Fuel injector for an engine

A fuel injector connected to a high pressure fuel source, comprising:

• a needle having one end which controls the opening operation of a nozzle hole and having another end opposite to said one end;
• a piston having one end and a rear face opposite to said one end of said piston, the other end of said needle and the one end of said piston defining a pressure control chamber therebetween;
• a fuel passage having a restricted flow area and connecting said pressure control chamber to the high pressure fuel source to feed fuel under pressure in the high pressure fuel source into said pressure control chamber;
• a high pressure fuel chamber to which the rear face of said piston is exposed, said high pressure fuel chamber being filled with fuel under pressure and having a pressure which is substantially equal to that of the fuel under pressure in said pressure control chamber to urge said piston toward said pressure control chamber;
• and
• actuating means for actuating said piston to increase a volume of said pressure control chamber, to thereby cause said nozzle hole to be opened by said needle and to decrease the volume of said pressure control chamber, to thereby cause said nozzle hole to be closed by said needle, wherein
• said piston is slidably inserted in a cylinder, and a clearance between said piston and said cylinder is sealed, said high pressure fuel chamber being connected to the high pressure fuel source;
• said cylinder comprising a reduced diameter cylinder portion and an increased diameter cylinder portion, and said piston comprising a reduced diameter piston portion slidably inserted in said reduced diameter cylinder portion, and an increased diameter piston portion slidably inserted in said increased diameter cylinder portion, said reduced diameter piston portion defining said pressure control chamber, said increased diameter piston portion forming said rear face thereon.