Alternator energized electric towing dynamometer

The national goals of more fuel efficient automobiles are being achieved in part by smaller and lighter vehicles resulting in demands for smaller and compatible instrumentation. Previously designed towing dynamometers for regular-sized vehicles were unable to provide adequately low drawbar levels for small cars like the Chevette. The dynamometer trailer provides a controllable retarding force on the passenger car to simulate hill climbing. This paper describes electrical and mechanical characteristics and operation of a dynamometer specifically designed for contemporary vehicles. An improved method is outlined for supplying controlled electrical power to eddy-current retarders used on the dynamometer. The improved system uses a 24 volt production alternator to supply controlled direct current to the eddy-current retarder. The current delivered to the eddy-current retarder is controlled by adjusting the alternator's field current. Rotational energy to turn the alternator is derived from forward motion of the dynamometer trailer. The improved system eliminates the need for the previously used gasoline-powered generator and silicon-controlled rectifier system. The improved method greatly reduces initial hardware cost, operating and maintenance cost, and noise level.