JPH0452615Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to, for example, a Stirling refrigerator that cools an infrared detection element to an extremely low temperature.

[Conventional technology]

FIG. 4 shows an example of the configuration of a conventional Stirling refrigerator. The Stirling refrigerator shown in the figure is called a split type Stirling refrigerator, and is a typical example of a Stirling refrigerator.

In FIG. 4, the split type Stirling refrigerator is roughly composed of one compressor, two cold fingers, and a connecting pipe 3 connecting them.
The compressor 1 includes a cylinder 4 and a piston 5,
The piston 5 is driven by an electric motor (not shown) via a connecting rod 6 and a crank 7 to reciprocate inside the cylinder 4. In order to reduce the amount of gas leaking through the gap between the cylinder 4 and the piston 5, the gap is made so that the difference in diameter is small, for example, 20 microns or less. A cylinder head 8 is attached to the upper part of the cylinder 4, and the cylinder 4, the piston 5, and the cylinder head 8
The internal space defined by this is called a compression chamber 9. Mechanical members such as the crank 7 that drive the piston 5 are housed in a housing 10, and a space inside the housing 10 partitioned from the compression chamber 9 by the piston 5 is called a bulk chamber 11. The cylinder 4, the cylinder head 8, and the housing 10 are joined to each other so as to maintain airtightness from the outside, and the compression chamber 9 and the bulk chamber 11 inside are filled with high-pressure working gas such as helium or hydrogen. It is enclosed. In addition, the cylinder 4
Fins 13 are provided on the outer surface of the housing to improve heat dissipation to the outside. The above is the configuration of the compressor 1. On the other hand, the cold finger 2 has a cylindrical low-temperature cylinder 14, and a displacer 15 that reciprocates slidably within the low-temperature cylinder 14. The space inside the low temperature cylinder 14 is divided into two by the displacer 15,
The space above the displacer 15 is called a low temperature room 16, and the space below is called a high temperature room 17. A regenerator 18 and a gas passage hole 19 are provided inside the displacer 15, and a regenerator 18 and a gas passage hole 19 are provided inside the displacer 15.
7 communicates with the regenerator 18 via the gas passage hole 19, and the regenerator 18 is filled with a cold storage material 20 such as a copper wire mesh. A seal ring 21 is fitted into the side of the displacer so that the working gas does not pass through the gap between the low temperature cylinder 14 and the displacer 15. A control cylinder 22 and a control chamber 23 are provided at the lower part of the cold finger 2, and a control piston 24 attached to the lower end of the displacer 15 passes through the high temperature chamber 17 and the control cylinder 22, and passes through the high temperature chamber 17 and the control cylinder 22. It projects into the control room 23. A seal ring 25 is attached to the control cylinder 22 to prevent working gas from passing through the gap between the control cylinder 22 and the control piston 24. Like the compressor 1, each chamber of the cold finger 2 is filled with a high-pressure working gas such as helium or hydrogen. The above is the configuration of the cold finger 2, and the compressor 1
compression chamber 9 and high temperature chamber 1 of the cold finger 2
7 are in communication via the connecting pipe 3. Also,
The compression chamber 9, the space inside the connecting pipe 3, the low temperature chamber 17, the regenerator 18, and the gas passage hole 19 communicate with each other, and these chambers are collectively referred to as a working chamber 26.

The operation of the conventional refrigerator configured as described above will be explained. The piston 5 moves from the compression chamber 9 to the cold room 1 by reciprocating inside the cylinder 4.
A sinusoidal wave is applied to the gas pressure in the working chamber 26 up to 6. On the other hand, since the volume of the bulk chamber 11 is sufficiently larger than the stroke volume of the piston 5, the internal gas pressure does not change much even when the piston 5 reciprocates. Control cylinder 22 of cold finger 2
The seal ring 25 attached to the working chamber 26 is almost completely sealed against short-period pressure changes such as the pressure waves of the gas in the working chamber 26, but the sealing is incomplete over a long period of time. The gas pressure in the control chamber 23 is maintained at approximately the average value of the gas pressure in the working chamber 26.

FIGS. 5 to 8 explain the operating principle of the conventional device in the order of the refrigeration cycle.

During one stage of the cycle shown in FIG. 5, the piston 5 of the compressor 1 is located below in the cylinder 4, and the displacer 15 of the cold finger 2 is located above the cold cylinder 14. During the transition from FIG. 5 to FIG. 6, the piston 5 rises and compresses the gas in the working chamber 26. The heat generated by this compression is released to the outside from the fins 13 on the outer periphery of the cylinder 5. At the time of Fig. 6, the working chamber 26
The gas pressure in the control chamber 23 is greater than that in the control chamber 23, and this pressure difference causes the control piston 2 to
The downward force generated at the displacer 1 overcomes the static frictional force of the seal rings 21 and 25.
5 begins to move downward, moving it to the bottom of the cold cylinder 14 as shown in FIG. As the displacer 15 moves, the gas in the high temperature chamber 17 passes through the regenerator 18 and moves to the low temperature chamber 16, and at this time, the regenerator 18 is filled with a cold storage material 20 that absorbs heat from the passing gas. Lowers the temperature of the gas. In the process from FIG. 7 to FIG. 8, the piston 5 of the compressor 1 descends and expands the gas in the working chamber 26. Due to this expansion, the temperature of the gas in the cold chamber 16 further decreases, and the upper part of the cold finger absorbs heat from its surroundings. This endothermic action plays a role in cooling the object to be cooled as a refrigerator. Since the pressure in the working chamber 26 decreases due to the expansion of the gas, the gas pressure is higher in the control chamber 23 than in the working chamber 26 at the time of FIG. The piston 2 is controlled by this differential pressure.
The upward force applied to displacer 1 overcomes the static friction force of seal rings 21 and 22, and
5 begins to move upward, moving it to the top of the cold cylinder 14 as shown in FIG. As the displacer 15 moves, the low temperature gas in the low temperature chamber 16 passes through the regenerator 18, stores cold heat in the cold storage material 20 in the regenerator 18, and the gas itself flows into the high temperature chamber 17 while increasing in temperature. . Refrigeration operation is performed by repeating the above-described cycle.

[Problem that the invention attempts to solve]

The conventional device as described above has the following problems. Cylinder 4 and piston 5 of compressor 1
Since there is a small gap between them, gas leaks little by little while the refrigerator is operating. That is, when the piston 5 rises and the gas pressure in the compression chamber 9 becomes higher than the gas pressure in the bulk chamber 11, it moves from the compression chamber 9 to the bulk chamber, and conversely, the piston moves down and the pressure in the compression chamber 9 becomes lower than that in the bulk chamber 11. Then, gas leaks from the bulk chamber 11 to the compression chamber 9. Here, since the gas leaking from the compression chamber 9 to the bulk chamber 11 has a higher density than the gas leaking from the bulk chamber 11 to the compression chamber 9, the mass flow rate of the gas leaks from the compression chamber 9 to the bulk chamber 11. The case is larger.
As a result, the pressures in the working chamber 26 as a whole and in the bulk chamber 11 behave as shown in FIG. 9 during operation.

In the figure, A indicates the pressure in the working chamber 26, B indicates its time average value, and C indicates the pressure in the bulk chamber 11. , the balance between the two is maintained. As mentioned above, the volume of the bulk chamber 11 is generally sufficiently large compared to the stroke volume of the piston 5.
Even during operation of the refrigerator, the pressure in the bulk chamber 11 is approximately constant or pulsates only slightly, and is approximately equal to the gas pressure before operation. Therefore, the time average value (b) of the gas pressure in the working chamber 26 during operation of the refrigerator is lower than the gas filling pressure before operation. If the compression ratio of the compressor 1 is the same, the higher the time average value of the pressure in the working chamber 26, the greater the amount of refrigeration generated in the cold room 16. Therefore, in order to obtain the required amount of refrigeration, it is necessary to The refrigerator must be filled with gas at a pressure higher than the average gas pressure in the working chamber 26. However, if the gas filling pressure is increased, it is necessary to increase the pressure resistance of the housing 10, etc., resulting in an increase in weight. Furthermore, because helium gas, which is commonly used as a working gas, has small molecules, it is difficult to keep it sealed at high pressure for long periods of time. When using or storing a refrigerator, more frequent gas replenishment is required, which leads to the problem of deteriorating the maintenance and operability of the refrigerator.

This invention was made to solve this problem, and proposes a Stirling refrigerator in which the time average pressure in the working chamber 26 is high during operation even if the gas filling pressure is low.

[Means for solving problems]

The Stirling refrigerator according to this invention has a compressor equipped with a cylinder that is tapered so that the inner diameter becomes smaller as it approaches the cylinder head.

[Effect]

With this design, gas leaks are more likely to occur between the cylinder and the piston when the piston is near bottom dead center than when it is near top dead center, so during operation, gas leakage occurs more easily from the bulk chamber to the working chamber. Gas leakage increases and equilibrium is maintained with the time average value of the gas pressure in the working chamber being higher than the pressure in the bulk chamber. Therefore, in order to obtain the same performance as the conventional device, the pressure of the gas sealed in the refrigerator may be lower than that of the conventional device.

〔Example〕

FIG. 1 is a diagram showing an embodiment of this invention.
In the illustrated embodiment, only four cylinders differ from the conventional device shown in FIG. 4, and the other parts are exactly the same as the conventional device. The cylinder 4 is tapered so that the inner diameter thereof has a diameter difference of, for example, about 5 μm to 20 μm between the upper end and the lower end,
It is attached so that the side with the smaller inner diameter faces the cylinder head 8.

In the Stirling refrigerator of this invention constructed as described above, the principle of generating refrigeration is exactly the same as that of the conventional apparatus shown in FIGS. 4 to 8. However, since the inner diameter of the cylinder 4 is tapered, when the piston 5 is located near the top dead center as shown in FIG. 2, the gas pressure is higher in the working chamber 26 than in the bulk chamber 11. In this case, the gap between cylinder 4 and piston 5 is small, so gas is difficult to leak, but as shown in Figure 3, piston 5
When is located near the bottom dead center, that is, when the gas pressure in the bulk chamber 11 is higher than that in the working chamber 26, the gap between the cylinder 4 and the piston 5 is large, so gas tends to leak. In other words, during operation, gas tends to move from the bulk chamber 11 to the working chamber 26, and as shown in FIG. Balance is maintained in high embodiments. Since the gas pressure in the bulk chamber 11 during operation is approximately equal to the gas filling pressure in the refrigerator before operation, pressure waves equivalent to those of the conventional apparatus can be obtained with a lower gas filling pressure than the conventional apparatus.

As explained above, in the device of this invention, since the sealed gas pressure is low, the pressure resistance of the housing 10 and the like is relatively unnecessary, so that the weight of the compressor 1 can be reduced. Furthermore, the lower the gas filling pressure, the less gas leaks from the refrigerator to the outside.
When using or storing a refrigerator for a long period of time, there is an advantage in terms of maintenance and operation that the frequency of gas replenishment can be reduced.

Incidentally, in the above explanation, the case where this invention is applied to a split-type Stirling refrigerator has been described, but it goes without saying that this invention can also be applied to other known Stirling refrigerators.

[Effect of idea]

This idea has a simple structure consisting of a cylinder with a tapered inner diameter, which allows a higher time-average pressure in the working chamber during operation to be obtained with a lower filling pressure of the working gas. It is possible to reduce the weight of components that require pressure-resistant strength, and at the same time, the lower the gas sealing pressure, the less gas leaks to the outside of the refrigerator. This has the effect of reducing the frequency of replenishment and significantly improving the maintainability and operability of the refrigerator.

[Brief explanation of the drawing]

Figures 1 to 3 show an embodiment of this invention, Figures 4 to 8 show a conventional Stirling refrigerator, and Figure 9 shows the pressure and pressure in the working chamber of a conventional Stirling refrigerator. FIG. 10 is a diagram showing temporal changes in the pressure in the working chamber and the pressure in the bulk chamber in the Stirling refrigerator of this invention. In the figure, 1 is a compressor, 4 is a cylinder, 5 is a piston, and 8 is a cylinder head. It should be noted that the same or corresponding parts in the figures are indicated by the same reference numerals.

Claims (1)

[Scope of utility model registration request] A Stirling refrigerator comprising: a cylinder having a tapered inner circumferential surface; a cylinder head that closes an end surface with a smaller inner diameter of the cylinder; and a compressor having a piston that reciprocates within the cylinder. .