System for controlling heating unit of exhaust monitor in IC engine

摘要

A system for controlling (13) the heating unit of an air/fuel sensor (11) monitoring the exhaust circuit (107) of an IC engine (10) optimises the energisation of the heater element (112) without reference to the cooling water temperature (142) during starting when th semiconductor switch (122) controlling the power supply (121) is maintained closed for an initial period. The duration of this period is determined by measuring the voltage and current in the element (112) to derive a resistance value for use as a temperature limiting threshold. At a time after starting which depends on other environmental and operating conditions e.g. RPM, throttle opening, atmosphere, etc. the ensuing control responds to these variables and to engine temperature.