Transmission

A series hydrostatic transmission for a vehicle, the vehicle comprising a plurality of wheels, the transmission comprising:

• a first hydraulic pump and a hydraulic motor each of which has a pumping mode in which it operates as a hydraulic pump and a motoring mode in which it operates as a hydraulic motor, the first hydraulic pump and the hydraulic motor each comprising a plurality of cylinders of cyclically varying working volume in which the displacement of hydraulic fluid through each cylinder is regulated by one or more electronically controllable valves, on each cycle of cylinder working volume, and in phased relationship to cycles of cylinder working volume with reference to a phase signal provided by a phase sensor, the pump being torque connected or torque connectable to at least one prime mover, the motor being torque connected or torque connectable to one or more of the wheels by way of a torque transmitting device, wherein the transmission has at least a first mode in which the pump and motor are fluidly connected to each other such that fluid pressurised by the pump drives the motor, a second mode in which energy from hydraulic fluid pressurised by the motor in the pumping mode is transferred to an energy store, and a third mode in which energy from the energy store drives the motor, and wherein the motor comprises a valve assembly disposed between a high pressure line and a working chamber of the motor, the valve assembly comprising:
• a main valve having a main valve element providing sealing contact with a valve seat;
• and a pilot valve for equalising pressure across the main valve element by placing the working chamber in direct fluid communication with the high pressure line.