GB1562894A

GB1562894A - Road vehicle suspension

Info

Publication number: GB1562894A
Application number: GB916978A
Authority: GB
Original assignee: FRUEHAUF CRANE Ltd
Current assignee: FRUEHAUF CRANE Ltd
Priority date: 1978-03-08
Filing date: 1978-03-08
Publication date: 1980-03-19

Description

(54) ROAD VEHICLE SUSPENSION (71) We, CRANE FRUEHAUF LIMITED, a British Company of Norwich Road, Dereham Norfolk NR20 3AU, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement-: The present invention relates to a suspension for a road vehicle, for example a trailer or semi-trailer goods vehicle.

Conventional multiple axle suspensions for heavy goods road vehicles employ two or more independently sprung beam axles spaced longitudinally of the vehicle. Each axle is supported at either end on leaf springs positioned symmetrically about the longitudinal centre line of the vehicle. The outer ends of the leaf springs are supported directly within a hanger bracket assembly secured to the vehicle and the inner ends of the leaf springs are supported within an equaliser carried on a hanger bracket secured to the vehicle and pivoted about a shaft parallel to the axles. The function of the equaliser is to equalise the load on the axles during normal road operation. Such arrangements are employed on the majority of semi-trailer road vehicles currently in use in the U.K.However, with European standards for vehicle suspensions and in particular recent EEC brake directives there has been a need to reconsider vehicle suspension design and in particular to provide a suspension wherein an approximately equal load on each axle is maintained over a wide range of braking conditions.

We have described in U.K. Patent Specification N. 882,954 a tandem axle suspension wherein the axles were each supported in trailing arms and were interconnected via a lead spring and rubber bushes. However, this suspension only provided one spring on each side of the vehicle.

The present invention provides a suspension system for a road vehicle comprising first and second axles arranged in tandem, first and second leaf springs secured adjacent each end of each axle, each first leaf spring being located by engagement of its outer end within a first hanger bracket positioned on the side of the first axle remote from the second axle and by a radius rod secured at opposite ends between the first spring chair and the first hanger bracket to control the location of the first axle so as to permit axle articulation and allow a difference in level between a wheel on one end of the first axle and a wheel on the other end, each second leaf spring which is secured adjacent its outer end to the second axle being located by engagement at an intermediate longitudinal position in a second hanger bracket positioned between the first and second axles and by a radius rod secured at opposite ends between the second spring chair and the second hanger bracket to control the location of the second axle so as to permit axle articulation and to allow differences in level between a wheel on one end of the second axle and a wheel on the other end, each second leaf spring extending inwardly of the second hanger bracket towards the respective first leaf spring and the inner ends of respective first and second leaf springs being engaged or operatively connected in relatively movable force transmitting relationship such that upward load at the inner end of the first leaf spring is balanced by downward load at the inner end of the second leaf spring.

Other preferred features of the invention are set out in the appended claims, to which attention is hereby directed.

Embodiments of the invention will now be described, by way of example only, with reference to Figures 1 and 2 of the accompanying diagrammatic drawings which are side views of tandem axle arrangements for a heavy goods vehicle e.g. a semi-trailer goods vehicle, and in which corresponding parts are denoted by the same reference numerals.

In Figure 1 a front beam axle 10 and a rear beam axle 12 are supported on respective laminated steel leaf springs 1-3 and 14 and are fastened thereto in conventional- manner by respective U-bolts 15 and 16, spring chairs 17 and 18 and clamping plates 19 and 20. The leading ends of the front springs 13 which are upeardly concave, are supported on bearer plates 21 in front hanger brackets 22 and front radius rods 23, which are almost horizontally directed, are pivotally secured at their front ends by bolts 24 to hanger brackets 22 and at their rear ends to forwardly and downwardly extending yoke portions of the spring chairs 17 so as to control the location of the axle and permit axle articulation. The bolts 24 and 25 pass through rubber bushes to permit a difference in level between a wheel at one end of the axle and a wheel at the other end.The springs 13 shown in the figure are multi-leaf springs and the number of leaves may be selected in accordance with the desired spring rating or, if desired single leaf springs may be used. The rear springs 14 are upwardly convex and are supported at an intermediate longitudinal position on bearer pads 30 within rear hanger brackets 31. The hanger brackets 31 are of conventional construction and comprise inner and outer plates secured to the vehicle chassis and the bearer pad 30 secured between them.The rear axle 12 is located behind the rear hanger brackets 31 by means of radius rods 32 directed almost horizontally and fastened at opposite ends to the spring chairs 18 and to the rear hanger brackets 31 between the inner and outer plates by means of respective rubber bushed bolts 34 and 33 which again control the location of the axle and permit a difference in level between a wheel at one end of the axle and a wheel at the other end. The rear springs 14 are of constant stiffness in the region between the rear axle and the rear hanger bracket and are of reducing stiffness between the hanger bracket and the front end of the spring. In the embodiment shown in Figure 1, the rear springs 14 are made up of ten leaves and extend well forward of the rear hanger brackets 31.All ten leaves are present in the trailing portion of the spring but the leaves terminate in succession forwardly of the rear hanger bracket, the uppermost leaf being the shortest and the lowermost three (which are of equal length) being the longest. The number of leaves in the springs 14 may of course, vary depending upon the desired load rating and single leaf springs may be used instead of the laminated springs shown. The leading ends of the rear springs 14 have on their lower surface bearer pads 36 which rest on the upper surfaces of the front springs 13 at the rear ends thereof, the system being dimensioned and arranged so that the upward load at the rear ends of the front springs is balanced out by the downward load at the front ends of the rear springs.

The embodiment shown in Figure 2 is similar to that in Figure 1 except that the rear ends of the front springs 13 are positioned above the front ends of the rear spring 14 and the said ends are connected together by shackles 40. Rubber bushed pins 41 and 42 at opposite ends of the shackles received in fixings (not shown) permit limited relative movement of the springs and the shackles.

Again the system is dimensioned and arranged so that the upward thrust at the rear ends of the front springs is balanced out by the downward load at the front ends of the rear springs.

Both embodiments of suspension have the advantages that large axle movement is possible and that there is very low reaction under braking, the axle weights remaining substantially constant. Furthermore, the portion of each rear spring between the rear hanger bracket and the rear axle is very stiff and it imparts high roll stiffness to the rear axle. The embodiment shown in Figure 1 has the advantage that it is of simple construction, whereas the embodiment shown in Figure 2 is more flexible in that it can provide for a variety of different axle spreads merely by alteration of the length of the shackle 40.

Various modifications may be made to the embodiments described herein without departing from the invention. For example, although the two suspensions illustrated in the drawings have been described as fitted to a vehicle with the axle 10 forwardly of the axle 12 in the forward direction of travel of the vehicle, the suspension could also be fitted the other way around which might be an advantage on lowloader vehicles where minimal clearance is required in front of the leading axle. The suspension may also be provided with means for temporarily lifting the rear axle from the ground. This feature has been provided in some semi-trailer goods vehicle suspensions in recent years because vehicle loading regulations may require the use of tandem axles when the vehicle is fully laden but may permit the unladen vehicle to travel on a single axle when unladen.If one axle can be lifted from ground contact while the vehicle is unladen, there is a saving in tyre wear. In the present suspension, the rear axle can be raised if means, e.g. a hydraulic ram or an inflatable air bag, is provided for forcing the bearer pad 36 or shackle 40 downwardly away from the chassis of the vehicle. It is sometimes convenient to form the suspension on a subframe, which may be assembled separately and subsequently bolted on to the chassis of the vehicle.

WHAT WE CLAIM IS: 1. A suspension system for a road vehicle comprising first and second axles arranged in tandem, first and second leaf springs secured adjacent each end of each axle, each first leaf spring being located by engagement of its outer end within a first hanger bracket positioned on the side of the first axle remote from the second axle and by a radius rod secured at opposite ends between the first spring chair and the first hanger bracket to control the location of the first axle so as to permit axle articulation and allow a difference

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. front radius rods 23, which are almost horizontally directed, are pivotally secured at their front ends by bolts 24 to hanger brackets 22 and at their rear ends to forwardly and downwardly extending yoke portions of the spring chairs 17 so as to control the location of the axle and permit axle articulation. The bolts 24 and 25 pass through rubber bushes to permit a difference in level between a wheel at one end of the axle and a wheel at the other end. The springs 13 shown in the figure are multi-leaf springs and the number of leaves may be selected in accordance with the desired spring rating or, if desired single leaf springs may be used. The rear springs 14 are upwardly convex and are supported at an intermediate longitudinal position on bearer pads 30 within rear hanger brackets 31.The hanger brackets 31 are of conventional construction and comprise inner and outer plates secured to the vehicle chassis and the bearer pad 30 secured between them. The rear axle 12 is located behind the rear hanger brackets 31 by means of radius rods 32 directed almost horizontally and fastened at opposite ends to the spring chairs 18 and to the rear hanger brackets 31 between the inner and outer plates by means of respective rubber bushed bolts 34 and 33 which again control the location of the axle and permit a difference in level between a wheel at one end of the axle and a wheel at the other end. The rear springs 14 are of constant stiffness in the region between the rear axle and the rear hanger bracket and are of reducing stiffness between the hanger bracket and the front end of the spring.In the embodiment shown in Figure 1, the rear springs 14 are made up of ten leaves and extend well forward of the rear hanger brackets 31. All ten leaves are present in the trailing portion of the spring but the leaves terminate in succession forwardly of the rear hanger bracket, the uppermost leaf being the shortest and the lowermost three (which are of equal length) being the longest. The number of leaves in the springs 14 may of course, vary depending upon the desired load rating and single leaf springs may be used instead of the laminated springs shown.The leading ends of the rear springs 14 have on their lower surface bearer pads 36 which rest on the upper surfaces of the front springs 13 at the rear ends thereof, the system being dimensioned and arranged so that the upward load at the rear ends of the front springs is balanced out by the downward load at the front ends of the rear springs. The embodiment shown in Figure 2 is similar to that in Figure 1 except that the rear ends of the front springs 13 are positioned above the front ends of the rear spring 14 and the said ends are connected together by shackles 40. Rubber bushed pins 41 and 42 at opposite ends of the shackles received in fixings (not shown) permit limited relative movement of the springs and the shackles. Again the system is dimensioned and arranged so that the upward thrust at the rear ends of the front springs is balanced out by the downward load at the front ends of the rear springs. Both embodiments of suspension have the advantages that large axle movement is possible and that there is very low reaction under braking, the axle weights remaining substantially constant. Furthermore, the portion of each rear spring between the rear hanger bracket and the rear axle is very stiff and it imparts high roll stiffness to the rear axle. The embodiment shown in Figure 1 has the advantage that it is of simple construction, whereas the embodiment shown in Figure 2 is more flexible in that it can provide for a variety of different axle spreads merely by alteration of the length of the shackle 40. Various modifications may be made to the embodiments described herein without departing from the invention. For example, although the two suspensions illustrated in the drawings have been described as fitted to a vehicle with the axle 10 forwardly of the axle 12 in the forward direction of travel of the vehicle, the suspension could also be fitted the other way around which might be an advantage on lowloader vehicles where minimal clearance is required in front of the leading axle. The suspension may also be provided with means for temporarily lifting the rear axle from the ground. This feature has been provided in some semi-trailer goods vehicle suspensions in recent years because vehicle loading regulations may require the use of tandem axles when the vehicle is fully laden but may permit the unladen vehicle to travel on a single axle when unladen.If one axle can be lifted from ground contact while the vehicle is unladen, there is a saving in tyre wear. In the present suspension, the rear axle can be raised if means, e.g. a hydraulic ram or an inflatable air bag, is provided for forcing the bearer pad 36 or shackle 40 downwardly away from the chassis of the vehicle. It is sometimes convenient to form the suspension on a subframe, which may be assembled separately and subsequently bolted on to the chassis of the vehicle. WHAT WE CLAIM IS:

1. A suspension system for a road vehicle comprising first and second axles arranged in tandem, first and second leaf springs secured adjacent each end of each axle, each first leaf spring being located by engagement of its outer end within a first hanger bracket positioned on the side of the first axle remote from the second axle and by a radius rod secured at opposite ends between the first spring chair and the first hanger bracket to control the location of the first axle so as to permit axle articulation and allow a difference

in level between a wheel on one end of the first axle and a wheel on the other end, each second leaf spring which is secured adjacent its outer end to the second axle being located by engagement at an intermediate longitudinal position in a second hanger bracket positioned between the first and second axles and by a radius rod secured at opposite ends between the second spring chair and the second hanger bracket to control the location of the second axle so as to permit axle articulation and to allow differences in level between a wheel on one end of the second axle and a wheel on the other end, each second leaf spring extending inwardly of the second hanger bracket towards the respective first leaf spring and the inner ends of respective first and second leaf springs being engaged or operatively connected in relatively movable force transmitting relationship such that upward load at the inner end of the first leaf spring is balanced by downward load at the inner end of the second leaf spring.

2. A suspension system according to Claim 1, wherein the inner ends of the first and second leaf springs overlap.

3. A suspension system according to Claim 1 or 2, wherein the second leaf spring is of constant stiffness in the region between the second axle and the second hanger bracket and extends inwardly of the second hanger bracket with stiffness which decreases with increasing distance therefrom.

4. A suspension system according to Claim 3, wherein the second leaf spring is an upwardly convex laminated spring supported at its top point in the second hanger bracket, all the laminations extending between the second hanger bracket and the second axle and the upper laminations terminating inwardly of the second hanger bracket in succession with increasing distance therefrom.

5. A suspension system according to Claim 2, 3 or 4, wherein the inner end of the second leaf spring overlies the inner end of the first leaf spring and has secured to its lower surface a bearer pad which engages the upper surface of the first leaf spring.

6. A suspension system according to any of Claims 1 to 4, wherein a shakle is secured in force transmitting relationship between the inner ends of the first and second leaf springs by fastening means which allow limited relative movement between the springs and between each end of the shackle and the respective spring.

7. A suspension system for a road vehicle having first and second axles arranged in tandem, substantially as hereinbefore described with reference to and as illustrated in Figure 1 of the accompanying drawings.

8. A suspension system for a road vehicle having first and second axles arranged in tandem, substantially as hereinbefore described with reference to and as illustrated in Figure 2 of the accompanying drawings.

9. A trailer or semi-trailer road vehicle or a sub-frame for a road vehicle fitted with a suspension system as claimed in any one of Claims 1 to 8. - - - -