Rigid body modeling of three wheel vehicle to determine the dynamic stability — A practical approach

The dynamic stability of a vehicle is of profound significance which has led three wheel vehicles to be used for only low speed application. Static Stability Factor (SSF) is a commonly used safety rating for vehicles. In this paper, stability of a three-wheeled vehicle with two wheels on the front (2F1R), a three-wheeled vehicle with two wheels on the rear (1F2R) and a standard four-wheeled vehicle are compared. A particularized formula for SSF of a three wheel vehicle is derived. Critical cornering conditions for lift-off are identified for both three wheeler configurations. Three wheelers with tilting wheel mechanism are seen as a potential solution for high speed stability. The mathematical model is derived for dynamic load transfer in case of tilting wheels. A comparison is carried out for cornering stability enhancements that can be achieved through tilting mechanism during critical cornering conditions. It is observed that SSF for a three wheel vehicle can be raised equivalent to that of a four wheel vehicle by implementing tilting mechanism. Difference in dynamic stability characteristics of 1F2R and 2F1R configurations are evaluated and presented in velocity vs. critical turning radius plots. Computation is required for operation of hydraulic cylinder of tilting mechanism. For this, a simple and practical approach is suggested in the paper. Rigid body analysis is performed to find the value of commonly used safety rating, SSF of a vehicle.