Abstract

The braking system is one of the major factors affecting a vehicle’s performance. The future of the automotive industry thrives by the creation of a greener, more efficient and lightweight braking mechanisms. Research on utilizing electromechanical brakes have shown potential due to their superior performance and controllability. The magnetorheological Brake (MRB) is a promising electromechanical brake which can provide variable damping through variation of the MR fluids’ apparent viscosity and yield strength using the applied magnetic field. Fast response time, low power requirement and large dynamic range are among unique features of MRBs making them an ideal candidate for vehicle applications. While some design configurations have been proposed for applying MRBs in the automotive industry, the commercial application has not yet been fully realized mainly due to the existence of their zero-field viscous torque. The focal purpose of this study is to propose and develop a novel real-size vehicle model of the MRB design with absolutely no energy loss in terms of viscous torque generation. The design is achieved using permanent magnets which force the MR fluid volume to shift locations between the brake’s operating modes – ‘on’ and ‘off’ – to allow complete de-coupling. The performance of the proposed design compared with the conventional design is demonstrated on a 2-disk-type MRB configuration. The Herschel-Bulkley constitutive model is adopted for the MR fluid to derive the mathematical equations governing the systems’ braking torques as a function of the rotational speed, geometric properties, and applied electrical current. The MR fluid selected for the proposed designs is MRF-132DG from Lord Corporation. Analytical magnetic circuit analysis of the MRB design has been conducted which allows to approximately derive the relation between the magnetic field intensity and the electric current as a function of number of coil turns and the brake’s geometric variables. The analytical model is then verified using an electromagnetic finite element model developed in open source FEMM software. An equation relating densities of the materials used in the MRB and their corresponding dimensions is also derived to estimate the weight of the proposed MRB. Subsequently, a multidisciplinary design optimization problem has been formulated to identify the optimal brake geometrical parameters to maximize the dynamic range of the MRBs under weight, size and magnetic flux density constraints. The optimization problem has been solved using Genetic Algorithm (GA) followed by the Sequential Quadratic Programming (SQP) technique implemented in the MATLAB environment to achieve the true global optimal design. It is shown that the proposed MRB design provides better performance specifications under the required design constraints while having zero viscous torque generation making it suitable for application in real commercial vehicles. Finally, a simple dynamic quarter-vehicle model integrated with the optimally designed MRB has been considered to investigate the brake performance in automotive application. A PID control scheme has been designed for optimal wheel slip control over different road surface conditions. The objective is to obtain the highest value possible for the road-friction coefficient. This is possible through regulating and maintaining the slip ratio to a desired value whether driving on dry, wet, snowy or icy roads. The controller is purposed to enhance the overall braking properties of a vehicle through reducing the stopping distance and time, enhancing stability, and avoiding wheel lockup.