Reversible pneumatically driven expander

Abstract

A pneumatically driven cryogenic refrigerator, primarily operating on a Gifford-McMahon (GM) cycle, switches from cooling to heating via a switching valve between a rotary valve and a drive piston that causes the displacer to reciprocate. The rotary valve has ports at two radii: one circulates flow to the displacer, and the second circulates flow to the drive piston. Both ports circulate flow to the top of the drive piston; the "cooling" port optimizes the cooling cycle, while the "heating" port provides a good heating cycle. The switching valve that changes flow from one port to the other can be linearly or rotary actuated. The rotary valve does not reverse direction.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to U.S. Provisional Application No. 63 / 071,669, filed on August 28, 2020, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to a pneumatic drive mechanism for a reciprocating cryogenic expander, which incorporates a valve that switches between generating cooling or heating. Background Technology

[0004] Semiconductors are manufactured in vacuum chambers, which are typically evacuated using cryogenic pumps cooled by Gifford-McMahon (GM) coolers. A typical cryogenic pump has a warm panel cooled to approximately 80 K (Group I gases, including water vapor frozen on the warm panel); and a cold panel cooled to approximately 20 K (Group II gases, such as nitrogen and oxygen frozen on the cold panel). Charcoal on the back side of the cold panel adsorbs lighter gases, hydrogen, and helium. After several days or weeks of operation, the cryogenic pump must be reheated to remove frozen deposits. Combustible gaseous compositions can accumulate in the cryogenic pump, so heaters are avoided inside the pump; the cryogenic panels are typically heated indirectly by heaters located outside the pump housing. Most GM-type expanders currently in use generate cooling when running in one direction and continue to generate cooling at a reduced rate when running in the opposite direction. Cryogenic pumps with expanders that can alternately generate heating allow for faster heating, reduced costs, or both.

[0005] U.S. Patent 3,045,436 ("'436 Patent") by Wegeifford and HOMcMahon describes the GM cycle. The systems described herein primarily operate on the GM cycle, generally with an input power between 5 and 15 kW, but larger and smaller systems can fall within the scope of this invention. GM cycle and many Brayton cycle refrigerators use oil-lubricated compressors designed for air conditioning applications to supply gas (helium) to a reciprocating cryogenic expander. The GM expander circulates the gas to the cryogenic expansion chamber via inlet and outlet valves at room temperature and a regenerator, while the Brayton cycle expander has a counter-current heat exchanger for gas entry and exit at room temperature and cold inlet and outlet valves for circulating the gas to the cryogenic expansion chamber. The displacer in the expander is driven mechanically or pneumatically.

[0006] Gifford's U.S. Patent 3,205,668 ("Patent No. '668") describes a GM expander with a rod attached to the warm end of a displacer, which drives the displacer up and down by means of a rotary valve that causes the pressure circulation above the drive rod to be inconsistent with the pressure in the expansion chamber. With the valve rotating in the forward direction, the cycle might be assumed to begin with the displacer down (minimum cold displacement volume), at low pressure, and with high pressure above the rod. The pressure of the displacer is switched to high pressure, and then, after a short delay, the pressure of the drive rod is switched to low pressure. This causes the displacer to move upward, drawing high-pressure gas through a regenerator into the cold displacement volume. The high-pressure valve of the displacer is typically closed before the displacer reaches the top, and the gas expands partially upon reaching the top. The low-pressure valve of the displacer then opens, and the expanded gas cools. The pressure above the drive rod is then converted to high pressure and pushes the displacer down, forcing the cold, low-pressure gas through a cold-end heat exchanger and back through the regenerator, completing the cycle. When the pressure to the displacer switches, the pressure drop through the regenerator generates a force in the same direction as the force on the drive rod. When the pressure-displacement relationship, PV, is plotted on a graph, the order of the relationship is clockwise, and the area equals the cooling generated per cycle. When the rotary valve of patent '668 runs in reverse, the pressure to the drive rod switches before the pressure to the displacer, and the PV order remains clockwise, but the cooling effect is reduced due to the poor timing. At each stage of the cycle, when the pressure in the displacer and the pressure on the drive rod are equal, there is no net force to move the displacer.

[0007] Longsworth's U.S. Patent 8,448,461 ("'461 Patent") describes a Brayton cycle expander with a pneumatically driven rod on its displacer / piston, which can switch from a cooling cycle to a heating cycle using the mechanism of the present invention. The mechanism of the present invention can also be used to implement adjustment of the orifice controlling the speed of the up-and-down movement of the displacer / piston to optimize cooling during the cooling period. Most Brayton cycle expanders have a piston with a seal that separates the cold displacement volume from the warm displacement volume, while '461 Patent has a piston with a regenerator that balances the pressure in the cold and warm displacement volumes, hence the term "displacer."

[0008] In order for the expander to generate heat during reverse operation, the displacement device must be at or near the top when the pressure switches from low to high, and must remain there even when there is a downward force due to a drop in regenerator pressure, so that the cold displacement volume is heated by the compressed gas. This high-pressure hot gas is pushed out through the regenerator, and the pressure is converted to low pressure as the displacement device descends. This is accomplished by the Scotch Yoke driven displacement device with a rotary valve described in Asami's U.S. Patent 5,361,588 ("'588 Patent"). Regardless of the pressure, the Scotch Yoke drive keeps the displacement device in place as the motor rotates. As the valve rotates in the forward direction, the timing of gas inflow and outflow through the valve is optimized to produce refrigeration. The rotary valve disc has a surface that slides on the port of the valve seat and is rotated by a valve motor having a shaft with a pin that engages with a groove on the back side of the valve disc. The valve disc of the '588 Patent has an annular groove that changes the engagement angle between the pin and the groove. This causes the high-pressure port to open when the displacer is at the top and moving downwards, and the low-pressure port to open when the displacer is at the bottom and moving upwards. The PV sequence is counterclockwise. The valve timing is designed to achieve near-optimal heating cycles.

[0009] As the cooling capacity of expanders for cooling larger cryogenic pumps increases, Scotch Yoke drives become much larger and more expensive than pneumatic drives, thus creating a need for more efficient pneumatically driven expanders that can switch from cooling cycles to heating cycles.

[0010] U.S. Patent 7,191,600 ("Patent 600") by Gao and Longsworth describes a pulse tube expander with separate rotary valves for flow to a regenerator and flow to the pulse tube. When the valve motor rotates in the forward direction, a phase difference between the two valves generates cooling, while when rotated in the opposite direction, a phase difference between the two valves generates heating. Patent application WO2018 / 168305 ("Application 305") describes a valve configuration different from that of the pulse tube expander described in Patent 600, which generates heating during reverse operation.

[0011] The principle of patent '588 is that the mechanism (Scotch Yoke) that drives the displacement device up and down is independent of the valve (rotary valve), which switches the pressure applied to the displacement device. The phase of the pressure switching changes when the direction of rotation is changed. Patent application WO2018 / 168304 ("'304 application") describes a pneumatic drive for a displacement device having a piston attached to a drive rod, which is larger than the drive rod and connected to inlet and outlet valves different from those connected to the displacement device. The valve is a concentric disc sliding on a fixed valve seat. The inner disc switches the flow towards the displacement device, and the outer disc switches the flow towards the top of the drive piston. When the valve motor reverses, the outer disc rotates a fixed angle relative to the inner disc, providing the phase shift required to generate heating rather than cooling. Figures 8a-8d The '304 application' is shown respectively. Figure 1 8(a), 8(c), and 9(c). For example... Figure 8a As shown, the gas on the back side of the drive piston in volume 48 is trapped between the seals 50 and 32 on the drive piston and drive rod. It circulates around an average pressure, which depends on volume 48. To achieve... Figure 8c The rectangular PV diagram shown must have a volume 48 that is at least twice the size of the volume above the drive piston 46. Figure 8b The diagram illustrates that valves V3 and V4 control the flow to the drive rod, opening with a 180° difference and remaining open for the same duration, while valve V2 opens approximately 100° after V1 and remains open for the same duration. While this asymmetry may provide optimal timing for cooling, it results in less than ideal timing for heating, which is reflected in… Figure 8d The smaller PV diagram is shown below. An important aspect of the invention is that the timing of opening and closing the valve, which corresponds to the drive lever, can be different when switching from cooling to heating. Summary of the Invention

[0012] The object of this invention is to switch a pneumatically driven GM-type expander from cooling to heating without reversing the direction of the drive motor, while providing valve timing for both cooling and heating, thereby achieving good efficiency in both processes. High efficiency in cooling and heating is achieved by: using a drive piston to reciprocate the expander displacement unit, driving it to the end of its stroke regardless of the pressure within the displacement unit; using a rotary valve with a separate track for switching the pressure between the displacement unit and the drive piston; and having a separate switching valve that changes the flow from a port on the drive piston track that leads to cooling to a second port that leads to heating. The switching valve can be actuated by a linear or rotary drive. The drive piston can be single-acting or double-acting, and the actuator can simply switch the flow to the drive piston or be connected to a controller that can also change the pressure drop through the switching valve to control the speed of the displacement unit's up-and-down movement.

[0013] These advantages can be achieved using a cryogenic expander that receives gas at a first pressure from a compressor and returns the gas at a second pressure. The cryogenic expander includes a pneumatically driven, reciprocating displacement assembly and a valve assembly capable of providing cooling and heating modes to generate cooling and heating, respectively. The displacement assembly includes: a displacement unit in a displacement cylinder that reciprocates between a warm end and a cold end of the displacement cylinder; a drive rod attached to the warm end of the displacement unit and extending through a rod sleeve; and a drive piston having a top and a bottom, the bottom of which is attached to the top end of the drive rod, reciprocating within a drive piston cylinder. The diameter of the drive piston may be larger than the diameter of the drive rod. Gas flows between a warm displacement volume and a cold displacement volume through a regenerator. The valve assembly includes a valve seat and a valve disc that rotates on the valve seat. The valve seat has a port at a first radius connected to the displacement cylinder or a valve actuator, a port at a second radius connected to the drive piston cylinder, and a central port connected to the compressor at the second pressure. The valve disc has a groove that alternately connects gases at a first pressure and a second pressure to ports at first and second radii. The port at the second radius includes a cooling port and a heating port. The direction of rotation of the valve disc remains constant. The valve assembly also includes a switching valve between the port at the second radius and the top volume above the drive piston. The switching valve is configured to connect either the cooling port or the heating port to the top volume above the drive piston to provide a cooling mode or a heating mode. Attached Figure Description

[0014] The accompanying drawings illustrate one or more embodiments according to the concepts of this application by way of example only and not by way of limitation. In these drawings, similar reference numerals refer to the same or similar elements.

[0015] Figure 1 This is a schematic diagram of a cryogenic refrigeration system 100, which includes a pneumatically actuated GM cycle expander having a single-acting drive piston, a rotary valve, and a switching valve, supplying gas from a compressor through interconnected pipes.

[0016] Figure 2 This is a schematic diagram of a cryogenic refrigeration system 200, which includes a pneumatically actuated GM cycle expander having a double-acting drive piston, a rotary valve, and a switching valve, supplying gas from a compressor through interconnected pipes.

[0017] Figure 3 This is a schematic diagram of a cryogenic refrigeration system 300, which includes a pneumatically actuated Brayton cycle expander having a single-acting drive piston, a rotary valve, and a switching valve, supplying gas from a compressor through interconnected pipes.

[0018] Figure 4 A cross-sectional view of the rotary valve, switching valve, and drive piston of system 100 is shown.

[0019] Figure 5 A cross-sectional view of the rotary valve, switching valve, and drive piston of system 200 is shown.

[0020] Figure 6a The diagram shows a pattern of grooves superimposed on the valve disc on the valve seat when the displacer in system 100 is about to be discharged to a low pressure.

[0021] Figure 6b This illustrates the sequence in which the grooves on the valve disc of system 100 pass through the ports in the valve seat as the expander generates cooling.

[0022] Figure 6c The PV diagram of the cooling cycle is shown, with points on the cycle as follows: Figure 6b The location number is shown.

[0023] Figure 7a The diagram shows a pattern of grooves superimposed on the valve disc on the valve seat when the displacer in system 100 is about to be pressurized to high pressure.

[0024] Figure 7b This illustrates the sequence in which the grooves on the valve disc of system 100 pass through the ports on the valve seat as the expander generates heat and the valve disc of system 100 rotates.

[0025] Figure 7c The PV diagram of the heating cycle is shown, with points on the cycle as follows: Figure 7b The location number is shown.

[0026] Figures 8a-8d The '304 application' is shown respectively. Figure 1Figures 8(a), 8(c), and 9(c). Detailed Implementation

[0027] In this section, some embodiments of the invention will be described more fully with reference to the accompanying drawings, in which preferred embodiments of the invention are illustrated. However, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to make this disclosure thorough and complete and to convey the scope of the invention to those skilled in the art. Similar reference numerals refer to similar elements throughout, and apostrophes are used to denote similar elements in alternative embodiments. Identical or similar portions in the drawings are labeled with the same reference numerals and are generally not described repeatedly.

[0028] Cryogenic expanders typically operate with the cold end facing downwards; therefore, the terms "upper" and "lower," as well as "top" and "bottom," refer to this orientation. Identical components in the diagram use the same numbering, and subscripts are used to distinguish equivalent components with different configurations.

[0029] refer to Figure 1 The diagram shows a schematic of a cryogenic refrigeration system 100, illustrating in detail the relationship between the core features of the invention and other parts of the system. The core features are the valve and the drive piston. The other parts of the system are the displacer 20a in cylinder 30 and the compressor 15, which supplies gas at a first pressure (Ph) to the rotary valve 2 via line 16 and receives gas at a second pressure (Pl) from the rotary valve 2 via line 17. The rotary valve 2 has ports on a rotating disc, which pass through ports on a fixed seat. A port at a first radius 10a on the seat circulates gas to the warm end of the displacer cylinder 30 via line 9, and a port at a second radius 11a circulates gas to the top of the drive piston cylinder 6a via a switching valve 1 and line 18. Line 18a originates from a first port on the second radius 11a of the valve seat, designated as a cooling port, and line 18b originates from a second port on the second radius 11a of the valve seat, designated as a heating port. A schematic diagram of switch valve 1 shows it fixed in the cooling position and rotated 90° counterclockwise for heating. A schematic diagram of valve 2 shows gas at high pressure Ph in line 9 connected to cylinder 30 and gas at low pressure Pl in line 18 connected to cylinder 6a as displacement device 20a moves upward.

[0030] Displacer 20a reciprocates between a warm end and a cold end within cylinder 30, generating a warm displacement volume 25 and a cold displacement volume 26. Gas flows between volumes 25 and 26 through port 23 at the warm end, regenerator 22a, and port 24 at the cold end in displacement body 21a. Seal 27 prevents gas from bypassing regenerator 22a. Displacer 20a is driven up and down by drive rod 7, which connects at its bottom end to the top end of displacement 20a and at its top end to the bottom end of drive piston 5a. Drive piston 5a is driven by the pressure difference between the circulating gas pressure in volume 12a above drive piston 5a and the pressure in buffer volume 13a below drive piston 5a acting on the area outside drive rod 7. Since drive piston 5a is driven only by the pressure on one side of the piston changing from high pressure Ph to low pressure Pl, it is described as a single-acting piston. Seal 31 in drive piston 5a keeps the gas in volume 12a separate from the gas in volume 13a. The seal 28 in the sleeve 8 keeps the gas in volume 13a separate from the gas in volume 25.

[0031] Typical operating pressures are a supply pressure Ph of approximately 2.2 MPa and a return pressure Pl of 0.8 MPa, resulting in a pressure ratio of 2.8. Therefore, the buffer volume 13a must be at least three times larger than the displacement volume 12a to allow the drive piston 5a to complete its full stroke. However, a larger volume is needed to reduce pressure variations within volume 12a so that the pressure across the drive piston 5a remains nearly constant throughout its full stroke. This large volume of buffer volume 13a relative to volume 12a is schematically shown as a volume separate from the displacement volume below the drive piston 5a.

[0032] refer to Figure 2 The diagram shows a schematic of a cryogenic refrigeration system 200, which differs from system 100 in that it has a double-acting drive piston 5b. When the pressure at the top is high pressure Ph, the pressure at the bottom of the drive piston 5b is low pressure Pl, and when the pressure at the top is low pressure Pl, the pressure at the bottom of the drive piston 5b is high pressure Ph. In system 100, the line 18b from the heating port in rotary valve 2 is blocked at switching valve 1 during cooling, but in system 200, it is connected to the volume 13b below the drive piston 5b via switching valve 3 and line 19. The diameter of the double-acting drive piston 5b can be smaller than that of the single-acting drive piston 5a because the full pressure difference Ph-Pl acts on it, and the volumes 12b and 13b above and below the drive piston 5b can be as small as the volume displaced by the drive piston 5b.

[0033] Rotary valve 4 is similar to rotary valve 2 in that it has a port at a first radius 10b on the valve seat leading to line 9 and a port at a second radius 11b leading to lines 18a and 18b and to line 18. Switching valve 3 is configured such that when gas from cooling line 18a is connected to line 18, gas from heating line 18b in rotary valve 4 is connected to line 19, thereby switching the pressure above and below the drive piston 5b to opposite pressures as valve disc 4 rotates.

[0034] Switch valve 3 is fixed in the position shown for cooling and rotated 90 degrees counterclockwise for heating. The schematic diagram of valve 4 shows that as the displacementr 20a moves upward, the gas in line 9 connected to cylinder 30 is at high pressure Ph, the gas in line 18 connected to the top of cylinder 6b is at low pressure Pl, and the gas in line 19 connected to the bottom of cylinder 6b is at high pressure Ph. While the mechanism for switching a pneumatically driven cryogenic expander from cooling to heating is most suitable for cryogenic pumps cooled by GM cycle expanders, it can also be applied to pneumatically driven Brayton cycle expanders, such as… Figure 3 As shown.

[0035] refer to Figure 3 The diagram shows a schematic of a cryogenic refrigeration system 300, which includes a pneumatically actuated Brayton cycle expander with a single-acting drive piston. The Brayton cycle expander of system 300 has a main inlet valve and outlet valves 9a and 9b at the cold end of cylinder 30b. Gas flows from compressor 15 from high-pressure line 16 through counter-current heat exchanger 50 to inlet valve 9a, and returns from outlet valve 9b through heat exchanger 50 and low-pressure line 17. Displacer 21b has a regenerator 22b that circulates gas from cold-end volume 26 to warm-end volume 25 to maintain nearly equal pressure above and below displacementr 21b and allows the valve mechanism and drive piston mechanism of system 100 or system 200 to generate cooling or heating. The ports on rotary valves 2' at a first radius 10c are relatively small because they circulate only a small amount of gas to pneumatic actuators 29a and 29b, which open and close the cold inlet and outlet valves 9a and 9b. Pneumatic actuator 29a opens valve 9a when connected to high pressure Ph and closes it when connected to low pressure Pl. The same applies to actuator 29b and valve 9b.

[0036] refer to Figure 4The diagram shows a cross-sectional view of the switching valve 1, rotary valve 2, and drive piston 5a of system 100. The rotary disc 2a is rotated by a valve motor 40, a motor shaft 41, and a pin 42, which engages with a slot 44 in the top of the disc 2a. The valve disc shown in this invention has two cycles per revolution and therefore two symmetrical high-pressure and low-pressure slots. The valve seat has two symmetrical ports for flow to the displacer, but may only have one pair of ports for flow to the drive piston. The bottom of the valve disc 2a contacts the valve seat 2b and shows a slot 17a that connects the low-pressure return port 17 to a line 18a to drive the piston volume 12a via a spool 1b. This is the cooling mode. When the linear actuator 1a pulls the spool 1b to the right so that the line 18b connects to the drive piston volume 12a, system 100 switches to the heating mode. Lines 18a and 18b may have different flow resistances, so the speed at which the drive piston 12a moves up and down may differ in heating and cooling modes. Different flow resistances can be determined by the degree of opening of the switching valve or by fixing the port size. Controlling the degree of opening of the switching valve can be used to control the piston speed.

[0037] The switching valve 1 can be configured such that, when the expander is in cooling mode, only the cooling port 18a is in fluid communication with the top volume 12a above the drive piston 5a, and when the expander is in heating mode, only the heating port 18b is in fluid communication with the top volume 12a above the drive piston 5a. The linear activation actuator 1a can be configured to control the pressure drop through the switching valve 1 to control the speed at which the displacer 20a moves up and down.

[0038] refer to Figure 5 The diagram shows a cross-sectional view of the switching valve 3, rotary valve 4, and drive piston 5b of system 200. The bottom of valve disc 4a contacts valve seat 4b and shows grooves 16a and 17a. Groove 16a connects high-pressure supply port 16 to line 18b to drive piston volume 12b via spool 3b and line 18b. Groove 17a connects low-pressure return port 17 to line 18a to drive piston volume 13b via spool 3b and line 19. This is the heating mode. When rotary actuator 3a rotates spool 3b 90° so that line 18a connects to drive piston volume 12b and line 18b connects to piston volume 13b, system 200 switches to cooling mode.

[0039] Figure 6a and 7a The rotary valves of system 100-300 in two positions are shown as an example. Figure 6b For cooling, and Figure 7b For heating, the timing of the high-pressure and low-pressure channels in the valve disc passing through the ports on the valve seat is shown, which is equivalent to opening and closing the valve. Figure 6c and 7cThe opening and closing of the valve are shown on the PV diagram for cooling and heating. Figure 6a and 7a The grooves 16a and 17a in the surface of the valve disc 2a, viewed from the valve motor and rotating counterclockwise against the valve seat 2b, are shown. The port 9 at a first radius 46 in the valve seat 2b connects to the displacement cylinder 30 and opens as valve V1 when the high-pressure groove 16a passes through (see...). Figure 6b The valve 1 opens as low-pressure valve V2 when low-pressure tank 17a passes through it. Pipes 18a and 18b with a second radius 45 in valve seat 2b are connected to the top of the drive piston cylinder 6a, and open as valves V3a and V3b when high-pressure tank 16a passes through them, and as low-pressure valves V4a and V4b when low-pressure tank 17a passes through them. Switch valve 1 blocks flow from pipe 18b when the expander is cooling, and blocks flow from pipe 18a when the expander is heating.

[0040] Figure 6a , 6b Figures 6c and 6c show the cooling cycle starting from the end of the expansion phase, where the cold displacement volume 26 reaches its maximum, the displacementr 20a is at the top, and the pressure is greater than the low pressure Pl. Figure 6b and 6c The numbers 1-8 in the diagram indicate the valve timing and the corresponding PV cycle, which are summarized below.

[0041] 1: Valve V2 opens, causing the pressure in the displacer to drop to low pressure Pl.

[0042] 2: After the pressure drops to Pl, V3a opens, and the pressure difference across the drive piston pushes the displacer to the bottom.

[0043] 3: Before the displacement device reaches the bottom, V2 closes, causing the pressure to increase as cold gas moves to the warm end, while the displacement device moves to the bottom for the rest of its stroke.

[0044] 4: V1 opens, causing the pressure to increase to high pressure Ph.

[0045] 5: V3 is off.

[0046] 6: V4 opens, and the pressure difference across the drive piston pushes the displacer to the top.

[0047] 7: Before the displacement device reaches the top, V1 closes, causing the pressure to decrease as the warm gas moves to the cold end, while the displacement device moves to the top for the rest of its travel.

[0048] 8: V4 is off.

[0049] This cycle follows two principles: first, the pressure in the drive piston is switched after the pressure in the displacement device is switched; second, valves V1 and V2 are closed before the displacement device reaches the end of its stroke, both at the top and bottom of the stroke.

[0050] Figure 7a , 7b Figures 7c and 7c show a heating cycle starting from the low-pressure stage, where the displacement volume 26 is at its minimum, the displacementr 20a is at the bottom, and the pressure is greater than the low-pressure Pl. Figure 7b and 7c The numbers 1-8 in the diagram indicate the valve timing and the corresponding PV cycle, which are summarized below.

[0051] 1: Valve V2 opens, causing the pressure in the displacer to drop to P1. Note that valve V3b remains open, maintaining high-pressure gas on the drive piston 5a to suppress it.

[0052] 6: After the pressure drops to Pl, V4b opens, causing the pressure difference across the drive piston to pull the displacer to the top.

[0053] 3: Before the displacement device reaches the top, V2 closes, causing the pressure to increase as warm gas moves to the bottom, while the displacement device moves to the top for the rest of its stroke.

[0054] 4: V1 opens, therefore, the pressure increases to high pressure Ph. Note that V4b remains open, causing the drive piston to hold the displacer at the top.

[0055] 7: V1 is closed, and then the pressure drops as the displacement device moves to the bottom and the gas moves from the cold end to the warm end.

[0056] This cycle follows three principles. First, when valves V1 and V2 switch pressures, the pressure above the drive piston holds the displacer at the top or bottom. Second, the pressure above the drive piston switches after reaching high or low pressure. Third, valves V1 and V2 are closed before the displacer reaches the top or bottom. It is important to note that optimizing the cooling cycle by allowing V2 to open longer than V1 and V1 to open more than 90° after V2 does not negatively impact the heating cycle, as the heating line 18b can be located more than 90° away from the cooling line 18a.

[0057] The valve timing of system 300 can be the same as that of system 100. The description of the valves and valve timing of system 200 shows more symmetry because the pressure above and below the drive piston 5b must switch at the same time. Therefore, a trade-off is needed to balance good cooling circulation and good heating circulation.

[0058] The scope of the following claims is not limited to the specific components referenced. For example, the linearly actuated switching valve 1 shown could be replaced with a rotary-activated valve. The heating port on the second radius could be changed to be on the third radius. Within the scope of these claims, operational limitations that are not optimal for simplifying mechanical design are also included. The terminology and descriptions used herein are for illustrative purposes only and are not intended to be limiting. Those skilled in the art will recognize that many variations are possible within the spirit and scope of the invention and the embodiments described herein.

Claims

1. A cryogenic expander for receiving gas at a first pressure from a compressor and returning the gas at a second pressure, comprising: Displacement device assembly, pneumatically driven and reciprocating, the displacement device assembly comprising: The displacement device is located in the displacement device cylinder and reciprocates between the warm end and the cold end of the displacement device cylinder, generating a warm displacement volume and a cold displacement volume in the displacement device cylinder, and the gas flows between the warm displacement volume and the cold displacement volume through the regenerator. A drive rod, the drive rod being attached to the warm end of the displacement device and extending through a rod sleeve; and A drive piston having a top and a bottom, the bottom of the drive piston being attached to the top of a drive rod, reciprocating within a drive piston cylinder, the drive piston having a diameter larger than that of the drive rod, the drive piston separating a top volume above the drive piston from a bottom volume below the drive piston; and A valve assembly capable of providing a cooling mode and a heating mode to generate cooling and heating respectively, the valve assembly comprising: Valve seat; A valve disc, rotating on a valve seat, wherein the valve seat has a port at a first radius connected to the displacer cylinder or valve actuator, a port at a second radius connected to the drive piston cylinder, and a central port connected to the compressor under a second pressure; the valve disc has grooves that alternately connect gas at a first pressure and a second pressure to the ports at the first and second radii, and the port at the second radius includes a cooling port and a heating port; and wherein the rotation direction of the valve disc remains constant. A switching valve located between the port at the second radius and the top volume above the drive piston, wherein the switching valve is configured to connect the cooling port or the heating port to the top volume above the drive piston to provide a cooling mode or a heating mode.

2. The cryogenic expander according to claim 1, wherein the switching valve is configured to: connect the heating port to the bottom volume below the drive piston when the expander is in cooling mode; and connect the cooling port to the bottom volume below the drive piston when the expander is in heating mode.

3. The cryogenic expander according to claim 2, wherein the switching valve is configured to: connect the cooling port to the top volume above the drive piston when the expander is in cooling mode; and connect the heating port to the top volume above the drive piston when the expander is in heating mode.

4. The cryogenic expander according to any one of claims 2-3, wherein the switching valve includes a spool configured to rotatably switch the connection between the heating port and the cooling port and the bottom volume below the drive piston.

5. The cryogenic expander according to any one of claims 2-3, wherein the switching valve is configured such that: when the expander is in cooling mode, only the cooling port is in fluid communication with the top volume above the drive piston; and when the expander is in heating mode, only the heating port is in fluid communication with the top volume above the drive piston.

6. The cryogenic expander of claim 5, wherein the switching valve comprises a spool configured to linearly switch communication between the cooling port and the heating port and the top volume above the drive piston.

7. The cryogenic expander according to any one of claims 2-3, wherein the pipelines connecting the cooling port and the heating port to the top volume above the drive piston have different flow resistances.

8. The cryogenic expander according to any one of claims 2-3, wherein the switching valve comprises: A spool for connecting the cooling port or the heating port to the top volume above the drive piston; as well as An actuator for linearly or rotaryly actuating the spool.

9. The cryogenic expander of claim 8, wherein the linearly activated actuator is configured to control the pressure drop through the switching valve to control the speed at which the displacer moves upward and downward.

10. The cryogenic expander of claim 9, wherein the linearly activated actuator is configured to control the degree to which the switching valve opens to control the pressure drop.

11. The cryogenic expander according to any one of claims 2-3, wherein during cooling and heating, the displacer remains at the warm end or cold end of the displacer cylinder until the pressure reaches the first pressure or the second pressure, and then the displacer moves to the other end.

12. The cryogenic expander according to any one of claims 2-3, wherein the port at the first radius is connected to the warm displacement volume of the displacement cylinder.

13. The cryogenic expander according to any one of claims 2-3, wherein the displacer assembly further comprises a cold inlet valve and a cold outlet valve connected to the cold displacement volume of the displacer cylinder, and wherein: The port at the first radius is connected to the valve actuator; The valve actuator includes a first valve actuator, which, when connected to a first pressure of the compressor, is used to open the inlet valve; and The valve actuator includes a second valve actuator, which, when connected to the first pressure of the compressor, is used to open the outlet valve.

14. The cryogenic expander according to any one of claims 2-3, wherein the heating port is located at one of the ports closer to the first radius than the cooling port.

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