Fuel injection nozzle for two-stage fuel injection

Claim 1

A fuel injection nozzle, comprising: a nozzle body defining a first chamber which is selectively subjected to a fuel injection pressure from a fuel injection pump, a second chamber which is subjected to a back pressure substantially lower than said fuel injection pressure from a fuel supply, and a fuel injection hole for injecting fuel into a combustion chamber of an internal combustion engine; a fuel passage provided in said nozzle body for conducting fuel placed under said fuel injection pressure from said first chamber to said fuel injection hole; a needle valve received in said nozzle body and provided with a first pressure receiving surface for receiving said fuel injection pressure and a valve element adapted to cooperate with a valve seat provided in said fuel passage upstream of said fuel injection hole; a pressure spring urging said needle valve against said valve seat, said needle valve being lifted away from said valve seat in an upward lift stroke against the spring force of said pressure spring when said fuel injection pressure applied to said first pressure receiving surface of said needle valve is more dominant than the spring force of said pressure spring; and a cylindrical plunger member which is passed through a wall member separating said first chamber from said second chamber so as to be slidable between a first position and a second position and is provided with a head at its one end which abuts said wall member from said first chamber by way of projections provided on an underside of said head when said plunger member is at said first position, said needle valve coming into contact with a free end of said plunger member located in said second chamber when said needle valve is at an intermediate point of the upward lift stroke thereof, and moving said plunger member to said second position as said needle valve reaches the end of said upward lift stroke.