DOC AIRBUS | AMM A320FFAN DRIVE GEARBOX (FDG) - DESCRIPTION AND OPERATION
** ON A/C NOT FOR ALL
** ON A/C NOT FOR ALL
1. General
A. Fan Drive Gearbox (FDG)
(1) The FDG is a planetary gear unit in a "star" arrangement that decreases the fan shaft speed from the Low Pressure Turbine (LPT) shaft. The FDG gets the torque from the LPT and uses it to turn a sun gear. This sun gear then turns the five planet gears against an outer ring gear set which is connected to the gearbox front shaft. The gearbox front shaft is connected to the fan rotor.
(2) There are journal bearings at each planet gear position. With these bearings, the cylindrical surfaces of the gear inner diameters turn against their mating pivots. The gears are housed in a carrier which is attached at the rear to the Fan Intermediate Case (FIC) by inner and outer assemblies. Pins through the inner carrier function as a radial support.
(3) The journal bearings, FDG gears and inner pins are lubricated with pressure oil from an oil manifold at the rear of the FDG. Oil from the journal oil shuttle valve goes through the oil manifold, journal bearing oil supply tubes and journal bearing oil filters to the journal bearings. The Variable Oil Reduction Valve (VORV) controls the flow of oil through the VORV oil manifold to the gear oil filters and nozzles and then to the FDG gears and the inner pins.
(4) A windmill pump, which turns at fan speed, is located in the compartment. The gravity valve in the front of the assembly changes the flow of oil during flight conditions. During normal engine operation (when the main oil pump pressure supplies the FDG bearings sufficiently), the gravity valve lets oil from the compartment auxiliary reservoir be sent by the windmill pump to the main oil tank through the journal oil shuttle valve. During windmill conditions, the gravity valve lets oil from the sump go through the windmill pump to the journal bearings through the journal oil shuttle valve. During zero and negative G conditions, the gravity valve lets oil from the auxiliary reservoir go through the windmill pump to the journal bearings through the journal oil shuttle valve.
2. Description of the Fan Drive Gearbox (FDG) Module
Fan Drive Gearbox (FDG) ModuleA. The FDG is a planetary gear reduction unit that takes the torque from the LPT and uses it to turn a sun gear.
(1) This sun gear then turns the star gears against an outer ring gear that is connected to the fan hub.
(2) There is a ratio of LPC/LPT to fan hub speed of approximately three to one, and the fan turns in the opposite direction from that of the LPC/LPT.
NOTE: The fan hub turns clockwise as seen from the rear of the engine, and the LPC/LPT system turns counterclockwise as seen from the rear. This gives the effect of a straighter gaspath.
B. The No. 1 and No. 1.5 bearing support assembly hold the No. 1 and No. 1.5 bearing compartment.
(1) The No. 1 and No. 1.5 bearings are tapered roller bearings that hold the gearbox shaft from the Fan Drive Gearbox (FDG) axially and radially.
(a) There are labyrinth and carbon-face seals at the No. 1 bearing side to control the oil and airflow.
(b) The No. 1 bearing is oil-damped and uses a pressurized oil film around its outer race to absorb fan vibration.
C. In the PW1100G design, the FDG gears and the carrier to which they are attached do not move around the sun gear.
(1) The sun gear engages the star gears and turns them in a direction that causes the ring gear (and fan) to turn in the opposite direction from the sun gear (and LPC/LPT) at a lower speed.
(2) This design keeps rotating masses to a minimum and keeps centrifugal loads away from the star gear bearings. The most important effect of this is a lower fan speed and a higher LPC speed, which increases compressor efficiency.
(3) The FDG uses journal bearings at each star gear position.
(a) With these bearings, the cylindrical surfaces of the gear inner diameters turn against their mating pivots with no balls or rollers.
(b) These bearings are lubricated with pressure oil from a manifold at the rear of the FDG. Oil which goes through the gear bearing areas is caught in an oil channel around the circumference of the FDG and goes by centrifugal force to the auxiliary oil tank in the No. 1 bearing support and to the sump.
(4) A windmill pump is installed in the No. 1 bearing support.
(a) This pump engages a pump drive gear on the gearbox shaft and turns at fan speed.
(b) Under conditions when it is possible that the flow of oil from the main oil pump to the FDG will not be continuous (for example after shutdown when wind could turn the fan), oil from the sump is distributed to the windmill pump and from there to the FDG to keep oil pressure in the gear bearings.
(c) During usual engine operation, the main oil pump pressure supplies the FDG bearings sufficiently.
1 Under zero and negative G conditions, oil from the auxiliary oil tank and the sump go through the windmill pump to the FDG gears.
(5) Struts in the No. 1 bearing support give access to the bearing compartment for oil, air and instrumentation components.
(6) The FDG is attached at its rear side to the fan intermediate case by a torque frame and flex mount. This makes it possible for the FDG to align easily with the LPC at the rear and the fan at the front.