H.
Steering Collar and Torsion Links (Detail A, Fig. 7)

_________________________________
 (1)  
The nose gear steering collar is mounted on the shock strut outer cylinder and is retained by the actuator lower trunnion support plate.

 (2)  
Both steering actuator rod ends are connected to the steering collar, which in turn is connected to the upper end of the upper torsion link. When force is applied to the steering collar by either or both actuators, the collar rotates on the shock strut and also imparts motion through the torsion links to turn the shock strut inner cylinder and nose gear wheels.

 3. Operation
_________
 A. Functional Description (Fig. 2)
 (1)  
The landing gear control lever must be in the DOWN position to make hydraulic pressure available from the landing gear down line to the steering valve.

 (2)  
Tiller steering operation.

 (a)  
When the tiller is rotated the steering cables (NWS) move and displace the steering metering valve piston.

 (b)  
Hydraulic fluid is directed by the metering valve through swivel valves to the steering actuators.

 (c)  
The steering actuators provide a turning movement on the steering collar which is transmitted to the wheels by the torsion links.

 (d)  
Continued movement of the metering valve piston combined with the steering actuator swivel valves produces a maximum of 65 degrees of wheel turn for 360 degrees of tiller rotation.

 (e)  
During the turn, the metering valve slide is displaced until the required angle of nose wheel turning is reached and is then returned to the center position by follow-up action of the cable.

 (3)  
Rudder pedal steering operation.

 (a)  
Rudder pedal steering is activated by the piston position system when the nose gear is compressed 3 inches or more.

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757
MAINTENANCE MANUAL

 (b)  
The compression movement is transmitted by linkage (cables and spring cartridge) to move the interconnect mechanism cable drum and reposition the eccentric arm allowing the clutch arm to contact stops mounted on the steering crank.

 (c)  
In this position, any movement of the rudder pedals is transmitted from the steering arm to the quadrant.

 (d)  
The quadrant moves the nose wheel steering cables displacing the steering metering valve slide for the required turn.

 (e)  
Rudder pedal steering will cause the tiller to be back driven an equivalent amount, however the tiller can override the rudder pedal command at any point in its travel.

 (4)  
Hydraulic actuator operation

 (a)  
At the start of a turn, hydraulic fluid is directed by the metering valve module to the head end of one actuator and the rod end of the other actuator. Refer to Fig. 7, Steering Actuator Operation Schematic.

 (b)  
When a turn of approximately 30 degrees is reached, the actuator with rod end pressure has contracted to its minimum length and the turning motion of its trunnion mounting moves the swivel valve to supply pressure to both ends causing the rod cross section to be the effective area. This allows the actuator to extend to the maximum steering angle helping the other actuator which pushes through the full 65 degrees.

 (c)  
Coming out of a turn, the actuator which has crossed over center now has only return pressure at both ends, so the other actuator does all the work from 65 degrees to 30 degrees.

 (d)  
As the angle gets less than 30 degrees, the swivel valve in the actuator approaching dead center opens up pressure to its head end and both actuators again are in a push-pull attitude.

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757 FAULT ISOLATION/MAINT MANUAL
NOSE WHEEL STEERING SYSTEM
COMPONENT  SHT 102 FIG.  QTY  ACCESS/AREA  REFERENCE 
ACTUATOR - STEERING  3  2  NOSE LANDING GEAR  32-51-11 
CABLES - STEERING  2  4  113AL, FWD EQUIP COMPT, NOSE LANDING GEAR  32-00-05 
COLLAR - STEERING  3  1  NOSE LANDING GEAR  32-51-00 
CARTRIDGE - SPRING  3  1  NOSE LANDING GEAR  32-51-08 
DRUM AND LINK - STEERING CONTROL  3  1  NOSE LANDING GEAR  32-51-06 
DRUM - TORQUE LIMITER  2  1  113AL, FWD EQUIP COMPT, L SIDE  32-51-02 
MECHANISM - RUDDER PEDAL STEERING INTERCONNECT  3  1  113AL, FWD EQUIP COMPT  32-51-05 
　
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本文鏈接地址：757 AMM 飛機維護手冊 起落架 CHAPTER 32 - LANDING GEAR 3(98)