US Patent 7870941 Friction engaging device

An outer plate 31, which is used under a lubricated environment of a differential gear oil including a friction adjuster, is made of a SC tempered material which is subjected to nitriding treatment to suppress chemical adsorption of the friction adjuster. An inner plate 33 has paper on a surface thereof. The outer plate 31 and the inner plate 33 are provided to apply or release the torque between an outer differential case 3 and an inner differential case 5 of a rear differential device 1 having the outer differential case 3 and the inner differential case 5 capable of relatively rotating to the inside and the outside.