JP2013044255A - Closed compressor and refrigerator using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a sliding loss generated between a cylinder and a piston.SOLUTION: A closed compressor includes an airtight container, and a compression element and an electric element, which are housed in the airtight container. The compression element, which is driven by the electric element via a crankshaft, comprises the cylinder 1 which forms a cylinder chamber, the piston 4 which reciprocates in the cylinder, and a connecting rod 2 which connects the crankshaft and the piston together. In addition, a lower limit of a rotational speed range, in which the electric element is operated, is set at 1,500 minor less, and a central axis line 1c of the cylinder is offset with respect to the center 7n of rotation of the crankshaft. Furthermore, the amount D of offset is set larger than 2 mm.

Description

  The present invention relates to a hermetic compressor used in a refrigeration cycle such as a refrigerator and a refrigerator using the same.

  As a conventional hermetic compressor, for example, there is one described in Japanese Patent No. 3437376 (Patent Document 1). This hermetic compressor is a reciprocating compressor using HFC refrigerant as a refrigerant. One member of the sliding part is subjected to nitriding treatment and manganese phosphate coating treatment, and the other member is not treated. Carbon steel is used. Specifically, manganese phosphate coating is applied to the cylinder side, carbon steel is used for the piston, and the center axis of the cylinder is offset by 2 mm from the axis of the crankshaft that transmits the rotational torque from the motor. The cylinder is arranged to pass through.

  Another conventional hermetic compressor is described in Japanese Patent Application Laid-Open No. 2009-62864 (Patent Document 2). This hermetic compressor is a reciprocating compressor using a ball joint, and the cylinder is offset so that the axis of the compression chamber does not intersect the axis of the main shaft.

  Further, another conventional hermetic compressor is disclosed in Japanese Patent No. 4538307 (Patent Document 3). This hermetic compressor has a stepped portion extending from the crankshaft side end portion to a range of 0.2 to 0.4 times the total length of the piston on the outer peripheral surface of the piston.

Japanese Patent No. 3437376 JP 2009-62864 A Japanese Patent No. 4538307

The problems described in the above patent documents have the following problems.
In recent years, some refrigerators have operated the compressor by inverter control in order to reduce the power consumption, and the rotation speed of the compressor is operated at a considerably lower rotation speed than that without inverter control. There are many cases. Moreover, the heat insulation technology of the refrigerator is also progressing, and the temperature in the refrigerator can be maintained even when the compressor is operated at a lower rotational speed than before. For this reason, the lower limit of the rotational speed of the compressor tends to be reduced in order to reduce the power consumption of the refrigerator.

In the above background, in the hermetic compressor described in Patent Document 1, the cylinder is offset as described above in order to reduce the surface pressure acting on the cylinder sliding portion. Further, in this Patent Document 1, test results at a rotational speed of 3600 min ⁻¹ are shown as test conditions for the compressor alone with the offset amount set to 2 mm. However, when the compressor is operated by inverter control, for example, when it is frequently operated at a rotational speed range of 2000 min ⁻¹ or less, the structure described in Patent Document 1 has sufficient surface pressure acting on the cylinder sliding portion. There is a possibility that it cannot be lowered, and consideration for reducing the sliding loss generated between the cylinder and the piston is not sufficient. Note that if the offset amount is large, no consideration is given to the possibility that a part of the piston ball seat portion may interfere with the connecting rod.

  In the hermetic compressor described in Patent Document 2, in order to reduce loss at the sliding portion, the cylinder is offset so that the shaft center of the compression chamber does not intersect the shaft center of the main shaft portion, and the rod portion The center of the shaft is not crossed with the center of the ring portion connecting the rod and the shaft. However, as will be described later, the sliding loss may increase depending on the offset amount, and there is a risk that the performance may be adversely affected particularly when the inverter is operated in a wide rotational speed range.

  In the hermetic compressor described in Patent Document 3, if the range of the stepped portion provided in the piston is excessively increased, the contact area between the piston and the cylinder is reduced, and should exist between the piston and the cylinder. The lubricating oil film tends to break during low-speed operation, and the solid surfaces of the piston and cylinder may come into contact with each other, which may increase sliding loss. For this reason, in the case of a compressor used in low-speed operation, it is necessary to secure a certain area of the stepped portion of the piston, and the sliding loss cannot be sufficiently reduced.

  An object of the present invention is to obtain a hermetic compressor capable of reducing a sliding loss generated between a cylinder and a piston, and a refrigerator using the same.

In order to achieve the above object, the present invention includes a sealed container, a compression element and an electric element housed in the closed container, and the compression element is driven by the electric element via a crankshaft. In a hermetic compressor including a cylinder that forms a cylinder chamber, a piston that reciprocates in the cylinder, and a connecting rod that connects the crankshaft and the piston, the lower limit of the rotational speed range in which the electric element is operated is 1500 min ⁻ together constitute ^one or less, the central axis of the cylinder is offset with respect to the center of rotation of the crankshaft, characterized by further amount of said offset (offset amount) constitute greater than 2 mm.

  Another feature of the present invention is a refrigerator using isobutane (R600a) as a refrigerant to form a refrigeration cycle and using the above-described hermetic compressor as a hermetic compressor used in the refrigeration cycle. .

  ADVANTAGE OF THE INVENTION According to this invention, the hermetic compressor which reduced the sliding loss generate | occur | produced between a cylinder and a piston can be obtained. In addition, a refrigerator with low power consumption can be obtained by mounting a hermetic compressor having the above characteristics on a refrigerator.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectional view showing a first embodiment of a hermetic compressor according to the present invention. The longitudinal cross-sectional view which shows the Example of the refrigerator of this invention carrying the hermetic compressor of FIG. The schematic diagram explaining the operation | movement at the time of the compression stroke of the part of the cylinder and piston shown in FIG. The schematic diagram explaining operation | movement when a piston moves to the bottom dead center from the top dead center of the cylinder and piston part shown in FIG. The schematic diagram explaining the direction of the typical force which acts on a piston. The diagram explaining the relationship between offset amount and compressor performance. The schematic diagram explaining the operation | movement at the time of the compression stroke of the part of a cylinder and a piston at the time of using a piston pin for the connection of a connecting rod and a piston. FIG. 3 is a schematic perspective view showing the shape of a piston in the first embodiment. FIG. 6 is a schematic perspective view showing the shape of a piston in Embodiment 2.

  Specific embodiments of the present invention will be described below with reference to FIGS. In addition, the part which attached | subjected the same code | symbol in each figure shows the part which is the same or corresponds.

A first embodiment of the present invention will be described with reference to FIGS.
First, the overall configuration of the hermetic compressor of this embodiment will be described with reference to FIG. FIG. 1 is a longitudinal sectional view showing a hermetic compressor according to the present embodiment.

  The hermetic compressor 50 is a reciprocating compressor in which the compression element 20 and the electric element 30 are vertically arranged in the hermetic container 3 and connected by the crankshaft 7. The compression element 20 and the electric element 30 are elastically supported in the sealed container 3.

  The electric element 30 is disposed below the frame 1 b and includes a stator 5 and a rotor 6. The rotor 6 is composed of a rotor core 6 a on which electromagnetic steel plates are laminated and is fixed to the crankshaft 7. The stator 5 is fixed to the frame 1b. A crankpin 7 a that is eccentric from the center of rotation is provided at the upper end of the crankshaft 7.

  The crankshaft 7 extends from the lower side of the frame 1b through the radial bearing portion 1a, and is provided so that the crank pin 7a is located on the upper side of the frame 1b. The lower part of the crankshaft 7 is connected to the rotor 6, and the crankshaft 7 is rotated by the power of the electric element 30. When the crankshaft 7 rotates, the crankpin 7 a rotates eccentrically, and the piston 4 reciprocates via the connecting rod 2.

  The compression element 20 includes a cylinder 1 that forms a cylinder chamber, the piston 4 that reciprocates in the cylinder 1, the connecting rod 2 that drives the piston 4, and a discharge valve device 40 that is attached to the end face of the cylinder 1. And a head cover 17 for forming a discharge chamber space. The cylinder 1 is integrally formed with the radial bearing portion 1a and the frame 1b. The piston 4 is connected to the crankpin 7a via the connecting rod 2, and reciprocates in the cylinder chamber by the eccentric rotation of the crankpin 7a.

  The refrigerant sucked into the cylinder 1 is compressed by the reciprocating motion of the piston 4, and the compressed gas refrigerant is sent to a discharge pipe 18 communicating with the outside of the compressor. Reference numeral 21 denotes an oil supply piece attached to the lower end of the crankshaft 7.

Next, the refrigerator 60 equipped with the hermetic compressor 50 will be described with reference to FIG.
FIG. 2 is a longitudinal sectional view showing an embodiment of the refrigerator 60 of the present invention on which the hermetic compressor 50 of the present embodiment is mounted. The refrigerator 60 includes a refrigerator compartment 62, an upper freezer compartment 63, a lower freezer compartment 64, and a vegetable compartment 65. The positional relationship among the refrigerator compartment 62, the upper freezer compartment 63, the lower freezer compartment 64, and the vegetable compartment 65 is not limited to that shown in FIG.

  The refrigerant discharged from the hermetic compressor 50 passes through a condenser and a decompression mechanism (both not shown) provided in the refrigerator 60, absorbs heat in the refrigerator by the cooler 66, and evaporates. It is returned to the compressor 50 again. In the refrigeration cycle including the hermetic compressor 50, the condenser, the decompression mechanism, the cooler 66, and the like, a hydrocarbon-based refrigerant such as propane (R290) or isobutane (R600a) is used. In the refrigerator of the present embodiment, isobutane is used as a refrigerant for the refrigeration cycle.

  FIG. 3 is a schematic diagram for explaining the operation of the cylinder and piston portions shown in FIG. 1 during the compression stroke, and the positional relationship between the cylinder 1 and the piston 4 and the crankshaft 7 will be described with reference to FIG.

  The piston 4 is connected to the connecting rod 2 via a ball joint 2a, and the connecting rod 2 is connected to a crankpin 7a via a rod large end 2b. The ball joint 2a is connected to the piston 4 so as to slide in a piston inner spherical surface 4c formed in the piston 4 in a substantially spherical shape. The piston inner sphere 4c is provided with a piston inner sphere cut portion 4d, whereby the piston inner sphere 4c has an asymmetric shape.

  The center axis of the crank pin 7a is separated from the rotation center (center axis) 7n of the crank shaft 7 by an eccentric amount R, and the crank pin 7a has a radius R about the rotation center 7n as the crank shaft 7 rotates. Rotating on the circumference of With the rotational movement of the crank pin 7a, the connecting rod 2 swings and reciprocates the piston 4. The center axis 1c of the cylinder 1 is offset by a distance D with respect to the rotation center 7n of the crankshaft. When the piston 4 is moving from the bottom dead center to the top dead center, the cylinder center axis 1c is offset in the direction in which the crank pin 7a is located when viewed from the rotation center 7n of the crankshaft. . FIG. 3 shows an example in which the crankshaft 7 rotates clockwise as viewed from above in FIG.

  Next, the positional relationship between the piston 4 and the connecting rod 2 in the stroke in which the piston 4 moves from the top dead center to the bottom dead center will be described with reference to FIG. FIG. 4 is a schematic diagram for explaining the operation when the piston moves from the top dead center to the bottom dead center of the cylinder and piston shown in FIG.

  In the stroke in which the piston 4 moves from the top dead center to the bottom dead center, the crank pin 7a is located on the opposite offset side. Therefore, when the offset amount D between the center axis 1c of the cylinder 1 and the shaft rotation center 7n is large, the connecting rod 2 has an edge portion of the piston inner spherical surface 4c and an edge portion on the bottom dead center side of the outer periphery of the piston 4 ( The structure is easy to interfere with the cylindrical portion. In particular, when the offset amount D exceeds 2 mm, this interference is likely to occur. Therefore, in the present embodiment, the piston inner spherical surface 4c is provided with a piston inner ball cut portion 4d so as to avoid interference with the connecting rod 2, that is, in the direction opposite to the offset side. A piston notch 4e is similarly provided in the edge portion of the lower end. Thereby, there is no possibility that the connecting rod 2 interferes with the piston 4.

A typical direction of force applied to the piston 4 will be described with reference to FIG. 3 and FIG.
FIG. 5 is a schematic diagram for explaining the direction of a typical force applied to the piston 4 in the compression stroke. A load (refrigerant compression load) 70 received from the compressed refrigerant acts on the compression chamber side of the piston 4. Further, the piston 4 receives a force 71 from the connecting rod 2 in a direction that changes in accordance with the swing angle θ of the connecting rod 2. For this reason, as the reaction force, the piston 4 receives a reaction force 72 from the wall surface of the cylinder 1. In accordance with the reaction force 72 from the cylinder wall surface and the reciprocating motion of the piston 4, a frictional force 73 is generated between the cylinder 1 and the piston 4, and a sliding loss is generated.

  In FIG. 3, when the offset amount D takes a positive value, that is, when the piston 4 is moving from the bottom dead center to the top dead center, the crank pin 7a is located when viewed from the rotation center 7n of the crankshaft. When the cylinder center shaft 1c is offset in the direction, the swing angle θ when the refrigerant compression load 70 is the same can be made smaller than when the offset amount D is zero. Thereby, the component force of the direction perpendicular | vertical with respect to the cylinder wall surface of the force 71 received from the connecting rod 2 can be made small, and the reaction force 72 from a cylinder wall surface can be made small.

  On the other hand, in the process in which the piston 4 moves from the top dead center to the bottom dead center (reexpansion process), the reaction angle 72 received from the cylinder wall surface may increase because the swing angle θ increases. That is, in the process of one rotation of the crankshaft 7, when the offset amount D takes a positive value, the sliding loss generated between the piston 4 and the cylinder 1 is smaller than that when the offset amount D is zero. There will be a decreasing interval and an increasing interval. When the offset amount D is small, the reduction amount of the sliding loss in the compression process becomes larger than the increase amount of the sliding loss in the re-expansion process, and as a result, the entire sliding loss can be reduced. However, when the offset amount D is large, the sliding loss reduction amount in the compression process is smaller than the sliding loss increase amount in the re-expansion process, and as a result, the overall sliding loss may increase. . From this, it can be seen that there is an offset amount D that minimizes the sliding loss.

  Here, the force 71 received from the connecting rod 2 includes the piston 4 and the connecting rod 2 in addition to the resultant force calculated from the refrigerant compression load 70 and the frictional force 73 between the cylinder and the piston and the swing angle θ. Inertial force is added. Therefore, even if the refrigerant compression load 70 is constant, the magnitude and direction of the force 71 that the piston 4 receives from the connecting rod 2 changes according to the rotational speed of the compressor. That is, the optimum offset amount D changes depending on the rotational speed.

FIG. 6 is a diagram for explaining the relationship between the offset amount D and the performance of the compressor. The horizontal axis represents the offset amount D, and the vertical axis represents the improvement rate of the coefficient of performance (COP) obtained by dividing the refrigeration capacity of the compressor by the input. This figure shows the relationship between the offset amount D and the COP improvement rate at each of the two rotational speeds N1 and N2. Further, the rotational speed N1 is smaller than 2000 min ⁻¹ , and N2 is a rotational speed larger than 2000 min ⁻¹ . In the example shown in FIG. 6, the amount of eccentricity R is 9 mm.

From FIG. 6, at a relatively large rotational speed N2 exceeding 2000 min ⁻¹ , when the offset amount D is increased, the sliding loss increases rapidly and the COP tends to decrease. However, when the rotational speed N1 is less than 2000 min ⁻¹ , the influence of the inertial force of the piston 4 and the connecting rod 2 is reduced, the range of the offset amount D in which COP is improved, and the offset amount is made larger than 2 mm. Has been found to improve COP.

In recent refrigerators, the number of rotation speeds frequently used in electric elements of compressors is less than 2000 min ⁻¹ , and the lower limit (minimum number of rotations) of the rotation speed is 1500 min ⁻¹ or less. There are also things. In such a case, it is desirable to set the offset amount D to a value exceeding 2 mm in order to fully exhibit the effect of the cylinder 1 being offset. However, when operating at a rotational speed exceeding 2000 min ⁻¹ , such as during quick freezing operation in a refrigerator, when the offset amount D is set to 4 mm or more, for example, as shown in FIG. 6, at a rotational speed exceeding 2000 min ^−1. Performance will deteriorate rapidly.

Therefore, when importance is attached to the performance at an operation speed of 2000 min ⁻¹ or less, the offset amount D should be a value exceeding 2 mm (however, the preferable upper limit is 9 mm or less). When the performance during the refrigeration operation must also be emphasized, the offset amount D is desirably 4 mm or less, preferably 3 mm or less.

Thus, by setting the offset amount D to be larger than 2 mm and not larger than 4 mm (preferably 3 mm), it is possible to improve the performance of a refrigerator having a specification in which the rotational speed of a frequently used compressor is smaller than 2000 min ^−1. Even when operating at a rotational speed exceeding 2000 min ⁻¹ , such as during quick freezing operation, it is possible to obtain an effect capable of suppressing deterioration in performance.

  FIG. 7 is a schematic diagram for explaining the operation during the compression stroke of the cylinder and the piston when a piston pin is used to connect the connecting rod and the piston. As a means for connecting the connecting rod 2 and the piston 4, the piston The operation when the pin 2c is used will be described with reference to FIGS. 3 and 5 and FIG.

  In FIG. 7, the piston pin 2 c is a columnar or cylindrical member and is inserted through the piston 4, and therefore the piston top surface is considered when considering the axial length in which the piston 4 seals the inside of the cylinder 1. The length from 4b to the insertion position of the piston pin 2c is shortened. For this reason, in order to improve the sealing performance of the gap between the piston 4 and the cylinder 1, the distance L from the piston top surface 4b to the axial center of the piston pin 2c must be secured above a certain level. 7, the axis of the piston pin 2c is likely to be closer to the crankshaft 7 than the position of the center of gravity of the piston 4, and the axis of the piston pin 2c and the center of gravity of the piston 4 do not coincide with each other. End up. For this reason, a moment around the axial center of the piston pin 2c is generated in the piston 4, and one-sided contact is likely to occur between the piston 4 and the cylinder 1, and the sliding loss increases.

  In contrast to the connection method using the piston pin shown in FIG. 7, as described in FIGS. There is no need to provide a hole for inserting the piston pin. Therefore, it is possible to easily secure the axial length in which the piston 4 seals the inside of the cylinder 1, and the ball center of the ball joint 2 a is on the side opposite to the crankshaft 7 of the piston 4 (near the piston top surface 4 b). It can be easily installed. Accordingly, the ball center of the ball joint 2a and the center of gravity of the piston 4 can be made to coincide with each other. In particular, as in this embodiment, the center axis 1c of the cylinder 1 and the rotation center 7n of the crankshaft are offset. Since the reaction force 72 that the piston 4 receives from the wall surface of the cylinder 1 is small, it is difficult for the piston 4 and the cylinder 1 to come into contact with each other, and the sliding loss between the piston 4 and the cylinder 1 can be effectively reduced.

FIG. 8 is a schematic perspective view showing the shape of the piston in the first embodiment. With reference to FIG. 8, the shape of the piston 4 will be described with reference to FIGS.
As described with reference to FIG. 3, the piston 4 includes the inner ball cut portion 4 d and the piston 4 so that the connecting rod 2 and the piston 4 do not interfere with each other even when the offset amount D takes a large value exceeding 2 mm. A piston notch 4e is provided at the outer peripheral lower end. The piston 4 is provided with a piston recess region 4a on the outer peripheral surface of the piston 4 at a portion including a portion in the direction of the bottom dead center with respect to the central position of the axial length of the piston 4 so as not to contact the inner peripheral surface of the cylinder. ing. In this example, the piston recessed area 4a is formed with a depth of 200 μm from the sliding surface of the piston 4. The depth of the piston recess area 4 is preferably 50 μm or more from the sliding surface.

  When the rotational speed of the compressor is low, the speed at which the piston 4 reciprocates decreases. When the sliding speed on the sliding surface is reduced, it is difficult to form an oil film of lubricating oil, and the sliding state is likely to deteriorate. That is, the lubricating oil film that should exist in the gap between the piston 4 and the cylinder 1 is likely to break during low-speed operation, and the solid surfaces of the piston 4 and the cylinder 1 come into contact with each other, and the sliding loss tends to increase. In particular, when the contact surface pressure between the piston 4 and the cylinder 1 is large, there is an increased risk that the solid surfaces come into contact with each other and the sliding loss increases.

  For this reason, in the case where the conventional offset is not provided, a certain contact area between the piston 4 and the cylinder 1 is secured in order to prevent an increase in sliding loss between the piston 4 and the cylinder 1 during low-speed operation of the compressor. There was a need to do. In particular, on the outer peripheral surface of the piston 4, a sufficiently large contact area is necessary for a portion that receives the reaction force 72 (see FIG. 5) from the cylinder wall surface.

  On the other hand, in the present embodiment, since the center axis 1c of the cylinder 1 is offset from the shaft rotation center 7n by a distance D, the contact surface pressure between the piston 4 and the cylinder 1 is not offset. And can be reduced. As a result, the contact area between the piston 4 and the cylinder 1 can be greatly reduced as compared with the one with an offset amount of 0, and the sliding loss between the piston 4 and the cylinder 1 can be reduced. . As shown in FIG. 8, in this embodiment, the piston recess area 4a that is not in contact with the cylinder inner peripheral surface is provided on the outer peripheral surface of the piston 4 to effectively reduce the sliding loss. To be able to. The piston axial length L2 of the piston recess area 4a is, for example, 60% of the piston total length L1. In particular, if the piston recessed area 4a is provided on the outer peripheral surface on the side receiving the reaction force 72 from the cylinder wall surface, the effect can be further improved.

  Also, by providing the piston recessed area 4a, the lubricating oil scattered from the crank pin 7a can be easily introduced into the sliding surface between the piston 4 and the cylinder 1 through the recessed area 4a. As a result, it is possible to improve the anti-seizure effect and improve the sealing performance in the cylinder. Thus, by making a piston shape into the structure shown in FIG. 8, the efficiency of the airtight compressor 50 can be improved and the power consumption of the refrigerator 60 carrying this can be reduced.

  A second embodiment of the hermetic compressor according to the present invention will be described with reference to FIG. FIG. 9 is a schematic perspective view showing the shape of the piston in the second embodiment. The basic configuration of the hermetic compressor is the same as that of the above-described first embodiment, and only differences from the first embodiment will be described with reference to FIG.

  As shown in FIG. 9, on the outer peripheral surface of the piston 4, a piston recess region 4a that is not in contact with the inner peripheral surface of the cylinder at a portion including a portion in the bottom dead center direction with respect to the central position of the piston axial length. Is provided. The piston recess area 4 a is formed over the entire circumference of the piston 4 and occupies half or more of the area of the outer peripheral surface of the piston 4. In this embodiment, the piston recessed area 4 a occupies about 60% of the area of the outer peripheral surface of the piston 4.

  With this configuration, in contrast to the piston shape of the first embodiment shown in FIG. 8, in the second embodiment, the piston recess region 4 a is formed on the cylinder wall surface which is the main sliding load surface of the piston 4. Since it is provided not only on the part that receives the reaction force 72 from the side but also on the entire circumference of the piston, it is possible to effectively reduce the sliding area and reduce the sliding loss. Further reduction can be achieved. Therefore, according to the present embodiment, the efficiency of the hermetic compressor 50 can be further improved, and the power consumption of the refrigerator 60 equipped with the same can be further reduced.

DESCRIPTION OF SYMBOLS 1 ... Cylinder, 1a ... Radial bearing part, 1b ... Frame, 1c ... Center axis of a cylinder,
2 ... Connecting rod, 2a ... Ball joint, 2b ... Large end of rod,
2c ... Piston pin,
3 ... Sealed container,
4 ... piston, 4a ... piston recessed area, 4b ... piston top surface,
4c ... spherical surface of piston, 4d ... spherical cut portion of piston, 4e ... piston notch,
5 ... Stator, 6 ... Rotor, 6a ... Rotor core,
7 ... crankshaft, 7a ... crankpin, 7n ... center of rotation of the crankshaft,
17 ... head cover,
18 ... discharge pipe,
20 ... compression element, 21 ... oiling piece, 30 ... electric element, 35 ... lubricating oil,
40 ... discharge valve device,
50 ... Hermetic compressor,
60 ... Refrigerator, 61 ... Refrigerator body, 62 ... Refrigerator room, 63 ... Upper freezer room,
64 ... lower freezer room, 65 ... vegetable room, 66 ... cooler,
70: Refrigerant compression load,
71 ... The force received from the connecting rod
72 ... Reaction force from cylinder wall surface,
73: Friction force between cylinder and piston.

Claims (13)

An airtight container, and a compression element and an electric element housed in the airtight container. The compression element is driven by the electric element via a crankshaft, and a cylinder forming a cylinder chamber is disposed in the cylinder. In a hermetic compressor including a reciprocating piston and a connecting rod connecting the crankshaft and the piston,
The lower limit of the rotational speed range in which the electric element is operated is configured to 1500 min ⁻¹ or less,
Offset the center axis of the cylinder with respect to the center of rotation of the crankshaft;
Further, the hermetic compressor is characterized in that the amount of offset (offset amount) is larger than 2 mm. 2. The hermetic compressor according to claim 1, wherein a rotational speed at which the electric element is frequently operated is less than 2000 min ⁻¹ .   2. The hermetic compressor according to claim 1, wherein the offset amount is greater than 2 mm and not greater than 4 mm.   The hermetic compressor according to claim 3, wherein the offset amount is 3 mm or less.   2. The hermetic compressor according to claim 1, wherein a piston recess region that is not in contact with the cylinder inner peripheral surface is formed on the outer peripheral surface of the piston at least on a portion that receives a reaction force from the cylinder wall surface. A hermetic compressor characterized by   6. The hermetic compressor according to claim 5, wherein the piston recess region is formed in a portion including a portion in a lower dead center direction than a central position of an axial length of the piston. Mold compressor.   The hermetic compressor according to claim 6, wherein the piston recess region is formed over the entire circumference of the piston.   8. The hermetic compressor according to claim 7, wherein an area of the piston recess region formed on the outer peripheral surface of the piston is formed so as to occupy half or more of an area of the piston outer peripheral surface. A hermetic compressor.   6. The hermetic compressor according to claim 5, wherein the piston recessed area is formed at a depth of 50 μm or more from a sliding surface of the piston.   2. The hermetic compressor according to claim 1, wherein the connecting rod and the piston are connected to each other by a ball joint that slides in an inner spherical surface of the piston formed in a substantially spherical shape on the piston. Hermetic compressor.   11. The hermetic compressor according to claim 10, wherein a piston inner sphere formed on the piston is provided with a piston inner sphere cut portion to form an asymmetric shape.   12. The hermetic compressor according to claim 11, wherein the piston has a piston notch at the lower end of the outer periphery of the piston so that the connecting rod and the piston do not interfere with each other.   A refrigerator comprising the refrigeration cycle using isobutane (R600a) as a refrigerant and using the hermetic compressor according to claim 1 as the hermetic compressor used in the refrigeration cycle.

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