The present invention relates to a method and apparatus for controlling the torque of an internal combustion engine.
It is known that there can occur conditions which result in the engine speed of a vehicle oscillating which in turn causes an oscillation in the torque output from the engine. The torque oscillation can sometimes be audible or even result in a physical oscillation of the vehicle which is commonly called "kangarooing" in the United Kingdom. In some vehicles, torque oscillation of the engine occurs due to a mismatch of the resonant frequencies of the engine, transmission and final drive and this is inherent at certain vehicle and engine speeds. It has already been proposed to mitigate the effects of this torque oscillation by monitoring the rate of change of engine speed and to alter the ignition timing so as to alter the torque output of the engine. In other words, when a drop in engine speed is detected by the monitoring operation, engine torque is increased by advancing the ignition in order to counteract the drop. An increase in engine speed is likewise counteracted by retarding the ignition so as to damp out the oscillation.
This system is only possible because the resonant conditions are known and also the amount of phase shift between engine and wheel speed of the vehicle is a constant under these conditions. The requisite ignition timing variation can therefore be evaluated.
There exists another set of conditions which may induce "kangarooing" and that is during acceleration. Here, the phase shift between engine and wheel speed is not constant and so the technique proposed above cannot be used.