Study On The Electro-mechanical Brake System Based On CAN Bus

There are so many shortcomings of traditional hydraulic or pneumatic brakingforms,they are unable to meet the gradual expansion of the braking function.A newform of electro-mechanical brake system thus emerge.As one form of brake-by-wiretechnology,EMB system has many advantages,such as advanced performance,stableand reliable,fast response,simple structure,compact,high transmission efficiency and soon.There is no brake fluid leakage risks,making it more safe and environmental andhas a high value and market development prospect.Foreign companies such asContinental Teves,Bosch and Siemens have acquired some research achievements anddeveloped its own prototype in this field.In contrast,domestic research starts later andis still in the laboratory stage.The research in paper will contribute to promote thedevelopment of this technology.Paper adds fieldbus technology to EMB system,which use CAN bus ascommunication carrier and apply distributed structure arrangement with master-slavenodes.As a high rate, high reliability and multi-master communication form,CAN bushas been widely used in automotive electronic communication.Adding it to the controlof vehicle braking system provides a new way to study the EMB system.First of all,paper introduces the background and development status of EMBsystem,analyses the basic concept and working principle of CAN bus.According tofunctional requirement of braking system,the overall design of the master and slavenodes is proposed.Paper focuses on three aspects of mechanical structure,hardwarecircuit and software programming.Mechanical structure includes electronic brake pedaland actuator.Electronic brake pedal generates brake signal by the angular displacementsensor.Actuator contains drive motor,deceleration and torque increasing device andmotion conversion device.The best transmission scheme is choosed and parametricdesign is made.Hardware circuit chooses STM32F103chip produced by STM company as coreprocessor for master-slave nodes when designing.BxCAN module,AD convertionmodule,serial communication circuitembed in the processor and so on embedded inprocessor contribute to simple circuit.Advanced timer can generate PWM pulse widthmodulated signal to control motor.In addition to minimum system and peripheralcircuits,functional circuit contains angular displacement signal acquisition and processing circuit,motor drive circuit and CAN bus interface circuit.Three-phasefull-bridge inverter control circuit is designed for motor.According to CANcommunication structure of master-slave nodes,system designs integrated and separatecommunication interface circuits respectively.Modular design thinking is used in software design.Master node contains mainprogram structure and flow chart,angular displacement acquisition algorithm,ADCconversion program,CAN bus communication program.Slave nodes contain mainprogram structure and flow chart,motor PWM control procedures,CAN buscommunication program.EMB system in the paper utilizes angular displacement sensor to acquire pedalangular displacement signal.STM32F103chip generates control signal and controlsfour slave nodes to output PWM pulse signal after processing the angular displacementsignal.PWM pulse signal drives motor to generate torque with motor drive circuit.Afterdeceleration,torque increasing and motion conversion,braking force is exerted to thebrake caliper and achieves wire controlling braking effect.