Two-stage fuel injection valve

A two-stage fuel injection valve for injecting a fuel into a combustion chamber of a cylinder head, the valve comprising:

• a valve body having a plurality of main fuel nozzle holes and a plurality of auxiliary fuel nozzle holes radially formed at points axially spaced apart from the front end based on the same center axis, a main fuel inflow passage formed from a main fuel inlet to a point adjacent to the main fuel nozzle hole, a first main fuel chamber axially formed to communicate with the main fuel inflow passage, an auxiliary fuel inflow passage formed from an auxiliary fuel inlet to a point adjacent to the auxiliary fuel nozzle hole, and an auxiliary fuel discharge passage formed from another point adjacent to the auxiliary fuel nozzle hole;
• a plunger inserted into the first main fuel chamber of the valve body to be axially slidable so that an auxiliary fuel pressurizing chamber is formed between the front end and the valve body to communicate with the auxiliary fuel nozzle hole, advancing forwards with the pressure of a main fuel applied to the first main fuel chamber to pressurize an auxiliary fuel in the auxiliary fuel pressurizing chamber, and allowing the main fuel inflow passage to communicate with the main fuel nozzle hole after an auxiliary fuel injection completion point;
• a plunger spring for elastically pressurizing the plunger in a retreating direction;
• a needle inserted into the center of the plunger to be slidable in an axial direction, the needle having a needle end at the front end thereof to close the auxiliary fuel nozzle hole, the needle retreating by means of pressure increase of the auxiliary fuel pressurizing chamber so that the auxiliary fuel pressurizing chamber communicates with the auxiliary fuel nozzle hole;
• and
• a needle spring interposed between the rear end of the needle and the plunger to elastically pressurize the needle in the advancing direction.