METHODS AND SYSTEMS FOR A FUEL SYSTEM

Abstract

Methods and systems for an evaporative emissions fuel system (EVAP system) are provided. In one example, a system for the EVAP system includes a differential pressure sensor disposed between a first purge line coupled to a first canister and a second purge line coupled to a second canister arranged in parallel with the first canister.

Description

FIELD OF TECHNOLOGY

[0001] This description generally relates to methods and systems for a fuel system including parallel vapor canisters. GENERAL STATE OF THE ART

[0002] Vehicle emission control systems may be configured to store vapors from fuel tank refueling and diurnal engine operation in a vapor canister. The stored vapors may be purged during a later engine operating condition. The stored vapors may be directed to an engine intake for combustion, which may increase fuel efficiency.

[0003] The amount of vapor stored onboard the vehicle can be proportional to the fuel tank size. As the fuel tank size increases, the canister size can be increased to store a greater amount of vapor. However, larger canisters can increase vapor line restriction, which can shut off a fuel pump before a fuel level index of 100% is reached. To address this issue, some systems with larger fuel tanks can utilize at least two vapor canisters.

[0004] However, the inventors have identified some problems with the approaches described above. For example, including two vapor canisters may still be susceptible to the same problems faced by single-canister systems during refueling. For example, canisters may contain natural variability in their restriction, or one canister may develop a greater restriction over time due to more purging, degradation of a carbon bed due to vibration, and the like. If one canister is more restrictive than the other, vapor flow will preferentially favor the less restrictive canister. During some refueling events, the less restrictive canister may become overloaded and release vapors into the atmosphere, increasing emissions. Thus, a method for balancing the loading of parallel vapor canisters is desired. SUMMARY

[0005] In one example, the problems described above may be solved by a system including a differential pressure sensor disposed between a first purge line coupled to a first canister and a second purge line coupled to a second canister arranged parallel to the first canister. In this way, a load of the canisters may be comparatively determined, and purging and / or filling of the canisters may be adjusted based on feedback from the differential pressure sensor.

[0006] As one example, when a purge event occurs, a canister vent valve of a less loaded canister may be oscillated between an open and a closed position. A canister vent valve of a more heavily loaded canister may be held open to promote a greater amount of purge (e.g., vapor flow) from the more heavily loaded canister to the engine compared to the less heavily loaded canister. As another example, when a refueling event occurs, the canister vent valve of the more heavily loaded canister may be oscillated between an open and a closed position. The canister vent valve of the less heavily loaded canister may be held open to promote a greater amount of vapor flow to the less heavily loaded canister.This can reduce the pressure difference between the less loaded canister and the more heavily loaded canister during the purging event and / or the refueling event.

[0007] It should be understood that the foregoing summary is provided to introduce, in simplified form, a selection of concepts that are described in more detail in the detailed description. It is not intended to identify important or significant features of the claimed subject matter, the scope of which is defined solely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that overcome any of the disadvantages recited above or in any part of this disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The advantages described in this document will become more fully apparent from reading an example of an embodiment, referred to in this document as the detailed description, when read alone or with reference to the drawings, in which: Fig. Figure 1 illustrates a schematic of an engine included in a hybrid vehicle. Fig. 2. illustrates a prior art example of an engine incorporating a single canister. Fig. 3 illustrates the engine, which includes canisters arranged in parallel. Fig. Figure 4 illustrates a method for operating canister vent valves of canisters arranged in parallel in response to a differential pressure sensed during a purge event. Fig. Figure 5 illustrates a method for operating canister vent valves of canisters arranged in parallel in response to a differential pressure sensed during a refueling event. Fig. 6 graphically illustrates an engine operating sequence illustrating changes in canister vent valve operation during a refueling event. DETAILED DESCRIPTION

[0009] The following description relates to systems and methods for directing vapors to parallel canisters of an evaporative emission control (EVAP) system. Fig. Figure 1 illustrates a schematic of an engine included in a hybrid vehicle. Fig. 2. illustrates a prior art example of an engine incorporating a single canister. Fig. 3 illustrates the engine, which includes canisters arranged in parallel. Fig. Figure 4 illustrates a method for operating canister vent valves of canisters arranged in parallel in response to a differential pressure sensed during a purge event. Fig. Figure 5 illustrates a method for operating canister vent valves of canisters arranged in parallel in response to a differential pressure sensed during a refueling event. Fig. 6 graphically illustrates an engine operating sequence illustrating changes in canister vent valve operation during a refueling event.

[0010] The Fig. 1-3 show example configurations with relative positioning of the various components. When shown as directly touching or directly coupled to one another, such elements may be referred to as directly touching or directly coupled, respectively, in at least one example. Similarly, elements shown contiguous or adjacent to one another may be contiguous or adjacent to one another, respectively, in at least one example. As one example, components that are in surface-sharing contact with one another may be referred to as being in surface-sharing contact. As another example, elements that are positioned apart from one another, with only a space between them and no other components, may be so referred to, respectively, in at least one example.As yet another example, elements shown above / below each other, on opposite sides of each other, or left / right of each other may be so referred to relative to each other. Further, as shown in the figures, in at least one example, a topmost element or point of an element may be referred to as a "top" of the component, and a bottommost element or point of the element may be referred to as a "bottom" of the component. As used herein, top / bottom, upper / lower, over / under may be relative to a vertical axis of the figures and may be used to describe the positioning of elements of the figures relative to each other. Thus, in one example, elements shown above other elements are positioned vertically above the other elements. As yet another example, shapes of the elements shown within the figures may be referred to as having those shapes (such as a circle).B. as circular, straight, planar, curved, rounded, beveled, angled, or the like). Further, elements shown intersecting one another may be referred to as intersecting elements or intersecting one another in at least one example. Still further, an element shown inside another element or outside another element may be referred to as such in an example. It is understood that one or more components referred to as "substantially similar and / or identical" differ from one another according to manufacturing tolerances (e.g., within 1-5% variation).

[0011] Fig. 1 illustrates an example vehicle propulsion system 100. The vehicle propulsion system 100 includes a fuel-burning engine 110 and an electric motor 120. As a non-limiting example, the engine 110 comprises an internal combustion engine, and the electric motor 120 comprises an electric motor. The electric motor 120 may 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 electric motor 120 may consume electrical energy to produce an electric motor output. Accordingly, a vehicle including the propulsion system 100 may be referred to as a hybrid electric vehicle (HEV).

[0012] The vehicle propulsion system 100 may utilize a variety of different operating modes depending on the operating conditions the vehicle propulsion system is subjected to. Some of these modes may allow the engine 110 to be maintained in a deactivated state (e.g., set to a deactivated state), in which the combustion of fuel in the engine is suspended. For example, under selected operating conditions, the electric motor 120 may propel the vehicle via a drive wheel 130, as indicated by arrow 122, while the engine 110 is deactivated.

[0013] During other operating conditions, the engine 110 may be set to a shut-down state (as described above), while the electric motor 120 may be operated to charge an energy storage device 150. For example, the electric motor 120 may receive wheel torque from the drive wheel 130, as indicated by arrow 122, where the electric motor may convert the vehicle's kinetic energy into electrical energy for storage in the energy storage device 150, as indicated by arrow 124. Thus, in some examples, the electric motor 120 may provide a generator function. However, in other examples, a generator 160 may instead receive wheel torque from the drive wheel 130, where the generator may convert the vehicle's kinetic energy into electrical energy for storage in the energy storage device 150, as indicated by arrow 162.

[0014] During still other operating conditions, the engine 110 may be operated by combusting fuel received from a fuel system 140, as indicated by arrow 142. For example, the engine 110 may be operated to propel the vehicle via the drive wheel 130, as indicated by arrow 112, while the electric motor 120 is off. During other operating conditions, both the engine 110 and the electric motor 120 may each be operated to propel the vehicle via the drive wheel 130, as indicated by arrows 112 and 122, respectively. A configuration in which both the engine and the electric motor can selectively propel the vehicle may be referred to as a parallel-type vehicle propulsion system.It should be noted that in some examples, the electric motor 120 may propel the vehicle through a first set of drive wheels and the engine 110 may propel the vehicle through a second set of drive wheels.

[0015] In other examples, the vehicle propulsion system 100 may be configured as a series-type vehicle propulsion system, whereby the engine does not directly drive the drive wheels.

[0016] Rather, the engine 110 may be operated to power the electric motor 120, which in turn may propel the vehicle via the drive wheel 130, as indicated by arrow 122. For example, during select 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 electric 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 electric 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 in the energy storage device 150 for later use by the electric motor.

[0017] The fuel system 140 may include one or more fuel storage tanks 144 for storing fuel onboard 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 onboard 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 (e.g., E10, E85, etc.) or a mixture of gasoline and methanol (e.g., M10, M85, etc.), which fuels or fuel mixtures may be delivered to the engine 110, as indicated by arrow 142. Other suitable fuels or fuel mixtures may be supplied to the engine 110, which may be combusted in the engine to produce an engine output.The engine output may be used to propel the vehicle, as indicated by arrow 112, or to charge the energy storage device 150 via the electric motor 120 or the generator 160.

[0018] In some examples, energy storage device 150 may be configured to store electrical energy that may be supplied to other on-board vehicle electrical loads (other than the electric motor), including interior heating and air conditioning, engine starting, headlights, interior video and audio systems, etc. As a non-limiting example, energy storage device 150 may include one or more batteries and / or capacitors.

[0019] A control system 190 may communicate with one or more of the engine 110, the electric 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 electric motor 120, the fuel system 140, the energy storage device 150, and the generator 160. Further, in response to this sensory feedback, the control system 190 may send control signals to one or more of the engine 110, the electric motor 120, the fuel system 140, the energy storage device 150, and the generator 160. The control system 190 may receive an indication of an operator-requested output of the vehicle propulsion system from a vehicle operator 102. For example, the control system 190 may receive sensory feedback from a pedal position sensor 194 that communicates with a pedal 192.Pedal 192 may schematically refer to a friction pedal and / or a foot-drive pedal. Furthermore, in some examples, control system 190 may be in communication with a remote engine start receiver 195 (or transceiver) that receives wireless signals 106 from a remote key fob 104 having a remote start button 105. In other examples (not shown), a remote engine start may be initiated via a mobile phone or smartphone-based system, where a user's mobile phone sends data to a server, and the server communicates with the vehicle to start the engine.

[0020] The energy storage device 150 may periodically receive electrical energy from a power source 180 external to the vehicle (e.g., not part of the vehicle), as indicated by arrow 184. As a non-limiting example, the vehicle propulsion system 100 may be configured as a plug-in hybrid electric vehicle (PHEV), whereby electrical energy may be supplied to the energy storage device 150 from the power source 180 via an electrical energy transmission cable 182. During a recharging operation of the energy storage device 150 from the power source 180, the electrical transmission cable 182 may electrically couple the energy storage device 150 and the power source 180. While the vehicle propulsion system is operating to propel the vehicle, the electrical transmission cable 182 between the power source 180 and the energy storage device 150 may be disconnected.The control system 190 may identify and / or control the amount of electrical energy stored in the energy storage device, which may be referred to as the State Of Charge (SOC).

[0021] In other examples, the electrical transmission cable 182 may be omitted, and electrical energy may be received at the energy storage device 150 wirelessly from the power source 180. For example, the energy storage device 150 may receive electrical energy from the power source 180 via one or more of electromagnetic induction, radio waves, and electromagnetic resonance. Accordingly, it is understood that any suitable approach for recharging the energy storage device 150 from a power source that is not part of the vehicle may be used. In this way, the electric motor 120 may propel the vehicle using a different energy source than the fuel used by the engine 110.

[0022] The fuel system 140 may periodically receive fuel from a fuel source located external to the vehicle. As a non-limiting example, the vehicle propulsion system 100 may be refueled by receiving fuel via a fuel dispenser 170, as indicated by arrow 172. In some examples, the fuel tank 144 may be configured to store the fuel received from the fuel dispenser 170 until it is delivered to the engine 110 for combustion. In some examples, the control system 190 may 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), may be communicated to the vehicle operator via, for example, a fuel gauge or an indication on a vehicle instrument panel 196.

[0023] The vehicle propulsion system 100 may also include an ambient temperature / humidity sensor 198 and a stability control sensor, such as lateral and / or longitudinal acceleration and / or yaw rate sensor(s) 199. The vehicle instrument panel 196 may include indicator light(s) and / or a text-based display on which messages are displayed to an operator. The vehicle instrument panel 196 may also include various input portions for receiving operator input, such as buttons, touchscreens, voice input / recognition, etc. For example, the vehicle instrument panel 196 may include a fueling button 197 that may be automatically actuated or pressed by a vehicle operator to initiate fueling.For example, in response to the vehicle operator pressing the refueling button 197, the pressure in a fuel tank in the vehicle may be reduced to allow refueling to occur.

[0024] In some examples, the vehicle propulsion system 100 may include one or more in-vehicle cameras 135. The in-vehicle cameras 135 may communicate photographs and / or video images, for example, to the control system 190. In-vehicle cameras may be used in some examples to record images within a predetermined radius around the vehicle, for example.

[0025] The vehicle system 100 may also include an in-vehicle navigation system 132 (e.g., a global positioning system) with which an operator of the vehicle may interact. The navigation system 132 may include one or more location sensors to assist in estimating vehicle speed, vehicle altitude, vehicle position / location, etc. This information may be used to derive engine operating parameters, such as local barometric pressure. As discussed above, the control system 190 may be further 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 vehicle location, traffic information, etc. to be collected about the vehicle.

[0026] Vehicle system 100 may be in wireless communication with a wireless network 131. Control system 190 may communicate with wireless network 131 via a modem, router, radio signal, or the like. Data regarding various vehicle system conditions may be communicated between control system 190 and the wireless network. Additionally or alternatively, wireless network 131 may communicate conditions of other vehicles to control system 190.

[0027] Fig. 2 shows a schematic diagram of a prior art vehicle system 206. 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 evaporative emission system 251) includes a fuel vapor canister or fuel system canister 222 that may be used to capture and store fuel vapors. In some examples, the vehicle system 206 may be a hybrid electric vehicle system, such as the vehicle propulsion system 100 of Fig. 1. Therefore, the motor 210 can be replaced by the motor 110 Fig. 1, while the control system 214 consists of Fig. 2 the same as the control system 190 from Fig. can be 1.

[0028] 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 the intake manifold 244. Fresh intake air enters an intake passage 242 and flows through an air filter 253. The air filter 253 disposed in the intake passage 242 may clean the intake air before the intake air is directed to the intake manifold 244. Cleaned intake air exiting the air filter 253 may flow via the intake passage 242 past the throttle 262 (also referred to as an intake throttle 262) into the intake manifold 244. As such, the intake throttle 262, when fully open, may allow a greater degree of fluid communication between the intake manifold 244 and the intake passage 242 downstream of the air cleaner 253.An amount of intake air provided to intake manifold 244 may be controlled via throttle 262 based on engine conditions. Engine exhaust 225 includes an exhaust manifold 248 leading to an exhaust passage 235 that directs exhaust gas to the atmosphere. Engine exhaust 225 may include one or more emission control devices 270 that may be mounted at a near-engine location in the exhaust. One or more emission control devices may include a three-way catalyst, a lean NOx converter, or a combined exhaust system. x trap, a diesel particulate filter, an oxidation catalyst, etc. It is understood that other components may be included in the engine, such as a variety of valves and sensors.

[0029] Each cylinder 230 may be operated by one or more valves. In the present example, each cylinder 230 includes a corresponding intake valve 264 and an exhaust valve (not shown). Each intake valve 264 may be held in a desired position via a corresponding spring. The engine system 208 further 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 may be actuated to operate the intake valve 264. In some embodiments where the intake valves of a plurality of cylinders 230 are coupled to a common camshaft, the intake camshaft 268 may be actuated to operate all intake valves of all coupled cylinders.

[0030] The intake valve 264 is operable between an open position allowing intake air into the corresponding cylinder and a closed position substantially blocking intake air from the cylinder. The intake camshaft 268 may be included in an intake valve actuation system 269. The intake camshaft 268 includes an intake cam 267 having a cam lift profile for opening the intake valve 264 during a defined intake duration. The lift profile may affect cam lift, cam duration, and / or cam timing. A controller, such as controller 212, may be capable of switching the intake valve duration by moving the intake camshaft 268 longitudinally and switching between cam profiles.

[0031] It is understood that the intake and / or exhaust camshafts may be coupled to cylinder subsets, and multiple intake and / or exhaust camshafts may be present. The intake valve actuation system 269 may further include pushrods, rocker arms, lifters, etc. Accordingly, the intake valve actuation system may include a plurality of electromechanical actuators. Such devices and features may control the actuation of the intake valve 264 by converting the rotational movement of the cams into a sliding movement of the valves. As previously discussed, the valves may also be actuated via additional cam lift profiles on the camshafts, where the cam lift profiles may provide varying cam lift, cam duration, and / or cam timing between the different valves. However, alternative camshaft arrangements (overhead and / or pushrod) may be used if desired.Further, in some examples, cylinders 230 may each have more than one intake valve. In still other examples, each intake valve 264 of one or more cylinders may be actuated by a common camshaft. Still further, in some examples, some of the intake valves 264 may be actuated by their own independent camshaft or other device.

[0032] The engine system 208 may include variable valve timing systems, such as a variable cam timing (VCT) system 260. Accordingly, the VCT system 260 may be operatively and communicatively coupled to the intake valve actuation system 269. The VCT system 260 may include an intake cam phaser 265 coupled to the common intake camshaft 268 to change the intake valve timing. The VCT system 260 may be configured to advance or retard the valve timing by advancing or retarding the 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.

[0033] The valve / cam control devices and systems described above may be hydraulically driven, electrically actuated, or combinations thereof. In one example, a camshaft position may be changed via cam phasing of an electric actuator (e.g., an electrically actuated cam phaser) with a precision exceeding that of most hydraulically actuated cam phasers. Signal lines may send control signals to and receive cam timing and / or cam selection measurement from the VCT system 260. Accordingly, the valve actuation systems described above may enable the intake valves to close to block fluid flow therethrough when desired.

[0034] Although this is Fig. 2, the vehicle system 206 may also include an exhaust gas recirculation (EGR) system to direct a desired portion of the exhaust gas via an EGR passage from the exhaust passage 235 to the intake manifold 244. The amount of EGR provided may be varied by the controller 212 via adjusting an EGR valve in the EGR passage. By introducing exhaust gas into the engine 210, the amount of available oxygen for combustion is reduced, thereby, for example, reducing combustion flame temperatures and reducing the formation of NO x is reduced.

[0035] The fuel system 218 may include a fuel tank 220 coupled to a fuel pump system 221. The fuel pump system 221 may include one or more pumps for pressurizing fuel delivered to the injectors of the engine 210, such as the example injector 266. While only a single injector 266 is illustrated, additional injectors are provided for each cylinder. It should be understood that the fuel system 218 may be a no-return fuel system, a return fuel system, or various other types of fuel systems.The fuel tank 220 can hold a variety of fuel mixtures, including fuel with a range of alcohol in terms of relative amounts of alcohol within a solution or in a particular volume of space, such as various gasoline-ethanol blends, including E10, E85, gasoline, etc., and combinations thereof. A fuel level sensor 234 located within the fuel tank 220 can provide an indication of the fuel level ("fuel level input") to a controller 212. As depicted, the fuel level sensor 234 can include a float connected to a rheostat. Alternatively, other types of fuel level sensors can be used.

[0036] The vapors generated in the fuel system 218 may be routed via a vapor recovery line 231 to the evaporative emission control system 251, which includes a fuel vapor canister 222. The fuel vapor canister 222 may also be referred to simply as canister 222 herein. Fuel vapors stored in the fuel vapor canister 222 may be purged to the engine intake 223 at a later time. The vapor recovery line 231 may be coupled 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 coupled to the fuel tank 220 via one or more, or a combination, of conduits 271, 273, and 275.

[0037] Further, in some examples, one or more fuel tank vent valves may be located in conduits 271, 273, or 275. Among other functions, fuel tank vent valves may allow a fuel vapor canister of the emissions control system to be maintained at a low pressure or vacuum without increasing the rate of fuel evaporation from the tank (which would otherwise occur if the fuel tank pressure were lowered). For example, conduit 271 may include a grade vent valve (GVV) 287, conduit 273 may include a fill level venting valve (FLVV) 285, and conduit 275 may include a grade vent valve (GVV) 283. Further, in some examples, recovery line 231 may be coupled to a fuel fill system 219 (or refueling system 219).In some examples, the fuel filling system may include a fuel cap 205 for sealing the fuel filling system from the atmosphere. The refueling system 219 is coupled to the fuel tank 220 via a fuel filler tube or fuel filler neck 211.

[0038] Further, the refueling system 219 may include a refueling lock 245. In some embodiments, the refueling lock 245 may be a fuel cap locking mechanism. The fuel cap locking mechanism may be configured to automatically lock the fuel cap in a closed position so that the fuel cap cannot be opened. For example, the fuel cap 205 may remain locked via the refueling lock 245 while the pressure or vacuum in the fuel tank is above a threshold. In response to a refueling request, e.g., a request initiated by a vehicle operator, the pressure in the fuel tank may be reduced and the fuel cap unlocked after the pressure or vacuum in the fuel tank drops below the threshold.A fuel cap locking mechanism may be a clutch that, when engaged, prevents removal of the fuel cap. The clutch may be locked electrically, for example, by a solenoid, or may be locked mechanically, for example, by a pressure diaphragm.

[0039] In some embodiments, the refueling lock 245 may be a filler tube valve located at an opening of the fuel filler neck 211. In such embodiments, the refueling lock 245 may not prevent removal of the fuel cap 205. Instead, the refueling lock 245 may prevent insertion of a refueling pump into the fuel filler tube 211. The filler tube valve may be electrically locked, for example, by a solenoid, or mechanically locked, for example, by a pressure diaphragm.

[0040] In some embodiments, the refueling lock 245 may be a fuel door lock, such as a clutch that locks a fuel door located in a body panel of the vehicle. The refueling door lock may be electrically locked, for example, by a solenoid, or mechanically locked, for example, by a pressure diaphragm.

[0041] In embodiments where the refueling lock 245 is locked using an electrical mechanism, the refueling lock 245 may be unlocked by commands from the controller 212, for example, when a fuel tank pressure decreases below a pressure threshold. In embodiments where the refueling lock 245 is locked using a mechanical mechanism, the refueling lock 245 may be unlocked via a pressure gradient, for example, when a fuel tank pressure decreases to atmospheric pressure.

[0042] The evaporative emissions control system 251 may include one or more emissions control devices, such as one or more fuel vapor canisters 222 (also referred to as canisters 222) filled with a suitable adsorbent. The canisters are configured to temporarily contain fuel vapors (including vaporized hydrocarbons) during fuel tank refueling operations and "run-loss" (i.e., fuel vaporized during vehicle operation). In one example, the adsorbent used is activated carbon. The evaporative emissions system 251 may further include a canister vent path or conduit 227 that can direct gases from the canister 222 to the atmosphere when storing or trapping fuel vapors from the fuel system 218.

[0043] The vent line 227 may allow fresh air to be drawn into the canister 222 when stored fuel vapors are purged from the canister 222 to the engine intake 223 via a purge line 228 and a canister purge valve 261 (also referred to as purge valve 261). For example, the purge valve 261 may be normally closed but opened during certain conditions so that vacuum from the engine intake manifold 244 is provided to the fuel vapor canister 222 for purging.

[0044] A fuel tank isolation valve (FTIV) 252 may be positioned between the fuel tank and the fuel vapor canister within the conduit 278. The FTIV 252 may be a normally closed valve that, when open, allows fuel vapors to vent from the fuel tank 220 into the canister 222. Fuel vapors may be stored within the canister 222, and air from which fuel vapors have been extracted may then be vented to the atmosphere via the vent line 227. Fuel vapors stored in the fuel vapor canister 222 may be purged along the purge line 228 via the canister purge valve 261 to the engine intake 223 at a later time when purge conditions exist. Accordingly, the FTIV 252, when closed, can isolate and seal the fuel tank 220 from the evaporative emission system 251.It is noted that certain vehicle systems may not include the FTIV 252.

[0045] The fuel system 218 can be operated in a variety of modes by the controller 212 through selective adjustment of the various valves and solenoids. For example, the fuel system can be operated in a fuel vapor storage mode (e.g., during a fuel tank refueling operation and when the engine is not running), where the controller 212 can open the FTIV 252 while closing the canister purge valve (CPV) 261 to direct refueling vapors into the canister 222 and prevent the fuel vapors from being directed into the intake manifold.

[0046] As another example, the fuel system may be operated in a refueling mode (e.g., when refueling of the fuel tank is requested by a vehicle operator), where the controller 212 may open the FTIV 252 while keeping the CPV 261 closed to reduce the pressure in the fuel tank before allowing fuel to be added. Thus, the FTIV 252 may be kept open during the refueling process to allow refueling vapors to be stored in the canister. After refueling is complete, the FTIV may be closed.

[0047] As yet another example, the fuel system may be operated in a canister purge mode (e.g., after an emission control device light-off temperature has been reached and while the engine is running), where the controller 212 may open the CPV 261 while closing the FTIV 252. Here, the vacuum generated by the intake manifold of the operating engine may be used to draw fresh air through the vent line 227 and through the fuel vapor canister 222 to purge the stored fuel vapors into the intake manifold 244. In this mode, the fuel vapors purged from the canister are combusted in the engine. Purging may continue until the amount of stored fuel vapors in the canister is below a threshold. The FTIV 252 may be closed during the purge mode.

[0048] The controller 212 may include a portion of a control system 214. The 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, the sensors 216 may include a manifold absolute pressure sensor (MAP sensor) 224, a barometric pressure sensor (BP sensor) 246, an exhaust gas sensor 226 located in the exhaust manifold 248 upstream of the emissions control device, a temperature sensor 233, a fuel tank pressure sensor 291 (also referred to as a fuel tank pressure transducer or FTPT), and a canister temperature sensor 232.Other sensors, such as pressure, temperature, air-fuel ratio, and composition sensors, may be coupled to various locations in the vehicle system 206. As another example, the actuators may include the CPV 261, the fuel injector 266, the throttle 262, the FTIV 252, the fuel pump 221, and the refueling interlock 245. The control system 214 may include a 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 an instruction or code programmed therein corresponding to one or more routines.

[0049] The controller 212 receives signals from the various sensors Fig. 2 and exposes the various actuators Fig. 2 to adjust engine operation based on the received signals and instructions stored in a 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 vapors therethrough. Accordingly, the controller 212 may communicate a signal to the actuator (e.g., the canister purge valve solenoid) of the canister purge valve based on a desired purge flow rate. Accordingly, the canister purge valve solenoid may be opened (and pulsed) in a specific duty cycle to allow flow of stored vapors from the canister 222 to the intake manifold 244 via the purge line 228.

[0050] With reference now to Fig. 3 shows this one embodiment of a fuel system 300. The fuel system 300 can be used in the engine system of Fig. 1 and / or 2. 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 the fuel tank 220 of Fig. 2. The fuel tank 302 may include a port 304 to which a loading line 306 is fluidly coupled. The loading line 306 may be configured to flow fuel vapors to and / or from the fuel tank 302. An FTPT 308 may be coupled to the fuel tank 302 at a location proximal to the loading line 306.

[0051] In contrast to the example from Fig. 2, which includes only a single canister coupled to a loading line (e.g., line 278), the fuel system 300 includes a first canister 320 and a second canister 340 coupled to the loading line 306. In one example, the fuel system 300 is similar to the fuel system 218 of Fig. 2, except that the fuel system 300 includes at least two canisters and the fuel system 218 includes only one canister. In this way, the first and second canisters 320, 340 can replace the single canister from Fig. 2 in the vehicle system 206.

[0052] The first loading line 306 may bifurcate and be fluidly coupled to a first loading line 312 and a second loading line 314. The first loading line 312 may be fluidly coupled to a first loading port 322 of the first canister 320. The second loading line 314 may be fluidly coupled to a second loading port 342 of the second canister 340.

[0053] Each of the first canister 320 and the second canister 340 may be coupled to a CPV 316. In one example, the CPV 316 may be coupled to the CPV 261 of Fig. 2. The CPV 316 may direct vapors to an engine intake during conditions such as when combustion is occurring and fuel is being consumed. The first canister 320 may include a first canister purge line 324 and the second canister 340 may include a second canister purge line 344. The first canister purge line 324 may be coupled to the first canister 320 at a first canister purge port 326. The second canister purge line 344 may be coupled to the second canister 340 at a second canister purge port 346. The first canister purge line 324 and the second canister purge line 344 may intersect upstream of the CPV 316 relative to a direction of vapor flow.

[0054] Each of the first canister 320 and the second canister 340 may further include respective vent lines. The first canister 320 may include a first canister vent line 328 coupled to a first canister vent valve (CVV1) 330. The second canister 340 may include a second canister vent line 348 coupled to a second canister vent valve (CVV2) 350. The first and second vent lines may converge to form a common vent line 360. A dust box 362 may be disposed in the common vent line 360 upstream of the atmosphere with respect to a gas flow direction.

[0055] As described in more detail below, the fuel system 300 may be operated to equalize loading of the first canister 320 and the second canister 340 during a refueling event and / or a purge event. The refueling event may include admitting fuel into the fuel tank 302. The purge event may include directing vapors from the first canister 320 and the second canister 340 to an engine via opening the CPV 316. In doing so, the engine may perform combustion during the purge event to consume vapors purged through the first canister 320 and the second canister 340. In one example, a method may include oscillating a canister vent valve (CVV) of a less loaded one of the first canister 320 and the second canister 340 between an open position and a fully closed position during the purge event.Another method may include oscillating a canister vent valve (CVV) of a less loaded one of the first canister 320 and the second canister 340 between an open position and a fully closed position during the refueling event. The less loaded canister may be purged less during the purge event than the more heavily loaded canister. During the refueling event, the less loaded canister may hold more vapors.

[0056] In one example, a length and diameter of the lines to and from the canisters may be substantially identical. That is, a length and diameter of the first loading line 312 and the second loading line 314 may be identical. A length and diameter of the first canister purge line 324 and the second canister purge line 344 may be identical. A length and diameter of the first canister vent line 328 and the second canister vent line 348 may be identical. A size and volume, including the carbon bed, of the first canister 320 and the second canister 340 may be identical. As a result, constrictions of the canisters may be substantially identical, thereby promoting more uniform vapor flow.

[0057] Comparatively, a load of the canisters can be determined via a differential pressure sensor 310. The differential pressure sensor 310 can be coupled to the first canister purge line 324 and the second canister purge line 344. An imbalance (e.g., a pressure difference) detected by the differential pressure sensor 310 corresponds to a difference in the load of one of the first canister 320 and the second canister 340.

[0058] In some examples, the operation of CVV1 330 and CVV2 350 may additionally or alternatively be based directly on feedback from differential pressure sensor 310. If a pressure difference is detected by differential pressure sensor 310 indicating an imbalance between first canister 320 and second canister 340, a CVV of a less loaded canister may be oscillated during a purge event. Alternatively, if a pressure difference is detected by differential pressure sensor 310 during a refueling event, a CVV of a more heavily loaded canister may be oscillated. The operation of CVV1 330 and CVV2 350 during purge and refueling events based on feedback from differential pressure sensor 310 is described in more detail below.

[0059] With reference now to Fig. 4, this illustrates a method 400 for adjusting operation of the CVV1 of the first canister or the CVV2 of the second canister in response to an imbalance detected during a purge event. Instructions for performing the method 400 and the other methods included herein may be executed by a controller based on instructions stored in 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 the Fig. 1 and Fig. 3. The controller may use motor actuators of the engine system to adjust engine operation according to the methods described below.

[0060] Method 400 begins at 402, which includes determining whether a purge event is occurring. The purge event may include routing fuel vapors from the canisters to the engine. In doing so, CVV1 and CVV2 may be signaled to open, and CPV may be signaled to open.

[0061] If no purge event occurs, method 400 may proceed to 502 of method 500, as described in the following Fig. 5. When a purge event occurs, method 400 may include measuring a pressure differential at 404. The pressure differential may be measured via the differential pressure sensor coupled to the first canister vent line and the second canister vent line. The differential pressure sensor may be configured to measure a difference (e.g., a pressure differential) between the first and second canister vent lines. In some examples, the pressure differential may be correlated to a respective load of the canisters.

[0062] At 406, method 400 may include determining whether P1 is equal to P2. P1 may correspond to a pressure sensed in the first canister vent line, and P2 may correspond to a pressure sensed in the second canister vent line. If P1 is equal to P2, there is no pressure differential and the canister loads are balanced.

[0063] At 408, method 400 may include maintaining CVV1 and CVV2 open during the purge event. Each of the first canister and the second canister may be purged equally.

[0064] Returning to 406, if P1 is not equal to P2, method 400 may include determining whether P1 is greater than P2 at 410. During the purge event, a negative pressure may develop in the evaporative emissions system. If a positive pressure differential is detected (e.g., P1>P2), the second canister is more restricted and contains a higher load than the first canister.

[0065] If P1 is greater than P2, method 400 may include oscillating CVV1 between a closed and an open position at 412. In doing so, the CVV of the less loaded canister is oscillated. In one example, the open positions are less than fully open positions where 100% flow is allowed. An amount of opening of the open position may be inversely related to the sensed pressure differential. For example, a more positive pressure differential may include a less open position of CVV1. As another example, a less positive pressure differential may include a more open position of CVV1. In doing so, a purge amount of the first canister may be adjusted based on an amount of restriction in the second canister.In one example, the first canister may be purged less during the purge event because the second canister is more restricted, further increasing the imbalance. The lesser purging of the first canister may involve oscillating the CVV1 between a fully closed position and a less open position.

[0066] Additionally or alternatively, a flushing level can be further adjusted by setting the time period during which the CVV1 remains in the fully closed position and the open position. Thus, the CVV1 can be a two-position valve, whereby the time period during which the CVV1 remains fully closed can be reduced as the pressure differential approaches zero.

[0067] At 414, method 400 may include opening the CVV2. The CVV2 may be opened to a fully open position to allow for complete purging of the second canister. In this way, equilibrium between the first canister and the second canister may be achieved more quickly.

[0068] At 416, method 400 may include increasing an opening amount of CVV1. CVV1 may continue to oscillate between an open and a closed position. However, the size of the opening of the open position may increase. As the method progresses, the first canister may be increasingly purged, and the imbalance between the first canister and the second canister decreases.

[0069] At 418, method 400 may include determining whether P1 is equal to P2. If P1 is still not equal to P2, method 400 may continue to oscillate CVV1 and increase its opening amount when in the open position until equilibrium is reached and no pressure differential is detected.

[0070] If P1 is equal to P2, method 400 may include maintaining CVV1 open at 420. In doing so, the first canister and the second canister may be purged relatively evenly once the pressure differential is no longer sensed and the first canister is balanced with the second canister. This may prevent the purge time for the first canister from being missed during the purge event while achieving balance between the first canister and the second canister.

[0071] Again, at 410, if P1 is not greater than P2, then P2 is greater than P1. The first canister is more constricted than the second canister. Therefore, it may be desirable to oscillate the CVV of the less loaded canister, such as the second canister.

[0072] At 422, method 400 may include oscillating the CVV2 between a closed and an open position. In one example, the open positions are less than fully open positions (e.g., 100% flow). An amount of opening of the open position may be inversely related to the sensed pressure differential. For example, a more negative pressure differential may include a less open position of the CVV2. As another example, a less negative pressure differential may include a more open position of the CVV2. In doing so, a purge amount of the second canister may be adjusted based on an amount of restriction in the first canister. In one example, the second canister may be purged less during the purge event because the first canister is more restricted, further increasing the imbalance.The lesser purging of the second canister may involve oscillating the CVV2 between a fully closed position and a less open position such that the second canister is at least partially purged during the purge event.

[0073] Additionally or alternatively, a purge level can be further adjusted by adjusting the time the CVV2 remains in the fully closed position and the open position. In some examples, the CVV2 may be a two-position valve, and the time the CVV2 remains fully closed may be reduced as the pressure differential approaches zero. In this way, manufacturing resources of the evaporative emissions system may be reduced.

[0074] At 424, method 400 may include opening the CVV1. The CVV1 may be opened to a fully open position to allow for complete purging of the first canister. In this way, equilibrium between the first canister and the second canister may be achieved more quickly.

[0075] At 426, method 400 may include increasing an opening amount of the CVV2. The CVV2 may continue to oscillate between an open and a closed position. However, the size of the opening of the open position may increase. As the method progresses, the second canister may be increasingly purged, and the imbalance (e.g., the pressure differential) between the first canister and the second canister decreases.

[0076] At 428, method 400 may include determining whether P1 is equal to P2. If P1 is not equal to P2, method 400 may continue to oscillate CVV2 and increase its opening amount if it is in the open position until equilibrium is reached and no pressure differential is detected. CVV1 may remain fully open.

[0077] If P1 is equal to P2, method 400 may include holding CVV2 open at 430. In doing so, CVV2 may no longer be oscillated. In one example, CVV2 may be opened to an identical position to CVV1.

[0078] With reference now to Fig. 5 illustrates a method 500 for adjusting operation of the CVV1 of the first canister or the CVV2 of the second canister in response to an imbalance detected during a refueling event.

[0079] The procedure 500 starts at 502, after at 402 from Fig. 4, it has been determined that no purge event is occurring. At 502, method 500 includes determining whether a refueling event is occurring. The purge event may include supplying fuel to a fuel tank of the vehicle. The fuel tank may be fluidly coupled to the evaporative emissions system, including the first canister and the second canister. During the refueling event, a pressure of the fuel tank may be increased, and removal of fuel vapors generated therein may be desired to achieve a fuel tank fill level.

[0080] If no refueling event occurs, method 500 may proceed to 504 of method 500, which includes not pulsing the CVV1 or CVV2. In doing so, the CVV1 and / or CVV2 may be maintained in closed or open positions. The vehicle may be operating in a coasting mode, an all-electric mode, or another mode in which purging and refueling do not occur.

[0081] If no purge event occurs, method 500 may include measuring a pressure differential at 506. The pressure differential may be measured via the differential pressure sensor coupled to the first canister vent line and the second canister vent line. The differential pressure sensor may be configured to measure a difference (e.g., a pressure differential) between the first and second canister vent lines. In some examples, the pressure differential may be correlated to a respective load of the canisters.

[0082] At 508, method 500 may include determining whether P1 is equal to P2. P1 may correspond to a pressure sensed in the first canister vent line, and P2 may correspond to a pressure sensed in the second canister vent line. If P1 is equal to P2, there is no pressure differential and the canister loads are balanced, and method 500 proceeds to 504. During the refueling event, where the first canister and the second canister are balanced and no pressure differential is sensed, CVV1 and CVV2 may be commanded to identical positions. This may maintain balance.

[0083] If P1 is not equal to P2, method 500 may include determining at 510 whether P1 is greater than P2. During the refueling event, overpressure may develop in the evaporative emissions system. If a positive pressure differential is detected (e.g., P1>P2), the first canister is more restricted and contains a higher load than the second canister.

[0084] If P1 is greater than P2, method 500 may include oscillating CVV1 between a closed and an open position at 512. In doing so, the CVV of the more heavily loaded canister is oscillated during the refueling event. In one example, the open positions are less than fully open positions (e.g., 100% flow). An amount of opening of the open position may be inversely related to the sensed pressure differential. For example, a more positive pressure differential may include a less open position of CVV1. As another example, a less positive pressure differential may include a more open position of CVV1. In doing so, an amount of vapor flow of the first canister may be adjusted based on the restriction of the first canister.In one example, the first canister may hold less fuel vapor during the refueling event because the first canister is more restricted, further increasing the imbalance. The lower loading of the first canister may involve oscillating the CVV1 between a fully closed position and a less open position.

[0085] Additionally or alternatively, a loading level can be further adjusted by setting a time period during which the CVV1 remains in the fully closed position and a fully open position.

[0086] At 514, method 500 may include opening the CVV2. The CVV2 may be opened to a fully open position to allow maximum vapor flow to the second canister. In this way, equilibrium between the first canister and the second canister may be achieved more quickly.

[0087] At 516, method 500 may include increasing an opening amount of CVV1. CVV1 may be oscillated between an open and a closed position. However, the size of the opening of the open position may increase. In doing so, the first canister may accommodate more vapor flow over the course of the method, and the imbalance between the first canister and the second canister decreases.

[0088] At 518, method 500 may include determining whether P1 is equal to P2. If P1 is not equal to P2, method 500 may continue to oscillate CVV1 and increase its opening amount when in the open position until equilibrium is reached and no pressure differential is detected.

[0089] If P1 is equal to P2, method 500 may include maintaining CVV1 open at 520. This may allow the first canister and the second canister to be loaded relatively evenly once the pressure differential is no longer sensed and the first canister is equal to the second canister. This may allow both canisters to be loaded during the refueling event, which may improve customer satisfaction and canister longevity.

[0090] Again, at 510, if P1 is not greater than P2, then P2 is greater than P1. The second canister is more constricted than the first. Thus, it may be desirable to oscillate the CVV of the more heavily loaded canister, such as the second canister.

[0091] At 522, method 500 may include oscillating the CVV2 between a closed and an open position. In one example, the open positions are less than fully open positions (e.g., 100% flow). An amount of opening of the open position may be inversely related to the sensed pressure differential. For example, a more negative pressure differential may include a less open position of the CVV2. As another example, a less negative pressure differential may include a more open position of the CVV2. In doing so, a loading amount of the second canister (e.g., vapor flow thereto) may be adjusted based on an amount of restriction in the second canister. In one example, the second canister may be less loaded during the refueling event because the second canister is more restricted, further increasing the imbalance.The lower loading of the second canister may involve oscillating the CVV2 between a fully closed position and a less open position so that the second canister is loaded to a lesser degree during the refueling event compared to the first canister.

[0092] Additionally or alternatively, a purge level can be further adjusted by adjusting the time the CVV2 remains in the fully closed position and the open position. In some examples, the CVV2 may be a two-position valve, and the time the CVV2 remains fully closed may be reduced as the pressure differential approaches zero. In this way, manufacturing resources of the evaporative emissions system may be reduced.

[0093] At 524, method 500 may include opening the CVV1. The CVV1 may be opened to a fully open position to allow for a high loading level of the first canister. In this way, equilibrium between the first canister and the second canister may be achieved more quickly as the first canister is progressively constricted.

[0094] At 526, method 500 may include increasing an opening amount of CVV2. CVV2 may continue to oscillate between an open and a closed position. However, the size of the opening of the open position may increase. As the method progresses, the second canister may become increasingly loaded, and the imbalance (e.g., the pressure differential) between the first canister and the second canister decreases.

[0095] At 528, method 500 may include determining whether P1 is equal to P2. If P1 is not equal to P2, method 500 may continue to oscillate CVV2 and increase its opening amount if it is in the open position until equilibrium is reached and no pressure differential is detected. CVV1 may remain fully open.

[0096] If P1 is equal to P2, method 500 may include holding CVV2 open at 530. In doing so, CVV2 may no longer be oscillated. In one example, CVV2 may be opened to an identical position to CVV1. In this way, the first canister and the second canister may be loaded evenly.

[0097] With reference now to Fig.6 depicts an operating sequence 600 graphically illustrating a refueling event. Trace 610 indicates whether a refueling event is occurring. Trace 620 indicates a first pressure (P1) sensed in a vent line coupled to a first canister. Trace 630 indicates a second pressure (P2) sensed in a vent line coupled to a second canister. Trace 640 indicates a pressure differential sensed by a differential pressure sensor. Trace 650 indicates operation of a first CVV (CVV1) of the first canister. Trace 660 indicates operation of a second CVV (CVV2) of the second canister. Time increases from a left side to a right side of the figure.

[0098] A refueling event occurs before t1. P1 and P2 are sensed via a differential pressure sensor. A pressure difference based on P1 and P2 is positive, indicating that the first canister is more restricted than the second canister. The canister restriction may be proportional to a canister load, with the restriction increasing with increasing load. In this way, the first canister is more heavily loaded than the second canister. To balance the canister during the refueling event while vapors are still flowing to both canisters, it may be desirable to oscillate CVV1 to reduce vapor flow to the first canister while still allowing partial loading of the first canister.

[0099] At t1, the CVV2 is moved to a fully open position. This involves moving the CVV of the less loaded canister to the fully open position during the refueling event. Between t1 and t2, the CVV1 is oscillated between a fully closed position and open positions with varying degrees of opening. For example, as the pressure differential approaches 0, the CVV1 can be commanded to slightly more open positions than an open position of a previous oscillation. Additionally, the amount of time spent in the open position is increased. This allows for more accurate balancing of the first canister and the second canister and prevents overloading of the second canister.

[0100] At t2, the pressure difference is 0. P1 is equal to P2, indicating equilibrium between the first canister and the second canister. CVV1 is commanded to the fully open position.

[0101] After t2, CVV1 and CVV2 are both in fully open positions, allowing both canisters to be evenly loaded during the remainder of the refueling event.

[0102] The technical effect of adjusting the operation of a CVV based on feedback from a differential pressure sensor is to provide additional opportunities for canister equalization due to reduced engine runtime in hybrid vehicles. The CVV of a less loaded canister may be oscillated during purge events to allow a more heavily loaded canister to undergo a relatively larger purge volume while still purging the less loaded canister. The CVV of a more heavily loaded canister may be oscillated during refueling events to allow a less loaded canister to be more heavily charged while still charging the more heavily loaded canister.

[0103] The disclosure provides support for a system including a differential pressure sensor disposed between a first purge line coupled to a first canister and a second purge line coupled to a second canister arranged parallel to the first canister. A first example of the system further includes where the first canister and the second canister are fuel vapor canisters. A second example of the system, optionally including the first example, further includes where a first canister vent valve (CVV1) is configured to control vapor flow between a first canister vent line and the first canister.A third example of the system, optionally including one or more of the preceding examples, further includes a second canister vent valve (CVV2) configured to control vapor flow between a second canister vent line and the second canister. A fourth example of the system, optionally including one or more of the preceding examples, further includes a controller having instructions stored in persistent memory thereof that, when executed, cause the controller to command opening and closing a canister vent valve of a less loaded canister during a purge of the first canister and the second canister, wherein a loading of the first canister and the second canister is comparatively measured via the differential pressure sensor.A fifth example of the system, optionally including one or more of the preceding examples, further includes where the instructions further cause the controller to command opening and closing a canister vent valve of a more heavily loaded canister during a refueling event. A sixth example of the system, optionally including one or more of the preceding examples, further includes where the instructions further cause the controller to command the canister vent valve to more open positions during an oscillation between open and closed as a pressure differential sensed by the differential pressure sensor approaches zero.

[0104] The disclosure provides additional support for a method that includes oscillating a canister vent valve of a less loaded canister between an open position and a closed position during purging of at least two canisters arranged in parallel, wherein a load of the at least two canisters is comparatively measured via a differential pressure sensor arranged between purge lines of the at least two canisters. A first example of the method further includes wherein the oscillating further comprises increasing an opening amount of the canister vent valve as a differential pressure sensed by the differential pressure sensor approaches zero. A second example of the method, optionally including the first example, further includes wherein a canister vent valve of a more loaded canister is fully open during purging of the at least two canisters.A third example of the method, optionally including one or more of the preceding examples, further includes oscillating a canister vent valve of a more heavily loaded canister during a refueling event. A fourth example of the method, optionally including one or more of the preceding examples, further includes fully opening the canister vent valve of the less heavily loaded canister during the refueling event. A fifth example of the method, optionally including one or more of the preceding examples, further includes the refueling event comprising directing fuel to a fuel tank fluidly coupled to the at least two canisters.A sixth example of the method, optionally including one or more of the preceding examples, further includes wherein purging comprises directing vapors from the at least two canisters to an engine of a vehicle. A seventh example of the method, optionally including one or more of the preceding examples, further includes wherein the canister vent valve is disposed in a purge line of the less loaded canister.

[0105] The disclosure further provides support for a system including a first canister arranged in parallel with a second canister, a differential pressure sensor coupled to purge lines of the first canister and the second canister, and a controller including instructions in memory that cause the controller to oscillate a canister vent valve between an open position and a closed position of a less loaded one of the first canister and the second canister during a purge event. A first example of the system further includes further opening the open position as a pressure difference sensed by the differential pressure sensor approaches zero.A second example of the system, optionally including the first example, further includes where the instructions further cause the controller to fully open the canister vent valve in response to a pressure difference sensed by the pressure difference sensor being zero. A third example of the system, optionally including one or more of the preceding examples, further includes where the canister vent valve is one of two canister vent valves, each of the two canister vent valves being disposed in a corresponding vent line of the first canister and the second canister. A fourth example of the system, optionally including one or more of the preceding examples, further includes where the first canister and the second canister are fluidly coupled to an engine during the purge event.

[0106] It should be noted that the example control and estimation routines included in this document may be used with various engine and / or vehicle system configurations. The control methods and routines disclosed in this document may be stored as executable instructions in non-transitory memory and may be executed by the control system including the controller in combination with the various sensors, actuators, and other engine hardware. The specific routines described in this document may represent one or more of any number of processing strategies, such as event-driven, interrupt-driven, multitasking, multithreading, and the like. Accordingly, various illustrated acts, operations, and / or functions may be performed in the illustrated sequence or in parallel, or in some cases, may be omitted.Likewise, 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 illustrated acts, operations, and / or functions may be performed repeatedly depending on the particular strategy employed. Further, the described acts, operations, and / or functions may graphically represent code to be programmed into non-transitory memory of the computer-readable storage medium in the engine control system, wherein the described acts are performed by executing the instructions in a system including the various engine hardware components in combination with the electronic controller.

[0107] It should be understood that the configurations and routines disclosed herein are exemplary in nature and that these specific embodiments are not to be considered limiting, as numerous variations are possible. For example, the foregoing technique may be applied to V6, I4, I6, V12, horizontally opposed 4-cylinder, and other engine types. The subject matter of the present disclosure includes all novel and non-obvious combinations and subcombinations of the various systems and configurations, as well as other features, functions, and / or characteristics disclosed herein.

[0108] In this context, the term “approximately” is intended to mean plus or minus five percent of the range, unless otherwise specified.

[0109] The following claims particularly point out specific combinations and subcombinations that are considered novel and non-obvious. These claims may refer to "a" element or "a first" element, or the equivalent thereof. Such claims are to be construed as including the inclusion of one or more such elements and 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 amending the present claims or by filing new claims in this or a related application.Such claims, whether broader, narrower, equal, or different in scope than the original claims, are also considered to be included within the subject matter of the present disclosure.

[0110] According to the present invention, a system is provided comprising: a differential pressure sensor disposed between a first purge line coupled to a first canister and a second purge line coupled to a second canister disposed parallel to the first canister.

[0111] According to one embodiment, the first canister and the second canister are fuel vapor canisters.

[0112] According to one embodiment, a first canister vent valve (CVV1) is configured to control vapor flow between a first canister vent line and the first canister.

[0113] According to one embodiment, a second canister vent valve (CVV2) is configured to control vapor flow between a second canister vent line and the second canister.

[0114] According to one embodiment, the invention is further characterized by a controller having instructions stored in a persistent memory thereof that, when executed, cause the controller to command opening and closing of a canister vent valve of a less loaded canister during purging of the first canister and the second canister, wherein a loading of the first canister and the second canister is comparatively measured via the differential pressure sensor.

[0115] According to one embodiment, the instructions further cause the controller to command opening and closing of a canister vent valve of a more heavily loaded canister during a refueling event.

[0116] According to one embodiment, the instructions further cause the controller to command the canister vent valve to more open positions during an oscillation between open and closed as a pressure difference sensed by the differential pressure sensor approaches zero.

[0117] According to the present invention, a method includes: oscillating a canister vent valve of a less loaded canister between an open position and a closed position during purging of at least two canisters arranged in parallel, wherein a load of the at least two canisters is comparatively measured via a differential pressure sensor arranged between purge lines of the at least two canisters.

[0118] In one aspect of the invention, oscillating further comprises increasing an opening amount of the canister vent valve as a differential pressure sensed by the differential pressure sensor approaches zero.

[0119] In one aspect of the invention, a canister vent valve of a more heavily loaded canister is fully opened during purging of the at least two canisters.

[0120] In one aspect of the invention, the method includes oscillating a canister vent valve of a more heavily loaded canister during a refueling event.

[0121] In one aspect of the invention, the canister vent valve of the less loaded canister is fully opened during the refueling event.

[0122] In one aspect of the invention, the refueling event comprises directing fuel to a fuel tank fluidly coupled to the at least two canisters.

[0123] In one aspect of the invention, purging comprises directing vapors from the at least two canisters to an engine of a vehicle.

[0124] In one aspect of the invention, the canister vent valve is arranged in a purge line of the less loaded canister.

[0125] According to the present invention, a system is provided comprising: a first canister arranged in parallel with a second canister; a differential pressure sensor coupled to purge lines of the first canister and the second canister; and a controller including instructions in memory that cause the controller to oscillate a canister vent valve between an open position and a closed position of a less loaded one of the first canister and the second canister during a purge event.

[0126] According to one embodiment, the open position is further opened when a pressure difference detected by the differential pressure sensor approaches zero.

[0127] In one embodiment, the instructions further cause the controller to fully open the canister vent valve in response to a pressure differential sensed by the pressure differential sensor being equal to zero.

[0128] According to one embodiment, the canister vent valve is one of two canister vent valves, each of the two canister vent valves being arranged in a corresponding vent line of the first canister and the second canister.

[0129] According to one embodiment, the first canister and the second canister are fluidly coupled to an engine during the purge event.

Claims

[1] System comprising: a differential pressure sensor disposed between a first purge line coupled to a first canister and a second purge line coupled to a second canister disposed parallel to the first canister. [2] The system of claim 1, wherein the first canister and the second canister are fuel vapor canisters. [3] The system of claim 1, wherein a first canister vent valve (CVV1) is configured to control vapor flow between a first canister vent line and the first canister. [4] The system of claim 3, wherein a second canister vent valve (CVV2) is configured to control vapor flow between a second canister vent line and the second canister. [5] The system of claim 1, further comprising a controller having instructions stored in a persistent memory thereof that, when executed, cause the controller to command opening and closing of a canister vent valve of a less loaded canister during purging of the first canister and the second canister, wherein a loading of the first canister and the second canister is comparatively measured via the differential pressure sensor. [6] The system of claim 5, wherein the instructions further cause the controller to command opening and closing of a canister vent valve of a more heavily loaded canister during a refueling event. [7] The system of claim 5, wherein the instructions further cause the controller to command the canister vent valve to more open positions during an oscillation between open and closed as a pressure differential sensed by the differential pressure sensor approaches zero. [8] Method comprising: Oscillating a canister vent valve of a less loaded canister between an open position and a closed position during purging of at least two canisters arranged in parallel, wherein a load of the at least two canisters is comparatively measured via a differential pressure sensor arranged between purge lines of the at least two canisters. [9] The method of claim 8, wherein oscillating further comprises increasing an opening amount of the canister vent valve as a differential pressure sensed by the differential pressure sensor approaches zero. [10] The method of claim 8, wherein a canister vent valve of a more heavily loaded canister is fully opened during purging of the at least two canisters. [11] The method of claim 8, further comprising oscillating a canister vent valve of a more heavily loaded canister during a refueling event. [12] The method of claim 11, wherein the canister vent valve of the less loaded canister is fully opened during the refueling event. [13] The method of claim 11, wherein the refueling event comprises directing fuel to a fuel tank fluidly coupled to the at least two canisters. [14] The method of claim 8, wherein purging comprises directing vapors from the at least two canisters to an engine of a vehicle. [15] The method of claim 8, wherein the canister vent valve is located in a purge line of the less loaded canister.

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