Method and system for engine control

#The present application relates to improving engine restarts during high torque demand in hybrid vehicles.

#Reduced engine operation times in hybrid vehicles enable fuel economy and fuel emissions benefits. However, having the internal combustion engine off when the vehicle is driven in an electric mode and then performing a smooth engine restart can delay the delivery of torque from the engine. The delay can be exacerbated in engines operating on a Miller cycle where a boosting device (such as a turbocharger or a supercharger) has to spool up before delivering high pressure air to the air intake system.

#One example approach for reducing the delay in turbocharger spool-up (also referred to as turbo lag) is shown by Berger et al. in U.S. Pat. No. 7,314,043. Therein, compressed air is delivered from a dedicated source to an engine intake manifold during selected conditions to provide an increase in cylinder charge when a turbocharger has not yet attained sufficient speed to provide the desired boost pressure. In this way, flow amplification is implemented until the turbocharger comes up to speed.

#FIG. 1 illustrates an example hybrid vehicle system.

#FIG. 2 illustrates an example internal combustion engine coupled in the hybrid vehicle system of FIG. 1.

#FIG. 3 shows an example embodiment of a pressure accumulator coupled to the engine of FIGS. 1-2.

#The following description relates to systems and methods for operating a hybrid electric vehicle, such as the plug-in hybrid electric vehicle of FIG. 1. During selected conditions, such as a pedal tip-in to wide-open pedal, vehicle wheels may be transitioned from being propelled using motor torque to being propelled using engine torque, such as from the engine of FIG. 2. A controller may be configured to perform a control routine, such as the routine of FIG. 4, to restart the engine by cranking while operating the engine with intake valve timing advanced. The controller may also discharge compressed air from a high pressure air accumulator, such as the accumulator of FIG. 3, to the engine intake manifold while advancing intake valve timing to expedite turbine spool-up and maximum engine torque output. A timing of opening an accumulator valve to discharge the compressed air may be coordinated with the fueling of a first firing cylinder during the engine restart. An example engine restart is shown with reference to FIG. 5. In this way, a smooth engine restart is provided in a hybrid vehicle system.

#FIG. 1 illustrates an example vehicle propulsion system 100. Vehicle propulsion system 100 includes a fuel burning engine 10 and a motor 20. As a non-limiting example, engine 10 comprises an internal combustion engine and motor 20 comprises an electric motor. Motor 20 may be configured to utilize or consume a different energy source than engine 10. For example, engine 10 may consume a liquid fuel (e.g. gasoline) to produce an engine output while motor 20 may consume electrical energy to produce a motor output. As such, a vehicle with propulsion system 100 may be referred to as a hybrid electric vehicle (HEV). Specifically, propulsion system 100 is depicted herein as a plug-in hybrid electric vehicle (PHEV).

#Vehicle propulsion system 100 may be operated in a variety of different modes depending on vehicle operating conditions. Some of these modes may enable engine 10 to be maintained in an off state (or deactivated state) where combustion of fuel at the engine is discontinued. For example, under select operating conditions, motor 20 may propel the vehicle via drive wheel 30 while engine 10 is deactivated. Therein, the vehicle wheels are driven with motor torque.