JP2007137086A - Method, device and tire for estimating road friction state - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and a device capable of accurately estimating a friction state between a tire and a rod with a simple constitution, and a tire for estimating a road friction condition used for estimating the road friction state. <P>SOLUTION: Ground pressure detection means 11 is made of conductive rubber. Signal of outputs of the ground pressure detection means 11 are processed, so as to extract a peak value p<SB>1</SB>on a treading side in a ground pressure variation waveform acting on a tread rubber of the tire and a bottom value q generated near a part immediately below the tread, and transmit them to a road friction state estimating device 20. A peak/bottom ratio R=(q/p<SB>1</SB>) is calculated by the road friction state estimating device 20, so that an friction state between the road, on which a vehicle is traveling, and a tire is estimated based on the calculated peak/bottom ratio R, and a map 23M stored in storage means 23. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method and apparatus for estimating a friction state between a road surface on which a vehicle travels and a tire, and a tire used for estimation of a road surface friction state, and more particularly to a ground load or a ground contact acting on a tire tread rubber. The present invention relates to a method and apparatus for estimating a road surface friction state from pressure.

In order to improve the running stability of automobiles, it is required to accurately estimate the condition of the road surface on which the vehicle is traveling or the friction coefficient between the tire and the road surface (road friction coefficient) and feed it back to the vehicle control. ing. In particular, if the road surface condition and the value of the road surface friction coefficient can be estimated in advance before the risk avoidance operation such as braking / driving or steering, the accuracy of vehicle control technology such as ABS and VSC can be improved. The nature is expected to increase further.
Conventionally, as a method of estimating the road surface friction coefficient, there is a method of estimating the road surface condition, particularly the maximum friction coefficient of the road surface from the relationship between the change in the slip ratio when the accelerator or the brake operation is performed and the vehicle body acceleration. Proposed. This is based on the fact that the magnitude of the road surface friction coefficient μ corresponds to the vehicle body acceleration Ab. The low μ road previously obtained in the stable region of the vehicle body acceleration Ab-wheel slip S characteristic curve. Compared with the Ab / S value when traveling on a medium μ road or a high μ road, the state of the road surface during traveling is estimated. Thereby, the magnitude | size of road surface friction coefficient (micro | micron | mu) can be easily estimated from vehicle body acceleration Ab (for example, refer patent document 1).

On the other hand, in order to develop a highly safe block pattern, a pressure-sensitive conductive rubber body is embedded in the tread portion of a pneumatic tire, and the resistance change of the pressure-sensitive conductive rubber body deforms when the tread surface touches the ground. A method has been proposed in which the relationship between the forces acting on the tread block is examined by detecting the above (see, for example, Patent Document 2). Specifically, as shown in FIG. 5, the tread block 50 includes a first sensor 50A provided with a pressure-sensitive conductive rubber body 50S whose resistance value decreases when compressed in the tire radial direction, and in the tire width direction. A second sensor 50B having a pressure-sensitive conductive rubber body whose resistance value decreases when compressed, and a third sensor having a pressure-sensitive conductive rubber body whose resistance value decreases when compressed in the tire circumferential direction 50C is attached, and each change in current value due to the resistance change of the pressure-sensitive conductive rubber body 50S when the tread block 50 is grounded is detected and transmitted to the vehicle mounting unit 60 on the vehicle body side. In the vehicle mounting unit 60, in the calculation unit 61, from the outputs of the sensors 50A to 50C, the tire radial force Fv, the width force Fw acting on the tread block at the time of tire contact, and the circumferential force The force Fc is calculated and displayed on the display unit 62.
Further, since the Fv corresponds to the vertical drag acting on the tread block at the time of ground contact, the calculation unit 61 is provided with a friction coefficient estimation means 61k, and the calculated radial force Fv and width-direction force Fw The friction coefficient in the tire width direction is estimated from the ratio (Fw / Fv), and the friction coefficient in the tire circumferential direction is estimated from the ratio (Fc / Fv) between the radial force Fv and the circumferential force Fc. Thereby, in addition to the forces Fv, Fw, and Fc acting on the tread block 50, the grip force of the tire can be evaluated, so that a block pattern with improved safety can be designed.
JP-A-7-112659 JP 2005-82010 A

However, in the method of estimating the road surface friction coefficient from the vehicle body acceleration of the vehicle, the road surface friction coefficient can be estimated only when the driver performs a certain operation such as acceleration or deceleration. Since the coefficient cannot be estimated, it is not suitable for estimating the road surface condition in real time.
On the other hand, in the method of embedding the sensors 50A to 50C including the pressure-sensitive conductive rubber bodies 50k having different detection directions in the tread block 50, it is necessary to attach at least three pressure-sensitive conductive rubber bodies 50k with different sensitivity directions. As a result, the configuration of the detection part is not only complicated, but also during steady running, the sensitivity in the tire width direction and the tire circumferential direction is small, so the road surface friction coefficient cannot be accurately estimated. It was.

  The present invention has been made in view of the conventional problems. A method and apparatus capable of accurately estimating the friction state between the tire and the road surface with a simple configuration, and estimation of the road friction state. An object of the present invention is to provide a road surface friction state estimation tire used for the vehicle.

The inventors compared the time-varying waveforms of the force (compression force due to contact load or contact pressure) that acts on the tread rubber when the tread surface treads on the ground when traveling on various road surface conditions. The ground pressure fluctuation is small on the high μ road with high frictional force, but the ground pressure fluctuation is large on the low μ road, and the ground pressure just below the ground is much smaller than when stepping on or kicking out. The present inventors have found that it is possible to accurately estimate the friction state between the tire and the road surface by detecting the variation state of the applied contact load or contact pressure.
That is, the invention according to claim 1 of the present application is a method for estimating a friction state between a tire and a road surface, and measures a contact load or a contact pressure acting on a tread rubber of a running tire, The friction state between the tire and the road surface is estimated based on the time change of the measured contact load or contact pressure.
The invention according to claim 2 is the road surface friction state estimation method according to claim 1, wherein the magnitude of the peak value generated near the stepping-on point or the kicking-out point of the time-varying waveform of the measured contact load or contact pressure. In addition, the friction state between the tire and the road surface is estimated from the magnitude of the bottom value generated near the bottom of the ground.

The invention according to claim 3 is an apparatus for estimating a friction state between a tire and a road surface, the means for detecting a contact load or a contact pressure acting on a tread rubber of a running tire, Means for detecting a peak value generated near the stepping-off point or the kicking-out point of the ground load or the ground pressure and a bottom value generated immediately below the ground from the time-varying waveform of the detected ground load or pressure, and the peak value And a bottom value and a road surface friction state estimating means for estimating a friction state between the tire and the road surface using the calculated value.
According to a fourth aspect of the present invention, there is provided the road surface friction state estimating device according to the third aspect, wherein means for determining the slipperiness of the road surface is provided on the basis of a calculated value obtained from the peak value and the bottom value. It is a thing.
The invention according to claim 5 is the road surface friction state estimation device according to claim 3 or claim 4, wherein the calculated values obtained from the peak value and the bottom value, and various road surface states, prepared in advance. And a road surface friction state estimating unit for estimating the friction state between the tire and the road surface using the calculated value and the map.

A sixth aspect of the present invention is a tire used in the road surface friction state estimation method according to the first or second aspect, wherein the tire has a land portion at a center in a width direction of the tire tread, and the tread of the land portion is used. Means for detecting a grounding load or a grounding pressure acting on the tread rubber is disposed in the rubber.
According to a seventh aspect of the present invention, in the road surface friction state estimation tire according to the sixth aspect, the means for detecting the ground load or the ground pressure is positioned at a position within 10 mm in the depth direction from the ground surface of the land portion. It is arranged.

  According to the present invention, means for measuring the ground load or the ground pressure acting on the tread rubber of the running tire is disposed in the tread rubber of the land portion of the tire tread, and the time of the ground load or ground pressure is set. From the calculated value obtained by detecting the change waveform and the peak value generated near the stepping-on point or the kick-out point and the bottom value generated near the ground contact point in the time-change waveform of the contact pressure, the tire Therefore, the friction state between the tire and the road surface can be accurately estimated with a simple configuration.

Hereinafter, the best mode of the present invention will be described with reference to the drawings.
FIG. 1 is a functional block diagram showing a configuration of a road surface friction state estimation system according to the best mode. In FIG. 1, reference numeral 10 denotes a ground pressure detecting means 11 for detecting a ground pressure acting on a tread rubber of the tire; A signal processing device 12 for extracting the fluctuation value of the ground pressure acting on the tread rubber of the tire by performing signal processing on the output of the ground pressure detection means 11, and transmission for transmitting the extracted fluctuation value of the ground pressure to the vehicle body side. A road surface friction state estimation tire 20 to which a measurement unit 14 including means 13 is attached, 20 is provided on the vehicle body side and is running from the fluctuation value of the ground pressure transmitted from the road surface friction state estimation tire 10. A road surface friction state estimation device for estimating a friction state between a tire and a road surface.
In this example, conductive rubber is used as the contact pressure detecting means 11 and the measurement unit 14 is embedded in the land portion 10b located at the center in the width direction of the tread portion 10a of the tire as shown in FIG. Then, the force in the direction perpendicular to the road surface acting on the tread rubber constituting the land portion 10b, that is, the tire contact pressure is detected. At this time, it is important that the ground pressure detecting means 11 is buried within 10 mm from the ground surface of the land portion 10b in the depth direction. Is unfavorable because it decreases.

Specifically, the signal processing device 12 provided in the road surface friction state estimation tire 10 includes a ground pressure waveform detecting unit 12a that detects a ground pressure waveform in which output levels of the ground pressure detecting unit 11 are arranged in time series, and A ground pressure value extracting means 12b for extracting a peak value p ₁ generated at the stepping point and a bottom value q generated near the ground contact point from the ground pressure waveform is provided. The extracted peak value p ₁ and the bottom The data of the value q is transmitted from the transmission means 13 to the road surface friction state estimating device 20 on the vehicle body side.
Further, the road surface friction state estimating apparatus 20 includes a receiving means 21 for receiving data of the peak value p ₁ and the bottom value q which is transmitted from the tire 10, a ratio between the peak value p ₁ and the bottom value q A peak / bottom ratio calculating means 22 for calculating a certain peak / bottom ratio R; a storage means 23 for storing a map 23M indicating a relationship between a road surface friction state and a peak / bottom ratio R obtained in advance; Road surface friction which is calculated by the bottom ratio calculation means 22 and estimates the friction state between the road surface on which the vehicle is running and the tires based on the peak / bottom ratio R received by the receiving means 21 and the map 23M. and a state estimation unit 24, a road surface friction condition based on the peak value p ₁ and the bottom value q of the ground pressure acting on the tread rubber which is transmitted from the road surface friction condition estimating tire 10 A constant.

FIGS. 3A to 3C are examples of a time waveform of a contact pressure acting on the tread rubber of the land portion 10b located at the center of the tread portion 10a and the ground contact state of the road surface friction state estimation tire 10 according to the present invention. FIG. 5B is a diagram showing a change in the contact pressure during DRY asphalt running on a high μ road, and FIG. 5C is a diagram showing a change in the contact pressure during ICE road running on a low μ road. is there.
The road surface friction is generated between the rubber on the tire tread surface and the road surface. As shown in FIG. 3 (a), when the tire rolls and the tread comes into contact with the ground, it is almost cylindrical except for the ground surface. Since the shape that has been shaped is deformed on a flat surface, the tread receives a compressive force in the circumferential direction. At this time, on the high μ road, the frictional force with the road surface is large, and the tread is strongly restrained by the road surface. Therefore, the compression force is absorbed as a shear strain of the tread. On the other hand, on the low μ road, it is not possible to generate a force that opposes the compressive force. Therefore, the tread is greatly compressed, and reverse bending deformation (buckling) occurs in the tire. As a result, as shown in FIGS. 3 (b) and 3 (c), the fluctuation of the ground pressure between the stepping-in and the kicking-out is small on the high μ road, but on the low μ road because of the above buckling, The contact pressure is smaller than when stepping on or kicking out.
Therefore, the use of the fact that the ground pressure fluctuation varies depending on the road friction state makes it possible to estimate the road friction state with high accuracy and good responsiveness.

Next, the road surface friction state estimation method according to the best mode will be described.
First, the contact pressure detecting means 11 detects the contact pressure acting on the tread rubber of the land portion 10b, and the output is sent to the contact pressure waveform detecting means 12a to contact the land portions 10b arranged in time series. seeking pressure waveform at the ground pressure value extracting extracting unit 12b, the grounding peak value p ₁ occurs pressure waveform depression points and bottom and the peak value p ₁ after extracting bottom value q that occurs in the vicinity of the ground immediately below the Data of the value q is transmitted to the road surface friction state estimation device 20 via the transmission means 13.
In the road surface friction state estimating device 20, the data of the peak value p ₁ and the bottom value q is received by the receiving means 21, and the peak / bottom ratio calculating means 22 receives the peak / bottom ratio R = (q / p ₁ ). Is calculated by the road surface friction state estimating means 24 based on the peak / bottom ratio R and the map 23M stored in the storage means 23, and the friction state between the road surface on which the vehicle is running and the tire. Is estimated.

As described above, according to the best mode, the contact pressure detecting means 11 made of conductive rubber and the fluctuation waveform of the contact pressure acting on the tire tread rubber by signal processing the output of the contact pressure detecting means 11. The peak value p ₁ on the depression side and the bottom value q generated in the vicinity immediately below the ground are extracted and transmitted to the road surface friction state estimation device 20, and the road surface friction state estimation device 20 calculates the peak / bottom ratio R = (q / p ₁ ) is calculated, and the friction state between the road surface on which the vehicle is running and the tire is estimated based on the calculated peak / bottom ratio R and the map 23M stored in the storage means 23. Therefore, the friction state between the tire and the road surface can be accurately estimated with a simple configuration.
Further, in this example, the road surface friction state is estimated from the fluctuation of the contact pressure acting on the tread rubber of the tire. Therefore, even when the slip ratio is substantially zero, the road surface friction state can be estimated. For this reason, there is an advantage that an appropriate initial braking force can be determined before the start of braking.

In the above-described best mode, the road surface friction state is estimated from the contact pressure obtained by the contact pressure detecting means 11. However, instead of the contact pressure detecting means 11, a contact load detecting means such as a load cell is provided, and this contact load detecting means. The road surface friction state may be estimated based on the ground contact load obtained by the above.
Further, if there is one contact pressure detecting means 11 on the circumference, the road surface friction state is estimated every time the vehicle travels along the tire circumference, so that the road surface friction state can be updated each time the vehicle travels. That is, the road surface friction state can be updated for each rotation of the tire without depending on the vehicle speed. If a plurality of contact pressure detecting means 11 are provided on the circumference, the update distance of the road surface friction state can be easily shortened.
In the above example, the peak value p ₁ on the depression side is used as the peak value for calculating the peak / bottom ratio R, but the same effect can be obtained by using the peak value p ₂ generated near the kicking point. Can be obtained.
Further, instead of the peak-to-bottom ratio R, as a peak value, a difference between a peak value p ₁ on the stepping side or a peak value p ₂ occurring near the kicking point and a bottom value q occurring near the ground contact point is used. Also good.

In the best mode, the peak / bottom ratio calculating means 22 is provided in the road surface friction state estimating device 20 and the peak / bottom ratio R = (q / p ₁ ) is calculated on the vehicle side. The ratio calculation means 22 may be provided in the signal processing device 12 of the road surface friction state estimation tire 10 to calculate the peak / bottom ratio R on the tire side and transmit the result to the vehicle body side. Incidentally, conceivable configuration for extracting the bottom value q outputs were sent directly to the vehicle body, a peak value p ₁ of leading side detects the ground pressure waveform at the vehicle body side of the ground immediately below the ground pressure detecting means 11 it is, but in this case, since the transmission data increases, as in the present embodiment, it is preferable to adopt a configuration that transmits to the vehicle body by extracting and the peak value p ₁ and the bottom value q on a tire side .
Further, in the above example, the road surface friction state is estimated using the map 23M indicating the relationship between the peak / bottom ratio R and the road surface friction state obtained in advance, but instead of the map 23M, the determination with respect to the peak / bottom ratio R is performed. If the value is set and the peak-to-bottom ratio R is equal to or less than the determination value, the road surface is slippery, and if the value exceeds the determination value, determination means is provided to determine that the road surface is slippery road surface. You may make it estimate the slipperiness of. Alternatively, a plurality of threshold values K1 and K2 are provided, and road surface condition determining means for determining a high μ road surface if R ≦ K1, a medium μ road surface if K1 <R ≦ K2, and a low μ road surface if K2 <R is provided. Good.

  A vehicle equipped with the road surface friction state estimation system of the present invention was allowed to enter the ICE road surface (μ≈0.1) from the DRY asphalt road surface (μ≈1) at a constant speed, and the time change of the peak / bottom ratio was measured. . The result is shown in FIG. In the figure, the horizontal axis represents time, and the vertical axis represents the peak / bottom ratio. As is apparent from the figure, the peak-to-bottom ratio increases at the same time as entering the ICE road surface. Therefore, it was confirmed that the slipperiness of the road surface can be easily determined by providing an appropriate threshold value as in the determination line of FIG.

  As described above, according to the present invention, it is possible to estimate the road surface friction state from the tire behavior robustly with respect to the temperature and speed even during steady running, so if the information on the estimated road surface friction state is used, In addition to alerting the driver, the accuracy of vehicle control such as ABS and VSC can be greatly improved, so that the driving safety of the vehicle can be greatly improved.

It is a functional block diagram which shows the structure of the road surface friction state estimation system concerning the best form of this invention. It is a figure which shows an example of the mounting position of a ground pressure detection means. It is a figure which shows an example of the time waveform of the contact pressure which acts on the tread rubber of the land part located in the contact state of a tire, and the tread part center. It is a figure which shows the time change of a peak / bottom ratio when the vehicle carrying the road surface state estimation system of this invention is approached from the DRY asphalt road surface to the ICE road surface at a constant speed. It is a figure which shows the estimation method of the conventional road surface friction state.

Explanation of symbols

10 tires for estimating the road surface friction state, 10a tread portion, 10b center land portion,
11 ground pressure detecting means, 12 signal processing device, 12a ground pressure waveform detecting means,
12b Ground pressure value extracting means, 13 transmitting means, 14 measuring unit,
20 road surface friction state estimating device, 21 receiving means, 22 peak / bottom ratio calculating means,
23 storage means, 23M map, 24 road surface friction state estimation means.

Claims (7)

  The contact load or contact pressure acting on the tread rubber of the running tire was measured, and the friction state between the tire and the road surface was estimated based on the above measured contact load or contact pressure fluctuation state. A road surface friction state estimation method characterized by the above.   Estimate the frictional condition between the tire and the road surface from the measured time-varying waveform of the contact load or contact pressure based on the peak value generated near the stepping-on or kick-out point and the bottom value generated immediately below the contact point. The road surface friction state estimation method according to claim 1, wherein:   From the means for detecting the contact load or contact pressure acting on the tread rubber of the running tire and the time-varying waveform of the detected contact load or contact pressure, in the vicinity of the stepping or kicking point of the contact load or contact pressure. Means for detecting a peak value generated in the vicinity of the vehicle and a bottom value generated immediately below the ground contact, means for calculating a calculated value using the peak value and the bottom value, and a friction state between the tire and the road surface using the calculated value A road surface friction state estimation device comprising: a road surface friction state estimation means for estimating the road surface friction state.   4. A road surface friction state estimating apparatus according to claim 3, further comprising means for determining the slipperiness of the road surface based on a calculated value obtained from the peak value and the bottom value.   In addition to storing a map that shows the relationship between the calculated value obtained from the peak value and the bottom value and various road surface conditions, which is created in advance, the road surface frictional state estimating unit provides the calculated value and the 5. The road surface friction state estimation device according to claim 3, wherein the road surface friction state estimation device is configured to estimate a friction state between a tire and a road surface using a map.   A tire used in the road surface friction state estimation method according to claim 1 or 2, wherein the tire tread has a land portion at a center in a width direction, and acts on the tread rubber in the tread rubber of the land portion. A road surface friction state estimating tire characterized in that means for detecting a contact load or a contact pressure is provided. 7. The road surface friction state estimating tire according to claim 6, wherein the means for detecting the contact load or contact pressure is disposed at a position within 10 mm in the depth direction from the contact surface of the land portion.

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