GB2605451A

GB2605451A - Hydraulic cylinder cushioning

Info

Publication number: GB2605451A
Application number: GB2104754.3A
Authority: GB
Inventors: Lakshminarayanan Rameshkrishnan; Steven Goslovich Kurt
Original assignee: Caterpillar Global Mining LLC
Current assignee: Caterpillar Global Mining LLC
Priority date: 2021-04-01
Filing date: 2021-04-01
Publication date: 2022-10-05
Anticipated expiration: 2041-04-01
Also published as: AU2022201886A1; GB202104754D0; GB2605451B

Abstract

A pin assembly 47 for a piston of a hydraulic cylinder (30, Figure 2) is provided. The pin assembly 47 provides cushioning for the cylinder. The pin assembly 47 comprises: a pin 48; a floating bush 60 mounted on the pin 47; and a locking nut 90 releasably engaged with the pin 47. The floating bush 60 is movable radially and axially and has a tapered section (70, Figure 5) having first and second tapered portions (71, 72 Figure 5) comprising first and second taper angles (α1, α2 Figure 5) with the angle of taper of the first portion is less than the angle of taper of the second portion. A hydraulic cylinder incorporating such a pin assembly is also disclosed.

Description

HYDRAULIC CYLINDER CUSHIONING

Technical Field

The present disclosure relates to hydraulic cylinder cushioning, and more particularly to a pin assembly for a piston of a hydraulic cylinder, which provides cushioning.

Background

Conventionally machines which perform digging or loading functions, such as backhoe loaders, excavators and mining shovels, may have an implement assembly controlled by an operator via hand operated levers or other control devices. Typically, the control devices are coupled to a linkage assembly. A movement in the control devices may be transmitted to a hydraulic valve assembly via the linkage assembly to actuate one or more hydraulic cylinders associated with the operation of the implement assembly. Generally, the hydraulic valve assembly may be coupled to the linkage assembly via a linkage joint. The hydraulic valve system may move the hydraulic pistons in two directions with great force, enabling significant loads to be moved.

When pressurised fluid is directed into the rod end of a hydraulic cylinder, this causes the cylinder to retract (the retracting stroke) and when pressurised fluid is directed into the cap end; this causes the cylinder to exlend (the extending stroke). When the hydraulic cylinders reach the end of their stroke, the pressure rises quickly, creating a shock wave in the hydraulic circuit. The area, of the rod end piston face (i.e. the face of the piston which is attached to the rod) is generally smaller than that of the cap end piston face (i.e. the face of the piston which is no attached to the rod), so the extension force is generally greater lhan retraction force. Furthermore, the total cylinder volume is less with the cylinder fully retracted; due to the presence of the rod within the cylinder, than when the cylinder is fully extended. As such, a cylinder generally retracts faster than it extends. As a consequence. the hydraulic cylinders used in such machines may be subjected to significant shock loads, as they may have to stop high inertial forces at the end of a stroke, particularly at the cap end of the cylinder when the cylinder is retracting.

Hydraulic cylinders may therefore be provided with cushioning, to reduce this shock and to prevent structural damage to the cylinders and to the load being moved. The cushioning may be provided by a pin assembly (also known as a cushion assembly), usually located in the cap end, so that the cap end piston face does not collide with the cap end. The pin assembly may provide a damping effect to the movement of the piston as it approaches the cap end, thereby avoiding heavy end impact loads and preventing shock waves and vibration loads being transmitted to the machine and the operator. Such cushioning may help to increase structural life of the hydraulic cylinder and the machine components.

US-B-9784292 describes a pin assembly which uses a cylindrical floating bush, which aligns with the cap port of the cylinder housing prior to entering the cap port, and which dampens the movement of the piston towards the cap end of the hydraulic cylinder housing. As the floating bush enters the cap port, it creates an additional resistance to the fluid leaving the piston chamber, providing deceleration of the piston. The floating bush is located about a sleeve which surrounds the support pin. The sleeve holds the floating bush in position.

However there is always a need to provide improved cushioning for hydraulic cylinders to further improve the life of the hydraulic cylinder and machine components, to prevent damage to the hydraulic cylinder and machine components, to provide better operator comfort and to enable ease of service, especially for machines which may be required to move significant payloads.

Summary

According to the present disclosure there is provided pin assembly for a piston of a hydraulic cylinder. The pin assembly comprises a pin, a floating bush and a locking nut. The pin comprises a pin body, a flanged portion at a first end of the pin body, a piston engaging portion projecting axially from the flanged portion configured to releasably engage with a piston of a hydraulic cylinder, and a locking section projecting axially from an opposing second end of the pin body. The locking nut is configured to releasably engage with the locking section. The floating bush has an first surface having an inwardly tapered section. The floating bush is disposed about the pin body and is movable radially and axially relative to the pin body between the flanged portion and the locking nut and a fluid passage is defined between a second surface of the floating bush and a surface of the pin body. The tapered section of the floating bush has a first tapered portion and a second tapered portion, said first tapered portion having a length greater than a length of the second tapered portion and an angle of taper of the first tapered portion is less than an angle of taper of the second tapered portion.

According to the present disclosure there is also provided a hydraulic cylinder comprising: a cylinder housing defining an axially extending cylinder bore and a cap port having a cushion bore. A piston rod is located in the cylinder bore and is axially movable therein. A piston is attached to an end of the piston rod, said piston comprising a socket, and said socket comprising a counterbore and a pin engaging portion. The hydraulic cylinder further comprises a pin assembly as described above. The piston engaging portion of the pin is releasably engaged with the pin engaging portion of the piston, such that the flanged portion of the pin is located in the counterbore.

Brief Description of the Drawings

Aspects of the present disclosure are described below, by way of example only, with reference to the following drawings, in which: Figure 1 is pictorial view of a mining shovel mass excavator; Figure 2 is a part cross-sectional side elevation of a hydraulic cylinder of the mining shovel mass excavator of Figure 1; Figure 3 is cross sectional side elevation of a pin assembly of the present disclosure mounted in an end of a piston and projecting into the cushion bore of the hydraulic cylinder of Figure 2; Figure 4 is a side elevation of a pin of the pin assembly of Figure 3; Figure 5 is a cross sectional side elevation of a floating bush of the pin assembly of Figure 3; Figure 6 is an end elevation of the floating bush of Figure 5; Figure 7 is a pictorial view of a locking nut of the pin assembly of Figure 3; Figure 8 is a cross sectional side elevation of the locking nut of Figure 7; Figure 9 is a cross sectional plan view of the locking nut of Figure 7; and Figure 10 is a cross sectional plan view of a portion of an intersection between a flange of the pin assembly and the piston forming a threaded bore.

Detailed Description

Figure 1 illustrates a non-limiting example of a machine 10, in this case a mining shovel mass excavator, which utilises first, second and third hydraulic actuators 24, 25, 26, at least one of which may be provided with the pin assembly 47 of the present disclosure, which provides cushioning at an end of a retracting stroke. The machine 10 may, however, be another type of machine, vehicle or indeed another type of apparatus which utilises hydraulic cylinders. The machine 10 may comprise a main unit 11 having an operator cabin 12 for an operator and a power unit (not shown in Figure 1), such as an internal 4 -combustion engine, for providing power to ground engaging means 13, such as tracks or wheels. The machine 10 may comprise an implement 14, in this example a bucket, coupled to an implement assembly 15 (a backhoe) by means of a suitable coupling arrangement 16, thereby connecting the implement 14 to the main unit 11. The machine 10 may also comprise other implements (not shown) attached to the main unit 11 via other implement assemblies. The implement 14 may be manoeuvred by means of one or more hand operated levers 19 located in the operator cabin 12 connected to suitable linkage assemblies.

The implement assembly 15 may include a boom 22 pivotally connected to the main unit 11 of the machine 10, a stick 23 pivotally connected to the boom 22, and the implement 14 pivotally connected to the stick 23. The boom 22 may be actuated by a first hydraulic actuator 24 to enable a raising and a lowering of the boom 22. The stick 23 may be drawn towards and away from the machine 10 by a second hydraulic actuator 25. A third hydraulic actuator 26 may be configured to curl and uncurl the implement 14. The machine 10 may further include a pair of fourth hydraulic actuators (not shown) disposed on each side of the boom 22 and coupled to the main unit 11. The pair of fourth hydraulic actuators may be configured to enable a swing of the implement assembly 15 with respect to the machine 10.

The hydraulic cushioning of the present disclosure provided by the pin assembly 47 may be particularly suitable for use in the third hydraulic actuator 26 (also known as the stick cylinder but may be used on the other hydraulic actuators 24, 25 or indeed any other hydraulic actuators used in entirely different applications. The terms hydraulic actuator and hydraulic cylinder are, in the context of this specification, synonymous, and the hydraulic cylinder 30 described below may be used as any of the aforementioned hydraulic actuators 24, 25, 26.

Referring to Figure 2, the hydraulic cylinder 30 may comprise a cylinder housing 31 defining a cylinder bore 32 extending axially therethrough. The hydraulic cylinder 30 may also comprise a piston rod 33 located in the cylinder bore 32 and axially moveable therein. A piston 34 may be attached at its proximal end to one end of the piston rod 33. The piston 34 may have a first surface 35 at its distal end and a second surface 36 at its proximal end. The second surface 36 and a head end 37 of the cylinder housing 31 may together define a rod chamber 38. The first surface 35 and a cap end 39 of the cylinder housing 31 may together define a piston chamber 40. The cylinder housing 31 may be provided with a head

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port 41 and a cap port 42. The head port 41 may be disposed in fluid communication with the rod chamber 38 while the cap port 42 may be disposed in fluid communication with the piston chamber 40. Movement of the piston 34 along the cylinder bore 32 towards the cap end 39 of the cylinder housing 31 during a retracting stroke may be accomplished by routing pressurised fluid via the head port 41 to the rod chamber 38. Movement of the piston 34 along the cylinder bore 32 towards the head end 37 of the cylinder housing 31 during an expanding stroke may be accomplished by routing pressurised fluid via the cap port 42 to the piston chamber 40.

As shown in Figure 3, a socket 44, may be formed in the piston 34 extending into the piston 34 from the first surface 35. The socket 44 may be co-axial with the piston rod 33. The socket 44 may have a counterbore 45 and pin engaging portion 46 for engaging with the pin assembly 47, which may include an internal thread.

The pin assembly 47 may include a pin 48 (see also Figure 4) which may comprise a pin body 49. The pin body 49 may be substantially cylindrical and may have a first end 50 and an opposing second end 56. The pin 48 may also comprise a flanged portion 51 adjacent the first end 50 of the pin body 49, and the flanged portion 51 may be configured to be received in the counterbore 45 of the socket 44. The pin 48 may further include a piston engaging portion 52 projecting axially from the flanged portion 51. The piston engaging portion 52 is configured to releasably engage with the pin engaging portion 46 of the socket 44. When the pin engaging portion 46 comprises an internal thread, the piston engaging portion 52 may have a complementary external thread. A pair of slotted grooves 53 may be provided on the pin body 49, configured to allow the use of tools (not shown) e.g. a torque wrench, for engaging the pin 48 in, or removing it from, the socket 44. Other alternative suitable means may also be used to facilitate this. When the pin 48 is fully engaged in the socket 44, one or more fasteners 54, such as screws, may be used to secure the pin 48 to the piston 34 to prevent further rotation. In the example shown, a single fastener 54 may be axially mounted in a threaded bore 43 which is formed at an intersection of the flanged portion 51 of the pin 48 and the piston 34. One part of the threaded bore 43 may be formed in the radial edge of the flanged portion 51 and the other part of the threaded bore 43 may be formed in the radial internal face of the counterbore 45, as shown in Figure 10. The one or more fasteners 54 may be screws provided with complementary locking threads. 6 -

The pin 48 may further comprise a locking section 55 projecting axially from the second end 56 of the pin body 49 and configured to releasably engage with a locking nut 90 (described in detail below). The locking section 55 may have a locking nut engagement portion 57 located at its proximal end, which is adjacent the second end 56 of the pin body 49, and a cap 58 located at its distal end. The locking nut engagement portion 57 may have an external thread. The locking section 55 may also have a neck 59 between the locking nut engagement portion 57 and the cap 58. The neck 59 may have an external diameter which is less than an external diameter of the cap 58. The external diameter of the neck 59 may also be less than an external diameter of the locking nut engagement portion 57.

The pin assembly 47 may further comprise a floating bush 60 disposed directly about the pin body 49 such that a fluid passage is defined between an internal surface 63 of the floating bush 60 and an external surface 73 of the pin body 49. As shown in Figure 5, the floating bush 60 may have a first end 61, which may be located towards the first end 50 of the pin body 49 and the flanged portion 51. The floating bush 60 may also have a second end 62, which may be located towards the second end 56 of the pin body 49. The floating bush 60 may have an internal diameter 64 which may be greater than the external diameter 65 of the pin body 49. The internal diameter 64 of the floating bush 60 and the external diameter 65 of the pin body 49 may be selected to provide a radial clearance between the floating bush 60 and the pin body 49, which may enable the floating bush 60 to move radially relative to the pin body 49. The radial clearance may be in the range of 0.5 to 0.6mm. The length 66 of the floating bush 60 may also be less than the length 67 of the pin body 49. The lengths 66, 67 may be selected to enable the floating bush 60 to move axially relative to the pin body 49. The axial movement may be in the range of 0.725 to 2.175mm.

In one example the axial movement is about 1.45mm. The internal diameter 64 of the floating bush 60 may also be less than the external diameter of the flanged portion 51 of the pin body 49, such that the flanged portion 51 provides a first end stop to the axial movement of the floating bush 60.

The floating bush 60 may have an external surface 68, which may have a substantially cylindrical section 69 extending from the first end 61 of the floating bush 60, and a tapered section 70, extending from the cylindrical section 69 to the second end 62 of the floating bush 60. The external surface 68 tapers inwardly along the tapered section 70, such that the external diameter of the floating bush 60 is greater at its first end 61 than at its second end 62. The floating bush 60 may, alternately, have no cylindrical section 69 and the tapered section 70 may extend along the full length of the floating bush 60 from the first 7 -end 61 to the second end 62. The tapered section 70 may have a first tapered portion 71, which extends from the cylindrical section 69, if one is present, or from the first end 61, if no cylindrical section 69 is present, and a second tapered portion 72 which extends from the first tapered portion 71 towards the second end 62. The length 66 of the floating bush 60 may be in the range of 25 to 150mm. The length of the tapered section 70 may lie in the range 01 10 to 100% of the length of the floating bush 60. The length of the tapered section 70 may lie in the range of 57.96% to 60.50% of the length of the floating bush 60 and may be 59%. The first tapered portion 71 may have a length which is greater than the length of the second tapered portion 72. The length 66 of the first tapered portion 71 may lie in the range of 10 to 90% of the length 66 of the floating bush 60. The length of the second tapered portion 72 may be 2 to 20% of the length 66 of the floating bush 60. In one example, the length 66 of the floating bush 60 may be 44mm, the length of the cylindrical section 69 may be 16mm and the length of the tapered section 70 may be 26mm. The length of the first tapered portion 71 may be 24mm and the length of the second tapered portion 72 may be 2mm. The angle of taper al of the first tapered portion 71 (from the cylindrical section 69, if one is present, or from the first end 61, if no cylindrical section 69 is present) may be less than the angle of taper az of the second tapered portion 72 (from the first tapered portion 71). The ratio of the angle of taper al to angle of taper az may be 1:6. The angle of taper al may be in the range of 1 to 7°. The angle of taper az may be in the range of 15 to 45°. In one example, the angle of taper ai may be 2.5° and the angle of taper az may be 15°.

The cap port 42 of the hydraulic cylinder 30 may include a cushion bore 75 at one end thereof. During operation of the hydraulic cylinder 30, the floating bush 60 of the pin assembly 47 is configured to be slidably received within the cushion bore 75 as the piston 34 approaches the cap end 39 of the cylinder housing 31 during a retracting stroke. The internal diameter 76 of the cushion bore 75 may be greater than the external diameter 77 of the cylindrical section 69 of the floating bush 60. The internal diameter 76 of the cushion bore 75 may be in the range of 30 to 70mm. The external diameter 77 of the cylindrical section 69 may be in the range of 29.7 to 69.7mm. In one example, the internal diameter 76 of the cushion bore 75 may be 50mm and the external diameter 77 of the cylindrical section 69 may be 49.7mm. This may provide an annular clearance which allows limited radial movement of the floating bush 60 relative to the pin body 49, once the floating bush 60 is fully located within the cushion bore 75 (as shown in Figure 3). 8 -

The first end 61 of the floating bush 60 may be provided with a rim 80, which extends axially from the cylindrical section 69. An internal diameter 81 of the rim 80 may be greater than the internal diameter 64 of the floating bush 60 and an external diameter 82 of the rim 80 may be the same as the external diameter 77 of the cylindrical section 69 of the floating bush 60. An external chamfer 84 may be provided on the distal end of the rim 80. The rim may be provided with a plurality of radial relief slots 83. In one example there may be four radial relief slots 83 evenly spaced around the rim 80.

The surface roughness and finish of the floating bush 60 may be selected to provide cushioning without much noise. The surface roughness is important to control the fluid friction with the floating bush surface. Too fine or too rough would cause an abnormal noise, so a suitable roughness profile may be selected to avoid this. The floating bush 60 may therefore be treated to improve its hardness and to improve its scratch resistance. One suitable treatment may be Nitrocarburization in salt melts.

As shown in Figures 7 to 9, the locking nut 90 of the pin assembly 47 may have a body 91, which may be substantially cylindrical, and which may have an internal bore 97. Located towards a first end 93 of the locking nut 90 may be a cap receiving section 98. The body 91 may comprise a pair of slotted grooves 92 (only one of which can be seen in Figure 7). The slotted grooves 92 may be located externally in the cap receiving section 98 of the locking nut 90, and be configured to allow the use of tools (not shown) e.g. a torque wrench, for engaging the locking nut 90 with, or removing it from, the locking nut engagement portion 57 of the locking section 55. Other alternative suitable means may also be used to facilitate this. Located towards a second end 94 of the locking nut 90 may be a pin engagement section 95, which may be configured to releasably engage with the locking nut engagement portion 57 of the locking section 55 of the pin 48. When the locking section 55 of the pin 48 is provided with an external thread, the pin engagement section 95 may have a complementary internal thread.

The locking nut 90 may be provided with a pair of opposing apertures 96 extending radially through the body 91 for receiving fastening means (not shown). The apertures 96 may be internally threaded and the fastening means may be screws, which may have a complementary locking thread. The apertures 96 may be located between the pin engagement section 95 and the cap receiving section 98. The apertures 96 may be offset from each other, such that one aperture 96 lies on one side of a longitudinal central plane X-X (see Figure 9) and the other aperture 96 lies on the other side of the longitudinal central plane X-X.

The internal bore 97 of locking nut 90 may be stepped, such that it has a first diameter in the pin engagement section 95 which is greater than a second diameter in the cap receiving section. The second diameter may be greater than an external diameter of the cap 58 of the pin 48.

Industrial Applicability

The pin assembly 47 of the present disclosure may be particularly suitable for use in backhoe loaders and face shovel hydraulic mining machines, due to the high payloads which they may have to move during digging or loading operations, which may subject the hydraulic cylinders to high forces and impacts.

The design of the pin assembly 47 may be such that it is easy to install, and may therefore be suitable for retrofitting in the field, and may be easy to service,as it may be easy to access all of the components of the pin assembly 47. The pin assembly 47 may comprise three main components, namely the pin 48, the floating bush 60 and the locking nut 90. To install the pin assembly 47 in the piston 34, the piston engaging portion 52 of the pin 48 may first be engaged with the pin engaging portion 46 of the socket 44 in the piston 34, for example by screwing the piston engaging portion 52 into the socket 44, until the flanged portion of the pin 48 lies in the counterbore 45 of the piston 34. The assembly torque applied to the pin 48 may depend on the actual size of the components of the pin assembly and may range from 100 to 2000Nm. In one example, the assembly torque may be in the range of 440 to 460 Nm. The assembly torque may be 450Nm. An adhesive may be applied to the pin engaging portion 46 prior to engagement with the When the piston engaging portion 52 is correctly located in the socket 44, the threaded bore 43 may be formed, for example by machining, across the interface of the flanged portion 51 of the pin 48 and the counterbore 45, such that one part of the threaded bore 43 is in the flanged portion 51 and one part is in the counterbore 45. The fastener 54 may then be screwed into the threaded bore 43.

The floating bush 60 may then be placed around the pin body 49, such that the first end 61 or the floating bush 60 is located adjacent the flanged portion 51 of the pin 48. The locking nut 90 may then be engaged with the locking nut engagement portion 57 of the locking -10 -section 55. When the locking nut 90 is correctly engaged with the locking section 55, the second end 94 of the locking nut 90 abuts the second end 56 of the pin body 49 and the cap 58 may extend through the internal bore 97 in the cap receiving section 98. The cap 58 may protrude slightly from the first end 93 of the locking nut 90. The fasteners may be inserted into the apertures 96, such that one end of the fasteners protrude into the neck 59 of the locking section 55, thereby locking the locking nut 90 in place in a locked position by preventing further rotational movement of the locking nut 90 relative to the pin 48. In this locked position, the second end 94 of the locking nut 90 may project radially beyond the second end 56 of the pin body 49 to provide a second end stop to the axial movement of the floating bush 60. When the locking nut 90 is in the locked position, axial movement of the floating bush 60 relative to the pin body 49 may thus be constrained between the flanged portion 51 of the pin 48 and the locking nut 90. No pre-assembly of the pin assembly 47 is therefore required prior to attachment to the piston 34.

The design of the pin assembly 47 is such that it may be secure and stable when it has been installed and may prevent damage which may arise as a result of any looseness between the components. Furthermore, the design of the pin assembly 47, utilising only three main components, may enable the diameter of the pin 48 to be increased, as compared to prior art pins, which may enable the pin assembly 47 to withstand greater forces.

In use, the pin assembly 47 of the present disclosure may provide cushioning in the hydraulic cylinder 30 at the end of the retraction stroke, by providing controlled deceleration of the piston 34 to reduce deceleration and inertial forces. As the hydraulic cylinder 30 reaches the end of a retracting stroke, the distal end of the pin assembly 47 (which comprises the pin body 49, the floating bush 60 and the locking section 55) may be pushed into the cushion bore 75 in the cap port 42, until the first surface 35 of the piston 34 abuts the cap end 39. As the floating bush 60 approaches the cushion bore 75, the flow of hydraulic fluid to the cap port 42 may be restricted through the annular area formed between the external surface 68 of the floating bush 60 and the internal surface of the cushion bore 75. The clearances between the floating bush 60 and the pin body 49 may enable the floating bush 60, which is suspended in hydraulic fluid, to move axially and radially relative to the pin body 49. This may enable the floating bush 60 to easily move to align with the cushion bore 75. When the retracting stroke is occurring at a maximum functional speed of the implement assembly 15, the speed of the piston 34 may be dampened, or reduced, as a result of a gradual restriction of the flow passage formed by the annular area. The annular area may reduce at different rates as the floating bush 60 progresses further into the cushion bore 75 as a result of the first and second tapered portions 71, 72 of the floating bush 60 having different angles of taper al, a2, such that the pin assembly 47 provides a variable orifice area curve. The axial movement of the floating bush 60 may help to provide an adjustment to attain the equilibrium of flow forces without having any stick slip situation or hydraulic locking The second tapered portion 72, having the greater angle of taper 02, may play a greater role in providing a smooth entry of the floating bush 60 into the cushion bore 75 and preventing sudden shocks, whilst the first tapered portion 71, having the shallower angle of taper al, may play a greater role in ramping down the speed of the piston 34. The variable orifice area curve and rate of reduction in the annular area may cause an increase in the fluid pressure within the cap port 42 (cushion pressure) which may enable the speed of the piston 34 to be reduced by up to a third of its initial velocity. The rest of the kinetic energy may be dissipated by heat, pressure and strain energy. The orifice area curve may provide a rate of reduction in the velocity of the piston 34 and increase in cushion pressure occurring during the retraction stroke and may achieve an optimum dampening effect which may avoid shock loads and may improve the life of the pin assembly 47 and the hydraulic cylinder 30.

The location of the floating bush 60 directly around the pin body 49, such that a fluid passage is defined between an internal surface 63 of the floating bush 60 and an external surface 73 of the pin body 49, may provide a continuous passage for the pressurised fluid, which may avoid fluid locking. The radial relief slots 83 in the rim 80 of the floating bush 60 may also help to relieve hydraulic fluid entrapped inside the floating bush 60 when the retracting stroke is about to be, or has been, completed. The radial relief slots 83 may allow hydraulic fluid inside the floating bush 60 to pass back into the cushion bore 75. The radial relief slots 83 may further assist in balancing the hydraulic fluid flow force during the retracting stroke and maintain the floating bush 60 in a stable substantially centralised position.

Claims

-12 -CLAIMS: 1. A pin assembly for a piston of a hydraulic cylinder, said pin assembly comprising: a pin, said pin comprising: a pin body; a flanged portion at a first end of the pin body; a piston engaging portion projecting axially from the flanged portion configured to releasably engage with a piston of a hydraulic cylinder; and a locking section projecting axially from an opposing second end of the pin body; a locking nut configured to releasably engage with the locking section; and a floating bush having a first surface having an inwardly tapered section; wherein the floating bush is disposed about the pin body and is movable radially and axially relative to the pin body between the flanged portion and the locking nut and a fluid passage is defined between a second surface of the floating bush and a surface of the pin body, and further wherein the tapered section of the floating bush has a first tapered portion and a second tapered portion, said first tapered portion having a length greater than a length of the second tapered portion and an angle of taper of the first tapered portion is less than an angle of taper of the second tapered portion.
2. A pin assembly as claimed in claim 1, wherein the ratio of the angle of taper of the first tapered portion to the angle of taper of the second tapered portion is 1:6.
3. A pin assembly as claimed in claim 1 or claim 2, wherein the angle of taper of the first tapered portion lies in the range 1 to 72 and the angle of taper of the second tapered portion lies in the range 15 to 452.
4. A pin assembly as claimed in any one of the preceding claims, wherein the length of the tapered section may lie in the range of 10 to 100% of the length of the floating bush.
5. A pin assembly as claimed in any one of the preceding claims, wherein the length of the first tapered portion lies in the range of 10 to 90% of the length of the floating bush.
6. A pin assembly as claimed in any one of the preceding claims, wherein the length of the second tapered portion lies in the range of 2 to 20% of the length of the floating bush.
7. A pin assembly as claimed in any one of the preceding claims, wherein the length of the floating bush 60 is in the range of 25 to 150mm.
8. A pin assembly as claimed in any one of the preceding claims, wherein an internal diameter of the floating bush and external diameter of the pin body provide a radial clearance in the range of 0.5 to 0.6mm between the floating bush and the pin body.
9. A pin assembly as claimed in any one of the preceding claims, wherein the floating bush is able to move axially relative to the pin body between the flanged portion and the locking nut by 0.725 to 2.175 mm.
10. A pin assembly as claimed in any one of the preceding claims, wherein the floating bush is able to move axially relative to the pin body between the flanged portion and the locking nut by 1.45mm.
11. A pin assembly as claimed in any one of the preceding claims, wherein the floating bush further comprises a rim, which extends axially from the cylindrical section, said rim comprising a plurality of radial relief slots.
12. A pin assembly as claimed in claim 10, in which the rim comprises four radial relief slots evenly spaced around the rim. 25
13. A pin assembly as claimed in any one of the preceding claims, wherein the locking nut comprises a body and a pair of opposing apertures extending radially through the body, each aperture being configured to receive a fastener, wherein the apertures are offset relative to each other, such that one aperture lies on one side of a longitudinal central plane and the other aperture lies on the other side of the longitudinal central plane.
14. A pin assembly as claimed in any one of the preceding claims, wherein the locking section of the pin projects axially from the second end of the pin body, said locking section comprising a locking nut engagement portion located at a proximal end of the locking section, and a cap located at a distal end of the locking section, wherein a neck is formed -14 -between the locking nut engagement portion and the cap, said neck having an external diameter which is less than an external diameter of the cap.
15. A hydraulic cylinder comprising: a cylinder housing defining an axially extending cylinder bore and a cap port having a cushion bore; a piston rod located in the cylinder bore and being axially movable therein; a piston attached to an end of the piston rod, said piston comprising a socket, and said socket comprising a counterbore and a pin engaging portion; and a pin assembly as claimed in any one of the preceding claims, wherein the piston engaging portion of the pin is releasably engaged with the pin engaging portion of the piston, such that the flanged portion of the pin is located in the counterbore.
16. A hydraulic cylinder as claimed in claim 15, wherein the first surface of the floating bush and a surface of the cushion bore define a variable area fluid passage, which decreases as the floating bush is pushed into the cushion bore.
17. A hydraulic cylinder as claimed in claim 15 or claim 16, wherein an assembly torque in the range of 100 to 2000 Nm is applied to the pin to engage the piston engaging portion with the pin engaging portion.
18. A hydraulic cylinder as claimed in claim 17, wherein the assembly torque is 440 to 460 Nm.