Hydraulic transmission system

Claim 1

An hydraulic transmission system comprising a pump having a housing, a rotor supported therein, a plurality of radial pistons slidable in the rotor, a ring surrounding the rotor engageable by the pistons and displacable to vary its eccentricity with respect to the rotor, a pair of ports in the rotor for fluid displaced by the pistons, passages communicating with the said ports and with a motor driven, in use, by the pump, a flow restrictor in one of said passages, actuating means responsive to the difference in the fluid pressures on opposite sides of the restrictor to displace said ring and means for biassing the ring towards one extremity of its displacement, said actuating means comprising a pair of actuating elements slidable in diametrally opposite bores in the housing within said ring, said actuating elements engaging said ring internally and said bores communicating with said one passage on opposite sides of said flow restrictor, the arrangement being such that an increase in the said fluid pressure difference urges the ring against the biassing means in a direction to reduce the stroke of the pistons.