Combustion control system for internal combustion engine

Abstract

In engine idle, a throttle valve is set to an intermediate position between the closed position and the open position, which provides a substantial opening for air flow. When an accelerator is initiated, the sufficient air flow amount and speed are already attained in the engine, the engine rotation quickly increases in response to the accelerator movement. During the period before the accelerator arrives at a pick-up position, an electric control unit controls ignition timing in response to the accelerator movement. The amount of fuel injected to the engine is also controlled depending on the accelerator movement. Also during this period, one or more cylinders are set to be inactive by not supplying the fuel thereto. Thus, the engine rotation speed is controlled to be low at idle. In engine deceleration, when the engine is in the range where a backfire tends to occur, the rate of change in the ignition delay and the amount of fuel injection are adjusted depending on the engine rotation speed, the ignition delay and the other physical parameters. In the range where backfire is likely to happen, the rate of change in the ignition delay timing is controlled to be smaller and the amount of fuel injection is controlled to be larger, which will suppress the backfire in deceleration.