| 摘要 |
PROBLEM TO BE SOLVED: To improve an acoustic life and reduce a rotation torque. SOLUTION: Contact surface stress is reduced, seizure is prevented for a long term, and the surface is prevented from roughing by setting a radius of curvature on an inner wheel raceway surface to more than 50.5% and less than 52% of a ball diameter. An area of the contact surface is reduced to reduce a differential slide, and low torque and long life is realized by setting a radius of curvature on an outer wheel raceway surface to more than 53% and less than 55% of the ball diameter. Since a rolling element is made of ceramics, inertia is reduced to reduce slide and abrasion, whereby friction is reduced and low torque is realized. Durability in a high temperature area is improved by using ester oil as a base oil of a pre-charged grease. Since a retainer is made of synthetic resin, torque can be reduced due to a light weight, and generation of heat and abrasion powder is prevented thereby enhancing a long life.
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