Parameter Conversion Between Controlled Pass-By Method And Alternative .

Appl. Sci. 2020, 10, x FOR PEER REVIEW 3 of 13 Appl. Sci. 2020, 10, 5679 3 of 13 Campillo-Davo et al. [17,18] defined the alternative close proximity trailer method (A-CPX) to evaluate the sound power level emitted by a specific tire/road combination and to extrapolate the sound pressure level obtained taxiing on thethe roadside. 10 dB (A). Campillo-Davo et al.by [17,18] defined alternative close proximity trailer method (A-CPX) The CPB method for level measuring theby maximum pressure level of aand vehicle passing by to evaluate the soundused power emitted a specificsound tire/road combination to extrapolate is simple, and uses a microphone placed on the side of the road. Its disadvantages include a long the sound pressure level obtained by taxiing on the roadside. experiment cycle and high experiment cost. The CPB method cannot obtain a stable and accurate The CPB method used for measuring the maximum sound pressure level of a vehicle passing noise spectrum. closeplaced proximity (A-CPX) the accuracy and by is simple, andThe usesalternative a microphone on the side of method the road.considers Its disadvantages include cost-effectiveness of the experiment. Its advantage is that it can exclude or ignore other noise a long experiment cycle and high experiment cost. The CPB method cannot obtain a stable and components except tire noise. Through close data proximity processing,(A-CPX) it can obtain accuratethe and stable accurate noise spectrum. The alternative methodan considers accuracy spectrum. The experiment is short,Itsand the experiment and theordependence the and cost-effectiveness of thecycle experiment. advantage is that it cost can exclude ignore otheronnoise experiment road surface form are low. If the relationship between the experiment results of these components except tire noise. Through data processing, it can obtain an accurate and stable spectrum. two methods cancycle be determined [1,7], CPB experiment can be predicted from the A-CPX The experiment is short, and the the experiment cost andresults the dependence on the experiment road noise experiment data. This would shorten the experiment cycle and reduce the cost of tire noise surface form are low. If the relationship between the experiment results of these two methods can be experiments [2]. the CPB experiment results can be predicted from the A-CPX noise experiment data. determined [1,7], previous research, we conducted CPBthe and A-CPX on five mainstream This Based would on shorten the experiment cycle and reduce cost of tire experiments noise experiments [2]. passenger car tires on the market. The correlation between the noise data of the two experimental Based on previous research, we conducted CPB and A-CPX experiments on five mainstream methods Tomarket. study the conversion between of the passengerwas car analyzed. tires on the Theparameter correlation between the noise the dataexperiment of the two results experimental two experiment methods, conducted acoustic radiationbetween propagation experiments in theofhalf-free methods was analyzed. Towe study the parameter conversion the experiment results the two field. experiment methods, we conducted acoustic radiation propagation experiments in the half-free field. 2. Real Real Vehicle Vehicle Experiment Experimental Site Site 2.1. Experimental CPB and A-CPX were conducted conducted on on aa common common cement cement road, road, Dangssang Dangssang Road, Road, Gunsan, Gunsan, Korea. Korea. thethe A-CPX method waswas a straight roadroad section at least 1.2 m1.2 away The experimental experimental track trackofofCPB CPBand and A-CPX method a straight section at least m from large objects on the side of the road. Figure 1 shows the measurement location and road surface away from large objects on the side of the road. Figure 1 shows the measurement location and road of the CPB andCPB the and A-CPX surface of the the methods. A-CPX methods. (a) Measurement location (b) Measurement road surface Figure 1. Measurement location and and road surface of the controlled pass-by (CPB) and the alternative close proximity (A-CPX) method. close proximity (A-CPX) method. 2.2. Experimental Experimental Vehicle Vehicle and and Tires Tires for 2.2. for CPB CPB and and A-CPX A-CPX Methods Methods To ensure To ensure that that the the tire/road tire/road surface surface noise noise was was not not affected affected by by the the structure structure of of the the experimental experimental vehicle, the vehicle was cleaned before the experiment to ensure that it was free of soil and vehicle, the vehicle was cleaned before the experiment to ensure that it was free ofpollutants, soil and and the sound-absorbing materials inadvertently added in theadded experimental phase were removed. pollutants, and the sound-absorbing materials inadvertently in the experimental phase were The experimental vehicle was a Korando sports (SsangYong Company, Pyeongtaekho, Korea). removed. The wheelbase of the vehicle was 3060 mm. Thesports rim width code wasCompany, 8.5J 18 and the tire specification The experimental vehicle was a Korando (SsangYong Pyeongtaekho, Korea). was 235/60R18. The parameters of the tires selected for the experiment are in the Table 1. The wheelbase of the vehicle was 3060 mm. The rim width code was 8.5J shown 18 and tire The referencewas inflation pressure of parameters the experimental was 250 kPa. specification 235/60R18. The of thetire tires selected for the experiment are shown in Table 1. The reference inflation pressure of the experimental tire was 250 kPa.

Appl. Sci. 2020, 10, 5679 4 of 13 Table 1. Parameters of experimental tires. Designation Tire Manuf. Tread Size Tire Category Labelling Noise Level a b c d e Michelin Goodyear Bridgestone Hankook Kumho LATITUDE TOUR HP EAGLE RS-A DUELER H/P SPORT Dynapro HP2/KA33 SOLUS/KL21 235/60R18 103V 235/60R18 102H 235/60R18 103W 235/60R18 103V 235/60R18 102H Snow(M S) Snow(M S) Normal Snow(M S) Snow(M S) / / 71 dB / / 2.3. Experimental Equipment In the CPB experiment, the noise measuring equipment was NL 42 (RION, Tokyo, Japan), a common sound level meter. The vehicle speed was measured using VELOCITY (Bushnell, Overland Park, KS, USA) multi-functional handheld radar speedometer. The track temperature was measured using a 561 (FLUKE, Everett, WA, USA). Wind speed was measured using an AVM-01/03 anemometer (TES, Taiwan, China). Tire inflation pressure was measured using an H.S-NO.90 needle inflator gage (HYUP SUNG PRECISION Company, Incheon, Korea). In the A-CPX experiment, vehicle speed and track temperature were measured with the same equipment as in the CPB method. Tire inflation and pressure measurements used an automatic E21 inflation and deflator (MAX, Seoul, Korea). The specific parameters of sound measurement devices are listed in Table 2. Table 2. Parameters of sound measurement devices of A-CPX method. Description Manufacturer/Modal Number Prepolarized microphone Preamplifier Data acquisition modal PCB PIEZONTRONICS/377B02 PCB PIEZONTRONICS/426E01 National instruments/NI 9234 2.4. Experimental Conditions The average tire load used in the CPB and A-CPX experiment was 55% (467.5 kg) of the reference load, which met the requirement for the experimental load of each tire being in the range of 50–90% of the reference load. The average inflation pressure of the tire was 55% (190 kPa), which was no higher than the reference inflation pressure. The background noise was less than the experimental noise, at 10 dB. The wind speed was lower than the required 5 m/s. The atmospheric temperature met the required range of 5–40 C, and the surface temperature met the required range of 5–50 C. The background noise and meteorological conditions met the experimental requirements. 2.5. Experimental Procedure Before the experiment, we closed the trunk lid, skylight, all windows, and ventilation devices for air intake and exhaust. There were no other sundries in the vehicle except for the experimental personnel and equipment. Before the series of experimental runs, the vehicle was driven for 15 min to warm up the tires. During each experiment, the driving direction of the vehicle was consistent and the experimental section was fixed to maintain the reliability of the experiment [19]. During the CPB experiment, when the front end of the vehicle reached the starting line of the experimental area, the experimental vehicle, which was equipped with the experimental tire, passed the specified experimental area at the specified experimental speed at a constant speed with the engine on. The test distance was about 50 m. Two sound level meters were placed on both sides of the track 7.5 m from the track centerline and 1.2 m above the ground. During the experiment, the sound level meter recorded the maximum sound pressure level of the A-weighted noise as a single measurement result. Experiments were conducted four times at a speed lower and higher than the reference speed of 80 km/h.

Appl. Sci. 2020, 10, 5679 5 of 13 During the A-CPX experiment, to conveniently, quickly, and safely complete the tire/road noise experiment, a xbracket forREVIEW mounting the microphone acoustic probe was installed on the spindle of Appl. Sci. 2020, 10, FOR PEER 5 of 13 the right rear wheel. The position of the microphone in the A-CPX method refers to the position of the microphone American Standard OBSIOBSI test program [20]. The acoustic wasprobe positioned the microphoneininthethe American Standard test program [20]. The probe acoustic was 90 mm above the road surface and 150 mm away from the tire sidewall, 100 mm behind the centerline positioned 90 mm above the road surface and 150 mm away from the tire sidewall, 100 mm behind of the tire [21].ofThe forThe holding thefor acoustic probe was constructed so that the sound the centerline thebracket tire [21]. bracket holding the acoustic probe was constructed so pressure that the could be measured close the trailing edges of the tire/pavement patch. Probe location and sound pressure could be to measured close to the trailing edges of contact the tire/pavement contact patch. equipment configuration of theconfiguration A-CPX is shown Figureis2.shown The test distance 250 m. Probe location and equipment of theinA-CPX in Figure 2. was The about test distance The vehicle traveled the vehicle experimental section a uniform speed under experimental conditions was about 250 m. The traveled the at experimental section at athe uniform speed under the with the engine on. The experiment was conducted three times under the same working experimental conditions with the engine on. The experiment was conducted three times conditions. under the The equivalent sound pressure of the two microphones were recorded, and the average value same working conditions. Thelevels equivalent sound pressure levels of the two microphones were was takenand as athe single experimental result. recorded, average value was taken as a single experimental result. (a) Probe location (b) Equipment configuration Figure Figure 2. 2. Probe Probelocation locationand andequipment equipmentconfiguration configuration of of the the A-CPX A-CPX method. method. 3. Results Resultsand andCorrelation CorrelationAnalysis Analysis 3. The tire tire noises noises recorded recorded between between CPB CPB and and the the A-CPX A-CPX method method after after linear linear regression regression correction correction The are compared compared in in Table Table 3. 3. We We found found that that the the tire/pavement tire/pavement noise noise recorded recorded by by the the A-CPX A-CPX method method on on are the cement road was about 32 dB higher than that of the CPB (Table 3). However, the ranking of the tire the cement road was about 32 dB higher than that of the CPB (Table 3). However, the ranking of the assigned by the twotwo experimental methods waswas the same. tire assigned by the experimental methods the same. Table 3. 3. Comparison Comparison of of tire tire noise noise between between CPB CPB and and A-CPX A-CPX methods. methods. Table Tire Type a b a bc d c e Tire Type d e CPB Experimented CPB Experimented Value/dB Value/dB 76.1 78.0 76.1 79.4 78.0 77.1 79.4 78.0 77.1 78.0 A-CPX Experimented A-CPX Experimented Value/dB Value/dB 108.1 110.2 108.1 111.2 110.2 108.9 111.2 110.1 108.9 110.1 Difference Value/dB Difference Value/dB 32.0 32.2 32.0 31.8 32.2 31.8 31.8 32.1 31.8 32.1 To study the feasibility of using the A-CPX experiment results to predict the CPB tire noise value, we first examined the correlation between the experimental results of the two methods. The To study the feasibility of using the A-CPX experiment predict theisCPB tire in noise value, correlation coefficient between the noise experiment results results of CPBto and A-CPX shown Figure 3, we first examined the correlation between the experimental results of the two methods. The correlation which was 0.973. Therefore, the noise experiment results of the CPB method can be predicted using coefficient between the noiseobtained experiment results of CPBmethod. and A-CPX is shown in Figure 3, which was the noise experiment results using the A-CPX 0.973. Therefore, the noise experiment results of the CPB method can be predicted using the noise experiment results obtained using the A-CPX method.

Appl. Sci. 2020, 10, 5679 x FOR PEER REVIEW Appl. Sci. 2020, 10, x FOR PEER REVIEW 6 of 13 6 of 13 Figure 3. Tire noise correlation of CPB and A-CPX methods. Figure methods. Figure3.3.Tire Tirenoise noisecorrelation correlationof ofCPB CPBand andA-CPX A-CPX methods. 4. Analysis of Parameter Conversion Relationship between the Noise Experiment Results of CPB 4. of Parameter Conversion Relationship between the Noise Experiment Results of CPB 4. Analysis Analysis and A-CPX of Parameter Conversion Relationship between the Noise Experiment Results of CPB and A-CPX and A-CPX The CPB CPB method method is is used used to to determine determine four four tires’ tires’ pass-by pass-by noise noise in in aa semi-free semi-free field. field. The The A-CPX A-CPX The TheisCPB method is used the to determine four tires’ pass-by noise in the a semi-free field.relationship The A-CPX method used to determine noise of a single tire. To determine quantitative method is used to determine the noise of a single tire. To determine the quantitative relationship method is determine the noise of a single tire.inTo determine thepath quantitative relationship between theused two to methods, the between the two methods, the attenuation attenuation relationship relationship in the the propagation propagation path must must be be determined, determined, between the two methods, the attenuation relationship in the propagation path must be determined, including the theattenuation attenuationofof sound pressure at frequency each frequency and the correction of the including thethe sound pressure levellevel at each and the correction of the number including the attenuation of the sound pressure level at each frequency and the correction of the number of sound sources and other factors [22]. of sound sources and other factors [22]. number of sound sources and otherisfactors [22]. experiment and the CPB method is a far-field Because theA-CPX A-CPX method a near-field Because the method is a near-field experiment and the CPB method is a far-field experiment, Because the A-CPX method is a near-field experiment and the CPB method is a far-field experiment, process of predicting noise near-field noise is essentially an the process of the predicting far-field noise fromfar-field near-field noisefrom is essentially an extrapolation process [12]. experiment, the process of predicting far-field noise from near-field noise is essentially an extrapolation process [12]. The physical configuration of near-field noise extrapolated to far-field The physical configuration of near-field noise extrapolated to far-field noise is shown in Figure 4 [12]. extrapolation process [12]. The configuration of near-field noisebetween extrapolated to far-field noise is shown in Figure 4 relationship [12]. physical To discuss the transmission relationship noise To discuss the transmission between near-field noise and far-field noise near-field and to simplify noise is shown in Figure 4 [12]. To discuss the transmission relationship between near-field noise and far-field noise and to simplify the theoretical derivation of the extrapolation process, the theoretical derivation of the extrapolation process, we assumed that the statistical characteristicswe of and far-field noise and to characteristics simplify the theoretical derivation of were the extrapolation process, we assumed that sources the statistical four tires’ sources consistent and all of them the four tires’ were consistent and of all the of them were incoherent noise. We also assumed that assumed that thenoise. statistical of thethe four tires’ sources consistent and tires all ofofthem were incoherent We characteristics also assumed that contributions of were the front and rear the the contributions of the front and rear tires of the vehicle to the far-field sound pressure measurement were incoherent noise. We also assumed that the contributions of the front and rear tires of the vehicle to the far-field sound pressure measurement were the same. were the same. vehicle to the far-field sound pressure measurement were the same. Figure 4. The Thephysical physicalconfiguration configurationfor forthe theextrapolation extrapolation signals acquired proximity of of of signals acquired by by thethe proximity of the Figure 4. The physical configuration for the extrapolation of signals acquired by the proximity of the the signals. tire tire signals. tire signals. 4.1. Theoretical Derivation Derivation of 4.1. Theoretical of the the Propagation Propagation Relationship Relationship between between Near-Field Near-Field and and Far-Field Far-Field Noise Noise 4.1. Theoretical Derivation of the Propagation Relationship between Near-Field and Far-Field Noise We We assumed assumed that that tire tire noise noise is is aa spherical spherical wave. wave. The The expression expression of of spherical spherical wave wave attenuation attenuation with at temperature We assumed that tire noise is ais: spherical wave. The expression of spherical wave attenuation with distance distance at normal normal temperature is: with distance at normal temperature is: (1) SPLCPBi SPL SPL CPXi SPL 20lgr 20lgri kk (1) (1) SPL SPL 20lgr k where SPLCPBi is the far-field noise of the i-th tire measured by the CPB method (dB); SPLCPXi is the where is the far-field noise of the i-th tire measured by the CPB method (dB); SPL is the is CPBi where SPL SPLnoise CPBi is the far-field noise of the i-th tire measured by the CPB method (dB); SPLCPXiCPXi near-field of the i-th tire measured by the A-CPX method (dB); ri is the distance from the the near-field noise of the i-th tire measured by the A-CPX method (dB); r is the distance from i near-field microphone noise of the to i-ththe tire measured by the A-CPX method ri isand thekdistance from the near-field far-field microphone (m), where i (dB); 1,2,3,4; is the correction near-field microphone to the far-field microphone (m), where i 1,2,3,4; and k is the correction factor. In free space, k 11; in semi-free space, k 8. factor. In free space, k 11; in semi-free space, k 8.

Appl. Sci. 2020, 10, 5679 7 of 13 the near-field microphone to the far-field microphone (m), where i 1,2,3,4; and k is the correction factor. In free space, k 11; in semi-free space, k 8. When the distances between the near-field and far-field microphones are r1 and r2 , the far-field tire noise measured by the CPB method can be expressed as follows: SPLCPB1 SPLCPX1 20lgr1 k (2) SPLCPB2 SPLCPX2 20lgr2 k (3) The difference in the sound pressure level between them can be expressed as follows: L SPLCPB1 SPLCPB2 r 20lg 2 r1 ! (4) Ignoring the shielding effect of the vehicle body on tire noise, the above equation is used to calculate the sound attenuation values in the sound propagation path from the near-field microphone to the far-field microphone corresponding to the four tires. The theoretical value of far-field tire noise can be obtained by removing the sound attenuation value in the propagation path from the value of near-field tire noise. Since the distance between the near-field and the far-field microphones of T1 and T3, and T2 and T4 tires is the same, the theoretically calculated noise attenuation values in the propagation path are the same. The total noise prediction value at the far-field measurement point can be calculated using the four tires’ noises using the superposition equation. The noise superposition equation can be expressed as: n X 0.1SPL CPBi SPLCPB 10 log10 10 (5) i 1 where SPLCPB is the far-field noise of four tires measured by the CPB method (dB). The difference between the predicted noise and the measured noise at the far-field experiment point of five tread patterns is shown in Table 4. Table 4 shows that although assumptions were made in theoretical analysis, the difference between the measured value and the theoretically predicted value was still large. The average difference was about 6.56 dB. Therefore, it is not advisable to theoretically deduce the quantitative relationship between the noise experiment results of the two methods. Table 4. Prediction value and difference value between predicted value and experimental value at far field measurement point. Tire Type SPLCPB Experimental Value/dB SPLCPB Predicted Value/dB Difference Value

noise and tire noise. The contribution rate of tire noise is high when the vehicle is running at a constant speed of 50 km/h, reaching 86-100%, indicating tire noise is the main noise source [1]. Therefore, reducing tire noise is important for reducing the overall noise of the vehicle and controlling noise pollution [2].