EP1015761B1 - Improvements in and relating to hydraulic pumps and motors - Google Patents
Improvements in and relating to hydraulic pumps and motors Download PDFInfo
- Publication number
- EP1015761B1 EP1015761B1 EP98908221A EP98908221A EP1015761B1 EP 1015761 B1 EP1015761 B1 EP 1015761B1 EP 98908221 A EP98908221 A EP 98908221A EP 98908221 A EP98908221 A EP 98908221A EP 1015761 B1 EP1015761 B1 EP 1015761B1
- Authority
- EP
- European Patent Office
- Prior art keywords
- slipper
- piston
- pad
- annular ring
- polymer
- 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
Links
Images
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
- F04B1/122—Details or component parts, e.g. valves, sealings or lubrication means
- F04B1/124—Pistons
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
- F05C—INDEXING SCHEME RELATING TO MATERIALS, MATERIAL PROPERTIES OR MATERIAL CHARACTERISTICS FOR MACHINES, ENGINES OR PUMPS OTHER THAN NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES
- F05C2225/00—Synthetic polymers, e.g. plastics; Rubber
Definitions
- the present invention relates to hydraulic pumps and motors, and more especially to an improved slipper design for use therein.
- a known hydraulic pump comprises an outer casing, a cylindrical block keyed to a drive shaft and a plurality of piston assemblies each mounted within a respective axially extending bore in the cylinder block.
- Each piston assembly comprises a hollow piston which is slidable back and forth within its bore and a slipper which is mounted on a ball joint at the end of the piston. The slippers are supported against an angled swash plate which is fixed in position relative to the rotatable cylinder block.
- a port plate which is fixed in position relative to the rotatable cylinder block.
- the port plate has in it an inlet port through which water is supplied to the piston bores in the cylinder block and an outlet port through which water is expelled from piston bores under pressure.
- the cylinder block is rotatably driven by means of a prime mover connected to the drive shaft.
- a prime mover connected to the drive shaft.
- water is drawn into the bore, as the piston is moved along the length of the bore by the action of the slipper on the angled surface of the swash plate which at this point in the cycle of rotation is extending away from the cylinder block.
- the open end thereof is closed off with a quantity of water in it.
- each slipper passes up the angled surface of the swash plate which is now extending towards the cylinder block. This has the effect of causing the piston connected to the slipper to be driven back down the bore in which it is located, compressing the volume of water contained therein.
- the bore passes into alignment with the outlet port in the port plate the water in the bore is expelled therethrough under pressure. In this way water entering the pump under relatively low pressure is pumped out at high pressure.
- the water pump described hereinabove can also function as an hydraulic motor.
- the pump is simply operated in reverse; water under high pressure is applied to the inlet port which has the effect of driving each of the pistons in turn down its respective bore.
- the slipper connected to the end of each piston passes over the angled surface of the swash plate it has the effect of causing the cylinder block and the drive shaft connected to it to turn.
- slippers of conventional design a circular polymer slipper pad is secured to the front face of the slipper, conveniently by means of a grub screw, or is moulded onto the front face of the slipper.
- the front surface of the slipper pad defines a centrally located recess or pocket and into the centre of this recess a capillary sized through bore opens.
- the through bore extends from the recessed surface of the slipper pad, through the slipper and the ball shaped foot on which it is mounted, and connects with the hollow section of the piston.
- liquid is supplied from the cylinder bore in which a piston assembly is mounted through to the front surface of the slipper pad associated with that piston assembly.
- the liquid in the recess of the slipper pad serves to create a hydrostatic bearing between the slipper pad and the angled swash plate against which it is supported when the hydraulic pump/motor is in use.
- This hydrostatic bearing causes the slipper pad to lift off the swash plate into a hydrostatically balanced condition as each piston assembly sees pressure.
- the film of liquid in the recess of each slipper pad also serves to lubricate and allow free movement of the slipper pad over the surface of the angled swash plate.
- the circular polymer slipper pad of conventional slipper designs is not very tolerant of the pressure changes which take place across its surface as a result of the pressure changes which are inherent in an axial piston pump/motor.
- the slipper pad covers substantially all of the front face of the slipper it is subject to considerable bending moments and these can lead to premature failure due to fatigue stresses.
- mechanical fixing means e.g. a countersunk screw
- this has the effect of reducing the overall piston ball seat area the end of the screw must be accommodated in the area of the piston ball seat. This reduces the load taking area and results in increased piston ball seat stresses.
- a piston assembly for an axial displacement pump or motor comprising a piston having at one end a ball shaped piston foot, and a slipper, the rear end of which defines a piston ball seat in which the ball shaped piston foot is received, characterised in that a centrally located annular groove or cylindrical bore is provided in the front end of the slipper, within which is located an annular slipper pad of polymer material which defines a sliding contact surface.
- the slipper defines a planar front face in which is provided an annular groove and the annular ring, the axial length of which is greater than the depth of the annular groove, is mounted in the annular groove.
- the slipper itself can be much thicker at the centre than is the case with conventional designs where a recess must be provided in the slipper to accommodate the circular slipper pad. It will be apparent that this increased thickness gives the slipper a much more rigid construction and reduces the likelihood of bending at the piston ball to piston ball seat interface.
- the slipper design in accordance with the present invention allows for much improved load carry capacity over conventional slipper designs with the result that the working life of a hydraulic pump/motor can be extended for existing typical working loads or pressures.
- a piston assembly according to claim 1 characterised in that the slipper comprises a metal annular ring, the inner diameter of which is substantially equal to the outer diameter of the polymer annular ring pad, and the axial length of which is less than that of the polymer annular ring pad, wherein the polymer annular ring pad is received co-axially within the metal annular ring, such that the hoop stresses in the polymer annular ring pad are constrained by the metal annular ring.
- the slipper is essentially defined by a ring of polymer, the slipper to swash plate load is decreased, thereby reducing the surface stresses in the slipper ring to swash plate interface. This results in lower friction, giving improved starting performance and reduced slipper ring wear.
- the water pump/motor comprises cylindrical outer casing 1 which is closed at one end by a port end covering 2 and at the opposite end by a mounting flange plate or snout 3.
- Bolts (not shown) hold the port end covering 2 and the snout 3 to the outer casing 1 and O-rings 4 seal the joints therebetween and prevent any leakage of liquid.
- An aperture is provided in the centre of the snout 3 within which is mounted a drive shaft 5.
- the drive shaft 5 is held in place by means of a seal housing 6 which is recessed into the front face of the snout 3 and held in place by means of socket head capscrews 7 (only one of which is shown for ease of illustration).
- An O-ring 8 between the seal housing 6 and the snout 3 prevents liquid from leaking therebetween.
- the seal housing 6 also supports a seal 9 which prevents liquid from leaking past the drive shaft 5.
- the drive shaft 5 is rotatably supported within the aperture in the snout 3 by means of front and rear bearings 10 and 11.
- a dummy shaft 1 Keyed to the inner end of the drive shaft 5 is a dummy shaft 1 and keyed onto the dummy shaft 11 is a cylinder block 12.
- the cylinder block is rotatable with the drive shaft 5 within the cavity defined by the outer casing 1, the port end covering 2 and the snout 3.
- a snout bush 13 allows free rotation of the cylinder block 12 on the inner end of the snout 3.
- the cylinder block 12 carries a plurality of piston assemblies 14 (only two of which are actually shown for ease of illustration). Each of the piston assemblies 14 is mounted within a respective axially extending piston bore in the cylinder block 12 and is axially slidable back and forth therein. Each of the piston assemblies 14 comprises a piston 15 having a hollow body and a ball shaped piston foot 16 at one end on which is mounted a slipper 17. The slippers 17 are supported against and are slidable over the surface of an angled swash plate 30 secured to the inner face of the snout 3.
- Each slipper 17 is held in place on the ball shaped piston foot 16 by a retaining cap of the type commonly referred to as a "top hat", and a split ring retaining bush.
- a circular slipper pad 20 is secured to the front surface of the slipper by means of a countersunk screw,
- a piston ball seat supports the slipper on the ball shaped piston foot.
- a frictionless sleeve around the body of the piston 15 ensures free movement of the piston assembly 14 back and forth within its respective piston bore.
- a capillary sized bore 23 is provided from the front surface of the slipper pad 20 through to the hollow body of the piston 15. As shown, this capillary sized bore 23 passes through the screw which secures the slipper pad 20 to the slipper 17.
- the slipper pad 20 may be over moulded onto the slipper 17.
- a through hole must be provided from the piston seat to the front surface of the slipper through which the polymer can flow during moulding.
- the capillary sized through bore must be maintained in this hole.
- a slipper 41 having a piston ball seat 42 mounted in a cavity in the rear surface thereof which facilitates connection of the slipper to the ball shaped piston foot of a piston (not shown).
- the front surface of the slipper is planar except for a circumferential groove 43 machined in it.
- a ring shaped slipper pad 44 comprised of a polymer material.
- the ring shaped slipper pad 44 is retained in the groove 43 by a friction fit.
- the depth of the circumferential groove 43 is such that the ring shaped slipper pad 44 stands proud of the planar surface of the slipper 41 itself.
- ring shaped slipper pad 44 which engages with the surface of the swash plate in an axial displacement pump or motor.
- a capillary sized through bore 45 is provided in the slipper 41 from the front face thereof through to the piston ball seat 42.
- the slipper does not have a large hole at the centre to accommodate the screw or the shaft of polymer which are required to secure conventional circular slipper pads in place, it is much thicker at the centre than a conventional slipper. This gives it a much more rigid construction, reducing bending of the piston ball seat to piston ball interface and repetitive stress cycles due to metal deformation.
- a slipper which consists of an inner ring of polymer 51 and an outer ring of metal 52.
- the inner ring 51 is of slightly greater length axially than the outer ring 52 such that it defines a ring shaped slipper pad 53 at one end. In use, this ring shaped slipper pad 53 is supported against a swash plate.
- the inner surface of the inner ring is shaped to define a piston ball seat 54. The ball shaped piston foot of a piston is received within the inner ring 51 against the ball seat 54.
- the outer ring 52 of metal is provided to constrain hoop stresses in the inner ring 51.
- Leakage between the piston ball and piston ball seat is minimised by manufacturing the inner ring from a polymer which is deformable, at least in the region of the piston ball seat.
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Reciprocating Pumps (AREA)
- Hydraulic Motors (AREA)
- Fluid-Pressure Circuits (AREA)
Description
Claims (6)
- A piston assembly for an axial displacement pump or motor comprising a piston (15) having at one end a ball shaped piston foot (16), and a slipper (41), the rear end of which defines a piston ball seat (42) in which the ball shaped piston foot (16) is received, characterised in that a centrally located annular groove or cylindrical bore is provided in the front end of the slipper (41), within which is located an annular slipper pad (44) of polymer material which defines a sliding contact surface.
- A piston assembly according to claim 1, characterised in that the slipper (41) defines a planar front face in which is provided an annular groove (43) and the annular ring (44), the axial length of which is greater than the depth of the annular groove (43), is mounted in the annular groove (43).
- A piston assembly according to claim 2 characterised in that the annular ring (44) retained in the annular groove (43) by a friction fit.
- A piston assembly according to claims 2 or 3, characterised in that a cylindrical cavity is provided in the rear end of the slipper (41), in which is received a piston ball seat (42).
- A piston assembly according to claim 1 characterised in that the slipper comprises a metal annular ring (52), the inner diameter of which is substantially equal to the outer diameter of the polymer annular ring pad (53), and the axial length of which is less than that of the polymer annular ring pad (53), wherein the polymer annular ring pad (53) is received co-axially within the metal annular ring (52), such that the hoop stresses in the polymer annular ring pad (53) are constrained by the metal annular ring.
- A piston assembly according to claim 5 characterised in that the rear end of the polymer annular ring pad (53) defines a piston ball seat (54).
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GBGB9704678.3A GB9704678D0 (en) | 1997-03-06 | 1997-03-06 | Improvements in and relating to hydraulic pumps and motors |
GB9704678 | 1997-03-06 | ||
PCT/GB1998/000655 WO1998039568A1 (en) | 1997-03-06 | 1998-03-03 | Improvements in and relating to hydraulic pumps and motors |
Publications (2)
Publication Number | Publication Date |
---|---|
EP1015761A1 EP1015761A1 (en) | 2000-07-05 |
EP1015761B1 true EP1015761B1 (en) | 2002-09-11 |
Family
ID=10808821
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP98908221A Expired - Lifetime EP1015761B1 (en) | 1997-03-06 | 1998-03-03 | Improvements in and relating to hydraulic pumps and motors |
Country Status (9)
Country | Link |
---|---|
EP (1) | EP1015761B1 (en) |
JP (1) | JP2001513865A (en) |
AU (1) | AU719300B2 (en) |
CA (1) | CA2282424A1 (en) |
DE (1) | DE69807903T2 (en) |
DK (1) | DK1015761T3 (en) |
GB (1) | GB9704678D0 (en) |
WO (1) | WO1998039568A1 (en) |
ZA (1) | ZA981899B (en) |
Families Citing this family (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
ITPD20030012U1 (en) * | 2003-02-25 | 2004-08-26 | Lavorwash Spa | AXIAL PISTON PUMP OPERATED BY AN ELECTRIC MOTOR |
DE102006057364B4 (en) | 2006-12-04 | 2011-08-25 | Danfoss A/S | Water hydraulic machine |
Family Cites Families (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB1141605A (en) * | 1965-04-10 | 1969-01-29 | Dowty Technical Dev Ltd | Hydraulic apparatus |
DE2909248C2 (en) * | 1979-03-09 | 1984-03-15 | J.M. Voith Gmbh, 7920 Heidenheim | Working piston for a hydrostatic piston machine |
DE4301123C2 (en) * | 1993-01-18 | 1995-05-18 | Danfoss As | Hydraulic machine and method for assembling a piston-shoe unit |
DE19601721C3 (en) * | 1996-01-18 | 2003-07-24 | Brueninghaus Hydromatik Gmbh | Weight-optimized, multi-part sliding shoe |
-
1997
- 1997-03-06 GB GBGB9704678.3A patent/GB9704678D0/en active Pending
-
1998
- 1998-03-03 JP JP53826898A patent/JP2001513865A/en active Pending
- 1998-03-03 DE DE69807903T patent/DE69807903T2/en not_active Expired - Fee Related
- 1998-03-03 EP EP98908221A patent/EP1015761B1/en not_active Expired - Lifetime
- 1998-03-03 DK DK98908221T patent/DK1015761T3/en active
- 1998-03-03 AU AU66302/98A patent/AU719300B2/en not_active Ceased
- 1998-03-03 WO PCT/GB1998/000655 patent/WO1998039568A1/en active IP Right Grant
- 1998-03-03 CA CA002282424A patent/CA2282424A1/en not_active Abandoned
- 1998-03-05 ZA ZA9801899A patent/ZA981899B/en unknown
Also Published As
Publication number | Publication date |
---|---|
EP1015761A1 (en) | 2000-07-05 |
CA2282424A1 (en) | 1998-09-11 |
DK1015761T3 (en) | 2002-11-18 |
AU6630298A (en) | 1998-09-22 |
WO1998039568A1 (en) | 1998-09-11 |
DE69807903D1 (en) | 2002-10-17 |
AU719300B2 (en) | 2000-05-04 |
JP2001513865A (en) | 2001-09-04 |
GB9704678D0 (en) | 1997-04-23 |
DE69807903T2 (en) | 2003-05-28 |
ZA981899B (en) | 2000-06-27 |
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