Abstract:
An active thrust management system varies pressure responsive to changes in rotor assembly thrust to maintain a desired position. The system includes a bearing supporting rotation of a rotor assembly within a pressurizing chamber. The rotor assembly is supported on a cushion of air generated between the bearing and the rotor assembly. Pressure within a cavity adjacent the rotor assembly opposes a thrust force to maintain a desired position of the rotor assembly. Modulating airflow into the pressurizing chamber adjacent the rotor assembly compensates for changes in the thrust generated by the rotor assembly to maintain the desired rotor assembly position.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention generally relates to a thrust bearing. More particularly, this invention relates to an active thrust bearing for a turbine engine.  
         [0002]     Machinery such as generators and compressors that operate at relatively high speeds require low friction bearing assemblies that produce little heat. Hydraulic and air bearings are often utilized for such applications and provide the desired low friction. A conventional air bearing assembly includes a bearing element that contacts and supports a rotating member at rest. A cushion of air formed between the bearing element and the rotating member lifts the bearing elements off of the rotating member such that the rotating member is rotating and supported on the cushion of air. The cushion of air supporting the rotating element provides minimal friction, and therefore produces minimal heat.  
         [0003]     Typically, the rotating member generates a thrust force that moves the rotating element from a desired position. Typically, the generator or compressor rotates at a fixed rotational speed such that the configuration of the air bearing can be designed to accommodate the thrust force and maintain the desired position of the rotating member. However, variations in thrust force that may result from operational mode changes or from changes in loading levels cannot be accommodated by the fixed configuration of the typical air bearing. Disadvantageously, such difficulties limit the use of air bearings to devices that operate at a fixed rotational speed and constant thrust force.  
         [0004]     For this reason is it desirable to develop a low friction bearing system capable of adapting to variation in thrust forces generated by a rotating member.  
       SUMMARY OF THE INVENTION  
       [0005]     This invention is an active bearing assembly for a turbine engine-producing variable thrust forces. The active bearing assembly varies a pressure responsive to changes in thrust that balances and maintains a desired position of a rotating member.  
         [0006]     The bearing assembly includes a plurality of bearing assemblies supporting rotation of a rotor assembly. A portion of the rotor assembly along with the bearing assemblies are disposed within a pressurizing chamber. A film of air between the bearing assemblies and the rotor assembly support rotation. Pressure within the chamber adjacent the rotor assembly opposes a thrust force generated by rotation of the rotor assembly. A fixed orifice generates a known flow rate out of the chamber. An airflow valve regulates airflow into the chamber to produce a desired pressure to counterbalance the thrust force exerted by the rotor assembly.  
         [0007]     Sensors disposed on either side of the rotor assembly provide position information that is utilized by a controller to adjust air pressure within the chamber to balance against the thrust force from the rotor assembly. Continuous adjustment of pressure within the chamber provides for countering of changing thrust force levels produced by the rotor assembly. Further, the controller actuates the airflow valve in anticipation of known thrust levels. Pressure within the chamber and adjacent the rotor assembly is raised to the anticipated level followed by fine adjustments made in view of position feedback from the sensors.  
         [0008]     The active thrust bearing assembly of this invention accommodates variable thrust by modulating pressure within a chamber in response to anticipated thrust levels and positional feedback information.  
         [0009]     These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a schematic view of a turbine engine with an example bearing assembly according to this invention.  
         [0011]      FIG. 2  is a schematic view of an example thrust bearing assembly. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0012]     Referring to  FIG. 1 , a gas turbine engine assembly  11  is schematically illustrated and includes a compressor  19  providing compressed air to a combustor  17 . Fuel mixes with compressed air within the combustor  17  and generates hot gases traveling at a high speed. The hot gases discharged from the combustor  17  drive a turbine  13 . A rotor assembly  12  supported both axially and radially by air bearing assemblies  10 A,  10 B driven by the turbine  13  drives the compressor  19 . The axial thrust bearing  10 A maintains a desired axial position of the rotor assembly. The radial thrust bearing  10 B maintains a desired radial position of the rotor assembly  12 . The operation of a gas turbine engine assembly  11  is well known, and the description of components and operation is by way of example only. Further, a worker versed in the art with the benefit of this disclosure will understand that other applications for the example bearing assemblies  10 A,  10 B are within the contemplation of this invention. The bearing arrangement shown is for example only. The bearing position and number of bearings is determined by requirements of the specific application.  
         [0013]     Referring to  FIG. 2 , a schematic view of the example air bearing assembly  10  is shown and includes the rotor assembly  12  supported for rotation within a chamber  14 . A first thrust bearing  16  and a second thrust bearing  18  are disposed within the chamber  14  to support rotation of the rotor assembly  12 . The first and second thrust bearings  16 , 18  are shown schematically. The thrust bearings  16 ,  18  are mounted within the chamber  14 . Further, although an air thrust bearing assembly  10 A is shown in the exemplary embodiment, a worker with the benefit of this disclosure would understand the application to other bearing assemblies.  
         [0014]     The chamber  14  and first and second thrust bearings  16 ,  18  are supplied with pressurized air from an air supply  20 . Seals  28  seal against the rotor assembly  12  to prevent air from escaping around the rotor assembly  12 . A small leakage airflow  40  escapes through the seals  28  at a known rate. The air supply  20  is preferably a regulated air supply to an air valve  21 . Further, use of alternate sources of air pressure such as engine compressor bleed air, are known and within the contemplation of this invention.  
         [0015]     The air valve  21  regulates air from the air supply  20  and is commanded by a controller  22  to produce a desired airflow  36  to the pressurizing chamber  15 . A first sensor  24  and a second sensor  26  communicate with the controller  22  to provide information on the position of the rotor assembly  12 . The example first and second sensors  24 ,  26  measure a distance between the rotor assembly  12  and a side of the chamber  14 . If the distances are equal than the rotor assembly  12  is in the desired position. A difference between measurement distances indicates a movement from the desired center position.  
         [0016]     At rest, the rotor assembly  12  is in contact with the first and second bearings  16 ,  18 . As the rotor assembly  12  begins to rotate a cushion of air builds along the surface of the rotor assembly  12  and between the bearing assemblies  16 ,  18 . The bearing assemblies  16 ,  18  lift off the rotor assembly  12  such that the rotor assembly  12  rotates on a cushion of air without contacting the bearing assemblies  16 ,  18 .  
         [0017]     Rotation of the rotor assembly  12  generates a thrust force  25  that drives the rotor assembly  12  away from a centered position within the chamber  14 . The chamber  14  includes a pressurizing chamber  15  adjacent one side of the rotor assembly  12 . Pressure within the pressurizing chamber  15  exerts a counter force  27  on the rotor assembly  12  opposing the thrust force  25  produced by the rotor assembly  12 . The combination of the thrust force  25  and the counter force  27  produce a resultant force  29  that provides the desired balance and position of the rotor assembly  12 .  
         [0018]     The rotor assembly  12  includes an orifice  34  in communication with the pressurizing chamber  15 . The orifice  34  is of a known size that produces a known flow for a given pressure. Air pressure within the pressurizing chamber  15  is maintained by balancing incoming airflow  36  against outgoing airflow  38 . The outgoing airflow  38  is exhausted from the pressurizing chamber  15  through the orifice  34 , and seals  28 . The size of the orifice  34  is determined according to application specific parameters. With a known size of the orifice  34  and known leakage  40 , the controller  22  can provide the volume of incoming airflow  36  required to provide the desired pressure within the pressurizing chamber  15  at any given time.  
         [0019]     In operation, the rotor assembly  12  begins rotating such that the bearings  16 ,  18  lift off of the rotor assembly  12 . Airflow  36  is regulated to provide a desired pressure within the pressurizing chamber  15  that maintains a desired position of the rotor assembly  12 . The pressure within the pressurizing chamber  15  is maintained by balancing incoming airflow  36  with outgoing airflow through the orifice  34  and leakage  40 . Greater incoming airflow  36  relative to outgoing airflow  38  and leakage  40 , produces an increase in pressure within the pressurizing chamber  15 . Reducing incoming air flow  36  relative to outgoing airflow  38  and leakage  40  reduces pressure within the pressurizing chamber  15 . The pressure within the pressurizing chamber  15  produces the desired counter force  27 .  
         [0020]     The rotor assembly  12  rotates at various speeds depending on the specific operating conditions. Variation of rotor assembly speed causes a variation in the thrust force  25  exerted by the rotor assembly  12  in a direction perpendicular to axial rotation. Increases in thrust force  25  moves the rotor assembly  12  toward the bearing  18 . Decreases in thrust force  25  without a corresponding decrease in counter force  27  produced within the pressurizing chamber  15  will result in movement of the rotor assembly  12  toward the bearing  16 . The controller  22  modulates the air valve  21  responding to measured movement of the rotor assembly  12  to adjust pressure with the pressurized chamber  15  and thereby the counter force  27  that maintains a desired position of the rotor assembly  12 .  
         [0021]     The first and second sensors  24 ,  26  communicate the position of the rotor assembly  12  to the controller  22 . The controller  22  utilizes the position information communicated from the sensors  22  to determine what pressure is required and if an increase or decrease in pressure within the pressurizing chamber  15  are required. The air valve  21  is modulated to produce the airflow  36  that results in the desired pressure within the pressurizing chamber  15 . A reduction in pressure in the pressurizing chamber  15  will result in movement of the rotor assembly  12  toward the bearing  18 , and an increase in pressure will result in movement toward the bearing  16 . The airflow  36  stabilizes as the rotor assembly  12  reaches the desired centered position.  
         [0022]     The example controller  22  uses a proportional plus integral plus differential control to determine the command signal to modulate the air valve  21 . The controller  22  is as known, and a worker versed in the art would understand how to program a commercially available microprocessor to provide the desired commands for the air valve  21 .  
         [0023]     The rotor assembly  12  generates a known thrust force  25  during known operating parameters; such as for example during start up. A schedule of thrust dynamics  42  is utilized by the controller  22  to anticipate the magnitude of the thrust force  25  for a known time. The schedule of thrust dynamics  42  correlates an operation time or sequence with a know magnitude of thrust force  25 . In the example schedule of thrust dynamics  42 , a thrust force  44  is provided relative to a time  46 . The controller  22  utilizes this known relationship for modulating the air valve  21  to provide pressure within the pressurizing chamber  15  that will produce the required counter force  29  that maintains the desired position of the rotor assembly  12 .  
         [0024]     The example schedule of thrust dynamics  42  relate thrust  44  to time  46 , however, other relationships affecting thrust force  25 , such as turbine engine load can be utilized to form a relationship providing for anticipation of the thrust force  25 . The anticipated counter force provided from the schedule of thrust dynamics  42  provides an initial setpoint and the sensors  26 ,  24  provide positional feed back to the controller  22 , such that the controller  22  can make further adjustments to airflow  36  required to maintain the rotor assembly  12  in the desired position.  
         [0025]     The example active bearing assembly  10  counters variable thrust forces to enable use of air bearing assemblies in variable thrust machines such as the example turbine engine assembly  11 .  
         [0026]     Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.