Research On Cogging Torque Characteristics Of Electric Power Steering Permanent Magnet Brushless Direct Current Motor

In the more than one century of automobile development,with the continuous updating of technology and the continuous improvement of people's performance requirements,the steering system that directly affects the driving comfort of the car has experienced four stages of development:from the initial mechanical steering system.(MS)evolved into a hydraulic power steering system(HPS),followed by an electronically controlled hydraulic power steering system(EHPS)and an electric power steering system(EPS).Electric power steering systems have become a new trend in all automotive industries.The assisted motor also becomes the main power output of the steering system.However,due to the inherent torque fluctuation of the motor itself,it will affect the comfort when driving.Therefore,improving the torque ripple of the motor has become the focus.However,the main influencing factor of torque fluctuation is the cogging torque of the motor.Therefore,from the theory to the actual situation,the article seeks to improve the cogging torque of the motor through simulation and actual verification.First introduced the definition of the steering system of the car,the role of the steering system in the car,and traced the history of the development of the car steering system,from understanding its importance and safety.At the same time,with the pictures or schematics,the classification of the steering system and the advantages and disadvantages of each steering system are explained.Point out the problems and difficulties that exist in the steering system.Then the concept of cogging torque is given.Using the energy method,the equation of cogging torque is derived according to the theory.Then,according to the expressions derived above,several commonly used methods for reducing the cogging torque are analyzed and studied,including the stator-slant oblique groove method and the optimization of the stator notch width.The magnet is designed with unequal thickness.Use the magnet to cut the angle and add the auxiliary slot method on the top of the stator to understand the direction of improving the cogging torque.After introducing several improvement measures,an electric power steering motor was designed according to a given motor specification.Through preliminary calculation of the main parameters of the motor,and then input the parameters into the simulation software,analyze some performance parameters of the initial scheme and the cogging torque.Under the condition that the initial scheme does not meet the requirements,the motor is optimized and the stator is improved.The tooth width and the stator slot width are simultaneously segmented by the armature,and then simulated and optimized to meet the design specifications.Based on the optimization design based on the above simulation,an improvement scheme for the stator chip processing technology is proposed.The full-circle stator chip is used to increase the twisted piece.At the same time,the heat treatment process is applied to the stator chip to eliminate the stamping stress of the chip,The rotor lamination is changed from a glued method to an injection molded plastic part,and then respectively make the actual prototype to test and compare,and get the feasibility of the scheme.