Patent Publication Number: US-11378011-B2

Title: Decoupler assemblies for engine starter

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application is a continuation of U.S. patent application Ser. No. 15/595,371, filed May 15, 2017, and now allowed, which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     An aircraft engine, for example a gas turbine engine, is engaged in regular operation to an air turbine starter. The internal components of both the gas turbine engine and the air turbine starter spin together and can each include gearboxes allowing for step down or step up ratios between consecutive parts. To prevent back drive, an overrunning clutch is placed between the air turbine starter output shaft and the air turbine starter gearbox section. Back drive events can occur with an overrunning clutch failure in the engaged position, when the engine drives the output shaft of the air turbine starter resulting in over spinning a turbine rotor in the air turbine starter. In a back drive event, it can be desirable to decouple the air turbine starter from the gas turbine engine. 
     BRIEF DESCRIPTION 
     In one aspect, the present disclosure relates to an air turbine starter for starting an engine, comprising a housing defining an inlet, an outlet, and a flow path extending between the inlet and the outlet for communicating a flow of gas there through, a turbine member journaled within the housing and disposed within the flow path for rotatably extracting mechanical power from the flow of gas, a gear train drivingly coupled with the turbine member, a drive shaft operably coupled with the gear train and having ramped teeth on its output end, and a decoupler, comprising an output shaft having a first end with mating ramped teeth that are selectively operably coupled to the drive shaft and a second end configured to be operably coupled to and rotate with the engine, the ramped teeth allow for driving torque transfer from the drive shaft to the output shaft and the ramped teeth slide on each other when back driving torque is transmitted such that the output shaft is moved away from the drive shaft, and a connector having a body with a first and second end and extending between the output shaft and the drive shaft a magnetic coupling selectively linking the drive shaft to the output shaft via the connector, when driving torque is transmitted the connector is magnetically linked to one of the output shaft or the drive shaft via the magnetic coupling and when back driving torque is transmitted the connector is moved away from at least a portion of the magnetic coupling. 
     In another aspect the present disclosure relates to an air turbine starter for starting an engine, comprising a housing defining an inlet, an outlet, and a flow path extending between the inlet and the outlet for communicating a flow of gas there through, a turbine member journaled within the housing and disposed within the flow path for rotatably extracting mechanical power from the flow of gas, a gear train drivingly coupled with the turbine member, a drive shaft operably coupled with the gear train and having an output end, an intermediate connector having a body with a first end operably coupled to the output end of the drive shaft and a second end, opposite the first end, having ramped teeth, an output shaft having a first end with mating ramped teeth that are selectively operably coupled to the intermediate connector and a second end configured to be operably coupled to and rotate with the engine, the ramped teeth allow for driving torque transfer from the intermediate connector to the output shaft and the ramped teeth slide on each other when back driving torque is transmitted such that the intermediate connector is moved away from the output shaft, a connector having a first end coupled to the intermediate connector and a second end selectively operably coupled to the output shaft; and a magnetic coupling dipole mounted within the drive shaft and configured to magnetically couple with at least one of the intermediate connector or the connector. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  is a schematic isometric view of a turbine engine with an accessory gearbox and a starter in accordance with various aspects described herein. 
         FIG. 2  is an enlarged cross-sectional view of the starter of  FIG. 1  in accordance with various aspects described herein. 
         FIG. 3  is an isometric view of a portion of a decoupler assembly that can be utilized in the starter of  FIG. 2 . 
         FIG. 4  is a cross-sectional view of the decoupler assembly of  FIG. 3  in a first position. 
         FIG. 5  is a cross-sectional view of the decoupler assembly of  FIG. 4  in a second decoupled position. 
         FIG. 6  is a cross-sectional view of a decoupler assembly that can be utilized in the starter of  FIG. 2 , in a first position. 
         FIG. 7  is a cross-sectional view of the decoupler assembly of  FIG. 6  in a second decoupled position. 
         FIG. 8  is a cut away isometric view of a decoupler assembly that can be utilized in the starter of  FIG. 2 , in a first position. 
         FIG. 9  is an isometric view of a portion of the decoupler assembly from  FIG. 8 . 
         FIG. 10  is a cross-sectional view of the decoupler assembly of  FIG. 8  in a first position. 
         FIG. 11  is a cross-sectional view of the decoupler assembly of  FIG. 8  in a decoupled position. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The present disclosure is related to a driving mechanism generating kinetic motion in the form of a rotating shaft coupled with a piece of rotating equipment. One non-limiting example is coupling a starter containing more than one component onto an accessory gear box. The starter can have various applications including starting a gas turbine engine. While the examples described herein are directed to application of a turbine engine and a starter, the disclosure can be applied to any implementation of a driving mechanism that generates rotational motion at a driving output and provides the rotational motion to another piece of rotating equipment. 
     All directional references (e.g., radial, upper, lower, upward, downward, left, right, lateral, front, back, top, bottom, above, below, vertical, horizontal, clockwise, counterclockwise) are only used for identification purposes to aid the reader&#39;s understanding of the disclosure, and do not create limitations, particularly as to the position, orientation, or use thereof. Connection references (e.g., attached, coupled, connected, and joined) are to be construed broadly and can include intermediate members between a collection of elements and relative movement between elements unless otherwise indicated. As such, connection references do not necessarily infer that two elements are directly connected and in fixed relation to each other. The exemplary drawings are for purposes of illustration only and the dimensions, positions, order and relative sizes reflected in the drawings attached hereto can vary. 
     As used herein, the term “forward” or “upstream” refers to moving in a direction toward the engine inlet, or a component being relatively closer to the engine inlet as compared to another component. The term “aft” or “downstream” refers to a direction toward the rear or outlet of the engine relative to the engine centerline. Additionally, as used herein, the terms “radial” or “radially” refer to a dimension extending between a center longitudinal axis of the engine and an outer engine circumference. It should be further understood that “a set” can include any number of the respectively described elements, including only one element. 
     Referring to  FIG. 1 , a starter motor or air turbine starter  10  is coupled to an accessory gear box (AGB)  12 , also known as a transmission housing, and together are schematically illustrated as being mounted to a turbine engine  14  such as a gas turbine engine. This assembly is commonly referred to as an Integrated Starter/Generator Gearbox (ISGB). The turbine engine  14  comprises an air intake with a fan  16  that supplies air to a high pressure compression region  18 . The air intake with a fan  16  and the high pressure compression region collectively are known as the ‘cold section’ of the turbine engine  14  upstream of the combustion. The high pressure compression region  18  provides a combustion chamber  20  with high pressure air. In the combustion chamber, the high pressure air is mixed with fuel and combusted. The hot and pressurized combusted gas passes through a high pressure turbine region  22  and a low pressure turbine region  24  before exhausting from the turbine engine  14 . As the pressurized gases pass through the high pressure turbine (not shown) of the high pressure turbine region  22  and the low pressure turbine (not shown) of the low pressure turbine region  24 , the turbines extract rotational energy from the flow of the gases passing through the turbine engine  14 . The high pressure turbine of the high pressure turbine region  22  can be coupled to the compression mechanism (not shown) of the high pressure compression region  18  by way of a shaft to power the compression mechanism. The low pressure turbine can be coupled to the fan  16  of the air intake by way of a shaft to power the fan  16 . 
     The turbine engine can be a turbofan engine, such as a General Electric GEnx or CF6 series engine, commonly used in modern commercial and military aviation or it could be a variety of other known turbine engines such as a turboprop or turboshaft. The turbine engine can also have an afterburner that burns an additional amount of fuel downstream of the low pressure turbine region  24  to increase the velocity of the exhausted gases, and thereby increasing thrust. 
     The AGB  12  is coupled to the turbine engine  14  at either the high pressure or low pressure turbine region  22 ,  24  by way of a mechanical power take-off  26 . The mechanical power take-off  26  contains multiple gears and means for mechanical coupling of the AGB  12  to the turbine engine  14 . Under normal operating conditions, the power take-off  26  translates power from the turbine engine  14  to the AGB  12  to power accessories of the aircraft for example but not limited to fuel pumps, electrical systems, and cabin environment controls. The air turbine starter  10  can be mounted on the outside of either the air intake region containing the fan  16  or on the core near the high pressure compression region  18 . 
     Referring now to  FIG. 2 , the air turbine starter  10 , which can be mounted to the AGB  12  is shown in greater detail. Generally, the air turbine starter  10  includes a housing  30  defining an inlet  32 , an outlet  34 , and a flow path  36  extending between the inlet  32  and outlet  34  for communicating a flow of gas there through. In one non-limiting example the gas is air and is supplied from either a ground-operating air cart, an auxiliary power unit, or a cross-bleed start from an engine already operating. The air turbine starter  10  includes a turbine member  38  journaled within the housing  30  and disposed within the flow path  36  for rotatably extracting mechanical power from the flow of gas along the flow path  36 . A gear box  42  is mounted within the housing  30 . Further, a gear train  40 , disposed within the gear box  42  and drivingly coupled with the turbine member  38 , can be caused to rotate. 
     The gear train  40  includes a ring gear  46  and can further comprise any gear assembly including for example but not limited to a planetary gear assembly or a pinion gear assembly. A turbine shaft  50  couples the gear train  40  to the turbine member  38  allowing for the transfer of mechanical power to the gear train  40 . The turbine shaft  50  is coupled to the gear train  40  and rotatably supported by a pair of turbine bearings  52 . The gear train  40  is supported by a pair of carrier bearings  53 . The gear box interior  54  can contain a lubricant, including, but not limited to, a grease or oil to provide lubrication and cooling to mechanical parts contained therein such as the gear train  40 , ring gear  46 , and bearings  52 ,  53 . 
     There is an aperture  56  in the gear box  42  through which the turbine shaft  50  extends and meshes with a carrier shaft  58  to which a clutch  60  is mounted and supported by a pair of spaced bearings  62 . A drive shaft  64  extends from the gear box  42  and is coupled to the clutch  60  and additionally supported by the pair of spaced bearings  62 . The drive shaft  64  is driven by the gear train  40  and coupled to the AGB  12 , such that during a starting operation the drive shaft  64  provides a driving motion to the AGB  12 . 
     The clutch  60  can be any type of shaft interface portion that forms a single rotatable shaft  66  comprising the turbine shaft  50 , the carrier shaft  58 , and the drive shaft  64 . The shaft interface portion can be by any known method of coupling including, but not limited to, gears, splines, a clutch mechanism, or combinations thereof. An example of a shaft interface portion is disclosed in U.S. Pat. No. 4,281,942 to General Electric and is incorporated herein by reference in its entirety. 
     The starter  10  can be formed by any materials and methods, including, but not limited to, die-casting of high strength and lightweight metals such as aluminum, stainless steel, iron, or titanium. The housing  30  and the gear box  42  can be formed with a thickness sufficient to provide adequate mechanical rigidity without adding unnecessary weight to the air turbine starter  10  and, therefore, the aircraft. 
     The rotatable shaft  66  can be constructed by any materials and methods, including, but not limited to extrusion or machining of high strength metal alloys such as those containing aluminum, iron, nickel, chromium, titanium, tungsten, vanadium, or molybdenum. The diameter of the turbine shaft  50 , carrier shaft  58 , and drive shaft  64  can be fixed or vary along the length of the rotatable shaft  66 . The diameter can vary to accommodate different sizes, as well as rotor to stator spacing. 
     As described herein, air supplied along the flow path  36  rotates the turbine member  38  for driving the rotation of the rotating shafts  50 ,  58 ,  64 . Therefore during starting operations, the starter  10  can be the driving mechanism for the turbine engine  14  via rotation of the rotating shafts  50 ,  58 ,  64 . The non-driving mechanism, that is, the equipment being driven by the driving mechanism, can be understood as rotating equipment utilizing the rotational movement of the rotating shafts  50 ,  58 ,  64 , for example to generate electricity in the starter  10 . 
     The drive shaft  64  is further coupled to a decoupler assembly  70  including a back drive decoupler  72  having an output shaft  74 . The output shaft  74  is configured to be operably coupled to and rotate with the engine  14 . A connector  76  is coupled to the output shaft  74  and can extend into a magnetic coupling  78  of the drive shaft  64  to selectively couple the connector  76  to the drive shaft  64 . Further, the connector  76  can provide alignment between both the drive shaft  64  and output shaft  74 . 
     Turning to  FIG. 3 , the output shaft  74  is illustrated in more detail. A first end  79  includes a set of teeth  80 . Each tooth  80  includes a tooth portion  82  and a ramped portion  84 . The ramped portion  84  can be, in non-limiting examples, an inclined portion, an angled portion, or an otherwise oriented portion of the tooth  80  to enable engagement in one direction. While three teeth are illustrated, more or less teeth are contemplated. The teeth  80  circumscribe a cylindrical body  86  of the output shaft  74  at the first end  79 . The cylindrical body  86  has an interior  88  and terminates in a second end  90 . The second end  90  can include any type of coupling mechanism (not shown) to couple the output shaft  74  to the AGB  12 . The second end  90  can be of varying lengths depending on the AGB  12  to which it is coupled. 
     A blocking mechanism  92  can be provided at the first end  79  of the output shaft  74 . The blocking mechanism  92  can include a biasing mechanism  94  illustrated in an expanded position. The biasing mechanism  94  is illustrated, by way of non-limiting example, as a compressive spring  96 . While shown within the output shaft  74 , it is contemplated that the blocking mechanism can be provided on the drive shaft  64  where the first end  79  of the output shaft  74  meets the drive shaft  64 . 
       FIG. 4  further illustrates portions of the starter  10  with the decoupler assembly  70  in a first position  100  under normal driving conditions. It is more easily seen, that the drive shaft  64  terminates in a secondary shaft  102  having an output end  104  with complementary teeth  106  for mating with the teeth  80  of the output shaft  74 . While not illustrated, the teeth  106  are complementary such that they also include a tooth portion and a ramped portion. The compressive spring  96  illustrated in a retracted position is located within the output shaft  74  at the teeth  80 . The secondary shaft  102  further includes an interior  108  in which a sheath  110  is located. The sheath  110  is an open cylinder having an opening  111  through which the fuse  76  can slide. The sheath  110  can be a hollow cylinder made of a highly magnetic permeable material. The sheath  110  can be made of, for example but not limited to, cobalt-iron, copper, ferrite, ferritic stainless steel, or a permalloy. 
     The connector  76  has a body  112  extending to the interior  108  of the drive shaft  64  and through the interior  88  of the output shaft  74  via the opening  111  where the connector  76  terminates in a first end  114  coupled to the output shaft  74 . The connector  76  can be made of any magnetic material, by way of non-limiting example steel. The connector  76  is secured to the output shaft  74  mechanically at the first end  114 . The portion of the body  112  that is located within the interior  108  extends through the sheath  110  and beyond where the connector  76  terminates in a second end  116  that extends into the magnetic coupling  78 . 
     The magnetic coupling  78  includes a magnetic dipole  120  formed between, for 3example but not limited to, a collection of permanent magnets  122  and the connector  76 . The permanent magnets  122  are arranged circumferentially as magnetic rings around the connector  76  within the secondary shaft  102  of the drive shaft  64 . The connector  76  is selectively axially coupled to the drive shaft  64  with the magnetic coupling  78  by the magnetic dipole  120 . 
     A torque path illustrated with arrows  124  runs from the drive shaft  64  through the output end  104  with teeth  106 , and the teeth  80  of the output shaft  74 , through output shaft  74 , and finally continuing to the AGB  12  and engine  14 . The teeth  106  and the teeth  80  enable high torque transfer in one direction along the torque path  124 . Under normal operating conditions, the torque path  124  allows the drive shaft  64  to provide torque to the AGB  12  to start the engine  14 . 
     Turning to  FIG. 5 , in the event of a back drive condition where the torque path  125  reverses direction, the output end  104  at the drive shaft  64  and output shaft  74  rotates in an opposite direction. As they rotate in opposite directions, the teeth  106  of the drive shaft  64  and the teeth  80  of the output shaft  74  slip against each other due to the ramped portions  84  of the teeth  80 ,  106 . The teeth  80  slide over the teeth  106  causing the output shaft  74  to lift away from the drive shaft  64 . 
     As the connector  76  is coupled with the output shaft  74 , it also moves away from the drive shaft  64 , out of the magnetic coupling  78 , and into the sheath  110 . The sheath  110  redirects the magnetic field lines to break the magnetic dipole  120  between the connector  76  and the permanent magnets  122 . Upon breaking the magnetic dipole  120  the output shaft  74  is decoupled from the drive shaft  64 . When the output shaft  74  is lifted away from the drive shaft  64 , the biasing mechanism  94  moves from a retracted position ( FIG. 4 ) to an expanded position illustrated in  FIG. 5 . The compressive spring  96  expands to hold the output shaft  74  away from the drive shaft  64  after decoupling to prevent a possible recoupling. 
       FIG. 6  illustrates another exemplary decoupler assembly  170  that can be utilized in the starter  10 . The decoupler assembly  170  is similar in function to the decoupler assembly  70  illustrated in  FIG. 4 , therefore like parts will be identified with like numerals increased by 100. It should be understood that the description of the like parts of the decoupler assembly  70  applies to the other exemplary decoupler assembly  170  unless otherwise noted. 
     As with the previously described decoupler, the output shaft  174  terminates in a first end  179  having mating ramped teeth  180 . The teeth  180  circumscribe a cylindrical body  186  of the output shaft  174  at the first end  179 . One difference is that the cylindrical body  186  further includes a sheath  210  within an interior  188  of the output shaft  174 . The sheath  210  can be a hollow cylinder made of a highly magnetic permeable material. The sheath  210  can be made of, for example but not limited to, cobalt-iron, copper, ferrite, ferritic stainless steel, or a permalloy. Another difference is that a magnetic coupling  178  is formed from a collection of, by way of non-limiting example, permanent magnets  222  circumferentially arranged within the cylindrical body  186  and adjacent to the sheath  210 . 
     The drive shaft  164  terminates in a secondary shaft  202  having an output end  204  with complementary teeth  206  that can mate with the teeth  180  of the output shaft  174 . The secondary shaft  202  further includes an interior  208 . A connector  176  has a body  212  with a first end  214  and a second end  216 . The second end  216  is mechanically coupled to the drive shaft  164 . When the decoupler  170  is in the first position, the connector  176  extends from the drive shaft  164  through the interior  208  of the secondary shaft  202  and through the sheath  210  to terminate at the first end  214  within the magnetic coupling  178 . The magnetic coupling  178  includes a magnetic dipole  220  formed between the collection of permanent magnets  222  and the first end  214  of the connector  176 . In this manner, the connector  176  is selectively axially coupled to the output shaft  164  with the magnetic coupling  178  by the magnetic dipole  220 . 
     A torque path  224  runs from the drive shaft  164  through the teeth  206  and the mating ramped teeth  180  to the output shaft  174  continuing to the AGB  12  and engine  14 . Under normal operating conditions, the torque path  224  allows the drive shaft  164  to provide torque to the AGB  12  to start the engine  14 . 
     Turning to  FIG. 7 , similar to the decoupler assembly  70 , the decoupler assembly  170  enables the output shaft  174  to decouple from the drive shaft  164  in the event of a back drive condition. In the decoupler assembly  170 , the connector  176  is mechanically connected to the drive shaft  164  while the magnetic coupling is located in the output shaft  174 . During a back drive event, as the teeth  206  and  180  lift the output shaft  174  away from the drive shaft  164 , the connector  176  does not move. Rather, the magnetic coupling  178  and the sheath  210  move with the output shaft  174 . As the sheath  210  passes over the first end  214  of the connector  176  the magnetic dipole  220  between the connector  176  and the permanent magnets  222  is broken. This completely decouples the output shaft  174  from the drive shaft  164 . Again, a biasing mechanism  194  can be used to maintain separation. 
       FIG. 8  illustrates a cut away isometric view of another exemplary decoupler assembly  270 . The decoupler assembly  270  is similar in function to the decoupler assembly  70  illustrated in  FIG. 4 , therefore like parts will be identified with like numerals increased by 200. It should be understood that the description of the like parts of the decoupler assembly  70  applies to the other exemplary decoupler assembly  270  unless otherwise noted. 
     The decoupler assembly  270  includes a drive shaft  264  terminating in an output end  330 . A plurality of permanent magnets  322  are arranged circumferentially within an interior base  332  of the drive shaft  264  to form a magnetic coupling  278 . The drive shaft  264  further includes a spline coupler  345  in which spline features  334  can be received. 
     An output shaft  274  terminates in a first end  279  having teeth  280 . The teeth  280  circumscribe a cylindrical body  286  of the output shaft  274  at the first end  279  of the output shaft  274 . The first end  279  of the cylindrical body  286  is supported by a set of bearings  336  provided within a tip  338  of the drive shaft  264 . 
     A connector  276  has a body  312  with a first end  314  coupled to the output shaft  274  and a second end  316  coupled to an intermediate connector  340 . The connector  276  provides additional axial stability. The connector  276  in one non-limiting example is a tensile fuse. Portions of the output shaft  274  and intermediate connector  340  are located within an interior portion  308  of the output end  330  of the drive shaft  264 . 
     The intermediate connector  340  is illustrated in more detail in an isometric view of  FIG. 9  and it can more clearly be seen that the plurality of splines  344  circumscribe a base  348  of the connector  340 . A projection  346  defines the base  348  of the intermediate connector  340  upon which the plurality of splines  344  terminates. A face  304  having complementary teeth  306  for mating with the teeth  280  of the output shaft  274  is provided at an end  350  opposite the base  348  of the intermediate connector  340 . The intermediate connector  340  is coupled to the drive shaft  264  via the spline coupler  334  and plurality of splines  344 . The intermediate connector  340  extends towards the output shaft  274  terminating in the face  304  to be selectively coupled to the output shaft  274 . The intermediate connector  340  is made of a highly magnetic permeable material, for example but not limited to, cobalt-iron, copper, ferrite, ferritic stainless steel, or a permalloy. During normal operation, the projection  346  of the intermediate connector  340  limits axial movement of the intermediate connector  340  towards the output shaft  274 . 
     Turning to  FIG. 10 , the decoupler assembly  270  is illustrated in cross-section in a first position  300 . During normal operation, a torque path  324  runs from the drive shaft  264  through the intermediate connector  340 , the teeth  306  and the mating ramped teeth  280  to the output shaft  274  continuing to the AGB  12  and engine  14 . The teeth  306  of the intermediate connector  340  and output shaft  274  allow for high torque transfer in one direction and slipping in the other. Under normal operating conditions, the torque path  324  allows the drive shaft  164  to provide torque to the AGB  12  to start the engine  14 . 
     In a back drive event, the decoupler assembly  270  enables the output shaft  274  to decouple from the intermediate connector  340  as illustrated in  FIG. 11 . During back drive, when the torque path  324  reverses, the teeth  306  and the teeth  280  slide over each other, pushing the intermediate connector  340  further into the drive shaft  264  and away from output shaft  274 . As the intermediate connector  340  moves away from the output shaft  274  the connector  276  is configured to shear during the back driving and breaks allowing the intermediate connector  340  to move. The intermediate connector  340  moves within the permanent magnets  322 . A magnetic coupling dipole  320  is formed between the permanent magnets  322  and the intermediate connector  340 . The intermediate connector  340  is held by the magnetic coupling dipole  320  away from the output shaft  274  such that the output shaft  274  is allowed to spin freely and be decoupled from the drive shaft  264 . 
     Advantages associated with the decoupler assemblies described herein include minimizing the possibility of unintentional re-engagement of the output shaft. This includes preventing undesirable back driving of the starter for a turbine engine. By preventing back driving, wear to the parts described herein, in particular the drive shaft and output shaft decrease. Decreasing wear in turn increases the life of the parts. The decoupler assemblies as described herein enable lower maintenance cost and easy repair. 
     The connector can provide alignment between both the drive shaft and output shaft. The connector interfaces with the magnetic coupling dipole to offer axial connectivity. Utilizing magnetic dipoles and a connector helps to reduce any impulse associated with back driving. A reduction in impulse also Reduces vibrational noise at the starter which increases efficiency and overall performance. 
     Additionally with respect to the decoupler assembly including the intermediate connector, when restrictions of drive shaft axial movement towards the AGB occur, the intermediate connector can be placed in between the output shaft and drive connector. 
     To the extent not already described, the different features and structures of the various aspects can be used in combination with each other as desired. That one feature cannot be illustrated in all of the aspects is not meant to be construed that it cannot be, but is done for brevity of description. Thus, the various features of the different aspects can be mixed and matched as desired to form new examples, whether or not the new examples are expressly described. Moreover, while “a set of” various elements have been described, it will be understood that “a set” can include any number of the respective elements, including only one element. Combinations or permutations of features described herein are covered by this disclosure. Many other possible embodiments and configurations in addition to that shown in the above figures are contemplated by the present disclosure. Additionally, the design and placement of the various components such as starter, AGB, or components thereof can be rearranged such that a number of different in-line configurations could be realized. 
     This written description uses examples to disclose aspects, including the best mode, and also to enable any person skilled in the art to practice aspects of disclosure, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims, and can include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.