Abstract:
In a sealed casing ( 2 ) there are provided a bimetal disc ( 8 ) which carries out the switching of an electric current path by snapping between oppositely dished configurations in conformity with the level of the electric current that flows therethrough and ambient temperature by moving a movable contact ( 10 ) into and out of the electric current path. A fuse terminal ( 14, 15, 141, 142, 143, 144 ) is connected in series with the bimetal disc ( 8 ) and shuts off the current path by being melted by an over-current. The fuse terminal ( 14 ) in one embodiment is fixed on one surface of a support member ( 3 ) that serves as a heater. The fuse terminal ( 14 ) and the bimetal disc ( 8 ) are connected through a connective pin ( 12 ) which is provided through the support member ( 3 ) electrically insulated therefrom. In another embodiment the bimetal disc ( 8 ) and the fuse terminal ( 15 ) are disposed on opposite face surfaces of support member ( 3 ).

Description:
FIELD OF THE INVENTION 
     This invention relates generally to a motor protector which is to be used in a compressor or the like to be employed, for instance, in air conditioners, and more particularly to a motor protector of the type to be used inside of the motor that is to be protected. 
     BACKGROUND OF THE INVENTION 
     Examples of prior art motor protectors of this type are shown in FIGS.  9 ( a ) through  9 ( c ). As shown in FIGS.  9 ( a ) and  9 ( b ), a typical motor protector  101  has a support  103  having a heater  103   a  disposed in the main body  102   a  of a casing  102  made of steel. A terminal pin  104  which has been fixed to the support member  103  extends out of a header  105  that has been provided at the opening of casing  102 , with the gap between this terminal pin  104  and header  105  being sealed by a glass seal  106  and an epoxy pellet  107 . A bimetal disc  108  is fixed to support member  103  by means of a slug  109 , with its movable contact  110  engageable with a stationary contact  111  mounted inside of casing  102 . 
     In applications in which a motor protector as described is to be installed in a motor compressor of the sealed type (hereafter referred to as the electromotive compressor  100 ), first and second electric wires  112  are connected respectively to terminal pin  104  and casing  102 . Motor protector  101  is disposed inside of an insulating sleeve  113  and, as shown in FIG.  9 ( c ), is connected to windings  114  (main winding  114   a  and auxiliary winding  114   b ). Thus, motor protector  101  is serially connected with driving circuit  130  of electromotive compressor  100  connectable to an alternating current source  115 . 
     Bimetal disc  108  snaps from one dished configuration to an opposite dished configuration due to the generation of heat by the bimetal disc stemming from overload current or, otherwise, by an elevation of the ambient temperature within the protector including the generation of heat by heater  103   a , with a consequence that the driving circuit is opened thereby preventing any possible damage from being inflicted on electromotive compressor  100 . 
     Nevertheless, such conventional motor protectors  101  have the following problem: 
     In the event that an abnormal state, as described above, develops in electromotive compressor  100 , electromotive compressor  100  is protected from heat generation or possible burning as the motor protector  101  repeatedly conducts and interrupts the electric current. In the case where the situation is not remedied, motor protector  101  continues its protection of electromotive compressor  100  above and beyond the designed number of cycles of its life expectancy. Under such circumstances, when motor protector  101  eventually exceeds its expected product life, melting and welding of movable contact  110  and stationary contact  111  of the bimetal disc  108  occur, thereby bringing about a state of continuous current flow. If such a state continues, winding  114  in electromotive compressor  100  will become over-heated, with a result that the electrical insulating resin of winding  114  will be melted by the heat, thereby bringing about a short-circuited state. This results in a marked increase in electric current and concomitant lowering of the resistance value of the driving circuit  130 , with a resultant abnormally heated state due to a large current flowing in the inner circuit of electromotive compressor  100 . As a consequence of such abnormal heating, winding  114  of electromotive compressor  100  can be burned producing carbide soot which adheres to the surface of glass  106  of the fusite pin  104 , thereby bringing about a loss of electrical insulation between the fusite pin  104  and header  105 . 
     In the worst case, tracking develops on the surface of glass  106  causing the glass to soften and melt due to the heat generated by the passage of electric current, culminating in the blow-out of fusite pin  104  which is no longer able to withstand the inner pressure of electromotive compressor  100  in some cases. In order to cope with such a problem, it is conceivable to provide a fuse, for example, for the purpose of de-energizing driving circuit  130  prior to the possible blow-out of the fusite pin. In such case, there is also a concern that the arc that is generated in connection with the melting of the fuse could ignite the gas in the electromotive compressor  100 , thereby causing a possible explosion. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a motor protector which solves the problem of the prior art described above. Another object of the invention is the provision of a motor protector which is capable of ultimately avoiding a dangerous situation even in the case where the contacts of a motor protector weld. Yet another object of the invention is the provision of a motor protector which is capable of preventing any possible adverse affect of an arc, generated when the driving circuit has been interrupted, on the various environments of the electromotive compressor. 
     Briefly stated, a motor protector made in accordance with the invention comprises a casing that can be tightly sealed, a first switch provided inside the casing that carries out the switching of a movable contact in an electric path as a snap-acting disc snaps from one dished configuration to an opposite dished configuration in response to a selected level of electric current and the ambient temperature, and a second switch which is connected in series with the first switch inside of the casing and which opens the current path when it is melted by a predetermined overflow of electric current. 
     In cases where the contacts of the first switch melt and weld in the conductive state, a large electric current is generated. According to the invention, however, the second switch will melt, thereby de-energizing the motor. Therefore, it becomes possible to prevent the possible burning of the electromotive compressor of the sealed type and any damage from being inflicted on the sealing terminal of the protector, thereby making it possible to prevent the possible adhesive tracking of carbide to the vicinity of the sealing terminal. As a consequence of this, it becomes possible by means of the invention to prevent the possible melting of the glass portion as induced from the tracking phenomenon caused by the loss of electrical insulating characteristics of the glass seal and prevent any possible blow-out of the fusite pin caused by the loss of holding characteristic of the glass. Further, by means of the invention, there is no adverse affect on the various environments of the electromotive compressor of the sealed type by the arc generated upon melting of the second switch since the second switch is disposed in an air-tight casing. 
     According to a feature of the invention, a heater generates heat in dependence on the level of electric current that flows in the electric current path so that it is possible to elevate the atmospheric temperature inside the casing by the heat generated by the heater and to adjust the characteristics of the motor protector by suitably selecting the material of the heater and the temperature responsive characteristics. According to another feature of the invention, accurate adjustment of the characteristics of the protector is enhanced when the second switch also serves as a heater and when the first and second switches are connected via a connective member extending through the support member which serves as the heater. According to yet another feature of the invention, the heater can be used to satisfactorily generate heat by arranging the first and second switches to sandwich the support member, for example, thereby making it possible to easily adjust the characteristics as desired. The first switch can be supported on the support member and the second switch can be arranged on the opposite side of the support member relative to the first switch. According to an alternative feature of the invention, the second switch can be arranged on the same side of the support member as the first switch so that it becomes possible to easily maintain the distance between the second switch and the inner wall of the casing, thereby making it possible to expand design flexibility and, at the same time, to accurately prevent a possible short-circuiting after the melting. According to yet another feature, the second switch as described above, can have a meltable portion that has been formed by reducing the cross-sectional area forming a meltable part which has a large electric resistance which melts when a selected level of electric current flows therethrough. In this case, it becomes easily possible to form the meltable portion of the second switch by providing a notch cut on the sides of the plate member. In addition, the second switch can have a plurality of meltable parts formed at prescribed locations to obtain motor protectors of various characteristics, with different melting temperatures, with the meltable parts provided in conformity with the motor to be protected, as the melting characteristics will change when a plurality of meltable parts are provided. According to a feature of the invention, the second switch can be constructed employing a cylindrical member to easily prepare the second switch and minimize the cost of metal molds and materials and which allows having the meltable parts comprise fusing material being formed and cut at a desired location and, at the same time, to obtain motor protectors of various properties by changing the size of the electric current that flows to the meltable part. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, advantages and details of the novel and improved motor protector of the invention appear in the following detailed description of preferred embodiments of the invention, the detailed description referring to the drawings in which: 
     FIG.  1 ( a ) is a cross-sectional front elevational view showing the inner construction of a motor protector made in accordance with the first embodiment of the invention; 
     FIG.  1 ( b ) is a partial cross-sectional bottom plan view showing the inner construction of the FIG.  1 ( a ) motor protector; 
     FIG.  1 ( c ) is a cross-sectional view taken on line A—A of FIG.  1 ( b ); 
     FIG.  1 ( d ) is a schematic circuit diagram showing a motor driving circuit to which the invention applies and a motor protector made according to the first embodiment; 
     FIG.  2 ( a ) is a front elevational view showing a connective pin member fixed to the support member according to the first embodiment of the invention; 
     FIG.  2 ( b ) is a bottom plan view including a cross-section taken along line B—B in FIG.  2 ( a ); 
     FIG.  3 ( a ) is a front elevational view showing an example of the fuse terminal used in the first embodiment of this invention; 
     FIG.  3 ( b ) is a bottom plan view showing the FIG.  3 ( a ) fuse terminal; 
     FIG.  4 ( a ) is a cross-sectional front elevational view showing the inner construction of a motor protector according to a second embodiment of the invention; 
     FIG.  4 ( b ) is a cross-sectional top plan view showing the inner construction of the FIG.  4 ( a ) motor protector; 
     FIG.  4 ( c ) is a cross-sectional view taken along line B—B in FIG.  4 ( b ); 
     FIG.  5 ( a ) is a front elevational view showing a fuse terminal used in the second embodiment of the invention; 
     FIG.  5 ( b ) is a right side view of the FIG. 5 fuse terminal; 
     FIG.  6 ( a ) is a front elevational view showing another embodiment of a fuse terminal which can be used in the invention; 
     FIG.  6 ( b ) is a bottom plan view showing the FIG.  6 ( a ) fuse terminal; 
     FIG.  7 ( a ) is a front elevational view showing still another embodiment of a fuse terminal which can be used in the invention; 
     FIG.  7 ( b ) is a top plan view showing the FIG.  7 ( a ) fuse terminal; 
     FIG.  8 ( a ) is a partial cross-section showing still another embodiment of a fuse terminal which can be used in the invention; 
     FIG.  8 ( b ) is a partial cross-section showing still another embodiment of a fuse terminal which can be used in the invention; 
     FIG.  9 ( a ) is a cross-sectional front elevational view showing the inner construction of a motor protector according to the prior art; 
     FIG.  9 ( b ) is a cross-sectional top plan view of the FIG.  9 ( a ) motor protector; and 
     FIG.  9 ( c ) is a schematic circuit diagram of a motor driving circuit and motor protector made according to the prior art. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the motor protector made according to the invention will be explained in detail below with reference to the accompanying drawings. 
     With reference to FIGS.  1 ( a ) through  1 ( d ),  2 ( a ),  2 ( b ),  3 ( a ) and  3 ( b ), a motor protector  1  made in accordance with the first embodiment comprises a plate like support member  3  having opposed face surfaces lying in respective planes which also functions as a heater and is accordingly composed of a metal of high electrical resistance, such as iron. Support member  3  is disposed inside a tubular casing  2  of suitable material such as steel having an open end. At one end of support member  3 , a terminal pin  4 , made of a stainless steel pin having a core of copper, for example, is fixed for connection with external circuits. A header  5  made of a steel plate is installed, as by welding, at the open end of casing  2  in electrical engagement therewith. Terminal pin  4  extends outwardly beyond header  5  and has an opposite distal end disposed within casing  2 . The annular gap between terminal pin  4  and header  5  is sealed by means of a glass seal  6 . The outer part of glass seal  6  preferably is further covered by an epoxy pellet  7 . An inert gas may be introduced into casing  2  in order to set the dielectric value and the pressure of the atmosphere inside the casing  2  at a preselected value. 
     A connective pin member  12  preferably in the shape of a cylinder, made of stainless steel, to cite an example, extends through support member  3  approximately at its center, preferably extending beyond the planes in which the opposed face surfaces lie, as best shown in FIG.  2 ( b ). Connective pin member  12  is fixed to the inner wall of a cylindrically shaped aperture  3   a  that has been formed in the support member  3  by using suitable sealing material made of an electrically insulating material such as glass or ceramic, for example, thereby making it possible for connective pin member  12  and support member  3  to be electrically isolated from each other. To fixedly attach connective pin member  12  to support member  3 , a ring-shaped glass pellet and connective pin member  12  can be placed in hole  3   a  of support member  3  and heated to a temperature of 700 degrees centigrade, for example, while held in the described position. Cooling is then effected after melting of the glass pellets. In the described arrangement, the thermal expansion coefficient of connective pin member  12  is selected so that it is somewhat higher than the thermal expansion coefficient of support member  3 . 
     On one side or face surface (the lower side in FIG.  1 ( b )) of the support member  3 , a dished thermostatic disc such as bimetal disc  8  made of a plate formed by bonding layers of steel and copper, for example, is provided. In this case, a slug  9  is fixed at one of the ends of the bimetal disc  8  and, at the same time, this slug is fixed to the connective pin member  12 , thereby making it possible for the bimetal disc  8  to be supported in such a fashion as to snap between oppositely dished configurations. A movable contact  10  is fixed at a free distal end of bimetal disc  8 , i.e., at a location which is removed from slug  9  on the lower surface of the disc as seen in FIG.  1 ( b ). 
     A stationary contact  11  is mounted on the inner wall of casing  2  at a location aligned with movable contact  10  of bimetal disc  8  so that movable contact  10  can move into and out of electrical engagement with stationary contact  11  in conformity with the snap action of bimetal disc  8 . On the other face surface (the upper surface in FIG.  1 ( b )) of support member  3 , a longitudinally extending fuse terminal (second switch)  14  made of suitable fusing metal material of low resistance such as a copper alloy, for example, is provided. Terminal portions  14   a  and  14   c  are formed at opposite ends in the longitudinal direction as is shown in FIGS.  3 ( a ) and  3 ( b ), and a meltable portion  14   b  is integrally formed between terminal portions  14   a  and  14   c . Meltable portion  14   b  is formed to extend in an oblong configuration by pressing, for example, between terminal portion  14   a  and terminal portion  14   c , with the cross-sectional area being made smaller than the cross-sectional area of each of the terminal portions  14   a  and  14   c . One terminal portion  14   a of the fuse terminal  14  is fixed to connective pin member  12  mounted on support member  3  as shown in FIGS.  1 ( a ) and  1 ( b ) and, the other terminal portion  14   c  of fuse terminal  14  is fixed to one of the terminals of support member  3 , by welding, for example, in both cases. 
     In the motor protector made according to this embodiment, electric current flows from terminal pin  4  to fuse terminal  14  through support member  3  as shown in FIGS.  1 ( b ) and  1 ( d ) and, moreover, through connective terminal member  12 , through movable contact  10  of bimetal disc  8 , stationary contact  11  and casing  2 , by means of a series electrical current path. 
     In FIG.  1 ( d ), connective pin member  12 , on the electrical side of the casing  2 , is connected to the windings  51  (main winding  51  a and auxiliary winding  51   b ) of the rotor (not shown in the drawing) of the motor, for example, and on the electrical side of the terminal pin member  4 , is connected to an alternating current power source  52 , thereby connecting motor protector  1  in series with the driving circuit  30  of electromotive compressor  50 . It is mentioned in this connection that reference number  53  in FIG.  1 ( d ) indicates a capacitor used for motor starting purposes. 
     In a motor protector made according to this embodiment, if melting and welding develops between movable contact  10  of bimetal disc  8  and stationary contact  11 , a large electric current would be generated if coil  51  of electromotive compressor  50  becomes short-circuited. However, in such case, fuse terminal  14  will be destroyed by melting, the driving circuit  30  of the electromotive compressor  50  is shut off and electromotive compressor  50  is de-energized. Accordingly, damage to the electromotive compressor  50  and destruction of the sealed terminal and the like are prevented, thereby making it possible to avoid having adhesion of carbide to the vicinity of the sealed terminal. According to this embodiment, melting of the glass part induced from the tracking phenomenon that stems from loss of electrical insulative characteristics of the glass seal  6  is avoided along with the possible blow-out of the fusite pin due to an elevated pressure level inside the electromotive compressor  50 , thereby making it possible to ultimately avoid a dangerous state. Further, fuse terminal  14  is provided inside sealed casing  2  so that there is no adverse affect on the various environments of the electromotive compressor  50  by the arc that is generated when the fuse terminal  14  is melted and destroyed. Thus, motor protector  1  can be produced easily in a simple construction without drastically modifying the basic construction of conventional motor protectors (such as casing  2 , support member  3 , terminal pin  4 , bimetal disc  8 , and the like). Support member  3  which functions as a heater and fuse terminal  14  are connected in series in the current path, thereby making it possible for the atmospheric temperature inside the casing to increase by the heat generated by the heater, so that it becomes possible to adjust the characteristics of the motor protector in the optimal state by properly selecting the material of the heater and the temperature responsive characteristics. Bimetal disc  8  and fuse terminal  14  are connected via a connective pin member  12  that extends through but is electrically isolated from support member  3 , thereby making it possible for the heat to be fully generated by employing the heating function of support member  3  as a whole and to easily adjust the suitable characteristics. 
     FIGS.  4 ( a )- 4 ( c ),  5 ( a ) and  5 ( b ) show a motor protector and parts thereof made in accordance with a second embodiment of the invention. The following explanation will be given using the same reference characters for those parts that correspond to the previously described embodiment. As shown in FIGS.  4 ( a ) through  4 ( c ), motor protector  1 A made according to this embodiment is different from the first embodiment insofar as fuse terminal  15  is provided on the same side of support member  3  as bimetal disc  8 . As shown in FIGS.  5 ( a ) and  5 ( b ), fuse terminal  15  in this embodiment is made of the same material as fuse terminal  14  in the first above-described embodiment. It is formed in the shape of a discontinuous ring, with terminal portions  15   a  and  15   c  being provided at opposite ends thereof. One terminal portion  15   a  of fuse terminal  15  is fixed by means of welding or the like to terminal pin  4  and the other terminal portion  15   c  is fixed to slug  9  also by means of welding or the like, thereby serially connecting fuse terminal  15  to terminal pin  4  and bimetal disc  4 . A meltable portion  15   b  is formed by reducing the cross-sectional area of its center to such an extent that it is smaller than the cross-sectional area of the terminal portions  15   a  and  15   c.    
     In motor protector  1 A made according to this embodiment, a series electric current path is formed so that electric current flows from terminal pin  4  to fuse terminal  15 , bimetal disc  8 , movable contact  10 , stationary contact  11  and casing  2 . Support member  3  is used for the purpose of supporting bimetal disc  8  and is so constructed that bimetal disc  8  may be actuated by the heat generated by the fuse terminal  15  itself. According to this embodiment, it becomes possible to prevent the possible burning of electromotive compressor  50  and damage to the sealed terminal of the protector and the like as in the case of the above described embodiment, thereby making it possible to ultimately avoid a dangerous state. Fuse terminal  15  is provided on the same side of support member  3  as bimetal disc  8 , thereby making it possible to obtain sufficient distance vis-a-vis the inner wall of the casing  2 . Accordingly, there will be an increase in design flexibility and it becomes possible to prevent fuse terminal  15  from becoming short-circuited by contacting the inner wall of the casing  2  due to a deformation in connection with the melting process. Otherwise, the description is the same as in the case of the above embodiment. Accordingly, a repetition of the details will be omitted. 
     According to the invention, it becomes possible to suitably change the shape of the fuse terminal, that is, the second switch, in conformity with the motor to be protected, and the like, and the value of the calibrated electric current. Below, examples of a fuse terminal which can be used in the motor  30  protector of this invention will be explained by referring to FIGS.  6 ( a ) through  8 ( b ). 
     As shown in FIGS.  6 ( a ) and  6 ( b ), fuse terminal  141  in this embodiment can be formed by providing a notch cut on both sides between the terminal portions  141   a  and  141   c  at opposite ends, thereby making it possible for the cross-sectional area of the meltable portion  141  b to become smaller than the cross-sectional area of the terminal portions  141   a  and  141   c . Fuse terminal  141  of this embodiment makes is possible to easily carry out an adjustment of the electrical isolation distance to the casing after melting and the melting time as compared with the fuse terminal  14  shown in FIGS.  3 ( a ) and  3 ( b ). 
     It is also possible to provide a plurality (such as two) of meltable portions  142   b  whose form is the same as the meltable portion  141   b  of fuse terminal  14  between the terminal portions  142   a  and  142   c  as in the case of fuse terminal  142  shown in FIGS.  7 ( a ) and  7 ( b ). Melting takes place more easily than in the case of fuse terminal  141  in the above embodiment by providing a plurality of meltable portions  142   c . Accordingly, it becomes possible to obtain motor protectors of various properties with different melting temperatures by providing the meltable portions in conformity with the motor to be protected. 
     FIGS.  8 ( a ) and  8 ( b ) are partial cross-sectional views showing still other embodiments of the fuse terminal that can be used in this invention. Fuse terminals  143  and  144  in these embodiments are formed in a longitudinal form, with the terminal portions  143   a ,  144   a  and  143   c ,  144   c  at opposite ends being fixed to the respective terminal pin  4  and slug  9  by means of welding or the like. Fuse terminal  143  shown in FIG.  8 ( a ) is integrally formed by using fusion material which is the same as in the various examples described above. In this case, the center of the fuse terminal  143  becomes the meltable portion  143   b . Preparation is facilitated compared with the above-described fuse terminals  14 ,  15 ,  141  and  142 . This is more advantageous from the standpoint of cost of metal molds and materials used for the fuse terminal. In the case of the fuse terminal  144  shown in FIG.  8 ( b ), on the other hand, the meltable portion  144   b , made of the same fusing material as in the various examples described above, is fixed by welding or the like in such a manner as to be sandwiched by the terminal portions  144   a  and  144   c  which are made of material of low electrical resistance. According to fuse terminal  144  of this embodiment, it is possible to melt and separate at a desired location and to obtain motor protectors of various characteristics by changing the size of the electric current that flows to the melt portion  144   b.    
     The invention is not restricted to the forms of the above-mentioned embodiment and can be changed in various ways. For example, the fuse terminals which are shown in FIGS. 6 through 8 can be used in any of the forms of the above-mentioned first and second embodiments. In addition, it becomes possible to provide an electrically insulative part on the inner wall of the casing and on the surface of the backside support member, by way of example, to prevent short-circuiting by the fuse terminal that has been melted and separated. According to the invention described above, it becomes possible to offer a motor protector which is capable of ultimately avoiding a dangerous state even when melting and welding occurs between the contacts. According to the invention, moreover, it becomes possible to offer a motor protector which is capable of preventing any adverse affect upon the various environments of the electromotive compressor by the arc that is generated at the time of a de-energization of the driving circuit. 
     It will be understood that the invention includes all modifications and equivalents of the described embodiments falling within the scope of the appended claims.