FORM 2
The Patents Act 1970
(39 of 1970)
&
The Patent Rules 2003
COMPLETE SPECIFICATION
(See Section 10 and rule 13)
TITLE OF THE INVENTION:
TRISTABLE COMPLIANT CIRCUIT BREAKER MECHANISM
APPLICANT:
LARSEN & TOUBRO LIMITED
L&T House, Ballard Estate, P.O. Box No. 278,
Mumbai, 400 001, Maharashtra,
INDIA.
PREAMBLE OF THE DESCRIPTION:
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED

A) TECHNICAL FIELD
[0001] The present invention generally relates to a circuit breaker and
particularly to trip free tristable compliant circuit breaker mechanism. The present invention more particularly relates to a usage of compliant joints in the circuit breaker to achieve manual independent operation.
B) BACKGROUND OF THE INVENTION
[0002] Circuit Breaker is a mechanical switching device, capable of making
(i.e. switching ON), carrying and breaking (i.e. switching OFF) current under normal circuit conditions and more specifically breaking current (tripping) during abnormal circuit conditions such as during short-circuit. Generally, the short circuit current is sensed automatically and the signal is given to the circuit breaker mechanism as a TRIP command which leads to opening of the contacts. However, during normal ON-OFF and OFF~ON operation, the input to the circuit breaker mechanism is given through the rotation of knob by manual means. In all the three cases (ON-FF-TRIP), the contact velocity is independent of speed at which the knob is rotated.
[0003] Initially, the rotation of the knob leads to storing potential energy in
the spring member while restricting the contact movement during the charging operation. At a specified instance, the potential energy of spring is released in the form of kinetic energy through mechanical linkages leading to the rotation of the contacts at high velocity.
[0004] In conventional circuit breakers, the ON, OFF, and TRIP positions are
achieved by transmitting motion through mechanical linkages. The links are connected by rigid joints like revolute or sliding which results in higher friction and also wear and tear. Also the circuitry demands large number of components.

[0005] The conventional bistable compliant circuit breaker mechanism uses
flexural pivots to transfer the motion, equivalent four bar linkage and flexible segment as energy storing member.
[0006] Hence there is a need to provide a circuit breaker with tristable
mechanism including the minimal number of components. Also there exists a need for a circuit breaker mechanism to provide for less friction and wear and tear during operation.
[0007] The above mentioned shortcomings, disadvantages and problems are
addressed herein and which will be understood by reading and studying the following specification.
C) OBJECTS OF THE INVENTION
[0008] The primary object of the present invention is to provide manually
independent tristable circuit breaker mechanism with built-in trip free condition.
[0009] Another object of the present invention is to provide a circuit breaker
mechanism with reduced number of components.
[0010] Yet another object of the present invention is to provide a circuit
breaker mechanism where the mechanical linkages, joints and supports are formed out of a single member.
[0011] Yet another object of the present invention is to provide a circuit
breaker mechanism to achieve ON, OFF and TRIP position by transmitting motion through rigid elements connected with flexible leaf and torsional elements.
[0012] Yet another object of the present invention is to provide a circuit
breaker mechanism to reduce the assembly time.

[0013] Yet another object of the present invention is to provide a circuit
breaker mechanism to reduce the wear and tear losses in the assembly.
[0014] These and other objects and advantages of the present invention will
become readily apparent from the following detailed description taken in conjunction with the accompanying drawings.
D) SUMMARY OF THE INVENTION
[0015] The various embodiments of the present invention provide a manually
independent tristable mechanism which also suffices requirement of trip free condition. According to one embodiment of the present invention, a tristable circuit breaker mechanism comprises a housing element, a fork element, a driveshaft element to connect circuit breaker contacts to the housing element, a lower link element, an upper link element, a latch element, a trip element and a spring arrangement. The circuit breaker consists of a compliant arrangement where all mechanical linkages, joints and supports are formed out of a single member. A charging of the spring arrangement beyond a dead centre position of the actuating mechanism flips the tristable circuit breaker such that the circuit breaker contacts attain at least one of the ON, OFF and TRIP position.
[0016] According to one embodiment of the present invention, the fork
element comprising a knob sub-element to provide for various positions of the circuit breaker, a torsional fork element to connect the fork element to the housing element, a spring sub-element and a resetting arm.
[0017] According to one embodiment of the present invention, the drive shaft
element comprising a first flexible leaf element to connect the driveshaft element to the lower link element. The lower link element comprising a second flexible leaf element to connect the lower link element to the upper link element. The upper link

element comprising a third flexible leaf element to connect the latch element to the upper link element.
[0018] According to one embodiment of the present invention, the latch
element comprising a locking segment and a latch torsional element to connect the latch element with the housing element.
[0019] According to one embodiment of the present invention, the trip
element comprising a rigid trip element to act as a push button to provide a trip input to the circuit breaker, a rigid latch bracket element to lock the latch element, a fourth flexible leaf element to connect the rigid trip element and the rigid latch bracket element and a trip torsional element to connect trip element to the housing element.
[0020] According to one embodiment of the present invention, the housing
element further comprises a snap arm to lock the housing element. The housing element functions as a guide to rotary motion of torsional elements and the fork element of the circuit breaker mechanism during operation.
[0021] According to one embodiment of the present invention, the resetting
arm is adapted to resettle the latch element to a locked position when the knob element is rotated from TRIP position to OFF position. The upper link element decides the dead centre position during ON-OFF and OFF-ON operation. The third flexible leaf element connects the latch element to the upper link element.
[0022] According to one embodiment of the present invention, the latch
element rotates during a TRIP operation to convert an equivalent four bar arrangement to an equivalent five bar arrangement. The rigid trip element is adapted to function as a push button to provide input to the circuit breaker.

[0023] According to one embodiment of the present invention, the flexible
leaf element converts the sliding motion of the rigid trip element to rotary motion of the rigid latch bracket element.
[0024] According to one embodiment of the present invention, the at least
one end of the spring is connected to the spring sub-element of the fork and other end is connected to the lower link element. A clockwise rotation of the knob element from an ON position of the circuit breaker contacts charges the spring until a dead centre position. The spring energy is converted to rotary motion of the circuit breaker contacts through the rigid and flexible leaf elements to attain an OFF position of the breaker contacts. An anticlockwise rotation of the knob element from an OFF position of the circuit breaker contacts charges the spring until a dead centre position. The spring energy is converted to rotary motion of the circuit breaker contacts through the rigid and flexible leaf elements to attain an ON position of the breaker contacts.
E) BRIEF DESCRIPTION OF THE DRAWINGS:
[0001] The other objects, features and advantages will occur to those skilled
in the art from the following description of the preferred embodiment and the accompanying drawings in which:
[0002] FIG. 1 illustrates a perspective view of a instable complaint circuit
breaker mechanism without the front cover attached to the housing according to one embodiment of the present invention.
[0003] FIG. 2 illustrates an isometric view of a tristable complaint circuit
breaker mechanism with the front cover attached to the housing according to one embodiment of the present invention.

[0004] FIG. 3 illustrates the isometric view of a tristable complaint circuit
breaker mechanism at ON position according to one embodiment of the present invention.
[0005] FIG. 4 illustrates the isometric view of a tristable complaint circuit
breaker mechanism at OFF position according to one embodiment of the present
invention.
[0006] FIG. 5 illustrates the isometric view of a tristable complaint circuit
breaker mechanism at TRIP position according to one embodiment of the present
invention.
[0007] Although specific features of the present invention are shown in some
drawings and not in others. This is done for convenience only as each feature may be combined with any or all of the other features in accordance with the present invention.
F) DETAILED DESCRIPTION OF THE INVENTION
[0008] In the following detailed description, reference is made to the
accompanying drawings that form a part hereof, and in which the specific embodiments that may be practiced is shown by way of illustration. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments and it is to be understood that the logical, mechanical and other changes may be made without departing from the scope of the embodiments. The following detailed description is therefore not to be taken in a limiting sense.
[0009] The various embodiments of the present invention provide a circuit
breaker mechanism for trip free manually independent tristable circuit breaker. According to one embodiment of the present invention, the circuit breaker housing comprises of a fork element, a driveshaft element, a lower link element, an upper link element, a latch element, a trip element and at least one spring.

[0010] The fork element comprises of a knob sub-element which acts as
handle to operate the circuit breaker mechanism. The circuit breaker mechanism further comprises a fork torsional element to connect the fork element with the housing element and a spring sub-element. The spring is the energy storing element. The spring is connected to a spring pin sub-element oil fork element and lower link element.
[0011] The driveshaft element which connects the circuit breaker contacts to
the circuit breaker mechanism is allowed to rotate about z-axis. The mechanism further comprises a flexible leaf element which connects the drive shaft element to the lower link element and allows rotation of the elements about z-axis.
[0012] The lower link element is connected to another end of energy storing
element, the spring. A.flexible leaf element connects lower link element to an upper link element and allows rotation of these elements in X-Y plane (axis).
[0013] The upper link element decides the position of dead-centre during
ON-OFF and OFF-ON operation. During the ON-OFF and OFF-ON operation and TRIP operation one end of the upper element remains stationary.
[0014] A latch element rotates during the TRIP operation converting
equivalent four bar arrangement into equivalent five bar arrangement. The latch element comprises a locking segment wherein the latch segment is locked by means of latch bracket segment of a trip element during ON-OFF and OFF-ON operation. The latch element is connected to the housing element by a flexible element called latch torsional element. The latch torsional element allows rotary motion of the latch during TRIP operation.

[0015] The circuit breaker farther comprises a trip element which comprises
a rigid trip element which has a push button to give trip input to the circuit breaker. A flexible leaf element which connects the rigid trip element and the rigid latch bracket element. The flexible leaf element converts the sliding motion of the rigid trip element into rotary motion of a rigid latch bracket element. The rigid latch bracket element locks the latch element during ON-OFF and OFF-ON operation and releases latch element during TRIP operation. Further the trip element is connected to the housing through a trip torsional element. Further the trip torsional element allows rotary motion of latch bracket segment.
[0016] The housing further comprises at least one spring, which is the energy
storing element. The one end of the spring is connected to spring sub-element of fork element and other end of the spring is connected to lower link element.
[0017] When the circuit breaker state is moved from the ON position to OFF
position, the knob element of the fork element is rotated in a clockwise direction. During this process, the springs get charged until the knob element reaches a dead centre position. The dead centre is an equilibrium condition of actuating mechanism. In dead centre condition the mechanism spring is fully charged and beyond this point the mechanism flips and operates independently due to energy discharged by mechanism spring. After the dead centre, the potential energy in the spring is converted into rotary motion of contacts through rigid and flexible leaf elements thus moving the circuit breaker from the first stable ON position to the second stable OFF position.
[0018] When the circuit breaker state is moved from second stable position;
that is from the OFF position to ON position, the knob element of the fork element is rotated in an anticlockwise direction which allows the springs to get charged until the dead centre position is reached. When the knob element reaches dead centre position, the potential energy is converted into rotary motion of contacts through rigid and

flexible leaf elements mechanism. Thus the circuit breaker comes to first stable position that is ON position from the second stable position that is the OFF position.
[0019] Further when the trip input is given through the rigid trip element in
case of short circuit, the latch bracket element starts rotating in an anticlockwise direction and unlocks the latch element. Hence the latch element is allowed to rotate in anticlockwise direction due to residual spring energy at ON position. At the end of this operation, the third stable position that is the TRIP position is achieved.
[0020] The resetting operation facilitates resetting of the circuit breaker
mechanism to OFF position from the TRIP position. During the resetting, the knob element of fork element is rotated in clockwise direction. During this process, the springs get charged and latch element gets locked with latch bracket element of trip element and breaker mechanism comes to second stable position that is the OFF position.
[0021] FIG. 1 illustrates an isometric view of a tristable complaint circuit
breaker mechanism without the front cover attached to the housing according to one embodiment of the present invention. With respect to FIG. 1, the circuit breaker mechanism comprises a circuit breaker housing 101. The circuit breaker housing 101 encloses a fork element 201, a driveshaft element 301, a lower link element 401, an upper link element 501, a latch element 601, a trip element 701 and at least one spring 801.
[0022] The fork element 201 further comprises of a knob sub-element 202
which acts as handle to operate the circuit breaker mechanism, a fork torsional element 203 which is a flexible element connecting fork element 201 to the housing element 101, a spring pin sub-element 204 and a resetting arm 205. Here, the latch element 601 gets resettled to lock position through the resetting arm 205.

[0023] The driveshaft element 301 which connects the circuit breaker
contacts to the circuit breaker mechanism arrangement is allowed to rotate about a z-axis. The circuit breaker mechanism further comprises a flexible leaf element 302 which connects drive shaft element 301 to the lower link element 401 and allows rotation of these elements about z-axis.
[0024] The lower link element 401 is connected to another end of the energy
storing element which is the spring 801. A flexible leaf element 402 connects the lower link element 401 to an upper link element 501 and allows rotation of these elements in X-Y plane (axis).
[0025] The upper link element 501 decides the position of dead-centre during
ON-OFF and OFF-ON operation. During the ON-OFF, OFF-ON operation, and TRIP operation one end of the upper link element remains stationery.
[0026] A latch element 601 rotates during the TRIP operation, converting an
equivalent four bar arrangement into equivalent five bar arrangement. The latch element 601 comprises a locking segment 602 wherein the latch segment 601 is locked by means of a latch bracket segment of a trip element 701 during ON-OFF and OFF-ON operation. The latch element 601 is connected to the housing element 101 by a flexible element called latch torsional element 603. The latch torsional element 603 allows rotary motion of the latch 601 during TRIP operation.
[0027] The circuit breaker further comprises a trip element 701 which
comprises a rigid trip element 702 which acts as a push button to give trip input to circuit breaker, a flexible leaf element 703 which connects rigid trip element 702 and rigid bracket element 704. The flexible leaf element 703 converts the sliding motion of the rigid trip element 702 into rotary motion of a rigid latch bracket 704 element. The rigid latch bracket element 704 locks the latch element 701 during ON-OFF and

OFF-ON operation and releases latch element during TRIP operation. Further the trip element 701 is connected to the housing through a trip torsional element 705. Further the trip torsional element 705 allows rotary motion of latch bracket segment 704.
[0028] The housing further comprises at least one spring 801, which are the
energy storing elements. The one end of the spring 801 is connected to spring sub-element 204 of fork element 201 and other end of the spring 801 is connected to lower link element 401.
[0029] FIG. 2 illustrates the isometric view of a tristable complaint circuit
breaker mechanism with the front cover attached to the housing according to one embodiment of the present invention. With respect to FIG. 2, the housing element 101 supports elements of the circuit breaker mechanism. The housing element 101 acts as a guide to rotary motion of torsional elements of mechanism and fork element during the operation. The housing element l0l also guides the rotary and sliding motion of the trip element during TRIP operation. The housing is provided with a snap arm 102 for the purpose of locking with the front cover 901.
[0030] FIG. 3 illustrates the isometric view of a tristable complaint circuit
breaker mechanism at ON position according to one embodiment of the present invention. When the circuit breaker state is moved from the ON position to the OFF position, the knob element 202 of the fork element 201 is rotated in a clockwise direction. During this process the springs 801 get charged until the knob reaches a dead centre position. The dead centre is an equilibrium condition of the actuating mechanism. In dead centre condition, the mechanism spring is fully charged and beyond this point the circuit breaker mechanism flips and operates independently due to energy discharged by the mechanism spring. In the present circuit breaker mechanism, after the dead centre, spring's potential energy is converted into rotary motion of the contacts through rigid and flexible leaf elements. This moves the circuit breaker from ON position to OFF position.

[0031] FIG. 4 illustrates the isometric view of a tristable complaint circuit
breaker mechanism at OFF position according to one embodiment of the present invention. When the circuit breaker state is moved from the OFF position to the ON position the knob element 202 of the fork element 201 is rotated in an anticlockwise direction which allows the springs 801 to get charged until the knob reaches a dead centre position. When the knob element 202 reaches dead centre position the potential energy is converted into rotary motion of contacts through rigid and flexible leaf elements in the circuit breaker mechanism. This moves the circuit breaker from ON position to OFF position.
[0032] FIG. 5 illustrates the isometric view of a tristable complaint circuit
breaker mechanism at TRIP position according to one embodiment of the present
invention. Further when the trip input is given through the rigid trip element 702
in case of short circuit, the latch bracket element 704 starts rotating in anticlockwise direction and unlocks the latch element 601. Hence the latch element 601 is allowed to rotate in anticlockwise direction due to residual spring energy at ON position. At the end of this operation the third stable position that is the TRIP position is achieved.
G) ADVANTAGES OF THE INVENTION
[0033] The various embodiments of the present invention provide a circuit
breaker mechanism for trip free manually independent tristable circuit breaker. The flexible leaf segment and torsional elements are used to connect rigid elements which results in significant reduction in the number of components being used. The flexible leaf segment and torsional elements i.e. flexible joints offer almost zero friction and hence less wear and tear in the mechanism occurs. Further, the flexible leaf segment and torsional elements i.e. flexible joints offers almost zero friction, resulting in less wear and tear in the mechanism. Moreover, due to less number of components, there is a reduction in the assembly time of the circuit breaker mechanism,

[0034] Although the invention is described with various specific
embodiments, it will be obvious for a person skilled in the art to practice the invention with modifications. However, all such modifications are deemed to be within the scope of the claims.
[0035] It is also to be understood that the following claims are intended to
cover all of the generic and specific features of the present invention described herein and all the statements of the scope of the invention which as a matter of language might be said to fall there between.

CLAIMS
What is claimed is:
1. A tristable circuit breaker mechanism comprising:
a housing element;
a fork element;
a driveshaft element to connect circuit breaker contacts to the housing element;
a lower link element;
an upper link element;
a latch element;
a trip element; and
a spring arrangement;
Wherein a charging of the spring arrangement beyond a dead centre position of the
actuating mechanism flips the tristable circuit breaker such that the circuit breaker
contacts attain at least one of the ON, OFF and TRIP position.
2. The mechanism according to claim 1, wherein the fork element comprising:
a knob sub-element to provide for various positions of the circuit breaker;
a fork torsional element to connect the fork element to the housing element; a spring sub-element; and a resetting arm.
3. The mechanism according to claim 1, wherein the drive shaft element comprising a first flexible leaf element to connect the driveshaft element to the lower link element.
4. The mechanism according to claim 1, wherein the lower link element comprising a second flexible leaf element to connect the lower link element to the upper link element.

5. The mechanism according to claim 1, wherein the upper link element comprising a third flexible leaf element to connect the latch element to the upper link element.
6. The mechanism according to claim 1, wherein latch element comprising: a locking segment; and
a latch torsional element to connect the latch element with the housing element.
7. The mechanism according to claim 1, wherein the trip element comprising:
a rigid trip element to act as a push button to provide a trip input to the circuit
breaker;
a rigid latch bracket element to lock the latch element;
a fourth flexible leaf element to connect the rigid trip element and the rigid latch
bracket element;
a trip torsional element to connect trip element to the housing element.
8. The mechanism according to claim 1, wherein the housing element further comprising a snap arm to lock the housing element.
9. The mechanism according to claim 1, wherein the housing element is a guide to
rotary motion of torsional elements of the fork element and latch bracket element of
the circuit breaker mechanism during operation.
10. The mechanism according to claim 1, wherein the resetting arm is adapted to resettle the latch element to a locked position when the knob element is rotated from TRIP position to OFF position.
11. The mechanism according to claim 1, wherein the upper link element decides the dead centre position during ON-OFF and OFF-ON operation.

12. The mechanism according to claim 5, wherein the third flexible leaf element connects the latch element to the upper link element.
13. The mechanism according to claim 1, wherein the latch element rotates during a TRIP operation to convert an equivalent four bar arrangement to an equivalent five bar arrangement.
14. The mechanism according to claim 7, wherein the rigid trip element is adapted to function as a push button to provide input to the circuit breaker.
15. The mechanism according to claim 7, wherein the flexible leaf element converts the sliding motion of the rigid trip element to rotary motion of the rigid latch bracket e\ernem.
16. The mechanism according to claim 1, wherein the at least one end of the spring is connected to the spring sub-element of fork element and other end is connected to the lower link element.
17. The mechanism according to claim 1, wherein a clockwise rotation of the knob element from an ON position of the circuit breaker contacts charges the spring until a dead centre position.
18. The mechanism according to claim 9, wherein the Spring energy is converted to rotary motion of the circuit breaker contacts through the rigid and flexible leaf elements to attain an OFF position of the breaker contacts.
19. The mechanism according to claim 1, wherein an anticlockwise rotation of the knob element from an OFF position of the circuit breaker contacts charges the spring until a dead centre position.

20. The mechanism according to claim 11, wherein the spring energy is converted to rotary motion of the circuit breaker contacts through the rigid and flexible leaf elements to attain an ON position of the breaker contacts.