GB2062770A

GB2062770A - Improvements in Hydraulic Pumps

Info

Publication number: GB2062770A
Application number: GB7938572A
Authority: GB
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1979-11-07
Filing date: 1979-11-07
Publication date: 1981-05-28

Abstract

An hydraulic pump comprises two plungers (15, 16) working in parallel bores (7, 8) and an eccentric drive mechanism (23) acting on the plungers through a common lever (19) which is mounted to rock about a fixed pivot (20). The parallel arrangement of the plungers allows the side thrust imparted by the drive mechanism on the plungers to be minimised. The effective sizes of the plungers can be increased substantially in comparison with known pumps having a radial arrangement of bores. The eccentric drive mechanism (23) acts on the rocking lever (19) through a reciprocating block (28) slidably received in a slot (29) in the lever. The friction of the block sliding in the slot is transferred to the fixed pivot and not to the plungers, thereby avoiding any tendency for the plungers to "scrub" the bores in which they work. <IMAGE>

Description

SPECIFICATION Improvements In Hydraulic Pumps This invention relates to improvements in hydraulic pumps for hydraulic systems of the kind in which at least two pump plungers are adapted to be reciprocated in different bores in a housing by means of a common eccentric drive mechanism.

In one known hydraulic pump of the kind set forth, the bores are radially arranged and are spaced circumferentially with respect to each other. Noise consideration apart, in such a known construction, for reliability, it is necessary to maintain within acceptable limits the side thrust which the eccentric drive mechanism imparts to the plungers. Since the side thrust is a function of operating pressure and the size of the plungers, it follows that there is a limit to the maximum size of the plungers which will be compatible with the required degree of reliability.

In addition, the arrangement of the radial bores may necessitate the provision of complicated cross-drillings to link delivery chambers. This is particularly complicated where three or more bores are provided in the common housing.

According to our invention an hydraulic pump of the kind set forth incorporates two plungers which work in substantially parallel bores in the housing and the eccentric drive mechanism acts on the plungers through a common lever which is mounted to rock about a fixed pivot in the housing.

By providing a "binocular" arrangement and by utilising a rocking lever, the geometry can be so arranged that side thrust is minimised. This has the advantage that the effective sizes of plungers can be increased substantially in comparison with known pumps in which the bores are relatively spaced circumferentially. In fact two plungers operated by a rocking lever can provide the pump with a capacity which is substantially equivalent to that of a pump having four plungers which are relatively spaced circumferentially. In addition the geometry can be arranged such that the plungers are loaded centrally.

The eccentric drive mechanism acts on the rocking lever through a block which is reciprocably mounted in a slot in the lever in which it is slidably received.

This has the advantage that the friction of the block sliding in the slot is transferred to, and is taken by, the fixed pivot. Thus any tendency for this to be transmitted to the plunger in avoided, thereby avoiding any tendency for the plungers to "scrub" the bores in which they work.

The slot in which the block reciprocates may be located on the inboard side of the pivot, between the pivot and the plungers, or it may be located on the outboard side of the pivot remote from the plungers.

The lever is provided on opposite sides of the pivot with a pair of arms. Where the slot is located on the outboard side of the pivot, the arms can act directly on the plungers. Where the slot is located on the inboard side of the pivot, the arms can act indirectly on the plungers through thrust members of which the ends are adapted to rock in complementary recesses in the arms and in the plungers.

Some embodiments of our invention are illustrated in the accompanying drawings in which: Figure 1 is a longitudinal section through an hydraulic pump; Figure 2 is a transverse section through the same; Figure 3 is a longitudinal section through another hydraulic pump; Figure 4 is a section on the line 4-4 of Figure 3; Figure 5 is a section on the line 5-5 of Figure 3; Figure 6 is a view similar to Figure 3 but with the lever in a different position; Figure 7 is a longitudinal section through a further hydraulic pump incorporating a regulator valve; Figure 8 is a section on the line 8-8 of Figure 7; Figure 9 is a section on the line 9-9 of Figure 8; and Figure 10 is a view similar to Figure 7 but with the lever in a different position and incorporating a modification.

The pump illustrated in Figures 1 and 2 of the drawings comprises a housing in the form of a valve block 1, and an end cover 2 which is bolted to the one end of the block to define a chamber 3 which is connected through a port 4 in the cover to a tank containing hydraulic fluid.

A pair of two-piece sleeves 5 and 6 of generally cup-shaped outline are guided for limited axial sliding movement in a pair of parallel blind bores 7, 8 in the block 1.

A plate valve housed in each sleeve 5, 6 comprises a plate 9 which abuts against the closed end of the sleeve 5, 6, against a seating 11 in the sleeve to cut-off communication between the remainder of the bore of the sleeve 5, 6 and radial outlet ports 12 in the walls of the sleeves 5, 6. A transverse passage 13 in the block 1 interconnects the two sets of outlet ports 12, which in addition, communicate all times with an outlet port 14 in the block 1 for connection to services, for example an hydraulic accumulator.

A hollow pump plunger 15, 16 of cup-shaped outline works in the bore of each respective sleeve 5, 6 and is urged outwardly at its closed end by a return spring 17, 18 which acts between the plunger 15, 1 6 and the respective plate 9.

A lever 19 of generally semi-circular outline is mounted in the chamber 3 for rocking movement about a fixed pivot 20. The lever 19 is provided on opposite sides of the pivot 20 with thrust transmitting portions 21, 22 of arcuate outline which engage with the closed outer ends of the plungers 15, 1 6.

The lever 1 9 is adapted to rock about the pivot 20 by operation of a drive mechanism 23. The mechanism 23 comprises a transverse shaft 24 which is rotatably mounted at opposite end portions in bushings 25, 26 in the walls of the end cover 2 on opposite sides of the chamber 3. An integral eccentric 27 on the shaft between the end portions is rotatable in a circular opening in a parallel sided block 28 which is slidably received in a parallel sided slot 29 in the lever 19. The slot 29 is symmetrically arranged in the lever 1 9 with respect to the pivot 20, on the outboard side of the lever 19 from the pivot 20 which is remote from the plungers 1 5, 1 6.

Rotation of the eccentric 27 with the shaft 24 causes the block 28 to reciprocate in the slot 29, and the lever 19 to rock about the pivot 20 thereby urging the plungers 1 5, 1 6 altenately inwardly against the loading in the return springs 17,18.

As shown in the drawings, when the plunger 16 is moved by the spring 18 into the B.D.C.

position shown, the respective plate valve 9 is closed and a pump chamber 30 defined within the sleeve 1 6 is in open communication with the chamber 3, and hence the tank, through radial supply ports 31 in the plunger, so that fluid is drawn into the pump chamber 30. As the plunger 1 6 is moving into the B.D.C. position the plunger 1 5 is being moved by the lever 1 9 inwardly of the sleeve 5, initially to close the supply ports 31 and thereafter to force the fluid from a pump chamber 32 defined within the sleeve 5 to the outlet port 14 and through the corresponding plate valve 9 which then opens.

The action of the pump is controlled by a pressure regulator 33 which is incorporated in the valve block 1. The regulator 33 comprises a spool 34 which is normally urged by a spring 35 in an inwards direction to isolate chambers 36, 37 between the closed ends of the sleeves 5, 6 and the bores 7, 8, from the passage 13 through an axial bore 38, and to place the chambers 36, 37 in communication with the tank through a chamber 39 in the valve block 1 in which the spring 35 is housed.

The spring 35 is pre-loaded such that the spool 34 does not move until a predetermined pressure, of say 2000 p.s.i., has been developed in the bore 38. At that point the spool 34 moves axially against the loading in the spring 35 to isolate the chambers 36 and 37 from the tank.

At some higher pressure, determined by the stiffness of the spring 35, the spool 34 has moved sufficiently in the same direction to allow pressure fluid from the bore 38 to flow into the chambers 36 and 37. This pressure fluid acts on the sleeves 5 and 6 to urge them away from the closed ends of the bores 7 and 8 into stalled positions such that, during reciprocation of the plungers 1 5, 1 6, the ports 31 are at all times closed by the bores of the sleeves 5, 6. Pumping therefore ceases.

Thereafter the only additional fluid supplied to the chambers 36 and 37 is the amount necessary to allow the spool 34 to retract slightly to a neutral position in which the two chambers 36 and 37 are isolated from the tank and the outlet port 14.

The pressure in the chambers 36, 37 is determined by the spring 35.

When the sleeves 5 and 6 are in their stalled positions, the force on the eccentric 27 is minimised since the forces in the springs 1 7, 1 8 are balanced.

As the pressure in the bore 38 reduces, for example due to the use of powered equipment, the spool 34 will move in the opposite direction until, at a cut-in point at 2000 p.s.i., the chambers 36 and 37 are connected again to the tank. The springs 1 7, 1 8 are operative to urge the sleeves 5 and 6 into their initial positions and pumping will re-commence as described above. The springs 1 7, 1 8 therefore act as return springs for the sleeves 5 and 6, and for the plungers 1 5, 16.

In the pump of Figures 3-6 the drive mechanism 23 is located on the inboard side of the pivot 20 adjacent to the plungers 1 5, 1 6. The lever 19 has a pair of opposed arms 40, 41 and each arm acts on a respective plunger 1 5, 1 6 through a thrust member 42, 43 of which opposite ends are adapted to rock in part spherical recesses 44, 45 in the lever 19 and in the plunger 1 5, 1 6. The plate valve 9 and the springs 10 are omitted, and a one-way valve 46 is disposed between each sleeve 5, 6 and the outlet port 14.

The pressure regulator 35 is also omitted and fluid under pressure from an external regulator is adapted to supply fluid under pressure to the chambers 36 and 37 to disable the pump through a connection 47 in the valve block 1.

Figure 3 shows the lever 19 in a neutral position, and Figure 6 shows the relative dispositions of the components when the plunger 1 5 is at T.D.C and the plunger 16 at B.D.C.

The construction and operation of the pump of Figures 3-6 is otherwise the same as that of Figures 1 and 2 and corresponding reference numerals have been applied to corresponding parts.

The pump illustrated in Figures 7-9 is similar to that illustrated in Figures 3-6 except that the pump incorporates a pressure regulator 50. The pressure regulator 50 comprises a stationary sleeve 51 which is housed in a central blind bore 52 in the valve block 2 and the open outer end of the bore 52 is closed by a plug 53. A spool 54 is normally held in the inoperative position shown by a pre-loaded compression spring 55 which acts between the sleeve 51 and an abutment plate 56 which, in turn, is coupled to the inner end of the spool 54. In this position a chamber 57 between the plug 53 and the sleeve 51 and connected to the tank communicates with the chambers 36, 37 through a radial passage 58 in the sleeve 51, and the chambers 36, 37 are isolated by the spool 54 from a chamber 59 in which the spring 55 is housed and which is in communication with the outlet port 14.

As in the pump of Figures 1 and 2, when the pressure in the chamber 59 acting on the spool 54 is sufficient to overcome the pre-load in the spring 55, for example at a pressure of 2000 p.s.i., the spool 54 moves towards the plug 53 to isolate the chambers 36 and 37 from the tank by closing the inner end of the radial passage 58.

Thereafter, at a higher pressure, the spool 54 moves further in the same direction to place chamber 59, via passage 58, in communication with the chambers 36 and 37, anddnddnddnddnd the sleeves 5 and 6 move axially as described above to cause the pump to idle.

The construction and operation of the pump of Figures 7-9 is otherwise the same as that of Figures 3-6, and corresponding reference numerals have been applied to corresponding parts.

In the pump of Figure 10 the pressure regulator 50 is replaced by a solenoid-operated spool valve 60 of which the solenoid 61 is adapted to be energised to urge the spool 62 into a position to cause the pump to idle as described above.

Energisation of the solenoid 61 is achieved by a signal from suitable means, for example representing flow, pressure volume, height, depth, width and the like. This means that the pump is particularly suitable for use in hydraulic vehicle systems where the ride height of a vehicle is adjusted by pressurisation of suspension struts from a pump.

The construction and operation of the pump of Figure 10 is otherwise the same as that of Figures 7-9, and corresponding reference numerals have been applied to corresponding parts.

Claims

1. An hydraulic pump of the kind set forth in which two plungers work in substantially parallel bores in the housing and the eccentric drive mechanism acts on the plungers through a common lever which is mounted to rock about a fixed pivot in the housing.

2. An hydraulic pump as claimed in Claim 1, in which the eccentric drive mechanism acts on the rocking lever through a block which is reciprocably mounted in a slot in the lever in which it is slidably received.

3. An hydraulic pump as claimed in Claim 2, in which the slot in which the block reciprocates is located on the inboard side of the pivot, between the pivot and the plungers.

4. An hydraulic pump as claimed in Claim 2, in which the slot in which the block reciprocates is located on the outboard side of the pivot remote from the plungers.

5. An hydraulic pump as claimed in Claim 3, in which the lever is provided on opposite sides of the pivot with a pair of arms which act indirectly on the plungers through thrust members of which the ends are adapted to rock in complementary recesses in the arms and in the plungers.

6. An hydraulic pump as claimed in Claim 4, in which the lever is provided on opposite sides of the pivot with a pair of arms which act directly on the plungers.

7. An hydraulic pump as claimed in Claim 6, in which the lever is of substantially semi-circular outline and is provided on opposite sides of the pivot with thrust transmitting portions of arcuate outline which engage with closed ends of the plungers.

8. An hydraulic pump as claimed in any preceding claim in which a pair of two-piece sleeves of generally cup-shaped outline are guided for limited axial sliding movement in a pair of parallel blind bores in the housing, a radial outlet port being provided in the wall of each sleeve and a transverse passage interconnecting the ports which, in turn, communicate with an outlet port for connection to services.

9. An hydraulic pump as claimed in Claim 8, in which a plate valve is housed in each sleeve to cut off communication between the bore of the sleeve and the radial outlet port.

10. An hydraulic pump as claimed in Claim 8, in which a one-way valve is disposed between each sleeve and the outlet port.

11. An hydraulic pump as claimed in Claim 9 or Claim 10, in which a hollow pump plunger of generally cup-shaped outline works in the bore of each respective sleeve and is urged outwardly at its closed end by a return spring.

12. An hydraulic pump as claimed in any one of the Claims 8-11 1 in which there is provision for fluid under pressure from a regulator to be supplied to chambers between the closed ends of the sleeves and the closed ends of the bores, the fluid acting on the sleeves to urge them away from the closed ends of the bores into stalled positions causing the pump to idle.

13. An hydraulic pump as claimed in Claim 12, in which the fluid under pressure is supplied to said chambers from an external pressure regulator.

14. An hydraulic pump as claimed in Claim 12, in which the pressure regulator is incorporated in the housing.

1 5. An hydraulic pump as claimed in Claim 14, in which the pressure regulator comprises an axial bore housing a spool which is normally urged by a pre-loaded spring into a position so as to place the chambers between the closed ends of the sleeves and the bores in communication with the supply tank of hydraulic fluid through a supply chamber in the housing, said spool isolating said chambers from an outlet chamber in communication with the outlet port.

1 6. An hydraulic pump as claimed in Claim 15, in which the spool does not move until a predetermined pressure is reached in the outlet chamber when the fluid in the outlet chamber acts on the spool against the loading in the spring to move the spool to a position in which the chambers between the closed ends of the spools and bores are isolated from the supply tank, and at a higher pressure the spool moves further in the same direction to place the said chambers in communication with the outlet chamber, causing the sleeves to move axially and the pump to idle.

1 7. An hydraulic pump as claimed in Claim 16, in which the spool is normally urged in an inwards direction by the spring acting between the outer end of the axial bore and the spool.

18. An hydraulic pump as claimed in Claim 16, in which the spool is contained within a stationary sleeve housed in the axial bore and the spring acts between said sleeve and an abutment plate which is coupled to the inner end of the spool.

19. An hydraulic pump as claimed in Claim 12, in which the pressure regulator comprises a solenoid-operated spool valve of which the solenoid is adapted to be energised to urge the spool into a position to cause the pump to idle.

20. An hydraulic pump as claimed in Claim 19, in which the solenoid is energised by a signal from a monitoring device.

21. An hydraulic pump substantially as hereinbefore described with reference to and as illustrated by Figures 1 and 2 of the accompanying drawings.

22. An hydraulic pump substantially as hereinbefore described with reference to and as illustrated by Figures 3 to 6 of the accompanying drawings.

23. An hydraulic pump substantially as hereinbefore described with reference to and as illustrated by Figures 7 to 9 of the accompanying drawings.

24. An hydraulic pump substantially as hereinbefore described with reference to and as illustrated by Figure 10 of the accompanying drawings.