GB2066188A - Trailer jacking system - Google Patents

Abstract

A trailer jacking system comprises a pressurised hydraulic fluid source 27 and at least two hydraulically operated jacks 1..4 for location on a trailer, hydraulic fluid connecting means connect said source to said jacks through a selector valve 11 operable to connect selectively pressurised fluid from the source to any one of said jacks. Each jack may have an associated check valve to reduce unwanted pressure loss. <IMAGE>

Description

SPECIFICATION Trailer jacking system This invention relates to jacking systems for trailers and more particularly concerns a jacking system for a caravan.

Conventional caravans include a steady at each corner in order to support the caravan when it is parked and in order to maintain the caravan in a level condition. Such steadies are normally pivoted at one end to the caravan chassis and have a foot at the other end. They are adjusted by means of an arm pivoted to the leg or steady between the foot and the pivot and said arm being movable relative to the caravan chassis by means of a screw arrangement.

The levelling of a caravan with such legs or steadies is both inconvenient and time consuming and often requires considerable physical strength.

According to the present invention we provide a trailer jacking or steady system which comprises a source of pressurised hydraulic fluid, at least two hydraulically operated jacks for location on a trailer, hydraulic fluid connecting means for connecting said source to said jacks and a selector valve operable to connect selectively pressurised fluid from the source to any one of said jacks.

Preferably, the source of pressurised fluid comprises a fluid pump which is operated by an electric motor. The motor may be controlled by control means in the form of a two-position switch which can be operated so as to either raise or lower each jack.

In a preferred embodiment the motor control switch and the selector valve are mounted in a single casing and this may, if desired, be provided with a level indicator to facilitate levelling of the caravan from a single position.

The jack may be arranged to be fixed at one end to the trailer chassis and may carry a ground-engaging foot. In one embodiment the jack comprises a conventional type of trailer leg or steady pivoted to the chassis at its end opposite the foot and a hydraulic cylinder pivoted between the chassis and a point intermediate the ends of the leg.

In an alternative form of the invention the jacks comprise a leg pivoted to a member associated with the hydraulic cylinder and a strut pivoted at one end to said leg and at its other end to the frame of the trailer. By suitable choice of the pivot points this arrangement enables the leg to be raised and lowered with a very small transverse movement of the ground-engaging end of the leg.

Reference is now made to the accompanying drawings, in which: Figure 1 is a perspective view of one form of a control unit in accordance with the present invention; Figure 2 is a diagrammatic side elevation of one corner steady for a caravan; Figure 3 is a cross section of one form of check valve for use in association with each jack; and Figures 4 and 5 are schematic diagrams of the hydraulic circuits for a caravan having four corner jacks.

Figure 6 is a perspective view an alternative form of steady for a caravan; Figure 7 is a cross-section on the line 7-7 of Figure 6; and Figure 8 is a schematic diagram of a hydraulic circuit for use with steadies as shown in Figures 6 and 7.

Referring to Figure 1 the control unit comprises a casing 10 having motor control means in the form of two way electric switch 11 with a centre "OFF" position and a selector valve operated by a rotatable control knob 12.

The upper surface of the casing carries a level indicator 13 comprising mutually perpendicular bubble cylinders.

Referring to Figure 2 each jack at each corner of the caravan is in the form of a steady comprising a leg 14 having a ground engaging foot 15 at the opposite end of the pivot 16 by which the leg is pivoted to the chassis. A hydraulic cylinder 17 of the double acting type is connected between the chassis and the leg at pivots 18 and 19.

Referring to Figure 4 the two position switch 11 is spring-biassed towards the centre "OFF" position.

The electrical connections are shown in dashed lines and the circuit includes a battery 20 (which in practice will be a battery carried by the trailer and/or a towing vehicle) and a pair of solenoid valves 21 and 22.

Actuation of the switch 11 will cause the motor 23 to rotate and drive hydraulic pump 24 which has two simultaneous outputs connected to relief valves 25 and 26. One of the solenoid valves will connect pressurised fluid from the pump to the rotary selector valve and the other solenoid valve will connect the other output to fluid reservoir 27.

Solenoid valve 21 is actuated to connect pressurised fluid to the selector valve 28 when the switch 11 is in the "RAISE" position and in this position solenoid valve 22 connects return fluid to the reservoir 27.

When the switch 11 is in the "LOWER" position the solenoid valve 22 will connect pressurised fluid to the common fluid line 29 and return fluid from selected cylinder 1,2,3 or 4 will be returned to the reservoir 27 via the rotary selector valve 28 and solenoid valve 21.

Each cylinder 1,2,3 and 4 is associated with a jack which comprises a corner steady for a trailer and pressurised fluid can be connected to any one of the cylinders by appropriate positioning of the valve 28.

The positions 1,2,3 and 4 of the selector valve 28 are connected by individual fluid lines to cylinders 1,2, 3 and 4 respectively and the application of pressurised fluid in these lines causes the respective cylinder to cause a raising action of the jack. The pressurised fluid for the raising action will normally be applied to the full area of the piston in the cylinder and all the return flows from the annular area side of the piston are connected to common line 29. Application of pressurised fluid to the common line 29, normally to the annular sides of the pistons, will cause a lowering action of the jack comprising the cylinder selected by the rotary selector valve 28 since return flow of fluid from the other side of the piston will be possible only through the line connected to reservoir 27 by the selector valve 28.

It is possible, of course, to replace or supplement the electric motor 23 and pump 24 by hand pump and to select the direction of flow of pressurised fluid by means of a suitable hydraulic valve.

The corner steadies of a trailer such as a caravan may have to remain in a load-supporting condition for an extended period and thus it is necessary to reduce as far as possible any tendency for the fluid pressure to leak away. To this end each hydraulic cylinder 1,2,3 and 4 has an associated check valve 1A, 2A, 3A, and 4A respectively. Each such check valve may be as shown in Figure 3 of the accompanying drawings.

The valve comprises a valve body 30 having a connection 31 to the cylinder "extend" line and a connection 32 to the cylinder "retract" line. The body 30 includes a poppet valve member 33 biassed towards its valve seat by a spring 34 retained by a ring 35. A ball 36 is in contact with the poppet 33 and co-operates with a valve seat 37.

The cylinder 38 receives a piston 39 a sealing ring 40 and connected to a piston rod 41. When pressure is applied to cause "retraction" the pressurised fluid will cause the ball 36 to lift the poppet 33 from its seat against the pressure of spring 34. The pressurised fluid is applied to the annular area of the piston (i.e. the piston rod side) to cause retraction and the lifting of the poppet 33 permits fluid from the other side of the piston to return to the reservoir via the "extend" line connection 31.

Pressure applied to the "extend" line connection 31 causes the poppet 33 to lift from its seat and act upon the full area of the piston. Fluid from the annular side of the piston returns to the reservoir via the "retract" connection 32.

The use of such a valve serves to considerably reduce the tendency for pressurised fluid to leak and thus fail to maintain the steadies in the desired positions.

In the drawings (Figure 4) a fifth position of the selector switch is shown for an auxiliary jack. This auxiliary jack may be used in a fixed position or as a mobile jack and is particularly useful for initially levelling the trailer in a transverse direction before the corner steadies are lowered. The use of a jack intermediate the corner steadies also helps to prevent chassis distortion which tends to occur when the corner steadies are raised to a height which appreciably reduces the load on one wheel of a two wheeled trailer.

An alternative form of power supply to that shown in Figure 4 is shown in Figure 5. In this embodiment the switch 11 selector valve 28 and the cylinder circuits are as shown in Figure 4 but the motor 43 is arranged to drive the pump 44 in one of the two directions depending upon the position of switch 11.

This arrangement requires a different valve arrangement to that shown in Figure 4. When the battery 40 is connected to drive the motor and the pump to cause pressurised fluid to be supplied via the valve 28 to extend the hydraulic cylinders pressurised fluid is delivered through pilot operated check valve 49 and fluid from the other side of the pistons is returned via pilot operated check valve 48.

When pressurised is supplied to retract the hydraulic cylinders by reversing the rotation of the motor M the fluid flows through valve 48 and returns via valve 49.

The valve 49 is, however, connected to the full area side of the pistons in the hydraulic cylinders and thus a larger quantity of fluid returns via valve 49 than is passed by valve 48. This excess of fluid is returned to the reservoir 47 by means of a further pilot operated check valve 50. The connections for the pilot operation of valves 48,49 and 50 are shown in dashed lines.

Two simple check valves 51 and 52 are provided to permit the pump 44 to draw fluid from the reservoir 47 and one-way pressure relief valves 45 and 46 provide a connection to the reservoir 47 in the event of the build up of excess pressure.

An alternative form of corner steady having the advantage that the ground-engaging end of the leg moves up and down in a substantaillyvertical direction is shown in Figure 4.

A conventional channel section leg 60 has a ground-engaging foot 61 pivoted at its lower end and is pivoted at 62 to a leg carrier 63 mounted on the piston rod (not shown) of the hydraulic cylinder 64. The leg carrier 63 is secured to a guide member 65 which can slide along guide bar 66 to define the path of movement of the leg carrier 63 as the piston rod is extended and retracted. This guide arrangement serves to prevent undue loading being applied to the piston rod in a transverse direction which may cause misalignment.

A pair of cranked struts 67 are pivoted at 68 to the leg 60 and at 69 to a bracket 70 rigid with the plate 71 which is secured to the caravan chassis frame by conventional means (not shown).

When the leg is raised the cylinder is disposed in the channel section and thus protected from damage and dirt during trailing.

The operation of the system is described below with reference to Figures 7 and 8 common reference numerals being used for identical features in each of Figures 6,7 and 8.

Figure 8 shows a schematic hydraulic circuit diagram illustrating four caravan corner steadies, but for simplicity the operation of only one of these steadies will be described.

The switch 72 has a central "OFF" position, which isolates the power pack 73 from the battery supply, and two "ON" positions corresponding to "leg raise" and "leg lower".

The power pack 73 comprises a pump 74, a reservoir for hydraulic fluid 75 and a motor 76, the motor being connected to the switch 72 so that in the "leg raise" position of the switch pressurised fluid will be delivered from port 77 and will return to the reservoir 75 via port 78.

In this position the fluid is delivered to the inlet of the selector valve 79 and delivered to the selected output, in this case 80. It wil be appreciated that the operation described below will be similarfor each position of the selector valve 79. The fluid from outlet 80 is connected by line 81 to check valve inlet 82, the pressure causing ball 83 to be lifted from its seat allowing the fluid to pass into the annulus port of the cylinder 64 to retract the piston rod into the cylinder and cause the leg 60 to be extended. Fluid from the other side of the piston is returned to the reservoir by way of the port 84, bridge line 85, T-connector 86 and line 87 to port 78.

When the switch 72 is moved to the "leg lower" position pressurised fluid is delivered by the pump 74 to the port 78 thereby applying pressurised fluid to the line 87 to all four hydraulic cylinders. This applies pressure to port 84 of the cylinder to urge the piston to the extended position, this being permitted by the operation of the check valve. Pressurised fluid is also applied via T-connector 86 to inlet 88 which urges actuator 89 to move to the right in the bore 90.

The actuator 89 includes a seal 91, a reduced diameter portion 92 and a projection 93 which contacts the ball 83 to lift it from its seat. This allows the fluid to escape from the annular side of the cylinder via port 82 to line 81.

It will be appreciated that this occurs for all cylinders as line 87 is common but only the selected one of the cylinders will be allowed to extend as the fluid path back to reservoir 75 is by way of a selector valve 79 and port 77.

The use of a check valve is necessary to ensure that loss of pressure in the cylinders is reduced to a minimum as caravan steadies are required to maintain the caravan in the desired position for extended periods of time. The check valve described above has been found satisfactory for this purpose and yet also provides for rapid extension by virtue of the actuator 89.

Whilst in the foregoing description the use of an electrically operated pump has been described it would be possible to utilise a manually operated pump which would provide a cheaper system.

It will be appreciated that the present invention provides an extremely convenient means for steadying and/or levelling a trailer. It can be operated from a single position and does not require any physical effort other than the operation of a switch and the rotation of the selector valve control knob.

The system can be supplied as original equipment or it can be supplied as a kit to be added to an existing system which utilises conventional manuallyoperated corner steadies.

Claims (16)

1. A trailer jacking or steady system which comprises a source of pressurised hydraulic fluid, at least two hydraulically operated jacks for location on a trailer, hydraulic fluid connecting means for connecting said source to said jacks and a selector valve operable to connect selectively pressurised fluid from the source to any one of said jacks.

2. A system according to Claim 1 in which the jacks are double-acting jacks so that hydraulic pressure can be applied either to raise or lower the jacks.

3. A system according to Claim 1 or 2 in which the source of pressurised fluid is a fluid pump operated by an electric motor.

4. A system according to Claim 3 incorporating control means in the form of a two-position switch so that the pump can be driven in either selected one of two directions.

5. A system according to any of Claims 1 to 4 in which each jack is associated with a check valve which reduces any tendency for the pressurised fluid to leak away from the pressurised side of the hydraulic cylinder whilst the jack is under load.

6. A system according to any of Claims 1 to 5 in which the selector valve includes at least one inlet for pressurised fluid, at least one outlet for each jack in the system and selector means operable to connect said inlet to any selected one of said outlets.

7. A system according to Claim 6 in which the selector means is a rotary selector means.

8. A system according to any of Claim 1 to 7 in which said selector valve controls the flow of pressurised fluid to the cylinders and also the flow of pressurised fluid from the cylinders.

9. A system according to any of Claims 1 to 8 incorporating a check valve associated with each cylinder to reduce unwanted loss of pressure.

10. A system according to any of of Claims 1 to 9 in which the jacks each comprise a leg adapted to be pivoted to a trailer frame and a hydraulic cylinder arranged to move said leg about said pivot.

11. A system according to any of Claims 1 to 9 in which the jacks each comprise a leg pivoted to a member associated with the hydraulic cylinder and a strut pivoted at one end to said leg and adapted to be pivoted at its other end to a trailer frame.

12. A system according to any of Claims 1 to 11 incorporating four jacks.

13. A system according to any of Claims 1 to 11 incorporating five jacks, one of which is a movable jack.

14. A system according to any of Claims 1 to 13 in which the selector valve and any control means are mounted in a single casing.

15. A trailer jacking or steady system substantially as herein described with reference to and as shown in Figures 2,3 and 4; 2,3 and 5; 2,7 and 8; 6, 3 and 4; 6,3 and 5; or 6,7 and 8 of the accompanying drawings.

16. Atrailer incorporating a system as claimed in any of Claims 1 to 13.