Analysis and experimentation of variable gap magnetorheological transmission device driven by electromagnetic force

To solve the problems of poor transmission performance and small torque regulation range of traditional MR device, a variable working gap MRF transmission device driven by electromagnetic force is proposed. The device uses electromagnetic force driving the squeeze disk to move axially to squeeze the MRF, thereby changing the number of working gaps and effective working thickness of the MRF to improve the transmission performance of the MR device. Based on the coil magnetization effect, the relationship between current, magnetic field intensity, and electromagnetic force is established. According to the driving characteristics of electromagnetic force and the rheological characteristics of MRF, a nonlinear function relationship between electromagnetic force and MRF working gap thickness and working volume is derived. Using the finite element method, a theoretical analysis of the magnetic circuit design, magnetic field distribution and temperature change profile in different parts of MRF device with different currents was conducted, the MRF torque transfer equations were deduced and calculated, and experimentally verified the correctness of the theoretical equations. Finally, the transmission performance of the variable working gap MRF transmission device is tested through the established testing system. Results show that, the required squeeze force is 6.65 kN when the MRF thickness reaches 1 mm in both working gaps. As the current increases from 0.5 to 3.0 A, the electromagnetic force increases from 0.65 to 6.77 kN, with an increase of 972.3%, the average temperature of the MRF in working gap I increases from 25.2°C to 71.2°C and the MRF in working gap II increases from 23.5°C to 48.3°C. When the current is 1.5 A, the MRF in the working gap I reaches magnetic saturation, continue to increase the current to 3.0 A, the MRF thickness in both working gaps is 1 mm, and the MR device transmits torque reach 376.6 N·m, which is 72.3% higher than that of the traditional MR device.