阅读说明：本技术 抽取控制方法和系统 (Extraction control method and system ) 是由 艾德·杜道尔 于 2020-02-11 设计创作，主要内容包括：本公开提供了“抽取控制方法和系统”。提供了用于降低滤罐抽取期间的发动机失速发生率的方法和系统。以较高的抽取缓变率向一个或多个气缸被选择性停用的发动机抽取燃料蒸气滤罐。响应于潜在或部分发动机失速的指示,重新启动所述停用的气缸并且降低所述滤罐抽取缓变率。(The present disclosure provides an extraction control method and system. Methods and systems for reducing the incidence of engine stall during canister purging are provided. The fuel vapor canister is purged at a higher purge ramp rate to the engine with one or more cylinders selectively deactivated. In response to an indication of a potential or partial engine stall, the deactivated cylinders are reactivated and the canister purge ramp rate is reduced.)

1. A method for an engine of a vehicle, the method for an engine of a vehicle comprising:

deactivating one or more cylinders in response to a request to purge fuel vapor from a canister; and

deactivating the extraction and reactivating the one or more deactivated cylinders in response to an indication of engine stall.

2. The method of claim 1, further comprising selecting a number of the one or more cylinders to deactivate as a function of a vehicle occupancy level, the number increasing as the occupancy level decreases.

3. The method of claim 2, further comprising: purging the fuel vapor from the canister to the engine having the one or more deactivated cylinders and remaining active cylinders at a first purge ramp rate prior to deactivating the purging, the first purge ramp rate based on a canister load, the selected number of the one or more deactivated cylinders.

4. The method of claim 1, wherein reactivating the one or more deactivated cylinders comprises injecting fuel into the deactivated cylinders prior to Intake Valve Opening (IVO) and combusting previously inducted air charges in the deactivated cylinders.

5. The method of claim 3, further comprising: temporarily disabling fuel flow to the remaining active cylinders in response to the indication of engine stall; pumping at least some purge fuel vapor from an intake manifold of the engine to a tailpipe via the reactivated cylinder; and resuming fuel flow in the remaining active cylinders after the pumping.

6. The method of claim 3, further comprising: restarting the purging after a duration based on the number of the one or more deactivated cylinders, the duration increasing as the number decreases.

7. The method of claim 6, further comprising:

after restarting the purging, purging the fuel vapor from the canister to the engine with all cylinders restarted at a second purge ramp rate that is lower than the first purge ramp rate.

8. The method of claim 7, wherein the second decimation ramp rate is decreased relative to the first decimation ramp rate as cylinder deactivation volume increases.

9. The method of claim 1, wherein the indication of engine stall comprises an indication of partial engine stall or an expectation of full engine stall.

10. A vehicle system, the vehicle system comprising:

an engine having a plurality of cylinders, each cylinder having a selectively deactivatable fuel injector;

an engine speed sensor;

a fuel system including a fuel tank, a fuel vapor canister, and a purge valve coupling the canister to an engine air intake;

an occupancy sensor coupled to a vehicle cabin; and

a controller having computer-readable instructions stored on a non-transitory memory that, when executed, cause the controller to:

deactivating the plurality of cylinders and operating the purge valve at a first duty cycle to purge canister fuel vapor to remaining active cylinders in response to the canister load being above a threshold; and

in response to an indication of stall in one or more of the remaining active cylinders, restarting the plurality of cylinders and closing the purge valve and disabling fuel flow to the remaining active cylinders for a duration of time.

11. The system of claim 10, wherein the controller comprises further instructions that when executed cause the controller to:

selecting the plurality of cylinders to be deactivated in accordance with an output of the occupancy sensor;

deactivating the plurality of cylinders by disabling fuel flow through the corresponding fuel injectors and keeping the corresponding intake and exhaust valves closed; and

restarting the plurality of cylinders by enabling fuel flow through the corresponding fuel injectors prior to opening the corresponding intake valves.

12. The system of claim 11, wherein the controller comprises further instructions that when executed cause the controller to:

after the duration, resuming fuel flow to the remaining active cylinders and re-operating the purge valve at a second duty cycle that is less than the first duty cycle, the second duty cycle being reduced relative to the first duty cycle in accordance with a cylinder deactivation amount.

Technical Field

The present description relates generally to methods and systems for controlling a vehicle engine to reduce engine stall during fuel vapor canister purging.

Background

Vehicle fuel systems may include a fuel vapor canister filled with an adsorbent for adsorbing fuel tank vapors. Adsorbed fuel tank vapors may include refueling vapors, diurnal vapors, and vapors released during tank depressurization. By storing fuel vapor in the canister, fuel emissions are reduced. Later, when the engine is in operation, the stored vapor may be drawn into the engine intake manifold for use as fuel. The purge fuel vapor may be ramped at a defined purge rate such that the target fuel vapor flow level is gradually reached. The gradual extraction improves engine stability by reducing the likelihood of engine stall, which may occur if the canister being extracted is loaded.

Various methods have been developed to accelerate the release of fuel vapor from a fuel system canister. An exemplary method is shown in US 6,820,597 to Cullen et al. Wherein the purge fuel vapor is directed to one or more groups of cylinders of the engine based on the purge load. Specifically, when the purge load is low, purge fuel vapor is directed to a group of cylinders operating at a leaner air-fuel ratio, while the remaining group of cylinders continues to operate at stoichiometry.

However, the inventors herein have recognized potential problems with this approach. As one example, engine stall may occur even with selective purging. Specifically, when purging is first initiated since the engine has been cranking in a drive cycle, the canister load state may not be known with certainty, resulting in a significant air-fuel ratio shift. For example, if the fuel tank is refueled and the vehicle is parked for a long time in an area where the solar load is high, the canister may be under high load. Therefore, a rich air-fuel ratio shift may occur when the canister purge valve is opened. Several seconds of transport delay may be required before the exhaust gas oxygen sensor responds to the rich excursion and for the engine controller to learn how rich the canister is and compensate for injector fueling based on the learned excursion. Thus, during this duration of time that extraction occurs "open-loop" without exhaust gas oxygen sensor feedback, the risk of engine stall may increase. This problem may be exacerbated when the decimation rate is ramped. Additionally, vehicle motion may cause fuel sloshing, during which vapor mass from the fuel tank may enter the engine air intake. If a vapor bolus is inferred, the controller may turn off purge control to avoid rich excursions that may stall the engine. However, closing the purge control may cause interference and may result in increased emissions. As a result, it may become difficult to balance and coordinate engine stall, extraction control, and exhaust emission control.

Another problem is that the lower ramp rate of extraction to provide higher engine stability may result in incomplete canister cleaning, especially in hybrid and start/stop vehicles where engine operating time is limited. Exhaust emissions may be affected if the canister is not fully drawn during engine operation.

Disclosure of Invention

The inventors herein have recognized that the problem of engine stalling due to initial canister conditions being rich may be addressed by utilizing selective deactivation of the engine cylinders. In particular, engines may be configured with variable displacement (also referred to as variable displacement engines, or VDEs), wherein certain cylinders may be selectively deactivated at low loads to reduce fuel consumption. Fueling of the selected cylinder may be deactivated and the intake and exhaust valves of the deactivated cylinder may remain closed while the piston continues to move up and down from crankshaft momentum. Thus, the deactivated cylinders act as air springs, reducing pumping losses, relative to the situation where the cylinders are not sealed but are propelled by the active cylinders. Selective cylinder deactivation thus substantially seals the selected cylinder and prevents scavenged vapors (which may cause engine stall) from reaching the selected cylinder. Thus, in one example, engine stall during canister purging may be addressed by a method for an engine of a vehicle, the method comprising: deactivating one or more cylinders in response to a request to purge fuel vapor from a canister; and deactivating extraction and reactivating the deactivated cylinders in response to an indication of engine stall.

As one example, after engine start-up, the controller may deactivate a threshold number of engine cylinders before an initial "open loop" canister purging operation in order to protect them from ingestion of rich canister vapors. The threshold number of deactivated cylinders may be based at least on vehicle occupancy, the number of deactivated cylinders increasing as the vehicle occupancy decreases. To further reduce the risk of potential engine stall, the extraction ramp rate may be increased relative to a default rate during open-loop extraction control. If after the canister purging is initiated, engine operating conditions indicate a potential engine stall (such as in response to a drop in engine speed), canister purging may be temporarily suspended and deactivated cylinders may be reactivated and fueled to prevent a complete engine stall. By resuming fueling to all engine cylinders, rich vapor may be extracted from the "stalled" cylinders and exhausted from the tailpipe. Canister purging may then be resumed at a lower purge ramp rate in view of the learned rich excursions.

In this way, engine stall due to canister purging may be avoided. A technical effect of purging a canister of unknown load status from an engine in which one or more cylinders are selectively deactivated is that the deactivated cylinders may be protected from rich excursions and associated stall. In addition, the extraction may be performed at a higher extraction ramp rate, which allows for faster canister extraction. This may allow for more complete cleaning of the canister during the limited engine operating time available in a hybrid vehicle. By restarting cylinders in response to a parameter indicative of potential stall, rich purge vapor may be extracted from active cylinders that ingested vapor, and a complete engine stall may be avoided. Further, engine stall due to vapor mass during fuel sloshing can also be avoided.

It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.

Drawings

FIG. 1 illustrates an exemplary engine system in a hybrid vehicle.

FIG. 2 illustrates an exemplary fuel vapor recovery system coupled to the engine system of FIG. 1.

FIG. 3 depicts a high level flow chart of an exemplary method for selectively deactivating and reactivating engine cylinders during purging of a fuel system canister.

FIG. 4 illustrates a prophetic example for addressing engine stall during purging of a fuel system canister by selectively deactivating and reactivating engine cylinders.

Detailed Description

The following description relates to systems and methods for reducing engine stall during purging of a fuel system canister coupled in the engine system of FIG. 1 (such as in the fuel vapor recovery system of FIG. 2). The controller may be configured to execute a control routine, such as the exemplary routine of FIG. 3, to purge the canister at a higher purge rate to the engine in which one or more cylinders are selectively deactivated. In response to an indication of a potential engine stall, the deactivated cylinders may be reactivated and the extraction rate may be decreased.

Turning now to FIG. 1, an exemplary embodiment 100 of a combustion chamber or cylinder of an internal combustion engine 10 is shown. The engine 10 may be coupled to a propulsion system, such as a vehicle system 5 configured for driving on a roadway. Engine 10 may receive control parameters from a control system including controller 12 and input from a vehicle operator 130 via an input device 132. In this example, the input device 132 includes an accelerator pedal and a pedal position sensor 134 for generating a proportional pedal position signal PP. The cylinders (also referred to herein as "combustion chambers") 14 of the engine 10 may include combustion chamber walls 136 with pistons 138 positioned in the combustion chamber walls 136. Piston 138 may be coupled to crankshaft 140 such that reciprocating motion of the piston is translated into rotational motion of the crankshaft. Crankshaft 140 may be coupled to at least one drive wheel of the passenger vehicle via a transmission system (not shown).

Cylinder 14 may receive intake air via a series of intake air passages 142, 144, and 146. Intake passage 146 may also communicate with other cylinders of engine 10 in addition to cylinder 14. In some embodiments, one or more of the intake ports may include a boosting device, such as a turbocharger or a supercharger. For example, FIG. 1 shows engine 10 configured with a turbocharger including a compressor 174 disposed between intake passages 142 and 144 and an exhaust turbine 176 disposed along exhaust passage 148. Where the boosting device is configured as a turbocharger, compressor 174 may be at least partially powered by exhaust turbine 176 via shaft 180. However, in other examples, such as where engine 10 is provided with a supercharger, exhaust turbine 176 may optionally be omitted, where compressor 174 may be powered by mechanical input from a motor or the engine. A throttle 20 including a throttle plate 164 may be disposed along an intake passage of the engine to vary the flow rate and/or pressure of intake air provided to the engine cylinders. For example, throttle 20 may be disposed downstream of compressor 174, or alternatively, may be disposed upstream of compressor 174.

Exhaust passage 148 may receive exhaust gases from other cylinders of engine 10 in addition to cylinder 14. Exhaust gas sensor 128 is shown coupled to exhaust passage 148 upstream of emission control device 178. Exhaust gas sensor 128 may be selected from a variety of suitable sensors for providing an indication of exhaust gas air/fuel ratio, such as a linear oxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), a two-state oxygen sensor or EGO (as shown), a HEGO (heated EGO), a NOx sensor, an HC sensor, or a CO sensor. Emission control device 178 may be a Three Way Catalyst (TWC), NOx trap, various other emission control devices, or combinations thereof.

Each cylinder of engine 10 may include one or more intake valves and one or more exhaust valves. For example, the cylinder 14 is shown to include at least one poppet-type intake valve 150 and at least one poppet-type exhaust valve 156 located in an upper region of the cylinder 14. In some embodiments, each cylinder of engine 10 (including cylinder 14) may include at least two intake poppet valves and at least two exhaust poppet valves located in an upper region of the cylinder.

Intake valve 150 may be controlled by controller 12 via cam actuation system 151. Similarly, exhaust valve 156 may be controlled by controller 12 via cam actuation system 153. Cam actuation systems 151 and 153 may each include one or more cams and may utilize one or more of Cam Profile Switching (CPS), Variable Cam Timing (VCT), Variable Valve Timing (VVT), and/or Variable Valve Lift (VVL) systems that may be operated by controller 12 to vary valve operation. Operation of intake valve 150 and exhaust valve 156 may be determined by valve position sensors (not shown) and/or camshaft position sensors 155 and 157, respectively. In alternative embodiments, the intake and/or exhaust valves may be controlled by electric valve actuation. For example, cylinder 14 may alternatively include an intake valve controlled via electric valve actuation and an exhaust valve controlled via cam actuation including a CPS system and/or a VCT system. In other embodiments, the intake and exhaust valves may be controlled by a common valve actuator or actuation system or a variable valve timing actuator or actuation system.

In some embodiments, each cylinder of engine 10 may include a spark plug 192 for initiating combustion. Ignition system 190 can provide an ignition spark to cylinder 14 via spark plug 192 in response to spark advance signal SA from controller 12, under select operating modes. In other embodiments, the cylinder may not include a spark plug, such as where compression ignition is used to initiate combustion in the cylinder.

In some embodiments, each cylinder of engine 10 may be configured with one or more injectors for delivering fuel to the cylinder. As a non-limiting example, cylinder 14 is shown to include two fuel injectors 166 and 170. Fuel injectors 166 and 170 may be configured to deliver fuel received from fuel system 8 via a high pressure fuel pump and a fuel rail. Alternatively, fuel may be delivered at a lower pressure by a single stage fuel pump, in which case the timing of the direct fuel injection is more limited during the compression stroke than if a high pressure fuel system were used. Further, the fuel tank may have a pressure sensor that provides a signal to controller 12.

Fuel injector 166 is shown coupled directly to cylinder 14 for injecting fuel directly therein in proportion to the pulse width of signal FPW-1 received from controller 12 via electronic driver 168. In this manner, fuel injector 166 provides what is known as direct injection (hereinafter "DI") of fuel into combustion cylinder 14. Although FIG. 2 shows injector 166 positioned to one side of cylinder 14, the injector may alternatively be located overhead of the piston, such as near spark plug 192. Such a location may improve mixing and combustion when operating an engine using an alcohol-based fuel due to the lower volatility of some alcohol-based fuels. Alternatively, the injector may be located overhead and near the intake valve to improve mixing.

As described in detail below, engine 10 may be a variable displacement engine wherein fuel injectors 166 are selectively deactivated in response to an operator torque request to operate the engine at a desired air intake ratio.

Fuel injector 170 is shown disposed in intake passage 146 rather than in cylinder 14 in a configuration that provides so-called port injection of fuel (hereinafter "PFI") into the intake passage upstream of cylinder 14. Fuel injector 170 may inject fuel received from fuel system 8 in proportion to the pulse width of signal FPW-2 received from controller 12 via electronic driver 171. Note that a single electronic driver 168 or 171 may be used for both fuel injection systems, or multiple drivers may be used, such as electronic driver 168 for fuel injector 166 and electronic driver 171 for fuel injector 170, as shown.

During a single cycle of the cylinder, fuel may be delivered to the cylinder through both injectors. For example, each injector may deliver a portion of the total fuel injection combusted in cylinder 14. Thus, the injected fuel may be injected from the intake port and the direct injector at different timings, even for a single combustion event. Further, multiple injections of the delivered fuel per cycle may be performed for a single combustion event. Multiple injections may be performed during a compression stroke, an intake stroke, or any suitable combination thereof.

As described above, FIG. 1 shows only one cylinder of a multi-cylinder engine. Thus, each cylinder may similarly include its own set of intake/exhaust valves, fuel injectors, spark plugs, and the like. It should be appreciated that engine 10 may include any suitable number of cylinders, including 2, 3, 4, 5, 6,8, 10, 12, or more cylinders. Further, each of these cylinders may include some or all of the various components described and illustrated by fig. 1 with reference to cylinder 14.

The engine may further include one or more exhaust gas recirculation passages for recirculating a portion of the exhaust gas from the engine exhaust port to the engine intake port. Thus, by recirculating some exhaust gas, engine dilution may be affected, which may improve engine performance by reducing engine knock, peak cylinder combustion temperatures and pressures, throttling losses, and NOx emissions. In the illustrated embodiment, exhaust gas may be recirculated from exhaust passage 148 to intake passage 144 via EGR passage 141. The amount of EGR provided to intake passage 144 may be varied by controller 12 via EGR valve 143. Further, an EGR sensor 145 may be disposed within the EGR passage and may provide an indication of one or more of pressure, temperature, and concentration of exhaust gas.

In some examples, the vehicle system 5 may be a hybrid vehicle having multiple torque sources available to one or more wheels 55. In other examples, the vehicle system 5 is a conventional vehicle having only an engine, or an electric vehicle having only an electric machine. In the illustrated example, the vehicle system 5 includes an engine 10 and an electric machine 52. The electric machine 52 may be a motor or a motor/generator. When one or more clutches 56 are engaged, a crankshaft 140 of engine 10 and motor 52 are connected to wheels 55 via transmission 54. In the illustrated example, the first clutch 56 is disposed between the crankshaft 140 and the motor 52, while the second clutch 56 is disposed between the motor 52 and the transmission 54. Controller 12 may send a clutch-engaging or clutch-disengaging signal to an actuator of each clutch 56 to connect or disconnect crankshaft 140 from motor 52 and components connected thereto, and/or to connect or disconnect motor 52 from transmission 54 and components connected thereto. The transmission 54 may be a gearbox, a planetary gear system, or another type of transmission. The powertrain may be configured in various ways, including being configured as a parallel, series, or series-parallel hybrid vehicle.

The electric machine 52 receives power from the traction battery 58 to provide torque to the wheels 55. The electric machine 52 may also operate as a generator to provide electrical power to charge the battery 58, for example, during braking operations.

The vehicle 5 may include a cabin 184. The number of vehicle cabin occupants (i.e., occupancy level) may be sensed via an occupancy sensor 186 coupled to the vehicle cabin. The sensors 186 may include seat sensors, seat belt sensors, door sensors, or any other sensors.

The controller 12 is shown as a microcomputer including a microprocessor unit 106, an input/output port 108, an electronic storage medium for executable programs and calibration values (shown in this particular example as a read-only memory chip 110), a random access memory 112, a keep alive memory 114 and a data bus. In addition to those signals previously discussed, controller 12 may receive various signals from sensors coupled to engine 10, including measurements of Engine Coolant Temperature (ECT) from temperature sensor 116 coupled to cooling sleeve 118; a surface ignition pickup signal (PIP) from Hall effect sensor 120 (or other type) coupled to crankshaft 140; a Throttle Position (TPS) from a throttle position sensor; and a manifold absolute pressure signal (MAP) from sensor 124. Engine speed signal, RPM, may be generated by controller 12 from signal PIP. Manifold pressure signal MAP from a manifold pressure sensor may be used to provide an indication of vacuum or pressure in the intake manifold. Other sensors may include a fuel level sensor and a fuel composition sensor coupled to a fuel tank of the fuel system.

The storage medium read-only memory chip 110 may be programmed with computer readable data representing instructions executable by the microprocessor unit 106 for performing the methods described below as well as other variants that are anticipated but not specifically listed.

One or more cylinders of engine 10 may be selected for selective deactivation during selected conditions, such as when full torque capacity of the engine is not required. This may include selectively deactivating one or more cylinders of a group of cylinders. In one example, where the engine cylinders are divided into two cylinder groups, one or more cylinders of a cylinder group may be deactivated. The number and identity of deactivated cylinders on a given cylinder group may be symmetric or asymmetric. By adjusting the number of deactivated cylinders, the air intake ratio set at the engine may be changed. The cylinders may be deactivated by closing the respective direct fuel injectors while maintaining operation of the intake and exhaust valves so that air may continue to be pumped through the selected cylinders. In some examples, the cylinders may be deactivated based on a specified control algorithm to provide a particular intake ratio or firing pattern.

One or more cylinders of engine 10 may be selected for selective deactivation (also referred to herein as individual cylinder deactivation) during selected conditions, such as when full torque capacity of the engine is not required. This may include selectively deactivating one or more cylinders of the cylinder bank 15. The number and identity of deactivated cylinders on a cylinder bank may be symmetric or asymmetric. By adjusting the number of deactivated cylinders, the air intake ratio set at the engine may be changed.

In addition to deactivating fuel injectors, controller 12 may also close individual cylinder valvetrains, such as intake and exhaust valvetrains. The cylinder valves may be selectively deactivated via hydraulically actuated lifters (e.g., lifters coupled to valve pushrods), via a cam profile switching mechanism (where no lifted cam lobes are used for deactivated valves), or via electrically actuated cylinder valvetrains coupled to each cylinder. Additionally, spark to the deactivated cylinders may be deactivated.

When the selected cylinder is disabled, the remaining enabled or active cylinders continue to burn with the fuel injectors and cylinder valvetrain active and operating. To meet the torque demand, the engine produces the same amount of torque on the active cylinders. This requires higher manifold pressures, resulting in reduced pumping losses and increased engine efficiency. Moreover, the lower effective surface area exposed to combustion (from the active cylinder only) reduces engine heat loss, thereby improving the thermal efficiency of the engine.

FIG. 2 shows a schematic diagram of a vehicle system 200 including an engine system 208 coupled to an emissions control system 251 and a fuel system 218. Emission control system 251 includes a fuel vapor container, such as fuel vapor canister 222, that may be used to capture and store fuel vapor. In some examples, the vehicle system 5 may be a hybrid electric vehicle system, such as the vehicle system 100 of fig. 1, and the fuel system 218 may include the fuel system 8 of fig. 1.

The engine system 208 may include an engine 210 having a plurality of cylinders 230. In one example, engine 210 includes engine 10 of FIG. 1. The engine 210 includes an engine intake 223 and an engine exhaust 225. Engine intake 223 includes a throttle 262 fluidly coupled to an engine intake manifold 244 via an intake passage 242. The engine exhaust ports 225 include an exhaust manifold 248 that leads to an exhaust passage 235, which exhaust passage 235 directs exhaust gases to the atmosphere. The engine exhaust 225 may include one or more emission control devices 270, and the emission control devices 270 may be mounted at close-coupled locations in the exhaust. The one or more emission control devices may include a three-way catalyst, a lean NOx trap, a diesel particulate filter, an oxidation catalyst, and/or the like. It should be appreciated that other components may be included in the engine, such as various valves and sensors.

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 injectors of the engine 210, such as the exemplary injector 266 shown. Although only a single injector 266 is shown, additional injectors are provided for each cylinder. It should be appreciated that the fuel system 218 may be a returnless fuel system, or various other types of fuel systems. Injector 266 may be a direct injector that may be selectively deactivated, such as injector 166 of FIG. 1. By deactivating the injector 266, the corresponding cylinder may be deactivated.

Vapors generated in the fuel system 218 may be directed to an evaporative emissions control system 251 including a fuel vapor canister 222 via a vapor recovery line 231 before being purged to the engine air intake 223. Vapor recovery line 231 may be coupled to 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, vapor recovery line 231 may be coupled to fuel tank 220 via one or more of conduits 271, 273, and 275, or a combination thereof.

Further, in some examples, one or more tank vent valves may be positioned in conduits 271, 273, or 275. Among other functions, the fuel tank vent valve may allow the fuel vapor canister of the emission control system to be maintained at a low pressure or vacuum without increasing the fuel vaporization rate of the fuel tank (which would otherwise occur if the fuel tank pressure were reduced). For example, conduit 271 may include a Grade Vent Valve (GVV)287, conduit 273 may include a Fill Limit Vent Valve (FLVV)285, and conduit 275 may include a Grade Vent Valve (GVV) 283. Further, in some examples, the recovery line 231 may be coupled to the fuel fill system 219. In some examples, the fuel fill system may include a fuel cap 205 for sealing the fuel fill system from the atmosphere. Fueling system 219 is coupled to fuel tank 220 via fuel filler tube 211 or neck 211.

Further, the fueling system 219 may include a fueling lock 245. In some embodiments, the refuel lock 245 may be a fuel tank cap locking mechanism. The fuel cap locking mechanism may be configured to automatically lock the fuel cap in the closed position such that the fuel cap cannot be opened. For example, the fuel tank cap 205 may remain locked via the refueling lock 245 when the pressure or vacuum in the fuel tank is greater than a threshold. In response to a refueling request, such as a request initiated by a vehicle operator via actuation of a refueling button on a vehicle dashboard, the fuel tank may depressurize and the fuel tank cap may unlock after the pressure or vacuum in the fuel tank falls below a threshold. Herein, unlocking the refueling lock 245 may include unlocking the fuel tank cap 205. A fuel cap locking mechanism may be a latch or clutch that, when engaged, prevents removal of the fuel cap. The latch or clutch may be electrically locked, for example by a solenoid, or may be mechanically locked, for example by a pressure diaphragm.

In some embodiments, the fueling lock 245 may be a filler pipe valve located at the mouth of the fuel filler pipe 211. In such embodiments, the refueling lock 245 may not prevent removal of the fuel tank cap 205. Rather, fueling lock 245 may prevent the insertion of the fueling pump into fueling pipe 211. The fill pipe valve may be electrically locked, for example by a solenoid, or mechanically locked, for example by a pressure diaphragm.

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

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

Emission control system 251 may include one or more fuel vapor canisters 222 (also referred to herein simply as canisters) filled with a suitable adsorbent that are configured to temporarily trap fuel vapors (including vaporized hydrocarbons) generated during fuel tank refill operations and "run-away" vapors (i.e., fuel vaporized during vehicle operation). In one example, the adsorbent used is activated carbon. The emissions control system 251 may also include a canister vent path or vent line 227, which canister vent path or vent line 227 may direct gas from the fuel vapor canister 222 to the atmosphere when storing or trapping fuel vapor from the fuel system 218.

The vent line 227 may also allow fresh air to be drawn into the canister 222 as stored fuel vapor is purged from the fuel system 218 to the engine air intake 223 via the purge line 228 and the purge valve 261. For example, purge valve 261 may be normally closed, but may be opened during certain conditions (such as certain engine operating conditions) such that vacuum from engine intake manifold 244 is applied to the fuel vapor canister for purging. In some examples, the vent line 227 may include an optional air filter 259 disposed therein upstream of the canister 222. The flow of air and vapor between the canister 222 and the atmosphere may be regulated by a canister vent valve 229.

The fuel tank 220 is fluidly coupled to the canister 222 via a conduit 276, which conduit 276 includes a Fuel Tank Isolation Valve (FTIV)252 for controlling the flow of fuel tank vapors into the canister 222. The FTIV 252 may be normally closed such that fuel tank vapors (including run-off and diurnal losses) may be retained in the fuel tank, such as in the ullage space of the fuel tank. In one example, the FTIV 252 is a solenoid valve.

In configurations where the vehicle system 200 is a Hybrid Electric Vehicle (HEV), the fuel tank 220 may be designed as a sealed fuel tank that can withstand pressure fluctuations (e.g., steel fuel tanks) typically encountered during normal vehicle operation and diurnal temperature cycles. Additionally, the canister 222 may be reduced in size to account for shortened engine operating times in hybrid vehicles. However, for the same reason, HEVs may have limited opportunity for fuel vapor canister purging operations. Thus, the use of a sealed fuel tank with a closed FTIV (also referred to as a NIRCOS or non-integrated refueling canister only system) prevents diurnal and run-away vapor loading of the fuel vapor canister 222 and limits fuel vapor canister loading via refueling vapor only. FTIV 252 may be selectively opened in response to a fueling request to depressurize fuel tank 220 before fuel may be received into the fuel tank via fuel filler pipe 211.

In some embodiments, an additional pressure control valve (not shown) may be configured in parallel with the FTIV 252 to relieve any excess pressure created in the fuel tank, such as when the engine is operating, or even to vent excess pressure from the fuel tank when the vehicle is operating in an electric vehicle mode, such as in the case of a hybrid electric vehicle.

When open, the FTIV 252 allows fuel vapor to drain from the fuel tank 220 to the canister 222. Fuel vapor may be stored in canister 222 while air stripped from the fuel vapor is vented to the atmosphere via canister vent valve 229. When engine conditions permit, fuel vapor stored in canister 222 may be purged to engine intake 223 via canister purge valve 261.

The fuel system 218 may be operated in multiple modes by the controller 212 by selectively adjusting various valves and solenoids. For example, the fuel system may be operated in a fuel vapor storage mode (e.g., during a fuel tank refueling operation and when the engine is not running) wherein the controller 212 may open the FTIV 252 and the canister vent valve 229 while closing the Canister Purge Valve (CPV)261 to direct refueling vapors into the canister 222 while preventing fuel vapors from being directed into the intake manifold.

As another example, the fuel system may be operated in a refueling mode (e.g., when a vehicle operator requests refueling of the fuel tank), wherein the controller 212 may open the FTIV 252 and the CVV 229 while maintaining the canister purge valve 261 closed to depressurize the fuel tank before allowing refueling to be effected therein. Accordingly, the FTIV 252 may remain open during a refueling operation to allow refueling vapors to be stored in the canister. After fueling is complete, the isolation valve may be closed.

As yet another example, the fuel system may be operated in a canister purge mode (e.g., after the emission control device light-off temperature has been reached and the engine is running), where the controller 212 may open the Canister Purge Valve (CPV)261 and the Canister Vent Valve (CVV)229 while closing the isolation valve 252. Herein, the vacuum created by the intake manifold of an operating engine may be used to draw fresh air through the vent line 227 and through the fuel vapor canister 222 to draw stored fuel vapor into the intake manifold 244. In this mode, fuel vapor purged from the canister is combusted in the engine. Purging may continue until the amount of fuel vapor stored in the canister is below a threshold. The learned vapor amount/concentration may be used to determine the amount of fuel vapor stored in the canister during purging, and then during later portions of the purging operation (when the canister is sufficiently purged or emptied), the learned vapor amount/concentration may be used to estimate the load state of the fuel vapor canister. For example, one or more oxygen sensors (not shown) may be coupled to canister 222 (e.g., downstream of the canister), or positioned in the engine intake and/or engine exhaust, to provide an estimate of canister load (i.e., the amount of fuel vapor stored in the canister). The purge flow rate may be determined based on canister load, and further based on engine operating conditions, such as engine speed-load conditions.

When purging is first initiated since the engine has been cranking during a drive cycle, the canister load condition may not be known with certainty, resulting in a significant air-fuel ratio excursion. For example, if the fuel tank is refueled before the start of a given driving cycle and the vehicle is parked for a long time in an area where the solar load is high, the canister may be under high load. Therefore, when CPV 261 is open, a rich air-fuel ratio shift may occur. It may take several seconds of transport delay before the exhaust gas oxygen sensor responds to the rich excursion and for engine controller 212 to learn how rich the canister is and compensate for injector fueling based on the learned excursion. Thus, during this duration, purging occurs "open-loop" without feedback from an exhaust gas oxygen sensor (such as sensor 128 of FIG. 1). This may increase the risk of engine stall. To reduce risk, the extraction rate may be reduced, however this may reduce the likelihood that the canister will be completely cleaned during limited engine operating times of the hybrid vehicle. This problem may be exacerbated when the decimation rate is ramped. Additionally, vehicle movement may cause fuel sloshing, during which vapor slugs from the fuel tank may enter the engine air intake and trigger engine stall.

As detailed herein with reference to fig. 3, to reduce the incidence of engine stall during canister purging, the canister 222 may be purged with selective deactivation of one or more cylinders 230. The number of deactivated cylinders may be based on an occupancy level of the cabin, such as based on input from sensor 186. Because the intake and exhaust valves of the deactivated cylinders remain closed while the pistons continue to move up and down from the crankshaft momentum, the deactivated cylinders are sealed against ingestion of rich purge vapors to avoid engine stalling. Further, if engine stall is anticipated, the deactivated cylinders may be reactivated and purging may be temporarily disabled. Thus, the active engine cylinder can extract the intake vapor.

The vehicle system 206 may also include 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 an exhaust gas sensor 237, a temperature sensor 233, a fuel tank pressure sensor (FTPT) or pressure sensor 291, and a canister temperature sensor 243 located upstream of the emission control device. Thus, pressure sensor 291 provides an estimate of fuel system pressure. In one example, the fuel system pressure is a fuel tank pressure, such as the pressure within fuel tank 220. 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 fuel injector 266, throttle 262, FTIV 252, and pump 221. The control system 214 may include a controller 212. The controller may receive input data from various sensors, process the input data, and trigger the actuator in response to the processed input data based on instructions or code programmed in the input data corresponding to one or more routines. An exemplary control routine is described herein with respect to FIG. 3. The controller 212 receives signals from the various sensors of fig. 1-2 and employs the various actuators of fig. 1-2 to adjust vehicle operation based on the received signals and instructions stored on the controller's memory.

For example, in response to the canister load being above a threshold, the controller may command the CPV 261 to open and disable the injectors 266 in a number of engine cylinders, the number selected based on input from the occupancy sensor 186. Specifically, as the occupancy level decreases, the number of deactivated cylinders increases. Further, in response to an indication of engine stall, as inferred from a drop in engine speed sensed via a speed sensor (e.g., sensor 120 in fig. 1), the deactivated cylinders may be reactivated and the CPV may be commanded off to temporarily suspend canister purging.

In this way, the components of fig. 1-2 implement a system comprising: an engine having a plurality of cylinders, each cylinder having a selectively deactivatable fuel injector; an engine speed sensor; a fuel system including a fuel tank, a fuel vapor canister, and a purge valve coupling the canister to an engine air intake; an occupancy sensor coupled to a vehicle cabin; and a controller having computer readable instructions stored on a non-transitory memory that, when executed, cause the controller to: deactivating the plurality of cylinders and operating the purge valve at a first duty cycle to purge canister fuel vapor to remaining active cylinders in response to the canister load being above a threshold; and in response to an indication of stall in one or more of the remaining active cylinders, reactivating the plurality of cylinders and closing the extraction valve and disabling fuel flow to the remaining active cylinders for a duration of time. Additionally or optionally, the controller includes further instructions that when executed cause the controller to: selecting the plurality of cylinders to be deactivated in accordance with an output of the occupancy sensor; deactivating the plurality of cylinders by disabling fuel flow through the corresponding fuel injectors and keeping the corresponding intake and exhaust valves closed; and restarting the plurality of cylinders by enabling fuel flow through the corresponding fuel injectors prior to opening the corresponding intake valves. Further, the controller may include instructions that, when executed, cause the controller to: after the duration, resuming fuel flow to the remaining active cylinders and re-operating the purge valve at a second duty cycle that is less than the first duty cycle, the second duty cycle being reduced relative to the first duty cycle as a function of the number of deactivated cylinders. That is, the second extraction rate is decreased in proportion to the cylinder deactivation amount. For example, if half of the cylinders are deactivated, the extraction rate is reduced to 50%.

Turning now to FIG. 3, an exemplary method 300 for purging a canister to an engine while reducing the occurrence of engine stall by utilizing selective cylinder deactivation is illustrated. The instructions for performing the method 300 may be executed by the controller based on instructions stored on a memory of the controller in conjunction with signals received from sensors of the engine system (such as the sensors described above with reference to fig. 1-2). The controller may employ engine actuators of the engine system to adjust engine operation according to the methods described below.

At 302, the method includes confirming an engine start from an engine standstill. In one example, the engine may be restarted from an off state in response to an operator inserting an active key into the ignition slot, actuating a start/stop button to a start setting, or inserting a passive key into the cabin. Still further, in engines configured to automatically shut down and restart in response to engine operating conditions, the engine may be restarted in response to a torque demand, a need to operate an air conditioning compressor, or a need to charge a system battery. If the engine start condition is not met, then at 304, the engine is maintained off. The method then exits.

If the engine start conditions are met, the engine is cranked via the starter motor to restart the engine at 306. For example, cranking the engine until a threshold speed (such as 400rpm) is reached, after which engine fueling may be resumed to maintain engine rotation.

After starting the engine via cranking of the starter motor, and before resuming cylinder fueling, it is determined at 308 whether a purge condition exists. In one example, the purge condition is confirmed if the inferred canister load at the end of the last travel cycle is above a non-zero threshold load (such as when the canister is in the range of 20% to 100% more load). In another example, the canister purge condition may be confirmed at any time the engine is operating to produce torque to propel the vehicle. If the canister purge condition is not satisfied, at 310, the method includes maintaining the canister purge valve closed and beginning delivery of fuel to the engine cylinder. The engine may be operated with a number of cylinders deactivated, the number being determined based on the torque demand. Specifically, the number of deactivated cylinders may increase as the operator torque request decreases. The routine then ends.

If the extraction condition is satisfied, at 312, the method includes retrieving the most recent canister load condition from the memory of the controller. Additionally, an occupancy level of the cabin is determined based on the occupancy sensor input. At 314, the method includes selecting a plurality of cylinders to deactivate during canister purging based on vehicle conditions (including occupancy level). Thus, there is a tradeoff between the number of deactivated cylinders and the risk of engine stall. In one example, as the number of occupants in the cabin decreases (such as below a non-zero threshold), the number of deactivated cylinders may increase. As an example, when the occupancy level is 50%, the engine may be operated at an air intake ratio of 0.5. As another example, when the occupancy level is 25%, the engine may be operated at an air intake ratio of 0.25. The maximum number of cylinders may be deactivated if the vehicle is operating autonomously without the driver and passengers.

Therefore, cylinder deactivation and restart involves NVH disturbances. Thus, for occupants in the cabin, it may be necessary to deactivate one cylinder at a time, or it may be necessary to time the VDE under rough road conditions in order to mask NVH. However, in the event of an impending engine stall, priority is given to preventing such an undesirable condition, and cylinder deactivation is performed without considering NVH. VDE may be performed to prevent engine stall, whether unoccupied or most occupied.

In some cases, the actual canister load at the beginning of a canister draw may be higher than expected (e.g., higher than the last retrieved value). This may occur, for example, due to refueling the fuel tank prior to the current driving cycle. This may instead occur due to the vehicle being parked for a long period of time in an area with a high solar load, resulting in the generation of additional daytime vapours. If the canister load is higher than expected, a rich excursion may occur at the start time of the initial canister purge before the exhaust gas sensor can sense and compensate for the rich excursion. The rich excursions may cause the engine to stall. Because the intake and exhaust valves of the deactivated cylinders remain closed, the deactivated cylinders are prevented from ingesting purge vapor, including any rich vapor. Thus, by selectively deactivating a portion of all of the engine cylinders while purging the canister to the engine, engine stalling due to the canister purging rich excursion is avoided.

At 318, a purge ramp rate is selected based on the last retrieved canister load condition and the number of deactivated cylinders. The draw ramp rate may include an initial draw rate, and a defined step-wise increase in the draw rate over the duration of the canister draw. For example, a default extraction rate may be initially determined based on canister load, and then the extraction ramp rate may be increased with a gain determined from the number of deactivated cylinders. Thus, as the number of cylinders deactivated at canister purging increases, the purge ramp rate may be increased relative to the default purge ramp rate. The controller may use an algorithm, model, or look-up table that uses canister load and air intake ratio as inputs to determine the decimation ramp rate as an output. For example, the decimation steps and the ramp-up rate may be determined by engine speed and canister load conditions. The engine can handle vapor ingestion better at higher engine speeds than at low engine speeds. The ramp rate may be increased when the engine speed is high. For a loaded canister, the ramp rate is reduced, thereby reducing excessive ingestion of fuel vapor. The rate of increase depends on the propagation delay (typically a few seconds) of the UEGO response. Increasing the extraction rate (relative to the default) allows more air to flow into the canister, which cleans the canister faster in a given drive cycle. By purging the canister to the engine while selectively deactivating a portion of all of the engine cylinders, the deactivated cylinders are protected from rich purge excursions, thereby allowing an overall higher than otherwise possible canister purge rate. This allows the canister to be purged more thoroughly even if the engine run time is limited, such as may occur in hybrid vehicles and vehicles having start/stop configurations, without causing combustion instability in the engine.

At 320, canister purging is performed to the engine with the selected number of cylinders deactivated according to the determined purge rate. Specifically, the controller may command the CPV to open (while also commanding the CVV to open) and adjust the duty cycle of the CPV to provide the determined ramp rate of decimation. At the same time, a selected number of cylinders are deactivated while the remaining active cylinders are fueled.

At 322, it is determined whether there is a potential engine stall. Alternatively, it may be determined whether there is a partial engine stall and whether there is a possibility of a complete engine stall. In one example, a potential (or partial) engine stall may be inferred in response to the engine speed first increasing during a cranking and then decreasing (or a downward engine speed trajectory) after delivery of fuel and purge vapor to the active engine cylinders. For example, the engine speed may initially increase from engine rest for a first duration at a rate above the threshold, and then after the purging is initiated, the engine speed may decrease at a rate above the threshold for a second duration immediately after the first duration. Partial engine stall may occur due to engine stall of at least one cylinder in the active portion of cylinders.

In this context, the engine stall may be a partial engine stall in which the engine speed starts to drop (slowly) after the cranking is stopped. As described in detail below, remedial action is taken whenever a drop in engine speed begins to occur so that the engine does not spin to a standstill and cause a complete engine stall. Instead, the engine can recover from a potential full engine stall.

In one example, a cylinder balancing test may be used to determine which cylinders are about to stall. The cylinder balancing test may use a crankshaft position sensor (CKP sensor) and measure the rate of change of crankshaft position to infer torque output from each cylinder.

Engine stall may occur due to vapor slugs. In particular, under hot weather conditions (e.g., above a threshold ambient temperature), the fuel present in the fuel tank may become hot. When the vehicle is in motion, there may be fuel sloshing. The combination of fuel sloshing due to vehicle motion and hot fuel due to elevated ambient temperatures may cause vapor slugs generated in the fuel tank to enter the engine intake and stall the engine cylinders that are receiving the purge vapor. In particular, a richer than expected excursion caused by a sudden ingestion of a large amount of concentrated fuel vapor may stall the engine. The controller may monitor pedal displacement and drive patterns to infer whether a vapor bolus and associated engine stall is likely to occur. For example, if there is rapid vehicle acceleration or deceleration (e.g., above a threshold rate of pedal displacement), the controller may infer the generation of an vapor bolus and predict engine stall. As another example, if a sudden change in fuel tank pressure occurs (e.g., an increase or decrease above a threshold), the controller may infer the generation of a vapor bolus and predict engine stall.

If no engine stall is indicated or expected, at 324, the method includes maintaining an extraction ramp rate above a threshold and continuing to extract canisters from the engine with one or more cylinders selectively deactivated. During purging, the controller may continuously update the canister load based on feedback from the exhaust gas sensor. Alternatively, the controller may continuously update the canister load based on the draw conditions (such as draw rate).

At 326, it may be determined whether the draw is complete, such as may occur when the inferred or sensed canister load is less than the threshold load. In one example, the purge condition is considered to be satisfied when the canister load is above an upper threshold, and the purge is considered to be complete when the canister load is below a lower threshold. The change in canister load may be sensed by a sensor (such as a pressure sensor or a hydrocarbon sensor) coupled to the canister (or elsewhere in the fuel system). Alternatively, a change in canister load may be inferred based on the duration of canister draw, the duty cycle of the CPV, and the inferred or sensed canister load at the beginning of the canister draw.

If the extraction is complete, at 328, the method includes restarting the cylinder that was deactivated during the canister extraction. This includes resuming delivery of fuel to the cylinders. Thereafter, the engine cylinders may be selectively deactivated based on the torque demand. Wherein as the torque demand decreases, the number of selectively deactivated cylinders increases and the torque demand is satisfied via a smaller number of active cylinders. At 340, after restarting the cylinder, the controller may (fully) turn off the CPV to disable further purging and update the canister load status in the controller's memory at the end of the purging operation. The method then exits.

Returning to 322, if engine stall is anticipated, at 330, the method includes (fully) closing the CPV to disable further canister purging. By limiting further ingestion of the rich canister purge vapor, a complete engine stall is avoided. At 332, the method includes restarting the selectively deactivated cylinders and starting a timer. In one example, the deactivated cylinders are reactivated together. In another example, deactivated cylinders are reactivated in sequence. In another example, the controller may restart the cylinder furthest from the CPV valve. This allows the vapor to diffuse within the intake port rather than concentrating at one cylinder and causing a rich misfire. The stalled cylinder is the cylinder deactivated by the VDE hardware. Reactivating the deactivated cylinders may include injecting fuel into the deactivated cylinders and combusting a previously inducted air charge prior to Intake Valve Opening (IVO). This reduces accidental ingestion of rich purge fuel vapor by deactivated cylinders.

In addition to restarting the deactivated cylinders, the controller may temporarily disable fuel injector flow to the stalled cylinders that are rich in hydrocarbons from canister purge vapors at 334. Herein, a stalled cylinder may be a portion of a previously active cylinder and may include less than all of the engine cylinders. The stalled cylinder may be identified based on its piston position. In one example, fuel flow to a stalled cylinder may be shut off for a short duration (e.g., a few seconds). This allows the rich vapors ingested in the stalled engine cylinders to be extracted and discharged to the tail pipe. The controller may then resume fueling all of the engine cylinders once rich vapor has been drawn from the stalled cylinder. In this way, when fuel flow is temporarily inhibited to the stalled cylinder, the restarted cylinder (previously deactivated) continues to be fueled, thereby allowing the restarted cylinder to provide the engine torque needed to meet the torque demand.

At 336, after the rich vapor has been purged from the stalled engine cylinders, the controller may resume canister purging by opening the CPV. In addition, the decimation ramp rate can be reduced. This includes decreasing the initial extraction rate, and the gradual increase in the extraction rate relative to the extraction rate initially applied during canister extraction (at 318) to an engine having at least some deactivated cylinders. In one example, the reduced ramp rate of extraction applied after cylinder reactivation varies with the increased ramp rate of extraction applied after cylinder deactivation. As an example, the purge ramp rate decreases in proportion to the cylinder deactivation amount.

In this way, purging may continue even if engine stall is expected due to rich fuel vapor from the loaded canister or due to hot fuel vapor slugs. By mitigating engine stall with selective cylinder deactivation and restart, the need to disable purging in response to vapor slugs is avoided.

From 336, the method moves to 338 to determine if the extraction is complete. As at 326, it may be determined that the draw is complete when the inferred or sensed canister load is less than a threshold load (e.g., below a lower threshold). The change in canister load may be sensed by a sensor (such as a pressure sensor or a hydrocarbon sensor) coupled to the canister (or elsewhere in the fuel system). Alternatively, a change in canister load may be inferred based on the duration of canister draw, the duty cycle of the CPV, and the inferred or sensed canister load at the beginning of the canister draw.

If the draw is complete, at 340, the controller may (fully) turn off the CPV to disable further draw and update the canister load status in the controller's memory at the end of the draw operation. The method then exits. If the draw is not complete, at 342, the CPV is maintained open and the reduced draw ramp rate is maintained. The method then exits.

Turning now to FIG. 4, a prophetic example of canister purging operation in a vehicle having an engine with VDE technology is shown. The vehicle may be a hybrid vehicle, such as the exemplary vehicle system of FIG. 1. Graph 400 shows engine speed at curve 402. The fuel vapor canister load condition is shown relative to a threshold (Thr, dashed line) at curve 404. The canister purge rate is shown at curve 406. The fraction of total engine cylinders active is shown in curve 408. A fraction of 1.0 indicates that all cylinders are active. As the number of deactivated cylinders increases, the fraction decreases. The AFR of the active cylinder is shown relative to the stoichiometric air-fuel ratio (AFR) (dashed line) at curve 410. When more air is present than fuel relative to the stoichiometric AFR, the degree of rarefaction (and absolute value) of the AFR increases. When more fuel than air is used relative to the stoichiometric AFR, the enrichment of the AFR increases and the absolute value of the AFR decreases. All curves are shown along the x-axis over time.

Before t1, the vehicle is not moving. For example, the vehicle may be parked with the engine off. The canister load stored in the memory of the controller may reflect the last canister load learned by the vehicle controller prior to shut down. At shutdown, it is determined that the canister load is above the purge threshold, requiring purging of the canister for the next drive cycle.

At t1, the engine is restarted, such as in response to an operator requesting an engine restart by firing the vehicle. Between t1 and t2, the engine is cranking via the starter motor. At this point, no fuel is delivered to the engine. At t2, engine fueling may be resumed and the canister may be purged in response to the engine speed exceeding a threshold cranking speed (e.g., 400 rpm). To enable canister purging with reduced incidence of engine stall, one or more cylinders of the engine are selectively deactivated. The number of cylinders is selected based on a vehicle occupancy level. In the illustrated example, half of all of the engine cylinders are deactivated while the remaining cylinders remain active (at curve 408, a fraction of 0.5). However, in other examples, the score may vary. For example, if the vehicle occupancy level is higher (than the level corresponding to curve 408), more cylinders will be deactivated to provide a smaller active cylinder fraction (shown at 409 b). As another example, if the vehicle occupancy level is low (below the level corresponding to curve 408), fewer cylinders will be deactivated to provide a greater active cylinder fraction (shown at 409 a).

In addition, the canister extraction rate and extraction ramp rate achieved during extraction are increased relative to the default extraction rate and extraction ramp rate (shown at dashed segment 412). The default extraction rate may correspond to the extraction rate and the extraction ramp rate used when all of the engine cylinders are active. As the number of deactivated cylinders increases, the increased extraction rate is increased relative to the default extraction rate. Increasing the decimation rate includes operating the CPV at a larger duty cycle (represented by a higher final step value). Increasing the decimation ramp rate includes increasing the size of each step of the ramp as well as the ramp rate (as indicated by the steeper slope of the ramp). As the canister is pumped, the canister load begins to drop.

When the canister is purged, the fueling of the active cylinder is adjusted according to the amount of fuel vapor ingested (determined based on the canister purge rate and the canister load) to maintain the AFR of the active cylinder at or near stoichiometric.

Shortly before t3, engine stall is predicted when the canister is extracted for the engine with half of all cylinders deactivated. Specifically, one or more (but not all) of the active cylinders may stall shortly before t3, causing a sudden drop in engine speed. Engine stalls may be due to ingestion of rich fuel vapors from the canister, resulting in a temporary rich AFR excursion. In one example, this may occur due to the canister being more loaded than originally intended (such as due to the vehicle being parked in an area of high solar load for a long time before t 1).

In response to an indication of a potential engine stall, at t3, the deactivated cylinders are reactivated. This results in the fraction of active cylinders moving to 1. By reactivating the deactivated cylinders, the engine may be restarted in operation via cylinders that are not drawing rich fuel vapor. As a result, the entire engine stall (to zero speed) is avoided and the engine speed may begin to recover. In particular, even if the engine performance is somewhat hesitant, depending on how many cylinders are deactivated, the entire engine stall can be avoided.

By closing the CPV, the canister extraction is also disabled at t 3. Also at t3, fuel is temporarily inhibited from going to the stalled engine cylinder that has ingested rich vapor to allow rapid purging of rich fuel vapor from the cylinder to the tailpipe. Shortly after t3, when rich fuel vapor is purged, stoichiometric fueling of the stalled engine cylinder is resumed.

Between t3 and t4, the CPV remains closed as rich vapor is being extracted from the stalled cylinder, causing the extraction rate to drop to 0. Also, since no draw occurs, the canister load is maintained between t3 and t 4. At t4, canister purging resumes once rich vapor is purged from the stalled cylinder. However, the canister is drawn at a lower draw rate and draw ramp rate than when the canister draw is started at t 2. The lower decimation ramp rate includes a smaller size of each step of the ramp, and a lower ramp rate (as indicated by the shallower slope of the ramp) than the decimation ramp rate applied at t2-t 3. As the canister is pumped, the canister load begins to drop. At t5, the canister is purged of fuel vapor and canister purging is disabled.

After t5, loading of the canister with fuel vapor during engine operation resumes. Also, after t5, the fraction of engine cylinders selectively deactivated varies according to torque demand and is independent of canister load.

In this manner, engine stall that may occur during canister purging may be minimized. A technical effect of deactivating one or more cylinders of an engine in response to a request to purge fuel vapor from a canister is that the deactivated cylinders may be sealed from ingestion of potentially rich canister vapors, particularly during open loop control phases of purging when canister load conditions are not reliably known. Further, engine stall due to vapor mass caused by fuel sloshing can be avoided in advance. By increasing the purge ramp rate when purging a canister to an engine having one or more deactivated cylinders, the canister may be emptied more quickly during the drive cycle. A technical effect of reactivating deactivated cylinders in response to an indication of potential engine stall is that the engine may be quickly recovered from an entire engine stall by fueling the cylinders that are not ingesting rich vapors. By reducing the extraction ramp rate when extracting canisters from an engine in which all cylinders are active, engine stability during the remainder of the extraction operation is improved. By increasing canister extraction efficiency, exhaust emissions may be improved.

An exemplary method for an engine of a vehicle includes: deactivating one or more cylinders in response to a request to purge fuel vapor from a canister; and deactivating the extraction and reactivating the one or more deactivated cylinders in response to an indication of engine stall. In the foregoing example, additionally or alternatively, the method further comprises selecting a number of the one or more cylinders to deactivate as a function of a vehicle occupancy level, the number increasing as the occupancy level decreases. In any or all of the foregoing examples, additionally or optionally, the method further comprises: purging the fuel vapor from the canister to the engine with one or more cylinders deactivated and remaining cylinders active at a first purge ramp rate prior to deactivating the purging, the first purge ramp rate based on a canister load, the selected number of the one or more deactivated cylinders. In any or all of the foregoing examples, additionally or alternatively, reactivating the deactivated cylinder includes injecting fuel into the deactivated cylinder prior to Intake Valve Opening (IVO) and combusting a previously inducted air charge in the deactivated cylinder. In any or all of the foregoing examples, additionally or optionally, the method further comprises: temporarily disabling fuel flow to the remaining active cylinders in response to the indication of engine stall; pumping at least some purge fuel vapor from an intake manifold of the engine to a tailpipe via the reactivated cylinder; and resuming fuel flow in the remaining active cylinders after the pumping. In any or all of the foregoing examples, additionally or optionally, the method further comprises: restarting the purging after a duration based on the number of the one or more deactivated cylinders, the duration increasing as the number decreases. In any or all of the foregoing examples, additionally or optionally, the method further comprises: after restarting the purging, purging the fuel vapor from the canister to the engine with all cylinders restarted at a second purge ramp rate that is lower than the first purge ramp rate. In any or all of the foregoing examples, additionally or optionally, the second extraction ramp rate is decreased relative to the first extraction ramp rate as the cylinder deactivation amount increases. In any or all of the foregoing examples, additionally or optionally, the indication of engine stall comprises an indication of partial engine stall or an expectation of total engine stall.

Another exemplary method for a vehicle engine includes: operating in a first purging mode, the first purging mode including purging fuel vapors from a canister at a first purging ramp rate to an engine in which a plurality of cylinders are deactivated and remaining cylinders are active; and operating in a second purging mode that includes purging fuel vapors from the canister to the engine with all cylinders active at a second purge ramp rate that is lower than the first purge ramp rate. In any or all of the foregoing examples, additionally or optionally, the method further comprises: transitioning from the first extraction mode to the second extraction mode in response to an indication of a potential engine stall. In any or all of the foregoing examples, additionally or optionally, the transitioning comprises: reactivating the plurality of deactivated cylinders and temporarily disabling fuel flow to the remaining active cylinders. In any or all of the foregoing examples, additionally or optionally, after fuel vapor is drawn from the engine intake manifold to the tailpipe via the plurality of deactivated cylinders for a duration of time, fuel flow is redirected to the remaining active cylinders. In any or all of the foregoing examples, additionally or optionally, operating in the first extraction mode is in response to a canister load being above a threshold load upon completion of an engine cranking after the engine is started from rest. In any or all of the foregoing examples, additionally or optionally, operating in the first extraction mode further comprises selecting a number of deactivated cylinders as a function of vehicle occupancy level, the number increasing as the vehicle occupancy level decreases. In any or all of the foregoing examples, additionally or alternatively, operating the engine with the selected number of deactivated cylinders comprises: disabling the fuel injector, and closing each of the intake and exhaust valves of each of the selected number of deactivated cylinders. In any or all of the preceding examples, additionally or optionally, the first decimation ramp rate includes a first decimation step size and a first rate of change between successive steps, and wherein the second decimation ramp rate includes a second decimation step size that is less than the first decimation step size and a second rate of change between successive steps that is less than the first rate of change between successive steps.

Another exemplary vehicle system includes: an engine having a plurality of cylinders, each cylinder having a selectively deactivatable fuel injector; an engine speed sensor; a fuel system including a fuel tank, a fuel vapor canister, and a purge valve coupling the canister to an engine air intake; an occupancy sensor coupled to a vehicle cabin; and a controller having computer readable instructions stored on a non-transitory memory that, when executed, cause the controller to: deactivating the plurality of cylinders and operating the purge valve at a first duty cycle to purge canister fuel vapor to remaining active cylinders in response to the canister load being above a threshold; and in response to an indication of stall in one or more of the remaining active cylinders, reactivating the plurality of cylinders and closing the extraction valve and disabling fuel flow to the remaining active cylinders for a duration of time. In any or all of the foregoing examples, additionally or optionally, the controller includes further instructions that when executed cause the controller to: selecting the plurality of cylinders to be deactivated in accordance with an output of the occupancy sensor; deactivating the plurality of cylinders by disabling fuel flow through the corresponding fuel injectors and keeping the corresponding intake and exhaust valves closed; and restarting the plurality of cylinders by enabling fuel flow through the corresponding fuel injectors prior to opening the corresponding intake valves. In any or all of the foregoing examples, additionally or optionally, the controller includes further instructions that when executed cause the controller to: after the duration, resuming fuel flow to the remaining active cylinders and re-operating the purge valve at a second duty cycle that is less than the first duty cycle, the second duty cycle being reduced relative to the first duty cycle in accordance with a cylinder deactivation amount.

In a further representation, the vehicle system is a hybrid vehicle system or an autonomous vehicle system.

Note that the example control and estimation routines included herein may be used with various engine and/or vehicle system configurations. The control methods and routines disclosed herein may be stored as executable instructions in a non-transitory memory and may be executed by a control system, including a controller, in conjunction 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, and the like. As such, various acts, operations, and/or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing 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 illustrated acts, operations, and/or functions may be repeatedly performed depending on the particular strategy being used. Further, the described acts, operations, and/or functions may graphically represent code to be programmed into the non-transitory memory of the computer readable storage medium in the engine control system, wherein the described acts are performed by executing instructions in conjunction with the electronic controller in the system including the various engine hardware components.

It will be appreciated that the configurations and routines disclosed herein are exemplary in nature, and that these specific embodiments are not to be considered in a limiting sense, because numerous 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 nonobvious combinations and subcombinations of the various systems and configurations, and other features, functions, and/or properties disclosed herein.

As used herein, the term "about" is to be construed as representing ± 5% of the range, unless otherwise specified.

The following claims particularly point out certain combinations and subcombinations regarded as novel and nonobvious. 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 through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure.

According to the invention, a method for an engine of a vehicle comprises: deactivating one or more cylinders in response to a request to purge fuel vapor from a canister; and deactivating the extraction and reactivating the one or more deactivated cylinders in response to an indication of engine stall.

According to one embodiment, the invention is further characterized by: selecting a number of the one or more cylinders to deactivate as a function of a vehicle occupancy level, the number increasing as the occupancy level decreases.

According to one embodiment, the invention is further characterized by: purging the fuel vapor from the canister to the engine having the one or more deactivated cylinders and remaining active cylinders at a first purge ramp rate prior to deactivating the purging, the first purge ramp rate based on canister load, the selected number of the one or more deactivated cylinders.

According to one embodiment, reactivating the one or more deactivated cylinders includes injecting fuel into the deactivated cylinders prior to Intake Valve Opening (IVO) and combusting previously inducted air charges in the deactivated cylinders.

According to one embodiment, the invention is further characterized by: temporarily disabling fuel flow to the remaining active cylinders in response to the indication of engine stall; pumping at least some purge fuel vapor from an intake manifold of the engine to a tailpipe via the reactivated cylinder; and resuming fuel flow in the remaining active cylinders after the pumping.

According to one embodiment, the invention is further characterized by: restarting the purging after a duration based on the number of the one or more deactivated cylinders, the duration increasing as the number decreases.

According to one embodiment, the invention is further characterized by: after restarting the purging, purging the fuel vapor from the canister to the engine with all cylinders restarted at a second purge ramp rate that is lower than the first purge ramp rate.

According to one embodiment, the second extraction ramp rate is decreased relative to the first extraction ramp rate as the cylinder deactivation amount increases.

According to one embodiment, said indication of engine stall comprises an indication of partial engine stall or an expectation of total engine stall.

According to the invention, a method for a vehicle engine comprises: operating in a first purging mode, the first purging mode including purging fuel vapors from a canister at a first purging ramp rate to an engine in which a plurality of cylinders are deactivated and remaining cylinders are active; and operating in a second purging mode that includes purging fuel vapors from the canister to the engine with all cylinders active at a second purge ramp rate that is lower than the first purge ramp rate.

According to one embodiment, the invention is further characterized by: transitioning from the first extraction mode to the second extraction mode in response to an indication of a potential engine stall.

According to one embodiment, the transitioning comprises: reactivating the plurality of deactivated cylinders and temporarily disabling fuel flow to the remaining active cylinders.

According to one embodiment, after fuel vapor is drawn from the engine intake manifold to the tailpipe via a plurality of deactivated cylinders for a duration, fuel flow is redirected to the remaining active cylinders.

According to one embodiment, operating in the first extraction mode is in response to a canister load being above a threshold load upon completion of an engine cranking after the engine is started from rest.

According to one embodiment, operating in the first extraction mode further comprises selecting a number of deactivated cylinders in dependence on a vehicle occupancy level, the number increasing as the vehicle occupancy level decreases.

According to one embodiment, operating an engine having a selected number of deactivated cylinders comprises: disabling the fuel injector, and closing each of the intake and exhaust valves of each of the selected number of deactivated cylinders.

According to one embodiment, the first decimation ramp rate includes a first decimation step size and a first rate of change between successive steps, and wherein the second decimation ramp rate includes a second decimation step size that is less than the first decimation step size and a second rate of change between successive steps that is less than the first rate of change between successive steps.

According to the present invention, there is provided a vehicle system having: an engine having a plurality of cylinders, each cylinder having a selectively deactivatable fuel injector; an engine speed sensor; a fuel system including a fuel tank, a fuel vapor canister, and a purge valve coupling the canister to an engine air intake; an occupancy sensor coupled to a vehicle cabin; and a controller having computer readable instructions stored on a non-transitory memory that, when executed, cause the controller to: deactivating the plurality of cylinders and operating the purge valve at a first duty cycle to purge canister fuel vapor to remaining active cylinders in response to the canister load being above a threshold; and in response to an indication of stall in one or more of the remaining active cylinders, reactivating the plurality of cylinders and closing the extraction valve and disabling fuel flow to the remaining active cylinders for a duration of time.

According to one embodiment, the controller includes further instructions that when executed cause the controller to: selecting the plurality of cylinders to be deactivated in accordance with an output of the occupancy sensor; deactivating the plurality of cylinders by disabling fuel flow through the corresponding fuel injectors and keeping the corresponding intake and exhaust valves closed; and restarting the plurality of cylinders by enabling fuel flow through the corresponding fuel injectors prior to opening the corresponding intake valves.

According to one embodiment, the controller includes further instructions that when executed cause the controller to: after the duration, resuming fuel flow to the remaining active cylinders and re-operating the purge valve at a second duty cycle that is less than the first duty cycle, the second duty cycle being reduced relative to the first duty cycle in accordance with a cylinder deactivation amount.