Fuel tank with improved mechanical resistance

1. A fuel tank comprising:

two opposite wall portions; and

at least one reinforcing element connecting the two wall portions,

wherein the reinforcing element includes a hollow pillar having a ratio of at least 1.8 between a diameter of its cross section at its ends and a diameter of its cross section at at least one intermediate point.

2. A fuel tank according to claim 1 , which is a plastic fuel tank.

3. A fuel tank according to claim 1 , wherein the two opposite wall portions respectively are a lower wall portion, aimed at facing downwards in a vehicle where the tank would be mounted, and an upper wall portion, aimed at facing upwards in the vehicle where the tank would be mounted.

4. A fuel tank according to claim 1 , wherein the intermediate point with a reduced diameter does not extend over more than 90% of an entire length of the pillar and is located to cover a location of maximum stress in the pillar.

5. A fuel tank according to claim 4 , wherein the diameter of the cross section in the area of the intermediate point is not constant from one cross section to another.

6. A fuel tank according to claim 1 , wherein both ends of the pillar include connecting flanges.

7. A fuel tank according to claim 6 , wherein the pillar comprises two transition portions where the diameter of its cross section is not constant: a first transition portion in a flange area and a second transition portion substantially in the center of the pillar.

8. A fuel tank according to claim 1 , wherein the pillar has an axis of symmetry in rotation and a cross section such that when viewed in a vertical plane comprising the axis, the cross section comprises a portion that has a shape of a diabolo or of two opposite parabola linked by a middle portion of constant diameter or of a diameter which decreases from the parabola tops towards the center of the portion.

9. A fuel tank according to claim 8 , wherein the parabolic surface on each side of the middle portion of the diabolo is prolonged by a cylindrical portion extending up to a connecting flange, and wherein the ratio between the diameter of the flange and the diameter of the cylindrical portion is of at least 1.25 and the ratio between the diameter of the cylindrical portion and the diameter of the central portion is of at least 1.5.

10. A fuel tank according to claim 1 , wherein the pillar includes two different materials, and wherein two parts made of the different materials are overmolded.

11. A fuel tank according to claim 10 , wherein the pillar comprises two transition portions where the diameter of its cross section is not constant: a first transition portion in an overmolding area and a second transition portion substantially in the center of the pillar.

12. A fuel tank according to claim 1 , wherein the hollow pillar has an internal volume delimited by one external wall in a shape of a hollow pillar.

13. A fuel tank according to claim 1 , wherein the hollow pillar has an internal volume between plural ribs of material, an external envelope of which having a shape of a hollow pillar.

14. A fuel tank according to claim 1 , wherein the ratio of the diameters is between 1.8 and 5.