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. 