1. Field of the Invention
The invention relates to a transfer case for all-wheel drive vehicles and, more particularly, to a transfer case which is provided with a self actuated, locking limited slip planetary differential. 2. Summary of Related Art
It is well known that all-wheel drive vehicles conventionally employ front and rear driving axles having front and rear differentials, respectively, drivingly connected to front and rear pairs of wheels through a transfer case including a third, inter-axle differential powered by the vehicle engine. Thus, should either the front or the rear drive axle experience a low friction condition, high torque could not be transmitted to the other wheel due to the constitution of the inter-axle differential. To avoid this, there is provided a differential lock up or limiting mechanism which effects a torque transfer to the drive axle in the higher friction condition, thus increasing the total available tractive force for propelling the vehicle and thereby improving the mobility and performance thereof.
To this end, the transfer cases employed previously have typically included a viscous coupling, or an electronically controllable clutch mechanism which may vary the amount of clutch force applied. Such mechanisms have generally performed adequately, but are unduly complex.