| 摘要 |
PURPOSE:To control the detection error at the time of incomplete combustion by eliminating the valley type temperature characteristics in regard to CO which is incidental to the exhaust gas temperature fluctuation by disposing a gas sensor behind a heat exchanger and causing the power applied to a heater in the gas sensor to be regularly changed. CONSTITUTION:A gas sensor 2 which makes use of the change in resistance level of metallic oxide semiconductor is disposed behind a heat exchanger 06. A timer 28 operates in, for instance, 60 second cycles to control a switch 20 which cyclically changes the power applied to a heater 6. During the initial 20 seconds, the switch 20 is turned on to heat-clean the sensor 2, and, during the following 40 seconds, the switch 20 is turned off to maintain the sensor 2 at a lower temperature. In 40 seconds from the moment the switch 20 is turned off, the temperature of the sensor 2 will be 120 deg.C when the exhaust gas temperature is 100 deg.C. On the basis of the resistance level of the sensor 2 at the 40th second, the CO level is measured. This way, the temperature- dependency of the sensor in the lower temperature zone changes drastically, and it does not indicate the valley type temperature characteristics any more even if the exhaust gas temperature fluctuates. |
