GB2305972A - Rotary Pump - Google Patents

Abstract

In a rotary pump 10 for pumping fluid such as oil in a vehicle engine E, a housing 14, (16, Fig 2) has an inlet port (24) and an outlet port (26) in communication with a pumping chamber in which a first driven gear 32 and a second cooperating gear 30 effect the pumping. Means in the form of grooves 44, (50, Fig 3) connected by bores 46 help to balance any fluid pressure differential across the first gear 32, to achieve a reduced and more uniform wear of the gear and a reduction in leakage across sealing faces. Grooves may be provided instead in the housing wall adjacent gear 32.

Description

ROTARY PUMP This invention relates to a rotary pump for pumping fluids such as oil in a vehicle engine. More particularly it relates to rotary gear pumps having an inner driven gear and outer idling gear.

It is known to use rotary gear pumps to pump the oil through a vehicle engine in which the rotary pump comprises cf an inner and outer rotor which are meshed together within a pumping chamber. The pumping of fluid from an inlet port to an outlet port is effected by driving the inner rotor on a drive shaft thereby effecting rotary movement of a clearance space, or changing volume, between the two meshed gears about the drive shaft. This produces a positive displacement of fluid under pressure between the inlet and outlet ports.

However, it has been found that uneven wear of opposite faces of the inner rotor can occur and also that leakage of cil can be a problem.

It is an object of the invention to reduce inner rotor wear and oil leakage.

According to the invention there is provided a rotary oear pump for pumping fluid, the pump comprising a housing having a pumping chamber, an inlet port and an outlet port in communication with the pumping chamber, a first driven rotor, a second idling rotor in meshing engagement with the riven rotor to effect pumping of fluid from the inlet port the outlet port and balancing means to reduce the pressure differential across the first driven rotor wherein said balancing means comprises a first circumferentially extending groove in a first surface within the pumping chamber, a second circumferentially extending groove in a second surface within the pumping chamber and at least one extending through said first rotor for co-operation with said first and second circumferentially extending grooves.

The first and second grooves may be circumferentially csntinuous.

Preferably, the first and second grooves may be formed in opposing radial side faces of said first rotor.

There may be three equispaced bores extending between the opposing radial side faces of the first rotor.

At least one of the circumferentially extending grooves nay be semi-circular in cross-section.

At least one of the circumferentially extending grooves may be formed in a radially extending end surface of the pumping chamber.

An embodiment of the invention will now be described, by way of example with reference to the accompanying drawing, in which: Figure 1 is a schematic front elevation view of part of a rotary pump according to the invention in an engine; Figure 2 is a schematic front elevation view of another part of the rotary pump shown in Figure 1; Figure 3 is a schematic sectional view of a rotary pump comprising the ports shown in Figures 1 and 2; and Figures 4A to 4F schematically represent the fluid pressure at different radial positions along the faces of an inner rotary gear.

Referring to Figure 1, there is shown part of a rotary pump 10 according to the invention housed in part of an engine E of a vehicle. The rotary pump 10 comprises a housing 12 consisting of a front plate, 14 shown in Figure 1 and a back plate, 16 shown in Figure 2. The front and back plates 14 and 16 both have annular faces 18 which abut one another when the two components are joined and a number of apertures 20 around their periphery to enable them to be secured to one another by nuts and bolts or fixing screws.

The front and back plates 14 and 16 both have a central aperture 22 to allow for the passage of a drive shaft 38, and each has a crescent shaped inlet port 24 and a crescent shaped outlet port 26 in substantially radially extending circular faces 25 and 27 respectively.

The front and back plates 14 and 16 together define a central pumping or working chamber having an outer, cylindrical surface 28 and radially extending ends walls formed by the circular faces 25, 27.

The working chamber houses an outer idling rotor 30 and inner driven rotor 32.

The rotor 32 has a number of circumferentially spaced teeth 34 which co-operate by meshing engagement with indentations 36 formed on the inner circumference of the idling rotor 30. The co-operation of the teeth 34 and the indentations 36, when the rotor is driven, produces positive fluid displacement through the pump from the inlet ports 24 to the outlet ports 26.

As can best be seen in Figure 1, the rotor 32 has a central aperture 40 shaped to drivingly engage with the shaft 38 and a first radially extending face 42 in which is formed an annular groove 44. The annular groove 44 is semi-circular in cross-section and has three equispaced bores 46 therein which extend through the rotor 32 to the opposite radially extending side face 48.

With reference to Figure 3, it can be seen that the rotor 32 also has an annular groove in the form of an undercut 50 in the second radial face 48.

The undercut 50 extends between the side face 48 of the rotor 32 and a collar 39 which is used to couple the rotor 32 to the drive shaft 38. The undercut 50 improves the ease of manufacture of the rotor 32 by means of a sintering process and is also utilised to assist with balancing the pressure. A seal 60 is provided between the shaft 38 and the housing 12 to prevent leakage along the shaft 38.

In use, the rotor 32 is driven by the shaft 38 causing rotation relative to the idling gear 30 and hence movement of the space between it and the idling gear 30. The movement of the space caused by movement of teeth 34 relative to the indentations 36 effects a positive displacement of fluid from the inlet ports 24 to the outlet ports 26. This is due to the creation of a partial vacuum at inlet port 24 and the creation of a positive pressure effecting positive displacement at the outlet port 26.

During operation the oil pressures at the inlet and outlet ports change radially across the face of the rotor 32. That is, a substantially neutral pressure can be found at the interface between the shaft 38 and the rotor 32 such that pressure gradients exists across the face of the rotors 32, 30 from the shaft 38 to the inlet and outlet ports 24 and 26.

These pressure gradients are shown in figures 4A and 4B respectively for the outlet and inlet side of the pump for face 42 of the rotor 32 without a balancing groove 44.

The diagrams show how pressure varies along the horizontal, or x axis, versus position along vertical radial axes of the pump. Thus, it can be seen that a positive pressure exists near the inner edge of port 26 whilst a neutral pressure is present at the interface between the rotor 32 and the shaft 38, see figure 4A.

Similarly, a negative pressure is present at the inner surface of ports 24 whilst a neutral pressure is present at the interface between the shaft 38 and the rotor 32, see figure 4B.

The presence of the undercut 50 affects the pressure gradients due to the fluid communication which takes place circumferentially within the undercut 50 and thus between the radially opposite, inlet and outlet sides of the pump.

Accordingly, a pressure gradient similar to that shown in Figures 4C and 4D across face 48 of inner gear 32 is established in the undercut 50. Thus, a positive pressure exists at the inner edge of outlet 26 whilst a lower positive pressure exists at the radially outer edge of undercut 50 as shown in Figure 4C, and a negative pressure exists at the inner edge of inlet 24, see Figure 4D.

In the absence of the balancing groove 44, the radial side face 42 of the rotor 32 has a pressure gradient across it as shown in figures 4A and B, and the opposite radial side face 48, having the undercut 50, has a pressure gradient across it as shown in figures 4C and 4D.

Accordingly, there exists a pressure differential axially across the rotor 32 between opposite parts of faces 42 and 48.

The addition of the groove 44 changes the pressure gradient across face 42 to become substantially similar to that shown in Figures 4E and 4F and thus substantially similar to the pressure gradients across face 48 as shown in Figures 4C and 4D. The use of the bores 46 between the grooves 44 and 50 enables the pressure gradient between the faces 42, 48 to be reduced.

By balancing the pressures between the two faces 42 and 48, the total leakage past the sealing faces will be reduced as any leakage which does occur has the opportunity to travel along the annular balancing groove 44 and enter the inlet port via the clearance between the rotor 32 and its housing. Also, the reduction in pressure variation results in less wear on the rotor 32 and any wear is much more uniform thus increasing the useful life of the rotor 32.

It will be appreciated that the shape of groove 44 need not be semi-circular in cross-section but could for example be triangular.

Although the use of three bores 46 is a preferable number, since this beneficially provides good fluid communication between the opposite sides 42 and 48 of gear 32 whilst minimising manufacturing costs of the gear, other numbers of bores could be used.

It will also be appreciated that it is possible not to include the grooves 44 or 50 in the rotor 32 but instead to provide one or more similar grooves within the radial faces 25 and 27 of the housing. For example, a circumferentially extending or annular groove can be provided in either of the faces 25 or 27 and a balancing groove can be provided in the rotor 32 on the opposite side of the rotor 32 to the location of the groove in one of the faces 25 or 27.

Claims (7)

1. A rotary gear pump for pumping fluid, the pump comprising a housing having a pumping chamber, an inlet port and an outlet port in communication with the pumping chamber, a first driven rotor, a second idling rotor in meshing engagement with the driven rotor to effect pumping of fluid from the inlet port to the outlet port and balancing means to reduce the pressure differential across the first driven rotor wherein said balancing means comprises a first circumferentially extending groove in a first surface within the pumping chamber, a second circumferentially extending groove in a second surface within the pumping chamber and at least one bore extending through said first rotor for co-operation with said first and second circumferentially extending grooves.

2. A rotary gear pump as claimed in Claim 1 in which the first and second grooves are circumferentially continuous.

3. A rotary gear pump as claimed in Claim 1 or in Claim 2 in which the first and second grooves are formed in opposing radial side faces of said first rotor.

4. A rotary gear pump as claimed in Claim 3 in which there are three equispaced bores extending between the opposing radial side faces of the first rotor.

5. A rotary pump as claimed in any of Claims 1 to 4 in which at least one of the circumferentially extending grooves is semi-circular in cross section.

6. A rotary gear pump as claimed in Claim 1 or in Claim 2 in which at least one of the circumferentially extending grooves is formed in a radially extending end surface of the pumping chamber.

7. A rotary gear pump substantially as described herein with reference to the accompanying drawing.