Under-frame for a motor vehicle seat

1. An under-frame apparatus for a motor vehicle seat including:

a basic body;

a seat frame adjustable relatively with respect to the basic body between an utmost rear position and an utmost front position;

a pair of front and rear vibration levers joint-connected to the basic body and the seat frame, respectively;

an adjustment arm joint-connected one of the front and rear vibration levers and including a saw teeth engagement part on a free end region thereof;

an adjustment device rotatably coupled to the seat frame and engaged to the free end region of the adjustment arm so as to adjust a position of the seat frame with respect to the basic body, wherein the adjustment device includes a pinion gear engaged to the adjustment arm and driven by an operation unit; and

an elastic member attached to the seat frame and applying a restoring force to the seat frame toward a starting position,

wherein the operation unit includes an operation lever coupled to a clamping roller,

wherein the elastic member is a torsion bar spring fixed to a seat frame cross arm and a seat frame side part, and

wherein the torsion bar spring applies the restoring force to the seat frame toward the starting position such that the rear vibration levers progress upwards with respect to the basic body.

2. The under-frame apparatus for the motor vehicle seat of claim 1 , wherein the pinion gear is driven by a driving shaft attached to the pinion gear, the driving shaft being coupled to the operation unit.

3. The under-frame apparatus for the motor vehicle seat of claim 1 , wherein the driving shaft has a connection region for arranging the operation unit.

4. The under-frame apparatus for the motor vehicle seat of claim 1 , wherein the adjustment arm is connected to the one of the front or rear vibration levers between first and second connections of the one of the front or rear vibration levers to the basic body.

5. The under-frame apparatus for the motor vehicle seat of claim 1 , wherein the basic body includes two side members arranged to each other at a predetermined distance and the two side members are connected to each other through at least one seat frame cross arm.

6. The under-frame apparatus for the motor vehicle seat of claim 5 , wherein a receiving member is arranged for fixing a belt to one of side members and/or one of front and rear vibration levers.

7. The under-frame apparatus for the motor vehicle seat of claim 1 , wherein the seat frame includes two seat frame side parts arranged to each other at a predetermined distance and the two seat frames side parts are connected to each other through at least one seat frame cross arm.

8. The under-frame apparatus for the motor vehicle seat of claim 7 , wherein the front and rear vibration arms are joint-connected to at least two seat frame cross arms.

9. The under-frame apparatus for the motor vehicle seat of claim 1 , wherein the front vibration levers are connected to each other through a first support cross arm and the rear vibration levers are connected to each other through a second support cross arm.

10. The under-frame apparatus for the motor vehicle seat of claim 1 , wherein the rear vibration levers rotate from the starting position to the respective rotation directions till 75°.