Four-wheel drive vehicle having differential-limiting control

A four-wheel drive vehicle comprising:

• a first differential mechanism for distributing engine drive force to front drive wheels and rear drive wheels, either the front drive wheels or the rear drive wheels being used as main drive wheels and the other drive wheels being used as slave drive wheels;
• a second differential mechanism for distributing the engine drive force that has been distributed by the first differential mechanism to left and right main drive wheels, the main drive wheels get more drive force than the slave drive wheels;
• first differential-limiting means for operating differential-limiting control of the first differential mechanism;
• second differential-limiting means for operating differential-limiting control of the second differential mechanism;
• rotational speed detection means for detecting rotational speed of each drive wheel;
• turn direction detection means for detecting the direction of a turn that the vehicle is making;
• and
• control means for, based on detection signals from the rotational speed detection means and the turn direction detection means, controlling differential-limiting force provided by the second differential-limiting means according to a difference between the rotational speed of the left main drive wheel and that of the right main drive wheel, determining front and rear drive wheels on the outer side in the turn direction, and controlling differential-limiting force provided by the first differential-limiting means according to only a rotational speed difference between the front and rear drive wheels on the outer side in the turn direction.

A method of distributing engine torque to front and rear drive wheels of a four-wheel drive vehicle, comprising:

• determining which drive wheels, front or rear, are used as main drive wheels;
• detecting rotational speed of each drive wheel;
• detecting a direction of turn that a vehicle is making;
• determining front and rear drive wheels on the outer side in the turn direction based on the detected rotational speed and direction of turn;
• distributing engine torque to the front and rear drive wheels in such a manner that larger engine torque is distributed to the main drive wheels, based on only a rotational speed difference between the front and rear drive wheels on the outer side in the turn direction;
• and
• distributing engine torque that has been distributed to the main drive wheels further to left and right main drive wheels based on a difference between the rotational speed of the left main drive wheel and that of right main drive wheel.