DOC AIRBUS | AMM A320FELEVATOR AND HYDRAULIC ACTUATION - DESCRIPTION AND OPERATION
** ON A/C NOT FOR ALL
** ON A/C NOT FOR ALL
1. General
Two electrohydraulic servocontrols hydraulically actuate each elevator.
** ON A/C NOT FOR ALL Two electrohydraulic servocontrols hydraulically actuate each elevator.
2. Component Location
** ON A/C NOT FOR ALL 
Location of Elevator Servocontrol| FIN | FUNCTIONAL DESIGNATION | PANEL | ZONE | ACCESS DOOR | ATA REF |
|---|---|---|---|---|---|
| ** ON A/C ALL | |||||
| 34CE1 | SERVO CTL-L ELEVATOR, INBD G | 335 | 27-34-51 | ||
| 34CE2 | SERVO CTL-R ELEVATOR, INBD Y | 345 | 27-34-51 | ||
| 34CE3 | SERVO CTL-L ELEVATOR, OUTBD B | 335 | 27-34-51 | ||
| 34CE4 | SERVO CTL-R ELEVATOR, OUTBD B | 345 | 27-34-51 | ||
3. Component Description
(1) General
Each elevator is equipped with two interchangeable fixed-body electrically-controlled servo controls.
Each servo control is connected to two ELACs and to two SECs.
NOTE: vibrations could occur in the following configuration:
Each elevator is equipped with two interchangeable fixed-body electrically-controlled servo controls.
Each servo control is connected to two ELACs and to two SECs.
NOTE: vibrations could occur in the following configuration:
- vibrations along the cabin and in the cockpit and
- elevator control with SECs active and ELACs not active,
No trouble shooting is necesary (elevator oscillations are wider in SEC mode than ELAC mode).
Each elevator is actuated by a servo control in the active mode, while the other is in the damping mode.
the active computer achieves the closed loop control of one servo control and commands the damping mode on the adjacent servo control.
In the normal configuration, the inboard servo control is in the active mode.
4. Operation
A. General
Each servo control has three operating modes:
Each servo control has three operating modes:
- the active mode which permits the actuation of the elevator depending on electrical orders,
- the damping mode which prevents the appearance of flutter in the event of multiple failures (mainly dual hydraulic or electrical failures, disconnection of one servocontrol associated to the hydraulic or electrical failure of the other servo control),
- the centering mode which permits to bring back and hold the elevator in the 0 position in the event of a loss of the electrical control of the two servo controls of a surface.
B. Normal operation with the servocontrol pressurized.
The pressurization of the servocontrol involves the opening of the pressure-line closing valve (2) and of the return-line closing valve (3).
Thus, the servovalve (4) is supplied from the HP system and the return system of the servocontrol is connected to the LP system.
The pressurization of the servocontrol involves the opening of the pressure-line closing valve (2) and of the return-line closing valve (3).
Thus, the servovalve (4) is supplied from the HP system and the return system of the servocontrol is connected to the LP system.
(1) Servocontrol in the active mode.
In this case, the two solenoid valves (1) are de-energized and let out the HP flow which sets the mode selector valve (5) in the active mode.
Thus, the two actuator chambers are connected to the servovalve control line and the servovalve passes in the active mode.
The mode selector-valve transducer (11) supplies an electrical signal which identifies this change of state.
The feedback transducer (10) gives the servoloop feedback.
In this case, the two solenoid valves (1) are de-energized and let out the HP flow which sets the mode selector valve (5) in the active mode.
Thus, the two actuator chambers are connected to the servovalve control line and the servovalve passes in the active mode.
The mode selector-valve transducer (11) supplies an electrical signal which identifies this change of state.
The feedback transducer (10) gives the servoloop feedback.
NOTE: If two feedback transducers are installed, one of the two feedback transducers gives the servoloop feedback. The other is in standby and used in case of failure.
NOTE: If three feedback transducers are installed, the third is not used.
The elevator position transducer-unit is used for the monitoring.
The servovalve transducer (12) is also used for the monitoring.
The elevator position transducer-unit is used for the monitoring.
The servovalve transducer (12) is also used for the monitoring.
(2) Servocontrol in the damping mode.
One solenoid valve at least is energized and the mode selector is displaced in the damping mode under the action of its spring.
This causes the interconnection of the two actuator chambers through the damping orifice (6).
The mode selector-valve transducer identifies this change of state.
The check valve (7) and the fluid reserve (9) hold the volume of fluid in the actuator chambers :
One solenoid valve at least is energized and the mode selector is displaced in the damping mode under the action of its spring.
This causes the interconnection of the two actuator chambers through the damping orifice (6).
The mode selector-valve transducer identifies this change of state.
The check valve (7) and the fluid reserve (9) hold the volume of fluid in the actuator chambers :
- if the temperature of the hydraulic fluid changes,
- if there is a leakage.
(3) Servocontrol in the centering mode.
With the solenoid valves and servovalve de-energized the servovalve control valve is centered to the neutral position by its mechanical input.
The mechanical input is always positioned by the linkage (13) so as to give a control order opposed to the preceding electrical control order.
Thus the servocontrol goes back and stays in the zero position.
With the solenoid valves and servovalve de-energized the servovalve control valve is centered to the neutral position by its mechanical input.
The mechanical input is always positioned by the linkage (13) so as to give a control order opposed to the preceding electrical control order.
Thus the servocontrol goes back and stays in the zero position.
(4) Differential pressure indicator
The purpose of differential pressure indicator (16) is to check the return relief valve (8). It controls:
The purpose of differential pressure indicator (16) is to check the return relief valve (8). It controls:
- that the return relief valve provides a differential pressure greater or equal to 4 +-0.5 bar or -+0.5 bar (58.0151 +-7.2519 psi or -+7.2519 psi).
- that the return relief valve does not stick in the open position.
- that the return relief valve closes properly.
C. Operation after a simple electrical failure.
In this case, the solenoid valve is energized and the servocontrol operates in the damping mode (Ref. para. (2) (b)).
In this case, the solenoid valve is energized and the servocontrol operates in the damping mode (Ref. para. (2) (b)).
D. Operation after a total electrical failure.
In this case, the solenoid valves and the servovalves are de-energized and the servocontrol operates in the centering mode (Ref. para. (2) (c)).
In this case, the solenoid valves and the servovalves are de-energized and the servocontrol operates in the centering mode (Ref. para. (2) (c)).
E. Operation after a hydraulic failure.
The closing valves (2) and (3) close and isolate the servocontrol from the aircraft hydraulic system.
If there is a rupture of the aircraft return line, the return relief- valve holds the fluid volume in the fluid reserve. The mode selector- valve is set to the damping mode under the action of its spring.
Thus, the servocontrol operates in the damping mode.
The closing valves (2) and (3) close and isolate the servocontrol from the aircraft hydraulic system.
If there is a rupture of the aircraft return line, the return relief- valve holds the fluid volume in the fluid reserve. The mode selector- valve is set to the damping mode under the action of its spring.
Thus, the servocontrol operates in the damping mode.
F. Special case
After hydraulic depressurization, a difference in droop speed and travel between the two elevators is possible.
This is because of the variations of friction in the attachments and the servo control.
This difference is correct.
After hydraulic depressurization, a difference in droop speed and travel between the two elevators is possible.
This is because of the variations of friction in the attachments and the servo control.
This difference is correct.
G. Maintenance and rigging facilities.
The maintenance is "on condition".
The items given below are Line Replaceable Units:
This is done through the adjustment of the rod eye-end length.
The maintenance is "on condition".
The items given below are Line Replaceable Units:
- Filter
- Mode selector-valve transducer
- Solenoid valves
- Servovalve
- Actuator eye-end.
Some servocontrols are fitted with a rod eye-end with a regreasable roller bearing. This roller bearing is lubricated through grease nipples.
This is done through the adjustment of the rod eye-end length.
H. Particular points.
During flight, vibrations may occur with the current elevator neutral setting combined with backlash at the elevator servo control attachments. To avoid this situation, the elevator zero position is shifted 0.5 deg nose-up, trailing edge upwards.
During flight, vibrations may occur with the current elevator neutral setting combined with backlash at the elevator servo control attachments. To avoid this situation, the elevator zero position is shifted 0.5 deg nose-up, trailing edge upwards.