| Magnetorheological fluid(MRF)is a kind of artificial intelligence material,which is widely used in damper,prosthetic joint,transmission device,shock absorber and other industrial products.It is mainly used in suspension and brake of automobile,with the advantages of rapid response,strong reversibility,low energy consumption and convenient control.In this paper,the design of magnetorheological fluid brake for micro electric vehicle is carried out,the system structure is optimized by magnetic field simulation,and the performance of magnetorheological fluid brake is analyzed by combining with the temperature field simulation in the brake braking process.Firstly,the density,sedimentation stability and rheological properties of MRF are tested,the relationship between shear stress,viscosity and shear rate of MRF under zero magnetic field is analyzed,and the relationship between shear stress and current of MRF under different magnetic fields is analyzed,The speed range of the platform is200～600r/min,the output torque range was 15～50N·m,and the moment of inertia was0～1.59kg·m~2.A micro electric vehicle is selected as the research object,and the target braking torque is determined according to the requirements of braking laws and regulations;the braking moment of a single brake disc of MRF Brake is analyzed by Bingham plastic equation and micro element method,and the relationship model of shear stress and braking torque is established;then the structure parameters such as diameter,working clearance and number of brake discs of multi disc magnetorheological fluid brake are determined;The basic structure of multi disk magnetorheological fluid brake was designed.Then,ANSYS Maxwell is used to simulate the magnetic field of the designed magnetorheological fluid brake,and the magnetic induction intensity at the working gap is analyzed.According to the magnetic saturation and magnetic density index,the thickness of the outer magnetic guide ring and the position of the fixed disk air field are optimized.The results show that the outer magnetic guide ring is thickened to 21mm,and the position of the air field in the fixed disk moves 4mm along the y-axis with respect to the middle position.At this time,the magnetorheological fluid magnetic induction strength is the largest at the working gap.Finally,the temperature field of the magnetorheological fluid brake is analyzed.Combined with the main heat sources of the magnetorheological fluid brake,the heat and heat exchange of the brake are analyzed by the thermodynamic law.Using ANSYS Workbench conducts steady-state and transient simulation on the temperature field of the optimized magnetorheological fluid brake;analyzes the steady-state temperature of the heat absorption and heat dissipation balance of the brake when the vehicle is running normally without braking.Under the simulation conditions,the maximum temperature of the magnetorheological fluid brake appears at the working gap between the fixed disc and the brake disc,which is 45.25℃;the transient of the magnetorheological fluid brake under the emergency braking condition is analyzed the temperature of the state is 45.5℃at the end of the brake.The transient temperature of the magnetorheological fluid brake is analyzed under the continuous braking condition.The temperature of the working clearance reaches 188.45℃after 15 consecutive braking times,which exceeds the maximum value of the working temperature of the magnetorheological fluid. |
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