CA1159338A - Pilot-operated priority valve - Google Patents
Pilot-operated priority valveInfo
- Publication number
- CA1159338A CA1159338A CA000394011A CA394011A CA1159338A CA 1159338 A CA1159338 A CA 1159338A CA 000394011 A CA000394011 A CA 000394011A CA 394011 A CA394011 A CA 394011A CA 1159338 A CA1159338 A CA 1159338A
- Authority
- CA
- Canada
- Prior art keywords
- priority
- fluid
- pressure
- valve
- pilot
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Landscapes
- Fluid-Pressure Circuits (AREA)
Abstract
I Abstract of the Disclosure A priority valve includes a valve element which is shifted between a closed position blocking pump flow from a non-priority circuit and an open position establishing substantially non-restricted communication between the pump and the non-priority circuit. The valve element is shifted from its closed to its open position in response to a pressure drop being established there across, the pressure drop occurring in response to the flow of fluid through a restricted passage in the valve element. The flow of fluid through this restricted passage is governed by a pilot valve having a valve bore connected in fluid communication with the restricted passage and with the non-priority circuit and including a valve spool which is pilot-operated by fluid pressure in the priority circuit so as to establish an open path for fluid to flow from the restricted passage to the non-priority circuit only when the pressure in the priority circuit is above a pre-determined minimum pressure.
Description
33~
The present invention relates to vehicle hydraulic control systems and more particularly relates to pilot-operated priority valves for such systems.
Vehicle steering and brakes require priority over other hydraulic functions on most industrial machines. The conven-tional method of assuring priority is to use a priority valve which restricts the non-priority circuit to maintain a minimum pump outlet pressure (typically 80% of the system pressure). The disadvantage o~ this system is that all non-priority functions require the pump to operate at priority pressure regardless of the pressure required by the load. This results in a horsepower loss at light loads.
Summary of the Invention According to the present invention, there is provided an improved pilot-operated priority valve for use in vehicle hydrau-lic systems. Specifically, the priority valve of the present invention is connected between priority and non-priority circuits.
The priority valve includes a valve element mounted for pilot operation between a closed position, wherein it blocks flow to the non-priority circuit from the pump, and an open position, wherein it permits substantially non-restricted flow to the non-priority circuit. Pilot operation of the valve element is accom-plished by means of a pilot fluid passage which is connected for establishing a pressure drop across the valve element when flow occurs through the passa~e and flow through the passage is con-trolled by a pilot-operated valve which is connected for opera-tion in response to priority circuit pressure so as to establish a ~low path through the pilot fluid passage only when the pressure in the priority circuit is above a predetermined minimum.
An object of the present invention is to provide a priority valve which functions to establish a substantially non-restricted flow path to the non-priori-ty circui-t when the pressure in the priority circuit i.s above a predetermined minimum.
~5 A more specific objec-k is -to provide a priori-ty valve having a pressure-shitabl~ valve elemellt arranged for movemen-t between a closed posi-ti~n wherein it prevents fluid from being communi-cated from a supply pump to the non-priority circuit and an open position wherein it permi-ts subs-tantially unres-tricted flow ~o ~ -the non-priority circuit; and to also provide a restricted :Eluid - : :
.
: : . , , 1 passage for establishing a pressure drop across the valve element for causing it to shift to its open position in response to fluid flow through the restricted passage and to provide a pilot-operated valve for permitting flow through the restricted passage only when the pressure in the priority circuit is above a pre-determined minimum.
It is a further object of the invention to provide a priority valve having a valve element as described above wherein the restricted passage has its opposite ends connected to the priority circuit and the non-priority circuit.
These and other objects will become apparent from a reading of the ensuing description, together with the appended drawing.
Brief Description of the Drawing . _ _ _ _ The sole figure is a schematic representation of a pertinent portion of the vehicle hydraulic system and showing the priority valve in longitudinal section.
Description of the Pre~erred Embodiment Referring now to the drawing, therein is shown a vehicle hydraulic sys~em 10 including a single variable displacement pump 12 for supplying fluid both to non-priority functions such as lift cylinders and to priority functions such as brake and steer-ing cylinders. To insure that fluid is always available for the priority functions, there is provided a pilot-operated priority valve 14. The priority valve 14 lncludes a valve body 16 which, as viewed in the drawing, defines an upper or priority fluid cavity 18 and a lower or non-priority fluid cavity 20. ~rxanged in axial alignment with each other are a cylindrical passage 22 which joins the priority and non-priority fluid cavities 18 and 20 and a cyLindrical chamber 24 which forms a lower continuation of the non-priority fluid cavity 20. ~ sleeve 26 is press-fit in the cylindrical passage 22 and a pilot-operated poppek valve 28 has its upper and lower ends respec-tively slidably mounted in the sleevc 26 and in the cylindrical chamber
The present invention relates to vehicle hydraulic control systems and more particularly relates to pilot-operated priority valves for such systems.
Vehicle steering and brakes require priority over other hydraulic functions on most industrial machines. The conven-tional method of assuring priority is to use a priority valve which restricts the non-priority circuit to maintain a minimum pump outlet pressure (typically 80% of the system pressure). The disadvantage o~ this system is that all non-priority functions require the pump to operate at priority pressure regardless of the pressure required by the load. This results in a horsepower loss at light loads.
Summary of the Invention According to the present invention, there is provided an improved pilot-operated priority valve for use in vehicle hydrau-lic systems. Specifically, the priority valve of the present invention is connected between priority and non-priority circuits.
The priority valve includes a valve element mounted for pilot operation between a closed position, wherein it blocks flow to the non-priority circuit from the pump, and an open position, wherein it permits substantially non-restricted flow to the non-priority circuit. Pilot operation of the valve element is accom-plished by means of a pilot fluid passage which is connected for establishing a pressure drop across the valve element when flow occurs through the passa~e and flow through the passage is con-trolled by a pilot-operated valve which is connected for opera-tion in response to priority circuit pressure so as to establish a ~low path through the pilot fluid passage only when the pressure in the priority circuit is above a predetermined minimum.
An object of the present invention is to provide a priority valve which functions to establish a substantially non-restricted flow path to the non-priori-ty circui-t when the pressure in the priority circuit i.s above a predetermined minimum.
~5 A more specific objec-k is -to provide a priori-ty valve having a pressure-shitabl~ valve elemellt arranged for movemen-t between a closed posi-ti~n wherein it prevents fluid from being communi-cated from a supply pump to the non-priority circuit and an open position wherein it permi-ts subs-tantially unres-tricted flow ~o ~ -the non-priority circuit; and to also provide a restricted :Eluid - : :
.
: : . , , 1 passage for establishing a pressure drop across the valve element for causing it to shift to its open position in response to fluid flow through the restricted passage and to provide a pilot-operated valve for permitting flow through the restricted passage only when the pressure in the priority circuit is above a pre-determined minimum.
It is a further object of the invention to provide a priority valve having a valve element as described above wherein the restricted passage has its opposite ends connected to the priority circuit and the non-priority circuit.
These and other objects will become apparent from a reading of the ensuing description, together with the appended drawing.
Brief Description of the Drawing . _ _ _ _ The sole figure is a schematic representation of a pertinent portion of the vehicle hydraulic system and showing the priority valve in longitudinal section.
Description of the Pre~erred Embodiment Referring now to the drawing, therein is shown a vehicle hydraulic sys~em 10 including a single variable displacement pump 12 for supplying fluid both to non-priority functions such as lift cylinders and to priority functions such as brake and steer-ing cylinders. To insure that fluid is always available for the priority functions, there is provided a pilot-operated priority valve 14. The priority valve 14 lncludes a valve body 16 which, as viewed in the drawing, defines an upper or priority fluid cavity 18 and a lower or non-priority fluid cavity 20. ~rxanged in axial alignment with each other are a cylindrical passage 22 which joins the priority and non-priority fluid cavities 18 and 20 and a cyLindrical chamber 24 which forms a lower continuation of the non-priority fluid cavity 20. ~ sleeve 26 is press-fit in the cylindrical passage 22 and a pilot-operated poppek valve 28 has its upper and lower ends respec-tively slidably mounted in the sleevc 26 and in the cylindrical chamber
2~. Upper arld lower counterbores 30 and 32 are respec-tively Pormecl in -the upper and lower ends oE -the poppek valve 28 and a restricted passage 34 extends axially through the valve 28 -to permit the ~low o~ Pluid Prom the pxiori-ty ~luid cavity 18 to -the non-priority fluid cavity 20. Compressed be-tween a washer 36 sea-ted in the lower coun-terbore 32 and a lower encl wall 38 oP the ~ cylindrical chamber 24 is a coil compression spring 39 which .
- :;. ':'' :
- ~
33i3 1 biases the poppet val~e 28 to an upper closed position wherein an upwardly facing annular seat 40 of the valve 28 is engaged with an annular seat at the lower sur~ace of the sleeve 26. Radial openings 41 are located in the upper counterbore 30 above the seat 40. When flow is occurring through the restricted passage 34, a pressure drop exists across the valve 28 and it is shifted downwardly to an open position wherein the radial openings 41 are located, as shown in dashed lines, in fluid communication with the non priority fluid cavity 20. The flow of fluid through the restricted passage 34 and hence the shifti:ng of the pilot-operated valve 28 to its open position is governed or controlled by means of a pilot valve 42 forming part of the priority valve 14 and including a valve bore 44 defined by the valve body 16.
Intersecting the valve bore 44 is an inlet port 46 which is connected in fluid communication with the chamber 24 by means of a passage 48. Also intersecting the valve bore 44 is an outlet port 50 which is connected to the non-priority fluid cavity 20 through means of a conduit 52. A pilot-prPssure port 54 is in fluid communication with an upper end of a pilot pin 56 reciprocably mounted in the valve body 16 i.n axial alignment with . and having its lower end extending into the upper end of the valve bore 44. Positioned in the valve bore 44 so as to be operated by the pilot pin 56 is a valve spool 58 having a plurallty of lands formed therealong for controlling the flow of fluid between the inlet port 46 and the outlet port 50. A coil compression spring 60 is compressed between a lower end surface of the valve spool 58 and a plug 62 closing the lower end of the valve bore 44. The spring 60 normally biases the spool to an upper, closed position, as shown, wherein fluid communication between the inlet and outlet ports 46 and 50 is blocked. The pump 12 delivers fluid to a priority circuit conduit 64 and connected between the conduit 64 and the pilot-pressure port 54 is a pilot-pressure conduit 66. Whenever the pressure in the priority clraui-t conduit 64 is above a prede-term.ined minimum p~essure, -the pilo-t pin 56 is pressuxized aga:ins-t the spool 58 with ~orce su~:~i.aient to o~ercome the coil compression spring 60 and to shif-t the spool 58 downwardly to an open position wherei.n :~luid communica-t:ion is established between the inle-t and outlet ports 46 and 50.
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,, ~ .
:
.. ~ .~ ~ ;.: .
33~3 1 While the use of the pilot pin 56 is pre~erred, the pin could be omitted so as to let pilot pressure in the passage 54 to act directly on the top of the spool 58. Such an alternate structure would require the spring 60 to be stiffer to compensate for the additional pressure force acting on the spool.
To insure the availablity of priority fluid pressure, an accumulator 68 is connected to the priority circuit conduit 64.
A check valve 70 is connected in the priority circuit conduit 64 ~or preventing any fluid discharged from the accumulator 68 from flowing to the non-priority circuit by way of the valve element 20, it being noted that a non-priority circuit conduit 72 is connected, as by an outlet port 74, to the non-priority fluid cavity 20.
It is noted that Eluid stored in the accumulator will dis-charge to make up for system leakage and that the pump 12 will operate to recharge the accumulator upon a certain amount of its precharge being lost. While the use of the accumulator 68 is preferred, it could be omitted in which case the pump 12 would supply the fluid directly for making up that lost through leakage.
The operation of the priority valve 14 is brie~ly described below. Assuming the pump 12 to be in operation and that a pri-ority function such as the steering or brakes have just been actuated, the pressure in the priority circuit conduit 64 and hence in the pilot-pressure conduit 66 will be below the pre-determined minimum value and the priority valve 14 will be in its condition illustrated with the valve spool 58 of the pilot valve ~2 and the pilot operated valve 28 being in their respective closed positions to thereby prevent the fluid outputted by the pump 12 from being communicated to the non-priority circuit. As the demand for fluid by the priorlty Eunctions diminishes, the pressure will increase in the priority circuit conduit 6~ until it rises above the predetermined minimum value and this increase in pressure will be conveyed to -the upper end of the pilot pin by the pilo-~-pressure conduit 66 and resul-t in -the pin 56 uryiny the valve spool 58 downwardly agains-t the opposition o~ the coil compression spriny 60 so as -to shi~t the valve spool 58 to i-ts operl position wherein i-t es-tablishes ~luid communica-tion between -the inle-t and outlet ports ~6 and 50. Flow will th~n occur ~rom -the priority cavi-ty 18 to the non-priority cavi-ty 20 by way o~
~ the res-tricted passage 3~ in the valve 28, -the passage ~8 leading ., ~
' 33~
1 to the valve bore 44 and the conduit 52 leading from the valve bore 44 to the non-priority fluid cavity. A pressure drop will then be established across the valve 28 which results in the latter being shifted downwardly to its open position so as to establish a relatively non-restricted path between the priority cavity 18 and the non-priority cavity 20 so that the flow from the pump 12 is now available for operating non-priority functions connected to the non-priority cavity 20 by way of the non-priority circuit conduit 72. It is here noted that the relatively unrestricted flow from the pump to the non-priority circuit is accomplished by the proper selection of the upper and lower cross-sectional areas Al and A2, respectively, of the valve 28 and the proper selection of the spring 39 so that an extremely low pressure drop across the valve 28 will shift it completely from its closed to its fully open position.
~5 ,,
- :;. ':'' :
- ~
33i3 1 biases the poppet val~e 28 to an upper closed position wherein an upwardly facing annular seat 40 of the valve 28 is engaged with an annular seat at the lower sur~ace of the sleeve 26. Radial openings 41 are located in the upper counterbore 30 above the seat 40. When flow is occurring through the restricted passage 34, a pressure drop exists across the valve 28 and it is shifted downwardly to an open position wherein the radial openings 41 are located, as shown in dashed lines, in fluid communication with the non priority fluid cavity 20. The flow of fluid through the restricted passage 34 and hence the shifti:ng of the pilot-operated valve 28 to its open position is governed or controlled by means of a pilot valve 42 forming part of the priority valve 14 and including a valve bore 44 defined by the valve body 16.
Intersecting the valve bore 44 is an inlet port 46 which is connected in fluid communication with the chamber 24 by means of a passage 48. Also intersecting the valve bore 44 is an outlet port 50 which is connected to the non-priority fluid cavity 20 through means of a conduit 52. A pilot-prPssure port 54 is in fluid communication with an upper end of a pilot pin 56 reciprocably mounted in the valve body 16 i.n axial alignment with . and having its lower end extending into the upper end of the valve bore 44. Positioned in the valve bore 44 so as to be operated by the pilot pin 56 is a valve spool 58 having a plurallty of lands formed therealong for controlling the flow of fluid between the inlet port 46 and the outlet port 50. A coil compression spring 60 is compressed between a lower end surface of the valve spool 58 and a plug 62 closing the lower end of the valve bore 44. The spring 60 normally biases the spool to an upper, closed position, as shown, wherein fluid communication between the inlet and outlet ports 46 and 50 is blocked. The pump 12 delivers fluid to a priority circuit conduit 64 and connected between the conduit 64 and the pilot-pressure port 54 is a pilot-pressure conduit 66. Whenever the pressure in the priority clraui-t conduit 64 is above a prede-term.ined minimum p~essure, -the pilo-t pin 56 is pressuxized aga:ins-t the spool 58 with ~orce su~:~i.aient to o~ercome the coil compression spring 60 and to shif-t the spool 58 downwardly to an open position wherei.n :~luid communica-t:ion is established between the inle-t and outlet ports 46 and 50.
~0 -3-: . . .: . .
,, ~ .
:
.. ~ .~ ~ ;.: .
33~3 1 While the use of the pilot pin 56 is pre~erred, the pin could be omitted so as to let pilot pressure in the passage 54 to act directly on the top of the spool 58. Such an alternate structure would require the spring 60 to be stiffer to compensate for the additional pressure force acting on the spool.
To insure the availablity of priority fluid pressure, an accumulator 68 is connected to the priority circuit conduit 64.
A check valve 70 is connected in the priority circuit conduit 64 ~or preventing any fluid discharged from the accumulator 68 from flowing to the non-priority circuit by way of the valve element 20, it being noted that a non-priority circuit conduit 72 is connected, as by an outlet port 74, to the non-priority fluid cavity 20.
It is noted that Eluid stored in the accumulator will dis-charge to make up for system leakage and that the pump 12 will operate to recharge the accumulator upon a certain amount of its precharge being lost. While the use of the accumulator 68 is preferred, it could be omitted in which case the pump 12 would supply the fluid directly for making up that lost through leakage.
The operation of the priority valve 14 is brie~ly described below. Assuming the pump 12 to be in operation and that a pri-ority function such as the steering or brakes have just been actuated, the pressure in the priority circuit conduit 64 and hence in the pilot-pressure conduit 66 will be below the pre-determined minimum value and the priority valve 14 will be in its condition illustrated with the valve spool 58 of the pilot valve ~2 and the pilot operated valve 28 being in their respective closed positions to thereby prevent the fluid outputted by the pump 12 from being communicated to the non-priority circuit. As the demand for fluid by the priorlty Eunctions diminishes, the pressure will increase in the priority circuit conduit 6~ until it rises above the predetermined minimum value and this increase in pressure will be conveyed to -the upper end of the pilot pin by the pilo-~-pressure conduit 66 and resul-t in -the pin 56 uryiny the valve spool 58 downwardly agains-t the opposition o~ the coil compression spriny 60 so as -to shi~t the valve spool 58 to i-ts operl position wherein i-t es-tablishes ~luid communica-tion between -the inle-t and outlet ports ~6 and 50. Flow will th~n occur ~rom -the priority cavi-ty 18 to the non-priority cavi-ty 20 by way o~
~ the res-tricted passage 3~ in the valve 28, -the passage ~8 leading ., ~
' 33~
1 to the valve bore 44 and the conduit 52 leading from the valve bore 44 to the non-priority fluid cavity. A pressure drop will then be established across the valve 28 which results in the latter being shifted downwardly to its open position so as to establish a relatively non-restricted path between the priority cavity 18 and the non-priority cavity 20 so that the flow from the pump 12 is now available for operating non-priority functions connected to the non-priority cavity 20 by way of the non-priority circuit conduit 72. It is here noted that the relatively unrestricted flow from the pump to the non-priority circuit is accomplished by the proper selection of the upper and lower cross-sectional areas Al and A2, respectively, of the valve 28 and the proper selection of the spring 39 so that an extremely low pressure drop across the valve 28 will shift it completely from its closed to its fully open position.
~5 ,,
Claims (2)
1. In a hydraulic control system including a priority valve connected to a pump and to primary and secondary circuits for controlling the flow of fluid from the pump to -the primary and secondary circuits, the improvement comprising: said priority valve including a pressure-responsive valve element normally disposed in a closed position, wherein it blocks fluid communi-cation between the pump and the secondary circuit, and being shiftable, in response to a predetermined pressure drop -there across, to an open position wherein it establishes fluid communi-cation between the pump and the secondary circuit; a restricted pilot-pressure passage means connected across the valve element and to a source of pilot-pressure fluid for establishing said pressure drop across the valve element when fluid flows through the passage means; a pilot flow control valve means connected in the passage means and to the primary circuit and including a shiftable element means normally being positioned in an open position permitting flow through the pilot passage means, when the pressure in the primary circuit is above a predetermined minimum pressure, and being shiftable to a closed position pre-venting flow through the pilot passage means when the pressure in the primary circuit is at or below said predetermined minimum pressure.
2. In a hydraulic control system including a priority valve connected to a pump and non-priority and priority circuits for controlling the flow of fluid from the pump to said circuits, the improvement comprising: a valve body defining a priority fluid cavity and a non-priority fluid cavity joined by a cylindrical passage; a cylindrical chamber joined to the non-priority fluid cavity in axial alignment with the cylindrical passage; a priority valve element having opposite ends respectively, reciprocably mounted in the cylindrical passage and the cylindrical chamber; a spring urging the valve element to a closed position blocking fluid communication between the priority and non-priority fluid cavities; a restricted fluid passage extending through the valve element and interconnecting the priority fluid cavity and the cylindrical chamber; a pilot valve means connected to the cylindrical chamber and to the non-priority circuit and including a pressure-shiftable pilot valve element shiftable between closed and open positions respectively blocking and establishing fluid communication between the cylindrical chamber and the non-priority fluid circuit; and a pilot pressure conduit connected between the priority circuit and the pilot valve element for shifting the latter to its open position only upon the priority circuit pressure falling below a predetermined minimum pressure.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000394011A CA1159338A (en) | 1982-01-12 | 1982-01-12 | Pilot-operated priority valve |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000394011A CA1159338A (en) | 1982-01-12 | 1982-01-12 | Pilot-operated priority valve |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1159338A true CA1159338A (en) | 1983-12-27 |
Family
ID=4121809
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000394011A Expired CA1159338A (en) | 1982-01-12 | 1982-01-12 | Pilot-operated priority valve |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1159338A (en) |
-
1982
- 1982-01-12 CA CA000394011A patent/CA1159338A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |