F0RM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)
1. Title of the invention: IMPROVED SPRING ASSEMBLY FOR USE IN CIRCUIT
BREAKER
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
This invention relates generally to the field of circuit breakers. More particularly, the present invention relates to an improved spring assembly for use in circuit breaker. This invention finds its application in switch gear industry.
BACKGROUND AND THE PRIOR ART
Most switchgear manufacturer uses extension springs as a basic source of power and also to enable smooth operation of mechanism. In some applications, to achieve intended function within a given space constraint, concentric extension spring assembly is required. The same is generally achieved by joining extra metal plates/inserts at both ends of the concentric extension springs having only basic spring body or coils, as there are no separate hooks.
JP2001357768 aims to improve reliability of a breaker action by aiming at life elongation of an open-close spring by improving the spring shape so that fatigue is hard to be generated even when repeated loads are applied while securing the required spring constant. In a tension spring consisted of U-shaped hooks 6b formed at both ends of a coil part 6a of the open-close spring assembled into a main contact point open-close mechanism of a circuit breaker, and whose hooks are hung on pins 7, 8 and stretched across a toggle link of the main contact point open-close mechanism, a bending diameter rl of the hooks is formed as a smaller diameter than a coil diameter D of the coil, and the hooks at the both ends are formed in the reverse directions with each other, and the stress concentration of the hooks accompanied by the open-close action of the circuit breaker is reduced to make fatigue-fracture of the spring hard to be generated.
Conventionally such concentric extension spring assemblies are made either by using metal inserts or sheet metal components at either ends/sides of the concentric springs. This requires secondary operations for joining/fitment of the end parts. Thus, final assembly comprises of total four parts, (i.e. two springs -inner & outer and two end parts.) Inner Spring with only body (i.e. without hooks at both ends) and outer spring with only body (i.e. without hooks at both ends). Further metal inserts are assembled at both ends to form spring assembly. Therefore in totality

four parts are required for assembly. Further a few end coils/turns of both springs are required to engage with metal inserts at both ends. Hence there is always reduction in number of effective/useful turns of each spring.
There are few drawbacks/disadvantages of the same which are listed below :
• Reduction in no of effective/useful turns.
• More no of parts required for complete spring assembly.
• Increased cost of spring assembly due to more no of parts and joining process involved in a spring assembly.
• Increased assembly time due to secondary process of spring joining.
This invention overcomes / improves on above mentioned drawbacks and deficiencies of the conventional available solutions as mentioned above. These points are as follows:
• Complete utilization of turns as there are no ineffective turns.
• No extra parts are required for spring assembly as novel hook design itself takes care of an assembly.
• Reduced cost of spring assembly since there are no extra parts required for assembly and hence no separate joining process required to make spring assembly.
• Reduced assembly time as no secondary process of spring joining is required. The same can be achieved during manufacturing of outer spring itself.
The current invention uses a different method / process to join two concentric extension springs having customized hook design to facilitate basic assembly process of springs - without using any other external parts. Since the springs are assembled together with each other, it can finally act as a single conventional spring, enabling to use for varieties of applications.
The current assembly process allows assembly of two concentric extension springs without using external members. This also involves re-orientation of hooks to facilitate assembly of two
springs.

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 concentric extension spring assembly for use in circuit breakers.
Yet another object of the present invention is hook means to restrict movement of internal spring of Concentric Extension Spring Assembly.
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
The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the present invention. It is not intended to identify the key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concept of the invention in a simplified form as a prelude to a more detailed description of the invention presented later.
There is provided an improved concentric extension spring assembly for use in circuit breakers.
According to one aspect of the present invention, there is provided hook means to restrict movement of internal spring of Concentric Extension Spring Assembly.
Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.

BRIEF 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 inner Extension Spring (Front View) is illustrated.
Fig 2 illustrates Inner Extension Spring (Isometric View)
Fig 3 illustrates Outer Extension Spring (Front View)
Fig 4 illustrates Outer Extension Spring (Isometric View)
Fig 5 illustrates Concentric Extension Spring Assembly (with different views)
Fig 6 illustrates Concentric Extension Spring Assembly (Isometric view)
Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may have not been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure. Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures.
DETAILED DESCRIPTION OF THE INVENTION
The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but

these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.
The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.
It is to be understood that the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.
By the term "substantially" it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide.
Accordingly the present invention provides a Concentric Extension Spring Assembly for operation of circuit breaker.
The current invention uses a different method / process to join two concentric extension springs having customized hook design to facilitate basic assembly process of springs - without using any other external parts. Since the springs are assembled together with each other, it can finally act as a single conventional spring, enabling to use for varieties of applications.
The purpose of the invention is a means to assemble two Concentric Extension Springs in a more efficient manner and also to meet design intent within a given space envelop.

The current assembly process allows assembly of two concentric extension springs without using external members. This also involves re-orientation of hooks to facilitate assembly of two springs.
The process first involves in manufacturing of inner spring and then placing the spring when outer spring is being made. This is done in such a way that the inner spring is retained inside once the outer spring is completely manufactured. Arrangement of hooks doesn't allow inner spring to separate out from the outer spring.
The same assembly is also possible to make by first manufacturing both springs (inner and outer) completely and then assemble them by using assembly fixture. Since there are no external parts required for assembly, final spring assembly comprises of only two parts, (i.e. two springs -inner & outer.)
The invention comprises of a Concentric Extension Spring assembly (3), consisting of an Inner Spring (1), and an Outer Spring (2). The same can be used for intended application. Inner Spring 1 is an extension spring with German type of hook construction at both ends. Both hook ends have an angle 11 & 12 with reference to center line of the spring as shown in figure. Outer Spring (2) is an extension spring with German type of hook construction at both ends. Both hook ends have an angle 21 & 22 with reference to center line of the spring as shown in figure 3.
Fig 5 shows concentric extension spring assembly 3. Springs in assembly have same nominal values of free length 31 to enable work them together at intended deflection in the actual application. Features 11,12, 21 & 22 as mentioned above aids assembly of springs without interference of hooks of at both ends. This also helps to maintain same nominal values of free lengths of both springs.
Mean diameters of both springs have been designed so as to make them concentric 32 with each other. Both springs are arranged in such a way that there is a positive clearance 33 between

hooks of both springs. This enables both springs work together at a time without any interference between the hooks. Direction of winding of coils 34 is different in both springs so as to allow smooth working without interference and to avoid entanglement between the two. Fig 6 Shows isometric view of the complete assembly ready for use in the actual application. Spring assembly can be mounted directly on application by using hooks at both ends. Once loaded, both springs act together to produce desired load values.
ADVANTAGES:
• Complete utilization of turns as there are no ineffective turns.
• No extra parts are required for spring assembly as novel hook design itself takes care of an assembly.
• Reduced cost of spring assembly since there are no extra parts required for assembly and hence no separate joining process required to make spring assembly.
• Reduced assembly time as no secondary process of spring joining is required. The same can be achieved during manufacturing of outer spring itself.
• Maximum utilization of space available inside outer spring which otherwise could have been wasted in a conventional single extension spring.
• Compact design, hence can be used when space is a constraint and also when design intent to be met within a given space.
• Since already it's an assembly, it can be directly used at the required location in the actual application.
• No need of extra end pieces required for assembly of both springs.
Concentric extension spring assembly in the present invention is comprising of an inner extension spring; a German type of hooks set at an angle (with reference to axis of spring body) at both ends of the said inner extension spring; a outer extension spring; a German type of hooks set at an angle (with reference to axis of spring body) at both ends of the said outer extension spring ; a concentric extension spring assembly; concentric assembly of above said inner extension spring and outer extension spring to form the said concentric extension spring assembly; same nominal values of free lengths of above said inner extension spring and outer extension springs in the above said concentric extension spring assembly; an inner extension

spring and a outer extension spring having opposite direction of coil winding (i.e. left and right handed) in the above said concentric extension spring assembly.
A concentric extension spring assembly as above wherein a typical type of hook construction with hooks set at a relative angle with each other which avoid interference between them during and after assembly - same can also be achieved by different orientation or design of hooks; the same nominal value of free length of an inner extension spring and outer extension spring allows simultaneous loading of both springs.
Since there are two separate springs, both have same nominal values of free lengths. This allows
simultaneous loading of both springs.
This involves typical type of hook construction with hooks of both springs set at a relative angle with each other to :
A) Avoid interference between them during and after assembly.
B) Enable interlocking of two springs. This also helps to restrict movement of inner spring with reference to outer spring so that it can not come out of outer spring. This ensures that both springs together act as an assembly without using any other external means (like metal inserts at both ends.)
Since there are no separate metal inserts at the ends, all available turns in both springs are functional and hence there is no reduction in the number of total effective turns/coils in both springs (i.e. inner & outer ). Only two springs are required for assembly.
No extra metal inserts required for assembly. Hence there is reduced cost of spring assembly due to less number of parts and less assembly time as no joining process with separate metal inserts involved in a spring assembly. It provides a unique arrangement of hooks of both springs ensures that they remain as an assembly during handling operation. This is achieved by interlocking hooks of both springs with reference to each other.

Further the hook profile is set at an angle with reference to axis of spring. This facilitates smooth assembly of both springs without interference. It allows maintaining same nominal free length of both springs so that both springs can be loaded simultaneously. It ensures that both springs, once assembled, acts as an assembly, since hooks are designed in such a way so as to interlock with each other, thereby also locking the springs with each other.
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 invention.
It is also to be understood that the description is 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 CLAIMS
1. An improved spring assembly for use in circuit breaker, said assembly comprising:
an inner spring means;
an outer spring means;
wherein said inner spring means and said outer spring means concentrically placed;
wherein said inner spring means and said outer spring means having a pair of hook ends each, said hook ends placed at an angle with reference to axis of said spring means.
2. Assembly as claimed in claim 1 wherein said spring means are substantially extension spring means.
3. Assembly as claimed in claim 1 wherein said spring means having german type of hook construction at both ends.
4. Assembly as claimed in claim 1 wherein said hook ends placed at an angle with reference to axis of said spring means adapted to facilitate interlocking of said inner and outer spring means.
5. Assembly as claimed in claim 1 wherein said inner spring means and said outer spring means having substantially same nominal values of free length thereby enabling both said spring means to work together at intended deflection.
6. Assembly as claimed in claim 1 wherein said inner spring means and said outer spring means having a positive clearance there between thereby preventing interference between said hooks.

7. Assembly as claimed in claim 1 wherein both said spring means having direction of winding of coils substantially different thereby facilitating smooth working without interference and avoiding entanglement between both said spring means.
8. An improved spring assembly for use in circuit breaker as herein described and illustrated with reference to accompanying drawings.