EP0081902A1

EP0081902A1 - A gear pump or motor

Info

Publication number: EP0081902A1
Application number: EP19820305754
Authority: EP
Inventors: Hideo Teruyama
Original assignee: Kayaba Industry Co Ltd
Current assignee: KYB Corp
Priority date: 1981-10-31
Filing date: 1982-10-28
Publication date: 1983-06-22
Also published as: JPS5867994U

Abstract

A gear pump or motor, comprising a pair of gears (20, 21), engaged with each other with their external teeth, the shafts (22, 24) of the gears being supported bearings provided on both sides in a housing, a seal block (31) being provided between the tooth tops of said gears and the inside wall surface of the housing, arranged to the tooth tops of the gears by a high pressure acting on the outside surface of the seal block, and side plates (36) being provided to cover both the sides of said gears at least on the high pressure side to closely contact, at their outside ends, the inside surface of said seal block and to contact, at their inside ends, the circumferential surfaces of protrusions (26a, 28a) of said bearings, whereby the inside diameter of the curved surfaces of the side plates in contact with the circumferential surfaces of the protrusions of said bearings is made larger than the outside diameter of the protrusions of the bearings.

Description

The present invention relates to a gear pump or motor having gears which engage each other with their external teeth.
More particularly, it relates to a gear pump or motor with a cover and a mounting flange provided on both sides of a housing, the shafts protruding on both sides of the two gears and being supported by the bearings provided in the cover and the mounting flange, and with a seal block arranged on the high pressure side of the housing, to seal the tooth tops of the gears on the delivery side.
In a gear pump or motor of this kind known hitherto, the seal block is supported by the side plates, and the side plates form curved surfaces to accurately fit the bearings as bushings protruding a little toward the chamber of the housing and contact the surface of the seal block which is in contact with the tooth tops on the side opposite to the bushings.
When- the seal block is supported by the side plates in this way, the tooth top clearances between said seal block and the gears are kept in an optimum condition.
Therefore, if any dimensional error exists in any of said side plates, the surface of the seal block in contact with the tooth tops may be deeply shaven off by the gears, so as to impair the sealing function.
For this reason, the dimensions of said side plates and bushings are strictly controlled, to let the inside diameter of the curved surfaces of the side plates perfectly coincide with the outside diameter of the bushings.
However, to attain perfect coincidence in these dimensions is difficult, and some dimensional errors occur actually.
If any dimensional error occurs in spite of the effort to attain perfect dimensional coincidence, the respective components such as side plates interfere with one another when they are going to be assembled, so as not to allow assembling, which is a disadvantage.
Objects-of the invention :
A first object of the present invention is to provide a gear pump or motor, in which the inside diameter of said curved surfaces of said s.ide plates is made larger than the outside diameter of the bearings, so that said curved surfaces may contact the bearings at one point of each of said curved surfaces when they are assembled, to prevent the interference of the respective components during assembling, allowing the optimum control of the tooth top clearances.
A second object of the present invention is to provide agear pump or motor, in which the inside diameter of said side plates is made larger beforehand than the outside diameter of the bearings, so that said side plates may contact the bearings with an optimum condition kept when the gear pump or motor is operated.
A third object of the present invention is to provide a gear pump or motor, in which the tooth top clearances can be automatically corrected even if the housing expands or contracts due to temperatures during operation.

Summary of the invention:

To attain the above objects, in the present invention, the inside diameter of the curved surfaces of the side plates is made larger than the outside diameter of the bearings, to prevent the interference of the respective components during assembling, and to let said curved surfaces contact said bearings at one point of each of said curved surfaces, for controlling the radial positions of the side plates and the seal block. Brief description of the drawings:

Fig. 1 is a longitudinal sectional view showing an example of the gear pump of the present invention.
Fig. 2 is a sectional view along the 2 - 2 line of Fig. 1.
Fig. 3 is a sectional view along the 3 - 3 line of Fig. 1.
Fig.4 is an illustration showing the relation between the side plates and the bearings.
Fig. 5 is a sectional view showing anotherexample corresponding to said Fig. 3.

Detailed description of the invewntion:
In Fig. 1 a gear pump 10 according to the present invention has a housing 11 consisting of a casing 12, a cover 13 and a mounting flange 14.
Said casing 12 is cylindrical, and is closed by the cover 13 on one side and by the mounting flange 14 on the ather side. The cover 13 and the mounting flange 14 are connected with both the ends of the casing 12 respectively through seal members 15 and 16 by fitting joints 18 and 19, being fastened firmly by bolts 17. In this joining, dowel pins as used in the ordinary gear pump are not required.
The cover 13 and the mounting flange 14 are made of aluminium alloy and the casing 12 is made of steel.
The cover and the mounting flange are formed by die casting to enhance the dimensional accuracy, and to be suitable for die casting, aluminium alloy is used as the material. The use of aluminium alloy is intended also to reduce the weight.
Steel is selected as the material of the casing to secure high strength.
The casing 12 contains a pair of gears 20 and 21 engaged with each other as pumping components. The gears 20 and 21 are provided with shafts 22 & 23, and 24 & 25 respectively on both sides. These shafts 22 to 25 are supported rotatably by bearings 28 & 27 and 28 & 29 as bushings fitted in the cover 13 and the mounting flange 14. These bearings 26 to 29 are protruded at their inner ends to some extent from the cover 13 and the mounting flange 14, to form protrusions 26a, 27a, 28a and 29a.
The shaft 25 on one side of said gear 21 is protruded outward through the mounting flange 14, and can be connected with a power source outside the gear pump 10.
In the portion of the mounting flange 14 through which the shaft 25 is passed through, an oil seal 30 is fitted, to seal the clearance between the shaft 25 and the mounting flange 14.
And as can be seen from Fig. 3 on the delivery side of the gear pump 10, a seal block 31 is provided between the inside wall of the casing 12 and the tooth tops of the gears 20 and 21.
The outside curved surface of the seal block 31 is formed to suit the inside wall surface of the casing 12, and inwardly curved surfaces are formed inside to suit the outside contours of the gears 20 and 21.
On the outside curved surface of the seal block 31, there is a high pressure area 33 sectioned by a seal member 32, and the high pressure area 33 communicates to the delivery side of the gears 20 and 21 through a radial high pressure introducing hole 34 and an axial high prssure groove 35 formed in the seal block 31.
The other portions of the circumferential surfaces of the gears 20 and 21 than the portions facing the inwardly curved surfaces of the seal block 31 have a space against the inside wall of the casing 12, being open to the suction side of the gears 20 and 21.
Said seal block 31 is almost equal to the overall width of the chamber in the casing 12 containing the gears 20 and 21 as can be seen from Fig. 2 . Therefore, the seal block 31 is limited in its axial movement by the inside wall surfaces of the cover 13 and the mounting flange 14, but is arranged to be able to move radeally to some extent in the range between the inside wall surface of the casing 12 and the tooth tops of the gears 20 and 21.
The gears 20 and 21 are made of steel to maintain the strength, and are made to be somewhat more narrow than the overall width in said casing 12. Thus, clearances are formed between the side surfaces of the gears and the cover 13 and the mounting flange 14, by narrowing the width of the gears 20 and 21, and in the clearances, side plates 36 and 37 made of steel are provided. The side plate 38 is positioned between the cover 13 and the side surfaces of the gears 20 and 21 facing it, while the side plate 37 is positioned between the mounting flange 14 and the side surfaces of the gears 20 and 21 facing it.
Since the side plates 36 and 37 are the same in form, the side plates 36 only will be described below.
The side plate 36, as can be seen from Fig. 3, consists of a central portion 36a and branching portions 36b and 36c. The central portion 38a is positioned between said protrusions 26a and 28a of the bearings 26 and 28, and the branching portions 36b and 38c are formed to suit the circumferences of the protrusions 26a and 28a. The inside diameter of the curved surfaces 36d and 36e formed by the inward curves of the central portion 38a and the branching portions 36b and 36c is made a little larger thah the outside diameter of the protrusions 26a and 28a of the bearings 28 and 28, and at points P and Q, said curved surfaces 38d and 36e contact the protrusions 26a and 28a.
Said points P and Q can be selected freely as far as they contact the circumferences of the bearings 26 and 28 at one point each to control the radial movement. To be specific, the distance S between the points P and Q is only required to be longer than the clearance ℓ₂ between the bearings 26 and 28.
However, as shown in Fig. 3 , it is ideal that the distance S between both the points P and Q satisfies the following relation with the distance ℓ ₁between the axial centers 0 ₁and 0 ₂ of the shafts 22 and 24 and with the distance ℓ₂ between the bearings 28 and 28.
The reason will be described later.
The outwardly curved surfaces of said branching portions 36b, 36c, 37b and 37c of the side plates are the same in form as the outside contours of the gears 20 and 21, viz. as the inwardly curved surfaces of the seal block. 31, and support the inwardly curved surfaces of the seal block 31.
In this case, the outwardly curved surfaces of the side plates 36 and 37 keep arcs dimensionally somewhat smaller than the outside contours of the gears 20 and 21, when the curved surfaces 38d, 36e, 37d and 37e of the side plates 36 and 37 are supported by the circumferential surfaces of the protrusions 26a to 29a of the bearings 26 to 29.
Since both the sides of the gears 20 and.21 are sealed by the side plates 36 and 37 on the delivery side, pressure areas 40 and 41 sectioned by seal members 38 and 39 are formed in the inside wall portions of the cover 13 and the mounting flange 14 respectively adjacent to the side plates 36 and 37.
Thus, if the gear pump 10 is operated, the pressure medium is sucked toward the suction side of the chamber in the casing 12 through an axial passage 43 from an inlet port 42 provided at-one side of the cover 13 (see Fig.1), and is carried toward the delivery side by the gears 20 and 21 rotating mutually in the other directions.
The pressure medium carried as mentioned above is fed from the high pressure groove 35 formed in the seal block 31 through an axial passage 44 formed in the cover 13 and an outlet port 45 opening toward the other side of the cover 13(see Fig. 1), to an actuator not illustrated.
The high pressure generated in the delivery side of the gears 20 and 21 in this wayactsfrom the high pressure groove 35 of the seal block 31 onto the pressure areas 40 and 41 at the rear of the side plates 36 and 37.
This loads the side plates at the rear at-high pressure, causing them to adhere to both the sides of the gears 20 and 21 on the delivery side with a good sealing effect.
At the same time, said high pressure acts also on the pressure area 33 at the rear of the seal block 31 through the high pressure introducing hole 34, and the seal block 31, being loaded with the high pressure on the rear side, is pressed against the tooth tops of the gears 20 and 21.
Thus, the seal block 31 is shaved off on the inwardly curved surfaces by the tooth tops of the gears 20 and 21, and the tooth tops of the gears 20 and 21 slightly bite the seal block 31, for good sealing of the tooth tops of the gears 20 and 21.
The depth of bite by the tooth tops of the gears 20 and 21 into the seal block 31 is as far as the inwardly curved surfaces of the seal block 31 are supported in contact with the outwardly curved surfaces of the side plates 38 and 37.
The above state is secured during the initial adaptation operation of the gear pump 10. Therefore, in the ordinary state of operation of the gear pump 10, the seal block 31 is always supported through the side plates 36 and 37 by the circumferential surfaces of the protrusions 26a to 29a of the bearings 26 to 29.
Therefore, if the side plates 36 and 37 have some play, the seal block 31 cannot be positioned, and furthermore, the tooth tops of the gears 20 and 21 cannot be sealed, to lower the pump efficiency.
For this reason, the side plates 36 and 37 must be assembled accurately against the protrusions 26a to 29a of the bearings.
However, as mentioned above, if the curved surfaces 36d, 36e, 37d and 37e of the side plates are designed, to let their inside diameter coincide with the outside diameter of said protrusions 26a to 29a, a slight dimensional error in said curved surfaces 36d, 36e, 37d and 37e causes the gears, etc. to interfere with each other, not allowing them to be assembled.
The-refore, to overcome the above disadvantage, in this example, the inside diameter of the curved surfaces 36d, 36e, 37d and 37e of the seal blocks is made beforehand larger than the outside diameter of the protrusions of the bearings 26 to 29, and one point is selected at the position where each side plate does not play, for pressure contact with said protrusions only at the pressure contact point.
If the curved surfaces of the side plates are formed in this way, the severe dimensional control of the one each pressure contact point only can eliminate the mutual interference among the respective components even if there are some dimensional errors in the other portions.
In this case, said pressure contact points of the curved surfaces 36d and 38e, for example, are most desirable to be so selected that the distance S between the pressure contact point P and Q satisfies the relation of ℓ₂ < S <ℓ₁ with the distance ℓ₁ between the axial centers 0 ₁and 0 ₂ of the shafts 22 and 24 and with the clearance ℓ₂ between both the bearings 26 and 28.
If the basic dimensional relation is kept, the tangential lines passing through the pressure contact points P and Q form a wedge, as shown in Fig. 4 .
If the gear pump 10 composed as mentioned above is used, for example, at low temperatures, the cover 13 and the mounting flange 14 contract, and therefore the clearance ℓ₂ between the bearings supported by them becomes shorter than that at room temperature. However, since the gears and side plates made of steel are smaller in the coefficient of contraction than the cover and the mounting flange made of aluminium alloy, the correlation between the gears and the side plates on one hand and the cover and the mounting flange on the other hand becomes irregular.
Thus, if the clearance ℓ₂ becomes short, the pressure contact points P and Q move along said tangential lines, causing the side plate to be pressed out of the position between the shafts 22 and 24.
If the side plate is pressed out as mentioned above, the sealing clearance between the seal block 31 and the tooth tops of the gears 20 and 21 becomes large as a result, and this is desirable on the contrary for the following reason, especially when an oil is used as the pressure medium.
On oily pressure medium becomes higher in viscosity at low temperatures as mentioned above. Therefore, even if the sealing clearance becomes large to some extent, the leak through the clearance does not increase.
Furthermore, if the gear pump 10 is operated with the pressure medium at a high viscosity as mentioned above, bubbles are generated in the spaces of the gears 20 and 21, causing the pressure in the spaces to vary greatly, and for this reason, the load to the seal block becomes too large momentarily. If the load to the seal block becomes too large, the gear tracks of the seal block formed by the tooth tops of the gears become abnormally deep.
However, since the side plates move to make the sealing clearance between the seal block and the tooth tops of the gears large as mentioned above, said gear tracks do not become deep even if the load to the seal block becomes large.
On the other hand, at high temperatures, since said clearance J2.2 becomes wide, the side plate is pressed into the position between the shafts 22 and 24, receiving the loading action of the seal block .
If the side plate is pressed into the position between the shafts 22 and 24, the seal block 31, too, moves accordingly, to make said sealing clearance narrow.
However at high temperatures, since the viscosity of said oily pressure medium drops, the narrow sealing clearance reduces the leak, providing a good condition on the contrary.
Inanotherexample shown in Fig. 5 , the inside diameter of the curved surfaces 50d and 50e of the side plate 50 is made larger than the outside diameter of the protrusions of the bearings 28 to 29, and said curved surfaces 50d and 50e are arranged not to contact said protrusions during assembling.
Furthermore, on the outwardly curved surfaces of the side plate 50 in both the branching portions 50b and 50c, a sufficiently large constriction 50f is formed, to correspond to said high pressure groove 35.
The formation of said constriction 50f decreases the rigidity of the branching portions 50b and 50c at the portion corresponding to the constriction.
Therefore, if the gear pump 10 is operated as mentioned above, a high pressure acts on said constriction 50f, to bend the side plate 50, allowing the pressure contact points P and Q to be obtained as in said example.
If the pressure contact points P and Q are obtained like this, the tangential lines passing through the points P and Q are as shown in Fig. 4 , giving quite the same result as obtained in said example.
In the example shown in Fig. 5 , since the curved surfaces 50d and 50e of the side plate 50 are arranged not to contact the bearings at all during assembling, the dimensional control is not required to be so severe as that for the example shown in Fig. 3.

Claims

1. A gear pump or motor, comprising a pair of gears (20, 21) engaged with each other with their external teeth, a housing (11) forming a chamber to contain the gears (20, 21), bearings (26, 27, 28, 29) provided on both sides in the housing to support the respective shafts (22, 23, 24, 25) of said gears, with protrusions (26a, 27a, 28a, 29a) at the inner ends toward the chamber, a seal block (31) provided between the tooth tops of said gears and the inside wall surface of the housing, with its inside surface formed to suit the outside contours of the gears and arranged to be pressed to the tooth tops of the gears by a high pressure acting on the outside surface of the seal bluck, and side plates (36, 37) provided to cover both the sides of said gears, at least on the high pressure side, to closely contact, at their outside ends, the inside surface of said seal block, having the same form as the outside contours of the gears, and to contact, at their inside ends, the circumferential surfaces of the protrusions of said bearings supporting the shafts of the gears, thereby positioning said seal block at a predetermined position in relation to the protrusions of the bearings, wherein the inside diameter of the curved surfaces (36d, 36e) of the side plates in contact with the circumferential surfaces of the protrusions of said bearings is made larger than the outside diameter of the protrusions of the bearings, and the distance S between the points P and Q at which said curved surfaces are brought into pressure contact with the protrusions of said bearings is larger than the distance between the protrusions of said bearings, at least during operation.

2. A gear pump or motor according to Claim 1, wherein siad pressure contact points P and Q at which the protrusions of said bearings contact the curved surfaces (36d, 36e) of the side plates are arranged to satisfy the relation Q₂< S < ℓ₁ with ℓ₁ being the distance between the axial centers O₁ and 0₂ of the gears and with ℓ₂ being the distance between said protrusions.

3. A gear pump or motor according to Claim 2, wherein the inside diameter of the curved surfaces of said side plates is made larger than the outside diameter of the bearings, such that said curved surfaces do not contact the circumferential surfaces of the bearings when said side plates are assembled, and a sufficiently large constriction is formed in the position corresponding ro the high pressure groove (35) of said seal block (31), so that when a high pressure acts on the constriction, the side plate may be bent, to let one point of each of said curved surfaces correspond to each of said pressure contact points P and Q.