Camber effect study on combined tire forces

Abstract: Considering the more and more concerned climate change issues to which the greenhouse gas emission may contribute the most, as well as the diminishing fossil fuel resource, the automotive industry is paying more and more attention to vehicle concepts with full electric or partly electric propulsion systems. Limited by the current battery technology, most electrified vehicles on the roads today are hybrid electric vehicles (HEV). Though fully electrified systems are not common at the moment, the introduction of electric power sources enables more advanced motion control systems, such as active suspension systems and individual wheel steering, due to electrification of vehicle actuators. Various chassis and suspension control strategies can thus be developed so that the vehicles can be fully utilized. Consequently, future vehicles can be more optimized with respect to active safety and performance. Active camber control is a method that assigns the camber angle of each wheel to generate desired longitudinal and lateral forces and consequently the desired vehicle dynamic behavior. The aim of this study is to explore how the camber angle will affect the tire force generation and how the camber control strategy can be designed so that the safety and performance of a vehicle can be improved. As the link between the vehicle and the road, the tire ultimately determines the dynamic characteristics of the vehicle. Researchers in the automotive industry have developed various tire models to describe the force and torque generation of a tire. The semi-empirical Magic Formula tire model and the simple physical brush tire model are two common and widely used tire models. In this study, a quick review of the Magic Formula tire model and the brush tire model is firstly presented. Bearing the advantages and disadvantages of the two models in mind, a new multi-line brush tire model, which places its focus on camber effect on longitudinal and lateral force generation, is developed according to the brush model theory. The newly developed multi-line brush tire model describes longitudinal and lateral force generation at different camber angles accurately and provides some essential information of the effect of camber angle. However, the multi-line brush tire model consumes huge amount of computational effort thus it is not suitable for real time vehicle level simulations. In order to explore how the camber control strategy can be designed, a simple magic formula model is developed by curve fitting to the multi-line brush tire model. The simple magic formula model takes much less computational effort but represents the force generation at different camber angles quite well as the multi-line brush tire model does. With the help of the simple magic formula model, real time vehicle level simulations are conducted to find the optimal camber control strategies with respect to safety and performance.