Vehicle seat assembly with a spring-biased pivotable seat back

1. A vehicle seat having two opposite sides,

a seat back mounted on a seat cushion to pivot about a transverse horizontal pivot axis X-X by a recliner mechanism that can be moved between

a locked position in which the recliner mechanism prevents the seat back from moving relative to the seat cushion, and

an unlocked position in which the recliner mechanism allows the seat back to pivot relative to the seat cushion about the pivot axis, the seat assembly comprising

a torsion bar subassembly with one or more elongate torsion bars extending along an axis Y-Y at least partially between the opposite sides,

each bar of the torsion bar subassembly having

an end affixed to one of the seat back and the seat cushion and

another end affixed respectively to the seat cushion and the seat back so that the torsion bar subassembly exerts a forwardly directed force on the seat back over a limited range of arcuate travel;

each bar of the torsion bar subassembly having a central portion extending substantially parallel to the pivot axis X-X between first and second lever arms,

the first lever arm formed at one end of a central portion extending perpendicular thereto and being attached to a seat cushion, and the second lever arm formed at the other end of the central portion also extending perpendicularly thereto and being attached to the seat back,

each of the first and second lever arms being secured by a pivot bracket that anchors the associated lever arm and allows it to rotate therewithin during forward and rearward arcuate movement of the seat back,

wherein the axis Y-Y is located rearwardly of axis X-X.

2. A seat according to claim 1 , in which the one or more torsion bars is limited to one torsion bar.

3. A seat according to claim 1 , in which the one or more torsion bars is limited to two torsion bars.

4. A seat according to claim 3 , in which the two torsion bars are wrapped around each other by one turn.

5. A seat according to claim 4 , in which each torsion bar lies parallel to the other when the seat back lies in a forward position that is about 30 degrees ahead of a generally vertical position.

6. A seat according to claim 1 , in which the seat back is adapted to pivot relative to the seat cushion under the influence of the torsion bar subassembly over a range of zero to about 20 degrees.

7. A seat according to claim 6 , in which the seat back is adapted to pivot relative to the seat cushion between a table position in which said back is folded down substantially horizontally over the seat cushion, and a recumbent position in which the back is tilted rearwardly into a substantially horizontal position.

8. A seat according to claim 1 , in which the torsion bars are made of steel and have a diameter lying in the range 5.70 mm to 6.30 mm.