GB2229983A - A fifth wheel mounting structure - Google Patents

Abstract

A mounting frame for connecting a fifth wheel to a tractor comprises a base (4) securable to the tractor and to the fifth wheel and a plate (6) attached to the base (4) either removably or permanently. The base (4) and the plate (6) are so arranged and dimensioned that the connection between the fifth wheel and the tractor has a certain given maximum strength. Preferably only the size of the plate (6) need be varied to give the required down-rating, all the other parts required for the mounting frame, being standard. In order to simplify the relationship between the variable dimension of the plate and the strength of the connection at least one aperture (32) is preferably provided in the base beneath, and symmetrically arranged with respect to, the plate (6). <IMAGE>

Description

IMPROVEMENTS IN AND RELATING TO FIFTH WHEELS This invention relates to the fifth wheel couplers for coupling a tractor vehicle to a trailer or semi-trailer and in particular to a frame for mounting a fifth wheel coupler to a tractor.

Fifth wheel couples are well known and generally comprise a plate with a slot and a locking mechanism to hold a king pin fixed to the trailer or semitrailer in the apex of the slot. Fifth wheel couples are secured to the tractor, generally to the chassis thereof, by a mounting frame.

The cost of road taxing large tractors is very high and can add considerably to their running costs.

However, such tractors are more useful since the range of trailers with which they can be employed is wider and moreover they are found to be preferred by drivers. One known way of overcoming the problem of the expense involved in taxing large tractors involves fixing the fifth wheel mounting frame to the tractor chassis with a certain number and size of bolts which sets an upper limit to the size of trailer which can be attached to the tractor. The tractor is then rated at a lower value and so costs less to tax. This procedure is known as "down-rating".

This arrangement is relatively complicated, requiring a large number of bolts of different sizes to be kept readily to hand to allow the rating of the tractors to be varied. It requires the mounting frames to be formed with holes capable of receiving bolts of different sizes. The arrangement has to be very carefully checked to ensure that the bolting is such as to conform with the rating for which tax has been paid.

A mounting frame for connecting a fifth wheel to a tractor in accordance with the invention comprises a base securable to the tractor and to the fifth wheel, a plate attached to the base either removably or permanently, the base and the plate being so dimensioned and arranged that the connection has a certain given maximum strength.

The advantage of this is that a single base of constant dimensions together with a single means for securing the base to the tractor and fifth wheel are required, since only the size of the plate need be varied to give the required down-rating. If a number of plates of varying dimension are provided then the down-rating is adjusted simply by changing the size of plate attached to the base. Alternatively, to change the down-rating the mounting frame can be replaced by another with a different size of plate which will be a relatively simple operation since, as noted above, no variation in the attachment means is required.

The plate will hereinafter be referred to as the "rating plate" to aid clarity.

The strength of the connection between the fifth wheel and the tractor is fairly complicated to evaluate. In order to simplify the evaluation the base may have at least one cut-out, in the general shape of two isosceles triangles connected at their apexes, provided in the region where the plate is attached to the base. This has been found to aid computation of the mounting frame strength and determination of the required plate dimensions. The shape of the cut-out is suitably computer generated and conveniently provides a direct correlation between at least one dimension, preferably the width, of the rating plate and the required down rating which the mounting frame is to provide. The thickness and length of the different rating plates may therefore be kept constant while the width is varied.

Preferably the base includes apertures whereby it may be bolted to the fifth wheel and to the tractor, suitably to the chassis of the latter. The same quantity and size of bolts is always employed no matter what down-rating is required and the problems discussed above are therefore obviated.

The base may comprise two members, each of which comprises two parallel, laterally spaced arms, the length of which is equal to, or greater than, the width of the tractor chassis. These arms are employed to secure the members to the tractor chassis, suitably by bolting them thereto. Each member further includes a support plate, the plane of which is parallel to, but vertically spaced from, those of the arms, the support plate being positioned intermediate the arms.

A connecting plate positioned at an angle to the axes of the arms is secured at one edge along one of the longitudinal edges of the support plate and at the other to one of the arms. The arms, support plate and connecting plates may be integral. By employing a two member base, chassis flexibility is increased.

In use, the two members may be positioned side by side with their axes parallel. The rating plate rests on top of the support plates and preferably has integral arms at right-angles thereto, the ends of which are connected to the outer arms of the base members by, for example, welding. As mentioned previously cut-outs may be provided in the support plates of the base members.

The fifth wheel is secured to the base by bolts, by way of suitably positioned apertures in the support plates of the base members.

The invention will now be further described by way of example with reference to the accompanying drawings in which: Figure 1 is a plan view of a mounting frame in accordance with the invention; Figure 2 is a side view of the mounting frame of Figure 1 and Figure 3 is a schematic view of the mounting frame of Figure 1 employed to mount a fifth wheel to a tractor.

The mounting frame 2 comprises a base 4 and a rating plate 6. The base 4 comprises two identical members 8 and 10, each of which comprises two laterally spaced parallel arms 12 and 14 joined by connecting plates 16, 18 to a support plate 20, the plane of which is parallel to, but vertically spaced from, those of the arms 12 and 14. The length of each member 8 or 20 is equal to, or greater than, the width of the tractor chassis to which a fifth wheel is to be mounted via the frame 2. The base 4 is connected across the chassis, illustrated in dotted outline at 22 in Figure 3, by bolting it thereto through apertures 24 provided in the arms 12, 14 of the members 8 and 10. The form of the base 4, that is in two separate parts, increases the flexibility of the chassis.

The rating plate 6 rests on the support plates, 20 and includes integral arms 26, 28 at rightangles to the plane thereof by which it can be secured to the outer arms 12 of the base 4, by, as illustrated, welding. The longitudinal axis 30 of the rating plate 6 is preferably aligned with the lateral axes of the support plates 20 to ensure that the transfer of loading is symmetrical.

In the region where the rating plate 6 is attached the support plates 20 have cut-outs 32, each of which comprises a generally oval aperture 34, the major axis of which is aligned with the lateral axes of the support plates 20. Two rectangular apertures 36 intersect the oval aperture 34 on either side thereof and each extends for a distance before diverging to form a trapezoidal aperture 38. The cutouts 32 could be described as resembling a bow-tie or a propeller in overall shape.

The shape of the cut-outs 32 is such that it aids calculation of bending strengths of the mounting frame 2. In particular, the width of the cut-out considered parallel to the longitudinal axis 30 of the rating plate 6 varies, which has been found in practice to be important in aiding the calculation of the rating plate dimensions.

The rating plates 6 employed with the mounting frame 2 are preferably of the same thickness and length no matter what down rating is required. The only dimension which is varied is then the width and this is suitably such that there is a direct correlation between the width and the desired down rated gross weight, for example a 38 cm width rating plate would be employed with a 380000 kg gross weight unit. This correlation can be evaluated relatively easily, owing to the shape of the cut-outs 32.

The support plates 20 contain further apertures 40 whereby a fifth wheel, illustrated in dotted outline at 42 in Figure 3 may be secured thereto. The frame 2 thus provides the connection between the chassis 22 and the fifth wheel 42. To strengthen the frame 2, bracing plates 44 may be welded between the arms 12, 14 and the connecting plates 16, 18 of the base members 8 and 10.

The mounting frame 2 is robust but relatively simple to construct. It is always connected to the tractor with which it is to be employed by the same number of type of bolts. It allows down-rating to be achieved in a straight forward and practical manner without requiring a large number of varying component parts. Identification of the mounting frame required for a particular job is simplified by the correlation between rating width and required rating.

Claims (8)

CLAIMS:

1. A mounting frame for connecting a fifth wheel to a tractor, the frame comprising a base securable to the tractor and the fifth wheel and plate attached to the base either removably or permanently, the base and plate being so dimensioned and arranged that the connection has a certain given maximum strength.

2. A frame as claimed in Claim 1 wherein one dimension of the plate is directly related to the required maximum strength.

3. A frame as claimed in either Claim 1 or 2 in which the base comprises at least one member having laterally spaced arms and a support surface positioned intermediate the arms, the plane of which is parallel to but spaced from the arms, the plate resting on top of the support surface and being secured to the base.

4. A frame as claimed in Claim 3 wherein the support surface of the or each member includes at least one cut-out positioned beneath, and symmetrically arranged with respect to, the plate.

5. A frame as claimed in Claim 4 wherein the cutouts are in the general shape of two isosceles -triangles connected at their apices beneath the centre line of the plate.

6. A frame as claimed in either Claim 3, 4 or 5 wherein the base comprises two such members.

7. A frame as claimed in any preceding claim wherein the base is provided with apertures through which bolts may pass in order to secure the base to the tractor and the fifth wheel.

8. A mounting frame substantially as described herein with reference to the accompanying drawings.