DOC AIRBUS | AMM A320FPOWER - DESCRIPTION AND OPERATION
** ON A/C NOT FOR ALL
** ON A/C NOT FOR ALL
** ON A/C NOT FOR ALL
1. General
This chapter deals with the N1, N2 and EPR indications.
The other engine indications related to the power management parameters are described in chapter 73-25-00.
** ON A/C NOT FOR ALL This chapter deals with the N1, N2 and EPR indications.
The other engine indications related to the power management parameters are described in chapter 73-25-00.
2. N1 Indicating System
A. General
The measurement channel for the low-pressure rotor speed is designed as follows:
The measurement channel for the low-pressure rotor speed is designed as follows:
- the speed sensor on the engine sends a signal to the EEC,
- the EEC uses this signal in engine control computation and also transmits it to the ECAM through the ARINC 429 data bus (Ref. AMM D/O 73-25-00-00).
B. N1 Speed Sensors
Fan Speed (N1) Indicating System(1) General
The fan speed (N1) indicating system has four sensors:
The fan speed (N1) indicating system has four sensors:
- Two of them are used to provide EEC channels A and B with N1 rotational speed signals.
- One sensor acts as a spare for either EEC channel (it can be actuated by a changeover connector at a junction box mounted on the fan case).
This sensor cannot be used in place of the N1 sensor dedicated to the Engine Vibration Monitoring Unit (see below). - One sensor provides the Engine Vibration Monitoring Unit with N1 analog signals (trim balance sensor).
- The N1 speed sensors and the trim balance sensor are installed on the front brackets attached to the No. 2 bearing support in the front bearing compartment.
They are installed in line with an LP compressor phonic wheel attached to the LP stub shaft. - The N1 electrical harness tube goes through the inner strut of the No. 3 strut of the intermediate structure and to the terminal block.
The electrical leads from each sensor go through the N1 tube and connect to the terminal block. The terminal block is connected by the engine electrical harness to an interface connector located on the bifurcation panel. From the interface connector,
the fan speed wiring is connected to the EEC via a changeover connector mounted on the fan case. - The fan speed and trim balance sensors are of the variable reluctance type ; magnetic discontinuity is caused by the phonic wheel. For the fan speed sensors, one turn of the LP shaft causes the 60 teeth on the phonic wheel to go through its sensors one time for each turn ; for the trim balance sensor, this causes one slot in the phonic wheel to go through its sensor one time for each turn
(2) Fan speed sensors
(a) Description
The three fan speed sensors are installed on the front brackets attached to the No. 2 bearing support in the front bearing compartment
They are installed in line with an LP compressor phonic wheel attached to the LP shaft. Only two of the three fan speed sensors are connected to the ECU and two indicator circuits (Ref. Fig. 1).
The remaining sensor is an alternative sensor to be used if there is a failure of one of the two connected sensors.
The fan speed sensors consist of a permanent magnet, two pole pieces and a sensor coil assembly.
They are all assembled with expoxy resin in a capsule in the sensor body made of glass-filled polyamide.
The sensor body has two stainless steel contact pads which are used to install the sensor in the engine and give the electrical output terminal.
The distance between the center of the two holes of the contact pads is shorter than that of the trim balance sensor to prevent incorrect installation.
Both the fan speed sensor and the trim balance sensor have an identical body shape, but the trim balance sensor is offset along the engine axis in relation to the fan speed sensors.
This prevents the sensors from being installed the wrong way round.
The three fan speed sensors are installed on the front brackets attached to the No. 2 bearing support in the front bearing compartment
They are installed in line with an LP compressor phonic wheel attached to the LP shaft. Only two of the three fan speed sensors are connected to the ECU and two indicator circuits (Ref. Fig. 1).
The remaining sensor is an alternative sensor to be used if there is a failure of one of the two connected sensors.
The fan speed sensors consist of a permanent magnet, two pole pieces and a sensor coil assembly.
They are all assembled with expoxy resin in a capsule in the sensor body made of glass-filled polyamide.
The sensor body has two stainless steel contact pads which are used to install the sensor in the engine and give the electrical output terminal.
The distance between the center of the two holes of the contact pads is shorter than that of the trim balance sensor to prevent incorrect installation.
Both the fan speed sensor and the trim balance sensor have an identical body shape, but the trim balance sensor is offset along the engine axis in relation to the fan speed sensors.
This prevents the sensors from being installed the wrong way round.
(b) Operation
The distance between the two pole pieces is equal to the two pitches of the teeth on the phonic wheel.
The air gap between the pole pieces and the teeth gives a path of lower reluctance when they are directly opposite. A path of larger reluctance is given when the phonic wheel moves to the teeth between the pole pieces.
Thus the flux change caused in the magnetic circuit causes a voltage into the coil, and a pulse is given at the output terminal.
The pulse frequency is equal to the rate at which the teeth go through the pole pieces, and therefore directly in proportion to the rotation speed of the phonic wheel which has 60 teeth. That is, the pulse frequency is equal to N1 rpm.
The distance between the two pole pieces is equal to the two pitches of the teeth on the phonic wheel.
The air gap between the pole pieces and the teeth gives a path of lower reluctance when they are directly opposite. A path of larger reluctance is given when the phonic wheel moves to the teeth between the pole pieces.
Thus the flux change caused in the magnetic circuit causes a voltage into the coil, and a pulse is given at the output terminal.
The pulse frequency is equal to the rate at which the teeth go through the pole pieces, and therefore directly in proportion to the rotation speed of the phonic wheel which has 60 teeth. That is, the pulse frequency is equal to N1 rpm.
(3) Trim balance sensor
(a) Description
The trim balance sensor is installed on the front brackets attached to No. 2 bearing support and installed in line with the fan speed sensors
The trim balance sensor has the following components : a permanent magnet, one pole piece and a sensor coil assembly.
They are all assembled with epoxy resin in a capsule in the sensor body, which is the same shape and made of the same material as the fan speed sensor.
The trim balance sensor is installed on the front brackets attached to No. 2 bearing support and installed in line with the fan speed sensors
The trim balance sensor has the following components : a permanent magnet, one pole piece and a sensor coil assembly.
They are all assembled with epoxy resin in a capsule in the sensor body, which is the same shape and made of the same material as the fan speed sensor.
(b) Operation
The operation of the trim balance sensor is the same as that of the fan speed sensors without one pole piece. For the trim balance sensor, there is only one slot on the phonic wheel. The trim balance sensor therefore gives one pulse for each turn of the phonic wheel.
The operation of the trim balance sensor is the same as that of the fan speed sensors without one pole piece. For the trim balance sensor, there is only one slot on the phonic wheel. The trim balance sensor therefore gives one pulse for each turn of the phonic wheel.
C. N1 Indication
The N1 rotational speed value is permanently displayed in green on the upper ECAM display unit in analog and digital form.
When the N1 red line value (100%) is exceeded:
The N1 rotational speed value is permanently displayed in green on the upper ECAM display unit in analog and digital form.
When the N1 red line value (100%) is exceeded:
- the indication becomes red
- the MASTER CAUT light comes on accompanied by the single chime
- a warning message appears on the ECAM display unit.
3. N2 Indicating System
A. General
The N2 indicating system provides the signals proportional to the High Pressure (HP) shaft rotational speed to the EEC for use in engine control computation, to the ECAM for visual display in the cockpit and to the Engine Vibration Monitoring Unit for use in processing engine vibration data.
The N2 indicating system provides the signals proportional to the High Pressure (HP) shaft rotational speed to the EEC for use in engine control computation, to the ECAM for visual display in the cockpit and to the Engine Vibration Monitoring Unit for use in processing engine vibration data.
(1) General
The N2 signals originate from the dedicated alternator which is driven from the main accessory gearbox.
The dedicated alternator is installed on the front of the main gearbox.
The dedicated alternator consists of a magnetic rotor running in a stator. The stator has four independent windings, two of which provide three-phase frequency AC electrical power to respectively channel A and B of the EEC.
The third winding of the dedicated alternator provides a single-phase AC analog signal proportional to N2 which is taken by separate wiring to the Engine Vibration Monitoring System. The forth winding provides a dedicated N2 signal to channel A of the EEC for low speed indication.
The N2 signals originate from the dedicated alternator which is driven from the main accessory gearbox.
The dedicated alternator is installed on the front of the main gearbox.
The dedicated alternator consists of a magnetic rotor running in a stator. The stator has four independent windings, two of which provide three-phase frequency AC electrical power to respectively channel A and B of the EEC.
The third winding of the dedicated alternator provides a single-phase AC analog signal proportional to N2 which is taken by separate wiring to the Engine Vibration Monitoring System. The forth winding provides a dedicated N2 signal to channel A of the EEC for low speed indication.
(2) Operation
The dedicated alternator gives an analog signal from the N2 windings when it rotates. The frequency of this signal is 0.2376 of N2 rpm.
This signal is sent through the EEC for in the cockpit.
The dedicated alternator gives an analog signal from the N2 windings when it rotates. The frequency of this signal is 0.2376 of N2 rpm.
This signal is sent through the EEC for in the cockpit.
C. N2 Indication
The N2 rotational speed indication is permanently in green on the upper ECAM display unit in digital form. If N2 exceeds the N2 red line value (100% not displayed), a red cross appears next to the digital indication. There is an associated red MASTER CAUT light and a single chime with a warning message to warn the crew that N2 overspeed has occurred. If an indicating failure occurs, the N2 value is replaced by amber crosses.
The N2 rotational speed indication is permanently in green on the upper ECAM display unit in digital form. If N2 exceeds the N2 red line value (100% not displayed), a red cross appears next to the digital indication. There is an associated red MASTER CAUT light and a single chime with a warning message to warn the crew that N2 overspeed has occurred. If an indicating failure occurs, the N2 value is replaced by amber crosses.
4. EPR (Engine Pressure Ratio) Indicating System
A. General
The Engine Pressure Ratio (EPR) indicating system consists of one combined P2/T2 sensor and eight pressure ports located in three LP turbine exhaust case struts (24 total).
The pressures from these sensors are routed to the EEC pressure transducers. The signals are then converted into a digital format. The Electronic Engine Control (EEC) processes the pressures to form actual EPR (P4.9/P2) and transmits the EPR value to the ECAM system through it digital data bus. Each of the two EEC channels performs this operation independently.
The Engine Pressure Ratio (EPR) indicating system consists of one combined P2/T2 sensor and eight pressure ports located in three LP turbine exhaust case struts (24 total).
The pressures from these sensors are routed to the EEC pressure transducers. The signals are then converted into a digital format. The Electronic Engine Control (EEC) processes the pressures to form actual EPR (P4.9/P2) and transmits the EPR value to the ECAM system through it digital data bus. Each of the two EEC channels performs this operation independently.
(1) P2/T2 Sensor
The P2/T2 sensor is installed in the inlet air stream of the engine forward of the engine front flange. It is in the area of the engine top centerline. A manifold connects the sensor to the Electronic Engine Control.
The P2/T2 sensor is installed in the inlet air stream of the engine forward of the engine front flange. It is in the area of the engine top centerline. A manifold connects the sensor to the Electronic Engine Control.
(2) P4.9 Sensors
The P4.9 sensor and manifold has three probes which measure the total pressure of the exhaust gas stream. The probes are installed in to the exhaust gas vanes at the N°4, 7 and 10 positions (the vanes are numbered from the top viewed from the rear of the engine). Each of the three vanes has eight holes in its leading edge to let the exhaust gas in to the vanes. The pressure is supplied through a hole in each of the probes. This measurement is sent through the manifold to one of the EEC pressure transducers.
The P4.9 sensor and manifold has three probes which measure the total pressure of the exhaust gas stream. The probes are installed in to the exhaust gas vanes at the N°4, 7 and 10 positions (the vanes are numbered from the top viewed from the rear of the engine). Each of the three vanes has eight holes in its leading edge to let the exhaust gas in to the vanes. The pressure is supplied through a hole in each of the probes. This measurement is sent through the manifold to one of the EEC pressure transducers.
C. EPR Indication
All indications concerning the EPR are permanently displayed on the upper ECAM display unit in analog and digital form.
All indications concerning the EPR are permanently displayed on the upper ECAM display unit in analog and digital form.
- Actual EPR is displayed in green in analog and digital form.
- EPR Max : indicated by a thick amber mark across the EPR scale ; represents the EPR limit value corresponding to the full forward throttle position.
- EPR limit : This value is displayed in digital form ; it represents the maximum EPR value corresponding to the thrust limit mode selected by the FADEC as a function of TRA, MN and ALT.
- EPR REF : Indicated by a small white circle in front of the EPR scale value corresponding to the predicted EPR value according to the throttle resolver angle selected position.
- Thrust limit mode : Displayed in digital form, it indicates the mode in which the EPR limit value will be computed.
TO = Take-Off Mode
GA = Go-Around Mode
FLX = Flexible Take-Off Mode
MCT = Maximum Continuous Thrust Mode
CL or CLB = Climb Mode - Flex temp : Displayed in cyan in digital form, it indicates the fictitious TAT take-off temperature entered by the crew through the FMS-MCDU.
Appears only in FLX mode.
- Reversion into N1 mode:
The actual EPR indications (analog and digital) will be replaced by amber crosses.
EPR REF (or CMD when A/THR is engaged) will disappear.
The indication N1 MODE and N1 limit value will be displayed on the upper ECAM display unit in place of the EPR limit. - Transition between EPR and N1
The primary mode of setting power is provided by controlling the fuel flow to set the engine pressure ratio (EPR) as illustrated
An EPR reference (EPR REF) is calculated as a function of the Trottle Resolver Angle (TRA), the ambient temperature (T2), the mach number and the altitude. The EPR reference is compared to the sensed EPR and dynamic compensation is then applied to this EPR error.
The result is that fuel flow is modulated until the EPR error is eliminated.
If the control is unable to sense the EPR or calculate EPR REF, automatic transition to an N1 reversionary control mode will take place.
In the event of this transition, EEC logic is incorporated to prevent thrust perturbation when control is transfered from EPR to the reversionary control mode. The rotor speed reference (N1 REF) will be scheduled as a function of the Throttle Resolver Angle (TRA) and T2.