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32-41-00
ALL ú ú 01 Page 5 ú Oct 25/84
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
B.
C.
D.
A
737-300/400/500MAINTENANCE MANUAL
When the brake pedals are depressed, through the mechanical linkage, cables and actuating lever, an inward movement is imparted to the metering valve slide. As the slide moves in, the return port is closed and the pressure port opens to direct hydraulic pressure to the brakes (Fig. 4). Brake hydraulic pressure through a passage in the valve slide enters the reaction chamber. The pressure in the reaction chamber acts on the end of the slide creating a feedback force tending to close the valve. This feedback force varies with the intensity of braking pressure and provides a feel at the pedals. Cable stretch and variation of pedal position permit the valve slide to move back until actuating force and feedback pressure are equal. At this point braking effect remains constant. When the pedals are released the pressure in the compensating chamber and the return spring move the valve slide out and the return line opens. As the return line opens, pressure in the brake line falls, the brakes are released and return force on the valve slide is relieved. The desired braking effect is obtained by depressing the brake pedals to actuate the main wheel brakes as needed based on required stopping distance and holding steady pressure. If a wheel goes into a skid, the antiskid system will reduce pilots metered brake pressure by electrically controlling the antiskid control valve to maintain maximum braking pressure and efficiency over all types of runway braking conditions.Automatic braking of main gear wheels upon gear retraction is done through hydraulic system gear up pressure (Fig. 4). The pressure is routed to the "A" ports of each of the two alternate brake metering valves. The pressure drives the slide to meter reduced pressure from hydraulic system A through the alternate antiskid units to halt the wheels before they enter the wheel well. During gear retraction the alternate antiskid circuitry is disabled by the landing gear handle up switch so that the system will not sense a skid and release brake pressure.A brake feel augmentor is mounted on each normal brake metering valve and is used to provide increased brake pedal feel force at low metered pressure to improve brake pressure control during taxi conditions. The augmentor consists of a slide attached to a plunger. The slide is hydraulically connected to the output pressure line of the brake metering valve and the plunger is connected by a roller and lever to the shaft of the metering valve control quadrant. Operation of the brakes will pressurize the brake metering valve output line causing fluid to push against the augmentor slide and plunger. This generates a resistance to pedal force proportional to the amount of metered brake pressure. This feature is not available to the alternate braking system.
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú
32-41-00
ALL ú ú 02 Page 6 ú Oct 25/86
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
LEVER ASSY
UP
PRESSURE FEEDBACK OR REACTION CHAMBER
PRESSURE FEEDBACK OR REACTION CHAMBER
PRESSURE FEEDBACK OR REACTION CHAMBER
ALTERNATE BRAKE
METERING VALVE
BRAKE METERING VALVES
PRESSURE BRAKE RETURNPB RA
VALVE CLOSED - BRAKES RELEASED PB RA
VALVE OPEN - BRAKES APPLIED PB RA
PRIMARY BRAKE METERING VALVE
CONTROL QUADRANT SHAFT
A SYSTEM PRESSURE (ALTERNATE BRAKE METERING VALVE) OR
B RETURN NORMAL)
VALVE SLIDE
BRAKE PEDAL INPUT
VALVE OPEN - WHEELS DESPIN - ALTERNATE BRAKE METERING VALVE ONLY
FLOW SCHEMATIC
BRAKE METERING VALVE
Brake Metering Valve
Figure 4
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：737-300 400 500 AMM 飞机维护手册 起落架 LANDING GEAR 3(3)
