JPH05223382A - Stirling freezer - Google Patents

Abstract

PURPOSE:To maintain maximum freezing efficiency by keeping a phase difference between a compressor and a displacer both constituting a freezer with respect to a pressure loss change caused by the long term operation of a free piston type stirling freezer. CONSTITUTION:A compressor 1 provides a pressure change to operation gas 7 by reciprocating motion of a piston 2. A driver 8 sets the number of repetition of the reciprocating motion of the piston 2, i.e., driving frequency. The operation gas 1 to which the pressure change is imparted forces a displacer 4 of a cold head 3 to be rendered to a reciprocation motion. The displacer 4 includes an orifice 6 mounted thereon and is fixed to a casing of the cold head 3 through a spring 5. A temperature sensor 10 obtains cooling temperature information from the cold head 3 and supplies it to a driving frequency control part 11, and the driving frequency control part 11 keeps a phase difference between the displacer 4 and the piston 2 at an optimum value correspondingly to the cooling temperature information of the driving frequency by a driver 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Stirling refrigerator, and more particularly to a free piston Stirling refrigerator.

[0002]

2. Description of the Related Art Conventionally, this type of free piston type Stirling refrigerator utilizing a Stirling cycle as a refrigeration cycle has a built-in piston and a compressor for compressing a working gas such as pure helium gas and an operation by the compressor. A cold head that generates a desired low temperature in response to a change in gas pressure and a drive device that drives a built-in piston of a compressor are provided, and the cold head cools an object to be cooled to a predetermined low temperature.

FIG. 2 is a schematic diagram showing a conventional free piston type Stirling refrigerator.

In FIG. 2, a compressor 1 contains a working gas 7 such as pure helium gas, and reciprocates the piston 2 to repeatedly compress and expand the working gas 7, thereby giving a pressure change.

The driving machine 12 drives the directly connected piston 2 at a constant frequency and a constant amplitude in a form of changing a rotary motion by a rotary machine such as a motor into a linear reciprocating motion.

The cold head 3 has a porous and cylindrical displacer 4, and at one end of the displacer 4 is attached a disc-shaped orifice 6 having an opening at the center, and the displacer 4 and the orifice 6 as a whole are The spring 5 locks the case of the cold head 3.

The cold head 3 takes in the working gas 7 contained in the compressor 1, and the pressure change thereof causes the displacer 4 to reciprocate, thereby making one end of the displacer 4 a cooling end of a predetermined low temperature.

In this case, the pressure change of the working gas 7 and the frequency of the reciprocating motion of the displacer 4 are the same, but since a pressure loss occurs inside the cold head 3, the working gas 7, that is, the piston 2 and the displacer 4 are generated. There is a phase difference between the two.

The pressure change that causes the phase difference can be changed by changing the diameter of the opening 61 of the orifice 6 attached to the displacer 4, and thus the phase difference can also be changed.

In the case of a Stirling refrigerator, the above-mentioned phase difference greatly affects the refrigerating performance, and the diameter of the opening 61 of the orifice 6 is ensured so that the optimum phase difference can be ensured under a constant frequency of the driving machine 12. Is set.

[0011]

The relationship between the repetition frequency of the piston drive by the drive unit and the phase difference between the piston and the displacer in the conventional Stirling refrigerator described above is as shown in FIG.

As shown in FIG. 4, the initial state characteristic is C0,
The relationship between the driving frequency f0 of the piston 2 by the driving machine 12 and the phase difference ψ0 between the piston 2 and the displacer 4 is indicated by the operating point P0.

Thereafter, the initial state characteristic C0 changes and changes with the characteristics C1 and C2 as the operation continues for a long time. This change is brought about by an increase in pressure loss due to gas contained in the components of the cold head 3 itself, that is, so-called outgas emission.

Due to this increase in pressure loss, the operating point becomes P
1 and P2, and the phase difference correspondingly changes from ψ0 to ψ
There is a drawback that the cooling performance is significantly deteriorated by deviating from the optimum state.

An object of the present invention is to eliminate the above-mentioned drawbacks and to provide a Stirling refrigerator capable of maintaining a constant phase difference and maintaining optimum cooling performance.

[0016]

A refrigerating machine of the present invention comprises a piston and a compressor containing a working gas which undergoes a pressure change due to the reciprocating motion of the piston, a driving device for driving the piston, and a working gas for the working gas. In a free piston type Stirling refrigerator having a cold head for ensuring a predetermined low temperature state by incorporating a displacer that reciprocates in response to a pressure change, it is applied to the built-in displacer of the cold head brought about by long-term operation. A means for changing the driving frequency of the piston by the driving machine to compensate for the deterioration of the cooling function due to the pressure loss of the working gas, and holding the phase difference between the piston and the displacer at a predetermined optimum value. Composed.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention.

In the embodiment shown in FIG. 1, in addition to the compressor 1 and the cold head 3 which are the same as those in the conventional example shown in FIG. The cooling body 9, the temperature sensor 10 for detecting the cooling temperature of the cold head 3, and the piston by the driving machine 8 so as to keep the phase difference between the piston 2 and the displacer 4 at an optimum value according to the temperature detected by the temperature sensor 10. Two
And a drive frequency controller 11 for controlling the drive frequency.

Of the above-mentioned components, the compressor 1 and the cold head 3 are exactly the same as those of the conventional example shown in FIG. 2, so detailed description of each of them will be omitted.

Next, the operation of this embodiment will be described.

The piston 2 of the compressor is given a reciprocating motion by the driver 8 and gives a pressure change to the working gas 7 utilizing pure helium gas.

The driving machine 8 changes the rotary motion of a rotary machine using a DC motor into a reciprocating motion to drive the piston 2. The repetition of the reciprocating motion of the piston 2 is determined according to the drive frequency of the drive machine 8, and the drive machine 8 is controlled by the control signal output from the drive frequency controller 11 to control the power supply voltage of the DC motor. The rotation speed, that is, the drive frequency is controlled.

The driving frequency controller 11 includes a temperature sensor 10
The temperature information regarding the cooling temperature of the cold head 3 is obtained from the above, and the drive frequency of the drive machine 8 is controlled based on this temperature information so that the phase difference between the piston 2 and the displacer 4 is maintained in the optimum state.

FIG. 2 is a characteristic diagram showing the relationship between the drive frequency and the phase difference in the embodiment of FIG.

In the case of this embodiment, the initial state of the phase difference between the piston 2 and the displacer 4 is operated with P0 determined by the drive frequency f0 and the initial state characteristic C0 as the operating point.

The relationship between the drive frequency and the phase difference fluctuates and changes with the characteristics C1 and C2 with the long-time operation.

In this embodiment, based on the temperature information obtained by the temperature sensor 10, the drive frequency is changed from f0 to f1 and f2 so as to keep the phase difference at a constant value of ψ0. Control signal for drive frequency controller 1
It occurs in 1.

As a result, the characteristic changes to C1 and C2,
Piston 2 is always operated even when the operating point changes to P1 and P2.
Thus, the phase difference between the displacer 4 and the displacer 4 can be maintained at the optimum ψ0, and the optimum cooling effect can be secured.

[0030]

As described above, according to the present invention, the drive frequency of the drive unit in the free piston type Stirling refrigerator is changed so as to compensate for the decrease in cooling efficiency due to the change in the pressure loss of the working gas in the cold head. By doing so, there is an effect that the optimum cooling performance can be maintained for a long time.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a Stirling refrigerator according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a conventional Stirling refrigerator.

3 is a characteristic diagram showing the relationship between the drive frequency and the phase difference between the piston and the displacer in the embodiment of FIG.

FIG. 4 is a characteristic diagram showing a relationship between a conventional drive frequency and a phase difference between a piston and a displacer.

[Explanation of symbols]

 1 Compressor 2 Piston 3 Cold head 4 Displacer 5 Spring 6 Orifice 7 Working gas 8 Driver 9 Cooled object 10 Temperature sensor 11 Driving frequency controller 12 Driver

Claims (1)

[Claims] 1. A built-in compressor including a piston and a working gas that undergoes a pressure change due to the reciprocating motion of the piston, a drive device that drives the piston, and a displacer that reciprocates due to a pressure change of the working gas. In a free piston type Stirling refrigerator having a cold head that secures a predetermined low temperature state, a cooling function based on the pressure loss of the working gas applied to the built-in displacer of the cold head caused by long-term operation A Stirling refrigerator comprising means for changing a driving frequency of the piston by the driving machine so as to compensate for the decrease so as to maintain a phase difference between the piston and the displacer at a predetermined optimum value.