Advanced Automotive Engine Using Maglev Technology English Language Essay

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Nowadays electromagnetically levitating superconducting systems are an emerging trend in automotives. This is due to their frictionless motion and lower power consumption. A small-scale proof prototype of the proposed concept has been designed and built as the next stage in the development of a novel magnetic non-combustible engines using superconductivity concept. This prototype demonstrates on how the maglev and suspension technology using superconductors can also be adopted for the real time large scale manufacture of magnetic engines for various applications in industries. Key design features and performance characteristics of the prototype are analyzed and their control strategies are devised. Various simulation results and experimental outcomes are substantiated.

INTRODUCTION

Traditional IC engines are expensive due to ecological incompatibility of its exhaust .Presence of noise and vibrations invoke high maintenance of IC engines. Hence the alternative technologies such as electric motor drives were introduced, but the requirements of high voltage batteries, large size convertors, inability in driving heavy loads and their high power demands to cover long distances have made them ineffective for automotive drives.

An attempt has been made to overcome all these drawbacks using superconducting maglev and suspension technologies. Our proposed design and its control strategy offer an innovative solution in the field of automotive drives. This idea implies modification of conventional IC engines by replacing the combustible part with a magnetically controllable system. Here the force required for the movement of piston is obtained with the help of magnetic attraction and repulsion forces aided by superconducting cylindrical walls of the engine. A brief description of the proposed design is provided subsequently.

THE DESIGN APPROACH

The outer structure of the model is quite similar to that of conventional IC engine with a cylindrical top connected with crank case. The entire outer structure is hollow where the internal moving and stationary parts are placed as shown in Fig.1.

Fig.1.Design structure

This design consists of two electromagnets fixed inside at the upper and lower sections of the cylinder. The excitation is controlled using PWM technique, where the upper electromagnet consists of copper wire wounded on a cylindrical pole core with a concave shaped cylindrical disc as pole shoe thereby reducing the reluctance of the magnetic path hence spreading out the flux in the air gap radially. And the lower electromagnet is similar to upper electromagnet with a round rectangular cut at the center with a clearance for piston rod to move freely during reciprocating motion. Both the pole core and pole shoe are fabricated by laminations of annealed steel. The piston consists of two NdFeB (Neodymium) magnets in disc and donut shape. Where the disc shaped magnet is mounted over the donut shaped magnet (collectively known as the permanent magnet) and a piston rod connected to it with help of a hinge. This piston is free to move up and down between the two electromagnets during the reciprocating action producing a circular motion to shaft {8} connected inside crank case. The inner cylindrical walls between the two electromagnets are made up of Yttrium barium copper oxide (YBCO) a crystalline chemical compound which is a high temperature superconductor with a critical temperature above 77K. The Fig.2 shows the structure of YBCO synthesized by heating a mixture of the metal carbonates at temperatures between 1000 K and 1300 K by equation below.

4BaCO3 + Y2(CO3)3 + 6 CuCO3 + (1/2−x) O2 → 2YBa2Cu3O7−x + 13 CO2

The selected superconductor (YBCO) is economical and easy to fabricate providing good diamagnetic levitation effect. Also the NdFeB magnet's is selected such that it is kept below the critical magnetic field of superconductor (YBCO) to maintain superconductivity property given by equation below.

The Working Principle

The superconducting Maglev-suspension engine basically works on the principle of "forces of electromagnetic attraction and repulsion"(in simple terms magnetic pull and push forces) aided by superconducting repulsive forces (miessner effect [4]). Since the upper electromagnet {1} and the lower electromagnet {6} are supplied with electrical energy, an unit pole (both electromagnets must not have the same pole at any given instant of time) is assumed to be generated at the near end{10,15} of electromagnets, relative to the permanent magnet{14}.Thus one electromagnet pushes the permanent magnet{14} and the other pulls it, where the repulsive maglev force produced due to movement of permanent magnet{14} by interaction with superconducting walls aids the reciprocating action[3]. The field strength of the permanent magnet {14} is so weak the it ranges only a few millimeters from its axis, therefore it is evident that it assists its motion only during the time of repulsion when the polarity of the near end changes at position {13, 5}.The mechanism of the shaft {8} rotation can be described as under (refer Fig.2):

1. First stroke.

2. Second stroke.

The First Stroke:

Conventionally the permanent magnet {14} is assumed to be placed at position {5}, (i.e.) at the near end {10} of the lower electromagnet {6}) with its S pole facing the lower electromagnet{6}. When the Maglev-suspension engine is started by turning ON the control circuits (refer art.IV) at an instant T=0, both the lower electromagnet {6} and the upper electromagnet {1} acquire the analogous polarity i.e.) S pole at their near ends {10, 15} during the first stroke. Hence the permanent magnet {14} experiences a force of repulsion (since face {3} has same polarity to that at near end {10}).Till, when T=T1 the permanent magnet {14} experiences a strong repulsive force (pushing force) at near end {10} and undergoes an upward motion. At T=T1, the permanent magnet {14} reaches a position {16} (near the centre of the cylindrical portion) at which the permanent magnet {14} begins to experience a force of attraction due to the upper electromagnet {1}, this incidentally marks the end of the first half cycle of the first stroke(see Fig,2(a)) where the shaft connected to the permanent magnet{14} completes one quarter of the revolution.

Fig.2.(a) First stroke Fig.2.(b) Second stroke

During the beginning of the second half cycle, the permanent magnet {14} is pulled i.e.) attracted by the opposite polarity of the upper electromagnet {1} at the near end {15}. (Since the face {2} (side nearer to the upper electromagnet {1}) has N pole and the upper electromagnet's near end {15} has S pole).Till, when T=T2, the permanent magnet {14} undergoes upward motion. When T=T2, the permanent magnet {14} gets to the near end {15} and reaches the position {13} and the shaft attached to the piston rod {11} connected to the permanent magnet {14} completes another quarter part of the revolution. This marks the end of the first stroke. Hence at the end of the first stroke,

(i) Permanent magnet {14} moves from position {5} to position {13} undergoing upward motion.

(ii).The shaft {8} connected to the connecting rod {9} it complete one half of the entire revolution.

The Second Stroke:

The second stroke (see Fig.2(b)) is just similar to that of the first stroke but the difference lies in the fact that the permanent magnet {14} moves downwards due to repulsion since the polarity at the near ends {15,10} is changed(from S to N)by the control circuits. At T=T3 once again the permanent magnet {14} reaches position{16} mean while the shaft {8} completes three fourths of the revolution and marks the end of first half of the second stroke. When T>T3 the permanent magnet is attracted by the near end {10} of the lower electromagnet {6} (Since face {3} is an S pole and near end {10} is an N pole) and at T=T4, the permanent magnet {14} reaches its initial position {5} marking the end of a complete revolution of the shaft {8}.

The Force expressions and

calculations

Assumptions

The diamagnetic levitating force provided by the superconductor {12} at the side walls is considered to be much greater than G force. Hence G force is considered negligible. Also as the motion is linear (against or assisted by gravity) the variation of the potential energy of the permanent magnet {14} also plays a major part, but since the change in height is not very much appreciable (i.e. negligible) it is not considered into account [1]. In order to calculate the push and pull forces it is necessary to introduce two terminologies:

Magneto motive force F

It is the magnetic potential difference between any two points. The pulling and pushing operations of the permanent magnet depends on F. For an electromagnet this force is related to the number of turns, the core material used and the amount of current. So in order to pull a magnet from distance it is necessary to know the potential at the near ends {15, 10} and at the faces {2, 3}.Hence to find the force at a point from the electromagnet it is essential to find H.

Magnetic Field Intensity H

It is the amount of force exerted at a point by a magnet. This depends on the flux density and the permeability of the medium.

(10) In order to get the required force from eqn (7) it is evident that by varying amount of current the criterion is satisfied. The value of field intensity at every instant required to fix a particular force for a given speed was calculated using MAXWELL 3D simulation software and VIZIMAG software.

Expression for Torque:

For a particular speed, the corresponding torque can be found by knowing the relative position of the permanent magnet {14} with respect to any one of the electromagnet.

CONTROL SYSTEM

The control system consists of a µc AT89C51 interfaced with an electromagnet driver LMD18200T IC, Two IR sensors and a pressure transducer act as inputs. The Fig.4 shows the block diagram of the control system. When the engine is started the µc first checks the lower IR sensor and energies both the coils with same polarity (south) which in turn forces the piston upwards. Now the piston cuts upper IR ray and µc changes the polarity of the both coils (done by reversing the current direction), thereby forcing the piston downwards and this process continues [2]. For speed control, the force is converted into a proportional analog signal using pressure transducer. This signal is amplified and converted to digital data and given to the µc as in the new input. The control system is designed in such a way that when it is turned OFF, the µc sends the required signals to bring the piston to its original position (i.e. in the vicinity of the near end {10}).Thus µc generates three signals (PWM, direction & brake (refer Fig.6)) to the driver IC for controlling the excitation of the electromagnets which gets the input from the source.

RESULTS

A miniaturized model (prototype) of our projected design was practically implemented. A similar software generated setup for the piston movement (crank and shaft {8} arrangements are not shown for clarity) is shown in Fig.8 and the flux density spectrum of the electromagnets is shown in Fig.9.

Fig.8.Simulation of our Model

The experiment's scope is actually limited to the prototype and an all-encompassing analysis is done using MAXWELL 3D, VIZIMAG and PROTEUS ISIS simulation softwares for future enhancement of the design due to its rigid hardware nature [5]. The simulation's focal aim is to provide an unambiguous idea on the distribution of the magnetic parameters (H, B specifically).The scrutinized trace of H Vs distance for the electromagnets is shown (see trace Fig.10.)

Fig.9.Magnetic Flux Simulation

On further investigation the following fallouts were observed.

The magnetic field intensity (H) is a function of space (decreases with distance).

The required force for levitation and suspension decreases as the distance between them decreases since area of CS decreases. (Eqn. 6 substantiates this statement).

The superconducting forces too were simulated and their presence was found to favor the movement of the piston thereby increasing the overall efficiency.

The projected control system provides an optimized control over the entire arrangement (refer art. IV).

On further exploration the losses due to friction and the requirements for maintenance are found to be lesser compared to other engines.

Since the setup is energized from a supply, this suffers from magnetic losses (core loss, eddy current losses) hence obviously a trade-off exists between the magnetic losses and mechanical losses (e.g. friction which is not prominent here), but on the whole this provides a lucid solution for environmental problems leaving no residues.

Fig.10.Field intensity graph

CONCLUSION

This model is aimed at providing a long term solution for automotive drives from a different perspective. The initial experimental and simulation results were found to be satisfactory and the further enrichment aspects are also provided. Hope this design marks a new era in automobiles.

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