This invention concerns joints between two parts or more, and aims at improving the mechanical strength of such joints, particularly in cases where at least one of the assembled parts is relatively thin, such as the joining of a sheet metal part to another more rigid part. It applies to joints between various parts used in the frames of automobile seats, and notably the joining of a hinge mechanism between the seat back and seat pan to a flange on the seat back or pan. Such hinge mechanisms, moreover, are well known and provide possibilities of adjusting the tilt angle of the seat back with respect to the seat pan, and locking it in various positions.
These joints are conventionally made by welding, riveting, bolting or crimping.
Welded joints generally display good mechanical strength, but welding processes cannot be used, for example, to assemble dissimilar metals such as aluminium parts to steel parts. Furthermore, welding cannot be used to join painted or coated parts or, for example, to assemble two parts of an automobile seat that have already been padded.
The other methods of assembly sometimes do not ensure adequate mechanical strength, particularly when one of the parts, such as the flange, is thin.
In automobile seat applications, the joint between the mechanisms hinging the seat back on the seat pan and pan frames made of relatively thin sheet metal must be particularly strong and free of any play liable to create grating noises or any other form of discomfort.
We know, for example, of bolted attaching systems in which the hinge mechanism comprises two half-shells, usually in the form of a disk, that are interconnected and can pivot with respect to each other around the pivoting axis of the seat back, and comprising between them, in a manner known in itself, the mechanical components for position adjustment and locking. Each half-shell is attached to the corresponding frame of the seat back or pan by shouldered bolts, aligned parallel with the axis and therefore subjected to shear stresses under the forces tending to pivot the seat back. The inevitable play between the bolts and the seat pan or seat back frames is eliminated by the tightening of the bolts, creating friction between the hinge mechanism and the sheet metal frame. However, the duration of absence of play depends on controlling bolt tightness and the friction at the interfaces, which is impossible to achieve in practice under mass production assembly conditions.
We know of yet other attaching systems in which the hinge mechanisms feature in addition tapered bosses on the outer face of the half-shells, which fit into raised collars provided on the sheet metal of the seat back or seat pan, to avoid the risk of play between the hinge mechanism and the seat frame. A bolted attachment is then applied, for example, on other bosses provided for this purpose. The elimination of play in this case results from the tapered boss coming into contact with an internal edge of the corresponding collar, which risks leading to the development of play due to plastic deformation of the very limited area of contact. Moreover, the areas used for tightening and those used for positioning to eliminate the play, are different, and in principle are distributed around the circumference. The consequence of this is that the flatness tolerances of the parts and the relative flexibility of the frame sheet metal do not always ensure good tapered boss-to-collar contact on all the bosses.
We also know, through document FR-A-2734609, of a system for joining one part to another thin part, for example a thin sheet, by means of an assembly component connected to the first part and passing through a hole in the second part, and a thrust component connected to the said assembly component such that it is applied axially against the second part to push it up against the first. In order to increase the cross-sectional area subjected to shear stresses when a force is directed along the plane of the contact surface between the parts, the hole features a raised collar formed directly in the sheet metal of the second part, which is gripped radially in a bore made in the thrust component, such as a nut.
We also know, for example through document DE-A-1217144, of sheet metal attaching systems using a bolt or taper-headed stud placed in a raised collar made on a sheet, where the bolt head abuts axially on the rounded edge between the sheet and the raised collar. The part to be attached to the plate is held against the sheet by a nut screwed onto the said bolt. The nut is shaped so as to bear against the second part only around the collar and not directly on it. Alternatively, a conventional nut can be used, but in this case with the addition of a special bell-shaped washer that covers the collar without actually pressing on it. This system does not however solve the problem of lateral play that might subsist or appear between the assembled parts when the assembly is in service.
The aim of this invention is to provide a solution to the problems mentioned above, in particular for attachments on relatively thin sheets such as seat frame flanges. It aims more specifically at improving the strength of joints made using assembly components that pass through the assembled parts, notably in the direction transverse to the axis of the assembly component. It also aims at preventing any lateral play between the assembled parts and the means of assembly, and guaranteeing this absence of play even further to repeated shear loads in alternating direction, such as those to which the hinges between an automobile seat back and pan are exposed, and this without complicating the assembly operations.
With these aims in view, the subject of the invention is an automobile seat featuring a seat back flange and a seat pan flange linked by a hinge mechanism attached to at least one of the said flanges by a joining system comprising at least one assembly component connected to the hinge mechanism and passing through a hole in the flange, said hole featuring a raised collar that is gripped radially in a bore made in a thrust component connected to the assembly component such that it applies axial thrust against the flange,
characterised in that
the raised collar is tapered, at least in part,
the assembly component features a tapered male section of appropriate diameter to fit into the tapered collar when the hinge mechanism is assembled with the flange, and
the bore of the thrust component is also tapered to form a female tapered section that grips the tapered collar of the said bore and the said male tapered part when the thrust component is pressed up against the flange.
The raised collar preferably has an apex taper angle of between 15 and 30xc2x0.
This angle is preferably of the roughly same value as that of the tapered part of the assembly component, which means that the assembly component fits into the raised collar with slight play to begin with, then tends to centre automatically as the two tapered sections fit together.
The dimensions and tapers of the bore of the raised collar and the tapered section of the assembly component are such that, at least during the first assembly, the hinge mechanism abuts against the flange before the female cone of the collar tightens on the male cone of the assembly component. In the most common application of the invention, where several Joining systems are used to assemble the mechanism on the flange, this guarantees correct and constant positioning of these two parts in the direction of the hinge axis, for all the joining systems.
The dimensions and tapers of the bore of the raised collar and the tapered section of the assembly component are also such that, when the two parts are bearing against each other in their final assembly position, there is no lateral play whatsoever between the raised collar and the assembly component. On the other hand, the lateral play existing between the smaller diameter part of the male tapered section and the larger diameter section of the collar at the start of fitting, ensures the fitability, that is to say allows at least the start of engagement of the male tapered section in the collar, even if the collar and the assembly component are not perfectly aligned, which can happen frequently owing to the manufacturing tolerances of each part, when the two parts are assembled at several points as indicated above, or when their relative positioning is otherwise ensured.
The taper of the bore of the thrust component enables it to fit easily over the tapered external surface of the collar and if necessary to press the said collar axially until the flange abuts on the mechanism, then radially press the collar between the male cone of the assembly component and the female cone of the thrust component causing plastic deformation of the said collar, which is designed to be deformable for this very purpose.
If the collar is centered exactly on the assembly component and the thrust component, and has the same taper, there is simply compressive plastic deformation of the collar material between the components.
In the event of misalignment, taper defects, or even an intentional difference in the tapers of the tapered section of the assembly component and the collar, the gripping of the thrust component causes plastic deformation of the collar in order to take up the lateral play and ensure an adequate contact area between the tapered sections to prevent any later plastic deformation that could cause such play to develop again. One can thus, for example, give the collar a different pre-assembly taper to that of the tapered section of the assembly component, or even make a virtually cylindrical collar, and then make use of its deformability, so that during assembly it is pressed by the thrust component and perfectly matches the taper of the tapered male section of the assembly component.
If there is an offset between the axes of the collar and the assembly component, the deformability of the collar can also compensate for this by moving laterally in its entirety with respect to the flange, to fit precisely over the tapered part of the assembly component connected to the hinge mechanism.
Whatever the case, the plastic deformation of the collar creates a stress on the thrust component that will jam it and prevent any future loosening.
In a preferential arrangement, the assembly component is threaded, for example such as a stud fixed to the hinge mechanism, and the thrust component is a nut. The thrust component could nevertheless be riveted to the assembly component.
In a complementary preferential arrangement, the stud has a head and a bushing that carries the said tapered section and abuts against the hinge mechanism when the head is joined to the hinge mechanism. The stud head is preferentially riveted to the hinge mechanism.
In other arrangements:
the stud is fixed on a boss of the hinge mechanism, with the flange in axial abutment on the boss.
the nut has a tapered seat in which is cut a tapered bore.
Other characteristics and advantages will be presented in the description given as an example of one method of producing the invention, and its application to the assembly of the hinge between an automobile seat pan and back.