A new formulation of the understeer gradient and stability margin to analyse vehicle steady-state cornering behaviour

Abstract

The understeer gradient is a measure that describes a vehicle's cornering behaviour as either understeer, neutral, or oversteer. Several formulations of this measure have been developed, all of which are reviewed in this paper. It has been found that all of these formulations rely essentially on the lateral acceleration of the vehicle. While the understeer gradient provides a useful connection to vehicle stability, its reliance on lateral acceleration can result in numerical instability and error at high levels of lateral acceleration. To address this issue, a new formulation of the understeer gradient is proposed in this paper. This new formulation is based on vehicle speed and is suitable for all maneuvers. Unlike previous formulations, it does not rely on lateral acceleration or provide a direct connection to vehicle stability. To address the issue of vehicle stability, a new measure called the stability margin is also proposed in this paper. The stability margin provides a more precise measurement of a vehicle's stability than the understeer gradient alone. By combining the stability margin with the new formulation of the understeer gradient, a more comprehensive picture of a vehicle's cornering behaviour and stability can be obtained.

Keywords:

• Understeer gradient
• stability margin
• steady-state cornering behaviour

Disclosure statement

No potential conflict of interest was reported by the author(s).