Design and Fabrication of Magneto-Rheological Braking system – Mechanical Project
The aim of this project work is to develop a magneto-rheological brake (MRB) system that has performance advantages over the conventional hydraulic brake system. The proposed brake system consists of rotating disks immersed in a MR fluid and enclosed in an electromagnet, which the yield stress of the fluid varies as a function of the magnetic field applied by the electromagnet. The controllable yield stress causes friction on the rotating disk surfaces, thus generating a retarding brake torque. The braking torque can be precisely controlled by changing the current applied to the electromagnet. In this paper, an optimum MRB design with two rotating disks is proposed based on a design optimization procedure using simulated annealing combined with finite element simulations involving magneto static, fluid flow and heat transfer analysis. The performance of the MRB in a vehicle was studied using a quarter vehicle model. A sliding mode controller was designed for an optimal wheel slip control, and the control simulation results show fast anti-lock braking.
In this project, we propose a MR actuator for the brake in each wheel. The actuator consists of a rotating disk immersed in a MR fluid, enclosed in an electromagnet. In principle, the brake torque can be controlled by changing the DC current applied to the electromagnet. Magneto rheological fluid – compound containing fine iron particles stiffens in the presence of a magnetic field. Two important characteristics of MR fluids are: (i) they exhibit linear response, i.e., the increase in stiffness is directly proportional to the strength of the applied magnetic field and (ii) they provide fast response, i.e., MR fluid changes from a fluid state to a near-solid state within milliseconds of exposing a magnetic field. CHB systems exhibit about 200–300 ms of delay between the time the brake pedal is pressed by the driver and the corresponding brake response is observed at the wheels due to pressure build-up within the hydraulic lines. An electric brake system has the potential to drastically reduce this time delay, consequently bringing a reduction in braking distance.
Imagine some materials have the ability to change shape or size simply by adding a little bit of heat, or to change from a liquid to a solid almost instantly when near a magnet; these materials called smart materials. Smart materials have one or more properties that can be dramatically altered. Most everyday materials have physical properties, which cannot be significantly altered; for example if oil is heated it will become a little thinner, whereas a smart material with variable may turn from a liquid state which flows easily to a solid. Each individual type of smart material has a different property which can be significantly altered, such as viscosity, volume or conductivity. The rheological properties of fluid change when a magnetic field is applied across it. When in normal conditions the MR fluid behaves like a Newtonian fluid, but when magnetic field is applied across it the viscosity of the fluid changes and it shows semisolid like a characteristic.
Components of MR Fluid
• Iron Particle: micron or nano size
• Carrier fluids: synthetic oil, silicone or water
• Binder Material (to prevent the iron particles from settling down): special grease
MAGNETO REHOLOGICAL BRAKING SYSTEM
The automotive industry has a commitment to build safer, cheaper and better performing vehicles. For example, the recently introduced drive by wire technology has been shown to improve the existing mechanical systems in automobiles. In other words, the traditional mechanical systems are being replaced by improved electromechanical systems that are able to do the same tasks faster, more reliably and more accurately. The proposed brake is a magneto rheological brake (MRB) that potentially has some performance advantages over conventional hydraulic brake (CHB) systems. A CHB system involves the brake pedal, hydraulic fluid; transfer lines and brake actuators (e.g. disk or drum brakes). When the driver presses on the brake pedal, the master cylinder provides the pressure in the brake actuators that squeeze the brake pads onto the rotors, generating the useful friction forces (thus the braking torque) to stop a vehicle. However, the CHB has a number limitations, including,
(i) delayed response time (200–300 ms) due to pressure build up in the hydraulic lines,
(ii) bulky size and heavy weight due to its auxiliary hydraulic components such as the master cylinder,
(iii) brake pad wear due to its frictional braking mechanism, and
(iv) low braking performance in high speed and high temperature situations. The MR brake operates in a direct-shear mode, shearing the MR fluid filling the gap between the two surfaces (housing and rotor) moving with respect to one another. Rotor is fixed to the shaft, which is placed in bearings and can rotate in relation to housing. Resistance torque in the MR brake depends on viscosity of the MR fluid that can be changed by magnetic field. MR brake allows for continuous control of torque. When there is no magnetic field the torque is caused by viscosity of carrier liquid, bearings and seals.
MR Braking System consists of rotor fixed to the shaft, which is placed in bearings and can rotate in relation to housing. Wires allow supplying electric current to the coil. Between rotor and housing there is a gap filled with MR fluid. Construction of the brake and location of the coil makes the gap to be in the magnetic field generated by the coil. MR fluid being in the brake is suspension of magnetic particles in the liquid (water, oil or some other kind of liquid). Magnetic particles are dissipated in the liquid when field strength is equal to zero but when the field strength is grater then zero particles are magnetized, they gather in chains and make liquid flow through them to be difficult. Operation of MR brake is based on the effect. MR fluid changes viscosity when it is in magnetic field. Shows MR fluid in the gap during working in clutch (direct-sheer) mode, when there is magnetic field applied. This kind of working takes place in the brake.
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Authors Sridhar.V, 2 Subash Chandra Bose B, 3 Syed Ibrahim S, and 4 Vijay S Guided By – Assistant professor Mr.Sachin S Raj
Gnanamani College of Technology, Namakkal, Tamilnadu, India
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