Two stage fuel injector nozzle assembly

A closed nozzle injector assembly for injecting fuel at high pressure into the combustion chamber of an engine, comprising:

• an injector body containing an injector cavity forming a nozzle cavity at one end of said injector body and a plurality of injector orifices communicating with said nozzle cavity to discharge fuel into the combustion chamber, said plurality of injector orifices including a first set of orifices and a second set of orifices, said injector body including a fuel transfer circuit for transferring supply fuel to said nozzle cavity, said infector body containing a spring cavity;
• a first and a second biasing springs positioned in said spring cavity for biasing said first and said second nozzle valve elements toward the closed positions, respectively;
• a spring guide and seat member removably positioned in said spring cavity and formed separately from the said injector body, said spring guide and seat member including a first integral abutment surface for alignment with said first biasing spring, and a second integral abutment surface for alignment with said second biasing spring;
• a nozzle valve means positioned in said nozzle cavity adjacent said plurality of injector orifices for controlling fuel flow through said plurality of injector orifices, said nozzle valve means including a first nozzle valve element and a first valve seat formed on said injector body, said first nozzle valve element movable from a closed position against said first valve seat blocking flow through said first set of injector orifices to an open position permitting flow through said first set of injector orifices, said first nozzle valve element containing a cavity opening into a lower end of said first nozzle valve element, said nozzle cavity surrounding a lower portion of said first nozzle valve element, said nozzle valve means further including a second nozzle valve element and a second valve seat formed on said injector body, said second nozzle valve element movable from a closed position against said second valve seat blocking flow through said second set of injector orifices to an open position permitting flow through said second set of injector orifices, said second nozzle valve element positioned within said cavity of said first nozzle valve element, said fuel transfer circuit including an annular recess formed between said first nozzle valve element and said second nozzle valve element, said fuel transfer circuit further including a transverse passage formed in said first nozzle valve element for directing fuel from said nozzle cavity to said annular recess for delivery to said first set of injector orifices;
• and
• valve opening means for moving said first and said second nozzle valve elements into said respective open positions, said valve opening means including a first pressure surface area formed on said first nozzle valve element and positioned in said nozzle cavity and a second pressure surface area formed on said second nozzle valve element and positioned in said annular recess, wherein fuel in said nozzle cavity increases from a low pressure level to a high pressure level during an injection event, said first and said second pressure surface areas being sized to open one of said first and said second nozzle valve elements during the injection event in response to the low pressure level and maintain the one nozzle valve element in the open position throughout the injection event and to open the other of said first and said second nozzle valve elements during the injection event in response to the high pressure level.