GB2241936A - Improved lifting arrangement - Google Patents

Abstract

In order to achieve simultaneous and constant raising of a roof, e.g. a vehicle roof at all corners or edges (in order to prevent warping) at least two, preferably four, hydraulic jacks 10, 20, 30, 40 each including a slideably piston rod 12, 22, 32 42, linked together to form a "closed system". One connecting tube 54 passes through a pump 50 which can be operated to displace fluid within the system. When the pump 50 is actuated fluid will be supplied to a first jack 10 causing a displacement of the piston 12. This displacement forces fluid out of the first jack 10 and into the second jack 20 causing a corresponding piston displacement. Thus the third and fourth jacks 30, 40 are also subject to piston displacement by movement of the fluid. <IMAGE>

Description

IMPROVED LIFTING ARRANGEMENT This invention relates to an improved lifting arrangement especially for the raising and lowering of a vehicle roof of, for example a cargo compartment of a commercial vehicle, for example a container truck or similar.

In order to provide maximum usage of available space in a cargo carrying vehicle, for example a commercial truck or wagon, it is known to provide lifting means operable to raise and lower the roof of such a vehicle such that cargo may be stacked between the support beams of the roof structure itself. Such lifting arrangements commonly use pneumatic or hydraulic jacking arrangements, at least one such jack being provided at each corner of the roof.

A problem inherent in such an arrangement is achieving the simultaneous control of each of the jacks such that no one corner of the roof is raised or lowered faster than another in order to avoid warping or stressing of the roof. Such a problem is magnified where an uneven load is spread over the surface of the roof as would be common for example when snow or ice is present on the roof surface.

Previously known solutions to this problem have revolved around provision of a single two way ram directly controlled by the vehicle's operator. In turn movement of this ram simultaneously causes displacement of rams in hydraulic jacks causing raising or lowering of the roof. By use of a solid plate connecting the two way ram with each of four displacement rams any movement in the two way ram can be directly transmitted to the displacement rams which are each moved an equal distance.

In this way equal movement of the roof jacks positioned at each corner of the vehicle roof can be achieved.

Such a method is however, cumbersome and requires use of an additional two way jack and the balancing apparatus required to transmit the movement of the two way ram to each of the single action displacement rams can be subjected to uneven stresses caused by snow etc on the vehicle roof.

Similar requirements and problems are found in other applications of hydraulic jacks as lifting means, for example car inspection ramps.

It is an object of the present invention to provide an improved lifting arrangement which is simple in construction and is operative to balance its displacement equally across an attached surface.

With this object in view the present invention provides an improved lifting arrangement comprising at least two hydraulic jacks, each having a piston and an associated piston rod, attached to a vertically displaceable surface, the jacks being connected to each other by fluid transfer pipes such that fluid expelled from one jack by displacement of its piston rod will be supplied to a second jack causing displacement of its respective piston rod, the arrangement further including means to cause displacement of at least one piston rod in the arrangement. In a first aspect of the invention the arrangement further includes pump means operative to receive fluid from one jack in the arrangement and supply it to a second jack thereby to cause a displacement of the second jack's piston rod.

It will be appreciated with the arrangement described there will always be a fixed amount of fluid within the arrangement such that activation of the pump will supply fluid to a first jack, displacement of which will cause expulsion of fluid therefrom to a second jack, which will cause consequent expulsion of further fluid into either a third jack, if present, or back to the pump.

The net result of actuation of the pump will, therefore, be a simultaneous movement in each of the jacks disposed in the arrangement by an equal amount.

A second aspect of the invention includes lifting means operative to raise or lower the attached surface thereby causing a displacement of at least one piston rod attached thereto.

It will be understood that in this arrangement the lifting means can be located near one corner or edge of the surface and that the force exerted thereon is equalised across the surface by the corresponding movement of the associated jacks.

In order that each of the jacks is moved by an equal amount it is advantageous to provide an hydraulic jack in which the piston rod extends throughout the jack's cylinder. In this way the volume on each side of the piston head is equal and, therefore, the fluid displacement between opposing sides of the piston head from jack cylinder to jack cylinder is of an equal amount.

For the case where the cylinder jacks only include a piston rod on one side of the piston head the interconnection of the jacks is preferably such so that alternate jacks are simultaneously extended and retracted. By connection of those jacks which are retracted to a sliding bracket arrangement such that the roof of the vehicle is practically pulled upwards the motion of each jack can be translated into a raising or lowering of the surface.

Preferably the arrangement includes four jacks disposed at respective corners of a vehicle's roof to cause raising and lowering of same.

The invention will be described further by way of example the accompanying drawings in which: Fig. 1 is a diagrammatic representation of a first preferred embodiment of the improved vehicle roof lifting arrangement; and Fig. 2 is a diagrammatic representation of a second embodiment of the arrangement of the invention.

Referring firstly to Fig. 1, a first preferred embodiment of ta first aspect of the invention includes four hydraulically operated jacks 10, 20, 30, 40. Each jack 10, 20, 30, 40 comprises a piston rod 12, 22, 32, 42 arranged to be slidably displaceable within the cylinder 14, 24, 34, 44. A piston head 16, 26, 36, 46 is rigidly secured to the piston rod 12, 22, 32, 42 and enclosed within the cylinder 14, 24, 34, 44. The piston head is thereby effective to define within the cylinder a first space 17, 27, 37, 47 and a second space 18, 28, 38, 48 arranged on opposing sides of the piston head.

It will be appreciated that the volume within each cylinder 14, 24, 34, 44 is constant regardless of the positioning of piston head 16, 26, 36, 46. Thus movement thereof only serves to alter the volume ratio between first space 17, 27, 37, 47 and second space 18, 28, 38, 48. In operation each of the cylinders is filled by a fluid media (not shown).

The arrangement according to the invention also includes a pump 50 which is connected to first space 17 jof first cylinder 10 by a tube 52. The pump is also connected by a further tube 54 to second space 48 of fourth hydraulic jack 40. Additional tubes are also provided connecting first space 47 of the fourth jack to the second space 38 of the third jack, the first space 37 of the third jack 30 to second space 28 of second jack 20 and first space 27 of second jack 20 to second space 18 of first jack 10.

It will be apparent that operation of the pump to either draw fluid from first space 17 of first jack 10 and to supply same to second space 48 of fourth jack 40 will result in a movement of all four piston rods 12, 22, 32, 42. This will be caused by piston head 46 being moved upward by addition of fluid to second space 48 causing the expelling of fluid from first space 47 into the third jack 30. A corresponding amount of fluid will be expelled from first space 37 and third jack 30 into second jack 20 and so on. In this way each of the jacks rises by a corresponding amount as the total volume of fluid within the arrangement is constant at all times.

As the pressure on any one of the four jacks 10, 20, 30, 40 is equalised across the arrangement by way of the common fluid flow there can be no disproportionate raising or lowering causing flexing or warping of an attached vehicle roof.

Turning now to Fig. 2 a second embodiment of the first aspect of the invention also contains four hydraulically operated jacks essentially similar to those of the first embodiment and similar parts will therefore be identified using the same reference numerals as in the first embodiment. The second embodiment includes four hydraulically operated jacks 10, 20, 30, 40 each having piston rods, cylinders and piston heads as in the first embodiment. In the second embodiment, however, the piston head is located at the end of the piston rod whilst still operative to define two spaces within each cylinder of its respective jack. With such an arrangement the volume of the first and second spaces will not be equal and therefore a displacement of fluid from a first space of one jack into a second space of an adjacent jack will not produce an identical displacement in the piston rod.

Accordingly a modified coupling is required whereby two of the jacks 20, 40 are inverted. In this arrangement the pump 50 receives fluid from first space 17 of first jack 10 and supplies it to second space 48 of fourth jack 40, first space 47 of jack 40 is connected to second space 38 of the third jack 30, first space 37 is connected to second space 28 of second jack 20 and first space 27 is connected to second space 18 of first jack 10.

The second and fourth jacks' pistons rods 22, 42 are attached to a vehicle roof (not shown) by way of a slidable connecting bracket arrangement. Furthermore their inversion relative to first and third jacks 10, 30 is such that when piston rods 12, 32 are extended piston rods 22, 42 are retracted. The connecting bracket thus effects a relative pulling up of the attached roof with respect to second and fourth jacks 20, 40.

It will be understood that by reversing the direction of flow of fluid through the pump the piston rods can be made to move in an opposing direction thus lowering or respectively raising the roof as required.

An improved lifting arrangement according to a second aspect of the invention may use either of the jack arrangements previously described. The arrangements are modified by omitting the pump 50 such that the jacks complete a sealed system. A mechanical lifting device is attached to one corner of the vehicle roof so as to be operable to raise or lower the said roof. The lifting device may be any convenient known device such as an hydraulic or pneumatic cylinder, a pulley/chain system, a screw or cantilever jack etc.

It will be appreciated that normally operation of such a lifting device on only one corner of the vehicle roof would result in warpage or damage to the roof surface. This would result since the other three corners would tend to remain in their rest positions when the device weas operated. Thus it would normally be necessary as previously explained to synchronise independent lifting devices located at separate corners of the roof to achieve an even raising or lowering of the roof surface.

In the arrangement according to this second aspect of the invention, however, the sealed system jack arrangement is operative to transfer the lifting force exerted by the device on the attached corner across the entire roof surface. Thus as the device is operated, to raise or lower the roof, the jack located adjacently is constrained to move in accordance therewith. Movement of this jack causes explusion of a quantity of liquid and simultaneously draws in, by suction, a similar quantity of liquid from the adjacent connected jack.

The movement of the one jack located adjacent to the device is thus transmitted via the arrangement of this invention to the jacks located at each corner of the roof.

The roof is therefore raised by action on all four of its corners thereby avoiding warping etc.

The invention is not confined to the foregoing details and variations are possible. For example only two or three hydraulic jacks may be required for certain uses such as in a car inspection ramp arrangement. For other uses five or more jacks may be required where there is a large surface to be lifted or the expected load is very large. Bleed valves may be necessary in order to provide a smooth and steady lowering of the system. Other variations may also be possible.

Claims (8)

1. An improved lifting arrangement comprising at least two hydraulic jacks, each having a piston and an associated piston rod, attached to a vertically displaceable surface, the jacks being connected to each other by fluid transfer pipes such that fluid expelled from one jack by displacement of its piston rod will be supplied to a second jack causing displacement of its respective piston rod, the arrangement further including means to cause displacement of at least one piston rod in the arrangement.

2. An improved lifting arrangement as claimed in claim 1 in which the arrangement further includes pump means operative to receive fluid from one jack in the arrangement and supply that fluid to a second jack thereby to cause a displacement of the second jack's piston rod.

3. An improved lifting arrangement as claimed in claim 1 in which the arrangement further includes lifting means operative to displace the surface and thereby to cause a displacement of at least one piston rod attached to the said surface.

4. An improved lifting arrangement as claimed in claims 1, 2 or 3 in which each hydraulic jack is provided with a piston rod which extends through the jack's cylinder.

5. An improved lifting arrangement as claimed in claims 1, 2 or 3 in which each hydraulic jack includes a piston rod on one side of the piston head only and the jacks are interconnected so that adjacently located jacks are simultaneously moved in opposed direction.

6. An improved lifting arrangement as claimed in claim 5 in which there are four jacks, two of which are connected to a sliding bracket arrangement such that the roof of the vehicle is raised by a retraction of the piston of each said jack.

7. An improved lifting arrangement as claimed in any preceding claim in which there are four jacks disposed at respective corners of a vehicle's roof.

8. An imrpoved lifting arrangement substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.