Drive force distribution system for four wheel independent drive vehicle

• US 7,440,834 B2
• Filed: 06/27/2005
• Issued: 10/21/2008
• Est. Priority Date: 07/13/2004
• Status: Expired due to Fees

• Current Assignee: Nissan Motor Co., Ltd.
• Original Assignee: Nissan Motor Co., Ltd.
• Inventors: Deguchi, Yoshitaka, Inoue, Hideaki, Yamaguchi, Ichiro
• Primary Examiner(s): Beaulieu; Yonel
• Application Number:
  US11/166,741
• Publication Number:
  US 20060015236A1
• Time in Patent Office: 1,212 Days
• Field of Search: 701/69, 701/81, 701/89, 180233-234, 180/6.2, 180/242, 303/143
• US Class Current: 701/69
• CPC Class Codes: B60K 17/356 having fluid or electric motor, for driving one or more wheels disposition of motor in, or adjacent to, traction wheel B60K7/00
• CPC Class Codes: B60K 17/358 all driven wheels being steerable
• CPC Class Codes: B60K 23/0808 for varying torque distribution between driven axles, e.g. by transfer clutch
• CPC Class Codes: B60K 7/0007 the motor being electric
• CPC Class Codes: B60T 8/1769 specially adapted for vehicles having more than one driven axle, e.g. four-wheel drive vehicles
• CPC Class Codes: B60W 2520/26 Wheel slip
• CPC Class Codes: B60W 2530/10 Weight
• CPC Class Codes: B60W 2552/40 Coefficient of friction

Abstract

A drive force distribution system for a four wheel independent drive vehicle is configured to suppress changes in longitudinal and lateral accelerations and change in yaw moment about the center of gravity of the vehicle that occur when the brake/drive force of one wheel changes or is changed deliberately. The drive force distribution system is configured such that when the brake forces and the drive forces determined by the brake/drive force determining section based on the motion requirements of the vehicle are to be changed, the drive force revising section revises the brake/drive forces of the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel by amounts, respectively, based on the sensitivities of the tire lateral forces of each of the wheels estimated by the tire lateral force sensitivity estimating section so as to satisfy the motion requirements of the vehicle.

Claims

1. A drive force distribution system for controlling a four wheel independent drive vehicle comprising:

a brake/drive force determining section configured to determine a brake/drive force to be applied to each of the four wheels based on motion requirements of the vehicle;

a tire lateral force sensitivity estimating section configured to estimate a sensitivity k1, k2, k3, and k4 of a tire lateral force with respect to a change in the brake/drive force for each of a left front wheel, a right front wheel, a left rear wheel, and a right rear wheel, respectively; and

a drive force revising section configured to revise the brake/drive forces to be applied to the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel based on the sensitivities k1, k2, k3, k4 estimated by the tire lateral force sensitivity estimating section, and

the drive force revising section being further configured to correct the brake/drive forces to be applied to the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel by drive force correction amounts Δ

Fx1, Δ

Fx2, Δ

Fx3, and Δ

Fx4, respectively, based on the sensitivities k1, k2, k3, and k4 estimated by the tire lateral force sensitivity estimating section so as to satisfy the motion requirements of the vehicle, when the brake/drive forces determined by the brake/drive force determining section are to be changed.

2. The drive force distribution system as recited in claim 1, wherein

the drive force revising section is further configured to set the drive force correction amounts for the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel such that following relationships are satisfied:

$\frac{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>1}{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>2}=\frac{k<br><br><br><br>2}{-k<br><br><br><br>2};<br><br>\mathrm{and}<br><br><br><br>\frac{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>2}{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>3}=\frac{-k<br><br><br><br>1}{-k<br><br><br><br>2};<br><br>\mathrm{and}<br><br><br><br>\frac{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>3}{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>4}=\frac{-k<br><br><br><br>2}{k<br><br><br><br>1}$

when the tire lateral force sensitivities estimated by the tire lateral force sensitivity estimating section are such that a difference between a product of the sensitivities k1 and k4 of the left front wheel and the right rear wheel and a product of the sensitivities k2 and k3 of the right front wheel and the left rear wheel is approximately 0.

3. The drive force distribution system as recited in claim 2, wherein

the drive force revising section is further configured to set the drive force correction amounts for the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel such that following relationships are satisfied:

$\frac{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>1}{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>2}=\frac{1}{-1};<br><br>\mathrm{and}<br><br><br><br>\frac{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>2}{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>3}=\frac{-<br><br>1}{-1};<br><br>\mathrm{and}<br><br><br><br>\frac{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>3}{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>4}=\frac{-1}{<br><br>1}$

when the tire lateral force sensitivities estimated by the tire lateral force sensitivity estimating section are such that a difference between the sensitivities k1 and k2 of the left front wheel and the right front wheel is approximately 0, or a difference between sensitivities k3 and k4 of the left rear wheel and the right rear wheel is approximately 0.

4. The drive force distribution system as recited in claim 2, wherein

the drive force revising section is further configured to set the drive force correction amounts for the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel such that following relationships are satisfied:

$\frac{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>1}{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>2}=\frac{k<br><br><br><br>4}{-k<br><br><br><br>3};<br><br>\mathrm{and}<br><br><br><br>\frac{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>2}{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>3}=\frac{-k<br><br><br><br>3}{-k<br><br><br><br>4};<br><br>\mathrm{and}<br><br><br><br>\frac{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>3}{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>4}=\frac{-k<br><br><br><br>4}{k<br><br><br><br>3}$

when the tire lateral force sensitivities estimated by the tire lateral force sensitivity estimating section are such that the sensitivities k1 and k2 of the left front wheel and the right front wheel are both approximately 0.

5. The drive force distribution system as recited in claim 1, wherein

the drive force revising section is further configured to determine the drive force correction amounts Δ

Fx1, Δ

Fx2, Δ

Fx3, and Δ

Fx4 for the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel based on the sensitivities k1, k2, k3, and k4 estimated by the tire lateral force sensitivity estimating section such that ratios of the drive force correction amounts Δ

Fx1, Δ

Fx2, Δ

Fx3, and Δ

Fx4 satisfy following relationships;

$\frac{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>1}{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>2}=\frac{\left(\mathrm{Lt}/L\right)<br><br>\left(k<br><br><br><br>4-k<br><br><br><br>2\right)+k<br><br><br><br>2<br><br>\left(k<br><br><br><br>4-k<br><br><br><br>3\right)<br><br>}{-\left(\mathrm{Lt}/L\right)<br><br>\left(k<br><br><br><br>3-k<br><br><br><br>1\right)-k<br><br><br><br>1<br><br>\left(k<br><br><br><br>4-k<br><br><br><br>3\right)};<br><br>\mathrm{and}$ $\frac{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>2}{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>3}=\frac{-\left(\mathrm{Lt}/L\right)<br><br>\left(k<br><br><br><br>3-k<br><br><br><br>1\right)+k<br><br><br><br>1<br><br>\left(k<br><br><br><br>4-k<br><br><br><br>3\right)}{-\left(\mathrm{Lt}/L\right)<br><br>\left(k<br><br><br><br>4-k<br><br><br><br>2\right)-k<br><br><br><br>4<br><br>\left(k<br><br><br><br>2-k<br><br><br><br>1\right)};<br><br>\mathrm{and}$ $\frac{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>3}{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>4}=\frac{-\left(\mathrm{Lt}/L\right)<br><br>\left(k<br><br><br><br>4-k<br><br><br><br>2\right)+k<br><br><br><br>4<br><br>\left(k<br><br><br><br>2-k<br><br><br><br>1\right)}{\left(\mathrm{Lt}/L\right)<br><br>\left(k<br><br><br><br>3-k<br><br><br><br>1\right)-k<br><br><br><br>3<br><br>\left(k<br><br><br><br>2-k<br><br><br><br>1\right)}$

 

where Lt is a tread length and

L is a wheelbase of the four wheel independent drive vehicle.

6. The drive force distribution system as recited in claim 1, wherein

the tire lateral force sensitivity estimating section is further configured to estimate the sensitivity k1, k2, k3, and k4 of the tire lateral force for each of the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel, respectively, with respect to a change in the brake/drive force based on at least one of a wheel load, a road surface friction coefficient, and a lateral slip angle of each of the wheels.

7. The drive force distribution system as recited in claim 1, wherein

the drive force revising section is further configured revise the brake/drive forces to be applied to the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel based on steering angles δ

1, δ

2, δ

3, and δ

4 of the left front wheel, the right front wheel, the left rear wheel and the right rear wheel; and

the drive force revising section being further configured to revise the brake/drive forces of the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel by the drive force correction amounts Δ

Fx1, Δ

Fx2, Δ

Fx3, and Δ

Fx4, respectively, based on the steering angles δ

1, δ

2, δ

3, and δ

4 of the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel and the sensitivities k1, k2, k3, and k4 estimated by the tire lateral force sensitivity estimating section so as to satisfy the motion requirements of the vehicle, when the brake/drive forces determined by the brake/drive force determining section are to be changed.

8. The drive force distribution system as recited in claim 7, wherein

the drive force revising section is further configured to set the drive force correction amounts Δ

Fx1, Δ

Fx2, Δ

Fx3, and Δ

Fx4 for the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel such that ratios of the drive force correction amounts Δ

Fx1, Δ

Fx2, Δ

Fx3, and Δ

Fx4 satisfy following relationships;

$\frac{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>1}{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>2}=\frac{\left(\cos <br><br><br><br>\mathrm{\delta <br><br>}<br><br><br><br>3-k<br><br><br><br>3<br><br>\sin <br><br><br><br>\mathrm{\delta <br><br>}<br><br><br><br>3\right)}{-\left(\cos <br><br><br><br>\mathrm{\delta <br><br>}<br><br><br><br>3-k<br><br><br><br>3<br><br>\sin <br><br><br><br>\mathrm{\delta <br><br>}<br><br><br><br>3\right)};<br><br>\mathrm{and}<br><br>$ $\frac{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>2}{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>3}=\frac{-\left(\cos <br><br><br><br>\mathrm{\delta <br><br>}<br><br><br><br>3-k<br><br><br><br>3<br><br>\sin <br><br><br><br>\mathrm{\delta <br><br>}<br><br><br><br>3\right)}{-\left(\cos <br><br><br><br>\mathrm{\delta <br><br>}<br><br><br><br>1-k<br><br><br><br>1<br><br>\sin <br><br><br><br>\mathrm{\delta <br><br>}<br><br><br><br>1\right)};<br><br>\mathrm{and}$ $\frac{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>3}{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>4}=\frac{-\left(\cos <br><br><br><br>\mathrm{\delta <br><br>}<br><br><br><br>1-k<br><br><br><br>1<br><br>\sin <br><br><br><br>\mathrm{\delta <br><br>}<br><br><br><br>1\right)}{\left(\cos <br><br><br><br>\mathrm{\delta <br><br>}<br><br><br><br>1-k<br><br><br><br>1<br><br>\sin <br><br><br><br>\mathrm{\delta <br><br>}<br><br><br><br>1\right)}$

when the steering angles δ

1 and δ

2 of the left and right front wheels are substantially equal to each other, the steering angles δ

3 and δ

4 of the left and right rear wheels are substantially equal to each other, a difference between the sensitivities k1 and k2 of the left and right front wheels is approximately 0, and a difference between the sensitivities k3 and k4 of the left and right rear wheels is approximately 0.

9. The drive force distribution system as recited in claim 7, wherein

the drive force revising section is further configured to set the drive force correction amounts Δ

Fx1, Δ

Fx2, Δ

Fx3, and Δ

Fx4 for the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel such that;

the sum of the drive force correction amounts for the left and right front wheels and the sum of the drive force correction amounts for the left and right rear wheels are both approximately 0, and

as the steering angles δ

1 and δ

2 of the left and right front wheels become larger in comparison with the steering angles δ

3 and δ

4 of the left and right rear wheels, the smaller the drive force correction amount of each of the left and right rear wheels is in comparison with the drive force correction amount of a diagonally opposite front wheel,

when the steering angles δ

1 and δ

2 of the left and right front wheels are substantially equal to each other, the steering angles δ

3, δ

4 of the left and right rear wheels are substantially equal to each other, and the tire lateral force sensitivities k1, k2, k3, and k4 estimated by the tire lateral force sensitivity estimating section are all approximately 0.

10. The drive force distribution system as recited in claim 7, wherein

the drive force revising section is further configured to set the drive force correction amounts Δ

Fx1, Δ

Fx2, Δ

Fx3, and Δ

Fx4 for the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel such that ratios of the drive force correction amounts Δ

Fx1, Δ

Fx2, Δ

Fx3, and Δ

Fx4 satisfy following relationships;

$\frac{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>1}{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>2}=\frac{\cos <br><br><br><br>\mathrm{\delta <br><br>}<br><br><br><br>3}{-\cos <br><br><br><br>\mathrm{\delta <br><br>}<br><br><br><br>3};<br><br>\mathrm{and}<br><br><br><br>\frac{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>2}{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>3}=\frac{-\cos <br><br><br><br>\mathrm{\delta <br><br>}<br><br><br><br>3}{-\cos <br><br><br><br>\mathrm{\delta <br><br>}<br><br><br><br>1};<br><br>\mathrm{and}<br><br><br><br>\frac{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>3}{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>4}=\frac{-\cos <br><br><br><br>\mathrm{\delta <br><br>}<br><br><br><br>1}{\cos <br><br><br><br>\mathrm{\delta <br><br>}<br><br><br><br>1}$

when the steering angles δ

1 and δ

2 of the left and right front wheels are substantially equal to each other, the steering angles δ

3 and δ

4 of the left and right rear wheels are substantially equal to each other, and the tire lateral force sensitivities k1, k2, k3 and k4 estimated by the tire lateral force sensitivity estimating section are all approximately 0.

11. The drive force distribution system as recited in claim 7, wherein

the drive force revising section is further configured to set the drive force correction amounts Δ

Fx1, Δ

Fx2, Δ

Fx3, and Δ

Fx4 for the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel in such a manner that the ratios of the drive force correction amounts Δ

Fx1, Δ

Fx2, Δ

Fx3, and Δ

Fx4 satisfy the following relationships;

$\frac{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>1}{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>2}=\frac{1}{-<br><br>1};<br><br>\mathrm{and}<br><br><br><br>\frac{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>2}{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>3}=\frac{-1}{-\left(\cos <br><br><br><br>\mathrm{\delta <br><br>}<br><br><br><br>1-k<br><br><br><br>1<br><br><br><br>\sin <br><br><br><br>\mathrm{\delta <br><br>}<br><br><br><br>1\right)};<br><br>\mathrm{and}$ $\frac{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>3}{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>4}=\frac{-\left(\cos <br><br><br><br>\mathrm{\delta <br><br>}<br><br><br><br>1-k<br><br><br><br>1<br><br><br><br>\sin <br><br><br><br>\mathrm{\delta <br><br>}<br><br><br><br>1\right)}{\left(\cos <br><br><br><br>\mathrm{\delta <br><br>}<br><br><br><br>1-k<br><br><br><br>1<br><br><br><br>\sin <br><br><br><br>\mathrm{\delta <br><br>}<br><br><br><br>1\right)}$

when the steering angles δ

1 and, δ

2 of the left and right front wheels are substantially equal to each other, the steering angles δ

3 and δ

4 of the left and right rear wheels are both approximately 0, the difference between the sensitivities k1 and k2 of the left and right front wheels is approximately 0, and the difference between the sensitivities k3 and k4 of the left and right rear wheels is approximately 0.

12. The drive force distribution system as recited in claim 7, wherein

the drive force revising section is further configured to set the drive force correction amounts Δ

Fx1, Δ

Fx2, Δ

Fx3, and Δ

Fx4 for the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel such that;

a sum of the drive force correction amounts for the left and right front wheels and a sum of the drive force correction amounts for the left and right rear wheels are both approximately 0; and

as the steering angles δ

1 and δ

2 of the left and right front wheels becomes larger, the smaller the drive force correction amount of each rear wheel is in comparison with the drive force correction amount of a diagonally opposite front wheel,

when the steering angles δ

1 and δ

2 of the left and right front wheels are substantially equal to each other, the steering angles δ

3 and δ

4 of the left and right rear wheels are both approximately 0, the sensitivities k1 and k2 of the left and right front wheels are both approximately 0, and the sensitivities k3 and k4 of the left and right rear wheels are substantially equal to each other.

13. The drive force distribution system as recited in claim 7, wherein

the drive force revising section is further configured to set the drive force correction amounts Δ

Fx1, Δ

Fx2, Δ

Fx3, and Δ

Fx4 for the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel in such a manner that the ratios of the drive force correction amounts Δ

Fx1, Δ

Fx2, Δ

Fx3, and Δ

Fx4 satisfy the following relationships;

$\frac{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>1}{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>2}=\frac{1}{-<br><br>1};<br><br>\mathrm{and}<br><br><br><br>\frac{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>2}{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>3}=\frac{-1}{-\cos <br><br><br><br>\mathrm{\delta <br><br>}<br><br><br><br>1};<br><br>\mathrm{and}<br><br><br><br>\frac{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>3}{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>4}=\frac{-\cos <br><br><br><br>\mathrm{\delta <br><br>}<br><br><br><br>1}{\cos <br><br><br><br>\mathrm{\delta <br><br>}<br><br><br><br>1}$

when the steering angles δ

1 and δ

2 of the left and right front wheels are substantially equal to each other, the steering angles δ

3 and δ

4 of the left and right rear wheels are both approximately 0, the sensitivities k1 and k2 of the left and right front wheels are both approximately 0, and the sensitivities k3 and k4 of the left and right rear wheels are substantially equal to each other.

14. The drive force distribution system as recited in claim 7, wherein

the drive force revising section is further configured to set the drive force correction amounts Δ

Fx1, Δ

Fx2, Δ

Fx3, and Δ

Fx4 for the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel based on the steering angles δ

1, δ

2, δ

3, and δ

4 of the left front wheel, right front wheel, left rear wheel, and right rear wheel and the sensitivities k1, k2, k3, and k4 estimated by the tire lateral force sensitivity estimating section such manner that ratios of the drive force correction amounts Δ

Fx1, Δ

Fx2, Δ

Fx3, and Δ

Fx4 satisfy following relationships;

$\frac{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>1}{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>2}=\frac{\left[\left(\mathrm{Lt}/L\right)<br><br>\left(h<br><br><br><br>4-h<br><br><br><br>2\right)+h<br><br><br><br>2<br><br>\left(h<br><br><br><br>4-h<br><br><br><br>3\right)\right]/\left(\cos <br><br><br><br>\mathrm{\delta <br><br>}<br><br><br><br>1-k<br><br><br><br>1<br><br><br><br>\sin <br><br><br><br>\mathrm{\delta <br><br>}<br><br><br><br>1\right)}{-\left[\left(\mathrm{Lt}/L\right)<br><br>\left(h<br><br><br><br>3-h<br><br><br><br>1\right)+h<br><br><br><br>1<br><br>\left(h<br><br><br><br>4-h<br><br><br><br>3\right)\right]/\left(\cos <br><br><br><br>\mathrm{\delta <br><br>}<br><br><br><br>2-k<br><br><br><br>2<br><br><br><br>\sin <br><br><br><br>\mathrm{\delta <br><br>}<br><br><br><br>2\right)};<br><br>$ $\mathrm{and}$ $\frac{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>2}{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>3}=\frac{-\left[\left(\mathrm{Lt}/L\right)<br><br>\left(h<br><br><br><br>3-h<br><br><br><br>1\right)+h<br><br><br><br>1<br><br>\left(h<br><br><br><br>4-h<br><br><br><br>3\right)\right]/\left(\cos <br><br><br><br>\mathrm{\delta <br><br>}<br><br><br><br>2-k<br><br><br><br>2<br><br><br><br>\sin <br><br><br><br>\mathrm{\delta <br><br>}<br><br><br><br>2\right)}{-\left[\left(\mathrm{Lt}/L\right)<br><br>\left(h<br><br><br><br>4-h<br><br><br><br>2\right)+h<br><br><br><br>4<br><br>\left(h<br><br><br><br>2-h<br><br><br><br>1\right)\right]/\left(\cos <br><br><br><br>\mathrm{\delta <br><br>}<br><br><br><br>3-k<br><br><br><br>3<br><br><br><br>\sin <br><br><br><br>\mathrm{\delta <br><br>}<br><br><br><br>3\right)};<br><br>$ $\mathrm{and}$ $\frac{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>3}{\mathrm{\Delta <br><br>}<br><br><br><br>F\times <br><br>4}=\frac{-\left[\left(\mathrm{Lt}/L\right)<br><br>\left(h<br><br><br><br>4-h<br><br><br><br>2\right)+h<br><br><br><br>4<br><br>\left(h<br><br><br><br>2-h<br><br><br><br>1\right)\right]/\left(\cos <br><br><br><br>\mathrm{\delta <br><br>}<br><br><br><br>3-k<br><br><br><br>3<br><br><br><br>\sin <br><br><br><br>\mathrm{\delta <br><br>}<br><br><br><br>3\right)}{\left[\left(\mathrm{Lt}/L\right)<br><br>\left(h<br><br><br><br>3-h<br><br><br><br>1\right)+h<br><br><br><br>3<br><br>\left(h<br><br><br><br>2-h<br><br><br><br>1\right)\right]/\left(\cos <br><br><br><br>\mathrm{\delta <br><br>}<br><br><br><br>4-k<br><br><br><br>4<br><br><br><br>\sin <br><br><br><br>\mathrm{\delta <br><br>}<br><br><br><br>4\right)}$

 

where Lt is the tread length and

L is the wheel base of the four wheel independent drive vehicle and

hi=(sin δ

i+ki cos δ

i)/(cos δ

i−

ki sin δ

i).

15. A drive force distribution system for controlling a four wheel independent drive vehicle comprising:

brake/drive force determining means for determining a brake/drive force to be applied to each of the four wheels based on motion requirements of the vehicle;

tire lateral force sensitivity estimating means for estimating a sensitivity k1, k2, k3, and k4 of a tire lateral force with respect to a change in the brake/drive force for each of a left front wheel, a right front wheel, a left rear wheel, and a right rear wheel, respectively, and

drive force revising means for revising the brake/drive forces to be applied to the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel based on the sensitivities k1, k2, k3, and k4 estimated by the tire lateral force sensitivity estimating means; and

the drive force revising means further configured to correct the brake/drive forces to be applied to the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel by drive force correction amounts Δ

Fx1, Δ

Fx2, Δ

Fx3, and Δ

Fx4, respectively, based on the sensitivities k1, k2, k3, and k4 estimated by the tire lateral force sensitivity estimating means so as to satisfy the motion requirements of the vehicle, when the brake/drive forces determined by the brake/drive force determining means are to be changed.

16. The drive force distribution system as recited in claim 15, wherein

the drive force revising means is further configured to revise the brake/drive forces to be applied to the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel based on the steering angles δ

1, δ

2, δ

3, and δ

4 of the left front wheel, the right front wheel, the left rear wheel and the right rear wheel; and

the drive force revising section being further configured to correct the brake/drive forces of the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel by drive force correction amounts Δ

Fx1, Δ

Fx2, Δ

Fx3, and Δ

Fx4, respectively, based on the steering angles δ

1, δ

2, δ

3, and δ

4 of the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel and the sensitivities k1, k2, k3, and k4 estimated by the tire lateral force sensitivity estimating means so as to satisfy the motion requirements of the vehicle, when the brake/drive forces determined by the brake/drive force determining means are to be changed.

18. The drive force distribution system as recited in claim 15, wherein

the revising of the brake/drive forces to be applied to the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel is further based on the steering angles δ

1, δ

2, δ

3, and δ

4 of the left front wheel, the right front wheel, the left rear wheel and the right rear wheel; and

the correcting of the brake/drive forces of the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel by the drive force correction amounts Δ

Fx1, Δ

Fx2, Δ

Fx3, and Δ

Fx4, respectively, is further based on the steering angles δ

1, δ

2, δ

3, and δ

4 of the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel and the sensitivities k1, k2, k3, and k4 that were estimated to satisfy the motion requirements of the vehicle, when the brake forces and drive forces are to be changed.

17. A method of controlling drive force distribution of a four wheel independent drive vehicle comprising:

determining a brake/drive force to be applied to each of the four wheels based on motion requirements of the vehicle;

estimating a sensitivity k1, k2, k3, and k4 of a tire lateral force with respect to a change in the brake/drive force for each of a left front wheel, a right front wheel, a left rear wheel, and a right rear wheel, respectively;

revising the brake/drive forces to be applied to the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel based on the sensitivities k1, k2, k3, and k4 that were estimated; and

correcting the brake/drive forces to be applied to the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel by drive force correction amounts Δ

Fx1, Δ

Fx2, Δ

Fx3, and Δ

Fx4, respectively, based on the sensitivities k1, k2, k3, and k4 that were estimated by to satisfy the motion requirements of the vehicle, when the brake/drive forces are to be changed.