Vehicle speed control system with dual interrupt safety circuit

Abstract

A motor drives a fuel supply control element, typically the throttle of an automotive-type gasoline engine through a solenoid controlled coupling. Upon brake, clutch, manual switch, or other interrupting operation, the solenoid is de-energized so that a spring can permit interruption of the coupling and a throttle return spring can return the throttle to idle position. To prevent dangerous conditions from arising, and run-away of the engine in case of malfunction of the coupling, an electronic circuit is provided to introduce a signal to the speed control system which tends to move the throttle positioning motor to change the position of the throttle to idle speed condition if a disabling signal is sensed. Preferably, additionally, a first timing circuit interrupts energization of the positioning motor servo loop after a predetermined period of time; a second timing circuit may be provided which has a time constant which is long with respect to the return time of the throttle under its spring connection and controlling a malfunction memory which provides a visual indication of malfunction in the system.