| 摘要 |
PROBLEM TO BE SOLVED: To prevent seizure of a sliding frictional surface and pitching of a differential gear by forming an electroless Ni-coating layer on whole of the surface of a blank of a differential gear, cutting the layer surface to obtain a gear member which has teeth surfaces with exposed blank, and then performing cementation hardening and tempering. SOLUTION: Mesh-like oil grooves are formed on outer peripheries of blanks of pinion gears 17, 19 by knurling. The outer peripheries are polished for finely finishing the surfaces. An electroless Ni-coating layer is formed on whole of the surfaces of the blanks. The layer surface is cut to form a gear member having teeth surfaces 17e, 19e each having an exposed blank. Cementation hardening and tempering are carried out to obtain surface hardness of the teeth surfaces 17e, 19e of HRC50 to 60, and layer surface hardness of HRC 64 to 68. Even under a severe sliding surface pressure condition influenced by driving force and differential braking force, abrasion ane seizure are prevented due to sliding of the coating layer, so that pitching resistance is improved.
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