_________________________
(1)
The truck positioner actuator is a hydraulic piston-type actuator. It operates hydraulically in one direction. This actuator applies the force to put the truck assembly at an angle to permit clearance with the structure when the landing gear moves to the extended or retracted position. The actuator is installed on the aft side of the shock strut near the truck assembly. The head end attaches to the shock strut inner cylinder, and the rod end attaches to the truck beam.
I.
Truck Positioner Shuttle Valve (Fig. 8)
______________________________
Truck Positioner Actuator
Figure 7
32-32-00
ALL ú ú 10 Page 8 ú Mar 20/90
A
757
MAINTENANCE MANUAL
SEE A
SEE B MAIN LANDING LINK GEAR STABILIZING
LANDING MAIN GEAR BEAM
MAIN LANDING A BEARING TRUNNION GEAR FORWARD UP FWD SPAR WING REAR
MAIN LANDING LINK GEAR STABILIZING
VALVE SHUTTLE POSITIONER TRUCK
FWD B
Truck Positioner Shuttle Valve Figure 8
32-32-00
ALL ú ú 01 Page 9 ú Mar 20/90
A
757
MAINTENANCE MANUAL
(1)
The left truck positioner shuttle valve is a flow-limited control valve. Normally, this valve permits free flow of hydraulic fluid to the truck positioner actuator. If a low pressure input is received from the lines between the valve and the actuator, fluid flow to the actuator is blocked. This is done with a hydraulic fuse.
(2)
The extension and retraction system for the right main landing gear has two hydraulic fuses installed. There is one fuse installed in the the landing gear up and one installed in the landing gear down control lines. On these airplanes the right truck positioner shuttle valve fuse is not installed. If a low pressure input is received, the related fuse will stop flow to the full system. This will prevent the loss of the other airplane systems supplied by the left hydraulic system because of a break or a leak.
J.
Uplock Assembly (Fig. 4)
_______________
(1) The uplock assembly is a spring-loaded hook and linkage mechanism. This assembly locks the landing gear up in the wheel well after it is retracted. The uplock hook engages in the uplock roller which is installed on the shock strut. The mechanism is operated by the uplock actuator. The uplock assembly is installed on the outboard fairing of the wheel well for the main landing gear.
3. Operation (Fig. 9)
_________
A. Functional Description
(1)
Landing Gear Retraction
(a)
The retraction cycle starts with the landing gear down and locked and the main landing gear door closed and locked. With the control lever in UP, hydraulic fluid flows through the selector valve to pressurize the hydraulic lines for landing gear retraction.
(b)
Hydraulic fluid flows through the truck positioner shuttle valve to the truck positioner actuator. The actuator extends to put the truck the at an angle for entry into the wheel well.
(c)
Hydraulic fluid flows through the uplock-operated and downlock-operated sequence valves to the door actuator. The mechanical lock in the door actuator is released. Then the door actuator extends to open the main landing gear door.
(d)
When the door is approximately 90 per cent open, the door-operated sequence valve sends hydraulic fluid to the downlock and retract actuators. The downlock actuator retracts to move the downlock links out of the locked position. Then, the retract actuator retracts to retract the landing gear.
32-32-00
ALL ú ú 05 Page 10 ú Mar 20/91
A
757
MAINTENANCE MANUAL
HYDRAULIC POWER LEFT HYDRAULIC
TRANSFER UNIT SYSTEM POWER
P PR
3 DOWN
UP OFF
RESTRICTOR
RELIEF VALVE
LANDING GEAR
SELECTOR VALVE
TO THERIGHT MAINLANDING GEARSYSTEM AND NOSELANDING GEARHYDRAULIC
SYSTEM FUSE
CLOSED URD TRANSIT OPENDR
U1HYDRAULIC
FUSE
2
LEFT MAIN
LEFT MAIN LANDING GEAR DOOR
I OLEFT MAIN LANDING
UC DC UNLK
LANDING
OPERATED GEAR SEQUENCE VALVE
GEAR DOWNLOCKGEAR TRUCK OPERATED DOORIDU
POSITIONERSEQUENCE VALVESHUTTLE
LEFTVALVE
MAIN LANDINGGEAR UPLOCKOPERATED DOOR
SEQUENCE VALVERCO
UNLOCK LEFT MAINLANDING GEARUPLOCK ACTUATOR
UP LEFT MAIN LANDINGGEAR DOOR SAFETY INTERNAL LOCK
VALVE
LEFT MAIN LANDING GEAR(PRESSURE
RETRACT ACTUATOR RELEASED)
中国航空网 www.aero.cn
航空翻译 www.aviation.cn
本文链接地址：757 AMM 飞机维护手册 起落架 CHAPTER 32 - LANDING GEAR 2(42)
