T53 – Oil & Lubrication System

System Design

The engine lubrication system consists of main oil pressure supply and the oil scavenge system. Principal components of the lubrication system are lube oil filter assembly, power drive rotary (oil) pump, power driven rotary (booster) pump, and associated external hoses assemblies and internal passages.

Main oil pressure supply system. Engine lubricating oil is supplied from an aircraft mounted oil tank. Oil enters power driven rotary (oil) pump mounted on accessory drive gearbox and is discharged through internal passages to lube oil filter assembly. Filtered oil is directed into two main flow paths. One oil path passes through internal passages in inlet housing to supply lubricating oil to front section of engine including reduction gearing, torquemeter, accessory drive gearing, No. 1 main bearing, and power shaft forward bearing. The second oil flow path is through external oil pressure hose assemblies to rear section of engine for lubrication of No. 2, 3, and 4 main bearings and seals at bearing positions.

In inlet housing section, oil is directed through accessory drive carrier flanges into annular passage located in rear support flang of carrier. Oil from this passage is directed to oil transfer assembly for forced feed spray lubrication of reduction gears through three oil transfer tubes. Passages in housing provide lubrication to output shaft bearings. No. 1 main bearing and accessory drive pinion gear and power shaft forward bearing are lubricated by a transfer tube from accessory drive carrier assembly. Oil under constant pressure lubricates support bearing. 011 passes through oil transfer tube in oil nozzle located on rear face of front cover housing. Oil flows through two jets in nozzle to lubricate output gearshaft support bearings.

A third transfer passage from accessory drive carrier is directed up through an inlet housing strut to power driven rotary (booster) pump, which is mounted on, and driven by, the overspeed governor and tachometer drive assembly. This assembly includes a pressure regulating valve that governs output pressure of power driven rotary (booster) pump by circulating excess pressurized oil back to inlet housing. Pressurized oil from power driven rotary (booster) pump is directed back through an inlet housing strut and a strainer to torquemeter valve located on torquemeter cylinder.

An offset passage in overspeed governor mounting flange supplies oil to strainer and metering cartridge in overspeed governor which directs metered oil to overspeed governor and tachometer drive gear train. An additional transfer passage from main transfer support assembly directs oil through internal passages in inlet housing to power takeoff mounting flange. This oil, as required, passes through a strainer and metering orifice to lubricate engine drive accessories on power takeoff mounting flange.

Oil flows to rear section of engine is supplied from an oil pressure port at the 5 o’clock position on inlet housing through an external flexible oil hose assembly to lube pressure manifold mounted on forward face of diffuser housing. Oil is directed from bottom of diffuser housing to No. 2 main bearing and forward and aft seals. Oil is directed from top of manifold through a hose assembly and strainer through upper strut in exhaust diffuser to lubricate No. 3 and 4 main bearings.

All internal scavenge oil from inlet housing section drains through hollow support struts to bottom strut in inlet housing, through a screen and transfer tube, and into accessory drive gearbox. Scavenge oil from output reduction carrier and gear assembly flows by gravity into hollow inlet housing struts.

Scavenge oil from No. 2 main bearing flows through a scavenge oil tube in diffuser housing and is directed to accessory drive gearbox by an external scavenge oil hose assembly. Scavenge oil from No. 3 and 4 bearings, aided by two impellers located in bearing housing, flows through oil tube that extends through bottom of exhaust diffuser and is directed to the accessory drive gearbox by an external scavenge oil hose assembly. Scavenge portion of the power driven rotary oil pump returns scavenge oil from accessory drive gearbox through aircraft oil cooler and back to oil storage tank.

The torquemeter is a hydro-mechanical torque measuring device located in the reduction gearing section of the inlet housing.The torquemeter uses lubricating oil boosted to a high pressure by the power driven rotary booster pump. It consists of a stationary plate, a movable plate attached to planet gear carrier, and 18 steel balls positioned in conical pockets located in both plates. Resistance to rotation of planetary gears, due to load on output shaft, causes carrier mounted plate to rotate slightly. Torquemeter balls are displaced from their individual pockets, forcing rear torquemeter plate to move rearward. Rearward motion of torquemeter plate unseats a spring loaded poppet valve, permitting high pressure oil to enter cylinder chamber and equalize force tending to cause rearward movement of torquemeter plate. Torquemeter oil pressure from the cylinder and the gearbox air pressure is directed to the aircraft torquemeter gage which indicates differential torque oil pressure in psi. Differential torque oil pressure is proportional to torque delivered to output gearbox.