777 AMM 飞机维护手册 起落架 Landing Gear(17)

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The MLG uplock actuator is a two-position piston-type actuator. It retracts to unlock the gear and extends during gear uplock operation.
The MLG uplock-operated sequence valve is a two-position sequence valve (LOCKED AND UNLOCKED). A mechanical linkage from the uplock mechanism moves the sequence valve.
Location
The MLG uplock assembly is on the ceiling on the outboard edge of each wheel well. The uplock assembly is aft of the door uplock assembly.
The MLG uplock actuator attaches horizontally above the MLG uplock mechanism.
The MLG uplock-operated sequence valve attaches vertically above the MLG uplock mechanism.
Functional Description
During gear retraction, the roller on the MLG shock strut engages the hook in the uplock assembly. The motion of the gear starts to move the uplock mechanism to the over-center locked position. This also moves the MLG uplock-operated sequence valve to the lock position.
The MLG uplock-operated sequence valve then supplies pressure to the extend side of the MLG uplock actuator. This makes sure the uplock mechanism moves to the over-center locked position.
Lock springs hold the mechanism in this position.
During gear extension, the MLG uplock actuator moves the uplock mechanism to the unlocked position. This releases the gear from the up and locked position.
EFFECTIVITY BEJ ALL  32-32-00 
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MLG EXTENSION-RETRACTION -MLG UPLOCK ASSY, UPLOCK ACTUATOR, AND UPLOCK-OPERATED SEQUENCE VALVE

EFFECTIVITY BEJ ALL  32-32-00 
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MLG EXTENSION-RETRACTION -MLG DRAG BRACE-OPERATED SEQUENCE VALVE

Purpose
The MLG drag brace-operated sequence valve controls MLG door close operation during landing gear extension.
Physical Description
The MLG drag brace-operated sequence valve has two positions: GEAR DOWN and GEAR NOT DOWN. Linkage from the upper drag brace spindle moves the valve.
Location
The MLG drag brace-operated sequence valve is in the MLG wheel well on the wing rear spar.
EFFECTIVITY BEJ ALL  32-32-00 
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MLG EXTENSION-RETRACTION -MLG DRAG BRACE-OPERATED SEQUENCE VALVE

EFFECTIVITY BEJ ALL  32-32-00 
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D633W101-BEJ  Jan 05/2002 

MLG EXTENSION-RETRACTION -MLG TRUCK POSITIONER ACTUATOR

Purpose
The MLG truck positioner actuator moves the main landing gear truck to 13 degrees forward wheels up (TILT) when the airplane is in the air and the landing gear is down and locked.
The actuator also moves the truck to approximately 5 degrees forward wheels down (STOW) during a gear retraction. The gear stays in this position during flight.
During a landing gear extension, the actuator holds the truck in the STOW position until the gear is down and locked.
Physical Description
The MLG truck positioner actuator has a main piston and a floating piston. The floating piston can move between stops on the main piston.
Pressure operated valves control the hydraulic flow to the actuator.
A pressure operated relief valve protects the actuator from high pressure caused by thermal expansion and touch down loads.
Location
The MLG truck positioner actuator is on the forward end of the MLG truck. The head end attaches to the main gear shock strut. The rod end attaches to a bracket on the MLG truck beam.
EFFECTIVITY BEJ ALL  32-32-00 
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D633W101-BEJ  Sep 05/2002 

 

MLG EXTENSION-RETRACTION -MLG TRUCK POSITIONER ACTUATOR

EFFECTIVITY BEJ ALL  32-32-00 
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D633W101-BEJ  Jan 05/2002 

MLG EXTENSION-RETRACTION -MLG TRUCK POSITIONER ACTUATOR -FUNCTIONAL DESCRIPTION

General
The MLG truck positioner actuator retracts to move the MLG truck to the TILT position and extends to move the MLG truck to the STOW position.
Tilt Position
When the landing gear is down and locked, hydraulic pressure goes to both sides of the floating piston and the rod side of the main piston. This retracts the truck positioner actuator which moves the truck to 13 degrees forward wheels up (airplane in the air).
Stow Position
During gear retraction, hydraulic pressure goes between the floating piston and the rod side of the main piston. This makes the pistons move apart until the floating piston touches the rod shoulder.
Since the floating piston has a larger surface area than the main piston, the actuator extends until the floating piston touches the stops on the cylinder rod end. This moves the truck to the 5 degrees forward wheels down position.
After the landing gear is up and locked, the pressure in the truck positioner actuator keeps the gear in the STOW position.
　
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