Necessity of Body Torsional Rigidity of Personal Mobility Vehicles (PMVs) with an Inward Tilting Mechanism

In traditional four-wheeled automobiles, the imbalance between the roll moment, which is the product of the centrifugal force during a turn acting on the center of gravity and the height of the center of gravity, and roll stiffness, which is the product of the left-right difference in tire vertical load and the tread width and commonly used among automotive suspension engineers, of the front and rear sections necessitates body torsional rigidity. However, there is a lack of specific cases and guidelines for constructing the body structure of three-wheeled PMVs (Personal Mobility Vehicles) with a tilting mechanism from the perspective of vehicle dynamics characteristics. In this paper, the basic considerations related to the dynamics of such three-wheeled PMVs are investigated. We use the term “torsional rigidity” to refer to the stiffness as the torsional deformation of the body itself, and the term “roll stiffness” to refer to the moment that counteracts the roll moment during a turn and suppresses the vehicle’s roll in accordance with the terminology commonly used among automotive suspension engineers. In this paper, “torsional rigidity” and “roll stiffness” are clearly distinguished. Through a systematic comparative analysis with conventional four-wheeled automobiles, this study theoretically formulates the concept of mechanical equilibrium for the body torsional rigidity of three-wheeled PMVs, resulting in fundamental guidelines governing their body structure. The findings that the tilting function does not seem to impose torsional loads on the body during steady turning as analyzed through static analysis, shows that torsional rigidity around the longitudinal axis may be unnecessary. However, under actual dynamic conditions, a different scenario emerges. Dynamic simulations under real-world conditions demonstrate significant torsional loads on the body, emerging the necessity of torsional rigidity around the longitudinal axis. In three-wheeled PMVs, body torsion directly influences dynamic vehicle response. Therefore, to accurately delineate the structural requirements for body design, quantitative evaluation of the necessary body torsional rigidity under dynamic conditions is essential. Future efforts will involve creating a dynamic simulation model that integrates considerations for body torsion based on these initial study outcomes. Ultimately, this research aims to bridge the gap between theoretical understanding and practical implementation, contributing to comprehensive guidelines for the body design of three-wheeled PMVs.