System for discrimination of spurious crank encoder signals

A method for discrimination of spurious crankshaft encoder signals in an internal combustion engine having a crankshaft and a target wheel mounted for rotation with said crankshaft, said target wheel having a predetermined number of spaced apart teeth, each tooth having a rising edge and falling edge, said engine further having a crankshaft position encoder for generating a pulsed signal indicative of rotational performance of the crankshaft, and an engine controller for receiving the pulsed signal from the encoder and for controlling the timing of engine functions including but not limited to spark and fuel injection timing,

• the method comprising the following steps:
• a) triggering an interrupt service routine that generates a pulsed signal from every falling and rising edge of each tooth;
• b) calculating and storing a period of interrupt from each successive pulsed signal;
• c) comparing the periods of interrupt from successive pulsed signals to calculate engine speed and an instantaneous rate of acceleration or deceleration of the engine;
• d) using the calculated rate of engine acceleration or deceleration and the engine speed to calculate a predicted a time window for reception of the next successive pulsed signal;
• e) recognizing a next successive pulsed signal arriving within the predicted time window;
• and
• f) rejecting as spurious a next successive pulsed signal arriving outside the predicted time window.