Developing Evaluation Model of Tire Pattern Impact Noise

Transcription

1 Developing Evaluation Model of Tire Pattern Impact Noise Nobutaka TSUJIUCHI 1 ; Akihito ITO 2 ; Atsushi MASUDA 3 ; Hamiyu SEKI 4 ; Hisashi TAKAHASHI Doshisha University, Japan 5 Toyo Tire & Rubber Co., Ltd., Japan ABSTRACT Demand for noise-reduced tires has been increasing globally due to the European Union's tire noise regulation ECE R117. Therefore, it is crucial for tire manufacturers to comply and to improve the problem of tire noise. Tire noise consists of several noise sources. This paper focuses on tread impact noise because the noise generating mechanism of each tread pattern when contacting the road is unclear. It is important to clarify the mechanism of tread pattern and road impact noise in order to develop a noise-reduced tire. Thus, this paper focused on impact noise and aimed to construct an evaluation model. We made a tire with only one tread block on its circumference in order to examine the characteristics of impact noise. According to our experiment, there is a proportional relationship between sound pressure and acceleration of the tire tread surface. We also constructed a model from the simplified phenomenon of the impact between the tread block and the road to identify the maximum acceleration of the tire tread surface. Then, we compared the calculated values and the measured values. Our results showed that the calculated values qualitatively coincided with the measured values, therefore confirming the validity of our model. Keywords: Vehicle noise, Tire, Tire-road noise, Vibration, Impact noise, Model analysis I-INCE Classification of Subjects Number(s): INTRODUCTION Automobile ownership is currently on the rise. The automobile has become a necessity of life. However, this accelerating motorization is causing many problems, including health hazards, environmental contamination, and noise pollution, all of which are important. The World Health Organization (WHO) has reported that there is a relationship between road noise and serious diseases, such as myocardial disease. Because of these recent road noise issues, automobile noise regulations will continue to tighten (1). Vehicle noise consists of several noise sources, such as the engine, cooling system, exhaust system, drive system, and tires. However, recent technology has made it possible to reduce engine noise, which is the primary vehicle noise source. Accordingly, the contribution ratio of tire noise has increased. Therefore, tire manufacturers are pressured to create a noise-reduced tire that complies with the European Union s (EU s) tire noise regulation UN/ECE R117 (2). Tire noise consists of several noise sources. This paper focuses on pattern vibration noise that occurs when the tire pattern makes contact with the road. Although pattern vibration noise has been reduced by creating a different type of pattern block on the tread surface (3), the mechanism of the noise for each pattern when it contacts the road is still unclear. Therefore, constructing an evaluation model of pattern and road impact noise is important. This paper focuses on the impact noise that occurs when each pattern makes contact with the road with the aim of constructing an evaluation model of it. Pattern vibration noise is analyzed by splitting the impact noise and restoration noise. To do this, two types of experimental tires are created. The first is the short tread block tire, which has only one tread block on the tire circumference. This tire is used to examine how noise generates from the short tread block. The second is the long tread block 1 ntsujiuc@mail.doshisha.ac.jp 2 aito@mail.doshisha.ac.jp 3 duo0546@mail4.doshisha.ac.jp 4 duq0557@mail4.doshisha.ac.jp 5 his-taka@toyo-rubber.co.jp 2969

2 tire, whose length is halfway around the tire circumference. This tire is made to separate the impact vibration noise and restoration vibration noise. An accelerometer is installed to each experimental tire and a drum test is conducted. According to the experiment, there is a proportional relationship between sound pressure and acceleration of the tire tread surface. Second, a model from the simplified phenomenon of the impact between the tread block and road is constructed to identify the maximum acceleration of the tire tread surface. Then, the calculated values and the measured values are compared. 2. The Tire Noise Experiment 2.1 An Outline of the Experiment Experimental Tire First of all, two different types of experimental tires, the short tread block tire and long tread block tire, were made in order to separate impact vibration noise and restoration vibration noise. The short tread block tire has only one tread block on the tire circumference. A schematic of the short tread block tire is shown in Figure 1. Generally, a tire is composed of many tread blocks on its circumference. This structure generates a pattern vibration noise from each tread block continually contacting the road. However, using a short tread block tire prevents this from happening. The long tread block tire has a long tread block halfway around the tire circumference. A schematic of the long tread block is shown in Figure 2. Installing the long tread block halfway around separates the impact vibration noise and restoration vibration noise because the length of both ends is physically separated. In addition, the main groove is filled with urethane in order to prevent air-column resonance. The short and long tread block tires were made by processing a 265/65R17 tire. The measurements of the tread block are shown in Figure 1, Figure 2, and Table 1. l w h w h Figure 1 Short tread block tire Figure 2 Long tread block tire Table 1 Size of tread block Block width (w) [mm] Block span (l) [mm] Groove width (h) [mm] Short tread block tire Long tread block tire 30 Half around Tire noise test The noise and acceleration of the short tread block tire in a semi-anechoic chamber were measured using an accelerometer and drum rolling device. The testing condition for the internal tire pressure was 200 kpa, imposing 3923 N of vertical load 2970

3 when contacting the ground, with the drum resembling a smooth road surface. A uniaxial piezoelectric accelerometer PCB 352C23 (0.2 g) was set at three different places on the edge of the block. The placement for the three accelerometers on the short tread block tire is shown in Figure 3. The placement of the three accelerometers on the long tread block tire is shown in Figure 4. The sampling frequency of the accelerometer was set to Hz. A microphones used in the experiment is PCB 377B02 (1/2 inch) microphones. The rotating direction is defined as front. The front side is labeled as Leading, vertical to the tire as Center, and back side as Trailing. The sound pressure was measured from two different distances and three different directions. The tire noise test procedure was referenced from JASO C606 and measured the sound pressure from a 1000-mm radius from the tire contact patch. At the same time, the vicinity sound pressure was measured from a 350-mm radius from the tread block contact patch. The location of the tire and microphones is shown in Figure 5. The tire s rotating velocity was changed from 20 km/h to 100 km/h at increments of 10 km/h. Thereafter, the arithmetic mean for the sound pressure data and acceleration data was calculated for each velocity. Figure 3 Placement of accelerometers on the short block tire (blue: Circumferential direction; green: Circumferential direction; red: Radial direction) Figure 4 Position of accelerometers on the long block tire (blue: Circumferential direction; green: Width direction; red: Radial direction) Leading mic Trailing Center mic Figure 5 Placement of microphone 2971

4 2.2 Results and considerations of tire noise test Comparison of radial acceleration and sound pressure of short tread tire and long tread tire Figure 6 shows the relationship between the radial acceleration and sound pressure of the short and long tread block tires at a velocity of 40 km/h. The horizontal axis shows the time and the vertical axis represents the acceleration and sound pressure. As shown in Figure 6, there are three peaks for the short tread block tire, but there are only two peaks found in the long tread block tire. This is because the long tread block separates the impact vibration noise and restoration vibration noise. Therefore, the third peak found in the short tread block tire can be considered a restoration vibration noise caused by desorption. Next, the impact behavior of the tires is divided into four parts, as shown in Figures 6 and 7. The first is the impact of the tread block end, the second is the impact with the complete ground, the third is the desorption of the tread block end, and the last is complete desorption of the tread block. According to Figure 6, the major noise source is from 1 through 2. Therefore, this paper focused on the impact of the tread block end to impact with the complete ground. Figure 6 Relationship between radial acceleration and sound pressure of short tread block tire and long tread block tire at a velocity of 40 km/h Tire Tire :Accelerometer :Accelerometer Drum Drum Impact of Tread Block End Impact to Complete Ground Tire Tire :Accelerometer :Accelerometer Drum Drum Desorption of Tread Block End Complete Desorption of Tread Block Figure 7 Four different impact behaviors of tire The relationship between sound pressure and radial acceleration The relationship between vicinity sound pressure measured from the center mic and radial acceleration at 40 km/h is shown in Figure 8(a) and Figure 8(b). The horizontal axis shows the tire angle, for which 0 degrees represents the tread block position when the block is at the bottom. The 2972

5 vertical axis shows the acceleration in Figure 8(a) and sound pressure in Figure 8(b). In Figure 8(a) and Figure 8(b), there are peaks found in both acceleration and sound pressure at around -13 degrees, indicating collision between the tread block and drum. This peak can be opined as the excited vibration and sound factor. In addition, similar characteristics were observed at another rotation velocity. To verify the relationship between sound pressure and radial acceleration, the peaks of the sound pressure and acceleration for each velocity was acquired. Figure 8(b) shows the relationship between the absolute value of the peak and velocity. The horizontal axis shows the radial acceleration and the vertical axis shows the sound pressure. According to Figure 9, there is a proportional relationship between sound pressure and radial acceleration. Acceleration waveform Sound pressure waveform (a) short-block, center-mic (b) short-block, Radial direction Figure 8 Example of sound pressure and acceleration waveform. 40 km/h Figure 9 Acceleration to radial direction vs sound pressure at moment of impact. 3. The Tire Pattern Noise 3.1 Impact noise As discussed in Section 2, there is a proportional relationship between the tread surface vibration excited by collision and impact noise. This paper refers to the experimental results to analyze the sound generating mechanism when the tread block collides with the drum. Igarashi et al. analyzed the noise generating mechanism of a collision between a ball and plate (4). First, pulsive contact force acts between the ball and plate as a result of their collision. This contact force then causes the plate to instantly deform vertically to the plate surface, generating the pulsive sound. Thereafter, the free vibration of the plate radiates into the air and pulsive noise is generated. This noise generating mechanism was adapted to the generating mechanism of the tire pattern noise in our study. The ball is deemed as the pattern block and the plate as the tread surface. That is to say, during the tire pattern collision, the first pattern block collides with the road and pulsive noise is generated due to the deformation of the tread surface in the radial direction. Then, contact force disperses to the tire structure, resulting in the structural vibration sound. 2973

6 3.2 Phenomenon analysis of tire pattern during collision Figure 10 shows the vicinity sound of the center mic. A time frequency analysis of the sound pressure shown in Figure 10 was conducted and the result indicated that approximately 200 Hz of sound was generated during collision. Thereafter, noise at low frequency ranges near the eigenfrequency of the tire structure is generated. From this, the mechanism of tread block impact noise is divided into pulsive noise and structural vibration noise. In this paper, pulsive noise is considered as impact noise and conducted phenomenon analysis and modelling. Sound Pressure [Pa] Angle[ ] Sound of Pulse Sound after Pulse Figure 10 Sound pressure waveform during impacting, 40 km/h, short-block, center-mic. 3.3 Genesis timing of impact noise Figure 10 shows that the peak of the sound pressure has a negative value. Therefore, collision of the pattern block and road compressively deforms the tire structure in the radial direction, creating the negative sound pressure. It is conceivable that the compressive deformation originates from the tread block itself or the tread surface. To specify the noise source, the genesis timing of the vicinity sound pressure and radial accelerometer placed on the tread surface were compared. The results are shown in Table 2. Table 2 shows the time of the acceleration peak, the time of the sound pressure peak, and their differences by rotation speed. The time difference of the sound speed is believed to synchronize the accelerometer and microphone. According to Table 2, the peak of acceleration generates earlier or at the same time as the sound pressure. If the collision s sound source is caused by the block deformation, then the sound will be measured before the acceleration. Therefore, deformation of the tread surface is the main source of the impact noise. Table 2 Comparison of time between acceleration peaks and sound peaks Speed [km/h] Time of Acceleration Peak [s] Time of Sound Pressure Peak [s] Time Difference [s] Model Analysis of tire pattern impact noise 4.1 Evaluation model of tire pattern impact noise It is important to develop a prediction technique for tire pattern vibration noise, one of the main sources of tire road noise, to meet the recent demand for a noise-reduced tire. As discussed in Section 3, tire pattern noise is generated when the tread surface is compressively deformed radially to the tread surface. Moreover, from Section 2.1.1, there is a proportional relationship observed between acceleration in the radial direction and sound pressure. That is to say, calculating the radial acceleration at impact can assist us in predicting the pulsive noise. In this paper, the collision phenomenon of the tread block was modeled and the radial acceleration of the tread surface were calculated. 2974

7 4.1.1 Evaluation model of simplified phenomenon To calculate the radial acceleration of collision, the tread block collision phenomenon as shown in Figure 11 was modelled. The phenomenon is simplified as the tread surface only deforms in the radial direction. Also, the tread block is treated as a rigid body because the stiffness of the tread block is much higher than the tread surface. Moreover, it is assumed that pressure acts on the tread surface in a uniform distribution to the area of the tread block and that the sidewall is an infinite elastic body with a tread surface. Each parameter is a sidewall radial spring constant k[n/m], the equivalent mass of the deformed area of the sidewall during collision is M, and the deformation of the sidewall during collision is x. Before impact Sidewall After impact x Road surface Tread block Figure 11 Simplified model of impact Calculation of radial acceleration from static model The radial acceleration from the model proposed in was calculated. The force acting between the tread block and sidewall is F = -kx. Considering the relationship between momentum change before and after the collision and the impulse acted on an equivalent mass during collision time!, if the radial deformation of the sidewall generated by the collision is x = x(t), then the relationship between the impulse and momentum change before and after the collision is *! " # -" 0 = - '" () +. (1) The deformation is! " = $" % + '" + (. (2) The radial deformation acceleration of the sidewall during collision set as a[m/s^2]. Then, the equation of motion for the sidewall is!" = $ = -&'. (3) The acceleration will be at its maximum when the deformation is at its maximum. Therefore, the maximum acceleration can be found from Equation (3) because there is a proportional relationship between the maximum acceleration and sound pressure. Substituting the M in Equation (3) gives! "#$ = - '( "#$ ) = 12$ 2%& ' + 3%& + 6+, -./. (4) 4.2 Parameter identification of model equation The unknown parameters p, q, and r, maximum deformation x max, and collision time T from Equation (2) need to be identified in order to obtain the acceleration in Equation (4). 2975

8 4.2.1 Strain distribution of sidewall during collision The strain distribution of the sidewall before and after the collision was measured to identify the unknown parameters. Using the short block tire, a rolling test at 20, 40, and 80 km/h under the same conditions specified in Section 2 were conducted. In this experiment, an image near collision was captured using a GX-1 PLUS high-speed camera from NAC Image Technology Inc. From the captured images, a digital image correlation method was used to measure the sidewall s strain distribution using the Vic-3D digital correlation system from Correlated Solutions, Inc. for image analysis. The sidewall s radial deformation was identified from the strain distribution measured from the sidewall. Figure 12 shows the strain distribution at the start of the collision and the maximum deformation at 40 km/h. The X axis is the front-back direction of the tire, the Y axis is the vertical direction of the tire, and the color map shows the strain distribution in the vertical direction. The deformation of the y axis direction was calculated from the mean value of the strain measured from the arbitrary area and the coordinates of the y axis. The considered area of deformation is the area with more than 18% of strain. The deformation of the y axis was calculated for every frame, which indicated the collision start to the maximum deformation, and regarded it as the time variation of the sidewall s radial deformation. The maximum deformation is further treated as x max and the collision start to maximum deformation as collision time T. The same process was repeated at 20, 40, and 80 km/h. (a) Beginning of impact (b) Maximum deformation Figure 12 Strain distribution during the tire pattern impact Derivation of parameters p, q, and r The least squares method was used to calculate the quadratic approximation formula from the time variation of the radial deformation, which was obtained from the strain distribution analysis, to obtain each of the parameters in Equation (2). First, the conditions are set as No deformation at moment of collision and Deformation velocity is zero at maximum deformation. Therefore,! 0 = 0 (5)! " = 0. (6) From, Equation (2) and (5)! = 0. (7) Also, from Equation (2) and (6) 2976

9 ! " = 2%" + ' = 0 (8) " = 2&'. Substituting Equations (7) and (8) for Equation (2) gives us! " = $" % -2$(". (9) Deformation Equation (8) gives us!-# $ % -2'$ = 0. (10) Considering A as p, gives us! = -$ (11) The sum of the squares of the error E(x, t) is! + # $ % -2($ = 0. (12) -! ", $ = " & + ( $ & ) -2,$ & ) &./. (13) The minimum of!(#, %) can be obtained by conducting the partial differentiation for A to make Equation (13) zero. -!"!# = 2 & '( -2*' + 2# ' ( -2*' ( = 0./0 " = - -./0 * +,- % & ' -2)& * +,- & ' -2)& '. Substituting calculated values to Equation (14) gives us A. Finally, from A, Equations (8) and (11) gives us the parameters p, q, and r. 4.3 Calculated value of acceleration from model Computation of calculated value Figure 13 (a)~(c) shows the time variation of the deformation and approximate curve for each velocity obtained from Section The approximation formulas for x 1, x 2, and x 3 are shown in the title of the figure. These coefficients were considered as unknown parameters p, q, and r. Each parameter is shown in Table 3. Table 3 Identified parameters and calculated acceleration values p q r x max T α max 20 km/h km/h km/h (14) 2977

10 Measured value Quadratic approximating curve Measured value Quadratic approximating curve 2 2 (a)20 km/h, x ( t) = t t (b)40 km/h, x ( t) = t t Measured value Quadratic approximating curve 2 (c)80 km/h, x ( t) = t t 3 + Figure 13 Fitted curves of deformation volumes Comparison and examination of calculated value and measured values Table 4 shows the calculated value of the maximum acceleration and measured value of the accelerometer placed on the tread surface when the edge of the tread block impacts the road. The value that divided the measured value by the calculated value is also shown. The results reveal that the calculated value is smaller than the measured value. This is because the proposed model only considers the simplified phenomenon of the tire s radial direction. There are, in fact, many other phenomena that should have been considered, such as centrifugal force, reaction force from the drum, and shearing force. Moreover, the fitted curve of the deformation volume shown in Figure 13 does not show the impulsive phenomenon that observed with the accelerometer. This is also why each value did not quantitatively coincide. However, the scale factor of the calculated value and measured value is equal for each velocity, and the calculated value increases when the quadratic function is the same as the measured value. This trend denotes that the calculated value qualitatively coincides with the measured value. Therefore, we can say that this model is valid for analyzing partial collision phenomena. In the future, we will develop a model that includes phenomena we did not presently consider. Table 4 Comparison between calculated values and measured values α max α mea α mea / α max 20 km/h km/h km/h

11 5. Conclusion This study focused on developing an evaluation model of tire pattern impact noise, which is important for the development of a noise-reduced tire. We conducted an experiment that focused on pattern vibration noise and measured the vibration acceleration and sound pressure during collision. We found that the radial acceleration of the tread surface and impact noise are proportional. Therefore, we developed our evaluation model of tread surface radial acceleration and compared the calculated value and measured value. In sum: 1. The pattern impact noise and impact vibration were analyzed using a short tread block tire and a long tread block tire. 2. Two kinds of sound were generated when the tread block collides with the drum, specifically, pulsive noise, which is generated when the tread surface deforms radially, and structural vibration, which is generated when the contact force disperses to the tire structure. 3. Impact noise can be predicted by predicting the radial acceleration because there is a proportional relationship between the radial acceleration of the tread surface and sound pressure. 4. The tread surface acceleration was calculated using a model that simplified the collision phenomenon. The calculated value qualitatively coincided with the measured value. Therefore, it is concluded that the developed model is valid. 5. In future study, we will develop a complete evaluation model including centrifugal force, reaction force from the drum, and shearing force. REFERENCES 1. Vercammen S,Bianciardi F,Kindt P,Desmet W,Sas P. Characterization of tyre exterior noise radiation, Proceedings of International Conference on Noise and Vibration Engineering 2014; No. 388; pp Abhishek K, P. M, Prashant V, U. D. B, Dinesh T. Comparative Study of Sound Absorption Coefficients on Different Types of Road Surfaces Using Non-Destructive Method as per ISO :2010, Physical Review & Research International 2011; 1(2):pp Nakajima Y, Method of determining a pitch arrangement of a tire. US A,1998. Available from: -bool.html&r=1&f=g&l=50&d=pall&refsrch=yes&query=pn/ Igarashi T, Goto M, Kawasaki A. Study on Impact Sound: 1st Report, Collision of Ball against Plate, Transactions of the Japan Society of Mechanical Engineers Series C 1984; Vol. 50; No. 453; pp