Design of a magnetorheological brake system based on magnetic circuit optimization




Karakoc, Kerem

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Conventional hydraulic brake (CHB) systems used in automotive industry have several limitations and disadvantages such as the response delay, wear of braking pad, requirement for auxiliary components (e.g. hydraulic pump, transfer pipes and brake fluid reservoir) and increased overall weight due to the auxiliary components. In this thesis, the development of a novel electromechanical brake (EMB) for automotive applications is presented. Such brake employs mechanical components as well as electrical components, resulting in more reliable and faster braking actuation. The proposed electromagnetic brake is a magnetorheological (MR) brake. The MR brake consists of multiple rotating disks immersed into an MR fluid and an enclosed electromagnet. When current is applied to the electromagnet coil, the MR fluid solidifies as its yield stress varies as a function of the magnetic field applied by the electromagnet. This controllable yield stress produces shear friction on the rotating disks, generating the braking torque. This type of braking system has the following advantages: faster response, easy implementation of a new controller or existing controllers (e.g. ABS, VSC, EPB, etc.), less maintenance requirements since there is no material wear and lighter overall weight since it does not require the auxiliary components used in CHBs. The MRB design process included several critical design steps such as the magnetic circuit design and material selection as well as other practical considerations such as cooling and sealing. A basic MRB configuration was selected among possible candidates and a detailed design was obtained according to a set of design criteria. Then, with the help of a finite element model (FEM) of the MRB design, the magnetic field intensity distribution within the brake was simulated and the results were used to calculate the braking torque generation. In order to obtain an optimal MRB design with higher braking torque generation capacity and lower weight, the key design parameters were optimized. The optimization procedure also consisted of the FEM, which was required to calculate the braking torque generation in each iteration. Two different optimization search methods were used in obtaining the minimum weight and maximum braking torque: (i) a random search algorithm, simulated annealing, was first used to find an approximate optimum design and (ii) a gradient based algorithm, sequential quadratic programming, was subsequently used to obtain the optimum dimensional design parameters. Next, the optimum MRB was prototyped. The braking performance of the prototype was tested and verified, and the experimental results were shown. Also, experimental results were compared with the simulation results. Due to the lack of accurate material property data used in the simulations, there were discrepancies between the experimental and the simulation results. Other possible sources of errors are also discussed. Since the prototype MRB generates much lower braking torque compared to that of a similar size CHB, possible design improvements are suggested ton further increase the braking torque capacity. These include the relaxation of the optimization constraints, introduction of additional disks, and the change in the basic magnetic circuit configuration.



Magnetorheological Brake, Magnetorheological Fluids, Magnetic Circuit, Magnetic Circuit Optimization, Simulated Annealing, Sequential Qadratic Programming