JP7712846B2 - Tire contact condition evaluation method - Google Patents

Description

The present invention relates to a method for evaluating the tire contact condition when driving on wet road surfaces below freezing.

As described in Patent Documents 1 and 2, a method for evaluating the ground contact state of a tire on a wet road surface includes a step of grounding a rubber test piece with a fluorescent liquid interposed between a ground contact surface provided on one side of a transparent plate and having unevenness equivalent to an actual road surface, and a step of 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, and measuring the luminance distribution of the fluorescence emitted from the fluorescent liquid.

However, conventional fluorescent liquid freezes at temperatures below freezing, making it difficult to measure the tire contact condition at temperatures below freezing.

JP 2018-84428 A JP 2019-74335 A

In view of the above, the present invention aims to provide a method for evaluating the tire contact condition when traveling on a wet road surface below freezing.

The tire contact condition evaluation method according to the present invention includes the steps of: placing a rubber test piece on a contact surface having irregularities equivalent to an actual road surface provided on one side of a transparent plate, with fluorescent liquid A interposed therebetween; irradiating the fluorescent liquid A interposed between the contact surface and the rubber test piece with excitation light from the opposite side of the transparent plate to the contact surface; and measuring the luminance distribution of the fluorescence emitted from the fluorescent liquid A. The fluorescent liquid A contains an antifreeze agent that is water-soluble and non-volatile at sub-freezing points, in addition to a water-soluble fluorescent agent.

The antifreeze agent may be a dihydric alcohol, a chloride salt, or an acetate salt.

The tire ground contact condition measuring method according to the present invention is a measuring method using a water-soluble fluorescent agent, fluorescent liquid A containing a water-soluble and non-volatile antifreeze agent at sub-zero temperatures, and fluorescent liquid B containing a water-soluble fluorescent agent but no antifreeze agent, and includes the steps of: grounding a rubber test piece with the fluorescent liquid A interposed between a ground contact surface provided on one side of a transparent plate and having irregularities equivalent to an actual road surface at a temperature higher than 0°C; irradiating the fluorescent liquid A 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 while changing the ground contact pressure of the rubber test piece, and measuring the luminance distribution A of the fluorescence emitted from the fluorescent liquid A; grounding a rubber test piece with the fluorescent liquid B interposed between a ground contact surface provided on one side of a transparent plate and having irregularities equivalent to an actual road surface; and irradiating the fluorescent liquid B 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 while changing the ground contact pressure of the rubber test piece. the fluorescent liquid A is irradiated with excitation light from the transparent plate and a luminance distribution B of the fluorescence emitted from the fluorescent liquid B is measured; the luminance distribution B is arbitrarily set to a threshold B and binarized to obtain a correlation between ground contact pressure and contact area; the threshold A is set so that the correlation between ground contact pressure and contact area in the luminance distribution A matches the correlation between ground contact pressure and contact area obtained in the luminance distribution B; below freezing point, a rubber test piece is grounded on a contact surface having irregularities equivalent to an actual road surface provided on one side of a transparent plate, with the fluorescent liquid A interposed therebetween; while changing the contact pressure of the rubber test piece, an excitation light is irradiated from the opposite side of the transparent plate to the fluorescent liquid A interposed between the contact surface and the rubber test piece, and a luminance distribution C of the fluorescence emitted from the fluorescent liquid A is measured; and the luminance distribution C is set to a threshold A and binarized to obtain a correlation between ground contact pressure and contact area.

The evaluation method of the present invention makes it possible to evaluate with high accuracy the tire contact condition when traveling on wet road surfaces below freezing.

1 is a simplified diagram showing the configuration of a fluorescence measuring device that performs a tire ground contact state evaluation method according to an embodiment. The brightness distribution was obtained by photographing the contact surface at a specific contact pressure using fluorescent liquid A at 5°C and 22°C. The brightness distribution was obtained by photographing the contact surface at a specific contact pressure using fluorescent liquid B at 5°C and 22°C. 1 is a histogram showing the relationship between luminance and frequency obtained from a luminance distribution A obtained using fluorescent liquid A and a luminance distribution B obtained using fluorescent liquid B. Graph showing the correlation between contact pressure and contact area at 5° C. Graph showing the correlation between contact pressure and contact area at 22° C. Graph showing the correlation between contact pressure and contact area at −5° C.

Below, a tire contact condition evaluation method according to one embodiment of the present invention will be described with reference to Figures 1 to 7.

The tire ground contact state evaluation method of this embodiment includes the steps of: grounding a rubber test piece with fluorescent liquid A on a contact surface having irregularities equivalent to an actual road surface provided on one side of a transparent plate; and irradiating the fluorescent liquid A interposed between the contact surface and the rubber test piece with excitation light from the opposite side of the contact surface of the transparent plate, and measuring the luminance distribution of the fluorescence emitted from the fluorescent liquid A. The fluorescent liquid A contains an antifreeze agent that is water-soluble and non-volatile at sub-freezing points in addition to a water-soluble fluorescent agent.

As the fluorescent agent, various hydrophilic fluorescent dyes can be dissolved in water and used, but from the viewpoint of obtaining excellent measurement accuracy, it is preferable to use an aqueous solution containing a hydrophilic fluorescent dye whose peak wavelength difference between the excitation spectrum and the fluorescence spectrum is 100 nm or more. Specific examples of hydrophilic fluorescent dyes whose peak wavelength difference between the excitation spectrum and the fluorescence spectrum is 100 nm or more include pyranine, DY-481XL-Carboxylic Acid and DY-521XL-Carboxylic Acid manufactured by Dyomics, and ATTO 490LS carboxy manufactured by ATTO-TEC. From the viewpoint of safety and cost, pyranine can be preferably used. In addition, in the case of a hydrophilic fluorescent dye whose excitation spectrum and/or fluorescence spectrum have multiple peak wavelengths, a filter or the like may be used for the excitation spectrum and/or fluorescence spectrum to select the peak wavelength so that the difference between the peak wavelength between the excitation spectrum and the fluorescence spectrum is 100 nm or more.

The concentration of the hydrophilic fluorescent dye in the fluorescent solution is not particularly limited, but when pyranine is used, it is preferably 100 to 10,000 mg/L.

Antifreeze agents are not particularly limited as long as they are water-soluble and non-volatile below freezing point, but examples include dihydric alcohols such as ethylene glycol and propylene glycol, sugars 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, of which dihydric alcohols, chloride salts and acetate salts are preferred.

When a dihydric alcohol is used as an antifreeze agent, its melting point is not particularly limited, but is preferably -130 to -10°C, and more preferably -60 to -12°C.

The molecular weight of the antifreeze agent is not particularly limited, but is preferably 200 or less, and 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 the amount that can be mixed into the fluorescent liquid.

There are no particular limitations on the concentration of antifreeze in the fluorescent liquid, and the amount that will cause a drop in the freezing point to the temperature of use can be selected appropriately depending on the type. For example, when using ethylene glycol or propylene glycol to lower the freezing point to below -10°C, the concentration is preferably 30 to 40% by mass; when using sodium chloride or calcium chloride, the concentration is preferably 15 to 20% by mass; and when using sodium acetate or magnesium acetate, the concentration is preferably 15 to 20% by mass.

If the fluorescent liquid contains any components other than the hydrophilic fluorescent dye and antifreeze, the fluorescence intensity may decrease, so it is preferable that the fluorescent liquid does not contain any components other than the hydrophilic fluorescent dye and antifreeze.

Figure 1 is a simplified diagram showing the configuration of a fluorescence measuring device that performs the tire ground contact condition evaluation method of this embodiment.

Arranged below the transparent plate installation stand 18 are the fluorescence measuring device 20, which includes 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 an imaging means 13 that measures the fluorescence that has passed through the filter 17.

The method for producing the transparent plate 1 with a contact surface having the same unevenness as an actual road surface is not particularly limited, and it can be produced, for example, by making a vacuum casting silicon mold out of silicone rubber from asphalt that corresponds to the actual road surface, pouring a transparent resin into this mold, and curing it in a vacuum degassed state. An example of the transparent resin is a urethane-based resin.

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

The tire contact condition evaluation method of this embodiment can be carried out as follows, using, for example, fluorescent liquid A (0.1% by mass pyranine, 30% by mass propylene glycol) containing pyranine as a hydrophilic fluorescent dye and propylene glycol as an antifreeze agent, and fluorescent liquid B (0.1% by mass pyranine) containing pyranine as a hydrophilic fluorescent dye and no antifreeze agent.

That is, fluorescent liquid 11 is placed between transparent plate 1, which has unevenness corresponding to the actual road surface, and the flat surface of rubber test piece 2 is pressed against it. The tire contact condition is measured while pressure is applied to rubber test piece 2 on transparent plate 1.

An ultraviolet LED (peak wavelength 365 nm) is used as the light source 12 to irradiate excitation light, and the filter 16 (400 nm low-pass filter) separates excitation light with a wavelength of 400 nm or less. The separated excitation light is reflected by the dichroic mirror 14, and the excitation light is irradiated from the opposite side of the transparent plate 1 to the ground surface of the fluorescent liquid 11 between the rubber test piece 2 and the ground surface, causing the pyranine contained in the fluorescent liquid 11 to transition from the ground state to the excited state. The excited pyranine then returns to the ground state, emitting fluorescence at that time. The emitted fluorescence passes through the dichroic mirror 14, is reflected by the mirror 15, and the filter 17 (480 nm high-pass filter) separates fluorescence with a wavelength of 480 nm or more. The separated fluorescence is photographed by the photographing means 13 to obtain a luminance distribution (fluorescence intensity image).

The light source 12 can be appropriately selected according to the excitation spectrum of the hydrophilic fluorescent dye used, and is not particularly limited. However, it is preferable that the light source 12 has a peak wavelength near the peak wavelength of the excitation spectrum of the hydrophilic fluorescent dye used, and it is more preferable that the light source 12 has a single wavelength. When the hydrophilic fluorescent dye 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 according to the excitation spectrum and fluorescence spectrum of the hydrophilic fluorescent dye used. Examples of the filters 16 and 17 include a wavelength-selective fluorescent filter that removes noise when detecting fluorescence, a high-pass filter (long-pass filter) that cuts out light on the shorter wavelength side than a specified wavelength and transmits light on the longer wavelength side, a low-pass filter (short-pass filter) that cuts out light on the longer wavelength side than a specified wavelength and transmits light on the shorter wavelength side, and a band-pass filter that transmits only light in a certain wavelength range and cuts out light on the shorter and longer wavelength sides.

Figure 2 shows the luminance distribution A obtained using fluorescent liquid A at 5°C and 22°C and a specific ground pressure, and Figure 3 shows the luminance distribution B obtained using fluorescent liquid B.

The tire contact condition evaluation method of this embodiment sets a specific brightness as a threshold based on the brightness distribution obtained above, and can obtain a binarized image in which the areas where the brightness is below the threshold are areas where the rubber test piece 2 is in contact with the contact surface.

As shown in the histogram in Figure 4, fluorescent liquid A contains an antifreeze agent, which weakens the fluorescent intensity, and the histogram of luminance distribution A is shifted to the lower luminance side compared to the histogram of luminance distribution B. As a result, if the same threshold value is set for luminance distribution A and luminance distribution B, there is a problem that the contact area between the rubber test piece and the road surface is overestimated in luminance distribution A. Therefore, the contact area calculated based on luminance distribution A was corrected by carrying out the following operation.

Specifically, in the brightness distribution B obtained for each contact pressure, for example, brightness 40 was set as the threshold value, and the correlation between contact pressure and contact area was obtained.

Next, in the luminance distribution A obtained for 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 obtained. As shown in Figures 5 and 6, there was a discrepancy between the correlation between the contact pressure and the contact area in the luminance distribution B obtained using the luminance of 40 as the threshold value and the correlation between the contact pressure and the contact area in the luminance distribution A obtained using the luminance of 40 as the threshold value.

Therefore, in the luminance distribution A obtained at each contact pressure, a threshold value of luminance 34 or luminance 35 was set, and the correlation between the contact pressure and the contact area was obtained. As shown in Figures 5 and 6, the correlation between the contact pressure and the contact area in the luminance distribution B obtained with a threshold value of luminance 40 was consistent with the correlation between the contact pressure and the contact area in the luminance distribution A obtained with a threshold value of luminance 34 or luminance 35. Here, in this specification, the correlation being consistent means that the difference in the contact area at each contact pressure is ±5% or less, based on the luminance distribution B.

Next, the luminance distribution was obtained using the same method as above, except that measurements were taken below freezing point using fluorescent liquid A.

Specifically, measurements were taken at -5°C to obtain luminance distribution C. Then, luminance 34 and luminance 35 were set as thresholds, and the correlation between contact pressure and contact area was calculated and shown in Figure 7.

As described above, by measuring luminance distribution A and luminance distribution B for fluorescent liquid A and fluorescent liquid B at temperatures above 0 degrees and setting a threshold value so that the contact areas obtained from each luminance distribution match, it is possible to accurately measure the tire contact state on a wet road surface even below freezing. In this way, by setting a threshold value so that the contact areas calculated based on the luminance distributions obtained from fluorescent liquid A and fluorescent liquid B are compatible, it is possible to evaluate the temperature dependence of the contact area from below freezing to room temperature.

Although an embodiment of the present invention has 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 gist of the invention. These embodiments and their modifications are included within the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims.

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

Reference Signs List 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 mounting stand 20: Fluorescence measuring device

Claims (3)

a step of grounding a rubber test piece on a contact surface having projections and depressions corresponding to an actual road surface provided on one side of a transparent plate, with fluorescent liquid A interposed therebetween;
a step of irradiating the fluorescent liquid A present between the ground surface and the rubber test piece with excitation light from an opposite side of the ground surface of the transparent plate, and measuring a luminance distribution of the fluorescence emitted from the fluorescent liquid A;
The method for measuring a tire ground contact state, wherein the fluorescent liquid A contains, in addition to a water-soluble fluorescent agent, an antifreeze agent which is water-soluble and non-volatile below freezing point. The tire contact state measuring method according to claim 1, wherein the antifreeze agent is a dihydric alcohol, a chloride salt, or an acetate salt. A method for measuring a tire ground contact state using a fluorescent liquid A containing a water-soluble fluorescent agent and an antifreeze agent that is water-soluble and non-volatile at sub-zero temperatures, and a fluorescent liquid B containing a water-soluble fluorescent agent but not containing the antifreeze agent,
At temperatures above 0° C.
a step of grounding a rubber test piece with the fluorescent liquid A interposed therebetween on a contact surface having projections and depressions corresponding to an actual road surface provided on one side of a transparent plate;
a step of irradiating the fluorescent liquid A present between the contact surface and the rubber test piece with excitation light from the opposite side of the transparent plate to the contact surface while changing the contact pressure of the rubber test piece, and measuring a 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 therebetween on a contact surface having projections and depressions corresponding to an actual road surface provided on one side of a transparent plate;
a step of irradiating the fluorescent liquid B present between the contact surface and the rubber test piece with excitation light from the opposite side of the transparent plate to the contact surface while changing the contact pressure of the rubber test piece, and measuring a luminance distribution B of the fluorescence emitted from the fluorescent liquid B;
A step of determining a correlation between contact pressure and contact area by arbitrarily setting a threshold value B in the luminance distribution B and binarizing the luminance distribution B;
setting a threshold value A such that a correlation between contact pressure and contact area in the luminance distribution A coincides with a correlation between contact pressure and contact area obtained in the luminance distribution B;
a step of grounding a rubber test piece with the fluorescent liquid A interposed therebetween at a temperature below freezing, the rubber test piece being grounded on a contact surface having projections and depressions corresponding to an actual road surface and provided on one side of a transparent plate;
a step of irradiating the fluorescent liquid A present between the contact surface and the rubber test piece with excitation light from the opposite side of the transparent plate to the contact surface while changing the contact pressure of the rubber test piece, and measuring a luminance distribution C of the fluorescence emitted from the fluorescent liquid A;
a step of determining a correlation between contact pressure and contact area by setting a threshold A and binarizing the brightness distribution C.