EP0216999A2

EP0216999A2 - An external gear pump or gear motor unit of the asymmetric radial floating type

Info

Publication number: EP0216999A2
Application number: EP86108080A
Authority: EP
Inventors: Anqiang Cheng
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-09-29
Filing date: 1986-06-13
Publication date: 1987-04-08
Also published as: CN85107186B; EP0216999A3; JPS6275086A; CN85107186A

Abstract

On the basis of asymmetry theory the low-pressure zone is enlarged and the high-pressure zone is reduced; the performance of said gear pump or gear motor is optimized by means of an asymmetric axial and radial floating compensation device (5); the realization of axial and radial floating compensation provides higher volumetric efficiency; by adopting the integral structure higher mechanical efficiency is obtained and the noise is reduced; the stable radial floating device makes the high-pressure radial sealing practicable. The high-pressure zone is reduced, the radial force is reduced and the lifetime of said gear pump or gear motor is prolonged. With the invention, the gear type hydraulic machinery can be pressurized up to 321 kg·cm² level.

Description

The invention relates to an external gear pump or gear motor unit of asymmetric radial floating type, which can be used in a hydraulic system.
The external gear pump has been a key element of the hydraulic system for a considerably long time. Its evloution shows that axial floating compensation was realized as early as in 1930's and 1940's while radial compensation still remains a challenge. Although various structures of radial floating type have been developed, no satisfactory radial floating compensation concept is accepted because the existing structures of radial floating compensation are all of symmetric type. The inherent disadvantage of the symmetric structure is that it is difficult to maintain radial balance of the radial floating block and the pump performance is unsatisfactory.
It is an object of the present invention to provide an asymmetric radial floating device beyond the existing symmetric structure for optimizing performance of the gear pump or gear motor unit.
The attached figures are:

Fig. 1 Schematic diagram of a symmetric radial compen- sation device
Fig. 2 Schematic diagram of an asymmetric radial compensation device
Fig. 3 Structure drawing of an asymmetric floating gear pump
Fig. 4 Sectional view taken along line A-A of Fig. 3
Fig. 5 Sectional view taken along line B-B of Fig. 3
Fig. 6 Partial sectional view taken along line C-C of Fig. 4
Fig. 7 Gear motor with an asymmetric radial floating device, able to rotate in either forward or backward direction

Fig. 1 is a schematic diagram of a symmetric radial floating device. Fig. 2 is a schematic diagram of an asymmetric radial floating device comparison-between _Fig. 1 and Fig. 2 shows the principle and structural features of the asymmetric radial floating device.
As can be seen from Fig. 1, the so-called symmetric radial floating devices means that the included angles θ₁ and θ₂ (hereafter called opening angles), formed by the line 0₂0₁ connecting the centers of the two arcs and the lines connecting respectively the two arc ends to centers 0₂ and 1, are equal, i.e. θ₂ = θ₁. The asymmetric radial floating device, as the term suggests, has unequal opening angles, i.e. θ₂ ≠ θ₁. First of all, let us analyse the problems that exist in the symmetric radial floating device.
As shown in Fig. 1, a and b are a pair of intermeshing gears, a is a drive gear, b is a driven gear, c is a housing, d is a radial sealing inserted between the gears and the housing. When the gears rotate in the direction indicated in the figure, the recess between a and b brings the oil into a sealing zone formed by the gear pair and the radial sealing block. Being squeezed, the oil turns into high-pressure oil and comes out from the oil pump outlet through the central passage of the sealing shoe. The oil pressure existing between the tooth tips and the radial sealing shoe gives the sealing block a push force, which makes the sealing shoe tend to leave the tooth tips and is called radial separating force (F (1) or F₂ (II) in Fig. 1). To balance this radial separating force, a backpressure chamber is disposed at the back of the sealing shoe and is sealed by a sealing ring h. The backpressure chamber forms a compensating force F₂to balance the said force F₁(I) or F (II). That is basic principle of raidal floating. Fig. 1 (I) shows the instantaneous state of a certain tooth tip (such as of tooth X in the figure) of the driven gear which has just left the end of the sealing arc. Fig. 1(II) shows the instantaneous state of a certain tooth tip (such as of tooth Y in the figure) of the drive gear which has just left the end of the sealing arc. It is known from what is said above that the gear pump bring the oil into the sealing zone, then the oil is squeezed by the tooth to form a high pressure up to the exist pressure of the oil pump. As shown in Fig. 1(I), the tooth tip of tooth X has left the end of the sealing arc of the sealing block and the recess of tooth X is open into zone P where the oil pressure has reached the the output pressure of the oil pump, but tooth Y has not yet left the sealing zone because of the position difference of gear drive. it is obvious that the high- pressure zone at the driven gear side is larger than that at the drive gear side, so the said force F₁(I) is not on the symmetric central line g, but is inclined to the driven gear side as shown in Fig. l(I). similarly, when the gear pump runs into the state shown in Fig. l(II), the said force F₁(II) is inclined to the drive gear side as shown in Fig. l(II). It is thus clear that during the operation of the gear pump the position of the said force F₁ is always changing. The position of F₁ varies from the driven gear side to the drive gear side, then comes back to the driven gear side. The process will repeat, changing periodically with frequency of nz (n is the rotational speed of the gear pump, z is the number of gear teeth). The position of the backpressure chamber is constant and the position of the compensating force F₂ generated by the oil pressure within the said chamber is always on the central line g. Although F₁ and P₂ both act on the radial sealing shoe, they are not on the same straight line and cannot offset each other. This causes unstability and swinging of the symmetric radial floating device, resulting in abnormal wear and low efficiency.
To overcome the shortcomings of the symmetric radial compensation device, the invention proposes an asymmetric radial floating compensation device wherein a pair of intermeshing gears are also mounted in a housing c, a sealing block d is inserted between the gear and the housing. The only difference is θ₁≠θ₂, one differs from another by ½·360°/z, that is θ₁=θ₂+180°/z. Thus the tooth tips of both drive and driven gears leave the ends of two sealing arcs of the radial sealing block simultaneously. i.e. both teeth leave the sealing zone simultaneously. Moreover, the two sealing arcs of the sealing block are equal, i.e. α₁=α₂ (hereafter called enveloping angles). The change makes the high-pressure zone at the drive gear side always larger than that at the driven gear side, in other words, the radial separating force F₁ is always inclined to the drive gear side. Then, the position of the backpressure chamber is also inclined to the drive gear side, because it depends on the position of the radial separating force F₁. The invention proposes a circular backpressure chamber sealed by means of a sealing ring h. The eccentricity e between the central line of the backpressure chamber and the symmetric central line g is determined by the position of the radial separating force F₁. To prevent the lateral force, a planar back of the radial sealing shoe should be adopted instead of a curved one. Since the radial separating force F₁ and the radial compensating force F₂ act on the same straight line, they can offset each other. In this way the inherent radial unbalance of the symmetric floating structure is eliminated.
The specific structure of the invention is shown in Figures 3-7. Fig. 3_' is a lateral sectional view. Fig. 4 is a sectional view along line A-A of Fig. 3. As can be seen from the figures, the internal hole of the housing 1 is a hole of irregular shape composed of two holes arranged in ∞ form and an internal plane 2. The housing configuration is of a squarish cylinder. Inside the housing are arranged a pair of intermeshing gears 3 and 4. And an asymetric radial sealing shoe 5 is inserted between the external circular surface of the gear pair and the internal plane 2. The opening angle at the drive gear side is larger than that at the driven gear side. The enveloping angles are equal. The back surface of the radial sealing block 5 is a plane with a circular backpressure slot in it, a sealing 0-ring 6 and a spacer 7 are provided for high pressure sealing. There exists eccentricity e between the central line 8 of the circular backpressure slot and the symmetric central line 9 of the gear pair, the magnitude of eccentricity e depends on the deviation position of the radial separating force from the symmetric central line 9. The centers of the oil inlet port 10 and the oil outlet port 11 coincide with the central line 8 to keep the fluid flow freely. Shaft 12 is a drive shaft. The drive gear and the driven gear are supported by four bearings 13 which are pressed in four sleeves (three short sleeves 14 and a long sleeve 15), the length of the sleeve internal hole is shorter than the width of the bearing 13. On the projecting part of the bearing 13 are inlaid a front side plate 16 and a rear side plate 17. There is a step end face 18 on both sleeves 15 and 14. Fig. 5 is a sectional view along line B-B of Fig. 3. As shown in Fig. 5, the step end face 18 limits the position of the sealing shoe 5 to prevent axial movement of the sealing block. Four sleeves with four bearings on them, the front side plate, the gear side plate and the radial sealing block are all disposed within the hole of irregular shape in the housing 1 to form an integral part. It can also be seen from Fig. 3 and Fig. 5 that the two arcs of the radial sealing block 20 and 21 coincide with the external circular surface of the gear pair on the front side plate 16 and the rear side plate 17, and with the step-like external circular surfaces of the sleeves 14 and 15 so sealing along the axial direction can be obtained by means of the side plate and bearings which limit the position of the sealing block as shown in Fig. 6. Fig. 6 is a partial sectional view along line C-C of Fig. 4. It illustrates the configuration of the axial backpressure chamber. There is provided an asymmetric λ-form slot at the back of the rear side plate 17. The external cylindric surface of the bearing 13 supporting the side plates and two arcs 20 and 21 of the radial sealing block 5 form an asymmetric A-form axial backpressure chamber, wherein an asymmetric A-form sealing shoe 22 and a spacer 23 (shown in Fig. 4, not in Fig. 6) form an axial floating sealing device. The axial floating sealing devices on the front side plate and the rear side plate are identifical. On the side plate there is a hole 24, through which the pressure oil flows from the front into the axial backpressure chamber forming an axial compensating force which overcomes the axial separating force from the front of the side plate and makes the front side plate 16 and the rear side plate 17 abut against the end faces of the gears 3 and 4 to prevent axial leakage and to realize axial and hydraulic floating sealing.
It can also be seen from Fig. 4 that among the four sleeves the sleeve 15 mounted on the drive gear shaft near the drive shaft is a longer one, its extending portion determines the position of the front cover 25. The rear pump cover 26 closes the housing. The housing 1, the front cover 25 and the rear cover 26 are fixed by means of bolts 27 to form an integral part.
When the gear pump is running the gear 3 rotates in the direction indicated in Fig. 3. Through the oil inlet port 10 the oil enters into the sealing zone between the radial sealing block 5 and the gears 3 and 4, than is squeezed by the teeth, turns into high-pressure oil and comes out from the oil outlet port through the passage 27 of the radial sealing block. Being pushed by the oil pressure of the backpressure chamber, the said sealing block 5 overcomes the radial separating force and keeps the raidal sealing stable and reliable in the high-pressure zone.
The above is described according to the mode of operation as a pump. If the pressure oil enters in from the oil outlet port 11 of the oil pump, a torque can be obtained on the output shaft 12, and the gear pump turns into a gear motor. Generally, the hydraulic motor should rotate forward and backward, so Fig. 7 illustrates the lateral sectional view of the gear motor which can rotate in both forward and backward directions. As shown in the figure, the housing should be a bidirectional housing 28 having two internal planes 29 and 30, and two radial sealing block 5 should be installed. The rest is identical with what is in the gear pump.
The invention enlarges low-pressure zone and reduces high-pressure zone on the basis of asymmetric theory, improves the engineering level of the gear pump or gear motor by means of the asymmetric axial and radial floating compensation device, gives higher volumetric efficiency because of realization of the bidirectional (axial and radial) floating compensation, has higher mechanical efficiency and reduces the noise due to adopting the integral configuration. The stable radial floating device makes radial sealing of the high-pressure zone practicable. The high-pressure zone is reduced, the radial force is reduced, the lifetime of the gear pump or gear motor is prolonged. According to the invention the gear type hydraulic machinery can be pressurized up to 32lkg/cm 2 level.
A series of products can be manufactured with the technique of the invention according to the different flow rate. Also, single-stage pumps, double pumps and triple pumps can be manufactured in accordance with different operating modes. In a word, the invention develops a wider operating area for the pump or gear motor unit.

Claims

1. An external gear pump or gear motor unit of the asymmetric radial floating type, wherein an asymmetric radial sealing shoe (5) is disposed between the housing (1) and the pair of gears (3 and 4); side plates (16 and 17) are mounted on the two end faces of the said gears; the said plates (16 and 17) are inlaid on the projecting part of the bearing (13); by means of the oil pressure the said side plates (16 and 17) are pressed against the two faces of said gears (3 and 4); said sealing block pressing against said gears (3 and 4), side plates (16 and 17) and sleeves (14 and .15) form an asymmetric type device for both radial and axial floating compensation.

2. A unit according to claim 1, including said radial sealing block, wherein the opening angles are not equal, and θ₁ = θ₂ + 180°/z.

3. A unit according to claim 1 or 2, wherein enveloping angle α₁ = α₂, that is the arcs (20 and 21) equal in length.

4. A unit according to any one of claims 1 to 3, including said radial sealing block, wherein the central line (8) of the circular backpressure chamber does not coincide with the symmetric central line (9) of the two arcs (20 and 21), with an eccentricity (e) between them.

5. A unit according to claim 4, including said backpressure chamber, wherein said central line (8) is at the drive gear side of said symmetric central line (9).

6. A unit according to any one of claims 1 to 5, especially as a pump, wherein an asymmetric - form axial sealing device is composed of an axial backpressure chamber, which is formed by the axial backpressure slot of said side plates (16 and 17), the external circular surface of said bearing (13) and the curved surfaces of the two arcs, together with the λ- form sealing block (22) and the spacer (23).

7. A unit according to any one of claims 1 to 6 wherein said housing (1) is of cylindrical configuration of which the cross section is a hole of irregualr shape, which is composed of two holes arranged in ∞ form and an internal plane (2).

8. A unit according to claim 1, wherein a longer sleeve (15) is used as a positioning device for the housing (1) and the front cover (25).

9. A unit according to any one of claims 1 to 8, characterized in that it is designed such that the pump turns into an asymmetric radial floating gear motor if the high pressure oil enters in from the outlet (11).

10. A unit according to any one of claims 1 to 9 wherein the two asymmetric radial sealing blocks are mounted center-symmetrically, thus turning the said motor able to run in either forward or backward direction.

11. A unit according to claim 10 wherein the housing (28) is an irregular chamber which is composed of two holes arranged in ∞ form and two inner planes (29 and 30) parallel to said holes.