Method for producing a covered steering wheel for a vehicle

Abstract

A method for producing a covered steering wheel for a vehicle. A steering wheel skeleton is overmolded with a matrix material. A covering material is coated on its non-visible side with an activatable material. The coated covering material is applied to the overmolded steering wheel skeleton so that its non-visible side faces the overmolded steering wheel skeleton. Longitudinal edges of the covering material are joined together. The activatable material is activated with creation of an integral connection between the covering material and the matrix material.

Claims

1. A method for producing a covered steering wheel for a vehicle, the method comprising: providing an overmolded steering wheel skeleton by overmolding a steering wheel skeleton with a matrix material; coating a covering material on a non-visible side with an activatable material to form a coated covering material; applying the coated covering material to the overmolded steering wheel skeleton so that the non-visible side faces the overmolded steering wheel skeleton; joining longitudinal edges of the coated covering material together; and activating the activatable material to form an integral connection between the covering material and the matrix material after the joining of the longitudinal edges of the coated covering material, wherein the activatable material is a foamable material that foams when activated.

2. The method according to claim 1, wherein the joining of the longitudinal edges of the coated covering material includes a closure of a zipper, the zipper including zipper halves that were attached to the longitudinal edges of the coated covering material prior to the applying of the coated covering material to the overmolded steering wheel skeleton.

3. The method according to claim 2, wherein the zipper is a coil zipper or a plastic coil zipper.

4. The method according to claim 2, wherein the matrix material enclosing the steering wheel skeleton has a recess in a region directly underneath the joined longitudinal edges of the coated covering material, the zipper being disposed inside of the recess.

5. The method according to claim 1, wherein the activatable material is an activatable adhesive, and wherein the integral connection is an adhesive bond.

6. The method according to claim 1, wherein the activating of the activatable material is accomplished by thermal treatment and/or irradiation.

7. The method according to claim 1, wherein the joining of the longitudinal edges of the coated covering material includes stitching.

8. The method according to claim 1, wherein the joining of the longitudinal edges of the coated covering material includes a closure of zipper halves of a zipper, and in a later process step includes a stitching of the longitudinal edges by overstitching of the zipper.

9. The method according to claim 1, wherein the overmolding of the steering wheel skeleton includes a foam-coating of the steering wheel skeleton with the matrix material.

10. The method according to claim 1, wherein the covering material is cut to size before or after coating and prior to application to the overmolded steering wheel skeleton.

11. The method according to claim 1, wherein, prior to the application of the coated covering material to the overmolded steering wheel skeleton, the matrix material is also coated at least in regions with the activatable material or with a different activatable material.

12. The method according to claim 1, wherein instead of the covering material, it is the matrix material that is coated on an exterior with an activatable material after the overmolding of at least sections of the steering wheel skeleton, and wherein the covering material is applied to the overmolded steering wheel skeleton so that the coated exterior of the matrix material faces the covering material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:

(2) FIGS. 1A-1F illustrates a process sequence of a method for producing a steering wheel according to a first form of the invention: (1A) steering wheel skeleton in a perspective view and as a sectional view; (1B) blank of the covering material in a top view and as a sectional view before and after coating; (1C) steering wheel skeleton (cross-section) with overmolded or foam-coated matrix; (1D) steering wheel after application and joining of the covering material; 1(E) finished steering wheel after activation of the activatable material in a first variant embodiment, and (1F) finished steering wheel after activation of the activatable material in a second variant embodiment; and

(3) FIGS. 2A-2G process sequence of a method for producing a steering wheel according to a second form of the invention: (2A) steering wheel skeleton in a sectional view; (2B) steering wheel skeleton with overmolded or foam-coated matrix; (2C) coated covering material in a top view with zipper; (2D) application of the covering material; (2E) steering wheel with partially closed zipper; (2F) sectional view of the steering wheel after closure of the zipper in a first variant embodiment and (2G) of the steering wheel after closure of the zipper in a second variant embodiment.

DETAILED DESCRIPTION

(4) The process sequence of a first embodiment of the method according to the invention for producing a steering wheel shall be described below with reference to FIGS. 1A-1F on the basis of the intermediate products in different process stages.

(5) To start with, in a first step of the method, a steering wheel skeleton, which is labeled as a whole with 10 in FIG. 1A, is provided. The steering wheel skeleton 10 includes a steering wheel hub 11, from which any desired number (here: two) of steering wheel spokes 12 proceed radially and transition into a circumferential steering wheel rim 13. On the right-hand side of FIG. 1A, the steering wheel rim 13 is shown in a sectional view. It can be seen that the steering wheel rim 13 in this example is designed as an essentially U-shaped profile. Normally, the steering wheel skeleton is made of a metallic material, for example magnesium or a magnesium alloy, and can be obtained in a die casting process, for example. Subsequently, the steering wheel skeleton 10, in particular the steering wheel rim 13, is to be overmolded with a matrix material and enclosed with a covering material.

(6) In another step, a cutting to size and coating (lamination) of the covering material with an activatable material takes place. On the left-hand side, FIG. 1B shows a top view of an unrolled blank of a covering material 14. For example, leather, artificial leather, a textile material, or any desired type of artificial material may serve as covering material. Shown on the right-hand side of FIG. 1B is a sectional view of the covering material 14 before and after it has been coated. The covering material has a visible side 15 and a non-visible side 16. The activatable material 17 is applied to the non-visible side 16. The letter X identifies a height, the height of the coating (coating thickness). It can be any desired thickness, for example 20 to 2000 m, and is dependent on a variety of requirements and the material used, etc.

(7) A material that is capable, after a suitable activation (see below), of producing an integral connection with the covering material 14 and also with the matrix material of the overmolded steering wheel rim 10 is used as the activatable material 17. The activatable material can develop adhesive characteristics, which is to say that an activatable adhesive, for example a hot melt adhesive, is used as the activatable material 17. Suitable hot melt adhesives include, e.g., ethylene vinyl acetate (EVA), ethylene vinyl acetate copolymers, modified polyolefins, polyester, etc. Additional suitable adhesive substances include polyurethanes, polymers based on acrylate or acrylic acid monomers, polyvinyl alcohol, silicones, synthetic elastomers, and natural rubber compositions. A thermoplastic polyurethane composition (mixture of polyol and isocyanate) can be used, which can be employed as a powder, in particular.

(8) The coating technique can, in principle, be configured in any desired manner, and depends on the type of activatable material 17, in particular on whether this material is used in the form of a powder, a melt, a solution or dispersion, as a preformed layer in the form of a film or a mesh, or a mat, for example spun-bonded fabric. Accordingly, wet and dry coating, coatings with or without solvents, thermal coating, and other options are employed. If the activatable material 17 is available as a powder, solution, dispersion, or melt, then doctor-blade or spray techniques can be used. If the activatable material 17 is already preformed as a layer in the form of a film or a mesh or the like, then laminating or lining techniques are used, wherein the material 17 can also be provided on a carrier film in order to prevent the activatable material 17 from adhering prematurely. This carrier film is removed before or after the coating.

(9) The coating of the non-visible side 16 of the covering material 14 with the activatable material 17 can take place before the covering material is cut to size in its exemplary shape shown in FIG. 1B; in other words, it is first coated and then the coated covering material 14 is cut to size (prefabricated). The cutting-to-size may be accomplished by cutting or stamping.

(10) In a further process step, the result of which is shown in FIG. 1C, an overmolding, for example, a foam-coating, with a matrix material 18 occurs of the steering wheel skeleton 10 or of parts thereof, in particular of the steering wheel rim 13. Known injection molding processes using injection molds are employed for this process step. The product of this process step is thus a matrix 18, in which the steering wheel skeleton is present and embedded. The matrix 18 defines the desired shape of the steering wheel and in doing so takes into account, in particular, ergonomic requirements, safety requirements, and visual design aspects. A foam-coated steering wheel skeleton is also referred to as a foam steering wheel part in the technical terminology. One of the materials mentioned for the activatable material, for instance, may be used as the matrix material 18. In particular, a thermoplastic polymer, for example polyurethane, is employed. All of the aforementioned materials can be foamed with a physical foaming process, for example by saturating the polymer mass with supercritical CO.sub.2 and releasing the latter under a sudden drop in pressure and/or sudden increase in temperature. Some of the aforementioned materials can also be foamed chemically, for example in that the polymer composition releases a gaseous component under heating. Chemical and physical foaming processes or foam-coating processes are known to the person skilled in the art.

(11) In a next process step, an application of the coated material 14 to the overmolded steering wheel skeleton 13 (the foam steering wheel part), in particular the steering wheel rim 13, takes place. In this process, the covering material 14 is arranged such that its non-visible side, which is to say its coated side, faces the overmolded steering wheel skeleton 10, 13. The short ends of the blank of the coating material 14 can be joined to one another, for example stitched, glued, or welded, prior to the application of the coated covering material 14 to the overmolded steering wheel skeleton 10. This process can be performed mechanically. After the application of the coated covering material 14 to the overmolded steering wheel skeleton 10, the longitudinal edges 22 of the covering material 14 are joined together to produce a joint or seam 23. Here, too, the joining can be accomplished by, for example, sewing, gluing, or welding. The result of the application of the covering material 14 to the overmolded steering wheel rim 13 is illustrated in FIG. 1D. Here, reference number 17 identifies the as-yet-unactivated activatable material, and 23 identifies the seam of the longitudinal sides 22 of the covering material 14.

(12) In a next process step, an activation of the activatable material 17 takes place in order to create an integral connection between the covering material 14 and the matrix material 18 enclosing the steering wheel skeleton 10. The type of activation is determined by the type of activatable material, and can include the application of heat, irradiation, in particular infrared irradiation, application of pressure, pressing, chemical activation, etc. If, for instance, the activatable material 17 is a hot melt adhesive, the activation of the adhesive bond is accomplished by external heat input, for example in an oven, or by IR irradiation. In a special embodiment, the steering wheel is equipped with a steering wheel heater. In this case, the thermal activation of the activatable material 17 can take place using the steering wheel heater. The activation temperature employed should be matched to the temperature resistance of the covering material.

(13) The result of the activation step is shown in FIG. 1E. Here, 17 identifies the activated, and in this example foamed, material, which has only undergone slight expansion as a result of the activation in the example shown. FIG. 1F shows an alternative example, in which the activated material 17 is expanded (foamed) to a much greater degree. The extent of foaming and expansion can be regulated by factors including the coating thickness x (see FIG. 1B), with which the activatable material 17 has been applied to the covering material 14. It is also possible to provide different coating thicknesses x over the area of the covering material 14 that is to be coated in order to obtain different degrees of expansion in the product. In this way, different haptic characteristics, for example, can be produced along the circumference of the steering wheel rim 13.

(14) After activation, the steering wheel 100 is an end product, and can be installed, in particular in a motor vehicle, if applicable with additional equipment.

(15) An embodiment of the method according to the invention for producing a steering wheel 100 is illustrated in FIGS. 2A-2G on the basis of different process stages and intermediate products. Corresponding elements are labeled here with the same reference characters as in FIG. 1, and are not explained again in detail. Only the differences are discussed below. The method in FIG. 2 differs from the one in FIG. 1 in that a zipper is used for joining the longitudinal edges of the covering material.

(16) FIG. 2A again shows a sectional view through the steering wheel rim 13 of a steering wheel skeleton 10. The latter is overmolded or foam-coated with a matrix 18 (see FIG. 2B), as described in FIG. 1. In the present optional embodiment, the matrix 18 is designed with a recess or groove 19, which extends, in particular, along a rear side of the steering wheel rim 13. The purpose of the recess 19 is to accommodate the zipper and prevent it from causing a bump.

(17) According to the embodiment of the invention illustrated here, the covering material 14 is equipped with zipper halves 20 (FIG. 2C) on its non-visible side 16, which has already been coated with the activatable material 17. For example, the zipper halves 20 are arranged along the longitudinal edges 22 of the covering material 14 and joined, for example stitched, thereto. In this case, the zipper halves 20 are arranged such that the zipper teeth 21 face toward the open longitudinal edges 22 of the covering material 14. The zipper teeth 21 can be concealed by the longitudinal edges 22 of the covering material 14 or be exposed. Unlike what is shown in FIG. 2C, the coating of the covering material 14 with the activatable material 17 can also take place after the application of the zipper halves 20. This is associated with a higher process cost, however.

(18) FIG. 2D shows the process step of applying the covering material 14 that has been coated and provided with the zipper halves 20 to the steering wheel skeleton 10 that has been overmolded with the matrix material 18. The application takes place in such a manner that the zipper halves 20 are arranged over the recess 19 of the matrix material 18. Next, the zipper halves 20 are closed by passing a zipper slider over the rows of teeth of the zipper halves 20 so that the teeth 21 mutually engage one another in a known manner. FIG. 2E shows the state in which the zipper is partially closed. FIG. 2F shows a sectional view through the steering wheel rim 13 with covering material 14 applied and zipper 20 already closed. It can be seen that the zipper halves 20 are accommodated in the recess 19 of the matrix 18 such that the zipper does not bulge outward in the product. It can also be seen that the longitudinal edges 22 of the covering material 14 butt against one another as abutting edges, and conceal the zipper halves 20. Thus, the zipper 20 can neither be seen nor felt in the finished steering wheel.

(19) FIG. 2G shows a variant of the embodiment from FIG. 2F. Here, the recess 19 in the matrix 18 is designed with a greater depth. This makes it possible for the zipper to be pushed into the recess 19 after being closed, and thus be completely contained by the recess 19. In this variant embodiment, the zipper halves 20 are not initially concealed by the longitudinal edges 22 of the covering material 14. Instead, they are only concealed by the longitudinal edges 22 of the covering material 14 after the zipper halves have been closed and pushed into the recess 19. The use of a deeper recess 19 in the matrix 18 also permits the use of profiled zipper types, which are thicker than coil zippers. In this embodiment, as well, the zipper 20 can neither be seen nor felt in the finished steering wheel.

(20) In contrast to the embodiments in FIG. 2E or 2F, the zipper can also be exposed, however, and hence visible. This makes it possible to create special design effects, for example with regard to color design through the use of zippers that have contrasting colors or are fluorescent.

(21) Finally, in the embodiment of the method shown in FIG. 2 as well, the activation of the activatable material 17 takes place to produce an integral connection, in particular an adhesive connection, between the covering material 14 and the matrix 18, and to obtain the finished steering wheel 100. The joining of the longitudinal edges 22 after application of the covering material is considerably simplified through the use of the zipper in comparison with, for example, a manual stitching process. Furthermore, closure by means of a zipper has better reproducibility with regard to smaller tolerances and ensures a uniform closing force.

(22) The finished steering wheel 100 has the following layer sequence: steering wheel skeleton 10/matrix 18/activated material 17 (integral connection)/covering material 14. Optionally, a primer can also be provided between the covering material 14 and the activatable or activated material 17, for example preventing show-through or penetration of the activatable material 17 through the covering material 14 on its visible side 15. The invention shall be explained below using concrete exemplary embodiments.

Example 1

(23) A thermoplastic polyurethane powder was rolled or dusted onto the back side of a dermis (covering material) as the activatable material and permanently bonded to the leather as lamination by means of IR radiation. The leather thus coated was then cut to size by stamping. Zipper halves were stitched onto the longitudinal edges of the leather. The leather blank thus equipped was applied to a steering wheel rim of a steering wheel skeleton foam-coated with a polyurethane matrix, and the zipper halves were closed. Activation of the polyurethane powder took place by means of infrared irradiation at 100 to 120 C. for 5 minutes. After cooling, a uniform adhesive bond between the leather and the polyurethane matrix with high adhesive strength was obtained.

Example 2

(24) A polyimide copolymer powder was rolled onto a carrier mesh and fused at 130 C. The laminate thus obtained was then applied to the non-visible side of leather with the application of light pressure and heat. Next, the leather was cut to size and zipper halves were stitched onto longitudinal edges of the leather blank. In one variant, no zipper halves were used. After application of the leather to a steering wheel foam-coated with a polyurethane matrix, the zipper was closed, or in the variant with no zipper the longitudinal edges were stitched. The structure was heated in an oven at 115 C. for 10 minutes to activate the polyimide copolymer powder. After cooling, a uniform and stable connection of the leather to the polyurethane matrix was obtained.

(25) The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.