Hydraulic variable speed drive

Variable speed drive assembly of the type that comprise an hydraulic pump and an hydraulic motor, in which the power transmission is achieved by means of a fluid circulating in close circuit between them, such that the flow rate displaced by the hydraulic pump must be received by the hydraulic motor and subsequently returned to the hydraulic pump, and in which both the hydraulic pump and the hydraulic motor are vane pumps, constituted by a cylinder (29,39) and a rotor (40,50) from which emerge radially vanes (41,51) which, by extending outwards to fit against the inner wall of said cylinder (29,39) and laterally to fit against two covers (30,55), form cells that are fluidtight from each other, one or both of said covers being provided with a central opening to let the shafts of the rotors (40,50) protrude outwards therethrough, any rotation ratio between the rotor (40) of the hydraulic pump and the rotor (50) of the hydraulic motor, between zero and a maximum value, being achieved by varying the eccentricity of the rotor (40) of the hydraulic pump, of the rotor (50) of the hydraulic motor or of both, characterized in that:

• the cylinder (29) of the hydraulic pump, the cylinder (39) of the hydraulic motor and their respective end covers (30,55) form an integral body constituting the variable drive assembly, the cylinders having geometric axes (65,66) that are parallel but not coincident, and the only possible movement of said variable drive assembly being rotation with respect to a third geometric axis (23) that is static with respect to a support member (10,11) and parallel to said geometric axes (65,66) of the cylinders;
• the rotor (40) of the hydraulic pump and the rotor (50) of the hydraulic motor have a common geometric axis (22), with a static and eccentric position with respect to said support member (10,11), parallel to the geometric axes (65,66) of the cylinders of the hydraulic pump and the hydraulic motor and displaced a distance (E) with respect to said third geometric axis (23), both rotors (40,50) being able to turn independently from each other with respect to said common geometric axis (22);
• the rotation of said variable drive assembly is actuated from the outside and causes, through a variation of the eccentricity of the rotors (40,50) with respect to their respective cylinders (29,39), the effect of variation of said rotation ratio between the rotor (40) of the hydraulic pump and the rotor (50) of the hydraulic motor, the position of the variable drive assembly with respect to said support member being defined by an angle .alpha., .alpha.=0 corresponding to a starting position in which the cylinder (29) of the hydraulic pump and its rotor (40) are concentric.