Four wheel drive system having driving force distribution control responsive to vehicle lateral acceleration

Claim 1

A four wheel drive system for a vehicle having an engine, a transmission, and first and second wheel pairs, comprising: a transfer means having an input rotational member for receiving torque from said transmission, a first output rotational member connected with said input member for driving said first wheel pair, a second output rotational member for driving said second wheel pair, and a transfer clutch provided between said input member and said second output member for varying torque transmitted from said input member to said second output member by varying a clutch engagement force, a cornering behavior sensor for sensing a corner behavior of said vehicle and producing a signal representing a lateral acceleration of said vehicle, a vehicle speed sensor for sensing a vehicle speed of said vehicle, an accelerator sensor for sensing a position of an accelerator of said engine, a gear position sensor for sensing a gear position of said transmission, and driving force distribution control means for determining a driving force distribution ratio between a driving force for said first wheel pair in accordance with said signal of said vehicle cornering behavior sensor, estimating a total driving force transmitted from said engine to said input member of said transfer through said transmission from the vehicle speed, accelerator position and gear position sensed by said vehicle speed sensor, accelerator sensor and gear position sensor, determining a desired magnitude of the torque transmitted through said transfer clutch from said distribution ratio and said total driving force, and controlling the torque transmitted through said transfer clutch in accordance with said desired magnitude, wherein said control means continuously decreases a share of the driving force apportioned to said second wheels as the vehicle lateral acceleration increases.