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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500
MAINTENANCE MANUAL
NOSE LANDING
GEAR SNUBBER
SEE A
FWD
NUT
WASHER
SUPPORT SPRING
SNUBBER BLOCK
SPACER (2 AT EACH FASTENER LOCATION)
1
BOLT (6 LOCATIONS)
NOSE LANDING GEAR SNUBBER
TWO SPACERS IS THE STANDARD
CONFIGURATION. HOWEVER, SOME
1
A
AIRPLANES HAVE EITHER ONE OR
THREE SPACERS THAT SEPARATE
THE PAD AND THE SPRING
Nose Landing Gear Snubber Installation
Figure 201
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ALL ú ú 01 Page 203 ú Jul 15/92
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
NOSE WHEEL STEERING SYSTEM - DESCRIPTION AND OPERATION
______________________________________________________
1. General_______
A. Nose wheel steering is provided for airplane directional control during ground maneuvers and taxiing. Hydraulic power from system A is used to turn the nose wheels to either side from zero to 78 degrees. In addition, on some airplanes system B may also be used to turn the nose wheels. An alternate nose wheel steering system, activated by a switch on the captain's forward panel (Fig 1), allows power from hydraulic system B to turn the nose wheels if power from hydraulic system A is lost. Steering is controlled by a wheel on the left side of the control cabin and by an interconnect mechanism from the rudder pedals. The steering system is spring-loaded to the center position. The airplane can be towed through turns up to 78 degrees without disconnecting the torsion links or depressurizing the hydraulic system. Internal cams in the shock strut center the nose gear when the nose gear shock strut is fully extended, therefore turning the wheels or towing should not be attempted unless the shock strut is compressed more than two inches.
B. Normal steering is accomplished by using the steering wheel located on the left sidewall forward of the captain's position (Fig. 1). Movement of the steering wheel in either direction is transmitted by cables to a steering metering valve which directs 3000 psi hydraulic fluid to the nose wheel steering actuators for turning the steerable portion of the nose gear. A steering wheel movement of 95 degrees will give 78 degrees of nose wheel turning.
C. Rudder pedal steering is available during takeoff, landing, and taxiing when small directional changes are required. Full deflection of the rudder pedals produces about 7 degrees of nose wheel steering. The rudder pedal steering mechanism is engaged for steering by the squat switch located on the nose gear shock strut. When the nose gear is compressed, the movement of the torsion link is transmitted to the squat switch. This causes the actuator motor to reposition the stops mounted on the clutch crank in the rudder pedal steering mechanism (Fig. 3). In this position, any movement of the rudder pedals will be transmitted into ground directional control of the nose wheel.
2. Steering Metering Valve_______________________
A. The steering metering valve is a piston and sleeve type valve located on the nose gear. A pair of swivel valves are combined with the metering valve to direct hydraulic fluid for turns. The piston and sleeve assembly is ported to direct 3000 psi hydraulic fluid through the swivel valves to the steering actuators. Movement of the control cable positions the valve piston for the required turn. When the wheels reach the required turn angle, the piston is returned to neutral position by follow-up action of the control cable.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
B. During steering operation, hydraulic fluid is directed by the metering valve to one side of the right actuator piston and to the opposite side of the left actuator piston producing a push-pull action on the steering collar (Fig. 2). This push-pull action continues as long as the valve piston is displaced or until approximately 33 degrees of steering. At this point the pulling actuator has reached the end of its stroke and the turning motion of the actuator has closed off the hydraulic pressure and return lines in the steering actuator swivel valve. Continued pushing by the other actuator moves the pulling actuator past the null point. Above 33 degrees of steering, hydraulic pressure for the steering cylinder that is overcenter has been closed off and both ports have been ported to return. Further turning from 33 degrees to the maximum of 78 degrees is provided by the pushing actuator only. The steering wheel must be turned 95 degrees to obtain the maximum turning angle of 78 degrees.
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本文链接地址：737-300 400 500 AMM 飞机维护手册 起落架 LANDING GEAR 3(113)
