Electromagnetic Shock Absorber

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Electromagnetic Shock Absorber

  1. 1. ELECTROMAGNETIC SHOCK ABSORBER PROJECT REPORT Submitted by AJITH ARAVIND (AXAKEME002) JESBIN JOHNSON (AXAKEME018) VINOD K J (AXAKEME035) VISHNU T SAJEEVAN (AXAKEME038) in partial fulfillment for the award of the degree of BACHELOR OF TECHNOLOGY in MECHANICAL ENGINEERING AXIS COLLEGE OF ENGINEERING & TECHNOLOGY, AMBANOLY 2014
  2. 2. Project ’14 Electromagnetic Shock Absorber ii Dept of Mechanical Engg AXISCET DEPARTMENT OF MECHANICAL ENGINEERING CERTIFICATE This is to certify that the Project titled ELECTROMAGNETIC SHOCK ABSORBER was prepared and presented by AJITH ARAVIND (AXAKEME002) JESBIN JOHNSON (AXAKEME018) VINOD K J (AXAKEME035) VISHNU T SAJEEVAN (AXAKEME038) of the Eighth Semester Mechanical Engineering in partial fulfillment of requirement for the award of Degree of Bachelor of Technology in Mechanical Engineering under the University of Calicut during the year 2010-2014 PROJECT GUIDE HEAD OF THE DEPARTMENT
  3. 3. Project ’14 Electromagnetic Shock Absorber iii Dept of Mechanical Engg AXISCET ACKNOWLEDGEMENT We express our deep sense of gratitude and indebtedness to Asst Prof. Manu Mohan Nair, Head of Department, Mechanical Engineering for his valuable advice, constant encouragement, for being our internal guide in the design and implementation of our project, constructive criticism during the course of the project and also during the preparation of this manuscript. We are highly indebted to the staff members of Mechanical Department, especially Asst.Professors Jineesh.V.V, Clint.K.S, Joffin Jose, Midhun Joy, Ridhik Radh for their wholehearted support and co-operation. We also express our indebt thanks to our Mechanical workshop superintendent Mr.Velayudhan, and trade instructors Mr.Sooraj and Mr.Jacob, for their helpful mind during the work. We also express our sincere thanks to all the classmates for their support and co-operation in completing the project work. Above all, we should express our supreme gratitude to almighty God.
  4. 4. Project ’14 Electromagnetic Shock Absorber iv Dept of Mechanical Engg AXISCET ABSTRACT A shock absorber in common parlance (or damper in technical use) is a mechanical device designed to smooth out or damp sudden shock impulse and dissipate kinetic energy. It is analogous to a resistor in an electric circuit. Shock absorbers must absorb or dissipate energy. One design consideration, when designing or choosing a shock absorber is where that energy will go. Magnetic shock absorber is an advanced area that can be used to absorb the heavy shock loads which will occur in automobiles. In magnetic shock absorber, repulsive forces from same poles of permanent magnets/electro magnets are used for absorbing the heavy shock loads. Two magnets are fixed permanently in top and bottom end cover of the magnetic shock absorber. Another one magnet is mounted on the movable rod. This magnet will move up and down vertical direction with the rod. All magnets are fixed like same poles are facing each other. This will help to create the repulsive force for absorbing the shock. Top end cover is fixed with body of the vehicle by using bolt connections and movable rod is fixed at the end with the axle of the vehicle. When the vehicle experiences the sudden shock, movable rod slides vertically inside the cylinder along with the magnet. The same poles of the fixed and movable magnets are creating the strong repulsive force. This repulsive force is used for absorbing the heavy shock load and magnetic shock absorber will act as a damping device for vehicle. When the heavy shocking load decreases, the movable magnet comes into the original position. The variable magnet movement depends on the magnitude of the shock load. In this way, this magnetic shock absorber absorbs the heavy load in the vehicle. High grade “Neodymium” [NdFeB] materials are available, having good magnetic property. Along with stainless steel can used for other components in the magnetic shock absorber. This non magnetic stainless steel will not disturb the magnetic field and magnets inside the shock absorber. The non-magnetic material will hold the magnet in both the sides.
  5. 5. Project ’14 Electromagnetic Shock Absorber v Dept of Mechanical Engg AXISCET TABLE OF CONTENT CHAPTER TITLE PAGE ACKNOWLEDGEMENT iii ABSTRACT iv LIST OF TABLES vii LIST OF FIGURES vii 1 INTRODUCTION 1 1.1 Different shock absorbers in use 3 1.2 Types of suspension system 5 1.2.1 Rigid axle front suspension 5 1.2.2 Independent front suspension 6 1.2.3 Torque rod 8 1.2.4 Stabilizer 8 1.3 Permanent magnetic shock absorber 8 2 LITERATURE REVIEW 12 2.1 Investigations of shock absorber 12 2.2 MR Fluids 17 2.3 Concept & modelling eddy current damper 18 2.4 Design considerations 20 2.4.1 Manufacturability 20 2.4.2 Cost 20 2.4.3 Durability 21 2.4.4 Heat dissipation 21 2.4.5 Assembly/Disassembly considerations 21 2.4.6 Sealing 21 2.5 Theoretical Approaches 22 3 PROBLEM STATEMENT 25
  6. 6. Project ’14 Electromagnetic Shock Absorber vi Dept of Mechanical Engg AXISCET 4 COMPONENTS AND DESCRIPTION 27 4.1 Mechanical components 27 4.1.1 Frame structure 27 4.1.2 Cylinder and piston 27 4.1.3 Permanent magnet 30 4.1.4 Coil spring 35 4.2 Electrical components 38 4.2.1 Battery 38 4.2.2 Electromagnet 40 5 RESULTS AND DISCUSSIONS 52 5.1 Electromagnetic force 53 5.2 Repulsive force between magnets 54 5.3 Critical damping coefficient 55 5.4 Design of shock absorber 55 5.5 Billing 57 6 SCOPE AND FUTURE OF PROJECT 58 REFERENCES 60
  7. 7. Project ’14 Electromagnetic Shock Absorber vii Dept of Mechanical Engg AXISCET LIST OF TABLES Table Number TITLE PAGE 4.1 Physical properties of neodymium magnet 34 4.2 Battery specifications 39 5.1 Billing table 57 LIST OF FIGURES Figure Number TITLE PAGE 1.1 Telescopic shock absorber 2 1.2 Schematic Representation 9 1.3 Magnetic Shock Absorber with Regeneration11 2.1 Force vs. Peak Velocity at A Constant Frequency of 20 Hz 14 2.2 MR Effects 18 2.3 Velocity Profiles across the Annular Duct 18 2.4 Illustration of Arrangement of Magnetic Field 19 4.1 Cylinder top view 28 4.2 Cylinder top and cover 28 4.3 Piston 29 4.4 Neodymium magnet 32 4.5 Coil spring 36 4.6 Battery 39 4.7 Magnetic wire 41 4.8 Typical EI lamination 46 4.9 Electromagnet 49 5.1 Shock absorber attached on frame 52 5.2 Repulsion of magnets 53 5.3 Piston and cylinder view 55 5.4 Damper 56
  8. 8. Project ’14 Electromagnetic Shock Absorber 1 Dept of Mechanical Engg AXISCET CHAPTER I INTRODUCTION A shock absorber in common parlance (or damper in technical use) is a mechanical device designed to smooth out or damp sudden shock impulse and dissipate kinetic energy. It is analogous to a resistor in an electrical circuit. Shock absorbers must absorb or dissipate energy. One design consideration, when designing or choosing a shock absorber is where that energy will go. In most dashpots, energy is converted to heat inside the viscous fluid. In hydraulic cylinders, the hydraulic fluid will heat up. In air cylinders, the hot air is usually exhausted to the atmosphere. In other types of dashpots, such as electromagnetic ones, the dissipated energy can be stored and used later. Shock absorbers are an important part of automobile and motorcycle suspensions, aircraft landing gear, and the supports for many industrial machines. Large shock absorbers have also been used in structural engineering to reduce the susceptibility of structures to earthquake damage and resonance. Shock absorbers, linear dampers, and dashpots are devices designed to provide absorption of shock and smooth deceleration in linear motion applications. They may be mechanical (e.g., elastomeric or coil spring) or rely on a fluid (gas, air, hydraulic), which absorbs shock by allowing controlled flow from outer to inner chamber of a cylinder during piston actuation. In conventional shock absorbers the piston rod is typically returned to the unloaded position with a spring. Shock absorbers typically contain either a fluid or mechanical dampening system or a return mechanism to the unengaged position. They vary from small device application to large industrial and civil engineering uses. Linear dampers is an inclusive term that can be applied to many forms of dashpots and shock absorbers; typically used for devices designed primarily for reciprocating motion attenuation rather than absorption of large shock loads. Dashpots are typically distinct in that while they use controlled fluid flow to dampen and decelerate motion, they do not necessarily incorporate an integral return mechanism such as a spring. Dashpots are often relatively small, precise devices used for applications.
  9. 9. Project ’14 Electromagnetic Shock Absorber 2 Dept of Mechanical Engg AXISCET Fig No 1.1 Telescopic Shock Absorber Shock absorbers or damper types for shock absorbers, linear dampers and dashpots can be hydraulic, air, gas spring, or elastomeric. The absorption or damping action can be compression or extension. Important parameters to consider when searching for shock absorbers, linear dampers and dashpots include absorber stroke, compressed length, extended length, maximum force, and maximum cycles per minute. Absorber or spring stroke is difference between fully extended and fully compressed position. Compressed length is the minimum length of shock (compressed position). Extended length is the maximum length of shock (extended position). The maximum rated force for shock absorber or damper, referred to as the force. The maximum cycles per minute are the rated frequency of compression or extension. Important physical specifications to consider when searching shock absorbers, linear dampers and dashpots include the cylinder diameter or maximum width, the rod diameter, mounting, and body material. The cylinder diameter or maximum width refers to the desired diameter of housing cylinder. The rod diameter refers to the desired diameter of extending rod. Mounting choices include ball and socket, rod end, clevis, eyelet, tapered end, threaded, and bumper
  10. 10. Project ’14 Electromagnetic Shock Absorber 3 Dept of Mechanical Engg AXISCET or rod end unattached. Choices for body materials include aluminum, steel, stainless steel, and thermoplastic. Common features for shock absorbers, linear dampers and dashpots include adjustable configuration, reducible, locking, and valve. An adjustable configuration allows the user to fine tune desired damping, either continuously or at discrete settings. A reducible shock absorber, linear damper or dashpot has an adjustment style for gas shocks in which gas is let out to permanently reduce force capacity. In a locking configuration the position can be locked at ends or in the middle of stroke. Valves can be included for fluid absorbers, a valve or port, which can be used to increase or decrease fluid volume or pressure. 1.1 DIFFERENT SHOCK ABSORBERS IN USE 1. There are several commonly-used approaches to shock absorption: 2. Hystersis of structural material, for example the compression of rubber disks, stretching of rubber bands and cords, bending of steel springs, or twisting of torsion bars. Hysteresis is the tendency for otherwise elastic materials to rebound with less force than was required to deform them. Simple vehicles with no separate shock absorbers are damped, to some extent, by the hysteresis of their springs and frames. 3. Dry friction as used in wheel brakes, by using disks (classically made of leather) at the pivot of a lever, with friction forced by springs. Used in early automobiles. Although now considered obsolete, an advantage of this system is its mechanical simplicity; the degree of damping can be easily adjusted by tightening or loosening the screw clamping the disks, and it can be easily rebuilt with simple hand tools. A disadvantage is that the damping force tends not to increase with the speed of the vertical motion. 4. Solid state, tapered chain shock absorbers, using one or more tapered, axial alignment(s) of granular spheres, typically made of metals such as nitinol, in a casing.
  11. 11. Project ’14 Electromagnetic Shock Absorber 4 Dept of Mechanical Engg AXISCET 5. Fluid friction, for example the flow of fluid through a narrow orifice (hydraulics), constitutes the vast majority of automotive shock absorbers. An advantage of this type is that using special internal valving the absorber may be made relatively soft to compression (allowing a soft response to a bump) and relatively stiff to extension, controlling “jounce”, which is the vehicle response to energy stored in the springs; similarly, a series of valves controlled by springs can change the degree of stiffness according to the velocity of the impact or rebound. Some shock absorbers allow tuning of the ride via control of the valve by a manual adjustment provided at the shock absorber. In more expensive vehicles the valves may be remotely adjustable, offering the driver control of the ride at will while the vehicle is operated. The ultimate control is provided by dynamic valve control via computer in response to sensors, giving both a smooth ride and a firm suspension when needed. Many shock absorbers contain compressed nitrogen, to reduce the tendency for the oil to foam under heavy use. Foaming temporarily reduces the damping ability of the unit. Another variation is the magneto rheological damper which changes its fluid characteristics through an electromagnet. 6. Compression of a gas, for example pneumatic shock absorbers, which can act like springs as the air pressure is building to resist the force on it. Once the air pressure reaches the necessary maximum, air dashpots will act like hydraulic dashpots. In aircraft landing gear air dashpots may be combined with hydraulic damping to reduce bounce. Such struts are called oleo struts (combining oil and air). 7. Magnetic effects. Eddy current dampers are dashpots that are constructed out of a large magnet inside of a non-magnetic, electrically conductive tube. 8. Inertial resistance to acceleration, for example prior to 1966 the Citroen 2cv had shock absorbers that damp wheel bounce with no external moving parts. These consisted of a spring-mounted 3.5 kg (7.75 lb) iron weight inside a vertical cylinder and are similar to, yet much smaller than versions of the tuned mass dampers used on tall buildings
  12. 12. Project ’14 Electromagnetic Shock Absorber 5 Dept of Mechanical Engg AXISCET 9. Composite hydro-pneumatic devices which combine in a single device spring action, shock absorption, and often also ride-height control, as in some models of the Citroen automobile. 10. Conventional shock absorbers combined with composite pneumatic springs with which allow ride height adjustment or even ride height control, seen in some large trucks and luxury sedans such as certain lincoln and most land rover automobiles. Ride height control is especially desirable in highway vehicles intended for occasional rough road use, as a means of improving handling and reducing aerodynamic drag by lowering the vehicle when operating on improved high speed roads. 1.2 TYPES OF SUSPENSION SYSTEM 1.2.1 RIGID AXLE FRONT SUSPENSION It shows a typical rigid axle font wheel suspension. This type of suspension was universally used before the introduction of independent front wheel suspension. It may use either two longitudinal leaf spring, or on transverse spring, usually in conjunction with shock absorbers. These assemblies are mounted similarly to rear leaf spring suspensions. In this type of suspension, the front wheel hubs rotate on anti – fiction bearings on steering spindles, which are attached to the steering knuckles. To permit the wheels to be tuned by the steering gear, the steering spindle and the steering knuckle assemblies are hinged on the axle ends. The pin that forms the pivot of this hinge is usually referred to as the kingpin or steering knuckle pin. Where the forked portion is integral with the steering knuckle and fits over the end of the axle, the construction is known as reverse Elliot. In Elliot type construction, the ends of the axle are forked to hold the steering knuckle extension between the ends.
  13. 13. Project ’14 Electromagnetic Shock Absorber 6 Dept of Mechanical Engg AXISCET 1.2.2 INDEPENDENT FRONT SUSPENSION In the independent type of front suspension, a coil, torsion bar or leaf spring independently supports each front wheel. Almost all the passenger cars now use the independent front suspension, in which the coil spring arrangement is the most common. There are three types of coil spring front suspension: 1. In the first type, the coil spring is located in between the upper and lower control arms. The lower control arm has one point attachment to the car frame. 2. In the second type, the coil spring is located in between the upper and lower control arms. The lower arms have two points to attachment to the car frame. 3. In the third type, the coil spring is between the upper control arm and spring tower or housing that is part of the front – end sheet – metal work. Other types of front suspension, besides coil spring type, are also in use. The twin I – beam construction is another type, used on some models of Ford trucks. Each front wheel is supported at the end by a separate I – beam. The ends of the I – beams are attached to the frame by pivots. The wheel ends of the two I – beams are attached to the frame by radius arms, which prevent backward or forward movement of the wheels. This type of suspension provides more flexibility. Single I – beam front suspension is used in larger trucks. The I-beam has a hole in each end through which a kingpin is assembled to hold the steering knuckle in place. Each end of the I-beam is supported by a leaf spring. In this type of suspension system, a steel rod, known as a torsion bar, act as a spring to hold the upper and lower control arms parallel under load. The front end of the rod is of hexagonal shape to fit tightly into an opening in the lower
  14. 14. Project ’14 Electromagnetic Shock Absorber 7 Dept of Mechanical Engg AXISCET control arm. Its rear reaction is also of the hexagonal shape to fit tightly into an opening in an anchor attached to the frame cross member. A seal hides the hexagonal shaped end of the torsion bar. The torsion bar twisted due to the forces on the wheel assembly outer end of the lower control arm. The torsion bar is designed to balance these forces so that the lower arm is kept at a designated height. The height can be adjusted by a tightening mechanism at the anchor end, which twists the rod by means of an adjusting bolt and swivel. A strut rod is used to keep the suspension in alignment. This type of suspension is able to cushion road shocks by causing the lower arm to twist the torsion bar. When the wheels are no larger under stress, the arm returns to normal. It simplifies the independent front suspensions using coil, torsion bar and leaf spring. Basically, the system is known as parallelogram type independent front suspension. It consists of an upper and lower link connected by the stub axle carrier. In general, the lower link is larger than the upper and they may not be parallel. This arrangement maintains the track width as the wheel rise and fall and so minimize tyre wear caused by the wheel scrubbing sideways. Strut and link type suspension system is particularly for integral body construction, because the loading points are widely spaced. The normal top link is replaced by a flexible, mounting, and a telescopic damper acts as the kingpin. This system, known as the Mac Pherson system has little rolling action and absorbs shocks readily. Trailing arm independent front suspension maintains constant track and wheel attitude with a slight change in wheelbase and caster angle. A coil spring is attached to the trailing arm which itself is attached to the shaft carrying the wheel hub. When the wheel moves up and down, it winds and unwinds the spring. A torsion bar has also been used in certain designs in place of the coil spring. In sliding type suspension system, the stub axle can move up and down as well as rotate in the frame members. Track, wheel attitude and wheelbase remain unchanged throughout the rise and fall of the wheel. In vertical guide suspension system, the kingpin is attached directly to the cross member of the frame. It can slide up and down, thus compressing and expanding the springs.
  15. 15. Project ’14 Electromagnetic Shock Absorber 8 Dept of Mechanical Engg AXISCET 1.2.3 TORQUE ROD The torque rod is used to maintain correct alignment of the axle with the frame. It also serves to remove all the stresses on the springs. One end of the torque rod is rigidly fixed to the axle or axle housing, and the other end is attached to the frame by means of a pivoted mounting. The torque rod is also known as torque rod. 1.2.4 STABILIZER A stabilizer or a sway bar, is necessarily is used in all independent front-end suspension. It reduces the tendency of the vehicle to roll or tip on either side when taking a turn. This tendency has been increased due to the use of softer springs and independent front-end suspension. A stabilizer is simply a bar of alloy steel with arms at each end connected to the lower wishbone of the independent suspension or axle. It is supported in bush bearings fixed to the frame, and is parallel to the cross member. When both the wheels deflect up or down by the same amount, the stabilizer bar simply turns in the bearings. When only one wheel deflects, then only one end of the stabilizer moves, thus twisting the stabilizer bar, which acts as a spring between the two sides of the independent suspension. In this way, the stabilizer reduces heeling or tipping of the vehicle on curves. 1.3 PERMANENT MAGNET SYSTEM SHOCK ABSORBER A permanent magnetic suspension apparatus for maintaining a spaced relationship between a first movable member and a second fixed member, wherein the motion of the movable member requires dampening, cushioning, stabilizing, harmonic balancing, and/ or reflexive re-centring. The suspension apparatus includes a plurality of sets of permanent magnets located within a case, which is coupled to one of the members. The sets of permanent magnets are coupled to an elongated support member, which is
  16. 16. Project ’14 Electromagnetic Shock Absorber 9 Dept of Mechanical Engg AXISCET couple to the second member. The support member extends within the case, with the support member and the case being adapted for relative axial movement. The sets of permanent magnets are arranged in bidirectional repulsion configuration with additional magnet fixed within the case. The sets of permanent magnets are being moved relative to the fixed permanent magnets, such that the magnetic forces of repulsion produced by the permanent magnets are increased in response to relative movement between the support member and the case, creating dampening, cushioning, stabilizing, harmonic balancing, and/or re-centring forces. Fig No 1.2 Schematic Representation In one embodiment, the control mechanism is coupled between the frame of a vehicle and a wheel support assembly. The permanent magnetic suspension apparatus, however, is for use with any type of equipment or machinery having a movable and non-movable, or fixed, member. This includes, but is not limited to, cars, trucks, motorcycles, scooters, all terrain vehicles, semi-tractors, semi-trailers, and the like, as well as, but not limited to, industrial equipment and machinery, hospital and office machinery and equipment, such as being coupled between the frame of an office chair and the chair seat. A regenerative electromagnetic shock absorber comprising: a linear electromagnetic generator comprised of a central magnet array assembly comprising a central magnet array comprised of a plurality of axially-aligned, stacked cylindrical magnets having like magnetic poles facing one another, a plurality of high magnetic permeability, high saturation magnetization, central
  17. 17. Project ’14 Electromagnetic Shock Absorber 10 Dept of Mechanical Engg AXISCET cylindrical spacers positioned at each end of stacked central magnet array and between adjacent stacked central magnets, and a magnet array support for mounting magnets and spacers. An inner coil array comprising a plurality of concentric cylindrical coil windings positioned adjacent to central spacers and magnetic poles of central magnets, inner coil windings surrounding an outside perimeter of central spacers. The inner coil array mounted on a movable coil support, movable coil support providing for reciprocating linear motion of coil array relative to magnet array. And an outer magnet array assembly comprising an outer magnet array comprised of a plurality of axially-aligned, stacked concentric toroidal magnets having like magnetic poles facing each other, outer magnet array surrounding inner coil array, stacked outer concentric magnets being aligned and positioned essentially coplanar with stacked central cylindrical magnets with the magnetic poles of outer magnets aligned with and facing opposing magnetic poles of central cylindrical magnets, and a plurality of high permeability, high saturation magnetization, outer concentric toroidal spacers positioned at each end of stacked outer magnet array and between adjacent stacked outer magnets, outer magnet array assembly attached to magnet array support; wherein a predetermined location, configuration and orientation of central magnet magnetic poles, central spacers, inner coil windings, outer magnet magnetic poles and outer spacers provide for superposition of a radial component of a magnetic flux density from a plurality of central and outer magnets to produce a maximum average radial magnetic flux density in the inner coil windings; and a voltage conditioning circuit electrically connected to coil windings, voltage conditioning circuit providing an output voltage and output current to an electrical load.
  18. 18. Project ’14 Electromagnetic Shock Absorber 11 Dept of Mechanical Engg AXISCET Fig No 1.3 Magnetic Shock Absorber with Regeneration
  19. 19. Project ’14 Electromagnetic Shock Absorber 12 Dept of Mechanical Engg AXISCET CHAPTER II LITERATURE REVIEW Andrzej Milecki , Miko" Aj Hauke, 2012,Application Of Magnetorheological fluid In Industrial Shock Absorbers, discussed: Magnetorheological (MR) fluid, which is capable of controlling the stopping process of moving objects, e.g. on transportation lines. The proposed solution makes it possible to adjust the braking force (by electronic controller) to the kinetic energy of the moving object . The paper presents an overview of passive shock absorbers. Next, the design concept of a semi- active shock absorber with the MR fluid is proposed. Theoretically the optimal breaking process occurs when the breaking force is constant on the whole stroke of the absorber. The passive shock absorbers which are in use now do not guarantee this. The braking force of these absorbersis not constant, and, as a result, the stopping process is not optimal. Therefore there is a need for improvement. Recently, semi- active devices, also called ‘‘intelligent’’ devices, have been proposed for the damping of vibrations and oscillations.The parameters of these devices, like the movement opposite force, can be continuously changed with minimal energy requirements. They utilise electrorheological (ER) or magnetorheological (MR) fluids. Such fluids can be quite attractive for industrial applications in the stopping of moving elements on production lines. Compared to conventional electrorheological solutions, MR devices are stronger and can be operated directly from low-voltage power supplies this is why MR fluids are much more often used. 2.1 INVESTIGATIONS OF SHOCK ABSORBER WITH MAGNETORHEOLOGICAL FLUID A bypass valve with a cylindrical gap was mounted on the interface plate. The complete shock absorber is approximately 310 mm long and contains approximately 0.05 dm3 of the MR fluid. An electro-hydraulic servo drive was applied to control the velocity of the piston. The MR shock absorber and the drive were attached to a plate that was mounted on a strong floor. A Linear Variable
  20. 20. Project ’14 Electromagnetic Shock Absorber 13 Dept of Mechanical Engg AXISCET Differential Transducer (LVDT) was used to measure the displacement (linearity 0.5%) and an HBM 5 kN transducer was used to measure the braking force. The measured signals (force and displacement) were transformed into a digital form by a 16-bit analogue/digital (ADC0 and ADC1) converter placed in an input/output card, and then sent to the computer and recorded in its memory. The displacement signal was differentiated in order to obtain the piston velocity. The same computer was used to control the electro-hydraulic servo system velocity (DAC1) and the MR shock absorber coils current (DAC0). Babak Ebrahimi , Mir Behrad Khamesee , M. Farid Golnaraghi, 2008,Design And Modeling Of A Magnetic Shock Absorber Based On Eddy Current Damping Effect, studied: Eddy currents are generated in a conductor in a time-varying magnetic field. They are induced either by the movement of the conductor in the static field or by changing the strength of the magnetic field, initiating motional and transformer electromotive forces (emfs), respectively. Since the generated eddy currents create a repulsive force that is proportional to the velocity of the conductor, the moving magnet and conductor behave like a viscous damper. Graves et al have derived a mathematical representation for eddy current dampers, based on the motional and transformer emf, and have developed an analytical approach to compare the efficiency of the dampers in terms of these two sources. For more than two decades, the application of eddy currents for damping purposes has been investigated, including magnetic braking systems , vibration. Control of rotary machinery, structural vibration suppression , and vibration isolation enhancement in levitation systems. The newly developed analytical model is used to design high-performance dampers for a variety of applications. The damping characteristic of the proposed system can be easily changed by either re-positioning the conductor or choosing the appropriate conductor size and the air-gap distance between the magnets. The novel magnetic spring–damper described in this article is a non-contact device with adjustable damping characteristics,no external power supply requirement and suitable for different vibrational structures for high accuracy and simple implementation. The proposed magnetic spring damper can be modified in terms of size, material , and topological design for different applications. Future work might involve extending
  21. 21. Project ’14 Electromagnetic Shock Absorber 14 Dept of Mechanical Engg AXISCET the magnetic spring–damper design for vehicle suspension systems, since the damper is oil free, inexpensive, requires no external power, and is simple to manufacture. Fig No 2.1 Peak Force vs. Peak Velocity at A Constant Frequency of 20 Hz Alberdi-Muniain , N. Gil-Negrete , L. Kari, 2012,Direct Energy flow Measurement In Magneto-Sensitive Vibration Isolator Systems, learned: The effectiveness of highly non-linear, frequency, amplitude and magnetic field dependent magneto-sensitive natural rubber components applied in a vibration isolation system is experimentally investigated by measuring the energy flow into the foundation. The energy flow, including both force and velocity of the foundation, is a suitable measure of the effectiveness of a real vibration isolation system where the foundation is not perfectly rigid. The vibration isolation system in this study consist s of a solid aluminium mass supported on four magneto- sensitive rubber components and is excited by an electro-dynamic shaker while applying various excitation signals, amplitudes and positions in the frequency range of 20–200 Hz and using magneto sensitive components at zero-field and at magnetic saturation. The energy flow through th e magneto-sensitive rubber isolators is directly measured by inserting a force transducer below each isolator and an accelerometer on the foundation close to each isolator. Bart.L.J.Gysen, Johannes.J.H.Paulides, Jeroen.L.G.Janssen, 2010, Active Electromagnetic Suspension System For Improved Vehicle Dynamics studied:
  22. 22. Project ’14 Electromagnetic Shock Absorber 15 Dept of Mechanical Engg AXISCET Due to the change in vehicle concepts to the more electric car, the suspension system becomes ever more important due to changes in the sprung and unsprung masses. Active electromagnetic suspension systems can maintain the required stability and comfort due to the ability of adaptation in correspondence with the state of the vehicle. Specifications are drawn from on-and off road measurements on a passive suspension system, and it can be concluded that, for ARC, a peak force of 4kN and an RMS force of 2kN (dutycycleof100%) are necessary for th front actuators. Furthermore, the necessary peak damping power is around 2kW; however, the RMS damping power is only 16W during normal city driving. The maximum bound and rebound strokes are 80 and 58mm, respectively. The on road measurements, which are mimicked on a quarter car setup by means of electromagnetic actuation, a good tracking response, and measurement of the frequency response of the tubular actuator, prove the dynamic performance of the electromagnetic suspension system Georgios Tsampardoukas, Charles W.Stammers, Emanuele Guglielmino, 2008, Hybrid Balance Control Of A Magnetorheological Truck Suspension, discussed: The paper concerns an investigation into the use of controlled magnetorheological dampers for a semi active truck suspension. A control strategy targeted to reduce road damage without penalizing driver comfort is presented. A half truck model is employed and system performance investigated via numerical simulation. A balance control algorithm (variable structure type algorithm) based on dynamic tyre force tracking has been devised. Algorithm robustness to parametric variations as well as to real life implementation issues such as feedback signals noises are investigated as well. The magnitude of total road damage reduction (over three axles)on a simulated random road varies with vehicle speed. The reduction was found to be 6% at 7.5m/s, 19% at 17.5m/s and 9% at 25m/s. Kirk T. McDonald, Joseph Henry Laboratories, Princeton University, Princeton, NJ08544 (April14,2012)Magnetic Damping discussed: When a conductor moves through a non uniform, external magnetic field, the magnetic flux varies through loops fixed inside the conductor, so an electromotive force is induced around the loops, according to Faraday’s law (in the rest frame of the conductor), and eddy
  23. 23. Project ’14 Electromagnetic Shock Absorber 16 Dept of Mechanical Engg AXISCET currents flow. The Lorentz force on these eddy currents, due to the external magnetic field, opposes the motion, and one speaks of magnetic braking/damping. This effect is (ultra) relativistic, being of order v2/c2, where v is the speed of the conductor and c is the speed of light in vacuum. While such relativistic effects are generally small for “ordinary” velocities, the eddy current density obeys J=σE, where the conductivity σf or good conductors approaches c2/v2 when measured in Gaussian units, such that eddy current braking is a rare example of an important (ultra) relativistic correction at low velocities. In the present problem the magnetic field is spatially uniform, so the magnetic flux through a moving loop does not change, and no eddy currents develop. Yet, there exists a very weak magnetic damping effect. Zekeriya Parlak, Tahsin Engin, Ismail Çallı, 2012, Optimal Design Of MR Damper Via Finite Element Analyses Of Fluid Dynamic And Magnetic Field, studied: The purpose of the study was to optimize MR damper geometrically in accordance with two objectives, target damper force as 1000N and maximum magnetic flux density. The optimization studies were carried out by finite element method using electromagnetic and CFD tools of ANSYSv12.1. The FEM analyses were employed to get desired optimal values in ANSYS Goal Driven Optimization tool. Values of optimal of the design parameters of the MR damper were searched between lower and upper boundaries in both electromagnetic and CFD analyses. The parameters were geometrical magnitudes, current excitation and yield stress. In the electromagnetic analysis gap width, flange length, gap length, piston head housing thickness, radius of piston core, the number of coil turns and the applied current were selected as design parameters to be able to get maximum magnetic flux density. The values were used in CFD analysis to obtain damper force under optimal conditions
  24. 24. Project ’14 Electromagnetic Shock Absorber 17 Dept of Mechanical Engg AXISCET 2.2 MR FLUIDS When a magnetic field is applied to the fluid, particles in the fluid form chains, and the suspension becomes like a semi-solid material in a few millisecond. Under the magnetic field, an MR fluid behaves as a non-Newtonian fluid with controllable viscosity. However, if the magnetic field is removed, the suspension turns to a Newtonian fluid and the transition between these two phases is highly reversible, which provides a unique feature of magnetic field controllability of the flow of MR fluids. The chains form causes about 50 kPa of yield stress depending on type of MR fluids in a few millisecond, the case creates a resistance against the fluid flow. If a force is applied on the chains form, the shape of the form changes in terms of magnitudes of the force and magnetic field. The pressure reaction on MR fluid is called ‘‘MR effect’’. In figure as can be seen that the particles are scattered randomly in the liquid carrier, when magnetic field applied, the particle array in the direction of the magnetic flux lines to resist the flow, and the chains form is changed in term of force applied to the particles. Fig No 2.2 MR Effect Magnetic field in the gap, the fluid acts like a rigid body below dynamic yield stress considering the Bingham plastic model. This plug region is called the pre-yield. In the pre-yield region, the local shear stresses have not yet exceeded
  25. 25. Project ’14 Electromagnetic Shock Absorber 18 Dept of Mechanical Engg AXISCET the dynamic yield stress. When the local shear stresses exceed the dynamic yield stress, these regions are called the post-yield region and then the fluid acts like a viscous fluid. The pre- and post-yield regions are shown in figure with the velocity profile. As can be seen in figure, the velocity profile is divided into three regions. Fig No 2.3 Velocity Profiles Across the Annular Duct Lei Zuo, Xiaoming Chen, Samir Nayfeh, 2011,Design And Analysis Of A New Type Of Electromagnetic Damper With Increased Energy Density, learned: 2.3 CONCEPT AND MODELLING OF A NEW EDDY CURRENT DAMPER In this section, we first present the concept of the proposed eddy current dampers, and then derive an analytical model for its damping coefficient. Concept Illustration: Alternative Arrangement of Magnetic Poles. It is a common practice in the design o transformers or electromagnetic motors to use laminated steel to reduce the eddy current losses. The reason is that by splitting the conductor, we can increase the electrical resistance of the current loops. In an eddy current damper, we would like to reduce the loop electrical resistance; that is why the area of conductors is usually several times larger than the area of the magnetic field. Inspired by the approach of “splitting the conductor” to reduce the eddy current in transformer design, we can “split the magnets” to increase the eddy current via alternating the magnetic poles. To illustrate this idea, consider two extreme cases as follows. Figure1 as how’s a moving conductor in a uniform magnetic field of the same width. In figure the magnetic field is split into two with alternative pole directions. When the
  26. 26. Project ’14 Electromagnetic Shock Absorber 19 Dept of Mechanical Engg AXISCET conductor is moving at position as shown in the figure, instantaneous electric charges are induced in both cases, as indicated in figure. However, eddy current loop and damping exist only in second case, but not in first case. It is similar to two identical batteries connected Fig No 2.4 Illustration of two types of arrangements of magnetic field for eddy current dampers: case a uniform magnetic field and case b alternating magnetic field R. Zalewski , J. Nachman , M. Shillor , J. Bajkowski, 2013, Dynamic Model For A Magnetorheological Damper, discussed: Lumped mass thermo-mechanical model for the dynamics of a damper filled with a magnetorheological fluid is described, analyzed, and numerically simulated. The model includes friction and temperature effects, and consists of a differential inclusion for the piston displacements coupled with the energy balance equation for the temperature. The fluid viscosity is assumed to be a function the temperature and electrical current, which in practice may be used as the control variable. Numerical simulations of the system behaviour are presented. In particular, the simulations of an initial impact show how the subsequent oscillations can be effectively damped.
  27. 27. Project ’14 Electromagnetic Shock Absorber 20 Dept of Mechanical Engg AXISCET Michael James Atherden,2004, Formula Sae Shock Absorber Design, The University Of Queensland, discussed: 2.4 DESIGN CONSIDERATIONS To form accurate conclusions as to the feasibility of the production of a customised set of dampers, certain design issues must first be taken into account. The factors which require consideration include manufacturability, cost, durability, heat dissipation, assembly and disassembly procedures and sealing. 2.4.1 Manufacturability For the design of the new damper to be feasible, the design must be such that it can be manufactured, preferably in house at the university. As expressed previously, dampers require exacting tolerances to be adhered to if quality items are to be produced. The mechanical engineering workshop has the ability to machine parts to average accuracy, such that I believe it would be possible to manufacture a set of dampers with the current tooling. 2.4.2 Cost The overall cost of the dampers can be reduced if careful consideration is given to the component designs. One area where potential savings exist over purchased dampers is in assembly, with students being able to assemble to units when the components have been manufactured. An actual costing analysis of the damper production will be performed after the design has been presented. In Formula SAE competition, teams are required to complete a cost report based on the competition rules. To summarize, purchased items must be costed at recommended retail price, regardless if the team received a discount from the supplier. For a manufactured item however, the cost of the item includes the raw cost of the material, the machining operations included and the labour to machine and assemble the component. If the team were to manufacture its own set of dampers, significant savings could be made to the final cost of the car, a figure worth 30/100 points for the cost event.
  28. 28. Project ’14 Electromagnetic Shock Absorber 21 Dept of Mechanical Engg AXISCET 2.4.3 Durability Dampers need to be designed with durability in mind as they from the compliant link between the suspension and the chassis. As dampers are usually one of the most expensive items on the vehicle, it is beneficial to be able to re-use them. To be able to reuse the dampers, they should be designed such that major components do not wear to the point where replacement is necessary. This may mean increasing the weight of some components to extend their fatigue life and exerting higher tolerances on machined parts, both of which increase the cost of the damper. 2.4.4 Heat Dissipation Dampers produce a resistive force by passing oil through narrow passages. As time passes, frictional forces within the fluid and damper mechanisms generate heat which raises the temperature of the oil. Short term temperature variations will affect the viscosity of the damper oil, in some cases drastically altering the performance of the damper. Long term thermal cycling of oil eventually degrades its performance as its chemical properties change, thus good heat dissipation prolongs the life of the damper, requiring less frequent maintenance. Heat dissipation away from dampers is usually left to the vehicle designer, who must provide adequate airflow around the unit. 2.4.5 Assembly / Disassembly Considerations As the damper consists of many smaller components, due consideration must be given as to how the damper is going to be assembled or disassembled. Most components are circular by nature and hence threads are prolific. Accessing these threads, by virtue of being able to apply enough torque to tighten or loosen them, must be considered. 2.4.6 Sealing Dampers generate resistive forces by generate large internal pressures. To contain the contents of the damper under these pressures, adequate sealing must be
  29. 29. Project ’14 Electromagnetic Shock Absorber 22 Dept of Mechanical Engg AXISCET provided. Static seals usually consist of rubber O-rings fitting into machined groves with specific dimensions as to provide sufficient ‘squish’ to form a seal. Another type of seal often found in dampers is the sliding seal. Sliding seals are used around the piston, the main shaft and possibly in the external reservoir. These sliding seals usually perform dual functions, providing both a sealing surface and axial support for the particular component. 2.5 THEORETICAL APPROACHES There are several commonly used approaches to shock absorption: 1. Hysteresis of structural material, for eg. the compression of rubber disks stretching of rubber bands and cords, bending of steel springs, or twisting of torsion bars. Hysteresis is the tendency for otherwise elastic materials to rebound with less force than was required to deform them. Simple vehicles with no separate shock absorbers are damped, to some extent, by the hysteresis of their springs and frames. 2. Dry friction as used in wheel brakes, by using disks (classically made of leather) at the pivot of a lever, with friction forced by springs. Used in early automobiles such as the Ford Model T, up through some British cars of the 1940s. Although now considered obsolete, an advantage of this system is its mechanical simplicity; the degree of damping can be easily adjusted by tightening or loosening the screw clamping the disks, and it can be easily rebuilt with simple hand tools. A disadvantage is that the damping force tends not to increase with the speed of the vertical motion. 3. Solid state, tapered chain shock absorbers, using one or more tapered, axial alignment(s) of granular spheres, typically made of metals such as nitinol, in a casing. 4. Fluid friction, for example the flow of fluid through a narrow orifice (hydraulics), constitutes the vast majority of automotive shock absorbers. This design first appeared on Morsracing cars in 1902. One advantage of this type is, by using special internal valving, the absorber may be made relatively soft to compression (allowing a soft response to a bump) and
  30. 30. Project ’14 Electromagnetic Shock Absorber 23 Dept of Mechanical Engg AXISCET relatively stiff to extension, controlling "rebound", which is the vehicle response to energy stored in the springs; similarly, a series of valves controlled by springs can change the degree of stiffness according to the velocity of the impact or rebound. Specialized shock absorbers for racing purposes may allow the front end of a dragster to rise with minimal resistance under acceleration, then strongly resist letting it settle, thereby maintaining a desirable rearward weight distribution for enhanced traction. Some shock absorbers allow tuning of the ride via control of the valve by a manual adjustment provided at the shock absorber. In more expensive vehicles the valves may be remotely adjustable, offering the driver control of the ride at will while the vehicle is operated. The ultimate control is provided by dynamic valve control via computer in response to sensors, giving both a smooth ride and a firm suspension when needed. Many shock absorbers are pressurized with compressed nitrogen, to reduce the tendency for the oil to cavitate under heavy use. This causes foaming which temporarily reduces the damping ability of the unit. In very heavy duty units used for racing or off-road use, there may even be a secondary cylinder connected to the shock absorber to act as a reservoir for the oil and pressurized gas. 5. In electrorheological fluid damper, an electric field changes the viscosity of the oil. This principle allows semi-active dampers application in automotive and various industries. 6. Other principles use magnetic field variation magneto rheological damper which changes its fluid characteristics through an electromagnet. 7. Compression of a gas, for example pneumatic shock absorbers, which can act like springs as the air pressure is building to resist the force on it. Once the air pressure reaches the necessary maximum, air shock absorbers will act like hydraulic shock absorbers. In aircraft landing gear air shock absorbers may be combined with hydraulic damping to reduce bounce. Such struts are called oleo struts (combining oil and air). 8. Inertial resistance to acceleration, for example prior to 1966 the Citroën 2CV had shock absorbers that damp wheel bounce with no external
  31. 31. Project ’14 Electromagnetic Shock Absorber 24 Dept of Mechanical Engg AXISCET moving parts. These consisted of a spring-mounted 3.5 kg (7.75 lb) iron weight inside a vertical cylinder and are similar to, yet much smaller than versions of the tuned mass dampers used on tall buildings. 9. Composite hydropneumatic devices which combine in a single device spring action, shock absorption, and often also ride-height control, as in some models of the Citroën automobile. 10. Conventional shock absorbers combined with composite pneumatic springs which allow ride height adjustment or even ride height control, seen in some large trucks and luxury sedans such as certain Lincoln and most Land Rover automobiles. Ride height control is especially desirable in highway vehicles intended for occasional rough road use, as a means of improving handling and reducing aerodynamic drag by lowering the vehicle when operating on improved high speed roads.
  32. 32. Project ’14 Electromagnetic Shock Absorber 25 Dept of Mechanical Engg AXISCET CHAPTER 3 PROBLEM STATEMENT The automobile chassis is mounted on the axles, not direct but through some form of springs. This is done to isolate the vehicle body from the road shocks which may be in the form of bounce, pitch, roll or sway. These tendencies give rise to an uncomfortable ride and also cause additional stress in the automobile frame and body. All the parts which perform the function of isolating the automobile from the road shocks are collectively called a suspension system. It includes the springing device used and various mountings for the same. Broadly speaking, suspension system consists of a spring and a damper. The energy of road shock causes the spring to oscillate. These oscillations are restricted to a reasonable level by the damper, which is more commonly called a shock absorber. A springing device must be a compromise between flexibility and stiffness. Springs are placed between the road wheels and the body. When the wheel comes across a bump on the road, it rises and deflects the spring, thereby storing energy therein. On releasing, due to the elasticity of the spring material, it rebounds thereby expending the stored energy. In this way springs starts vibrating, of course, with amplitude decreasing gradually on account of internal friction of the spring material and friction of the suspension joints, till vibrations die down. The name Shock absorber is rather misleading since it is the spring and not the shock absorber that initially absorbs the shocks. The ‘Shock Absorber’ absorbs the energy of shock converted into vertical movement of the axle by providing damping and dissipating the same into heat. Thus it merely serves to control the amplitude and frequency of spring vibrations. It cannot support weight and has zero resilience. Therefore, ‘Damper’ is a better term technically to describe the ‘Shock Absorber’. In Magneto-rheological fluid type suspension system, fluid passes through an orifice, which can be restricted by applying an electrical field across it. The fluid consists of magnetically soft particles suspended in a synthetic fluid. When current is applied to an electromagnetic coil inside the shock absorbers piston, the
  33. 33. Project ’14 Electromagnetic Shock Absorber 26 Dept of Mechanical Engg AXISCET resulting magnetic field changes the resistance of flow (rheology) of the fluid which produces a very responsive and controllable damping action without any valves. In the Magneto-suspension system, the damping effect is produced by the theory of magnetic repulsion. The fluidized damping system in the ‘Telescopic- shock absorbers’, is replaced by the introduction of magnetic field. The magnets are placed in such a way that, the mating surfaces are fitted with the same poles of magnet, thereby producing the repulsive effect on the damper system
  34. 34. Project ’14 Electromagnetic Shock Absorber 27 Dept of Mechanical Engg AXISCET CHAPTER 4 COMPONENTS AND DESCRIPTION The components of Electromagnetic shock absorbers are mainly categorized in to two; 1. Mechanical Component 2. Electrical Component 4.1 MECHANICAL COMPONENTS 1. Frame Structure 2. Cylinder and Piston 3. Permanent Magnet 4. Coil Spring 4.1.1Frame Structure It is just to support the shock absorber arrangement. The whole parts are fixed in to this frame stand with suitable arrangement. It is made up of hollow MS pipes which are cut and welded at desired positions. 4.1.2 Cylinder and Piston A cylinder is the central working part of space in which a piston travels. It has two heads. The top head accommodate the electromagnetic coil and core, which will produce the repulsive force when excited. At the top head its just bored to increase diameter, that will help to accommodate the electromagnet. Connection to the coil is passed through the top hole that is drilled at the top.The material of cylinder is usually mild steel, due to easy for machining
  35. 35. Project ’14 Electromagnetic Shock Absorber 28 Dept of Mechanical Engg AXISCET Fig.No 4.1 Cylinder top view Fig. No 4.2 Cylinder and top cover
  36. 36. Project ’14 Electromagnetic Shock Absorber 29 Dept of Mechanical Engg AXISCET The piston is a cylindrical member of certain length which reciprocates inside the cylinder. The diameter of the piston is slightly less than that of the cylinder bore diameter and it is fitted to the top of the piston rod. It is one of the important part which converts the pressure energy into repulsive force in this shock absorber. The piston is equipped with a ring suitably proportioned and it is relatively soft rubber which is capable of providing good sealing with low friction at the operating pressure. The purpose of piston is to provide means of conveying the pressure. Generally piston is made up of 1. Aluminium alloy-light and medium work. 2. Brass or bronze or CI-Heavy duty. The piston is double acting type. The piston moves forward when the high- pressure air is turned from the right side of cylinder. The piston moves backward when high pressure acts on the piston from the left side of the cylinder. The piston should be as strong and rigid as possible. The efficiency and economy of the machine primarily depends on the working of the piston. It must operate in the cylinder with a minimum of friction and should be able to withstand the high compressor force developed in the cylinder and also the shock load during operation. The piston should posses the following qualities. 1. The movement of the piston not creates much noise. 2. It should be frictionless. 3. It should withstand high pressure. Fig. No 4.3 Piston
  37. 37. Project ’14 Electromagnetic Shock Absorber 30 Dept of Mechanical Engg AXISCET 4.1.3 Permanent Magnet A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials like iron and attracts or repels other magnets. A permanent magnet is an object made from a material that is magnetized and creates its own persistent magnetic field. An everyday example is a refrigerator magnet used to hold notes on a refrigerator door. Materials that can be magnetized, which are also the ones that are strongly attracted to a magnet are called ferromagnetic (or ferrimagnetic). These include iron, nickel, cobalt, some alloys of rare earth metals, and some naturally occurring minerals such as lodestone. Although ferromagnetic (and ferrimagnetic) materials are the only ones attracted to a magnet strongly enough to be commonly considered magnetic, all other substances respond weakly to a magnetic field, by one of several other types of magnetism. Ferromagnetic materials can be divided into magnetically "soft" materials like annealed iron which can be magnetized but don't tend to stay magnetized, and magnetically "hard" materials, which do. Permanent magnets are made from "hard" ferromagnetic materials which are subjected to special processing in a powerful magnetic field during manufacture, to align their internal microcrystalline structure, making them very hard to demagnetize. To demagnetize a saturated magnet, a certain magnetic field must be applied and this threshold depends on coercivity of the respective material. "Hard" materials have high coercivity whereas "soft" materials have low coercivity. An electromagnet is made from a coil of wire which acts as a magnet when an electric current passes through it, but stops being a magnet when the current stops. Often an electromagnet is wrapped around a core of ferromagnetic material like steel, which enhances the magnetic field produced by the coil. The overall strength of a magnet is measured by its magnetic moment, or alternately the total magnetic flux it produces. The local strength of the magnetism in a material is measured by its magnetization
  38. 38. Project ’14 Electromagnetic Shock Absorber 31 Dept of Mechanical Engg AXISCET Magnetic field: The magnetic field (usually denoted B) is a vector field. The magnetic field vector at a given point in space is specified by two properties: 1. Its direction, which is along the orientation of a compass needle. 2. Its magnitude (also called strength), which is proportional to how strongly the compass needle orients along that direction. In SI units, the strength of the magnetic field is given in teslas. Magnetic moment: A magnet's magnetic moment (also called magnetic dipole moment, and usually denoted μ) is a vector that characterizes the magnet's overall magnetic properties. For a bar magnet, the direction of the magnetic moment points from the magnet's south pole to its north pole, and the magnitude relates to how strong and how far apart these poles are. In SI units, the magnetic moment is specified in terms of A·m. A magnet both produces its own magnetic field and it responds to magnetic fields. The strength of the magnetic field it produces is at any given point proportional to the magnitude of its magnetic moment. In addition, when the magnet is put into an external magnetic field, produced by a different source, it is subject to a torque tending to orient the magnetic moment parallel to the field. The amount of this torque is proportional both to the magnetic moment and the external field. A magnet may also be subject to a force driving it in one direction or another, according to the positions and orientations of the magnet and source. If the field is uniform in space, the magnet is subject to no net force, although it is subject to a torque.A wire in the shape of a circle with area A and carrying current I is a magnet, with a magnetic moment of magnitude equal to IA. Magnetization: The magnetization of a magnetized material is the local value of its magnetic moment per unit volume, usually denoted M, with units A/m. It is a vector field, rather than just a vector (like the magnetic moment), because different areas in a magnet can be magnetized with different directions and strengths (for example, because of domains, see below). A good bar magnet may
  39. 39. Project ’14 Electromagnetic Shock Absorber 32 Dept of Mechanical Engg AXISCET have a magnetic moment of magnitude 0.1 A·m2 and a volume of 1 cm3 , or 1×10−6 m3 , and therefore an average magnetization magnitude is 100,000 A/m. Iron can have a magnetization of around a million amperes per meter. Such a large value explains why iron magnets are so effective at producing magnetic fields. The permanent magnet used in this shock absorber is Neodymium magnet. A neodymium magnet (also known as NdFeB, NIB or Neo magnet), the most widely used type of rare-earth magnet, is a permanent magnet made from an alloy of neodymium, iron and boron to form the Nd2Fe14B tetragonal crystalline structure. Developed in 1982 by General Motors and Sumitomo Special Metals, neodymium magnets are the strongest type of permanent magnet commercially available. They have replaced other types of magnet in the many applications in modern products that require strong permanent magnets, such as motors in cordless tools, hard disk drives and magnetic fasteners. Some important properties used to compare permanent magnets are: remanence (Br), which measures the strength of the magnetic field; coercivity (Hci), the material's resistance to becoming demagnetized; energy product (BHmax), the density of magnetic energy; and Curie temperature (TC), the temperature at which the material loses its magnetism. Neodymium magnets have higher remanence, much higher coercivity and energy product, but often lower Curie temperature than other types. Neodymium is alloyed with terbium and dysprosium in order to preserve its magnetic properties at high temperatures. The table below compares the magnetic performance of neodymium magnets with other types of permanent magnets. Fig. No 4.4 Neodymium magnet
  40. 40. Project ’14 Electromagnetic Shock Absorber 33 Dept of Mechanical Engg AXISCET Neodymium magnets are graded according to their maximum energy product, which relates to the magnetic flux output per unit volume. Higher values indicate stronger magnets and range from N35 up to N52. Letters following the grade indicate maximum operating temperatures. Grades of Neodymium magnets: 1. N35-N52 2. 33M-48M 3. 30H-45H 4. 30SH-42SH 5. 30UH-35UH 6. 28EH-35EH Neodymium magnet used is N4518, the easy availability and desirable properties are the reason to choose it. Property Neodymium Remanence (T) 1–1.3 Coercivity (MA/m) 0.875–1.99
  41. 41. Project ’14 Electromagnetic Shock Absorber 34 Dept of Mechanical Engg AXISCET Relative permeability 1.05 Temperature coefficient of remanence (%/K) −0.12 Temperature coefficient of coercivity (%/K) −0.55..–0.65 Curie temperature (°C) 320 Density (g/cm3 ) 7.3–7.5 CTE, magnetizing direction (1/K) 5.2×10−6 CTE, normal to magnetizing direction (1/K) −0.8×10−6 Flexural strength (N/mm2 ) 250 Compressive strength (N/mm2 ) 1100 Tensile strength (N/mm2 ) 75 Vickers hardness (HV) 550–650 Electrical resistivity (Ω·cm) (110–170)×10−6 Table No 4.1 Physical properties of neodymium magnet
  42. 42. Project ’14 Electromagnetic Shock Absorber 35 Dept of Mechanical Engg AXISCET 4.1.4 Coil Spring A coil spring, also known as a helical spring, is a mechanical device, which is typically used to store energy due to resilience and subsequently release it, to absorb shock, or to maintain a force between contacting surfaces. They are made of an elastic material formed into the shape of a helix which returns to its natural length when unloaded. Springs can be classified depending on how the load force is applied to them: 1. Tension/Extension spring – the spring is designed to operate with a tension load, so the spring stretches as the load is applied to it. 2. Compression spring – is designed to operate with a compression load, so the spring gets shorter as the load is applied to it. 3. Torsion spring – unlike the above types in which the load is an axial force, the load applied to a torsion spring is a torque or twisting force, and the end of the spring rotates through an angle as the load is applied. 4. Constant spring - supported load will remain the same throughout deflection cycle 5. Variable spring - resistance of the coil to load varies during compression The suspension coil springs combined with shock absorbers prevent undesired vertical movement of the vehicle and suppress jolts and vibrations. An optimum design, an improved production process and a new type of primary material make it possible to reduce the suspension coil spring weight by up to 50%. One type of coil spring is a torsion spring: the material of the spring acts in torsion when the spring is compressed or extended. The quality of spring is judged from the energy it can absorb. The spring which is capable of absorbing the greatest amount of energy for the given stress is the best one. Metal coil springs
  43. 43. Project ’14 Electromagnetic Shock Absorber 36 Dept of Mechanical Engg AXISCET are made by winding a wire around a shaped former - a cylinder is used to form cylindrical coil springs. A spring is an elastic object used to store mechanical energy. Springs are usually made out of spring steel. Small springs can be wound from pre-hardened stock, while larger ones are made from annealed steel and hardened after fabrication. Some non-ferrous metals are also used including phosphor bronze and titanium for parts requiring corrosion resistance Fig. No 4.5 Coil Spring
  44. 44. Project ’14 Electromagnetic Shock Absorber 37 Dept of Mechanical Engg AXISCET This spring is obtained from a dismantled fluid shock absorber. Two end caps are made with sheets two cover the ends and attach with the piston rod. The properties of the spring taken are follows: Material: spring steel Wire dia= 10mm Outer dia= 70mm Inner dia= 50mm Pitch= 23.2mm No.of turns= 11 Length= 230mm Stiffness of spring= 41.72×10^3 N/m
  45. 45. Project ’14 Electromagnetic Shock Absorber 38 Dept of Mechanical Engg AXISCET 4.2 ELECTRICAL COMPONENTS Electrical components are the other important parts of this system. These include: 1. Battery 2. Electromagnet 4.2.1 Battery In isolated systems away from the grid, batteries are used for storage of excess solar energy converted into electrical energy. The only exceptions are isolated sunshine load such as irrigation pumps or drinking water supplies for storage. In fact for small units with output less than one kilowatt. Batteries seem to be the only technically and economically available storage means. Since both the photo-voltaic system and batteries are high in capital costs. It is necessary that the overall system be optimized with respect to available energy and local demand pattern. To be economically attractive the storage of solar electricity requires a battery with a particular combination of properties: 1. Low cost 2. Long life 3. High reliability 4. High overall efficiency 5. Low discharge 6. Minimum maintenance a. Ampere hour efficiency b. Watt hour efficiency We use lead acid battery for storing the electrical energy from the solar panel for lighting the street and so about the lead acid cells are explained below. Since the shock absorber is installed in automobile, the easy power source will be the rechargeable battery. It will recharge automatically when engine is on. Usually 12V batteries are available for the use. And current will vary. Two wheelers have 7A and four wheelers have 40A. We use a 7a battery for this demonstration purpose.
  46. 46. Project ’14 Electromagnetic Shock Absorber 39 Dept of Mechanical Engg AXISCET Fig. No 4.6 Battery Feature Data Voltage 12V Current 40A Type 50B20R Table No 4.2 Battery Specifications
  47. 47. Project ’14 Electromagnetic Shock Absorber 40 Dept of Mechanical Engg AXISCET 4.2.2 Electromagnet An electromagnet is a type of magnet in which the magnetic field is produced by electric current. The magnetic field disappears when the current is turned off. Electromagnets are widely used as components of other electrical devices, such as motors, generators, relays, loudspeakers, hard disks, MRI machines, scientific instruments, and magnetic separation equipment, as well as being employed as industrial lifting electromagnets for picking up and moving heavy iron objects like scrap iron. An electric current flowing in a wire creates a magnetic field around the wire, due to law. To concentrate the magnetic field, in an electromagnet the wire is wound into a coil with many turns of wire lying side by side. The magnetic field of all the turns of wire passes through the center of the coil, creating a strong magnetic field there. A coil forming the shape of a straight tube (a helix) is called a solenoid. Much stronger magnetic fields can be produced if a "core" of ferromagnetic material, such as soft iron, is placed inside the coil. The ferromagnetic core increases the magnetic field to thousands of times the strength of the field of the coil alone, due to the high magnetic permeability μ of the ferromagnetic material. This is called a ferromagnetic-core or iron-core electromagnet. The direction of the magnetic field through a coil of wire can be found from a form of the right-hand rule. If the fingers of the right hand are curled around the coil in the direction of current flow (conventional current, flow of positive charge) through the windings, the thumb points in the direction of the field inside the coil. The side of the magnet that the field lines emerge from is defined to be the North Pole. The main advantage of an electromagnet over a permanent magnet is that the magnetic field can be rapidly manipulated over a wide range by controlling the amount of electric current. However, a continuous supply of electrical energy is required to maintain the field.
  48. 48. Project ’14 Electromagnetic Shock Absorber 41 Dept of Mechanical Engg AXISCET The cost of an electric machine depends upon its size and weight and primarily on the weight of magnetic and conducting materials as these being most costly ones. The weight of the magnetic materials is influenced by the size of the magnetic circuit of the machine. To a great extent, the size and the weighty of the machine depends upon the assigned values of specific magnetic loading, which is limited by the saturation and core losses of the magnetic materials used in the machine. However an increased value of specific magnetic loading could be assigned for designing an electrical machine, provided the magnetic materials has a comparatively higher saturation limit and lower core losses per kg of the material. The main components of electromagnets are insulated magnet wire and a soft iron core. Magnet wire or enameled wire is a copper or aluminium wire coated with a very thin layer of insulation. It is used in the construction of transformers, inductors, motors, speakers, hard disk, head actuators, potentiometers, electromagnets and other applications which require tight coils of wire. Fig No 4.7 Magnetic wire The wire itself is most often fully annealed, electrolytically refined copper. Aluminium magnet wire is sometimes used for large transformers and motors. An aluminium wire must have 1.6 times the cross sectional area as a copper wire to
  49. 49. Project ’14 Electromagnetic Shock Absorber 42 Dept of Mechanical Engg AXISCET achieve comparable DC resistance. Due to this, copper magnet wires contribute to improving energy efficiency in equipment such as electric motors. Smaller diameter magnet wire usually has a round cross section. This kind of wire is used for things such as electric guitar pickups. Thicker magnet wire is often square or rectangular (with rounded corners) to provide more current flow per coil length. Although described as "enameled", enameled wire is not, in fact, coated with either a layer of enamel paint nor with vitreous enamel made of fused glass powder. Modern magnet wire typically uses one to four layers (in the case of quad-film type wire) of polymer film insulation, often of two different compositions, to provide a tough, continuous insulating layer. Magnet wire insulating films use (in order of increasing temperature range) polyvinyl formal (Formvar), polyurethane, polyamide, polyester, polyester-polyimide, polyamide- polyimide (or amide-imide), and polyimide. Polyimide insulated magnet wire is capable of operation at up to 250°C. The insulation of thicker square or rectangular magnet wire is often augmented by wrapping it with a high- temperature polyimide or fiberglass tape, and completed windings are often vacuum impregnated with an insulating varnish to improve insulation strength and long-term reliability of the winding. Other types of insulation such as fiberglass yarn with varnish, aramid paper, kraft paper, mica, and polyester film are also widely used across the world for various applications like transformers and reactors. In the audio sector, a wire of silver construction, and various other insulators, such as cotton (sometimes permeated with some kind of coagulating agent/thickener, such as beeswax) and polytetrafluoroethylene (Teflon) can be found. Older insulation materials included cotton, paper, or silk, but these are only useful for low- temperature applications (up to 105°C). For ease of manufacturing, most new magnet wire has insulation that acts as a flux (metallurgy) when burnt during soldering. [1] This means that the electrical connections at the ends can be made without stripping off the insulation first. Older magnet wire is normally not like this, and requires sandpapering or scraping to remove the insulation before soldering.
  50. 50. Project ’14 Electromagnetic Shock Absorber 43 Dept of Mechanical Engg AXISCET Why must use an insulated copper wire for coils of an electromagnet? A single coil of wire produces an electromagnetic field. Multiple coils add their electromagnetic fields together for a stronger field. Using uninsulated copper wire in the coils would resemble a single large coil because current would not flow evenly through all the copper wires. Also, without insulation the resistance to the flow of electricity would be reduced to near zero drawing too much current and perhaps blowing a fuse or tripping a circuit breaker. E = IR and I = E/R, I (current) is equal to E (voltage)/R(resistance) and I is large if R is small for a given voltage. A magnetic core is a piece of magnetic material with a high permeability used to confine and guide magnetic fields in electrical, electromechanical and magnetic devices such as electromagnets, transformers, electric motors, generators, inductors, magnetic recording heads, and magnetic assemblies. It is made of ferromagnetic metal such as iron, or ferrimagnetic compounds such as ferrites. The high permeability, relative to the surrounding air, causes the magnetic field lines to be concentrated in the core material. The magnetic field is often created by a coil of wire around the core that carries a current. The presence of the core can increase the magnetic field of a coil by a factor of several thousand over what it would be without the core. The use of a magnetic core can enormously concentrate the strength and increase the effect of magnetic fields produced by electric currents and permanent magnets. The properties of a device will depend crucially on the following factors: 1. The geometry of the magnetic core. 2. The amount of air gap in the magnetic circuit. 3. The properties of the core material (especially permeability and hysteresis). 4. The operating temperature of the core. 5. Whether the core is laminated to reduce eddy currents. In many applications it is undesirable for the core to retain magnetization when the applied field is removed. This property, called hysteresis can cause
  51. 51. Project ’14 Electromagnetic Shock Absorber 44 Dept of Mechanical Engg AXISCET energy losses in applications such as transformers. Therefore 'soft' magnetic materials with low hysteresis, such as silicon steel, rather than the 'hard' magnetic materials used for permanent magnets, are usually used in cores. Commonly used core structures are: Air core: A coil not containing a magnetic core is called an air core coil. This includes coils wound on a plastic or ceramic form in addition to those made of stiff wire that are self-supporting and have air inside them. Air core coils generally have a much lower inductance than similarly sized ferromagnetic core coils, but are used in radio frequency circuits to prevent energy losses called core losses that occur in magnetic cores. The absence of normal core losses permits a higher Q factor, so air core coils are used in high frequency resonant circuits, such as up to a few megahertz. However, losses such as proximity effect and dielectric losses are still present. Straight cylindrical core: Most commonly made of ferrite or a similar material, and used in radios especially for tuning an inductor. The rod sits in the middle of the coil, and small adjustments of the rod's position will fine tune the inductance. Often the rod is threaded to allow adjustment with a screwdriver. In radio circuits, a blob of wax or resin is used once the inductor has been tuned to prevent the core from moving. The presence of the high permeability core increases the inductance but the field must still spread into the air at the ends of the rod. The path through the air ensures that the inductor remains linear. In this type of inductor radiation occurs at the end of the rod and electromagnetic interference may be a problem in some circumstances. Single "I" core: Like a cylindrical rod but square, rarely used on its own. This type of core is most likely to be found in car ignition coils. "C" or "U" core: U and C-shaped cores are used with I or another C or U core to make a square closed core, the simplest closed core shape. Windings may be put on one or both legs of the core. "E" core: E-shaped core are more symmetric solutions to form a closed magnetic system. Most of the time, the electric circuit is wound around the center leg,
  52. 52. Project ’14 Electromagnetic Shock Absorber 45 Dept of Mechanical Engg AXISCET whose section area is twice that of each individual outer leg. A core shape derived from E shape is used in this model. When the core is subjected to a changing magnetic field, as it is in devices that use AC current such as transformers, inductors, and AC motors and alternators, some of the power that would ideally be transferred through the device is lost in the core, dissipated as heat and sometimes noise. This is due primarily to two processes: 1. Hysteresis - When the magnetic field through the core changes, the magnetization of the core material changes by expansion and contraction of the tiny magnetic domains it is composed of, due to movement of the domain walls. This process causes losses, because the domain walls get "snagged" on defects in the crystal structure and then "snap" past them, dissipating energy as heat. This is called hysteresis loss. It can be seen in the graph of the B field versus the H field for the material, which has the form of a closed loop. The amount of energy lost in the material in one cycle of the applied field is proportional to the area inside the hysteresis loop. Since the energy lost in each cycle is constant, hysteresis power losses increase proportionally with frequency. 2. Eddy currents - If the core is electrically conductive, the changing magnetic field induces circulating loops of current in it, called eddy currents, due to electromagnetic induction. The loops flow perpendicular to the magnetic field axis. The energy of the currents is dissipated as heat in the resistance of the core material. The power loss is proportional to the area of the loops and inversely proportional to the resistivity of the core material. Eddy current losses can be reduced by making the core out of thin laminations which have an insulating coating, or alternately, making the core of a nonconductive magnetic material, like ferrite.
  53. 53. Project ’14 Electromagnetic Shock Absorber 46 Dept of Mechanical Engg AXISCET Having no magnetically active core material (an "air core") provides very low inductance in most situations, so a wide range of high-permeability materials are used to concentrate the field. Most high-permeability material are ferromagnetic or ferrimagnetic. The most common core materials are follows: Soft iron:"Soft" (annealed) iron is used in magnetic assemblies, electromagnets and in some electric motors; and it can create a concentrated field that is as much as 50,000 times more intense than an air core. Iron is desirable to make magnetic cores, as it can withstand high levels of magnetic field without saturating (up to 2.16 tesla at ambient temperature) It is also used because, unlike "hard" iron, it does not remain magnetized when the field is removed, which is often important in applications where the magnetic field is required to be repeatedly switched. Unfortunately, due to the electrical conductivity of the metal, at AC frequencies a bulk block or rod of soft iron can often suffer from large eddy currents circulating within it that waste energy and cause undesirable heating of the iron. Laminated silicon steel: Because iron is a relatively good conductor, it cannot be used in bulk form with a rapidly changing field, such as in a transformer, as intense eddy currents would appear due to the magnetic field, resulting in huge losses (this is used in induction heating). Two techniques are commonly used together to increase the resistivity of iron: lamination and alloying of the iron with silicon. Lamination: Fig No 4.8 Typical EI Lamination
  54. 54. Project ’14 Electromagnetic Shock Absorber 47 Dept of Mechanical Engg AXISCET Laminated magnetic cores are made of thin, insulated iron sheets, lying, as much as possible, parallel with the lines of flux. Using this technique, the magnetic core is equivalent to many individual magnetic circuits, each one receiving only a small fraction of the magnetic flux (because their section is a fraction of the whole core section). Because eddy currents flow around lines of flux, the laminations prevent most of the eddy currents from flowing at all, restricting any flow to much smaller and thinner and thus higher resistance regions. From this, it can be seen that the thinner the laminations, the lower the eddy currents. This type of plates are used here to make the core materials. Silicon alloying: A small addition of silicon to iron (around 3%) results in a dramatic increase of the resistivity, up to four times higher. Further increase in silicon concentration impairs the steel's mechanical properties, causing difficulties for rolling due to brittleness. Among the two types of silicon steel, grain-oriented (GO) and grain non- oriented (GNO), GO is most desirable for magnetic cores. It is anisotropic, offering better magnetic properties than GNO in one direction. As the magnetic field in inductor and transformer cores is static (compared to that in electric motors), it is possible to use GO steel in the preferred orientation. Carbonyl iron: Powdered cores made of carbonyl iron, a highly pure iron, have high stability of parameters across a wide range of temperatures and magnetic flux levels, with excellent Q factors between 50 kHz and 200 MHz. Carbonyl iron powders are basically constituted of micrometer-size spheres of iron coated in a thin layer of electrical insulation. This is equivalent to a microscopic laminated magnetic circuit (see silicon steel, above), hence reducing the eddy currents, particularly at very high frequencies. A popular application of carbonyl iron-based magnetic cores is in high- frequency and broadband inductors and transformers. Iron powder: Powdered cores made of hydrogen reduced iron have higher permeability but lower Q. They are used mostly for electromagnetic
  55. 55. Project ’14 Electromagnetic Shock Absorber 48 Dept of Mechanical Engg AXISCET interference filters and low-frequency chokes, mainly in switched-mode power supplies. Ferrite: Ferrite ceramics are used for high-frequency applications. The ferrite materials can be engineered with a wide range of parameters. As ceramics, they are essentially insulators, which prevents eddy currents, although losses such as hysteresis losses can still occur. Vitreous Metal: Amorphous metal is a variety of alloys that are non-crystalline or glassy. These are being used to create high efficiency transformers. The materials can be highly responsive to magnetic fields for low hysteresis losses and they can also have lower conductivity to reduce eddy current losses. China is currently making wide spread industrial and power grid usage of these transformers for new installations. Soft iron has a far greater magnetic permeability than steel. Meaning it provides a stronger magnetic field for a given magnetization current (up to saturation). It has a much lower retentivity than steel - when the current is switched off the remaining field strength is very weak (objects held by iron will be released , but probably held by the significant 'permanent' field retained by steel). That’s why soft iron core is used for core material. During the last few years, considerable developments have place in the field of magnetic materials. Presently magnetic materials having very high permeability’s and low specific iron losses are available. These materials are much superior and result into a reduced size of the machine with a lower overall cost. As such they are replacing the poor magnetic materials previously used in electrical machines. The most suitable magnetic materials for electrical machines, which give a considerable reduction in size and cost, are silicon steel of various grades.
  56. 56. Project ’14 Electromagnetic Shock Absorber 49 Dept of Mechanical Engg AXISCET Fig No 4.9 Electromagnet The force exerted by an electromagnet on a section of core material is: F= (B²A)/ (2μₒ) The magnetic field created by an electromagnet is proportional to both the number of turns in the winding, N, and the current in the wire, I, hence this product, NI, in ampere-turns, is given the name magneto motive force. For an electromagnet with a single magnetic circuit, of which length Lcore of the magnetic field path is in the core material and length Lgap is in air gaps, Ampere's Law reduces to: Where is the permeability of free space (or air) For a closed magnetic circuit (no air gap), such as would be found in an electromagnet lifting a piece of iron bridged across its poles, equation becomes: B= (NIμ)/L
  57. 57. Project ’14 Electromagnetic Shock Absorber 50 Dept of Mechanical Engg AXISCET F= (μ²N²I²A)/(2μₒL²) The above methods are inapplicable when most of the magnetic field path is outside the core. For electromagnets (or permanent magnets) with well defined 'poles' where the field lines emerge from the core, the force between two electromagnets can be found using the 'Gilbert model' which assumes the magnetic field is produced by fictitious 'magnetic charges' on the surface of the poles, with pole strength m and units of Ampere-turn meter. Magnetic pole strength of electromagnets can be found from: The force between two poles is: The variables of the electromagnet are: Permeability,μ =1.2567×10^-6 H/m Number of turns,N =250 Current,I =7amp Radius of core ,R =3cm Area of cross section, A =Πd²/4 = 7.06×10^-4 m² Permeability of free space,μₒ = 4Π×10^-7 N/A² Length of core,L = 6cm
  58. 58. Project ’14 Electromagnetic Shock Absorber 51 Dept of Mechanical Engg AXISCET Calculating the attractive or repulsive force between two magnets is, in the general case, an extremely complex operation, as it depends on the shape, magnetization, orientation and separation of the magnets. The Gilbert model does depend on some knowledge of how the 'magnetic charge' is distributed over the magnetic poles. It is only truly useful for simple configurations even then. Fortunately, this restriction covers many useful cases. For two cylindrical magnets with radius , and height , with their magnetic dipole aligned and the distance between them greater than a certain limit, the force can be well approximated (even at distances of the order of ) by, Where is the magnetization of the magnets and is the distance between them. For small values of , the results are erroneous as the force becomes large for close-to-zero distance.
  59. 59. Project ’14 Electromagnetic Shock Absorber 52 Dept of Mechanical Engg AXISCET CHAPTER 5 RESULTS AND DISCUSSIONS Electromagnet is made by winding the insulated copper coil around the soft iron piece. To end of the coil is leads to connections. The permanent magnet is attached at the centre of piston head, with adhesives. According to the outside pole of the permanent magnet electromagnet is connected to the battery, such that the poles are identical and repel each other when comes closer. After that cylinder and piston are arranged. Then the spring is aligned on the piston rod with end covers. And fixed on the frame. Fig. No 5.1 Shock absorber attached on frame
  60. 60. Project ’14 Electromagnetic Shock Absorber 53 Dept of Mechanical Engg AXISCET Since we have no exact equation to find the repulsive force between two non identical magnet, its assumed that both magnets have shape, size, magnetic force approximately same. For two cylindrical magnets with radius , and height , with their magnetic dipole aligned and the distance between them greater than a certain limit, the force can be well approximated (even at distances of the order of ) by, Fig No. 5.2 Repulsion of magnets 5.1 ELECTROMAGNETIC FORCE The magnetic force generated by the electromagnet is calculated by formula F= (μ²N²I²A)/(2μₒL²) Permeability,μ =1.2567×10^-6 H/m Number of turns, N =250 Current, I =7amp Diameter of core ,d =3cm Area of cross section, A =Πd²/4 = 7.06×10^-4 m² Permeability of free space,μₒ = 4Π×10^-7 N/A²
  61. 61. Project ’14 Electromagnetic Shock Absorber 54 Dept of Mechanical Engg AXISCET Length of core, L = 6cm Force, F = 300.48N 5.2 REPULSIVE FORCE BETWEEN MAGNETS Radius of electromagnet, R = 3cm Permeability of free space,μₒ = 4Π×10^-7 N/A² Height of magnet, H =6cm At normal condition the permanent magnet rest at distance of 10cm from the core, and the minimum distance when it comes during shock is 3cm. So there is a maximum and a minimum force, between these repulsion forces varies. As the distance between magnets decreases the force will increase. But when it comes closer the magnet will attract. So in order to avoid such situation a rubber bush is placed over the electromagnet. Magnetisation, M =Nm/V, m-unit vector in that direction =(250/54)*m = 4.62 A/m Therefore Repulsive force, When x =x1 i.e., x =3cm, Repulsive force will be maximum Fmax = 4.23×10^-6 N When x =x2 i.e., x =10 cm, Repulsive force will be minimum Fmin = 3.748×10^-7 N
  62. 62. Project ’14 Electromagnetic Shock Absorber 55 Dept of Mechanical Engg AXISCET 5.3 CRITICAL DAMPING COEFFICIENT Stiffness of spring, K = 41720 N/m Mass of spring, m = 0.650kg Linear resonance frequency, fres =127Hz Angular natural frequency, ωn = 797.96 rad/s Critical damping coefficient, Cc =2 ( ) = 2 ( ) =329.35 5.4 DESIGN OF SHOCK ABSORBER Fig No 5.3 Piston and cylinder view
  63. 63. Project ’14 Electromagnetic Shock Absorber 56 Dept of Mechanical Engg AXISCET Fig No 5.4 Damper
  64. 64. Project ’14 Electromagnetic Shock Absorber 57 Dept of Mechanical Engg AXISCET 5.5 BILLING No ITEM No. of ITEMS COST ₹ 1 Cylinder & Piston 1 650 2 Coil Spring 1 250 3 Neodymium Magnet 1 350 4 Copper Coil 10mtrs 100 5 Insulated plate 15 30 6 Wire 3mtrs 20 7 Machining cost 100 Total, ₹ 1500 Table 5.1 Billing table
  65. 65. Project ’14 Electromagnetic Shock Absorber 58 Dept of Mechanical Engg AXISCET CHAPTER 6 SCOPE AND FUTURE OF PROJECT The riding comfort ability is one of the main factors that considered in designing. Shock absorbers, linear dampers, and dashpots are devices designed to provide absorption of shock and smooth deceleration in linear motion applications. The road conditions are different at places. An automobile is designed to perform best at all places. Suspension system will help to maintain better stability at any state. Hydraulic and gas charged shock absorbers are commonly used now a days. But at severe shock load the hydraulic shock absorbers may fail. The fluids get leaked. So in introducing magnets in the shock absorber to provide damping effect is an efficient method. During the shock loads the damper will absorbs the energy, in case of the fluidic type it take time. These create an unstable condition. And the passengers want to suffer its after effects. In case of racing cars, the loads are suddenly fluctuating type and the vibrations wants to remove as soon as possible. General principle similar poles deflect; can be applied to absorb the damping effect by providing the magnets. And there is no contact between parts inside the damper, so the friction is negligible. The absence of conductive medium will also help to remove hysteresis effect. The design can be varied to the required conditions and the component such as electromagnets are available on the requirement. While considering the additional cost for fabrication it’s not large when compared with the performance. The levitation based researches are presently takes place. So more improved magnetic parts will be available easily in future. Actually now it’s a conceptual model. We are not included the features such as sensor to detect the deflection of the coil spring. Depending on the deflection magnetic field with required strength can be induced, that will help to make the repulsive force to dampen the shock loads in few seconds. During this project we had studied various method of suspension system, using the magnetic properties.
  66. 66. Project ’14 Electromagnetic Shock Absorber 59 Dept of Mechanical Engg AXISCET We had noticed that when any two leads of the three phase induction motor were shorted then we had to apply more force to rotate the shaft. If it is coupled with the suspension system like a torque arm suspension system, we can damper the force without any expenditure of energy. The only requirement will be the shorting circuit. We hope these high performance suspension systems will incorporate in coming generation vehicles, which will remove the defects caused by the current models.
  67. 67. Project ’14 Electromagnetic Shock Absorber 60 Dept of Mechanical Engg AXISCET REFERENCES 1. Andrzej Milecki , Miko Aj Hauke,2012, Application Of Magnetorheological fluid In Industrial Shock Absorbers, Mechanical Systems And Signal Processing 28,528–541 2. Babak Ebrahimi , Mir Behrad Khamesee , M. Farid Golnaraghi,2008, Design And Modeling Of A Magnetic Shock Absorber Based On Eddy Current Damping Effect, Journal Of Sound And Vibration 315, 875–889. 3. Alberdi-Muniain , N. Gil-Negrete , L. Kari, 2012,Direct Energy flow Measurement In Magneto-Sensitive Vibration Isolator Systems, Journal Of Sound And Vibration 331,1994–2006 4. Bart.L.J.Gysen, Johannes.J.H.Paulides, Jeroen.L.G.Janssen, 2010, Active Electromagnetic Suspension System For Improved Vehicle Dynamics, IEEE Transactions On Vehicular Technology, Vol.59.No.3 5. Georgios Tsampardoukas, Charles W.Stammers, Emanuele Guglielmino, 2008,Hybrid Balance Control Of A Magnetorheological Truck Suspension, Journal Of Sound And Vibration31.7 ,514-536 6. Kirk T. Mcdonald, Joseph Henry Laboratories, Princeton University, Princeton, NJ08544,2012, Magnetic Damping 7. Zekeriya Parlak, Tahsin Engin, Ismail Çallı, 2012,Optimal Design Of MR Damper Via Finite Element Analyses Of Fluid Dynamic And Magnetic Field, Mechatronics 22, 890–903 8. Lei Zuo, Xiaoming Chen, Samir Nayfeh, 2011,Design And Analysis Of A New Type Of Electromagnetic Damper With Increased Energy Density, Journal Of Vibration And Acoustics, Vol.133/041006-1 9. R. Zalewski , J. Nachman , M. Shillor , J. Bajkowski,2013, Dynamic Model For A Magnetorheological Damper, Applied Mathematical Modelling 10. Pinjarla.Poornamohan, Lakshmana Kishore.T,2012, Design And Analysis Of A Shock Absorber,IJRET,Vol 1,Issue 4, 578-592
  68. 68. Project ’14 Electromagnetic Shock Absorber 61 Dept of Mechanical Engg AXISCET 11. Michael James Atherden,2004, Formula Sae Shock Absorber Design, The University Of Queensland, BE thesis, 51-54 12. Bogdan Sapinski,2009, Magnetorheological Damper in Vibrational Control of Mechanical Structures, Mechanics,Vol 1, No 1,18-25

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