JP2002371959A - Linear compressor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a linear compressor capable of preventing a collision of a piston and a cylinder head, and preventing a flaw or collision noise generated between the piston and the cylinder head, even when impact force working at the time of transporting. SOLUTION: In this linear compressor, a compression mechanism compressing gas or liquid and a linear motor actuating the compression mechanism are provided in a sealed container. The compression mechanism has a cylinder and a piston, and the linear motor has a fixed portion connected to the cylinder and a movable portion connected to the piston. The linear compressor is provided with a coil spring connected to the piston or the movable portion at one end, connected to the cylinder and the fixed portion at the other end, and supporting the piston so as to move in an axial direction. The coil spring is used as a compression spring, and the elastic force of the coil spring keeps the piston pressing against one end side of the cylinder.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a linear compressor for compressing gas by reciprocating a piston fitted in a cylinder by a linear motor, and more particularly to a direction perpendicular to the reciprocating direction of the piston. The present invention relates to a linear compressor in which a load hardly acts on the compressor.

[0002]

2. Description of the Related Art It is said that an HCFC-based refrigerant represented by R22 used in a refrigeration cycle destroys an ozone layer due to the stability of its physical properties. In recent years, HC
Although an HFC-based refrigerant is used as an alternative refrigerant to the FC-based refrigerant, the HFC-based refrigerant has a property of promoting a warming phenomenon. Therefore, recently, HC-based refrigerants that do not significantly affect the destruction of the ozone layer and the global warming phenomenon have begun to be adopted. However, since the HC-based refrigerant is flammable, it is necessary to prevent explosion and ignition from the viewpoint of ensuring safety. Therefore, it is required to reduce the amount of the refrigerant used as much as possible. On the other hand, the HC-based refrigerant has no lubricity as the refrigerant itself, and has a property of being easily dissolved in a lubricant. From the above, when an HC-based refrigerant is used, an oilless or oil-poor compressor is required. The linear compressor is known as a compressor in which a piston movable part has a free piston stroke in which a piston position is freely determined by a motor thrust applied to a motor and an operating pressure condition, and a load in a direction orthogonal to the axis of the piston. And the sliding surface pressure is small. Therefore, compared to reciprocating compressors, rotary compressors, and scroll compressors that have been widely used in the past, this type is easier to be oilless.

[0003]

However, since this linear compressor has a free piston stroke and is not mechanically restrained by other members, the piston tip is not affected by an external impact force during transportation or the like. May collide with a cylinder head or the like, generating a collision sound and possibly damaging a piston or the like. In addition, since the linear compressor has a free piston stroke, even when the compressor is operating, the piston behavior becomes unstable if it exceeds the original stroke range of the piston. Also, in this linear compressor, a sliding surface exists between the cylinder and the piston. The quality of the sliding property of the sliding surface affects the efficiency and durability of the linear compressor. Therefore, in order to make the linear compressor oilless, only a simple one-way frictional force acts between the cylinder and the piston, for example, minimizing the generation of twisting force by the spring mechanism supporting the piston. is important.

Accordingly, an object of the present invention is to prevent a collision between a piston and a cylinder head even when an impact force acts during transportation, for example, and to prevent a scratch or a collision sound generated between the piston and the cylinder head. I do. Another object of the present invention is to make the piston behave stably within the original stroke range of the linear motor during the operation of the compressor.
Another object of the present invention is to provide a simple linear compressor having high efficiency and high reliability by preventing an increase in sliding surface pressure between a piston and a cylinder wall surface due to a twist or the like.

[0005]

According to a first aspect of the present invention, there is provided a linear compressor including a compression mechanism for compressing a gas or a liquid, and a linear motor for operating the compression mechanism in a closed container. The mechanism has a cylinder and a piston, the linear motor has a fixed part connected to the cylinder and a movable part connected to the piston, and has one end connected to the piston or the movable part and the other end. A linear compressor having a coil spring that supports the piston movably in an axial direction in connection with the cylinder or the fixed portion, wherein the coil spring is used as a compression spring, and the elastic force of the coil spring is It is characterized in that a state in which the piston is constantly pressed against one end of the cylinder is maintained. According to a second aspect of the present invention, in the linear compressor according to the first aspect, a compression space is formed in the cylinder at one end of the piston, and a spring is connected to the fixing portion at the other end of the piston. A member is provided, the coil spring is constituted by a single coil spring, one end of the coil spring is abutted on the other end surface of the piston, and the other end of the coil spring is abutted on the spring fixing member. It is characterized by having done. According to a third aspect of the present invention, in the linear compressor according to the second aspect, the position of the piston when the coil spring is most compressed is set as an allowable movable position on the bottom dead center side of the piston. Features. According to a fourth aspect of the present invention, in the linear compressor according to the second aspect, at least one end of the coil spring is fixed so as not to rotate in a circumferential direction. According to a fifth aspect of the present invention, in the linear compressor according to the second aspect, the other end surface of the piston with which one end of the coil spring contacts, and the spring fixing member with which the other end of the coil spring contacts, A protrusion having a thread groove is provided, and the coil spring is connected by the protrusion. According to a sixth aspect of the present invention, in the linear compressor according to the second aspect, the other end surface of the piston with which one end of the coil spring abuts and the spring fixing member with which the other end of the coil spring abuts. A projection is provided, a detent claw is formed on the other end surface of the piston and the spring fixing member, and the coil spring is press-fitted into each of the projections. The present invention described in claim 7 is based on claim 1.
In the above-described linear compressor, a direct current is supplied to the linear motor when the compressor is started, and then the alternating current is superimposed on the linear motor to drive the piston. According to an eighth aspect of the present invention, in the linear compressor according to the first aspect, a DC current is supplied to the linear motor when the compressor is stopped, and thereafter the DC current component is gradually reduced.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In a first embodiment of the present invention, a coil spring is used as a compression spring, and a state in which a piston is constantly pressed against one end of a cylinder by the elastic force of the coil spring is maintained. In this way, by assembling with the coil spring in a state where the piston tip surface is in contact with the cylinder head surface and a preload is generated in the coil spring,
The movement of the piston movable part can be restricted by the preload applied to the piston against the impact force in the axial direction of the piston at the time of transportation or dropping, and the reliability at the time of transportation can be greatly improved. In addition, since the coil spring is assembled in a state where a preload has already been applied, the coil spring does not have a free length or a tension state in any operating state of the linear compressor, so that the durability of the coil spring can be increased. .

According to a second embodiment of the present invention, in the linear compressor according to the first embodiment, a compression space is formed in a cylinder at one end of a piston, and the compression space is connected to a fixed portion at the other end of the piston. A spring fixing member is provided, the coil spring is constituted by a single coil spring, one end of the coil spring is brought into contact with the other end surface of the piston, and the other end of the coil spring is placed in contact with the spring fixing member. is there. As described above, according to the present embodiment, since the configuration is a single coil spring having the same axis, the compressor has a simple structure, and a compressor having a small number of parts can be configured.

In a third embodiment of the present invention, in the linear compressor according to the second embodiment, the position of the piston when the coil spring is most compressed is defined as the allowable movable position on the bottom dead center side of the piston. It was done. According to the present embodiment, the position of the piston at the contact height of the coil spring is
By selecting and assembling a coil spring that matches the allowable movable point on the bottom dead center side of the piston, the operation can always be driven within the possible movable range of the linear motor during operation, so that stable piston operation can be realized.

According to a fourth embodiment of the present invention, at least one end of the coil spring is fixed so as not to rotate in the circumferential direction in the linear compressor according to the second embodiment. According to the present embodiment, by positioning and fixing the coil spring at an optimum position so that the coil spring does not rotate in the circumferential direction and the cylinder axis is aligned with the coil spring axis, the circumferential position generated by the coil spring can be improved. The directional force and the side force applied to the cylinder wall from the piston are reduced, and the sliding loss between the piston and the cylinder wall is reduced.

According to a fifth embodiment of the present invention, there is provided a linear compressor according to the second embodiment, wherein the other end surface of the piston with which one end of the coil spring abuts, and the spring fixing member with which the other end of the coil spring abuts. Are provided with protrusions each having a thread groove, and the coil springs are connected by the respective protrusions. According to the present embodiment, the coil spring is prevented from rotating in the circumferential direction, the circumferential force transmitted to the piston and the side force applied from the piston to the cylinder wall surface are suppressed, and a high machine with low sliding loss between the piston and the cylinder is provided. It becomes an efficient compressor.

According to a sixth embodiment of the present invention, there is provided a linear compressor according to the second embodiment, wherein the other end surface of the piston with which one end of the coil spring abuts, and the spring fixing member with which the other end of the coil spring abuts. Are provided with protruding portions, a detent claw portion is formed on the other end surface of the piston and the spring fixing member, and a coil spring is press-fitted into each protruding portion. According to the present embodiment, the rotation preventing claw prevents the coil spring from rotating in the circumferential direction, suppresses the circumferential force transmitted to the piston and the side force applied from the piston to the cylinder wall surface. It is easy to align the centers of the generated spring forces, so that the piston movable portion can be smoothly driven, and a highly reliable linear compressor with small sliding loss can be realized.

According to a seventh embodiment of the present invention, in the linear compressor according to the first embodiment, a direct current is supplied to the linear motor at the time of starting the compressor, and then the alternating current is superimposed to drive the piston. Things. According to the present embodiment, a direct current is supplied to the linear motor when the linear compressor is started, so that the piston tip surface pressed against the cylinder head surface can be separated from the cylinder head surface. Therefore, by superimposing an alternating current thereafter, it is possible to prevent a collision between the piston tip surface and the cylinder head at the time of start-up, and to realize a low-noise linear compressor in which a collision between the piston and the cylinder head is prevented.

In an eighth embodiment of the present invention, in the linear compressor according to the first embodiment, a direct current is supplied to the linear motor when the compressor is stopped, and then the direct current component is gradually reduced. . According to the present embodiment, when the linear compressor is stopped, a direct current is supplied to the linear motor to move the piston tip surface to the side opposite to the cylinder head, thereby preventing the piston tip from colliding with the cylinder head when stopped. I do.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the linear compressor according to the present invention will be described below with reference to the drawings. First, the overall structure of the linear compressor of the present invention will be described with reference to FIG. This linear compressor is roughly divided into a cylinder 10, a piston 20, a movable section 40 and a fixed section 50 that constitute a linear motor section,
It is composed of a spring mechanism 30 composed of a coil spring, a head cover 80, a support mechanism 90, and a closed container 100. The cylinder 10 includes a cylinder head 11 to which a valve element (not shown) is assembled, a flange 14, and a boss 12 protruding from the flange 14 toward one side (leftward in the figure). The piston 20 includes a frame 22 forming a recess for accommodating the support 21 and the coil spring 30. Piston 2
Reference numeral 0 denotes a protrusion 23 provided on the bottom surface in the recess of the frame 22. A compression space 13 is formed between one end of the piston 20 and the cylinder head 11.

The linear motor section includes a movable section 40 and a fixed section 5.
It consists of 0. The movable section 40 includes a permanent magnet 41, a cylindrical holding member 42, and the like. The fixing portion 50 includes an inner yoke 51, an outer yoke 52, a coil 53, and the like. The permanent magnet 41 is held by a cylindrical holding member 42. The cylindrical holding member 42 is disposed concentrically with the piston 20 and is fixed by the frame 22. The inner yoke 51 is formed of a cylindrical body, and the boss 1 of the cylinder 10 is formed.
2 is circumscribed and fixed. Note that a small gap is formed between the outer periphery of the inner yoke 51 and the cylindrical holding member 42.
The coil 53 is provided on the outer yoke 52. On the other hand, the outer yoke 52 is also formed of a cylindrical body, is arranged concentrically so as to form a minute gap on the outer periphery of the cylindrical holding member 42, and is fixed to the flange 11 of the cylinder 10. As described above, the movable part 40 and the fixed part 50 are concentrically held with high precision, and the reciprocating motion can be performed smoothly.

The spring mechanism 30 is composed of a single coil spring having a predetermined spring rigidity. This coil spring 3
0 is used as a compression spring which is always used in a state of being compressed more than the natural length. One end 31 of the coil spring 30
Is connected to a protrusion 23 formed on the other end surface of the piston 20. The other end 32 of the coil spring 30 is connected to the spring fixing member 6.
It is coupled to the second protrusion 63. The coil spring 30 is used to generate a preload due to compression deflection.
The coil spring 30 is pressed against the piston 20 by the spring fixing member 62 until the spring contacts the cylinder head 11.
The spring fixing member 62 is provided in a state of being bridged over an outer yoke 52 serving as a fixing portion 50 of the linear motor portion, and is fixedly connected to an end thereof. Therefore, even if an external impact force is applied to the piston 20 during transportation or the like, the coil spring 3
The vibration of the piston 20 is regulated by the preload due to the zero compression deflection, and a highly reliable compressor against external impact can be realized. Also, since the coil spring 30 is assembled by applying a preload due to compression deflection, the piston 2
0 is always the coil spring 30 in all operating modes.
Can be driven in a compressed state. Further, since the coil spring 30 is constituted by one spring, a highly reliable linear compressor can be constituted.

The closed container 100 is formed of a cylindrical container, and has a space 101 formed therein. This space 101
The components of the linear compressor are housed therein. Further, the closed container 100 is provided with a suction pipe (not shown) and a discharge pipe (not shown). The support mechanism section 90 has a plurality of coil springs 91 disposed between the components of the linear compressor and the closed casing 100, and prevents transmission vibration from the cylinder 10 to the closed casing 100.

In a linear compressor in which the position of the piston 20 is determined by the balance between the operating pressure condition and the applied output supplied to the linear motor, the piston 20 is located at a position equal to or higher than the set bottom dead center position of the piston. May move. As a result, the piston 20 may move beyond the allowable stroke of the linear motor, and may make the behavior of the piston 20 unstable.

FIG. 2 shows that the position of the piston 20 when the coil spring 30 is most compressed is the bottom dead center 29 of the piston 20 (allowable maximum stroke position of the linear motor) in order to solve the above-mentioned disadvantage. Is assembled. This allows the piston 20 to move within the allowable stroke range of the linear motor during operation.
Does not exceed the allowable stroke range of the linear motor. Therefore, the behavior of the piston 20 can be stabilized.

FIG. 3 shows a rotation for preventing the coil spring 30 from rotating in the circumferential direction by connecting and fixing the coil spring 30 to the projection 23 on the inner bottom surface of the recess of the piston 20 and the projection 63 of the spring fixing member 62. The prevention means is shown. In the figure, the protrusion 23 on the inner bottom surface of the recess of the piston 20 and the protrusion 63 of the spring fixing member 62 are respectively threaded portions 25, 65 so as to match the coil spiral of the coil spring 30.
Is provided. Thus, both ends of the coil spring 30 are formed by the threaded portion 25 of the projection 23 of the piston and the spring fixing member 6.
2, the coil spring 30 is prevented from rotating in the circumferential direction, the circumferential force applied to the piston 20 is reduced, and the piston 2
A compressor with small sliding loss between the cylinder 0 and the cylinder 10 can be realized.

FIG. 4 shows another embodiment of the above-described rotation preventing means. In the figure, the protrusion 2 of the piston 20
3 is provided with a detent claw 24 and a spring fixing member 62.
A detent claw portion 64 is provided on the end face of the projection 63.
Thus, the inner peripheral surfaces of the both ends of the coil spring 30 correspond to the protrusions 23 of the piston 20 and the protrusions 63 of the spring fixing member 62.
, And the winding start portion 3 of both ends of the coil spring 30
3 is positioned and fixed to the detent claws 24 and 64. This prevents the coil spring 30 from rotating in the circumferential direction, so that it is easy to align the axial center of the piston 20 with the center axis of the coil spring 30 that generates the spring force, and to drive the piston 20 smoothly. This realizes a highly reliable linear compressor with small sliding loss.

In the case of a linear compressor placed horizontally as shown in FIG.
Zero misalignment to the lower surface occurs. In this case, the center position of the spring force of the coil spring is inclined in advance in consideration of the misalignment due to weight, and the coil spring 30 is positioned as shown in FIGS.
Since the center axes of the piston 20 and the coil spring 30 can be aligned concentrically, the piston 2 in the cylinder 10
0 can be driven smoothly and sliding loss can be reduced.

Next, the operation of the linear compressor of this embodiment will be described. First, when the coil 53 of the fixed portion 50 is energized,
A thrust proportional to the current is generated between the movable part 40 and the permanent magnet 41 in accordance with Fleming's left-hand rule. Due to the generation of this thrust, a driving force that retreats along the axial direction acts on the movable portion 40. Since the cylindrical holding member 42 of the movable portion 40 is connected to the piston 20, the piston 20 smoothly retreats along its axial direction.

Here, as shown in FIG. 5, by supplying a DC current 55 to the linear motor when the compressor is started,
The distal end surface of the piston 20 pressed against the cylinder head 11 surface can be separated from the cylinder head 11 surface. Thereafter, the alternating current 56 is gradually increased. This prevents a collision between the tip end surface of the piston 20 and the cylinder head 11 at the time of starting the compressor, and makes it possible to provide an excellent low-noise linear compressor without a collision sound between the piston 20 and the cylinder head 11. After start-up, the center position of the piston stroke undergoes compression deflection in the direction of the coil spring 30 due to the differential pressure between the suction pressure and the discharge pressure due to the compressed gas pressure due to the reciprocating motion of the piston 20. Piston 20
After a certain start-up time at a position where the tip does not collide with the end face of the cylinder head 11, the operation is performed only with the AC current without adding the DC current 55 component.

When the linear compressor is stopped,
As shown in FIG. 6, a DC current 58 is supplied to the linear motor to move the front end surface of the piston toward the side opposite to the cylinder head, thereby gradually reducing the DC current 58 component. Thereby, it is possible to prevent the piston tip from suddenly colliding with the cylinder head at the time of stop, and it is possible to reduce noise due to the collision. The alternating current in energizing the coil 53 is given as a sine wave, and forward and reverse thrusts are alternately generated in the linear motor unit. The piston 20 reciprocates by the alternately generated forward and reverse thrusts.

The refrigerant is introduced from the suction pipe (not shown) into the closed container 100 shown in FIG. The refrigerant introduced into the sealed container 100 enters the compression space 13 from the suction side space of the head cover 80 through a suction valve (not shown) attached to the cylinder head 11. And this refrigerant,
It is compressed by the piston 20 and discharged from a discharge pipe (not shown) through a discharge side space of the head cover section 80 from a discharge valve (not shown) assembled to the cylinder head 11. In addition, the vibration of the cylinder 10 caused by the reciprocating motion of the piston 20
Damped by 1.

As described above, the piston 20 is assembled by pressing the tip end surface 22 of the piston 20 against the cylinder head 11 by the preload of the coil spring 30 against external impact force during transportation or the like. Since the amplitude is regulated, it is possible to avoid collision with the cylinder head 11 and the like, which can contribute to improvement in reliability.

In addition, a preload is applied to a single coil spring 30 by a compression deflection, and the coil spring is always subjected to a compression deflection in all operation modes, so that a simple configuration of a single highly reliable coil spring is obtained. .

Further, in addition to the state in which the preload is already applied,
Further, by positioning and fixing the coil spring at the optimum position so that the coil spring does not rotate in the circumferential direction, the circumferential force generated by the coil spring is reduced, and the sliding loss between the piston and the cylinder wall surface is reduced.

Also, the linear compressor is assembled so that the spring length of the coil spring 30 at the time of compression becomes the allowable maximum stroke position of the linear motor located at the bottom dead center 24 of the piston under any operating conditions. This allows the linear motor to operate within the allowable stroke range during operation. Therefore, the behavior of the piston 20 is stabilized without the piston 20 exceeding the allowable stroke range of the linear motor, and a highly reliable compressor can be realized.

Further, by preventing the coil spring 30 from rotating in the circumferential direction, it is easy to align the axial center of the piston 20 with the center axis of the coil spring 30 for generating the spring force. The working force is reduced, and a highly efficient and highly reliable linear compressor with small sliding loss is obtained.

Further, by supplying DC currents 55 and 58 to the linear motor at the time of starting and stopping, the distal end surface of the piston 20 pressed against the cylinder head surface is separated from the cylinder head 11 surface, and the Since the collision between the cylinder heads 11 can be prevented, a linear compressor with low noise and excellent reliability can be realized. In the above-described embodiment, the explanation has been made using the refrigerant. However, a gas or a liquid other than the refrigerant may be used.

[0033]

According to the present invention, the preload of the coil spring is generated by bringing the tip end surface of the piston into contact with the cylinder head surface, and the spring fixing member is assembled to the fixing portion, so that it can be transported or dropped. In response to the impact force in the axial direction of the piston, the movement of the piston movable portion can be restricted by the preload applied to the piston, and the reliability during transportation can be greatly improved. According to the invention, in addition to the state in which the coil spring is already applied, the circumferential force generated by the coil spring is fixed by positioning and fixing the coil spring at an optimum position so as not to rotate in the circumferential direction. And reduce the sliding loss between the piston and the cylinder wall. Further, according to the present invention, a simple structure of a single spring can be provided by applying a preload to one coil spring and assembling the coil spring to assemble the coil spring with one coil spring. Thus, a compressor having a small number of parts can be configured. Further, according to the present invention, by selecting a coil spring whose contact height position of the coil spring coincides with the allowable movable point of the linear motor located at the piston bottom dead center side, the possible movable range of the linear motor during operation is selected. The operation can be always driven without deviating from the inside, so that stable piston operation can be realized. Further, according to the present invention, the protrusion of the piston and the protrusion of the spring fixing member that are joined to the coil spring are subjected to thread processing corresponding to the coil spiral of the coil spring, and the protrusion of the piston and the protrusion of the fixing member are formed on the coil spring By screwing the coil spring into the screw, the coil spring is prevented from rotating in the circumferential direction, the circumferential force transmitted to the piston is suppressed, the sliding loss between the piston and the cylinder is reduced, and the mechanical efficiency can be improved. According to the present invention, the protrusion of the piston fixed to the coil spring is pressed into the protrusion of the piston and the protrusion of the spring fixing member. By forming a detent claw on the end face, the coil spring is prevented from rotating in the circumferential direction, and it becomes easy to align the center of the piston axis with the center of the generated spring force of the coil spring. And a highly reliable linear compressor with even smaller sliding loss.
According to the present invention, by supplying a DC current to the linear motor when the linear compressor is started, the piston tip surface pressed against the cylinder head surface is separated from the cylinder head surface to increase the AC current. Prevents collision between piston tip surface and cylinder head at startup,
No collision noise between the piston and the cylinder head. Also, when the linear compressor is stopped, a direct current is supplied to the linear motor to move the piston tip surface to the opposite side of the cylinder head, thereby gradually reducing the DC current component. Collision can be prevented, and noise due to collision can be reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an overall configuration of a linear compressor according to one embodiment of the present invention.

FIG. 2 is a cross-sectional view showing an overall configuration of a linear compressor according to another embodiment of the present invention.

FIG. 3 is an enlarged sectional view of a main part showing a rotation preventing means of the present invention.

FIG. 4 is an enlarged sectional view of a main part showing another rotation preventing means of the present invention.

FIG. 5 is a current waveform diagram at the time of startup according to an embodiment of the present invention.

FIG. 6 is a current waveform diagram at the time of stoppage according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Cylinder 13 Compression space which performs compression work 20 Piston 23 Projection part 24 Detent part 25 Screw processing part 30 Coil spring 40 Movable part 41 Permanent magnet 42 Cylindrical holding member 50 Fixed part 51 Inner yoke 52 Outer yoke 53 Coil 62 Spring fixing member 63 Projecting part 64 Detent part 65 Screw processing part 80 Head cover part 90 Support mechanism part

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H02P 7/00 H02P 7/00 101T F04B 49/02 331B 331F (72) Inventor Nobuaki Ogawa Kazuma, Osaka 1006 Kadoma Matsushita Electric Industrial Co., Ltd. F-term (reference) HH22 JA02 JA04 JA05

Claims (8)

[Claims] 1. A compression mechanism for compressing a gas or a liquid, and a linear motor for operating the compression mechanism are provided in a closed container. The compression mechanism has a cylinder and a piston, and the linear motor is mounted on the cylinder. It has a fixed portion connected to the piston and a movable portion connected to the piston, and has one end connected to the piston or the movable portion and the other end connected to the cylinder or the fixed portion to move the piston in the axial direction. A linear compressor having a coil spring freely supported,
A linear compressor, wherein the coil spring is used as a compression spring, and the piston is constantly pressed against one end of the cylinder by the elastic force of the coil spring. 2. A compression space is formed in the cylinder at one end of the piston, a spring fixing member connected to the fixing portion is provided at the other end of the piston, and the coil spring is a single coil spring. The linear compressor according to claim 1, wherein one end of the coil spring is abutted on the other end surface of the piston, and the other end of the coil spring is abutted on the spring fixing member. . 3. The linear compressor according to claim 2, wherein the position of the piston when the coil spring is most compressed is an allowable movable position on the bottom dead center side of the piston. 4. The linear compressor according to claim 2, wherein at least one end of said coil spring is fixed so as not to rotate in a circumferential direction. 5. A protrusion having a thread groove is provided on each of the other end surface of the piston with which one end of the coil spring abuts and the spring fixing member with which the other end of the coil spring abuts. The linear compressor according to claim 2, wherein the coil spring is connected by a portion. 6. A projection is provided on each of the other end surface of the piston with which one end of the coil spring contacts and the spring fixing member with which the other end of the coil spring contacts, and the other end surface of the piston is fixed with the spring. The linear compressor according to claim 2, wherein a detent claw portion is formed on the member and the coil spring is press-fitted into each of the protrusion portions. 7. The linear compressor according to claim 1, wherein a direct current is supplied to the linear motor when the compressor is started, and then the alternating current is superimposed to drive the piston. 8. The linear compressor according to claim 1, wherein a direct current is supplied to the linear motor when the compressor is stopped, and then the direct current component is gradually reduced.