Normal Braking - Electrical Control Schematic
Figure 041
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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,
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decrease the pilot workload during landing,
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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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(b) Indicating
Each lighted pushbutton switch is divided into two parts:
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the lower part (ON legend) comes on blue to show that the pushbutton switch has been selected and the system armed,
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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:
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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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