JP2009127519A - Piston engine and Stirling engine - Google Patents

Abstract

[PROBLEMS] To reduce the possibility of contact between a piston and a cylinder.
A piston 20 reciprocates in a cylinder 30. A gas bearing GB is formed between the piston 20 and the cylinder 30. The piston 20 is formed such that the outer diameter from the top surface 20Tt to the piston-side stepped portion Kp toward the top-surface opposite end portion 20Bt is smaller than the outer diameter from the piston-side stepped portion Kp to the top surface opposite-side end portion 20Bt. The reduced diameter part 21 is provided. The annular member 50 is fitted into the reduced diameter portion 21. The annular member 50 is made of a material having a smaller coefficient of thermal expansion than the material of the reduced diameter portion 21 of the piston 20.
[Selection] Figure 4-1

Description

  The present invention relates to a piston engine and a Stirling engine in which a piston reciprocates in a cylinder without using a piston ring or lubricating oil.

  In recent years, Stirling engines with excellent theoretical thermal efficiency have attracted attention in order to recover exhaust heat and factory exhaust heat of internal combustion engines mounted on vehicles such as passenger cars, buses, and trucks. Patent Document 1 discloses a Stirling engine in which a step portion is provided on the top surface side of the high temperature side piston by making the outer diameter on the top surface side of the high temperature side piston smaller than the outer diameter on the skirt side. .

Japanese Patent Laid-Open No. 2005-106012

  However, in the Stirling engine disclosed in Patent Document 1, the clearance between the piston and the cylinder at the stepped portion is abruptly narrowed, and the thermal expansion of the stepped portion may cause contact between the piston and the cylinder at the stepped portion. is there. The present invention has been made in view of the above, and has a configuration in which contact between the piston and the cylinder due to thermal expansion of the piston is avoided by enlarging the clearance between the piston and the cylinder on the top surface side of the piston. In the above, an object is to reduce the possibility that the piston and the cylinder come into contact with each other at the step portion where the clearance between the piston and the cylinder is enlarged.

  In order to achieve the above-described object, a piston engine according to the present invention is a piston engine including a piston that reciprocates in a cylinder, and is located at a predetermined position from the top surface of the piston toward the end opposite to the top surface of the piston. A reduced diameter portion formed so that the outer diameter of the portion up to the predetermined position is smaller than the outer diameter of the end opposite to the top surface of the piston, and an annular member fitted into the reduced diameter portion. It is characterized by. In this piston engine, since the thermal expansion in the radial direction of the piston is suppressed by the annular member, the clearance between the piston and the cylinder is increased in the configuration that avoids the contact between the piston and the cylinder due to the thermal expansion of the piston. The possibility that the piston and the cylinder come into contact with each other at the step portion can be reduced.

  As a preferred aspect of the present invention, in the piston engine, the annular member is preferably made of a material having a smaller coefficient of thermal expansion than a material constituting the piston in the reduced diameter portion.

  As a preferred aspect of the present invention, in the piston engine, it is desirable that the outer diameter of the annular member is the same as the outer diameter of the piston from the predetermined position to the end opposite to the top surface.

  As a preferred aspect of the present invention, in the piston engine, it is desirable that a gas bearing be interposed between the piston and the cylinder.

  In order to achieve the above-described object, a Stirling engine according to the present invention includes a heater that heats a working fluid, a regenerator that is connected to the heater and through which the working fluid passes, and is connected to the regenerator. A heat exchanger including a cooler for cooling the working fluid; a cylinder into which the working fluid that has passed through the heat exchanger flows in and out; a piston that reciprocates in the cylinder; A reduced diameter portion in which an outer diameter of a portion from the top surface to a predetermined position toward the end on the opposite side of the top surface of the piston is smaller than an outer diameter of the end on the opposite side of the top surface of the piston from the predetermined position. An annular member that is made of a material having a smaller coefficient of thermal expansion than the material constituting the piston in the reduced diameter portion, and is fitted into the reduced diameter portion, the cylinder, and the piston, Characterized in that it comprises a and a gas bearing intervening therebetween. In this Stirling engine, thermal expansion in the radial direction of the piston is suppressed by an annular member made of a material having a smaller thermal expansion coefficient than that of the material in the reduced diameter portion of the piston. In the configuration for avoiding the contact, it is possible to reduce the possibility that the piston and the cylinder come into contact with each other at the step portion where the clearance between the piston and the cylinder increases.

  As a preferred aspect of the present invention, in the Stirling engine, it is desirable that the outer diameter of the annular member is the same as the outer diameter of the piston from the predetermined position to the end opposite to the top surface.

  As a preferred aspect of the present invention, in the Stirling engine, the piston is preferably supported by an approximate linear mechanism.

  The present invention increases the clearance between the piston and the cylinder on the top surface side of the piston, thereby avoiding the contact between the piston and the cylinder due to the thermal expansion of the piston. The possibility that the piston and the cylinder come into contact with each other at the stepped portion of the expanding portion can be reduced.

  Due to the stepped portion provided in the piston or cylinder, the clearance between the piston and cylinder abruptly narrows, so the surface temperature of the side periphery of the piston suddenly increases from the opposite side of the piston toward the top surface. It was found to rise. Then, it is found that the surface temperature of the side peripheral portion of the piston suddenly rises, so that the thermal expansion in the radial direction of the piston becomes larger than that of other portions, which may cause the piston and the cylinder to come into contact with each other. It was done. The present invention has been completed with this point in mind.

  Hereinafter, the present invention will be described in detail with reference to the drawings. The present invention is not limited by the best mode for carrying out the invention (hereinafter referred to as an embodiment). In addition, constituent elements in the following embodiments include those that can be easily assumed by those skilled in the art, those that are substantially the same, and those in a so-called equivalent range.

  In the following, a Stirling engine is taken as an example of a piston engine, but the piston engine is not limited to this. Moreover, although the example which collect | recovers exhaust heat of the internal combustion engine mounted in a vehicle etc. using the Stirling engine which is a piston engine is demonstrated, the collection | recovery object of exhaust heat is not restricted to an internal combustion engine. For example, the present invention can also be applied to recovering waste heat from a factory, plant, or power generation facility.

  This embodiment is applied to a piston engine having a configuration in which the clearance between the piston and the cylinder is enlarged on the top surface side of the piston in order to avoid contact between the piston and the cylinder due to thermal expansion of the piston. In this embodiment, the outer diameter of the portion from the top surface of the piston to the predetermined position toward the end opposite to the top surface of the piston is larger than the outer diameter of the end portion on the opposite side of the piston from the predetermined position. It is characterized in that an annular member is fitted to a reduced diameter portion formed to be small.

  FIG. 1 is a cross-sectional view showing a configuration of a Stirling engine that is a piston engine according to the present embodiment. FIG. 2 is an explanatory diagram illustrating a configuration example of a gas bearing included in the Stirling engine that is the piston engine according to the present embodiment, and a piston support structure. A Stirling engine 100 that is a piston engine according to this embodiment is a so-called α-type in-line two-cylinder Stirling engine. In this embodiment, the Stirling engine 100 arranges the heat exchanger 108 in the heater case 3 that functions as a passage through which the exhaust gas Ex of the internal combustion engine passes, and recovers thermal energy from the exhaust gas Ex of the internal combustion engine. Used as a device.

  In the Stirling engine 100, a high temperature side piston 20H housed in the high temperature side cylinder 30H and a low temperature side piston 20L housed in the low temperature side cylinder 30L are arranged in series. Hereinafter, the high temperature side cylinder 30H and the low temperature side cylinder 30L are referred to as the cylinder 30 when not distinguished from each other, and the high temperature side piston 20H and the low temperature side piston 20L are referred to as piston 20 when not distinguished from each other.

  The high temperature side cylinder 30 </ b> H and the low temperature side cylinder 30 </ b> L are supported or fixed directly or indirectly on the substrate 111 which is a reference body. In the Stirling engine 100 according to the present embodiment, the substrate 111 serves as a position reference for each component of the Stirling engine 100. By comprising in this way, the relative positional accuracy of each said component can be ensured. Further, as will be described later, the Stirling engine 100 according to the present embodiment interposes the gas bearing GB between the high temperature side cylinder 30H and the high temperature side piston 20H and between the low temperature side cylinder 30L and the low temperature side piston 20L. .

  The Stirling engine 100 according to the present embodiment can maintain the clearance between the piston and the cylinder with high accuracy by directly or indirectly attaching the high temperature side cylinder 30H and the low temperature side cylinder 30L to the substrate 111 which is a reference body. Can do. Thereby, the function of the gas bearing GB can be sufficiently exhibited. Further, the Stirling engine 100 can be easily assembled.

  Between the high temperature side cylinder 30H and the low temperature side cylinder 30L, a heat exchanger 108 including a substantially U-shaped heater (heater) 105, a regenerator 106, and a cooler 107 is provided. Thus, by making the heater 105 substantially U-shaped, the heater 105 can be easily disposed in a relatively narrow space such as in the exhaust passage of the internal combustion engine. Further, by arranging the high temperature side cylinder 30H and the low temperature side cylinder 30L in series as in the Stirling engine 100, the heater 105 can be disposed relatively easily in a cylindrical space such as the exhaust gas passage of the internal combustion engine. can do.

  One end of the heater 105 is disposed on the high temperature side cylinder 30H side, and the other end is disposed on the regenerator 106 side. The heater 105 heats the working fluid (in this embodiment, air). The regenerator 106 has one end disposed on the heater 105 side and the other end disposed on the cooler 107 side, through which the working fluid flowing from the heater 105 or the cooler 107 passes. One end of the cooler 107 is disposed on the regenerator 106 side, and the other end is disposed on the low temperature side cylinder 30L side. The cooler 107 cools the working fluid. The working fluid that has passed through the heat exchanger 108 flows into and out of the high temperature side cylinder 30H and the low temperature side cylinder 30L.

  A working fluid is sealed in the high temperature side cylinder 30H, the low temperature side cylinder 30L, and the heat exchanger 108, and a Stirling cycle is constituted by the heat supplied from the heater 105 to drive the Stirling engine 100. Here, for example, the heater 105 and the cooler 107 can be configured by bundling a plurality of tubes made of a material having high thermal conductivity and excellent heat resistance. The cooler 107 may be air-cooled or water-cooled. Moreover, the regenerator 106 is comprised with a porous heat storage body, for example. Note that the configurations of the heater 105, the cooler 107, and the regenerator 106 are not limited to this example, and a suitable configuration can be selected depending on the heat conditions of the exhaust heat recovery target, the specifications of the Stirling engine 100, and the like.

  The high temperature side piston 20H and the low temperature side piston 20L are supported in the high temperature side cylinder 30H and the low temperature side cylinder 30L via a gas bearing GB. That is, the piston is supported in the cylinder without using a piston ring and without using lubricating oil. Thereby, the friction between the piston 20 and the cylinder 30 can be reduced, and the efficiency of the Stirling engine 100 can be improved. Further, by reducing the friction between the piston 20 and the cylinder 30, for example, even when the Stirling engine 100 is used under a low heat source and low temperature difference operating condition such as exhaust heat recovery of an internal combustion engine, the Stirling engine 100 is used. The heat energy can be recovered from the exhaust heat.

  In order to constitute the gas bearing GB, as shown in FIG. 2, there is a predetermined gap between the piston 20 (high temperature side piston 20H, low temperature side piston 20L) and the cylinder 30 (high temperature side cylinder 30H, low temperature side cylinder 30L). A clearance tc is provided. The clearance tc is set to several μm to several tens of μm over the entire circumference of the piston 20. The reciprocating motion of the high temperature side piston 20H and the low temperature side piston 20L is transmitted to the crankshaft 110, which is the output shaft, by the connecting rod 61, where it is converted into rotational motion.

  Here, since the gas bearing GB has a low ability (load ability) to withstand the force in the radial direction (lateral direction, thrust direction) of the piston 20, it is preferable that the side force Fs of the piston 20 is substantially zero. For this reason, it is necessary to increase the linear motion accuracy of the piston 20 with respect to the axis (center axis) of the cylinder 30. In order to realize this, in the present embodiment, the high temperature side piston 20H and the low temperature side piston 20L are supported by an approximate linear mechanism (for example, a grasshopper mechanism) 60 shown in FIG. In the present embodiment, for example, the approximate linear mechanism 60 supports most of the side force Fs, and the side force Fs generated when the reciprocating motion of the piston 20 deviates from the approximate linear motion is supported by the gas bearing GB. In the present embodiment, a grasshopper mechanism is used as the approximate linear mechanism 60.

  The approximate linear mechanism 60 has a first arm 62 whose one end is rotatably attached to the casing 100C of the Stirling engine 100, and a second arm whose one end is rotatably attached to the casing 100C of the Stirling engine 100. 63, and a third arm 64 having one end rotatably connected to the end of the connecting rod 61 and the other end rotatably connected to the other end of the second arm 63. The connecting rod 61 is rotatably connected to the end of the third arm 64 at an end different from the end that is rotatably attached to the crankshaft 110. Further, the other end of the first arm 62 is rotatably connected between both ends of the third arm 63.

  If such an approximate linear mechanism 60 is used, the high temperature side piston 20H and the low temperature side piston 20L can be reciprocated substantially linearly. As a result, since the side force Fs of the piston 20 becomes almost zero, the piston 20 can be sufficiently supported even by the gas bearing GB having a small load capacity. The approximate linear mechanism that supports the piston 20 is not limited to the grasshopper mechanism, and a watt link or the like may be used.

  Here, the glass hopper mechanism, which is a kind of approximate linear mechanism, requires a smaller dimension of the mechanism to obtain the same linear motion accuracy than other linear approximate mechanisms. For this reason, when a grasshopper mechanism is used as the approximate linear mechanism 60, there is an advantage that the entire Stirling engine 100 becomes compact. In particular, when the Stirling engine 100 is installed in a limited space such as using the Stirling engine 100 for exhaust heat recovery of an internal combustion engine mounted on a vehicle and disposing the heat exchanger 108 in the exhaust gas passage of the internal combustion engine, The degree of freedom of installation is improved when the entire Stirling engine 100 is compact. Further, the grasshopper mechanism is advantageous in terms of improving the thermal efficiency because the mass of the mechanism necessary for obtaining the same linear motion accuracy is lighter than other mechanisms. Furthermore, since the grasshopper mechanism is relatively simple in structure, it is advantageous in that it can be easily manufactured and assembled, and the manufacturing cost can be reduced.

  As shown in FIG. 1, components such as the high temperature side cylinder 30H, the high temperature side piston 20H, the connecting rod 61, and the crankshaft 110 that constitute the Stirling engine 100 are stored in a housing 100C. The casing 100C of the Stirling engine 100 includes a crankcase 114A and a cylinder block 114B. The housing 100C is filled with gas. In the present embodiment, the gas is the same as the working fluid of the Stirling engine 100. The gas filled in the housing 100C is pressurized by a pump 115 that is a pressure adjusting means. The pump 115 may be driven by, for example, an internal combustion engine that is an exhaust heat recovery target of the Stirling engine 100, or may be driven using a driving unit such as an electric motor.

  In the Stirling engine 100, when the temperature difference between the heater 105 and the cooler 107 is the same, the higher the average pressure of the working fluid, the larger the pressure difference between the high temperature side and the low temperature side, so that a higher output can be obtained. The Stirling engine 100 is configured to take out more output from the Stirling engine 100 by holding the working fluid in the working space MS at a high pressure by pressurizing the gas filled in the housing 100C. . As a result, even when only a low-quality heat source can be used, such as exhaust heat recovery, more output can be extracted from the Stirling engine 100. Here, the output of the Stirling engine 100 increases substantially in proportion to the pressure of the gas filled in the housing 100C.

  In the Stirling engine 100, a seal bearing 116 is attached to the housing 100C, and the crankshaft 110 is supported by the seal bearing 116. The Stirling engine 100 pressurizes the gas filled in the housing 100C, but the seal bearing 116 can minimize leakage of the gas filled in the housing 100C. The output of the crankshaft 110 is taken out of the housing 100C via a flexible coupling 119 such as an Oldham coupling, for example.

  As shown in FIGS. 1 and 2, in the present embodiment, gas (same air as working fluid in the present embodiment) A is provided from the air supply port HE provided in the side peripheral portions of the high temperature side piston 20H and the low temperature side piston 20L. Is blown out to form the gas bearing GB. As shown in FIGS. 1 and 2, a high temperature side piston internal space 20HI and a low temperature side piston internal space 20LI are formed inside the high temperature side piston 20H and the low temperature side piston 20L, respectively. When they are not distinguished from each other, they are simply referred to as a piston internal space 20I.

  The high temperature side piston 20H is provided with a gas inlet HI for supplying the gas A to the high temperature side piston internal space 20HI, and the low temperature side piston 20L is supplied with the gas A to the low temperature side piston internal space 20LI. A gas inlet HI is provided. A gas supply pipe 118 is connected to each gas inlet HI. One end of the gas supply pipe 118 is connected to the gas bearing pump 117 and guides the gas A discharged from the gas bearing pump 117 to the high temperature side piston internal space 20HI and the low temperature side piston internal space 20LI.

  The gas A introduced into the high temperature side piston internal space 20HI and the low temperature side piston internal space 20LI flows out from the air supply port HE provided in the side periphery of the high temperature side piston 20H and the low temperature side piston 20L, and flows through the gas bearing GB. Form. In addition, although this gas bearing GB is a static pressure gas bearing, in this embodiment, the structure of the gas bearing GB is not limited thereto, and may be a dynamic pressure gas bearing.

  Further, a gas intake hole is provided on the top surfaces of the high temperature side piston 20H and the low temperature side piston 20L, and the gas A as a working fluid is taken into the high temperature side piston internal space 20HI and the low temperature side piston internal space 20LI from the gas intake hole, The gas bearing GB may be configured by flowing out from the air supply port HE. In addition, although the gas bearing GB of this embodiment is a static pressure gas bearing, you may use a dynamic pressure gas bearing.

  FIG. 3 is an explanatory diagram showing the surface temperature and thermal expansion of the piston during operation of the Stirling engine. FIG. 3 shows a surface temperature (piston surface temperature) Tp of a piston (high temperature side piston) 200 of a Stirling engine (for example, an α-type Stirling engine as shown in FIG. 1), a piston 200 and a cylinder (high temperature side cylinder) 300. The simulation result of the thermal expansion in the radial direction is shown.

  The center of FIG. 3 shows the surface temperature (piston surface temperature) Tp of the side periphery of the piston 200, and the piston surface temperature Tp increases as it approaches the top surface 200Tt of the piston 200. Tp_K is the piston surface temperature at the piston side stepped portion Kp. The left side of FIG. 3 shows the state of thermal expansion of the piston 200 and the cylinder 300 before operating the Stirling engine. Further, the right side of FIG. 3 shows a state of thermal expansion of the piston 200 and the cylinder 300 during operation of the Stirling engine. R on the left side and the right side in FIG. 3 indicates a distance from the central axis of the piston (same as the central axis of the cylinder).

  During operation of the Stirling engine, the working fluid of the Stirling engine constantly applies heat to the top surface 200Tt of the piston 200, so that a heat flow from the top surface 200Tt toward the side peripheral portion 200S is generated. A temperature gradient of the piston surface temperature Tp as shown in the center is formed. This piston 200 is provided with a piston-side stepped portion Kp and a cylinder-side stepped portion Ks, which will be described later, and the clearance between the piston 200 and the cylinder 300 is expanded more than the region where the gas bearing GB is formed. Avoid side thermal expansion.

  Here, in the piston side stepped portion Kp, the clearance between the piston 200 and the cylinder 300 changes abruptly. Specifically, at the piston-side stepped portion Kp, the clearance between the piston 200 and the cylinder 300 is rapidly reduced at the end 200Bt on the side opposite to the top surface from the piston-side stepped portion Kp. As a result, as shown in the center of FIG. 3, the piston surface temperature Tp rises rapidly as it goes from the top surface opposite end portion 200 Bt side to the top surface 200 Tt at the piston side stepped portion Kp. Here, Tp_K in FIG. 3 is the temperature of the piston side stepped portion Kp.

  As a result, during operation of the Stirling engine, as shown on the right side of FIG. 3, the thermal expansion of the piston-side stepped portion Kp in the radial direction of the piston 200 becomes larger than the other portions, and the piston 200 and the cylinder 300 Even if the clearance is made larger than the region where the gas bearing GB is formed, the piston 200 and the cylinder 300 come into contact with each other at the piston side stepped portion Kp. Therefore, in this embodiment, the outer diameter of the portion from the top surface of the piston to the predetermined position toward the end on the opposite side of the top surface of the piston is larger than the outer diameter of the end on the opposite side of the top surface of the piston from the predetermined position. Further, by adopting a structure in which the annular member is fitted and attached to the reduced diameter portion formed to be smaller, the thermal expansion in the radial direction of the piston side stepped portion Kp is suppressed. Next, this structure will be described in detail.

  FIG. 4A is an enlarged view showing a configuration of a piston and a cylinder included in a Stirling engine that is a piston engine according to the present embodiment. FIG. 4-2 is a plan view showing an annular member attached to the piston according to the present embodiment. FIG. 5A is a schematic diagram illustrating a configuration of a piston according to the present embodiment. FIG. 5B is a schematic diagram illustrating the configuration of the cylinder according to the present embodiment. 4-1, FIG. 4-2, FIG. 5-1, and FIG. 5-2 show the high temperature side piston 20H and the high temperature side cylinder 30H of the Stirling engine 100 shown in FIG. 20 and cylinder 30. The configuration of the piston and the cylinder according to this embodiment is particularly preferably applied to the high temperature side piston 20H and the high temperature side cylinder 30H, but may be applied to the low temperature side piston 20L and the low temperature side cylinder 30L shown in FIG. .

  The piston 20 that reciprocates in the cylinder 30 includes a top surface 20Tt and a side peripheral portion 20S connected to the top surface 20Tt. The top surface 20Tt of the piston 20 is a surface on which the piston 20 contacts the working fluid. Further, the end portion of the piston 20 opposite to the top surface 20Tt is the top surface opposite end portion 20Bt of the piston 20. One end of the heater 105 of the heat exchanger 108 shown in FIG. 1 is connected to the top end 30Tt of the cylinder 30. The top portion side end portion 30Tt of the cylinder 30 is an end portion that is closest to the top surface 20Tt of the piston 20 when the piston 20 comes to the top dead center among the two end portions of the cylinder 30. The end of the cylinder 30 opposite to the top end 30Tt is the top 30 opposite end 30Bt of the cylinder 30. Further, the surface of the cylinder 30 facing the side peripheral portion 20S of the piston 20 is a cylinder inner peripheral surface 30S.

  A stepped portion (piston side stepped portion) Kp is provided on the side peripheral portion 20S on the top surface 20Tt side of the piston 20. The piston side stepped portion Kp is provided at a predetermined position from the top surface 20Tt of the piston 20 toward the end 20Bt on the opposite side of the top surface of the piston 20. Here, the distance from the top surface 20Tt of the piston 20 to the piston side stepped portion Kp is L1. The outer diameter Dp1 of the piston 20 from the top surface 20Tt of the piston 20 to the piston-side stepped portion Kp is smaller than the outer diameter Dp2 of the piston 20 from the piston-side stepped portion Kp to the end 20Bt on the piston 20 opposite to the top surface. That is, the piston 20 has an outer diameter Dp1 of a portion from the top surface 20Tt to a predetermined position toward the top surface opposite end 20Bt of the piston 20 so that the top surface opposite end 20Bt of the piston 20 from the predetermined position. It has the reduced diameter part 21 formed smaller than the outer diameter Dp2. By this reduced diameter portion 21, the side peripheral portion 20 </ b> S on the top surface 20 </ b> Tt side of the piston 20 is formed in a stepped shape so that the outer diameter on the top surface 20 </ b> Tt side of the piston 20 becomes small.

  Further, in the present embodiment, a step portion (cylinder side step portion) Ks is provided on the cylinder inner peripheral surface 30S of the cylinder 30 that faces the side peripheral portion 20S on the top surface 20Tt side of the piston 20 at the top dead center. . The distance from the top side end portion 30Tt of the cylinder 30 to the cylinder side stepped portion Ks is L2, and L1 <L2. Further, the inner diameter of the cylinder 30 from the top side end 30Tt of the cylinder 30 to the cylinder side stepped portion Ks is Ds1, and the inner diameter of the cylinder 30 from the cylinder side stepped portion Ks to the top opposite end 30Bt of the cylinder 30 is Ds2. It is. In the present embodiment, the cylinder side stepped portion Ks may not be provided.

  By configuring the piston 20 and the cylinder 30 as described above, a portion from the top surface 20Tt of the piston 20 to the position of the predetermined distance L1 from the top surface opposite end portion 20Bt of the piston 20 (piston side stepped portion Kp The clearance tce is formed between the piston 20 and the cylinder 30 in FIG. Further, a clearance tc is formed between the piston 20 and the cylinder 30 from the position of the predetermined distance L1 to the end 20Bt on the opposite side of the top surface of the piston 20. The clearance tce is larger than the clearance tc (tce> tce). Here, the clearance tce is (Ds1-Dp1) / 2, and the clearance tc is (Ds2-Dp2) / 2. A gas bearing GB is interposed in a clearance tc formed between the piston 20 and the cylinder 30 from the position of the predetermined distance L1 to the top surface opposite end 20Bt.

  The top surface of the high temperature side piston 20 </ b> H shown in FIG. 1 is in thermal expansion because it contacts the high temperature working fluid heated by the heater 105. In the piston 20 in which the side peripheral portion 20S on the top surface 20Tt side of the piston 20 is formed in a stepped shape by the piston-side stepped portion Kp, as described above, the thermal expansion of the piston-side stepped portion Kp toward the radial direction of the piston 20 occurs. Since it becomes larger than other parts, there exists a possibility that piston 20 and cylinder 30 may contact. Therefore, in this embodiment, as shown in FIGS. 4-1 and 5-1, the annular member 50 shown in FIG. 4-2 is fitted to the reduced diameter portion 21 formed on the top surface 20Tt side of the piston 20. To suppress the thermal expansion of the piston-side stepped portion Kp toward the radial direction of the piston 20. This avoids contact between the piston 20 and the cylinder 30 due to thermal expansion of the piston 20 in the radial direction.

  The outer diameter of the annular member 50 is Dro, and the inner diameter is Dri. Since the annular member 50 is fitted and attached to the reduced diameter portion 21 formed on the top surface 20Tt side of the piston 20, the inner diameter Dri of the annular member 50 is set to be equal to or less than the outer diameter Dp1 of the reduced diameter portion 21. For example, when the annular member 50 is attached to the reduced diameter portion 21 of the piston 20 by tight fitting, the inner diameter Dri of the annular member 50 is made smaller than the outer diameter Dp1 of the reduced diameter portion 21. In this case, shrink fitting is used by heating the annular member 50 so that the temperature of the annular member 50 is higher than the temperature of the reduced diameter portion 21 of the piston 20 or cooling the reduced diameter portion 21 of the piston 20. A cold fit is used in which the temperature of the ring member 50 is lower than the temperature of the annular member 50.

  The annular member 50 is made of a material having a smaller coefficient of thermal expansion than the material constituting the reduced diameter portion 21 of the piston 20. Thereby, the thermal expansion of the reduced diameter portion 21 in the radial direction of the piston 20 can be effectively suppressed. In the present embodiment, for example, stainless steel is used for the reduced diameter portion 21 of the piston 20, and titanium (Ti) or a titanium alloy having a smaller thermal expansion coefficient than stainless steel is used for the annular member 50.

  Further, the outer diameter Dro of the annular member 50 and the outer diameter of the piston 20 in the region where the gas bearing GB of the piston 20 is formed, that is, the region from the piston-side stepped portion Kp to the top surface opposite end portion 20Bt of the piston 20. Dp2 or less. Preferably, the outer diameter Dro of the annular member 50 and the outer diameter Dp2 of the region where the gas bearing GB of the piston 20 is formed have the same size. When the thermal expansion toward the radial direction of the piston 20 is restricted by the annular member 50, the annular member 50 is caused by its own thermal expansion and the stress toward the circumferential direction of the annular member 50 generated when regulating the thermal expansion of the piston 20. The annular member 50 also increases in the radial direction. That is, the outer diameter Dro of the annular member 50 is larger than before the piston 20 is thermally expanded.

  Therefore, by setting the outer diameter Dro of the annular member 50 to be equal to or smaller than the outer diameter Dp2 of the region where the gas bearing GB of the piston 20 is formed, the annular member 50 and the cylinder are increased even if the outer diameter Dro of the annular member 50 is increased. Contact with 30 can be avoided. Further, if the outer diameter Dro of the annular member 50 and the outer diameter Dp2 of the region where the gas bearing GB of the piston 20 is formed have the same size, the surface of the side peripheral portion 20S of the piston 20 and the side surface of the annular member 50 50S is the same. As a result, the region where the gas bearing GB is formed increases by the thickness Lr of the annular member 50, so that the load capacity of the gas bearing GB increases accordingly. Here, the thickness Lr of the annular member 50 is a dimension of the annular member 50 in the piston central axis Zp direction. In addition, the thickness Lr of the annular member 50 is not more than the dimension L1 of the reduced diameter portion 21 in the piston central axis Zp direction.

  FIG. 6 is an explanatory diagram showing the surface temperature and thermal expansion of the piston during the operation of the Stirling engine according to the present embodiment. FIG. 6 shows a simulation result of the piston surface temperature Tp of the high temperature side piston 20H provided in the Stirling engine 100 shown in FIG. 1, the thermal expansion in the radial direction of the high temperature side piston 20H, and the high temperature side cylinder 30H. Here, FIG. 6 is a result of the high temperature side piston 20H in which the annular member 50 shown in FIGS. 4-1 and 5-2 is attached to the reduced diameter portion. FIG. 6 is for the high temperature side piston 20H and the high temperature side cylinder 30H of the Stirling engine 100 shown in FIG. 1, but in the following, for convenience of explanation, they are simply referred to as the piston 20 and the cylinder 30.

  FIG. 7 is an explanatory view showing the thermal expansion of the piston. FIG. 7 shows the amount of thermal expansion in the radial direction of the piston 20 with and without the annular member 50 in relation to the piston surface temperature. The amount of thermal expansion describes the value when the distance from the piston central axis Zp to the piston side stepped portion Kp when the piston surface temperature is −50 ° C. is set as a reference with respect to the piston surface temperature. That is, the amount of thermal expansion becomes 0 when the piston surface temperature is −50 ° C. The solid line de_r in FIG. 7 is the amount of thermal expansion when the annular member 50 shown in FIGS. 4-1, 4-2, and 5-1 is attached, and the dotted line de_wr in FIG. The amount of thermal expansion when not attached. FIG. 7 shows simulation results when the piston 20 is manufactured from SUS303 and the annular member 50 is manufactured from titanium.

  The center of FIG. 6 shows the surface temperature (piston surface temperature) Tp of the piston 20. The left side of FIG. 6 shows a state of thermal expansion of the piston 20 and the cylinder 30 before operating the Stirling engine 100 shown in FIG. 6 shows the state of thermal expansion of the piston 20 and the cylinder 30 during operation of the Stirling engine 100 shown in FIG. R on the left and right sides of FIG. 5 indicates the distance from the piston center axis Zp (same as the cylinder center axis Zs) shown in FIG.

  During operation of the Stirling engine 100 shown in FIG. 1, the working fluid constantly heats the top surface 20Tt of the piston 20 to generate a heat flow from the top surface 20Tt toward the side peripheral portion 20S. A temperature gradient of the piston surface temperature Tp as shown in the center of FIG. In this case, as described above, at the piston side stepped portion Kp, the clearance between the piston 20 and the cylinder 30 changes abruptly, and as shown in the center of FIG. The piston surface temperature Tp increases rapidly toward the top surface 20Tt.

  In the case where the annular member 50 is not attached, for example, when the piston surface temperature is around 110 ° C., the piston and the cylinder are galling by about 3 μm. That is, the distance from the piston center axis Zp to the piston side stepped portion Kp is about 3 μm larger than the distance from the cylinder center axis Zs (which coincides with the piston center axis Zp) to the inner peripheral surface of the cylinder. However, as shown in FIG. 7, for example, when the piston surface temperature is around 110 ° C., the piston 20 (FIG. 4-1) in which the annular member 50 having a lower coefficient of thermal expansion than the reduced diameter portion 21 is attached to the reduced diameter portion 21. In FIG. 5-2), the amount of thermal expansion is reduced by about 6 μm as compared with the case where the annular member 50 is not attached. That is, δ = (de_wr−de_r) is approximately 6 μm near the piston surface temperature Tp = 110 ° C.

  As a result, when the annular member 50 is attached to the piston 20, for example, when the piston surface temperature is around 110 ° C., the distance from the piston central axis Zp to the piston side stepped portion Kp is equal to the cylinder central axis Zs (the piston central axis Zp and About 3 μm smaller than the distance from the inner peripheral surface of the cylinder. As described above, in the piston 20 in which the annular member 50 having a lower thermal expansion coefficient than the reduced diameter portion 21 is attached to the reduced diameter portion 21, the thermal expansion in the radial direction of the piston 20 (particularly the thermal expansion of the piston side stepped portion Kp). ) Is regulated by the annular member 50. As a result, as shown on the left side of FIG. 6, contact between the piston-side stepped portion Kp of the piston 20 and the cylinder 30 (particularly the cylinder-side stepped portion Ks) is avoided. Therefore, even if thermal expansion of the piston-side stepped portion Kp in the radial direction of the piston 20 occurs during the operation of the Stirling engine 100 shown in FIG. 1, the piston 20 and the cylinder 30 contact with each other at the piston-side stepped portion Kp. Since this can be avoided, the Stirling engine 100 is stably operated.

FIG. 8A is an explanatory diagram illustrating a relationship between the piston surface temperature and the distortion of the material of the piston and the material of the annular member. 8-2 is explanatory drawing which shows the relationship between piston surface temperature and the stress of the material of a piston, and the material of an annular member. When the annular member 50 is fitted and attached to the reduced diameter portion 21 of the piston 20 to suppress thermal expansion in the radial direction of the piston 20, tensile stress is generated in the annular member 50 and tensile strain is generated. Compressive stress is generated in 20 and compressive strain is generated. FIGS. 8-1 and FIGS. 8-2 have shown the simulation result about the piston 20 which fitted and attached the annular member 50 shown to FIGS. 4-1 and FIGS. 5-1. The simulation conditions are as follows.
(1) The material of the piston 20 is stainless steel, more specifically, SUS303, and the material of the annular member 50 is titanium.
(2) Piston surface temperature Tp shall be -50 degreeC-150 degreeC. At Tp = −50 ° C., the annular member 50 is fitted onto the piston 20 so that the inner diameter Dri of the annular member 50 and the outer diameter Dp1 of the reduced diameter portion 21 of the piston 20 coincide. Then, considering the use conditions of the Stirling engine 100 shown in FIG.
(3) The outer diameter of the reduced diameter portion 21 of the piston 20 is 85.5 mm, and the radial thickness of the piston 20 in the reduced diameter portion 21 is 0.75 mm.
(4) The dimension of the annular member 50 in the radial direction is 0.25 mm. In addition, the dimension in the radial direction of the annular member 50 can be obtained by (Dro-Dri) / 2 in FIG.
(5) The maximum tolerance of the piston 20 and the annular member 50 is 10 μm.
(6) The maximum tightening allowance is 20 μm. Here, the maximum tightening allowance is the reduced diameter portion when the annular member 50 can be manufactured with the minimum tolerance before the annular member 50 is assembled to the piston 20 and the reduced diameter portion 21 of the piston 20 is manufactured with the maximum tolerance. 21 is the difference between the outer diameter of 21 and the inner diameter of the annular member 50.

  In FIG. 8A, εmax_ti is the maximum strain of Ti, εu_ti is the strain of Ti at the upper limit of tolerance, ε_ti is the strain of Ti when the tolerance is 0, εmax_su is the maximum strain of SUS303, εu_su is the strain of SUS303 at the upper limit of tolerance, ε_su is the strain of SUS303 when the tolerance is zero. 8-2, σ_0.2_ti is the 0.2% proof stress of Ti, σu_ti is the stress of Ti at the upper limit of tolerance, σ_ti is the stress of Ti when the tolerance is 0, and σ_0.2_su is the 0.2% proof stress of SUS303. , Σu_su is the stress of SUS303 at the upper limit of tolerance, and σ_su is the stress of SUS303 when the tolerance is zero.

  As can be seen from FIG. 8A, under the above conditions, the strain of titanium constituting the annular member 50 and the strain of SUS303 constituting the piston 20 are both elastic regions. Under the above conditions, both the stress generated in titanium constituting the annular member 50 and the stress generated in SUS 303 constituting the piston 20 are values smaller than 0.2% proof stress. Thus, under the above-mentioned conditions considering the use conditions of the Stirling engine 100 shown in FIG. 1, both the annular member 50 and the piston 20 can be used without any problem in strength.

  FIG. 9 is a schematic diagram showing a configuration example when the Stirling engine according to the present embodiment is used for exhaust heat recovery of an internal combustion engine. In the present embodiment, the output of the Stirling engine 100 is input to the internal combustion engine transmission 4 via the Stirling engine transmission 5 and is combined with the output of the internal combustion engine 1 to be taken out.

  In the present embodiment, the internal combustion engine 1 is mounted on a vehicle such as a passenger car or a truck, and serves as a power source for the vehicle. The internal combustion engine 1 generates an output as a main power source while the vehicle is running. On the other hand, the Stirling engine 100 cannot produce the minimum necessary output unless the temperature of the exhaust gas Ex reaches a certain level. Therefore, in the present embodiment, the Stirling engine 100 collects thermal energy from the exhaust gas Ex of the internal combustion engine 1 to generate an output when the temperature of the exhaust gas Ex discharged from the internal combustion engine 1 exceeds a predetermined temperature. Drive the vehicle. Thus, the Stirling engine 100 is a power source that the vehicle follows.

  The heater 105 provided in the Stirling engine 100 is disposed in the exhaust passage 2 of the internal combustion engine 1. A regenerator (see FIG. 1) 106 of the Stirling engine 100 may be disposed in the exhaust passage 2. The heater 105 provided in the Stirling engine 100 is provided in a hollow heater case 3 provided in the exhaust passage 2.

  In the present embodiment, the thermal energy of the exhaust gas Ex recovered using the Stirling engine 100 is converted into kinetic energy by the Stirling engine 100. A crank shaft 110 that is an output shaft of the Stirling engine 100 is attached with a clutch 6 that is a power interrupting means, and the output of the Stirling engine 100 is transmitted to the Stirling engine transmission 5 via the clutch 6.

  The output of the internal combustion engine 1 is input to the internal combustion engine transmission 4 via the output shaft 1 s of the internal combustion engine 1. The internal combustion engine transmission 4 synthesizes the output of the internal combustion engine 1 and the output of the Stirling engine 100 output from the Stirling engine transmission 5 and outputs the resultant to the transmission output shaft 9. The drive wheel 11 is driven via

  Here, the clutch 6 serving as the power interrupting means is provided between the internal combustion engine transmission 4 and the Stirling engine 100. In this embodiment, it is provided between the input shaft 5 s of the Stirling engine transmission 5 and the crankshaft 110 of the Stirling engine 100. The clutch 6 engages and disengages, thereby interrupting mechanical connection between the crankshaft 110 of the Stirling engine 100 and the input shaft 5s of the Stirling engine transmission 5. Here, the clutch 6 is controlled by the engine ECU 50.

  When the clutch 6 is engaged, the crankshaft 110 of the Stirling engine 100 and the output shaft 1 s of the internal combustion engine 1 are directly connected via the Stirling engine transmission 5 and the internal combustion engine transmission 4. As a result, the output generated by the Stirling engine 100 and the output generated by the internal combustion engine 1 are combined by the internal combustion engine transmission 4 and taken out from the transmission output shaft 9. On the other hand, when the clutch 6 is released, the output shaft 1s of the internal combustion engine 1 is separated from the crankshaft 110 of the Stirling engine 100 and rotates.

  The piston (at least the high temperature side piston) included in the Stirling engine 100 shown in FIG. 9 has the above-described configuration. This suppresses a sudden decrease in the clearance between the piston and the cylinder in the stepped portion provided in at least one of the piston and the cylinder even if the heat is constantly received from the high-temperature working fluid and thermally expanded in the radial direction. The contact between the piston and the cylinder can be avoided. As a result, even if the Stirling engine 100 mounted on the vehicle receives vibration and the clearance between the piston and the cylinder changes, the piston and the cylinder in the stepped portion are generated due to thermal expansion in the radial direction of the piston. And the effect of a sharp decrease in clearance is reduced.

  As a result, when the Stirling engine 100 is being operated while the vehicle is running, the possibility of contact between the piston and the cylinder can be reduced, so that the Stirling engine 100 can be stably operated and the durability of the piston and cylinder can be reduced. Reduction can be suppressed. Thus, when the Stirling engine 100 according to the present embodiment is used for exhaust heat recovery of the internal combustion engine 1 mounted on a vehicle, exhaust heat can be recovered stably and sufficient durability can be ensured.

  As described above, in the present embodiment, in the configuration in which the clearance between the piston and the cylinder is enlarged on the top surface side of the piston, the direction of the bottom dead center of the piston from the step formed on at least one of the piston and the cylinder (that is, the piston A predetermined range is formed in a taper shape in which the clearance between the piston and the cylinder is gradually narrowed (in the direction of the end opposite to the top surface). Thereby, when large thermal expansion toward the radial direction of the piston occurs at the stepped portion, the possibility that the piston and the cylinder come into contact with each other is suppressed, and the piston engine can be operated stably. In particular, in a configuration in which a gas bearing is interposed between the piston and the cylinder, the clearance between the piston and the cylinder is very small, so that the piston and the cylinder are likely to contact each other due to the thermal expansion of the piston. However, according to the present embodiment, the possibility that the piston and the cylinder come into contact with each other can be suppressed, and the function of the gas bearing can be surely exhibited.

  As described above, the piston engine and the Stirling engine according to the present invention are useful for a piston engine that supports a piston in a cylinder by a gas bearing without using a piston ring, and particularly avoids contact between the piston and the cylinder. Suitable for that.

It is sectional drawing which shows the structure of the Stirling engine which is a piston engine which concerns on this embodiment. It is explanatory drawing which shows the structural example of the gas bearing with which the Stirling engine which is a piston engine which concerns on this embodiment is provided, and the support structure of a piston. It is explanatory drawing which shows the surface temperature and thermal expansion of a piston during the driving | operation of a Stirling engine. It is an enlarged view which shows the structure of the piston and cylinder with which the Stirling engine which is a piston engine which concerns on this embodiment is provided. It is a top view which shows the annular member attached to the piston which concerns on this embodiment. It is a schematic diagram which shows the structure of the piston which concerns on this embodiment. It is a schematic diagram which shows the structure of the cylinder which concerns on this embodiment. It is explanatory drawing which shows the surface temperature and thermal expansion of a piston during the driving | operation of the Stirling engine which concerns on this embodiment. It is explanatory drawing which shows the thermal expansion of a piston. It is explanatory drawing which shows the relationship between piston surface temperature and the distortion | strain of the material of a piston, and the material of an annular member. It is explanatory drawing which shows the relationship between piston surface temperature and the stress of the material of a piston, and the material of an annular member. It is a mimetic diagram showing the example of composition in the case of using the Stirling engine concerning this embodiment for exhaust heat recovery of an internal-combustion engine.

Explanation of symbols

20 Piston 20Bt Top side opposite end 20H High temperature side piston 20L Low temperature side piston 20S Side circumference 20Tt Top 21 Reduced diameter part 30 Cylinder 30Bt Top opposite side end 30H High temperature side cylinder 30L Low temperature side cylinder 30S Cylinder inner peripheral face 30Tt Top portion side end portion 50 annular member 50S side surface 100 Stirling engine 100C casing 105 heater 106 regenerator 107 cooler 108 heat exchanger

Claims (7)

In a piston engine having a piston that reciprocates in a cylinder,
The outer diameter of the portion from the top surface of the piston to the predetermined position toward the end opposite to the top surface of the piston is formed smaller than the outer diameter of the end portion on the opposite side of the top surface of the piston from the predetermined position. A reduced diameter part,
An annular member fitted to the reduced diameter portion;
A piston engine comprising:   2. The piston engine according to claim 1, wherein the annular member is made of a material having a smaller coefficient of thermal expansion than a material constituting the piston in the reduced diameter portion.   3. The piston engine according to claim 1, wherein an outer diameter of the annular member is the same as an outer diameter of the piston from the predetermined position to an end portion on the opposite side to the top surface.   The piston engine according to any one of claims 1 to 3, wherein a gas bearing is interposed between the piston and the cylinder. A heat exchanger comprising: a heater that heats the working fluid; a regenerator that is connected to the heater and through which the working fluid passes; and a cooler that is connected to the regenerator and cools the working fluid. When,
A cylinder into which the working fluid that has passed through the heat exchanger flows in and out;
A piston that reciprocates in the cylinder;
The outer diameter of the portion from the top surface of the piston to the predetermined position toward the end opposite to the top surface of the piston is formed smaller than the outer diameter of the end portion on the opposite side of the top surface of the piston from the predetermined position. A reduced diameter part,
An annular member made of a material having a smaller coefficient of thermal expansion than the material constituting the piston in the reduced diameter portion, and fitted into the reduced diameter portion;
A gas bearing interposed between the cylinder and the piston;
Stirling engine characterized by including.   The Stirling engine according to claim 5, wherein an outer diameter of the annular member is the same as an outer diameter of the piston from the predetermined position to an end portion on the opposite side to the top surface.   The Stirling engine according to claim 5 or 6, wherein the piston is supported by an approximate linear mechanism.

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