The hydraulic brakes presently used in cars exhibit several important limitations. These include the slow response to the driver's command;​ difficulties in control due to the hydraulic nature of the system;​ and a large number of components spread throughout the car with critical components such as the disk surface, the brake pads and the fluid pipings vulnerable to damage from gravel or other external sources. To overcome these problems, intrinsic to the concept of hydraulic brakes, a new system must be devised. Solutions are sought in the use of smart materials, including the application of piezoelectric or electrostrictive materials and electrorheological or magnetorheological fluids to car brakes. A detailed study of each material is carried out, in terms of their possibilities and limitations. It is seen that present piezoelectric and electrostrictive materials are unable to meet the performance requirements needed for application to car brakes and that electrorheological fluids are less suitable than magnetorheolical fluids for this application. Consequently, an innovative car braking system is designed using rnagnetorheological fluids.

The design procedure comprises the study of theoretical models for the performance of a magnetorheological brake and, given the absence of closed-form solutions for the braking torque of an arbitrary brake system, finite element models are built to provide a means to analyse the performance of the magnetorheological brake system. The formulation of these models (including the definition of the geometry, material properties, boundary conditions and meshing process, as well as necessary assumptions) are described. The results obtained with the finite element models are presented and analysed.

In order to obtain an optimum design, i.e. one with high braking power and low weight, an optimisation procedure is carried out, centred on the finite element analysis. Three different optimisation methods are used (subproblem approximation, first order and simulated annealing). Their performance and relative methods are compared.

Based on the results of the optimisation problem, a final design is proposed, taking into account manufacturing constraints and a study of its longevity and reliability is carried out. A scaled-down prototype is also proposed to serve as a proof of concept.

Finally, the strengths and weaknesses of magnetorheological brakes and the expected evolution of this techonology are discussed, as well as conclusions regarding the use of piezoelectric or electrostrictive materials for brake actuators.