DOC AIRBUS | AMM A320FHPT ACTIVE CLEARANCE CONTROL SYSTEM - DESCRIPTION AND OPERATION
** ON A/C NOT FOR ALL
1. General
The engine High Pressure Turbine Active Clearance Control (HPTACC) system uses High Pressure Compressor (HPC) bleed air from stages 4 and 9 to heat or cool the High Pressure Turbine (HPT) shroud support structure. The purpose of the system is to maximize turbine efficiency during cruise and to minimize Exhaust Gas Temperature (EGT) peak during throttle bursts.
** ON A/C NOT FOR ALL The engine High Pressure Turbine Active Clearance Control (HPTACC) system uses High Pressure Compressor (HPC) bleed air from stages 4 and 9 to heat or cool the High Pressure Turbine (HPT) shroud support structure. The purpose of the system is to maximize turbine efficiency during cruise and to minimize Exhaust Gas Temperature (EGT) peak during throttle bursts.
HPTACC - Schematic2. Description
The HPTACC is a closed loop system based on shroud temperature.
The Electronic Control Unit (ECU) first calculates the HPTACC valve position to control the temperature of the shroud to the desired level. Then, the ECU sends an electrical signal to the Hydromechanical Unit (HMU) to move the HPTACC valve. The HPTACC valve is an hydraulic actuator linked with the 4th and the 9th stage butterfly valves which control air flow to the HPT shroud support structure. Two Linear Variable Differential Transformers (LVDT) are connected to the actuator to give valve position feedback to the two thermocouples which are embedded in the HPT shroud support structure and provide temperature feedback to the ECU.
On engine start, the HPTACC valve moves to the 9th stage bleed position which unloads the compressor to improve engine acceleration. At and above ground idle, the HPTACC valve position is determined by the closed loop shroud temperature control. When the engine is shut down, the valve extends to a failsafe no air position.
** ON A/C NOT FOR ALL The HPTACC is a closed loop system based on shroud temperature.
The Electronic Control Unit (ECU) first calculates the HPTACC valve position to control the temperature of the shroud to the desired level. Then, the ECU sends an electrical signal to the Hydromechanical Unit (HMU) to move the HPTACC valve. The HPTACC valve is an hydraulic actuator linked with the 4th and the 9th stage butterfly valves which control air flow to the HPT shroud support structure. Two Linear Variable Differential Transformers (LVDT) are connected to the actuator to give valve position feedback to the two thermocouples which are embedded in the HPT shroud support structure and provide temperature feedback to the ECU.
On engine start, the HPTACC valve moves to the 9th stage bleed position which unloads the compressor to improve engine acceleration. At and above ground idle, the HPTACC valve position is determined by the closed loop shroud temperature control. When the engine is shut down, the valve extends to a failsafe no air position.
3. HPT Active Clearance Control Valve
The HPTACC valve has integrated dual butterfly valves driven by a single fuel powered actuator. Position feedback to the ECU is provided by a dual channel LVDT installed on the actuator. One butterfly valve controls the flow from 4th stage compressor bleed while the other butterfly valve controls the flow from the 9th stage compressor bleed. The 4th stage air is mixed with the 9th stage air downstream of the valve. The main valve modes are defined in the table that follows:
The HPTACC valve has integrated dual butterfly valves driven by a single fuel powered actuator. Position feedback to the ECU is provided by a dual channel LVDT installed on the actuator. One butterfly valve controls the flow from 4th stage compressor bleed while the other butterfly valve controls the flow from the 9th stage compressor bleed. The 4th stage air is mixed with the 9th stage air downstream of the valve. The main valve modes are defined in the table that follows:
| --------------------------------------------------------------------------- |
| ! Actuator ! Mode ! 4th Stage ! 9th Stage ! |
| ! Stroke ! ! Butterfly ! Butterfly ! |
| !-------------------------------------------------------------------------! |
| ! 0 percent ! No Air ! Closed ! Closed ! |
| ! Failsafe ! ! ! ! |
| !-----------------!---------------!-------------------!-------------------! |
| ! 22 percent ! Full 9th ! Closed ! Fully open ! |
| !-----------------!---------------!-------------------!-------------------! |
| ! 42 percent ! Regular 9th ! Closed ! Intermediate ! |
| !-----------------!---------------!-------------------!-------------------! |
| ! 42-100 percent ! Mixed ! Intermediate ! Intermediate ! |
| !-----------------!---------------!-------------------!-------------------! |
| ! 100 percent ! Full 4th ! Fully open ! Closed ! |
| --------------------------------------------------------------------------- |