GB2067667A - Rotary positive-displacement fluid-machines - Google Patents

Abstract

A gear pump, or motor, has a pair of externally-toothed gears (20, 21) with shafts (22-25) supported by plain bearings (26-27), the crests of the teeth of said gears being engaged by a seal block (31) on the high- pressure side. The face of the seal block in contact with the tooth crests is in engagement with side plates (36, 37) in sealing contact with the side faces of the gears at least at the high- pressure side. Edge faces of the side plates are in contact with the outer circumferential faces of the bearings. This arrangement permits use of thin low-cost side plates. <IMAGE>

Description

SPECIFICATION A seal-block supporting device for gear pumps or motors The present invention relates to a gear pump or motor wherein a pair of gears meshing mutually by means of their circumferential teeth are mounted on shafts; each shaft is supported at both ends in holes in the housing; the said two gears are sealed at the crests of their teeth on the delivery side by a seal block on the high pressure side that is fitted to the outside surface of the gears and subject to the working pressure at the high-pressure side, while the other portion of the outer circumferential face of the gears is not in contact with the housing and is connected with the low-pressure side.

In the case of a gear pump or motor of this type, crests are the high-pressure side of the two gears may be effectively sealed by a simple sealblock mechanism. Nevertheless, the seal block is forced into contact with the inside faces on the crests of the gears as it is continuously backloaded by the working pressure during operation of the gear pump or motor. This has the defect that the interior face of the seal block is rapidly worn away by the crests of the gears due to this load, and the back face of the seal block ceases to remain in contact with the inside walls of the housing after a short period of time, thus permitting the seal member sealing the working pressure on the high pressure side of the back to ride up, leaving the inside walls of the housing and resulting in the loss of the seal between the seal block and the gear crests.

Therefore, in order to hold the said seal block in a given position and reduce the load upon the gears during operation of the gear pump or motor, measures are taken to seal both side faces of the gears by using side plates and thus to locate the said block. For example, in the case of a gear type pump or motor known from the Specifications of U.S. Patent No. 3,986,800, both sides of the gears are sealed by means of side plates which are movable in the axial direction under the action of the working pressure at the high-pressure side.

The high pressure side edge faces of these side plates are in contact with the gear-side face of the said seal block, while the opposite low-pressure side edge faces are in contact with inside walls of the bowel which holds the gears in the housing.

The said defect is therefore resolved by the side plates as they enable the inside walls of the housing to support the seal block.

However. the major disadvantage of this device lies in the cor.siderable distance between the side wall face at the low-pressure side of the bowel of the housing which supports the side plates and the area of contact between the seal block and the side plates upon which it presses. Side plates with low manufacturing cost made, for example, by punching thin steel sheet, bend during operation of the gear pump or motor because of their lack of rigidity, and fail to hold the seal block precisely and continuously at a given position.

Of measures designed to minimise this difficulty, none are known other than that in the said Specifications of U.S. Patent No. 3,986,800, where notches are cut into the inside wall face opposite to the seal block so as to introduce continuously the working pressure of the high pressure side and so as to reduce the load of the seal block pressing upon the gears, or that seen in a gear pump or motor known from the Specifications of U.S. Patent No. 3,847,519, where highly rigid bushes are inserted into the bowel of the housing so as to support the gear shafts and so as to support the seal block by the outer circumferential faces of these bushings.

However, each of these measures has a defect; the structure becomes complex in the former, while the pump itself becomes large in size in the latter.

The purpose of the present invention is, therefore, to offer gear pumps or motors of the type described above which are not only simple in structural form but also makes it possible to position the seal block precisely by means of lowcost side plates such as may be made of thin steel sheet.

This purpose is attained in the following invention as follows. Each bearing supporting the gear shaft projects a certain amount into the interior of the bowel of the housing, and the side plates are disposed so as to seal both side faces of the gears only at the high pressure side. Each edge face of these side plates opposite to that contacting the seal block is in close contact with the corresponding outer face of the part of the bearings supporting the gear shafts that projects into the bowel.

Thus, the width of the side plate between the edge face in contact with the outer circumferential face of the bearings and the other edge face in contact with the seal block is reduced. It therefore becomes possible to support a heavy seal-block load and to maintain the seal block continuously in the correct position even using such low-cost side plates as may be made of thin steel sheet, achieving a high performance pump or motor with a low-cost device.

In the following, an example of this invention will be detailed with reference to the attached drawings. Although the description is made with regard to a gear pump, the principles are, of course, equally applicable to gear motors.

Fig. 1 is a side elevation showing a cross section of a gear pump according to this invention.

Fig. 2 is a section along the line 2-2 of Fig. 1.

Fig. 3 is a section along the line 3-3 of Fig. 1.

Fig. 4 is a section along the line 4-4 of Fig. 1.

In Fig. 1, a gear pump 10 according to this invention has a housing 11 consisting of a casing 12, end cover 13 and mounting flange 14. The casing 12 is a thick-walled cylinder bolted securely, so as to form liquid-tight seals, by bolts 7 to the end cover 13 on one side and to the mounting flange 14 on the other, using seal members 1 5 and 16 respectively. The end cover 13 and the mounting flange 14 are connected to both ends of the casing 12 by means of fit joints 18, 19, which grip the seal members 1 5, 1 6 respectively. These fit joints 1 8, 1 9, enable the casing 12 to conform to the end cover 13 and the mounting flange 14 without the use of dowels, etc.

The casing 12 houses two mutually meshing gears 20 and 21. These gears 20, 21 are mounted on shafts 22, 23 and 24, 25 that extend on both sides of the respective gears. The shafts 22-25 are supported. rotating freely, by bearings 26, 27 and 28, 29, respectively. Bearings 26, 28 and 27, 29 consist of wound bushes mounted in the end cover 13 and the mounting flange 14, respectively. One shaft, 25, of gear 21 extends outwards through mounting flange 14 and may be connected to a power source outside gear pump 10. That part of the mounting flange 14 through which shaft 25 extends is provided with an oil seal 30 to seal the clearance between shaft 25 and mounting flange 1 4.

As shown in Fig. 2, a seal block 31 is located between the inside walls of the casing 12 and the tooth crests of the gears 20, 21 at the delivery side of gear pump 10. The outer circumferential face of this seal block 31 conforms to the inside face of the wall of casing 12, while its inner face conforms to the exterior profile of the gears 20, 21. The outer circumferential face of seal block 31 has a pressure zone 33 partitioned off by a seal member 32. This pressure zone 33 is connected to the delivery side of gears 20, 21 via a radial high pressure feed hole 34 and an axial high pressure groove 35 through the seal block 31. The circumferential faces of gears 20, 21, other than the parts facing the inner face of the seal block 31, are not in contact with the inner wall of the casing 12, and are connected to the low-pressure side of gears 20,21.

As shown in Fig. 4, the total height of seal block 31 is almost identical with that of the chamber housing gears 20,21 in casing 12, and thus its movement is limited axially by the end cover 1 3 and the mounting flange 14. Radially, however, it is free to move until it comes into contact with the inside face of the wall of casing 12 and the tooth crests of gears 20, 21. The total height of gears 20, 21 is made slightly smaller than that of the chamber in casing 12, and the space thus formed houses side plates 36, 37 at the delivery side. Side plate 36 is placed between the end cover 13 and the corresponding side face of gears 20, 21, while side plate 37 is placed between the mounting flange 14 and the corresponding side face of gears 20,21.

Since the two side plates 36, 37 are essentially identical, only side plate 36 will be described in full detail. As shown in Fig. 2, side plate 36 consists of a central section 36a and side sections 36b, 36c branching in opposite directions. The central section 36a extends between bearings 26, 28 that support the freely rotating shafts 22, 24 of the gears 20, 21, while the inner edges of sections 36b, 36c contact the circumferential faces of these bearings 26, 28. Also, bearings 26-29 project a certain distance from the end cover 13 and from the inner wall of the mounting flange 14 into the chamber in casing 12, forming projections 26a, 27a, 28a and 29a.

In the side plates 36 (and similarly for 37), the part extending from the central section 36a to the inner edges of sections 36b, 36c conforms approximately to the outer circumferential faces of the projections 26a-29a of bearings 26-29, enabling the projections to support the side plates 36 (and 37) at the inner edge faces. Each outer edge of sections 36b, 36c and 37b, 37c of side plates 36, 37 also conforms to the exterior profile of gears 20, 21, and thus to the interior surface of the seal block 31, so enabling the outer edge faces of these sections 36b, 36c and 37b, 37c to support seal block 31 at its interior surface.The dimensions of side plates 36, 37 are chosen so that the outer edge faces supporting the interior surface of the seal block 31 form an arc rather smaller than the exterior profile of gears 20, 21, and so that their inner edge faces are supported by the corresponding circumferential faces of the projections 26a-29a of the bearings 26-29.

In order to seal the deiivery-side faces of both gears 20,21 using side plates 36, 37, pressure zones 40, 41 are partitioned off by seal members 38, 39 in the inner walls of the end cover 13 and the mounting flange 14 adjacent to side plates 36, 37 respectively. Fig. 3 shows pressure zone 40 on the side of the end cover 1 3. The other pressure zone 41 on the side of the mounting flange 14 is precisely similar.

Thus, as the gear pump 10 commences operation, the hydraulic medium is drawn into the low-pressure side of the chamber in casing 12 through the passage 43 (see Fig. 1 and Fig. 3) that passes radially from an inlet port 42 to one side face of the end cover 13, and is sent to the deliver side under the action of the contra-rotating gears 20, 21. The hydraulic fluid is then supplied to the device using it, not shown in the drawing, via the high pressure groove 35 in the seal block 31, the passage 44 passing axially through the end cover 13, and an outlet port 45 (see Fig. 1 and Fig. 3) opening into the other side face of the end cover 13.

The high pressure produced at the delivery side of gears 20,21 acts upon the pressure zones 40, 41 behind side plates 36, 37 via the high pressure groove 35 through seal block 31. Thus, the pressure on the back surfaces of side plates 36, 37 forces them into contact with both of the delivery side faces of gears 20, 21, producing an excellent seal. Simultaneously, the high pressure also acts upon the pressure zone 33 at the back of seal block 31 ,which is therefore also forced into contact with the tooth crests of gears 20,21. As the tooth crests of gears 20, 21 shave the inside face of seal block 31 , they tend to form a slight depression in it, again producing a satisfactory seal. This action of the tooth crests of gears 20, 21 continues until the interior surface of seal block 31 comes into contact with the outer edge surfaces of the side plates 36, 37 and is supported by them. This is performed while the gear pump 10 is being run in. Under normal operation of gear pump 10, therefore, seal block 31 is continuously supported by the outer circumferential faces of the projections 26a-29a of the bearings 26-29 through the medium of the side plates 36,37.

By this means it becomes possible to form the side plates 36, 37 that support the seal block 31 from parts with smaller physical dimensions than conventional ones, with the result that side plates 36, 37 can be punched out of thin sheet steel at low cost and still ensure excellent pumping action while continuously maintaining seal block 31 in the correct position.

It is advantageous not only costwise, as mentioned above, but also for the following reasons to make the side plates 36, 37 by punching thin steel sheet. That is, since the gears 20, 21 are commonly made of steel for strength, both the gears 20, 21 and the side plates 36, 37 thus all have the same structural material.

Therefore, no matter what the temperature conditions under which the gear pump 10 may be operated, high or low, the fact that the gears 20, 21 and the side plates 36,37 share the same coefficient of expansion means that the seal block 31 can always be held in the correct position relative to the tooth crests of the gears 20,21.

However, in cases where side plates 36, 37 made of steel are used, their coefficient of sliding friction with the side faces of the gears 20, 21 is high, and this lowers the mechanical efficiency of the pump.

For this reason, the inner faces of side plates 36, 37 in the present invention, which are in sliding contact with the gears 20, 21, are completely covered with a lining of such materials as copper or aluminum alloy to give a low sliding frictional resistance.

Since the projections 26a-29a of the bearings 26-29 that support the shafts 22-25 of gears 20, 21 support the seal block 31 through the medium of the side plates 36,37, if these projections 26a-29a are too rigid, the seal block 31 may fail to follow the movement of the tooth crests of the gears 20, 21 as they are moved to the low-pressure side during operation of the gear pump 10 under high pressure, causing the hydraulic medium flowing from the delivery side to the low-pressure side to leak from the tooth crest part of the gears 20, 21.This will degrade the volumetric efficiency of the gear pump 1 0. On the other hand, if the rigidity of the projections 26a-29a is too low, the rate of motion of the seal block 31, supported by these projections 26a-29a through the medium of the side plates 36, 37, exceeds that of the gears 20,21 which are pushed to the low-pressure side during operation of the gear pump 10 under high pressure, thus permitting tooth crests of the gears 20,21 to shave the interior surface of the seal block 31.

Therefore, when the gear pump 10 is operated subsequently at working or lower pressures, a clearance will have been formed due to erosion between the tooth crests of the gears 20, 21 and the interior surface of the seal block 31, and the hydraulic oil on the delivery side will leak to the low-pressure side through this clearance, thus reducing the volumetric efficiency of the gear pump 10.

In order to remove this defect, therefore, it is preferable to select an appropriate wall thickness for the bearings 26-29 made of a bearing material or to insert collars 48, 49, 50, 51 made of another material into the end of the bearings 26-29 as shown in the preferred embodiment so as to give the proper rigidity to the projections 26a-29a.

In addition, in the case of the above preferred embodiment, the side plates 36, 37 are designed to cover the sides of the gears 20,21 only on the delivery side. However, as shown by line 52 in Fig. 2, side plates 136, 137 may be designed to cover the entire side areas of the gears 20, 21 with or without extensions.In this case, however, it is necessary to permit the said side plates 1 36, 1 37 to maintain a clearance between their side edges at the low-pressure side and the inside surface of the wall of the casing 12 at the lowpressure side so that the side plates 136,137 are supported by the protrusions 26a--29a of the bearings 26-29 which support the shafts 22-25 of the gears 20,21 lest the side plate 36, 37 should contact the inside surface of the wall of the casing 12 at the side edge on the lowpressure side, and form there a bearing face to support the seal block 31.

Although we have described a preferred embodiment of the present invention, it is obvious as previously noted that the present invention is applicable, without modification, to gear motors of the same structural type, or gear pumps or motors of a type such as that described in the Specifications of U.S. Patent No. 3,986,800 that employs a casing provided with two holes partially overlapping each other and conforming to the outer profile of the gears.

Claims (5)

1. A seal-block supporting device for gear pumps or motors, consisting of a pair of gears with mutually meshing circumferential teeth, a housing which forms a chamber to house these gears, bearings which are inserted into both sides of the housing so as to support the respective shafts of the said gears and are provided with projections extending into the chamber at their inner ends, a seal block which is located between the tooth crests of the said gears and the inner surface of the walls of the housing so that its interior surface may conform to the outside profile of the gears and is pressed into contact with the crests of the gears as its back surface is subject to the working pressure of the high-pressure side, and side plates which cover either both sides of the gears or at least those sections of them located on the highpressure side; so that their outside edges conform to the outside profile of the gears and can come into close contact with the interior surface of the said seal block, that their inside edges can come into contact with the respective circumferential faces of the projections of the said bearings supporting the respective shafts of the gears and that the said seal block can thus be maintained in a given position between the projections of the bearings.

2. A device as claimed in Claim 1, wherein the said side plates are made of a material of the same type as the gears and their inside faces in sliding contact with the side faces of the gears are covered with a lining material of low sliding frictional resistance.

3. A device as claimed in Claim 2, wherein the said side plates cover the whole side faces of the gears with or without extensions while keeping a clearance between their outside edge at the lowpressure side and the inside surface of the wall of the housing at the low-pressure side.

4. A device as claimed in any one of Claims 1 to 3, wherein each of the projections of the bearings supporting the gear shafts is formed by a collar made of another material inserted into the inside end of each bearing.

5. A seal-block supporting device for gear pumps or motors substantially as hereinbefore described with reference to the drawings.