Method for evaluating tire vibration characteristic

Abstract

To provide a method for evaluating tire vibration characteristics, that includes a method for efficiently acquiring data of a normal direction relative to a tire surface, regarding vibration, for a plurality of measurement points.SOLUTION: A method for evaluating tire vibration characteristics includes a step of applying excitation to a tire T and measuring vibration with respect to the applied excitation, and analyzing the vibration of the tire T based on a result of the measurement. The method for evaluating tire vibration characteristics is characterized in including: measuring, by a vibration measuring instrument 30 having a fixed position and a fixed direction, vibration in three directions in an orthogonal coordinate system at a plurality of measurement points respectively of a tire surface; obtaining a unit vector of a normal vector relative to the tire surface at the plurality of measurement points respectively; and as said analysis, obtaining a transfer function expressing vibration in a direction of the normal vector with respect to the applied excitation, based on the unit vector, a frequency characteristic of the vibration and a frequency characteristic of force of the applied excitation, for the measurement points respectively.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a tire vibration characteristic evaluation method. [Background technology]

[0002] A method is known in which a pneumatic tire (hereinafter referred to as "tire") is vibrated, the vibration of the tire surface (hereinafter referred to as "tire surface") caused by the vibration is measured, and the vibration is analyzed and evaluated.

[0003] Specifically, as described in Non-Patent Document 1, a tire with wheels is laid on its side, and the wheels are placed on a stand so that the tire does not come into contact with the stand. In this state, the center position in the axial direction of the tire tread is excited by an input device, and the vibration of the tire surface caused by the excitation is measured by one laser Doppler vibrometer.

[0004] In Non-Patent Document 1, the laser Doppler vibrometer is positioned to measure vibrations in the normal direction to the tire surface at one measurement point on the tire surface. [Prior art documents] [Patent documents]

[0005] [Non-Patent Document 1] Bolton J. Stuart, Kim Yong-Joe."Visualization of Tire Vibration and Sound Radiation and Modeling of TireVibration with an Emphasis on Wave Propagation". University TransportationCenters Program (US). Published Date 2003-08-01. Report NumberSQDH2003-4;HL2003-15. https: / / rosap.ntl.bts.gov / view / dot / 34133, (referenced 2023-10-26) Summary of the Invention [Problem to be solved by the invention]

[0006] However, the above method was inefficient for measuring vibrations at multiple measurement points: after completing a measurement at one measurement point, an operator had to move the laser Doppler vibrometer and reposition it so that the next measurement point could measure vibrations in the normal direction to the tire surface.

[0007] Therefore, an object of the present invention is to provide a tire vibration characteristic evaluation method that includes a method for efficiently acquiring data regarding vibrations in the normal direction to the tire surface for a plurality of measurement points. [Means for solving the problem]

[0008] The present invention includes the embodiments set forth below.

[0009] [1] A tire vibration characteristic evaluation method including the steps of: vibrating a tire, measuring the vibration in response to the vibration, and analyzing the vibration based on the measurement results, the tire vibration characteristic evaluation method comprising the steps of: measuring the vibration in three directions of a Cartesian coordinate system at each of a plurality of measurement points on the tire surface using a vibration measuring device whose position and orientation are fixed; determining a unit vector of a normal vector to the tire surface at each of the plurality of measurement points; and determining a transfer function representing the vibration in the direction of the normal vector to the vibration for each of the measurement points based on the unit vector, the frequency characteristics of the vibration, and the frequency characteristics of the vibration force.

[0010] [2] The tire vibration characteristic evaluation method described in [1], in which the normal vector at the starting point is obtained by calculating the cross product of two vectors whose origin is one of the measurement points and whose end points are two measurement points located in different directions next to the starting point.

[0011] [3] A tire vibration characteristic evaluation method according to [1] or [2], wherein the measurement points are set in a line in the tire axial direction and the tire circumferential direction, two or more measurement points are set in the tire axial direction, and the distance between adjacent measurement points in the tire circumferential direction is a length equivalent to an angle around the tire rotation axis of 45° or less.

[0012] [4] The tire vibration characteristic evaluation method according to any one of [1] to [3], further comprising the steps of: applying vibration at a plurality of vibration points set on a tire surface; and measuring the vibration in response to each of the vibrations. Effect of the Invention

[0013] In the tire vibration characteristic evaluation method according to the embodiment, data on vibrations in the normal direction to the tire surface can be efficiently obtained for a plurality of measurement points. [Brief description of the drawings]

[0014] [Figure 1] FIG. 2 is a view of the vibration measuring device from the axial direction of the tire. [Diagram 2] FIG. 2 is an enlarged view of the table and the vibrator in FIG. 1. [Diagram 3] FIG. [Figure 4] FIG. 2 is a diagram showing a first curve, a second curve and a third curve. [Diagram 5] View of the top plate from above. [Figure 6] View of the top plate from underneath. [Figure 7] A diagram showing the positions of some of the measurement points. (a) is a diagram of the tire as seen from the front-rear direction, and (b) is a diagram of the tire as seen from the axial direction. [Figure 8] FIG. 4 is a diagram showing normal vectors with respect to the tire surface at measurement points. [Figure 9] FIG. 4 is a diagram showing the magnitude of a transfer function with respect to the tire circumferential position and frequency. [Figure 10] FIG. 4 is a diagram showing the magnitude of a transfer function with respect to a circumferential mode number and a frequency. [Figure 11] A diagram showing the vibration of a tire in the circumferential mode, as seen from the tire axial direction. (a) shows the tire change for order 1, (b) for order 2, and (c) for order 3. [Figure 12] FIG. 13 is a view of the vibration measuring device of the modified example viewed from the horizontal direction. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The embodiments will be described with reference to the drawings. Note that the embodiments described below are merely examples, and any appropriate modifications that do not depart from the gist of the present invention are included in the scope of the present invention.

[0016] As shown in FIG. 1, the vibration measuring device of the embodiment includes a stand 10 on which a tire T is placed, a vibrator 20 that vibrates the tire T, a vibration measuring device 30 that measures the vibration of the tire T, and an analysis device (not shown) that collects and analyzes vibration data. The direction in which the tire T can move when it rotates is referred to as the "tire front-rear direction" or simply the "front-rear direction". However, in this embodiment, the tire T does not actually move. Also, the direction perpendicular to the front-rear direction on a horizontal plane is referred to as the "left-right direction". In this embodiment, the left-right direction coincides with the tire axial direction. Also, excitation means to vibrate.

[0017] The platform 10 comprises a top plate 11 as a ground contact member on which the tire T comes into contact, and one leg 12 that supports the top plate 11. The top plate 11 is a plate-shaped member, and its upper surface is a horizontal plane. The leg 12 extends downward from the underside of the top plate 11 and is in contact with the floor of the test room. Spaces are formed below the top plate 11 and on both sides of the leg 12 in the front-to-rear direction. The location below the top plate 11 and on one side of the leg 12 in the front-to-rear direction (this side is defined as the front) is a vibration exciter arrangement space 13.

[0018] A vibration exciter 20 is disposed in the vibration exciter arrangement space 13. The vibration exciter 20 comprises a stinger 21 which is a rod-shaped member that moves up and down to advance and retreat toward the tire T, a force sensor 22 fixed to the upper end of the stinger 21 with a fastener (e.g., a screw), and an oscillator 23 which moves the stinger 21. A part of the oscillator 23 is placed in the vibration exciter arrangement space 13 below the top plate 11.

[0019] The force sensor 22 is a vibration member that vibrates the tire T. The force sensor 22 is located slightly forward of the front end of the top plate 11, and is fixed to the tire T with an adhesion means (e.g., adhesive). The vibration of the oscillator 23 is transmitted to the tire T through the stinger 21 and the force sensor 22, thereby vibrating the tire T. The force sensor 22 has a circular shape with a diameter of 10 mm or less when viewed from above (see FIG. 5), and this circular part is in contact with the tire T, and the magnitude of the vibration force during vibration is measured by the force sensor 22. A gap L1 (see FIG. 5) between the force sensor 22 and the front end of the top plate 11 is 5 mm or less.

[0020] 2, the length of the vibration exciter 20 in the front-to-rear direction is Wa, the height of the remaining part of the vibration exciter 20 excluding the part that moves up and down (i.e., the oscillator 23) is Ha, the length of the top board 11 of the platform 10 in the front-to-rear direction is Wb, the length of the feet 12 in the front-to-rear direction is Tb, and the height of the feet 12 is Hb. In this case, (Wb-Tb)≧Wa, Hb>Ha.

[0021] The vibration measuring device 30 is configured by combining three laser Doppler vibrometers. This configuration makes it possible to measure the coordinates of multiple measurement points on the tire surface and the vibration velocity of each measurement point. The coordinate system is an orthogonal coordinate system consisting of three mutually orthogonal coordinate axes, the front-rear direction, the up-down direction, and the tire axial direction. The velocities in the three directions of the orthogonal coordinate system, i.e., the front-rear direction, the up-down direction, and the tire axial direction, are measured as the vibration velocity.

[0022] Once installed, the vibration measuring device 30 can measure the coordinates and vibration velocity of multiple measurement points on the tire surface without changing the position of the vibration measuring device 30. Therefore, there is no need to move the vibration measuring device 30 or the laser Doppler vibrometer that constitutes it in order to measure the coordinates and vibration velocity of multiple measurement points.

[0023] The analysis device is a computer that is made up of an output device, an input device, a storage device, a processing device, etc. The analysis and evaluation of this embodiment are carried out by the processing device executing a program stored in the storage device.

[0024] The vibration measuring device configured as above measures the vibration of tires T of various shapes and sizes. Therefore, the top plate 11 is created for each tire T to be measured so that the shape and size of the top plate 11 approximately matches the shape and size of the contact surface of each tire T.

[0025] As a method for this, first, an operator obtains the shape and size of the contact surface of the tire T to be subjected to vibration measurement when a static load is applied, using a known method. As a method for obtaining the shape and size of the contact surface, for example, there is a method in which a specific sheet is laid on a transparent glass plate, the tire T is placed on the sheet, a load is applied, and the contact surface of the tire T that can be recognized from under the glass plate is photographed with a camera. There is also a method in which the tire T is placed on a specific surface and a load is applied, a pressure distribution on the surface is obtained, and the contact surface is recognized based on the pressure distribution. There is also a method in which a model of the tire T is used to obtain the contact surface by performing a numerical analysis such as a finite element analysis.

[0026] The contact surface thus obtained for the creation of the top plate 11 is referred to as the "reference contact surface." The reference contact surface is indicated by the reference symbol 50 in FIG. 3. The internal pressure and load applied to the tire T when obtaining the reference contact surface 50 are the same as the internal pressure and load applied during the vibration measurement described below. The load applied at this time is the same in both magnitude and direction. In addition, the surface on which the tire T contacts the ground when obtaining the reference contact surface 50 is a surface of the same shape as the surface on which the tire T contacts the ground during the vibration measurement, and in this embodiment, it is a flat surface like the upper surface of the top plate 11. The reference contact surface 50 obtained in this manner can be regarded as having the same shape and size as the contact surface of the tire T on the top plate 11 during the vibration measurement.

[0027] Next, the worker identifies the portion of the contour line of the reference contact patch 50 from point A where the contour line intersects with the tire equator line E to point B on one of the tire contact ends in the axial direction as a line segment 51 shown in Fig. 3. In Fig. 3, the line segment 51 is shown thicker than other portions of the contour line of the reference contact patch 50.

[0028] Next, the worker sets three reference points on the line segment 51. The three reference points can be selected arbitrarily, for example, reference point P1 on the tire equator line E, reference point P3 at the tire axial end, and reference point P2 between reference points P1 and P3. Note that reference point P1 coincides with point A, and reference point P3 coincides with point B. Furthermore, if an inflection point exists on the line segment 51, reference point P2 may be set at the inflection point.

[0029] Then, the worker specifies the curve that passes through these three reference points as the first curve. The first curve extends from point A to point B in the same range as the line segment 51. The first curve can be specified by a quadratic function or a circular arc. The quadratic function or the circular arc can be expressed with the tire axial direction as the x direction and the front-rear direction (which can also be said to be the tire circumferential direction) as the y direction. Furthermore, the worker creates a third curve by connecting the first curve with a second curve, which is a line segment that is symmetrical to the first curve with respect to the tire equator line E. For reference, in FIG. 4, the range of the first curve is indicated by reference numeral 41, the range of the second curve by reference numeral 42, and the range of the third curve by reference numeral 43.

[0030] The third curve thus completed is similar in shape and size to a tire front-rear direction ground contact end 53, which is a tire front-rear direction portion of the contour of a ground contact surface 52 that contacts the top plate 11 of the tire T. The ground contact surface 52 is indicated by a two-dot chain line in Fig. 5 and by a dashed line in Fig. 6.

[0031] Next, the worker prepares the top plate 11. At this time, the worker matches the shape and size of a part of the front end of the top plate 11 (specifically, the central part in the left-right direction) to the shape and size of the third curve. In this way, the part of the front end of the top plate 11 that has the same shape and size as the third curve is set as the ground contact end shape edge 14. As a result, when the tire T to which a predetermined internal pressure is applied (described later) is grounded on the top plate 11 and a predetermined load (described later) is applied, the entire tire front-rear direction ground contact end 53 of the ground contact surface 52 of the tire T will be aligned with the entire ground contact end shape edge 14 of the top plate 11. In FIG. 5, the tire front-rear direction ground contact end 53 of the ground contact surface 52 of the tire T and the ground contact end shape edge 14 of the top plate 11 are shown with thicker lines than the other lines. The worker may also match the shape and size of the rear end 15 of the top plate 11 to the shape and size of the third curve. In addition, the worker makes the length of the top plate 11 in the front-rear direction slightly longer than the length of the contact surface 52 of the tire T that comes into contact with the top plate 11 in the front-rear direction.

[0032] Also, the worker preferably makes the length of the top plate 11 in the left-right direction (tire axial direction) slightly longer than the length in the tire axial direction of the contact surface 52 of the tire T that comes into contact with the top plate 11. However, the worker may make the length of the top plate 11 in the left-right direction the same as the length in the tire axial direction of the contact surface 52 of the tire T that comes into contact with the top plate 11, and make the entire front end of the top plate 11 the ground contact end shape edge 14.

[0033] The worker attaches legs 12 to the completed top plate 11 to form a stand 10, and places the stand 10 in a predetermined position on the vibration measuring device.

[0034] Vibration measurement is performed using the vibration measuring device configured as described above. First, an operator sets a tire T in the vibration measuring device as shown in FIG. 1. In detail, the operator places the tire T on the top plate 11 with the tire axial direction horizontal, thereby causing the tire to touch the ground. At this time, the operator applies a predetermined internal pressure to the tire T. Furthermore, the operator applies a predetermined load in a downward direction to the tire T that is in contact with the top plate 11.

[0035] Here, the predetermined internal pressure is the air pressure determined for each tire by each standard in the standard system including the standard on which the tire is based, and in the case of truck and bus tires and light truck tires, it is the maximum air pressure in the case of JATMA, the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the case of TRA, and "INFLATION PRESSURE" in the case of ETRTO. In addition, if the tire is for passenger cars, the internal pressure is usually 180 kPa, but in the case of tires described as Extra Load or Reinforced, the internal pressure is 220 kPa.

[0036] The predetermined load can be selected according to the purpose, and may be a normal load or the load of the vehicle on which the tire is mounted. The normal load is a load determined for each tire by each standard in the standard system including the standard on which the tire is based, and is the "maximum load capacity" for JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" for TRA, and "LOAD CAPACITY" for ETRTO. In addition, when the tire is for passenger cars, the normal load is a load equivalent to 88% of the above-mentioned "load determined for each tire by each standard." In addition, when the tire is for racing karts, the normal load is 392N.

[0037] Furthermore, the worker adjusts the position of the tire T so that when the tire T to which a predetermined internal pressure has been applied is placed on the top plate 11 and a predetermined load is applied, the ground contact edge 14 at the front end of the top plate 11 and the tire front-rear direction ground contact edge 53 of the ground contact surface 52 of the tire T are close to each other. Specifically, the worker adjusts the position of the tire T so that the front-rear distance L2 (see Figs. 5 and 6) from the ground contact edge 14 at the front end of the top plate 11 to the tire front-rear direction ground contact edge 53 of the ground contact surface 52 of the tire T is 5 mm or less at any position in the tire axial direction.

[0038] The worker sets the tire T on the top plate 11, and then fixes the force sensor 22 to the tire T. After fixing the force sensor 22, the worker operates the vibration measuring device to vibrate the tire T. In this embodiment, the vibration is applied at a plurality of vibration points along the tire front-rear ground edge 53. The vibration points are parts where the force sensor 22, which is a vibration application member, is in contact and vibration is applied. The vibration points are set outside the ground contact surface 52 and within 10 mm in the front-rear direction from the tire front-rear ground edge 53. The vibration points are set on the tread. By vibrating the tread near the tire front-rear ground edge 53 in this way, the vibration when the tire T is in contact with the road surface is reproduced.

[0039] In this embodiment, the multiple excitation points are three points: a center excitation point Q1 on the tire equator line E, a shoulder excitation point Q3 on one of the shoulder parts (for example, shoulder rib parts) on both axial sides of the tire, and an intermediate excitation point Q2 between the center excitation point Q1 and the shoulder excitation point Q3, as shown in Fig. 6. Excitation is performed on these three excitation points in order, and each time, vibration velocities are measured at multiple measurement points on the tire surface.

[0040] In detail, first, excitation is performed at the first excitation point. Specifically, the tire T is excited by applying the vibration of the oscillator 23 to the first excitation point through the stinger 21 and the force sensor 22. The force sensor 22 measures the magnitude of the excitation force during excitation. Furthermore, the vibration of the tire surface caused by this excitation is measured by the vibration measuring device 30. The vibration measuring device 30 measures the coordinates of multiple measurement points on the tire surface and the vibration velocity of each measurement point. Furthermore, for each measurement point, vibrations in the front-rear direction, the up-down direction, and the tire axial direction, which are perpendicular to each other, are measured. Since measurement is performed for one measurement point for each excitation, excitation is performed the same number of times as there are measurement points. The operator does not move the vibration measuring device 30 until measurements are completed at the number of measurement points required for the analysis and evaluation described below. In other words, the vibration measuring instrument 30 keeps its position and orientation (more precisely, the position and measurement direction of each of the three laser Doppler vibrometers that make up the vibration measuring instrument 30) fixed until measurements are completed at the number of measurement points required for the analysis and evaluation described below.

[0041] Similarly, excitation is performed on the second and third excitation points, and the vibrations caused by the excitation are measured. The operator does not move the vibration measuring device 30 when changing the excitation point.

[0042] The measurement points are set to line up in the tire axial direction and the tire circumferential direction. Some example positions of the measurement points are illustrated in FIG. 7 with black circles. As shown in FIG. 7, two or more measurement points are set in the tire axial direction. The interval θ between adjacent measurement points in the tire circumferential direction is a length equivalent to an angle around the tire rotation axis of 45° or less. In other words, the interval L3 between adjacent measurement points in the tire circumferential direction (see FIG. 7(b)) satisfies the following formula, where r is the radius of tire T. Here, the interval L3 between adjacent measurement points in the tire circumferential direction refers to the arc length between two measurement points adjacent in the tire circumferential direction.

[0043]

number

[0044]

number

[0045]

number

[0046] The analysis device analyzes and evaluates the vibration of tire T based on the measured data. Analysis means clarifying the components and elements of vibration based on the measured data. Evaluation means clarifying the differences in vibration characteristics due to differences in conditions and tires T, and specific examples include differences in vibration characteristics of tire T due to differences in excitation points and differences in vibration characteristics due to differences in the structure of tire T. Here, vibration characteristics refer to characteristics related to vibration that are clarified by analysis.

[0047] The analyses include a transfer function in the normal direction of the tire surface with respect to the excitation (this direction is referred to as the "tire normal direction"), a transfer function in the tire normal direction with respect to the tire circumferential position and frequency, a transfer function in the tire normal direction with respect to the circumferential mode order and frequency, etc. These analyses are performed for each excitation point.

[0048] In order to analyze the transfer function in the tire normal direction, first, a unit vector of a normal vector to the tire surface at each measurement point is obtained. To obtain the normal vector, as shown in FIG. 7 and FIG. 8, a measurement point S0 as a starting point, a measurement point S1 adjacent to the measurement point S0 in the tire axial direction and serving as the first end point, and a measurement point S2 adjacent to the measurement point S0 in the tire circumferential direction and serving as the second end point are specified. Then, as shown in FIG. 8, a cross product of a vector S01 from the measurement point S0 as the starting point to the measurement point S1 as the first end point, and a vector S02 from the measurement point S0 as the starting point to the measurement point S2 as the second end point is calculated, thereby obtaining a normal vector N to the tire surface at the measurement point S0. A unit vector of the normal vector N is obtained from the obtained normal vector N. By this method, a unit vector of a normal vector to the tire surface is obtained for all measurement points on all tire surfaces.

[0049] Next, the magnitude of the transfer function at each measurement point is calculated as the square root of the sum of the squares of the transfer function in the front-rear direction, the transfer function in the up-down direction, and the transfer function in the tire axial direction.

[0050] Next, the transfer function in the tire normal direction at each measurement point is calculated from the unit vector of the normal vector and the magnitude of the transfer function. The transfer function in the tire normal direction at each measurement point is obtained for the excitation at each of the excitation points Q1, Q2, and Q3.

[0051] Based on the transfer functions in the tire normal direction at each measurement point thus obtained, the magnitude of the transfer function in the tire normal direction with respect to the tire circumferential position and frequency is obtained. Here, the tire circumferential position is the angle (°) around the tire rotation axis starting from the lowest point of the tire T.

[0052] Fig. 9 is based on the transfer function in the tire normal direction at a plurality of measurement points arranged in the tire circumferential direction at a predetermined position in the tire axial direction (for example, the positions where measurement points S0 and S2 in Fig. 7 are provided) when excitation is performed at one excitation point. In this figure, the horizontal axis indicates the position in the tire circumferential direction, and the vertical axis indicates the frequency. Also, in this figure, the brightness indicates the magnitude of the transfer function in the tire normal direction as a level, and the higher the brightness (i.e., the brighter it is), the greater the magnitude of the transfer function.

[0053] Here, the magnitude of the transfer function expressed in terms of a level is obtained as M' by the following formula, where M is the magnitude of the transfer function.

[0054]

number

[0055] Such magnitude of the transfer function in the tire normal direction versus tire circumferential position and frequency can be obtained for excitation at each of excitation points Q1, Q2, and Q3. From the results, differences in the vibration characteristics of tire T due to differences in excitation points can be evaluated. In addition, vibration measurements are performed on a number of tires with different structures, and based on the respective results, the magnitude of the transfer function in the tire normal direction versus tire circumferential position and frequency can be obtained. From the results, differences in the vibration characteristics of each tire can be evaluated.

[0056] The structure here refers to the structure of the tread and the internal structure radially inward of the tread, including the arrangement of various grooves including sipes, and the shapes and sizes of ribs and blocks.

[0057] Furthermore, the transfer function in the tire normal direction for the circumferential mode number and frequency can be obtained by Fourier transforming the transfer function in the tire normal direction according to the following equation.

[0058]

number

[0059]

number

[0060] Fig. 10 is a diagram created based on data on the magnitude of the transfer function in the tire normal direction versus the tire circumferential position and frequency shown in Fig. 9. In this diagram, the horizontal axis indicates the circumferential mode order, and the vertical axis indicates the frequency. In addition, in this diagram, the luminance is expressed as a level of the magnitude of the transfer function V(p, m) calculated using Equation 5 above, and is calculated using the same formula as Equation 4, with M substituted for the magnitude |V(p, m)| of the transfer function calculated based on Equation 5 above. It means that the greater the luminance (i.e., the brighter it is), the greater the magnitude of the transfer function.

[0061] In Fig. 10, the bright areas are connected to form multiple lines. Each line represents a vibration mode that appears as a characteristic deformation on the tire axial cross section. Certain of these lines represent vibration modes that contribute to the sound radiation from tire T.

[0062] Such magnitudes of the transfer functions for the circumferential mode order and frequency can be obtained for excitation at each of the excitation points Q1, Q2, and Q3. From the results, it is possible to evaluate the difference in vibration characteristics of the tire T due to the difference in the excitation point. For example, it is possible to evaluate the difference in the magnitude of the transfer function of a specific vibration mode that contributes to radiated sound due to the difference in the excitation point.

[0063] In addition, vibration measurements are performed on a number of tires with different structures, and the magnitude of the transfer function for the circumferential mode order and frequency can be obtained based on the respective results. From the results, differences in vibration characteristics due to differences in tire structure can be evaluated. For example, the magnitude of the transfer function of a specific vibration mode that contributes to radiated sound due to differences in tire structure can be evaluated.

[0064] These evaluation results are used in tire design, etc. For example, the difference in the magnitude of the transfer function of a specific vibration mode due to the difference in excitation point or the difference in tire structure is used in tire design to reduce tire vibration radiation sound. As a more specific example, when excitation is performed at any one of excitation points Q1, Q2, and Q3, if the magnitude of the transfer function of a specific vibration mode that contributes to the radiation sound is large, a design change is made to the rib or the like that has that excitation point in order to reduce tire vibration radiation sound.

[0065] According to the present embodiment described above, by using a vibration measuring device whose position and orientation are fixed to measure vibrations in three directions of a Cartesian coordinate system at each of a plurality of measurement points on the tire surface, it is possible to efficiently obtain vibration data at the plurality of measurement points.

[0066] However, in this embodiment, since the vibration measuring device 30 is installed once and then measured for multiple measurement points without moving it, it is not possible to measure vibrations in the normal direction to the tire surface at most of the measurement points. The vibration measuring device 30 only measures vibrations in three directions in a Cartesian coordinate system.

[0067] Therefore, in this embodiment, a unit vector of a normal vector to the tire surface at each of the multiple measurement points is obtained. Then, for each measurement point, a transfer function representing vibration in the normal vector direction to the excitation force is obtained based on the obtained unit vector, the frequency characteristics of the vibration, and the frequency characteristics of the excitation force. In this way, data on the vibration in the normal direction to the tire surface can be efficiently obtained for the multiple measurement points.

[0068] As described above, two vectors are identified, each of which has a starting point at one measurement point and ends at two measurement points adjacent to the starting point in different directions. The normal vector at the starting point is then calculated from the cross product of these two vectors. This makes it possible to efficiently identify the normal vector with respect to the tire surface at each of the multiple measurement points.

[0069] As described above, excitation is performed at each of a plurality of excitation points set on the tire surface, the vibrations for each excitation are measured, and the measurement results are analyzed. This makes it possible to evaluate differences in vibration characteristics based on differences in excitation points, and the results can be utilized in tire design.

[0070] As described above, vibration measurements are performed on a plurality of tires T with different structures, and the measurement results are analyzed. This makes it possible to evaluate differences in vibration characteristics based on differences in structure, and to utilize the results in tire design.

[0071] Various modifications can be made to the above embodiment. Any one of the modifications described below may be applied to the above embodiment, or any two or more of them may be combined and applied to the above embodiment. Combinations can be freely made.

[0072] <Change Example 1> The vibration measurement may be performed with the tire T laid horizontally as shown in FIG.

[0073] In this modified example, a wheel with a tire T attached thereto is placed horizontally on a stand 110 provided in the vibration measuring device. As a result, the tire axial direction is vertical. The tire T is given the same internal pressure as in the above embodiment. Note that the tire T does not come into contact with the stand 110.

[0074] A ground contact member 111 having the same shape and size as the top plate 11 of the above embodiment is disposed near the platform 110 with the surface on which the tire T comes into contact being vertical. The tire T comes into contact with the ground contact member 111, and a load of the same magnitude as in the above embodiment is applied to the tire T. The load is applied in a direction that presses the tire T against the ground contact member 111.

[0075] The same vibrator 20 as in the above embodiment is disposed next to the ground contact member 111. However, in this modification, the stinger 21 of the vibrator 20 extends horizontally, and a force sensor 22 is provided at its tip. The contact portion between the force sensor 22 and the tire T is within 10 mm in the tire longitudinal direction from the tire longitudinal direction ground contact edge 53, as in the above embodiment.

[0076] In this modified example as well, the vibration of the oscillator 23 is transmitted to the tire T through the stinger 21 and the force sensor 22, thereby exciting the tire T, and the vibration measuring device 30 measures the vibration of the tire surface caused thereby.

[0077] <Change Example 2> The number and positions of the excitation points in the vibration measurement method are not limited to those in the above embodiment. For example, excitation may be performed at five points, namely, the center excitation point, the shoulder excitation points on both sides in the tire axial direction, and the middle excitation points on both sides in the tire axial direction. Also, excitation may be performed at only one of the excitation points.

[0078] <Change Example 3> In the above embodiment, the vibration velocity of the tire surface is measured as the vibration, but acceleration may be measured instead of the velocity and used for analysis.

[0079] <Change Example 4> The positions of the measurement points for vibration measurement are not limited to those in the above embodiment, and can be set arbitrarily.

[0080] Regardless of the location of the measurement point, the normal vector to the tire surface at the starting point can be obtained by calculating the cross product of two vectors whose origin is one measurement point and whose end points are two measurement points next to the starting point in different directions.

[0081] <Change Example 5> A wide range of vibration measurements can be performed by an operator moving the vibration measuring device 30 and measuring vibrations from multiple different locations with the vibration measuring device 30. To be more specific, the vibration measuring device 30 can measure vibrations at multiple measurement points in one location. By an operator moving the vibration measuring device 30 and measuring vibrations at multiple measurement points from each location, it is possible to measure vibrations at more measurement points in a wider range.

[0082] Alternatively, an operator can place a plurality of vibration measuring devices 30 around the tire T to perform vibration measurement over a wide range.

[0083] <Change Example 6> The normal vector with respect to the tire surface at each measurement point can also be obtained using a built-in function of MATLAB (registered trademark), which is numerical analysis software from MathWorks, Inc.

[0084] Specifically, three measurement points forming a triangle are specified by the built-in function triangulation. The three measurement points are, for example, measurement points S0, S1, and S2 in Fig. 8. Then, the built-in function vertexNormal acquires a normal vector at one of the three measurement points, for example, measurement point S0 in Fig. 8. [Explanation of symbols]

[0085] E... tire equator line, T... tire, 10... base, 11... top plate, 12... foot, 13... vibration exciter placement space, 14... ground contact edge shape edge, 15... rear end, 20... vibration exciter, 21... movable shaft, 22... force sensor, 23... oscillator, 30... vibration measuring instrument, 41... first curve, 42... second curve, 43... third curve, 50... reference ground contact surface, 51... ground contact contour line, 52... contour line, 53... tire front-rear ground contact edge, 110... base, 111... ground contact member

Claims

1. 1. A tire vibration characteristic evaluation method comprising the steps of: vibrating a tire; measuring the vibration caused by the vibration; and analyzing the vibration based on a measurement result, Using a vibration measuring device whose position and orientation are fixed, the vibrations are measured in three directions of a Cartesian coordinate system at each of a plurality of measurement points on the tire surface; A unit vector of a normal vector with respect to the tire surface at each of the plurality of measurement points is obtained; The tire vibration characteristic evaluation method is characterized in that, as the analysis, a transfer function representing the vibration in the direction of the normal vector to the excitation is calculated for each of the measurement points based on the unit vector, the frequency characteristics of the vibration, and the frequency characteristics of the excitation force.

2. 2. The tire vibration characteristic evaluation method according to claim 1, wherein the normal vector at the starting point is obtained by calculating the cross product of two vectors whose starting point is one of the measurement points and whose ending points are two of the measurement points adjacent to the starting point in different directions.

3. 3. The tire vibration characteristic evaluation method according to claim 1, wherein the measurement points are set in a line in the tire axial direction and the tire circumferential direction, two or more measurement points are set in the tire axial direction, and the interval between adjacent measurement points in the tire circumferential direction is a length equivalent to an angle around the tire rotation axis of 45° or less.

4. 3. The tire vibration characteristic evaluation method according to claim 1, further comprising the steps of: exciting a tire at a plurality of exciting points set on a tire surface; measuring the vibrations caused by each exciting point; and analyzing the tire vibrations based on the respective measurement results.

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