Detection of hill grade and feed-forward distribution of 4WD torque bias to improve traction on a low MU surfaces during climbing of such hill grade

• US 20070129871A1
• Filed: 12/06/2005
• Published: 06/07/2007
• Est. Priority Date: 12/06/2005
• Status: Active Grant

• Current Assignee: Honda Motor Co., Ltd. (Honda Motor Company)
• Original Assignee: Honda Motor Co., Ltd. (Honda Motor Company)
• Inventors: Kang, Xiaodi, Klaus, Theodore, Post, James
• Granted Patent: US 8,321,110 B2
• Time in Patent Office: Days
• US Class Current: 701/69
• CPC Class Codes: B60K 23/0808 for varying torque distribution between driven axles, e.g. by transfer clutch
• CPC Class Codes: B60K 28/165 acting on elements of the vehicle drive train other than the propulsion unit and brakes, e.g. transmission, clutch, differential acting on brakes B60T8/17
• CPC Class Codes: B60W 2520/14 Yaw
• CPC Class Codes: B60W 2520/263 Slip values between front and rear axle
• CPC Class Codes: B60W 2552/15 Road slope, i.e. the inclination of a road segment in the longitudinal direction
• CPC Class Codes: B60W 2720/30 Wheel torque

Abstract

A feed forward method for controlling the distribution of torque between the front and rear axle in a four wheel drive vehicle where the slope of a hill upon which the vehicle is traveling is calculated based on measured vehicle longitudinal acceleration and estimated longitudinal acceleration. The hill slope estimation is made and implemented before the wheels of the vehicle begin to slip due to the slope and low friction coefficient of the road surface. Under conditions of high vehicle speeds or sever vehicle turning, the change of torque distribution is not implemented because there is a lesser tendency for the vehicle to slip on the hill surface.

Claims

1. A method of changing torque distribution between front and rear axles of a four wheel drive vehicle on a hill comprising:

measuring the speed of individual wheels;

calculating an estimated value of longitudinal acceleration using the measured wheel speed;

measuring the longitudinal acceleration of the vehicle using a sensor;

calculating an estimated value of hill slope based on the estimated value of longitudinal acceleration and measured value of longitudinal acceleration; and

using the estimated value of hill slope to shift torque from the front axle of the vehicle to the rear axle of the vehicle.

2. The method of claim 1, wherein torque is shifted from the front axle to the rear axle of the vehicle before the front wheels of the vehicle slip due to the slope and coefficient of friction of the hill.

3. The method of claim 1, wherein the step of measuring the speed of individual wheels includes measuring the speed of all four vehicle wheels.

4. The method of claim 1, further including the step of measuring the speed of the vehicle and mitigating the shift of torque if the speed exceeds a threshold value.

5. The method of claim 1, further including the step of measuring the yaw rate of the vehicle and mitigating the shift of torque if the vehicle is not traveling in a generally straight ahead direction.

6. The method of claim 1, wherein the step of measuring the speed of individual wheels includes measuring the speed of the wheels on the rear axle at two separate times and the step of calculating an estimated value longitudinal acceleration includes calculating the rate of speed change of the wheels on the rear axle between the separate times.

7. The method of claim 6, wherein torque is shifted from the front axle to the rear axle of the vehicle before the front wheels of the vehicle slip due to the slope and coefficient of friction of the hill.

8. The method of claim 6, further including the step of measuring the speed of the vehicle and mitigating the shift of torque if the speed exceeds a threshold value.

9. The method of claim 6, further including the step of measuring the yaw rate of the vehicle and mitigating the shift of torque if the vehicle is not traveling in a generally straight ahead direction.

10. The method of claim 1 further including the step of controlling slippage of the vehicle wheels in a feed back based manner.