KR20170075430A - Piston and linear compressor including the same - Google Patents

Abstract

The present invention relates to a cylinder assembly and a linear compressor including the same.
A cylinder assembly according to an embodiment of the present invention includes: a cylinder; And a piston reciprocating in an inner space of the cylinder, wherein a concavo-convex portion is formed on an outer circumferential surface of the piston, wherein a plurality of convex portions and a plurality of curved portions are alternately arranged.

Description

[0001] The present invention relates to a cylinder assembly and a linear compressor including the same,

The present invention relates to a cylinder assembly and a linear compressor including the same.

The cooling system is a system that generates cool air by circulating a coolant, and repeats the process of compressing, condensing, expanding, and evaporating the coolant. To this end, the cooling system includes a compressor, a condenser, an expansion device and an evaporator. The cooling system may be installed in a refrigerator or an air conditioner as a household appliance.

Generally, a compressor is a mechanical device that receives power from a power generating device such as an electric motor or a turbine to increase pressure by compressing air, refrigerant or various other operating gases. .

Such a compressor is broadly classified into a reciprocating compressor that compresses the refrigerant while linearly reciprocating the piston inside the cylinder so as to form a compression space in which a working gas is sucked and discharged between the piston and the cylinder. A rotary compressor for compressing the refrigerant while the roller is eccentrically rotated along the inner wall of the cylinder and a compression space for sucking and discharging the working gas between the roller and the cylinder, a scroll compressor in which a compression space in which an operating gas is sucked and discharged is formed between a fixed scroll and a fixed scroll and the orbiting scroll rotates along the fixed scroll to compress the refrigerant.

In recent years, among the reciprocating compressors, there has been developed a linear compressor in which a piston is directly connected to a driving motor that reciprocates linearly, so that compression efficiency can be improved without mechanical loss due to motion switching and a simple structure is constructed.

Normally, the linear compressor is configured to suck and compress the refrigerant while discharging the refrigerant while moving the piston in the sealed shell by reciprocating linear motion within the cylinder by the linear motor.

The linear motor is configured such that a permanent magnet is positioned between an inner stator and an outer stator, and the permanent magnet is driven to linearly reciprocate by the mutual electromagnetic force between the permanent magnet and the inner (or outer) stator. As the permanent magnet is driven in the state of being connected to the piston, the piston linearly reciprocates in the cylinder, sucks the refrigerant, compresses the refrigerant, and discharges the refrigerant.

Regarding a conventional linear compressor, the present applicant has been registered by applying a patent application (hereinafter referred to as Prior Art 1).

[Prior Art 1]

1. Registration No. 10-1454549, Date of registration: October 17, 2014, Title of the invention: Linear compressor

Hereinafter, the configuration of a conventional linear compressor will be described with reference to the drawings.

1 and 2 show the construction of a conventional cylinder assembly of a linear compressor.

Referring to FIG. 1, a conventional cylinder assembly 1 includes a cylinder 2 and a piston 3 that reciprocates linearly in the axial direction within the cylinder 2.

The piston 3 is provided with a piston body 4 having a substantially cylindrical shape and disposed inside the cylinder 2 and a permanent magnet (not shown) extending in a radial direction from one end of the piston body 4, And a flange portion 6 joined thereto.

The piston body 4 includes a front portion 5 on which a suction portion 5a is formed. The refrigerant flowing in the piston body 4 can be sucked into the compression space through the suction portion 5a. The compression space is understood as a space formed between the front part 5 and the discharge valve (not shown). The suction unit 5a may be provided with a suction valve (not shown).

The front portion 5 further includes a fastening portion 5b to which a predetermined fastening member (not shown) is coupled to fasten the suction valve to the front portion 5.

The flange portion 6 includes a plurality of holes 7, 8. The plurality of holes 7 and 8 are provided with at least one fastening hole 7 into which a predetermined fastening member to be fastened to a part around the piston 3 is inserted and a flow resistance generated around the piston 3 And at least one through hole 8 for reducing the thickness of the through hole.

2, a gap is formed between the outer circumferential surface of the piston body 4 and the inner circumferential surface of the cylinder 2. The gap may have oil acting as a bearing.

The conventional linear compressor is operated at a relatively high frequency, and recently it is structured so as to be able to operate at a high frequency while getting smaller. In one example, the high frequency may be 100 Hz.

When the linear compressor is operated at the high frequency, the piston 3 reciprocates at a high speed in the cylinder 2. In this process, the movement of the piston in the radial direction is caused, A friction loss due to friction between the cylinders 2 is generated.

The piston 3 or the cylinder 2 is abraded by the friction and the reliability of the resulting oil bearing is lowered so that the force that the piston 3 floats in the cylinder 2 The injured force) was lowered. As a result, the friction between the piston 3 and the cylinder 2 becomes worse.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a cylinder assembly and a linear compressor including the cylinder assembly.

A cylinder assembly according to an embodiment of the present invention includes: a cylinder; And a piston reciprocating in an inner space of the cylinder, wherein a concavo-convex portion is formed on an outer circumferential surface of the piston, wherein a plurality of convex portions and a plurality of curved portions are alternately arranged.

The concave-convex portion is provided so as to have a sawtooth shape.

Further, the hill part guides the oil to be gathered in the curved part.

The concavo-convex portion may include a first connecting portion extending from one of the plurality of convex portions to the convex portion. And a second connection part extending from the other of the plurality of mountain parts to the curved part, wherein the first connection part and the second connection part form a groove angle about the curved part.

Further, the groove angle is in the range of 60 deg. To 70 deg..

The concavo-convex portion is disposed at a front portion of the piston with respect to a center line (lc) of the axial length of the piston.

An inclined portion extending from the front portion in an increasing direction of the outer diameter; And a first extending portion extending from the inclined portion so as to have the same outer diameter toward the rear.

In addition, a second extending portion extending rearward from the first extending portion and having an outer diameter larger than the outer diameter of the first extending portion is further included, and the concave and convex portion is formed in the second extending portion.

Further, the concave-convex portion forms a front end portion of the second extended portion.

The concavo-convex portion may include: a first concavo-convex portion provided at a front portion of the piston; And a second concavo-convex portion provided at a rear portion of the piston.

According to the present invention, a serrated irregular portion is formed on the outer circumferential surface of the piston, and oil is concentrated (compressed) on the concavo-convex portion to increase the pressure, so that the levitation force to lift the piston in the cylinder may increase Effect appears.

Particularly, the convex portion and the convex portion are repeatedly formed, and oil can be effectively concentrated while flowing from the mountain portion toward the valley portion in the process of advancing the piston.

Since the concavo-convex part is disposed in the front part from the central part of the axial length of the piston body, the floating force can be greatly applied in the process of moving the piston forward, that is, in compressing the refrigerant.

In addition, the concave-convex portion may be provided on the front portion and the rear portion of the piston, respectively, so that the pressure and the levitation force can be increased in accordance with concentration of the oil in the process of advancing and retracting the piston.

Further, since the front portion of the piston is provided with the inclined portion extending so as to linearly decrease the outer diameter towards the front portion, the effect of reducing the gap between the piston and the cylinder when the piston is advanced is displayed. As a result, the gap between the piston and the cylinder is compressed by the reduced gap, so that the pressure can be increased, thereby increasing the lifting force of the piston.

In addition, since the angle formed by the first and second connecting portions extending to the adjacent mountain portion around the valley portion of the concave-convex portion, that is, the groove angle is set within the set range, there is an advantage that the friction loss between the reciprocating motion of the piston can be reduced.

1 and 2 are views showing a configuration of a cylinder assembly included in a conventional linear compressor.
3 is a perspective view showing a configuration of a piston according to a first embodiment of the present invention.
4 is a side view showing the configuration of the piston according to the first embodiment of the present invention.
5 is a cross-sectional view showing a configuration of a cylinder assembly according to a first embodiment of the present invention.
6A and 6B are simulation drawings showing a state in which the floating pressure (supporting load) is improved as compared with the conventional art by the construction of the piston according to the first embodiment of the present invention.
FIGS. 7A and 7B are graphs showing experimental results showing that the floating pressure (supporting load) of the gap between the piston and the cylinder is improved by the construction of the piston according to the first embodiment of the present invention.
8 is an experimental graph showing the variation of the friction loss according to the groove angle of the concavo-convex portion according to the first embodiment of the present invention.
9 is a view showing the configuration of a piston according to a second embodiment of the present invention.

Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. It is to be understood, however, that the spirit of the invention is not limited to the embodiments shown and that those skilled in the art, upon reading and understanding the spirit of the invention, may easily suggest other embodiments within the scope of the same concept.

FIG. 3 is a perspective view showing the configuration of a piston according to a first embodiment of the present invention, FIG. 4 is a side view showing the configuration of a piston according to the first embodiment of the present invention, FIG. 5 is a cross- Fig. 5 is a cross-sectional view showing the arrangement of the piston and the cylinder according to Fig.

3 to 5, the piston 100 according to the first embodiment of the present invention may be reciprocally movable in the internal space of the cylinder 200. As shown in FIG.

In detail, the piston 100 includes a piston body 110 having a substantially cylindrical shape and extending in the axial direction, and a piston flange 155 extending radially from the rear end of the piston body 110.

Define the direction.

The axial direction can be understood as a direction in which the piston 100 reciprocates, and the radial direction can be understood as a direction perpendicular to the axial direction. The term " forward " can be understood as a direction in which the piston 100 moves in the direction of compressing the refrigerant, and the term " rear " The definition of such a direction can be equally applied throughout the specification.

For example, the direction from the front portion 120 of the piston body 110 to the piston flange 155 may be defined as the rear direction, and the opposite direction as the front direction.

The piston main body 110 includes a front portion 120 forming a front end portion of the piston main body 110 and having a suction portion 121 and a coupling portion 125 formed therein. A suction valve is installed in the suction part 121 and a fastening member (not shown) for fastening the suction valve to the front part 120 may be coupled to the fastening part 125.

The refrigerant flowing in the piston body 110 may be sucked into the compression space through the suction portion 121. The compression space is understood as a space formed between the front portion 120 and the discharge valve (not shown).

The piston body 110 further includes an inclined portion 130 extending obliquely rearward from the front portion 120. The inclined portion 130 may be inclined so that the outer diameter of the piston body 110 is larger than the outer diameter of the front portion 120. That is, the piston body 110 may be inclined by the inclined portion 130 in a direction in which the outer diameter of the piston body 110 increases toward the rear from the front portion 120.

In detail, the inclined portion 130 may extend so as to linearly increase its outer diameter toward the rear. In other words, the inclined portion 130 may extend so as to linearly decrease its outer diameter toward the front side.

The outer diameter of the inclined portion 130 increases toward the rear so that the gap between the piston 100 and the cylinder 200 may be gradually reduced toward the rear. According to this configuration, when the piston 100 moves forward, the oil can be gradually compressed along the decreasing gap. As a result, the pressure of the oil is increased, and the force of lifting the piston 100 from the inner circumferential surface of the cylinder 200 is increased by the increased pressure.

The piston body 110 includes a first extension 135 extending rearward from the slope 130. The outer diameter of the first extension 135 is constant.

The piston body 110 further includes a second extension 140 extending rearward from the first extension 135 toward the piston flange 150. The outer diameter of the second extending portion 140 may be larger than the outer diameter of the first extending portion 135. The outer diameter of the second extension part 140 may be constant.

The second extending portion 140 includes a concave / convex portion 160. The concave and convex portion 160 may surround the outer periphery of the piston body 110 to increase the pressure of the oil during the movement of the piston 100. For example, the concave-convex portion 160 may have a saw-tooth shape.

The concave-convex portion 160 forms a front end portion of the second extension portion 140. The concave and convex portion 160 may have a shape protruding in the radial direction from the first extending portion 135. In other words, the uneven portion 160 may be formed in a boundary region between the first extending portion 135 and the second extending portion 140.

In detail, the convex portion 160 is formed with a convex portion 161 and a curved portion 165.

A plurality of the crests 161 and the valleys 165 are provided. The plurality of crests 161 and the plurality of curved portions 165 are arranged alternately along the outer peripheral surface of the piston body 110.

Specifically, the curved portion 165 may be positioned between two adjacent hill portions 161, that is, the hill portion of any one of the plurality of hill portions 161 and the other hill closest to the one hill . The concave and convex portion 160 is provided with a first connecting portion 166 extending from the convex portion 161 to the curved portion 165 of the adjacent two convex portions 161 and a second connecting portion 166 extending from the adjacent two convex portions 161 And a second connection portion 167 extending from the hill portion 161 to the curved portion 165 is included.

The first connection portion 166, the curved portion 165, and the second connection portion 167 have a V shape. The first connection portion 166 and the second connection portion 167 form a predetermined angle with respect to the curved portion 165.

The plurality of hill portions 161 may be disposed forward of the plurality of curved portions 165, that is, closer to the front portion 120. Accordingly, in the process of moving the piston 100 forward, the oil first meets the plurality of hill portions 161 and is gathered on the hill portions 165 while being divided on both sides of the mountain portions 161 . That is, the plurality of peak portions 161 can be understood as a configuration for guiding the oil to be gathered toward the curved portion 165 side.

Accordingly, the oil is compressed in the valley portion 165, so that the pressure of the oil is increased and the levitation force for floating the piston 100 or the supporting load for supporting the piston 100 is increased.

The piston flange 150 extends radially from the rear end of the second extension 140 and has a substantially ring shape.

Defines an imaginary extension line (lc) extending in the radial direction with respect to the axial center of the piston body (110). The distance from the extension line lc to the front portion 120 is L1 and the distance from the extension line lc to the rear end of the piston body 110 is 2 * And the distance to the end portion may be L1.

The concave-convex portion 160 may be formed on the front side with respect to the extension line lc. According to such a configuration, the lifting force in the front portion of the piston body 110 can be improved. The refrigerant flows forward from the rear of the piston body 110 and flows toward the discharge valve through the suction port 121. [

Therefore, a higher pressure than the rear portion of the piston body 110 closer to the discharge valve side can be formed. Further, the possibility that the performance of the oil bearing is deteriorated by the high pressure becomes high.

Accordingly, the piston lifting force at the front portion of the piston body 110 needs to be increased. In this embodiment, the concave-convex portion 160 is positioned in the front portion of the piston body 110, so that the oil pressure can be increased and the floating force can be improved.

5, the bold arrows indicate the movement of the piston 100 forward, and the dotted arrows indicate that the oil existing between the piston 100 and the cylinder 200 is in contact with the inclined portion 130 and the concave- 160).

6A and 6B are simulation drawings showing a state in which the floating pressure (supporting load) is improved as compared with the conventional art by the construction of the piston according to the first embodiment of the present invention.

6A shows a simulation of the magnitude of the pressure acting on the outer circumferential surface of the piston body, that is, the levitation force when the concave / convex portion is not formed in the piston body. Specifically, Fig. 6A shows a portion corresponding to the front portion of the piston body, and Fig. 6B shows a portion corresponding to a part of the outer circumferential surface of the piston body.

In the above (A) and (B), a relatively low surface pressure acts. For example, the surface pressure may range from 3 * 10 ⁶ to 1 * 10 ⁷ (kgf / mm 2).

On the other hand, FIG. 6B shows a simulation of the pressure acting on the outer circumferential surface and the concavo-convex portion of the piston body, that is, the magnitude of the levitation force, when the concavo-convex portion is formed in the piston body, as in this embodiment. 6B, a portion corresponding to the front portion 120 of the piston main body 110, (B ') a portion corresponding to a part of the outer peripheral surface of the piston main body 100, and (C') A portion corresponding to the first connection portion 166 or the second connection portion 167, and (D ') a portion corresponding to the curved portion 165.

The surface pressures of (A ') and (B') have a pressure similar to the surface pressure of (A) and (B) of FIG. 6A. On the other hand, relatively high surface pressure acts on (C ') and (D'). For example, the surface pressure may range from 1.3 * 10 ⁷ to 1.6 * 10 ⁷ (kgf / mm 2).

The surface pressure acting on the surfaces (C ') and (D') is such that the oil existing between the cylinder 200 and the piston 100 during the reciprocating movement of the piston 100 is supplied to the protrusions 160, It can be understood that the pressure is concentrated especially on the curved portion 165.

The high surface pressure acting on (C ') and (D') may mean that the piston 100 has a large force of rising from the inner circumferential surface of the cylinder 200. As a result, it can be seen that when the concave-convex structure according to the present embodiment is implemented in the piston 100, the floating pressure acting on the piston 100 can be increased.

FIGS. 7A and 7B are graphs showing experimental results showing that the floating pressure (supporting load) of each gap between the piston and the cylinder is improved, compared with the prior art, by the construction of the piston according to the first embodiment of the present invention.

The graph abscissa in Figs. 7A and 7B represents the time (msec) in which the piston 100 advances forward, and the ordinate axis represents the force (supporting load, N) for supporting the piston 100. Fig. As described above, the support load is understood as a value corresponding to the lifting force of the piston 100. [

On the other hand, the respective diagrams shown in the respective graphs show the clearances (H, mm) between the outer circumferential surface of the piston 100 and the inner circumferential surface of the cylinder 200. For example, the gap H was tested for 0.2 mm, 0.4 mm, 0.6 mm, 0.8 mm and 1 mm.

7A shows a change in the support load with respect to time in the structure in which the concavo-convex portion 160 is not formed on the outer circumferential surface of the piston 100. Fig. Regardless of the change in the gap H, the support load was formed within the range of 0 to 150N.

 When the support load rises, the time decreases again at about 0.5 msec as the acceleration of the piston 100 changes from + to -.

On the other hand, FIG. 7B shows a change in the support load with respect to time in the structure in which the concave and convex portions 160 are formed on the outer circumferential surface of the piston 100. It can be seen that the range of the support load is largely different according to the gap H.

For example, when H = 1 mm, that is, when the gap H is relatively large, it can be seen that the support load N is close to zero. On the other hand, when the gap H is 0.8 mm, the maximum value of the support load N is about 80 N and the gap H is 0.6 mm, the maximum value of the support load N is about 150 N, The maximum value of the supporting load N was measured to be about 750 N when the maximum value of the supporting load N was about 300 N and the gap H was 0.2 mm.

Likewise, the support load increases gradually in the interval of about 0.5 msec at the advance time 0, and the support load decreases gradually in the interval of 0.5 msec to 1 msec. It is understood that the supporting load increases when the forward acceleration of the piston 100 is positive and decreases when the forward acceleration is negative.

As described above, when the structure of the concave and convex portion 160 according to the present invention is realized in the piston 100, it can be seen that the floating pressure acting on the piston 100 can be increased. As the gap H between the outer circumferential surface of the piston 100 and the inner circumferential surface of the cylinder 200 becomes smaller, the levitation pressure rises more remarkably.

8 is an experimental graph showing the variation of the friction loss according to the groove angle of the concavo-convex portion according to the first embodiment of the present invention.

Fig. 8 shows a graph showing that the friction loss W changes according to the change of the groove angle according to the first embodiment of the present invention.

In the graph of FIG. 8, the axis of abscissas represents the angle formed by the first connecting portion 166 and the second connecting portion 167 around the curved portion 165, that is, the groove angle (). The vertical axis represents the friction loss W generated between the piston 100 and the cylinder 200. Of course, the smaller the friction loss W, the better the performance of the compressor.

Prior to the experiment, in order to realize the required performance of the compressor, a friction loss equal to or less than the set value W0 was previously determined. For example, the set value may be 1.5W.

As a result of the experiment, when the groove angle is 60 degrees, the friction loss is 1.43 W, the friction loss is 1.47 W when the groove angle is 70 degrees, the friction loss is 1.51 W when the groove angle is 80 degrees, °, the friction loss is 1.54 W, and the friction loss increases as the groove angle is increased to 90 ° or more.

Through this, the following interpretation can be made.

First, if the groove angle is too large, the concentration of oil into the valley portion 165 is not easily performed and the increase of the oil pressure is limited. As a result, it is difficult to raise the lifting force of the piston 100.

On the other hand, if the groove angle is too small, the oil passage toward the curved portion 165 is not properly formed. That is, when the concave and convex portions 160 are formed to be too dense, it is difficult to concentrate the oil into the curved portions 165. As a result, it can be seen that the increase of the oil pressure in the valley portion 165 is limited, and thus the lift force of the piston 100 is difficult to rise.

Therefore, in this embodiment, the groove angle range is set within the range of 60 to 70 degrees, and the number of the concave-convex portions 160 is appropriately adopted according to the circumferential length of the piston 100 . With such a configuration, it is possible to prevent a large friction loss between the piston 100 and the cylinder 200 from occurring.

Hereinafter, a second embodiment of the present invention will be described. Since the present embodiment differs from the first embodiment only in some configurations, differences are mainly described, and the description and the reference numerals of the first embodiment are used for the same portions as those of the first embodiment.

9 is a view showing the configuration of a piston according to a second embodiment of the present invention.

Referring to Fig. 9, the piston 100a according to the second embodiment of the present invention includes a plurality of protrusions 160a and 160b. In detail, the plurality of concave-convex portions 160a and 160b are provided with a first concave-convex portion 160a provided at a front portion of the piston 100a and a second concave-convex portion 160b provided at a rear portion of the piston 100a ).

The first concavo-convex part 160a is positioned in front of the center line lc and the second concavo-convex part 160b is positioned in front of the center line lc of the piston 100a, And can be positioned at the rear.

The piston 100a is provided with a first inclined portion 130a extending obliquely from the front portion 120 in the direction of increasing the outer diameter and a second inclined portion 130b extending rearward from the first inclined portion 130a to have the same outer diameter A first extension 140a and a second extension 140b extending rearward from the first extension 140a and having an outer diameter larger than the outer diameter of the first extension 140a.

The first concavo-convex portion 160a forms a front end portion of the second extension portion 140b and may be installed in a boundary region between the first extension portion 140a and the second extension portion 140b. The first convex portion 160a includes a first convex portion 161a and a first convex portion 165a. The description of the first concavo-convex portion 160a explains the configuration of the concavo-convex portion 160 of the first embodiment. Accordingly, the first concavo-convex portion 160a can function to concentrate the oil into the valley portion 165 when the piston 100a moves forward.

The piston 100a further includes a second inclined portion 130b extending obliquely downward in a direction in which the outer diameter of the piston 100a decreases from the second extended portion 140b toward the rear.

The piston 100a further includes a third extension 140c extending rearward from the second slope 130b so as to have the same outer diameter. The center line lc may be formed to pass through the third extension portion 140c.

The piston 100a is provided with a third inclined portion 130c extending obliquely so as to increase its outer diameter from the third extended portion 140c toward the rear and an outer diameter of the third inclined portion 130c And further includes a fourth extension portion 140d which is constantly extended.

At the rear end of the fourth extension part 140d, the second concave-convex part 160b is formed. The second convex portion 160b includes a second convex portion 161b and a second convex portion 165b. The second concave-convex portion 160b may be configured such that when the piston 100a moves backward, the oil is concentrated to the second curved portion 165b. The description of the configuration of the second concave-convex portion 160b is omitted from the description of the concave-convex portion 160 of the first embodiment.

The piston 100a is provided with a fifth extending portion 140e extending to the rear from the fourth extending portion 140d so as to have the same diameter and having an outer diameter larger than the outer diameter of the fourth extending portion 140d . The second concavo-convex portion 160b may be formed in a boundary region between the fourth extension portion 140d and the fifth extension portion 140e.

The piston 100a is provided with a fourth inclined portion 130d extending obliquely to reduce its diameter from the fifth extended portion 140e toward the rear and a fourth inclined portion 130d extending rearward from the fourth inclined portion 130d And further includes a sixth extension 140f.

According to the configuration of the piston 100a according to the present embodiment, when the piston 100a advances, the oil is concentrated in the first concave / convex portion 160a, and the pressure of the oil increases, The power can be increased. When the piston 100a moves backward, the oil is concentrated on the second concave and convex portion 160b, so that the pressure of the oil increases and thus the lifting force of the piston 100a can be increased.

As a result, the lifting force of the piston 100a may be increased by the first and second convex and concave portions 160a and 160b in the front portion and the rear portion of the piston 100a during the reciprocating motion of the piston 100a, The friction loss between the cylinder 200 and the cylinder 200 can be reduced and the reliability of the oil bearing can be increased.

100: Piston 110: Piston body
120: front part 121: suction part
125: fastening part 130:
135: first extension part 140: second extension part
150: piston flange 160: concave /
160a: first irregular portion 160b: second irregular portion
161: Mountain part 165:
166: first connection part 167: second connection part
200: Cylinder

Claims (18)

A cylinder having an inner space; And
A piston reciprocating in an internal space of the cylinder,
In the piston,
A front portion forming a front end portion of the piston and provided with a suction valve;
A piston body extending rearward from the front portion;
A piston flange extending radially from a rear portion of the piston body; And
And a concave portion formed on an outer circumferential surface of the piston body for guiding the concentration of oil located between the outer circumferential surface of the piston and the inner circumferential surface of the cylinder. The method according to claim 1,
The concavo-
And the piston assembly is provided so as to surround the outer periphery of the piston body. The method according to claim 1,
Wherein the concavo-convex part has a saw-tooth shape. The method of claim 3,
In the concave-
A mountain portion forming a front portion of the concave-convex portion; And
And a curved portion which is located at the rear of the mountain and on which oil guided by the mountain is collected. 5. The method of claim 4,
Wherein a plurality of the mountain portions and the valley portions are alternately arranged. 6. The method of claim 5,
In the concave-
A first connection part extending from the mountain part to the valley part of the plurality of mountain parts; And
And a second connection part extending from the other of the plurality of mountain parts to the curved part,
And the first connecting portion and the second connecting portion form a groove angle about the curved portion. The method according to claim 6,
Wherein the groove angle is in the range of 60 to 70 degrees. The method according to claim 1,
The concavo-
Is disposed at a front portion of the piston with respect to a center line (lc) of the axial length of the piston. The method according to claim 1,
An inclined portion extending in a direction in which an outer diameter of the front portion increases; And
And a first extending portion extending from the inclined portion so as to have the same outer diameter rearward. 10. The method of claim 9,
Further comprising a second extending portion extending rearward from the first extending portion and having an outer diameter larger than an outer diameter of the first extending portion,
And the uneven portion is formed in the second extending portion. 11. The method of claim 10,
Wherein the concave and convex portion forms a front end portion of the second extension portion. The method according to claim 1,
In the concave-
A first concavo-convex portion provided at a front portion of the piston; And
And a second concave portion provided on a rear portion of the piston. 13. The method of claim 12,
A first inclined portion extending obliquely in a direction of increasing the outer diameter from the front portion;
A first extension extending rearwardly from the first inclined portion so as to have the same outer diameter;
A second extending portion extending rearward from the first extending portion and having an outer diameter larger than the outer diameter of the first extending portion; And
And a second ramp extending rearwardly from the second extension in an inclined manner in a direction in which the outer diameter thereof decreases. 14. The method of claim 13,
And the first concavo-convex part is installed in the second extension part. 14. The method of claim 13,
A third inclined portion extending rearwardly from the second extending portion so as to be inclined to increase its outer diameter;
A fourth extending portion extending rearward from the third inclined portion and extending to have the same outer diameter;
A fifth extending portion extending rearward from the fourth extending portion and having an outer diameter larger than the outer diameter of the fourth extending portion; And
Further comprising: a fourth inclined portion extending rearwardly from the fifth extending portion so as to be inclined to decrease its outer diameter. 16. The method of claim 15,
And the second concavo-convex part is installed in the fourth extension part. A linear compressor having the cylinder assembly of any one of claims 1 to 16. A cylinder having an inner space; And
A piston reciprocating in an internal space of the cylinder,
On the outer peripheral surface of the piston,
And a plurality of convex and concave portions arranged alternately in a plurality of convex portions and a plurality of curved portions are formed.

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