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THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)
1 Title of the invention. - IMPROVED VARIABLE INDUCTION COIL MECHANISM
2. Applicant(s)
(a) NAME : LARSEN & TOUBRO LIMITED
(b) NATIONALITY: An Indian Company.
(c) ADDRESS: L & T House, Ballard Estate, Mumbai 400 001,
State of Maharashtra, India
3. PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed:

TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to induction coil mechanism and more particularly to an improved variable induction coil mechanism providing a wide range of continuous inductance values.
BACKGROUND AND THE PRIOR ART
Conventionally a variable multilayer inductor is provided with tapping to change the number of turns of the coil thus changing the value of inductance. Tapping is an additional joint in the coil which deforms the windings and is the cause for inter-turn shorting. The number of tapping provided in the conventional method is fixed and changing it is a lengthy process. Hence only discrete values of inductance are obtained. Another method is by using a variable core material, in this case a sliding core is used which can be moved in and out of the coil in order to change the inductance. However, this is not possible in case of air core reactors. Figure 1 shows a conventional variable multilayer inductor.
US 6317021 disclose a variable inductor with a saturable core having three legs, including a center leg and two outer legs. A control winding is wound on the center leg and two outer windings are connected in parallel and wound on the outer legs. The inductances of the windings on the outer legs vary with the current through the control winding. The current through the control winding varies the saturation level of the outer legs. In one embodiment, the inductance of the control winding is substantially constant with a change in current in the control winding. In another embodiment, the outer legs are saturated and the center leg is not saturated. Portions of the core connecting the three legs are tapered down from the cross-section of the center leg to the cross-sections of the outer legs. The invention further includes methods of varying the inductance of an inductive circuit element in accordance with

a control current. In which, the inductance of the inductive circuit element is varied by means of an electrical signal. However, mechanical movement of the series inductor coils was not known in the prior art.
US 5999077 disclose a voltage controlled variable inductor provides a rapidly variable inductance for high power frequency dependent circuit applications. Continuously variable inductance values having a high Q factor are obtainable with the application of only a minimal amount of control power. It corresponds to the invention of voltage controlled variable inductor using a variable air gap to control inductance. In this case the air gap between the magnets is varied by controlling the voltage.
US 4620144 discloses an electric power apparatus, namely a variable inductor comprising a magnetic core provided with a center limb and two outer limbs all having first and second ends. The first ends are interconnected through a first common point of the magnetic core, and the second ends through a second common point of this core. Two primary windings disposed respectively around the two outer limbs are connected in series and supplied with an alternating current, while two control windings also connected in series are respectively superposed to the two primary windings. The alternating current of the primary windings is rectified through a diode bridge for supplying with direct current the control windings. The direction of the different windings along with their interconnections are selected so that the alternating and direct currents induce in one of the two outer limbs alternating and direct current magnetic fluxes which assist each other or which are in opposition and in the other of these two limbs alternating and direct current magnetic fluxes which are in opposition or which assist each other, respectively, depending on the positive or negative value of the alternating current. Each outer limb comprises an air gap traversed by the resultant magnetic flux induced in this limb, and preferably disposed in the center of the corresponding primary and control windings. It relates to

variable iron core inductor consisting of three fixed limbs. However, the number and position of the limbs are variable which was not known in the prior art.
Although the tapings provides variable inductance, only the fix values of inductance can be obtained from the tapping. Thus, there is a need to overcome the problems of conventionally existing inductance loads of the prior art. Therefore, the present inventors have developed an improved variable induction coil whose inductance would vary over a wide range of continuous values. It would provide more compact and easily accessible for maintenance.
OBJECTS OF THE INVENTION
A basic object of the present invention is to overcome the disadvantages/drawbacks of the known art.
Another object of the present invention is to provide an improved variable induction coil.
Other object of the present invention is to provide continuous range of inductance.
These and other advantages of the present invention will become readily apparent from the following detailed description read in conjunction with the accompanying drawings.
SUMMARY OF THE INVENTION
There is provided induction coil mechanism.

According to one embodiment of the present invention, there is provided an improved variable induction coil mechanism providing a wide range of continuous inductance values. Mechanism comprising a plurality of inductor coils connected in series, said coils stacked closely thereby providing mutual induction
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
In the appended drawings:
Fig 1 illustrates a conventional variable multilayer inductor.
Fig 2 illustrates an improved variable induction coil.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The following drawings are illustrative of particular examples for enabling methods of the present invention, are descriptive of some of the methods, and are not intended to limit the scope of the invention. The drawings are not to scale (unless so stated) and are intended for use in conjunction with the explanations in the following detailed description.
Reference is first invited to Fig 1 where the prior art of the present field of invention is shown.
Fig. 2 shows the mutual distance between the coils and the variation in inductance value.
The invention therefore provides an improved variable induction coil mechanism providing a wide range of continuous inductance values.

DETAILED DESCRIPTION OF THE INVENTION
Accordingly in the present invention there is provided an improved variable induction coil. As shown in figure 2, the improved variable induction coil used various inductor coils in series in place of a single coil.
The total inductance of a series inductor circuit is given by Lt=Ll +L2+L3+....Ln
As these inductors are stacked close to each other, the magnetic flux of one links with the other resulting into mutual inductance between the coils. The effect of this mutual inductance depends on the distance apart of the coils and their orientation to each other. If the current flowing through the two coils in the same direction then the mutual inductance aids to the total inductance of the circuit, whereas if the current in the two coils are flowing in opposite direction then the mutual inductance opposes the total inductance of the circuit.
For cumulatively coupled coils the total inductance is given by Lt=Ll+L2+M12
For differentially coupled coils the total inductance is given by Lt=Ll+L2-M12
The mutual inductance depends on the distance between the two coils. Thus by changing the distance between the two coils one can vary the inductance over a continuous range of values.
Thus, it is able to achieve a higher value of inductance by cumulatively coupling two or more coils. This results in saving of the coil material. Unlike the conventional multilayered coils, this inductor is less susceptible to heating and ageing effects.

Also, as the coils are connected in series for maintenance purpose there is no need to disconnect the entire circuit, only the faulty coil can be removed from the circuit thus preventing interruption during maintenance.
ADVANTAGES:
1. Vary over a wide range of continuous values.
2. More compact
3. Easily accessible for maintenance.
4. Heating of the winding is less in turn resulting into greater life of the winding.
Although the embodiments herein are described with various specific embodiments, it will be obvious for a person skilled in the art to practice the embodiments herein with modifications. However, all such modifications are deemed to be within the scope of the claims.
It is also to be understood that the following claims are intended to cover all of the generic and specific features of the embodiments described herein and all the statements of the scope of the embodiments which as a matter of language might be said to fall there between.

WE CLAIM:
1. An improved variable induction coil mechanism providing a wide range of continuous inductance values, wherein said mechanism comprising a plurality of inductor coils connected in series, said coils stacked together having intermediate spaces between the coils wherein said space the coils is adjustable either manually or through an automated system so as to achieve a favorable value of mutual inductance between the coils which in turn provides the desired value of total coil inductance..
2. Mechanism as claimed in claim 1 wherein said coils are adjusted to provide a varying range of mutual induction which depends on the distance between said coils and their orientation.
3. Mechanism as claimed in claim 1 wherein said coils are cumulatively or differentially coupled to provide a required value of inductance.
4. An improved variable induction coil mechanism providing a wide range of continuous inductance values as herein described and illustrated with reference to accompanying drawings.