JP2023169602A - reciprocating compressor - Google Patents

Abstract

To provide a reciprocating compressor that can reduce wear of a piston and a piston ring, and has high reliability.SOLUTION: A reciprocating compressor 50 according to the present invention comprises: a cylinder 1 constituting a compression chamber 40; a piston 4 in proximity to or in sliding contact with a cylinder inner wall surface 1n, and for making reciprocating motion and oscillating motion; and a connecting rod 2 fixed to the piston 4, and connecting the piston 4 and a crankshaft 5. A piston ring 6 in sliding contact with the cylinder inner wall surface 1n is fitted to the piston 4. In the piston 4, at least surfaces 4c and 4d in proximity to the cylinder inner wall surface 1n have an approximately spherical shape. The piston ring 6 is located at a position where a center line 6o of a width dimension s1 thereof and a spherical center 4o of the piston 4 approximately coincide, and is arranged at a center βho of an oscillating range βh of the piston 4.SELECTED DRAWING: Figure 1

Description

The present invention relates to a reciprocating compressor.

Conventionally, as a compressor for compressing fluid, there is a reciprocating compressor in which a piston reciprocates linearly.
There are two types of reciprocating compressors: a normal piston type and a swinging piston type as described below.
Usually, the piston type has a bearing provided at the end of the connecting rod on the compression chamber side, and a piston supported by the bearing so as to be able to swing.
The swing piston type does not have a bearing on the compression chamber side of the connecting rod, but has a seal ring on the piston integrated with the connecting rod that deforms elastically to seal compressed fluid.

The rocking piston method has a simpler structure than the regular piston method because it does not have bearings or piston pins, there are no design restrictions due to bearing temperature, and the mass of reciprocating movement can be reduced. It has many advantages.

JP 2021-055647 (Figure 2, Figure 3B, paragraph 0024, etc.)

However, on the other hand, especially in compressors with large strokes, the range of angles at which the connecting rod tilts during one rotation of the crankshaft (oscillation angle) becomes large, causing wear and tear on the piston due to contact between the piston and cylinder, increased vibration, and sealing. This causes problems such as decreased performance.
These are generally issues with the swinging piston system. For example, as shown in Patent Document 1, a technology is proposed in which the top of the piston (33) is made into a spherical shape to prevent excessive contact and deterioration of sealing performance due to swinging motion. It has been known.

In Patent Document 1, a piston ring (37) is installed on the outer periphery of the piston (33) in order to improve the sealing performance between the piston (33) and the cylinder (22). Since the piston ring (37) is installed approximately perpendicular to the connecting rod axis (32), at the angular position where the swing angle becomes large, the spherical piston (33), rather than the piston ring (37), has a cylindrical surface. Line contact with cylinder (22). Therefore, it is necessary to select a material for the piston (33) that simultaneously satisfies lubricating properties to reduce friction and strength properties to reduce wear.

In addition, airtightness inside and outside the compression chamber must be maintained by sealing through line contact between the piston and the cylinder. The structure is such that the swing angle in the compression stroke is made small by being arranged offset from the other hand. For this reason, in the suction stroke, the swing angle increases, the contact range of the piston (33) increases, and there is a concern that problems such as wear of the piston (33) may occur. Therefore, it may be necessary to replace the piston (33) together with the piston ring (37) to ensure reliability.

The present invention was devised in view of the above-mentioned circumstances, and an object of the present invention is to provide a highly reliable reciprocating compressor that can reduce wear on pistons and piston rings.

In order to solve the above problems, the reciprocating compressor of the present invention includes a cylinder that constitutes a compression chamber, a piston that moves reciprocatingly and swings in close proximity to or in sliding contact with the inner wall surface of the cylinder, and a piston that is fixed to the piston, A connecting rod connecting the piston and a crankshaft is provided, the piston is equipped with a piston ring that makes sliding contact with the inner wall surface of the cylinder, and the piston has at least a substantially spherical surface adjacent to the cylinder. The piston ring is located at a position where the center line of its width dimension substantially coincides with the center of the spherical surface of the piston, and is located at the center of the swing range of the piston.

According to the present invention, it is possible to provide a highly reliable reciprocating compressor that can reduce wear on pistons and piston rings.

1 is a vertical cross-sectional view of essential parts of an air compressor using a crank mechanism according to Embodiment 1 of the present invention. A schematic diagram of a crankshaft, a connecting rod, a piston, and a cylinder showing the swing angle of a connecting rod during a compression stroke of an air compressor. FIG. 2 is a perspective view of a piston according to Embodiment 1. FIG. 2 is a perspective view of a piston ring of Embodiment 1. A schematic diagram of a crankshaft, a connecting rod, a piston, and a cylinder showing the swing angle of a connecting rod during the expansion stroke of an air compressor. FIG. 2 is a schematic diagram of a piston and a connecting rod of Embodiment 1. FIG. 3 is a diagram showing a time history change of the rocking angle with respect to the crank angle in the first embodiment. FIG. 2 is a sectional view of a cylinder portion of an air compressor using a piston according to a second embodiment of the present invention.

The present invention relates to a reciprocating compressor in which a piston reciprocates within a cylinder.
Embodiments of the present invention will be described below with reference to the accompanying drawings. Similar components are given the same reference numerals, and similar descriptions will not be repeated.

<<Embodiment 1>>
FIG. 1 shows a vertical cross-sectional view of a main part of an air compressor 50 using a crank mechanism according to a first embodiment of the present invention.
The air compressor 50 of the first embodiment is a device that compresses air, which is a fluid.
In the air compressor 50, the crankshaft 5 is rotated by a drive source such as an electric motor (not shown).

The crankshaft eccentric portion 5 a is connected to a connecting rod large end portion 2 b at one end of the connecting rod 2 via a large end bearing 9 .
Examples of the big end bearing 9 include rolling bearings and sliding bearings. The big end bearing 9 may be configured to be separate from the connecting rod 2 and the crankshaft 5, or may be configured to be integrated with the connecting rod 2 and the crankshaft 5.
A piston 4 for compressing fluid is connected to a connecting rod small end 2e at the other end of the connecting rod 2. The piston 4 is made of a different member from the connecting rod 2.

The piston 4 is configured to reciprocate and swing within the cylindrical cylinder 1.
In order to smoothly reciprocate and swing within the cylindrical cylinder 1, the piston 4 has a substantially spherical shape at a portion where it comes into close or sliding contact with the inside of the cylindrical cylinder 1.
The upper surface 4b of the tip edge of the piston 4 and the inside of the inner wall surface 1n of the cylindrical cylinder 1 form a compression chamber 40 in which fluid is compressed.

When the crankshaft 5 rotates (arrow α11 in FIG. 1), the piston 4 reciprocates and oscillates within the cylinder 1 together with the connecting rod 2.
Through this series of operations, the compression chamber 40 within the cylinder 1 repeatedly expands and compresses, thereby functioning as a compressor.
As the compression chamber 40 expands and compresses, the volume inside the crankcase 3 also repeats expansion and compression. Therefore, the inside and outside of the crankcase 3 are structured to communicate with each other.

A cylinder head 7 having a reed valve type suction valve 10 and a discharge valve (not shown) attached to one end face of the cylinder 1 is assembled.
The cylinder head 7 has a suction port 7a and a discharge port 7b. The suction port 7a sucks in the air of the fluid to be compressed, and the discharge port 7b discharges the air of the compressed fluid.
The suction valve 10 and the discharge valve (not shown) open and close in accordance with the expansion and compression of the compression chamber 40. That is, outside air is taken into the compression chamber 40 through the suction valve 10 and through the suction port 7a. On the other hand, the air compressed in the compression chamber 40 is discharged from the compression chamber 40 through the discharge valve and the discharge port 7b into a discharge space (not shown) constituted by the cylinder head 7 and the head cover 8. be done.

When the crankshaft 5 rotates (arrow α11 in FIG. 1), the piston 4 is restrained within the cylinder 1, so there is a reciprocating motion component in the axis (center axis 1a) direction of the cylinder 1 and a component around the crankshaft eccentric center 5a1. It has a rotational motion component.
At this time, if the center of rotational movement 2a (see FIG. 2) of the small end 2e of the connecting rod is always kept at a constant position with respect to the connecting rod 2, the ideal external shape of the piston 4 will be a spherical shape.

FIG. 2 is a schematic diagram of the crankshaft 5, the connecting rod 2, the piston 4, and the cylinder 1 showing the swing angle β of the connecting rod 2 during the compression stroke of the air compressor 50.
On the other hand, it is also possible to design such that the center of rotational movement 2a of the small end portion 2e of the connecting rod moves according to the rotational angle θ of the crankshaft 5 (see FIG. 2). In that case, the outer shape of the piston 4 is not a sphere, but a distorted shape from a sphere in which the center of rotational motion 2a has moved. The external shape of the piston 4 can be arbitrarily designed depending on the sliding characteristics and sealing characteristics between the piston 4 and the cylinder 1.

<Piston 4 and piston ring 6>
FIG. 3 shows a perspective view of the piston 4 of the first embodiment.
FIG. 4 shows a perspective view of the piston ring 6 of the first embodiment.

An annular piston ring 6 is fitted into the center of the piston 4 shown in FIG. 1 .
The piston 4 shown in FIG. 3 is formed with an annular groove 4a for fitting a piston ring 6 (see FIG. 4).

The outer peripheral surface 6g of the piston ring 6 shown in FIG. 4 is a substantially cylindrical surface. The outer diameter D1 of the piston ring 6 is set so that when the piston 4 is attached to the piston 4, it slides smoothly inside the cylinder 1, and at the same time, the airtightness of the compression chamber 40 inside the cylinder 1 is maintained during compression. A dimensional relationship with the inner diameter d1 of the cylinder 1 (see FIG. 1) is determined.

The piston ring 6 shown in FIG. 4 has a substantially C-shape that is substantially annular. The piston ring 6 has an abutment 6a forming a substantially C-shaped end.
In a natural state where no external force is applied to the piston ring 6, its outer diameter is slightly larger than the inner diameter d1 of the cylinder 1 (see FIG. 1). However, when the piston ring 6 is attached to the annular groove 4a (see FIG. 3) of the piston 4 and inserted into the cylinder 1 as shown in FIG. Due to the reaction force (expansion force) due to contraction and deformation, the outer circumferential surface 6g of the piston ring 6 comes into pressure contact with the inner wall surface 1n of the cylinder 1 and comes into substantially close contact with it. Thereby, the airtightness of the compression chamber 40 formed by the inner wall surface 1n of the cylinder 1, the piston ring 6, and the piston 4 is maintained.

By the way, when the piston ring 6 is not attached to the piston 4, the contact between the piston 4 and the cylinder 1 is a linear contact because the piston 4 has a substantially spherical shape and the inner wall surface 1n of the cylinder 1 is a cylindrical surface. becomes.

On the other hand, when the piston ring 6 is attached to the piston 4, the outer circumferential surface 6g of the piston ring 6 is a substantially cylindrical surface, and the inner wall surface 1n of the cylinder 1 is a cylindrical surface. Become.
Therefore, by using the piston ring 6 having a substantially cylindrical outer circumferential surface 6g, the piston ring 6 comes into substantially surface contact with the cylinder 1, so that the compression chamber 40 can have a structure with excellent sealing properties.

<Piston 4 and connecting rod 2>
In the structure of the first embodiment, the gas pressure (air pressure) in the compression chamber 40 is mainly applied to the upper surface 4b of the piston 4 (see FIG. 1). The force applied to the piston 4 is generally applied in the axial direction of the connecting rod 2, which is substantially perpendicular to the upper surface 4b of the piston 4. A part of the gas pressure within the compression chamber 40 acts between the inner wall surface 1n of the cylinder 1 wall surface and the piston 4. Here, as shown in FIG. 1, the parts where the piston 4 can slide on the inner wall surface 1n of the wall surface of the cylinder 1 are the piston upper curved surface 4c and the piston lower curved surface 4d shown in FIG.

When the piston 4 is constructed without using lubricating oil, the piston 4 can be made of a material with excellent solid lubricity. By configuring the piston 4 without using lubricating oil, there is an advantage that lubricating oil is not mixed into the compressed gas (air) in the compression chamber 40.
An example of a material with excellent solid lubricity used for the piston 4 is a material made by adding a filler such as glass fiber to a fluororesin such as polytetrafluoroethylene to improve mechanical properties such as strength and toughness. Conceivable.

On the other hand, the connecting rod 2 shown in FIG. 1 is a part to which a compression reaction force is applied by the compressed fluid (air) based on the gas pressure in the compression chamber 40, and is required to have mechanical strength. Therefore, it is desirable that the connecting rod 2 be made of a material with high mechanical strength. Examples of materials with high mechanical strength include metal materials such as iron-based materials and aluminum-based materials.
In the first embodiment, the piston 4 and the connecting rod 2 are made of different members in order to achieve both the mechanical strength of the connecting rod 2 and the sliding characteristics of the piston 4 in an environment without using lubricating oil.

<Swinging angle β of connecting rod 2>
FIG. 5 shows a schematic diagram of the crankshaft 5, the connecting rod 2, the piston 4, and the cylinder 1, showing the swing angle β of the connecting rod 2 during the expansion stroke of the air compressor 50.
Next, the swing angle β of the connecting rod 2 will be explained. The swing angle β is the angle formed by the connecting rod 2 with respect to the central axis 1a of the cylinder 1 (see FIGS. 2 and 5).
In the first embodiment, as shown in FIGS. 2 and 5, the crankshaft rotation axis 5b and the cylinder center axis 1a do not intersect, but are offset by an offset amount δ. By offsetting, the external force in the direction perpendicular to the reciprocating movement of the piston 4 toward the piston 4 can be reduced in the compression process, and smooth reciprocating movement of the piston 4 becomes possible.

In FIG. 2, the crankshaft 5 rotates counterclockwise (arrow α11 in FIG. 2), but the cylinder center axis 1a is rotated at the crankshaft eccentric portion 5a in the compression stroke (FIG. 2) with respect to the crankshaft rotation axis 5b. is offset by an offset amount δ to the side where is located (right side in the paper).
Here, we will focus on the swing angle β, which is the angle formed by the connecting rod 2 and the cylinder center axis 1a. The swing angle β is an angle formed between the connecting rod 2 and the cylinder center axis 1a, and changes during the cycle of the piston 4.
When the cylinder center axis 1a and the crankshaft rotation axis 5b intersect (when there is no offset and the offset amount δ is 0), the maximum swing angle in the compression stroke (the state in Figure 2) and the suction stroke (in the state in Figure 5) The maximum swing angles in the state) are the same.

On the other hand, when an offset (offset amount δ) is provided as in Embodiment 1, the oscillating motion between the compression stroke (Fig. 2) and the expansion stroke (Fig. 5) is As shown in 5, the cylinder is asymmetrical with respect to the cylinder center axis 1a. In the case of the first embodiment, the maximum swing angle βc in the compression stroke shown in FIG. 2 is smaller than the maximum swing angle βs in the suction stroke shown in FIG.

In the first embodiment, as shown in FIG. 1, a piston ring 6 is attached to a piston 4 that swings.
A substantially spherical center 4o of the piston 4 is located on the centerline 2o of the connecting rod 2. A center line 6o that equally divides the width s1 of the piston ring 6 passes through the substantially spherical center (spherical center) 4o of the piston 4.

<Piston 4 and connecting rod 2>
FIG. 6 shows a schematic diagram of the piston 4 and connecting rod 2 of the first embodiment.
A straight line perpendicular to the center line 2o of the connecting rod 2 is defined as a straight line 2h. While the connecting rod 2 swings (between the compression stroke in FIG. 2 and the expansion stroke in FIG. 5), the piston ring 6 slides on the inner wall surface 1n of the cylinder 1 evenly with respect to the center line 6o of the piston ring 6. A piston ring 6 is attached to the piston 4 in such a manner. That is, the piston ring 6 is attached to the annular groove 4a (see FIG. 3) of the piston 4 that is inclined at an angle α with respect to a straight line 2h perpendicular to the centerline 2o of the connecting rod 2. In other words, the piston ring 6 is attached to the piston 4 with its center line 6o inclined at an angle α with respect to a straight line 2h perpendicular to the connecting rod 2 (center line 2o).

When the swing range of the center line 6o of the piston ring 6 is βh, the center line 6o of the piston ring 6 is positioned in the middle or almost in the middle with respect to the straight line 2h perpendicular to the center line 2o of the connecting rod 2. The piston ring 6 is attached to the annular groove 4a (see FIG. 3) of the piston 4 at an angle α.
As a result, the positional relationship between the piston 4 and the piston ring 6 during the compression process in FIG. 2 and during the expansion process in FIG. 5 is as follows.

While the connecting rod 2 swings (from the compression stroke in FIG. 2 to the expansion stroke in FIG. 5), the piston ring 6 slides ( contact).

The maximum swing angle β of the connecting rod 2 during the compression process shown in FIG. 2 is β=βc.
During the expansion process in FIG. 5, the maximum swing angle β of the connecting rod 2 is β=βs.
Since the piston ring 6 is fixed to the piston 4, it swings together with the piston 4 relative to the cylinder 1.

<Time history change of rocking angle β with respect to crank angle θ>
FIG. 7 shows a time history change of the swing angle β, which is the angle formed by the connecting rod 2 with respect to the central axis 1a of the cylinder 1 (see FIGS. 2 and 5), with respect to the crank angle θ. The horizontal axis of the graph in FIG. 7 represents the crank angle θ, and the vertical axis represents the rocking angle β.
The crank angle θ of the crankshaft 5 (see FIGS. 2 and 5) is defined as 0° (0 on the horizontal axis) when the connecting rod large end 2b reaches the lowest point during the expansion stroke in FIG. The counterclockwise direction of the crankshaft 5 is defined as the positive direction.

In FIG. 5, it is assumed that the swing angle β takes a positive value when the connecting rod large end 2b is located on the left side of the cylinder center axis 1a.
As described above, in the first embodiment, the crankshaft rotating shaft 5b and the cylinder center axis 1a are offset by an offset amount δ.
Therefore, the rocking motion of the connecting rod 2 is asymmetrical with respect to the cylinder center axis 1a, unlike in the case where there is no offset. Therefore, as shown in FIG. 7, the time history change of the swing angle β becomes vertically asymmetrical with respect to the horizontal axis (X-axis).

In the case of Embodiment 1, the maximum swing angle βc in the compression stroke (the stroke in which the piston 4 moves from the bottom dead center (at the time of maximum expansion) to the top dead center (at the time of maximum compression) shown in FIG. It becomes smaller than when it is 0. This reduces the force applied to the piston 4 in the direction perpendicular to the central axis 1a of the cylinder 1 and the force applied to the piston 4 in the direction perpendicular to the reciprocating motion during compression, when the pressure is highest.

<Operation of piston 4 during suction stroke>
Next, the operation in the suction stroke shown in FIG. 5 will be explained.
In the suction stroke in which the piston 4 descends, since the piston 4 is offset by the offset amount δ, the swing angle β becomes larger than that in the compression stroke, as shown in FIG. In the large swing angle β range shown in FIG. Contact.

When the outer peripheral surface 4g of the piston 4 comes into contact with the inner wall surface 1n of the cylinder 1, wear and material deterioration at the contact portion of the piston 4 are likely to occur. This causes a decrease in the reliability of the air compressor 50.
Furthermore, since the piston ring 6 is not in contact with the inner wall surface 1n of the cylinder 1, the flow rate of gas leaking from between the piston ring 6 and the inner wall surface 1n of the cylinder 1 increases, and the sealing characteristics deteriorate.
Furthermore, vibrations and noise are likely to occur due to changes in the contact state of the piston 4. These problems become even more noticeable as the wear of the contact portion of the piston 4 with the inner wall surface 1n of the cylinder 1 increases.

<Relationship between the swing angle β of the connecting rod 2 and the angle α at which the piston ring 6 is installed>
The relationship between the swing angle β and the angle α at which the piston ring 6 is installed will be explained using FIG.
In order to reduce the wear of the piston 4, the range in which the outer circumferential surface 4g of the piston 4 contacts the inner wall surface 1n of the cylinder 1 is made as small as possible, and the contact range of the outer circumferential surface 4g of the piston ring 6 is made large.
To this end, in the first embodiment, the piston ring 6 is arranged at a position where the center of rotational motion 2a of the small end portion 2e of the connecting rod and the spherical center 4o of the piston 4 approximately coincide (substantially coincide).

Further, the piston ring 6 is arranged to be inclined by an angle α, which is the piston ring installation angle, from a plane 2h perpendicular to the central axis 2o of the connecting rod 2. The angle α is made to match the average swing angle βm shown in FIG.
Therefore, the piston ring 6 is disposed approximately at the center of the contact range of the outer circumferential surface 4g of the piston 4 due to the rocking movement of the connecting rod 2 to which the piston 4 is fixed. Therefore, the contact surface between the outer circumferential surface 4g of the piston 4 and the inner wall surface 1n of the cylinder 1 becomes smaller, and wear and tear on the piston 4 is reduced. This prevents or suppresses an increase in leakage of compressed gas within the cylinder 1. Therefore, good sealing properties are maintained, and increases in vibration and noise can be prevented or suppressed.

When maintaining the air compressor 50, it is necessary to replace the piston ring 6 as appropriate depending on the condition of the piston ring 6, but the frequency of replacing the piston 4 can be significantly extended.
As described above, according to the first embodiment, it is possible to provide the air compressor 50 having a highly reliable and highly efficient reciprocating mechanism.
Moreover, the maintainability of the air compressor 50 is improved, and maintenance costs can be reduced. The reciprocating mechanism of the first embodiment is applicable to the air compressor 50 and other devices.

<<Embodiment 2>>
FIG. 8 shows a cross-sectional view of a cylinder section using the piston 4 of an air compressor 50 according to Embodiment 2 of the present invention.
In the second embodiment, the height 26h (size or range of the piston ring 26) of the piston ring 26 is greater than or equal to the swing range βh of the piston 4, unlike the first embodiment shown in FIG.

In the second embodiment, the same components as in the first embodiment are denoted by the same reference numerals, and different components are denoted by the numerals in the 20s.
In the second embodiment, the piston ring 26 is arranged at a position where the rotational movement center 2a of the connecting rod small end 2e and the spherical center 4o of the piston 4 approximately coincide.
Then, after arranging the piston ring 26 so as to be inclined by an angle α which is an average swing angle βm from a plane perpendicular to the central axis 2o of the connecting rod 2, the piston ring 26 is placed within a height 26h (size) range. It is specified that the swing range of the piston 4 is not exceeded from . In other words, the swinging range βh of the piston 4 is set within the range of the height 26h of the piston ring 26.

Therefore, the range of contact between the outer circumferential surface 4g of the piston 4 and the inner wall surface 1n of the cylinder 1 (see FIG. 1) due to the rocking movement of the connecting rod 2 to which the piston 4 is fixed is only the range of the piston ring 6.
Therefore, the outer peripheral surface 4g of the piston 4 does not come into contact with the inner wall surface 1n of the cylinder 1, and the piston 4 does not wear out. This eliminates the need to replace the piston 4 as a maintenance part.

Therefore, according to the second embodiment, it is possible to provide the air compressor 50 having a reciprocating mechanism (reciprocating mechanism) with high reliability and low maintenance cost.

<<Other embodiments>>
1. In the first and second embodiments described above, air is used as an example of the fluid, but fluids other than air may be used.

2. The present invention is not limited to the configurations of the first and second embodiments described above, and various modifications and specific forms are possible within the scope of the appended claims.

1 Cylinder 1a Cylinder center axis (center axis of cylinder inner wall surface)
1n Cylinder inner wall surface (cylinder inner wall surface)
2 Connecting rod 2a Center of rotational movement of the small end of the connecting rod 4 Piston 4c Piston upper curved surface (proximate surface of the piston)
4d Piston lower curved surface (piston proximal surface)
4o Center of approximately spherical shape of piston 4 (center of spherical surface of piston)
5 Crankshaft 5b Crankshaft rotation axis (crankshaft rotation axis)
6 Piston ring 6o Center line of piston ring width dimension 26h Piston ring height (piston ring size)
40 Compression chamber 50 Air compressor (reciprocating compressor)
s1 Piston ring width dimension α Piston ring installation angle β Swing angle βh Piston swing range βho Center of piston swing range δ Offset amount

Claims (4)

A cylinder that constitutes a compression chamber;
a piston that reciprocates and oscillates in close proximity to or in sliding contact with the inner wall surface of the cylinder;
a connecting rod fixed to the piston and connecting the piston and the crankshaft;
The piston is equipped with a piston ring that makes sliding contact with the inner wall surface of the cylinder,
The piston has a substantially spherical shape at least at a surface adjacent to the cylinder inner wall surface,
In the reciprocating compressor, the piston ring is located at a position where a center line of its width dimension substantially coincides with a spherical center of the piston, and is disposed at the center of a swing range of the piston. The reciprocating compressor according to claim 1,
The reciprocating compressor is configured such that a center axis of the inner wall surface of the cylinder and a rotation axis of the crankshaft are offset from each other. A cylinder constituting a compression chamber, a piston that slides on the inner wall surface of the cylinder and makes reciprocating and rocking movements, and a connecting rod that is fixed to the piston and connects the piston and the crankshaft,
A piston ring is attached to the piston,
The piston has at least a sliding surface having a substantially spherical shape,
The central axis of the cylinder inner wall surface and the rotation axis of the crankshaft are offset,
A reciprocating compressor in which the piston ring is located at the center of the swing range of the piston. The reciprocating compressor according to claim 1 or 3,
A reciprocating compressor in which the swing range of the piston does not exceed the range of the piston ring.

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