Injection rate shaping nozzle assembly for a fuel injector

A closed nozzle fuel injector adapted to inject fuel at high pressure into the combustion chamber of an engine, comprising:

• an injector body containing an injector cavity and an injector orifice communicating with one end of said injector cavity to discharge fuel into the combustion chamber, said injector body including a fuel transfer circuit for transferring supply fuel to said injector orifice, a low pressure drain circuit for draining fuel from said injector cavity and a nozzle housing having a seating surface;
• a nozzle valve element positioned in one end of said injector cavity adjacent said injector orifice, said nozzle valve element movable between an open position in which fuel may flow from said fuel transfer circuit through said injector orifice into the combustion chamber and a closed position in which fuel flow through said injector orifice is blocked, movement of said nozzle valve element from said closed position to said open position and from said open position to said closed position defining an injection event during which fuel may flow through said injector orifice into the combustion chamber, said nozzle valve element including an inner portion having a valve surface facing said seating surface, said seating surface and said valve surface extending at different angles in a nonparallel relationship;
• a rate shaping control means for producing a predetermined time varying change in the flow rate of fuel injected into the combustion chamber during said injection event to create a low injection flow rate through said injector orifice followed by a high injection flow rate greater than said low injection flow rate during said injection event, said rate shaping control means including an injection spill circuit for spilling a portion of the fuel to be injected from said fuel transfer circuit to said low pressure drain circuit during said injection event to create said low injection flow rate;
• a spill circuit purge means for providing a flow of purge gas through said injection spill circuit so as to remove fuel from said injection spill circuit, said spill circuit purge means including a cylinder gas purge passage for directing cylinder gas from the combustion chamber of the engine into said injection spill circuit, said cylinder gas purge passage including an annular clearance gap formed between said seating surface and said valve surface by the nonparallel relationship and sized, when said nozzle valve element is in said closed position, to restrict the purge gas flow to ensure sufficient fuel removal from said injection spill circuit while avoiding excessive purge gas flow.