Hydraulic drive for construction machine

A hydrostatic transmission comprising:

• a hydraulic motor comprising:
• a fixed casing comprising principle fluid supply and exhaust conduits,
• a reaction member fast with the casing,
• a cylinder block mounted for relative rotation about an axis of rotation with respect to said reaction member and which comprises a plurality of cylinder and piston assemblies, disposed radially with respect to the axis of rotation and capable of being supplied with fluid under pressure,
• an inner fluid distributor valve fast with the casing with respect to rotation about the axis of rotation, and comprising distribution conduits capable of placing the cylinders in communication with the principal fluid supply and exhaust conduits, and
• a driving shaft having a first end and a second end, and extending inside the casing coaxially to the axis of rotation and capable of being driven in rotation with the cylinder block,
• the hydraulic motor being a low-speed, high-torque motor, and further comprising, disposed inside the casing:
• a coupling member fast in rotation with the cylinder block,
• first mechanical engagement means for connecting the coupling member and the driving shaft in rotation,
• a step-up gear comprising at least one step-up member, capable of driving the driving shaft in rotation and mounted on a secondary shaft having an axis parallel to the axis of rotation of the motor, and
• second mechanical engagement means for connecting the coupling member and the step-up gear in rotation,
• the coupling member being mobile between a first position in which the first mechanical engagement means are activated, while the second mechanical engagement means are de-activated, and a second position in which the second mechanical engagement means are activated, while the first mechanical engagement means are de-activated,
• the motor comprising means for controlling the displacement of the coupling member between said first and second position,
• the driving shaft is a through shaft capable of forming a portion of a main shaft of a transmission of a vehicle, and
• wherein the first and second ends of the driving shaft are respectively connected to a first and to a second axle of a vehicle.