FIELD OF THE INVENTION

This invention pertains to the field of miniature circuit breakers and, in particular, to an instantaneous tripping device with a stepped lever for a miniature circuit breaker.

BACKGROUND OF THE INVENTION

Circuit breakers protect electrical circuits from damage caused by current surges by interrupting or breaking the current path between the input terminals and output terminals. A conventional miniature circuit breaker comprises a pair of contacts located in a main current path between a line terminal for connecting to a power supply and a load terminal for connecting to a load to be powered by the power supply. The conventional miniature circuit breaker further includes an instantaneous tripping mechanism to sense short circuit condition in which there is a large surge of over current through the main current path. Tripping mechanisms provide a command to mechanisms for opening the contacts. The contacts include a fixed contact and a moving contact. The movable contact is attached to a contact arm that can be pivoted.

Instantaneous trip mechanisms generally include an electromagnet and an armature that, when a short circuit occurs, pushes a plunger into the contact arm of the movable contact, pivoting the contact arm and thereby breaking the circuit. The plunger has linear motion while the trip mechanism requires rotary motion to pivot the act arm resulting in a loss of energy in this transformation process in the conventional mechanism.

This background information is provided to make known information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention. SUMMARY OF THE INVENTION

An object of the present invention is to provide an instantaneous tripping device for a miniature circuit breaker and miniature circuit breaker comprising the same. In accordance with an aspect of the invention, there is provided an instantaneous tripping device for a miniature circuit breaker comprising a solenoid with a L-shaped plunger.

In accordance with another aspect of the invention, there is provided a miniature circuit breaker comprising a solenoid with a L-shaped plunger and a trip lever configured to rotate when activated by the L-shaped plunger. In one embodiment, the trip lever is stepped.

DESCRIPTION OF THE DRAWINGS Embodiments of the invention will now be described, by way of example only, by reference to the attached Figures, wherein:

Figure 1 illustrates a miniature circuit breaker (1 ) in accordance with one aspect of the invention detailing the handle spring (2), handle (3), connect rod (4), contact support (10), base (1 1 ) and instantaneous tripping device (21 ). Also shown are the trip lever (7), moving contact (22), contact pressure spring (19), opening spring (20) and the fixed contact (23) as well as part of the housing. Flexible braid component of circuit is not shown.

Figure 2 illustrates components of the instantaneous tripping device in cross section including the moving core (12), yoke brush (13), yoke (14), plunger (15) with retaining spring (18), fixed core (16), the coil of the solenoid (17). Also shown is the fixed contact (23) on the fixed contact arm (24) and the on/input terminal (25).

Figure 3 illustrates the miniature circuit breaker assembly at ON condition detailing the handle (3), trip lever (7), base (1 1 ), contact pressure spring (19), opening spring (20), instantaneous tripping device (21 ), and moving contact (22). Also shown are the fixed contact (23), connect rod (4) and part of the housing. Flexible braid component of circuit is not shown.

Figure 4A and 4B illustrates the shape of the trip lever (7). Figure 5 illustrates the miniature circuit breaker assembly in normal or ON conditions (A) and immediately following the fault condition such that the contacts are separated but the handle has yet to move to the OFF position (B). A close-up of the contacts is shown in (C).

Figure 6 illustrates the current path (shaded in dark) from the in terminal (25) through the solenoid coil (17), the fixed contact (23), moving contact (22), through the flexible braid (61 ) to the bimetal (62).

DETAILED DESCRIPTION OF THE INVENTION

This invention provides a miniature circuit breaker (1 ) having an instantaneous tripping device (21 ) that efficiently transforms linear forces into a rotary force to rotate the moving contact for quick opening of the electrical contacts. In particular, the unique configuration of the trip lever and the plunger efficiently converts the linear motion of the plunger to rotary motion via the trip lever to facilitate the rapid separation of the fixed and moving contacts. The miniature circuit breaker by rapidly opening the contacts reduces the energy inside breaker to the minimal level during clearance of fault. Referring to the figures, a miniature circuit breaker (1 ) is provided with an instantaneous tripping device (21 ) for opening the contacts in over current conditions. The miniature circuit breaker (1 ) comprises a housing or casing, optionally provided in two connectable halves, and the breaker assembly provides a main current path between the input terminal and the output terminal. Appropriate housings or casings are known in the art. Housing or casings are generally plastic and include appropriate mounting and insulation elements. The breaker assembly includes an instantaneous tripping device (21 ) operatively connected to a handle assembly, fixed and moving contacts. The handle assembly is movable between a normal and abnormal or fault position (indicative of the circuit being tripped) and includes the operator or handle (3) and associated handle spring (2). The handle assembly is connected to the trip lever by connect rod (4).

The handle spring (2) is configured to bring the handle (3) to the OFF position when the miniature circuit breaker (1 ) is tripped.

As illustrated in the figures, the fixed contact is attached to the lateral edge of the yoke (14) by a fixed contact arm (24). The moving contact (22) is configured to rotate into and out of contact with the fixed contact and is supported by the contact support arm (10) and trip lever. Contact pressure spring (19) is operatively associated with the moving contact and the trip lever and is configured to maintains the desired value of contact pressure with the fixed contact at the ON condition.

Referring to figure 2, the instantaneous tripping device (21 ) includes an electromagnetic mechanism comprising a yoke (14) having a first end and second end, yoke brush (3), a solenoid having a coil (17), a hollow fixed core (16), a moving core or armature (12), retaining spring (18) and plunger (15). In particular, the yoke (14) surrounds the solenoid (17) which is connected to the electric circuit. The hollow fixed core (16) is riveted to the yoke at the second end and extends axially into the coil. The plunger is an "L"- type plunger (15) that extends axially through the hollow center of the fixed core (16) and is optionally held in place in the moving core (12) by interference fit. Also provide is a retaining compression spring (18) as shown in the figure 2.

Under normal operating conditions as shown in figure 3, i.e. ON conditions, the retaining spring (18) holds the moving core (12) and associated plunger (15) in place. The plunger (15) abuts the trip lever (7). The fixed contact and moving contact (22) are in contact and the circuit is open. The moving contact (22) is attached to the rest of the circuit by a metal braid (61 ).

Referring to figure 5, when there is a large surge of over current (i.e. a short circuit over current) through the main current path, instantaneous tripping device (21 ) generates a magnetic field which acts on the moving core (12) with a force that overcomes the retaining force of the retaining spring (18) such that the moving core (12) and the associated plunger (15) move laterally in the direction of the fixed core (16). The plunger (15) activates the trip lever (7) causing it to rotate.

Referring to figure 4A and figure 4B, the trip lever (7) includes a first wall (71 ) and second wall (72) and a floor (73) there between. The floor is stepped and is configured to be engaged by the plunger (15) such that when an short circuit over current occurs the plunger engages the steps to rotate the trip lever counterclockwise. The trip lever includes a circular opening (74) and is rotatably mounted onto housing by a contact support and mechanism pin (75). The trip lever includes a rotatable contact support arm (10) and two spring contact points. The first spring contact point is a raised lip (76) around the circular opening (74) sized to fit within the coil of the spring and the second contact point is a raised nub (77) with groove (78) configured to receive a free end of the spring. The second free end of the spring hooks over the moving contact.

The trip lever is configured to transform the linear force of the moving plunger (15) to rotary force by acting on the stepped trip lever (7). When the opening mechanism is activated, the trip lever (7) rotates counterclockwise into the arm of the moving contact (22) thereby transferring the rotational force to the arm of the moving contact (22) and forcibly separating the moving contact (22) from the fixed contact. Opening spring (20) facilitates separation of the contacts by providing the required opening velocity for rotating the moving contact (22) during OFF (TRIP) operation. The instantaneous tripping device (21 ) is configured to break the circuit quickly by separating the two contacts such that when the opening mechanism is first activated the handle (3) is still in the ON position because of inertia. As the moving contact (22) continues its counterclockwise movement, the handle spring (2) through its operable connection of the trip lever (7) via the connect rod (4) moves the handle (3) to the OFF position. The cam profile in the tripping lever and contact support together lock the connect rod (4) from slipping away during normal ON-OFF operation.

When a very large short circuit over current flows through the main current path the coil of the solenoid (17) generates a large magnetic field and thereby produces a large force which acts on the moving core (12). This moves the plunger (15) at high speed into contact with the trip lever (7) thus triggering the contact opening mechanism in a very short period of time.

Moreover, because the moving core (12) moves at high speed, the plunger (15) strikes the trip lever (7) with a large amount of force which causes the trip lever (7) to quickly rotate into contact with the moving contact (22) so as to mechanically assist in the opening of the contacts, i.e. in addition to triggering the contact opening mechanism. This mechanical assistance helps to prevent the contacts from being welded together due to the very large current flowing between the contacts. This welding together of the contacts is known as "tack" welding and is a danger at very large short circuit currents, e.g. 1000A to 2000A.

Although the invention has been described with reference to certain specific embodiments, various modifications thereof will be apparent to those skilled in the art without departing from the spirit and scope of the invention. All such modifications as would be apparent to one skilled in the art are intended to be included within the scope of the following claims.