Patent Application
20100257857
The disclosure of Japanese Patent Application No. 2009-095350 filed on Apr. 9, 2009, including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to a Stirling engine and, more particularly, to a Stirling engine that includes a plurality of crankcase pressurizing α-type Stirling cycle mechanisms.
2. Description of the Related Art
In order to recover exhaust heat of an internal combustion engine mounted on a vehicle, such as an automobile, a bus and a truck, or exhaust heat from a factory, a Stirling engine that is excellent in theoretical thermal efficiency receives attention. A Stirling engine is expected to exhibit high thermal efficiency and is an external combustion engine that externally heats working fluid, so the Stirling engine is advantageous in that it can use various low temperature difference alternative energies, such as solar, geothermal heat and exhaust heat, irrespective of a heat source, and is useful for energy savings.
Japanese Patent Application Publication No. 2005-54640 (JP-A-2005-54640), Japanese Patent Application Publication No. 2008-223555 (JP-A-2008-223555) and Japanese Patent Application Publication No. 2006-118406 (JP-A-2006-118406), for example, describe such a Stirling engine that includes a plurality of Stirling-cycle mechanisms coupled to each other via a common rotary shaft. JP-A-2005-54640 describes that the same rotational phase difference (for example, 90°) is set between cylinders in the same Stirling cycle mechanism, while a selected rotational phase difference may be set between the Stirling cycle mechanisms. Other than the above, Japanese Patent Application Publication No. 2005-351242 (JP-A-2005-351242) and Japanese Patent Application Publication No. 2005-351243 (JP-A-2005-351243), for example, describe a crankcase pressurizing α-type Stirling engine.
Incidentally, in an α-type Stirling cycle mechanism, the amplitude of in-cylinder pressure is large as compared with a net work. Therefore, the α-type Stirling cycle mechanism has a characteristic that variations in output torque are large. Thus, in a Stirling engine that includes an α-type Stirling cycle mechanism, not only when the number of the mechanisms is one but also when the number of the mechanisms is multiple, it is necessary to sufficiently consider variations in output torque and suppress the variations. Note that it is conceivable that, for example, a flywheel or a damper is used to suppress variations in output torque. However, in this case, there is a problem that the size or weight of the Stirling engine increases and, as a result, vehicle mountability deteriorates.
The invention provides a Stirling engine that is able to desirably suppress variations in output torque when the Stirling engine includes a plurality of α-type Stirling cycle mechanisms coupled to each other via a common rotary shaft.
As aspect of the invention relates to a Stirling engine. The Stirling engine includes a plurality of α-type Stirling cycle mechanisms, each of which includes a first piston and a second piston and pressurizes a crankcase space. The mechanisms are coupled to each other via a common rotary shaft so that each of the mechanisms generates a torque variation waveform in which the number of periods per rotation is two.
With the Stirling engine according to the aspect of the invention, when the Stirling engine includes a plurality of α-type Stirling cycle mechanisms coupled to each other via a common rotary shaft, variations in output torque may be desirably suppressed.
The foregoing and further objects, features and advantages of the invention will become apparent from the following description of example embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:
An upper space of the high temperature cylinder 22 is an expansion space. Working fluid heated by a heater 47 flows into the expansion space. Specifically, the heater 47 is arranged inside an exhaust pipe 200 of a gasoline engine mounted on a vehicle in the present embodiment. An upper space of the low temperature cylinder 32 is a compression space. Working fluid cooled by a cooler 45 flows into the compression space. A regenerator 46 exchanges heat with working fluid that reciprocally moves between the expansion space and the compression space. Specifically, the regenerator 46 receives heat from working fluid when the working fluid flows from the expansion space to the compression space, and radiates stored heat when working fluid flows from the compression space to the expansion space. The expansion space and the compression space constitute a working gas space. The crankcase 60A forms a crankcase space that is common to the high temperature-side cylinder 20 and the low temperature-side cylinder 30. The working gas space and the crankcase space are partitioned by the expansion piston 21 and the compression piston 31. Air is used as the working fluid. However, the working fluid is not limited to air; instead, gas, such as He, H2 and N2, may be, for example, used as the working fluid.
An introducing pipe 71 is provided as a working fluid introducing portion that introduces working fluid into the working gas space. In terms of this point, the introducing pipe 71 is specifically provided for the low temperature cylinder 32. The introducing pipe 71 provides fluid communication between the compression space of the low temperature cylinder 32 and the outside of the Stirling engine 10A. The introducing pipe 71 is provided with a filter 72 and a check valve 73. The filter 72 traps impurities. The check valve 73 allows circulation only in a direction from the outside toward the compression space, and transfers pressure.
Next, the operation of the Stirling engine 10A will be described. When working fluid is heated at the heater 47, the working fluid expands to press the expansion piston 21 downward. By so doing, a drive shaft (crankshaft) 113A is rotated. The drive shaft 113A that corresponds to a rotary shaft. Subsequently, when the expansion piston 21 enters the upstroke, working fluid passes by the heater 47 and is conveyed to the regenerator 46. Then, the working fluid radiates heat at the regenerator 46 and flows to the cooler 45. Working fluid cooled at the cooler 45 flows into the compression space, and further compressed with the upstroke of the compression piston 31. The working fluid compressed in this way then absorbs heat from the regenerator 46 to increase in temperature, and flows into the heater 47. Then, the working fluid is heated and expanded at the heater 47 again. That is, the Stirling engine 10A operates through reciprocal flow of the working fluid.
On the other hand, as reciprocal flow of working fluid occurs with reciprocation of the two pistons 21 and 31, the proportion of working fluid in the expansion space and working fluid in the compression space varies and the total internal volume also varies, so pressure variations occur. In terms of this point, when pressures are compared for each of the two pistons 21 and 31 at the same position, the pressure during downstroke is considerably higher than the pressure during upstroke in the case of the expansion piston 21; whereas the pressure during downstroke is lower than the pressure during upstroke in the case of the compression piston 31. Therefore, it is necessary that the expansion piston 21 does positive work (expansion work) to the outside and the compression piston 31 receives work (compression work) from the outside. Part of the expansion work is used for the compression work, and the remainder is extracted as output through the drive shaft 113A.
Incidentally, in the present embodiment, the heat source of the Stirling engine 10A is exhaust gas from the internal combustion engine of the vehicle, so the amount of heat obtained is restrictive, and it is necessary to operate the Stirling engine 10A within the range of the amount of heat obtained. Then, in the present embodiment, the internal friction of the Stirling engine 10A is reduced as much as possible. Specifically, in order to eliminate a friction loss due to a piston ring that gives the largest friction loss within the internal friction of the Stirling engine 10A, gas lubrication is performed between the cylinder 22 and the piston 21 and between the cylinder 32 and the piston 31.
In the gas lubrication, air pressure (distribution) occurs in a small clearance between the cylinder 22 and the piston 21 and a small clearance between the cylinder 32 and the piston 31 is utilized to float the pistons 21 and 31 in the air. Gas lubrication provides extremely small sliding resistance, so it is possible to greatly reduce the internal friction of the Stirling engine 10A. Specifically, the gas lubrication for floating an object in the air may be, for example, static pressure gas lubrication that jets pressurized fluid to generate static pressure to thereby float an object. However, the gas lubrication is not limited to the static pressure gas lubrication; it may be, for example, dynamic pressure gas lubrication.
Each of the clearances between the cylinder 22 and the piston 21 and between the cylinder 32 and the piston 31, for which gas lubrication is performed, is set at several tens of micrometers. Then, working fluid of the Stirling engine 10A is present in the clearances. The pistons 21 and 31 are respectively supported in a non-contact state with the cylinders 22 and 32 or in an allowable contact state through gas lubrication. Thus, no piston ring is provided around the piston 21 or 31, and no lubricating oil that is generally used together with a piston ring is used. In the gas lubrication, airtightness of each of the expansion space and the compression space is maintained by the small clearances to achieve clearance seal with no ring or oil.
Furthermore, both the pistons 21 and 31 and the cylinders 22 and 32 are made of metal, and, in the present embodiment, specifically, metal having the same coefficient of linear expansion (here, stainless steel) is used for the associated piston 21 and cylinder 22 and the associated piston 31 and the cylinder 32. By so doing, even when thermal expansion occurs, appropriate clearances may be maintained to perform gas lubrication. In addition, the pistons 21 and 31 and the cylinders 22 and 32 form the above small clearances to implement throttles that can ensure airtightness necessary for the working gas space while providing fluid communication between the working gas space and the crankcase space. In the Stirling engine 10A, the pistons 21 and 31 and the cylinders 22 and 32 correspond to a first communication portion.
Incidentally, in the case of gas lubrication, load capability is small, so the side forces of the pistons 21 and 31 should be substantially reduce to zero. That is, when gas lubrication is performed, withstanding capability (pressure resistant capability) against force in the diameter direction (lateral direction, thrust direction) of each of the cylinders 22 and 32 is low, so it is necessary that the accuracy of linear motion of each of the pistons 21 and 31 with respect to the axis of a corresponding one of the cylinders 22 and 32 is high.
Therefore, in the present embodiment, a grasshopper mechanism 50 is employed for each piston-crank portion. A mechanism for implementing linear motion includes not only the grasshopper mechanism 50 but also, for example, a Watt's mechanism. However, the grasshopper mechanism 50 may have a small-size mechanism necessary for obtaining the same accuracy of linear motion in comparison with another mechanism, so the grasshopper mechanism 50 has an advantageous effect that the device as a whole is compact. Particularly, the Stirling engine 10A according to the present embodiment is installed in a limited space, that is, an underfloor of an automobile, so the flexibility of installation increases when the device as a whole is compact. In addition, the grasshopper mechanism 50 has a characteristic that the weight of the mechanism necessary for obtaining the same accuracy of linear motion may be reduced as compared with another mechanism, so it is advantageous in terms of fuel economy. Furthermore, the configuration of the grasshopper mechanism 50 is relatively simple, so the grasshopper mechanism 50 is advantageous in that it is easy to construct (manufacture, assemble) the mechanism.
The reciprocating motion of the expansion piston 21 is transmitted to the drive shaft 113A by the connecting rod 110, and is converted into the rotating motion by the drive shaft 113A. The connecting rod 110 is supported by the grasshopper mechanism 50, and linearly reciprocate the expansion piston 21. In this way, by supporting the connecting rod 110 by the grasshopper mechanism 50, the side force F of the expansion piston 21 becomes almost zero. Therefore, even when gas lubrication having small load capability is performed, it is possible to sufficiently support the expansion piston 21.
Incidentally, the Stirling engine 10A is a crankcase pressurizing Stirling engine. In terms of this point, the operation for pressurizing the crankcase space is as follows. Here, the in-cylinder pressure P, which is the pressure of working fluid, normally varies to repeatedly obtain a region lower than a working gas mean pressure Pm (from the latter half of expansion stoke to the first half of compression stroke) and a region higher than the working gas mean pressure Pm (from the latter half of compression stroke to the first half of expansion stroke) as shown in
As shown in
In terms of this point, the pistons 21 and 31 and cylinders 22 and 32, which correspond to the first communication portion, have the function of balancing the pressure in the working gas space and the pressure in the crankcase space. Then, the introducing pipe 71, which corresponds to the working fluid introducing portion, and the pistons 21 and 31 and cylinders 22 and 32, which correspond to the first communication portion, serve as a pressurization enabling portion that enables the crankcase space to be pressurized so that the crankcase pressure Pcr is equal to the working gas mean pressure Pm. Note that, instead of providing the pressurization enabling portion, it is also applicable that the crankcase pressure Pcr becomes equal to the working gas mean pressure Pm by hermetically sealing high-pressure gas in the Stirling engine 10A in a state where the pistons 21 and 31 and cylinders 22 and 32, which correspond to the first communication portion, are provided. Specifically, the Stirling engine 10A has an α-type Stirling cycle mechanism that includes the high temperature-side cylinder 20, the low temperature-side cylinder 30, the cooler 45, the regenerator 46, the heater 47, the crankcase 60A, the approximate linear mechanism, the introducing pipe 71, the filter 72 and the check valve 73.
Next, the function and advantageous effects of the Stirling engine 10A will be described with reference to
In addition, in the case of the Stirling engine 10X that does not pressurize the crankcase space, the pistons 21 and 31 each carry a pressure difference between the in-cylinder pressure P and the atmospheric pressure Po as pressure loading (see
A Stirling engine 10B according to a second embodiment will be described with reference to
The communication pipe 75 provides fluid communication between the crankcase spaces of the respective Stirling engines 10A. In terms of this point, instead of providing the communication pipe 75, the Stirling engine 10B may be configured like a Stirling engine 10B′ in which, for example, as shown in
Next, the concept of reducing variations in output torque when the plurality of α-type Stirling cycle mechanisms are provided will be described with reference to
In the Stirling engine 10B, on the basis of the above concept, specifically, as described as follows, a phase difference β between the Stirling engines 10A (in other words, α-type Stirling cycle mechanisms) is set. Specifically, the phase difference β is a phase difference between the expansion pistons 21 (or, in other words, the compression pistons 31) of the adjacent Stirling engines 10A.
In terms of this point, in the waveforms W11 and W12, which are the torque variation waveforms of the Stirling engines 10A, specifically, the maximum point and the minimum point are present alternately at an interval of about 90°. Therefore, in the Stirling engine 10B, the phase difference β is further specifically set at 90°. On the other hand, the phase difference β is set using the drive shaft 113B. In terms of this point, specifically, in the Stirling engine 10B, as shown in
Next, the function and advantageous effects of the Stirling engine 10B will be described. In the Stirling engine 10B, the phase difference β is set as described above, so the waveforms W11 and W12 are synthesized to desirably cancel each other. Then, as a result, the torque variation waveform of the Stirling engine 10B becomes a waveform W13 of which variations in output torque are desirably suppressed by synthesizing the waveforms W11 and W12 as shown in
In addition, in the Stirling engine 10B, the communication pipe 75 provides fluid communication between the crankcase spaces of the respective Stirling engines 10A. Therefore, in the Stirling engine 10B, the working gas mean pressure Pm may be equal between the Stirling engines 10A. By so doing, in the Stirling engine 10B, in the Stirling engines 10A, pressure loadings applied to the pistons 21 and 31 may be equal to each other. In addition, by so doing, in the Stirling engine 10B, the shapes of the torque variation waveforms of the Stirling engines 10A may be similar to each other. Thus, the Stirling engine 10B is able to desirably suppress variations in output torque as described above.
Note that, to set the phase difference β at 90°, for example, it may be set as follows. That is, for example, as shown in
A Stirling engine 10C according to a third embodiment will be described with reference to
In the Stirling engine 10C, phase differences 13 are set as follows. FIG. 15 is a graph that shows the torque variation waveforms before and after the three Stirling engines 10A are coupled to each other. In
In terms of this point, in the waveforms W21, W22 and W23, which are the torque variation waveforms of the Stirling engines 10A, specifically, the maximum point and the minimum point are present alternately at an interval of about 90°. Therefore, further specifically, in the Stirling engine 10C, the phase differences β each are set at 60°. On the other hand, the phase differences β are set using the drive shaft 113C. In terms of this point, specifically, in the Stirling engine 10C, as shown in
Next, the function and advantageous effects of the Stirling engine 10C will be described. In the Stirling engine 10C, the phase differences β are set as described above, so the waveforms W21, W22 and W23 are synthesized to desirably cancel each other. Then, as a result, the torque variation waveform of the Stirling engine 10C becomes a waveform W24 of which variations in output torque are desirably suppressed by synthesizing the waveforms W21, W22 and W23 as shown in
Note that, when the three Stirling engines 10A are coupled to each other, the phase differences β each may be set so as to be about four thirds (4/3) of the angular difference θ. That is, the phase differences β may be set at 120°. In this case, for example, as shown in
On the other hand, when the drive shaft 113C′ is provided instead of the drive shaft 113C, the torque variation waveforms before and after the three Stirling engines 10A are coupled to each other are those shown in
A Stirling engine 10D according to a fourth embodiment will be described with reference to
In the Stirling engine 10D, the phase differences β are set as follows.
Then, when the Stirling engines 10A are coupled to each other, in the Stirling engine 10D, the phase differences β are set so as to be substantially equal to multiples of the angular difference θ. In addition, in the Stirling engine 10D, the phase differences β are set so that the phases of the expansion pistons 21 (in other words, the compression pistons 31) of the respective Stirling engines 10A do not overlap each other. In addition, in the torque variation waveforms W41, W42, W43 and W44 of the Stirling engines 10A, specifically, the maximum point and the minimum point are present alternately at an interval of about 90°. In terms of this point, more specifically, in the Stirling engine 10D, the phase differences β are set at 90°.
On the other hand, the phase differences β are set using the drive shaft 113D. In terms of this point, specifically, in the Stirling engine 10D, as shown in
Next, the function and advantageous effects of the Stirling engine 10D will be described. In the Stirling engine 10D, the phase differences β are set as described above, so the waveforms W41, W42, W43 and W44 are synthesized to desirably cancel each other. Then, as a result, the torque variation waveform of the Stirling engine 10D becomes a waveform W45 of which variations in output torque are desirably suppressed by synthesizing the waveforms W41, W42, W43 and W44 as shown in
Note that, when the four Stirling engines 10A are coupled to each other, the phase differences β may be set using a combination of 90° and 180°.
In the above described embodiments, the drive shaft (for example, the drive shaft 113B) formed of the plurality of drive shafts 113A coupled to each other is a common rotary shaft. However, the aspect of the invention is not limited to this configuration; the rotary shaft may be formed of a single member.
In addition, in the above described third embodiment, in order to set the phase differences β at any one of 60° and 120°, the phases of the expansion piston 21 of the Stirling engines WA are advanced by 60° or 120° sequentially. However, the aspect of the invention is not limited to this configuration; for example, the phase differences β may be set at any one of 60° and 120° by delaying the phases of the expansion pistons 21 of the Stirling engines 10A by 60° or 120° sequentially.
In addition, in the above described embodiments, it is advantageous in pressurizing the crankcase spaces in terms of cost, or the like, so the introducing pipe 71 introduces outside air at the atmospheric pressure P0 into the working gas space as working fluid. However, the aspect of the invention is not limited to this configuration, the working fluid introducing portion may, for example, introduce working fluid, which is used in the Stirling engine and is other than outside air, into the working gas space or may introduce working fluid having a pressure higher than the atmospheric pressure into the working gas space.
In addition, in the above described embodiments, because of rationality in terms of configuration, and the like, the pistons 21 and 31 and cylinders 22 and 32, which form small clearances, serve as the first communication portion. However, the aspect of the invention is not limited to this configuration; the first communication portion may be, for example, a communication portion, such as a pipe, that has a throttle that is able to ensure airtightness necessary for the working gas space and that provides fluid communication between the working gas space and the crankcase space.
While the invention has been described with reference to example embodiments thereof, it is to be understood that the invention is not limited to the described embodiments or constructions. The invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the disclosed invention are shown in various example combinations and configurations, other combinations and configurations, including more, less or only a single element, are also within the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-095350 | Apr 2009 | JP | national |
