Abstract:
Method and apparatus for controlling sump pressurization in a gas turbine bearing sump by controllably restricting or actively venting air flow from said sump cavity to maintain a continuous air flow from said sump cavity through a sump vent in all operating conditions.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates generally to gas turbine engines, and, more particularly, to control of air pressure within a bearing oil sump during all operating conditions.  
         [0002]     A gas turbine engine typically includes at least one bearing assembly that supports a rotatable shaft. Each bearing assembly is housed within a sump to which lubricating oil is supplied from a supply pump and from which lubricating oil is scavenged and passed through an oil/air separator and a heat exchange system for cleaning and cooling before being returned to the lubricating oil supply system. To control oil leakage from the sump, some gas turbine engines employ bearing sumps housed within pressurized cavities sealed with circumferential labyrinth seals and supplied with air under pressure to minimize oil leakage. Certain aero-derivative gas turbine engines, such as the LMS100, sold by the assignee of this case, require vent sump pressure control to prevent escape of lubricating oil from an oil sump and to prevent oil consumption when operating at high power and corresponding high inlet pressure.  
         [0003]     In some prior art gas turbine engines, as shown, for example, in U.S. Pat. No. 6,470,666 B1, issued Oct. 29, 2002 to Przytulski et al. and assigned to the assignee of the present case, a sump evacuation system is employed to lower air pressure inside a sump pressurization cavity to prevent oil leakage during low power or idle operation. As the power levels of gas turbines has been raised, a system to control oil leakage at high power is needed.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0004]     Method and apparatus for controlling sump pressurization in a gas turbine bearing sump by controllably restricting or actively venting air flow from said sump cavity to maintain a continuous air flow from said sump cavity through a sump vent in all operating conditions. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]      FIG. 1  is a schematic illustration of an exemplary gas turbine engine having a sump evacuation system;  
         [0006]      FIG. 2  is a schematic illustration of an exemplary sump evacuation apparatus;  
         [0007]      FIG. 3  is a schematic cross-sectional view of an exemplary sump vent pressure control system for a gas turbine engine;  
         [0008]      FIG. 4  is a schematic, enlarged, cross-sectional view of one exemplary bearing sump incorporating a vent pressure control system;  
         [0009]      FIG. 5  is a schematic, enlarged, cross-sectional view of a second exemplary bearing sump incorporating a vent pressure control scheme;  
         [0010]      FIG. 6  is a block diagram illustration of a first exemplary operation of a sump vent pressure control system; and  
         [0011]      FIG. 7  is a block diagram illustration of a second exemplary operation of a sump vent pressure control system. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]      FIG. 1  is a schematic illustration of a gas turbine engine  10 , including a low pressure compressor  12 , a high pressure compressor  14 , a combustor  16 , a high pressure turbine  18 , and a low pressure turbine  20 . Low pressure compressor  12  is connected to low pressure turbine  20  by a first shaft  24 , and high pressure compressor  14  is connected to high pressure turbine  18  by a second shaft  22 . A plurality of bearing assemblies rotatably support first shaft  24  and second shaft  22  for concentric rotation around longitudinal axis  26 . Each bearing assembly is contained within an oil sump. Controlling air pressure within each oil sump aids in maintaining adequate bearing lubrication during all rotational speeds, from sub-idle to maximum power. “Idle” is defined as the lowest rotational operating speed range at which a gas turbine engine operates in a stable mode. For example, “idle” speed for the LMS100 engine is a rotational speed in the range between approximately 6000 and 7000 rpm and in other gas turbine engines may range between about 2500 and 6500 rpm. “Sub-idle” is an engine rotational speed below idle or below the minimum rotational speed at which the engine can sustain stable operation on its own and requires a starter motor to maintain rotation, used for example, for cooling the engine and for engine check out before ignition. Maximum power is the highest speed and highest power output, in the LMS100 approximately 10,400 to 10,600 rpm. Each oil sump is vented via a respective sump vent tube  34 ,  36  and  38 , via air tubes  40  and  42 , controlled by respective adjustable valves  35 ,  37 ,  39  connecting respective oil sumps to a pressure control system  30  driven by a gear box  32 . Each of valves  35 ,  37  and  39  may be individually activated to a setting appropriate to provide control of air flow through respective sump vent tubes  34 ,  36  and  38  and minimize oil consumption.  
         [0013]      FIG. 2  is a schematic illustration of a sump evacuation system  90  used with lubrication system  28 , including a sump oil cavity  44  pressurized by air flow from an oil pressurization cavity  80 . Cavity sump vent  70  is connected by vent tube  82  to intake  95  of air/oil separator  92  driven by an accessory drive or gear box  32 . Air/oil separator  92  receives a mixture of air and entrained lubricating oil from each sump oil cavity  44 . Separator exhaust  96  is coupled to intake  98  of blower  94  via pipe  93  incorporating adjustable valve  91 . Blower  94  exhausts air at output  100  to a vent system  102 , which may be incorporated into the engine exhaust gas flow. As described in more detail hereinafter, during idle or sub-idle operation, adjustable valve  91  is set to its open position and blower  94  is turned on to maintain a positive pressure on labyrinth seals to minimize oil leakage. During powered operation above idle rotational speed, including maximum power operation, adjustable valve  91  is set to a partially closed position and blower  94  is turned off to allow air flow into the air/oil separator  92  to be driven by pressurized air flow.  
         [0014]      FIGS. 3, 4  and  5  schematically illustrate an exemplary bearing assembly sump vent pressure control system. Bearing assemblies  110 ,  120  and  130  rotatably support rotor shaft  141 . Booster output  54  is connected in flow communication through passages within strut  134  and opening  135  with air cavity  140  which is connected through opening  136  and duct  142  to sump pressurization cavity  138 . Sump pressurization cavity  138  is in flow communication with a sump cavity chamber  114  via labyrinth seal  146  and is sealed by labyrinth seal  148  to minimize oil consumption by leakage, shown by arrow  149 , into engine interior cavity  150  exterior to sump pressurization cavity  138 . Bearing assembly  110  is surrounded by a sump cavity  112  comprising sump cavity chamber  114  in flow communication through opening  115  with sump cavity chamber  116  which is also in flow communication through opening  117  with sump cavity chamber  118 . Bearing assembly  120  is surrounded by a sump cavity  122  comprising sump cavity chambers  118  and  124  in flow communication through opening  152  through chamber wall  154 , as shown enlarged in  FIG. 4 . Bearing assembly  130  is surrounded by a sump cavity  132 , comprising sump cavity chambers  126  and  128  in flow communication through opening  184  through housing wall  186 , as shown enlarged in  FIG. 5 . Booster air flow passages through strut  134  are in flow communication through opening  162  with air cavity  160  and through opening  164  with sump pressurization cavity  166 . Sump pressurization cavity  166  is sealed from leakage into engine turbine interior cavity  168  as shown by arrow  165  by labyrinth seal  170  and is connected in flow communication with sump cavity chamber  128  through labyrinth seal  172 . Sump pressurization cavity  166  supplies pressurized air as shown by arrow  177  through opening  178  into sump pressurization cavity  180  which directs pressurized air flow to labyrinth seal  176 , as shown by arrow  182 .  
         [0015]     During engine operation above idle, sump cavity  112  is pressurized by compressed air from engine booster output  54  supplied through passages within strut  134  through opening  135 , shown by arrow  133 , into air cavity  140 , and through opening  136 , shown by arrow  137 , and duct  142  along the sump wall  144  of forward sump cavity chamber  116  and air cavity  140  into sump pressurization cavity  138 , as shown by arrow  145 . Compressed air flows through labyrinth seal  146 , as shown by arrow  147 , into sump cavity chamber  114 , into sump cavity chamber  116  through opening  115 , as shown by arrow  113 , and through opening  117  into sump cavity chamber  118 , as shown by arrow  119 .  
         [0016]     Sump cavity  122  is pressurized by the air flow into sump cavity chamber  118  and via opening  152  through chamber wall  154 , as shown by arrow  151 , into sump cavity chamber  124 . Pressurized air flow through sump pressurization cavity  180  as shown by arrow  182  also enters sump cavity chamber  124  through labyrinth seal  176 , as shown by arrow  179 , as shown in  FIG. 4 .  
         [0017]     Booster air flow, shown by arrow  55 , through passages within strut  134  through opening  162  as shown by arrow  161  pressurizes air cavity  160  and through opening  164 , as shown by arrow  188 , pressurizes sump pressurization cavity  166 . Air flow from sump pressurization cavity  166  provides pressurized air to sump cavity chamber  128  through labyrinth seal  172 , as shown by arrow  174 , as shown in  FIG. 5 . Sump pressurization cavity  166  supplies pressurized air as shown by arrow  177  through opening  178  via sump pressurization cavity  180  which is connected in flow communication with sump cavity chamber  124  via labyrinth seal  176 , as shown by arrow  179 , and through opening  184  as shown by arrow  190  into sump cavity chamber  126 . Sump cavity chamber  126  is vented to sump cavity chamber  124  as shown by arrow  192 .  
         [0018]     Air flow from interconnected sump cavities  112  and  122  along the path shown by arrows  113 ,  119  and  151  into sump cavity chamber  124  and from sump cavity  132  shown by arrow  192  into sump cavity chamber  124  connects the sump cavities  112 ,  122  and  132  to sump pressure control system through sump vent tube  200  in flow communication with a sump air evacuation system as shown in  FIG. 2 .  
         [0019]      FIG. 6  illustrates in block diagram form the active control scheme used to control pressurization of the sump cavities  112 ,  122 ,  132  in order to avoid oil consumption, during all above idle rotational speeds. Air pressure provided by air flow from booster  54  raises air pressure within sump pressurization cavities  138 ,  166  and  180 , and will force a mixture of air with entrained oil to flow through sump cavities  112 ,  122  and  132  to sump cavity chamber  124  and sump vent tube  200  to the air/oil separator  92 . Air/oil separator  92  removes oil from the mixture and returns it to oil tank  86  and oil sump cavities  112 ,  122  and  132 . Pressure inside the sump cavities  112 ,  122 , and  132  will typically be between 18 and 24 psia (pounds per square inch absolute) at maximum power driven by air flow through labyrinth seals  146 ,  176  and  172 , which would be pressurized to approximately 42 psia in sump pressurization cavity  138  and 33 psia in sump pressurization cavities  166  and  180 , as shown in  FIG. 6 . These increased air pressures may tend to accelerate air flow through sump cavities  112 ,  122  and  132  and increase the quantity of entrained oil flowing to air/oil separator  92 . Avoiding excessive oil consumption would require a large capacity air/oil separator and oil tank adding significant size and weight to the engine system. To control the air flow to the air/oil separator  92  adjustable valve  91  is set to a partially closed position and blower  94  is turned off. This holds air pressure within sump cavity chamber  124  at approximately 24.7 psi guage and restricts air and oil flow to an quantity which can be readily processed by air/oil separator  92  to remove oil and deposit it into oil tank  86  for recirculation to bearing assemblies  110 ,  120  and  130 .  
         [0020]      FIG. 7  illustrates in block diagram form the active control scheme used to control pressurization of the sump cavities  112 ,  122 ,  132  when a gas turbine engine is operating at idle or sub-idle. Air pressure within sump pressurization cavities  138 ,  166  and  180  is approximately atmospheric pressure as shown and is inadequate to maintain continuous flow from the sump cavities  112 ,  122 ,  132  through sump vent tube  200  to air/oil separator  92 . In order to maintain minimum necessary air flow through labyrinth seals  146 ,  176  and  172 , in idle or sub-idle operation adjustable valve  91  is set to a fully open position and blower  94  is turned on. Blower  94  draws air flow through the vent tube to lower pressure inside the sump cavities  112 ,  122 , and  132  to approximately 14.0 psi. and draw an air-oil mixture to the air/oil separator  92  which removes the oil from the mixture which is returned to the oil sump cavities  112 ,  122  and  132  through oil tank  86 .  
         [0021]      FIGS. 3, 6  and  7  illustrate schematically a system having three sump cavities  112 ,  122 , and  132 , but it is to be understood that the oil sump pressurization system described can be employed to control pressurization of a single sump cavity surrounding a single bearing assembly or a large number of bearing assemblies, or can be used with a plurality of separate vent tubes including a separately controlled valves connected individually to separate bearing assemblies, so that each may be individually controlled.,  FIG. 1  illustrates an sump lubrication system in which air flow through sump vent tubes  34 ,  36  and  38  is separately controlled by respective adjustable valves  35 ,  37  and  39 . Each of adjustable valves  35 ,  37  and  39  may be set to a unique setting to restrict flow in each respective sump vent tube  34 ,  36  and  38  at a separate flow rate from the other flow tubes to allow a predetermined air flow through the respective sump vent tubes  34 ,  36  and  38  to maintain oil/air flow into the air/oil separator during all operating conditions. Certain operating conditions may require that one of the adjustable valves  35 ,  37  or  39  be set to a restricted flow setting with the blower turned off, while allowing another adjustable valve to be set at its fully open position with its blower turned on. The flexibility of pressure control provided by the controllable blower and valve combination to each bearing assembly or combination of bearing assemblies offers maximum protection to the bearing assembly lubrication system.  
         [0022]     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.