Protective device for a hermetic motor-driven compressor

A protective device for a hermetic motor-driven compressor comprises a protective device main body and an insulating layer made of a heat-resisting insulating material having a heat-resisting temperature of 155.degree. C. or higher, wherein the insulating layer surrounds the main body.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an improvement in a current temperature 
sensitive type overload protective device to be mounted on a motor for a 
hermetic motor-driven compressor and an improvement in a method of 
attaching the same. 
2. Description of the Related Art 
There has been known a current/temperature sensitive type overload 
protective device (hereinafter, referred to a protective device) which is 
provided in the casing of a hermetic motor-driven compressor so as to 
electrically disconnect a motor for the compressor from a power source by 
sensing predetermined temperature values of the motor and a refrigerant 
gas as well as a predetermined value of overcurrent in a case that the 
hermetic motor-driven compressor is operated under a condition of 
overload. 
FIGS. 5 to 10 show examples of attaching a conventional protective device 
to a typical hermetic motor-driven compressor as disclosed in, for 
instance, Japanese Unexamined Utility Model Publication 175581/1981. A 
protective device 5 is placed in contact with the surface of a motor end 
coil 3 and is fixed thereto by means of a binding string 4. 
FIGS. 5, 6 and 8 show the examples that the protective device 5 is attached 
to the upper end portion of the motor end coil 3, and FIGS. 9 and 10 show 
the examples that the protective device 5 is attached to a side area of 
the motor end coil 3. 
FIG. 7 is an enlarged perspective view showing a conventional protective 
device 5 wherein the main body of the protective device 5 which is an 
electrically charged portion is covered by an insulating layer 6 of a hard 
film material such as polyester film. As shown in FIG. 5, the insulating 
layer 6 of a polyester film is wrapped around the protective device 5 in a 
cylindrical form with both ends being opened wherein overlapping portions 
are bonded. The length l.sub.1 in the axial direction of the cylindrically 
formed insulating layer 6 is generally 1.5 -2 times as long as the length 
l.sub.0 of the protective device 5 in order to keep a sufficient distance 
of the space for electric insulation. 
Since the insulating layer 6 is hardly deformed when it is attached to the 
motor end coil 3, the dimension of l.sub.1 is necessary. 
Since hermetic motor-driven compressors are generally of a small size, it 
was difficult to attach a protective 
Further, there was a problem that since the protective device 5 was placed 
near a portion where an upper casing 1 and a lower casing 2 were welded 
together to form a hermetic casing, a polyester film used generally as an 
insulating layer 6 for the protective device 5 was easily molten by heat 
of radiation at the time of welding to thereby lose the function of 
insulation. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a protective device 
having an insulating layer excellent in heat resistance and facilitating 
attachment to a motor end coil. 
In accordance with the present invention, there is provided a protective 
device for a hermetic motor-driven compressor which comprises a protective 
device main body and an insulating layer made of a heat-resisting 
insulating material having a heat-resisting temperature of 155.degree. C. 
or higher, wherein the insulating layer surrounds the main body.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
An embodiment of the protective device for a hermetic motor-driven 
compressor of the present invention will be described with reference to 
FIGS. 1 to 4 wherein the same reference numerals as in FIGS. 5 to 10 
designate the same parts. 
A protective device 5 which is the subject to be protected is in contact 
with the surface of a motor end coil 3 and is fixed thereto by means of a 
binding string 4. 
FIG. 3 shows the protective device 5 according to the present invention. 
The main body constituting an electrically charged portion of the 
protective device 5 is covered by an insulating layer 6. A sheet of 
aromatic polyamide (an aramid sheet) is used as the insulating layer 6. 
The insulating layer is formed into a cylindrical shape. Both end portions 
of the cylindrically shaped insulating layer 6 are respectively closed to 
be in a form of a bag so that the protective device 5 is entirely 
surrounded in it. The closed end portions 8a, 8b are melt-welded by 
applying ultrasonic waves. As shown in FIG. 1, the protective device 5 
having its dimension l.sub.0 in the longitudinal direction is attached to 
the motor end coil 3. In this case, the insulating layer 6 can be easily 
deformed by winding the binding string 4 around the motor end coil 3 so 
that the dimension l.sub.2 of the insulating layer 6 can be substantially 
the same as the dimension l.sub.0 of the protective device 5. 
In the above-mentioned embodiment, the aramide sheet is used as a material 
for the insulating layer 6. However, another material may be used so long 
as the materials has a heat resistance property of 155.degree. C. or 
higher. For instance, a sheet of polyimide resin may be used. 
Thus, in accordance with the present invention, the protective device main 
body is surrounded by the insulating layer made of a heat resisting 
material having a heat resisting temperature of 155.degree. C or higher. 
Accordingly, the insulating layer can withstand heat of radiation when a 
hermetic casing is prepared by welding. 
Further, the aramid sheet is used for the insulating layer and both ends of 
the insulating layer are respectively melt-bonded by ultrasonic waves to 
have a shape of bag. Accordingly, it is unnecessary to use an adhesive and 
therefore the protective device of the present invention is not chemically 
attacked even when it is used in an atmosphere of refrigerant.