Collaborative optimization of multi-mode composite gain and variable-angle transmission ratio parameter sets for steer-by-wire system

The design of the variable steering ratio for steer-by-wire (SBW) systems must balance multi-scenario adaptability and control robustness, enhancing both the human-vehicle interaction experience and closed-loop performance of intelligent driving vehicles. To optimize the variable steering ratio in an SBW system for adaptive adjustment of steering characteristics under various driving conditions, this paper proposes a multi-mode composite gain variable steering ratio control method. Three distinct steering modes—stability-oriented, sport-oriented, and race-oriented—are designed through a weighted fusion of constant yaw-rate gain and constant lateral-acceleration gain. The analytic hierarchy process (AHP) is applied to configure differentiated sub-indicators within a vehicle handling stability evaluation framework, thereby constructing fitness function metrics. Genetic algorithms (GA) are then applied to determine optimal parameter sets for the variable steering ratio designs across these modes. The approach is validated through CarSim/Simulink co-simulation under step-steering and double lane-change (DLC) conditions, supplemented by real-vehicle subjective evaluations. Results show that the proposed method significantly improves steering performance across different scenarios. This effectively balances personalized driving preferences with handling stability and provides core technical support for steering control strategies in intelligent driving systems.