The paper presents a new electromechanical brake system for vehicles using magnetorheological fluid. The brake system designed for the electric vehicle has some advantages over the conventional brake system. The brake system is made up of a brake disk, shells, magnetorheological fluid (MRF) and the electromagnets. The brake disk is immersed in the MRF whose yield stress changes as the applied magnetic field. The braking torque of this system can be linearly adjusted by the current in just a few milliseconds without the conventional vacuum booster. This system has a quick response and precise control performance with a low hysteresis. Besides, the system has adopted the original complicated structure to save space and cost. In this paper, the configuration of MRF brake types is described. The braking torques of the MRF brakes is derived based on the MRF theoretical model which is firstly raised. Some braking simulation based on the theoretical model is also shown. Then the research focuses on optimal design of different types of magnetorheological brakes using the method of finite element.
Smart Lockwire: A Shape Memory Alloy Lockwire for Improved Reliability in Bolted Fixing in Automotive and Aeronautical Applications
Shape memory alloys (SMA) have a unique behavior due to a reversible phase transformation between two solid crystalline structures: martensite (low temperature and low stiffness phase) and austenite (high temperature and a higher stiffness phase). This transformation can occur either as a result of temperature change or mechanical stress load, both above characteristic critical values of these materials. Due to the reversible nature of this phenomenon, direct transformation occurs when austenite transforms into martensite and reverse transformation when martensite transforms into austenite. The latter is induced by raising the temperature and it is this process that occurs during the generation of significant associated forces through the undergone deformation recovering of the material, being of fundamental importance for the use as actuators. The use of lockwires is common in aviation and automotive industries as an extra precaution to prevent possible screw loosening (due to vibration, temperature increase or other external forces) in bolted joints where it is not possible to use locking nuts.
Chassis performance greatly influences driving in the turn inn movement. Spec of the active damper is simulated to achieve a chassis that satisfies various requirements. In this paper, an MR-damper (Magneto-Rheological fluid damper), which is high-response active damper, is chosen. The MR-damper is mounted in FSAE vehicles and controlled vehicle behavior electronically in a simulator. As a result, the MR-damper brought a big effect to pitch action rather than roll action, and an initial damping force effected vehicle behavior more than damping force change ratio.
Effect of Cylinder Diameter of Monotube-Type MR-Damper on the Damping Force Changing Ratio and the Response Time
MR-damper (Magneto-Rheological fluid damper) is used an actuator with high speed in response to control the movement of four-wheel vehicles. In this paper, performances of two MR-dampers were measured. These dampers had difference in diameter of cylinder, length of piston and orifice. These changes will influence the damping force, the damping force change ratio and the response time of damping force change. As a result, a larger damper showed 1.4 times damping force change ratio of smaller one and shorter response time in compression.
Magneto-rhelological(MR) dampers are devices that use rheological fluids to modify the mechanical properties of fluid absorber. The mechanical simplicity, high dynamic range, large force capacity, lower power requirements, robustness and safe manner of operation have made MR dampers attractive devices for semi-active real-time control in civil, aerospace and automotive applications. Landing gear is one of the most essential components of the aircraft, which plays an extreme important role in preventing the airframe from vibration and excessive impact forces, improving passenger comfortable characteristics and increasing aircraft flight safety. In this paper, the semi-active system used in landing gear damping controller design, simulation, and the vibration test-bed are discussed and researched. The MR dampers employed in landing gear system were designed, manufactured and characterized as available semi-active actuators. On the basis of a large number of experimental data, a mathematical model based on the Bouc-Wen hysteresis model was adopted to predict both the force-displacement behavior and the complex nonlinear force-velocity response of the MR dampers.
Magneto-rheological fluid squeeze mode investigations at CVeSS have shown that MR fluids show large force capabilities in squeeze mode. A novel MR squeeze mount was designed and built at CVeSS, and a dynamic mathematical model was developed, which considered the inertial effect and was validated by the test data. A variant engine mount that will be used for isolating vibration, based on the MR squeeze mode is proposed in the paper. The mathematical governing equations of the mount are derived to account for its operation with MR squeeze mode. The design method of a robust H✓ controller is addressed for the squeeze mount subject to parameter uncertainties in the damping and stiffness. The controller parameter can be derived from the solution of bilinear matrix inequalities (BMIs). The displacement transmissibility is constrained to be no more than 1.05 with this robust H✓ controller. The MR squeeze mount has a very large range of force used to isolate the vibration.
Piezoelectric materials are smart materials that can undergo mechanical deformation when electrically or thermally activated. An electric voltage is generated on the surfaces when a piezoelectric material is subjected to a mechanical stress. This is referred to as the ‘direct effect’ and finds application as sensors. The external geometric form of this material changes when it is subjected to an applied voltage, known as ‘converse effect’ and has been employed in the actuator technology. Such piezoelectric actuators generate enormous forces and make highly precise movements that are extremely rapid, usually in the micrometer range. The current work is focused towards the realization and hence application of the actuator technology based on piezoelectric actuation. Finite element simulations are performed on different types of piezoelectric actuations to understand the working principle of various actuators. The displacements produced by the multilayered actuators are sometimes insufficient compared with the total displacement requirements such as in injector control valve applications in automotive engine environment, therefore it calls for design of an amplification system to increase the stroke using existing multilayered stacks.
Smart material is a suitable candidate for adaptive airfoil design as it can be customized to generate a specific response to a combination of inputs. Shape memory alloy (SMA) in particular is lightweight, produces high force and large deflection which makes it a suitable candidate for actuator in the adaptive airfoil design. By attaching SMA wires inside the airfoil, they can be activated to alter the shape of the airfoil. Placement of the actuator is crucial in obtaining the desired change of the airfoil camber. This paper proposed a design for the morphing wing aimed at changing the camber of the airfoil during cruise in order to increase the lift-to-drag ratio. Finite Element Method (FEM) analysis predicted the deformed airfoil geometry when the SMA wires were fully actuated. Numerical results are presented along with issues related to the fabrication of the morphing wing and implementation of the SMA actuator.
The Anatomy of Smart Materials and Structures and Their Influence on Design Practices in Automotive Engineering
This paper presents an exposition on the embryonic eclectic field of smart materials and structures, prior to discussing how this class of biomimetic materials will influence design practices in the field of automotive engineering. The development of smart structures typically involves the macroscopic synthesis of materials with both functional and structural properties by exploiting biomimetic philosophies. The most innovative class of these macroscopically adaptive materials typically feature combinations of actuators, sensors, and microprocessing capabilities which enable these materials to actively change their mass, stiffness and energy-dissipation characteristics in real-time. Such capabilities are particularly relevant to the numerous automotive systems that must operate under variable service conditions and in unstructured environments.