-
the anti-skid function (to give maximum braking efficiency)

 -
the automatic braking of the main gear wheels during the L/G retraction

 -
the test of the brake system and nose wheel steering system before a landing

 -
the nose wheel steering (Ref. 32-51-00).

 The BSCU also has these secondary functions, it:
 -monitors the temperature of each brake
 -calculates the wheel speed
 -uses Built-In Test Equipment (BITE) to do software controlled tests when the aircraft is on the ground
 -supplies data to other systems in the aircraft.
 The BSCU has two systems, System 1 and System 2. These systems are isolated from each other and each connects to its related electrical sub-system. Only one system (the active system), controls the operation of the braking system. The other system (the standby system) is available if the active system becomes unserviceable. If available, the two systems monitor the operation of the braking system.
 When the BSCU is supplied with power system 1 becomes active. After each landing the BSCU makes a record in an Electrically Erasable Programmable Read-Only Memory (EEPROM) that identifies which system was active during the landing. Before the next landing, the BSCU reads the EEPROM and makes active the system that was in standby mode during the last landing.
 A tachometer is installed in the end of each MLG axle. A drive assembly connects the tachometer to the related wheel. The tachometer measures the speed of the wheel and sends this data to the BSCU. The BSCU uses this data to control the hydraulic pressure supply to the related brake for anti-skid and autobrake functions.
 1EFF : 401-499, 1 32-42-00Page 5 1 1 Config-2 Aug 01/05 1 1 1CES 1 C. Hydraulic System Components

 The components that control the supply of hydraulic power to the system are installed on a manifold that is located in the hydraulics compartment. These components are:
 -selector valve 23GG
 -high pressure filter 2584GM
 -pressure transducer 96GG.
 A manifold installed on each MLG includes the necessary components to control the hydraulic pressure at its related brakes.
 The selector valve 23GG is attached to the GREEN PTU manifold 1113GM (Ref. 29-11-00). The selector valve is solenoid operated and controls the supply and release of the Green hydraulic pressure in the brake system. When the valve is de-energized it connects the system to the Green LP manifold 1003GM to release the pressure in the system.
 The BSCU energizes the selector valve 23GG to connect the Green hydraulic pressure to the system when:
 -
the brake pedals move more than a specified limit

 -
the conditions necessary for an automatic braking program are available

 -
the landing gear is set to UP (retraction braking). The selector valve 23GG stays energized for 3 seconds or until the NLG is not down-locked.

 -it does a test of the normal braking system (this occurs before each landing or when a specified BITE test (Ref. 32-46-00) is set).
 The high pressure filter 2584GM and pressure transducer 96GG are installed downstream of the selector valve 23GG. The filter prevents contamination of the braking system components. The transducer measures the hydraulic pressure in the system and supplies the data to the BSCU and to the ABCU (to give the condition of the selector valve).
 The hydraulic line divides to supply the two Normal Brake Servovalve Manifold assemblies 2612GM and 2613GM installed on the MLG.
 The manifold assemblies are the same. They have an inlet port that includes a filter, a return port and two outlet ports that each supply a related brake. At the filter outlet, the hydraulic supply divides equally to supply two sets of components that are attached to the manifold (one set for each brake). Each set of components includes a servovalve, a safety valve and a pressure transducer.
 Each servovalve has an electrically operated solenoid. The active channel of the BSCU supplies the servovalve control current to the related coil to:
 -get the correct quantity of pressure in the brake line
 1EFF : 401-499, 1 32-42-00Page 6 1 1 Config-2 Aug 01/05 1 1 1CES 1 -connect the brake line to return to release the pressure.

 If a leak of hydraulic fluid occurs downstream of the safety valve, the valve automatically closes to prevent loss of fluid in the related brake line. The pressure transducer measures the hydraulic pressure in the related brake line and supplies an input to the BSCU. The input is in proportion to the pressure.
 Each manifold assembly has a return line with a check valve. The return line from each MLG manifold connects the related manifold to the Green LP Manifold 1003GM. The check valves isolate the related manifold from the other return pressures.
　
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