GB2294527A - Assembly of gear pump and load-sensing priority flow valve - Google Patents

Abstract

A gear pump 10 and a load-sensing priority flow valve 20 are each self-contained with their own housing, but can be clamped together so that an outlet port 1 of the pump housing communicates directly with an inlet port 22 of the load sensing priority flow valve housing. The valve 20 is particularly switching spool valve which is controlled by a pilot valve responsive to an excessive pressure in a chamber (34) at one end of the valve spool (Fig. 2, not shown) or in a priority flow outlet (30) (Fig. 6, not shown). <IMAGE>

Description

TITLE: Assembly of gear pump and load sensing priority flow valve Field of the invention The invention relates to gear pumps for providing pressurized fluid to either a priority flow or a non -priority flow output device, as dictated by the operation of a load sensing priority flow control valve.

GB 2238355B discloses a gear pump and load sensing priority flow control valve in a single housing. That Patent Specification teaches the incorporation of the load sensing priority flow control valve in a cover member which is part of the housing defining the gear pump body, with the stated objective of reduction in pipework when the assembly is used in, for example, an agricultural tractor. The tractor could have, for example, power steering and other hydraulics such as a lifting bucket. As a matter of priorities, it would be desired to maintain hydraulic flow to the power steering in preference to flow to the bucket.To that end, GB 2238355B teaches the use of a load sensing priority flow control valve which sends hydraulic flow preferentially to a priority outlet port feeding the power steering system, as opposed to a non-priority outlet port which feeds other less critical hydraulic equipment such as the lifting bucket. In proposing the integration of the gear pump and load sensing priority flow control valve into a single housing to reduce pipework, GB 2238355B has increased the cost of the gear pump and considerably decreased its design flexibility, since a different gear pump would have to be designed and constructed for differential commercial applications which might require different load sensing priority flow control valve characteristics.

It is an object of the invention to provide a gear pump assembly which avoids the design constraints of GB 2238355B while providing further advantages not envisaged in that Patent Specification.

The invention provides an assembly of a gear pump in association with a load sensing priority flow valve, comprising: a gear pump having a pump housing defining a gear chamber containing meshing gear elements of the gear pump, and a load output passage machined in the housing from the gear chamber to an outlet port on an external face of the pump housing; and a load sensing priority flow valve having a valve housing formed separately from the pump housing but secured to the pump housing over the outlet port thereof, and a valve member axially movable in a valve chamber in the valve housing for selectively directing hydraulic flow from the outlet port of the pump housing to a priority outlet or a non-priority outlet of the load sensing priority flow valve in response to a hydraulic pressure load signal applied to a sensing port of the load sensing priority flow valve.

The flexibility of the above arrangement will become apparent when it is appreciated that a single gear pump can be used in operative association with any of a wide range of load sensing flow control valves. The priority flow valve may be static, in which case the hydraulic pressure load signal applied to the sensing port is a single signal transmitted from, for example, the output side of a control valve controlling the operation of a power steering mechanism. Alternatively the priority flow valve may be a dynamic control valve, in which the hydraulic pressure load signal is a composite signal incorporating elements of the output of the priority flow outlet port of the flow valve and the outlet of the above power steering control valve.Such a composite signal would typically be established by feeding hydraulic fluid through a flow restriction orifice from the priority outlet of the load sensing priority flow control valve to the sensing port, to modulate the external load signal applied to the same sensing port.

Other variants of the load sensing priority flow control valve that can be used in association with the original gear pump are those in which the valve housing incorporates an integral pilot relief valve, for dumping to drain the hydraulic pressure applied to the sensing port when that pressure exceeds a predetermined threshold, or those incorporating in the valve housing an integral full flow pressure relief valve for dumping to drain the hydraulic pressure established at the priority flow outlet of the valve when that pressure exceeds a given threshold. In each case, the overpressure can be returned to a drain reservoir through an external conduit, or can very conveniently be returned to the inlet side of the pump by means of cooperating bores in the path housing and pump housing.

Furthermore, the gear pump housing and priority valve housing may be made of differing materials to suit respective needs of their functions. They are conveniently bolted together, and the gear pump itself has sufficient flexibility of design that it can be used without the load sensing priority flow control valve in other applications, simply by unbolting that flow control valve and either replacing it with another pressure control valve suited for the application, or replacing it with a gear pump outlet connection which bolts to the gear pump external face in the same way as the load sensing priority flow control valve used in the assembly of the invention.

Drawings Figure 1 is a partially cutaway side view of an assembly according to the invention.

Figure 2 is an axial section taken along the line A-A of Figure 1 through the load sensing priority flow control valve of Figure 1, drawn to an enlarged scale; Figure 3 is a section similar to that of Figure 2 but with the priority flow control valve in the condition in which it sends flow to the non-priority outlet port; Figure 4 is a side view of the valve spool of Figures 2 and 3; Figure 5 is an axial section through the valve spool of Figure 4, in slightly greater detail than is shown in Figures 2 and 3; and Figures 6 and 7 are sections similar to those of Figures 2 and 3 respectively but through an alternative load sensing priority flow control valve for use in the assembly of Figure 1.

Figure 1 depicts the general arrangement of a gear pump 10 in association with a load sensing priority flow valve 20, in an assembly according to the invention. The gear pump 10 is conventional internally, with a pair of meshing gears 11,12 rotating in a gear chamber 13 defined in a pump housing 14. End plates 15,16 complete the housing and are retained in position by clamping bolts 17. The gear 12 is a driven gear, driven by a splined input shaft 18; and the gear 11 is an idler gear.

Many other gear arrangements are possible within the scope of the invention, for example arrangements with two or more sets of gears on common rotational axes, or gear pumps working on epicyclic principles.

The inlet port for the gear pump 10 is not illustrated in Figure 1, but the outlet port is illustrated in Figure 1 as a passage 19 leading to an external face of the end pressure plate 16 of the housing. That end face has been machined flat, and on it is mounted the load sensing priority flow valve 20, by means of four mounting bolts 21.

It will be understood that although in Figure 1 the outlet passage 19 is shown as terminating on an outer face of the end plate 16, it would be equally feasible for the passage 19 to terminate on a suitably flat portion of the side wall of the main housing body 14, provided that side wall could be machined flat to provide a good seal with the load sensing priority flow valve 20 which also has a flat machined face for abutment with the flat face of the housing of the gear pump. An inlet passage 22 for the priority flow valve 20 is provided in alignment with the passage 19 of the gear pump, and an Oring seal 23 around the passage 22 forms a fluid tight seal when the priority flow valve 20 is mounted on the gear pump 10.

The load sensing priority flow control valve 20 is illustrated in greater detail in Figures 2 and 3. Four through-holes 24 in a housing 25 of the priority flow valve receive the mounting bolts 21. The inlet passage 22 communicates with a central gallery 26 around a central axial bore 27 in the housing 25. On one side of the central gallery 26 is a priority flow gallery 28 communicating via a bore 29 with a priority outlet port 30. On the other side of the central gallery 26 is a non-priority flow gallery 31 communicating through a bore 32 with a non-priority outlet port 33.

One end of the bore 27 is blanked off by a plug 34 sealed by an O-ring 35. The other end is closed by a cap 36 and O-ring 37, the cap 36 incorporating a sensing port 38 tapped for a hydraulic connection with an external load as described below. The sensing port 38 is in hydraulic communication with a pressure chamber 39 in the valve body 25, responsive to the variable pressure caused by variable demand at the priority device with which the valve is to be associated in use.

Axially movable in the bore 27 is a valve spool 40, shown in greater detail in Figures 4 and 5. The valve spool 40 comprises a priority flow gallery 41 and a non-priority flow gallery 42 separated by a land 43. The shoulders between the central land 43 and the galleries 41 and 42 are formed with metering notches 44 in the embodiment illustrated which are shallow angle flats machined on the outer surface of the land 43. At each end of the central land 43 there are formed four such metering notches 44, equally spaced around the periphery of the valve spool, with the metering notches communicating with the priority flow gallery 41 being offset by 45C from those communicating with the non-priority flow gallery 42.This offset, or asymmetry between the priority and nonpriority edges of the land 43, provides for improved flow performance and stability of valve operation. A variety of shapes and configurations may be chosen for the metering notches. For example, the shallow angles illustrated may be deepened, or the notches may be milled as V-shaped, semicircular or flat-bottomed notches.

A central blind bore 45 in the valve spool 40 communicates at one end with the priority flow gallery 41 through a radial bore 46; and at the other end with the end face of the valve spool at the non-priority flow gallery end thereof. Hydraulic communication between the priority flow gallery 41 and the opposite axial end of the valve spool 40 is through a restricted orifice 47 in a plug member 48 screwed into an end of the valve spool; and a filter member 49 is trapped between the plug 48 and the valve spool 40 to prevent clogging of the orifice 47.

In the rest condition shown in Figure 2, the valve spool 40 is in its rest condition, urged to the left by a spring 50 in compression between the valve spool 40 and the cap 36.

In this valve condition, the pump outlet is delivered preferentially to the priority outlet port 30 through the central gallery 26, the metering notches 44 (shown dotted in Figure 2 because they are in fact out of the plane of the section), the overlapping galleries 41 and 28, and the bore 29. As the pump outlet pressure rises, so that pressure increase is communicated via the radial bore 46, the axial bore 45 and the flow restriction orifice 47 of the valve spool 40 to a pump outlet pressure chamber 51 at the left hand end of the valve spool 40.If that pump outlet pressure is not countered by a pilot pressure at the sensing port 38, the valve spool 40 will move to the right, compressing the spring 50, until the condition of Figure 3 is reached in which flow to the priority outlet port 30 is terminated and all of the pump output goes to the non-priority outlet port 33 via the central gallery 26, the metering notches 44, the overlapping galleries 31 and 42, and the bore 32.

When there is a requirement for power consumption at the priority device connected to the priority outlet port 30, the hydraulic pressure at the sensing port 38 will rise and flow is again provided preferentially to the priority outlet port 30.

Also illustrated in Figure 2 in phantom lines is a connecting passage 60, including a flow restriction orifice 61, between the priority flow outlet port 30 and the pressure chamber 39. The provision of this connecting passage is optional. Inclusion of this connecting passage means that the load sensing priority flow valve operates as a dynamic flow control valve, with a constant flow of a small amount of hydraulic fluid through the sensing port 38 to the priority device. This ensures that the pressure chamber 39 is constantly replenished, thus ensuring that the oil temperature and viscosity is substantially uniform throughout the system.

If the connecting passage 60 is omitted, then the load sensing priority flow control valve operates as a static control valve, being responsive as already described to the varying pressure at the output side of the priority load device, but without the benefit of constant movement of the hydraulic fluid in the pressure chamber 39.

Figures 2 and 3 also illustrate the provision of an integral pilot relief valve 70 operating to control the hydraulic pressure in the pressure chamber 39 in such a manner that when the pressure at the sensing port 38 exceeds a set limit, the hydraulic fluid in the pressure chamber 39 is dumped to drain to cause the valve spool to move to the position of Figure 3, passing all of the pump output to the non-priority port 33 until such time as the pressure at the sensing port 38 is reduced below the said set limit. The pilot relief valve 70 comprises a valve seat 71 and a valve member 72 biased by a spring 73. When the valve member 72 lifts away from its seat 71, hydraulic fluid can flow from the pressure chamber 39 to a discharge passage 74.The pilot relief valve 70 is used in conjuction with a flow restriction 75 between chambers 38 and 39, to provide a pressure differential between the load sensing line and the chamber 39 when the valve member 72 is unseated. The discharge passage 74 may lead to the same machined face of the valve housing 25 as does the inlet passage 22, for delivering the dumped fluid directly to the inlet of the pump 10; or it may lead to an external face for conduit connection to a reservoir.

As an alternative to the integral pilot relief valve 70, Figures 6 and 7 show an integral full flow pressure relief valve 80 operating on the priority flow outlet port 30 in such a manner that when the pump outlet pressure at the priority flow outlet port 30 exceeds a set limit, the relief valve 80 causes the priority flow to be passed from the service line leading to the priority flow device to a passage 81 in the housing 25.

The passage 81 may connected to the inlet side of the pump 10 or via an external conduit to a reservoir, in exactly the same manner as described in detail above with reference to the passage 74 of the integral pilot relief valve 70 of Figures 2 and 3.

In the embodiments described, the pilot ports and outlet ports 30,33 and 38 are shown on the side walls of the pressure control valve 20 as viewed in Figure 1. It will, however, be appreciated that any one or more of those ports could be provided on the top face of the load sensing priority flow control valve 20, so that differently constructed priority flow control valves, but operating on exactly the same principles, can be made available for specific end use applications when the geometry of the installation might dictate different positions for those ports.

Each of the gear pump 10 and the load sensing priority flow control valve 20 has its own housing, and is in itself a self-contained unit. Therefore a given pump can be used with any of a variety of load sensing priority flow control valves of which a selection has been described above (with or without the dynamic flow connecting passage 60; with or without the integral pilot relief valve 70; or with or without the integral full flow pressure relief valve 80). Similarly any given load sensing priority flow control valve can be used with a variety of gear pumps. The flexibility of the concept provides immense design advantages not previously attainable in prior art designs.

Claims (12)

CLAIMS:

1. An assembly of a gear pump in association with a load sensing priority flow valve, comprising: a gear pump having a pump housing defining a gear chamber containing meshing gear elements of the gear pump, and a load output passage machined in the housing from the gear chamber to an outlet port on an external face of the pump housing; and a load sensing priority flow valve having a valve housing formed separately from the pump housing but secured to the pump housing over the outlet port thereof, and a valve member axially movable in a valve chamber in the valve housing for selectively directing hydraulic flow from the outlet port of the pump housing to a priority outlet or a non-priority outlet of the load sensing priority flow valve in response to a hydraulic pressure load signal applied to a sensing port of the load sensing priority flow valve.

2. A gear pump assembly according to claim 1, wherein the valve member of the load sensing priority flow valve comprises a valve spool with external annuli defining the priority and non-priority flow paths to the priority and non-priority outlets respectively of the valve.

3. A gear pump assembly according to claim 2, wherein the valve spool has an axial drilling communicating with one of the external annuli, for transmitting the priority output port pressure to one end of the valve spool, the other end being exposed to the hydraulic pressure load signal at the sensing port, and to a spring bias.

4. A gear pump assembly according to claim 2 or claim 3, wherein within the valve spool and across the axial drilling therein is provided a mesh screen to prevent undesired blocking of a flow restriction member carried by the valve spool, for restricting the hydraulic flow between the priority output port and the said one end of the spool.

5. A gear pump assembly according to any of claims 2 to 4, wherein the external annuli define priority and non-priority flow control edges of the valve spool, each such edge being provided with a circumferential array of metering notches to establish a variable gain in flow versus valve spool travel.

6. A gear pump assembly according to claim 5, wherein the metering notches on one valve control edge are angular displaced from those on the other.

7. A gear pump assembly according to claim 6, wherein there are four metering notches each mutually displaced by 90" on each of the valve control surfaces, and one set of metering notches is angularly displaced by 45" from the other.

8. A gear pump assembly according to any of claims 2 to 7, wherein anti-stiction grooves are formed around valve lands at opposite ends of the valve spool.

9. A gear pump assembly according to any preceding claim, wherein the valve housing has a communicating bore incorporation a flow restriction which provides limited hydraulic communication between the priority outlet port and the sensing port, so that the load sensing priority flow valve functions as a dynamic priority flow control valve.

10. A gear pump assembly according to any preceding claim, wherein the valve housing incorporates a pilot relief valve in association with the sensing port, effective so that when the hydraulic pressure load signal applied to the sensing port exceeds a given threshold, the hydraulic pressure in the sensing port is reduced, thereby increasing hydraulic flow to the non-priority outlet.

11. A gear pump assembly according to any of claims 1 to 9, wherein the valve housing incorporates a full flow pressure relief valve connected to the priority flow outlet port, such that when the priority outlet pressure is above a given threshold, fluid flow into the priority flow port from the pump is diverted to drain or to the pump inlet.

12. A gear pump assembly comprising a gear pump in association with a load sensing priority flow valve, substantially as described herein with reference to the drawings.