Hydrostatic drive with radially-nested radial-roller pump and motor having common displacement control ring

An adjustable hydrostatic drive unit, particularly for the auxiliary units of motor vehicle internal combustion engines, comprising a pump and a motor arranged radially one inside the other in a common housing around a drive shaft and an eccentric control ring, having inner and outer curved ring surfaces, arranged between said pump and said motor, said pump and motor being connected together hydraulically and having delivery volumes adjustable in opposite senses, characterized in that the drive shaft passes through the side plates of the housing and has a projecting end that rotates in an inner bushing that receives said shaft end and has an eccentric, sickle-shaped shoulder that engages in a throughbore in a front face of said control ring, and said inner bushing is coaxially surrounded by an outer bushing having a nose that projects into a radial groove in said control ring, whereby relative rotation of said inner and outer bushings effects radial or rotary displacement of said control ring.