JP2001253334A - Device and method for determining coefficient of road surface friction - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device for determining a road surface friction coefficient capable of enhancing vehicle performance and safety by determining a coefficient of friction between a road surface and a tire based on rotation information of tire wheels. SOLUTION: This device comprises a rotational speed detecting means for regularly detecting a rotational speed of four wheel tires of a vehicle, a first computing means for calculating a slip ratio based on a value determined by the rotational speed detecting means, a second computing means for finding a relational expression showing the relation between the slip ratio and acceleration/deceleration of a vehicle, and a friction coefficient determining means for determining a coefficient of friction between a road and a tire based on the gradient in the relation found by the second computing means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an apparatus and a method for determining a road surface friction coefficient. More specifically, a road surface friction coefficient determining device that can improve the performance and safety of a vehicle by determining a friction coefficient (road surface friction coefficient) between a road surface and a tire using rotation information of four tire wheels. And methods.

[0002]

2. Description of the Related Art When a vehicle is suddenly accelerated or braked on a slippery road surface, there is a risk that tires may slip and spin. Also, sudden steering may cause the vehicle to skid or spin.

[0003] Conventionally, before the braking force between the tire and the road surface exceeds the maximum value and the tire is locked, the brake torque acting on the wheel is reduced to prevent the wheel from being locked, An anti-lock brake device for controlling the number of rotations of a wheel at which a maximum braking force is obtained has been proposed (Japanese Patent Application Laid-Open No. 60-99757, Japanese Patent Application Laid-Open No. Hei 1-9957).
249559).

For example, in the control of the anti-lock brake device, a slip ratio is calculated from a judgment speed of a vehicle and a detected wheel speed (rotation speed), and the calculated slip ratio matches a predetermined reference slip ratio. The braking force is controlled so as to follow the maximum braking force.

In the control of such an ABS device or the like, the friction coefficient μ of the road surface is used. That is, according to the road surface friction coefficient μ (road surface μ), for example, the control content is changed between the case of high μ and the case of low μ to perform optimal control.

[0006]

The above-mentioned JP-A-60-99
In the device disclosed in Japanese Patent No. 759, a vehicle acceleration is obtained from a driven wheel when a slip occurs, and the road surface μ is determined using the acceleration.

That is, according to this publication, when the vehicle acceleration is A and the vehicle weight is W at the time of slip, the driving force F required for accelerating the vehicle can be obtained by F = WAA / g (g is Gravitational acceleration). On the other hand, the driving force F is determined by the frictional force between the driving wheel and the road surface, and is calculated by using the load Wr applied to the driving wheel and the road surface μ to obtain F = μ ·
Wr. From these two equations, the road surface μ
Is determined as μ = W / Wr · g × A.

However, the road surface μ obtained by this equation
Is the road surface μ at the time of calculating the vehicle acceleration A by replacing the acceleration of the driven wheel obtained by simply differentiating the rotational speed of the driven wheel with the vehicle acceleration A, and the road surface between the actual road surface and the tires. Whether it is μ or not, the probability is very high if it is not.

Therefore, if various types of vehicle motion control such as ABS are performed based on such a road surface μ, the control does not correspond to the actual road surface μ, and there is a possibility that inappropriate control may be performed. Further, even when the driver is warned of a slippery road surface, there is a possibility that an erroneous report may be issued on the determined road surface μ. Furthermore, since the slip ratio at which the maximum braking force is obtained differs depending on the road surface μ, when the follow-up control is performed with a fixed reference slip ratio, the braking distance may be long or the tire may be locked. .

As a countermeasure, it is necessary to determine the road surface condition and change the reference slip ratio in accordance with the determined road surface μ. However, there is no technique for determining the road surface μ with high accuracy.

The present invention provides a road friction coefficient determining apparatus and method capable of improving the performance and safety of a vehicle by determining a friction coefficient between a road surface and a tire using rotation information of four tire wheels. The purpose is to provide.

[0012]

According to the present invention, there is provided a road surface friction coefficient determining apparatus comprising: a rotation speed detection unit for periodically detecting rotation speeds of four tires of a vehicle; and a measured value obtained by the rotation speed detection unit. First calculating means for calculating a slip ratio;
A second equation for obtaining a relational expression between the slip ratio and the acceleration / deceleration of the vehicle
It is characterized by comprising arithmetic means and friction coefficient determining means for determining a friction coefficient between the road surface and the tire based on the slope of the relational expression obtained by the second arithmetic means.

The method of determining a coefficient of road friction according to the present invention includes the steps of periodically detecting the rotational speeds of four tires of a vehicle, calculating a slip ratio from the measured rotational speeds, A step of obtaining a relational expression between the ratio and the acceleration / deceleration of the vehicle; a step of comparing a slope of the relational expression with a preset threshold value; and judging a coefficient of friction between the road surface and the tire from a result of the comparison. And a step of performing

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an apparatus and a method for determining a road friction coefficient according to the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a block diagram showing an embodiment of a road friction coefficient determining apparatus according to the present invention, FIG. 2 is a block diagram showing an electric configuration of the road friction coefficient determining apparatus in FIG. 1, and FIG.
Is a schematic diagram showing a relationship between a road surface μ and a slip ratio, FIG. 4 is a flowchart according to the present embodiment, and FIG. 5 is a diagram showing a change over time of a regression coefficient when a road surface condition is different.

As shown in FIG. 1, a road friction coefficient determining apparatus according to an embodiment of the present invention periodically determines the rotational speeds of wheel tires provided on tires FLW, FRW, RLW and RRW of a four-wheeled vehicle. The output of the rotational speed detecting means S is transmitted to a control unit 1 such as an ABS. As shown in FIG. 2, the control unit 1 is connected to an alarm display 2 which is a display means such as a liquid crystal display, a plasma display, or a CRT. Three
Is an initialization switch operated by the driver.

The rotation speed detecting means S generates power by using a rotation such as a wheel speed sensor or a dynamo which generates a rotation pulse using an electromagnetic pickup or the like and measures the rotation speed from the number of pulses. An angular velocity sensor including one that measures the rotation speed from this voltage can be used.

As shown in FIG. 2, the control unit 1 has an I / O interface 1a required for transmitting and receiving signals to and from an external device, and a C functioning as a center of arithmetic processing.
A PU 1b, a ROM 1c in which a control operation program of the CPU 1b is stored, and a RAM 1d from which data and the like are temporarily written when the CPU 1b performs a control operation, and from which the written data and the like are read. I have.

In the present embodiment, the control unit 1
A first calculating means for calculating a slip ratio (a ratio of a wheel speed of a front wheel tire to a wheel speed of a rear wheel tire) from a value measured by the rotation speed detecting means S; A second calculating means for obtaining a relational expression between the ratio and the acceleration / deceleration of the vehicle; and a friction coefficient determination for determining a frictional coefficient μ between the road surface and the tire based on a slope of the relational expression obtained by the second calculating means. Means. The friction coefficient determining means includes a comparing means for comparing the slope of the relational expression obtained by the second calculating means with a preset threshold value.

In the present embodiment, the rotational speed of the four tires is detected in 0.1 seconds or less, preferably in 0.05 seconds or less. Although the acceleration / deceleration of the vehicle can be measured by a G sensor, it is preferable to calculate from the average wheel speed of four wheels or driven wheels from the viewpoint of cost.

Next, the slip ratio and the acceleration / deceleration of the vehicle are determined by moving average for each sampling time as an average value of data for a fixed time, for example, data of at least 0.1 second or more. Based on (a fixed number of slip ratios and acceleration / deceleration of the vehicle), a relational expression between the slip ratio and the acceleration / deceleration of the vehicle is obtained.

Further, using the moving averaged slip ratio and vehicle acceleration / deceleration data, for example, at least five or more pieces of data, mutual linear regression coefficients and correlation coefficients of the slip ratio and the vehicle acceleration / deceleration are used. Ask for. Here, if the slip ratio obtained by the moving average is equal to or greater than a certain value or equal to or less than a certain value (for example, equal to or greater than 0.07 or equal to or less than -0.07), the slip ratio is not used for calculating the regression coefficient. Instead, an alarm may be issued as a slip alarm.

If the value of the correlation coefficient is equal to or greater than the set value, the regression coefficient is updated and held, and the value of the regression coefficient is compared with a preset threshold value to determine the difference between the tire and the road surface. Determine the coefficient of friction.

In this embodiment, when the road surface friction coefficient determining means determines that the road surface is low μ, an alarm is issued by the alarm display 2.

Hereinafter, the operation of the road friction coefficient determining apparatus according to the present embodiment will be described in accordance with the following procedures.

Four-wheel tires FLW, FRW, RL of the vehicle
From the rotational speeds of W and RRW, the wheel speed (V
1 _n , V 2 _n , V 3 _n , V 4 _n ).

For example, each wheel tire FLW, FRW, RLW,
The wheel speed data at a certain point in the RRW is calculated based on the wheel speeds V1 _n , V1
2 _n , V 3 _n , and V 4 _n .

Next, the average wheel speeds (Vf ₁ , Vd _n ) of the driven wheels and the drive wheels are calculated.

In the case of front-wheel drive, wherein the average wheel speeds Vf _n1, Vd _n of the driven wheel and the driving wheel at a certain time following (1), obtained by (2). _{Vf n = (V3 n + V4} n) / 2 ··· (1) Vd n = (V1 n + V2 n) / 2 ··· (2)

[0030] To followed calculates Af _n (acceleration ie vehicle) average wheel acceleration of the driven wheels.

Assuming that the average wheel speed Af _{n -1} is obtained from the wheel speed data immediately before the average wheel speed Vf _{n of} the driven wheel, the average wheel acceleration / deceleration Af _n of the driven wheel is _expressed by the following equation (3). Desired. Af _n = a · (Vf _n −Vf _n−1 ) / Δt / g (3)

Here, Δt is a time interval (sampling time) between the wheel speeds Vf _n and Vf _n−1 calculated from the wheel speed data, g is a gravitational acceleration, and a is a wheel speed (k
m / h) and a constant (1 / 3.6) for matching the unit of acceleration (m / s). The sampling time needs to be 0.1 second or less in order to reduce the variation in data and make a determination in a short time. More preferably, the time is 0.05 seconds or less.

Next, a slip ratio is calculated in accordance with the value of the acceleration / deceleration Af _n of the vehicle.

First, when the vehicle is slipping with the driving wheels locked in the acceleration state (Vd _n = 0, Vf _n ≠ 0), the driving wheels cause wheel spin when the vehicle is stopped in the deceleration state. and when that _{(Vf n = 0, Vd n} ≠ 0) include, but are not occur, the slip ratio S _n the following formula (4),
Calculate from (5). If it is af _n ≧ 0 and _{Vd n ≠ 0, S n =} (Vf n -Vd n) / Vd n ··· (4) If it is af _n <0 and _{Vf n ≠ 0, S n =} (Vf _{n -Vd n) / Vf n ···} (5) otherwise said, the S _n = 1.

Next, the data of the slip ratio and the acceleration / deceleration of the vehicle are subjected to a moving average process for each sampling time.

Since the road surface μ during actual running is not constant and changes every moment, it is necessary to estimate the road surface μ in a short time. In the case of performing linear regression, the reliability of the obtained regression coefficients is poor unless the number of data exceeds a certain value. Therefore, data is sampled every single sampling time, for example, every several tens of milliseconds, and the moving average of the data having a large variation obtained in this sampling time is reduced, thereby reducing the data variation without reducing the number of data. can do.

As for the slip ratio, MS _n = (S ₁ + S ₂ +... + S _n ) / N (6) MS _{n + 1} = (S ₂ + S ₃ +... + S _{n + 1} ) / N (7) MS _{n + 2} = (S ₃ + S ₄ +... + S _{n + 2} ) / N (8)

Regarding the acceleration / deceleration of the vehicle, MAf _n = (Af ₁ + Af ₂ +... + Af _n ) / N (9) MAf _{n + 1} = (Af ₂ + Af ₃ +... + Af _{n + 1} ) / N (10) MAf _{n + 2} = (Af ₃ + Af ₄ +... + Af _{n + 2} ) / N (11)

Next, the first-order regression coefficients of the slip ratio and the acceleration / deceleration of the vehicle, that is, the regression coefficient K1 of the slip ratio for the acceleration / deceleration of the vehicle and the regression coefficient K2 of the acceleration / deceleration of the vehicle for the slip ratio are expressed by the following equations, respectively. (1
2) Calculate from (13).

[0040]

(Equation 1)

[0041]

[Table 1]

The correlation coefficient R is as follows: R = K1 × K2 (14)

The correlation coefficient is set to a set value, for example, 0.6
If so, the value of the regression coefficient K1 is updated.

Here, the relationship between the slip ratio and the acceleration / deceleration of the vehicle is the same as the μ-s curve of a general tire and the road surface, and the difference between the road surfaces μ (high μ road R1, middle μ road R2 ,
As shown in FIG. 3 by the low μ road R3). The regression coefficients K1 and K2 are obtained by calculating the gradient of the μ-s curve. Although the μ-s curve is originally a curve, it is substantially a straight line in a range of a slip ratio generated during actual running. That is, the μ-s curve can be represented by the equation y = aX + b. The coefficient a at this time is the regression coefficient (K1, K2), which means the gradient of the straight line.
Here, depending on whether y is a slip ratio or an acceleration,
a = K1 or a = K2. In the present embodiment, the road surface μ is determined by the value of K1 with y as the slip ratio. Of course, the road surface μ can also be determined from the regression coefficient K2.

The reason why the correlation coefficient R is obtained is to determine whether or not the obtained value of the regression coefficient is appropriate. That is, when the value of the correlation coefficient R is large, there is a correlation between the slip ratio and the acceleration, and the obtained regression coefficient is appropriate. However, when the value of the correlation coefficient R is small, the correlation between the two is obtained. Since the regression coefficient obtained without correlation is inappropriate, the road surface μ is not determined based on the value.

Next, the value of the road surface μ is calculated based on the value of the regression coefficient K1.
Is estimated.

For example, K1 ≦ 0.1 High μ road (μ = 0.7 or more) 0.1 <K1 ≦ 0.16 Medium μ road (μ = 0.3 to 0.7) 0.16 <K1 Low μ road (μ = 0.3 or less)

The threshold value of the regression coefficient K1 can be obtained, for example, from experimental data up to now.

Next, the driver is warned of road surface information (such as slipperiness).

Further, the condition of the road surface is determined by an ABS device or a TR.
Used to control the C device.

Next, the present invention will be described based on examples, but the present invention is not limited to only these examples.

[0052]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a studless tire (Glass Pick D manufactured by Sumitomo Rubber Industries, Ltd.) was used as a four-wheel tire for a front wheel drive vehicle.
Using S-1), the vehicle is placed on dry asphalt road R1,
The vehicle traveled on the snow compacted road R2 and the frozen asphalt road R3. The traveling condition at this time is traveling around 50 km / h on each road surface. Regarding the sampling time of the wheel speed of the wheel, in order to increase the number of data and to eliminate variations and measurement errors, for example, the sampling time is set to 40 ms because 1 second is too long.

Then, as shown in FIG. 4, based on the wheel speed pulse output from the rotation speed detecting means, the wheel speed is taken in, and the average wheel acceleration / deceleration of the driven wheels (vehicle acceleration / deceleration) every 40 ms and the front and rear The wheel slip ratio was calculated (steps S1, S2, S3).

Next, the average wheel acceleration / deceleration of the driven wheels and the slip ratio of the front and rear wheels were averaged over 25 data for one second, and determined as a moving average value for each sampling time (40 ms) (steps S4 and S5). ). here,
If the slip ratio becomes 0.05 or more or -0.05 or less, a slip warning is issued at that time (step 6). In other cases, the average wheel acceleration / deceleration of the driven wheel with respect to the slip ratio is set to 1 based on the data of the averaged wheel acceleration / deceleration of the driven wheel and the slip ratio of 50 pieces.
The next regression coefficient K1 was obtained (step S7).

Further, the correlation coefficient R at this time is obtained (step 8). If the correlation coefficient R is 0.6 or more, the value of the regression coefficient K1 is updated and held (step 9). FIG. 5 shows the change over time of the regression coefficient obtained on each road surface at this time. In the case of dry asphalt R1, the regression coefficient K1 constantly changes below 0.12,
On the compacted snow road R2, it changes between about 0.1 and 0.2. On the frozen asphalt road R3, the regression coefficient K1
It can be seen that the value of fluctuates greatly. This is because the state of the road surface is not constant. In fact, the road surface evaluated was apparently black and asphalt, but when it got off the car, it was frozen everywhere and was very slippery.

Then, the value of the regression coefficient K1 is compared with a preset threshold value (0.12 and 0.18) to determine the friction coefficient μ between the tire and the road surface. The calculation of the regression coefficient K1 and the correlation coefficient R takes a sampling time (40 ms)
The road surface μ was determined by the following threshold values (steps 10, 11, and 12).

K1 ≦ 0.12 High μ road (neither alarm nor warning is issued) 0.12 <K1 ≦ 0.18 Medium μ road (slip warning is issued) 0.18 <K1 Low μ road (slip alarm Emits)

As a result, in the case of dry asphalt, neither a slip warning nor a slip warning was generated. On snow-covered roads, almost always a slip warning was issued and, in rare cases, a slip warning. On frozen asphalt, slip warnings as well as slip warnings were issued frequently.

In this embodiment, the number of data for obtaining the regression line is set to 50, but the present invention is not limited to this. However, if the number of data is too small, reliable results will not be obtained. Therefore, at least five or more are necessary. Conversely, if the number of data is too large, sampling time will be longer and the condition of the road surface will be reduced. If it changes one after another, the data will vary and the correlation coefficient will be low, which will increase the number of cases where the road surface μ cannot be determined. Therefore, it is desirable to determine this in consideration of the sampling time.

As described above, by using the present system, the road surface μ can be determined accurately and in a short time, and the driver can be informed that the vehicle is in a slippery and dangerous state.

Then, the information of the determined road surface μ is represented by A
Road surface μ by using for BS equipment and TRC equipment
The most suitable control can be performed according to. In addition, low μ
If it is determined that the road is a road, the driver can be warned that the road is slippery.

[0062]

As described above, according to the present invention,
Since the road surface μ can be determined accurately and in a short time only by the wheel rotation speed information of the four wheels, the performance and safety of the vehicle can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an embodiment of a road surface friction coefficient determining apparatus according to the present invention.

FIG. 2 is a block diagram showing an electrical configuration of the road surface friction coefficient determining device in FIG.

FIG. 3 is a schematic diagram showing a relationship between a road surface μ and a slip ratio.

FIG. 4 is a flowchart according to the embodiment.

FIG. 5 is a diagram illustrating a change over time of a regression coefficient when a road surface state is different.

[Explanation of symbols]

 Reference Signs List 1 control unit 2 alarm display 3 initialization switch FLW, FRW, RLW, RRW tire

[Procedure amendment]

[Submission date] March 27, 2000 (2003.
7)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0028

[Correction method] Change

[Correction contents]

Next, the average wheel speeds ( Vf _n , Vd _n ) of the driven wheels and the drive wheels are calculated.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0029

[Correction method] Change

[Correction contents]

In the case of front-wheel drive, the average wheel speed Vf _n of the following wheels and the driving wheels at a certain time, the Vd _n of the following formula (1),
It is determined by (2). _{Vf n = (V3 n + V4} n) / 2 ··· (1) Vd n = (V1 n + V2 n) / 2 ··· (2) ──────────────── ─────────────────────────────────────

[Procedure amendment]

[Submission date] May 24, 2000 (2005.2.
4)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0040

[Correction method] Change

[Correction contents]

[0040]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0041

[Correction method] Change

[Correction contents]

[0041]

Claims (6)

[Claims] 1. A rotational speed detecting means for periodically detecting rotational speeds of four tires of a vehicle; a first calculating means for calculating a slip ratio from a measured value by the rotational speed detecting means; Coefficient calculating means for determining a relational expression between the vehicle and the acceleration / deceleration of the vehicle, and friction coefficient determining means for determining a coefficient of friction between the road surface and the tire based on the inclination of the relational expression determined by the second calculating means A road surface friction coefficient determining device comprising: 2. A step of periodically detecting rotational speeds of four tires of a vehicle, a step of calculating a slip ratio from the measured rotational speed, and a relationship between the slip ratio and the acceleration / deceleration of the vehicle. Road surface friction comprising a step of obtaining an equation, a step of comparing the slope of the relational expression with a preset threshold value, and a step of determining a friction coefficient between the road surface and the tire from the result of the comparison. Coefficient determination method. 3. The method according to claim 1, wherein the detection of the rotation speed is at least 0.1.
3. The method for determining a road surface friction coefficient according to claim 2, which is performed in seconds or less. 4. The road surface friction coefficient determining method according to claim 2, wherein the acceleration / deceleration of the vehicle is calculated from the measured values of the rotational speed detecting means of the four tires. 5. The slip ratio and the vehicle acceleration / deceleration are determined by moving average for each sampling time as an average value of data for a fixed time, and the slip ratio and the vehicle speed are determined based on the moving average value. The road surface friction coefficient determining method according to claim 2, 3 or 4, wherein a relational expression with respect to acceleration / deceleration is obtained. 6. A first-order regression coefficient and a correlation coefficient between the slip ratio and the acceleration / deceleration of the vehicle are obtained using the moving averaged slip ratio and data of the acceleration / deceleration of the vehicle, and the correlation coefficient is obtained. When the value of is equal to or greater than a set value, the regression coefficient is updated and held, and the coefficient of friction between the tire and the road surface is determined by comparing the value of the regression coefficient with a preset threshold value. The road surface friction coefficient determination method described in the above.