The present invention relates to a differential apparatus to which driving force is to be cut off in a part-time four(4)-wheel drive car when in two(2)-wheel drive. More particularly, the invention relates to a differential apparatus having a mechanism for reducing frictional loss of the apparatus when not driven.
In prior art part-time four-wheel drive cars of this kind, a differential apparatus such as shown in FIG. 1 is used. Such an apparatus is disclosed in Japanese Utility Model Publication (kokai) No. 63-193929.
In FIG. 1, assembled so as to rotate in a first casing 401 relatively is a second casing 403 in which a pinion shaft 405, a pinion gear 407 and left and right side gears 409, 411 etc. are arranged. A sleeve 413 is arranged so as to slip on the outer periphery of the first casing 401. With the slipping movement of the sleeve 413, both casings 401, 403 can be either operatively associated with, or separated from, each other.
When it is desired to switch from four-wheel drive into two-wheel drive, due to a driver's manipulation of a controller in a vehicle cabin, the sleeve 413 is shifted to the left side of FIG. 1 by a switching unit 417 provided on a differential carrier 415. Consequently, the association between the first casing 401 and the second casing 403 is released, so that the casings can rotate relatively to each other.
In this way, while the second casing 403, the pinion shaft 405, the pinion gear 407 and the left and right side gears 409, 411 etc. race independent of tire rotation due to the vehicle's traveling, the surrounding first casing 401 and a ring gear 419 etc. do not race since the power transmission is cut off by switching of a transfer unit. Thus, racing loss and occurrence of noise can be reduced.
In the above-mentioned differential apparatus, however, since the switching unit 417 for switching between 4-wheel/2-wheel driving operation is disposed outside the differential carrier 415, it has been unavoidable that the differential carrier 415 is subjected to detailed remodeling to install a mechanism for sliding the sleeve 413 in the carrier 415.
Furthermore, the known art has to ensure a space allowing the axial sliding of the sleeve 413 in the first casing 401. For this reason, the first casing 401 is apt to have a one-sided weight imbalance and deviated configuration. Thus, an ill balanced configuration is caused in the differential apparatus.