GB2297128A - Closed centre hydraulic system - Google Patents

Closed centre hydraulic system Download PDF

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Publication number
GB2297128A
GB2297128A GB9424317A GB9424317A GB2297128A GB 2297128 A GB2297128 A GB 2297128A GB 9424317 A GB9424317 A GB 9424317A GB 9424317 A GB9424317 A GB 9424317A GB 2297128 A GB2297128 A GB 2297128A
Authority
GB
United Kingdom
Prior art keywords
pump
air
purge valve
charge pump
closed centre
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.)
Granted
Application number
GB9424317A
Other versions
GB9424317D0 (en
GB2297128B (en
Inventor
Ian David Patterson
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Danfoss Power Solutions Ltd Great Britain
Sauer Danfoss Swindon Ltd
Original Assignee
Sauer Sundstrand Ltd
Sauer Sundstrand UK Holdings Ltd
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Sauer Sundstrand Ltd, Sauer Sundstrand UK Holdings Ltd filed Critical Sauer Sundstrand Ltd
Priority to GB9424317A priority Critical patent/GB2297128B/en
Publication of GB9424317D0 publication Critical patent/GB9424317D0/en
Publication of GB2297128A publication Critical patent/GB2297128A/en
Application granted granted Critical
Publication of GB2297128B publication Critical patent/GB2297128B/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
    • F04C14/00—Control of, monitoring of, or safety arrangements for, machines, pumps or pumping installations
    • F04C14/06—Control of, monitoring of, or safety arrangements for, machines, pumps or pumping installations specially adapted for stopping, starting, idling or no-load operation
    • 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
    • F04B23/00—Pumping installations or systems
    • F04B23/04—Combinations of two or more pumps
    • F04B23/08—Combinations of two or more pumps the pumps being of different types
    • F04B23/10—Combinations of two or more pumps the pumps being of different types at least one pump being of the reciprocating positive-displacement type
    • 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
    • F04B53/00—Component parts, details or accessories not provided for in, or of interest apart from, groups F04B1/00 - F04B23/00 or F04B39/00 - F04B47/00
    • F04B53/06—Venting
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
    • F04C15/00—Component parts, details or accessories of machines, pumps or pumping installations, not provided for in groups F04C2/00 - F04C14/00
    • F04C15/0053—Venting means for starting
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B21/00—Common features of fluid actuator systems; Fluid-pressure actuator systems or details thereof, not covered by any other group of this subclass
    • F15B21/04—Special measures taken in connection with the properties of the fluid
    • F15B21/044—Removal or measurement of undissolved gas, e.g. de-aeration, venting or bleeding

Abstract

A hydraulic system which prevents the entrainment of air in closed system hydraulic fluid by eliminating that air in the charge circuit for the closed system includes a closed centre pump (3) for delivering fluid to a load (4) and a charge pump (1) for delivering hydraulic fluid to the closed centre pump. An air purge valve (5) in close proximity to an inlet of the closed centre pump (3) diverts the charge pump output away from the closed centre pump to drain when that output contains significant amounts of entrapped air. A restrictor (6) in the flow path to the drain (2) creates a pressure difference across the valve. When the fluid has entrained air the pressure difference is insufficient to operate the valve but when substantially air free fluid is flowing, pressure builds up causing the valve to changeover and direct fluid to the pump (3).

Description

TITLE: Closed Centre Hydraulic Systems DESCRIPTION: Field of the invention The invention relates to closed centre hydraulic systems incorporating automatic air bleed facilities, and to closed centre hydraulic pump assemblies for such systems.
Prior Art A well known problem with closed centre hydraulic systems results from the introduction of air into the system. Air can be introduced as the pumps, valves, controls and associated pipework drain their hydraulic fluid back into the reservoir during periods when the system is shut down, and on start-up the entrapped air is then pumped into any closed-circuit system that is selected. The result can be a considerable entrainment of air in the hydraulic fluid that is pumped around the system, causing the system to lose efficiency and become slow and spongy.
There may also be excessive noise.
Depending on the nature of the hydraulic circuit, it may take considerable time and effort for the air to be purged from the closed centre system once it has become introduced in the above manner.
The Invention The invention has as its object the creation of a hydraulic system which prevents the entrainment of air in closed system hydraulic fluid by eliminating that air in the charge circuit for the closed system.
The invention provides a closed centre hydraulic system comprising: a closed centre pump for delivering hydraulic fluid to a load; and a charge circuit for delivering hydraulic fluid to the closed centre pump, the charge circuit comprising: a charge pump for drawing hydraulic fluid from a reservoir and delivering it at charge pressure to the closed centre pump, and an air purge valve in close proximity to an inlet gallery of the closed centre pump, for diverting the charge pump output away from the closed centre pump to drain in response to the detection of significant amounts of entrapped air in fluid passing therethrough.
The detection of significant amounts of entrapped air in the fluid passing through the air purge valve is preferably achieved by passing that fluid flow through a restricted orifice one side of which is at drain pressure and the other side of which is at the charge pump output pressure. The orifice allows free passage or relatively unrestricted passage of air or aerated oil, so that the pressure differential across the orifice is maintained at a low value when there is a significant amount of entrapped air in fluid passing through the orifice. When the air has been purged from the system and hydraulic fluid alone tries to pass through the orifice to drain, the pressure at the charge pump side of the orifice rises and can be used as a signal to actuate closure of the air purge valve.
The air purge valve may be a spool valve spring-biased to an open position but closable when the pressure from the upstream side of the above orifice acts against and overcomes the bias of the spring. If desired the orifice may be provided in the valve spool itself.
The closed centre pump may be for example a variable displacement piston pump. The charge pump may suitably be a gear pump.
The diversion of the charge pump output to drain when a significant amount of entrapped air is detected may be by opening a flow passage to drain while maintaining open the main hydraulic flow connection between the charge pump and the closed centre pump; or it may be by synchronously opening a flow passage to drain while disconnecting the charge pump from the closed centre pump. The former is sufficient to reduce the pressure at the output side of the charge pump below a working minimum for the closed centre pump, so as to ensure that the air and aerated oil at the start-up is passed selectively through the air purge valve to drain. The latter may have the advantage of protecting the very small volume between the air purge valve and the inlet gallery of the closed centre pump from loss of hydraulic fluid while the system is shut down.
Drawings The accompanying drawings are both schematic flow systems only, and use the same reference numerals for similar or identical parts.
Figure 1 is a flow chart illustrating a first embodiment of a system of the invention; and Figure 2 is a flow chart illustrating a second embodiment of a system of the invention.
In the drawings, a charge pump 1 draws hydraulic fluid from a reservoir 2 and delivers it to a closed centre variable displacement piston pump 3 which supplies a closed centre load circuit 4.
In Figure 1, an air purge valve 5 is positioned close to the inlet gallery of the pump 3 to establish, when open, a drain path for hydraulic fluid from the charge pump, via a restricted orifice 6. The orifice 6 in Figure 1 is shown in a valve spool of the valve 5, but it could alternatively be downstream or upstream of the valve 5.
Downstream of the orifice 6 the hydraulic fluid is at tank pressure, passing directly back to the reservoir 2.
Upstream, the pressure is dependent on the flow through the orifice. When the charge pump delivers either air or aerated oil to the valve 5, the pressure differential across the orifice is small. As the air content diminishes, the pressure upstream of the orifice rises until that upstream pressure at 7 is sufficient to move the valve spool to a closed position against the bias of a spring 8. Thereafter the air-free oil is passed in usual manner to the pump 3.
Figure 2 shows an alternative embodiment in which in the rest position of the valve 5 the passage to the inlet gallery of the closed centre pump 3 is closed, so that hydraulic fluid is charged to the pump only when the valve 5 moves to its position closing the bypass passage through the orifice 6 to drain.

Claims (8)

CLAIMS:
1. A closed centre hydraulic system comprising: a closed centre pump for delivering hydraulic fluid to a load; and a charge circuit for delivering hydraulic fluid to the closed centre pump, the charge circuit comprising: a charge pump for drawing hydraulic fluid from a reservoir and delivering it at charge pressure to the closed centre pump, and an air purge valve in close proximity to an inlet gallery of the closed centre pump, for diverting the charge pump output back to the reservoir on initial start-up; means for detecting significant amounts of entrapped air in fluid passing through the air purge valve; and means for closing the air purge valve and passing the charge pump output to the closed centre pump when the detecting means no longer detects significant amounts of entrapped air in fluid passing through the air purge valve.
2. A hydraulic system according to claim 1, wherein the air purge valve includes a restricted orifice in the flow path from the charge pump through the air purge valve to the reservoir, one side of the restricted orifice being at charge pump pressure and the other side being at reservoir pressure; the orifice being sized to permit free or relatively unrestricted passage of air or aerated oil but to provide a flow restriction for unaerated oil, the pressure at the charge pump side of the orifice providing the detection of significant amounts of entrapped air in fluid passing through the air purge valve.
3. A hydraulic system according to claim 2, where the air purge valve is a spool valve spring-biased to a first position in which it opens an air bleed passage from the charge pump to the reservoir.
4. A hydraulic system according to claim 3 wherein: the pressure at the charge pump side of the orifice acts against the bias of the spring, and when this pressure is sufficiently high to indicate that there is not a significant amount of entrapped air in the fluid passing through the air purge valve, the pressure overcomes the bias of the spring and moves the spool valve to a second position in which it closes an air bleed passage from the charge pump to the reservoir.
5. A hydraulic system according to any preceding claim wherein when the air purge valve is open, the charge pump is disconnected from the closed centre pump.
6. A hydraulic system according to any preceding claim wherein the closed centre pump is a variable displacement piston pump.
7. A hydraulic system according to any preceding claim wherein the charge pump is a gear pump.
8. A hydraulic system substantially as described herein with reSrence to the drawings.
GB9424317A 1994-12-01 1994-12-01 Closed centre hydraulic systems Expired - Lifetime GB2297128B (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB9424317A GB2297128B (en) 1994-12-01 1994-12-01 Closed centre hydraulic systems

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB9424317A GB2297128B (en) 1994-12-01 1994-12-01 Closed centre hydraulic systems

Publications (3)

Publication Number Publication Date
GB9424317D0 GB9424317D0 (en) 1995-01-18
GB2297128A true GB2297128A (en) 1996-07-24
GB2297128B GB2297128B (en) 1998-08-05

Family

ID=10765308

Family Applications (1)

Application Number Title Priority Date Filing Date
GB9424317A Expired - Lifetime GB2297128B (en) 1994-12-01 1994-12-01 Closed centre hydraulic systems

Country Status (1)

Country Link
GB (1) GB2297128B (en)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1403531A1 (en) * 2002-09-25 2004-03-31 Caterpillar Inc. Hydraulic pump circuit
EP1847721A1 (en) * 2005-02-08 2007-10-24 Komatsu Ltd Hydraulic shovel
US20140352822A1 (en) * 2013-05-31 2014-12-04 Eaton Corporation Air bleed valve float arrangement with restrictor

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1410812A (en) * 1971-11-25 1975-10-22 Langen Co Thomas K H Automatic air bleeder means for piston pumps
US4021155A (en) * 1975-11-13 1977-05-03 Sundstrand Corporation Oil burner pumping system with air purging valve

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1410812A (en) * 1971-11-25 1975-10-22 Langen Co Thomas K H Automatic air bleeder means for piston pumps
US4021155A (en) * 1975-11-13 1977-05-03 Sundstrand Corporation Oil burner pumping system with air purging valve

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1403531A1 (en) * 2002-09-25 2004-03-31 Caterpillar Inc. Hydraulic pump circuit
EP1847721A1 (en) * 2005-02-08 2007-10-24 Komatsu Ltd Hydraulic shovel
EP1847721A4 (en) * 2005-02-08 2012-02-08 Komatsu Mfg Co Ltd Hydraulic shovel
US20140352822A1 (en) * 2013-05-31 2014-12-04 Eaton Corporation Air bleed valve float arrangement with restrictor

Also Published As

Publication number Publication date
GB9424317D0 (en) 1995-01-18
GB2297128B (en) 1998-08-05

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Legal Events

Date Code Title Description
730A Proceeding under section 30 patents act 1977
732E Amendments to the register in respect of changes of name or changes affecting rights (sect. 32/1977)
732E Amendments to the register in respect of changes of name or changes affecting rights (sect. 32/1977)
732E Amendments to the register in respect of changes of name or changes affecting rights (sect. 32/1977)
PE20 Patent expired after termination of 20 years

Expiry date: 20141130