Cryocooler and rotary valve unit for cryocooler

A cryocooler includes a displacer capable of reciprocating in an axial direction, a cylinder that accommodates the displacer, a drive piston that drives the displacer in the axial direction, a drive chamber that accommodates the drive piston, a rotary valve that includes a first valve element that is one of a valve rotor rotatable around a rotary valve rotation axis and a valve stator, and a second valve element that is the other of the valve rotor and the valve stator, a reversible motor that is coupled with the rotary valve so as to rotate the rotary valve around the rotary valve rotation axis. The rotary valve includes a coupling mechanism that couples the first component and the second component with each other. The first relative angle is designed to cool the cryocooler, and the second relative angle is designed to heat the cryocooler.

RELATED APPLICATIONS

The content of Japanese Patent Application No. 2017-047748, and of International Patent Application No. PCT/JP2018/004999, on the basis of which priority benefits are claimed in an accompanying application data sheet, is in its entirety incorporated herein by reference.

BACKGROUND

Technical Field

Certain embodiments of the present invention relate to a cryocooler and a rotary valve unit for a cryocooler.

Description of Related Art

A Gifford McMahon (Gifford-McMahon, GM) cryocooler serving as a representative cryocooler is mainly divided into two types such as a gas-driven type and a motor-driven type, depending on a drive source of a displacer. A typical gas-driven type GM cryocooler has a rotary valve disposed to control a pressure of a working gas expansion chamber, and a valve drive motor mechanically coupled so as to rotate the rotary valve. The displacer is mechanically disconnected from the motor, and the displacer is driven using a gas pressure. Not only an expansion chamber pressure but also a drive gas pressure is controlled by the rotary valve. The motor rotates the rotary valve. In this manner, a periodic volume change in the working gas expansion chamber and a periodic pressure oscillation in an expansion chamber are properly synchronized with each other, thereby forming a refrigerating cycle. In this way, the gas-driven type GM cryocooler is cryogenically cooled.

On the other hand, in a motor-driven type GM cryocooler, the displacer is mechanically coupled with a displacer drive motor. The displacer is caused to reciprocate in an axial direction by the motor. In this manner, a volume of the working gas expansion chamber is periodically changed. The displacer drive motor is also mechanically coupled with the rotary valve for controlling the pressure of the working gas expansion chamber. The motor rotates the rotary valve, and drives the displacer. In this manner, the periodic volume change in the working gas expansion chamber and the periodic pressure oscillation in the expansion chamber are properly synchronized with each other, thereby forming the refrigerating cycle. In this way, the motor-driven type GM cryocooler is cryogenically cooled.

In the motor-driven type GM cryocooler, a so-called rearward rotation heating technique is known in the related art. When the displacer drive motor is rotated forward, the refrigerating cycle is formed by expansion of a working gas. On the other hand, when the motor is rotated rearward, a heating cycle is formed by compression of the working gas. Rotation directions of the motor are switched therebetween, thereby enabling the GM cryocooler to switch between the refrigerating cycle and the heating cycle. In the heating cycle, the adiabatic compression of the working gas occurs in the expansion chamber. As a result, compression heat is generated. Based on the generated compression heat, the GM cryocooler can be heated. For example, the cooled GM cryocooler can be heated so as to recover a room temperature by using rearward rotation heating.

SUMMARY

According to an aspect of the present invention, there is provided a cryocooler including a displacer capable of reciprocating in an axial direction, a cylinder that accommodates the displacer, a drive piston that drives the displacer in the axial direction, a drive chamber that accommodates the drive piston, a rotary valve that includes a first valve element that is one of a valve rotor rotatable around a rotary valve rotation axis and a valve stator, and a second valve element that is the other of the valve rotor and the valve stator, in which the first valve element includes a first component configured to alternately connect the cylinder to a compressor discharge port and a compressor suction port by being rotated relative to the second valve element, and a second component configured to alternately connect the drive chamber to the compressor discharge port and the compressor suction port by being rotated relative to the second valve element, and a reversible motor that is coupled with the rotary valve so as to rotate the rotary valve around the rotary valve rotation axis. The rotary valve includes a coupling mechanism that couples the first component and the second component with each other so that the first component holds a first relative angle with the second component around the rotary valve rotation axis when the reversible motor is rotated forward, and so that the first component holds a second relative angle with the second component around the rotary valve rotation axis when the reversible motor is rotated rearward. The first relative angle is designed to cool the cryocooler. The second relative angle is designed to heat the cryocooler. The coupling mechanism is configured to switch between the first relative angle and the second relative angle in response to a reverse in a rotation direction of the reversible motor.

According to another aspect of the present invention, there is provided a rotary valve unit for a cryocooler. The rotary valve unit includes a rotary valve that includes a first valve element that is one of a valve rotor rotatable around a rotary valve rotation axis and a valve stator, and a second valve element that is the other of the valve rotor and the valve stator, in which the first valve element includes a first component configured to alternately connect a first gas chamber to a compressor discharge port and a compressor suction port by being rotated relative to the second valve element, and a second component configured to alternately connect a second gas chamber to the compressor discharge port and the compressor suction port by being rotated relative to the second valve element, and a reversible motor that is coupled with the rotary valve so as to rotate the rotary valve around the rotary valve rotation axis. The rotary valve includes a coupling mechanism that couples the first component and the second component with each other so that the first component holds a first relative angle with the second component around the rotary valve rotation axis when the reversible motor is rotated forward, and so that the first component holds a second relative angle with the second component around the rotary valve rotation axis when the reversible motor is rotated rearward. The first relative angle is designed to cool the cryocooler. The second relative angle is designed to heat the cryocooler. The coupling mechanism is configured to switch between the first relative angle and the second relative angle in response to a reverse in a rotation direction of the reversible motor.

DETAILED DESCRIPTION

The present inventors have intensively and repeatedly studied the gas-driven type GM cryocooler. As a result, the following problems have been recognized. For example, even if the rotation direction of the valve drive motor is reversed in the gas-driven type GM cryocooler used in the related art in the same manner as the motor-driven type GM cryocooler, the rearward rotation heating cannot be realized. The reason is as follows. Not only working gas pressure of the expansion chamber but also the drive gas pressure of the displacer is determined by the rotation of the valve drive motor. According to the gas-driven type GM cryocooler used in the related art, the heating cycle is not effectively formed even if the motor is rotated rearward. This results from a fundamental difference between both the motor-driven type and the gas-driven type. According to the motor-driven type, the displacer is mechanically coupled with the motor so as to be forcibly moved by driving the motor. In contrast, according to the gas-driven type, the displacer can be moved only by an operation of the gas pressure. Therefore, there no precedent example in which the rearward rotation heating available in the motor-driven type is applied to the gas-driven type. Without being limited to the gas-driven type GM cryocooler, this problem may arise to other cryocoolers in which the displacer is driven using the gas pressure.

It is desirable to provide a new heating technique for a cryocooler.

An aspect of the present invention may effectively adopt any combination of the above-described configuration elements or those in which configuration elements or expressions according to the present invention are substituted with each other in methods, devices, and systems.

According to the aspect of the present invention, it is possible to provide a new heating technique for a cryocooler.

Hereinafter, embodiments according to the present invention will be described in detail with reference to the drawings. In the description and the drawings, the same reference numerals will be given to the same or equivalent configuration elements, members, and processes, and repeated description thereof will be appropriately omitted. A scale or a shape of each illustrated portion is conveniently set in order to facilitate the description, and is not to be interpreted as being limited unless otherwise specified. The embodiments are merely examples, and do not the scope of the present invention. All characteristics or combinations thereof described in the embodiments are not necessarily essential to the invention.

FIG. 1is a view schematically illustrating a gas-driven type GM cryocooler according to an embodiment.

A GM cryocooler10includes a compressor12which compresses working gas (for example, helium gas) and a cold head14which cools the working gas through adiabatic expansion. The compressor12has a compressor discharge port12aand a compressor suction port12b. The cold head14is also called an expander.

As will be described in detail later, the compressor12supplies high-pressure (PH) working gas from the compressor discharge port12ato the cold head14. The cold head14includes a regenerator15which precools the working gas. The precooled working gas is further cooled through expansion inside the cold head14. The working gas is collected to the compressor suction port12bthrough the regenerator15. The working gas cools the regenerator15when the working gas passes through the regenerator15. The compressor12compresses the recovered low-pressure (PL) working gas, and supplies the working gas to the cold head14again.

The illustrated cold head14is a single stage type. However, the cold head14may be a multi-stage type.

The cold head14is a gas-driven type. Accordingly, the cold head14includes an axially movable body16serving as a free piston driven using gas pressure, and a cold head housing18configured to be airtight and accommodating the axially movable body16. The cold head housing18supports the axially movable body16so as to be capable of reciprocating in an axial direction. Unlike a motor-driven type GM cryocooler, the cold head14does not have a motor for driving the axially movable body16, and a coupling mechanism (for example, a scotch yoke mechanism).

The axially movable body16includes a displacer20capable of reciprocating in the axial direction (upward-downward direction inFIG. 1, indicated by an arrow C), and a drive piston22coupled with the displacer20so as to drive the displacer20in the axial direction. The drive piston22is located coaxially with and apart from the displacer20in the axial direction.

The cold head housing18includes a displacer cylinder (simply referred to as a cylinder in some cases)26which accommodates the displacer20, and a piston cylinder28which accommodates the drive piston22. The piston cylinder28is located coaxially with and adjacent to the displacer cylinder26in the axial direction.

Although details will be described later, a drive part of the cold head14which is a gas-driven type is configured to include the drive piston22and the piston cylinder28. In addition, the cold head14includes a gas spring mechanism that operates the drive piston22so as to relieve or prevent collision or contact between the displacer20and the displacer cylinder26.

In addition, the axially movable body16includes a coupling rod24that rigidly couples the displacer20with the drive piston22so that the displacer20reciprocates integrally with the drive piston22in the axial direction. The coupling rod24extends coaxially with the displacer20and the drive piston22from the displacer20to the drive piston22.

The drive piston22has a smaller dimension than that of the displacer20. An axial length of the drive piston22is shorter than that of the displacer20, and a diameter of the drive piston22is smaller than that of the displacer20. The diameter of the coupling rod24is smaller than that of the drive piston22.

A volume of the piston cylinder28is smaller than that of the displacer cylinder26. The axial length of the piston cylinder28is shorter than that of the displacer cylinder26, and the diameter of the piston cylinder28is smaller than that of the displacer cylinder26.

A dimensional relationship between the drive piston22and the displacer20is not limited to the above-described relationship, and may be different therefrom. Similarly, the dimensional relationship between the piston cylinder28and the displacer cylinder26is not limited to the above-described relationship, and may be different therefrom. For example, the drive piston22may be a tip portion of the coupling rod24, and the diameter of the drive piston22may be equal to the diameter of the coupling rod24.

An axial reciprocating movement of the displacer20is guided by the displacer cylinder26. In general, the displacer20and the displacer cylinder26are cylindrical members which respectively extend in the axial direction, and an inner diameter of the displacer cylinder26coincides with or slightly larger than an outer diameter of the displacer20. Similarly, the axial reciprocating movement of the drive piston22is guided by the piston cylinder28. In general, the drive piston22is a columnar member which extends in the axial direction. The piston cylinder28is a cylindrical member which extends in the axial direction, and the inner diameter of the piston cylinder28coincides with or slightly larger than the outer diameter of the drive piston22.

The displacer20and the drive piston22are rigidly coupled with each other in the axial direction by the coupling rod24. Accordingly, an axial stroke of the drive piston22is equal to an axial stroke of the displacer20, and both of these integrally move over all strokes. A position of the drive piston22relative to the displacer20is unchanged during the axial reciprocating movement of the axially movable body16.

In addition, the cold head housing18includes a coupling rod guide30which connects the displacer cylinder26to the piston cylinder28. The coupling rod guide30extends coaxially with the displacer cylinder26and the piston cylinder28from the displacer cylinder26to the piston cylinder28. The coupling rod24penetrates the coupling rod guide30. The coupling rod guide30is configured to serve as a bearing which guides the axial reciprocating movement of the coupling rod24.

The displacer cylinder26is coupled with the piston cylinder28in an airtight manner through the coupling rod guide30. In this way, the cold head housing18is configured to serve as a pressure vessel for the working gas. The coupling rod guide30may be considered to be a portion of either the displacer cylinder26or the piston cylinder28.

A first seal portion32is disposed between the coupling rod24and the coupling rod guide30. The first seal portion32is mounted on one of the coupling rod24and the coupling rod guide30, and slides on the other of the coupling rod24and the coupling rod guide30. For example, the first seal portion32is configured to include a seal member such as a slipper seal or an O-ring. In addition, instead of the seal member, a gap may be extremely reduced between the coupling rod24and the coupling rod guide30so that the gap functions as a clearance seal. The piston cylinder28is configured to be airtight relative to the displacer cylinder26by the first seal portion32. In this way, the piston cylinder28is fluidly isolated from the displacer cylinder26, and there is no direct gas circulation between the piston cylinder28and the displacer cylinder26.

The displacer cylinder26is divided into an expansion chamber34and a room temperature chamber36by the displacer20. The displacer20forms the expansion chamber34with the displacer cylinder26in one end in the axial direction, and forms the room temperature chamber36with the displacer cylinder26in the other end in the axial direction. The expansion chamber34is located on a bottom dead center LP1side, and the room temperature chamber36is located on a top dead center UP1side. In addition, the cold head14is provided with a cooling stage38fixed to the displacer cylinder26so as to wrap the expansion chamber34.

The regenerator15is incorporated in the displacer20. An upper lid portion of the displacer20has an inlet flow path40which allows the regenerator15to communicate with the room temperature chamber36. In addition, a cylinder portion of the displacer20has an outlet flow path42which allows the regenerator15to communicate with the expansion chamber34. Alternatively, the outlet flow path42may be disposed in a lower lid portion of the displacer20. In addition, the regenerator15includes an inlet retainer41inscribed in the upper lid portion, an outlet retainer43inscribed in the lower lid portion, and a regenerator material interposed between both the retainers. InFIG. 1, the regenerator material is illustrated as a dotted region interposed between the inlet retainer41and the outlet retainer43. The regenerator material may be a copper wire mesh, for example. The retainer may be a wire mesh which is coarser than the regenerator material.

A second seal portion44is disposed between the displacer20and the displacer cylinder26. For example, the second seal portion44is a slipper seal, and is mounted on the cylinder portion or the upper lid portion of the displacer20. A clearance between the displacer20and the displacer cylinder26is sealed with the second seal portion44. Accordingly, there is no direct gas circulation (that is, a gas flow bypassing the regenerator15) between the room temperature chamber36and the expansion chamber34.

When the displacer20moves in the axial direction, the expansion chamber34and the room temperature chamber36complementarily increase and decrease respective volumes. That is, when the displacer20moves downward, the expansion chamber34is narrowed, and the room temperature chamber36is widened. And vice versa.

The working gas flows into the regenerator15from the room temperature chamber36through the inlet flow path40. More precisely, the working gas flows into the regenerator15from the inlet flow path40through the inlet retainer41. The working gas flows into the expansion chamber34from the regenerator15by way of the outlet retainer43and the outlet flow path42. When the working gas returns to the room temperature chamber36from the expansion chamber34, the working gas passes a reverse path thereof. That is, the working gas returns to the room temperature chamber36from the expansion chamber34through the outlet flow path42, the regenerator15, and the inlet flow path40. The working gas trying to flow into the clearance after bypassing the regenerator15is blocked by the second seal portion44.

The piston cylinder28includes a drive chamber46whose pressure is controlled to drive the drive piston22, and a gas spring chamber48divided from the drive chamber46by the drive piston22. The drive piston22forms the drive chamber46with the piston cylinder28in one end in the axial direction, and forms the gas spring chamber48with the piston cylinder28in the other end in the axial direction. When the drive piston22moves in the axial direction, the drive chamber46and the gas spring chamber48complementarily increase and decrease the respective volumes.

The drive chamber46is located on a side opposite to the displacer cylinder26in the axial direction with respect to the drive piston22. The gas spring chamber48is located on a side the same as the displacer cylinder26in the axial direction with respect to the drive piston22. In other words, the drive chamber46is located on a top dead center UP2side, and the gas spring chamber48is located on a bottom dead center LP2side. An upper surface of the drive piston22receives the gas pressure of the drive chamber46, and a lower surface of the drive piston22receives the gas pressure of the gas spring chamber48.

The coupling rod24extends to the coupling rod guide30from the lower surface of the drive piston22through the gas spring chamber48. Furthermore, the coupling rod24extends to the upper lid portion of the displacer20through the room temperature chamber36. The gas spring chamber48is located on the side the same as the coupling rod24with respect to the drive piston22, and the drive chamber46is located on the side opposite to the coupling rod24with respect to the drive piston22.

A third seal portion50is disposed between the drive piston22and the piston cylinder28. For example, the third seal portion50is a slipper seal, and is mounted on to side surface of the drive piston22. A clearance between the drive piston22and the piston cylinder28is sealed with the third seal portion50. Accordingly, there is no direct gas circulation between the drive chamber46and the gas spring chamber48. In addition, since the first seal portion32is provided, there is no gas circulation between the gas spring chamber48and the room temperature chamber36. In this way, the gas spring chamber48is formed to be airtight relative to the displacer cylinder26. The gas spring chamber48is sealed with the first seal portion32and the third seal portion50.

The gas spring chamber48is narrowed when the drive piston22moves downward. At this time, the gas of the gas spring chamber48is compressed, and the pressure increases. The pressure of the gas spring chamber48acts upward on the lower surface of the drive piston22. Accordingly, the gas spring chamber48generates a gas spring force which acts against the downward movement of the drive piston22. Conversely, the gas spring chamber48is widened when the drive piston22moves upward. The pressure of the gas spring chamber48decreases, and the gas spring force acting on the drive piston22decreases.

The third seal portion50may not be provided. The clearance may be held between the drive piston22and the piston cylinder28. The clearance may act as flow path resistance against the gas circulation between the drive chamber46and the gas spring chamber48.

The cold head14is installed in an illustrated direction at a job site where the cold head14is used. That is, the cold head14is located vertically upward by locating the displacer cylinder26below in the vertical direction and locating the piston cylinder28above in the vertical direction. In this way, the GM cryocooler10has the highest refrigeration capacity when the cooling stage38is installed by adopting a downward facing posture in the vertical direction. However, an arrangement of the GM cryocooler10is not limited thereto. Conversely, the cold head14may be installed by adopting a posture in which the cooling stage38faces upward in the vertical direction. Alternatively, the cold head14may be installed sideways or in any other direction.

In a case where the cold head14is installed by adopting a posture in which the cooling stage38faces downward in the vertical direction, gravity acts downward as illustrated by an arrow D. Therefore, an empty weight of the axially movable body16acts to assist the downward drive force of the drive piston22. A stronger drive force acts on the drive piston22when the drive piston22moves downward, compared to when the drive piston22moves upward. Accordingly, in the typical gas-driven GM cryocooler, collision or contact between the displacer and the displacer cylinder is likely to occur at the bottom dead center of the displacer.

However, the cold head14is provided with the gas spring chamber48. The gas stored in the gas spring chamber48is compressed when the drive piston22moves downward, thereby increasing the pressure. The pressure acts in a direction opposite to the gravity. Accordingly, the drive force acting on the drive piston22decreases. It is possible to slow down the speed immediately before the drive piston22reaches the bottom dead center LP2.

In this way, it is possible to avoid contact or collision between the drive piston22and the piston cylinder28, and/or the displacer20and the displacer cylinder26. Alternatively, even if the collision occurs, collision sound is minimized since collision energy is reduced by the decreasing speed of the drive piston22.

Furthermore, the GM cryocooler10includes a working gas circuit52which connects the compressor12to the cold head14. The working gas circuit52is configured to generate a pressure difference between the piston cylinder28(that is, the drive chamber46) and the displacer cylinder26(that is, the expansion chamber34and/or the room temperature chamber36). The pressure difference causes the axially movable body16to move in the axial direction. If the pressure of the displacer cylinder26is lower than that of the piston cylinder28, the drive piston22moves downward, and consequently, the displacer20also moves downward. Conversely, if the pressure of the displacer cylinder26is higher than that of the piston cylinder28, the drive piston22moves upward, and consequently, the displacer20also moves upward.

The working gas circuit52includes a rotary valve54. The rotary valve54may be located in the cold head housing18so as to be connected to the compressor12by using a pipe. The rotary valve54may be located outside the cold head housing18so as to be connected to each of the compressor12and the cold head14by using a pipe.

The rotary valve54includes a main pressure switching valve60and an auxiliary pressure switching valve62. The main pressure switching valve60has a main intake on-off valve V1and a main exhaust on-off valve V2. The auxiliary pressure switching valve62has an auxiliary intake on-off valve V3and an auxiliary exhaust on-off valve V4.

The main pressure switching valve60is located in a main intake/exhaust flow path64which connects the compressor12to the room temperature chamber36of the cold head14. The main intake/exhaust flow path64is bifurcated to the main intake path64aand the main exhaust path64bin the main pressure switching valve60. The main intake on-off valve V1is located in the main intake path64a, and connects the compressor discharge port12ato the room temperature chamber36. The main exhaust on-off valve V2is located in the main exhaust path64b, and connects the compressor suction port12bto the room temperature chamber36.

The main pressure switching valve60is configured so that the compressor discharge port12aor the compressor suction port12bselectively communicates with the room temperature chamber36of the displacer cylinder26. In the main pressure switching valve60, the main intake on-off valve V1and the main exhaust on-off valve V2are respectively and exclusively opened. That is, the main intake on-off valve V1and the main exhaust on-off valve V2are inhibited from being opened at the same time. When the main intake on-off valve V1is open, the main exhaust on-off valve V2is closed. The working gas is supplied from the compressor discharge port12ato the displacer cylinder26through the main intake/exhaust flow path64. On the other hand, when the main exhaust on-off valve V2is open, the main intake on-off valve V1is closed. The working gas is collected to the compressor suction port12bfrom the displacer cylinder26through the main intake/exhaust flow path64. The main intake on-off valve V1and the main exhaust on-off valve V2may be temporarily closed together. In this way, the displacer cylinder26is alternately connected to the compressor discharge port12aand the compressor suction port12b.

The auxiliary pressure switching valve62is located in the auxiliary intake/exhaust flow path66which connects the compressor12to the drive chamber46of the piston cylinder28. The auxiliary intake/exhaust flow path66is bifurcated to the auxiliary intake path66aand the auxiliary exhaust path66bin the auxiliary pressure switching valve62. The auxiliary intake on-off valve V3is located in the auxiliary intake path66a, and connects the compressor discharge port12ato the drive chamber46. The auxiliary exhaust on-off valve V4is located in the auxiliary exhaust path66b, and connects the compressor suction port12bto the drive chamber46.

The auxiliary pressure switching valve62is configured so that the compressor discharge port12aor the compressor suction port12bselectively communicates with the drive chamber46of the piston cylinder28. The auxiliary pressure switching valve62is configured so that the auxiliary intake on-off valve V3and the auxiliary exhaust on-off valve V4are respectively and exclusively opened. That is, the auxiliary intake on-off valve V3and the auxiliary exhaust on-off valve V4are inhibited from being opened at the same time. When the auxiliary intake on-off valve V3is open, the auxiliary exhaust on-off valve V4is closed. The working gas is supplied from the compressor discharge port12ato the drive chamber46through the auxiliary intake/exhaust flow path66. On the other hand, when the auxiliary exhaust on-off valve V4is open, the auxiliary intake on-off valve V3is closed. The working gas is collected to the compressor suction port12bfrom the drive chamber46through the auxiliary intake/exhaust flow path66. The auxiliary intake on-off valve V3and the auxiliary exhaust on-off valve V4may be temporarily closed together. In this way, the drive chamber46is alternately connected to the compressor discharge port12aand the compressor suction port12b.

Although details will be described later, a group of the valves (V1to V4) can be operated in accordance with a cooling valve timing for cooling the GM cryocooler10, or in accordance with a heating valve timing for heating the GM cryocooler10.

The group of valves (V1to V4) is incorporated in the rotary valve54, and is synchronously driven. The rotary valve54is configured so that the valves (V1to V4) are properly switched by rotational sliding of the valve disc (or the valve rotor) with respect to the valve main body (or the valve stator). The group of valves (V1to V4) is switched in the same cycle during the operation of the GM cryocooler10, thereby causing the four on-off valves (V1to V4) to periodically change an open/closed state. The four on-off valves (V1to V4) are open and closed in respectively different phases.

The GM cryocooler10includes a reversible motor56coupled with the rotary valve54so as to rotate the rotary valve54around the rotary valve rotation axis. The reversible motor56is mechanically coupled with the rotary valve54. The rotary valve54is configured to be operated in accordance with the cooling valve timing, when the reversible motor56is rotated forward, and to be operated in accordance with the heating valve timing, when the reversible motor56is rotated rearward.

The GM cryocooler10may include a motor control unit58that controls the rotation direction of the reversible motor56. The motor control unit58may be configured to switch the rotation directions of the reversible motor56in accordance with an input from a user. For example, the motor control unit58may include a switching switch operated by the user. The switching switch is operated, thereby reversely changing the rotation direction of the reversible motor56(switching from forward rotation to rearward rotation, or rearward rotation to forward rotation).

The rotary valve unit for the GM cryocooler10includes the rotary valve54and the reversible motor56. The rotary valve unit may include the motor control unit58. The rotary valve unit may be integrally mounted on the cold head14of the GM cryocooler10. Alternatively, the rotary valve unit may be provided separately from the cold head14so as to be connected to the cold head14by using a pipe.

FIG. 2is a schematic perspective view illustrating the rotary valve unit according to the embodiment. In order to facilitate understanding, a portion of an internal structure is illustrated using a broken line.

The rotary valve54includes a valve stator150and a valve rotor152. In a case where the rotary valve54is accommodated in the cold head housing18, the valve stator150is fixed to the cold head housing18. In a case where the rotary valve54is provided separately from the cold head14, the valve stator150is fixed to a valve housing which accommodates the rotary valve54or other stationary portions.

The valve stator150includes a first valve stator150aand a second valve stator150b. Both the first valve stator150aand the second valve stator150bare fixed to the cold head housing18or other stationary portions. The first valve stator150aand the second valve stator150bare formed in a cylindrical shape, and are arranged coaxially with a rotary valve rotation axis (hereinafter, referred to as a rotation axis)156. The second valve stator150bis located outside the first valve stator150aso as to surround the first valve stator150a. The cylindrical surface disposed inside the second valve stator150bis in contact with the cylindrical surface disposed outside the first valve stator150a.

In this way, the valve stator150is divided into two stator components. However, the dividing is not essential, and the valve stator150may be a single component.

The valve stator150has a cylinder port158and a drive chamber port160. The rotary valve54is connected to the room temperature chamber36illustrated inFIG. 1through the cylinder port158, and fluidly communicates with the displacer cylinder26. The cylinder port158corresponds to the main intake/exhaust flow path64illustrated inFIG. 1. In addition, the rotary valve54is connected to the drive chamber46illustrated inFIG. 1through the drive chamber port160, and fluidly communicates with the piston cylinder28. The drive chamber port160corresponds to the auxiliary intake/exhaust flow path66illustrated inFIG. 1.

The cylinder port158and the drive chamber port160are open on a cylinder side surface of the second valve stator150b. The cylinder port158and the drive chamber port160are arranged on mutually opposite sides across the rotation axis156. The cylinder port158penetrates both the contact surfaces from the second valve stator150bto the first valve stator150a. In order to seal the cylinder port158and the drive chamber port160with each other by using a seal member such as an O-ring on the contact surface between the second valve stator150band the first valve stator150a, the cylinder port158and the drive chamber port160are located at different positions in a direction of the rotation axis156.

In addition, the valve stator150has a high-pressure port162. The rotary valve54is connected to the compressor discharge port12aillustrated inFIG. 1through the high-pressure port162, and fluidly communicates with the compressor12. The high-pressure port162corresponds to the main intake path64aand the auxiliary intake path66aillustrated inFIG. 1. The high-pressure port162is open on a bottom surface (that is, surface on a side opposite to the valve rotor152in the direction of the rotation axis156) of the first valve stator150a.

The valve rotor152is coupled with the reversible motor56so as to be rotated around the rotation axis156relative to the valve stator150. For example, the valve rotor152is coupled with an output shaft of the reversible motor56via a rotation transmission mechanism166such as a crank mechanism, on one end side in the direction of the rotation axis156. The valve rotor152may be directly coupled with the output shaft of the reversible motor56. As illustrated by an arrow R, the valve rotor152can be rotated around the rotation axis156in both forward and rearward directions.

In addition, the valve rotor152is in surface contact with the valve stator150so as to rotationally slide on the valve stator150, on the other end side in the direction of the rotation axis156. The surface contact between the valve rotor152and the valve stator150holds airtightness of the working gas circulating through the valve stator150and the valve rotor152. In other words, the contact surface pressure between the valve rotor152and the valve stator150is used. In this manner, a high-pressure gas flow path and a low-pressure gas flow path which penetrate a rotational sliding surface between the valve rotor152and the valve stator150are sealed with each other.

The valve rotor152includes a first valve rotor152aand a second valve rotor152b. The first valve rotor152aand the second valve rotor152bare coupled with the reversible motor56so as to be rotated around the rotation axis156relative to the valve stator150. The first valve rotor152ais configured to be rotated so as to alternately connect the displacer cylinder26to the compressor discharge port and the compressor suction port. The second valve rotor152bis configured to be rotated so as to alternately connect the piston cylinder28to the compressor discharge port and the compressor suction port. An internal flow path configuration of the rotary valve54will be described later.

The first valve rotor152aand the second valve rotor152bare formed in a cylindrical shape, and are arranged coaxially with the rotation axis156. The second valve rotor152bis located outside the first valve rotor152aso as to surround the first valve rotor152a. The cylindrical surface disposed inside the second valve rotor152bis in contact with the cylindrical surface disposed outside the first valve rotor152a. The second valve rotor152bis configured so that one end side is closed, and the other end side is open in the direction of the rotation axis156, and has a recess portion to which the first valve rotor152ais fitted. An upper surface (surface on a side opposite to the valve stator150in the direction of the rotation axis156) of the first valve rotor152ais in contact with a closed end portion of the second valve rotor152b.

In this way, the valve rotor152is divided into two rotor components.

The valve rotor152has a main low-pressure port164and an auxiliary low-pressure port165. The rotary valve54is connected to the compressor suction port12billustrated inFIG. 1through the main low-pressure port164and the auxiliary low-pressure port165, and fluidly communicates with the compressor12. The main low-pressure port164corresponds to the main exhaust path64billustrated inFIG. 1. The auxiliary low-pressure port165corresponds to the auxiliary exhaust path66billustrated inFIG. 1. The main low-pressure port164and the auxiliary low-pressure port165are open on the upper surface of the second valve rotor152b. In the drawing, the main low-pressure port164includes two gas outlets, but the number of the gas outlets may be only one.

The first valve rotor152ais in surface contact with the first valve stator150aso as to rotationally slide on the first valve stator150a. The outer diameter of the first valve rotor152acoincides with the outer diameter of the first valve stator150a. The second valve rotor152bis in surface contact with the second valve stator150bso as to rotationally slide on the second valve stator150b. The inner diameter and the outer diameter of the second valve rotor152bcoincide with the inner diameter and the outer diameter of the second valve stator150b. The second valve rotor152band the second valve stator150bmay have mutually different outer diameters.

A combination of the first valve stator150aand the first valve rotor152aconfigures the main pressure switching valve60illustrated inFIG. 1, that is, the main intake on-off valve V1and the main exhaust on-off valve V2. A combination of the second valve stator150band the second valve rotor152bconfigures the auxiliary pressure switching valve62illustrated inFIG. 1, that is, the auxiliary intake on-off valve V3and the auxiliary exhaust on-off valve V4.

The first valve rotor152aand the second valve rotor152bare coupled with each other by a valve rotor coupling mechanism168. The valve rotor coupling mechanism168couples the first valve rotor152aand the second valve rotor152bwith each other as follows. When the reversible motor56is rotated forward, the first valve rotor152aholds a first relative angle with the second valve rotor152bso that both the valve rotors are rotated around the rotation axis156. When the reversible motor56is rotated rearward, the first valve rotor152aholds a second relative angle with the second valve rotor152bso that both the valve rotors are rotated around the rotation axis156. The rotation of the reversible motor56is transmitted to the second valve rotor152bvia the rotation transmission mechanism166(or directly), and the rotation of the second valve rotor152bis transmitted to the first valve rotor152avia the valve rotor coupling mechanism168. In this way, the first valve rotor152aand the second valve rotor152bare integrally rotated.

The valve rotor coupling mechanism168is configured to change a relative position between the first valve rotor152aand the second valve rotor152bin response to a reverse in rotation direction of the reversible motor56. More specifically, the valve rotor coupling mechanism168is configured to switch between the first relative angle and the second relative angle in response to the reverse in rotation direction of the reversible motor56. Details of the valve rotor coupling mechanism168will be described later.

The second relative angle is different from the first relative angle. Although details will be described later, the first relative angle is designed to cool the GM cryocooler10. The second relative angle is designed to heat the GM cryocooler10. The second relative angle may be shifted from the first relative angle as much as an angle selected from a range of 30° to 60°. The second relative angle may be shifted from the first relative angle as much as approximately 45°. In this case, when the reversible motor56is rotated forward, the rotary valve54can be operated in accordance with the cooling valve timing. When the reversible motor56is rotated rearward, the rotary valve54can be operated in accordance with the heating valve timing.

The flow path configuration of the rotary valve54will be described with reference toFIGS. 3A to 5B.

FIGS. 3A to 3Eare schematic plan views illustrating the rotational sliding surface of the rotary valve unit according to the embodiment.FIG. 3Aillustrates a surface of the valve stator150coming into surface contact with the valve rotor152, andFIGS. 3B to 3Eillustrate a surface of the valve rotor152coming into surface contact with the valve stator150.FIGS. 3B to 3Eillustrate some examples of the relative position between the first valve rotor152aand the second valve rotor152bwith regard to the valve rotor152.

FIGS. 4A, 4B, 5A, and 5Bare schematic sectional views for describing the internal flow path configuration of the rotary valve54. In order to facilitate understanding, as an example of the valve rotor152illustrated inFIG. 3D,FIG. 4Aillustrates a state where the main intake on-off valve V1and the auxiliary intake on-off valve V3are open (that is, a state where the main exhaust on-off valve V2and the auxiliary exhaust on-off valve V4are closed). In addition, as an example of the valve rotor152illustrated inFIG. 3D,FIG. 4Billustrates a state where the main exhaust on-off valve V2and the auxiliary exhaust on-off valve V4are open (that is, a state where the main intake on-off valve V1and the auxiliary intake on-off valve V3are closed).

In addition, as an example of the valve rotor152illustrated inFIG. 3E,FIG. 5Aillustrates a state where the main intake on-off valve V1and the auxiliary intake on-off valve V3are open (that is, a state where the main exhaust on-off valve V2and the auxiliary exhaust on-off valve V4are closed). In addition, as an example of the valve rotor152illustrated inFIG. 3E,FIG. 5Billustrates a state where the main exhaust on-off valve V2and the auxiliary exhaust on-off valve V4are open (that is, a state where the main intake on-off valve V1and the auxiliary intake on-off valve V3are closed).FIGS. 4A to 5Billustrate each cross section including the rotation axis156.

As illustrated inFIG. 3A, the first valve stator150ahas a first stator flat surface170a, and the second valve stator150bhas a second stator flat surface170b. The first stator flat surface170ais an end surface of the first valve stator150a, and the second stator flat surface170bis an end surface of the second valve stator150b. As described above, the valve stator150has a double cylindrical structure having the first valve stator150aand the second valve stator150bwhich serve as inner and outer cylinders. Accordingly, the first stator flat surface170ahas a circular region, and the second stator flat surface170bhas an annular region surrounding the first stator flat surface170a. The first stator flat surface170aand the second stator flat surface170bare located at substantially the same height in the direction of the rotation axis156. Accordingly, the first stator flat surface170aand the second stator flat surface170bare on substantially the same plane.

The high-pressure port162and the cylinder port158are open on the first stator flat surface170a. The high-pressure port162is located at the center of the first stator flat surface170a. That is, the high-pressure port162penetrates the first valve stator150ain the direction of the rotation axis156. The cylinder port158penetrates from the outer peripheral portion of the first stator flat surface170ato the cylinder side surface of the second valve stator150b. That is, the cylinder port158enters the first valve stator150ain the direction of the rotation axis156, is bent outward in the radial direction, and is open on the cylinder side surface of the first valve stator150a. Then, the cylinder port158is connected to a hole penetrating the second valve stator150bin the radial direction.

The drive chamber port160is open on the second stator flat surface170b. The drive chamber port160is located on a side opposite to the cylinder port158across the high-pressure port162(that is, the rotation axis156). The drive chamber port160enters the second valve stator150bfrom the second stator flat surface170bin the direction of the rotation axis156, is bent outward in the radial direction, and penetrates the cylinder side surface of the second valve stator150b.

As illustrated inFIG. 3B, the first valve rotor152ahas a first rotor flat surface172acoming into surface contact with the first stator flat surface170a, and the second valve rotor152bhas a second rotor flat surface172bcoming into surface contact with the second stator flat surface170b. The first rotor flat surface172ais an end surface of the first valve rotor152a, and the second rotor flat surface172bis an end surface of the second valve rotor152b. As described above, the valve rotor152has a double cylindrical structure having the first valve rotor152aand the second valve rotor152bwhich serve as inner and outer cylinders. Accordingly, the first rotor flat surface172ahas a circular region, and the second rotor flat surface172bhas an annular region surrounding the first rotor flat surface172a. The first valve stator150aand the second valve stator150bare located at substantially the same height in the direction of the rotation axis156. Accordingly, the first valve stator150aand the second valve stator150bare on substantially the same plane.

A first rotor high-pressure flow path174is open on the first rotor flat surface172a. The first rotor high-pressure flow path174defines a rectangular or oblong gas inlet extending outward in the radial direction from a center portion of the first rotor flat surface172a, on the first rotor flat surface172a. The gas inlet extends in the radial direction of the first rotor flat surface172a. However, the first rotor high-pressure flow path174does not reach the cylinder side surface of the first valve rotor152a. A radial length of the first rotor high-pressure flow path174is substantially equal to a radial length from the high-pressure port162to the cylinder port158on the first stator flat surface170a. The outer peripheral portion of the first rotor high-pressure flow path174and the cylinder port158are located on substantially the same circumference around the rotation axis156.

The center portion of the first rotor high-pressure flow path174penetrates from the first rotor flat surface172ato the upper surface (end surface on a side opposite to the first rotor flat surface172a) of the first valve rotor152ain the direction of the rotation axis156(refer toFIG. 4A). The first rotor high-pressure flow path174is always connected to the high-pressure port162.

In addition, the first rotor low-pressure flow path176is open on the first rotor flat surface172a. The radial length from the rotation axis156to the first rotor low-pressure flow path176on the first rotor flat surface172ais substantially equal to the radial length from the rotation axis156to the cylinder port158on the first stator flat surface170a. The first rotor low-pressure flow path176and the cylinder port158are located on substantially the same circumference around the rotation axis156. The first rotor low-pressure flow path176is located on a side opposite to the rotation axis156relative to the first rotor high-pressure flow path174. The first rotor low-pressure flow path176penetrates from the first rotor flat surface172ato the upper surface of the first valve rotor152ain the direction of the rotation axis156(refer toFIG. 4A).

The auxiliary low-pressure port165and the second rotor high-pressure flow path178are open on the second rotor flat surface172b. The auxiliary low-pressure port165, the second rotor high-pressure flow path178, and the drive chamber port160on the second stator flat surface170bare located on substantially the same circumference around the rotation axis156. The auxiliary low-pressure port165penetrates up to the upper surface of the second valve rotor152bin the direction of the rotation axis156. The second rotor high-pressure flow path178is bent inside the second valve rotor152b, and extends to the first rotor high-pressure flow path174(refer toFIG. 4A). The second rotor high-pressure flow path178is always connected to the first rotor high-pressure flow path174on the upper surface of the first valve rotor152a.

As illustrated inFIG. 4A, the main low-pressure port164penetrates the second valve rotor152bfrom the upper surface of the second valve rotor152b. Then, the main low-pressure port164includes an arc-shaped low-pressure groove180. In the arc-shaped low-pressure groove180, the first valve rotor152ais formed on a surface (that is, a surface of the second valve rotor152bfacing the upper surface of the first valve rotor152a) coming into contact with the second valve rotor152b(illustrated by a broken line). As also illustrated inFIG. 7, the arc-shaped low-pressure groove180and the first rotor low-pressure flow path176are located on substantially the same circumference around the rotation axis156. The first rotor low-pressure flow path176is always connected to the main low-pressure port164through the arc-shaped low-pressure groove180. In this way, the main low-pressure port164is formed in the second valve rotor152bso as to avoid the second rotor high-pressure flow path178.

FIG. 3Billustrates a relative position between the first valve rotor152aand the second valve rotor152bwhen the reversible motor56is rotated forward. The first valve rotor152ahas a first relative angle68with respect to the second valve rotor152b. While the first valve rotor152aholds the first relative angle68with the second valve rotor152baround the rotation axis156, the valve rotor152is rotated in a forward rotation direction72. In this manner, the rotary valve54is operated at the cooling valve timing.FIG. 3Bsimultaneously illustrates a center line74of the first rotor flat surface172apassing through the first rotor high-pressure flow path174and the first rotor low-pressure flow path176, and a center line76of the second rotor flat surface172bpassing through the auxiliary low-pressure port165and the second rotor high-pressure flow path178. The first relative angle68can be represented as an angle formed between the center line74of the first rotor flat surface172aand the center line76of the second rotor flat surface172b. Here, the first relative angle68is 45°.

FIG. 3Cillustrates a relative position between the first valve rotor152aand the second valve rotor152bwhen the reversible motor56is rotated rearward. The first valve rotor152ahas a second relative angle70with respect to the second valve rotor152b. While the first valve rotor152aholds the second relative angle70around the second valve rotor152band the rotation axis156, the valve rotor152is rotated in a rearward rotation direction80. In this manner, the rotary valve54is operated at the heating valve timing. The second relative angle70can be represented as an angle formed between the center line74of the first rotor flat surface172aand the center line76of the second rotor flat surface172b. Here, the second relative angle70is 90°. Therefore, the second relative angle70is shifted from the first relative angle68as much as 45°.

In this way, angular relative positional relationships between the first valve rotor152aand the second valve rotor152bare different from each other at the cooling valve timing and the heating valve timing. As will be understood from the comparison betweenFIGS. 3B and 3C, the first valve rotor152ais rotated 45° with respect to the second valve rotor152b.

As another example,FIG. 3Dillustrates a case where a relative angle between the first valve rotor152aand the second valve rotor152bis 0°.FIG. 3Eillustrates a case where the relative angle between the first valve rotor152aand the second valve rotor152bis 180°.

As illustrated inFIG. 3B, the first valve rotor152ahas a first cylindrical surface173a, and the second valve rotor152bhas a second cylindrical surface173b. The first cylindrical surface173ais a side surface of the first valve rotor152a, and the second cylindrical surface173bis an inner side surface of the second valve rotor152b. The first cylindrical surface173aand the second cylindrical surface173bare in contact with each other.

The rotary valve54is configured so that the inlet/outlet of the working gas flow path does not exist on either the first cylindrical surface173aor the second cylindrical surface173b. The whole working gas flow path of the first valve rotor152apenetrates from the first rotor flat surface172aserving as the rotational sliding surface to the upper surface which is a surface opposite thereto. The working gas flow path of the second valve rotor152bpenetrates from the second rotor flat surface172bserving as the rotational sliding surface to the upper surface or the contact surface of the first valve rotor152a.

In this case, the working gas flow path does not exist. Accordingly, it is not necessary to provide a seal member such as an O-ring between the first cylindrical surface173aand the second cylindrical surface173b. If the seal member is provided, the relative rotation of the second valve rotor152bwith respect to the first valve rotor152amay cause the seal member to be undesirably deformed. As a result, durability of the seal member may be affected.

In a certain embodiment, the rotary valve54may be configured so that the inlet/outlet of the working gas flow path exists on the first cylindrical surface173aand the second cylindrical surface173b. In this case, the seal member such as the O-ring may be provided between the first cylindrical surface173aand the second cylindrical surface173b.

In order to improve slidability in the relative rotation, it is desirable that the first valve rotor152aand the second valve rotor152bare formed of mutually different materials. Similarly, in order to achieve satisfactory slidability, it is desirable that the valve stator150and the valve rotor152are formed of mutually different materials. For example, in a case where one of two sliding components is formed of a metal material (for example, aluminum or iron) and the other is formed of a resin material (for example, an engineering plastic material or a fluorine resin material), the satisfactory slidability can be achieved.

Therefore, the first stator flat surface170amay be formed of the resin material, the second stator flat surface170bmay be formed of the metal material, the first rotor flat surface172amay be formed of the metal material, and the second rotor flat surface172bmay be formed of the resin material. Alternatively, the first stator flat surface170amay be formed of the metal material, the second stator flat surface170bmay be formed of the resin material, and the first rotor flat surface172amay be formed of the resin material, the second rotor flat surface172bmay be formed of the metal material. Here, only a portion of the valve rotor including the rotor flat surface or only a portion of the valve stator including the stator flat surface may be formed of a desired material. Alternatively, the whole valve stator or the whole valve rotor may be formed of the desired material.

In the rotary valve54, the main intake on-off valve V1is configured to include the high-pressure port162, the first rotor high-pressure flow path174, and the cylinder port158. When the first rotor high-pressure flow path174overlaps the cylinder port158during the rotation of the valve rotor152, the high-pressure port162is connected to the cylinder port158. The high-pressure working gas can flow into the cylinder port158from the high-pressure port162through the first rotor high-pressure flow path174. This is an open state of the main intake on-off valve V1(refer toFIGS. 4A and 5A). On the other hand, when the first rotor high-pressure flow path174does not overlap the cylinder port158, the high-pressure port162is disconnected from the cylinder port158. Accordingly, the working gas cannot flow into the cylinder port158from the high-pressure port162. This is a closed state of the main intake on-off valve V1(refer toFIGS. 4B and 5B).

The main exhaust on-off valve V2is configured to include the cylinder port158, the first rotor low-pressure flow path176, and the main low-pressure port164. When the first rotor low-pressure flow path176overlaps the cylinder port158during the rotation of the valve rotor152, the cylinder port158is connected to the main low-pressure port164. The low-pressure working gas can flow to the main low-pressure port164from the cylinder port158through the first rotor low-pressure flow path176. This is an open state of the main exhaust on-off valve V2(refer toFIGS. 4B and 5B). On the other hand, when the first rotor low-pressure flow path176does not overlap the cylinder port158, the main low-pressure port164is disconnected from the cylinder port158. Accordingly, the working gas cannot flow to the main low-pressure port164from the cylinder port158. This is a closed state of the main exhaust on-off valve V2(refer toFIGS. 4A and 5A).

The auxiliary intake on-off valve V3is configured to include the high-pressure port162, the first rotor high-pressure flow path174, the second rotor high-pressure flow path178, and the drive chamber port160. When the second rotor high-pressure flow path178overlaps the drive chamber port160during the rotation of the valve rotor152, the high-pressure port162is connected to the drive chamber port160. The high-pressure working gas can flow into the drive chamber port160from the high-pressure port162through the first rotor high-pressure flow path174and the second rotor high-pressure flow path178. This is an open state of the auxiliary intake on-off valve V3(refer toFIGS. 4A and 5A). On the other hand, when the second rotor high-pressure flow path178does not overlap the drive chamber port160, the high-pressure port162is disconnected from the drive chamber port160. Accordingly, the working gas cannot flow to the drive chamber port160from the high-pressure port162. This is a closed state of the auxiliary intake on-off valve V3(FIGS. 4B and 5B).

The auxiliary on-off valve V4is configured to include the drive chamber port160and the auxiliary low-pressure port165. When the auxiliary low-pressure port165overlaps the drive chamber port160during the rotation of the valve rotor152, the drive chamber port160is connected to the auxiliary low-pressure port165. Accordingly, the low-pressure working gas can flow to the auxiliary low-pressure port165from the drive chamber port160. This is an open state of the auxiliary exhaust on-off valve V4(refer toFIGS. 4B and 5B). On the other hand, when the auxiliary low-pressure port165does not overlap the drive chamber port160, the drive chamber port160is disconnected from the auxiliary low-pressure port165. Accordingly, the working gas cannot flow to the auxiliary low-pressure port165from the drive chamber port160. This is a closed state of the auxiliary exhaust on-off valve V4(refer toFIGS. 4A and 5A).

An exemplary configuration of the valve rotor coupling mechanism168will be described with reference toFIGS. 6 and 7.FIG. 6is a schematic perspective exploded view illustrating the valve rotor152according to the embodiment, andFIG. 7is a schematic perspective view illustrating the second valve rotor152baccording to the embodiment.FIG. 7illustrates a recess portion formed in the second valve rotor152bfor receiving the first valve rotor152a, together with the second rotor flat surface172b.

The valve rotor coupling mechanism168includes a coupling pin guide groove182, a coupling pin184, and a coupling pin fixing hole186. The coupling pin guide groove182is formed on an upper surface188of the first valve rotor152a. The coupling pin guide groove182is formed in an arc shape around the rotation axis156. The coupling pin guide groove182has a first groove end portion182aand a second groove end portion182b. The first groove end portion182aand the second groove end portion182bcorrespond to both ends of the coupling pin guide groove182in the circumferential direction. A size of a central angle of the coupling pin guide groove182corresponds to a phase difference between the first relative angle and the second relative angle. Therefore, the size of the central angle of the coupling pin guide groove182is an angle selected from a range of 30° to 60°, for example. In the present embodiment, the size of the central angle of the coupling pin guide groove182is approximately 45°.

The coupling pin184is fixedly supported by the second valve rotor152b. The coupling pin184extends parallel to the rotation axis156. One end of the coupling pin184is inserted into the coupling pin guide groove182, and the other end is attached to the coupling pin fixing hole186. The coupling pin184may be fitted and fixed to the coupling pin fixing hole186, or may be inserted into the coupling pin fixing hole186with slight play. The coupling pin fixing hole186is formed in the second valve rotor152b. The coupling pin fixing hole186is formed on a contact surface190where the second valve rotor152bcomes into contact with the upper surface188of the first valve rotor152a. The coupling pin guide groove182and the coupling pin fixing hole186are located on the same circumference around the rotation axis156. The coupling pin fixing hole186is also located on the circumference the same as that of the arc-shaped low-pressure groove180.

The coupling pin184engages with the first groove end portion182aof the coupling pin guide groove182so that the first valve rotor152aholds the first relative angle with the second valve rotor152bwhen the reversible motor56illustrated inFIGS. 1 and 2is rotated forward. In addition, the coupling pin184engages with the second groove end portion182bof the coupling pin guide groove182so that the first valve rotor152aholds the second relative angle with the second valve rotor152bwhen the reversible motor56is rotated rearward. The coupling pin guide groove182is formed so as to guide the coupling pin184from the first groove end portion182ato the second groove end portion182bwhen the reversible motor56is switched from the forward rotation to the rearward rotation, and so as to guide the coupling pin184from the second groove end portion182bto the first groove end portion182awhen the reversible motor56is switched from the rearward rotation to the forward rotation.

Therefore, when the reversible motor56is switched from the forward rotation to the rearward rotation, the second valve rotor152bis angularly displaced with respect to the first valve rotor152a, and the relative angles between both the valve rotors are switched from the first relative angle to the second relative angle. In addition, when the reversible motor56is switched from the rearward rotation to the forward rotation, the second valve rotor152bis angularly displaced with respect to the first valve rotor152a, and the relative angles between both the valve rotors are switched from the second relative angle to the first relative angle.

In this case, a relatively simple structure such as a combination of the coupling pin guide groove182and the coupling pin184enables the relative angles between the first valve rotor152aand the second valve rotor152bto be switched.

The coupling pin guide groove182may be formed in the second valve rotor152b, and the coupling pin184may be fixedly supported by the first valve rotor152a. The coupling pin fixing hole186may be formed in the first valve rotor152a.

FIG. 7illustrates the arc-shaped low-pressure groove180formed on the contact surface190of the second valve rotor152b. A central angle of the arc-shaped low-pressure groove180may be larger than or equal to a phase difference between the first relative angle and the second relative angle. In the present embodiment, the central angle of the arc-shaped low-pressure groove180is approximately 270°, and is larger than approximately 45° of the phase difference between the first relative angle and the second relative angle. In this case, even if the relative angles of both the valve rotors are switched, the main low-pressure port164can be always connected to the first rotor low-pressure flow path176through the arc-shaped low-pressure groove180.

An operation of the GM cryocooler10according to the embodiment will be described with reference toFIGS. 8A to 9C.FIGS. 8A to 8Care views for describing the cooling valve timing of the GM cryocooler10, andFIGS. 9A to 9Care views for describing the heating valve timing of the GM cryocooler10.

FIG. 8Aillustrates a timing chart of the GM cryocooler10, and this illustrates an example of the cooling valve timing.FIG. 8Aillustrates a valve open/closed state of the GM cryocooler10in time series per one cycle. One cycle is associated with 360°. When the valve rotor152illustrated inFIG. 3Bis rotated in the forward rotation direction72with respect to the valve stator150, the rotary valve54can realize the cooling valve timing illustrated inFIG. 8A. As illustrated, the rotary valve54is open and closed in the order of the auxiliary intake on-off valve V3, the main intake on-off valve V1, the auxiliary exhaust on-off valve V4, and the main exhaust on-off valve V2. A phase difference (for example, 45°) between a phase for opening the auxiliary intake on-off valve V3and a phase for opening the main intake on-off valve V1is determined, based on the first relative angle between the first valve rotor152aand the second valve rotor152b.

FIG. 8Billustrates an operation waveform per one cycle of the GM cryocooler10which is obtained when the GM cryocooler10is operated in accordance with the cooling valve timing illustrated inFIG. 8A. A solid line represents a pressure waveform of the displacer cylinder26, a dashed line represents a pressure waveform of the drive chamber46, and a dotted line represents a position waveform of the displacer20.

The pressure waveform of the displacer cylinder26is 45° behind the pressure waveform of the drive chamber46. As a result, a differential pressure is generated between the working gas chamber (that is, the expansion chamber34and the room temperature chamber36) of the displacer cylinder26and the drive chamber46, thereby enabling the displacer20to be moved. As illustrated, when the displacer20is located at the bottom dead center LP1, an inspiratory process is performed in the displacer cylinder26. When the displacer20is located at the top dead center UP1, an exhaust process is performed in the displacer cylinder26. That is, when the expansion chamber34has the maximum volume, the high pressure (PH) working gas is expanded and decompressed. Therefore, similarly to a normal refrigeration cycle, the GM cryocooler10can generate cold.

FIG. 8Cis a PV diagram obtained when the GM cryocooler10is operated in accordance with the cooling valve timing illustrated inFIG. 8A. The PV diagram illustrates a figure closed clockwise. Accordingly, the working gas absorbs heat from the outside. Based on this diagram, it can be understood that the GM cryocooler10generates the cold when the GM cryocooler10is operated in accordance with the cooling valve timing.

FIG. 9Aillustrates a timing chart of the GM cryocooler10, and this illustrates an example of the heating valve timing. When the valve rotor152illustrated inFIG. 3Cis rotated in the rearward rotation direction80with respect to the valve stator150, the rotary valve54can realize the heating valve timing illustrated inFIG. 9A. The rotary valve54is rotated rearward by the reversible motor56. Accordingly, as illustrated, the rotary valve54is open and closed in the order of the main exhaust on-off valve V2, the auxiliary exhaust on-off valve V4, the main intake on-off valve V1, and the auxiliary intake on-off valve V3. The heating valve timing inFIG. 9Ais a valve opening and closing sequence reverse to the cooling valve timing inFIG. 8B. A phase difference between a phase for opening auxiliary intake on-off valve V3and a phase for opening the main intake on-off valve V1is determined, based on the second relative angle between the first valve rotor152aand the second valve rotor152b.

FIG. 9Billustrates an operation waveform per one cycle of the GM cryocooler10which is obtained when the GM cryocooler10is operated in accordance with the heating valve timing illustrated inFIG. 9A. Similarly toFIG. 8B, a solid line represents a pressure waveform of the displacer cylinder26, a dashed line represents a pressure waveform of the drive chamber46, and a dotted line represents a position waveform of the displacer20.

The pressure waveform of the displacer cylinder26is 90° ahead of the pressure waveform of the drive chamber46. As a result, a differential pressure is generated between the working gas chamber (that is, the expansion chamber34and the room temperature chamber36) of the displacer cylinder26and the drive chamber46, thereby enabling the displacer20to be moved. As illustrated, when the displacer20is located at or in the vicinity of the bottom dead center LP1, an exhaust process is performed in the displacer cylinder26. When the displacer20is located at or in the vicinity of the top dead center UP1, an inspiratory process is performed in the displacer cylinder26. That is, when the expansion chamber34has the maximum volume, the high pressure (PH) working gas is introduced and decompressed. Therefore, the GM cryocooler10can generate the heat.

FIG. 9Cis a PV diagram obtained when the GM cryocooler10is operated in accordance with the heating valve timing illustrated inFIG. 9A. The PV diagram illustrates a figure closed counterclockwise. Accordingly, the working gas generates the heat to the outside. Based on this diagram, it can be understood that the GM cryocooler10generates the heat when the GM cryocooler10is operated in accordance with the heating valve timing.

In this way, according to the GM cryocooler10of the embodiment, when the rotary valve54is rotated forward by the reversible motor56, the refrigeration cycle is formed in the GM cryocooler10, and the GM cryocooler10is cooled. Then, when the rotation direction of the reversible motor56is switched from the forward rotation to the rearward rotation, the relative angle between the first valve rotor152aand the second valve rotor152bis switched from the first relative angle to the second relative angle. When the rotary valve54is rotated rearward by the reversible motor56, the heating cycle is formed in the GM cryocooler10, and the GM cryocooler10can be heated, based on the compression heat of the working gas.

According to the GM cryocooler10of the embodiment, similarly to the rearward rotation heating of the motor-driven type GM cryocooler, the gas-driven type GM cryocooler can be first heated, based on the compression heat of the working gas. The compression heat of the working gas is used. Accordingly, compared to natural heating, the GM cryocooler10can be efficiently heated within a short time. In addition, the GM cryocooler10can be heated to a temperature higher than the room temperature without adding a heating element such as an electric heater.

Hitherto, the present invention has been described, based on the embodiment. The present invention is not limited to the above-described embodiment, and various design changes can be made. It will be understood by those skilled in the art that various modification examples can be made, and the modification examples also fall within the scope of the present invention.

In the above-described embodiment, the inner cylinder portions (the first valve stator150aand the first valve rotor152a) of the rotary valve54configure the main pressure switching valve60, and the outer cylinder portions (the second valve stator150band the second valve rotor152b) of the rotary valve54configure the auxiliary pressure switching valve62. However, the inner cylinder portions of the rotary valve54can configure the auxiliary pressure switching valve62, and the outer cylinder portions of the rotary valve54can configure the main pressure switching valve60. In addition, the internal flow path configuration of the rotary valve54is not limited to the above-described configuration, and various specific configurations can be adopted.

In the above-described embodiment, the valve rotor152is divided into two components, and the relative positions between the two components can be switched. However, the present invention is not limited thereto.FIG. 10is a schematic sectional view illustrating the valve stator according to another embodiment. In a certain embodiment, the valve stator150may be divided into two components, and the relative positions between the two components may be switchable. In this case, the valve rotor152may be a single component in which the first valve rotor152aand the second valve rotor152bare integrated with each other. The rotary valve54may include a valve stator coupling mechanism92which couples the first valve stator150aand the second valve stator150bwith each other so that the first valve stator150aholds the first relative angle with the second valve stator150bwhen the reversible motor56is rotated forward, and so that the first valve stator150aholds the second relative angle with the second valve stator150bwhen the reversible motor56is rotated rearward (refer toFIG. 10).

The valve stator coupling mechanism92may be configured to couple the first valve stator150awith the second valve stator150bby using a fastener such as a bolt, and may be configured to be switchable between the first relative angle and the second relative angle. For example, the valve stator coupling mechanism92may be manually detachable from the valve stator150, and may be attachable to the valve stator150again after the relative angles are switched therebetween.

In the above-described embodiment, the valve rotor152is divided into two components, and the relative angles around the rotation axis156can be switched as the relative positions between the two components. However, the present invention is not limited thereto. If applicable, the rotary valve54may be configured to switch between the cooling valve timing and the heating valve timing by relatively moving in the rotation axis direction of the first valve rotor152aand the second valve rotor152b. In addition, the rotary valve54may be configured to switch between the cooling valve timing and the heating valve timing by relatively moving in the rotation axis direction of the first valve stator150aand the second valve stator150b.

FIGS. 11A and 11Bare schematic sectional views illustrating the rotary valve54according to still another embodiment. For the convenience of description, the internal flow path of the rotary valve54is omitted inFIGS. 11A and 11B.

In the illustrated rotary valve54, in a case where a first resin valve member is surrounded by a first metal valve member, the first resin valve member protrudes in the axial direction with respect to the first metal valve member. In this manner, the rotational sliding surface of the first resin valve member is located at an axial height which is different from that of the rotational sliding surface of the first metal valve member. In addition, in a case where a second metal valve member is surrounded by a second resin valve member, the second resin valve member protrudes in the axial direction with respect to the second metal valve member. In this manner, the rotational sliding surface of the second resin valve member is located at an axial height which is different from that of the rotational sliding surface of the second metal valve member.

The second metal valve member is located to rotationally slide with the first resin valve member. The diameter (for example, the outer diameter) of the first resin valve member is smaller than the diameter (for example, the outer diameter) of the second metal valve member. In addition, the first metal valve member is located to rotationally slide with the second resin valve member. The diameter (for example, the outer diameter) of the second resin valve member is smaller than the diameter (for example, the outer diameter) of the second metal valve member.

As a result, a portion including the rotational sliding surface in the first resin valve member enters a recess portion surrounded by the second resin valve member. The first resin valve member has a gap with the second resin valve member in the radial direction. The first metal valve member is located away from the second metal valve member in the axial direction.

The first resin valve member and/or the second resin valve member may be worn due to long-term use of the rotary valve54. However, the first metal valve member is located away from the second metal valve member in the axial direction. Accordingly, even if the resin valve member is slightly worn, the first metal valve member and the second metal can be avoided from coming into contact with each other.

For example, in the rotary valve54illustrated inFIG. 11A, the first valve stator150ais formed of a metal material, and the second valve stator150bis formed of a resin material. The first valve rotor152ais formed of a resin material, and the second valve rotor152bis formed of a metal material. The second valve stator150bprotrudes in the axial direction with respect to the first valve stator150a. Therefore, the axial height of the second stator flat surface170bis higher than that of the first stator flat surface170a(in the drawing, the second stator flat surface170bis located above the first stator flat surface170a). The first valve rotor152aprotrudes in the axial direction with respect to the second valve rotor152b. Therefore, the axial height of the first rotor flat surface172ais higher than that of the second rotor flat surface172b(in the drawing, the first rotor flat surface172ais located below the second rotor flat surface172b).

The diameter of the first valve rotor152ais smaller than the diameter of the first valve stator150a. Therefore, the inner diameter of the second valve rotor152bis smaller than the inner diameter of the second valve stator150b. In addition, the outer diameter of the second valve stator150bis smaller than the outer diameter of the second valve rotor152b.

Therefore, an end portion including the first rotor flat surface172ain the first valve rotor152aenters a recess portion surrounded by the second valve stator150b. The first valve rotor152ahas a gap94with the second valve stator150bin the radial direction. The second valve rotor152bis located away from the first valve stator150ain the axial direction. The axial height of the gap94corresponds to the axial distance from the first valve stator150ato the second valve rotor152b.

In the rotary valve54illustrated inFIG. 11B, the second valve stator150bis formed of the metal material, and the first valve stator150ais formed of the resin material. The second valve rotor152bis formed of the resin material, and the first valve rotor152ais formed of the metal material. The first valve stator150aprotrudes in the axial direction with respect to the second valve stator150b. Therefore, the axial height of the first stator flat surface170ais higher than that of the second stator flat surface170b. The second valve rotor152bprotrudes in the axial direction with respect to the first valve rotor152a. Therefore, the axial height of the second rotor flat surface172bis higher than that of the first rotor flat surface172a.

The diameter of the first valve stator150ais smaller than the diameter of the first valve rotor152a. Therefore, the inner diameter of the second valve stator150bis smaller than the inner diameter of the second valve rotor152b. In addition, the outer diameter of the second valve rotor152bis smaller than the outer diameter of the second valve stator150b.

Therefore, an end portion including the first stator flat surface170ain the first valve stator150aenters a recess portion surrounded by the second valve rotor152b. The first valve stator150ahas a gap94with the second valve rotor152bin the radial direction. The first valve rotor152ais located away from the second valve stator150bin the axial direction. The axial height of the gap94corresponds to the axial distance from the second valve stator150bto the first valve rotor152a.

In a certain embodiment, the rotary valve may include a first valve element serving as one of the valve rotor rotatable around the rotary valve rotation axis and the valve stator, and a second valve element serving as the other of the valve rotor and the valve stator. The first valve element may include a first component configured to alternately connect the displacer cylinder to the compressor discharge port and the compressor suction port by being rotated relative to the second valve element, and a second component configured to alternately connect the drive chamber to the compressor discharge port and the compressor suction port by being rotated relative to the second valve element. The rotary valve may include a coupling mechanism that couples the first component and the second component with each other so that the first component holds a first relative angle with the second component around the rotary valve rotation axis when the reversible motor is rotated forward, and so that the first component holds a second relative angle around the second component and the rotary valve rotation axis when the reversible motor is rotated rearward. The first relative angle may be designed to cool the cryocooler, and the second relative angle may be designed to heat the cryocooler. The coupling mechanism may be configured to switch between the first relative angle and the second relative angle in response to a reverse in rotation direction of the reversible motor.

The first valve element may be the valve rotor, the second valve element may be the valve stator, and the first component and the second component may be respectively the first valve rotor and the second valve rotor. Alternatively, the first valve element may be the valve stator, the second valve element may be the valve rotor, and the first component and the second component may be respectively the first valve stator and the second valve stator.

The above-described embodiments have been described with reference to the gas-driven type GM cryocooler as an example. However, the present invention is not limited thereto. The rotary valve unit according to the embodiments may be applicable to the other cryocoolers in which the displacer is driven using the gas pressure. In addition, without being limited to a single stage cryocooler, the rotary valve unit according to the embodiments is applicable to a multi-stage cryocooler having two or more stages.

The present invention can be used in a field of the cryocooler and the rotary valve unit for the cryocooler.