Vehicle part intended to be welded to a bodywork element

Abstract

A part of a motor vehicle is made from plastic material and includes at least one wall configured to be welded to a bodywork element. The wall includes at least one protruding element defining a weld surface configured to form a point of contact with said bodywork element. The part includes, around the protruding element, at least one stress relief area for relieving stresses experienced by the protruding element.

Claims

1. Part of a motor vehicle made from plastic material, comprising at least one wall to be welded to a bodywork element, said wall comprising at least one protruding element defining a weld surface to form a point of contact with said bodywork element, wherein the part comprises, around said protruding element, at least one stress relief area for relieving stresses experienced by the protruding element.

2. Part according to claim 1, wherein the stress relief area is a flexible area of the wall, configured to relieve the stresses in the three dimensions in space.

3. Part according to claim 1, wherein the stress relief area comprises at least one flexibility element, chosen alone or in combination from at least one of the following elements: a smaller cross-section than a local cross-section of the wall, a recess of material, a cutout, and a portion made from a material that is more flexible than a local material of the wall.

4. Part according to claim 3, wherein the at least one flexibility element forms a ring around the protruding element.

5. Part according to claim 4, wherein the stress relief area comprises several flexibility elements distributed around the protruding element.

6. Part according to claim 1, wherein the protruding element locally forms a protrusion of height approximately 1.5 mm.

7. Part according to claim 1, wherein the part is made from one of the following materials: polypropylene (PP), polycarbonate-acrylonitrile butadiene styrene (PC-ABS), and acrylonitrile styrene acrylate (ASA).

8. Part according to claim 1, wherein the at least one protruding element comprises at least three protruding elements.

9. Part according to claim 3, comprising at least two flexibility elements.

10. Part according to claim 9, wherein each of the at least two flexibility elements have a circular arc shape and the at least two flexibility elements are arranged to substantially form a ring around the protruding element.

11. Part according to claim 9, wherein each of the at least two flexibility elements have a U-shape and the at least two flexibility elements are arranged to substantially form a ring around the protruding element.

12. Part according to claim 11, wherein at least one of the at least two flexibility elements is a different size than at least one other of the at least two flexibility elements.

13. An assembly comprising a bodywork element and a part according to claim 1.

14. Assembly according to claim 13, wherein the bodywork element is made from one of the following materials: polypropylene (PP), polycarbonate-acrylonitrile butadiene styrene (PC-ABS), acrylonitrile butadiene styrene (ABS).

15. Assembly according to claim 13, forming a bodywork part of a motor vehicle.

16. Assembly according to claim 15, wherein the assembly is a tailgate.

17. Assembly according to claim 15, wherein the assembly is a spoiler, the bodywork element is a spoiler outer surface, and the bodywork part is a spoiler reinforcement.

18. Assembly according to claim 15, wherein the assembly is a bumper.

19. Assembly according to claim 13, wherein the protruding element is bonded to the bodywork part.

20. Assembly according to claim 13, wherein the bodywork element is welded to the part.

Description

(1) The invention will be better understood on reading the accompanying figures, which are given solely by way of example and not limiting in any way, in which:

(2) FIG. 1 illustrates an example of a part of a motor vehicle made from plastic material according to the invention, and a bodywork element to which the part is intended to be welded;

(3) FIG. 2A illustrates a particular embodiment, in which the stress relief area comprises four flexibility elements, from the circular arc-shaped openings, arranged so as to substantially form a ring around the protruding element;

(4) FIG. 2B illustrates another particular embodiment, in which the stress relief area comprises two flexibility elements, from the U-shaped openings, arranged so as to substantially form a ring around the protruding element;

(5) FIGS. 3A and 3B illustrate a detail of a weld area, in cross-section; FIG. 3A illustrates the arrangement of the part and the bodywork element before welding; FIG. 3B illustrates the arrangement of the part and the bodywork element after welding.

(6) We now refer to FIG. 1 which illustrates an example of a part 10 of a motor vehicle made from plastic material according to the invention, and a bodywork element 20 to which the part 10 is intended to be welded. According to the example, it is a spoiler reinforcement intended to be welded to a spoiler outer surface to form a spoiler. The part 10 comprises at least one wall 30 intended to be welded to the bodywork element 20.

(7) The part 10 can be made from one of the following materials: polypropylene (PP), polycarbonate-acrylonitrile butadiene styrene (PC-ABS), acrylonitrile styrene acrylate (ASA), acrylonitrile butadiene styrene (ABS).

(8) We now refer to FIG. 2A which illustrates a detail of the part 10 of a motor vehicle and we also refer to FIG. 2B which illustrates a design alternative of the same detail of the part 10 of a motor vehicle. The wall 30 comprises at least one protruding element 40 defining a welding surface intended to form a point of contact 50 with the bodywork element 20. The protruding element 40 forms a protrusion, for example having a height “h” between 0.1 and 5 mm (measurement taken between the two planes, see FIG. 3A) for a nominal thickness of the part 10 of 2.4 to 3.8 mm. This protrusion allows freedom of movement of the part 10. The welding area 50 has a thickness of 1.0 to 3.8 mm.

(9) The part 10 generally comprises a set of protruding elements 40, in order to weld the part 10 to the bodywork element 20.

(10) The part 10 comprises around this protruding element 40 at least one stress relief area 60 for relieving stresses experienced by the protruding element 40. Preferably, this area 60 relieves the stresses in the three dimensions in space.

(11) The “stress relief area” designates an area of the wall 30 used to relieve at least some of the stresses experienced by the protruding element 40. These stresses may be due to: the pressure applied to press the part 10 and the bodywork element 20 against each other during the welding operation; a differential expansion between the part 10 and the bodywork element 20 once welded together.

(12) According to one embodiment, the stress relief area 60 is a flexible area of the wall 30, configured to relieve the stresses in the three dimensions in space. Due to its flexibility, this area allows the point of contact to move in all directions (angular flexibility).

(13) The flexibility of the stress relief area 60 is obtained by providing the wall 30 locally with flexibility elements 70.

(14) These flexibility elements 70 are chosen alone or in combination from the following elements: a smaller cross-section than the local cross-section of the wall; to increase the mechanical strength, ribs may be added locally; a recess of material; such a recess may be formed when moulding the part 10, or during a rework operation such as punching or machining for example; a cutout; a portion made from a material more flexible than the local material of the wall.

(15) The position relative to the protruding element 40, the shape and the number of flexibility elements 70 around the welding area, i.e. around the protruding element 40, depend on the required flexibility of the area 60. This shape and this number also depend on the design constraints of the part 10. There could therefore be between 1 and 8 flexibility elements 70 around the protruding element 40. Depending on the moulding constraints and the space available on the part, the shape of the flexibility elements 70 may be different. An element 70 may thus be circular or rectangular, without these shapes being limiting. To ensure good efficiency, the element 70 will be located near the protruding element 40. According to a preferred embodiment, the one or more flexibility elements 70 substantially form a ring around the protruding element 40. If the stress relief area 60 comprises several flexibility elements 70, they are distributed around the protruding element 40.

(16) The flexibility elements 70 also allow “flat spring” type areas 90 to be located inside the stress relief area 60. The material cross-section of the wall 30 is in fact reduced locally by the elements 70 and this stress relief area 60 therefore deforms more easily than the rest of the wall 30. We now refer to FIGS. 3A and 3B which illustrate a detail of a weld area 80. FIG. 3A illustrates the arrangement of the part 10 and of the bodywork element 20 before welding. We see that the contact between the point of contact 50 and the bodywork element 20 is not sufficient (it is not flat on flat). Pressure must therefore be applied to the part 10 and/or the bodywork element 20. FIG. 3B illustrates the arrangement of the part 10 and of the bodywork element 20 after applying this pressure (the arrow on FIG. 3B shows the direction of this pressure), and after welding. The stresses applied to the protruding element 40 are relieved by the stress relief area 60.

EMBODIMENT

(17) FIG. 2A illustrates a particular embodiment, in which the stress relief area 60 comprises four flexibility elements 70. Each flexibility element 70 is a recess of material in the shape of a comma or circular arc. The flexibility elements 70 have different sizes and are arranged so as to substantially form a ring around the protruding element 40. In this case, there are 6 “flat spring” type areas 90 inside the stress relief area 60.

(18) FIG. 2B illustrates another particular embodiment, in which the stress relief area 60 comprises two flexibility elements 70. Each flexibility element 70 is a U-shaped recess of material. The flexibility elements 70 have different sizes and are arranged so as to substantially form a ring around the protruding element 40. A single U-shaped recess could be considered if it is directed so as to allow angular flexibility in the locally most relevant axis of rotation to place the surfaces in contact and allow welding under good conditions. In this case, there are 2 “flat spring” type areas 90 inside the stress relief area 60. The invention also concerns an assembly of a bodywork element 20 and a part 10 according to the invention. The bodywork element can be made from one of the following materials: polypropylene (PP), polycarbonate-acrylonitrile butadiene styrene (PC-ABS).

(19) According to one embodiment, the assembly forms a bodywork part of a motor vehicle such as a tailgate, a bumper or a spoiler.

(20) In the case of a spoiler for example, the bodywork element 20 is the spoiler outer surface, and the part 10 is the spoiler reinforcement.

(21) The welding method consists of several steps. The reinforcement is positioned against the bodywork part. A stress is applied to press the two parts together at various points, locally. According to the invention, the special design allows the surface to be welded to move so that the plane of the area to be welded is in the plane of the bodywork part, locally, i.e. at the location where the weld will be made.

(22) The overall direction of the reinforcement and of the bodywork part remains unchanged. Welding is then carried out. The stresses applied to the reinforcement and the bodywork part can be released. The residual stresses are reduced by the design according the invention compared with a conventional design. Less material in fact tends to return to its initial shape, so there is less elastic return. Consequently, the bodywork part is less deformed locally by these residual stresses on the welded surface, but it is in particular the local area of the reinforcement which undergoes the deformation. This local area of the reinforcement follows the direction of the wall of the bodywork part more easily due to the freedom of movement provided by the flexibility areas. The local behaviour is similar to that of a flat spring.

LIST OF REFERENCES

(23) 10: part of a motor vehicle made from plastic material 20: bodywork element to which the part 10 is intended to be welded 30: wall of the part 10 intended to be welded to the bodywork element 20 40: protruding element 40 of the wall 30 50: area of contact of the protruding element with the bodywork element 20 defining a welding surface 60: stress relief area for relieving stresses experienced by the protruding element 40 70: flexibility element of the stress relief area 60 80: weld area 90: “flat spring” type area of the stress relief area 60