Patent ID: 8851050
Filing Date: 2014-10-07
Classification: F02B,F02D,Y02T

Abstract:
1. A method of controlling a spark-ignition engine which comprises a detection device for detecting a preignition which is a phenomenon that an air-fuel mixture self-ignites before a spark-ignited normal combustion initiation timing, an injector for directly injecting fuel into a cylinder, and a variable mechanism for variably setting an intake valve closing timing, the method comprising the steps of: executing a first preignition avoidance control as a control mode to be performed when the preignition is detected based on a detection value of the detection device, and it is ascertained that an engine speed is less than a predetermined value; and executing a second preignition avoidance control as a control mode to be performed when the preignition is detected based on the detection value of the detection device, and it is ascertained that the engine speed is equal to or greater than the predetermined value, wherein; the first preignition avoidance control includes an A/F control operation of increasing a fuel injection amount from the injector to enrich an air/fuel ratio in the cylinder, a compression ratio control operation of, when the preignition is detected even after the A/F control operation, shifting the intake valve closing timing using the variable mechanism to reduce an effective compression ratio of the engine; the second preignition avoidance control includes an A/F control operation of increasing a fuel injection amount from the injector to enrich the in-cylinder air/fuel ratio, an injection timing control operation of, when the preignition is detected even after the A/F control operation, retarding an injection timing of a part of fuel to be injected from the injector, to the medium or later phase of the compression stroke; the first preignition avoidance control is executed in such a manner as to enrich the air/fuel ratio in a multi-stage manner, and then, when the preignition is detected even after maximally enriching the air/fuel ratio, to reduce the effective compression ratio; and the second preignition avoidance control is executed in such a manner as to enrich the air/fuel ratio in a multi-stage manner, and then, when the preignition is detected even after maximally enriching the air/fuel ratio, to retard the injection timing of a part of the fuel.