Protective device for a hermetic motor-driven compressor

Abstract: A protective device for a hermetic motor-driven compressor comprises a protective device main body (5) and an insu­ lating layer (6), which is made of a heat-resisting insu­ lating material having a heat-resisting temperature of 155°C or higher, and entirely encloses the main body.

Description: 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. 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 the 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. Figures 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. Figures 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 Figures 9 and 10 show the examples that the protective device 5 is attached to a side area of the motor end coil 3. Figure 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 Figure 5, the insulating layer 6 of the 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 ₁ in the axial direction of the cylindrically formed insulating layer 6 is generally 1.5 - 2 times as long as the length ℓ 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 ₁ is necessary. Since hermetic motor-driven compressors are generally of a small size, it was difficult to attach a protective device 5 to a motor end coil 3 in assembling operations. 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. 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°C or higher and the insulating layer is formed from a cylindrically shaped insulating sheet into a bag to receive therein said main body and that opposing end portions of said insulating layer are melt-bonded by ultra-sonic welding. In the drawings: Figure 1 is a front view partly cross-sectioned of a hermetic motor-driven compressor on which a protective device according to the present invention is mounted; Figure 2 is an enlarged side view partly omitted which shows an example of attaching a protective device to a motor end coil; Figure 3 is enlarged front view showing the protective device; Figure 4 is a longitudinal cross-sectional view partly omitted of a hermetic motor-driven compressor on which the protective device according to the present invention is mounted; Figure 5 is a plane view partly cross-sectioned of a hermetic motor-driven compressor on which a conventional protective device is mounted; Figure 6 is an enlarged side view which shows an example of attaching a conventional protective device to a motor coil end; Figure 7 is an enlarged perspective view showing the conventional protective device; Figures 8 and 9 are respectively longitudinal cross-sectional views partly omitted of hermetic motor-driven compressor in which a conventional protective device is mounted; and Figure 10 is a partly enlarged view when viewed from the direction P in Figure 9. An embodiment of the protective device for a hermetic motor-driven compressor of the present invention will be described with reference to Figures 1 to 4 wherein the same reference numerals as in Figures 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. Figure 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 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 Figure 1, the protective device 5 having its dimension ℓ₀ 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 ℓ₂ of the insulating layer 6 can be substantially the same as the dimension ℓ₀ 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°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°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.

Claims: A protective device for a hermetic motor-driven compressor which comprises a protective device main body (5) and an insulating layer (6) made of a heat-resisting insulating material, characterized in that said insulating material has a heat-resisting temperature of 155°C or higher, that said insulating layer (6) is formed from a cylindrically shaped insulating sheet into a bag to receive therein said main body (5) and that opposing end portions (8a, 8b) of said insulating layer (6) are melt-bonded by ultra-sonic welding. The protective device according to claim 1, characterized in that said insulating layer (6) is an aromatic polyamide sheet.

Inventors: MURAMATSU SHIGERU, YAMADA HIDEHIKO, MURAMATSU, SHIGERU, YAMADA, HIDEHIKO
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1989
Main classification: H02K11
IPC codes: F04C29, H02K11, F04B39