GB2195589A

GB2195589A - Vehicle leaf spring suspension

Info

Publication number: GB2195589A
Application number: GB08722761A
Authority: GB
Inventors: Andrew Pollard
Original assignee: GKN Technology Ltd
Current assignee: GKN Technology Ltd
Priority date: 1986-10-04
Filing date: 1987-09-28
Publication date: 1988-04-13
Also published as: AU8033987A; WO1988002315A1; ES2005374A6; GB8722761D0

Abstract

A vehicle suspension having a leaf spring (10, 30, 110) connected at its ends to the vehicle structure (15, 35, 113) and between its ends to an axle part (11, 31, 117), wherein the spring has an extension portion (20, 42, 119) beyond one of its ends, arranged to engage an abutment (21, 41, 120) to give an increased spring rate when the spring is deflected by a load exceeding a predetermined value. The extension portion may be provided at an end of the spring pivoted to a fixed part (14) of the vehicle structure, at a shackle arrangement (38), or at a slipper end (114, 115, 116).

Description

SPECIFICATION Vehicle suspension This invention relates to a suspension for supporting a vehicle axle part relative to the structure of a vehicle, comprising a leaf spring having a first end portion pivotally connected to the vehicle structure, a second end portion supported by the vehicle structure and able to undergo generally pivotal movement relative thereto, and an axle part connected to the spring between said end portions thereof. The second end portion of the spring may be supported by the vehicle structure (a chassis part or an appropriate part of an integral bodychassis structure) by either a pivoted shackle arrangement or an arrangement generally known as a "slipper end", wherein the spring bears against a part of the vehicle structure for sliding movement lengthwise of the spring.

The provision of a pivoted shackle or a slipper end is necessary to accommodate the effective change in distance between the end portions of the spring as the spring deflects under changing load conditions in use. The ability of the end portions of the spring to move pivotally relative to the vehicle structure is, of course, necessary for the changes in spring shape which occur under changing loads.

When we refer to an axle part, we include any appropriate part of a vehicle axle arrangement, e.g. of a live axle or a dead axle beam, which may be supported by a leaf spring in a vehicle suspension. In the most common suspension arrangement, identical leaf springs at each side of the vehicle support an axle extending transversely of the vehicle.

Conventional leaf spring suspension arrangements of this type have a constant spring rate, i.e. a linear relationship between axle load and the height at which the vehicle frame is supported by the suspension. Since the degree of vertical movement of the suspension arrangement is constrained to lie within certain design limits, corresponding limitations are placed on the range of axle loads tolerated by the suspension arrangement and for which the ride characteristics of the vehicle remain acceptable. Accordingly, many attempts have been made to increase the range of axle loads by providing a vehicle axle suspension arrangement whose spring rate either increases steadily with increasing axle loads, or has two or more values depending upon the axle load.

Such suspension arrangements with an increasing spring rate, or with dual or multiple spring rates, are complex and costly to produce, particularly with the advent of leaf springs made of fibre-reinforced plastics materials. There is a need for a vehicle axle suspension arrangement with a spring rate which increases with increasing axle loads, and which is simpler and less costly to produce than previous arrangements of this type.

It is the object of the present invention to provide a suspension which meets the above described need.

According to the present invention, we provide a suspension for an axle of a vehicle, comprising a leaf spring having a first end portion pivotally connected to the vehicle structure, a second end portion supported by the vehicle structure and able to undergo generally pivotal movement relative thereto, and an axle part connected to the spring between the said end portions thereof, wherein the spring is provided with a portion extending beyond one of said end portions thereof and arranged to engage an abutment when the spring is deflected by a load exceeding a predetermined value, said engagement resisting further pivotal movement of the spring end portion to provide an increased spring rate.

In a suspension according to the invention, an increased spring rate for a certain part of the range of available axle movement given by the suspension is readily achieved in a simple manner. Various design details may be provided to enable different characteristics to be obtained, as described hereafter.

The end portion of the spring which is provided with the extension portion may be that which is pivotally connected to a fixed part of the vehicle structure. The abutment then is preferably fixed to the vehicle structure.

Alternativeiy, the end portion of the spring which is provided with the extension portion may be pivotally connected to a shackle assembly, the shackle assembly itself being pivotally mounted to the vehicle structure. In this case, the abutment preferably is fixed to the shackle assembly, although it would be possible to provide an abutment fixed to the vehicle structure and engagable by the extension portion of the spring.

In yet a further construction, the end portion of the spring which is provided with the extension portion may be a slipper end thereof, with the extension portion of the spring being provided beyond a spring portion which has sliding engagement with the vehicle structure.

In this case, the abutment may comprise an element in the form of a roller, to accommodate the movement lengthwise of the spring which the spring undergoes relative to the vehicle structure.

The abutment may be a rigid element. In this case, the spring rate until the abutment is engaged by the extension portion of the spring is determined by the stiffness of the spring between the end portions thereof.

When the abutment has been engaged, the spring rate depends on the stiffness of the spring between the end portions, and the stiffness of the extension portion thereof. A dual spring rate is thus obtained with a first constant or substantially constant value up to the pre-determined load and thereafter a second, higher, constant or substantially constant value.

Alternatively, the abutment may be a resilient element. In this case, after the extension portion of the spring has engaged the abutment, the effective spring rate is determined by the stiffness of the main part of the spring, the stiffness of the extension portion thereof, and the resilient characteristics of the abutment.

In particular, the abutment may be of a material and/or configuration arranged to provide a progressively increasing resistance to deformation by the springs engagement therewith, e.g. an elastomeric element. In this way, a progressively increasing spring rate may be obtained, and the abutment may be engaged by the extension portion of the spring for all or substantially all loads likely to be encountered in use.

As above referred to, the invention is particularly advantageous when the spring is of fibre-reinforced plastics material, and the extension portion is integral with the rest of the spring, extending substantially in line with the immediately adjacent part of the spring (although it will be appreciated that a leaf spring usually is of generally arcuate configuration and the extension portion itself may be of such configuration).

The invention will now be described by way of example with reference to the accompanying drawings, of which: Figure 1 is a diagrammatic elevation of one embodiment of suspension according to the invention; Figure 2 is a view as Figure 1, of a further embodiment of the invention; Figure 3 is a view as Figure 1, of yet a further embodiment of the invention; Figure 4 shows a modification of the suspension of Figure 3.

Referring firstly to Figure 1, there is shown a leaf spring 10 which is of composite, fibrereinforced plastics, material. To the spring in the centre region thereof there is secured an axle part indicated diagrammatically at 11, the securing being effected by- means such as Ubolts clamping the axle parts to the spring.

Adjacent one end of the spring, it is provided with an eye 12 affording an aperture receiving a pin 13 by which the spring is pivotally secured to a bracket 14 depending from a part of a vehicle structure indicated generally at 15. The vehicle structure 15 may be a chassis or an appropriate part of an integral bodychassis structure. At its other end, the spring is formed with an eye 16 receiving a pin by which the spring is pivotally connected to a shackle assembly 1 7 which in turn is pivotally connected, by a pin 18, to a further bracket 19 depending from the vehicle structure.

Beyond the eye 12, the spring is formed with an extension portionn 20, which extends to a position-to be engagable with a resilient block 21 which is supported from the vehicle structure by a bracket 22.

As illustrated in Figure 1, the spring and the rest of the suspension is shown in a typical position it will assume when under no load.

The extension portion 20 of the spring is free.

Under increasing suspension load, the spring 10 will straighten from its generally arcuate unloaded shape, until the extension portion 20 engages the resilient block 21 supported from the vehicle structure. The block 21 resiliently resists the anti-clockwise pivotal movement of the spring about the pin 13 resulting from the straining of the spring, and thus provides an additional stiffness in the suspension.

The resilient block 21 is preferably of an elastomeric material, itself being compressible so as to provide a resistance to deflection which increases with deflection and hence with the increasing load. This provides the suspension with a spring rate which increases progressively under loads above the predetermined threshold load at which the spring continuation 20 contacts the block 21.

As an alternative, the block 21 could be a rigid abutment, to provide an increase in suspension stiffness above the predetermined load but not one which progressively increases.

Referring now to Figure 2 of the drawings, there is shown a leaf spring 30, to which an axle part 31 is secured. At one end, the spring is formed with an eye 32 affording an aperture receiving a pin 33 so that the spring is pivotally secured to a bracket 34 depending from vehicle structure 35. At its other end, the spring is formed with an eye 36 for a pin 37 securing the spring to a shackle 38 itself pivoted, by a pin 39, to a bracket 40.

The shackle 38 further provides an abutment 41 engagable by a portion 42 of the spring forming a extension beyond the eye 38. Under loads below a predetermined threshold, the leaf spring pivots about the pin 37 until the extension 42 of the spring engages the abutment 41, whereafter such pivoting is resisted. Thereby an increasing resistance to the spring deflection is provided.

Referring now to Figure 3 of the drawings, a spring 110 is in the form of a single leaf of composite, fibre-reinforced plastics, material.

One end of the spring is provided with an attachment eye 111 by which the spring is pivotally mounted to a bracket 112 secured to or forming part of the chassis or integral body-chassis structure 113 of a vehicle.

The opposite end portion 114 of the spring is provided on its upper surface with an abrasion resistant pad 115 which bears against an abutment 116 secured to the vehicle structure. Between the ends of the spring, an axle indicated diagrammatically at 117 is secured to the spring, e.g. by clamping U-bolts 118.

The second end portion 114 of the spring has an extension portion 119 whose undersurface is engagable with an abutment in the form of a cylindrical or spherical element 120 which is supported from beneath by a part of the vehicle structure. Initially the spring extension portion 119 is clear of abutment 120, but after a certain increase in axle load (which it will be appreciated causes the axle to move upwardly relative to the vehicle structure, straightening the spring 110 from its initial part-elliptic form and causing pivoting of its first end 111 about the bracket 113 and a complex pivoting and sliding motion of the second end portion 114 of the spring about abutment 116) the extension portion 119 of the spring engages the abutment 120. Thereafter, the spring rate is determined by the stiffness of the spring as constrained by the abutment 120. Because of the constraint of the spring, an increase in spring rate is obtained.

Referring now to Figure 4 of the drawings, there is shown the second end portion 124 of a spring, with an abrasion resistant pad 125 on its upper surface engaging an abutment 126 analogous to the abutment 116 of Figure 3. When the element 130 is engaged by the spring extension, an increased spring rate is obtained, as determined by the stiffness of the spring and the resilience of-element 130.

A resilient element as 130 may be shaped or otherwise arranged to provide an increasing resistance to deformation, and hence give a progressively rising spring rate when engaged by the spring. Such a resilient element may even be engaged by the spring during all or virtually all axle displacements normally encountered in use, to give a rising spring rate under all normal conditions.

Claims

1. A suspension for an axle of a vehicle, comprising a leaf spring having a first end portion pivotally connected to the vehicle structure, a second end portion supported by the vehicle structure and able to undergo generally pivotal movement relative thereto, and an axle part connected to the spring between the said end portions thereof, wherein the spring is provided with a portion extending beyond one of said end portions thereof and arranged to engage an abutment when the spring is deflected by a load exceeding a predetermined value, said engagement resisting further pivotal movement of the spring end portion to provide an increased spring rate.

2. A suspension according to Claim 1 wherein the end portion of the spring which is provided with the extension portion is that which is pivotally connected to a fixed part of the vehicle structure.

3. A suspension according to Claim 2 wherein the abutment is fixed to the vehicle structure.

4. A suspension according to Claim 1 wherein the end portion of the spring which is provided with the extension portion is pivotally connected to a shackle assembly pivotally mounted to the vehicle structure.

5. A suspension according to Claim 4 wherein the abutment is fixed to the shackle assembly.

6. A suspension according to Claim 1 wherein the end portion of the spring which is provided with the extension portion is a slipper end thereof, the extension portion of the spring being provided beyond a spring portion which has sliding engagement with the vehicle structure.

7. A suspension according to Claim 6 wherein the abutment comprises an element in the form of a roller.

8. A suspension according to any one of the preceding claims wherein the abutment is a rigid element

9. A suspension according to any one of Claims 1 to 7 wherein the abutment is a resilient element. In this case, after the extension portion of the spring has engaged the abutment, the effective spring rate is determined by the stiffness of the main part of the spring, the stiffness of the extension portion thereof, and the resilient characteristics of the abutment.

10. A suspension according to Claim 9 wherein the abutment is of a material and/or configuration arranged to provide a progressively increasing resistance to deformation by the spring's engagement therewith.

11. A suspension according to Claim 10 wherein the abutment is engaged by the extension portion of the spring for all or substantially all loads likely to be encountered in use.

12. A suspension according to Claim 10 or Claim 11 wherein the abutment is an elastomeric element.

13. A suspension according to any one of the preceding claims wherein the spring is of fibre-reinforced plastics material, and the extension portion is integral with the rest of the spring, extending substantially in line with the immediately adjacent part of the spring.

14. A suspension substantially as hereinbefore described with reference to Figure 1, Figure 2 or Figure 3 or 4 of the accompanying drawings.