Patent ID: 7261088

Claim:
A fuel pump ( 4 ) for an internal combustion engine, the fuel pump ( 4 ) comprising at least one cylinder ( 11 ); a variable-volume pump chamber ( 22 ) defined inside the cylinder ( 11 ); a piston ( 12 ) defining the bottom of the pump chamber ( 22 ) and movable with respect to the cylinder ( 11 ) in a pumping direction ( 35 ); at least one one-way intake valve ( 26 ) only permitting fuel flow into the pump chamber ( 22 ); at least one one-way delivery valve ( 27 ) only permitting fuel flow from the pump chamber ( 22 ); and an actuating device ( 13 ) for moving the piston ( 12 ) back and forth with respect to the cylinder ( 11 ) and in the pumping direction ( 35 ) to cyclically vary the volume of the pump chamber ( 22 ); wherein the actuating device ( 13 ) is a fluid-actuated actuating device, which uses the thrust produced by a pressurized control fluid to move the piston ( 12 ) back and forth with respect to the cylinder ( 11 ) and in the pumping direction ( 35 ), and comprises a first actuating chamber ( 34 ) located beneath the pump chamber ( 22 ) with respect to the pumping direction ( 35 ), a control member ( 47 ) for connecting the first actuating chamber ( 34 ) to a pressurized control fluid tank ( 45 ) and to a control fluid drain tank ( 41 ), and return means ( 37 ) for exerting thrust on the piston ( 12 ) in the pumping direction ( 35 ) and in the opposite direction to the thrust exerted by the pressurized control fluid in the first actuating chamber ( 34 ); wherein the return means ( 37 ) comprise a second actuating chamber ( 37 ) located above the first actuating chamber ( 34 ) with respect to the pumping direction ( 35 ), and which receives pressurized control fluid.