DOC AIRBUS | AMM A320FHP COMPRESSOR AIRFLOW CONTROL SYSTEM - DESCRIPTION AND OPERATION
** ON A/C NOT FOR ALL
1. General
This system consists of the Variable Stator Vane Actuator, the HPC bleed air tubes and the HPC stage 7 and 10 solenoid valves and bleed valves. The variable stator vanes and the 7th and 10 t stage HP compressor bleeds are used to improve engine performance and stability during engine starting, acceleration and deceleration. The variable stator vanes are modulated open or closed by a hydraulic actuator controlled by the Electronic Engine Control (EEC). The 7th and 10th HP compressor bleed valves are pneumatically actuated by two position air shut-off valves which are actuated by EEC solenoids.
** ON A/C NOT FOR ALL This system consists of the Variable Stator Vane Actuator, the HPC bleed air tubes and the HPC stage 7 and 10 solenoid valves and bleed valves. The variable stator vanes and the 7th and 10 t stage HP compressor bleeds are used to improve engine performance and stability during engine starting, acceleration and deceleration. The variable stator vanes are modulated open or closed by a hydraulic actuator controlled by the Electronic Engine Control (EEC). The 7th and 10th HP compressor bleed valves are pneumatically actuated by two position air shut-off valves which are actuated by EEC solenoids.
2. Description
A. Variable Stator Vane System
Variable Stator Vane Actuator(1) General
The purpose of this system is to position the Inlet Guide Vanes (IGV) and stator vanes, using a fuel driven hydraulic actuator, in response to electrical signals provided by the EEC.
The purpose of this system is to position the Inlet Guide Vanes (IGV) and stator vanes, using a fuel driven hydraulic actuator, in response to electrical signals provided by the EEC.
(2) Description
(a) Variable Stator Vane Actuator
The stator vane actuator accurately controls vane movement with respect to a torque motor current supplied by the EEC.
Operation of the stator vanes in regulated by accurate control of high pressure fuel flow to one or other side of a differential area piston.
The piston has an externally adjustable low speed stop at the extended end of its travel. The high speed stop is formed by a collar which limits piston retraction. Provision is made to lock the piston with a rigging pin for setting purposes.
A control servo valve and piston type pressure drop regulator regulate the flow to either side of the piston.
The stator vane actuator accurately controls vane movement with respect to a torque motor current supplied by the EEC.
Operation of the stator vanes in regulated by accurate control of high pressure fuel flow to one or other side of a differential area piston.
The piston has an externally adjustable low speed stop at the extended end of its travel. The high speed stop is formed by a collar which limits piston retraction. Provision is made to lock the piston with a rigging pin for setting purposes.
A control servo valve and piston type pressure drop regulator regulate the flow to either side of the piston.
1 Servo Valve
The control servo valve is a spring-centered spool valve which contains the metering and transfer ports. The metering ports set an orifice size proportional to the valve of the servo valve.
If the servo valve moves away from null in one direction the metering ports are opened to reveal one leg of the axial characteristics, similarly if the servo valve moves in the other direction the opposite leg of the characteristic will be revealed.
The control servo valve is a spring-centered spool valve which contains the metering and transfer ports. The metering ports set an orifice size proportional to the valve of the servo valve.
If the servo valve moves away from null in one direction the metering ports are opened to reveal one leg of the axial characteristics, similarly if the servo valve moves in the other direction the opposite leg of the characteristic will be revealed.
2 Pressure Drop Regulator
The pressure drop regulator controls the main flow, supplied to the control servo valve, to maintain a constant 68 psi pressure drop across the metering ports.
The pressure drop regulator senses pressure downstream of the metering ports in the control servo valve and throttles the high pressure supply flow to maintain the pressure drop.
The pressure drop regulator controls the main flow, supplied to the control servo valve, to maintain a constant 68 psi pressure drop across the metering ports.
The pressure drop regulator senses pressure downstream of the metering ports in the control servo valve and throttles the high pressure supply flow to maintain the pressure drop.
3 Torque Motor
The servo flow to the torque motor is supplied from the FMU high pressure supply via a constant pressure valve which regulates the servo pressure to 180 psi above the low pressure return.
The dual wound torque motor is polarised by permanent magnets and contains an armature which is connected to the flapper coils generating a torque on the armature. The armature and flapper are mounted onto a flexure sleeve which provides a frictionless pivot and also serves to isolate the hydraulic and electro-magnetic section of the valve.
A hydraulic bridge circuit is formed by supplying pressure to the fixed orifices via a filter and downstream of each of these, the two variable orifices formed by the nozzle/flapper interfaces of the torque motor.
The servo flow to the torque motor is supplied from the FMU high pressure supply via a constant pressure valve which regulates the servo pressure to 180 psi above the low pressure return.
The dual wound torque motor is polarised by permanent magnets and contains an armature which is connected to the flapper coils generating a torque on the armature. The armature and flapper are mounted onto a flexure sleeve which provides a frictionless pivot and also serves to isolate the hydraulic and electro-magnetic section of the valve.
A hydraulic bridge circuit is formed by supplying pressure to the fixed orifices via a filter and downstream of each of these, the two variable orifices formed by the nozzle/flapper interfaces of the torque motor.
4 Linear Variable differential Transformer (LVDT)
A Dual Wound Linear Variable Differential Transformer (LVDT) is located in the center of the actuator piston rod and is directly driven by the piston through a bearing assembly to allow for possible rotation of the piston. The LVDT completes the electronic control loop by providing a signal of actuator position to the Engine Electronic Control.
A Dual Wound Linear Variable Differential Transformer (LVDT) is located in the center of the actuator piston rod and is directly driven by the piston through a bearing assembly to allow for possible rotation of the piston. The LVDT completes the electronic control loop by providing a signal of actuator position to the Engine Electronic Control.
5 Engine Linkage with the VSV Actuator
The engine IGV and Stator Vane linkage is connected to a fork end on the piston rod of the VSVA unit. The securing pin of link on to fork end.
The engine IGV and Stator Vane linkage is connected to a fork end on the piston rod of the VSVA unit. The securing pin of link on to fork end.
6 Operation of the VSV Actuator
Dual wound torque motors convert electrically isolated drive signals from each channel of the Electronics Engine Control (EEC) into hydraulic drive signals to position the actuator piston.
Each winding of the torque motor translates the drive current from the corresponding channel of the EEC into the appropriate hydraulic drive signal. The dual Linear Variable Differential Transformer (LVDT) is mechanically connected to the piston to provide electrically isolated position feedback signals to each channel of the EEC. Each of the two EEC chanels controls one of the torque motor coils thus providing system redundancy. Feedback is provided to each channel from one of the redundant LVDT assemblies and the wiring for each channel is handled through separate electrical connectors. If power to the stator vane actuator torque motor is lost, the stator vane actuator will go to the full open position.
Dual wound torque motors convert electrically isolated drive signals from each channel of the Electronics Engine Control (EEC) into hydraulic drive signals to position the actuator piston.
Each winding of the torque motor translates the drive current from the corresponding channel of the EEC into the appropriate hydraulic drive signal. The dual Linear Variable Differential Transformer (LVDT) is mechanically connected to the piston to provide electrically isolated position feedback signals to each channel of the EEC. Each of the two EEC chanels controls one of the torque motor coils thus providing system redundancy. Feedback is provided to each channel from one of the redundant LVDT assemblies and the wiring for each channel is handled through separate electrical connectors. If power to the stator vane actuator torque motor is lost, the stator vane actuator will go to the full open position.
(b) Variable Stator Vane Actuation Mechanism
The variable geometry operating mechanism for the compressor comprises the following elements:
The crankshaft is mounted onto the front casing with suitable brackets. The crankshaft is a steel tube onto which the front three crankshaft levers are brazed. The stator 5 lever is bolted onto the rear end of the crankshaft and positioned by a dowel.
The unison rings are formed from hollow square-section titanium tubing into circular arcs. Bridge pieces of the same material are used to complete the rings over the split casing flanges. The joints are secured by steel brackets with bolts and located by dowels.
The unison rings and bridge pieces are cross-drilled at equal intervals to provide location for the spindle lever pins.
The vane spindle levers, which convert the circumferential movement of the unison rings into rotation of the vane, are bolted onto the vane spindles. The unison ring movement is transmitted to these levers by riveted titanium pins. The levers are designed to accommodate the small, but inherent, goemetrical imperfection between the lever pin and unison ring movements by twisting.
The variable geometry operating mechanism for the compressor comprises the following elements:
- actuator/crankshaft drag link
- crankshaft (steel)
- four crankshaft/unison ring drag links
- four unison rings
- spindle levers (titanium)
- variable IGVs and stage 3, 4, and 5 variable stators (nimonic).
The crankshaft is mounted onto the front casing with suitable brackets. The crankshaft is a steel tube onto which the front three crankshaft levers are brazed. The stator 5 lever is bolted onto the rear end of the crankshaft and positioned by a dowel.
The unison rings are formed from hollow square-section titanium tubing into circular arcs. Bridge pieces of the same material are used to complete the rings over the split casing flanges. The joints are secured by steel brackets with bolts and located by dowels.
The unison rings and bridge pieces are cross-drilled at equal intervals to provide location for the spindle lever pins.
The vane spindle levers, which convert the circumferential movement of the unison rings into rotation of the vane, are bolted onto the vane spindles. The unison ring movement is transmitted to these levers by riveted titanium pins. The levers are designed to accommodate the small, but inherent, goemetrical imperfection between the lever pin and unison ring movements by twisting.
B. HP Compressor Bleed Valves System
(1) General
HP compressor bleed valves are required for stability of engine operation during starting and transient conditions. Three bleed valves for the seventh stage and one for the tenth stage of the HP compressor redirect a portion of HP compressor air into the fan stream.
HP compressor bleed valves are required for stability of engine operation during starting and transient conditions. Three bleed valves for the seventh stage and one for the tenth stage of the HP compressor redirect a portion of HP compressor air into the fan stream.
(2) Description/Operation
(a) Bleed valves
The bleed valves are mounted onto the outside of the HP compressor case. Each valve has a spring loaded open position. The piston has holes to permit a flow of air through the valve when it is open. When the valve is closed the piston is held against a plate which is part of the valve body. This shuts off the air bleed from the compressor.
The piston is held in the open position by spring and compressor delivery (P3) pressures. When the P3 pressure is released by the controlling solenoid valve, the bleed valve is closed by compressor air pressure.
The bleed valves are mounted onto the outside of the HP compressor case. Each valve has a spring loaded open position. The piston has holes to permit a flow of air through the valve when it is open. When the valve is closed the piston is held against a plate which is part of the valve body. This shuts off the air bleed from the compressor.
The piston is held in the open position by spring and compressor delivery (P3) pressures. When the P3 pressure is released by the controlling solenoid valve, the bleed valve is closed by compressor air pressure.
(b) Bleed valve solenoid valves
Each air bleed valve has its own controlling solenoid valve which is installed on the fan case. The solenoid valve is connected to the bleed valve by a tube. This tube transmits P3 pressure to or from the bleed valve. The solenoid valve is controlled by electrical signals from the EEC through two separate coils.
With either or both of the solenoid coils energized, the service port is connected to vent. In this position the bleed valve is held closed.
With both solenoid coils de-energized the solenoid valve connects the engine supplied air to the service port holding the bleed valve open.
The accessories which do the power distribution are divided into four groups: engine group I, engine group II, autostart group and reverser group.
Each air bleed valve has its own controlling solenoid valve which is installed on the fan case. The solenoid valve is connected to the bleed valve by a tube. This tube transmits P3 pressure to or from the bleed valve. The solenoid valve is controlled by electrical signals from the EEC through two separate coils.
With either or both of the solenoid coils energized, the service port is connected to vent. In this position the bleed valve is held closed.
With both solenoid coils de-energized the solenoid valve connects the engine supplied air to the service port holding the bleed valve open.
The accessories which do the power distribution are divided into four groups: engine group I, engine group II, autostart group and reverser group.