and second canister 201 to purge stored fuel vapors into intake manifold 244. In this mode, fuel vapors purged from the canister are combusted in the engine. Purging may continue until the amount of fuel vapor stored in the canister is below a threshold. FTIV 252 may be closed during the purge mode.

[0053] Controller 212 may include a portion of control system 214. Control system 214 is shown receiving information from a plurality of sensors 216 (various examples of which are described herein) and sending control signals to a plurality of actuators 281 (various examples of which are described herein). As one example, sensors 216 may include manifold absolute pressure (MAP) sensor 224, barometric pressure (BP) sensor 246, exhaust gas sensor 226 located in exhaust manifold 248 upstream of emission control device, temperature sensor 233, fuel tank pressure sensor 291 (also referred to as fuel tank pressure sensor or FTPT), and canister temperature sensors 232, 203. Other sensors (such as pressure, temperature, air-fuel ratio, and composition sensors) may be coupled to various locations in vehicle system 206. As another example, actuators may include CPV 261, fuel injector 266, throttle 262, FTIV 252, fuel pump 221, and refuel lock 245. Control system 214 may include controller 212. The controller may receive input data from the 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.

[0054] The controller 212 Figure 2 Various sensors receive signals and use Figure 2 Controller 212 may control various actuators of the canister purge valve to adjust engine operation based on the received signals and instructions stored on the memory of the controller. For example, adjusting the canister purge valve may include adjusting an actuator of the canister purge valve to adjust a flow rate of fuel vapor therethrough. Thus, controller 212 may transmit a signal to an actuator of the canister purge valve (e.g., a canister purge valve solenoid) based on a desired purge flow rate. Thus, the canister purge valve solenoid may be opened (and pulsed) at a particular duty cycle to allow stored vapor to flow from the canister via purge line 228 to intake manifold 244.

[0055] Now turn to Figure 3 , which shows an embodiment of a fuel system 300. The fuel system 300 may be used in Figure 1 and / or Figure 2 In an engine system of the invention, the fuel system 300 may include a fuel tank 302 configured to store one or more fuels. In one example, the fuel tank 302 may be similar to Figure 2 20. In one example, fuel tank 302 is a non-integrated refueling canister system (NIRCOS) fuel tank. Fuel tank 302 may include a first port 304 to which a first loading line 306 is fluidly coupled. First loading line 306 may be configured to flow fuel vapor to and / or out of fuel tank 302. FTPT 308 may be coupled to fuel tank 302 at a location proximate first loading line 306.

[0056] Fuel tank 302 may also include a second port 305 to which a second loading line 307 is fluidly coupled. Second loading line 307 may be configured to flow fuel vapor to and / or out of fuel tank 302.

[0057] The fuel tank 302 may also include a first fuel limit vent valve (FLVV) 301 at the first port 304. A second FLVV 303 may be disposed at the second port 305. In one example, a gradient vent valve (GVV) that would otherwise be disposed at the second port 305 may be omitted. By doing so, the weight of the second FLVV 303 may be offset.

[0058] The fuel system 300 includes a first canister 320 and a second canister 340 coupled to a first loading line 306 and a second loading line 307, respectively. Figure 2 The fuel system is separated.

[0059] A first fuel tank isolation valve (FTIV) 310 may be disposed at a junction between the first loading line 306 and the first canister loading line 312. The first canister loading line 312 may be coupled to the first FTIV 310 and the first canister inlet port 322. The second FTIV 309 may be coupled to the second canister loading line 314 and the second loading line 307. The second canister loading line 314 may be coupled to the second FTIV 309 and the second canister inlet port 342. In some embodiments, the first FTIV 310 and the second FTIV 309 may be combined and the fuel system 300 may be modified to include Figure 2 A multi-position FTIV 252 is positioned to control multiple flows to the canister.

[0060] The first FTIV 310 and the second FTIV 309 can be actuated to a fully open position, a fully closed position, or a position therebetween. In some examples, the first FTIV 310 and the second FTIV 309 can be adjusted based on the loading of the first canister 320 and the second canister 340 in response to conditions, such as in Figure 5 and Figure 6 In one example, the first FTIV 310 and the second FTIV 309 are multi-position two-way valves.

[0061] Each of the first canister 320 and the second canister 340 can be coupled to the CPV 316. In one example, the CPV 316 can be coupled to the Figure 2The CPV 316 may be the same as the CPV 261 of the engine. The CPV 316 may direct vapors to the engine intake during various conditions, such as when combustion occurs and fuel is consumed. The first canister 320 may include a first canister extraction line 324, and the second canister 340 may include a second canister extraction line 344. The first canister extraction line 324 may be coupled to the first canister 320 at a first canister extraction port 326. The second canister extraction line 344 may be coupled to the second canister 340 at a second canister extraction port 346. The first canister extraction line 324 and the second canister extraction line 344 may cross upstream of the CPV 316 relative to the direction of vapor flow toward the engine intake. When vapor flows from one or more of the first canister 320 and the second canister 340 through the CPV 316 and flows to the engine, canister cleaning is occurring and the loading of the canister may be reduced to a less loaded state.

[0062] Each of the first canister 320 and the second canister 340 may also include a corresponding exhaust line. The first canister 320 may include a first canister exhaust line 328 coupled to a first canister exhaust port 330 and a first canister exhaust valve (CVV1) 332. The second canister 340 may include a second canister exhaust line 348 coupled to a second canister exhaust port 350 and a second CVV (CVV2) 352. The first canister exhaust line 328 and the second canister exhaust line 348 may be fluidly separated from each other.

[0063] An evaporative leak check module (ELCM) 362 may be fluidly coupled to each of the first canister exhaust line 328 and the second canister exhaust line 348 at a position downstream of CVV1 332 and CVV2 352 relative to the direction of vapor flow through the combined exhaust passage 360. An ELCM sensor 364 may be disposed between the ELCM 362, CVV1 332, and CVV2 352. In one example, the ELCM 362 and the ELCM sensor 364 may be used to perform leak detection diagnostics of the fuel system 300. In some examples, such as in an example where the vehicle includes only an internal combustion engine, the ELCM 362 and the ELCM sensor 364 may be omitted, and each of the first canister exhaust line 328 and the second canister exhaust line 348 may be led to the atmosphere. If the ELCM 362 is omitted, a dust box or similar device may be included between the fuel system and the atmosphere.

[0064] In one example, the lengths and diameters of the lines in and out of the canister can be substantially the same. That is, the lengths and diameters of the first loading line 312 and the second loading line 314 can be the same. The lengths and diameters of the first canister extraction line 324 and the second canister extraction line 344 can be the same. The lengths and diameters of the first canister exhaust line 328 and the second canister exhaust line 348 can be the same. The size, shape, and volume (including the carbon bed) of the first canister 320 and the second canister 340 can be the same. By doing so, the restrictions of the canisters can be substantially the same, thereby promoting a more uniform vapor flow.

[0065] Now turn to Figure 4 , which shows a fuel system 400. The fuel system 400 may include Figure 3 The components of the fuel system 300 are identical to one or more components. Figure 3 The unchanged parts are Figure 4 are numbered similarly.

[0066] The fuel system 400 may include a fuel tank 402. The fuel tank 402 may include a first port 304 and a second port 305 arranged at different heights. In one example, the first port 304 may include a first FLVV 301, and the second port 305 may include a second FLVV 303. The fuel tank 402 may include a step 404 or other protrusion on which the second port 305 and thus the second FLVV 303 are arranged to distinguish their heights from the first port 304. By doing so, the condition of the first FLVV 301 and the second FLVV 303 may be determined via a diagnostic procedure or other procedure.

[0067] In some examples, the shape and configuration of fuel tank 402 may additionally or alternatively be Figure 3 The fuel tanks 302 are the same. The fuel tanks 402 may be arranged at an angle or slope to arrange the FLVV at different heights.

[0068] Fuel system 400 may also include third canister 420. Third canister 420 may differ from first canister 320 and second canister 340 in one or more of size and shape. In one example, third canister 420 is smaller than first canister 320 and second canister 340.

[0069] The third canister 420 may include a third canister inlet port 422 fluidly coupled to a third loading line 424. The third loading line 424 may extend from the third canister inlet port 422 to the first FTIV 410. A connecting passage 426 may extend from the third loading line 424 to the second canister exhaust line 348. Thus, a four-way intersection may exist between the first canister exhaust line 328, the third loading line 424, and the connecting passage 426.

[0070] The third canister 420 may also include a third canister purge port 434. A cap 436 may be coupled to the third canister purge port 434. The cap 436 may hermetically seal the third canister purge port 434.

[0071] The third canister 420 may also include a third canister exhaust port 430. The third canister exhaust port 430 may be fluidly coupled to a third canister exhaust line 438. The third canister exhaust line 438 may fluidly couple the third canister 420 to the atmosphere. Additionally or alternatively, the ELCM 362 may be disposed between the third canister exhaust port 430 and the atmosphere. Furthermore, the third canister 420 is positioned between the atmosphere and each of the first canister 320 and the second canister 340.

[0072] In one example, operation of fuel system 400 may include operating third canister 420 as an emission restriction device, wherein third canister 420 captures vapors that would otherwise flow to the atmosphere. Thus, canister cleaning may include prioritizing cleaning third canister 420 before cleaning first canister 320 and second canister 340. Figure 3 The fuel system 400 and the method of the fuel system 300 are provided.

[0073] In the example of the fuel system 400, the first FTIV 410 may be a multi-position valve configured to control fluid connections between the fuel tank 402 and one or more of the first canister charge line 312, the third canister charge line 424, the first canister vent line 328, and the second canister vent line 348. The fully closed position of the first FTIV 410 may hermetically seal the fuel tank 402 from each of the first main canister 320, the second main canister 340, and the third canister 420. The first open position of the first FTIV 410 may fluidly couple the fuel tank 402 to the first canister charge line 312.

[0074] The second open position of first FTIV 410 may fluidly couple fuel tank 402 to third canister charge line 424. When in the second open position, the positions of CVV1 332 and CVV2 352 may be adjusted to control vapor flow into and out of first and second primary canisters 320 and 340, respectively.

[0075] The third open position of first FTIV 410 may fluidly couple fuel tank 402 to each of first canister charge line 312 and third canister charge line 424. Thus, when first FTIV 410 is in the third open position, at least each of first main canister 320 and third canister 420 are fluidly coupled to the fuel tank.

[0076] Additionally or alternatively, in the example of fuel system 400, second FTIV 412 may be a multi-position valve configured to control fluid coupling between fuel tank 402 and one or more of second canister charge line 314 and second canister vent line 348. Due to the configuration of second canister vent line 348, second FTIV 412 may also control fluid coupling between fuel tank 402, third canister charge line 424, and first canister vent line 328.

[0077] Second FTIV 412 may include a fully closed position that seals fuel tank 402 from each of second canister charge line 314 and second canister vent line 348. Second FTIV 412 may also include a first open position that fluidly couples fuel tank 402 to second canister charge line 314 only.

[0078] Second FTIV 412 may also include a second open position that fluidly couples fuel tank 402 only to second canister vent line 348. Thus, fuel tank 402 may be hermetically sealed from second canister charge line 314 when second FTIV 412 is in the second open position.

[0079] The second FTIV 412 may also include a third open position that fluidly couples the fuel tank 402 to each of the second canister charge line 314 and the second canister exhaust line 348 .

[0080] In one example, when the first FTIV 410 is in the third open position, the CVV 1332 can be commanded closed. Additionally or alternatively, when the first FTIV is in the second open position and / or the third open position, the second FTIV 412 can be commanded to one of the first open position or the fully closed position.

[0081] In another example, additionally or alternatively, when the second FTIV 412 is in the third open position, the CVV 2352 can be commanded closed. Additionally or alternatively, when the second FTIV 412 is in the second open position or the third open position, the first FTIV 410 can be commanded to the first open position or the fully closed position.

[0082] For each of the associated open positions, the first FTIV 410 and the second FTIV 412 can be actuated to different opening amounts. The different opening ranges can range from greater than 0% open to 100% open. Thus, precise control of vapor flow through the passage can be achieved.

[0083] Now go to Figure 5 , which shows a method 500 for adjusting a fuel tank vapor flow path based on the loading of multiple canisters during depressurization. Instructions for carrying out method 500 and the remainder of the methods included herein may be executed by a controller based on instructions stored on a memory of the controller and in conjunction with signals received from sensors of the engine system, such as those described above with reference to Figures 1 to 4 The controller may employ engine actuators of the engine system to adjust engine operation according to the methods described below.

[0084] Method 500 begins at 502 and includes determining operating parameters. The operating parameters may include, but are not limited to, one or more of vehicle speed, engine speed, selected gear, and air / fuel ratio.

[0085] At 504, method 500 may include determining whether a refueling is requested. Refueling may be requested if the refueling door is open, if the operator requests the refueling door to be opened, and if the vehicle is located at a gas station. The refueling door may be opened or requested to be opened via an operator pressing against the exterior of the refueling door, pressing a button in the interior of the vehicle, and / or via selection through an electronic device (such as a phone, laptop, tablet computer, navigation system, etc.). It may be determined based on data provided by a position sensor and / or a navigation system that the vehicle will be located at a refueling station. The position sensor may be a global positioning satellite (GPS) sensor or other type of sensor.

[0086] If refueling is not requested, then at 506 , the method may include where the fuel tank is not depressurized and vapors may be contained therein. Therefore, each of the FTIV valves may remain in a fully closed position.

[0087] If refueling is requested, method 500 may proceed to 508, which includes determining whether the fuel tank pressure is less than a threshold pressure. The threshold pressure may correspond to a fuel tank pressure where the depressurization time is longer than the desired duration. If the fuel tank pressure is not less than the threshold pressure, depressurizing the fuel tank by opening only one FTIV may take longer than the desired duration, and method 500 may proceed to 510, which includes initiating fuel tank depressurization.

[0088] At 512, method 500 may include opening both FTIVs. Thus, the first FTIV is opened and the second FTIV is opened, and both the first main filter canister and the second main filter canister are fluidly connected to the fuel tank. In one example, the first FTIV and the second FTIV are opened to corresponding first open positions. By doing so, vapors from the fuel tank may not flow directly to the third filter canister. More specifically, during decompression, the third filter canister can be isolated and sealed from the fuel tank. The first FTIV can be in its first open position so that fuel vapors from the fuel tank can only flow to the first main filter canister and prevent vapors from flowing to the third filter canister. The second FTIV can be in its first open position so that fuel vapors from the fuel tank can only flow to the second main filter canister. In this way, the third filter canister can be in a position to capture vapors that may leak from the first main filter canister and / or the second main filter canister.

[0089] At 514 , method 500 may include flowing vapors to both the first and second main canisters. The method may continue to monitor the fuel tank pressure, and once the pressure is less than a threshold pressure, only the less loaded of the two main canisters may receive fuel tank vapors, as will be described below.

[0090] Returning to 508, if the fuel tank pressure is less than the threshold pressure, decompression of the fuel tank may occur over a shorter period than the expected duration when only one FTIV is open. Method 500 proceeds to 516 (yes at 508), which includes determining the loading of the first main filter canister and the second main filter canister. The loading of the filter canister may be determined based on one or more of the temperature of the filter canister, feedback from an oxygen sensor positioned at the inlet of the filter canister, and feedback from a hydrocarbon sensor positioned at the inlet of the filter canister. Additionally or alternatively, the loading of the filter canister may be tracked over time based on one or more of ambient temperature, fuel tank pressure, and engine operating time.

[0091] At 518 , method 500 may include initiating fuel tank depressurization.

[0092] At 520, method 500 may include flowing fuel vapor to a less loaded main canister in the first main canister and the second main canister. Thus, the loading of the first main canister and the second main canister may be compared, and the canister with the lower loading may be selected to receive vapor from the fuel tank during decompression. Thus, the FTIV corresponding to the canister with the lower loading may be opened, and the FTIV corresponding to the canister with the higher loading may be kept closed. For example, if the first main canister includes a lower loading than the second main canister, the first FTIV may be opened to a first open position, and the second FTIV may be kept closed. Alternatively, if the second main canister includes a lower loading than the second main canister, the first FTIV may be kept closed and the second FTIV may be opened to a first open position.

[0093] If the first main canister and the second main canister are equally loaded, the method may include selecting one of the two canisters to receive vapor. The selected canister may be based on canister age and one or more of the previously selected canisters. In one example, the canister with the shorter canister age may be selected. Additionally or alternatively, the method may alternate between the selected canisters such that if the first main canister was selected during a previous decompression period, the second main canister may be selected to receive vapor during a current decompression period.

[0094] At 522, method 500 may optionally include flowing vapor to both canisters once the canister loading is equal. Flowing vapor to both primary canisters may include opening the first FTIV and the second FTIV to respective first open positions. Additionally or alternatively, the loading of the primary canisters may be balanced by flowing vapor directly from one canister to the other canister based on actuation of respective exhaust valves. If the third canister is included in the execution Figure 5 In the fuel system of method 500 , a third canister charging valve may optionally be disposed in the third charging line to control vapor flow to the third canister.

[0095] Now go to Figure 6 , which shows a method 600 for reverse purging one or more filter canisters of a fuel system. Method 600 begins at 602, which may include determining whether fuel tank vacuum is available. Fuel tank vacuum may be available if the temperature of the fuel tank changes by a threshold amount. The threshold amount may be equal to 10 degrees, or 20 degrees, or 30 degrees, or 40 degrees, or 50 degrees or greater. Additionally or alternatively, fuel tank vacuum may be available at night (e.g., after sunset and before sunrise) when the ambient temperature is lower. Additionally or alternatively, fuel tank vacuum availability may be determined via a pressure sensor. If fuel tank vacuum is not available, then at 604, method 600 may include not reverse purging the filter canister. Therefore, vapors from the filter canister are not directed to the fuel tank via vacuum.

[0096] If fuel tank vacuum is available, at 606 , method 600 may include determining the loading of the canister.

[0097] At 608, method 600 may include determining whether each of the canisters is clean. The canisters may be cleaned during a purge event, which may include flowing vapor from the primary canister to the engine, where the vapor is combusted. The third canister may be cleaned by flowing vapor therefrom to one or more of the first primary canister and the second primary canister.

[0098] If the canister is clean, method 600 may proceed to 604 and reverse purging may not occur. If each of the canisters is not clean, method 600 proceeds to 610, which includes determining whether the third canister is dirty. If the third canister load is greater than a lower threshold load, the third canister is dirty. In one example, the lower threshold load is equal to 0. Additionally or alternatively, the lower threshold load may be based on a percentage of the capacity of the third canister, such as 5%, or 3%, or 1%.

[0099] If the third canister is dirty, method 600 proceeds to 612, which includes opening the first FTIV to a second open position that fluidly couples the fuel tank to only the third canister. In this way, vacuum flow is preferentially directed to the third canister. Additionally or alternatively, CVV1 and CVV2 may be maintained fully closed to prevent vacuum from entering the first main canister and the second main canister. The second FTIV may be maintained fully closed.

[0100] In some examples, additionally or alternatively, the second FTIV may be actuated to the second open position and CVV1, CVV2, and the first FTIV may be maintained fully closed to allow vacuum to flow to the third canister. In other examples, additionally or alternatively, each of the first FTIV and the second FTIV may be actuated to the corresponding second open position and CVV1 and CVV2 may be maintained closed to allow vacuum to flow only to the third canister.

[0101] At 614 , method 600 may include flowing vacuum to the third canister.The vacuum may flow through the first charge line, through the first FTIV, through the third charge line, through the third canister inlet port, and into the third canister.

[0102] At 616, method 600 may include flowing vapor from the third canister to the fuel tank. Thus, the loading of the third canister is reduced. Method 600 may continue to monitor the third canister loading, and once the third canister is no longer dirty, vacuum from the fuel tank may be supplied to one or more of the primary canisters.

[0103] Returning to 610, if the third canister is not dirty (e.g., its load is less than or equal to the lower threshold load) or if the third canister has been cleaned via the fuel tank vacuum, at 618, method 600 may include opening the FTIV associated with the more loaded primary canister of the primary canisters. For example, if the second primary canister is more loaded than the first primary canister, the second FTIV may be opened to its first open position and the first FTIV may remain closed. As another example, if the first primary canister is more loaded than the second primary canister, the first FTIV may be opened to its first open position and the second FTIV may remain closed.

[0104] At 620 , method 600 may include flowing vacuum to the more loaded primary canister. Vacuum may flow from the fuel tank, through the corresponding charge line, through the corresponding FTIV, and into the more loaded primary canister.

[0105] At 622 , method 600 may include flowing vapors to the fuel tank. The vapors may flow in an opposite direction to the vacuum. The more loaded the primary canister is, the less loaded it is.

[0106] At 624 , method 600 may include opening the other FTIV once the main canisters are equally loaded. In this way, each of the first and second FTIVs may be opened to a corresponding first open position such that vacuum flows to the first and second main canisters.

[0107] Additionally or alternatively, one of the first FTIV or the second FTIV can be commanded to a third open position and the other FTIV remains fully closed. For example, if the first FTIV is commanded to the third open position, the second FTIV can remain closed. Additionally, CVV1 can remain closed and CVV2 can be commanded to an open position. In this configuration, vacuum can continue to flow to the third canister, which may increase the likelihood of cleaning the third canister. In another example, if the first FTIV is commanded to its third open position, the first FTIV can remain closed. Additionally, CVV1 can be commanded to open and CVV2 can be commanded to close. Vacuum can flow to the third canister.

[0108] At 626 , method 600 may include flowing vacuum to the first main canister and the second main canister.

[0109] At 628 , method 600 may include flowing vapor from the main canister to the fuel tank. In this way, the loading of the first main canister and the second main canister may be reduced. In one example, the loading of the first main canister and the second main canister are reduced simultaneously.

[0110] Now turn to Figure 7, which shows a graph 700 illustrating an operating sequence of a fuel system including multiple canisters. Graph 710 shows a first FTIV position. Graph 720 shows a second FTIV position. Graph 730 shows the first main canister loading, and dashed line 732 shows the loading when the first main canister loading is equal to the second main canister loading. Graph 740 shows the second main canister loading. Graph 750 shows the third canister loading. Graph 760 shows the fuel tank pressure. As the fuel tank pressure decreases, more vacuum is available for reverse extraction. Time increases from the left side of the graph to the right side.

[0111] Before t1, the fuel tank pressure begins to decrease. This may be due to a decrease in ambient temperature, which may occur after sunset and before sunrise. Therefore, a vacuum may be created in the fuel tank. At t1, the first FTIV may be commanded to move from a fully closed position to a second open position. Therefore, the fuel tank may be fluidly connected to the third filter canister, and vacuum flows from the fuel tank to the third filter canister. In one example, the second open position may also allow gas to flow only between the fuel tank and the third filter canister. In this way, the first main filter canister and the second main filter canister may be isolated and sealed from the fuel tank and the third filter canister.

[0112] Between t1 and t2, the fuel tank vacuum flows to the third canister. Vapors from the third canister are purged and directed to the fuel tank. Thus, the third canister loading is reduced.

[0113] At t2, the third canister is cleaned and its load is less than the lower threshold. Therefore, the third canister may no longer request reverse extraction. The first FTIV is commanded from the second open position to the first open position. By doing so, the third canister is isolated and sealed from the fuel tank, and the first main canister is fluidly connected to the fuel tank. Since the first canister load is greater than the second canister load, the first main canister can receive vacuum before the second main canister.

[0114] Between t2 and t3, fuel tank vacuum flows to the first main canister. Vapors from the first main canister flow to the fuel tank, thereby increasing fuel tank pressure and reducing the loading of the first main canister.

[0115] At t3, the first main canister loading is equal to the second main canister loading. The second FTIV is commanded to an open position. Each of the first main canister and the second main canister is fluidly coupled to a fuel tank.

[0116] Between t3 and t4, fuel tank vacuum flows to each of the first main canister and the second main canister. The loading of the first main canister and the second main canister decreases at substantially equal rates. The fuel tank pressure increases.

[0117] At t4, the first main filter canister and the second main filter canister are clean. The main filter canister may no longer need to be reversed. Therefore, the first FTIV and the second FTIV can be moved to the fully closed position. In this way, the fuel tank can be isolated and sealed from each of the first main filter canister, the second main filter canister, and the third main filter canister.

[0118] After t4, the fuel tank pressure remains constant. The canister load remains unchanged.

[0119] It should be noted that the example 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 combination with various sensors, actuators and other engine hardware. The specific routines described herein may represent one or more of any number of processing strategies (such as event-driven, interrupt-driven, multi-tasking, multi-threading, etc.). Therefore, the various actions, operations and / or functions shown may be executed in the sequence shown, executed in parallel, or omitted in some cases. Similarly, the processing order is not necessarily required to achieve the features and advantages of the example embodiments described herein, but is provided for ease of illustration and description. One or more of the actions, operations and / or functions shown may be repeatedly performed according to the specific strategy used. In addition, the actions, operations and / or functions may be graphically represented as codes in a non-transitory memory of a computer-readable storage medium to be programmed into an engine control system, wherein the actions are implemented by executing instructions in a system including various engine hardware components in conjunction with an electronic controller.

[0120] It should be understood that the configurations and routines disclosed herein are exemplary in nature, and these specific embodiments should not be construed in a limiting sense, as many variations are possible. For example, the above techniques may be applied to V-6, I-4, I-6, V-12, opposed 4, 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 properties disclosed herein.

[0121] As used herein, unless otherwise specified, the term "about" is interpreted to mean a range of ±5%.

[0122] The appended claims particularly point out certain combinations and subcombinations regarded as novel and non-obvious. These claims may refer to "an" element or "a first" element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and subcombinations of the disclosed features, functions, elements, and / or properties may be claimed by amendment of the present claims or by presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, are also deemed to be included in the subject matter of the present disclosure.

[0123] According to the present invention, a fuel system is provided, the fuel system having: a fuel tank; a first filter canister; a second filter canister; a third filter canister; and a first fuel tank isolation valve (FTIV), the FTIV being configured to fluidly connect the fuel tank to the first filter canister exhaust line, the second filter canister exhaust line, and the third filter canister exhaust line.

[0124] According to one embodiment, the above invention also features a second FTIV configured to fluidly couple the fuel tank to the second canister charge line and the first canister exhaust line.

[0125] According to one embodiment, the first FTIV is further configured to fluidly couple the fuel tank to the first canister charge line.

[0126] According to one embodiment, the third canister is positioned between the atmosphere and each of the first canister and the second canister.

[0127] According to one embodiment, the first canister and the second canister are identical, and wherein the third canister is different than the first canister and the second canister.

[0128] According to one embodiment, the fuel tank comprises a first fuel limit vent valve (FLVV) and a second FLVV.

[0129] According to one embodiment, the above invention is further characterized by a controller having instructions stored on its memory that, when executed, enable the controller to cause vacuum to flow from the fuel tank to one or more of the first canister, the second canister, and the third canister.

[0130] According to one embodiment, the instructions further enable the controller to adjust a depressurization rate of the fuel tank based on loading of the first canister, the second canister, and the third canister.

[0131] According to the present invention, a method includes: in response to a fuel tank pressure being less than a threshold pressure, causing fuel tank vapor to flow to a less loaded canister of a first canister and a second canister during a depressurization event; and in response to a loading of a third canister being less than a lower threshold loading, causing fuel tank vacuum to flow to a more loaded canister of the first canister and the second canister.

[0132] According to one embodiment, the above invention is further characterized by causing the fuel tank vacuum to flow only to the third canister when the loading of the third canister is greater than a lower threshold loading.

[0133] According to one embodiment, the above invention is further characterized by flowing fuel tank vapor to each of the first canister and the second canister when one or more of the loading of the first canister is equal to the loading of the second canister and the fuel tank pressure is greater than or equal to a threshold pressure.

[0134] According to one embodiment, the above invention is further characterized by flowing fuel tank vacuum to each of the first canister and the second canister when the loading of the first canister is equal to the loading of the second canister and the loading of the third canister is less than a lower threshold loading.

[0135] According to one embodiment, the above invention is further characterized by adjusting a position of a fuel tank isolation valve (FTIV) to adjust fuel tank vapor and fuel tank vacuum flow to each of the first canister, the second canister, and the third canister.

[0136] According to one embodiment, the above invention is further characterized by purging the third canister only to one or more of the fuel tank, the first canister, and the second canister.

[0137] According to one embodiment, the evaporative leak check module is disposed between the third canister and the atmosphere, and wherein the third canister is disposed between the atmosphere and the first canister and the second canister.

[0138] According to the present invention, a system is provided, the system having: a fuel tank; a first filter canister, the first filter canister being fluidly connected to a first port of the fuel tank; a second filter canister, the second filter canister being fluidly connected to a second port of the fuel tank; a third filter canister, the third filter canister being fluidly connected to one or more of a first filter canister vent line and a second filter canister vent line; a first fuel tank isolation valve (FTIV), the FTIV being configured to control vapor flow between the fuel tank, the first filter canister, the second filter canister, and the third filter canister; and a controller, the controller having computer-readable instructions stored on a non-transitory memory, the computer-readable instructions, when executed, causing the controller to: when the third filter canister is loaded with more than a lower threshold load, adjust the first FTIV so that fuel tank vacuum flows only to the third filter canister; and when the third filter canister is loaded with less than or equal to the lower threshold load, adjust the first FTIV so that fuel tank vacuum flows only to the filter canister with more load among the first filter canister and the second filter canister.

[0139] According to one embodiment, the instructions further cause the controller to adjust the first and second FTIVs to flow fuel tank vacuum to each of the first and second canisters when the third canister loading is less than or equal to a lower threshold loading and the first canister loading is equal to the second canister loading.

[0140] According to one embodiment, the instructions further cause the controller to flow fuel tank vapors only to the less loaded canister of the first canister and the second canister in response to the fuel tank pressure being less than an upper threshold pressure during fuel tank depressurization.

[0141] According to one embodiment, the instructions further cause the controller to flow fuel tank vapors only to each of the first canister and the second canister in response to the first canister loading being equal to the second canister loading during fuel tank depressurization.

[0142] According to one embodiment, the instructions further cause the controller to flow fuel tank vapors to one of the first canister and the second canister in response to the fuel tank pressure being greater than or equal to the upper threshold pressure during fuel tank depressurization.

Claims

1. A fuel system comprising: Fuel tank; First filter tank; Second filter tank; The third filter tank; as well as A first fuel tank isolation valve (FTIV) is configured to fluidly couple the fuel tank to the first, second, and third canister vent lines. 2 . The fuel system of claim 1 , further comprising a second FTIV configured to fluidly couple the fuel tank to a second canister charge line and the first canister exhaust line. 3 . The fuel system of claim 1 , wherein the first FTIV is further configured to fluidly couple the fuel tank to a first canister charge line. 4 . The fuel system of claim 1 , wherein the third canister is positioned between atmosphere and each of the first canister and the second canister. 5 . The fuel system of claim 1 , wherein the first canister and the second canister are identical, and wherein the third canister is different than the first canister and the second canister.

6. The fuel system of claim 1, wherein the fuel tank includes a first fuel limit vent valve (FLVV) and a second FLVV.

7. The fuel system of claim 1 further comprising a controller having instructions stored on a memory thereof that, when executed, enable the controller to cause vacuum to flow from the fuel tank to one or more of the first canister, the second canister, and the third canister. 8 . The fuel system of claim 7 , wherein the instructions further enable the controller to adjust a depressurization rate of the fuel tank based on loading of the first canister, the second canister, and the third canister.

9. A method comprising: causing fuel tank vapors to flow only to the less loaded canister of the first canister and the second canister in response to the fuel tank pressure being less than a threshold pressure during a depressurization event; and Fuel tank vacuum is directed to flow to the more loaded canister of the first canister and the second canister in response to the loading of the third canister being less than a lower threshold loading. 10 . The method of claim 9 further comprising directing fuel tank vacuum to flow only to said third canister when said loading of said third canister is greater than said lower threshold loading.

11. The method of claim 9 further comprising flowing fuel tank vapors to each of the first canister and the second canister when one or more of the loading of the first canister is equal to the loading of the second canister and the fuel tank pressure is greater than or equal to the threshold pressure.

12. The method of claim 9 further comprising flowing fuel tank vacuum to each of the first canister and the second canister when the loading of the first canister is equal to the loading of the second canister and the loading of the third canister is less than the lower threshold loading.

13. The method of claim 9 further comprising adjusting a position of a fuel tank isolation valve (FTIV) to adjust fuel tank vapor and fuel tank vacuum flow to each of the first canister, the second canister, and the third canister.

14. The method of claim 9 further comprising purging the third canister only to one or more of a fuel tank, the first canister, and the second canister. 15 . The method of claim 9 , wherein an evaporative leak check module is disposed between the third canister and atmosphere, and wherein the third canister is disposed between atmosphere and the first canister and the second canister.

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