Gear Pump Or Motor

Abstract

In the gear pump or motor including a pair of intermeshing single-helical pump gears, the thrust acting on the intermeshing gears is balanced with liquid pressure from the higher pressure side of the pump or motor which is applied to one end of the respective gear shafts.

Description

BACKGROUND OF THE INVENTION

This invention relates to hydraulic gear pumps or motors, and more particularly to an improved means for balancing the thrusts acting on the intermeshing gears of gear pumps or motors using a pair of intermeshing single-helical gears.

As for the tooth form of the intermeshing gears for gear pumps or motors, continuous curves such as arc and sine curve have become widely used since they are effective to preclude the so-called "confinement" phenomenon. Even in the case of using such continuous curve toothform, if straight tooth or spur gears are used continuous meshing cannot be assured. It is, therefore, required to use helical gears having a phase shift, i.e. lead, of at least one-half pitches by the tooth width. Preferably, the lead should be just one pitch.

With high pressure gear pumps, however, the high bearing loads make it impossible to increase the tooth width, resulting in an increase in the helical angle. Such an increase in the helical angle in turn results in increasing the axial component of the meshing force and also increasing the axial unbalanced force exerted due to the inclination of the tooth grooves. Since these unbalanced forces act as a high thrust load, it has been impossible heretofore to increase the pump pressure.

In order to solve these problems, an attempt has been made to use double-helical gears so that said axial unbalanced thrusts can be counteracted. The gear pumps or motors with the double-helical gears are, however, disadvantageous in that a higher meshing accuracy which results in an increase in cost is required. In addition, the double helical gears are not utilizable for higher pressure pumps because they suffer from higher bearing loads due to an increase in the tooth width.

The primary object of the invention is to provide new and improved gear pumps or motors including a pair of intermeshing single-helical pump gears in which the above mentioned disadvantages with known gear pumps or motors can be avoided.

Another object of the invention is to provide new and improved gear pumps or motors including a pair of single helical pump gears in which the thrusts acting on the intermeshing helical gears due to various factors are all conveniently balanced though the utilization of the liquid pressure of the higher pressure side of the pumps or motors.

A further object of the invention is to provide improved means for applying liquid pressure from the higher pressure side of gear pumps or motors to the one end of the gear shafts thereof in such a manner that different total pressures are applied to the one end of the gear shafts according to the different total thrusts acting on those gear shafts.

SUMMARY OF THE INVENTION

In the gear pump or motor according to the invention, the thrusts acting on the intermeshing helical gears are balanced with a liquid pressure. The source for such liquid pressure for balancing the thrusts acting on the gears may be the higher pressure side of the gear pump or motor. The liquid pressure is applied to the one end of each of the gear shafts. In a preferred embodiment of the invention, the one end of each of the gear shafts is engaged with a piston axially slidable in a cylinder which is formed in the casing. Each of the cylinder is communicated with the higher pressure side of the pump or motor so as to apply the liquid pressure to the pistons in the respective cylinders. The liquid pressure receiving areas at the one ends of the gear shafts are so dimensioned as to balance the respective thrusts of different magnitudes.

In a gear pump, the liquid pressure receiving area at the one end of the drive gear shaft is approximately three times the liquid pressure receiving area at the one end of the driven gear shaft.

Other features of the invention will be described herein after in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a central vertical longitudinal sectional view of a typical form of the gear pump embodying the present invention; and

FIG. 2 is an enlarged view of the portion indicated by the lines of 2--2 of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, first particularly to FIG. 1, the present invention is illustrated in connection with a gear pump, but it should be understood that the invention may be utilized in connection with a gear motor.

The pump includes a pair of intermeshing helical 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. Hereinafter one end closure 15 is referred to as the front head while the other end closure 16 is referred to 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 (not shown) which extends through the inside of the cylindrical body 14 from the cover plate 16 to the front head 15. Though not shown in the drawings, the ends of bolts may terminate at the front head 15 and be screw-secured thereto.

The front head 15 is recessed to contain a roller-bearing 19 and a suitable oil-seal assembly 20. A drive shaft 21 extends through the oil-seal assembly 20 and the roller-bearing 19 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 needle bearings 26 and 27 which are in turn received within bores 28 and 29 recessed in the front head 15 and the end cover plate 16, respectively. A driven shaft 25 is supported on the opposite sides of the driven gear 12 by a pair of needle bearings 30 and 31 which are in turn received within bores 32 and 33 recessed in the front head 15 and the end cover plate 16, respectively.

The intermeshed helical gears 11 and 12 are supported between a pair of side sealing plates 34 and 35. The side sealing plates 34 and 35 are at their inner ends in sliding contact and in sealing relationship with the end faces of the intermeshing gears 11 and 12 and abut at their outer ends the end wall 36 of the front head 15 and the end wall 37 of the end cover plate 16 via seat plates 38 and 39. The seat plates 38 and 39 are always in contact with the end wall 36 of the front head 15 and the end wall 37 of the end cover plate 16, respectively. The reference numerals 40 and 41 indicates sealing means which are inserted between the side sealing plate 34 and the seat plate 38, and, between the side sealing plate 35 and the seat plate 39, respectively.

The contact pressure for securing the sealing engagement between each of the side sealing plates 34, 35 and the intermeshing gears 11, 12 is given by liquid pressure applied to the outer end of each of the side sealing plates 34, 35. In other words, liquid pressure from the higher pressure side of the pump is introduced to the gaps, which may exist between the side sealing plates 34, 35 and their respective facing seat plates 38, 39, from their peripheries. Sealing means 40 and 41 define the liquid pressure receiving areas of the side sealing plates 34 and 35, respectively. In the embodiment of the invention illustrated in FIG. 1, the liquid pressure receiving area at the outer end of the side sealing plate 34 is larger than that at the outer end of the side sealing plate 35 since the thrust force of the liquid introduced between the intermeshing gear teeth is larger at the side of the plate 34 than at the side of the plate 35. This system for urging the side sealing plates to the intermeshing gears through the utilization of the liquid pressure of the higher pressure side of the pump is known as "Balanced Pressure Loading." No further explanation would therefore be necessary.

Now I consider the thrusts which act on the intermeshing helical gears 11 and 12. In FIG. 1, the arrows A and B denote the thrusts which act on the helical gear 11 and 12, respectively. The thrust A which act on the drive gear 11 is represented by the sum of a thrust Fa due to the intermeshing torque T and a thrust Fp exerted by the liquid on the side sealing plates 34 and 35.

The discharge volume D of the pump per revolution is expressed by the following formula:

D = 2 .pi. rhb

wherein r is the pitch radius of each of the gears 11, 12, h is the tooth height of the gears 11, 12 and b is the tooth width of the gears 11, 12. The transmission torque T of the gears 11, 12 is given by the following formulas:

2 .pi. T = Dp.apprxeq. 2 .pi. rbhp, accordingly,

T .apprxeq. rbhp

wherein p is the liquid pressure.

The tangential intermeshing force Ft of the gears 11 and 12 is then expressed as follows:

Ft = T/2r .apprxeq. 1/2 bhp

Accordingly, the thrust Fa due to the intermeshing torque is given as follows:

Fa = Ft.sup.. tan.theta. .apprxeq. 1/2 bhp tan .theta.

wherein .theta. is the helical angle of the gears 11 and 12.

On the other hand,

Fp = btan .theta..sup.. hp = 2Fa

Accordingly,

A = Fa + Fp = 3Fa .apprxeq. 1/2 bhp tan .theta. (1)

Since the direction of the thrust due to the intermeshing torque T of the gear 12 is opposite to that of the gear 11, the thrust B which acts on the gear 12 is expressed by the following formula:

B = -Fa + Fp = Fa = 1/2 bhptan .theta. (2)

It will be seen from the above that the ratio of A to B is approximately 3:1.

According to the invention, the above mentioned thrusts A and B acting on the gears 11 and 12 are balanced with the liquid pressure from the higher pressure side of the pump which is applied to the one end of the respective gear shafts 21 and 25. The gear shafts 21 and 25 are engaged at their respective one ends with pistons 51, 52 via pressure receiving plate 53, 54. The pistons 51 and 52 are slidable in axial directions within the respective cylinders 55, 56 recessed in the end cover plate 16. The cylinders 55 and 56 are communicated with pressure chambers 57, 58 which are in turn communicated with the higher pressure side of the pump through passages 59, 60 and common port 61. This construction is more clearly illustrated in FIG. 2.

Referring to FIG. 2, the drive shaft 21 with the drive gear 11 is formed at its end face 62 with a shallow recess 63 at which the pressure receiving plate 53 is attached and carried. The pressure receiving plate 53 is in turn in contact with the piston 51 which is slidably carried in a cylinder 55 which is recessed in the end cover plate 16. The reference numeral 64 indicates an O-ring attached to the piston 51. The cylinder 55 is opened to a pressure chamber 57 to which a liquid pressure is supplied through the passage 59 and the port 61 from the higher pressure side (not shown) of the pump. The piston 51 has a central small opening 65 which communicates the cavity formed between the surface of the pressure receiving plate 53 and the piston 51 with the pressure chamber 57. The piston 51, the cylinder 55 and the pressure chamber 57 are all elongated in the direction of an extension of the central axis of the shaft 21. The pressure receiving plate 54, the piston 52, the cylinder 56 and the pressure chamber 58 are arranged with respect to the driven shaft 25 is in the same manner as those for the drive shaft 21.

The same liquid pressure is applied to the pressure chambers 57 and 58. However, since the ratio of the pressure receiving area of the piston 51 to that of the piston 52 is approximately 3:1, the drive and driven shafts 21 and 25 receive different total liquid pressures which can effectively and substantially exactly balance with the different thrusts A and B acting on the shafts, respectively.

Thus, according to the invention, it has become possible to obtain a perfect and reliable balance between the thrust acting on each of the intermeshing helical gears and the counteracting liquid pressure. The utilization of piston means separated from the gear shafts is advantageous in that there is no need of carrying out an exact alignment of each of the gear shafts with the cylinder to which pressure liquid is supplied and dispersed with the provision of an extremely fine sealing means for preventing pressurized liquid from leaking along the gear shafts.

It should, however, be noted that since the gist of the invention resides in directly or indirectly constituting the end of the gear shaft as a pressure receiving surface, the presence of a balancing piston and pressure receiving surface is not absolutely necessary. It is also possible to directly admit pressurized liquid to the gear shaft end surface by providing a seal mechanism of superior performance in the bearing part. In this case, the gear shaft end surface itself constitutes a pressure receiving surface. Concerning all modified embodiments constituting other pressure surfaces including these modified forms, the invention will comprehend them.

It should also be noted that the arrangement is not necessarily limited to the one shown in the drawing. As for the piston area ratio, for example, it is not absolutely necessary to make it 3:1 and such area may be formed depending upon the unbalanced force acting on the corresponding shaft. Further, although the static pressure bearing mechanism has been constructed with pressure receiving plates interposed, such pressure receiving plates are not absolutely necessary and the balancing pistons may be disposed directly opposed to the shaft ends and it is possible to effect simpler engagement in lieu of the static pressure receiving mechanism.

Further, in the present invention, the arrangement of the side seating plates of the bearing mechanism for the gear shafts, etc. is not limited to the one shown in the drawing. The liquid handled by the gear mechanism for feeding of liquid will not be limited to oil.

Further, as for the toothform of the gears of the gear pump embodying the present invention, the case described above is one in which a continuous curve toothform is used, but the invention can also be embodied in a gear pump using an involute toothform or the like which is in wide use, and the technical scope of the invention is in no sense limited with regard to these toothforms.

It will be a matter of course that the present invention comprised of the arrangement described so far can be used not only as a gear pump but also as a gear motor.

Claims

What is claimed is:

1. In a gear pump or motor including a drive shaft, a driven shaft, a pair of intermeshing drive and driven helical gears fixedly mounted on the drive and driven shaft respectively, which drive and driven gears react an axial force on the drive and driven shaft, a casing housing the gears, the improvement comprising pressure chambers formed in said casing in alignment with and spaced from the end of each of the gear shafts toward which the axial force is directed, means outside the casing for providing communication between each pressure chamber and the higher pressure side of the pump or motor so as to have a liquid pressure supplied from the higher pressure side of the pump or motor to each pressure chamber, axially movable means located in each pressure chamber for engaging the end of the gear shaft adjacent the pressure chamber and sealing the pressure chamber, whereby the thrust from the end of the gear shaft and the liquid pressure in the pressure chamber bear against the opposite ends of the axially movable means to balance the thrust on the ends of the drive and driven shafts.

2. A gear pump or motor as in claim 1 wherein the axial movable means located in each chamber is a piston and an annular O-ring on the outer surface of the piston.

3. A gear pump or motor according to claim 2 further comprising a pressure-receiving plate interposed between each shaft end and each piston.

4. A gear pump or motor according to claim 3 further comprising a central cavity formed in the front end surface of each piston engaging a pressure-receiving plate, and a central port formed in each piston to provide communication between the central cavity and the pressure chamber.

5. A gear pump or motor according to claim 4 wherein the liquid pressure receiving area of the piston engaging with the drive gear shaft is approximately three times the liquid pressure receiving area of the piston engaging with the driven gear shaft.