| 摘要 |
PURPOSE:To control sensor temperature to a constant value in the entire air fuel ratio range and to improve measurement accuracy by switching a heater to duty control when a sensor output indicates an air fuel ratio range nearby an ideal air fuel ratio point. CONSTITUTION:The ideal air fuel ratio range (0.95<=lambda<=1.05) where a pumping current becomes extremely small is detected from the sensor output and the heater is switched to the duty control system. Namely, the heater control duty ratio is set constant. In another way, a microcomputer judges operation condition from an engine rotating speed, negative pressure, and water temperature and corrects the heater control duty ratio to a proper value. Consequently, the heater is brought under the duty control only nearby the ideal air fuel ratio point where the pumping current Ip becomes extremely small to disable temperature detection by a detecting element and switched to a feedback system in the range wherein temperature control is possible by a conventional system. The sensor temperature is controlled to the constant value without any defect in the temperature control throughout the entire range including a fuel rich range, the ideal air fuel ratio range, and a fuel lean range and the measurement accuracy is improved. |
