EP1766247A1

EP1766247A1 - Hydraulic cylinder

Info

Publication number: EP1766247A1
Application number: EP05742443A
Authority: EP
Inventors: Nigel Moorcroft; Trevor Hornsby; Raymond Hardy
Original assignee: Parker Hannifin PLC
Current assignee: Parker Hannifin Manufacturing Ltd
Priority date: 2004-05-14
Filing date: 2005-05-06
Publication date: 2007-03-28
Also published as: GB2414043A; GB0410848D0; WO2005111432A1

Abstract

A hydraulic cylinder (10) is disclosed. The hydraulic cylinder has a tube (20) provided with a cap (30) attached to a first axial end portion of the tube (20) and a head (40) attached to the other axial end portion of the tube (20). A piston (55) is slideable axially within the tube (20) and is arranged to seal against the inside surface of the tube as it slides. The piston (55) has a rod (60) attached thereto which passes through and seals against the head (40) as it moves with the piston (55). Conduits (31, 41) are provided to be connected, in use, to sources of hydraulic fluid via suitable supply lines to control fluid pressure on at least one side of the piston (55) within the tube (20) to control axial movement of the piston (55) within the tube (20). End portions (21, 22) of the tube (20) are mechanically formed into engagement with at least one of the cap (30) and the head (40) to fix the tube in a permanent and fluid tight manner thereto. A method of assembling a hydraulic cylinder (10) is also disclosed.

Description

HYDRAULIC CYLINDER

The present invention relates to a hydraulic cylinder and to a method of assembling a hydraulic cylinder.

Hydraulic cylinders are used in a variety of applications, such as in mobile industries including mechanical diggers, bulldozers and fork-lift trucks to provide movement of articulated arms, scoops, lifting apparatuses etc. Hydraulic cylinders are also used in industrial applications such as for various types of machines, pumps etc.

Hydraulic cylinders generally comprise a tube provided with a cap attached to a first axial end portion of the tube and a head attached to the other axial end portion of the tube. A piston is provided within the tube with the piston being slidable axially within the tube. The piston is arranged to seal against the inside surface of the tube as it slides and has a rod attached thereto which passes through and seals against the head as it moves with the piston. One or more conduits are provided through which, in use, fluid is applied to control fluid pressure on at least one side of the piston within the tube to force the piston back and forth within the tube to thus also force the rod back and forth to perform some useful function, such as those described earlier.

The cap and head are generally attached to the tube by welding or via a threaded connection. However, welded connections are susceptible to failure by weld fatigue, are generally time consuming to prepare and the produced weld is sensitive to decontamination. Threaded connections are generally rather expensive to produce and are, at least to some extent, susceptible to fatigue.

It is an aim of the present invention to provide a hydraulic cylinder and a method of assembling a hydraulic cylinder which alleviates or overcomes at least some of the problems discussed above. According to a first aspect of the present invention, there is provided a hydraulic cylinder comprising a tube provided with a cap attached to a first axial end portion of the tube, a head attached to the other axial end portion of the tube, a piston provided within the tube, the piston being slidable axially within the tube, being arranged to seal against the inside surface of the tube as it slides and having a rod attached thereto which passes through and seals against the head as it moves with the piston and one or more conduits through which, in use, fluid is applied to control fluid pressure on at least one side of the piston within the tube, wherein the tube is mechanically formed into engagement with at least one of the cap and the head to fix the tube in a permanent and fluid tight manner thereto.

Mechanically forming (crimping) the tube into engagement with at least one of the cap and the head provides a reliable joint which is less expensive and simpler than either welded or threaded joints and has greater resistance to fatigue.

The head preferably has a bore through which the rod passes, with at least a portion of the bore having sufficient clearance from the rod to accommodate any deformation produced by the mechanical deformation of the tube into it, such that it will not be deformed into such a position that it would otherwise obstruct, impede or engage any moving parts of the hydraulic cylinder such as the rod.

The head preferably has a bore with a first portion with at least one annular rod seal to seal against the outside surface of the rod and a second portion axially aligned with the portion of the head onto which the tube is mechanically formed, wherein the annular rod seal is axially spaced from the second portion of the bore. The axial spacing prevents the mechanical deformation from adversely affecting the annular rod seal. The axial spacing may be at least 10mm, at least 8mm, at least 6mm, at least 4mm or at least 3mm for example. The second portion of the bore may have a wider diameter than the first portion of the bore. The at least one of the cap and the head with which the tube is mechanically formed preferably has an annular groove formed in its outer surface into which the tube is mechanically deformed. The groove preferably includes a sharp entry radius and a curved sidewall to the bottom of the groove. The sharp entry radius provides enhanced fatigue resistance and the curve reduces tensile stress.

The at least one of the cap and the head with which the tube is mechanically deformed preferably has a radially outward projecting flange to engage an end of the tube to which it is attached to locate the at least one of the cap and the head relative to the tube so that appropriate predetermined portions of the tube and the at least one of the cap and the head are mechanically formed into engagement.

The tube may be mechanically formed into engagement with one of the cap and the head and screw threaded to the other of the cap and the head to enable the screw threaded portion to be removed when required such as for maintenance.

According to a second aspect of the present invention, a method of assembling a hydraulic cylinder comprises providing a tube, inserting a cap into one end of the tube, inserting a head with a rod arranged therein into the other end of the tube with the rod having a piston at one end to reciprocate within the tube and to seal against the inside surface of the tube and mechanically forming the tube into engagement with at least one of the cap and the head to fix the tube in a permanent and fluid tight manner thereto.

An example of the present invention will now be described with reference to the accompanying drawings, in which: Figure 1 shows a perspective view of a hydraulic cylinder illustrating the present invention; Figure 2 shows a cross-sectional view of the hydraulic cylinder shown in Figure 1 ; Figure 3 shows a perspective view of a cap to be provided at one end of a hydraulic cylinder; Figure 4 shows a cross-sectional view of the cap shown in Figure 3; Figure 5 shows a perspective view of a head to be provided at the other end of a hydraulic cylinder and Figure 6 shows a cross-sectional view of the head shown in Figure 5.

As shown in Figures 1 and 2, a hydraulic cylinder 10 comprises a tube 20 provided with a cap 30 attached to a first axial end portion of the tube 20 and a head 40 attached to the other axial end portion of the tube 20. As shown in the cross-sectional view of the hydraulic cylinder 10 of Figure 2, a piston 55 is slidable axially within the tube 20 and is arranged to seal against the inside surface of the tube 20 as it slides. The piston 55 has a rod 60 attached thereto which passes through and seals against the head 40 as it moves with the piston 55. Conduits 31, 41 are provided to be connected, in use, to sources of hydraulic fluid via suitable supply lines (not shown) to control fluid pressure on at least one side of the piston 55 within the tube 20 to control axial movement of the piston 55 within the tube 20. As shown in Figure 2, end portions 21, 22 of the tube 20 are mechanically formed or crimped into engagement with the cap 30 and the head 40 to fix the tube in a permanent and fluid tight manner to the cap 30 and the head 40. If desired, only one end portion of the tube 20 may be mechanically formed into engagement with one of the cap 30 and head 40. The other end portion of the tube 20 may then be connected to the cap 30 or head 40 as appropriate by some other means such as a screw thread (not shown) to enable it to be removed when required such as for maintenance.

As shown in Figures 2, 3 and 4, cap 30 is provided with an annular groove 32 formed on an outer surface of a portion of the cap 30 to be inserted into the tube 20. The annular groove 32 has the first end portion 21 of the tube 20 mechanically deformed into it in a permanent and fluid type manner. The annular groove 32 has a sharp entry radius 33 to provide enhanced fatigue resistance and a curved sidewall 34 to the bottom of the groove to reduce tensile stress.

The cap 30 has a radially outward projecting flange 35 to engage the end of the first end portion 21 of the tube 20 into which it is inserted. The flange 35 locates the inserted cap 30 relative to the tube 20 in a predetermined manner so that the first end portion 21 of the tube 20 can be mechanically deformed into the annular groove 32 which will be at a known position relative to the first end portion 21 of the tube 20. This provides reliable and consistent mechanical deformation of the first end portion 21 of the tube 20 into the annular groove 32 of the cap 30 to provide a reliable connection.

The cap 30 is provided with an annular seal 36 to seal against the inside surface of the tube 20. The annular seal 36 is provided a sufficient axial distance away from the point at which the tube 20 is deformed (in this example at groove 32) to not be detrimentally affected by the mechanical deformation of the tube 20. In this example annular seal 36 is in the form of an O-ring.

The cap 30 is provided with a bearing 37, in this example a radial spherical plain bearing, to enable the cap 30 of the hydraulic cylinder 10 to be secured to a suitable component, such as the body of a vehicle for example. A grease nipple 38 is provided to lubricate the bearing.

At the other end of the tube 20 from the cap 30 is the head 40. Like the cap 30, in this example, the head 40 is provided with an annular groove 42 formed on an outer surface of a portion of the head 40 to be inserted into the tube 20. The annular groove 42 has the second end portion 22 of the tube 20 mechanically deformed into it into in a permanent and fluid tight manner. The annular groove 42 has a sharp entry radius 43 to provide enhanced fatigue resistance and a curved sidewall 44 to the bottom of the groove 42 to reduce tensile stress. The head 40 has a bore 45 through which the rod 60 is passed. The bore 45 has a predetermined minimum diameter to provide a clearance around the rod 60 and to accommodate any internal deformation that may result from the deformation of the tube 20 onto the head 40 so that it will not obstruct, impede or engage the rod 60. The bore 45 of the head preferably has a clearance of at least 3mm from the outside surface of the rod 60, but may have a clearance of at least 2mm or at least 1mm if distortion of the head 40 is likely to be less severe.

The head 40 has a radially outward projecting flange 46 to engage the end of the second end portion 22 of the tube 20 into which it is inserted. Like the flange 35 on the cap, the flange 46 locates the inserted head 40 relative to the tube 20 in a predetermined manner so that the second end portion 22 of the tube 20 can be mechanically deformed into the annular groove 42 which will be at a known position relative to the second end portion 22 of the tube 20. This provides reliable and consistent mechanical deformation of the second end portion 22 of the tube 20 into the annular groove 42 of the head 40 to provide a reliable connection.

The head 40 is provided with an annular seal 47 to seal against the inside surface of the tube 20. The annular seal 47 is provided a sufficient axial distance away from the point at which the tube 20 is deformed (in this example at groove 42) so that it is not detrimentally affected by the mechanical deformation of the tube 20. In this example annular seal 47 is

The head 40 has an annular rod seal 48 to seal against the outside surface of the rod 60. The annular rod seal 48 is provided a sufficient axial distance away from the point at which the tube 20 is deformed (in this example at groove 42) so that it is not detrimentally affected by the mechanical deformation of the tube 20. The annular rod seal 48 is preferably at least 10mm from the deformation of the tube 20, but could be closer, such as at least 8mm, at least 6mm, at least 4mm or at least 3mm. In this example annular rod seal 48 is in the form of an O-ring. A wear ring 49 is provided on one side of the annular rod seal 48 and a wiper ring 50 is provided on the other side of the annular rod seal 48.

Piston 55 has a generally smooth outer surface with one or more annular channels or grooves formed therein to receive a sealing ring 56 and a wear ring 57 to maintain a fluid tight seal as the piston reciprocates in the tube 20.

A first end portion 61 of rod 60 is secured to and supported by the piston 55 and the other second end portion 62 of rod 60 is passed through the annular rod seal 48 in head 40 so that the rod is supported concentrically within the tube 20. The second end portion 62 of rod 60 supports a rod end 63 with a bearing 64 to enable the rod 60 to be secured to a suitable component, such as an articulated arm of a vehicle for example. A grease nipple 65 is provided to lubricate bearing 62.

Figure 3 shows a perspective view of the cap 30 and Figure 4 shows a cross-sectional view in which some of the details can be seen more clearly. The shape of the groove 32 in particular with its sharp entry radius 33, curved sidewall 34 and flat bottom is clearly visible.

Figure 5 shows a perspective view of the head 40 and Figure 6 shows a cross-sectional view in which some of the details can be seen more clearly. Like the groove 32 in the cap 30, the groove 42 with its sharp entry radius 43, curved sidewall 44 and flat bottom is clearly visible. The annular rod seal 48, wear ring 49 and wiper ring 50 are also clearly shown. The bore 45 is shown having a narrower diameter 45a in the area of the head which is not subject to deformation, in this example incorporating annular rod seal 48, and a wider diameter 45b in the portion of the head 40 into which the tube 20 is deformed. The bore 45 has a wider diameter portion 45b to accommodate any possible deformation of this portion of the head 40 when the tube 20 is mechanically deformed into engagement with it, such that it will still not obstruct, impede or engage the rod 60. The annular rod seal 48 is provided in a portion of the head 40 which is not subject to deformation so that the seal between the head 40 and rod 60 is not compromised. The difference in diameter between the narrower diameter portion 45 a and the wider diameter portion 45b will depend upon the likely extent of deformation of the wider diameter portion 45b during mechanical engagement of the tube 20. However, it can be 1mm or more, 2mm or more, 3mm or more, 4mm or more or 5mm or more for example.

The hydraulic cylinder 10 shown in Figure 1 is assembled by providing a tube 20, inserting a cap 30 into one end of the tube 20 and a head 40 with a rod 60 arranged therein into the other end of the tube 20. The rod 60 has a piston 55 at one end to reciprocate within the tube 20 and to seal against the inside surface of the tube 20. Each end of the tube 20 with the cap 30 or head 40 inserted therein is then inserted into the jaws of a crimping machine and mechanically formed into engagement with the cap 30 and head 40.

Many variations may be made to the example described above whilst still falling within the scope of the present invention. For example, only one end of the tube 20 need be mechanically deformed into engagement with the cap 30 or head 40, with the other end being engaged in some other way, for example using a screw thread to enable subsequent removal. For example the tube 20 may be mechanically formed into engagement with the head 40 and screw threaded with the cap 30. Conduit 41 could be omitted with fluid only provided via conduit 31 and if desired a resilient member such as a spring provided to urge the piston 55 towards the cap 30.

Claims

1. A hydraulic cylinder comprising a tube provided with a cap attached to a first axial end portion of the tube, a head attached to the other axial end portion of the tube, a piston provided within the tube, the piston being slidable axially within the tube, being arranged to seal against the inside surface of the tube as it slides and having a rod attached thereto which passes through and seals against the head as it moves with the piston, and one or more conduits through which, in use, fluid is applied to control fluid pressure on at least one side of the piston within the tube, wherein the tube is mechanically formed into engagement with at least one of the cap and the head to fix the tube in a permanent and fluid tight manner thereto.

2. A hydraulic cylinder according to claim 1, wherein the head has a bore through which the rod passes, with at least a portion of the bore having sufficient clearance from the rod to accommodate any deformation produced by the mechanical formation of the tube onto the head.

3. A hydraulic cylinder according to claim 2, wherein the bore has a first portion with at least one annular rod seal to seal against the outside surface of the rod and a second portion axially aligned with the portion of the head onto which the tube is mechanically formed, wherein the annular rod seal is axially spaced from the second portion of the bore.

4. A hydraulic cylinder according to claim 3, wherein the annular rod seal is axially spaced at least 10mm from the second portion of the bore.

5. A hydraulic cylinder according to claim 3 or claim 4, wherein the second portion of the bore has a wider diameter than the first portion of the bore.

6. A hydraulic cylinder according to any one of the preceding claims, wherein the at least one of the cap and the head with which the tube is mechamcally formed has an annular groove formed in its outer surface into which the tube is mechanically formed.

7. A hydraulic cylinder according to claim 6, wherein the groove has a sharp entry radius and a curved sidewall to the bottom of the groove.

8. A hydraulic cylinder according to any one of the preceding claims, wherein the at least one of the cap and the head with which the tube is mechanically formed has a radially outward projecting flange to engage an end of the tube to which it is attached.

9. A hydraulic cylinder according to any one of the preceding claims, wherein the tube is mechamcally formed into engagement with one of the cap and the head and screw threaded to the other of the cap and the head.

10. A method of assembling a hydraulic cylinder, the method comprising providing a tube, inserting a cap into one end of the tube, inserting a head with a rod arranged therein into the other end of the tube with the rod having a piston at one end to reciprocate within the tube and to seal against the inside surface of the tube and mechanically forming the tube into engagement with at least one of the cap and the head to fix the tube in a permanent and fluid tight manner thereto.

11. A method of assembling a hydraulic cylinder according to claim 10, wherein one end of the tube is mechanically formed into engagement with one of the cap and the head and the other end of the tube is screw threaded to the other of the cap and the head.

2. A method of assembling a hydraulic cylinder according to claim 10 or 11 , wherein the tube is mechanically formed into engagement with the at least one of the cap and the head by being inserted into the jaws of and acted upon by a crimping machine.