Joints and connections – Utilizing thermal characteristic – e.g. – expansion or...
Reexamination Certificate
1999-03-29
2001-07-10
Kim, Harry C. (Department: 3629)
Joints and connections
Utilizing thermal characteristic, e.g., expansion or...
C403S329000, C403S353000
Reexamination Certificate
active
06257794
ABSTRACT:
The present invention relates to a plastics material piece suitable for being mounted in sliding manner on a support.
BACKGROUND OF THE INVENTION
Motor vehicle bodywork parts are secured to the structure of the vehicle by add-on mounts which hold them in position throughout all stages of manufacture of the vehicle subsequent to them being put into place, and also throughout the lifetime of the vehicle.
The steps in vehicle manufacture subsequent to bodywork parts being put into place include the step of electrophoresis which consists in immersing the entire vehicle, including its bodywork parts, in a bath, and then passing the vehicle through an oven at a temperature lying in the range about 180° C. to 220° C. so as to treat the structure of the vehicle and all of the metal parts it includes against corrosion, and also a painting step which comprises a stage of baking at a temperature lying in the range about 140° C. to 170° C.
Those various operations are designed for bodywork parts made of sheet metal.
However, bodywork parts made of plastics material withstand such treatment less well, particularly the baking treatment for paintwork.
During heating, the plastics material parts expand to a much greater extent than do the structural parts of the vehicle, and as a result a large amount of differential expansion arises between the structure of the vehicle and the bodywork parts that are mounted thereon. As a result the bodywork parts made of plastics material deform and warp or form corrugations that spoil the appearance of the vehicle.
In addition, differential expansion can occur during the lifetime of the vehicle, given that its parts can reach temperatures of close to 80° C., and that also needs to be taken into account in the way bodywork parts are mounted to the structure of a vehicle.
Finally, another problem arises because of the shrinkage to which thermoplastics material parts are subject after a rise in temperature and over time, which phenomenon is known as “post-shrinkage”, giving rise to bodywork parts moving relative to the structure of the vehicle, independently of phenomena of differential expansion.
To solve those drawbacks, add-on mounts are used that enable a bodywork part to slide relative to the structure of the vehicle. Such mounts are referred to as “sliding mounts”.
French patent application No. 96 04317, published under the number 2 747 091, describes such a sliding mount, which is provided with spring blades for returning it towards a privileged position.
That sliding mount gives rise to various problems which are associated with the presence of said spring blades.
The privileged position of the sliding mount corresponds to an equilibrium position in which the spring blades exert opposite forces of the same amplitude on the mount. Consequently, this position depends on the stiffnesses of the two blades and can vary from one mount to another if the stiffnesses of the blades are not stable in production.
Furthermore, the plastics material used for making the sliding mount is preferably creep-resistant, thereby making it rather brittle and not very flexible, whereas the spring blades need on the contrary to be elastically deformable.
As a result, in order to make the sliding mount, it is necessary to select an intermediate plastics material that provides a compromise between those two contrary requirements, or else the spring blades must be made of an elastic material that is different from the remainder of the sliding mount.
OBJECTS AND SUMMARY OF THE INVENTION
The present invention seeks to provide a novel sliding mount which presents the advantages of being easy to put into place on a bodywork part, and of prepositioning itself relative to said part so as to facilitate the engagement of members for mounting the bodywork part in their housings, without representing the above-mentioned drawbacks.
The present invention provides a sliding mount for a part made of plastics material and having at least one thin wall that is to be mounted in sliding manner on a support via its thin wall, the thin wall having an elongate opening therein with two longitudinal edges that are substantially parallel at least over a portion of their length, the mount comprising a spacer that is separate from the part, that is thicker than the thin wall, and that is suitable for sliding in the opening between the two longitudinal edges thereof, wherein the spacer comprises an elastically deformable portion bearing slidably against the thin wall of the part when the spacer slides in the opening, the thin wall having a coupling shape organized in such a manner that when the spacer is in a privileged position relative to the opening, the deformable portion of the spacer couples with the thin wall.
In other words, while the spacer is sliding in the opening, the elastically-deformable portion snaps into the coupling shape of the thin wall, thus defining a hard point in the stroke of the spacer corresponding to the privileged position of the spacer relative to the opening.
It will be understood that the privileged position of the invention is defined as being the prepositioning position of the spacer on the bodywork part.
In the invention, the term “thin wall” is used to mean a portion of the piece which has one dimension that is very small compared with its other two dimensions.
Preferably, the area of the spacer that bears against the support is large enough to prevent any creep of the spacer, including when its temperature is high.
This area is selected as a function of the conditions desired and as a function of the material used.
In the event of the spacer being secured to the support by means of a screw, an appropriate choice of bearing area makes it possible, in particular, to avoid using a lock washer as is commonly used for keeping a screw tight.
In a particular embodiment, the spacer has tabs for holding the thin wall within the thickness of the spacer, and one of the longitudinal edges of the opening has one or more notches shaped to correspond to the shape of the tab(s) of the spacer, thereby enabling the spacer to be put into place in the opening.
In this embodiment, the position in which the spacer is put into place in the opening is remote from its privileged position.
Preferably, provision is made for the tabs to be asymmetrical on opposite sides of the spacer so that the notches in the opening allow the spacer to be inserted in a single orientation only in which the elastically deformable portion of the spacer and the coupling shape of the thin wall are on the same side.
In a preferred embodiment of the invention, the elastically deformable portion of the spacer is constituted by a resilient tongue provided with an outwardly directed projection which bears against one of the longitudinal edges of the opening, the longitudinal edge in question having, as its coupling shape, an indentation in which the projection of the resilient tongue engages when the spacer is occupying its privileged position relative to the opening.
According to the invention, the privileged position of the spacer relative to the opening is such that the spacer can move inside the opening in a first direction to compensate for post-shrinkage of the thermoplastic material, and in a second direction, opposite to the first, to compensate for differential expansion between the part made of thermoplastic material and the support.
Since expansion differences are preponderant, the stroke available to the spacer in the opening in the second direction is preferably greater than that available to it in the first direction.
In a preferred embodiment of the invention, the elastically deformable portion of the spacer, e.g. the resilient tongue provided with a projection, is integrally molded with the spacer.
In a particular embodiment of the invention, the spacer has a head covering it completely, the head being wider than the opening so as to be incapable of passing through it, in order to maintain the thin wall in the thickness of the spacer.
REFERENCES:
patent: 3456706 (1969-07-01), Ollis
patent: 4436269 (198
Courtois Sébastien
Gobled Patrice
Jacquemard Claude
Rossetto Marc
Compagnie & Plastic Omnium
Kim Harry C.
Schweitzer Cornman Gross & Bondell LLP
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