Hydrostatic self-regulating drive system

Claim 2

A hydrostatic drive system comprising: an internal combustion engine; a main pump driven by the engine and having a control element displaceable to vary the pump displacement; a control pump driven by the engine; an output motor having a control element displaceable to vary the motor displacement and having a rotary output; conduits interconnecting the main pump and output motor for driving of the motor by the pump; a speed-measuring pump connected to the motor output and producing a pressure differential corresponding to the speed of the motor output; pump control means powered by the control pump and connected to the pump control element for adjusting the pump displacement; motor control means connected to the motor control element for adjusting the motor displacement; and engine control means including a first engine cylinder connected to the speed-measuring motor and operable thereby for adjusting the engine speed and a second engine cylinder connected to the control pump and operable thereby for affecting engine speed.

Claim 3

The drive system defined in claim 1 wherein the motor control means includes a motor cylinder connected to the motor control element; and a proportional valve connected between the control pump and the motor cylinder and pressurized on one side by the speed-measuring motor and on the other side by the main pump.

Claim 4

The drive system defined in claim 1, further comprising: means including respective pressure-relief valves connected to the conduits and to the pump control means for changing pump displacement when the pressure in either conduit exceeds the limit of the respective relief valve; and a changeover valve between the conduits and the motor control means for varying motor displacement when pressure in either conduit exceeds the limit of the respective relief valve.

Claim 5

A hydrostatic drive system comprising: an internal combustion engine having a control element displaceable to vary engine speed; a main pump driven by the engine and having a control element displaceable to vary the pump displacement; a control pump driven by the engine; an output motor having a control element displaceable to vary the motor displacement and having a rotary output; conduits interconnecting the main pump and output motor for driving of the motor from the pump; a speed-measuring pump connected to the motor output and producing a pressure differential corresponding to the speed of the motor output; a speed-setting valve connected to the speed-measuring pump for varying the pressure differential created thereby in accordance with desired speed; pump control means including a pump valve powered by the control pump, and a pump cylinder connected to the pump control element and pressurizable therethrough, actuators connected to the speed-measuring pump and effective to apply the pressure differential across the pump valve for adjusting pump displacement in accordance with desired speed; motor control means including a motor valve powered by the control pump, and a motor cylinder connected to the motor control element and pressurizable therethrough, respective actuators connected to the speed-measuring pump and to the conduits adjusting motor displacement in accordance with both the desired speed and the pressure in the conduits; engine control means including an idle cylinder connected to the engine control element and to the control pump and pressurizable by the control pump for establishing a predetermined minimum engine speed, and an engine cylinder connected to the speed-measuring pump for varying engine speed in accordance with desired speed; and valve means connected between both conduits and the pump valve for reducing pump displacement when the pressure in the conduit exceeds a predetermined limit.

Claim 6

A hydrostatic drive system comprising: an internal combustion engine having a control element displaceable to vary engine speed; a main pump driven by the engine and having a control element displaceable to vary the pump displacement; a control pump driven by the engine; an output motor having a control element displaceable to vary the motor displacement and having a rotary output; conduits interconnecting the main pump and output motor for driving of the motor from the pump; a speed-measuring pump connected to the motor output and producing a pressure differential corresponding to the speed of the motor output; a speed-setting valve connected to the speed-measuring pump for varying the pressure differential created thereby in accordance with desired speed; pump control means including a pump valve powered by the control pump, and a pump cylinder connected to the pump control element and pressurizable therethrough, actuators connected to the speed-measuring pump and effective to apply the pressure differential across the pump valve for adjusting pump displacement in accordance with desired speed; motor control means including a motor valve powered by the control pump, and a motor cylinder connected to the motor control element and pressurizable therethrough, respective actuators connected to the speed-measuring pump and to the conduits adjusting motor displacement in accordance with both the desired speed and the pressure in the conduits; engine control means including an idle cylinder connected to the engine control element and to the control pump and pressurizable by the control pump for establishing a predetermined minimum engine speed, and an engine cylinder connected to the speed-measuring pump for varying engine speed in accordance with desired speed; and valve means connected between both conduits and the pump valve for reducing pump displacement when the pressure in the conduit exceeds a predetermined limit.