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Methods and systems are provided for expediting EGR purging in a hybrid vehicle during transient operations, such as tip-out to lower load conditions. In response to decreasing engine torque demand, engine fueling is disabled and a motor is used to spin the engine unfueled until a desired LP-EGR rat

Methods and systems are provided for expediting EGR purging in a hybrid vehicle during transient operations, such as tip-out to lower load conditions. In response to decreasing engine torque demand, engine fueling is disabled and a motor is used to spin the engine unfueled until a desired LP-EGR rate is achieved. Alternatively, engine operation is maintained with EGR disabled until the desired LP-EGR rate is achieved, and the excess engine torque generated is stored in a system battery.

대표청구항 ▼

1. A method for a hybrid vehicle, comprising: in response to decreasing engine torque demand while operating an engine with EGR, disabling EGR; anduntil EGR in an engine intake is less than a threshold, operating the engine, fueled, with EGR disabled and propelling the vehicle with engine output tor

1. A method for a hybrid vehicle, comprising: in response to decreasing engine torque demand while operating an engine with EGR, disabling EGR; anduntil EGR in an engine intake is less than a threshold, operating the engine, fueled, with EGR disabled and propelling the vehicle with engine output torque higher than demanded torque for vehicle propulsion; andcharging a system battery. 2. The method of claim 1, wherein operating the engine with EGR includes operating the engine with low pressure EGR (LP-EGR) provided at a fixed rate relative to airflow, the LP-EGR including cooled exhaust residuals recirculated from an exhaust manifold, downstream of an exhaust turbine, to the engine intake, upstream of an intake compressor via an EGR passage. 3. The method of claim 2, wherein operating the engine with EGR includes operating the engine with an EGR valve in the EGR passage open. 4. The method of claim 3, wherein disabling EGR includes closing the EGR valve. 5. The method of claim 1, wherein the threshold is based on an EGR tolerance of the engine at low engine load conditions. 6. The method of claim 1, wherein the decreasing engine torque demand is in response to an operator pedal tip-out. 7. The method of claim 1, wherein operating the engine with engine output torque higher than demanded includes operating the engine at an engine speed based on a state of charge of the battery and an EGR level at the decreasing engine torque demand. 8. The method of claim 1, wherein charging the system battery includes charging the battery with the engine output torque in excess of demanded torque generated during engine operation with EGR disabled. 9. The method of claim 8, wherein charging the system battery includes operating a generator using the excess engine output torque, the generator coupled to the battery. 10. The method of claim 1, further comprising, when EGR in the intake is less than the threshold, deactivating fuel to the engine and spinning down the engine to rest while propelling the vehicle using motor torque. 11. The method of claim 1, wherein operating the engine with EGR includes operating the engine boosted, with low pressure EGR flowing, and with fuel delivered to the boosted engine via direct injection. 12. The method of claim 1, wherein the hybrid vehicle is a power split hybrid vehicle. 13. A method for a hybrid vehicle system, comprising: during a tip-out from operating an engine with EGR flowing, while a battery state of charge is lower than a threshold charge, charging a battery while propelling a vehicle by operating the engine with EGR disabled until an engine intake EGR level is lower than an EGR threshold, the engine operated to generate more torque than demanded for vehicle propulsion. 14. The method of claim 13, wherein operating the engine with EGR flowing includes operating the engine with an EGR valve coupled in a low pressure EGR passage open, and wherein operating the engine with EGR disabled includes operating the engine with the EGR valve closed. 15. The method of claim 14, wherein the threshold charge is based on an EGR level of the intake at the tip-out, the threshold charge lowered as the EGR level increases. 16. The method of claim 15, further comprising, after the engine intake EGR level is lower than the EGR threshold, discontinuing engine operation and discontinuing battery charging, and continuing to propel the vehicle using motor torque. 17. A hybrid vehicle system, comprising: an engine including an intake and an exhaust;an intake throttle;an electric motor/generator coupled to a battery;vehicle wheels propelled using torque from one or more of the engine and the motor;a direct fuel injector coupled to an engine cylinder;a turbocharger including an intake compressor driven by an exhaust turbine;an EGR passage for flowing EGR from the exhaust, downstream of the turbine, tothe intake, upstream of the compressor, via an EGR valve; anda controller with computer readable instructions for: in response to an operator pedal tip-out while operating the engine with EGR flowing, estimating a battery state of charge; andif the estimated battery state of charge is lower than a threshold charge, closing the EGR valve;operating the engine with the EGR valve closed for a duration until EGR in the engine is lower than a threshold, the engine operated to propel the vehicle and to generate more torque than demanded; andcharging the battery with excess engine torque generated while operating the engine with the EGR valve closed. 18. The system of claim 17, wherein operating the engine with the EGR valve closed includes spinning the engine at an engine speed based on one or more of the battery state of charge at the tip-out and an intake EGR level at the tip-out. 19. The system of claim 18, wherein operating the engine with the EGR valve closed until EGR in the engine is lower than a threshold includes operating the engine until EGR flow is at zero flow. 20. The system of claim 19, wherein the controller includes further instructions for: if the estimated battery state of charge is higher than the threshold charge, disabling the fuel injector;fully opening the EGR valve and the intake throttle; andusing torque from the generator to meet operator torque demand and spin the engine unfueled until EGR in the engine is lower than the threshold.