HYDROSTATIC GEAR MACHINE

A hydrostatic gear machine is described which comprises a pair of gear wheels meshing with one another, one of the gear wheels being an internally toothed annular gear wheel and the other an externally toothed pinion, the tooth profile of at least one of said wheels being at least substantially trochoidal; the tooth profile of a first one of the two wheels being defined as being obtained by rolling the first wheel with meshing on the other wheel. The teeth of at least one of said wheels bear the thus defined profile only on a limited zone having a length just sufficient for the ratio of the angles of rotation of the two wheels to be constant throughout rotation of the wheels, and have their profile set back, outside the said limited zone, by a sufficient distance to eliminate contact, outside the limited zone, with the teeth of the other gear wheel.