Claims:We claim:

1. A miniature slip clutch assembly (100) for a motor operator (150) of a circuit breaker (200), the motor operator (150) having a shaft (140), the shaft (140) having a motor (130) and a pinion (120) rotably fitted thereon, the pinion (120) having a metal insert (110) configured thereon, the shaft (140) being adapted to transfer the torque of the motor (130) to a gear train (117), the miniature slip clutch assembly (100) comprising:
• a fixed clutch plate (20) retained on the shaft (140);
• a friction plate (40) sandwiched between the fixed clutch plate (20) and
the metal insert (110), the metal insert (110) acting as an interfacing plate for the
friction plate (40);
• a metal washer (60) fitted on a step of the shaft (140); and
• at least one clutch spring (80) coiled on the shaft (140) for resting between
the metal washer (60) and the pinion (120), the at least one clutch spring (80)
adapted to press the pinion (120) along with the metal insert (110) against the
friction plate (40),

wherein, the miniature slip clutch assembly (100) being mounted on the shaft (140) and integrated within the pinion (120) to act as a torque limiter to allow the shaft (140) to slip/rotate freely without transmitting any torque to the gear train (117) and thus preventing the motor momentum to affect the gears upon completion of the breaker operation as well as upon experiencing a sudden abnormal stop thereby eliminating the voltage variation associated with uncertainty in a feedback or cut-off system of the motor operator (150) due to variability in breaker to breaker force and travel and making the gearing safe against sudden impact.

2. The miniature slip clutch assembly (100) as claimed in claim 1, wherein the pinion (120) is made of a plastic material.

3. The miniature slip clutch assembly (100) as claimed in claim 1, wherein the metal insert (110) is made up of stainless steel.

4. The miniature slip clutch assembly (100) as claimed in claim 1, wherein the fixed clutch plate (20) is retained on the shaft (140) through a dowel pin (10).

5. The miniature slip clutch assembly (100) as claimed in claim 1, wherein the at least one clutch spring (80) is selected from any one of a compression type spring, concentric compression springs, a Belleville spring and Belleville washers placed in series and parallel combinations.

6. The miniature slip clutch assembly (100) as claimed in claim 1, wherein the motor operator (150) is a direct drive type motor operator.

7. The miniature slip clutch assembly (100) as claimed in claim 1, wherein the circuit breaker (200) is a molded case circuit breaker
, Description:MINIATURE SLIP CLUTCH ASSEMBLY FOR MOTOR OPERATOR OF CIRCUIT BREAKER

Field of the invention

The present invention generally relates to circuit breakers and more particularly to a miniature slip clutch assembly for a motor operator of a circuit breaker.

Background of the invention

Electrical switching devices such as an electrical-power switchgear, a molded case circuit breaker (MCCB) and the like need to switchover from one desired source to the other. These devices usually mounted inside a board / enclosure / panel board for added safety to a worker are operated either from outside or by opening the enclosure for a switching operation thereof. These devices include operators / operating mechanisms for power switches and even for switches at overhead (or pole-top) locations. The operators include a drive system that facilitates switching operation of the power switches by force derived from a motor of the operator or by manually applied force.

In today’s scenario response, the time required for electrical switching devices to switchover from one desired source to the other is gaining importance. Thus with a view of lesser operational time and remote operation and space of the switching device, a direct driven type or stored energy type motor mechanism is used. Direct drive motor operators work by transmitting the power through motor to the gearing system, and from the gearing system to the drive system which can either be a crank slotted lever mechanism or a rack and pinion arrangement which converts the rotary motion to reciprocating motion and eventually drive the knob of the MCCB.

The gearing assembly is designed to meet the torque required to operate the molded case circuit breaker and a feedback or cut-off switch which gauges the completion of breaker operation and signals the system for next operation. Following this system of operation where the motor is cut-off after the MCCB is toggled or operation is complete, the feedback system needs to be very apt for controlling the motor cut-off or else the motor shaft still maintains to rotate and deliver torque to the gearing system due to the momentum of motor shaft. This exerts impact force on the gearing system thus causing the gears to stress. The impact changes when the motor operator is operated at elevated voltages, as motor speed is directly proportional to voltage.

And with variability in operating forces and knob travel of breaker to breaker, the effect of impact is considerable. In order to minimize the effect, feedback or cut-off system must be very apt with all variability taken into consideration. Also, gear jamming or sudden stop due to any reason with no cut-off in place yet, causes a heavy impact force on the gearing system and reaction force on the motor shaft.

In order to arrest this fallout, a torque limiting mechanism or over-running clutch or adjustable slip clutch is deployed in the past for providing protection against overloading, sudden shocks which are either separately placed in series with driving and driven shaft. For example, ‘US3105371’ describes an adjustable miniature slip adapted to provide against overloading of rotary components such as switches, potentiometers used in control systems. ‘US3091951’ relates to a miniature slip clutch used for slippage of shafts relative to each other which is very desirable. When placed in a gear train, gearing mechanism protects the gear train and other delicate instruments from mechanical overloads and sudden shocks. ‘CN101657869B’ relates to an electrical switching apparatus operating mechanism and more particularly to a loading motor provided in the operating mechanism and the operating mechanism is loaded clutch (one way, over-running clutch) between the handle. However, the systems described above usually have more numbers of components and occupy considerable place thus increases complexity and size of the operator.

Accordingly, there is a need of a miniature slip clutch assembly for a motor operator of a circuit breaker that overcomes the above mentioned drawbacks of the prior art.

Objects of the invention

An object of the present invention is to achieve the required torque limiting characteristics with minimal numbers of components and in lesser operational time.

Another object of the present invention is to integrate complete clutch assembly within a motor pinion space thus making the overall product light and compact.

Still another object of the present invention is to achieve various values of limiting torques with appropriate selection of spring design and frictional material.

Summary of the invention

Accordingly, the present invention provides a miniature slip clutch assembly for a motor operator of a circuit breaker. The circuit breaker is a molded case circuit breaker. The motor operator is a direct drive type motor operator and comprises a shaft, a motor and a pinion. The motor and the pinion are rotably fitted on the shaft. The pinion is made of a plastic material and includes a metal insert made up of stainless steel configured thereon. The shaft is adapted to transfer the torque of the motor to a gear train.

The miniature slip clutch assembly comprises a fixed clutch plate, a friction plate
a metal washer and at least one clutch spring (herein after ‘the clutch spring). The fixed clutch plate is retained on the shaft through a dowel pin. The friction plate is sandwiched between the fixed clutch plate and the metal insert. The metal insert acts as an interfacing plate for the friction plate. The metal washer is fitted on a step of the shaft.

The clutch spring is selected from any one of a compression type spring, concentric compression springs, a Belleville spring and Belleville washers placed in series and parallel combinations. The clutch spring is coiled on the shaft for resting between the metal washer and the pinion. The clutch spring is adapted to press the pinion along with the metal insert against the friction plate.

The miniature slip clutch assembly is mounted on the shaft and integrated within the pinion to act as a torque limiter for allowing the shaft to slip/rotate freely without transmitting any torque to the gear train and thus preventing the motor momentum to affect the gears upon completion of the breaker operation as well as upon experiencing a sudden abnormal stop thereby eliminating the voltage variation associated with uncertainty in a feedback or cut-off system of the motor operator due to variability in breaker to breaker force and travel and making the gearing safe against sudden impact.

Brief description of the drawings

Other features as well as the advantages of the invention will be clear from the following description.
In the appended drawings:
Figure 1 shows a direct drive motor operator for a molded case circuit breaker, in accordance with the present invention;

Figure 2 shows a user interface of the direct drive motor operator, in accordance with the present invention;
Figures 3A - 3B show an internal architecture of the direct drive motor operator, in accordance with the present invention;

Figure 4 shows a motor assembly of the direct drive motor operator, in accordance with the present invention; and

Figures 5 - 7 show various components of a miniature slip clutch assembly mounted on a motor shaft integrated within a motor pinion, in accordance with the present invention.

Detailed description of the invention

The foregoing objects of the present invention are accomplished and the problems and shortcomings associated with the prior art, techniques and approaches are overcome by the present invention as described below in the preferred embodiment.

The present invention provides a miniature slip clutch assembly for a motor operator of a circuit breaker. The miniature slip clutch assembly with minimal numbers of components is integrated within a motor pinion space thus making the overall product light and compact. The miniature slip clutch assembly achieves the required torque limiting characteristics in lesser operational time with appropriate selection of spring design and frictional material.

The present invention is illustrated with reference to the accompanying drawings, throughout which reference numbers indicate corresponding parts in the various figures.

Referring to figures 1-7, a miniature slip clutch assembly (100) for a motor operator (150) of a circuit breaker (200) in accordance with the present invention is shown. Specifically, the circuit breaker (200) is a molded case circuit breaker and the motor operator (150) is a direct drive type motor operator. The motor operator (150) is superimposed on the circuit breaker (200) for remote operations thereof. A user interface of the motor operator (150) includes an operating handle / knob (111), a toggle switch (112) for changing the operating modes, an indication window (113) for true breaker state indication, a bezel cover (114) and safety interlocks (not numbered) such as a padlock (115) and a key lock (116).

The motor operator (150) comprises a motor unit (not numbered), a gearing unit (not numbered) and allied mechanism (not numbered) for functionality as shown in figure 3A. The motor unit of the motor operator (150) comprises a shaft (140), a motor (130) and a pinion (120). The motor (130) and the pinion (120) are rotably fitted on the shaft (140). The motor (130) is a universal motor designed to operate at different voltages and frequency and deliver a specific torque and speed at specified input voltage. The shaft (140) is adapted to transfer the torque of the motor (130) to a gear train (117) of the gearing unit. The gear train (117) (refer figure 3A) is coupled to an output member that drives a rack (118) (refer figure 3B) that eventually accommodates the operating knob (111) of the circuit breaker (200). The rack (118) is continuously connected with the gear train and the gear train with the pinion (120).

The pinion (120) includes a metal insert (110) configured thereon. In an embodiment, the pinion (120) is made of a plastic material and the metal insert (110) is made up of stainless steel. The miniature slip clutch assembly (100) (herein after ‘the assembly (100)’) is mounted on the shaft (140) and integrated within the pinion (120) of the motor unit of the motor operator (150).

The assembly (100) comprises a fixed clutch plate (20), a friction plate (40), a metal washer (60) and at least one clutch spring (80) (herein after ‘the clutch spring (80)’). The fixed clutch plate (20) is retained on the shaft (140) for example by a dowel pin (10). The friction plate (40) is sandwiched between the fixed clutch plate (20) and the metal insert (110). The metal insert (110) acts as an interfacing plate for the friction plate (40). In an embodiment, the fixed clutch plate (20) is made of a stainless steel material and the friction plate (40) is made from a RoHS (Restriction of Hazardous Substance) compliant SBR (synthetic replacement for natural rubber) based friction material. The metal washer (60) is fitted to sit freely on a step (not numbered) of the shaft (140).

The clutch spring (80) is coiled on the shaft (140) for resting between the metal washer (60) and the pinion (120). The clutch spring (80) is adapted to press the pinion (120) along with the metal insert (110) against the friction plate (40). The clutch spring (80) is designed for pressure required to maintain the torque to operate the circuit breaker (100) but allowing the friction plate (40) to slip against a sudden stop or high torque requirement.

In an embodiment, the clutch spring (80) is selected from any one of a simple compression spring, two concentric compression springs, a Belleville spring, Belleville washers placed in series and parallel combinations. The clutch spring (80) combination is capable of being changed to readily adjust assembly (100) for different torque limit values. Thus, by changing different concentric springs and arrangements in case of Belleville washers, different torque values are adjusted. In a brief, by changing the compressed length of the clutch spring (80) by addition of washers or by different arrangements, a combination array is achieved. And with same set of springs but different arrangement, the clutch is used for different torque values.

With variation in voltage parameters, the speed of the motor (130) varies while maintaining the same torque. The working principle of the assembly (100) is based on a uniform pressure theory of single plate friction clutches. Thus, the assembly (100) is designed to deliver an output torque of that of the motor (130) and slipping against extra torque requirement. Based on co-efficient of friction of the material used for the friction plate (40) and spring force achieved at required deflection of the clutch spring (80), the output torque obtained from the assembly (100) is easily varied for required torque limit. If the demand on the lower side of the gearing unit increases beyond a specified limit, the friction plate (40) tends to slip freely against the fixed clutch plate (20), thus avoiding sudden impact or extra torque being applied on the gears.

The assembly (100) being mounted on the shaft (140) and integrated within the pinion (120) acts as a torque limiter to allow the shaft (140) to slip freely without transmitting any torque to the gear train (117) whenever the breaker operation is completed and end stops are reached. This assembly (100) also allows the shaft (140) to rotate freely upon experiencing a sudden abnormal stop thus preventing the motor momentum to affect the gears thereby eliminating the voltage variation associated with uncertainty in a feedback or cut-off system of the motor operator (150) that occurs due to variability in breaker to breaker force and travel. Thus, the assembly (100) makes the gearing safe against sudden impact by eliminating the voltage variation.

Advantages of the invention

1. The required torque limiting characteristics are achieved with minimal components. The numbers of component are reduced by using the metal insert (110) that acts as interfacing plate for the friction plate (40).
2. The complete assembly (100) with minimal numbers of components is integrated within the motor pinion space thus making the overall product light and compact.
3. By selecting appropriate spring design and frictional material, various values of limiting torques are easily achieved.
4. The integration of the assembly (100) within the motor pinion (120) of the motor operator (150) for the circuit breaker (200) enables remote operations thereof for transmission and distribution of electrical power within industrial / domestic segment.
5. The assembly (100) is capable of being readily adjusted for different torque limit values by changing the clutch spring (80) combination.

The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, and to thereby enable others skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omissions and substitutions of equivalents are contemplated as circumstances may suggest or render expedient, but such omissions and substitutions are intended to cover the application or implementation without departing from the spirit or scope of the claims of the present invention.