DOC AIRBUS | AMM A320FALTERNATE BRAKING WITH ANTI SKID - DESCRIPTION AND OPERATION
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1. General
The Alternate braking system is a secondary electrohydraulic system. It is manually operated (no autobrake function available) and used to decrease the speed of the aircraft when it moves on the ground with engine power. It gives automatic anti skid protection, if available from BSCU, when the aircraft moves at more than ten meters per second.
The system automatically becomes available during braking if:
If the Green hydraulic supply goes back to more than 150 bar (2176 psi) after braking the ABCU will give back the control to the BSCU (Normal Brake System) once the pedals have been fully released to prevent transient during a braking phase.
Braking inputs are made at the brake pedals (Ref. AMM D/O 32-42-00-00) through the transmitter unit 103GG (Capt's pedals). The ABCU uses these inputs to control the Alternate servovalves (Direct Drive Valves) in the system. This system causes the Yellow main hydraulic power supply (Ref. AMM D/O 29-13-00-00) to go to the second set of pistons in the brakes (Ref. AMM D/O 32-42-00-00). The pressure that goes to the brakes is in proportion to the travel of each brake pedal.
The BSCU supplies the anti skid function to the ABCU when necessary to prevent wheel locking.
The BSCU continuously monitors the alternate braking system to make sure that it is serviceable.
If specified failures occur in the system, control automatically changes to its alternative mode of operation, Alternate Braking Without Anti Skid (Ref. 32-44-00).
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Alternate Braking with Anti SkidThe Alternate braking system is a secondary electrohydraulic system. It is manually operated (no autobrake function available) and used to decrease the speed of the aircraft when it moves on the ground with engine power. It gives automatic anti skid protection, if available from BSCU, when the aircraft moves at more than ten meters per second.
The system automatically becomes available during braking if:
- specified failures occur in the Normal braking system (Ref. AMM D/O 32-42-00-00)
and - the pressure of the Green Main Hydraulic Power System (Ref. AMM D/O 29-11-00-00) is less than 90 bar (1305 psi).
If the Green hydraulic supply goes back to more than 150 bar (2176 psi) after braking the ABCU will give back the control to the BSCU (Normal Brake System) once the pedals have been fully released to prevent transient during a braking phase.
Braking inputs are made at the brake pedals (Ref. AMM D/O 32-42-00-00) through the transmitter unit 103GG (Capt's pedals). The ABCU uses these inputs to control the Alternate servovalves (Direct Drive Valves) in the system. This system causes the Yellow main hydraulic power supply (Ref. AMM D/O 29-13-00-00) to go to the second set of pistons in the brakes (Ref. AMM D/O 32-42-00-00). The pressure that goes to the brakes is in proportion to the travel of each brake pedal.
The BSCU supplies the anti skid function to the ABCU when necessary to prevent wheel locking.
The BSCU continuously monitors the alternate braking system to make sure that it is serviceable.
If specified failures occur in the system, control automatically changes to its alternative mode of operation, Alternate Braking Without Anti Skid (Ref. 32-44-00).
2. Component Location
** ON A/C NOT FOR ALL | FIN | FUNCTIONAL DESIGNATION | PANEL | ZONE | ACCESS DOOR | ATA REF |
|---|---|---|---|---|---|
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| 95GG | ABCU | 126 | 32-43-34 | ||
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| 95GG | ABCU | 122 | 32-43-34 | ||
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| 97GG | SERVOVALVE-ALTN BRK, L | 171 | 32-43-35 | ||
| 98GG | SERVOVALVE-ALTN BRK, R | CR N | 671 | 32-43-35 | |
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| 99GG | SEL VALVE-ALTN BRK | 198 | 32-43-51 | ||
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| 99GG | SEL VALVE-ALTN BRK | 671 | 32-43-51 | ||
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| 100GG | PRESS XDCR-BRK, YELLOW R | 671 | 32-44-19 | ||
| 101GG | PRESS XDCR-BRK, YELLOW L | 571 | 32-44-19 | ||
| 2853GM | MANIFOLD-ALTN BRK, L | 571 | 32-43-32 | ||
| 2852GM | MANIFOLD-ALTN BRK, R | 671 | 32-43-32 | ||
| 3016GM | MANIFOLD | 198 | 32-44-17 | ||
| 3067GM | BRAKE RELIEF VALVE | 198 | 32-44-15 | ||
| 3058GM | CHECK VALVE Y | 198 | 27-20-00 | ||
| 3068GN | HYDR. PRESSURE TRANSMITTER | 198 | 29-32-11 | ||
3. System Description
The alternate braking with anti skid system is an electrohydraulic system that automatically becomes available when the normal braking system (Ref. AMM D/O 32-42-00-00) is not available. Braking inputs are made only at the brake pedals. The hydraulic power to operate the brakes is supplied from the Yellow Main Hydraulic Power System (Ref. 29-13-00). The BSCU (Ref. 32-42-00) controls the operation of the system and its anti skid function and also monitors the system to make sure that it is serviceable.
The system includes these primary components:
The system also uses the components that follow to supply the braking inputs or control functions necessary for the operation of the system:
The alternate manifold assemblies 2853GM and 2852GM are located in the wing shroud boxes and include:
The manifold has two supply ports.One supply port is for the alternate braking system and one for the parking brake system (Ref. AMM D/O 32-45-00-00). The service port connects to the brakes. The manifold also includes a filter.
The DDV operates when necessary to:
The ABCU sends the necessary control current to the Alternte servovalve (Direct Drive Valve) to:
The pressure output from the DDV goes through its related shuttle valve to isolate the pressure in the service line from the parking brake. The safety valve in the manifold acts as an hydraulic fuse. If a large leak occurs downstream of the safety valve, it closes to stop the flow for each pair of brakes. The pressure transducer measures the pressure that goes to the brakes and sends the data to the BSCU, ABCU and the Triple Pressure Indicator.
This lets the BSCU know if the operation of the applicable Alternate servovalve (Direct Drive Valve) is correct.
The alternate brake system connects to one of the two sets of pistons in each brake. The other set of pistons connect to the Normal brake system. A half-coupling connects each brake service line to a half-coupling on the brake. Each half-coupling seals automatically when disconnected to prevent a decrease of system fluid and/or fluid contamination.
The alternate HP manifold provides the interface between the alternate braking system and the parking brake system.
A tachometer is installed in each axle of the main landing gears to measure the speed of the wheel and send the data to the BSCU. The BSCU uses this data to compute the antiskid current given to the ABCU.
** ON A/C NOT FOR ALL The alternate braking with anti skid system is an electrohydraulic system that automatically becomes available when the normal braking system (Ref. AMM D/O 32-42-00-00) is not available. Braking inputs are made only at the brake pedals. The hydraulic power to operate the brakes is supplied from the Yellow Main Hydraulic Power System (Ref. 29-13-00). The BSCU (Ref. 32-42-00) controls the operation of the system and its anti skid function and also monitors the system to make sure that it is serviceable.
The system includes these primary components:
- a left alternate brake manifold
- a righ alternate brake manifold
- a HP manifold assembly
- a return manifold .
The system also uses the components that follow to supply the braking inputs or control functions necessary for the operation of the system:
- the transmitter unit 103GG at the brake pedals
- the selector valve 99GG
- the tachometer in each axle (Ref. AMM D/O 32-42-00-00)
- the second set of pistons at the brake units (32-42-00)
- the pressure transducers (100 GG and 101 GG) at each manifold assembly .
- it lets the hydraulic supply go to the system when braking inputs are made
- it lets the hydraulic pressure in the system go to the return manifold when braking inputs are not made.
The alternate manifold assemblies 2853GM and 2852GM are located in the wing shroud boxes and include:
- a manifold
- a servovalve (Direct Drive Valve)
- a safety valve (hydraulic fuse)
- a shuttle valve
- a pressure transducer.
The manifold has two supply ports.One supply port is for the alternate braking system and one for the parking brake system (Ref. AMM D/O 32-45-00-00). The service port connects to the brakes. The manifold also includes a filter.
The DDV operates when necessary to:
- connect the necessary hydraulic pressure through a safety valve to the related service port
- connect the service port to return.
The ABCU sends the necessary control current to the Alternte servovalve (Direct Drive Valve) to:
- give the correct pressure at the related brakes
- give the anti skid control.The ABCU substracts antiskid currents given by the BSCU to the pressure control current (function of the pedal angle) computed by the ABCU.
- connect the brakes to the return line.
The pressure output from the DDV goes through its related shuttle valve to isolate the pressure in the service line from the parking brake. The safety valve in the manifold acts as an hydraulic fuse. If a large leak occurs downstream of the safety valve, it closes to stop the flow for each pair of brakes. The pressure transducer measures the pressure that goes to the brakes and sends the data to the BSCU, ABCU and the Triple Pressure Indicator.
This lets the BSCU know if the operation of the applicable Alternate servovalve (Direct Drive Valve) is correct.
The alternate brake system connects to one of the two sets of pistons in each brake. The other set of pistons connect to the Normal brake system. A half-coupling connects each brake service line to a half-coupling on the brake. Each half-coupling seals automatically when disconnected to prevent a decrease of system fluid and/or fluid contamination.
The alternate HP manifold provides the interface between the alternate braking system and the parking brake system.
A tachometer is installed in each axle of the main landing gears to measure the speed of the wheel and send the data to the BSCU. The BSCU uses this data to compute the antiskid current given to the ABCU.
4. Power Supply
B. Hydraulic Power Supply
The hydraulic pressure is supplied from the Yellow Main Hydraulic Power system (Ref. AMM D/O 29-13-00-00).
The hydraulic pressure is supplied from the Yellow Main Hydraulic Power system (Ref. AMM D/O 29-13-00-00).
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6. Component Description
A. Alternate Brake Manifold Assembly FIN: 2852-GM FIN: 2853-GM
The manifold assembly is installed in the wing shroud box.The primary components of the manifold assembly are:
The manifold assembly is installed in the wing shroud box.The primary components of the manifold assembly are:
- An alternate brake manifold
- Three filters
- A check valve
- A shuttle valve
- A safety valve
- A servovalve (Direct Drive Valve (DDV))
- A pressure transducer.
(1) Manifold
The manifold has four ports which have union type connectors:
The manifold has internal bores that contain:
It also has external faces for the DDV and the pressure transducer. The filter protect the components installed in and on the manifold. A sealed plug keeps the filter in position.
The manifold has four ports which have union type connectors:
- Two supply ports A and D
- One service port B
- One return port C.
The manifold has internal bores that contain:
- The two inlet filters
- The shuttle valve
- The safety valve
- The check valve
- The filter at the service port.
It also has external faces for the DDV and the pressure transducer. The filter protect the components installed in and on the manifold. A sealed plug keeps the filter in position.
(2) Shuttle valve
The shuttle valve isolates the parking brake supply from the alternate brake supply.
The shuttle valve has a body that is installed in the manifold block. The body holds a valve and a spring. An end plug keep these items in the body and supplies a seat for the valve. Usually the spring keep the valve against the seat to let the alternate brake hydraulic supply go through the related brakes. When the parking brake is set, the parking brake hydraulic supply moves the valve against the spring. This lets the parking brake supply go through the related brakes and isolates the alternate brake supply.
The shuttle valve isolates the parking brake supply from the alternate brake supply.
The shuttle valve has a body that is installed in the manifold block. The body holds a valve and a spring. An end plug keep these items in the body and supplies a seat for the valve. Usually the spring keep the valve against the seat to let the alternate brake hydraulic supply go through the related brakes. When the parking brake is set, the parking brake hydraulic supply moves the valve against the spring. This lets the parking brake supply go through the related brakes and isolates the alternate brake supply.
(3) Safety valves
If a large leak occurs downstream of the safety valve, the valve closes to stop the flow of the hydraulic fluid to its related brakes. The safety valve has a valve, a spring and a plug. The plug holds the valve and the spring in the manifold, the spring keeps the valve off the valve seat. A flange around the valve has holes through it to let the hydraulic fluid go through the brakes.
When the fluid goes through the safety valve, the pressure at the rear of the flange (and in chamber X) moves the valve nearer the seat. This movement stops when the pressure in chamber X and the valve seat are equal. If a leak occurs downstream of the valve, the pressure at the valve seat decreases. This lets the pressure in chamber X move the valve against the seat to close the valve. The pressure in chamber X will keep the valve in the closed position until the plug is removed sufficiently to release it. When this occurs the spring moves the valve back to its initial position.
If a large leak occurs downstream of the safety valve, the valve closes to stop the flow of the hydraulic fluid to its related brakes. The safety valve has a valve, a spring and a plug. The plug holds the valve and the spring in the manifold, the spring keeps the valve off the valve seat. A flange around the valve has holes through it to let the hydraulic fluid go through the brakes.
When the fluid goes through the safety valve, the pressure at the rear of the flange (and in chamber X) moves the valve nearer the seat. This movement stops when the pressure in chamber X and the valve seat are equal. If a leak occurs downstream of the valve, the pressure at the valve seat decreases. This lets the pressure in chamber X move the valve against the seat to close the valve. The pressure in chamber X will keep the valve in the closed position until the plug is removed sufficiently to release it. When this occurs the spring moves the valve back to its initial position.
(4) Alternate servovalves (DDV)
The alternate servovalve (DDV) receives an input current from the ABCU which corresponds to the pressure necessary in the brakes.
In the alternate servovalve (DDV) an electronic stage controls a hydraulic stage. At the outlet port inside the alternate servovalve (DDV), there is a pressure transmitter. The information from the transmitter is sent to the electronic stage which compares it to the current sent by the ABCU and corrects its action on the hydraulic stage if necessary to get continuously the necessary braking pressure.
The alternate servovalve (DDV) is a three-way servo valve of the pressure control type. The alternate servovalve (DDV) has electrical and hydraulic assemblies.
The electrical assembly has:
The hydraulic assembly has:
The electronic assembly is installed in a housing on top of the valve body. Clamps and screws attach the torque motor to the valve body. The pressure transducer has a support that connects it to the valve body. The electronic amplifier has a circuit board to which the pressure transducer and the external electrical connector are connected.
The valve body has a distribution bore with drilling that connect to the pressure transducer and external ports P (supply), U (service) and R (return). The bore contains a liner assembly that has a slide valve, a spring and two end fittings. The slide valve can connect two ports at the same time as it moves in the bore. The torque motor has an eccentric shaft which engages vertically with the slide valve through a hole in the body. The spring is installed at one end of the slide valve to take up the clearance between the torque motor shaft and the slide valve. The end fittings seal the liner assembly in the bore.
The electronic amplifier receives a control current of between 0 mA to 32 mA through the electrical connector. The pressure transducer is permanently connected to the port U and gives an output signal in relation to the service pressure at port U. The electronic amplifier receives the output signal from the transducer and, in relation to the control current, supplies a current to the torque motor. The torque motor shaft then moves the slide valve to adapt the service pressure to the control current set.
When the alternate servovalve (DDV) is de-energized (0 mA input current), the slide valve is at the return position. Ports U and R are connected until the service pressure at port U is stable at 7 bar (101 psi).
When the alternate servovalve (DDV) is fully energized (32 mA input current), the torque motor moves the slide valve to the supply position. Ports P and U are connected until the service pressure at port U is stable at 175 bar (2538 psi). The return port R is isolated.
The pressure transducer continuously monitors the service pressure at port U. If the pressure is more or less than a set value, the electronic amplifier changes the control current to the torque motor. The slide valve moves between the supply position and the return position until the pressure at port U becomes stable at the set value. The return port R is isolated.
A change of the control current changes the control current to the torque motor. The slide valve moves until the pressure at port U becomes stable in relation to the control current set. For each change of control current, a different service pressure is supplied. The higher the current, the higher the service pressure at port U.
The alternate servovalve (DDV) receives an input current from the ABCU which corresponds to the pressure necessary in the brakes.
In the alternate servovalve (DDV) an electronic stage controls a hydraulic stage. At the outlet port inside the alternate servovalve (DDV), there is a pressure transmitter. The information from the transmitter is sent to the electronic stage which compares it to the current sent by the ABCU and corrects its action on the hydraulic stage if necessary to get continuously the necessary braking pressure.
The alternate servovalve (DDV) is a three-way servo valve of the pressure control type. The alternate servovalve (DDV) has electrical and hydraulic assemblies.
The electrical assembly has:
- A torque motor
- A pressure transducer
- An electronic amplifier
- A plug-in type electrical connector.
The hydraulic assembly has:
- A valve body
- A liner assembly.
The electronic assembly is installed in a housing on top of the valve body. Clamps and screws attach the torque motor to the valve body. The pressure transducer has a support that connects it to the valve body. The electronic amplifier has a circuit board to which the pressure transducer and the external electrical connector are connected.
The valve body has a distribution bore with drilling that connect to the pressure transducer and external ports P (supply), U (service) and R (return). The bore contains a liner assembly that has a slide valve, a spring and two end fittings. The slide valve can connect two ports at the same time as it moves in the bore. The torque motor has an eccentric shaft which engages vertically with the slide valve through a hole in the body. The spring is installed at one end of the slide valve to take up the clearance between the torque motor shaft and the slide valve. The end fittings seal the liner assembly in the bore.
The electronic amplifier receives a control current of between 0 mA to 32 mA through the electrical connector. The pressure transducer is permanently connected to the port U and gives an output signal in relation to the service pressure at port U. The electronic amplifier receives the output signal from the transducer and, in relation to the control current, supplies a current to the torque motor. The torque motor shaft then moves the slide valve to adapt the service pressure to the control current set.
When the alternate servovalve (DDV) is de-energized (0 mA input current), the slide valve is at the return position. Ports U and R are connected until the service pressure at port U is stable at 7 bar (101 psi).
When the alternate servovalve (DDV) is fully energized (32 mA input current), the torque motor moves the slide valve to the supply position. Ports P and U are connected until the service pressure at port U is stable at 175 bar (2538 psi). The return port R is isolated.
The pressure transducer continuously monitors the service pressure at port U. If the pressure is more or less than a set value, the electronic amplifier changes the control current to the torque motor. The slide valve moves between the supply position and the return position until the pressure at port U becomes stable at the set value. The return port R is isolated.
A change of the control current changes the control current to the torque motor. The slide valve moves until the pressure at port U becomes stable in relation to the control current set. For each change of control current, a different service pressure is supplied. The higher the current, the higher the service pressure at port U.
(5) Brake Yellow Pressure Transducers 100GG and 101GG
The pressure transducers send data to the BSCU, ABCU and to the Triple Indicator (right & left side).
The description is the same as the pressure transducer 96GG (Refer to 32-42-00-00).
The pressure transducers send data to the BSCU, ABCU and to the Triple Indicator (right & left side).
The description is the same as the pressure transducer 96GG (Refer to 32-42-00-00).
B. Alternate HP Manifold Assembly 3016GM
The manifold assembly is installed in the MLG bay, hydraulic compartment, on wall C47 right side.
The primary component parts of the manifold assembly are:
The manifold assembly is installed in the MLG bay, hydraulic compartment, on wall C47 right side.
The primary component parts of the manifold assembly are:
- the alternate brake manifold
- the alternate selector valve 99GG
- the pressure relief valve 3067GM
- the check valve 3058GM
- the pressure transmitter 3068GN
(1) Alternate Selector Valve 99GG
The description of the alternate selector valve is the same as the normal selector valve 23GG (Ref 32-42-00-00).
The description of the alternate selector valve is the same as the normal selector valve 23GG (Ref 32-42-00-00).
(2) Pressure Relief Valve 3067GM
The pressure relief valve returns the fluid directly to the reservoir in the case of overpressure.
It limits the pressure to 237 bars (3436 psi) if a thermal expansion occurs, and is also used for manual pressure release.
The pressure relief valve returns the fluid directly to the reservoir in the case of overpressure.
It limits the pressure to 237 bars (3436 psi) if a thermal expansion occurs, and is also used for manual pressure release.
(3) Check Valve 3058GM
The check valve isolates the supply line
The check valve isolates the supply line
(4) Yellow Accumulator Pressure Transmitter 3068GN
It is installed in the common supply line.It transmits data on the hydraulic fluid pressure to the third input of the brake Yellow-pressure triple indicator and to the ABCU.
It is installed in the common supply line.It transmits data on the hydraulic fluid pressure to the third input of the brake Yellow-pressure triple indicator and to the ABCU.
C. Alternate Brake Yellow - HP Filter 2862GM
The filter is installed in belly fairing area between frames C46 and C47 right side. It is the same as the Normal HP Filter (Refer to 32-42-00-00).
The filter is installed in belly fairing area between frames C46 and C47 right side. It is the same as the Normal HP Filter (Refer to 32-42-00-00).
D. Alternate-Brake Pedal Transmitter-Unit 103GG
The alternate-brake pedal transmitter-unit is installed at the captains pedals. It transmits the manual braking inputs to the ABCU. It is the same as the normal-brake pedal transmitter-unit 9GG (Refer 32-42-00-00).
Two sets of potentiometers are used for alternate braking, a third set is used for braking during towing operation.
The alternate-brake pedal transmitter-unit is installed at the captains pedals. It transmits the manual braking inputs to the ABCU. It is the same as the normal-brake pedal transmitter-unit 9GG (Refer 32-42-00-00).
Two sets of potentiometers are used for alternate braking, a third set is used for braking during towing operation.
(1) General
The ABCU is located in the right hand avionics bay.
The ABCU controls and monitors the alternate braking system with and without anti-skid protection.
When NORMAL system is activated, braking control and antiskid protection are provided by the BSCU.
When ALTERNATE braking circuit is activated, braking control is provided by the ABCU.Antiskid protection is still provided by the BSCU, which sends antiskid orders to the ABCU.
When PARKING brake circuit is activated , braking is controlled directly by the PARKING brake circuit.
The ABCU is automatically activated if:
The ABCU is located in the right hand avionics bay.
The ABCU controls and monitors the alternate braking system with and without anti-skid protection.
When NORMAL system is activated, braking control and antiskid protection are provided by the BSCU.
When ALTERNATE braking circuit is activated, braking control is provided by the ABCU.Antiskid protection is still provided by the BSCU, which sends antiskid orders to the ABCU.
When PARKING brake circuit is activated , braking is controlled directly by the PARKING brake circuit.
The ABCU is automatically activated if:
- the A/SKID & N/W STRG switch is selected to OFF position
- the BSCU is not serviceable (both system 1 and 2 failures)
- the normal braking system has failed
- only the batteries supply the aircraft.
(2) Alternate Braking
When ALTERNATE braking is activated:
The ABCU inhibits such braking orders according to a logic based on alternate pressure transducer and park on signals. Such inhibition prevents the alternate brake servovalves (Direct Drive Valve) from operating in low hydraulic
When ALTERNATE braking is activated:
- The ABCU energises the alternate brake selector valve and indicates to the BSCU that braking is activated on the ALTERNATE braking system.
- The ABCU determines the braking orders according to the brake pedal deflections measured by the brake pedal transmitter unit.
- The ABCU determines if antiskid protection is inhibited according to a predeterminated logic.If antiskid protection is not inhibited, the unit combines these braking orders with the antiskid orders sent by the BSCU.
The ABCU inhibits such braking orders according to a logic based on alternate pressure transducer and park on signals. Such inhibition prevents the alternate brake servovalves (Direct Drive Valve) from operating in low hydraulic
(3) Emergency Braking
When Emergency braking is activated the ABCU inhibits the antiskid protection and maintains a predeterminated level of braking even when the brake pedals are fully released.
When Emergency braking is activated the ABCU inhibits the antiskid protection and maintains a predeterminated level of braking even when the brake pedals are fully released.
(4) Monitoring of inputs
The ABCU continuously monitors the specific inputs, coming from the alternate brake pedal transmitter unit and the park accumulator pressure transducer and sends the indications to the BSCU or SDACs in case of failure detection with outputs discretes.
The ABCU continuously monitors the specific inputs, coming from the alternate brake pedal transmitter unit and the park accumulator pressure transducer and sends the indications to the BSCU or SDACs in case of failure detection with outputs discretes.
(5) Functional Test
During each flight, before landing and after downlocking of the NLG, the BSCU activates a functional test of the normal braking system.
Six seconds later, the BSCU sends functional test orders to the ABCU in a predetermined sequence to test the alternate braking capability. When the ABCU receives these orders, it modifies the selected inputs with predetermined stimuli, so as to be in various operational configurations leading to:
During each flight, before landing and after downlocking of the NLG, the BSCU activates a functional test of the normal braking system.
Six seconds later, the BSCU sends functional test orders to the ABCU in a predetermined sequence to test the alternate braking capability. When the ABCU receives these orders, it modifies the selected inputs with predetermined stimuli, so as to be in various operational configurations leading to:
- opening and closing of the alternate brake selector valve (99GG) and
- activation of the alternate brake servovalves (Direct Drive valves) (97GG) and (98GG).
One consequence of these stimuli is a fluctuation of the left and right side pressure values that can be seen on the Yellow brake pressure triple-indicator (60GG).
The BSCU monitors the proper performance of the functional test with specific pressure sensors located in the Alternate system.
(6) Services
The ABCU provides electrical power supply to alternate servovalves(Direct Drive Valves) and to the normal brake selector valve pressure transmitter (96GG).
Electrical power supply of the alternate servovalve (Direct Drive Valve) is cut by the ABCU in case of load short circuit.
The ABCU provides electrical power supply to alternate servovalves(Direct Drive Valves) and to the normal brake selector valve pressure transmitter (96GG).
Electrical power supply of the alternate servovalve (Direct Drive Valve) is cut by the ABCU in case of load short circuit.
(7) Unit architecture
The ABCU is composed of two functional modules:
The ABCU is composed of two functional modules:
- the power supply selection module (PSSM)
- the main functional module (MFM)
- DC Essential power supply (101PP).
- DC Battery power supply (701PP)
7. Operation/Control and Indicating
A. Control
To provide anti skid protection, the BSCU needs to know that the Yellow Main Hydraulic Power supply (Ref. AMM D/O 29-13-00-00) is available. It reads the input from the pressure switch (3151GN) to get this data. If the BSCU cannot give or control the anti skid function, the caption ANTI SKID shows in amber on the system display (WHEEL page). The braking system then operates in the Alternate Braking without Anti Skid mode (Ref. AMM D/O 32-44-00-00).
The regulators used for the Normal system are also used for anti skid regulation.
A pressure transducer 3068GN (on the Alternate HP Brake Manifold Assembly) continuously measures the (Yellow) pressure available in the Alternate braking system. The top gage of the triple pressure indicator (Ref. AMM D/O 32-44-00-00) shows this pressure.
When the ABCU gets an input from the brake pedal transmitter 103GG it:
The operation of the selector valve causes the Yellow hydraulic pressure to go to the Alternate Brake Manifold Assembly at each landing gear.
At the same time that the selector valve is energized, the BSCU sends a control current through the ABCU to the applicable Alternate servovalves (Direct Drive Valves) .The control current is set for the necessary pressure at the related brakes. The pressure output from each alternate servovalve (Direct Drive Valve) goes through its related shuttle valve to isolate the supply from the parking brake system. The safety valves let the pressure go through to the second set of pistons in the brakes. The pistons extend and the brakes operate to decrease the speed of the wheels.
A pressure transducer in the supply line to each pair of brakes measures the hydraulic pressure in the brake supply line. The bottom two gages of the triple pressure indicator show the pressure in the brake supply lines (Ref. AMM D/O 32-44-00-00).
To provide anti skid protection, the BSCU needs to know that the Yellow Main Hydraulic Power supply (Ref. AMM D/O 29-13-00-00) is available. It reads the input from the pressure switch (3151GN) to get this data. If the BSCU cannot give or control the anti skid function, the caption ANTI SKID shows in amber on the system display (WHEEL page). The braking system then operates in the Alternate Braking without Anti Skid mode (Ref. AMM D/O 32-44-00-00).
The regulators used for the Normal system are also used for anti skid regulation.
A pressure transducer 3068GN (on the Alternate HP Brake Manifold Assembly) continuously measures the (Yellow) pressure available in the Alternate braking system. The top gage of the triple pressure indicator (Ref. AMM D/O 32-44-00-00) shows this pressure.
When the ABCU gets an input from the brake pedal transmitter 103GG it:
- energizes the alternate brake selector valve 99GG
- sends the necessary control current to the alternate servovalves (Direct Drive Valves) in the system to get the correct pressure (set at the brake pedal/s) at the related brakes.
The operation of the selector valve causes the Yellow hydraulic pressure to go to the Alternate Brake Manifold Assembly at each landing gear.
At the same time that the selector valve is energized, the BSCU sends a control current through the ABCU to the applicable Alternate servovalves (Direct Drive Valves) .The control current is set for the necessary pressure at the related brakes. The pressure output from each alternate servovalve (Direct Drive Valve) goes through its related shuttle valve to isolate the supply from the parking brake system. The safety valves let the pressure go through to the second set of pistons in the brakes. The pistons extend and the brakes operate to decrease the speed of the wheels.
A pressure transducer in the supply line to each pair of brakes measures the hydraulic pressure in the brake supply line. The bottom two gages of the triple pressure indicator show the pressure in the brake supply lines (Ref. AMM D/O 32-44-00-00).
B. Braking during towing operation
A function in the ABCU allows to brake the aircraft during towing operation. The ABCU is able to switch from DC Essential Power Supply to the Hot bus Power Supply when no electrical power supply is available and the pedals are depressed.The ABCU is connected to a third set of potentiometers in the alternate BPTU and a connection to the Hot bus Power Supply is done.Park Brake can be applied, as well without electricity on board (batteries only).
A function in the ABCU allows to brake the aircraft during towing operation. The ABCU is able to switch from DC Essential Power Supply to the Hot bus Power Supply when no electrical power supply is available and the pedals are depressed.The ABCU is connected to a third set of potentiometers in the alternate BPTU and a connection to the Hot bus Power Supply is done.Park Brake can be applied, as well without electricity on board (batteries only).
C. Indicating
(1) Wheel Page
If the Normal Braking system is not available, the BSCU will automatically select the Alternate Braking with Anti Skid system. When the Normal Braking system is not available:
If none of these conditions are met, nothing is displayed on the WHEEL PAGE.
If the Normal Braking system is not available, the BSCU will automatically select the Alternate Braking with Anti Skid system. When the Normal Braking system is not available:
- the WHEEL page shows the caption NORM BRK in amber and the caption ALTN BRK in green
- the AUTO BRK pushbutton light extinguishes.
- the alternate braking mode is available (loss of the normal braking), the green or yellow pressure are not low and both BSCU channels are faulty or the anti-skid switch is set to off,
- or, the NORM BRK message is displayed,
- or, the AUTO BRK message is displayed.
If none of these conditions are met, nothing is displayed on the WHEEL PAGE.
(2) Alternate Braking System Warnings
Each condition shown below causes:
Each condition shown below causes:
- the master caution light to come on
- a single aural chime to operate
- the WHEEL page to show on SYSTEM DISPLAY
- the EWD to show the related message
(a) BRAKES NORM+ALTN FAULT
- Normal braking and Alternate braking mode failure
- SC, MAST CAUT, message on EWD and SD
The conditions, which trigger this warning, are: - A normal braking fault,
- or, a green low pressure,
- or, an anti-skid fault or A/SKID & N/W STRG switch selected OFF,
and - an alternate braking fault,
- or, an anti-skid fault or A/SKID & N/W STRG switch selected OFF,
- or, a yellow low pressure
and - a yellow accumulator low pressure.
(b) BRAKES ALTN BRK FAULT
In case of ALTN L and ALTN R RELEASED fault
In case of ALTN L and ALTN R RELEASED fault
(c) BRAKES ALTN L(R) RELEASED
This message warns the crew that the braking will be asymmetric in case of normal braking failure.
This message warns the crew that the braking will be asymmetric in case of normal braking failure.