JP3635897B2 - Electromagnetic drive type reciprocating mechanism - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is directed to, for example, a Stirling refrigerator applied to a cryocooler that cools an infrared detection element to a cryogenic temperature, and an electromagnetically driven reciprocating motor that drives a compressor, a reciprocating piston built in an expander, and a displacer. Related to the dynamic mechanism.
[0002]
[Prior art]
First, the configuration of the Stirling refrigerator mentioned above is shown in FIGS. 3 (a) and 3 (b). In the figure, reference numeral 1 denotes a compressor having a reciprocating piston 1b built in a cylinder portion of a housing 1a, and 2 denotes an expander (cooling) having a reciprocating displacer 2c having a regenerator 2b built in the cylinder portion of the housing 2a. (Finger) 3 is a refrigerant (helium gas) connecting pipe piped between the compression space of the compressor 1 and the expander 2. The piston 1a of the compressor 1 and the displacer 2b of the expander 2 are driven to reciprocate in the axial direction by a linear motor electromagnetic actuator 4 incorporated in the housings 1b and 2b.
[0003]
Here, the electromagnetic actuator 4 includes a permanent magnet 4a and a stator composed of yokes 4b and 4c that are coupled to the magnetic pole end face of the permanent magnet 4a to form a closed magnetic path, and a gap (magnetic path opening) between the yokes 4b and 4c. Part) is a kind of linear motor comprising a mover provided with a solenoid coil 4d that enters and exits from the side. The stator is inside the housings 1a and 2a of the compressor 1 and the expander 2, and the mover is The piston rod 1c connected to the piston 1b of the compressor 1 and the piston rod 2d connected to the displacer 2c of the expander 2 are respectively fixed.
[0004]
The piston rods 1c and 2d are guided and supported so as to be displaceable in the axial direction via suspension springs 5 disposed on two sides of the electromagnetic actuator 4. As shown in FIG. 3 (b), the suspension spring 5 has a ring-shaped plate spring made of a highly elastic thin metal plate (for example, beryllium copper alloy) as a base and a plurality of spiral slits 5a on the plate surface. Formed and formed between the slits 5a and the arm portion 5b that can be bent in the direction perpendicular to the plate surface, and after assembling together with a spacer between the inner and outer peripheries of a plurality of leaf springs arranged in parallel, The inner peripheral end is coupled to the piston rod 1c of the compressor 1 and the displacer rod 2d of the expander 2, and the outer peripheral end is coupled to the end surface of the support cylinder 6 disposed on the outer peripheral side of the mover of the electromagnetic actuator 4, The base of the support cylinder 6 is fixedly supported on the yoke end surface of the electromagnetic actuator 4.
[0005]
In addition, 1d is a position detector of the piston 1b, 2e is a position detector of the displacer 2b, and 2f is an active balancer attached to the expander 2. In addition, the housings 1a and 2a of the compressor 1 and the expander 2 and the support cylinder 6 of the suspension spring 5 are made of an aluminum alloy material in order to reduce the weight.
The operation principle of the Stirling refrigerator having such a configuration is well known, and when the solenoid coil 4d of the electromagnetic actuator 4 is excited at a predetermined frequency from an AC power source (not shown), the exciting current and the stator that flow through the solenoid coil 4d. The piston 1b and the displacer 2c reciprocate in the cylinder by the electromagnetic force due to the interaction with the gap magnetic field between the yokes 4b / 4c and the spring action of the suspension spring 5, and are enclosed in the working space in the cylinder. Compresses and expands gas (helium gas). As a result, cold heat having a Kelvin temperature of about 70K is generated on the cylinder end surface 2g of the expander 2, and an infrared detection element (photoelectric element: InSb, HgCdTe, etc.), which is a body to be cooled, installed at this cold heat generation site And a minute heat radiation signal is detected with a high S / N ratio.
[0006]
[Problems to be solved by the invention]
By the way, in the Stirling refrigerator applied to the cryocooler of the infrared detecting element described above, a gap (magnetic path opening) between the yoke 4b and 4c constituting the stator of the electromagnetic actuator 4 and the solenoid coil 4d of the mover enters and exits. For this reason, a leakage magnetic flux is generated in the peripheral region from the magnetic path opening, and this causes magnetic disturbance as described below. That is, the leakage magnetic flux of the electromagnetic actuator 4 acts as noise on a minute signal detected by an infrared detecting element installed at the tip of the cylinder of the expander 2, and a signal line wired around the compressor 1 and the expander 2. It also acts as noise on electrical signals that flow through the electromagnetic actuator drive control circuit (including the piston and displacer position detection circuit). For this reason, if the leakage magnetic flux of the electromagnetic actuator 4 is left as it is, not only the measurement accuracy of the infrared sensor is lowered due to the magnetic disturbance, but also the operation control of the refrigerator as a cryocooler may be hindered.
[0007]
Therefore, as a measure for preventing magnetic disturbance caused by leakage magnetic flux of the electromagnetic actuator, a method of surrounding the compressor and expander housings with a high permeability material such as permalloy, for example, or shielding the housing itself with a soft iron or other high magnetic material. Although a method of using a magnetic material with magnetic permeability is conceivable, any of the methods has a drawback that the reciprocating mechanism (a Stirling refrigerator compressor or expander) increases in size or increases in weight.
[0008]
The present invention has been made in view of the above points, and is intended to implement an electromagnetically driven Stirling refrigerator applied to the cryocooler of the infrared detection element described above without causing an increase in size and weight of the apparatus. And it aims at providing the electromagnetic drive type reciprocating mechanism improved so that the leakage magnetic flux of an electromagnetic actuator could be suppressed without changing a basic structure.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, a reciprocating electromagnetic actuator is used as a drive unit for a compressor and a displacer in a compressor and an expander such as a Stirling refrigerator. In an electromagnetically driven reciprocating mechanism, in which a piston and a displacer rod are juxtaposed with the electromagnetic actuator and supported in a movable manner in the axial direction via a suspension spring incorporated in the housing, the leakage of the electromagnetic actuator As the magnetic shielding means against magnetic flux, the suspension spring located near the magnetic path opening of the actuator or the supporting member of the suspension spring is made of a high permeability material (Claim 1). Specifically, the suspension spring is deposited. Consists of hardened stainless steel (Claim 2) and suspension Pensions spring support member electromagnetic soft iron, is comprised of low carbon steel or silicon steel (claim 3).
[0010]
With the above configuration, the basic structure of the reciprocating mechanism remains the same, and a new magnetic shielding material is added, and the compressor and expander housing materials that incorporate electromagnetic actuators are made of lightweight aluminum alloy and heavy. Without changing to soft iron or the like, the material of the suspension spring located near the magnetic path opening of the electromagnetic actuator, or the support member of the suspension spring (part of the structural members of the reciprocating mechanism) is made of high permeability material, electromagnetic soft iron To effectively prevent magnetic disturbance to the external electrical signal system by blocking the leakage flux of the electromagnetic actuator by simply changing to (relative permeability μ _o = 200 to 300), silicon steel (μ _o ≈500), etc. Can do.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described based on the embodiment of FIG. In FIG. 1, the same members as those in FIG.
FIG. 1 shows a compressor of the Stirling refrigerator in FIG. 3, and its basic structure is the same as that in FIG. Here, the precipitation spring type stainless steel, which is a material having high permeability from a conventional beryllium copper alloy, is used for the suspension spring 5 disposed in the vicinity of the magnetic path opening of the electromagnetic actuator 4 and incorporated in the housing 1a of the compressor 1. It is configured to change to. Further, the support cylinder 6 which is a support member of the suspension spring 5 is also made of electromagnetic soft iron, low carbon steel, silicon steel or the like, which is also a high permeability material.
[0012]
As a result, the suspension spring 5 and its support cylinder 6 function as a magnetic shield with respect to the magnetic path opening of the electromagnetic actuator 4 and suppress leakage of magnetic flux to the surroundings. FIG. 2 is a characteristic diagram showing the result of analyzing the magnetic field in the peripheral region of the compressor 1 by the three-dimensional magnetic moment method in order to evaluate and confirm the effect of the magnetic shield. Here, the horizontal axis is the distance L in the radial direction with the point P (outer peripheral surface of the housing 1a) in FIG. 1 as the measurement reference point of the leakage magnetic flux density, the vertical axis is the magnetic flux density, and the characteristic line A is the illustrated embodiment. A characteristic line B represents a case of a conventional structure (the suspension spring 5 is made of a beryllium shell alloy and the support drum 6 is made of an aluminum alloy).
[0013]
As can be seen from the analysis diagram of the magnetic flux distribution shown in FIG. 2, the suspension spring 5 and the support cylinder 6 arranged in the vicinity of the magnetic path opening of the electromagnetic actuator 4 are made of electromagnetic soft iron (relative magnetic permeability μ _o = 200 to 300), the leakage magnetic flux density in the housing peripheral area is reduced to about 1/5 to 1/7 as compared with the conventional structure.
[0014]
【The invention's effect】
As described above, according to the present invention, the electromagnetically driven reciprocating motion for reciprocating the piston and the displacer built in the compressor, the expander for the Stirling refrigerator applied to the cryocooler of the infrared detecting element is an object. As a mechanism, a reciprocating electromagnetic actuator is incorporated in the housing of the compressor and expander, and the piston and displacer rod are juxtaposed with the electromagnetic actuator and moved in the axial direction via a suspension spring incorporated in the housing. The suspension spring located near the magnetic path opening of the actuator or the suspension spring support member as a magnetic shielding means against the leakage flux of the electromagnetic actuator is made of a high permeability material. Do not lead to large size and significant increase in weight , It can effectively reduce the magnetic flux leaking from the electromagnetic actuator to the outside peripheral area, thereby preventing the infrared detection element is cooled by the expander, and a compressor, the magnetic disturbance to an electric circuit which is arranged around the expander.
[Brief description of the drawings]
1 is a cross-sectional view of a compressor of a Stirling refrigerator according to an embodiment of the present invention. FIG. 2 shows an analysis result of a leakage magnetic field in a compressor peripheral region expressed by comparing the embodiment of FIG. 1 with a conventional example. FIG. 3 is a configuration diagram of a Stirling refrigerator that is an object of implementation of the present invention, (a) is a sectional view of the entire configuration of the refrigerator, and (b) is a plan view of a suspension spring incorporated in the refrigerator. Explanation of]
DESCRIPTION OF SYMBOLS 1 Stirling refrigerator compressor 1a Housing 1b Piston 1c Piston rod 2 Stirling refrigerator expander 2a Housing 2c Displacer 2d Displacer rod 4 Electromagnetic actuator 5 Suspension spring 6 Support cylinder

Claims (3)

This is an electromagnetically driven reciprocating mechanism that reciprocates pistons and displacers built into compressors and expanders such as Stirling refrigerators, and reciprocating electromagnetics within the housings of compressors and expanders as piston and displacer drive units. Actuator as a magnetic shielding means against leakage flux of electromagnetic actuator in which actuator is incorporated and piston and displacer rods are arranged in parallel to the electromagnetic actuator and supported in a movable manner in the axial direction via a suspension spring incorporated in the housing An electromagnetically driven reciprocating mechanism characterized in that the suspension spring located near the magnetic path opening or a support member for the suspension spring is made of a high magnetic permeability material. 2. The electromagnetically driven reciprocating mechanism according to claim 1, wherein the suspension spring is made of precipitation hardening stainless steel. 2. A reciprocating mechanism according to claim 1, wherein the suspension spring support member is made of electromagnetic soft iron, low carbon steel, or silicon steel.

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