Design And Research Of Pure Electric Vehicle Control Unit

Vehicle control unit is the core control unit of pure electric vehicle,responsible for coordinating the orderly and efficient operation of the remaining electronic control unit.With the increasing complexity of the electronic control system,the risk of failure has increased.Based on the functional safety ISO 26262 standards,designing the hardware of the vehicle control unit can effectively avoid the risks and reduce harm brought by the risks.Firstly,the thesis describes the structure of the vehicle control system and functional safety standards.The vehicle control system is divided into three layers,of which the vehicle control unit as the middle layer,collects the pedal signal,the gear signal,the key switch signal and the CAN bus motor speed,battery SOC,battery charge and discharge power and other signals,and then,sends instructions to the underlying control unit with all the signals calculated through the control strategy,thus,achieving the control of the vehicle.Referring to the SAE J1939 protocol,a CAN communication protocol is designed between the vehicle control unit and the remaining control units.Automotive safety lifecycle and automotive safety integrity level of functional safety ISO 26262 standards are briefly described.Secondly,the control strategy of vehicle control unit is researched,and the working process of vehicle control unit is divided into 6 categories,a total of 13 modes.The dual-mode control strategy under the starting conditions can effectively ensure the smooth and steady start of the automotive.Under acceleration conditions,the acceleration pedal opening,the rate of change of opening,the battery SOC,the speed of the motor,and the efficiency of motor are taken into consideration.The expected torque of the driver is calculated by using the algorithm of the base torque plus the compensation torque to obtain better dynamic performance.Under braking condition,based on the requirements of ECE braking regulations,parallel braking force distribution strategy is adopted,and in the case of medium-intensity braking,the fuzzy control strategy is used to calculate the braking force of the motor.According to the above control strategy,a model of MATLAB/Simulink is established to perform a co-simulation with the vehicle dynamics model.The results show that the control strategy adopted in this thesis can effectively meet the driver’s driving demand.At the same time,braking energy can be effectively recovered when the vehicle is braking,so the mileage can be extended.Then,the vehicle control unit is analyzed by FMEA and FTA,so as to determine the vehicle control system architecture.Starting from the functional requirements of the vehicle control unit,at the same time,based on the functional safety ISO 26262 standards,hardware circuits of vehicle control unit are designed.Hardware architecture indicators and random hardware failure indicators of the hardware circuits are calculated to meet ASIL C-level requirements.Application layer software is automatically generated from the MATLAB/Simulink control strategy model,while the underlying software is prepared manually,both of which are integrated to design the vehicle control unit software.Finally,hardware-in-the-loop test is performed on the vehicle control unit,including NEDC operating conditions and fault diagnosis test.The test results show that the vehicle control unit designed in this thesis meets the design requirements and has reference significance for the development of vehicle control unit.