Hybrid hydraulic drive system with engine integrated hydraulic machine

A hybrid hydraulic drive system for a motor vehicle, said system operable in three modes of operation including a driving mode, a retarding mode and a neutral mode, said system comprising:

• a prime mover and a transmission connecting said prime mover to drive wheels;
• at least one fluid energy storage accumulator operable to store and release a pressurized fluid;
• a reversible hydraulic machine operatively coupled to an output shaft of said prime mover upstream of the transmission, said reversible hydraulic machine being in fluid communication with said at least one energy storage accumulator;
• and
• said hybrid hydraulic drive system being arranged such that in said retarding mode said reversible hydraulic machine retards the drive wheels of the vehicle by pumping fluid into said at least one energy storage accumulator, in said driving mode said reversible hydraulic machine supplies a supplementary power to the drive wheels of the vehicle using said pressurized fluid from said at least one energy storage accumulator to assist propulsion of said vehicle, and in said neutral mode said reversible hydraulic machine is disconnected from said prime mover to render said reversible hydraulic machine substantially inoperative to exert any significant driving or retarding influence on said drive wheels;
• said hybrid hydraulic drive system thereby in use being adapted to supply said supplementary regenerative power and retardation to said drive wheels substantially independently of said prime mover.