EP3825388B1

EP3825388B1 - Hermetic refrigerant compressor and freezing/refrigerating apparatus using same

Info

Publication number: EP3825388B1
Application number: EP19837799.6A
Authority: EP
Inventors: Masanobu Gondo; Hirotaka Kawabata; Hiroto Hayashi
Original assignee: Panasonic Appliances Refrigeration Devices Singapore Pte Ltd
Current assignee: Panasonic Appliances Refrigeration Devices Singapore Pte Ltd
Priority date: 2018-07-20
Filing date: 2019-07-02
Publication date: 2023-11-15
Anticipated expiration: 2039-07-02
Also published as: JP2021080925A; EP3825388A1; CN115614253A; CN112639061A; WO2020017319A1; JPWO2020017319A1; JP6922109B2; EP4303441A2; JP7307065B2; CN112639061B; EP3825388A4; EP4303441A3

Description

Technical Field

The present invention relates to a hermetic refrigerant compressor for use in, for example, a refrigerator or an air conditioner and also to a refrigerator-freezer using the hermetic refrigerant compressor.

Background Art

In recent years, from the viewpoint of global environment conservation, the development of a high-efficient hermetic refrigerant compressor that uses less fossil fuels has been conducted. For example, in order to realize high efficiency, it has been proposed to form various films on sliding surfaces of slide members included in the hermetic refrigerant compressor, and to use lubricating oil having a reduced viscosity.
The hermetic refrigerant compressor includes a sealed container in which the lubricating oil is stored. The sealed container also accommodates an electric element and a compression element. The compression element includes, as the slide members, for example, a crank shaft, a piston, and a connecting rod serving as a coupler. A main shaft of the crank shaft and a main bearing, the piston and a bore, a piston pin and the connecting rod, and an eccentric shaft of the crank shaft and the connecting rod, etc., form slide parts with each other.
For example, Patent Literature 1 discloses a reciprocating compressor (hermetic refrigerant compressor) using lubricating oil having a low viscosity. The reciprocating compressor is configured such that, among the slide members, the piston and the connecting rod are each made of a ferrous sintered material and are steam-treated, and then a steam layer is removed from the surface of the piston by cutting, whereas the connecting rod is subjected to nitriding after being steam-treated. In Patent Literature 1, the lubricating oil used in the reciprocating compressor thus configured has a kinematic viscosity in the range of 3 mm²/S to 10 mm²/S at 40°C. Patent Literature 2 discloses a refrigeration apparatus including a hermetic sealed compressor with a lubricating oil that has a kinematic viscosity of 0.1 - 5.1 mm²/s at 40°C.
If the lubricating oil has a low viscosity, an oil film is not easily formed. In this respect, in the hermetic refrigerant compressor disclosed by Patent Literature 1, the surfaces of the slide members forming the slide parts are subjected to special treatment so that even with the use of the lubricating oil having a low viscosity, wear or seizing of the piston and the connecting rod will be prevented.

Citation List

Patent Literature

PTL 1: Japanese Laid-Open Patent Application Publication No. 2011-021530 PTL 2: International Patent Application WO 2018/101246

Summary of Invention

Technical Problem

As mentioned above, if the lubricating oil has a reduced viscosity, the oil film is not easily formed. Therefore, in such a case, it is possible that the oil film partially breaks, and that the sliding surfaces contact each other more frequently. If the sliding surfaces contact each other more frequently, then there are concerns that at least one of the sliding surfaces may become worn, causing increase in frictional coefficient and that heat generated by the slide parts may increase, causing abnormal wear, such as adhesion. In other words, if the oil film formed by the lubricating oil breaks easily, it lowers the wear resistance of the slide parts.
The above-described reciprocating compressor (hermetic refrigerant compressor) disclosed by Patent Literature 1 uses the low-viscosity lubricating oil, which has a kinematic viscosity in the range of 3 mm²/S to 10 mm²/S at 40°C. However, wear resistance to be improved in Patent Literature 1 is the wear resistance of only the piston and the connecting rod. Therefore, with the technique of Patent Literature 1, the lowering of wear resistance at slide parts different from the piston and the connecting rod cannot be addressed sufficiently.
The present invention has been made in order to solve the above-described problems. An object of the present invention is to provide a hermetic refrigerant compressor that makes it possible to favorably suppress the lowering of wear resistance at slide parts even with the use of lubricating oil having a reduced viscosity.

Solution to Problem

In order to solve the above-described problems, a hermetic refrigerant compressor according to the present invention includes a sealed container in which lubricating oil having a kinematic viscosity in a range of 1 mm²/S to 10 mm²/S at 40°C is stored, the sealed container accommodating an electric element and a compression element, the compression element being driven by the electric element and configured to compress a refrigerant. The lubricating oil has a surface tension in a range of 23 mN/m to 45 mN/m.
According to the above configuration, the lubricating oil stored in the sealed container has a low viscosity and a high surface tension. Accordingly, at slide parts included in the compression element, an oil film formed between sliding surfaces can be retained as a thinner film. Therefore, the breakage of the oil film can be effectively suppressed even though the oil film is formed as a thin film. Consequently, the lowering of wear resistance at the slide parts can be favorably suppressed while realizing increased efficiency of the hermetic refrigerant compressor.
A refrigerator-freezer according to the present invention includes a refrigerant circuit including: the hermetic refrigerant compressor configured as above; a radiator; a decompressor; and a heat absorber. In the refrigerant circuit, the hermetic refrigerant compressor, the radiator, the decompressor, and the heat absorber are connected by piping in an annular manner.
According to the above configuration, since the hermetic refrigerant compressor uses the lubricating oil having a low viscosity and a high surface tension, favorable wear resistance is realized at the slide parts. Therefore, by including the hermetic refrigerant compressor having such an advantage in the refrigerator-freezer, the power consumption of the refrigerator-freezer can be reduced, and also, the refrigerator-freezer can be made highly reliable.
The above and other objects, features, and advantages of the present invention will more fully be apparent from the following detailed description of preferred embodiments with accompanying drawings.

Advantageous Effects of Invention

The present invention is configured as described above, and has an advantage of being able to provide a hermetic refrigerant compressor that makes it possible to favorably suppress the lowering of wear resistance at the slide parts even with the use of lubricating oil having a reduced viscosity.

Brief Description of Drawings

FIG. 1 is a schematic sectional view showing one example of the configuration of a hermetic refrigerant compressor according to an embodiment of the present disclosure.
FIG. 2 is a graph showing relationships between the kinematic viscosity and surface tension of lubricating oils used in the hermetic refrigerant compressor according to the embodiment of the present disclosure.
FIG. 3 is a schematic diagram showing one example of the configuration of a refrigerator-freezer including the refrigerant compressor shown in FIG. 1.

Description of Embodiments

A hermetic refrigerant compressor according to the present disclosure includes a sealed container in which lubricating oil having a kinematic viscosity in a range of 1 mm²/S to 10 mm²/S at 40°C is stored, the sealed container accommodating an electric element and a compression element, the compression element being driven by the electric element and configured to compress a refrigerant. The lubricating oil has a surface tension in a range of 23 mN/m to 45 mN/m.
According to the above configuration, the lubricating oil stored in the sealed container has a low viscosity and a high surface tension. Accordingly, at slide parts included in the compression element, an oil film formed between sliding surfaces can be retained as a thinner film. Therefore, the breakage of the oil film can be effectively suppressed even though the oil film is formed as a thin film. Consequently, the lowering of wear resistance at the slide parts can be favorably suppressed while realizing increased efficiency of the hermetic refrigerant compressor.
In the hermetic refrigerant compressor configured as above, the surface tension of the lubricating oil may be in a range of 25 mN/m to 35 mN/m.
According to the above configuration, the surface tension of the lubricating oil stored in the sealed container is within a more preferable range. Therefore, the breakage of the thin oil film at the slide parts can be more effectively suppressed. Consequently, the lowering of wear resistance at the slide parts can be favorably suppressed while realizing increased efficiency of the hermetic refrigerant compressor.
In the hermetic refrigerant compressor configured as above, the lubricating oil may contain a surface tension adjusting agent that is either a sulfur-based compound or a phosphorus-based compound.
According to the above configuration, since the low-viscosity lubricating oil contains the surface tension adjusting agent, the surface tension can be adjusted within the aforementioned range. Therefore, the breakage of the thin oil film at the slide parts can be more effectively suppressed. Consequently, the lowering of wear resistance at the slide parts can be favorably suppressed while realizing increased efficiency of the hermetic refrigerant compressor.
In the hermetic refrigerant compressor configured as above, the electric element may be inverter-driven at a plurality of operating frequencies.
According to the above configuration, in the case where the electric element is inverter-driven, regardless of whether low-speed operation is being performed or high-speed operation is being performed, the thin film of the lubricating oil having a low viscosity and a high surface tension is retained at the slide parts. Therefore, at the slide parts, favorable wear resistance can be realized, which makes it possible to improve the reliability of the hermetic refrigerant compressor.
A refrigerator-freezer according to the present disclosure includes a refrigerant circuit including: the hermetic refrigerant compressor configured as above; a radiator; a decompressor; and a heat absorber. In the refrigerant circuit, the hermetic refrigerant compressor, the radiator, the decompressor, and the heat absorber are connected by piping in an annular manner.
According to the above configuration, since the hermetic refrigerant compressor uses the lubricating oil having a low viscosity and a high surface tension, favorable wear resistance is realized at the slide parts. Therefore, by including the hermetic refrigerant compressor having such an advantage in the refrigerator-freezer, the power consumption of the refrigerator-freezer can be reduced, and also, the refrigerator-freezer can be made highly reliable.
Hereinafter, representative embodiments of the present invention are described with reference to the drawings. In the drawings, the same or corresponding elements are denoted by the same reference signs, and repeating the same descriptions is avoided below.

(Embodiment 1)

[Configuration of Refrigerant Compressor]

First, a representative configuration example of a hermetic refrigerant compressor according to Embodiment 1 of the present disclosure is specifically described with reference to FIG. 1. FIG. 1 is a schematic sectional view showing one example of the configuration of a hermetic refrigerant compressor 100 according to Embodiment 1 of the present disclosure (hereinafter, the hermetic refrigerant compressor 100 may be simply referred to as "refrigerant compressor 100").
As shown in FIG. 1, the refrigerant compressor 100 includes a sealed container 101 filled with a refrigerant that is, for example, R600a. Mineral oil is stored in the bottom of the sealed container 101 as lubricating oil 103. In the present disclosure, the lubricating oil 103 has a kinematic viscosity in the range of 1 mm²/S to 10 mm²/S at 40°C, and has a surface tension in the range of 23 mN/m to 45 mN/m. It should be noted that, in Embodiment 1, although the lubricating oil 103 is low-viscosity mineral oil, the lubricating oil 103 is not limited to mineral oil as described below.
The sealed container 101 also accommodates an electric element 106 and a compression element 107. The electric element 106 is constituted by a stator 104 and a rotor 105. The compression element 107 is a reciprocating element driven by the electric element 106. The compression element 107 includes, for example, a crank shaft 108, a cylinder block 112, and a piston 120.
The crank shaft 108 is constituted by a main shaft 109 and an eccentric shaft 110. The rotor 105 is fixed to the main shaft 109 by press-fitting. The eccentric shaft 110 is formed such that it is eccentric with the main shaft 109. In Embodiment 1, the outer peripheral surface of the main shaft 109 of the crank shaft 108 serves as a sliding surface. In the present disclosure, the term "sliding surface" means an outer peripheral surface or an inner peripheral surface of each of slide members forming a slide part, and the outer or inner peripheral surface slidably contacts the other inner or outer peripheral surface. An unshown oil-feeding pump is provided at the lower end of the crank shaft 108.
In Embodiment 1, for example, the cylinder block 112 is made of cast iron. The cylinder block 112 forms a substantially cylindrical bore 113, and includes a main bearing 114, which pivotally supports the main shaft 109 of the crank shaft 108. The inner peripheral surface of the main bearing 114 is slidably in contact with the outer peripheral surface, i.e., the sliding surface, of the main shaft 109. Accordingly, the inner peripheral surface of the main bearing 114 also serves as a sliding surface. It should be noted that the entirety of the outer peripheral surface of the main shaft 109 or the entirety of the inner peripheral surface of the main bearing 114 may serve as a sliding surface. Alternatively, not the entirety but a part of the outer peripheral surface of the main shaft 109 or a part of the inner peripheral surface of the main bearing 114 may serve as a sliding surface.
It should be noted that, as shown in FIG. 1, the eccentric shaft 110 of the crank shaft 108 is positioned in the upper side of the refrigerant compressor 100, whereas the main shaft 109 of the crank shaft 108 is positioned in the lower side of the refrigerant compressor 100. Therefore, this upper-lower positional relationship (direction) is utilized herein when describing positions on the crank shaft 108. For example, the upper end of the eccentric shaft 110 faces the inner upper surface of the sealed container 101, and the lower end of the eccentric shaft 110 is connected to the main shaft 109. The upper end of the main shaft 109 is connected to the eccentric shaft 110, and the lower end of the main shaft 109 faces the inner lower surface of the sealed container 101. The lower end portion of the main shaft 109 is immersed in the lubricating oil 103.
A non-sliding outer peripheral surface 111c constitutes a part of the outer peripheral surface of the main shaft 109. However, unlike a first sliding surface 111a and a second sliding surface 111b of the outer peripheral surface of the main shaft 109, the non-sliding outer peripheral surface 111c is a surface that is recessed (or receding) from the sliding surfaces (the first sliding surface 111a and the second sliding surface 11 1b), such that the non-sliding outer peripheral surface 111c is not in contact with the inner peripheral surface of a bearing part. In other words, the portions of the main shaft 109 serving as the sliding surfaces are greater in diameter or radius than the portion of the main shaft 109 serving as the non-sliding outer peripheral surface 111c.
The piston 120 is inserted in the bore 113 in a reciprocable manner, and thereby a compression chamber 121 is formed. A piston pin 115 having, for example, a substantially cylindrical shape is disposed parallel to the eccentric shaft 110. The piston pin 115 is locked to a piston pin hole formed in the piston 120 in a non-rotatable manner.
A coupler 117 is, for example, constituted by an aluminum casting product. The coupler 117 includes an eccentric bearing 119, which pivotally supports the eccentric shaft 110, and the coupler 117 couples the eccentric shaft 110 and the piston 120 via the piston pin 115. The end face of the bore 113 is sealed by a valve plate 122.
It should be noted that, in the present disclosure, the main shaft 109 and the eccentric shaft 110 included in the crank shaft 108 are collectively referred to as a "shaft part". Also, the main bearing 114 of the cylinder block 112, which pivotally supports the main shaft 109, and the eccentric bearing 119 of the coupler 117, which pivotally supports the eccentric shaft 110, are collectively referred to as the aforementioned "bearing part".
A cylinder head 123 forms an unshown high-pressure chamber, and is fixed to the valve plate 122 at the opposite side to the bore 113. An unshown suction tube is fixed to the sealed container 101, and also connected to the low-pressure side (not shown) of a refrigeration cycle, such that the suction tube leads the refrigerant gas into the sealed container 101. A suction muffler 124 is held in a sandwiched manner between the valve plate 122 and the cylinder head 123.
The main shaft 109 of the crank shaft 108 and the main bearing 114, the piston 120 and the bore 113, the piston pin 115 and a connecting rod of the coupler 117, and the eccentric shaft 110 of the crank shaft 108 and the eccentric bearing 119 of the coupler 117, etc., form slide parts with each other.
In the refrigerant compressor 100 thus configured, first, electric power is supplied from an unshown commercial power supply to the electric element 106 to cause the rotor 105 of the electric element 106 to rotate. The rotor 105 causes the crank shaft 108 to rotate, and eccentric motion of the eccentric shaft 110 from the coupler 117 drives the piston 120 via the piston pin 115. The piston 120 makes reciprocating motion in the bore 113, sucks the refrigerant gas that has been led into the sealed container 101 through the suction tube from the suction muffler 124, and compresses the sucked refrigerant gas in the compression chamber 121.
It should be noted that a specific method adopted for driving the refrigerant compressor 100 is not particularly limited. For example, the refrigerant compressor 100 may be driven by simple on-off control, or may be inverter-driven at a plurality of operating frequencies. In the case where the refrigerant compressor 100 is inverter-driven, in order to optimize the operation control of the refrigerant compressor 100, low-speed operation or high-speed operation is performed. When the low-speed operation is performed, the amount of oil fed to each slide part decreases, whereas when the high-speed operation is performed, the rotation speed of the electric element 106 increases. In the refrigerant compressor 100, the wear resistance of the main shaft 109 can be improved as described below. Consequently, the reliability of the refrigerant compressor 100 can be improved.
Among the plurality of slide parts included in the refrigerant compressor 100, the main shaft 109 of the crank shaft 108 is rotatably fitted to the main bearing 114, and thereby a slide part is formed. Similarly, the eccentric shaft 110 of the crank shaft 108 is rotatably fitted to the eccentric bearing 119, and thereby a slide part is formed. Further, the piston 120 and the bore 113, or the piston pin 115 and the coupler 117, also form a slide part. In accordance with the rotation of the crank shaft 108, the oil-feeding pump feeds the lubricating oil 103 to each of these slide parts.

[Configuration of Lubricating Oil]

Next, a more specific configuration of the lubricating oil 103 stored in the sealed container 101 is specifically described.
The lubricating oil 103 according to the present disclosure is not limited to a particular type of lubricating oil, so long as the lubricating oil 103 has a kinematic viscosity in the range of 1 mm²/S to 10 mm²/S at 40°C and has a surface tension in the range of 23 mN/m to 45 mN/m.
Typically, for example, at least one oil substance selected from the group consisting of mineral oil, alkyl benzene oil, and ester oil can be suitably used as the lubricating oil 103. Only one of these oil substances may be used as the lubricating oil 103, or a suitable combination of two or more of the oil substances may be used as the lubricating oil 103. The definition of the combination of two or more of the oil substances herein includes not only a combination of two or more different oil substances that are, for example, mineral oils, but also a combination of, for example, one or more oil substances each of which is a mineral oil and one or more oil substances each of which is an alkyl benzene oil (or one or more oil substances each of which is an ester oil).
As previously mentioned, the lubricating oil 103 according to the present disclosure is required to have a kinematic viscosity in the range of 1 mm²/S to 10 mm²/S at 40°C. A preferable example of the range of the kinematic viscosity at 40°C is 1 mm²/S to 9 mm²/S. If the kinematic viscosity at 40°C is less than 1 mm²/S, the viscosity of the lubricating oil 103 becomes too low. In such a case, even if the lubricating oil 103 has a surface tension in the range of 23 mN/m to 45 mN/m, an oil film that is favorably retainable on the slide parts cannot be formed. On the other hand, if the kinematic viscosity at 40°C is greater than 10 mm²/S, the lubricating oil 103 is no longer "low-viscosity oil", which affects the sliding of slide members with each other, and consequently, the realization of increased efficiency of the slide parts may be hindered.
As previously mentioned, the lubricating oil 103 according to the present disclosure is required to have a surface tension in the range of 23 mN/m to 45 mN/m. A preferable example of the range of the surface tension is 25 mN/m to 35 mN/m. If the surface tension of the lubricating oil 103 is less than 23 mN/m, the surface tension is too low. In such a case, an oil film that is favorably retainable on the slide parts cannot be formed. On the other hand, if the surface tension of the lubricating oil 103 is greater than 45 mN/m, the surface tension is too high, which affects the sliding of slide members with each other, and consequently, the realization of increased efficiency of the slide parts may be hindered.
An actual machine reliability test was actually conducted on the refrigerant compressor 100, in which the low-viscosity and high-surface-tension lubricating oil 103 was used. In this test, R600a was used as the refrigerant gas, and as shown in FIG. 2, a total of seven types of lubricating oils 103, each having a kinematic viscosity in the range of 1 mm²/S to 10 mm²/S at 40°C and a surface tension in the range of 20 mN/m to 45 mN/m, were used. As a slide part to be evaluated, the main shaft 109 of the crank shaft 108 and the main bearing 114 were selected, and a high-temperature and high-load intermittent operation mode in which start and stop are repeated within a short period of time in a high temperature environment was adopted as an operation mode in order to accelerate wear of the main shaft 109.
After completion of the actual machine reliability test, the refrigerant compressor 100 was disassembled, and the crank shaft 108 was removed. Then, the slide part was observed. As a result, as indicated by symbols "X" in FIG. 2, in the test results (of comparative examples) in which the surface tension of each lubricating oil 103 was less than 23 mN/m, it was confirmed that the main shaft 109 was significantly worn. On the other hand, as indicated by "circle" and "triangle" symbols in FIG. 2, in the test results (of working examples) in which the surface tension of each lubricating oil 103 was greater than or equal to 23 mN/m, almost no wear or only minor wear of the main shaft 109 was observed.
However, in the test results indicated by the "triangle" symbol in FIG. 2, although the surface tension of the lubricating oil 103 was about 42 mN/m, the degree of the wear of the main shaft 109 was greater than in the test results indicated by the "circle" symbols. Thus, in the present disclosure, in which the lubricating oil 103 is required to have a surface tension in the range of 23 mN/m to 45 mN/m, it is understood that a preferable example of the range of the surface tension is 25 mN/m to 35 mN/m. It should be noted that a method adopted for measuring the surface tension is not particularly limited. In the present embodiment, the du Noüy ring method defined in JIS K2241 is used, and DY-300 (trade name) manufactured by Kyowa Interface Science Co., LTD. is used as a surface tension measuring device.
A method adopted for adjusting the surface tension of the lubricating oil 103 according to the present disclosure to fall within the aforementioned range is not particularly limited. For example, a commercially available oil substance satisfying the aforementioned kinematic viscosity and surface tension may be used as the lubricating oil 103 as it is, or a plurality of oil substances may be blended together to adjust the kinematic viscosity and surface tension of the resulting oil substance mixture to the aforementioned kinematic viscosity and surface tension. Moreover, a surface tension adjusting agent may be added to (or contained in) one or more oil substances, and thereby the surface tension may be adjusted. Thus, the lubricating oil 103 used in the refrigerant compressor 100 according to the present disclosure is required to contain at least one oil substance (as its major component(s)), and may be a lubricating oil composition that is constituted by, at least, one or more oil substances and a surface tension adjusting agent.
The specific type of the surface tension adjusting agent is not particularly limited, so long as when the surface tension adjusting agent is added to a known oil substance (i.e., when the surface tension adjusting agent and the known oil substance constitute the lubricating oil composition), the surface tension adjusting agent allows the surface tension of the oil substance (the lubricating oil composition) to fall within the aforementioned range.
Representative examples of the surface tension adjusting agent include sulfur-based compounds and phosphorus-based compounds. Specific examples of the sulfur-based compounds include, but are not particularly limited to, a sulfurized olefin, a sulfide-based compound (e.g., dibenzyl disulfide (DBDS)), a xanthate, a thiadiazole, a thiocarbonate, a sulfurized oil or fat, a sulfurized ester, a dithiocarbamate, and a sulfurized terpene. Specific examples of the phosphorus-based compounds include, but are not particularly limited to, tricresyl phosphate (TCP), tributyl phosphate (TBP), and triphenyl phosphate (TPP). Only one of these compounds may be used as the surface tension adjusting agent, or a suitable combination of two or more of these compounds may be used as the surface tension adjusting agent.
The surface tension adjusting agent content in the lubricating oil composition is not particularly limited, and can be suitably set in accordance with various conditions, such as the type(s) of the oil substance(s), the required range of surface tension, and a more specific configuration of the refrigerant compressor 100. In general, if the total amount of the lubricating oil composition is 100% by weight, then the lubricating oil composition is required to contain 0.01 to 8% by weight of the surface tension adjusting agent. As a more preferable example, the lubricating oil composition may contain 1 to 3% by weight of the surface tension adjusting agent. If the surface tension adjusting agent content in the lubricating oil composition is less than 0.01% by weight, then although depending on various conditions, there is a risk that the surface tension cannot be adjusted to a desired value, and thereby the oil film may break. On the other hand, if the surface tension adjusting agent content in the lubricating oil composition is greater than 8% by weight, the surface tension may not vary although it depends on various conditions.
In addition to the above-described oil substance and surface tension adjusting agent, various additives may be added to the lubricating oil 103 (lubricating oil composition) according to the present disclosure. Those known in the field of the lubricating oil 103 can be suitably used as the various additives to be added to the lubricating oil 103. Typical examples of such additives include an extreme-pressure additive, an oily agent, an anti-wear agent, an antioxidant, an acid-acceptor, a metal deactivator, a defoaming agent, an anti-corrosive agent, and a dispersant. Specific types and specific addition amounts of these additives are not particularly limited, and they may be added within known ranges.
Next, the lubricating function of the lubricating oil 103 is described by referring to operations of the refrigerant compressor 100 configured as described above. Electric power is supplied from a commercial power supply (not shown) to the electric element 106 to cause the rotor 105 of the electric element 106 to rotate. The rotor 105 causes the main shaft 109 of the crank shaft 108 to rotate, and eccentric motion of the eccentric shaft 110 from the coupler 117 drives the piston 120 via the piston pin 115. The piston 120 makes reciprocating motion in the bore 113, sucks the refrigerant gas that has been led into the sealed container 101 through the suction tube (not shown) from the suction muffler 124, and compresses the sucked refrigerant gas in the compression chamber 121.
In accordance with the rotation of the crank shaft 108, the unshown oil-feeding pump feeds the lubricating oil 103 to each slide part, and thereby each slide part is lubricated. Slide members forming the slide parts are, for example, the main shaft 109 and the main bearing 114, the eccentric shaft 110 and the eccentric bearing 119 (of the coupler 117), the piston pin 115 and the coupler 117, and the piston 120 and the bore 113. The lubricating oil 103 is supplied to the sliding surfaces of these slide members. It should be noted that the lubricating oil 103 also serves to seal between the piston 120 and the bore 113.
For the refrigerant compressor 100 in recent years, in order to further improve the efficiency thereof, several measures have been taken, such as using lubricating oil having a reduced viscosity as the lubricating oil 103 and designing the length of the sliding surface of each of the slide members forming the slide parts to be shorter. For these reasons, the sliding condition is getting more severe. Specifically, the oil film between the slide members tends to be made thinner, or the oil film between the slide members tends to break more easily. Accordingly, the breakage of the oil film tends to occur at the slide parts, for example, between the main shaft 109 of the crank shaft 108 and the main bearing 114, and consequently, the metals of the sliding surfaces come into contact with each other more frequently.
In this respect, in the refrigerant compressor 100 according to the present disclosure, the lubricating oil 103 has a kinematic viscosity in the range of 1 mm²/S to 10 mm²/S at 40°C, and has a surface tension in the range of 23 mN/m to 45 mN/m. The use of the lubricating oil 103 having such features makes it possible to favorably retain a thin oil film at each slide part and effectively suppress the breakage of the oil film. Therefore, the lowering of wear resistance at the slide parts can be favorably suppressed while realizing increased efficiency of the hermetic refrigerant compressor.
It should be noted that, as previously mentioned, the refrigerant compressor 100 according to the present disclosure may be inverter-driven at a plurality of operating frequencies. In the case where the refrigerant compressor 100 is inverter-driven, there are two operation modes of the electric element 106, in one of which the electric element 106 is operated at a low rotation speed (low-speed operation), and in the other of which the electric element 106 is operated at a high rotation speed (high-speed operation). When the electric element 106 is operated at a low rotation speed, the amount of lubricating oil 103 supplied to the main shaft 109 of the crank shaft 108 and the main bearing 114 (i.e., the slide part of the main shaft 109) decreases. In this respect, in the present disclosure, since the lubricating oil 103 has a low viscosity and a high surface tension as described above, even when the amount of lubricating oil 103 supplied to the slide part of the main shaft 109 decreases, favorable wear resistance at the slide part of the main shaft 109 can be realized.
Also, even when the rotation speed of the electric element 106 shifts from the low rotation speed to the high rotation speed (i.e., even when the rotation speed of the electric element 106 increases), favorable wear resistance at the slide part of the main shaft 109 can be realized. Therefore, in the case where the refrigerant compressor 100 is inverter-driven, regardless of whether the low-speed operation is being performed or the high-speed operation is being performed, favorable wear resistance at the slide part can be realized. Consequently, the reliability of the refrigerant compressor 100 can be improved, and also, the operating efficiency can be improved.

(Embodiment 2)

In Embodiment 2, one example of a refrigerator-freezer that includes the refrigerant compressor 100 described above in Embodiment 1 is specifically described with reference to FIG. 3. FIG. 3 is a schematic diagram showing a schematic configuration of the refrigerator-freezer including the refrigerant compressor 100 according to Embodiment 1. Therefore, in Embodiment 2, only a fundamental configuration of the refrigerator-freezer is described briefly.
As shown in FIG. 3, the refrigerator-freezer according to Embodiment 2 includes, for example, a body 275, a dividing wall 278, and a refrigerant circuit 270. The body 275 is constituted by a thermally-insulated box, a door, and so forth. The box is configured to have one opening face, and the door is configured to open/close the opening of the box. The interior of the body 275 is divided by the dividing wall 278 into a product storage space 276 and a machinery room 277. An unshown air feeder is provided in the storage space 276. It should be noted that the interior of the body 275 may be divided into, for example, spaces that are different from the storage space 276 and the machinery room 277.
The refrigerant circuit 270 is configured to cool the inside of the storage space 276. For example, the refrigerant circuit 270 includes the refrigerant compressor 100 described above in Embodiment 1, a radiator 272, a decompressor 273, and a heat absorber 274, which are connected by piping in an annular manner. The heat absorber 274 is disposed in the storage space 276. Cooling heat of the heat absorber 274 is stirred by the unshown air feeder so as to circulate inside the storage space 276 as indicated by a dashed arrow in FIG. 3. In this manner, the inside of the storage space 276 is cooled.
As described above in Embodiment 1, the lubricating oil 103 used in the refrigerant compressor 100 included in the refrigerant circuit 270 has a kinematic viscosity in the range of 1 mm²/S to 10 mm²/S at 40°C, and has a surface tension in the range of 23 mN/m to 45 mN/m. Accordingly, favorable wear resistance at the slide parts included in the refrigerant compressor 100 can be realized. Consequently, the reliability of the refrigerant compressor 100 can be improved.
As described above, the refrigerator-freezer according to Embodiment 2 includes the above-described refrigerant compressor 100 according to Embodiment 1. In the refrigerant compressor 100, the low-viscosity lubricating oil 103 is used; the sliding area of the slide parts of the shaft part is reduced; and the shaft part has high reliability. Since the refrigerator-freezer includes the hermetic refrigerant compressor, which is highly efficient and highly reliable, the power consumption of the refrigerator-freezer can be reduced, and also, the refrigerator-freezer can be made highly reliable.
It should be noted that the present invention is not limited to the embodiments described above, and various modifications can be made within the scope of Claims. Embodiments obtained by suitably combining technical means that are disclosed in different embodiments and variations also fall within the technical scope of the present invention.
From the foregoing description, numerous modifications and other embodiments of the present invention are obvious to one skilled in the art. Therefore, the foregoing description should be interpreted only as an example and is provided for the purpose of teaching the best mode for carrying out the present invention to a person skilled in the art.

Industrial Applicability

As described above, the present invention makes it possible to provide a refrigerant compressor that uses low-viscosity lubricating oil and yet has excellent reliability and to provide a refrigerator-freezer using the refrigerant compressor. Therefore, the present invention is widely applicable to various equipment that uses a refrigeration cycle.

Reference Signs List

100: refrigerant compressor
101: sealed container
103: lubricating oil
106: electric element
107: compression element
108: crank shaft
109: main shaft (slide member)
110: eccentric shaft (slide member)
112: cylinder block
113: bore (slide member)
114: main bearing (slide member)
115: piston pin (slide member)
119: eccentric bearing (slide member)
120: piston (slide member)
121: compression chamber
270: refrigerant circuit
272: radiator
273: decompressor
274: heat absorber

Claims

A hermetic refrigerant compressor (100) comprising a sealed container (101) in which lubricating oil (103) having a kinematic viscosity in a range of 1 mm²/S to 10 mm²/S at 40°C is stored, the sealed container (101) accommodating an electric element (106) and a compression element (107), the compression element (107) being driven by the electric element (106) and configured to compress a refrigerant, wherein
the lubricating oil (103) has a surface tension in a range of 23 mN/m to 45 mN/m when the surface tension is measured by the du Noüy ring method defined in JIS K2241.
The hermetic refrigerant compressor (100) according to claim 1, wherein
the surface tension of the lubricating oil is in a range of 25 mN/m to 35 mN/m.
The hermetic refrigerant compressor (100) according to claim 1 or 2, wherein
the lubricating oil (103) contains a surface tension adjusting agent that is either a sulfur-based compound or a phosphorus-based compound.
The hermetic refrigerant compressor (100) according to any one of claims 1 to 3, wherein
the electric element (106) is inverter-driven at a plurality of operating frequencies.
A refrigerator-freezer comprising a refrigerant circuit (270) including:
the hermetic refrigerant compressor (100) according to any one of claims 1 to 4;

a radiator (272);

a decompressor (273); and

a heat absorber (274), wherein

in the refrigerant circuit (270), the hermetic refrigerant compressor (100), the radiator (272), the decompressor (273), and the heat absorber (274) are connected by piping in an annular manner.