Downhill safety assistance control for hybrid electric vehicles based on the downhill driver’s intention model

Abstract

Assisting the control of a vehicle’s speed while driving downhill improves the vehicle’s safety and reduces the driver’s workload in both internal-combustion engine vehicles and hybrid electric vehicles. The current technology widely used in internal-combustion engine vehicles is a hill descent control system. However, hill descent control can be achieved only at lower speeds, but it may also lead to thermal wear of the brake components during prolonged intensive braking. There is currently no effective downhill safety assistance control technology for hybrid electric vehicles that is effective across the full range of speeds and can take advantage of regenerative braking. To address the limitations of previous studies, a novel downhill safety assistant control strategy for hybrid electric vehicles, which adapts to the characteristics of different drivers and takes advantage of all braking subsystems of hybrid electric vehicles, is proposed in this paper to improve the vehicle safety, the fuel economy and the ride comfort for the full range of speeds. To adapt to the characteristics of different drivers, the downhill driver’s intention model is established on the basis of a statistical data analysis of questionnaires and experiments, which is used to determine the control mode’s switching conditions and the control objective for downhill safety assistant control. To improve the vehicle safety, the fuel economy and the ride comfort for the full speed range, a coordinated control strategy for the electric motor’s braking subsystem, the engine’s braking subsystem and the hydraulic braking subsystem is developed, which includes six braking assistant modes, an identifying strategy and torque control of the electric motor based on coordinated control strategies. Simulations and experimental results show that the proposed control strategy improves the vehicle safety, the fuel economy and the ride comfort of hybrid electric vehicles during downhill driving.