Study of Variable Thickness Magnetorheological Transmission Performance of Electrothermal Shape Memory Alloy Squeeze

Abstract

This paper designs a new composite transmission device for improving the transmission torque by squeezing magnetorheological fluid (MRF) with an electrothermal shape memory alloy (SMA) spring. Based on the finite element method, a numerical analysis of the magnetic circuit and magnetic field distribution of the magnetorheological (MR) transmission is presented, as well as a theoretical derivation and calculation of the squeezing force output by the electrothermal SMA spring and the transfer torque of the variable thickness MR transmission. In addition, the output characteristics of the electrothermal SMA spring at different temperatures are analyzed, as are the torque characteristics of the variable thickness MR transmission. The research shows that the electrothermal SMA springs exhibit a highly non-linear squeezing force output during the temperature rise, and the increase in current affects the martensite phase transition quality, and thus the phase transition temperature. The squeezing force generated by the springs increases significantly when the temperature is within the martensitic phase transformation interval, with a maximum squeezing force of 318.43 N when the SMA temperature reaches 100 °C. The proposed variable thickness MR transmission can increase the maximum torque by 4.88 times under SMA spring squeezing force, and its maximum transmitted torque is increased from 15.08 to 73.56 N·m. By squeezing the MRF with an electrothermal SMA spring, the torque of the variable thickness MR transmission can be increased quickly and effectively.

Analysis of electromagnetic-thermal coupling braking properties of combined electromagnetic friction and shape memory alloy brake

“…The above research provides a certain theoretical basis for the analysis, design and optimization of electromagnetic friction brakes, fewer research on improving brake torque. Based on the previous research on SMA, for instance, Ma et al [20] designed an offset SMA spring actuator, it provided theoretical support for the design and application of SMA springs; Xiong et al [21] proposed an SMA force driver for low-torque magnetorheological fluid (MRF) brakes, to solve the problem of the MRF performance degradation at high temperatures; Chen et al [22] designed an electrothermal SMA spring displacement actuator, when temperature is too high, increase the torque of the transmission by changing the effective working clearance of the MRF; the above research has laid the foundation for the application of SMA in transmission, but there is a device torque is lower, large limitations in use, low energy utilization of the device and other problems. In this paper, SMA springs are used in combination with conventional electromagnetic friction brakes for the first time, take advantage of the thermal-mechanical energy conversion of the SMA, it effectively solves the problem of severe heat generation of traditional brakes without changing the original brake size, insufficient braking performance and poor braking stability, etc.…”