# Automotive Seat Comfort and Vibration Performance Evaluation in Dynamic Settings
## 1 Introduction  
Whether it is in conventional driving or riding in an autonomous vehicle, the automotive seat continuously supports the vehicle occupants and has the greatest effect on the overall ride-and-drive comfort. Of all the components within the seat, the foam consists of the most volume, has the largested contact areas as a primary interface between the seat and occupants, and provides the most direct support to the occupant. Therefore, it plays a key role in the occupants' seating comfort. Foam mechanical properties, including density and firmness, are known to affect contact pressure, buttocks tissue oxygenation, and perceived seating comfort [1, 2, 3]. In addition, previous studies have shown that these foam properties can also mitigate vibration being transmitted from the vehicle floor to the occupants, and therefore impact the occupants' perceptions on their riding experiences [4, 5]. Extensive research has indicated that foam mechanical properties such as firmness and vibration transmissibility can significantly affect the occupants' seating comfort and body discomfort [6, 7, 8, 9, 10]. However, these studies also have some notable limitations. For example, the standardized vibration testing for seat comfort evaluations specified by SAE [11] uses a sine sweep input, rather than actual field-measured vibration profiles. Therefore, such tests only measure the seat mechanical properties and do not directly translate to the occupants' perceptions on seating comfort in real-life driving or riding scenarios. Additionally, most studies which evaluated the effects of the foam characteristics on seating comfort havebeen conducted in static, short term, laboratory settings [11; 12]. Because commonly-used automotive seating foams (open cell polyurethane foam) have time dependent viscoelastic material properties [13; 14; 15; 16], the existing short-term evaluations may not provide accurate implications for longer-term dynamic comfort. Hence, it is of great importance to evaluate seating comfort with suitable time durations to account for time-dependency nature of the foam mechanical properties. The foam mechanical properties are known to affect the occupants' vibration exposures. The vibration transmitted from a vehicle to the human body is defined as whole body vibration (WBV) [17]. WBV has long been associated with various adverse health outcomes, especially in the lower back and neck regions [18; 19; 20; 21]. Other studies have indicated that WBV substantially affects a vehicle occupant's perceptions of seating comfort, fatigue, and alertness, especially for longer-term (>45 min) driving and riding scenarios [4; 5; 22; 23]. Extensive research on WBV has been carried out on commercial vehicles which widely use active, mechanical or pneumatic suspension systems to mitigate vibration [21; 24; 25]. On the contrary, passenger vehicles mostly rely on the seat cushion foam for damping and vibration isolation [26]. Because the seat foam is a sole source for vibration mitigation in passenger vehicles, it is important to understand how different mechanical properties of the seat foam affect WBV and associated seating comfort. While previous studies evaluated the effects of foam properties on WBV and related comfort measures, those comfort studies used rigid laboratory-built testing seats or disassembled incomplete automotive seats in laboratory settings [8; 27; 28]. Such incomplete testing seats usually have inferior surface, bolstering, and body support compared to those currently in the market, which can significantly affect WBV exposures and associated comfort measures. Moreover, as occupants' perceived seating comfort is affected by both physical and psychologoial factors [29], the existing laboratory studies may not accurately characterize realistic seating comfort as compared to field-based studies on the real road. Therefore, those existing comfort study results may be confounded with potential noises due to those unrealistic settings (i.e., laboratory and incomplete seats).