Abstract: Autocalibration of the camshaft phasing sensor of a closed-loop variable valve timing system of an internal combustion engine. The camshaft phasing adjustment mechanism comprises a cam that changes the camshaft phasing. This cam is provided with a dwell that occurs at a known true phasing of the camshaft. The cam is commanded to operate to the dwell, and the lack of change in the sensor output indicates when the dwell is reached. At this time the sensor output should exactly indicate the known camshaft phasing that is produced by the adjustment cam dwell. If it does not, the difference is calculated and forms an offset that is algebraically applied to the sensor output thereby calibrating the sensor.

Abstract: A variable camshaft timing system for an internal combustion engine varies the relative angular position between the intake camshaft and the exhaust camshaft by controlling the path of the timing belt means. A first belt means is interconnected at one end of the engine between the crankshaft and the exhaust camshaft. At the other end of the engine the intake camshaft and the exhaust camshaft are connected by a second belt means for rotating the intake camshaft from the rotational drive supplied via exhaust camshaft. Idler arms are positioned for controlling the path and tension in the second belt means for varying the timing of the intake camshaft relative to the exhaust camshaft. A motor means operates to position the idler arms through a positioning cam means.