This paper introduces a high accuracy method of measuring crankshaft angular position of an I-C engine. The method uses a sensor which couples magnetically to the starter ring gear. There are many automotive applications of this measurement of crankshaft angular position including ignition timing reference, engine performance measurement and certain diagnostic functions. The present paper disusses only the ignition timing application. Engine performance measurements are reported in refs. (1,2,3). The diagnostic application is discussed in refs. (4-5).
The passage of a starter ring gear tooth past the sensor axis causes a pulse to be generated in the sensor output. The waveform of this sensor voltage is independent of engine angular speed (including zero speed). However, this waveform is a function of gear tooth profile and is consequently influenced by gear wear.
The present method uses a finite state machine to process the sensor output signal. This method is highly versatile and is readily adaptable to provide a signal having suitable format for timing reference for an arbitrary electronic ignition system. The method is particularly well suited for a distributorless ignition system.
Another benefit of the finite state machine signal processing is its ability to correct for sensor errors. Sensor errors can occur randomly due for example to electrical noise and, in extreme cases, to broken ring gear teeth. The error correcting feature makes this method highly fault tolerant and essentially insensitive to the condition of the ring gear.