US3851288A

US3851288A - Thermostatic switch

Info

Publication number: US3851288A
Application number: US00361053A
Authority: US
Inventors: J Stoll
Original assignee: Portage Electric Products Inc
Current assignee: Portage Electric Products Inc
Priority date: 1973-05-17
Filing date: 1973-05-17
Publication date: 1974-11-26
Anticipated expiration: 1991-11-26

Abstract

A thermostatic switch having a bimetallic electric-contactcarrying blade with a dish-shaped snap portion is provided. ''''Creep'''' opening of the contacts prior to snap-open action is substantially eliminated by forming the terminal arm opposite the one that carries the bimetallic blade of a bimetal positioned to deflect in response to temperature change in the same direction that the bimetallic blade deflects and at a faster rate.

Description

O United States Patent 1191 1111 3,851,288 Stoll Nov. 26, 1974 THERMOSTATIC SWITCH 3,104,296 9/1963 Moksu CI al. 337/89 [75] Inventor: James E. Stoli, Canton, Ohio v I Primary ExaminerJ. D. Miller [73] Assignee. gortilgecElectrlcoProducts, lnc., Assistant Examiner l:red E Bell anton hlo Attorney, Agent, or Firm-Ryder, McAulay, Fields, 1 Filed: May 17, 1973 Fisher & Goldstein 1211 Appl. No.1 361,053

'[ 57] ABSTRACT [52] U.S. Cl 337/89, 337/343 337 5 A thermostatic switch having a bimetallic electric-con- 337 tact-carrying blade with a dish-shaped snap portion is 51 1111. C1. H0ih 61/00 Provided p Opening of the Contacts prior to [58] Field Of Search 337/89, 91, 93, 94, 343, pp action Substantially eliminated by form- 337/347 3 5 372 ing the terminal arm opposite the one that carries the bimetallic blade of a bimetal positioned to deflect in [56] Referen e Ci response to temperature change in the same direction UNITED STATES PATENTS that the bimetallic blade deflects and at a faster rate.

3,095,486 6/1963 Perry 337/89 3 Claims, 1 Drawing Figure PAIENTELHUVZBISH 3,851,288

Z A fza I 20 4 /a n g THERMOSTATIC SWITCH BACKGROUND OF THE INVENTION The present invention relates to thermostatic switches such as those used for overload protection purposes with small electric motors, home appliances, etc. Heretofore, attempts have been made to secure positive, quick-opening (and closing) action in thermostats of this general type by providing a dish-shaped portion in the contact carrying, bimetallic blade (see U.S. Pat.'No. 2,820,870). Such assemblies, however, are subject to creep" which is the tendency for the electric contacts to separate slightly as temperature increases prior to the snap action occurring. Such creep action can cause sparking which is destructive to the contacts and destroys the intended beneficial effect of the snap action, which is to rapidly separate the electric contacts when a predetermined temperature has been reached.

In the past, thermostatic switches of the type described were formed with a pair of rigid arms with one arm carrying a fulcrum designed to bear down on the dish-shaped portion of the bimetallic blade. Various attempts were made to minimize and compensate for the tendency of the contacts to creep by varying the relationship between the fulcrum and dish-shaped portion (see U.S. Pat. No. 3,443,259). The present invention provides a novel approach at solving this same creep problem.

The principal object of the present invention is to provide an inexpensive thermostatic switch which may readily be mass-produced and is virtually creepless.

SUMMARY OF THE INVENTION includes a fulcrum means adapted to bear on the stripand is formed of a material which is relatively unaffected by variations in temperature. The other arm is formed of a bimetal positioned to deflect in response to temperature change in the same direction that the bimetallic blade deflects in response to the same temperature change but at a quicker rate thereby insuring that the blade and other arm remain in contact until the snap action occurs.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawing is a simplified sectional view of a switch in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference is now .made to the drawings wherein the Intermediate the ends of arm 18 is a dished-out portion 24 of blade 18 which is located fairly close to the.

center of the blade. Arm 14 carries at its forward end 26 a fulcrum 28 which contacts the blade. As is well known in the art, and as described in the above cited patents, as the blade 18 heats up, the fulcrum exerts increasing pressure on the blade l8'until the dished-out portion snaps into a concave position at which time contacts 20 and 22 separate. To this end, the bimetallic material chosen for blade 18 is positioned such that an increase in temperature causes it to curl upwardly in .the direction indicated by arrow A.

In accordance with the present invention, the first arm 14 which carries blade 18 is formed of a rigid material which remains relatively unchanged by temperature changes. The second arm 16 is formed of a bimetal positioned to creep in the direction indicated by arrow B, the same as the direction of the blades creep. The bimetallic material for arm 16 is chosen so that its creep toward arm 14 is at a rate equal to or greater than the creep of blade 18 away from arm 16. In this manner, the blade contact 20 is maintained in engagement with contact 22 virtually up until the moment the dished portion 24 reverses itself so as to minimize and virtually eliminate any creep and hence sparking at the contacts. Accordingly, the above objective is effectively attained.

Having thus described the invention, what is claimed 1. In a thermostatic snap switch of the type comprising: a mounting member; first and second terminal arms supported by said mounting member extending out therefrom in spaced relationship with each other; an elongated bimetal blade adapted to deflect in response to a temperature change having one end coupled to the first arm and the other end free extending along the side of the first arm directed toward the second arm, said blade having a part thereof dished to provide a snap-acting portion; and fulcrum means carried by the first arm and bearing on the strip; the improvement wherein said second arm is formed of a bimetal positioned to deflect in response to temperature change in the same direction as that which the bimetal blade deflects in response to the same temperature change. I

2. The thermostatic switch in accordance with claim I wherein the second arm deflects at a rate equal to or greater than the rate at which the blade deflects.

3. The switch in accordance with claim I wherein the second arm deflects toward the first arm with an increase in temperature and said bimetal blade deflects toward the first arm with the same increase in tempera ture.

Claims

1. In a thermostatic snap switch of the type comprising: a mounting member; first and second terminal arms supported by said mounting member extending out therefrom in spaced relationship with each other; an elongated bimetal blade adapted to deflect in response to a temperature change having one end coupled to the first arm and the other end free extending along the side of the first arm directed toward the second arm, said blade having a part thereof dished to provide a snap-acting portion; and fulcrum means carried by the first arm and bearing on the strip; the improvement wherein said second arm is formed of a bimetal positioned to deflect in response to temperature change in the same direction as that which the bimetal blade deflects in response to the same temperature change.

2. The thermostatic switch in accordance with claim 1 wherein the second arm deflects at a rate equal to or greater than the rate at which the blade deflects.

3. The switch in accordance with claim 1 wherein the second arm deflects toward the first arm with an increase in temperature and said bimetal blade deflects toward the first arm with the same increase in temperature.