Stirling engine

Abstract

To reduce a piston load by making (average) pressures of two spaces sandwiching a power piston during movement of the power piston come close to each other.SOLUTION: A Stirling engine is constituted by providing a seal structure in a power piston. The Stirling engine includes: a body that accommodates the power piston and has an operation space and a buffer space on a surface side and a rear face side of the power piston; and two communication passages for communicating the operation space and the buffer space so as to enable flowing of work gas. The respective two communication passages have check valves in which work gas flowing directions are reverse to each other.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a Stirling engine. [Background technology]

[0002] For example, Patent Document 1 discloses a free-piston type Stirling engine that does not have a crank mechanism. In the above Stirling engine, the following configuration is adopted to make the average pressure on both sides of the power piston approximately equal. That is, a pressure balance control valve, in which an orifice and a one-way valve are arranged in series, is provided in the middle of the gas flow path connecting the working space and the buffer space that sandwich the power piston. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2011-163688 A Summary of the Invention [Problem to be solved by the invention]

[0004] The Stirling engine of Patent Document 1 is based on a configuration without a seal structure in the power piston, and assumes a case where the average pressure in the working space is lower than the average pressure in the buffer space. In this configuration, since there is no seal structure, energy loss occurs due to gas leakage from the working space. In order to reduce energy loss and increase the thermal efficiency of the engine, a gas seal in the working space is necessary.

[0005] However, if a seal structure is provided for the power piston, the seal is so good that the pressure in the working space cannot be released even if it becomes high. As a result, the working space pressure is always greater than the buffer space pressure, and the load required to move the power piston (piston load) increases.

[0006] The present invention has been made to solve the above problems, and its purpose is to provide a Stirling engine that can bring the (average) pressures in the two spaces on either side of the power piston closer to each other when the power piston moves, thereby reducing the piston load. [Means for solving the problem]

[0007] A Stirling engine according to one aspect of the present invention is a Stirling engine having a seal structure on a power piston, and includes a main body that houses the power piston and has a working space and a buffer space on the front and back sides of the power piston, and two communication passages that connect the working space and the buffer space so that a working gas can flow between them, and the two communication passages each have a check valve that allows the working gas to flow in opposite directions. Effect of the Invention

[0008] According to the above-mentioned configuration, the (average) pressures in the two spaces sandwiching the power piston when the power piston moves can be made closer to each other, thereby reducing the piston load of the power piston. [Brief description of the drawings]

[0009] [Figure 1] 1 is an explanatory diagram showing a schematic configuration of a Stirling engine according to an embodiment of the present invention; [Diagram 2] FIG. 2 is an explanatory diagram showing changes in pressure and volume in an expansion space within the main body of the Stirling engine. [Diagram 3] FIG. 4 is an explanatory diagram showing changes in pressure and volume in a compression space in the main body. [Figure 4] FIG. 2 is an explanatory diagram showing a schematic detailed configuration of an engine section of the Stirling engine. [Figure 5A] 6 is a graph showing a change in pressure in the working space in Comparative Example 1. [Figure 5B]4 is a graph showing changes in pressure in the working space and the buffer space in the first embodiment. [Figure 6] 4 is an explanatory diagram showing the relationship between the volume of a compression space and a pressure difference when a compression piston moves; FIG. [Figure 7A] 13 is a graph showing changes in pressure in the working space and in the buffer space in Comparative Example 2. [Figure 7B] 10 is a graph showing changes in pressure in the working space and the buffer space in Example 2. [Figure 8] 10A and 10B are explanatory diagrams showing other examples of the arrangement of orifices arranged in the communication passage. [Figure 9] FIG. 2 is an explanatory diagram illustrating a schematic connection relationship between a thermosiphon and the main body. [Figure 10] FIG. 4 is an explanatory diagram showing the positional relationship between the buffer tank and the main body together with the stand. [Figure 11] FIG. 11 is an explanatory diagram showing another example of the stand. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings.

[0011] <1. Basic structure of Stirling engine> 1 is an explanatory diagram showing a basic configuration of a Stirling engine 100 according to an embodiment of the present invention. The Stirling engine 100 includes a thermosiphon 1 and an engine unit 20.

[0012] (1-1. Thermosyphon) Thermosiphon 1 contains a heat medium that receives heat from a heat source HS. The heat source HS can be, for example, factory waste heat. The heat source HS may also be solar heat or geothermal heat. The heat source HS moves through a flow path FP. The flow path FP is, for example, composed of a heat exhaust pipe.

[0013] Thermosiphon 1 has a first pipe 1a, a second pipe 1b, and a third pipe 1c as pipes through which a heat medium flows. First pipe 1a is located inside flow path FP. Second pipe 1b and third pipe 1c are located outside flow path FP. Thus, a portion of thermosiphon 1 is disposed in flow path FP.

[0014] The second pipe 1b is located downstream of the first pipe 1a in the direction in which the heat medium flows. The first pipe 1a and the second pipe 1b are connected via a first connection part 11. The first connection part 11 is provided on a wall surface of the flow path FP. The end of the second pipe 1b opposite to the end connected to the first pipe 1a is connected to an upper part of the main body 30 of the engine part 20.

[0015] The third pipe 1c is located upstream of the first pipe 1a in the direction in which the heat medium flows. The first pipe 1a and the third pipe 1c are connected via a second connection part 12. The second connection part 12 is provided on the wall surface of the flow path FP. The end of the third pipe 1c opposite to the end connected to the first pipe 1a is connected to the lower part of the main body 30.

[0016] The heat transfer medium contained in the thermosiphon 1 is, for example, water. Water is liquid at room temperature, but at high temperatures it boils and turns into gaseous steam. Steam also condenses into water (condensed water). Therefore, steam and condensed water are also included in the heat transfer medium. The heat transfer medium, in either a liquid or gaseous state, flows through the piping of the thermosiphon 1 and circulates between the heat source HS (flow path FP) and the engine section 20.

[0017] More specifically, when the heat medium (here, water) in the first pipe 1a is heated by the heat source HS (for example, exhaust heat), the water evaporates and becomes steam. The steam passes from the first pipe 1a through the second pipe 1b and is introduced from above into the main body 30 of the engine section 20. The steam releases condensation heat to a heater 40 (described later) in the main body 30, thereby heating the heater 40. After releasing the condensation heat, the steam condenses and becomes water (condensed water). The water is discharged from the bottom of the main body 30 and passes through the third pipe 1c, and is returned to the first pipe 1a. In other words, the condensed water enters the flow path FP of the heat source HS. The above process is repeated thereafter. The heat medium contained in the thermosiphon 1 may be a liquid other than water (for example, alcohol).

[0018] In this way, the thermosiphon 1 receives heat from the heat source HS and exchanges heat with the heater 40. Such a thermosiphon 1 is also called a primary heat exchanger.

[0019] (1-2. Engine Configuration) The engine section 20 has a main body 30. The main body 30 is a cylinder that contains a working gas G. The working gas G is, for example, helium. Since helium has a large specific heat capacity, engine output per volume can be increased by increasing the density by applying high pressure to the helium. The working gas G may be a gas other than helium (for example, air, hydrogen, etc.). Within the main body 30, a heater 40, a cooler 50, and a regenerator 60 are arranged linearly in the horizontal direction.

[0020] The heater 40 is formed of, for example, a shell-and-tube type heat exchanger. The heater 40 is also referred to as a secondary heat exchanger in comparison with the thermosiphon 1 which is a primary heat exchanger. The heater 40 has a heater tube 41 through which the working gas G flows. The heater tube 41 is, for example, a metal tube. The metal constituting the heater tube 41 may be appropriately selected from metals with excellent thermal conductivity, such as aluminum, copper alloy, and stainless steel. In this embodiment, a plurality of heater tubes 41 are provided, but it is sufficient that at least one heater tube 41 is provided.

[0021] Steam introduced from thermosiphon 1 into main body 30 flows around each heater tube 41. This heats each heater tube 41, and the working gas G flowing inside each heater tube 41 is heated. In other words, heater 40 imparts heat transferred by the heat medium of thermosiphon 1 to working gas G.

[0022] One end of the heater 40 communicates with the expansion space ES, and the other end communicates with one end of the regenerator 60. That is, the heater 40 is located between the expansion space ES and the regenerator 60 within the main body 30. The expansion space ES is a space in which the working gas G expands when it is heated by the heater 40.

[0023] The cooler 50 is also configured with a shell-and-tube type heat exchanger similar to the heater 40. That is, the cooler 50 has a cooling pipe 51 through which the working gas G flows. The cooling pipe 51 is a metal pipe similar to the heater pipe 41. In this embodiment, a plurality of cooling pipes 51 are provided, but it is sufficient that at least one cooling pipe is provided.

[0024] When a refrigerant is supplied to the cooler 50 from the cooling equipment 70 installed outside the main body 30 via the refrigerant piping 71, the refrigerant flows around each cooling tube 51. This cools each cooling tube 51, and the working gas G flowing through each cooling tube 51 is cooled. In other words, the cooler 50 cools the working gas G with the refrigerant. The above refrigerant is, for example, water, but a refrigerant other than water may also be used. The refrigerant flows through the refrigerant piping 71 and circulates between the cooler 50 and the cooling equipment 70.

[0025] One end of the cooler 50 communicates with the compression space CS, and the other end of the cooler 50 communicates with the other end of the regenerator 60. That is, the cooler 50 is located between the regenerator 60 and the compression space CS within the main body 30. The compression space CS is a space where the working gas G is compressed by a compression piston CP described later.

[0026] The regenerator 60 is disposed between the heater 40 and the cooler 50. The regenerator 60 is formed, for example, of a mesh-shaped flow path. This allows the working gas G in the main body 30 to circulate between the expansion space ES side and the compression space CS side via the regenerator 60. In other words, the regenerator 60 allows the working gas G to circulate between the expansion space ES and the compression space CS. Note that the regenerator 60 is not limited to a mesh-shaped flow path. For example, the regenerator 60 can also be formed of a heat storage material such as a laminated wire mesh, a thin plate aligned with the flow, or a porous body.

[0027] An expansion piston EP serving as a power piston PP is disposed in the main body 30 on the opposite side of the expansion space ES to the heater 40. Also, a compression piston CP serving as a power piston PP is disposed in the main body 30 on the opposite side of the compression space CS to the cooler 50. That is, in the main body 30, the expansion piston EP is disposed via the heater 40 and the expansion space ES of the working gas G, and the compression piston CP is disposed via the cooler 50 and the compression space CS of the working gas G. Thus, a two-piston type Stirling engine 100 having two pistons (expansion piston EP, compression piston CP) serving as a power piston PP is also called an α-type Stirling engine.

[0028] Piston rings PR are fitted around the outer periphery of the expansion piston EP and the compression piston CP. The piston rings PR act as a gas seal. In other words, the piston rings PR prevent leakage of the working gas G from the gap between the expansion piston EP and the main body 30 and the gap between the compression piston CP and the main body 30 (gas leakage).

[0029] An expansion-side piston rod 81 of the expansion piston EP is connected to an expansion-side crosshead piston 82. The expansion-side crosshead piston 82 is connected to an expansion-side crankshaft 84 via an expansion-side connecting rod 83. The expansion-side piston rod 81 is provided penetrating one end face 30a of the main body 30. Therefore, the expansion-side crosshead piston 82, the expansion-side connecting rod 83, and the expansion-side crankshaft 84 are located outside the main body 30.

[0030] The expansion-side crosshead piston 82, the expansion-side connecting rod 83, and the expansion-side crankshaft 84 constitute an expansion-piston-side crank mechanism 85. The expansion piston EP is connected to the expansion-piston-side crank mechanism 85 via the expansion-side piston rod 81. On one end surface 30a of the main body 30, an expansion-side gas seal portion 31a is provided around a through hole through which the expansion-side piston rod 81 passes.

[0031] A compression-side piston rod 86 of the compression piston CP is connected to a compression-side crosshead piston 87. The compression-side crosshead piston 87 is connected to a compression-side crankshaft 89 via a compression-side connecting rod 88. The compression-side piston rod 86 is provided penetrating the other end face 30b of the main body 30. Therefore, the compression-side crosshead piston 87, the compression-side connecting rod 88, and the compression-side crankshaft 89 are located outside the main body 30.

[0032] The compression side crosshead piston 87, the compression side connecting rod 88, and the compression side crankshaft 89 constitute a compression piston side crank mechanism 90. The compression piston CP is connected to the compression piston side crank mechanism 90 via a compression side piston rod 86. On the other end surface 30b of the main body 30, a compression side gas seal portion 31b is provided around a through hole through which the compression side piston rod 86 passes.

[0033] The expansion piston side crank mechanism 85 and the compression piston side crank mechanism 90 are connected to each other so as to be capable of transmitting power through a power transmission unit 91. More specifically, the expansion side crankshaft 84 of the expansion piston side crank mechanism 85 is connected to the output shaft SH through a first belt 92 so as to be capable of transmitting power. Furthermore, the compression side crankshaft 89 of the compression piston side crank mechanism 90 is connected to the output shaft SH through a second belt 93 so as to be capable of transmitting power. In other words, the first belt 92, the output shaft SH, and the second belt 93 constitute the above-mentioned power transmission unit 91. Note that the power transmission unit 91 may be configured to have a chain, gears, etc., other than or in addition to the belt.

[0034] The output shaft SH is, for example, a rotating shaft of a work machine M. The work machine M is composed of, for example, a generator and a motor. For example, the work machine M operates as a motor only at start-up, and operates as a generator after independent operation.

[0035] (1-3. Engine operation) In the above configuration, when steam flowing through the first pipe 1a and the second pipe 1b of the thermosiphon 1 is introduced into the main body 30 of the engine section 20, the heat of condensation of the steam is imparted to the heater 40, heating the heater 40. The heating of the heater 40 heats the working gas G in the heater tube 41. As a result, the working gas G expands, increasing the pressure in the expansion space ES and pressing against the expansion piston EP. Here, the pressure in the expansion space ES is defined as P E (Pa), and the volume of the expansion space ES is V E (m 3 ), the work load in the expansion process is W E (J) is W E =∫P E dV E It is expressed as:

[0036] As the expansion piston EP is pressed and moved, the expansion-side piston rod 81 and the expansion-side crosshead piston 82 rotate the expansion-side crankshaft 84 in the positive direction via the expansion-side connecting rod 83. The rotation of the expansion-side crankshaft 84 rotates the first belt 92, causing the output shaft SH to rotate in the positive direction. When the output shaft SH rotates, the second belt 93 rotates, causing the compression-side crankshaft 89 to rotate in the positive direction.

[0037] By the rotation of the compression side crankshaft 89, the compression side connecting rod 88 presses the compression side crosshead piston 87 and the compression side piston rod 86, and pushes the compression piston CP into the main body 30. As a result, the compression space CS is compressed, and the working gas G in the compression space CS flows into the cooler 50, and the working gas G is cooled by the cooler 50. Here, the pressure in the compression space CS is expressed as P C (Pa), and the volume of the compression space CS is V C (m 3 ), the work load in the compression process is W C (J) is W C =-∫P C dV C It is expressed as:

[0038] Therefore, when the amount of work required to rotate the output shaft SH (for example, the amount of work required to generate electricity) is W (J), the amount of work W is the amount of work W during the expansion process. E and the work load in the compression process W C and a predetermined mechanical efficiency η of the engine unit 20, the following equation is used: W = (W E +W C ) η=(∫P E dV E -∫P C dV C )·η

[0039] The expansion and compression steps are repeated by the reciprocating movements of the expansion piston EP and the compression piston CP. At this time, the pressure P E and volume V E In the compression space CS, the pressure PC and volume V C This changes as shown in FIG.

[0040] (1-4. Timing) As described above, the power imparted to the expansion piston side crank mechanism 85 by the movement of the expansion piston EP shown in FIG. 1 is transmitted to the compression piston side crank mechanism 90 via the first belt 92, the output shaft SH, and the second belt 93.

[0041] Here, the expansion piston EP and the compression piston CP reciprocate within the main body 30 with a predetermined phase difference. The phase difference corresponds to the difference between the crank angle of the expansion piston-side crank mechanism 85 and the crank angle of the compression piston-side crank mechanism 90. Therefore, for example, when the rotation angle (crank angle) of the expansion-side crankshaft 84 from a reference position is θ (°), the rotation angle (crank angle) of the compression-side crankshaft 89 from a reference position is expressed as (θ-β), where β (°) is a phase lag. The phase lag β is, for example, 90°, but is not limited to 90°.

[0042] The expansion piston side crank mechanism 85 and the compression piston side crank mechanism 90 are pre-timed to realize the above-mentioned phase difference. Such timing can be achieved, for example, by connecting the expansion side crankshaft 84 to the output shaft SH via a first belt 92 at a predetermined rotational position, and connecting the compression side crankshaft 89 to the output shaft SH via a second belt 93 at a predetermined rotational position.

[0043] Specifically, the expansion side crankshaft 84 and the first belt 92 are provided with marks for alignment. The compression side crankshaft 89 and the second belt 93 are provided with marks for alignment. Therefore, by aligning the marks of the expansion side crankshaft 84 and the first belt 92 and connecting them, and aligning the marks of the compression side crankshaft 89 and the second belt 93 and connecting them, the expansion side crankshaft 84 can be connected to the output shaft SH via the first belt 92 at a predetermined rotational position, and the compression side crankshaft 89 can be connected to the output shaft SH via the second belt 93 at a predetermined rotational position. The first belt 92 and the second belt 93 used at this time are preferably toothed belts, i.e., timing belts. In this manner, timing is performed. That is, the expansion piston side crank mechanism 85 and the compression piston side crank mechanism 90 are connected to each other via the power transmission unit 91 so as to be capable of timing.

[0044] In this embodiment, the expansion piston side crank mechanism 85 and the compression piston side crank mechanism 90 are connected via a power transmission unit 91 so as to be capable of transmitting power and adjusting timing, but it is sufficient that they are connected so as to enable at least one of power transmission and timing.

[0045] <2. Configuration for reducing piston load> Fig. 4 is an explanatory diagram showing a schematic diagram of the detailed configuration of the engine section 20 in the Stirling engine 100 of this embodiment. For convenience, the piston ring PR and the power transmission section 91 shown in Fig. 1 are omitted in Fig. 4, and the expansion side and the compression side are shown inverted from Fig. 1. Also, members located in the power transmission path between the power piston PP and the power transmission section 91 are shown with hatching.

[0046] In this embodiment, as described above, the Stirling engine 100 (particularly the engine section 20) has a compression piston CP and an expansion piston EP as the power piston PP. Since a piston ring PR (see FIG. 1) is provided on the outer periphery of the expansion piston EP and the compression piston CP, it can be said that each power piston PP is provided with a seal structure.

[0047] The main body 30, which houses the two power pistons PP, has an operating space AS and a buffer space BS. The operating space AS and the buffer space BS are spaces on the front and back sides, respectively, of the power pistons PP.

[0048] Here, the surface side refers to the heater 40 or cooler 50 side of the power piston PP within the main body 30. Therefore, since the compression space CS is located on the cooler 50 side of the compression piston CP, which is the power piston PP, it becomes the space on the surface side of the power piston PP and constitutes the working space AS. Also, since the expansion space ES is located on the heater 40 side of the expansion piston EP, which is the power piston PP, it becomes the space on the surface side of the power piston PP and constitutes the working space AS.

[0049] On the other hand, the back side refers to the opposite side of the power piston PP from the front side within the main body 30. Here, the space located on the opposite side of the cooler 50 from the compression piston CP and the space located on the opposite side of the heater 40 from the expansion piston EP are the spaces on the back side of the power piston PP, and each of them constitutes a buffer space BS.

[0050] The two buffer spaces BS on the rear side of the power piston PP in the main body 30 are connected to a buffer tank BT. The buffer tank BT contains the same gas (e.g., helium) as the working gas G in the main body 30.

[0051] In this embodiment, the working space AS (compression space CS) on the front surface side of the compression piston CP and the buffer space BS on the back surface side of the compression piston CP are communicated by two communication passages 32. The two communication passages 32 communicate the working space AS and the buffer space BS so that the working gas G can flow therethrough.

[0052] A check valve 33 and an orifice 34 are disposed in each of the two communication passages 32. The check valve 33 includes a first check valve 33A and a second check valve 33B. The orifice 34 includes a first orifice 34A and a second orifice 34B. Each communication passage 32 will be described in more detail below.

[0053] Of the two communication passages 32, one communication passage 32 is referred to as a first communication passage 32A, and the other communication passage 32 is referred to as a second communication passage 32B. A first check valve 33A and a first orifice 34A are arranged in series in the first communication passage 32A. The first check valve 33A is a one-way valve that allows the working gas G to flow from the buffer space BS to the working space AS (compression space CS) in the first communication passage 32A, but prevents the working gas G from flowing from the working space AS (compression space CS) to the buffer space BS.

[0054] The first orifice 34A is a throttle that regulates the flow rate of the working gas G flowing through the first communication passage 32A. In the first communication passage 32A, the first orifice 34A is disposed downstream of the first check valve 33A in the flow direction of the working gas G, that is, on the side of the working space AS (compression space CS) that becomes high pressure.

[0055] In the second communication passage 32B, a second check valve 33B and a second orifice 34B are arranged in series. The second check valve 33B is a one-way valve that allows the working gas G to flow from the working space AS (compression space CS) to the buffer space BS in the second communication passage 32B, while blocking the flow of the working gas G from the buffer space BS to the working space AS (compression space CS). Therefore, it can be said that the two communication passages 32 each have a check valve 33 that allows the working gas G to flow in opposite directions.

[0056] The second orifice 34B is a throttle that regulates the flow rate of the working gas G flowing through the second communication passage 32B. In the second communication passage 32B, the second orifice 34B is disposed upstream of the second check valve 33B in the flow direction of the working gas G, i.e., on the side of the working space AS (compression space CS) that becomes high pressure.

[0057] 5A is a graph showing the change in pressure P1 in the working space AS (e.g., compression space CS) when the engine section 20 is driven in a case where the buffer tank BT and the two communication passages 32 are not provided (Comparative Example 1). Note that, since the pressure is constant (the same) at any position between the expansion piston EP and the compression piston CP in the main body 30, in FIG. 5A, the horizontal axis represents the crank angle (θ) of the expansion piston-side crank mechanism 85, and the change in pressure P1 is shown as the change in pressure relative to the change in the phase of the expansion piston EP (the same applies to the following drawings).

[0058] If the buffer tank BT and the two communicating passages 32 are not provided, the pressure P2 on the back side of the compression piston CP is approximately atmospheric pressure (P2 ≒ 0.1 MPa), and therefore, when the engine section 20 is driven, a pressure difference ΔPa is generated between P1 and P2 as indicated by the arrows in FIG. 5A.

[0059] 5B is a graph showing the change in pressure P1 in the working space AS (e.g., compression space CS) and the change in pressure P2 in the buffer space BS on the back side of the compression piston CP when the engine section 20 is driven in the case where a buffer tank BT and two communication passages 32 are provided as in this embodiment (Example 1 as opposed to Comparative Example 1). Note that the two communication passages 32 are provided with a check valve 33 and an orifice 34.

[0060] When the buffer tank BT and two communication passages 32 are provided, if the pressure of the compression space CS as the working space AS becomes relatively higher than the buffer space BS on the back side, the working gas G in the compression space CS flows through one communication passage 32 (the second communication passage 32B in FIG. 4) into the buffer space BS and toward the buffer tank BT. Conversely, if the pressure in the buffer space BS becomes relatively higher than the compression space CS, the working gas G in the buffer tank BT passes through the buffer space BS and flows through the other communication passage 32 (the first communication passage 32A), and the working gas G is introduced into the compression space CS.

[0061] As a result, when the engine unit 20 is driven, the pressures P1 and P2 change as shown in Fig. 5B, and the pressure difference ΔPb between them becomes smaller than ΔPa, and the difference between the average pressure in the compression space CS and the average pressure in the buffer space BS on the back side of the compression piston CP becomes smaller. In the examples of Figs. 5A and 5B, the maximum value of the pressure difference ΔPb is about 1 / 4 of the maximum value of the pressure difference ΔPa. Therefore, when the engine unit 20 is driven, the load (piston load) required to move the compression piston CP is reduced to about 1 / 4 of that in Comparative Example 1.

[0062] FIG. 6 is an explanatory diagram showing the relationship between the volume V of the compression space CS and the pressure difference ΔP (=P1-P2) when the compression piston CP moves. In FIG. 6, the above relationship in Comparative Example 1 is shown by a dashed line, and the above relationship in Example 1 is shown by a solid line. It can be seen from the figure that the trajectory (shape) of the cycle showing the above relationship does not change whether the pressure difference ΔP is large or small. Therefore, it can be said that in the case of Example 1, it is possible to perform approximately the same amount of work (∫P·dV) while reducing the piston load compared to Comparative Example 1.

[0063] 7A and 7B are graphs showing the change in pressure P1 in the working space AS (e.g., compression space CS) and pressure P2 in the buffer space BS on the back side of the compression piston CP when the engine section 20 is driven, in the case where the power piston PP is provided with a seal structure and a communication passage 32. However, FIG. 7A shows a case where the communication passage 32 is only the first communication passage 32A (Comparative Example 2), and FIG. 7B shows a case where the communication passage 32 is provided with two communication passages, the first communication passage 32A and the second communication passage 32B (Example 2 in contrast to Comparative Example 2). From FIG. 7A and FIG. 7B, it can be seen that when the power piston PP is provided with a seal structure, in the configuration of Comparative Example 2 in which the communication passage 32 is only the first communication passage 32A, the discrepancy between the pressures P1 and P2 cannot be eliminated, but in the configuration of the Example in which the two communication passages 32 are provided, the discrepancy is eliminated, and the difference in the average pressures of the pressures P1 and P2 is reduced. By reducing the difference in the average pressure, the piston load of the compression piston CP can be reduced. Note that Examples 1 and 2 have the same configuration as that shown in this embodiment (the same configuration).

[0064] As described above, in this embodiment, when a pressure difference occurs between the compression space CS and the buffer space BS, the working gas G flows in both directions through the two communication passages 32 (the working gas G flows in the opposite directions through the two communication passages 32), so that the (average) pressures in the two spaces (compression space CS, buffer space BS) sandwiching the compression piston CP when the compression piston CP moves can be made closer to each other. This makes it possible to reduce the piston load when the compression piston CP moves. As a result, it becomes possible to reduce the size of the compression piston CP, which is the power piston PP, and its drive mechanism (compression piston side crank mechanism 90). In addition, when the piston load is constant, the output of the engine unit 20 by driving the power piston PP can be increased.

[0065] In the above, the two communication passages 32 are provided on the compression side of the main body 30, but they may be provided on the expansion side. In other words, the two communication passages 32 may be configured to communicate the working space AS (expansion space ES) on the front side of the expansion piston EP with the buffer space BS on the back side of the expansion piston EP.

[0066] Therefore, the Stirling engine 100 of this embodiment is provided with two communication passages 32 that connect the working space AS on the front side of one of the two power pistons PP, i.e., the compression piston CP and the expansion piston EP, to the buffer space BS on the back side of the one of the power pistons PP so that the working gas G can flow through them, and the two communication passages 32 each have a check valve 33 that allows the working gas G to flow in opposite directions.

[0067] However, the working space AS (expansion space ES) on the surface side of the expansion piston EP is a space where thermal expansion of the working gas G occurs, and becomes hotter than the compression space CS. For this reason, if two communication passages 32 and a check valve 33 are provided on the expansion side of the main body 30, the two communication passages 32 and the check valve 33 will be affected by heat, and there is a concern that this will lead to a decrease in reliability due to damage, etc.

[0068] Therefore, from the viewpoint of improving reliability by eliminating the influence of heat on the two communication passages 32 and the check valve 33, it is desirable to provide the two communication passages on the compression side of the main body 30. In other words, it is desirable for the two communication passages 32 to communicate between the working space AS (compression space CS) on the front side of the compression piston CP and the buffer space BS on the back side of the compression piston CP.

[0069] 4, in this embodiment, the two communication passages 32 each have an orifice 34. Specifically, the first communication passage 32A has a first orifice 34A, and the second communication passage 32B has a second orifice 34B.

[0070] If the amount of working gas G moving between the working space AS and the buffer space BS becomes greater than necessary, the excess flowing working gas G is wasted in performing work by the power piston PP. By providing the orifices 34 in the two communication passages 32, the movement of the working gas G is regulated (restricted), and the excessive movement of the working gas G is suppressed. Therefore, an increase in the working gas G that is wasted in performing work is suppressed.

[0071] In this embodiment, in the first communication passage 32A, the first orifice 34A is disposed downstream of the first check valve 33A in the flow direction of the working gas G, but may be disposed upstream. In the second communication passage 32B, the second orifice 34B is disposed upstream of the second check valve 33B in the flow direction of the working gas G, but may be disposed downstream.

[0072] 8 is an explanatory diagram showing another example of the arrangement of the orifice 34. As shown in the figure, in the first communication passage 32A, the first orifice 34A may be arranged both upstream and downstream of the first check valve 33A in the flow direction of the working gas G. Although not shown, in the second communication passage 32B, the second orifice 34B may be arranged both upstream and downstream of the second check valve 33B in the flow direction of the working gas G.

[0073] That is, in each communication passage 32, the orifice 34 may be disposed at least on either the upstream side or the downstream side of the check valve 33 in the direction in which the working gas G flows.

[0074] However, if the working gas G in the working space AS leaks more than necessary to the outside (e.g., the buffer space BS) through the communication passage 32 or enters from the buffer space BS, the pressure fluctuation range in the working space AS narrows when the engine section 20 is driven. As a result, there is a concern that the efficiency of output extraction (thermal efficiency) of the engine section 20 due to heat exchange in the main body 30 will decrease. From the viewpoint of avoiding such a decrease in thermal efficiency, it is desirable to effectively suppress excessive leakage of the working gas G from the working space AS to the outside and excessive inflow of the working gas G from the outside into the working space AS. From this viewpoint, it is desirable that the orifice 34 in each of the two communication passages 32 is disposed on the working space AS side with respect to the check valve 33.

[0075] In addition, since the pressure in the working space AS changes significantly due to pulsation, it is effective to provide the orifice 34 on the side closer to the working space AS than the check valve 33 in order to efficiently absorb the effects of such pulsation.

[0076] Incidentally, the primary heat exchanger of a Stirling engine is usually exposed to a heat source of about 800°C or higher. For this reason, the primary heat exchanger also reaches a high temperature of nearly 800°C, raising concerns about damage, corrosion, and the like due to the heat. In the Stirling engine 100 of this embodiment, a thermosiphon 1 is used as the primary heat exchanger. The heat medium in the thermosiphon 1 is a liquid (usually water). Because liquids have high heat exchange properties and the heat of vaporization can be used, the temperature of the thermosiphon 1 is kept at about 300°C. Therefore, by using the thermosiphon 1 as the primary heat exchanger as in this embodiment, damage, corrosion, and the like due to the heat of the heat medium in the primary heat exchanger are reduced.

[0077] <3. Piping for draining condensed water> 9 is an explanatory diagram showing a schematic diagram of the connection relationship between the thermosiphon 1 and the main body 30 of the engine section 20. The heater 40 in the main body 30 has, in addition to the heater tube 41 (see FIG. 1) described above, a steam inlet 42 and a condensed water outlet 43. The second pipe 1b of the thermosiphon 1 is connected to the steam inlet 42. The steam inlet 42 is located above the condensed water outlet 43. The third pipe 1c of the thermosiphon 1 is connected to the condensed water outlet 43.

[0078] In the above configuration, steam as a heat medium supplied from thermosiphon 1 flows through second pipe 1b, and is then introduced from above into heater 40 via steam inlet 42. Inside heater 40, the steam releases condensation heat to heater tube 41, thereby heating heater tube 41.

[0079] On the other hand, when the steam releases condensation heat to the heater tube 41, the steam condenses to become condensed water. The condensed water generated inside the heater 40 moves downward by gravity, is discharged from each condensed water discharge port 43, and returns to the first pipe 1a via the third pipe 1c. Therefore, the third pipe 1c constitutes a condensed water introduction pipe that guides the condensed water discharged from the condensed water discharge port 43 to the first pipe 1a in the flow path FP of the heat source HS.

[0080] 9, in this embodiment, the second connection part 12, which is a connection part of the third piping 1c with the flow path FP of the heat source HS, is located below the condensed water discharge port 43. Note that, as long as the above-mentioned vertical positional relationship between the second connection part 12 and the condensed water discharge port 43 can be realized, the third piping 1c may have a horizontal part midway along the piping.

[0081] When the second connection part 12 and the condensed water discharge port 43 are in the above-mentioned positional relationship, the direction in which the condensed water flows from the condensed water discharge port 43 to the second connection part 12 in the third pipe 1c can be easily set to a direction from the upper side to the lower side, that is, a natural direction in which the condensed water flows without resisting the direction of gravity. This further improves the drainage of the condensed water from the heater 40.

[0082] <4. Positional relationship between the buffer tank and the main body> 10 is an explanatory diagram showing a schematic positional relationship between the buffer tank BT and the main body 30. The Stirling engine 100 of this embodiment may further include a stand PE. The stand PE supports the main body 30 from below. The stand PE includes, for example, a metal frame or a metal plate, and has the strength to support the main body 30.

[0083] Moreover, the pedestal PE is installed on the floor surface with the buffer tank BT housed therein. Therefore, the buffer tank BT is built into the pedestal PE. The buffer tank BT does not have to be supported by the pedestal PE. For example, the buffer tank BT may be installed on the floor surface, and the periphery of the buffer tank BT may simply be covered by the pedestal PE. Even in such a form, as long as the pedestal PE covers the buffer tank BT, the buffer tank BT is considered to be built into the pedestal PE.

[0084] In this manner, in a configuration in which the main body 30 is supported from below by the stand PE incorporating the buffer tank BT, the buffer tank BT and the main body 30 are positioned so as to overlap each other in the vertical direction via the stand PE. This makes it easy to efficiently arrange the buffer tank BT and the main body 30 in a limited installation space.

[0085] Fig. 11 is an explanatory diagram showing another example of the pedestal PE. As shown in Fig. 11, the pedestal PE itself that supports the main body 30 from below may be composed of a buffer tank BT. In this case, the buffer tank BT is composed of, for example, a metal container to store the working gas G, but may be composed of a resin container as long as the strength can be ensured.

[0086] In a configuration in which the buffer tank BT is used as the stand PE, there is no need to prepare a separate dedicated stand for supporting the main body 30, and therefore the configuration of the Stirling engine 100 is simplified. In addition, if the buffer tank BT is a metal container, it is easier to increase the rigidity of the stand compared to a configuration in which the main body 30 is supported using a stand constructed by assembling a frame. The buffer tank BT and the main body 30 are positioned so as to overlap each other in the vertical direction, which makes it easy to efficiently arrange the buffer tank BT and the main body 30 within a limited installation space, as in the case of the configuration of FIG. 10.

[0087] <5. Supplementary Information> In this embodiment, as shown in FIG. 1, the expansion piston EP and the heater 40 are arranged in a straight line in the movement direction of the expansion piston EP in the main body 30. In addition, the cooler 50 and the compression piston CP are arranged in a straight line in the movement direction of the compression piston CP in the main body 30. The movement direction of the expansion piston EP refers to the direction in which the expansion piston EP reciprocates in the main body 30 due to the expansion of the working gas G in the main body 30 and the rotation of the expansion side crankshaft 84. On the other hand, the movement direction of the compression piston CP refers to the direction in which the compression piston CP reciprocates in the main body 30 due to the compression of the working gas G in the main body 30 and the rotation of the compression side crankshaft 89. In this case, the entire expansion space ES between the expansion piston EP and the heater 40 can be made to contribute to the pressing of the expansion piston EP. In addition, the entire compression space CS between the cooler 50 and the compression piston CP can be made to contribute to the retraction of the compression piston CP. Therefore, there is no void space in the expansion space ES that does not contribute to the pressing of the expansion piston EP. Moreover, in the compression space CS, there is no void space that does not contribute to the drawing in of the compression piston CP. As a result, by heating the working gas G by the heater 40 and cooling the working gas G by the cooler 50, the Stirling engine 100 (particularly the engine section 20) can be driven efficiently, and the output of the engine section 20 (specifically the rotation speed of the output shaft SH) can be increased.

[0088] Therefore, from the viewpoint of reducing the dead space and increasing the output of the engine section 20, it is desirable that the expansion piston EP and the heater 40 are arranged in a straight line within the main body 30, and that the cooler 50 and the compression piston CP are also arranged in a straight line within the main body 30.

[0089] Furthermore, if there is a bend in the flow path inside the main body 30, there is a concern that pressure loss will occur at the bend, which will result in a decrease in the output of the engine section 20. From the perspective of avoiding a decrease in the output of the engine section 20 due to the pressure loss, it is desirable to arrange the expansion piston EP, heater 40, cooler 50, and compression piston CP in a straight line inside the main body 30, as shown in FIG.

[0090] In addition, when it is more important to realize a compact layout than to prevent a reduction in the output of the engine unit 20 due to pressure loss, the main body 30 may have a curved portion. For example, when the regenerator 60 is positioned extending in one direction within the main body 30, the expansion piston EP and the heater 40 may be arranged side by side in a direction intersecting the one direction within the main body 30, and the cooler 50 and the compression piston CP may also be arranged side by side in a direction intersecting the one direction within the main body 30. In other words, the expansion piston EP and the heater 40, and the cooler 50 and the compression piston CP may be arranged side by side in parallel.

[0091] In the description of this embodiment, a so-called α-type Stirling engine in which the power piston is divided into a compression piston and an expansion piston has been taken as an example. However, the configuration of this embodiment can also be applied to so-called β-type Stirling engines, γ-type Stirling engines, and double-acting Stirling engines in which the power piston is not divided into a compression piston and an expansion piston.

[0092] <6. Notes> The Stirling engine described in this embodiment can also be expressed as follows.

[0093] The Stirling engine in Appendix (1) is A Stirling engine having a seal structure on a power piston, a main body that houses the power piston and has an operating space and a buffer space on a front side and a back side of the power piston; two communication passages that communicate the working space and the buffer space so that a working gas can flow therebetween; The two communication passages each have a check valve through which the working gas flows in an opposite direction to each other.

[0094] The Stirling engine of appendix (2) is the Stirling engine of appendix (1), The power piston includes a compression piston and an expansion piston, and the two communication passages communicate the working space on the front surface side of the compression piston with the buffer space on the back surface side of the compression piston.

[0095] The Stirling engine of appendix (3) is the Stirling engine of appendix (1) or (2), The two communication passages each have an orifice.

[0096] The Stirling engine of appendix (4) is the Stirling engine of appendix (3), The orifice is disposed at least one of the upstream side and the downstream side in the flow direction of the working gas relative to the check valve.

[0097] The Stirling engine of appendix (5) is the Stirling engine of appendix (4), In each of the two communication passages, the orifice is disposed on the working space side with respect to the check valve.

[0098] A Stirling engine according to claim (6) is a Stirling engine according to any one of claims (1) to (5), a primary heat exchanger that receives heat from a heat source; the main body has a heater as a secondary heat exchanger that imparts the heat transferred from the heat source via the primary heat exchanger to the working gas, The primary heat exchanger is a thermosiphon that contains a heat medium that transfers the heat received from the heat source to the heater.

[0099] The Stirling engine of appendix (7) is the Stirling engine of appendix (6), The heater has a condensed water discharge port for discharging condensed water condensed from the steam serving as the heat transfer medium, The thermosiphon has a condensed water introduction pipe that introduces the condensed water discharged from the condensed water discharge port to a pipe in a flow path of the heat source, A connection portion of the condensed water introduction pipe with the flow path of the heat source is located below the condensed water discharge port.

[0100] A Stirling engine according to claim (8) is a Stirling engine according to any one of claims (1) to (7), The buffer tank may further include a base having a built-in buffer tank connected to the buffer space. The main body is supported from below by the stand.

[0101] A Stirling engine according to claim (9) is a Stirling engine according to any one of claims (1) to (7), Further comprising a stand supporting the main body from below, The frame is constituted by a buffer tank connected to the buffer space.

[0102] Although the embodiment of the present invention has been described above, the scope of the present invention is not limited to this, and the invention can be expanded or modified without departing from the spirit of the invention. [Industrial Applicability]

[0103] The present invention can be used in a Stirling engine that utilizes heat from a heat source such as exhaust heat and performs heat exchange to drive an engine section. [Explanation of symbols]

[0104] 1 Thermosyphon (primary heat exchanger) 1a First pipe 1b Second piping 1c Third pipe (condensate introduction pipe) 12 Second connection part 30 Main unit 32 Communication path 32A 1st communication passage 32B 2nd communication passage 33 Check valve 33A First check valve 33B Second check valve 34 Orifice 34A First Orifice 34B Second orifice 40 Heater (secondary heat exchanger) 41 Heater tube 43 Condensate drain 100 Stirling Engine AS working space BS Buffer Space BT Buffer Tank CP Compression Piston (Power Piston) CS Compressed Space EP Expansion Piston (Power Piston) ES Expansion Space FP flow path G Working gas HS heat source PE Mount PP Power Piston

Claims

1. A Stirling engine having a seal structure on a power piston, a main body that houses the power piston and has an operating space and a buffer space on a front side and a back side of the power piston; two communication passages that communicate the working space and the buffer space so that a working gas can flow therethrough; a Stirling engine, wherein the two communication passages each have a check valve through which the working gas flows in a direction opposite to each other.

2. 2. The Stirling engine according to claim 1, wherein the power piston includes a compression piston and an expansion piston, and the two communication passages communicate between the working space on a front surface side of the compression piston and the buffer space on a back surface side of the compression piston.

3. 2. The Stirling engine according to claim 1, wherein each of the two communication passages has an orifice.

4. 4. The Stirling engine according to claim 3, wherein the orifice is disposed at least one of an upstream side and a downstream side in a flow direction of the working gas relative to the check valve.

5. 5. The Stirling engine according to claim 4, wherein in each of the two communication passages, the orifice is disposed on a side of the working space with respect to the check valve.

6. a primary heat exchanger that receives heat from a heat source; the main body has a heater as a secondary heat exchanger that imparts the heat transferred from the heat source via the primary heat exchanger to the working gas, 2. The Stirling engine of claim 1, wherein the primary heat exchanger is a thermosiphon containing a heat transfer medium that transfers the heat received from the heat source to the heater.

7. The heater has a condensed water discharge port for discharging condensed water condensed from the steam serving as the heat transfer medium, The thermosiphon has a condensed water introduction pipe that introduces the condensed water discharged from the condensed water discharge port to a pipe in a flow path of the heat source, 7. The Stirling engine according to claim 6, wherein a connection portion of the condensed water inlet pipe with the flow path of the heat source is located below the condensed water outlet.

8. The buffer tank may further include a base having a built-in buffer tank connected to the buffer space.

8. The Stirling engine according to claim 1, wherein the main body is supported from below by the base.

9. Further comprising a stand supporting the main body from below, 8. The Stirling engine according to claim 1, wherein the frame is constituted by a buffer tank connected to the buffer space.

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