Patent ID: 8186724

Claim:
A connecting head structure for a high-pressure fuel injection pipe, the connecting head structure comprising: a steel pipe having a pipe wall with inner and outer substantially cylindrical surfaces defining a wall thickness t and an outer diameter D selected so that t/D 0.3; a spherical seat surface having a spherical radius R and defining a connecting head end at an axial end of the pipe; an annular flange spaced from the spherical seat surface in an axial direction and having a back face facing away from the spherical seat surface, the annular flange having an outer diameter D 1 and the back face being spaced from the connecting head end in an axial direction by a distance L 1 ; a conical surface extending from the spherical surface toward the annular flange and being tapered toward the spherical seat surface, wherein the connecting head structure is configured so that the distance L 1 in the axial direction from the connecting head end to the back face of the annular flange is 0.38D to 0.6D, the spherical radius R of the spherical seat surface is 0.45D to 0.65D, and the outer diameter D 1 of the annular flange is 1.2D to 1.4D; and wherein the connecting head structure has an inner peripheral surface defining a substantially straight cylindrical face with a diameter substantially conforming to an inner diameter of the inner cylindrical surface of the pipe rearward of the connecting head structure or defining a conical face.