Control system for a hydrostatic transmission

Claim 2

A fluid system comprising a pump, a fluid motor connected in a circuit with and driven by the output of said pump, means for varying the fluid capacity of said circuit, and an auxiliary pump wherein the auxiliary pump feeds hydraulic fluid through a throttle orifice and a feed pipe into the circuit to make good leakage loss, and part of the hydraulic fluid delivered by the auxiliary pump is tapped off by a bleeder valve and diverted through a bleeder pipe for controlling said means for varying the fluid capacity, the bleeder valve having a first port connected to the bleeder pipe and a second port connected to exhaust and a valve member for controlling the pressure in the bleeder pipe and which is displaceable in one direction by the pressure drop across the throttle orifice, against the resistance of a restoring spring, to open the first port and to connect the bleeder pipe to the auxiliary pump delivery, and in the opposite direction to open the second port and to connect the bleeder pipe to exhaust, the valve member having at least one additional working face to which the pressure in the bleeder pipe is applied in the same direction as the spring force and wherein the valve member is in the form of a piston and contains the throttle orifice.

Claim 3

A fluid system comprising a pump, a fluid motor connected in a circuit with and driven by the output of said pump, means for varying the fluid capacity of said circuit, and an auxiliary pump wherein the auxiliary pump feeds hydraulic fluid through a throttle orifice and a feed pipe into the circuit to make good leakage loss, and part of the hydraulic fluid delivered by the auxiliary pump is tapped off by a bleeder valve and diverted through a bleeder pipe for controlling said means for varying the fluid capacity, the bleeder valve having a first port connected to the bleeder pipe and a second port connected to exhaust and a valve member for controlling the pressure in the bleeder pipe and which is displaceable in one direction by the pressure drop across the throttle orifice, against the resistance of a restoring spring, to open the first port and to connect the bleeder pipe to the auxiliary pump dElivery, and in the opposite direction to open the second port and to connect the bleeder pipe to exhaust, the valve member having at least one additional working face to which the pressure in the bleeder pipe is applied in the same direction as the spring force and wherein the valve member is in the form of a piston whereof a face of said piston adjacent the inlet forms a control edge cooperating with said first port to control communication from the inlet to the bleeder pipe.

Claim 4

A fluid system comprising a pump, a fluid motor connected in a circuit with and driven by the output of said pump, means for varying the fluid capacity of said circuit, and an auxiliary pump wherein the auxiliary pump feeds hydraulic fluid through a throttle orifice and a feed pipe into the circuit to make good leakage loss, and part of the hydraulic fluid delivered by the auxiliary pump is tapped off by a bleeder valve and diverted through a bleeder pipe for controlling said means for varying the fluid capacity, the bleeder valve having a first port connected to the bleeder pipe and a second port connected to exhaust and a valve member for controlling the pressure in the bleeder pipe and which is displaceable in one direction by the pressure drop across the throttle orifice, against the resistance of a restoring spring, to open the first port and to connect the bleeder pipe to the auxiliary pump dElivery, and in the opposite direction to open the second port and to connect the bleeder pipe to exhaust, the valve member having at least one additional working face to which the pressure in the bleeder pipe is applied in the same direction as the spring force and wherein the valve member is in the form of a piston whereof a face of said piston adjacent the inlet forms a control edge cooperating with said first port to control communication from the inlet to the bleeder pipe.

Claim 5

A fluid system comprising a pump, a fluid motor connected in a circuit with and driven by the output of said pump, means for varying the fluid capacity of said circuit, and an auxiliary pump wherein the auxiliary pump feeds hydraulic fluid through a throttle orifice and a feed pipe into the circuit to make good leakage loss, and part of the hydraulic fluid delivered by the auxiliary pump is tapped off by a bleeder valve and diverted through a bleeder pipe for controlling said means for varying the fluid capacity, the bleeder valve having a first port connected to the bleeder pipe and a second port connected to exhaust and a valve member for controlling the pressure in the bleeder pipe and which is displaceable in one direction by the pressure drop across the throttle orifice, against the resistance of a restoring spring, to open the first port and to connect the bleeder pipe to the auxiliary pump delivery, the valve member having at least one additional working face to which the pressure in the bleeder pipe is applied in the same direction as the spring force and wherein the valve member is in the form of a stepped piston having a step and a shoulder formed by the step and the shoulder communicates with the bleeder pipe and provides a control edge cooperating with said second port to control communication from the bleeder pipe to exhaust.

Claim 6

A fluid system comprising a pump, a fluid motor connected in a circuit with and driven by the output of said pump, means for varying the fluid capacity of said circuit, and an auxiliary pump wherein the auxiliary pump feeds hydraulic fluid through a throttle orifice and a feed pipe into the circuit to make good leakage loss, and part of the hydraulic fluid delivered by the auxiliary pump is tapped off by a bleeder valve and diverted through a bleeder pipe for controlling said means for varying the fluid capacity, the bleeder valve having a first port connected to the bleeder pipe and a second port connected to exhaust and a valve member for controlling the pressure in the bleeder pipe and which is displaceable in one direction by the pressure drop across the throttle orifice, against the resistance of a restoring spring, to open the first port and to connect the bleeder pipe to the auxiliary pump delivery, the valve member having at least one additional working face to which the pressure in the bleeder pipe is applied in the same direction as the spring force and wherein the valve member is in the form of a stepped piston having a step and a shoulder formed by the step and the shoulder communicates with the bleeder pipe and provides a control edge cooperating with said second port to control communication from the bleeder pipe to exhaust.