US3746479A

US3746479A - Hydraulic motor with minimum break-away torque

Info

Publication number: US3746479A
Application number: US00189399A
Authority: US
Inventors: P Spencer; J Hovanchak
Original assignee: TRW Inc
Current assignee: Northrop Grumman Space and Mission Systems Corp
Priority date: 1971-10-14
Filing date: 1971-10-14
Publication date: 1973-07-17
Anticipated expiration: 1990-07-17

Abstract

A hydraulic motor device particularly characterized as exhibiting minimum break-away torque under starting or accelerating conditions. The device comprises a housing having an inlet, an outlet at opposite sides. The device also contains a pair of rotary gears in said housing having shaft means disposed on axes of rotation concentric to the bore walls, each rotary gear having alternating gear teeth and gear tooth spaces and being in full meshing engagement with one another. Also present are means to pump fluid under pressure through said inlet and against said teeth whereby said gears are rotated, and at least one arcuate circumferential groove in each bore wall connected to the inlet, and communicating with the teeth of said gears, but having a width less than the width of said teeth. The presence of fluid in the groove reduces startup and running friction at the tips of the gear teeth.

Description

United States Patent 1191 Spencer et a1.

1451 July 17,1973

HYDRAULIC MOTOR WITH MINIMUM BREAK-AWAY TORQUE Inventors: Phillip B. Spencer, Royal Oak; John A. Hovanchak, Detroit, both of Mich.

Assignee: TRW Inc., Cleveland, Ohio Filed: Oct. 14, 1971 Appl. No.: 189,399

Related U.S. Application Data Continuation of Ser. No. 887,212, Dec. 22, 1969 abandoned.

Trick Aspelin Vickers 418/74 3,285,188 11/1966 Kita 418/74 Primary Examiner-Carlton R. Croyle Assistant Examiner-John J. Vrablik Attorney-Hill, Sherman, Meroni, Gross & Simpson 57 ABSTRACT A hydraulic motor device particularly characterized as exhibiting minimum break-away torque under starting or accelerating conditions. The device comprises a housing having an inlet, an outlet at opposite sides. The device also contains a pair of rotary gears in said housing having shaft means disposed on axes of rotation concentric to the bore walls, each rotary gear having alternating gear teeth and gear tooth spaces and being in full meshing engagement with one another. Also present are means to pump fluid under pressure through said inlet and against said teeth whereby said gears are rotated, and at least one arcuate circumferential groove in each bore wall connected to the inlet, and communicating with the teeth of said gears, but having a width less than the width of said teeth. The presence of fluid in the groove reduces startup and running friction at the tips of the gear teeth.

8 Claims, 6 Drawing Figures PAIENTED JULI 7 i975 sum 1 or 2 HYDRAULIC MOTOR WITH MINIMUM BREAK-AWAY TORQUE This a continuation, of application Ser. No. 887,2l2, filed Dec. 22, 1969 now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is concerned with a hydraulic motor device constructed so as to exhibit minimum break-away torque under starting and accelerating conditions by reducing startup and running friction.

2. Description of the Prior Art One of the more serious problems found with use of a hydraulic motor device is that of excessive breakaway torque when one initially starts the device or under condition of acceleration. The primary cause for increase in torque under these conditions is due to the fact that there is an undesirably high level of friction between the bore walls and the tips of the gear teeth.

A number of proposals have been made to reduce break-away torque in hydraulic motor devices. However, for the most part these have been unsatisfactory for a number of reasons. In some cases, the construction of the device is unsatisfactory from the standpoint of complexity, being therefore exceptionally costly to manufacture. In other situations, hydraulic motor devices which have been specifically modified to reduce break-away torque nevertheless still exhibit an undesirably high level of torque. Thus, the problem has not been completely solved.

It would therefore be a substantial advance in the art if a hydraulic motor device were devised which obviated the above problem by means of a simple modification of a conventional hydraulic motor device. Moreover, if the device could be simply made such as by casting, it would find ready acceptance in the art.

SUMMARY OF THE INVENTION In view of the above, a hydraulic motor device has been provided which is particularly characterized as exhibiting minimum break-away torque under starting or accelerating conditions. The device comprises a housing having an inlet, and outlet at opposite sides. The device also contains a pair of rotary gears in said housing having shaft means disposed on axes of rotation concentric to the bore walls, each rotary gear having alternating gear teeth and gear tooth spaces and being in full meshing engagement with one another. Also present are means to pump fluid under pressure through said inlet and against said teeth whereby said gears are rotated, and at least one arcuate circumferential groove in each bore wall connected to the inlet, and communicating with the teeth of said gears, but having a width lessthan the width of said teeth. The presence of fluid in the groove reduces startup and running friction at the tips of the gear teeth.

It therefore becomes an object of the invention to provide an improved hydraulic motor device.

A more specific object of the invention is to provide a hydraulic motor device so constructed that startup and running friction at the tips of the gear teeth contacting the bore is considerably reduced leading to minimum break-away torque under starting or accelerating conditions.

"A still further specific object of the invention is to construct a hydraulic motor device which has grooved bore walls, which grooves communicate with the gear teeth and when filled with fluid reduce friction between the tips of said gear teeth and the bore walls.

Other objects, features and advantages of the invention will be readily apparent from the following description of certain preferred embodiments thereof taken in conjunction with the accompanying drawings, although variations and modifications may be effected without departing from the spirit and scope of the novel concepts of this disclosure, and in which:

FIG. 1 is a vertical cross section of the hydraulic motor device of the invention;

FIG. 2 is a cross section taken across line lI-ll of FIG. 1;

FIG. 3 is another cross section taken across line II-II of FIG. 1 illustrating an alternate construction;

FIG. 4 is another vertical cross section of a further embodiment of the hydraulic motor device of the in vention;

FIG. 5 is a cross section taken along lines lV-IV of FIG. 4; and

FIG. 6 is another cross section taken along line IV-IV of FIG. 4 illustrating an altemate construction.

Turning now to the drawings, FIG. 1 illustrates one embodiment of the invention in which there is shown generally the hydraulic motor device at 10 which comprises a housing member I2 formed with an inlet 14 and an outlet 16,- said inlet and outlet being at opposite sides from one another in the housing at I8 and 20.

A pair of rotary gears 22 and 24 are rotatably journalled in the housing 12 and are carried by shaft members shown respectively at 26 and 28. The

shafts

26 and 28 are disposed on axes of rotation which are concentric with respect to the bore walls of the lobe 20 and lobe I8 and each respective rotary gear is particularly characterized by the formation of the peripheral surface thereof of alternating gear teeth 30 and gear tooth spaces 32. Thus, the gears 22 and 24 are in full meshing engagement in a nip area of intermesh disposed be tween the inlet 14 and outlet 16. The inlet 14 communicates with one side of the nip between the gears while the outlet 16 communicates with "the other side of the nip. The inlet and outlet sides of the nip are separated by the intermeshed gear teeth.

In each

bore wall

34 and 36, there is shown a

groove

37 and 38 communicating with the inlet 14 at

points

40 and 42. The grooves do not extend the full circumference of the bore but rather terminate at

points

44 and 46. There is a seal then running from point 44 to 48 and from 46 to 50, respectively, defining sealing lands. In the usual case, the sealing lands are approximately 1% tooth spaces from the motor outlet.

The arcuate circumferential constant depth relief notches or grooves are filled with pressurized fluid and vent the peripheries of the gears to inlet fluid pressure to reduce the startup'and running friction at the tips of the gear teeth, whereby the motor device then exhibits minimum break-away torque under starting or acceler ating conditions. Inlet pressure thus acts on the gear teeth well beyond the inlet nip area to increase the gear driving area. By use of such grooves, in effect, the tooth tip contact area is reduced, while driving faces of the gear teeth are more exposed to the pressurized fluid. The location of the groove also forces the gears to one side of the bearings in a direction that will not tend to reduce the seal width between the sealing teeth and the housing, thereby reducing the tendency to seize as pressures are increased.

The relationship between the grooves and the bores and teeth is better shown in FIG. 2. Here there is shown

grooves

37 and 38, respectively, in

bore walls

34 and 36. Also shown is tooth 52 communicating with groove 37 and tooth 54 communicating with groove 38. There is also shown a still further embodiment of the invention wherein

bearings

56, 58, 60 and 62 are provided at each of the first four journal support points to further remove friction. These bearings, which are preferably low-friction needle bearings are between housing 12 and

shafts

26 and 28.

In FIG. 3 there is shown an alternate device as a section through line IIII of FIG. 1 wherein each bore has two grooves. The

grooves

64 and 66 and bore wall 34 communicate with tooth 52.

Grooves

68 and 70 and bore wall 36 communicate with tooth 54. Again

needle bearings

56, 58, 60 and 62 are shown between the shafts 26 and housing 12.

In a further embodiment shown in FIG. 4, the hydraulic motor device of the invention is so modified to permit dual direction. In addition to the structures already described there is shown here

grooves

72 and 74. Groove 74 is connected to the source of fluid, in this case by port 76 and line 78 to pump means 80. Line 78 extends through the housing to connect with the port 76 which in turn connects with groove 74. Likewise, there is shown groove 72 connecting with line 82 through port 84. Again, this groove is supplied with fluid from pump 80 which also is connected to the inlet means 14. Thus, again groove 72 is supplied with fluid through the inlet means, specifically by means of pump 80. By the presence of fluid in

grooves

72 and 74 the start-up and running friction at the tips of the gear teeth is greatly reduced.

In this embodiment, the inlet of FIG. 4 is shown at 14 and outlet 16. However, depending on the rotation required, the inlet means and outlet means can be reversed with

ports

76 and 84 being connected to whatever chamber shown in the inlet chamber by means of pump 80. An external valve arrangement (not shown) can be utilized to shift the

feed lines

78 and 82 from pump 80 to the new inlet when direction is changed.

FIGS. and 6 are cross sections of FIG. 4 through line IVIV of FIG. 4. FIG. 5 illustrates the concept of a single groove. FIG. 6 graphically shows two arcuate circumferential grooves communicating with each rotary gear.

As shown in FIG. 5, line 82 connects to groove 72 by means of port 84. Also shown in bore wall 34 and tooth 86. Again, on the opposite side, line 78 connects with groove 74 through port 76 where there is also shown bore wall 36 and tooth 88. Again,

needle bearings

56, 60 and 62 are positioned between housing 12 and

shafts

26 and 28 at each of the four points to further reduce friction.

FIG. 6 illustrates an embodiment of the invention utilizing two grooves in the dual directional motor device. These grooves are shown at 90 and 92 at the top of the drawing and 94 and 96 at the bottom of the drawing.

It has been determined that the width of the abovediscussed groove should have a width less than the width of the gear teeth. If such is not the case, too much of the tooth surface would be exposed to pressure causing excessive bearing loads and failure. For optimum safe loading the groove width should be of a width less than the width of the teeth, and most preferably is about one-half of the width of the gear teeth. In those situations where two grooves are employed are present, the total width of the two grooves again should be less than the width of the gear teeth, and is most satisfactorily about one-half the width of the gear teeth. It is understood, of course, that one may utilize any number of grooves other than just one or two grooves as specifically discussed here.

The device discussed above may be used wherever a low-break-away torque hydraulic motor is required. Low friction at high speeds makes the device particularly desirable for use as blowers, fans, gear reduction mechanisms and power rotary devices.

We claim as our invention:

1. A hydraulic motor device exhibiting a minimum break-away torque under starting and accelerating conditions, said device comprising a housing having an inlet and outlet at opposite sides, said housing having formed internally therein a double lobed cavity be tween said outlet and inlet, a pair of rotary gears in said housing having shaft means disposed on axes of rotation concentric to the bore wall of each lobe, each rotary gear having alternating gear teeth and gear teeth spaces between and in full meshing engagement with one another, means to pump fluid under pressure through said inlet and against said teeth whereby said gears are rotated, at least one arcuate circumferential groove in each bore wall in communication with said means to pump fluid and surrounding the teeth of said gears, said groove extending to a cutoff point spaced before the outlet and having a width less than the width of said teeth with the tips of the gear teeth engaging the bore walls of the lobes adjacent the groove along the entire length of the groove whereby the presence of pressurized fluid in said groove vents the driving sides of the gear teeth and the peripheries of the gears to inlet fluid pressure to reduce the startup and running friction at the tips of the gear teeth.

2. A hydraulic motor device according to claim 1, wherein there are present a pair of holes in the housing communicating with said grooves in each bore, said feed holes being connected with the inlet means.

3. A hydraulic motor device according to claim I, wherein the groove extends directly from the inlet to the cutoff point.

4. A hydraulic motor device according to claim 3, wherein the width of said groove in each bore wall is approximately one-half the width of the teeth and surrounds the central portion of the gear teeth.

5. A hydraulic motor device according to claim 1, wherein each bore has a pair of grooves whose total width is less than the width of the teeth with each groove positioned at an end of a gear.

6. A hydraulic motor device according to claim 5, wherein the total width of said pair of grooves in each bore is approximately one-half the width of the teeth.

7. A hydraulic motor device exhibiting a minimum break-away torque under starting and accelerating con ditions, said device comprising a housing having an inlet and outlet at opposite sides, said housing formed internally therein a double lobed cavity between'said inlet and outlet, a pair of rotary gears in said housing having shaft means disposed on axes of rotation concentric to the bore wall of each lobe, each rotary gear having alternating gear teeth and gear teeth spaces being in full meshing engagement with one another, means to pump fluid under pressure through said inlet and against said teeth whereby said gears are rotated,

said grooves vents the peripheries of the gears to inlet fluid pressure to reduce the startup and running friction at the tips of the gear teeth and to force the gears in a direction that will not reduce the seal width of the meshing gear teeth.

8. A hydraulic motor device according to claim 7, wherein the total width of the grooves in each bore wall is approximately one-half the width of the teeth.

Claims

1. A hydraulic motor device exhibiting a minimum break-away torque under starting and accelerating conditions, said device comprising a housing having an inlet and outlet at opposite sides, said housing having formed internally therein a double lobed cavity between said outlet and inlet, a pair of rotary gears in said housing having shaft means disposed on axes of rotation concentric to the bore wall of each lobe, each rotary gear having alternating gear teeth and gear teeth spaces between and in full meshing engagement with one another, means to pump fluid under pressure through said inlet and against said teeth whereby said gears are rotated, at least one arcuate circumferential groove in each bore wall in communication with said means to pump fluid and surrounding the teeth of said gears, said groove extending to a cutoff point spaced before the outlet and having a width less than the width of said teeth with the tips of the gear teeth engaging the bore walls of the lobes adjacent the groove along the entire length of the groove whereby the presence of pressurized fluid in said groove vents the driving sides of the gear teeth and the peripheries of the gears to inlet fluid pressure to reduce the startup and running friction at the tips of the gear teeth.

3. A hydraulic motor device according to claim 1, wherein the groove extends directly from the inlet to the cutoff point.

7. A hydraulic motor device exhibiting a minimum break-away torque under starting and accelerating conditions, said device comprising a housing having an inlet and outlet at opposite sides, said housing formed internally therein a double lobed cavity between said inlet and outlet, a pair of rotary gears in said housing having shaft means disposed on axes of rotation concentric to the bore wall of each lobe, each rotary gear having alternating gear teeth and gear teeth spaces being in full meshing engagement with one another, means to pump fluid under pressure through said inlet and against said teeth whereby said gears are rotated, a pair of separated parallel arcuate circumferential grooves in each bore wall in direct communication with said inlet means and surrounding the peripheries of the gear teeth at the outer tips of the teeth, said grooves extending from the inlet to a cutoff point spaced before the outlet and having a total width less than the width of said teeth and said gear teeth riding on the cavity walls adjacent the grooves along the entire length of the grooves whereby the presence of pressurized fluid in said grooves vents the peripheries of the gears to inlet fluid pressure to reduce the startup and running friction at the tips of the gear teeth and to force the gears in a direction that will not reduce the seal width of the meshing gear teeth.