Engine/Gearbox Couplings
The engine/gearbox couplings system transmits rotational power from the engine to the mast and transmission assembly system. It is a flexible coupling that adjusts to and accommodates for the constant movement of the mast and transmission system as it moves due to changing flight attitudes and buffeting loads. During autorotation, it disengages the engine from the drive train so that the main rotor system can become the rotational power source for the mast and transmission assembly system and the tail rotor system.
The system of the engine/gearbox couplings has the components that follow:
Main driveshaft
The main driveshaft assembly is of a KAflex-type that has an assembly of four steel Flex frames on both ends of a hollow tubular steel shaft. The Flex frames are attached together and to the flanges of the shaft with bolted joints. At the forward end of the main driveshaft assembly, the Flex frame assembly connects to the input quill at the rear of the of the transmission assembly, and at the aft end of the main driveshaft assembly, the Flex frame assembly connects to the output shaft of the freewheel assembly.
Freewheel assembly
The forward end of the freewheel assembly attaches to the aft end of the main driveshaft, and the aft end of the freewheel assembly attaches to the forward driveshaft assembly of the tail rotor drive system.
The freewheel assembly includes the primary components that follow:
Input shaft
Clutch assembly
Output shaft
Housing assembly
The forward end of the freewheel assembly attaches to the aft end of the main driveshaft, and the aft end of the freewheel assembly attaches to the forward driveshaft assembly of the tail rotor drive system.
The splines of the input shaft engage with the engine Reduction Gear Box (RGB) from which it receives power during normal operation. When receiving power from the RGB, the sprags in the clutch assembly move to cause power to be transmitted from the input shaft to the output shaft. The output shaft in turn transmits power both aft and forward.
During autorotation, the RGB does not supply power to the freewheel assembly. When not receiving power from the RGB, the sprags in the clutch assembly move to disengage the input shaft from the output shaft which removes the RGB from the drive train. Removing the RGB from the drive train allows the main driveshaft, now being powered by the main rotor, to provide power to the tail rotor.
The housing assembly serves as a casing and an oil sump for the lubrication of the freewheel assembly. The transmission oil system supplies pressurized oil for the lubrication of the freewheel assembly. The housing assembly also has mount points for the components of the freewheel indicating system.
Operation
During normal operation the freewheel assembly receives power from the engine and distributes it to the main driveshaft assembly and to the forward driveshaft of the tail rotor drive system. The main driveshaft assembly then transmits power to the mast and transmission assembly system, and the forward driveshaft of the tail rotor drive system transmits power to the tail rotor.
The input shaft receives power from the engine. When the input shaft turns, sprags in the clutch assembly engage the output shaft and allow power to be transmitted to the output shaft which then transmits power both aft and forward. On the forward side, the output shaft connects to the main driveshaft assembly of the main rotor drive system. On the aft side, the output shaft connects to the forward driveshaft assembly of the tail rotor drive system. The housing assembly serves as a casing and an oil sump for the lubrication of the freewheel assembly. The transmission oil system supplies pressurized oil for the lubrication of the freewheel assembly. The housing assembly also has mount points for the components of the freewheel indicating system.
The splines of the input shaft on the freewheel assembly engage the engine power drive gear shaft. Power is then transmitted to the output shaft through the sprags of the clutch assembly.
During autorotation, the output shaft disengages from the input shaft through the effect of the clutch assembly. Thus, the engine power source no longer drives the output shaft and the main rotor then takes over to drive the mast and transmission system, its accessories, and the forward driveshaft of the tail rotor drive system.
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