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

Abstract

The invention relates to a method for manufacturing a composite leaf spring comprising a leaf body having a lower surface and, at each end, an attachment end piece for fastening the leaf spring to a suspension system, wherein the leaf body is produced by curing a fibre-reinforced matrix, characterised in that, prior to the operation for curing the matrix, deformable reinforcing fibres 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 fibres being arranged in parallel with one another and extending along the curvature of the support surface (40) in order to form, after curing, an arrangement of continuous reinforcing fibres which are parallel to one another and oriented in the longitudinal direction of the leaf body.

Description

METHOD FOR MANUFACTURING A COMPOSITE SPRING LEAF AND USE OF SUCH A LEAF IN A VEHICLE SUSPENSION SYSTEM TECHNICAL FIELD OF THE INVENTION

[0001] The invention relates to a method of manufacturing a composite spring blade comprising a blade body having an intrados surface and, at each end, a tip for attachment to a suspension system.

[0002] The leaf spring manufactured using the method according to the invention is intended to be used in a vehicle suspension system and in particular, but not exclusively, in a suspension system of a cycle, an automobile, a scooter or a motorcycle. STATE OF THE ART

[0003] The purpose of vehicle suspension is to compensate for irregularities in the surface on which the vehicle is moving by reducing the impact on the machine, avoiding mechanical fatigue and excessive wear, maintaining contact between the wheels and the ground despite its irregularities and improving driving comfort.

[0004] As is known, in the case of a cycle, a suspension is composed of an energy dissipation system guaranteeing shock absorption, classically ensured by hydraulic rolling or mechanical friction, and an elastic system opposing the movement of the wheel and guaranteeing its return to the balance point.

[0005] The elastic system must allow for weak opposition to the movement of the wheel around its equilibrium position in order to guarantee high sensitivity to small shocks (vibration filtration) but also be able to firmly oppose larger shocks in order to avoid the bottoming phenomenon, i.e. the suspension reaching the stop, which then no longer plays its role. The visualization of the force (in N) of the elastic system in opposition to the movement of the wheel in the absence of energy dissipation (i.e. without considering the energy dissipation system) is called the static compression curve (or traction in the case of a "pulled" elastic system). We then speak of the static behavior of the suspension.

[0006] Among the elastic systems used, we know the one used in the suspension system described in application WO2016 / 207570, and presented in the form of an elastic blade elastically deformable between a rest state in which the blade has a curved profile and a maximum extension state in which the blade has an elongated profile whose length corresponds to that of the neutral fiber of said blade, the blade passing from the rest state to the extension state via intermediate extension states in which the blade has profiles that are less and less curved.

[0007] The advantage of such a leaf spring is in particular to offer a suspension system whose reliability, size and performance are improved but also whose behavior is adaptable according to the sensitivity, travel, stiffness, progressiveness, type of use etc. desired.

[0008] The invention aims to provide improvements to the elastic system proposed in the aforementioned application in terms of resistance and behavior. SUBJECT OF THE INVENTION

[0009] To this end, the invention proposes a method for manufacturing a composite spring blade having an intrados surface and, at each end, an attachment end piece for fixing the spring blade to a suspension system, in which the blade body is produced by subjecting a fiber-reinforced matrix to hardening, the method being remarkable in that, prior to the matrix hardening operation, deformable reinforcing fibers are applied to a support surface having a curvature defining the intrados surface of the spring blade in the rest state, the reinforcing fibers being arranged parallel to each other and extending along the curvature of the support surface to form, after hardening, an arrangement of continuous reinforcing fibers, parallel to each other and oriented in the direction of the length of the blade body, at least at the intrados surface of the blade body.

[0010] In the present description, the term "deformable fiber" means a fiber having elastic elongation properties of at least 2%.

[0011] Thus, by giving the reinforcing fibers the correct shape before assembling them together by positioning them on the support surface corresponding to the intrados surface of the desired spring blade, and by orienting them unidirectionally on the support surface, a spring blade is produced having all the reinforcing fibers perfectly aligned and oriented in the direction of the blade length (0° relative to the longitudinal axis of the blade).

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

[0013] Advantageously, the plurality of layers of fibers is obtained by successive folding(s), folding(s) or winding(s) of one or more strips of fabric arranged on the support surface and containing unidirectional reinforcing fibers extending in the direction of the length of the strips.

[0014] Advantageously, the attachment tips are made by placing an axis on the strip(s) of fabric, prior to folding, folding down or rolling them up, on either side of the support surface. Depending on whether the axes are then kept in the finished spring blade or removed from it, we will obtain respectively either a spring blade in which the insert is integrated into the blade, or even "embedded" in the fiber, or a 100% composite spring blade. In the case of integration of the insert, it will have a tubular section.

[0015] Advantageously, the attachment tips are secured to the blade body once it has been produced.

[0016] Advantageously, the method further comprises an operation of lacing the reinforcing fibers by one or more retaining fibers over all or part of the length of the fibers, the lacing being carried out so as to arrange the retaining fiber at a non-zero angle relative to the orientation of the fibers (i.e. so as to arrange the retaining fiber not aligned with the reinforcing fibers).

[0017] Advantageously, the holding fiber(s) are laced around the reinforcing fibers at the junction of the attachment tips and the blade body. Lacing the reinforcing fibers makes it possible to avoid or at least limit the effects of delamination. The "lacing" in fact makes it possible to "recover" the delamination forces, making the blade less sensitive to them.

[0018] Advantageously, the lacing is carried out so as to arrange the holding fiber at an angle of between 45 and 90 degrees relative to the orientation of the reinforcing fibers, and preferably at 90 degrees.

[0019] Advantageously, the holding fiber has a rigidity greater than that of the reinforcing fibers.

[0020] Advantageously, the method comprises a step of assembling a plurality of elementary blade bodies or elementary single-piece blades arranged contiguous laterally and / or abutting each other. By single-piece blade, we mean a blade whose attachment tips are formed in one piece with the blade body.

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

[0022] Advantageously, the supporting fiber is a carbon fiber.

[0023] The invention also relates to a composite spring blade obtained according to the manufacturing method described above. The composite spring blade manufactured according to the method is advantageously a blade elastically deformable between a rest state in which the blade has a curved profile and a state of maximum extension in which the blade has an elongated profile whose length corresponds to that of the neutral fiber of said blade. Such a blade is referred to as a "pulled" blade.

[0024] The invention also relates to the use of a spring blade obtained according to the manufacturing method previously described in a suspension system. It is thus an initially curved blade which is stretched / pulled. BRIEF DESCRIPTION OF THE FIGURES

[0025] Other characteristics and advantages of the invention will emerge from the detailed description of the invention which follows with reference to the appended figures and in which:

[0026] The figure represents a schematic perspective view of 3 / 4 of a composite spring blade obtained using the manufacturing method according to the invention;

[0027] The represents a perspective view of a template used to produce the spring blade of the;

[0028] It represents a sectional view of the template following the median plane;

[0029] Illustrates the steps for producing a three-layer composite blade according to a first embodiment;

[0030] Illustrates a schematic view of the arrangement of the unidirectional fibers to form the blade body before the lacing operation with the holding fiber;

[0031] It represents a three-layer composite spring blade according to an embodiment variant;

[0032] The representation of a three-layer composite spring blade according to another embodiment variant;

[0033] It represents a four-layer composite spring blade, obtained using another folding variant;

[0034] The figure represents a composite spring blade according to an alternative embodiment of the invention.

[0035] For clarity, identical or similar elements of the different embodiments are identified by identical reference signs throughout the figures. DETAILED DESCRIPTION OF THE INVENTION

[0036] In relation to the figures, a method is described for manufacturing a composite leaf spring 1 comprising a leaf body 2 provided, at each end, with an attachment end piece 3 allowing the attachment of the leaf spring 1 to a suspension system of a cycle-type vehicle.

[0037] The spring blade 1, in the embodiment described, is formed from a plurality of layers of unidirectional fibers, advantageously continuous over the entire length of the strip, said fibers being laced in whole or in part by a holding fiber, a plurality of fibers or a holding strip containing holding fibers. By unidirectional fibers is meant fibers oriented in the same direction.

[0038] Unidirectional fibers are deformable fibers chosen to provide the desired degree of flexibility for the composite blade. In order to ensure that the unidirectional fibers are held together, the holding fiber advantageously has a greater rigidity than the unidirectional fibers. This thus makes it possible to avoid delamination of the spring blade. Advantageously, the unidirectional fibers are glass, Kevlar®, aramid, polyethylene and / or PBO Zylon® fibers; the holding fiber(s) is (are) preferably carbon fibers.

[0039] Figures 1 and 2 illustrate an elastically deformable spring blade 1 obtained according to the production method which is the subject of the invention. The spring blade 1, illustrated in the rest state, has a curved shape defining an outer convex surface (extrados surface) and an inner concave surface (intrados surface).

[0040] In the following, the manufacturing method is described according to a non-limiting example in which the layers of unidirectional fibers are layers of pre-impregnated unidirectional fiber fabric. The method according to the invention is of course not limited to the use of impregnated fabrics, the infusion technique for producing the blade body can be implemented without departing from the scope of the invention. Depending on whether the layers applied are pre-impregnated fabrics, dry fabrics containing fibers or fibers positioned individually, the conventional steps of the process implemented will then be carried out (“pre-impregnated” process: cooking, possibly under vacuum, to ensure the polymerization of the resin contained in the layer(s) of pre-impregnated fabrics; “infusion” process: placing the dry fabrics or fibers under vacuum in a tarpaulin and suction and diffusion of the resin in the tarpaulin under the effect of the vacuum).

[0041] The spring blade is produced on a template arranged to give the desired shape and curvature of the blade. Figures 2 and 3 illustrate an example of template 4. This has a convex support surface 40 having an arc of curvature corresponding to the profile of the spring blade 1 in the rest state once it has been obtained. The curvature of the support surface 40 defines the intrados shape of the spring blade 1 in the rest state.

[0042] In the example described, the template comprises two receiving notches 41, 42 located on either side of the support surface 40 intended to house respectively an insert or axis for producing the attachment tips. This is of course an exemplary embodiment, the support on which the fibers are shaped may not include such notches.

[0043] In the embodiment which will be described below, and the steps of which are illustrated in the, the spring blade 1 is a spring blade comprising three layers 10A, 10B, 10C of pre-impregnated unidirectional fiber fabric 100 obtained from a single strip 10 of pre-impregnated fabric of a length greater than the length of the support surface 40 of the template. This is of course a non-limiting embodiment, the dimensions of the template being able to be greater than or equal to that of the fabric strip.

[0044] The spring blade 1 is produced by placing the pre-impregnated fabric strip 10 on said support surface 40, the portions extending outside the template 4 being substantially of the same length (figure 4a). As illustrated in the, the fabric strip 10 is placed so that the unidirectional fibers 100 of said strip extend parallel to each other along the curvature of the support surface 40.

[0045] Two tubular inserts 6 are then positioned on the strip 10, at the level of each of the receiving notches 41, 42 provided for this purpose in the template 4 (figure 4b). Once in place, the inserts 6 delimit the strip of fabric into three parts: a so-called central part 10B extending between the two inserts 6 and resting on the support surface 40, and two parts extending on either side of the inserts 6 (designated flaps or end panels 10A, 10C). Each of these parts will define the layers 10A, 10B and 10C.

[0046] The three layers 10A, 10B, 10C are then obtained by folding the fabric strip 10, by folding one of the end flaps 10A over the central portion 10B of the strip and then folding the opposite end flap 10C over the folded end flap 10A (Figures 4c and 4d). The length of the fabric strip will be chosen in order to obtain three superimposed layers after folding the end portions, the three layers being formed from the superposition of the so-called central portion and the end portions. The fabric strip will advantageously have a length approximately 3 to 3.5 times greater than the length of the spring blade 1 obtained, in its resting state. The advantage of this folding draping technique makes it possible to obtain a functional thickness of the central portion defining the blade body three times greater than the thickness at the ends. The spring blade obtained thus has compact ends.

[0047] Since it is a pre-impregnated fabric, the layers stick together under the pressure exerted when the layers are placed and folded over each other.

[0048] At the end of the folding operation, the inserts 6, integrated between the layers, form the attachment ends 3 of the spring blade 1. According to an alternative embodiment, so-called temporary axes may be provided, intended to be removed after completion of the operation of folding the fabric strips, either before the operation of draping the blade body 2 with a holding strip, or after the draping operation.

[0049] The formed assembly is then removed from the template 4. A retaining fiber is then laced around the superimposed layers, at least at the junction of the blade body 2 and the attachment tip, this part being the most sensitive to delamination forces. The retaining fiber is placed on the pre-impregnated fabric layers to present a fiber orientation different from that of the pre-impregnated fabric layers. The retaining fiber, thus positioned relative to the pre-impregnated fabric layers, ensures the retention of the fibers of the layers regardless of the stress state of the spring blade when it is implemented in a suspension system (rest, compression or traction), preventing the separation of the unidirectional fibers from each other and thus reducing the risks of delamination of the fabric layers.

[0050] According to an advantageous embodiment, the holding fiber is arranged around the pre-impregnated fabric layers so that the holding fiber is oriented in a range between 45 degrees and 90 degrees relative to the fibers of the pre-impregnated fabric layers, and advantageously 90 degrees. In the example illustrated, the holding fiber is arranged at 90 degrees relative to the unidirectional fibers of the pre-impregnated fabric layers (Figure 5e). The holding fiber illustrated is advantageously positioned at each end of the blade body 2, at the tip and blade body junction (Figure 5e). It is of course obvious that this is an exemplary embodiment, and that it may be provided to drape the blade body 2 over all or part of its length with a holding strip. Indeed, the larger the surface area covered by the lacing, the more the delamination forces are recovered and the more efficient the spring blade is.

[0051] In the example just described, the spring blade is a three-layer blade formed from a single strip of fabric by draping by folding. Illustrates an example of the embodiment of a spring blade according to the invention comprising three layers of fabric pre-impregnated with unidirectional fibers made from three separate strips of fabric (draping by superposition).

[0052] The spring blade is made as follows. The strips of fabric are arranged on the support surface 40 of the template 4, superimposed on each other. As previously, two inserts 6 are then positioned on the strip, at the level of each of the insert receiving notches respectively. The inserts may be inserts 6 remaining permanently, or temporary inserts. Each strip is then folded down, starting with the upper strip, and ending with the lower strip. By upper strip, we mean the strip furthest from the template 4, and by lower strip, the strip closest to the template 4 (in the example, this is the strip in contact with the template 4). In this example, the strips have a defined length so that the ends of the end parts, once the latter have been folded down, are positioned in the vicinity of the inserts 6. The operation of draping the layers with the holding strip is then carried out.

[0053] In the case of superposition draping, layers of fibers of different stiffness can be superimposed on the support surface. The energy storage compactness of the spring blade will thus be all the better as the stiffness of the fibers increases away from its intrados surface.

[0054] In the embodiments described above, the attachment tips 3 are formed by the folded portions of the strips. They are thus formed in one piece with the blade body 2 (integrated tips). The choice of producing integrated tips and thus producing a single-piece blade makes it possible to improve the reliability of the latter, the risk of failure of separation of the blade and the tips being reduced.

[0055] According to another alternative embodiment, the attachment tips are elements attached to the blade body 2. An example of the embodiment of a three-layer spring blade 1 of this type is illustrated in the figure. In this example, the spring blade 1 is a three-layer blade made 10, 20, 30 by superimposing three separate strips of pre-impregnated fabric. The strips have a length substantially corresponding to the length of the blade body 2. In the example described, the length corresponds to the length of the support surface 40 of the template 4. The spring blade 1 is produced by first producing the blade body 2. To do this, the same operations are carried out as in the example previously described, namely the operation of superimposing the strips of fabric 10, 20, 30, then the operation of covering all or part of the layers by affixing one or more retaining strips around said layers.Once the blade body 2 has been produced, an attachment end piece 3A, 3B is secured to each end of the blade body 2. The securing will be carried out by any means known to those skilled in the art.

[0056] The examples previously described relate to the production of a spring blade whose blade body 2 is made up of three layers of pre-impregnated fabric. It is of course obvious that the spring blade 1 is not limited to three layers of pre-impregnated fabric, it can comprise one or two layers, or more than three layers, these can be produced by folding strips, or by a number of strips corresponding to the number of layers desired. In the case of production by folding several strips, the layers of pre-impregnated fabric are obtained by successively folding down portions of the ends of the strips onto the upper strip, from the upper strip to the lower strip.

[0057] Furthermore, the production of the pre-impregnated fabric layers is not limited to the folding just described, other types of folding can be carried out without departing from the scope of the invention, such as for example an accordion fold or a winding of one or more strip(s). An example of winding a strip is illustrated. The advantage of draping by winding is that it allows for easier automation.

[0058] Similarly, in the examples described above, the layers of pre-impregnated fabric are made with or without a folding technique. It is of course obvious that a spring blade 1 may be formed from a combination of layers from folded strips and layers from individual unfolded strips.

[0059] In the illustrated examples, the layers and strips are shown, during the production of the spring blade or once it has been produced, separated from each other for the purpose of understanding the process. It is of course obvious that the layers or strips are in contact with the directly adjacent layer or strip.

[0060] According to an alternative embodiment illustrated in the, the spring blade 1 can be formed from a plurality of blade bodies called elementary blade bodies 2A, 2B, 2C (three in the example illustrated) or, when the end pieces are integrated, from blades called elementary monobloc blades, produced according to the method previously described.More particularly, the spring blade according to the illustrated and non-limiting variant is produced according to the following steps: production of the three elementary blade bodies 2A, 2B, 2C: production of three series of layers of unidirectional reinforcing fibers 100 to obtain blade bodies preferably having a thickness identical to the width of the layers, said fibers of the layers being shaped on the template, prior to their assembly, assembly of the reinforcing fibers 100 of each series by lacing with at least one holding fiber 7A, 7B, 7C, impregnation of the reinforcing fibers of each series with a matrix (for example an epoxy resin), bagging of the three elementary blade bodies arranged contiguous laterally and / or abutting each other in a structural element 8 (showing the contiguous blade bodies). baking of the reinforcing fibers assembled together.

[0061] The impregnation operation (step (b)) can advantageously be carried out in conjunction with the baking operation (step (e)). The baking step can be carried out in one go, after step (d), or in two stages, with a first baking operation of the elementary blade bodies prior to their bagging and a second baking operation after the assembly of the blade bodies together by bagging.

[0062] Bagging can be carried out for example with a fabric using the pre-impregnated or infusion technique. Other assembly techniques can be implemented without departing from the scope of the invention. In particular, as a replacement for bagging, provision may be made to assemble the elementary blade bodies or the elementary single-piece blades by gluing.

[0063] The advantage of a spring blade made from a plurality of elementary blade bodies or elementary single-piece blades is increased performance.

[0064] In the variant just described, the blade bodies or elementary monobloc blades have a square section. It may be provided, according to a particularly advantageous embodiment, to produce a spring blade with a rectangular section from elementary blade bodies or elementary monobloc blades with a circular section. The advantage of a blade formed from sub-parts (blade bodies or elementary blades) with a circular section is to offer more effective recovery of delamination forces. Indeed, a disc being the shape which has the best surface / circumference ratio, any deformation of a circular section with a constant cross-sectional surface (i.e. the same quantity of non-compressible material) necessarily leads to an increase in its circumference. By bagging the sub-parts with a circular section, the circumferences are made non-deformable, thus preventing the effects of delamination.

[0065] Likewise, in the above, the manufacturing method has been described according to a non-limiting example in which the layers of unidirectional fibers are layers of pre-impregnated unidirectional fiber fabric. The method just described can of course be implemented indifferently and in an identical or similar manner with layers of dry fabrics containing fibers or with fibers positioned individually.

[0066] The invention is described in the foregoing by way of example. It is understood that those skilled in the art are able to carry out different variant embodiments of the invention without departing from the scope of the invention.

Claims

Method for manufacturing a composite spring blade (1) elastically deformable between a rest state in which the blade has a curved profile and a maximum extension state in which the blade has an elongated profile whose length corresponds to that of the neutral fiber of said blade, said spring blade comprising a blade body (2) having an intrados surface and, at each end, an attachment end piece (3) for fixing the spring blade (1) to a suspension system, in which the blade body (2) is produced by subjecting a fiber-reinforced matrix (100) to hardening, characterized in that, prior to the matrix hardening operation, deformable reinforcing fibers (100) are applied to a support surface (40) having a curvature defining the intrados surface of the spring blade in the rest state,the reinforcing fibers being arranged parallel to each other and extending along the curvature of the support surface (40) to form, after hardening, an arrangement of continuous reinforcing fibers (100), parallel to each other and oriented in the direction of the length of the blade body, at least at the intrados surface of the blade body (2)., Manufacturing method according to claim 1, characterized in that the blade body is formed from one or more layers of superimposed reinforcing fibers. Manufacturing method according to claim 2, characterized in that the plurality of layers of fibers is obtained by successive folding(s), folding(s) or winding(s) of one or more strips of fabric arranged on the support surface (40) and containing unidirectional fibers extending in the direction of the length of the strips. Manufacturing method according to claim 3, characterized in that the attachment tips (3) are produced by placing an axis on the strip(s) of fabric, prior to their folding, folding down or rolling up, on either side of the support surface (40). Manufacturing method according to any one of claims 1 to 3, characterized in that the attachment tips (3) are secured to the blade body (2) once the latter has been produced. Manufacturing method according to any one of the preceding claims, characterized in that it further comprises an operation of lacing the reinforcing fibers by one or more retaining fiber(s) over all or part of the length of the fibers, the lacing being carried out so as to arrange the retaining fiber at a non-zero angle relative to the orientation of the fibers. Manufacturing method according to claim 6 when it depends on claims 4 or 5, characterized in that the holding fiber(s) are laced around the reinforcing fibers at the junction of the attachment tips and the blade body. Manufacturing method according to claim 6 or claim 7, characterized in that the lacing is carried out so as to arrange the holding fiber at an angle of between 45 and 90 degrees relative to the orientation of the reinforcing fibers, and preferably at 90 degrees. Manufacturing method according to any one of claims 6 to 8, characterized in that the holding fiber has a rigidity greater than that of the reinforcing fibers. Manufacturing method according to any one of claims 6 to 9, characterized in that the holding fiber is a carbon fiber. Manufacturing method according to any one of the preceding claims, characterized in that it comprises a step of assembling a plurality of elementary blade bodies (2A, 2B, 2C) or elementary blades provided with blade bodies formed in a single piece with the attachment ends, called elementary monobloc blades, arranged contiguous laterally and / or abutting each other. Manufacturing method according to any one of the preceding claims, characterized in that the reinforcing fibers are glass, Kevlar®, aramid, polyethylene and / or PBO Zylon® fibers.

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