Energy analysis and optimization design of vehicle electro-hydraulic compound steering system

Abstract

In order to reduce the vehicle steering energy consumption and improve the steering road feeling, this work proposes an electro-hydraulic compound steering (EHCS) system, which combines the functions of electric power steering (EPS) and electro-hydraulic power steering (EHPS). For this novel steering system, there is a complex mechanical-electro-hydraulic coupling relationship that affects the steering performance. Thus, how to choose the appropriate parameters to ensure the system of good energy-saving characteristics and steering road feeling is one of the key issues. The power flow of mechanical, electrical and hydraulic subsystems is used to test the coupling relationship between the parameters of the motor, hydraulic pipe, hydraulic valve, power cylinder, and mechanical steering structure, and analyze their influence on the steering energy consumption. According to the results of energy consumption sensitivity analysis, the main coupling parameters are selected as design variables, and the steering energy consumption, steering road feeling and steering wheel return error are taken as optimization objectives. To add population diversity and accelerate convergence velocity, the improved competitive multi-objective particle swarm optimization (CMOPSO) algorithm is proposed and used for optimization. The optimization results illustrate that the CMOPSO has better convergence compared with the basic MOPSO, and the EHCS system optimized by CMOPSO has a better steering economy, with better steering road feeling and smaller steering wheel return error. To verify the comprehensive steering performance, the optimized EHCS system is installed on the vehicle for an on-field road test. Compared with original EHPS, the road test results show that the energy consumption of the modified vehicle under the steering condition significantly decreases, and can also meet the steering assistance and driver road feeling requirements. Furthermore, the real road traffic scene around Nanjing University of Aeronautics and Astronautics is reconstructed to analyze the relationship between the whole vehicle energy consumption and energy characteristics of the EHCS system in the intelligent traffic environments, which verifies the steering energy consumption is reduced by 51.7% under the 15 km test road.