System and method for automatic control of a vehicle speed to a geschwünschte cruising speed with the disconnection function.

摘要

PURPOSE:To make it possible to surely release control of constant running when a vehicle speed is less than a predetermined value, by cutting off power supply to an actuator for driving a throttle valve when it is discriminated that an actual vehicle speed is less than a predetermined value. CONSTITUTION:A control unit 30 controls an actuator 31 in accordance with turn-on and -off from a clutch switch 11, a normally closed brake switch 12, a constant speed running set/coast switch 17, an accelerator switch 18, a cancel switch and the like, and accordingly, the throttle valve is driven to carry out constant speed running. In this arrangement, there is provided a vehicle speed discriminating circuit 40, and a relay 43 having normally open contacts are connected between the control unit 30 and the actuator 31. When the circuit 40 discriminates an actual vehicle speed which is less than a predetermined value, the relay 43 is turned off so as to cut off power supply to a battery 1 to the actuator 31.