Hydrostatic transmission drive system

摘要

An improved drive system includes a pair of hydrostatic transmissions which are driven by a common engine or prime mover and are drivingly connected with different tracks of a vehicle. The input to output speed ratios of the hydrostatic transmissions are simultaneously varied by operating a single speed control valve to port control fluid pressure to pressure responsive secondary or control motors in pump and motor actuators of the hydrostatic transmissions. A pair of charge pumps are provided to charge the hydrostatic transmissions and provide control fluid. If the fluid pressure output of either of the charge pumps falls below a predetermined level, a control arrangement reduces the control fluid pressure transmitted to the pump and motor actuators by the speed control valve to deswash or destroke both of the transmissions. The control arrangement also short circuits the hydrostatic loops interconnecting the pump and motor units. In addition, the brakes of the vehicle are engaged to stop the vehicle. When the vehicle is to be stopped during normal operation, actuation of the brakes causes the control arrangement to effect a deswashing of the pump and motor units and a short circuiting of the hydrostatic loops.