Hybrid Transmission

A method of operating a transmission for a vehicle which includes a ground engaging structure driven from an output member of the transmission, the transmission including a first input member connected to a prime mover, and a second input member drivable by the operation of a hydraulic drive motor, and the transmission being operable to transmit drive from the first input member to the output member in mechanical drive mode, and from the second input member to the output member in hydrostatic drive mode, the first input member providing a drive input from the prime mover to a mechanical drive train which includes a gear ratio selection apparatus, and for mechanical drive mode, the gear ratio selection apparatus providing for one of a plurality of alternative gear ratios to be selected by the engagement and/or disengagement of at least one power-shift clutch device, and the second input member being connected via a drive path to the output member, and there being a power-shift clutch device between the hydraulic drive motor and the second input member which is operative when the transmission is in hydrostatic drive mode, to transmit drive established by the operation of the hydraulic drive motor to the second input member, the method including operating the transmission in hydrostatic drive mode with the power-shift, hydrostatic drive, clutch device engaged and no gear ratio selected by the gear ratio selection apparatus, and while the vehicle is still traveling, selecting a gear ratio of the mechanical drive train by engaging or disengaging at least one power-shift clutch device of the gear ratio selection apparatus and disengaging the power-shift, hydrostatic drive, clutch device and continuing to drive the vehicle, in mechanical drive mode.