GB2192689A

GB2192689A - Leaf spring

Info

Publication number: GB2192689A
Application number: GB08716748A
Authority: GB
Inventors: Kevin David Potter
Original assignee: BP PLC
Current assignee: BP PLC
Priority date: 1986-07-17
Filing date: 1987-07-16
Publication date: 1988-01-20
Also published as: GB8617538D0; GB8716748D0

Abstract

A leaf spring suitable for use in a vehicle suspension system comprising a plurality of leaves 1,2, the end portions of adjacent leaves having means 4,5 for engaging each other which allow relative longitudinal movement but restrain relative lateral movement. <IMAGE>

Description

SPECIFICATION Leaf spring The present invention relates to leaf springs and more particularly relates to end fittings for leaf springs.

It is known to fabricate leaf springs, for example for use in vehicles, from fibre reinforced composite materials. Composite leaf springs have potential advantages of weight and performance over conventional metal leaf springs. Thus suitably engineered leaf springs of composite material have advantages of decreased weight and enhanced performance characteristics.

For use in vehicles, substantial lateral stiffness capability is required in the leaf spring.

The present invention relates to an improved composite leaf spring which has advantages in coping with lateral loading for example when the lateral stiffness of a single leaf is insufficient to enable the proper spring characteristics to be achieved.

Thus according to the present invention there is provided a leaf spring suitable for use in a vehicle suspension system, the leaf spring comprising a plurality of leaves of fibre reinforced composite material, the end portions of adjacent leaves having means for engaging each other, the engaging means allowing relative longitudinal movement between adjacent leaves and restraining relative lateral movement between the leaves.

In a particular embodiment of the invention, the leaf spring comprises a pair of leaves comprising a fibre reinforced composite material, the end portions of the adjacent leaves having means for engaging each other, the means comprising a first part attached to the upper leaf and engaging with, and capable of sliding within a complementary keying recess in the lower leaf, the engaging means allowing relative longitudinal movement between the upper and lower leaf and restraining relative lateral movement between the leaves, the engaging means also being adapted to locate the leaf spring on the chassis of the vehicle.

The shape and form of the keying recess allows the leaves to share vertical, lateral, and 'wind-up' loads. Clearly the linkage may also take up the complementary form i.e. with the upper leaf having a keying recess and the lower leaf having a complementary engaging projection.

The keying recess enables movement of the leaves under vertical and "wind-up" or end loading by its ability to slide as well as rotate.

The engaging means also provide positive location between each leaf individually and the chassis fixing point. This provides a fail-safe mode in case of the leaf failure or breakage.

This is not generally the case with conventional metal leaf springs and fixings.

The arrangement also enables the leaves to share tensile (downward) loads resulting from the wheels of the vehicle temporarily leaving the road surface.

The engaging means may be integral with the leaves or may be attached by known means such as glueing etc.

The leaves may be fabricated from a suitable fibre reinforced composite material, for example, fibre resin combinations such as glass fibre, carbon fibre and thermosetting resin formualtions. The leaves may be homogeneous or be comprised of layers of differing characteristics such as having oriented or nonoriented fibres.

The invention will now be described by way of example only and with reference to the accompanying drawings.

Figure 1 shows a vertical section through one end of a composite leaf spring according to the invention.

Figure 2 shows side and end views of the end fixings of the leaf spring and Fig. 3 shows the allowed and disallowed movement of the leaves.

In the drawings, a leaf spring has an upper leaf (1) and a lower leaf (2) fabricated from a fibre-reinforced composite material. The leaves are held together by a clamp at the centre of the leaf spring (not shown).

The ends of the upper and lower leaves are held together by an end fixing (3). The end fixing (3) is in the form of a projection (4) attached to and protruding from the bottom face of the upper leaf which engages with a keying recess or groove (5) in the top face of the lower leaf. The end fixing also extends (6) above the upper leaf and locates on the underside of the vehicle chassis (not shown).

During use of the leaf spring, under loading the upper and lower leaves may be moved relative to each other along the longitudinal axis of the leaf spring, the projection sliding along the recess to take up the movement (Fig. 3a). Also the projection/recess enables twisting or wind up of the leaves relative to each other to be accommodated (Fig. 3b).

However the arrangement does not allow separation of the leaves in either of the non-longitudinal axes (Figs. 3c and 3d).

1. A leaf spring suitable for use in a vehicle suspension system, the leaf spring comprising a plurality of leaves of fibre reinforced composite material, the end portions of adjacent leaves having means for engaging each other, the engaging means allowing relative longitudinal movement between adjacent leaves and restraining relative lateral movement between the leaves.

2. A leaf spring according to claim 1 in which the leaf spring comprises a pair of leaves.

3. A leaf spring according to claim 2 in which the engaging means comprises a first

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Leaf spring The present invention relates to leaf springs and more particularly relates to end fittings for leaf springs. It is known to fabricate leaf springs, for example for use in vehicles, from fibre reinforced composite materials. Composite leaf springs have potential advantages of weight and performance over conventional metal leaf springs. Thus suitably engineered leaf springs of composite material have advantages of decreased weight and enhanced performance characteristics. For use in vehicles, substantial lateral stiffness capability is required in the leaf spring. The present invention relates to an improved composite leaf spring which has advantages in coping with lateral loading for example when the lateral stiffness of a single leaf is insufficient to enable the proper spring characteristics to be achieved. Thus according to the present invention there is provided a leaf spring suitable for use in a vehicle suspension system, the leaf spring comprising a plurality of leaves of fibre reinforced composite material, the end portions of adjacent leaves having means for engaging each other, the engaging means allowing relative longitudinal movement between adjacent leaves and restraining relative lateral movement between the leaves. In a particular embodiment of the invention, the leaf spring comprises a pair of leaves comprising a fibre reinforced composite material, the end portions of the adjacent leaves having means for engaging each other, the means comprising a first part attached to the upper leaf and engaging with, and capable of sliding within a complementary keying recess in the lower leaf, the engaging means allowing relative longitudinal movement between the upper and lower leaf and restraining relative lateral movement between the leaves, the engaging means also being adapted to locate the leaf spring on the chassis of the vehicle. The shape and form of the keying recess allows the leaves to share vertical, lateral, and 'wind-up' loads. Clearly the linkage may also take up the complementary form i.e. with the upper leaf having a keying recess and the lower leaf having a complementary engaging projection. The keying recess enables movement of the leaves under vertical and "wind-up" or end loading by its ability to slide as well as rotate. The engaging means also provide positive location between each leaf individually and the chassis fixing point. This provides a fail-safe mode in case of the leaf failure or breakage. This is not generally the case with conventional metal leaf springs and fixings. The arrangement also enables the leaves to share tensile (downward) loads resulting from the wheels of the vehicle temporarily leaving the road surface. The engaging means may be integral with the leaves or may be attached by known means such as glueing etc. The leaves may be fabricated from a suitable fibre reinforced composite material, for example, fibre resin combinations such as glass fibre, carbon fibre and thermosetting resin formualtions. The leaves may be homogeneous or be comprised of layers of differing characteristics such as having oriented or nonoriented fibres. The invention will now be described by way of example only and with reference to the accompanying drawings. Figure 1 shows a vertical section through one end of a composite leaf spring according to the invention. Figure 2 shows side and end views of the end fixings of the leaf spring and Fig. 3 shows the allowed and disallowed movement of the leaves. In the drawings, a leaf spring has an upper leaf (1) and a lower leaf (2) fabricated from a fibre-reinforced composite material. The leaves are held together by a clamp at the centre of the leaf spring (not shown). The ends of the upper and lower leaves are held together by an end fixing (3). The end fixing (3) is in the form of a projection (4) attached to and protruding from the bottom face of the upper leaf which engages with a keying recess or groove (5) in the top face of the lower leaf. The end fixing also extends (6) above the upper leaf and locates on the underside of the vehicle chassis (not shown). During use of the leaf spring, under loading the upper and lower leaves may be moved relative to each other along the longitudinal axis of the leaf spring, the projection sliding along the recess to take up the movement (Fig. 3a). Also the projection/recess enables twisting or wind up of the leaves relative to each other to be accommodated (Fig. 3b). However the arrangement does not allow separation of the leaves in either of the non-longitudinal axes (Figs. 3c and 3d). CLAIMS

3. A leaf spring according to claim 2 in which the engaging means comprises a first part attached to the upper leaf and engaging with and capable of sliding within a complementary keying recess in the lower leaf.

4. A leaf spring according to claim 2 in which the engaging means comprise a first part attached to the lower leaf and engaging with and capable of sliding within a complementary keying recess in the upper leaf.

5. A vehicle suspension system having a leaf spring according to any of the preceding claims.

6. A leaf spring as hereinbefore described and with reference to the accompanying drawings.