Patent Publication Number: US-9837231-B2

Title: Thermal switch, method of manufacturing the same and device for adjusting height of movable contact

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This Non-Provisional patent application is National Stage Entry into the United States Patent and Trademark Office from International Patent Application No. PCT/JP2013/051076, having an international filing date of Jan. 21, 2013, the entire contents of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a thermal switch having a contact switching mechanism using a thermally responsive plate such as a bimetal in a pressure-proof hermetic container including a metal housing and a header plate, a method of manufacturing the same and a device for adjusting a height of a movable contact. 
     DESCRIPTION OF RELATED ART 
     Thermal switches of the above-mentioned type are disclosed in Japanese Patent No. JP-B-2519530, Japanese Patent No. JP-B-2860517, and the like. The thermal switch described in each document comprises a thermally responsive plate assembly including a thermally responsive plate, a movable contact and a metal support all housed in a closed container including a metal housing and a header plate. The movable contact is secured to one of two ends of the thermally responsive plate, and the metal support is secured to the other end of the thermally responsive plate. The thermally responsive plate reverses a direction of curvature thereof at a predetermined temperature. An electrically conductive terminal pin is inserted through a through hole of the header plate and hermetically fixed in the hole by an electrically insulating filler such as glass. A fixed contact constituting switching contacts together with the movable contact is attached to a distal end of the terminal pin located in the closed container. 
     The thermal switch is mounted in a closed housing of a hermetic electric compressor thereby to be used as a thermal protector for an electric motor of the compressor. In this case, windings of the motor are connected to the terminal pin or the header plate. The thermally responsive plate reverses the direction of curvature when a temperature around the thermally responsive switch becomes unusually high or when an abnormal current flows in the motor. When the temperature drops to or below a predetermined value, the contacts are re-closed such that the compressor motor is energized. A temperature at which the thermally responsive plate reverses the direction of curvature thereof is configured to be calibrated by crushing a secured part (a calibration part) of the metal support to the closed housing from the outside (hereinafter, “crushing temperature adjustment”). 
     Japanese Patent No. 2860517 discloses a thermal switch having a construction similar to the above-described thermal switch. In this thermal switch, the conductive terminal pin has a distal end located in the closed housing. A metal fixed contact support has one end secured to the distal end of the conductive terminal pin and the other end to which the fixed contact is secured. The fixed contact has a height above a back surface or a front surface of the fixed contact support. The height of the fixed contact is adjusted to a predetermined value. The fixed contact has a contact surface with the movable contact, which contact surface is formed into a predetermined shape. This can reduce variations in a contact height caused in the welding of the fixed contact to the fixed contact support and variations in a contact pressure after the assembly, thereby rendering a temperature calibrating work after the assembly easier. 
     Japanese Patent Application Publication No. H05-36335 discloses a thermal switch including a fixed contact secured to a header plate and an electrical conductor fixed through the header plate and having a distal end located in a closed housing. A thermally responsive plate support has one end secured to the distal end of the conductor. The thermally responsive plate support is provided with a supporting portion to which one end of a thermally responsive plate is secured. A movable contact is secured to the other end of the thermally responsive plate. A calibrating piece made of an electrically insulating material is inserted near the other end of the thermally responsive plate support. 
     SUMMARY OF THE INVENTION 
     In the thermal switches described in the above-referenced patent documents, there is also a problem of variations in the shape of the thermally responsive switch and in the secured position of the thermally responsive plate as well as variations in the height of the fixed contact. The thermally responsive plate used in the thermal switches is made of a bimetal, for example and has a part located near the center thereof and drawn into a dish shape. In this construction, variations in the characteristics of the bimetal, processing variations caused by the drawing or the like result in variations in a curved shape of the thermally responsive plate after the drawing. 
     Further, in the process of forming a thermally responsive plate assembly using the thermally responsive plate and securing the assembly to the housing or the conductor, variations in shape, finished dimensions and the like occur in a welded part between the thermally responsive plate and the metal support, a welded part between the thermally responsive plate and the movable contact, a welded part between the metal support and the housing or the conductor. When there are variations in the shape or dimensions, variations also occur in an initial contact pressure between the contacts after the assembly. With this, variations also occur in an amount of deformation (an amount of crush) of the calibration portion during the above-mentioned temperature calibration. 
     In the thermal switch described in Japanese Patent Application Publication No. H05-36335, the supporting portion of the thermally responsive plate support includes a root portion. The root portion is deformed so that the movable and fixed contacts are located so as to be in slight contact with each other or opposed to each other with a slight gap therebetween before a cover is welded to the header plate. According to this adjustment, the position adjustment is allowed before assembly except for the contact between the movable and fixed contacts. However, further positional adjustment is disallowed when the movable and fixed contacts have been brought into contact with each other, with the result that an initial contact pressure cannot be imparted to the movable and fixed contacts, and variations in the contact pressure cannot be adjusted. This excessively increases an amount of crush in the temperature adjustment by the crushing or results in variations in the amount of crush. 
       FIG. 9  explains variations in the amount of crush in Japanese Patent No. 2519530 and Japanese Patent Application Publication No. H10-144189. Time t 1  refers to the time when the thermally responsive plate assembly is mounted to the housing, and the vertical axis denotes a height H of the movable contact above an open end of the housing. The height of the movable contact has a variation of ΔH (0.5 mm, for example) by the foregoing cause. Time t 2  refers to the time when the header plate is secured to the housing and the temperature adjustment by the crushing is carried out, and the vertical axis denotes a crush amount C with reference to a height position at time t 1 . 
     Since a position (HA) of the movable contact above the open end of the housing at the time of the mounting of the thermally responsive plate assembly is excessively high in product A, the movable contact is spaced away from the fixed contact at the time of assembly. The calibrating part is then crushed such that the movable contact is brought into contact with the fixed contact, with the result that the product A is calibrated to a specified operating temperature. An amount of crush in this case is referred to as “CA.” On the other hand, since a position (HB) of the movable contact above the open end of the housing at the time of the mounting of the thermally responsive plate assembly is excessively low in product B, the movable contact is already in contact with the fixed contact at the time of assembly. The calibrating part is then crushed such that the product B is calibrated to a specified operating temperature. An amount of crush in this case is referred to as “CB.” A variations ΔC in the amount of crush is substantially equal to a variation ΔH in the height of the movable contact except for a variation in the contact pressure required to obtain a specified operating temperature. 
     When an amount of deformation in the calibrating part becomes excessively large as in the above-mentioned product A, there is the possibility of a defect that the metal support secured near the calibrating part would come off, a defect that stress would be concentrated on a neighborhood of the calibrating part with the result of reduction in the strength and durability of the closed container, or the like defect. Further, when the contact pressure before temperature calibration during the assembly has already exceeded a value corresponding to a reversing temperature, the temperature calibration by the crushing cannot be carried out. Still further, in a thermal switch of the type that a heater is provided in the closed container, a distance between the thermally responsive switch and the heater differs depending upon an amount of deformation of the calibrating part. Accordingly, a short time trip (S/T or ST operating time) varies as a variation ΔC in the amount of crush becomes large. The short time trip refers to a time period required until the opening of the contacts in a case where an excessively large current flows such as a case where a rotor of the motor is locked. 
     The present invention was made in view of the foregoing circumstances and an object thereof is to provide a thermal switch in which an amount of deformation of the calibrating part to calibrate the operating temperature can be rendered substantially constant and a stable protecting performance can be achieved, and a method of manufacturing the thermal switch and a device for adjusting a height of the movable contact. 
     A thermal switch according to one embodiment includes a housing assembly and a header plate. The housing assembly includes a metal housing having an open bottom and a thermally responsive plate assembly housed in the metal housing and including a thermally responsive plate, a movable contact secured to one of two ends of the thermally responsive plate, and a metal support secured to the other end of the thermally responsive plate. The thermally responsive plate includes a part located near a middle thereof and formed into a dish shape by drawing. The metal support has an end secured in the housing. The header plate assembly includes a header plate secured to the end of the open bottom, so that a pressure-proof closed container is formed by the header plate and the housing. The header plate has at least one through hole through which at least one conductive terminal pin is inserted and fixed in the hole by an electrically insulating filler. The header plate assembly further includes a fixed contact secured to the conductive terminal pin. The header plate assembly is hermetically secured to the housing assembly, so that switching contacts are formed by the movable contact and the fixed contact, and thereafter, a neighborhood of a part of the housing to which part the thermally responsive plate assembly is secured is deformed, whereby an operating temperature is calibratable. The pressure-proof closed container has a part secured to the metal support and provided with a calibrating part. Before the header plate assembly is hermetically secured to the housing assembly, the metal support of the thermally responsive plate assembly is deformed from an initial shape so that a position of the movable contact in the housing assembly is adjusted so as to be within a predetermined height range relative to the open end of the housing. As a result of the height adjustment, when the header plate assembly has hermetically been secured to the housing assembly, the movable contact is returned by a predetermined distance by contact with the fixed contact, so that a contact pressure between the switching contacts is produced. The calibrating part has a height falling within a predetermined range on a basis of an underside of the header plate. 
     According to the above-described thermal switch, the position of the movable contact in the housing assembly is adjusted before the header plate assembly is secured to the housing assembly, so that the specified contact pressure can be produced between the movable contact and the fixed contact when the header plate assembly is secured to the housing assembly. Accordingly, an amount of deformation of the calibrating part in the temperature calibration can be rendered smaller and substantially constant even when a curved shape of the thermally responsive plate after the drawing, the dimensions of the thermally responsive plate and the like vary from one product to another. This can avoid a reduction in the strength of the pressure-proof closed container due to deformation and conditions where the temperature calibration is impossible, and a stable protecting performance can be obtained after the temperature calibration. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various embodiments of the present invention will now be described in connection with the accompanying drawings, in which: 
         FIG. 1  is a longitudinal section of a thermal switch of a first embodiment in accordance with the present invention; 
         FIG. 2  is a cross section taken along line II-II in  FIG. 1 ; 
         FIG. 3  is a side view of the thermal switch; 
         FIG. 4  is a plan view of the thermal switch; 
         FIG. 5  is a configuration diagram showing a device for adjusting a height of the movable contact; 
         FIG. 6  is an explanatory illustration of the height adjustment and a crushing temperature adjustment; 
         FIG. 7  is a graph showing the relationship between the height of the calibrating part after execution of the crushing temperature adjustment and the ST operating time; 
         FIG. 8  is an explanatory illustration of a manner of adjusting the height of the movable contact, showing a second embodiment according to the invention; and 
         FIG. 9  is an explanatory illustration of a crushing temperature adjustment, showing a prior art. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENT(S) OF THE INVENTION 
     A first embodiment of the present invention will be described with reference to  FIGS. 1 to 7 . 
       FIGS. 3 and 4  are a side view and a plan view of a thermal switch respectively.  FIG. 1  is a longitudinal section of the thermal switch and  FIG. 2  is a transverse section taken along line II-II in  FIG. 1 . A thermal switch  1  includes a pressure-proof closed container  2  (hereinafter, “closed container  2 ”) constructed of a metal housing  3  and a header plate  4 . The housing  3  is formed into an elongate dome shape by drawing an iron plate or the like by a press machine so as to have both lengthwise ends each formed into a substantially spherical shape and a middle portion connecting the ends. The header plate  4  is formed by shaping an iron plate thicker than the housing  3  into an oval and is hermetically sealed to an open end of the housing  3  by the ring projection welding or the like. 
     The thermal switch  1  is constructed of a housing assembly  5  and a header plate assembly  6 . The housing assembly  5  includes the housing  3  and a thermally responsive plate assembly  7  housed and fixed in the housing  3 . The thermally responsive plate assembly  7  includes a thermally responsive plate  8 , a movable contact  9  secured to one of two ends of the thermally responsive plate  8  by welding and a plate-shaped metal support  10  (hereinafter, “support  10 ”) secured to the other end of the thermally responsive plate  8  by welding. The support  10  has an end which is opposed to its end secured to the thermally responsive plate  8  and is secured to an upper surface end in the housing  3  by welding. 
     The thermally responsive plate  8  is formed by drawing a thermally responsive member such as a bimetal or trimetal into a shallow dish shape and is configured to reverse a direction of curvature with a snap action when the thermally responsive plate  8  reaches a predetermined temperature. The closed container  2  includes a part (a calibrating part  2 A) to which the support  10  is secured. A contact pressure between the movable contact  9  and a fixed contact  11  (as will be described later) is adjustable by externally crushing the part (the calibrating part  2 A) of the closed container  2 , so that a temperature at which the thermally responsive plate  8  reverses its curvature can be calibrated into a desirable specified value (crushing temperature adjustment). 
     Next, the header plate assembly  6  will be described. The header plate  4  is formed with through holes  4 A and  4 B. Electrically conductive terminal pins  13 A and  13 B are inserted through and hermetically fixed in the respective holes  4 A and  4 B by an electrically insulating filler  9  such as glass in view of a thermal expansion coefficient by a well-known hermetic compression sealing. Heat-resistant inorganic insulating members  14  each comprising ceramics and zirconia (zirconium oxide) are closely fixed to upper surfaces of the fillers  12  respectively. Each heat-resistant inorganic insulating member  14  is shaped in consideration of electrical strength against creeping discharge and physical strength such as heat resistance to sputtering. The heat-resistant inorganic insulating member  14  can improve a dielectric strength between the terminal pins  13 A and  13 B and the header plate  4  and prevent generated arc from transition to a space between the terminal pin  13 B and the header plate  4  or a space between the terminal pins  13 A and  13 B. 
     A contact support  15  is secured to a part of the terminal pin  13 A near the distal end of the pin inside the closed container  2 . The fixed contact  11  is secured to a part of the contact support  15  opposed to the movable contact  9 . A heater  16  serving as a heating element has two ends one of which is fixed to a portion of the terminal pin  13 B located near the distal end of the terminal pin inside the closed container  2 . The other end of the heater  16  is fixed to the header plate  4 . The heater  16  is disposed so as to be substantially parallel to the thermally responsive plate  8  along the terminal pin  13 B, so that heat generated by the heater  16  is efficiently transmitted to the thermally responsive plate  8 , as shown in  FIG. 2 . 
     The heater  16  is provided with a fusing portion  16 A (see  FIG. 2 ) having a smaller sectional area than the other part thereof. The fusing portion  16 A is prevented from being fused by an operating current of an electric motor during a normal operation of a compressor serving as equipment to be controlled. The fusing portion  16 A is further prevented from being fused upon occurrence of a locked rotor condition of the motor since the thermally responsive plate  8  reverses the direction of curvature thereby to open the contacts  9  and  11  in a short period of time. However, when the thermal switch  1  repeats the opening and closure of the contacts  9  and  11  for a long period of time such that the number of times of switching exceeds a guaranteed number of switching operations, the movable and fixed contacts  9  and  11  are sometimes welded together thereby to be inseparable from each other. In this case, when a rotor of the motor is locked, a temperature of the fusing portion  16 A is increased by an excessively large current, so that the fusing portion  16 A is fused, whereupon power supply to the motor can reliably be cut off. 
     When current flowing into the motor is a normal operation current including a short-duration starting current, the contacts  9  and  11  of the thermally responsive switch  1  remain closed, so that the motor continues running. On the other hand, the thermally responsive plate  8  reverses the direction of curvature thereof to open the contacts  9  and  11  thereby to cut off the motor current when a current larger than a normal current flows continuously into the motor as the result of an increase in the load applied to the motor, when the motor is constrained such that an extremely large constraint current flows into the motor continuously for more than several seconds, or when the temperature of a refrigerant in the hermetic housing of the compressor becomes extremely high. Subsequently, when the internal temperature of the thermally responsive switch  1  drops, the thermally responsive plate  8  again reverses the direction of curvature thereof such that the contacts  9  and  11  are closed, whereupon energization to the motor is re-started. 
     The following will describe the height adjustment of the movable contact  9  in an assembly process and a process of calibrating a reversing temperature of the thermally responsive plate  8  after the assembling. The manufacture of the thermal switch  1  includes the assembly process and a calibration process. In the assembly process, the thermally responsive plate assembly  7  is made and mounted to the housing  3 , so that the housing assembly  5  is manufactured. With this, the header plate assembly  6  is manufactured. Subsequently, the header plate assembly  6  is hermetically secured to the housing assembly  5  while the housing assembly  5  is filled with a gas at a predetermined pressure. In the subsequent calibration process, a calibrating part  2 A of the container  2  is externally crushed in an oil which is kept at a specified reversing temperature, until the thermally responsive plate  8  reverses its curvature (the crushing temperature adjustment). 
     Variations in the curved shape of the thermally responsive plate  8  result from variations in the characteristics of the thermally responsive plate  8 , processing variations due to drawing or the like, as described above. Further, variations resulting from welding or the like occur in the shape and dimensions of the thermally responsive plate  8  when the thermally responsive plate assembly  7  is made and when the thermally responsive plate assembly  7  is mounted to the housing  3 . Still further, the shape of the support  10  slightly varies. When the crushing temperature adjustment is carried out in this state, an amount of deformation (an amount of crush) of the calibrating part  2 A becomes excessively large with the result that the strength and durability of the closed container  2  are reduced, and the amount of crush varies for every product with the result that the ST operating time required until the opening of the contacts  9  and  11  varies. 
     In view of the problems, the support  10  mounted to the housing  3  in the assembly process is deformed from an initial shape so that an amount of crush in the crushing temperature adjustment becomes substantially constant and the amount of crush is reduced, whereby the position of the movable contact  9  is adjusted so as to be within a predetermined height range relative to the open end of the housing  3  even if the height of the movable contact  9  varies at the time of manufacture of the housing assembly  5 . When the header plate assembly  6  is hermetically secured to the housing assembly  5 , the movable contact  9  is pressed against the fixed contact  11  as the result of the height adjustment, so that a contact pressure (an initial contact pressure) is produced between the switching contacts. 
       FIG. 5  shows the construction of a height adjuster  17  for adjusting the height of the movable contact  9 . The height adjuster  17  includes a holding part  18 , a pressing device  19 , a position measuring device  20  and a control device  21 . The holding part  18  holds the housing assembly  5  with the open end thereof up. The pressing device  19  includes a press cylinder having a servomotor or the like serving as a drive source and a rod  19 A. In response to a command signal from the control device  21 , the rod  19 A is caused to thrust forward to press, from above, a neighborhood of a part of the support  10  in one direction, to which part the thermally responsive plate  8  is secured, namely, inward from the open end of the housing  3 . The position measuring device  20  includes a differential transformer and measures a height H of the movable contact  9  from the open end in the housing assembly  5 . The control device  21  controls the pressing device  19  so that the rod  19 A is thrust downward until the value H measured by the position measuring device  20  equals a specified value H 1 , thereby deforming the support  10  from an initial shape. 
       FIG. 6  is an explanatory illustration of the height adjustment and a crushing temperature adjustment. Time t 0  refers to the time when the thermally responsive plate assembly  7  is mounted to the housing  3 . The vertical axis denotes the height of the movable contact  9  above the open end of the housing  3 . An initial height H (a range from HA to HB) of the movable contact  9  is set to be smaller than the defined value H in every product though having variations within ΔH (0.5 mm, for example) as in the prior art (HA, HB&lt;H 1 ). 
     Time t 1  refers to the time when the height adjustment of the movable contact  9  is completed by the height adjuster  17 . The movable contact  9  is adjusted to be located at the position (within an acceptable error range) spaced away by the specified value H 1  from the open end of the housing  3  in each one of all the products. The specified value H 1  is set so that the contact with the fixed contact  11  returns the movable contact  9  by a predetermined distance when the header plate assembly  6  has been secured to the housing assembly  5  after time t 1 . The return results in a specific initial contact pressure between the movable contact  9  and the fixed contact  11 . 
     Time t 2  refers to the time when the crushing temperature adjustment is completed while the header plate assembly  6  is hermetically secured to the housing assembly  5 . The vertical axis denotes a crush amount C with reference to the height position at time t 1 . Since the height adjustment of the movable contacts  9  has been carried out, the contact pressure at the time of assembly becomes substantially equal to one another among the products. Variations in the crush amount in the crushing temperature adjustment (ΔC=CA−CB) becomes extremely small, so that the crush amount can be prevented from differing to a large extent over all the products. Further, since the initial contact pressure is set beforehand, the crush amount can be rendered as small as possible in the crushing temperature adjustment. 
       FIG. 7  shows the relationship between the height E (see  FIG. 2 ) of the calibrating part  2 A after execution of the crushing temperature adjustment and the ST operating time required until the opening of the contacts  9  and  11  when an excessive current flows. When the crush amount is small and the height E of the calibrating part  2 A with reference to an underside of the header plate  4  is high, the distance between the thermally responsive plate  8  and the heater  16  is increased with the result that the ST operating time is rendered longer. On the other hand, when the crush amount is large and the height E of the calibrating part  2 A is low, the distance between the thermally responsive plate  8  and the heater  16  is reduced with the result that the ST operating time is rendered shorter. When the height adjustment of the movable contact  9  is performed prior to the crushing temperature adjustment, the height E of the calibrating part  2 A after the crushing temperature adjustment falls within the range of 6.9±0.3 mm with the result that variations in the ST operating time can be reduced as compared with the prior art. 
     As described above, the thermal switch  1  of the embodiment is assembled through the process of deforming the support  10  of the thermally responsive plate assembly  7  mounted to the housing  3 , from the initial shape. Accordingly, the position of the movable contact  9  in the housing assembly  5  is controlled to correspond to the predetermined height H 1  relative to the open end of the housing  3 , so that a crush amount in the crushing temperature adjustment can be rendered as small as possible. Consequently, the crush amount of the calibrating part  2 A in the crushing temperature adjustment after the assembling can be rendered substantially constant, with the result that a stable motor protecting performance can be obtained while variations in the ST operating time among the products are reduced. 
     Further, the crush amount in the crushing temperature adjustment can be rendered as small as possible by setting the height H 1  of the movable contact  9  in the crushing temperature adjustment so that a specific initial contact pressure is ensured between movable contact  9  and the fixed contact  11  after the assembling process. This can reduce strain applied to a neighborhood of the calibrating part  2 A in the crushing temperature adjustment and can accordingly prevent reductions in the strength and durability of the closed container  2  disposed in the compressor interior which is a high-temperature and high-pressure environment. 
     The height of the movable contact  9  is adjusted after the support  10  of the thermally responsive plate assembly  7  has been welded to the housing  3 . Accordingly, the height of the movable contact  9  can be adjusted in consideration of variations in the shape and the dimensions resulting from the welding of the support  10  to the housing  3  as well as the variations in the shape and the dimensions of the thermally responsive plate assembly  7 . This can realize a constant crush amount with further accuracy in the crushing temperature adjustment. 
     The thermally responsive plate  8  is secured via the support  10  to the housing  3 . The height of the movable contact  9  is adjusted by deforming the support  10 . Since a bending angle of the support  10  made of a metal is changed, application of deformation to the thermally responsive plate  8  causes no variations in the reversing characteristics thereof, so that a stable motor protecting performance without variations can be obtained through a subsequent crushing temperature adjustment. Further, since the thermally responsive plate  8  is deformed by pressing it in one direction inward from the open end of the housing  3 , the construction of the height adjuster  17  can be simplified. 
     A second embodiment of the invention will be described with reference to  FIG. 8 . In the embodiment, the height adjustment of the movable contact  9  is performed before the thermally responsive plate assembly  7  is mounted to the housing  3 .  FIG. 8  is an explanatory illustration of the height adjustment. The thermally responsive plate assembly  7  is disposed on the holding part, and the movable contact  9  is adjusted so as to be located at a predetermined height L 1  with reference to the surface of the support  10  secured to the housing  3 . The height adjustment is carried out by pressing a part of the support  10  secured to the thermally responsive plate  8 , in one direction from above by the rod  19 A of the pressing device  19 . After the height adjustment, the thermally responsive plate assembly  7  is mounted to the housing  3 , so that the housing assembly  5  is completed. 
     In this case, the position of the movable contact  9  in the housing assembly  5  is within the predetermined height range relative to the open end of the housing  3 . The contact with the fixed contact  11  returns the movable contact  9  by a predetermined distance when the header plate assembly  6  is hermetically secured to the housing assembly  5 . The return results in a specified initial contact pressure between the movable contact  9  and the fixed contact  11 . In other words, the height L 1  is set so that the specified initial contact pressure is generated. 
     In the second embodiment, the crush amount in the crushing temperature adjustment after the assembling is also rendered substantially constant and smaller by the same operation as in the first embodiment. In the second embodiment, dimensional variations caused by the welding of the support  10  and the housing  3  cannot be reduced by the above-described height adjustment. Accordingly, these dimensional variations are reduced by adjustment of the crush amount in subsequent crushing temperature adjustment. 
     The invention should not be limited to the foregoing embodiments. The embodiments may be modified as follows. The closed container  2  should not be limited to the elongate dome shape but may not be formed into the elongate dome shape when a certain strength is obtained by provision of ribs provided along the lengthwise direction of the container. 
     The support  10  is fixed to one end of the closed container  2 . However, when the size of the thermal switch is further reduced, the support  10  may be fixed to a neighborhood of the central part of the closed container  2 . The support  10  may be formed into a button shape. 
     The support  10  need not be formed into the plate shape. 
     The heater  16  and the heat-resistant inorganic insulating member  14  may be provided as the need arises. 
     Although two conductive terminal pins  13 A and  13   b  are provided on the header plate  4 , a single conductive terminal pin may be provided and the metal header plate  4  may serve as the other terminal. 
     Two or more pairs of the switching contacts each including the movable contact  9  and the fixed contact  11  may be provided. The electric motor with which the thermal switch is used should not be limited to the single-phase induction motor but may be another motor such as a three-phase induction motor. 
     As described above, the thermal switch of the invention is useful as a thermal protector for a compressor motor.