GB2238355A

GB2238355A - An hydraulic pump

Info

Publication number: GB2238355A
Application number: GB9021793A
Authority: GB
Inventors: Graham Scott; Stephen Brian Turner
Original assignee: Ultra Hydraulics Ltd
Current assignee: Ultra Hydraulics Ltd
Priority date: 1989-10-21
Filing date: 1990-10-08
Publication date: 1991-05-29
Anticipated expiration: 2010-10-08
Also published as: GB8923775D0; GB2238355B; GB9021793D0

Abstract

The pump, e.g. a gear pump, has a load sensing priority flow control valve 13 provided in end cover member 2 of the pump. The valve has an inlet port (12, Fig. 1) communicating with the outlet side of the pump, a first outlet port 24 communicating with a first fluid pressure actuated device, a second outlet port 25 communicating with a second fluid pressure actuated device, and a valve spool 15 biassed by spring 29 to a position in which substantially all of the fluid entering the inlet port flows to the first outlet port. A load sensing port 26 communicates a pressure signal from downstream of a variable orifice in the first device to exert a biasing force on the spool to supplement the spring. This is opposed by a pressure signal from upstream of the variable orifice. The valve 13 will ensure that the first device is always given priority over the second device and, whenever possible, receives the required amount of fluid, no more and no less. <IMAGE>

Description

An hydraulic Pump This invention relates to an hydraulic pump.

According to one aspect of the present invention, there is provided an hydraulic pump having a load sensing priority flow control valve formed as an integral part of the pump.

Preferably, the pump is a fixed displacement pump, typically a gear pump.

Advantageously, the pump includes a pump body which is open at least one end and a cover member closing said one end of the pump body, and the load sensing priority valve is provided in said cover member.

According to another aspect of the present invention, there is provided an hydraulic pump in combination with an integral flow control valve, the valve having an inlet port communicating with an outlet side of the pump, a first outlet port for fluid communication with a first fluid pressure actuated device, a second outlet port for fluid communication with a second fluid pressure actuated device, valve means to control fluid flow from the inlet port to the outlet ports, spring means biasing the valve means to a position in which the valve means permits all or substantially all of the fluid entering the inlet port to flow to the first outlet port, a load sensing port for communicating a pressure signal from downstream of a variable orifice in the first fluid pressure actuated device to exert a biasing force on the valve means to supplement the biasing force of the spring means, and means for communicating a pressure signal from upstream of the said variable orifice to exert a biasing force on the valve means to oppose the biasing force of the spring means.

Preferably, the valve means comprises an axially movable spool and, in this case, advantageously, said means for communicating the pressure signal from upstream of the variable orifice is provided in the spool.

Preferably, the pump is a fixed displacement pump, typically a gear pump.

Advantageously, the pump includes a pump body which is open at least one end and a cover member closing said one end of the pump body, and the flow control valve is provided in said cover member.

The invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a side view of one embodiment of an hydraulic pump according to the present invention, with parts thereof sectioned, Figure 2 is a section taken along line II-II of Figure 1, and Figure 3 is an hydraulic circuit diagram showing the pump of Figures 1 and 2 in use.

Referring now to the drawings, the hydraulic pump shown therein is a fixed displacement pump, more particularly a gear pump, and comprises a pump body 1 open at opposite ends and two cover members 2 and 3, closing the opposite ends of the body 1, respectively.

The pump body 1 defines two mutually intersecting parallel working chambers 4 and 5. Two meshing pump rotors 6 and 7 are mounted for rotation in the two chambers 4 and 5, respectively, by bearings 8 supported in bearing supports 9. The pump body 1 also has an inlet port 10 communicating with the inlet side of the working chambers 4 and 5, and passage 11 communicating with the outlet side of the working chambers 4 and 5.

The cover member 2 defines the body of a load sensing priority valve designated by the general reference number 13. The valve 13 has a bore 14 in which a valve spool 15 is slidably mounted. The spool 15 has three axially spaced lands 16, 17 and 18 with annular recesses 19 and 20 therebetween. The valve bore 14 has three annular grooves 21, 22 and 23. The groove 22 communicates with an inlet port 12 of the valve 13, the groove 21 communicates with a priority flow outlet port 24 of the valve 13, and the groove 23 communicates with an auxiliary flow outlet port 25 of the valve 13.

The inlet port 12 extends through the base of the cover member 11 and communicates with the outlet side of the pump via passage 11.

A load sensing port 26 is provided in a nipple 27 which is screwthreadably engaged in one end of the bore 14 and the other end of the bore 14 is closed by a screwthreaded plug 28.

The valve spool 15 is biased towards the plug 28, i.e. to the right as seen in Figure 2, by a compression spring 29 and by fluid pressure at the load sensing port 26.

The valve spool 15 has a gallery comprising radial passages 30 and 31 and an axial passage 32 which provides communication both between the two passages 30 and 31 and between the passages 30 and 31 and the end of the spool 15 adjacent to the plug 28 so that fluid pressure in the gallery will oppose the biasing force of the spring 29 and fluid pressure at the load sensing port 26.

As shown in Figure 3,. the pump/valve combination described above is used to supply hydraulic fluid to a first fluid pressure actuated device 40, such as a power steering system of a fork lift truck, having an associated control valve 41 including a variable flow control orifice 42, and to a second fluid pressure actuated device 43, such as a lifting ram of the fork lift truck. Tile priority flow outlet port 24 of the valve 13 is connected to the fluid pressure actuated device 40 via the control rralve 41 and the auxiliary flow outlet port 25 is connected to the fluid pressure actuated device 43. The load sensing port 26 is connected to the downstream side of the variable orifice 42 for a reason which will become apparent hereinafter.

When there is no flow from the pump, the spring 29 will move the valve spool 15 fully to the right as shown in Figure 2. In this position the land 17 will co-operate with the bore 14 to cut-off fluid communication between the inlet port 12 and the auxiliary flow outlet port 25, and the inlet port will communicate with the priority flow outlet port 24 via the gallery in the spool 15 and the recess 19. If the pump is started with the variable orifice 42 in the control valve 41 of the first fluid pressure actuated device closed, hydraulic fluid will communicate via the gallery in the spool 15 with the right hand end of the spool 15.Fluid pressure at the right hand end of the spool will oppose the biasing force of the spring 29 and will move the spool 15 to the left to open the inlet port to the auxiliary flow outlet port 25 via the grooves 22 and 23, yet at the same time maintain some flow communication between the inlet port and the priority flow outlet port 24 via the groove 21. Now, if the variable orifice 42 in the control valve 41 of the first fluid pressure actuated device 40 is partially opened, a pressure signal from downstream of the variable orifice will be communicated to the load sensing port 26.This pressure signal will supplement the biasing force of the spring 29 and the spool 15 will adopt a position in which the forces applied to opposite ends of the spool are balanced and the fluid flow demanded by the variable orifice 42 is fed to the priority flow outlet port 24, with any excess flow going to the auxiliary flow outlet port 25.

If the variable orifice 42 is then opened further to demand a higher fluid flow from the valve 13, the pressure drop across the variable orifice will decrease and the fluid pressure at the load sensing port 26 will increase relative to the fluid pressure on the right hand end of the spool 15 so that the spool 15 will move further to the right to increase flow between the inlet port and the priority flow outlet port 24 and decrease flow to the auxiliary flow outlet port 25. On the other hand, if the variable orifice 42 is made smaller to demand a lower fluid flow from the valve 13, the pressure drop across the variable orifice will increase and the fluid pressure at the load sensing port 26 will decrease relative to the fluid pressure on the right hand end of the spool 15 so that the spool 15 will move to the left to decrease flow between the inlet port and the priority flow outlet port 24 and increase flow between the inlet port and the auxiliary flow outlet port 25.

Also, if the outlet flow from the pump decreases, the spool 15 will move to the right to reduce flow to the auxiliary flow outlet port 25 and maintain flow as demanded by the variable orifice 42 to the priority flow outlet port 24, and, if the outlet flow from the pump increases, the spool 15 will move to the left to increase flow to the auxiliary outlet port 25 and maintain flow as demanded by the variable orifice 42 to the priority flow outlet port 24.

Thus, the valve 13 ensures that the first fluid pressure actuated device 40 is always given priority over the second pressure actuated device 43 and, whenever possible, receives the required amount of fluid, no more and no less.

By combining the pump and valve 13 into a single unit, costs are kept low and hydraulic fluid lines are kept to a minimum.

The above embodiment is given by way of example only and various modifications will be apparent to persons skilled in the art without departing from the scope of the invention. For example, the body 1 and one or other of the cover members 2, 3 of the pump could be formed as an integral casting. Also, the end of the spool adjacent to the plug 28 could be connected externally of the valve 13 to the upstream side of the variable orifice 42 instead of the internal connection described above between the spool gallery and the end of the spool adjacent to the plug 28.

Claims

1. An hydraulic pump having a load sensing priority flow control valve formed as an integral part of the pump.

2. An hydraulic pump as claimed in Claim 1, wherein the pump is a fixed displacement pump.

3. An hydraulic pump as claimed in Claim 2, wherein the pump is a gear pump.

4. An hydraulic pump as claimed in any one of Claims 1 to 3, including a pump body which is open at at least one end and a cover member closing said one end of the pump body, the load sensing priority valve being provided in said cover member.

5. An hydraulic pump in combination with an integral flow control valve, the valve having an inlet port communicating with an outlet side of the pump, a first outlet port for fluid communication with a first fluid pressure actuated device, a second outlet port for fluid communication with a second fluid pressure actuated device, valve means to control fluid flow from the inlet port to the outlet ports, spring means biasing the valve means to a position in which the valve means permits all or substantially all of the fluid entering the inlet port to flow to the first outlet port, a load sensing port for communicating a pressure signal from downstream of a variable orifice in the first fluid pressure actuated device to exert a biasing force on the valve means to supplement the biasing force of the spring means, and means for communicating a pressure signal from upstream of the said variable orifice to exert a biasing force on the valve means to oppose the biasing force of the spring means.

6. The combination of Claim 5, wherein the valve means comprises an axially movable spool.

7. The combination of Claim 6, wherein said means for communicating the pressure signal from upstream of the variable orifice is provided in the spool.

8. The combination of any one of Claims 5 to 7, wherein the pump is a fixed displacement pump.

9. The combination of Claim 8, wherein the pump is a gear pump.

10. The combination of any one of Claims 5 to 9, wherein the pump includes a pump body which is open at at least one end and a cover member closing said one end of the pump body, and the flow control valve is provided in said cover member.

11. An hydraulic pump in combination with an integral flow control valve, substantially as hereinbefore described with reference to the accompanying drawings.