Fuel injection system

A fuel injection system comprising:

• a valve main body having a needle guide cavity with the distal end thereof formed as an injection aperture, fuel passing through said needle guide cavity to be injected through said injection aperture;
• a pressure control chamber filled with a pressure transmitting medium;
• a piston for changing the fluid pressure of said pressure transmitting medium in said pressure control chamber;
• a needle valve having one end thereof located in said needle guide cavity and the other end thereof located in said pressure control chamber, said needle valve being installed in such a manner that it is allowed to move to open or close said injection aperture;
• a pressure receiving section which is provided on a portion of said needle valve located in said pressure control chamber and which is subjected to said fluid pressure;
• a pre-loading means for pre-loading said needle valve in a direction for closing said injection aperture;
• and
• a piezoelectric element which changes said fluid pressure of said pressure transmitting medium by driving said piston, applies said changed fluid pressure to said pressure receiving section, and moves said needle valve in a direction for opening or closing said injection aperture so as to start or stop the flow of an injection fuel through said injection aperture,
• wherein a flow channel for said injection fuel is airtightly independent from said pressure control chamber, and
• wherein said pressure transmitting medium is completely sealed off from said injection fuel by a sealing member.