摘要 |
PURPOSE:To detect oxygen concentration accurately by providing a heater-power controlling means which controls power supplied to a heater so that the power is increased to a higher value than the lower limit value when the detected power supplied to the heater is less than the lower limit value of the power. CONSTITUTION:Power PW which is supplied to an oxygen sensor OS is controlled so that the resistance value RH of a heater HT in the sensor OS becomes a specified value RT. When the power PW supplied to the heater HT which is detected with a heater-power detecting means M1 is less than a lower limit value PO, the power PW is controlled so that the power PW supplied to the heater HT becomes higher than the value PO with a heater- power controlling means M4. The lower limit value of the power PO is determined in correspondence with the operating state which is detected with an operating-state detecting means M2. Namely, the PO is determined in consideration of the power value where the temperature of the sensor OS becomes too low to expect the normal operation of the sensor OS when the power PW supplied to the heater becomes lower than the value PO under the operating state. |