DOC AIRBUS | AMM A320FHP/LP TURBINE ACTIVE CLEARANCE CONTROL (ACC) SYSTEM - DESCRIPTION AND OPERATION
** ON A/C NOT FOR ALL
** ON A/C NOT FOR ALL
1. General
The HP/LP Turbine Active Clearance Control (ACC) system uses fan air to cool the HP and LP cases for blade tip clearance control in order to improve engine performance and maximize the turbine cases life time.
Fan air is drawn from a common HP/LP turbine ACC air scoop in the fan duct.
This air is divided into HP and LP cooling air and passes through individual short ducts to the Active Clearance Control Valves which direct air for both HP and LP turbine case cooling.
** ON A/C NOT FOR ALL The HP/LP Turbine Active Clearance Control (ACC) system uses fan air to cool the HP and LP cases for blade tip clearance control in order to improve engine performance and maximize the turbine cases life time.
HP/LP Active Clearance Control System SchematicFan air is drawn from a common HP/LP turbine ACC air scoop in the fan duct.
This air is divided into HP and LP cooling air and passes through individual short ducts to the Active Clearance Control Valves which direct air for both HP and LP turbine case cooling.
2. Description
The LP and HP Turbine ACC Systems function in the same manner.
Cooling air passes through the tube perforations, located on the inner surfaces of the tubes, and impinges on the case outer surface.
The cool air reduces the temperature and the thermal expansion of the cases under some operating conditions.
The LPT/HPT ACC system consists of the following components:
The LP and HP Turbine ACC Systems function in the same manner.
Cooling air passes through the tube perforations, located on the inner surfaces of the tubes, and impinges on the case outer surface.
The cool air reduces the temperature and the thermal expansion of the cases under some operating conditions.
The LPT/HPT ACC system consists of the following components:
- one HP turbine ACC manifold
- two LP turbine ACC manifolds
- Four HPT ACC perforated tubes
- height LPT ACC perforated tube
- one LP turbine supply pipe
- one LP/HP turbine valve (composed of a HPT control valve and a LPT control valve)
- one LP/HP turbine ACC actuator
A. HP Turbine ACC Manifold
The HP turbine ACC manifold is attached to the HP/LP control valve The HP turbine ACC Manifold directs air into an arrangement of four perforated tubes on each side of the engine for HP turbine case cooling.
The tubes on each side of the case cover 180 degrees of the case circumference.
The HP turbine ACC manifold is attached to the HP/LP control valve The HP turbine ACC Manifold directs air into an arrangement of four perforated tubes on each side of the engine for HP turbine case cooling.
The tubes on each side of the case cover 180 degrees of the case circumference.
B. LP Turbine ACC Manifold
The LP turbine ACC manifolds are connected to the HP/LP control valve by a supply pipe.
There are two LP Turbine ACC Manifolds, one situated at the top and one at the bottom of the LP Turbine Case. The top and bottom tube arrangements each cover 180 degrees of the case circumference.
The LP turbine ACC manifolds are connected to the HP/LP control valve by a supply pipe.
There are two LP Turbine ACC Manifolds, one situated at the top and one at the bottom of the LP Turbine Case. The top and bottom tube arrangements each cover 180 degrees of the case circumference.
C. LP/HP Turbine ACC Valve
The valve is installed on the bottom of the diffuser case.
The ACC valve has two butterfly valves. One butterfly valve controls the airflow for the active clearance of the HP turbine. The other butterfly valve controls the airflow for active clearance control of the LP turbine.
The ACC valve is driven by the ACC actuator through a set of linkages making both valves schedules dependent upon each other.
The valve is installed on the bottom of the diffuser case.
The ACC valve has two butterfly valves. One butterfly valve controls the airflow for the active clearance of the HP turbine. The other butterfly valve controls the airflow for active clearance control of the LP turbine.
The ACC valve is driven by the ACC actuator through a set of linkages making both valves schedules dependent upon each other.
D. ACC Actuator
The ACC actuator includes four primary components:
The torque motor and jet pipe pilot valve set the position of the servo valve.
The ACC actuator is connected to the Fuel Metering Unit (FMU) for fuel supply and return.
The ACC actuator receives torque motor current to adjust valve position as a function of N2 and altitude. The torque motor has two coils in order to provide failsafe operation. In the failsafe position, the actuator position is such that the HP valve is closed and the LP valve is 45 percent open.
The ACC actuator includes four primary components:
- A torque motor with two coils
- A servo valve
- An actuator piston
- two linear voltage differential transformers (LVDT) also the ACC actuator has four connections:
- An electrical connector
- A fuel supply connection
- A fuel return connection
- A fuel drain connection
The torque motor and jet pipe pilot valve set the position of the servo valve.
The ACC actuator is connected to the Fuel Metering Unit (FMU) for fuel supply and return.
The ACC actuator receives torque motor current to adjust valve position as a function of N2 and altitude. The torque motor has two coils in order to provide failsafe operation. In the failsafe position, the actuator position is such that the HP valve is closed and the LP valve is 45 percent open.
3. Operation
A. Normal Operation
The torque motor of the ACC actuator has springs to hold the jet pipe at neutral bias position. The torque motor current from the EEC changes the jet pipe direction. This direction change of the jet pipe makes a higher pressure on one side of the servo valve. This higher pressure moves the servo valve and it changes the fuel passage to the actuator piston.
The pressure difference between two sides of the actuator piston and the spring load moves the actuator piston to the required position.
The actuator piston drives the butterfly valves in the ACC valve. The butterfly valves thus control the airflows for the HP/LP turbine ACC manifolds. The LVDT's transmit the valve position to the EEC.
The torque motor of the ACC actuator has springs to hold the jet pipe at neutral bias position. The torque motor current from the EEC changes the jet pipe direction. This direction change of the jet pipe makes a higher pressure on one side of the servo valve. This higher pressure moves the servo valve and it changes the fuel passage to the actuator piston.
The pressure difference between two sides of the actuator piston and the spring load moves the actuator piston to the required position.
The actuator piston drives the butterfly valves in the ACC valve. The butterfly valves thus control the airflows for the HP/LP turbine ACC manifolds. The LVDT's transmit the valve position to the EEC.
B. Fail Safe Operation
When there is no torque motor current or no fuel servo pressure, the actuator piston moves to the point A.
The actuator piston remains at this point at all defective actions.
When there is no torque motor current or no fuel servo pressure, the actuator piston moves to the point A.
The actuator piston remains at this point at all defective actions.
C. Mode of Operation
The butterfly valves of the ACC valve are driven by the same actuator in the modes given below
The butterfly valves of the ACC valve are driven by the same actuator in the modes given below
(1) Engine stop
With the engine stop, the position of the actuator piston is at point A
At this point:
The butterfly valve for the HP turbine ACC is closed.
The butterfly valve for the LP turbine ACC is not less than 45 per cent opened.
With the engine stop, the position of the actuator piston is at point A
At this point:
The butterfly valve for the HP turbine ACC is closed.
The butterfly valve for the LP turbine ACC is not less than 45 per cent opened.
(2) Engine operation
During engine operation, the EEC controls the position of the actuator piston between point B and point E.
During engine operation, the EEC controls the position of the actuator piston between point B and point E.
(3) Take-off
During take-off, the position of the actuator piston is at point C
At this point:
The butterfly valve for the HP for the HP turbine ACC is closed The butterfly valve for the LP turbine ACC is not less than 70 per cent opened.
During take-off, the position of the actuator piston is at point C
At this point:
The butterfly valve for the HP for the HP turbine ACC is closed The butterfly valve for the LP turbine ACC is not less than 70 per cent opened.
NOTE: The failure of the HP/LP valve in the closed position have no adverse effect on the engine thrust nor on the engine rotation: only the abradable parts of the turbine can be affected (leading to a reduction on engine performance).