Hermetical type thermally responsive switch

In a hermetic type thermally responsive switch comprising a fixed contact support having a fixed contact at its end and cantilever disposed in a hermetically sealed vessel, a elongated support supporting a thermally responsive disk which has a movable contact and cantilever disposed in said vessel through a connecting means; said fixed contact support comprises laminated metallic sheets each having different elastic modulus, while a spacer means is interposed in electrically, thermally insulated relationship between said elongated support and said connecting means so as to calibrate the snap temperature of said disk.

BACKGROUND OF THE INVENTION 
(1) Field of the Art 
This invention relates to a thermally responsive switch having a thermally 
responsive element enclosed in a hermetically sealed vessel, said 
thermally responsive element being warped for snap action in response to 
ambient temperature. 
A thermally responsive switch of this type thus far introduced, comprises a 
fixed contact disposed in a hermetically sealed vessel and a movable 
contact secured to a thermally responsive disk disposed in said vessel, 
with the disk being of bi- or tri-metallic element. Said switch is, for 
example, embedded into the winding of an electric motor with the disk in 
series with the winding. At the time of overloaded condition, the disk 
snaps to separate the movable contact from the fixed contact so as to 
interrupt the motor circuit for protection in response to the temperature 
rise owing to abnormally increased current flowing through the motor. 
In so doing, said fixed contact support is in cantilever relationship with 
the vessel. Such is the construction that the fixed contact support has a 
tendency to bounce when the movable contact is brought into engagement 
with the fixed contact upon the moving-back action of the disk. The bounce 
thus induced allows both the contacts to be exposed to welding force 
caused by arcing. As a result, the contacts suffer from undesirably large 
quantity of consumption loss. 
Further, it is important to insure a short response time for the disk to 
snap when its temperature reaches a predetermined value in protecting 
appliances to be protected against overcurrency. 
In addition, it is necessary to maintain uniform response time in spite of 
having a means to adjust ultimate trip current value. 
SUMMARY OF THE INVENTION 
A first object of the invention is to provide a hermetic type thermally 
responsive switch which is compact and capable of preventing a fixed 
contact support from bouncing when a movable contact engages a fixed 
contact upon the moving-back action of a thermally responsive element. 
Accordingly, the invention provides a hermetic type thermally responsive 
switch which is capable of curbing welding force from being induced 
between contacts and eventually reducing consumption loss of the contacts. 
A second object of the invention is to provide a hermetic type thermally 
responsive switch which substantially maintains a short response time of 
its thermally responsive element in spite of having a means to adjust the 
ultimate trip current value. 
To achieve the first object, a fixed contact support placed in a hermetic 
vessel is comprised of composite laminated metallic sheets each having 
different elastic modulus. Such is the structure that the support is 
curbed from bouncing when the movable contact is brought into engagement 
with the fixed contact upon the moving-back action of the element. 
On the other hand, to achieve the second object, the thermally responsive 
switch carries a connecting means secured between a thermally responsive 
element and on elongated support supporting the element, and a space 
determiner secured between the connecting means and the support so as to 
adjust point pressure of the contacts which governs snap temperature of 
the element. The space determiner is constructed so as to thermally and 
electrically insulate between the connecting means and the support. Such 
is the configuration that the space determiner avoids current flowing 
through the connecting means from being bypassed. As a result, effective 
Joule heat is generated at the connecting means, while heat generated from 
the thermally responsive element is deterred from moving toward the 
support, so that the short responsive time of the element is maintained. 
Other and further objects, features and advantages of the invention will be 
apparent more fully from the following description.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIG. 1, a vessel designated by the numeral 1 is formed from an 
iron sheet by means of drawing to have open left end 1a as depicted, a 
circular lid plate 2 formed form, for example, an iron sheet by means of 
stamping is hermetically secured to the open end 1a by means of ring 
projection welding or the like. The lid plate 2 has aperture 2a to which 
an electrically conductive column-shaped terminal pin 4 is air-tightly 
secured in electrically insulated relationship with the plate 2 by means 
of glass sealant 3 or the like. The portion of the terminal pin 4 
positioned outside from the vessel 1 has a connector 9b adapted to be 
connected to power supply source or appliance to be protected. While the 
other portion of the pin 4 positioned inside of the vessel 1 has a fixed 
contact support 5 having a silver-alloy clad semi-spherical fixed contact 
5a at its end. Said support 5, as shown in FIG. 3, is comprised of a 
composite material, that is, three metal sheet layers unseparably 
laminated to each other, both the upper and lower layers 51, 53 are of 
iron: the middle layer 52 being of copper. In this situation, the lower 
part of said fixed contact 5a has projections 5b welded to the upper layer 
51 of the support 5. The portion of the lid plate 2 facing the interior of 
the vessel 1 has an L-shaped metallic support 8 cantilever mounted by 
means of welding or the like. To the free end of said support 8 is one end 
of a crank-shaped metallic connecting means 7 secured, the other end of 
which being secured to the peripheral end of a thermally responsive disk 
6. 
The disk 6 comprises bi- or tri-metallic element formed into centrally 
concave-shaped configuration, and has a movable contact 6a remote from the 
connecting means 7 so as to be in registeration with the fixed contact 5a. 
The disk 6 is adapted to warp with snap action from the solid line position 
to the dotted line position so as to separate the movable contact 6a from 
the fixed contact 5a at the temperature of, for example, 120.degree. C., 
and move back from said contact open position to the solid line contact 
closed position when the temperature falls to, for example, 80.degree. C. 
as seen in FIG. 1. Between the support 8 and the disk 6 is a space 
determiner 10 which comprises a screwed stud 10a and an insulator 10b 
fixed to the stud 10a. The stud 10a is driven into the screwed hole (not 
shown) formed in the free end of the disk 6, while the insulator 10b made 
from, for example, aluminous procelain engages with the end of the 
connecting means 7. 
In this situation, turning the stud 10a in one direction or another allows 
the width portion 7a of the means 7 to deform to different degrees for the 
reason that the insulator 10b pushes the connecting means 7 with different 
forces in magnitude, thus allowing the point pressure between contacts 5a, 
6a to change. This makes it possible to adjust the point pressure so as to 
ensure the snap action of the disk 6 upon calibrating the ultimate trip 
current value as described hereinafter in detail. 
Incidentally, it is noted if the stud 10a is made from an electrically 
insulating material, the insulator 10b may, of course, be eliminated. 
Reverting to the lid plate 2 of FIG. 1, another connector 9a is attached to 
the outer surface of the lid 2 by means of welding or the like. 
With the structure thus far described, it may be apparent that an operator 
should connect the switch in series with, for example, an electric motor, 
and at the same time, connectors 9a, 9b to a power supply source with the 
switch installed in thermally exchangeable relation to the winding of the 
motor. 
As a consequence, the current flows from the support 8 through the 
connecting means 7, the thermally responsive disk 6, the movable contact 
6a, the fixed contact 5a, and the fixed contact support 5 to the terminal 
pin 4, while the switch is subjected to the heat generated by the winding. 
In so doing, the temperature of the disk 6 rises due to the heat from the 
members noted above causing the disk 6 to snap to the dotted line contact 
open position so as to interrupt the motor circuit, thus protecting the 
winding of the motor against abnormal temperature rise. 
Note that the support 8 is secured to the lid plate 2, while the support 5 
is secured to the pin 4 as seen FIG. 1, but alternatively, the support 8 
may be secured to the pin 4, while the support 5 is secured to the lid 
plate 2. 
The thermally responsive disk 6, as stated hereinbefore, snaps and moves 
back at the predetermined temperatures, however, the movable contact 6a, 
may for short periods of time, bounce against the fixed contact 5a when 
the former engages the latter. 
General theory shows that usual contact closed condition unavoidably 
accompanies slight welding between the contacts owing to the intensive 
current flowing through microscopic projections presented on the surface 
of the contacts. Taking this theory into consideration, if the movable 
contact 6a bounces the contacts are subjected to additional welding 
because of the repeated arcing between the contacts and the intensive 
current flowing through the microscopic projections, thus resultantly 
increases consumption loss of contacts. 
Now, the dimension of the switch according to the embodiment is as follows: 
The switch is a little smaller than half the scale of the illustration, the 
fixed contact support 5 being 12 mm long, 4.5 mm wide with both the upper 
and lower layers 0.2 mm thick, the middle layer 52 being 0.4 mm thick. The 
contact 5a is 6 mm in diameter with the projecting 5b being 3.8 mm in 
diameter. The thermally responsive disk 6 is, as described hereinbefore, 
formed into central concave-shaped configuration by means of stamping from 
a bi-metallic sheet of 26 mm long, 14.5 mm wide and 0.25 mm thick. In the 
meanwhile, the point pressure exerting against the contact 5a from the 
contact 6a is substantially 100 gram, the magnitude of which being 
tantamount to slight displacement (about 0.1 mm) at the end of the support 
5. Apparently a larger quantity of the displacement than that occurs 
though, when the disk 6 moves back to bring the contact 6a into engagement 
with the contact 5a, however, the allowable maximum displacement is 
previously designed to be within elastic limit of the support 5. When the 
engagement between the contacts occurs, the support 5 is allowed to 
resiliently deflect, although extremely slightly, in timed relationship 
with the moving-back action of the disk 6 to alleviate the impact between 
said contacts. 
The following is the method of ascertaining whether the welding between 
contacts is present or not, 65 amp current is supplied to the switch 
through the connectors 9a, 9b from a constant current power supply with 
the switch installed in 25.degree. C. atmospheric temperature. 
And the contacts 5a, 6b are repeatedly on-off actuated in combination with 
the consecutive snap action of the disk 6. 
In so doing, the on-sustained and off-sustained times are counted to 
measure each deviation of both these times. The extent of the deviation, 
of course, depends upon the magnitude of welding. 
Actually the count of the on-sustained and off-sustained times is first 
begun after the disk 6 snaps and moves back 10 times to accommodate itself 
to the atmospheric temperature. 
Now, FIGS. 8 and 9 show the experimental results obtained from the above 
measurements in which FIG. 8 is for a thermally responsive switch in 
accordance with the invention of FIGS. 1 through 3, while FIG. 9 is for a 
prior art switch similar to this invention except for that a fixed contact 
support is made of a phosphor bronze piece. In FIGS. 8 and 9, axis of 
ordinates is on- and off-sustained times (sec) between the contacts 5a, 6a 
while axis of abscissa are on-off counted number between the same. 
Accordingly, curves represented by X1, Y1, of the graphic illustrations 
show the on-sustained time, while curves by X2, Y2 show the off-sustained 
time when the presently embodied switch and a prior art switch are 
respectively energized with low voltage (5 V) a.c. source. In the 
meanwhile, curves expressed by X3, Y3 show the on-sustained time, curves 
by X4, Y4 being off-sustained time when said switches are energized with 
high voltage (18 V) d.c. source. 
The following is the discussion of contact "bouncing phenomenon". 
As seen at X3, X4 of FIG. 8, the on-sustained time is within the boundary 
of 5-5.4 (sec), while the off-sustained time being within the boundary of 
30.3-30.5 (sec) with the on-off counted number from 10 to 20. 
Contrary to that, in the prior art in which a fixed contact support 
comprises phosphor bronze, the on-sustained time is within the boundary 
4.2-6.8 (sec), while off-sustained time being within the boundary of 
25.8-36.9 (sec) as seen at Y3, Y4 of FIG. 9 with the number of count from 
10 to 20. 
As readily understood from the foregoing description, the more extensive 
deviation is found within the boundary of 25.8-36.9 (sec) in the prior art 
compared to the present invention. 
Incidentally, a fixed contact support made from other material than 
phoshpor bronze, for example, iron metal sheet, shows an extensive 
deviation similar to that of the phosphor bronze as a result of the 
experiment. 
In the meanwhile, the observation of the on-off actuation between contacts 
through C.R.T. display shows that if a fixed contact support is made from 
composite material, the bouncing attenuates in shorter periods of time. If 
the phenomenon in which the bouncing is shortly attenuated is termed as 
anti-bounce effect for the sake of convenience, further investigation 
indicates that the anti-bounce effect involves in elastic modulus (Young's 
modulus), namely the anti-bounce effect is strengthened in line with the 
increase of difference between elastic modulus of the metallic layers. 
By way of example, the elastic modulus are 12,000 Kg/m.sup.2 for copper, 
21,000 Kg/m.sup.2 for iron and 1600 Kg/m.sup.2 for lead. 
If lead metal is employed for the support 5 instead of copper, the 
anti-bounce effect will be further enhanced due to the large difference 
between the elastic modulus. 
In this way, properly selective combination of materials renders more 
improved anti-bounce effect when no problem is compounded with electrical 
resistance and heat resistivity taken into account. 
Note that instead of three-laminated layer, two-laminated layer is, of 
course, effective in thwarting the bouncing, and further increased number 
of laminations will expectantly bear more advantageous effects in 
abstaining the bouncing. 
In addition, the layer may be of alloy, to say briefly, the anti-bounce 
effect is obtained so long as each of layers has different elastic 
modulus, so that the contacts are deterred from welding to each other. It 
is appreciated that so long as elastic modulus of one layer is 1.2-1.3 
times as large as that of another layer, a practical anti-bounce effect is 
obtained. 
Now, generally a thermally responsive switch has ultimate trip current 
value (referred to U T C hereinafter) and short time trip (referred to S/T 
hereinafter) as a characteristic required in protecting devices such as an 
electric motor. The S/T is an elapse time spent to actually open the 
contacts when the temperature reaches high enough to snap the disk 6 when 
the current a few times as intensive as the U T C is supplied. 
As is well known the U T C must be accorded with the rated load current of 
the motor. If the U T C is smaller than the rated load current, the 
operability of the motor reduces due to the frequently repeated warping 
action of the disk. To the contrary, if the U T C is, say 1.5 times higher 
than the rated load current, there is a hazard that the insulation of the 
winding deteriorates owing to the heat generated especially in case where 
the motor is in overloaded condition. 
In consequence, the U T C is determined within the boundary of 105-125 
percent of the rated load current. 
Secondly, when a loaded torque is applied to the motor, the rotor is in the 
locked condition, while current a few times as intensive as the rated 
current flows through the winding. In this situation, a prompt 
interruption of current supply is necessary to protect the winding against 
overheat. This involves the characteristic of the S/T of the thermally 
responsive switch. It is necessary to determine each dimension and 
resistance value of the assembly members of the switch in a bid to accord 
the U T C with the rated load current of the motor, while considering the 
mechanical strength of the members. To merely determine the U T C in a 
manner stated above is relatively easy. However, a short S/T is a 
requirement since the winding of the motor is vulnerable to overload 
current (at the time the rotor is locked). This signifies that to shorten 
the S/T without altering the U T C is desired. 
Investigation shows that a member providing high ratio of resistance to the 
total resistance (total resistance between the connectors 9a, 9b) must be 
a disk in obtaining a short S/T. Subsequently, it has been found that 
relatively high resistivity is required for the connecting means 7 so as 
not to release the heat of the disk 6 through thermal conduction. A 
connecting means of high resistivity effectively intercepts thermal 
transfer from the disk 6 to the support 8. In consequence, the resistivity 
of the means 7 depends upon the magnitude of the S/T. 
The measurement of the U T C is carried out as follows: A thermally 
responsive switch is placed in an atmosphere having a temperature of 60 
deg.C and allowed to adjust to that temperature. Then current is supplied 
to the switch through the connectors 9a, 9b. The current value is adapted 
to be intensified by one ampere per ten minutes, and read when contacts 
open. 
On the other hand, the measurement of the S/T is as follows: The same 
switch is placed into a constant temperature bath of 25.degree. C. to 
accommodate itself to the atmosphere. Then 60 ampere current is supplied 
to the switch through the connector 9a, 9b. 
And the time spent until the contacts open when energized, is counted. 
The specimens subjected to the measurement are as follows: One is a 
presently embodied switch seen in FIG. 1, another being a prior art switch 
similar to that except that a space determiner comprises a screw means 
made from brass metal. 
In the switch disclosed here, 2.5 (m.OMEGA.) is the totaled resistance in 
which 1.2 (m.OMEGA.) being for the disk 6; 0.3 (m.OMEGA.) each for the 
connecting means 7 and the supports 5, 8; 0.2 (m.OMEGA.) each for the 
terminal pin 4 and the contacts 5a, 6a including their point resistance. 
In the prior art switch, 2.5 (m.OMEGA.) is the totaled resistance in which 
1.2 (m.OMEGA.) being for a disk; 0.01 (m.OMEGA.) for a connecting means 
0.59 (m.OMEGA.) for an elongated support; 0.3 (m.OMEGA.) for a fixed 
contact support; 0.2 (m.OMEGA.) each for a terminal pin and contacts 
including their point resistance. The experimental results show that the U 
T C is 34.5 ampere and the S/T being 12 seconds for the switch presently 
embodied, while the former is 34.3 ampere; the latter being 16 seconds for 
the prior art switch. 
This signifies that the S/T is shortened by 25 percent compared with that 
of the prior art to effectively protect the motor against the hazardous 
temperature rise at the time of overloaded condition. 
The description thus far conducted is why high resistivity is required for 
a connecting means to obtain a short S/T among the totaled resistance 
between the connectors 9a, 9b. However, one of the objects of the 
invention resides in providing a structure which is capable of calibrating 
snap temperatures, while maintaining the advantage of the connecting means 
7. 
With the structure thus described, the gap adjustment between the support 8 
and the connecting means 7 by means of the space determiner 10, permits 
adjusting the temperature at which the movable contact 6a separates from 
the fixed contact 5a. In this situation, the connecting means 7 generates 
enough heat, while regulating thermal release from the disk 6 to the 
support 8 for the reason that the space determiner 10 is electrically, 
thermally insulated, and thus allows a short length of S/T with 
substantially uniform U T C. 
It is noted that instead of the space determiner 10 shown in FIG. 1, a 
space determiner may constructed as illustrated in FIG. 4. Thus, a 
wedge-shaped space determiner 15, made of insulating material such as a 
procelain or the like, is interposed between the connecting means 7 and 
the support 8, and said determiner 15 being horizontally slidable relative 
to support 8. A generally arcuate arm 16 is attached at its end to the 
support 8 by means of welding or the like and at its other end to the 
determiner 15. 
In FIG. 6, a column-shaped terminal pin 40 is attached to the aperture 2a 
by means of the glass sealant 3. 
To the exterior end of the pin 40 from the vessel 1 is a connector 90b spot 
welded at N1, while to the interior end of the pin 40 from the vessel 1 is 
a fixed contact support 50 spot welded at N2. Said terminal pin 40 is, as 
seen in FIG. 7, a composite metallic bar consisting of an outer cylinder 
40a and an inner column 40b, the cylinder 40a is made from nickel-ferrous 
alloy with nickel ingredient some ten percent while the column 40b being 
from copper, and said cylinder 40a and column 40b are tightly attached to 
each other by means of hot or cold roll. The glass sealant 3 is of 
soda-containing glass, for example, soda-lime glass, the terminal pin 40 
being of nickel ferrous alloy having thermal expansional coefficient 
smaller than that of the sealant 3. 
In this situation, the lid plate 2 is placed into a furnace of about 
1000.degree. C., so that the sealant 3 is sufficiently molten to present 
wetting condition between the pin 40, the sealant 3 and the aperture 2a. 
Lowering the lid plate 2 to the normal temperature allows hermetically 
sealed condition between said pin 40, the sealant 3 and the aperture 2a as 
is well known. In this condition, the sealant 3 air-tightly engages the 
terminal pin 40 by its strong contraction. For this reason, the pin 40 is 
somewhat smaller than the sealant 3 in coefficient of thermal expansion. 
To suffice the above requirement, the nickel ferrous alloy is most 
compatible for the terminal pin 40. 
However, the nickel ferrous alloy is 30-50 times greater than copper in 
electrical resistance, and generates heat when energized, which is not 
preferable. For the reason of curbing the heat thus generated from the 
alloy, the terminal pin 40 is made of so-called clad material, that is, 
copper metal clad by cylindrical nickel ferrous alloy as described 
hereinbefore. But, such clad material as nickel ferrous alloy generally 
has such bad machinability that multiple machining processes are needed, 
thus being prohibitively costly. Also, a lot of care must be taken to 
check on the air-tightness between the copper metal and the alloy on the 
production line. 
The present invention includes a provision of a novel mounting structure 
which obviates the above drawbacks; that is, a terminal pin is made of 
nickel ferrous alloy without using clad material, while maintaining the 
electrical resistances of the elements not more than the same level of the 
prior art while securing sufficient strength of the elements. For this 
purpose, the electrical resistance values of the mounting structure 
involving the terminal pin, is measured to discuss the measurements. 
By way of example, the dimensions and electrical resistance values 
involving the prior art terminal pin 40 are as follows: 1.6 (mm) in 
diameter is the central copper 40b; 3.2 (mm) in diameter is the nickel 
ferrous alloy 40a; 9 (mm) long is the distance between N1 (nugget portion) 
and N2 (nugget portion). While, 0.24 (m.OMEGA.) is the electrical 
resistance of the alloy between N1 and N2; 0.077 (m.OMEGA.) is the 
electrical resistance of the copper 4b between N1 and N2. The above 
measurements show that 0.24 (m.OMEGA.) of the alloy 40a is greater 
compared with 0.077 (m.OMEGA.) of the copper 4b, and 0.163 (m.OMEGA.) is 
the resistance from the portion N1 (N2) to the copper 40b through the 
thickness dimension of the alloy 40a. 
On the other hand, the mounting structure involving a terminal pin 
according to the invention, is on the basis of the following fact: In a 
thermally responsive switch of the sort, it has not been contemplated at 
all to, for example, weld the members to the ends of the pin by means of 
surface-to-surface contact since there is a risk that the hermetically 
sealed portion of the pin may be thermally damaged to lose air-tightness 
at the time of welding. However, experimental results show that if the 
diameter of the pin 4 is predetermined longer than the mounted portion of 
the pin 4 to the sealant 3, and the total length of the pin 4 is not more 
than twice as great as the diameter of the pin 4, the members such as a 
connector and a fixed contact support may be attached to both ends of the 
pin 4 by means of surface-to-surface contact. 
Dimensions and electrical resistances of the mounting structure of the 
terminal pin 4 are as follows: 3.5 (mm) long is the total length of the 
pin 4; 3.8 (mm) is the diameter of the pin 4. 0.22 (m.OMEGA.) is the 
electrical resistance between the mounting surface of the connector 9b and 
that of the fixed contact support 5 including their thickness seen FIG. 1. 
0.22 (m.OMEGA.) measured as above signifies the surface-to-surface contact 
is advantageous considering that the resistance of the above mounting 
surfaces are slight 0.04 (m.OMEGA.) since that of the pin 4 is 0.18 
(m.OMEGA.). In this situation, the connector 9b and the fixed contact 
support 5 are identical to those of the prior art in dimension and 
material. 
The invention thus far described provides an inexpensive and quality-wise 
switch because a costly clad material is eliminated with the amount of a 
nickel ferrous alloy reduced, while the elimination of the clad material 
is free from the air-tightness problem between a copper metal and a nickel 
ferrous alloy. The pin of relatively short length lessens the projecting 
length of the support 5 from the lid plate 2, thus permitting the vessel 1 
to be short in depth so as to be of compactness as a whole. 
By way of illustration in which a third terminal pin is added to FIG. 1 as 
described in FIG. 5 which depicts a third embodiment of the invention. In 
FIG. 5, a U-shaped filament 11 is attached at one end to the elongated 
support 8 and at other end to the lid plate 2, while another connector 9c 
is attached to the closed end of the vessel, and the support 8 being 
attached to a terminal pin 17. Said terminal pin 17 is secured to the 
aperture 2b by means of glass sealant 18 in the manner similar to the 
terminal pin 4. With the structure, across the connectors 9c and 9a, is 
the auxiliary winding of the motor connected, so that the disk 6 will snap 
promptly with the assist of the hot filament 10 at the time of abnormal 
conditions. 
Note that operation and other reference numerals of the parts are identical 
to FIG. 1, therefore the detailed description is omitted. 
It is to be understood that variations and modifications of the present 
invention may be made without departing from the scope thereof. It is also 
to be understood that the present invention is not to be limited by the 
specific embodiments disclosed herein but only in accordance with the 
appended claims when read in light of the foregoing specification.