GB2298902A

GB2298902A - Pump with integral priority pressure regulating valve

Info

Publication number: GB2298902A
Application number: GB9505453A
Authority: GB
Inventors: Roderick Howell Spurry
Original assignee: Sauer Sundstrand Ltd
Current assignee: Sauer Danfoss Swindon Ltd
Priority date: 1995-03-17
Filing date: 1995-03-17
Publication date: 1996-09-18
Anticipated expiration: 2015-03-17
Also published as: GB9505453D0; GB2298902B

Abstract

A fluid pump has main and auxiliary output ports (18 and 20), flow to which is controlled by a priority pressure regulating valve having a valve spool (14) axially movable within housing (10) for feeding fluid preferentially to the main output port (18) while the pressure at the main output port is less than a predetermined working pressure. Thereafter the valve spool (14) feeds fluid to the auxiliary output port (20). The priority pressure regulating valve is incorporated in the housing (10).

Description

TITLE: Pump with integral priority pressure regulating valve DESCRIPTION: Field of the invention The invention relates to fluid pumps, and in particular to gear pumps and other positive displacement hydraulic pumps, which can be used to deliver hydraulic fluid to two different sets of hydraulic loads. A priority valve is needed to distinguish between the two loads, and deliver hydraulic fluid preferentially to a first load up to a first working pressure, and only then deliver hydraulic fluid to the second load which is a non -preferential load.

Prior Art Priority valves are known which divide the flow from a hydraulic pump into preferred and non-prefered flows for servicing two loads as indicated above. Previously all such priority valves have been connected in series with the pump output, being connected to the pump by conduits and to the first and second loads by further conduits.

It is an object of the invention to provide a fluid pump having an integral priority pressure regulating valve.

The invention The invention provides a fluid pump having main and auxiliary output ports, flow to which is controlled by a priority pressure regulating valve, wherein the priority pressure regulating valve is a spool valve within a pump housing for feeding fluid delivered by the pump preferentially to the main output port while the pressure at the main output port is less than a predetermined working pressure; and for feeding fluid delivered by the pump to the auxiliary output port whenever the pressure at the main output port is at the predetermined working pressure.

It is a significant advantage of the invention that the pump housing itself has two output ports. The main output port delivers hydraulic fluid to a priority load, and the auxiliary output port delivers fluid to the non-priority load. The valve spool of the priority pressure regulating valve is axially movable in a suitably shaped bore formed in the pump housing, which location reduces the amount of conduit required in most applications, and reduces significantly the chance of leakage of the high pressure fluid delivered by the pump.

The predetermined working pressure may be greater than or less than the working pressure to be established at the auxiliary outlet port (the second working pressure), which may itself be limited by a pressure control valve for returning excess hydraulic fluid to drain, or may be unlimited in which case the second working pressure becomes the pump rated pressure. If a pressure relief valve is used, it may be contained within the pump housing in the same way as the priority pressure regulating valve, or it may be placed externally of the pump housing, in the fluid line to drain.

Drawings: Figure 1 is a transverse section through a pump according to the invention, taken along the axis of a priority pressure regulating valve of the pump; Figure 2 is an enlarged detail of a part of the valve spool of the priority pressure regulating valve, in an axial position in which it delivers hydraulic output fluid preferentially to the main output port; Figure 3 is a similar detail with the valve spool in a position in which it delivers fluid to the auxiliary output port, while maintaining the predetermined working pressure at the main output port.

Referring first to Figure 1, there is shown a housing 10 of a gear pump. The pumping elements of the gear pump are not shown, but are conventional. Indeed the housing 10 could be of any conventional positive displacement hydraulic fluid pump. The pump delivers hydraulic fluid at high pressure to a high pressure chamber 12, from that high pressure chamber 12 the hydraulic fluid is controlled by an integral priority pressure regulating valve 14 which is a spool valve fitted into an accurately machined bore in the pump housing 10.

The valve spool of the spool valve 14 is biassed to a rest position as shown in Figure 2 by a regulating spring 16. The spool valve 14 controls the hyraulic flow to a main output port 18 and to an auxiliary output port 20, with the preferential flow being to the main output port 18.

In use, high pressure hydraulic fluid from the high pressure chamber 12 flows to an annulus 22 around the valve spool 14. The spool 14 is biassed to the left by the spring 16, to the position shown in Figure 2, and the high pressure fluid from the chamber 12 is therefore delivered initially past a land 24 of the valve spool 14 to an annulus 26 which communicates with the main output port 18. At this stage a second land 28 of the valve spool 14 blocks hydraulic flow to the auxiliary output port 20.

The pressure at the main output port 18 is used to control the axial position of the valve spool 14 by means of a drilling 30 which passes radially through the valve spool 14 to connect with a blind axial drilling 32 to communicate the pressure at the output port 18 with the left hand end face of the valve spool 14. The hydraulic pressure at the left hand end of the valve spool 14 acts to oppose the bias of the spring 16, and urge the valve spool 1 to the right. Figures 1 and 3 show the valve spool 14 in its extreme right hand position, in which a shoulder portion 34 of the valve spool 14 abuts a stop washer 36 that is retained in position by a screw end cap 38 which closes the right hand end of the bore in which the valve spool 14 is axially movable.A short drilling 38 between a chamber in which the right hand end of the valve spool 14 moves and a pump low pressure chamber 40 ensures that the hydraulic pressure at the right hand end of the valve spool 14 does not rise, on axial movement of the valve spool, to resist the hydraulic pressure at the left hand end.

When the hydraulic pressure at the main output port 18 reaches a desired predetermined working pressure, established by the compression force of the spring 16, the hydraulic pressure acting on the left hand face of the valve spool 14 is sufficient to overcome the bias in the spring and move the valve spool 14 to the position shown in Figure 3. In that position, the hydraulic communication between the high pressure chamber 12 and the main output port 18 is interrupted by a valve land 42, and hydraulic communication is established between the high pressure chamber 12 and the auxiliary output port 20. The pressure at the auxiliary output port 20 can then rise either to the maximum rated output pressure of the pump or to such lower pressure as may be dictated by the load or by a pressure relief valve (not shown).

Thus the spool valve 14 feeds preferentially the main output port 18 with a regulated pressure supply. When the supply is satisfied so that the pressure in the main output port reaches a predetermined working pressure, the spool valve 14 moves so that hydraulic fluid delivered by the pump continues to be delivered, but to the auxiliary output port 20 rather than exclusively to the main output port 18. The pressure at the auxiliary output port 20 can be greater than or less than the pressure at the main output port 18. If the predetermined working pressure, being the pressure required at the main output port 18, is less than the working pressure at the auxiliary output port 20 then the latter pressure can be allowed to rise until it reaches the maximum rated output pressure of the pump. Alternatively the working pressure at the auxiliary output port 20 can be limited by a pressure relief valve (not shown in the drawings) with excess hydraulic fluid being returned to drain.

The pump illustrated is much simpler to install than one requiring a separate priority pressure regulating valve to be inserted in the pipeline or conduit between the pump and the main and auxiliary loads, and there is a much lesser tendency for fluid leakage.

Claims

CLAIMS:

1. A fluid pump having main and auxiliary output ports, flow to which is controlled by a priority pressure regulating valve, wherein the priority pressure regulating valve is a spool valve within a pump housing for feeding fluid delivered by the pump preferentially to the main output port while the pressure at the main output port is less than a predetermined working pressure; and for feeding fluid delivered by the pump to the auxiliary output port whenever the pressure at the main output port is at the predetermined working pressure.

2. A pump according to claim 1, being a positive displacement hydraulic pump.

3. A pump according to claim 2, being a gear pump.

4. A pump according to any of claims 1 to 3, wherein housing is a metal casting in which operative elements of the pump move.

5. A pump according to any of claims 1 to 3, wherein the priority pressure regulating valve is provided in a mounting flange portion of the housing, being a portion of the pump housing by means of which the pump is mounted and supported in use.

6. A pump according to any of claims 1 to 3, wherein the priority pressure regulating valve is provided in a cover member which forms an integral part of the pump housing.

7. A pump according to any of claims 1 to 3, wherein the priority pressure regulating valve is provided in a sandwich plate portion of the pump housing, being a housing portion which links together a number of such pumps

8. A pump according to any preceding claim, wherein the working pressure attainable at the auxiliary output port is greater than the prdetermined working pressure at the main output port.

9. A pump according to claim 8, wherein the working pressure attainable at the auxiliary output port is the pump rated pressure.

10. A pump according to claim of claims 1 to 7, wherein the working pressure attainable at the auxiliary output port is less than the predetermined working pressure.

11. A pump according to claim 8, wherein when the pressure at the auxiliary output port reaches a desired working pressure, excess fluid delivered by the pump is dumped to drain through a pressure relief valve.

12. A pump according to claim 11, wherein the pressure relief valve is contained within the pump housing.

13. A fluid pump and integral priority pressure regulating valve, substantially as described herein with reference to the drawings.