Patent ID: 6994072

Claim:
A method for expanding the mid load operation limit in a four-stroke gasoline direct-injection controlled auto-ignition combustion engine having at least one cylinder with direct fuel injection and containing a piston reciprocably connected with a crank and defining a variable volume combustion chamber including an intake valve controlling communication with an air intake and an exhaust valve controlling communication with an exhaust outlet, the method comprising: operating the engine with two sequential pairs of expansion and contraction strokes during two revolutions of the crank, said two revolutions of the crank defining a combustion cycle; operating the engine with an overall stoichiometric air/fuel ratio and external EGR dilution; employing a variable valve actuating system for variably actuating the intake and exhaust valves, said valve actuating system being capable of operating the intake and exhaust valves with one of an exhaust re-compression valve strategy or an exhaust re-breathing valve strategy; providing a spark plug that extends into said combustion chamber, said spark plug having a spark gap; employing a fuel injector in communication with said combustion chamber, said fuel injector having multiple injection capability for injecting more than one fuel charge per combustion cycle; injecting a first fuel charge into the combustion chamber to form a lean air-fuel mixture throughout the combustion chamber; injecting a second fuel charge into the combustion chamber adjacent the spark plug a period of time after said first fuel charge to form a stratified air-fuel mixture having an ignitable mixture located near said spark plug; and igniting the ignitable mixture at the spark gap, thereby causing spark-ignition combustion, the spark-ignition combustion causing a rise in cylinder pressure and temperature that triggers auto-ignition of the remaining lean air-fuel mixture, and controlling the combustion phasing and burn rate such that higher engine load is attainable before a pressure rise rate in the combustion chamber exceeds a prescribed threshold value.