Method and system for controlling engine fuel supply

Abstract

The present disclosure provides a method and system for controlling engine fuel supply. A method and system are provided for tracking the mass of the fuel puddle in the intake tract of a deactivated engine cylinder. Differences in fuel vaporization rates in the deactivated cylinder's intake are accounted for by applying different time constants and gain values ​​to a transient fuel compensation model. Once the intake vapor pressure in the intake tract of the deactivated cylinder reaches a saturation pressure limit, the fuel vapor content is reduced.

Description

Technical Field

[0001] The present description generally relates to methods and systems for controlling fueling of engine cylinders to compensate for fueling dynamics. Background Art

[0002] Internal combustion engines are controlled to maintain a desired air-fuel ratio (AFR) in the combustion chamber to reduce emissions. For example, fuel is delivered via electronically controlled fuel injectors, which can be located inside each engine cylinder or in the cylinder's intake manifold. However, not all of the injected fuel enters the combustion chamber. Instead, some fuel accumulates in the engine's intake manifold, leading to a phenomenon commonly known as "wall wetting." For example, in an engine equipped with port fuel injection, fuel is injected into the intake manifold behind the closed intake valve during the cylinder's non-intake stroke. The injected fuel quickly evaporates due to heat from the valve and mixes with the intake air. The air-fuel mixture is then introduced into the cylinder during the intake stroke. However, fuel evaporation in the intake manifold is a function of wall temperature and manifold pressure. Therefore, depending on engine operating conditions, the injected fuel will impact the rear wall, and a portion of the fuel will cause wall wetting or form a fuel pool in the intake manifold. Some of the liquid fuel may remain in the intake manifold throughout the cycle, resulting in a net delay in fuel injection.

[0003] During steady-state engine operation, the fuel film is in a quasi-equilibrium state, where the amount of fuel added to the film per cycle by the fuel injection device is equal to the fuel removed by evaporation and film flow. However, if an engine throttle transient occurs, airflow and fuel injector response may be very fast (e.g., limited only by manifold aerodynamics), while the net fuel flow to the engine cylinders may be limited by variations in the fuel film properties. This delay in fuel in the intake tract can lead to AFR excursions during throttle transients. Furthermore, this problem can be exacerbated in engines with selectively deactivatable cylinders.

[0004] Various methods have been developed for controlling the engine air-fuel ratio during steady-state and transient engine operation by accounting for the fuel puddle in the intake manifold. An exemplary attempt is presented by Song et al. in US Pat. No. 7,111,593. There, transient fuel wall wetting characteristics of a running engine are determined while accounting for cylinder valve deactivation. Specifically, the fuel evaporation effect of fuel vapor that leaves the fuel puddle in the deactivated cylinder and migrates to the activated cylinder is taken into account when calculating the fueling offset for the activated cylinder.

[0005] However, the inventors have recognized potential issues with such a system. Even with Song's adjustments, the intake air-fuel ratio of the enabled cylinders may fluctuate. As an example, the evaporation rate of fuel from a cylinder's melt pool can vary based on whether a given cylinder was ignited and ingested in the last event. If a cylinder has not been ingested and ignited, the number of events that have passed since the last ignition event in a given cylinder may also affect the evaporation rate of fuel from the melt pool of that cylinder. In addition, vapor accumulation in the intake tract may be affected by the vapor pressure relative to the saturation vapor pressure. Specifically, if a cylinder is deactivated for an extended period of time, all of the melt pool or film mass may not evaporate. Conversely, vapor accumulation in the intake runners of the deactivated cylinders can quickly reach the saturation vapor pressure limit. Thereafter, vapor pressure accumulation can be limited. As another example, any disturbance in manifold pressure may cause vapor to escape into the engine's intake manifold and cause additional AFR fluctuations. Summary of the Invention

[0006] In one example, the aforementioned issues may be addressed by a method for an engine that includes adjusting fuel injection in response to reaching vapor saturation conditions in an intake port of a deactivated cylinder of the engine. In this manner, fuel dynamics may be more accurately determined.

[0007] As an example, an engine may be configured with variable displacement, which is activated via selectively deactivated engine cylinders. Based on torque demand, the engine can operate with different air-intake ratios, and thus, cylinders can be skipped or fired for each event. For each cylinder, the engine controller can track the estimated fuel puddle mass and fuel vapor content (e.g., the amount of fuel present in the liquid phase relative to the vapor phase) using calibrated gains and time constants. The gains and time constants can be calibrated using an X-Tau model based on engine operating conditions, including manifold pressure, engine speed, injected fuel mass, and engine temperature. The model can assume that the metered fuel is proportional to the airflow, and that a defined percentage of this fuel impacts the existing puddle and forms a liquid film. The X-Tau model is used to determine the evaporation rate of the fuel from this liquid film based on the film thickness or size. For deactivated cylinders, with deactivated intake and exhaust valves, the lower airflow in the deactivated cylinder's flow path results in a slower evaporation rate. Therefore, a different time constant is applied for each skipped cylinder event compared to an activated cylinder. Furthermore, based on the number of skip events for a cylinder, it can be determined whether the fuel vapor pressure has reached a saturation limit (e.g., when the fuel vapor content reaches the saturation vapor pressure). Saturation pressure is also affected by intake duct temperature and manifold pressure. Therefore, once the saturation limit is reached, further fuel vaporization from the intake duct can be restricted. Therefore, once the saturation limit is reached, the melt pool mass and vapor content of the deactivated cylinder can be reduced. For example, it can be noted that the melt pool mass and vapor content have not changed further, and the last estimated melt pool fuel mass and vapor content can be retained until the cylinder is reactivated. When the deactivated cylinder is reactivated, fuel supply to the cylinder is restored based on the reduced melt pool mass and vapor content. For example, the fuel supply is adjusted to compensate for the amount of fuel vapor pressure caused by the reduced melt pool mass and vapor content. Simultaneously, independent of the calculations in one or more deactivated cylinders, the fuel pool mass and vapor content in the remaining activated cylinders can continue to be estimated based on the vapor pressure of those cylinders. Therefore, in the activated cylinders, the cylinder fuel supply can continue to be adjusted to account for the wall wetting effects of the fuel pool.

[0008] In this way, transient fuel compensation can be improved by adjusting the fuel puddle dynamics of a deactivated cylinder based on the charge state of the deactivated cylinder relative to the activated cylinder. The technical effect of applying different time constants and gains accounts for the different fuel vaporization rates of activated and skipped cylinders, making it easier to understand the fuel puddle volume. By clipping the fuel puddle estimate when the vapor pressure at the puddle reaches the saturation vapor pressure limit, cylinder fueling errors are reduced, particularly when fueling is resumed to the deactivated cylinder. Consequently, more accurate air-fuel ratio control is provided with fewer AFR disturbances. By tracking and updating the vapor content and puddle fuel mass at each skipped cylinder event, more accurate fueling can be provided to the cylinder upon reactivation. Overall, the fuel economy of the variable displacement engine can be improved.

[0009] It should be understood that the above summary is provided to introduce in simplified form a series of concepts that will be further described in the detailed description. It is not intended to identify key or essential features of the claimed subject matter, the scope of which is solely defined by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that address any disadvantages noted above or in any part of this disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 An exemplary embodiment of an engine system layout is shown.

[0011] Figure 2 A partial engine view is shown.

[0012] Figure 3 A high-level flow chart of an example method for updating fuel puddle dynamics for each cylinder based on the cylinder's intake state is shown.

[0013] Figure 4 Example gain values ​​that may be applied during estimation of fuel puddle dynamics are shown.

[0014] Figure 5 Example time constant values ​​that may be applied during the estimation of fuel puddle dynamics are shown.

[0015] Figure 6 An example of how the fuel film quality at the cylinder runner varies with the relative vapor content is shown.

[0016] Figure 7 A prophetic example of regulating cylinder fueling in a variable displacement engine while accounting for variations in fuel puddle mass as intake conditions change is shown. DETAILED DESCRIPTION

[0017] Provided is a method for operating an engine configured for selective cylinder deactivation, such as Figure 1 and Figure 2 Method and system for regulating the amount of fuel delivered to the engine cylinders when the engine system is running. The engine controller can execute a control program such as Figure 3 An exemplary procedure is provided for updating the fuel pool dynamics for each cylinder based on the cylinder's charge state and based on the firing history of a given cylinder. The controller may select gains and time constants to apply to the X-Tau model for transient fuel compensation, such as based on Figure 4 and Figure 5 The controller can also reduce the fuel pool mass once the fuel vapor content of the cylinder reaches the saturation vapor pressure limit, such as Figure 6 As shown. Figure 7 An exemplary fuel supply adjustment is shown in the prophetic example of , which takes into account the changing fuel pool dynamics. In this way, air-fuel ratio disturbances associated with incorrect transient fuel compensation are reduced.

[0018] Figure 1 An exemplary engine 10 is shown having a cylinder bank 15. In the depicted example, the engine 10 is an inline four (I4) cylinder engine having a cylinder bank with four cylinders 14. The engine 10 has an intake manifold 16 having a throttle valve 20, and an exhaust manifold 18 coupled to an emission control system 30. The emission control system 30 includes one or more catalysts and an air-fuel ratio sensor, such as a reference Figure 2 As a non-limiting example, engine 10 may be included as part of a propulsion system for a passenger vehicle, such as hybrid vehicle system 5 .

[0019] Engine system 10 may have cylinder 14 having a selectively deactivatable intake valve 50 and a selectively deactivatable exhaust valve 56. In one example, intake valve 50 and exhaust valve 56 are configured for electric valve actuation (EVA) via electric single-cylinder valve actuators. While the depicted example shows each cylinder having a single intake valve and a single exhaust valve, in alternative examples, such as Figure 2 As described in detail in , each cylinder may have multiple selectively deactivatable intake valves and / or multiple selectively deactivatable exhaust valves.

[0020] During selected conditions, such as when the full torque performance of the engine is not required, one or more cylinders of engine 10 may be selectively deactivated (also referred to herein as single cylinder deactivation). This may include selectively deactivating one or more cylinders on cylinder bank 15. The number and characteristics of cylinders deactivated across the cylinder banks may be symmetrical or asymmetrical. By adjusting the number of cylinders deactivated, the charge ratio set at the engine may be varied.

[0021] During deactivation, selected cylinders can be deactivated by closing individual cylinder valvetrains (such as the intake valvetrain, the exhaust valvetrain, or a combination of both). Cylinder valves can be selectively deactivated via hydraulically actuated lifters (e.g., lifters coupled to valve pushrods), via a cam profile switching mechanism (where a cam lobe without lift is used for the deactivated valve), or via electrically actuated cylinder valvetrains coupled to each cylinder. Additionally, fuel flow and spark can be stopped to the deactivated cylinders, such as by deactivating cylinder fuel injectors.

[0022] In some examples, engine system 10 may have selectively deactivatable (direct) fuel injectors, and selected cylinders may be deactivated by turning off corresponding fuel injectors while maintaining operation of intake and exhaust valves so that air may continue to be pumped through the cylinders.

[0023] When a selected cylinder is disabled, combustion continues in the remaining open or enabled cylinders, with their fuel injectors and cylinder valvetrains enabled and operating. To meet torque demands, the engine produces the same amount of torque on the enabled cylinders. This requires higher manifold pressure, resulting in reduced pumping losses and improved engine efficiency. Furthermore, the lower effective surface area exposed to combustion (from only the open cylinders) reduces engine heat losses, thereby improving engine thermal efficiency.

[0024] Cylinders can be deactivated to provide a specific intake (or ignition) pattern based on a specified control algorithm. More specifically, the selected deactivated working cylinders do not take in air and therefore do not ignite, while the other enabled working cylinders take in air and therefore ignite. The intake pattern can be defined in one or more engine cycles and repeatedly defined if the same pattern is maintained. An overall pattern can be defined for one cycle of the engine, where an example of a four-cylinder engine with cylinders having position numbers of 1-4 (where 1 is at one end of the line and 4 is at the other end of the line) and a firing order of 1-3-4-2 has a pattern of 1-S-4-S, where "S" represents non-intake (or deactivated or skipped mode), and the numbering indicates that the cylinder is supplied with fuel and ignited. Another different pattern can be S-3-S-2. Other patterns can be 1-SS-4, S-3-4-S, 1-3-4-S, and 1-S-4-2, and so on. Another scenario is a pattern that extends over multiple engine cycles, such as 1-SS-2-SS-4-SS-3-SS, where the pattern changes in each cycle to create a rolling pattern. Even though each of these patterns operates at the same average intake manifold pressure, the cylinder charge of a given cylinder may depend on the intake pattern, specifically whether the cylinder fired or not in the previous engine cycle.

[0025] Engine 10 may be operated on a variety of substances, which may be delivered via fuel system 8. Engine 10 may be controlled at least in part by a control system 13 including controller 12. Controller 12 may be coupled to engine 10 (and reference Figure 2 The sensors 16 receive various signals and send control signals to the sensors 16 connected to the engine and / or vehicle (as described in reference Figure 2 The various actuators 81 described above may include motors, solenoids, etc. coupled to engine actuators such as the intake throttle, fuel injectors, intake and exhaust valve actuators, etc. The various sensors may include, for example, various temperature, pressure, and air-fuel ratio sensors.

[0026] The engine controller 12 may include a drive pulse generator and a sequencer for determining a cylinder mode based on the engine output desired under the current engine operating conditions. For example, the drive pulse generator may use adaptive predictive control to dynamically calculate a drive pulse signal indicating which cylinders will be fired and at what intervals to obtain the desired output (i.e., cylinder firing / non-firing mode). The cylinder firing mode may be adjusted to provide the desired output without generating excessive or inappropriate vibrations within the engine. Thus, the cylinder mode may be selected based on the configuration of the engine (such as based on whether the engine is a V-type engine, an in-line engine), the number of engine cylinders present in the engine, and the like. Based on the selected cylinder mode, the single-cylinder valve mechanism of the selected cylinder may be closed, while simultaneously stopping the supply of fuel flow and spark to the cylinder.

[0027] The engine cylinder charge ratio is the actual total number of cylinder firing events during a predetermined actual total number of cylinder compression strokes divided by the actual total number of cylinder compression strokes. As used herein, a cylinder activation event refers to a cylinder firing during a cylinder cycle with the intake valve open and the exhaust valve closed, while a cylinder deactivation event refers to a cylinder not firing during a cylinder cycle with the intake and exhaust valves remaining closed. An engine event can be the cylinder stroke that occurs (e.g., intake, compression, power, exhaust), the timing of intake or exhaust valve opening or closing, the timing of ignition of the air-fuel mixture in the cylinder, the position of the piston in the cylinder relative to the crankshaft position, or other engine-related events. An engine event number corresponds to a specific cylinder. For example, engine event number one may correspond to the compression stroke of cylinder number one. Engine event number two may correspond to the compression stroke of cylinder number three. A cycle number refers to an engine cycle, which includes one event (activation or deactivation) in each cylinder. For example, the first cycle is completed when engine events are passed through in the firing order in each cylinder of an 8-cylinder engine (a total of eight engine events). The second loop begins when the second engine event occurs in the first cylinder in the firing order (ie, the ninth engine event counted from the initial engine event).

[0028] The decision to activate or deactivate a cylinder and to open or close its intake or exhaust valve can be made a predetermined number of cylinder events (e.g., one cylinder event, or alternatively, one cylinder cycle or eight cylinder events) before the cylinder is to be activated or deactivated, to allow time for the estimated process of opening and closing the intake and exhaust valves of the cylinder to begin. For example, for an eight-cylinder engine with a firing order of 1-3-7-2-6-5-4-8, the decision to activate or deactivate cylinder number seven can be made during the intake or compression stroke of cylinder number seven, one engine cycle before cylinder number seven is activated or deactivated. Alternatively, the decision to activate or deactivate a cylinder can be made a predetermined number of engine events or cylinder events before the selected cylinder is activated or deactivated.

[0029] Now turn Figure 2 , showing an internal combustion engine 10 (such as Figure 1 200 of an exemplary embodiment of a combustion chamber or cylinder of an engine 10). Figure 1 The components described in the drawings are similarly numbered. The engine 10 may be coupled to a propulsion system, such as a vehicle system 5 configured for traveling on a road. The engine 10 may be controlled from a controller 12 (such as Figure 1 A control system (controller 12) receives control parameters and input from a vehicle operator 130 via an input device 132. In this example, input device 132 includes an accelerator pedal and a pedal position sensor 134 for generating a proportional pedal position signal PP. Cylinder 14 of engine 10 (also referred to herein as a "combustion chamber") may include combustion chamber walls 136 with a piston 138 positioned therein. Piston 138 may be coupled to a crankshaft 140 so 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 a passenger vehicle via a transmission system (not shown).

[0030] Cylinder 14 can receive intake air via a series of intake passages 142, 144, and 146. Intake passage 146 can also communicate with other cylinders of engine 10 in addition to cylinder 14. In some embodiments, one or more of the intake passages may include a boosting device, such as a turbocharger or a supercharger. For example, Figure 2 Engine 10 is shown 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. Compressor 174 may be powered at least in part by exhaust turbine 176 via shaft 180, wherein the boosting device is configured as a turbocharger. However, in other examples, such as where engine 10 is provided with a supercharger, exhaust turbine 176 may optionally be omitted, wherein compressor 174 may be powered by a mechanical input from a motor or the engine. A throttle 20 including a throttle plate 164 may be disposed along the 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, upstream of compressor 174.

[0031] 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, which is part of emission control system 30, as shown. Figure 1As shown. Exhaust gas sensor 128 can be selected from various suitable sensors for providing an indication of the 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 depicted), a HEGO (Heated EGO), a NOx, HC, or CO sensor. Emission control device 178 can be a three-way catalyst (TWC), a NOx trap, various other emission control devices, or combinations thereof.

[0032] Each cylinder of engine 10 may include one or more intake valves and one or more exhaust valves. For example, cylinder 14 is shown including at least one poppet-type intake valve 150 and at least one poppet-type exhaust valve 156 located at an upper region of 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 at an upper region of the cylinder.

[0033] Intake valve 150 may be controlled by controller 12 via cam actuation 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 a cam profile switching system (CPS), variable cam timing (VCT), variable valve timing (VVT), and / or variable valve lift (VVL) system, which 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 via 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 and / or 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.

[0034] As reference Figure 1 As described in detail, engine 10 may be a variable displacement engine in which intake and exhaust valves may be selectively deactivated in response to operator torque demand to operate the engine at a desired charge / charge ratio in a selected cylinder deactivation (or firing) mode.

[0035] In some embodiments, each cylinder of engine 10 may include a spark plug 192 for initiating combustion. Under select operating modes, 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. In other embodiments, such as where compression ignition is used to initiate combustion in the cylinder, the cylinder may not include a spark plug.

[0036] In some embodiments, each cylinder of engine 10 may be configured with one or more injectors for providing fuel to the cylinder. As a non-limiting example, cylinder 14 is shown as including 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 during the compression stroke may be more restrictive than when using a high-pressure fuel system. Additionally, the fuel tank may have a pressure sensor that provides a signal to controller 12.

[0037] 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 (hereafter referred to as "DI") of fuel into combustion cylinder 14. Figure 2 Injector 166 is shown positioned to one side of cylinder 14, but the injector may alternatively be located on top of the piston, such as near spark plug 192. Due to the lower volatility of some alcohol-based fuels, such a location may improve mixing and combustion when the engine is operated on alcohol-based fuels. Alternatively, the injector may be located on top and near the intake valve to improve mixing.

[0038] As reference Figure 2 As described in detail, engine 10 may be a variable displacement engine wherein fuel injector 166 is selectively deactivated in response to operator torque demand to enable engine operation at desired air intake ratios in selected cylinder deactivation (or firing) modes.

[0039] Fuel injector 170 is shown arranged in intake passage 146 rather than in cylinder 14 and is configured to provide what is known as port injection of fuel (hereinafter referred to as "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 depicted.

[0040] During a single cycle of a cylinder, fuel can be delivered to the cylinder via two injectors. For example, each injector can deliver a portion of the total fuel injection for combustion in cylinder 14. Thus, even for a single combustion event, the injected fuel from the port and direct injectors can be injected at different timings. Furthermore, for a single combustion event, multiple injections of the delivered fuel can be performed per cycle. Multiple injections can be performed during the compression stroke, the intake stroke, or any suitable combination thereof.

[0041] As mentioned above, Figure 2 Only one cylinder of a multi-cylinder engine is shown. Thus, each cylinder may similarly include its own set of intake / exhaust valves, one or more fuel injectors, spark plugs, etc. It should be understood that engine 10 may include any suitable number of cylinders, including 2, 3, 4, 5, 6, 8, 10, 12, or more cylinders. Furthermore, each of these cylinders may include reference cylinder 14 through Figure 2 Some or all of the various components described and depicted.

[0042] The engine may also include one or more exhaust gas recirculation passages for recirculating a portion of the exhaust gas from the engine exhaust to the engine intake. Thus, by recirculating some of the 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 depicted 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. Additionally, EGR sensor 145 may be disposed within the EGR passage and may provide an indication of one or more of the pressure, temperature, and concentration of the exhaust gas.

[0043] In some examples, vehicle 5 may be a hybrid vehicle with multiple torque sources available to one or more wheels 55. In other examples, vehicle system 5 is a conventional vehicle with only an engine, or an electric vehicle with only one or more electric motors. In the illustrated example, vehicle system 5 includes engine 10 and electric motor 52. Electric motor 52 may be a motor or a motor / generator. When one or more clutches 56 are engaged, crankshaft 140 of engine 10 and electric motor 52 are connected to wheels 55 via transmission 54. In the depicted example, a first clutch 56 is positioned between crankshaft 140 and electric motor 52, and a second clutch 56 is positioned between electric motor 52 and transmission 54. Controller 12 can send signals to the actuators of each clutch 56 to engage or disengage the clutch, thereby connecting or disconnecting crankshaft 140 from electric motor 52 and its connected components, and / or connecting or disconnecting electric motor 52 from transmission 54 and its connected components. Transmission 54 may be a gearbox, a planetary gear system, or another type of transmission. The powertrain can be configured in various ways, including parallel, series, or series-parallel hybrid vehicles.

[0044] The electric machine 52 receives power from the traction battery 58 to provide torque to the wheels 55. The electric machine 52 can also operate as a generator to provide power to charge the battery 58, such as during braking operations.

[0045] Controller 12 is shown as a microcomputer, including a microprocessor unit 106, input / output ports 108, an electronic storage medium for executable programs and calibration values ​​(shown in this particular example as a read-only memory chip 110), random access memory 112, keep-alive memory 114, and a data bus. In addition to those signals previously discussed, controller 12 may also receive various signals from sensors coupled to engine 10, including a measurement of engine coolant temperature (ECT) from a temperature sensor 116 coupled to a cooling sleeve 118; a surface ignition pickup signal (PIP) from a Hall effect sensor 120 (or other type) coupled to a 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 based on 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 fuel composition sensors coupled to one or more fuel tanks in the fuel system.

[0046] Storage medium read-only memory chip 110 can be programmed with computer readable data representing instructions executable by microprocessor unit 106 for performing the methods described below as well as other variants that are anticipated but not specifically listed.

[0047] The controller 12 Figures 1 to 2 Various sensors receive signals and use Figures 1 to 2 The controller may control various actuators to adjust engine operation based on received signals and instructions stored in the controller's memory. For example, in response to a driver torque demand, as inferred from a pedal position sensor, the controller may send a signal to a throttle actuator to adjust throttle opening, with the throttle opening increasing as torque demand increases. As another example, in response to a desired air intake ratio determined based on the driver torque demand, the controller may send signals to selected cylinder fuel injectors and valves to selectively deactivate those cylinders according to a cylinder deactivation pattern that provides the desired air intake ratio.

[0048] Therefore, not all port-injected fuel enters the combustion chamber. Some fuel is stored in the engine's intake manifold, such as in the intake port. This phenomenon is known as wall wetting. Specifically, during the non-intake stroke of the corresponding cylinder, fuel is injected from the port injector behind the closed intake valve. Heat from the valve rapidly vaporizes the port-injected fuel and mixes with the intake air, and the mixture is introduced into the cylinder during the intake stroke. Because this evaporation of fuel in the intake port is a function of the wall temperature and manifold pressure, under certain engine operating conditions, this injected fuel may impact the rear of the wall, and a portion of this fuel may cause wall wetting or form a fuel pool in the intake port. A portion of the liquid fuel may remain in the intake port throughout the cycle, resulting in a net delay in fuel injection. During steady-state engine operation, the fuel film is in a quasi-equilibrium state, where the amount of fuel added to the film by the fuel injection device per cycle is equal to the amount removed by evaporation and liquid film flow. However, if an engine throttle transient occurs, the airflow and fuel injector response are very fast (limited only by the manifold aerodynamics), but the net fuel flow to the engine cylinders is limited by the varying properties of the fuel thin. Fuel delays in the intake port cause air / fuel ratio (AFR) excursions during throttle transients. To reduce AFR excursions due to transient operation, the controller can use, for example, an X-Tau model for transient fuel control, a gain-time constant model, and / or a multi-component puddle model (such as "wall wetting") to accurately estimate the mass of the fuel puddle on each intake port for each cylinder event. As shown in reference Figure 3 As detailed in the routine, the controller may also adjust model parameters based on whether a cylinder is fired or skipped for a given cylinder event, thereby accounting for differences in fuel evaporation rates in the intake ports of fired or skipped cylinders.

[0049] In this way, Figure 1 and Figure 2 An engine system is provided, comprising a first cylinder; a second cylinder; a first fuel injector coupled to a first intake port of the first cylinder; a second fuel injector coupled to a second intake port of the second cylinder; and a controller. The controller may be configured with computer-readable instructions stored on a non-transitory memory, the computer-readable instructions configured to: selectively deactivate the second cylinder in response to a decrease in torque demand while continuing to supply fuel to the first cylinder for a plurality of cylinder events; and for each of the plurality of cylinder events, update a value of a first fuel pool in the first intake port via a first set of fuel vaporization constants; update a value of a second fuel pool in the second intake port via a second, different set of fuel vaporization constants until the fuel pool is at a saturation limit, and then maintain the value of the second fuel pool; and adjust a pulse width commanded to the first fuel injector based on the value of the first fuel pool. Additionally, in response to an increase in torque demand, the controller may reactivate the second cylinder and adjust the pulse width commanded to the second fuel injector based on the value of the second fuel pool. In another example, updating the value of the first fuel pool in the first intake passage may include updating the fuel pool mass and fuel vapor pressure in the first intake passage, respectively, and updating the value of the second fuel pool in the second intake passage may include updating the fuel pool mass and fuel vapor pressure in the second intake passage, respectively, wherein the fuel pool being at a saturation limit includes the fuel vapor pressure in the second intake passage being at a saturated vapor pressure. In another example, the controller may further include further instructions for calculating the saturated vapor pressure based on the fuel alcohol content, the temperature of the second intake passage, and the ambient pressure, respectively. The controller may further include further instructions for retrieving a first set of fuel vaporization constants from memory based on engine speed and load; calculating a second set of fuel vaporization constants based on engine speed and load; and using either the first set or the second set of constants based on the activation state of the corresponding cylinder.

[0050] Now turn Figure 3 , a method 300 for accurately estimating fuel puddle dynamics prior to a cylinder fueling event is shown. The method enables accurate control of cylinder fueling while taking into account wall wetting effects. Instructions for executing method 300 and the remaining methods included herein may be provided by a controller based on instructions stored on a memory of the controller and in conjunction with information from sensors of the engine system (such as those described above). Figures 1 to 2 The controller may use the engine actuators of the engine system to adjust the engine operation according to the method described below. It should be understood that the controller may be repeated before each cylinder event during engine operation. Figure 3 program.

[0051] At 302, the method includes estimating and / or measuring engine operating conditions. These may include, for example, vehicle speed, engine speed, engine load, accelerator pedal position, driver torque demand, ambient conditions (including ambient temperature, humidity, and pressure), boost pressure, EGR, manifold pressure, manifold airflow, etc. The driver torque demand may be based on accelerator pedal position and vehicle speed. For example, accelerator pedal position and vehicle speed may be the basis for indexing a table or function in controller memory. The table or function outputs the driver-requested engine torque based on empirically determined values ​​stored in the table.

[0052] At 304, a target air intake ratio or desired engine cylinder firing fraction may be selected based on engine operating conditions. For example, as driver torque demand decreases, the number of cylinders that need to be fired to meet the torque demand may be reduced, and the number of cylinders that may be skipped (i.e., operated with selective fuel deactivation) while the torque demand is being met may be increased. As used herein, a desired engine cylinder firing fraction or target air intake ratio refers to the ratio of the total number of cylinder events being charged in a predetermined actual total number of cylinder compression strokes divided by the actual total number of cylinder compression strokes. In one example, the target air intake is determined based on the requested engine torque. In particular, the allowable air intake ratios may be stored in a table or function that may be indexed by the desired engine torque and engine speed.

[0053] In addition to selecting a target intake ratio, the controller can also determine whether to fire or skip each cylinder based on the selected intake ratio. For example, a determination is made regarding the next cylinder event and whether to fire or skip the cylinder in the upcoming cylinder event to support the desired intake ratio. This determination is based on the engine's previous intake history and the desired intake ratio. If the intake ratio remains constant for an extended period, the resulting determination will provide a pattern corresponding to the intake ratio. In other words, the controller determines whether to fire or skip in the next cylinder event to provide the determined target intake ratio. In one example, if the most recent cylinder event was a fire event and the target intake ratio requires the next cylinder event to be an intake event, the next cylinder is fired and fired. Otherwise, if the target intake ratio requires the next cylinder event to be a skip event, the next cylinder is skipped and not fired. In some examples, a cylinder deactivation pattern that provides the target intake ratio or the desired engine cylinder firing fraction can also be selected.

[0054] At 306, the method includes retrieving parameters for modeling wall wetting. In particular, a first set of model parameters can be retrieved. In one example, the first set of model parameters can be default settings that are determined as a function of engine speed and load. As an example, the controller can retrieve a gain factor (e.g., X) and a fuel vaporization time constant (e.g., Tau) for the wall wetting model. These values ​​can be retrieved from a lookup table stored in a memory of the controller. The gain and Tau values ​​can be predetermined based on engine speed and MAP. These values ​​can be adjusted based on intake manifold runner control (IMRC), variable cam timing (VCT) position, and estimated valve temperature. In a cylinder deactivation mode, these parameters can be further adjusted based on the number of engine cycles or events in which a cylinder has been deactivated.

[0055] At 308 , it can be determined whether the next cylinder event is a firing event or a skip event. Specifically, based on the selected airflow ratio, it can be determined whether the next cylinder will burn fuel. In one example, if the airflow ratio is 1.0, all cylinders are operated and the next cylinder is a firing event. In another example, if the airflow ratio is 0.5, every other cylinder is skipped. Therefore, if the previous cylinder event was a firing event, the upcoming cylinder event may be a skip event. Similarly, if the previous cylinder event was a skip event, the upcoming cylinder event may be a firing event.

[0056] If the next cylinder event is a firing event, then at 310 , the method includes estimating the air charge (m_air) of the firing cylinder. In one example, estimating the air charge of the firing cylinder includes measuring intake manifold pressure and using a representation of engine volumetric efficiency to infer the amount of air trapped in the cylinder. The air charge estimate may be modified based on the cylinder's previous deactivation history. At 312 , the method includes estimating a desired fuel mass for the firing cylinder based on the estimated cylinder air charge and a target air-fuel ratio (AFR). In one example, where the target AFR is stoichiometric, a desired fuel mass for the cylinder (Mf_desired) may be calculated based on the estimated cylinder air charge to set the air charge to fuel mass ratio to 14.7:1. Other AFRs are possible, such as richer than stoichiometric (less air than stoichiometric) or leaner than stoichiometric (more air than stoichiometric), and the fuel mass calculation may be adjusted accordingly. The target AFR may also be selected based on engine operating conditions. As an example, the desired fuel mass for a stoichiometric AFR may be determined as: Mf_Desired = AFR_Stoichiometric * Air.

[0057] At 314, the method includes updating the melt pool mass and vapor content in the intake runner of the firing cylinder based on the last estimated melt pool state and the retrieved time constant and gain values. Here, the retrieved time constant and gain values ​​may be a first set of time constants and gain values. In one example, the update includes estimating the melt pool mass and vapor content via a model (such as an X-Tau model) while applying a first set of model parameters (in this example, a first set of time constants and gain values) due to the cylinder being in an active state. In one example, the retrieved gain value applied may be 0.07, and the retrieved time constant may be 4. The first set of model parameters may include other parameters such as engine coolant temperature (ECT), IMRC, and VCT compensation gain. The first set of model parameters may be based on engine speed and load, ECT, IMRC position, VCT position, the cylinder's intake state, and / or the number of cylinder shutdown events. As an example, the controller may update the melt pool mass by taking into account fuel evaporated from the previous melt pool and additional fuel added to the melt pool during the current injection. The net fuel in the melt pool is used in subsequent transient fuel calculations. In this manner, the controller may estimate the fuel puddle mass and fuel vapor content in the intake port of each cylinder separately based on cylinder events, including based on the intake state of each cylinder.

[0058] At 316, the controller may estimate fuel vapor received in the intake runner of a given cylinder from adjacent deactivated cylinders. Specifically, the controller may estimate fuel migration from one or more deactivated engine cylinders to a given activated cylinder of the engine. At 318, the controller may calculate the fuel mass to be delivered to the firing cylinder based on the desired fuel mass, puddle mass, and fuel vapor content, as well as the fuel vapor received from the deactivated cylinders. Optionally, a transient fueling compensation value may be combined with feedback correction from an exhaust gas oxygen sensor to allow the combustion air-fuel ratio to more accurately approximate the target air-fuel ratio. The feedback may be proportional, integer, or other suitable forms. Additionally, additional feedforward compensation, such as compensation for airflow dynamics, may be employed. For example, the controller may adjust fuel delivery to a given activated cylinder based on the estimated fuel puddle mass, fuel vapor content, and fuel migration, as described in detail below. At 320, the method includes adjusting at least one fuel amount port injected into a given activated cylinder based on the estimated fuel puddle mass and fuel vapor content. For example, a pulse width signal corresponding to the calculated fuel mass to be delivered can be commanded to a fuel injector (e.g., a port fuel injector) coupled to a firing cylinder. In one example, as the fuel puddle mass and vapor content increase, the amount of fuel required to be port injected can be reduced, and the pulse width commanded to the port fuel injector can be reduced accordingly. In other examples, the amount of direct fuel injected can be reduced.

[0059] In general, a cylinder (or port)-specific transient fuel model can be used to derive fuel injection compensation for the firing cylinder. The parameters x and τ are used to describe the transient behavior of the injected fuel and the fuel film at the port. However, a different set of x and τ values ​​is retrieved for each cylinder / port. The model assumes that a portion (1-x) of the mass flow rate (dmf / dt) of the injected liquid fuel enters the cylinder, while the remainder (xdmf / dt) remains on the surface of the port / ports, forming a liquid film or pool mass. Additionally, vapor from the remaining fuel in the port can be included in the model and contribute to the fuel mass (mp) in the port, thus allowing the fuel pool mass at the port to have a broader meaning. The fuel supply dynamics model uses a fuel mass balance for each port, with the model development illustrated using the equations presented here. Specifically, the mass balance is written based on the fuel injector / port / cylinder. The incoming fuel mass is the mass flow rate (dmf / dt) of the fuel injected from the injector. The mass flow rate of fuel leaving the puddle is expressed as (dme / dt), which is assumed to be proportional to the mass of fuel in the puddle (mp) (via the parameter 1 / τ). Writing the mass balance when substituting for the flow into the cylinder gives:

[0060] dmp / dt=χdmf / dt-mp / τ

[0061] However, while time-based models / compensations can be used, discrete formats (event-based) can also be used in engine control applications. The event-based approach gives:

[0062] mp(k+1)=mp(k)+χmf(k)-mp(k) / Nr

[0063] where k is an event index, updated, for example, at each engine ignition or each engine revolution, or after a certain number of crank (or cam) shaft revolutions; mp is the mass of fuel remaining in the intake tract; and x is the fraction of the injected fuel that remains in the intake tract as a liquid film or vapor; mf is the amount of fuel injected into the intake tract during a given sampling period; Nr is the characteristic time of fuel vaporization over a number of engine events; and τ is a time constant describing the speed at which fuel in the intake tract leaves the intake tract.

[0064] At steady state, the amount of fuel trapped in the intake duct equals the amount of fuel leaving the duct, which is known as equilibrium. At equilibrium, the injected fuel equals the fuel introduced into the cylinder. As noted above, the mass flow rate of fuel entering the cylinder that joins the combustion process (dmfcyl / dt) can be described as the sum of the fuel leaving the melt pool and the portion of fuel from the injector that does not enter the melt pool via the following equation:

[0065] dmfcyl / dt=(1-χ)dmf / dt+mp / τ

[0066] where dmfcyl / dt is the mass flow rate of fuel entering the cylinder.

[0067] Note that transport delays for fuel injection, intake, combustion, and exhaust can be increased if desired.

[0068] Returning to 308, if the upcoming cylinder event is not a firing event but a skip event, the method proceeds to estimating the fuel puddle mass and fuel vapor content in the intake port of the skipped cylinder based on the cylinder event (based on the deactivated intake state of the cylinder), respectively. The estimating includes estimating via a model by applying a second set of different model parameters (compared to the first set of model parameters applied to the activated cylinders) when the cylinder is deactivated, the model parameters including one or more of a fuel vaporization time constant and a gain value.

[0069] Specifically, at 322, the method includes the controller calculating new values ​​for the gains and time constants using a forgetting factor (γ). The forgetting factor may be a blending ratio that is used to blend between the active cylinder values ​​(X, tau for the active cylinder) and the deactivated cylinder values ​​(X, tau for the deactivated cylinder) to calculate the new values. Ideally, there should be no blending between the two, as this is an event-based phenomenon. As an example, when the forgetting factor or blending ratio is 1, the values ​​may switch instantaneously. This may be a recommended calibration for all non-stationary modes. The blending ratio may be useful for software VDE systems.

[0070] As an example, the first set of values ​​applied during fuel compensation for the firing cylinders may be ignored and, instead, a second set of values ​​may be selected and applied. By mixing the first set of parameter values ​​for the enabled cylinders with the first set of parameter values ​​for the disabled cylinders, the controller may use a forgetting factor to calculate the second set of model parameter values. While the first set of model parameters is based on engine speed and load, the second set of model parameters may be based on the amount of vapor in the intake tract and the number of events that the cylinder has been disabled. In one example, the vaporization time constant and gain values ​​in the first set (for the enabled cylinders) are smaller than the vaporization time constant and gain values ​​in the second set for the disabled cylinders. Alternatively, the vaporization time constant and gain values ​​may be obtained from a mapping map such as Figure 4 and Figure 5A new (second set of) time constant and gain values ​​are retrieved from a map (using a map). Maps 400 and 500 depict exemplary gain and time constant values, respectively, for a base, preheated engine (e.g., with an ECT of 180 degrees Celsius). In one example, the new gain values ​​applied may be between 0.2 and 0.4, while the new time constants may be between 2 and 7 events. The time constants may be expressed in terms of events, with compensation derived based on the number of cylinder shutoff events. The number of events in the calibration is adjusted to account for RPM effects.

[0071] At 324, the melt pool fuel mass and vapor content in the runner of the deactivated cylinder may be updated based on the new time constant and gain values ​​and also based on the duration since the last firing event in the current cylinder. For example, the fuel vapor content may increase as the duration since the last firing event in the deactivated cylinder increases.

[0072] For engines with VDE functionality, some of the expected dynamics that may occur during cylinder deactivation include changes in evaporation rate, vapor accumulation in the intake manifold, and vapor escape into other cylinders, based on melt pool mass evaporation from the intake manifold. Since there is no air flow in the intake manifold of a deactivated cylinder, the evaporation rate of the fuel film in the intake manifold from the last firing event may be different compared to an intake cylinder with constant airflow. Therefore, at least the time constant values ​​for the deactivated cylinders can be set differently. Furthermore, if a specific cylinder is deactivated for multiple events, vapor accumulated in the intake manifold can quickly reach saturation vapor pressure limits. Any potential perturbation in the MAP could then cause vapor to escape into the intake manifold and cause AFR fluctuations in other intake cylinders. To account for potential impacts on AFR control due to melt pool mass estimation and transient fueling control in VDE engines, the transient fuel compensation model can be adjusted using new time constants and gain values ​​when updating the melt pool mass for the deactivated cylinder. By updating the algorithm, a software-only solution can be provided to accurately compensate for fuel supply affected by the melt pool mass / vapor content in the intake port of the deactivated cylinder.

[0073] In the updated fuel puddle mass and vapor content estimates for deactivated cylinders, it is assumed that the metered fuel is proportional to the airflow and that a certain percentage ('X') of this fuel impacts the existing puddle and forms a liquid film. It is also assumed that the fuel evaporates from this liquid film and that the evaporation rate depends on the film thickness / size. The continuity equation is written as the X-Tau model - Where X is determined as a function of MAP, ECT, and engine speed, and τ is determined as a function of MAP, ECT, and intake airflow. For example, the controller may reference a lookup table that calculates the values ​​of X and τ based on the corresponding parameters. Also in the above equation, Mp is the mass of the fuel puddle, and Mf is the mass of fuel injected per cylinder.

[0074] To track the fuel puddle and vapor in the intake for each cycle, for each current event "k" and for cylinder / injector "i", the amount of expected fuel mass can be expressed as 'mf des (k, i)', the molten pool mass is expressed as 'm p (k, i)', the steam quality is expressed as 'm vap (k, i)', the actual injected fuel is expressed as 'mf inj (k, i)', the fuel introduced into the cylinder is represented by 'mf cyl (k, i)', and X k &τ k Represents the corresponding fuel fraction and time constant values ​​for the current firing event.

[0075] So for the current event:

[0076]

[0077]

[0078] Injected fuel quantity mf inj Yes, so that mf cyl Equal to the desired fuel mass mf des , such that:

[0079]

[0080] Thus, for each cylinder, the controller can keep track of the melt pool mass. Thus, using calibrated X and Tau values ​​according to each engine operating condition, the controller can accurately compensate the amount of fuel injected so that the engine operates at stoichiometry (or another desired AFR) during transient operation.

[0081] As previously discussed, for standard VDE and rolling VDE cases based on torque demand, there are different intake ratios, and each cylinder can be fired or skipped, i.e., enabled or deactivated for the current event. For deactivated cylinders, with the intake and exhaust valves deactivated, there is no airflow through the valves or intake runners. Without airflow in the runners, the evaporation rate of the melt pool mass is different (specifically, slower) than the value used in the lookup table for conventionally fired cylinders. Different time constants (τ) are used for the current skipped / deactivated event 'k'.k ) is applied to the deactivated cylinders by referencing a different lookup table than the firing cylinders. Also, note that for the currently deactivated cylinder mf inj (k, i)=0.

[0082] Using the melt pool fuel mass equation:

[0083]

[0084] The vapor accumulated in the intake runner of the deactivated cylinder can be given as:

[0085]

[0086] In this way, the controller can keep track of the melt pool quality and vapor content in the flow path of the deactivated cylinder on an event-by-event basis.

[0087] Return to Figure 3 , at 326, the method includes calculating the saturated vapor pressure (SVP) and the actual vapor pressure (VP) of the flow passage for a given event. In addition, the relative vapor percentage can be determined as the ratio of the actual vapor pressure to the SVP. For example, the controller can calculate the saturated vapor pressure (also referred to herein as the saturation limit) of the cylinder based on the alcohol content of the injected fuel, the temperature of the intake passage of the cylinder, and the ambient pressure, respectively. The saturated vapor pressure can increase / decrease with one or more of an increase in the alcohol content of the injected fuel, an increase in the ambient pressure, and an increase in the intake passage temperature. At 328, the relative vapor percentage can be compared with a threshold. In one example, the threshold is 100%. If the relative vapor percentage is 100%, it means that the actual vapor pressure is at the saturated vapor pressure limit.

[0088] If the relative vapor percentage is below the threshold, the method continues updating the melt pool mass and fuel vapor content for the deactivated cylinder at 330 . Specifically, the routine returns to 324 and resumes updating the melt pool mass and fuel vapor content based on the new (e.g., second set) time constant and gain values. Otherwise, if the relative vapor percentage reaches the threshold, the method includes reducing the melt pool mass and fuel vapor content values ​​at 332 . Specifically, the current state can be determined to be equal to the last determined value. In this way, the controller can estimate and update the fuel pool mass and fuel vapor content in the intake port of the deactivated cylinder on a cylinder event basis, then maintain the (most recent) estimated fuel pool mass and fuel vapor content after the estimated fuel vapor content reaches the cylinder's saturation limit. The controller can then adjust fuel supply to the deactivated cylinder based on the estimated fuel pool mass and fuel vapor content upon reactivation. For example, upon reactivation, the controller can adjust the amount of fuel injected from the intake port to the cylinder based on the estimated fuel pool mass and fuel vapor content.

[0089] As the controller keeps track of the melt pool mass and vapor in the runners, it compares the vapor pressure in the runners to the saturation vapor pressure. This is because, in most cases, if the cylinders are deactivated for an extended period, such as for multiple events, it cannot be assumed that all of the melt pool or film mass will eventually evaporate and be ingested at the next firing event. Depending on the intake port temperature and the MAP at which the engine is operating, the vapor pressure in the runners can reach a saturation limit, after which further evaporation of the melt pool mass may become limited.

[0090] The saturated vapor pressure of a fuel (e.g. gasoline) at a given intake manifold temperature can be calculated using the Antoine equation as follows:

[0091]

[0092] Where: A, B and C are constants for the fuel type, T 进气道 is the air temperature in the intake device and Pv is the saturated vapor pressure.

[0093] Considering that at a steady MAP and engine speed the air mass in the runner (for the deactivated cylinder) is the same as the air charge of the intake cylinder, the controller can then calculate the vapor pressure in the runner as follows:

[0094]

[0095] Where MF(mf vap ) is the mole fraction of the vaporized melt pool mass, MF(air) is the mole fraction of air, and MAP is the current manifold absolute pressure.

[0096] Using the saturated vapor pressure and vapor pressure, the relative vapor concentration percentage in the flow channel can be determined as:

[0097]

[0098] This value is compared to a threshold limit (e.g., 100%) to check whether the vapor content in the flow path has reached the saturation limit. If so, the melt pool mass and vapor content values ​​for the deactivated cylinder are reduced. In other words, the melt pool mass and vapor content values ​​for the deactivated cylinder are updated as long as the relative vapor percentage is below the threshold, and once the relative vapor percentage reaches the threshold, the values ​​are maintained at the last determined values. These values ​​remain at the last determined values ​​until the cylinder is reactivated and its status changes to a firing cylinder.

[0099] It will be appreciated that as the charge state of the cylinder changes, the controller may continue to update the fuel puddle estimate in each cylinder on a cylinder event (or cylinder cycle) basis. Therefore, after 320 , if an activated cylinder is deactivated, the fuel puddle state of the currently deactivated cylinder may be tracked by switching from estimating using the model using the first set of model parameters to estimating using the second set of model parameters. Similarly, once the deactivated cylinder is reactivated, the fuel puddle state of the currently activated cylinder may be tracked by switching from estimating using the model using the second set of model parameters to estimating using the first set of model parameters.

[0100] As used herein, a cylinder event or cylinder cycle refers to the completion of the last four strokes (intake, compression, power, and exhaust strokes) in a given cylinder. In contrast, an engine event or engine cycle refers to the completion of a cylinder cycle for each cylinder of the engine. For example, in a four-cylinder engine, the engine cycle is complete when each of the four cylinders completes the intake stroke, compression stroke, power stroke, and exhaust stroke.

[0101] In this way, the engine controller can adjust fuel injection in response to reaching a vapor saturation state in the intake port of a deactivated cylinder of the engine. In one example, adjusting fuel injection includes adjusting fuel injection for the deactivated cylinder upon reactivation. In another example, adjusting fuel injection includes adjusting fuel injection for other activated cylinders of the engine on a per-cylinder basis while the deactivated cylinder remains deactivated. For example, adjusting fuel injection can first be based on increasing vapor release into the intake port of the deactivated cylinder over multiple consecutive cylinder cycles until vapor saturation is reached, and then based on no increasing vapor release into the intake port of the deactivated cylinder. In another example, adjusting fuel injection for activated cylinders includes adjusting fuel injection based on vapor migration from the intake port of the deactivated cylinder to each activated cylinder. The controller can estimate the fuel pool mass and vapor content in the intake port of the deactivated cylinder separately via a model, and indicate a vapor saturation state when the estimated vapor content reaches a saturation vapor pressure. The saturation vapor pressure may be estimated based on each of the fuel alcohol content, ambient pressure, and the intake port temperature of the deactivated cylinder. Furthermore, the controller may estimate the fuel pool mass and vapor content in the intake ports of the other activated cylinders, respectively, using a model. The controller may apply a first set of vaporization time constants and gain values ​​to each activated cylinder, while applying a second, different set of vaporization time constants and gain values ​​to the deactivated cylinders.

[0102] exist Figure 6An example of tracking the fuel vapor content of a deactivated cylinder and reducing the vapor content once the vapor pressure reaches the saturation limit is shown in FIG. Map 600 depicts the desired fuel mass for the cylinder at 610, with curves 602-606 depicting different amounts of fuel injection mass. Map 600 depicts updated film mass at 620, with curves 612-616 depicting the fuel puddle mass for three different fuel injection masses, represented by 602, 604, and 606, respectively. Map 600 also depicts relative vapor percentages at 630, with curves 622-626 depicting the relative saturation vapor pressure in the flow channel. All curves are plotted along the x-axis over time. For an injection of mass 602, a puddle mass of 612 results in a vapor pressure 622 above 100%, indicating that fuel vaporization is reaching a limiting condition. For the case of fuel injection masses 604 and 606, the melt pool mass is low enough (614, 616) not to exceed the relative vapor pressure (624, 626) above 100% and therefore does not limit evaporation of the fuel.

[0103] Now turn Figure 7 , shows an exemplary map 700 for updating the port fuel puddle mass based on the activation status of the cylinders and adjusting engine fueling accordingly. Map 700 depicts torque demand at curve 702, airflow ratio at curve 704, and compares the selection of a second (deactivated) cylinder at curve 707 (solid line), and model parameter selection for the first (activated) cylinder at curve 706 (dashed line). For example, the selected model parameters may include time constants and gain values. Map 700 depicts cylinder firing determination at curve 708 and cylinder number per cylinder event at curve 709. Map 700 also depicts the change in port fuel puddle mass for the first cylinder at curve 710 (dashed line) and the change in port fuel puddle mass for the second cylinder at curve 712 (solid line). The intake port vapor content of the first cylinder is shown at curve 714 (dashed line), and the intake port vapor content of the second cylinder is shown at curve 716 (solid line), both of which are related to the saturation vapor pressure limit (Thr). The desired fuel mass in the first cylinder based on the torque demand is shown at curve 718 (solid line), while the actual fuel injection amount is shown, while the consideration of the fuel pool and vapor content is shown at curve 720 (dashed line). It can be noted that for the case of the deactivated cylinder with the intake ratio 704, the fuel pool mass evaporates (712) to the saturation vapor pressure (716) and is reduced when the vapor pressure threshold Thr is reached. All curves are plotted along the x-axis over time (and engine events).

[0104] The depicted example is for an eight-cylinder, four-stroke engine (having cylinders 1-8) with a firing order (or combustion order) of 1, 3, 7, 2, 6, 5, 4, 8. An engine event (also referred to herein as an engine cylinder event) can be a stroke occurring in a cylinder (e.g., intake, compression, power, exhaust), the timing of an intake or exhaust valve opening or closing, the timing of ignition of the air-fuel mixture in a cylinder, the position of a piston in a cylinder relative to the crankshaft position, or other engine-related events. Cylinder events are shown in their firing order. If a particular cylinder in the firing order is fired, it is shown as a solid circle at plot 708. If a particular cylinder in the firing order is skipped, it is shown as an open circle at plot 708. Graph 709 depicting firing decisions reflects the selected firing mode, with cylinder activation events (e.g., firing with the intake and exhaust valves opening and closing during a cylinder cycle) represented by solid circles, and cylinder deactivation events (e.g., no firing with the intake and exhaust valves remaining closed during a cylinder cycle) represented by hollow circles. The decision to activate or deactivate a cylinder and to open and close its intake and exhaust valves can be made a predetermined number of cylinder events (e.g., one cylinder event, or alternatively, one cylinder cycle or eight cylinder events for an eight-cylinder engine) before the cylinder is to be activated or deactivated, to allow time for the process of opening and closing the intake and exhaust valves of the estimated cylinder to begin. For example, for an eight-cylinder engine with a firing order of 1, 3, 7, 2, 6, 5, 4, 8, the decision to activate or deactivate cylinder number seven can be made during the intake or compression stroke of cylinder number seven, one engine cycle before cylinder number seven is deactivated. Alternatively, the decision to activate or deactivate a cylinder can be made a predetermined number of engine events or cylinder events before the selected cylinder is activated or deactivated. When a firing determination is indicated by a solid circle (and the firing determination value is 1), the cylinder on the compression stroke corresponding to the cylinder event is activated. When a firing determination is indicated by an open circle (and the firing determination value is 0), the cylinder on the compression stroke corresponding to the numbered event is deactivated.

[0105] Prior to t1, the engine is off. At t1, in response to an increase in torque demand (such as due to a depressing the accelerator pedal), the engine is turned on. Due to the high torque demand (plot 702), an intake air ratio of 1.0 is selected at t1 (plot 704). That is, the engine operates with all cylinders active. Between t1 and t2, when the engine operates with all cylinders firing, the fuel puddle mass (plots 710, 712) and intake port vapor content (plots 714, 716) of the first and second cylinders, respectively, are tracked via a fuel puddle estimation model using a first set of model parameters (plots 706, 707). Furthermore, fuel injection into the first cylinder (shown at plot 720) and the second cylinder (not shown) is adjusted based on the estimated fuel puddle mass and vapor content to set a desired fuel mass (plot 718) that achieves a target air flow rate (such as stoichiometric). For example, shortly after the accelerator pedal is depressed, fuel exceeding a desired fuel mass is injected into the first cylinder to account for some fuel remaining in the intake tract and to replenish the fuel puddle. Then, once the fuel puddle is formed, fuel less than the desired fuel mass is injected into the first cylinder to account for some fuel drawn from the fuel puddle into the intake tract.

[0106] At t2, in response to a decrease in torque demand (such as due to a release of the accelerator pedal), the air ratio is reduced (e.g., from 1.0 to 0.5). That is, the engine is operated with some cylinders selectively deactivated, and in particular, with each spare cylinder deactivated. An air ratio of 0.5 is set via a stationary mode, wherein the characteristics of the cylinders deactivated in successive cycles remain the same (e.g., in this case, cylinders 1, 6, and 4 would be skipped, while cylinders 2, 5, and 8 would be fired in each cycle). In the depicted example, a first cylinder (e.g., which could be cylinder 8) remains activated, while a second cylinder (e.g., which could be cylinder 1) is deactivated in response to the decrease in torque demand. The second cylinder can be deactivated by deactivating fuel delivery to the cylinder and disabling cylinder valve operation.

[0107] Between t2 and t3, the fuel pool mass and intake port vapor content of the activated first cylinder continue to be tracked via the fuel pool estimation model while using the first set of model parameters. However, to account for the slower evaporation rate from the now-deactivated cylinder, the fuel pool mass and vapor content of the second cylinder are simultaneously tracked via the fuel pool estimation model using a second set of model parameters that are different from the first set of model parameters. In one example, the second set includes time constants and gain values ​​that are smaller than those included in the first set. In the depicted example, after deactivation, the fuel pool mass in the second cylinder begins to decrease as fuel evaporates into the intake port. Simultaneously, the fuel vapor content begins to rise as a portion of the liquid fuel from the fuel pool transitions to the vapor phase.

[0108] Likewise, between t2 and t3, fuel injection to the first cylinder continues to be adjusted based on the estimated fuel puddle mass and vapor content to provide the desired fuel mass. As torque demand decreases, the load on the first cylinder increases to improve engine performance due to fewer cylinders being active, and accordingly, the desired fuel mass in the first cylinder increases. In the depicted example, due to the formation of the fuel puddle, between t2 and t3, less fuel than the desired fuel mass is injected into the first cylinder to account for some fuel drawn into the intake port from the fuel puddle and for fuel vapor migration from the deactivated second cylinder to the intake port of the activated first cylinder.

[0109] At t3, in response to a further decrease in torque demand, the air ratio is further reduced (e.g., from 0.5 to 0.33). That is, the engine operates with more cylinders selectively deactivated. Here, the engine operates with every third cylinder ignited. The air ratio of 0.33 is set by a non-stationary mode, in which the characteristics of the enabled and disabled cylinders vary in successive cycles (e.g., in this case, cylinders 3 and 6 are ignited in the first cycle and skipped in the next cycle). In the depicted example, the first cylinder (e.g., cylinder 8) continues to be enabled, while the second cylinder (e.g., cylinder 1) continues to be deactivated in response to a further decrease in torque demand. When the torque demand decreases, since a smaller number of cylinders are enabled to operate, the load on the first cylinder is further increased to improve engine performance, and accordingly, the desired fuel mass in the first cylinder increases. The fuel puddle and vapor contents in the first and second cylinders continue to be estimated using the first and second sets of model parameters, respectively, and fuel injection to the first cylinder continues to be updated based on the fuel puddle dynamics of the intake port of the first cylinder.

[0110] At t4, while the second cylinder remains deactivated, the fuel vapor content of the second cylinder reaches a saturation limit, Thr. Here, the saturation limit corresponds to the saturation vapor pressure of the fuel injected into the intake tract of the second cylinder, which is determined based on the fuel in the fuel pool (e.g., its alcohol content, octane rating, etc.) and the temperature of the intake tract of the second cylinder. Therefore, once the saturation limit is reached, further evaporation of fuel from the intake tract of the second cylinder becomes limited. Therefore, at t4, the estimated fuel pool mass and vapor content values ​​are reduced. Specifically, while the cylinder remains deactivated, the most recent values ​​of the fuel pool mass and vapor content estimated immediately before t4 are retained. Simultaneously, the fuel pool mass and vapor content of the first cylinder continue to update.

[0111] At t5, in response to an increase in torque demand (such as due to a depressing of the accelerator pedal), the charge ratio is increased (e.g., from 0.5 to 1.0), and the engine is operated with all cylinders active. That is, while the first cylinder continues to be active, the second cylinder is reactivated in response to the increase in torque demand. Consequently, the fuel pool and vapor content estimation in the second cylinder using the first set of model parameters is resumed, while the fuel pool and vapor content estimation in the first cylinder using the first set of model parameters continues. As torque demand increases, the load on the first cylinder decreases due to the greater number of cylinders being active, and accordingly, the required fuel mass in the first cylinder decreases. Fuel injection to the first cylinder continues to be updated based on the fuel pool dynamics of the first cylinder's intake port. For example, fuel supply to the first cylinder is increased to account for the lower amount of fuel vapor migrating from the second cylinder to the first cylinder. When cylinder fueling is resumed, fuel injection to the second cylinder is updated to account for the fuel pool dynamics of the second cylinder's intake port (not shown). For example, fuel may be delivered to the second cylinder in excess of a desired fuel mass to account for fuel that may be lost to the intake port of the second cylinder to create a fuel puddle (and other associated wall wetting losses).

[0112] In this way, Figure 7The example illustrates how, in response to the selective deactivation of engine cylinders, an engine controller can adjust the fuel puddle mass and fuel vapor content in the intake tract of the deactivated cylinder for each skipped cylinder event; and when the fuel vapor content reaches a threshold, the controller can maintain the fuel puddle mass and fuel vapor content until the cylinder is reactivated. As an example, the threshold can be a function of the cylinder's saturation limit, estimated based on the alcohol content of the injected fuel and the temperature of the intake tract of the deactivated cylinder. The saturation limit can increase with increasing temperature or alcohol content. Furthermore, the controller can adjust the fuel puddle mass and fuel vapor content in the intake tract of the activated cylinder for each skipped cylinder event based on a first vaporization time constant and a first gain value. In contrast, adjustments to the fuel puddle mass and fuel vapor content in the intake tract of the deactivated cylinder can be based on a second vaporization time constant and a second gain value, respectively. The controller can calculate the first vaporization time constant and the first gain value, respectively, based on engine speed and load. Furthermore, in response to reactivation of the deactivated cylinder, the controller may adjust at least the amount of port injected fuel delivered to the cylinder based on the maintained fuel puddle mass and fuel vapor content. In some examples, such as where the engine is a PFDI engine, the controller may also adjust the amount of direct injected fuel delivered to the cylinder based on the maintained fuel puddle mass and fuel vapor content to operate the engine at a desired air-fuel ratio.

[0113] In this way, the fuel puddle mass and fuel vapor content of the intake runners of each cylinder of a PFI or PFDI engine system can be better tracked. The technical effect of using different lookup tables (including different time constants and gain values ​​for deactivated cylinders relative to activated cylinders) is that the difference in vaporization rate between the firing cylinder and the skipped cylinder can be better accounted for during transient fuel puddle compensation. By tracking vapor accumulation in the deactivated cylinders and comparing the vapor pressure to a saturation pressure limit, the state of the puddle or film mass in the intake runner can be better determined. In particular, when the tracked vapor pressure reaches the saturation pressure limit, the vapor content is reduced, thereby reducing the error in the fuel puddle estimation and the associated AFR disturbance during torque transients.

[0114] An exemplary method for an engine includes adjusting fuel injection in response to reaching a vapor saturation condition in an intake port of a deactivated cylinder of the engine. In the preceding examples, additionally or optionally, adjusting fuel injection includes adjusting fuel injection for the deactivated cylinder upon reactivation. In any or all of the preceding examples, additionally or optionally, adjusting fuel injection includes adjusting fuel injection for other activated cylinders of the engine on a single cylinder basis while the deactivated cylinder remains deactivated. In any or all of the preceding examples, additionally or optionally, adjusting fuel injection includes first adjusting fuel injection based on increasing vapor release into the intake port of the deactivated cylinder over a plurality of consecutive cylinder cycles until vapor saturation is reached, and then adjusting fuel injection based on no increasing vapor release into the intake port of the deactivated cylinder. In any or all of the preceding examples, additionally or optionally, adjusting fuel injection for activated cylinders includes adjusting fuel injection based on vapor migration from the intake port of the deactivated cylinder to each activated cylinder. In any or all of the foregoing examples, additionally or optionally, the method further includes estimating, via a model, a fuel puddle mass and vapor content in the intake port of the deactivated cylinder, and indicating a vapor saturation state when the estimated vapor content reaches a saturation vapor pressure. In any or all of the foregoing examples, additionally or optionally, estimating the saturation vapor pressure based on the fuel alcohol content, ambient pressure, and intake port temperature of the deactivated cylinder, and further includes estimating, via a model, a fuel puddle mass and vapor content in the intake port of the other activated cylinders. In any or all of the foregoing examples, additionally or optionally, estimating via the model includes applying a first set of vaporization time constants and gain values ​​to each activated cylinder and applying a second, different set of vaporization time constants and gain values ​​to the deactivated cylinder, the vaporization time constants and gain values ​​in the first set being smaller than the vaporization time constants and gain values ​​in the second set. In any or all of the foregoing examples, additionally or optionally, adjusting fuel injection includes adjusting port fuel injection by adjusting a pulse width commanded to a port fuel injector.

[0115] Another example method includes, in response to selective deactivation of an engine cylinder, updating estimates of fuel puddle mass and vapor content in an intake port of the deactivated cylinder for each skipped cylinder event until a vapor saturation limit is reached; and thereafter maintaining the estimates until the cylinder is reactivated; and adjusting fuel injection to the cylinder upon reactivation based on the maintained estimates. In the foregoing examples, additionally or optionally, the vapor saturation limit is based on an alcohol content, ambient pressure, and temperature of the injected fuel in the intake port of the deactivated cylinder. In any or all of the foregoing examples, additionally or optionally, the method further includes updating estimates of fuel puddle mass and vapor content in an intake port of another activated cylinder for each cylinder event via a model using a first vaporization time constant and a first gain value, wherein updating for the deactivated cylinder is performed via a model using a second, different vaporization time constant and a second, different gain value. In any or all of the foregoing examples, additionally or optionally, the method further includes selecting first and second vaporization time constants and first and second gain values ​​based on engine speed and load, and also based on intake state. In any or all of the foregoing examples, additionally or optionally, the method further includes adjusting fuel injection to the activated cylinders based on estimates of fuel puddle mass and vapor content in the intake ports of the activated cylinders and further based on fuel vapor migration from the intake ports of the deactivated cylinders to the intake ports of the activated cylinders. In any or all of the foregoing examples, additionally or optionally, updating includes decreasing the estimate of fuel puddle mass and increasing the estimate of vapor content in the intake ports for each skipped cylinder event until a vapor saturation limit is reached.

[0116] Another exemplary engine system includes: a first cylinder; a second cylinder; a first fuel injector coupled to a first intake port of the first cylinder; a second fuel injector coupled to a second intake port of the second cylinder; and a controller having computer-readable instructions stored on non-transitory memory for: selectively deactivating the second cylinder in response to a decrease in torque demand while continuing to supply fuel to the first cylinder for a plurality of cylinder events; and for each of the plurality of cylinder events, updating a value of a first fuel pool in the first intake port via a first set of fuel vaporization constants; updating a value of a second fuel pool in the second intake port via a second, different set of fuel vaporization constants until the fuel pool is at a saturation limit and then maintaining the value of the second fuel pool; and adjusting a pulse width commanded to the first fuel injector based on the value of the first fuel pool. Additionally or alternatively to the foregoing example, the controller includes further instructions for reactivating the second cylinder in response to an increase in torque demand; and adjusting a pulse width commanded to the second fuel injector based on the value of the second fuel pool. In any or all of the foregoing examples, additionally or optionally, updating the value of the first fuel pool in the first intake passage includes updating the fuel pool mass and the fuel vapor pressure in the first intake passage, respectively, wherein updating the value of the second fuel pool in the second intake passage includes updating the fuel pool mass and the fuel vapor pressure in the second intake passage, respectively, and wherein the fuel pool being at a saturation limit includes the fuel vapor pressure in the second intake passage being at a saturation vapor pressure. In any or all of the foregoing examples, additionally or optionally, the controller includes further instructions for calculating the saturation vapor pressure based on the fuel alcohol content, the temperature of the second intake passage, and the ambient pressure, respectively. In any or all of the foregoing examples, additionally or optionally, the controller includes further instructions for retrieving a first set of fuel vaporization constants from memory based on engine speed and load; and calculating a second set of fuel vaporization constants based on the first set of fuel vaporization constants by applying a forgetting factor.

[0117] In other representations, a method for an engine includes estimating a fuel puddle mass and fuel vapor content in an intake port of each cylinder based on cylinder events (including based on each cylinder's intake state); and, for deactivated cylinders, maintaining the estimated fuel puddle mass and fuel vapor content after the estimated fuel vapor content reaches a saturation limit for the cylinder. In the foregoing examples, additionally or optionally, the estimated fuel puddle mass and fuel vapor content are maintained until the deactivated cylinder is reactivated. In any or all of the foregoing examples, additionally or optionally, the method further includes adjusting fuel supply to activated cylinders based on the estimated fuel puddle mass and fuel vapor content, and adjusting fuel supply to deactivated cylinders based on the estimated fuel puddle mass and fuel vapor content upon reactivation. In any or all of the foregoing examples, additionally or optionally, adjusting fuel supply includes adjusting an amount of fuel injected into the intake port based on the estimated fuel puddle mass and fuel vapor content. In any or all of the foregoing examples, additionally or optionally, estimating also includes estimating fuel migration from deactivated cylinders to activated cylinders of the engine. In any or all of the foregoing examples, additionally or optionally, estimating includes estimating via a model, and wherein estimating based on the intake state includes applying a first set of model parameters when the cylinder is activated and applying a second, different set of model parameters when the cylinder is deactivated, including one or more of a fuel evaporation time constant and a gain value. In any or all of the foregoing examples, additionally or optionally, the evaporation time constant and gain value in the first set are smaller than the evaporation time constant and gain value in the second set. In any or all of the foregoing examples, additionally or optionally, applying the first set of model parameters includes retrieving the first set from a memory of an engine controller, and wherein applying the second set includes calculating the second set of model parameters from the first set of parameters using a forgetting factor. In any or all of the foregoing examples, additionally or optionally, the first set of model parameters is based on engine speed and manifold pressure, and the second set of model parameters is based on a number of cylinder deactivation events. In any or all of the foregoing examples, additionally or optionally, the method further includes calculating a saturation limit for the cylinder based on an alcohol content of the injected fuel and a temperature of an intake port of the cylinder. In other embodiments, the engine system is coupled to a hybrid electric vehicle.

[0118] Note that the exemplary control and estimation routines included herein can be used with various engine and / or vehicle system configurations. The control methods and routines disclosed herein can be stored as executable instructions in a non-volatile memory and can be executed by a control system including a controller in conjunction with various sensors, actuators, and other engine hardware. The specific routines described herein can represent one or more of any number of processing strategies (such as event-driven, interrupt-driven, multi-tasking, multi-threaded processing strategies, etc.). Therefore, the various actions, operations, and / or functions shown can be performed in the order shown, in parallel, or omitted under certain conditions. Similarly, the processing order is not necessarily required to achieve the features and advantages of the exemplary embodiments described herein, but is provided for ease of illustration and description. One or more of the actions, operations, and / or functions shown can be repeatedly performed depending on the specific strategy used. In addition, the described actions, operations, and / or functions can graphically represent code to be programmed into the non-volatile memory of a computer-readable storage medium in an engine control system, where the described actions are implemented by executing the instructions in conjunction with an electronic controller in a system including various engine hardware components.

[0119] It should be understood that the configurations and procedures disclosed herein are exemplary in nature, and that these specific embodiments should not be construed in a limiting sense, as many variations are possible. For example, the above-described techniques can be applied to V-6, I-4, I-6, V-12, opposed 4-cylinder, and other engine types. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations and other features, functions, and / or properties disclosed herein.

[0120] The following claims specifically point out certain combinations and subcombinations believed to be novel and non-obvious. These claims may refer to "an" element or "a first" element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and subcombinations of the disclosed features, functions, elements, and / or properties may be claimed by amendment of the present claims or by presentation of new claims in this or a related application. Such claims, whether broader, narrower, the same, or different in scope to the original claims, are likewise deemed to be included within the subject matter of the present disclosure.

[0121] According to the present invention, a method for an engine includes adjusting fuel injection in response to reaching vapor saturation conditions in an intake port of a deactivated cylinder of the engine.

[0122] According to one embodiment, the invention is further characterized in that regulating the fuel injection includes regulating fuel injection of the deactivated cylinders when reactivated.

[0123] According to one embodiment, the invention is further characterized in that regulating the fuel injection includes regulating fuel injection of other activated cylinders of the engine on a single cylinder basis while the deactivated cylinder remains deactivated.

[0124] According to one embodiment, the present invention is further characterized in that regulating the fuel injection includes first regulating the fuel injection based on increasing vapor release into the intake duct of the deactivated cylinder in multiple consecutive cylinder cycles until the vapor saturation state is reached, and then regulating the fuel injection based on no increasing vapor release into the intake duct of the deactivated cylinder.

[0125] According to one embodiment, the invention is further characterized in that regulating fuel injection to the activated cylinders includes regulating fuel injection based on vapor transport from an intake port of the deactivated cylinders to each of the activated cylinders.

[0126] According to one embodiment, the present invention is further characterized by separately estimating the fuel pool mass and vapor content in the intake port of the deactivated cylinder via a model, and indicating the vapor saturation state when the estimated vapor content reaches a saturation vapor pressure.

[0127] According to one embodiment, the saturated vapor pressure is estimated based on the fuel alcohol content, the ambient pressure and the intake port temperature of the deactivated cylinder, respectively, and the method further includes estimating the fuel pool mass and the vapor content in the intake port of the other activated cylinders, respectively, via the model.

[0128] According to one embodiment, estimating via the model comprises applying a first set of evaporation time constants and gain values ​​to the activated cylinders, respectively, and applying a second, different set of evaporation time constants and gain values ​​to the deactivated cylinders, the evaporation time constants and gain values ​​in the first set being smaller than the evaporation time constants and gain values ​​in the second set.

[0129] According to one embodiment, the invention is further characterized in that adjusting the fuel injection includes adjusting the port fuel injection via adjusting a pulse width commanded to the port fuel injector.

[0130] According to the present invention, a method includes: in response to selective deactivation of an engine cylinder, updating an estimate of fuel puddle mass and vapor content in an intake port of the deactivated cylinder for each skipped cylinder event until a vapor saturation limit is reached; and thereafter maintaining the estimate until the cylinder is reactivated; and adjusting fuel injection to the cylinder upon reactivation based on the maintained estimate.

[0131] According to one embodiment, the vapor saturation limit is based on the alcohol content of the injected fuel, the ambient pressure and the temperature of the intake port of the deactivated cylinder.

[0132] According to one embodiment, the invention is further characterized by updating the estimate of the fuel puddle mass and vapor content in the intake tract of another enabled cylinder for each cylinder event via a model using a first vaporization time constant and a first gain value, wherein the updating of the deactivated cylinder is performed via a model using a second, different vaporization time constant and a second, different gain value.

[0133] According to one embodiment, the present invention is further characterized by: selecting the first evaporation time constant and the first gain value according to engine speed and manifold pressure; and applying a forgetting factor to the first evaporation time constant and the first gain value to calculate the second evaporation time constant and the second gain value.

[0134] According to one embodiment, the present invention is further characterized in that fuel injection to the enabled cylinder is regulated based on an estimate of the fuel pool mass and vapor content in the intake duct of the enabled cylinder, and also based on the migration of fuel vapor from the intake duct of the deactivated cylinder to the intake duct of the enabled cylinder.

[0135] According to one embodiment, the updating comprises decreasing the estimate of the fuel puddle mass and increasing the estimate of the vapor content in the intake tract for each skipped cylinder event until the vapor saturation limit is reached.

[0136] According to the present invention, an engine system is provided, which has: a first cylinder; a second cylinder; a first fuel injector connected to a first intake port of the first cylinder; a second fuel injector connected to a second intake port of the second cylinder; and a controller having computer-readable instructions stored on a non-volatile memory, the computer-readable instructions being used to: selectively deactivate the second cylinder in response to a decrease in torque demand while continuing to supply fuel to the first cylinder for multiple cylinder events; and for each of the multiple cylinder events, update the value of the first fuel pool in the first intake port via a first set of fuel vaporization constants; update the value of the second fuel pool in the second intake port via a second, different set of fuel vaporization constants until the fuel pool is at a saturation limit and then maintain the value of the second fuel pool; and adjust the pulse width commanded to the first fuel injector based on the value of the first fuel pool.

[0137] According to one embodiment, the controller includes further instructions for: reactivating the second cylinder in response to the increase in torque demand; and adjusting a pulse width commanded to the second fuel injector based on the value of the second fuel puddle.

[0138] According to one embodiment, updating the value of the first fuel pool in the first intake channel includes updating the fuel pool mass and the fuel vapor pressure in the first intake channel, respectively, wherein updating the value of the second fuel pool in the second intake channel includes updating the fuel pool mass and the fuel vapor pressure in the second intake channel, respectively, and wherein the fuel pool being at the saturation limit includes the fuel vapor pressure in the second intake channel being at the saturation vapor pressure.

[0139] According to one embodiment, the controller includes further instructions for calculating the saturated vapor pressure based on the alcohol content of the fuel, the temperature of the second intake passage, and the ambient pressure, respectively.

[0140] According to one embodiment, the controller includes further instructions for: retrieving the first set of fuel vaporization constants from the memory based on the engine speed and load; and

[0141] The second set of fuel evaporation constants is calculated from the first set of fuel evaporation constants by applying a forgetting factor.

Claims

1. A method for an engine, comprising: adjusting fuel injection in response to reaching vapor saturation conditions in an intake port of a deactivated cylinder of the engine; Wherein adjusting the fuel injection includes adjusting fuel injection to the deactivated cylinder based on an estimated fuel puddle mass and a fuel vapor content when the deactivated cylinder is reactivated. 2 . The method of claim 1 , wherein adjusting the fuel injection comprises adjusting fuel injection to other activated cylinders of the engine on a cylinder-by-cylinder basis while the deactivated cylinder remains deactivated.

3. The method of claim 2 , wherein adjusting the fuel injection comprises first adjusting the fuel injection based on increasing vapor release into the intake port of the deactivated cylinder over a plurality of consecutive cylinder cycles until the vapor saturation state is reached, and then adjusting the fuel injection based on no increasing vapor release into the intake port of the deactivated cylinder. 4 . The method of claim 3 , wherein adjusting fuel injection to the activated cylinders includes adjusting fuel injection based on vapor transport from the intake port of the deactivated cylinder to each of the activated cylinders.

5. The method of claim 2 further comprising estimating fuel pool mass and vapor content in the intake port of the deactivated cylinder via a model, respectively, and indicating the vapor saturation state when the estimated vapor content reaches a saturation vapor pressure.

6. The method of claim 5 , wherein the saturated vapor pressure is estimated based on the fuel alcohol content, the ambient pressure, and the intake port temperature of the deactivated cylinder, respectively, and the method further comprises estimating the fuel pool mass and the vapor content in the intake port of the other activated cylinders, respectively, via the model.

7. The method of claim 6, wherein the estimating via the model comprises: A first set of evaporation time constants and gain values ​​is applied to each of the activated cylinders, and a second, different set of evaporation time constants and gain values ​​is applied to the deactivated cylinders, the evaporation time constants and gain values ​​in the first set being smaller than the evaporation time constants and gain values ​​in the second set. 8 . The method of claim 1 , wherein adjusting the fuel injection comprises adjusting port fuel injection via adjusting a pulse width commanded to a port fuel injector.

9. An engine system comprising: First cylinder; Second cylinder; a first fuel injector coupled to a first intake port of the first cylinder; a second fuel injector coupled to a second intake port of the second cylinder; and a controller having computer-readable instructions stored on a non-transitory memory, the computer-readable instructions for: In response to a decrease in torque demand, selectively deactivating the second cylinder while continuing to supply fuel to the first cylinder for a plurality of cylinder events; and For each event of the plurality of cylinder events, updating a value of a first fuel puddle in the first intake passage via a first set of fuel vaporization constants; updating the value of a second fuel pool in the second intake passage via a second different set of fuel vaporization constants until the second fuel pool is at a vapor saturation limit and then maintaining the value of the second fuel pool; and A pulse width commanded to the first fuel injector is adjusted based on the value of the first fuel puddle.

10. The system of claim 9, wherein the controller includes further instructions for: In response to the increase in torque demand, reactivating the second cylinder; and The pulse width commanded to the second fuel injector is adjusted based on the value of the second fuel puddle.

11. The system of claim 9 , wherein updating the value of the first fuel pool in the first intake duct comprises updating a fuel pool mass and a fuel vapor pressure in the first intake duct, respectively, wherein updating the value of the second fuel pool in the second intake duct comprises updating the fuel pool mass and the fuel vapor pressure in the second intake duct, respectively, and wherein the fuel pool being at the saturation limit comprises the fuel vapor pressure in the second intake duct being at a saturated vapor pressure. 12 . The system of claim 11 , wherein the controller includes further instructions for calculating the saturated vapor pressure based on fuel alcohol content, temperature of the second intake passage, and ambient pressure, respectively.

13. The system of claim 12, wherein the controller includes further instructions for: retrieving the first set of fuel vaporization constants from the memory based on engine speed and load; and The second set of fuel evaporation constants is calculated from the first set of fuel evaporation constants by applying a forgetting factor.

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