Patent ID: 7850099

Claim:
An electronic unit injector comprising a housing with a fuel pressure chamber, a mechanically operated plunger reciprocating in the housing chamber to pressurize fuel in the chamber, an electronically controlled valve for venting fuel from the chamber when it is open and thereby preventing high pressurization of fuel in the chamber by the plunger and allowing the plunger to pressurize fuel in the chamber to an injection pressure when it is closed, a spray tip including a valve seat communicating with the fuel pressurization chamber, a needle valve arranged to close on the seat to prevent discharge of fuel from the spray tip or to open off the seat to dispense fuel from the spray tip, a spring biasing the needle valve to a closed position on the valve seat, a spring seat disposed between the spring and the needle valve, the needle valve being arranged to overcome the biasing force of the spring when the pressure in the pressure chamber reaches a predetermined level as a result of the electronically controlled valve closing, the spring and seat being disposed in a cage, the cage having a port area circumferentially arranged about said spring and said spring seat to allow fuel from a low pressure source to supply fuel to the area occupied by said spring and spring seat to reduce the risk of cavitation in said spring cage, said cage having a cylindrical wall and said port area comprising a series of radial holes distributed about the circumference of said cylindrical wall, the collective area of said holes being at least about one-quarter of the area of the spring seat.