Four-wheel drive control system and method

1. A four-wheel drive control system comprising:

a driving force distribution mechanism for transmitting a driving force from a power source to main driving wheels of a vehicle and capable of distributing the driving force to auxiliary driving wheels of the vehicle;

a rotational speed difference detector for detecting a rotational speed difference between the main and auxiliary driving wheels; and

a driving force distribution controller for controlling a distribution of the driving force to the main and auxiliary driving wheels on the basis of the rotational speed difference, the driving force distribution controller comprising:

a rotational difference driving torque determining section for determining a rotational difference-dependent driving torque on the basis of the rotational speed difference;

an output driving torque determining section for determining an output-dependent driving torque on the basis of the output of the power source and the longitudinal load distribution; and

a distribution determining section for determining a larger one of the rotational difference-dependent driving torque and the output-dependent driving torque to be the driving torque to be transmitted to the auxiliary driving wheels,

wherein the driving force distribution controller determines a driving force to be transmitted to the auxiliary driving wheels on the basis of an output of the power source, a longitudinal load distribution in the vehicle and the rotational speed difference.

2. A four-wheel drive control system according to claim 1 , wherein the output driving torque determining section alters a longitudinal load distribution component for determining the output-dependent driving torque, on the basis of a longitudinal acceleration of the vehicle.

3. A four-wheel drive control system comprising:

a driving force distribution mechanism for transmitting a driving force from a power source to main driving wheels of a vehicle and capable of distributing the driving force to auxiliary driving wheels of the vehicle;

a rotational speed difference detector for detecting a rotational speed difference between the main and auxiliary driving wheels;

a driving force distribution controller for controlling a distribution of the driving force to the main and auxiliary driving wheels on the basis of the rotational speed difference;

a longitudinal acceleration detector for detecting a longitudinal acceleration of the vehicle; and

a four-wheel slip detector for detecting substantially simultaneously whether the main and auxiliary driving wheels are all in a slipping state;

wherein the driving force distribution controller determines a driving torque to be transmitted to the auxiliary driving wheels in accordance with the longitudinal acceleration and the rotational speed difference when the main and auxiliary driving wheels are all in a slipping state.

4. A four-wheel drive control system comprising:

a driving force distribution mechanism for transmitting a driving force from a power source to main driving wheels of a vehicle and capable of distributing the driving force to auxiliary driving wheels of the vehicle;

a rotational speed difference detector for detecting a rotational speed difference between the main and auxiliary driving wheels;

a driving force distribution controller for controlling a distribution of the driving force to the main and auxiliary driving wheels on the basis of the rotational speed difference;

a longitudinal acceleration detector for detecting a longitudinal acceleration of the vehicle; and

a four-wheel slip detector for detecting whether the main and auxiliary driving wheels are all in a slipping state;

wherein the driving force distribution controller determines a driving torque to be transmitted to the auxiliary driving wheels in accordance with the longitudinal acceleration and the rotational speed difference when the main and auxiliary driving wheels are all in a slipping state, and

wherein the driving force distribution controller comprises:

a rotational difference driving torque determining section for determining a rotational difference-dependent driving torque on the basis of the rotational speed difference;

an acceleration driving torque determining section for determining an acceleration-dependent driving torque on the basis of the longitudinal acceleration when the main and auxiliary driving wheels are all in a slipping state; and

a distribution determining section for determining a larger one of the rotational difference-dependent driving torque and the acceleration-dependent driving torque to be the driving torque to be transmitted to the auxiliary driving wheels.

5. A four-wheel drive control system according to claim 4 , further comprising a vehicle climbing detector for detecting climbing of the vehicle, wherein the driving torque distribution controller further comprises a sloping road driving torque determining section for determining a sloping road-dependent driving torque at the time of climbing, and wherein the distribution determining section determines a largest one of the rotational difference-dependent driving torque, the acceleration-dependent driving torque and the sloping road-dependent driving torque to be the driving torque to be transmitted to the auxiliary driving wheels.

6. A four-wheel drive control method for a vehicle having a driving force distribution mechanism for transmitting a driving force from a power source to main driving wheels of a vehicle and capable of distributing the driving force to auxiliary driving wheels of the vehicle, the method comprising:

detecting a rotational speed difference between the main and auxiliary driving wheels; and

controlling a distribution of the driving force to the main and auxiliary driving wheels on the basis of the rotational speed difference, the controlling comprising:

determining a rotational difference-dependent driving torque on the basis of the rotational speed difference;

determining an output-dependent driving torque on the basis of the output of the power source and the longitudinal load distribution, and

determining a larger one of the rotational difference-dependent driving torque and the output-dependent driving torque to be the driving torque to be transmitted to the auxiliary driving wheels,

wherein the controlling comprises determining a driving force to be transmitted to the auxiliary driving wheels on the basis of an output of the power source, a longitudinal load distribution in the vehicle and the rotational speed difference.

7. A four-wheel drive control method according to claim 6 , wherein the determining of the output-dependent driving torque comprises altering a longitudinal load distribution component for determining the output-dependent driving torque, on the basis of a longitudinal acceleration of the vehicle.

8. A four-wheel drive control method for a vehicle having a driving force distribution mechanism for transmitting a driving force from a power source to main driving wheels of a vehicle and capable of distributing the driving force to auxiliary driving wheels of the vehicle, the method comprising:

detecting a rotational speed difference between the main and auxiliary driving wheels;

controlling a distribution of the driving force to the main and auxiliary driving wheels on the basis of the rotational speed difference;

detecting a longitudinal acceleration of the vehicle; and

detecting substantially simultaneously whether the main and auxiliary driving wheels are all in a slipping state;

wherein the controlling comprises determining a driving torque to be transmitted to the auxiliary driving wheels in accordance with the longitudinal acceleration and the rotational speed difference when the main and auxiliary driving wheels are all in a slipping state.

9. A four-wheel drive control method for a vehicle having a driving force distribution mechanism for transmitting a driving force from a power source to main driving wheels of a vehicle and capable of distributing the driving force to auxiliary driving wheels of the vehicle, the method comprising:

detecting a rotational speed difference between the main and auxiliary driving wheels;

controlling a distribution of the driving force to the main and auxiliary driving wheels on the basis of the rotational speed difference;

detecting a longitudinal acceleration of the vehicle; and

detecting whether the main and auxiliary driving wheels are all in a slipping state;

wherein the controlling comprises;

determining a driving torque to be transmitted to the auxiliary driving wheels in accordance with the longitudinal acceleration and the rotational speed difference when the main and auxiliary driving wheels are all in a slipping state;

determining a rotational difference-dependent driving torque on the basis of the rotational speed difference;

determining an acceleration driving torque on the basis of the longitudinal acceleration when the main and auxiliary driving wheels are all in a slipping state; and

determining a larger one of the rotational difference-dependent driving torque and the acceleration-dependent driving torque to be the driving torque to be transmitted to the auxiliary driving wheels.

10. A four-wheel drive control method for a vehicle having a driving force distribution mechanism for transmitting a driving force from a power source to main driving wheels of a vehicle and capable of distributing the driving force to auxiliary driving wheels of the vehicle, the method comprising:

detecting a rotational speed difference between the main and auxiliary driving wheels;

controlling a distribution of the driving force to the main and auxiliary driving wheels on the basis of the rotational speed difference;

detecting a longitudinal acceleration of the vehicle;

detecting whether the main and auxiliary driving wheels are all in a slipping state; and

detecting climbing of the vehicle,

wherein the controlling comprises;

determining a driving torque to be transmitted to the auxiliary driving wheels in accordance with the longitudinal acceleration and the rotational speed difference when the main and auxiliary driving wheels are all in a slipping state;

determining a rotational difference-dependent driving torque on the basis of the rotational speed difference;

determining an acceleration-dependent driving torque on the basis of the longitudinal acceleration when the main and auxiliary driving wheels are all in a slipping state;

determining a sloping road-dependent driving torque at the time of climbing; and

determining a largest one of the rotational difference-dependent driving torque, the acceleration-dependent driving torque and the sloping road-dependent driving torque to be a driving torque to be transmitted to the auxiliary driving wheels.