Convertible juvenile vehicle seat

1. A vehicle seat for children, comprising

a base and an armchair, the armchair including a seat and a seat back,

the seat back includes an upper portion having at least one chest strap passage integral to the seat back and having an upward facing opening, the at least one chest strap passage configured to receive a chest strap of a safety belt of a motor vehicle,

the at least one chest strap passage is configured to receive the chest strap in a forward-facing position and in a rear-facing position of the armchair, and that the chest strap circulates in the at least one chest strap passage included on the upper portion of the seat back in the forward-facing position and in the rear-facing position,

wherein the base is fixed in a single position and the armchair is movable between the forward-facing and rear-facing positions in relation to the base;

wherein the base includes a ventral strap slot configured to receive vertical ventral strap, the ventral strap slot including a downward-facing opening through which the ventral strap passes, and the ventral strap slot being fixed in the same position on the base relative to a seat of the motor vehicle when the armchair is in the forward-facing position and in the rear-facing position; and

wherein the ventral strap slot is formed on a lower face of the base that is in contact with the seat of the motor vehicle.

2. The vehicle seat according to claim 1 , wherein the at least one chest strap passage includes two chest strap passages, each of the two chest strap passages located on one of two lateral edges of the seat back.

3. The vehicle seat according to claim 2 , wherein the two chest strap passages are chest strap passage slots crossing the lateral edges.

4. The vehicle seat according to claim 1 , wherein the at least one chest strap passage includes at least two separate zones, each of the at least two separate zones configured to receive the chest strap on a chest strap passage bearing surface.

5. The vehicle seat according to claim 4 , wherein when the chest strap is set into place, the chest strap circulates in a first zone of the strap passage slot of a first of the lateral edges and circulates in a second zone of the strap passage slot of a second of the lateral edges.

6. The vehicle seat according to claim 5 , wherein the chest strap passage slots have two slot portions, an entry portion and a bottom portion, the portions forming a non-zero angle, and corresponding respectively to the first and to the second zones.

7. The vehicle seat according to claim 6 , wherein the entry portion is substantially vertical and defines at least one chest strap passage bearing surface for the portion of the chest strap closest to a reel of the chest strap.

8. The vehicle seat according to claim 7 , wherein the entry portion is reinforced in such a way that the chest strap is configured to bear on two lips of the entry portion, when the armchair is in the forward-facing position or in the rear-facing position.

9. The vehicle seat according to claim 6 , wherein the bottom portion is directed towards the rear of the seat back and defines a chest strap passage bearing surface for the portion of the chest strap farthest from a reel of the chest strap.

10. The vehicle seat according to claim 1 , wherein the base has a bevelled section configured to at least partially offset an inclination of the seat of the motor vehicle.

11. The vehicle seat according to claim 1 , wherein the ventral strap slot includes a bearing surface and a retaining zone located on the bearing surface to retain the ventral strap in the ventral strap slot.

12. The vehicle seat according to claim 11 , wherein the bearing surface is inclined relative to a substantially vertical plane that intersects substantially transversely with a lower surface of the base.