Electricity: electrothermally or thermally actuated switches – Electrothermally actuated switches – With bimetallic elements
Reexamination Certificate
2001-12-04
2003-05-27
Vortman, Anatoly (Department: 2835)
Electricity: electrothermally or thermally actuated switches
Electrothermally actuated switches
With bimetallic elements
C337S097000, C337S059000, C337S037000, C335S023000, C335S035000, C218S158000
Reexamination Certificate
active
06570481
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a circuit breaker having a base constituting a molded case employed to protect the electric cables and lines and a crossbar supported onto this base to hold a movable contact and, more particularly, a circuit breaker, for example, a molded case circuit breaker stipulated in IEC60947-2, that has a function of executing quick-make and quick-break of the movable contact by swinging the crossbar by virtue of an accumulated force of a toggle link mechanism regardless of an ON/OFF operation speed of a handle, and is excellent in the prevention of contact point deposition in the open/close operation and the concurrent closing of respective contacts.
BACKGROUND ART
As set forth in Patent Application Publication (KOKAI) Hei 09-161641, for example, the circuit breaker in the prior art comprises a molded case consisting of a base and a cover, a movable contact provided to the inside of the molded case to have a movable contact point, a fixed contact having a fixed contact point that is connected/disconnected to/from the movable contact point, a crossbar that is molded out of the insulating material and supported onto the base in the closed state of the circuit breaker to hold the movable contact swingably, a switching mechanism portion for opening/closing the movable contact via this crossbar, a spring for pushing the movable contact point against the fixed contact point in the closed state of the circuit breaker, etc.
The contact points are worn away and eroded away by the arc that is generated by the repetition of the opening/closing operations and the opening/closing in the current supply in the actual use due to the electrical and mechanical or both factors. In order to maintain the stability of contact between the contact points even when the contact points are worn away and eroded away in this manner, a predetermined overtravel is provided. Where the “overtravel” is an amount of movement of the movable contact point before and after the removal, i.e., an amount that indicates the contacting margin of the contact point when the fixed contact and the fixed contact point are removed in the closed state of the circuit breaker, and is about one to two times a thickness of the contact point.
The crossbar and the base as constituent parts of the circuit breaker, that are formed of thermosetting resin as a principal component, were employed since the mechanical strength, the thermal resistance, the insulating property, etc. are required of them. For example, as the 30 ampere-frame circuit breaker, the crossbar was molded out of the material containing phenol 52 wt %, glass fiber 15 wt %, inorganic filler 10 wt %, wood flour 15 wt %, and pigment and others 8 wt %, and the base was molded out of the material containing phenol 50 wt %, wood flour 30 wt %, inorganic filler 15 wt %, and pigment and others 5 wt %.
In the circuit breaker in the prior art, since the base that occupies most of the volume of the plastic parts is constructed by the thermosetting resin such as phenol resin, unsaturated polyester resin, etc. as a principal component, the reduction in thickness of the parts is difficult to disturb the reduction in size and the reduction in weight.
In particular, in the base constructed by the thermosetting resin as a principal component, portions constituting the base interior need a predetermined thickness or more because of the molding restriction irrespective of the size of the base. Thus, such portions constituting the base interior are formed excessively thick and thus the reduction in size of the base becomes difficult. For example, in the small circuit breaker having 225 ampere-frame or less in which the interpole pitch is less than 35 mm, the pressure of the spring between the contact points is less than 20 N, etc., the rib having a height of more than 2 mm needs the thickness of more than about 2 mm because of the molding restriction and thus the portions constituting the base interior are formed excessively thick. Here the rib thickness of 2 mm is such a value that is decided with a minute margin to satisfy the minimum thickness standard of more than 1 mm to 3 mm of the thermosetting resin, that is normally well known.
Also, since the base of the circuit breaker in the prior art contains the thermosetting resin as a principal component, the flash generated in the molding, the sprue and the runner generated in the injection molding, etc. must be destroyed by fire or buried under the ground.
Then, for the reasons that the molding precision of details can be increased, etc., it is examined to employ the moldings that contain the thermoplastic resin as a principal component. However, if the thermoplastic resin is applied particularly to the base, such resin did not sufficiently satisfy the characteristics that are required for the base. For example, the moldings containing the thermoplastic resin set forth in Patent Application Publication (KOKAI) Hei 08-171847, the inorganic compound that has the dehydration reaction at 200° C. or more, and the reinforcement is excellent in the flame retardance and the insulating performance after the electrodes are opened/closed, and thus is suitable for the moldings of the circuit breaker. However, in case the thermoplastic resin is applied to the base which is used at the higher temperature and the higher stress than the cover, the handle, etc., especially the base whose temperature exceeds 100° C. at the time of current supply and which is subjected to the heavy stress via the crossbar, such thermoplastic resin is not sufficient since the reduction of overtravel in which the creep deformation generated under various conditions between the base and the crossbar takes part mutually is large.
Therefore, as the result of trial and error, the inventors of the present invention found that it is possible to employ the base that has the small reduction of overtravel, in which the creep deformation generated under various conditions takes part mutually, and that contains the thermoplastic resin as a principal component. Thus, the finding will be reported hereinafter.
The present invention has been made to overcome such problems, and it is an object of the present invention to provide a circuit breaker that is capable of decreasing the reduction of overtravel and thinning a thickness of the base and is gentle to the environment.
DISCLOSURE OF THE INVENTION
A circuit breaker according to the present invention comprises fixed contacts each having a fixed contact point; movable contacts each having a movable contact point that is connected/disconnected to/from the fixed contact point; a spring for applying a pushing force to both contact points when both contact points come into contact with each other; a crossbar formed integrally of insulating resin as a principal component to hold the movable contact swingably, and coupled to a lower link of a toggle link mechanism to swing around its swing axis with a motion of the toggle link mechanism; a switching mechanism portion for releasing an accumulated energy of a spring of the toggle link mechanism in response to a handle operation to execute quick-make and quick-break of the movable contact; and a molded case constructed by a base that fixes/supports the switching mechanism portion and a cover covered on the base from a handle side; wherein the base is a moldings that contains thermoplastic resin as a principal component to have a bending modulus of elasticity Eb at an ordinary temperature/ordinary humidity, and the crossbar is a moldings that has a bending modulus of elasticity Ec at an ordinary temperature/ordinary humidity, and following relationships are satisfied.
Eb+Ec≧
17000 MPa (1)
8000 MPa≦
Eb
(2)
9000 MPa≦
Ec
(3)
Therefore, the reduction of overtravel is small, the thickness and the weight of the base can be reduced, and this circuit breaker is gentle to the environment.
Also, the bending moduli of elasticity Eb, Ec satisfy following relationships.
Eb+Ec≧
205000 MPa (4)
9000 MPa&l
Fukuya Kazunori
Katsube Shunichi
Mitsubishi Denki & Kabushiki Kaisha
Sughrue & Mion, PLLC
Vortman Anatoly
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