JP2022102035A - Sound source survey method - Google Patents

Abstract

To precisely specify the sound source of noise generated from a tire.SOLUTION: A sound source survey method includes the steps of: setting a road surface model, a tire model grounding on the road surface model, a plurality of sound source points of sounds generated when the tire model rolls, and a plurality of measurement points for the sounds, and performing acoustic analysis to find frequency response functions of the sounds from the sound source points to the measurement points; measuring sounds during actual rolling of the tire at the measurement points; and finding a distribution of the sounds at the plurality of sound source points based upon the sounds measured at the positions of the measurement points and the frequency response functions.SELECTED DRAWING: Figure 1

Description

The present invention relates to a sound source exploration method.

A microphone array in which a large number of microphones are arranged vertically and horizontally on a plane is known. The sound pressure of noise generated from a rotating tire is measured by a large number of microphones constituting the above microphone array, acoustic holography is processed on the measured data, and the surface including the ground contact portion of the tire ( A method for obtaining the sound pressure distribution on the sound source surface) is known (see, for example, Patent Document 1). The position where the sound pressure is large in the obtained sound pressure distribution is specified as a noise source.

Japanese Patent No. 5089253

By the way, near the measurement surface and the sound source surface, there are a tire surface and a sound reflecting surface called a road surface. However, the conventional method of obtaining the sound pressure distribution on the sound source surface using acoustic holography based on the measurement result at the location (measurement surface) of the microphone array is to transmit sound in a free sound field without a sound reflection surface. It was a premised method. Therefore, the sound pressure distribution obtained by the conventional method does not reflect the reflection of sound on the tire surface and the road surface, and there is room for improvement in accuracy.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a sound source exploration method capable of accurately identifying a sound source of noise generated from a tire.

In the sound source exploration method of the embodiment, a road surface model, a tire model that touches the road surface model, a plurality of sound source points of a sound generated when the tire model rolls, and a plurality of measurement points of the sound are set. The step of obtaining the frequency response function of the sound from the sound source point to the measurement point by performing acoustic analysis, the step of actually measuring the sound at the time of rolling of the tire at the position of the measurement point, and the step of measuring the measurement point. It is characterized by including a step of obtaining a distribution of sounds at a plurality of the sound source points based on the sound actually measured at a position and the frequency response function.

According to the sound source search method of the present embodiment, it is possible to accurately identify the sound source of the noise generated from the tire.

The figure which looked at the state of the acoustic test from the tire axis direction. The figure which looked at the state of the acoustic test from the direction of arrow A of FIG. The figure which shows the structure of the sound source exploration apparatus. The figure which shows the measurement position by a microphone. Flowchart of sound source exploration method. Flow chart of sound pressure measurement. Flow chart of acoustic analysis. The figure which looked at the contact patch of the tire model for acoustic analysis from the bottom. The mesh is not shown. The figure which looked at the grounding part of the tire model for acoustic analysis and the drum model for acoustic analysis from the microphone side. The mesh is not shown. The figure which shows the distribution of the volume velocity at a sound source point. The figure which shows the structure of the sound source exploration apparatus of a modification example. The figure which shows the microphone array. The figure which looked at the state of the acoustic test of the modified example from the tire axial direction.

The embodiment will be described with reference to the drawings. It should be noted that the embodiments described below are merely examples, and those appropriately modified without departing from the spirit of the present invention shall be included in the scope of the present invention.

1. 1. Configuration of Sound Source Exploration Device FIGS. 1 to 3 show the sound source exploration device 10 of the present embodiment. The sound source exploration device 10 includes a drum D for rolling the tire T, a drum control device 12 to which the drum D is connected, two microphones 17 and 18 for measuring the sound pressure of the sound from the tire T, and a microphone. An acoustic measuring device 13 to which 17 and 18 are connected, a mobile control device 19 that holds and moves a mobile microphone 17 that is one of the microphones 17 and 18, a computer 14 connected to the acoustic measuring device 13, and a computer 14. It has an input device 15 connected to the computer 14, an output device 16 connected to the computer 14, and a reference signal device 11 connected to the acoustic measurement device 13.

Of the sound source exploration devices 10, at least the drum D and the microphones 17 and 18 are arranged in an environment suitable for sound measurement, for example, an anechoic chamber or a semi-anechoic chamber. In that environment, an acoustic test is performed in which the noise generated when the drum D and the tire T are rotated is measured by the microphones 17 and 18.

As shown in FIGS. 1 and 2, the drum D has a cylindrical shape, and the tire T comes into contact with the outer peripheral surface D1 thereof. Although not shown, a load-bearing device for pressing the tire T against the outer peripheral surface D1 of the drum D with a force of a predetermined magnitude is provided with respect to the rotation shaft S of the tire T. The outer peripheral surface D1 of the drum D is smooth, and even when a large number of minute irregularities are present on the outer peripheral surface D1, it is preferable that the height difference between the convex portion and the concave portion adjacent to the convex portion is 1 mm or less. Examples of such an outer peripheral surface D1 include a safety walk or a steel road surface.

The start of rotation of the drum D, the end of rotation, and the change of the rotation speed are performed by the drum control device 12. The drum control device 12 is connected to the computer 14 and controls the rotation of the drum D based on the instruction from the computer 14. Although omitted in FIGS. 1 and 2, a large number of grooves are formed in the tread portion of the tire T. When the drum D rotates while the tire T is in contact with (grounded) the drum D, the tire T rolls in the direction opposite to the rotation direction of the drum D, and noise is generated from the grounded portion G of the tire T.

As a device for measuring the sound pressure of noise generated from the ground contact portion G of the tire T, one movable mobile microphone 17 and one reference microphone 18 having a fixed position are provided. The measurement data of these microphones 17 and 18 are collected by the acoustic measuring device 13 and sent to the computer 14.

As the mobile microphone 17, a microphone having a small measuring portion at the tip is used. For example, the mobile microphone 17 is a probe microphone having a tip measuring portion having a diameter of, for example, 0.8 mm to 1.2 mm, or a 1/2, 1/4 or 1/8 inch microphone (that is, a tip measuring portion having a diameter of 1 /). 2, 1/4 or 1/8 inch microphone), or MEMS (Micro-Electrical-Mechanical Systems) microphone.

The moving microphone 17 is arranged so that the measuring portion at the tip thereof approaches the ground contact portion G of the tire T with respect to the drum D. The position of the measuring portion at the tip of the moving microphone 17 is preferably a position 25 mm to 100 mm away from the ground contact portion G of the tire T in the tangential direction of the tire T in the ground contact portion G (left-right direction in FIG. 1).

The mobile microphone 17 is located in front of or behind the tire T. A more preferred location for the mobile microphone 17 is a location below the tire T in front of or behind the tire T as shown in FIG. 1 (in other words, in front of or behind the tire T and with the tread surface T1 of the tire T). A place sandwiched between the outer peripheral surface D1 of the drum D).

The mobile microphone 17 is held by a holding unit (not shown) of the movement control device 19, and is moved by the control of the movement control device 19. The movement control device 19 is, for example, a robot. The movement control device 19 is connected to the computer 14 and controls the movement of the movement microphone 17 based on an instruction from the computer 14.

The measuring unit at the tip of the moving microphone 17 moves on a plane having a predetermined area. This plane is the sound pressure measuring surface 20 by the moving microphone 17 (see FIG. 2). The measurement surface 20 is, for example, a plane perpendicular to the traveling direction of noise generated from the ground contact portion G of the tire T, and when the moving microphone 17 is arranged in front of or behind the tire T, the measurement surface 20 is in the front-rear direction of the tire T. It is a plane perpendicular to.

FIG. 4 shows an enlarged measurement surface 20 by the mobile microphone 17. In FIG. 4, the movable path of the moving microphone 17 is indicated by a broken straight line, and the stop position is indicated by a solid line circle. The movable path draws a grid (preferably a grid forming a square as shown in FIG. 4), and the stop positions are periodically arranged vertically and horizontally. There are multiple stop positions in both the vertical and horizontal directions.

The mobile microphone 17 stops at all the stop positions shown in FIG. 4, but the route of movement for that purpose is not limited. As an example, as shown by the arrow in FIG. 4, the mobile microphone 17 moves the movement path of the top row to the right, the movement path of the second row from the top to the left, and the third from the top. Moves the movement path of the column to the right, moves the movement path of the fourth column from the top to the left, and stops at all stop positions during those movements.

The mobile microphone 17 measures the sound pressure while it is stopped at each stop position. That is, the stop position indicated by the solid circle in FIG. 4 is also the sound pressure measurement position. The rectangular portion surrounded by the outermost measurement position and the movable path in FIG. 4 is defined as the measurement surface 20.

The distance L between the vertically and horizontally adjacent measurement positions (that is, the stop position of the moving microphone 17) is preferably 1 mm to 10 mm, and more preferably 4 mm to 5 mm. The movement path and stop position of the moving microphone 17 as described above are preset in the sound source search device 10.

The position where the reference microphone 18 is fixed is not limited, but is, for example, the position at the center of the measurement surface 20 in the vertical direction. Further, the position of the reference microphone 18 in the left-right direction is not limited, but is, for example, within the range of the measurement surface 20 or within the range of the interval L outward from either the left or right end of the measurement surface 20 as shown in FIG. The position.

Various microphones can be applied as the reference microphone 18, but for example, a 1/2, 1/4 or 1/8 inch microphone is used.

The reference signal device 11 is, for example, a rotary encoder provided on the rotation axis S of the tire T as shown in FIG. When the tire T and its rotation axis S rotate, a pulse signal corresponding to the rotation angle of the rotation axis S is generated from this rotary encoder and sent to the computer 14. For example, a pulse signal is generated once for each rotation of the tire T and its rotation axis S, that is, 360 °.

This pulse signal is used as a reference signal for starting and ending the sound pressure measurement by the mobile microphone 17. Therefore, the relationship between the start of the measurement by the mobile microphone 17 and the pulse signal and the relationship between the end of the measurement by the mobile microphone 17 and the pulse signal are preset. For example, the pulse signal of the predetermined time (for example, the first time) after the mobile microphone 17 moves to the new measurement position is set as the reference signal for starting the measurement, and another predetermined time after the mobile microphone 17 moves to the new measurement position. The pulse signal (for example, the second or third time) is set as the reference signal for the end of measurement.

Since such a relationship is set, the mobile microphone 17 is operated from the time when the reference signal (pulse signal) at the start of measurement is emitted until the reference signal (pulse signal) at the end of measurement is emitted at each measurement position. The measurement will be performed. Therefore, the sound pressure can be measured at all the measurement positions during the same rotation speed of the tire T, and the measurement conditions by the moving microphone 17 at each measurement position can be matched.

The acoustic measuring device 13 collects the measurement data by the mobile microphone 17 and the measurement data by the reference microphone 18 and sends them to the computer 14. In the acoustic measuring device 13, the measurement data at each measurement position by the mobile microphone 17 and the measurement data measured by the reference microphone 18 at the same time as the measurement at each measurement position by the mobile microphone 17 are associated with each other. Then, the associated data is sent to the computer 14.

The computer 14 has a processing device and a storage device, and the processing device reads and executes a program stored in the storage device, so that the sound pressure data acquisition unit 31, the device control unit 32, and the volume velocity distribution are created. It functions as a device having a unit 33 and an acoustic analysis unit 40.

The device control unit 32 controls the movement control device 19 and the drum control device 12.

Further, the sound pressure data acquisition unit 31 acquires the measurement data at each measurement position by the mobile microphone 17 and the measurement data by the reference microphone 18 associated with the measurement data from the acoustic measurement device 13.

Further, the acoustic analysis unit 40 performs acoustic analysis using a model that reproduces the above acoustic test. The acoustic analysis unit 40 is a numerical analysis method using a model having nodes divided into elements, specifically, from a sound source point set in the model to a measurement point set in the model by finite element analysis or boundary element analysis. Analyze sound transmission.

As shown in FIG. 3, the acoustic analysis unit 40 includes a grounding analysis unit 41, an acoustic analysis model acquisition unit 42, a sound source setting unit 43, a measurement point setting unit 44, and a frequency response function calculation unit 45.

The ground contact analysis unit 41 uses the above-mentioned finite element model for the tire T and the drum D to obtain the shape of the ground contact surface and the deformed shape of the tire T when the tire T is pressed against the drum D.

The acoustic analysis model acquisition unit 42 acquires a model for acoustic analysis of the tire T and the drum D (for example, a finite element model when performing finite element analysis). Further, the sound source setting unit 43 sets a plurality of sound source points in the acoustic analysis at positions corresponding to the vicinity of the ground contact portion G of the tire T. Further, the measurement point setting unit 44 sets a plurality of measurement points in the acoustic analysis at positions corresponding to the measurement positions of the mobile microphone 17 in the above acoustic test.

The frequency response function calculation unit 45 uses the model acquired by the acoustic analysis model acquisition unit 42 to transmit sound from the sound source point set by the sound source setting unit 43 to the measurement point set by the measurement point setting unit 44. And calculate the frequency response function.

The volume velocity distribution creating unit 33 performs the above acoustic test based on the measurement data on the measurement surface 20 acquired by the sound pressure data acquisition unit 31 and the frequency response function calculated by the frequency response function calculation unit 45 of the acoustic analysis unit 40. The distribution of the sound at the position corresponding to the above sound source point at the time of, and the distribution of the volume velocity in the present embodiment are created.

The input device 15 is a keyboard or the like for a person to input to the computer 14, and the output device 16 is a display or the like that outputs the calculation result of the computer 14.

2. 2. Sound source exploration method Figure 5 shows the flow of the sound source exploration method of this embodiment. First, an acoustic test is performed in which the tire T is rolled to measure noise (S1).

In the acoustic test, first, as shown in FIG. 1, the tire T is arranged so as to touch the drum D. Next, the rotation of the drum D starts, and the rotation of the tire T in contact with the drum D starts. When the rotation of the tire T starts, noise starts to be generated. Further, a pulse signal as a reference signal is generated according to the rotation angle of the tire T and the rotation axis S.

Next, the sound pressure is measured by the microphones 17 and 18. The measurement of sound pressure will be described with reference to FIG.

First, the moving microphone 17 moves to the first measurement position (S1-1) and stands by at that measurement position (S1-2). Then, when the reference signal for starting measurement is emitted during standby (YES in S1-3), the mobile microphone 17 starts measuring the sound pressure (S1-4). Next, when the reference signal for the end of measurement is emitted during the measurement of sound pressure (YES in S1-5), the mobile microphone 17 ends the measurement of sound pressure (S1-6). As a result, the mobile microphone 17 performs the measurement from the time when the reference signal for starting the measurement is emitted until the reference signal for the end of the measurement is emitted.

After that, if the measurement at all the measurement positions is not completed (NO in S1-7), the mobile microphone 17 moves to the next measurement position (S1-1), and the steps from S1-2 to S1-6 are performed. Will be carried out again. If the measurement at all the measurement positions is completed (YES in S1-7), the sound pressure measurement is completed.

On the other hand, the sound pressure measurement by the reference microphone 18 may be performed at least in synchronization with the sound pressure measurement by the mobile microphone 17. Therefore, the reference microphone 18 may continue to measure the sound pressure from the start of the measurement at the first measurement position by the mobile microphone 17 to the end of the measurement at the last measurement position. Further, each time the mobile microphone 17 starts or stops the measurement based on the reference signal, the reference microphone 18 may also start or stop the measurement.

Since the measurement by the mobile microphone 17 and the measurement by the reference microphone 18 are performed in synchronization in this way, the measurement data at each measurement position by the mobile microphone 17 and the measurement data by the corresponding reference microphone 18 are linked. Will be done. That is, the measurement data at a certain measurement position by the mobile microphone 17 and the measurement data by the reference microphone 18 when the mobile microphone 17 is measuring at the measurement position are associated with each other.

Since the sound pressure is measured at each measurement position over a predetermined time, the measurement data at each measurement position is time series data.

After the sound pressure measurement is completed in this way, acoustic analysis is then performed (S2 in FIG. 5). The acoustic analysis will be described with reference to FIG.

First, the ground contact analysis unit 41 acquires a finite element model of the tire T (hereinafter referred to as “tire FE model”) and a finite element model of the drum D (hereinafter referred to as “drum FE model”) (S2-1). .. These finite element models are created from the 3D CAD model of the tire T used in the acoustic test and the 3D CAD model of the drum D used in the acoustic test. These finite element models may be stored in advance in the storage device of the computer 14, may be acquired by input from the input device 15, or may be acquired via a network (not shown) or the like. .. In the finite element model, the physical property values of the actual tire T and the drum D and the conditions necessary for the finite element analysis are set.

Next, the grounding analysis unit 41 performs grounding analysis (S2-2). Specifically, the ground contact analysis unit 41 brings the tire FE model into contact with the drum FE model, applies the same load to the tire FE model as in the acoustic test, and performs a calculation to deform the tire FE model. Then, the shape of the deformed tire FE model, the shape of the contact patch between the tire FE model and the drum FE model, and the contact area are acquired.

Next, the acoustic analysis model acquisition unit 42 refers to a model for acoustic analysis of the tire T (hereinafter referred to as "tire model for acoustic analysis") and a model for acoustic analysis of drum D (hereinafter referred to as "drum model for acoustic analysis"). ) Is acquired (S2-3). The drum model for acoustic analysis is a kind of road surface model that models the road surface that the tire T contacts.

These models for acoustic analysis are models that are divided into elements and have nodes, and are capable of numerical analysis such as finite element analysis and boundary element analysis. These models for numerical analysis are created from a three-dimensional CAD model. These numerical analysis models may be stored in advance in the storage device of the computer 14, may be acquired by input from the input device 15, or may be acquired via a network (not shown) or the like. good.

The tire model for acoustic analysis is a three-dimensional model of the tire T used in the acoustic test, and is a model having the same deformed shape as the deformed tire FE model acquired by ground contact analysis. In the tire model for acoustic analysis, a plurality of main grooves 22 extending in the tire circumferential direction and a land portion 23 partitioned by the main grooves 22 are formed (see FIGS. 8 and 9). The drum model for acoustic analysis is a three-dimensional model of the drum D used in the acoustic test.

The tire model for acoustic analysis is arranged in a posture pressed against the drum model for acoustic analysis. The shape and contact area of the ground contact surface between the tire model for acoustic analysis and the drum model for acoustic analysis are the same as the shape and contact area of the ground contact surface acquired in the ground contact analysis.

Further, the mesh size of the model for acoustic analysis is a size that can reproduce the deformed shape of the tire T and the ground contact shape between the tire T and the drum D.

Necessary boundary conditions are set for the tire model for acoustic analysis and the drum model for acoustic analysis. For example, a tire model for acoustic analysis and a drum model for acoustic analysis are set as a complete reflector that does not absorb sound but reflects 100%. Further, the tire model for acoustic analysis and the drum model for acoustic analysis are set as rigid body models that do not deform.

When the acoustic analysis is performed by the finite element analysis, the tire FE model and the drum FE model used in the ground contact analysis may be used as they are as the acoustic analysis model.

Further, the acoustic analysis model acquisition unit 42 divides the acoustic space in which the tire model for acoustic analysis and the drum model for acoustic analysis do not exist into elements and provides nodes (S2-4). The mesh size of the acoustic space is set to 1/6 or less of the wavelength of the upper limit of the frequency to be evaluated by acoustic analysis. For example, when the upper limit of the frequency is set to 2000 Hz, the wavelength is 340 (sound velocity) /2000 = 0.17 m when the frequency is 2000 Hz, so the mesh size is 0.17 / 6 = 0.028 m or less. ..

Next, the sound source setting unit 43 sets a plurality of sound source points in the vicinity of the ground contact portion G between the tire model for acoustic analysis and the drum model for acoustic analysis (S2-5). In the acoustic test of the present embodiment, the sound pressure is measured by the microphones 17 and 18 in the front-rear direction (traveling direction and the opposite direction) of the tire T. In this case, it can be assumed that the noise source is near the ground contact end (the end of the ground contact surface of the tire T and the drum D) on the measurement position side by the microphones 17 and 18 in the front-rear direction of the tire T. Therefore, in the acoustic analysis, the sound source setting unit 43 sets the sound source point near one of the ground contact ends in the front-rear direction of the tire model for acoustic analysis. The setting of the sound source point to the model by the sound source setting unit 43 is performed via the operation from the input device 15.

The set sound source points are shown by black dots in FIGS. 8 and 9. Although not shown, the tire model t for acoustic analysis, the drum model d for acoustic analysis, and the acoustic space in FIGS. 8 and 9 are divided into elements and nodes are set.

The sound source point is an input point of volume velocity (m ³ / sec) in acoustic analysis. The frequency of fluctuations in the volume velocity of the sound source point can be changed.

One or more sound source points are set for one land portion 23, and one or more points are set for one main groove 22. Further, the sound source points are set for all the land portions 23 and all the main grooves 22.

The sound source point set for the land portion 23 is set to the node closest to the grounding end of the land portion 23 among the nodes in the acoustic space. It is preferable that the plurality of sound source points set for the plurality of land portions 23 all have the same distance in the front-rear direction (the traveling direction of the tire T and the opposite direction) from the ground contact end. Further, the plurality of sound source points set for the plurality of land portions 23 are all heights from the outer peripheral surface (tread surface) of the tire model t for acoustic analysis (distance in the direction perpendicular to the tread surface). Is preferably the same.

Further, as shown in FIGS. 8 and 9, the sound source point set for the main groove 22 is the opening of the main groove 22 at the position of the ground contact end of the tire model t for acoustic analysis among the nodes of the acoustic space. Set on the edge. Here, the opening end of the main groove 22 is the opening of one hollow tube 24 (see FIG. 9) formed by the outer peripheral surface of the acoustic analysis drum model d and the main groove 22 of the acoustic analysis tire model t. It's the edge. The sound source point is preferably set at the center of the open end.

Next, the measurement point setting unit 44 sets the measurement point of the sound pressure in the acoustic analysis (S2-6). The measurement points are set to the same positions as all the measurement positions by the moving microphone 17 at the time of the acoustic test. Although not shown, the measurement point is set in the upper part of FIG. The setting of the measurement point to the model by the measurement point setting unit 44 is performed via the operation from the input device 15.

Next, the frequency response function calculation unit 45 executes acoustic analysis by a well-known method (S2-7). In the acoustic analysis, the volume velocity (m ³ / sec) is input to a plurality of sound source points set by the sound source setting unit 43, and the sound pressure (Pa) at the plurality of measurement points set by the measurement point setting unit 44 is calculated. It is calculated. The frequency of the fluctuation of the sound pressure at the measurement point obtained by calculation is the same as the frequency of the fluctuation of the volume velocity at the sound source point.

Volume velocities at n sound source points are q ₁ , q ₂ , ... q _n (m ³ / sec), and sound pressures at _m measurement points are p ₁ , p ₂ , ... pm ( If Pa), the following relationship can be obtained by acoustic analysis.

ここで、

here,

は、ｎ個の音源点からｍ個の測定点への周波数応答関数である。周波数応答関数Ｈにおいて、ｈ_ｍｎはｎ番目の音源点からｍ番目の測定点への伝達を表す。このように、音響解析の結果として、周波数応答関数Ｈが求まる（Ｓ２－８）。

Is a frequency response function from n sound source points to m measurement points. In the frequency response function H, h _mn represents the transfer from the nth sound source point to the mth measurement point. As described above, the frequency response function H can be obtained as a result of the acoustic analysis (S2-8).

The frequency response function H is obtained for each frequency of the fluctuation of the volume velocity at the sound source point. Therefore, the frequency response function H can be obtained for each frequency at predetermined frequencies from the lower limit value to the upper limit value of the frequency to be evaluated. When the frequency response function H is obtained, the acoustic analysis ends.

Next, the volume velocity distribution creation unit 33 is based on the measurement data on the measurement surface 20 acquired by the sound pressure data acquisition unit 31 and the frequency response function H obtained by the frequency response function calculation unit 45 of the acoustic analysis unit 40. , The volume velocity distribution in the vicinity of the ground contact portion G of the tire T at the time of the above acoustic test is created (S3).

Specifically, first, time-series data of the sound pressure at the m measurement points measured at the time of the acoustic test (in the case of the acoustic test, the sound pressure is measured at each measurement point over a predetermined time, so that the sound pressure is measured over a predetermined time. (Acquisition of time-series data of sound pressure) is performed by Fourier conversion, and data of sound pressures P ₁ , P ₂ , ... P _m (Pa) for each frequency are acquired. Next, for each frequency, the following are based on the sound pressures P ₁ , P ₂ , ... P _m (Pa) and the inverse function H ^-1 of the frequency response function H obtained by the frequency response function calculation unit 45. From the equation, the volume velocities Q ₁ , Q ₂ , ... Q _n (m ³ / sec) at n sound source points are calculated.

ここで、

here,

は、周波数応答関数Ｈの逆関数である。なお、周波数応答関数Ｈは周波数応答関数算出部４５が求めたものである。また、この計算において、音圧Ｐ_１、Ｐ_２、・・・Ｐ_ｍ（Ｐａ）と同じ周波数についての周波数応答関数Ｈが使用される。また、体積速度Ｑ_１、Ｑ_２、・・・Ｑ_ｎ（ｍ^３／秒）の周波数は音圧Ｐ_１、Ｐ_２、・・・Ｐ_ｍ（Ｐａ）の周波数と同じである。

Is the inverse function of the frequency response function H. The frequency response function H is obtained by the frequency response function calculation unit 45. Further, in this calculation, the frequency response function H for the same frequency as the sound pressures P ₁ , P ₂ , ... P _m (Pa) is used. Further, the frequencies of the volume velocities Q ₁ , Q ₂ , ... Q _n (m ³ / sec) are the same as the frequencies of the sound pressures P ₁ , P ₂ , ... P _m (Pa).

The calculation according to the equation 3 may be performed for each frequency at predetermined frequencies from the lower limit value to the upper limit value of the frequency to be evaluated. Further, the calculation by Equation 3 may be performed only for the specific frequency of interest.

The volume velocities Q ₁ , Q ₂ , ... Q _n obtained by the equation 3 can be regarded as the volume velocities of the sound generated at the positions of the respective sound source points at the time of the acoustic test. In this way, the distribution of the volume velocity at the positions of the plurality of sound source points can be obtained for each frequency. Then, the sound source point having a large volume velocity is identified as the source of noise at that frequency (S4). The noise source may be specified by a person or by the computer 14 based on the distribution of the volume velocity.

FIG. 10 illustrates the distribution of volume velocities Q ₁ , Q ₂ , ... Q _n at a certain frequency obtained by Equation 3. The black circle is the sound source point, and the larger the circle, the higher the volume velocity. Since the circles are large in the shoulder land on both sides in the tire axial direction, it can be seen that the sound source at this frequency is the shoulder land.

Based on the specific result of the noise source, the tread pattern can be redesigned to reduce the noise generated by the tire.

3. 3. Effect of Embodiment In this embodiment, a drum model for acoustic analysis, which is a road surface model, a tire model for acoustic analysis that touches the drum model for acoustic analysis, and a plurality of sounds generated when the tire model for acoustic analysis rolls. The sound source point of the above and a plurality of measurement points for measuring the above sound are set and acoustic analysis is performed to obtain the frequency response function H of the sound from the sound source point to the measurement point. Further, an acoustic test is performed in which the sound of the actual rolling of the tire T is actually measured at the position of the measurement point, and a plurality of sounds are measured based on the sound measured at the position of the measurement point and the frequency response function H in the acoustic test. Find the distribution of sound (volume velocity) at the sound source point.

In this way, since acoustic analysis is performed using the acoustic analysis drum model and the acoustic analysis tire model, the frequency response function from the sound source point to the measurement point in the form affected by the sound reflection in these models. H can be obtained. Further, the measurement data at the measurement points in the acoustic test is the data affected by the sound reflected by the tire T and the drum D. Since the distribution of the sound (volume velocity) at a plurality of sound source points is obtained from the measurement data and the frequency response function H obtained by acoustic analysis, the obtained distribution reflects the reflection of the sound on the tire T and the drum D. The sound is high and the accuracy is high. Since the sound source of the noise generated from the tire is specified based on the obtained distribution, the accuracy of specifying the sound source is good.

Further, since one or more sound source points in the acoustic analysis are set for each of the main groove 22 and the land portion 23 of the tire model for acoustic analysis, the noise generated from the main groove 22 and the noise generated from the land portion 23 are taken into consideration. Can be used for acoustic analysis.

Further, the sound source point set for the land portion 23 is set at the node closest to the ground contact end of the land portion 23 among the nodes in the acoustic space. Therefore, the acoustic analysis can be performed by assuming that the noise is generated from the land portion 23. Even so, acoustic analysis can be performed with the setting that the sound source point is not in the object but in the acoustic space, so there is no calculation cost.

Here, the plurality of sound source points set for the land portion 23 have the same distance from the ground contact end of the land portion 23 in the front-rear direction of the tire, and the height from the outer peripheral surface of the tire model for acoustic analysis is also the same. Since they are the same, the volume velocities from all the sound source points are treated equally and the acoustic analysis is performed, and the accuracy of the analysis result is improved.

Further, since the sound source point is set at the open end of one hollow tube 24 formed by the outer peripheral surface of the drum model for acoustic analysis and the main groove 22 of the tire model for acoustic analysis, resonance in the tube is assumed. Can perform acoustic analysis.

4. Example of change a. Change example 1
A flat belt type tire tester may be used instead of the drum D as a device for rotating the tire T at the time of an acoustic test. In the flat belt type tire testing machine, since the portion in contact with the tire T is the flat portion of the rotating belt, it is possible to specify the sound source of noise when the tire T rolls on the flat surface.

The surface of the rotating belt is smooth, and it is preferable that the height difference between the convex portion and the concave portion adjacent to the convex portion is 1 mm or less even when a large number of minute irregularities are present.

When a flat belt type tire tester is used during acoustic testing, the rotating belt model is used as the road surface model in ground contact analysis and acoustic analysis.

stomach. Change example 2
The tire model for acoustic analysis may be set to absorb sound to some extent, instead of being a perfect reflector as in the above embodiment. Such a setting is realized by setting a sound absorption coefficient larger than 0% and smaller than 100% on the surface of the tire model for acoustic analysis as a boundary condition. As the sound absorption coefficient, it is preferable to use the sound absorption coefficient of the rubber on the surface of the tire T used in the acoustic test.

By setting a predetermined sound absorption coefficient to the tire model for acoustic analysis in this way, the acoustic analysis reproduces the actual acoustic test more accurately, and the frequency response function calculated by the acoustic analysis is the actual acoustic test. It becomes closer to the frequency response function of the sound in, and the identification of the sound source becomes more accurate.

Even when a predetermined sound absorption coefficient is set for the tire model for acoustic analysis, the drum model for acoustic analysis may be set as a complete reflector. Since the surface of the actual drum D has high sound reflectance, even if the drum model for acoustic analysis is set as a perfect reflector, the specific accuracy of the sound source is not significantly affected.

hare. Change example 3
In this modification, the rotation speed of the tire T is used instead of the pulse signal of the above embodiment as the reference signal that serves as a reference for the start and end of the measurement by the mobile microphone 17. Therefore, as the reference signal device 11, a rotation speedometer for measuring the rotation speed of the tire T is provided.

Then, the first rotation speed and the second rotation speed, which are two different rotation speeds of the tire T, are preset as reference signals. Then, at each measurement position, the moving microphone 17 measures from the time when the rotation speed of the tire T is the first rotation speed to the time when the rotation speed is the second rotation speed.

As a specific example, the first rotation speed is set as the reference signal at the start of measurement, and the second rotation speed slower than the first rotation speed is set as the reference signal at the end of measurement. Then, the tire T is rotated on the drum D at a speed higher than the first rotation speed, and the power of the motor for rotating the drum D is turned off in that state. Then, the rotation speeds of the drum D and the tire T gradually decrease. Then, when the rotation speed of the tire T drops to the first rotation speed, the measurement by the moving microphone 17 starts, and when the rotation speed of the tire T further drops to the second rotation speed, the measurement by the moving microphone 17 ends. Thereby, it is possible to specify the sound source of the noise when the rotation speed of the tire T is the average speed of the first rotation speed and the second rotation speed in the state where the sound of the motor is muted.

As another specific example, the first rotation speed is set as the reference signal at the start of measurement, and the second rotation speed faster than the first rotation speed is set as the reference signal at the end of measurement. Then, the rotation speed of the tire T was gradually increased, and when the rotation speed of the tire T increased to the first rotation speed, the measurement by the moving microphone 17 was started, and the rotation speed of the tire T further increased to the second rotation speed. Sometimes the measurement with the mobile microphone 17 ends. Thereby, it is possible to specify the sound source of noise when the rotation speed of the tire T is accelerated from the first rotation speed to the second rotation speed.

In this modification, the rotation speed of the drum D may be used as the reference signal instead of the rotation speed of the tire T.

workman. Change example 4
In this modification, the axial force acting on the rotation axis S of the tire T is used instead of the pulse signal of the above embodiment as the reference signal that serves as a reference for the start and end of the measurement by the mobile microphone 17. Therefore, as the reference signal device 11, an axial force meter for measuring the axial force acting on the rotating shaft S of the tire T is provided.

Then, an axial force of a predetermined magnitude is preset as a reference signal. Then, at each measurement position, the moving microphone 17 measures while the measured axial force is equal to or greater than the predetermined magnitude. That is, the measurement of the moving microphone 17 is started when the axial force gradually increases and exceeds the predetermined magnitude, and then when the axial force gradually decreases and exceeds the predetermined magnitude, the moving microphone is moved. The measurement of 17 is completed. Since the magnitude of the axial force corresponds to the controlling driving force, it is possible to specify the sound source of noise when a braking force or driving force of a predetermined magnitude or more is generated by this method.

E. Change example 5
In this modification, instead of the mobile microphone 17, a microphone array 111 in which microphones are fixed at a plurality of measurement positions is used.

FIG. 11 shows a sound source exploration device 110 used to carry out the sound source exploration method of this modified example. The difference between the sound source exploration device 110 of this modification and the sound source exploration device 10 of the above-described embodiment is that, as a device for measuring sound pressure, a plurality of measurement microphones 112 and one reference are used instead of the mobile microphone 17 and the reference microphone 18. The point is that the microphone 114 is provided. The plurality of measurement microphones 112 and reference microphones 114 are connected to the sound pressure data acquisition unit 31.

As shown in FIG. 12, the microphone array 111 is composed of a plurality of measurement microphones 112 (indicated by a solid single circle in FIG. 12) and one reference microphone 114 (indicated by a solid double circle in FIG. 12). Has been done. In the microphone array 111, the microphones 112 and 114 are arranged in a grid pattern (preferably in a grid pattern forming a square as shown in FIG. 12), and are periodically arranged vertically and horizontally. The positions of the microphones 112 and 114 are the measurement positions for measuring the sound pressure. It is preferable that there are two or more measurement positions in the vertical direction and four or more in the horizontal direction. The distance L between the vertically and horizontally adjacent measurement positions is, for example, 15 mm to 35 mm.

Examples of the measuring microphone 112 and the reference microphone 114 include a probe microphone having a measuring portion having a diameter of 0.8 mm to 1.2 mm at the tip, a 1/2, 1/4 or 1/8 inch microphone, or a MEMS (Micro-Electrical-). Mechanical Systems) Microphones, etc. can be used.

The outermost surface of the microphone array 111 surrounded by the measurement microphone 112 is the sound pressure measurement surface 130. The measurement surface 130 is arranged, for example, perpendicular to the traveling direction of the noise generated from the ground contact portion G of the tire T.

As shown in FIG. 13, the microphone array 111 is arranged so as to approach the ground contact portion G of the tire T with respect to the drum D. The sound pressure measurement position by the microphone array 111 (that is, the position of the measurement unit at the tip of each of the microphones 112 and 114 constituting the microphone array 111) is in the tangential direction of the tire T at the ground contact portion G (left-right direction in FIG. 13). It is preferable that the position is 25 mm to 200 mm away from the ground contact portion G of the tire T.

The microphone array 111 is arranged in front of or behind the tire T. A more preferred location for the microphone array 111 is a location below the tire T in front of or behind the tire T as shown in FIG. 13 (in other words, in front of or behind the tire T and with the tread surface T1 of the tire T). A place sandwiched between the outer peripheral surface D1 of the drum D). It is preferable that the microphone array 111 is arranged so that the measurement surface 130 is perpendicular to the front-rear direction of the tire T.

In such a microphone array 111, all the measurement microphones 112 and the reference microphone 114 simultaneously measure the sound pressure. Therefore, the measurement of the sound pressure in the acoustic test can be completed in a short time. The measured sound pressure data is taken into the sound pressure data acquisition unit 31.

After that, as in the above embodiment, the volume velocity distribution creating unit 33 calculates the measurement data on the measurement surface 130 acquired by the sound pressure data acquisition unit 31, and the frequency calculated by the frequency response function calculation unit 45 of the acoustic analysis unit 40. Based on the response function, the volume velocity distribution in the vicinity of the ground contact portion G of the tire T at the time of the acoustic test is created.

D ... Drum, d ... Drum model for acoustic analysis, D1 ... Outer surface, G ... Grounding part, S ... Rotating axis, T ... Tire, t ... Tire model for acoustic analysis, T1 ... Tread surface, 10 ... Sound source exploration device, 11 ... Reference signal device, 12 ... Drum control device, 13 ... Sound measurement device, 14 ... Computer, 15 ... Input device, 16 ... Output device, 17 ... Mobile microphone, 18 ... Reference microphone, 19 ... Mobile control device, 20 ... Measurement surface, 22 ... Main groove, 23 ... Land part, 24 ... Tube, 31 ... Sound pressure data acquisition unit, 32 ... Device control unit, 33 ... Volume velocity distribution creation unit, 40 ... Acoustic analysis unit, 41 ... Ground analysis unit , 42 ... Sound analysis model acquisition unit, 43 ... Sound source setting unit, 44 ... Measurement point setting unit, 45 ... Frequency response function calculation unit, 110 ... Sound source search device, 111 ... Microphone array, 112 ... Measurement microphone, 114 ... Reference microphone , 130 ... Measurement surface

Claims (5)

Acoustic analysis is performed by setting a road surface model, a tire model that touches the road surface model, a plurality of sound source points of the sound generated when the tire model rolls, and a plurality of measurement points of the sound, and the sound source. The step of finding the frequency response function of the sound from the point to the measurement point, and
The step of actually measuring the sound when the tire rolls at the position of the measurement point, and
A step of obtaining a distribution of sounds at a plurality of sound source points based on the sound actually measured at the position of the measurement point and the frequency response function, and
Sound source exploration methods, including. The tire model has a main groove extending in the tire circumferential direction and a land portion partitioned by the main groove.
The sound source search method according to claim 1, wherein one or more sound source points in the acoustic analysis are set for each of the main groove and the land portion. The acoustic analysis is performed by providing a plurality of nodes in a space including the road surface model, the tire model, the sound source point, and the measurement point.
The sound source search method according to claim 2, wherein the sound source point set for the land portion is provided at a node closest to the contact end of the tire model with respect to the road surface model. The third aspect of claim 3, wherein the plurality of sound source points set with respect to the land portion have the same distance from the ground contact end in the front-rear direction of the tire and the same height from the outer peripheral surface of the tire model. The described sound source exploration method. In the ground contact portion of the tire model with respect to the road surface model, a pipe is formed by the road surface model and the main groove.
The sound source search method according to claim 2, wherein the sound source point set for the main groove is provided at the open end of the tube.

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