IDLE ENGINE SPEED CONTROLLER

摘要

PROBLEM TO BE SOLVED: To prevent the excessive increase of an idling engine speed and to properly issue and alarm about a failure even during any failure which makes it impossible to shut off the flowing of electricity from a switching element to a coil. SOLUTION: A first transistor Tr1 switched ON/OFF by a duty ratio which is based on an objective idling engine speed at the time is connected to the ground side of the coil 6a of an ISC valve 6 and a second transistor Tr2 switched ON/OFF by a prescribed duty ratio when shutting of electricity flowing to the coil 6a by the first transistor Tr1 is made impossible is connected to the battery side of the coil 6a. A CPU 21 detects a failure which makes it impossible to shut off electricity flowing to the coil 6a by the first transistor Tr1 based on the existence of the edge of the comparator output of a voltage level determination circuit 32. Also, the CPU 21 lights a failure alarming lamp when the failure is detected and limits the increase of an idling engine speed based on a prescribed engine speed higher than the objective idling engine speed.