A320飞机维护手册 AMM LANDING GEAR 起落架4(40)

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 (c) Extension Body
 The extension body is installed on the upper end of the actuating cylinder. The body has three hydraulic unions and contains two internal annuli. One of these annuli is connected to the actuator-supply port. The other annuli contains the restrictor.
 Two annuli in the body, aligned with two annuli in the cylinder, provide the hydraulic connection between the components.
 (d) Retraction Body
 The body assembly contains a hydraulic union and an annuli. The annuli contains a restrictor.
 An annuli in the body, in line with an annuli in the cylinder, provides the hydraulic connection between the components.
 (e) External Hydraulic Fittings
 The actuating-cylinder extension-body has connections for the extension and retraction hydraulic-fluid supply-hoses. The extension and retraction bodies are connected together by a hydraulic pipe. This pipe is attached to the cylinder assembly.
 (2) Operation
 (a) Retraction
 To retract the NLG, pressurized hydraulic fluid goes through the restrictor into the annular side of the actuating-cylinder. This causes the piston rod to retract to move the NLG. The hydraulic fluid on the other side of the piston goes to the hydraulic system return through the main return orifice and the restrictor. As the piston gets near to the end of its travel, it closes the return orifice in the actuating cylinder. This decreses the flow of hydraulic fluid to the hydraulic system return, which damps the end of piston-rod travel.
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 (b) Extension
 During the extension of the NLG, the aerodynamic loads, and the weight of the NLG, cause the NLG to extend. The restrictor on the annular side of the piston decreases the return flow of the fluid from the actuating-cylinder. This causes a damping-pressure on the annular side of the piston and thus controls the rate of NLG extension.
 A restrictor valve (2691GM) keeps a limit on the damping-pressure. To do this, the valve decreases the flow of pressurized fluid to the extend side of the actuating-cylinder.
 G. MLG Door Actuating Cylinder (2523GM, 2522GM)
 (Ref. Fig. 028, 029)
 (1) Description
 The door actuator is a hydraulic actuator with rate control devices. The piston and piston rod are contained in a cylinder. A damping piston, on each side of the piston, goes into a damping bore at the end of the extend and retract strokes.
 The door-actuating cylinder attaches to the center-fuselage keel-structure at the fixed end, and to the hinged door at the piston end.
 (a) Actuating Cylinder
 The actuating cylinder has a:
 -cylinder assembly
 -restrictor housing
 -piston.
 The cylinder assembly has a cylinder closed at one end by a fixed end fitting. At the other end it is closed by a gland housing and a piston. The fixed end fitting and the gland housing are internally machined to form damping chambers. The piston is shaped to fit inside the damping chambers, at the end of the assembly.
 (b) Damping Chamber
 The damping chamber in:
 -the fixed end fitting has two diametrically opposite damping holes and two diametrically opposite axial feed slots
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 MLG Door Actuating Cylinder (2523GM,2522GM) Figure 028
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 MLG Door Actuating Cylinder - Schematic Figure 029
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 -the gland housing has two damping holes that are axially displaced to provide progressive damping.
 The restrictor housing is installed on the fixed end fitting. It has two port connectors that contain restrictors to control fluid flow. A service line connects port B on the restrictor housing to the gland housing.
 The actuating cylinders range of travel is controlled by:
 -the door stops and the door uplock when the door closes
 -an internal stop (the piston head touches the internal face of the gland housing) when the door opens.
 (2) Operation
 (a)
 Doors Closed

 When main gear doors 'closed' is selected, hydraulic fluid from port B passes through the restrictor and the damping holes. The hydraulic pressure is applied to the piston flange and the annular face of the piston. The piston retracts slowly (due to the restricted fluid flow) until it opens the second damping hole which increases the piston speed. The speed increases until the piston is free of the damping chamber.

 (b)
 Doors Open

 When main gear doors 'open' is selected, hydraulic fluid from port A passes through a restrictor and the axial feed slots. At the same time the hydraulic fluid passes through the damping holes.The piston then extends slowly due to the restricted fluid flow. Piston speed increases until the piston goes into the gland-housing damping chamber.
　
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