Description

1. TASK 72-60-00-990-501 Description And Operation Of The External Gearbox Module

   1. External gearbox

      1. The primary parts of the external gearbox module (Figure) are:

         1. Main gearbox

         2. Angle gearbox

      2. The external gearbox is installed at the bottom of the intermediate case module. Four flexible support links, three on the main gearbox and one on the angle gearbox support, attach the external gearbox to the intermediate case flanges. The links have spherical bearings at each end to permit any necessary mount flexibility.

   2. Main gearbox

      1. The main gearbox is installed forward of the angle gearbox and is attached to the angle gearbox by an angle gearbox support and to the intermediate case flange by three joint links.

         1. The angle gearbox support is a casting which houses the layshaft and rigidly connects the angle gearbox with the main gearbox. A pad on the support is used for the installation of the oil scavenge pump.

         2. The main gearbox has a cast aluminum housing that has a gear train, carbon seals and mounting pads for the airframe and engine accessories. An external deoiler is installed on the front face of the main gearbox. Each of the accessory drive gear train sections is individually replaceable.

      2. The metered oil nozzles are installed on a gearbox housing and supply pressure oil to the bearings and gears in the gearbox.

      3. An external oil tank is attached at the left-hand flange of the main gearbox.

      4. Drive pads on the forward face of the gearbox are used to install these that follow:

         Hydraulic pump

         Starter

         Oil pressure pump

         Permanent magnet alternator (PMA)

         Provision for remote cranking of the HPC rotor is also located on the front face.

      5. Drive pads on the rear face of the gearbox are used to install these that follow:

         Integrated drive generator system (IDGS)

         Fuel pump

         Oil scavenge pump (on the angle gearbox support)

      6. Drive gearshaft rotation

         NOTE

         The direction of gearshaft rotation is when you face the mounting pad being described.

         1. Hydraulic pump drive gearshaft

            Direction of drive rotation is counterclockwise. The gearshaft receives the motion through the adjacent idler gearshaft. If the hydraulic pump is not installed, the ID gearshaft is sealed and the pad cover is installed.

         2. Starter drive gearshaft

            Direction of drive rotation is counterclockwise. The gearshaft receives the motion through the adjacent crank gearshaft.

         3. Oil pressure pump

            The oil pressure pump is a removable assembly installed on the front flange of the gearbox. The pump has a separate housing that has two bush-mounted drive gear assemblies and the seat for the oil pressure filter.

            Direction of drive rotation is counterclockwise. The oil pressure pump receives the motion through the fuel pump drive gearshaft.

            The pump supplies oil under pressure to the engine bearings and accessory drives.

         4. PMA gearshaft

            Direction of drive rotation is counterclockwise. The gearshaft receives the motion through the adjacent input gearshaft.

         5. IDGS gearshaft

            Direction of drive rotation is counterclockwise. The gearshaft receives the motion through the starter gearshaft. When the IDGS is not installed, the ID gearshaft is sealed and the mount pad cover is installed.

         6. Fuel pump drive gearshaft

            Direction of drive rotation is counterclockwise. The gearshaft receives the motion through the hydraulic pump drive gearshaft.

         7. Oil scavenge pump

            The oil scavenge pump is a removable assembly installed on the flange of the angle gearbox support. The pump has a separable housing that has a bush-mounted drive gear assembly which moves two pump gear stages.

            The pump receives the motion through the idler gearshaft. The direction of drive rotation is counterclockwise.

            The oil scavenge pump increases the scavenge capacity of the oil pump module and sends the scavenge oil to the oil tank.

         8. External deoiler

            Direction of drive rotation is counterclockswise. The deoiler receives the motion through the IDGS gearshaft.

            The oil/air mixture flows through the deoiler that, with the centrifugal action, removes the air from the oil. The deaerated oil goes back to the oil system and the clean air is bled overboard.

   3. Angle gearbox

      1. The angle gearbox is installed at the rear of the main gearbox and engages with the powershaft on the engine.

      2. The cast aluminum angle gearbox houses a bevel gearset. The bevel gearset transmits the power to and from the engine through a powershaft which is engaged to the HPC rotor stubshaft. The bevel gearset has a spiral gear mesh which drives a horizontal input gearshaft in the main gearbox.

      3. Two metered jets supply pressure oil to the bearings and gears in the angle gearbox.

2. Operation

   1. The external gearbox at run condition, transmits the power from the power shaft which rotates at high speed, to the accessories installed on the main gearbox.

      At starter condition, the external gearbox transmits the power from the starter to the engine.

      The external gearbox supplies the necessary speeds, torques and data checking for the accessories to perform their various functions.

3. Module Sub-Assemblies

   Listed below are the module build groups with the associated work groups (marked *). The work group level is where piece parts are cleaned, inspected and repaired/reworked.

SNS		Part
Location		External Gearbox Module Nomenclature
72-60-10		Main gearbox assembly
72-60-21	*	Main gearbox case assembly
72-60-22	*	Starter drive gear, bearings, and housing assembly
72-60-23	*	Hydraulic pump drive gear, bearings, and housing assembly
72-60-24	*	Extension layshaft gear and bearing assembly
72-60-25	*	Fuel pump drive gear, bearings, and housing assembly
72-60-26	*	Oil scavenge oil pump drive gear and bearings assembly
72-60-27	*	Starter idler gear and bearing assembly
72-60-28	*	IDG drive gear, bearings, and housing assembly
72-60-29	*	Deoiler gear, impeller, bearings, and housing assembly
72-60-31	*	Deoiler case assembly
72-60-32	*	Angle gearbox support assembly
72-60-33	*	PMA drive gear, bearings, and support assembly
72-60-40		Angle gearbox assembly
72-60-41	*	Angle gearbox case
72-60-42	*	Angle gearbox driving gear, bearings, and support assembly
72-60-43	*	Angle gearbox driven gear, bearings, and layshaft assembly

Figure: External gearbox

External gearbox