WO2015104615A1 - A jack - Google Patents

Abstract

The invention relates to a jack with an extendable lifting structure. A fluid driven telescopic ram having a cylinder (90) preferably provides a biasing mechanism for an extendable prop (91) slidably engaged in the cylinder (90). The cylinder (90) is pivotably secured to a base, and the prop (91) to a rigid support harness (60). Two spaced apart posts (10) connected to a lifting head (70) extend slidably through the harness (60) and are adjustably securable relative to the harness (60). A rigid guide collar (50) is fixed at an end of the cylinder (90) opposite the base and the posts (10) extend slidably through the guide collar (50). The posts (10) are hollow and fit over guide rods that are also pivotably secured to the base. The lower end of each post (10) is adjustably securable to the harness (60) through an elongate fastening member provided as a chain. The harness (60) includes a passage for each chain with a chain engaging member removably locatable into the passage. This provides for extension of the lifting structure, which may also take place after an initial stroke of the ram under a load using stops to lock the posts (10) in place on the guide rods, retracting the ram, and re-securing of the harness (60) with the posts (10) in an extended position for a further advance by a second stroke of the ram. The biasing mechanism is secured to the base by a spacer where an increased length of the lifting structure is required for use with the same size biasing mechanism.

Description

A JACK

FIELD OF THE INVENTION

The invention relates to a jack, preferably with a hydraulic ram, which will be used to lift and support a load for recovery of vehicles stuck in off-road conditions and/or for rescue operations which would include extraction of people from wreckage at an accident scene (particularly where a vehicle is trapped beneath a heavy truck and/or trailer) or any in other situation that requires load displacement. BACKGROUND TO THE INVENTION

The use of specialised jacks is common where people take vehicles into off-road conditions. This is particularly so in the case of military vehicles, which are also larger and heavier than most commercially available off-road vehicles. The conditions and circumstances which can lead to a vehicle becoming stuck are numerous, depending on terrain and also weather.

Heavy trucks are commonly involved in motor vehicle accidents. Medical attention can only be provided to the injured once extracted from the wreckage. Even with cutting equipment (such as the "jaws of life") and spreading bar rescue equipment, extraction can still be difficult and time consuming. New developments in vehicle technology can be a problem with high strength body/structural parts making cutting or bending more difficult. The problems and delays are compounded where extraction of injured people is required from vehicles trapped under heavy trucks and/or trailers. Delay in receiving the required medical treatment as a result of being trapped in the wreckage leads to a number of unnecessary fatalities.

A jack which allows relatively easy and quick height adjustment and which can also lift a load to a relatively high level would find application in both of the situations (recovery/rescue) referred to. Such a jack would also, for example, find application in a mine, where there is heavy equipment and/or rock structures which may need to be lifted or shifted and where rescue operations also commonly require moving heavy loads.

OBJECT OF THE INVENTION

It is an object of the present invention to provide a jack which is suited for use in a variety of circumstances. It is a further object of the invention to provide a jack that allows for convenient height adjustment before engaging a load and provides a suitable degree of structural integrity when under the load.

SUMMARY OF THE INVENTION

In accordance with the invention there is provided a jack with an extendable lifting structure comprising: an extensible prop located on a biasing mechanism; the biasing mechanism secured to a base at one end with the prop extending from the other end and secured to a rigid support harness; a post with a lifting head extending slidably through the harness and adjustably securable relative to the harness; with the prop and the post slidably guided between the harness and the base. The invention further provides for a jack as defined in which the biasing mechanism is secured to the base by a spacer; and which includes a fluid driven telescopic ram having a cylinder providing the biasing mechanism with the prop slidably engaged in the cylinder.

Further features of the invention provide for a jack as defined in which a rigid guide collar is fixed at an end of the cylinder opposite the base and the post extends slidably through the guide collar; in which the post is hollow and fits over a guide rod secured to the base; in which the guide rod extends to adjacent the guide collar; and in which a stop for an end of the post opposite the lifting head is adjustably securable along the guide rod.

Further features of the invention provide for a jack as defined in which the cylinder is pivotably secured to the base; and in which the cylinder and guide rod are pivotably secured to the base.

Further features of the invention provide for a jack as defined in which an end of the post opposite the lifting head is adjustably securable to the harness; in which an end of an elongate fastening member is secured to the end of the post opposite the lifting head and a body of the fastening member is releasably securable at positions along the body to the harness; in which the fastening member is a chain; in which the harness includes a passage for the chain with a chain engaging member removably locatable into the passage. Further features of the invention provide for a jack as defined in which the post has a profiled cross-section and extends through correspondingly profiled guide passages in the harness and guide collar to prevent axial rotation of the post relative to the harness and guide collar; and in which the post has a square cross- section and extends through square profiled guide passages in the harness and guide collar. Further features of the invention provide for a jack as defined in which a pair of parallel spaced apart posts extends from the lifting head through the harness and guide collar with the posts respectively located on either side of the ram; in which the harness and guide collar brace the spaced apart posts; in which the harness is provided as a crossbar secured to the end of the prop with the guide passages for the posts on either side; and in which the guide collar is provided as a crossbar secured to the cylinder with the guide passages for the post on either side.

Further features of the invention provide for a jack as defined in which a pair of spaced apart rams are provided with cylinders that extend from the base to the guide collar and the post is located between the rams; in which the harness extends between ends of two props; in which the guide collar is secured to the base; in which the guide collar is secured to the base by suitably tensioned ties; and in which the guide collar is secured to the base by belt ties with ratchet fasteners.

In accordance with a further aspect of the invention there is provided a jack with an extendable lifting structure comprising: a fluid driven ram secured to a base; an extension post slidably guided for movement along the ram relative to the base; the ram having a harness adjustably securable to the post for a first advance of the post by at least part of a stroke of the ram; the post securable relative to the base for release of the harness, retraction of the ram, and re-securing of the harness with the post in an extended position for a second advance of the post by at least part of a stroke of the ram. BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the invention will become more apparent from the following description, made by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a perspective view of a jack with a ram in a partially extended position and a lifting structure in a partially extended condition;

Figure 2 shows a front view of the jack in Figure 1 ;

Figures 3 & 4 show exploded views of the lifting structure of the jack;

Figure 5 shows perspective views of a base for the jack in exploded and assembled condition;

Figure 6 shows a front view of the jack with the ram in a retracted position and the lifting structure in a retracted condition;

Figure 7 shows a front view of the jack with the ram moved into an extended position and the lifting structure in a retracted condition together with details of a post locking mechanism; Figure 8 shows details of a mechanism to adjustably secure the posts to a harness of the ram;

Figure 9 shows a front view of the jack with the ram in a retracted position and the lifting structure in an extended condition;

Figure 10A shows a front view of three versions of the jack with lifting structures of different length;

Figure 10B shows a front view of an alternative embodiment of a jack with the ram in an extended position and the lifting structure in a partially extended condition;

Figures 1 1 & 12 show a pair of jacks arranged to lift a trailer body; and

Figure 13 shows a jack arranged to lift a military vehicle. DETAILED DESCRIPTION OF THE INVENTION

Referring to Figures 1 to 9 of the drawings, a first embodiment of a jack (1 ) in accordance with the invention includes an extendable lifting structure (1 1 ) as described below. A hydraulic telescopic ram (90; 91 ) is pivotably mounted onto a base comprising a footplate (100) located on a base plate (30). The ram includes a cylinder (90) secured to the base (30; 100) at one end and an extensible prop (91 ) that protrudes from the other end of the cylinder (90) and is connected into the lifting structure (1 1 ).

Figures 3 and 4 illustrate details of the components of the lifting structure (1 1 ) of the jack (1 ) and Figure 5 illustrates the components of the base (30; 100). A free end of the prop (91 ) is fitted with a rigid support harness (60). A pair of spaced apart posts (10) extends slidably through the harness (60). A lifting head (70) is mounted across the free, upper ends of the posts (10) and carries a load engaging formation (80) that serves to engage (or be secured to) a structure to be lifted or displaced by the jack (1 ).

The posts (10) are adjustably securable relative to the harness (60), which in turn links them to the prop (91 ) of the ram (90; 91 ). A guide collar (50) is fixed to the cylinder (90) adjacent the prop (91 ) and the posts (10) extend slidably through the guide collar (50). The posts (10) are located on either side of the ram (90; 91 ) and these three components are substantially coplanar in this embodiment. The posts (10) are slidably guided between the harness (60) and the base (30; 100) by the guide collar (50) and a pair of guide rods (20).

Each post (10) has a profiled cross-section and extends through correspondingly profiled guide passages in the harness (60) and guide collar (50) to prevent axial rotation of the posts (10) relative to the harness (60) and guide collar (50). More specifically, each post (10) has a square cross-section and extends through a square profiled guide passage in the harness (60) and guide collar (50). The posts (10) are accordingly provided as two spaced apart square tubes (10). The tubes (10) are hollow and respectively fit over the guide rods (20) which are secured to the footplate (100) of the base (30; 100). The guide rods consist of two round tubes (20) that extend slidably into the square tubes (10). The guide rods (20), which guide the posts (10) internally, extend to adjacent the guide collar (50), which guides the posts (10) externally. The guide rods (20) are also pivotably secured to the base (30; 100). The prop (91 ) is guided by the guide collar (50) and by the inside of the cylinder (90).

The lifting head (70) has a square socket (74) to receive a square spigot of the load engaging formation (80), which is secured using a pin through a hole (76). This may alternatively be provided as a round socket to receive a round spigot on the load engaging formation. The round components will allow rotation of the load engaging formation (80) relative to the lifting head (70). This feature provides for rotational adjustment of the position of the load engaging formation (80) where required or desirable for lifting operations.

Two square sockets (78.1 ; 78.2) in the underside of the lifting head (70) receive ends of the posts (10). The square tubes (10) each have at their upper ends a pair of holes (10.1 ) for engagement within the sockets (78.1 ; 78.2) of the lifting head (70).

The round tubes of the guide rods (20) have a number of equally spaced apart holes (20.2) along their length and, adjacent the top end, a hole (20.1 ) to receive a pin that retains an oil based round nylon guide (22) sized to bear against the inside of the walls of the square posts (10). At the bottom end is a base bracket hole (20.3).

An elongate fastening member (120) is secured to the end of the post (10) opposite the lifting head (70) and a body of the fastening member (120) is releasably securable at positions spaced along the body to the harness (60). The fastening member in this embodiment is a chain (120). The harness (60) includes a passage (63) for the chain (120) with a chain engaging member or fastener (69) removably locatable into the passage (63).

The bottom or lower ends of the two square tubes (10) have load supports (40) welded in place. The chains (120) are secured to the supports (40). This arrangement provides for the end of each post (10) opposite the lifting head (70) to be adjustably securable to the harness (60) through engagement of the elongate body of the chain (120) in the passages (63). Each bottom support (40) of the posts (10) consists of front and back plates (44; 42), with side plates (41 ; 43) and two top plates (45.1 ; 45.2). Chain link anchor brackets (46) are provided on the front plate (44). A pair of holes (47.1 ; 47.2) is positioned below the anchor brackets (46) with a corresponding pair of holes in the back plate (42).

An oil based nylon guide (48) with a round bore (48.1 ) is fitted into the bottom end of each support (40) and secured in place with bolts and nuts located through corresponding holes (48.2; 48.3) and (47.1 ; 47.2). The guide (48) provides for smooth longitudinal telescopic movement of the round tube (20) through the bottom end of the post (10).

The harness (60) is provided as a crossbar (61 ) secured to the free end of the prop (91 ) with the two guide passages (62) for the posts (10) provided therethrough. An oil based nylon guide (68) is positioned in each of the guide passages (62) providing a close guided sliding fit to the posts (10).

The two spaced apart chain passages (63) are provided as channel formations (63) on the crossbar (61 ), which slidably receive the two chain fasteners (69). The chain fasteners (69) are slidable over two chain port holes (65) provided through lugs (67) provided across the channel formations (63). The lugs (67) provide an upwardly facing shoulder around each hole (65) forming a seat against which the chain fasteners (69) bear when the jack (1 ) is in use. The fasteners (69) are retained by two pins (66).

Positioned centrally between the two guide passages (62), in the underside of the harness (60), is a round socket (64) - see Figure 2 - for engagement onto the prop (91 ).

The guide collar (50) is also provided as a crossbar (51 ) securely mounted on the cylinder (90) with the guide passages (52) for the posts (10) located on either side. Two oil based nylon guides (68) are also positioned within the passages (52) providing a close guided sliding fit to the posts (10).

The harness (60) and guide collar (50) brace the spaced apart posts (10), maintain the posts (10) in parallel relationship and resist axial rotation of the posts (10) during operation of the jack (1 ).

The harness (60) accordingly provides a brace for the lifting structure (1 1 ) and guides the posts (10) during an adjustment operation as the posts (10) and lifting head (70) are moved from a retracted condition to an extended condition [relative to the harness (60)] as described below. The guide collar (50) provides a brace which guides the posts (10) as the prop (91 ) is moved from a retracted position to an extended position in the lifting or biasing operation [wherein the lifting head (70) is moved with the harness (60)] as described below. The hydraulic ram (90; 91 ) has a custom fitted pivoting bracket (94), a control valve (93), and a shoulder formation (92) for engagement with the guide collar (50) adjacent the extendable prop (91 ). The ram (90; 91 ) is fitted onto the footplate (100) and the prop (91 ) placed into position extending through a hollow spigot (54) with the shoulder formation (92) abutting a corresponding shoulder (not shown) inside the guide collar (50). A suitable power pack or hydraulic pump unit with controls (not shown) will be connected through the valve (93). The operation of two stops (24) providing anchor brackets securable to the guides (20) and the chain engaging members (69) will be described in more detail below, with reference to Figures 7 and 8.

Referring to Figure 5, the base plate (30) has four anchor spigots (31.1 ; 31 .2; 31 .3; 31 .4), two ratchet assembly brackets (34; 35), two base plate handles (32; 33) and three anchor brackets (36; 37; 38). The anchor brackets (36; 37; 38) will be used if necessary during lifting (or rescue and recovery) operations for to secure the base plate (30) against slipping out from a position required for lifting or displacing vehicles that are stuck (or trapped vehicle bodies). The footplate (100) has four holes (100.1 ; 100.2; 1 00.3; 100.4) adjacent its corners that will be fitted over the spigots (31 .1 ; 31 .2; 31.3; 31 .4) when located onto the base plate (30). Two ratchet assembly brackets (102; 103) are provided at opposite ends of the footplate (100). A ram mounting bracket (107) is centrally positioned on the footplate (100) between two guide rod mounting brackets (106; 108). The load lifting structure (1 1 ) and ram (90; 91 ) are secured to the footplate (100) with appropriate pins and/or bolt and nuts (not detailed specifically in the drawings) at relevant brackets (106; 107; 108).

The footplate (100) is then fitted onto the base plate (30) over the spigots (31 .1 ; 31 .2; 31 .3; 31 .4). Figure 5(c) shows the foot plate (100) fitted onto the base plate (30). The spigots (31 .1 ; 31.2; 31 .3; 31 .4) do not show any specific securing means but are each provided with a hole for a pin, bolt and nut or other suitable fastener that may be used. The guide collar (50) is also secured to the base (30; 100) separately from its connection through the base-mounted cylinder (90). In this embodiment, the guide collar (50) is secured to the base plate (30) by a web-belts (57) and ratchet fasteners (56). These ratchet assemblies also serve to tie the bottom-mounted cylinder (90) to which the guide collar (50) is secured to the base and hold the footplate (100) which carries the cylinder (90) against the base plate (30). The two ratchet fasteners (56) are fitted to brackets (55) on the guide collar (50) and J-hooks (58) on the ends of the web-belts (57) are connected to brackets (34; 35) on the base plate (30). The two ratchet fasteners (56) are used to tension the web-belts (57). The connection of the ram (90; 91 ) and lifting structure (1 1 ) to the base (30; 100) allows for pivoting between these components where this is required during operation. This is, for example, relevant where one side of a vehicle is lifted and moves in an arc relative to the side which remains in contact with the ground. A person skilled in the art will understand and appreciate the relevance of this feature of pivoting with the load in other circumstances.

Where the jack (1 ) is to be used in a confined space for a lifting (rescue/recovery) operation, this may be done using only the footplate (100), removed from the base plate (30). In such a case, the two ratchet assembly brackets (102; 103) on the footplate are used to tether the guide collar (50). When the jack (1 ) is not in use, the base plate (30) may also be removed for easy storage of the equipment.

In a development of the embodiment illustrated, a pair of cables will be secured between the collar (50) and footplate (100). The cables will be located beneath or on the inside of the web-belts (57) to either side of the collar (50). The cables will extend between and be connected to brackets of the kind used for the ratchet fasteners (56) and J-hooks (58) and may include turnbuckles to apply a suitable tension. The web-belts (57) or cables as referred to secure the cylinder (90) to the base (30; 100) and provide support to the lifting structure (1 1 ) lateral to the plane of pivoting. During operation, the web-belts (57) or cables will also provide a tactile and/ or visual indication of any such lateral loading of the jack (1 ).

Each chain (120) is permanently fitted to the load lifting structure (1 1 ) and includes a chain handle (120.1 ) that prevents the chain (120) from sliding through and out of the ports (65) on the harness (60). The chain (120) is anchored to the bottom load support (40) by a chain link (120.2) secured to the chain anchor brackets (46).

Referring to Figure 6, the jack (1 ) is shown with the prop (91 ) in the lowered, retracted position with the harness (60). The prop (91 ) rests on the hollow spigot (54) of the guide collar (50) which is fixed to the cylinder (90) and the lifting head (70) locates against the harness (60) when the lifting structure (1 1 ) is in the retracted condition. In this drawing, the chains (120) have been positioned and engaged by the fastening members (69) in a manner that provides only a small gap between the harness (60) and lifting head (70) - the lifting structure (1 1 ) is thus substantially in a fully retracted condition.

In Figure 7 the ram (90; 91 ) has been actuated, moving the prop (91 ) out of the cylinder (90), into the extended position with the lifting structure (1 1 ) in the retracted condition.

During operation of the jack (1 ) it may be necessary (for safety and/or practical reasons) to anchor the posts (10) to guide rods (20) under or against a lifted or displaced load.

The stops (24) are provided as channel sections that will be attached to the guides (20) below the supports (40) of the posts (10). The stops (24) are locked to the guide rods (20) by fitting pins (124) though any of spaced apart holes (24.1 ; 24.2; 24.3) which will be aligned with a hole (20.2) through the guide rod (20). The spaced apart holes (24.1 ; 24.2; 24.3) facilitate location of a top shoulder of the stop (24) in close proximity to the bottom of the post (10). Each specific rescue/recovery operation will have a required height to which a load will be lifted. The supports (40) may thus, during use, be located at varying positions spaced from the holes (20.2) in the guide rods (20). In the insert/detailed view of Figure 7(b), this spacing is small in the drawing on the left and larger in the drawing of the right (as indicated by the arrows). Each stop (24), with its spaced holes design, accommodates this varied spacing and enables close location to the supports (40) by selecting any of three different positions relative to the closest hole (20.2). The adjustable engagement of the stops (24) to the guide rods (20) accordingly fills (to an available degree) the space between the supports (40) and the closest hole (20.2).

Once the stops (24) are secured in place on the guide rods (20) an operator will lower the ram (90; 91 ) in a controlled manner to bring the supports (40) to rest against the stops (24). The full load will then be carried by the lifting head (70), posts (10) and guide rods (20).

The stops (24) may alternatively be provided as cylindrical sleeves with spaced apart openings that are fitted onto the guide rods (20) below the posts (10). Where adjustment for varied spacing is not required, the stops (24) may be provided by pins that locate through the holes (20.2).

Referring to Figure 8(a), the chain fastener (69) includes a handle (69.1 ), a planar body (69.2) provided as a plate with a chain anchor slot (69.3) and two stops (69.4; 69.5). During assembly, the retaining pins (66) will be inserted after the fasteners (69) have been located onto the lugs (67) across the passages (63).

Figure 8(b) shows the chain (120) engaged by the fastener (69) which has been pressed into the passage (63) with a link of the chain (120) aligned and within the chain slot (69.3). A link of the chain (120) above the fastener (69) is maintained transverse to the slot (69.3) and locked in place. With the fastener (69) properly inserted, the chain (120) is engaged to the harness (60), which is in turn connected to the support (40).

Referring to Figure 8(c), the chain fastener (69) is pulled back and withdrawn from the chain port (65) to allow travel of the chain through the passage (63) and repositioning of the chain (120) [and thus the posts (10)] relative to the harness (60).

This procedure for re-positioning of the chains (120) allows initial extension of the lifting structure (1 1 ) before the jack (1 ) is used but with the jack (1 ) under a load, can only be completed once the lifted load tension has been released from the chains (120) by lowering the prop (91 ) and allowing the load to be transferred to the guide rods (20) through the stops (24). During operation and after the tension from a lifted load has been released from the chains (120), with the supports (40) resting on the stops (24), the chain anchor bracket (69) the chain anchor bracket handle (69.1 ) is pulled back until the two stops (69.4; 69.5) rest against the retaining pin (66). The chain anchor slot (69.3) will be clear from the chain links and the operator uses the chain handle (120.1 ) to reset the chain (120) in the desired position.

Referring to Figure 9, the load lifting structure (1 1 ) has been moved into an extended condition with the posts (10) connected to the harness (60) by the chains (120).

It will be understood that the jack (1 ) can be placed in this extended condition either: i. for an initial lifting stroke of the ram (90; 91 ) to reach a suitable load engaging height before lifting; or

ii. after an initial stroke executed in a substantially retracted condition [as shown from Figure 6 to Figure 7] the lifting structure (1 1 ) can be secured using the stops (24), the ram (90; 91 ) moved back to a retracted position, the chains (120) adjusted (shortened) relative to the harness (60) to reengage the posts (10) and a second stroke of the ram (90; 91 ) can be executed in an extended condition to obtain a further lift.

A person skilled in the art will appreciate how this adjustable feature of the jack (1 ) can be used to obtain different lifts from different initial load engaging heights either in a single stage or in two or more stages.

It will also be appreciated that the chain (120) which is used to obtain the adjustable connection between the harness (60) and posts (10) may be replaced with other mechanical locking means such as a rack and pinion gear bar, and/or any custom designed mechanical link mechanism that will effectively link and secure the harness (60) to the supports (40). In a development of the invention, the posts (10) may be engaged directly by the harness (60) through suitable locking means, such as pins that extend through holes in the posts (10) above the harness (60). Such a change would allow the necessary adjustable engagement of the harness (60) relative to the posts (10). The structure would then not involve the transfer of the lifting load from the harness through tension in a chain (or other elongate member) to the bottom ends of the posts. Instead, the lifting head, posts, harness and prop would resist the lifting load in compression.

A bottom end of the extendable prop (91 ) provides a point at which the jack lifting structure (1 1 ) is actuated to lift a load. In the illustrated preferred embodiment, the hydraulic cylinder (90) with a piston (not shown) to which a foot of the prop (91 ) at the bottom end is secured provides the biasing mechanism for the jack (1 ). It will be appreciated that this may be replaced by an alternative biasing mechanism (located between a base and the prop) such as a screw type jack, a scissor jack, a rack and pinion type jack, or any other suitable load lifting device. Referring to Figure 10A, the jack on the left (1 a) is equivalent to the one illustrated in the previous drawings. The two versions of the jack in the middle (1 b) and on the right (1 c) illustrate the use of a spacer (300b; 300c). The spacer (300b; 300c) enables the use of a lifting structure (312b; 312c) with extended posts (310b; 310c) and guide rods (not shown). Apart from the use of longer chains (320b; 320c) the construction is substantially the same as that of the jack (1 a), without a spacer (300b; 300c). The spacer (300b; 300c) enables the use of a longer lifting structure (312b; 312c) with a ram (301 ) of given length that can be advanced by more than two stages or strokes of the ram. These variations of the invention further illustrate how the jack provides a feed mechanism for the extension of the lifting structure under a load or a manual mechanism for extension to a given height for initial engagement of a load.

The lifting structure can either be fully extended before lifting and then the lifting is effected for a single extension of the ram or a load can be engaged with the lifting structure fully retracted and then incrementally extended for further lifting until both the lifting structure and ram are fully extended, which represents the full displacement of the jack. The invention accordingly provides a jack with an extendable lifting structure comprising: a a fluid driven ram secured to a base;

b an extension post slidably guided for movement along the ram relative to the base;

c the ram having a harness adjustably securable to the post for a first advance of the post by at least part of a stroke of the ram;

d the post securable relative to the base for release of the harness, retraction of the ram, and re-securing of the harness with the post in an extended position for a second advance of the post by at least part of a stroke of the ram. Referring to Figure 10B, a second embodiment of a jack (2) with an extendable lifting structure (12) is illustrated. The jack (2) includes a pair of spaced apart rams (81 ; 82) with cylinders (82) that extend from a base (3) to a guide collar (4). A single post (10) with a lifting head (107) is located between the rams (81 ; 82) and over a guide rod (150). A rigid harness (130) extends between ends of two extendable props (81 ) which protrude from the cylinders (82).

A chain (200) is secured at (200.2) to a load support (40) on the bottom of the post (10). The chain (100) is adjustably securable at (136) to the harness (130). The free end of the chain has a handle (200.1 )

This configuration of the jack (2) provides an alternative to that of the first embodiment with the symmetrical, balanced arrangement of the rams and posts reversed. The operation of this jack will be substantially the same as that of the first embodiment and not repeated.

A number of accessories may be used with the jack (1 ). Referring to the examples of use illustrated in Figures 1 1 to 13, these may include various chain assembly units (121 ) with D-shackles or chain links (123) and various types of polyester type slings and web-belt ties (126) with ratchet fasteners.

The configuration of the load engaging formation (80) that is fitted to the lifting head (70) may be varied depending on the specific rescue and/or recovery operation to be performed. The load engaging formation (80) may also be adapted for use with fastening accessories (as will be illustrated in Figure 13 described below). Formations (80) of varied configuration will preferably be provided with the jack (1 ).

In Figures 1 1 and 12, two jacks (1 ) are shown arranged on opposite sides of a trailer body (140). The trailer body (140) is detailed with its wheel-base (146) removed in Figure 1 1 to illustrate the cross-connection between the jacks (1 ). The jacks (1 ) will each be placed under the trailer body (140) at selected load lifting points (142; 144). Exact positioning will depend on the circumstances. The operators will position the lifting head (70) with an L-shaped load engaging formation (129) at the load lifting points (142; 144). This is done by adjustably securing the chains (120) to the harness (80). Alternatively, where the height of the points (142; 144) does not require extension of the lifting structure (1 1 ), the ram (90; 91 ) can be operated to place the load engaging formations (129) in contact with the points (142; 144).

The load engaging formations (129) will be secured in position by attachment of restraining devices such as chain assembly units (121 ) and ratchet and web-belt ties (126). In this example, the restraints are connected between the jacks (1 ) below the body (140). Once the load engaging formations (129) are secured in position, the operators can proceed with the controlled lifting of the trailer body (140) through extension of the rams (90; 91 ).

With the trailer body (140) lifted the operators can secure the load lifting structure (1 1 ) into a safe locked position by securing the stops (24) below the bottom load supports (40) and controlling retraction of the ram (90; 91 ) to bring the posts (10) to rest against the stops.

Retraction of the rams (90; 91 ) will also release the load tension in the chains (120) and resetting of the chains (120) can take place on either or both sides if further lifting is required using the second stage lifting feature of the invention. With the chains (120) repositioned on the lowered harness (60) the operator actuates a second stroke of the ram (90; 91 ). The stops (24) will then need to be moved up the guide rods to lock the lifting structure (1 1 ) in the second, higher position. To enable the lowering of the lifted trailer body (140) once the rescue/recovery process is completed the operators will perform the following procedures:

- If the lifting process was completed with a single stage, the operator extends the ram (90; 91 ) to lift the bottom load supports (40) off the stops (24) which are then removed to enable lowering of the lifting structure (1 1 ). Once the load is supported on the ground (230) and the tension on the chain (120) has been fully released the operator will remove the jack (1 ) from the trailer body (140).

- If the lifting process was completed with an additional stage involving extension of the lifting structure (1 1 ) while the jack (1 ) is under the load, the operators will similarly lift the supports (40) to remove and reposition the stops (24) to allow lowering of the ram (90; 91 ) by approximately a full stroke for re-engagement of the lowered stops (24) with the bottom supports (40).

The tension in the chains (120) is released and the chain engaging members (69) are disengaged. The operator extends the prop (90; 91 ) to a position where the harness (60) is just short of the lifting head (70) or approximately 10 centimetres from a fully extended position. The chains (120) are re- secured to the harness (60) and the ram (90; 91 ) lifted slightly to allow removal of the stops (24) once again. The ram (90; 91 ) is lowered until the load rests on the ground (230). In this manner, a two stage lowering process is performed to undo the two stage lifting process of the jack (1 ).

In Figure 13 a jack (1 ) is placed in engagement with the front of a military type heavy-duty vehicle (250).

Recovery of military type vehicles (250) will usually take place in off-road (typically, sandy, muddy or rocky) conditions where the surface (230) will be unstable or the terrain uneven. The recovery of military vehicles (250) will primarily be executed by engaging the side, front or rear of the vehicle (250) as opposed to lifting from under the vehicle. The recovery procedure in this example employs custom attachment brackets (79.1 ; 79.2) fitted onto the lifting head (70), which is used without an engaging formation (80).

As most military vehicles (250) have adequate front and back lifting hooks (252) the jack (1 ) is placed in position in front of the vehicle (250). The required lifting accessories such as a chain assembly units (121 ) and D-shackles (122) will be attached to the attachment bracket (79.1 ; 79.2) and to the lifting hooks (252).

The lifting and lowering operation of the jack (1 ) for the military vehicle (250) to enable a safe "de-bogging" of the tires (254) will be the same as discussed for the trailer body (140) recovery operations and are not be repeated. As already implied, recovery of the military (250) type vehicles can also be done from any side of the military vehicle (250) and is not restricted to the image shown. It will be appreciated that a number of variations may be made to the features of the described embodiments without departing from the scope of the invention.

The jack may be used as lifting/structural support such as a prop in an underground mine, for example, and suitable modifications may be made for such use.

Specifics of operation will depend on particular variations and also the circumstances and preference of or procedures provided to the operators of the jack.

Claims

1. A jack with an extendable lifting structure comprising:

a. an extensible prop located on a biasing mechanism;

b. the biasing mechanism secured to a base at one end with the prop extending from the other end and secured to a rigid support harness; c. a post with a lifting head extending slidably through the harness and adjustably securable relative to the harness;

d. with the prop and the post slidably guided between the harness and the base.

2. A jack as claimed in claim 1 in which the biasing mechanism is secured to the base by a spacer.

A jack as claimed in claim 1 or claim 2 which includes a fluid driven telescopic ram having a cylinder providing the biasing mechanism with the prop slidably engaged in the cylinder.

A jack as claimed in claim 3 in which a rigid guide collar is fixed at an end of the cylinder opposite to the base and the post extends slidably through the guide collar.

5. A jack as claimed in claim 3 or claim 4 in which the post is hollow and fits over a guide rod secured to the base.

6. A jack as claimed in claim 5 in which the guide rod extends to adjacent the guide collar.

7. A jack as claimed in claim 5 or claim 6 in which a stop for an end of the post opposite the lifting head is adjustably securable along the guide rod.

8. A jack as claimed in claim 3 or claim 4 in which the cylinder is pivotably secured to the base.

9. A jack as claimed in any one of claims 5 to 7 in which the cylinder and guide rod are pivotably secured to the base.

10. A jack as claimed in any one of claims 1 to 9 in which an end of the post opposite the lifting head is adjustably securable to the harness.

1 1 . A jack as claimed in claim 9 in which an end of an elongate fastening member is secured to the end of the post opposite the lifting head and a body of the fastening member is releasably securable at positions along the body to the harness.

12. A jack as claimed in claim 1 1 in which the fastening member is a chain.

13. A jack as claimed in claim 12 in which the harness includes a passage for the chain with a chain engaging member removably locatable into the passage.

14. A jack as claimed in claim 4 in which the post has a profiled cross-section and extends through correspondingly profiled guide passages in the harness and guide collar to prevent axial rotation of the post relative to the harness and guide collar.

15. A jack as claimed in claim 14 in which the post has a square cross-section and extends through square profiled guide passages in the harness and guide collar.

16. A jack as claimed in claim 4 in which a pair of parallel spaced apart posts extends from the lifting head through the harness and guide collar with the posts respectively located on either side of the ram. A jack as claimed in claim 16 in which the harness and guide collar brace the spaced apart posts.

A jack as claimed in claim 17 in which the harness is provided as a crossbar secured to the end of the prop with the guide passages for the posts on either side.

A jack as claimed in claim 17 or claim 18 in which the guide collar is provided as a crossbar secured to the cylinder with the guide passages for the post on either side.

A jack as claimed in claim 4 in which a pair of spaced apart rams are provided with cylinders that extend to the guide collar and the post is located between the rams.

A jack as claimed in claim 20 in which the harness extends between ends of two props.

A jack as claimed in any one of claims 14 to 21 in which the guide collar is secured to the base.

A jack as claimed in claim 22 in which the guide collar is secured to the base by suitably tensioned ties.

A jack as claimed in claim 23 in which the guide collar is secured to the base by belt ties with ratchet fasteners.

A jack with an extendable lifting structure comprising

a. a fluid driven ram secured to a base; b. an extension post slidably guided for movement along the ram relative to the base;

c. the ram having a harness adjustably securable to the post for a first advance of the post by at least part of a stroke of the ram;

d. the post securable relative to the base for release of the harness, retraction of the ram, and re-securing of the harness with the post in an extended position for a second advance of the post by at least part of a stroke of the ram.