Hinge mechanism for a vehicle seat, and a seat including such a mechanism

A hinge mechanism for a vehicle seat comprises first and second cheek plates connected to each other via a hypocycloid gear driven by a first control shaft, and further comprising a third cheek plate which guides toothed slugs that are normally maintained in engagement with a set of teeth of the second cheek plate by a resiliently biased cam. In this way, the second and third cheek plates are normally secured to each other; however, by actuating a second control shaft secured to the cam, the slugs can be released, thereby enabling the third cheek plate to rotate freely relative to the second cheek plate, thereby enabling the seat to be adjusted quickly.

FIELD OF THE INVENTION 
The present invention relates to hinge mechanisms for vehicle seats and to 
vehicle seats including such mechanisms, each mechanism presenting two 
portions that are mounted to pivot relative to each other. 
The hinge mechanisms in question may be fitted in particular to the front 
seats of cars. 
Of such hinge mechanisms, the invention relates more particularly to those 
which comprise: 
first and second cheek plates that are rotatable relative to each other; 
a hypocycloid gear having first and second circular sets of teeth that mesh 
with each other and that are respectively mechanically linked with the 
first and second cheek plates so that rotation between said first and 
second sets of teeth corresponds to corresponding rotation between said 
first and second cheek plates, the two sets of teeth having respective 
central axes that are parallel and offset relative to each other, referred 
to respectively as the first axis and the second axis; 
a first cam which is mounted to rotate about the first axis to drive 
relative rotation between the first and second sets of teeth; and 
a first control shaft for rotating the first cam. 
BACKGROUND OF THE INVENTION 
An example of such a hinge mechanism is given in particular in document 
EP-A-0 505 229. 
Such a hinge mechanism makes it possible to obtain very precise adjustment 
of the seat, but allows the moving portion of the seat under its control 
to move only relatively slowly, and as a result quite a long time is 
required to move the moving portion through a large distance. 
In addition, when the hinge mechanism is actuated by hand, it is tiring for 
the user to move the moving portion of the seat through such a large 
displacement. 
OBJECTS AND SUMMARY OF THE INVENTION 
A particular object of the present invention is to mitigate those 
drawbacks. 
To this end, the invention provides a hinge mechanism of the kind in 
question which further comprises: 
a third cheek plate which is mounted to rotate relative to the second cheek 
plate about a third axis parallel to the above-mentioned first and second 
axes, the three cheek plates extending in parallel planes perpendicular to 
said axes, the second cheek plate being disposed between the first and 
third cheek plates, one of the second and third cheek plates being secured 
to a third set of teeth extending over at least an arc of a circle 
centered on the third axis and directed radially inwardly, and the first 
and third cheek plates being securable to the above-mentioned portions of 
the seat, respectively; 
at least one slug provided with an outwardly-directed set of teeth suitable 
for co-operating with the third set of teeth, said slug being guided to 
slide in a radial direction by at least one guide secured to that one of 
the second and third cheek plates which is not secured to the third set of 
teeth, and said slug being displaceable between an engaged position where 
it co-operates with the third set of teeth to prevent relative rotation 
between the second and third cheek plates, and a retracted position in 
which said slug does not co-operate with the third set of teeth; 
a second cam for controlling sliding of the slug, said second cam being 
urged by resilient means towards a rest position in which it places the 
slug in its engaged position; and 
a control member for moving the second cam from its rest position towards 
an actuated position in which it enables the slug to slide towards its 
retracted position. 
By means of these dispositions, when the user of the seat seeks to move the 
moving portion of the seat under the control of the hinge mechanism 
through a large displacement, it suffices to actuate the control member 
for the second cam, thereby leaving the first and second cheek plates free 
to rotate relative to each other. The user can then adjust the seat by 
acting directly on the moving portion concerned. 
In contrast, in order to obtain fine adjustment of the seat, the first 
control shaft is actuated, thereby giving rise to relative rotation 
between the first and second cheek plates by means of the hypocycloid 
gear. 
In preferred embodiments of the hinge mechanism of the invention, use is 
also made of one or more of the following dispositions: 
one of the first and second sets of teeth is secured to the first cheek 
plate while the other is secured to the second cheek plate; 
the second set of teeth is secured to a ring gear also including a fourth 
circular set of teeth of diameter different from the diameter of the 
second set of teeth and engaging with a fifth circular set of teeth, one 
of the first and fifth sets of teeth being secured to the first cheek 
plate while the other is secured to the second cheek plate; 
the second cam is mounted to rotate about the third axis, and the control 
member of said second cam is a second control shaft extending 
longitudinally along the third axis; 
one of the first and second control shafts is hollow and receives the other 
of the first and second control shafts; 
the second control shaft is hollow and receives the first control shaft, 
the first shaft being secured to a control knob and the second shaft being 
secured to a handle extending radially outwards between the control knob 
and the cheek plates immediately beyond the periphery of the control knob; 
the first and second control shafts extend in opposite directions; and 
the third set of teeth is secured to the second cheek plate while the guide 
for the slug is secured to the third cheek plate. 
The invention also provides a vehicle seat comprising two portions, in 
particular a seat proper and a seat back, which portions are mounted to 
pivot relative to each other by means of a hinge mechanism as defined 
above, one of said two portions being secured to the first cheek plate 
while the other of said two portions is secured to the third cheek plate.

MORE DETAILED DESCRIPTION 
FIG. 1 is a diagram of a motor vehicle front seat 1 having firstly a seat 
cushion mounted on the floor 3 of the vehicle, and secondly a seat back 4 
which is mounted to pivot relative to the seat cushion 2 about a 
horizontal transverse axis X. 
In this manner, the seat back 4 is displaceable forwards or backwards along 
the directions indicated by double-headed arrow 5, by means of a hinge 
mechanism 6, a first embodiment of which is shown in FIGS. 2 to 5. 
The hinge mechanism 6 comprises: 
a first metal cheek plate 7 that is substantially circular, extending in a 
plane perpendicular to the axis X and, in the example shown, secured to 
the framework 2a of the seat cushion; 
a second metal cheek plate 8 that is likewise circular in shape and that 
extends parallel to the first cheek plate 7, said second plate 8 being 
mounted to rotate about the axis X; 
a third metal cheek plate 9 that is circular in shape and that extends 
parallel to the first two cheek plates, the second cheek plate 8 being 
sandwiched between the first cheek plate 7 and the third cheek plate 9, 
and the third cheek plate 9 being secured to the framework 4a of the seat 
back in the example shown; 
a metal band 10 having an inwardly open channel section profile surrounding 
the periphery of the first and third cheek plates 7, 9 so as to co-operate 
therewith to form a closed box; 
a hypocycloid gear 11 interposed between the first and second cheek plates; 
and 
a locking mechanism 12 interposed between the second and third cheek 
plates. 
Firstly, in conventional manner, the hypocycloid gear 11 comprises the 
following: 
a circular metal first cam 13 extending in a plane perpendicular to the X 
axis and eccentric relative to said axis; 
a control shaft 14 extending longitudinally along the X axis through the 
first cheek plate 7 and secured to the first cam 13, said control shaft 
being actuated in the example described by manually rotating a control 
knob 15 fixed to the end thereof; and 
a ring gear 16 having two outside sets of teeth and mounted to rotate 
freely on the first cam 13, having both a first circular external set of 
teeth 17 centered on the axis 13a of the first cam, and a second external 
circular set of teeth 18 likewise centered on the axis 13a or the first 
cam, but smaller in diameter than the first set of teeth 17. 
The first set of teeth 17 of the ring gear engages with an 
inwardly-directed circular set of teeth 19 on the first cheek plate 7, 
while the second set of teeth 18 of the ring gear engages with an 
inwardly-directed circular set of teeth 20 on the second cheek plate, both 
of said sets of teeth 19 and 20 being centered on the X axis. 
Also, the locking mechanism 12 further comprises, likewise in conventional 
manner: 
an inwardly-directed circular set of teeth 21 belonging to the second cheek 
plate 8 and preferably centered on the X axis (or optionally centered on a 
third axis that is different from the X axis and from the axis 13a), said 
set of teeth 21 being formed on the side of the second cheek plate that 
faces the third cheek plate 9; 
three metal slugs 22, each having an outwardly-directed set of teeth 23 
suitable for engaging in the inwardly-directed set of teeth 21 of the 
second cheek plate, said three slugs being guided in radial sliding by 
projections 24 belonging to the third cheek plate; 
a second cam 25 that is rotatable about the X axis, consisting in a cutout 
metal plate disposed in the same radial plane as the slugs 22, the second 
cam 25 being angularly displaceable between a cam rest position in which 
it urges the slugs towards an engaged position in which the 
outwardly-directed teeth 23 of the slugs co-operate with the 
inwardly-directed teeth 21 of the second cheek plate, and a cam actuated 
position in which the second cam enables the slugs 22 to reverse towards a 
retracted position in which their outwardly-directed sets of teeth no 
longer co-operate with the inwardly-directed teeth 21 of the second cheek 
plate; 
three metal springs 26 urging the second cam towards its rest position; and 
a control shaft 27 secured to the second cam 25 and extending 
longitudinally along the X axis through the third cheek plate 9. 
In the example shown, the control shaft 27 is secured to a radial lever 28 
whose free end is extended axially by a handle 29, which handle projects 
to the outside of the seat back 4 through a circularly arcuate slot 30 
formed in the framework 4a of the seat back. 
By means of the above dispositions, by turning the control knob 15 
manually, it is possible to perform fine adjustment of the inclination of 
the seat back, while by actuating the handle 29, the seat back is allowed 
to pivot freely, thereby making it possible to achieve large angular 
displacement of said seat back quickly and easily. 
In the variant shown in FIG. 6, the hinge mechanism 6 differs from the 
mechanism shown in FIGS. 2 and 5 solely in the following respects: 
the first cheek plate 7 is secured to the framework 4a of the seat back 
while the third cheek plate 9 is secured to the framework 2a of the seat 
proper, said third cheek plate being disposed towards the outside of the 
seat; 
the control shaft 27a of the second cam 25 is pierced by a central bore, 
and said control shaft extends towards the outside of the seat through the 
third cheek plate 9 and through the framework 2a of the seat proper; 
the control shaft 14 of the first cam 13 extends towards the outside of the 
seat through the central bore of the above-mentioned control shaft 27a, 
rather than through the first cheek plate 7; and 
the lever 28 extends radially outwards between the control knob 15 and the 
framework 2a of the seat cushion, immediately outside the periphery of the 
control knob 15. 
In the second embodiment of the invention (FIG. 7), the hinge mechanism 6 
differs from the hinge mechanism of FIGS. 2 to 5 in the following 
respects: 
the hypocycloid gear 11 does not have a ring gear 16, the 
outwardly-directed teeth 17 being secured to the second cheek plate 8, 
which second cheek plate is mounted to rotate freely on the first cam 13; 
and 
the second and third cheek plates 8 and 9, the inwardly-directed set of 
teeth 21, the second cam 25, and the control shaft 27 are all centered on 
the axis 13a of the first cam, and no longer on the X axis. 
In this latter embodiment, when the control knob 15 is rotated, the second 
and third cheek plats 8 and 9 are rotated with nutating motion about the X 
axis.