Research On Modeling And Control Strategy Of A Novel Electro-Hydraulic Brake System

In recent years,new energy vehicles and intelligent networked vehicles have become the hot spots in the automotive industry,which has greatly promoted the development of brake systems towards electronic control,integration,and modularization.Due to the limitation of its structure and working principle,the traditional vacuum-assisted braking system cannot realize the decoupling of man-machine braking force,nor can it meet the requirements of electric vehicles and intelligent vehicles on fault-tolerant,response speed,and boosting ability.Therefore,it is bound to be replaced by the brake-by-wire system.The existing electro-hydraulic brake system does not consider the adverse effects of pedal feel simulator failure on the driver,brake system,and vehicle driving safety.Therefore,a novel EHB system is proposed,and its control strategy is studied.The main research contents are as follows:(1)Considering the impact of the failure of the pedal feel simulator on the driver,the brake system,and driving safety of the vehicle,a novel electro-hydraulic brake system which can realize the decoupling of human-machine braking force and has various failure backup schemes is proposed.According to the proposed structure scheme,the brake system model is established,the parameters of the system are matched,and the AMESim simulation model is established.The braking performance and cylinder pressure response in each working mode of the brake system are verified.The simulation results show that the braking performance of the system complies with the regulations,and the pressure build-up rate is not less than 32MPa/s except the manual backup mode,which can meet the design requirements of the brake system.(2)Referring to the pedal characteristic parameters of a passenger car,a pedal feel simulation strategy based on motor torque control is proposed.To make the pedal feel conform to the driver’s expectation,braking conditions are divided based on time-to-collision parameters,and a pedal characteristic switching control strategy is proposed.To avoid the adverse effects of the failure of pedal feel simulator on the driver,the performance of the brake system,and driving safety of the vehicle,and to avoid sudden change of pedal characteristics before and after the failure of pedal feel simulation motor,a backup scheme for the pedal feel failure is proposed.The AMESim simulation model is built to verify the effectiveness and feasibility of the proposed control strategy and the failure backup scheme.(3)Aiming at the proposed electro-hydraulic brake system,the identification method of the driver’s braking intention is studied based on the fuzzy control strategy.A sensor failure backup scheme is proposed for pedal travel sensor failure.According to the structural characteristics of the brake system,the corresponding wheel cylinder pressure control strategy is put forward.Based on this,the brake distribution strategy based on dynamic load and anti-lock braking control strategy based on slip rate threshold are studied.The Car Sim/AMESim/Simulink co-simulation model was built to validate the cylinder pressure control strategy,braking force distribution strategy,and anti-lock braking control strategy of the brake system.(4)To improve driver acceptance of collision avoidance system,improve braking comfort and improve vehicle following efficiency,the characteristics of several existing safety distance models are analyzed.Considering factors such as driver,self-driving,and road surface comprehensively,a calculation method of minimum following distance is put forward,and then a man-machine cooperative longitudinal collision avoidance control strategy based on changing time-to-collision parameters is put forward in combination with extension control theory.The simulation results show that the proposed strategy can significantly improve driving comfort and improve vehicle following efficiency under medium and low-speed conditions.Under high-speed conditions,the proposed strategy can improve driving comfort and at the same time achieve higher braking strength.In addition,the weight of driver control is always higher than that of the auxiliary system during collision avoidance,and the longitudinal auxiliary system gradually takes over control rights,which can improve the acceptance of the driver to the collision avoidance system.Figure [65] Table [16] Reference [82]...