Method of manufacturing a composite leaf spring and use of such a leaf spring in a vehicle suspension system

Abstract

The present invention relates to a method for manufacturing a composite leaf spring comprising a spring body having a lower surface and attachment end pieces at each end for fixing the leaf spring to a suspension system, the method being characterized in that the spring body is manufactured by curing a fiber-reinforced matrix, and that prior to the operation of curing the matrix, deformable reinforcing fibers are applied to a support surface (40) having a curvature that defines the lower surface of the leaf spring in its rest state, the reinforcing fibers being arranged parallel to one another and extending along the curvature of the support surface (40) to form, after curing, an arrangement of continuous reinforcing fibers that are parallel to one another and oriented in the longitudinal direction of the spring body.

Description

[Technical Field]

[0001] The present invention relates to a method of manufacturing a composite leaf spring that includes a spring body having a lower surface and mounting end pieces at each end for attachment to a suspension system.

[0002] The leaf springs manufactured according to the method of the present invention are intended for use in vehicle suspension systems, particularly, but not exclusively, in suspension systems for bicycles, automobiles, scooters, or motorcycles. [Background technology]

[0003] The purpose of a vehicle suspension is to compensate for the unevenness of the surface on which the vehicle drives, reduce its impact on the vehicle, prevent mechanical fatigue and excessive wear, maintain contact between the wheels and the ground despite the unevenness, and improve driving comfort.

[0004] As is known, in the case of a bicycle, the suspension consists of an energy dissipation system that ensures shock absorption, typically provided by hydraulic fluid pressure or mechanical friction, and an elastic system that counteracts wheel displacements and ensures their return to an equilibrium point.

[0005] The elastic system must be able to flexibly oppose the displacement of the wheel around its equilibrium position to ensure high sensitivity to small shocks (vibration filtering), but also to firmly oppose larger shocks to prevent bottoming out, i.e., the suspension reaching the end of its travel and no longer performing its purpose. The visualization of the force (in N) of the elastic system opposing the wheel displacement in the absence of energy dissipation (i.e., without considering the energy dissipation system) is called the static compression curve (or traction force in the case of a "tensioned" elastic system). This is called the static suspension behavior.

[0006] Among the elastic systems used, those used in the suspension system described in WO 2016 / 207570 are known, in which the leaf spring takes the form of an elastic leaf that is elastically deformable between a rest state with a curved profile and a state of maximum extension with an elongated profile, the length of which corresponds to the length of the neutral axis of the spring, from which the leaf passes to the extended state via intermediate states of extension with a curved profile such that the leaf gradually decreases in length.

[0007] The advantages of this type of leaf spring are, among others, improved reliability, compactness and performance, and the provision of a suspension system whose behavior can be adapted depending on the desired sensitivity, travel, stiffness, gradualness, type of use, etc. Summary of the Invention [Problem to be solved by the invention]

[0008] The object of the present invention is to improve the elastic system proposed in the above application in terms of strength and behavior. [Means for solving the problem]

[0009] To this end, the invention provides a method for manufacturing a composite leaf spring having a lower surface and attachment end pieces at each end for fixing the leaf spring to a suspension system, the spring body being formed by curing a fiber-reinforced matrix, the method being characterized in that, before the step of curing the matrix, deformable reinforcing fibers are applied to a support surface having a curvature that defines the lower surface of the leaf spring in its rest state, the reinforcing fibers being arranged parallel to one another and extending along the curvature of the support surface so as to form, after curing, an arrangement of continuous reinforcing fibers that are parallel to one another and oriented in the longitudinal direction of the spring body at least on the lower surface of the spring body.

[0010] As used herein, the term "deformable fiber" means a fiber that has an elongation property of at least 2%.

[0011] Thus, by positioning the reinforcing fibers on a support surface that corresponds to the underside of the desired leaf spring, by giving the reinforcing fibers the correct shape before combining them with each other, and by orienting the reinforcing fibers in one direction on the support surface, a leaf spring is produced in which all reinforcing fibers are perfectly aligned and oriented in the longitudinal direction of the leaf section (0° to the longitudinal axis of the leaf spring).

[0012] Advantageously, the spring body is formed from one or more superimposed layers of reinforcing fibers.

[0013] Advantageously, the superimposed layers of reinforcing fibers are obtained by one or more successive steps of folding, recurring or winding a strip of one or more fibrous material that is placed on a support surface and includes unidirectional reinforcing fibers extending in the longitudinal direction of the strip.

[0014] Advantageously, the attachment end pieces are manufactured by placing pins on one or more strips of fibrous material on either side of the support surface before folding, folding back or winding. Depending on whether the pins are retained in the finished leaf spring or removed therefrom, either an insert is integrated into the leaf, or a leaf spring "embedded" in the fibers, or a 100% composite leaf spring is obtained. If the insert is integrated, it has a tubular cross section.

[0015] Advantageously, the attachment end piece is secured to the spring body after the spring body has been formed.

[0016] Advantageously, the method further comprises the step of weaving the reinforcing fibers together with one or more supporting fibers over all or part of the length of the fibers, the weaving being performed so as to position the supporting fibers at a non-zero angle relative to the orientation of the fibers (i.e., so as to position the supporting fibers so as not to be aligned with the reinforcing fibers).

[0017] Advantageously, one or more retaining fibers are woven around the reinforcing fibers at the point where the attachment end piece joins the spring body. The weaving of the reinforcing fibers prevents or at least reduces the effects of delamination. The "weaving" "absorbs" the delamination forces, making the plate less sensitive to delamination forces.

[0018] Advantageously, the weaving is carried out so as to place the supporting fibres at an angle between 45 and 90°, preferably at 90°, to the orientation of the reinforcing fibres.

[0019] Advantageously, the retaining fibers have a higher stiffness than the reinforcing fibers.

[0020] Advantageously, the method comprises the step of assembling a plurality of elementary spring bodies or elementary integral plates arranged laterally adjacent to one another and / or abutting one another, integral plates being plates whose mounting end pieces are formed integrally with the spring body.

[0021] Advantageously, the reinforcing fibers are glass, Kevlar, aramid, polyethylene, and / or PBO Zylon fibers.

[0022] Advantageously, the retaining fibers are carbon fibers.

[0023] The present invention also relates to a composite leaf spring obtained using the above-described manufacturing method. The composite leaf spring manufactured according to this method is advantageously a leaf spring that is elastically deformable between a rest state in which the leaf spring has a curved profile and a fully extended state in which the leaf spring has an elongated profile, the length of which corresponds to the length of the neutral axis of the leaf spring. Such a leaf spring is known as a "tension" leaf spring.

[0024] The invention also relates to the use of a leaf spring obtained according to the manufacturing method described above in a suspension system, whereby it is the initially curved leaf portion that is subjected to tension. [Brief explanation of the drawings]

[0025] Other features and advantages of the present invention will become apparent from the following detailed description of the invention which refers to the accompanying drawings. [Figure 1] FIG. 1 is a perspective view of a composite leaf spring obtained by the manufacturing method of the present invention, viewed from an angle of approximately 45 degrees. [Figure 2] FIG. 2 is a perspective view of a jig used to manufacture the leaf spring of FIG. [Figure 3] FIG. 3 is a cross-sectional view taken along the mid-plane of the fixture of FIG. [Figure 4] 4(a) to (e) are diagrams illustrating steps in the manufacture of a three-layer composite leaf spring according to a first embodiment. [Figure 5] FIG. 5 shows a schematic diagram of the arrangement of unidirectional fibers to form the spring body of FIG. 1 prior to the step of weaving the retaining fibers. [Figure 6] FIG. 6 is a diagram showing a three-layer composite leaf spring according to a modified example. [Figure 7] FIG. 7 is a diagram showing a three-layer composite leaf spring according to another modified example. [Figure 8] FIG. 8 shows a four-layer composite leaf spring obtained according to another folding variant. [Figure 9] FIG. 9 is a diagram showing a composite leaf spring according to a modified example of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0026] For greater clarity, identical or similar elements of the various embodiments are designated by the same reference numerals in all figures.

[0027] With reference to the figures, a method of manufacturing a composite leaf spring 1 will be described, comprising a spring body 2 provided at each end with a mounting end piece 3 that allows the leaf spring 1 to be mounted in the suspension system of a bicycle-type vehicle.

[0028] The leaf spring 1 is formed in the described example from several layers of unidirectional fibers, which are advantageously continuous over the entire length of the strip, and which are fully or partially interwoven with the retaining fiber, several retaining fibers, or a retaining strip containing retaining fibers. Unidirectional fibers are fibers oriented in the same direction.

[0029] The unidirectional fibers are deformable fibers selected to impart a desired degree of flexibility to the composite plate. To ensure that the unidirectional fibers are held together, the retaining fibers advantageously have a higher stiffness than the unidirectional fibers, thereby preventing delamination of the leaf spring. Advantageously, the unidirectional fibers are glass, Kevlar®, aramid, polyethylene, and / or PBO Zylon® fibers, and one or more of the retaining fibers are preferably carbon fibers.

[0030] 1 and 2 show an elastically deformable leaf spring 1 obtained according to the method that is the subject of the present invention. The leaf spring 1, shown at rest, has a curved shape that defines an outer convex surface (upper surface) and an inner concave surface (lower surface).

[0031] In the following, the manufacturing method will be described according to a non-limiting example in which the layer of unidirectional fibers is a layer of resin-impregnated unidirectional fibers. The method according to the invention is, of course, not limited to the use of resin-impregnated fiber material; any infusion technique for forming the spring body can be implemented without departing from the scope of the invention. Depending on whether the applied layer is resin-impregnated fiber, a dry fiber material containing fiber, or a single positioned fiber, the conventional steps of the process are carried out (the "resin impregnation" process, i.e., curing, optionally under vacuum, to ensure polymerization of the resin contained in one or more layers of resin-impregnated fiber, and the "infusion" process, i.e., placing the dry fiber material or fiber in a bag under vacuum and drawing and diffusing the resin through the bag as a result of the vacuum).

[0032] The leaf springs are manufactured on a jig configured to give the leaf spring the desired shape and curvature. Figures 2 and 3 show an example of a jig 4, which has a convex support surface 40 with an arc of curvature that corresponds to the contour of the leaf spring 1 once it is at rest. The curvature of the support surface 40 defines the shape of the underside of the leaf spring 1 in its rest state.

[0033] In the example described, the fixture has two receiving notches 41, 42 located on either side of the support surface 40, each intended to receive an insert or pin for forming an attachment end piece. Of course, this is just one example, and the support on which the fibers are formed may not include such notches.

[0034] In the exemplary embodiment described below, the steps of which are shown in Figure 4, the leaf spring 1 is a leaf spring that is longer than the length of the support surface 40 of the jig and includes three layers 10A, 10B, 10C of resin-impregnated unidirectional fibers 100 obtained from one and the same strip of resin-impregnated fibers 10. This is, of course, a non-limiting example, and the dimensions of the jig may be equal to or greater than the dimensions of the strip of fiber material.

[0035] The leaf spring 1 is manufactured by placing resin-impregnated fibrous strips 10 on a support surface 40, with the portions extending outside the jig 4 being of substantially the same length (FIG. 4(a)). As shown in FIG. 5, the fibrous strips 10 are positioned so that the unidirectional fibers 100 of the strips run parallel to one another along the curvature of the support surface 40.

[0036] Two tubular inserts 6 are then positioned on the strip 10, one in each of the receiving notches 41, 42 provided in the jig 4 for this purpose (FIG. 4(b)). Once in place, the inserts 6 divide the strip of fibrous material into three sections: a central section 10B extending between the two inserts 6 and resting on the support surface 40, and two sections extending on either side of the inserts 6 (called end flaps 10A, 10C). Each of these sections defines a layer 10A, 10B, 10C.

[0037] The three layers 10A, 10B, and 10C are then obtained by folding the textile strip 10, i.e., by folding one of the end cuffs 10A over the central portion 10B of the strip, and then folding the opposite end cuff 10C over the folded end cuff 10A (FIGS. 4(c) and 4(d)). The length of the textile strip is selected so as to obtain three overlapping layers after folding the end portions, which are formed by overlapping the central and end portions. Advantageously, the textile strip is approximately 3 to 3.5 times longer than the length of the resulting leaf spring 1 when in a resting state. The advantage of this folding and laminating technique is that the functional thickness of the central portion defining the spring body is three times greater than the thickness of the end portions. The resulting leaf spring therefore has compact end portions.

[0038] Since this is a resin-impregnated fiber, the layers bond together under the influence of the pressure exerted when the layers are placed on top of each other and folded.

[0039] At the end of the folding step, the inserts 6 incorporated between the layers form the mounting end pieces 3 of the leaf spring 1. According to one variant, temporary pins can be provided, which are intended to be removed after the completion of the folding operation of the textile strips, either before or after the lamination step, of the spring body 2 with the retaining strips.

[0040] The formed assembly is then removed from the jig 4. Retaining fibers are then woven around the overlapping layers, at least where the attachment end piece joins the spring body 2, as this area is most susceptible to delamination forces. The retaining fibers are positioned on top of the resin-impregnated fiber layer so that they have a fiber orientation different from that of the resin-impregnated fiber layer. Retaining fibers positioned in this way relative to the resin-impregnated fiber layer ensure that the fibers of the layer are held in place whatever the state of stress (rest, compression, or tension) of the leaf spring when used in a suspension system, and prevent unidirectional fibers from separating from each other, thereby reducing the risk of delamination of the fiber material layers.

[0041] According to one advantageous embodiment, the retaining fibers are arranged around the resin-impregnated fibrous layer so that they are oriented at an angle between 45° and 90° relative to the fibers of the resin-impregnated fibrous layer, preferably at 90°. In the example shown, the retaining fibers are arranged at 90° relative to the unidirectional fibers of the resin-impregnated fibrous layer (FIG. 4(e)). The illustrated retaining fibers are advantageously positioned at each end of the spring body 2, at the points where the attachment end pieces join to the spring body (FIG. 4(e)). Of course, this is merely an example, and the spring body 2 can be laminated with retaining strips over all or part of its length. In fact, the larger the area covered by the weave, the greater the absorption of delamination forces and the higher the performance of the leaf spring.

[0042] In the illustrated example, the leaf spring is a three-layer leaf formed from a single fiber strip via folded lamination. Figure 6 shows an example of a leaf spring according to the present invention that includes three layers of resin-impregnated unidirectional fiber fabricated from three separate fiber strips (overlapping lamination).

[0043] The leaf springs are manufactured as follows: Strips of fibrous material are placed on the support surface 40 of the jig 4 and overlap each other. As previously described, two inserts 6 are positioned on the strips in each of the insert-receiving notches. The inserts may be either permanent or temporary. Each strip is then folded over, starting with the upper strip and ending with the lower strip. The upper strip is the strip farthest from the jig 4, and the lower strip is the strip closest to the jig 4 (in this example, this is the strip in contact with the jig 4). In this example, the strips have a defined length so that the ends of the end sections are positioned near the inserts 6 after folding. The layers are then stacked together with the retaining strips.

[0044] In the case of overlapping stacks, layers of fibers of different stiffness can be stacked on the support surface. The compactness of the energy storage of the leaf spring therefore increases as the stiffness of the fibers increases away from the lower surface.

[0045] In the above-described embodiment, the attachment end pieces 3 are formed by folded portions of the strips. They are therefore formed integrally with the spring body 2 (integral end pieces). The choice to form integral end pieces and therefore to manufacture an integral leaf spring improves its reliability, as the risk of leaf / end piece separation failure is reduced.

[0046] In another variant, the attachment end piece is an additional element to the spring body 2. An example of such a three-layer leaf spring 1 is shown in FIG. 7. In this example, the leaf spring 1 is a three-layer leaf spring 10, 20, and 30 manufactured by overlapping three separate resin-impregnated fiber strips. The length of the strips substantially corresponds to the length of the spring body 2. In the example described, this length corresponds to the length of the support surface 40 of the jig 4. The leaf spring 1 is manufactured by first forming the spring body 2. To do this, the same steps as in the previous example are performed: overlapping the fiber strips 10, 20, and 30, followed by covering all or part of the layer by placing one or more retaining strips around the layer. Once the spring body 2 is formed, end pieces 3A and 3B are attached to each end of the spring body 2 by any means known to those skilled in the art.

[0047] The above example relates to the manufacture of a leaf spring in which the spring body 2 is composed of three layers of resin-impregnated fiber. The leaf spring 1 is not limited to three layers of resin-impregnated fiber, but may have one, two, or more than three layers, and can be manufactured by folding a strip or by using a number of strips corresponding to the desired number of layers. When manufactured by folding multiple strips, the layers of resin-impregnated fiber are obtained by continuously folding the ends of the strips over the upper strip, from the upper strip to the lower strip.

[0048] Furthermore, the formation of the resin-impregnated fiber layer is not limited to the above-described folding, and other types of folding, such as folding one or more strip-shaped members into an accordion shape or wrapping, can be performed without departing from the scope of the present invention. Figure 8 shows an example of wrapping a strip-shaped member. The advantage of wrapping lamination is that it is easy to automate.

[0049] Similarly, in the above examples, the resin-impregnated fiber layers may be formed with or without folding techniques, and it goes without saying that the leaf spring 1 may also be formed from a combination of layers obtained from folded strips and layers obtained from individual unfolded strips.

[0050] In the illustrated examples, the layers and strips are shown separated from one another during or after the manufacture of the leaf spring to facilitate understanding of the method, although it will be appreciated that layers or strips may be in contact with immediately adjacent layers or strips.

[0051] According to the variant shown in Figure 9, the leaf spring 1 can be formed from several spring bodies (three in the example shown), called basic spring bodies 2A, 2B, 2C, or, if the end pieces are integrated, from a plate part, called basic integrated plate part, manufactured according to the method described above. More specifically, the leaf spring according to the shown non-limiting variant can be produced by the following steps: a: The three basic spring bodies 2A, 2B, and 2C are forming three sets of unidirectional reinforcing fiber layers 100, preferably to obtain a spring body having a thickness equal to the width of the layers, the fibers of the layers being shaped on a jig before being combined; combining the reinforcing fibers 100 of each series by interweaving them with at least one holding fiber 7A, 7B, 7C; b) impregnating each set of reinforcing fibers with a matrix (e.g., epoxy resin); c) Packing three laterally consecutive and / or abutting spring bodies into a structural element 8 (FIG. 9 shows a continuous spring body); d. curing the combined reinforcing fibers.

[0052] The impregnation step (step (b)) can advantageously be carried out together with a curing step (step (e)), which can be carried out in a single step after step (d) or in two stages, i.e. a first step to cure the elementary spring body before bagging it, and a second curing step after the spring bodies have been combined together by bagging.

[0053] The encapsulation can be carried out with the fibrous material, for example using resin impregnation or infusion techniques. Other assembly techniques can be implemented without departing from the scope of the invention. In particular, as an alternative to encapsulation, the basic spring body or basic one-piece plates can be glued together.

[0054] The advantage of a leaf spring made from multiple elementary spring bodies or elementary one-piece leaf sections is improved performance.

[0055] In the above-mentioned variants, the spring body or basic one-piece leaf has a square cross section. In a particularly advantageous embodiment, a leaf spring with a rectangular cross section can be manufactured from a basic spring body or basic one-piece leaf with a circular cross section. The advantage of a leaf spring composed of subcomponents (spring body or basic leaf) with a circular cross section is that it absorbs delamination forces more efficiently. Specifically, since a circle is the shape with the highest surface / circumference ratio, any deformation of a circular cross section with a constant cross-sectional area (i.e., the same amount of incompressible material) necessarily results in an increase in its circumference. By encasing a subcomponent with a circular cross section, the circumference is rendered non-deformable, thereby preventing delamination effects.

[0056] Similarly, above, the manufacturing method has been described according to a non-limiting example in which the unidirectional layer of fibers is a layer of resin-impregnated unidirectional fibers. Of course, the above-described method can equally be carried out in the same or similar way with a dry fibrous material layer containing fibers or with individually positioned fibers.

[0057] The present invention has been described above in an illustrative manner, and it is understood that those skilled in the art can make different modified embodiments of the present invention without departing from the scope of the present invention.

Claims

1. 1. A method for manufacturing a composite leaf spring (1), the leaf spring being elastically deformable between a rest state having a curved profile and a maximum extension state having an elongated profile corresponding to the length of the neutral axis of the leaf spring, the leaf spring comprising a spring body (2) having a lower surface and attachment end pieces (3) at each end for fixing the leaf spring (1) to a suspension system, the spring body (2) being manufactured by curing a fiber-reinforced matrix reinforced with reinforcing fibers (100), characterized in that prior to the step of curing the fiber-reinforced matrix, the deformable reinforcing fibers (100) are applied to a support surface (40) having a curvature that defines the lower surface of the leaf spring in the rest state, the reinforcing fibers being arranged parallel to one another and extending along the curvature of the support surface (40) to form, after curing, an arrangement of continuous reinforcing fibers (100) that are parallel to one another and oriented in the longitudinal direction of the spring body at least on the lower surface of the spring body (2).

2. The method of claim 1 , wherein the spring body is formed from one or more overlapping layers of the reinforcing fibers.

3. 3. The method of claim 2, wherein the superimposed layers of reinforcing fibers are obtained by one or more successive steps of folding, recurring or winding the strips of one or more fibrous material that are arranged on the support surface (40) and that include unidirectional fibers extending in the longitudinal direction of the strips.

4. 4. A method according to claim 3, characterized in that the attachment end pieces (3) are produced by placing pins on the one or more strips of fibrous material on both sides of the support surface (40) before folding, turning over or winding them.

5. 4. A manufacturing method according to any one of claims 1 to 3, characterized in that the attachment end piece (3) is fixed to the spring body (2) after the spring body (2) has been manufactured.

6. 6. The method of claim 1, further comprising weaving the reinforcing fibers with one or more supporting fibers over all or part of the length of the fibers, the weaving being performed to position the supporting fibers at a non-zero angle relative to the orientation of the fibers.

7. 7. A method according to claim 6 when dependent on claim 4 or claim 5, wherein the one or more retaining fibres are woven around the reinforcing fibres at the point where the attachment end piece joins the spring body.

8. 8. The method according to claim 6 or 7, characterized in that the weaving is carried out so as to position the supporting fibers at an angle of 45 to 90°, preferably at 90°, relative to the orientation of the reinforcing fibers.

9. The manufacturing method according to claim 6 , wherein the holding fibers have a higher rigidity than the reinforcing fibers.

10. The manufacturing method according to any one of claims 6 to 9, characterized in that the supporting fibers are carbon fibers.

11. 11. A manufacturing method according to any one of claims 1 to 10, characterized in that it comprises a step of assembling a plurality of elementary spring bodies (2A, 2B, 2C) arranged laterally consecutive to one another and / or abutting one another, or elementary one-piece plates with the spring bodies formed integrally with the mounting end pieces.

12. 12. A method according to any one of claims 1 to 11, characterized in that the reinforcing fibres are glass, Kevlar, aramid, polyethylene and / or PBO Zylon fibres.

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