Research On Magnetorheological Elevator Brake Device With Self-protection And Heat Dissipation

With the rapid development of China's urbanization level,the elevator procurement requirements continue to be released,the existing traditional elevator brake device has the disadvantages of large vibration impact,large noise and insufficient safety protection,coupled with the support of the government of new elevator brake device,so in recently years,based on the traction elevator magnetorheological(MR)brake device came into being.MR brake device uses the controllable magnetic shear stress of MR fluid to control the braking torque,which has the advantages of stable torque,fast response and low noise etc.However,because of the braking torque only can be produced under the condition of excitation current,it is difficult to ensure the safety of the device under the condition of power failure.In order to enhance the device performance and braking safety,in this paper,based on the magneto rheological effect and the principle of permanent magnet braking,a new type of self-protection elevator brake device based on MR effect is proposed.Initially,the performance of MR fluid is investigated according to the braking characteristics of elevator brake device in this paper.Experimental study on MR fluid performance and friction performance of MR fluid with different additives is carried out based on the different operating conditions of elevator.The variation law of the magnetic shear stress and the zero field viscosity before and after the friction of MR fluid is studied to choose the MR fluid material suitable for elevator braking device and establish the mathematical model of shear yield strength and magnetic induction.Furthermore,the main structure types and parameters of the braking device are determined through the analysis of the braking principle of the new braking and the specific structural parameters of the elevator.According to the structure design of the excitation coil and the permanent magnet structure and the analysis of the magnetic circuit,the design of the internal coolant flow passage of the brake shaft can reduce the temperature rise of the MR fluid.And the braking moment of braking device based on structural parameters is analysed.Additionally,the magnetic flux density distribution of the MR fluid gap is investigated by the simulation of the double magnetic field generator.The mathematical model of braking torque is established,and the change trend of braking time and rotational speed is analyzed under different initial conditions and braking conditions.The numerical simulation of temperature field of braking device under different braking conditions is carried out.Finally,the prototype of the brake device is developed and tested.Combined with the braking condition of the elevator brake device,the test scheme is determined and the performance test platform of the braking device is set up,The braking performance,the temperature rise characteristic and the noise performance of the test prototype are carried out to verify the rationality of the design.The innovation of this paper as follows:On the basis of the existing MR braking device and the permanent magnet braking technology,a MR brake device with self-protection and heat dissipation function is designed.On the one hand,the permanent magnet structure can be combined with the excitation coil in the normal operation to form a double magnetic field to improve the braking torque of the brake device,on the other hand,in the case of power failure,the permanent magnet structure provides the braking torque to form the self-protection function.In addition,the design of the device in the brake shaft inside the cooling fluid channel designed to ensure the effective temperature control of MR fluid.This research not only provides a new idea for the development of the new type of traction brake device,but also helps to broaden design ideas of MR brake device.