FORM 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 PIVOT JOINT ASSEMBLY FOR USE IN ELECTRICAL SWITCHING DEVICES
2. Applicant(s)
(a) NAME: LARSEN & TOUBRO LIMITED
(b) NATIONALITY: An Indian Company.
(c) ADDRESS; L & T House, BaJJard 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 switching devices and more particularly to an improved pivot joint assembly for use in electrical switching devices to reduce friction and increasing consistency of transmitted forces.
BACKGROUND AND THE PRIOR ART
An electrical switching device may be defined as a unit designed to connect, carry and disconnect electrical supply. An electrical circuit breaker may be defined as a unit designed to connect, carry, disconnect and protect the equipments connected in the electrical circuit from damage caused by overload, under-voltage or short circuit etc. A circuit breaker is a commonly used electrical switching device. The operating mechanism of a circuit breaker having a moving contact and a stationary contact is switched ON (closed) or OFF (tripped) by using energy stored in a compressed or stretched spring. When the circuit breaker is closed, energy is stored in the contact springs. This energy is locked with latching arrangement through a set of linkages. When the latching arrangement is de-latched by moving the linkages, the energy stored in the springs is released to trip the breaker.
US 7703984 discloses a rolling bearing comprises a roller, a roller shaft provided inwardly of the roller, and rolling elements provided between the roller and the roller shaft, the roller shaft having a nitrogen-rich layer and is configured such that its race surface, on which the rolling elements run, has not smaller than 11 in the JIS austenite grain size number and not smaller than HV653 in the Vickers hardness number, at both ends not greater than HV300, and at its core beneath a widthwise midpoint of the race surface not smaller than HV550.
US 7867281 disclose use of bearing surfaces of differential hardness for joint replacement in particular a hip prosthesis. It uses two surfaces of different

hardness which slide over each other. However, rollers roll over the surface of bearing member, joints are under constant static load and also a unique shape and size of the joint was not known from the prior art.
In the mechanism of circuit breakers, initially main springs are charged either manually or electrically to store energy. This energy is used to close the breaker. When the breaker is closed, simultaneously a set of contact springs get charged due to the closing force, thus storing the energy. These set of springs are locked in the charged condition by the linkage assembly by a latching arrangement. This arrangement can be de-latched by operating the linkages whenever required, to release the spring energy for tripping the breaker. In the linkages arrangement certain links are pivoted on shafts. Pivoted joints consisted of plain journal bearing on shafts. In switchgear application the command to operate the linkages can be given both manually or electrically through an electromechanical device.
During switching ON of the breaker the linkages pass through a toggle point. At the toggle point very high forces are observed by the linkages one due to main closing springs which are getting discharged and closing the breaker and second, opposing force by contact springs which are getting charged due to closing of the breaker. 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. But when linkages are under high force for very long time and suddenly the mechanism is operated, the pivots of linkages may respond differently than expected due to static friction and also depending on the condition of the journal bearing surfaces of the pivot due to adhesive wear or galling effect. This results in inconsistency of the forces transferred by the linkages. Thus the output of the breaker and force required to

move the linkages both cannot be accurately determined. Thus the entire linkage assembly and electromechanical device used for operating the mechanism will have to be designed with very high safety margin rendering it uneconomical. Also due to high static friction at the pivoted joints and if the torque arm is very close to the centre of the pivot the links may seize when suddenly operated after a long time resulting in failure of operation. The bearing surfaces of the pivoted joints will only deteriorate with number of operations resulting in high frictional forces. Also in the switchgear application there is limitation of oil lubrication. Even grease lubrication can only be done before the assembly of the mechanism. Once the mechanism is assembled lubrication on certain pivoted joints is inaccessible. Thus it becomes very important to design the pivoted joints of linkages such that there is very low friction, also the bearing surfaces do not deteriorate with operations i.e. life of the breaker. Such pivots design needs to very economical; also it should adhere with the space limitations of the mechanism.
The disadvantages of the prior art technologies are as follows:
1. If a bearing with both inner and outer race is used for the application, there are no commercially available standard bearings with both rings which fit into size of this particular mechanism thus rendering it unviable and uneconomical.
2. If a journal bearing is used, its frictional value is higher compared to a needle roller bearing thus requiring higher force. Journal bearings are more susceptible to adhesive wear compared to needle rollers. Also static friction observed in journal bearings is high compared to needle rollers.
3. 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 becomes very uneconomical and space consuming and it also does not provide reliability in transmission of forces.
4. If only needles with cage are used it is very difficult to incorporate into the shown assembly also the effective load carrying capacity will be less.

Some provisions for holding the cage in its position will have to be incorporated which makes it uneconomical.
Thus, there is a need to overcome the problems of the prior art. Therefore, the present inventors have developed an improved pivot joint assembly for use in electrical switching devices to reduce static friction, dynamic friction and also to improve the condition of the bearing surface with life of the breaker so as to increase the consistency of transmitted forces through linkages also increasing the reliability of operation and enhancing the life of the mechanism of a circuit breaker.
OBJECTS OF THE INVENTION
An object of the present invention is to overcome the problems/disadvantages of the prior art.
Another object of the present invention is to provide an improved pivot joint assembly for use in electrical switching devices.
These and advantages of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings.
SUMMARY OF THE INVENTION
There is provided a pivot joint assembly.
Other embodiment of the present invention provides an improved pivot joint assembly for use in electrical switching devices to reduce friction and increasing consistency of transmitted forces, said assembly comprising a shaft; a link assembly having a needle roller bearing attached therein; a bush; a spring means

exerting force thereby locking said link assembly; wherein said link assembly and said shaft forming an oscillating pivoted joint and said needle roller adapted to roll over said shaft under load during mechanism operation.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
In the appended drawings:
Figure 1 illustrates a diagrammatic representation of the linkages for an Air Circuit Breaker for transmission of forces in ON condition of the breaker.
Figure 2 illustrates a sectional diagrammatic representation of the improved pivoted joint with shaft and needle bearing for the Air Circuit Breaker.
Figure 3 illustrates a diagrammatic representation of the link with needle bearing for the Air Circuit Breaker.
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 a diagrammatic representation of the linkages for an Air Circuit Breaker for transmission of forces in ON condition of the breaker is shown.
Fig. 2 shows a sectional diagrammatic representation of the improved pivoted joint with shaft and needle bearing for the Air Circuit Breaker.

Fig. 3 shows a diagrammatic representation of the link with needle bearing for the Air Circuit Breaker.
The invented system is thus an improved pivot joint assembly for use in electrical switching devices to reduce friction and increasing consistency of transmitted forces.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention there is provided an improved pivot joint assembly for use in electrical switching devices. The improved pivoted joint of linkages in the mechanism of an air circuit breaker comprises of a shaft of material En 24 steel with through-hardness about (35-40) RC with surface finish of 1.6 micron, a link assembly consisting of a needle bearing without inner ring with hardness of the needle rollers about 60 RC, the link and the shaft form an oscillating pivoted joint in the mechanism, and the width of the joint is 15mm; the diameter of the shaft and Inner diameter of the needle roller is 10mm. and the outer diameter of the needle roller is 14mm.
As and when the link oscillates whenever the mechanism is operated, the needle rollers with higher hardness roll over the surface of the shaft under load, creating a fine surface on shaft due to rolling action. The rollers of relatively high hardness and strength compared to the shaft reduce the microscopic irregularities on the shaft surface thus improving its Ra value to improve the surface finish of the shaft with operations. Also due to the strength and hardness of the rollers small amount of strain hardening also occurs on the shaft to certain extent.
Thus the surface and strength of the shaft will only be progressively improved through its life as the number of operations takes place. The needle bearing also absorbs the load created during the toggle point and avoids adhesive wear of the

bearing surface of the shaft. This increases the efficiency of force transfer since the needle bearings have very low frictional values. Also the direction of transmission of force remains consistent as per design. Thus reliability of force transfer increases even if the torque arm passes very close to the centre of the pivot.
The special consideration is given to the length of the rollers and material of the shaft for a case in which the breaker is considerably ON for a long period of time thus the links will be in constant force without movement. In such case the length of the rollers are decided such that sufficient material of the shaft take the load (i.e. pressure is decreased) so that there is no piercing of the rollers into the surface of the shaft under constant load, also the material of the shaft is En 24 steel through hardened to (35-40) RC to have enough toughness and hardness to resist denting or piercing of the rollers. This fine balance of hardness, material specification, type of motion, pressure and forces allow to achieve an application wherein one of the bearing surface improves in strength and surface finish when other bearing surface rolls over it, at the same time it also resist deformation under constant load.
Thus from a switchgear perspective a very high consistent performance and reliability of operation is achieved. Hence the mechanism linkages and the electromechanical device to operate the mechanism can be designed according to the requirements as economical as possible. Also the needle bushes without inner rings provide a very compact (suitable for very small size of the mechanism) as well as economical design. Also because of very low friction the necessity of lubrication of the pivoted joint is considerably reduced. And the most important aspect is that it provides reliability of operation of the breaker as a safety device to operate in critical condition even if the breaker is not operated for a very long time.

According to a preferred embodiment of the invention, there is provided an improved pivot joint assembly for use in electrical switching devices. Referring to Figure 1, Figure 2(a) and Figure 2 (b), the like numerals assigned to the parts shown in various figures indicate the like parts. According to the embodiment of the present invention, the improved pivoted joint assembly for the electrical switching device comprises a set of linkages (1), (2), (3) and (4), a shaft (8) of En 24steel material of hardness about (35-40) RC, a bush(9) and a needle roller(7), a shaft (6) for locking the linkage assembly, and pivoted joint is represented by (5).
The arrangement of links when the breaker is ON and can be tripped is as shown in the figure. In the ON (closed) condition, the energy stored in the springs from the contacts is transmitted from the linkages (1) to (3) (shown as Fl). Further linkage (3) exerts a force on linkage (4) (shown as F2). This force from linkage (3) passes through the body of the shaft but at a distance from the centre thus imparts a torque on linkage (4) (shown as F3). Thus linkage (4) tends to rotate, but this rotation of the linkage (4) is stopped by shaft (6). Thus the entire link arrangement is locked in this position due to forces from the spring and locking by the shaft (6) and the arrangement remains in the static equilibrium. There consists a slot in the shaft (6) in line (i.e. in the same plane) with (4). When (6) is rotated about its axis the slot is exposed to the link (4), allowing it to pass through the slot under the action of spring forces which is transmitted to (4) through (3). Hence the breaker gets tripped.
When this arrangement is in equilibrium before rotating the shaft, the entire spring forces is reduced in stages due to the shape of linking assembly and finally a force is exerted on (6) to get the locking and thus the equilibrium. The force required to rotate shaft (6) when it is under the influence of force from linkage (4) is referred to as tripping force. In this arrangement (4) is pivoted about shaft (8) by a needle roller bearing (7) with each roller hardness about 60 RC.

The dimensions of the bearing are as follows: Outer diameter 14mm, inner diameter 10mm, bearing width 15mm. In needle roller bearing (7) the shaft (8) acts as a journal and is made of steel En24. Bush (9) is riveted in linkage (4) and needle roller bearing (7) is press fitted in bush (9) made of Enl steel material.
The present invention refers to the bearing area between shaft (8) and needle roller bearing (7). Since the force F2 passes through the body of the shaft the bearing area is more subjected to wear but with the improved surface finish, low friction in this area the force F3 will be consistent. Also due slight strain hardening the surface strength improves with operation thus performance improves with life of the device.
The present invention provides an improved pivot joint that provides optimum design margin for mechanism linkages and operating system for the electrical switching device. It eliminates the excess power requirement for operation, assures reliability even in extreme conditions such as dust, lack of lubrication etc. also the performance enhances life of circuit breaker. Therefore, the incorporated design makes the system sturdy. The present invention may also be extended for use in other linkages of any circuit breaker where similar conditions prevail.
ADVANTAGES:
• Improving the surface of the shaft with operations
• Enhanced reliability in transmission of direction of forces
• Enhanced reliability of operation
• Improvement in strength of the shaft to a certain extent
• Enhanced reliability of operation even under no lubrication
• Protection of shaft surface against rusting
• Compact size of needle roller bearing which can be fitted easily into a compact mechanism assembly

• An economical option as bearing is readily commercially available at a low cost
• Ease of assembly of bearing into the link assembly
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 pivot joint assembly for use in electrical switching devices to
reduce friction and increasing consistency of transmitted forces, said
assembly comprising:
a shaft (8);
a link assembly having a needle roller bearing and bush(9) attached therein;
a spring means exerting force thereby locking said link assembly;
wherein said link assembly and said shaft forming an oscillating pivoted joint and said needle roller adapted to roll over said shaft, under load during mechanism operation.
2. Assembly as claimed in claim 1 wherein said needle roller bearing is adapted for absorbing load.
3. Assembly as claimed in claim 1 wherein said link assembly comprising plurality of linkages.
4. Assembly as claimed in claim 1 wherein said needle roller having length such that sufficient material of the shaft take the load so that there is no piercing of the rollers into the surface of the shaft under constant load.
5. Assembly as claimed in claim 1 comprising a shaft (6) adapted to lock said link assembly.

6. An improved pivot joint assembly for use in electrical switching devices to
reduce friction and increasing consistency of transmitted forces as herein described and illustrated with reference to the accompanying drawings.