EP0369807A2

EP0369807A2 - A miniature circuit breaker

Info

Publication number: EP0369807A2
Application number: EP89311920A
Authority: EP
Inventors: Declan Lyons; Joseph Michael Walsh; Gerard Finlay
Original assignee: NATIONAL ELECTRICAL DESIGNS Ltd
Current assignee: NATIONAL ELECTRICAL DESIGNS Ltd
Priority date: 1988-11-18
Filing date: 1989-11-17
Publication date: 1990-05-23
Also published as: BE1001735A7; EP0369807A3

Abstract

A miniature circuit breaker is disclosed with has a double biasing connector which can bias the movable contact to either the off position or to provide contact pressure in the on position. Switching between effective directions of action is achieved instantaneously and is effected by operation of an operating handle in the miniature circuit breaker. The double biasing connector may take the form of a spring acting on a movable contact via a switch arm pivotally connected to the movable contact. If the free end of the switch arm is held by the operating handle, the spring provides contact pressure, however, when the switch arm is released by the operating handle, the spring acts to pull the movable contact to the off position.

Description

The present invention relates to miniature circuit breakers generally. More particularly, the invention relates to a breaker assembly having an operating handle co-operating with a movable contact for a miniature circuit breaker comprising a housing, an over current sensing arrangement and a fixed contact.
Possibly the most important criterion for a miniature circuit breaker is the speed with which the movable contact separates from the fixed contact on detection of a fault. This criterion is clearly important for both the safety and the reliability aspects as relatively slow separation may cause welding of the contacts. It is also important that the contacts have a good contact pressure when in the on position to prevent accidental tripping and arcing which can damage the contacts. In many miniature circuit breakers, these two criteria have been mutually exclusive as a spring acting on the movable contact, say to bias the movable contact to the off position will reduce contact pressure in the on position. Conversely, a spring biasing the movable contact to the on position will reduce the speed of separation of the contacts.
In an attempt to overcome this problem, miniature circuit breakers such as those described in United States Patent Specification No. 3774129 and German Patent Specification No. 2047223 include a movable contact having an elongate slot which engages a pivot pin secured to the housing. This is known as a "floating pivot". In this arrangement, a single spring acting on the movable contact gives both contact pressure and off biasing pressure depending on the pivot position of the movable contact which changes between the floating pivot and another position on the movable contact which is generally held in position by the operating handle. This arrangement is not entirely satisfactory, however, because there is a delay in the switching off action while the movable contact moves at the floating pivot between the opposing end positions. Further, because the movable contact is loosely pivoted to the housing there is little consistency in positioning of the movable contact, which can cause pitting of the contacts.
The present invention is directed towards providing a breaker assembly for a miniature circuit breaker which provides for relatively quick switching off action and for good contact pressure. Other objects of the invention are that the breaker assembly has a relatively small number of components and is relatively simple to manufacture.
According to the invention there is provided a breaker assembly for a miniature circuit breaker comprising a housing, an over current sensing means, and a fixed contact, the breaker assembly comprising:
a movable contact arranged to be pivotally connected to the housing for movement between on and off positions;
an operating handle for the movable contact; and
a double biasing connector between an anchorage on the housing and an anchorage on the movable contact, the connector comprising a spring secured to one anchorage and to a switch arm which is in turn secured to the other anchorage and releasably engageable with the operating handle at a position defining an auxiliary fulcrum, the relative positions of the anchorages and the auxiliary fulcrum being such that when the switch arm and the operating handle are engaged the connector biases the movable contact in one direction and when disengaged in the opposite direction.
The double biasing connector allows a spring to provide both contact pressure and off pressure without the need for a floating pivot. This has been achieved because the action of the double biasing connector is always in one direction only or another about the single movable contact pivot connection to the housing.
In one embodiment the switch arm anchorage is a pivot connection to the movable contact and the spring anchorage is on the housing, the spring acting on the pivot connection and the auxiliary fulcrum when the switch arm engages the operating handle to bias the movable contact to the on position, and biasing the movable contact to the off position via the switch arm pivot connection when the switch arm disengages the operating handle.
The switch arm is disposed between the spring and the movable contact and immediately changes the effective direction of action of the spring on the movable contact when the switch arm engages and disengages the operating handle. It is our understanding that this has been achieved because for the on position the spring acts on both the switch arm anchorage and the auxiliary fulcrum in one direction about the movable contact pivot. When the auxiliary fulcrum is removed the spring acts about the switch arm anchorage pivot in the opposite direction about the movable contact. As a result a single spring can provide both off and contact pressure without changing direction and thereby having no over-centre. Accordingly, for switching off, the over-current sensing means must simply disengage the operating handle and the switch arm to instantaneously change the effective direction of action of the spring.
In another embodiment a stop is provided on the movable contact for abutment with the switch arm for biasing of the movable contact to the off position.
When the operating handle and switch arm are disengaged, the spring acts to pull the movable contact to the off position via the switch arm. By providing a stop on the movable contact for abutment with the switch arm, effective connection between the spring and the movable contact is improved, thus increasing the speed of switching off.
Ideally, the breaker assembly further comprises a latch lever for connection with the over current sensing means and arranged to disengage the operating handle and the switch arm on over current detection.
A latch lever is a simple and effective connection between the over-current sensing means and the operating handle to cause disengagement of the operating handle and the switch arm.
Preferably, the switch arm is engageable with the operating handle via a link pivotally connected to the operating handle.
A link pivotally connected to the operating handle is a simple and effective connection between the operating handle and the switch arm.
In an alternative embodiment, the switch arm anchorage is connected to the housing and the spring anchorage is connected to the movable contact.
In this embodiment, the spring is connected directly to the movable contact and the switch arm is disposed at the opposite end of the spring which changes the direction of action of the spring on use or otherwise of the auxiliary fulcrum. Again, there is no need for a floating pivot and the spring will provide both contact pressure and off pressure according to whether or not the switch arm engages the operating handle. This embodiment may be described as a reverse of the above-described embodiments. In this arrangement, as in the other embodiments, it is important that there is no over-centre action of the spring as this slows opening of the contacts. As stated above, it is our understanding of the principle that the spring acts on one anchorage to have one line of action. When the spring acts on both the anchorage and the auxiliary fulcrum, its effective line of action is changed. It appears therefore, that the arrangement can be reversed as defined in this embodiment.
The invention will be more clearly understood from the following description of some preferred embodiments thereof, given by way of example only with reference to the accompanying drawings in which:

Fig. 1 is a plan view of a miniature circuit breaker incorporating a breaker assembly of the invention,
Figs. 2 and 3 are plan views of the breaker assembly of Fig. 1 in the off and on positions, respectively,
Figs. 4 and 5 are schematic views of an alternative construction of breaker assembly in the off and on positions, respectively,
Figs. 6 and 7 are schematic views of a still further construction of breaker assembly in the on and off positions, respectively, and
Fig. 8 is a schematic view of another construction of breaker assembly.

Referring to the drawings, and initially to Fig. 1, there is illustrated a miniature circuit breaker 1 incorporating a breaker assembly 1(a) of the invention. The miniature circuit breaker 1 comprises a housing 2 and components forming a conducting path for current, namely, an input terminal 4, a bi-metallic element 5, a movable contact 6 pivotally connected by a pivot pin 7 to the housing 2, a fixed contact 8, a solenoid 9 and an output terminal 10. An arc stack 11 is also mounted in the housing 2.
The miniature circuit breaker 1 further comprises a breaker assembly 1(a) including an operating handle 12 biased to rotate in the clockwise direction by a helical tension spring 13. A transverse pivot pin 14 pivotally connects the operating handle 12 to a latch lever 15 arranged to be tripped by a plunger 16 for the solenoid 9 and by a rod 17 connected to the bi-metallic element 5.
The breaker assembly 1(a) also includes the above-mentioned movable contact 6 and a double biasing connector acting on the movable contact 6. The breaker assembly 1(a) is more clearly illustrated in Figs. 2 and 3, in which parts similar to those described with reference to Fig. 1 are identified by the same reference numerals. The double biasing connector comprises a torsion spring 18 which has an anchorage 19 on the housing 2. The spring 18 is secured to a switch arm 20 which has an anchorage pivotally connected to the movable contact 6 at a pivot pin 21. The switch arm 20 has a free end 22 which is arranged to engage the operating handle 12 via a link 23 pivotally connected to the operating handle 16 at the pivot pin 14. The latch lever 15 abuts against the link 23 adjacent the pivot pin 14. The link 23 includes a notch 24 for engagement with the free end 22 of the switch arm 20.
In the off position, the link 23 and the switch arm 20 are effectively disengaged as the link 23 does not act on the switch arm 20. It will be seen, however, that the switch arm free end 22 and notch 24 are in contact. In this position, the torsion spring 18 biases the switch arm 20 to rotate about the pivot pin 21 to abut against a surface 25 of the movable contact 6 which acts as a stop for the switch arm 20. Thus, the switch arm 20 and the movable contact 6 are effectively integral and the torsion spring 18 biases the movable contact 6 to the off position about the pivot pin 7.
To move the movable contact 6 to the on position, the operating handle 16 is rotated in the anti-clockwise direction, engaging the link 23 and the switch arm 20. The link 23 rotates the switch arm 20 and the movable contact 6 (which two components may still be regarded as being integral) about the pivot pin 7 until the movable contact 6 touches the fixed contact 8. Thereafter, the movable contact 6 cannot rotate any further and thus the switch arm 20 begins to rotate about the pivot pin 21 in the clockwise direction. Immediately when the switch arm 20 moves from the stop surface 25 the spring 18 acts on both the pivot pin 21 and on the engaged free end 22 which is an auxiliary fulcrum. Because of the relative positions of the anchorages, the spring urges the pivot pin 21 about the pivot pin 7 in the clockwise direction to provide contact pressure. This position is illustrated in Fig. 3 in which the operating handle 16 has been turned to the full extent.
On detection of a fault the latch lever 15 is pushed downwards, causing the link 23 to disengage from the switch arm free end 22 and thus the spring 18 again biases the switch arm in the anti-clockwise direction to abut against the stop surface 25 and bias the movable contact in the anti-clockwise direction to provide off pressure. It will be appreciated therefore that the double biasing connector acts on the movable contact 6 in either the clockwise or anti-clockwise directions about the pivot pin 7 to give either contact or off pressure, respectively and that the change-over is instantaneous, limited only by design requirements. This advantage is achieved by the fact that the spring does not itself change direction by going through an over-centre or toggle position.
It is our understanding that this has been achieved because the spring 18 in the off position acts on the switch arm pivot 21 and thus the movable contact pivot 7 alone. In the on position the spring 18 acts on both the switch arm pivot 21 and the free end 22 of the switch arm 20 which acts as an auxiliary fulcrum. Accordingly the spring has a different line of action for both positions and thus can switch between providing off and contact pressure without going through an over-centre. This is very important for speed of opening.
Referring now to Figs. 4 and 5 there is illustrated in schematic form an alternative construction of breaker assembly according to the invention indicated generally by the reference numeral 30. The breaker assembly 30 includes an operating handle 31 acted on by a tension spring 32 which is connected to a combined latch/link arm 33 at a transverse pivot pin 34. The breaker assembly 30 also includes a movable contact 35 pivotally connected at a pivot pin 36 to a housing, and a fixed contact 37. In this embodiment, a double biasing connector comprises a tension spring 40 having a fixed anchorage 41 and acting on a switch arm 42 having an anchorage pivotally connected to the movable contact 35 at a pivot pin 43. The switch arm 42 has a free end 44 for engagement with the latch/link arm 33 and at the opposite end thereof includes an extension arm 45 to which the tension spring 40 is secured. In this embodiment, the switch arm 42 is disposed within a slot in the movable contact 35, the slot having an end-surface 46 which forms a stop for abutment with the switch arm 42.
The breaker assembly 30 is dynamically equivalent to the breaker assembly of Figs. 1 to 3. The differences are in design of various components and in the manner in which they are connected. It will be seen, for example, that the connection of a tension spring to the extension arm 45 on one side of the pivot pin 43 is equivalent to the connection, as in Figs. 1 to 3 of a torsion spring to the switch arm on the opposite side of the pivot pin 43. The use of an integral latch/link arm provides for ease of assembly although the arm must be manufactured within a smaller tolerance range than if they were separate as in Figs. 1 to 3.
Referring now to Figs. 6 and 7 there is illustrated a still further construction of breaker assembly of the invention indicated generally by the reference numeral 50. The breaker assembly 50 includes an operating handle 51 acted on by a tension spring 52 at a transverse pivot pin 53 which also supports a combined latch/link arm 54. The breaker assembly 50 also includes a movable contact 55, pivotally connected at a pivot pin 56 to a housing, and a fixed contact 57. In this embodiment the fixed contact 57 is disposed on the opposite side of the movable contact with reference to the operating handle 51. A spring 60 having a fixed anchorage 61 is connected to a switch arm 62 having an anchorage pivotally connected at a pivot pin 63 to the movable contact 55. The switch arm 62 has a free end 64 which forms a notch for contact with the latch/link arm 54. A stop 65 is secured to the movable contact 55 adjacent the pivot pin 63.
In operation, the spring 60 biases the movable contact 55 to the off position when the switch arm free end 64 is disengaged from the latch/link lever 54, allowing the switch arm 62 to abut against the stop 65. For movement to the on position, the operating handle 51 is rotated in the anti-clockwise direction, causing the latch/link lever 54 to engage the switch arm free end 64 to push the movable contact 55 against the fixed contact 7. When this happens, further rotation of the operating handle 51 rotates the switch arm 62 away from the stop 65 causing the spring 60 to act on the pivot pin 63 and the free end 64 which forms an auxiliary fulcrum thus biasing the movable contact 55 in the anti-clockwise direction about the pivot pin 56 to provide contact pressure for the movable contact 55.
Referring now to Fig. 8 there is illustrated a still further breaker assembly of the invention indicated generally by the reference numeral 70. The breaker assembly 70 includes an operating handle 71 acted on by a torsion spring 72. A latch/link arm 73 is pivotally connected to the operating handle 71 at a pivot pin 74. The breaker assembly 70 also includes a movable contact 75 pivotally connected at a pivot pin 76 to a housing, and a fixed contact 77. In this embodiment a double biasing connector is provided by a compression spring 80 having a fixed anchorage 81 connected to a switch arm 82 having an anchorage pivotally connected at a pivot pin 83 to the movable contact 75. The movable contact 75 includes a stop 84 adjacent a pivot pin 83.
In operation, the compression spring 80 biases the movable contact 70 to the off position by action on the switch arm 82 and the stop 84 when the switch arm 82 is disengaged from the latch/link lever 73. When the operating handle is rotated in the anti-clockwise direction, the latch/link lever 73 engages the switch arm 82 to rotate the movable contact 75 in the clockwise direction about the pivot pin 76. When the movable contact 75 touches the fixed contact 77 and cannot rotate any further, the switch arm 82 is forced to rotate in the clockwise direction away from the stop 84. When this happens, the compression spring 80 acts to urge the movable contact 75 via the pivot pin 83 in the clockwise direction about the pivot pin 76.
The invention has been described for the embodiments whereby the switch arm anchorage is on the movable contact and the spring anchorage is on the housing. It appears to us, however, that this arrangement may be reversed with the switch arm anchorage on the housing and the spring anchorage on the movable contact, thus changing the effective line of action of the spring. It is important that the spring acting on the movable contact would not go through an over-centre when changing from acting in one direction to the other direction.
It will be appreciated that the invention provides a breaker assembly of relatively simple construction in which only one spring acts on the movable contact and this spring provides both contact pressure and off pressure without a switching delay such as the delay associated with a floating pivot. Further, as there is no play in the pivot connection at the movable contact to the housing, movement of the various parts of the breaker assembly are consistent and a good contact with the fixed contact is ensured.
The invention is not limited to the embodiments hereinbefore described and indeed, many different arrangements based on the same principle would be apparent to one skilled in the art.

Claims

1. A breaker assembly 1(a) for a miniature circuit breaker comprising a housing (2), an over current sensing means (5,9), and a fixed contact (8), the breaker assembly comprising:
a movable contact arranged (6) to be pivotally connected to the housing (2) for movement between on and off positions;
an operating handle (12) for the movable contact (6); and
a double biasing connector between an anchorage on the housing (19) and an anchorage on the movable contact (21), the connector comprising a spring (18) secured to one anchorage and to a switch arm (20) which is in turn secured to the other anchorage and releasably engageable with the operating handle (12) at a position defining an auxiliary fulcrum (22), the relative positions of the anchorages (19,21) and the auxiliary fulcrum (22) being such that when the switch arm (20) and the operating handle (12) are engaged the connector biases the movable contact (6) in one direction and when disengaged in the opposite direction.

2. A breaker assembly (1(a)) as claimed in claim 1 wherein the switch arm anchorage (21) is a pivot connection to the movable contact and the spring anchorage (19) is on the housing, the spring (20) acting on the pivot connection (21) and the auxiliary fulcrum (22) when the switch arm engages the operating handle (12) to bias the movable contact (6) to the on position, and biasing the movable contact (6) to the off position via the switch arm pivot connection (21) when the switch arm (20) disengages the operating handle (12).

3. A breaker assembly as claimed in claim 2 in which a stop (25) is provided on the movable contact (6) for abutment with the switch arm (20) for biasing of the movable contact (6) to the off position.

4. A breaker assembly as claimed in any preceding claim further comprising a latch lever (15) for connection with the over current sensing means (5,9) and arranged to disengage the operating handle (12) and the switch arm (20) on over current detection.

5. A breaker assembly as claimed in any preceding claim wherein the switch arm (20) is engageable with the operating handle (12) via a link (23) pivotally connected to the operating handle.

6. A breaker assembly as claimed in claim 1 wherein the switch arm anchorage is connected to the housing and the spring anchorage is connected to the movable contact.