DESC:TECHNICAL FIELD

[001] The present subject matter described herein, in general, relates to circuit breakers and/or switchgears and more particularly to a joint linkage for improving the latching mechanism in an electrical switching device.

BACKGROUND

[002] An electrical switching device may be defined as a unit designed to connect, carry and disconnect electrical supply so as to protect the equipments connected in the electrical circuit from damage caused by overload, under-voltage or short circuit etc. Circuit breakers are well-known electrical switching devices used to provide automatic circuit interruption, to a monitored circuit, when circuit fault conditions occur.

[003] Circuit breaker operating mechanism permits breaker to store the energy by compressing springs that are linked to the contact assembly of breaker by latching different links. Stored energy of springs and latching between the linkages allows breaker to make the contacts, hence completing the electrical circuit (closing of breaker) and break the contacts, hence interrupting the electrical circuit (tripping of breaker). Switchgear mechanisms use methods of latching for storing the spring energy and achieving its intended motion. In the linkages arrangement certain links are pivoted on shafts. Pivoted joints consisted of plain journal bearing on shafts. Also in switchgear applications it is possible that a breaker once ON (closed) will be kept in that state for several months continuously. Hence the mechanism and linkages are under constant static force for several months without operation. Hence the linkages undergo very high dynamic forces followed by a constant static force for a long period. In this condition when the mechanism is operated after several months, being a safety device it is very critical that the linkages move exactly as expected to trip the breaker.

[004] Currently, the switchgear manufacturers provide a linkage with journal bearing at its pivot. But, journal bearings are more susceptible to adhesive wear and high static friction is observed in journal bearings. Also, if journal bearing is made of high hardness and shaft of high hardness is used then the method of incorporating a journal bearing in the linkage assembly, it becomes very uneconomical and space consuming and it also does not provide reliability in transmission of forces.

[005] Thus, keeping in view the above drawbacks of the existing journal bearing linkages in latch assembly, there is a need to provide a latch assembly with improved joint linkage that provides optimized static friction at its pivot points to enable smooth latching.

SUMMARY OF THE INVENTION

[006] 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.

[007] An object of the present invention is to provide an improved latch assembly to overcome the above drawbacks of a journal bearing linkages in the latch assembly to enable smooth latching.

[008] Another object of the present invention is to provide an improved joint linkage in a latch assembly to overcome constant static forces when the linkages are under constant load for a long period.

[009] Accordingly, the present invention provides an improved latch assembly with optimized static friction at its pivot points for smooth latching and thereby overcome the drawbacks of the journal bearing linkage at the pivots points.

[0010] In one implementation, the present invention provides an improved joint linkage which further comprises a needle roller bearing member that overcome stiction and enhances the reliability in transmission of forces in an electrical switching device.

[0011] In one implementation, the present invention provides an improved mechanism for latching comprising a latch assembly, which further comprises a closing latch and a needle roller bearing member that enables a loss free motion due to stiction when an electrical switching device is made ON by collapsing the linkages after a long span of time.

[0012] Accordingly, in one implementation, a circuit breaker comprising at least one operating mechanism comprising at least one pivot shaft, at least one close shaft, and at least one slot, is disclosed. The circuit breaker comprises at least one latch assembly having at least one closing latch and at least one needle roller bearing member flushed completely in at least one riveted bush housing (12) such that a width of said needle roller bearing member (13) and a width of said riveted bush housing (12) are same.. Hence there is no guiding wall for bearing member which helps in improving the collar friction between latch (11) and corresponding mating components in the same axis.

[0013] In contrast to the existing mechanism and circuit breaker, the present invention solves the problem of losses in force distribution due to very high dynamic forces of kinematic linkages. Also, the present invention solves the problem of overcoming constant static force when the linkages are under load for a long period.

[0014] In contrast to the existing mechanism and circuit breaker, the present invention provides a bearing member with each roller hardness of about 60 RC press fitted on the riveted bush housing made of En1 steel material. The dimensions of the bearing are as follows: Outer diameter 16mm, inner diameter 12mm, bearing width 10mm. Pivot shaft 21 acts as a journal.

[0015] In contrast to the existing mechanism and circuit breaker, the present invention provides the latch assembly pivoted rigidly on the pivot shaft conforming only single degree of freedom on its own axis. The bearing member of the latch assembly ensures proper engagement of the bearing needle rollers on the pivot shaft. Hence the need for lubrication needed at the interaction is avoided using the present invention. On rotation of latch assembly on its axis ensures change in position of individual needle rollers on the direction of force (F1) every time, hence overcomes phenomenon of stiction when mechanism is latched for longer period. The consistency in the torque transmission could be achieved by reducing the static friction losses of the joint by introducing the bearing member in the closing circuit which has 0.001 coefficient of static and rolling friction as against 0.1 in case of journal bearing.

[0016] 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 above and other aspects, features, and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings in which:

[0017] Figure 1 illustrates the arrangement of links when a circuit breaker is charged and made ON, in accordance with an embodiment of the present subject matter.

[0018] Figure 2 illustrates the joint links that is incorporated in a latching assembly, in accordance with an embodiment of the present subject matter.

[0019] Figure 3 illustrates the cross sectional view of a latch assembly pivoted on a pivot shaft, in accordance with an embodiment of the present subject matter.

[0020] 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 PRESENT INVENTION

[0021] The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary.

[0022] 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 of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.

[0023] 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.

[0024] It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

[0025] 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.

[0026] Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments.

[0027] It should be emphasized that the term “comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0028] Figure 1 illustrates the arrangement of links when a circuit breaker is charged and made ON. A person skilled in the art will appreciate that for understanding purpose the present invention is explained with the help of circuit breaker however the disclosed method shall not be considered as the limiting factor for the scope of present invention.

[0029] Figure 2 illustrates the joint links that is incorporated in a latching assembly. A person skilled in the art will appreciate that for understanding purpose the present invention is explained with the help of circuit breaker however the disclosed method shall not be considered as the limiting factor for the scope of present invention.

[0030] Figure 3 illustrates the cross sectional view of a latch assembly pivoted on a pivot shaft. A person skilled in the art will appreciate that for understanding purpose the present invention is explained with the help of circuit breaker however the disclosed method shall not be considered as the limiting factor for the scope of present invention.

[0031] Referring now to figure 1 and figure 2, in one implementation, in the charged condition of an electrical switching device, the energy stored in the springs from the main springs is transmitted to close shaft (31) through latch assembly (1). Force (F1) is transmitted from linkages to latch assembly (1) as shown in figure 1. This creates a torque (T1) on member (21). Thus latch assembly (1) tends to rotate, but this rotation of (1) is stopped by close shaft (31). Thus the entire link arrangement is locked in this position due to forces from the spring and locking by the shaft (31) and the arrangement remains in the static equilibrium. There consists a slot in the shaft (32) in line (i.e., in the same plane) with (1). When close shaft 31 is rotated about its axis the slot is exposed to the link (11) as shown in figure 2, allowing it to pass through the slot under the action of spring forces which is transmitted to (F1). Hence the breaker gets ON.

[0032] Referring now to figure 2, in one implementation, a bearing member (13) with needle roller hardness of about 60 RC is press fitted on the riveted bush housing (12) made of En1 steel material.

[0033] In one implementation, the dimensions of the bearing member (13) are as follows: Outer diameter 16 mm, inner diameter 12 mm, bearing width 10mm. Pivot shaft 21 acts as a journal and is made of steel En1 steel material. However, it may be understood by the person skilled in that the art that depending on the applicability and as per the requirement, the diameter and width may vary and hence fall within the claims scope of the present invention.

[0034] Referring now to figure 3, the latch assembly (1) is pivoted rigidly on the pivot shaft (21) conforming only single degree of freedom on its own axis. The needle roller bearing member (13) ensures proper engagement of the bearing needle rollers on the pivot shaft (21). Hence there is no need for lubrication needed at the interaction. On rotation of latch assembly (1) on its axis ensures change in position of individual needle rollers on the direction of force F1 every time hence overcomes phenomenon of stiction when mechanism is latched for longer period.

[0035] In one implementation, the consistency in the torque transmission is achieved by reducing the static friction losses of the joint using the bearing member (13) in the closing circuit of latch assembly (1) which has 0.001 coefficient of static and rolling friction as against 0.1 in case of journal bearing.

[0036] In one implementation, the electrical switching device is a circuit breaker.

[0037] Some of the important features of the present invention, considered to be noteworthy are mentioned below:
1. Enhanced reliability in transmission of direction of forces.
2. Enhanced reliability of operation even under no lubrication.
3. With fine balance of hardness selection of a needle roller member there is always a consistency in the torque transmitted.
4. The collapsing force required for de-latch an electrical switching system remains consistent throughout its life.
5. An economical option as compact size of needle roller bearing which can be fitted easily into a compact mechanism assembly
,CLAIMS:1. A switching device comprising:
at least one operating mechanism (2) comprising at least one pivot shaft (21), at least one close shaft (31), and at least one slot (32); and
said switching device CHARACTERIZED IN THAT comprising at least one latch assembly (1) having at least one closing latch (11) and at least one needle roller bearing member (13) flushed completely in at least one riveted bush housing (12) such that a width of said needle roller bearing member (13) and a width of said riveted bush housing (12) are same.

2. The switching device as claimed in claim 1, wherein said needle roller bearing member (13) comprises at least one needle roller of a specific hardness, said hardness is preferably of 60 RC.

3. The switching device as claimed in claim 1, wherein said needle roller bearing member (13) comprises at least one roller is coupled on said riveted bush housing (12) made preferably of En1 steel material.

4. The switching device as claimed in claim 1, wherein said needle roller bearing member (13) comprises:
an outer diameter, preferably of 16 mm;
an inner diameter, preferably of 12 mm; and
a bearing width, preferably of 10 mm.

5. The switching device as claimed in claim 1, wherein said pivot shaft (21) acts as a journal and passes through said needle roller bearing member (13).

6. The switching device as claimed in claim 1, wherein said latch assembly (1) is pivoted on said pivot shaft (21) of said operating mechanism (2) conforming only single degree of freedom on its axis.

7. The switching device as claimed in claims 1 and 2, wherein said needle roller, on rotation of said latch assembly (1) on its axis, changes position, said change in position is based on the direction of force under the action of at least one charging spring.

8. The switching device as claimed in claims 1, characterized in that comprises said needle roller bearing member (13) with at least one needle roller of a specific hardness and comprises 0.001 coefficient of static and rolling friction.