Abstract:
A journal bearing provides lubrication to planetary gears during windmilling operation of a fan section. A primary oil pump provides oil from an oil supply during driven operation of the fan and a secondary oil pump driven by a generator provides oil during windmilling operation of the fan. The generator acts as a dynamic brake when the aircraft is grounded to prevent windmilling. A switch selects between the primary and secondary oil pump and controls the brake application.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to an arrangement for protecting journal bearings of the fan drive systems for turbofan engines by preventing undesired rotation and supplying oil to the journal bearings during rotation. 
     Turbofan engines include fan sections driven by planetary gear systems. Journal bearings in the systems reduce friction between planetary gears and corresponding support shafts. An oil system supplies oil to lubricate each of the journal bearings. An oil pump maintains pressure within the oil system to ensure each of the journal bearings receives an adequate supply of oil. 
     Turbofan engines may be used to propel a multi-engine aircraft. In such an aircraft, one of the turbofan engines may shut-down during flight if a fault condition occurs. The oil pump also shuts down when the turbofan engine is not operating. Although the turbofan engine is shut down, airflow through the moving engine may continue to rotate (i.e., windmill) the fan section of the turbofan engine. Without some oil supply, the journal bearings may seize and harm the turbofan engine or prevent operation of the turbofan engine. Preventing windmilling while the aircraft is in the air causes drag as the stationary fan section impedes airflow through the turbofan engine. 
     When the aircraft is on the ground, airflow through the turbofan engine may cause the fan section to windmill. Without some oil supply while windmilling, the journal bearings may seize and harm the turbofan engine. 
     Accordingly, it is desirable to provide an arrangement for lubricating journal bearings when the fan section is windmilling during flight, and to prevent the fan section from windmilling when an aircraft is not in flight. 
     SUMMARY OF THE INVENTION 
     An example system provides an arrangement for preventing undesired rotation of the fan section of a turbofan engine and for supplying oil to the journal bearings during rotation of the fan section as a result of windmilling. 
     During engine operation, a fan section for a turbofan engine is driven by a fan drive system that includes a planetary gear system. An oil supply system supplies oil to lubricate the planetary gear system. When the engine in not operating, wind passing over the fan can cause the fan to rotate (i.e., windmill) even though the fan is not being driven by the fan drive system. 
     The engine includes a three-way switch controlled by an engine control system. The engine control system senses the engine status and the altitude of the aircraft to determine the desired switch position. When the engine is operating and the fan is being driven the switch maintains an “open” position. The oil supply system includes a primary oil pump, which provides oil from an oil supply during driven operation of the fan. 
     The switch is located between the engine control system and a generator for operating a secondary oil pump. When the engine control system senses an engine shut-down during flight, the switch moves to activate the generator and power the secondary oil pump. The secondary oil pump supplies oil that protects the journal bearings if the fan section begins to windmill. 
     If the engine is shut down and the engine control system senses that the aircraft is on the ground, the switch is set to apply a brake to prevent rotation of the fan. Specifically, the engine control system moves the switch to short the generator, and to provide a dynamic brake. Because the generator is connected to the fan drive gear system this creates drag on the fan and prevents the fan from rotating. 
     A spring brake can also be mounted around the rotor shaft. A solenoid, receiving power from the engine control system, maintains the brake in a released position. When the switch moves to the brake application position, the solenoid no longer receives power and the brake is released which clamps the rotor shaft to prevent rotation. 
     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 
         FIG. 1  is a schematic view of a portion of an example turbofan engine; 
         FIG. 2  illustrates an example gear system; 
         FIG. 3  schematically illustrates a fan drive for a fan system of the example turbofan engine; 
         FIG. 4A  illustrates an example rotor brake; 
         FIG. 4B  shows another view of the  FIG. 4A  brake; 
         FIG. 4C  shows yet another view of the  FIG. 4A  brake. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  is a schematic view of a portion of a turbofan engine  10 . The turbofan engine  10  includes a compressor section  12  with compressor blades  14  that rotate about an axis A driven by a turbine shaft  16 . A fan section  18  is supported on a fan shaft  20  and driven by the turbine shaft  16  using a planetary gear set  22 . 
     Referring now to  FIG. 2 , a fan drive gear system  26  rotates a fan shaft  20  to drive the fan section  18 . The fan drive gear system  26  includes a sun gear  30  and a plurality of planetary gears  32  that engage the sun gear  30 . Journal bearings  34  are located between the planetary gears  32  and support shafts  36  to reduce friction. The planetary gears  32  rotate relative to the journal bearings  34 . 
     When the engine  10  is running, a primary oil pump  40  pumps oil from an oil supply  38  to lubricate the fan drive gear system  26  as shown in  FIG. 3 . The oil from the primary oil pump  40  communicates along an oil flow path  42  to the journal bearings  34 . 
     An engine control system  44  senses the status of the engine  10  and controls a switch  46  to manage the oil supply to the journal bearings  34  and a fan braking system  24 . A person skilled in the art would be able to develop an engine control system  44  capable of monitoring aircraft altitude and status of the engine  10 . Using the status of the engine  10  and the altitude of the aircraft, the engine control system  44  determines an appropriate position of the switch  46 . In one example, the switch  46  is a three-way switch. 
     When the engine  10  is operating, and the turbine shaft  16  is driving the fan section  18 , the switch  46  is “open” (position  1 ). In this position, the primary oil pump  40  is powered by the engine  10  and provides oil for the journal bearings  34 . 
     The switch  46  is located between the engine control system  44  and a generator  48  for powering a secondary oil pump  50 . When the engine control system  44  senses shut-down of the engine  10  and the aircraft is at a flight altitude, the switch  46  moves to position  2 , a position that activates the secondary oil pump  50 . In this position, the secondary oil pump  50  provides oil to the journal bearings  34 . The oil prevents the fan section  18  from seizing as the fan section  18  windmills when the engine  10  is shut-down, such as when an engine  10  shuts down when the aircraft is moving through the air. The generator  48  provides power to drive the secondary oil pump  50 , which communicates oil from the oil supply  38  through the oil flow path  42 . Alternatively, the secondary oil pump  50  may utilize oil supply lines separate from the primary oil pump  40 . 
     The engine control system  44  can be set to move the switch  46  to position  2  to activate the secondary oil pump  50  when the engine  10  is cycled on and off. In this manner, the secondary oil pump  50  will be ready for use if needed when the aircraft is in flight. 
     Various sources of air flowing though the fan section  18  cause windmilling in an unpowered engine  10 . For example, wind moving though the fan section  18  when the aircraft is at a ground altitude may cause the fan section  18  to windmill. If the engine  10  is shut down and the engine control system  44  senses that the aircraft is at a ground altitude, the switch  46  may move to position that brakes the fan shaft  20  by inhibiting rotation of the fan section  18 . In this example, the engine control system  44  moves the switch  46  to a position  3 , a position that shorts the generator  48 . The generator  48  is connected to the fan drive gear system  26  through a spur gear  54 . Because the generator  48  is connected to the fan drive gear system  26 , the fan section  18  must overcome the torque of the generator  48  to rotate. In this manner, the generator  48  brakes the fan section  18 , and prevents wind moving though the engine  10  from moving the fan section  18 . A person skilled in the art would be able to position the generator  48  to achieve this result. 
     In some situations, such a very strong winds, the generator  48  alone is not enough to brake the fan section  18 .  FIG. 4A  illustrates an end view of an example embodiment for braking the generator shaft  62  using a spring brake  60  and a solenoid  39 . The spring brake  60  provides braking power to the fan section  18  and may be used if the generator  48  alone is unable to brake the fan section  18 . 
       FIG. 4B  illustrates a cross section of the spring brake  60  and the solenoid  39  mounted to the generator shaft  62 . In this example, the spring brake  60  mounts around a generator shaft  62  and is shown in an unbraked position. Energizing a coil  66  within the solenoid  39  creates a magnetic field that urges a wedge lever  63  toward the center of the coil  66 . The wedge lever  63  includes angled faces  67 , as shown in the top view of  FIG. 4C . The angled faces  67  abut the brake pad arms  64 , and move the upper portion of the brake pad arms  64  toward each other as the wedge lever  63  is urged toward the center of the coil  66 . Moving the brake pad arms  64  toward each other compresses a spring  68 , and causes lower portion of the brake pad arms  64  to move away from the generator shaft  62  pivoting about points  65 . 
     The engine control system  44  powers the solenoid  39  to maintain the brake pad arms  64  in a released position by urging the wedge lever  63  toward the center of the coil  66 . The solenoid  39  receives power from the engine control system  44  when the switch  46  is in position to operate the primary oil pump  40  (position  1 ) or the secondary oil pump  50  (position  2 ). When the switch  46  moves to position that shorts the generator  48  (position  3 ), such as when the engine  10  is not powered and on the ground, the solenoid  39  no longer receives power. As a result, the solenoid  39  does not urge the wedge lever  63 , and the spring  68  forces the brake pad arms  64  to rotate about points  65  to clamp the brake pad arms  64  to the generator shaft  62 . The spring  68  causes the brake pad arms  64  to apply a consistent force to the generator shaft  62 , even when the brake pad arms  64  are worn. For example, repeated application of the brake pad arms  64  may cause wear on the brake liners (not shown) of the brake pad arms  64 . The spring  68  ensures consistent braking force on the generator shaft  62  even if the liners are worn. 
     As described in the above embodiment, the generator shaft  62  is connected to the fan drive gear system  26  through the spur gear  54 . Thus, preventing rotation of the generator shaft  62  using the spring brake  60  prevents rotation of fan section  18 . 
     Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art may 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 of coverage available for this invention.