Drainage behavior analysis method

Abstract

To provide a drainage behavior analysis method that is able to visualize the drainage behavior of a tire by photographing the flow of water in the groove of the tire.SOLUTION: A drainage behavior analysis method comprises: a first step of acquiring an image of a tread surface of a tire on a wet road surface; a second step of generating a luminance histogram of the image acquired in the first step; and a third step of analyzing a range of 80% of a tire ground contact length, with a center of the ground contact length of the image of the tread surface as a center of an analysis range, for a portion corresponding to the groove of the tire of the luminance histogram generated in the second step. In the luminance histogram generated in the second step, a ratio of a gradation of a peak corresponding to a portion other than the groove of the tire to a gradation of a peak corresponding to the groove of the tire is greater than 0 and equal to or less than 0.3.SELECTED DRAWING: Figure 19

Description

[Technical field]

[0001] The present invention relates to a method for analyzing drainage behavior. [Background technology]

[0002] There are known methods for visualizing the drainage behavior of tires. For example, in Patent Document 1, a vehicle runs on a road surface on which a water film is formed, and the tire of the vehicle is photographed to visualize the drainage behavior of the tire. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2005-201851 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, when the analysis method described in Patent Document 1 is adopted, depending on the imaging conditions, it becomes difficult to capture the flow of water inside the tire grooves.

[0005] The present invention has been made in consideration of the above, and its object is to provide a drainage behavior analysis method that can photograph the flow of water inside the grooves of a tire and visualize the drainage behavior of the tire. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems and achieve the objectives, a drainage behavior analysis method according to one embodiment of the present disclosure includes a first step of acquiring an image of a tire tread on a wet road surface, a second step of generating a brightness histogram of the image acquired in the first step, and a third step of analyzing a range of 80% of the tire contact length for a portion of the brightness histogram generated in the second step corresponding to the tire grooves, with the center of the contact length of the image of the tread as the center of the analysis range, wherein the ratio of the gradation of the peak corresponding to the portion other than the tire grooves to the gradation of the peak corresponding to the tire grooves in the brightness histogram generated in the second step is greater than 0 and less than or equal to 0.3. Effect of the Invention

[0007] According to the present invention, it is possible to photograph the flow of water inside the grooves of a tire and visualize the drainage behavior of the tire. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing the configuration of an apparatus for implementing a tire drainage behavior analysis method according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is a diagram showing the configuration of an apparatus for implementing the tire drainage behavior analysis method according to the embodiment of the present disclosure. [Diagram 3] FIG. 3 is a diagram showing an example of an image captured by the camera in FIG. [Figure 4] FIG. 4 is a diagram illustrating an example of the analysis range. [Diagram 5] FIG. 5 is a diagram showing an example of a brightness histogram for an image captured by a camera. [Figure 6] FIG. 6 is a diagram showing an example of a gradation histogram. [Figure 7] FIG. 7 is a diagram showing an example of the spread of the base from the peak portion of a tone histogram. [Figure 8] FIG. 8 is a diagram showing an example of the spread of the base from the peak portion of the gray scale histogram. [Figure 9] FIG. 9 is a diagram showing a state in which the gradation on the X axis shown in FIG. 6 is divided into four equal parts. [Figure 10] FIG. 10 is a diagram for explaining the ratio of the density of the solvent to the density of the tracer. [Figure 11] FIG. 11 is a diagram for explaining the ratio of the density of the solvent to the density of the tracer. [Figure 12] FIG. 12 is a diagram for explaining the concentration of the tracer. [Figure 13] FIG. 13 is a diagram for explaining the concentration of the tracer. [Figure 14] FIG. 14 is a diagram for explaining the change in a solution containing a tracer. [Figure 15] FIG. 15 is a diagram for explaining the change in a solution containing a tracer. [Figure 16] FIG. 16 is a diagram for explaining the change in a solution containing a tracer. [Figure 17] FIG. 17 is a diagram showing an example of the shape of a tracer. [Figure 18] FIG. 18 is a diagram for explaining the movement of the tracer. [Figure 19] FIG. 19 is a flowchart showing the steps of the drainage behavior analysis method of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, the embodiments of the present invention will be described in detail with reference to the drawings. In the following description of each embodiment, the same or equivalent components as those in other embodiments are given the same reference numerals, and their description will be simplified or omitted. The present invention is not limited to each embodiment. In addition, the components of each embodiment include those that are replaceable and easy for a person skilled in the art, or those that are substantially the same. In addition, the configurations described below can be appropriately combined. In addition, the configurations can be omitted, replaced, or modified within the scope of the gist of the invention.

[0010] 1 and 2 are diagrams showing the configuration of an apparatus for carrying out a tire drainage behavior analysis method according to an embodiment of the present disclosure. In Fig. 1 and Fig. 2, the subject of analysis is a tire 11 mounted on a vehicle 10. The vehicle 10 runs on a road plate 1. The road plate 1 is a plate that imitates the road surface on which the vehicle 10 runs. The vehicle 10 can move on the road plate 1 in the direction indicated by the arrow Y11.

[0011] (Image Acquisition) A camera 4 is provided below the road plate 1. The camera 4 is provided, for example, underground. A glass 2 is provided on the road plate 1 at a position corresponding to the camera 4. The glass 2 is, for example, transparent glass. The camera 4 can photograph tires 11 of a vehicle 10 passing above the glass 2 from below the glass 2 in the direction indicated by arrow Y12 in FIG. 1. That is, the camera 4 can photograph the tires 11 through the glass 2. The camera 4 is a high-speed camera.

[0012] Fig. 2 is a diagram showing the configuration shown in Fig. 1 as viewed in the direction of arrow Y13, i.e., from above. When the vehicle 10 moves, the tire 11 mounted on the vehicle 10 passes over the surface of the glass 2. That is, the glass 2 is provided at a position where the tire 11 passes over.

[0013] As shown in Figures 1 and 2, a water film 3 is provided on the surface of the glass 2. By providing the water film 3 on the surface of the glass 2, a wet road surface is formed. Therefore, when a tire 11 passes over the top of the glass 2, the behavior of the tire 11 and the water film 3 can be photographed. Furthermore, as shown in Figure 2, the water film 3 on the surface of the glass 2 contains a plurality of tracers 5. The tracers 5 are marker particles that are added to examine the movement of water.

[0014] When the tire 11 passes over the glass 2, the water in the water film 3 moves, and the tracer 5 moves at the same time. The movement of the tracer 5 accompanying the movement of the water in the water film 3 is photographed by the camera 4. In the tire drainage behavior analysis method according to this embodiment, the brightness distribution and peaks are compared and analyzed for the part corresponding to the tire and the part corresponding to the groove. During the analysis, the difference in brightness between the tire and the tracer is focused on to capture the water flow. When the correlation coefficient between an image at a certain time and an image at a later time is high, it can be evaluated that the accuracy of tracking the water flow is high.

[0015] (Example of a photo) FIG. 3 is a diagram showing a schematic example of an image captured by the camera 4 in FIG. 1. In FIG. 3, the hatched portion is the area corresponding to the tire, and the white portion is the area corresponding to the water of the water film 3. In the image shown in FIG. 3, the analysis target is a range of 40% each forward and backward in the tire contact length direction from the center LC of the tire contact length in the groove portion. The tire contact length direction is the vehicle travel direction indicated by the arrow Y31. The range L1 of 40% each forward and backward in the tire contact length direction is a range of 80% of the tire contact length L, with the center LC of the contact length in the image of the tread as the center of the analysis range. The tire contact length is the longest part of the contact surface in the image.

[0016] The analysis range is preferably 30% in both the front and rear directions in the tire contact length direction, i.e., 60% of the tire contact length with the center LC of the contact length of the tread image as the center of the analysis range.The analysis range is more preferably 25% in both the front and rear directions in the tire contact length direction, i.e., 50% of the tire contact length with the center LC of the contact length of the tread image as the center of the analysis range.

[0017] If the analysis range is wider than the above range, it will include the front and rear ends of the contact area, so the shape of the histogram may be affected by splashes of water, and the correlation coefficient may deteriorate.If the analysis range is narrower than the above range, it will be difficult to confirm the brightness of the entire inside of the groove, so the shape of the histogram may be affected and the correlation coefficient may deteriorate.

[0018] FIG. 4 is a diagram showing a schematic example of an analysis range. In FIG. 4, the hatched portion is an area corresponding to the tire, and the white portion is an area corresponding to the water of the water film 3. In FIG. 4, the analysis range is a range W1 corresponding to the surface of the tire and a range W2 inside the groove. The range W2 includes the water inside the groove and the tracer 5. Regarding the range W1 corresponding to the surface of the tire, the range W1 is selected so that the sipes and grooves are not included in the rib or land portion adjacent to the groove to be analyzed. The range W1 is the part corresponding to the smallest gradation. In the drainage behavior analysis method of the present disclosure, the range W2 inside the groove is analyzed based on the gradation of this range W1. In the analysis by the drainage behavior analysis method of the present disclosure, as described later, the similarity of the local concentration pattern between images is obtained by cross-correlation, and the movement position of the tracer 5 is determined from the peak value.

[0019] It is also possible to reverse the magnitude of the gradation, so that the large gradation represents black, i.e., the tire, and the small gradation represents white, i.e., the inside of the groove. In this case, the magnitude of the gradation can be defined before performing the analysis process.

[0020] (Histogram example) FIG. 5 is a diagram showing an example of a luminance histogram for an image acquired by the camera 4. The histogram can be generated by using a predetermined image processing program and specifying the groove to be analyzed. In FIG. 5, the horizontal axis, i.e., the X-axis, indicates the luminance gradation, and the vertical axis, i.e., the Y-axis, indicates the frequency [%] of each gradation. When the luminance gradation is expressed in 8 bits, the gradation value is 256 gradations from "0" to "255". In this example, "0", which is the small gradation on the left side of the horizontal axis, corresponds to black, and "255", which is the large gradation on the right side of the horizontal axis, corresponds to white. The frequency [%] is the percentage of the ratio of each gradation value. The frequency [%] can be calculated by the number of pixels of that gradation / total number of pixels x 100.

[0021] 5, the solid line is histogram HT corresponding to the tire, and the dashed line is histogram HM corresponding to the inside of the tire groove. Here, as shown by arrow Y51, the grayscale value corresponding to the peak part of histogram HT is set to PT. Also, as shown by arrow Y52, the grayscale value corresponding to the peak part of histogram HM is set to PM.

[0022] The ratio PT / PM of the gradation value PT to the gradation value PM is preferably greater than 0 and in the range of 0.3 or less. If the ratio PT / PM is in this range, it is possible to distinguish between the tire and the inside of the groove, and the correlation coefficient can be improved. If the ratio PT / PM is greater than this range, it becomes difficult to distinguish between the inside of the groove and the tire, making it impossible to measure the amount of movement, and the correlation coefficient deteriorates. If the ratio of the gradation of the peak value inside the groove and the gradation of the peak value of the tire is in the above range, the correlation coefficient can be improved and good analysis can be achieved. It is more preferable that the ratio PT / PM is greater than 0 and in the range of 0.25 or less.

[0023] FIG. 6 is a diagram showing an example of a gradation histogram. In this example, the histogram HT corresponding to the tire is shown by a solid line, and the histogram HM corresponding to the inside of the groove is shown by a dashed line. In FIG. 6, the point TP is the peak value of the part corresponding to the tire. Also, the point M1P is the peak value of the part corresponding to the inside of the groove. The point M1P is the peak value of the gradation corresponding to white. The point M2P is the peak value of the part corresponding to the inside of the groove. The point M2P is the peak value of the gradation corresponding to light gray (light gray) rather than white. In the inside of the groove, there are parts that look white due to water (i.e., the gradation value is maximum) and parts that look light gray due to the small amount of water, and the point M2P is the part corresponding to the latter. Note that in this example, the frequency of the point M1P is higher than the frequency of the point M2P, but depending on the image to be analyzed, the frequency of the point M2P may be higher than the frequency of the point M1P.

[0024] In order to distinguish between the tire and the inside of the grooves, the peaks of the two must be separated from each other in the gradation histogram, and the bases of the two must be separated from each other. Figures 7 and 8 are diagrams showing examples of the spread of the bases from the peaks of the gradation histogram.

[0025] 7, the peak of histogram HT corresponding to the tire and the peak of histogram HM corresponding to the inside of the groove are separated. The bases of these peaks are also separated. As shown in FIG. 7, if the bases of the peaks are separated, it is possible to easily distinguish between the tire and the inside of the groove.

[0026] On the other hand, referring to Fig. 8, the peak of histogram HT corresponding to the tire and the peak of histogram HM corresponding to the inside of the groove are separated. However, the bases of these peaks overlap, as shown by the dashed-dotted circle in Fig. 8. When the bases of the peaks overlap, as shown in Fig. 8, it is not possible to distinguish between the tire and the inside of the groove well, and this may result in a poor correlation coefficient.

[0027] Returning to FIG. 6, the maximum frequency, i.e., the peak value, of the portion corresponding to the tire is designated as point TP. The point located on the high gradation side of the portion corresponding to the tire is designated as point T5. The intersection point of the line connecting points TP and T5 with the X-axis is designated as point T0. The range of point T5 is preferably 3% to 7% of point TP. The range of point T5 is more preferably 4% to 6% of point TP.

[0028] The maximum frequency, i.e., the peak value, of the portion corresponding to the groove is designated as point M1P. The point located on the lower gradation side of the portion corresponding to the groove is designated as point T130. The intersection of the line connecting points M1P and T130 with the X-axis is designated as point M10. The range of point T130 is preferably 28% or more and 32% or less of point M1P. The range of point T130 is more preferably 29% or more and 31% or less of point M1P.

[0029] When the second highest frequency of the portion corresponding to the groove is 60% or more of the maximum frequency, the second highest frequency is designated as point M2P. The point located on the side of the smaller gradation of the second highest frequency is designated as point M230. The intersection of the line connecting point M2P and point M230 with the X-axis is designated as point M20. In this case, the range of point M230 is preferably 28% or more and 32% or less of point M2P. It is more preferable that the range of point M230 is 29% or more and 31% or less of point M2P.

[0030] Furthermore, it is preferable that M10>T0 and M20>T0. If T0 is larger than M10 or larger than M20, it becomes difficult to distinguish between the tire and the inside of the groove, and the correlation coefficient may deteriorate. In FIG. 6, by satisfying the above conditions, the bases of the peaks are separated from each other, as explained with reference to FIG. 7, and the tire and the inside of the groove can be easily distinguished.

[0031] FIG. 9 is a diagram showing a state where the X-axis gradation shown in FIG. 6 is divided into four equal parts. In FIG. 9, the X-axis gradation is divided into four equal parts from the low gradation side to the high gradation side, and the low gradation side to the high gradation side are designated as a first block B1, a second block B2, a third block B3, and a fourth block B4. When divided into four equal parts like this, the ratio of the sum of the frequencies in the second block B2 to the sum of the frequencies in the fourth block B4 is preferably in the range of 0.1 or more and less than 1.0, and more preferably in the range of 0.2 or more and 0.5 or less. When the ratio of the sum of the frequencies in the second block B2 to the sum of the frequencies in the fourth block B4 is in the above range, it is possible to judge the similarity of the density patterns inside the grooves, and the correlation coefficient can be improved. The reason why the second block B2 is the target is because the second block B2 is close to the tire and includes a color close to gray.

[0032] If the ratio is lower than the range, the frequency of block B4 will be too high (i.e., bright), making it difficult to judge the similarity of the density patterns inside the grooves, which may lead to a deterioration in the correlation coefficient since the amount of movement cannot be measured.

[0033] On the other hand, if the ratio is higher than the above range, the frequency of the second blocks B2 will be too high (i.e., dark), making it difficult to judge the similarity of the density patterns inside the grooves, and therefore making it impossible to measure the amount of movement, which may result in a poor correlation coefficient.

[0034] (Tracer) As described with reference to Figs. 1 and 2, in the drainage behavior analysis method of this example, a water film 3 containing a plurality of tracers 5 is formed on the surface of glass 2, and this is used as a wet road surface. In other words, the water film forming the wet road surface contains tracers 5, i.e., particles. It is preferable that the ratio S of the density of the solvent to the density of the tracers 5 is 0.6 or more and 3.0 or less. If the ratio S is smaller than this range, the tracers 5 may not move even if the solvent flows into the groove, and the amount of movement of the tracers 5 inside the groove cannot be measured, so the correlation coefficient may deteriorate. If the ratio S is larger than this range, the number of tracers 5 increases, and the amount of movement of the tracers 5 inside the groove cannot be measured, so the correlation coefficient may deteriorate. The density of the tracers 5 is 0.4 g / cm 3 More than 1.2g / cm 3 It is preferable that:

[0035] 10 and 11 are diagrams for explaining the ratio S of the density of the solvent to the density of the tracer 5. In FIG. 10 and FIG. 11, the black parts correspond to the tire 11, and the white parts between the rectangles correspond to the inside of the groove of the tire 11. The same applies to the following figures. If the ratio S of the density of the solvent is larger than the above range, as shown in FIG. 10, the tracer 5 may not move even if the solvent flows in the groove, and the movement amount of the tracer 5 in the groove cannot be measured, so the correlation coefficient may deteriorate. On the other hand, if the ratio S of the density of the solvent is smaller than the above range, as shown in FIG. 11, the number of tracers 5 increases, and the movement amount of the tracer 5 in the groove cannot be measured, so the correlation coefficient may deteriorate.

[0036] Furthermore, the concentration C of the tracer 5 is preferably 0.3 wt% or more and 1.5 wt% or less. If the concentration C of the tracer 5 is lower than this range, the amount of tracer 5 in the groove will be small, and the amount of movement will not be measured, which may result in a poor correlation coefficient. If the concentration C of the tracer 5 is higher than this range, the amount of tracer 5 will be large, and the amount of movement of the tracer 5 inside the groove will not be measured, which may result in a poor correlation coefficient. It is more preferable that the concentration C of the tracer 5 is 0.4% or more and 0.8% or less.

[0037] 12 and 13 are diagrams for explaining the concentration C of the tracer 5. When the concentration C of the tracer 5 is higher than the above range, as shown in FIG. 12, the amount of the tracer 5 inside the groove increases, and it may be impossible to trace the tracer 5 inside the groove and measure the amount of movement of the tracer 5 inside the groove. Therefore, when the concentration C of the tracer 5 is high, the correlation coefficient may deteriorate. On the other hand, when the concentration C of the tracer 5 is lower than the above range, as shown in FIG. 13, even if the tracer 5 inside the groove is traced, it may be impossible to measure the amount of movement of the tracer 5 inside the groove.

[0038] As for the tracer 5, by making the ratio S and the concentration C satisfy the above conditions, the relationship between the tire 11 and its groove can be maintained in a good condition, and therefore the correlation coefficient improves.

[0039] (Changes in solution containing tracer) Incidentally, it is preferable that the solution containing the tracer 5 changes little over time. For example, when a plurality of tracers 5 are put into a container containing a solvent, sealed, and shaken, and then the gradation and frequency of the peak of the brightness histogram after 10 seconds are compared with the gradation and frequency of the peak of the brightness histogram after 30 minutes, it is preferable that there is no change of 10% or more (the change is less than 10%). More specifically, a solution having a concentration that satisfies the gradation condition described with reference to FIG. 9 is prepared, a still image of the solution after 10 seconds is taken, and a brightness histogram is created. Similarly, a still image of the solution after 30 minutes is taken, and a brightness histogram is created. The gradation and frequency of the peak of the brightness histogram are compared.

[0040] 14 to 16 are diagrams for explaining changes in a solution containing a tracer. FIG. 14 shows a state in which a solvent 60 is contained in a container 7 and 10 seconds have passed since a plurality of tracers 5 were poured into the solvent 60. FIG. 15 and FIG. 16 show a state in which 30 minutes have passed since a plurality of tracers 5 were poured into the solvent 60. FIG. 15 shows a state in which the dye of the tracer 53 has leaked and the solvent 61 has discolored. FIG. 16 shows a state in which the tracer 54 in the solvent 60 has expanded. When comparing the gradation and frequency of the peaks of the luminance histogram in the state of FIG. 14 with the gradation and frequency of the peaks of the luminance histogram in the state of FIG. 15 or FIG. 16, it is preferable that there is no change of 10% or more.

[0041] If the tracer pigment is lost over time, the brightness of the entire water film may change. In that case, the amount of movement of the particles inside the groove cannot be measured, and the correlation coefficient may deteriorate. In addition, if the particles absorb the solvent and expand over time, the brightness of the entire water film may change. In that case, the amount of movement of the particles inside the groove cannot be measured, and the correlation coefficient may deteriorate. If the change in the solution containing the tracer satisfies the above conditions, the relationship of the histograms for the tire and the inside of the groove can be maintained, and the correlation coefficient improves. It is more preferable that the gradation and frequency of the peaks of the brightness histogram do not change by 5% or more.

[0042] The container is preferably a container with a lid. For example, a 500 ml plastic bottle can be used as the container. If a plastic bottle is used as the container, it is easy to seal and easy to shake.

[0043] (Tracer shape) FIG. 17 is a diagram showing an example of the shape of the tracer 5. In FIG. 17, when the tracer 5 is a sphere, the diameter R is preferably, for example, 600 μm. For the tracers 55, 56 that are not spherical, the maximum width of the particle is called the major axis, and the minimum width is called the minor axis. The ratio of the major axis RL to the minor axis RS (RS / RL) is preferably 0.6 or more and 1 or less. In addition, the ratio RL / Sr of the major axis RL of the tracer 5 to the spatial resolution Sr (mm / pix) of the image of the tire tread is preferably 1.5 or more and 3.0 or less.

[0044] If the ratio RL / Sr is smaller than this range, it is difficult to track. In that case, the amount of movement cannot be measured, and the correlation coefficient may deteriorate. If the ratio RL / Sr is larger than this range, the tracer may get stuck in the sipes of the tire, which may worsen the water flow. Furthermore, the tracer may not be able to follow the water flow as well, which may worsen the correlation coefficient. For this reason, it is desirable that the size of the tracer is 75% or less of the groove width or sipe width of the groove to be analyzed. For example, when photographing with a spatial resolution Sr = 0.3 (mm / pix), particles with a major axis RL of 0.6 mm are desirable. Note that a sipe is a cut formed on the tread surface, and generally has a sipe width of less than 1.0 mm and a sipe depth of 2.0 mm or more, and is closed when the tire comes into contact with the ground.

[0045] When the major axis RL of the tracer 5 satisfies the above condition, it becomes possible to measure the amount of movement of the tracer 5 following the water, and the correlation coefficient improves. It is more preferable that the ratio RL / Sr is 1.8 or more and 2.2 or less.

[0046] (Tracer movement distance) Here, in order for the range of the movement amount Mv (pix) of the tracer that moves from a certain captured image (X) to the captured image (X+1) captured thereafter to satisfy 0.5≦Mv≦11, it is preferable that the relationship between the speed Sv (m / s), spatial resolution Sr (mm / pix), and capture speed Ss (fps) of the vehicle 10 satisfies Mv=Sv / (Sr×Ss). Note that if the vehicle speed is increased, the movement speed of the tracer increases, and the movement amount Mv of the tracer increases.

[0047] FIG. 18 is a diagram for explaining the movement of the tracer. In FIG. 18, the tracer 5 included in the first image P(X) captured at the first time moves as indicated by the arrow Y18 in the second image P(X+1) captured at the second time after the first time. In order for the amount of movement Mv of the tracer between the first image P(X) and the second image P(X+1) to be 0.5 pixels or more and 11 pixels or less, it is preferable that Mv=Sv / (Sr×Ss). When the amount of movement of the tracer satisfies the above condition, it becomes possible to track the tracer, and the correlation coefficient can be improved. For example, the speed Sv of the vehicle 10 is set to about 16.7 (m / s) or more and about 19.4 (m / s) or less (60 km / h or more and 70 km / h or less), the spatial resolution is set to 0.3 (mm / pix), and the shooting speed Ss is set to 20,000 (fps) (i.e., one image is shot every 50 μs).

[0048] The amount of movement Mv of the tracer is preferably 1 pixel or more and 11 pixels or less. If the amount of movement Mv of the tracer is smaller than this range, the amount of movement of the particle cannot be measured, and the correlation coefficient may deteriorate. If the amount of movement of the tracer is larger than this range, the particle cannot be tracked due to its large amount of movement, and the correlation coefficient may deteriorate. It is more preferable that the amount of movement Mv of the tracer is 5 pixels or more and 10 pixels or less.

[0049] The speed Sv of the vehicle 10 is preferably 10 (m / s) or more and 20 (m / s) or less, more preferably 13 (m / s) or more and 20 (m / s) or less, and further preferably 15 (m / s) or more and 19 (m / s) or less.

[0050] The spatial resolution Sr of the image is preferably 0 (mm / pix) or more and 0.8 (mm / pix) or less, more preferably 0 (mm / pix) or more and 0.5 (mm / pix) or less, and further preferably 0 (mm / pix) or more and 0.4 (mm / pix) or less.

[0051] The shooting speed Ss is preferably 3,000 (fps) or more and 70,000 (fps) or less, more preferably 5,000 (fps) or more and 30,000 (fps) or less, and further preferably 10,000 (fps) or more and 20,000 (fps) or less.

[0052] (Evaluation of tracking accuracy inside the groove) The tracking accuracy inside the ditch by the drainage behavior analysis method disclosed herein can be evaluated by a correlation coefficient. More detailed operating principles and classification of detailed methods for evaluating the tracking accuracy inside the ditch are disclosed in, for example, the document "PIV Handbook (2nd Edition)" published by the Visualization Society of Japan, Morikita Publishing Co., Ltd. on May 31, 2018. The evaluation method disclosed in the document can be adopted for the drainage behavior analysis method disclosed herein. PIV (Particle Image Velocimetry) is an indirect measurement method that restores the velocity field by recording images of tracer particles mixed in the flow.

[0053] (summary) FIG. 19 is a flowchart showing the procedure of the drainage behavior analysis method of the present disclosure described above. In FIG. 19, the drainage behavior analysis method of the present disclosure includes a first step ST1 of acquiring an image of the tire tread on a wet road surface, a second step ST2 of generating a brightness histogram of the image acquired in the first step ST1, and a third step ST3 of analyzing a range of 80% of the tire contact length of the tire contact length of the portion of the brightness histogram generated in the second step ST2 corresponding to the tire groove, with the center of the contact length of the image of the tread as the center of the analysis range. In the brightness histogram generated in the second step ST2, the ratio of the gradation of the peak corresponding to the portion other than the tire groove to the gradation of the peak corresponding to the tire groove is greater than 0 and is equal to or less than 0.3. According to the drainage behavior analysis method shown in FIG. 19, the flow of water inside the tire groove can be photographed to visualize the drainage behavior of the tire.

[0054] [Example] In the embodiment, the correlation coefficient was calculated and evaluated for the range in which the ratio PT / PM of the gradation value PT to the gradation value PM was greater than 0 and less than or equal to 0.3, and the results are summarized in Tables 1 to 3. In Tables 1 to 3, the evaluation results were calculated as an index value with the "Comparative Example" being set to "100". The larger the number, the higher the tracking accuracy inside the groove. The "Comparative Example" in Table 1 has a ratio PT / PM of 0.4, the frequency of point M10 is equal to the frequency of point T0 (M10=T0), a ratio of the frequency of block B2 / the frequency of block B4 is 2.1, a density ratio S is 2.1, a concentration C is 0.2, a rate of change after 30 minutes is 12%, a ratio of major axis / spatial resolution RL / Sr is 1, and a tracer movement amount Mv is 0.3.

[0055] According to each embodiment of Tables 1 to 3, it was found that good results were obtained when the frequency relationship was M10>T0 and M20>T0, when the ratio of frequency of block B2 / frequency of block B4 was 0.1 or more and 1.0 or less, when the density ratio S was 0.6 or more and 3.0 or less, when the concentration C was 0.3 (wt%) or more and 1.5 (wt%) or less, when the rate of change after 30 minutes was less than 10%, when the ratio of long axis / spatial resolution RL / Sr was 1.5 or more and 3.0 or less, and when the amount of tracer movement Mv was 0.5 (pix) or more and 11 (pix) or less.

[0056] [Table 1]

[0057] [Table 2]

[0058] [Table 3]

[0059] With respect to the claims, the present disclosure may take the following forms. <1> a first step of acquiring an image of a tire tread on a wet road surface; a second step of generating a brightness histogram of the image acquired in the first step; and a third step of analyzing a range that is 80% of the tire contact length, with the center of the contact length of the image of the tread as the center of an analysis range, for a portion of the brightness histogram generated in the second step that corresponds to the tire grooves. Including, In the brightness histogram generated in the second step, the ratio of the gradation of a peak corresponding to a portion other than the tire groove to the gradation of a peak corresponding to the tire groove is greater than 0 and is equal to or less than 0.3. Method for analyzing drainage behavior. <2> The brightness histogram has brightness gradations on the X axis and the frequency of each gradation on the Y axis. In the luminance histogram, a point TP being the maximum frequency of the portion corresponding to the tire, a point T5 being a point located on the larger gradation side of the portion corresponding to the tire, and a point TO being an intersection of a line connecting the point TP and the point T5 with the X-axis, the range of the point T5 is 3% or more and 7% or less of the point TP, When the maximum frequency of the portion corresponding to the groove is defined as point M1P, a point located on the smaller gradation side of the portion corresponding to the groove is defined as point T130, and the intersection point of the line connecting point M1P and point T130 with the X-axis is defined as point M10, the range of point T130 is 28% or more and 32% or less of point M1P, when the second highest frequency in the portion corresponding to the groove is 60% or more of the maximum frequency, the second highest frequency is designated as point M2P, a point located on the smaller gradation side of the second highest frequency is designated as point M230, and an intersection point between a line connecting point M2P and point M230 and the X-axis is designated as point M20, the range of point M230 is 28% or more and 32% or less of point M2P, Furthermore, M10>T0 and M20>T0; <1> The wastewater behavior analysis method described in. <3> The brightness histogram has brightness gradations on the X axis and the frequency of each gradation on the Y axis. When the gradation of the X-axis is divided into four equal parts from the low gradation side to the high gradation side, and the low gradation side to the high gradation side are defined as a first block to a fourth block, the ratio of the sum of the frequencies in the second block to the sum of the frequencies in the fourth block is 0.1 or more and less than 1.0. <1> or <2> The wastewater behavior analysis method described in. <4> In the first step, the wet road surface is formed by a solvent containing particles, a ratio of the density of the solvent to the density of the particles is 0.6 or more and 3.0 or less; The concentration of the particles is 0.3 wt% or more and 1.5 wt% or less; <1> from <3> 13. A method for analyzing wastewater behavior according to claim 12. <5> The particles are placed in a container containing the solvent, sealed, and shaken, and then when comparing the gradation and frequency of the peak in the luminance histogram after 10 seconds with the gradation and frequency of the peak in the luminance histogram after 30 minutes, there is no change of 10% or more. <4> The wastewater behavior analysis method described in. <6> The ratio of the major axis of the particle to the spatial resolution of the image is 1.5 or more and 3.0 or less. <4> or <5> The wastewater behavior analysis method described in. <7> A movement amount Mv of the particle between a first image captured at a first time and a second image captured at a second time after the first time is 0.5 pixels or more and 11 pixels or less, and a relationship between a speed Sv of a vehicle equipped with the tire, a spatial resolution Sr of the image, and a capturing speed Ss is Mv=Sv / (Sr×Ss). <4> from <6> 13. A method for analyzing wastewater behavior according to claim 12. [Explanation of symbols]

[0060] 1 Road board 2. Glass 3 Water film 4. Camera 5, 53, 54, 55 Tracer 7 containers 10 Vehicles 11 Tires 60, 61 Solvent

Claims

1. a first step of acquiring an image of a tire tread on a wet road surface; a second step of generating a brightness histogram of the image acquired in the first step; and a third step of analyzing a range that is 80% of the tire contact length, with the center of the contact length of the image of the tread being set as the center of an analysis range, for a portion of the brightness histogram generated in the second step that corresponds to the tire grooves. Including, In the brightness histogram generated in the second step, a ratio of a gradation of a peak corresponding to a portion other than the tire groove to a gradation of a peak corresponding to the tire groove is greater than 0 and is equal to or smaller than 0.

3. Method for analyzing drainage behavior.

2. The brightness histogram has brightness gradations on the X axis and the frequency of each gradation on the Y axis. In the luminance histogram, a point TP is a maximum frequency of the portion corresponding to the tire, a point T5 is a point located on the larger gradation side of the portion corresponding to the tire, and a point TO is an intersection of a line connecting the point TP and the point T5 with the X-axis, the range of the point T5 is 3% or more and 7% or less of the point TP, When the maximum frequency of the portion corresponding to the groove is defined as point M1P, a point located on the smaller gradation side of the portion corresponding to the groove is defined as point T130, and an intersection point between a line connecting point M1P and point T130 and the X-axis is defined as point M10, the range of point T130 is 28% or more and 32% or less of point M1P, when the second highest frequency in the portion corresponding to the groove is 60% or more of the maximum frequency, the second highest frequency is designated as point M2P, a point located on the smaller gradation side of the second highest frequency is designated as point M230, and an intersection point between a line connecting point M2P and point M230 and the X-axis is designated as point M20, the range of point M230 is 28% or more and 32% or less of point M2P, Further, M10>T0 and M20>T0; The method for analyzing drainage behavior according to claim 1 .

3. The brightness histogram has brightness gradations on the X axis and the frequency of each gradation on the Y axis.

3. The drainage behavior analysis method according to claim 1, wherein when the X-axis gradation is divided into four equal parts from the low gradation side to the high gradation side, and the low gradation side to the high gradation side are designated as a first block to a fourth block, a ratio of the sum of the frequencies in the second block to the sum of the frequencies in the fourth block is 0.1 or more and less than 1.

0.

4. In the first step, the wet road surface is formed by a solvent containing particles; a ratio of the density of the solvent to the density of the particles is 0.6 or more and 3.0 or less; 3. The method for analyzing wastewater behavior according to claim 1, wherein the concentration of the particles is 0.3 wt % or more and 1.5 wt % or less.

5. 5. The method for analyzing drainage behavior according to claim 4, wherein, when the particles are placed in a container containing the solvent, sealed, and shaken, the gradation and frequency of the peak in the brightness histogram after 10 seconds have elapsed are compared with the gradation and frequency of the peak in the brightness histogram after 30 minutes have elapsed, and there is no change of 10% or more.

6. The method for analyzing drainage behavior according to claim 4 , wherein a ratio of a major axis of the particles to a spatial resolution of the image is equal to or greater than 1.5 and equal to or less than 3.

0.

7. The drainage behavior analysis method according to claim 4, wherein the relationship between the speed Sv of the vehicle on which the tire is mounted, the spatial resolution Sr of the image, and the shooting speed Ss is Mv = Sv / (Sr x Ss), so that the amount of movement Mv of the particles between a first image taken at a first time and a second image taken at a second time after the first time is 0.5 pixels or more and 11 pixels or less.

Images