This invention is directed generally to electrical switch mechanisms. More particularly, this invention pertains to a latching mechanism that prevents circuit breaker nuisance tripping due to shock or vibration forces without impeding the intended circuit trip function.
Circuit breakers are well-known devices used to provide automatic circuit interruption, to a monitored circuit, when circuit fault conditions occur. Fault conditions include, but are not limited to, current overload, ground faults, over voltage conditions and arcing faults. The release or disengaging of circuit breaker contacts to interrupt a monitored circuit is commonly referred to as tripping. The current interruption is usually achieved by having a movable contact (attached to a movable blade) that separates from a stationary contact (attached to a stationary blade). The movable contact is under considerable spring tension to move away from the stationary contact to open the circuit. When the movable contact separates from the stationary contact, it is important that this physical action occurs quickly and reliably to minimize arcing. If the arcing is too intense, it can affect the ability of the circuit breaker to open the faulted circuit. It is also important, in the design of circuit breaker trip mechanisms, that the force required to trip or open the circuit breaker mechanism is minimized.
In typical circuit breakers a latching mechanism is used to provide engagement of the circuit breaker contacts. When the circuit breaker contacts are closed or engaged, the latching mechanism holds the spring-loaded circuit breaker contacts together, and thus must resist the considerable spring force that causes the circuit breaker contacts to open when the latch is released. At the same time, the latching mechanism must be sensitive enough to trip and open the contacts with minimal force.
One of the disadvantages of many latching devices, is that the required sensitivity of the tripping mechanism makes them liable to inadvertent tripping due to shock and vibration. One of the sources of local shock vibrations is the actual act of manually closing the circuit breaker contacts. Since the breaker contacts must be closed as rapidly as they are released, the snap of closing the circuit breaker contacts sets up a shock vibration within the circuit breaker unit itself. This local vibration can cause an immediate nuisance trip. Therefore, various design solutions can be used to stabilize the breaker mechanism against shock and vibration forces. These designs, however, typically require greater energy to perform the intended trip function, which is undesirable.
In accordance with the present invention, there is provided an electrical circuit breaker including a latching mechanism for a movable member. The movable member is mounted for movement between first and second positions. The latching mechanism includes (1) a primary latching mechanism mounted for movement between a latched position where the primary latching mechanism engages the movable member to allow the movable member to move between the first and second positions, and an unlatched position where the movable member is disengaged for movement to the second position, and (2) a secondary latching element engaging the first latching mechanism to hold the primary latching mechanism in the latched position. The secondary latching element is movable to move the primary latching mechanism to the unlatched position.
The latching mechanism resists inadvertent forces tending to open the circuit breaker contacts when in the closed position, and thus makes the circuit breaker resistant to shock and vibration forces acting on the circuit breaker. Nuisance tripping of the breaker contacts can be virtually eliminated.
The latching mechanism can also be used in applications other than circuit breakers, where the movable member controls items other than circuit breaker contacts.
The foregoing and other advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings.
a is a perspective view of a circuit breaker incorporating one embodiment of the present invention, in the disengaged or tripped condition;
b is the same perspective view shown in
a is a side elevation of the circuit breaker as shown in
b is a side elevation of the circuit breaker as shown in
c is the same side elevation shown in
a is an enlarged side elevation of the primary latching mechanism in the circuit breaker as shown in
b is an enlarged side elevation of the primary latching mechanism in the circuit breaker as shown in
a is an enlarged side view of the secondary latching mechanism in the circuit breaker as shown in
b is an enlarged side view of the secondary latching mechanism in the circuit breaker as shown in
a is an enlarged side view of the secondary latching mechanism and the tripping mechanism in the circuit breaker as shown in
b is an enlarged side view of the secondary latching mechanism and the tripping mechanism in the circuit breaker as shown in
While the invention is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. It should be understood, however, that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
Turning now to the drawings, and referring initially to
The hand toggle 106 has three positions, center (
The automated tripping mechanism is triggered when a fault condition is detected. If the hand toggle 106 is in the “on” position, the tripping mechanism releases the latching mechanism, causing the breaker contacts to open and the hand toggle 106 to be moved to the center position shown in
a, 2a, 3a and 4a show the circuit breaker with the hand toggle 106 in the center position, which means the breaker has been triggered to release the latching mechanism and open the breaker contacts. In this condition, a conventional crochet-link assembly 110 that controls movement of the movable breaker contact is in its raised position, as shown in
The two main components of the latching mechanism are a latch bar 120 and a latch plate 130. The latch bar 120 is mounted for pivoting movement about the axis of a shaft 122, and is biased in the clockwise direction by a light biasing spring (not shown). The latch plate 130 is mounted for pivoting movement about the axis of a shaft 132, and is biased in the clockwise direction by a light biasing spring (not shown). The plate 130 includes a lateral projection 134 that forms a lower surface 136 for engaging a shoulder 114 on the opposed edge of the crochet 110a, as shown in
In the latched condition shown in
The trip pin 128 extends laterally outwardly from one end of the latch bar 120 into a cam slot 142 in a secondary latching element 140 mounted on the outer surface of the chassis plate 102a. When the latching mechanism is in its latched condition, engaging the crochet 110a and holding it in its lowered position as shown in
In many applications, the latch bar 120 can experience shocks on the order of 10 G's during the engagement process of bringing the crochet link assembly 110, the latch plate 130, and the latch bar 120 into mutual contacting positions.
To release the primary latching mechanism formed by the latch bar 120 and the latch plate 130, the secondary latching element 140 is pivoted in a counterclockwise direction so that the lower edge of the cam slot 142 pushes the trip pin 128 upwardly, thereby pivoting the latch bar 120 in a counterclockwise direction. This pivoting movement of the latching element 140 is caused by a trip mechanism (described below) that engages a depending arm 146 formed as an integral part of the latching element 140. The depending arm 146 provides a lever to rotate the secondary latching element 140 around the axis of its shaft 144 with minimal force.
The tripping of the latching mechanism by the upward movement of the trip pin 128 releases the crochet-link assembly 110 for movement to its raised position, as described previously.
Likewise in the closed state, any shock force attempting to rotate the latch bar 120 will exert a shock on the secondary latching element 140. By designing the upper left portion of the cam slot 142 as an arc about the shaft 144, there is no net moment created to try to rotate latch element 140 during a shock, thereby not allowing latch bar 120 rotation.
During a shock, if the cam slot 142 surface were to produce a clockwise moment on element 140, this would increase the required tripping force. If the cam slot 142 surface were to cause a counterclockwise shock moment, this would reduce the required tripping force, but would also increase the potential for an unintentional and undesired trip.
a and 5b show the relationship of the secondary latching element 140 with a trip mechanism 150. The user manually places the primary latching mechanism into the engaged state, as described previously. During the engagement process, the trip mechanism 150 is turned slightly counterclockwise, as shown. Surface 152 of the trip mechanism 150, in contact with the arm 146 of the secondary latching element 140, then allows the element 140 to rotate clockwise. The clockwise movement of the secondary latching element 140 places the trip pin 128 in the secure portion of the cam slot 142 to prevent inadvertent movement of the primary latching elements as described above. The trip mechanism 150 maintains this position while in the engaged state.
The disengagement of the primary latching mechanism occurs when the trip mechanism 150 is rotated clockwise to the position shown in
While particular embodiments and applications of the present invention have been illustrated and described, it is to be understood that the invention is not limited to the specific embodiments disclosed herein and that various modifications, changes, and variations may be apparent from the foregoing descriptions without departing from the spirit and scope of the invention as defined in the appended claims.
This application claims benefit to U.S. Provisional Application No. 60/533,552, filed on Dec. 31, 2003, which is incorporated by reference in its entirety.
Number | Name | Date | Kind |
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4001739 | Powell et al. | Jan 1977 | A |
6628185 | Raabe et al. | Sep 2003 | B2 |
Number | Date | Country | |
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20050140479 A1 | Jun 2005 | US |
Number | Date | Country | |
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60533552 | Dec 2003 | US |