JPS5734426A - Misfire detector - Google Patents

Abstract

PURPOSE:To improve misfire detection in stability and reliability, by measuring the lowering of the exhaust temperature and resulting from a misfire. CONSTITUTION:Thermocouple temperature detectors 1A and 1B are attached near the exhaust ports of respective cylinders of an internal-combustion engine, one for each of said cylinders. The ends 2A and 2B of the thermocouples, having the same polarity, are connected together, while the ends 3A and 3B having the opposite polarity are connected across an exciting coil 5 of a reed relay 4. An auxiliary exciting coil 6 is wound on the outside of the exciting coil 5,and a power source whose current direction changes every given time is connected across said coil 6. When there is no misfire, the temperature in the respective cylinders are approximately equal to each other, so that the electromotive forces of the respective thermocouples 1A and 1B are approximately equal to each other. When there is a misfire, however, a large temperature difference, approximately 500 deg.C, arises between the insides of the respective cylinders. Consequently, an electromotive force difference arises, so that a current flows in the exciting coil 5, from the 3B side to the 3A side. When said current direction and the current direction changed over by a timer 8 coincide with each other, the magnetic force increases, so that a reed switch 7 is closed to turn on a lamp 11. When the circuit is changed over after a given time by means of the timer 8, the current direction of the auxiliary coil side is reversed, so that the switch 7 is opened to turn off the lamp 11, which repeats on-off operation thereafter.