The present invention relates to seat rails in a motor vehicle, and more particularly to a method of manufacturing optimised seat rails.

Customarily a seat slide assembly in a vehicle comprises a first elongated (bottom) rail fastened to the vehicle floor and a second elongated (top) rail mounted on the first rail in a sliding and locking manner. The second rail is also applied for fastening of seats and safety belts for occupants of the vehicle.

Due to a general tendency to reduce the vehicle weight rails extruded in light metals, e.g. made of Al-alloys, have recently replaced rails made of steel. A drawback of the applied extrusion manufacturing technique is that the provided rails exhibit uniform cross-sections along their longitudinal extension. Since the load imposed on the rails varies significantly along their longitudinal extension, the rear part of the second (top) rail accommodating fastening means (apertures) for the safety belts exhibits larger dimension than the remaining front part of the rail. Currently applied solutions to achieve the above configuration of the seat rails are either to provide a whole rail with sufficient wall thickness and thus accidentally increase the weight or to remove

Another viable way to go is to reinforce the rear part of the rail by attachment of external members, thus increasing the complexity and number of components in the rail assembly.

Consequently, it is an object of the present invention to provide a novel manufacturing method/principle resulting in an optimised design of seat rails characterized by a unitary, light weight rail manufactured with minimum material spill.

This and other objects of the present invention are achieved by provision of a manufacturing method and the resulting seat rail as claimed in the accompanying claims 1 and 5, respectively.

The invention will be described in details with reference to the attached drawings, Figs. 1-3, where

Figs. 1a,b,c,d show in a vertical cross-sectional view a different configuration of an intermediate extruded shape usable for manufacturing of rails according to the invention,

Fig. 2 illustrates schematically the cutting step resulting in provision of two identical rails, and

Fig. 3 shows in a partial perspective view the seat rail applied as the top rail in a seat rail assembly.

Referring to Fig. 1a two co-extruded rails (1 ,2) of identical cross-sectional configuration covering the requested sliding and fastening functions are inter-

connected along a reinforcing rib 3 laterally protruding from the side of the vertical rail wall 4. This unitary shape extruded in Al-alloy in one simple operation provides an intermediate product for the following single cutting operation as illustrated in Fig. 2 by the resulting separated rails 1 ,2. By alternately moving the cutting tool (not shown in the Figure) back and forth (up and down), thus following the upper side and the bottom side of the reinforcing rib 3, two identical rails ready to use are provided in one single cutting operation. Fastening apertures 11 ,22, respectively will then be provided in a conventional manner in the vertical side walls in the vicinity of the provided reinforcing rib 3.

Fig. 1 b shows an alternative cross-sectional configuration of the intermediate extruded shape comprising two co-extruded rails 1 ,2 where the reinforcing rib 3 protrudes laterally from both sides of the vertical rail wall 4.

Another variant of the intermediate extruded shape illustrated in Fig. 1 c exhibits no reinforcing rib between the co-extruded rails 1 ,2.

This particular embodiment will, after applying the above cutting pattern described in connection with Fig. 2, also result in two identical rails exhibiting different heights along their longitudinal extension and where the "elevated" part of the rails represent a local reinforcement of the rail in the area of fastening apertures (not shown in the Figure).

There is also a possibility to conduct "an asymmetric" longitudinal cut so that two rails having different longitudinal extension of the elevated part can be provided in one operation without spill of the material.

Still another configuration of the extruded intermediate shape is shown in Fig. 1d. Two rails of non-identical cross-sectional configuration 1 ,2 are co-extruded comprising in common a reinforcing rib 3 laterally protruding from the vertical rail wall 4.

An apparent advantage of this altemative configuration is the possibility to provide two different rails in a simple step cutting operation by the alternating movement of the cutting tool along the upper and the bottom side of the reinforcing rib 3.

Fig. 3 illustrates in a perspective view the special design of the resulting rail applied as a top rail 1 comprising a higher part provided with the laterally extending top rib 3 representing the reinforced part of the rail exhibiting fastening apertures 11 for safety belts.

A perpendicularly movable locking means 5 ensures in a conventional manner attachment of the top rail 1 to the bottom rail 7.

The new method of manufacturing seat rails as illustrated above by way of examples of cutting different embodiments of the intermediate extruded shapes according to the present inventive principle results in a reduced number of processing/- manufacturing steps, less use of material and consequently in substantial costs savings.