Components torque detection device for a belt transmission

An arrangement for detecting torque in a belt-driven system inexpensively and with high precision makes use of the fact that belt tension varies with the torque load. The tension may be measured from the corresponding stretch of the belt, which allows a small variation with torque in the relative speeds of a driving and a driven or idle pulley. The arrangement shown detects the total torque imposed on a vehicle engine 1 by multiple accessories driven by a crankshaft pulley 6 via a belt transmission 7. The rotational speeds W1, W2 of the pulley 6 and an idle pulley 10 are detected and fed to a torque detector 400 which calculates the total torque of all the accessories and provides a signal to an engine controller 500. Alternatively, the belt tension is determined from the axle load on a belt tensioning device, or from its tension arm position. An automatic calibration system is described, which makes use of the known load imposed on an alternator when a rear screen heater is switched on.