GB2116924A - Third axle unit for tractor - Google Patents

Abstract

A third axle unit for converting a two axle, four wheel tractor into a three axle, six wheel tractor comprises a forwardly-extending, substantially horizontal frame mounted on a wheeled axle adjacent the rear of said frame. The frame includes a pair of opposed, parallel side members (6) extending fore and aft of the unit for location one to each side of the chassis of the associated tractor, the distance between distance pieces attached to the opposed faces of the side members (6) being adjustable to suit tractors of different widths. The unit includes a suspension system (32 to 48) reacting between the frame and the axle which is located substantially above and rearwardly of the axle whereby the space forward of said axle and between the wheels (18) of the unit is empty. Instead of being used to tow a trailer, the third axle unit may have mounted thereon a skip, cement mixer or vehicle recovery crane. <IMAGE>

Description

SPECIFICATION Third-axle units for tractors This invention relates to third axle units for attachment to tractors, in particular two axle, four wheel heavy goods vehicle tractors to convert said tractors to three axle, six wheel units.

In order to increase the load-carrying capacity of two axle, four wheel heavy goods vehicle tractors it has, amongst other things, been proposed to provide a 'dolly' or extension module for attachment to the tractor intermediate the tractor and its trailer to convert the tractor into a three axle, six wheel unit.

Conventional tractors of this type incorporate leaf-spring rear suspension systems which extend fore and aft of the tractors and project rearwardly beyond the confines of the rear wheels of said tractors. Further, the chassis of such tractors can be of different shapes and sizes.

Known 'dollies' for the above-mentioned purpose comprise a forwardly-extending frame fitted with a king-pin for location in the Fifth Wheel of the tractor, the frame itself carrying a further Fifth Wheel in which can be located the king-pin of the associated trailer. The frame is mounted on a two wheel single rear axle, the suspension between the frame and the axle being of the conventional leaf-spring type.

Whilst such 'dollies' serve the purpose of increasing the load-carrying capacity of the tractors, they suffer from a number of disadvantages. Because of the differing configurations of tractors, each 'dolly' has to be purpose-buiit to suit the particular tractor in question, and in particular the Fifth Wheel installation. Thus, for a fleet of different tractors, there must be as many 'dollies' provided as there are tractors.

Further, the provision of leaf-spring type suspension systems on both the tractor and the 'dolly', and in particular the rearward extension of the tractor suspension, as well as the chassis itself, beyond the rear wheels of the tractor, prevents the wheels of the 'dolly' being located as close to the rear wheels of the tractor as would be desirable - the suspension units would interfere one with the other and with the tractor chassis with closer location. The result is a substantial gap between the rear wheels of the tractor and the wheels of the 'dolly', undesirably increasing the overall length of the tractor-trailer combination, while tyre-scrub is a further problem with such an arrangement.

It would be desirable to be able to increase the load-carrying capacity of a tractor by providing a third-axle unit which could be fitted to any one of a number of different tractors without unnecessarily increasing the length of the combination.

According to the present invention there is provided a third axle unit for attachment to a receiving plate on a chassis of an associated tractor, the unit comprising a frame extending fore and aft of the unit, the forward end of said frame being provided with a depending pin member for location in a socket on said receiving plate, the frame including a pair of opposed, parallel side members extending longitudinally of the unit for location one to each side of the chassis of the trailer, said side members being adapted for attachment thereto of any one or more of a series of associated distance pieces whereby the effective distance between the inside faces of the side members can be altered to suit the width of the chassis of an associated tractor, the unit further comprising a wheeled axle and a suspension system for the axle, said suspension system being located substantially above and rearwardly of said axle and including a series of transversely-spaced resilient suspension members reacting between the rear regions of the frame and the axle.

A preferred suspension system includes two pairs of suspension members, one pair for each side of the unit, each suspension member comprising a pair of rigid parallel end plates between which is secured a resilient body portion, conveniently of rubber, the two end plates of each suspension member being transversely spaced one from the other and vertical ly displaced relative to each other.

Preferably the end plates of the suspension members make acute angles with the vertical, the members of each pair being arranged such that the central axes of the body portions thereof define a V.

The suspension system may further include, for each side of the unit, a pair of torsion bars one above the other extending fore and aft of the unit rearwardly of the rear axle and reacting between the frame and the rear axle. The torsion bars of one of said pairs may be adjustable in length.

Conveniently the side members may be further adapted such that the fore and aft loction of the associated distance pieces thereon may be varied.

Preferably the depending pin member at the forward end of the frame can be located in any one of a plurality of different operative position on the frame to suit the associated tractor.

By way of example only, an embodiment of the invention will now be described in greater detail with reference to the accompanying drawings of which: Figure 7 is a side view of a third axle unit according to the invention; Figure 2 is a longitudinal vertical section on the centreline of the unit of Figure 1; Figure 3 is a rear view of the unit of Figure 1; Figure 4 is a plan view of the unit of Figure land Figures 5a and 5b show the unit of Figure 1 awaiting attachment to, and attached to a tractor respectively.

Referring to Figures 1 to 4 of the drawings, the illustrated third axle unit comprises a substantially horizontal frame indicated generally at 2 and including a pair of opposed, parallel side members 4, 6 in the form of U-section beams extending fore and aft of the unit.

A pin member 8 for effecting connection of the unit to an associated tractor depends from the front central regions of the frame 2, said pin member 8 being secured, for example by welding, in either one of two longitudinally spaced receiving apertures 10, 10' formed in a plate 12 secured to the frame, the aperture used depending upon the construction of the associated tractor. Clearly more than two apertures such as 10 may be provided if required or desired.

A conventional receiving plate or Fifth Wheel 14 is mounted on top of the frame 2 rearwardly of the plate 12 for connection thereto of the trailer (not shown) to be associated with the tractor.

The unit further includes a single rear axle 16 on each end of which are carried a pair of road wheels 18.

A pair of support arms 20 are pivotally secured one to each side of the frame 2 adjacent the front regions thereof in such a manner that, when the unit is disconnected from a tractor, the arms 20 can be located in their operative, ground-engaging positions shown in Figures 1 to 3 to support the unit as shown. On attchment of the unit to a tractor, the arms 20 can be pivoted, as indicated by the dotted line in Figure 1,to a stored position extending along and parallel with the side members 4,6 of the frame 2.

The distance D, Figure 3, between the inside faces of the side members 4, 6 may correspond with the width of the chassis of the tractor to which the unit is to be attached, in which case said members 4, 6, on attachment of the unit to a tractor, can be positioned one to either side of said chassis to locate the unit laterally relative to the tractor.

However, the widths of the chassis of tractors can vary and may be less than said distance D. In such cases, distance pieces such as those shown at 22 can be used to reduce the distance D to D' (Figure 4), the width of the associated tractor, and thereby to maintain the possibility of controlled relative vertical movement between the unit and the tractor whilst preventing undesirable relative lateral movement therebetween.

More particularly, the distance pieces 22 each comprise a substantially right-angled bracket in one plate 24 of which are formed a pair of holes 26 by means of which the bracket can be bolted to the associated side member 4 or 6 in which are formed correspondingly spaced holes, the other plate of said bracket abutting the inside face of the side member.

Said other plate has secured thereto, by means of, for example, a series of ribs 28, an abutment plate 30, the distance between the abutment plates 30 of the two distance pieces 22 being equal to the desired distance D'. A series of distance pieces 22 each with different length ribs 28 may be provided to enable any desired distance D' to be achieved.

A series of longitudinally spaced holes may be formed in the upper flanges of the side members 4,6 to enable the longitudinal position of the distance pieces 22 on the frame to be varied to suit particular requirements.

The unit includes a suspension system reacting between the frame 2 and the axle 16 and located substantially above and rearwardly of the axle whereby the space between the wheels 18 in front of the axle 16 is substantially empty.

More particularly, the suspension system includes a box-section support member 32 welded to, to extend parallel with and substantially the length of, the axle 16 such that the forces applied to the axle are distributed along the full length thereof rather than being concentrated adjacent the ends of the axle as occurs in conventional arrangements.

The suspension system further includes two pairs of suspension members 34, one pair for each side of the unit, said suspension members reacting between the frame 2 and the support member 32. Each suspension member 34 comprises a pair of parallel end plates 36,38 between which is secured a resilient body portion comprising series of layers 40 of rubber interconnected by metal sub-plates 42.

The two suspension members 34 of each pair are positioned transversely of the unit with the central axes of the body portions thereof defining a V-shape as best seen in Figure 3. One plate 36 of each member is secured to the frame 2 to make an acute angle with the vertical, while the other plate 38 of each member is secured to the support member 32 to make the same acute angle with the vertical.

It will thus be appreciated that the suspension members 34, which are disposed transversely of the unit immeditely above the axle 16, can absorb vertical loads applied to the axle, the application of such loads resulting in compression of the body portions of the members 34 between the associated plates 36, 38 which are moved towards one another as the frame lowers on the axle.

Additionally, the configuration and transverse location of the members 34 is such that any lateral force or side thrust applied to the unit is also absorbed by the suspension system, eliminating the necessity for rigid A-frames and the like as are normally provided for such purposes.

The suspension system is completed by two pairs of torsion bars 44,46, one pair for each side of the unit. One end of the bars of each pair are pivotally mounted to an associated rigid bracket 48 depending from the rear end of the frame 2, the upper bar 44 of each pair extending fore and aft of the unit from said bracket 48 to a pivot point above the rear axle adjacent the junction between the two associated suspension members 34, and the lower bar 46 of each pair extending fore and aft of the unit from the bracket 38 to a pivot point just below the axle 16. It will be appreciated that the torsion bars 44,46 absorb longitudinal forces on the unit such as those resulting from braking.

Conveniently the bars 44,46 of one of said pairs are adjustable in length in such a manner as to enable accurate relative positioning between the frame 2 and the axle 16.

Thus it will be appreciated that the suspension system for the third axle unit is located immediately above and rearwardly of the axle 16 whereby the space in front of said axle and between the inner wheels 18 is empty and available to receive therein any rearwardly projecting components of the associated tractor.

Referring to Figure 5a, there is shown a conventional tractor of which the rear leaf spring suspension and the rear regions of the chassis project rearwardly of the rear wheels of the tractor. The third axle unit is shown unattached to the tractor and supported by its arms 20.

Figure 5b shows the third axle unit attached to the tractor, with the rearward extents of the tractor suspension and the rear regions of the tractor chassis projecting into the free space between the wheels of the unit whereby the wheels of the unit can be positioned very close to the rear wheels of the tractor, Such an arrangement keeps the length of the tractor-third axle unit combination to a minimum and also considerably reduces tyre-scrub compared with established arrangement in which the wheels of the 'dolly' and the tractor are spaced a substantial distance apart.

Figure 1 shown in dotted lines the position of the rear wheel of the tractor on attachment of the unit to the tractor, the distance 'X' between the wheels of the unit and the tractor being able to be kept to a minimum.

The described third axle unit may be used between a tractor and an associated trailer to enable a tractor to transport heavier loads than heretofore, or said unit may have mounted thereon any one of a number of different mechanisms, such as skips, cement mixers, vehicle recovery cranes and the like, thus enabling a tractor to be readily convertible for any one of a number of different purposes.

Claims (9)

1. Athird axle unit for attachment to a receiving plate on the chassis of an associated tractor, the unit comprising a frame extending fore and aft of the unit, the forward end of said frame being provided with a depending pin member for location in a socket on said receiving plate, the frame including a pair of opposed, parallel side members extending longitudinally of the unit for location one to each side of the chassis of the tractor, said side members being adapted for attachment thereto of any one or more of a series of associated distance pieces whereby the effective distance between the inside faces of the side members can be altered to suit the width of the chassis of an associated tractor, the unit further comprising a wheeled axle and a suspension system for the axle, said suspension system being located substantially above and rearwardly of the axle and including a series of transversely spaced resilient suspension members reacting between the rear regions of the frame and the axle.

2. A third axle unit as claimed in claim 1 in which the suspension system includes two pairs of suspension members, one pair for each side of the unit, each suspension member comprising a pair of rigid parallel end plates between which is secured a resilient body portion, the end of each suspension member being transversely spaced one from the other and vertically displaced relative to each other, one plate being secured to the frame and the other, lower plate being secured to the axle.

3. Athird axle unit as claimed in claim 2 in which the end plates of each suspension member make an acute angle with the vertical, the members of each pair being arranged such that the central axes of the body portions thereof extend transversely of the unit and define a V.

4. Athird axle unit as claimed in claim 2 or claim 3 in which the body portion of each suspension member comprises a series of resilient sub-portions bonded to each other by means of intermediate plate portions each extending parallel with the end plates of the associated suspension member.

5. A third axle unit as claimed in any one of claims 1 to 4 in which the suspension system further includes, for each side of the unit, a pair of torsion bars one above the other extending fore and aft of the unit rearwardly of the rear axle and reacting between the frame and the rear axle.

6. A third axle unit as claimed in claim 5 in which the torsion bars of one of said pairs are adjustable in length.

7. Athird axle unit as claimed in any one of claims 1 to 6 in which the side members of the frame are further adapted such that the fore and aft location of the associated distance pieces thereon can be varied.

8. A third axle unit as claimed in any one of claims 1 to 7 in which the depending pin member at the forward end of the frame can be located in any one of a plurality of different operative positions on the frame.

9. A third axle unit substantially as described with reference to and as illustrated by the accompanying drawings.