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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 squeaki... |
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 enteri... |
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 betwe... |
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., ... |
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 rea... |
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 st... |
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... |
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 ... |
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 T... |
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 thi... |
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 Figur... |
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, ... |
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 ... |
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... |
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 thi... |
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 visc... |
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 compressi... |
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 ser... |
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... |
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... |
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... |
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 materi... |
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 (δ... |
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... |
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 t... |
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 ana... |
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 propo... |
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