US3730656A

US3730656A - Hydraulic apparatus

Info

Publication number: US3730656A
Application number: US00126553A
Authority: US
Inventors: D Lambeth
Original assignee: Dowty Technical Developments Ltd
Current assignee: Dowty Technical Developments Ltd
Priority date: 1971-03-22
Filing date: 1971-03-22
Publication date: 1973-05-01
Anticipated expiration: 1990-05-01

Abstract

A hydraulic displacement device such as an internal gear pump having an internally toothed gear in mesh with an externally toothed gear, a high pressure zone and a low pressure zone defined within the internally toothed gear and separated by the meshing position of the gears and an end bearing member loaded by liquid at the pressure of the high pressure zone to engage the end surfaces of the gears. In order to reduce excessive friction between the end bearing member and the gears the bearing member has an area of engagement with an end surface of the gears in the vicinity of the high pressure zone with part of its boundary at a position intermediate the tooth root radius and the periphery of the internally toothed gear.

Description

United States Patent 1 Lambeth [54] HYDRAULIC APPARATUS [75] Inventor: Dennis Ernest Lambeth, Benhall,

Cheltenham, England [73] Assignee: Dowty Technical Developments Limited, Cheltenham, England [22] Filed: Mar. 22, 1971 [21] Appl. No.: 126,553

UNITED STATES PATENTS 3,496,877 2/1970 Eckerle et a1. ..4l8/13l 2,405,061 7/1946 Shaw ..418/l32 1,802,527 4/1931 Nichols ..4l8/169 3,204,564 9/1965 Elitze ..4l8/l70 2,808,785 10/1957 Hilton "418/132 3,303,793 2/1967 Morita ..4l8/132 1 May 1, 1973 2,855,854 lO/l958 Aspelin .418/126 Primary ExaminerCarlton R. Croyle Assistant Examiner-John J. Vrablik Attorney Young & Thompson [57] ABSTRACT A hydraulic displacement device such as an internal gear pump having an internally toothed gear in mesh with an externally toothed gear, a high pressure zone and a low pressure zone defined within the internally toothed gear and separated by the meshing position of the gears and an end bearing member loaded by liquid at the pressure of the high pressure zone to engage the end surfaces of the gears. In order to reduce excessive friction between the end bearing member and the gears the bearing member has an area of engagement with an end surface of the gears in the vicinity of the high pressure zone with part of its boundary at a position intermediate the tooth root radius and the periphery of the internally toothed gear.

2 Claims, 4 Drawing Figures Patented May 1, 1973 3,730,656

2 Sheets-Sheet 1 INVENTOR 0.6mm: fen/3 7' La M15577;

BY (4M7, r L, /5544 [ATTORNEYS Patented May 1, 1973 1 3,130,656

2 Sheets-Sheet 2 INVENTOR fii/wv/s fen/asrla/vaz/v %:I7 YUM ATTORNEYS HYDRAULIC APPARATUS This invention relates to a hydraulic displacement device having an internally-toothed gear in mesh with an externally-toothed gear, a high-pressure zone and a low-pressure zone defined within the internally toothed gear and separated by the meshing position of the gears, a high pressure connection for the high-pressure zone and a low pressure connection for the low-pressure zone and at least one end bearing member being loaded by liquid at the pressure of the high pressure zone to engage end surfaces of the gears. Thiskind of hydraulic displacement device will hereinafter be referred to as a pressure loaded internal gear device.

Where a pressure loaded internal gear device is provided for operation at high pressure the internallytoothed gear must be of substantial radial thickness in order to provide adequate strength to resist the action of pressure in the high pressure zone which will tend to distort the internally-toothed gear out of its circular form.

The present invention has for its object to provide an improved form of pressure loaded internal gear device for reliable and efficient operation at high pressures.

in accordance with the present invention, a pressure loaded internal gear device comprises a casing, an internally toothed gearand an externally toothed gear both rotatably mounted within the casing with teeth in mesh, the externally toothed gear being supported by a pair of shafts extending c-axially from the ends thereof into bearings within the casing, an end bearing member mounted within the casing for axial floating movement to enable a flat bearing surface thereof to engage the flat ends of the gears adjacent to one shaft, a load reacting member forming part of the casing having a flat reacting surface adjacent to a flat loading surface formed on the bearing member opposite to the bearing surface, sealing means located between the loading surface and the reacting surface to define a balancing zone, a passage connecting high pressure liquid from the high pressure zone between the gears to the balancing zone whereby the end bearing member is urged against the end surfaces of the gears to seal the high pressure zone within the gears, a groove in the bearing surface of the end bearing member connecting the low pressure zone between the gears to some of the intertooth spaces of the gear teeth not in mesh with one another, the area of engagement between the flat bearing surface of the end bearing member and the flat end surfaces of the gears in the neighborhood of the high pressure zone terminating between the tooth root radius and the periphery of the internally toothed gear.

Where a land is located in between the gears having curved surfaces to engage the gear tooth tips at nonmeshing positions thereof, the low pressure zone may be connected to some of the inter-tooth spaces of teeth not in mesh with one another be means of a groove in the surface of the land.

One embodiment of the invention for use as a pump will now be particularly described with reference to the accompanying drawings, in which,

FIGS. 1 and 2 are longitudinal cross-sections lying at right angles to one another through the pump,

FIG. 3 is a cross-section on the line Ill-III in FIG. 1, and

FIG. 4 is a cross-section on the line IV--IV in FIG. 1.

The pump casing comprises an annular member 1 in ternally bored to receive a thin plain metal bearing 2 having an internal cylindrical bearing surface 3. A pair of end covers 4 and 5 are secured to the annular member 1 by a plurality of bolts 6. The end covers 4 and 5 are provided respectively with extensions coaxially known in parallel to the axis of the member 1 but eccentric relative thereto the bores being provided with cylindrical bearing sleeves 7 and 8. The bearing sleeves 7 and 8 carry two

parts

9 and 11 ofa hollow drive shaft which are integrally formed with an externally-toothed driving gear 12. The driving gear 1.2 meshes with an internally-toothed gear ring 14 whose cylindrical external surface 10 fits closely within the bearing surface 3 for rotation therein. The teeth 15 of the gear 12 and the teeth 16 of the gear ring 14 are accurately shaped in a .manner well known in standard gear technology to minimize sliding contact between the gear teeth. The radial thickness of the gear ring 14' from the tooth roots to the outer periphery is quite substantial having regard to the high operating pressure intended for the pump.

The eccentric location of the gear 12 relative to the gear 14 is such that at one position, indicated at 17 in FIG. 4, the

teeth

15 and 16 are in full mesh. A crescentshaped space exists between the paths swept by the

teeth

15 and 16, the space being occupied by a crescent-shaped land 18 which has a pair of part

cylindrical surfaces

19 and 21 which are spaced with a very small clearance from the tips of the

teeth

15 and 16 respectively in the crescent-shaped space to provide effectively fluid-tight engagement between the

surfaces

19 and 21 and the tips of the teeth. The land 18 is firmly secured in position as will be described further in this specification.

The end surfaces of the two

gears

12 and 14 are accurately finished plane surfaces the axial length of the two gears measured between the end surfaces being exactly the same. A thin sheet metal bearing member 22 is secured to the inner surface of the end cover 5 to engage one pair of end faces of the gears. The sheet metal bearing member 23 is mounted on the internal surface of the end cover 4 with the ability to move a small degree in the axial direction. The land 18 is secured by bolts 24 to the end cover 5, such bolts passing through the bearing member 22 into the land 18, the tension in the bolts tightly gripping the. bearing member 22 between the land 18 and the end cover 5. Accurate location forthe land 18 is ensured by dowel pins 20 (see FIG. 4).

A pair of ports 25 and 26 (see FIG. 2) are formed through the bearing member 22 and co-operate with the end faces of the gears, the port 25 in the high pressure zone where the gears approach the fully meshed position 17 and the port 26 in the low pressure zone where the gears move away from the fully meshed position 17. The port 25 is formed as two holes through the bearing member 22, the portion of bearing member between the holes forming a strengthening member against the action of high pressure.

The end cover 5 on to which the bearing member 22 is attached is formed with-inlet and delivery connections 28 and 29 (see FIG. 2) which co-operate with the

ports

26 and 25 in the bearing member 22 respectively.

The port 31 is formed in bearing member 23 (see FIG. 2) at a'position corresponding to the inlet port 26 in the bearing member 22. The inner surface of end cover 4 (see FIG. 2) includes a recess 32 which feeds inlet liquid from the inlet port 28 to the port 31 through a pair of passages 33 in the member 1. A recess 30 similar to recess 32 is also formed in the end cover to extend from the inlet connection 28 to the passages 33. A hole 34 in the bearing member 23 is shaped so as to fit around an extension 35 on the end of the crescent land 18. The extension 35 is so arranged as to leave a shoulder 36 around the crescent-shaped land. The length of the land measured in the direction of the rotation axis from shoulder 36 to bearing member 22 is as accurately as possible the same as the axial length of the gears between their end surfaces.

A pair of bolts 38 extend through the end cover 4 and the extension 35 into the land and during assembly of the pump the two sets of

bolts

38 and 24 are tightly screwed into position to help the two end covers 4 and 5 to resist any outward forces generated by hydraulic liquid in the pump.

In order to provide pressure loading on the bearing member 23 a continuous groove 39 (see FIGS. 2 and 3) is formed on the inner surface of the end cover 4. A rubber seal 41 (FIG. 2) fits into the groove 39 and engages against the bearing member 23 to define a loading zone 40 on the side of the bearing member 23 opposite to the high pressure zone in between the gear teeth and 16 as they are coming to the full meshing point 17 during rotation. Liquid at pressure is fed through hole 42 in bearing member 23 from the high pressure zone.

Both bearing

members

22 and 23 are circular in form and their peripheries respectively 44 and 45, engage the end surfaces of the gear ring 14 at positions intermediate the tooth root radius and the cylindrical bearing surface 3. This arrangement ensures that the high pressure zone between the

meshing teeth

15 and 16 is sealed against outward leakage but at the same time ensures that the area of contact between the end surfaces of the gear ring 14 and the bearing

members

22 and 23 is kept to a reasonable minimum thus reducing frictional losses. The extension 35 has a thickness very slightly greater than the thickness of the bearing member 23 so that when the bolts 38 are tightened the bearing member 23 is still capable of very slight axial movement.

Rubber sealing rings

46 and 47 carried in

grooves

48 and 49 in end covers 4 and 5 seal against the end surfaces of the annular member 1.

When in use the gears as seen in FIG. 4 will rotate in a clockwise direction the gear 12 being the driver gear. Liquid enters the pump through connection 28 and through

port

26 and 31 in the

bearing members

22 and 23 into the low pressure zone. Liquid fills the spaces between the gears and as the gear teeth meet the

curved surfaces

19 and 21 of the crescent land the spaces between the teeth will be sealed. As the teeth move into the high pressure zone towards the meshing position 17, the teeth 15 enter spaces between the teeth 16 and the teeth 16 enter the spaces between the teeth 15 thus reducing the effective volume for liquid and creating pressure in the liquid. This pressure will react on the teeth 16 to urge the gear ring 14 against the driving force exerted by the teeth 15. The

teeth

15 and 16 at their meshing positions will seal one against the other to prevent the high pressure liquid from passing the meshing point of the teeth towards the low pressure zone. The high pressure liquid is then urged out of port 25 into the delivery connection 29. Some of the liquid at pressure will pass through the small port 42 into the loading zone 40 defined by the seal 41. The pressure in this zone will then react on the bearing member 23 to urge it against the adjacent end surfaces of the

gears

12 and 14 and at the same time to urge the gears to the right as seen in FIGS. 2 and 3 so that their opposite end surfaces engage the bearing surface 22. This pressure loading ensures good sealing of the pressure zone between the

gears

12 and 14 and helps to reduce leakage losses within the pump. The pressure in the loading zone will also urge the bearing member 23 against the shoulder 36 of the crescent-shaped land at that end of the land which helps to define the high pressure zone.

The described pump is suitable for operation at high speed and high pressure. Its ability to operate at high speed results from the fact that the relative rubbing speed between the teeth is extremely low due to the fact that the gears are internally meshing. Its ability to operate at high pressure results from the fact that the relative curvatures of the engaging surfaces of the gears are such that the Hertz stress is low having regard to the pressure generated. For dealing with very high pressures the two gears need to be made of very hard metals such for example as tool steel.

It is desirable to limit the high pressure zone between the gears to control the magnitude and direction of the forces acting within the pump. For this purpose grooves are provided to connect some inter-tooth spaces to the low pressure zone at positions where these inter-tooth spaces are normally completely sealed. The groove may be provided as a pair of

grooves

53 and 54 in the

surfaces

19 and 21 of the crescent-shaped land extending from the low pressure end thereof and terminating short of the high pressure zone so that at least one inter-tooth space maybe sealed adjacent to the high pressure zone. These grooves may alternatively be provided as indicated at 55 in one or the otheror both bearing

members

22 and 23.

Whilst the illustrated embodiment of pressureloaded internal gear device is intended for use as a pump it is equally possible within the invention to provide a structure for use as a motor.

I claim:

1. A pressure loaded internal gear device comprising a casing, an internally toothed gear and an externally toothed gear both rotatably mounted within the casing with teeth in mesh, the externally toothed gear being supported by a pair of shafts extending co-axially from the ends thereof into bearings within the casing, an end bearing member mounted within the casing for axial floating movement to enable a flat bearing surface thereof to engage the flat ends of the gears adjacent one shaft, a load reacting member forming part of the casing having a flat reacting surface adjacent to a flat loading surface formed on the bearing member opposite to the bearing surface, sealing means located between the loading surface and the reacting surface to define a balancing zone, a passage connecting high pressure liquid from the high pressure zone between the gears to the balancing zone whereby the end bearing member is urged against the end surfaces of the gears to seal the high pressure zone within the gears, a groove in the bearing surface of the end bearing member connecting the low pressure zone between the gears to some of the inter-tooth spaces of the gear teeth not in mesh with one another, the area of engagement between the flat bearing surface of the end bearing member and the flat end surfaces of the gears in the neighborhood of the high pressure zone terminating between the tooth root radius and the periphery of the internally toothed gear.

2. A pressure loaded internal gear device comprising a casing, an internally toothed gear and an externally toothed gear both rotatably mounted within the casing with teeth in mesh, the externally toothed gear being supported by a pair of shafts extending co-axially from the ends thereof into bearings within the casing, an end bearing member mounted within the casing for axial floating movement to enable a flat bearing surface thereof to engage the flat ends of the gears adjacent one shaft, a load reacting member forming part of the casing having a flat reacting surface adjacent to a flat loading surface formed on the bearing member opposite to the bearing surface, sealing means located between the loading surface and the reacting surface to define a balancing zone, a passage connecting high pressure liquid from the high pressure zone between the gears to the balancing zone whereby the end bearing member is urged against the end surfaces of the gears to seal the high pressure zone within the gears, a land located in between the gears having curved surfaces to engage the gear tooth tips at non-meshing positions of the gear teeth, securing means holding the land to the casing independently of the end bearing member, and a groove in the surface of the land connecting the low pressure zone between the gears to some of the inter-tooth spaces of teeth not in mesh with one another, the area of engagement between the flat bearing surface of the end bearing, member and the flat end surfaces of the gears in the neighborhood of the high pressure zone terminating between the tooth root radius and the periphery of the internally toothed gear.

Claims

2. A pressure loaded internal gear device comprising a casing, an internally toothed gear and an externally toothed gear both rotatably mounted within the casing with teeth in mesh, the externally toothed gear being supported by a pair of shafts extending co-axially from the ends thereof into bearings within the casing, an end bearing member mounted within the casing for axial floating movement to enable a flat bearing surface thereof to engage the flat ends of the gears adjacent one shaft, a load reacting member forming part of the casing having a flat reacting surface adjacent to a flat loading surface formed on the bearing member opposite to the bearing surface, sealing means located between the loading surface and the reacting surface to define a balancing zone, a passage connecting high pressure liquid from the high pressure zone between the gears to the balancing zone whereby the end bearing member is urged against the end surfaces of the gears to seal the high pressure zone within the gears, a land located in between the gears having curved surfaces to engage the gear tooth tips at non-meshing positions of the gear teeth, securing means holding the land to the casing independently of the end bearing member, and a groove in the surface of the land connecting the low pressure zone between the gears to some of the inter-tooth spaces of teeth not in mesh with one another, the area of engagement between the flat bearing surface of the end bearing member and the flat end surfaces of the gears in the neighborhood of the high pressure zone terminating between the tooth root radius and the periphery of the internally toothed gear.