WO2005080131A1

WO2005080131A1 - Tensioner

Info

Publication number: WO2005080131A1
Application number: PCT/AU2005/000209
Authority: WO
Inventors: Maurice John Matthews
Original assignee: Matthews International Pty. Ltd.
Priority date: 2004-02-19
Filing date: 2005-02-21
Publication date: 2005-09-01

Abstract

A tensioner (31) for a flexible elongated element or elements such as a chain (32) comprising at least one fluid ram (13) comprising a cylinder and a piston assembly and coupling means (19, 20) at opposite ends of the tensioner (31) adapted to be coupled to the elongated element or elements at spaced apart positions such that fluid pressure applied to the ram (14) causes retraction of the ram and tensioning of the chain (32). The tensioner (31) may include a pair of rams (12) which are spaced apart and connected at opposite ends by bridging members (19, 20) which define the coupling means. In another embodiment, releasable restraining means in the form of a ratchet are provided to prevent extension of the ram to maintain tension in the tensioned flexible element.

Description

TENSIONER Technical Field This invention relates to a tensioner which has particular but not. exclusive application as a tensioner for use in load restraint applications where a load is restrained by elongated flexible restraining elements such as chains or webbing, robe or wire such as for example where a load is restrained on a vehicle. The present invention however has many other applications where tension is required to be applied to and/or maintained in an elongated flexible element. Background Art Chains are commonly used for restraining loads on commercial vehicles for example for restraining loads on low loaders, lorries or other load carrying vehicles. For applying and maintaining tension in the chain and thereby the load securely held to the vehicle, it is common to employ chain "dogs". The common form of chain dog comprises a mechanically operated device which is coupled to the chain which is applied about the load. The device usually includes a lever which through a pivoting and over-centre action can apply tension to the chain. The device then remains attached to the chain maintaining tension until it is desired to removed the load from the vehicle. A disadvantage of the known type of chain dog as referred to above is that the device is required to be operated manually which can necessitate a substantial application of manual force. Further an operator is required to take care whilst operating the device because of the risk of recoil of the device whilst tensioning the chain. In addition, this type of chain dog has limitations in the extent of tension to which it can apply to a chain. A further disadvantage arises where the operator wishes to release the tension in the chain. In such circumstances, the operator must take great care in releasing the lever to avoid recoil due to the existing tension in the chain. Similar disadvantages occur where a load is restrained by other elongated restraining elements such as webbing, rope or wire. Again in these circumstances it is difficult not only to tension the elements but also to ensure that tension is maintained in the elements so that the restrained load is securely held. Summary of the Invention The present invention aims to overcome or alleviate one or more of the above disadvantages by providing a tensioner which enables tension to be applied to an elongated flexible load restraining element in a safe, effective and reliable manner. The present invention in a further aspect aims to provide a tensioner which allows for safe release of tension in the restraining element. Other objects and advantages of the invention will become apparent from the following description. The present invention in a first aspect provides a tensioner for a flexible elongated element or elements, said tensioner comprising at least one fluid ram, said ram having a cylinder and a piston assembly, coupling means at opposite ends of said tensioner and connected to said cylinder and said piston assembly respectively, said coupling means being adapted to be coupled to said elongated element or elements at spaced apart positions whereby fluid pressure applied to said ram causes retraction of said piston assembly relative to said cylinder and tensioning of said element or elements. The piston assembly comprises a piston movable within the cylinder and preferably means are provided to resist the retraction of the piston to return to the piston to an extended position after fluid pressure has been removed or released. Such means may comprise resilient or elastic means or other form of biasing means. Typically such means may comprise springs within the cylinder between the piston and one end of the cylinder. Alternatively such means may comprise an elastically compressible gas such as nitrogen. In a particularly preferred form, the tensioner comprises first and second fluid rams, each having a cylinder and a piston assembly movable relative to the cylinder with the fluid rams extending substantially parallel to and being laterally spaced from each other. Preferably, first interconnecting means are provided at one end of the tensioner for interconnecting the cylinders. Preferably also second interconnecting means are provided at the other end of the tensioner for interconnecting the piston assemblies. The respective interconnecting means may be rigidly connected to the cylinders and piston assemblies respectively. Alternatively at least one of the interconnecting means may be pivotally or hingedly connected to the cylinders or piston assemblies respectively. The pivot or hinged connection may provide for limited pivotal movement of the interconnecting means about an axis extending transversely and suitably normal to the cylinders and piston assemblies. Preferably stop means are provided to limit the pivotal movement of the pivotal interconnecting means. The interconnecting means suitably comprise bridging members which bridge the respective cylinders and piston assemblies of the respective rams. Preferably, the rams are spaced apart transversely to define a passage extending substantially parallel to the rams and along which the element to be tensioned may pass. The rams are typically arranged symmetrically on opposite sides of the passage. The means which interconnect the cylinders and piston assemblies may be transversely offset relative to the longitudinal axis of the tensioner. The piston assemblies may have piston rods connected to or formed integrally with the pistons which extend out of the cylinders and which are interconnected by the second interconnecting means. The coupling means may be connected to the interconnecting means or may be incorporated in the interconnecting means. Where the coupling means are connected to the interconnecting means, they are suitably pivotally connected to the interconnecting means for pivotal movement about an axis extending normal to the longitudinal axes of the rams. Fluid passage means suitably fluidly interconnect the respective cylinders to enable fluid pressure to be applied to the respective cylinders to cause retraction of the pistons. The fluid passage means suitably interconnect the respective cylinders such that fluid pressure can be applied simultaneously to the cylinders. Preferably the fluid passage means is defined by a hollow member which extends transversely between the respective cylinders. A fluid port provided on the hollow member suitably communicates with the fluid passage means to allow the simultaneous application of fluid pressure to the respective cylinders and therefore cause simultaneous retraction of the rams. The hollow member suitably comprises a gripping handle which may be gripped to permit manipulation of the tensioner. The tensioner is particularly suited to tensioning chains and the coupling means suitably include chain couplers. Where a chain coupler is a coupler incorporated in an interconnecting means, it is suitably defined by a slot to receive a chain link and an abutment face rearwardly of the slot for cooperation with the next chain link adjacent to the link received in the slot. The present invention provides in a further preferred aspect, a tensioner for a flexible element or elements comprising a fluid ram having a cylinder and a piston movable in said cylinder, coupling means for coupling said cylinder and said piston to said flexible element or elements at spaced apart positions and restraining means between said cylinder and said piston normally permitting said piston to move relative to said cylinder in a first direction for tensioning said element or elements and preventing movement of said piston in a direction opposite said first direction to maintain tension in said element or elements and releasing means selectively actuable to release said restraining means for releasing tension in said element or elements. Preferably, the restraining means comprises ratchet means. The ratchet means suitably comprises a plurality of teeth fixed for movement with one of the piston and cylinder and one or more pins or engagement members engageable with the teeth fixed for movement with the other of the piston and cylinder. The releasing means suitably comprises means for moving the one or more pins or engagement members out of engagement with one or more of the teeth. Preferably, the releasing means is rotatable about a longitudinal axis relative to the longitudinal axis of the ram and direction of movement of the piston to release the one or more pins or engagement members from the one or more teeth. The releasing means may carry the one or more pins or engagement member or may carry the teeth. Most preferably, the one or more pins or engagement members are fixed for movement with the cylinder and the teeth are fixed for movement with the piston. Preferably, the cylinder terminates at one end in an end member and the end member carries the one or more pins or engagement members. The end member may be releasably attachable to the one end of the cylinder. Typically the end member may be threadably engageable with the one end of the cylinder. Preferably the releasing means comprises a sleeve coaxial with the longitudinal axis of the ram and located around the end member, the sleeve being fixed for longitudinal movement with the piston. Suitably the sleeve carries the teeth for engagement by the one or more pins or engagement members and is rotatable about the longitudinal axis relative to the piston and cylinder. Biasing means are suitably provided to provide a rotational bias to the sleeve to normally urge the teeth into engagement with the one or more pins or engagement members. The biasing means suitably is provided between the end member and sleeve. The biasing means suitably comprises a spring or other resilient or elastic means normally urging the sleeve in a first rotational direction about the longitudinal axis to maintain the teeth in engagement with the one or more pins or engagement members. Connecting means for connecting the cylinder to a source of fluid pressure are suitably provided on the end member. Passage means are suitably provided in the end member for connecting the connecting means to the cylinder. The connecting means suitably extends radially of the end member. The sleeve suitably is provided with a longitudinally extending slot to receive the connecting means and permit longitudinal movement of the connecting means relative to the sleeve. The connecting means suitably comprises a conventional hydraulic connector. The slot also allows limited rotations movement of the connector. Preferably the piston is provided with a piston rod to which the sleeve is connected for longitudinal movement with the piston rod and rotational movement about a longitudinal axis relative to the piston rod. The piston rod suitably extends through the end member so as to be movable longitudinally relative to the end member. Preferably the free end of the piston rod is connected to the sleeve. Suitably, the sleeve has an end wall through which the free end of the piston rod projects. Bearing means are suitably provided between the free end of the piston rod and end wall of the sleeve to facilitate the rotational movement of the sleeve relative to the piston and piston rod. Suitably a cover is provided over the sleeve to facilitate gripping thereof. The respective coupling means are suitably provided at the free end of the piston rod and outer end of the cylinder. The coupling means may be pivotally connected to the piston rod and cylinder. For engagement with a chain, the coupling means suitably comprises chain couplers. The elongated flexible element or elements may typically comprise a chain or chains and the coupling means at opposition ends of the tensioner are adapted to be coupled to spaced links of the chain or links of respective chains. The coupling means may comprise female claw hooks for engagement with the chain links. Other forms of coupling means may be provided for coupling the tensioner to other forms of elongated flexible elements such as webbing or rope. Brief Description of the Drawings In order that the invention may be more readily understood and put into practical effect, reference will now be made to the accompanying drawings which illustrate a preferred embodiment of the invention. The tensioners of the embodiment of the invention have been described in relation to the tensioning of chains. It will be appreciated however that the tensioners may be used for tensioning other elongated flexible elements and thus the reference to chains is to be understood as including other elongated flexible elements such as webbing, robe or wire. Figs. 1 and 2 are opposite perspective views of a tensioner according to a first embodiment of the invention; Fig. 3 is a longitudinal cross sectional view of portion of the tensioner of Figs. 1 and 2 in the region of the gripping handle; Fig. 4 is an enlarged view of the piston rod end of the tensioner of Figs. 1 and 2; Fig. 5 is an enlarged view of the cylinder end of the tensioner showing a bridging member between the respective cylinders and the manner of its engagement with a chain; Figs. 6 and 7 illustrate the manner in which a tensioner similar to the embodiment of Figs. 1 and 2 is use for tensioning a chain; Figs. 8 and 9 illustrate in perspective view, a second embodiment of chain tensioner of according to the invention in a retracted and extended position respectively; Fig. 10 is a schematic sectional elevational view of the chain tensioner of Figs. 8 and 9; Fig. 11 is a perspective partly cut away view of the chain tensioner of Figs .8 and 9; Figs. 12 and 13 are opposite cut-away perspective views of portion of the chain tensioner of Figs. 8 and 9 showing the manner in which the ratchet is disengaged; and Fig. 14 illustrates the manner in which the chain tensioner of Figs. 8 and 9 is applied to a chain and tensions the chain about a load. Detailed Description of the Preferred Embodiment Referring to the drawings and firstly to Figs. 1 and 5, there is illustrated a tensioner 10 according to a first embodiment of the invention comprising a pair of spaced apart arms 11 which extend substantially parallel to each other in a longitudinal direction and which are transversely spaced apart symmetrically to define therebetween a passage 12 along which an elongated flexible element to be tensioned may be passed. Each arm 11 is defined by a fluid ram 13 comprising a cylinder 14 and a piston assembly comprising a piston 15 within the cylinder 14 and a piston rod 16 which extends through a gland 17 at one end of the cylinder 14, the gland 17 typically being in threaded engagement with the cylinder 14. The region between the piston 15 and closed end of the cylinder 14 opposite the gland 17 contains an elastically compressible gas which normally biases the piston 15 towards the gland 17 and thus the piston rod 16 outwardly of the cylinder 14. Alternatively, a compression spring may be provided in the cylinder 14 to serve the same function. A flexible boot 18 surrounds the piston rod 16 to provide protection to or shield the piston rod 16 during its movement. The rams 13 are connected and held parallel to each other by a first end bridging member 19 which rigidly connects the outer ends of the cylinders 14 through a bolt connection and a second end bridging member 20 which interconnect the outer ends of the piston rods 16. The second bridging member 20 is either rigidly connected to the piston rods 16 as in the embodiment of Figs. 6 and 7 or alternatively, the bridging member 20 is pivotally connected via clevis connectors 21 to the ends of the piston rods 16. The pivot pins 22 of the clevis connectors 21 define a pivot axis for the bridging member 20 which extends substantial normal to the longitudinal axis of the tensioner 10. The clevis connectors 21 include stops 23 which limits pivotal movement of the bridging member 20 by cooperating with opposing portions 24 of the bridging member 20. The limited pivotal movement of the bridging member 20 allows the tensioner 10 to engage portions of a flexible element or separate flexible elements arranged in other than a non-linear orientation. The bridging members 19 and 20 additionally include slots 25 which extend centrally through the end walls 26 of the bridging members 19 and 20 for receipt of a chain link as shown in Fig. 5, the slot 25 being of a width slightly greater than the diameter of the arms of the chain link. Recesses 27 are provided in the bridging members 19 and 20 rearwardly of the slots 25 for accommodating a chain link next to a link received within a slot 25. The inner faces of the end walls 26 act as abutment faces for engagement by the chain links within the recesses 27. In an alternative arrangement, the bridging members 19 and 20 can be provided with outwardly extending lugs for pivotal connection to coupling devices for coupling the tensioner 10 to the element to be tensioned. Where the element is a chain, the coupling devices may be chain claw couplers of known form. Extending between and joined rigidly to the cylinders 14 of the opposite rams 11 is transversely extending member 28 which forms a gripping handle 29. The member 28 comprises a hollow tubular member 29 which is connected to the cylinders 14 such that the transversely extending portion which defines the handle 29 thereof is spaced laterally from the rams 11. The hollow tubular member 28 serves as a fluid passage to interconnect the cylinders 14 of each ram 11 on the gland side of the pistons 15. A fluid connector 30 such as a conventional hydraulic connector is provided on the member 28 to enable connection of the tensioner 10 to a fluid pressure source. Thus fluid pressure applied to the connector 30 is applied simultaneously to both rams 13 through the hollow member 28. Referring now to Figs. 6 an 7, there is illustrated a slightly modified form of tensioner 31 which is similar to the embodiment of Figs. 1 and 2 and thus like components have been given like numerals. The tensioner 31 has a slightly modified form of tubular member 28 which forms the gripping handle 29 and both bridging members 19 and 20 are fixed rigidly to the cylinder and piston assemblies of the rams 13. The tensioner 31 is typically applied to tension an element such as a chain 32 as shown in Figs. 6 and 7 which may be in joined or separate lengths. The chain 32 may be at least partially tensioned about a load. The tensioner 31 is positioned relative to the chain 32 such that the ram assemblies 13 are arranged symmetrically on opposite sides of the chain 32 with the portion 33 of the chain 32 located in and extending along the passage 12. Spaced apart chain links of the chain 32 are also positioned in the slots 25 of the bridging members 19 and 20. Fluid pressure is then applied to the connector 30 which will cause the pistons 15 and thus piston rods 16 to be retracted simultaneously into the cylinders 14 against the bias of the gas or springs therein. This will move the bridging members 19 and 20 towards each other and thus tension the chain 32 on the outer sides of the bridging members 19 and 20 with the portion 33 of the chain 32 becoming de-tensioned. A connecting link (shown in dotted outline in Fig. 7) can then be provided to span the looped de-tensioned portion 33 of the chain to reduce the effective length of the chain 32. Fluid pressure can then be relieved at a controlled rate through the connector 30 to permit the piston rods 16 to be extended from the cylinders 14 under the bias of the compressed gas in the cylinders 14. Tension however will remain in the chain 32 due to the fact that the effective length of the chain 32 about the load has been reduced by the connecting link. Where the chain 32 is to be detached from the load or tension released, the tensioner 31 in the Fig. 6 position is re-engaged with the tensioned chain 32 in the above described manner and fluid pressure applied to retract the pistons 15 and piston rods 16 and thus move bridging members 19 and 20 towards each other. This will allow the connecting link to be released and the pressure in the rams 13 may then be reduced thereby allowing the bridging members 19 and 20 to move away from each other and thereby de-tension the chain 32. Whilst the tensioners 10 and 31 are typically used for tensioning chain which holds a load on a vehicle such as hay bales on a vehicle, it may be used in any load restraining applications or other applications where tension is to be applied to a chain or portions of a chain. The tensioners 10 or 31 may also be used to tension other elongated elements such as webbing, wires, or ropes by using appropriate connectors to engage the element at spaced positions. In another application, the chain 32 may be in separate lengths each of which is engaged by a respective bridging member 19 and 20. When the tensioner 10 or 31 is retracted, the respective chain lengths may be urged towards each other and may be interconnected. Referring now to Figs. 8 to 10, there is illustrated a chain tensioner 34 according to a further embodiment of the present invention comprising a pneumatic or hydraulic ram assembly 35 which comprises a cylinder 36, and a piston 37 slidably movable in the cylinder 36 and having a piston rod 38 extending coaxially of the cylinder 36. The cylinder 36 has a closed end 39 which carries an external clevis 40 or other connector which connects via a pivot pin 41 to a chain coupler 42 as shown in Figs. 8 and 9. A return spring 43 is provided in the cylinder 36 between the end 39 and piston 37 to normally urge the piston 37 away from the end 39 and extend the piston rod 38 from the cylinder 36. Alternatively, the return spring 43 may be replaced by an elastically compressible gas. The opposite end of the cylinder 36 is closed by a gland nut 44 which is in threaded engagement with the cylinder 36 as at 45. A bore 46 coaxial with the cylinder 36 is provided in the gland nut 44 to accept the piston rod 38 which extends through the bore 46. Seals (no shown) may be provided to seal the piston rod 38 in the bore 46. Seals may also be provided between the gland nut 44 and cylinder 36 to seal the gland nut 44 to the cylinder 36. A fluid supply passage 47 is provided in the gland nut 44 for the supply of fluid typically hydraulic oil to the cylinder 36, the passage 47 opening at 48 to the inner or cylinder end of the gland nut 44 and terminating in a supply port 49 in a circumferential side wall of the gland nut 44. A connector 50 for connection to a supply of pressurised fluid is connected such as by a threaded connection to the supply port 49 and extends radially outwardly of the gland nut 44. The gland nut 44 additionally includes a series of outwardly projecting ratchet pins 51 (in this case three) on opposite sides for a purpose which will become apparent further below. A ratchet sleeve 52 is coaxial with and surrounds the end of the cylinder 36 containing the gland nut 44. A radially extending end wall 53 is provided at the outer end of the sleeve 52. The end wall 53 is either fixed to or formed integrally with the sleeve 52. A central opening 54 is formed in the end wall 53 to accept a clevis 55 which has a stepped thrust bearing surface 56 in bearing contact with the wall of, or surrounding, the opening 54 so that the clevis 55 may rotate relative to the sleeve 52. A circlip 57 is provided in a groove 58 in the clevis 55 on the outside of the end wall 52 to capture the sleeve 52 to the clevis 55. The clevis 55 is fixed rigidly to the outer end of the piston rod 38 such as by means of a threaded connection and is adapted to be coupled to a chain coupler 59 by a pin 60 (see Figs. 8 and 9) in a similar manner to the connection of the clevis 40 to the coupler 42. The sleeve 52 includes on opposite sides in substantial alignment with the ratchet pins 61 on opposite sides of the gland 44, longitudinally extending slots 61 (shown in dotted outline in Fig. 1) which accommodate longitudinal movement of the pins 51 and thus the gland 44 relative to the sleeve 52. The lower sides of the slots 61 are provided with a series of ratchet teeth 62 adapted to cooperate with the ratchet pins 51. The teeth 62 are concave on one side and convex on their opposite sides. When one or more ratchet pins 51 are engaged with the teeth 62, the gland 44 and thus attached cylinder 36 are locked in position against movement in one longitudinal direction preventing outward extension of the cylinder 36 from the sleeve 52 which is attached to the piston 37. Movement of the gland 44 and cylinder 36 however is allowed in the opposite direction with the respective ratchet pins 51 during this movement riding up over the convex sides of the respective ratchet teeth 62 and engaging with the next set of ratchet teeth 62 in turn. The sleeve 52 is also provided on its upper side with a longitudinally extending slot 63 for accommodating longitudinal movement of the connector 50 during longitudinal movement of the cylinder 36 (and gland 44) relative to the sleeve 52. The slot 63 is also of sufficient width in a circumferential direction to permit limited rotational movement of the sleeve 52 about the longitudinal axis of the cylinder 36 as described further below. So that the ratchet pins 51 carried by the gland 44 are normally in engagement with the ratchet teeth 62, a biasing means in the form of a spring 64 is fixed at one end to the gland 44 and extends circumferentially in a groove around the gland 44. The opposite free end 65 of the spring 64 abuts one side of the slot 63 (as is more apparent in Figs. 11 to 13). A rotational biasing force thus will be applied to the sleeve 52 to normally urge it in a clockwise direction in Figs.12 and 13 to maintain the teeth 61 engaged with the pins 51. The circumferential width of the slot 63 is sufficient to allow the sleeve 52 to be rotated against the bias of the spring 64 to disengage the ratchet pins 51 from the ratchet teeth 62 without the connector 50 inhibiting this movement by contact with the side of the slot 63. To facilitate rotation of the sleeve 52, a handgrip 65 (see Figs. 8, 9 and 11) is provided around and fixed to sleeve 52 to enable it to be more readily grasped and twisted. In use and as shown in Fig.14, a chain 67 for securing a load 68 such as a vehicle or other load (only a portion of which is shown) is attached between the load 68 and an anchoring point 69 such as an anchoring point of a vehicle tray. The chain tensioner 34 in the extended position of Fig. 9 is then applied to a section of the chain 67 with opposite chain couplers 42 and 60 being coupled to spaced chain links of the chain 67. An hydraulic fluid line is then connected to the connector 50 on the tensioner 34 and fluid pressure applied to the connector 50. This will cause the piston 37 to be advanced relatively into the cylinder 36 against and compressing the return spring 43 and at the same time the gland 44 is moved further into the sleeve 52. During this movement, the respective ratchet pins 51 on the gland 44 will move along the surfaces of the ratchet teeth 62 against the bias of the spring 64 to "click" into position behind the next set of teeth 62 under the influence of the bias of the spring 64. Movement of the gland 44 into the sleeve 52 will also move the chain couplers

42 and 60 relatively towards each other and thus move the chain links to which they are coupled towards each other thereby applying tension to the chain 67. This procedure will continue with the ratchet pins 51 moving successively into the respective ratchet teeth 62 towards the end wall 53 of the sleeve 52 until sufficient tension is established in the chain 67 to firmly secure the load 68 to the anchoring point 69. The section of chain 67 between the couplers 42 and 60 will adopt or maintain a tension free state and form a loose section or loop 70 of chain 67. When sufficient tension is established in the chain 67 to secure the load 68, the fluid supply is disconnected from the connector 50 or the fluid pressure reduced however the engagement between the ratchet pins 51 and ratchet teeth 62 will maintain the tensioner 40 in the retracted tensioning position and thus the chain 67 tensioned. When it is desired to release the load 68, the connector 50 is reconnected to the hydraulic fluid supply to urge the piston 37 further into the cylinder 36 against the spring 43 so that the tension in the chain 69 is taken by the ram 35. This will relieve the engagement between the ratchet pins 5 land teeth 62 and thus permit the handgrip 66 to be grasped by the user and twisted or rotated against the bias of the spring 64 in the direction of the arrows of Figs.12 and 13. This action will rotate the sleeve 52 anti-clockwise to therefore move the ratchet teeth 62 relatively away from the pins 51 to disengage the ratchet. The hydraulic pressure may then be slowly released and as the ratchet has now been disengaged, the spring 43 combined with the tension in the chain 67 causes the piston 37 and the attached sleeve 52 to move away from the cylinder 36 and thus the chain couplers 42 and 60 away from each other. Tension in the chain 67 is thus released which also releases the load 68. When the handgrip 66 is released, the sleeve 52 will again be rotated by the spring 64 in a clockwise direction to re-engage the pins 51 with the teeth 62. If necessary a pair of chain tensioners 10, 31 or 34 may be associated with a single length of chain for example on opposite sides of the load. In another arrangement, a chain tensioner 10, 31 or 34 may be used to span respective lengths of chain and apply a tension thereto which may then be maintained by any suitable connection between the chain lengths. For example one chain length may be provided with a chain coupler which can be connected to the other chain length after the chain lengths are tensioned by a tensioner 10, 31 or 34. Furthermore whilst the chain tensioner 34 has been described in an application to the restraint of loads on a vehicle, it may be used in many other situations where a multi-link chain is to be tensioned or where any other elongated flexible element is to be tensioned. Usually hydraulic fluid is used to apply the retraction force to the tensioner. In some situations however, the tensioner may be actuated by pneumatic pressure. The terms "comprising" or "comprises" or derivatives thereof as used throughout the specification and claims are taken to specify the presence of the stated features, integers and components referred to but not preclude the presence or addition of one or more other feature/s, integer/s, component/s or group thereof. Whilst the above has been given by way of illustrative embodiment of the invention, all such variations and modifications thereto as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of the invention as defined in the appended claims.

Claims

1. A tensioner for a flexible elongated element or elements, said tensioner comprising at least one fluid ram, said ram having a cylinder and a piston assembly, coupling means at opposite ends of said tensioner and connected to said cylinder and said piston assembly respectively, said coupling means being adapted to be coupled to said elongated element or elements at spaced apart positions whereby fluid pressure applied to said ram causes retraction of said piston assembly relative to said cylinder and tensioning of said element or elements.

2. A tensioner as claimed in claim 1 and including means for resisting retraction of the piston assembly to return to the piston assembly s to an extended position after fluid pressure has been released.

3. A tensioner as claimed in claim 2 wherein said biasing means comprise resilient or elastic means within the cylinder between the piston assembly and one end of the cylinder.

4. A tensioner as claimed in claim 3 wherein said biasing means comprises an elastically compressible gas.

5. A tensioner as claimed in any one of claims 1 to 4 and comprising first and second fluid rams, each said ram having a cylinder and a piston assembly, said fluid rams extending substantially parallel to, and being laterally spaced from, each other.

6. A tensioner as claimed in claim 5 and including first interconnecting means at one end of the tensioner for interconnecting the cylinders and second interconnecting means at the other end of the tensioner for interconnecting the piston assemblies.

7. A tensioner as claimed in claim 6 wherein said interconnecting means are rigidly connected to the cylinders and piston assemblies respectively.

8. A tensioner as claimed in claim 6 wherein at least one of said interconnecting means is pivotally or hingedly connected to the cylinders or piston assemblies respectively.

9. A tensioner as claimed in claim 8 wherein said pivot or hinged connection provides for limited pivotal movement of the interconnecting means about an axis extending transversely to the cylinders and piston assemblies.

10. A tensioner as claimed in any one of claims 6 to 9 wherein said coupling means are connected to the interconnecting means.

11. A tensioner as claimed in any one of claims 6 to 9 wherein said coupling means are incorporated in the interconnecting means.

13. A tensioner as claimed in any one of claims 5 to 12 and including fluid passage means for fluidly interconnecting the respective cylinders to enable fluid pressure to be applied to the respective cylinders to cause retraction of the pistons.

14. A tensioner as claimed in claim 13 wherein said fluid passage means is defined by a hollow member which extending transversely between the respective cylinders.

15. A tensioner as claimed in claim 13 or claim 14 and including a fluid port communicating with said fluid passage means to allow the simultaneous application of fluid pressure to the respective cylinders and therefore cause simultaneous retraction of the rams.

16. A tensioner for a flexible element or elements comprising a fluid ram having a cylinder and a piston movable in said cylinder, coupling means for coupling said cylinder and said piston to said flexible element or elements at spaced apart positions and restraining means between said cylinder and said piston normally permitting said piston to move relative to said cylinder in a first direction for tensioning said element or elements and preventing movement of said piston in a direction opposite said first direction to maintain tension in said element or elements and releasing means selectively actuable to release said restraining means for releasing tension in said element or elements.

17. A tensioner as claimed in claim 16 wherein said restraining means comprises ratchet means.

18. A tensioner as claimed in claim 17 wherein said ratchet means comprises a plurality of teeth fixed for movement with one of the piston and cylinder and one or more pins or engagement members engageable with the teeth fixed for movement with the other of the piston and cylinder.

19. A tensioner as claimed in claim 18 wherein said releasing means comprises means for moving the one or more pins or engagement members out of engagement with one or more of the teeth.

20. A tensioner as claimed in claim 19 wherein said releasing means is rotatable about a longitudinal axis relative to the longitudinal axis of the ram to release the one or more pins or engagement members from the one or more teeth.

21. A tensions as claimed in claim 19 or claim 20 wherein said releasing means carries the teeth.

22. A tensioner as claimed in claim 19 or claim 20 wherein said releasing means carries the one or more pins or engagement members

23. A tensioner as claimed in any one of claims 18 to 21 wherein said one or more pins or engagement members are fixed for movement with the cylinder and the teeth are fixed for movement with the piston.

24. A tensioner as claimed in claim 23 wherein said cylinder terminates at one end in an end member and wherein said end member carries the one or more pins or engagement members.

25. A tensioner as claimed in claim 24 wherein said releasing means comprises a sleeve coaxial with the longitudinal axis of said ram and located around the end member, the sleeve being fixed for longitudinal movement with the piston.

26. A tensioner as claimed in claim 25 and including biasing means for providing a rotational bias to the sleeve to normally urge the teeth into engagement with the one or more pins or engagement members.

27. A tensioner as claimed in claim 26 wherein said biasing means is provided between the end member and sleeve, said biasing means normally urging the sleeve in a first rotational direction about the longitudinal axis to maintain the teeth in engagement with the one or more pins or engagement members.

28. A tensioner as claimed in claim 27 a connector for connecting the cylinder to a source of fluid pressure on said end member, said sleeve having a longitudinally extending slot receiving said connector and permitting longitudinal movement of the connector relative to the sleeve.

29. A tensioner as claimed in any one of claims 25 to 28 wherein said piston is provided with a piston rod to which the sleeve is connected for longitudinal movement with the piston rod and rotational movement about a longitudinal axis relative to the piston rod.

30. A tensioner as claimed in any one of the preceding claims wherein said coupling means comprise female claw hooks for engagement with the chain links of a chain or chains comprising said elongated flexible element or elements.