Research On Electro-hydraulic Hybrid Braking System Of Wire Control Chassis Based On Functional Safety

With the rapid economic development of today’s society,automobiles have entered thousands of households.With the increase of road vehicles,traffic accidents have become more frequent.According to statistics,35% of traffic accidents are caused by the delayed intervention of the vehicle braking system or the failure of the brake.Therefore,it is very necessary to design a new type of vehicle braking system to improve vehicle driving safety.Based on functional safety technology and guided by the ISO 26262 standard,this paper proposes a wire-controlled chassis electro-hydraulic hybrid braking system based on electronic hydraulic braking system and an electronic mechanical braking system.First,the existing electronic hydraulic brake system and the electronic mechanical brake system are compared in structure,and the target of the hybrid brake system is determined.According to the steps and requirements of the conceptual design stage of the ISO 26262 standard,the development of the conceptual stage was carried out.Through the hazard analysis and risk assessment of the four hazards of brake failure,unintentional braking,inconsistent braking intention and braking delay,it was determined The functional safety goals are derived,the functional safety requirements are derived,and the functional safety goals are assigned.Secondly,in accordance with the step requirements of system design and hardware design in the ISO 26262 standard,parameter design and simulation model construction of the hydraulic brake subsystem and mechanical brake subsystem of the electro-hydraulic hybrid brake system are carried out,combined with the selected target models The component parameters were determined.The CAN bus interface circuit,vehicle speed signal acquisition circui t and logic level conversion circuit are designed.Then,taking the vehicle speed signal acquisition circuit as an example,two evaluation indicators of "hardware architecture measurement" and "random hardware failure measurement" in functional safety tech nology are selected,combined with three evaluation factors of single point failure measurement,latent failure measurement and random hardware failure probability,The safety integrity level evaluation of the designed hybrid braking system is carried out,and the calculation results are compared with the ASIL C level standard in the ISO 26262 standard,and the designed hybrid braking system meets the ASIL C level standard.Finally,on the basis of the force analysis of the braking process of the car,the method of Carsim and Matlab/Simulink software joint modeling and simulation was used to establish a car model and a tire model that meet the requirements of functional safety,driving in a straight line and a curve respectively Under the two driving paths,the model injected wheel speed sensor failure,communication network failure,ECU failure,and the failure response of traditional ABS braking and the designed hybrid braking system are compared.The results show that the designed hybrid braking system is effective.It has obvious advantages in shortening the braking distance,reducing braking time,and ensuring driving stability,which can effectively improve the stability and safety of the vehicle braking process.