DOC AIRBUS | AMM A320FVARIABLE BLEED VALVE SYSTEM (VBV) - DESCRIPTION AND OPERATION
** ON A/C NOT FOR ALL
** ON A/C NOT FOR ALL
** ON A/C NOT FOR ALL
1. General
The variable bleed valve (VBV) position is related to the high pressure compressor (HPC) operation. It is directly controlled by the angular setting of the variable compressor stator vanes at steady-state operation and during acceleration. The bleed valves open during low and transient operations to increase the booster mass flow and to improve booster and HPC matching. The bleed valves are fully open during fast decelerations. The bleed valve control system includes the following:
The variable bleed valve (VBV) position is related to the high pressure compressor (HPC) operation. It is directly controlled by the angular setting of the variable compressor stator vanes at steady-state operation and during acceleration. The bleed valves open during low and transient operations to increase the booster mass flow and to improve booster and HPC matching. The bleed valves are fully open during fast decelerations. The bleed valve control system includes the following:
Variable Bleed Valve SystemA. A mechanical transmission system which includes:
A stop mechanism
A bleed valve main flexible shaft assembly located between the master ballscrew actuator and fuel gear motor.
A master ballscrew actuator
Eleven ballscrew actuators
Eleven bleed valve flexible shaft assemblies located between the bleed valve and ballscrew actuators.
A stop mechanism
A bleed valve main flexible shaft assembly located between the master ballscrew actuator and fuel gear motor.
A master ballscrew actuator
Eleven ballscrew actuators
Eleven bleed valve flexible shaft assemblies located between the bleed valve and ballscrew actuators.
A. Description of the System.
The VBV actuation system provides an angular output through fuel gear motor assembly, master ballscrew actuator assembly and 11 ballscrew actuator assemblies. The system is interconnected by 11 flexible shaft assemblies. Eleven ferrules are installed in the engine struts to provide support for the flexible shaft assemblies.
The system is designed to open, close, or modulate the 12 VBV doors to an intermediate position in response to an input command signal. The VBVs remain fully synchronized throughout their complete stroke by the continuous mechanical flexible shaft arrangement. High pressure fuel hydraulically activates the VBV actuation system. The VBV position sensor provides VBV position bias to the ECU. The master ballscrew actuator assembly is connected by a push-pull feedback rod to the VBV position sensor.
The VBV actuation system provides an angular output through fuel gear motor assembly, master ballscrew actuator assembly and 11 ballscrew actuator assemblies. The system is interconnected by 11 flexible shaft assemblies. Eleven ferrules are installed in the engine struts to provide support for the flexible shaft assemblies.
The system is designed to open, close, or modulate the 12 VBV doors to an intermediate position in response to an input command signal. The VBVs remain fully synchronized throughout their complete stroke by the continuous mechanical flexible shaft arrangement. High pressure fuel hydraulically activates the VBV actuation system. The VBV position sensor provides VBV position bias to the ECU. The master ballscrew actuator assembly is connected by a push-pull feedback rod to the VBV position sensor.
B. Operation of the System
The system performs 4 primary functions :
The system performs 4 primary functions :
(1) Positions the bleed valves in response to a differential fuel pressure through the motor of the fuel gear motor assembly.
(2) Mechanically synchronizes the 12 bleed valves throughout the stroke.
(3) Limits the bleed valve position at the end of each stroke.
(4) Provides the feedback of the VBV position sensor (RVDT) to the ECU.
C. Modulating Operation
The motor, actuated by the HMU, drives the system to the commanded position with the required power. The pressure across the motor is reduced as the system approaches the commanded position. The electrical position feedback to the ECU directs the fuel control valve to its null position or minimum opening needed to neutralize the bleed valve loads.
The motor, actuated by the HMU, drives the system to the commanded position with the required power. The pressure across the motor is reduced as the system approaches the commanded position. The electrical position feedback to the ECU directs the fuel control valve to its null position or minimum opening needed to neutralize the bleed valve loads.
D. End-of-Stroke Operation
(1) Bleed valves closing.
The feedback electrical mechanism relays the bleed valve position to the ECU as the system approaches the commanded closed ECU position.
The fuel control valve is moved towards the null position as the bleed valve approaches the end of its stroke. This reduces motor speed and allows the motor to engage the end-of-stroke stops at a low impact force.
The closed bleed valve position is within 0.3 percent of the stroke of the ballscrew actuator assembly utilizing the mechanical stops.
The feedback electrical mechanism relays the bleed valve position to the ECU as the system approaches the commanded closed ECU position.
The fuel control valve is moved towards the null position as the bleed valve approaches the end of its stroke. This reduces motor speed and allows the motor to engage the end-of-stroke stops at a low impact force.
The closed bleed valve position is within 0.3 percent of the stroke of the ballscrew actuator assembly utilizing the mechanical stops.
(2) Bleed valves opening
The feedback electrical mechanism relays the bleed valve position to the ECU as the system approaches the commanded open position. The fuel control valve is positioned to decelerate the motor.
The same type of mechanical stops is used at the opening end of the stroke. The open bleed valve position is within one percent of the stroke of the ballscrew actuator assembly utilizing the mechanical stops. All 12 bleed valves are mechanically synchronized.
The feedback electrical mechanism relays the bleed valve position to the ECU as the system approaches the commanded open position. The fuel control valve is positioned to decelerate the motor.
The same type of mechanical stops is used at the opening end of the stroke. The open bleed valve position is within one percent of the stroke of the ballscrew actuator assembly utilizing the mechanical stops. All 12 bleed valves are mechanically synchronized.
3. Component Description
A. Main Flexible Shaft Assembly
(1) Description.
The main flexible shaft assembly is an unshielded power core which has a hexagon fitting on one end and a splined end fitting on the other.
The main flexible shaft assembly is an unshielded power core which has a hexagon fitting on one end and a splined end fitting on the other.
B. Flexible Shaft Assemblies.
(1) Description
The flexible shaft assembly is an unshielded power core which has a hexagon fitting on one end and an 8-point fitting on the other.
The flexible shaft assembly is an unshielded power core which has a hexagon fitting on one end and an 8-point fitting on the other.
C. Bleed Valve Fuel Gear Motor Assembly
(1) General.
- The bleed valve fuel gear motor assembly consists of a positive displacement gear motor and end-of-stroke stop mechanism. The motor converts pressurized fuel into rotary shaft power driving the gear reduction stage of the bleed valve and master ballscrew actuator assembly through the bleed valve stop mechanism. The bleed valve fuel gear motor is located on the fan frame aft face at the 9:00 o'clock position.
(2) Description.
- The motor controls the position of the bleed valves. It is a gear motor driven by high pressure fuel. It consists of 2 spur gears guided during rotation by needle bearings. Sealing at the drive gear shaft is provided by carbon seals. A secondary lip seal is installed on the output shaft for further sealing. A drain system collects fuel leaks which could occur past the different sealing provisions.
D. Bleed Valve Stop Mechanism Assembly
The function of the bleed valve stop mechanism assembly is to limit the number of revolutions of the bleed valve fuel gear motor to the number of revolutions required for a complete cycle (opening-closing) of the VBV doors. It is located between the bleed valve fuel gear motor and the bleed valve and ballscrew actuator on the aft face of the fan frame at the 9 o'clock position aft looking forward.
The function of the bleed valve stop mechanism assembly is to limit the number of revolutions of the bleed valve fuel gear motor to the number of revolutions required for a complete cycle (opening-closing) of the VBV doors. It is located between the bleed valve fuel gear motor and the bleed valve and ballscrew actuator on the aft face of the fan frame at the 9 o'clock position aft looking forward.
NOTE: The bleed valve stop mechanism includes a protecting dust cover boot to protect the shaft and ball bearing (PRE CFM56-5B SB 75-0010); the bleed valve mechanism which includes packed sealed bearings has not a protecting dust cover boot (POST CFM56-5B SB 75-0010).
E. Bleed Valve and Master Ballscrew Actuator Assembly
The bleed valve and master ballscrew actuator is the unit which transfers the driving input from the bleed valve fuel gear motor to the 11 ballscrew actuators system. It consists of a speed reduction gearbox and a ballscrew actuator linked to a hinged door. The master ballscrew actuator is located on the fan frame under fan duct panel at the 9:00 o'clock position, aft looking forward.
The bleed valve and master ballscrew actuator is the unit which transfers the driving input from the bleed valve fuel gear motor to the 11 ballscrew actuators system. It consists of a speed reduction gearbox and a ballscrew actuator linked to a hinged door. The master ballscrew actuator is located on the fan frame under fan duct panel at the 9:00 o'clock position, aft looking forward.
F. Bleed Valve and Ballscrew Actuator Assembly
(1) General
Eleven bleed valve and ballscrew actuator units are attached to the fan frame. They are controlled by the ECU and open at low and transient power settings to increase the booster mass flow and improve booster and HP compressor matching. Each bleed valve and master ballscrew actuator consists of a bevel gear speed reduction gearbox and a ballscrew unit linked to a hinged door.
Eleven bleed valve and ballscrew actuator units are attached to the fan frame. They are controlled by the ECU and open at low and transient power settings to increase the booster mass flow and improve booster and HP compressor matching. Each bleed valve and master ballscrew actuator consists of a bevel gear speed reduction gearbox and a ballscrew unit linked to a hinged door.
G. Transducer Variable Bleed Valve (VBV) Position Feedback
The VBV position sensor is of the Rotary Variable Differential Transducer (RVDT) type. It is installed on the VBV stop mechanism. It sends an angular position to the ECU.
The VBV position sensor is of the Rotary Variable Differential Transducer (RVDT) type. It is installed on the VBV stop mechanism. It sends an angular position to the ECU.