Hydraulic actuation systems

A method controlling a hydraulic actuation system for an automated transmission system having;

• a hydraulic clutch actuator for controlling engagement of a clutch;
• a gear engagement actuator for controlling engagement of a gear;
• an accumulator;
• an electric motor driven constant displacement pump, an output of the motor driven pump being connected to the accumulator for charging thereof via a non-return valve,
• a main control valve for selectively connecting the accumulator to the hydraulic clutch actuator and/or the gear engagement actuator;
• a pressure transducer arranged to measure pressure of fluid in the accumulator;
• and
• a control means, said control means controlling energisation of the main control valve to effect a gear change;
• said method comprising;
• upon initiation of a gear change opening the clutch actuator to the accumulator to effect disengagement of the clutch;
• isolating the clutch actuator from the accumulator in order to clamp the clutch in a disengaged position at a point where the clutch is disengaged to an extent that it does not transmit torque but has not reached the extent of movement of the clutch actuator in the disengagement direction;
• switching on the pump motor to provide a predetermined accumulator pressure at a predetermined stage of the gear change;
• and
• reconnecting the clutch actuator to the accumulator to maintain the predetermined pressure or to change the pressure from the predetermined pressure in controlled manner.