Method of controlling rear wheels of a four-wheel steering motor vehicles
First Claim
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1. A method of controlling steering operations of rear road wheels of a four-wheel steering motor vehicle, comprising the steps of:
- detecting a steering angle of the vehicle'"'"'s front road wheels;
detecting a lateral acceleration of the vehicle;
determining a steer angle ratio of a rear wheel steering angle to a front wheel steering angle dependent on the detected lateral acceleration;
determining a rear wheel steering angle dependent on said detected front wheel steering angle and said determined steer angle ratio; and
steering the vehicle'"'"'s rear road wheels according to the determined rear wheel steering angle;
said steer angle ratio being further determined so as to be in a range defined by;
space="preserve" listing-type="equation">f1(yo)-g(yo)·
f2(yo)≧
0whereyo=vehicle lateral acceleration while the motor vehicle is making a steady-state turn;
g(yo)=steer angle ratio;
f1(yo)=Cfo/mf;
f2(yo)=Cro/mr;
Cfo, Cro are equivalent cornering powers of the tires of the front and rear road wheels while the motor vehicle is making a steady-state turn; and
mf, mr are equivalent masses at the front and rear axles of the motor vehicle.
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Abstract
The rear road wheels of a four-wheel steering motor vehicle are controlled so that a steer angle ratio of a rear wheel steer angle to a front wheel steer angle is variably controlled depending on the lateral acceleration. The steer angle ratio is selected so as to be in a range defined by:
f1(yo)-g(yo) ·f2(yo)≧0
where
f1(yo)=Cfo/mf;
f2(yo)=Cro/mr;
Cfo, Cro are equivalent cornering powers of the tires of the front and rear road wheels while the motor vehicle is making a steady-state turn; and
mf, mr are equivalent masses at the front and rear axles of the motor vehicle.
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Citations
6 Claims
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1. A method of controlling steering operations of rear road wheels of a four-wheel steering motor vehicle, comprising the steps of:
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detecting a steering angle of the vehicle'"'"'s front road wheels; detecting a lateral acceleration of the vehicle; determining a steer angle ratio of a rear wheel steering angle to a front wheel steering angle dependent on the detected lateral acceleration; determining a rear wheel steering angle dependent on said detected front wheel steering angle and said determined steer angle ratio; and steering the vehicle'"'"'s rear road wheels according to the determined rear wheel steering angle; said steer angle ratio being further determined so as to be in a range defined by;
space="preserve" listing-type="equation">f1(yo)-g(yo)·
f2(yo)≧
0where yo=vehicle lateral acceleration while the motor vehicle is making a steady-state turn; g(yo)=steer angle ratio; f1(yo)=Cfo/mf; f2(yo)=Cro/mr; Cfo, Cro are equivalent cornering powers of the tires of the front and rear road wheels while the motor vehicle is making a steady-state turn; and mf, mr are equivalent masses at the front and rear axles of the motor vehicle.
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2. A method of controlling a rear wheel steer angle of a four-wheel steering motor vehicle having front road wheels, rear road wheels, a steering wheel, a front wheel steering mechanism for turning the front road wheels in response to steering action of the steering wheel, and a rear wheel steering mechanism for turning the rear road wheels in response to the turning of the front road wheels, said method comprising the steps of:
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detecting a lateral acceleration and a front wheel steer angle; determining a final ratio of said rear wheel steer angle to said front wheel steer angle based on the detected lateral acceleration; determining a target rear wheel steer angle from said final ratio and said front wheel steer angle; turning said rear road wheels to said target rear wheel steer angle; and determining said final ratio such that a transient yaw rate gain represented by a ratio of an increase in a yaw rate to an increase in said front wheel steer angle immediately after the motor vehicle is steered is positive while the lateral acceleration is smaller than a predetermined value. - View Dependent Claims (3, 4, 5, 6)
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Specification