JP3119010B2 - Road friction coefficient detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a road friction coefficient detecting device for detecting a friction coefficient between a tire of an automobile and a road surface.

[0002]

2. Description of the Related Art Various methods have been proposed for detecting a road surface friction coefficient. For example, JP-A-61-
Japanese Patent Publication No. 94864 discloses a method of detecting a road surface friction coefficient from a relationship between a sprung wheel load and a brake torque when a wheel slips. As another method, the estimated yaw rate and the estimated lateral acceleration are calculated from the front wheel steering angle, the rear wheel steering angle, and the vehicle speed, and the slip determination is performed by comparing the yaw rate and the lateral acceleration actually obtained from the sensor with each other. A method of detecting the road surface friction coefficient from the actual lateral acceleration when the slip determination is made over 100 msec or more has also been proposed.

[0003]

Among the above prior arts, the former does not consider the lateral movement, so that the accuracy of detecting the road surface friction coefficient at the time of turning is deteriorated and the wheel must be slippery. For example, since the road surface friction coefficient cannot be detected, there is a problem that there is almost no opportunity to detect the road surface friction coefficient in a normal traveling state. In the latter case, since the road surface friction coefficient cannot be detected unless the tire is in a slip state, there is almost no opportunity to detect the road surface friction coefficient in a normal running state. Since the acceleration is obtained, there is a problem that the detection accuracy of the road surface friction coefficient is not high.

On the other hand, according to the present invention, when the vehicle is turning when actual lateral acceleration occurs, the tire may be in either a tire grip state where the tire is not running idle or a slip state where the tire is running idle. Also make it possible to obtain the road surface friction coefficient. Accordingly, an object of the present invention is to increase opportunities for detecting a road surface friction coefficient during driving of an automobile. Still another object of the present invention is to improve the detection accuracy of the road surface friction coefficient.

[0005]

In order to achieve the above object, the present invention utilizes the fact that the lateral acceleration obtained from the relationship between the slip angle and the cornering force is a function of the road surface friction coefficient. The present invention provides means for estimating a wheel slip angle from outputs of various sensors, means for estimating a cornering force from the slip angle, and means for obtaining an estimated lateral acceleration from the cornering force. The ratio between the lateral acceleration and the actual lateral acceleration obtained from the means for detecting the actual lateral acceleration is determined, and the road surface friction coefficient is determined from this ratio.

[0006]

According to the above-described means, the present invention can be applied to any of a tire grip state where the tire is not spinning and a slip state where the tire is idling, when the vehicle is turning in which actual lateral acceleration occurs. The road surface friction coefficient can be obtained. This increases the chances of detecting the road surface friction coefficient while driving the vehicle. Further, since the map can be used when estimating the cornering force from the slip angle, the accuracy of the estimation of the cornering force can be improved, and accordingly, the accuracy of detecting the road surface friction coefficient can be improved.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a diagram illustrating the system configuration of the present embodiment.
As each sensor, a wheel speed sensor 1 is provided for each wheel rotor, a yaw rate sensor 2 is provided near the center of gravity of the vehicle, and a steering angle sensor 2 'and an acceleration sensor 3 are further provided. Output signals of these sensors are input to the control device 4. The control device 4 estimates the road surface friction coefficient from the output signal of each sensor by an estimation algorithm described below, and displays the road surface friction coefficient on the display device 5 to inform the driver of the road surface condition.

FIG. 1 shows an algorithm for estimating a road surface friction coefficient. Output signals of the wheel speed sensor 1, the yaw rate sensor 2, the steering angle sensor 2 ', and the acceleration sensor 3 are input to the control device 4. The control device 4 includes a slip angle estimating means 6, a cornering force estimating means 7, an estimated lateral acceleration calculating means 8, and a road surface friction coefficient estimating means 9.

Hereinafter, the operation of each means in the control device 4 will be described. The slip angle estimation means 6 calculates the following [Equation 1] to [Equation 1] from the wheel speed of each wheel obtained from the wheel speed sensor 1, the yaw rate obtained from the yaw rate sensor 2, and the steering angle obtained from the steering angle sensor 2 '. The slip angle of the front wheel and the rear wheel is estimated using Expression 3]. The tire slip angle is represented by the following [Equation 1] and [Equation 2] from a vehicle motion model having two degrees of freedom.

[Equation 1] β _f = δ− (β + I _f γ / V) [Equation 2] β _r = β−I _r γ / V

Here, β _f : front wheel slip angle (rad) β _r : rear wheel slip angle (rad) β: center of gravity point slip angle (rad) δ: front wheel tire angle (rad) _If : distance between front wheel axle center of gravity. (m) I _r: rear wheel axle distance between the centers of gravity (m) gamma: yaw rate (rad / sec) V: vehicle speed (m / sec) [Equation 1] [Equation 2] in I _f, I _r is determined by the vehicle Things. The vehicle speed V can be obtained from a wheel speed signal obtained from the wheel speed sensor 1. The front wheel tire angle δ can be obtained from the steering angle.

The center-of-gravity point slip angle β in [Equation 1] and [Equation 2]
Is obtained by the following [Equation 3]. [Equation 3] β = ∫ (K _R G _Y / V−γ) dt where K _R : roll component correction coefficient of lateral acceleration G _Y : lateral acceleration (m / s ² ) γ: yaw rate (rad / sec)

Next, the cornering force estimating means 7
Is a slip angle beta _f estimated for the front wheels, the slip angle beta _r estimated for the rear wheels, for estimating a cornering force Cf with the map shown in FIG. The map of the slip angle-Cf characteristic is determined based on data obtained from vehicle experiments. First, a lane change test is performed with the front-rear slip ratio set to zero, and a slip angle-Cf characteristic map is determined. Next, the same test is performed by changing the front-rear slip ratio, and the test is performed at a required front-rear slip ratio.

FIG. 3 shows three values obtained by changing the front-back slip ratio.
Is shown. Curve with front / rear slip ratio = 0
Is shown at the top, and the slip ratio before and after increases
The lower the characteristic curve moves. Estimate about the front wheels
Slip angle β_fAnd the slip angle estimated for the rear wheel
β _rFrom, using the map, the cornering force Cf
When estimating, the front and rear wheel speed sensors 1
Calculate the calculated front-rear slip ratio and calculate the front-rear slip ratio.
Cf is estimated from the slip angle as a parameter.

In this embodiment, Cf is calculated from the slip angle.
Is obtained, the estimated lateral acceleration close to the actual lateral acceleration can be obtained even in a region where the slip angle is large. If the slip angle and Cf are treated as having a proportional relationship as in the above-described conventional example, the accuracy of the estimated lateral acceleration obtained in a region where the slip angle is large is reduced. However, in this embodiment, an estimated lateral acceleration close to the actual lateral acceleration can be obtained even in a region where the slip angle is large.

Further, in the present embodiment, when Cf is obtained from the slip angle, the characteristic curve is changed using the longitudinal slip ratio as a parameter. As a result, not only can the road surface friction coefficient be obtained by using Cf at the time of tire grip when the wheel does not spin, but also the road surface friction coefficient can be obtained in consideration of the Cf that has decreased during wheel idling. Therefore, according to the present embodiment, the detection accuracy of the road surface friction coefficient can be improved.

The cornering force Cf obtained as described above is a force acting in a direction perpendicular to the traveling direction of the vehicle. Therefore, since the sum of Cf of the four tires is equal to the force acting in the lateral direction of the vehicle, the following equation (Equation 4) holds. The estimated lateral acceleration calculating means 8 calculates the following [Equation 4] from the sum of the cornering forces Cf at each wheel.
Is used to calculate the estimated lateral acceleration. [Equation 4] G _Y = C _f / M where G _Y : lateral acceleration (m / s ² ) M: vehicle weight (kg)

The road friction coefficient estimating means 9 calculates the ratio of the estimated lateral acceleration obtained from the estimated lateral acceleration calculating means 8 to the actual lateral acceleration obtained from the acceleration sensor 3 and calculates the ratio of (actual lateral acceleration / The road surface friction coefficient μ is estimated using the estimated lateral acceleration) -μ characteristic. This (actual lateral acceleration / estimated lateral acceleration)
The -μ characteristic indicates that on a road surface having a high road friction coefficient μ, the actual lateral acceleration is substantially equal to the estimated lateral acceleration, and on a road surface having a low road friction coefficient μ, the actual lateral acceleration is smaller than the estimated lateral acceleration. We are using.

The road friction coefficient obtained by the road friction coefficient estimating means 9 is input to the display device 5 as an output signal of the control device 4. The display device 5 displays the input road surface friction coefficient on the screen to notify the driver of the road surface condition. Then, when the road surface friction coefficient becomes dangerous for driving, the driver is notified of the danger to encourage safe driving.

[0020]

According to the present invention, the estimated lateral acceleration is calculated, and the road surface friction coefficient is detected by comparing the actual lateral acceleration with the estimated lateral acceleration. For this reason, if the vehicle is turning at which the actual lateral acceleration occurs, the road surface friction coefficient can be detected in any of the tire grip state where the tire is not idling and the slip state where the tire is idling. Therefore, the chance of detecting the road surface friction coefficient increases. Therefore, the opportunity for notifying the driver of the vehicle of the road surface condition is increased, and safe driving can be promoted. In addition, since the lateral motion of the vehicle is taken into account when calculating the road surface friction coefficient, it is possible to prevent deterioration of the estimation accuracy at the time of turning.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an algorithm for estimating a road friction coefficient according to an embodiment of the present invention.

FIG. 2 is a system configuration diagram of an embodiment of the present invention.

FIG. 3 is a map used in the Cf estimating means of FIG. 1;

FIG. 4 is a map used by a road surface friction coefficient estimating unit in FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Wheel speed sensor 2 ... Yaw rate sensor 2 '... Rudder angle sensor 3 ... Acceleration sensor 4 ... Control device 5 ... Display device 6 ... Slip angle estimation means 7 ... Cornering force estimation means 8 ... Estimated lateral acceleration calculation means 9 ... Road surface friction Coefficient estimation means

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-63-284066 (JP, A) JP-A-4-126667 (JP, A) JP-A-4-325357 (JP, A) JP-A-4- 126670 (JP, A) JP-A-4-135923 (JP, A) JP-A-6-206563 (JP, A) JP-A-5-502421 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B62D 6/00-6/06 B62D 7/14

Claims (1)

(57) [Claims] 1. A means for estimating a slip angle of a wheel, a means for estimating a cornering force from an obtained slip angle, a means for calculating an estimated lateral acceleration from an obtained cornering force, a means for detecting an actual lateral acceleration, and A device for detecting a road surface friction coefficient, comprising: means for estimating a road surface friction coefficient from the estimated lateral acceleration and the actual lateral acceleration.