GB2332480A - Hydraulic apparatus - Google Patents

Hydraulic apparatus Download PDF

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Publication number
GB2332480A
GB2332480A GB9824206A GB9824206A GB2332480A GB 2332480 A GB2332480 A GB 2332480A GB 9824206 A GB9824206 A GB 9824206A GB 9824206 A GB9824206 A GB 9824206A GB 2332480 A GB2332480 A GB 2332480A
Authority
GB
United Kingdom
Prior art keywords
cylinder
fluid
volume
piston
hydraulic apparatus
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.)
Withdrawn
Application number
GB9824206A
Other versions
GB9824206D0 (en
Inventor
Anthony Roger Davies
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.)
Smiths Group PLC
Original Assignee
Smiths Group PLC
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 Smiths Group PLC filed Critical Smiths Group PLC
Publication of GB9824206D0 publication Critical patent/GB9824206D0/en
Publication of GB2332480A publication Critical patent/GB2332480A/en
Withdrawn legal-status Critical Current

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Classifications

    • 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
    • F15B15/00—Fluid-actuated devices for displacing a member from one position to another; Gearing associated therewith
    • F15B15/08—Characterised by the construction of the motor unit
    • F15B15/14—Characterised by the construction of the motor unit of the straight-cylinder type
    • F15B15/149—Fluid interconnections, e.g. fluid connectors, passages
    • 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
    • F15B11/00—Servomotor systems without provision for follow-up action; Circuits therefor
    • F15B11/02—Systems essentially incorporating special features for controlling the speed or actuating force of an output member
    • F15B11/024—Systems essentially incorporating special features for controlling the speed or actuating force of an output member by means of differential connection of the servomotor lines, e.g. regenerative circuits
    • 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
    • F15B7/00—Systems in which the movement produced is definitely related to the output of a volumetric pump; Telemotors
    • F15B7/005—With rotary or crank input
    • F15B7/006—Rotary pump input
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61G—TRANSPORT, PERSONAL CONVEYANCES, OR ACCOMMODATION SPECIALLY ADAPTED FOR PATIENTS OR DISABLED PERSONS; OPERATING TABLES OR CHAIRS; CHAIRS FOR DENTISTRY; FUNERAL DEVICES
    • A61G7/00—Beds specially adapted for nursing; Devices for lifting patients or disabled persons
    • A61G7/002—Beds specially adapted for nursing; Devices for lifting patients or disabled persons having adjustable mattress frame
    • A61G7/018—Control or drive mechanisms
    • 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
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/20—Fluid pressure source, e.g. accumulator or variable axial piston pump
    • F15B2211/205—Systems with pumps
    • F15B2211/20507—Type of prime mover
    • F15B2211/20515—Electric motor
    • 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
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/20—Fluid pressure source, e.g. accumulator or variable axial piston pump
    • F15B2211/205—Systems with pumps
    • F15B2211/2053—Type of pump
    • F15B2211/20561—Type of pump reversible
    • 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
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/30—Directional control
    • F15B2211/305—Directional control characterised by the type of valves
    • F15B2211/30505—Non-return valves, i.e. check valves
    • F15B2211/3051—Cross-check valves
    • 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
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/30—Directional control
    • F15B2211/305—Directional control characterised by the type of valves
    • F15B2211/3056—Assemblies of multiple valves
    • F15B2211/30565—Assemblies of multiple valves having multiple valves for a single output member, e.g. for creating higher valve function by use of multiple valves like two 2/2-valves replacing a 5/3-valve
    • F15B2211/3058—Assemblies of multiple valves having multiple valves for a single output member, e.g. for creating higher valve function by use of multiple valves like two 2/2-valves replacing a 5/3-valve having additional valves for interconnecting the fluid chambers of a double-acting actuator, e.g. for regeneration mode or for floating mode
    • 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
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/30—Directional control
    • F15B2211/315—Directional control characterised by the connections of the valve or valves in the circuit
    • F15B2211/3157—Directional control characterised by the connections of the valve or valves in the circuit being connected to a pressure source, an output member and a return line
    • F15B2211/31576—Directional control characterised by the connections of the valve or valves in the circuit being connected to a pressure source, an output member and a return line having a single pressure source and a single output member
    • 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
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/30—Directional control
    • F15B2211/32—Directional control characterised by the type of actuation
    • F15B2211/329—Directional control characterised by the type of actuation actuated by fluid pressure
    • 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
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/50—Pressure control
    • F15B2211/505—Pressure control characterised by the type of pressure control means
    • F15B2211/50509—Pressure control characterised by the type of pressure control means the pressure control means controlling a pressure upstream of the pressure control means
    • F15B2211/50518—Pressure control characterised by the type of pressure control means the pressure control means controlling a pressure upstream of the pressure control means using pressure relief valves
    • 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
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/50—Pressure control
    • F15B2211/515—Pressure control characterised by the connections of the pressure control means in the circuit
    • F15B2211/5157—Pressure control characterised by the connections of the pressure control means in the circuit being connected to a pressure source and a return line
    • 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
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/50—Pressure control
    • F15B2211/55—Pressure control for limiting a pressure up to a maximum pressure, e.g. by using a pressure relief valve
    • 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
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/60—Circuit components or control therefor
    • F15B2211/61—Secondary circuits
    • F15B2211/613—Feeding circuits
    • 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
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/70—Output members, e.g. hydraulic motors or cylinders or control therefor
    • F15B2211/705—Output members, e.g. hydraulic motors or cylinders or control therefor characterised by the type of output members or actuators
    • F15B2211/7051—Linear output members
    • F15B2211/7053—Double-acting output members

Landscapes

  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Fluid Mechanics (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Actuator (AREA)

Abstract

Hydraulic apparatus has an outer cylinder 10 slidable up and down and supported by two slide bearings 15 and 16, the upper end of the cylinder being attached to a load 6. Inside the cylinder 10, a piston assembly 20 comprising a piston head 21 supported on a fixed, hollow piston rod 31, opens through apertures 33 into the cylinder below the piston head. Within the rod 31, a pipe 27 opens through an aperture 25 into the volume above the piston head 21. The piston head 21 includes a one-way valve 24. A pump 41 is operable in either direction and has outlets 42 and 43 connected to the pipe 27 and to the inside of the piston rod 31. When the pump 41 is operated in one direction fluid flows through the pipe 27 to both the volume above the piston head 21 and to the volume below, thereby extending the piston assembly. When the pump 41 is operated in the opposite direction, fluid flows through the rod 31 to only the volume below the head, thereby retracting the piston assembly.

Description

1 HYDRAULIC APPARATUS This invention relates to hydraulic apparatus.
2332480 Hydraulic apparatus is used in many lifting and other applications, hydraulic fluid being supplied to a cylinder to cause relative movement between the cylinder and its piston. Where a single-acting hydraulic cylinder is used, fluid may be supplied to extend the cylinder and lift the load, retraction of the cylinder often being achieved by venting the cylinder to the hydraulic reservoir or tank and allowing the applied load to cause retraction, without any applied fluid pressure. There are various problems associated with previous hydraulic apparatus. For example, it can be difficult to control the speed of relative movement in both directions. Also, wear on bearings used with the apparatus may impede movement.
It is an object of the present invention to provide improved hydraulic apparatus.
According to one aspect of the present invention there is provided hydraulic apparatus comprising a cylinder assembly and an hydraulic supply, the cylinder assembly comprising an outer cylinder and a piston assembly movable longitudinally relative to one another, the outer cylinder having an annulus at one end and being closed at its opposite end, the piston assembly including a piston head that divides the space between the cylinder and the piston assembly into a first volume and a second volume, and the apparatus being arranged to supply fluid to both the first and second 2 volumes to cause extension of the cylinder assembly, and to supply fluid to only the second volume to cause retraction of the cylinder assembly.
The piston head preferably includes a one-way valve allowing fluid to flow from the first volume to the second volume but preventing flow in the opposite direction. The piston assembly may include a first fluid inlet passageway communicatina with the first volume and a second fluid inlet passageway communicating with the second volume, the first passageway extending longitudinally Within the second passageway. The hydraulic supply preferably includes a pump that is operable in two directions, the apparatus being arranged such that fluid is supplied to the first and second volumes when the pump is operated in one direction and is supplied only to the second volume when the pump is operated in the opposite direction. The piston assembly may be fixed and the cylinder assembly may be movable and attached with a load. The apparatus preferably includes at least one sliding bearing engaging the outer surface of the outer cylinder. The apparatus preferably includes two fluid lines conununicating with the first and second volumes respectively, both fluid lines including a check valve, and the fluid line communicating with the first volume being a pilot-operated check valve operated by pressure in the other fluid line.
Hydraulic apparatus for a patient lift, will now be described, by way of example, with reference to the accompanying drawing, which shows the apparatus schematically.
3 The apparatus comprises an hydraulic cylinder assembly 1 connected to an hydraulic fluid supply 2. The cylinder assembly 1 is fixed at its lower end on a mount 30 and is connected at its upper end to one end 3 of a lateral bar 4. The other end 5 of the bar 4 supports a chair 6 in which a patient can sit, such as to be lifted into and out of a bath. The apparatus could, alternatively, be used in other applications.
The cylinder assembIly 1 comprises an outer cylinder 10, which is closed at its upper end 11 and has a annulus 12' at its lower end 12 providing a circular opening 13) with a sealing ring 14. The cylinder 10 is supported against lateral displacement by 0 two annular slide bearings 15 and 16 spaced from one another and engaging the outside of the cylinder in a manner that allows vertical, sliding movement of the cylinder. The bearings 15 and 16 and the cylinder 10 also allow the cylinder to be rotated about a vertical axis so that the arm 4 can be swung in an arc.
The cylinder assembly 1 also includes a piston assembly 20 slidable relative to the cylinder 10. At its upper end, the piston assembly 20 has a piston head 21 having an annular sealing ring 22 located in a groove 23 extending around its outer surface. The sealing ring 22 makes a sliding, sealing fit with the inside of the cylinder 10 but, because the pressure difference across the piston head 21 is not high, the seal provided by the ring need not have a high efficiency. The piston head 21 has a oneway check valve 24 within it, which allows fluid to flow from the upper surface of the piston head to its lower surface, but prevents flow in the opposite direction. The piston head 21 also has a central orifice 25 on its upper surface opening into a bore 26 on its opposite surface. The bore 26 is sealed to the upper end of a central pipe 27 4 extending coaxially of the cylinder 10 and fixed at its lower end to the mount 30. The lower end of the pipe 27 provides one inlet 28 of the cylinder assembly 1.
The piston assembly 20 is completed by a tubular piston rod 3 1, extending coaxially about the central pipe 27. The piston rod '31 is fixed at its upper end to the underside of the piston head 2 1, and at its lower end to the mount 30. The internal diameter of the piston rod 3) 1 is greater than the external diameter of the central pipe 27 so that an annular recess 3)2 of fixed volume is formed between them. The outlet of the one- way valve 24 opens within the recess 32. At the upper end of the rod 3 1, the recess 3) 2 opens through side apertures 33) into an outer annular recess 34 of variable volume between the outside of the rod 3 1 and the inside of the cylinder 10. At its lower end, the inner recess 32 provides the second fluid inlet 35 of the cylinder assembly 1.
The fluid supply system 2 is connected to the two inlets 28 and 35 of the cylinder assembly 1. The fluid supply system 2 includes a reversible electric motor 40 coupled to an hydraulic pump 41 having two ports 42 and 43, which act as either an outlet or an inlet according to the direction in which the pump is driven. The fluid supply system has two fluid lines 44 and 45 connected to the inlets 28 and 35 respectively. Each line 44 and 45 contains a check valve, the valve 46 in line 44 being a pilot- operated one-way check valve opened by pressure in line 45, whereas the other valve 47 is a simple one-way check valve. The lines 44 and 45 connect with respective ports 42 and 43) of the pump 4 1, the ports also being connected to a fluid reservoir 50, firstly via a filter 51 and respective one-way check valve 52 and 53, and secondly via respective pressure relief valves 54 and 55. An additional low pressure relief valve 56 is connected between lines 44 and 45 to allow flow of fluid from line 45 to line 44 when pressure in line 45 rises above that in line 44 by more than the opening pressure of the valve. The opening pressure of the valve 56 is set at a much lower value than that of the pressure relief valve 55.
If the apparatus is initially switched to cause extension of the cylinder assembly 1 (raising the cylinder 10), the motor 40 and pump 41 are operated in a forward direction such that the left-hand port 42 is the outlet and fluid is drawn from the reservoir 50 via the valve 53 to the inlet 43 of the pump. The pump 41 supplies this fluid via line 44 and the check valve 46 to the inlet 28 of the cylinder assembly 1. Fluid flows via the pipe 27 and the orifice 25, which may be selected to provide a restriction to fluid flow, to the closed end 11 of the cylinder 10 above the piston head 2 1. The check valve 24 in the piston head 21 allows this fluid to flow into the annular space.' 3 4 via the annular space J3) 2 and the apertures 33). Flow of fluid out of the inlet 35 at the lower end of the annular space 32 is prevented by the one-way check valve 47. Fluid supplied to the cylinder assembly 1 via the inlet 28 flows, therefore, into the space above the piston head 21 and into the outer annular space 34, so that these volumes can be regarded as integral. For a volume V of fluid supplied to the cylinder assembly 1 via the inlet 2 8, the cylinder 10 will be displaced up by a distance equal to V/A,, where A, is the external cross-sectional area of the rod 3 1. The rate of extension is, therefore, dependent on the external diameter of the rod 3 1. If pressure in the fluid line 44 rises above a predetermined value, such as caused by an obstruction to upward movement of the cylinder 10, the pressure relief valve 54 opens allowing 6 fluid pressure to flow to the reservoir 50 and halting movement of the cylinder. If the fluid supply 2 should fail, the valves 46 and 47 close and prevent the cylinder assembly 1 retracting.
To retract the cylinder assembly 1, the motor 40 and pump 41 are reversed, so that the pump supplies fluid to the other inlet 35. This inlet 35 communicates directly with the annular space 32 and with the space 34 via the apertures 3 33. The one-way valve 24 in the piston head 21 prevents fluid flowing to the space at the closed end 11 of the cylinder 10 above the upper surface of the piston head. Fluid supplied to the cylinder assembly 1 via the inlet 35, therefore, flows into the variable volume of the outer annular space 34 causing the cylinder 10 to move down relative to the piston assembly 20. Fluid trapped in the upper, closed end of the cylinder 10 flows out through the check valve 24 when pressure above the piston head 21 exceeds that below it. For a volume V of fluid supplied to the cylinder assembly 1 via the inlet 35, the cylinder 10 will be displaced down by a distance equal to V/A2, where A2 is the crosssectional area of the annulus 12'. Alternatively, by appropriately selecting the ratio between these two areas, the retraction and extension speeds can be set at any ratio. This is achieved without the need to alter the speed of the pump between extension and retraction. The rate of retraction, therefore, can be made equal to the rate of extension by making the external cross-sectional area A, of the rod 31 equal to the area A2 of the annulus 12'. If pressure in the fluid line 45 rises above a predetermined value, such as caused by an obstruction to downward movement of the cylinder 10, the pressure relief valve 56 opens allowing fluid pressure in the two lines 7 44 and 45 to equalize, thereby halting movement of the cylinder. The relief valve 55 provides a safety relief if pressure in line 45 should continue to rise.
The piston head 21 divides the space between the cylinder 10 and the piston assembly 20 into two volumes, namely a first volume provided by the space above the piston head and a second volume provided by the space below the head between the outside of the rod 3 3 1 and the inside of the cylinder 10. Extension of the cylinder assembly is achieved by supplying fluid pressure to both these volumes, whereas retraction is achieved by supplying pressure to only the second volume. The apparatus, therefore, acts in a dual mode: as a differential, single-acting cylinder on extension; and as an annular-fed, double-acting cylinder on retraction. This is achieved even though fluid connection is made to only one end of the cylinder assembly 1, avoiding external hoses extending along the cylinder assembly.
The load applied by the weight of the patient in the chair 6 is at one end of the lateral bar 4 so a considerable sideways force is exerted on the cylinder assembly 1 and the bearings 15 and 16. Because the bearings 15 and 16 engage the large area of the outer surface of the cylinder 10, the force is distributed more evenly. If wear of the bearings 15 and 16 should cause frictional resistance, the present invention reduces the risk of movement being prevented, because both extension and retraction are powered.
The apparatus of the present invention supplies power both to retract as well as to extend the cylinder assembly, thereby making retraction of the cylinder 8 assembly independent of the applied load. The apparatus also enables the maximum retraction force to be set independently of the extension force. This is a useful safety feature because it enables the maximum retraction force set by the relief valve 56 to be set at a relatively low value, reducing the risk of injury or damage on lowering the load.
It will be appreciated that the invention could be used in many applications other than patient lifts.
9

Claims (9)

  1. Hydraulic apparatus comprising a cylinder assembly and an hydraulic supply, wherein the cylinder assembly comprises an outer cylinder and a piston assembly movable longitudinally relative to one another, wherein the outer cylinder has an annulus at one end and is closed at its opposite end, wherein the piston assembly includes a piston head that divides the space between the cylinder and the piston assembly into a first volume and a second volume, and wherein the apparatus is arranged to supply fluid to both the first and second volumes to cause extension of the cylinder assembly, and to supply fluid to only the second volume to cause retraction of the cylinder assembly.
  2. Hydraulic apparatus according to Claim 1, wherein the piston head includes a oneway valve allowing fluid to flow from the first volume to the second volume but preventing flow in the opposite direction.
  3. Z"> Hydraulic apparatus according to Claim 1 or 2, wherein the piston assembly includes a first fluid inlet passageway communicating with the first volume and a second fluid inlet passageway communicating with the second volume, and wherein the first 0 passageway extends longitudinally within the second passageway.
  4. 4. Hydraulic apparatus according to any one of the preceding claims, including a pump that is operable in two directions, and wherein the apparatus is arranged such that fluid is supplied to the first and second volumes when the pump is operated in one direction and is supplied only to the second volume when the pump is operated in the opposite direction.
  5. 5.
    Hydraulic apparatus according to any one of the preceding claims, wherein the piston assembly is fixed and the cylinder assembly is movable and attached with a load.
  6. Hydraulic apparatus according to Claim 5 including at least one sliding bearing engaging the outer surface of the outer cylinder.
  7. 7. Hydraulic apparatus according to any one of the preceding claims, including two fluid lines communicating with the first and second volumes respectively, wherein both fluid lines include a check valve, and wherein the fluid line communicating with the first volume is a pilot-operated check valve operated by pressure in the other fluid line.
  8. 8. Hydraulic apparatus substantially as hereinbefore described with reference to the accompanying drawing.
  9. 9. Any novel and inventive feature as hereinbefore described.
GB9824206A 1997-12-16 1998-11-04 Hydraulic apparatus Withdrawn GB2332480A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GBGB9726517.7A GB9726517D0 (en) 1997-12-16 1997-12-16 Hydraulic apparatus

Publications (2)

Publication Number Publication Date
GB9824206D0 GB9824206D0 (en) 1998-12-30
GB2332480A true GB2332480A (en) 1999-06-23

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GBGB9726517.7A Ceased GB9726517D0 (en) 1997-12-16 1997-12-16 Hydraulic apparatus
GB9824206A Withdrawn GB2332480A (en) 1997-12-16 1998-11-04 Hydraulic apparatus

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Application Number Title Priority Date Filing Date
GBGB9726517.7A Ceased GB9726517D0 (en) 1997-12-16 1997-12-16 Hydraulic apparatus

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2006012017A1 (en) * 2004-06-30 2006-02-02 Ebihara Daniel T Fluid-operated power generating system
GB2422862A (en) * 2005-02-03 2006-08-09 Schlumberger Holdings Apparatus for actuating downhole tools

Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1473420A (en) * 1973-07-31 1977-05-11 Peiner Masch Schrauben Control means for hydraulically driven grabs
GB1473123A (en) * 1973-07-31 1977-05-11
GB1514891A (en) * 1976-05-03 1978-06-21 Dewandre Co Ltd C Hydraulic cab tilting systems
GB1526563A (en) * 1977-06-17 1978-09-27 Davy Loewy Ltd Fluid operable piston-cylinder device
GB1579287A (en) * 1976-06-10 1980-11-19 Sanyo Kiki Kk Speed-up devices for reciprocating cylinders
GB2080421A (en) * 1980-07-02 1982-02-03 Annegarn Joseph M J Fluid operated piston and cylinder assembly and metal drawing apparatus embodying same
US5370038A (en) * 1992-12-21 1994-12-06 Caterpillar Inc. Regeneration circuit for a hydraulic system
GB2294505A (en) * 1994-10-25 1996-05-01 Nisshin Spinning Hydraulic circuit for driving the ram of a hydraulic press

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1473420A (en) * 1973-07-31 1977-05-11 Peiner Masch Schrauben Control means for hydraulically driven grabs
GB1473123A (en) * 1973-07-31 1977-05-11
GB1514891A (en) * 1976-05-03 1978-06-21 Dewandre Co Ltd C Hydraulic cab tilting systems
GB1579287A (en) * 1976-06-10 1980-11-19 Sanyo Kiki Kk Speed-up devices for reciprocating cylinders
GB1526563A (en) * 1977-06-17 1978-09-27 Davy Loewy Ltd Fluid operable piston-cylinder device
GB2080421A (en) * 1980-07-02 1982-02-03 Annegarn Joseph M J Fluid operated piston and cylinder assembly and metal drawing apparatus embodying same
US5370038A (en) * 1992-12-21 1994-12-06 Caterpillar Inc. Regeneration circuit for a hydraulic system
GB2294505A (en) * 1994-10-25 1996-05-01 Nisshin Spinning Hydraulic circuit for driving the ram of a hydraulic press

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2006012017A1 (en) * 2004-06-30 2006-02-02 Ebihara Daniel T Fluid-operated power generating system
US7159396B2 (en) 2004-06-30 2007-01-09 Ebihara Daniel T Fluid-operated power generating system
GB2422862A (en) * 2005-02-03 2006-08-09 Schlumberger Holdings Apparatus for actuating downhole tools

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GB9726517D0 (en) 1998-02-11
GB9824206D0 (en) 1998-12-30

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