A novel magnetorheological braking system with variable magnetic particle volume fractioncontrolled by utilizing shape memory alloy

Abstract

To address the shortcomings of decreasing shear yield stress of magnetorheological fluid due to temperature increase, magnetic saturation phenomenon under the action of a strong magnetic field, and decreasing performance of magnetorheological brake due to magnetic particle settling, a braking system of variable particle volume fraction of magnetorheological fluid modulated by shape memory alloy spring is proposed, which solves the shortcomings of constant particle volume fraction magnetorheological brakes. The brake temperature rises and automatically increases the volume fraction of magnetorheological fluid, leading to increase in the braking torque and ensuring stable braking performance at high temperatures. The magnetorheological fluid particle settling stability is enhanced, and energy consumption at idle is reduced. Based on the shape memory effect of shape memory alloy, the relationship between the output displacement of shape memory alloy spring and temperature, squeezing pressure and volume fraction of magnetic particles is established. Based on the microscopic body-centered tetragonal structure of magnetorheological fluid, the relationship between the volume fraction of magnetic particles and the magnetic permeability of magnetorheological fluid was established. Based on the rheological characteristics of magnetorheological fluid, the relationship between the braking torque of magnetorheological fluid and the magnetic permeability and the volume fraction of magnetic particles is established; and the finite element method was applied to simulate and analyze it. The results show that the magnetic permeability increases with the increase of the volume fraction of magnetic particles and the braking torque increase with the increase of the volume fraction of magnetic particles during the evolution of the magnetorheological fluid microstructure from single chain to body-centered tetragonal structure. When the volume fraction of magnetic particles in the magnetorheological fluid increased from 15% to 45%, the magnetorheological brake torque increased to 10.1N·m, and the braking performance of the magnetorheological brake improved by 14.3%. The experimental and theoretical analyses provide a theoretical basis for the design and manufacture of magnetorheological fluid brakes with variable particle volume fractions.