Hydraulic device

Abstract

 Hydraulic device comprising pistons rotatable in a first plane, piston sleeves arranged around the pistons in a sealing manner, a drum plate rotatable around a rotation axis in a second plane with a drum plate surface for sealingly supporting the piston sleeves, whereby the piston sleeves are resiliently pressed by first spring means against the drum plate surface and whereby the first plane and the second plane intersect forming an angle and the piston, the piston sleeve and the drum plate form a chamber which has a changing volume during rotation of the pistons and whereby the device further is provided with second spring means that press the piston sleeves at a contact point on the outer circumference of a piston sleeve in direction of the rotation axis.

Description

[0001] The invention relates to a hydraulic device as described in the not pre-published application PCT/NL2005/050062 of the same applicant. This document describes the hydraulic device with piston sleeves that are arranged around pistons and that rotate at a high speed. At high rotation speed of the pistons there is a risk that the sleeves tilt on the drum plate due to the centrifugal force on the sleeve. This is not allowable as this causes leakage and reduction in efficiency. To prevent this tilting the document proposes first spring means in order to clamp the sleeve against the drum plate. Although this measure reduces the leakage between the sleeves and the drum plate and improves efficiency it is not sufficient for high rotation speeds such as above 5000 rotations per minute. In order to improve on this the hydraulic device is in accordance with claim 1. It has been found that this combination of first spring means and second spring means ensures that the sleeves do not tilt against the drum plate surface so that there is no leakage between the sleeves and the drum plate.

[0002] In accordance with an embodiment the hydraulic device is according to claim 2. In this way the second spring means directly compensate the centrifugal forces on the sleeves.

[0003] In accordance with an embodiment the hydraulic device is according to claim 3. In this way stability of the sleeve is ensured, as otherwise the second spring means would tilt the sleeves at low rotation speeds.

[0004] In accordance with an embodiment the hydraulic device is according to claim 4. In this way a proper sealing between the sleeves and the drum plate is ensured.

[0005] In accordance with an embodiment the hydraulic device is according to claim 5. The sleeves are placed in an oval on the drum plate where the sleeves move during rotation to and from the rotation axis. The circumference around the sleeves does hardly change so a flexible support with an elliptical shape whereby the elliptical shape rotates with the sleeves keeps a more or less constant distance from the sleeves. Spring means attached between such a support and a sleeve will exert a more or less constant force on the sleeve, independent from the rotational position of the oval. As the centrifugal force on the sleeves is also independent from the rotational position a flexible ring surrounding the sleeves as a support for the second spring means ensures that the forces on the ring are independent from the rotational position.

[0006] In accordance with an embodiment the hydraulic device is according to claim 6. An elastic band directly around the contact points of the sleeves is a simple solution for arranging forces directed towards the rotation axis.

[0007] In accordance with an embodiment the hydraulic device is according to claim 7. The grooves on the sleeves position the ring in an easy way.

[0008] In accordance with an embodiment the hydraulic device is according to claim 8. In this way easy to mount second spring means are obtained.

[0009] In accordance with an embodiment the hydraulic device is according to claim 9. In this way the spring means are made from a single part and are easy to assemble.

[0010] The invention will be explained in more detail below with reference to an exemplary embodiment by means of a drawing, in which:

Fig. 1 shows a perspective view of the internal parts of a pump or hydromotor according to a first embodiment of the invention;

Fig. 2 shows a section of a chamber shown in figure 1 at the location where the chamber has a minimal volume;

Fig. 3 shows a top view of the path of the piston sleeves on a drum plate,

Fig. 4 shows a perspective view of a drum plate with piston sleeves of a pump or hydromotor according to a second embodiment of the invention;

Fig. 5 shows a section of a chamber shown in figure 4 at the location where the chamber has a minimal volume;

Fig. 6 shows a perspective view of a drum plate with piston sleeves of a pump or hydromotor according to a third embodiment of the invention; and

Fig. 7 shows a section of a chamber shown in figure 6 at the location where the chamber has a minimal volume.

[0011] Fig. 1 and 2 show the internal parts of a hydraulic device, such as a pump or hydromotor, which can be fitted into a housing (not shown) in a known manner. With regard to the method of fitting the internal parts, which will be known to those skilled in the art, reference is here made, for the sake of completeness, to prior publications by the applicant, such as WO 03/058035 and EP 1508694 and to the prior application PCT NL92 050062.

[0012] The internal parts are provided with a first face plate 4 and a second face plate 17 which are fitted inside the housing. Bearings 2 are fitted inside the housing on both sides of the housing. The housing is provided on the one side with an opening with a shaft seal in a known manner, so that the end of a shaft 1, which is provided with a toothed shaft end 18, protrudes from the housing. A motor can be coupled to the toothed shaft end 18 if the hydraulic device is a pump, and a driven tool can be coupled thereto if the hydraulic device is a motor.

[0013] Approximately in the centre between the bearings 2, the shaft 1 is provided with a flange 14. Pistons 13 are fitted on both sides of the flange 14; in the embodiment shown, twelve pistons 13 on either side. The pistons 13 rotate in a plane of rotation 9 which is at right angles to the shaft 1. A piston sleeve 11, 12 is fitted around each piston, the piston sleeve 11, 12 consists of a sleeve bottom 11 and a sleeve jacket 12. The piston sleeve 11, 12 is fastened in a sealing manner around a spherical seal 28, which forms part of the piston 13. On the one side of the pump or hydromotor, the sleeve bottom 11 rests against a first drum plate 7 and on the other side of the pump or hydromotor, against a second drum plate 16. Together with the piston 13 the drum plate 7 or 16 forms with the interior of the piston sleeve 11, 12 a chamber 10. The first drum plate 7 and the second drum plate 16 are fitted around the shaft 1 by means of a ball hinge 23 and are coupled to the shaft 1 by means of coupling means, such as a key connection, so that the first drum plate 7 and the second drum plate 16 rotate with the shaft 1.

[0014] The first drum plate 7 rests on a supporting surface 5 of the tapering first face plate 4 by the side remote from the piston sleeve 11, 12, so that the first drum plate 7 pivots about the ball hinge 23 during rotation with the shaft 1. A wedge angle α is situated between the plane of rotation 9 and the supporting surface 5, so that the rotation axes of the piston sleeves 11, 12 and the piston 13 make a wedge angle α as well. In the embodiment is the wedge angle α approximately 9 degrees.

[0015] A spring plate 24 is connected to the first drum plate 7, another spring plate 24 is connected to the second drum plate 16. The drum plate 24 is provided with spring arms 25 having contact surfaces 15 which press against a top edge 33 of the sleeve jacket 12 on two sides and thus press the piston sleeves 11, 12 against the first drum plate 7 or the second drum plate 16. In the embodiment shown, the contact surfaces 15 are designed as small pads of material having a low sliding resistance which are connected to the spring arms 25 by riveting. In another design the contact surfaces 15 can be formed by local deformation of the spring arm 25.

[0016] The piston sleeves 11, 12 are pressed against the pivoting first drum plate 7 during rotation of the shaft 1, so that the volume of the chamber 10 changes. The chamber 10 is in communication with line connections for the supply and discharge of fluids, such as oil, in a known manner via a drum plate gate 6 and a face plate gate 3.

[0017] If the shaft 1 rotates quickly or if the rotational speed of the shaft 1 changes rapidly, the piston sleeves 11, 12 may tilt about the spherical seal 28 by the effect of centrifugal forces or by the effect of acceleration forces and deceleration forces. This is prevented by the fact that the piston sleeve 11, 12 is pressed against the first drum plate 7 by the spring arms 25. However, if the forces become too great, there would still be a risk of tilting. In order to compensate for the centrifugal forces the piston sleeves 11, 12 are resiliently pushed towards the rotation axis of the drum plate 4 or 16. In the embodiment shown in figure 1 and 2 the sleeve jackets 12 have a groove 34 at the height of the gravity centre of the piston sleeves 11, 12 and a ring shape spring 35 surrounds the piston sleeves 11, 12.

[0018] As shown in figure 3 the piston sleeves 11, 12 move in different more or less elliptical paths 36 on the drum plate 7 or 16 as a result of the rotation of the piston 13 and the wedge angle α between the rotation axes of the pistons and the piston sleeves 11, 12. For an explanation of the different shapes of these paths 36 see the patent application EP 1508694. The projection of the path of the pistons 13 on the plane of the drum plate 7 or 16 is an ellipse and is shown as the interrupted line e. For reasons of clarity the paths 36 of the pistons and the ellipse e are shown in the situation whereby the wedge angle α is 40 degrees. In the embodiment of figure 1 and 2 the wedge angle α is 9 degrees so that the paths of the piston sleeves 11, 12 on the drum plate 16 are considerably smaller.

[0019] It has been found that with a constant wedge angle α the length of the polygon surrounding the piston sleeves 11, 12 is more or less independent of the rotative position of the pistons 13, so the length of the ring shaped spring 35 is more or less constant and the ring shaped spring 35 exerts a more or less constant force in the direction of the rotation axis which compensates the centrifugal force at the piston sleeves 11, 12. In practice the force exerted by the ring shaped spring 35 on the piston sleeve 11, 12 is less than the force exerted by the spring arms 25. Preferably this force is more or less 50% of the force exerted by the spring arms 25 on the piston sleeve 10,11.

[0020] By compensating for the centrifugal force in the above way the tilting is prevented or reduced so that higher rotational speeds of axis 1 are allowable. The spring arms 25 can slide over the top edge 33 of the sleeve jacket 12 and the ring shaped spring 35 can slide in the grooves 34 so that the piston sleeve 11, 12 is able to rotate about its axis and wear resulting from friction between the inside of the sleeve jacket 12 and the spherical seal 28 is distributed evenly over the circumference.

[0021] The piston sleeve 11, 12 seals against the first drum plate 7 having an annular sealing surface 21, which forms part of the side of the sleeve bottom 11 facing the first drum plate 7. In order to further reduce tilting, the outermost circumference of the sleeve bottom 11 forms a supporting surface 22. A relieving groove 20 is provided between the supporting surface 22 and the sealing surface 21 in order to prevent pressure building up between the supporting surface 22 and the drum plate 7. The dimensions of the sealing surface 21 are chosen such that the resultant of all the forces acting on the piston sleeve 11, 12 and depending on the pressure in the chamber 10 more or less equals zero, so that the piston sleeve 11, 12 is pressed against the first drum plate 7 mainly by the force exerted by the contact surfaces 15 in the direction of the first drum plate 7.

[0022] It will be clear to those skilled in the art that the details as discussed in connection with the first face plate 4, the first drum plate 7 and the piston sleeves 11, 12 resting on them apply to the second face plate 17 and the second drum plate 16 in a corresponding manner.

[0023] Fig. 2 shows the piston sleeve 11, 12 and the second drum plate 16 in more detail. The sleeve bottom 11 is provided with a thin clamping edge 27 which is clamped in the inner diameter of the sleeve jacket 12. Radial grooves 32 are provided between the sleeve bottom 11 and the sleeve jacket 12 which ensure that no build-up of pressure occurs between the underside of the sleeve jacket 12 and the sleeve bottom 11. The thin clamping edge 27 is deformable and increases its clamping force as the pressure in the chamber 10 increases, so that the clamping action between the sleeve bottom 11 and the sleeve jacket 12 is maintained even as the pressure increases. Since the clamping edge 27 is thin and the sleeve jacket 12 is much thicker, the clamping edge 27 thus follows the increase in diameter of the sleeve jacket 12 by the effect of the pressure.

[0024] The dimensions of the clamping edge 27 and the supporting surface 21 are in addition matched to one another such that the surface of the clamping edge 27, when viewed as a projection on the drum plate 7, is approximately half the size of the surface of the sealing surface 21. Because the pressure between the chamber 10 and the relieving groove 20 decreases more or less linearly along the drum plate 7, the forces directed at the drum plate 7 acting on the clamping edge 27 are approximately equal to the forces directed away from the drum plate acting on the sealing surface 21 and there are approximately no forces which are dependent on the pressure in the chamber 10 exerted on the piston sleeve 11, 12.

[0025] In the embodiment shown, the piston sleeve 11, 12 is designed in two parts. This has the advantage that both parts can be produced differently and may be made of different materials. The sleeve jacket 12 may be made from tube in a simple manner with the groove 34 and an exactly calibrated inner diameter and a height which is ground to size. Preferably, the sleeve jacket 12 is made of material of as high a stiffness as possible, such as steel, so that as little deformation as possible occurs in the chamber 10 by the effect of the pressure. The sleeve bottom 11 may be made of flat material, the clamping edge 27 being formed by pressing. The chosen material may be a type of bronze as this has good sliding properties and can slide over the drum plate 7 with little resistance. The drum plate 7 may in that case be made from steel and the face plate 4 may, in turn, be for example made from bronze. An additional advantage of the use of bronze as material is that the material is less stiff, as a result of which the clamping edge 27 is better able to follow the increase in diameter of the sleeve jacket 12 when the pressure increases and the clamping between the sleeve jacket 12 and the sleeve bottom 11 is tighter.

[0026] The spring plate 24 is attached to the drum plate 7 or 16 by means of bolts 31 inserted through mounting holes 19. In this case, washers 30 are arranged between the spring plate 24 and the drum plate 7 or 16. By making the washers 30 thicker or thinner, the force used to press the spring arms 25 against the piston sleeve 11, 12 can be adjusted. Fig. 2 also shows a keyway 29 which is arranged in the drum plate 16 and interacts with a key placed in the shaft 1, and which ensures that the drum plate 16 rotates together with the shaft 1.

[0027] Figure 4 and 5 show a second embodiment of the springs that push the piston sleeves 11, 12 towards the rotation axis. A flexible ring 38 is positioned around the second drum plate 16 and is coupled thereto at two facing positions with pins 39, whereby the pins 39 are fixed in the second drum plate 16 and the flexible ring 38 is provided with a slot 40 through which the pin 39 extends. The flexible ring 38 has at the location of each piston sleeve 11, 12 a spring arm 37 which pushes the piston sleeve 11, 12 at the height of its gravity centre towards the rotation axis. The piston sleeves 11, 12 each move in an elliptical path 36 relative to the second drum plate 16 whereby the circumference around all sleeve jackets 12 is more or less elliptical. The spring arms 37 press against the sleeve jackets 12 and as a result of the spring forces the flexible ring 38 takes a similar elliptical shape. Due to the play of the pin 39 in the slot 40 the flexible ring 38 can follow the movements of the sleeve jackets 12, whereby the spring arms 37 have a constant height above the second drum plate 16, so they press at the height of the gravity center of the piston sleeves 11, 12. It will be clear that in a similar way a flexible ring 38 is mounted around the first drum plate 7 for containing the piston sleeves 11, 12 that are supported by the first drum plate 7. The spring arms 37 are designed such that the force on the circumference of a sleeve jacket 12 is approximately half of the force exerted on the top edge 33 of the sleeve jacket 12 by the spring arm 25 on the piston sleeve 10,11.

[0028] Figures 6 and 7 show a third embodiment of springs that push the piston sleeves 11, 12 towards the rotation axis. The flexible ring 38 is connected in the same way as described above around the second drum plate 16. The flexible ring 38 has at the location of the sleeve jacket 12 an opening 41 and at the height of the gravity centre of the piston sleeve 11, 12 the edge of the flexible ring 38 is bent inwards and forms a counter bent strip 42, which presses against the sleeve jacket 12 with a force that is approximately half of the force exerted by the spring arm 25 on the top edge 33 of the sleeve jacket 12. If necessary for making a soft spring the counter bent strip 42 is only fastened to the flexible ring 38 at one end. For the first drum plate 7 the construction is similar.

[0029] In the above embodiments the pump or hydraulic motor has a fixed wedge angle α which leads to a fixed displacement of the pump or motor. In case the pump or hydraulic motor needs a variable displacement in many cases this is achieved by making the wedge angle α variable. In the disclosed embodiments this would mean a wedge angle α which varies between 0 and 9 degrees. In that situation the circumference around the piston sleeves 10,11 is slightly reduced at the maximum wedge angle α when compared to the situation when the wedge angle α is zero. This means that the design of the ring shaped spring 35, the spring arms 37 and the counter bent strip 42 should be so that with this variance in the circumference a proper spring force towards the rotation axis is maintained.

Claims

1. Hydraulic device comprising pistons (13) rotatable in a first plane (9), piston sleeves (11,12) arranged around the pistons in a sealing manner, a drum plate (7,16) rotatable around a rotation axis in a second plane with a drum plate surface for sealingly supporting the piston sleeves, whereby the piston sleeves are resiliently pressed by first spring means (25) against the drum plate surface and whereby the first plane and the second plane intersect forming an angle (α) and the piston, the piston sleeve and the drum plate form a chamber (10) which has a changing volume during rotation of the pistons and whereby the device further is provided with second spring means (35;37;42) that press the piston sleeves at a contact point on the outer circumference of a piston sleeve in direction of the rotation axis.

2. Hydraulic device in accordance with claim 1 whereby the distance between the centre of gravity of a piston sleeve (11,12) and the drum plate surface is more or less equal to the distance between the contact point and the drum plate surface.

3. Hydraulic device in accordance with claim 1 or 2 whereby the spring force exerted on a piston sleeve (11,12) by the first spring means (25) is greater than the force exerted on the piston sleeve by the second spring means (35;37;42).

4. Hydraulic device in accordance with claim 3 whereby the spring force exerted on the sleeve by the first spring means (25) is approximately twice the force exerted on the sleeve by the second spring means (35; 37; 42).

5. Hydraulic device in accordance with claim 1, 2, 3 or 4 whereby the second spring means are attached to a flexible ring (35;38) surrounding the piston sleeves (11,12).

6. Hydraulic device in accordance with claim 5 whereby the second spring means are formed by the ring (35), whereby the ring is elastically extendable and placed around the contact points.

7. Hydraulic device in accordance with claim 6 whereby the piston sleeves (11,12) have a groove (34) on the outside circumference for positioning the ring (35).

8. Hydraulic device in accordance with claim 5 whereby the ring has coupling means (39,40) for positioning the ring relative to the drum plate (7,16) and is provided with springs (37;42) that are connected to the ring (38) in such a way that each spring presses against a contact point.

9. Hydraulic device in accordance with claim 8 whereby the springs (37;42) are bended parts of the flexible ring.

Drawing