GB2042676A - Torsion Bar Spring with Thicker Portion - Google Patents

Abstract

An L-shaped torsion bar spring consisting of a torsion arm 15 and a lever arm 17 has, in the region of the elbow of the two arms, a part of greater cross-sectional area than the torsion arm. The increased cross-sectional area of the elbow accommodates increased stresses in the bar allowing a bar with shorter arms to be used without approaching the elastic limit of the bar undesirably closely. The spring is used to bias a tiltable cab structure of a truck into the tilted position. <IMAGE>

Description

SPECIFICATION Torsion Bar for Tiltable Cab This invention relates to a torision bar for biasing a tiltable cab of a truck from a normal position towards a position tilted in relation to a frame or body member of the truck: the cab is tilted to enable access to be gained to the engine or other components beneath the cab.

Our earlier British Patent Specification No.

992604 discloses and claims a torsion bar counterbalance arrangement having an L-shaped torsion bar of uniform cross-section, one arm canstituting a torsion arm fixed at its free end and rotatably mounted at the other end in the cab of the truck; the other arm constituting a lever arm in engagement with the truck body; and the cab is biased by the torsional stress in the torsion arm and the bending stress in the lever arm.

The utilization of the resiliency of both arms of the bar enables a bar whose torsion arm is of a certain length and cross-section to bias the cab member through a larger angle than would be the case if the torsional resiliency of the torsion arm alone were used. The torsional and bending stresses required to bias the cab through a desired angle increase as the lengths of the arms of the torsion bar decrease. In order to avoid stressing the bar undesirably closely to its elastic limit, the arms of the torsion bar are made as long as possible. However, the maximun lengths of the arms are dictated by the dimensions of the cab.

When the cab is of relatively small dimensions, the bar must be capable of withstanding relatively high torsional and bending stresses without its elastic limit being approached too closely. By increasing the cross-sectional area of the torsion bar, the elastic limit of the bar is increased, thus allowing greater stresses to be applied to it.

However, the deflection, or strain, produced by any given stress on the torsion bar decreases as the diameter of the bar increases. Consequently, a bar of relatively large cross-sectional area would not bias the cab through as large an angle as a bar of smaller cross-sectional area.

According to the present invention there is provided a torsion bar for biasing a tiltable cab structure of a truck from a normal position towards a position tilted in relation to the body structure of the truck, the said bar being L shaped, one arm constituting a torsion arm and the other arm constituting a lever arm, characterized in that the part of the bar in the region of the elbow of the two arms is of greater cross-sectional area than the torsion arm.

The increased cross-sectional area of the elbow accommodates increased stresses applied to the bar without reducing significantly the strain produced by any given stress on the torsion bar.

Consequently, the torsion bar of the present invention may have shorter arms than the bar disclosed in British Patent Specification No.

992,604 whilst still biasing the cab through the required angle and without stressing the bar to a degree which is undesirably close to the elastic limit of the bar.

Preferably the cross-sectional area of the bar in the region of the elbow is from 10 to 30% e.g. 10 to 20%, greater than that of the torsion arm. For example, torsion arm and elbow may be of circular crosssection, in which case the diameter of the elbow may be about 24 mm and the diameter of the arms may be about 21 mm.

The cross-sectional shapes of the arms may be similar, e.g. square, or rectangular. Alternatively the cross-sectional shape of the torsion arms may be different. Thus, since a bar of rectangular or square cross-section has a greater resistance to bending stresses than a circular-section bar of identical cross-sectional area, and a bar of circular cross-section has a greater resistance to torsion than a square-section bar of identical crosssectional area, preferably the lever arm is of rectangular or square cross-section, and the torsion arm is of circular cross-section. The elbow region will preferably have a cross-section similar to that of the arm of larger cross-sectional area.

The torsion bar is connected with a truck as an assembly comprising a series of mountings adapted to be secured to the cab or body structure of the truck. Usually, the assembly will include two torsion bars the lever arms being on opposite sides of the assembly. A first mounting for the or each bar is fixed towards the free end of the or each torsion bar and is adapted to be secured to the cab or body structure, preferably the body structure. A second mounting for the or each bar is rotatably mounted on the elbow region of the bar at the other end of the torsion arm and is adapted to be secured to the same structure as the first mounting. A third mounting for the or each bar is fixed towards the free end of the lever arm and is adapted to be secured to the opposite structure to that to which the torsion arm is attached, preferably the cab structure.

When the torsion bars are used in the assembly the first mounting for each bar may be formed in the same fitting as the second mounting to the other bar. The same fitting may also provide a pivot for the cab structure.

In order to provide secure attachments of the ends of the torsion bar to their respective first mountings, the free ends of the bar are preferably of non-circular, e.g. square, rectangular, hexagonal or splined cross-section.

The invention also includes a truck having a body structure, a cab structure mounted thereon for movement between normal position and a position tilted in relation thereto and a torsion bar assembly of the invention acting between the cab and the body structures.

The invention is hereafter particularly described with reference to the accompanying drawings in which: Figure 1 is a perspective view of a torsion bar assembly according to the invention; Figure 2 is an exploded perspective view of part of the assembly of Figure 1; and Figure 3 is a side view of part of an alternative assembly according to the invention.

The torsion bar assembly is fitted in a conventional truck having a body structure which includes a frame 1 composed of longitudinal members 3 and transverse members 5, and a cab structure (not shown) and which is tiltable from a normal position to give access to the engine (not shown). The cab structure is biased towards its tiltable position by the torsion bar assembly.

The torsion bar assembly comprises a left hand torsion bar 7, a right hand torsion bar 9, a left hand fitting 11 and a right hand fitting 13. The bars and fittings are similar, and accordingly only one will be described.

Each bar is L-shaped and has a torsion arm 1 5 and a lever arm 1 7 which rubs against a mounting 6 which is connected to the cab structure.

A mounting bracket 21 is welded to the front part of each longitudinal member 3, and overlies the member 3 to which it is welded. The upper surface of the bracket is formed in two rearwardly downwardly inclined parts 22 and 23 (Figure 2); the part 22 makes a smaller angle with the horizontal than the part 23. The two brackets are symmetrically arranged on opposite sides of the vehicle centre line.

Each fitting 11 or 13, is attached to a bracket 21 by means of a bolt 24, which passes through the part 22, and a bolt 26 which passes through the part 23, the nuts 25, 27 screwing on to the ends of the bolts. Each fitting has a journal bearing 29 for a pivot (not showm) of the tiltable cab structure and two mountings for the torsion bars. One mounting comprises a square aperture 31 for anchoring the free end of the torsion arm 1 5 of a torsion bar. The other mounting comprises a split bush 35 having a circular aperture 37 which receives the elbow of the bar at the end of the torsion arm, the bush 35 being rotatably mounted in a circular aperture 33 in the fitting.

The bearings 29, recesses 31, and apertures 33 in the two fittings 11 and 13 are symmetrically located on opposite sides of the vehicle centre line. Figure 3 illustrates an alternative fitting the various parts of which have been given like reference numerals to the corresponding parts of the fitting shown in Figure 2. The fitting of Figure 3 is formed as an integral casting. The mounting for the elbow of the bar at the end of the torsion arm is positioned between the journal bearing 29 for the pivot of the cab structure and the aperture 31 in which the free end of the torsion arm is fixed. This fitting permits a longer lever arm 1 7 to be used.

The torsion bars are of circular cross-section along all their length, except at the free ends of the torsion arms 15, which are of square crosssection. The part of the bars in the region of the elbow 35 between the two arms 1 7, 1 5 is of greater diameter than the torsion arm 1 5 but equal in diameter to the lever arm 17. In the embodiment illustrated, the torsion arm has a diameter of 20 mm and the lever arm and the elbow region have a diameter of 24 mm.

The free end of the torsion arm 1 5 of the bar 7 fits non-rotatably in the recess 31 in the fitting 11. The elbow region of the end of the torsion arm 1 5 of the bar 7 is received in the aperture 37 in the split bush 35 in the fitting 1 3. Lock bolts 39 are screwed into fittings to engage the ends of the bars located in the aperture 31.

Since the fittings 11 and 1 3 are symmetrically located on opposite sides of the vehicle centre line, the torsion arm 1 5 of each bar is bent at 41 so as to permit the arms 1 5 to cross over.

The weight of the cab bends each lever arm adjacent the bend between the arms 1 5 and 17, (that is, outboard of and adjacent the bush 35 through which it extends) and also twists the torsion arms 1 5 of each bar. The elbow of the bar is subjected to both torsional and bending stresses, and the increased diameter of the bar in this region prevents damage to the bar as a result of the total stress in the bar exceeding the elastic limit at this point. As a result the bar can be stressed more highly than the bar described in our earlier Patent Specification No. 992604 thus allowing a bar with shorter arms to be used. The fittings 11, 13 can therefore be positioned directly on the main frame members 3, thus reducing the overall width of the vehicle.

Claims (10)

Claims

1. A torsion bar for biasing a tiltable cab structure of a truck from a normal position towards a position tilted in relation to body structure of the truck, the said bar being L shaped, one arm constituting a torsion arm and the other arm constituting a lever arm, characterized in that the part of the bar in the region of the elbow of the two arms is of greater cross-sectional area than the torsion arm.

2. A torsion bar according to Claim 1 wherein the cross-sectional area of the bar in the region of the elbow is from 15 to 20 per cent greater than that of the torsion arm.

3. A torsion bar according to Claim 1 or Claim 2 wherein the arms and elbow are of circular cross-section.

4. A torsion bar according to any one of Claims 1 to 3 wherein the free ends of the arms are of non-circular cross-section.

5. A torsion bar substantially as hereinbefore described and illustrated in the drawings.

6. A torsion bar assembly comprising a torsion bar according to any one of Claims 1 to 5 and mountings adapted to be secured to the cab or body structure of the truck, a first mounting being fixed to the free end of the torsion bar and adapted to be secured to one of the cab or body structures, a second mounting connected to the elbow region of the bar at the other end of the torsion arm, and adapted to be secured to the said one of the cab or body structures to allow rotation of the said end of the torsion arm, and a third mounting engaging the free end of the lever arm and adapted to be secured to either of the cab or body structures.

7. A torsion bar assembly according to Claim 6 including two torsion bars, the lever arms being symmetrically located on opposite sides of the assembly.

8. A torsion bar assembly substantially as hereinbefore described and as illustrated in the drawings.

9. A truck having a body structure, a cab structure mounted on the body structure for movement between a normal position and a position tilted in isolation to body structure, and a torsion bar assembly according to any one of Claims 6 to 8 acting between the cab and body structure.

10. A truck according to Claim 9 wherein the first and second mounting are secured to the body structure.