Improvement of Cornering Characteristic Using VariableSteering Ratio

Abstract

A variable steering ratio (VSR) is introduced for a purpose of improving cornering characteristic of a vehicle. Two degree-of-freedom vehicle models are used for derivation and calculation of the VSR gain, and simulating the vehicles cornering characteristic, with and without adjustable gain. Approximated bounds of validity for a specific case of a car using VSR is justified using Dugoff’s tire model. A sample of two dimensional look-up table is generated within the bound. Understeer, neutral steer, and oversteer vehicles are tested within the bound of validity of VSR to see effects of this variable gain. A constant steer angle testing is also used with an understeer vehicle model with and without VSR to confirm the effects of the gain. Results show that, within the bound of validity, understeer and oversteer vehicles with VSR units have neutral steer characteristic. The improvement of cornering characteristic is also evident from the numerical simulations.