Synchronizer sleeve used in power transmission and press-forming apparatus for the same

A press-forming apparatus for a synchronizer sleeve formed at its inner periphery with first inner spline teeth for meshing engagement to be meshed with a clutch gear of a change-speed gear train and second inner spline teeth for synchronization shorter in axial direction than the first inner spline teeth and positioned among them in a circumferential direction to be meshed with a synchronizer ring, comprising:

• an upper die having first and second outer spline teeth formed to be coupled with the first and second inner spline teeth of said synchronizer sleeve, the first outer spline teeth of said upper die being formed at their upper ends with a first chamfer forming portion for forming a pair of chamfers on each distal end of the first inner spline teeth of said synchronizer sleeve respectively, and the second outer spline teeth of said upper die being formed at their upper ends with a second chamfer forming portion smaller in depth than the first chamfer forming portion for forming a pair of chamfers on each distal end of the second inner spline teeth of said synchronizer sleeve respectively, wherein a small diameter portion of the second chamfer forming portion is formed smaller than a small diameter portion of the first chamfer forming portion;
• a lower die having first and second outer spline teeth formed to be coupled with the first and second inner spline teeth of said synchronizer sleeve, the first outer spline teeth of said lower die being formed at their lower ends with a first chamfer forming portion for forming a pair of chamfers on the other distal ends of the first inner spline teeth of said synchronizer sleeve respectively, and the second outer spline teeth of said lower die being formed at their lower ends with a second chamfer forming portion smaller in depth than the first chamfer forming portion for forming a pair of chamfers on the other distal ends of the second inner spline teeth of said synchronizer sleeve respectively, wherein a small diameter portion of the second chamfer forming portion is smaller than a small diameter portion of the first chamfer forming portion;
• wherein the synchronizer sleeve is pressed in a condition where the first and second inner spline teeth of said synchronizer sleeve have been vertically coupled at their one ends with the first and second outer spline teeth of said lower die and at their other ends with the first and second outer spline teeth of said upper die thereby to form a pair of chamfer surfaces on opposite ends of the first and second inner spline teeth of said synchronizer sleeve respectively and to form the second inner spline teeth of said synchronizer sleeve shorter in axial length than the first inner spline teeth of said synchronizer sleeve.