Patent ID: 7370636

Claim:
A fuel injection system fuel injection system selectively connecting a pressure control chamber formed on an inside end of a needle valve and an intermediate chamber of a booster piston for increasing the injection pressure through a two-position switching type three-way valve to the inside of a common rail or a fuel discharge passage, discharging high pressure fuel inside the common rail supplied into the pressure control chamber into the fuel discharge passage so as to open the needle valve and inject fuel, and discharging high pressure fuel inside the common rail supplied into the intermediate chamber into the fuel discharge passage so as to operate the booster piston and increase the fuel injection pressure, wherein an intermediate chamber control valve operated by the fuel pressure in the common rail is arranged in a fuel flow passage connecting the three-way valve and intermediate chamber, and said intermediate chamber control valve controls the flow area of the fuel flow passage in accordance with the fuel pressure in the common rail to operate the booster piston when the fuel pressure in the common rail is in a high pressure side fuel region higher than a predetermined fuel pressure and to weaken the booster action by the booster piston as compared with when the fuel pressure in the common rail is in the high pressure side fuel region or stop the operation of the booster piston when the fuel pressure in the common rail is in a low pressure side fuel region lower than the predetermined fuel pressure.