Variable set point speed control for hydrostatic transmissions

Claim 2

A control system for hydraulic transmissions having a variable displacement pump driving a hydraulic motor in a hydraulic system comprising: a regulated air pressure signal; sensing means in said hydraulic system for creating a fluid pressure signal responsive to the flow of hydraulic fluid in said hydraulic system; two opposing pistons, one being responsive to said regulated air signal and the other being responsive to the fluid pressure signal of said sensing means; and means responsive to said opposing pistons for controlling the displacement of said variable displacement pump.

Claim 3

The apparatus of claim 1 wherein said sensing means is a venturi in that part of said hydraulic system which exhausts said hydraulic motor.

Claim 4

The apparatus of claim 1 further comprising: a high pressure air signal; and means for controlling said air responsive piston which when in a first position exhausts one side of said piston such that said air responsive piston opposes said fluid pressure responsive piston, and which when in a second position directs said high pressure air signal to one side of said air responsive piston for movement in opposition to the movement caused by said regulated air pressure signal on the other side of said air responsive piston.

Claim 5

The apparatus of claim 3 wherein said air responsive piston controlling means is a diaphragm operated valve operated by said regulated air signal which shifts from said second position to said first position when said regulated air signal exceeds a predetermined pressure, and which returns to said second position when said regulated air signal is reduced to said predetermined pressure.

Claim 6

In a hydraulic transmission system which includes a variable displacement pump having an adjustable control lever which controls the displacement of the pump, a hydraulic motor, a high pressure conduit conducting hydraulic fluid from the pump to the motor, and a low pressure conduit conducting hydraulic fluid from the motor to the pump, the combination comprising: a regulated pressurized air signal; two opposing pistons connected to each other wherein movement in one causes a corresponding movement in the other; controlling means for biasing the first of said opposing pistons in a first direction in response to said regulated pressurized air signal; sensing means for creating a pressure differential across the second piston of said opposing pistons in response to the flow of hydraulic fluid in said hydraulic transmission system thereby biasing said opposing pistons in a second direction opposite to said first direction; and means connected to said adjustable control lever responsive to movement in said opposing pistons for changing said control lever thereby changing the displacement of said variable displacement pump until movement of said opposing pistons ceases.

Claim 7

In a hydraulic transmission system which includes a variable displacement pump having an adjustable control lever which controls the displacement of the pump, a hydraulic motor, a high pressure conduit conducting hydraulic fluid from the pump to the motor, and a low pressure conduit conducting hydraulic fluid from the motor to the pump, the combination comprising: a regulated pressurized air signal; two opposing pistons connected to each other wherein movement in one causes a corresponding movement in the other; controlling means for biasing the first of said opposing pistons in a first direction in response to said regulated pressurized air signal; sensing means for creating a pressure differential across the second piston of said opposing pistons in response to the flow of hydraulic fluid in said hydraulic transmission system thereby biasing said opposing pistons in a second direction opposite to said first direction; and means connected to said adjustable control lever responsive to movement in said opposing pistons for changing said control lever thereby changing the displacement of said variable displacement pump until movement of said opposing pistons ceases.

Claim 8

The apparatus of claim 5 wherein said controlling means includes a two-position means for biasing said first piston in the first direction when in a first position, and for biasing said first piston in the second opposite direction when in a second position.

Claim 9

The apparatus of claim 5 wherein said sensIng means comprises a venturi in said hydraulic system, a fluid conduit communicating fluid pressure from the mouth of said venturi to one side of said second piston, and a fluid conduit communicating fluid pressure from the throat of said venturi to the second side of said second piston.

Claim 10

The apparatus of claim 5 wherein said sensing means is placed in said low pressure conduit.

Claim 11

In a hydraulic transmission system having: a reversible variable displacement pump having an adjustable control lever with a zero stroke position, a forward stroke range wherein the displacement of said pump is varied in the forward direction, and a reverse stroke range wherein the displacement of said pump is varied in the reverse direction; a hydraulic motor; and a hydraulic conduit system wherein hydraulic fluid is carried from said pump to said motor and returned from said motor to said pump; the combination comprising: a regulated air pressure signal; two opposing pistons connected to each other wherein movement in one causes a corresponding movement in the other; a two-position controlling means for biasing the first of said opposing pistons in a first direction in response to said regulated air pressure signal when said controlling means is in a first position, and for biasing said first piston in a second direction opposite to said first direction in response to said air signal when said controlling means is in a second position; a forward sensing means for creating a pressure differential in response to the flow of hydraulic fluid in said hydraulic conduit system when said controlling means is in the first position; a reverse sensing means for creating a pressure differential in response to the flow of hydraulic fluid in said hydraulic conduit system when said controlling means is in the second position; switching means for placing the pressure differential of said forward sensing means across said second piston so that said second piston is biased in said second direction when said controlling means is in the first position, and for placing the pressure differential of said reverse sensing means across said second piston so that said second piston is biased in said first direction when said controlling means is in the second position; and means connected to said adjustable control lever responsive to movement in said opposing pistons for changing said control lever thereby changing the displacement of said reversible variable displacement pump in either the forward or reverse stroke ranges until movement of said opposing pistons ceases.

Claim 12

In a hydraulic transmission system having: a reversible variable displacement pump having an adjustable control lever with a zero stroke position, a forward stroke range wherein the displacement of said pump is varied in the forward direction, and a reverse stroke range wherein the displacement of said pump is varied in the reverse direction; a hydraulic motor; and a hydraulic conduit system wherein hydraulic fluid is carried from said pump to said motor and returned from said motor to said pump; the combination comprising: a regulated air pressure signal; two opposing pistons connected to each other wherein movement in one causes a corresponding movement in the other; a two-position controlling means for biasing the first of said opposing pistons in a first direction in response to said regulated air pressure signal when said controlling means is in a first position, and for biasing said first piston in a second direction opposite to said first direction in response to said air signal when said controlling means is in a second position; a forward sensing means for creating a pressure differential in response to the flow of hydraulic fluid in said hydraulic conduit system when said controlling means is in the first position; a reverse sensing means for creating a pressure differential in response to the flow of hydraulic fluid in said hydraulic conduit system when said controlling means is in the second position; switching means for placing the pressure differential of said forward sensing means across said second piston so that said second piston is biased in said second direction when said controlling means is in the first position, and for placing the pressure differential of said reverse sensing means across said second piston so that said second piston is biased in said first direction when said controlling means is in the second position; and means connected to said adjustable control lever responsive to movement in said opposing pistons for changing said control lever thereby changing the displacement of said reversible variable displacement pump in either the forward or reverse stroke ranges until movement of said opposing pistons ceases.

Claim 13

The apparatus of claim 9 wherein said forward sensing means is located in that part of said hydraulic conduit system which returns hydraulic fluid from said motor to said pump when said movable control is in the forward stroke range, and said reverse sensing means is located in that part of said hydraulic conduit system which returns hydraulic fluid from said motor to said pump when said movable control is in the reverse stroke range.

Claim 14

The apparatus of claim 10 wherein said forward sensing means comprises a first check valve passing hydraulic fluid when said pump is in the forward stroke range and blocking hydraulic fluid when said pump is in the reverse stroke range, a first venturi in series with said first check valve, and a first bypass valve bypassing hydraulic fluid around said first check valve and said first venturi when said pump is in the reverse stroke range and directing hydraulic fluid through said first check valve and said first venturi when said pump is in the forward stroke range; and said reverse sensing means comprises a second check valve passing hydraulic fluid when said pump is in the reverse stroke range and blocking hydraulic fluid when said pump is in the forward stroke range, a second venturi in series with said second check valve, and a second bypass valve bypassing hydraulic fluid around said second check valve and said second venTuri when said pump is in the forward stroke range and directing hydraulic fluid through said second check valve and said second venturi when said pump is in the reverse stroke range.

Claim 15

The apparatus of claim 11 wherein said switching means comprises: a first valve means for communicating hydraulic fluid from the mouth of said first venturi to the first side of said second piston when said pump is in the forward stroke range, and for communicating hydraulic fluid from the throat of said second venturi to the first side of said second piston when said pump is in the reverse stroke range; and a second valve means for communicating hydraulic fluid from the throat of said first venturi to the second side of said second piston when said pump is in the forward stroke range, and for communicating hydraulic fluid from the mouth of said second piston when said pump is in the reverse stroke range.

Claim 16

The apparatus of claim 9 further comprising: stop means responsive to said two-position controlling means for preventing said opposing pistons from moving said adjustable control lever into the reverse stroke range when said controlling means is in its first position, and for preventing said opposing pistons from moving said adjustable control lever into the forward stroke range when said controlling means is in its second position.

Claim 17

The apparatus of claim 13 further comprising: shut-off means responsive to said regulated air signal for moving said first piston in the direction opposite to the direction said first piston is being biased by said regulated signal when said regulated air signal is below a predetermined minimum pressure until said opposing pistons are prevented from moving further by said stop means.

Claim 20

In a hydraulic transmission system having a hydraulic motor being driven by hydraulic fluid pumped by a reversible variable displacement pump, the method of changing the speed of said hydraulic motor from a speed in the forward direction to a set speed in the reverse direction comprising the steps of: creating a first force responsive to a regulated air signal; creating a second force responsive to the flow of said hydraulic fluid in the forward direction; decreasing the displacement in the forward direction of said reversible variable displacement pump responsive to said first force and said second force until zero displacement of said variable displacement pump is reached; reversing the displacement of said variable displacement pump responsive to said first force; creating a third force responsive to the flow of said hydraulic fluid in the reverse direction; opposing said first force with said third force; and increasing the displacement in the reverse direction of said reversible variable displacement pump responsive to said opposing first and third forces until said opposing forces are balanced.

Claim 21

In a hydraulic transmission system having a hydraulic motor being driven by hydraulic fluid pumped by a reversible variable displacement pump, the method of changing the speed of said hydraulic motor from a speed in the forward direction to a set speed in the reverse direction comprising the steps of: creating a first force responsive to a regulated air signal; creating a second force responsive to the flow of said hydraulic fluid in the forward direction; decreasing the displacement in the forward direction of said reversible variable displacement pump responsive to said first force and said second force until zero displacement of said variable displacement pump is reached; reversing the displacement of said variable displacement pump responsive to said first force; creating a third force responsive to the flow of said hydraulic fluid in the reverse direction; opposing said first force with said third force; and increasing the displacement in the reverse direction of said reversible variable displacement pump responsive to said opposing first and third forces until said opposing forces are balanced.