Researchand Development Of Magneto-rheological Braking System For Electric Vehicle

Magneto-rheological(MR)fluids is a type of suspension with micron-sized magnetic particles dispersed in nonmagnetic liquids.When an external magnetic field is applied to MR fluid,rapid,continuous,and reversible changes in rheological properties will be happened.Given the favorable properties,MR fluids are widely used in mechanical components,such as dampers,brakes,valves,clutches,and building shock absorbers.MR braking system for vehicle has accurate and fast driving/braking torque response,which is favorable for improving the brake efficiency and stability.Hence itis meaningful to conduct research on the key technologies of MR braking system which has broad application prospects.This research is based on the project named "Research and Development of Magneto-rheological Braking System for Electric Vehicle" supported by Major State Basic Research Development Program.Somefundamentalperformance of MRF were studied and three MRF braking prototypes were designed based on a variety of models and simulation results.The prototypes were tested and compared with the traditional braking system in the aspects of performace.At last,the control method and strategy of the MRF braking system were studied in order to improve the performance of MRF brake system for vehicle.In this paper,the performance of MR fluids was studied,proposing the fitting method of the performance and the design method of the brake.This thesis analyzed its magnetic,mechanical and thermal properties.The paper also proposed a fitting method of the sheering stress with a high degree of precision at both high shear rate and high magnetic field.The design method of magnetorheological fluid brake was presented.The structure of brake was selected and designed based on the power law model obtained by experiments and understanding of the MR fluids.The parameters of MR brake was optimized under the constraint of the functional requirements,which was helpful to make the structure meet the braking requirements.The experimental results and simulation results were compared and verified.The design method can effectively reduce the computation time and satisfy therequirement of the real time solution satisfying the accuracy of calculation.Various brake structures were designed in this research.The counter-position MR brake utilized multi-path magnetic circuits,which enhanced braking effect and reduce the response time.Self-energizing MR braking cost low energy consumption,and possess the function of energy regeneration which can satisfy the energy demand of braking.Exterior-coil MR braking can provide a larger brake torque with relatively accurate control.Brake test platform was built and tested.Driving system was realized by motor,at the same time,braking torque was realized by braking system.Brake torque was tested by torque sensor.A vehicle control unit based on single chip microcontroller is in charge of the control algorithm and the coordinated control system and the experiment platform can simulate the braking process.Corresponding control algorithm for MR braking system was designed.This algorithm can effectively reduce the braking time for braking system and improve braking efficiency.After the ABS control algorithm was transplanted into this system,experimental results showed that the braking system can improve the braking efficiency,as well as enhance comfort level under the situation of emergency braking.