GB2187687A - Trailer with damped caster wheel - Google Patents

Abstract

A trailer 10 includes a first pair of wheels each wheel being positioned adjacent one side of the trailer adjacent one end thereof and at least one caster wheel 11 which is pivotally mounted adjacent the other end of the trailer 10. Damping means 15 is provided for damping pivotal movement of the or each caster wheel 11, said damping means 15 being adjustable to vary the degree of damping. A tow bar 32 is pivotally attached to the trailer 10 for movement in a vertical plane and spring means 39 resiliently loads the tow bar 32 downwardly. <IMAGE>

Description

SPECIFICATION Trailers The present invention relates to trailers.

In orderto permit cornering, trailers for motor vehicles are normally provided with wheels on only one axle or perhaps wheels on two closely-spaced axles. As a result the towing vehicle must take some ofthe load ofthetrailer, which may place undesirable stresses on the vehicle suspension and cause problems with the levelling ofthevehicle.Such trailers are also likely to sufferfrom snaking when towed and are also difficult to reverse. Where the trailer has only two wheels, there is also a safety problem should one ofthe wheels puncture. Problems also arise in the loading and distribution of load where the trailer is not adequately supported at the front and rear.

To overcome these problems, it has been prop owed to provide wheels adjacent each corner of the trailer, a pairatthe rearofthetraileron a fixed axle and a pair of caster wheels adjacent the front corners ofthetrailer,which are pivotted individuallytothe trailer. The caster wheels are pivottablethrough 360 degrees and permit manoeuvering ofthe trailer in all directions. In orderto avoid oscillation ofthecaster wheels when travelling at speed, it is necessary to damp the pivotting action of the casterwheels.Un- fortunatelythisdamping inhibits pivotting ofthecas terwheelsduringslowmanoeuvering,forexample when reversing around corners, when it is desirable that the caster wheels should be freely pivotable.

According to one aspect of the present invention a trailer includes a first pair of wheels positioned one adjacent either side of the trailer adjacent one end thereof and at least one furtherwheel adjacent the other end ofthetrailer, saidfurtherwheel being independently pivotted with respect to the trailer about a vertical or nearvertical pivot, the wheel axle trailing the pivot and the wheel and pivot being sub stantiallycoplanar, damping means being associated with each pivot to damp rotation thereof, said damping means being adjustabletovarythedegree of damping applied to the pivot.

The independently pivotted wheel will act as a casterto provide self steering so that the trailer is free to manoeuvre in spite of having longitudinallysepar- ated wheels. The caster wheel may be positioned on the longitudinal axis ofthetrailer. However, preferably a pair of caster wheels are provided, one adjacent each side of the trailer.

In a preferred embodiment, the caster wheels will be able to rotate through 360 degrees on the pivot, the damping means also operating through 360 degrees.

The caster wheels may be mounted on axles rigidly mounted with respect to the pivot, although preferably they will be mounted to provide a compliant suspension. This may be achieved by mounting the wheel axle on a swinging arm which is hinged with respect to the pivot or a support member attached to the pivot, to allow vertical movement, spring and damping means being provided between the swinging arm and a rigid support memberassociated with the pivot.

With wheels at each end ofthe trailer provision must be made for vertical articulation of the tow bar between thetrailerand towing vehicle in order to ac commodate relative vertical movement there between.

According to a further aspect ofthe present invention a trailer includes a first pair of wheels positioned one adjacent either side ofthe trailer adjacent one end thereof; at least onefurtherwheel adjacent the otherendofthetrailer,saidfurtherwheel being independently pivotted with respect to the trailer about a vertical or near vertical pivot, the wheel axle trailing the pivot and the wheel and pivot being substantially complanar, damping means being associated with each pivot to damp rotation thereof; and a tow bar pivotally attached to thetrailerfor movement in a vertical plane, means being provided to resiliently load the tow bar downwardly.

An embodimentofthe invention is now described, byway of example only, with reference to the accompanying drawings, in which Figure lisa diagrammatic sectional side elevation ofthe front wheel suspension assembly of a trailer formed in accordance with the present invention; Figure2 is an illustration, on enlarged scale, of an adjustment mechanism for the damping means of the assembly illustrated in figure 1; and Figure 3 is an illustration in side elevation of a tow barassemblyforthetrailerillustrated in figure 1.

in accordance with one embodiment ofthe present invention a trailer 10 is provided with fourwheels, one adjacent each corner ofthe trailer. The rear wheels (not shown) are attached to the trailer by conventional suspension means,forexampleatrailing arm hinged to thetrailer base frame so that itwill swing in a vertical plane, spring and damping means being connected between the arm and the base frame,to provide a compliantsuspension.

As illustrated in figure 1,the front wheels 11 are each mounted onto the base frame 12 ofthetrailer 10 by means ofa hub I3which is pivotally secured to the base frame 12 by means of a stub axle 14. Each stub axle 14 is bolted to the base frame 12 so that it extends downwardly and is inclined at about 10 degrees to the vertical, away from the front ofthe trailer.

The hub 13 is providdwith a drum brake assembly 15, said assembly comprising a drum 16 which is mounted on the hub 13 for rotation therewith and a pair of brake shoes 26 supported non-rotatably by backing plate 17 which is secured to the trailer base frame 12. A lever mechanism 27 is provided by which the brake shoes 26 may be expanded against the inner surface of the brake drum l6therebyproduc- ing a frictional force damping rotation ofthe drum 16, or maybe contracted awayfromthe drum 16to leave it freely rotatable. Said lever mechanism 27 is controlled by cable 18.

Asupport member 20 is mounted on the drum 16 and extends downwardly therefrom. Atrailing swinging arm 21 is secured at one end to the support member 20 about a horizontal pivot 22 which allows the arm to swing in a vertical plane. Astub axle 23 for the wheel 11, is provided atthefree end of arm 21. A spring/damping unit 24 is mounted between the arm 21 adjacent the stub axle 23 and a rigid extension 25 ofthe support member20. The arm 21 isoffsetfrom the pivot axis ofthe hub 13 so thatwhen wheel 11 is mounted on the stub axle 23, the pivot axis 13 will lie in the plane of the wheel 11.

In the arrangement described above, the front wheels 11 ofthe trailerwill act as casters, being free to rotate aboutthe pivot axes of hubs 13to followthe direction oftravel ofthe towing vehicle. The drum brake assembly 15will control rotation of the hubs 13 and will prevent oscillation ofthe wheels 11. Inclination ofthe stub axles 1 4will produce a selfcentering effect when the direction of travel ofthe vehicle is straight ahead.

Clearance is provided between the wheel 11 and the body of the trailer 10 to permit 360 degree rota- tion ofthewheel. This will permitfull movement of the wheel on cornering in boththeforward and reverse directions.

The swinging arms 21 and spring/damping unit 24 will provide a compliant suspension which will smooth out undulations in the road surface.

As illustrated in figure 2,the cable 18 will normally be kept undertension by hand lever 28 in orderto apply the brake shoes againstthe inner surface ofthe drum 16. The linkage mechanism 27 may be adjusted so thatthe frictional engagement between the drum 16 and the shoes is sufficient to provide the required degree of damping to the hub 13, to prevent oscillation ofthewheel when travelling atspeed. Springs 29, which will be normally under compression are provided between an abutment 30 on the hand lever 28 and the end ofthe cable 18, to maintain frictional engagement between the shoes 26 and drum 16 as the shoes 26 wear.

For slow speed manoeuvering, a hand lever 28 is released to release tension in the cable 18 and thereby allow the lever mechanism 27 to contract the brake shoes 26 sothatthe hub 13 and wheel 11 become freely rotatable about the stub axle 14.

Alternatively, the spring means maintaining the shoes in engagement with the drum 16 may be positioned internallyofthedrum,thecableactuating means serving to overcome the action of the spring.

Furthermore release ofthe brake 15 to remove the damping effect may be achieved automatically, for example on reversing by,forexample,asolenoidac- tuatorenergised by the reversing light circuit ofthe towing vehicle.

In orderto permit adjustment of the brake mech anism 15to provide an appropriate degree of dam ping overthe life ofthefriction linings 32, it may be necessary to replace the conventional frictional lin ings with linings of lowerfrictionall co-efficient, for example nylon. Alternatively, conventional friction linings may be impregnated with lubricating mat erial.

In order to accommodate relative vertical move ment between the towing vehicle and trailer, a tow bar 32 in the form of an A4rame, is pivotally attached at the end of each leg, to longitudinally extending chassis members 31 on the trailer, as illustrated in figure 3. The pivot pins 33 permit movement ofthe tow bar 32 in the vertical plane. A bridge structure 34 interconnects the legs of the A4rame adjacentthe pivotted ends thereof and extends substantially parallelto averticallyextending chassis member36 on the trailer, when the tow bar 32 is positioned in its normal position for towing. An adjusting screw 35 is mounted on the chassis member 36 so that it is capable of pivotting relative thereto in a vertical plane.

The screw 35 extends through an oversize hole in the bridge structure 34. A spherical seat member 37 is provided on the screw 35 so that it abuts the bridge structure 34 and adjusting nut 38 engages the seat member 37. A compression spring 39 is positioned about the screw 35 between the chassis member 36 and the bridge structure 34 and acts to resiliently load the tow bar 32 downwardly.

The screw adjuster may be used to raise and lower the tow bar 32 to hitch and unhitch the trailerfrom the towing vehicle. It may also be used to adjustthe tow bar 32, so that underthe influence of the spring 39 it imposes a maximum downward load,typically 75kg,onthetowingvehicle.

Damping means may also be provided between the trailer and the tow bar 32 in ordertodampen transmission of vibrations from trailerto towing vehicle.

Various modifications may be made without departing from the invention. Forexample,while in the embodiment described above, damping is removed completely for low speed manoeuvrability, therelease mechanism may be arranged to only partially reduce damping, or may be arranged to reduce the damping to a varying degreefordifferentmanoeuvr- ing situations. Adjustable damping arrangements otherthan the drum brake assembly described above, for example external shoe drum brakes or disk brake assemblies may also be used.

Furthermore, wheels pivotted in accordance with the present invention may be provided at the rear of the trailer rather than the front.

While it is preferred to provide a compliant sus- pension system, both the front and rear wheels ofthe trailer may be mounted rigidly. The form of compliant suspension may also be varied, for example instead of using a trailing arm 21, a leading arm may be pivotted to the end of support member 25 remote from pivot 13, and directed forwardly, provided that the wheel axle does not extend in front of the pivot axes of hub 13. Also, ratherthan using a combined spring/damper unit 24 as illustrated, separate springs and dampers may be used. The form of those springs and dampers may also be varied, for example by using rubber, torsion or leaf springs and hydraulic or pneumatic dampers.

This invention is applicable to any form oftrailer which would not normally be provided with a stee red axle. For example, car trailers, horse boxes, cattle trailers, boat trailers, caravans and general purpose trailers.

Claims (19)

1. Atrailerincluding afirstpairofwheelsposi- tioned one adjacent either side ofthetrailer adjacent one end thereof and at least one further wheel adja cent the other end ofthe trailer, said furtherwheel being independently pivotted with respect to thetrai- ler about a vertical or nearvertical pivot, the wheel axle trailing the pivot and the wheel and pivot being substantially coplanar, damping means being associated with each pivot to damp rotation thereof, said damping means being adjustabletovarythedegree of damping allied to the pivot.

2. Atraileraccording to claim 1 in which a pair of furtherwheels are provided, one adjacent each side of the trailer.

3. A trailer according to claim 1 or 2 in which release means is provided to partially ortotally reduce the damping on the wheel pivots.

4. Atraileraccordingto anyone of claims 1 to 3 in which the wheel is pivotally mounted upon a hub, means being associated with said hub by which rotation thereof may be damped.

5. Atraileraccording to claim 4 in which said means comprises a drum brake mechanism, the shoes ofthe drum brake mechanism being expanded by biasing means into engagementwith the drum thereby damping rotation of the hub.

6. Atraileraccordingto claim 5 in which means is provided for overriding the biasing means, to release the brake shoes from the drum and remove damping from the hub.

7. Atraileraccording to claim 6 in which the release means is cable operated.

8. Atraileraccording to claim 7 in which the cable is controlled buy a hand lever.

9. Atraileraccording to claim 7 in which the cable is controlled automatically.

10. Atraileraccording to claim 9 in which the cable is controlled by means of a solenoid, in responseto reversing ofthevehicle.

11. Atrailer according to anyone of claims 1 to 10 in which the wheels are mounted with respect to the pivot in a mannerwhich will permit relative vertical movement, spring and damping means being provided between the wheel and pivotto provide a compliant suspension.

12. Atraileraccordingtoanyoneofthepreced- ing claims in which the axis of rotation ofthe pivot is inclined downwardly at upto 10 degrees from the horizontal, away from the front of the trailer.

13. Atraileraccordingto anyoneofthepreceding claims in which the pivotted wheels are provided adjacentthe front of the trailer.

14. Atrailer according to any one ofthe preced- ing claims having a tow bar by means of which the trailer may be attached to a towing vehicle, said tow bar being pivotted with respect ofthe trailerfor movement in a vertical plane, means being provided to resiliently load the tow bar downwardly.

15. Atrailer including a first pair of wheels positioned one adjacent either side of the trailer adjacent one end therereof; at least one furtherwheel adIa- centthe other end ofthetrailer,saidfurtherwheel being independently pivotted with respect to the trailer about a vertical or near vertical pivot, the wheel axle trailing the pivot and the wheel and pivot being substantiallycomplanar, damping means being associated with each pivot to damp rotation thereof; and a tow bar pivotally attached to the trailerfor movement in avertical plane, means being provided to resiliently load the tow bar downwardly.

16. Atrailer according to claim 14 or 15 in which spring means acts between the tow bar and the trailer.

17. Atraileraccording to claim 16 in which screw adjusting means is provided to pre-load the tow bar.

18. Atraileraccordingto anyoneofclaims 14to 17 which damping means is provided betweenthe trailer and tow bar.

19. Atrailer substantially as described herein with reference to and as shown in figures 1 to 3 of the accompanying drawings.