US3834842A

US3834842A - Hydraulic power translating device

Info

Publication number: US3834842A
Application number: US00205164A
Authority: US
Inventors: D Dorff; J Santi
Original assignee: HYDRAULIC PROD Inc
Current assignee: Parker Hannifin Corp
Priority date: 1971-12-06
Filing date: 1971-12-06
Publication date: 1974-09-10
Anticipated expiration: 1991-09-10
Also published as: DE2249395A1; FR2164331A5; JPS4865504A; JPS5532914B2; IT965256B

Abstract

A hydraulic power translating device of the gerotor type having inner and outer rotatable partially meshing gear elements with a pressure fluid passage surrounding a major part of the exterior periphery of the outer gear element to obtain radial balance of the outer gear element upon start up in motor operation and with a plurality of recesses formed in the case of the device and at the cross-over areas which operate as fluid accumulators of limited capacity to reduce the noise of operation of the device as well as torque variations and to compensate for tolerance and natural frequency variations in the mechanical structure and to also axially balance the gear elements.

Description

O United States Patent 11 1 1111 3,834,842 Dorfl et a1. Sept. 10, 1974 [54] HYDRAULIC POWER TRANSLATING 3,427,983 2/1969 Brundage 418/171 DEVICE 3,680,989 8/1972 Brundage 418/171 X [75] Inventors: Donald R. Dorff, Union Grove; iprima ry Exammer-W1ll1am L. Freeh 3. Sana Racme both of Assistant Examiner-Michael Koczo, Jr.

Attorney, Agent, or FirmWegner, Stellman, McCord, [73] Assignee: Hydraulic Products Incorporated, Wiles & Wood Sturtevant, Wis.

22] Filed: Dec. 6, 1971 ABSTRACT [21] AppL NOJ 205,164 A hydraulic power translating device of the gerotor type havmg mner and outer rotatable partially meshing gear elements with a pressure fluidv passage sur- U.S-

rounding a major part of the exterior periphery of the 418/189 outer gear element to obtain radial balance of the uter gear element upon tart up in motor operation 1 Field Of Search 413/166, 171, and with a plurality of recesses formed in the case of 413/79 the device and at the cross-over areas which operate as fluid accumulators of limited capacity to reduce the References C'ted noise of operation of the device as well as torque vari- UNITED STATES PATENTS ations and to compensate for tolerance and natural 1,793,577 2/1931 Wilsey 418/75 frequenc! variations in the mechanical Structure and 3,007,418 11/1961 Brundage..... 418/ 189 X to also axially balance the gear elements. 3,034,448 5/1962 Brundage..... 418/189 X 3,303,792 2/1967 Littlewood 418/189 10 3 Drawmg Flgures PATENIEDSEPWIBM Sama -a2 SHEEY a {I}? 2 HYDRAULIC POWER TRANSLATING DEVICE BACKGROUND OF THE INVENTION This invention pertains to hydraulic power translating devices and, more particularly, to a hydraulic pump or motor of the gear type and particularly the gerotor type with partially meshing inner and outer gear elements rotatable within a case and with the outer gear element being eccentric of the inner gear element and to improvements therein providing for smoother, quieter operation with reduction .in torque variations and with provision for improvement in starting torque when the device is used as a motor.

A gerotor type of pump or motor is well-known. Existing units have had a resistance to starting when used as a motor. This has resulted from a radial imbalance of forces on the outer gear element when fluid pressure is applied to the motor with the result that the outer gear element tends to bind against the adjacent wall of the case. Additionally, such devices when used as a pump have been noisy in operation and have had torque variations with these conditions resulting from the trapped condition of fluid in the cross-over areas of the device. The foregoing shortcomings of the prior art devices are overcome by the invention disclosed herein.

SUMMARY An object of this invention is to provide a new and improved hydraulic power translating device which overcomes the shortcomings of the prior art in providing for a smoother, quieter operating device and which when used as a motor has improved starting torque characteristics.

Another object of the invention is to provide a hydraulic power translating device wherein the improvements in the starting torque characteristics of the device when used as a motor are provided by means subjecting the peripheral exterior of the outer gear element to fluid pressure by means of a limited fluid flow giving a controlled pressure drop to obtain radial balance thereof upon initial start-up of the motor.

Another object of the invention is to provide a hydraulic power translating device as defined in the preceding paragraphs wherein the improved sound and operating characteristics are provided by accumulator means of limited capacity positioned at the cross-over areas which communicate with opposite sides of both the inner and outer gear elements of the device as well as any space existing therebetween whereby fluid pressure is applied to the opposite sides of said gear elements for axial balance thereof and the accumulator means provide for utilization of the bulk modulus of the fluid to effectively provide variation in the total space confining the fluid in the cross-over areas.

A further object of the invention is to provide a hydraulic translating device as defined in the preceding paragraph of the gerotor type wherein the radial balancing of the outer gear element and the provision of accumulator means are provided by simple machining operations on the case of the device to provide flow passages from the inlet and outlet ports of the device to the space exteriorly of the outer gear element and to provide relatively small cavities formed in the walls of the case at opposite sides of the inner and outer gear elements for the accumulator means.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an elevational view of the hydraulic power translating device with a part thereof being shown as a section taken generally along the: line ll in FIG. 2;

FIG. 2 is a vertical section, taken generally along the line 2-2 in FIG. 1; and

FIG. 3 is a section, taken generally along the line 3-3 in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT The hydraulic power translating device is shown in particular in FIGS. 1 and 2 wherein a multi-part case has outer parts and .11 mounting a case ring 12 therebetween with a fluid seal between the parts being provided by O-rings l4 and 15. The case ring 12 of the case is aligned with outer case part 1 0 by a series of aligning pins and with there being a series of bolts 21 extending between the outer case parts l0, l1 and through the case ring 12 to hold the case in fluid-tight assembled relation. The

outer case parts

10 and 11 each have a bearing 25 and 26, respectively, rotatably mounting a shaft which is a drive shaft when the device is operating as a pump and which is an output shaft when the device is operating as a motor.

Disposed between the

outer case parts

10 and 11 and surrounded by the case ring 12 are a pair ofgear elements of the gerotor type. These elements include an inner gear element which is keyed to the shaft30 and is concentric with the axis of rotation of the shaft. The second element is an outer gear element 36 which is rotatably mounted within a chamber defined by opposed faces of the

outer case parts

10 and 11 and by an internal wall 37 of the case ring 12. This internal wall is cylindrical, but has its center offset eccentrically from the axis of rotation of the shaft 30 and the inner gear element 35. This is conventional in a gerotor-type hydraulic power translating device. With the six teeth 40 on the inner gear element 35 and the seven internal teeth 41 on the outer gear element 36 there is thus established a plurality of fluid chambers in spaces between the gear elements.

The outer case part 11 has a pair of fluid passages having threaded openings 45 and 46 at the outer ends thereof for pipe connections and at their internal ends are shaped to define a pair of kidney-shaped fluid ports in the face of the outer case part 11 adjacent to one side of the gear elements 35 and 36. One of these fluid ports 50 is shown in FIG. I and in broken'line in FIG. 2. With rotation of the gear elements in a clockwise direction as viewed in FIG. 2, the leading end of the fluid port 50 is at 51, while the terminus thereof is at 52. When the device is operating as a pump, this is a suction port connected to a source of fluid. The second fluid port is shown in broken line in FIG. 2 and, with the direction of rotation of the gear elements as set forth above, has a leading end 56 and a terminus 57. In the pump application, this is the [pressure port. The relation of the gear elements provides for two cross-over areas wherein fluid communication between the fluid ports 50 and 55 is blocked as well as communication between fluid chambers which are then in fluid communication with the respective fluid ports.

In FIG. 2, a tooth 41a of the outer gear element 36 is shown in close relation with the mating tooth space of the inner gear element at one cross-over area. The other cross-over area is defined by engagement of a pair of teeth a and 40b of the inner gear element 35 with teeth 41b and 410 of the outer gear element 36. Again with the rotation of the gear elements in a clockwise direction, there is a gradually increasing space between the gear elements in moving from the cross-over area defined by tooth 41a of the outer gear element to the other cross-over area to draw fluid into the pump and with the fluid chambers beyond the latter crossover area gradually decreasing in size to pump fluid from the device until they reach the cross-over area having tooth 41a.

As is well known, the fluid connections to the device can be reversed to have the fluid port 50 connected to a source of fluid under pressure whereby the device will function as a motor to drive the output shaft 30.

The face of the outer case part 10 is provided with kidney-shaped recesses 60 and 61 shaped similarly to the fluid ports 50 and 55 to balance forces acting on the gear elements because of the fluid ports 50 and 55.

When the hydraulic power translating device is operated as a motor with pressure fluid supplied to port 50, there is a hydrostatic condition existing on start-up wherein the forces applied hydraulically to the gear elements resultingly force the outer gear element 36 generally in the direction of the arrow A, shown in FIG. 2. This tends to bind the outer gear element 36 on startup. Improvements in starting torque are obtained by exerting fluid pressure on the exterior periphery of the gear element 36. The pressure is applied on the exterior of the outer gear element by a restricted fluid flow through a conducting passage surrounding the outer gear element and defined therewith by the adjacent faces of the

outer case parts

10, 11 and the wall 37 of the case ring 12. The restricted flow provides a controlled pressure drop to obtain radial balance of the outer gear element 36 by the particular location of the entry and exit points of the fluid flow into the path partially surrounding the outer gear element 36. As shown particularly in FIGS. 1 and 2, the fluid port 50 is the pressure port when the device is operating as a motor and a passage 70 connects the inlet opening with a recess 71 formed in the internal wall 37 of the case ring 12. Controlled limited flow then passes about the exterior of the outer gear element 36 until the flow reaches a recess 72 formed on the internal wall 37 of the case ring 12. The recess 72 communicates with the fluid outlet 46 through a passage 73 in the outer case part 11.

The film of fluid rolls with the outer gear element 36 and moves the latter element away from the case ring 12.

The location of recesses 71 and 72 is approximately coincident with the beginning 51 of fluid port and the terminus 57 of fluid port 55. With the entry of pressure at location 71 there is a force acting in opposition to the lockup force represented by arrow A.

The hydraulic power translating device also has improved structure providing for reduced torque variations or torque ripple with quieter, smoother operation. This structure is in the form of accumulator means of limited capacity defined by a series of recesses formed in the faces of

outer case parts

10 and 11. These are arranged to axially balance the inner-and outer gear elements. The accumulator means is in the form of three pairs of recesses with one recess of each pair being formed in the outer case part 10 and the other recess of each pair being formed in the outer case part 11. These pairs of recesses are shown in FIG. 3 with a first pair of recesses being identified at and 81, the second pair at 82 and 83, and the third pair at 84 and 85. with the

recesses

80, 82 and 84 being in outer case part 10 and

recesses

81, 83, and being in outer case part 1 l.

The pair of

recesses

80 and 81 are located in the cross-over area having the tooth 41a of the outer gear element 36 and with the center of the circularlydimensioned recess being centered on the root diameter of the inner gear element 35 whereby fluid within the

recesses

80 and 81 act equally upon generally equal areas of the sides of both the inner and outer gear elements.

The second and third pair of recesses are at the other cross-over area. The pair of

recesses

82 and 83 are centered on the root diameter of the inner gear element 35, while the third pair of

recesses

84 and 85 are centered at the root diameter of the outer gear element 36. The pairs of recesses communicate with the fluid chambers at the cross-over areas wherein trapped fluid is subjected to compression as well as cavitation. The pairs of recesses provide additional fluid-holding areas wherein the bulk modulus of fluid held therein can function to provide an accumulator action to compensate for compression, cavitation, and tolerance and natural frequency variations in the mechanical structure. Additionally, the recesses function as balancing ports to provide axial balance for the inner and outer gear elements 35 and 36.

The capacity of the recess pairs 82-85 must be limited to a fluid-holding capacity since, if too large, the action provided thereby would be too slow (in trying to control the rate of compression) and result in a sloppy system.

The recesses must be of sufficient capacity whereby the total effect of the bulk modulus of the fluid will provide the desired results. By test it has been found that satisfactory operation will occur if recesses 82-85 have a total fluid volume in a range generally 3-20 percent of the volume of a fluid chamber of maximum size, with optimum capacity being preferably in the range of 5-l0 percent.

The pairs of recesses 80-85 are out of communication with the fluid ports 50 and 55 at all times. The series of recesses formed in each of the case parts lie along a line which is radial of the shaft 30 and inner gear element 35 and which is also the line along which the gear elements are eccentrically offset.

We claim:

1. A hydraulic power translating device comprising, a case, partially meshing inner and outer gear elements rotatably mounted in said case with said outer gear element being internally toothed and eccentrically mounted relative to the inner gear element whereby a series of fluid chambers are defined between said gears and with said gears having their teeth interrelated at two cross-over areas wherein fluid communication is blocked between said fluid chambers at either side of said cross-over areas, a pair of kidney-shaped fluid ports in said case intermediate said cross-over areas, means subjecting the circumferential exterior of said outer gear to fluid pressure to obtain radial balance thereof, and accumulator means positioned at said cross-over areas communicating with opposite sides of both the inner and outer gear elements and with the space defined therebetween whereby said elements are axially balanced and noise of operation is reduced as well as torque variations.

2. A hydraulic power translating device as defined in claim 1 wherein said device is a motor and said means for obtaining radial balance of the outer gear element includes means defining a restricted fluid flow path from the fluid port receiving pressure fluid to the outlet fluid port with said path extending around the exterior of the outer gear element from a location near the leading end of the pressure fluid port to a location near the terminus of the outlet fluid port.

3. A hydraulic power translating device as defined in claim 2 wherein said restricted fluid flow path includes a pair of passages in said case extending one from each of said fluid ports and each communicating with one of a pair of recesses formed one at each of said locations in a part of the case surrounding said outer gear.

4. A hydraulic power translating device as defined in claim 1 wherein said accumulator means comprises recesses formed in said case.

5. A hydraulic power translating device as defined in claim 1 wherein said accumulator means comprises three pairs of recesses with the recesses of a pair being formed in said case at opposite sides of said gear elements, all three pairs of recesses being in the cross-over areas with one pair of recesses being centered on the root diameter of the inner gear element at the cross over area where the tip of an outer gear element tooth and the adjacent root of the mating tooth space of the inner gear element are closely adjacent, the second and third pair of recesses being at the other cross-over area, the second pair of recesses being centered on the root diameter of the inner gear element and the third pair of recesses being centered on the root diameter of the outer gear element, and all of said recesses at one side of the gear elements lying along a line which is radial of said inner gear element.

6. A hydraulic pump of the gerotor type comprising, a case, an inner gear element and an outer gear element rotatably mounted in said case with said outer gear element eccentrically mounted relative to the inner gear element whereby a series of fluid chambers are defined between said gears and with said gears having their teeth interrelated at two cross-over areas wherein fluid communication is blocked between said fluid chambers at either side of said cross-over areas, a pair of kidneyshaped fluid ports intermediate said cross-over areas for completing a flow path through the device, and recesses in said case for fluid positioned at said cross-over areas communicating with opposite sides of both the inner and outer gear elements and with the space defined therebetween whereby said elements are axially balanced and noise of operation is reduced as well as torque ripple.

7. A hydraulic power pump as defined in claim 6 wherein there are three pairs of said recesses with a recess of each pair being formed in said case at a side of said gear elements, a pair of recesses being at opposite sides of said gear elements, all three pairs of recesses being in the cross-over areas with one pair of recesses being centered on the closely adjacent tip of an outer gear element tooth and the adjacent root of the mating tooth space of the inner gear element at one cross-over area, a second pair of recesses being bisected by a mating tooth space on the inner gear element, the third pair of recesses being bisected by a mating tooth space of the outer gear element, and the last two pairs of recesses being at the other cross-over area.

8. A hydraulic power pump as defined in claim 7 wherein the last two pairs of recesses are generally circular limited depth recesses to hold a limited amount of fluid in the range of generally 3-20 percent of the volume of a maximum fluid chamber size and preferably in the range of 5-10 percent.

9. A hydraulic pump of the gerotor type as defined in claim 6 wherein there are three pairs of said recesses of limited size with the recesses of a pair being formed in said case at opposite sides of said gear elements, all three pairs of recesses being in the cross-over areas with one pair of recesses being centered on the root diameter of the inner gear element at the cross-over area where the tip of an outer gear element tooth and the adjacent root of the mating tooth space of the inner gear element are closely adjacent, the second and third pair of recesses being at the other cross-over area the second pair of recesses being centered on the root diameter of the inner gear element and the third pair of recesses being centered on the root diameter of the outer gear element, the second and third pair of recesses having a total volume of approximately 10 percent of the volume of a fluid chamber of maximum size, and all of said recesses at one side of the gear elements lying along a line which is radial of said inner gear element.

10. A hydraulic pump of the gerotor type comprising, a case, an inner gear element and an outer gear element rotatably mounted in said case with said outer gear element eccentrically mounted relative to the inner gear element whereby a series of fluid chambers are defined between said gears and with said gears having their teeth interrelated at two cross-over areas wherein fluid communication is blocked between said fluid chambers at either side of said cross-over areas, a pair of kidneyshaped fluid ports intermediate said cross-over areas, a pair of recesses formed in said case at one of said crossover'areas, two additional pairs of recesses in said case at the other of said cross-over areas where there is a maximum size fluid chamber, all of said recesses communicating with opposite sides of both the inner and outer gear elements and with the space defined therebetween whereby said elements are axially balanced and said recesses provide small fluid accumulators to reduce the noise of operation as well as torque variations.

Claims

5. A hydraulic power translating device as defined in claim 1 wherEin said accumulator means comprises three pairs of recesses with the recesses of a pair being formed in said case at opposite sides of said gear elements, all three pairs of recesses being in the cross-over areas with one pair of recesses being centered on the root diameter of the inner gear element at the cross-over area where the tip of an outer gear element tooth and the adjacent root of the mating tooth space of the inner gear element are closely adjacent, the second and third pair of recesses being at the other cross-over area, the second pair of recesses being centered on the root diameter of the inner gear element and the third pair of recesses being centered on the root diameter of the outer gear element, and all of said recesses at one side of the gear elements lying along a line which is radial of said inner gear element.

6. A hydraulic pump of the gerotor type comprising, a case, an inner gear element and an outer gear element rotatably mounted in said case with said outer gear element eccentrically mounted relative to the inner gear element whereby a series of fluid chambers are defined between said gears and with said gears having their teeth interrelated at two cross-over areas wherein fluid communication is blocked between said fluid chambers at either side of said cross-over areas, a pair of kidney-shaped fluid ports intermediate said cross-over areas for completing a flow path through the device, and recesses in said case for fluid positioned at said cross-over areas communicating with opposite sides of both the inner and outer gear elements and with the space defined therebetween whereby said elements are axially balanced and noise of operation is reduced as well as torque ripple.

10. A hydraulic pump of the gerotor type comprising, a case, an inner gear element and an outer gear element rotatably mounted in said case with said outer gear element eccentricaLly mounted relative to the inner gear element whereby a series of fluid chambers are defined between said gears and with said gears having their teeth interrelated at two cross-over areas wherein fluid communication is blocked between said fluid chambers at either side of said cross-over areas, a pair of kidney-shaped fluid ports intermediate said cross-over areas, a pair of recesses formed in said case at one of said cross-over areas, two additional pairs of recesses in said case at the other of said cross-over areas where there is a maximum size fluid chamber, all of said recesses communicating with opposite sides of both the inner and outer gear elements and with the space defined therebetween whereby said elements are axially balanced and said recesses provide small fluid accumulators to reduce the noise of operation as well as torque variations.