GB2207102A - Trailer foot assembly - Google Patents

Abstract

A foot assembly (20, 40, 50), suitable for use in supporting the front end of an unhitched trailer (10) of an articulated vehicle comprises an upper member (22) on a support leg (16) of the trailer, and a lower member (24) which, during use for supporting the trailer, remains in substantially stationary contact with the ground and supports the upper member (22) and hence the trailer; the construction and arrangement being such that the lower member (24) is held captive in relation to the upper member (22) such as by springs (36) and/or links (26), yet relative longitudinal movement is permitted between the upper and lower members, to accommodate longitudinal movement of the unhitched trailer due to loss of pressurised fluid from its suspension and/or due to loading thereof. <IMAGE>

Description

Trailer Foot Assembly Description of Invention This invention relates to means for supporting a trailer of a commercial vehicle of the kind in which a cab/tractor unit may be releasably connected to the trailer, typically in an articulated manner, in order to pull or manoeuvre the trailer.

Typically such a trailer comprises one or more pairs of wheels at or near a rear portion thereof, and a leg-like support at or near a front portion thereof, whereby the trailer may be left free-standing (unattended and with the cab/tractor disconnected) on said wheels and a foot portion of said leg. It will be appreciated that such a foot may bear a substantial proportion of the weight of such a free-standing trailer.

Where such a trailer is fitted with a suspension system in which a pressurised fluid medium is utilised to maintain a chassis frame of the vehicle at a suitable height above the wheels or ground, problems can arise when the trailer is left free-standing for long periods and/or where the trailer is loaded while free-standing. In particular, should there be gradual undesired leakage of the fluid medium from the suspension system, or if the free-standing trailer is loaded heavily in the absence of a supply of additional fluid medium for such suspension, undesired movements of suspension components relative to the chassis frame may occur, for example upward angular movements of 0 0 up to between about 10 and about 15 , which result in undesired longitudinal movements of the chassis frame, generally in a forward direction.

Various designs of foot have been proposed for accommodating such longitudinal movements, but have proved to be unsatisfactory.

Conventionally, taking as an example a pneumatic suspension system in which the fluid medium is air, axles carrying the wheels are carried on generally longitudinal suspension elements which are pivotally connected to a chassis frame of the vehicle at their forward ends, and connected to the chassis at their rearward ends via the intermediary of air bags of the pneumatic suspension system, the pressure in the air bags being varied during normal operation of the complete vehicle in order to maintain the chassis ride height generally constant.

When parked, the air bags should ideally remain pressurised to maintain the chassis at an appropriate height, but since air for pressurising the air bags is derived from a compressed air source carried by the cab/tractor unit, no additional air is available once the cab/tractor unit has been disconnected Thus, should air leak from the pneumatic suspension when the trailer is left unattended with the cab/tractor unit disconnected, or should there be inadequate air to support a load placed on the unattended trailer, the chassis will become lower in the vicinity of the wheels, and said longitudinal elements will be caused to pivot, the end result being that the effective longitudinal separation between said foot and the points of contact of the wheels with the ground must change.The geometry is generally such that said separation must increase in such circumstances, typically by about 10cam or so.

In systems where a parking brake of the trailer is operated from the some pneumatic system as the suspension, the air leak results in a simultaneous reduced braking effect, which enables the required change to be accommodated by mere forced rotation of the wheels, without requiring any movement of the foot.

However, in more safety-conscious systems, it is arranged that the parking brake is maintained "on" by mechanical (e.g. spring-biased) means, wholly independently of the pneumatic suspension, which brake thus constrains the wheels against rotation in relation to their axles and hence forces said change to be accommodated by longitudinal movement of said foot relative to the ground.

Prior foot designs have made no provision for such movement, leading potentially to dangerous fracturing of the leg, or, in attempts to accommodate such movement, have utilised (i) a base plate on the foot which simply scrapes undesirably along the ground, or (ii) elastomeric connections of inadequate flexibility, or (iii) small unbraked wheels carried by the leg and which are themselves prone to damage and which can sink into, or damage, the ground, or (iv) pivoted feet, with arcuate ground-contacting flanges, which contact the ground over only a small area.

It is an object of the invention to provide a new and improved trailer foot assembly.

According to the present invention, there is provided a foot assembly suitable for use in supporting a trailer, comprising an upper member on, integrally formed with, or mountable on, a support leg or the like of the trailer, and a lower member which, during use for supporting the trailer, remains in substantially stationary contact with the ground and supports the upper member and hence the trailer, the construction and arrangement being such that the lower member is held captive in relation to the upper member yet relative longitudinal movement is permitted between the upper and lower members.

In this manner, in use, the lower member remains substantially stationary on the ground, so avoiding scraping of ground, and the upper member is able to move longitudinally, whilst still offering support to the trailer, in order to accommodate longitudinal movement of the trailer due to suspension movement.

The invention is particularly applicable to trailers having pressurisedfluid-medium (e.g. pneumatic) suspension systems, in which such suspension movements can arise in such circumstances as have hereinbefore been described.

Preferably, in at least one position of the members, a generally horizontal surface of the upper member is supported directly on a generally horizontal surface of the lower member so as to transmit substantially the entire support force of the foot i.e. substantially without support force transmission through a means by which the lower member is held captive.

In this manner, at least in the aforesaid position, the support force may be "spread" over relatively extensive surfaces of members of the foot assembly, so avoiding undue stress concentrations in the foot assembly itself, and in particular, where the construction and arrangement permits the members to occupy such a position at the time when the trailer is disconnected from a tractor unit, enabling the foot assembly to cope with such dynamic/shock forces as may arise if the trailer drops when being so disconnected.

Preferably spring means is provided, operative to urge the members towards each other, the spring means preferably also being operative to bias the members to a relative position such as will be desired intially as a trailer is left free-standing and from which said longitudinal movement may be accommodated.

Such spring bias has the advantage that the lower member will be returned to its original position automatically by the spring(s) when load is removed from the leg e.g. during hitching of a trailer to a tractor unit or when lifting the leg.

In preferred embodiments of the invention the upper and lower members remain in continuous sliding contact during said longitudinal movement.

Thus, at least in such embodiments, said generally horizontal surfaces transmit substantially the entire support force of the foot throughout said longitudinal movement.

Said sliding may be facilitated through provision of a low friction surface on at least one of the members, which surface may be of nylon or other low friction material.

At least in such preferred embodiments of the invention, the lower member may be held captive on the upper member solely by said spring means.

In other embodiments of the invention the lower member is held captive on the upper member by one or more links (e.g. one on either side of the foot) pivotally mounted on the members.

In this manner, during longitudinal relative movement between the members, the members may move between extreme positions in which the members engage each other directly, through intermediate positions wherein the support force is transmitted by a said link(s).

The lower surface of the upper member may have a convex surface (as seen from below), for accommodating any changes of upper member orientation between positions in which it lies directly on the lower member and also for accommodating uneven ground.

In any embodiment of the invention, the lower member in use preferably lies flat on the ground, which is important for safety, over a sufficient area to spread the support force, preferably by way of a base plate of the lower member.

The invention also provides a trailer having such a foot assembly, and a method of modifying a trailer by providing the trailer with such a foot assembly.

Three embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: FIGURE I is a side elevational view of a trailer, showing the position of a foot assembly in accordance with the invention and including a simplified perspective view of the foot assembly to a larger scale; FIGURES 2 to 4 are side elevational views of the foot assembly shown in Figure 1, to a greatly enlarged scale, showing three relative positions of members of the foot assembly during use; FIGURE 5 is a schematic side elevational view of an alternative foot assembly in accordance with the invention; FIGURE ó is an exploded view of a third embodiment of the invention; FIGURES 7 and 8 show the foot of Figure 6 in two positions thereof; and FIGURES 9 and 10 correspond to Figures 7 and 8, but with an alternative arrangement of spring means of said foot.

The general technical features, problems and requirements in the field of supporting a free-standing trailer are described in the introduction to this specification, to which reference is expressly directed.

Referring first to Figure I of the drawings, there is illustrated a trailer 10, the trailer being shown free-standing, in a parked condition, a cabitractor unit capable of being connected to the trailer in an articulated manner having being disconnected (i.e. unhitched).

The trailer 10 comprises a chassis 12 on which two sets of wheels 14 are mounted, the wheels being carried by axles mounted on longitudinal suspension elements II which are pivotally mounted on the chassis at their left-hand ends (in relation to the drawings) and which support the chassis at right-hand ends thereof through the intermediary of air bags 15 of a pneumatic suspension system.

The trailer 10 is provided with a parking brake (not shown) which under mechanical bias of a spring (not shown) is maintained "on" irrespective of the state of the pneumatic suspension, so long as the trailer remains parked.

The trailer, in addition to being supported on the rearwardly located wheels 14, is supported on a retractable leg 16 located below a forward portion of the chassis.

The problems which can arise with such a trailer, due to longitudinal movement caused by upward movement of suspension components relative to the chassis due to suspension air leaks (or excessive loading) with the wheels locked by the brake, and prior proposals for trailer support feet and their disadvantages, are described in the introduction to this specification, to which reference is again expressly directed.

The trailer is provided, on the leg 16, with a new and improved foot assembly 20 in accordance with the invention, shown in detail in Figures 2 to 4.

The assembly 20 comprises an upper member 22 mounted on (or alternatively integrally formed with) the support leg 16 of the trailer, and a lower member 24 which during the illustrated use for supporting the trailer remains in substantially stationary contact with the ground. The lower member 24 is held captive in relation to the upper member 22 by links 26 (one on each side) pivotally connected (at 28 and 30) to the members 22 and 24, which links permit relative arcuate (but generally longitudinal) movement between the lower and upper members, between a first extreme position shown in Figure 2, through an intermediate position shown in Figure 3, to a second extreme position shown in Figure 4, and back again when appropriate.

Thus, in use, with the lower member 24 substantially stationary on the ground, so that it does not scrape the ground, the upper member 22 is able to move substantially longitudinally, whilst still being supported by the lower member 24 and offering support to the trailer, in order to accommodate longitudinal movement of the trailer frame such as may arise as hereinbefore described.

In each of the extreme positions (Figures 2 and 4) of the members, an extensive generally horizontal surface 32 of the upper member is supported directly on an extensive generally horizontal surface 34 of the lower member 24, so as to transmit substantially the entire support force of the foot through the surfaces 32 and 34 i.e. substantially without support force transmission through the links 26 or through the springs 36 described later.

In this manner, for said extreme positions, the support force is "spread" over relatively extensive surfaces of said members, which enables the foot to cope with dynamic/shock forces, such as may arise if the front of the trailer drops when being disconnected from a tractor unit, without damage to the pivots 28, 30.

The lower member 24 has a generally flat base plate 25 which is either unperforated or perforated only by one or more water drainage holes.

The lower member 24, in use, lies flat on the ground, on said base plate 25, which is important for safety, over a sufficient area to spread the support force and thereby avoid sinking into, or damage to, the ground.

In use, the trailer is left parked and unattended with the members 22, 24 in the Figure 2 position, and subsequent longitudinal movement of the trailer chassis frame, if any, causes the generally longitudinal movement of the member 22 through the Figure 3 position, ultimately to the Figure 4 position if the movement is exceptional (e.g. if the air bag is compressed so much that bump stops therein engage each other.) Whilst in Figure 2, the members 22, 24 engage directly, in the intermediate position as shown in Figure 3, the support force is transmitted via the links 26.

Springs 36 (four in total, two in each side) are provided, and are operative to urge the members 22, 24 towards each other, and also, more specifically, to bias the members to the Figure 2 relative position, such as will be desired initially when a trailer is left free-standing, and from which said longitudinal movement is required to be accommodated.

Such spring bias has the advantage that the lower member will be retracted automatically, e.g. by being raised by the springs 36, relative to the member 22, under guiding constraint of the links 26, when load is removed from the leg. e.g. during hitching or when lifting the leg 16.

The lower surface 32 of the upper member 22 has a convex curvature (as seen from below), for accommodating changes of upper member orientation between the positions in Figures 2 and 4 in which it lies directly on the lower member, and also for accommodating uneven ground.

In an alternative foot assembly 40 in accordance with the invention, shown in Figure 5, no such links 26 are provided, but the members (correspondingly numbered) 22, 24 are held captive together solely by springs 36, arranged as shown, the upper and lower members in this example remaining in continuous direct sliding contact with each other throughout the relative longitudinal movement so that relatively extensive, mutually engaging generally horizontal surfaces 22a and 24a of the respective members 22 and 24 transmit substantially the entire support force of the foot 40 throughout said longitudinal movement. The member 24 comprises a nylon low friction upper surface 24a on which the member 22 slides, to facilitate such movement and avoiding sliding steel-on-steel sliding contact and potential associated corrosion and wear problems. Use of the surface 24a also reduces noise (e.g. rattling) during transit.

It will be appreciated that in any such direct contact position between members 22 and 24, for any of the above embodiments, high impact loads will not damage or weaken connections between the members 22 and 24.

Although in Figure 5 the foot assembly 40 is shown as being connected to leg 16 by way of a pivot P, this pivot P is not shown by way of limitation and is present only for accommodating uneven ground, rather than for accommodating said longitudinal movement of the trailer. Said longitudinal movement of the trailer is accommodated by said sliding movement between the members 22 and 24. The state or quality of pivot P is of no consequence to said sliding movement and indeed all that is required is some (controlled) lack of rigidity for accommodating uneven ground.Thus, as an alternative to the pivot P, the foot assembly 40 could for example be connected to the leg by flexible and/or resilient means to cater for uneven ground, or flexible and/or resilient means may be incorporated between parts of the leg or in mountings therefore on the trailer chassis, for achieving such controlled lack of rigidity.

Should dirt, mud or the like become deposited on the nylon syrface 24a of the foot assembly 40, longitudinal sliding of the member 22 over that surface during use of the assembly 40 for supporting the trailer is effective to sweep clear the surface 24a, any dirt, mud or other foreign matter being pushed onto the extremities of the base plate 25 of the member 24 at the front and rear extremities of the surface 24a from which it may be washed away naturally by rain or road surface water or by manual hosing, generally in a lateral directions.

An alternative foot assembly 50 in accordance with the invention, in which flexible resilient means (not shown) between telescoping parts of leg 16 is used for accommodating uneven ground, is shown in Figures 6 to 10, being otherwise a development of the embodiment illustrated in Figure 5, and being correspondingly numbered where appropriate.

Referring to the exploded perspective view, Figure 6, of the foot assembly 50, the upper member 22 of the assembly 50 comprises a generally horizontal plate welded to the lower end of the leg 16 (and which may be formed by cutting to size a conventional such plate such as would conventionally be provided at the lower end of such a leg), affording a downwardly presented generally horizontal surface 22a. Said plate being rigid with a lower portion of the leg 16.

The lower member 24 of the assembly 50 is formed from a channel section base plate 25, of steel, to which are welded respective lateral side pieces 51, also of steel, said welding being carried out at each end of each side piece; and along the lower edge of each side piece, and a front-top piece 52, of steel plate, is then welded to the upper front edge of the base plate 25 and along front portions of upper edges of the respective side pieces 51. Two strips 24a of nylon, affording low friction upper surfaces, are rivetted to the lower portion of the base plate 25 prior to welding in position of the plate 52.

The rivets used are countersunk into the strips 24a so as not to protrude above said low friction surfaces. The strips 24a are spaced slightly apart, and spaced slightlly from the respective adjacent side pieces 51, and also spaced from front and rear end walls of the base plate 25, and the side pieces 51 have trunkated lower corners both to facilitate positioning during aseembly and to provide drainage outlets for foreign matter.

Brackets 53 are welded to opposite lateral sides of said lower portion of the leg 16, and cross bars 54 and 55 are inserted through respective throughholes 56 and 57 in the brackets 53. The cross bars are provided with "turned grooves" to receive and trap hook portions at the ends of appropriate springs 36.

The upper member 22, on the leg 16, is then introduced into the space between the plate 52 and the base plate 25, and one pair of the springs 36 is then connected between the grooves on the bar 55 and respective hookreceiving through holes 58 in the base plate 25, and the other pair of springs 36 is connected between the outer most grooves on the bar 54 and respective through holes 59 in the plate 52.

Thus, as with the assembly 40 hereinbefore described, the lower member 24 is held captive in relation to the upper member 22 of the foot assembly 50, by the springs 36.

The construction of the lower member 24, with the channel crosssection base plate 25, side pieces 51 and front-top plate 52, affords a lower member of great rigidity, which is especially important on uneven ground.

The normal "rest" position of the members 22 and 24 of the foot 50 is as shown in Figure 5, in which the springs 36 are under tension and act to hold the members in said position. In use, in response to longitudinal movement of the trailer when parked, the leg 16 is able to slide forwardly (the cce4#icient of friction between the surfaces 22a and 24a being less than that between the base plate 25 and the ground), eventually to the position shown in Figure 6, the support force of the foot being transmitted throughout entirely by the direct contact between the relatively extensive generally horizontal surfaces 22a and 24a, as for the assembly 40.

In an alternative arrangement, shown in Figures 9 and 14 the springs connected to the holes 58 are instead connected to the inner grooves on the bar 54, and the bar 55 and apertures 57 in such a construction may be dispensed with.

In either case, dirt, mud or foreign matter which enters the lower member 24, is urged off the strips 24 by movement of the member 22, and application of a water hose for example may drive it out, laterally, through the drainage holes afforded at the lower corners of the member 24.

In either case, the lower member returns to its original position when the weight of the trailer is taken from the foot, when the trailer is reconnected to a cab/tractor unit.

It will be appreciated that the more upright of the springs 36 serves to hold the member 24 against the member 22, whilst the more horizontal of the springs 36 serves this purpose to some extent but also serves to return the lower member 24 to its original position when appropriate.

In each of the illustrated embodiments the springs 36 shown are tension springs, but in alternative constructions they could be replaced by compression springs or torsion'springs.

It will be appreciated that such foot assemblies may be fitted to a leg of an existing trailer by removing the existing foot or foot portion of such leg, and replacing it with a foot assembly in accordance with the invention.

Although the trailer 10 illustrated utilises a pneumatic suspension system, the invention is also applicable to trailers having suspension systems which utilise any other pressurised fluid medium.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, or a class or group of substances or compositions, as appropriate, may, separately or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims (17)

CLAIMS:

1. Afoot assembly suitable for use in supporting a trailer, comprising an upper member on, intergrally formed with, or mountable on, a support leg or the like of the trailer, and a lower member which, during use for supporting the trailer, remains in substantially stationary contact with the ground and supports the upper member and hence the trailer, the construction and arrangement being such that the lower member is held captive in relation to the upper member yet relative longitudinal movement is permitted between the upper and lower members.

2. A foot assembly according to Claim I wherein, in at least one position of the members, a generally horizontal surface of the upper member is supported directly on a generally horizontal surface of the lower member so as to transmit substantially the entire support force of the foot.

3. A foot assembly according to Claim 2 wherein the construction and arrangement permits the members to occupy such a position at the time when the trailer is disconnected from a tractor unit.

4. A foot assembly according to any one of Claims I to 3 wherein spring means is provided, operative to urge the members towards each other.

5. A foot -assembly according to Claim 4 wherein the spring means is also operative to bias the members to a relative position such as will be desired initially as a trailer is left free-standing and from which said longitudinal movement may be accommodated.

6. A foot assembly according to Claim 5 wherein such a spring bias is such that the lower member is returned to its original position automatically by the spring(s) when load is removed from the leg.

7. A foot assembly according to any one of Claims I to 6 wherein the upper and lower members remain in continuous sliding contact during said longitudinal movement.

8. A foot assembly according to Claim 7 wherein said sliding is facilitated through provision of a low friction surface on at least one of the members.

9. A foot assembly according to Claim 8 wherein said surface is of nylon or other low friction material.

10. A foot assembly according to any one of Claims 7 to 9 wherein the lower member is held captive on the upper member solely by said spring means.

II. A foot assembly according to any one of Claims I to 6 wherein the lower member is held captive on the upper member by one or more links pivotally mounted on the members.

12. A foot assembly according to Claim 11 wherein the lower surface of the upper member has a convex surface (as seen from below).

I 3. A foot assembly according to any one of the preceding claims wherein the lower member in use lies flat on the ground over a sufficient area to spread the support force.

14. A foot assembly substantially as hereinbefore described with reference to and/or as illustrated in the accompanying drawings.

15. A trailer having a foot assembly according to any one of Claims I to 14.

16. A method of modifying a trailer by providing the trailer with a foot assembly according to any one of Claims I to 14.

17. Any novel feature or novel combination of features described herein and/or illustrated in the accompanying drawings.