JP2541406B2 - Free piston reciprocating compressor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a free piston reciprocating compressor for compressing a refrigerant to be supplied to an expander in a Stirling refrigerator having an expander which produces a cryogenic level of refrigeration by reciprocating motion of a displacer. In particular,
The present invention relates to an opposed type having a pair of opposed pistons.

[0002]

2. Description of the Related Art Heretofore, this free displacer type Stirling refrigerator has been known as a kind of small refrigerator for generating an extremely low temperature. For example, as shown in FIG. 5, this refrigerator is a combination of a compressor (a) that compresses a refrigerant gas and an expander (k) that expands the refrigerant gas discharged from the compressor (a). Is.
The compressor (a) is, for example, a closed casing (b).
And a cylinder (c) formed in the casing (b)
A piston (e) that is reciprocally fitted in the cylinder (c) and partitions and forms a compression chamber (d) in the internal space of the cylinder (c); and a drive source that reciprocally drives the piston (e). And a linear motor (f). This linear motor (f) has an annular permanent magnet (g) arranged around the cylinder (c), and this magnet (g) allows a cylindrical gap (magnetic gap) concentric with the center of the cylinder (c). )
To generate a magnetic field. A substantially inverted cup-shaped bobbin (h) integrally fixed to the piston (e) at the center of the gap is reciprocally disposed, and a drive coil (i) is provided around the bobbin (h). Is wrapped around. Further, a piston formed of a coil spring for elastically supporting the piston (e) so as to reciprocate between the outer bottom surface of the bobbin (h) (opposite side of the piston (e)) and the inner bottom surface of the casing (b). A spring (j) is installed, and by applying an alternating current of a predetermined frequency to the drive coil (i), the coil (i) and the bobbin (h) are driven by the action of the magnetic field passing through the gap to drive the piston ( The e) is reciprocated in the cylinder (c) to generate a gas pressure of a predetermined cycle in the compression chamber (d).

On the other hand, the expander (k) has a cylindrical cylinder (l), and the inside space of the cylinder (l) is defined as an expansion chamber (m) and a working chamber (n) in the cylinder (l). A free displacer (o) which is divided into two is fitted so as to be reciprocally movable. The displacer (o) is filled with a metal regenerator (o1) (regenerative heat exchanger) and communicates the regenerator (o1) with the expansion chamber (m) and the working chamber (n). The communication holes (o2) and (o3) are opened. A displacer spring (p), which is a coil spring elastically supporting the displacer (o) so as to reciprocate, is disposed in the working chamber (n). Further, the working chamber (n) is connected to the compression chamber (d) of the compressor (a) via the coupling pipe (q), and the displacer (o) is driven by the refrigerant gas pressure from the compressor (a). ) Is reciprocated to expand the refrigerant gas in the expansion chamber (m) to generate cold in the cold head at the tip of the cylinder (l) (for example, “Refr
igerator for Cryogenic Sensors ”, NASA Conference
See Publication 2287 etc.).

In the compressor (a), since one piston (e) reciprocates in the cylinder (c), the vibration is large, and among various devices operated at a cryogenic level,
It has a drawback that it cannot be used in a device such as an infrared sensor that is sensitive to vibration.

For this reason, as shown in Japanese Patent Publication No. 2-8155, an opposed piston type compressor is conventionally known. In this compressor, a pair of opposed pistons are reciprocally fitted in a cylinder to form a compression chamber between the pistons, and the pistons are respectively attached to a linear motor and a spring arranged on the back side thereof. In this configuration, as shown in FIG. 4, the coils (14) and (14) of both linear motors (10) and (10) are connected.
Are connected in series to an AC power supply (31) by a power supply circuit (32 '), and power of a predetermined frequency is supplied in synchronization with both coils (14), (14). (36) is an operation switch for operating the compressor.

[0006]

However, when the present inventor studied the above opposed piston type compressor,
As shown in FIG. 6, there is no problem when the power supply frequency (operating frequency) supplied to the linear motor is stable at the set frequency, but if the power supply frequency deviates from the set frequency due to fluctuations or external factors under specific conditions. When the phase difference between both pistons is greatly deviated, and in a serious case, the vibration mode becomes an antiphase mode in which both pistons move in the same direction, and a phenomenon occurs in which gas is not compressed at all. Then, once the piston vibrates in the antiphase mode, it becomes difficult to return to the inphase mode thereafter, and there is a problem that the original effect of the opposed piston compressor cannot be obtained.

That is, to explain this problem in detail, generally, in a linear motor compressor, the spring constant of the spring is (Km) and the gas spring constant of the compression chamber is (Km).
g), where the weight of the movable part is (M), the operating frequency (f) of the compressor is expressed by the following equation.

F = (1 / 2π) · {(Km + Kg) / M} ^1/2 And the coil which is one of the constituent parts of the voice coil type linear motor has a solid inductance and a resistance difference. There is some variation due to the above, and even in the mechanical parts of the compressor, there are variations in the weight of the movable part and the spring constant of the spring.

Therefore, in the opposed piston type compressor, the potential difference between both ends of each coil and the power factor are different due to variations in the specifications of the coils of the two linear motors, and the effective power consumed by each coil is reduced. There is a difference. When the operating frequency (f) is changed and the compressor is operated in the vicinity of the resonance point obtained from the weight of the spring and the movable part, the subtle difference in behavior due to the individual difference of the linear motor is amplified by the resonance phenomenon of the spring system. Therefore, the two linear motors cannot be synchronized with each other, and an abnormal operating state with different amplitudes occurs. In this abnormal operation state, one of the linear motors has a large amplitude and synchronizes with the pressure wave, and does not work the gas filled in the system. At this time, a large amount of counter electromotive force is generated and the power factor is extremely reduced, so that the effective power is also reduced. For this reason, part of the electric power that should be originally consumed by one linear motor is regenerated by the other linear motor, and the power factor of that linear motor increases and the effective power increases. However, when the absolute value of the current reaches its maximum, the position of the moving part of the linear motor becomes the dead point, and the coil largely protrudes from the magnetic gap.Therefore, the linear motor obtained by the product of the current value, the magnetic flux density and the coil length is obtained. Does not mean that the driving force is generated effectively and the amplitude does not increase.

Therefore, in order to properly control the phases of such two pistons, a power supply circuit needs a phase control circuit for energizing the coil, but in that case, the structure of the compressor becomes complicated. However, the cost is inevitable.

The present invention has been made in view of the above points, and an object thereof is to improve the power supply circuit in the above-mentioned opposed piston type compressor without the need for a phase control circuit. Is suppressed in order to oscillate in the anti-phase mode to ensure that the compressor performs the gas compression operation.

[0012]

In order to achieve the above object,
In the invention of claim 1, the coils of both linear motors are connected in parallel to the power source.

Specifically, the compressor of the present invention, as shown in FIGS. 1 and 2, has a casing (2), a cylinder (5) provided in the casing (2), and the cylinder (5). ) Reciprocatingly fitted inside, and a pair of opposed pistons (6), (6) defining and defining a compression chamber (15) in the space inside the cylinder (5) between each piston, and each piston (6). Elastic support means (1) for elastically supporting the casing (2) so that the cylinders (6) and (6) can reciprocate in the cylinder (5).
8) and (20), a magnet (12) and a coil (14), and by supplying alternating current of a predetermined frequency to the coil (14), each piston (6) is opposed to the opposing piston (6). A pair of linear motors (10) and (10) that are reciprocally driven so as to come close to and separate from each other are provided, and the coils (14) of both the linear motors (10) and (10) have an AC power supply (3).
It is characterized in that it is connected in parallel to 1).

According to the second aspect of the invention, the operation of the compressor is stopped when the coil of one of the linear motors is broken.

That is, according to the present invention, the linear motor (1
The power supply circuit (32) connecting the coils (14), (14) of (0), (10) and the AC power supply (31) has a disconnection detecting means (3) for detecting disconnection of each coil (14).
3) and an energization interruption means (34) for stopping energization to the other coil (14) when one coil (14) is broken.

[0016]

With the above construction, in the invention of claim 1, the coils (14), (1) of both linear motors (10), (10) are
Since 4) are connected in parallel, currents independently flow from the power supply (31) to the coils (14) and (14), and it is difficult for power imbalance to occur. Moreover, since the power supply circuit (32) to each coil (14) is independent of each other, even if the behavior of one linear motor (10) changes, electric power is regenerated as in the case of series connection. Is not used as electric power for the other linear motor (10). That is, two linear motors (10), (1
0) operates electrically independently. Therefore, both pistons (6) and (6) do not move in opposite phases, and therefore the gas can be reliably compressed by the compressor.

Moreover, a phase control circuit for controlling the phases of the coils (14) and (14) is not required, so that the structure can be simplified and the cost can be reduced.

According to the second aspect of the present invention, when the coil (14) of one of the linear motors (10) is broken, the fact is detected by the detecting means (33), and at the time of this breaking, the energization interruption means (34) is used for the other. The power supply to the coil (14) is stopped. Therefore, the linear motor (10) in which the coil (14) is not broken does not vibrate continuously and a large vibration is not generated, and the cooling target can be protected from the vibration.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 shows a compressor (1) for a Stirling refrigerator according to an embodiment of the present invention. This compressor (1) is an opposed piston type reciprocating compressor, and is combined with a conventionally known free displacer type expander (see FIG. 5) to form a refrigerator. The compressor (1) has a cylindrical casing (2), and this casing (2) has a pair of left and right cylindrical casing assemblies (3) of substantially the same configuration.
(3) are arranged concentrically, and an annular center base (4) is sandwiched between both casing assemblies (3), (3) in an airtight manner, so that both casing assemblies (3), (3) Is made of pure iron. Inside each of the casing assemblies (3), (3), there is provided a cylindrical cylinder (5) made of stainless steel, the ends of which are open. The cylinder (5) is a pair of left and right opposing cylinder members. It is composed of (5L) and (5R). Each of the cylinder members (5L) and (5R) has a flange portion (5a) at the end portion on the opposite cylinder member (5R) and (5L) side, and the flange portion (5a) is the center base (4). Is airtightly fitted and fixed to the flange (5
The a) and (5a) are in close contact with each other by sandwiching a regulation plate (22), which will be described later, so that both cylinder members (5L),
(5R) are concentrically connected to each other and are integrally connected. Inside the cylinder (5), a pair of left and right cylindrical pistons (6), (6) each having a bottomed central hole (6a) are slidably fitted. A portion surrounded by the cylinder (5) between 6) and (6) is a compression chamber (15). A concave groove (7) extending in the radial direction from the inner peripheral surface to the outer peripheral surface of the flange portion (5a) is correspondingly formed on the facing surface of the flange portion (5a) of each of the cylinder members (5L) and (5R). The space between the concave grooves (7) and (7) forms a gas passage (8) communicating with the compression chamber (15). Further, a gas passage (9) having an inner end communicating with the gas passage (8) is formed through the center base (4), and an outer end of the gas passage (9) is expanded through a coupling pipe (not shown). It is connected to the.

The left and right pistons (6) and (6) are drivingly connected to linear motors (10) and (10) as driving sources for reciprocatingly driving the pistons (6) and (6), respectively. That is, each linear motor (10) has a cylindrical member (11) made of pure iron fitted and fixed around each of the cylinder members (5L) and (5R), and the outer circumference of the cylindrical member (11). There is a gap between the inner circumference of the casing assembly and the inner circumference of the casing assembly (3). An annular permanent magnet (12) is fixed to the outer circumference of the cylindrical member (11) with a predetermined gap from the inner circumference of the casing assembly (3).
With this magnet (12), a cylindrical member (1
1) and the casing assembly (3) are used as yokes to generate a magnetic field of a predetermined strength in the gap (magnetic gap) between the magnet (12) and the inner peripheral surface of the casing assembly (3).

Further, each piston (6) has a flange portion (6b) extending radially outward from the opening side end portion of the center hole (6a), and the piston is provided on the outer periphery of the flange portion (6b). A substantially bottomed cylinder extending concentrically to the center of the left and right sides and having a tip portion reciprocally movable in the left-right direction in the gap between the magnet (12) and the inner peripheral surface of the casing assembly (3). Bobbins (13) are connected by an inward flange portion (13a). This bobbin (13)
Is made of thin-walled stainless steel as a non-magnetic material, and a coil winding portion (13b) is formed on the outer periphery of the tip end portion thereof by cutting out the outer peripheral surface over a predetermined width so as to correspond to the magnet. A coil (1
4) is wrapped around. The pistons (6) and (6) are turned into coil springs (to be described later) by energizing the coils (14) and (14) of the linear motors (10) and (10) with an alternating current of a predetermined frequency. 18) is configured to reciprocate in the same phase in opposite directions at a cycle determined by the spring constant of 18) and the gas spring constant of the gas in the compression chamber (15) to generate a gas pressure of a predetermined cycle in the compression chamber (15). Has been done.

The opening of each casing assembly (3) is closed by a spring assembly (16), and a spring holder (17) is attached to the center of the inner surface of the spring assembly (16). ) And the bottom surface of the center hole (6a) of the piston (6), a coil spring (18) is installed between the piston and the piston (6).
Is held at the neutral position of the reciprocating motion.

A restriction mechanism (21) is provided for restricting vibrations in the antiphase mode in which the pistons (6), (6) move in the same direction in the cylinder (5). The regulation mechanism (21) has a regulation plate (22) made of a thin circular plate having the same diameter as the flange portion (5a) of each of the cylinder members (5L) and (5R). The cylinder members (5L) and (5R) are sandwiched between the flange portions (5a) and (5a) and are arranged in the center of the compression chamber (15).
The restriction chamber (22) divides the compression chamber (15) into two chambers, a left chamber (15L) and a right chamber (15R), at the center of the cylinder (5). Further, since the regulation plate (22) is sandwiched between the flange portions (5a) and (5a), the above-mentioned flange portions (5a) and (5a) are formed by the regulation plate (22).
The gas passage (8) between them is also divided into a left branch passage (8L) and a right branch passage (8R) along the length direction, and the left branch passage (8L) is connected to the left chamber (15L) of the compression chamber (15). The right branch passage (8R) communicates with the right chamber (15R). Both branch passages (8L) and (8R) are communicated with each other through the gas passage (9) of the center base (4), and the branch passages (8L), (8R) and the gas passage (9) are connected to each other. , Left and right chambers (15L) of the compression chamber (15)
), (15R) communicate with each other. The flow passage resistances of the branch passages (8L), (8R) and the gas passages (9) that connect the left and right chambers (15L) and (15R) of the compression chamber (15) are the same as those of the compression chamber (15). Gas passage (8) (both branch passages (8L), which connects the expansion chamber to the expansion chamber of the expander,
(8R), the gas passage (9) and the connecting pipe are made larger than the overall flow passage resistance, and this large flow passage resistance causes the pistons (6) and (6) to vibrate in the antiphase mode. Are regulated.

Further, the coil (14) of each of the linear motors (10) is connected to a conductive wire (not shown) which is provided between the inward flange portion (13a) of the bobbin (13) and the spring assembly (16). It is connected. As a feature of the present invention, as shown in FIG. 1, the coils (14) and (14) are connected in parallel to the AC power source (31).

Further, the power supply circuit (3) between the coil (14) of each of the linear motors (10) and the AC power supply (31).
Branch circuit (32a) to each coil (14) in 2)
A relay (33) as a disconnection detecting means for detecting the disconnection of each coil (14) is arranged in series. Further, in the circuits other than the both branch circuits (32a) and (32a), the relay switch (3) which is always turned off by exciting the relays (14) and (14), respectively.
4) and (34) are arranged in parallel, and both of the relay switches (34) and (34) enable the coil (1)
At the time of disconnection of 4), the branch circuit (32) of the coil (14)
With the demagnetization of the relay (33) in a), the relay (1)
By turning off the relay switch (34) corresponding to 4), an energization cutoff unit for stopping energization to the other coil (14) is configured. In FIG. 1, reference numeral (35) is a start switch connected in parallel with both relay switches (34), (34), which are coils (14), (14) only at the start of operation of the compressor (1). O to energize
N is operated.

Next, the operation of the above embodiment will be described. With the start of operation of the refrigerator, the coils (14) of both linear motors (10), (10) in the compressor (1),
AC power of a predetermined frequency (50 Hz) is energized in synchronization with (14). With this energization, the magnets (12), (1
2) by the action of the magnetic field generated by the coil (1
4), (14) and pistons (6), (6) reciprocate in the same phase in opposite directions while expanding and contracting the first and second coil springs (18), (20), respectively. The volumes of the compression chamber (15) increase / decrease as the compression chambers (6) and (6) come into contact with and separate from each other in the cylinder (5).
A pressure wave having a predetermined period is generated within 5). This compression chamber (1
Since 5) communicates with the expansion chamber of the expander via both gas passages (8) and (9) and the connecting pipe, the displacer of the expander reciprocates at the same cycle as the pressure wave of the compression chamber (15). It moves and the expansion of the gas in the expansion chamber produces cold,
By repeating the reciprocating movement of the displacer, the cold head at the tip of the cylinder is cooled to a cryogenic level.

In this embodiment, both linear motors (1
0) and (10) coils (14) and (14) are power sources (3
Since it is connected in parallel to 1), even if it is operated at a frequency near the resonance point of the moving parts of the compressor (1) and the coil springs (18), (20), two linear motors (1
The phenomenon that 0) and (10) cannot be synchronized does not occur. That is, the power source (31) and the coils (14), (1
Since 4) and 4) are connected in parallel, currents independently flow from the power source (31) to the coils (14) and (14), which makes it difficult for power imbalance to occur. Moreover, since the power supply circuit (32) to each coil (14) is independent of each other, even if the behavior of one linear motor (10) changes, electric power is regenerated as in the case of series connection. Is not used as electric power for the other linear motor (10). Therefore, as shown in FIG. 3, even if the operating frequency of the power supply (31) deviates from the set frequency, the phase difference between the pistons (6) and (6) is maintained at zero.

Even if both pistons (6) and (6) try to oscillate in the same direction in antiphase mode, both chambers (15L) and (15R) of the compression chamber (15) move with the movement thereof.
) Gas is the branch passage (8L) of the gas passage (8).
), (8R) and the gas passage (9). However, in that case, each branch passage (8L
), (8R) and the flow passage resistance in the gas passage (9) are composed of the gas passage (8), the gas passage (9) and the connecting pipe which communicate between the compression chamber (15) and the expansion chamber of the expander. Since the flow path resistance is larger than the flow path resistance, the pistons (6) and (6) vibrate in the same phase mode because the pistons (6) and (6) are prevented from moving in opposite phases due to the large flow path resistance. As a result, the vibrations of the two pistons (6) and (6) in opposite phases can be regulated, and the gas can be reliably compressed by the compressor (1).

Further, since the parallel connection of the coils (14) and (14) to the power source (31) and the flow path resistance restrict the vibrations of both pistons (6) and (6) in the opposite phase, A phase control circuit for controlling the phases of the coils (14) and (14) is not required, the structure of the compressor (1) can be simplified, and the cost can be reduced.

In the compressor (1), at the start of operation, the coil (14) of each linear motor (10) is energized by turning on the start switch (35), which energizes each relay (33). Then, the relay switch (34) corresponding to this relay (33) is turned on. After this, the starting switch (35) is returned to the OFF state, but the coils (14) are continuously energized via the relay switch (34) which is in the ON state. When one of the coils (14) of the linear motors (10) and (10) is broken, the relay (33) that has been in the excited state until then is demagnetized, and the demagnetization of the relay (33) causes the relay (33) to demagnetize. The relay switch (34) corresponding to (33) is switched from the ON state to the OFF state, whereby the conduction between the power source (31) and the coil (14) is cut off. Therefore, when one coil (14) is disconnected, the energization to the other coil (14) is stopped, and the linear motor (10) in which the coil (14) is not disconnected continues to vibrate, causing large vibration. It can be prevented from being generated and the object to be cooled can be protected from vibration.

In the above embodiment, the piston (6),
Although the restriction mechanism (21) for restricting the anti-phase vibration of (6) is provided, it is not always necessary in the present invention. However, in order to more reliably prevent the vibrations of the two pistons (6) and (6) in the antiphase mode, the regulation mechanism (21) is preferable.

Further, in the above embodiment, when the coil (14) of one of the linear motors (10) is broken, the coil of the other linear motor (10) is broken by the relay (33) and the relay switch (34) opened and closed by the relay (33). Although power supply to (14) is stopped, instead of this, for example, a sensor for electronically detecting disconnection of each coil (14) and a switch means for connecting and disconnecting the power supply circuit are provided, and the sensor is a coil. When the disconnection of (14) is detected, the control circuit may switch off the power supply circuit by the switch means.

[0033]

As described above, according to the first aspect of the invention, the Stirling refrigerating machine has a pair of opposed pistons which vibrate in the cylinder in the same phase mode to compress the gas in the compression chambers between them. For a free piston reciprocating compressor for a machine, the coils of both linear motors were connected in parallel to the power supply, and both pistons were restricted from oscillating in antiphase mode. By operating the motor electrically completely independently, both pistons can surely vibrate in the same phase mode without the need for a phase control circuit, simplifying the structure of the opposed piston compressor and reducing the cost. It is possible to reliably perform the gas compression while achieving the above.

According to the second aspect of the present invention, when one of the coils is disconnected, the other coil is deenergized, so that the operation of the compressor can be stopped when the coil is disconnected. Therefore, the vibration of the cooling target can be protected.

[Brief description of drawings]

FIG. 1 is a linear motor power supply circuit diagram of a compressor according to an embodiment of the present invention.

FIG. 2 is an enlarged sectional view of a compressor.

FIG. 3 is a characteristic diagram showing a phase difference between both pistons with respect to an operating frequency.

FIG. 4 is a view corresponding to FIG. 1 showing a conventional example.

FIG. 5 is a sectional view showing a conventional example of a Stirling refrigerator.

FIG. 6 is a view corresponding to FIG. 3 showing a conventional example.

[Explanation of symbols]

 (1) ... Compressor (2) ... Casing (5) ... Cylinder (6) ... Piston (8) ... Gas passage (8L), (8R) ... Branch passage (9) ... Gas passage (10) ... Linear motor ( 12) ... Magnet (14) ... Coil (15) ... Compression chamber (15L), (15R) ... Chamber (18), (20) ... Coil spring (elastic support means) (31) ... AC power supply (32) ... Power supply Circuit (33) ... Relay (disconnection detection means) (34) ... Relay switch (energization interruption means)

Claims (2)

(57) [Claims] 1. A casing (2), a cylinder (5) provided in the casing (2), and a cylinder (5) interposed between the cylinder (5) and the cylinder (5) so as to be reciprocally movable. A pair of opposed pistons (6), (6) partitioning and forming a compression chamber (15) in an internal space, and each piston (6) is reciprocally movable in a cylinder (5) in a casing (2). Elastic support means (18) for elastically supporting the (2)
0), a magnet (12) and a coil (14), and by supplying alternating current of a predetermined frequency to the coil (14), the pistons (6) are brought into contact with and separated from the opposing pistons (6). A pair of linear motors (1
0), (10), and both linear motors (1
The free piston reciprocating compressor, wherein the coils (14) and (14) of 0) and (10) are connected in parallel to the AC power source (31). 2. A power supply circuit (32) for connecting the coils (14), (14) of the linear motors (10), (10) and the AC power supply (31), each coil (14) being disconnected. A disconnection detecting means (33) for detecting a current is provided, and an energization interruption means (34) for stopping energization to the other coil (14) when one coil (14) is disconnected. The free piston reciprocating compressor according to claim 1.