JP2003194430A - Stirling engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a Stirling engine where the amplitude center position of a piston hardly fluctuates even when the operation state of a refrigerator is changed. <P>SOLUTION: A flow pass 1 to intercommunicate a back pressure space 19 and the internal space of the cylinder 12 is formed in the cylinder 12. Communicating flow passages 2 and 3 running from a working space 18 to the outer peripheral surface of the piston 15 are formed in a piston 15. The communicating flow passages 2 and 3 are provided with a flow passage 2 having an opening part formed in a working space 18 and the flow passage 3 having an opening part formed in the outer peripheral surface of the piston 15 and extending in a direction different from that of the flow passage 2. The size of the opening, formed in the outer peripheral surface of the piston 15, of the flow passage 3 is larger than that of the opening, formed in the internal part of the cylinder 12, of the flow passage 1. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Stirling engine, and more specifically, to a free piston type Stirling refrigerating machine having a piston and a displacer which are reciprocally movable in a cylinder containing a working gas. It is about machines.

[0002]

2. Description of the Related Art Generally, a vapor compression type refrigeration cycle is adopted as the refrigeration cycle. In such a vapor compression refrigeration cycle, Freon is used as a refrigerant as a working medium, and the required cooling performance is obtained by utilizing the condensation and evaporation of Freon.

However, it has been pointed out that CFC used as a refrigerant reaches the stratosphere and destroys the ozone layer when it is released into the atmosphere. Therefore, in recent years, the use and production of CFCs for specific CFCs have been regulated. Therefore, the reverse Stirling refrigeration cycle is drawing attention as an alternative to the refrigeration cycle using CFCs.

The reverse Stirling refrigeration cycle employs a gas such as helium gas, hydrogen gas, and nitrogen gas that does not adversely affect the global environment as a working medium, and obtains a low temperature by the reverse Stirling cycle. This Stirling refrigerator is known as a kind of small refrigerator that produces a cryogenic level of cold. Hereinafter, a conventional Stirling refrigerator will be described.

FIG. 6 is a sectional view schematically showing the structure of a conventional Stirling refrigerator. Referring to FIG. 6, piston 15 and displacer 13 are arranged so as to be able to slide back and forth on the inner peripheral wall surface of cylinder 12. The piston 15 and the displacer 13 are coaxially arranged and can smoothly reciprocate on the inner circumference of the cylinder 12.

The cylinder 12 is fixedly supported by the pressure vessel 11. The displacer 13 is elastically supported on the pressure vessel 11 by a displacer support spring 16 via a displacer rod 14 penetrating the sliding hole of the piston 15. The piston 15 is elastically supported by the pressure vessel 11 by a piston support spring 17.

The space formed by the pressure vessel 11 and the cylinder 12 is divided into two by the piston 15. 1
One is the working space 1 on the displacer 13 side of the piston 15.
8 and the other is a back pressure space 19 on the opposite side of the displacer 13. The two spaces 18 and 19 are filled with a working medium such as high-pressure helium gas.

The piston 15 is reciprocated by the linear motor 10 in a predetermined cycle. As a result, the working medium is compressed and expanded in the working space 18. The displacer 13 is driven by the pressure change of the working medium that is compressed / expanded in the working space 18, and reciprocates with the piston 15 with a phase difference of generally 90 °.

There is a minute gap between the inner wall of the cylinder 12 and the outer wall of the piston 15, and the reciprocating motion of the piston 15 causes pressure fluctuations in both the working space 18 and the back pressure space 19. Further, since the magnitude and volume of pressure fluctuations in the working space 18 and the back pressure space 19 are not the same, the working space 18
The outflow amount and the inflow amount of the working medium into the back pressure space 19 viewed from above are not the same amount.

If the outflow amount of the working medium from the working space 18 to the back pressure space 19 is larger than the inflow amount, the pressure in the working space 18 gradually decreases and the pressure in the back pressure space 19 gradually increases, and the piston 15 reciprocates. The vibration center position of the movement gradually moves to the working space 18 side. When the piston 15 shifts from the initial amplitude center position of the reciprocating motion, the piston 1
5 and the displacer 13 may collide with each other.

US Pat. No. 4,583,364 discloses a method of keeping the pressure balance of the working medium in the working space and the back pressure space and suppressing the fluctuation of the piston amplitude center position. In the technique disclosed in USP 4,583,364, the working medium flow passage is provided inside the piston, and when the piston is at the initial amplitude center position, the working space and the back pressure space are formed by the working medium flow passage inside the piston. It is configured to be connected. When the piston reciprocates, the working medium flows from the high pressure space to the low pressure space between the working space and the back pressure space each time the piston passes through the initial amplitude center position. This corrects the pressure difference between the two spaces and maintains the piston amplitude center position.

[0012]

However, when the free piston type Stirling refrigerator is operated, the operating condition changes depending on the required cold heat. When a large amount of cold heat is required, the piston reciprocates with large amplitude. On the other hand, when a small amount of cold heat is required, the piston reciprocates with a small amplitude. When the working fluid flow path provided in the piston is formed in a constant shape, the reciprocating motion of the piston with a large amplitude shortens the connection time between the working space and the back pressure space, and sometimes the required working medium weight cannot be obtained. Further, when the piston reciprocates with a small amplitude, the connection time between the working space and the back pressure space becomes long, and as a result, the working medium flows regardless of compression / expansion, resulting in loss during operation of the refrigerator. .

The present invention has been made to solve the above problems, and an object of the present invention is to provide a Stirling engine in which the center position of the piston amplitude does not easily fluctuate even when the operating condition of the refrigerator changes.

[0014]

The Stirling engine of the present invention is a free piston type Stirling engine having a piston reciprocally movable in a cylinder filled with a working gas, in which the cylinder has a back pressure space outside the cylinder. And a first flow path that communicates with the internal space of the cylinder are formed, and a communication flow path that connects the working space to the outer peripheral surface of the piston is formed in the piston.
Is arranged so that the working space and the back pressure space communicate with each other by communicating with each other, and the communicating flow path is the second flow path having an opening in the working space and the outer peripheral surface of the piston. A third opening having an opening and extending in a direction different from that of the second flow path.
And the opening size of the third flow path on the outer peripheral surface of the piston is larger than the opening size of the first flow path inside the cylinder.

According to the Stirling engine of the present invention, the first
Since the opening size of the channel is smaller than the opening size of the third channel, it is possible to suppress the amount of gas movement. As a result, the gas flow rate in the process unrelated to the refrigerating machine cycle can be reduced, and the increase in miscellaneous loss can be prevented.

Further, the second and third flow passages influence the position of the center of movement of the piston, and in particular, the opening of the third flow passage has the first
Since it faces the opening of the third flow path, the opening of the third flow path is set to be large so that the time when the opening of the first flow path and the opening of the third flow path face each other is extended. It is possible to control the movement amount of the gas so that the piston moves at the movement center position.

By reducing the opening size of the first flow path in this way, it is possible to prevent an increase in the amount of miscellaneous loss, and to make the opening size of the third flow path larger than the opening size of the first flow path. As a result, fluctuations in the center position of the piston movement can be suppressed, and the refrigeration cycle can be performed without any practical problems.

In the above Stirling engine, preferably, the diameter of the third flow passage is larger than that of the second flow passage.

As a result, it is possible to further suppress the fluctuation of the movement center position of the piston. In the above Stirling engine, preferably, the second flow path extends in the movement direction of the piston.

This facilitates the processing and formation of the second flow path in the piston. In the above Stirling engine, preferably, the third flow passage extends in the direction perpendicular to the second flow passage.

As a result, it becomes easy to form the third flow path into the piston. In the above Stirling engine, preferably, the opening shape of the third flow path that is opened on the outer peripheral surface of the piston is either a circular shape, a shape spreading in the circumferential direction of the piston, or a shape spreading in the movement direction of the piston. Is.

As described above, various shapes can be selected as the opening shape of the third flow path. In the above Stirling engine, preferably, the second flow path provided in the piston corresponds to the second flow path of the other piston when the diameter of the piston is larger than the diameter of the other piston of the other Stirling engine. Larger than the diameter of the channel.

As a result, it is possible to obtain a Stirling refrigerator in which the fluctuation of the piston amplitude center position is small without increasing the gas flow loss of the free piston type Stirling engine.

In the above Stirling engine, preferably, when the diameter of the piston is smaller than the diameters of other pistons of another Stirling engine, the second flow passage provided in the piston is the second flow passage of the other piston. Is smaller than the diameter of the channel corresponding to.

As a result, it is possible to obtain a Stirling refrigerator in which the fluctuation of the piston amplitude center position is small without increasing the gas flow loss of the free piston type Stirling engine.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is a sectional view schematically showing the structure of a Stirling refrigerator according to Embodiment 1 of the present invention, and FIG. 2 is a working space and back pressure in the Stirling refrigerator of FIG. It is a figure which shows the flow path which connects with space.

Referring to FIG. 1, the Stirling refrigerator of the present embodiment has a pressure vessel 11, a cylinder 12, a displacer 13, a displacer rod 14, a piston 15, a displacer support spring 16, and a piston support spring. 17 and the linear motor 10 are mainly included.

The Stirling refrigerator of this embodiment is different from the conventional example shown in FIG. 6 in that a flow path connecting the working space and the back pressure space is provided.

Referring to FIG. 2, this flow path is formed in the cylinder 1.
2 has a flow passage 1 provided therein, and a communication flow passage 2, 3 provided in the piston 15. The flow path 1 has a back pressure space 19
Is formed in the cylinder 12 so as to communicate with the internal space of the cylinder 12. Further, the communication passages 2 and 3 are formed in the piston 15 so as to communicate with the outer peripheral surface of the piston 15 from the working space 18.

The communication channels 2 and 3 have a channel 2 having an opening in the working space 18 and a channel 3 having an opening on the outer peripheral surface of the piston 15. The flow paths 2 and 3 extend in different directions, the flow path 2 extends, for example, in the movement direction of the piston 15, and the flow path 3 extends, for example, in a direction perpendicular to the extending direction of the flow path 2. There is. Piston 1
The opening dimension (diameter, opening area) L1 of the flow path 3 on the outer peripheral surface of the channel 5 is set larger than the opening dimension (diameter, opening area) L2 of the flow path 1 inside the cylinder 12.

The opening of the flow path 3 on the outer peripheral surface of the piston 15 is reciprocally moved by the piston 15 so that the cylinder 1
2 is opposed to the opening of the flow channel 1 on the inner peripheral surface of the flow channel 2, whereby the flow channel 1 and the communication flow channels 2, 3 communicate with each other, and the working space 18 and the back pressure are communicated through the flow channel 1 and the communication flow channels 2, 3. Space 1
And 9 are connected.

Since the other structures are almost the same as those of the conventional example shown in FIG. 6, the same members are designated by the same reference numerals and the description thereof will be omitted.

The inventors of the present invention calculated the deviation amount of the piston amplitude center position from the initial position and the miscellaneous loss reduction amount when the flow path diameters of the flow paths 1 to 3 were changed in the Stirling refrigerator shown in FIGS. Examined. As a result, the results shown in Tables 1 and 2 below were obtained.

[0035]

[Table 1]

[0036]

[Table 2]

From these results, the amount of deviation of the piston amplitude center position from the initial position becomes smaller when the flow passage diameter of the flow passage 3 is made larger than when it is made equal to the flow passage diameter of the flow passage 1, and It was found that the amount of miscellaneous loss is also small.

The reason why the above results are obtained will be described below. When the piston 15 reciprocates, the gas moves from a minute gap (tens of μm) between the piston 15 and the cylinder 12. The amount of gas movement at that time is proportional to the pressure difference between the working space 18 and the back pressure space 19.

Due to the structure of the refrigerator, the volume of the working space 18 is smaller than the volume of the back pressure space 19 (about 1/10). Therefore, when the piston 15 moves in the direction of the working space 18, the working space 18 is compressed, and a pressure difference P1 is generated between the working space 18 and the back pressure space 19, and the piston 15
The gas moves from the working space 18 to the back pressure space 19 through the gap between the cylinder 12 and the cylinder 12. Piston 15 is back pressure space 1
When moving in 9 directions, a pressure difference P2 similarly occurs between the working space 18 and the back pressure space 19.

However, when the piston 15 moves to the back pressure space 19, the size of the back pressure space 19 causes the back pressure space 19 to move.
, The pressure difference becomes smaller and the pressure difference P2 becomes smaller than P1. Therefore, the total amount of gas moving from the back pressure space 19 to the working space 18 due to the pressure difference P2 is smaller than the total amount of gas moving from the working space 18 to the back pressure space 19 due to the pressure difference P1. As a result, the piston 1 is placed in the back pressure space 19.
Each time the gas 5 reciprocates, gas accumulates, which causes the piston 15 to be pushed in the direction of the working space 18, and the movement center position of the piston 15 (that is, the amplitude center position) shifts in the working space 18 direction.

In order to improve this, it is necessary to properly return the gas accumulated in the back pressure space 19 to the working space 18. Therefore, the channels 1 to 3 exist. Return of these gases is necessary for the operation of the refrigerator, but it is a gas flow that is not related to the original compression process, equal volume process, expansion process, and equal volume process of the refrigerator cycle, and it causes miscellaneous loss. It becomes the amount.

Further, if the amount of gas returned is not sufficient, there is a risk that the center position of the amplitude of the piston 15 moves toward the working space 18 and collides with the displacer 13. Therefore, the flow paths 1 to 3 are designed so that the amount of miscellaneous loss is as small as possible.
It is necessary to determine the diameter of.

Since the flow passage 1 is located at the boundary between the working space 18 and the back pressure space 19, if the diameter of the flow passage 1 is large, the amount of gas movement increases, and in a process not related to the refrigerator cycle. The gas flow rate increases and the amount of miscellaneous loss increases. Since the flow path 1 greatly affects the amount of miscellaneous loss, it must be made as small as possible.

On the other hand, the size of the diameters of the flow passages 2 and 3 is influenced by the center position of the amplitude of the piston 15. Especially channel 3
Since the opening of the channel 3 faces the opening of the channel 1, the opening of the channel 3 is set to be large, and the time when the opening of the channel 1 and the opening of the channel 3 face each other (overlap). It is necessary to control the amount of movement of the gas so that the piston 15 moves at the center position of the amplitude by increasing the length of time during which the gas moves.

When all of the flow passages 1 to 3 have the same diameter, if the flow passage diameter is increased in order to hold the piston 15 at the amplitude center position, the amount of miscellaneous loss in the cycle will increase. If the diameters of all the flow paths 1 to 3 are reduced to reduce the amount of miscellaneous loss, it becomes difficult to hold the piston 15 at the amplitude center position. In order to satisfy the two contradictory conditions, it is necessary to make the opening size L1 of the flow path 3 larger than the opening size L2 of the flow path 1 as described above.

That is, it is possible to prevent an increase in miscellaneous loss by reducing the opening size L2 of the flow passage 1, and increase the opening size L1 of the flow passage 3 so that the center position of the amplitude of the piston 15 becomes normal. It is possible to hold it in position.

However, the amount of miscellaneous loss is not increased at all, and the amplitude center position of the piston 15 is not changed at all. By setting the diameters of the flow passages 1 to 3 as described above, it is possible to operate the refrigerator without any problem, without lowering the refrigerator performance at the actual use level.

(Embodiment 2) In the free piston type Stirling refrigerator in this embodiment, the flow passage diameter (diameter) of the flow passage 3 is larger than the flow passage diameter (diameter) of the flow passage 2 in FIGS. 1 and 2. It is set.

The rest of the configuration is almost the same as the configuration of the above-described first embodiment, and therefore its explanation is omitted.

In the present embodiment, the flow path diameter of the flow path 3 is set larger than the flow path diameter of the flow path 2, so that the deviation of the vibration center position of the piston from the initial vibration center position can be further suppressed. It will be possible.

(Third Embodiment) FIG. 3 is a front view schematically showing the structure of a piston of a free piston Stirling refrigerator according to a third embodiment of the present invention. Referring to FIG. 3, flow path 3 provided in piston 15 in the present embodiment has an elliptical opening shape having a circumferentially widened outer peripheral surface of piston 15.

The rest of the configuration is almost the same as the configuration of the first embodiment described above, and therefore the description thereof is omitted.

Further, the flow path 3 may have an elliptical shape having a spread in the movement direction of the piston 15, as shown in FIG.

As shown in FIGS. 3 and 4, the piston 15
Even when the opening shape of the flow path 3 on the outer peripheral surface of the flow path 3 is elliptical, the opening size L1 of the flow path 3 is equal to the opening size L2 of the flow path 1.
If it is larger, the Stirling refrigerator can be operated with the amplitude center position of the piston 15 close to the initial amplitude center position without increasing the miscellaneous loss amount of the Stirling refrigerator as described above.

(Fourth Embodiment) FIG. 5 is a diagram showing a flow path connecting a working space and a back pressure space of a free piston Stirling refrigerator in a fourth embodiment of the present invention. Figure 5
With reference to, in the present embodiment, the extending direction of flow path 3 is different from that in the first embodiment. Flow path 3 of the present embodiment
Does not extend in a direction perpendicular to the extending direction of the flow path 2 (movement direction of the piston 15), but extends in a predetermined selected angular direction. As a result, the flow path 3 enters the outer peripheral surface of the piston 15 from an oblique direction and opens.

The rest of the configuration is almost the same as the configuration of the above-described first embodiment, and therefore its explanation is omitted.

In this embodiment, the flow passage 3 is connected to the piston 15
By extending in a direction tilted by a predetermined angle with respect to the movement direction of, the opening size of the flow passage 3 in the outer peripheral surface of the piston 15 can be made larger than the actual flow passage diameter of the flow passage 3. As a result, similarly to the first embodiment, it is possible to operate the Stirling refrigerator without increasing the miscellaneous loss amount of the Stirling refrigerator and suppressing the deviation of the amplitude center position of the piston 15.

Further, the diameter of the flow passage 3 and the diameter of the flow passage 2 can be further reduced by forming the flow passage 3 at a predetermined angle.

(Fifth Embodiment) The inventors of the present application investigated the amount of deviation of the piston amplitude center position from the initial position by changing the flow passage diameters of the passages 2 and 3 in each of the pistons 15 having different diameters. The results are shown in Table 3.

[0060]

[Table 3]

From this result, it has been found that when the diameter of the piston 15 changes, the deviation amount of the piston amplitude center position from the initial position can be suppressed by changing the diameters of the flow paths 2 and 3.

That is, when the diameter of the piston 15 is increased, the amount of deviation of the piston amplitude center position from the initial position is simply increased by increasing the diameters of the flow paths 2 and 3 without changing the diameter of the flow path 1. Therefore, the stable operation of the Stirling refrigerator can be performed without increasing the amount of miscellaneous loss of the Stirling refrigerator.

On the contrary to the above, even when the diameter of the piston 15 is reduced, the diameter of the flow path 1 is not changed and the flow path 2 is not changed.
The amount of deviation of the piston amplitude center position from the initial position can be suppressed simply by reducing the diameters of the flow path 3 and the flow path 3, so that stable Stirling refrigerator operation can be performed without increasing miscellaneous loss of the Stirling refrigerator. Become.

In this way, by changing the flow passage diameters of the flow passages 2 and 3 according to the diameter of the piston 15,
A stable Stirling refrigerator suitable for each design can be obtained.

The embodiments disclosed this time are to be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description but by the claims, and is intended to include meanings equivalent to the claims and all modifications within the scope.

[0066]

According to the Stirling engine of the present invention, since the opening size of the first flow path is smaller than the opening size of the third flow path, the amount of gas movement can be suppressed. As a result, the gas flow rate in the process unrelated to the refrigerating machine cycle can be reduced, and the increase in miscellaneous loss can be prevented.

Further, the second and third flow paths influence the position of the center of motion of the piston, and in particular, the opening of the third flow path has the first position.
Since it faces the opening of the third flow path, the opening of the third flow path is set to be large so that the time when the opening of the first flow path and the opening of the third flow path face each other is extended. It is possible to control the movement amount of the gas so that the piston moves at the movement center position.

By thus reducing the opening size of the first flow path, it is possible to prevent an increase in the miscellaneous loss amount, and to make the opening size of the third flow path larger than the opening size of the first flow path. As a result, fluctuations in the center position of the piston movement can be suppressed, and the refrigeration cycle can be performed without any practical problems.

In the above Stirling engine, preferably, the flow path diameter of the third flow path is larger than the flow path diameter of the second flow path. As a result, it is possible to further suppress the fluctuation of the movement center position of the piston.

In the above Stirling engine, preferably, the second flow passage extends in the movement direction of the piston.
This facilitates the processing and forming of the second flow path on the piston.

In the above Stirling engine, preferably, the third flow passage extends in the direction perpendicular to the second flow passage. This facilitates the formation of the third flow path in the piston.

In the above Stirling engine, preferably, the opening shape of the third flow path which is opened to the outer peripheral surface of the piston is circular, the shape spreading in the circumferential direction of the piston, and the shape spreading in the moving direction of the piston. Is one of. In this way, various shapes can be selected as the opening shape of the third flow path.

In the above Stirling engine, preferably, when the diameter of the piston is larger than the diameters of other pistons of another Stirling engine, the second flow passage provided in the piston is the second flow passage of the other piston. Is larger than the diameter of the channel corresponding to. Accordingly, it is possible to obtain a Stirling refrigerator in which the fluctuation of the piston amplitude center position is small without increasing the gas flow loss of the free piston type Stirling engine.

In the above Stirling engine, preferably, when the diameter of the piston is smaller than the diameter of the other piston of the other Stirling engine, the second flow passage provided in the piston is the second flow passage of the other piston. Is smaller than the diameter of the channel corresponding to. Accordingly, it is possible to obtain a Stirling refrigerator in which the fluctuation of the piston amplitude center position is small without increasing the gas flow loss of the free piston type Stirling engine.

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing a configuration of a free piston type Stirling refrigerator in a first embodiment of the present invention.

FIG. 2 is a diagram showing a flow path connecting an operating space and a back pressure space in the Stirling refrigerator of FIG.

FIG. 3 is a front view schematically showing an example of a piston configuration of a free piston Stirling refrigerator according to a third embodiment of the present invention.

FIG. 4 is a front view schematically showing another example of the configuration of the piston of the free piston type Stirling refrigerator in the third embodiment of the present invention.

FIG. 5 is a diagram showing a flow path connecting an operating space and a back pressure space in a free piston type Stirling refrigerator according to a fourth embodiment of the present invention.

FIG. 6 is a schematic cross-sectional view showing the configuration of a conventional free piston Stirling refrigerator.

[Explanation of symbols]

1, 2 and 3 flow paths, 10 linear motors, 11 pressure vessels, 12 cylinders, 13 displacers, 14 displacer rods, 15 pistons, 16 displacer support springs, 17 piston support springs, 18 working spaces, 19 back pressure spaces.

Claims (7)

[Claims] 1. A free piston type Stirling engine having a piston provided so as to be able to reciprocate in a cylinder filled with a working gas, wherein a back pressure space outside the cylinder and an internal space of the cylinder communicate with the cylinder. A first flow path is formed, a communication flow path is formed in the piston from the working space to the outer peripheral surface of the piston, and the communication flow path and the first flow path are mutually The working space and the back pressure space are arranged so as to communicate with each other by communicating with each other, and the communication flow passage has a second flow passage having an opening in the working space and an outer peripheral surface of the piston. A third flow path having an opening and extending in a direction different from the second flow path, wherein the opening size of the third flow path in the outer peripheral surface of the piston is the first flow path. The cylinder of the road A Stirling machine characterized by being larger than the opening size inside. 2. The flow path diameter of the third flow path is larger than the flow path diameter of the second flow path.
Stirling agency described in. 3. The first flow path according to claim 1, wherein the second flow path extends in a movement direction of the piston.
Stirling agency described in. 4. The first flow path, wherein the third flow path extends in a direction perpendicular to the second flow path.
The Stirling engine according to any one of 3 above. 5. The opening shape of the third flow path opened on the outer peripheral surface of the piston has a circular shape, a shape expanded in the circumferential direction of the piston, and a shape expanded in the movement direction of the piston. The Stirling engine according to any one of claims 1 to 4, which is any one of the above. 6. The second flow passage provided in the piston is arranged in the second flow passage of the other piston when the diameter of the piston is larger than the diameter of another piston of another Stirling engine. Stirling engine according to any of claims 1 to 5, characterized in that it is larger than the diameter of the corresponding flow path. 7. When the diameter of the piston is smaller than the diameter of another piston of another Stirling engine, the second flow passage provided in the piston is the second flow passage of the other piston. Stirling engine according to any of claims 1 to 5, characterized in that it is smaller than the diameter of the corresponding channel.