Fuel injector with pressure balanced needle valve

A fuel injector for injecting high pressure fuel into a combustion chamber of an internal combustion engine, comprising:

• an injector body containing an injector cavity, an injector orifice communicating with one end of said injector cavity and a fuel supply circuit for supplying pressurized fuel to be injected through said injector orifice;
• a needle valve element positioned in said injector cavity adjacent said injector orifice, said needle valve element operable to be placed in 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 needle 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;
• a needle valve actuating means for moving said needle valve element between said open position and said closed position independent of the pressure of the fuel to be injected;
• and
• a fuel pressure balancing means for balancing fuel pressure forces acting on said needle valve element, said fuel pressure balancing means including a balancing cavity formed in said needle valve element for receiving supply fuel and pressure balancing surfaces formed on said needle valve element and positioned in said balancing cavity, said pressure balancing surfaces having an effective cross-sectional area for balancing the fuel pressure biasing forces acting on said needle valve element during an injection event, said fuel pressure balancing means further including a closed position balancing means for balancing fuel pressure forces on said needle valve element when said needle valve element is in said closed position.