Abstract:
A switch is shown having a thermostatic member which deforms in response to variations in temperature to thereby control the state of energization of the switch. The thermostatic member is shown cantilever mounted or centrally mounted using material to affix the member to a support which melts at a selected temperature to cause the member to separate from the support upon the occurrence of selected conditions.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates in general to a switch device and in particular to a switch device that carries out an opening and closing action in conformity with variations in temperature. 
     2. Brief Description of the Prior Art 
     Electrical appliances such as motors generate heat when they are subjected to an overload and if they are continuously used despite such overload the insulating coating of the coil is burnt, thereby demaging the motor and making it impossible for them to function any longer. In order to prevent this it is conventional to use a switch device (protective device) that employs a bimetal which opens a movable contact due to abnormal electric current and abnormal temperature, thereby bringing about the OFF state. 
     Examples of the above-described switch device are shown in FIGS. 9 through 11. 
     In the switch device 41 which is shown in FIG. 9, a bimetal disc 7 is fixed to a bolt 5 via a washer 30. This fixing is effected by deforming the head 5c of the bolt 5 (or by screwing the same). The bolt 5 is screwed to a female screw 5b which extends through a bore in bottom wall 3 of electrically insulative housing 2 and is secured to the bottom wall 3 as it is tightened by means of a lock nut 6. In the insulative housing 2, terminals 13b and 14b of the fixed contact point 13a and 14a are fixed as by staking and the insulative housing 2 is covered by an electrically insulative lid 16. 
     At the time when the motor is in normal operation, the movable contacts 8 and 8 which are mounted on the bimetal disc 7 are in engagement with the stationary contacts 13a and 14a and the terminals 13B and 14B that protrude under the insulative housing 2 are electrically connected through the stationary contacts 13a and 14a, movable contacts 8 and 8 and bimetal disc 7. Switch device 41 is installed at a common terminal of the motor and, if the motor happens to be in an abnormal or overload state, an abnormal electric current flows to the common terminal, with a result that the bimetal generates heat (Joule&#39;s law), is heated and snaps open with the movable contacts 8 and 8 moving out of engagement with the stationary contacts 13a and 14a, thereby electrically deenergizing terminals 13b and 14b. 
     The interior of the switch device 41 is heated to a suitable temperature by means of a heater 15a so that the deformation or snapping of the bimetal disc 7 at the time of a fault condition may take place early. In the drawing, 15b  is the terminal of the heater 15a. In this manner, the motor is maintained in an acceptable temperature range. 
     In a switch device 42 shown in plan view in FIG. 10 and in FIG. 11 which is a cross section taken along line 11--11 of FIG. 10, there is located a can 26 electrically isolated from a metal plate 22 via an insulation sheet 24. Metal plate 22 and the can are fixed mutually in such a manner that the lower portion 26a of the can 26 may clamp the metal plate 22 via an electrically insulative gasket 29. A stationary contact 23a is mounted on plate 22 and a terminal 23b is formed thereon. One end of the bimetal strip 27 is fixed to the inner wall of the can 26. 
     In the drawing, numeral 31 stands for a rivet head that mounts a bimetal strip 27 and its shank 31a is inserted through an aperture in the can 26 and welded to the can. As a result, the bimetal strip 27 is firmly fixed to the can 26. A heater 25a is wound on the peripheral surface of the can 26 and one terminal 25c of the heater 25a is connected with the can 26 by means of welding. 
     At the time when the motor is functioning normally, a movable contact 28 that is provided at the other end of the bimetal strip 27 is in contact with the stationary contact 23a and the terminal 23b and the terminal 25b of the heater 25a are electrically connected via the metal plate 22, stationary contact 23a, movable contact 28, bimetal strip 27, can 26 and the heater 25a. 
     The method for using the switch device 42 and the principle governing its action are the same as those of the switch device 41 described in FIG. 9. 
     In the case of a comparatively large-sized motor of more than one half HP, for example, the switch device 41 or 42 is electrically connected with the common terminal of the motor and is ordinarily used as shown in FIGS. 8a and 8b. 
     At the time when the motor is functioning normally, the contacts of the switch device are in engagement conducting the operating current. At the time when the motor load is excessive, however, the overload electric current is detected and the circuit is opened. 
     At the time when the motor experiences some trouble and the rotary element is locked, thereby causing an electric current which is several times as large as the normal operating current to flow, the switch device responds to the said abnormal electric current, with a result that the circuit is opened. 
     In the case of an overload state and a fault such as the locked state, etc., the switch device opens the electric circuit, thereby protecting the motor from being burnt. The temperature setting of the bimetal is so arranged that an automatic return of the switch device may be effected, with a result that the OFF/ON is repeated until the abnormal state is removed. 
     Since there is a limit to the life of the switch device, however, there are cases where the abnormal condition may not be removed indefinitely. In such a case, the switch may fail in the contacts closed position and the abnormal current will be passed continuously to the motor, with a result that the motor may be burnt or set on fire. 
     SUMMARY OF THE INVENTION 
     This device is invented in view of the aforementioned circumstances. It is an object of the invention that when the life of a switch device has come to an end and it has stopped functioning, the electric circuit is automatically opened in order to protect the electric appliance. 
     Briefly, in accordance with the invention, a switch device having a deformable member that deforms in response to variations in the temperature is used to control the movement of a movable contact into and out of engagement with a stationary contact that corresponds to this movable contact, characterized in that the aforementioned deformable member and a support member that supports this deformable member are mutually fixed by means of a meltable material, which melts at the time of an emergency, with a result that the aforementioned deformable member is dismounted, thereby effecting switching and opening of the circuit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 through 7 show several embodiments of this invention. 
     FIG. 1 is a vertical cross section of a switch device. 
     FIG. 2 is a cross section taken along line 2--2 in FIG. 1. 
     FIG. 3 is a cross section of the bimetal disc and a bolt that supports the same before securing the disc to the bolt. 
     FIG. 4 is an equilibrium state of a tin-lead dual element alloy. 
     FIG. 5 is a vertical cross section of a switch device in an alternate embodiment. 
     FIG. 6 is a top plan view of a switch device according to still another embodiment. 
     FIG. 7 is a cross section taken along line 7--7 in FIG. 6. 
     FIGS. 8a and 8b are circuit diagrams showing the connection between the switch device and the motor windings. 
     FIGS. 9 through FIG. 11 show prior art examples. 
     FIG. 9 is a vertical section of a prior art switch device. 
     FIG. 10 is a plan view showing another prior art switch device. 
     FIG. 11 is a cross section taken along line 11--11 in FIG. 10. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 1 through 3, switch devices are shown having structures which are similar to the prior art switch device as explained in FIG. 9. FIG. 1 shows a vertical cross section and FIG. 2 is a cross section taken along line 2--2 in FIG. 1. Those parts which are common with FIG. 9 have been designated by the same numerals as used in FIG. 9. 
     Since the principle governing the action of the switch device 1 is the same as described for the switch device in FIG. 9 shown above, the explanation will not be repeated. 
     The electrically insulative housing 2 is cylindrical in shape and the bottom wall 3 is formed integrally with the housing 2. The bimetal is a bimetal disc 7 which is in the shape of a disc, with the movable contacts 8 and 8 being mounted on the extensions at corresponding locations of the disc. 
     This switch device 1 carries out the same action as explained with relation to FIG. 9. What should be noted in this example is the fact that, at the tip of a bolt 5, there is provided a protrusion 5a having a small diameter. The protrusion 5a is inserted through an aperture 7a at the center of the bimetal disc 7 as well as through an aperture in a fixed plate 9 located on the bimetal disc 7. Bolt protrusion 5a, bimetal disc 7 and the fixed plate 9 are soldered and secured by means of solder 10. 
     In addition, there is provided a coil spring 12 between the bimetal disc 7 and the bottom wall 3 and the bimetal disc 7 is given an upward bias as shown in the figure by means of coil spring 12. 
     FIGS. 8a and 8b are sketches showing an example of the installation of the switch device 1 for a motor. 
     Motor M comprises start winding SW and main winding MW connected between a line current source. Switch 1 can, for example, be used in conjunction with a starting relay as shown in FIG. 8b with the coil 6 of the relay coupled to switch 1 intermediate the disc and heater. FIG. 8a shows another example with switch 1 connected directly to the main winding terminal and to a capacitor coupled between the main and start windings. 
     If the operation of the motor becomes abnormal and the temperature of the motor windings rises or if an excessive electric current flows to the switch device, the ON and OFF state of the switch device 1 are repeated as described earlier, thereby repeating the deformation and release of the bimetal disc 7. Because of this repetition, the bimetal disc 7 comes to lose normal deformation capability due to fatigue and, if the movable contacts 8 and 8 remain in engagement with the stationary contacts 13a and 14a during an overload or if the contacts melt, the bimetal disc 7 is heated to a temperature which is higher than the temperature at which the normal deformation takes place. 
     At this point, the solder 10 melts, with a result that the fixing of the bimetal disc 7 to the bolt 5 is released and, as is shown by the phantom lines in FIG. 1, the bimetal disc 7 is dismounted and separated from the bolt 5 along with the fixed plate 9 and is raised therefrom. The movable contacts 8 and 8 are moved out of engagement with the stationary contacts 13a and 14a, with a result that the switch device 1 is brought into an OFF state. 
     The melting of the solder 10 is carried out by the heat conducted from the bimetal disc 7 and/or Joule&#39;s law heat that is generated in the solder 10. By setting the melting temperature of the solder 10 slightly higher than the temperature of the bimetal disc 7 at the OFF time, the switch device will be brought into an OFF state quickly at the time when the aforementioned emergency state takes place. In this manner, the motor will not be damaged and will be reliably protected. 
     The temperature at which the bimetal disc 7 snaps and the movable contacts 8 and 8 become separated from the stationary contacts 13a and 14a is selected by the design of the bimetal disc 7. In addition, the temperature at which the solder 10 melts is determined by the composition of the solder. 
     FIG. 4 shows the equilibrium state of the solder or the tin-lead dual element alloy. The temperature at which the solder melts is determined by the lead content of the solder. In the event that the melting is to be carried out at a temperature which is lower than the eutectic temperature of 182 degrees centigrade, a suitable amount of cadmium, for example, can be included to obtain melting in conformity with the temperature. 
     It is mentioned in this connection that the aforementioned melting temperature does not mean the temperature at which the production of the liquid phase begins or the temperature at which the solid phase starts disappearing but the temperature at which the solder melts and loses the aforementioned fixing capability for practical purposes. 
     The fixing of the bimetal disc 7 to the bolt 5 is carried out as shown in FIG. 3. The protrusion 5a and the small diameter of the bolt 5 is inserted through aperture 7a of the bimetal disc 7 and the protrusion 5a is further inserted into a through hole 9a of the fixed plate 9 which is in the shape of a dish. Next, the solder 11 in the shape of a flat washer is placed on the fixed plate 9 and the solder 11 is melted by heating same, the molten solder enters between the protrusion 5a and the fixed plate 9 and bimetal disc 7 and, when the solder solidifies by subsequent cooling, the bolt 5, bimetal disc 7 and fixed plate 9 are mutually firmly secured as shown in FIG. 1. 
     It will be noted in this connection that the coil spring 12 shown in FIG. 1 can be omitted. If the vertical orientation of the switch device in FIG. 1 is reversed as shown in FIG. 5, the bimetal disc 7 will become separated through its own weight together with the fixed plate 9 from the bolt 5. Plate 9 and disc 7 will fall when the solder melts with the movable contacts 8 and 8 separating themselves from the stationary contact 13a and 14a, with a result that this switch device is brought into an OFF state. 
     In this switch device, the coil spring is not required thereby lowering the manufacturing cost. 
     FIGS. 6 and 7 show switch devices having structures which are similar to those of the switch devices explained in FIGS. 10 and 11. FIG. 6 is a top plan view and FIG. 7 is a cross section taken along line 7--7 in FIG. 6. The parts which are common to FIGS. 10 and 11 are indicated by the same numerals. 
     Moreover, the structure and action of this switch device 21 have been explained in FIGS. 10 and 11 except for what is described below and, accordingly, any explanation of these will be omitted here. 
     As is shown in FIG. 6, a terminal side of the bimetal strip 27 is soldered and fixed to the inner surface of the can 26 by means of a solder 10. 
     When the bimetal strip 27 finally fatigues by the repetition of the deformation and the release of deformation, thereby losing its normal deformation capability, the bimetal 27 is not deformed even in the case where operation of such an electric apparatus as the motor may be abnormal and the movable contact 28 and the stationary contact 23a remain in the state of engagement. In this state, the bimetal strip 27 continues to increase in temperature and the solder 10 melts. As is shown by a phantom line in FIG. 7, the bimetal strip 27 becomes separated from the can 26 and drops. 
     Because of the above, the terminals 23b and 25b are electrically deenergized and the switch device 21 is brought into an OFF state, with a result that such an electric apparatus as the motor is not damaged but is accurately protected. 
     Materials used to secure the bimetals 7 and 27 to the support members that support same (such as the bolt 5 and can 26) can use electrically conductive or insulative thermoplastic adhesive materials in addition to the solders. 
     Various modifications can be made in addition to what has been described above on the basis of the technical concept of this invention. For example, the bimetal can have any suitable shape and the movable contact can be located at any suitable location in conformity with the structure and the shape of the switch device. In addition, some other members that deform in conformity with the variations in temperature can be used in the place of the bimetal. 
     As has been explained above, this invention is so constructed that a deformation member that is deformed in conformity with variations in temperature is fixed to a support member by means of a meltable material that melts at the time of an emergency, the aforementioned deformation member is displaced by the aforementioned melting and the switching is thereby carried out, with a result that switching can be effected reliably (such as the opening of the electric circuit, etc.) even in the case of an emergency such as the loss of the normal deformation ability due to the fatigue of the aforementioned deformation member, for instance, or even when the melting of the contact points may take place. 
     Accordingly, the supply of electricity to the electric apparatus is automatically terminated at the time of the aforementioned advent of an abnormal state, thereby effectively protecting the electric apparatus from being damaged and accurately protecting the same. 
     Though the invention has been described with respect to specific preferred embodiments thereof, many variations and modifications will immediately become apparent to those skilled in the art. It is therefore the intention that the appended claims be interpreted as broadly as possible in view of the prior art to include all such variations and modifications.