JPS57117010A - Constant speed running device for vehicle - Google Patents

Abstract

PURPOSE:To prevent hunting of a vehicle, by maintaining a shiftdown state of a gear until its engine suction pressure exceeds a prescribed value, even if it is repeated that a load put on the engine becomes heavy or light. CONSTITUTION:When a speed of a vehicle begins to be slower than a set car speed, a pulse signal whose duty ration is large is outputted from a comparing circuit 20 in accordance with a drop of the car speed. When this pulse signal exceeds a set level of a comparing circuit 51, an output of the circuit 51 turns on, an output of an OR circuit 52 turns on, and also a transistor 62 turns on. Subsequently, a solenoid 66 becomes a nonconducting state, a gear of an automatic speed changer is shifted down, and its constant speed running is maintained. After that, when the engine suction pressure becomes a set value or below, a contact of a switch 57 is closed, both a circuit 56 and a circuit 52 turn off, and the transistor 62 turns off. As a result, the gear of the automatic speed changer is shifted up, and the vehicle runs at a constant speed.