Multi-physics modelling of a magneto-rheological braking system

The topic of this Master Thesis is the multi-physics modelling of a magneto-rheological braking system developed by IEHV- Innovative Electric and Hybrid Vehicles - Research Group. This component is a part of ZEDS, the Zero-Emissions Driving System which can be used in electric vehicle to reduce the emissions generated by brakes. Such a component integrates an In-Wheel Electric Motor and a braking system. The functioning of this last one is based on the magneto-rheological properties of the fluid (MRF) placed between a rotor and a stator. Consequently, the emissions of the electric vehicles are drastically reduced because friction-based braking technology is no more used, as a consequence, no particulate matters emitted by such a component. The innovative braking system was already designed and a prototype was produced. Therefore, the aim of this thesis is the development of an electro-magnetic and fluid-dynamic model which can simulate the real behaviour of the system. This goal can be accomplished testing the functioning of the prototype in some peculiar working conditions, using a test bench already realized. Then, the experimental results have been compared to the simulation results, in order to validate the models. The first part of this dissertation consists of analysing the braking system and its functioning. The criticalities of the braking system simulation are related to the coupling between the electro-magnetic and fluid-dynamic fields. The operating principle of the brakes is the use of the magneto-rheological fluid, whose viscosity changes with the magnetic field. So, a traditional fluid-dynamic simulation is not sufficient if the effect of magnetic field needs to be considered. The coupling between electro-magnetic field and fluid-dynamic quantities is necessary to simulate the braking action of this system. For this reason, Ansys, whose software products are related to different physic fields and can perform multi-physics simulation, has been chosen. The simulations of the system are discussed in the second and third part of this dissertation. The software used are two: Ansys Electronics and Ansys Fluent, respectively for electro-magnetic and fluid-dynamic models. The magnetic simulation is performed using a 2D model of the system. The fluid-dynamic one, instead, is developed starting from a 3D slice of the system with a reduced thickness. The coupling between them is realized exporting the resulting magnetic map from the electro-magnetic simulation and importing it into the fluid-dynamic simulation. The viscosity in this last model is not considered constant, but function of the imported magnetic flux density and the shear rate of the fluid. Then, the obtained virtual models are validated using the experimental results of the test bench. The prototype has two sensors placed in two strategic positions. The measured magnetic field values are compared to the ones obtained from the simulation. Similarly, the braking torque calculated in the fluid-dynamic simulation is compared to the one measured in the prototype.