GB2199374A

GB2199374A - Pressure balancing seal in gear pump or motor

Info

Publication number: GB2199374A
Application number: GB08724540A
Authority: GB
Inventors: Angelo Zanardi; Gilberto Luppi
Original assignee: Sauer Sundstrand SpA
Current assignee: Sauer Sundstrand SpA
Priority date: 1986-10-20
Filing date: 1987-10-20
Publication date: 1988-07-06
Anticipated expiration: 2007-10-20
Also published as: FR2605361A1; IT8603547A0; FR2605361B1; DE8713996U1; IT1200232B; ES2008749A6; GB2199374B; GB8724540D0

Abstract

In a machine having two mutually engaging gear wheels (5 and 6, Fig. 1) supported by two bushes (13) in a casing (2) provided with two end plates (3) and 4, between each of the plates (3) and 4 and associated bushes (13) there are defined two interspaces, a first of which is delimited by an annular seal gasket 18, and the second 22, 22 of which is isolated from the first by a portion of the seal gasket which lies between points 26a and 26b and which is coupled to an antiextrusion gasket 27 constructed of hard material. The gasket 18 over the portion 26a to 26b is provided with a notch (31, Fig. 5) which receives the gasket 27. <IMAGE>

Description

GEAR XACHIKE FOR USE AS A PUXP OR MOTOR This invention relates to a gear machine for use as a pulp or rotor Currently available gear machines are known to comprise a machine casing within which two gear wheels, one the driven wheel and the other the drive wheel, are installed. The machine casing is closed on its two axial sides by respective closure plates in which respective annular seal gaskets are installed to laterally delimit a space between the plates and the support bushes for. the gear wheels. Pressurised fluid is present in this space, and this enables the clearance walls between the bushes and gear ends to be balanced and cowpensated.

Some manufacturers form the seal gasket in a single piece from soft material such as rubber. Unfortunately in such machines, if the operating pressure is high, gaps occur between the bushes and closure plates particularly along that portion of the gasket which separates the space containing high pressure fluid fron the space containing low pressure fluid, this latter always being defined between the plates and the respective bushes. If such gaps are present1 a gasket of soft material extrudes into the gaps, with the risk of becoming torn and cut. A hard material gasket cannot be installed because it would not form a seal, and therefore other manufacturers obviate the aforesaid drawback by combining the soft material gasket with second annular gasket

formed of hard material such as teflon.This totally obviates the extrusion drawback, but increases the assembly and overall oroductlon costs of the machines concerned. In this respect, as

such antiextrusion gaskets are constructed of teflon/ they have to be worked with machine tools.Moreover, the gasket seats1 which are provided in the closure plates, have a very varied perimetral profile, consisting of ailed straight and curved portions. Beither of the gaskets is shaped prior to asseably to coincide with the seats in which they are to be housed, and therefore their installation aust be carried out manually, requiring the use of labour suitable for such & sembly. Thus, although the use of the antiertrusion gasket on the one hand obviates the extrusion drawback, it leads on the other hand to relatively high costs in the form of the cost of the antiextrusion gasket plus the cost of the labour required for its installation.

The object of the present invention is to provide a gear machine for use as a pump or motor, which is free of the aforesaid drawbacks by virtue of preventing extrusion of the seal gasket at considerably reduced cost.

This object is attained according to the present invention by a gear machine for use as a pump or motor, of the type comprising: two mutually engaging gear wheels comprising respective hubs, one of which is connected to a motor output shaft; two bushes supporting said hubs and disposed to the sides of said gear wheels in such a manner as to define a respective clearance wall; a machine casing within which the assembly comprising the gear wheels and bushes is installed; and two closure plates for said machine casing, characterised in that between said plates and said bushes there are defined two respective interspaces, a first of which is delimited laterally by an annular seal gasket constructed of relatively soft material and housed in a seat formed in said plates and is in hydraulic communication with the inner opening of a first port traversed by a high pressure fluid, and the second of which is in hydraulic communication with the inner opening of a second port traversed by a low pressure fluid, between said interspaces there being disposed, of said annular seal gasket, a first portion which is coupled to an antiextrusion gasket constructed of relatively hard material and extending only along the boundary region between said interspaces.

The present invention will be more apparent from the description of a preferred embodiment thereof given herelnafter by way of non-limating example with reference to the acconpanying drawings, in which: Figure 1 is a section through a gear pump constructed in accordance with the present invention; Figure 2 is a section on the line II-II of Figure 1; Figure 3 is a section to a reduced scale on the line III-III of Figure 1; Figure 4 is a plan view of a seal assembly for the pump of Figure 1; and Figure 5 is a section to an enlarged scale on the line V-V of Figure 4.

In Figure 1, the reference numeral 1 indicates overall a gear punp constructed in accordance with the present invention. The pump 1 comprises a machine casing 2 closed on its two sides by respective closure plates 3 and 4 and having two mutually engaging gear wheels 5 and 6 installed in its interior. The gear wheel 5 is the driven wheel and comprises a hub 7 substantially as long as the machine casing 2. The gear wheel 6 is the drive wheel and comprises a hub 8 which extends at one end beyond the plate 3, where it is connected in any manner to the output shaft of a motor, not shown. For this purpose the plate 3 comprises a through bore 11 traversed by the hub 8 and housing a hydraulic seal assembly 12.The hubs 7 and 8 are supported by two support bushes 13 disposed on opposite sides of the gear wheels 5 and 6 to define, with the ends of the teeth of these latter, respective clearance walls 14.

With reference to Figures 1, 2 and 3, the machine casing 2 has an internal shape which reproduces the perimetral profile of the assembly formed from the two gear wheels 5 and 6, ie an "8"shaped profile. The bushes 13 are of analogous shape, each bush 13 comprising two parallel through bores 15 engaged by the hubs 7 and 8. In correspondence with the region of mutual engagement of the gear wheels 5 and 6, there are provided in the machine casing 2 a suction port 16 on one side and a delivery port 17 on the opposite side. The gear wheels 5 and 6 have respective teeth of known shape, such that within the engagement region there is no direct communication between the ports 16 and 17, and within the.

region of contact between the teeth and the inner wall of the machine casing 2 there is no fluid seepage between a region subtended by a pair of teeth and the regions to the sides thereof. The punp 1 is of self-compensating balanced type as will be apparent hereinafter. This means that there is no fluid seepage along the clearance walls 14.

Vith reference to Figures 1, 2, 3 and 4, as the fluid is drawn in at a predetermined pressure and delivered at a higher pressure than the preceding, the clearance walls 14 are subJected to a non-uniformly distributed hydrostatic pressure, which is a minium in correspondence with the inner opening of the suction port 16 and a saxismm in correspondence with the delivery port 17. For better understanding, hatching is used to indicate that surface of the bush 13 subJected to a pressure, known hereinafter as the internal pressure, which exceeds the mSniwum, ie is higher than the suction pressure. As the barycentre of the internal pressure does not lie on the axis of symmetry of the bush 13, due to the fact that the surface subjected to this internal pressure is shaped differently from the face (wall 14) of the bush 13, this latter would tend to oscillate about the hubs 7 and 8, to cause fluid seepage along the clearance walls 14. The bushes 13 are balanced by cowpensating on the opposite side of the bushes 13 the internal pressure exerted on these latter. For this purpose a respective interspace is formed in the inner face of the plates 3 and 4 which is delimited laterally by an annular seal gasket 18 and is in hydraulic coizaunication with the inner opening of the delivery port 17.This communication can be obtained by providing along the central part of the outer surface of the bushes 13 a cavity 21 shown by dashed lines in Figure 2. To the side of this interspace there is defined a second interspace connected to the inner youth of the suction port 16 by a second cavity also indicated by 21 formed on the opposite side of the bush 13 to the former. This second interspace comprises two circular cavities 22 formed in the plate 4 in correspondence with the hubs 7 and 8, and a cavity 23 which connects the cavities 22 together and comprises a portion facing the corresponding cavity 21. In the plate 3 there is however only one cavity 22 as the bore 11 is provided in correspondence with the other.

As shown in Figures 2 and 4, the annular gasket 18 comprises a first portion 25 which hugs the profile of the bush 13, and a second portion which hugs the two cavities 22. The gasket 18 therefore has a shape similar to the figure 3 In the plate 3, the portion 26 hugs the cavity 22 and the bore 11. The profile of the gasket 18 qnd thus of that surface of the bush 13 facing the interspace bounded by the gasket 18 is such that the resultant barycentre of the counter-pressure on the bush 13 is as close as possible to the resultant barycentre of the internal pressure. As shown in Figures 1 and 2, the portion 25 of the gasket 18 is interposed between the plates 3 and 4 and the corresponding end faces of the machine casing 2.The second portion 26 represents the boundary region between the two interspaces, ie it divides the interspace containing high pressure fluid from that containing low pressure fluid. The points of intersection of the geometrical shapes of the gasket 18 and bush 13 are indicated by 26a and 26b, and represent the ends of the boundary region between the two interspacee. Only along this boundary region are gaps present which could allow extrusion of the gasket 18. To overcome this problem, a second gasket 27 of antlextrusion type is coupled to the portion 26 along this boundary region. The gasket 18 is formed of soft material such as rubber or plastics material of elastic type, whereas the gasket 27 is constructed of hard material using suitable plastics materials possibly of silicone or nylon type.The two gaskets 18 and 27 are produced by moulding, and are thus already shaped before assenbly. A seat 28 is formed in the plates 3 and 4 to house the gasket 18, and has the same shape as this latter As shown in Figures 4 and 5, the portion 25 of the gasket 18 is of substantially rectangular cross-section with its two lower corners rounded, whereas the portion 26 differs in cross-section from the portion 25 by the provision along its outer side, with respect to the interspace which encloses it, of a notch 31 into which the gasket 27, of shape substantially complementary to that of the notch 31, is forced such that the portion 26 plus gasket 27 has a cross-section substantially similar to that of the portion 25.The notch 31 comprises in the lateral part of the portion 26 an upper face 32 which is perpendicular to the longitudinal axis of the gasket 18 and a lower face 33 which is oblique to this axis. That part of the gasket 27 which is housed in the notch 31 also has an upper face 34 perpendicular to the longitudinal axis of the gasket 27 and a lower face 35 which is oblique to this axis. Vben in the non-operating position shown in Figure 5, the upper faces 32 and 34 of the gaskets 18 and 27 mate. whereas the lower faces 33 and 35, being of different inclination, have a region of contact only in correspondence with their lower end. During assembly and subsequently when the pu 1 is in operation, the gasket 18 tends to deforn and said lower faces 33 and 35 tend to mate.As shown in Figure 2, to obtain correct isolation between the two said interspaces, the portion 26 of the gasket 18 and consequently the ends of the gasket 27 extend a very snall distance beyond the points of intersection 26a and 26b. Vith reference to Figure 1, along those faces of the machine casing 2 which face the plates 3 and 4 there is provided a respective seat 36 for a corresponding annular seal gasket 37, which because of the fact that the high pressure fluid is internal to the gasket 18 is not subjected to this pressure.

The operation of the pump 1 is entirely similar to that of already available pumps of the same type, and has already been described in the description given heretofore.

The advantages of the present invention are apparent from the aforegoing description.

In particular, the antiextrusion gasket is coupled to the seal gasket only along the boundary region between the interspaces formed between the plates 3 and 4 and the bushes 13. It should be noted that only along this boundary region could any extrusion of the seal gasket take place if the anti extrusion gasket were absent. This latter is therefore not annular and can be consequently produced by moulding. An antiextrusion gasket of this shape produced by this method enables both gaskets to be assembled by robots and does not require any machining by machine tools. fbis results in a lower overall pulp cost and lower maintenance costs, tn that the gaskets are easily replaceable.

Finally, it is apparent that modifications can be made to the pup 1 described and illustrated heretofore but without leaving the protective scope of the present invention.

Claims

PATENT CLAIMS

1. A gear machine for use as a pump or motor, of the type comprising: two mutually engaging gear wheels comprising respective hubs , one of which is connected to a rotor output shaft; two bushes supporting said hubs and disposed to the sides of said gear wheels in such a inner as to define a respective clearance wall a machine casing within which the assembly comprising the gear wheels and bushes is installed; and two closure plates for said machine casing characterised in that between said plates and said bushes there are defined two respective interspaces a first of which is delimited laterally by an annular seal gasket cotstructed of relatively soft material and housed in a seat formed in said plates and is in hydraulic co=jnication with the inner opening of a first port traversed by a high pressure fluid, and the second of which is in hydraulic communication with the inner opening of a second port traversed by a low pressure fluid, between said interspaces there being disposed, of said annular seal gasket, a first portion which is coupled to an antiertrusion gasket constructed of relatively hard material and extending only along the boundary region between said interspaces.

2. A machine as claimed in claim 1, characterised in that said annular seal gasket comprises said first portion and a second portion which bugs the perinetral profile of said bush and is thus interposed between said plates and the corresponding faces of said machine casing

3. A chine as claSsed in claim 2, characterised in that said second portion has a substantially rectangular crosssection, and said first portion has a substantially rectangular cross-section which along that lateral part facing said second interspace is provided with a notch in which said antiextrusion gasket is housed.

4. A machine as claimed in claims 3, characterised in that said anti extrusion gasket has a cross-section substantially similar to that of said notch 60 that the antiextrusion gasket plus the first portion together have a crosssection which is substantially sisNlar to that of said second portion

5.A machine as claimed in claim 4, characterised in that said notch comprises in the lateral part of said first portion an upper face which is perpendicular to the longitudinal axis thereof and a lower face which is oblique to said axis, that portion of said antiextrusion gasket which is housed in said notch having an upper face parallel to the upper face of said first portion and a lower face which is oblique in the same direction as that of said first portion but with a sligbtly different inclination so that wben in the non-operating state said upper faces mate perfectly and said lower faces are in contact only along tbeir lower end, whereas during operation said lower faces tod to mate by virtue of the deformation to which said first portion is subjected.

6. s machine as cla'sed in at least one of the preceding claima characterised in that said second interspace co1prises two first cavities formed in said plates in correspondence with the ends of said hubs , and a second cavity which connects the first cavities together and is in hydraulic communication with said second port ; said first portion bugglng said first cavities

7. A machine as claimed In at least one of the preceding clalis, characterised in that said antiextrusion gasket is constructed of plastics material such as nylon by ulding.

8. A machine as claimed in at least one of tbe preceding claims, characterised in that said seal gasket is constructed of rubber for example by moulding.

9. A seal gasket as described in the preceding claims for delimiting an interspace in which high pressure fluid is present, characterised by comprising a first portion for isolating said interspace fron a second interspace in which a low pressure fluid is present, and having a lateral notch for housing an anti extrusion gasket constructed of relatively hard material.

10. An antiextrusion gasket constructed of relatively hard material as described in the preceding claims.

11. A gear machine for use as a pump or motor as described and illustrated with reference to the accompanying drawings.