US2932254A

US2932254A - Gear pump

Info

Publication number: US2932254A
Application number: US505254A
Authority: US
Inventors: Booth Douglas Gerhard; Wood Robert Spurgeon
Original assignee: Plessey Co Ltd
Current assignee: Plessey Co Ltd
Priority date: 1955-05-02
Filing date: 1955-05-02
Publication date: 1960-04-12
Anticipated expiration: 1977-04-12

Description

I 'Api-il 12, 1960 D. s. BOOTH ETAL 2,932,254

GEAR PUMP Filed May 2, 1955 2 Sheets-Sheet 1 INVENTORS DOUCLAS GERHARD BOOTH. ROBERT SPVRGEON wool).

' A-r-rorauev April 9 D. G. BOOTH ETAL 2,932,254

GEAR PUMP Filed May 2, 1955 2 Sheets-Sheet 2 INVENTQQS DOUGLAS GERHARD BOOTH, ROBER RGEON W0 D.

was! $7 BY ATTORNEY GEAR PUMP 4 Claims. (Cl. 163-426) This'invention relates to gear pumps. A gear pump with which the present invention is concerned comprises a housing including twochambers which accommodate two inter-meshing, displacing gears.

Gear pumps have the advantage of simplicity of construction, but satisfactory operation at high delivery pressures can be achieved only by careful mechanical design, as the volumetric efficiency of such pumps tends to fall as the fluid pressure across the sealing faces, and hence the leakage, is increased.

Volumetric efficiency can be increased up to a point by machining the pump parts to a high degree of accuracy, but the improvement thereby attained is limited by the fact that the less the clearance employed between relatively moving parts the greater is the danger of the pump seizing in operation. Also, a pump having very small working clearances is unlikely to have a long working life and is liable to deteriorate rapidly in efficiency. I Some of the problems of design of gear pumps have been solved by pressure loading; in a pressure loaded pump the sealing member between the side faces of the gears and the adjacent stationary part defining the chamber is improved by loading that member against the gear face by a pressure which is related to the delivery pressure of the pump and hence to the pressure within the chamber. With accurate mechanical design, pressure loaded pumps can be used successfully with liquids of comparatively high viscosity such, for example,'as lubricating oils and fluids used in hydraulic transmission or control systems.

A new order of difliculty arises where it is desired to design a gear pump for use with fluids of low viscosity, such as kerosene or gasoline, even where the pressure involved is low in comparison with delivery pressures which can be achieved in gear pumps for high viscosity liquids.

The design of a gear pump which is efiicient when used with low viscosity fluid at high delivery pressures is a problem of great technical difficulty, and one which, so far as we are aware, has not hitherto been successfully achieved.

It is, therefore, an object of the present invention to provide improvements in gear pumps which, while they can be applied to gear pumps generally to improve their 'efficiency, can be used to produce an effective pump for low viscosity liquids. I

We have 'discoveredthat the low efficiency of hitherto known gear pumps for low-viscosity liquids, especially at high pressures, is due to a considerable extent to the fact that the pump housing becomes distorted by the pressure, thereby creating undesirable bearing friction.

Therefore a further object of the invention is to provide a gear pump in which effective sealing on or against the side faces of the gears is obtained by pressure loading, and in which the loss of efficiency of the pump due to distortion of the pump housing is minimised.

Another object of the'invention is to provide a gear pump in which the bearings are so mounted that mis-v States Patent 2,932,254 Patented Apr. 12, 1960 ice that side members and bearings are relatively movable both longitudinally and transversely of the journal axes.

-A related feature of the invention is that the bearings are mounted in the housing so as to be self aligning on the shafts; specifically, said bearings are mounted in the housing by engagement over an axial length which is less than the axial length of engagement between the bearings and the shaft and which is centrally disposed between the ends of the said latter axial length.

In carrying the present invention into effect it is advantageous to provide a reinforced sealing member on the outer faces of the side members for effecting high pressure and low pressure zones; the high pressure zone being in contact with fluid at high pressure from the outlet side of the pump and the low pressure zone receives fluid at low pressure from the inlet side of the .pump. In this way, the centre of pressure acting on the outer faces of the side members can be brought into sub stantial alignment with the centre of pressure acting on the inner faces of said side members.

The sealing means preferably consists of an endless flexible member which surmounts a rigid member of less thickness than the depth of said chamber and having a profile conforming to one of the pressure zones.

Features and advantages of the invention will also appear from the following description of embodiments thereof, given by way of example only, in conjunction V with the accompanying drawings in which:

Fig. 1 is a sectional elevation of a gear pump provided with bearing assembly in accordance with the invention,

Fig. 2 is a view in section on line 2-2 of Fig. 1,

Fig. 3 is a view in section on line 33 of Fig. 1,

Fig. 4 is a view in section on line 44 of Fig. 1,

Fig. 5 is a view in section of line 55 of Fig. 1, and

Fig. 6 is a detail of an alternative bearing support.

Referring to Figs. 1 to 5 of the drawing, a pump housing 1 is provided with two overlapping

cylindrical chambers

2 and 3 having

end covers

4 and 5 on each end thereof, the end covers being held tightly against the end faces of the housing by bolts, not shown.

A pair of

gears

6, 7 which mesh in the overlapping

cylinders

2 and 3 are provided with axially extending journals 8, and side plates 14 having clearance bores 8a for the journals 8 are inserted in the housing in contact with the outer faces of the

gears

6, 7 to form end walls of the pump chambers.

Housing plates 11 located within the housing 1 are provided for receiving the bearing bushes 9 for supporting the journals 8. Said bushes 9 are a slide fit in the housing plates ill but are held against rotation by means of keys 12 fitted into slots 13 in the housing plates 11. The housing plates 11 support the bushes 9 at a distance approximately midway along the length of the journals 8 and the width of said plates 11 at the point of contact with the bushes 9 is less than half the length of said bushes 9.

A chamber A is formed between the respective outer faces of the sides plates 14 and inner faces of the housing plates 11. Each chamber A is divided in two zones or chambers 15, 16 (Fig. 3) by means of a reinforced sealing member, and said side plates 11 are urged towards the

gears

6 and 7 by a side load derived from the pressures in the separate zones of

chambers

15, 16.

With the direction of rotation of the

gears

6, 7 as indicated by the arrows in Fig. 4, 17 is the inlet port and 18 is the outlet port.

The sealing members each consist of an endless flexible ring 19 which surrounds the low pressure chamber 16 and is adapted to be sealingly compressed between the outer faces of the side plates 14 and housing plates 11 to isolate the two

chambers

15, 16.

A separate pressure relief plate 20 of less depth than chamber 16 is provided to prevent each ring 19 from collapsing and has a configuration conforming to the peripheral shape of the low pressure chamber 16 which is bounded by the ring 19; and a guide plate 30 fixed to the housing in the high pressure chamber 15 assists in maintaining the shape of the ring as shown in Fig. 3.

The pressure relief plates 20 are provided with a port 23 adjacent the inlet 17 for the admission of low pressure fluid into the chamber 16 and the plate 30 has a similar port 31 adjacent the outlet port for the admission of high pressure fluid into the chamber 15.

The side plates 14 each have an opening 25 in line with the inlet port 17 and outlet port 18 respectively for the purpose of admitting fluid through the ports 23, 31.

Passageways or grooves 21 are provided in the side plates 11 (Fig. which communicate with the low pressure inlet 17 for the circulation of low pressure fluid through the helical groove 24 in the bearing bushes 9 on the low pressure side of the journal bearings. This will produce a circulation of the pump liquid to lubricate and cool the bearings due to the pumping effect of the relative movement of the journal and the bearing grooves, the static pressure in the chambers at the outer ends of the bearings being the same as at the inner ends due to their connection to the low pressure chamber 16. V

The side plates 14 and pressure relief plates 20 are provided with coinciding apertures for receiving dowels 32 whereby the said relief plates 20 can be easily located clear of the journals 8.

In the pump of the present invention, the effects of distortion are overcome firstly by making the bearings for the gear journals separate from the pressure loaded members engaging the sides of the gears. Thereby it becomes possible to accommodate the relative movements of the shaft and side members. Secondly, the bearings for the journals are mounted in the housing so that they can adapt themselves to the misalignment of the journals, due to the flexing. The necessary movement is small and in the embodiment of the invention described is provided by supporting the bearing bushes over a limited length of surface at 10, this surface being approximately centrally between the axial length of engagement of the bush with the journal. With such an arrangement the desired latitude of movement of the bush in the housing can be obtained without recourse to non-cylindrical engagement surfaces and without using a large clearance at the engaging surfaces 10.

It is also to be understood that the pressure areas of the side plates of the pump are accurately determined, so that the requisite degree of balance 'is obtained to secure proper sealing without excessive load, which may cause seizure.

In this connection it is advantageous to ensure that the centre of pressure loading coincides with the centre of pressure on the side plates tending to causing unloading, so that'the optimum sealing of the side plates with minimum end load is ensured.

The embodiment of the invention shown in Fig. 6 is generally similar to that described above, except that the support for the bearing bushes 9 is formed as an integral part of the cover 5 by providing bores 34 for receiving the bearing bushese 9 as an alternative to having separate housing plates as herein described with reference to Fig. 1.

The keys 12- are fitted into slots in the end cover 5 to maintain the angular position of said bushes 9 It will be apparent to those skilled in the art that modifications can be made to the pumps described above, which are to be taken as illustrative only, without departing from the spirit of the invention as defined by the scope of the following claims.

We claim:

1. A gear pump having an inlet and an outlet and comprising a housing having therein two chambers, two inter-meshing displacing gears mounted for rotation in said chambers, said gears each having journals extending axially therefrom, bearings engaging said journals over an axial length thereof, means for supporting said bearings in said housing, said supporting means only engaging each bearing over a portion of the axial length of said hearing which is intermediate the ends of the bearing and has an axial length less than half the said axial length of the bearing, while on the remainder of its axial length the bearing is unsupported so as to permit alignment of the bearings on said journals, side members each having two oppositely facing side surfaces one of which engages the side faces of said gears, said side members being mounted in said housing for limited movement in a direction axial of said journal and having bores through which said journals extend with radial play, and means for applying output fluid pressure to a predetermined area of the other side surface of at least one of said side members.

2. A gear pump according to claim 1 and comprising housing plates mounted in the housing and supporting the bearings.

3. A gear pump according to claim 1 and comprising end covers for said housing, said end covers supporting said bearings.

4; A gear pump having an inlet and an outlet and comprising a housing having therein two chambers, two intermeshing displacing gears mounted for rotation in said chambers, said gears each having journals extending axially therefrom, bearings engaging said journals over an axial length thereof, means for supporting said bearings in said housing, said means engaging each said bearing over an axial length of said bearing which is intermediate the ends of and equals less than half the said axial length of the journal bearing While the bearing is unsupported on the remainder of its axial length, so as to permit alignment of said hearings on said journals, side members each having two opposite side surfaces one of which engages the side faces of said gears, said side members being mounted in said housing for limited movement in a direction axial of said journals and having bores through which said journals extend with radial play, and means for applying output fiuid pressure to a predetermined area of the other side of each said member and comprising means for defining a high pressure area and a low pressure area on at least one of said members, whereby the centre of pressure on said side members coincides with the centre of pressure on said gears.

References Cited in the file of this patent UNITED STATES PATENTS 185,188 Pickering Dec. 12, 1876 385,288 Turner" u June 26, 1888 489,505 Silvey Jan. 10, 1893 1,771,863 Schmidt July 29, 1930 2,040,754 McLeod May 12, 1936 2,044,873 Beust June 23, 1936 2,487,732 Schanzlin Nov. 8, 1949 2,527,941 Lauck et al. Oct. 31, 1950 2,641,192 Liudberg' June 9, 1953 2,672,100 Harvey Mar. 16, 1954 2,682,836 Orr, Jr. July 6, 1954 (Other references on following page) 5 UNITED STATES PATENTS Compton Nov. 30,1954 Drennen May 3, 1955 Kane Aug. 9, 1955 Booth et a1 Feb. 21, 1956 Eames May 21, 1957 Miller et a1. Oct. 15, 1957 Jarvis Dec. 17, 1957 6 Compton Feb. 25, 1958 Banker Feb. 25, 1958 FOREIGN PATENTS Great Britain a. May- 26, 1938 France Nov. 28, 1939 France Nov. 28, 1939 France Mar. 2, 1955