| 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 providing a gas sensor disposed behind a heat exchanger with a heater, and causing the power applied to said heater to be cyclically changed so the power may be supplied to the heater at a lower temperature zone where the CO level is more suitably detected. CONSTITUTION: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 a sensor 2, and, the following 40 seconds, it is turned on at about 1/12 duty ratio to maintain the sensor 2 at a lower temperature. In the lower temperature zone, 160 deg.C is the temperature at which the CO sensitivity peaks, but there is little change in characteristics in the range of 130 to 200 deg.C. However, the NOx sensitivity increases below 130 deg.C. At the same time, the dependency on the exhaust gas temperature increases, and so does the dependency on the output to the incomplete combustion mode. Therefore, the power is applied to the heater 6 even in the lower temperature zone in order to prevent the sensor temperature from decreasing unnecessarily. |
