Driving force distribution control apparatus for four-wheel drive vehicle and driving force distribution control method for four-wheel drive vehicle

1. A driving force distribution control apparatus for a four-wheel drive vehicle including a driving force transmission path via which a driving force generated by a drive source is transferred to primary drive wheels and secondary drive wheels, and a driving force distribution apparatus disposed in the driving force transmission path between the drive source and the secondary drive wheels, the driving force distribution control apparatus comprising:

a basic distribution determination device configured to determine basic distribution of the driving force to the secondary drive wheels in accordance with the driving force and driving conditions of the vehicle, the basic distribution determination device comprising:

a tire force limit determination device configured to calculate a tire required acceleration in accordance with the driving conditions of the vehicle and configured to output a basic distribution adjustment signal having a characteristic that decreases a ratio of the basic distribution for the secondary drive wheels to zero in a transient region in which the calculated tire required acceleration is lower than a predetermined threshold value; and

an arithmetic device configured to adjust the basic distribution for the secondary drive wheels to a ratio corresponding to the basic distribution adjustment signal output from the tire force limit determination device; and

a servo controller configured to correct the driving force provided to the secondary drive wheels according to the basic distribution determined by the basic distribution determination device using a deviation between a measured value and a normative value of a rotational difference between an input shaft and an output shaft of the driving force distribution apparatus.

2. The driving force distribution control apparatus for a four-wheel drive vehicle according to claim 1 , wherein the servo controller includes a device configured to obtain a rotational speed theoretical value of the primary drive wheels and a rotational speed theoretical value of the secondary drive wheels based on a steering angle, a vehicle speed, a yaw rate and a slip angle of the four-wheel drive vehicle and calculate the normative value based on the two rotational speed theoretical values.

3. The driving force distribution control apparatus for a four-wheel drive vehicle according to claim 1 , wherein the tire force limit determination device is configured to calculate the tire required acceleration based on an acceleration of the vehicle in a front-rear direction and an acceleration of the vehicle in a lateral direction.

4. A driving force distribution control apparatus for a four-wheel drive vehicle including a driving force transmission path via which a driving force generated by a drive source is transferred to primary drive wheels and secondary drive wheels, and a driving force distribution apparatus disposed in the driving force transmission path between the drive source and the secondary drive wheels, the driving force distribution control apparatus comprising:

basic distribution determination means for determining basic distribution of the driving force to the secondary drive wheels in accordance with the driving force and driving conditions of the vehicle, the basic distribution determination means comprising:

tire force limit determination means for calculating a tire required acceleration in accordance with the driving conditions of the vehicle and for outputting a basic distribution adjustment signal having a characteristic that decreases a ratio of the basic distribution for the secondary drive wheels to zero in a transient region in which the calculated tire required acceleration is lower than a predetermined threshold value; and

arithmetic means for adjusting the basic distribution for the secondary drive wheels to a ratio corresponding to the basic distribution adjustment signal output from the tire force limit determination means; and

servo control means for correcting the driving force provided to the secondary drive wheels according to the basic distribution determined by the basic distribution determination means using a deviation between a measured value and a normative value of a rotational difference between an input shaft and an output shaft of the driving force distribution apparatus.

5. A driving force distribution control method for a four-wheel drive vehicle, the method comprising:

transferring a driving force generated by a drive source to primary drive wheels and secondary drive wheels via a driving force transmission path;

determining basic distribution of the driving force to the secondary drive wheels in accordance with the driving force and driving conditions of the vehicle;

calculating a tire required acceleration in accordance with the driving conditions of the vehicle;

outputting a basic distribution adjustment signal having a characteristic that decreases a ratio of the basic distribution for the secondary drive wheels to zero in a transient region in which the calculated tire required acceleration is lower than a predetermined threshold value;

adjusting the basic distribution for the secondary drive wheels to a ratio corresponding to the basic distribution adjustment signal; and

correcting the driving force provided to the secondary drive wheels according to the basic distribution determined by using a deviation between a measured value and a normative value of a rotational difference between an input shaft and an output shaft of the driving force distribution apparatus.