Fuel pump with an improved damping device for a direct injection system

1. A fuel pump for a direct injection system comprising:

at least one pumping chamber;

a piston which is mounted sliding inside the pumping chamber in order to vary cyclically the volume of the pumping chamber;

an intake duct connected to the pumping chamber and regulated by an inlet valve;

a delivery duct connected to the pumping chamber and regulated by a one-way delivery valve which allows exclusively a fuel flow outgoing from the pumping chamber; and

a damping device, which is placed along the intake duct upstream of the inlet valve, and comprises at least one elastically deformable damping body that has internally a closed chamber and is composed of two metal plates cup shaped and welded together in correspondence of their annular edges by an annular weld without interruptions;

wherein in the damping body the annular weld is created in a middle area of the annular edges of the plates so as to be at some distance from the outer ends of the annular edges themselves; and

wherein the annular edges of the plates have different shapes and sizes; a first annular edge of a first plate is larger than a second annular edge of a second plate and is bent into a “U” shape to embrace on both sides the second annular edge of the second plate.

2. A fuel pump according to claim 1 , wherein the damping device comprises a box of cylindrical shape, inside which a damping chamber is defined which houses the damping body.

3. A fuel pump according to claim 2 , wherein the box has a side input opening that can be connected to a inlet fuel duct and an lower output opening which flows into the intake duct.

4. A fuel pump according to claim 2 , wherein the damping device comprises two annular support elements which pinch together the external edges of the damping body on the outside of the annular welds.

5. A fuel pump according to claim 4 , wherein the set of the support elements is pressed pack inside the box by the pushing action of a lid of the box, the pushing actions is transmitted through a cup spring interposed between the lid and the set of the support elements.

6. A fuel pump according to claim 4 , wherein at least one support element has an axially elastic compressibility and the set of the support elements is pressed pack inside the box by the pushing action of a lid of the box.

7. A fuel pump according to claim 4 , wherein the support element has a number of through holes made through a cylindrical side wall to allow the flow of fuel through the support element.