Idling speed control system for internal combustion engines

摘要

An idling speed control system for controlling idling rotational speed of an internal combustion engine. A vacuum-operated actuator having a diaphragm defining a vacuum chamber controls opening and closing of a throttle valve in response to pressures supplied from a change-over control valve to the vacuum chamber. The change-over control valve selectively supplies the vacuum chamber with a first control pressure for opening the throttle valve and a second control pressure for closing same. An electronic control unit generates an on-off control pulse signal having a pulse repetition period corresponding to rotational speed of the engine, one of on-period or off-period of the on-off control pulse signal having a predetermined constant value, and supplies the change-over control valve with the on-off control pulse signal. A valve opening-correcting device is operatively connected to the throttle valve and responsive to at least one predetermined external load applied on the engine for correcting to a larger opening the opening of the throttle valve which is determined by the change-over control valve in response to the on-off control pulse signal.