Chairs and seats – Movable back – Tiltable
Patent
1993-11-24
1996-07-02
Cranmer, Laurie K.
Chairs and seats
Movable back
Tiltable
29735412, B60N 202
Patent
active
055315046
DESCRIPTION:
BRIEF SUMMARY
For seats, particularly for motor vehicles, that have adjustably reclining backrests, hinge mountings are known that comprise an external mounting, fitted externally on the seat, that can be pivoted, adjusted and secured by self-locking by means of an eccentric planetary gear.
In a hinge mounting of this kind according to German patent 1 680 128 it has been proposed to use a combined finishing stamping and extrusion moulding process to make the bridge part of the mounting integrally with the internal gear of the hinge member, and also the spur gear integrally with its associated hinge member, in each case with the width of the teeth being less than the thickness of the material of the hinge member by an amount corresponding to the extent of the pressing out. As shown by the mechanisms supplied according to this invention, and also as illustrated in the drawings, this difference amounts to about 30%. This reduction of the width of the teeth by about 30% of the thickness of the starting material is disadvantageous, as are the abrupt contours that are formed on the opposite side of the tooth systems that are used by the correspondingly offset protruding tooth system, which exhibit very large variations in cross-section and thereby lead to harmful stress concentrations in their connection regions. For this reason, to obtain adequate stability in such hinge mountings the starting material used has to be thicker than is required by the stresses to which these hinge members would be subjected if they had a more suitable form. This is undesirable on grounds of both weight and cost, particularly in motor vehicles.
To obviate these difficulties, the known German patent 28 34 492 proposes, in the case of the hinge members--likewise made by extrusion moulding--to line up the inner sides of the pressed-out areas with the outer sides of the hinge member in one plane, i.e. to make the width of the teeth the same as the thickness of the starting material and to make the connection between the two parts only through thin wall bridges that run round the fully pressed-out high tooth profile present on the sides of the mountings that are not used as rolling bodies. Because of the form of these tooth profiles extremely high additional bending stresses are introduced. This has the disadvantage that these relatively small wall bridges, which lie predominantly at right angles to the axis and carry bending and compressive loads, are highly stressed because of their small section. The unfavourable orientation of these stresses to the direction of loading also leads to high stress concentrations when they follow very different paths. This, combined with the high bending stresses and the notch effects introduced by the abrupt changes in section, further detracts from the load-bearing capacity, since cracks can also form and tearing can often occur, so that the high security against fracture that is required cannot be guaranteed under high loads. These unfavourable effects of the wall bridges, which are both thin and relatively long on the outside, substantially reduce the durability of the hinge mountings proposed in this patent in case of overloading in the so-called crash situation.
In addition, problems arise related to manufacturing technique owing to influences such as variations in the thickness and differences in the hardness of the starting material, machine settings, tool tolerances and tool wear in maintaining very high accuracy in the load-bearing small sections required by this proposal. For example, with an indentation that is only a few tenths of a millimeter too deep the wall bridges are too thin or are even locally broken through, since these thin places tear prematurely.
In the case of the known proposal in German patent 32 44 399 the unfavourable stress conditions for the tooth bodies again occur. The object here is to increase the width of the teeth of the load-bearing elements--again produced by extrusion moulding--relative to the thickness of the starting material, with the material required for this being made a
REFERENCES:
patent: 4573739 (1986-03-01), Schotter
patent: 4668013 (1987-05-01), Wahlmann
patent: 4717204 (1988-01-01), Tezuka
patent: 4786110 (1988-11-01), Mahling et al.
patent: 4874204 (1989-10-01), Walk
patent: 4895038 (1990-01-01), Pipon et al.
patent: 4986602 (1991-01-01), Blanchard
Hoge Ralf
Schmale Gerhard
Zynch Martin
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