Thermal protector for hermetic electrically-driven compressors

A thermal protector for a hermetic electrically-driven compressor including a hermetically sealed housing in which a power-supply terminal, an electric motor and a compressor are enclosed with a predetermined amount of refrigerant gas is disclosed. The thermal protector includes a thermally responsive switch having first and second lead terminal pins for securing first and second connecting terminals respectively and a holder formed from an electrically insulating material and including first, second and third cavities. Each of the first and second cavities has an opening in its one side. The first cavity accommodates the thermally responsive switch while the second cavity accommodates a secured portion between the lead terminal and the connecting terminal with a hardenable electrically insulating filler filling up the second cavity. Alternatively, the second connecting terminal is secured to a wall of the holder by an insert molding so as to extend through the wall, instead of use of the filler.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a thermal protector protecting, against an 
overcurrent and/or an overheat, an electric motor enclosed in a 
hermetically sealed housing of an electrically-driven compressor, the 
housing further enclosing a compressing means and a predetermined amount 
of refrigerant gas, and more particularly to such a thermal protector of 
the type that it is disposed in the compressor housing. 
2. Description of the Prior Art 
Various types of thermal protectors comprising a bimetal or other thermally 
responsive switch elements driving a switch have conventionally been used 
for protecting an electric motor against an overheating condition due to 
overload in hermetic electrically-driven compressors. In one of the types, 
the thermal protector is disposed in a hermetically sealed housing of the 
compressor so that better heat exchange can be achieved between the 
thermally responsive switch and the motor or the refrigerant gas. In this 
type, the thermal protector is closely bound to coils of the motor with 
strings, as shown in FIGS. 1 and 2 of Japanese Unexamined Utility Model 
Application No. 55-87170. Furthermore, the thermal protector is mounted on 
an elastic member further mounted on an inner wall of the compressor 
housing, as shown in Japanese Unexamined Utility Model Application No. 
60-95183. 
Binding the thermal protector to the motor coils with the strings is not 
easy but rather troublesome. On the other hand, the mounting is rendered 
easier when the thermal protector is mounted on the elastic member in the 
compressor housing. In this case, however, the elastic member and other 
mounting parts need to be previously provided in the compressor housing. 
Furthermore, since an excessive space for insulation is required between 
the compressor housing and the motor windings, the compressor housing is 
rendered large-sized. 
In view of the above-described disadvantages, U.S. Pat. No. 4,791,329 
issued Dec. 13, 1988 discloses a motor protector to which terminals in the 
form of tabs or receptacles are secured. The protector is enclosed in a 
socket or mounted on an outer face of the socket. Then, the terminals of 
the motor protector are directly connected to terminal pins of a 
glass-insulated power-supply terminal disposed in the compressor housing. 
The above-described motor protector is large in size although it is of a 
so-called plug-in type. Furthermore, its attachment to and detachment from 
the power supply terminal are not so easy as to be expected. Additionally, 
the manufacturing cost of the above motor protector is relatively high. In 
the above mounting structure, however, a force caused by vibration or the 
like during operation of the compressor acts on a secured portion between 
the protector and each terminal. Consequently, the secured portion between 
the protector and each terminal is distorted or bent. Thus, reliability in 
the mechanical strength of the secured portion is low. 
SUMMARY OF THE INVENTION 
Therefore, an object of the present invention is to provide an improved 
thermal protector wherein the mechanical strength of a portion of the 
protector connected to a power-supply terminal disposed in a hermetically 
sealed housing of a hermetic compressor can be improved. 
Another object of the invention is to provide an improved thermal protector 
wherein a space for insulation between the thermally responsive switch and 
conductive parts or portions around it can be reduced. 
In one aspect, the present invention provides a thermal protector for a 
hermetic electrically-driven compressor including a hermetically sealed 
housing in which a power-supply terminal is disposed and an electric motor 
and in which a compressor are enclosed with a predetermined amount of 
refrigerant gas. The thermal protector comprises a thermally responsive 
switch disposed in the housing of the compressor and including a metal 
casing accommodating therein a thermally responsive element and at least a 
pair of non-flexible lead terminals secured to the casing. A first 
non-flexible connecting terminal has one end connected to one of the lead 
terminals and the other end connected to the power-supply terminal. A 
second non-flexible lead terminal has an end connected to the other lead 
terminal. A holder is formed from an electrically insulating material and 
including a first cavity accommodating the casing of the thermally 
responsive switch, a second cavity adjacent to the first cavity in a 
communicating relation therewith and accommodating connected portions 
between the lead terminals and the first and second connecting terminals 
respectively, and a third cavity adjacent to the second cavity with a 
partition wall being provided therebetween, the other end of the first 
connecting terminal being fitted in the third cavity so as to be held 
therein. The cavities are open at one side of the holder. A hardenable 
electrically insulating filler is provided for filling a space defined by 
the inner peripheral face of the second cavity and a side of the casing 
facing the interior of the second cavity so that the connected portions 
between the lead terminals and the first and second connecting terminals 
are buried in the filler and so that the filler comes into contact with 
the side of the casing such that the casing, the lead terminals and the 
connecting terminals are integrally combined together by the filler 
hardened so as to be stationary relative to one another. 
According to the above-described construction, the secured portion between 
the lead terminal and the connecting terminal of the thermally responsive 
switch is fixed integrally to the holder by the electrically insulating 
filler in the second cavity. Transfer of vibration from the compressor to 
the thermally responsive switch is blocked at the secured portion. 
Consequently, distortion or bend of the secured portion due to the 
vibration can be prevented. 
Furthermore, since the thermally responsive switch is accommodated in the 
holder formed from the electrically insulating material, the space for 
insulation between the thermally responsive switch and the conductive 
parts or portions around it, such as the motor, can be reduced, which can 
enhance reduction in size of the compressor housing. 
Furthermore, in the condition that the connecting terminals are held on the 
power-supply terminal of the compressor by way of fitting or the like, the 
connecting terminal is reinforced when it is accommodated in the third 
cavity. Consequently, deformation of the connecting terminal due to the 
self-weight of the protector can be prevented. In another aspect of the 
present invention, the first non-flexible connecting terminal has one end 
located in the second cavity of the holder so that this end is exposed, 
the other end connected to the power-supply terminal and fitted in the 
third cavity of the holder so that this other end is held therein, and an 
intermediate fitted portion which is fitted with a wall constituting the 
holder. The second non-flexible connecting terminal has one end located in 
the second cavity of the holder so that this one end is exposed, the other 
end projecting out of the holder, and an intermediate portion extending 
through a wall of the holder defining the second cavity to be held in 
position by way of an insert molding. The lead terminals of the thermally 
responsive switch are welded to one end of the first connecting terminal 
in the second cavity and to one end of the second connecting terminal in 
the second cavity respectively under the condition that the casing is 
accommodated in the first cavity of the holder so that connection between 
the lead terminal and the second connecting terminal provides 
substantially integral connection between the casing of the thermally 
responsive switch and the holder. 
In a first preferred form, a member is provided in the first cavity of the 
holder for defining a gap between an inner peripheral face of the first 
cavity and an outer peripheral face of the casing of the thermally 
responsive switch, so that the refrigerant gas flows through the gap. 
In a second preferred form, one of the lead terminals comprises a part of 
the casing of the thermally responsive switch. 
In a third preferred form, the first cavity of the holder is open over two 
sides of the holder adjacent to each other.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A first embodiment of the present invention will be described with 
reference to FIGS. 1 to 6. Referring to FIG. 1, a hermetic 
electrically-driven compressor 1 comprises a hermetically sealed 
high-pressure housing 3 including a top cover 2A on which a thermal 
protector 11 of the first embodiment is mounted so as to be located in the 
housing 3, and a receptacle 2B. The housing 3 encloses therein a 
conventional electric motor 4 and a conventional compressing means 5 
driven by the motor 4. A suction pipe 6 extends through a lower peripheral 
wall of the housing 3 and is then connected to the compressing means 5 so 
that refrigerant gas delivered from an external heat exchanger (not shown) 
is introduced into the interior of the compressor housing 3. The 
refrigerant gas compressed by the compressing means 5 is discharged into 
the compressor housing 3, flowing along the periphery of the motor 4. The 
refrigerant gas is then circulated into the heat exchanger through a 
discharge pipe 7 extending through the cover 2A. A glass-insulated 
power-supply terminal 8 air-tightly extends through the cover 2B of the 
compressor housing 3 and is then secured in position by way of welding. 
The power-supply terminal 8 includes three electrically conductive pins 8A, 
8B and 8C. Three connecting tab terminals 8D are mounted on ends of the 
conductive pins 8A, 8B, 8C located in the compressor housing 3 
respectively, as shown in FIGS. 2 and 3. Lead wires 10 extending from 
windings of the motor 4 are connected to the conductive pins 8B, 8C 
respectively. The thermal protector 11 is connected to the other 
conductive pin 8A. 
The thermal protector 11 will now be described with reference to FIGS. 3 to 
6. The thermal protector 11 comprises a thermally responsive switch 12 and 
an electrically insulating holder 13 accommodating the thermally 
responsive switch 12, as shown in FIG. 5. The thermally responsive switch 
12 comprises a hermetically sealed metal casing 12D and a bimetallic 
thermally responsive element (not shown) enclosed in the casing 12D, as 
well known in the art. The structure of such a thermally responsive 
element is disclosed in U.S. Pat. No. 5,015,985, for example. 
The thermally responsive switch 12 has two lead terminal pins 12A and 12B 
each extending through a wall of the casing 12D and air-tightly fixed in 
position by a sealing material 12C such as glass or ceramic. Two 
connecting terminals 14A and 14B are connected to the respective lead 
terminal pins 12A, 12B by way of welding or the like. The connecting 
terminals 14A, 14B are to be further connected to the conductive pin 8A of 
the power-supply terminal 8 and a receptacle (not shown) connected to the 
lead wire 10 from the motor 4 respectively. 
The holder 13 is generally formed into the shape of a box and has an 
opening 13E in one side. An inner space of the holder 13 is partitioned by 
a rib 13A into a main accommodating section 13B or first cavity and a 
terminal accommodating section 13C or second cavity. The body of the 
thermally responsive switch 12 is enclosed in the main accommodating 
section 13B while the terminal pins 12A, 12B of the thermally responsive 
switch 12 are accommodated in the terminal accommodating section 13C. A 
terminal holding section 13D or third cavity having upper and lower open 
ends is provided to be adjacent to the terminal accommodating section 13C. 
The connecting terminals 14A, 14B are secured to the respective lead 
terminal pins 12A, 12B by welding. Thereafter, a distal end of the 
connecting terminal 14A is inserted into the terminal holding section 13D. 
Simultaneously, the casing 12D of the thermally responsive switch 12 is 
accommodated in the main accommodating section 13B and secured portion 
between the lead terminal pins 12A, 12B and the connecting terminals 14A, 
14B respectively are accommodated in the terminal accommodating section 
13C. A pushing protrusion 13F is formed on the inner wall of the main 
accommodating section 13B of the holder 13. One end face of the casing of 
the thermally responsive switch 12 accommodated in the main accommodating 
section 13B is pushed against the rib 13A by the protrusion 13F, whereupon 
the thermally responsive switch 12 is temporarily held by the holder 13 in 
the condition that a gap is defined between the inner peripheral face of 
the main accommodating section 13B and the outer periphery of the casing 
12D of the thermally responsive switch 12. In this condition, a 
predetermined amount of liquid electrically insulating filler 15 such as a 
mixture of an epoxy resin and a hardening agent is poured into the 
terminal accommodating section 13C so that the secured portions between 
the lead terminal pins 12A, 12B and the connecting terminals 14A, 14B 
respectively are covered by the filler 15. The filler 15 is hardened so 
that the thermally responsive switch 12 is fixed to the holder 13 as shown 
in FIGS. 4 and 6. The thermally responsive switch 12 thus accommodated in 
and fixed to the holder 13 is efficiently brought into contact with the 
refrigerant gas in the compressor housing 3 via the opening 13E of the 
holder 13, whereupon heat exchange is performed between the thermally 
responsive switch 12 and the refrigerant gas. 
The electrically insulating filler 15 serving as an integrating member may 
be poured into the main accommodating section 13B accommodating the 
thermally responsive switch 12 in the present invention. In the 
embodiment, however, the end face of the housing 12D of the thermally 
responsive switch 12 is caused to come into close contact with the rib 13A 
so that the filler 15 is prevented from flowing into the main 
accommodating section 13B. Accordingly, an amount of filler 15 used can be 
saved. Furthermore, since the refrigerant gas flows through a space around 
the thermally responsive switch 12 in the main accommodating section 13B, 
and through the gap around the casing 12D, the efficiency of heat exchange 
can be improved, which results in improvement in the thermal 
responsiveness of the thermally responsive switch to the heating due to an 
overheating condition of the motor or an abnormal condition of the 
compressing means. The heat exchange efficiency can be further improved 
when a plurality of through holes 13G are formed in side walls of the main 
accommodating section 13B of the holder 13 as shown as a second embodiment 
in FIG. 7. 
Referring to FIG. 8 showing a third embodiment, a thin plate portion 13A1 
may be provided to be opposite to the rib 13A in order that the thermally 
responsive switch 12 comes into more close contact with the holder 13. The 
thin plate portion 13A1 is caused to elastically come into contact with 
the thermally responsive switch 12 or an elastic material such as a 
silicon rubber may be provided instead of the thin plate portion 13A1 so 
that the insulating filler 15 poured into the terminal accommodating 
section 13C can be prevented from flowing into the main accommodating 
section 13B. Furthermore, the holder 13 may be formed from a material with 
sufficient elasticity. 
According to the above-described construction, the secured portions between 
the lead terminal pins 12A, 12B and the connecting terminals 14A, 14B 
respectively are accommodated in the terminal accommodating section 13C 
into which the hardenable electrically insulating filler 15 is then poured 
so that the secured portions are fixed in the section 13C. A force caused 
by the vibration of the compressor motor and resulting in distortion and 
bending is not transferred to the secured portions though the thermally 
responsive switch 12 which is held on the power-supply terminal 8 further 
held in the hermetically sealed housing 3 of the compressor 1. 
Consequently, the connecting terminals 14A, 14B can be prevented from 
dropping out of the thermally responsive switch 12. Furthermore, the 
above-described construction can reduce vibrational stress imposed on the 
sealing material 12C, such as glass or ceramic, holding the lead terminal 
pins 12A, 12B of the thermally responsive switch 12. Consequently, the 
thermally responsive switch 12 can be prevented from damage in the 
air-tightness thereof due to occurrence of a crack in the sealing material 
12C. 
The thermal protector 11 is held by a single connecting terminal 14A on the 
power-supply terminal 8 of the compressor 1. Accordingly, there is a 
possibility that a portion of the connecting terminal 14A or particularly, 
a bent portion 14A1 thereof may be deformed or broken when a force due to 
the self-weight of the thermal protector 11 subjected to the vibration of 
the compressor concentrates upon the portion of the connecting terminal 
14A. In the above-described construction, however, the connecting terminal 
14A is holding in the terminal accommodating section 13D of the holder 13, 
so that the connecting terminal 14A is reinforced so as not to be moved. 
Consequently, the bent portion 14A1 of the connecting terminal 14A can be 
prevented from being deformed or broken. 
Since the thermally responsive switch 12 is accommodated in the 
electrically insulating holder 13, the space for insulation can be reduced 
between the thermally responsive switch 12 and electrically conductive 
parts or portions around it. Furthermore, since the lead terminal pins 
12A, 12B and the connecting terminals 14A, 14B are embedded in the 
electrically insulating filler 15, the space for insulation between the 
terminals can be reduced, which enhances miniaturization of the thermal 
protector. 
FIGS. 9 to 16 describe a fourth embodiment of the invention. Since the heat 
capacity of the insulating filler 15 employed in the foregoing embodiments 
is relatively large, the heat generated by the thermally responsive switch 
12 is transferred to the holder 13. Consequently, a quick response of the 
thermally responsive switch 12 may not be expected. The fourth embodiment 
is directed to an improvement of this drawback. As shown in FIGS. 13, 14 
and 16, the holder 20 includes a main accommodating section 20G or first 
cavity, a terminal accommodating section 20K or second cavity and a 
terminal holding section 20B or third cavity. In the main accommodating 
section 20G, the upper face and one of side faces adjacent to the upper 
face are open. In particular, the second cavity 20K is located between 
positioning portions 20J provided in the first cavity 20G for positioning 
the casing of the thermally responsive switch 12 and the third cavity 20B 
and is contiguous to the first cavity 20G. The connecting terminal 21 is 
previously fixed on a terminal fixing section 20A by way of an insert 
molding. The terminal fixing section 20A is a part of a wall defining the 
second cavity 20K. In the fourth embodiment, the terminal fixing section 
20A thus serves as the integrating member. Both ends 21A and 21B of the 
connecting terminal 21 are exposed from the holder 20 for the purpose of 
electrical connection. The connecting terminal 22 is holding in the 
terminal accommodating section 20B. A bent portion 22A of the connecting 
terminal 22 is fitted with an upper portion of a wall 20C of the terminal 
holding section 20B as shown in FIG. 11. In this condition, a shoulder 22B 
of the connecting terminal 22 is elastically engaged with a stepped 
portion 20D formed on the inner wall of the terminal holding section 20B, 
whereby the connecting terminal 22 is held by the holder 20. A shelf 20E 
is provided for positioning an end of the connecting terminal 22 at the 
side of its welded zone 22C, as will be described later. 
Referring to FIGS. 10 and 12, the ends of the connecting terminals 21, 22 
located in the second cavity 20K of the holder 20 have weld zones 21A, 22C 
to which the lead terminal pins 12A, 12B are secured by welding, 
respectively. Through holes 20F are formed in the wall of the second 
cavity 20K of the holder 20 so as to correspond the respective weld zones. 
One of welding electrodes is inserted through each of the through holes 
20F. 
The thermally responsive switch 12 is accommodated in the main 
accommodating section 20G of the holder 20, as shown in FIGS. 10, 11 and 
14. The thermally responsive switch 12 is then positioned by the rib 20H 
and the positioning portions 20J. Thereafter, the lead terminal pins 12A, 
12B are welded to the weld zones 21A, 22C of the connecting terminals 21, 
22 previously fixed to the holder 20 respectively, whereby the thermally 
responsive switch 12 is fixed to the holder 20. The rib 20H provides a gap 
between the outer face of the casing 12D and the inner bottom face of the 
main accommodating section 20G of the holder 20 in the condition that the 
thermally responsive switch 12 is accommodated in the main accommodating 
section 20G. The gap permits the refrigerant gas to pass therethrough. In 
the welding, one of the welding electrodes is brought into contact with 
the lead terminal pin 12A or 12B from above as viewed in FIG. 12 while the 
other welding electrode is inserted through the through hole 20F from 
below and brought into contact with the underside of the welding zone 21A 
or 22C of the connecting terminal 21 or 22, so that an electric resistance 
welding is performed. In the fourth embodiment, particularly, an 
insulating material 23 such as an adhesive or resin is applied to a part 
of the wall of the thermally responsive switch near the lead terminal pins 
12A, 12B extending from the part for improvement in the withstand voltage 
between the lead terminal pin and the metal housing of the thermally 
responsive switch, as shown in FIGS. 11 and 14. Alternatively, a 
pelletized insulating material 23 is melted and hardened so that the 
insulation distance is increased between each of the lead terminal pins 
and the metal housing of the thermally responsive switch. 
Mounting the thermal protector 24 in the hermetic compressor 1 will now be 
described. The tab 8D of the conductive terminal pin 8A of the 
power-supply terminal 8 of the compressor 1 shown in FIG. 9 is inserted 
into the connecting terminal 22 of the thermal protector 24. The other 
connecting terminal 21 of the thermal protector 24 is connected to a 
receptacle (not shown) mounted on the distal end of one of the lead wires 
10 extending from the windings of the motor 4 shown in FIG. 1. Thus, the 
connection and fixing of the thermal protector 24 are completed. 
Upon operation of the compressor, a torsional or bending force caused by 
the vibration of the compressor is conventionally applied to the lead 
terminal pin of the thermal protector via the lead wires from the 
compressor motor or the power-supply terminal. In the fourth embodiment, 
however, the middle portion of the connecting terminal 21 is fixed to the 
holder 20 by way of the insert molding. Furthermore, the bent portion 22A 
of the connecting terminal 22 is elastically fitted with the wall 20C of 
the holder 20. Accordingly, the force caused by the vibration of the 
compressor is received by the whole holder 20. Thus, the force does not 
concentrate upon the secured or welded portions between the respective 
connecting terminals and the thermally responsive switch. Consequently, 
the secured portions can be prevented from being deformed or damaged. 
Furthermore, since the connecting portion between the connecting terminal 
22 and the power-supply terminal 8 is held by the terminal holding 
sections 20B, deflection and distortion of the connecting terminal 22 is 
limited, the connecting terminal 22 can be prevented from being deformed 
or damaged. 
A dome-shaped portion 12D1 of the housing 12D of the thermally responsive 
switch 12 is exposed around. The refrigerant gas in the compressor housing 
flows in direct contact with the thermally responsive switch 12, so that 
the thermal protector 24 can quickly respond to the change in the 
temperature of the refrigerant gas. Although the dome-shaped portion 12D1 
of the thermally responsive switch 12 is not electrically insulated, it is 
sufficiently distant from the cover 2A and the receptacle 2B of the 
compressor 1. Consequently, the dome-shaped portion 12D1 does not pose a 
problem of insulation. 
In the foregoing embodiments, each of the lead terminal pins 12A, 12B of 
the thermally responsive switch 12 is formed into the shape of a pin and 
extends through the wall of the switch housing to be fixed in position, 
electrically insulated from the housing wall. Alternatively, the switch 
housing itself may be used as a terminal. In this construction, one of the 
connecting terminals is welded to the switch housing. 
Although the present invention is applied to the electrically driven 
compressor comprising the hermetically sealed high-pressure housing in the 
foregoing embodiments, the invention may be applied to hermetically sealed 
low-pressure compressors. Furthermore, the types of the compressing means 
should not be limited to that described above. The invention can be 
applied to rotary, scroll and reciprocal compressing means. 
The foregoing disclosure and drawings are merely illustrative of the 
principles of the present invention and are not to be construed in a 
limiting sense. Various changes and modifications will become apparent to 
those of ordinary skill in the art. All such changes and modifications are 
seen to fall within the true spirit and scope of the invention as defined 
by the appended claims.