Abstract: A drive system has an engine that operates a control pump and a hydraulic variable-displacement drive pump having a control element and connected to a hydraulic motor. A servocylinder operates the control element of the drive pump and is pressurized through a control line connected to the control-pump output. A control valve is connected between the control line and the sump of the system and is connected to the hydraulic line between the motor and the drive pump to reduce pressure in the control line when the higher pressure of the line between the drive pump and the motor rises within a predetermined range. Thus it is possible with a substantially constant engine speed to produce a substantially constant output torque, with only the displacement of the pump and pressure in the lines between the pump and the motor varying by appropriate control of the control-line pressure.

Abstract: A hydrostatic transmission has an input connected to a prime mover and an output connected through a speed-change transmission to a load. A control element of this transmission is urged in a direction tending to increase the transmission ratio by a control cylinder pressurized from a hydraulic tachometer operated by the transmission input, and is urged in the opposite direction to decrease the ratio by a regulating cylinder connected via a feed line to the hydraulic network interconnecting the pump and motor of the transmission. During speed change the two cylinders are depressurized and the regulating cylinder is isolated from the network.

Abstract: A hydrostatic transmission having a variable displacement pump whose control element varies the transmission ratio and output direction of the transmission is controlled by a hydraulic servomechanism including a direction-reversing valve and a cylinder connected to this valve. A direction selector acts upon the valve and a mechanical or hydraulic locking mechanism is provided to prevent shifting of the valve until the control element of the pump has been restored to its neutral position before direction change.

Abstract: A hydrostatic torque converter has a hydrostatic transmission and a stepped or gear transmission shiftable under load by selective actuation of respective clutches assigned to the gear trains. The variable-displacement pump is controlled hydrostatically to follow the switchover between clutches with the control pressure to the servocontrolling the displacement of the pump being regulated in response to the fluid pressures of the clutches through respective pressure modulation valves. As a consequence, the hydrostatic transmission compensates for the jump resulting from the shifting of the steps of the gear transmission and follows the stepping of the gear transmission outside the forced actuation of the transmission (positive switching overlap of the shifting clutches) in dependence upon the progress of load transfer from the released to the engaged clutch.

Abstract: An automatic control for an automotive-vehicle hydrostatic transmission in which the engine drives a variable-displacement hydrostatic (axial-piston) pump which is connected with the motor by hydraulic lines. The hydrostatic (axial-piston) motor can be connected to the wheels of the vehicle. The control circuit comprises a filling pump, a metering throttle, a reversing valve and an adjusting device. The metering throttle is provided in a bypass between the filling pump and the reversing valve and is connected to the line communicating with the control element. A further throttle is provided in this line and has a diameter/length ratio less than 1.

Abstract: A system for controlling the operation of a reversible hydrostatic transmission including an engine-driven pump, particularly for a self-propelled utility vehicle such as a forklift truck, comprises a switchover member coupled with a setting lever of the hydrostatic pump which is biased by a pair of counteracting springs into a normal centered position. A shift lever, upon being moved from "neutral" to "forward" or "reverse", causes a displacement of the switchover member into a corresponding off-normal position by a fluidic or electromagnetic directive force generally proportional to engine speed.