GB1582453A - Hydraulic controller - Google Patents

Description

(54) HYDRAULIC CONTROLLER (71) We, BATON CORPORATION, a cor poration organised and existing under the laws of the State of Ohio, of 100 Erieview Plaza, Cleveland, Ohio 44114. United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the' method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a con trol for use with a variable displacement hydraulic pump or motor.

It is common in designing controls for hydrostatic transmissions to design a dis tinct control for each desired function. For example, a pressure override (P.O.R.) con trol is designed to monitor the high pres sure of a transmission to protect the trans mission from extended excessive overloads.

P.O.R. controls are well known in the art and will be disclosed, in part, in the present' application. Further, an anti-stall control is used to destroke the swashplate of a pump in response to loading of the prime mover of the pump. Anti-stall controls generally make use of governors (see U.S. Letters Patent 2,516,662 and 2,976,685) to directly control movement of a valve spool and thereby control fluid pressure. Another type of control is a phasing control which is used to first increase the displacement of the swashplate of a pump in a hydrostatic trans mission to its maximum and then decrease the displacement of the swashplate motor to a minimum during an increase in speed of the transmission and to reverse such process during a decrease in speed. Phasing controls generally make use of cams (see U.S. Letters Patent, 2,516,662).. Yet a further control is an input torque limiter (I.T L.) control which matches the torque of a hydrostatic transmission to that of the prime mover.

I.T.L. controls generally make use of cams to reset the compensating override pressure for each swashplate position to maintain a constant value of system pressure times pump displacement. Other known. I.T.L.

controls are hydraulic wherein a pressure drop across a compensating or override spool is maintained proportional to the pump displacement. This is generally accomplished by a variable orifice. Further, other known I.T.L. controls are electrical. In the electrical I.T.L. controls the displacement of the pump and the system pressure are each measured and then multiplied to produce a signal which is then used to control the displacement of the pump. All of the electrical I.T.L. controls which applicant is aware of make use of a pressure transducer.

Although each of the preceding referenced controls perform their respective functions satisfactorily, they are relatively cumbersome, complicated, difficult to adjust, and expensive. Further a separate, distinct control exists for each of the functions. Generally, the parts of each of the controls cannot be interchanged with parts from another control.

In accordance with the invention there is provided a control for use with a variable hydraulic pump unit or motor unit having a relatively high pressure fluid conduit and a relatively low pressure fluid conduit and fluid operable means for varying the displacement of said unit, a source of fluid at a substantially constant pressure irrespec tive -of the displacement of said unit and a drain, said control comprising: A. a housing defining an axially extending bore; B; a first port in said housing communicating with said bore and adapted for fluid communication with said fluid operable means; C. a second port in said housing communicating with said bore and adapted for fluid communication with'said source of fluid; D. a third port in said housing com- municating with said bore and adapted for fluid communication with said drain; - E. valve means in said bore and having a, first axial position communicating said first port with one of said second and third ports and a second axial position communicating said first port with the other of said second and third ports; F. spring biasing means to bias said valve means axially toward said first position; G. second biasing means to bias said valve means against said spring biasing means axially toward said second position, said second biasing means including (1) a fluid chamber, (2) inlet conduit means adapted to communicate said source of fluid under pressure with said fluid chamber, (3) inlet fluid flow restriction means within said inlet conduit means to re strict fluid flow from said source of fluid to said fluid chamber, (4) means responsive to the pressure of fluid within said fluid chamber to bias said valve means toward said second position, and (5) 'means responsive to a signal to vary the pressure of the fluid within said fluid chamber.

An arrangement embodying the invention will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 illustrates a hydrostatic transmission incorporating an electro-hydraulic control according to a feature of the invention, and Fig. 2 is a cross sectional view partly in schematic of the electro-hydraulic control illustrated in Fig. 1.

The hydrostatic transmission of Fig. 1 includes a variable displacement swashplate axial piston pump 10 hydraulically coupled to a fixed displacement motor 12 via conduits 14 and 16. Pump 10 is a well known type and includes an input shaft 18 which is used to drive the rotating group of the pump and also drive a charge pump 20 hydraulically coupled via check valves 22 and 24 respectively to conduits 14 and 16.

Pump 10 further includes a swashplate 26 which is movable cross center by a pair of known piston-cylinder servos 28 and 30.

Motor 12 includes an output shaft 32.

Hydraulically coupled in parallel with motor 12 is a known control mechanism 34 which includes a shuttle valve, a high pressure relief valve and a charge pressure relief valve. A charge pump relief valve 36 is hydraulically coupled to the output of charge pump 20. Pump 10, motor 12, and charge pump 20 are all in hydraulic communication with a reservoir 38. A filter 40 is provided in the drain conduit from pump 10 and motor 12 to reservoir 38.

Servos 28 and 30 are hydraulically coupled via conduits 42 and 44 to a manual servo control valve 46. Conduit 48 communicates the spring chamber of control valve 46 with the reservoir. Another conduit 50 communicates the bore of control valve 46 with the charge pump as is well known in the art. Control valve 46 includes a control lever 52 and linkage connecting the control valve spool 54 with swashplate 26 to center spool 54 when the position of the swashhplate matches the desired position set by control lever 52.

All of the preceding elements are well known in the art of hydrostatic transmission controls. Accordingly, a further description of the operation of these elements does not appear to be warranted. The remaining portion of the specification will therefore be directed toward a description of the electrohydraulic control 56 and its operation with the previously described portions of the hydrostatic transmission.

Electro-hydraulic control 56 includes a housing defining a first bore 58 and a second bore 60. A plurality of axially spaced annular grooves 62, 64, and 66 are provided in first bore 58 and respectively are in fluid communication with charge pump 20, servo control valve 46, and reservoir 38.

A spool 68 is located within bores 58 and 60 and includes a pair of axially spaced lands 70 and 72 in bore 58 and another land 74 in bore 60. An adjustable spring 76 resiliently biases spool 68 to the right in Fig. 1 to the stop position illustrated thereby opening communication between annular grooves 62 and 64.

A pair of chambers 80 and 82 are defined on opposite sides of land 74 within bore 60. Chamber 80 is always in fluid communication with reservoir 38 while chamber 82 is in fluid communication with charge pump 820 via an orifice 84 and with reservoir 38 via a conduit 86 and a variable force valve 88.

Valve 88 includes a spool 90 upon which a variable force is exerted. Progressive movement of spool 90 to the left in Fig. 1 results in the progressive closing of opening 92 thus creating a variable orifice. Accordingly, progressive movement of spool 90 to the right in Fig. 1 progressively opens opening 92.

The leftward force exerted on spool 90 is directly related to the amount of electrical current flowing from an electrical control 94.

Electrical control 94 is coupled to a power source 96 and in the illustrated embodiment to a swashplate position indicator 98. The swashplate position indicator includes a rheostat 100 and a pointer 102. Accordingly, an electrical signal indicative of swashplate position is provided via swashplate position indicator 98 to electrical control 94. As is well known, the position of swashplate 26 of pump 10 is directly related to the displacement of pump 10 and accordingly the volume of fluid flowing from pump 10 to motor 12 at a given speed of input shaft 18.

Electro-hydraulic control 56 further includes a roller needle 104 having one end in contact with land 74 and the other end hydraulically coupled via a shuttle valve 106 to the high pressure conduit 14 or 16.

Accordingly, the leftward force exerted by roller needle 104 on spool 68 will be directly proportional to the highest pressure within conduits 14 and 16. This pressure in most instances will be the pressure of the fluid flowing from pump 10 to motor 12 to drive output shaft 32.

The electro-hydraulic control 56 is illustrated as being connected as an input torque limited for the hydrostatic transmission. As will be hereinafter described it may be used in a number of other ways to control the operation of the hydrostatic transmission simply by providing different electrical controls 94 having different inputs.

As described electro-hydraulic control 56 operates in the following manner. It is well known in the hydraulic art that system pressure times displacement (volume of hydraulic fluid) is directly related to the torque of the hydraulic system. Therefore by maintaining the multiple of system pressure times displacement constant one can provide torque limiting means for the system and thereby match the maximum torque of the hydraulic system with the maximum torque provided by the prime mover used to drive input shaft 18. As illustrated, the displacement of pump 10 is provided via swashplate position indicator 98 to electrical control 94.

The system pressure is provided via shuttle valve 106 to a piston in the form of a needle roller 104. As the system pressure acting on the needle roller increases and overcomes the force of spring 76, the pressure of the fluid ported from charge pump 20 to servo control valve 46 is reduced. This occurs by movement of land 72 to a position in which annular grooves 64 and 66 are placed in commmunication with one another. As the pressure to servo control valvce 46 is reduced the centering moment of pump 10 and the springs within servos 28 and 30 act to decrease the displacement of the pump to that required to maintain the said system pressure. As the displacement is decreasing, however, an electrical signal is being fed via swashplate position indicator 98 to electrical control 94. This results in a decrease in leftward force on spool 90 thereby reducing the pressure of the fluid in chamber 82 and accordingly allowing spool 68 to move back to the right in Fig. 1 and port fluid from charge pump 20 to servo control valve 46.

Similarly, as system pressure is decreased, spool 68 will move to the right in Fig. 1 increasing the pressure of the fluid from charge pump 20 to control valve 46 and accordingly the displacement of pump 10.

However, as this is occurring, swashplate position indicator 98 will feed an electrical signal to electrical control 94 which will result in an increase in leftward force on spool 90 moving the spool toward opening 92 and thereby increasing the pressure in chamber 82. This increase in pressure will result in spool 68 moving to the left in Fig. 1 and returning to the desired position.

In operation, charge pump relief valve 36 is set to maintain a maximum charge pump pressure of about 200 psi. Variable force valve 88 is provided to maintain the pressure of the fluid within chamber 82 linearly from 10 psi to 150 psi depending upon the signal from electrical control 94. The high pressure relief valve in control mechanism 34 will generally be set in the area of 3500 psi to 6000 psi. Appropriate modification to the area of land 74 subject to fluid pressure in chamber 82 and the area of roller needle 104 subject to system pressure can be made by those skilled in the art. An operative design for the electronic circuit used in electrical control 94 may be made by those skilled in the art of electrical controls.

Referring now to Fig. 2 which illustrates a specific embodiment of an electro-hydraulic control according to the invention, charge pump 20 ports fluid to control 56 via passages 108 and 110. Passage 111 is in fluid communication with servo control valve 46 via conduit 50. A passage 112 fluidly communicates chamber 80 with reservoir 38.

Spool 68 is located in a multi-stepped bore 114, 116, and 118 and includes lands 120, 122, 124, 126, 128, and 130. Land 120 prevents fluid from flowing from bore 114 to the chamber housing adjustable spring 76. Land 122 or 124 contacts the wall of bore 114 depending upon the position of spool 68. Land 126 is spaced from the walls of bore 116 to allow fluid to flow from passage 111 through bore 114, bore 116 into chamber 80 and then through conduit 112 to the reservoir. Lands 128 and 130 are in contact with the wall of bore 1I8.

Variable force valve 88 is illustrated as a standard proportional pressure controller valve Model 80 provided by Fema Corporation, Portage, Michigan. The variable orifice defined by spool 90 and opening 92 in Fig. 1 is illustrated schematically in valve 88 by variable orifice 132. Orifice 132 as well as orifice 84 are component parts of the Fema valve. Passages 134 and 136 in control 56 are provided to direct fluid from passage 110 to orifice 84 via bore 118 and from there either to passage 86 or 112 depending upon the degree that variable orifice 132 is opened.

Adjustable- spring 76 includes an adjust able stop 138 which may be screwed into or out of control 56. The position of adjustable stop 138 will control the rightward force exerted by spring 76 on spool 68.

Briefly, in operation, the pressure of the fluid in chambers 82 and 140 of shuttle valve 106 will respectively be exerted against the areas of land 130 and needle roller 104 to bias spool 68 to the left in Fig. 2 against the force of spring 76. As spool 68 is moved to the left, the fluid flowing from charge pump 20 through passage 108 around land 122 to passage 111 and from there to servo control valve 46 is slowly restricted until a point is reached when land 122 makes contact with the wall of bore 114 to terminate such flow. At this point, land 124 begins to move away from the wall of bore 114 allow- - ing fluid communication between passage 111 and bore 116 to drain fluid from passage 111 into the reservoir. It may therefore readily be seen that the fluid pressure directed through passage 111 from charge pump 20 is directly dependent upon the position of spool 68 in control 56. The position of spool 68 is directly related to the force exerted by spring 76 and the force exerted by the pressure of fluid in chamber 82 against the area of land 130 and the force exerted by the pressure of fluid in chamber 140 against the area of needle roller 104.

Shuttle valve 106 may comprise a separate housing 142 which may be secured by bolts 144 to housing 146 of control 56. If desired, shuttle valve 106 may be removed and a flat plate may be bolted on housing 146 in its place. In this latter arrangement, the pressure of the fluid in chamber 82 and the force of spring 76 would be the only two factors used to position spool 68 within valve 56.

Various electrical controls can also be designed to operate variable force valve 88 and, accordingly, control the pressure of the fluid within chamber 82. These controls can have inputs from the positions of the swashplates of a variable displacement pump and/or a variable displacement motor.

Further, the pressure of the fluid in chamber 82 may be directly dependent upon system pressure by sealing passage 110 and removing needle roller 104 in the valve illustrated in Fig. 2. Electrical controls may also be operated by inputs from a prime mover rotating input shaft 18 of pump 10 and the position of swashplate 26 to prevent the prime mover from stalling during overload conditions. Other variations in the electrical controls are also contemplated.

By the foregoing, applicant has developed a single hydraulic control whose basic components may be readily changed to perform a number of control functions. It is to this hydraulic control that the following claims are directed. It should be appreciated that the orifice 132 may be varied in other ways, e.g., mechanically or hydraulically. Further, the fluid chamber 82 may be in communication with the spring end of spool 68 and.

be used to exert a force against the force, exerted by needle roller 104.

WHAT WE CLAIM IS:- 1. A control for use with a variable hydraulic pump unit or motor unit having a relatively high pressure fluid conduit and a relatively low pressure fluid conduit and fluid operable means for varying the displacement of said unit, a source of fluid at a substantially constant pressure irrespective of the displacement of said unit and a drain, said control comprising: A. a housing defining an axially extending bore; B. a first port in said housing communicating with said bore and adapted for fluid communication with said fluid operable means; C. a second port in said housing communicating with said bore and adapted for fluid communication with said source of fluid; D. a third port in said housing communicating with said bore and adapted for fluid communication with said drain; E. valve means in said bore and having a first axial position communicating said first port with one of said second and third ports and a second axial position communicating said first port with the other of said second and third ports; F. spring biasing means to bias said valve means axially toward said first position; G. second biasing means to bias -said valve means against said spring biasing means axially toward said, second position, said second biasing means including (1) a fluid chamber, (2) inlet conduit means adapted to communicate said source of fluid under pressure with said fluid chamber, (3) inlet fluid flow restriction means within said inlet conduit means to re strict fluid flow from said source of fluid to said fluid chamber, (4) means responsive to the pressure of fluid within said fluid chamber to bias said valve means toward said second position, and (5) means responsive to a signal- to vary the pressure of the fluid within said fluid chamber.

2. A circuit according to claim 1 further comprising: H. a pair of feed conduits communicating with said fluid operable means; and wherein I. said first port is connected for fluid

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. able stop 138 which may be screwed into or out of control 56. The position of adjustable stop 138 will control the rightward force exerted by spring 76 on spool 68. Briefly, in operation, the pressure of the fluid in chambers 82 and 140 of shuttle valve 106 will respectively be exerted against the areas of land 130 and needle roller 104 to bias spool 68 to the left in Fig. 2 against the force of spring 76. As spool 68 is moved to the left, the fluid flowing from charge pump 20 through passage 108 around land 122 to passage 111 and from there to servo control valve 46 is slowly restricted until a point is reached when land 122 makes contact with the wall of bore 114 to terminate such flow. At this point, land 124 begins to move away from the wall of bore 114 allow- - ing fluid communication between passage 111 and bore 116 to drain fluid from passage 111 into the reservoir. It may therefore readily be seen that the fluid pressure directed through passage 111 from charge pump 20 is directly dependent upon the position of spool 68 in control 56. The position of spool 68 is directly related to the force exerted by spring 76 and the force exerted by the pressure of fluid in chamber 82 against the area of land 130 and the force exerted by the pressure of fluid in chamber 140 against the area of needle roller 104. Shuttle valve 106 may comprise a separate housing 142 which may be secured by bolts 144 to housing 146 of control 56. If desired, shuttle valve 106 may be removed and a flat plate may be bolted on housing 146 in its place. In this latter arrangement, the pressure of the fluid in chamber 82 and the force of spring 76 would be the only two factors used to position spool 68 within valve 56. Various electrical controls can also be designed to operate variable force valve 88 and, accordingly, control the pressure of the fluid within chamber 82. These controls can have inputs from the positions of the swashplates of a variable displacement pump and/or a variable displacement motor. Further, the pressure of the fluid in chamber 82 may be directly dependent upon system pressure by sealing passage 110 and removing needle roller 104 in the valve illustrated in Fig. 2. Electrical controls may also be operated by inputs from a prime mover rotating input shaft 18 of pump 10 and the position of swashplate 26 to prevent the prime mover from stalling during overload conditions. Other variations in the electrical controls are also contemplated. By the foregoing, applicant has developed a single hydraulic control whose basic components may be readily changed to perform a number of control functions. It is to this hydraulic control that the following claims are directed. It should be appreciated that the orifice 132 may be varied in other ways, e.g., mechanically or hydraulically. Further, the fluid chamber 82 may be in communication with the spring end of spool 68 and. be used to exert a force against the force, exerted by needle roller 104. WHAT WE CLAIM IS:-

1. A control for use with a variable hydraulic pump unit or motor unit having a relatively high pressure fluid conduit and a relatively low pressure fluid conduit and fluid operable means for varying the displacement of said unit, a source of fluid at a substantially constant pressure irrespective of the displacement of said unit and a drain, said control comprising: A. a housing defining an axially extending bore; B. a first port in said housing communicating with said bore and adapted for fluid communication with said fluid operable means; C. a second port in said housing communicating with said bore and adapted for fluid communication with said source of fluid; D. a third port in said housing communicating with said bore and adapted for fluid communication with said drain; E. valve means in said bore and having a first axial position communicating said first port with one of said second and third ports and a second axial position communicating said first port with the other of said second and third ports; F. spring biasing means to bias said valve means axially toward said first position; G. second biasing means to bias -said valve means against said spring biasing means axially toward said, second position, said second biasing means including (1) a fluid chamber, (2) inlet conduit means adapted to communicate said source of fluid under pressure with said fluid chamber, (3) inlet fluid flow restriction means within said inlet conduit means to re strict fluid flow from said source of fluid to said fluid chamber, (4) means responsive to the pressure of fluid within said fluid chamber to bias said valve means toward said second position, and (5) means responsive to a signal- to vary the pressure of the fluid within said fluid chamber.

2. A circuit according to claim 1 further comprising: H. a pair of feed conduits communicating with said fluid operable means; and wherein I. said first port is connected for fluid

communication with at least one of said feed conduits.

3. A circuit according to claim 2, further comprising control valve means interposed between said first port and said feed conduits to selectively port fluid from said first port to one df said feed conduits and from said other feed conduit to drain, and to port fluid from said first port to said other feed conduit and from said one feed conduit to drain.

4. A control according to any preceding claim wherein said signal is electrical.

5. A control according to any one of the preceding claims further comprising: outlet conduit means in fluid communication with said fluid chamber and adapted for fluid communication with said drain; outlet fluid flow restriction means within said outlet conduit means to restrict fluid flow from said fluid chamber to said drain; and wherein said means responsive to a signal varies the amount of restriction of said outlet fluid flow restriction means to vary said pressure within said fluid chamber.

6. A control according to claim 5 wherein: said second biasing means further includes a fluid flow electrically responsive variable force valve defining a variable orifice in fluid communication with said outlet conduit; and said means responsive to a signal varies the force exerted by said variable force valve to vary said pressure within said fluid chamber.

7. A control according to any one of the preceding claims, wherein the signal is directly related to the displacement of said unit.

8. A control according to any one of the preceding claims further comprising: another fluid chamber; means responsive to pressure of fluid within said other fluid chamber to bias said valve means against said spring biasing means axially toward said second position; and conduit means adapted to communicate said relatively high pressure fluid conduit with said other fluid chamber.

9. A control for a hydrostatic transmission substantially as hereinbefore described with reference to the accompanying drawings.