DOC AIRBUS | AMM A320FTHS HYDRAULIC ACTUATION - DESCRIPTION AND OPERATION
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** ON A/C NOT FOR ALL
** ON A/C NOT FOR ALL
** ON A/C NOT FOR ALL
1. General
The Trimmable Horizontal Stabilizer (THS) actuator moves the control surface of the THS. The THS actuator is an electro-hydraulic unit that changes the mechanical or the electrical pitch-trim commands into mechanical movements.
The THS actuator has two hydraulic motors and a pitch-trim actuator. The pitch trim actuator controls the hydraulic actuation. Two hydraulic systems, Yellow and Green which supply power to the hydraulic motors. These systems have their independent fluid supplies.
Access door 312AR gives access to the THS actuator.
** ON A/C NOT FOR ALL The Trimmable Horizontal Stabilizer (THS) actuator moves the control surface of the THS. The THS actuator is an electro-hydraulic unit that changes the mechanical or the electrical pitch-trim commands into mechanical movements.
The THS actuator has two hydraulic motors and a pitch-trim actuator. The pitch trim actuator controls the hydraulic actuation. Two hydraulic systems, Yellow and Green which supply power to the hydraulic motors. These systems have their independent fluid supplies.
Access door 312AR gives access to the THS actuator.
2. Component Location
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Component Location| FIN | FUNCTIONAL DESIGNATION | PANEL | ZONE | ACCESS DOOR | ATA REF |
|---|---|---|---|---|---|
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| 9CE | ACTUATOR-THS | 311 | 27-44-51 | ||
| ** ON A/C NOT FOR ALL | |||||
| 9CE | ACTUATOR-THS | 312AR | 311 | 27-44-51 | |
3. System Description
The THS actuator moves the THS. The THS actuator is an electro-hydraulic unit. Its component parts are:
The THS actuator components are:
The THS actuator controls mechanically the deflection of the THS with a servo system. The input signal of the servo system has an electrical position sequence. The input signal is transmitted by the Elevator Aileron Computer (ELAC) and the Spoiler Elevator Computer (SEC). It is transmitted to the pitch trim actuator, which is part of the THS actuator, to move the gear trains of the control loop.
A mechanical input link is connected to the gear trains of the control loop through an override mechanism. This mechanism allows the pilot to override the ELAC and SEC signals with the pitch trim wheel in the cockpit.
If there is a loss of hydraulic power or control signal, the THS actuator makes sure that the THS is fully locked.
The two hydraulic systems supply fluid independently to the hydraulic motors. The output force from the hydraulic motors is transmitted to the screw shaft through a power differential gear followed by a reducing gear. Therefore, it is possible to operate one circuit at half of the maximum speed.
The double control loop-gear sends the input and reset signals to the valve blocks.
A comparison system makes sure that the THS actuator is locked if one of the control valves or one of the control gear loops locks.
In normal operation mode, the SEC and the ELAC transmit the signal to the pitch-trim actuator electrically or automatically. The signals activate one of the three electric motors of the pitch-trim actuator and the motor moves the double control gear loop.
If there is a failure of an upper primary load-path component, the ELSD is activated.
The THS actuator has the following items which make maintenance easier:
The THS actuator includes:
** ON A/C NOT FOR ALL The THS actuator moves the THS. The THS actuator is an electro-hydraulic unit. Its component parts are:
- two hydraulic motors,
- one pitch trim actuator,
- one fail-safe ball screwjack,
- one mechanical input shaft,
- two pressure-off brakes,
- two position transducer packs,
- one gear box,
- two hydraulic valve blocks.
The THS actuator components are:
- Two hydraulic motors
- One pitch trim actuator
- One fail-safe ball screw-jack
- One mechanical input shaft
- Two pressure-off brakes
- Two position transducer packs
- One gear box
- Two hydraulic valve blocks
- One upper secondary load-path detection-device (Electrical Load Sensing Device (ELSD)).
The THS actuator controls mechanically the deflection of the THS with a servo system. The input signal of the servo system has an electrical position sequence. The input signal is transmitted by the Elevator Aileron Computer (ELAC) and the Spoiler Elevator Computer (SEC). It is transmitted to the pitch trim actuator, which is part of the THS actuator, to move the gear trains of the control loop.
A mechanical input link is connected to the gear trains of the control loop through an override mechanism. This mechanism allows the pilot to override the ELAC and SEC signals with the pitch trim wheel in the cockpit.
If there is a loss of hydraulic power or control signal, the THS actuator makes sure that the THS is fully locked.
The two hydraulic systems supply fluid independently to the hydraulic motors. The output force from the hydraulic motors is transmitted to the screw shaft through a power differential gear followed by a reducing gear. Therefore, it is possible to operate one circuit at half of the maximum speed.
The double control loop-gear sends the input and reset signals to the valve blocks.
A comparison system makes sure that the THS actuator is locked if one of the control valves or one of the control gear loops locks.
In normal operation mode, the SEC and the ELAC transmit the signal to the pitch-trim actuator electrically or automatically. The signals activate one of the three electric motors of the pitch-trim actuator and the motor moves the double control gear loop.
If there is a failure of an upper primary load-path component, the ELSD is activated.
The THS actuator has the following items which make maintenance easier:
- Inspection windows, which allow a visual inspection of the power gear teeth
- A cranking shaft, which is used to manually crank the power differential output shaft.
The THS actuator includes:
- An oil drain port with a magnetic plug
- Fill and drain adaptors to replace oil
- An oil breather to keep the interior of the gear box at atmospheric pressure
- A grease nipple on the flange of the ball nut, which permits the lubrication of the nut
- A rigging pin located at the mechanical input, to keep the stabilizer at the zero degrees position
- A mechanical indicator, to show no-back wear
- Two mounting devices on each side of the gear box, which permit easier removal of the oil
- An oil level sight-glass to see the level of the oil in the gear box.
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5. Component Description
A. Hydraulic Motors FIN: 9-CE
Two hydraulic motors are installed on the THS actuator. The hydraulic motors are of fixed displacement type. The hydraulic fluid that enters into the pressure port turns the rotating group. The rotating group has nine pistons. The pistons, that move in the bores of the cylinder barrel, give the necessary torque. The torque is transmitted through a splined drive shaft to the gear box of the THS actuator.
Two drain tubes are installed below the flanges of the hydraulic motors. These drain tubes drain the leakage of the hydraulic motors.
Two hydraulic motors are installed on the THS actuator. The hydraulic motors are of fixed displacement type. The hydraulic fluid that enters into the pressure port turns the rotating group. The rotating group has nine pistons. The pistons, that move in the bores of the cylinder barrel, give the necessary torque. The torque is transmitted through a splined drive shaft to the gear box of the THS actuator.
Two drain tubes are installed below the flanges of the hydraulic motors. These drain tubes drain the leakage of the hydraulic motors.
B. Fail-Safe Ball Screw-Jack
(1) Fail safe system
The fail-safe tie bar goes through the center of the screw shaft and prevents the axial separation of the screw shaft. The fail-safe ball screw-jack has two load paths, the primary and the secondary. The primary load path transmits the load and the secondary path stays free of load. If the primary load path is axially separated, the secondary path retrieves the load and prevents damage to the ball screw-jack. Therefore, the two ends continue to turn if the screw shaft is fractured.
The fail-safe tie bar goes through the center of the screw shaft and prevents the axial separation of the screw shaft. The fail-safe ball screw-jack has two load paths, the primary and the secondary. The primary load path transmits the load and the secondary path stays free of load. If the primary load path is axially separated, the secondary path retrieves the load and prevents damage to the ball screw-jack. Therefore, the two ends continue to turn if the screw shaft is fractured.
(2) Ball screw-jack
The ball screw-jack is made up of the ball screw and the fail-safe ball nut. The fail-safe ball nut has three transport guides, a threaded fail-safe unit wiper and an ice chipper. The mechanical input shaft limits the range of travel of the screw-jack.
The ball screw-jack is made up of the ball screw and the fail-safe ball nut. The fail-safe ball nut has three transport guides, a threaded fail-safe unit wiper and an ice chipper. The mechanical input shaft limits the range of travel of the screw-jack.
(3) No-back system
The THS actuator with a no-back system has a no-back brake of ratchet and pawl type. The no-back brake holds the ball screw in its last position. It prevents movement of the ball screw under aerodynamic loads. A no-back wear detection device in the form of an indicator (no-back wear indicator) is installed on the lower side of the gear box. The indicator has a cam roller which faces the top edge of the claw-stop. This finds the gap which agrees with the wear limit to be detected.
If a high wear occurs, a compressive external load causes the top claw-stop to move up to a higher position. This causes the top claw-stop to touch the cam roller of the indicator. This makes the red finger of the indicator to "popout" and gives a visual wear alarm.
The THS actuator with a no-back system has a no-back brake of ratchet and pawl type. The no-back brake holds the ball screw in its last position. It prevents movement of the ball screw under aerodynamic loads. A no-back wear detection device in the form of an indicator (no-back wear indicator) is installed on the lower side of the gear box. The indicator has a cam roller which faces the top edge of the claw-stop. This finds the gap which agrees with the wear limit to be detected.
If a high wear occurs, a compressive external load causes the top claw-stop to move up to a higher position. This causes the top claw-stop to touch the cam roller of the indicator. This makes the red finger of the indicator to "popout" and gives a visual wear alarm.
(4) ELSD
If there is a failure of a component of an upper-primary load-path, the ELSD changes the THS actuator RVDT MON 2 signal. The signal change is detected by the Flight Control Computer (FCC). The message "ELAC2 PITCH FAULT" is shown on the Electronic Centralized Aircraft Monitoring (ECAM) display unit.
If there is a failure of a component of an upper-primary load-path, the ELSD changes the THS actuator RVDT MON 2 signal. The signal change is detected by the Flight Control Computer (FCC). The message "ELAC2 PITCH FAULT" is shown on the Electronic Centralized Aircraft Monitoring (ECAM) display unit.
C. Control Valve Blocks
The THS actuator has two control valve blocks. The two valve blocks control the operation of the THS actuator. Each valve block has:
The control valve blocks supply pressure to the hydraulic motors and the brake release piston. The control valve blocks can be installed on the left or on the right side of the THS actuator.
The THS actuator has two control valve blocks. The two valve blocks control the operation of the THS actuator. Each valve block has:
- A high pressure filter
- An inlet and outlet port
- Two input control shafts
- A control valve
- A shut-off valve
- A Pressure-Off Brake (POB) control valve
- A control device for the shut-off valve.
The control valve blocks supply pressure to the hydraulic motors and the brake release piston. The control valve blocks can be installed on the left or on the right side of the THS actuator.
D. Gearbox
The gearbox is in a split housing. The two housing parts are made of a light metal alloy. They are referred to as the upper casing and the lower casing. The upper casing holds the screw and the no-back housing assembly. It also supports the two hydraulic motors, the mechanical input lever and the control position transducer.
The lower casing supports:
The oil, which is necessary to lubricate the internal components, is in the gearbox. The level of the oil can be visually checked through an oil level sight-glass. The oil level sight-glass is on the upper casing.
The gearbox is in a split housing. The two housing parts are made of a light metal alloy. They are referred to as the upper casing and the lower casing. The upper casing holds the screw and the no-back housing assembly. It also supports the two hydraulic motors, the mechanical input lever and the control position transducer.
The lower casing supports:
- The pitch-trim actuator
- The monitor position transducer
- The two POBs
- Two hydraulic block valves
- The magnetic drain plug.
The oil, which is necessary to lubricate the internal components, is in the gearbox. The level of the oil can be visually checked through an oil level sight-glass. The oil level sight-glass is on the upper casing.
E. Pressure-Off Brakes
Each hydraulic motor shaft has a POB. Each POB is located at the output shaft of its related hydraulic motor. The POB is a dry brake with a hydraulic release which is used to lock the shaft of the motor. The shaft of the motor is locked if a failure occurs in the hydraulic system or in a hydraulic motor. Thus, this will help the second motor to fully control the ball screw through the power difference.
Each hydraulic motor shaft has a POB. Each POB is located at the output shaft of its related hydraulic motor. The POB is a dry brake with a hydraulic release which is used to lock the shaft of the motor. The shaft of the motor is locked if a failure occurs in the hydraulic system or in a hydraulic motor. Thus, this will help the second motor to fully control the ball screw through the power difference.
F. Pitch Trim Actuator
The pitch trim actuator has:
The pitch trim actuator has:
(1) Three brushless motors with an electro-magnetic clutch. In normal mode, one clutch will be applied (energized) and the others are de-clutched (de-energized). The output of the three motors is connected to move the input shaft through a reduction gear.
(2) Three electronic sets control each motor. The electronic sets also control the signal from the ELAC/SEC computers.
(3) An override mechanism with three microswitches. It is installed on the bottom of the reduction gearbox. The override mechanism is mechanically connected to the input shaft.
G. Position Transducer
The THS actuator has two inductive position-transducer packages: the command position transducer and the monitor position transducer.
The command position transducer is used to find the position of the override mechanism. It finds the position of the control system of the THS actuator through the output/input control sequence.
The monitor position transducer is used to find the position of the ball screw.
The THS actuator has two inductive position-transducer packages: the command position transducer and the monitor position transducer.
The command position transducer is used to find the position of the override mechanism. It finds the position of the control system of the THS actuator through the output/input control sequence.
The monitor position transducer is used to find the position of the ball screw.
H. Structural Components
The structural components include:
The THS actuator is connected to the horizontal stabilizer through the dual concentric axles, the attachment plates and the fail safe plates. These are installed on the trunnions of the ball nut.
A primary ring gimbal attaches the THS actuator to the structure. The primary ring gimbal is installed on the two linking axles of the no-back housing spigots.
The structural components have a two-path configuration. Usually, there is no load on the secondary load path.
The structural components include:
- The attachments to the horizontal stabilizer
- The attachments to the THS actuator and the structure
- The ball screw and the ball nut.
The THS actuator is connected to the horizontal stabilizer through the dual concentric axles, the attachment plates and the fail safe plates. These are installed on the trunnions of the ball nut.
A primary ring gimbal attaches the THS actuator to the structure. The primary ring gimbal is installed on the two linking axles of the no-back housing spigots.
The structural components have a two-path configuration. Usually, there is no load on the secondary load path.
I. Line Replaceable Units (LRU)
The Line Replaceable Units (LRU) connected to the THS actuator are as follows:
The LRUs connected to the THS actuator are as follows:
The Line Replaceable Units (LRU) connected to the THS actuator are as follows:
- electronic control module of each of the electric motors,
- pitch trim actuator,
- position transducer packs,
- filter,
- hydraulic motors.
The LRUs connected to the THS actuator are as follows:
- The electronic control module of each of the electric motors
- The pitch trim actuator
- The position transducer packs
- The filter
- The hydraulic motors
- The ELSD.
J. Technical Data
(1) Mechanical
| --------------------------------------------------------------------- |
| - THS actuator travel with a total |
| THS angular movement 17.5 degrees |
| - Operation travel 513.75 mm (20.23 in.) |
| - Stop-to-stop travel 531.75 mm (20.94 in.) |
| - Used travel of the electrical inputs 2105 rev |
| - Used travel of the mechanical inputs 6.13 rev |
| - Limit load |
| - Tensile 12.700 daN (28.550 lbf.) |
| - Compressive 19.000 daN (46.086 lbf.) |
| - Weight (when filled with fluid) 47.9 kg (105.4 lb.) |
(2) Hydraulic
| --------------------------------------------------------------------- |
| - Maximum flow for each circuit 27 l/min (7.02 USgal.mn) |
| - Maximum internal leakage 1 to 1.5 l/min |
| (0.264 to 0.396 USgal.mn) |
| - Maximum external leakage Nil |
| - Operation pressure of pressure-off |
| brake 100 bar (1450 psi) |
6. Operation
A. Normal Operation
The Green and Yellow hydraulic systems send hydraulic power through the valve blocks to the POB of the hydraulic motors. When the POB receives the hydraulic power, the hydraulic system releases the shafts of the hydraulic motors. Then, the two hydraulic motors are ready for operation.
The electrical pitch trim signal of the pitch trim actuator operates servo motor 1. This servo motor operates both control valves in the open configuration while the other two servo motors are in stand-by mode. Servo motor 1 operates through a path that includes:
Each of the separate gear paths includes:
The epicyclic control differential-output moves the control valve.
The control valve controls the hydraulic fluid flow to the hydraulic motors. Both hydraulic motors operate at the same time and move the ball screw through the power differential and the power gear train.
As the pitch-trim actuator output continues to rotate, it keeps the control valve open. Then, the hydraulic motors operate to move the ball screw.
When the pitch-trim actuator output gets to the position specified by the signal on the servo motor, the control differential input is stopped.
The feedback gears move the control differential output which decreases the opening of the control valve.
The control valve closes and the hydraulic flow to the motors stops. Then the ball screw-jack stops at the specified position.
The interval stops attached to the mechanical input keep the travel of the ball screw-jack shaft to a limit. The ball screw has claw-type stops attached to each end. The internal stops prevent mechanical overrun even if the internal stops do not operate.
The Green and Yellow hydraulic systems send hydraulic power through the valve blocks to the POB of the hydraulic motors. When the POB receives the hydraulic power, the hydraulic system releases the shafts of the hydraulic motors. Then, the two hydraulic motors are ready for operation.
The electrical pitch trim signal of the pitch trim actuator operates servo motor 1. This servo motor operates both control valves in the open configuration while the other two servo motors are in stand-by mode. Servo motor 1 operates through a path that includes:
- A pitch-trim actuator reduction-gear
- A mechanical override mechanism.
Each of the separate gear paths includes:
- A primary detent
- An epicyclic control differential
- A control gear train, which has an eccentric device
- A control valve detent
- A control valve command shaft.
The epicyclic control differential-output moves the control valve.
The control valve controls the hydraulic fluid flow to the hydraulic motors. Both hydraulic motors operate at the same time and move the ball screw through the power differential and the power gear train.
As the pitch-trim actuator output continues to rotate, it keeps the control valve open. Then, the hydraulic motors operate to move the ball screw.
When the pitch-trim actuator output gets to the position specified by the signal on the servo motor, the control differential input is stopped.
The feedback gears move the control differential output which decreases the opening of the control valve.
The control valve closes and the hydraulic flow to the motors stops. Then the ball screw-jack stops at the specified position.
The interval stops attached to the mechanical input keep the travel of the ball screw-jack shaft to a limit. The ball screw has claw-type stops attached to each end. The internal stops prevent mechanical overrun even if the internal stops do not operate.
B. Mechanical Control Operation
The input shaft, which is connected to the cable control, moves the mechanical servo loop mechanism through an override mechanism. The override mechanism installed in the pitch trim actuator makes sure that the mechanical control cancels the electrical control.
The input shaft, which is connected to the cable control, moves the mechanical servo loop mechanism through an override mechanism. The override mechanism installed in the pitch trim actuator makes sure that the mechanical control cancels the electrical control.
(1) Operation with the pitch trim actuator in OFF mode
If a manual command signal is applied with the handwheel to drive the THS actuator (the pitch trim actuator does not operate), the override mechanism stays off. The input signal is transmitted directly to the control valves of the valve block.
If a manual command signal is applied with the handwheel to drive the THS actuator (the pitch trim actuator does not operate), the override mechanism stays off. The input signal is transmitted directly to the control valves of the valve block.
(2) Operation of the override mechanism
If an electrical pitch-trim command controls the pitch-trim actuator servo motor, (the manual command signal applied through the mechanical input) it causes the override mechanism to break out. This mechanically disconnects the pitch-trim actuator output from the command loop of the THS actuator. Then, both control valves are driven through the manual command signal of the THS actuator.
The overriding procedure is possible when the THS actuator is controlled in a fixed position (the handwheel stays in the neutral position).
The overriding procedure is also possible when the THS actuator moves with a variable electrical command-signal (the handwheel turns).
If an electrical pitch-trim command controls the pitch-trim actuator servo motor, (the manual command signal applied through the mechanical input) it causes the override mechanism to break out. This mechanically disconnects the pitch-trim actuator output from the command loop of the THS actuator. Then, both control valves are driven through the manual command signal of the THS actuator.
The overriding procedure is possible when the THS actuator is controlled in a fixed position (the handwheel stays in the neutral position).
The overriding procedure is also possible when the THS actuator moves with a variable electrical command-signal (the handwheel turns).
C. Ground Operation from the Electric Pumps
In low fluid flow conditions, the pressure relief valve keeps the pressure-off brakes released.
In low fluid flow conditions, the pressure relief valve keeps the pressure-off brakes released.
D. Operation in Failure Conditions
(1) Operation with loss of hydraulic power
The THS actuator is independently supplied with power from the two hydraulic systems. When one hydraulic supply to the THS actuator does not operate, the related POB is activated.
If the POB stops and holds the hydraulic motor shaft, the THS actuator is operated by the other hydraulic system at half speed. But the performance will not change.
If a full loss of hydraulic power occurs, the POB and the no-back brake operate. They keep the ball screw-jack in the last specified position against the aerodynamic pressure.
The THS actuator is independently supplied with power from the two hydraulic systems. When one hydraulic supply to the THS actuator does not operate, the related POB is activated.
If the POB stops and holds the hydraulic motor shaft, the THS actuator is operated by the other hydraulic system at half speed. But the performance will not change.
If a full loss of hydraulic power occurs, the POB and the no-back brake operate. They keep the ball screw-jack in the last specified position against the aerodynamic pressure.
(2) Operation with a blocked control valve
When a control valve is blocked, the jamming protection device operates to stop the hydraulic power. The control valve opening in the defective circuit lets the hydraulic motor operate continuously. This causes the ball screw to operate and it moves the feed-back gear (after the serviceable control valve goes to the neutral position). This generates a break out of the primary detent in the defective control loop. The primary detent tries to open the serviceable control valve.
When the serviceable control valve is open, it activates the comparator, which is connected to the control valves. The piston of the comparator operates both shut-off valves. The shut-off valves isolate the hydraulic power supply from the THS actuator on the two circuits. This will stop the motor that is usually supplied by the defective valve. Thus, the POB is activated and it stops the ball screw.
If the control valve blocks in a position that is not in the limits of the protection device:
When a control valve is blocked, the jamming protection device operates to stop the hydraulic power. The control valve opening in the defective circuit lets the hydraulic motor operate continuously. This causes the ball screw to operate and it moves the feed-back gear (after the serviceable control valve goes to the neutral position). This generates a break out of the primary detent in the defective control loop. The primary detent tries to open the serviceable control valve.
When the serviceable control valve is open, it activates the comparator, which is connected to the control valves. The piston of the comparator operates both shut-off valves. The shut-off valves isolate the hydraulic power supply from the THS actuator on the two circuits. This will stop the motor that is usually supplied by the defective valve. Thus, the POB is activated and it stops the ball screw.
If the control valve blocks in a position that is not in the limits of the protection device:
- The two hydraulic motors can operate in the opposite direction at a low speed
- The THS actuator does not move
- The jamming detection is sensitive and makes sure that a permanent flow rate of fluid is supplied to prevent overheating.
(3) Operation with disconnected ball screw
If the ball screw is disconnected, the no-back brake holds it in the last signaled position.
If the ball screw is disconnected, the no-back brake holds it in the last signaled position.
7. Test
A. Ground Test
Different checks can be done when the Yellow and Green hydraulic systems are depressurized. The subsequent tests/checks are:
Different checks can be done when the Yellow and Green hydraulic systems are depressurized. The subsequent tests/checks are:
Different checks can be done when the Yellow and Green hydraulic systems are depressurized. The subsequent tests/checks are:
- The operational/test of the valve-jamming protection system.
- The functional test of the pressure off brake.
- The functional test of the no-back brake assembly.
- To check the integrity of the ball screw shaft and the tie bar.
- The visual inspection of the power gears in position with a borescope.
- The visual inspection of the oil level in the gear box through an oil level sight-glass.
Different checks can be done when the Yellow and Green hydraulic systems are depressurized. The subsequent tests/checks are:
- The Operational test of the valve-jamming protection system
- The Functional test of the pressure-off brake
- The Functional test of the no-back brake assembly
- The Check of the integrity of the ball screw shaft and the tie bar
- The Visual inspection of the power gears in position with a borescope
- The Visual inspection of the oil level in the gear box through an oil level sight-glass
- The ELSD integrity/functional test.