Bending spring element made of fiber plastic composite

Abstract

In a flexural spring element (1) made of a fiber plastic composite (4, 23), wherein the flexural spring element (1) has on both sides (9, 10) of a center plane respectively a functional layer (2, 3) made of a fiber plastic composite (4), in at least one longitudinal section (14) at least one matrix material output layer (17) is arranged parallel to both functional layers (2, 3) and extending in the longitudinal direction (7), which has at least a proportion of output layer fibers (18) which are arranged offset to the longitudinal direction (7) of the flexural spring element (1). In at least one bending section (13) of the flexural spring element (1) a first volume proportion of the bending spring fibers (5) in the functional layers (2, 3) is smaller, preferably several percent smaller, than a second volume proportion of the bending spring fibers (5) in the functional layers (2, 3) in the at least one longitudinal section (14).

Description

[0001] The present invention relates to a bending spring element made of fiber-plastic composite material, wherein the bending spring element has functional layers made of fiber-plastic composite material on two opposite sides of a central plane, wherein bending spring fibers in each functional layer are arranged at least in bundles parallel to each other and extend along the longitudinal direction of the bending spring element, wherein the bending spring element has at least one bending section in which the central plane of the unloaded bending spring element extending between the two functional layers extends in the longitudinal direction of the bending spring element with a bend greater than 90°, wherein the bending spring element has at least one longitudinal section in which the central plane of the unloaded bending spring element either has no obvious bend or has a bend reversal, and wherein when the bending spring element deflects as intended, the outwardly arranged functional layer section in the bending section is subjected to tensile stress, and the oppositely inwardly arranged functional layer section in the bending section is subjected to compressive stress.

[0002] Bending spring elements can be designed as a single unit to form a bending spring or bending spring assembly. Multiple bending spring elements can also be combined into a bending spring assembly and effectively connected to each other. For example, a single bending spring element can be designed in the shape of a rod with a straight or slightly curved direction. Bending spring elements with complex bending directions and, for example, C-shaped or S-shaped forms or multiple alternating bends designed to be zigzag are also known.

[0003] Bending spring elements can be made from various materials. For example, traditional bending spring elements are typically made from suitable spring steel. Such bending spring elements can be manufactured cost-effectively, and their shapes can be matched to specific purposes. Bending spring elements made of spring steel or other suitable metals are durable and possess advantageous spring properties.

[0004] The manufacture of bending spring elements from suitable fiber-plastic composites is also known and has been tested for various applications. Here, fiber-plastic composites are typically used, in which quasi-continuous fibers are embedded in a suitable plastic matrix material. Favorable spring performance can be promoted through the arrangement and alignment of the individual fibers, which are primarily responsible for transmitting tensile and compressive forces along the bending spring element. Here, depending on deformation, tensile or compressive forces are transmitted primarily through the bending spring fibers in the functional layers. Conversely, if deformation is as intended, no tensile or compressive forces are present in the center plane (also called the center fiber or zero line). Functional layers arranged on both sides of the center plane can be uniformly manufactured and fused together to form a monolithic bending spring element made of a uniform fiber-plastic composite. Compared to bending spring elements made of metal, bending spring elements made of fiber-plastic composites can have lower weight and better resistance to environmental conditions, especially moisture. Bending spring elements made of suitable fiber-plastic composites can be advantageously used in motor vehicles.

[0005] If a bending spring element is designed to have a uniform thickness or a uniform distance between two functional layers, then the thickness of the bending spring element must match the tensile and compressive stresses that may occur when the maximum expected force is applied to the bending section of the bending spring element. Significantly smaller stresses occur in adjacent longitudinal sections, making it impossible for the bending spring element to be too large if it has a uniform thickness in those sections. The weight and material cost of the bending spring element would then be excessive, which is particularly disadvantageous for lightweight constructions using fiber-reinforced plastic composites, which are typically sought after.

[0006] Manufacturing bending spring elements from fiber-reinforced plastic composites is typically associated with high manufacturing costs, which in turn lead to high production expenses. This is particularly true when the bending spring elements have varying thicknesses, where the costs are substantial and often decisive for the overall manufacturing cost. This arises from preparing large quantities of prefabricated fiber-reinforced plastic composite strips or prepregs of varying lengths, arranging them in molds, and subsequently pressing them.

[0007] For example, US 3,968,958 describes a bent spring element that is essentially designed as a planar leaf spring. The manufacture of prepregs of varying lengths, particularly arranging them in a mold and securing them during the curing process under pressure within the mold, is associated with enormous costs that are typically only possible manually. The middle section of the leaf spring is further reinforced by additional, shorter intermediate layers arranged between the outer functional layers.

[0008] Therefore, the object of the present invention is to design a bending spring element made of a plastic composite material such that the bending spring element can be manufactured cost-effectively, can be easily matched to the stresses that are commonly encountered in each section, and can have the most favorable spring performance possible.

[0009] According to the present invention, this objective is achieved by the following means: the bending spring element has at least one matrix material output layer in the at least one longitudinal section that is parallel to the two functional layers and extends along the longitudinal direction, the matrix material output layer having at least a certain proportion of output layer fibers that are arranged in a manner deviating from the longitudinal direction of the bending spring element, and a first volume proportion of bending spring fibers in the functional layers within the at least one bending section is smaller than, preferably a certain percentage smaller than, a second volume proportion of bending spring fibers in the functional layers within the at least one longitudinal section.

[0010] It has been shown that by locally matching the volume proportion of the bending spring fibers in the functional layers along the longitudinal direction of the bending spring element to the stresses that typically occur, particularly by making the volume proportion of the bending spring fibers in the longitudinal sections higher, optionally significantly higher, than in the at least one bending section, particularly advantageous spring performance can be achieved with less material and manufacturing cost. Advantageously, the volume proportion of the bending spring fibers is higher in all longitudinal sections than in all bending sections. Because the volume proportion of the bending spring fibers differs in the longitudinal sections compared to the bending sections, different important properties, such as bending stiffness or torsional stiffness, can be pre-defined for the bending spring and matched to the respective functions of the longitudinal and bending sections.

[0011] For example, a bending spring element according to the invention can be manufactured by placing a prepreg having unidirectional continuous bending spring fibers arranged along the longitudinal direction of the bending spring element in a mold. The prepreg is optionally impregnated with an additional matrix material and then heated and pressed until the matrix material cures. It has been shown that the still flowable matrix material within the functional layer flows substantially along the bending spring fibers embedded therein, and laterally therewith, the matrix material can only flow at a significantly lower rate because the bending spring fibers impede and intercept the matrix material.

[0012] To enable different volume ratios of bending spring fibers in different sections of the bending spring element, according to the present invention, a matrix material output layer is arranged in sections with a higher volume ratio. This matrix material output layer exhibits significantly lower transverse to longitudinal flow resistance compared to the adjacent functional layer during the curing operation of the matrix material when pressing the bending spring element. Thus, the matrix material that can still flow in the longitudinal section during pressing can first flow into the matrix material output layer and then rapidly flow out from the side of the bending spring element, while in the bending section, due to the bending spring fibers arranged longitudinally in the functional layer, it can flow substantially along the longitudinal direction of the bending spring element, but cannot, or in each case can only, exit from the side in a small proportion. By increasing the output of matrix material in the longitudinal section, the proportion of bending spring fibers increases here compared to the matrix material, while the proportion of bending spring fibers in the bending section remains almost unchanged compared to the matrix material during pressing and is decisively predetermined by the pre-prepared prepreg and the optional additional addition of matrix material.

[0013] Using a matrix material output layer has proven to be significantly more efficient and better controllable than other methods, such as applying varying compression pressures along the longitudinal direction of the bending spring element. Furthermore, the functional layers of the bending spring element can consist of uniform prepreg strips extending continuously along the entire length of the bending spring element, without the need for pre-setting and inserting locally different prepregs or varying numbers of prepreg sublayers. Alternatively, a prepreg with continuous bending spring fibers extending longitudinally throughout the bending spring element can be used, thereby enabling the manufacture of high-quality bending spring elements with low material costs.

[0014] According to one embodiment of the invention, the first volume proportion of the flexural spring fibers in the at least one curved section is less than 55%, preferably less than 52%, and the second volume proportion of the flexural spring fibers in the at least one longitudinal section is greater than 55%, preferably greater than 58%. It has been shown that a volume proportion of approximately 50% of the flexural spring fibers in the curved section and approximately 60% in the longitudinal section achieves advantageous performance for flexural spring elements in many applications, while maintaining a relatively low inherent weight.

[0015] The matrix material output layer can be composed of various materials or various material components. The basic requirements for a particularly suitable matrix material output layer are relatively high porosity and high resistance to deformation, so that the matrix material output layer is not over-compressed and densified during pressing, so that the flowable matrix material can flow quickly through the cavities within the matrix material output layer until it can exit from the side.

[0016] Advantageously, the matrix material output layer can have output layer fibers arranged along two or more directions extending at an angle to each other, wherein the average orientation of the output layer fibers is aligned along the longitudinal direction of the bending spring element. The average orientation of the output layer fibers refers to the orientation obtained by superimposing all the individual orientations of the individual output layer fibers. For example, if the same number of output layer fibers are arranged and extended in the longitudinal direction in the same manner toward a first longitudinal edge of the bending spring element and toward an opposing second longitudinal edge, the average orientation corresponds to the longitudinal direction of the bending spring element. The output layer fibers can, for example, be arranged relative to each other at an angle of 90°. To avoid pre-setting a preferred orientation for the matrix material transverse to the longitudinal direction during pressing (which could result in the proportion of bending spring fibers being designed to be uneven transverse to the longitudinal direction), the output layer fibers should be arranged symmetrically with respect to the two longitudinal edges, i.e., having, for example, angles of 45° relative to the longitudinal edges, or either aligned along the longitudinal direction or transverse to the longitudinal direction of the bending spring element. By increasing the proportion of output layer fibers aligned transverse to the longitudinal direction of the bending spring element, the flow resistance transverse to the longitudinal direction is reduced, allowing more matrix material to flow transversely to the longitudinal direction and exit laterally. Alternatively, it can be envisioned that the output layer fibers within the matrix material output layer are arranged equally toward the two longitudinal edges at an angle of 0° to 90° relative to the longitudinal direction, for example, with an angle of +20° or -20° relative to the longitudinal direction.

[0017] In an advantageous embodiment of the invention, the output layer fibers in the matrix material output layer are arranged isotropically. The output layer fibers may be arranged non-directionally within the matrix material output layer. Relatively short output layer fibers may also be used in the matrix material output layer. Optionally, the average length of the output layer fibers in the matrix material output layer may be less than the width of the bending spring element measured transversely to the longitudinal direction. The average length of the output layer fibers may also be significantly shorter than the width of the bending spring element measured transversely to the longitudinal direction, and for example, only a few millimeters.

[0018] The matrix material output layer can be, for example, a laid-out or knitted fabric. It can also be a textile. Particularly advantageously, the matrix material output layer has a nonwoven material. The fibers of each output layer can be bonded into a nonwoven material in various ways with or without a matrix material. The nonwoven material can be impregnated with the same matrix material as the functional layers or with a different matrix material.

[0019] It has been shown that a weight per unit area of ​​less than 200 g / m² is suitable. 2 Preferably less than 120 g / mm 2 Especially preferred is less than 80 g / mm 2 Nonwoven materials are particularly advantageous.

[0020] According to one embodiment of the invention, a spreading element, made of a material different from that of the two functional layers, is provided in at least one bending section of the bending spring element between two functional layers. This spreading element increases the thickness of the bending spring element, measured transversely to the longitudinal direction. The deformation force arising from the bending stress on the bending spring element under the intended load can be advantageously absorbed by the spreading element of the thus thickened bending section and converted into spring energy. By increasing the distance between the functional layers, measured transversely to the longitudinal direction, and thus increasing the distance between the functional layers and the central plane and the central fiber extending therein, the bending spring element exhibits greater resistance to deformation in the bending section than in the adjacent longitudinal section, without requiring additional intermediate layers extending only across the bending section between the functional layers for this purpose.

[0021] According to the invention, the extending element arranged between two functional layers in the bending section has a continuously varying thickness in the longitudinal direction, such that the extending element continuously thickens from a sharp first end, reaching its maximum thickness in the central region, and then gradually tapers and sharpens again at the opposite second end. In this way, abrupt changes in thickness in the bending spring element can be avoided, which empirically leads to stress peaks and typically high and optionally excessive stresses during the intended use of the bending spring element.

[0022] Advantageously, the diffuser element is made of a material that is as resistant to shear and shear stiffness as possible. In principle, it is conceivable that the diffuser element is made of, for example, wood or a suitable plastic material. The diffuser element can be prefabricated or manufactured in advance, wherein the diffuser element advantageously already has a shape that matches the shape or orientation of the unloaded bending spring element within the bending section.

[0023] In an advantageous embodiment according to the invention, the spacer element is made of a second fiber plastic composite material having fibers, each fiber having a length of less than 30 mm, preferably less than 10 mm, and particularly preferably less than 1 mm. This second fiber plastic composite material with such short fibers can be processed particularly advantageously and cost-effectively to form the desired shape of the spacer element. The individual fibers cannot transmit tensile or compressive forces across a large area, but this has proven unnecessary. By arranging the spacer element between two outer functional layers, the thickness of the bending spring element, measured transversely to the longitudinal direction of the bending spring element in the bending section, can be matched to the expected bending stress of the bending spring element and is designed to be significantly thicker than the total thickness of the two functional layers. The spacer element made of the second fiber plastic composite material can have a low inherent weight. Through the additional second fiber plastic composite material of the spacer element, the two significantly more expensive functional layers of the bending spring element can be designed to be relatively thin in the bending section and matched to the expected or anticipated maximum tensile and compressive stresses of the functional layers of the bending spring element within the bending section.

[0024] It has been found that bending spring elements exhibit particularly advantageous elastic properties when the fibers in the second fiber plastic composite are arranged in a non-directional manner. This non-directional arrangement of fibers in the matrix material embedded in the second fiber plastic composite is also referred to as random fibers. In many applications, the more uniformly the fibers are distributed in the second fiber plastic composite, the more advantageous the spring performance can be designed. The shorter the length of each fiber in the second fiber plastic composite, the easier it is to achieve the uniform distribution of fibers in the extension element according to the invention, as well as the uniform orientation of the fibers relative to each other.

[0025] In a particularly advantageous embodiment of the invention, the second fiber-plastic composite material has a plastic matrix material consistent with that of the two functional layers. By using the same plastic matrix material for both the functional layers and the spacer element disposed between them, a seamless and mating connection between the spacer element and the adjacent functional layers on both sides can be achieved. This prevents unintentional detachment of the functional layers from the spacer element, or at least makes it difficult, even when the bending spring element is subjected to high loads.

[0026] Extender elements can be manufactured by introducing a paste-like starting material between pre-fabricated and optionally pre-formed functional layers. Alternatively, depending on the material used, the extender elements can also be manufactured using known injection molding methods. The functional layers can then be joined with the extender elements disposed between them, thereby manufacturing the desired bending spring element. Alternatively, the extender elements can be introduced into the bending sections between functional layers already disposed in a mold using known injection molding methods. It is also conceivable that the extender elements be manufactured separately from the functional layers in a separate working step. The functional layers can then be joined with the extender elements disposed therebetween, forming and solidifying the desired bending spring element.

[0027] Optionally, the central plane of the at least one bending section of the bending spring element has a directional change of greater than 90°, preferably greater than 150°, and particularly preferably about 180°. In the case of bending sections whose orientation changes more than 150° in the longitudinal direction, preferably about 180°, the forces acting transversely to the two end regions of the bending section can be absorbed particularly effectively by the bending spring element within the bending section according to the expected deformation, and high spring restoring force and thus large spring effect are generated with low space requirements.

[0028] Advantageously, according to a variation of the invention, the bending spring element has at least two bending segments separated from each other by longitudinal sections and bent in opposite directions, such that the central plane has an S-shaped orientation across the two bending segments. A bending spring element having at least one S-shaped spring segment, and particularly a bending spring element having two or more S-shaped spring segments designed adjacent to each other, can achieve a particularly advantageous combination of high spring force and minimal space requirements for many applications. Multiple similar or structurally identical bending spring elements can be combined into a bending spring device that combines advantageous spring performance with high environmental tolerance and low inherent weight. The bending spring element according to the invention, or a bending spring device composed of multiple bending spring elements, is therefore also particularly suitable for use as a spring element in motor vehicles.

[0029] If the first fiber-reinforced plastic composite of the two functional layers has fibers unidirectionally arranged along the longitudinal direction of the bending spring element, the functional layers possess particularly advantageous properties. Through the unidirectional arrangement of fibers along the longitudinal direction, the functional layers can absorb particularly high tensile and compressive forces. Here, the functional layers can have fibers or fiber bundles extending parallel to the longitudinal direction or preferably at an acute angle to the longitudinal direction. Suitable fibers can be, for example, glass fibers, carbon fibers, ceramic fibers, basalt fibers, metal fibers, or natural fibers. A suitable matrix material can be a plastic material matched to the respective fibers, such as a suitable thermosetting plastic, elastomer, or thermoplastic. The extension element can have the same fibers as the functional layers or fibers made of different materials.

[0030] Optionally, the first fiber-reinforced plastic composite material has fibers whose length extends longitudinally across the entire bending spring element. Thus, the tensile or compressive stresses acting on the functional layer are distributed throughout the bending spring element by quasi-continuous fibers, thereby reducing the risk of breakage under excessive load.

[0031] The exemplary embodiments schematically illustrated in the accompanying drawings are explained in more detail below. They show:

[0032] Figure 1 A schematic cross-sectional view of a bending spring element, which has a tortuous path including multiple bending sections and longitudinal sections.

[0033] Figure 2 Figure 1 The bending spring element shown along Figure 1 A schematic cross-sectional view of line II-II in the middle.

[0034] Figure 3 Figure 1 The bending spring element shown along Figure 1 A schematic cross-sectional view of line III-III in the diagram.

[0035] Figure 4 A schematic cross-sectional view of the longitudinal section of the bending spring element according to the invention during pressing in the mold.

[0036] Figure 5 A schematic cross-sectional view of a bending spring element with different designs, including multiple bending sections and longitudinal sections. In each bending section, a spacer element is arranged to increase the thickness of the bending spring element within that bending section, measured transversely to longitudinally.

[0037] Figure 6 Figure 5 The bending spring element shown along Figure 5 A schematic cross-sectional view of the VI-VI line.

[0038] exist Figures 1 to 3 The bending spring element 1, shown in different views, has two functional layers 2 and 3, each made of a first fiber-plastic composite material 4. In these two functional layers 2 and 3, continuous bending spring fibers 5 are arranged in a plastic matrix material 6 such that the bending spring fibers 5 extend longitudinally 7 across the entire bending spring element 1. Figure 1 For clarity, only some of the bending spring fibers 5 are shown, and only in short sections along the longitudinal direction 7. The longitudinal direction 7 corresponds to the orientation of the central plane 8, which extends equidistantly from the two outward outer edges 9 and 10 of the two functional layers 2 and 3, respectively. In the exemplary embodiment shown, the orientation of the central plane 8 also corresponds to the orientation of the central fiber, which is unloaded at the two end regions 11 and 12 of the bending spring element 1, respectively, transverse to the longitudinal direction 7 under the expected force F.

[0039] The central plane 8 has a zigzag orientation. The bending spring element 1 includes three bending sections 13 with a bending orientation of approximately 180°, which are respectively arranged between two longitudinal sections 14. Two end regions 11, 12 are formed by the longitudinal sections 14, in which the bending spring element 1 has a generally straight or very flat orientation of the central plane 8 with only a slight S-shape. A longitudinal section 14 is also formed between the three bending sections 13, in which the central plane 8 extends generally straight or slightly S-shaped and has a bending reversal from the first bending section 13 to the adjacent second bending section 13.

[0040] The bending spring fibers 5 embedded in the matrix material 6 of functional layers 2 and 3 extend substantially parallel to the outer sides 9 and 10 of the respective functional layers 2 and 3 and extend along the longitudinal direction 7 throughout the bending spring element. Figure 2 and 3 In the cross-sectional view shown, the orientation of each fiber 5 is therefore perpendicular to the drawing plane and... Figure 1 The cross-sectional view shown extends in the drawing plane. Under the expected force F acting on the bending spring element, the bending spring fiber 5 is subjected to tensile stress substantially along the outermost segment 15 of its respective bending section 13, and compressive stress along the outermost portion 16 of the bending section 13. The closer the bending spring fiber 5 is to its respective outermost segments 9 and 10, the higher the tensile or compressive force that occurs and acts on the bending spring fiber 5 during the expected deformation.

[0041] In the longitudinal section 14, matrix material output layers 17 are arranged in the region of the central plane 8 between the two functional layers 2 and 3. The matrix material output layers 17 are made of materials with a thickness of less than 1 mm and a weight per unit area of ​​approximately 100 g / mm². 2The nonwoven layer consists of a consolidated layup of output layer fibers 18, which are uniformly distributed within the nonwoven layer and are arranged in a non-directional and isotropic or random and non-straightening manner. For clarity, the matrix material output layer 17 is not shown to scale in the figure and is noticeably thicker.

[0042] Figure 2 A cross-sectional view of the bending section 13 passing through the bending spring element 1 is shown. The two functional layers 2 and 3 are designed not to be separate from each other, but to be integral and without interface between them, so that the bending spring element 1 in the bending section 13 is composed of a fiber composite material designed to be uniform, wherein the bending spring fibers 5 are arranged perpendicular to the plane of the drawing.

[0043] Figure 2 A cross-sectional view is shown of the longitudinal section 14 passing through the bending spring element 1. A material matrix output layer 17 or a nonwoven layer is arranged between the two functional layers 2 and 3. The fibers 18 of each output layer extend randomly and non-directionally within the matrix material output layer 17.

[0044] To manufacture the bending spring element 1 according to the invention, for each of the functional layers 2, 3, a plurality of prepregs having continuous bending spring fibers 5 arranged unidirectionally along the longitudinal direction 7 are placed in the U-shaped lower portion 19 of the mold 20. A matrix material output layer 17 is placed and arranged between the two functional layers 2, 3. To press the bending spring element 1, a die 21 of the mold 20 is introduced into the lower portion 19 and the bending spring element 1 is pressed together between the die 21 and the lower portion 19 of the mold 20. During the curing operation, the matrix material 6 (typically a suitable resin), which is initially liquid, solidifies and cures to form the bending spring element 1 with the desired properties.

[0045] The still-flowable matrix material 6 is first absorbed by the matrix material output layer 17. Due to compression, additional matrix material 6 flows into the matrix material output layer 17. Because the matrix material 6 within the matrix material output layer can be transverse to the longitudinal direction 7 and therefore... Figure 4 The matrix material 6 flows particularly rapidly and with relatively little flow resistance along the direction of the drawing plane. As the pressing pressure increases, it flows out from the side of the matrix material output layer 17 and is pressed out of the mold 20 through the gap between the mold 21 and the lower part 19 of the surrounding mold 20, as if by... Figure 4 As indicated by the arrows in the diagram. Here, in the longitudinal section 14, due to the matrix material output layer 17 arranged only there, significantly more matrix material 6 is pressed out and output from the side than in the bending section 13. Therefore, the remaining volume proportion of matrix material 6 is smaller in the longitudinal section 14 than in the bending section 13. Consequently, the volume proportion of the bent spring fiber 5 is smaller in the bending section 13 than in the longitudinal section 14.

[0046] exist Figure 5 In the embodiment of the bending spring element 1, which is only schematically shown and includes multiple bending sections 13 and longitudinal sections 14, a distance-expanding element 22 is arranged in each of the bending sections 13, which increases the thickness of the bending spring element 1 in the bending section 13 as measured transversely to the longitudinal direction 7. The distance-expanding element 22 increases the distance between the outward outer section 15 and the inward outer section 16 of the two functional layers 2, 3 in the bending section 13, thereby achieving favorable spring performance of the bending spring element 1 in the region of the bending section 13.

[0047] The extender element 22 has a generally sickle-shaped shape. Arranged in the respective bending sections 13 between the two functional layers 2, 3, the extender element 22 here, according to the invention, has a continuously varying thickness in the longitudinal direction 7, such that the extender element 22 continuously thickens from a sharp first end, reaching its maximum thickness in the central region, and gradually tapers towards the opposite second end, also becoming sharp again. In this way, abrupt changes in thickness in the bending spring element 1 can be avoided, which empirically leads to stress peaks and typically high and optionally excessive stresses during the intended use of the bending spring element 1. The two extender elements 22 do not necessarily have to be designed symmetrically with respect to the central plane 8.

[0048] Each expansion element 22 is made of a second fiber-plastic composite material 23. The second fiber-plastic composite material 23 has the same matrix material 6 as the first fiber-plastic composite material 4, so that the expansion element 22 fits and is uniformly connected to the two adjacent functional layers 2, 3, without forming an interface between the expansion element 22 and the adjacent functional layers 2, 3 that may impair the mechanical strength of the bending spring element 1.

[0049] Figure 5 The cross-sectional diagrams II-II and III-III recorded in the middle correspond to Figure 2 and 3 The cross-sectional view shown. Figure 6 Cross-sectional views VI-VI are shown in the curved section 13, which has a cross-sectional view along... Figure 5 The spreading element 22 is embedded within the cutting line VI-VI. Short fibers 24, having a preferred uniform length of 1 mm to 5 mm, are arranged in the matrix material 6 of the second fiber-plastic composite 23. The short fibers 24 are arranged in a non-directional manner in the spreading element 22 so that there is a substantially uniform distribution of the short fibers 24 in the matrix material 6 of the second fiber-plastic composite 23 and a distribution along all directions.

[0050] In particular, the dimensions of the extension element 22 are arranged in terms of their respective thicknesses in the direction transverse to the central plane 8, so that the bending spring element 1 has advantageous spring performance within a predetermined range of normally occurring force action and substantially eliminates damage to the bending spring element 1. At the same time, the dimensions of the functional layers 2 and 3 are also determined so that the intended use of the bending spring element 1 can be achieved within a predetermined service life, but with as little material as possible for the functional layers 2 and 3 and the extension element 22, so that the bending spring element 1 according to the invention has advantageous spring performance and a particularly low inherent weight.

Claims

1. A bending spring element (1) made of fiber-plastic composite material (4, 23), wherein the bending spring element (1) has functional layers (2, 3) made of fiber-plastic composite material on two opposite sides (9, 10) of its central plane, wherein bending spring fibers (5) in each functional layer (2, 3) are arranged at least in bundles parallel to each other and extend along the longitudinal direction (7) of the bending spring element, wherein the bending spring element (1) has at least one bending section (13) in which the bending spring element (1) extends between the two functional layers (2, 3) without load. The center plane (8) of the extension extends in the longitudinal direction (7) of the bending spring element (1) with a bend greater than 90°, wherein the bending spring element (1) has at least one longitudinal segment (14) in which the center plane (8) of the unloaded bending spring element (1) either has no obvious bend or has a bend reversal, and wherein when the bending spring element (1) deflects as expected, the outwardly arranged functional layer segment (15) in the bending segment (13) is subjected to tensile stress, and the opposite and inwardly arranged functional layer segment (16) in the bending segment (13) is subjected to compressive stress, characterized in that, The bending spring element (1) has at least one matrix material output layer (17) in the at least one longitudinal section (14) that is parallel to the two functional layers (2, 3) and extends in the longitudinal direction (7). The matrix material output layer has at least a certain proportion of output layer fibers (18) that are arranged in a way that deviates from the longitudinal direction (7) of the bending spring element (1). The first volume proportion of the bending spring fibers (5) in the functional layers (2, 3) within the at least one bending section (13) is smaller than the second volume proportion of the bending spring fibers (5) in the functional layers (2, 3) within the at least one longitudinal section (14).

2. The bending spring element (1) according to claim 1, characterized in that, The first volume proportion of the bent spring fiber (5) in the at least one bent section (13) is less than 55%, and the second volume proportion of the bent spring fiber (5) in the at least one longitudinal section (14) is greater than 55%.

3. The bending spring element (1) according to claim 1 or claim 2, characterized in that, The matrix material output layer (17) has output layer fibers (18) arranged along two or more directions extending at an angle to each other, wherein the average orientation of the output layer fibers (18) is arranged along the longitudinal direction (7) of the bending spring element (1).

4. The bending spring element (1) according to any one of claims 1 or 2, characterized in that, The matrix material output layer (17) has output layer fibers (18) arranged along two output layer fiber directions that are arranged opposite each other at an angle of 90°.

5. The bending spring element (1) according to any one of claims 1 or 2, characterized in that, The output layer fibers (18) in the matrix material output layer (17) are arranged isotropically.

6. The bending spring element (1) according to claim 3, characterized in that, The matrix material output layer (17) has a nonwoven material.

7. The bending spring element (1) according to claim 6, characterized in that, The nonwoven material has a unit area weight of less than 200 g / m². 2 .

8. The bending spring element (1) according to any one of claims 1 or 2, characterized in that, The average length of the output layer fibers (18) in the matrix material output layer (17) is less than the width of the bending spring element (1) measured in the transverse direction (7).

9. The bending spring element (1) according to any one of claims 1 or 2, characterized in that, The bending spring element (1) has a distance-expanding element (22) arranged between two functional layers (2, 3) in at least one bending section (13), the distance-expanding element being made of a material different from the two functional layers (2, 3).

10. The bending spring element (1) according to claim 9, characterized in that, The material of the distance-expanding element (22) is a second fiber plastic composite material (23) with fibers (24) and the length of each fiber is less than 30 mm.

11. The bending spring element (1) according to claim 10, characterized in that, The fibers (24) in the second fiber-plastic composite material (23) are arranged in a non-directional manner.

12. The bending spring element (1) according to claim 10 or claim 11, characterized in that, The second fiber-reinforced plastic composite material (23) has a matrix material (6) that is consistent with the two functional layers (2, 3).

13. The bending spring element (1) according to any one of claims 1 or 2, characterized in that, The center plane (8) in at least one bending section (13) of the bending spring element (1) has a directional change of more than 90°.

14. The bending spring element (1) according to any one of claims 1 or 2, characterized in that, The bending spring element (1) has at least two bending sections (13) that are separated from each other by longitudinal sections (14) and bent in different directions, such that the central plane (8) has an S-shaped orientation across the two bending sections (13).

15. The bending spring element (1) according to any one of claims 1 or 2, characterized in that, The first fiber-plastic composite material (4) of the two functional layers (2, 3) has unidirectionally arranged bending spring fibers (5) along the longitudinal direction (7) of the bending spring element (1).

16. The bending spring element (1) according to claim 15, characterized in that, The first fiber-plastic composite material (4) has a bent spring fiber (5) whose length extends across the entire bent spring element (1) along the longitudinal direction (7).

17. The bending spring element (1) according to claim 1, characterized in that, The first volume proportion of the curved spring fiber (5) in the functional layer (2, 3) of the at least one curved section (13) is smaller than the second volume proportion of the curved spring fiber (5) in the functional layer (2, 3) of the at least one longitudinal section (14).

18. The bending spring element (1) according to claim 2, characterized in that, The first volume proportion of the bent spring fiber (5) in the at least one bent section (13) is less than 52%, and the second volume proportion of the bent spring fiber (5) in the at least one longitudinal section (14) is greater than 58%.

19. The bending spring element (1) according to claim 7, characterized in that, The nonwoven material has a unit area weight of less than 120 g / mm². 2 .

20. The bending spring element (1) according to claim 7, characterized in that, The nonwoven material has a unit area weight of less than 80 g / mm². 2 .

21. The bending spring element (1) according to claim 10, characterized in that, The material of the distance-expanding element (22) is a second fiber plastic composite material (23) with fibers (24) and the length of each fiber is less than 10 mm.

22. The bending spring element (1) according to claim 10, characterized in that, The material of the distance-expanding element (22) is a second fiber plastic composite material (23) with fibers (24), the length of which is less than 1 mm.

23. The bending spring element (1) according to claim 13, characterized in that, The center plane (8) in at least one bending section (13) of the bending spring element (1) has a directional change of more than 150°.

24. The bending spring element (1) according to claim 13, characterized in that, The center plane (8) in at least one bending section (13) of the bending spring element (1) has a 180° directional change.

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