Fuel injection apparatus

A fuel injection apparatus comprising:

• a valve body portion including a nozzle chip provided with a fuel injection port and a needle valve disposed movably back and forward within said nozzle chip for opening and closing said fuel injection port;
• a booster means for advancing a booster piston, movable back and forward and biased backwardly by a piston spring, against a biasing force of said piston spring by a pressure of working fluid introduced into a pressurizing chamber to increase the pressure of fuel within a booster chamber;
• a valve controlling means including a feeding port for communicating said pressurizing chamber and a working fluid supply source with each other, a discharge port for communication with said pressurizing chamber and a working fluid discharge passage, a booster valve for opening and closing said feeding port and said discharge port, a valve spring for closing said feeding port and biasing said booster valve toward a pressure decreasing position where said discharge port is released, and a solenoid for releasing said feeding port and moving said booster valve to a booster position where said discharge port is closed;
• a valve opening means for biasing said needle valve in a direction in which said fuel injection port is released by the increased pressure of fuel;
• and
• a valve closing means for biasing said needle valve in a direction in which said fuel injection port is closed by a pressure of working fluid introduced into a pressure controlling chamber and a biasing force of a needle spring;
• wherein a working fluid introducing/backing passage having a port for performing introduction and discharge of the working fluid is connected to said pressure controlling chamber, and a throttle portion for imparting a fluidization resistance to the working fluid is provided in said port;
• and
• wherein said port is adapted to become a condition in which it is in communication with said working fluid discharge passage only at the retracted position of said booster piston, to become a condition in which it is in communication with said pressurizing chamber only in the case where said booster piston is advanced through a predetermined distance or longer, and to become a closed condition in communication with none of said working fluid discharge passage and said pressurizing chamber from said retracted position to said position through said predetermined distance.