Fuel pump with an improved maximum-pressure valve for a direct-injection system
Fuel pump for a direct-injection system and having: a pumping chamber; a piston; an intake channel regulated by an intake valve; a delivery channel regulated by a delivery valve; and a drain channel that originates in the delivery channel and is regulated by a maximum-pressure valve having: a shutter, a valve body provided with a valve seat, a calibrated spring for pushing the shutter against the valve seat, and a plate that is arranged in contact with the shutter on the opposite side of the valve seat; the plate of the maximum-pressure valve has a first annular groove, which is arranged around the shutter; and the valve body of the maximum-pressure valve has a second annular groove, which is arranged around the shutter and at least partially faces the first annular groove of the plate.
1. A fuel pump ( 1 ) for a direct-injection system; the fuel pump ( 1 ) comprises:
at least one pumping chamber ( 14 );
a piston ( 15 ), which is mounted so as to slide inside the pumping chamber ( 14 ) to cyclically change the volume of the pumping chamber ( 14 );
an intake channel ( 17 ), which is connected to the pumping chamber ( 14 ) and is regulated by an intake valve ( 18 );
a delivery channel ( 22 ), which is connected to the pumping chamber ( 14 ) and is regulated by a one-way delivery valve ( 23 ), which only permits a fuel flow flowing out of the pumping chamber ( 14 ); and
a drain channel ( 32 ), which originates in the delivery channel ( 22 ) and is regulated by a one-way, maximum-pressure valve ( 33 ), which opens when the fuel pressure in the delivery channel ( 22 ) exceeds a threshold value;
wherein the maximum-pressure valve ( 33 ) comprises: a shutter ( 34 ), which is movable along the drain channel ( 32 ), a valve body ( 36 ), which is provided with a valve seat ( 35 ) designed to be engaged in fluid-tight manner by the shutter ( 34 ), a spring ( 38 ), which is calibrated to push the shutter ( 34 ) towards an engaging position where it engages the valve seat ( 35 ) in a fluid-tight manner; and a plate ( 39 ), which is arranged in contact with the shutter ( 34 ) on the opposite side of the valve seat ( 35 );
wherein the plate ( 39 ) of the maximum-pressure valve ( 33 ) has a first annular groove ( 42 ), which is arranged around the shutter ( 34 ); and
wherein the valve body ( 36 ) of the maximum-pressure valve ( 33 ) has a second annular groove ( 43 ), which is arranged around the shutter ( 34 ) and at least partially faces the first annular groove ( 42 ) of the plate ( 39 ).
2. A fuel pump ( 1 ) according to claim 1 , wherein the second annular groove ( 43 ) is, in its longitudinal section, bowl-shaped and has a curved profile without discontinuities.
3. A fuel pump ( 1 ) according to claim 2 , wherein, in its longitudinal section, the curved profile of the second annular groove ( 43 ) has an inner surface ( 46 ), which is arranged closer to the shutter ( 34 ) and has an end inclination directed towards an area of the plate ( 39 ) that is comprised between the shutter ( 34 ) and the first annular groove ( 42 ).
4. A fuel pump ( 1 ) according to claim 2 , wherein, in its longitudinal section, the curved profile of the second annular groove ( 43 ) has an outer surface ( 47 ), which is arranged farther from the shutter ( 34 ) and has an end inclination directed towards an annular meatus comprised between the plate ( 39 ) and an inner wall of the drain channel ( 32 ).
5. A fuel pump ( 1 ) according to claim 1 , wherein the first annular groove ( 42 ) is, in its longitudinal section, bowl-shaped and has a curved profile without discontinuities.
6. A fuel pump ( 1 ) according to claim 5 , wherein, in its longitudinal section, the curved profile of the first annular groove ( 42 ) has an inner surface ( 44 ), which is arranged closer to the shutter ( 34 ) and has an end inclination directed towards the valve seat ( 35 ).
7. A fuel pump ( 1 ) according to claim 5 , wherein, in its longitudinal section, the curved profile of the first annular groove ( 42 ) has an outer surface ( 45 ), which is arranged father from the shutter ( 34 ) and has an end inclination directed towards the second annular groove ( 43 ).
8. A fuel pump ( 1 ) according to claim 1 , wherein an inner edge of the second annular groove ( 43 ) arranged closer to the shutter ( 34 ) is arranged at an axial height that is different from the one of an outer edge of the second annular groove ( 43 ) arranged farther from the shutter ( 34 ), so that the inner edge of the second annular groove ( 43 ) is axially closer to the spring ( 38 ) than the outer edge of the second annular groove ( 43 ).
9. A fuel pump ( 1 ) according to claim 1 , wherein an inner edge of the first annular groove ( 42 ) arranged closer to the shutter ( 34 ) is arranged at an axial height that is different from the one of an outer edge of the first annular groove ( 42 ) arranged farther from the shutter ( 34 ), so that the inner edge of the first annular groove ( 42 ) is axially closer to the spring ( 38 ) than the outer edge of the first annular groove ( 42 ).
10. A fuel pump ( 1 ) according to claim 1 , wherein the plate ( 39 ) has a central seat ( 48 ), which is designed to house the shutter ( 34 ) and is surrounded by the first annular groove ( 42 ).
11. A fuel pump ( 1 ) according to claim 1 , wherein the calibrated plate ( 39 ) is interposed between an end of the spring ( 38 ) and an end of the shutter ( 34 ).
12. A fuel pump ( 1 ) according to claim 11 , wherein the calibrated plate ( 39 ) is provided with a rod ( 41 ), which is inserted inside the spring ( 38 ).
13. A fuel pump ( 1 ) according to claim 1 , wherein the drain channel ( 32 ) connects the delivery channel ( 22 ) to the pumping chamber ( 14 ).
14. A fuel pump ( 1 ) according to claim 1 , wherein the drain channel ( 32 ) connects the delivery channel ( 22 ) to the intake channel ( 17 ).
15. A fuel pump ( 1 ) according to claim 14 and comprising a compensating chamber ( 49 ), which is arranged along the intake channel ( 17 ), houses at least one elastically deformable compensating body ( 50 ) to attenuate the pulsations of the fuel flow, and receives an outlet end of the drain channel ( 32 ).