Patent ID: 9556836
Date: 2017-01-31
CPC Classifications: F02M,F04B,F16K

Claim:
1. A single plunger high pressure fuel pump including a low pressure infeed leading to a pumping chamber, a pumping plunger for pressurizing fuel in the pumping chamber during a pumping stroke, an outlet valve for delivering pressurized fuel from the pumping chamber to a high pressure outlet line during the pumping stroke, a piston, and an overpressure relief valve with a relief inlet connected to the high pressure outlet line and exit flow passage connected to the pumping chamber for over pressure relief into the pumping chamber; wherein the relief valve comprises a relief valve element that is spring biased to close against the relief inlet, and the spring is in a spring chamber that is fluidly isolated from the pumping chamber and said flow passage while the relief valve element is closed; the piston slides in a sleeve and comprises a front end confronting the relief valve element and back end that is subject to loading by said spring, whereby the front end urges the relief valve element to close against a seat and the back end projects from the sleeve into the spring chamber, the piston closely slides in a bore along a piston sealing diameter (D the sleeve has a front chamber in which the relief valve element and the front end of the piston are situated, a central bore in which a central portion of the piston slides, and a back chamber through which a back portion of the piston extends and which is in hydraulic communication with the spring chamber; and the piston has a front port in said front chamber, a back port sealed by said central bore at an actuation distance X adjacent the back chamber when the relief valve element is seated, and an hydraulic passage between the front and back ports, whereby sliding of the piston away from said front chamber at least said actuation distance exposes said back port to said back chamber.