Method and system for internal combustion engine oxygen sensor heating

Abstract

An internal combustion engine has an exhaust system and an oxygen sensor fitted to the exhaust system including a sensor element and an electrically powered heater for heating the sensor element. A method is disclosed for controlling the power supplied to the heater by determining a target value therefor according to engine operational parameters, by applying a smoothing correction to the target value to produce an actual value, and by supplying power to the heater in an amount according to this actual power value. The smoothing may be done by time-smoothing, and may be done by performing the calculation repeatedly in a cycle and by setting the actual power value amount equal to a function of this target power value and of values of this actual power value amount determined in previous cycles. This function may take the form of a weighted average, and as a special case such a weighted average may use only the actual power value amount determined in the previous cycle. Accordingly it is ensured that the heater is properly operated even in the case of quick variation in the engine operational parameters, which due to system inertia will only alter the exhaust gas temperature with a certain time lag. Thus, the oxygen sensor is properly kept heated up, even in such quick engine operational state alteration conditions, and engine performance and the quality of exhaust gas emissions at such a time are ensured to be good. A system is also described for implementing this method.