FORM 2
THE PATENTS ACT, 1970
COMPLETE SPECIFICATION
(See Section 10)
DIFFERENETIAL SLIDER FOR BIMETALLIC THERMAL
OVERLOAD RELAY
numbered as dated
INVENTORS:
1. SACHIN MOHAN SRI VATSAVA
2. H.L. CHAUDHARI
APPLICANT:
LARSEN & TOUBRO LIMITED
L&T House, Ballard Estate, P.O. Box No. 278,
Mumbai, 400 001, Maharashtra INDIA.


THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE
NATURE OF THE INVENTION

DIFFERENTIAL SLIDER FOR BIMETALLIC THERMAL
OVERLOAD RELAY
A) TECHNICAL FIELD
[0001] The present invention generally relates to overload relays and specifically relates to thermal overload relay trip mechanism. The present invention more particularly relates to a differential lever used for activating the trip mechanisms during the generation of overload and single phase faults.
B) BACKGROUND OF THE INVENTION
[0002] An over load relay is used to protect a motor against overload conditions. When a motor is mechanically over loaded, it will draw more current than its rated value. The over load conditions may also may be generated, when the supply voltage falls and the motor draws excessive current for the same load. Even when one of the phases is lost, the motor continues to run but draws excessive current through the remaining two phases. An over load relay is connected to the power circuit to protect a motor against the flow of excessive current.
[0003] A bimetallic thermal over load relay is widely used because of the simpler construction and minimal cost. The relay consists of three bimetallic strips with the current coils being wound on them. The whole assembly is mounted on a Bakelite enclosure. The bimetallic strips having two dissimilar metals with different thermal


coefficients of expansion are used for the three phases. The current flowing through the coil heats the bimetallic strips. The upper ends of the strips are firmly held while the lower ends of the strips are free to move. When the temperature of the strips increases due to the current flowing through the coils, the strips bend towards right due to the difference in expansion of metals. When the strips bend towards the right, the tripping mechanism gets actuated and opens the relay contact.
[0004] The thermal relays take car of two kinds of faults. The two kinds of faults are an overload fault and a single phase fault. The thermal assembly senses a fault to deflect a lever to trip a mechanism. The deflections of the levers due to the different faults are not uniform. Sometimes the lever is deflected in one fault condition, for example during over load fault, while the lever is not deflected during another fault condition, for example during single phase fault condition.
[0005] The currently available differential levers do not have proper guidance and supporting walls especially in the relay in which the thermal assemblies are vertically placed. Even the arrangement of the differential levers behind the thermal assembly is not an easy task.
[0006] Moreover the currently available differential levers experience problem due to the frictional forces. Due to the frictional forces the deflection of the levers are not uniform and the levers diverge irregularly. Moreover the number of operations performed using the currently available lever is also greatly reduced due to the frictional forces thereby decreasing the life of the levers.


[0007] Hence there is a need to develop a differential lever to which is deflected uniformly during both the fault conditions to activate a trip mechanism reliably. Also there is a need to assemble levers easily, quickly and firmly to ensure the reliability of the operation. Further, there is a need to develop the differential levers with non frictional material to enhance the life of the levers.
C) OBJECT OF THE INVENTION
[0008] The primary object of the present invention is to develop a differential lever which is deflected uniformly and reliably during the generation of both the fault conditions.
[0009] Another object of the invention is to develop a differential lever which may be assembled easily, quickly and reliably.
[0010] Yet another object of the invention is to develop a differential lever with non frictional surface to improve the frequency and the number of operations to enhance the life of the lever assembly.
[0011] Yet another object of the present invention is to develop a differential lever assembly for bimetallic thermal over load relay so that the differential lever assembly is positioned more accurately to improve the reliability of the more reliability of the lever during the generation of the three phase over load fault and single phase fault conditions.


[0012] Yet another object of the present invention is to develop a differential lever for a thermal over load relay to improve the reliability of the lever by avoiding the number of faults like divergence of levers and the tilting of levers.
[0013] Yet another object of the present invention is to develop a differential lever for a thermal over load relay to improve the reliability and the performance of the lever assembly by providing a separate assembly for differential levers in the housing of the relay device.
[0014] Yet another object of the present invention is to develop a differential lever for a thermal over load relay to resolve and improve the relay performance in a drastic manner and to simplify the function of differential levers and the relay device.
[0015] 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
[0016] The abovementioned shortcomings, disadvantages and problems are addressed herein and which will be understood by reading and studying the following specification


[0017] The various embodiments of the present invention provide a differential slider assembly including a pair of differential levers that are deflected by a thermal assembly during both the fault conditions to activate a trip mechanism.
[0018] According to one embodiment of the present invention, a differential slider assembly has a pair of differential levers provided between a thermal assembly and a trip mechanism. The differential levers are mounted on a base guiding plate using fastener such as metal rivet. The differential lever is made up of lesser frictional material. The thermal assembly senses the fault condition to deflect the lever to activate a trip mechanism to trip a circuit device during a faulty condition. There are two types of faults. One is an overload fault. In the over load fault excessive current may be drawn through the circuit. Another is a single phase fault. During the overload fault condition, the differential lever is deflected linearly while the lever is deflected angularly during the single phase fault condition.
[0019] The lever assembly is arranged as a separate assembly and fitted into the space between the thermal assembly and the trip mechanism. The components of the lever assembly are arranged over a base plate or a guiding plate. A cut or groove is provided in the housing which accommodates the thermal assembly and the trip mechanism. The lever assembly is made as a factory made assembly and fit into the cut or groove in the housing so that the deviation or tilting of the lever assembly in the unwanted directions are eliminated and the lever is defected reliably and uniformly along the desired direction during the generation of overload or single phase fault conditions to activate a trip mechanism. Thus the lever assembly can be made easily and compactly.


[0020] The lever assembly will be a factory fitted assembly and it doesn't require to be removed from the housing assembly. The usage of the assembly has solved the problem of frictional forces and the tilting and diverging problems of differential levers. The lever assembly is made up of non frictional surfaces. For example, the lever is made up of glass laminated material to provide a smooth glassy surface to prevent the generation of frictional forces to improve the life of the lever by reducing the wear and tear of the lever during the fault conditions. The levers are fixed on the base plate or guiding plate using the metallic rivets and are arranged in parallel to eliminate the problems of divergence generated during the faulty condition. The metallic rivets provide non frictional surfaces to the levers, while the deflection of differential levers and guiding plate of assembly help to give complete support for both the levers up to the complete deflection point.
[0021] Thus the present invention provides a differential lever which may be assembled easily and quickly. The lever has non frictional surfaces to increase the number of operations and hence the life of the lever assembly. The differential lever is deflected uniformly and reliable during the fault conditions to activate a trip mechanism to trip a circuit reliably and safely.
[0022] According to another embodiment of the present invention, a bimetallic thermal overload relay is provided with a differential slider assembly, a thermal assembly and a trip mechanism. The differential slider assembly is mounted between a thermal assembly and a trip mechanism in a housing. The housing has a cut into which the differential slider assembly is mounted. The differential slider assembly has


a pair of differential levers mounted in parallel on a base guiding plate using a metallic rivet. The thermal assembly detects a fault condition such as overload fault, single phase fault to deflect the differential lever to activate a trip mechanism to trip an electrical circuit in an external device. The lever is deflected linearly during an overload fault while the lever is deflected angularly during a single phase fault. The levers are made up of non frictional material like laminated glass material to avoid the generation of frictional forces during the deflection to improve the performance and the life of the slider assembly.
[0023] 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.
E) BRIEF DESCRIPTION OF THE DRAWINGS
[0024] 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:
[0025] FIGURE. 1 illustrates a front perspective view of slider assembly in a thermal over load relay according to one embodiment of the present invention.
[0026] FIGURE. 2 illustrates a top side perspective view of a relay assembly for a bimetallic thermal over load relay according to one embodiment of the present invention.


[0027] 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 PRESENT INVENTION
[0028] In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which the specific embodiments which 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.
[0029] The various embodiments of the present invention provide a differential slider which is deflected by a thermal assembly during both the fault conditions to activate a trip mechanism.
[0030] According to one embodiment of the present invention, a differential lever is provided between a thermal assembly and a trip mechanism. The differential lever is made up of non frictional material. The thermal assembly senses the fault condition to deflect the lever to activate a trip mechanism to trip a circuit device during a faulty condition. There are two types of faults. One type of fault is an overload fault. In the


over load fault excessive current may be drawn through the circuit. Another type of fault is a single phase fault. During the overload fault condition, the differential lever is deflected linearly, while the lever is deflected angularly during the single phase fault condition.
[0031] According to another embodiment of the present invention, a bimetallic thermal overload relay is provided with a differential slider assembly. The differential slider assembly is mounted between a thermal assembly and a trip mechanism. The differential slider assembly has a pair of differential levers mounted in parallel on a base guiding plate using a metallic rivet. The thermal assembly detects a fault condition such as overload fault and single phase fault to deflect the differential lever to activate a trip mechanism to trip an electrical circuit in an external device. The lever is deflected linearly during an overload fault while the lever is deflected angularly during a single phase fault. The levers are made up of laminated glass material to avoid the generation of frictional forces during the deflection to improve the performance and the life of the slider assembly.
[0032] The lever assembly is arranged as a separate assembly and fitted into the space between the thermal assembly and the trip mechanism. The components of the lever assembly are arranged over a base plate or a guiding plate. A cut or groove is provided in the housing which accommodates the thermal assembly and the trip mechanism. The lever assembly is made as a factory made assembly and fit into the cut or groove in the housing so that the deviation or tilting of the lever assembly in the unwanted directions are eliminated and the lever is defected reliably and uniformly along the desired direction during the generation of overload or single


phase fault conditions to activate a trip mechanism. Thus the lever assembly can be made easily and compactly.
[0033] The lever assembly will be a factory fitted assembly and it doesn't require to be removed from the housing assembly. The usage of the assembly has solved the problem of frictional forces and the tilting and divergence problems of differential levers. The lever assembly is made up of non frictional surfaces. For example the lever is made up of glass laminated material to provide a smooth glassy surface to prevent the generation of frictional forces and to improve the life of the life of the lever by reducing the wear and tear of the lever during the fault conditions. The levers are fixed on the base plate or guiding plate using the metallic rivets and are arranged in parallel to eliminate the problems of divergence generated during the faulty condition. The metallic rivets give non frictional surfaces to the levers, while the deflection of differential levers and guiding plate of assembly helps to give complete support for both the levers up to the complete deflection point.
[0034] Thus the present invention provides a differential lever which may be assembled easily and quickly. The lever has non frictional surfaces to increase the number of operations and hence the life of the lever assembly. The differential lever is deflected uniformly and reliable during the fault conditions to activate a trip mechanism to trip a circuit reliably and safely. The metallic rivets give non frictional surfaces, while the deflection of differential levers and guiding plate of deflection assembly helps to give a complete support for both the levers upto the complete deflection point.


[0035] FIGURE. 1 shows a front perspective view of a slider assembly in a thermal over load relay according to one embodiment of the present invention, while the FIGURE. 2 shows a top side perspective view of a relay assembly for a bimetallic thermal over load relay according to one embodiment of the present invention.
[0036] With reference to FIGURE. 1 and FIGURE.2, the slider assembly has a base plate or a guiding plate 1 on which an upper differential lever 3 and a lower differential lever 4 are mounted using the metallic step rivets 2 parallely so that the differential levers 3, 4 are deflected uniformly and without divergence during the generation of faults. The assembly is a factory fitted assembly and is not required to be removed from a thermal overload relay. The differential lever assembly is provided between a thermal assembly and a trip mechanism 5 that are arranged on a housing 6 of the thermal overload relay. The housing 6 has a cut or a groove in which the differential lever assembly is fit.
[0037] The thermal assembly senses a fault condition to deflect the lever assembly 7 to activate a trip mechanism. The fault condition may be an overload fault or a single phase fault. During the generation of over load fault condition, the lever 7 is deflected linearly to activate a trip mechanism to trip an electrical circuit. The lever 7 is deflected angularly during the generation of single phase fault condition to activate a trip mechanism. The lever 7 is made of non frictional material such as laminated glass material so that the lever 7 is operated smoothly without the generation of frictional forces thereby increasing the performance, the number of operations and the life of the lever assembly. Thus the tilting and the divergence of the differential levers due to


frictional forces are solved to improve the reliability and the performance of the levers.
[0038] The metallic rivets 2 provides non frictional surfaces to the differential levers 3, 4, while the deflection of differential levers 3, 4 and guiding plate of assembly helps to give complete support for both the levers upto complete deflection point.
G) ADVANTAGES OF THE PRESENT INVENTION
[0039] The differential lever assembly of the present invention is a factory fitted assembly. The differential movements of the levers are made only in one direction to improve the reliability and the performance of the relay. The differential levers assembly provides better deflection in one direction. The supporting guide provides more supporting area for levers so that levers will not tilt towards bottom surface. The rivet screws try to avoid the divergence of the levers in the unwanted directions and also prevent the lift up of the levers in the upward direction. The rivet also prevents the generation of the unwanted torque in the space. In other words the complete assembly also helps to check the planarity of bimetals.
[0040] The differential lever assembly is arranged separately from the relay assembly so that the differential assembly may be assembled by a person more accurately and easily. The differential lever assembly is fixed only once and that too in the factory itself so that the chances of misalignment of the lever assembly are almost negligible. The levers have a sharp tip contact with thickness 1mm to provide accurate results.


[0041] In single phase fault condition, the transmission of deflection from the bimetal to the trip mechanism is more accurate and precise to improve the efficiency and reliability of the operation. This differential lever assembly is more reliable because of the proper positioning of the levers at the tip of bimetals in the thermal assembly ensures accurate results in three phase over load condition and in single phase fault conditions. The divergence and the tilting of the levers are prevented to improve the reliability and the efficiency of the relay device.
[0042] The differential lever assembly of the present invention helps to improve the relay performance effectively and to simplify the operation of the relay operation efficiently. The components of the differential lever assembly are assembled easily and quickly as the differential lever assembly is arranged as a separate assembly. The differential lever assembly of the present invention is a factory fitted assembly thereby eliminating the need for removing the assembly from the housing of the relay assembly. The problems due to the frictional forces such as the reduction in operating frequency and performance, the divergence and the tilting of the differential lever, are greatly reduced by using the differential lever of the present invention. The usage metallic rivets to fix the differential levers with the base guiding plate provides non frictional surfaces and improves the performance and the frequency of the operation to enhance the life of the relay efficiently. The guiding plate of the differential lever provides a complete support for both levers upto complete deflection point.
[0043] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such


adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the appended claims.
[0044] 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 differential slider assembly for bimetallic thermal overload relay including a
bimetallic thermal assembly and a trip mechanism, comprising:
a base guiding plate; and
a differential lever assembly mounted on said base guiding plate; and
wherein said differential lever is deflected during generation of fault condition to activate a trip mechanism.
2. The differential slider assembly according to claim 1, further comprises a pair of differential levers.
3. The differential slider assembly according to claim 2, wherein the pair of differential lever comprises an upper differential lever and a lower differential lever.
4. The differential slider assembly according to claim 3, wherein the lower differential lever is mounted on the base guiding plate using a fastener.
5. The differential slider assembly according to claim 4, wherein the fastener is a metallic rivet.


6. The differential slider assembly according to claim 3, wherein the upper differential lever is mounted on the base guiding plate using a fastener.
7. The differential slider assembly according to claim 6, wherein the fastener is a rivet.
8. The differential slider assembly according to claim 3, the lower differential lever and the upper differential lever are arranged and moved in parallel.
9. The differential slider assembly according to claim 1, wherein the differential lever are deflected by said thermal assembly.
10. The differential slider assembly according to claim 9, wherein said thermal assembly detects a fault condition to deflect said differential lever.
11. The differential slider assembly according to claim 10, wherein the fault condition is an overload fault condition.
12. The differential slider assembly according to claim 10, wherein the fault condition is a single phase fault condition.
13. The differential slider assembly according to claim 1, wherein the differential lever is deflected linearly during the overload fault condition to activate the trip mechanism.


14. The differential slider assembly according to claim 1, wherein the differential
lever is deflected angularly during the single phase fault condition to activate a
trip mechanism.
15. The differential slider assembly according to claim 1, wherein the differential lever is made up of non frictional material.
16. The differential slider assembly according to claim 15, wherein the differential lever is made up of laminated glass material.
17. A bimetallic over load relay comprising:
a housing;
a trip mechanism arranged in said housing to trip an electrical circuit in an external device;
a thermal assembly arranged in said housing to detect a fault condition in said external device; and
a differential slider assembly mounted in said housing to activate said trip mechanism; and


wherein said thermal assembly senses a fault condition in said external device to deflect differential slider to activate said trip mechanism to trip electrical circuit in said external device.
18. The relay according to claim 17, wherein the differential slider assembly is arranged between said thermal assembly and said trip mechanism in said housing.
19. The relay according to claim 17, wherein the housing has a cut portion.
20. The relay according to claim 17, wherein the differential slider assembly is arranged in the cut portion.
21. The relay according to claim 17, wherein the differential slider assembly is assembled separately and mounted in said housing.
22. The relay according to claim 21, wherein the differential slider assembly is a factory fitted assembly.
23. The relay according to claim 17, wherein the differential slider assembly comprises
a base guiding plate; a lower differential lever; and


an upper differential lever;
24. The relay according to claim 23, wherein the lower differential lever is mounted on the base guiding plate using a fastener.
25. The relay according to claim 24, wherein the fastener is a metallic rivet.
26. The relay according to claim 23, wherein the upper differential lever is mounted on the base guiding plate using a fastener.
27. The relay according to claim 26, wherein the fastener is a metallic rivet.
28. The relay according to claim 23, the lower differential lever and the upper differential lever are arranged and moved in parallel.
29. The relay according to claim 23, wherein the lower and upper differential levers are deflected by said thermal assembly.
30. The relay according to claim 17, wherein said thermal assembly detects a fault condition to deflect said differential levers.
31. The relay according to claim 17, wherein the fault condition is an overload fault condition.


32. The relay according to claim 17, wherein the fault condition is a single phase fault condition.
33. The relay according to claim 23, wherein the lower and upper differential levers are deflected linearly during the overload fault condition to activate the trip mechanism.
34. The relay according to claim 23, wherein the lower and upper differential levers are deflected angularly during the single phase fault condition to activate a trip mechanism.
35. The relay according to claim 23, wherein the lower and the upper differential levers are made up of non frictional material.
36. The relay according to claim 23, wherein the lower and upper differential levers are made up of laminated glass material.

ABSTRACT
The various embodiments of the present invention provide a differential slider assembly for bimetallic thermal over load relay and a thermal over load relay. The slider assembly has upper and lower differential levers mounted on a guide plate through a metallic rivet. A thermal assembly containing bimetals senses a fault to deflect the differential levers to activate a trip mechanism to trip an electrical circuit in an external device. The differential levers are made up of glass laminated material.
36 Claims, 2 Drawing Sheets.