JP2000045867A - Stirling engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lower the friction of a sliding part of a piston cap and a displacer rod, and reduce a flow loss in the sliding part by forming the piston cap into a structure capable of being moved in the axial direction of the piston. SOLUTION: A large friction is generated between a piston cap 5a and a displacer rod 3 by a difference between their axes. A projecting part of the piston cap 5a is held with a clearance from a piston 4 holding part in the radial direction. In order to smoothly move the piston cap 5a relative to the piston 4, surface treatment such as Teflon coating is performed to at least one of the holding parts thereof so as to lower the sliding resistance, and the holding part can be moved in relation to a displacement of the core in the radial direction. In order to facilitate the movement, the piston cap 5a is made of the light material such as Al. With this structure, friction in the sliding part of the piston cap 5a and the displacer rod 3 is lowered, and a flow loss in the sliding part can be lowered.

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 particularly to a structure for improving the sliding reliability of a Stirling engine.

[0002]

2. Description of the Related Art FIG. 5 is a structural view of a conventional Stirling engine. As shown in FIG. 5, in a free-piston Stirling engine, one cylinder 1 contains a reciprocating piston 4 and a displacer 2. The piston 4 is linearly driven while supported by a piston spring 8, and the displacer 2 is connected to a displacer spring 9 and a displacer rod 3 to reciprocate. In the Stirling engine,
The reciprocating motion forms the compression space 18a and the expansion space 18b, and generates heat and heat by moving with a certain phase difference.

In the piston 4 and the displacer 2, a working gas flows from the compression space 18a through the one-way valves (6, 7) through the pressurizing chambers (10, 11) where a high pressure state is maintained. Have.

Using the gas in the pressurizing chamber, the piston 4
-Between the displacer 2 and the cylinder 1, a gas is blown out to the sliding portion to form a gas film, and the structure is designed to reduce friction.

In the sliding portion between the displacer rod 3 and the piston cap 5, at least one of the sliding portions is provided with a surface coating having a low friction coefficient (such as Teflon coating) to reduce the friction.

[0006]

However, as shown in FIG. 5, since the displacer rod 3 is integrally fixed to the displacer 2, a mounting error occurs when the displacer rod 3 is fixed. In addition, since the piston 4 and the displacer 2 balance their positions independently of the cylinder 1 due to the gas bearing effect, their respective axial centers may be greatly different, so that the piston cap 5 and the displacer rod 3 slide. In order to reduce the friction when moving, it was necessary to set the clearance of the sliding portion large.

For this reason, there has been a problem that the gas from the compression space 18a flows out to the back space 19 through the clearance of the sliding portion between the displacer rod 3 and the piston cap 5, which leads to a reduction in compression efficiency (generally, the gas is compressed). The outflow is proportional to the cube of the clearance).

[0008] Further, when the treatment of the sliding portion is performed only by surface coating, the temperature rise becomes large at the time of high-speed operation, and the hardness of the coating material decreases accordingly.
Wear becomes severe. Further, there have been cases where the surface coating film of the sliding portion is peeled off by the abrasion powder or the abrasion powder clogs the sliding portion to increase the frictional resistance.

Accordingly, an object of the present invention is to reduce a mechanical loss such as a frictional resistance of a sliding portion between the displacer rod 3 and the piston cap 5, and further reduce a gas flow loss at the sliding portion. It is therefore an object of the present invention to provide a structure that does not require a major change from the conventional structure and that can reduce friction between sliding parts and improve compression efficiency with a simple structure.

[0010]

SUMMARY OF THE INVENTION The present invention has been made to achieve the above-mentioned object, and the invention according to claim 1 comprises a cylinder, a piston reciprocating in the cylinder, and A Stirling engine including a displacer that reciprocates in the cylinder in conjunction with a piston, a piston cap held by the piston, and a displacer rod provided on the displacer and sliding with the piston cap. In the above Stirling engine, the piston cap has a structure movable in a radial direction of the piston.

[0011] According to the second aspect of the present invention, a cylinder,
A piston that reciprocates in the cylinder, a displacer that reciprocates in the cylinder in conjunction with the piston, a piston cap that is held by the piston, and a piston cap that is provided on the displacer and slides with the piston cap. In a Stirling engine provided with a moving display surrod, the piston cap has a structure capable of tilting in the axial direction of the piston.

According to a third aspect of the present invention, there is provided a cylinder, a piston reciprocating in the cylinder, a displacer reciprocating in the cylinder in conjunction with the piston, and held by the piston. In a Stirling engine provided with a piston cap and a displacer rod provided on the displacer and sliding on the piston cap, the gas compressed by the reciprocating motion of the piston is stored inside the piston or the displacer. A Stirling engine, wherein a pressurized chamber is formed and gas in the pressurized chamber is supplied to a sliding portion between the piston cap and the displacer rod.

According to a fourth aspect of the present invention, the gas stored in the pressurized chamber inside the displacer is ejected from a small hole on the surface of the displacer rod through a gas flow path provided inside the displacer rod. The Stirling engine according to claim 3, wherein

According to a fifth aspect of the present invention, there is provided the Stirling engine according to the third aspect, wherein the gas stored in the piston is jetted from a small hole provided in the piston cap.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited by this.

[First Embodiment] FIG. 1 is a structural view of a Stirling engine according to a first embodiment.

In the first embodiment, a high-pressure helium gas is filled as a refrigerant in a pressure vessel 23, and a piston 4 and a displacer 2 reciprocate in a cylinder 1. The space formed by the pressure vessel 23 and the cylinder 1 is divided into two spaces by the piston 4. One is a working space 1 on the displacer 2 side of the piston 4.
The other is a back space 19 opposite to the displacer 2 side of the piston 4. The working space 18 is further divided into two spaces by the displacer 2,
One is a compression space 18a sandwiched between the piston 4 and the displacer 2, and the other is an expansion space 18b at the tip of the cylinder 1. These two spaces are connected via a regenerator 17. The back space 19 is formed by the pressure vessel 23 so as to surround the cylinder 1.

At this time, the compression space 18a and the expansion space 18b
The pressure f varies with the displacement of the reciprocating motion of the piston 4 based on the gas pressure sealed in the pressure vessel 23.

The one-way valve (6,
The gas is blown out from the pressurized chambers (10, 11) flowing through 7) and maintained in a high pressure state to the sliding portion between the piston 4, the displacer 2 and the cylinder 1,
The piston 4 and the displacer 2 move by forming a gas film on the sliding portion. In addition, since the gas jetted from the pressurized chambers (10, 11) to the sliding portion has a reduced gas outflow amount using the orifices (14, 15), there is almost no flow loss, and the pressurized chamber (10 , 11) stores a gas pressure that is approximately equal to the maximum pressure of the gas pressure fluctuation in the compression space 18a.

The diameter of the piston 4 used this time is about 30 mm.
In contrast, the diametrical clearance of the sliding portion between the piston 4, displacer 2, and cylinder 1 is set to about 25 μm. This is a value that is easy to process and assemble and does not significantly affect the compression and expansion rates of gas.

The piston 4 is supported by a piston spring 8 and reciprocates in the cylinder 1 at a predetermined frequency by linear driving. . At this time, the piston cap 5a held by the displacer rod 3 and the piston 4
And are sliding with each other.

Here, since the displacer rod 3 is integrally fixed to the displacer 2 by screwing or the like, an assembling error occurs or the displacer 2 and the piston 4 are independent of each other in the cylinder 1 due to a gas bearing effect. Since the piston 4 is held in a balanced position, large friction may occur between the piston cap 5a and the displacer rod 3 connected to the displacer 2 due to a difference in the axial center.

Therefore, in order to reduce the friction between the displacer rod 3 and the piston cap 5a, the piston cap 5a is configured to be movable in the radial direction with respect to the piston 4. Specifically, the protrusion of the piston cap 5a is held with a gap provided in the radial direction with respect to the holding portion of the piston 4. Also, in order to allow the piston cap 5a to move smoothly with respect to the piston 4, at least one of these holding portions is subjected to a surface treatment such as Teflon coating to reduce sliding resistance, and the radial axis It is possible to move satisfactorily for the deviation.

Further, in order to facilitate the movement, the material of the piston cap 5a is a light material such as Al.
In this example, the piston 4 and the piston cap 5
The diameter gap provided between the holes a was 0.2 mm (the diameter of the holding portion of the piston cap 5a was about 20 mm). This value is considered to be a source of vibration during movement if the gap is made too large, and is a value determined in consideration of the processing accuracy of each component.

By adopting such a structure, the piston cap 5a follows the axis of the displacer rod 3 and can be driven with low friction. Therefore, in the conventional structure, the diametral clearance between the piston cap 5a and the displacer rod 3 is about 0.1 mm.
Is provided, but the structure is capable of absorbing assembly errors, so it may be about several μm. Therefore, the fluid loss of the gas is reduced together with the friction reducing effect, which leads to an improvement in performance.

Embodiment 2 FIG. 2 is a structural view of a Stirling engine according to Embodiment 2. Note that a detailed description of the same configuration as in the first embodiment will be omitted.

When the displacer rod 3 is attached to the displacer 2 at an angle, the coaxiality of the displacer rod 3 and the piston cap is greatly different, so that a large frictional resistance occurs.

As shown in FIG. 2, the piston cap 5b
The holding portions of the piston 4 and the piston 4 have the same curvature, and the piston cap has a structure capable of tilting in the axial direction of the piston. In order to allow the piston cap 5b to move smoothly inside the piston 4, a Teflon coat is applied to the holding portion.

By adopting such a structure, the piston cap 5b follows the displacer rod 3, and the axes of the sliding parts coincide with each other, so that it is possible to reduce the friction.

In the second embodiment, as in the first embodiment, the diametrical clearance between the piston cap 5b and the displacer rod 3 may be about several μm, and the fluid loss of gas is reduced. Connect.

As described above, by employing the structures shown in the first and second embodiments, the cylinder 1, the piston 4, the displacer 2, and the displacer rod 3 are processed with their axes shifted.
Even when assembled and moving, the piston cap moves with respect to the piston 4 to absorb the difference in the axial center, thereby preventing the occurrence of friction and prying and increasing the sliding loss. Thus, it is possible to prevent a decrease in the efficiency of the compressor and a decrease in the reliability of the sliding portion due to wear. Furthermore, since there is no need to make strict requirements on the processing accuracy and assembly accuracy of parts, cost can be reduced. Third Embodiment FIG. 3 is a structural diagram of a Stirling engine according to a third embodiment. In addition, about the same structure as Example 1,
Detailed description is omitted.

In the third embodiment, the pressure chamber 1 of the displacer 2
In this structure, the gas stored in the gas passage 0 passes through the gas flow path 12 inside the displacer rod 3 and is blown out of the gas from the small hole 13 existing in the sliding portion to reduce the friction.

If the diameter of the gas passage 12 provided in the displacer rod 3 is too large with respect to the displacer rod 3, the strength of the displacer rod 3 is undesirably reduced. Further, the gas flow path 12 can be easily created by finishing by drilling.

Small hole 13 provided in displacer rod 3
Was finished to an inner diameter of 100 μm with a drill to reduce gas fluid loss. In addition, the small holes 13 are distributed in four in the circumferential direction of the rod so as to be in a mechanically balanced state. FIG.
In the above, only one small hole 13 is arranged in the axial direction. However, in order to further improve the gas bearing effect, it is preferable to arrange two small holes 13 in the axial direction. The gas ejected from the small holes 13 to the sliding portion between the displacer rod 3 and the piston cap 5c flows out to the lower pressure side, and a gas film is formed on the sliding portion to produce a low friction effect.

Further, the gas flowing out from the compression space 18a to the back space 19 is blocked from flowing out because the gas pressure flowing out of the small holes 13 is high, so that the loss of the flow rate can be reduced. It is possible.

By employing this structure, it is possible not only to reduce the clearance of the sliding portion between the displacer rod 3 and the piston cap 5c, but also to reduce the outflow of gas from the compression space 18a. This leads to an improvement in compression efficiency.

Here, the magnitude of the frictional force of the sliding portion is proportional to the viscosity coefficient of the lubricant. Since the viscosity coefficient of gas is on the order of 1/1000 of ordinary lubricating oil, the frictional force of the sliding part is also 1
Therefore, by adopting the gas bearing effect between the displacer rod 3 and the piston cap 5d, it is possible to realize low friction.

Fourth Embodiment FIG. 4 is a structural diagram of a Stirling engine according to a fourth embodiment. Note that a detailed description of the same configuration as in the first embodiment will be omitted. The principle of low friction is based on the gas bearing effect as in the third embodiment. Hereinafter, points different from the third embodiment will be described.

As shown in FIG. 4, the piston cap 5d
Are provided with small holes 16. Piston 4 from this small hole 16
The gas stored in the pressurized chamber 11 is ejected to form a gas film on the sliding portion. The small hole shape at this time was also set to 100 μm in inner diameter for the same reason as in Example 3. Also, with this structure, similarly to the third embodiment, since there is an effect of blocking outflow of gas from the compression space 18a to the back space 19, it is possible to reduce the flow rate loss of the compression space 18a. It is.

The small holes shown in FIGS. 3 and 4 may be of a type used for a hydrostatic gas bearing such as a self-contained throttle or an orifice throttle. The small hole shape at this time is the piston 4
The flow path resistance is increased by reducing the diameter and increasing the length in order to reduce the loss of the gas stored inside. Further, small holes are equally distributed in the circumferential direction in order to maintain a mechanical balance in the sliding portion.

Also, the clearance of the sliding portion should be as small as possible in consideration of the surface roughness and working accuracy of the surfaces sliding with each other within a dynamically stable range so as to reduce the flow loss. It is good to set to an appropriate value.

Further, by combining the structures of the first, second, third, and fourth embodiments, an effect is further exhibited for reducing the friction of the sliding portion.

When a reliability test was performed on these examples, it was confirmed that scratches and the like on the sliding portions were greatly reduced.

[0044]

As described above, according to the first or second aspect of the present invention, the cylinder, the piston reciprocating in the cylinder, and the displacer reciprocating in the cylinder in conjunction with the piston. In a Stirling engine including a piston cap held by the piston and a displacer rod provided on the displacer and sliding on the piston cap, the piston cap is movable in a radial direction or an axial direction of the piston. By adopting a simple structure, it is possible to reduce the friction between the piston cap and the sliding part of the displacer rod, and further reduce the flow loss at the sliding part,
The compression efficiency is improved.

According to the third and fourth aspects of the present invention, the cylinder, the piston reciprocating in the cylinder,
A stirling provided with a displacer that reciprocates in the cylinder in conjunction with the piston, a piston cap held by the piston, and a displacer rod provided on the displacer and sliding with the piston cap. In the engine, a pressurized chamber for storing gas compressed by the reciprocating motion of the piston is formed inside the piston or the displacer, and the gas in the pressurized chamber slides between the piston cap and the displacer rod. By supplying the gas to the portion, a gas film is formed on the sliding portion, friction is reduced, and reliability is improved. At the same time, the clearance of the sliding portion can be reduced, and the flow loss in the clearance is reduced, and the efficiency is improved.

[Brief description of the drawings]

FIG. 1 is a structural diagram of a Stirling engine according to a first embodiment.

FIG. 2 is a structural diagram of a Stirling engine according to a second embodiment.

FIG. 3 is a structural diagram of a Stirling engine according to a third embodiment.

FIG. 4 is a structural diagram of a Stirling engine according to a fourth embodiment.

FIG. 5 shows a conventional Stirling engine structure.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cylinder 2 Displacer 3 Displacer rod 4 Piston 5, 5a-5d Piston cap 6, 7 One-way valve 8 Piston spring 9 Displacer spring 10, 11, Pressurizing chamber 12 Gas flow path 18a Compressed space 18b Expansion space 19 Back space 23 Pressure vessel

Claims (5)

[Claims] 1. A cylinder, a piston reciprocating in the cylinder, a displacer reciprocating in the cylinder in conjunction with the piston, a piston cap held by the piston, and a displacer. A Stirling engine provided with the piston cap and a display surrod that slides, wherein the piston cap has a structure movable in a radial direction of a piston. 2. A cylinder, a piston reciprocating in the cylinder, a displacer reciprocating in the cylinder in conjunction with the piston, a piston cap held by the piston, and a displacer. A Stirling engine provided with the piston cap and a display surrod that slides, wherein the piston cap has a structure capable of tilting in the axial direction of the piston. 3. A cylinder, a piston reciprocating in the cylinder, a displacer reciprocating in the cylinder in conjunction with the piston, a piston cap held by the piston, and a displacer. A stirling engine provided with the piston cap and a displacer rod that slides, wherein a pressurized chamber for storing gas compressed by reciprocation of the piston is formed inside the piston or the displacer, A Stirling engine for supplying gas in a pressurized chamber to a sliding portion between the piston cap and the displacer rod. 4. The gas stored in a pressurized chamber inside the displacer is ejected from a small hole on the surface of the displacer rod through a gas flow path provided inside the displacer rod. 3. The Stirling engine according to 3. 5. The gas stored inside the piston,
The Stirling engine according to claim 3, wherein the gas is ejected from a small hole provided in the piston cap.