Method for evaluating tire ground contact characteristics

Abstract

To provide a tire grounding state measuring device capable of measuring a grounding state of a rolling tire.SOLUTION: A tire ground contact characteristics evaluation method is a method for evaluating ground contact characteristics of a tire in which a circumferential groove 6 extending in a tire circumferential direction and a land portion 7 are provided on a tread, the method including a first step of bringing a tire 1 into contact with a pseudo road surface 56a of a pseudo road surface plate 56 having the pseudo road surface 56a having unevenness corresponding to an actual road surface, and a second step of detecting electromagnetic waves transmitted through the pseudo road surface plate 56 to perform optical imaging. The method includes a second step of photographing a ground contact portion of the tire 1 with respect to the pseudo road surface 56a to acquire an image, a third step of calculating a sum of brightness values of pixels at the same position in the tire axial direction with respect to the image and determining the positions of the circumferential groove 6 and the land portion 7 in the tire axial direction from the calculated sum of the brightness values, a fourth step of binarizing the image to acquire a binarized image, and a fifth step of evaluating the ground contact characteristics of the tire 1 based on the binarized image and the position of the land portion 7 in the tire axial direction.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a method for evaluating tire ground contact characteristics. [Background technology]

[0002] There is a demand for an accurate evaluation of tire contact characteristics on an uneven road surface that simulates an actual road surface, and various proposals have been made to address this demand. For example, Patent Document 1 discloses a method for measuring the tire contact state on a wet road surface, in which a tire is placed on a transparent plate having an uneven surface equivalent to the actual road surface with a fluorescent liquid interposed therebetween, the fluorescent liquid is irradiated with excitation light, and the fluorescence emitted from the fluorescent liquid is photographed. Patent Document 2 discloses a method for measuring the tire contact area using this measurement method and evaluating the tire contact state with high accuracy from the correlation between the contact area and the coefficient of friction. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-084428 [Patent Document 2] Japanese Patent Application Publication No. 2019-074335 Summary of the Invention [Problem to be solved by the invention]

[0004] Since many tires have circumferential grooves extending in the circumferential direction, when accurately evaluating the tire contact state using the measurement methods described in the above-mentioned documents 1 and 2, it is necessary to distinguish between groove-corresponding parts and land-corresponding parts in the obtained photographed image.

[0005] In view of the above, an embodiment of the present invention aims to provide a tire contact characteristic evaluation method that can easily distinguish between groove-equivalent parts and land-equivalent parts from an image taken of the contact state of a tire contacting a rough road surface that simulates an actual road surface. [Means for solving the problem]

[0006] The present invention includes the embodiments shown below.

[0007] [1] A tire ground contact characteristic evaluation method for evaluating the ground contact characteristics of a tire having circumferential grooves and land portions in its tread that extend circumferentially around the tire, comprising: a first step of placing the tire in contact with a pseudo road surface of a pseudo road plate having a pseudo road surface with unevenness equivalent to that of an actual road surface; a second step of photographing the tire's contact portion with the pseudo road surface using an imaging device that detects electromagnetic waves that have passed through the pseudo road plate and performs optical photography to obtain an image; a third step of calculating the sum of brightness values ​​of pixels that are located at the same position in the tire axial direction in the image and determining the axial positions of the circumferential grooves and the land portions from the calculated sum of brightness values; a fourth step of binarizing the image to obtain a binarized image; and a fifth step of evaluating the ground contact characteristics of the tire based on the binarized image and the axial positions of the land portions.

[0008] [2] A tire ground contact characteristic evaluation method as described in [1] above, wherein in the first step, a tire is rolled on the simulated road surface to make contact with the ground, and in the second step, a plurality of images are obtained by continuously photographing the contact portion of the tire rolling on the simulated road surface in contact with the simulated road surface, and in the third step, one image is selected from the plurality of images as a reference image, and the axial positions of the circumferential grooves and the land portions are determined from a numerical sequence obtained by summing the brightness values ​​of each pixel of the reference image in the tire circumferential direction for each pixel row in the tire axial direction.

[0009] [3] The tire ground contact characteristic evaluation method according to [2] above, wherein the sum of the brightness values ​​for each of the plurality of images is calculated, and the image with the smallest sum is selected as the reference image.

[0010] [4] A tire ground contact characteristic evaluation method as described in [2] or [3] above, wherein in the fourth step, the reference image and one or more images other than the reference image are binarized to obtain a plurality of the binarized images, and in the fifth step, the area of ​​the part of the land portion that is in contact with the pseudo road surface is calculated for each of the binarized images based on the plurality of binarized images and the axial position of the land portion, and the tire ground contact characteristic is evaluated based on the average value of the calculated areas. [Effects of the Invention]

[0011] According to this embodiment, groove-corresponding portions and land-corresponding portions can be easily distinguished from an image taken of the state of a tire in contact with an uneven road surface that simulates an actual road surface. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a front view schematically showing a measurement device used in a tire ground contact characteristic evaluation method according to an embodiment. [Figure 2] FIG. 2 is a plan view schematically showing the measurement device of FIG. 1; [Figure 3] Cross section AA of Figure 2 [Figure 4] Block diagram showing the control configuration of the measurement device of Figure 1. [Figure 5] 1 is a diagram showing an example of a tire contact shape; [Figure 6] 1(a) is a diagram showing brightness images G1 to G5 of a plurality of images captured by a photographing device, and FIG. 1(b) is a graph showing the total brightness values ​​of the brightness images G1 to G5. [Figure 7] 1 is a flowchart of a tire ground contact characteristic evaluation method according to an embodiment; [Figure 8] 1A is a diagram showing a luminance image of a reference image, and FIG. 1B is a graph showing the relationship between the position in the tire axial direction and the total luminance value of pixels at the same position in the tire axial direction for the luminance image of the reference image. [Figure 9] 1A is a diagram showing a reference binary image obtained by binarizing a reference luminance image, and FIG. 1B is a diagram showing a local region of interest in the reference binary image. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, a tire ground contact characteristic evaluation method according to an embodiment will be described with reference to the drawings.

[0014] The tire ground contact characteristic evaluation method of this embodiment involves rolling the tire 1 on a pseudo road surface plate 56, detecting electromagnetic waves that pass through the pseudo road surface plate 56, photographing the contact portion 3 of the tire 1 with the pseudo road surface 56a, and binarizing the obtained image to evaluate the ground contact characteristics.

[0015] FIG. 5 is a diagram showing an example of the contact shape of a tire 1 evaluated in this embodiment, illustrating the contour shape of a contact portion 3. A plurality of (four in this example) circumferential grooves 6 extending in the tire circumferential direction are provided on the surface of the tire tread. The circumferential grooves 6 define a plurality of tread land portions 7 in the tire tread. More specifically, a center land portion 7A located in the center, a pair of left and right quarter land portions 7B, 7B located on both sides of the center land portion 7A, and a pair of left and right shoulder land portions 7C, 7C located outside the quarter land portion 7B are provided. In this example, these tread land portions 7 are provided as ribs that are continuous around the entire circumference of the tire in the circumferential direction, but they may also be provided as block rows by providing lateral grooves that cross the ribs.

[0016] (1) Overall configuration of the measuring device 10 First, a measuring device 10 used in a tire ground contact characteristic evaluation method according to one embodiment will be described with reference to FIGS.

[0017] The measuring device 10 includes a track section 20 extending in a predetermined direction (hereinafter, this direction will be referred to as the X direction), a drive device 30 that runs on the track section 20, a road surface section 50 on which a tire 1 to be measured rolls, an irradiation device 81 that irradiates the tire 1 with electromagnetic waves, an imaging device 82 that detects the electromagnetic waves that have passed through a pseudo road surface plate 56, and a control unit 100 (see FIG. 4) that controls the measuring device 10. The measuring device 10 is a device that measures the ground contact state of the tire 1 rolling on the pseudo road surface plate 56 by having the irradiation device 81 irradiate the tire 1 with electromagnetic waves and the imaging device 82 detect the electromagnetic waves that have passed through the pseudo road surface plate 56 while the tire 1 rolls in the X direction on the pseudo road surface plate 56 provided on the road surface section 50.

[0018] Electromagnetic waves are a phenomenon in which periodic changes in electric and magnetic fields propagate through space as waves. Examples of electromagnetic waves include, but are not limited to, X-rays, ultraviolet rays, visible light, infrared rays, and radio waves (including terahertz waves).

[0019] As an embodiment, the following description will use as an example a measuring device 10 that measures the tire's contact state on a wet road surface. The measuring device 10 irradiates a fluorescent liquid interposed between the tire 1 and a simulated road surface 56a with excitation light and detects the fluorescence emitted from the fluorescent liquid to measure the tire's contact state. Each substance with fluorescent properties has its own specific absorption wavelength range and fluorescence wavelength range. The fluorescence used for imaging is generally in the visible light range, but electromagnetic waves invisible to the human eye, such as ultraviolet or infrared, can also be used. Ultraviolet or visible light is generally used as the excitation light, but the excitation light is selected to match the absorption wavelength range of the substance of interest.

[0020] (2) Track part 20 The track section 20 includes a plurality of linear guides 21 that guide the movement of the drive device 30 in the X direction, and a power section 22 that generates power. The power section 22 transmits the generated power to the drive device 30 via a belt mechanism (not shown) to drive the drive device 30 in the X direction.

[0021] (3) Drive unit 30 The drive unit 30 has a main frame 31 to which power is transmitted from the power section 22 of the track section 20, and is attached with a spindle section 32 that supports the wheel rim WR on which the tire 1 is mounted, and an alignment section 33 that adjusts the alignment and load of the tire 1 relative to the road surface section 50.

[0022] The spindle unit 32 is disposed above the road surface 50, and a wheel rim WR is attached to the spindle shaft 32a. Power generated by a spindle drive unit 32b (see FIG. 4), such as a motor, is transmitted to the spindle shaft 32a, which drives and rotates the tire 1 together with the wheel rim WR attached to the spindle shaft 32a. In other words, in this example, the spindle shaft 32a is a support shaft that supports the tire 1 above the road surface 50, and the spindle unit 32 is a shaft support unit that supports the support shaft, the spindle shaft 32a, horizontally in a rotatable state.

[0023] The spindle portion 32 is also provided with a six-component force sensor 32c that detects forces acting on the tire 1 in three orthogonal axial directions, namely the vertical direction, the rotational axis direction of the tire 1, and the X direction, as well as torque around each axis.

[0024] The alignment section 33 includes a load adjustment section 34, a slip angle adjustment section 35, and a camber angle adjustment section 36, and supports the spindle section 32 so that the position and angle of the spindle shaft 32a of the spindle section 32 can be changed.

[0025] The load adjustment unit 34 is a unit that moves the alignment unit 33 up and down to adjust the load applied to the tire 1 when the tire 1 attached to the wheel rim WR comes into contact with the road surface 50. The slip angle adjustment unit 35 rotates and moves the alignment unit 33 about a vertical line V to adjust the slip angle of the tire 1 attached to the wheel rim WR. The camber angle adjustment unit 36 ​​rotates and moves the spindle unit 32 about a rotation axis AC that is parallel to the X direction to adjust the camber angle of the tire 1 attached to the wheel rim WR.

[0026] In such a driving device 30, the load adjustment unit 34 applies a downward load to the spindle shaft 32a while moving the spindle shaft 32a horizontally, and the tire 1 is rolled on a pseudo road surface 56a provided on the road surface unit 50 while applying a ground contact load to the tire 1.

[0027] (4) Road surface section 50 1 and 3, the road surface portion 50 comprises a frame 51 and a road surface main body 52 supported on the upper side of the frame 51. The road surface main body 52 is made of a metal plate, a resin plate, or the like arranged so that the upper surface is horizontal, and a fixing jig 54 and a pseudo road surface plate 56 are provided in mounting holes 53 that pass through the road surface main body 52 from top to bottom.

[0028] A spacer 55 is provided on the periphery of the mounting hole 53. The spacer 55 is provided below the upper surface of the road surface body 52, and the upper surface of the spacer 55 is a surface on which the periphery of the fixing jig 54 is placed. The spacer 55 has a mounting step 55a. A light absorbing portion 55b made of a black colored layer or the like is provided on the surface of the spacer 55 facing the space below the fixing jig 54. The light absorbing portion 55b absorbs excitation light emitted from an irradiation device 81 (described later) and fluorescence emitted from a fluorescent liquid interposed between the tire 1 and the simulated road surface 56a, thereby suppressing stray light generated in the space below the fixing jig 54.

[0029] The fixing jig 54 is made of a metal member formed in a predetermined shape so as to be flush with the upper surface of the road surface main body 52. ​​The fixing jig 54 has an observation window 57 that penetrates from top to bottom. The peripheral edge of the observation window 57 has a window step 58 that is recessed downward from the upper surface of the fixing jig 54. The peripheral edge of the pseudo road surface plate 56 is placed on the upper surface of the window step 58, and the pseudo road surface plate 56 covers the observation window 57 from above.

[0030] The fixing jig 54 preferably has processability that allows for accurate formation of the observation window 57 into which the pseudo road surface plate 56 is fitted, is strong enough to support the load of the tire 1, has strength and durability that prevents deformation of the observation window 57 even when the pseudo road surface plate 56 is repeatedly attached and detached, and is light enough that an operator can replace the fixing jig 54 when changing stages. In order to satisfy such processability, high strength, high durability, and light weight, the fixing jig 54 is preferably formed from aluminum or an aluminum alloy.

[0031] The pseudo road surface plate 56 is made of a plate-like body that is permeable to electromagnetic waves, and is preferably a transparent plate. The pseudo road surface plate 56 is larger than the contact patch 3 of the tire 1 and is large enough to fit the entire contact patch 3 within it. The pseudo road surface plate 56 has a pseudo road surface 56a with irregularities equivalent to those of an actual road surface on at least one of its front and back surfaces, and in this example, the surface opposite the pseudo road surface 56a is flat. The pseudo road surface plate 56 is placed on the window step 58 of the fixing jig 54 with the pseudo road surface 56a facing upward. The thickness of the pseudo road surface plate 56 is adjusted so that the pseudo road surface 56a is flush with the road surface main body 52 and the upper surface of the fixing jig 54 when placed on the window step 58.

[0032] There are no particular limitations on the method for producing the transparent pseudo-road panel 56 with the pseudo-road surface 56a, and it can be produced, for example, by molding asphalt corresponding to the actual road surface using silicone rubber, pouring transparent resin into the mold, and curing it in a vacuum degassed state. Examples of transparent resins include urethane-based resins.

[0033] The simulated road surface plate 56 is replaceably installed on the window step 58 of the fixing jig 54. Multiple plates with various uneven shapes are prepared depending on the road surface to be tested, and one can be selected and installed. Note that the simulated road surface plate 56 may be adhesively fixed to the fixing jig 54 as necessary, for example, when a sealant is provided between the simulated road surface plate 56 and the observation window 57 of the fixing jig 54 to provide a liquid-tight seal. When fixing the simulated road surface plate 56 to the fixing jig 54, by preparing multiple fixing jigs 54 to which simulated road surface plates 56 with different uneven shapes are fixed, it is possible to measure the contact state for simulated road surfaces with a variety of uneven shapes.

[0034] (5) Irradiation device 81 and imaging device 82 Below the road surface portion 50, there is provided an irradiation device 81 for irradiating electromagnetic waves onto the contact portion 3 between the tire 1 and the pseudo road surface 56a through the pseudo road surface plate 56, and an imaging device 82 for detecting the electromagnetic waves that have passed through the pseudo road surface plate 56 and performing optical imaging.

[0035] As shown in FIG. 3, the irradiation device 81 includes a light source 83, a rod lens 84, and a dichroic mirror 85.

[0036] The light source 83 generates excitation light that is irradiated onto the fluorescent liquid 2 interposed between the tire 1 and the simulated road surface 56a.

[0037] The rod lens 84 converts the excitation light generated by the light source 83 into a planar light beam that spreads uniformly in a predetermined shape, such as a rectangle, and emits the light. The irradiation area of ​​the light beam emitted from the rod lens 84 is preferably larger than the area of ​​the contact portion 3 between the tire 1 and the simulated road surface 56a.

[0038] The dichroic mirror 85 reflects light in a specific wavelength band that includes the wavelength of the planar excitation light emitted from the rod lens 84, and transmits electromagnetic waves that pass through the pseudo road surface plate 56 and travel downward. The dichroic mirror 85 can be selected and used appropriately according to the excitation spectrum and fluorescence spectrum of the fluorescent dye used in the fluorescent liquid 2.

[0039] The wavelength of the excitation light emitted by the light source 83 is appropriately selected to match the excitation spectrum of the fluorescent dye contained in the fluorescent liquid 2, and a light source having a peak wavelength near the peak wavelength of the excitation spectrum is preferably used.

[0040] Any device may be used as the light source 83 as long as it is capable of generating electromagnetic waves in a wavelength band capable of exciting the fluorescent liquid 2. For example, when irradiating ultraviolet light as excitation light, a mercury lamp or an ultraviolet LED can be used as the light source 83, but an ultraviolet LED is preferably used as the light source 83 because the excitation light generated is highly monochromatic.

[0041] The image capturing device 82 detects electromagnetic waves that pass through the pseudo road surface plate 56 and travel downward from the contact portion 3 between the tire 1 and the pseudo road surface 56a.

[0042] In this example, the photographing device 82 detects the fluorescence emitted from the fluorescent liquid 2 present in the ground contact portion 3 and transmitted through the pseudo road surface plate 56. The photographing device 82 is equipped with a camera that photographs the fluorescence transmitted through the pseudo road surface plate 56 (see FIG. 3). The camera that constitutes the photographing device 82 may be, for example, a single-lens reflex camera, a high-speed camera, a CCD camera, a video camera, or the like.

[0043] In addition, the photographing device 82 may be a device that detects reflected waves formed when electromagnetic waves irradiated from the irradiation device 81 are reflected by the grounded portion 3, or a device that detects electromagnetic waves emitted from the grounded portion 3 due to the electromagnetic waves irradiated from the irradiation device 81.

[0044] In this example, a filter that transmits only light of a specific wavelength band and separates it from light of other wavelength bands may be provided between the light source 83 and the dichroic mirror 85, or between the dichroic mirror 85 and the imaging device 82.

[0045] The irradiation device 81 may be configured to be movable in the horizontal direction so that the position at which the planar excitation light is irradiated onto the contact portion 3 between the tire 1 and the simulated road surface 56a can be changed. The photographing device 82 may be configured to be movable in the horizontal direction in accordance with the movement of the irradiation device 81.

[0046] (6) Control unit 100 As shown in FIG. 4, the control unit 100 has a main control unit 100a and a memory unit 100b, and is connected to the power unit 22, the spindle drive unit 32b, the six-component force sensor 32c, the load adjustment unit 34, the slip angle adjustment unit 35, the camber angle adjustment unit 36, the light source 83 of the irradiation device 81, and the photographing device 82 via a communication interface.

[0047] The main control unit 100a is composed of a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory) for expanding programs, etc. The main control unit 100a executes a program stored in the storage unit 100b to control each unit connected to the control unit 100 and measure the contact state of the tire 1 rolling on the simulated road surface 56a of the simulated road surface plate 56.

[0048] Furthermore, the main control unit 100a executes a program stored in the storage unit 100b to realize an image processing unit 100c that processes image data acquired by the photographing device .

[0049] (7) Method for measuring the contact state of the tire 1 using the measuring device 10 Next, a method for measuring the contact state of the tire 1 rolling on the pseudo road surface plate 56 using the measuring device 10 will be described.

[0050] Before measuring the ground contact state of the tire 1, first, a pseudo road surface plate 56 is fixed to the window step 58 of the road surface portion 50 with the pseudo road surface 56a facing upward. Then, fluorescent liquid 2 is poured onto the uneven pseudo road surface 56a, filling the pseudo road surface 56a with fluorescent liquid 2. As the fluorescent liquid 2, for example, an aqueous solution containing a hydrophilic fluorescent dye (e.g., pyranine) whose excitation spectrum and fluorescence spectrum have a peak wavelength difference of 100 nm or more is used.

[0051] Next, the wheel rim WR with the tire 1 mounted thereon is attached to the spindle shaft 32a of the spindle portion 32, and the drive unit 30 is placed in an initial position set at a predetermined position in the X direction.

[0052] The tire 1 is inflated to an internal pressure. The internal pressure may be the air pressure determined for each tire by a standard system including the standard on which the tire is based, such as the maximum air pressure in the case of truck / bus tires and light truck tires in the case of JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the case of TRA, or "INFLATION PRESSURE" in the case of ETRTO, and typically 180 kPa, 220 kPa, etc. in the case of passenger car tires, or the air pressure set on an actual vehicle.

[0053] Next, with the tire 1 moving upward away from the road surface body 52 of the road surface portion 50, the slip angle adjustment unit 35 adjusts the slip angle to a preset value, and the camber angle adjustment unit 36 ​​adjusts the camber angle to a preset value.

[0054] Thereafter, the load adjustment unit 34 performs a first step of lowering the wheel rim WR to bring the tire 1 mounted on the wheel rim WR into contact with the upper surface of the road surface body 52, and applying a predetermined load to the tire 1.

[0055] When the load adjustment unit 34 applies a downward load to the tire 1, the six-component force sensor 32c functions as a load detection unit and detects the downward load acting on the tire 1. When the six-component force sensor 32c detects the load acting on the tire 1, the control unit 100 applies a predetermined load to the tire 1 by controlling the load adjustment unit 34 based on the detection result of the six-component force sensor 32c.

[0056] The load applied to the tire 1 may be a normal load, a load equivalent to that of an actual vehicle, or a value 0.2 to 1.5 times these loads, or any other value depending on the purpose of the ground contact characteristic evaluation. Alternatively, the load may be set at multiple levels, and the ground contact state may be measured at each load to evaluate the relationship between the load and the ground contact characteristic. The normal load here refers to the load determined for each tire by each standard in the standard system, including the standard on which the tire is based. For example, the normal load may be the maximum load capacity in the JATMA standard, the maximum value listed in the table above in the TRA standard, or the "LOAD CAPACITY" in the ETRTO standard. If the tire is for a passenger car, it may also be a load equivalent to 88% of these loads.

[0057] Next, the power unit 22 is driven, and the drive device 30 travels in the X direction at a predetermined speed. By setting the spindle drive unit 32b to an idling state in advance, the tire 1 rotates along with the drive device 30 at a peripheral speed substantially equal to the travel speed, and rolls freely on the pseudo road surface 56a of the pseudo road surface plate 56. At this time, by controlling the spindle drive unit 32b to apply a predetermined torque, the tire 1 rolls on the pseudo road surface 56a of the pseudo road surface plate 56 in a driving state or a braking state. In other words, in this embodiment, the spindle drive unit 32b functions as a tire torque adjustment unit that adjusts the driving force or braking force of the tire 1. The X direction in which the drive device 30 travels is set to a direction parallel to the tire circumferential direction when the tire 1 has a slip angle of 0°.

[0058] At least while the tire 1 is rolling on the pseudo road surface 56a, the irradiation device 81 emits excitation light from the light source 83, and the imaging device 82 detects the fluorescence emitted from the fluorescent liquid 2 present in the contact area 3 and transmitted through the pseudo road surface plate 56 at predetermined time intervals.

[0059] That is, the excitation light emitted from the light source 83 is reflected by the dichroic mirror 85 and irradiated from the underside of the pseudo road surface plate 56 onto the fluorescent liquid 2 interposed between the tire 1 and the pseudo road surface 56a. This causes the fluorescent pigment contained in the fluorescent liquid 2 to transition from the ground state to an excited state. The excited fluorescent pigment then returns to the ground state, emitting fluorescence. The emitted fluorescence is transmitted through the pseudo road surface plate 56 and the dichroic mirror 85 in this order, and then optically captured by the image capture device 82. The image capture device 82 performs a second step of capturing multiple images by continuously capturing images of the fluorescence transmitted through the pseudo road surface plate 56 and the dichroic mirror 85 at predetermined time intervals while the tire 1 passes over the pseudo road surface 56a, and stores the captured images in the memory unit 100b.

[0060] (8) Processing in the image processing unit 100c Next, a method for processing a plurality of images acquired by the photographing device 82 in the image processing unit 100c will be described with reference mainly to FIGS.

[0061] The image processing unit 100c converts the multiple images stored in the memory unit 100b into luminance images (fluorescence intensity images) that represent the luminance distribution of the fluorescence using a known method, and obtains multiple luminance images G1 to G6 as shown in Figure 6(a) (step S1 in Figure 7).

[0062] Then, the image processing unit 100c calculates the sum of the luminance values ​​for each luminance image. That is, the total luminance value is calculated for each image by adding up the luminance values ​​of all pixels that make up the luminance image. Then, the image processing unit 100c selects the image with the smallest total luminance value from the multiple images as the reference image (step S2 in FIG. 7).

[0063] When the luminance images G1 to G6 shown in Fig. 6(a) are acquired, the image processing unit 100c calculates the total luminance value of each of the six luminance images G1 to G6 as shown in Fig. 6(b), and selects the image corresponding to the luminance image G3 with the smallest total luminance value as the reference image. Note that the image obtained by converting the reference image selected in step S2 into a luminance image is called the reference luminance image.

[0064] Next, the image processing unit 100c performs a third step of determining the axial positions of the circumferential grooves and the tread land portions in the reference image (step S3 in FIG. 7).

[0065] Because the region corresponding to the circumferential groove 6 of the tire 1 in the reference image has a higher brightness than the region corresponding to the tread land portion 7, the image processing unit 100c calculates the sum of the brightness values ​​of pixels located at the same position in the tire axial direction in the reference brightness image as shown in FIG. 8(a), and obtains the sum of the brightness values ​​of pixels arranged in the tire circumferential direction for each pixel located at a different position in the tire axial direction. In other words, the image processing unit 100c sums the brightness values ​​of each pixel in the reference brightness image in the tire axial direction for each pixel row in the tire axial direction, and obtains a numerical string in which the sums of the brightness values ​​of the pixel rows are arranged in the tire axial direction. The image processing unit 100c then determines the axial positions of the circumferential groove and the tread land portion in the reference image from the tire axial position and the sum of the brightness values.

[0066] Specifically, the axial positions of the circumferential grooves and the tread land portions are determined by the following method.

[0067] For example, the image processing unit 100c may determine that an area where the sum of brightness values ​​in the circumferential direction of the tire is higher than a predetermined threshold value Th corresponds to the circumferential groove 6, and may determine that an area where the sum of brightness values ​​is lower than the threshold value Th corresponds to the tread land portion.

[0068] In addition, the image processing unit 100c may create a graph such as that shown in Figure 8(b) for the reference brightness image, which shows the relationship between the position in the tire axial direction and the sum of the brightness values ​​of pixels at the same position in the tire axial direction, and determine the axial positions of the circumferential grooves and the tread land portion from the created graph and a design pattern drawing of the tire 1 stored in advance in the memory unit 100b.

[0069] For example, the image processing unit 100c identifies positions P1, P2, P3, and P4 in the tire axial direction where the sum of brightness values ​​becomes an extreme value equal to or greater than a predetermined value in the created graph. Then, the image processing unit 100c may acquire the groove width of the circumferential groove from the design pattern drawing stored in the storage unit 100b, and determine that the region of the groove width acquired from the storage unit 100b, with positions P1, P2, P3, and P4 being the widthwise center positions of the circumferential groove 6, corresponds to the circumferential groove 6, and determine that the other regions correspond to the tread land portion 7.

[0070] Before calculating the sum of the luminance values ​​of pixels at the same position in the tire axial direction, the image processing unit 100c may perform trimming to cut out the area outside the contact patch 3 from the reference image as necessary.

[0071] Next, the image processing unit 100c performs a fourth step (step S4 in FIG. 7) of binarizing the reference luminance image to obtain a binarized image (hereinafter, this binarized image may also be referred to as a reference binarized image). The binarization of the reference luminance image can be performed by a computer program using a binarization algorithm. Preferably, the reference luminance image is binarized using a local adaptive thresholding algorithm. Generally, the background luminance of the reference luminance image varies between captured images. If a local adaptive thresholding algorithm is not used, it would be necessary to manually check the luminance histogram and reset the threshold value, which would increase the number of steps. In contrast, using a local adaptive thresholding algorithm reduces the number of manual steps and enables consistent processing.

[0072] The local adaptive threshold algorithm is a method for calculating a threshold for each small region in an image. For an image in which the brightness varies from region to region, a threshold is calculated for each region and binarized using that threshold, thereby clearly separating contact and non-contact regions with respect to the simulated road surface 56a. For example, regions below the threshold are binarized as "contact regions" because they have low brightness and a small thickness of the fluorescent liquid 2, while regions above the threshold are binarized as "non-contact regions" because they have high brightness and a large thickness of the fluorescent liquid 2. The adaptive threshold algorithm is described, for example, in Bradley, D., and G. Roth, "Adapting Thresholding Using the Integral Image," Journal of Graphics Tools, Vol. 12, No. 2, 2007, pp. 13-21, and any known algorithm can be used.

[0073] 9(a) shows a reference binarized image obtained by binarizing the reference luminance image using an adaptive threshold algorithm. In the reference binarized image, black areas represent areas that are in contact with the simulated road surface 56a (contact areas), and white areas represent areas that are not in contact with the simulated road surface 56a (non-contact areas).

[0074] Then, the image processing unit 100c performs a fifth step of evaluating the ground contact characteristics of the tire 1 based on the reference binarized image and the axial position of the tread land portion 7 determined in the third step (step S5 in FIG. 7).

[0075] For example, the image processing unit 100c classifies the reference binary image into an area corresponding to the circumferential groove and an area corresponding to the tread land portion based on the axial position of the tread land portion determined in the third step described above.

[0076] Then, the number of black pixels is counted for the region corresponding to the specific tread land portion in the reference binary image, and this number of black pixels is taken as the area of ​​the portion in contact with the pseudo road surface 56a. The number of black pixels is then divided by the total number of pixels in that region to calculate a standardized contact area occupancy rate ([number of black pixels in the region corresponding to the specific tread land portion] / [total number of pixels in the region corresponding to the specific tread land portion]). By calculating this contact area occupancy rate, the true contact area of ​​the tire 1 with the pseudo road surface 56a, which has irregularities simulating an actual road surface, can be evaluated.

[0077] Figure 9(b) shows an example of a tread land portion of interest, focusing on the center land equivalent region Ce surrounded by a rectangular frame in the center land portion 7A and the quarter land equivalent region Qu surrounded by a rectangular frame in the quarter land portion 7B.

[0078] By calculating the ratio of the number of black pixels to the total number of pixels in the center land equivalent area Ce, the true contact area in the center land equivalent area C can be evaluated from the contact area occupancy rate of the center land portion 7A with respect to the pseudo road surface 56a.

[0079] In addition, by calculating the ratio of the number of black pixels to the total number of pixels within the quarter land equivalent area Qu, the true contact area in the quarter land equivalent area Qu can be evaluated from the contact area occupancy rate of the quarter land portion 7B with respect to the pseudo road surface 56a.

[0080] (9) Effects In the embodiment described above, the sum of the brightness values ​​of pixels located at the same position in the tire axial direction is calculated for an image captured of the tire 1 in contact with a simulated road surface 56a, and the axial positions of the circumferential grooves 6 and the tread land portion 7 are determined from the calculated sum of brightness values. Therefore, the image processing unit 100c can easily distinguish between the groove-corresponding portion and the land-corresponding portion in the captured image, enabling the tire's ground contact characteristics to be evaluated simply and with high accuracy. By evaluating the tire's ground contact characteristics in this manner, it becomes possible to accurately evaluate differences in ground contact characteristics with a real road surface due to differences in design, such as the tread profile, tread pattern, tread rubber compounding, reinforcing fibers, and belt, and to obtain knowledge useful for design.

[0081] In this embodiment, the contact portion 3 of the tire 1 rolling on the pseudo road surface 56a is continuously photographed to obtain a plurality of images, one of the obtained images is selected as a reference image, and the axial positions of the circumferential grooves 6 and the tread land portion 7 are determined based on the selected reference image. Therefore, even in an image photographed of the contact state of the rolling tire 1, the image processing unit 100c can easily distinguish between the groove-corresponding portion and the land-corresponding portion, and the contact characteristics of the rolling tire can be evaluated simply and with high accuracy.

[0082] Furthermore, in this embodiment, the image with the smallest total brightness value among the multiple acquired images is used as the reference image, so the image processing unit 100c can accurately distinguish between groove-equivalent parts and land-equivalent parts, and the ground contact characteristics of the rolling tire can be evaluated with even greater accuracy.

[0083] (10) Example of change Next, modified examples will be described. Various modifications can be made to the above embodiment without departing from the spirit of the invention. In addition to the following modified examples, various omissions, substitutions, and modifications can be made without departing from the gist of the invention. Several modified examples will be described below, and any one of the modified examples may be applied to the above embodiment, or any two or more of the modified examples may be applied in combination.

[0084] (10-1) Change example 1 In the above embodiment, a reference image was binarized from among the multiple images acquired by the photographing device 82 to obtain a reference binary image, and the ground contact characteristics of the tire 1 were evaluated from the reference binary image, but images other than the reference image may also be binarized to obtain binary images, and the tire ground contact characteristics may be evaluated using the other images along with the reference image.

[0085] Specifically, in the fourth step, the image processing unit 100c binarizes the reference image and one or more images other than the reference image (hereinafter, these images may also be referred to as auxiliary images) from among the multiple images acquired by the photographing device 82 to obtain a binary image (hereinafter, this binary image may also be referred to as auxiliary binary image).

[0086] Then, the image processing unit 100c sets, in the auxiliary binary image, an area corresponding to the circumferential groove and an area corresponding to the tread land portion at the same positions as the axial positions of the circumferential groove and the tread land portion determined in the third step.

[0087] Then, in a fifth step, the image processing unit 100c counts the number of black pixels in the region corresponding to the specific tread land portion for the reference binary image and the auxiliary binary image, and calculates the area of ​​the portion in contact with the pseudo road surface 56a. Then, the normalized contact area occupancy rate is calculated by dividing the average value of the calculated area of ​​the reference binary image (the number of black pixels in the region corresponding to the specific tread land portion in the reference binary image) and the area of ​​the auxiliary binary image (the number of black pixels in the region corresponding to the specific tread land portion in the auxiliary binary image) by the total number of pixels in the region corresponding to the specific tread land portion.

[0088] If the pseudo road surface 56a has unevenness that simulates an actual road surface, the contact state will not be the same across multiple images, resulting in variation in the contact state of the tire 1. However, by averaging the areas calculated from multiple images as in this modified example, it is possible to reduce variation in the contact state caused by the unevenness of the pseudo road surface 56a, and more accurate evaluation results can be obtained.

[0089] (10-2) Change example 2 In the above embodiment, the contact area is relatively evaluated based on the contact area occupancy rate. 2 The contact area can also be evaluated absolutely using physical quantities such as

[0090] For example, a scale having a known length is photographed by the photographing device 82 to obtain an image, and the actual area value (mm 2 ) occupied by one pixel is calculated based on the obtained image. 2 ) is calibrated. Then, the contact area in physical quantities can be calculated by multiplying the number of black pixels corresponding to the portion in contact with the pseudo road surface 56a in the binarized image by the actual area value occupied by the acquired one pixel. [Explanation of symbols]

[0091] 1... tire, 2... fluorescent liquid, 3... ground contact portion, 10... measuring device, 20... track portion, 21... linear guide, 22... power portion, 30... carriage, 31... main frame, 32... spindle portion, 32a... spindle shaft, 32b... spindle drive portion, 32c... six-component force sensor, 33... alignment portion, 34... load adjustment portion, 35... slip angle adjustment portion, 36... camber angle adjustment portion, 50... road surface portion, 51... frame, 52... road surface body, 53... mounting hole, 54... fixing jig, 55... spacer, 55a... mounting step portion, 55b... light absorbing portion, 56... simulated road surface plate, 56a... simulated road surface, 57... observation window, 58... window step portion, 81... irradiation device, 82... photographing device, 83... light source, 84... rod lens, 85... dichroic mirror

Claims

1. A tire ground contact characteristic evaluation method for evaluating ground contact characteristics of a tire having a tread provided with circumferential grooves extending in the tire circumferential direction and land portions, a first step of bringing a tire into contact with a simulated road surface of a simulated road plate having irregularities equivalent to those of an actual road surface; a second step of photographing the contact portion of the tire with the simulated road surface using an imaging device that detects electromagnetic waves transmitted through the simulated road surface plate and performs optical imaging to obtain an image; a third step of calculating a sum of brightness values ​​of pixels at the same position in the tire axial direction in the image, and determining the tire axial positions of the circumferential groove and the land portion from the calculated sum of brightness values; a fourth step of binarizing the image to obtain a binarized image; and a fifth step of evaluating the ground contact characteristics of the tire based on the binarized image and the axial position of the land portion. Method for evaluating tire contact characteristics.

2. In the first step, the tire is rolled on the simulated road surface to make contact with the ground, In the second step, a plurality of images are obtained by continuously photographing a contact portion of the tire rolling on the simulated road surface, the contact portion being in contact with the simulated road surface; In the third step, one image is selected as a reference image from the plurality of images, and the axial positions of the circumferential groove and the land portion are determined from a numerical string obtained by summing the brightness values ​​of each pixel of the reference image in the tire circumferential direction for each pixel row in the tire axial direction. The tire ground contact characteristic evaluation method according to claim 1 .

3. The tire ground contact characteristic evaluation method according to claim 2 , further comprising the steps of: calculating a sum of brightness values ​​for each of the plurality of images; and selecting the image with the smallest sum as the reference image.

4. In the fourth step, the reference image and one or more images other than the reference image are binarized to obtain a plurality of the binarized images; 4. The tire ground contact characteristic evaluation method according to claim 2, wherein in the fifth step, an area of ​​the land portion in contact with the pseudo road surface is calculated for each of the binarized images based on a plurality of the binarized images and the axial positions of the land portion in the reference image, and the tire ground contact characteristics are evaluated based on an average value of the calculated areas.

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