US3113524A

US3113524A - Gear pump with trapping reliefs

Info

Publication number: US3113524A
Application number: US162124A
Authority: US
Inventors: John J Fulton
Original assignee: Roper Hydraulics Inc
Current assignee: Roper Hydraulics Inc
Priority date: 1961-12-26
Filing date: 1961-12-26
Publication date: 1963-12-10
Anticipated expiration: 1980-12-10

Description

Dec. 10, 1963 J. J. FULTON 3,113,524

GEAR PUMP WITH TRAPPING RELIEFS Filed Dec. 26, 1961 2 Sheets-Sheet 1 rm win find 5am WWW WW1; +01% United States Patent Oflfice Patented Dec. 10, 1963 3,113,524 GEAR hUMP WITH TRAPPING RELEFS John .1. Fulton, Rockford, EL, assignor to Roper Hydraulics, Ina, Commerce, Ga, a corporation of Georgia Filed Dec. 26, 1961, Ser. No. 162,124 6 Claims. (Ql. 163-12) This invention relates to fluid pump and particularly to a gear-type pump having trapping-relief grooves.

In pumps having intermeshing gears, problems are encountered due to entrapment of liquid in the intertooth spaces as the gear teeth move into meshing engagement, and trapping reliefs have heretofore been provided at the discharge side of the gear mesh for relieving the trapped liquid to the pump outlet. Problems are also encountered in completely filling the toothed spaces in such pumps as the gears move out of meshing engagement and inlet grooves have heretofore been provided in the end walls of the pump chambers for feeding liquid from the pump inlet along the ends of the gear teeth to the tooth spaces to assist in filling the same. However, the relatively low pressure at the pump inlet limits the rate at which the inlet fluid will flow into the tooth spaces and this has heretofore limited the maximum speed at which the pump could be driven, while still achieving complete filling of the tooth spaces.

An important object of this invention is to provide a pump having an improved arrangement for filling the tooth spaces at the inlet side of the pump to enable complete filling of the tooth spaces at higher pump speeds than can be achieved when the fluid at only pump inlet pressure is fed into the gear teeth.

Another object of this invention is to provide a gear pump having an improved arrangement for relieving the fluid trapped in the tooth spaces as the gear teeth move into meshing engagement, and for filling the tooth spaces at the inlet side of the pump as the gear teeth move out of meshing engagement.

A more particular object of this invention is to provide a gear pump having trapping relief recesses at the inlet side of the pump arranged to direct trapped fluid back into the tooth spaces as the gears move out of meshing engagement at the inlet side of the pump, to thereby have the trapped fluid assist in filling the tooth spaces.

Yet another object of this invention is to provide a pump in accordance with the foregoing objects and in which the trapped fluid is directed into the tooth spaces at the inlet side of the pump in such a manner that the trapped fluid does not oppose the normal flow of fluid from the pump inlet to the gear teeth.

These, together with various ancillary objects and advantages of this invention will be more readily appreci ated as the same becomes better understood by reference to the following detailed description when taken in connection with the accompanying drawings wherein:

FIG. 1 is a longitudinal sectional view through a pump embodying the trapping relief grooves of the present invention;

PEG. 2 is a transverse sectional view through the pump, taken on the plane 22 of FIG. 1;

FIGS. 3 and 4 are fragmentary sectional views illustrating the mesh point of the gears, with the gears in different positions;

FIG. 5 is a fragmentary sectional view taken on the plane 55 of FIG. 3; and

FIG. 6 is a fragmentary sectional view taken on the broken section line 6-6 of FIG. 3.

The present invention relates particularly to rotary gear pumps and, as shown herein, the pump includes a pump casing having a body 1% formed with intersecting

bores

11 and 12 and end walls 13 and 14 secured to opposite ends of the body. The end walls are conveniently detachably secured to the body as by bolts 15 which extend between the end Walls, and seals such as the 0 rings 16 are provided for sealing the interface between the end walls and the body. A pair of

meshing gears

21 and 22 are disposed in the

pump bores

11 and 12 respectively and have axially extending trunnions or

axles

23 and 24. The gears may be formed integrally With the trunnions or, can be formed separately therefrom and non-rotatably connected to the trunnions by suitable keys or splines.

End plates are provided at opposite ends of the

pump gears

21 and 22 in close running fit with the end faces of the gears. The end plates are preferably supported in the pump bores and the end plates at one or both ends of the gears are slidable in the bores to maintain a close running fit with the end faces of the gears. In order to facilitate machining of the end plates, the end plates are preferably in the form of two separate bushings designated 25 and 26 each having a generally circular peripheral portion 27 which are slidably received in the

respective bores

11 and 12 and a flat chordal portion designated 29, as best shown in FIG. 2. The chordal portions 29 etend tangent to the pitch circles of both gears at the mesh point thereof and abut each other at the intersection of the pump bores. The

gear trunnions

23 and 24 are rotatably supported in bearings 32 and 33 and which bearings are conveniently mounted in the

bushings

25 and 26 respectively. The interface between the

bushings

25 and 26 and the

respective pump bores

11 and 12 is sealed by a generally figure 8 shaped gasket 35 which is disposed in a groove 36 in the periphery of the circular portions 27 and 28 of the bushings. As best shown in FIGS. 1 and 5, the gasket is preferably formed with a channel shaped cross section and means described hereinafter is provided for maintaining the passage 36 under pressure to press the gasket outwardly into sealing engagement with the'pump bores.

' One of the gears such as the gear 21 is the drive gear and one of the journals 23 on the drive gear has an extension 4-1 which extends out of the pump housing through a shaft seal 42 and is adapted for connection at 43 to a pump drive mechanism (not shown). The pump is'provided with an inlet opening 45 and a discharge opening 46 at opposite sides of the gear mesh and the drive gear 21 is rotated in a direction (counterclockwise) as viewed in FIG. 2 to pump fluid from the inlet 45 to the outlet 46. As the gears are rotated, fluid is carried in the spaces between the

teeth

51 and 52 on the drive and driven

gears

21 and 22 respectively from the inlet 45 to the outlet 46. As the gear teeth move into meshing engagement, the lead faces 51a of the teeth on the drive gear 21 engage the trailing faces 52b of the teeth on the driven gear 22. This seals off the

intertooth spaces

51c and 52c in the drive and driven gears from the inlet and outlet. The fluid remaining in the spaces is thus trapped and, as the teeth move from the outlet side toward the plane through the axis of the gears, the trapped volume of the intertooth spaces decreases and, conversely, as the teeth move away from the plane through the axis of the gears toward the inlet side, the trapped volume of these intertooth spaces increases. As a practical matter, it is necessary to provide some backlash between the gears and, preferably, the gears are formed with more backlash than is normal practice so that the trailing face 51b of the teeth on the drive gear is spaced slightly from the lead face 52b of the teeth on the drive gear to intercommunicate the tooth spaces 51c in the drive gear with the tooth spaces 520 in the driven gear at the gear mesh. In order to relieve the excessive pressures which are otherwise developed in the intertooth spaces as they decrease in volume at the outlet side of the pump, it is the usual practice to provide trapping relief recesses at the outside or" the pump. It is also customary to provide inlet recesses at the inlet side of the pump for feeding fluid from the inlet along the ends of the gear teeth to the intertooth spaces as they increase in volume at the inlet side of the pump.

The pressure at the inlet of the pump is usually relatively low and there is a limit to the rate at which the fluid can flow under this low inlet pressure along the ends of the gear teeth and into the intertooth spaces to completely fill the same. This limits the maximum speed at which the pump can be operated with complete filling of the gear teeth. In accordance with the present invention, an improved trapping relief arrangement is provided which utilizes some of the trapped fluid to aid in filling the intertooth spaces at the inlet side of the pump, and in such a manner as to not interfere with the normal filling of the tooth spaces by the fluid entering the same from the pump inlet. As best shown in FIGS. 2-4, outlet trappin-g relief recesses 61 and inlet side trapping relief recesses 62 are provided in the end plates or bushings at at least one end of the pump gears, and preferably in the end plates or bushings at both ends of the pump gears. The outlet and inlet trapping relief recesses are spaced apart a distance suflicient to prevent open communication through the intertooth spaces in all positions of the pump gears and, preferably, the

inner side edges

61a and 62a of the outlet and inlet relief recesses are angularly spaced apart a distance such that, when the leading edge 51a of the tooth on one gear such as the drive gear begins to cover the outlet recess 61, the trailing edge such as 52b of the preceding tooth on the other gear begins to uncover the other recess 62. Thus, as shown in FIG. 2, the leading edge 51a of one tooth on the drive gear 21 is approaching a position which cuts off communication with the tooth space 51c and the outlet trapping relief recess 61, while the trailing edge 52!; on the next preceding tooth of the driven gear is approaching a position in which it will communicate the tooth space 520 with the inlet trapping relief recess 62. This angular spacing between the adjacent edges of the inlet and outlet trapping relief recesses is generally slightly less than the angular distance between corresponding teeth on the gear and, for the ten tooth gears shown, in which the spacing between the lead edges of the adjacent teeth is 36, the angular spacing between the

adjacent edges

51a and 62a of the outlet and inlet relief recesses is about 33. With this arrangement, the trapped spaces 51c and 520 will be relieved to the outlet relief recess 61 until the lead edge of the tooth on the drive gear moves across the edge 61a of the outlet relief recess. At about that time, the trailing edge of the preceding tooth on the driven gear 22 will uncover the inlet relief recess 62, as shown in FIG. 3, to relieve the trapped fluid to the inlet relief recess. The trapped fluid relieved to the inlet of the pump would normally be in a direction to oppose the flow of fluid from the pump inlet into the intertooth spaces so that it would not only reduce the pump efficiency but would also oppose proper filling of the tooth spaces with fluid. In accordance with the present invention, the inlet trapping relief recesses are shaped so as to deflect the trapped fluid back into the intertooth spaces at the inlet side of the pump to aid in filling the tooth spaces, and in a direction such that relieved fluid does not oppose the normal flow of fluid from the pump inlet into the tooth spaces. As best shown in FIG. 5, the inlet trapping relief recesses 62 are formed with a smoothly Iarcuate and preferably semi-cylindrical base wall which extends fromthe inlet edge 62a to the outlet edge 62b of the recess. Thus, trapped fluid which is discharged from the tooth spaces such as 520 into the inlet relief recesses 62 is deflected back into the intertooth spaces to aid in filling the same. As the fluid enters the intertooth spaces from the relief recesses, it is flowing in a direction generally normal to the direction of flow from the pump inlet to the gear teeth, and therefore does not oppose filling of the tooth spaces from the pump inlet. While the flow of trapped fluid through the relief recess 62 will vary in direction and magnitude as the gear teeth move past the relief recess, a typical flow passage for the relieved fluid is shown by arrows in FIG. 6 and designated by the letter R. As will be seen from a comparison of FIGS. 3 and 6, fluid in closing trapped space 510 in the drive gear passes through the backlash between the trailing face of one tooth on the drive gear and the lead edge of one tooth on the driven gear into the tooth space 52c, and is relieved through the inlet relief recess 62 into the tooth space 510 of the drive gear.

In order to properly direct the fluid into the tooth spaces at the inlet side of the gears, it is necessary that the inlet relief recesses 62 can be spaced inwardly of the addendum circle of the gears. The outer edge 62b of the inlet relief recesses thus intersect the chordal surfaces 29 at a point inwardly of the inlet edge thereof. These chordal surfaces are preferably disposed in a plane which is tangent to the pitch circles of both gears, and which plane thus extends perpendicular to a plane through the gear axes. For best performance, the inner edge of the recesses 62 is inclined to the tangent plane previously described so as to extend generally parallel to the edge of the tooth :base as the tooth moves thereacross. The portions of the inlet relief recess in each of the bushings are preferably similarly shaped and produce an overall chevron-shaped recess. These recesses with the arcuate base Walls can conveniently be formed by simple milling operation and extend inwardly to the root diameter of the teeth. At that point, they terminate in an abrupt semicircular end wall 62c, clearly shown in FIG. 5.

The trapping relief recesses 61 at the outlet side of the pump can conveniently be formed in the same manner and with the same shape as the inlet relief recesses previously described and, as shown, have an outer edge 61b which extends generally parallel to the inner edge 61a thereof and have an arcuate base Wall that extends between the inner and outer edges to deflect the trapped liquid into the outlet. Alternatively, the outlet tnapping relief recesses could extend all the way to the periphery of the bushings, if desired.

The outlet trapping relief recesses are advantageously communicated through a lateral passage 71 formed on. the chordal surfaces 29 of the bearing bushings with the gasket recess 36 in the bushings, to supply fluid at discharge pressure to the underside of the gasket 35. As previously described, this pressurizes the gasket outwardly against the walls of the pump bore to maintain a seal around the bushings.

The difference in pressure between the .pump outlet and pump inlet, acting on the gear peripheries, produces a radial hydraulic thrust in a direction generally toward the pump inlet. As is common practice, pressure angle adjusting grooves 72 are conveniently formed in the end faces of the bushings adjacent the roots of the teeth and extend from the outlet side of the pump and part way around the bushing and terminate short of the inlet, to distribute outlet pressure over a substantial portion of the gear peripheries.

From the foregoing, it is thought that the operation and construction of the device will be readily understood and further detailed description is deemed unnecessary. As will be noted, the fluid trapped in the intertooth spaces is alternately discharged through the outlet relief recesses 61 and the inlet relief recesses 62. The latter are shaped in such a manner to deflect the trapped fluid back into the tooth spaces at the inlet side of the pump to aid in filling the tooth spaces and in such a manner as to not oppose the normal filling of the tooth spaces from the pump inlet. This trapped fluid which is discharged back into the opening tooth spaces at the pump inlet is at substantially higher pressure than the fluid at the pump inlet and markedly aids in filling the tooth spaces so that the pump can be operated at substantially higher speeds than could otherwise be achieved, While still maintaining complete filling of the tooth spaces. This increases the overall pump efliciency and reduces cavitation and noise.

I claim:

1. A gear pump comprising, a pump casing having a pair of intersecting bores and end plates at opposite ends of said bores defining a pump chamber, a pair of meshing rotary gears in said pump bores having the ends thereof in running engagement with the faces of said end plates and including a drive gear and a driven gear, means in said casing providing an inlet on one side of the gear mesh and an outlet at the other side of the gear mesh, at least one of said end plates having a trapping relief recess at the inlet side of the pump disposed entirely within the addendum circle of the driven gear, said trapping relief recess having an inner side edge extending transverse to a common plane tangent to the pitch circles of both gears and intersecting said tangent plane at a point spaced from a plane through the gear axes toward the inlet side of the pump, said inner side edge of said recess extending to a point adjacent the root diameter of the driven gear and being angularly spaced from said plane through the gear axes a distance slightly less than one half the pitch of the teeth on the driven gear, said relief recess having an outer side edge intersecting said tangent plane at a point relatively farther from the said plane through the gear axes and spaced a substantial distance inwardly of the addendum circle of the gears, said recess having a curved base wall curving from said inner edge into the end plate and then back to said outer edge and extending substantially normal to the face of the end plate at said outer edge of the recess to direct the trapped liquid back into the tooth spaces at the inlet side of the pump in a direction substantially normal to the direction of fluid flow from the pump inlet to the gears to aid in filling the tooth spaces.

2. The combination of claim 1 wherein said inner and outer edges of the recess are inclined to said tangent plane to extend generally radially of said drive gear.

3. A gear pump comprising, a pump casing having a pair of intersecting pump bores and end plates at opposite ends of said bores defining a pump chamber, a pair of meshing rotary gears in said pump bores having the ends thereof in running engagement with thefaces of said end plates including a drive gear and a driven gear, means in said casing providing an inlet on one side of the gear mesh and an outlet at the other side of the gear mesh, at least one end plate comprising a pair of bushings having an outer diameter substantially equal to the addendum circle of the gears and slidably mounted in said bores to maintain the face thereof in close running fit with the end of the gears, said pair of bushings having flat chordal sur faces abutting each other at a common plane tangent to the pitch circles of both gears, said bushings each having an outlet trapping relief recess in the face thereof at the outlet side of the gear mesh, said bushings each having an inlet trapping relief recess in the face thereof at the inlet side of the gear mesh disposed entirely within the addendum circles of the gears and spaced inwardly of the Outer periphery of the respective bushing, said inlet and outlet relief recesses in each bushing each having an inner side edge extending transverse to the respective chordal surface and intersecting the latter at a point spaced from a plane through the gear axes toward the inlet side of the pump, the inner side edges of the inlet and outlet relief recesses in each bushing extending to a point adjacent the root diameter of the respective gear and being angularly spaced apart a distance slightly less than the pitch of the gear teeth to define a sealing land therebetween, said inlet relief recesses each having an outer side edge extending transverse to the respective chordal surface and intersecting the latter at a point relatively farther from the plane through the gear axes and spaced a substantial distance inwardly of the end of said chordal surface, said inlet relief recess in each bushing having a curved base wall curving from the inlet edge into the bushing and then back to the outlet edge and extending substantially normal to the face of the bushing at said outer edge to deflect the trapped liquid back into the tooth spaced at the inlet and in a direction transverse to the direction of fiow of liquid from the pump inlet to the gear teeth to aid in filling the gear teeth.

4. The combination of claim 3 wherein said inner edge of the inlet relief recess in each bushing is inclined to said chordal surface to extend generally radially of the respective bushing whereby the inlet relief recesses diverge relative to each other in a direction away from the inlet.

5. A gear pump comprising, a pump casing having a pair of intersecting pump bores and end plates at opposite ends of said bores defining a pump chamber, a pair of meshing rotary gears in said pump bores having the ends thereof in running engagement with the faces of said end plates including a drive gear and a driven gear, means in said casing providing an inlet on one side of the gear mesh and an outlet at the other side of the gear mesh, at least one end plate comprising a pair of bushings having an outer diameter substantially equal to the addendum circle of the gears and slidably mounted in said bores to maintain the face thereof in close running fit with the end of the gears, said pair of bushings having flat chordal surfaces abutting each other at a common plane tangent to the pitch circles of both gears, said bushings each having an outlet trapping relief recess in the face thereof at the outlet side of the gear mesh, said bushings each having an inlet trapping relief recess in the face thereof at the inlet side of the gear mesh disposed entirely within the addendum circles of the gears and spaced inwardly of the outer periphery of the respective bushing, said inlet and outlet relief recesses in each bushing each having an inner side edge extending transverse to the respective chordal surface and intersecting the latter at a point spaced from a plane through the gear axes toward the inlet side of the pump, the inner side edges of the inlet and outlet relief recesses in each bushing extending to a point adjacent the root diameter of the respective gear and being angularly Spaced apart a distance slightly less than the pitch of the gear teeth to define a sealing land therebetween, said inlet relief recesses each having an outer side edge extending transverse to the respective chordal surface and intersecting the latter at a point relatively farther from the plane through the gear axes and spaced a substantial distance in- War-dly of the end of said chordal surface, said inlet relief recess in each bushing having a generally semi-cylindrical configuration with the axis of each semi-cylindrical recess generally paralleling the face of the respective bushing, the axes of the inlet relief recess in both bushings be ing inclined to the chordal surface to extend generally radially of the respective bushing.

6. A gear pump comprising, a pump casing having a pair of intersecting pump bores and end plates at opposite ends of said bores defining a pump chamber, a pair of meshing rotary gears in said pump bores having the ends thereof in running engagement with the faces of said end plates including a drive gear and a driven gear, means in said casing providing an inlet on one side of the gear mesh and an outlet at the other side of the gear mesh, at least one end plate comprising a pair of bushings having an outer diameter substantially equal to the addendum circle of the gears and slidably mounted in said bores to maintain the face thereof in close running fit with the end of the gears, said pair of bushings having flat chordal surfaces abutting each other at a common plane tangent to the pitch circles of both gears, said bushings each having an outlet trapping relief recess in the face thereof at the outlet side of the gear mesh, said bushings each having an inlet trapping relief recess in the face thereof at the inlet side of the gear mesh disposed entirely within the addendum circles of the gears and spaced inwardly of the outer periphery of the respective bushing, said inlet and outlet relief recesses in each bushing each having an inner side edge extending transverse to the respective chordal surface and intersecting the latter at a point spaced from a plane through the gear axes toward the inlet side of the pump, the inner side edges of the inlet and outlet relief recesses in each bushing extending to a point adjacent the root diameter of the respective gear and being angularly spaced apart a distance slightly less than the pitch of the gear teeth to define a sealing land therebetween, said inlet relief recesses each having an outer side edge extending transverse to the respective chordal surface and intersecting the latter at a point relatively farther than the plane through the gear axes and spaced a substantial distance inwardly of the end of said chordal surface, said inlet and outlet relief recesses in each bushing having a generally semi-cylindrical configuration with the axis of each semi-cylindrical recess generally paralleling the face of the respective bushing, the axes of each relief recess being inclined to the chordal surface to extend generally radially of the respective bushing.

References Cited in the file of this patent UNITED STATES PATENTS 1,129,091 Hawley Feb. 23, 1915 1,659,771 Fox Feb. 21, 1928 1,719,025 Scherninger July 2, 1929 2,833,224 Meyer et al May 6-, 1958 2,870,720 Lorenz Jan. 27, 1959 2,884,864 Bobnar May 5, 1959 2,990,783 Oliver July 4, 19 61

Claims

1. A GEAR PUMP COMPRISING, A PUMP CASING HAVING A PAIR OF INTERSECTING BORES AND END PLATES AT OPPOSITE ENDS OF SAID BORES DEFINING A PUMP CHAMBER, A PAIR OF MESHING ROTARY GEARS IN SAID PUMP BORES HAVING THE ENDS THEREOF IN RUNNING ENGAGEMENT WITH THE FACES OF SAID END PLATES AND INCLUDING A DRIVE GEAR AND A DRIVEN GEAR, MEANS IN SAID CASING PROVIDING AN INLET ON ONE SIDE OF THE GEAR MESH AND AN OUTLET AT THE OTHER SIDE OF THE GEAR MESH, AT LEAST ONE OF SAID END PLATES HAVING A TRAPPING RELIEF RECESS AT THE INLET SIDE OF THE PUMP DISPOSED ENTIRELY WITHIN THE ADDENDUM CIRCLE OF THE DRIVEN GEAR, SAID TRAPPING RELIEF RECESS HAVING AN INNER SIDE EDGE EXTENDING TRANSVERSE TO A COMMON PLANE TANGENT TO THE PITCH CIRCLES OF BOTH GEARS AND INTERSECTING SAID TANGENT PLANE AT A POINT SPACED FROM A PLANE THROUGH THE GEAR AXES TOWARD THE INLET SIDE OF THE PUMP, SAID INNER SIDE EDGE OF SAID RECESS EXTENDING TO A POINT ADJACENT THE ROOT DIAMETER OF THE DRIVEN GEAR AND BEING ANGULARLY SPACED FROM SAID PLANE THROUGH THE GEAR AXES A DISTANCE SLIGHTLY LESS THAN ONE