Pressure responsive fuel injector actuated by pump

Claim 1

A fuel injector comprising: a body having a first cylinder bore, a second cylinder bore, and an injecting port for injecting fuel; a piezoelectric actuator confined in said body, said actuator expanding and contracting in response to an electric potential difference applied thereto; a piston slidably disposed in said first cylinder bore, one side of said piston engaging with said actuator, another side of said piston defining a pump chamber in said first cylinder bore, said piston moving according to the expansion and contraction of said actuator to change the volume of said pump chamber; a nozzle needle movably disposed in said second cylinder bore, said nozzle needle having a first surface subject to pressure in said pump chamber to urge said needle to close said port and having a second surface subject to another pressure to urge said needle to open said port, said nozzle needle being able to open and close said port by being subject to both said pressures; means for pressing said piston toward said pump chamber with a force lower than that developed by the pressure in said pump chamber, the reaction force of said pressing means being isolated from said actuator; and means for supplying pressurized fuel to said injecting port, said second surface of said nozzle needle, and said pump chamber.