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STUDY ON THE MULTIDISCIPLINARY DESIGN FOR SIMULTANEOUS REDUCTION OF WIND NOISE AND SQUEAK OF THE INNER BELT WEATHERSTRIP OF DOORS IN ELECTRIC VEHICLES

Noise, vibration, and harshness (NVH) are becoming crucial performances in electric vehicles (EVs), particularly an external wind noise. A high initial contact load of the door inner belt weatherstrip should be applied to prevent the wind noise from entering the interior of the vehicle. This in turn may cause a squeaking noise at the glass/weatherstrip interface. Thus, this study demonstrates a multidisciplinary design of the weatherstrip to simultaneously reduce the wind noise and squeak by designing thermoplastic vulcanizate (TPV) and friction material properties as well as the structural geometry of the weatherstrip. The minimum overlap value at the glass/weatherstrip was determined by considering the manufacturing deviation and deformation when the glass was stalled. The minimum contact load was measured experimentally at which the wind noise was kept constant. The compression set and damping properties of the TPV material were improved by 39% and 10%, respectively, by increasing the ethylene propylene diene monomer (EPDM) ratio and ethylidene norbornene (ENB) content. Moreover, flocking was applied on the surface of the weatherstrip which greatly reduced the squeaking noise by 89%. Furthermore, to predict the squeaking noise, friction-induced vibration was simulated using computer-aided engineering (CAE), and the CAD model was modified according to the design guide for reducing low noises. By evaluating vehicle level performances with the developed weatherstrip, simultaneous improvement in the wind noise (1.0–1.2 dB(A) reduction for the cabin and proximity noises) and squeaking noise (periodic noise in the frequency range of 0.1–1 kHz was disappeared) was found. This study can show enormous potential for the material and structural multidisciplinary design for NVH performances in next-generation vehicles such as autonomous EVs and urban air mobility.

INTRODUCTION

The widespread electrification of automobiles has introduced a significant challenge in designing noise, vibration, and harshness (NVH) of vehicles. Particularly, wind noise is becoming a major noise source in electric vehicles (EVs) due to the removal of engine noise. To prevent wind noise, water, and dust from entering the interior of the vehicle, a door inner belt weatherstrip is attached to the door trim and in contact with the side door glass through the elastomer-based part called lip. An appropriate compressive contact load must be applied between the lip and the door glass to ensure the insulation. Owing to the lip-glass contact load the squeaking noise can be generated by stick- and sprag-slip phenomena during the opening and closing of the glass (Chen and Trapp, 2012; Choi et al., 2018). Thermoplastic elastomers (TPEs), which can be recycled and have lighter weight than thermoset elastomers, are receiving great attention for the weatherstrip material. Among many TPEs, thermoplastic vulcanizates (TPVs) are in particular advantageous for mechanical properties in high temperatures, impact strength, and elasticity, which are fabricated through dynamic vulcanization of thermoset elastomers and thermoplastics; however, TPVs exhibit low material damping and compression set which can easily generate frictional noise and vibration in the lip-glass interface (Cho et al., 2021). For the wind noise the sound wave transmitted through the sealing system such as the inner belt weatherstrip significantly contributes to interior noise levels. The gap distance between the sealing system and the glass is considered a dominant factor for the noise, where acoustic leakage through the sealing parts occurs at high frequencies with intense aspiration noise (Zhu et al., 2016; Saf et al., 2020). Thus, a large initial contact load is desired between the weatherstrip and the glass with a low compression set property to ensure a stable sealing performance over time (Choi et al., 2013; Ryu et al., 2017); however, a large initial contact load may generate squeak by facilitating stick-slip in the interface. To control unwanted squeaking noise generation, Astalosch et al. (2012) proposed an optimal design of the weatherstrip geometry. They attempted to predict the lip compressive load and displacement of olefinic TPE during glass operation using computer aided engineering (CAE). Oumohand and Sartoni (2012) studied frictional effects of polyamid(PA)- and polyester(PE)-based fibers attached to the lip called flocking. They established a design rule for the noise-induced friction coefficient between the flocking-glass contact interface. A rough optimization study was conducted by Choi et al. (2018) to reduce the squeaking noise by selecting the design factors (shape of the inner belt lip and flocking specifications) using Taguchi optimization method. Cho et al. (2021) characterized the viscoelastic damping properties of TPV materials through vibration tests. Although these studies suggested design solutions for reducing the squeaking noise, simultaneous reduction of wind noise and squeaking noise was not shown. In this study, a comprehensive and multidisciplinary design of the inner belt weatherstrip concerning the TPV, flocking materials, and structural geometry is demonstrated to reduce both the wind noise and the squeaking noise simultaneously.

Composition of door inner belt weatherstrip

The structure of the inner belt weatherstrip can be divided into a carrier, upper and lower lip, and flocking for the upper and lower lips as shown in Figure 1(a). The carrier is fixed to the door body in white (BIW), and it is composed of polypropylene (PP) material. The lip contacts to the glass sealing the gap between the carrier and glass. The material candidates for the lip are TPV or ethylene propylene diene monomer (EPDM). Flocking, made of PE or PA, is attached to the lip to reduce friction with the glass surface. The overlap distance between the glass and the lip corresponds to dimension ⓐ in Figure 1(a). The contact load (L) is the reaction force generated when the inner belt lip contacts the glass, as shown in Figure 1(b).

Determination of minimum overlap distance

There are manufacturing deviations for the overlap distance depending on the manufacturing quality of each part of the door systems. To calculate the manufacturing deviations, the conventional design methods of assembly tolerance allocation typically use the root sum square (RSS) tolerance analysis method (Lin et al., 1997). Despite its limitations, such as one-dimensional calculation and quality control of the 3σ level of Gaussian distribution, it is widely used as a simple and practical analytical tool. When the i-th tolerance of the design parameters (DPs) is set to X_i and N number of associated DPs exist, manufacturing deviation is calculated using Equation (1). The typical tolerances of the DPs are shown in Table 1. The typical δ_ma is calculated to be 1.87 mm.The upward force of the side door glass due to the stall torque of the window regulator motor deforms the glass and the BIW. This changes the distance between the door inner belt and glass, making it smaller than the designed overlap dimension because the glass is deformed outwardly (Lee and Jeong, 2017; Miklos et al., 2017). This amount of deformation is denoted as δ_st. To measure the δ_st, the distance between the glass and the inner belt was measured using a laser point sensor, as shown in Figure 2. For conservative prediction of the δ_st, aged weatherstrips are prepared and 14.5 V was applied to the regulator rather than the rated voltage of 13.5 V. The measurement results are presented in Table 2. The amount of deformation is large when single rail regulator and laminated glass are used. Even among similar mid-sized vehicles, EVs exhibit large deformation because of the large door width. Despite the similar body size, EVs have a large wheel base to secure interior cabin space, and therefore, the door width is also larger than those of the existing internal combustion engine vehicles.According to ISO 315, the compression set of a material is defined as the permanent deformation retained after the removal of a force that was applied to it. For the inner belt weatherstrip, the initial overlap distance is denoted as ODi, and the overlap distance after aging is denoted as ODa; the compression set ηc is defined as the permanently deformed ratio according to Equation (2). The desired overlap ODdesired is defined as the sum of the stalled deformation (δst) and manufacturing deviation (δma).Because the designed minimum overlap distance must be larger than the desired overlap even after permanent deformation, by substituting Equation (3) into Equation (4), the minimum overlap requirement can be expressed as shown in Equation (5).The smaller the compression set of the elastomer material, the smaller the overlap required, and the smaller the change in the overlap distance, the better the performance maintenance. The ηc of general inner belt weather strip was restricted to within 30%. By substituting δma and δst obtained above into Equation (3) and (4), the ODdesired and ODmin are calculated to be 3.9 mm and 5.6 mm, respectively.

Determination of minimum contact load

Depending on the contact load, the amount of noise transmitted from the glass and the lower area of the lip can be determined. To estimate the minimum contact load (CLDmin), a few CAE methods have been studied and proposed (Saf et al., 2020). However, since these CAE methods produce inconsistent results, it is more reasonable to measure the proximity sound directly using a pin microphone according to the varied contact load with the aging condition of the inner belt weatherstrip through the wind tunnel. The test conditions for measuring noise were a wind speed of 110 kph and 11.3° yaw angle of the vehicle; the pin microphone was installed at a distance of 100 mm, and the parts that are not necessary to be measured were taped down to minimize the influx of noise. The measured noise was subjected to the fast Fourier transform (FFT) and converted to 1/3 octave band from 10 Hz to 10 KHz. The noise measurement results for the lip load are presented in Figure 3. At a lip load higher than 0.96 N/100 mm, there was no change in noise, whereas for values less than 0.96 N/100 mm, the performance dropped sharply in the high frequency area. The contact load decreases with time according to the stress relaxation characteristic represented by the Maxwell model of viscoelastic materials. Therefore, the initial contact load (CLDi) should be designed according to the minimum contact load maintained even after permanent deformation, as shown in Equation (6) and (7), where CLDa is the contact load after permanent deformation.

TPV AND FLOCKING MATERIAL DESIGN

A simple analytical model describing instable squeaking noise has been proposed, as shown in Figure 4(a) and Equation (8) (Eaton, 1975). The Figure of motion for mass M is given by,where X is the displacement of the mass (m) at time (t); ν is the drive velocity; c is the damping coefficient of dX/dt; k is the spring stiffness constant; F is the frictional resistance. The solution to this differential equation depends on the damping ratio ζ, where λ is the gradient of the friction versus speed curve (i.e., Stribeck curve), as shown in Figure 4(b). Equation (9) is summarized in the following section, and it gives a comprehensive explanation of the reasons for the generation of squeaks as well as the methods to control them (Reddyhoff et al., 2015). If ζ = 0, a marginally stable constant amplitude is considered; if 0 < ζ < 1, a stable amplitude with underdamped decaying oscillation is considered; if ζ ≥ 1, a stable amplitude with overdamped and non-oscillatory vibration is considered. To control the damping ratio, the value of damping coefficient (c) should be increased, and the value of the λ, i.e., – dμ/dν should be negative. To be precise, the TPV material should be developed to ensure a high degree of damping (loss factor), and the friction coefficient of surface should be changed from boundary friction to viscous friction, which is proportional to speed. Similarly, the compression set of the TPV material should have a low value to improve the wind noise insulation

Viscoelastic characterization of TPV

Material damping in polymers comes from the intrinsic viscoelastic properties, which exhibit both elastic and viscous behaviors that are characterized by storage modulus and loss modulus, respectively, in dynamic mechanical analysis (DMA). The ratio between the loss and storage moduli, i.e., tanδ is generally used as a material damping factor or a loss factor. To measure tanδ values of TPV material, DMA was performed under the following condition: temperature-ramp test from -70 to 80 °C with 3 °C /min heating rate at 10 Hz. The dynamic strain of 0.25% was selected for the DMA tests, which is confirmed to be stay within the linear viscoelastic regime (LVR) by the strain-sweep test. Compression set of TPV was measured in accordance with ISO 315 (25% strain, 70 ℃, 22 h). The material properties of the olefinic TPV can be determined by the following design factors: EPDM/PP ratio, EPDM crystallinity, EPDM crosslinking density, EPDM molecular weight distribution, PP crystallinity, crosslinking agent, filler, and process oil content and type. In this study, the EPDM/PP ratio and ENB content in the EPDM were chosen as the major factors among the design factors. The TPV material was fabricated using a twin-screw extruder. The mixing of the compound and crosslinking reaction of the EPDM were conducted simultaneously, so called a dynamic vulcanization process. After crosslinking, EPDM particles were dispersed in the PP matrix working as a physical crosslink of the TPV. Sheets of 2 mm thickness were manufactured using the prepared compositions with the aid of an injection molding machine.

EPDM and PP ratio design study

The EPDM and PP ratios were varied as shown in Table 3 to fabricate the TPV materials with Shore A hardness values of 60, 70, and 80. The compression set results according to the EPDM/PP ratio are also presented in Table 3. It was found that the compression set was proportional to the PP ratio. TPV 60 (35.35 %) with a low PP ratio exhibits a compression set value (35.35%) which is 22.2% lower than that of TPV 80 (45.44 %) with a high PP ratio because PP has a yield strain of approximately 15% which undergoes permanent deformation under the 25% strain applied in the compression set test (Hartmann et al., 1987). The temperature-dependent tanδ curves are shown in Figure 5, where two peaks can be observed indicating the glass transition temperature (Tg) of EPDM (approximately -35 °C) and PP (approximately 10 °C), respectively (Xu et al., 2018). The tan δ peak values at the Tg of PP were similar among the samples, whereas the tanδ peak values at the Tg of EPDM increased significantly as the EPDM ratio increased. Near the EPDM Tg region, the tanδ value of TPV 60 was 0.478 which was 88.2% higher than that of TPV 80 (0.254). This result is reasonable because a larger energy is required for the molecular mobility of EPDM polymer chains with a high EPDM loading fraction in the TPV.

EPDM crosslink density design study

To study the effect of the crosslink density of EPDM on the material properties of TPV, the ENB content was varied as presented in Table 4. The crosslink density was measured by swelling crumb TPV samples according to the ASTM D6815. It was observed that the crosslink density increased as ENB content increased in the TPV. Furthermore, as a result, a higher ENB content in the TPV lowered compression set due to enhanced elastic resilience of the EPDM crosslinks. ENB #3 (27.55 %) exhibited an improvement of approximately 12.4 % in the compression set compared to ENB #1 (31.45 %). Figure 6 presents the temperature-dependent tanδ curves for TPV samples with varied ENB content. The Tg of EPDM increased as the crosslink density increased (Tg of ENB #1, ENB #2, and ENB #3 were -41.2 °C, -39.0 °C, and -38.0 °C, respectively.). This can be attributed to the fact that more thermal energy is required for the glass transition of the EPDM polymer chins because of reduced chain mobility by higher crosslink density. As shown in the scanning electron microscopy (SEM) images in Figure 7, the average particle diameter observed was 0.85–2.10 μm. According to the related literatures (Katbab et al., 2000; Lim et al., 2017; Xu et al., 2018), the EPDM particle diameter of TPV is in the range of 0.5–5 μm. Therefore, the particle observed in this study can be considered as EPDM particles. The average diameter of the EPDM particles decreased as the EPDM crosslink density increased. ENB #3 exhibited an average diameter of 0.85 μm which was 59.5% smaller compared to ENB #1 (2.1 μm). For the same EPDM content, the specific surface area of an EPDM particle increases as the average particle diameter decreases, implying an increase in the interfacial area between EPDM and PP. Therefore, when the crosslinking density of EPDM is increased during the dynamic vulcanization reaction, the EPDM particles are broken down to smaller particles increasing EPDM/PP interfacial slip energy. This increased energy dissipation resulted in higher tanδ values above Tg of EPDM as shown in Figure 7. ENB #3 exhibited the largest tanδ value (0.11) at 24 °C, which is the standard temperature condition for vehicle vibration test.

Investigation of friction properties of flocking

To eliminate the squeaking noise, various methods have been proposed, such as adjusting the composition of the PE or PA materials or the diameter, length, and density of flocking. The application of a textile softener to the flocking surface has also been suggested (Oumohand and Sartoni, 2012; Choi et al. 2018). In this study, amino-modified silicone, which is widely used in textile engineering, was sprayed on to the flocking surface. To check the coating quality on the flocking surface, approximately 0.5 wt% of Bis(triazinyl amino) stilbene disulfonic acid, a fluorescent material, was added to the coating materials for coating amounts of 2 g/m2, 3 g/m2, and 5 g/m2. Flocking pile specification was 3.3dTex, and the pile length was 0.6 mm with PE materials. The coating material was supplied by Nicca Chemical (Japan) and Hwaseung Chemical (Korea), and the surface-coated flocking tape was supplied by Industrias Tapla, S.L. (Spain). Flocking tape was laminated to the above TPV compounds produced by Hwaseung Material (Korea).

Surface quality of flocking

Before the friction test, the coating quality was checked by irradiating the surface with ultraviolet rays. The micrograph presented in Figure 8 shows that the coating solution was well attached to the surface of the flocking pile (Shiny area in Figure 8(b) is where the coating was applied).

Friction coefficient measurement according to speed and normal force

In accordance with VDA 230-206 (VDA, 2007), the sample was prepared and attached to a semicircle aluminum jig with a length of 50 mm, using SSP-04 of Zins-Ziegler. The dynamic friction coefficient at a sliding speed of 1–150 mm/s was measured at normal loads of 2 N and 5 N. According to the test results shown in Figure 9, the dynamic friction coefficient of flocking exhibited four characteristics. First, the average dynamic coefficient was decreased approximately 60% as the normal load was increased from 2 N to 5 N for both non-coated and coated surfaces. Second, regardless of the type of coating, when applied to the flocking surface, it resulted in a reduction in the friction coefficient by more than 70%, on average (2 g/m2 is the minimum amount for Hwaseung Chemical’s coating). Third, when the spraying amount of the coating solution was increased, the friction coefficient showed a tendency to decrease. Based on the sample applied with Hwaseung Chemical’s coating, when the coating amount was increased from 2 g/m2 to 5 g/m2, the average coefficient of friction decreased by approximately 30% from 0.47 to 0.33, at a normal load of 2 N. Fourth, when the coating was not applied, the friction coefficient decreased as the sliding speed increased in the range of 21–150 mm/s at a normal load of 2 N. Therefore, λ is positive (λ = 4.01 x 10–4) as shown in Figure 5(b). Considering that the typical glass operation speed is 130–180 mm/s, this value of λ may lead to a negative damping ratio ζ (Figure (9)), thereby lowering the dynamic stability and causing vibration, which can result in squeaking noise. In the other cases, the value of λ is negative and that of the damping ratio is positive.

Friction coefficient measurement under semi-wet condition

The inner belt weatherstrip typically generates noise on rainy days; it is closely related to humidity, particularly when the glass is wet (Ma et al., 2021). Under wet condition, the friction coefficient is lower than that in the dry condition. However, when the glass is repeatedly lowered and raised, the water dries, and the friction coefficient converges to that of the dry state. However, a separate phenomenon exists, where squeak occurs owing to a rapid increase in the friction coefficient after a few cycles of operation or sufficient drying time has elapsed. This state is called the semi-wet state. (Oumohand and Sartoni, 2012). This is presumed to occur when the difference between the friction coefficients of wet and dry states is large. The wet area tends to slide easily, and the dry area tends to slide less owing to the relatively high friction coefficient. Consequently, the flocking surface needs to be modified to reduce the difference in the friction coefficient between the wet and dry conditions. It is difficult to simulate wet conditions using Ziegler’s SSP-04 equipment because the friction surface is perpendicular to the direction of gravity. Therefore, the equipment and test method suggested by Oumohand and Sartoni (2012) were used, except that the normal load for the test was 2 N, and the test speed was 50 mm/s. Consequently, the difference between the wet and dry friction coefficients could be reduced by increasing the coating amount from 2 g/m2 to 5 g/m2. This can be attributed to the larger drop in the dry friction coefficient compared to the wet friction coefficient, as shown in Figure 10. Because both manufacturers used amino-modified silicone to control surface friction, the performance difference between coatings from different manufacturers was insignificant

Friction induced vibration test

TPV 80, TPV 60 and ENB #3 TPV samples were subjected to friction tests with and without 5 g/m2 of Hwaseung Chemical’s coating according to the test conditions of the German Automobile Manufacturers Association (VDA 230-206, 2007), as shown in Figure 11, and acceleration (g) was measured. As shown in Figure 12(a), when the damping of the TPV material (uncoated flocking) was increased, the absolute maximum value of acceleration during the vibration decreased by approximately 40% from 1.19 g to 0.71 g. In contrast, the reduction was approximately 94.1–94.4% for TPV 60 (from 1.19 g to 0.07 g) and ENB #3 (from 0.71 g to 0.04 g) if coating is applied (Figure 12(b)). It was clearly seen that the effect of the coating on the flocking surface was more significant on squeaking noise than the effect of material damping.

Sprag slip theory

The belt and glass have similar brake system structures at wheels (Lee and Jeong, 2017). The friction force (F_f) and normal force (F_N) from the sprag slip phenomenon are described in Equation (10), which was first defined by Spurr (1961). Self-excited vibration due to the sprag slip mechanism generates vibration even if the coefficient of friction λ, i.e., – dμ/dν is negative. This phenomenon is caused by the instability of the geometric structure and boundary conditions. Here, the angle of the lip touching the glass is an important DP. From Equation (10), as the angle increases, the friction and normal force (L) also increase. When the denominator becomes 0, FN and Ff ≈ ∞, and the corresponding sprag slip criterion is shown in Equation (11). (Spurr, 1961; Ghazaly et al., 2014).

Determination of angle from measured friction coefficients and sprag slip theory

From Figure 9, the change in the dry-state friction coefficient of the flocking sample without spray coating at a normal load of 2 N is approximately 1.61 ± 0.3. According to Equation (11), the angle θ of vibration due to the sprag slip mechanism is 27.6–37.4. If the angle of the inner belt weatherstrip is within this range, vibration noise owing to sprag slip may occur. Even if the coating solution is attached to the flocking, with time, the coating solution on the surface will be removed by abrasion. Therefore, a design guide to avoid this angle range is required. Although the sprag slip is more advantageous at smaller angles, an angle of 0 is impossible owing to the structure of the belt. Therefore, optimization is necessary. Unless a glass surface is contaminated, it is difficult to have a coefficient of friction of higher than 3. Therefore, if the angle is designed to be less than 18.4° or the friction coefficient of lower than 3 can guarantee performance and sufficiently prevent sprag slip noise (Figure 13).

DEVELOPMENT OF CAE MODEL

The CAE model developed in this study was for the VDA 230-206 test machine to analyze the contact load and friction-induced vibration by reflecting the minimum overlap length and initial contact load that satisfy the requirements of preventing wind noise and squeaking noise. The model included the hyperelastic and viscoelastic models of the ENB #3 TPV material, and appropriate friction coefficient.

Hyperelastic material model

Cyclic tensile loading and unloading tests were performed to obtain a hyperelastic material model of the TPV. The fifth loading stress-strain curve was selected for fitting the model to remove the effect of stress-softening, so called Mullin’s effect, of the TPV material. Because TPV is a solid elastomer with compressibility, the Jel Jacobian value is 1. Therefore, the strain energy of the Mooney-Rivlin model can be represented as Equation (12), where I1 and I2 are 1st and 2nd invariant of the right Cauthy-Green strain tensor. The fitting results of the material constants for C10, C01 are listed in Table 5.

Viscoelastic material model

Fisher et al. (2004) and Ghoreishy (2012) conducted viscoelastic modeling using the Prony series, and in this study, modeling was carried out according to Fisher’s research methodology.From the generalized Maxwell model of the linear viscoelastic model, the Prony series can be obtained using Equation (13).The Prony series coefficients were determined in the following manner: First, frequency domain data in the range of 1 to 40 Hz (limited by the range of the DMA instrument) were collected under isothermal conditions at temperatures between -60 and 80 °C (increments of 5 °C). Subsequently, the time-temperature superposition principle was used to construct a master curve in a wide frequency range using the Williams-Landel-Ferry (WLF) Figure (Williams et al., 1955) as shown in Equation (14) and determine the shift factor aT (the horizontal translation factor). Tr is the reference temperature, which can be assigned by an operator, and the material constants were fitted, as shown in Table 6. Finally, these experimental reference curves were fitted with an 8-term Prony series using the linear least squares solver DYNAMFIT (Bradshaw and Brinson 1997), and the parameters are listed in Table 7.

Friction model

A linear friction Figure, Equation (15), was used to reflect Coulomb, Stribeck, and viscous friction in the CAE model. The fitted parameters from Figure (15) for the measured friction curves of each speed with 5 N normal force (Figure 9) are listed in Table 8. Despite the coefficient of determination being limited to 0.9, it was used to reflect the evaluation results on speed in CAE analysis for practical reasons.where μd is the dynamic friction of coefficient; μs is the static friction of coefficient; d is the decay coefficient; Cv is the viscous friction coefficient; ν is the drive velocity.

DEVELOPMENT OF CAE ANALYSIS MODEL AND VERIFICATION

The first step was based on the designed overlap distance, where the inner belt lip is pressed down by the rigid glass and the contact load is measured. In the second step, the acceleration was measured while sliding the glass at the same speed in the SSP-04 machine (Figure 14).To validate the CAE model, the results of VDA 230-206 from Figure 12 were simulated. For the CAE analysis, a commercialized finite element analysis software, Abaqus/Standard (Dassault Systemes) was used. The results obtained from the CAE model are compared with the test results in Figure 15 and Table 9, showing acceleration prediction error 0f 12%–59% and frequency prediction error of 57%–65%. Although the error ranges were large to take the absolute value, however, the tendency of the magnitude of the acceleration and frequency was similar to the test results; therefore, the developed CAE model was considered sufficient to be used as an auxiliary tool for designing the shape of inner belt weatherstrip to make a decision based on a relative comparison.

CAD MODEL DRAWING

According to the constraints of the DPs, CAD drawing was implemented as shown in Figure 16 and Table 10. To meet the design guide, the position of the boundary between PP and TPV and the shape of the lip were adjusted to decrease the lip angle and increase the overlap distance to 5.6 mm. Because the surface of flocking and the TPV material were changed, CAE analysis for the contact load and vibration of VDA 230-206 was performed to change the thickness of the lip and notch shape where the lip and carrier were connected. As a result of CAE, it was predicted that the maximum acceleration was reduced from 0.38 to 0.1g as shown in Figure 17

VALIDATION TEST

The door inner belt weatherstrip was manufactured using the following supply chain: Hwaseung Chmical (Korea) supplied the coating solution to Industrias Tapla, S.L. which produced a flocking tape with a coating. Tapla subsequently supplied them to Sedong (Korea), the inner belt weatherstrip manufacturer. The TPV material was supplied by Hwaseung Material. The different parts of the inner belt weatherstrip for the door were extruded, cut, and finished according to the specifications of the drawing in Sedong. The manufactured parts were installed on the driver's door of the Hyundai Motor Company’s EV. Subsequently, the parts were evaluated, and vehicle-level tests were conducted

Contact load and compression set

Before conducting the vehicle-level evaluation, the contact load distance and compression set were measured, which are component level tests. The compression set was measured under the condition of 80 ℃ and 45 h of soaking. As shown in Figure (5), additional tests were performed under typical manufacturing deviation (δma = 1.87) conditions (glass positions are nominal and nominal + 2 mm). This is because the contact of the glass must be maintained even in the deviation state where the manufacturing quality deteriorates, and there is no incomplete closure of the glass owing to a sudden increase in the contact load. In Table 11, the test results were found to satisfy the specification, in particular, it had a load of 0.96 N/100 mm or more even after the compression set; it was possible to obtain a result where contact with the glass was maintained even with manufacturing deviation. This can be attributed to the increase in the initial contact load owing to the decrease in the compression set of the material and increase in the initial overlap.

Friction induced vibration test

To properly consider the actual product shape and manufacturing state, the semi-circular VDA 230-206 standard test jig was replaced with a jig capable of installing the inner belt weatherstrip, and the test equipment was set up considering the amount of overlap of the inner belt. The test speed applied was 1–40 mm/s to obtain stable results. The evaluation results (Figure 18) showed that the magnitude of acceleration was reduced from 0.42 g to 0.24 g (43% reduction) compared to the base sample. Empirically, at an acceleration of 0.3 g or more, squeak is minimal. As the acceleration in the modified samples was less than this value, it can be predicted that there will be no squeaking noise under actual vehicle conditions.

Wind noise test

In the wind tunnel, the base and modified parts were installed on an EV (Hyundai Motor Company) to measure the cabin noise intercepted by the driver's inner ear and the proximity sound at a distance of 100 mm at a wind speed of 110 kph and a yaw angle of 10. Consequently, it was confirmed that the noise was improved to the level of 1.0 dB(A) and 1.2 dB(A) for the cabin noise and proximity noise, respectively (Figure 19). Vehicles of the same model were evaluated at Hyundai Motor Group California Proving Ground, USA. The crosswind speed was 32 kph, which was a suitable weather environment to test the fluctuation sound owing to wind variability. At 130 kph, both the cabin and proximity noise were measured in the same manner as in the wind tunnel test, and the improvement was clearly seen at a high frequency (2–8 kHz) area (Figure 20).

Glass sliding squeaking noise test

For the same vehicle model, a glass sliding squeaking noise evaluation was conducted. The position of the microphone was the same as that in the proximity wind noise test, at the center of the belt at a distance of 100 mm. The measured noise was converted into an SPL color map for time and frequency in the spectrum analysis, as shown in Figure 21. In the evaluation of the base sample, periodic noise was observed in the frequency range of 0.1 and 1 kHz, but in the revision sample, this noise was clearly disappeared.

CONCLUSION

This study proposed a multidisciplinary design of the inner belt weatherstrip of automobiles for the simultaneous reduction of wind noise and squeak of the glass window. The conclusions drawn from this study are as follows. Considering both the manufacturing deviation and deformation of the glass when stalled, we proposed the minimum overlap amount of the inner belt weatherstrip that maintains contact even in the event of permanent deformation. In addition, the value of the minimum contact load to maintain the wind noise when the CLD is reduced was proposed after experimental analysis. This value was proposed considering the degree of permanent deformation according to the viscoelastic characteristics of the TPV elastomer. Through the TPV material characterization, it was found that an increase in the loss factor was attributed to the higher ratio of EPDM. The lower PP ratio also decreased the compression set value because the amount of PP permanently deformed per unit area decreased. The loss factor tends to increase owing to the influence of the crosslinked network formed in the EPDM particles. SEM analysis revealed that the size of the EPDM particles decreased as the crosslinking density of the EPDM increased. This caused the increased interfacial area of EPDM particles with PP, thereby increasing the energy loss by intermolecular friction at the interface. Based on this study, it was possible to synthesize a new TPV compound, namely ENB #3, with a high loss factor (0.11 at 24 C, 10 Hz) and a low compression set (27.55). Through the flocking coating material characterization, it was established that the coefficient of friction of flocking tends to increase as the normal load decreases, and flocking without coating of dμ/dv has a negative slope at speeds higher than 40 mm/s under a normal load of 2 N. When amino-modified silicone is applied to the flocking surface, because dμ/dv has a positive value under all conditions, it leads to a positive and increased ζ, which stabilizes the vibration. In addition, the coefficient of friction is reduced by more than 70%, confirming that it helps to counter sprag slip. Moreover, the difference between the friction coefficient in the dry and wet states tends to decrease as the amount of coating solution increases. This effectively reduces squeak that occurs frequently on rainy days. To predict frictional vibration, the CAE methodology was devised by simulating the VDA 230-206 test, including not only the hyperelasticity of the TPV and flocking materials, but also the viscoelasticity and the change in the friction coefficient with respect to speed on the flocking surface. The CAE results were validated with the test results showing the same tendency of the magnitude of the acceleration and frequency with respect to different TPV materials. Based on the study of the TPV material damping and lip angle design, a new material and structural design of the inner belt weatherstrip was established and the actual parts were fabricated for further evaluation. In the component-level test, both permanent deformation and CLD satisfied the guide. Moreover, the enhanced damping of the TPV material with coating on the flocking surface (5 g/m2) significantly reduced the magnitude of acceleration from 0.42 g to 0.24 g (43% reduction) in the friction induced vibration test. Through the vehicle level performance tests, the newly developed inner belt weatherstrip exhibited better performances in both the wind noise (1.0 dB(A) and 1.2 dB(A) reduction for the cabin noise and proximity noise, respectively) and squeaking noise (periodic noise in the frequency range of 0.1 and 1 kHz was disappeared). This study demonstrated a multidisciplinary design for simultaneous reduction in wind noise and squeak of the inner belt weatherstrip, which can be applied to next-generation vehicles such as autonomous EVs and urban air mobility.

Research on Stick & Sprag-slip phenomenon of door waist belts

The squeak noise generated during the moving of the door glass has a influence on the performance of vehicles felt by the consumer. In order to improve the noise, it is necessary to understand the principle of a friction vibration. In this paper, it is confirmed that the principle on the belt is most closely related to Stick-slip and Sprag-slip among various vibration characteristics. Stick slip is expressed by energy accumulation and divergence due to difference in static and dynamic friction coefficient. Sprag-slip define instability of geometric structure due to angle of lips on the belt. In this paper, the physical model and the energy equation are established for the above two phenomena. Stick-slip can be solved by decreasing the difference of the static and dynamic friction coefficient. Sprag-slip is caused by the ratio of compressive and shear stiffness of the lips. The belt uses flocking to ensure durability, not coating. Therefore five factors that can be considered in the production of flocking are selected such as thickness. This study introduces an approach to improve the noise using DFSS. To predict the Sprag-slip, the lips was modeled by a spring-damper system, and the stiffness value could be derived by applying shear deformation after compression load. The shapes of the lips were designed with 18 cases and the guide for the optimum was provided. It is found that positional deviation occurs due to the equilibrium of forces rather than merely by the tolerance when the glass of the vehicles can be moved from 0 to 2.6 mm. The optimization was confirmed that no squeak noise occurred even under the condition of 3 mm.

Introduction

The noise / vibration generated at the descent of the door glass has a great influence on the performance of the goods which the consumer feels, and in order to improve this, it is necessary to understand the main mechanisms causing noise and vibration. Depending on the wet state between the door glass and the waist belt, the degree of vibration and noise varies with the change in friction characteristics, and therefore studies on the frictional properties to reduce this need to be made. The vibration of the brake and the vibration of the waist belt are similar to the principle of vibration in terms of the friction vibration of the object sandwiched between two objects and the principle of vibration is similar to the method of vibration reduction. Therefore, it is necessary to analyze the noise / vibration characteristics of the door glass based on the previous studies on the brake system. Nouby, Mohamed and Ibrahim(1) studied about the mechanisms of brake squeal. Figure 1 shows the similarity between the structure of the brakes and the structure of the glass belt. Figure 2 shows that the stick-slip and sprag-slip have the greatest effect on the brakes. In this paper, we will look at the principle of squeak noise generation on the waist belt, and based on the theory, how to make a prediction method and how to improve the problem if the coating and shape are changed

Coefficient of friction

The squeak noise generation on the waist belt is to cause friction-induced vibrations same as the brake system. As cited by Kinkaid (2) hypothesised that brake squeal originated because the dynamic friction coefficient is decreasing with increasing slipping velocity and leads to the steady state sliding becomes unstable and caused friction-induced vibrations. In order to understand friction, it is necessary to understand what friction coefficient is. The coefficient of friction is the ratio of the normal load to the load in the moving direction. As shown in Figure 3, there are four types of combinations depending on the velocity. The fiction coefficient is composed of 4 friction types; static friction when the slip speed is 0, the dynamic friction which occurs when slip occurs, and the viscous friction, which increases in size as the speed increases and the stribeck friction decreases as the speed increases. The function of the total friction coefficient is expressed by the equation (1). Stribeck friction is less effective when the difference between the static friction coefficient and the dynamic friction coefficient is small. In other words, it is advantageous that there is a small difference between the static and the dynamic friction coefficients.

Stick-slip Principle

Squeak noise is the noise generated by the stick-slip phenomenon in the relative movement between the glass and the waist belt. As shown in Figure 4, the maximum static friction is absorbed into the waist belt by the relative motion between the waist belt and the glass, and the lip is deformed to its maximum extent and this deformation is stored in the waist belt in the form of strain energy. When the waist belt exceeds the storage range, the energy is diverted to dynamic friction, and after the divergence, the static movement is stopped again and the relative motion is stopped. This operation will be repeated while achieving the cycle. Since there is a large difference between static and dynamic friction coefficient on the waist belt as the speed increases, this phenomenon can be explained by energy mechanism. The phenomenon is the same as the simulated 1-D physical model in which the mass fixed by spring is moving on the belt. From Figure 5, the relative motion of the belt and the mass is preserved in the form of strain energy while deforming in response to the stiffness, and is then dissipated into dynamic friction to form a stick-slip cycle that again performs the relative motion. In order to avoid such phenomena, it is necessary to eliminate the stick-slip cycle by eliminating the motion of the counterpart, adjusting the stiffness, absorbing all the energy, and changing the coefficient of friction.In the simple spring mass model shown in Figure 5, Equation (2) can be obtained because part of the divergent energy is converted into squeak noise in the process of transition from stationary state to motion state. In Equation (3), squeak noise is proportional to the difference between the static and dynamic friction coefficients, the mean value, and the load, and is inversely proportional to the stiffness. 〖N/k〗^2 is called the shape index because it is related to the shape, and 〖(μ〗_s-μ_d)×(〖(μ〗_s+μ_d))/2 is called the friction index because it is related to the characteristics of the friction surface. The total energy value, which is the sum of the two, is called the stick-slip index and the lower stick-slip index means the lower squeak noise. Next, in order to confirm the stability of the disappearance of the vibration, we can try the prediction with a simple spring-damping-mass one-dimensional model as shown in Figure 6 As shown in Fig. 6, the stribeck friction can be assumed to be a friction model in which the coefficient of friction decreases linearly as the slip rate increases. Therefore Equation 5 indicates that damping oscillation occurs when the -αN>0 , so that the damping value of the rubber material is larger. That is, the damped vibration is based on the tan δ of the rubber material. For example, if the material of the waist belt is changed from PVC to TPE, the damping characteristics are lowered and the noise generation ratio also increases. Also, the smaller value α of the stribeck curve is, the more the phenomenon disappears. When the static friction coefficient is the same, c>0, the system becomes stable

Sprag-slip Principle

As reported by Papinniemi(3), sprag-slip mechanism was first defined by Spurr(4). The mechanism causing the vibration between the two friction surfaces is not only stick-slip, but self-excited vibration generates vibration even if the coefficient of friction is constant. This phenomenon is caused by instability of the geometric structure and boundary conditions, and the angle of the lip is an important factor .That is, if μ 〖=cot〗⁡θ, the frictional force becomes infinite and can not move, which is called 'sprags'. The 'sprags' condition is indicated by the relationship between the friction force due to the geometric structure and the load when the rod is rigid. Since the lip of the waist belt is a deformable material with elasticity, the lip or door system, which is an actual structure, is deformed, and the accumulation and divergence of energy is repeated, resulting in vibration, which is called a sprag slip. As shown in Figure 8, it is possible to derive the lip angle which induces the spragging condition from the friction coefficient. (Highlighted range means that the lip angle of the waist belt when self energizing is 68~80 deg if the coefficient between the glass and the lip is 0.2~0.4). The smaller the lip angle is, the more advantageous it is, but the information about the possibility of vibration due to the geometrical structure is given but it does not show the information about the vibration aspect. The actual vibration pattern is because the lip is deformable and needs to be secured. In order for the waist belt's lip to slip well, the shear forece due to shear strain must be greater than the critical frictional force. That is, the lower μ and higher K_s/K_SDNF , which is called sprag-slip index, the more sprag slip avoidance designs are possible. And also equation (14) call sprag delta, which means shear strian. And the magnitude of noise that occurs when a Sprag slip is proportional to energy. To reduce sprag-slip noise, we confirmed that the sprag-delta should be small and the sprag-slip index should be large.

Principle Verification for Stick-slip phenomenon

As a result of implementing stick-slip using VBA with a MCK(mass, damper, coefficient) model between a spring(lip) and a block(glass), we were able to check various state variables related to the vibration surface of the block, and even though there is damping in the system. As shown in the Figure 9, it can be confirmed that the vibration surface is maintained by the phenomenon. If the spring constant of the door system including the regulator is K = ([20N / mm] / m) and the damping constant C = ([0.1Ns / mm] / m), the energy of the lip on waist belt included the initial peak value, the initial amplitude, and the final amplitude is output as shown in Figure 10. For the parameter study, we compared the initial peak values by increasing the static friction coefficient as shown in Figure 11. As a result, it can be seen that the larger the static friction coefficient, the larger the initial peak value. This is because the energy accumulation for generating the movement of the glass is large. Figure 12 shows that the larger the difference between static and dynamic friction coefficient, the larger the amplitude increase and the larger the rate of amplitude increase. It can be seen that the occurrence of the squeak noise due to the difference between the static friction and the dynamic friction is consistent with the vehicle evaluation result in Figure 13. In conclusion, the static friction coefficient and the normal force are the impulses given to the system. The difference between the static and dynamic friction coefficients and the normal force is the amount of energy added to the system in the event of stick-slip phenomenon and the slope of the static and dynamic friction coefficient affects the stability of the system

Principle Verification for Sprag-slip phenomenon

To confirm the vibrational behavior of the sprag-slip effect, modeling was carried out as shown in Figure 14. To predict the Sprag-slip, shear and normal stiffness must be known. Therefore, the value can be derived from the analysis according to the shape of the lip on the waist belt. First, normal force for each position is obtained, then shear stiffness K_s from shear force and normal stiffness K_SDNF from normal force when the door glass moving is obtained as well in Figure 15. As a result of the analysis with the stiffness ratio, the sprag slip effect shows a tendency that the vibration increases under the same friction coefficient condition even though the system has a damper in Figure 16.

Optimization Design of Waist belt

We have studied the basic principle of generating the squeak noise of the door waist belt. The major causes are the stick slip, which is a friction characteristic, and the Sprag slip, which is a structural feature. In this section, we propose an improvement way using the robust design using DFSS to optimize the friction characteristics and the structural characteristics. The optimum design method using DFSS is as follows: 1) setting of signal factor and output response, 2) noise strategy, 3) selection of control factor and level, and 4) optimization through performance verification after creation of orthogonal table

Friction characteristic

The contact surface of the door belt uses flocking rather than coating because of the abrasion and glass scratch when glass moving. The material of the flocking are divided into two specifications: whether to use PA series material or PE series. And other design parameter of flocking is thickness, length, and density. In Figure 17, it can be seen that different types of flocking are used in the type of excellent noise flocking. In general, since hydrophilic PA material is not good at wetting compared to PE, flocking of PE material is used. The signal factor for optimizing the friction characteristics is selected as the friction speed, and the output response was set as the friction index 〖(μ〗_s-μ_d)×(〖(μ〗_s+μ_d))/2 calculated as the friction coefficient. In this paper, the coefficient of friction of Figure 18 is set to 5,000mm / min as the signal factor close to the glass moving speed. We selected a wetting condition in which squeak noise easily occurs due to noise strategy. And L16 orthogonal table using five factors such as the material are shown in Table 1. The result of optimization through DFSS is Table 2. As a result of evaluating the evaluation value after the optimal manufacturing process, the reproducibility was as good as 90%

Structural characteristic

In order to improve the structural characteristics of the Sprag slip, the shape of the waist belt should be optimized, and an orthogonal table is created as shown in Table 3 based on the material hardness and lip shape. The signal and output responses are the Sprag-delta (μF_N0)/((K_s-〖μK〗_SDNF ) ) and Sprag-slip index K_s/K_SDNF mentioned above. The noise factor is the distance between the glass and the panel where the glass and waist belt are mounted. The shape of the 18 cases is designed, and the optimization specifications are derived by DFSS analysis of the results by analyzing Sprag delta and Sprag index. The result of optimization through DFSS is Table 4. In summary, we obtain how to make lower coefficient related to flocking and higher stiffness about the lip shape on the waist belt. The difficulty of the design of the waist belt is that the position of the glass is shifted when the door glass is moving. The position of the glass is not simply the sum of the glass curvature tolerance and the regulator tolerance, but the glass is in equilibrium And depending on whether the glass is rising or falling, its position changes depending on what type of regulator is used. Predicting the positional deviation of the glass is very difficult because the system is complicated and the normal force of the waist belt changes with time due to the viscous characteristic. Therefore, it is a practical method to view and ascertain the displacement of only statistically the actual vehicle. As shown in the figure, the position of the glass for the K model using the single rail regulator was found to vary up to 2.5 mm when it was narrowed. Therefore, it is necessary to design and verify that the sprag is prevented by considering the position deviation of the glass to 3 mm. The verification results are confirmed in the next section.

Performance verification result

Based on the optimized shape and flocking of the door waist belt, we predicted how it will change during glass moving. As shown in Figure 20, when the current waist belt is applied, it is confirmed that the sprag occurs, and it can be seen that the sprag is prevented by changing the shape of the lip. By reducing the friction coefficient by improving the flotation, the width of the vibration is reduced. As a result of evaluating the jig that can adjust the belt position by fabricating the actual waist belt on the basis of this, it was confirmed that there was no occurrence of the squeak noise even in the condition of 3 mm of the waist belt where the noise occurred at the narrow gap of 1 mm in Figure 21. The test method is an emotional evaluation if there is squeak noise or not. In addition, we applied the improvement method to the noise generation vehicle to evaluate the noise of the actual vehicle using the noise color map when a glass moving (The location of MIC is near the waist belt). We find that the optimized waist belt was satisfied in both the dry state and the wet condition of Figure 22.

Conclusion

In this paper, the energy equation for Stick slip and Sprag slip is established through the study of basic principle of squeak noise in door glass operation, and the robust design optimization is carried out by using DFSS tool. In summary, to improve the stick-slip phenomenon of the flocking, which is the friction characteristic of the door waist belt, it is necessary to reduce the difference between the static and dynamic friction coefficients and to lower the friction coefficient. Thus, the flocking of various specifications was mixed and the stick slip phenomenon was improved through the silicon coating treatment. In addition, we proposed an improvement to the sprag slip phenomenon caused by the structural characteristics by optimizing the lip shape of the waist belt during glass operation. Finally, the optimal design was verified through vehicle evaluation to ensure the noise quality that the customer could recognize.

Research on Airborne Noise of Battery Electric Vehicles Based on Transfer Path Analysis

With the popularity of battery electric vehicles, the engine of the vehicle disappears, so the problem of road noise in cars is becoming more and more prominent. Road noise into the car can be divided into structure-borne noise and airborne noise, this paper only focuses on the airborne noise above 500Hz, completely ignoring the structure-borne noise. A transfer path analysis model with ?쏧ntermediate Response Points??is proposed to accurately represent the transfer path of each airborne noise through the setting of ?쏧ntermediate Points?? In the Vehicle Semi-Anechoic Room With 4횞4 NVH Chassis Dyno, it is possible to create a working condition with only four tires running, so only the tire noise is considered in this paper. The frequency response function is tested in the Semi-Anechoic Chamber and the operating data is tested in the Vehicle Semi-Anechoic Room With 4횞4 NVH Chassis Dyno. The calculations are performed by the Conventional Transfer Path Analysis (CTPA) method and the Operational Transfer Path Analysis (OPA) method, respectively. The total responses were calculated for the three operating conditions of 60 kph, 90kph, and 120kph. Both the CTPA and OPA methods have errors within an acceptable range, but the CTPA method is more accurate. The CTPA method requires testing a large number of frequency response functions, which is time-consuming, while the OPA method is more efficient.

A Practical Approach towards Reducing the HVAC Flow Noise

Automotive heating ventilating and air conditioning (HVAC) noise is becoming a big concern area as the demand for acoustic comfort increases day by day. Vehicles are manufactured in recent years with quieter powertrain, reduced body leakage, better suspension. The other quieter technologies like electrification, hybridization of vehicle further complicate the whole subject of vehicle cabin noise issue. The HVAC noise is the major noise source inside the cabin. Hence designing a HVAC with very low sound pressure level is quite challenging and poses many difficulties in meeting other basic performances due to certain trade-off while meeting the noise requirement. However in recent years engineers have done extensive research and come up with various feasible and non-feasible solutions in order to reduce the HVAC noise significantly. Most commonly used tools and techniques are numerical simulation and experimental investigation or combined numerical simulation followed by experimental investigation. The present paper describes the way an existing HVAC noise is reduced by extensive experimental investigations. First the HVAC was dismantled and the flow path inside the HVAC was examined in details along with special features. Areas with chances of flow separations, vortices and high turbulent kinetic energy (TKE) were identified. Smoke tracing was also used in order to actually understand that phenomenon. After having deep investigation into those areas, existing HVAC was modified and series of experiments were carried out on this modified HVAC in a semi-anechoic chamber and noise data was captured at different voltages. In all these changes it is always aimed at keeping the airflow same or better than existing HVAC. It is observed that a significant improvement upto 3-4 dB(A) is achieved in overall noise level both at bench level and vehicle level. So this study provides a deeper insight into how HVAC overall noise level is reduced and hence further it can be very well applied at initial stage of design to make the noise level within desired limit.

Rattle and Squeak Investigation on the Interior Components of Automobile

Automotive rattle and squeak performance is an important factor affecting passenger comfort and perceived quality. In the current work, finite element simulation is developed to analyze the noise potential of adjacent interior components. The statistical ?????limit is adopted to assess the rattle risk at adjacent surfaces assuming a Gaussian distribution. The probability expressions about noise registration are derived for the symmetric and asymmetric tolerance zones of an initial nominal gap. Also the acoustical effects of material pairs are tested by stick-slip experiments. Results show modified polypropylene is compatible in frictional contact with itself but expresses noise when paired to adjacent components manufactured of modified acrylonitrile-butadiene-styrene terpolymer under multiple conditions.

Further Study of the Vehicle Rattle Noise with Consideration of the Impact Rates and Loudness

With the prevalent trend of the pure electric vehicle, vehicle interior noise has been reduced significantly. However, other noises become prominent in the cabin. Especially, the BSR noise generated by friction between parts and the clearance between components become the elements of complaints directly affect the quality of vehicles. Currently, the BSR noises are subjectively evaluated by experts, and the noise samples are simply labeled as ?쁰ualified??or ?쁴nqualified?? Therefore, it is necessary to develop an evaluation model to assess the BSR noise objectively. In this paper, we study the vehicle rattle noise intensively. Several types of rattle noise were recorded in a semi-anechoic room. The recorded signals were then processed in the LMS test lab. to extract the single impact segments. A pool of simulated signals with different impact rates (number of impacts per second) and various loudness was synthesized for analyzation. To verify the universality of the assessment, the in-vehicle background noises were also recorded. The in-vehicle background noises were added to the rattle noise samples to simulate the in-vehicle test environment. Sound metrics were calculated and compared for all the processed samples. Jury assessment with 5 experts were performed to evaluate the rattle noise samples. The correlation between the subjective evaluation and the impact rates as well as sound metrics were studied. Consequently, an objective assessing model for vehicle rattle noise was developed based on the above analysis. This study can be used to assess the rattle noise effectively, and it has bright prospect and great value in engineering.

Development of Tearing Pattern Prediction Model of Laser Scored Region on Invisible Passenger Side Airbag Door

The tear seam of invisible passenger side airbag door is made on the back of an instrument panel by laser scoring method and it is not shown outside. One of the requirements for the invisible passenger side airbag door is that the airbag module should deploy with no fragmentation at hot, room and cold temperature conditions. In this paper, a section model was developed by detail inspection of tearing phenomena at the laser-scored region. To validate the model, the finite elements of continuous and dot type laser-scored tear seam were built and analyzed in room and cold temperature conditions. Finally, a three-dimensional equivalent shell model was developed and it was proved that the section model and the equivalent shell model could represent well the tearing phenomena of the airbag door. It is expected that the tearing pattern prediction models developed in this study can be used to design the types of laser scoring and the airbag door with the minimum of real deployment tests.

Airflow Simulation Relative to Door-Closing Operability

Easiness in closing a vehicle door has been often evaluated on a physical vehicle body, and in most cases, has not been fully studied by computer-aided engineering (CAE) in an earlier developing stage. The authors have developed a numerical method for reproducing the behavior of a closing door with a high fidelity. Characteristics of this method are that moving grid is used to reproduce the unsteady air motion caused by closing the door, and that external reaction forces including cabin pressure are coupled with the equation of the door motion to achieve a high fidelity. This method has made it possible to quantitatively evaluate cabin pressure rise and determine minimum door closing velocity, and the method has turned out to be effective.

The Use of in Vehicle STL Testing to Correlate Subsystem Level SEA Models

For the assessment of vehicle acoustics in the early design stages of a vehicle program, the use of full vehicle SEA models is becoming the standard analysis method in the US automotive industry. One benefit is that OEM's and Tier 1 suppliers are able to cascade lower level acoustic performance targets for NVH systems and components. Detailed SEA system level models can be used to assess the performance of systems such as dash panels, floors and doors, however, the results will be questionable until test data Is available. Correlation can be accomplished with buck testing, which is a common practice in the automotive industry for assessing the STL (sound transmission loss) of vehicle level components. The opportunity to conduct buck testing can be limited by the availability of representative bodies to be cut into bucks and the availability of a transmission loss suite with a suitably large opening. In addition, the temporary fixture used to mount the test structure does not typically provide representative boundary conditions. Boundary conditions are particularly important when the in-vehicle performance is dependent on point connections at hinges / locking mechanisms and flexible seals at the perimeter of the system such as found in doors or lift-gate. In this paper the use of in-vehicle testing on prototype vehicles to assess the STL for the vehicle systems and the SEA models are discussed. Results are presented for a dash panel, floor system and door systems. The measurements are compared with predictions from system level SEA (Statistical Energy Analysis) models of the test systems. It is concluded that subsystem level SEA models can be used to assess the design and correlate well with STL measurements from in-vehicle tests.

Modular door system for side impact safety of motor vehicles

Side impact collision is one of the toughest safety challenges facing the Auto Industry today. Over thirteen thousand deaths, due to side impact, occurred during 1998 in the United States alone. The main difficulty in designing for side impact collisions is the limited crumple zone between the impacting vehicle and the impacted occupant. This paper presents a proprietary side impact protective door system within the space between the outer skin of a car door and the occupant, which will be as efficient as those already standard in frontal impact. The main objective for introducing the side impact structural system is to maximize energy absorption and minimize injury to the occupant. The developed structural side impact door system acts as a Primary Structure, to be assembled as a truly modular entity. This primary structure is also packaging modular in the sense that it acts as a carrier for the door latch, window regulator and hinges. A variation in safety and structural performance of the developed door system can be achieved by integrating the structural modular door with the vehicle body, using a patented integration system known as Door And Chassis-frame Integration Technology (DACIT). Unlike the traditional doors, that are just suspended weights, the modular door is truly structural and therefore adds strength to the vehicle body. When DACIT is used with the door system the vehicle door becomes part of the overall vehicle structure. The design and development of the side impact modular door system for different size vehicles with and without DACIT will be discussed. In addition, the five stars rating achieved during several side impact crash tests simulating Sport Utility Vehicles hitting mid-size vehicles, equipped with the developed modular door system, will be presented.

Simulation of Warm Forming Assisted Hemming to Study the Effect of Process Parameters on Product Quality

Current trends in the auto industry requiring tighter dimensional specifications combined with the use of lightweight materials, such as aluminum, are a challenge for the traditional manufacturing processes. The hemming process, a sheet metal bending operation used in the manufacturing of car doors and hoods, poses problems meeting tighter dimensional tolerances. Hemming is the final operation that is used to fasten the outer panel with the inner panel by folding the outer panel over the inner panel. Roll in/out is one of the main quality concerns with hemming, and keeping it under tolerance is a high priority issue for the auto manufacturers. Current hemming process technology, given the mechanical properties of current materials, has reached its saturation limit to deliver consistent dimensional quality to satisfy customers and at the same time meet government standards. Combining warm forming techniques with the traditional hemming process represents a new approach with the potential to overcome the current hemming limitation and to provide a satisfactory solution to all the requirements. The main objective of this research is to understand the effect of localized heating on the final quality in the hemming process by quantifying the influence of key geometrical and process parameters. To achieve this goal, a hemming finite element model, taking into consideration the mechanical properties as function of temperature is developed, and statistical methods to quantify the effect of key variables are employed. As an outcome to this study, the effectiveness of using warm forming techniques to improve hemming quality is assessed for A5182O aluminum, one of the most common used materials for this application.

Comparative Dimensional Quality of Doors: A Benchmarking Study

A comparative benchmarking study of the dimensional door quality 14 vehicles from Ford, General Motors, Daimler-Chrysler, Toyota, Nissan, BMW, Volvo, and Renault was conducted. Various aspects of the door design, manufacturing, assembly and hanging system were studied. This paper focuses on the dimensional quality of the doors and relates it to the final vehicle quality in terms of gaps and flush as well as customer satisfaction as established by J. D. Power Initial Quality Survey (IQS). For confidentiality reasons, all vehicles in the study are referred to by a coded designation.

Comparative Datuming and Hanging Strategies of Doors: A Benchmark Study

This paper discusses the results of a door benchmark study performed on 14 vehicles. The major focus is on the selection of datums or reference points and its impact on the product quality of the door system. The results indicate that there can be a relationship between datum utilization and quality metrics at any stage in the production process. Specific examples show the impact of various strategies on product performance.

Conductive Plastics Leading Fuel Door Technology

This paper will discuss, compare, and contrast current materials, designs, and manufacturing options for fuel filler doors. Also, it will explore the advantages of using conductive thermoplastic substrates over other materials that are commonly used in the fuel filler door market today. At the outset, the paper will discuss the differences between traditional steel fuel filler doors, which use an on-line painting process, and fuel filler doors that use a conductive thermoplastic substrate and require an in-line or off-line painting process. After reviewing the process, this paper will discuss material options and current technology. Here, we will highlight key drivers to thermoplastics acceptance, and look at the cost saving opportunities presented by the inline paint process option using a conductive thermoplastic resin, as well as benefits gained in quality control, component storage and coordination.

The Effect of Turbulence on Peak and Average Pressures on a Car Door

The influence of turbulence on automotive aerodynamics requires further investigation. This paper provides evidence that turbulence directly affects average and peak forces on the front door of a sedan automobile. Wind tunnel and several on-road test conditions were investigated. The results include instantaneous peak and average force coefficients, together with experimental pressure contour plots for a sedan front door. The pressure distribution over the front door of an automobile is important for efficient structural and door seal design. Door pressure distributions vary with flow turbulence characteristics. The results presented in this paper show that turbulent properties of the flow are of importance when investigating flow over the front door of a sedan automobile.

A Robust Solution for a Power-Train Mounting System for Automotive NVH Refinements

Production variations of a heavy duty truck for its vibrations were measured and then analyzed through an Ishikawa diagram. Noise and Control factors of the truck idle shake were indentified. The major cause was found to be piece to piece variations of its power-train (PT) rubber mounts. To overcome the same, a new nominal level of the mount stiffness was sought based on minimization of a cost function related to vibration transmissibility and fatigue damage of the mounts under dynamic loadings. Physical prototypes of such mounts were proved to minimize the variations of the driver's seat shake at idling among various trucks of the same design. These learning's are useful for design of various subsystems or components to refine the full vehicle-Noise Vibration Harshness (NVH) at the robust design level.

Structural Diffuse Field Excitation Synthesis by Synthetic Array (SFS-SA), Application to Cars Panels Contributions

Diffuse field or turbulent boundary layer excitations of vehicles are of huge interest in automotive industry. For such excitations reverberation chambers or wind tunnels are necessary, this means high cost experiments. The idea of sound field synthesis to create the acoustic effect corresponding to diffuse field or turbulent boundary layer excitation, is of major interest to reduce drastically the cost of experiments. Originally, techniques based on loudspeakers antenna were used, however, a major difficulty appeared due to driving simultaneously a huge number of sources. To avoid this difficulty a new technique based on synthetic antenna is used here; instead of an array of loudspeakers, just one source is used for scanning the surface where the acoustic field excite the structure. A post processing step, based on plane wave decomposition, is then applied to collected experimental data in order to get the response of the structure or the sound transmission through the structure. Validation of the method is presented by comparing synthetic antenna results to standard measurements of panels sound transmission between two reverberation chambers. The present paper is focusing on panels contributions in a car, leading to an experimental process avoiding the cumbersome masking technique generally used in automotive industry.

Engine Sound Reduction and Enhancement Using Engine Vibration

Over the past decade, there have been many efforts to generate engine sound inside the cabin either in reducing way or in enhancing way. To reduce the engine noise, the passive way, such as sound absorption or sound insulation, was widely used but it has a limitation on its reduction performance. In recent days, with the development of signal processing technology, ANC (Active Noise Control) is been used to reduce the engine noise inside the cabin. On the other hand, technologies such as ASD (Active Sound Design) and ESG (Engine Sound Generator) have been used to generate the engine sound inside the vehicle. In the last ISNVH, Hyundai Motor Company newly introduced ESEV (Engine Sound by Engine Vibration) technology. This paper describes the ESEV Plus Minus that uses engine vibration to not only enhance the certain engine order components but reduce the other components at the same time. Consequently, this technology would produce a much more diverse engine sound.

The Design of Wind Noise Transducers to Separate Acoustic and Turbulent Pressures

A four element wind noise transducer has been designed with surface mounted electret microphones in an array pattern which allows for the separate determination of the acoustic and turbulent pressures in wind noise. Three closely spaced transducers, defining an x-y coordinate system, are positioned to determine the velocity and direction of the turbulent flow. A fourth transducer is positioned at a greater distance such that the correlation of the turbulent flow will be diminished while the correlation of the acoustic pressure remains due to its longer wavelength. By averaging the cross-spectral densities of the pressure signals over time, the two contributors to wind noise can be differentiated. In addition, a wireless interface has been designed to minimize the flow disturbance of the transducer array.

Prediction of Automotive Air-Handling System Flow Noise Sound Quality Using Sub-System Measurements

This paper presents the methodology of predicting vehicle level automotive air-handling system air-rush noise sound quality (SQ) using the sub-system level measurement. Measurement setup in both vehicle level and sub-system levels are described. To assess the air-rush noise SQ, both 1/3 octave band sound pressure level (SPL) and overall Zwicker's loudness are used. The ?쏶ound Quality Correlation Functions (SQCF)??between sub-system level and vehicle level are developed for the specified climate control modes and vehicle segment defined by J.D. Power & Associates, while the Zwicker's loudness is calculated using the un-weighted predicted 1/3 octave band SPL. The predicting models are demonstrated in very good agreement with the measured data. The methodology is applied to the development of sub-system SQ requirement for upfront delivery of the optimum design to meet global customer satisfaction

A Unique Noise & Vibration Software Tool for Automotive Troubleshooting

A unique Matlab-based coded engineering software tool (Time-Frequency Analyzer Core짰) was developed that allows users to process acquired time data to help in identifying sources and paths of noise and vibration (in the experience of the authors). The Time-Frequency Analyzer Core (TFAC) software does not replace commercial off the shelf software/hardware NV specific tools such as modal analysis, ODS, acoustic mapping, order tracking, etc., rather it aims at providing basic, yet powerful data inspection and comparison techniques in a single software tool that facilitates drawing conclusions and identifying most effective next steps. The features and advantages of using this software tool will be explained, along with a description of its application to a few different cases (automotive and off highway/agricultural).

Operational Determination of Car Window Damping

Wind noise can be a significant event for automotive design engineers. The greenhouse glass plays an important role in the wind noise process. Robust estimates of the greenhouse glass damping are necessary for both understanding and modeling the role of the glass in the wind noise process. One unanswered question is whether the aerodynamic loads affect the window glass damping. To make this determination a method to assess the operational damping is required. The civil engineering community uses the random decrement technique to assess operational damping due to wind loads. The random decrement technique has been shown to be a normalized autocorrelation function. In this paper the damping is estimated directly from the autocorrelation function. In the first section the relationship between the damping and autocorrelation function is examined for white noise excitation. A single oscillator is examined as the first case. Extension to higher modal densities is discussed. Finally application to a car window is presented. The window results were limited by signal to noise problems.

An Experimental Study of Mechanism of Body Panel Vibration in Booming Noise Reduction of Passenger Vehicles

In a typical passenger vehicle, there can be different types of noises generated which are broadly categorized as Interior Noise and Exterior Noise. The interior noise sources can be further classified into noises which can be Structure Borne or Air Borne. One of the major sources of both structure borne and airborne noise generation is the powertrain of the vehicle. The structure-borne noise and vibrations generated from the powertrain is usually transferred to the vehicle body through its attachment points to the body and the powertrain driveline. These induced body vibrations can sometimes cause the acoustic cavity of the passenger cabin to go into resonance which results in an annoying and disturbing noise for the passengers, called Booming Noise. Very often, one or more than one vehicle body panels show a dominant contribution in inducing this acoustic cavity resonance. In this research, the backdoor of the selected passenger cars were identified to be one of the primary contributors in causing the booming noise phenomena. The objective of this research was to study the mechanism of the contribution of backdoor towards booming noise in these hatchback style passenger vehicles. The study was carried out on three differently styled hatchbacks namely Model A, Model B, and Model C. The study of the mechanism behind this contribution was carried out in three phases. The first phase included the response measurements of the individual grid points created on the backdoor which were excited using a low frequency sound source. In the second phase, a computer model of the grid structure of the backdoor was created and the response measurements obtained were superimposed on the geometry model to identify the modal parameters of the backdoor. The identification of the modal parameters helped in understanding the modal behavior of the backdoor which is causing the acoustic resonance of the cabin cavity thus creating the booming noise phenomena. In the third phase, in cabin acoustic measurements were carried out during vehicle acceleration tests and the results were correlated with the modal parameter data. This helped in identification of the dominant modal frequencies to be targeted for further design improvements during concept & vehicle design stage.

The Effects of Unsteady Flow Conditions on Vehicle in Cabin and External Noise Generation

A vehicle driving on the road experiences unsteady flow conditions which are not generally reproduced in the development environment. This paper investigates the potential importance of this difference to aeroacoustics and hence to occupant perception and proposes a methodology to enable better ranking of designs by taking account of wind noise modulation. Two approaches of reproducing the effects of unsteady wind on aeroacoustics were investigated: an active wind tunnel Turbulence Generation System (TGS) and a quasi-steady approach based on measurements at a series of fixed yaw angles. A number of tools were used to investigate the onset flow and its impacts, including roof-mounted probe, acoustic heads and surface microphones. External noise measurements help to reveal the response of separate exterior noise sources to yaw. The noise experienced by the driver or passenger ear facing the side-glass is dominated by increased sound pressure levels when the adjacent side-glass is the leeward side of the vehicle with some non-linear effects as leeward yaw produces first accelerated flow and then separation. In part because of non-linearity in response to yaw, a challenging parameter for a wind tunnel simulation of dynamic yaw is achieving a wide enough variation in yaw angle and this work suggests that considering an appropriate range of yaw angles is more important than capturing the dynamics. In terms of passenger perception, the most important effect of a time-varying onset flow was demonstrated to be the modulation of wind noise rather than the increase in time-averaged cabin noise. For the case considered, at 130 km/h, the impact of wind-noise modulation was found to be equivalent to an extra 1-2 dBA in terms of passenger perception, while the increment in time-averaged cabin noise would be only 0.2 dBA.

Daimler Aeroacoustic Wind Tunnel: 5 Years of Operational Experience and Recent Improvements

Since 2013 the new Daimler Aeroacoustic Wind Tunnel (AAWT) is in operation at the Mercedes-Benz Technology Center in Sindelfingen, Germany. This construction was the second stage of a wind tunnel center project, which was launched in 2007 and started with the climatic wind tunnels including workshop and office areas. The AAWT features a test facility for full-scale cars and vans with a nozzle exit area of 28 m2, a five-belt system, and underfloor balance to measure forces with best possible road simulation. With a remarkable low background noise level of the wind tunnel, vehicle acoustics can be investigated under excellent conditions using high-performance measurement systems. An overview is given about the building and the design features of the wind tunnel layout. The aerodynamic and aeroacoustic properties are summarized. During the first years of operation, further improvements regarding the wind tunnel background noise and vehicle handling were made. Changes in the surface of the contraction and the reduction of rough surfaces in the test section reduced the self-noise of the wind tunnel. For the standard test section configuration (used for daily operation) with smooth center belt, an overall sound pressure level of 57.2 dB(A) could be achieved, for a further optimized configuration with taped gaps and covered shutters and belts even 55.2 dB(A) were measured. Since the manual ride height adjustment of a vehicle in the test section showed to be very time-consuming, a new automatic ride height measuring system was developed. It significantly reduces the setup time before the first measurement. For the rising demands to document surface changes after a test campaign, a separate room for 3D surface scanning was already provided in the workshop area. The technical layout could only be finished with delay. Now the room houses a frontal area measurement system, vehicle lifts, and a robot for 3D surface scanning. This paper describes these new features and reports about the experiences of the first years of operation.

Surface treatment to reduce squeak noise in vinyl parts

It is a common practice of automotive industry to avoid dynamic contact between two surfaces with similar roughness for plastics and interior trim parts. That means reduce the friction and, consequently the squeak noise to the minimum level to meet zero noise level. Unfortunately, for design or economics reasons, that is not possible for some applications and a very disturbing noise may bother the costumer. A material incompatibility leads to an acute noise when two similar surfaces have relative movement due to multiple adherences between the surfaces, that is called stick-slip phenomenon. To characterize this noise, a Squeak and Rattle Evaluation testing should be performed in the worst case condition over the life of the vehicle. As a result, a scale of Risk Priority Number (RPN) provides a pass/fail judgement to implement any improvement required to address the issue. There are several ways to avoid this phenomenon during the product development: applying lubricants, tapes, coatings, material change or surface treatments. To solve this kind of undesirable user experience, an anti-squeak treatment was developed in water base using polymeric material, applied in a process similar to coating and cured thereafter by heat. The concept of this anti-squeak treatment is to reduce surface tension and the resistance of relative movement when fractioning similar material that leads to a reduction of noise, consequently. The aim of this paper is to show how this surface treatment can reduce the noise level related to material similarity, applying this into a vinyl surface, with no changes in mechanical properties and no need to run a new design verification plan. In the present study, it could be observed a reduction from 10 RPN to 2 RPN, related to an improvement from material match critical to material match in order. This corresponds to a customer satisfaction perception improvement from material audible annoying noise caused by stick- slip expected to not perceived noise.

Designing In-Cab Sound of Vehicles as per the Customer Driving Pattern on Roads

Vehicle refinement from point of view reduction in its Noise, Vibrations and Harshness (NVH) affects customer?셲 buying decision and it also directly influences his/her driving experience on road at different speeds. Customer voice, however, indicates that a traditional process of developing design solutions is not aligned with the customers??expectations. Traditionally the load cases for NVH development are focused only on quietness of passengers??cabin at idling and in 3rd gear wide open throttle cruising on smooth roads. In reality, the Driver of a premium sedan car or a Sports Utility Vehicle (SUV) or a Compact Utility Vehicle (CUV) expects something different than merely the low sound pressure level inside the cabin. His/her driving pattern over a day plays a crucial role. A vehicle-owner wishes to balance various attributes of the in-cab sound and tactile vibrations at a time. A single value Customer-Voice-Index (CVI) is developed here based on study of critical drive load cases faced by common customers classified with C: Critical to customer perception; O: Occurrence of each drive load case throughout running of the vehicle and D: Duration of each load case. Cost to Benefit Ratio of various design solutions then could be evaluated effectively in a vehicle by monitoring its CVI. This is demonstrated here on a new SUV to give the desired sound character of the vehicle with low cost solutions and thus make the customers fall in love with it during cruising on highways at high speeds.

Low Frequency In-Cab Booming Noise Reduction in the Passenger Car

In-cab booming noise is low frequency (20 Hz??00 Hz) phenomenon excites the cabin structure, which occurs mainly due to excitations from the powertrain, exhaust system, road input, etc. Annoyance due to booming noise affects the In-cab sound quality, which results in passenger discomfort. A diesel passenger car observed booming noise issue when operated at stationary as well as dynamic run-up conditions. In order to increase passenger comfort, experimental root cause analysis conducted on the vehicle to investigate the dominant sources for the cavity boom. Exhaust hanger and one of the engine mount identified as major reason for the booming noise in the cabin. A detailed study was carried out on dynamic property optimization of rubber hanger and possibility to relocate the hanger to improve the vibration transmissibility. Operational measurements conducted on vehicle by attaching finalized exhaust mount to confirm the significant booming noise reduction in the cabin.

Investigation of Cabin Noise while Accelerating on Low Mu Track through Simulation Approach Using Full Vehicle ADAMS/Car Model

Cabin noise is a significant product quality criteria which enables the customers for product differentiation. There are various sources of cabin noise such as wind, structures(panels), engine, suspension, tire and roads. During product development phase, extensive tests has been conducted to improve vehicle dynamics behavior on various climatic conditions. One such test is accelerating vehicle on low mu or icy surface. While performing acceleration manoeuvre (tractions) on a low mu tracks, Cabin noise with source identified from front underbody & low tractive torque build up is reported. This undesirable behavior may occur due to following reason (1) Excitation of coupled modes between suspension and powertrain which induces torque fluctuation. (2) Transmissibility of various subsystem can be the reason for above problem statement. (3) Poorly chosen tire compounds and design leads to fluctuation in torque. A detailed simulation based study using ADAMS/CAR has been performed to assess the contribution of various full vehicle sub-systems, primarily suspension & powertrain sub-system towards the said problem statement. The dynamic interaction between road, suspension, powertrain and BIW has been is the focus of study both in time and frequency domain. This simulation helped understand the factor effects and contribution levels and correlates well with the subjective feel observed on the physical vehicle on low-mu track. This model has been further used to provide design recommendation on the compliance parameters to overcome the issue at hand. Test has been conducted with recommended tire grip properties and suspension bushing parameters which lead to reduction in cabin noise

Design of Super Silent Enclosure for Diesel Genset Using Statistical Energy Analysis (SEA) Technique

Diesel engine generators are commonly used as a power source for various industrial and residential applications. While designing diesel generator (DG) enclosures requirements of noise control, ventilation and physical protection needs to be addressed. Indian legislation requirement demands DG enclosure insertion loss (IL) to be minimum 25 dB. However for certain critical applications like hospitals, residential apartments customer demands quiet DG sets than the statutory limits. IL targets for such application ranges between 35-40 dB. The objective of this paper is to develop methodology to design ?쁓uper Silent??enclosure with IL of 35 dB by Statistical Energy Analysis (SEA) approach for small capacity DG set. Major challenge was to achieve IL of 35 dB with single enclosure and making use of SEA technique for small size enclosure wherein modal densities is very less. Major airborne noise sources like engine, radiator fan and exhaust were modelled by capturing noise source test data. Structure-borne sources like panel vibrations were also modelled via vibration measurements. Noise control treatments (NCT) were sculpted using BIOT parameters. The predicted sound levels for an existing DG enclosure model were validated with its test data to ensure correctness of SEA model. Further critical noise paths identification and ranking was done through simulation. Based on results of above step, modifications were suggested on NCT, louvers, baffles, ducts and muffler to arrive at optimized enclosure. Proto for optimized enclosure was tested. Test showed IL of 35.5 dB against predicted IL of 35 dB showing very good correlation.

Computational Aeroacoustics Based on a Helmholtz-Hodge Decomposition

Using existing aeroacoustic wave equations, we propose a general hybrid aeroacoustic method, based on compressible flow data. By applying the Helmholtz-Hodge decomposition on arbitrary domains, we extract the incompressible projection (non-radiating base flow) of the compressible flow velocity by solving the vector valued curl-curl equation with the vorticity as forcing term. The resulting vortical flow part is used for computing the acoustic source term. This method maintains the favorable properties of the hybrid aeroacoustic method, while still considering acoustic feedback on the flow field.

Numerical Design of Loudspeaker Systems in a Car Cabin

These days loudspeaker systems in vehicles are gaining more and more of importance. Usually quite a few speakers are installed and driven in combination in order to obtain a convincing sound environment for the occupants/customers. Sometimes even a 3D sound experience shall be reached, where up to 20 loudspeakers might become necessary. No doubt that such a number of speakers and their proper placement in the car cabin is a rather challenging task, leading to extensive measurements in different cabin environments. In the current contribution, it is suggested to simulate the scenario by means of specially combined computer models. These allow not only a rather economic possibility to investigate different changes/variants without expensive new setups but also an additional gain of knowledge. For the numerical representation of the loudspeaker system a multiphysics approach is needed, namely physical aspects of electromagnetics, structural dynamics, and acoustics have to be considered and combined. Doing so, the different fields might be accounted for by models obeying different levels of detail, where the spectrum might reach from simple 1D approaches to highly detailed 3D models. In view of this, different methodologies such as the finite element method, the boundary element method or energy based formulations need to be coupled. In the current contribution a methodology for the numerical design of loudspeaker systems is developed and discussed by means of representative examples.

Correlation Analysis of Interior and Exterior Wind Noise Sources of a Production Car Using Beamforming Techniques

Beamforming techniques are widely used today in aeroacoustic wind tunnels to identify wind noise sources generated by interaction between incoming flow and the test object. In this study, a planar spiral microphone array with 120 channels was set out-of-flow at 1:1 aeroacoustic wind tunnel of Shanghai Automotive Wind Tunnel Center (SAWTC) to test exterior wind noise sources of a production car. Simultaneously, 2 reference microphones were set in vehicle interior to record potential sound source signal near the left side view mirror triangle and the signal of driver?셲 ear position synchronously. In addition, a spherical array with 48 channels was set inside the vehicle to identify interior noise sources synchronously as well. With different correlation methods and an advanced algorithm CLEAN-SC, the ranking of contributions of vehicle exterior wind noise sources to interested interior noise locations was accomplished. The results demonstrate that the advanced deconvolution algorithm CLEAN-SC has significant improvement against limitations of spatial resolution and dynamic range of conventional Beamforming technique. It has great potential for vehicle wind noise transmission path analysis and wind noise optimization work in the wind tunnel. In addition, Correlation analysis result of interior and exterior noise sources using virtual and real reference microphones was compared and discussed as well.

An Analysis on Automotive Side Window Buffeting Using Scale Adaptive Simulation

Automotive window buffeting is a source of vehicle occupant?셲 discomfort and annoyance. Original equipment manufacturers (OEM) are using both experimental and numerical methods to address this issue. With major advances in computational power and numerical modelling, it is now possible to model complex aero acoustic problems using numerical tools like CFD. Although the direct turbulence model LES is preferred to simulate aero-acoustic problems, it is computationally expensive for many industrial applications. Hybrid turbulence models can be used to model aero acoustic problems for industrial applications. In this paper, the numerical modelling of side window buffeting in a generic passenger car is presented. The numerical modelling is performed with the hybrid turbulence model Scale Adaptive Simulation (SAS) using a commercial CFD code. While the acoustic generation is modelled by solving compressible Navier-Stokes equation, integral method Ffowcs-Williams & Hawkings (FWH) is used to model acoustic propagation in the computational domain. Certain investigation on the influence of rear view mirror (RVM) & divide pillar on buffeting noises are analyzed using a few flow and spectral techniques. Differences in the noise levels between front and rear window buffeting are also investigated. A 3D-cavity test model is considered to validate the modelling methodology. Investigations have shown the installation of a divide pillar on window have significantly minimized noise levels and appendages like the glass mounted RVM have a minimizing effect on the buffeting intensity. Also the noise levels of rear window buffeting are found to be higher than front window buffeting. Modelling window buffeting using a SAS model have shown to be a reliable and computationally less expensive option. The investigations using spectral technique like Fast Fourier Transform (FFT) band analysis gave a better insight in to buffeting problem.

Acoustic Enclosure Optimization for a Higher Capacity Diesel Generator Set Using Statistical Energy Analysis (SEA) Based Approach

Diesel powered electric generators are used in a variety of applications, such as emergency back-up power, temporary primary power at industrial facilities, etc. As regulatory and customer requirements demand quieter designs, special attention is given to the design of acoustic enclosures to balance the need of noise control with other performance criteria like ventilation and physical protection. In the present work, Statistical Energy Analysis (SEA) approach augmented by experimental inputs is used to carry out Vibro-acoustic analysis of an enclosure for higher capacity Diesel generator set. The exterior sound radiated from an enclosed generator is predicted and further enclosure is optimized for an improved sound-suppression. The airborne sources such as engine, alternator, radiator fan and exhaust are modelled explicitly using experimental noise source characterization. Structure borne inputs are also captured in the test for improving modelling accuracy. The vibroacoustic performance of the enclosure and sound absorbers are modelled through Biot parameters and experimentally validated with a good agreement between test and simulated results within 2 dB for overall levels. Further, path contribution and sensitivity analysis has been done on base enclosure to find out major contributors to exterior radiated noise. Optimization is done using parameters like: noise path modifications (ducts, partitions), leakage minimization and acoustic louver designing based on preceding analysis results. Optimized enclosure has resulted in 3 dB reduction in overall noise level

Sound Quality Evaluation of a Brake and Clutch Pedal Assembly used for Automotive Applications

Sound Quality (SQ) of brake and clutch pedal assembly plays an important role in contributing to vehicle interior noise and perception of sound. Quiet operation of brake and clutch units also reflects the vehicle built and material quality. Noise emitted from these sub-assemblies has to meet certain acceptance criteria as per different OEM requirements. Not much work has been carried on this over the years to characterize and quantify the same. An attempt has been made in this paper to study the sound quality of brake and clutch pedal assemblies at component level and validate the same by identifying the parameters affecting SQ. Effect on noise at different environmental conditions was studied with typical operating cycles in a hemi-anechoic chamber. The effect of sensor switches integrated within the clutch and brake pedal on sound quality is analyzed. It is found that the operating characteristics of switches drives the noise and SQ. Wavelet analysis was carried out to correlate loudness sound quality metric with time-frequency amplitude modulations. Jury evaluation was performed to correlate subjective to objective data. Structural modifications were then suggested to improve the perception of sound. Significant improvement in the brake and clutch pedal assembly sound quality was achieved in product development with marginal impact on cost.

A Study on the Vehicle Body Effect on Brake Noise

Creep groan noise occurs in a just moving vehicle by the simultaneous application of torque to the wheel and the gradual release of brake pressure in-vehicle. It is the low frequency noise giving the driver a very uncomfortable feeling. Recently, the field claims regarding the creep groan noise are increasing. So far, creep groan noise has been improved by means of chassis modification the transfer system. But vehicle body the response system does not. In this paper, the effect between vibration characteristics of vehicle body, creep groan noise was analyzed. Then presented analysis method for vehicle body effect regarding creep groan noise.

C-17 Cargo Ramp and Door Automated Drilling & Fastening System - Project Overview

To further reduce airframe costs associated with fastener installation, an Automated Drilling & Fastening System (ADFS) has been implemented on the C-17 Program to enhance current Mold Line attachment processes. The ADFS will automate up to 90% of all Cargo Ramp and Door Mold Line fastener installations. Implementation of the C-17 ADFS captures a five goal technological approach identified at project onset: 1) Increase the use of automated drilling and fastening equipment, 2) System shall be Numerically Controlled, 3) High speed drilling techniques shall be used, 4) Minimize the use of current tooling, and 5) Design the system to use components common to other Boeing drilling & fastening machines.

Mechanical and Structural Aspects of the C-17 Cargo Ramp and Cargo Door ADFS

The cargo ramp and cargo door are two major C-17 components that are built in St. Louis, MO and shipped by rail for final assembly in Long Beach, CA. A major portion of the total build time for the ramp and door assemblies consisted of the hand installation of approximately 16,000 moldline fasteners and 19,400 moldline fasteners, respectively, attaching the skin to the substructure. In addition, several thousand fasteners are also installed in the floor sections of the ramp and door. A major cost savings opportunity existed to reduce the cost of the ramp and door assemblies by automating the installation of these fasteners. Boeing-St. Louis contracted Brotje Automation of Wiefelstede, Germany to design and build an automated drilling and fastening system (ADFS). Automation is expected to reduce cost by reducing the time required to build the ramp and door assemblies. In addition, automation is expected to improve fastener hole quality and fastener installation quality. Another important reason for undertaking this project was to enable Boeing-St. Louis to strengthen its position as an industry leader and innovator in aerospace manufacturing. This paper describes the mechanical and structural challenges (associated with hoisting and supporting the assemblies) that were overcome to implement this initiative.

A Direct Method for Designing Fuel Filler Door with Torsional Spring

A direct method is developed for designing a vehicle fuel filler door with torsional spring. The design parameters include the door's geometrical parameters and spring dimensions. The design requirements are based on the finger force curve during closing and opening, and the bending stress in the spring. An example is included to demonstrate the effectiveness of the new method.

An Ultra-Light Thin Sliding Door Design - A Multi-Product Multi-Material Solution

Sliding door designs are applied to rear side doors on vans and other large vehicles with a trend towards dual sliding doors with power operation. It is beneficial for the vehicle user to reduce the weight of and space occupied by these doors. Alcoa, in conjunction with Ford, has developed a multi-product, multi-material-based solution, which significantly reduces the cost of an aluminum sliding door and provides both consumer delight and stamping-assembly plant benefits. The design was successfully demonstrated through a concept readiness/technology demonstration program. The key findings of the joint effort demonstrated: Reduced system cost through parts reduction/consolidation and associated reduction of stamping and joining/assembly operations, gauge reduction and optimized material utilization Reduced thickness of the door by over 60mm and weight reduction by over 11kg, Equivalent functional performance to the current steel door Manufacturability using robust processes at desired quality and reliability levels. Improved quality and reliability of assembling the door hardware, which significantly improved serviceability over traditional designs. The basic door design concept is also applicable to other types of doors.

Integrated Test Platforms: Taking Advantage of Advances in Computer Hardware and Software

Ongoing hardware, software, and networking advances in low-cost, general-purpose computing platforms have opened the door for powerful, highly usable, integrated test platforms for demanding industrial applications. With a focus on the automotive industry, this paper reviews the pros and cons of integrated test platforms versus single-purpose and stand-alone testers. Potential improvements in in-process testing are discussed along with techniques for effectively using such testing to improve daily production quality, to maintain high production rates, to avoid unplanned downtime, and to facilitate process and product improvements and refinements through the use of monitoring, data collection, and analysis tools.

Optimal Design of Panel Reinforcing Material Using Practical Measurement Technique

Expandable reinforcing material such as that used for the outer panel of a door has been used to compensate for the lack of stiffness in automotive body panels. This material can improve panel stiffness and reduce vibration that causes radiated noise. Material properties in practical use have generally been evaluated by sensory methods. These properties, however, have not been sufficiently quantified to optimally design reinforcing material. We have developed evaluation methods aimed at ensuring reinforcement and also at reducing vibration and deformation in a panel. By employing these evaluation methods along with simulation of a material's basic properties, we are able to achieve the optimal design of materials for outer body panels.

Quantitative Assessment of Cosmetic and Structural Quality in Automotive Outer Body Panels Using ARAMIS Stereo Photogrammetry System

The methodology described enables high accuracy in the measurement of static and dynamic stiffness and dent resistance. Among the parameters being evaluated are: stiffness and dent resistance of the automotive outer body assembled panels ??under both static and dynamic loading and the effect of the stiffening features in the panel shape, upon its deformation characteristics under dynamic excitation and dynamic wave propagation following slow projectile impact. This methodology will help part and process designers to correctly position and manufacture outer and inner body features like door handle embossment shape and location, feature lines, lamp and mirror embossments, hemming lines and side bar locations. Measurements are carried out using the stereo photogrammetry system ARAMIS ??a fast and cost effective tool with a high accuracy of displacement measurement in both static and dynamic conditions. Measurements were performed in real time related to the phase of elastic wave generated by projectile impact. Parameters of the elastic wave were defined using laser displacement sensors and accelerometers with a linear accuracy of 0.5 關m.

Visualization and Classification of Strategy for Entering Car

This paper proposes a method for visualizing and classifying the variation in the motions of a person when entering a passenger vehicle. Entering behaviors vary greatly between individuals, especially if the vehicle door is designed to have large clearance. The present study was conducted with the aim of supporting the design process of seats and front doors by visualizing possible variations of entering motions using a motion database, rather than calculating a single representative movement. The motion database is consist of different motions caused by various seats, and the motions are classified by mapping them into two-dimensional plane according to the similarities between them. A representative entering motion for a clustered motion strategy group is synthesized and visualized on the 2D distribution plane by interpolating existing motions in the database.

Development and Application of High-Strength Steel for Auto Outer Panel in Baosteel

The characteristics of China's automotive steel sheets and high strength steels (including bake-hardening, high strength IF and isotropic steel) developed recently by Baosteel for automotive outer panels are briefly reviewed. Among these steels, bake-hardening (BH) steel is often used to make outer panel parts, such as hoods, decklids, and front and rear doors. In this paper, we present results from an investigation of the effect of baking process (temperature and time) on the bake hardening index value of BH220 steel, and through evaluation of tensile specimens cut from a production hood and simulated part. The results show that BH value is more than 30 MPa when the baking time is more than 2 minutes (at a temperature of 170째C) or the baking temperature is more than 90째C (for baking time of 20 minutes). Measurements on an actual hood and simulated part showed that baking has no effect to enhance the yield strength of the panel, but it can enhance the dent resistance. One needs to consider other factors when using the empirical equation (DR?쒴횞ta횞YS) to evaluate dent resistance of automotive panels.

Advanced High-Strength Steels and Hydroforming Reduce Mass and Improve Dent Resistance of Light Weight Doors In UltraLight Steel Auto Closures Project

In May 2000, the UltraLight Steel Auto Closure (ULSAC) Consortium unveiled a lightweight frameless steel door design that achieves 42 percent weight savings over the average benchmarked (1997 model year vehicles) frameless door and 22 percent savings over the lightest benchmark, a framed door. ULSAC was commissioned by this international consortium of 31 sheet steel producers to assist their automotive customers with viable lightweighting steel solutions. The ULSAC design and engineering team, Porsche Engineering Services, Inc. (PES), Troy, Michigan USA, accomplished this significant weight savings by using high and ultra high strength steels, combined with technologies such as tailored blanks and hydroforming. The door outer panel of this first round of demonstration hardware is made of stamped 0.7 mm Bake Hardenable (BH) 260 sheet steel. During the design and development of the ULSAC frameless door, the ULSAC Consortium evaluated further mass reduction, using sheet hydroforming for the door outer. Consequently, the ULSAC Validation Phase continued beyond May 2000 with sheet hydroforming process development for the door outer as a means to compile practical research documentation for this developmental process with mass reduction potential. Door structures were successfully manufactured with 0.6 mm Dual Phase (DP) 600 hydroformed steel outer panels achieving additional weight savings.

Economic Analysis of Two Different Door Architectures

In the past, materials selection for automotive components has been managed on a part-by-part basis. As a result, the economics of these selections have often been reduced to comparing material price/property ratios, rather than technological options. More recently, the debate around modular designs and their advantages and disadvantages has shifted the emphasis towards a higher level viewpoint that deals with more complex systems. This approach provides the opportunity to search for new combinations of product architecture and materials that may exploit specific material advantages better than the classic part-by-part replacement. This paper presents the results of an economic analysis for two different door designs. The door designs differ both with regards to their product architectures and with regards to the materials they employ. The economic analysis considers the following process steps: parts fabrication, subassembly, paint, and final assembly (trim) for two production scenarios. The case study reveals several findings. First, the analysis concludes that both door designs offer a potential economic advantage depending on the final production volume. Specifically, the conventional design is considered more appropriate for high volume production, whilst the alternative design is more cost effective at production volumes typical of niche and derivative vehicles. Second, since the choice of design architecture has an influence on all sub systems, meaningful comparisons between the architectures may be made only through the adoption of comprehensive cost models. For example, the case study demonstrates that the choice of certain product architectures can help mitigate disadvantages caused by higher input material costs. Finally, the case study finds that the cost savings from ?쁟ommonization??of components vary depending on the base production volume.

Open Bay Door Analysis Process for Hubble Space Telescope Servicing Mission 3B

During Servicing Mission 3B (SM3B) for the Hubble Space Telescope (HST) the Power Control Unit (PCU) will be replaced. The PCU was not originally designed to be replaced on orbit but was later identified as having the capability of being removed and replaced on orbit. The PCU has many connectors and bolts, some of which are difficult for the astronauts to reach. Due to the added difficulty, the replacement will take an entire six hour Extra Vehicular Activity (EVA) day. For four of these six EVA hours the door of the Support Systems Module (SSM) Equipment Section (ES) bay where the PCU is found will be open to allow the astronauts access to the PCU and its connectors. This bay, SSM ES Bay 4, also contains the four Power Distribution Units (PDUs), which house the busses, switching, fusing, and monitoring circuits that distribute power to the telescope. These PDUs are attached to the bay door and will be seeing a much colder than normal environment with the door open. The PCU controls power for the entire telescope and therefore when it is replaced all power to the telescope will be turned off. With power removed and the bay door open the PDUs will cool rapidly. In order to be sure that the PDUs remain above their turn-on and operating temperature limits during the change out, a detailed open bay door analysis was conducted. For this analysis a Thermal Synthesizer System (TSS) model was created of Bay 4 and it?셲 components. The model was used to calculate radiation couplings and heat rates with the bay door open. The FORTRAN code used to analyze the Servicing Mission timeline was modified and the new radiation couplings and heat rates added. This paper deals with the creation of the detailed TSS model as well as the modifications made to the timeline code in order to run the analysis. It will also present the temperature predictions for the PDUs during the PCU change out.

Passive Sensing of Driver Intoxication

A sensor that passively monitors the driver for intoxication has been demonstrated. The driver's blood alcohol concentration (BAC) is obtained by sensing alcohol and CO2 in air drawn from the vehicle cabin. With a legally drunk driver, the steady state alcohol concentration can be as low as 0.3 ppm, even with the doors and windows closed. The sensor uses infrared transmission to quantify alcohol vapor and CO2. A vapor concentrator increases alcohol sensitivity - an adsorber collects alcohol vapor and releases it as a concentrated burst at 1 minute intervals. A valid measure of driver BAC is ordinarily available 1.5 minutes after the driver gets in. Sensed CO2 must be above a threshold for a valid measurement.

The Truck that Jack Built: Digital Human Models and their Role in the Design of Work Cells and Product Design

Henry Ford is credited with the invention of the assembly line and for 100 years now we have manufactured high quality cars and trucks. The process to bring cars and trucks into production has seen many changes with the introduction of new technology, however the principle is still the same; designers draw concept designs and engineers transform these designs into functional parts. The first time the engineering community has a real feel for the design and process compatibility is at a physical prototype build. The money invested in the designs and prototype parts alone make the thought of a design change this late in the game, unbearable. The design of the manufacturing process along with product design has embraced virtual tools and digital human models to assess assembly feasibility. The major incentive to utilizing such tools is to reduce costly re-engineering of parts and to decrease prototype costs. Virtual technology allows ergonomists and engineers to perform ?쐖irtual builds?? This opens up doors for early ergonomic evaluation on the product design, process and tooling. Digital human models, motion capture technology, and biomechanical evaluations are all critical in performing accurate ergonomic analysis. This paper demonstrates how digital human technology is being utilized every day to drive sound engineering decisions in automotive manufacturing.

Low Gloss ABS Advancements for Automotive Interior Components

Automotive Original Equipment Manufactures (OEM's) desire interior plastic components being used on consoles, doors, trim areas, and instrument panels to have very low gloss levels. In fact, some OEM's have specified a 2.0 or lower sixty degree Gardner gloss level for most first surface interior components molded in color (MIC) and without paint or a secondary finishing process such as a vinyl wrap. While a trend in the industry is to move toward PP based materials because PP parts are believed to provide lower gloss aesthetics and lower gloss gradients, key features and benefits of ABS products such as dimensional stability, impact, load bearing at elevated temperatures, and scratch resistance, are compromised. Recently, Dow Automotive has developed lower gloss capable ABS resins which also exhibit typical ABS physical and thermal properties. This paper will detail the gloss and gloss gradient advantages of these new low gloss ABS products over a standard talc filled PP material and two traditional ABS products as observed in a glove box outer injection molding trial.

Child Safety via Anti-Trap Proximity Technology

Sir Galahad??anti-trap windows prevent injury and death, creating a new standard of care for automotive power closures. NHTSA estimates 500 people, approximately 50% of which are children, are treated in hospital emergency rooms each year for injuries related to power windows [11]. Sir Galahad??technology is easy to install and works on all applications, independent of window shape or geometry. The system is ideally suited for power windows, sunroofs, tailgates, sliding doors, trunks and any other power closures. This paper describes the design and operation of Sir Galahad??anti-trap windows, including experience of sensitivity response to both animate and inanimate objects. Also discussed are vehicle installation, performance test results, and competitive performance comparisons.

Tailor-Welded Aluminum Blanks for Liftgate Inner

Tailor welded steel blanks have long been applied in stamping of automotive parts such as door inner, b-pillar, rail, sill inner and liftgate inner, etc. However, there are few known tailor welded aluminum blanks in production. Traditional laser welding equipment simply does not have the capability to weld aluminum since aluminum has much higher reflectivity than steel. Welding quality is another issue since aluminum is highly susceptible to pin holes and undercut which leads to deterioration in formability. In addition, high amount of springback for aluminum panels can result in dimension control problem during assembly. A tailor-welded aluminum blank can help reducing dimension variability by reducing the need for assembly. In this paper, application of friction stir and plasma arc welded blanks on a liftgate inner will be discussed.

Use of SEA for Vehicle Target Setting and Efficient Realization of Vehicle Acoustic Goals

Statistical Energy Analysis (SEA) is an established technique for predicting vehicle NVH. Since SEA is more sensitive to certain parameters such as material properties, damping, absorption, and treatment thickness and coverage than to fine details of geometry, using SEA is especially practical and can be particularly advantageous in the early design phase of a vehicle development project. Different concepts for various vehicle subassemblies such as dash, doors, roof, floor, etc., can be effectively evaluated for feasibility at a very early stage in the design process. Such concept studies can prevent design failures and can also be used to improve subassembly NVH target setting. An introduction to SEA and summary of the established use of SEA for vehicle NVH design and development are presented. A proposed methodology for application of SEA to vehicle design is presented, addressing model validation, contribution analysis, target setting, design sensitivity analysis, and optimization for different design concepts and proposed configurations of the vehicle and vehicle subassemblies. A concrete example of an SEA vehicle subassembly model and modeling considerations is presented, followed by a summary and set of conclusions.

A New Approach for Best Fit Assembly Based on the Behaviour of Components

Best fit assembly is now a widely spread assembly technique that consists in finding an optimal position of measured components in order to get an assembly that fits its tolerance specifications. The rigid body assumption does not apply for compliant assemblies that can be slightly deformed and for which the geometrical variations are cleared by the flexibility of components to be assembled. We are proposing a best assembly process that takes into account through simulation the flexibility of components. Thanks to this more realistic simulation, the best fit application scope can be enlarged and confidently applied. It leads to reduced fitting times for over-constrained parts or interchangeable items, like doors, during assembly integration and in service replacements.

Two-Reference Beam Double-Pulsed Holographic Interferometry with Direct Phase Measurement in Transient Processes Study

Holographic interferometry has been successfully employed to characterize both static and dynamic behavior of diverse types of structure under stress. Double-exposure pulsed holographic interferometry has been extensively used in performing the vibration analysis and qualitative investigations of deformation of the non-stationary objects. One of the most important advantages of this technique is that it can be used for quantitative measurements of the transient processes (e.g. shock wave propagation). However, in conventional double-pulsed interferometry it is sometimes difficult to get phase information from a single set of holograms. Applying two-reference beam recording set-up to double-exposure pulsed holographic interferometry makes it possible to obtain phase-shifted interferograms from a single interferogram of the tested object and retrieve the phase information for OPD (optical path difference) map creation. Two-reference beam double-pulsed Ruby laser holographic interferometer has been adapted to transient and continuous phenomena studies. It is non-destructive, real-time, and definitive approach in identification of vibrational modes, displacements, and motion geometries. Results of a vibration study performed by double-pulsed Ruby laser holographic interferometry for wave excited by shaker with continuous sinusoidal excitation and propagated over the car door panel surface are presented in this paper.

Active vibration control of automotive like panels

Automotive panels can be great transmitter of undesired sound from external sources. The ability of controlling the noise and vibration performance of such panels is critical to the perceived quality of a vehicle. Passive vibration systems are currently used in vehicles, but they tend to be heavy in nature and capable of covering only a frequency range above 100-200 Hz. Active vibration control is a potential alternative to passive control. Its cost and adaptability of an active system has been the primary concern for implementation in the automotive sector. Recent developments in the control implementation and lower cost of electronics in general have made the gap between active and passive much smaller than before. An active vibration control has been developed and demonstrated into an automotive-like panel. Such panel was sized to represent a door of a military vehicle. Several excitation sources were considered and included engine excitation, road excitation and blast excitation due to the military design constraints. The active vibration control system is comprised of strain sensors, piezoelectric actuators, a control system and a power amplifier to drive the control actuators. Several control strategies were used depending on the source of excitation. Once of the primary features of all the control strategies used was their adaptability to the change in conditions. A 10 to 15 dB vibration reduction was obtained over the frequency range of interest. As the physically conditions changed (shift in frequency), the control algorithm adapted to the new conditions and vibration reduction could be obtained achieving the same level of performance as during the initial target. The cost of the solution was maintained to a minimum, and its potential production costs for automotive quantities was estimated to be in the order of few tens of dollars (US).

Analysis of Determining Parameters of Acoustical Comfort Inside Vehicles

The description of subjectively perceived acoustical comfort inside vehicle compartments is a complex challenge. On the one hand, it depends on physically measurable events like acoustical stimuli with a defined sound pressure level and frequency distribution. On the other hand, it is also strongly dependent on further factors like the customer's individual expectations, the previously made experiences and other contextual influences. Furthermore, many different driving conditions have to be considered for a customer-related assessment of driving comfort. In this paper, the mechanisms of acoustical comfort inside vehicle compartments are described on basis of various measurements, listening tests and qualitative assessments. The acoustical properties of driving noises at various driving conditions were taken into account as well as room-acoustical parameters of vehicle interiors and factors of speech communication between passengers. An interview-based qualitative assessment did confirm the importance of speech communication aspects for the comfort experience and well-being of both driver and passengers. These aspects are for example the speech intelligibility, the quality of conversational speech and further the increase in the vocal effort during a conversation in the presence of driving noises. In addition, the characteristics of driving noises at stationary and non-stationary driving conditions were under examination, both in a listening studio and on a test track. The results of the listening tests and customer surveys are connected to acoustical and psychoacoustical parameters to identify the customer-preferred properties of driving noises. This identification is further itemized to an empirically determined optimal ratio between the main noise components (powertrain-induced, chassis-induced and wind-induced noises). As a result of all these investigations, a prediction model of acoustical comfort will be developed in the future.

Research on the Application of Aluminum Door Beam for Automobiles

Door beams are attached inside car doors as one way to protect passengers from shock when the car is side impacted. Though door beams made of high tensile strength steel predominate now, the use of aluminum is growing rapidly to reduce weight. The effects of cross-section and types alloy on the performance of aluminum extrusions as door beams were investigated. As the result, aluminum door beams were developed which have bending proper2ties comparing favorably with those of door beams made of high tensile strength steel with a tensile strength of 1470 N/mm2. Since the shape of the cross-section of aluminum extrusions is versatile, non-symmetric cross-sections composed of regions with different wall thicknesses and lengths can be produced. On the basis of this technology, a technology to design door beams with required bending properties for any car model was developed. This technology is already been utilized in various automobiles. In this paper, the characteristics of these newly developed aluminum door beams will be introduced along with the results of practical use of them [1].

A Magnetorheological Door Check

Several shortcomings of mechanical door checks are overcome using a magnetorheological damper. Because the damper is electrically actuated, it can check in any desired position. The logical decision to activate or release the door check can be made either by passive circuitry based on input signals from switches attached to door handles or under microprocessor control, in which case the decision can take into account a variety of unconventional input factors, including the magnitude of the force applied to the door, the rate of change of the applied force, and the angle of door opening. With the addition of an appropriate proximity sensor, the controllable damper can prevent the door from inadvertently hitting a nearby obstacle. Details of the damper mechanism are described, and several implemented control strategies, both passive and microprocessor based, are discussed.

Enhanced Security Flight Deck Doors-Commercial Airplanes

In the wake of the 9/11/2001 hijacking events, the Federal Aviation Administration (FAA) has emphasized the need for enhanced flight deck doors on commercial airplanes. The paper describes enhanced flight deck door, which meets the new FAA requirements for intrusion resistance and ballistic protection. In addition, the new door meets the existing requirements for rapid decompression, flight crew security and rescue.