Tire Contact State Evaluation Method

Abstract

To provide an evaluation method of a tire ground contact state during traveling on a wet road surface below the freezing point.SOLUTION: A tire ground contact state evaluation method comprises the steps of: making a rubber test piece contact through fluorescent liquid A with a ground plane arranged on one surface of a transparent plate, which has irregularity corresponding to an actual road surface; and measuring brightness distribution of fluorescence emitted from the fluorescent liquid A by irradiating the fluorescent liquid A lying between the ground plane and the rubber test piece with exciting light from the opposite side to the ground plane of the transparent plate. The fluorescent liquid A contains an antifreezing agent which is water soluble below the freezing point and non-volatile in addition to water soluble fluorescence agent.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for evaluating the tire contact state during driving on a wet road surface below freezing point.

Background Art

[0002] As a method for evaluating the contact state of a tire on a wet road surface, as described in Patent Documents 1 and 2, a step of grounding a rubber test piece with a fluorescent liquid interposed on a contact surface having unevenness corresponding to an actual road surface provided on one surface of a transparent plate, and a step of irradiating excitation light to the fluorescent liquid interposed between the contact surface of the transparent plate and the rubber test piece from the side opposite to the contact surface of the transparent plate, and measuring the luminance distribution of the fluorescence emitted from the fluorescent liquid are included.

[0003] However, with conventional fluorescent liquids, since they freeze below freezing point, it has been difficult to measure the tire contact state below freezing point.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In view of the above points, an object of the present invention is to provide a method for evaluating the tire contact state during driving on a wet road surface below freezing point.

Means for Solving the Problems

[0006] The tire contact state evaluation method according to the present invention includes a step of bringing a rubber test piece into contact with a contact surface having unevenness equivalent to a real road surface provided on one surface of a transparent plate with a fluorescent liquid A interposed therebetween, and from the side opposite to the contact surface of the transparent plate, irradiating the fluorescent liquid A interposed between the contact surface and the rubber test piece with excitation light and measuring the luminance distribution of the fluorescence emitted from the fluorescent liquid A. The fluorescent liquid A contains, in addition to a water-soluble fluorescent agent, an antifreeze agent that is water-soluble and non-volatile at sub-zero temperatures.

[0007] The antifreeze agent can be a dihydric alcohol, a chloride salt, or an acetate salt.

[0008] The tire contact state measurement method according to the present invention is a measurement method using a water-soluble fluorescent agent, a fluorescent liquid A containing a water-soluble and non-volatile antifreeze agent under sub-zero temperatures, and a fluorescent liquid B containing a water-soluble fluorescent agent and not containing the antifreeze agent. The method includes the steps of: at a temperature higher than 0°C, grounding a rubber test piece on a contact surface having unevenness equivalent to a real road surface provided on one surface of a transparent plate with the fluorescent liquid A interposed therebetween; while changing the contact pressure of the rubber test piece, irradiating excitation light from the side opposite to the contact surface of the transparent plate to the fluorescent liquid A interposed between the contact surface and the rubber test piece, and measuring a luminance distribution A of the fluorescence emitted from the fluorescent liquid A; grounding a rubber test piece on a contact surface having unevenness equivalent to a real road surface provided on one surface of a transparent plate with the fluorescent liquid B interposed therebetween; while changing the contact pressure of the rubber test piece, irradiating excitation light from the side opposite to the contact surface of the transparent plate to the fluorescent liquid B interposed between the contact surface and the rubber test piece, and measuring a luminance distribution B of the fluorescence emitted from the fluorescent liquid B; in the luminance distribution B, arbitrarily setting a threshold B and binarizing it to obtain a correlation between the contact pressure and the contact area; setting a threshold A such that the correlation between the contact pressure and the contact area in the luminance distribution A coincides with the correlation between the contact pressure and the contact area obtained in the luminance distribution B; at sub-zero temperatures, grounding a rubber test piece on a contact surface having unevenness equivalent to a real road surface provided on one surface of a transparent plate with the fluorescent liquid A interposed therebetween; while changing the contact pressure of the rubber test piece, irradiating excitation light from the side opposite to the contact surface of the transparent plate to the fluorescent liquid A interposed between the contact surface and the rubber test piece, and measuring a luminance distribution C of the fluorescence emitted from the fluorescent liquid A; and in the luminance distribution C, setting the threshold A and binarizing it to obtain a correlation between the contact pressure and the contact area.

Effect of the Invention

[0009] According to the evaluation method of the present invention, the tire contact state during driving on a wet road surface can be evaluated with high accuracy under sub-zero temperatures.

Brief Description of the Drawings

[0010]

Figure 1

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Figure 7

Mode for Carrying Out the Invention

[0011] Hereinafter, a tire contact state evaluation method according to an embodiment of the present invention will be described with reference to FIGS. 1 to 7.

[0012] The tire contact state evaluation method of this embodiment includes a step of grounding a rubber test piece with fluorescent liquid A interposed on a contact surface having unevenness equivalent to a real road surface provided on one surface of a transparent plate, and from the side opposite to the contact surface of the transparent plate, irradiating excitation light on the fluorescent liquid A interposed between the contact surface and the rubber test piece, and measuring the brightness distribution of the fluorescence emitted from the fluorescent liquid A. The fluorescent liquid A contains a water-soluble fluorescent agent and a non-volatile antifreeze that is water-soluble below the freezing point.

[0013] As the fluorescent agent, various hydrophilic fluorescent dyes can be dissolved in water and used. From the viewpoint of obtaining excellent measurement accuracy, it is preferably an aqueous solution containing a hydrophilic fluorescent dye having a difference of 100 nm or more between the peak wavelengths of the excitation spectrum and the fluorescence spectrum. Specific examples of the hydrophilic fluorescent dye having a difference of 100 nm or more between the peak wavelengths of the excitation spectrum and the fluorescence spectrum include pyranine, DY-481XL-Carboxylic Acid, DY-521XL-Carboxylic Acid manufactured by Dyomics, and ATTO 490LS carboxy manufactured by ATTO-TEC. From the viewpoints of safety and cost, pyranine can be preferably used. In the case of a hydrophilic fluorescent dye having a plurality of peak wavelengths in the excitation spectrum and / or the fluorescence spectrum, for the excitation spectrum and / or the fluorescence spectrum, by using a filter or the like, the peak wavelengths may be selected and used so that the difference between the peak wavelengths of the excitation spectrum and the fluorescence spectrum is 100 nm or more.

[0014] The concentration of the hydrophilic fluorescent dye in the fluorescent liquid is not particularly limited, but when using pyranine, it is preferably 100 to 10,000 mg / L.

[0015] The antifreeze is not particularly limited as long as it is water-soluble and non-volatile below the freezing point, and examples include dihydric alcohols such as ethylene glycol and propylene glycol, saccharides such as glucose and sucrose, chloride salts such as sodium chloride, calcium chloride, and magnesium chloride, acetate salts such as sodium acetate, calcium acetate, magnesium acetate, and potassium acetate, and mixtures of these salts. Among these, dihydric alcohols, chloride salts, and acetate salts are preferred.

[0016] When using a dihydric alcohol as the antifreeze, its melting point is not particularly limited, but it is preferably -130 to -10 °C, and more preferably -60 to -12 °C.

[0017] The molecular weight of the antifreeze is not particularly limited, but is preferably 200 or less, more preferably 100 or less. The smaller the molecular weight, the less amount is required to lower the freezing point at the same temperature, and the smaller amount can be used when compounded in the fluorescent liquid.

[0018] The concentration of the antifreeze in the fluorescent liquid is not particularly limited, and the amount that causes the freezing point to drop to the use temperature may be appropriately selected according to the type. For example, when ethylene glycol or propylene glycol is used to lower the freezing point to -10 °C or lower, it is preferably 30 to 40% by mass. When sodium chloride or calcium chloride is used, it is preferably 15 to 20% by mass. When sodium acetate or magnesium acetate is used, it is preferably 15 to 20% by mass.

[0019] Since the fluorescence intensity may decrease if components other than the hydrophilic fluorescent dye and the antifreeze are included in the fluorescent liquid, it is preferably not to contain components other than the hydrophilic fluorescent dye and the antifreeze.

[0020] FIG. 1 is a schematic diagram showing the configuration of a fluorescence measuring apparatus for performing the tire contact state evaluation method of the present embodiment.

[0021] Below the transparent plate installation table 18, as the fluorescence measuring apparatus 20, there are arranged a light source 12, a filter 16 that transmits and separates only light of a specific wavelength from the light irradiated from the light source 12, a dichroic mirror 14 that reflects only light of a specific wavelength, a mirror 15 that reflects the fluorescence emitted from the fluorescent liquid 11, a filter 17 that transmits and separates only light of a specific wavelength from the emitted fluorescence, and photographing means 13 that measures the fluorescence transmitted through the filter 17.

[0022] The method for producing the transparent plate 1 having a contact surface with unevenness corresponding to the actual road surface is not particularly limited. For example, from asphalt corresponding to the actual road surface, a silicone mold for vacuum casting is molded with silicone rubber, and a transparent resin is poured into this mold and cured in a vacuum degassing state. Examples of the transparent resin include urethane resins.

[0023] The rubber test piece 2 is made of vulcanized rubber and has a flat surface that is pressed against the transparent plate 1, and may have grooves or tapers corresponding to tire grooves.

[0024] The method for evaluating the tire contact state of the present embodiment can be implemented as follows, for example, using a fluorescent liquid A (0.1% by mass of pyranine, 30% by mass of propylene glycol) containing pyranine as a hydrophilic fluorescent dye and propylene glycol as an antifreeze, and a fluorescent liquid B (0.1% by mass of pyranine) containing pyranine as a hydrophilic fluorescent dye and no antifreeze.

[0025] That is, the fluorescent liquid 11 is interposed between the transparent plate 1 having unevenness corresponding to the actual road surface, and the flat surface of the rubber test piece 2 is pressed against it. While applying pressure to the rubber test piece 2 on the transparent plate 1, the tire contact state is measured.

[0026] Using an ultraviolet LED (peak wavelength 365 nm) as the light source 12, excitation light is irradiated, and the excitation light with 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 onto the fluorescent liquid 11 interposed between the rubber test piece 2 and the ground contact surface from the side opposite to the ground contact surface of the transparent plate 1, thereby causing the pyranine contained in the fluorescent liquid 11 to transition from the ground state to the excited state. Thereafter, the excited pyranine returns to the ground state, and fluorescence is emitted at that time. The emitted fluorescence passes through the dichroic mirror 14, is then reflected by the mirror 15, and the fluorescence with a wavelength of 480 nm or more is separated by the filter 17 (480 nm high-pass filter). By photographing the separated fluorescence with the photographing means 13, a luminance distribution (fluorescent intensity image) can be obtained.

[0027] 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, it is preferably a light source 12 having a peak wavelength near the peak wavelength of the excitation spectrum of the hydrophilic fluorescent dye to be used, and more preferably 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.

[0028] The dichroic mirror 14 and the filters 16, 17 are not particularly limited and can be appropriately selected and used according to the excitation spectrum and fluorescence spectrum of the hydrophilic fluorescent dye to be used. Examples of the filters 16, 17 include a wavelength-selective fluorescent filter that removes noise when performing fluorescence detection, a high-pass filter (long-pass filter) that cuts light on the short-wavelength side of a specified wavelength and transmits light on the long-wavelength side, a low-pass filter (short-pass filter) that cuts light on the long-wavelength side of a specified wavelength and transmits light on the short-wavelength side, and a band-pass filter that transmits only light in a certain wavelength range and cuts light on the short-wavelength side and long-wavelength side other than that.

[0029] Here, at 5°C and 22°C, at a specific ground pressure, the luminance distribution A obtained using the fluorescent liquid A is shown in FIG. 2, and the luminance distribution B obtained using the fluorescent liquid B is shown in FIG. 3.

[0030] In the tire ground contact state evaluation method of the present embodiment, based on the luminance distribution obtained above, by setting a certain specific luminance as a threshold value, a binarized image can be obtained with the region where the luminance is below the threshold value as the region where the rubber test piece 2 is in contact with the ground surface.

[0031] As shown in the histogram of FIG. 4, since the antifreeze is blended in the fluorescent liquid A, the fluorescence intensity becomes weak, and the histogram of the luminance distribution A is shifted to the low-luminance side as compared with the histogram of the luminance distribution B. As a result, when the same threshold value is set for the luminance distribution A and the luminance distribution B, there is a problem that the contact area between the rubber test piece and the road surface is overestimated in the luminance distribution A. Therefore, the contact area calculated based on the luminance distribution A was corrected by performing the following operation.

[0032] Specifically, in the luminance distribution B obtained at each contact pressure, for example, a luminance of 40 was set as the threshold value, and the correlation between the contact pressure and the contact area was determined.

[0033] Next, in the luminance distribution A obtained at each contact pressure, for example, a luminance of 40 was set as the threshold value, and the correlation between the contact pressure and the contact area was determined. As shown in FIGS. 5 and 6, the correlation between the contact pressure and the contact area in the luminance distribution B obtained with a luminance of 40 as the threshold value and the correlation between the contact pressure and the contact area in the luminance distribution A obtained with a luminance of 40 as the threshold value were deviated.

[0034] Therefore, in the luminance distribution A obtained at each contact pressure, a luminance of 34 or a luminance of 35 was set as the threshold value, and the correlation between the contact pressure and the contact area was determined. As shown in FIGS. 5 and 6, the correlation between the contact pressure and the contact area in the luminance distribution B obtained with a luminance of 40 as the threshold value and the correlation between the contact pressure and the contact area in the luminance distribution A obtained with a luminance of 34 or a luminance of 35 as the threshold value were in agreement. Here, in this specification, the fact that the correlations are in agreement means that the difference in the contact area at each contact pressure is ±5% or less based on the luminance distribution B.

[0035] Next, a luminance distribution was obtained in the same manner as above except that the fluorescent liquid A was used for measurement under freezing conditions.

[0036] Specifically, it was measured at -5°C to obtain a luminance distribution C. Then, a luminance of 34 and a luminance of 35 were set as threshold values, and the correlation between the contact pressure and the contact area was determined and shown in FIG. 7.

[0037] As described above, at temperatures higher than 0°C, for the fluorescent liquid A and the fluorescent liquid B, the luminance distributions A and B are measured, and the threshold value is set so that the contact areas obtained from the respective luminance distributions match. Thus, even below the freezing point, the tire contact state on a wet road surface can be accurately measured. In this way, by setting the threshold value so that the contact areas obtained based on the luminance distributions from the fluorescent liquid A and the fluorescent liquid B are compatible, the temperature dependence of the contact area from below the freezing point to normal temperature can be evaluated.

[0038] Although the embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the invention described in the claims and its equivalent scope.

Industrial Applicability

[0039] The method for evaluating the tire contact state of the present invention can be used to evaluate the contact states of various tires such as passenger cars, light trucks, and buses.

Explanation of Signs

[0040] 1 ··· Transparent plate 2 ··· Rubber test piece 11 ··· Fluorescent liquid 12 ··· Light source 13 ··· Photographing means 14 ··· Dichroic mirror 15 ··· Mirror 16 ··· Filter 17 ··· Filter 18 ··· Transparent plate installation table 20 ··· Fluorescence measuring device

Claims

1. A step of grounding a rubber test piece with a fluorescent liquid A interposed on a grounding surface having unevenness corresponding to an actual road surface provided on one surface of a transparent plate; A step of irradiating excitation light to the fluorescent liquid A interposed between the grounding surface and the rubber test piece from the side opposite to the grounding surface of the transparent plate and measuring the luminance distribution of the fluorescence emitted from the fluorescent liquid A; The method for measuring the tire contact state, wherein the fluorescent liquid A contains a water-soluble fluorescent agent and a non-volatile antifreeze that is water-soluble below the freezing point.

2. The method for measuring the tire contact state according to claim 1, wherein the antifreeze is a dihydric alcohol, a chloride salt, or an acetate salt.

3. A method for measuring the tire contact state using a water-soluble fluorescent agent, a fluorescent liquid A containing a water-soluble and non-volatile antifreeze below the freezing point, and a fluorescent liquid B containing a water-soluble fluorescent agent and not containing the antifreeze, at a temperature higher than 0°C, a step of grounding a rubber test piece with the fluorescent liquid A interposed on a grounding surface having unevenness corresponding to an actual road surface provided on one surface of a transparent plate; a step of irradiating excitation light to the fluorescent liquid A interposed between the grounding surface and the rubber test piece from the side opposite to the grounding surface of the transparent plate while changing the grounding pressure of the rubber test piece and measuring the luminance distribution A of the fluorescence emitted from the fluorescent liquid A; a step of grounding a rubber test piece with the fluorescent liquid B interposed on a grounding surface having unevenness corresponding to an actual road surface provided on one surface of a transparent plate; a step of irradiating excitation light to the fluorescent liquid B interposed between the grounding surface and the rubber test piece from the side opposite to the grounding surface of the transparent plate while changing the grounding pressure of the rubber test piece and measuring the luminance distribution B of the fluorescence emitted from the fluorescent liquid B; a step of obtaining the correlation between the grounding pressure and the contact area by arbitrarily setting a threshold value B and binarizing it in the luminance distribution B; a step of setting a threshold value A so that the correlation between the grounding pressure and the contact area in the luminance distribution A coincides with the correlation between the grounding pressure and the contact area obtained in the luminance distribution B; a step of grounding a rubber test piece with the fluorescent liquid A interposed on a grounding surface having unevenness corresponding to an actual road surface provided on one surface of a transparent plate below the freezing point; While changing the contact pressure of the rubber test piece, excitation light is irradiated from the side opposite to the contact surface of the transparent plate onto the fluorescent liquid A interposed between the contact surface and the rubber test piece, and the luminance distribution C of the fluorescence emitted from the fluorescent liquid A is measured; In the luminance distribution C, a threshold value A is set and binarized to obtain the correlation between the contact pressure and the contact area; A method for measuring the tire contact state, comprising the steps of:

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