Methods and systems for improving the discharge of low-pressure EGR gases

Abstract

Method for venting low-pressure EGR gases during operation of a hybrid vehicle under low loads, comprising: in response to a decreasing power machine torque requirement when operating a power machine (10) with EGR (410) and a drop in the SOC of a system battery (411): a) Deactivating the EGR (422); b) Operating the engine (10) with fuel supply and EGR deactivated, and driving the vehicle at a higher drive torque of the engine (10) than the requested torque for vehicle propulsion until the EGR in an engine intake tract is below a threshold value (424); c) Charging a system battery (424); d) Determining when the threshold value of EGR gases has been undercut (426) and responding to such an undercutting; e) Deactivating the fuel supply to the engine (10), slowing down the engine (10) to standstill (428) and driving the vehicle by means of engine torque from the generator.

Description

[0001] This patent application relates to methods and systems for improving the venting of low-pressure EGR gases from an engine during operation at light loads.

[0002] Exhaust gas recirculation (EGR) systems recirculate a portion of the exhaust gases from an engine exhaust system to an engine intake system to improve vehicle fuel economy and emissions by reducing throttle losses and combustion temperatures. On turbocharged engines with direct injection, a low-pressure EGR (LP-EGR) circuit may be implemented. The LP-EGR circuit recirculates exhaust gases from an exhaust passage downstream of a turbine to an intake passage upstream of a turbocharger compressor.

[0003] Such an exhaust gas recirculation system is disclosed in connection with a hybrid vehicle in JP 2010-14 041 A.

[0004] However, due to the EGR supply upstream of the compressor, a significant transport delay between the EGR valve and the combustion chamber can occur. Specifically, exhaust gas residues may have to pass through the turbocharger compressor, high-pressure intake lines, an intercooler, and an intake manifold before reaching the combustion chamber. As a result of this transport delay, more dilution gas may be present in the intake tract than desired under conditions where EGR must be reduced very quickly, such as when the accelerator pedal is released at low load. The presence of increased intake air dilution at low loads can exacerbate combustion stability issues and the tendency to misfire.

[0005] An exemplary approach to managing excess residues is shown in US Pat. No. 6,014,959. This approach provides a rigid connection between an EGR throttle and a main air intake throttle, which makes the movement of the EGR throttle dependent on the movement of the main throttle. This allows EGR dilution gas to always be provided at a fixed proportion to the intake air flow.

[0006] However, the inventors here have recognized potential problems with such an approach. For example, the transport delay may not be adequately addressed, while at the same time the fuel economy benefits of LP EGR are limited. For example, linking EGR dilution to the intake airflow may result in LP EGR gases being provided at low-load points where no fuel economy benefit can be achieved from EGR. In some cases, providing LP EGR gases at a low-load point may even have a negative impact on fuel consumption. For example, in such systems, it may not be possible to quickly vent the LP EGR gases from the intake stroke without negatively impacting airflow.As another example, lower load points can limit the delivery of EGR gases at higher load points, as these are the points where the combustion system is most constrained in terms of dilution. Thus, this can limit the maximum achievable EGR rate under high load. The presence of too much dilution gas in the engine intake system can also make the compressor susceptible to corrosion and condensation from EGR gases remaining within it. Furthermore, increased condensation can occur at the intercooler of a turbocharged engine system due to the EGR flow through the cooler. This increased condensation may require additional anti-condensation measures.

[0007] The inventors have recognized that at least some of the above problems can be solved by operating a hybrid vehicle system in a battery charging mode to rapidly vent LP EGR gases. In one example, this is achieved by a method for a hybrid vehicle system comprising: In response to a decreasing engine torque demand when operating an engine with EGR and a system battery SOC falling below: a) Deactivation of the EGR; b) operating the engine with fuel supply and EGR deactivated and driving the vehicle at a higher engine drive torque than the requested torque for vehicle propulsion until the EGR in an engine intake tract is below a threshold value; c) charging a system battery; d) determining when EGR gases fall below the threshold and in response to the threshold being fallen below; e) Deactivating the fuel supply to the prime mover, slowing the prime mover down to a standstill and driving the vehicle using engine torque from the generator.

[0008] In this way, LP EGR gases can be released quickly without affecting the torque to the wheels.

[0009] As an example, under medium to high load conditions, a hybrid vehicle system may operate in an engine mode, where the engine combusts fuel to provide torque to drive the vehicle's wheels. Further, during the engine mode, low-pressure EGR (LP EGR) gases may flow from the engine's exhaust into the engine's intake tract to provide additional fuel economy and emissions benefits. In response to accelerator pedal release at lower load conditions, EGR may be deactivated by closing an EGR valve in a LP EGR passage. By operating the engine with the EGR valve closed, EGR in the intake tract can be quickly replaced with fresh intake air. Thus, during engine operation, the generated engine torque may be greater than the requested engine torque.The excess engine torque generated can be stored in a system battery if the battery has sufficient capacity to accept charge. The excess engine torque can be used, for example, to drive a motor / generator coupled to the battery. Engine operation and battery charging can continue until the LP EGR level falls below a threshold (e.g., all LP EGR has been replaced by fresh intake air). After that, the engine can be shut down, and the vehicle can be propelled using engine torque.

[0010] In this way, the venting of EGR gases from an engine's intake tract can be accelerated. By operating the engine with a closed EGR valve, EGR in the intake tract can be replaced with intake air. Furthermore, the higher engine torque can be advantageously used to charge a system battery. This makes it possible to maintain higher engine torque and battery charge while the EGR gases are vented. By quickly reducing the EGR level in the intake tract during low-load conditions when the engine is off, higher EGR rates can be achieved when the engine is subsequently restarted. This significantly improves engine efficiency, particularly in the mid- to high speed-load range.By replacing the EGR gases with fresh air, the evaporation of condensed water and hydrocarbons is increased, reducing their concentration in the engine and thus the need for anti-condensation measures. Furthermore, reducing condensation reduces corrosion and wear on the compressor and intercooler. Overall, the performance of a turbocharged engine is improved.

[0011] It should be noted that the above-mentioned summary is provided to introduce, in a simplified form, a selection of concepts that are described in more detail in the detailed description. The summary is not intended to identify key features or essential features of the claimed subject matter; the scope of the claimed subject matter is defined solely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that overcome disadvantages noted above or elsewhere in this disclosure. Fig. Figure 1 shows a schematic diagram of a hybrid electric vehicle system. Fig. Figure 2 shows a schematic representation of a combustion chamber of an engine system of Fig. 1. Fig. 3 shows an exemplary engine system equipped with exhaust gas recirculation (EGR) capability. Fig. Figure 4 shows a detailed flowchart for operating the hybrid vehicle system of Fig. 1 to accelerate the draining of low pressure EGR. Fig. Figure 5 shows exemplary EGR schemes at selected engine speed-load conditions. Fig. 6 shows exemplary operations in a hybrid electric vehicle for accelerating EGR purging according to the present invention.

[0012] The following description relates to systems and methods for using a motor / generator of a hybrid vehicle system (such as the vehicle system of Fig. 1) to allow the venting of EGR gases from an engine (such as the engine system of Fig. 2-3) to accelerate under low-load conditions. During operation of the hybrid vehicle in an engine mode with EGR flow, it may be necessary to quickly reduce the EGR supply to the engine in response to a decreasing engine load. Under such conditions, a controller may be configured to execute a control routine, such as the example routine of Fig. 4, to cut off fuel supply to the engine and propel the vehicle using engine torque. In addition, the controller may rotate the engine without fuel supply using engine torque until sufficient EGR gases are purged from the engine intake manifold. Alternatively, if the vehicle system battery can hold a charge, the controller may deactivate EGR and operate the engine with the EGR valve closed while storing the excess engine torque generated as battery charge. Example settings are described with reference to Fig. 6. In this way, higher EGR schemes can be achieved during subsequent engine operation, especially at medium to high engine speed-load conditions ( Fig. 5). Overall, the performance of a power machine is improved.

[0013] Fig. 1 illustrates a hybrid propulsion system 100 for a vehicle. In the illustrated embodiment, the vehicle is a hybrid electric vehicle (HEV). The propulsion system 100 includes an internal combustion engine 10 having a plurality of cylinders 30. Fuel may be provided to each cylinder of the engine 10 from a fuel system (not shown) that includes one or more fuel tanks, one or more fuel pumps, and fuel injectors 66.

[0014] Engine 10 delivers power to a transmission 44 via a torque input shaft 18. In the illustrated example, transmission 44 is a power-split transmission (or transmission axle) that includes a planetary gear set 22 and one or more rotating gear members. Transmission 44 further includes an electric generator 24 and an electric motor 26. The electric generator 24 and electric motor 26 may also be referred to as electric machines because they can each function as either a motor or a generator. Torque is output from transmission 44 via a power transfer gear 34, a torque output shaft 19, and a differential and axle assembly 36 to drive drive wheels 52 of the vehicle.

[0015] The generator 24 is drivably connected to the electric motor 26 so that the power generator 24 and the electric motor 26 can each be operated using electrical energy from an electrical energy storage device, shown here as the battery 54. In some embodiments, a power conversion device, such as an inverter, can be coupled between the battery and the motor to convert the direct current (DC) output of the battery into an alternating current (AC) output for the motor. However, in alternative embodiments, the inverter can be configured in the electric motor.

[0016] The electric motor 26 can be operated in a regenerative mode, i.e., as a generator, to capture energy from the motion of the vehicle and / or the engine and convert the captured kinetic energy into a form of energy suitable for storage in the battery 54. Furthermore, the electric motor 26 can be operated as a motor or as a generator, as needed, to supplement or capture the torque provided by the engine.

[0017] The planetary gear set 22 includes a ring gear 42, a sun gear 43, and a planetary carrier assembly 46. The ring gear and the sun gear may be coupled together via the carrier. A first input side of the planetary gear set 22 is coupled to the engine 10, while a second input side of the planetary gear set 22 is coupled to the generator 24. An output side of the planetary gear set is coupled to drive gears 52 of the vehicle via the power transfer gearbox 34, which includes one or more meshing gear elements 60-68. In one example, the meshing gear elements 60-68 may be stepped gears, with the carrier assembly 46 capable of distributing torque to the stepped gear. The gear elements 62, 64 and 66 are mounted on a countershaft 17, with the gear element 64 engaging with a gear element 70 driven by the engine.The electric motor 26 drives the gear member 70, which serves as the torque input for the countershaft transmission. In this way, the planetary carrier 46 (and consequently the engine and generator) may be coupled to the vehicle wheels and engine through one or more gear members. The hybrid propulsion system 100 may operate in various environments, including a full hybrid system, where the vehicle is powered only by the engine and generator together, or only by the electric motor, or a combination thereof. Alternatively, assist or mild hybrid embodiments may be employed, where the engine is the primary torque source and the electric motor selectively provides additional torque under certain conditions, such as during an accelerator pedal-pressing event.

[0018] For example, the vehicle may be driven in an engine mode in which the engine 10 may operate in conjunction with the electric generator (which provides reaction torque to the planetary gear set and enables a net planetary output torque for propulsion) and be used as the primary torque source to drive the wheels 52 (in motor mode, the generator may also provide torque to the wheels). During the engine mode, fuel may be supplied to the engine 10 from a fuel reservoir via the fuel injector 66, allowing the engine to rotate under fuel supply to provide torque to drive the vehicle. Specifically, engine power is supplied to the ring gear of the planetary gear set. Simultaneously, the generator supplies torque to the sun gear 43, thus creating reaction torque to the engine.Consequently, torque is delivered from the planetary carrier to the gears 62, 64, 66 on the countershaft 17, which in turn delivers power to the wheels 52. Additionally, the engine can be operated to deliver more torque than is needed for propulsion, in which case the additional power is absorbed by the generator (in power generation mode) to charge the battery 54 or to provide power for other loads in the vehicle.

[0019] In another example, the vehicle may be driven in an assist mode in which the engine 10 is operated as the primary torque source and used to drive the wheels 52, and the electric motor is used as an additional torque source to cooperate with the engine 10 and supplement the torque provided by it. During the assist mode, as in the engine mode, fuel is supplied to the engine 10 to rotate the engine under fuel supply and deliver torque to the vehicle wheels.

[0020] In yet another example, the vehicle may be operating in an engine-off or electric mode in which the battery-powered electric motor 26 is operated and utilized as the sole source of torque to drive the wheels 52. Therefore, during the electric mode, no fuel may be injected into the engine 10, regardless of whether the engine is rotating or not. The electric mode may be used, for example, during braking, at low speeds, at light loads, when stopped at a traffic light, etc. Specifically, engine power is delivered to the gear member 70, which in turn drives the gear members on the countershaft 17, thereby driving the wheels 52.

[0021] The drive system 100 may further include a control system with a controller 12 configured to receive information from a plurality of sensors 16 (various examples of which are described herein) and send control signals to a plurality of actuators 81 (various examples of which are described herein). As an example, sensors 16 may include various pressure and temperature sensors, a fuel level sensor, various exhaust gas sensors, etc. The various actuators may include, for example, the gear set, cylinder fuel nozzles (not shown), an air intake throttle coupled to the intake manifold of the engine (not shown), etc. Additional sensors and actuators are described in the Fig. 2-3. The controller 12 may receive input data from the various sensors, process the input data, and actuate the actuators in response to the processed input data based on instructions or code programmed therein according to one or more routines. An exemplary control routine is described with reference to Fig. 4 described.

[0022] Fig. 2 illustrates an exemplary embodiment of a combustion chamber or cylinder of engine 10 (of Fig. 1). The engine 10 may receive control parameters from a control system including the controller 12 as well as inputs from a vehicle operator 130 via an input device 132. In this example, the input device 132 includes an accelerator pedal and a pedal position sensor 134 for generating a proportional pedal position signal PP. The cylinder (also referred to herein as "the combustion chamber") 30 of the engine 10 may have combustion chamber walls 136 with the piston 138 disposed therein. The piston 138 may be coupled to a crankshaft 140 such that the reciprocating motion of the piston is translated into a rotational motion of the crankshaft. The crankshaft 140 may be coupled to at least one drive wheel of the passenger vehicle via an intermediate transmission system. Further, a starter motor may be coupled to the crankshaft 140 via a flywheel to enable starting operation of the engine 10. Specifically, the generator 24 (of Fig. 1) and the drive train including the engine 26 (from Fig. 1) be coupled to the crankshaft and provide torque for starting the engine.

[0023] Cylinder 30 may receive intake air through a series of intake air passages 142, 144, and 146. Intake air passage 146 may be in communication with other cylinders of engine 10 in addition to cylinder 30. In some embodiments, one or more of the intake passages may include a charging device, such as a turbocharger or a positive displacement supercharger. For example, Fig. 2 illustrates engine 10 in a turbocharger configuration with a compressor 174 disposed between intake passages 142 and 144 and with an exhaust turbine 176 disposed along exhaust passage 148. Compressor 174 may be driven at least partially by exhaust turbine 176 via a shaft 180, with the charging device configured as a turbocharger. However, in other examples, such as when engine 10 is equipped with a positive displacement supercharger, exhaust turbine 176 may optionally be omitted, with compressor 174 being driven by a mechanical input from an engine or the engine. A throttle 20 having a throttle valve 164 may be provided along an intake passage of the engine to vary the flow rate and / or pressure of intake air provided to the engine cylinders.For example, the throttle 20 may be located downstream of the compressor 174 as shown in FIG. Fig. 2, or alternatively, it may be provided upstream of the compressor 174. In some embodiments, as described with reference to Fig. 3, a charge air cooler (CAC) may be located downstream of the compressor 174 and upstream of the throttle 20 to cool a charge air charge delivered to the engine. Alternatively, the CAC may be located downstream of the throttle integrated into the intake manifold 146.

[0024] The exhaust passage 148 may receive exhaust gases from additional cylinders of the engine 10 in addition to cylinder 30. The exhaust gas sensor 128 is shown coupled to the exhaust passage 148 upstream of the emissions control device 178. The sensor 128 may be selected from various suitable sensors for providing an indication of an exhaust gas air / fuel ratio, such as a linear oxygen sensor or a UEGO (Universal or Wide-range Exhaust Gas Oxygen, unheated oxygen sensor), a binary oxygen sensor or EGO (as shown), a HEGO (Heated Oxygen Sensor), a NOx, HC, or CO sensor. The emissions control device 178 may be a three-way catalyst (TWC), a NOx storage catalyst, various other emissions control devices, or combinations thereof.

[0025] The exhaust temperature may be estimated from one or more temperature sensors (not shown) disposed in the exhaust passage 148. Alternatively, the exhaust temperature may be derived from engine operating conditions such as engine speed, load, air-fuel ratio (AFR), spark retard, etc. Further, the exhaust temperature may be calculated from one or more exhaust sensors 128. It should be appreciated that the exhaust temperature may alternatively be estimated using any combination of the temperature estimation methods listed herein.

[0026] Each cylinder of engine 10 may include one or more intake valves and one or more exhaust valves. For example, cylinder 30 is illustrated as having at least one intake poppet valve 150 and at least one exhaust poppet valve 156 located in an upper region of cylinder 30. In some embodiments, each cylinder of engine 10, including cylinder 30, may include at least two intake poppet valves and at least two exhaust poppet valves located in an upper region of the cylinder.

[0027] The intake valve 150 may be controlled by the controller 12 via cam actuation via a cam actuation system 151. Similarly, the exhaust valve 156 may be controlled by the controller 12 via a cam actuation system 153. The cam actuation systems 151 and 153 may each include one or more cams and may utilize one or more of the following systems operable by the controller 12 to vary valve operation: cam profile switching (CPS), variable cam timing (VCT), variable valve timing (VVT), and / or variable valve lift (VVL). The position of the intake valve 150 and the exhaust valve 156 may be determined using valve position sensors 155 and 157, respectively. In alternative embodiments, the intake valve and / or the exhaust valve can be controlled by an electric valve actuator.For example, cylinder 30 may alternatively include an intake valve controlled by an electric valve actuator and an exhaust valve controlled by camshaft actuation, including a CPS and / or VCT system. In still other embodiments, the intake valve and exhaust valve may be controlled by a common valve actuator or actuation system, or by a variable valve actuator or actuation system.

[0028] Cylinder 30 may have a compression ratio that is the ratio of the volumes when piston 138 is at bottom dead center to top dead center. Typically, the compression ratio is in the range of 9:1 to 13:1. However, in some examples where other fuels are used, the compression ratio may be higher. This may be the case, for example, when using higher octane fuels or fuels with higher latent heat of vaporization. The compression ratio may also be higher if direct injection is used, due to its effect on engine knock.

[0029] In some embodiments, each cylinder of engine 10 may include a spark plug 192 to initiate combustion. Ignition system 190 may provide an ignition spark to combustion chamber 30 via spark plug 192 in response to an ignition advance signal SA from controller 12 under certain operating conditions. However, in some embodiments, spark plug 192 may be omitted, such as when engine 10 initiates ignition via auto-ignition or fuel injection, as may be the case with some diesel engines.

[0030] In some embodiments, each cylinder of engine 10 may be configured with one or more fuel injectors to provide a knock or pre-ignition suppression fluid thereto. In some embodiments, the fluid may be a fuel, where the injector is referred to as a fuel injector. As a non-limiting example, cylinder 30 is shown with a single fuel injector 166. Fuel injector 166 is directly coupled to cylinder 30 to inject fuel directly therein, in proportion to the pulse width of the FPW signal received from controller 12 via electronic driver 168. In this manner, fuel injector 166 provides what is known as direct injection (hereinafter referred to as "DI") of fuel into combustion cylinder 30. Although Fig. While Figure 2 shows the fuel injector 166 as a side-mounted injector, it may alternatively be positioned above the piston, approximately near the position of the spark plug 192. This position may improve mixing and combustion when the engine is running on an alcohol-based fuel due to the lower volatility of some alcohol-based fuels. Alternatively, the injector may be positioned above and near the intake valve to improve mixing.

[0031] Fuel may be provided to fuel injector 166 via a high-pressure fuel system 8 including fuel tanks, fuel pumps, and a fuel rail. Alternatively, fuel may be supplied from a lower-pressure single-stage fuel pump, in which case the timing of direct fuel injection during the compression stroke may be more restricted than when using a high-pressure fuel system. Further, although not shown, the fuel tanks may include a pressure transducer that provides a signal to controller 12. It will be appreciated that in an alternative embodiment, fuel injector 166 may be a port injector that provides fuel into the intake port upstream of cylinder 30.

[0032] As described above, Fig. 2 only one cylinder of a multi-cylinder engine. Thus, each cylinder can include its own group of intake / exhaust valves, fuel injector(s), spark plug, etc.

[0033] Fuel tanks in fuel system 8 may contain fuel of different qualities, such as different compositions. These differences may include different alcohol contents, different octane ratings, different vaporization temperatures, different fuel blends, and / or combinations thereof, etc. In one example, fuels having different alcohol contents might include one fuel being gasoline and the other fuel being ethanol or methanol. In another example, the engine may use gasoline as the first substance and an alcohol-containing fuel blend such as E85 (equivalent to approximately 85% ethanol and 15% gasoline) or M85 (equivalent to approximately 85% methanol and 15% gasoline) as the second substance. Other alcohol-containing fuels could be a mixture of alcohol and water, a mixture of alcohol, water, and gasoline, etc.

[0034] Further, in the disclosed embodiments, an EGR system may direct a desired portion of exhaust gases from the exhaust passage 148 into the air intake passage 142. Fig. 2 shows a LP EGR system in which LP EGR gases are directed through an LP EGR passage 240 from downstream of the turbine 176 to upstream of the compressor 174. The amount of LP EGR provided into the intake passage 142 can be varied by the controller 12 via the LP EGR valve 242. Similarly, an HP EGR system (in Fig. 3) in which HP EGR gases are directed through an HP EGR passage from upstream of the turbine 176 to downstream of the compressor 174. The amount of HP EGR provided into the intake passage 146 can be varied by the controller 12 via a specific HP EGR valve. The HP EGR system can include an HP EGR cooler (see Fig. 3), and the LP-EGR system may include an LP-EGR cooler 246, for example, to remove heat from the EGR gases to the engine coolant.

[0035] Under some conditions, the EGR system may be used to regulate the temperature of the air-fuel mixture within combustion chamber 30. Therefore, it may be desirable to measure or estimate the EGR mass flow. EGR sensors may be disposed within EGR passages and may provide an indication of one or more of mass flow, pressure, temperature, O2 concentration, and exhaust gas concentration. In some embodiments, one or more sensors may be disposed within LP EGR passage 240 to provide an indication of one or more of pressure, temperature, and air-fuel ratio of the exhaust gases recirculated through the LP EGR passage. Exhaust gases rerouted through LP EGR passage 240 may be diluted with fresh intake air at a mixing point at the confluence of LP EGR passage 240 and intake passage 142.Specifically, by adjusting the LP EGR valve 242 in coordination with a throttle 230 of a low-pressure secondary air system (LP-SLS) (in . Fig. 3 further explained) a dilution of the EGR flow can be set.

[0036] A percentage dilution of the LP EGR flow can be derived from the output of a sensor 245 in the EGR gas stream. Specifically, the sensor 245 can be located downstream of the LP EGR valve 242 so that the LP EGR dilution can be precisely determined. For example, the sensor 245 can be an EGR delta pressure over orifice, delta pressure over valve, hot-wire anemometer, or hot-film anemometer flowmeter. An oxygen sensor, such as a UEGO sensor 372, can also be used to measure the EGR in the main intake passage 142 or 144.

[0037] The control 12 is in Fig. 2 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 example as a read-only memory chip 110, a random access memory 112, a retention memory 114, and a data bus. The controller 12 may, in addition to the signals discussed above, receive various signals from sensors coupled to the engine 10.This includes: measurement of induced mass air flow (MAF) from mass air flow sensor 122; measurement of engine coolant temperature (ECT) from a temperature sensor 116 coupled to a cooling sleeve 118; a profile ignition pickup (PIP) signal from Hall effect sensor 120 (or other sensor type) coupled to crankshaft 140; throttle position (TP) from a throttle position sensor; an absolute boost pressure (MAP) signal from sensor 124; the in-cylinder air-fuel ratio (AFR) from EGO sensor 128; and abnormal combustion from a knock sensor. The engine speed signal, RPM, may be generated by controller 12 from the PIP signal. The boost pressure signal, MAP, from a boost pressure sensor can be used to provide indications of vacuum or pressure in the intake manifold.

[0038] The read-only memory storage medium 110 may be programmed with computer-readable data representing instructions executable by a processor 106 to perform the methods described below, as well as other variations that are anticipated but not specifically listed.

[0039] Reference is now made to Fig. 3, in which an exemplary embodiment 300 of an engine system 10 (such as the engine system of Fig. 1-2) that includes a plurality of cylinder banks and an exhaust gas recirculation system. Embodiment 300 shows a turbocharged engine system including a multi-cylinder internal combustion engine 10 and two turbochargers 320 and 330. As a non-limiting example, engine system 300 may be part of the propulsion system of a passenger vehicle. Engine system 300 may receive intake air via intake passage 340. Intake passage 340 may include an air cleaner 356 and an EGR throttle valve 230. Engine system 300 may be a split engine system in which intake passage 340 downstream of EGR throttle valve 230 is split into first and second parallel intake passages, each including a turbocharger compressor.Specifically, at least a portion of the intake air is directed to the compressor 322 of turbocharger 320 via a first parallel intake passage 342 and at least another portion of the intake air is directed to the compressor 332 of turbocharger 330 via a second parallel intake passage 344 from intake passage 340.

[0040] The first portion of the total intake air, which is compressed by the compressor 322, can be provided via a first parallel, branched intake passage 346 into the intake manifold 360. Thus, the intake passages 342 and 346 form a first parallel branch of the engine's secondary air system. Similarly, a second portion of the total intake air can be compressed by the compressor 332, from which it can be provided via a second parallel, branched intake passage 348 into the intake manifold 360. Thus, the intake passages 344 and 348 form a second parallel branch of the engine's secondary air system. As shown in Fig. 3, the intake air from the intake ports 346 and 348 may be recombined via a common intake port 349 before entering the intake manifold 360, from where it is provided to the engine.

[0041] A first EGR throttle valve 230 may be disposed in the engine intake tract upstream of the first and second parallel intake passages 342 and 344, respectively, while a second air intake throttle valve 358 may be disposed in the engine intake tract downstream of the first and second parallel intake passages 342 and 344, respectively, and downstream of the first and second parallel branched intake passages 346 and 348, respectively, for example, in the common intake passage 349.

[0042] In some examples, intake manifold 360 may include an intake manifold pressure sensor 382 to estimate manifold pressure (MAP) and / or an intake manifold temperature sensor 383 to estimate manifold air temperature (MCT), both of which communicate with controller 12. Intake passage 349 may include a charge air cooler (CAC) 354 and / or a throttle (such as a second throttle valve 358). The position of throttle valve 358 may be adjusted by the control system via a throttle actuator (not shown) in communication with controller 12. An anti-surge valve 352 may be provided to selectively recirculate flow through the compressor stages of turbochargers 320 and 330 via recirculation passage 350.As an example, the anti-surge valve 352 may be opened to allow flow through the return passage 350 when the intake air pressure upstream of the compressors reaches a threshold.

[0043] Air duct 349 may further include an intake gas oxygen sensor 372. In one example, the oxygen sensor is a UEGO sensor. The intake gas oxygen sensor may be configured to provide an estimate of the oxygen content of the fresh air drawn into the intake manifold. Furthermore, as EGR gases flow, a change in oxygen concentration at the sensor may be used to infer an amount of EGR and for precise EGR flow control. In the depicted example, the oxygen sensor 372 is located upstream of the throttle 358 and downstream of the charge air cooler 354. However, in alternative embodiments, the oxygen sensor may be located upstream of the CAC. A pressure sensor 374 may be located adjacent to the oxygen sensor to estimate an intake pressure at which an output of the oxygen sensor is received.Since the oxygen sensor output is influenced by intake pressure, a reference oxygen sensor output may be learned at a reference intake pressure. In one example, the reference intake pressure is throttle inlet pressure (TIP), where pressure sensor 374 is a TIP sensor. In alternative examples, the reference intake pressure is manifold pressure (MAP) measured by MAP sensor 382.

[0044] The engine 10 may include a plurality of cylinders 30. In the depicted example, the engine 10 includes six cylinders arranged in a V-configuration. Specifically, the six cylinders are arranged in two banks 313 and 315, with each bank including three cylinders. In alternative examples, the engine 10 may include two or more cylinders, such as 3, 4, 5, 8, 10, or more cylinders. These various cylinders may be evenly spaced and arranged in alternative configurations, such as a V-configuration, in-line configuration, horizontally opposed configuration, etc. Each cylinder 30 may be equipped with a fuel injector 66. In the depicted example, the fuel injector 66 is a direct in-cylinder fuel injector. However, in other examples, the fuel injector 66 may be configured as an in-port fuel injector.

[0045] Intake air supplied to each cylinder 30 (also referred to herein as combustion chamber 30) via the common intake passage 349 may be used for fuel combustion, and combustion products may then be exhausted via bank-specific parallel exhaust passages. In the depicted example, a first cylinder bank 313 of the engine 10 may exhaust exhaust products of combustion via a first parallel exhaust passage 317, and a second cylinder bank 315 may exhaust exhaust products of combustion via a second parallel exhaust passage 319. Each of the first and second parallel exhaust passages 317 and 319, respectively, may further include a turbocharger turbine. Specifically, combustion products exhausted via the exhaust passage 317 may be directed through the exhaust turbine 324 of the turbocharger 320, which, in turn, may provide mechanical work to the compressor 322 via the shaft 326 to provide compression of the intake air.Alternatively, the exhaust gases flowing through exhaust passage 317 may be partially bypassed via turbine bypass passage 323 of turbine 324, as controlled by wastegate 328. Similarly, combustion products expelled via exhaust passage 319 may be directed through the exhaust turbine 334 of turbocharger 330, which in turn may provide mechanical work to compressor 332 via shaft 336 to provide compression of the intake air flowing through the second branch of the engine's intake system. Alternatively, the exhaust gases flowing through exhaust passage 319 may be partially bypassed via turbine bypass passage 333 of turbine 334, as controlled by wastegate 338.

[0046] In some examples, exhaust turbines 324 and 334 may be configured as variable geometry turbines, where controller 12 may adjust the position of the turbine blades (or vanes) to vary the amount of energy extracted from the exhaust stream and passed to the respective compressor. Alternatively, exhaust turbines 324 and 334 may be configured as variable nozzle geometry turbines, where controller 12 may adjust the position of the turbine nozzle to vary the amount of energy extracted from the exhaust stream and passed to the respective compressor. For example, the control system may be configured to independently vary the vane or nozzle position of exhaust turbines 324 and 334 via corresponding actuators.

[0047] Exhaust gases in the first parallel exhaust passage 317 may be directed to the atmosphere via the branched parallel exhaust passage 370, while exhaust gases in the second parallel exhaust passage 319 may be directed to the atmosphere via the branched parallel exhaust passage 380. The exhaust passages 370 and 380 may include one or more exhaust aftertreatment devices, such as a catalyst, and one or more exhaust gas sensors.

[0048] The engine 10 may further include one or more exhaust gas recirculation (EGR) passages, or loops, for recirculating at least a portion of the exhaust gases from the exhaust manifold to the intake manifold. These may include high-pressure EGR loops for providing high-pressure EGR gases (HP EGR) and low-pressure EGR loops for providing low-pressure EGR gases (LP EGR). In one example, HP EGR gases may be provided in the absence of boost pressure provided by the turbochargers 320, 330, while LP EGR gases may be provided in the presence of turbocharger boost pressure and / or when the exhaust gas temperature is above a threshold. In still other examples, both HP EGR and LP EGR gases may be provided simultaneously.

[0049] In the illustrated example, engine 10 may include a low-pressure EGR loop 202 for recirculating at least a portion of the exhaust gases from first branched, parallel exhaust passage 370 downstream of turbine 324 to first parallel intake passage 342 upstream of compressor 322. In some embodiments, a second (not shown) low-pressure EGR loop may similarly be provided for recirculating at least a portion of the exhaust gases from second branched, parallel exhaust passage 380 downstream of turbine 334 to second parallel intake passage 344 upstream of compressor 332. The LP EGR loop 202 may include an LP EGR valve 204 to regulate an EGR flow (i.e., a recirculated exhaust gas amount) through the loops, as well as an EGR cooler 206 to lower a temperature of the exhaust gases flowing through the EGR loop before being recirculated to the engine intake tract.Under certain conditions, the EGR cooler 206 may also be used to heat the exhaust gases flowing through the LP EGR loop 202 before the exhaust gases enter the compressor to prevent water droplets from entering the compressors.

[0050] The engine 10 may further include a first high-pressure EGR loop 208 for recirculating at least a portion of the exhaust gases from the first parallel exhaust passage 317 upstream of the turbine 324 to the first branched parallel intake passage 346 downstream of the compressor 322. Similarly, the engine may include a second high-pressure EGR loop (not shown) for recirculating at least a portion of the exhaust gases from the second parallel exhaust passage 318 upstream of the turbine 334 to the second branched parallel intake passage 348 downstream of the compressor 332. EGR flow through the HP EGR loops 208 may be regulated by the HP EGR valve 210. Under some operating conditions, HP EGR gases may be injected downstream of the engine throttle 358 to improve flowability. Alternatively, the HP EGR loop(s) may include an EGR cooler (not shown).

[0051] A PCV port 302 may be configured to supply crankcase ventilation gases (so-called blowby gases) via the second parallel intake passage 344 into the engine intake manifold. In some embodiments, the flow of PCV air through the PCV port 302 (e.g., PCV flow) may be regulated by a dedicated PCV port valve. Similarly, a vent port 304 may be configured to supply vented gases from a fuel system canister via the passage 344 into the engine intake manifold. In some embodiments, the flow of vented air through the vent port 304 may be regulated by a dedicated vent port valve.

[0052] Humidity sensor 232 and pressure sensor 234 may be present in only one of the parallel intake passages (shown here in the first parallel intake passage 342, but not the second parallel intake passage 344), downstream of the EGR throttle valve 230. Specifically, the humidity sensor and pressure sensor may be located in the intake passage that does not receive PCV or vent air. Humidity sensor 232 may be configured to estimate a relative humidity of the intake air. In one embodiment, humidity sensor 232 is a UEGO sensor configured to estimate the relative humidity of the intake air based on the sensor's output at one or more voltages. Because vent air and PCV air can corrupt the humidity sensor's readings, the vent port and PCV port are located in an intake passage remote from the humidity sensor.Alternatively, they may be located downstream of the humidity sensor. Pressure sensor 234 may be configured to estimate intake air pressure. In some embodiments, a temperature sensor may also be included in the same parallel intake passage, downstream or upstream of EGR throttle valve 230.

[0053] The intake oxygen sensor 372 can be used to estimate an oxygen concentration in the intake air and to estimate an amount of EGR flow through the engine based on a change in the intake oxygen concentration when the EGR valve 204 opens. Specifically, a change in the sensor's output when the EGR valve opens is compared to a reference point at which the sensor is operating without EGR (the zero point). Based on the change (e.g., decrease) in the amount of oxygen from the time of operation without EGR, a current EGR flow provided to the engine can be calculated. For example, when a reference voltage (Vs) is applied to the sensor, a pumping current (Ip) is output from the sensor.The change in oxygen concentration can be proportional to the change in pumping current (Delta Ip) output by the sensor in the presence of EGR gases relative to the sensor output in the absence of EGR gases (the zero point). Further EGR control can be performed based on the deviation of the estimated EGR flow from the expected (or target) EGR flow.

[0054] The position of the intake and exhaust valves of each cylinder 30 may be controlled via hydraulically actuated lifters coupled to valve pushrods or by a cam profile switching mechanism utilizing cam lobes. Specifically, the intake valve cam actuation system 325 may include one or more cams and utilize variable camshaft timing or lift for the intake and / or exhaust valves. In alternative embodiments, the intake valves may be controlled by electric valve actuators. Similarly, the exhaust valves may be actuated by cam actuation systems or electric valve actuators.

[0055] The engine system 300 may be controlled at least in part by a control system 15 having a controller 12, as well as by inputs from a vehicle operator via an input device (not shown). The control system 15 is illustrated receiving information from a plurality of sensors 16 (various examples of which are described herein) and sending control signals to a plurality of actuators 81. As one example, the sensors 16 may include the humidity sensor 232, the intake air pressure sensor 234, the MAP sensor 382, ​​the MCT sensor 383, the TIP sensor 374, and the intake air oxygen sensor 372. In some examples, the common intake passage 349 may further include a throttle inlet temperature sensor to estimate a throttle air temperature (TCT).In other examples, one or more of the EGR passages may include pressure, temperature, and hot-wire or hot-film anemometer flow sensors to determine EGR flow characteristics. As another example, actuators 81 may include fuel injector 66, HP EGR valve 210, LP EGR valve 204, throttle valves 358 and 230, and wastegate valves 328, 338. Additional actuators, such as various additional valves and throttles, may be coupled at various locations within engine system 300. Controller 12 may receive input data from the various sensors, process the input data, and actuate the actuators in response to the processed input data based on instructions or code programmed therein according to one or more routines. An example control routine is described with reference to FIG. Fig. 4 described.

[0056] Reference is now made to Fig. 4, in which an exemplary routine 400 for operating the vehicle system of Fig. 1. Specifically, the method according to Fig. 4, Low pressure EGR gases quickly from the engine system of the Fig. 2-3. A controller may operate a vehicle system generator during decreasing load conditions to spin the engine without fuel to quickly replace EGR gases in the intake tract with fresh intake air. Alternatively, if the system battery can accept a charge, the controller may operate the engine in a power generation mode with EGR disabled to replace EGR gases in the intake tract with fresh intake air while using the excess engine torque generated to recharge the battery. In either case, the engine system's dilution tolerance is improved, the likelihood of misfires is reduced, and the maximum achievable EGR rates during subsequent high-load operations are increased.

[0057] At 402, engine operating conditions and vehicle operating parameters are estimated and / or measured. These include, for example, a brake pedal position, an accelerator pedal position, an operator torque request, a battery state of charge (SOC), an engine temperature (Teng), an ambient temperature and humidity, a barometric pressure (BP), etc. In one example, the hybrid vehicle system is a power-split hybrid vehicle system.

[0058] At 404, a vehicle operating mode may be determined based on the estimated operating conditions. For example, based at least on the estimated driver torque request and the battery state of charge, it may be determined whether to operate the vehicle in an engine-only mode (where the engine drives the vehicle's wheels), an assist mode (where the battery assists the engine in driving the vehicle), or an all-electric mode (where the battery alone powers the vehicle). In one example, if the requested torque can be provided solely by the battery, the vehicle may operate in the all-electric mode. In another example, if the requested torque cannot be provided solely by the battery, the vehicle may operate in the engine mode or the assist mode.The vehicle can be operated accordingly in the specified operating mode.

[0059] At 406, it may be confirmed that the vehicle is in an engine-on mode. For example, it may be confirmed that the vehicle is in an engine-only mode, where the vehicle is propelled solely by engine torque. Alternatively, it may be confirmed that the vehicle is in an assist mode, where the vehicle is propelled at least partially by engine torque. If the engine-on mode is not confirmed, the routine may end.

[0060] At 408, fuel may be supplied to the engine to operate the engine and generate engine torque to propel the vehicle. Here, the engine output torque may correspond to a requested torque for vehicle propulsion. In one example, based on engine operating conditions, such as engine speed-load conditions, the engine may be operated boosted, with fuel supplied to the boosted engine via direct injection. Furthermore, the engine may be operated with EGR enabled or EGR flow. Here, operation with EGR includes operation with low-pressure EGR (LP EGR) flow. By flowing LP EGR gases during engine operation, fuel economy is improved by reducing pumping, mitigating knock, improving combustion efficiency, and reducing enrichment.Operation of the engine with low-pressure EGR includes operation of the engine with an open EGR valve coupled to a low-pressure EGR passage.

[0061] In one example, the LP EGR scheme may be a flat scheme where LP EGR gases are provided at a fixed rate relative to the airflow. The LP EGR gases include cooled exhaust gas residues recirculated from an engine exhaust manifold downstream of an exhaust turbine into an engine intake manifold upstream of an intake compressor.

[0062] For example, the amount of EGR (HP EGR, LP EGR, or a combination of both) delivered to the intake tract may be based on an engine speed-load map stored in the memory of the controller 12. In one example, the engine speed-load map may include at least two LP EGR modes, including a fixed mode and a variable mode. The fixed mode may include all engine speeds and loads across the normal engine operating range. The fixed mode may "dilute" the LP EGR gases at very high engine speeds and loads, including wide open throttle, to avoid conflicts with engine performance. In comparison, the variable EGR mode may allow variable EGR rates across the normal engine operating range.

[0063] At 410, it may be determined whether conditions of decreasing engine load exist. Specifically, it may be determined whether a decrease in engine torque request and conditions of decreasing engine torque request exist. For example, a decreasing engine load / request may be in response to the operator releasing the accelerator pedal. Thus, as the engine load / request decreases, airflow to the engine may be reduced and, accordingly, LP EGR to the engine may also be reduced. However, due to the large transport delay between the LP EGR valve and the combustion chamber, EGR may not be reduced as quickly as required. Specifically, because the LP EGR passage samples exhaust gases after the turbine and injects exhaust gases before the compressor, there is a large delay in venting the EGR gases from the intake manifold.The delay is further exacerbated by the presence of a large boost volume (e.g., six times the volume) above the engine displacement in some engine configurations. The delay in venting poses risks to combustion stability. For example, the presence of more dilution gases than required can increase the likelihood of misfiring.

[0064] The use of a flat EGR pattern, in which the EGR rate is kept constant relative to the airflow, helps mitigate some of the problems associated with delayed bleed. However, the use of a flat pattern results in the LP EGR operating at some lower load points where no fuel economy benefit is achieved. In fact, LP EGR operation can have a negative impact on fuel consumption at some lower engine speed-load points. In addition, the compressor can be exposed to EGR gases during low-load conditions, requiring measures to protect against corrosion and condensation. As EGR gases flow through the intercooler, additional condensation can occur, which may also require measures. Under some low-load conditions, a low-pressure air intake throttle may also be required to drive EGR flow.Furthermore, the lower load points limit the flat EGR pattern at higher load points, as the lower load points are the points where the combustion system is most limited in terms of dilution (EGR). For example, the flat pattern limits the maximum achievable EGR rate at higher engine speed-load conditions. This limits the fuel economy benefits of LP EGR.

[0065] Fig. 5 illustrates an exemplary flat EGR scheme in map 500. As illustrated therein, a flat scheme with EGR delivery at a fixed rate relative to airflow is applied in engine speed-load ranges corresponding to zone 502. Outside of zone 502, in zone 504, no LP EGR is used. Although the delivery of cooled LP EGR gases at a fixed rate in the mid-speed-load range (upper half of zone 502) yields significant fuel economy benefits, the benefit may be limited. Therefore, it may be desirable to operate with a larger amount of LP EGR in this range. However, this may not be achievable due to the large EGR transport delay.Furthermore, the flat pattern of map 500 results in the use of LP EGR at the engine's low speed-load conditions (lower half of zone 502), where fuel consumption may be adversely affected. Therefore, it may be desirable not to use EGR in this range. However, this may not be achievable due to the EGR supply upstream of the compressor and the resulting large EGR transport delay.

[0066] The inventors herein have discovered that EGR venting can be accelerated by utilizing an engine of the hybrid vehicle to replace the EGR vents in the intake manifold with fresh intake air. Specifically, in response to a decreasing engine torque demand or load when operating an engine with EGR flow, fuel to the engine can be shut off, and the engine can be cranked without fuel until sufficient EGR vents are vented from the intake manifold. Alternatively, if a system battery is capable of receiving a charge, EGR venting can be accelerated by disabling EGR and operating the engine in a power generation mode to replace EGR vents in the intake manifold with fresh air, while utilizing the excess engine torque generated to recharge the battery.

[0067] For example, by accelerating the discharge of LP EGR gases, an EGR scheme such as the scheme of map 550 of Fig. 5 can be achieved. Specifically, by allowing rapid venting of LP EGR gases during low-load conditions, it may be possible to operate without LP EGR in the low engine speed-load range, such as in Zone 554. By reducing the flow of cooled LP EGR gases at lower loads and relying on hot internal EGR instead, fuel economy and engine performance are improved in this operating range. Furthermore, by allowing rapid venting and reset of the EGR gases to essentially zero LP EGR conditions as engine loads decrease, higher maximum EGR rates can be achieved as engine loads subsequently increase. For example, it may be possible to operate with higher LP EGR rates in medium engine speed-load ranges, such as in Zone 552.

[0068] Reference is again made to Fig. 4; In response to a decreasing engine load and torque demand, at 411, the battery state of charge (SOC) may be estimated and / or measured and compared to a charge threshold. The routine further determines whether the battery state of charge is greater than a charge threshold. The charge threshold may be defined to allow a short additional engine-on time and subsequent charging to facilitate EGR venting.

[0069] If the battery state of charge is higher than the charge threshold, it may be determined that the battery is unable to accept further charge. Accordingly, at 412, in response to the decreasing engine torque request, fueling to the engine is disabled while a motor / generator of the hybrid vehicle system is operating. As a result, while the engine is off, the vehicle is propelled using engine torque instead of engine torque. At 414, the routine includes spinning the engine without fuel via the motor / generator to accelerate the venting of LP EGR gases from the engine intake manifold. For example, the engine may be spun without fuel via the generator for an additional 1-3 seconds.Furthermore, as long as the engine is running, both an EGR valve in a low-pressure EGR passage and an intake throttle in the intake passage can be fully open. By fully opening the EGR valve and intake throttle while running, the EGR system, as well as the secondary air system, can be emptied of exhaust residues and refilled with fresh intake air.

[0070] Turning the engine without fuel from the engine involves operating the generator using electrical energy from the system battery to turn the engine at the selected speed. The engine may be turned without fuel at a selected engine speed based on the engine speed before the fuel injectors were turned off. For example, the controller may operate the generator to maintain the engine speed at which the engine was turning immediately before the fuel injectors were turned off. As another example, the generator may turn the engine without fuel at an engine speed that is a function (e.g., a fraction) of the engine speed at which the engine was turning immediately before the fuel injectors were turned off.Alternatively, the selected engine speed can be a speed that affects both the engine and the transmission. Thus, the purge time required to completely purge the EGR gases depends on the engine speed and throttle position.

[0071] In an alternative example, the engine may be rotated without fuel at a speed based on the vehicle speed. For example, the engine speed may be set to be a calibratable speed stored in the controller's memory in a lookup table accessed based on the vehicle speed. In yet another example, the engine may be rotated at a speed based on a vehicle speed and a rotational speed (or a rotational speed limit) of the rotating components of the planetary gear train. Motor / generator settings may be adjusted to allow the engine to be rotated at a selected engine speed using engine torque.In some embodiments, both the generator and the motor may be operated to rotate the engine at the selected engine speed. In other embodiments, only the generator may need to be operated.

[0072] In yet another example, the engine may be rotated without fueling at an engine speed that is at least equal to an engine crankshaft speed. In addition to accelerating EGR venting, this allows the engine to be quickly restarted upon a driver change of mind operation (such as the operator releasing the accelerator pedal and shortly thereafter re-engaging the accelerator). For example, in response to an indication of an operator change of mind, the controller may begin fueling the engine and ramping the engine up from the crankshaft speed to meet the operator's torque request.

[0073] In still further examples, the engine may be spun without fuel at an engine speed that allows EGR gases to be vented as quickly as possible. Here, the engine speed may be selected based on the EGR level in the intake tract at a time of decreasing engine torque demand (e.g., the time the operator releases the accelerator pedal). For example, the engine speed may be temporarily increased to a maximum allowable engine speed that does not affect torque output but allows EGR gases to be vented as quickly as possible. In yet another example, the engine may be spun without fuel at an engine speed that allows EGR gases to be vented more slowly. For example, the operator releasing the accelerator pedal and the decreasing engine load / torque demand may occur when the vehicle is descending a hill.The operator can indicate a prolonged downhill section by pressing a button on the vehicle's instrument panel or via an interactive display in the vehicle's center console. By indicating a prolonged downhill section, the operator can indicate that the engine can be shut down for an extended period. Accordingly, the engine can be operated without fuel supply from the generator during the downhill section, allowing EGR purging to be completed by the time the downhill section is completed.

[0074] In further examples, instead of continuously rotating the engine until the EGR gases are vented, the engine may be rotated intermittently via the generator without fuel. For example, during a downhill descent, the engine may be pulsed via the generator without fuel to vent the EGR gases.

[0075] At 416, it may be determined whether the EGR gases have been sufficiently vented from the engine intake manifold. For example, it may be determined whether EGR gases (flow, amount, concentration, level, etc.) in the intake tract are lower than a threshold. In one example, an intake oxygen sensor, such as sensor 372 of Fig. 3, can be used to estimate the EGR concentration in the intake tract. A decrease in intake oxygen concentration can be used to infer an increase in the delivery of EGR dilution gases. In one example, the threshold is based on an engine EGR tolerance during low engine load conditions. For example, if the EGR tolerance increases, the threshold can be increased.

[0076] If the LP EGR gases are not below the threshold, control may spin the engine without fueling via the motor / generator until the EGR gases are sufficiently vented. If the EGR gases are below the threshold, the routine at 420 includes spinning the engine to a stop. For example, the engine may be spun to a stop via the motor, and then the engine may remain off until conditions for restarting the engine are met. Meanwhile, the vehicle may continue to be propelled using engine torque. This may reset the LP EGR rate (for example, to zero) so that upon engine restart, a known higher LP EGR rate can be realized to improve engine efficiency in the critical mid-load range of the speed-load map.

[0077] At 430, it may be determined whether engine restart conditions are met. For example, the engine may be restarted in response to one or more of a battery state of charge below a charge threshold, a received climate control request, an operator torque request above a threshold, etc. If engine restart conditions are not met, the engine may remain shut down and the vehicle may continue to be propelled by the engine. Otherwise, at 432, in response to the restart conditions being met, the engine may be restarted, and fueling to the engine may be resumed. Here, upon engine restart, EGR may be enabled, and higher EGR flow rates may be achieved since the engine has already been purged.

[0078] Returning to 411, if the battery SOC is lower than the charge threshold, it may be determined that the battery is capable of accepting further charge. Consequently, EGR bleed may be enabled by temporarily operating the vehicle in a power generation mode. Specifically, at 422, the routine includes disabling EGR in response to decreasing engine load conditions. Disabling EGR includes closing an EGR valve coupled to a LP EGR passage to prevent further recirculation of exhaust gas residues from the exhaust manifold downstream of the turbine to the intake manifold upstream of the compressor.

[0079] At 424, the routine includes operating the engine with EGR disabled and with engine output torque greater than a requested torque. This means that until the EGR gases in the engine intake are sufficiently vented, the engine continues to rotate while fueled with engine output torque generated in excess of the requested torque to propel the vehicle. By operating the engine while fueled with the EGR valve closed, fresh intake air drawn into the secondary air system may replace the EGR gases in the intake, thus accelerating EGR venting. In one example, the engine is operated while fueled with the EGR valve closed for 1-3 seconds.

[0080] Also at 424, the routine includes charging the system battery using excess engine output torque. This means charging the system battery using engine output torque generated when operating the engine with EGR disabled in excess of the requested torque. Charging the battery may include operating the generator using the excess engine output torque, where the generator is coupled to the battery. In one example, the engine is operated in the power generation mode for 1-3 seconds.

[0081] Operating the engine at greater than requested engine output torque includes operating the engine at an engine speed based on one or more of a system battery state of charge and an EGR level in the engine intake at a time of the decreasing engine torque request condition. For example, the engine speed may be based on a battery's ability to accept charge. Thus, as a difference between the battery's SOC and the charge threshold increases (and thereby the battery's charge acceptance capability increases), the engine speed at which the engine is operated may be increased. The engine speed may also be based on the EGR level in the intake at the time the operator releases the accelerator pedal.For example, if the EGR level increases when the accelerator pedal is released, more venting may be required, and consequently, engine speed may be increased. In still other examples, engine speed may be further adjusted based on vehicle speed.

[0082] At 426, as at 416, it may be determined whether the low-pressure EGR gases have been sufficiently vented from the engine intake manifold. For example, it may be determined whether EGR gases (flow, amount, concentration, level, etc.) in the intake tract are below a threshold. The threshold may be based on an engine EGR tolerance during low-load engine conditions.

[0083] If the LP EGR gases are not below the threshold, control may continue to operate the engine under fueled conditions, with EGR disabled and excess engine torque generated, and storing the excess torque as charge in a system battery until the EGR gases are sufficiently vented. At 428, if the intake EGR gases are below the threshold, the routine includes disabling fueling to the engine and spinning the engine down to a stop. Thereafter, the engine may remain off until conditions for restarting the engine are met. In the meantime, the vehicle may be propelled using engine torque from the motor / generator.This allows the LP EGR rate to be reset (e.g. to zero) so that when the engine is restarted, a known higher LP EGR rate can be realized in order to improve the efficiency of the engine in the important middle load range of the speed-load map.

[0084] From 428, the routine proceeds to 430 to determine if engine restart conditions are met and, if conditions are met, restart the engine at 432. Upon engine restart, EGR may be enabled, and higher EGR flow rates may be achieved because the engine has already been purged.

[0085] In this way, at 422-428, with the accelerator pedal released during engine operation with EGR flow, while a battery state of charge is below a charge threshold, a battery may be charged by operating the engine with EGR disabled until an EGR level in the engine intake tract is lower than a threshold, wherein the engine is operated to produce more torque than requested. Here, operating the engine with EGR flow includes operating the engine with an open (e.g., fully open) EGR valve coupled to a low-pressure EGR passage, and operating the engine with EGR disabled includes operating with the EGR valve closed (e.g., fully closed). Once the EGR level in the engine intake tract is lower than the threshold, engine operation and battery charging may be terminated.

[0086] It is clear that even if the routine of Fig. 4 illustrates the choice between venting LP EGR gases in a hybrid vehicle system by spinning the engine without fueling via a generator or operating an engine with fueling and EGR disabled and charging a battery based on a charge capacity (or SOC) of a system battery. In alternative examples, the controller may be configured to select based on the LP EGR level in the engine intake stroke during conditions with decreasing engine load / torque demand. For example, if the LP EGR level is higher at the time the operator releases the accelerator pedal, the controller may select venting by spinning the engine without fueling via the generator.Otherwise, if the LP EGR level is lower at the time the operator releases the accelerator pedal, the controller may select venting by operating the engine under fuel in a power generation mode with EGR disabled. Further still, the controller may be configured to select rotating the engine without fuel from the generator as the default venting option. The controller may then selectively replace the default venting option with the power generation mode venting option based on operator input.

[0087] It is clear that although the routine of Fig. 4 shows EGR venting in response to a decreasing engine load / torque demand (such as the operator releasing the accelerator pedal). In alternative examples, EGR venting may be initiated in anticipation of an engine shutdown. For example, the vehicle controller may determine an impending engine shutdown based on vehicle operating conditions and initiate EGR venting before the anticipated engine shutdown occurs. Here, EGR venting may occur independent of operator input, such as an operator releasing the accelerator pedal or a driver request. Instead, EGR venting may be performed based on vehicle operating conditions (e.g., vehicle speed, ambient humidity, etc.), which determine a frequency of engine shutdown and restart.By initiating EGR venting in anticipation of engine shutdown, additional venting delays are reduced.

[0088] In this way, under conditions of decreasing engine torque demand, the low-pressure EGR gases can be quickly vented and the EGR levels reset. This rapid venting reduces the combustion stability risks associated with residual EGR gases at low-load conditions. Furthermore, by resetting the EGR levels, higher EGR rates can be realized as the engine torque demand increases to medium-load conditions.

[0089] In one example, a hybrid vehicle system includes an engine having an intake and an exhaust tract; an intake throttle; an electric motor / generator coupled to a battery; and vehicle wheels driven by torque from one or more of the engine and the motor. The hybrid vehicle system further includes a direct fuel injector coupled to a cylinder of the engine; a turbocharger having an intake compressor driven by an exhaust turbine; and an EGR passage through which EGR gases flow from the exhaust tract downstream of the turbine to the intake tract upstream of the compressor via an EGR valve.The vehicle system may include a controller with computer-readable instructions for deactivating the fuel injector when the accelerator pedal is released during operation of an engine with EGR flow; fully opening both the EGR valve and the intake throttle; and utilizing engine torque to meet an operator torque request and rotate the engine without fueling, wherein rotating the engine continues for a duration until EGR gases in the engine are below a threshold. Here, rotating until LP EGR gases in the engine are below a threshold comprises rotating until an amount of LP EGR in an intake manifold of the engine is below the threshold, where the threshold is based on the torque request. In one example, rotating until LP EGR gases in the engine are below a threshold comprises rotating until LP EGR flow is at zero flow.Rotating the engine includes rotating the engine at an engine speed at or above an engine crankshaft speed. The controller may further include instructions to, after the duration, rotate the engine to a stop and keep the engine off while continuing to utilize engine torque to meet the torque request.

[0090] In another example, the controller of the hybrid vehicle system described above includes computer readable instructions to, in response to an operator releasing the accelerator pedal while operating the engine with EGR flow, estimate a state of charge of the battery; and if the estimated state of charge of the battery is below a threshold charge, close the EGR valve; operate the engine with the EGR valve closed for a duration until EGR gases in the engine are below a threshold, wherein the engine is operated to produce more torque than requested; and charge the battery with the excess produced torque when operating the engine with the EGR valve closed.Here, operating the engine with the EGR valve closed may include rotating the engine at an engine speed based on one or more of a battery state of charge at accelerator pedal release and an EGR level in the intake tract at accelerator pedal release. Further, operating the engine with the EGR valve closed until EGR gases in the engine are below a threshold may include operating the engine until EGR flow is at zero flow. The controller may further include instructions to, if the estimated battery state of charge is greater than the charge threshold, deactivate the fuel injector; fully open the EGR valve and intake throttle; and utilize torque from the generator to meet an operator torque request and rotate the engine without fuel until EGR gases in the engine are below the threshold.

[0091] Exemplary EGR bleed operations will now be described with reference to the example of Fig. 6. Specifically, map 600 represents engine speed at line 602, engine torque at line 604, LP EGR at line 606, fuel injection at line 608, a battery state of charge (SOC) at line 610, and a position of an LP EGR valve at line 614.

[0092] Before t1, the hybrid vehicle may be operating with a larger proportion of wheel torque provided by the engine and a smaller proportion of wheel torque provided by the motor. Accordingly, the engine may rotate under fueling (line 608) at an engine speed corresponding to operation in a medium-to-high load range (line 602) with only a little assistance from the engine (line 604). During operation in the medium-to-high load range, LP EGR gases may flow (line 606), for example, according to a flat pattern where EGR gases are provided at a fixed rate relative to airflow. Specifically, an LP EGR valve may be open (line 614). In the illustrated example, the LP EGR valve is shown as an on-off valve that can be switched between a fully open and a fully closed position.However, in other examples, an opening of the LP EGR valve may be variably adjusted based on the LP EGR demand. During engine operation prior to t1, the battery state of charge may be higher than a threshold 612, and the battery may not be able to accept further charge (line 610).

[0093] At t1, an operator may release the accelerator pedal, resulting in a reduction in engine load to low-load conditions. In response to the decreasing engine torque demand, EGR to the engine may be reduced. If an LP EGR valve is adjusted (e.g., closed) to decrease EGR gases, there may be a significant transport delay due to EGR delivery upstream of the compressor, and the EGR gases may not decrease as quickly as desired. For example, the EGR gases may decrease according to the profile of dotted line segment 609a. This would result in too much dilution gas in the engine intake manifold during low-load conditions, increasing the propensity for misfiring and combustion stability issues.

[0094] To improve the venting of LP EGR gases during low-load conditions and to enable a minimal EGR flow (e.g., zero flow) to be provided to the engine during low-load conditions, the EGR gases may be vented very quickly with assistance from a system generator. Here, venting with assistance from the generator may be requested due to the fact that the battery state of charge is higher than threshold 612. Specifically, at t1, fuel injection to the engine is deactivated, causing a drop in engine speed. In addition, the motor / generator power is increased to provide sufficient engine torque to propel the vehicle and meet the operator's torque request, while also providing sufficient engine torque to rotate the engine without fuel delivery.If the motor / generator is not running, the engine may slow down to a standstill according to the profile of dotted line segment 603. As long as the engine is running without fuel supply via the motor / generator, the LP EGR valve may remain fully open. In addition, an intake throttle (not shown) may be fully open. This allows EGR gases in the secondary air system to be quickly replaced with fresh intake air.

[0095] Rotating the engine without fueling includes rotating the engine at an engine speed 601. The engine speed 601 may be a crankshaft speed of the engine. Alternatively, the engine speed 601 may correspond to an engine speed prior to fuel injector deactivation or a function thereof. Still further, the engine speed 601 may correspond to an engine speed that is particularly efficient for the engine and transmission. Thus, the engine may be rotated via the motor for a duration between t1 and t2 until the LP EGR gases are sufficiently vented. For example, the engine may be rotated at the engine speed 601 until the LP EGR gases are at or below a minimum EGR level 611.In an alternative example, the EGR level 611 may not include EGR flow, such that no LP EGR gases are provided at lower engine load conditions.

[0096] At t2, once the EGR gases are sufficiently vented, the engine is allowed to stop. Furthermore, the LP EGR valve is closed. After that, the engine remains shut down until conditions for restarting the engine are met (at t3). In the meantime, between t2 and t3, engine operation may be adjusted to produce sufficient engine torque to propel the vehicle. Between t1 and t3, when the engine is not running and engine torque is being used to propel the vehicle and / or rotate the engine without fuel delivery, the battery SOC may decrease. For example, at t3, the battery SOC may fall below threshold 612.

[0097] At t3, in response to engine restart conditions (such as an increase in operator torque request), fuel injection to the engine may resume, and engine torque may be increased to propel the vehicle. At the same time, engine torque may be reduced because the vehicle is largely powered by engine torque. Although the illustrated example shows engine torque being reduced to a lower level, in an alternative example, engine torque may be eliminated entirely. Also at t3, the LP EGR valve is opened to reactivate EGR during engine operation. Furthermore, because LP EGR was reset at t2, higher peak LP EGR rates may be delivered upon restart to higher loads at t3.

[0098] Vehicle operation with the engine running and EGR gases supplied may continue until t4. This allows sufficient time to elapse between t3 and t4 (represented by dotted lines). At t4, the hybrid vehicle may operate in an engine-only mode where the wheel torque demand is met by the engine. The engine may rotate at an engine speed corresponding to operation in a medium to higher load range with LP EGR gases flowing (and the LP EGR valve open). For example, LP EGR gases may be provided according to a flat schedule with a fixed EGR rate relative to airflow. During engine operation at t4, the battery state of charge may be lower than threshold 612, and the battery may be able to accept further charge.

[0099] At t5, as at t1, an operator may release the accelerator pedal, resulting in a reduction in engine load to low-load conditions. In response to the decreasing engine load, EGR to the engine may be reduced. Specifically, the LP EGR valve is closed to reduce EGR. However, even if the EGR valve is closed, there may be a significant transport delay due to the EGR delivery upstream of the compressor, and the EGR gases may not decrease as quickly as desired. For example, the EGR gases may decrease according to the profile of dotted line segment 609b. This would result in too much dilution gas in the engine intake manifold at low-load conditions, increasing the propensity for misfiring and combustion stability issues.

[0100] To enhance the venting of LP EGR gases during low load conditions and to enable a minimal EGR flow (e.g., zero flow) to be provided to the engine during low load conditions, the EGR gases may be vented very quickly by operating the hybrid vehicle system in a power generation mode. Here, the venting may be requested by operating the engine in a power generation mode due to the fact that the battery state of charge is lower than threshold 612 and the battery is able to accept further charge. Specifically, at t5, fueling and operation of the engine are maintained, but with EGR disabled. Fuel injection to the engine is adjusted to produce more engine torque than required to propel the vehicle and meet the operator's torque request.This causes the engine to operate at a higher speed 605 than would otherwise be required to propel the vehicle (as represented by dashed line segment 607). By operating the engine at a higher speed with the EGR valve closed, the EGR gases in the secondary air system can be quickly replaced with fresh intake air, allowing for more rapid venting of the EGR gases. The excess torque generated by the engine is then used to charge the battery. Consequently, the battery state of charge may begin to increase after t5.

[0101] Operating the engine to generate excess torque includes rotating the engine at an engine speed 605. The engine speed 605 may be based on the LP EGR level at the time the operator releases the accelerator pedal (at t5) as well as the battery state of charge at the time the operator releases the accelerator pedal. As the battery state of charge decreases, a higher engine speed 605 (relative to the engine speed 607 otherwise required to propel the vehicle) may be applied, and higher levels of excess torque may be generated to vent the EGR gases as the battery is able to hold larger amounts of charge. Similarly, as the LP EGR level increases and more venting is required, the engine speed 605 may be further increased relative to the engine speed 607.

[0102] The engine operates with EGR deactivated and excess engine torque generated for a duration between t5 and t6 until the LP EGR gases are sufficiently vented. For example, the engine may continue to operate at engine speed 605 until the LP EGR gases are at or below the minimum EGR level 611. In an alternative example, the EGR level 611 may not include any EGR flow, such that no LP EGR gases are provided at lower engine load conditions. Additionally, between t5 and t6, the battery state of charge may continue to increase until it is above the threshold 612 at t6.

[0103] At t6, once the EGR gases have been sufficiently vented, the engine is allowed to stop. Specifically, fuel supply to the engine is deactivated and the engine is allowed to spin to a stop. Afterward, the engine remains shut down until conditions for restart are met (at t7). In the meantime, between t6 and t7, a motor in the vehicle system is operated to generate sufficient engine torque to propel the vehicle.

[0104] At t7, in response to engine restart conditions (such as an increase in operator torque request), fuel injection to the engine may resume, and engine torque may be increased to propel the vehicle. Concurrently, engine torque may be reduced (e.g., turned off) so that the vehicle is propelled with engine torque. Furthermore, because LP EGR was reset at t6, higher maximum LP EGR rates may be delivered upon restart to higher loads at t7.

[0105] In this way, during a first engine shutdown from EGR operation, a controller may disable fuel injection and spin the engine without fuel until EGR gases are below a threshold. In comparison, during a second engine shutdown from EGR operation, the controller may disable EGR and spin the engine with fuel until EGR gases are below the threshold, while using the excess engine torque to charge the battery.Here, during the first engine shutdown and while the engine is rotating without fuel, engine torque is used to propel the vehicle and rotate the engine. During the second engine shutdown and while the engine is rotating with fuel, engine torque is used to propel the vehicle and charge the battery. Furthermore, during the first engine shutdown, the battery's state of charge is above a charge threshold, whereas during the second engine shutdown, the battery's state of charge is below the charge threshold.During the first engine shutdown, the engine is rotated without fuel at an engine speed based on an engine speed before fuel injection was deactivated, whereas during the second engine shutdown with fuel, the engine is rotated at an engine speed based on an EGR level before EGR was deactivated.

[0106] In this way, under selected conditions with decreasing engine load / torque demand, the engine torque of a hybrid vehicle system can be advantageously used to vent EGR gases in a low-load range and improve EGR delivery in mid-load ranges. By controlling the engine speed to selectively rotate the engine after fuel supply is shut off, EGR gases trapped in the engine's charge volume can be quickly vented. During other conditions with decreasing engine load, the charge-carrying capacity of a hybrid vehicle's system battery can be advantageously used to vent EGR gases in the low-load engine range.By storing excess engine torque in the battery, the engine can operate at higher engine speeds (and with higher engine power) while EGR is deactivated, allowing EGR gases in the secondary air system to be quickly replaced with fresh intake air. By accelerating EGR venting, LP EGR rates can be reduced more quickly during low-load conditions. For example, LP EGR rates can be reset during low-load conditions. This reduces the tendency for misfiring and combustion instability due to the presence of excess dilution gases during low-load conditions. Accelerated venting also allows higher LP EGR rates to be achieved when the engine is restarted, thus allowing the engine to be used in the most efficient operating range.In particular, engine efficiency can be significantly improved in the mid-load range. The interaction of the turbocharged engine and the power-split hybrid application also enables the fuel-saving potential of LP EGR to be improved and reduces trade-offs in EGR rates, such as the need to run LP EGR at low-load conditions and the lower maximum EGR rates that can be achieved when operating with a flat schedule at medium to high load conditions. Overall, vehicle performance and engine fuel economy are improved.

[0107] It should be noted that the example control and estimation routines provided herein may be used for a wide variety of engine and / or vehicle system configurations. The control methods and routines disclosed herein may be stored in the form of executable instructions in non-volatile memory. The specific routines described herein may represent one or more of any number of processing strategies, such as event-driven, interrupt-driven, multitasking, multithreading, and the like. Therefore, various of the illustrated steps, operations, and / or functions may be performed in the sequence shown, in parallel, or may be omitted as appropriate.Similarly, the execution order is not required to achieve the features and advantages of the exemplary embodiments described herein, but is provided merely for convenience of illustration and description. One or more of the illustrated steps, operations, and / or functions may be performed repeatedly, depending on the particular strategy being pursued. Furthermore, the described steps, operations, and / or functions may represent, in graphical form, code that must be programmed into the non-transitory memory of the computer-readable storage medium in the engine control system.

[0108] It is understood that the configurations and routines disclosed herein are exemplary in nature and that these specific embodiments are not to be considered limiting, as numerous variations are possible. Thus, the technology described above may be applied to V-6, I-4, I-6, or V-12 engines, as well as horizontally opposed 4-cylinder engines and other engine types. The scope of the present disclosure includes all novel and non-obvious combinations and subcombinations of the various systems and configurations, as well as other features, functions, and / or characteristics disclosed herein.

[0109] The following claims specifically identify certain combinations and subcombinations that are considered novel and non-obvious. These claims may refer to "a" element or "a first" element, or the equivalent thereof. Such claims are to be construed as encompassing the inclusion of one or more such elements, neither requiring nor excluding two or more such elements.

[0110] Other combinations and subcombinations of the disclosed features, functions, elements, and / or properties may be claimed by amending or supplementing the present claims, or by presenting new claims in this or a related application. Such claims, whether broader or narrower, the same or different in scope as the original claims, are also considered to be encompassed by the present disclosure.

Claims

[1] A method for venting low-pressure EGR gases during operation of a hybrid vehicle under light loads, comprising: in response to a decreasing engine torque request when operating an engine (10) with EGR (410) and a system battery (411) falling below the SOC: a) Deactivation of the EGR (422); b) operating the engine (10) with fuel supply with EGR deactivated and driving the vehicle at a higher drive torque of the engine (10) than the requested torque for vehicle propulsion until the EGR in an engine intake tract is below a threshold value (424); c) charging a system battery (424); d) determining when EGR gases (426) have fallen below the threshold value and in response to falling below the threshold value; e) Deactivating the fuel supply to the prime mover (10), slowing down the prime mover (10) to a standstill (428) and driving the vehicle using engine torque from the generator. [2] The method of claim 1, wherein operating the engine (10) with EGR comprises operating the engine (10) with low-pressure EGR (LP-EGR) provided at a fixed rate relative to airflow, wherein the LP-EGR gases comprise cooled exhaust gas residues recirculated from an exhaust manifold downstream of an exhaust turbine into the engine intake tract upstream of an intake compressor via an EGR passage. [3] The method of claim 2, wherein operating the engine (10) with EGR comprises operating the engine (10) with an EGR valve (242) opened in the EGR passage. [4] The method of claim 3, wherein deactivating EGR comprises closing an EGR valve (242). [5] The method of claim 1, wherein the threshold is based on an EGR tolerance of the engine (10) at low load conditions of the engine (10). [6] The method of claim 1, wherein the decreasing engine torque request is in response to an operator releasing the accelerator pedal. [7] The method of claim 1, wherein operating the engine (10) at higher than requested engine drive torque comprises operating the engine (10) at an engine speed based on a battery state of charge and an EGR level at the decreasing engine torque request. [8] The method of claim 1, wherein charging a system battery comprises charging the battery when the engine (10) drive torque exceeds the requested torque generated during engine operation with EGR disabled. [9] The method of claim 8, wherein charging the system battery comprises operating a generator using the excess drive torque of the prime mover (10), the generator being coupled to the battery. [10] The method of claim 1, wherein operating the engine (10) with EGR comprises operating the engine (10) in a boosted state with low pressure EGR gases flowing and wherein fuel is delivered to the boosted engine (10) via direct injection. [11] The method of claim 1, wherein the hybrid vehicle system is a power-split hybrid vehicle system. [12] A method for venting low-pressure EGR gases during operation of a hybrid vehicle under light loads, comprising: with the accelerator pedal released during operation of an engine (10) with EGR flow while a state of charge of the battery is below a charge threshold, charging the battery while driving a vehicle by operating the engine (10) with EGR deactivated until an EGR level in the intake tract of the engine (10) is lower than an EGR threshold, wherein the engine (10) is operated to produce more torque than requested for vehicle propulsion, determining when the threshold level of EGR gases is exceeded and, in response to the threshold level being exceeded, deactivating the fuel supply to the engine (10), revving the engine (10) down to a standstill and driving the vehicle using engine torque from the generator. [13] The method of claim 12, wherein operating the engine (10) with EGR flow comprises operating the engine (10) with an open EGR valve (242) coupled to a low-pressure EGR passage, and wherein operating the engine (10) with EGR disabled comprises operating the engine (10) with the EGR valve (242) closed. [14] The method of claim 13, wherein the charge threshold is based on an intake EGR level upon release of the accelerator pedal, the threshold decreasing as the EGR level increases. [15] The method of claim 14, further comprising terminating engine operation and terminating battery charging when the EGR level in the intake tract of the engine (10) is lower than the threshold. [16] A hybrid vehicle system comprising: an engine (10) having an intake and an exhaust tract; an intake throttle; an electric motor / generator coupled to a battery; vehicle wheels (52) driven by torque from one or more of the engine (10) and the motor; a direct fuel injector coupled to a cylinder of the engine (10); a turbocharger having an intake compressor driven by an exhaust turbine; an EGR passage through which EGR gases flow from the exhaust tract downstream of the turbine to the intake tract upstream of the compressor via an EGR valve (242); and a controller having computer-readable instructions for: in response to an operator releasing the accelerator pedal while operating the engine (10) with EGR flow, estimating a state of charge of the battery;and if the estimated state of charge of the battery is below a charge threshold, closing the EGR valve (242); operating the engine (10) with the EGR valve (242) closed for a duration until EGR in the engine (10) is below a threshold, wherein the engine (10) is operated to propel the vehicle and produce more torque than requested; and charging the battery with the excess produced torque when operating the engine (10) with the EGR valve (242) closed, determining a drop in EGR gases below the threshold, and in response to a drop in EGR gases below the threshold, deactivating fuel supply to the engine (10), slowing down the engine (10) to a standstill, and propelling the vehicle using engine torque from the generator. [17] The system of claim 16, wherein operating the engine (10) with the EGR valve (242) closed comprises rotating the engine (10) at an engine speed based on one or more of a battery state of charge at accelerator pedal release and an EGR level in the intake tract at accelerator pedal release. [18] The system of claim 17, wherein operating the engine (10) with the EGR valve closed until EGR in the engine (10) is below a threshold comprises operating the engine (10) until EGR flow is at zero flow. [19] The system of claim 18, wherein the controller further comprises instructions to: if the estimated battery state of charge is greater than the charge threshold, deactivate the fuel injector; fully open the EGR valve (242) and the intake throttle; and utilize torque from the generator to satisfy an operator torque request and spin the engine (10) without fueling until the EGR gases in the engine (10) are below the threshold.

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