US3817117A

US3817117A - Gear pump or motor

Info

Publication number: US3817117A
Application number: US00283823A
Authority: US
Inventors: Y Kita; J Hida
Original assignee: Shimadzu Corp
Current assignee: Shimadzu Corp
Priority date: 1971-08-28
Filing date: 1972-08-25
Publication date: 1974-06-18
Anticipated expiration: 1991-06-18
Also published as: JPS4832201A; DE2242269A1; GB1400577A; FR2151943A5; DE2242269B2; DE2242269C3; JPS50702B2

Abstract

In a gear pump or motor, the tooth profile of the intermeshing gears is involutely formed at least on a torque transmitting side. The tooth profile of the intermeshing gears on a non-torque transmitting side is made steeper than an imaginary tooth profile which is symmetrical with that on the torque transmitting side.

Description

United States Patent Kita et al. June 18, 1974 4] GEAR PUMP OR MOTOR 2,752,751 7/1956 Vaucher 74/462 X [75] 5''" bmh FOREIGN PATENTS 0R APPLICATIONS 22,001 10/1907 G 'tB 't 74/462 731 Assignee: Shimadzu Seisakusho Ltd., Kyoto, m n m Japan G Primary Examiner-Leonard H. erin [22] 1972 Attorney, Agent, or Firm-Morgan, Finnegan, Durham [21] Appl. No.: 283,823 & Pine [30] Foreign Application Priority Data Aug. 28, 1971 Japan 46-66123 [57] ABS CT In a gear pump or motor, the tooth profile of the inter- 52] us. Cl. 74/462 meshing gears is involutely fomed at least on a torque [51] Illt. Cl. F1611 transmitting side The tooth profile of the intermesh [58] Fleld of Search 74/462, 460 g gears on a non torque transmitting Side is made steeper than an imaginary tooth profile which is sym- [56] uNlTE g gg z gs g rENTs metrical with that on the torque transmitting side.

462,073 10/1891 Beauregard 74/462 8 Claims, 6 Drawing Figures PATENTEDJUM 1 a 1914 SHEET 2 [1F 2 GEAR PUMP R MOTOR BACKGROUND OF THE INVENTION This invention generally relates to gear pumps or motors. In particular this invention relates to an improvement of the intermeshing gears of the gear pump or motor.

It is a common practice to use involute teeth for the intermeshing gears of the gear pump or motor for such reasons as easy workability, higher finishing accuracy, etc. However, a conventional gear pump or motor having involute tooth gears incorporated therein cannot escape a fluctuation in the fluid discharge which in turn leads to undesired as well as uncomfortable noise production during operation. Explained in detail, the amount of fluid discharged from the gear pump or motor changes from moment to moment and it reaches a maximum level at the instant when the gears intermesh with each other at the pitch point. While on the other hand, the amount of the discharged fluid at the instant when the gears intermesh with each other at points other than the pitch point is smaller than the maximum level. In other words, the fluid discharge of the gear pump or motor fluctuates from moment to moment and this fluctuation of the fluid discharge is a major, though not a sole, cause for the undesired noise production in the gear pump or motor during operation. This is particularly true when the gear pump or motor is operated at higher pressures.

It should be noted at this time that the undesired operating noise of the gear pump or motor is diminished to a great extent by reducing the fluctuation of the fluid discharge rate to a minimum level. In one way or other, the fluctuation in the fluid discharge, in turn, is effectively reduced by increasing the number of the gear teeth of the intermeshing gears. However, as can be readily understood by those skilled in the art, when the number of the gear teeth of a gear is increased with the pitch circle being the same, the height of the gear tooth is diminished in inverse proportion. On the other hand,

the amount of fluid discharged from the gear pump during one rotation of the gear (hereinafter referred to as displacement volume) changes in direct proportion to the tooth height of the gear. The result is that the displacement volume of the gear pump is substantially reduced if the number of the gear teeth of the intermeshing gears is increased with the pitch circles of the gears being the same. Thus, it is undesirably necessary to have a large-sized gear pump to obtain a particular displacement volume.

Meanwhile, public restrictions on the noise of hydraulic pumps and motors and other rotating machines are being tightened in recent years. Also there is an increasing demand for compact, low cost as well as highly efficient hydraulic pumps in the industry.

Accordingly, it is the principal object of this invention to provide a new and improved gear pump or motor having intermeshing gears of an involute tooth profile which enables to provide a geater number of the gear teeth on a gear sufficient to attenuate the operating noise of the gear pump or motor without causing the above mentioned undesirable reduction in the effective tooth height of the gears.

SUMMARY OF THE INVENTION According to this invention, a gear pump or motor includes a casing and at least one pair of intermeshing gears located within the casing as in any conventional gear pumps or motors. The tooth profile of the intermeshing gears according to this invention is involutely formed at least on the torque transmitting side, while on the opposite side, namely, the non-torque transmitting side it is not necessarily formed involutely. However, the tooth profile on the non-torque transmitting side is made at least steeper than an imaginary profile which is symmetrical with the profile on the torque transmitting side. By this arrangement of the tooth profile, it becomes possible to reduce tooth thickness without changing the tooth height, thereby making it possible to provide a greater number of the gear teeth on the gear. In other words, the tooth profile according to this invention is a kind of tall involute tooth profile which enables to form a gear of a smallest possible circular pitch without changing the tooth height.

In a preferred embodiment of this invention, for reasons of manufacture and assembly the tooth profile on the non-torque transmitting side may also be formed involutely. In such case, the pressure angle on the torque transmitting side is selected at a greater value than the pressure angle on the non-torque transmitting side, thus resulting in a non-symmetrical tooth form. For example, intermeshing gears of a non-symmetrical tooth profile having a pressure angle of 23 on the torque transmitting tooth surface and a pressure angle of on the non-torque transmitting tooth surface may be suitably used in accordance with this invention.

The invention itself together with advantages thereof may be better understood by referring to the following more detailed description taken in conjunction with the drawing,

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of a gear pump having incorporated therein intermeshing gears embodying this invention;

FIG. 2 is a schematic illustration of a prior-art standard basic rack;

FIG. 3 is a schematic illustration similar to FIG. 2 of another basic rack having an increased number of the gear teeth with the same pitch diameter and tooth height as in the basic rack of FIG. 2 and with a reduced circular pitch;

FIG. 4 is a schematic illustration similar to FIG. 2 of still another basic rack with a pressure angle on the torque transmitting side being made greater than a pressure angle on the non-torque transmitting side in accordance with this invention;

FIG. 5 is an elevational view of a pair of gears according to this invention arranged in a meshed relationship with each other to form a gear pump or motor; and

FIG. 6 is a fragmental view showing on an enlarged scale only one gear tooth profile of one of the intermeshing gears illustrated in FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, and in particular to FIG. 1, the invention is illustrated in connection with a gear pump, but it will be understood that the invention may be utilized in connection with a gear motor.

The pump includes a pair of intermeshing

gears

11 and 12 mounted within a cylindrical casing 13. The casing 13 comprises a cylindrical side wall body 14 and

end closures

15, 16 at opposite ends of the body 14. One end closure 15 is hereinafter referred to as the front head while the other end closure 16 is referred as the end cover plate. The cylindrical body 14 is clamped between the front head 15 and the end cover plate 16 by four bolts (only one of which is shown as 17) which extend through the cylindrical body 14 from the cover plate 16 to the front head 15. The end of the bolt 17 may terminate at the front head 15 and be screwthreaded thereinto.

The front head 15 is recessed to contain a roller bearing (not shown) and a suitable oil-seal assembly 18. A drive shaft 21 extends through the oil-seal assembly 18 and into the inside chamber of the casing 13 to engage and drive the drive gear 11. The gear 11 is keyed in a conventional manner to the shaft 21. The drive shaft 21 is supported on the opposite sides of the gear 11 by a pair of

bearing means

26 and 27 which are in turn received within the inside of the side wall body 14. A driven shaft is supported on the opposite sides of the driven gear 12 by a pair of bearing means 31) and 31 which are in turn received within the inside of side wall body 14.

The intermeshed

gears

11 and 12 are also supported between said pairs of

bearing means

26 and 27, and between and 31, respectively. The bearing means 26 and 30 are at their inner ends in sliding contact and in sealing relationship with the left end face of the

intermeshing gears

11 and 12 and abut at their outer ends the end wall 36 of the front head 15. The bearing means 27 and 31 are at their inner ends in sliding contact and in sealing relationship with the right end face of the

gears

11 and 12 and abut at their outer ends. The end eall 37 of the end cover plate 26. The reference numerals 40 and 41 indicates sealing means which are inserted between the end wall 36 of the front head 11 and bearing means 26, 30 and between the end wall of the cover plate 16 and bearing means 27, 31, 38, respectively.

, Inlet and outlet ports for the fluid under pressure (not shown) are provided in the casing 13, preferably in the front head 15 and they are communicated with a suction side and a discharge side of the meshed gears, respectively, via fluid passageways in a conventional manner. The fluid passageways may be arranged in any suitable manner. However, it is preferable to arrange those passageways such that the fluid under pressure may be introduced into the suction side of the

meshed gears

11, 12 and released from the discharge side thereof in an axial direction of the gears. Also, in order to avoid fluid entrapping when the two gears engage with each other at two points simultaneously, escape channels for the entrapped fluid may be suitably formed in bearing means 26, 27, 30 and 31.

Either spur or helical gears are used for the intermeshing gears. In accordance with this invention, the tooth profile at least on the torque transmitting side is involutely formed. In a preferred embodiment of this invention the tooth profile is formed involutely on both the torque transmitting and non-torque transmitting sides. In the latter case, the involute tooth profile is designed such that the pressure angle on the torque transmitting side is greater than the pressure angle on the non-torque transmitting side. By this unique design of the tooth profile, a tall involute tooth gear with a smallest possible pitch circle is obtained without reducing the original tooth height. When employed in a gear pump or motor, the tall involute tooth gear of this invention is effective to substantially reduce the fluctuation of the fluid discharge from the gear pump thereby attenuating the operating noise of the gear pump to a minimum level. For ease of understanding, the unique tall involute gear of this invention together with its noise reducing effect will be explained in more detail having reference to the basic racks which are schematically illustrated in FIGS. 2 to 4.

Generally, in the involute tooth profile of a standard tooth height, when the circular pitch is represented by 1rm the addendum and dedendum are respectively equal to m. FIG. 2 shows such a conventional standard basic rack. in order to increase the number of the gear teeth K times as many (where K 0) with the pitch diameter and the tooth height of the standard basic rack of FIG. 2 unchanged, the circular pitch thereof is decreased to UK. This basic rack is schematically illustrated in FIG. 3.

In the case of the basic racks shown in FIGS. 2 and 3 where the pressure angles on the opposite tooth surfaces of the profile are equal to each other, the available increase in the number of the gear teeth is determined as well as limited by the presence of a minimum allowable land thickness at the tooth top. If K is increased over this upper permissible limit without changing the originally selected pressure angles, the addendum is substantially reduced. If it is attempted to decrease the pressure angles on the other hand, the resulting undercut reduces the effective length of the involute curve at the dedendum. When the effective length of the involute curve at the dedendum is shortened beyond a predetermined critical point, the contact interval of the intermeshing gears become less than unity, failing to assure continuous meshing operation. For the two general reasons described above, there is little room for selecting values greater than unity for Kin the advanced tooth profiles of recent development.

The present invention has devised a unique tooth profile as shown in FIG. 4 on the basis of the fact that the higher pressure side in gear pumps is invariably predetermined in almost all applications and hence the tooth surface of the gear for transmitting driving force by meshing engagement with other mating gear is also predetermined (the tooth surface on the opposite side is just spaced away from the corresponding tooth surface of the mating gear by an amount equal to a backlash) and that the fluid discharge from a gear pump (including the instantaneous fluid discharge thereof) depends substantially on the profile of the tooth surface which transmits force by the meshing engagement.

In the basic rack illustrated in FIG. 4 the pressure angle 011 on the torque transmitting side of the gear tooth is maintained large enough to have a contact interval of not less than unity, while the pressure angle (12 on the non-torque transmitting side is made relatively smaller than the pressure angle al but large enough to secure a proper tooth top land for avoiding an excessive sharp tooth top which is harmful to satisfactory intermeshing operation of the gears. It should be noted at this point that even if the contact interval on the non torque transmitting side of the gear tooth is reduced to less than unity due to the presence of the larger undercut, it causes no harmful effect on the desired intermeshing operation of the gears.

Following is a more specific example of the preferred design of the gear according to this invention:

Pressure angle (11 on the torque transmitting side l4.5 Assuming the number of the gear teeth to be 12,

then; Tooth height module/pitch module z 1.3 This means that the displacement volume is increased by 30 percent. If it is attempted to obtain the same tooth height as in the gear of the present invention using the conventional standard tooth profile with the same pitch diameter, the number of the gear teeth is as follows;

Meanwhile, the percentage fluctuation or pulsation of the instantaneous fluid discharge of the gear pump using a pair of intermeshing gears having nine teeth, respectively, is approximately 24 percent, whereas it is approximately 18 percent when intermeshing gears each having twelve teeth is employed. Thus, by using the tooth profile of this invention, the fluctuation of the fluid discharge is effectively reduced to three-fourths of that when the conventional tooth profile is used. This results in a substantial reduction of noise which is produced during operation of the gear pump or motor.

The unique tooth profile has been explained hereinabove having reference to the basic racks. In actual practice, a pair of gears having gear teeth of the aboveexplained profile are arranged in an intermeshing rela tionship within a gear pump or motor casing as illustrated in FIG. 5. FIG. 6 shows in an enlarged scale the profile of only one gear tooth in one of the meshed gears of FIG. 5. In FIG. 5, a drive gear 11 is arranged in an intermeshing relationship with a driven gear 12 and is adapted to rotate in clockwise direction thereby to drive the driven gear in counter-clockwise direction. In the meshed section of the gears, the left hand tooth surface of each of the gear teeth in the drive gear 11 as seen in FIG. 5 is the torque transmitting tooth surface, while the right hand tooth surfaces of the same gear are the non-torque transmitting surfaces. The reverse is true with the driven gear 12. Thus, the torque transmitting tooth surfaces of the

gears

11 and 12 are indicated at 41, while the non-torque transmitting tooth surfaces are indicated at 42. As is apparent from the drawing, the pressure angle on the torque transmitting tooth surfaces 41 is made greater than the pressure angle on the other non-torque transmitting tooth surfaces 42. As the result, the tooth profile on the non-torque transmitting side is inclined steeper than an imaginary profile which is symmetrical with respect to that on the torque transmitting side.

In FIG. 6, the torque transmitting tooth surface 41 is involutely formed at the pressure angle of 23. On the non-torque transmitting side, the tooth surface 42 is involutely formed at the pressure angle of l4.5 along the addendum portion 42a. The dedendum portion 42b of the non-torque transmitting surface 42 is cut away to avoid undercutting interference with the gear teeth of the mating gear.

In the illustrated embodiment, the greater pressure angle on the torque transmitting side is selected at 23,

while the smaller pressure angle on the non-torque transmitting side at l4.5. However, different pressure angles may be suitably employed. In actual practice, the pressure angle on the torque transmitting side may be within the range of 14 to 30. Concerning the pressure angle on the non-torque transmitting side, there is no significance to define the pressure angle on this side since the non-torque transmitting tooth surface does not participate in the intermeshing engagement. However, it may be suitably determined depending on such factors, for example, as an amount of undercut, a minimum allowable tooth top land and tooth thickness necessary to maintain the desired tooth strength. In actual practice, it is preferred to select the pressure angle on the non-torque transmitting side within the range of 0 and 20. Also, in the illustrated embodiment, the tooth profile on the torque transmitting side has been formed involutely at least along its addendum. However, the tooth profile on the torque transmitting side is not necessarily be limited to the involute tooth profile and any other suitable tooth profile may be employed.

The important point is that the tooth profile on the non-torque transmitting side is formed steeper than the imaginary tooth profile which is symmetrical with the tooth profile on the torque transmitting side in order to reduce the tooth thickness to a possible minimum thereby to provide a tall tooth type intermeshing gear with a greatest possible number of gear teeth. Thus, any suitable form may be chosen as the tooth profile on the non-torque transmitting side including straight-line and cliff-like profiles.

It will be understood that the construction hereinabove described can be used not only as a gear pump but also as a gear motor.

As is apparent from the foregoing explanation, in the involute tooth profile for the intermeshing gears to be used in a gear pump or motor according to this invention the pressure angle on the torque transmitting side is made relatively greater than the pressure angle on the non-torque transmitting side. A gear pump which incorporates intermeshing gears of this invention pro duces only a substantially reduced noise while displacing an increased amount of fluid as compared to a gear pump having intermeshing gears of the conventional standard tooth profile with the same pitch diameter, tooth thickness and tooth height.

While only a few preferred embodiments have been described above, it is to be understood that this invention is not limited to the particular embodiment disclosed and that it is intended to cover all modifications which are within the true sprit and scope of the invention as claimed.

What is claimed is:

1. In a gear pump or motor including a casing and at least one pair of intermeshing gears arranged within said casing, an improvement in which the tooth profile of said intermeshing gears is formed involutely at least on the torque transmitting side and the tooth profile on the non-torque transmitting side is made steeper than an imaginary tooth profile which is symmetrical with that on the torque transmitting side.

2. An inprovement according to claim 1, in which the tooth profile is involutely formed! on both the torque transmitting and non-torque transmitting sides and the pressure angle on the non-torque transmitting side is made smaller than the pressure angle on the torque transmitting side.

3. An improvement according to claim 2, in which the pressure angle on the torque transmitting side is se lected within the range of 14 and 30 while the pressure angle on the non-torque transmitting side is selected within the range of and 20.

4. An improvement according to claim 3, in which the pressure angle on the torque transmitting side is selected at 24 while the pressure angle on the nontorque transmitting side is selected at l4.5.

5. In a gear pump or motor including a casing and at least one pair of intermeshing gears arranged within said casing, and wherein said intermeshing gears each include a plurality of teeth each having a top land surface portion of a non-symmetrical profile, the improvement therein which comprises: the non-torque transmitting side of each gear tooth profile has a steeper angle of inclination with respect to said top land than the angle of inclination of the torque transmitting side 8 of each gear tooth profile with respect to said top land.

side of the tooth profile is formed involutely.

Claims

2. An inprovement according to claim 1, in which the tooth profile is involutely formed on both the torque transmitting and non-torque transmitting sides and the pressure angle on the non-torque transmitting side is made smaller than the pressure angle on the torque transmitting side.

3. An improvement according to claim 2, in which the pressure angle on the torque transmitting side is selected within the range of 14* and 30* while the pressure angle on the non-torque transmitting side is selected within the range of 0* and 20*.

4. An improvement according to claim 3, in which the pressure angle on the torque transmitting side is selected at 24* while the pressure angle on the non-torque transmitting side is selected at 14.5*.

5. In a gear pump or motor including a casing and at least one pair of intermeshing gears arranged within said casing, and wherein said intermeshing gears each include a plurality of teeth each having a top land surface portion of a non-symmetrical profile, the improvement therein which comprises: the non-torque transmitting side of each gear tooth profile has a steeper angle of inclination with respect to said top land than the angle of inclination of the torque transmitting side of each gear tooth profile with respect to said top land.

6. The improvement as claimed in claim 5, wherein the profile of the torque transmitting side of each of said gear teeth is formed involutely at least along the addendum portion thereof.

7. The improvement as claimed in claim 6, wherein the dedendum portion of the profile of the non-torque transmitting side of each of said teeth is undercut with respect to the addendum portion thereof.

8. The improvement as claimed in claim 7, wherein the addendum portion of the non-torque transmitting side of the tooth profile is formed involutely.