EP0248804A1 - Assemblies of springs of composite material - Google Patents

Abstract

A leaf spring assembly comprising a first leaf (10, 110, 210) and a second leaf (9, 109, 209) of fiber-reinforced plastic composite material, the first leaf having an end portion (11, 111, 211) ) defining a transverse recess and held between upper and lower members (12, 112, 212 ,; 13, 113, 213) fixed one on the other to hold them on the blade. One of the members has a bearing surface (24, 124, 224) in which the second leaf of the spring engages.

Description

ASSEMBLIES OF SPRINGS OF COMPOSITE MATERIAL

This invention relates to leaf springs made of composite (fibre-reinforced plastics) material. More particularly, the invention relates to a leaf spring assembly including first and second spring leaves of composite material, and is concerned with the provision of means whereby such a spring assembly may be mounted in, for example, a motor vehicle where it is to be used.

Spring assemblies having two or more spring leaves are commonly required for use in motor vehicles where a single spring leaf cannot give the required suspension characteristic. Assemblies having a plurality of spring leaves made of steel are well known, but the methods used for mounting such assemblies in vehicles, _^and for holding the individual spring leaves together in the assembly, are not applicable to springs of composite material. In particular, the free end of a composite spring leaf cannot readily and economically be formed into a scroll to receive a mounting bolt. Any fasteners used to secure spring leaves together desirably should not penetrate spring leaves of composite material because of the disadvantageous effects of resulting discontinuities in the fibres of the spring leaf. Further, the effects of abrasion of the surface of spring leaves of composite material are undesirable and must be considered and, preferably, avoided.

With these considerations in view, it is the object of the present invention to provide an improved mounting arrangement for a leaf spring assembly having two spring leaves of composite material. According to the invention, we provide a leaf spring assembly comprising a first and a second spring leaf of composite material disposed in generally parallel relationship to one another and spaced in a principal direction of bending of the leaves in use, and a mounting assembly at an end of said leaves, said mounting assembly comprising:- an end portion of said first spring leaf, defining a recess extending transversely thereof; members engaging, respectively, upper and lower surfaces of said end portion, said members having a configuration which interfits with said surfaces including said recess and affording a formation adapted to engage a mounting element; fastening means holding said members to said end portion; . one of said members having an abutment surface associated therewith and arranged to be engaged by an end portion of said second spring leaf.

In an assembly according to the invention, the formation of the end portion of the first spring leaf to define a recess extending transversely of the spring leaf, together with the use of members engaging the upper and lower surfaces of such end portion and interfitting with such surfaces including the recess, provides effective transfer of loads between the spring and the members, and hence to the mounting element by which the assembly is secured to the member or structure where it is to be used, e.g. the chassis of a motor vehicle. There is great security against the members becoming detached from the first spring leaf. The engagement of the abutment surface on one of the members by an end portion of the second spring leaf provides effective load transfer between the second spring leaf and the mounting element and avoids a potential problem of abrasion of the first spring leaf which could arise if the spring leaves abutted one another directly. There remains, of course, the potential for abrasion of the second spring leaf but this can be overcome as hereafter described.

When we refer to upper and lower surfaces of the spring leaves, we mean surfaces which are spaced apart in the normal or principal direction of bending of the spring leaves in use. It will be appreciated that the most usual configuration of leaf springs used in motor vehicles is that of curves, typically of generally part- elliptic shape, secured to the vehicle chassis structure at their ends and extending downwardly between such ends to where an axle beam or the like .is carried. The principal direction of bending of• the spring leaves is that which tends to straighten them as vehicle load increases, although clearly the spring leaves have to withstand other loads, e.g. transverse loads, in service and thus will bend to a lesser extent in other directions. When we refer to upper and lower surfaces, and side surfaces, of the spring leaves hereafter, these relate to a typical installation as above described, but is to be appreciated that the invention is applicable to spring assemblies which may require to be used in some other orientation.

Said abutment surface, engaged by preferably the upper surface of said second spring leaf end portion, may be provided by an abutment element secured to said one of said members, which abutment element preferably includes an elastomeric material which is arranged to deform during relative lengthwise movement between the first and second spring leaf end portions. In use, many spring deflections are relatively small resulting in relatively little such lengthwise movement, which can be accommodated by incorporating elastomeric material in the abutment element and hence avoiding abrasion of the surface of the second spring leaf end portion. Larger spring deflections may cause such relative lengthwise movement greater than that which can be accommodated by the elastomeric material and hence results in rubbing of the second spring leaf end portion, but the cumulative effect of abrasion is nevertheless reduced.

There may be abutment means which cooperates with side surfaces of the second spring leaf end portion, to constrain transverse movement thereof, and the upper or lower surface thereof opposite that which engages said abutment surface, to constrain movement away from the first spring leaf end portion.

Preferably the fastening means holding said members together does not penetrate the first spring leaf end portion.

The invention will now be described by way of example with reference to the accompanying drawings, of which:

Figure 1 is a diagrammatic view of an assembly with first and second spring leaves, having mounting assemblies according to the invention;

Figure 2 is a side view, partly in cross-section, of part of the assembly of .Figure 1;

Figure 3 is an end view of the mounting assembly of Figure 1; Figure 4 is a side view of a further embodiment of spring mounting assembly according to the invention;

Figure 5 is a part section on 5-5 of Figure 4;

Figure 6 is a diagrammatic section through a further embodiment of spring mounting assembly according to the invention, on line 6-6 of Figure 7.

Figure 7 is a section on line 7-7 of Figure 6.

Referring firstly to Figure 1 of the drawings,, there is shown, diagrammatically, an assembly comprising two spring leaves of composite, fibre-reinforced plastics, material, disposed in spaced generally parallel relationship to one another. The leaves comprise an upper leaf 10 and a lower leaf 9, the drawings showing the assembly in the orientation in which it will typically be installed in a motor vehicle. At each end of the leaves there is a mounting assembly 2, described in greater detail hereafter. Generally at the centre of the spring leaves there is a structure by which an axle beam 8 is secured to the spring leaves. By way of example only, the arrangement at the centre of the assembly may be somewhat as disclosed in our published British Patent Application 2119725, the axle beam being held to the spring leaves by ϋ-bolts embracing them. In use, increasing vehicle load causes the spring leaves to bend so that they become more nearly straight than the curvature illustrated.

Although in Figure 1 the spring leaves 9, 10 are shown as relatively widely spaced from one another, it will be appreciated that they may be more closely spaced. or even contact one another at one or more positions along their lengths.

Referring now to Figures 2 and 3 of the drawings, there is illustrated an assembly which comprises the first spring leaf 10 and the second spring leaf 9, made of composite, fibre reinforced resin, material. An end portion 11 of the first leaf 10 defines a part- cylindrical recess, extending transversely of the spring. The end portion 11 of the leaf is clamped between upper and lower members 12, 13, of which the upper member 12 has welded thereto a generally ϋ-shaped part 14 whose lower surface is a close fit within the part-cylindrical recess defined by the portion 11 of the spring. A cylindrical bush 15 is received between the parts 14, 12, and provides for receiving a bolt or like element by which the assembly is secured to a motor vehicle in use. A metal-rubber-metal bush of known type may be utilized here. The lower member 13 has a surface 16 which fits closely to the lower surface of the end portion 11 of the leaf. Thus, when the members 12, 13 are clamped together the spring is firmly held therebetween.

The members 12, 13 are clamped together by fastening means comprising bolts. Two bolts 17 are provided at one end of the assembly, disposed at the sides of the spring so that there is no requirement for the spring to be penetrated by holes, which would weaken the spring. Further bolts 18 beyond the free end of the spring are less widely spaced. Spacers 26 between members 12, 13 prevent crushing of the spring leaf if the bolts 17, 18 were to be overtightened. Further, such spacers transmit loads between the lower member 13 (from leaf 9) directly to the upper member 12 and bush 15 without imposing additional forces on the upper leaf 10 which could damage the latter.

The second spring leaf 9 is, as above described, secured to the first spring leaf in the centre region thereof, considered longitudinally of the assembly of spring leaves. At the illustrated end of the spring leaves, vertically acting loads have to be transmitted between the leaves, and there is a requirement for the leaves to be able to move by a relatively small distance longitudinally relative to one another.

To provide such a connection, a generally ϋ-shaped sheet metal element 20 extends below the member 13, held thereto by pins or bolts 21. This defines an opening of generally rectangular cross-section through which the end portion of the spring leaf 9 extends. Abutment means in the form of bearing blocks 22 of a relatively hard and wear resistant plastics material, e.g. a suitable grade of nylon, are secured at* the side walls of the member 20 by rivets, and further abutment bearing blocks 23, 24 are secured to the lower wall of the member 20 and the undersurface of member 13, respectively, the block 24 being secured by a bolt 25. The dimensions of these blocks are such that the end of the spring leaf 9 is constrained to longitudinal movement therebetween, without being able to move transversely or vertically to any appreciable extent. As can be seen from Figure 1, the configuration of the block 23 is such that the small amount of angular movement about a transverse axis, which the spring leaf 9 undergoes in service relative to the • spring leaf 10, is permitted.

Bearing block 24, and possibly also blocks 23 and 22, may be of an elastomeric material, e.g. a suitable grade of rubber. They may possess sufficient resilience for relative longitudinal movement between the spring leaves to be accommodated by deflection of the blocks, without any rubbing occuring at the surface of spring leaf 9. This is advantageous in reducing wear due to abrasion of the spring leaves.

Referring now to the embodiment shown in Figures 4 and 5 of the drawings, this comprises upper and lower spring leaves 110, 109, respectively. An end portion 111 of upper spring leaf 110 is upwardly turried to define a transverse recess of quarter-cylindrical configuration. A member 112 is disposed on the upper surface of the upper spring leaf 110, and carries a cylindrical bush 115 which is a good fit within the recess defined by the leaf end portion 111. Beneath the end portion 111 there is disposed a lower member 113 of sheet metal, whose shape corresponds to that of the lower surface of the spring leaf end portion. Members 112, 113 are held together by a bolt or bolts 118 beyond the free end of the end portion, and a generally ϋ-shaped sheet metal element 126 and transverse pin 121 adjacent the end portion 111.

Beneath the lower member 113 there is disposed a bearing block 124 which may comprise an elastomeric element sandwiched between metal plates. The end portion of lower spring leaf 109 bears against this bearing block. A ϋ-shaped sheet metal element 120, held by pin 121 and bolts 118, extends down the sides and beneath the end portion of the lower spring leaf 109, to constrain it against movement downwardly or laterally away from leaf 110.

Referring now to Figures 6 and 7 of the drawings, this shows an assembly of upper and lower spring leaves 210, 209. The upper spring leaf has an end portion 211 of similar shape to the end portion 11 of spring leaf 10, and this end portion is held between upper and lower members 212, 213 analogous to the embodiment of Figures 2 and 3. Bolts 217, 218 hold the upper and lower members together.

In this embodiment, however, the lower spring leaf 209 is somewhat shorter than in the above described embodiments, and its end portion bears against a. bearing block 224 secured to lower member 230 adjacent the end portion 211 of the upper spring leaf, rather than directly beneath it. The bearing block 224 is preferably a metal-rubber-metal unit, as above described, so that relatively small lengthwise movements between the upper and lower spring leaves do not cause abrasion of the surface of the lower spring leaf through contact with the bearing block 224. It will be noted, in the embodiment of Figures 6 and 7, that because the spring leaves are relatively closer together than in the previous embodiments, such lengthwise movements inherently will be of smaller magnitude.

Downwardly extending parts 220 cooperate with the side surfaces of lower spring leaf 209, to prevent transverse movement thereof relative to the upper spring leaf 210.

In some designs of leaf spring assembly using two spring leaves, the leaves may not contact one another for load transmission at all times, but only when some load has been applied to the spring assembly. The invention is applicable to such a spring assembly.

Claims

1. A leaf spring assembly comprising a first and a second spring leaf of composite material disposed in generally parallel relationship to one another and spaced in a principle direction of bending of the leaves in use, and a mounting assembly at an end of said leaves, said mounting assembly comprising:- an end portion of said first spring leaf, defining a recess extending transversely thereof; members engaging, respectively, upper and lower surfaces of said end portion, said members having a configuration which interfits with said surfaces including said recess and affording a formation adapted to engage a mounting element; fastening means holding said members to said end " portion; one of said members having an abutment surface associated therewith and arranged to be engaged by an end portion of said second spring leaf.

2. An assembly according to Claim 1 wherein said abutment surface is provided by an abutment element secured to one of said members.

3. An assembly according to Claim 2 wherein said abutment element includes an elastomeric material, arranged to deform during relative lengthwise movement between said first and second spring leaf end portions.

4. An assembly according to any one of the preceding claims further comprising abutment means cooperable with side surfaces of said second spring leaf end portion to constrain transverse movement thereof.

5. An assembly according to any one of the preceding claims further comprising abutment means cooperable with said second spring leaf end portion to constrain movement thereof away from said first spring leaf end portion in said direction of bending.

6. An assembly according to any one of the preceding claims wherein said fastening means does not penetrate said first spring leaf end portion.

7. An assembly according to any one of the preceding claims wherein said recess is of part-cylindrical configuration.

8. An assembly according o Claim 7 wherein said formation for a mounting element comprises a transverse cylindrical bush, lying within said recess.

9. An assembly according to any one of the preceding claims wherein said first and second spring leaves are of substantially equal lengths, said second spring leaf engaging said member adjacent said recess in said first spring leaf end portion.

10. An assembly according to any one of Claims 1 to 8 wherein said second spring leaf is shorter than said first spring leaf.