Thermal protector for electric motors

A thermal protector comprising:

• a header plate having two through holes which is formed in the vicinity of longitudinal ends thereof respectively and in which two electrically conductive terminal pins are hermetically fixed by an electrically insulating filler so as to extend therethrough respectively;
• a metal housing having an open end hermetically welded to an peripheral edge of the header plate to thereby constitute a hermetic receptacle with the header plate, the housing being formed into a generally slender shape so as to be suited for mounting on end turns of a winding of an electric motor, the housing including an outer surface portion deformed for calibration of an operating temperature;
• two fixed contacts conductively secured to fixed contact supports further conductively secured to ends of the terminal pins located in the hermetic receptacle respectively;
• a metal thermally responsive element support secured to the inner surface of the housing at two longitudinally spaced apart portions thereof;
• an elastic plate electrically conductively and mechanically connected at one side thereof to a generally central portion of the thermally responsive element support;
• a thermally responsive element electrically conductively and mechanically connected to the other side of the elastic plate and including a generally shallow curved portion at which the element changes states of curvature with snap action in response to different ambient temperatures, the thermally responsive element having two movable contacts secured thereto to be disposed approximately symmetrically about a center of the curved portion so that the movable contacts are engageable with and disengageable from the fixed contacts respectively;
• a push piece disposed in the housing to exert a pushing force on a normally convex side of the thermally responsive element, the pushing force being adjusted by deforming the outer surface portion of the housing for calibration of the operating temperature, the push piece including a portion secured to an inner surface of the housing so as to correspond substantially to the deformed outer surface portion of the housing for calibration of the operating temperature.