A320飞机维护手册 AMM LANDING GEAR 起落架6(110)

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 Differential braking is available when the travel of the left and right brake pedals is different. The left pedal gives the quantity of braking at the left MLG. The right pedal gives the quantity of braking at the right MLG.
 When the output from the transmitter unit is more than a specified value, the BSCU:
 -energizes the brake selector valve to open the valve
 -sends a control current to the related servovalves in proportion to the pedal movement to give the specified pressure at the brakes (max 175 bar (2538 psi)).
 The brake selector valve opens to connect the Green hydraulic pressure to the normal braking system. The fluid goes through the HP filter and goes freely to the individual manifolds on the landing gear. The pressure transducer at the filter outlet sends data to the BSCU. This lets the BSCU make sure that the system is pressurized.
 At each manifold and valve assembly the hydraulic pressure divides equally to supply the servovalves. The servovalves are energized with the necessary control current to supply the correct hydraulic pressure to the individual brakes.
 The pressure transducers continuously monitor the pressure in their related brake service line. A signal that agrees with the pressure is sent to the BSCU. If the fluid pressure changes, the control current sent to the related servovalve is changed to adjust the pressure.
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 Normal Braking - Electrical Control Schematic
 Figure 041

 1EFF : 401-499, 1 32-42-00Page 73 1 1 Config-2 Aug 01/05 1 1 1CES 1

 Normal Braking Control (Principle)
 Figure 042

 1EFF : 401-499, 1 32-42-00Page 74 1 1 Config-2 Aug 01/05 1 1 1CES 1 When the brake pedals go back to their initial position, the output from the transmitter unit returns to a set value (set for the initial pedal position). When the output is less than a specified value this causes the BSCU to de-energize the brake selector valve. At the same time it decreases the control current it sends to the servovalves which releases the brakes.

 When the brake selector valve is de-energized, it connects the HP filter to the LP manifold (Port A) of the Green hydraulic system.
 When the servovalves are de-energized, they operate to connect their related brake service line to the LP manifold of the Green hydraulic system.
 B. Automatic Braking
 (1) Principle
 (a) Operation
 (Ref. Fig. 043)

 The automatic braking system has these functions:
 -generation of the arming or disarming orders to the system,
 -servoing of the aircraft deceleration to a programmed deceleration rate,
 -braking control when the spoiler signals are present, depending
 on the requested deceleration. When an autobrake mode (LO, MED or MAX) is selected, the BSCU sends a controlled pressure to the brakes until the deceleration measured by the IRUs matches the programmed deceleration. The anti skid system operates to avoid wheel lock-up. The auto brake system avantages are:
 -get the optimum deceleration rate compatible with the length of the runway,
 -
decrease the pilot workload during landing,

 -
decrease the number of pilot actions in case of rejected take-off (one action on throttle instead of two actions: braking + throttle)

 -improve passenger comfort. Before landing, the pilot sets the deceleration rate he thinks to be adapted to the runway. For this purpose, he uses the AUTO BRK LO and MED on the center instrument panel. The pilot can disengage the autobrake when he depresses the pedals or when he pushes again the AUTO BRK LO and MED. Before takeoff, the pilot selects the MAX mode.
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 Auto Brake Control
 Figure 043
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1  1  Config-2 Aug 01/05
 1  1
 1CES  1

 

 (b) Indicating
 Each lighted pushbutton switch is divided into two parts:

 -
the lower part (ON legend) comes on blue to show that the pushbutton switch has been selected and the system armed,

 -
the upper part (DECEL legend) comes on green: when 80% of the corresponding deceleration rate has been reached, (LO and MED pushbutton switches) or when you have a deceleration rate higher than 0.27 g (MAX pushbutton switch).

 (2) Auto brake logic (Ref. Fig. 044)
 The auto brake logic is located in the BSCU on the control and
 monitoring boards of the SYS 1 and SYS 2.
 The signals below are sent to the logic circuits of the auto brake:

 -
3 signals that the AUTO BRK LO/MED and MAX on the center instrument panel supply: 2 deceleration rates, LOW = 1.7 m/square second (LOW type 1) and MED = 3 m/ square second (2 m/square second in MED limited) , and a MAX = 10 m/square second (higher than the maximum possible deceleration of the aircraft) there is a LOW type 2 mode = 2m/square second depending of the aircraft pin programmation.
　
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