JPH09281030A - Apparatus for estimating coefficient of friction of road surface - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the estimation accuracy of a road surface frictional coeffe without bringing about an increase in calculation quantity by estimating the road surface frictional coeff. (μ) based only on yaw rate value at a time when a steering wheel is turned incrementally. SOLUTION: An interface 4 reads respective physical quantities of a steering angle, a tire rotational speed and a real yaw rate to operate a car speed and steering angular velocity and a steering discrimination circuit 6 discriminates a steering direction from the steering angle and the steering angular velocity. For example, when rightward steering is set to a positive direction, a steering angle always becomes a positive code in rightward steering and steering angular velocity is positive when a steering wheel is turned incrementally and becomes negative when turned to be returned. Therefore, in a negative case, return steering is discriminated to to inhibit the identification of a parameter and the previously sampled road surface μ estimate value held by a holding circuit 7 is outputted as a this time value. As a result, trouble such that the road surface μ estimate value becomes high at a time of return turning is eliminated and a true road surface μ is estimated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a road surface friction coefficient estimating device for estimating a road surface friction coefficient based on a comparison between a standard yaw rate value obtained from a steering angle and a vehicle speed and an actual yaw rate value obtained by a yaw rate sensor or the like. It is about.

[0002]

2. Description of the Related Art A road surface μ is estimated by utilizing a change in tire cornering force (or tire cornering power) under the same steering conditions in response to a change in road friction coefficient (hereinafter referred to as road surface μ). It is known how to do it. In particular, the present applicant traveled on a dry road surface (hereinafter referred to as high μ road) having a high friction coefficient calculated from the actual yaw rate obtained from the yaw rate sensor and the steering angle and the vehicle speed at that time, which was filed in Japanese Patent Application No. 7-240810. Parameter estimation based on the theoretical standard yaw rate (hereinafter referred to as yaw rate dry model) that may occur when estimating the road surface μ is the output of sensors commonly used in mass-produced vehicles. Since the value can be used as it is, its application range is expected to be large.

Specifically, as shown in FIG. 4, on the high μ road, the actual yaw rate (dotted line) becomes almost equal to the yaw rate dry model (solid line), while on the low μ road, the actual yaw rate is shown in FIG. As shown, due to the slip between the road surface and the tire, the gain of the actual yaw rate becomes lower than that of the yaw rate dry model, and the phase also becomes delayed. From the difference between the yaw rate dry model and the actual yaw rate, the road surface μ
However, since the road surface μ is estimated with the minimum amount of calculation, conventionally, the method of identifying the parameter for estimating the road surface friction coefficient using the gain difference as a ratio without adding the phase difference to the calculation has been proposed. Was being considered.

[0004]

However, according to the above-mentioned conventional method, the yaw rate dry model is used when relatively fast reverse steering is performed on a low μ road as shown in FIG. 6, for example. Since it is mainly calculated from the steering angle, it decreases instantaneously following changes in the steering angle, but the actual yaw rate does not decrease immediately after the turning point because it is accompanied by a phase delay. The actual yaw rate may be larger than that of the yaw rate, and even if the steering speed is low where the phase delay does not become extremely large, the actual yaw rate may be larger than that of the yaw rate dry model. An accurate estimate of the road surface μ can be obtained because the difference from the yaw rate is increasing, but when you start turning back the steering wheel,
Due to the phase delay of the actual yaw rate, the estimated value of the road surface μ was higher than it actually was.

An object of the present invention is to solve the problems of the prior art and to provide a road surface friction coefficient estimating device capable of improving the estimation accuracy of the road surface μ without increasing the calculation amount. It was issued.

[0006]

In order to achieve such an object, according to the present invention, the steering state at that time, that is, the state of increasing the steering angle or the state of returning the steering angle is determined, and the steering wheel is When starting to return, the road surface friction coefficient estimated value obtained just before turning back is held and output.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 shows a schematic structure of a road surface friction coefficient estimating device according to the present invention. This device is provided with a steering angle sensor 1 for a steering wheel, a tire rotation speed sensor 2,
In addition, the yaw rate sensor 3, an input interface 4 for inputting the output values of these sensors and converting it into a desired data amount, and a road surface for calculating an estimated value of the road surface μ based on each physical quantity processed by the input interface 4 The μ estimation circuit 5, the steering determination circuit 6 that determines the current steering state, that is, whether the steering angle is increased or returned, and the holding circuit 7 that holds the previously estimated road surface μ estimation value.
And the estimated value switching circuit 8 that selectively outputs the previous road surface μ value held by the holding circuit 7 and the current road surface μ value calculated by the road surface μ estimation circuit 5.

Next, a basic processing flow of the present invention will be described with reference to FIG. First, from the output of the steering angle sensor 1, the output of the tire rotation speed sensor 2, and the output of the yaw rate sensor 3, the input interface 4 reads the physical angles of the steering angle, the tire rotation speed, and the actual yaw rate (step 1). The vehicle speed and the steering angular velocity are calculated from these outputs (step 2). Next, the steering discrimination circuit 6
Calculates a by substituting the steering angle θ and the steering angular velocity V _H into the following equation (step 3). a = θ ・ V _H

From this result, the steering direction is determined by the sign of a (step 4). For example, if the right turn is in the positive direction, the steering angle θ always has a positive sign in the right turn.
The steering angular velocity V _H is positive when the steering is increased, but is negative when the steering is returned. Therefore, if the sign of a is negative here, it is judged to be the return steering and the parameter identification is prohibited (step 5), and the previously sampled road surface μ estimation value held by the holding circuit 7 is output as the current value. (Step 6).

On the other hand, when it is determined that the sign of a is positive, that is, it is increased, the parameters are identified (step 7), the road surface μ estimation circuit outputs the estimated value calculated this time, and the previous value is output. Is updated (step 8).

In this way, as shown by the chain double-dashed line in FIG. 3, by holding the value immediately before the return steering and outputting this, the yaw rate dry model ( The values of the thick line) and the actual yaw rate (dotted line) approach and reverse, and as a result, the road surface μ as shown by the solid line
The inconvenience that the estimated value becomes high at the time of switching back is solved, and the road surface μ that actually matches is output.

[0013]

As described above, according to the present invention, since the road surface μ is estimated based only on the yaw rate value when the steering wheel is increased, the yaw rate drive due to the phase delay of the actual yaw rate when returning the steering wheel is performed. The approach / reversal phenomenon of the ratio with the model is ignored, and the estimated value of the road surface μ is prevented from becoming higher than the actual value. In addition, in the estimation method for estimating the road surface μ by the ratio of the yaw rate dry model and the actual yaw rate during steering, basically, the larger the two amounts, the higher the S / N ratio and the higher the estimation accuracy. Become. Therefore, by adopting the value at the time when the steering wheel has the maximum turning angle and the yaw rate also has the maximum value, the estimation accuracy increases,
The reliability of the road surface μ estimation value can be further improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a device of the present invention.

FIG. 2 is a processing flowchart of the apparatus of the present invention.

FIG. 3 is a comparison diagram of μ estimated value, actual yaw rate, and yaw rate dry model.

FIG. 4 is a comparative diagram of a yaw rate on a high μ road and a yaw rate dry model.

FIG. 5 is a comparison diagram of an actual yaw rate on a low μ road and a yaw rate dry model.

FIG. 6 is a comparison diagram of an actual yaw rate and a yaw rate dry model when switching is performed on a low μ road.

[Explanation of symbols]

 1 Steering Angle Sensor 2 Tire Rotation Speed Sensor 3 Yaw Rate Sensor 4 Input Interface 5 Road Surface μ Estimating Circuit 6 Steering Discriminating Circuit 7 Holding Circuit 8 Estimated Value Switching Circuit

Claims (1)

[Claims] 1. A real yaw rate output means for outputting a real yaw rate signal of a vehicle, a yaw rate model output means for outputting a standard yaw rate signal that appears when a vehicle runs on a standard road surface with standard tires, and at least the actual yaw rate signal. And a standard yaw rate signal, the road surface friction coefficient estimating device is provided with a calculating means for estimating a road surface friction coefficient, the steering determining means for determining a steering state of a steering wheel, and the road surface friction coefficient estimation previously calculated. It has a value holding means and a switching means for selecting and outputting the value of the holding means and the road surface friction coefficient estimated value calculated this time, and the steering wheel turning back operation is discriminated by the steering discriminating means. And a value held by the holding means immediately before switching back is output from the switching means. .