# Multipole Multi-Layered Magnetorheological Brake with Intermediate Slots
###### Abstract  
Magnetorheological (MR) brakes are flourishing in low-torque applications due to their dynamic controllability nature. Researchers have introduced multi-layer and multipole concepts to increase the torque-volume ratio (TVR) of the MR brake. However, the combination of these two ideas did not exist due to the design limitations. Therefore, this study aims to design a brake that combines the multipole magnetic field and multi-layered structure concepts. The axial slots were introduced on the brake rotor and the stator drum axial surfaces to achieve a high TVR. These slots stop the flux bypass in the inner layers; therefore, the magnetic flux can also reach the brake's outer layers. This brake was designed with multiple stator and rotor drums and MR fluid layers. The number of poles was placed so that the magnetic field from these poles traveled in a closed loop via the stator, rotor, and MR layers. A 3D model of the brake was prepared for the virtual study. Electromagnetic simulations were conducted to analyze the effect of axial slots' and other design parameters of the brake. According to those simulation results, the axial slots' width and position significantly affect the brake output torque. The maximum torque obtained from the brake is 38 Nm, and the TVR value of the brake is 41 Nm/dm\({}^{3}\). Additionally, multiphysics simulations were performed to understand the Joule-heating effect of the magnetic coil and the frictional heating in MR fluid. Results showed that the maximum possible temperature in the brake is under the MR fluid temperature limits. Therefore, this multipole multi-layered (MPML) MR brake with axial slots idea is very useful for high-torque MR brake growth. magnetorheological brake; smart brake; multipole; multi-layered; drum brake +
Footnote †: journal: Applied sciences  
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Footnote 1: email: [EMAIL_ADDRESS]  
and absorb road shocks in vehicle structures [4; 5; 6]. Furthermore, MR valves offer a reliable alternative to mechanical valves in hydraulic actuation systems, boasting benefits such as reduced weight, simplified control, and the absence of moving parts. Researchers have made significant strides in optimizing the design and performance of MR valves. For instance, [PERSON] and [PERSON] [7] designed a high-efficiency MR valve, analyzing its performance through simulations and experiments. Building upon the reliable dynamic behavior of MR fluids, innovative applications such as engine valve trains have been explored. [PERSON] [8] introduced a groundbreaking magnetorheological valve device, enabling the achievement of variable valve actuation (VVA) in engine systems. The shear mode resistance principle is useful for MR clutches and brakes. These devices are emerging in the places of traditional low-torque clutches and brakes to achieve reasonable active control of torque transmission and braking force. [PERSON] developed a hybrid-mode MR brake for two-wheeler applications [9]. MR brakes are getting very popular in haptic, rehabilitation, and prosthetic applications [10; 11; 12]. This paper mainly focused on the MR brake. It is generally constructed with the stator, rotor, MR fluid, and magnetic field coil. MR fluid is filled in the space between the rotor and stator. When the current is supplied to the field coil, it generates a magnetic flux. This flux travels from the stator to the rotor via MR fluid. Therefore, the ferromagnetic particles in the fluid align in the field direction, and then the shear resistance in the MR fluid increases. That resistance acts as a braking force on the rotor. This force can be controlled with the magnitude of the coil current. Using this concept, there are several design models available, like single-layer drum type and disc type, hybrid T-shaped drum type, multiple layers of MR fluid type, multipole coil type, and multipole and bilayer MR brake type. Basic disc-type and drum-type MR brakes are the original designs for this technology. The significant difference between these two types is the geometry of the rotor.