Abstract:
An air turbine starter for starting an engine includes a housing, and a flow path communicating a flow of gas therethrough; a turbine member; a clutch; and a decoupler device at least partially housed within the output member of the clutch. The decoupler device includes a first shaft portion coupled to and rotating with the output member and a second shaft portion coupled to and rotating with the engine. The first and second shaft portions are axially aligned and configured to engage each another for rotation in a first direction and to separate from each other in a second direction to decouple the output member of the clutch from the engine. The starter further includes a bearing between the inner surface of the output member and the second shaft portion for reducing friction between the second shaft portion and the inner surface of the output member when the first and second shaft portions are decoupled.

Description:
TECHNICAL FIELD 
       [0001]    The present invention generally relates to decoupler devices of air turbine starters capable of driving in one direction only, and decoupling in response to a specific torque load in the opposite direction. 
       BACKGROUND 
       [0002]    Air turbine starters are known in the aviation field, and are commonly used to start propulsion turbine engines of modern aircraft. A starter typically includes a clutch that overruns when the turbine engine achieves a certain operating speed. Such overrunning can occur continuously during operation of the turbine engine. In some instances, if problems with the clutch occur, the clutch may transmit reverse torque and backdrive the air turbine starter. To prevent undesirable backdriving of the starter by the turbine engine, a decoupler device is conventionally provided in the power train between the starter and turbine engine. 
         [0003]    Unfortunately, a conventional decoupler device may suffer from one or more shortcomings. The conventional decoupler device may be overly large or complex in its construction, can provide a possible source of malfunction or breakdown, may undesirably reset automatically to a torque transmitting condition after it is tripped by a reverse torque, and/or may require extensive time consuming disassembly to reset after being tripped by a reverse torque incident. Moreover, portions of the decoupler device may wear and overheat the starter during a decoupled condition. Overheating of the starter may result in the decoupler device failing to prevent backdriving of the starter. 
         [0004]    Accordingly, it is desirable to provide improved decoupler devices for use with air turbine starters. Additionally, it is desirable to provide decoupler devices that reduce wear between the decoupler device and other portions of the starter. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention. 
       BRIEF SUMMARY 
       [0005]    In accordance with an exemplary embodiment, an air turbine starter is provided for starting an engine. The starter includes a housing defining an inlet, an outlet, and a flow path extending between the inlet and the outlet for communicating a flow of gas therethrough; a turbine member journaled within the housing and disposed within the flow path for rotatably extracting mechanical power from the gas flow, a gear train drivingly coupled with the turbine member; a clutch coupled with the gear train and including an output member with an inner surface; and a decoupler device at least partially housed within the output member of the clutch. The decoupler device includes a first shaft portion coupled to and rotating with the output member and a second shaft portion coupled to and rotating with the engine. Each of the first and second portions has outer surfaces. The first and second shaft portions are axially aligned and configured to engage each another for rotation in a first direction and to separate from each other in a second direction to decouple the output member of the clutch from the engine. The starter further includes a bearing between the inner surface of the output member and the second shaft for reducing friction between the second shaft portion and the inner surface of the output member when the first and second shaft portions are decoupled. 
         [0006]    In accordance with another exemplary embodiment, a decoupler device is provided for decoupling an output member of a starter from an engine. The decoupler device includes a first shaft portion configured to be coupled to and rotate with the output member; a second shaft portion configured to be coupled to and rotate with the engine, the first and second shaft portions being axially aligned and configured to engage each another for rotation in a first direction and to separate from each other in a second direction to decouple the output member from the engine; and a bearing arranged between the output member and the second shaft portion for reducing friction between the second shaft portion and the output member when the first and second shaft portions are decoupled. 
         [0007]    In accordance with yet another exemplary embodiment, an air turbine starter is provided for starting an engine. The starter includes a housing defining an inlet, an outlet, and a flow path extending between the inlet and the outlet for communicating a flow of gas therethrough; a turbine member journaled within the housing and disposed within the flow path for rotatably extracting mechanical power from the gas flow; a gear train drivingly coupled with the turbine member; a clutch coupled with the gear train and including an output member having an inner surface; and a decoupler device at least partially housed within the output member of the clutch. The decoupler device includes a first shaft portion fixed to the output member and a second shaft portion coupled to the engine, with each of the first and second portions having an outer surface. The first and second shaft portions are axially aligned and configured to engage each another for rotation in a first direction and to separate from each other in a second direction to decouple the output member of the clutch from the engine. The starter further includes a bushing positioned between the outer surface of the second shaft portion and the inner surface of the output member of the clutch for reducing friction between the second shaft portion and the inner surface of the output member and to restrict dynamic movement of the second shaft portion when the first and second shaft portions are decoupled. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and 
           [0009]      FIG. 1  is a cross-sectional view of an air turbine starter that includes a decoupler device in accordance with an exemplary embodiment; 
           [0010]      FIG. 2  is an enlarged, partial cross-sectional view of the decoupler device of  FIG. 1 ; 
           [0011]      FIG. 3  is an enlarged, partial cross-sectional view of a starter with a decoupler device in accordance with an alternate embodiment; 
           [0012]      FIG. 4  is an enlarged, partial cross-sectional view of a starter with a decoupler device in accordance with another alternate embodiment; and 
           [0013]      FIG. 5  is an enlarged, partial cross-sectional view of a starter with a decoupler device in accordance with yet another alternate embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description. 
         [0015]    Broadly, exemplary embodiments described herein provide decoupler devices in starters for engines, typically for aircraft. The decoupler devices function to decouple the starter from the engine during a failure event. Particular exemplary embodiments provide a bearing structure that reduces wear between the decoupler device and other portions of the starter. The bearing structures can include, for example, wear coatings, bushings, ball bearings, and roller bearings. 
         [0016]      FIG. 1  depicts a cross-sectional view of an exemplary air turbine starter  10 . The air turbine starter  10  includes a housing  12  defining an inlet  16  and an outlet  14 . The housing  12  further defines a flow path  18  extending between the inlet  16  and the outlet  14 . An axial flow turbine member  20  is rotatably journaled by the housing  12  in the flow path  18  for extracting mechanical energy from a flow of pressurized fluid conducted between the inlet  16  and the outlet  14  via the flow path  18 . The turbine member  20  is coupled to a rotatable shaft member  22  journaled by bearings  24  carried by the housing  12 . A gear member  26  is coupled to the shaft member  22  and engages a speed-reducing gear train  28 . The gear train  28  is coupled to a clutch  36 , which includes an output member  38 . The clutch  36  can be a sprag clutch of the inner-race-overrunning type or a pawl and ratchet clutch. 
         [0017]    The output member  38  is coupled to a decoupler device  58 , which is then coupled to a combustion turbine engine (not shown) such that energy extracted by the turbine member  20  can be used to start the engine. As described in further detail below, the decoupler device  58  functions to decouple the air turbine starter  10  from the engine (not shown) during a failure condition. The decoupler device  58  drivingly connects with output member  38  via respective inter-engaging male and female spline surfaces, generally indicated at  60 . The decoupler device  58  also defines a male spline surface  62  by which the air turbine starter  10  couples in driving relation with a combustion turbine engine (not shown). 
         [0018]    Viewing now  FIG. 2  in conjunction with  FIG. 1 , the decoupler device  58  includes a first axial shaft portion  64  and an adjacent, second axial shaft portion  66 . The first axial shaft portion  64  defines the male spline surface  60  that couples with output member  38 , while the second shaft portion  66  defines spline surface  62  that couples with the engine. The shaft portions  64 ,  66  cooperatively define a stepped axial through bore  68 . 
         [0019]    An elongate tensile bar member  82  is positioned within the through bore  68 . The tensile bar member  82  includes a head portion  84  coupled to the first shaft portion  64  and an end portion  86  is coupled to the second shaft portion  66 . An annular disk member  90  is carried upon the end portion  86  to fasten the tensile bar member  82  to the shaft portion  66 . The tensile bar member  82  connects the shaft portions  64  and  66  with a spring load from spring  95 , and it will be noted that tensile bar member  82  includes a neck portion  102  with a reduced diameter, the function of which will be further described below. 
         [0020]    The shaft portions  64 ,  66  each include matching interengageable surfaces  104 ,  106 , respectively. The surfaces  104 ,  106  can include alternating ramp and driving surfaces. The surfaces  104 ,  106  are configured such that first relative torques urge these surfaces into contact and the shaft portions  64 ,  66  rotate together. On the other hand, the surfaces  104 ,  106  are configured such that second relative torques urge the surfaces  104 ,  106  apart and separate shaft portions  64 ,  66 , as is depicted by arrow  108 . In other words, the surfaces  104 ,  106  of the shaft portions  64 ,  66  are configured to rotate together in a first direction, but to separate when the relative torques attempt to rotate the shaft portions  64 ,  66  in the opposite direction. 
         [0021]    Having described the structure of the air turbine starter  10 , attention may now be given to its operation. During a normal start cycle of a combustion turbine engine with both the air turbine starter  10  and the engine being stationary, a supply of pressurized fluid is connected to the inlet  16  of the air turbine starter  10 . Viewing  FIG. 1 , it will be seen that a flow of pressurized fluid through the housing  12  via the flow path  18  will cause the turbine member  20  to extract mechanical power there from and to deliver this power to the output member  38  of the clutch  32  via the gear train  28 . The output member  38  drivingly connects with the first shaft portion  64  of the decoupled device  58 . Engine starting torque applied to the first shaft portion  64  urges the surfaces  104 ,  106  of the shaft portions  64 ,  66  into engagement with each other such that the second shaft portion  66  conveys the engine starting power to the turbine engine substantially without axial force within the decoupler device  58 . Accordingly, the air turbine starter  10  delivers mechanical power to the decoupler device  58  thereof, and to the combustion turbine engine connected thereto, to accelerate the latter towards its self-sustaining speed. 
         [0022]    Upon the combustion turbine engine obtaining its self-sustaining speed, the supply of pressurized air to flow path  18  is shut off and the shaft of the engine will accelerate ahead of the output member  38  of the air turbine starter  10 . Consequently, torque loading within the clutch  36  will be eliminated, and the starter  10  overruns with respect to the engine. As a result, the turbine and drive train sections of the air turbine starter  10  coasts to a stop and remains stopped during operation of the turbine engine. The output section of the clutch  36  of the starter  10  continues overrunning as long as the engine operates. 
         [0023]    Certain events may cause a physical malfunction in the air turbine starter  10 . For example, one or more of the sprags of clutch  36  flips over center such that the turbine engine back drives the air turbine starter  10  to a high and destructive speed, or alternatively, one of the bearings  40  could fail and seize so that a high resisting torque load becomes imposed on the turbine engine. During these types of events, the decoupler device  58  can function to prevent further damage. Viewing  FIG. 2 , it will be seen that reverse torque applied to the shaft portion  66  urges the surfaces  104 ,  106  apart to result in an axial separation  108  between the shaft portions  64 ,  66 . Thereafter, further increased reverse torque can be transmitted from the second shaft portion  66  to the first shaft portion  64  only with the development of a directly related torsion force imposed on tensile bar member  82 . The neck portion  102  of tensile bar member  82  is sized such that the member  82  will fail in torsion at a predetermined stress level. That is, the tensile bar member  82  fractures at the neck portion  102  when a predetermined level of reverse torque is imposed upon decoupler device  58 . 
         [0024]    As a result of the tensile bar member  82  fracturing at the neck portion  102 , the shaft portions  64 ,  66  are allowed to rotate relative to one another in response to the reverse torque. The surfaces  104 ,  106  may additionally move the shaft portion  64  leftwardly in the view of  FIG. 2  and/or the shaft portion  66  rightwardly in the view of  FIG. 2 . In this position, the surfaces  104 ,  106  are disengaged from one another. As a result of the disengagement of the shaft portions  64 ,  66 , the first shaft portion  64  and output member  38  of the clutch  36  are no longer driven by the second shaft portion  66 , and the second shaft portion  66  rotates relative to the first shaft portion  64  and the output member  38 . 
         [0025]    One or more bearing structures can be provided to reduce wear between the second shaft portion  66  and the output member  38 . For example, in the embodiment of  FIG. 2 , a wear coating  150  is provided between the second shaft portion  66  and the output member  38 . The coating  150  can be provided on the some or all of the outer surfaces of the second shaft portion  66 , some or all of the inner surfaces of output member  38 , and/or some or all of both the outer surfaces of the second shaft portion  66  and the inner surfaces of the output member  38 . The coating  150  can be, for example, a tungsten-cobalt carbide coating, or any other coating suitable to reduce wear between the shaft portion  66  and the output member  38 . The coating  150  can have a thickness of, for example, 0.005-0.01 inches, although other thicknesses can be provided based on materials of the second shaft portion  66  and the output member  38 , starter conditions, and/or desired level of wear reduction or prevention. 
         [0026]      FIG. 3  is an enlarged cross-sectional view of a starter with a decoupler device  258  in accordance with an alternate exemplary embodiment from the decoupler device  58  of  FIG. 2 . In this embodiment, a bushing  250  is provided to reduce or prevent wear between the second shaft portion  266  and the output member  238 . The bushing  250  can be a cylindrically shaped sleeve or tube that can be mounted on the inner diameter of the output member  238  or the outer diameter of the shaft  266 . The bushing  250  can have a thickness of about 0.080 inches, although other thickness and shapes can be provided. The bushing  250  may also serve to constrain or restrict the dynamic movement of the second shaft portion  266 . 
         [0027]      FIG. 4  is an enlarged cross-sectional view of a starter with a decoupler device  358  in accordance with another alternate exemplary embodiment. In this embodiment, a ball bearing  350  is mounted between the second shaft portion  366  and the output member  338  to reduce or prevent wear. A housing element  351  can be provided to house the ball bearing  350 . The ball bearing  350  includes balls  352  and bearing rings  354 . The ball bearing  350  may also support both axial and radial dynamic and static loads between the second shaft portion  366  and the output member  338 . The ball bearing  350  can be manufactured from materials such as AISI52100 or AISI440C. 
         [0028]      FIG. 5  is an enlarged cross-sectional view of a starter with a decoupler device  458  in accordance with yet another alternate exemplary embodiment. In this embodiment, a roller bearing  450  is mounted between the second shaft portion  466  and the output member  438  to reduce or prevent wear. A thrust washer  475  is located between shaft portion  466  and bearing  450 . The roller bearing  450  includes rollers  452  and ring  454 . The roller bearing  450  in combination with the thrust washer  475  may also support both axial and radial dynamic and static loads between the second shaft portion  466  and the output member  438 . The roller bearing  450  can be manufactured from materials such as AISI52100, AISI440C or AISI1020. 
         [0029]    While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims.