Patent Grant
11098901
The present disclosure relates to a gas turbine combustor, particularly to the structure of a gas turbine combustor which has a plurality of combustors for combustion of a fuel by mixing with air and in which the combustors are connected by a crossfire tube assembly.
There is a system called multi-can type gas turbine in which a plurality of can type gas turbine combustors (hereinafter referred to as combustors) are provided for one gas turbine. Normally, the multi-can type gas turbine has a plurality of combustors arranged in an annular pattern around the gas turbine, one or more of the combustors are provided with an ignitor, while the remainder of the combustors have no individual ignitor. For ignition of the combustor having no ignitor, a tubing that connects two combustors adjacent to each other in the gas turbine circumferential direction, called crossfire tube assembly, is used. At the time of starting the gas turbine, a fuel made to flow into the combustor, and the ignitor is started to ignite the combustor which is provided with the ignitor. In the combustor thus ignited, a combustion exhaust gas at a high temperature is generated, resulting in a pressure higher than those inside the adjacent unignited combustors. This pressure difference is utilized to cause the high-temperature combustion exhaust gas to flow into the unignited combustor through the crossfire tube assembly connecting the adjacent combustors, and the combustion exhaust gas serves as an ignition source, whereby the unignited combustor is also ignited. Thus, through the crossfire tube assembly, ignition successively proceeds from the combustor provided with the ignitor to the adjacent combustors, and, finally, ignition in all the combustors is completed. When ignition in all the combustors is completed and the pressure difference between the individual combustors is lost, the flow of the combustion exhaust gas through the crossfire tube assembly ceases.
In general, the crossfire tube assembly is composed of a double tube including an inner tube and an outer tube. The inner tube connects combustion chambers of the adjacent combustors, and plays the role of making the high-temperature combustion exhaust gas to flow in the inside of the combustion chambers, thereby effecting flame propagation. The outer tube is provided on the outer periphery side of the inner tube, and connects combustion air flow passages of the adjacent combustors. With the outer tube provided, the pressure difference between the inside and the outside of the inner tube is reduced, whereby the inner tube is protected.
The crossfire tube assembly is a component part needed for the ignition operation, and, at the time of ignition, the high-temperature combustion gas should be made to flow through the inner tube, thereby securely performing ignition. On the other hand, since the inner tube is exposed to the high-temperature combustion exhaust gas, investigation of prevention of thermal deformation or fire damage should be made. In an ideal situation, after the temporary flow of the high-temperature combustion exhaust gas through the inner tube at the time of ignition, the pressure difference between the combustors would be eliminated and the combustion exhaust gas would not flow through the inner tube. In practice, however, a slight Pressure difference may be generated between the adjacent combustors, and the combustion exhaust gas may continue to flow through the inner tube. Therefore, cooling of the inner tube should be investigated, in order that the heat of the combustion exhaust gas will not influence ignition.
In addition, an investigation for coping with assembleability and deformation at the time of connecting the crossfire tube assembly between the combustors should be made. In the multi-can type gas turbine, generally, the combustors are disposed around a compressor at an inclination relative to a driving shaft, for shortening the length of the driving shaft. The distance between the adjacent combustors is comparatively short, and the crossfire tube assembly should be disposed in a comparatively narrow space surrounded by partition walls of the adjacent combustors. Besides, during operation, the partition walls constituting the combustors undergo thermal expansion due to a rise in the temperature thereof. Therefore, the combustor not only moves in the driving shaft direction but also moves in the radial direction of the driving shaft, so that the adjacent combustors are spaced away from each other by thermal expansion. As a result, the crossfire tube assembly connecting the adjacent combustors is extended in the axial direction. Coping with the deformation, such as provision of the crossfire tube assembly with extensibility in the axial direction should be made.
The related art concerning the cooling, assembleability and deformation problems of the crossfire tube assembly is described, for example, in JP-1999-14056-A and U.S. Pat. No. 6,705,088. According to JP-1999-14056-A, for cooling of a crossfire tube assembly, an inner tube is provided with air holes, and combustion air flowing within an outer tube is made to flow through the air holes into the inner tube, so as to cool the inner tube. In addition, the patent document proposes a method in which the inner tube is divided to provide a fitting portion of a telescopic structure at an intermediate portion of the crossfire tube assembly, in an attempt to cope with assembleability and deformation. By providing the telescopic structure and thereby making the length of the crossfire tube assembly variable in the axial direction, assembleability onto the combustors is enhanced, and thermal deformation is coped with. U.S. Pat. No. 6,705,088 presents a method in which the fitting portion of the inner tube is provided with channels, and combustion air is made to flow through the channels into the inner tube, thereby accelerating cooling of the fitting portion.
As described in the prior art documents, as a method for facilitating connection of the crossfire tube assembly between the combustors and coping with deformation, there is the method in which the inner tube is divided and the fitting portion of a telescopic structure is provided. In this method, the inside diameter of the inner tube on one side is set slightly larger than the outside diameter of the inner tube on the other side, and the inner tubes are combined with each other. In this instance, the dimensional difference between the inner tubes provide a gap, whereby is possible to flexibly cope with extension of the inner tube and with bending stress. In addition, combustion air (hereinafter referred to air) is made to flow through the gap at the fitting portion, whereby the fitting portion can be cooled.
In regard of cooling of the fitting portion, ideally, it is desirable to dispose the two inner tubes at the fitting portion concentrically, to form an annular gap therebetween, thereby permitting air to flow evenly. By the flow of air, the fitting portion can be cooled evenly in the circumferential direction. In addition, after passing through the fitting portion, the air flows along the inner tube on the downstream side of the fitting portion, resulting in a state of so-called film cooling such as to Protect the partition wall of the inner tube from the high-temperature combustion exhaust gas which flows through a central portion of the inner tube. The film cooling is high in cooling efficiency, whereby a wide range of the inner tube can be cooled with a smaller quantity of air.
In practice, however, the gap in the fitting portion is not always formed in a concentric shape. In many cases, a part where the two inner tubes contact with each other is formed in the fitting portion, so that the gap in the fitting portion is nonuniform. At the part where the two inner tubes contact with each other and the gap is eliminated, air does not flow and, therefore, temperature rises. In addition, in the surroundings of the part, also, a region of slight gap (for example, a gap of less than 0.3 mm) spreads. At the part where the gap is slight, air flow velocity is lowered due to viscosity of air, so that the cooling effect of air is lowered. Therefore, the temperature of the inner tube rises in a wide range centering on the part where the two inner tubes contact with each other, and the possibility of thermal deformation or fire damage is raised.
Meanwhile, on the wall surface of the inner tube, air flow velocity is zero due to the viscosity of air, and flow velocity increases in going away from the wall surface. Therefore, in the vicinity of the wall surface, an air flow velocity difference is particularly enlarged, and disturbance of air is enlarged. In other words, air is disturbed more easily as the surface area of the wall surface of the air flow passage increases, or, in other words, air is disturbed more easily as the length of wall surface appearing on the air flow passage side in a section increases.
As a method for securing a gap at the fitting portion, U.S. Pat. No. 6,705,088 presents a method in which channels are provided on one side or both side of the inner tubes at the fitting portion. In the case of this method, a gap through which air flows is secured by the provision of the channels, but, since the length of the wall surface in the radial-direction section (or a section perpendicular to the axial direction) of the inner tube is increased due to the channels, disturbance of air is increased as compared to the case where the channels are absent. Although a cooling-promoting effect is expected due to the increased disturbance of air at the fitting portion, mixing of air with the high-temperature combustion exhaust gas is promoted due to the increased disturbance of air on the downstream side of the fitting portion. In other words, on the downstream side of the fitting portion, the effect of protecting the inner tube by the film cooling is reduced, and the temperature of the combustion exhaust gas is lowered. In addition, the method of providing the channels leads to complication of a flow passage structure and to a rise in processing cost.
Thus, there is a need to cool a crossfire tube assembly for gas turbine combustors and to lower the possibility of thermal deformation or fire damage, without lowering the temperature of a combustion exhaust gas passing through the crossfire tube assembly.
In accordance with an aspect of the present disclosure, there is provided a gas turbine combustor including: a plurality of combustors each including a Partition wall constituting a combustion chamber, and an outer peripheral partition wall provided at an outer Periphery of the partition wall and defining a combustion air flow passage between itself and the partition wall; and a crossfire tube assembly connecting adjacent ones of the plurality of combustors, the crossfire tube assembly including an inner tube that connects the partition walls of the adjacent combustors, and an outer tube that is provided at an outer periphery of the inner tube and connects the outer peripheral partition walls of the adjacent combustors, the inner tube being divided in an axial direction into a first inner tube member and a second inner tube member, an end portion of the second inner tube member on the first inner tube member side having an enlarged portion that has an inside diameter greater than an outside diameter of the first inner tube member, and the first inner tube member and the second inner tube member forming a fitting portion such that part of the first inner tube member is located on an inner periphery side of the enlarged portion of the second inner tube member with a gap therebetween. In the gas turbine combustor, a sectional shape in a radial direction of either an inner peripheral surface of the second inner tube member or an outer peripheral surface of the first inner tube member at the fitting portion has a plurality of small-curvature portions having a curvature smaller than a reference curvature, the reference curvature being a curvature of a portion at a maximum distance from a center of the sectional shape.
According to the described aspect of the present disclosure, mixing of air and the high-temperature combustion exhaust gas flowing through a central portion of the inner tube is restrained; therefore, a cooling effect on the downstream side of the fitting portion is enhanced, and the possibility of thermal deformation or fire damage of the inner tube of the crossfire tube assembly can be lowered.
Gas turbines as embodiments of the present disclosure will be described below, referring to the drawings. Note that in the following description, the same component parts will be denoted bY=the same reference characters, and descriptions thereof may be omitted.
A gas turbine according to a first embodiment of the present disclosure will be described referring to
In
In general, the combustors 3A and 3B are composed of a plurality of multi-can type gas turbine combustors located between the compressor 2 and the turbine 4 and disposed in an annular pattern around the compressor 2 or the driving shaft 6.
Note that while a case where the number of the combustors is two is shown in
The gas turbine 1 of
The role of the crossfire tube assembly 20 at the time of ignition of the combustor will be described below.
At the time of ignition of the gas turbine 1, a mixture of the fuel and air in the combustion chamber 11A is ignited by the ignitor 17 disposed in the combustor 3A. While the pressure inside the combustion chamber 11A relatively raised by the generation of the combustion exhaust gas, the pressure inside the combustion chamber 11B is relatively low because ignition is not performed there. Therefore, the combustion exhaust gas 16 at a high temperature is sent from the combustion chamber 11A into the combustion chamber 11B through the inner tube 21 (crossfire tube assembly 20) connecting the combustion chambers 11A and 11B. In the combustion chamber 11B, a mixture of the fuel and air is ignited by the high-temperature combustion exhaust gas 16 flowing into the combustion chamber 11B through the inner tube 21. In this way, the unignited combustor 3 adjacent to the ignited combustor 3 is sequentially ignited through the crossfire tube assembly 20 (inner tube 21), whereby all the combustors 3 can be ignited.
Where the combustors 3 are the same in air amount, fuel flow rate and pressure, there is no pressure difference between the combustors 3 when ignition has been finished in all the combustors 3. In this case, the flow of the high-temperature combustion exhaust gas 16 flowing through the inner tube 21 of the crossfire tube assembly 20 becomes absent, and the time for which the high-temperature combustion exhaust gas 16 flows through the inner tube 21 is limited to a short time at the time of ignition. In practice, however, there may be variability in air amount, fuel flow rate, pressure or combustion state from combustor 3 to combustor 3. In this case, the pressure difference between the adjacent combustors 3A and 3B causes the high-temperature combustion exhaust gas 16 to continue flowing through the inner tube 21. The inner tube 21 is heated by the flow therethrough of the high-temperature combustion exhaust gas 16, to a high temperature. If this state is continued due to long-time operation of the gas turbine, inner tube 21 is liable to be deformed or damaged, and, therefore, the inner tube 21 should be cooled.
As the structures for positioning of the inner tube 21, stoppers 31A and 31B for positioning belong to the inner tube members 21A and 21B, in the case of
In addition, along the circumferential direction of side surfaces of the inner tube members 21A and 21B, pluralities of air holes 33A and 33B for introducing part of the combustion air flowing through the annular space 26 into the space 25 inside the inner tube 21 are provided. In the example of
On the radially inner side of the inner tube members 21A and 21B from the positions where the air holes 33A and 33B are provided, guide rings 34A and 34B which are partition walls extending along inside surfaces of the inner tube members 21A and 21B are provided. The guide rings 34A and 34B are cylinders concentric with the inner tube members 21A and 21B, and define annular spaces 26 between themselves and the inner tubes 21. End portions on the combustion chamber 11A, 11B side of the guide rings 34A and 34B in the axial direction are closed ends continuous with the inside surfaces of the inner tube members 21A and 21B, and end portions on the other side are open ends fronting on inside space 25 of the inner tube members 21A and 21B.
With the air holes 33A and 33B thus provided, part of the combustion air stagnating in the annular space 26 inside the outer tube 22 of the crossfire tube assembly 20 flows into the space 25 inside the inner tubes 21 where the pressure is lower, and the partition walls of the inner tube members 21A and 21B can be cooled by this combustion air. In this instance, the combustion air having passed through the air holes 33 flows through the annular flow passages between the guide rings 34A and 34B and the inner tube members 21A and 21B as flows 35A and 35B toward the opening ends of the guide rings 34A and 34B, whereby transfer of heat from the flow 16 of the combustion exhaust gas to the inner tube members 21A and 21B is restrained, and a rise in the temperatures of the inner tube members 21A and 21B can be restrained. Such a cooling system is called film cooling, since the flows 35A and 35B of air are formed in a film (layer) form along the inner peripheral surfaces of the inner tubes 21.
In the first embodiment of the present disclosure, the first inner tube member 21A of the two inner tube members 21A and 21B is connected to the combustion chamber 11A on one side nearer to itself, while the second inner tube member 21B on the other side is similarly connected to the combustion chamber 11B on the other side, and end surfaces of the opposite sides of the inner tube members 21A and 21B form the fitting portion 40 at a substantially central portion between the two combustion chambers 11A and 11B. An end portion (the left end portion in
In the case of
The present embodiment proposes a method in which in the case of contact between the inner tube members 21A and 21B at the fitting portion 40, the fitting portion 40 and the partition wall (enlarged inside diameter portion 43) near the fitting portion 40 of the second inner tube member 21B are cooled, to reduce the possibility of thermal deformation or fire damage of the inner tube 21.
In the first embodiment of the present disclosure, a plurality of plain surface portions 46 extending in an axial direction are provided, in a circumferential direction, on an outer peripheral surface of the first inner tube member 21A, near the fitting portion 40.
With the first inner tube member 21A thin provided with the plain surface portions 46 as small-curvature portions, a gap 41 between the two inner tube members 21A and 21B combined with each other at the fitting portion 40 is one of mainly the three types depicted in
Note that as a reference example for permitting easy grasping of the general shape of the first inner tube member 21A, a perspective view of a first inner tube member 21 formed with eight plain surface portions 46 is shown in
In the present embodiment, when the two inner tube members 21A and 21B contact with each other at the fitting portion 40, the circular arc portion or portions 47 of the first inner tube member 21A on the inner side make contact with the inner periphery of the second inner tube member 21B on the outer side. In this instance, in the vicinity of the Part or parts where the two inner tube members 21A and 21B contact with each other, the plain surface portion 46 formed by cutting the outer peripheral surface of the first inner tube member 21A on the inner side is present, whereby a part or parts are formed where the thickness in the radial direction of the gap between the two inner tube members 21A and 21B is enlarged. The gap part or parts have a sufficient thickness (for example, equal to or more than 0.3 mm), and, therefore, a sufficient air flow velocity is secured, and the inner tubes 21 can be cooled. Thus, a part where a sufficient gap thickness is secured and air cooling progresses is present at a part or parts circumferentially adjacent to the range or ranges 44 where the air flow velocity is low. In addition, the circumferential length of the range or ranges 44 where the air flow velocity is low is reduced as compared to the related art example depicted in
—Operation and Effect—
An air flow passage (gap) formed at the fitting portion 40 by the two inner tube members 21A and 21B in the Present embodiment is an annular flow passage which is shaped to be circular on the outer periphery side and be a combination of circular arcs (circular arc portions 47) and plain surfaces (plain surface portions 46) on the inner Periphery side, and of which the thickness in the radial direction gradually varies along the circumferential direction. Here, the sum total of the length of an outer peripheral surface (wall surface) of the first inner tube member 21A and the length of an inner peripheral surface (wall surface) of the second inner tube member 21B, in the radial-direction section of the fitting portion 40, is defined as the “boundary length in section of the gap.” The length of the outer peripheral surface of the first inner tube member 21A in the present embodiment is shorter as compared to the case of the circle circumference according to the related art depicted in
In addition, in the case of the present embodiment, the two inner tube members 21A and 21B are in contact with each other with circular arcs. Therefore, as contrasted to the case where the channels are provided, both members 21A and 21B are not liable to bite each other due to contact or vibration, so that abrasion of them can be reduced.
The enlarged inside diameter portion 43 located in a region on the downstream side of the fitting portion 40 in regard of air flow direction keeps the shape of the inside diameter Db of the second inner tube member 21B equal to that at the fitting portion 40, whereby disturbance of flow 42 of air flowing from the fitting portion 40 into the inner tube 21 is restrained, and the film cooling effect of the combustion air flowing into the fitting portion 40 is made to be easily maintained to the downstream side.
In addition, with the enlarged inside diameter portion 43 provided, the two inner tube members 21A and 21B can slide relative to each other in the axial direction. Therefore, at the time of assembling the combustors 3A and 3B, it is possible, by pushing the first inner tube member 21A into the second inner tube member 21B, to temporarily shorten the whole length of the inner tube 21 in the axial direction, which leads to enhanced assembleability.
The axial length Lb of the enlarged inside diameter portion 43 on the downstream side of the fitting portion 40 is desirably equal to or more than 1.5 times the axial length L1 of the fitting portion 40. This is because it has been found from the experimental results obtained by the Present inventors that the distance over which the effect of film cooling is maintained is about 1.5 times the length L1. In addition, with the length Lb secured, cooling on the second inner tube member 21B side proceeds owing to the flow 42 of air at the fitting portion 40. Therefore, in the case where the inner tube 21 is provided with the air holes 35A and 35B in both end portions thereof, a rise in the temperature of the second inner tube member 21B can be restrained even where the length of the second inner tube member 21B is set larger than the length of the first inner tube member 21A. Accordingly, it is desirable that the length of the second inner tube member 21B is 1.1 to 1.5 times the length of the first inner tube member 21A.
Besides, the axial length La of the plain surface portions 46 of the first inner tube member 21A is preferably larger than the axial length L1 of the fitting portion 40. Such a configuration ensures that an entrance for the flow 42 of air into the fitting portion 40 can be secured on the first inner tube member 21A, and it is easy for air to enter the fitting portion 40. In addition, with the air flowing along the outer surface of the inner tube 21, it is made easy to restrain disturbance of combustion air, and to maintain the film cooling effect to the downstream side. For this reason, it is desirable that the length La of the plain surface portions 46 is equal to or more than 1.1 times the length L1 of the fitting portion 40.
In addition, when the first inner tube member 21A on the inner side of the fitting portion 40 is formed with the plain surface portions 46 such that the radial-direction section thereof is a combination of circular arcs and plain surfaces, the two inner tube members 21A and 21B are in contact with each other with circular arcs, in the case where the two members 21A and 21B become eccentric at the fitting portion 40. Therefore, both members 21A and 21B are not liable to bite each other due to contact or vibration, so that abrasion of them can be reduced.
In the gas turbine combustors and the gas turbine provided with the crossfire tube assembly 20 as above-mentioned, the possibility of thermal deformation or fire damage of the inner tube 21 of the crossfire tube assembly 20 can be effectively lowered. Besides, abrasion at the fitting portion can be reduced. Therefore, the possibility of unexpected trouble or inspection of the combustors is lowered, whereby reliability of operation can be enhanced, and a reduction in operation cost can be realized.
While the first inner tube member 21A has been provided with the plain surface portions 46 in the first embodiment, the second inner tube member 21B may be provided with similar plain surface portions. An example of such a case will be described as a second embodiment. Note that the second embodiment is the same as the first embodiment except for the shapes in the radial-direction section of the two inner tube members 21A and 21B in the surroundings of the fitting portion 40, and the description of the same points will be omitted.
In the present embodiment, when the two inner tube members 21A and 21B contact with each other at the fitting portion 40, the second inner tube member 21B on the outer side contacts the outer periphery of the first inner tube member 21A at the plain surface portions 51. In this instance, in the vicinity of the contact part, parts where the thickness in the radial direction of the gap is enlarged due to the provision of the plain surface portions 51 of the second inner tube member 21B on the outer side are formed. Since the gap parts have a sufficient thickness (for example, equal to or more than 0.3 mm), a sufficient air flow velocity can be secured, and cooling can be performed. Thus, parts where the thickness of the gap in the radial direction is sufficient and air cooling progresses are present in the vicinity of the range 44 where the air flow velocity is low. In addition, the range 44 where the air flow velocity is low is narrower as compared to the related art example shown in
—Operation and Effect—
The air flow passage (gap) defined at the fitting Portion 40 by the two inner tube members 21A and 21B in the present embodiment is an annular flow passage which is polygonal in sectional shape due to a combination of the circle on the inner periphery side and the plain surface (plain surface portions 51) and the circular arcs (circular arc portions 52) on the outer periphery side, and of which the thickness in the radial direction gradually varies in the circumferential direction. The “boundary length in section of the gap” is shorter than that in the case where the inner peripheral surface of the second inner tube member 21B is entirely composed of a circular arc, since part of the circular arc in the inner peripheral surface is made to be plain surfaces. Therefore, disturbance of air flowing through the air flow passage (gap) at the fitting portion 40 is smaller than in the case of the circular annular shape depicted in
In addition, in the case of the present embodiment, the two inner tube members 21A and 21B are in contact with each other with circular arcs. Therefore, as contrasted to the case where the channels are provided, both members 21A and 21B are not liable to bite each other due to contact or vibration, so that abrasion of them can be reduced.
The enlarged inside diameter portion 43 located in a region on the downstream side of the fitting portion 40 in regard of air flow direction keeps the shape of the inside diameter Db of the second inner tube member 21B equal to that at the fitting portion 40, whereby disturbance of the flow 42 of air flowing from the fitting portion 40 into the inner tube 21 is restrained, and the film cooling effect of the combustion air flowing into the fitting portion 40 made to be easily maintained to the downstream side. In addition, with the enlarged inside diameter portion 43 provided, it is ensured that at the time of assembling the two inner members 21A and 21B into the combustors 3A and 3B, the length of the inner tube 21 can be temporarily shortened, which leads to enhanced assembleability.
The axial length Lb of the enlarged inside diameter portion 43 on the downstream side of the fitting portion 40 is desirably equal to or more than 1.5 times the axial length L1 of the fitting portion 40. This is because it has been found from the experimental results obtained by the present inventors that the distance over which the effect of film cooling is maintained is about 1.5 times the length L1. In addition, with the length Lb secured, cooling on the second inner tube member 21B side proceeds owing to the flow 42 of air at the fitting portion 40. Therefore, in the case where the inner tube 21 is provided with the air holes 35A and 35B in both end portions thereof, a rise in the temperature of the second inner tube member 21B can be restrained even where the length of the second inner tube 21B is set larger than the length of the first inner tube member 21A. Accordingly, it is desirable that length of the second inner tube 21B is 1.1 to 1.5 times the length of the first inner tube member 21A.
In addition, unlike in the first embodiment in which an angular portion present at the boundary between the plain surface portion 46 and the circular arc portion 47 may contact with the inner peripheral surface of the second inner tube member 21B, it is ensured in the second embodiment that the curved surface of the first inner tube member 21A and the plain surface portion 51 of the second inner tube member 21B contact with each other, and, therefore, generation of abrasion can be reduced.
In the gas turbine combustors and the gas turbine provided with the crossfire tube assembly 20 as above-mentioned, the possibility of thermal deformation or fire damage of the inner tube 21 of the crossfire tube assembly 20 can be effectively lowered. Besides, abrasion at the fitting portion can be reduced. Therefore, the possibility of unexpected trouble or inspection of the combustors is lowered, whereby reliability of operation can be enhanced, and a reduction in operation cost can be realized.
While the inner tube members 21A and 21B have been formed such that the plain surface portions 46 and 51 being straight lines in sectional shape appear at the fitting portion 40 in the above two embodiments, the shape by which the same effect as in the above embodiments is not limited to a straight line. For example, explaining by use of
The first inner tube member 21A in
Note that while a case where the outer peripheral surface of the first inner tube member 21A is provided with the small-curvature portion 49a has been described in the present embodiment, the same effect as above can naturally be obtained by providing the inner peripheral surface of the second inner tube member 21B with the small-curvature portions 49a in place of the straight line portions 51.
In addition, while the sectional shape of the inner tube member having the plain surface portions 46 or 51 has been a roughly hexagonal shape (an octagonal shape in
Besides, in the first embodiment, the sectional shape of the tubular members may be composed of only the plain surface portions 46 by omitting the circular arc portions 47. This applies also to the second embodiment.
In addition, the present disclosure is not limited to the above-described embodiments, and includes various modifications within the scope of the gist thereof. For example, the present disclosure is not limited to a mode including all the configurations described in the above embodiments, and includes modes in which part of the configurations is omitted. Besides, part of the configuration according to an embodiment may be added to or be replaced by a configuration of other embodiment.
| Number | Date | Country | Kind |
|---|---|---|---|
| JP2017-215444 | Nov 2017 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 6705088 | Martling | Mar 2004 | B2 |
| 6834491 | Coppola | Dec 2004 | B2 |
| 8220246 | Widener | Jul 2012 | B2 |
| 8813502 | Ishiguro | Aug 2014 | B2 |
| 8959925 | Romig | Feb 2015 | B2 |
| 20030188537 | Martling et al. | Oct 2003 | A1 |
| Number | Date | Country |
|---|---|---|
| 3 225 917 | Oct 2017 | EP |
| 3 306 198 | Apr 2018 | EP |
| 11-14056 | Jan 1999 | JP |
| WO 0192787 | Dec 2001 | WO |
| WO 2016036377 | Mar 2016 | WO |
| Entry |
|---|
| Extended European Search Report issued in counterpart European Application No. 18204927.0 dated Feb. 4, 2019 (nine (9) pages). |
| Number | Date | Country | |
|---|---|---|---|
| 20190137106 A1 | May 2019 | US |
