Method and apparatus for detecting friction coefficient of road surface, and method and system for four-wheel steering of vehicles using the detected friction coefficient of road surface
First Claim
1. A method for detecting a friction coefficient of a road surface on which a vehicle runs, the vehicle including front wheels, a steering wheel and a hydraulic power steering unit disposed between the front wheels and the steering wheel, the hydraulic power steering unit assisting the steering wheel in steering the front wheels, the method comprising the steps of:
- (a) detecting an operating angle of the steering wheel, a speed of the vehicle and an operating pressure of the hydraulic power steering unit, respectively;
(b) detecting a proper steering situation only when at least one of two conditions is satisfied during operation of the steering wheel, one condition being an increase in steering angle of the front wheels and the other condition being the holding of the front wheels at a steering position beyond a predetermined angle and(c) calculating a friction coefficient of the road surface on the basis of the data detected in said step (a) only when the proper steering situation is detected in said step (b), the friction coefficient of the road surface being calculated by using relationships of the following three conditions,(i) a slip angle of the front wheels is determined in accordance with the detected operating angle of the steering wheel, the detected vehicle speed and the friction coefficient of the road surface,(ii) a cornering force of the front wheels is determined in accordance with the slip angle and the friction coefficient of the road surface, and(iii) the cornering force is proportional to the detected operating pressure of the hydraulic power steering unit.
1 Assignment
0 Petitions
Accused Products
Abstract
A method for detecting a friction coefficient of the road surface includes a detection step of detecting an operating angle of the steering wheel of the vehicle, a vehicle speed and an operating pressure of the hydraulic power steering unit for the front wheels, and a calculation step of calculating the friction coefficient of the road surface on turning of the vehicle by considering relationships among a slip angle of the front wheel, the friction coefficient of the road surface and a cornering force of the front wheels. The method further includes a step of prohibiting the execution of the calculation step when the steering wheel is turned back, whereby the calculation step is executed only when the direction of the operating pressure of power steering unit is in the equiphase with the operating direction of the steering wheel. Also, a four-wheel steering system includes has a rear steering actuator for steering the rear wheels so as to increase the steering angle of the rear wheels as the friction coefficient of the road surface calculated by the above-described method decreases.
-
Citations
18 Claims
-
1. A method for detecting a friction coefficient of a road surface on which a vehicle runs, the vehicle including front wheels, a steering wheel and a hydraulic power steering unit disposed between the front wheels and the steering wheel, the hydraulic power steering unit assisting the steering wheel in steering the front wheels, the method comprising the steps of:
-
(a) detecting an operating angle of the steering wheel, a speed of the vehicle and an operating pressure of the hydraulic power steering unit, respectively; (b) detecting a proper steering situation only when at least one of two conditions is satisfied during operation of the steering wheel, one condition being an increase in steering angle of the front wheels and the other condition being the holding of the front wheels at a steering position beyond a predetermined angle and (c) calculating a friction coefficient of the road surface on the basis of the data detected in said step (a) only when the proper steering situation is detected in said step (b), the friction coefficient of the road surface being calculated by using relationships of the following three conditions, (i) a slip angle of the front wheels is determined in accordance with the detected operating angle of the steering wheel, the detected vehicle speed and the friction coefficient of the road surface, (ii) a cornering force of the front wheels is determined in accordance with the slip angle and the friction coefficient of the road surface, and (iii) the cornering force is proportional to the detected operating pressure of the hydraulic power steering unit. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
-
-
10. An apparatus for detecting a friction coefficient of a road surface on which a vehicle is running, the vehicle including front and rear wheels, a steering wheel and a hydraulic power steering unit disposed between the front wheels and the steering wheel, the hydraulic power steering unit assisting the steering wheel in steering the front wheels, and the apparatus comprising;
-
first means for detecting an operating angle of the steering wheel; second means for detecting a vehicle speed; third means for detecting an operating pressure of the hydraulic power steering unit in proportion to a cornering force of the front wheels; and calculating means for calculating a friction coefficient of the road surface on the basis of the operating angle of the steering wheel, the vehicle speed and the operating pressure detected by said first, second and third means, said calculating means including detection means for detecting a proper steering situation only when at least one of two conditions is satisfied during operation of wheel, one condition being an increase in steering angle of the front wheels and the other condition being the holding of the front wheels at a steering position beyond a predetermined angle, and fourth means for calculating a friction coefficient of the road surface by using relationships of the following three conditions, (i) a slip angle of the front wheels is determined in accordance with the detected operating angle of the steering wheel, the detected vehicle speed and the friction coefficient of the road surface, (ii) a cornering force of the front wheels is determined in accordance with the slip angle and the friction coefficient of the road surface, and (iii) the cornering force is proportional to the detected operating pressure of the hydraulic power steering unit.
-
-
11. A four-wheel steering method of a vehicle, the vehicle including a steering wheel, front wheels steered by the steering wheel, and hydraulic power steering unit disposed between the front wheels and the steering wheel, the hydraulic power steering unit assisting the steering wheel in steering the front wheels, and rear wheels which can be steered in accordance with the steering of the front wheels, the method comprising the steps of:
-
(a) detecting an operating angle of the steering wheel, a speed of the vehicle and an operating pressure of the hydraulic power steering unit, respectively; (b) detecting a proper steering situation only when at least one of two conditions is satisfied during operation of the steering wheel, one condition being an increase in the steering angle of the front wheels and the other condition being the holding of the front wheels at a steering position beyond a predetermined angle (c) calculating a friction coefficient of a road surface on which the vehicle is running on the basis of the data detected in said step (a) only when the proper steering situation is detected in said step (b); and (d) calculating an equiphase steering angle of the rear wheels for steering the rear wheels in the same direction as the steering direction of the front wheels on the basis of the detected operating angle of the steering wheel and the friction coefficient of the road surface determined in said step (c) when the front wheels are steered, the equiphase steering angle for the rear wheels calculated in said step (d) being increased by a predetermined amount as the friction coefficient of the road surface calculated in said step (c) decreases. - View Dependent Claims (12, 13, 14, 15, 16, 17)
-
-
18. A four-wheel steering system of a vehicle having front and rear wheels, comprising;
-
a steering wheel for steering the front wheels; a hydraulic power steering unit disposed between the front wheels and the steering wheel; first means for detecting an operating angle of the steering wheel; second means for detecting a vehicle speed; third means for detecting an operating pressure of the hydraulic power steering unit; fourth means for determining an equiphase steering angle of the rear wheels to steer the rear wheels in the same direction as the steering direction of the front wheels, on the basis of the detected operating angle of the steering wheel when the front wheels are steered; and rear steering means for steering the rear wheels in accordance with the equiphase steering angle of the rear wheels when the front wheels are steered, said rear steering means including fifth means for determining that a proper steering situation exists only when at least one of two conditions is satisfied during operation of the steering wheel, one condition being an increase in the steering angle of the front wheels and the other condition being the holding of the front wheels at a steering position beyond a predetermined angle, on the basis of the detected operating angle of the steering wheel, sixth means for calculating a friction coefficient of a road surface on which the vehicle is running on the basis of the detected operating angle of the steering wheel, the detected vehicle speed and the detected operating pressure only when at least one of the two conditions is satisfied, and seventh means for correcting the equiphase steering angle of the rear wheel so that it increases as the calculated friction coefficient of the road surface decreases.
-
Specification