GB2187423A - Semi-trailer landing gear - Google Patents

Abstract

A semi-trailer of an articulated lorry has rear suspension with trailing arms controlled by air bags. The brakes lock wheels to axles 11 that are fixed to the trailing arms. If the height of the suspension then changes, the wheels may roll along the ground, causing the whole semi-trailer to move forwards or backwards. Landing gear at the front of the semi-trailer has sectional arcuate feet 16 than then roll on the ground, taking up the movement and avoiding high horizontal stresses on the landing gear. <IMAGE>

Description

SPECIFICATION Improvements in and relating to articulated lorries The invention relates to articulated lorries, and more specifically to semi-trailers of such lorries.

The semi-trailer of an articulated lorry usually has one or more pairs of road wheels towards its rear end, and a landing geartowards its front end, on which the semi-trailer is supported when it is not connected to a tractor. The landing geartypicaily consists of a pair of legs that are telescopically collapsible and/or pivotally attached to the body of the semi-trailer and/or otherwise retractable so thatthey can be withdrawn clear of engagement with the ground when the semi-trailer is connected to a tractor.

It has previously been proposed to provide the lower end of each leg with ground-engaging means in the form of a small wheel or a flat plate. If a flat plate is used it may be pivotally connected to the leg so that it can lie flat on a surface that is not level. In United States Patent No. 2 926 889 (A.N. Obes) it was proposed to provide a pivotally-mounted foot with a ground-engaging surfaceintheformofaconvexarc of a cylinder, which was intended to rock in orderto find a firm seating on sloping ground.In orderto pre ventthefootfrom acting as a roller, andthusto prevent the semi-trailerfrom shifting position undesirably, Obes specified that the centre of curvature of the ground-engaging surface ofthefoot must be above the axis of pivoting of the foot to the leg, resulting in a self-centring action.

In recent years, the semi-trailers have been provided with air suspensions in which the road wheels are rotatably mounted on the ends of axles, the axles are fixedly mounted on radius arms, the radius arms are pivotally attached to the body ofthe semi-trailer at one end, and the body of the semi-trailer rests on the other ends of the radius arms through pneumatic suspension devices. When the semi-trailer is parked, parking brakes are applied to prevent the wheels from rotating on their axles, so that the radius arms, axle, and wheels then act as a single rigid unit pivotally connected to the trailer body and with its position governed by the air suspension.

A problem with a semi-trailerfitted with an airsuspension is that the trailer can move forwards or backwards, when the suspension is raised or lowered, by an amount equal to the vertical movement ofthe vehicle. Raising or lowering of the suspension can happen deliberately, or because of changes in the load on the trailer, or because of air leakage, and the consequent forward or backward movement often results in conventional landing legs' being broken.

It will therefore be appreciated that with a semitrailer fitted with an air suspension system as described above, it is imperative to provide means that permit the legs to move forwards or backwards relativelyfreely, at least over a distance of the order of the maximum height change that can resultfrom the air suspension, in order to ensure that the legs are not subjected to large bending stresses (They are designed to act substantially only in compression.) The use of wheels at the lower ends of the legs does not so Ive the problem because it is not practical to provide such wheels with a large radius of curvatureora large ground contactarea, and theytend to sink into tarmac surfaces to such an extentthat they will not roll.

Obes does not disclose the use of air suspension on a semi-trailer, and so is not concerned with the problem discussed above of enabling the legs to move forwards and backwards. In fact, Obes proposes an arrangement that is expressly intended to ensure that when the landing gear is in operation, that is to say, when the legs are lowered and supporting the front portion of the semi-trailer, there will be nodangerthatthe "truckbody",thatistosay,the body of the semi-trailer, will shift its position even when the ground on which the semi-trailer has been set down is sloping.Accordingly, Obes's intention is to provide, atthe lowerendsofthe legs, meansthat will prevent fore-and-aft movement of the semitrailer caused by the ground's being sloping, whereas the problem which the present invention is intended to overcome is that of providing means at the lower ends of the legs that will permitthetrailer to movefore-and-aft because ofthe operation of an air suspension system that can cause such movement even when the semi-trailer is set down on level ground.

The invention provides a semi-trailer that has road-wheels and landing-gear, wherein means defining the axes of rotation of the road wheels are connected to the body of the semi-trailer by radius arms and the landing gear is provided with one or more feet pivotally connected to the landing gear about axes that, at least when the landing gear is in use, are substantially parallel to the axes of rotation of the road-wheels and having ground-engaging surfaces thatform convex arcs as seen in section perpendiculartothe said axes.

Surprisingly, although the landing gear of a semitrailer according to the invention has a construction somewhatsimilarto that disclosed by Obes, it is found to provide a solution to a problem that is totally different from any problem that Obes was faced with, and the advantage that Obes was seeking to achieve, which would actually be a disadvantage in a semi-trailer according to the present invention, does not in practice prove to be significant.

The landing gear may comprisetwo legs that, at least when the landing gear is in use, are generally vertical and each of which has a respective said foot pivotallyconnectedto its lower end. The lengths of the legs of the landing gear are advantageously adjustable, so that the feet can be raised away from the ground when not in use. Instead or in addition, some other means for retracting the legs may be provided.

The or each said foot may be pivotally connected to a leg by a pivot that is substantially centred on alongitudinal axis of that leg. The or each said pivotthen advantageously comprises a pivot pin a central portion of which is received in bearing means on an end portion of the respective leg and opposite end portions of which are received in bearing means on the respective foot. The bearings do not then need to be able to cope with unbalanced loads, and can be made lighter and less likely to seize up than might otherwise be possible. Preferably, the said bearing means on the foot are provided on a pair ofwebs each of which extends from the pivot to a member defining the ground-engaging surface ofthefoot.

The ground-engaging surface of the or each said foot may lie substantially on a minor sector of a notional right-circular cylinderthe axis of which is substantially parallel to the axis of pivotal connection of the foot to the landing gear. The axis of pivotal connection is then advantageously between the cylinder axis and the ground-engaging surface, with a notional plane containing those two axes passing sub stantiallythrough the centre of the ground-engaging surface. In that way, it is possible to effectconsider- able savings in weight and space, and to have a comparatively large radius of curvature of the groundengaging surfaces, without giving rise to a self-centring action of sufficient magnitude to cause an undesirable resistance to rolling of the vehicle.

The semi-trailer may comprise means resiliently biasing the or each said foot into a position in which, in normal use, the ground is engaged by a central portion ofthe ground-engaging surface, advan tageouslyatension spring having one end so attached to the foot and the other end so attached to another part ofthe landing gearthatthe extension of the spring is ata minimum when the foot is in the said position. That both reduces any tendency ofthe feettoswing around when the feet are off the ground and makes it easier to ensure that the feet are in a central position when they are put down onto the ground. The said radius arms may be trailing arms.

Movement of the radius arms relative to the body of the semi-trailer may be controlled by air suspension means disposed between a distal end portion of each said radius arm and a member of the body and, as has been indicated above, the present invention is especially useful when that is the case.

The semi-trailer may comprise one or more axles, each having a said road wheel rotatably mounted on each end and being fixedly mounted on intermediate portions of a pair of radius arms.

The invention also provides an articulated lorry comprising a semi-trailer according to the invention and a tractor.

Two forms of semi-trailer constructed in accordance with the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a side elevation view of a semi-trailer; Figure 2 is a somewhat schematic side elevation view of a rear suspension assembly; Figure 3 is a front elevation view of a first form of landing gearfoot; Figure 4 is a side elevation view ofthefirstform of foot; Figure 5 is a view similarto Figure 4 showing the foot displaced; Figure 6is a viewsimilarto Figure 3 of a second form of landing gearfoot; and Figure 7is view similartb Figure 4 of the second form of foot.

Referring to the accompanying drawings, and init iallyto Figure 1, one form of semi-trailer according to the invention comprises a body indicated generally by the reference numeral 1, landing gear indicated generally by the reference numeral 2, and tandem road wheels, with respective suspension assemblies, each indicated generally by the reference num eras 3.

The body 1 comprises a platform 4 supported by a sub-frame 5 and has at a front end portion a coupling device 6 for connecting the semi-trailerto a tractor (not shown) which may be conventional.

Referring nowto Figure 2, each suspension assembly 3 comprises a pair of brackets 7 attached to the sub-frame 5, one on each side of the semi-trailer.

To each bracket 7 a trailing arm 8 is pivoted by means of a bearing 9 at the forward end ofthetrailing arm.

The bearings 9 permit the trailing arms 8 to rotate relative to the body 1 ofthe semi-trailer about a horizontal axis that is perpendiculartothe length ofthe semi-trailer and is common to the two trailing arms of the same suspension assembly 3. A respective air bag 10 is arranged to act in compression upwards on the sub-frame 5 and downwards on a rear portion of each trailing arm 8, and is supplied with air under pressure by conventional meansthathave been omitted for the sake of clarity.

An axle 11 is clamped rigidly to both ofthetrailing arms 8 of the respective suspension assembly 3 by clamping means 12, and dampers 13 extend between the clamping means 12 and the brackets 7. On each end of the axle 11 is rotatably mounted a road wheel 14, and brakes (not shown) are arranged to de celerate the vehicle, orto immobilisethe semi-trailer when parked, by resisting or preventing rotation of the wheels relative to the axle.

As may be seen from Figures 1 and 2, a large part ofthe weight ofthe semi-trailer and its load (not shown) is transmitted to the ground through the wheels 14, and is transmitted to the wheels partly through the bearings 9 and partly through the air bags 10, and any change in the degree of extension ofthe air bags 10 will entail a change in the height of the body 1 off the ground. As has been indicated above, such a change in any of the air bags may occur because air is deliberately introduced into, or released from, the air bag, because air leaks in or out, or because of a change in the compressive force acting on the air in the air bag caused by a change in the load on the platform 4.That last-mentioned cause occurs, of course, when cargo is being loaded onto, or unloaded from, the semi-trailer, and at such times the semi-trailer may well be parked without a tractor, resting on its landing gear.

As has been indicated above, when the vehicle is parked and the brakes are on, the wheels 14 are prevented from rotating on the axle 11 so that the wheels, axle, and radius arms 8 become in effect a single rigid unit, and any change in the air bags 10 must be accommodated by that unit's pivoting as a unit, relative to the body 1 about the axis of the bearings 9.Because the wheels 14 are resting on the ground under load, they will tend to roll ratherthan slip on the ground, and the whole of the rigid unit formed by the wheels 14, the axle 11, and the radius arms 8will rotate and move along the ground with them.The axis of the bearings 9 willtrace out a troch- oidal path, with its direction of motion relative to the ground being perpendicularto a line joining it to the point of contact of the wheels 14 and the ground.

Thus, in the arrangement shown in Figure 2, the axis of the bearings 9 will move forwards and downwards, or backwards and upwards, in a direction inclined at about 450 to the horizontal over the range of positions that is likely to occur in normal use.

Because, as has been explained above, the movement of the rigid unit relative to the body 1 is a rotation about the axis of the bearings 9, the movement of that axis relative to the ground must be accompanied by an identical movement of the body relative to the ground. That is to say, as the suspension rises or sinks, the adjacent part of the body 1 ofthe semi-trailer moves upwards and backwards, or downwards and forwards, respectively, atan angle of about 450 to the horizontal.The front end of the semi-trailer is prevented from rising and sinking with the rear by the landing gear 2 (Any resulting slight difference in level between the ends of the semitrailer can easily be accommodated by a slight rotation of the body 1.) but the front of the semi-trailer will move forwards and backwards over a distance approximately equal to the distance over which the back moves forwards and backwards. Thus, as has been indicated above, the front end of the semitrailer moves horizontally through a distance that is approximately equal to the distance through which the suspension bearings 9 move up or down, and that distance may typically be upto 150 mm.

Referring nowto Figures 1 and 3 to 5, the landing gear 2 comprises a pair of telescopic landing legs 15 that can be extended for use, or retracted clear of the ground when the semi-trailer is connected to a tractor, by conventional means (not shown). At the lower end of each leg 15 is a foot indicated generally by the reference numeral 16, which is pivotally attached to the leg 15 by a pin 17 that is received in a sleeve 18 welded to the bottom of the leg 15 and in a pairof bearings 1 9 on the foot. The axis ofthe pin 17 is sub stantially horizontal and perpendicular to the length of the semi-trailer.

The foot 16 has a sole plate 20 that is in the shape of a sector of a right-circularcylindrical shell with its axis 21 parallel to the axis ofthe pin 17. As shown in Figure 4, the axis 21 of the sole plate 20, the axis of the pin 17, the centre of gravity ofthefoot 16, and the centre ofthe sole plate 20 are one above another, in that order, in a common vertical plane.

The foot 16 comprises a pairofapproximatelysec- torial webs 22, which are supported on the bearings 19 and the arcuate lower edges of which abut the inner surface of the sole plate 20. The webs 22 are supported by outwardly extending flanges 23 at the side edges, a transverse stiffener 24 spanning the space between the webs attheircentres, and longitudinal stiffeners 25 lying against the insides of lower edge portions of the webs 22. Cross-braces 26 connect pairs of the flanges 23, spanning the space between the webs 22, nearthe upper ends thereof.

As an example of suitable dimensions, the radius of cu rvature of the sole plate 20may be350 mm,the distance from the axis of the pin 17 to the centre of thesole plate may be 250 mm, andthewidth ofthe sole plate may be 250 mm. Because thefoot 16 is directly below the leg 15 it is possible, without requiring an unacceptably heavy structure, to spread the load transmitted bythe leg over a greaterwidth of foot than would be the case with a wheel, which would have to be offset to one side of the leg.

In use, the foot 16 is allowed to hang from the leg 15 and the landing gear 2 is lowered until the foot 16 engages the ground. At least on flat, level ground the foot 16 is stable in the position shown in Figure 4, with the centre of the sole plate 20 directly underthe leg 15.

If the semi-trailer is left with the landing gear 2 in the condition shown in Figures 3 and 4 supporting the front end and with the wheels 14 braked, and if the height of the suspension subsequently alters, for example, as a result of the loading of cargo onto or the unloading of cargo from the platform 4then, as explained above, the forward part of the semi-trailer will move horizontally and the landing legs 15will move with it. Referring nowto Figure 5, the sole plate 20 of the foot 16 will tend to roll on the ground, allowing the leg 15 to move forwards or backwards, for example, to the position shown in Figure 5.

Because the sole plate 20 can have a larger effective width and a larger radius of curvature than would be practical with a conventional wheel, the foot 16 will tend to sink into tarmac or other comparably soft road surfaces less, and because of the larger radius of curvature its rolling will be less hindered by its having deformed the surface on which it is resting or by other small irregularities in the ground. Accordingly, the foot 16 will be able to rollwhereacon- ventional wheel would have stuck fast.

Because the centre of curvature 21 of the sole plate 20 is above the axis of the pin 17, when the foot 16 is displaced from the position shown in Figure 4 the pin 17 is raisedfurtherfrom the ground and as a result there is a self-centring action tending to oppose the displacement. It has been found, however, thatthe horizontal forces arising from the self-centring action are not sufficient to impose unacceptably high stresses on the landing legs 15.

Referring now to Figures 6 and 7 of the drawings, the second form of foot, indicated generally by the reference numeral 27, has generally the same structure and function as thefirst form 16, and in the interests of conciseness the description will not be repeated. The sole plate 28 of the second form of foot 27 is widerthan the sole plate 20, and extends round a larger arc. The webs 29 are further apart, the pivot pin 30 and the sleeve 31 in which it isjournalled are cor respondingly larger, and instead oftheflanges 23, transverse stiffener 24, and cross-braces 26 there are cross-braces 32 at the centre and 33 at the ends of the sole plate 28. A coil spring 34 acts in tension between a bracket 35 welded to the sleeve 31 and a rod 36 spanning the space between the two webs 29, urging the foot 27 into the central position shown in Figure 7.

Claims (16)

1. A semi-trailerthat has road wheels and landing gear, wherein means defining the axes of rotation of the road wheels are connected to the body of the semi-trailer by radius arms and the landing gear is provided with one or more feet pivotally connected to the landing gear about axes that, at least when the landing gear is in use, are substantially parallel to the axes of rotation of the road wheels and having ground-engaging surfaces that form convex arcs as seen in section perpendicular to the said axes.

2. A semi-trailer as claimed in claim 1,wherein the landing gearcomprisestwo legs that, at least when the landing gear is in use, are generallyvertical and each of which has a respective said foot pivotally connected to its lower end.

3. A semi-trailer as claimed in claim 2, wherein the lengths of the legs of the landing gear are adjustable.

4. A semi-trailer as claimed in any one of claims 1 to 3, wherein the or each said foot is pivotally connected to a leg by a pivot that is substantially centred on a longitudinal axis of that leg.

5. A semi-trailer as claimed in claim 4, wherein the or each said pivot comprises a pivot pin a central portion of which is received in bearing means on an end portion of the respective leg and opposite end portions of which are received in bearing means on the respective foot.

6. A semi-trailer as claimed in claim 5, wherein the said bearing means on the foot are provided on a pair of webs each of which extends from the pivot to a member defining the ground-engaging surface of the foot.

7. A semi-trailer as claimed in any one of claims 1 to 6, wherein the ground-engaging surface of the or each said foot lies substantially on a minor sector of a notional right-circular cylinderthe axis of which is substantially parallel to the axis of pivotal connection ofthefoot to the landing gear.

8. A semi-trailer as claimed in claim 7, wherein the axis of pivotal connection is between the cylinder axis and the ground-engaging surface, and a notional plane containing those two axes passes sub stantiallythrough the centre ofthe ground-engaging surface.

9. Asemi-trailerasclaimed in any one of claims 1 to8,which comprises means resiliently biasing the or each said foot into a position in which, in normal use, the ground is engaged by a central portion of the ground-engaging surface.

10. Asemi-trailer as claimed in claim 9, wherein the or each said resiliently biasing means comprises a tension spring having one end so attached to the foot and the other end so attached to another part of the landing gearthattheextension of the spring is at a minimum when the foot is in the said position.

11. A semi-trailer as claimed in any one of claims 1 to 10, wherein the said radius arms aretrailing arms.

12. A semi-trailer as claimed in any one of claims 1 to 11, wherein movementofthe radius arms relat- ive to the body of the semi-trailer is controlled by air suspension means disposed between a distal end portion of each said radius arm and a memberofthe body.

13. A semi-trailer as claimed in any one of claims 1 to 12, which comprises one or more axles each hav inS a said road wheel rotatably-mountedon each end and being fixedly mounted on intermediate portions of a pair of said radius arms.

14. A semi-trailer substantially as hereinbefore described with reference to, and as shown in, Figures 1 to 5 ofthe accompanying drawings.

15. A semi-trailer as claimed in claim 14, modified substantially as hereinbefore described with referenceto, and as shown in, Figures 6 and 7 ofthe accompanying drawings.

16. An articulated lorry comprising a semi-trailer as claimed in any one of claims 1 to 15 and a tractor.