JP3515040B2 - Road surface friction coefficient determination method - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates to relates to a road surface friction coefficient-size Sadakata <br/> method. More specifically, four by determining the coefficient of friction between the road surface and the tire (road friction coefficient) by using rotational information of the tire wheel, the road surface friction coefficient determination Priority determination that can enhance the performance and safety of the vehicle mETHODS about.

[0002]

2. Description of the Related Art When a vehicle is subjected to sudden acceleration or braking on a slippery road surface, there is a risk that the tires may slip and spin. In addition, sudden steering may cause the vehicle to slip or spin.

Therefore, 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 and the like for controlling the rotational speed of the wheel that provides the maximum braking force have been proposed (Japanese Patent Laid-Open No. 60-99757, Japanese Patent Laid-Open No. 1-99757).
249559, etc.).

For example, in the control of the anti-lock brake device, a slip ratio is calculated from the vehicle judgment speed and the detected wheel speed (rotational speed), and then the calculated slip ratio matches a preset reference slip ratio. The braking force is controlled so that the maximum braking force is followed.

In the control of such an ABS device, the friction coefficient μ of the road surface is used. That is, depending on the road surface friction coefficient μ (road surface μ), for example, the control content is changed between high μ and low μ to perform optimum control.

[0006]

The object of the invention is to be Solved by the Japanese Akira 60-99
In the device disclosed in Japanese Patent No. 759, the vehicle acceleration is obtained from the driven wheels when the slip occurs, and the road surface μ is determined using this acceleration.

That is, according to this publication, when the vehicle acceleration is A during slip and the vehicle weight is W, the driving force F required for accelerating the vehicle is obtained by F = W · A / 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 F = μ · is calculated by using the load Wr applied to the driving wheel and the road surface μ.
It can be expressed as Wr. From these two formulas, the road surface μ
Is calculated as μ = W / Wr · g × A.

However, the road surface μ obtained by this equation
Is the road surface μ at the time when the acceleration of the driven wheel, which is simply obtained by differentiating the rotational speed of the driven wheel, is replaced with the vehicle acceleration A, and the vehicle acceleration A is calculated. The road surface between the actual road surface and the tire is There is an overwhelming possibility when it is unknown whether it is μ or not stochastically.

Therefore, if various vehicle motion controls such as ABS are performed based on such a road surface μ, there is a possibility of executing an inappropriate control because the control does not correspond to the actual road surface μ. Further, even when the driver is warned that the road surface is slippery, there is a possibility that a false alarm 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, there is a risk that the braking distance will become longer or the tire will lock up. .

As a countermeasure against this, it is necessary to determine the road surface condition and change the reference slip ratio according to the determined road surface μ, but there is no technique for accurately determining the road surface μ.

The present invention, by determining the coefficient of friction between the road surface and the tires using the rotation information of the four wheels of the road surface friction coefficient-size Sadakata method can increase the performance and safety of the vehicle The purpose is to provide.

[0012]

The road surface friction coefficient judgment method of the present invention, in order to solve the problems] includes the steps of periodically detecting rotational speeds of tires of four wheels of the vehicle, the measured rotational speed or al, slip ratio a step of calculating, the step of obtaining a relational expression between acceleration of the slip ratio and the vehicle is set in advance and the inclination of the function engagement formula
And comparing the threshold, and a step of determining the coefficient of friction between the road surface and the tires from the result of the comparison, when a constant acceleration and deceleration of the slip ratio and the vehicle
As the average value of the data for the interval, for each sampling time
The moving average is used to obtain the moving average slip ratio.
And the vehicle acceleration / deceleration data are used to determine the slip ratio and the vehicle
Obtain the first-order regression coefficient and correlation coefficient of both acceleration and deceleration.
Therefore, if the value of the correlation coefficient is greater than or equal to the set value, the regression coefficient
Update and hold the value of the regression coefficient and preset
By comparing the threshold value, the friction coefficient between the tire and the road surface
Characterized that you determine the number.

[0013]

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, with reference to the accompanying drawings, illustrating the road surface friction coefficient-size Sadakata method of the present invention.

[0015] Figure 1 is a block diagram showing a road <br/> surface frictional coefficient determining equipment according to an embodiment of the present invention, FIG. 2 is a block diagram showing an electrical configuration of a road surface frictional coefficient determining unit in FIG. 1 3 is a schematic diagram showing the relationship between the road surface μ and the slip ratio,
FIG. 4 is a flow chart according to the present embodiment, and FIG. 5 is a diagram showing a change over time of the regression coefficient when the road surface condition is different.

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

As the rotation speed detecting means S, a rotation speed is generated using an electromagnetic pickup or the like to generate a rotation pulse and the rotation speed is measured from the number of pulses. An angular velocity sensor or the like 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 necessary for exchanging signals with an external device, and a C functioning as a center of arithmetic processing.
It comprises a PU 1b, a ROM 1c in which a control operation program for the CPU 1b is stored, and a RAM 1d in which data and the like are temporarily written when the CPU 1b performs a control operation and the written data and the like are read. There is.

In the present embodiment, the control unit 1
As a first solving means, there is provided a first calculating means for calculating a slip ratio (a ratio of a wheel speed of a front wheel tire and a wheel speed of a rear wheel tire) from a measured value by the rotation speed detecting means S, and the slip. Second calculation means for obtaining the relational expression between the ratio and the acceleration / deceleration of the vehicle, and friction coefficient determination for determining the frictional coefficient μ between the road surface and the tire based on the inclination of the relational expression obtained by the second calculation means. And means. The friction coefficient determining means includes 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 rotation speed of the tires of the four wheels is detected in 0.1 seconds or less, preferably 0.05 seconds or less. Although the acceleration / deceleration of the vehicle can be measured by the G sensor, it is preferable to calculate it from the average wheel speed of the four wheels or the driven wheels in terms of cost.

Next, the slip ratio and the acceleration / deceleration of the vehicle are obtained by moving averaging every sampling time as an average value of data for a certain period of time, for example, data of at least 0.1 second or more, and the moving averaged value is obtained. 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 data, the first-order regression coefficient and correlation coefficient of the slip ratio and the vehicle acceleration / deceleration are mutually obtained. Ask for. Here, if the slip ratio obtained by moving average is a certain value or more or a certain value or less (for example, 0.07 or more or −0.07 or less), use it for the calculation of the regression coefficient. Instead, an alarm may be issued as a slip alarm.

Then, when the value of the correlation coefficient is equal to or larger 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 compare the tire with the road surface. Determine the coefficient of friction.

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

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

Vehicle four-wheel tires FLW, FRW, RL
From the respective rotation speeds of W and RRW, the wheel speed (V
1 _n , V2 _n , V3 _n , V4 _n ) are calculated.

For example, each wheel tire FLW, FRW, RLW of the vehicle obtained from a sensor such as an ABS sensor,
The wheel speed data at a certain point of RRW is used as the wheel speeds V1 _n , V
_Let 2 _n , V3 _n , and V4 _n .

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

In the case of the front wheel drive, the average wheel speeds Vf _n and Vd _n of the driven wheels and the drive wheels at a certain point are _expressed by the following equation (1),
It is obtained by (2). Vf _n = (V3 _n + V4 _n ) / 2 (1) Vd _n = (V1 _n + V2 _n ) / 2 (2)

Next, the average wheel acceleration / deceleration (that is, vehicle acceleration / deceleration) Af _n of the driven wheels is calculated.

[0031] The average single from the previous wheel speed data from the wheel speed Vf _n of the following wheels and the average wheel speed V f _n-1, of each of the average wheel acceleration Af _n of the driven wheels following formula (3) Required by. 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.
It is a constant (1 / 3.6) for matching the unit of m / h) with the unit of acceleration (m / s). The sampling time needs to be 0.1 seconds or less in order to reduce the variation in data and to make a determination in a short time. More preferably, it is 0.05 seconds or less.

Then, the slip ratio is calculated according to the value of the acceleration / deceleration Af _n of the vehicle.

First, when the vehicle is slipping with the drive wheels locked in the acceleration state (Vd _n = 0, Vf _n ≠ 0), or in the deceleration state, the vehicle wheels are stopped and the drive wheels cause wheel spin. (Vf _n = 0, Vd _n ≠ 0), the slip ratio S _n is calculated by the following equation (4),
Calculate from (5). When Af _n ≧ 0 and Vd _n ≠ 0, S _n = (Vf _n −Vd _n ) / Vd _n (4) When Af _n <0 and Vf _n ≠ 0, S _n = (Vf _n− Vd _n ) / Vf _n (5) In other cases, S _n = 1.

Then, the data of the slip ratio and the acceleration / deceleration of the vehicle are subjected to moving averaging processing every sampling time.

Since the road surface μ during actual traveling is not constant and changes every moment, it is necessary to estimate the road surface μ in a short time. Further, when performing linear regression, the reliability of the obtained regression coefficient is poor unless there is a certain number of data. Therefore, data is sampled at short sampling time intervals, for example, every several tens of ms, and data with large variations obtained at this sampling time is subjected to a moving average, so that the number of data can be reduced without reducing the number of data. Can be reduced.

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

[0040]

[0041]

The correlation coefficient R is       R = K1 × K2 (14) Becomes

This correlation coefficient is a set value, for example, 0.6.
If it is above, 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 that of a general μ-s curve of a tire and a road surface, and a difference in road surface μ (high μ road R1, medium μ road R2). ,
Due to the low μ path R3), the result is as shown in FIG. The regression coefficients K1 and K2 are obtained by calculating the slope of the μ-s curve. This μ-s curve is originally a curve, but is substantially a straight line in the range of the slip ratio that occurs during actual traveling. That is, the μ-s curve can be expressed by the equation y = aX + b. The coefficient a at this time is a regression coefficient (K1, K2), which means the slope of a straight line.
Here, whether y is the slip ratio or the acceleration,
It may be 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 for obtaining the correlation coefficient R is to judge whether or not the value of the obtained 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, but when the value of the correlation coefficient R is small, the correlation coefficient R is large. Since the regression coefficient obtained without correlation is inappropriate, the road surface μ should not be judged by its value.

Then, according to the value of the regression coefficient K1, the road surface μ
To estimate.

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 the experimental data obtained so far.

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

Furthermore, the condition of the road surface can be measured by an ABS device or TR.
It is used to control the C device.

Next, the present invention will be explained based on examples, but the present invention is not limited to such examples.

[0052]

Example First, as a four-wheel tire for a front-wheel drive vehicle, a studless tire (Glass Pick D manufactured by Sumitomo Rubber Industries, Ltd.)
Use S-1) to drive the vehicle onto the dry asphalt road R1,
The compaction road R2 and the frozen Asfart road R3 were run. The running condition at this time is running around 50 km / h on each road surface. Regarding the sampling time of the wheel speed of the wheel, in order to eliminate the variation and the measurement error with a large number of data, for example, 1 second is too long, so the sampling time is set to 40 ms.

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

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

Further, the correlation coefficient R at this time is obtained (step 8), and 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, while the regression coefficient K1 has been constantly below 0.12,
In the snow-covered road R2, it has been transitioning between about 0.1 and 0.2. In the frozen asphalt road R3, the regression coefficient K1
It can be seen that the value of fluctuates greatly. This is because the condition of the road surface is not constant. In fact, the road surface that was evaluated seemed black and asphalt at first glance, but when I actually got out of 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 is performed at a sampling time (40 ms).
The road surface μ was determined based on the following threshold values (steps 10, 11, 12).

[0057]       K1 ≦ 0.12 High μ road (No alarm or warning is issued)       0.12 <K1 ≦ 0.18 Medium μ road (Slip warning is issued)       0.18 <K1 Low μ road (slip alarm is issued)

As a result, in the case of dry asphalt, neither slip warning nor slip warning occurred at all. In the case of a snow-covered road, a slip warning was issued almost constantly, and a slip warning was issued in rare cases. In frozen asphalt, not only slip warnings but also slip warnings were frequently issued.

In the present 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 cannot be obtained, so at least 5 or more are required, but if the number of data is too large, the sampling time will increase and the road surface condition will increase. In the case of successive changes, the data will be scattered and the correlation coefficient will be low on the contrary, resulting in more cases where the road surface μ cannot be discriminated. Therefore, it is desirable to decide in consideration of the sampling time.

As described above, by using the present system, the road surface μ can be accurately determined 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 set to A
By using it for BS equipment and TRC equipment, etc.
Optimal control can be performed according to Also, low μ
When the road is determined, the driver can be warned that the road surface is slippery.

[0062]

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

[Brief description of drawings]

1 is a block diagram showing a road surface friction coefficient determination equipment according to an embodiment of the present invention.

FIG. 2 is a block diagram showing an electrical configuration of the road surface friction coefficient determination 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 present embodiment.

FIG. 5 is a diagram showing a change over time in a regression coefficient when road surface conditions are different.

[Explanation of symbols]

1 control unit 2 alarm indicators 3 initialization switch FLW, FRW, RLW, RRW tires

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-7-112659 (JP, A) JP-A-6-298069 (JP, A) JP-A-8-216862 (JP, A) JP-A-7- 192086 (JP, A) JP-A-11-20649 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B60T 8/58 G01N 19/02

Claims (3)

(57) [Claims] 1. A step of periodically detecting the rotational speeds of four tires of a vehicle, a step of calculating a slip ratio from the measured rotational speeds, and a relationship between the slip ratio and the acceleration / deceleration of the vehicle. The method includes a step of obtaining an expression, a step of comparing a slope of the relational expression with a preset threshold value, and a step of determining a friction coefficient between a road surface and a tire from a result of the comparison , Adjust the slip ratio and vehicle acceleration / deceleration
As the average value of the data for a fixed time, the sampling time
And the moving average is calculated, and the moving averaged slip is calculated.
Using the ratio and vehicle acceleration / deceleration data, the slip ratio
And regression coefficient and correlation coefficient of acceleration and deceleration of vehicle
If the value of the correlation coefficient is greater than or equal to the set value, the regression coefficient
Update and hold the number, preset with the value of the regression coefficient
By comparing the threshold value with the
The road surface friction coefficient determining how to determine the friction coefficient. 2. The detection of the rotation speed is at least 0.1.
The road surface friction coefficient determination method according to claim 1, wherein performing a second. 3. A process according to claim 1 also <br/> 2 road surface friction coefficient determination method according to calculation from measured values of the rotational speed detecting means of the tire of the four-wheel acceleration or deceleration of the vehicle.