Leaf spring made of a fiber composite material having integrated bearing eyes and method of producing said leaf spring

Abstract

A leaf spring made of a fiber composite material having integrated bearing holes and a method for producing is disclosed. The method comprises the steps of cutting prepreg strips of a predetermined length from a prepreg strand, removing cut-outs from the particular prepreg strip in the axial ends where a bearing hole should be formed, laying a plurality of prepreg strips one over the other in a prepreg stack in alternation so that the surfaces of the prepreg strips are flush to form a raw leaf spring forming a bearing hole by deforming an axial end of the prepreg stack in a plane perpendicular to the longitudinal extension (L) and perpendicular to the transverse extension (B) of the prepreg stack, setting the raw sheet spring to form the finished leaf spring in a mold with a suitable setting pressure and a suitable setting temperature.

Claims

1. A leaf spring, consisting of a fiber composite material, in which a bearing eye is configured on at least one axial end, said leaf spring comprising: a plurality of prepreg strips constructed and arranged to be placed one on top of another in layers thereby forming a prepreg stack, wherein, for the formation of the bearing eye, said prepreg strips are bent with an axial end directed toward an axial middle of said prepreg stack and said prepreg strips being fixedly connected to a portion of the fiber composite material which is disposed toward a middle section of said leaf spring, in the axial direction.

2. The leaf spring of claim 1, wherein each prepreg strip of said plurality defines a cutout opening configured by a first cutout of fiber composite material, said cutout opening being positioned adjacent the axial end.

3. The leaf spring of claim 2, wherein said cutout opening is filled with fiber composite material wherein in this region, on the right side and on the left side, fibers of the prepreg strips are deformed inward forming indentations.

4. The leaf spring of claim 3, wherein the narrow end portions of the respective prepreg strips are jointly bent in the shape of a circle in the direction of the axial middle of the prepreg strips and are guided through the right-side or left-side indentations of the prepreg stack.

5. The leaf spring of claim 4, wherein the cross-sectional area of the narrow end portion of the respective prepreg strips is substantially the same with the cross-sectional area of the indentations.

6. The leaf spring of claim 5, wherein each prepreg strip of said plurality has its cutout opening located at a dimension from its axial end wherein said distance is different for each prepreg strip.

7. The leaf spring of claim 6, wherein the prepreg strips disposed between the bottommost and topmost prepreg strip in a prepreg stack respectively have a middle cutout opening, the distance of which from the axial end of the prepreg strips decreases with increasing proximity to the topmost prepreg strip.

8. The leaf spring of claim 7, which is produced from prepreg strips of a third prepreg strip variety stacked one upon the other, wherein, on these prepreg strips, a middle narrow end portion is formed by cutting out of a fourth cutout and fifth cutout on the right side and on the left side of an axial end, and in that these end portions of the prepreg stack are bent into a circle for the formation of the bearing eye and are stuck through the cutout opening created with the first cutout.

9. The leaf spring of claim 6 wherein said prepreg stack includes an uppermost prepreg strip and a lowermost prepreg strip and wherein the lowermost prepreg strip has the greatest cutout opening distance of all other prepreg strips of said plurality and the uppermost prepreg strip has the least cutout opening distance of all other prepreg strips of said plurality.

10. The leaf spring of claim 2, wherein the cutout opening in each prepreg strip of said plurality has a substantially oval, rectangular or diamond-shaped geometry.

11. The leaf spring of claim 1, wherein the leaf spring is made up of two prepreg strip varieties of geometrically different configuration at their axial end, wherein the prepreg strips of these two prepreg strip varieties are stacked alternately one upon the other.

12. The leaf spring of claim 11, wherein each prepreg strip of said plurality has at said axial end, for the formation of the bearing eye, a reduced transverse extent in comparison to a region of the leaf spring lying remote from the bearing eye.

13. The leaf spring of claim 12, wherein the prepreg strips of a first prepreg strip variety are shortened in their transverse extent at their axial end.

14. The leaf spring of claim 12, wherein the prepreg strips of a second prepreg strip variety are shortened in their transverse extent (B2) at their axial end.

15. The leaf spring of claim 1, wherein the fiber composite material of the prepreg strips consists of longitudinally directed fibers and a thermoset plastic or a thermoplastic.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a better understanding of the invention, a drawing is appended to the description, in which drawing:

(2) FIG. 1 shows a schematic side view of an inventively produced leaf spring made of a fiber composite material and having bearing eyes configured on the end of the leaf spring,

(3) FIG. 2 shows a schematic cross-sectional view of the leaf spring according to FIG. 1 along a sectional line A-A,

(4) FIGS. 3A-3E show the production of an inventive leaf spring according to basic method steps,

(5) FIGS. 4A-4D show slightly differently configured prepreg strips of two prepreg varieties in a schematic top view,

(6) FIG. 5 shows a first method step for producing a second variant of an inventively constructed leaf spring,

(7) FIG. 6 shows a second method step for producing a second variant of an inventively constructed leaf spring, and

(8) FIG. 7 shows a schematic side view of an inventive leaf spring in a, from the production engineering aspect, concluding cutting operation.

DESCRIPTION OF THE SELECTED EMBODIMENTS

(9) For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any alterations and further modifications in the described embodiments, and any further applications of the principles of the invention as described herein are contemplated as would normally occur to one skilled in the art to which the invention relates. One embodiment of the invention is shown in great detail, although it will be apparent to those skilled in the relevant art that some features that are not relevant to the present invention may not be shown for the sake of clarity.

(10) Accordingly, FIG. 1 shows in a schematic side view an inventively configured leaf spring 1, which is produced from a fiber composite material. This leaf spring 1 has a middle leaf spring portion 2, and two bearing eyes 3, 4, which are configured in the region of the axially outer ends 8, 9 of the leaf spring. These bearing eyes 3, 4 are produced such that their outer side 26 is formed by the material of the bottom side of the middle leaf spring portion 2 and their inner side 27 is formed by the material of the top side of the middle leaf spring portion 2. To this effect, the axial ends of the leaf spring 1, as indicated by the arrows, are turned axially inward in a circle shape and fixedly connected to the fiber composite material disposed farther toward the middle. This is also discussed in detail further below.

(11) As shown by the schematic cross section of FIG. 2 along the sectional line A-A according to FIG. 1, the leaf spring 1 consists of a plurality of prepreg strips 5, 6, 5′, 6′, which are deposited one on top of the other to form a prepreg stack 7. This prepreg stack 7 has a width B, a height H and a longitudinal extent L, and forms, after the creation of the bearing eyes 3, 4, a crude leaf spring 23, which in a pressing mold, with the application of a suitable setting pressure and suitable setting temperature, hardens into a finished leaf spring 1.

(12) FIGS. 3A-3E show schematically in a first illustrative embodiment the most important steps of the production process for producing an inventive leaf spring 1.

(13) First of all, prepreg strips 5, 6 having a predetermined length are cut off from a pre-produced prepreg strand of predefined width. These prepreg strips 5, 6 are next worked to form two geometrically somewhat different prepreg strip varieties, which then serve jointly for the construction of a prepreg stack 7 or for the construction of the crude leaf spring 23.

(14) After the prepreg strips 5, 6 have been cut off from the prepreg strand, in a method step C1 (see FIG. 3A) a here oval opening 24 is created in the region of the axial end of each individual prepreg strip 5, at which a bearing eye 4 is intended to be configured, by a first, roughly middle cutout 10. At the same time, a narrow end portion 21 of width B1 and length L2 is created at the axial end 19′ of the prepreg strip 5 by a second cutout 11.

(15) Equally, in a further method step C2 (see FIG. 3B), a here oval opening 24 is created in the region of the axial end of each individual prepreg strip 6, at which a bearing eye is intended to be configured, by a first, roughly middle cutout 10. At the same time, a narrow end portion 22 of width B2 and length L2 is created at the axial end 19 of the prepreg strip 6 by a second cutout 11.

(16) The cutouts 10 and 11, which have been cut out of the prepreg strip 5, 6, for instance, by a punching operation, are hereupon removed from the prepreg strip 5, 6. In this preferred illustrative embodiment, the width B1 of the narrow end portion 21 corresponds to the width B2 of the narrower end portion 22. Moreover, the narrow end portions 21, 22 of the prepreg strips 5 and 6 have the same axial length L2. The distance L1 of the oval opening 24 from the axial end 19, 19′ of the two narrow end portions 21 and 22 is in this example respectively identical, even though different axial distances are of advantage. This is further discussed in connection with FIGS. 4A-4D. The differential path ΔL between the distance L1 of the opening 24 from the axial end 19, 19′ of the prepreg strips 5, 6 and the axial length L2 of the narrow end portions 21, 22 is chosen such that this differential path ΔL corresponds to the respective circumference of the bearing eye 3, 4.

(17) The prepreg strips 5, 6 trimmed in method steps C1 and C2 are then in a step C3 (see FIG. 3C) laid alternately superficially flush one on top of the other, wherein a plurality of these prepreg strips 5, 6, 5′, 6′ form the prepreg stack 7 for the creation of a crude leaf spring 23 (see also FIG. 2). As FIG. 3C illustrates in representation of the method step C3, the narrow end portions 21, 22 of the two varieties of prepreg strips 5, 6 are in this illustrative embodiment so narrow that between them, in the prepreg stack 7, is formed a region which is free from fiber composite material.

(18) In a then following method step C4 (see FIG. 3D), the longitudinally directed margins 12 and 13 of the prepreg stack 7 and of the prepreg strips 5, 6, 5′, 6′, in the region of the oval opening 24, are compressed in the width B by means of a force F to the point where the thus displaced fiber composite material has closed off this opening 24. As a result of this deformation of the prepreg stack 7 or of the prepreg strips 5, 6, 5′, 6′, in the prepreg stack 7, in the region of the points of application for the force F, is respectively created an indentation or constriction 14, 15, which serve for the reception and, preferably, through-guidance, of the narrow end portions 21, 22.

(19) In a further method step C5 (see FIG. 3E), a bearing eye 4 is created on the prepreg stack 7 by bending over of its axial end in a plane oriented perpendicularly to the longitudinal extent L and perpendicularly to the transverse extent B of the prepreg stack 7. The narrow end portions 21, 22 and portion ΔL of the prepreg stack 7 are here bent in the shape of a circle in the direction of its axial middle and the narrow end portions 21, 22 are guided through the indentations 14, 15.

(20) Since the prepreg stack 7, prior to its setting, is still a comparatively soft structure, the bending of the axial end of the prepreg stack 7 is preferably realized in a mold or via a molded body 25 which can subsequently be removed. The narrow end portions 21, 22 are preferably stuck fully through the associated indentations 14, 15, so that these initially extend a short way beneath the prepreg stack 7. Following the setting or hardening of the crude leaf spring 23 under a suitable setting pressure and suitable setting temperature, this protrusion is cut off by means of a cutting device 28, as is represented, by way of example, in FIG. 7. The protrusion can also, however, remain on the leaf spring, forming a thickening, as has already been explained.

(21) In order to be able to use axially equally long prepreg strips 5, 6 of the two prepreg strip varieties for the production of the leaf spring 1, 23, it is of advantage to configure the opening 24, created by the first cutout 10, in the respective prepreg strips 5, 6, 5′, 6′ differently far away from the axial ends 19, 19′ thereof. Allowance is hereby made for the fact that a bearing eye has a smaller circumference on its radial inner side than on its outer side.

(22) Accordingly, it is provided according to FIGS. 4A-4D that the middle cutout opening 24 of each individual prepreg strip is differently far away from its axial end 19, 19′, wherein in the bottommost prepreg strip 5 of the prepreg stack 7, which subsequently forms the outer side 26 of the bearing eye 3, 4, the middle cutout opening 24 has the greatest distance L3 from the axial end 19, 19′ of the prepreg strip 5, and that the cutout opening 24, in the topmost prepreg strip 6′ of the prepreg stack 7, which subsequently forms the inner side 27 of the bearing eye 3, 4, has the least distance L6 from the axial end 19 of the prepreg strip 6′.

(23) This means that the prepreg strips 5, 6, 5′, 6′ of the prepreg stack 7, even after they have been turned up to form the bearing eye 4, despite different radial position and thus different circumferential length at the bearing eye 4 in the region of the indentations 14, 15, can be stuck through these with full length L2. This further means that that region ΔL in the prepreg stack 7 which is formed between the opening 24 and the start of the narrow end portions 21, 22 is sufficiently long to form the bearing eye 4 at a predetermined circumferential radius thereof.

(24) In order further to illustrate the geometric relationships, FIGS. 4A-4D show in its illustrations, by way of example, four prepreg strips 5, 6, 5′, 6′, which are laid superficially flush one upon the other to form a prepreg stack 7. The bottommost layer of the prepreg stack 7 is formed by the prepreg strip 5 according to FIG. 4A. In the case of this prepreg strip 5, the distance L3 between the opening 24 and the axial end 19 of the same is greatest in comparison to the other prepreg strips 6, 5′, 6′, since it forms the outer circumference of the bearing eye 4. In the case of the prepreg strips 6, 5′ and 6′ which then follow in the prepreg stack 7, the distance L4, L5 and L6 between the opening 24 and the axial end 19, 19′ of the same is respectively somewhat shorter, wherein the prepreg strip 6′ forms with its surface the inner side 27 of the future bearing eye 4.

(25) FIGS. 5 and 6 show that a fiber composite leaf spring to be produced according to the invention can also be constructed somewhat differently. Thus, to this effect, prepreg strips 16, 16′, 16″ which are geometrically identical with regard to their circumference are laid one on top of the other, forming a prepreg stack 7′. In the case of this prepreg strip 16, 16′, 16″, the narrow end portion 20 is formed centrally at the axial end of each individual prepreg strip 16, 16′, 16″ by punching out a third cutout 17 on the right side and a fourth cutout 18 on the left side. Moreover, these prepreg strips 16, 16′, 16″ likewise have a middle opening 24, which is here of rectangular configuration and has been created by punching out of the first cutout 10.

(26) As illustrated by FIG. 6, in one production step the axial ends 19 of the narrow end portions 20 and the strip portions ΔL of the prepreg stack 7′ are likewise bent in the shape of a circle in the direction of the axial middle of the prepreg stack 7′ and the end portions 20 are guided preferably fully through the opening 24. A bearing eye 4, initially supported by a molded body 25, is hereby created, wherein the regions of the narrow end portions 20 and of the rim of the opening 24, after the hardening of the leaf spring, form a strong bond.

(27) Also in the illustrative embodiment according to FIGS. 5 and 6, the opening 24 of each individual prepreg strip 16, 16′, 16″ is disposed differently far away from its axial end 19 in order to make allowance in the bearing eye 4 for the circumferential length, which is differently long in dependence on the position.

(28) While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes, equivalents, and modifications that come within the spirit of the inventions defined by following claims are desired to be protected. All publications, patents, and patent applications cited in this specification are herein incorporated by reference as if each individual publication, patent, or patent application were specifically and individually indicated to be incorporated by reference and set forth in its entirety herein.