Abstract: As a rotary pump, which is typically provided on an automobile, is provided with two alternative sources of motive power, typically including a driving connection to the automotive engine, and driving connection to an electric motor. These driving connections may be unidirectionally clutched in such a manner as to cause the electric motor to drive the rotary pump only when the pump is to be driven but the automotive engine is not operating up to a predetermined speed. Typically, the rotary pump is of the eccentrically mounted rotor type having radially outwardly protruding spring-loaded pistons effectively in contact with a camming ring. A slider is shown provided between the housing and the ring for effectively varying the magnitude of eccentricity of the rotor and thus for effectively smoothly varying the capacity of the pump.