FIBRE-REINFORCED AUTOMOTIVE SPRING

Abstract: A composite leaf spring for automotive use formed from fibre reinforced resin composite having a constant width and variable thickness. The fibre reinforcement may be either glass or carbon fibres while the resin is preferably epoxy. The spring comprises a core with randomly oriented fibres and outer layers of unidirectional fibres.

Description: FmI#:-RE:INFO#ED AUI###IVE SPRING The present invention relates to leaf springs and more particularly to leaf springs manufactured from fibre-reinforoed resin material such as glass fibre reinforcing members surrounded by a thermosetting resin, for example, epoxy. In U.S. Patent No. 3,142,598 there is described a resinimpregnated glass fibre leaf spring comprising a multiple leaf spring. In particular, the patent describes a glass fibre epoxy composite for use in forming constant thickness leaves which, in effect, duplicate conventional steel or metal spring leaves. A plurality of the leaves are assembled to form the spring in substantially the same manner as used with conventional metal leaf springs. While it is possible to form a leaf spring following the procedures described in the patent, in actual practice the movement and resulting wear between the individual leaves produces an abrasive layer between the individual leaves which in a short tine desttys the spring leaves. In an attempt to overcome the above problem of movement between the individual leaves of the spring, attempts have been made to form the spring from a single leaf. A spring of this type of construction is described in U.S. Patent No., 3,900,357. This patent describes a spring formed by using unidirectional longitudinal fibres for forming individual layers or plies of the spring. The innermost plies adjacent the neutral axis of the spring are made short while layers progressing outwardly are made longer. The final outermost plies or layers are made the full length of the spring. This composite of layers is impreg- nated with a resin and formed in a mould to provide a single leaf spring having a constant width and varying thickness. While this construction eliminates the pro'blems of nnnx3nent between the individual leaves, it produces a spring having low shear strength in the transverse direction and along the axis of the spring. Both of the above result from the use of unidirectional fibres for forming the spring. While unidirectional fibres are high in tensile and carpressive strength, the composite structure has low shear strength. The shear strength is dependent upon the strength of the resin and the strength of the mechanical bond between the theI=csetting resin and the outer surface of the reinforcing fibres. In an attempt to overcome the above deficiencies the patent suggests that the completed spring could be spirally wound with an oueer catering of reinforcing cloth or tape which would provide transverse strength for the spring. While this would increase the transverse shear strength of the spring, it would not increase the shear strength of the spring along its neutral axis. The present invention solves the above problems by providing a unitary leaf spring having an inner core formed fran a moulded composite material. The composite material is composed of randomly oriented fibres such as glass or carbon fibres impregnated with a thermosetting resin, for example, epoxy. The inner core is overlaid with outer layers formed from unidectional fibre reinforcing meibers that extend over the complete length of the spring. Preferably multiple longitudinal outer layers having substantially a uniform thickness are placed on the sides of the preformed core to complete the spring. The above construction provides a mono leaf spring that has both the required tension and compressive strength in a longitudinal direction as well as sufficient shear strength in all directions. Acxxrdüngly, the invention provides a unitary leaf spring for automotive applications having a substantially constant width and a variable thickness, said spring comprising: an inner core portion, formed of randomly oriented fibres and resin; and outer plies extending the length of said spring and formed of theerosetting resin and multiple layers of continuous longitudinal fibres positioned in a side-by-side relationship. In the attached drawings: Figure 1 is an elevation view of a leaf spring formed according to this invention. Figure 2 is a cross section taken along line 2-2 of Figure 1. Figure 3 is an enlarged section of the spring shown in Figure 1. Figure 4 is a plan view of a second embodimEnt of the spring of this invention. Figure 5 is an end view of the spring of Figure 4. Figure 6 is an elevation view of the spring of Figure 4 with the wing portions removed. Figure 7 is a plan view of the spring of Figure 4 showing the directions of the reinforcing fibres. Referring to the attached drawings, there is shown a mono-leaf spring formed from a composite of fibre reinforcing members impregnated with a thermosetting resin, preferably epoxy resin. Other types of resins, for example polyester or vinyl esters, may also be used. The fibre reinforcing members may be glass, carbon or any reinforcing fibres, although glass fibres are most preferred. The spring as shown in the attached figure comprises a core member 10 and multiple upper layers or plies 11 and lower layers or plies 12. The upper layers take the tension load of the spring while the lower layers 12 are normally in compression. The core member 10 is premoulded to a specific shape having a constant width and varying thickness which tapers toward both ends of the spring. The core is formed of randomly oriented fibres which are impregnated with a thermosetting resin. The fibres that may be loose fibres mixed with a suitable resin with the mixture being placed in a mould and heated to set the resin. An alternate procedure is the use of chopped fibreglass and mat material which is Impregnated with a thermosetting resin, then placed in a mould and set. The moulded core should preferably have a glass fibre content of 50 to 70 percent by weight. After the core is moulded, it is overlaid on its upper and lower surfaces with several layers or plies of unidirectional fibres. As shown in Figure 3, layers 13, 14, 15 and 16 comprise individual layers of longitudinal unidirectional fibres which are laid on the surfaces of the core. In particular, the unidirectional fibres of each layer should be laid in a side-byside relationship and extend from one end to the other end of the spring. It is preferable that the fibres be placed on the surfaces of the spring and impregnated with therrrosetting resin and then the complete spring placed in a suitable mould which may be heated to set the resin. When the core and unidirectional fibres are placed in the mould tension should be applied to the longitudinal fibres so that they retain their orientation and do not kink or beocce displaced. After the outer layers of the spring have been moulded onto the remoulded core 10, the spring is complete and suitable attachments or end fittings may be secured to the end of the spring. From the above description, it is seen that the spring is provided with upper and lower layers of unidirectional glass fibre reinforcing members having a high tensile and compressive strength. Thus, the spring will be capable of absorbing the tension and compression loads placed on it. The use of the premoulded core having randcmly oriented fibre reinforcing members provides a structure having both transverse as well as longitudinal shear strength in the completed spring. An alternate method for the constructing of single leaf springs is shown in Figures 4-7. The spring has a constant width and thickness sections 20 and 21 on the top and bottom surfaces of the spring 24. While the sections 20 and 21 have a constant cross section, the spring tapers as the wings 23 and 24 increase in width. The wings have a varying width and variable thickness as seen in Figure 4 over a portion of the spring 26 and a constant width over a portion 27. The wings extend over the ccmplete length of the spring to provide a cutting edge for assisting in removing the wings. After the spring is moulded the wings 23 and 24 are removed to provide a spring having a constant thickness in portion 25 and a varying or tapering thickness in portion 26 as seen in Figure 6. The above construction provides a spring having a constant width and a variable thickness in which the fibres in the outer layers are disposed longitudinally. The use of wings having a keysttoe cross section allows the fibres to exit from the spring at the cut portion at a very small angle a as shown in Figure 7. In contrast, if a wing having a constant thickness is used the fibres would exit from the spring at the cut portion at a larger angle ss. The small exit angle of the fibres prevents resin shear failure of the spring. Resin shear failure manifests itself as a cracking failure in the spring. The spring described above is preferably moulded in a heated metAl mould by placing the required reinforcing fibres and resin in the mould and the mould is then closed. When the mould is closed, the reinforcing fibres in the outermost layers or plies of the spring are held in tension to ensure that they remain straight and parallel from one end of the spring to the other. As the mould is closed the centre portion of the fibre reinforcement and resin will be forced outward to form the wings 23 and 24. The top portion 20 and bottom portion 21 have a constant cross section while the wings have a variable cross section. After the wings are roved by sawing or otherwise the spring will have a constant width and variable thickness. In addition, the spring will have continuous longitudinal fibres on the top and bottom surfaces in the areas of greatest stress. The invention also provides an automotive leaf spring assembly comprising the mcno leaf spring described hereinbefore and an end fitting which is formed fran fibre reinforced thermo setting resin, and which comprises an opening formed in one end of the fitting for receiving the means for fastening the spring to a vehicle, said opening being surrounded by an enlarged circular portion of the fitting, this portion being joined to two tapered sections that are spaced at a distance equal to the thickness of the end of the spring, to provide a close fitting to the end of the spring.

Claims: CLAIMS 1. A unitary leaf spring for automotive applications having a substantially constant width and a variable thickness, said spring comprising: an inner core portion, formed of fibres which are randomly oriented; and outer plies extending the length of said spring and formed of thermosetting resin and multiple layers of continuous longitudinal fibres positioned in a side-by-side relationship. 2. The espring of claim 1, wherein said thermosetting resin is an epoxy resin. 3. The spring of claim 1, wherein the reinforcing fibres are carbon fibres. 4. The spring of claim 1, wherein said reinforcing fibres are glass fibres. 5. The spring of any of claims 1 to 4, wherein said core member has a constant width and a vari#able thickness and the outer plies have a constant width and a constant thickness. 6. An automotive leaf spring assembly comprising a leaf as claimed in any of claims 1 to 5 and an end fitting which is formed from fibre reinforced thermOsetting resin, and which comprises an opening formed in one end of the fitting for receiving the means for fastening the spring to a vehicle, said opening being surrounded by an enlarged circular portion of the fitting, this portion being joined to two tapered sections that are spaced at a distance equal to the thickness of the end of the spring, to provide a close fitting to the end of the spring.

Inventors: GOTTENBERG, WILLIAM GEORGE, LO, KING HIM
Applicants: SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1984
Main classification: F16F1
IPC codes: F16F1, B60G11, B29D99