Traction distribution control system for four-wheel drive vehicle

1. A four-wheel drive vehicle, comprising:

a source of traction;

a device which transfers traction;

main driving wheels which receive traction from the source;

driven wheels which form at least a state of receiving smaller traction than traction transmitted to the main driving wheels through the device, the driven wheels receiving traction which can be changed through the device; and

an ECU which controls distribution of traction to the driven wheels, the ECU being so programmed as to:

form a control signal for operating the device in accordance with an input signal,

calculate a difference in spinning state between the main driving wheels, and

determine the control signal in accordance with the difference.

2. The four-wheel drive vehicle as claimed in claim 1 , wherein the difference comprises a difference in wheel speed.

3. The four-wheel drive vehicle as claimed in claim 1 , wherein the difference comprises a difference in wheel acceleration.

4. The four-wheel drive vehicle as claimed in claim 1 , wherein the difference comprises a difference in lateral acceleration of the vehicle.

5. The four-wheel drive vehicle as claimed in claim 1 , wherein the ECU is so programmed as to calculate a difference gain in accordance with the spinning-state difference, and determine the control signal by multiplying a control amount by the difference gain.

6. The four-wheel drive vehicle as claimed in claim 5 , wherein the control amount is calculated in accordance with a difference in average speed between the main driving wheels and the driven wheels.

7. The four-wheel drive vehicle as claimed in claim 5 , wherein the control amount is calculated in accordance with output torque of the source.

8. A four-wheel drive vehicle, comprising:

a source of traction;

means for transferring traction;

main driving wheels which receive traction from the source;

driven wheels which form at least a state of receiving smaller traction than traction transmitted to the main driving wheels through the transferring means, the driven wheels receiving traction which can be changed through the transferring means; and

means for controlling distribution of traction to the driven wheels, the controlling means comprising:

means for forming a control signal for operating the transferring means in accordance with an input signal,

means for calculating a difference in spinning state between the main driving wheels, and

means for determining the control signal in accordance with the difference.

9. The four-wheel drive vehicle as claimed in claim 8 , wherein the difference comprises a difference in wheel speed.

10. The four-wheel drive vehicle as claimed in claim 8 , wherein the difference comprises a difference in wheel acceleration.

11. The four-wheel drive vehicle as claimed in claim 8 , wherein the difference comprises a difference in lateral acceleration of the vehicle.

12. The four-wheel drive vehicle as claimed in claim 8 , wherein the controlling means comprise means for calculating a difference gain in accordance with the spinning-state difference, and means for determining the control signal by multiplying a control amount by the difference gain.

13. The four-wheel drive vehicle as claimed in claim 12 , wherein the control amount is calculated in accordance with a difference in average speed between the main driving wheels and the driven wheels.

14. The four-wheel drive vehicle as claimed in claim 12 , wherein the control amount is calculated in accordance with output torque of the source.

15. A four-wheel drive vehicle, comprising:

a source of traction;

a device which transfers traction;

main driving wheels which receive traction from the source;

driven wheels which form at least a state of receiving smaller traction than traction transmitted to the main driving wheels through the device, the driven wheels receiving traction which can be changed through the device;

an ECU which controls distribution of traction to the driven wheels, the ECU being so programmed as to:

form a control signal for operating the device in accordance with an input signal,

calculate a difference in spinning state between the main driving wheels,

calculate a difference gain in accordance with the spinning-state difference,

determine the control signal by multiplying a control amount by the difference gain, the control amount comprising greater one of a first control amount calculated in accordance with a difference in average speed between the main driving wheels and the driven wheels and a second control amount calculated in accordance with output torque of the source, and

determine the control signal in accordance with the difference.

16. A four-wheel drive vehicle, comprising:

a source of traction;

means for transferring traction:

main driving wheels which receive traction from the source;

driven wheels which form at least a state of receiving smaller traction than traction transmitted to the main driving wheels through the transferring means, the driven wheels receiving traction which can be changed through the transferring means; and

means for controlling distribution of traction to the driven wheels, the controlling means comprising:

means for forming a control signal for operating the transferring means in accordance with an input signal,

means for calculating a difference in spinning state between the main driving wheels,

means for calculating a difference gain in accordance with the spinning-state difference,

means for determining the control signal by multiplying a control amount by the difference gain, the control amount comprising greater one of a first control amount calculated in accordance with a difference In average speed between the main driving wheels and the driven wheels and a second control amount calculated in accordance with output torque of the source, and

means for determining the control signal in accordance with the difference.