CAR CHASSIS DESIGN

Car Chassis Design



Car Chassis Design

Introduction

Vehicle rollover is a serious problem in the area of ground transportation and a report published by the National Highway Traffic Safety Administration (NHTSA) has found that, even though rollover constitutes only a small percentage of all accidents, it does, however constitute a disproportionately large portion of severe and fatal injuries. Almost 11 million passenger cars, SUVs, pickups, and vans crashed in 2002, yet only 2.6% of these involved a rollover. However, the percentage of fatal crashes that involved the occurrence of rollover was about 21.1%, which is significantly higher than the corresponding percentages for other types of crashes (NHTSA, 2003). In order to help consumers understand a vehicle's likelihood of rollover, the rollover resistance rating program was proposed by NHTSA which uses the static stability factor (SSF), which is the ratio of half the track width to the height of the center of gravity (CG), to determine the rollover resistance rating. The SSF has been questioned by the automotive industry as it does not consider the effects of suspension deflection, tire traction aspects, or the dynamics of the vehicle control system. Accordingly, in 2002, NHTSA published another announcement with regard to a tentative dynamical rollover test procedure (NHTSA, 2001).

Car Chassis Design

Most existing rollover prevention technologies can be classified into two types, namely, (1) the type which directly controls the vehicle roll motion through an active suspension, an active anti-roll bar, or an active stabilizer (Chen & Hsu, 2008) which can prevent rollover by raising the rollover threshold; and (2) the type which indirectly influences roll motions by controlling the yaw motions through differential braking and active front steering (Wielenga & Chace, 2000). Several studies have been undertaken on rollover detection and its prevention and Hac et al. have proposed an algorithm that detects impending rollover and an estimator-based roll index (Hac, Brown, & Martens, 2004). Chen and Peng proposed an anti-rollover algorithm based on the time-to-rollover (TTR) metric (Chen & Peng, 2001). In this research, differential braking is selected as the actuation methodology. Ungoren and Peng evaluated a vehicle dynamics control (VDC) system for rollover prevention (Ungoren & Peng, 2004). Yang and Liu proposed a robust active suspension for rollover prevention (Yang & Liu, 2003) and Schofield and Hagglund proposed a method for rollover prevention that employs an optimal tire force distribution (Schofield & Hagglund, 2008). Yoon and Yi proposed a rollover index that indicates the danger of vehicle rollover as well as an index-based rollover mitigation control system to reduce the rollover index through Electronic Stability Control (ESC) (Yoon, Kim, & Yi, 2007). Since the lateral acceleration is the dominant factor in vehicle rollover, much research into rollover prevention has proposed the use yaw motion control to reduce the lateral acceleration. However, since these rollover prevention schemes only focus on reducing the lateral acceleration, vehicle maneuverability and lateral stability cannot be guaranteed (Yoon, Cho, Koo, & Yi, 2009). For instance, when the rollover prevention controller works to reduce the lateral acceleration, ...