Two Modes of Drag Reduction for Magnetorheological Fluids

Magnetorheological fluids (MRFs) show a millisecond-level reversible response controlled by an external magnetic field and are, thus, widely used in many areas, especially vehicle dampers, clutches, and brakes. However, in the standby state, the piston or rotor of these devices still moves in the MRF and generates damping force or torque, which will deteriorate the performance and even significantly increase the energy consumption of the entire vehicle. To solve these problems, we propose two working modes of MRFs based on rheology: vertical shear and parallel shear modes. We designed relevant magnetic circuit implementations for drum-type rotary magnetorheological (MR) devices to realize these new modes and verified the drag reduction effects by using a modified rheometer. The experimental results indicate that the vertical shear and parallel shear modes reduce the drag torque of the MRF by approximately 10% and 9% at magnetic field strengths of approximately 3.5 and 0.1 kA/m, respectively. Therefore, MR devices utilizing these drag reduction modes can reduce standby damping to improve performance. In addition, two mechanisms were developed to explain the significant decrease in damping torque with the increasing number of experiments under the vertical shear mode. In summary, research into these two modes promotes understanding of MRFs and the development of MR devices.