JP2003182553A - Road surface condition inferring method and device thereof and abs brake control method and device thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the erroneous operation of a system due to the degradation of the accuracy of an inferred value of a road surface friction coefficient in a condition in which a tire skids greatly and enhance the safety of a vehicle by discriminating the inferred road surface friction coefficient accurately. <P>SOLUTION: The vibration of a wheel is detected by a vibration sensor 11, and a vibration level of a vibration spectrum obtained by analyzing its frequencies is detected to infer a road surface friction coefficient continuously. A brake switch on/off detection means 16 is provided to detect the on/off of the brake switch. When it is discriminated that a brake is stepped on, the updating of the inferred value of the road surface friction coefficient is interrupted. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and a device for estimating a road surface condition during traveling, an ABS braking control method and a device for controlling an ABS brake based on the estimated road surface condition. .

[0002]

2. Description of the Related Art In order to improve the running stability of an automobile, it is required to accurately estimate a friction coefficient between a tire and a road surface (road surface friction coefficient) or a road surface condition and feed it back to vehicle control. In particular, if the road surface friction coefficient can be estimated in advance before a risk-avoidance operation such as braking / driving or steering is performed, for example, it will be possible to perform higher-level control of the ABS brake and further improve safety. To be In addition, it is possible to expect a reduction in accidents by allowing the driver to carry out a deceleration operation earlier by simply notifying the driver of the degree of danger. The applicant is, for example, Japanese Patent Application No. 200
In 0-190231 and Japanese Patent Application No. 2001-36048, the road surface condition during running is accurately estimated, and
A road surface state estimation method and apparatus, and a vehicle control method and apparatus, which can feedback-control the traveling state of the vehicle based on the estimated road surface state are proposed. These methods are based on the fact that the tires slip in the tread even during steady running, and the vibrations propagated to the tires, wheels and suspensions, or the gases in the propagated tires The minute fluctuation is detected, the frequency is analyzed, the vibration level or the pressure fluctuation level in at least one frequency band of the obtained vibration spectrum or pressure fluctuation spectrum is detected to estimate the road surface friction coefficient, and the above-mentioned estimation is performed. It controls the running state of the vehicle based on the road surface friction coefficient, which allows the road surface state to be maintained even on a rough road surface, which was difficult with the conventional technology, or even when the slip angle is zero. Accurate estimation can be performed, and vehicle safety can be further enhanced.

[0003]

However, in the above system, the road surface friction coefficient can be accurately estimated during straight traveling at a constant speed, or during gentle acceleration / deceleration or steering, but the slip of the tire with respect to the road surface becomes large. When the slip ratio, which is the ratio of the wheel speed of the tire to the vehicle body speed, becomes high, such as when accelerating or stepping on the brake, the estimated road surface friction coefficient Since the value of tends to be lower than the actual value, there is a possibility that the road surface condition and the risk may be erroneously determined when the slip is large.

The present invention has been made in view of the problems of the prior art, and by accurately determining the estimated road surface friction coefficient, the accuracy of the estimated value of the road surface friction coefficient in a state where the tire slips greatly is reduced. It is intended to prevent the malfunction of the system based on the above and to enhance the safety of the vehicle.

[0005]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that before the tire has a large slip,
That is, it is found that the malfunction of the system due to the above-mentioned slip can be prevented by detecting the road surface friction coefficient before starting the braking such as the sudden acceleration / deceleration and performing the appropriate vehicle control from the initial stage of the braking. It has arrived. That is, the road surface state estimating method according to claim 1 is
At least one of tire vibration, wheel vibration, suspension vibration, and tire pressure fluctuation is detected, and the vibration level of the vibration spectrum obtained by frequency analysis of this is detected, or the pressure fluctuation level of the pressure fluctuation spectrum is detected. The feature is that the road friction coefficient is estimated, the on / off of the brake switch is detected, and when it is determined that the brake is stepped on, the updating of the estimated road friction coefficient is interrupted. Thus, since it is possible to prevent the road surface friction coefficient from being estimated after the brake is depressed, it is possible to prevent the malfunction of the system due to the slip of the tire.

Further, in the road surface state estimating method according to the second aspect, instead of detecting the ON / OFF state of the brake switch, the speeds of the driving wheel and the driven wheels are detected to calculate the slip ratio, and the slip ratio is calculated. Is greater than a preset threshold value, the update of the estimated value of the road surface friction coefficient is interrupted. In the case of a two-wheel drive vehicle,
The slip condition of the tire can be grasped by detecting the slip ratio according to the speed difference between the driving wheel and the driven wheel caused by stepping on the brake, so the road friction coefficient can be estimated according to the slip condition of the tire. It is possible to prevent the malfunction of the system without fail.

Further, according to the road surface state estimating method of the third aspect, the engine speed is detected, and when the engine speed exceeds a preset threshold value, the update of the estimated value of the road surface friction coefficient is interrupted. It is characterized by doing so. In the case of a four-wheel drive vehicle, since all the drive wheels are used, the engine speed is detected, and when the engine speed becomes higher than the threshold value, the torque becomes extremely high, and it can be determined that the tires are slippery. It is possible to interrupt the estimation of the road surface friction coefficient according to the slip state of the tire, and it is possible to reliably prevent malfunction of the system. A road surface condition estimating method according to a fourth aspect of the present invention is the road surface condition estimating method according to the third aspect, wherein the threshold value of the engine speed is changed according to the connection state of the traveling gear and the clutch.

A road surface condition estimating method according to a fifth aspect of the present invention estimates the road surface friction coefficient from the data of the vibration level or the pressure fluctuation level using the following arithmetic expression. Road surface frictional coefficient estimated value = 1 / [1 + exp { - (a 0 + a 1 x 1 + a 2
_{x 2 + ‥‥ + a n x} n)}] where, a _{0; constant, a 1, a 2, ‥‥} , a n; coefficient x _i; vibration in the frequency band (f _i) level or pressure fluctuation levels

According to a sixth aspect of the road surface state estimating apparatus of the present invention, tire vibration, wheel vibration, suspension vibration,
Detecting at least one of the pressure fluctuations in the tire,
In a road surface state estimation device that estimates the road friction coefficient by detecting the vibration level of the vibration spectrum obtained by frequency analysis of this or the pressure fluctuation level of the pressure fluctuation spectrum, a means for detecting ON / OFF of the brake switch is provided. In the meantime, when it is determined that the brake is depressed, the updating of the estimated value of the road surface friction coefficient is interrupted.

A road surface state estimating apparatus according to a seventh aspect of the present invention detects at least one of tire vibration, wheel vibration, suspension vibration, and tire pressure fluctuation, and vibrates a vibration spectrum obtained by frequency analysis of the detected vibration. level,
Alternatively, in a road surface state estimating device that estimates the road surface friction coefficient by detecting the pressure fluctuation level of the pressure fluctuation spectrum,
Means for detecting the speed of the drive wheel and the driven wheel, and means for calculating the slip ratio from the detected speed of the drive wheel and the driven wheel, if the slip ratio exceeds a preset threshold, The update of the estimated value of the road surface friction coefficient is interrupted.

The road surface state estimating apparatus according to the present invention detects at least one of tire vibration, wheel vibration, suspension vibration, and tire pressure fluctuation, and frequency-analyzes the vibration to obtain a vibration spectrum vibration. level,
Alternatively, in a road surface state estimating device that estimates the road surface friction coefficient by detecting the pressure fluctuation level of the pressure fluctuation spectrum,
A means for detecting the engine speed is provided, and when the engine speed exceeds a preset threshold value, the updating of the estimated value of the road surface friction coefficient is interrupted. In the road surface state estimating device according to claim 9, since the load of the engine depends on the connection state of the running gear and the clutch, the road surface state estimating device according to claim 8 detects the connection state of the running gear and the clutch. A means is provided to change the threshold value of the engine speed according to the connection state of the traveling gear and the clutch, which enables more accurate control.

A road surface state estimating device according to a tenth aspect of the present invention is
The road surface state estimating device according to any one of claims 6 to 9, wherein the vibration or pressure fluctuation information signal is converted into a digital signal at a tire or a wheel portion or a suspension portion and then compressed, and then the vehicle body side. Sent to
The vehicle body receives the compressed signal, restores it, and analyzes the frequency.

The ABS braking control method according to claim 11 is a vibration obtained by detecting at least one of tire vibration, wheel vibration, suspension vibration, and tire internal pressure fluctuation, and performing frequency analysis on the detected vibration. The vibration level of the spectrum or the pressure fluctuation level of the pressure fluctuation spectrum is detected to continuously estimate the road surface friction coefficient, and according to the magnitude of the road surface friction coefficient estimated value immediately before the driver steps on the brake, the ABS It is characterized in that the threshold value of the brake hydraulic pressure that shifts to the control is changed. For example, when the road surface friction coefficient estimated value is low, the slip ratio increases and the braking force decreases. In this case, the threshold value of the brake hydraulic pressure that shifts to the ABS control is decreased to activate the ABS earlier. By controlling the slip ratio so that it does not increase, the safety of the vehicle is improved.

According to a twelfth aspect of the ABS braking control method of the present invention, tire vibration, wheel vibration, suspension vibration,
Detecting at least one of the pressure fluctuations in the tire,
The vibration level of the vibration spectrum obtained by frequency analysis of this or the pressure fluctuation level of the pressure fluctuation spectrum is detected to continuously estimate the road friction coefficient, and at the same time, the road friction coefficient is estimated immediately before the driver steps on the brake. It is characterized in that the degree of increase or decrease of the ABS brake oil pressure is adjusted according to the magnitude of the value.
It is possible to perform S braking stably.

The ABS braking control method according to a thirteenth aspect is the ABS braking control method according to the eleventh or the twelfth aspect, wherein the following arithmetic expression is used from the data of the vibration level or the pressure fluctuation level. The road surface friction coefficient is continuously estimated. Road surface frictional coefficient estimated value = 1 / [1 + exp { - (a 0 + a 1 x 1 + a 2
_{x 2 + ‥‥ + a n x} n)}] where, a _{0; constant, a 1, a 2, ‥‥} , a n; coefficient x _i; vibration in the frequency band (f _i) level or pressure fluctuation levels

According to a fourteenth aspect of the present invention, there is provided an ABS braking control device which detects at least one of tire vibration, wheel vibration, suspension vibration, and tire pressure fluctuation, and the detected vibration information signal or A means for detecting the vibration level of the vibration spectrum obtained by frequency analysis of the pressure fluctuation signal, or the pressure fluctuation level of the pressure fluctuation spectrum, and continuously calculating the estimated value of the road surface friction coefficient using the following arithmetic expression: , Turn on the brake switch
It is provided with means for detecting the off state and means for changing the threshold value of the brake hydraulic pressure for shifting to the ABS control according to the magnitude of the road surface friction coefficient estimated value immediately before the driver steps on the brake. Road surface frictional coefficient estimated value = 1 / [1 + exp { - (a 0 + a 1 x 1 + a 2
_{x 2 + ‥‥ + a n x} n)}] where, a _{0; constant, a 1, a 2, ‥‥} , a n; coefficient x _i; vibration in the frequency band (f _i) level or pressure fluctuation levels

The ABS braking control device according to a fifteenth aspect of the present invention is a tire vibration, a wheel vibration, a suspension vibration,
A means for detecting at least one of the pressure fluctuations in the tire, and a vibration level of a vibration spectrum obtained by frequency-analyzing the detected vibration information signal or pressure fluctuation signal, or a pressure fluctuation level of the pressure fluctuation spectrum. A means for continuously calculating the estimated value of the road surface friction coefficient using the following calculation formula, a means for detecting the on / off state of the brake switch, and an estimated value of the road surface friction coefficient immediately before the driver steps on the brake. And means for adjusting the degree of increase or decrease of the ABS brake hydraulic pressure according to the magnitude of the. Road surface frictional coefficient estimated value = 1 / [1 + exp { - (a 0 + a 1 x 1 + a 2
_{x 2 + ‥‥ + a n x} n)}] where, a _{0; constant, a 1, a 2, ‥‥} , a n; coefficient x _i; vibration in the frequency band (f _i) level or pressure fluctuation levels

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. Embodiment 1. FIG. 1 is a diagram showing a configuration of a road surface state estimating device 10 according to the first embodiment. In FIG.
Is a vibration sensor for detecting tire vibration, 12 is provided with a frequency band setting means 13 and a vibration level detecting means 14, and the vibration information signal of the wheel vibration detected by the vibration sensor 11 is frequency-analyzed to detect the vibration. A frequency range of the frequency spectrum (hereinafter referred to as vibration spectrum) in which the vibration level characteristically changes depending on the road surface condition and the running condition of the tire, that is, at least 10 to 10000H.
Frequency analysis means for detecting the vibration level of the frequency band included in the range of z, 15 is based on the vibration level data,
Estimated value of road surface friction coefficient (hereinafter,
road surface friction coefficient estimating means for calculating
Reference numeral 6 is a brake switch ON / OFF detection means for detecting the ON / OFF state of the brake switch, and 17 is a sequential update of the calculated μ estimated value based on the control signal from the brake switch ON / OFF detection means 16. And outputs it to the vehicle control means 50 that controls the traveling state of the vehicle.
It is an estimated value output means. In this example, FIG. 2 (a), (b)
As shown in FIG. 3, the vibration sensor 11 is attached to the tire-side recess of the wheel rim 2 of the wheel 1 to detect the vibration of the wheel propagated from the tire.

Next, the operation of the road surface state estimating device 10 having the above structure will be described. First, the vibration sensor 11 detects the vibration from the tire propagated to the wheel 1, and the frequency analysis means 12 analyzes the frequency of the detected vibration information signal to detect the vibration level in a predetermined frequency band. Specifically, the vibration level detected by the frequency analysis unit 12 has a center frequency in a frequency range in which the vibration level characteristically changes depending on the road surface condition or the running condition of the tire, that is, in the range of at least 10 to 10000 Hz. A vibration level of a frequency band having a predetermined bandwidth, for example, a vibration level of one frequency band having a relatively wide bandwidth such as 800 to 3500 Hz, or 800 to 1000 Hz, 1600 to 2000.
The vibration level (plurality) in a plurality of frequency bands having a relatively narrow bandwidth may be used, such as a vibration level in Hz, 3000 to 3500 Hz. In the frequency analysis means 12, the one or more frequency bands f _i (i = 1 to 1)
n) is set by the frequency band setting means 13, and the vibration level detecting means 14 detects the vibration level x _i (i = 1 to n). The detection of the vibration level x _i by the frequency analysis means 12 including the frequency band setting means 13 and the vibration level detection means 14 is usually performed by an FFT analyzer which is a frequency analysis device using a fast Fourier transform (FFT). realizable.

The road surface friction coefficient estimating means 15 calculates the μ estimated value from the detected vibration level x _i by the following calculation method. A test vehicle equipped with the vibration sensor 11 is run at a constant speed on a road surface having a different road surface friction coefficient μ to obtain a vibration spectrum of the wheel 1. From this vibration spectrum, at least one frequency band f _i (i = 1 to 1) is obtained. vibration level x _i (n = 1)
~ N) is detected, and the μ estimation value is calculated using the following equation (1). μ estimate = 1 / [1 + exp { - (a 0 + a 1 x 1 + a 2 x 2 + ‥‥ + a n x n)}] ‥‥ (1) where, a _0; constant, a _1, a _2, .., a _n ; coefficient Then, the correlation coefficient between the estimated μ value calculated by the above equation (1) and the road surface friction coefficient μ obtained in advance is calculated, and the above μ is set so that this correlation coefficient becomes the highest. A plurality of frequency bands f _i (i = 1 to n) for calculating the estimated value are set. In the road surface friction coefficient estimating means 15, the vibration level x _i (i) in each frequency band f _i (i = 1 to n) set by the above method, which is detected by the vibration level detecting means 14 of the frequency analyzing means 12. = 1 to n), the μ estimated value is calculated using the above equation (1).

The μ estimated value calculated by the road surface friction coefficient estimating means 15 is sent to the μ estimated value output means 17. In the μ estimated value output means 17, when the update interruption signal from the brake switch ON / OFF detection means 16 is not inputted, the μ sent from the road surface friction coefficient estimation means 15 is sent.
Based on the estimated value, the μ estimated value is sequentially updated and the vehicle control means 5
Output to 0. When the update interruption signal is input, the μ estimated value is not updated and the μ estimated value before the brake switch is depressed is output to the vehicle control means 50. The method of updating the μ estimated value will be described in more detail with reference to the flowchart of FIG. First, in step S10, the μ estimated value μ _n is calculated, and in step S11 the μ estimated value is updated to set the above μ _n as a new μ estimated value. In step S12, the brake switch ON / OFF detection means 16 detects the state of the brake switch. If the brake switch is in the OFF state, the process proceeds to step S13, in which the μ estimated value output means 17 determines μ _n by μ. The estimated value is output to the vehicle control means 50. Then, in step S14, after calculating the next μ estimated value μ _{n + 1} ,
Returning to step S11 by setting _{n + 1} to μ _n , the μ estimated value is updated and the above μ _n (μ _{n + 1} calculated in step S14) is set as a new μ estimated value, and the process proceeds to step S12 and again.
Detects ON / OFF of the brake switch. On the other hand, if the brake switch is ON, step S15
Then, the brake switch ON / OFF detection means 16 outputs an update stop signal to the μ estimated value output means 17 to interrupt the update of the μ estimated value, and thereafter, the μ estimated value before the update is interrupted. Vehicle control means 50 with μ _n as μ estimated value
Output to. After that, turn off the brake switch.
Is detected, the above step S
Returning to step 11, the μ estimation value is updated again. in this way,
If the brake is depressed and a sudden deceleration occurs, tire slippage is likely to occur.Therefore, the control after the brake is depressed is not the newly estimated μ estimated value μ _{n + 1} but the brake. Since it is performed using μ _n , which is the μ estimation value estimated immediately before stepping on, the malfunction of the system can be prevented.

As described above, according to the first embodiment, the vibration sensor 11 detects the vibration of the wheel 1 and frequency-analyzes the vibration to detect the vibration level of the vibration spectrum to determine the road friction coefficient. In addition to the estimation, the brake switch ON / OFF detection means 16 detects ON / OFF of the brake switch, and when it is determined that the brake is stepped on, the update of the estimated value of the road surface friction coefficient is interrupted. Therefore, the malfunction of the system due to the slip of the tire can be prevented.

In the first embodiment, the vibration sensor 11 is attached to the tire side of the wheel rim 2 to detect the vibration of the tire propagated to the wheel 1.
As shown in FIG. 4A, the vibration sensor 11 may be attached to the inner surface side 3a of the tire tread 3 to directly detect the vibration of the tire. Alternatively, as shown in FIG. 4B, the road surface condition may be estimated by detecting the vibration of the tire mounted on the suspension unit 4 and propagated to the suspension unit 4. Since a plurality of elastic members such as a rubber bush 5 are attached to the suspension portion 4 to absorb vibrations, in order to efficiently detect the propagated tire vibrations, the vibration sensor 11 is used as a suspension arm. It is preferable to mount it on the hub portion 6 to which the wheel 1 is mounted, rather than on the wheels 4a and 4b. Alternatively, instead of the vibration sensor 11, a pressure sensor is installed in the tire, a minute vibration component (AC component) on the time axis of the output of the pressure sensor is extracted, and the pressure of the gas filled in the tire is extracted. The fluctuation may be detected, the pressure fluctuation level of the pressure fluctuation spectrum obtained by frequency analysis of the fluctuation may be detected, and the μ estimated value may be calculated from the pressure fluctuation level by using the above-mentioned arithmetic expression (1). .

In the first embodiment, the on / off state of the brake switch is detected and the μ estimated value output means 17 is controlled to update the μ estimated value.
As shown in FIG. 5, the brake switch is turned on / off.
Instead of the detection means 16, wheel speed detection means 18a and 18b for detecting the rotational speeds of the drive wheel and the driven wheel, respectively, and the slip ratio S is calculated from the detected rotational speeds of the drive wheel and the driven wheel,
The road surface state estimating device 10S is provided with a slip ratio determining means 19 for comparing the value with a predetermined threshold value K to determine the magnitude of the slip ratio S, and the μ estimated value is calculated based on the magnitude of the slip ratio S. The update may be controlled. A method of updating the μ estimated value based on the slip ratio S will be described in detail with reference to the flowchart of FIG. First, in step S20, the μ estimated value μn is calculated, and step S2
In step 1, the μ estimation value is updated and the above μn is set as a new μ estimation value. In step S22, the rotational speed F1 of the driving wheel and the rotational speed F2 of the driven wheel are respectively detected, and in step S23, the slip ratio S is calculated by the following equation (2). S = | (a · F1-b · F2) / (a · F2) | (2) where F1 and F2 are the average values of the two wheels, and a and b
Is a coefficient for converting the rotation speed into the speed. Then, in step S24, it is determined whether or not the slip ratio S exceeds a preset threshold value K (here, K = 0.2). If S ≦ K, the process proceeds to step S25, where the μ estimated value output means 17 outputs the above μ.
_n is output to the vehicle control means 50 as a μ estimated value. Then, after calculating the next μ estimated value μ _{n + 1} in step S26, this μ _{n + 1} is set as μ _n and the process returns to step S21.
The μ estimated value is updated and the above μ _n (μ _{n + 1} calculated in step S26) is set as a new μ estimated value, and the process proceeds to step S22. On the other hand, if S> K, the process proceeds to step S27, in which the slip ratio determination means 19 causes the μ estimated value output means 17 to operate.
And outputs an update stop signal to interrupt the updating of the mu estimates, thereafter, the mu _n is an estimate mu before interrupting the update mu
The estimated value is output to the vehicle control means 50. If the slip ratio S becomes equal to or less than the threshold value K after that, the process returns to step S21 after a predetermined time has elapsed, and the update of the μ estimated value is restarted. As described above, the control after the tire slip ratio S exceeds the preset threshold value K due to the sudden acceleration / deceleration or the like is not the newly estimated μ estimated value μ _{n + 1} but S
It is possible to prevent the malfunction of the system by using μ _n, which is the μ estimated value estimated immediately before becoming> K.

In the case of a four-wheel drive vehicle, the method of calculating the slip ratio S from the rotational speeds of the driving wheel and the driven wheel as described above cannot be used, so the engine rotational speed R is detected to determine the engine rotational speed. When the number becomes higher than the predetermined threshold value R _z, it is determined that the torque becomes extremely high and the tire becomes slippery, and the update of the μ estimation value is interrupted. Regarding the method of updating the μ estimation value based on the engine speed,
This will be described in detail with reference to the flowchart of FIG. First, in step S30, the μ estimated value μ _n is calculated, and in step S31, the μ estimated value is updated to obtain the above μ _n as a new μ.
Estimated value. In step S32, the engine speed R
Is detected, and it is determined whether the detected engine speed R exceeds a predetermined threshold value R _z (for example, R _z = 4500 rpm). When R ≦ R _z , the process proceeds to step S33, and the μ estimated value output means 17 outputs the above μ _n to the vehicle control means 50 as the μ estimated value. Then, after calculating the next μ estimated value μ _{n + 1} in step S34, this μ _{n + 1} is calculated.
Is set as μ _n and the process returns to the step S31, the μ estimated value is updated, and the μ _n (μ _{n + 1} calculated in step S34) is set as a new μ estimated value. To detect. On the other hand, when R> R _z, the process proceeds to step S35, the update of the μ estimated value is interrupted,
After that, μ _n , which is the μ estimated value before the updating is interrupted, is output to the vehicle control means 50 as the μ estimated value. If the engine speed is reduced to R ≦ R _z after that, the process returns to step S31 after a predetermined time has elapsed, and μ
Restart the update of the estimated value. Therefore, even in the case of a four-wheel drive vehicle, malfunction of the system can be prevented by detecting the engine speed R, determining the slipping state of the tire, and controlling the update of the μ estimated value.

Example 1 FIG. 8 shows the test vehicle running at a constant speed on DRY asphalt, WET asphalt (water depth of about 1 mm), high pre-pool (concrete; water depth of about 10 mm), pressure snow road, and ice road. FIG. 6 is a diagram showing a result of calculating a μ estimation value on each road surface by using the vibration level in the optimum frequency band. In high prepool,
As the vehicle speed increases, the lifting phenomenon of the tire occurs and the ground contact area decreases, which causes μ to decrease, but this μ estimated value reflects such μ decrease and is calculated from the normal braking distance. It was confirmed that the road friction coefficient was almost the same. Next, when the test vehicle was gently accelerated in DRY asphalt, and the test vehicle was gently accelerated, as shown by the alternate long and short dash line in FIG.
It was confirmed that it was almost the same as the μ estimation value when the vehicle was driven at a constant speed shown in (4), and that the μ estimation value was not misjudged. However, in DRY asphalt,
When the test vehicle is fully accelerated, as shown by the broken line in FIG. 9, there is a region where the estimated μ value decreases. In these areas, the engine speed becomes high and immediately before the gear change. That is, it is a region where the engine torque is high and the tire slip ratio is high, and the tire slip ratio actually exceeds 20%. Therefore, the slip ratio S shown in FIGS.
The test flow is mounted on a test vehicle with a system incorporating the control flow logic according to the above and the control flow logic according to the engine speed, and the μ estimated value is obtained by fully accelerating the test vehicle in the DRY asphalt. In addition, it was confirmed that the updating of μ was interrupted and the μ value immediately before that was maintained while the slip ratio of the tire was high. The test vehicle used was an FF drive company of 1800 cc, and the threshold value of the slip ratio S was K = 0.2.
In addition, the threshold value R _z of the engine speed R was set to 4500 rpm.

Embodiment 2. FIG. 11 is an ABS that includes the respective means 11 to 17 of the road surface state estimating device 10 according to the present invention, and controls the ABS brake using the calculated μ estimated value.
It is a figure which shows one structural example of the braking control apparatus 20, and here the wheel side (rolling side) A to which the vibration sensor 11 was attached.
And the vehicle body side B which is a non-rolling side are wirelessly connected to each other, and the vibration information signal of the wheel 1 detected by the vibration sensor 11 is wirelessly transmitted to the vehicle body side B, and the vehicle body side B receives the signal and receives the frequency. The ABS estimated value is obtained by analyzing and the ABS brake is controlled. On the wheel side A, the vibration sensor 11, a circuit 21 for driving and detecting the vibration sensor 11, and a battery 22 are provided.
And an A / D converter 23 for digitally converting and compressing the vibration information signal of the wheel 1 detected by the vibration sensor 11
a, a transmission circuit 23 including an information compression circuit 23b and a transmitter 23c that wirelessly transmits the compressed signal to the vehicle body side B
And an antenna 23p for transmission. On the vehicle body side B, a receiver 24 and an antenna 24p for receiving the compressed signal, and a vibration level in a predetermined frequency band of a vibration spectrum obtained by frequency analysis after restoring the received compressed signal are detected. An FFT analyzer 25, an arithmetic circuit 26 for calculating a μ estimated value using the vibration level,
A brake switch ON / OFF detector 27 that detects the ON / OFF state of the brake switch, and a μ update circuit 28 that sequentially updates and outputs the μ estimated value based on the output of the brake switch ON / OFF detector 27. , ABS
And an ABS brake controller 29 for controlling the brake. The FFT analyzer 25 has a function equivalent to that of the frequency analyzing means 12 including the frequency band setting means 13 and the vibration level detecting means 14 of the first embodiment, and the arithmetic circuit 26 has the road surface friction coefficient. In the estimation means 15, the μ update circuit 28 is provided in the μ estimated value output means 17,
The brake switch ON / OFF detector 27 corresponds to the brake switch ON / OFF detecting means 16, respectively.
As a result, the vibration information signal detected on the wheel side A, which is the rolling side, can be processed on the vehicle body side B to estimate the road surface friction coefficient and control the ABS brake without providing a signal connection line. it can.

Next, the ABS braking control device 20 having the above structure.
The operation of will be described. First, the vibration information signal of the wheel 1 detected by the vibration sensor 11 and output from the vibration sensor circuit 21 is digitally converted by the A / D converter 23a, then compressed by the information compression circuit 23b, and transmitted from the transmitter 23c to the antenna. The compressed signal is wirelessly transmitted to the vehicle body side B via 23p. The transmitted compressed signal is received by the receiver 24 via the antenna 24p and sent to the FFT analyzer 25. In the FFT analyzer 25, the vibration level x _i (i = _i ) in a plurality of frequency bands f _i (i = 1 to n) of the vibration spectrum obtained by frequency analysis after restoring the compressed received signal
= 1 to n) are detected. Then, in the arithmetic circuit 26, in the same manner as in the first embodiment, the vibration level x _i (i =
1 to n), the μ estimated value is calculated and sent to the μ update circuit 28. In the μ update circuit 28, the μ estimated value is sequentially updated and output to the ABS brake controller 29. The ABS brake controller 29 controls the ABS brake using the updated μ estimated value. In this example also,
Brake switch is turned on in the same manner as in the first embodiment.
The / OFF detector 27 controls the update of the μ estimated value in the μ update circuit 28, and the μ estimated value for controlling the ABS brake can be changed. Therefore,
When the brake is not stepped on, the above-calculated μ estimated value is sequentially input to the ABS brake controller 29,
When the brake is depressed, the μ estimation value estimated immediately before the brake is depressed is input.

Generally, when a brake is applied on a low μ road, since the frictional force from the road surface is low, the wheel speed suddenly decreases and the slip ratio increases, as will be described later. If the slip ratio is too high, it causes a reduction in braking force and a drastic reduction in steering force, which is dangerous. Therefore, in the second embodiment,
In the ABS brake controller 29, if the estimated μ is low, the threshold for entering the ABS brake mode is lowered, and A
The BS is operated to perform control so that the slip ratio does not increase. At this time, when the brake is depressed, the μ estimation value estimated immediately before the brake is depressed is used to prevent the malfunction of the system. Also,
On low-μ roads, if the hydraulic pressure is applied rapidly even if the ABS mode is entered early, the slip ratio will be too high, which is dangerous. Therefore, on low-μ roads, the ABS mode will be entered early and the ABS In the brake controller 29, the brake hydraulic pressure is slowly increased.
On the contrary, when the pressure is reduced, the friction ratio is low on the low μ road, so that the slip ratio does not easily decrease (the acceleration of the tire is slow).

FIG. 12 is a schematic diagram showing the force applied to the tire. The frictional force from the road surface acts in the opposite direction to the braking force, as shown in FIG. For this reason,
When is low, the braking force becomes relatively strong, the rotation speed of the tire sharply decreases, and the slip ratio sharply increases. In extreme cases, the tires may lock up and be dangerous. When the tire locks, as shown in the S-μ curve showing the relationship between the slip ratio and the frictional force in FIG. 13, μ decreases, and the steering force also decreases to prevent bending. Thus, once the rotational speed of the tire decreases, the frictional force is low on a low μ road surface, and therefore it takes time for the slip ratio to return to an appropriate position even if the brake hydraulic pressure is loosened by the ABS control. That is, the braking distance becomes long, which is dangerous.

FIGS. 14 and 15 are graphs in which the vehicle speed and the wheel speed are measured by running the test vehicle on the WET road surface and the ICE road surface, respectively, and the slip ratio is obtained by dividing the speed difference between these values by the vehicle speed. become. It can be seen that the tire rotation speed is likely to decrease on the ICE road surface at the initial stage of braking and the slip ratio is higher than that on the WET road surface. Therefore, on low μ road surfaces, A
It is preferable that the threshold value of the hydraulic pressure at the time of shifting to the BS is lowered so that the brake hydraulic pressure does not rise excessively. Further, it is preferable to appropriately control the pressure increase and pressure decrease during ABS braking according to the road surface μ. Even in the normal ABS control, the ABS brake oil pressure is increased or decreased based on the information from the gear sensor. However, as in the present invention, the road surface μ is estimated in advance, and the increase or decrease of the oil pressure is adjusted based on the μ estimated value. By doing so, control errors can be reduced.

<Second Embodiment> FIG. 16 shows an AB according to the present invention.
A test vehicle equipped with the S braking control device 20 is run on an ICE road surface, an ABS braking test is performed, and a result of measuring a vehicle body speed and a wheel speed is shown. ABS braking control device 2 according to the invention
When the ABS brake was braked using 0, the wheel speed did not decrease with respect to the vehicle speed, and it was confirmed that the slip ratio was properly controlled.

[0033]

As described above, according to the present invention, at least any one of tire vibration, wheel vibration, suspension vibration, and tire pressure fluctuation is detected, and the vibration spectrum obtained by frequency analysis is detected. Vibration level,
Alternatively, the road friction coefficient is estimated by detecting the pressure fluctuation level of the pressure fluctuation spectrum, and if the brake switch is detected to be ON / OFF and it is determined that the brake pedal is stepped on, the estimated road friction coefficient Since the updating is interrupted, it is possible to prevent the road surface friction coefficient from being estimated after the brake is depressed, and to prevent the malfunction of the system due to the slip of the tire. Incidentally, instead of detecting the ON / OFF of the brake switch, the slip ratio is calculated by detecting the speeds of the driving wheels and the driven wheels, and when the slip ratio exceeds a preset threshold value, or
The same effect can be obtained by detecting the engine speed and interrupting the update of the estimated value of the road surface friction coefficient when the engine speed exceeds a preset threshold value. Further, the road surface friction coefficient is continuously estimated as described above, and the threshold value of the brake hydraulic pressure for shifting to the ABS control is changed according to the magnitude of the road surface friction coefficient estimated value immediately before the driver steps on the brake. Since it was set to AB
By operating S, it is possible to suppress an increase in the slip ratio. Further, the degree of increase or decrease in the ABS brake hydraulic pressure is adjusted according to the magnitude of the road surface friction coefficient estimated value immediately before the driver steps on the brake, so that the increase in the slip ratio can be reliably suppressed.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a road surface state estimating device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a mounting location of a vibration sensor.

FIG. 3 is a flowchart for updating control of an estimated μ value by detecting a brake switch.

FIG. 4 is a diagram showing another mounting location of the vibration sensor.

FIG. 5 is a diagram showing a configuration of a road surface state estimating device including a slip ratio determining means according to the present invention.

FIG. 6 is a flowchart for updating control of an estimated μ value based on a slip ratio.

FIG. 7 is a flowchart for updating control of μ estimated value based on engine speed.

FIG. 8 is a diagram showing calculation results of μ estimated values when the test vehicle is run on various road surfaces at a constant speed.

FIG. 9 is a diagram showing a calculation result of a μ estimated value when a test vehicle is accelerated on a dry asphalt road surface.

FIG. 10 shows μ according to the slip ratio and the engine speed.
It is a figure which shows the calculation result of the μ estimated value when updating control of the estimated value is performed.

FIG. 11 is a diagram showing a configuration example of an ABS braking control device according to a second embodiment of the present invention.

FIG. 12 is a schematic diagram showing a force applied to a tire.

FIG. 13 is an S-μ curve showing the relationship between the slip ratio and the frictional force.

FIG. 14 is a graph showing a result of measuring a vehicle body speed and a wheel speed by running a test vehicle on a WET road surface.

FIG. 15 is a graph showing a result of measuring a vehicle body speed and a wheel speed by running a test vehicle on an ICE road surface.

FIG. 16 is a test vehicle equipped with an ABS braking control device according to the present invention, in which a test vehicle is run on an ICE road surface.
It is a graph which shows the result of having measured body speed and wheel speed.

[Explanation of symbols]

1 wheel, 2 wheel rim, 3 tire tread, 3a inner side of tread, 4 suspension part,
4a, 4b suspension arms, 5 rubber bushes, 6 hubs, 10, 10S road surface condition estimation device, 1
1 vibration sensor, 12 frequency analysis means, 13 frequency band setting means, 14 vibration level detection means, 15 road surface friction coefficient estimation means, 16 brake switch ON / OF
F detection means, 17 μ estimated value output means, 18a wheel speed detection means (driving wheel), 18b wheel speed detection means (driven wheel),
19 Slip ratio determining means, 20 ABS braking control device, 21 Vibration sensor circuit, 22 Battery, 23
Transmitter circuit, 23a A / D converter, 23b Information compression circuit, 23c Transmitter, 23p Transmitter antenna, 24
Receiver, antenna of 24p receiver, 25 FFT analyzer, 26 arithmetic circuit, 27 brake switch ON / OFF detector, 28 μ update circuit, 29 ABS
Brake controller, 50 Vehicle control means.

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Claims (15)

[Claims] 1. A vibration level of a vibration spectrum obtained by detecting at least one of tire vibration, wheel vibration, suspension vibration, and pressure fluctuation in a tire, and performing frequency analysis of this, or pressure fluctuation of a pressure fluctuation spectrum. In the road surface condition estimation method that detects the level and estimates the road surface friction coefficient, when the brake switch is detected to be ON / OFF and it is determined that the brake pedal is pressed, the update of the road surface friction coefficient estimated value is suspended. A road surface condition estimation method characterized by the above. 2. A vibration level of a vibration spectrum obtained by detecting at least one of tire vibration, wheel vibration, suspension vibration, and tire internal pressure fluctuation and frequency-analyzing this, or pressure fluctuation of the pressure fluctuation spectrum. In the road surface state estimating method for estimating the road surface friction coefficient by detecting the level, the slip ratio is calculated by detecting the speeds of the driving wheels and the driven wheels, and when the slip ratio exceeds a preset threshold value, A method of estimating a road surface state, characterized in that updating of an estimated value of a road surface friction coefficient is interrupted. 3. A vibration level of a vibration spectrum obtained by detecting at least one of tire vibration, wheel vibration, suspension vibration, and pressure fluctuation in a tire, and performing frequency analysis of this, or pressure fluctuation of a pressure fluctuation spectrum. In the road surface condition estimation method that detects the level and estimates the road friction coefficient, the engine speed is detected, and if the engine speed exceeds a preset threshold value, the update of the road friction coefficient estimated value is interrupted. A method for estimating a road surface condition, which comprises: 4. The road surface condition estimating method according to claim 3, wherein the threshold value of the engine speed is changed according to the connection state of the traveling gear and the clutch. 5. The road surface state estimation according to claim 1, wherein the road surface friction coefficient is estimated from the vibration level or pressure fluctuation level data using the following arithmetic expression. Method. Road surface frictional coefficient estimated value = 1 / [1 + exp { - (a 0 + a 1 x 1 + a 2
_{x 2 + ‥‥ + a n x} n)}] where, a _{0; constant, a 1, a 2, ‥‥} , a n; coefficient x _i; vibration in the frequency band (f _i) level or pressure fluctuation levels 6. A vibration level of a vibration spectrum obtained by detecting at least one of tire vibration, wheel vibration, suspension vibration, and tire pressure fluctuation and frequency-analyzing this, or pressure fluctuation of the pressure fluctuation spectrum. In a road surface state estimating device that detects a level and estimates a road surface friction coefficient, a means for detecting ON / OFF of a brake switch is provided, and when it is determined that a brake is stepped on, the estimated value of the road surface friction coefficient is updated. A road surface state estimation device characterized in that the road surface state estimation device is interrupted. 7. A vibration level of a vibration spectrum obtained by detecting at least one of tire vibration, wheel vibration, suspension vibration, and tire pressure fluctuation and frequency-analyzing this, or pressure fluctuation of the pressure fluctuation spectrum. In a road surface condition estimating device for estimating a road surface friction coefficient by detecting a level, means for detecting speeds of driving wheels and driven wheels and means for calculating a slip ratio from the detected speeds of the driving wheels and driven wheels are provided. A road surface state estimating device, characterized in that, when the slip ratio exceeds a preset threshold value, updating of the estimated value of the road surface friction coefficient is interrupted. 8. A vibration level of a vibration spectrum obtained by detecting at least one of tire vibration, wheel vibration, suspension vibration, and pressure fluctuation in a tire, and performing frequency analysis of this, or pressure fluctuation of a pressure fluctuation spectrum. In a road surface state estimating device for estimating a road surface friction coefficient by detecting a level, a means for detecting an engine speed is provided, and when the engine speed exceeds a preset threshold value, the estimated value of the road surface friction coefficient is A road surface state estimating device characterized by suspending updating. 9. The method according to claim 8, further comprising means for detecting a connection state of the traveling gear and the clutch, wherein the threshold value of the engine speed is changed according to the connection state of the traveling gear and the clutch. The road surface condition estimating device described. 10. The vibration or pressure fluctuation information signal is converted into a digital signal at the tire or wheel portion or suspension portion and compressed, and then transmitted to the vehicle body side,
The road surface state estimating device according to any one of claims 6 to 9, wherein the vehicle side receives the compressed signal, restores the compressed signal, and analyzes the frequency. 11. At least one of tire vibration, wheel vibration, suspension vibration, and tire pressure fluctuation.
Just before the driver steps on the brake, while continuously detecting the vibration level of the vibration spectrum obtained by frequency analysis of this signal or the pressure fluctuation level of the pressure fluctuation spectrum to continuously estimate the road surface friction coefficient. The ABS braking control method characterized in that the threshold value of the brake hydraulic pressure that shifts to the ABS control is changed according to the magnitude of the road surface friction coefficient estimated value. 12. At least one of tire vibration, wheel vibration, suspension vibration, and tire pressure fluctuation.
Just before the driver steps on the brake, while continuously detecting the vibration level of the vibration spectrum obtained by frequency analysis of this signal or the pressure fluctuation level of the pressure fluctuation spectrum to continuously estimate the road surface friction coefficient. The ABS braking control method, wherein the degree of increase or decrease of the ABS brake hydraulic pressure is adjusted according to the magnitude of the road surface friction coefficient estimated value. 13. The ABS braking control according to claim 11 or 12, wherein the road surface friction coefficient is continuously estimated from the data of the vibration level or the pressure fluctuation level using the following arithmetic expression. Method. Road surface frictional coefficient estimated value = 1 / [1 + exp { - (a 0 + a 1 x 1 + a 2
_{x 2 + ‥‥ + a n x} n)}] where, a _{0; constant, a 1, a 2, ‥‥} , a n; coefficient x _i; vibration in the frequency band (f _i) level or pressure fluctuation levels 14. At least one of tire vibration, wheel vibration, suspension vibration, and tire pressure fluctuation.
And a vibration level of a vibration spectrum obtained by frequency-analyzing the detected vibration information signal or pressure fluctuation signal, or the pressure fluctuation level of the pressure fluctuation spectrum is detected, and the following arithmetic expression is used. Of the ABS according to the magnitude of the road friction coefficient estimated value immediately before the driver steps on the brake.
An ABS braking control device, comprising: means for changing a threshold value of a brake hydraulic pressure that shifts to control. Road surface frictional coefficient estimated value = 1 / [1 + exp { - (a 0 + a 1 x 1 + a 2
_{x 2 + ‥‥ + a n x} n)}] where, a _{0; constant, a 1, a 2, ‥‥} , a n; coefficient x _i; vibration in the frequency band (f _i) level or pressure fluctuation levels 15. At least one of tire vibration, wheel vibration, suspension vibration, and tire pressure fluctuation.
And a vibration level of a vibration spectrum obtained by frequency-analyzing the detected vibration information signal or pressure fluctuation signal, or the pressure fluctuation level of the pressure fluctuation spectrum is detected, and the following arithmetic expression is used. Of the ABS according to the magnitude of the road friction coefficient estimated value immediately before the driver steps on the brake.
An ABS braking control device, comprising: means for adjusting an increase / decrease degree of brake hydraulic pressure. Road surface frictional coefficient estimated value = 1 / [1 + exp { - (a 0 + a 1 x 1 + a 2
_{x 2 + ‥‥ + a n x} n)}] where, a _{0; constant, a 1, a 2, ‥‥} , a n; coefficient x _i; vibration in the frequency band (f _i) level or pressure fluctuation levels