JP2019074335A - Tire grounding condition evaluation method - Google Patents

Abstract

To provide a method of evaluating a tire grounding condition with high accuracy from a correlation between a tire contact area and a friction coefficient during traveling on a wet road surface.SOLUTION: A tire ground condition evaluation method includes the steps of: measuring a load when a rubber test piece is pressed through a fluorescent liquid against a ground contact surface having irregularities equivalent to an actual road surface provided on one surface of a transparent plate and is moved linearly while sliding, and a friction coefficient between the ground contact surface and the rubber test piece; irradiating the fluorescent liquid interposed between the ground contact surface and the rubber test piece with excitation light from the opposite side of the transparent plate to the ground contact surface to measure the luminance distribution of the fluorescence emitted from the fluorescent liquid; obtaining a binarized image by using an arbitrary luminance as a threshold on the basis of the obtained luminance distribution to determine a contact area; and obtaining an increase or decrease in the contact area from a difference between two or more types of binarized images in which measurement parameters are different from each other.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method of evaluating a tire contact state from the correlation between a tire contact area and a friction coefficient when traveling on a wet road surface.

  Conventionally, as a method of evaluating the contact state of the tire, a method of grounding the tire on a flat plate and visualizing and observing the contact shape at that time is used. Specifically, light interference method, total reflection method, etc. Visualization techniques are known.

  However, since tire characteristics when a tire is pressed on a flat plate and tire characteristics on an actual road surface are dissociated, a method that can be evaluated on a rough surface equivalent to the actual road surface is required. For that purpose, for example, in Patent Document 1, a method is proposed in which the tire is brought into contact with the ground contact surface provided with irregularities equivalent to the actual road surface, and the contact shape of the tire is photographed. It has also been proposed to fill the space portion on the ground contact surface with colored liquid to ground the tire and to photograph.

  In the method described in this patent document 1, although it is possible to evaluate the grounding condition on a wet road surface, in the method using a colored liquid, there is a problem in the measurement accuracy guaranteed in principle, and it is a problem in terms of expandability. was there.

  In particular, unevenness on the actual road is mixed with irregularities of various scales, and when the surface roughness of the surface of the actual road aggregate is measured with a contact roughness meter (Mitsutoyo Co., Ltd.), the arithmetic mean roughness (Ra) Was about 20 μm. In the dynamic sliding state, it is considered that the thin water film formed on the aggregate surface with such surface roughness is considered to be effective, and a method with excellent measurement accuracy that can detect even thin portions of film thickness Desired.

  Therefore, as a method of evaluating the ground contact state of a tire on a wet road surface having an uneven surface equivalent to an actual road surface, Non-Patent Document 1 proposes that the photoexcitation fluorescence method be adopted. In the photoexcitation fluorescence method, when the film thickness of the fluorescent liquid between the rubber test piece and the ground plane is thin, the luminance is proportional to the film thickness of the fluorescent liquid, so the measurement accuracy is excellent and the measurement example with a film thickness of 10 μm or less Has also been confirmed.

  However, there is a problem that the evaluation of the ground contact state of the tire in the stationary state on the uneven surface equivalent to the actual road surface can not be consistent with the evaluation of the ground contact state of the tire when traveling on the actual road surface.

JP 2003-240681 A JP 2012-154858 A JP 2004-9880 A JP, 2016-8950, A JP, 2017-58244, A

Eguchi Masao, "Rubber plate-analysis of indirect contact with uneven surface using light induced fluorescence method-Visualization and luminance histogram analysis-", Tribologist, 58, 10 (2013) 763-772.

  With regard to the evaluation method when running the tire, in Patent Document 2, the tire is in contact with the transparent plate provided with a liquid layer made of a white liquid on the surface, and the tire is moved relative to the front and rear direction. Although the method of image | photographing is disclosed, it is a measuring method using a coloring liquid like the said patent document 1, and the precision of evaluation is not enough. In addition, the main focus is on obtaining an outline of a dynamic ground contact surface shape in a flat glass flat plate, and it is not assumed to evaluate the ground contact state with the random unevenness of the actual road surface.

  In addition, even with tires that can obtain the same contact area on a wet road surface, there are cases where the friction coefficient contributing to grip performance and the like differ, and the present inventor has described not only simple magnitudes of contact area but also ground contact characteristics. I thought I needed to know Then, it has been found that the tire ground contact state can be evaluated with higher accuracy by evaluating the influence of other parameters from the correlation between the tire contact area and the friction coefficient. For example, even if the contact area is the same, a state in which there is a large or small relation between the friction coefficients is selected based on experimental parameter differences, and the characteristics of the contact state with high friction coefficient can be clarified by comparing the two. However, the difference between the two is predicted to be small, and a highly accurate measurement method is required.

  An object of the present invention is to provide a method of evaluating a tire grounding state with high accuracy from the correlation between a tire contact area and a friction coefficient during traveling on a wet road surface in view of the above points.

  Patent Document 3 describes an apparatus for measuring the ground contact shape of a tire tread during running of a tire, and Patent Document 4 has an observation method capable of observing the deformation of an elastic material such as rubber having a slip angle. Have been described.

  Further, according to Patent Document 5, the flat surface of the rubber test piece is pressed against the test road surface simulating the actual road surface including the aggregate, and the rubber test piece is moved straight while sliding on the flat test road surface. A rubber friction test method has been described which measures the load at the time and measures the coefficient of friction between a test road surface and a rubber test piece.

  However, these do not evaluate the characteristics of tires on wet road surfaces, and these methods can not be applied as they are to evaluation on wet road surfaces. Further, Patent Document 5 only measures the coefficient of friction, and does not disclose evaluating the correlation between the contact area of the tire and the coefficient of friction when traveling on a wet road surface.

  In the tire ground contact state evaluation method according to the present invention, a rubber test piece is pressed against a ground contact surface provided with unevenness corresponding to the actual road surface provided on one surface of a transparent plate, and a rubber test piece is pressed and moved straight while sliding. Measuring the friction load between the ground contact surface and the rubber test piece, and from the opposite side to the ground contact surface of the transparent plate, to the fluorescent liquid interposed between the ground contact surface and the rubber test piece The step of irradiating the excitation light to measure the luminance distribution of the fluorescence emitted from the fluorescent liquid and obtaining a binarized image with an arbitrary luminance as a threshold based on the obtained luminance distribution to determine the contact area It is assumed that there is a process and a process of obtaining an increase or decrease in the contact area from the difference between two or more types of binarized images having different measurement parameters.

  The different measurement parameters are at least selected from the group consisting of measurement time point, moving speed of rubber test piece, hardness of rubber test piece, pressure pressing rubber test piece against the ground surface, and shape of rubber test piece It can be one kind.

  The fluorescent liquid may contain a hydrophilic fluorescent dye having a peak wavelength difference of 100 nm or more between the excitation spectrum and the fluorescent spectrum, and the hydrophilic fluorescent dye is preferably pyranine.

  According to the evaluation method of the present invention, the tire ground contact state can be evaluated with high accuracy from the correlation between the tire contact area and the friction coefficient during traveling on a wet road surface.

BRIEF DESCRIPTION OF THE DRAWINGS The simplification figure which shows the whole structure of the testing machine which performs the tire grounding evaluation method based on one Embodiment. BRIEF DESCRIPTION OF THE DRAWINGS The simplification figure which shows the structure of the fluorescence measurement apparatus which performs the tire grounding evaluation method which concerns on one Embodiment. The simplified drawing which shows the relationship of the excitation spectrum at the time of using pyranine as a fluorescent dye, and a fluorescence spectrum.

  Hereinafter, the tire grounding state evaluation method of one embodiment concerning the present invention is explained based on Drawings 1-3.

  In the tire ground contact state evaluation method of this embodiment, a fluorescent liquid is interposed on a ground contact surface provided with irregularities corresponding to the actual road surface provided on one surface of a transparent plate, and a rubber test piece is pressed and moved straight while sliding. Measuring the friction load between the ground contact surface and the rubber test piece, and from the opposite side to the ground contact surface of the transparent plate, to the fluorescent liquid interposed between the ground contact surface and the rubber test piece The step of irradiating the excitation light to measure the luminance distribution of the fluorescence emitted from the fluorescent liquid and obtaining a binarized image with an arbitrary luminance as a threshold based on the obtained luminance distribution to determine the contact area It is assumed that there is a process and a process of obtaining an increase or decrease in the contact area from the difference between two or more types of binarized images having different measurement parameters.

  FIG. 1 is a simplified view showing the entire configuration of a testing machine that performs the tire grounding state evaluation method of the present embodiment.

  The testing machine 10 is a load device for pressing the rubber test piece 2 against the transparent plate 1, the holder 3 for holding the rubber test piece 2, and the transparent plate 1 provided with the ground contact surface having unevenness equivalent to the actual road surface on one side. 4 and a driving device 5 for moving the rubber test piece 2 relative to the transparent plate 1, a load sensor 6 for measuring the load acting on the rubber test piece 2, and control for controlling the operation necessary for the test And an apparatus 7. In addition, the transparent plate 1 is installed on the transparent plate installation stand 18, and the fluorescence measurement device 20 is provided under the transparent plate installation stand 18.

  The method of producing the transparent plate 1 having the ground contact surface having irregularities equivalent to the actual road surface is not particularly limited. For example, the silicone mold for vacuum casting is molded with silicone rubber from asphalt corresponding to the actual road surface It can be produced by pouring a transparent resin into a mold and curing it in a vacuum degassed state. As transparent resin, urethane-type resin can be mentioned, for example.

  The rubber test piece 2 is made of a vulcanized rubber and has a flat surface pressed against the transparent plate 1 and may have a groove or a taper corresponding to a tire groove.

  The holder 3 is connected to the load device 4. The load device 4 is configured to be capable of reciprocating the holder 3 along a Z direction (vertical direction in FIG. 1) perpendicular to the transparent plate 1. By appropriately setting the position of the holder 3 (the distance between the holder 3 and the transparent plate 1), the load in the Z direction input to the rubber test piece 2 can be adjusted, and thus the rubber test piece under a predetermined pressure condition 2 can be pressed against the transparent plate 1. The load device 4 is constituted by a servomotor, but other actuator mechanisms can also be used.

  The driving device 5 is configured to be capable of reciprocating the table 8 supporting the loading device 4 along the X direction (left and right direction in FIG. 1). The holder 3 is moved by the movement of the table 8 and can be moved while sliding the rubber test piece 2 on the transparent plate 1. The actuator 9 is configured to be capable of reciprocating the table 8 along the Y direction (direction perpendicular to the sheet of FIG. 1) perpendicular to both the X direction and the Z direction, and is transparent to the rubber test piece 2 in the Y direction. It is used for alignment with the board 1. In the present embodiment, the drive device 5 and the actuator 9 are respectively configured by servomotors, but the present invention is not limited to this.

  The load sensor 6 is capable of measuring a total of three component loads, a vertical component and a horizontal component, and the load in the Z direction (vertical force) acting on the rubber test piece 2, the load in the X direction (longitudinal force) and the Y direction Load (lateral force) can be measured. The load sensor 6 is configured of, for example, a load cell. In the present embodiment, the load sensor 6 is attached to the upper side of the holder 3 (opposite to the rubber test piece 2).

  The control device 7 includes an operation unit 7a that performs calculations necessary to measure the coefficient of friction, an operation control unit 7b that controls the operation of the load device 4 and the drive device 5, and an input unit 7c that receives an input from a test operator. And a display unit 7 d for displaying various information related to the operation and setting of the test machine 10 on the screen. The measured value by the load sensor 6 is sent to the control device 7, based on which the computing unit 7a calculates the coefficient of friction.

  Further, as shown in FIG. 2, a light source 12 and a filter 16 for transmitting and separating only light of a specific wavelength from the light irradiated from the light source 12 as a fluorescence measurement apparatus 20 under the transparent plate installation stand 18 , A dichroic mirror 14 that reflects only light of a specific wavelength, a mirror 15 that reflects fluorescence emitted from the fluorescent liquid 11, and a filter 17 that transmits and separates only light of a specific wavelength from the emitted fluorescence. An imaging means 13 for measuring the fluorescence transmitted through the filter 17 is disposed.

  The fluorescence measurement apparatus 20 may be fixed to the lower part of the transparent plate installation base 18, supported by the table 8, and configured to be capable of reciprocating along the X direction by the drive device 5 in conjunction with the load device 4. It may be

  The tire grounding state evaluation method of the present embodiment can be implemented as follows using, for example, pyranine as the hydrophilic fluorescent dye and using the above-described tester 10. That is, the fluorescent liquid 11 containing pyranine is interposed on the transparent plate 1 having irregularities corresponding to the actual road surface, the flat surface of the rubber test piece 2 is pressed, and the rubber test piece 2 is slid on the transparent plate 1 The load when moving straight is measured while measuring the coefficient of friction between the transparent plate 1 and the rubber test piece 2. Both static and dynamic friction coefficients can be measured. The pressure condition of the rubber test piece 2 pressed against the transparent plate 1 and the condition regarding the rectilinear movement such as the velocity and the path are controlled by the controller 7. The moving speed can be set so that the rubber test piece 2 can slide a predetermined section at a uniform speed.

  At that time, the excitation light is irradiated using an ultraviolet LED (peak wavelength 365 nm) as the light source 12, and the excitation light having a wavelength of 400 nm or less is separated by the filter 16 (400 nm low pass filter). The separated excitation light is reflected by the dichroic mirror 14, and the excitation light is irradiated to the fluorescent liquid 11 interposed between the rubber test piece 2 and the ground surface from the side opposite to the ground surface of the transparent plate 1. As a result, pyranine contained in the fluorescent liquid 11 is transitioned from the ground state to the excited state. The excited state pyranine then returns to the ground state, at which time fluorescence is emitted. The emitted fluorescence is transmitted through the dichroic mirror 14 and then reflected by the mirror 15, and the filter 17 (480 nm high-pass filter) separates the fluorescence having a wavelength of 480 nm or more. By photographing the separated fluorescence by the photographing means 13, a luminance distribution (fluorescence intensity image) can be obtained.

  The tire ground contact state evaluation method of the present embodiment further includes a step of binarizing using any luminance as a threshold with reference to the luminance distribution obtained above. Specifically, by setting a certain specific luminance as a threshold, a binarized image can be obtained as an area where the rubber test piece 2 is in contact with the ground contact area, in which the luminance is equal to or less than the threshold. From such a binarized image, for example, the area where the rubber test piece 2 and the ground contact surface are in contact can be calculated.

  By performing the above test, a coefficient of friction on a wet road surface and a binarized image showing the contact state between the wet road surface and the rubber test piece 2 can be obtained simultaneously, and the correlation between them can be obtained.

  The tire ground contact state evaluation method of the present embodiment includes, in addition to the above steps, a step of obtaining an increase or decrease in the contact area from the difference between two or more types of binarized images having different measurement parameters. By determining the increase or decrease of the contact area from the difference between the binarized images, it is possible to evaluate the influence of the measurement parameter on the grounding state. For example, in the case where there are binarized images having the same contact area but different friction coefficients, the comparison of the two can reveal the characteristics of the contact state having a high friction coefficient. Note that two or more types of binarized images are processed with the same threshold value.

  The measurement parameters include, for example, measurement time, moving speed of the rubber test piece 2, hardness of the rubber test piece 2, pressure pressing the rubber test piece 2 against the ground contact surface, shape of the rubber test piece 2, etc. . That is, two or more types of binarized images having different measurement parameters may be compared between different binarized images at the measurement time point obtained in one test, the moving speed of the rubber test piece 2, the rubber test Contrasting the binarized images obtained in different tests performed by changing measurement parameters such as the hardness of the piece 2, the pressure pressing the rubber test piece 2 against the ground contact surface, and the shape of the rubber test piece 2 It is also good.

  Although the case where pyranine is used as the hydrophilic fluorescent dye has been described in the above embodiment, the present invention is not limited to this. Although various hydrophilic fluorescent dyes can be used for the fluorescent liquid 11, from the viewpoint of obtaining excellent measurement accuracy, a hydrophilic fluorescent dye having a peak wavelength difference of 100 nm or more between the excitation spectrum and the fluorescence spectrum. It is preferable that it is an aqueous solution containing Specific examples of the hydrophilic fluorescent dye having a peak wavelength difference of 100 nm or more between the excitation spectrum and the fluorescence spectrum include pyranine, DY-481XL-Carboxylic Acid, DY-521XL-Carboxylic Acid, ATTO-TEC manufactured by Dyomics. Company-made ATTO 490LS carboxy etc. are mentioned, and it can use pyranine suitably from a safety or a viewpoint of cost. Also, in the case of a hydrophilic fluorescent dye having a plurality of peak wavelengths of the excitation spectrum and / or fluorescence spectrum, by using a filter or the like for the excitation spectrum and / or fluorescence spectrum, the peak wavelengths of the excitation spectrum and the fluorescence spectrum The peak wavelength may be selected and used so that the difference is 100 nm or more.

  Pyranine is a hydrophilic pH-sensitive fluorescent dye. When the pH is neutral to acidic, the peak wavelengths of the excitation spectrum appear near 365 nm and 400 nm, and when the pH is alkaline, the peak wavelength of the excitation spectrum appears near 450 nm . Further, the peak wavelength of the fluorescence spectrum is mainly around 510 nm regardless of the pH, and the fluorescence spectrum of 400 nm or less is hardly detected. Therefore, when pyranine is used as the hydrophilic fluorescent dye, the pH of the fluorescent solution 11 is preferably neutral to acidic, from the viewpoint of setting the difference in peak wavelength between the excitation spectrum and the fluorescence spectrum to 100 nm or more. Is more preferably 5-8. Further, in the present embodiment, the peak wavelength of the excitation spectrum of pyranine is mainly 365 nm by using the filter 16 transmitting only the wavelength of 400 nm or less for the excitation light, and the peaks of the excitation spectrum and the fluorescence spectrum The wavelength difference is up to 145 nm.

  As shown in FIG. 3, by using a fluorescent dye in which the difference in peak wavelength between the excitation spectrum and the fluorescence spectrum is 100 nm or more as the fluorescent liquid 11, overlapping of the wavelength ranges of the excitation spectrum and the fluorescence spectrum hardly occurs. Since the excitation spectrum and the fluorescence spectrum can be sufficiently separated, excellent measurement accuracy can be easily obtained.

  The concentration of the hydrophilic fluorescent dye in the fluorescent liquid is not particularly limited, but when pyranine is used, it is preferably 100 to 10000 mg / L.

  The light source 12 can be appropriately selected and used according to the excitation spectrum of the hydrophilic fluorescent dye to be used, and is not particularly limited. However, the peak wavelength is around the peak wavelength of the excitation spectrum of the hydrophilic fluorescent dye to be used It is preferable that it is the light source 12 which it has, and it is more preferable that it is a single wavelength. When the hydrophilic fluorescent dye to be used is pyranine, it is preferable that the peak wavelength of the irradiated light is 350 to 400 nm.

  The dichroic mirror 14 and the filters 16 and 17 are not particularly limited, and can be appropriately selected and used in accordance with the excitation spectrum and the fluorescence spectrum of the hydrophilic fluorescent dye to be used. The filters 16 and 17 may be, for example, a wavelength selective fluorescent filter that removes noise when performing fluorescence detection, or a high pass filter that cuts light on the short wavelength side of the specified wavelength and transmits light on the long wavelength side. (Long-pass filter), a low-pass filter (short-pass filter) that cuts light on the longer wavelength side than the specified wavelength and transmits light on the short wavelength side, transmits only light in a certain wavelength range, and other short wavelength sides And a band pass filter for cutting light on the long wavelength side.

  The tire ground contact state evaluation method of the present embodiment may further include the step of converting the obtained luminance distribution into the film thickness distribution of the fluorescent liquid 11. In this case, the film thickness distribution image is binarized to obtain a binarized image, and images of different measurement parameters are compared with each other. When the film thickness of the fluorescent liquid 11 between the rubber test piece 2 and the ground plane is thin, the luminance is proportional to the film thickness, so the obtained luminance distribution is converted into a film by converting the quantified luminance into a film thickness. It is possible to convert to a thickness distribution. In addition, the calibration of the brightness and the film thickness may be performed as a step before this process. For example, a calibration curve of film thickness and brightness is obtained using a glass plate of known dimensions, and the brightness can be converted to a film thickness by applying it. Thus, the present invention is applicable even when the luminance and the film thickness are not in a proportional relationship.

  While the embodiments of the present invention have been described, this embodiment is presented as an example and is not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and the gist of the invention, and are included in the invention described in the claims and the equivalent scope thereof.

  The tire contact state evaluation method of the present invention can be used to evaluate the contact state of various tires such as passenger cars and light trucks and buses.

DESCRIPTION OF SYMBOLS 1 ...... Transparent plate 2 ... Rubber test piece 3 ... Holder 4 ... Load apparatus 5 ... Drive apparatus 6 ... Load sensor 7 ... Control apparatus 8 ... Table 9 ... · Actuator 10 · · Test machine 11 · · Fluorescent solution 12 · · Light source 13 · · Imaging means 14 · · Dichroic mirror 15 · · Mirror 16 · · Filter 17 · Filter 18 · Transparent plate installation stand 20 · · Fluorescence measurement apparatus

Claims (4)

A fluorescent test piece is pressed against a ground contact surface with irregularities equivalent to the actual road surface provided on one side of a transparent plate, and a rubber test piece is pressed against it, and the load when moving straight while sliding is measured. Measuring the coefficient of friction with the rubber test piece;
Irradiating a fluorescent liquid interposed between the ground plane and the rubber test piece from the opposite side to the ground plane of the transparent plate with excitation light to measure the luminance distribution of the fluorescence emitted from the fluorescent liquid;
A step of obtaining a contact area by obtaining a binarized image with an arbitrary luminance as a threshold value based on the obtained luminance distribution;
A tire ground contact state evaluation method comprising the step of obtaining an increase or decrease of a contact area from the difference between two or more types of binarized images having different measurement parameters.   The different measurement parameters are at least selected from the group consisting of measurement time point, moving speed of rubber test piece, hardness of rubber test piece, pressure pressing rubber test piece against the ground surface, and shape of rubber test piece The tire grounding state evaluation method according to claim 1, wherein the tire grounding state is one type.   The tire grounding condition evaluation method according to claim 1 or 2, wherein the fluorescent liquid contains a hydrophilic fluorescent dye having a difference in peak wavelength between an excitation spectrum and a fluorescence spectrum of 100 nm or more. The tire grounding condition evaluation method according to any one of claims 1 to 3, wherein the hydrophilic fluorescent dye is pyranine.