Abstract: A cross drive transmission having a hydromechanical propulsion drive and hydrostatic steer drive. In the controls, a ratio governor has a set speed control wherein set speed is established in accordance with throttle position, steer request, engine power and brake torque. Advance and return signals regulate the speed ratio of the hydromechanical drive so input speed equals the set speed. A rate of change control provides fast increase of the return signal, slow increase of the advance signal in higher ratios and very slow increase of the advance signal in low ratio. Manual controls, return and advance signal control valves, shift signal valves and shift valves, in neutral, provide substantially zero displacement in the hydrostatic unit and neutral in the gear unit, and, in drive positions, coordinate hydrostatic ratio control and gear ratio control for continuous variable ratio change in the hydromechanical propulsion drive.

Abstract: A hydrostatic transmission, especially for a steer drive of a propulsion and steer drive transmission, having a variable displacement pump, a fixed displacement motor, and a pump displacement control, and including a low pressure fluid source supplying the charging and lubrication systems of the hydrostatic transmission and a high pressure source. The high pressure source, in a normal range of low hydrostatic power pressure values, provides control pressure regulated in proportion to high hydrostatic power pressure to meet the pressure requirements of the pump displacement control which increase with high hydrostatic power pressure. In an abnormal and lower range of low hydrostatic pressure values, the control pressure is regulated to decrease to zero as the low hydrostatic power pressure decreases to a minimum operating pressure value.