EP0226125B1 - Variable displacement pump system - Google Patents
Variable displacement pump system Download PDFInfo
- Publication number
- EP0226125B1 EP0226125B1 EP86116785A EP86116785A EP0226125B1 EP 0226125 B1 EP0226125 B1 EP 0226125B1 EP 86116785 A EP86116785 A EP 86116785A EP 86116785 A EP86116785 A EP 86116785A EP 0226125 B1 EP0226125 B1 EP 0226125B1
- Authority
- EP
- European Patent Office
- Prior art keywords
- pressure
- pump
- load
- sensing
- compensator
- 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 - Lifetime
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Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
- F04B1/00—Multi-cylinder machines or pumps characterised by number or arrangement of cylinders
- F04B1/12—Multi-cylinder machines or pumps characterised by number or arrangement of cylinders having cylinder axes coaxial with, or parallel or inclined to, main shaft axis
- F04B1/26—Control
- F04B1/30—Control of machines or pumps with rotary cylinder blocks
- F04B1/32—Control of machines or pumps with rotary cylinder blocks by varying the relative positions of a swash plate and a cylinder block
- F04B1/324—Control of machines or pumps with rotary cylinder blocks by varying the relative positions of a swash plate and a cylinder block by changing the inclination of the swash plate
Definitions
- This invention relates to a variable displacement pump control system comprising the features of the preamble to claim 1.
- Such a system is known from US-A-3,067,693 with a larger area piston as the controlled positioning piston and an opposing smaller area positioning piston without a spring biasing the piston.
- a spring is however known in the art (see Fig. 1).
- Such systems usually are also provided with a pressure compensator for operating a hydraulic positioning piston to decrease the displacement of the pump and for overriding the load sensing compensator which is active as the primary pump control except when the pressure of the pump is at the limit set by the pressure compensator.
- pump outlet is directly connected to the smaller area piston and to the supply line which includes the system valve.
- the problem underlying the present invention is to provide a variable displacement pump control system which is more stable.
- the load pressure as taken from a load sensing passage or downstream from the system valve is connected to the spring biased (or smaller area) piston rather than directly connecting the pump outlet to the spring biased piston.
- variable displacement pump from which an outlet 10 is shown may be of the variable axial piston type and comprises a yoke and a swash plate 11 that are movable to vary the stroke of axial pistons (not shown).
- a first smaller area spring biased positioning piston 12 is acted upon by pressure and yieldingly urges the yoke and the swash plate 11 to a maximum displacement position.
- a second larger area positioning piston 13 acts on the yoke and the swash plate 11 in opposition to the first spring biased positioning piston 12.
- Working fluid from the pump outlet 10 flows through a supply line 14 to a directional system or valve 15 and further to a load such as a hydraulic actuator.
- a short passage or line 16 connects the pump outlet 10 to the first spring biased positioning piston 12.
- pump outlet pressure is connected through a pump pressure sensing line 17 to a pressure compensator 18 and through a line section 17a, to a load sensing compensator 19.
- the pressure compensator 18 may include a pilot valve 22 which opens at the pressure limit, set by its spring force and relieves the spring chamber of the pressure compensator 18 so that the spool thereof travels to the right hand side connecting line 17 to a line section 17c and further to the larger area positioning piston 13 which destrokes the pump (protection against overpressure).
- Line section 17a of the pump pressure sensing line 17 is connected to the first spool end 19a of load sensing compensator 19 and to pump outlet pressure.
- the second spool end 19b is connected by a load pressure sensing line 20 downstream of the system valve 15 to the pressure of fluid being delivered to the load.
- compensator 19 which functions to modulate pump outlet pressure in lines 17, 17a and to deliver such modulated or control pressure via lines 17b, 17c to the second positioning piston 13. Modulation also depends on the spring preload of compensator 19.
- the second positioning piston 13 which is larger in cross section than the first positioning piston 12 determines the position of the yoke and swash plate 11 and therefore pump delivery rate.
- the displacement is varied in a manner to deliver exactly the load flow required by the actuator or actuators at the load pressure, which is, for example, 14 to 21 bar (200 to 300 p.s.i.) below the pump outlet pressure.
- the load pressure which is, for example, 14 to 21 bar (200 to 300 p.s.i.) below the pump outlet pressure.
- a load pressure line 21 is added which extends from the load pressure sensing line 20 downstream of the system valve 15 to the first positioning piston 12 which, therefore, is acted upon by load pressure.
- any change in the flow rate has a simultaneous influence on both positioning pistons 12 and 13, i. e. changes in the load pressure and in the modulated pressure will arrive practically simultaneously at the first positioning piston 12 and the second positioning piston 13, respectively, whereas it is believed that in the prior art system the influence on the first piston 12 (pump outlet pressure) is followed with a time lag by the influence on the second piston 13 (modulated or control pressure) so that the position of the swash plate 11 is changed in one direction immediately followed by a change in the other direction which might be the reason for the pulsations observed.
- variable displacement pump of the swash plate type
- pump adjusting mechanism for varying the displacement
- eccentric adjustment variable vane pumps and pumps using a rotating group housed in a tiltable yoke assembly.
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Control Of Positive-Displacement Pumps (AREA)
- Reciprocating Pumps (AREA)
- Fluid-Pressure Circuits (AREA)
Description
- This invention relates to a variable displacement pump control system comprising the features of the preamble to claim 1.
- Such a system is known from US-A-3,067,693 with a larger area piston as the controlled positioning piston and an opposing smaller area positioning piston without a spring biasing the piston. Using such a spring is however known in the art (see Fig. 1). Such systems usually are also provided with a pressure compensator for operating a hydraulic positioning piston to decrease the displacement of the pump and for overriding the load sensing compensator which is active as the primary pump control except when the pressure of the pump is at the limit set by the pressure compensator. In these known systems, pump outlet is directly connected to the smaller area piston and to the supply line which includes the system valve. When the system valve is shut down, pump pressure raises and the compensator controls the larger area positioning piston to destroke the pump, so that the smaller area piston displaces fluid into the supply line with a tendency to further raise the pump pressure. Conversly, when the system valve is opened, pump pressure falls and the compensator controls the larger area piston to onstroke the pump so that the smaller area cylinder sucks fluid from the supply line tending to further lower the pump pressure. Therefore, in both cases a positive feedback is brought about which means a destablilzing effect, especially under heavy loads and when the connecting lines are short. The control system oscillates causing hydraulic pulsations and resultant oscillating movement of the load or device being driven.
- Accordingly, the problem underlying the present invention is to provide a variable displacement pump control system which is more stable.
- In accordance with the invention, the load pressure as taken from a load sensing passage or downstream from the system valve is connected to the spring biased (or smaller area) piston rather than directly connecting the pump outlet to the spring biased piston.
- In the drawings:
- Fig. 1
- is a prior art control system, and
- Fig. 2
- an embodiment of the invention.
- The variable displacement pump from which an
outlet 10 is shown may be of the variable axial piston type and comprises a yoke and a swash plate 11 that are movable to vary the stroke of axial pistons (not shown). A first smaller area springbiased positioning piston 12 is acted upon by pressure and yieldingly urges the yoke and the swash plate 11 to a maximum displacement position. A second largerarea positioning piston 13 acts on the yoke and the swash plate 11 in opposition to the first springbiased positioning piston 12. Working fluid from thepump outlet 10 flows through asupply line 14 to a directional system or valve 15 and further to a load such as a hydraulic actuator. In the known control system as shown in Fig. 1, a short passage orline 16 connects thepump outlet 10 to the first springbiased positioning piston 12. - In Figs. 1 and 2, pump outlet pressure is connected through a pump
pressure sensing line 17 to apressure compensator 18 and through a line section 17a, to a load sensing compensator 19. Thepressure compensator 18 may include apilot valve 22 which opens at the pressure limit, set by its spring force and relieves the spring chamber of thepressure compensator 18 so that the spool thereof travels to the right handside connecting line 17 to aline section 17c and further to the largerarea positioning piston 13 which destrokes the pump (protection against overpressure). - Line section 17a of the pump
pressure sensing line 17 is connected to thefirst spool end 19a of load sensing compensator 19 and to pump outlet pressure. Thesecond spool end 19b is connected by a loadpressure sensing line 20 downstream of the system valve 15 to the pressure of fluid being delivered to the load. Thus the drop in pressure across the valve system 15 is sensed by compensator 19 which functions to modulate pump outlet pressure inlines 17, 17a and to deliver such modulated or control pressure vialines second positioning piston 13. Modulation also depends on the spring preload of compensator 19. Thesecond positioning piston 13 which is larger in cross section than thefirst positioning piston 12 determines the position of the yoke and swash plate 11 and therefore pump delivery rate. The displacement is varied in a manner to deliver exactly the load flow required by the actuator or actuators at the load pressure, which is, for example, 14 to 21 bar (200 to 300 p.s.i.) below the pump outlet pressure. When this difference of 14 to 21 bar is exeeded, the spring preload of the compensator 19 is surmounted and a modulated or control pressure produced which lowers the displacement of the pump so that the pressure difference is maintained. - It has been found that a hydraulic system as shown in Fig. 1 is unstable under high loads resulting in pulsation of the fluid and oscillating of the device being controlled, particularly when flows are small.
- In accordance with the invention as shown in Fig. 2, the usual
pump pressure line 16 of Fig. 1 is eliminated and aload pressure line 21 is added which extends from the loadpressure sensing line 20 downstream of the system valve 15 to thefirst positioning piston 12 which, therefore, is acted upon by load pressure. - It has been found that such a system overcomes the problem of stability of the prior art system.
- It is believed that any change in the flow rate has a simultaneous influence on both
positioning pistons first positioning piston 12 and thesecond positioning piston 13, respectively, whereas it is believed that in the prior art system the influence on the first piston 12 (pump outlet pressure) is followed with a time lag by the influence on the second piston 13 (modulated or control pressure) so that the position of the swash plate 11 is changed in one direction immediately followed by a change in the other direction which might be the reason for the pulsations observed. - Although the system has been described as used in connection with a variable displacement pump of the swash plate type, it will be understood by persons skilled in the art that it is also applicable to other types of pumps having differing pump adjusting mechanism for varying the displacement such as eccentric adjustment variable vane pumps and pumps using a rotating group housed in a tiltable yoke assembly.
Claims (2)
- A variable displacement hydraulic pump control system comprising(a) a variable displacement pump having an outlet (10) and an inlet and including a pump adjusting mechanism (11-13) comprising a controlled hydraulic positioning piston means (13) and spring biased positioning means (12) yieldingly opposing said controlled positioning piston means (13),(b) a supply line (14) with two sections including a system valve (15) therebetween,(c) load sensing compensator means (19) for providing control pressure,(d) pump pressure sensing passage means (17, 17a) connecting the outlet (10) of the pump to one end (19a) of said load sensing compensator means (19) for sensing the pressure at the outlet (10) of the pump,(e) load pressure sensing passage means (20) extending between the other end (19b) of said load sensing compensator means (19) and said system valve (15),(f) control pressure passage means (17b, 17c) extending between said load sensing compensator means (19) and said controlled positioning piston means (13) for moving said pump adjusting mechanism (11-13) in response to a change in control pressure,
characterized by(g) load pressure passage means (21) connecting load pressure downstream of said system valve (15) to said spring biased positioning piston means (12). - The variable displacement pump control system set forth in claim 1 including
pressure compensator means (18) having one end connected to said pump pressure sensing passage means (17) and being movable when pump pressure exceeds a predetermined amount whereby connecting said control pressure passage means (17c) to said pump pressure sensing passage means (17).
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US80852785A | 1985-12-13 | 1985-12-13 | |
US808527 | 1985-12-13 |
Publications (3)
Publication Number | Publication Date |
---|---|
EP0226125A2 EP0226125A2 (en) | 1987-06-24 |
EP0226125A3 EP0226125A3 (en) | 1989-07-05 |
EP0226125B1 true EP0226125B1 (en) | 1991-04-03 |
Family
ID=25199037
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP86116785A Expired - Lifetime EP0226125B1 (en) | 1985-12-13 | 1986-12-03 | Variable displacement pump system |
Country Status (6)
Country | Link |
---|---|
EP (1) | EP0226125B1 (en) |
JP (1) | JPH0819922B2 (en) |
CN (1) | CN1007542B (en) |
CA (1) | CA1248410A (en) |
DE (1) | DE3678538D1 (en) |
IN (1) | IN166532B (en) |
Families Citing this family (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5183393A (en) * | 1992-02-10 | 1993-02-02 | Schaffner Larey D | Power limiter control for a variable displacement axial piston pump |
US7797092B2 (en) * | 2006-11-06 | 2010-09-14 | Caterpillar Inc | Method and system for controlling machine power |
CN101865143B (en) * | 2010-07-08 | 2012-05-23 | 中国航天科技集团公司第六研究院第十一研究所 | Device for automatically adjusting power of turbine pump |
CN111911381B (en) * | 2020-07-26 | 2022-12-06 | 中国航发贵州红林航空动力控制科技有限公司 | Nozzle differential pressure valve mechanism with damping piston |
CN113266319B (en) * | 2021-07-01 | 2023-06-23 | 龙信阀业集团有限公司 | Gas lift valve suitable for pressure-variable gas lift process |
Family Cites Families (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US2502546A (en) * | 1947-03-28 | 1950-04-04 | Denison Eng Co | Hydraulic apparatus |
US3067693A (en) * | 1958-12-24 | 1962-12-11 | United Aircraft Corp | Control means for variable delivery pump |
SE323286B (en) * | 1967-12-04 | 1970-04-27 | Sperry Rand Corp | |
US4072442A (en) * | 1975-07-04 | 1978-02-07 | Takeshi Horiuchi | Variable delivery hydraulic pump |
-
1986
- 1986-12-02 IN IN870/CAL/86A patent/IN166532B/en unknown
- 1986-12-03 DE DE8686116785T patent/DE3678538D1/en not_active Expired - Fee Related
- 1986-12-03 EP EP86116785A patent/EP0226125B1/en not_active Expired - Lifetime
- 1986-12-11 JP JP61295683A patent/JPH0819922B2/en not_active Expired - Fee Related
- 1986-12-12 CN CN87105369A patent/CN1007542B/en not_active Expired
- 1986-12-12 CA CA000525243A patent/CA1248410A/en not_active Expired
Also Published As
Publication number | Publication date |
---|---|
CA1248410A (en) | 1989-01-10 |
EP0226125A2 (en) | 1987-06-24 |
IN166532B (en) | 1990-05-26 |
JPS62253980A (en) | 1987-11-05 |
CN1007542B (en) | 1990-04-11 |
JPH0819922B2 (en) | 1996-03-04 |
EP0226125A3 (en) | 1989-07-05 |
CN86108529A (en) | 1987-06-17 |
DE3678538D1 (en) | 1991-05-08 |
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