Method of machining injection hole in nozzle body, apparatus therefore, and fuel injection nozzle produced using the method and apparatus

A fuel injection nozzle, comprising:

• a nozzle body having,
• a plurality of injection holes, each injection hole having an entrance corner rounded with a larger curvature radius in an upstream region of fuel flow than in regions other than the upstream region of the fuel flow,
• a central hollow for accommodating a needle valve, and
• a tapered seat face formed in the central hollow at a forefront part of the nozzle body,
• wherein the tapered seat face has said plurality of injection holes in a circumferential direction thereon,
• wherein the nozzle body further includes,
• concave portions formed on the tapered seat face, the number of the concave portions being the same as that of said plurality of injection holes, each of the concave portions having a substantially straight part extending along generation lines of the tapered seat face in the nozzle body and a curved part continuing to the substantially straight part, and
• wherein the entrance corner of each injection hole is rounded with a larger curvature radius in a region continuing to the concave portion than in regions other than the region continuing to the concave portion.