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 A.  The nose gear door linkage transfers motion from the nose gear to open and close the nose gear wheel well doors (Fig. 7). Doors are open when gear is extended and close as the gear retracts. A link assembly connects a lug on the shock strut outer cylinder near the trunnion with the short arm of a bellcrank. A pushrod between a long arm on the crank and a fitting on the door completes the linkage. The lugs on the outer cylinder and the arms on the crank are positioned to pass over an overcenter positon for 80 percent of the gear travel. Therefore, except for a very slight further opening, the doors barely move during gear retraction. When the gear is moving over the last few inches of retraction, the long arm on the crank is almost at right angles to the pushrod connected to door. The doors then rapidly close as gear fully retracts. On gear extension, the initial extension movement opens the doors wide. At this point, lugs and cranks reach overcenter position and the doors remain open for the rest of the extension cycle.
PISTON RING SET PISTON CYLINDER

UP
DOWN
PORT
PORT
IN TRANSIT CONDITION

Transfer Cylinder Schematic
Figure 6

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
 10. Operation_________
 A. Retraction
 (1)  When the landing gear control lever is moved to UP position for gear retraction, hydraulic pressure is directed through the selector valve and the nose gear modular package to the gear and the lock actuators. Flow to the gear actuator is controlled by a flow limiting valve. Flow leaving the lock actuator is controlled by a restrictor (Fig. 8). The lock actuator starts retracting to apply a downward force to an extension on the lock link. The downward force pulls the lock link over center and starts both the lock strut and drag brace folding. As gear retraction proceeds, the lock link assembly swings through 90 degrees from horizontal to vertical position. In so doing, the lock link extension passes across an overcenter position with respect to the lock actuator. From this point, the lock actuator retracting force is opposed to lock link movement until the gear is almost retracted. During the opposition period, the larger main gear actuator overpowers the lock actuator. The unlock force provided by the lock actuator when the gear is down, becomes the locking force when gear is up. The changeover is caused by the lock link extension moving from the aft to the forward side of the lock link pivot (Fig. 9).
UPPER DRAG BRACE
LUG
BELL
CRANK

PUSHROD
DOOR
FITTING

LOWER DRAG
BRACE
RIGHT
DOOR

LEFT DOOR
Nose Gear Door Linkage Figure 7
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
(INTERNAL TO ACTUATOR) TWO WAY RESTRICTOR 
C1  C2  C1  C2  C1  C2  NOSE GEAR ACTUATOR  (PORT MOUNTED) TWO WAY RESTRICTOR 
CYLINDER TRANSFER  DOWN  UP  ACTUATOR NOSE GEAR LOCK 
R DOWN  P  R SELECTOR VALVE OFF P  R  UP  P  LIMITER FLOW  VALVE PRIORITY 

NOSE GEAR MODULAR PACKAGE
3550
3550
STEERING TO NOSE WHEEL  NOSE GEAR FUSE  RESTRICTOR TWO WAY 
TO MAIN GEAR  DOWN LINE  UP LINE  TO MAIN GEAR 
RETURN LEGEND:  DAMPER TO MAIN GEAR  R C1  P C  SELECTOR VALVE 
PRESSURE 
"B" SYSTEM  VALVE TRANSFER SYSTEM LANDING GEAR  LIMITER FLOW  VALVE BYPASS 
RETURN 
SYSTEM "A"  PRESSURE 

Nose Gear Extension and Retraction Hydraulic System Schmatic
Figure 8

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本文鏈接地址：737-300 400 500 AMM 飛機(jī)維護(hù)手冊(cè) 起落架 LANDING GEAR 2(107)