Electricity: electrothermally or thermally actuated switches – Thermally actuated switches – With bimetallic element
Patent
1996-08-19
1998-08-18
Picard, Leo P.
Electricity: electrothermally or thermally actuated switches
Thermally actuated switches
With bimetallic element
337 89, 337333, 337 52, 337388, H01H 3752, H01H 500
Patent
active
057963274
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention concerns improvements relating to electric switches and more particularly concerns thermally responsive electrical switches employing bimetallic elements as thermal actuators.
BACKGROUND OF THE INVENTION
Many kinds of electrical switches employing bimetallic actuators are known and likewise many different forms of bimetallic switch actuators are known. Early bimetallic switches simply employed a plain bimetal blade which moved relatively slowly in response to temperature changes and gave rise to arcing problems in the switch, and the development of the snap-acting bimetallic actuator, constructed as a dished bimetallic element capable of moving between oppositely curved configurations with a snap action, provided a major advance in the art. Various forms of snap-acting bimetallic actuators are known, such as those disclosed in GB 600055, GB 657434, GB 1064643, GB 1542252 and GB 2124429 for example. Likewise, various forms of electric switches employing such bimetallic actuators are known; GB 2124429 abovementioned for example discloses the utilization of a pear-shaped snap-acting bimetallic actuator in a current-sensitive switch where the heating of the bimetal by flow of electric current therethrough is designed to trip the switch in a current overload situation.
In WO 92/20086 there is described a miniature electrical switch employing a snap-acting bimetallic actuator, the switch being well suited to automatic manufacture and installation and comprising a minimum number of parts. The switch comprises a moulded plastics body portion which captures therein first and second terminal conductors, and a snap-acting bimetallic actuator is secured to one of the two conductors and carries a contact which constitutes the moving contact of the switch and is arranged for co-operation in switching operations with the other of the two conductors. The switch can be made highly current sensitive by use of a bimetallic material of very low thickness (eg. 0.003 inch: 0.076 mm) and the internal construction of the switch body can be designed to provide physical support for such a thin bimetallic element. The possibility is further described of providing a silver or silver alloy coating, for example a silver antimony coating as described in WO 92/14282 on the terminal conductor which co-operates with the moving switch contact carried by the bimetal so as to enable an otherwise plain conductor to be utilized without need for attachment of a discrete contact to the conductor.
To enhance the current sensitivity of the switch, the possibility is further disclosed to provide a series-connected heating element in the switch for injecting heat into the bimetallic actuator when the switch is in closed condition, and in a particularly convenient arrangement this is achieved by forming the heating element as a portion of one or other, or both, of the two terminal conductors. Yet another possibility is to provide a heating element in parallel with the switch conductors, for example by use of a conductive ink printed on the switch body portion, the effect of this being to inhibit resetting of the switch so long as its power supply remains connected.
OBJECTS AND SUMMARY OF THE INVENTION
One object of the present invention is to enable the provision of a thermally-responsive switch incorporating a bimetallic switch actuator, the switch obtaining the advantages of the switch of WO 92/20086 abovementioned and furthermore providing for increased current carrying capacity and preferably, though not essentially, for increased first break times to avoid nuisance tripping of the switch.
According to the present invention, in one of its aspects, there is provided a thermally-responsive switch comprising a moulded plastics body portion capturing therein first and second terminal conductors, a leaf spring secured to one of said conductors and carrying a contact which constitutes the moving contact of the switch and is arranged for co-operation in switching operations with the other of the two conductors
REFERENCES:
patent: 3242292 (1966-03-01), Malone
patent: 3573697 (1971-04-01), Dennis et al.
patent: 3936788 (1976-02-01), Uchiya
patent: 4013988 (1977-03-01), Holden
patent: 4507642 (1985-03-01), Blackburn
patent: 4914414 (1990-04-01), Ubukata et al.
patent: 5082997 (1992-01-01), Vialy
patent: 5196820 (1993-03-01), Ubukata
patent: 5367279 (1994-11-01), Sakai
Gandhi Jayprakash N.
Otter Controls Limited
Picard Leo P.
LandOfFree
Thermally responsive electrical switches does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Thermally responsive electrical switches, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Thermally responsive electrical switches will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1118386