Patent Application
20190164710
The present invention relates generally to magnetically actuated devices and particularly to miniature circuit breakers (MCBs) which utilize a solenoid in the trip mechanism.
Known circuit breaker products which utilize a solenoid in their trip mechanism typically use a movable solenoid plunger that is mechanically linked to the normal thermal/magnetic/electronic tripping system. These systems typically have a plunger arm in the solenoid that is captured therein and operates to press against or pull on a yoke mechanism of the trip assembly which typically includes at least the yoke, its associated latch plate, and a thermal trip bimetal; thereby delatching the trip lever and separating the movable contact from the stationary contact to remove power from the load. There are also known arrangements of magnetic-only coupled tripping solenoids where the plunger arm does not physically contact the trip assembly but instead acts upon it magnetically because the yoke or latch plate is ferromagnetic. Alternative solenoid arrangements from those known in the art may be desirable for a variety of reasons, especially in electronic miniature circuit breakers where physical space for components is at a premium.
Typically, NEMA-style miniature circuit breaker construction has the contact make or break mechanism, i.e. the trip lever and bias springs of the movable contact, on the high-expansion side of the bimetal, so that during fault conditions, the free end of the bimetal moves away from the contact make or break mechanism to disengage the circuit breaker latch. This arrangement is continued in some known MCBs with magnetic-only coupled tripping solenoids placed on the high expansion side of the bimetal, where the solenoid competes for room in the breaker with the contact make or break mechanism. Therefore either the solenoid or the make or break mechanism, or both, must be limited in size and may need to be made smaller than is considered ideal to withstand the voltage surge requirements for a miniature circuit breaker. Thus in existing systems an additional component, usually a relatively large MOV, is added to achieve the function of withstanding the required voltage surge. Accordingly, there is room for improvement in such systems.
The present invention provides an alternative miniature circuit breaker trip system with a magnetic-only coupling tripping solenoid with a moveable plunger assembly. The magnetic-only coupled plunger assembly has a floating plunger and frame that allows the magnetic gap between the solenoid and the yoke to be as small as possible, but lets the bimetal used for overcurrent thermal tripping move freely during short circuits to its full deflection by moving the plunger assembly of the solenoid out of its way. This aspect of the present invention allows a reduction of the physical and magnetic distance between the yoke and the trip solenoid with moveable frame and increases the magnetic attraction force between them. The floating plunger assembly can be in the forward or rearward position before the solenoid is energized. Thus, after the solenoid is energized a stronger pulling force is provided to move the trip assembly yoke and its attached latch plate, to de-latch the trip lever and trip the breaker, while the floating plunger is also movable to allow full deflection of the bimetal in a thermal trip condition. The present design also offers more flexibility in the positioning of the tripping solenoid than known systems and helps in the layout and assembly of the breaker by providing more possible positions in the limited space of the miniature circuit breaker.
In one aspect of the present invention a circuit breaker trip mechanism is presented, comprising: a trip assembly including a ferromagnetic yoke and a latch plate attached to the yoke; a trip lever held in the latch plate; a solenoid with a coil and a housing for the coil, and a plunger assembly of ferromagnetic material with a frame and a plunger rod attached to the frame, and the plunger rod passing through and floating in the solenoid coil when the solenoid is not activated; and the solenoid coil mounted adjacent to the ferromagnetic yoke at a known distance; whereby activating the solenoid pulls the frame to the housing of the solenoid coil thus placing the plunger rod at a magnetic gap distance from the trip assembly sufficient to magnetically attract the at least one of the ferromagnetic yoke and the latch plate to delatch the trip lever and trip the breaker. In another aspect of the present invention the circuit breaker trip mechanism may include the frame and plunger rod being integrated into a single piece. In another aspect of the present invention the circuit breaker trip mechanism may include the frame being U-shaped. In another aspect of the present invention the circuit breaker trip mechanism may include the frame and plunger rod being formed from a single material. In another aspect of the present invention the circuit breaker trip mechanism may further include a bimetal within the yoke, the plunger assembly facing the direction of yoke movement during a bimetal trip, and wherein the plunger assembly will yield under a motion of the bimetal causing a trip event.
The foregoing and other advantages of the disclosed embodiments will become apparent upon reading the following detailed description and upon reference to the drawings, wherein:
As an initial matter, it will be appreciated that the development of an actual commercial application incorporating aspects of the disclosed embodiments will require many implementation specific decisions to achieve the developer's ultimate goal for the commercial embodiment. Such implementation specific decisions may include, and likely are not limited to, compliance with system related, business related, government related and other constraints, which may vary by specific implementation, location and from time to time. While a developer's efforts might be complex and time consuming in an absolute sense, such efforts would nevertheless be a routine undertaking for those of skill in this art having the benefit of this disclosure.
It should also be understood that the embodiments disclosed and taught herein are susceptible to numerous and various modifications and alternative forms. Thus, the use of a singular term, such as, but not limited to, “a” and the like, is not intended as limiting of the number of items. Similarly, any relational terms, such as, but not limited to, “top,” “bottom,” “left,” “right,” “upper,” “lower,” “down,” “up,” “side,” and the like, used in the written description are for clarity in specific reference to the drawings and are not intended to limit the scope of the invention.
Further, words of degree, such as “about,” “substantially,” and the like may be used herein in the sense of “at, or nearly at, when given the manufacturing, design, and material tolerances inherent in the stated circumstances” and are used to prevent the unscrupulous infringer from unfairly taking advantage of the invention disclosure where exact or absolute figures and operational or structural relationships are stated as an aid to understanding the invention.
As understood in the art, for an electronic trip, the solenoid 21 is operated by the electronics (not shown) such as for AFCI/GFCI protection. For a thermal trip, within the yoke 55 is a bimetal 53 whose distortion under heat forces the latch plate 61 away from the trip lever 59.
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While particular aspects, implementations, and applications of the present disclosure have been illustrated and described, it is to be understood that the present disclosure is not limited to the precise construction and compositions disclosed herein and that various modifications, changes, and variations may be apparent from the foregoing descriptions without departing from the invention as defined in the appended claims.
