JPS5752399A - Driving circuit of electromagnetic clutch - Google Patents

Abstract

PURPOSE:To prevent a clutch from sliding while idling, by detecting the lowered r.p.m. of an engine below a normal value to increase a duty ratio of the intermittent driving current to flow to an electromagnetic coil of the clutch. CONSTITUTION:At a normal time the signals of an airconditioning temperature detector 8 and those of a setter 9 inside of a compartment are compared by a comparator 10 to control a transistor Q3 through a delay circuit 11 and a nonstable multivibrator 12 for driving an electromagnetic clutch for a vehicle air conditioning device 1 through a continuous current at a starting time and through an intermittent current after starting. And when idling, the lowering of the r.p.m. thereof is detected through a detector 13 to be given to a switching circuit 16 through a monostable multivibrator 14 and a comparator circuit 15 for changing a resistance value to be inserted into the nonstable multivibrator 12 to enlarge a duty ratio thereof. Accordingly at the time of the lowered r.p.m. the supply input to the electromagnetic clutch can be enlarged to eliminate sliding for performing constant and excellent air cooling.