JPH11247714A - Stirling cycle engine for driving displacer by using planetary gear - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the speed of a displacer near the top dead center/bottom dead center of a power piston so as to increase the regenerative calorific value by using a shaft eccentrically attached to a planetary gear when the displacer is driven, in a Stirling engine or a Stirling refrigerating machine/heat pump having a power piston and the displacer to be operated in different cylinders and promote heat exchange by repeatedly introducing operating gas in a cylinder to a heater or a cooler while oscillating the displacer at frequencies higher than the rotational speed of a power shaft in the expansion/compression stroke. SOLUTION: In a gear system in which the ratio of the number of teeth of a sum gear 4 and the number of teeth of a planetary gear 5 is 2:1 and an internal gear 3 is fixed, the sum gear 4 is rotated at the speed three times of a power shaft 7. A displacer is reciprocated by making use of a rotational motion of an eccentric shaft 2 attached to one of the planetary gears 5. At this time, the phase difference between the displacer and the power piston is taken as 90 deg., to constitute a Stirling cycle.

Description

Description: BACKGROUND OF THE INVENTION The Stirling engine is a new type of prime mover which has been gradually put into practical use in recent years, and in principle, extremely high thermal efficiency can be expected. Engine. It is suitable for using a relatively low temperature heat source, so it can be applied to a combined engine with a diesel engine or a small-scale cogeneration system. Stirling refrigerators are mainly used to make cryogenic temperatures (about the temperature of liquid helium), but their application to ordinary refrigerators and air conditioners is also expected due to the regulations for CFCs. 2. Description of the Related Art Stirling cycle engines that are currently manufactured are limited to those that change the working gas volume in a high-temperature section and a low-temperature section in a sinusoidal or nearly sinusoidal manner. In that case, the four basic steps of isothermal compression, isothermal heating, isothermal expansion, and isostatic cooling of the Stirling cycle are not clear. Therefore, even if it is assumed that heat transfer is sufficient, the output per cycle is only about 75% of the ideal value. When the four basic steps of the Stirling cycle, ie, isothermal compression, isothermal heating, isothermal expansion, and isocooling, are ideally performed, the work that can be taken out per cycle is maximum. become. However, in actual operation,
Since the power piston and displacer must move smoothly, the output will be somewhat lower than the ideal output. However, moving in a sinusoidal or near-sine-wave form, as is done in the past, reduces the output to be obtained more than necessary. Loss is large in processes other than equal-volume heating (in the case of an engine) between the type using separate high and low temperature cylinders of the same diameter and the type that moves the power piston and displacer in one cylinder. In the type that moves the power piston and displacer in cylinders of different diameters, the loss is large except for the compression stroke (in the case of an engine). The present invention aims to improve the thermal efficiency and the output per unit volume by reducing the phase width that changes in the middle of the four basic cycles as much as possible. [0004] The present invention is a technique applicable to a Stirling cycle engine of a type in which a power piston and a displacer are moved in different cylinders.
Since the pressure acting on the displacer is almost balanced and the driving force is not so large, this waveform can be devised to make it closer to the ideal. The points to be devised are to quickly move the displacer near the top and bottom dead center of the power piston to increase the change in the working gas average temperature due to the change in equal volume, and to minimize the movement of the displacer during compression and expansion. It is to suppress. In order to make the drive waveform as described above, a third harmonic is added to the drive waveform of the displacer, the peaks and valleys of the waveform are flattened, and the gradient at the point crossing the average value is made steep. . That is, the third harmonic-α ₃ cos 3φ is added to the waveform of α ₁ cos φ (ψ: phase). α ₁ / α ₃ = 1
/ 6 In the peaks and valleys, the displacement of the displacer is suppressed to 2% of the stroke over almost 90 ° of phase. Specifically, a planetary gear fixed to an internal gear having a ratio of the number of teeth of the sun gear to the number of teeth of the planetary gear of 2: 1 is provided.
In a planetary gear of this ratio, the orbital angular velocity and the rotation angular velocity of the planetary gear are 1/3 and 1 times the angular velocity of the sun gear, respectively. Therefore, the angular velocity of the sun gear is three times that of the power shaft (power piston crankshaft). , The center of the planetary gear rotates at a constant radius (α ₁ ) at the same angular velocity as the power shaft, while the rotation angular velocity of the planetary gear becomes three times this. Therefore, when mounting the eccentric axis eccentric by alpha ₃ one planetary gear, the position of this axis, because changes in waveforms applied three times harmonic as described above, such as to connect the connecting rod to the shaft To drive the displacer. α ₁ / α ₃ = 1 /
In the case of 6, the eccentric shaft trajectory is as shown in FIG. The mechanism that converts the rotary motion into a linear reciprocating motion is
In addition to the mechanism similar to the crank-piston mechanism described above, several well-known methods are available. The output work per cycle in the engine can be represented by an area surrounded by a closed curve formed by connecting state changes on a pressure-volume diagram. The differences between the ideal cycle, the conventional method, and the method according to the present invention are shown in FIG. 3 when the heat transfer is sufficiently performed. When the displacer is driven with a sinusoidal waveform, it is represented by a thin solid line, which is only about 75% of the ideal cycle represented by a broken line. On the other hand, in the method according to the present invention, when α ₁ / α ₃ = １ ／, it is represented by a thick solid line, and the output can be improved to about 90% of the ideal. Although the actual output of the engine is smaller than the value shown in the pressure-volume diagram due to the loss of friction and the like, the actual output is 30 to 40 because the degree of the decrease is not significantly affected by the drive waveform of the displacer. % Improvement is expected. In the method for driving a displacer according to the present invention, the displacer is swung at a frequency three times the rotational speed of the power shaft. Normally, it is difficult to heat and cool the working gas in the cylinder, but this swing sends the working gas in the cylinder into the heater or cooler,
Heat exchange can be enhanced. In particular, when the drive waveform is not vertically symmetrical, such as when a drive method similar to a piston-crank mechanism is used, the position of the eccentric shaft is set so that the swing becomes larger during expansion, which has a large amount of exchange heat compared to compression. Can be adjusted to achieve a more ideal cycle. FIG. 4 shows an embodiment. It consists of a displacer drive mechanism using planetary gears and a mechanism that increases the speed of the power piston three times. The phase difference between the planetary gear used to drive the displacer and the power piston is set to 90 °, and the phase of the planetary gear is set so that the eccentric shaft swings inward at the top dead center and bottom dead center of the displacer. The operation in the case of the engine is as follows. During the compression stroke, the displacer hardly moves when it is close enough to the heater side, and the working gas mainly in the low temperature part is compressed. When the power piston is near the top dead center, the displacer moves largely from the heater side to the cooler side, and sends out working gas to the high temperature side through the regenerator.
At this time, the amount of heat stored in the regenerator is given to the working gas, and the average temperature, that is, the pressure of the working gas rises. While the power piston is in the expansion stroke, the displacer hardly moves at a position sufficiently close to the cooler side, and the working gas mainly in the high temperature part expands to generate work. When the power piston is near the bottom dead center, the displacer moves largely from the cooler side to the heater side, and moves the working gas from the high temperature part to the low temperature part. At this time, heat is stored in the heat storage material in the regenerator. In order for the regeneration and heat storage to be performed sufficiently by equal volume heating and cooling, it is necessary to move more working gas between the hot and cold parts when the power piston is near the top dead center and bottom dead center. is there. As shown in FIG. 2, the moving volume of the working gas according to the present invention has a phase 6 between the top dead center and the bottom dead center.
Between 0 ° it is 77% of the stroke volume. This is a significant improvement over 50% when the displacer is moved with a sine wave. As the output work per cycle increases, the ratio of mechanical loss due to friction and the like decreases, and the output per engine volume and the thermal efficiency are remarkably improved. Originally, the Stirling cycle engine has a disadvantage that the manufacturing cost is higher than the internal combustion engine and the vapor compression refrigerator. However, if the thermal efficiency can be made sufficiently high, the advantages of fuel saving in the engine and high operating coefficient (COP) in the refrigerator will outweigh it, and the engine and the refrigerator will be economically sufficiently valuable. In particular, in a Stirling cycle engine in which the power piston and the displacer are moved in cylinders of different diameters, which is the object of the present invention, the compression / expansion by the power piston is performed by increasing the stroke volume of the displacer compared to that of the power piston. In this case, it is possible to reduce the rise and fall of the working gas temperature and to realize the isothermal process more ideally. Therefore, if the change in the equal volume approaches the ideal according to the present invention, it can be expected that an engine or a refrigerator utilizing the advantage of the inherently high thermal efficiency will be put to practical use.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 exemplifies a change in phase of a displacer position. [Explanation of Signs] 1. Waveform including third harmonic 2. Fig. 2 shows an example of a trajectory drawn by an eccentric axis. [Explanation of Codes] 1. Orbit of planetary gear Track 3 of the eccentric shaft compares the output work with the conventional method, the method according to the present invention, and the ideal case using the pressure-volume diagram, and shows the effect of the present invention. is there. [Explanation of Codes] 1. Improvement cycle according to the invention 2. Cycle by sine wave drive FIG. 4 is an example of an embodiment of the present invention, and is a perspective view. [Explanation of Codes] Connecting rod 2. Eccentric shaft 3. Internal gear 4. Sun gear 5. Planetary gear 6. Gears for speed increase7. Power shaft 8. Heater 9. Regenerator 10. Heat exchange cylinder 11. Cooler 12. Displacer 13. Compression / expansion cylinder 14. Power piston

Claims (1)

Claims 1. When a displacer is driven by a Stirling cycle engine (engine and refrigerator / heat pump), when the displacer is driven by using a shaft eccentrically mounted on a planetary gear, While moving faster, it moves with a waveform that is almost stationary and has a wider phase width.
The change in the average working gas temperature during the cooling process must be large. In the expansion / compression process, the working gas in the cylinder is repeatedly introduced into a heater or a cooler by oscillating the displacer at a frequency higher than the rotational speed of the power shaft, thereby enhancing heat exchange.