Telescopic hydraulic cylinder

Abstract

 The invention concerns a telescopic hydraulic cylinder comprising two or more concentric cylindrical tubes (14,20,21,22,23) and a piston (19); seals (37) between the cylindrical tubes and the piston whereby the cylindrical tubes and the piston can move in axial direction relative one another between a retracted position and an extended position, for in the extended position limiting further extending axial movement an inner tube (20,21,22,23) or piston has an outer stop ring (35) mounted in an outer groove in its outer surface and an outer tube or base tube has an inner stop ring (36) mounted in an inner groove in its inner surface. In accordance with the invention adjacent to the outer groove there is an outer relieve groove.

Description

[0001] The invention concerns a telescopic hydraulic cylinder in accordance with the preamble of claim 1. In the known telescopic hydraulic cylinders a sideways force on an extended piston or tube that results in a bending moment in the lower end of an inner tube and a similar bending moment in the adjacent top end of a concentric outer tube. This bending moment leads to bending stress in the tube and stress concentration in a sharp corner of the inner groove might lead to rupture of the tube. High fluid pressure in the telescopic hydraulic cylinders increases the risk of rupture as the high fluid pressure also leads to stress in the tubes and this adds to the bending stress. The stress concentration in the inner groove also applies to this added stress.

[0002] In order to increase the resistance of the telescopic hydraulic cylinder against bending forces the telescopic hydraulic cylinder is according to claim 1. In this way, stress concentration in a high loaded part of the tubes is avoided and the resistance against bending increases.

[0003] In accordance with an embodiment, the telescopic hydraulic cylinder is according to claim 2. In this way, the resistance against bending is further increased.

[0004] In accordance with an embodiment, the telescopic hydraulic cylinder is according to claim 3. In this way, the inner relief groove and/or the outer relief groove are not subjected to the axial load on the tubes but only to the bending moment in the tubes.

[0005] In accordance with an embodiment, the telescopic hydraulic cylinder is according to claim 4. In this way, the relief grooves are most effective for relieving the stress without reducing the minimum section surface of the tube.

[0006] In accordance with an embodiment, the telescopic hydraulic cylinder is according to claim 5. In this way, the minimum section surface of the tubes gradually increases thereby avoiding sudden increases that might lead to stress concentrations.

[0007] In accordance with an embodiment, the telescopic hydraulic cylinder is according to claim 6. In this way, the contact area between the stop rings in extended position is large so that surface stress between the stop rings is reduced.

[0008] In accordance with an embodiment, the telescopic hydraulic cylinder is according to claim 7. In this way, the inner stop ring groove and/or the outer stop ring groove are smaller, less deep and give less stress concentration.

[0009] In accordance with an embodiment, the telescopic hydraulic cylinder is according to claim 8 or 9. In this way, the tube has a small wall thickness so that the weight of the telescopic hydraulic cylinder is reduced.

[0010] The invention is explained with the aid of one or more embodiments using a drawing. In the drawing

Figure 1 shows a perspective view of a kipper with a telescopic hydraulic cylinder lifting a tipping body,

Figure 2 shows a perspective view of the telescopic hydraulic cylinder for lifting the tipping body,

Figure 3 shows a section of the telescopic hydraulic cylinder of figure 2 in retracted position,

Figure 4 shows a detail of the transition between two tubes of the telescopic hydraulic cylinder of figure 2 in extended position, and

Figure 5 shows various embodiments of the relief groove of a tube of the telescopic hydraulic cylinder of figure 2.

[0011] Figure 1 shows a kipper 1 comprising a tractor 4 and a trailer 5. A hinge 8 connects a frame of the trailer 5 and a tipping body 2 and a telescopic hydraulic cylinder 3 can lift the tipping body 2 to a tilted position for unloading the tipping body 2. The trailer 5 has axles with wheels to support the frame of the trailer 5 on the terrain. The terrain might have mounds 6, so that a rear axle 7 and with that the hinge 8 can be slightly inclined whereby the trailer 5 has a slight twist. The inclination of the hinge 8 can cause sideways movement of the tipping body 2 relative to the trailer 5 and in extreme situations this might lead to rolling over of the kipper 1 during lifting of the tipping body 2. By giving support to the tipping body 2 in a direction transverse to the trailer 5 the telescopic hydraulic cylinder 3 can reduce the sideways movement of the tipping body 2 relative to the trailer 5 during tipping.

[0012] Figure 2 and figure 3 show the telescopic hydraulic cylinder 3. Two chassis brackets 13 are mounted on the trailer 5 and support two chassis trunnions 12 that support a base tube 14. The base tube 14 can swivel around a base tube swivel axis 28 in the chassis brackets 13; the base tube swivel axis 28 is mounted parallel to the axis of hinge 8. The base tube 14 has a centreline 24, a bottom plate 29, and a high-pressure connection 15. A tube 23 can slide in the direction of the centreline 24 in the base tube 14. A tube 22 can slide in the direction of the centreline 24 in the tube 23. A tube 21 can slide in the direction of the centreline 24 in the tube 22. A tube 20 can slide in the direction of the centreline 24 in the tube 21. In retracted position of the telescopic hydraulic cylinder 3, the bottom plate 29 can support the tubes 20, 21, 22, and 23. A piston 19 can slide in the tube 20 in the direction of the centreline 24. The shown embodiment has four tubes that can slide relative to the piston 19 and the base tube 14, in other embodiments, this number of tubes can have any value above zero.

[0013] The piston 19 is made from a tube and is closed at the underside by a plate 30 and at the top by a plug 17. The plug 17 and a top plate 18 are connected and the top plate 18 is connected to a cover tube 9. A spherical ring 27 that is coupled to the cover tube 9 supports a lifting ring 16 with lifting trunnions 11 that swivably connect the lifting ring 16 to lifting brackets 10. The lifting ring 16 can rotate around a top swivel axis 25. The lifting brackets 10 couple the telescopic hydraulic cylinder 3 to the tipping body 2, whereby the top swivel axis 25 and the base tube swivel axis 28 are parallel to the axis of the hinge 8. A spherical bearing 27 between the lifting ring 16 and the spherical ring 27 compensates for alignment errors between the top swivel axis 25, the base tube swivel axis 28 and the axis of the hinge 8. As described the tipping body 2 and the piston 19 are coupled and the position of the tipping body 2 determines the position of the piston 19 in the telescopic hydraulic cylinder 3.

[0014] The base tube 14 and the tubes 20, 21, 22, and 23 have near the top end of their inside surface a groove into which a seal 37 is mounted to seal the gap between the base tube 14, the tubes 20, 21, 22, or 23 or the piston 19. Each seal 37 can slide over an outside surface of an adjacent tube 20, 21, 22, or 23 or the outside surface of the piston 19 and the seals 37 are suitable for the high pressure in the telescopic hydraulic cylinder 3 and seal the area inside the telescopic hydraulic cylinder 3 from the surroundings. The wipers 40, mounted in a groove at the top end of the inside surfaces of the base tube 14 and the tubes 20, 21, 21, 22, and 23, remove contaminations from the outside surfaces of the tubes 20, 21, 22, and 23 and the piston 19 and prevent dirt entering the gaps. For guiding the piston 19, the tubes 20, 21, 22, and 23 and the base tube 14 relative one another the inside surfaces have an upper wear ring 39 mounted at the top in grooves, under the upper wear ring 39 a lower wear ring 38, and at the bottom mounted in grooves in the outside surfaces a slider 33. The upper wear rings 39 and the lower wear rings 38 are mounted between the seal 37 and the wiper 40.

[0015] Filling the telescopic hydraulic cylinder 3 with pressurised fluid through the high pressure connection 15 causes the pressurized fluid to enter in the gaps between the base tube 14, the tubes 20, 21, 22, 23 and the piston 19 through holes 34 to the room between the piston 19 and the bottom plate 29. The pressurized fluid pushes the piston 19 and tubes 20, 21, 22, and 23 surrounding the piston 19 upwards. Inner lift rings 31 that interact with outer lift rings 32 or with a slider 33 ensure that the tubes 20, 21, 22 and 23 move together with the piston 19 in outward direction. The inner lift rings 31 are mounted in grooves in the inside surface of the tubes 20, 21, 22, and 23. The outer lift rings 32 are mounted in grooves in the outside surfaces of the piston 19 and the tubes 20 and 21. The slider 33 in tube 22 acts in a similar manner as an outer lift ring 31.

[0016] The upward movement of the tube 23 stops when an outer stop ring 35 of the tube 23 interacts with an inner stop ring 36 of the base tube 14 and the tube 23 has reached its maximum extension. The outer stop rings 35 are mounted in grooves in the outer surfaces of the piston 19 and the tubes 20, 21, 22, and 23. The inner stop rings 36 are mounted in grooves in the inner surface of the base tube 14 and the tubes 20, 21, 22, and 23.

[0017] Further filling of the telescopic hydraulic cylinder 3 with pressurized fluid pushes the piston 19 and tubes 20, 21, and 22 upwards until an outer stop ring 35 of the tube 22 interacts with an inner stop ring 36 of tube 23 and tube 22 has its maximum extension. Further filling of the telescopic hydraulic cylinder 3 brings one after the other tube 21, tube 20, and the piston 19 to their maximum extension. The telescopic hydraulic cylinder 3 then has its maximum extension and the tipping body 2 has its maximum tipping position.

[0018] Releasing pressurized fluid from the extended telescopic hydraulic cylinder 3 causes the piston 19 to move downwards in the tube 20 until the underside of the piston 19 interacts with an inner lift ring 31 of the tube 20. Further releasing of pressurize fluid causes the piston 19 and tube 20 to move downwards until an outer lift ring 32 of tube 20 interacts with an inner lift ring 31 of tube 21. In a similar way the tubes 21, 22 and 23 retract in the base tube 14 until the telescopic hydraulic cylinder 3 is in its retracted position.

[0019] Figure 4 shows the transition between tube 22 and tube 23 when they are in extended position and the inner stop ring 36 and the outer stop ring 35 interact. The shown transition is exemplary for the other transitions between the base tube 14, the tubes 20, 21, 22 and 23, and the piston 19 and the shown transition is similar between the other tubes 20, 21, the base tube 14, and the piston 19. As discussed earlier the telescopic hydraulic cylinder 3 stabilises the transversal movement of a lifted tipping body 2 by exerting a transverse force F_H on the tipping body 2. This transverse force F_H causes a bending moment M in the extended telescopic hydraulic cylinder 3 and this bending moment M is highest near the trailer 5. This bending moment M causes bending of the tubes 14, 20, 21, 22 and 23 in the longitudinal direction and deformation of the circular section of the tubes 14, 20, 21, 22 and 23 to a slightly oval section. This means that the bending moment M causes bending stress in the base tube 14 and the tubes 20, 21, 22, and 23.

[0020] At the location of the transition between tube 22 and tube 23, the bending moment is indicated as bending moment M_22-23. The bending moment M_22-23 causes a force P between the upper wear ring 39 and the outer surface of tube 22 and a force Q between the slider 33 and the inner surface of tube 23. This means that between the upper wear ring 39 and the slider 33 both tubes 22, 23 have to transfer the bending moment M_22-23 and both tubes are there subjected to the bending stress. In that area, the grooves of the outer stop ring 35 and the inner stop ring 36 reduce the strength of the tubes 22, 23 the grooves form the weakest part of the tubes, especially for the inside tube 22 that has the smallest diameter. As the tubes in the telescopic hydraulic cylinder 3 have relative thin walls in order to reduce its weight, the grooves can have a depth of more than 20 % of the wall thickness of the tube 22,23 for the outer groove and more than 25% of the inner groove to make it possible that the stop rings 35,36 transmit the axial forces between the adjacent tubes 22,23. A relief groove 41 reduces the stress in the bottom of the groove of the outer stop ring 35 and so reduces the risk of damages. In another embodiment, there is a relief groove 41 both adjacent to the groove of the outer stop ring 35 and adjacent to the groove of the inner stop ring 36.

[0021] Figure 5 shows various embodiments of the relief groove 41 in an outer surface of a tube. Figure 5a shows an embodiment wherein a small ridge limits the axial movement of the outer stop ring 35 and wherein the groove has a depth that is approximately equal to the depth of the groove for the outer stop ring 35. Figure 5b shows an embodiment with a relief groove 41 with a large radius form the bottom of the groove for the outer stop ring 35 to the outside diameter with a width of at least the twice the width of the groove for the outer stop ring 35. Figure 5c shows a similar embodiment with a relief groove 41 with a conical surface. The minimum diameter of the relief groove 41 is approximately equal to the diameter of the groove for the outer stop ring 35. In these latter embodiments, the outer stop ring 35 clamps around the tube to prevent axial movement. Figure 5d shows an embodiment of the relief groove 41 with a depth that is approximately equal to the depth of the groove for the outer stop ring 35 and that has a width that smaller than its depth and of which the bottom is a radius. As indicated with interrupted lines in figure 5d, in another embodiment a second and possibly a third narrow relief groove is adjacent to the first relief groove 41 wherein the second groove and the third groove have a decreasing depth. In the inner surface of a tube, the relief grooves will have similar dimensions.

Claims

1. Telescopic hydraulic cylinder (3) comprising two or more concentric cylindrical tubes (14,20,21,22,23) and a piston (19), seals (37) between the cylindrical tubes and the piston whereby the cylindrical tubes and the piston can move in axial direction relative one another between a retracted position and an extended position, for in the extended position limiting further extending axial movement an inner tube (20,21,22,23) or piston has an outer stop ring (35) mounted in an outer groove in its outer surface and an outer tube or base tube has an inner stop ring (36) mounted in an inner groove in its inner surface characterized in that adjacent to the outer groove there is an outer relieve groove (41).

2. Telescopic hydraulic cylinder in accordance with claim 1 wherein adjacent to the inner groove there is an inner relieve groove.

3. Telescopic hydraulic cylinder in accordance with claim 1 or 2 wherein the outer relieve groove (41) is at the side of the outer groove away from the end of the tube and/or the inner relieve groove is at the side of the inner groove away from the end of the tube.

4. Telescopic hydraulic cylinder in accordance with claim 1, 2 or 3 wherein the outer relief groove (41) has a depth that is approximately equal to the depth of the outer groove and/or the depth of the inner relief groove has a depth that is approximately equal to the depth of the inner groove.

5. Telescopic hydraulic cylinder in accordance with claim 4 wherein the outer relief groove (41) has a width of at least twice the width of the outer groove and/or the inner relief groove has a width of at least twice the width of the inner groove.

6. Telescopic hydraulic cylinder in accordance with one of the previous claims wherein the inner stop ring (36) and/or the outer stop ring (35) have a rectangular section.

7. Telescopic hydraulic cylinder in accordance with one of the previous claims wherein the inner stop ring and/or the outer stop ring have a hexagonal section.

8. Telescopic hydraulic cylinder in accordance with one of the previous claims wherein the outer groove has a depth of more than 20% or more than 30% of the wall thickness of the tube.

9. Telescopic hydraulic cylinder in accordance with one of the previous claims wherein the inner groove has a depth of more than 15% or more than 25 % of the wall thickness of the tube.

Drawing