Functional Safety Analysis And Control Software Implementation For EM-CVT

With the rapidly development of electronic technology,automotive electronics have been widely used in various fields of automobiles.The application of automotive electronic technology has brought a lot of convenience to consumers.At the same time,the application of electronic products has also increased the risk of electronic and electrical system failures in automobiles.In order to solve the automobile safety problems caused by electronic and electrical system failures,the International Standardization Organization(ISO)issued the ISO 26262 road vehicles functional safety standard in November 2011.This paper takes the ISO 26262 road vehicle functional safety standard as a guide,and implements the software functional safety design of the electronic control system of EMCVT in accordance with the requirements of the ISO 26262 standard,mainly completed the following work:Based on the requirements of third part of the ISO 26262 standards,implements the conceptual design of EM-CVT.Firstly,define the relevant items of EM-CVT,and analyze the functions,working environment,relevant regulations and common failure modes of the continuously variable transmission.Secondly,HARA analysis is performed on the speed regulation function and torque transmission function of the continuously variable transmission,the ASIL level is determined,and the safety goal of EM-CVT is obtained.Thirdly,based on the safety goal,derives the functional safety requirements and assigned the functional safety requirements.The technical safety requirements are derived according to the functional safety requirements.Finally,the common safety analysis methods in functional safety standards are compared,and FTA analysis is carried out on the hazardous events of "unexpected speed regulation" and "TCU torque mutation".Completed the design of EM-CVT electronic control system.Firstly,the software architecture design and software function division of the EM-CVT electronic control system are carried out,and the pins of TCU are defined.Secondly,analyzed the control requirements of the continuously variable transmission,determined the solution method of the target speed ratio,and built the solution model for calculating ratio.Finally,the EM-CVT speed regulation system is modeled,and the simulation model and control strategy of the EM-CVT speed regulation system are built.Completed the safety design of EM-CVT.As for the speed regulation function,adds the detection and monitoring modules of the input shaft speed sensor and the output shaft speed sensor.The real-time detection and fault level judgment of the output voltage for the speed sensor can reduce the risk of sensor failure.In addition,implements redundant design of the speed sensor.Built the calibration strategy of the angular displacement sensor and the calibrated the angular displacement sensor to reduce the risk which was caused by the failure of the speed sensor.In view of the torque transmission function,the torque monitoring system of EM-CVT was designed.Determines the required torque of the motor and built a calculation model of the required torque of the motor.The output torque of the transmission was detected,and the risk of "unexpected torque output" in the system was reduced by closed-loop control.Completed the functional test,safety test and performance test of EM-CVT.In terms of functional testing,the test and verification of speed ratio regulation accuracy,speed response time test,speed ratio following features test and torque following ability test are mainly carried out.In terms of safety test,the fault injection test of input shaft speed sensor and the output shaft speed sensor and the torque range test are carried out.In terms of performance test,the transmission efficiency of the continuously variable transmission under various operating conditions is mainly tested to verify the performance of continuously variable transmission.