Patent ID: 8430081

Claim:
A direct-injection system fuel pump comprising: at least one pumping chamber; a piston mounted to slide inside the pumping chamber to cyclically alter the volume of the pumping chamber; an intake channel connected to the pumping chamber and regulated by an intake valve; a delivery channel connected to the pumping chamber and regulated by a one-way delivery valve that only permits fuel flow from the pumping chamber; a drain channel which connects the delivery channel to the pumping chamber and serves as a fuel bleed in the event the fuel in the delivery channel exceeds a given maximum design pressure; a one-way, maximum-pressure valve, which regulates the drain channel, only permits fuel flow to the pumping chamber, opens when fuel pressure exceeds a threshold value to prevent the fuel in the delivery channel from exceeding the maximum design pressure, and comprises a shutter movable along the drain channel; a valve seat engaged in fluid tight manner by the shutter; a spring calibrated to push the shutter into a position engaging the valve seat in fluid tight manner; and a calibrated plate, which produces a local reduction in the fuel flow section of the drain channel; wherein the calibrated plate is sized so that a hydraulic pressure exerted on the calibrated plate and produced by a load loss astride the calibrated plate roughly equals an increase in the elastic pressure of the spring caused by compression of the spring as the maximum-pressure valve opens; and wherein the hydraulic pressure on the calibrated plate is exerted in the opposite direction to the elastic pressure of the spring, so that, as the opening of the maximum-pressure valve increases, the gradual increase in the elastic pressure of the spring is roughly compensated by a gradual increase in the hydraulic pressure on the calibrated plate.