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
2. Actuation System
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.
- POST CFM SB 72-310
To improve the flowpath and hail ingestion capacity.
- New VBV cast doors are installed (except the VBV door in front of the T25 sensor, at the 4:30 o'clock position).
- Eleven scoops and 9 slides are attached to the fan frame. - END OF CFM SB 72-310
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 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
(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. A spring is attached to the spring end. The spring holds the shaft assembly in position during operation and also permits easy removal of the shaft assembly
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. A spring is attached to the spring end. The spring holds the shaft assembly in position during operation and also permits easy removal of the shaft assembly
(1) Description
(a) 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. A spring is attached to the hexagon end. The spring holds the shaft assembly in position during operation and also permits easy removal of the shaft assembly.
(b) The ferrules are installed in the struts of the engine fan frame to support the flexible shaft assemblies during operation.
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
(1) General
The bleed-valve stop-mechanism assembly is a component of the Variable-Bleed-Valve (VBV) actuation system. It is located between the bleed-valve fuel gear-motor and master ballscrew actuator, on the aft face of the fan frame at the 9 o'clock position, aft looking forward.
The bleed-valve stop-mechanism assembly is a component of the Variable-Bleed-Valve (VBV) actuation system. It is located between the bleed-valve fuel gear-motor and master ballscrew actuator, on the aft face of the fan frame at the 9 o'clock position, aft looking forward.
(2) Description
(a) 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 exact number required for a complete cycle (opening-closing) of the VBV doors. This limiting function supplies the reference position for installing and adjusting the VBV actuators.
(b) The bleed-valve stop-mechanism consists of a housing for a hollow screw which is driven by the bleed-valve fuel gear-motor. This hollow screw shaft holds the main VBV flexible shaft which connects the bleed-valve fuel gear-motor to the master ballscrew actuator. A follower nut translates along the screw and stops the rotation of the bleed-valve fuel gear-motor when it reaches the ends of the screw threads.
NOTE: The bleed valve stop mechanism includes a protecting dust cover boot to protect the output shaft and ball bearing (PRE CFM56-5B SB 75-0038); the bleed valve mechanism which includes packed sealed bearings has not a protecting dust cover boot (POST CFM56-5B SB 75-0038).
(c) A location is provided on the aft end of the bleed-valve stop-mechanism for installation of a Rotary Variable Differential-Transformer (RVDT). This electrical equipment senses the angular position of the entire VBV system and sends a corresponding signal to the ECU.
E. Bleed-Valve and Master Ballscrew-Actuator Assembly
(1) General
(a) The bleed-valve and master ballscrew-actuator assembly is a component of the Variable-Bleed-Valve (VBV) actuation system.
(b) The master ballscrew-actuator is located on the fan frame under fan duct panel at the 9:00 o'clock position, aft looking forward.
(2) Description
(a) The master ballscrew-actuator is the unit which transfers the driving input from the bleed-valve fuel gear-motor to the ballscrew-actuator system. It consists of a speed-reduction gearbox and a ballscrew-actuator linked to a hinged door. Speed reduction is consecutively carried out through one pair of spur gears and then by 2 pairs of bevel gears. The last set of bevel gears drives the ballscrew.
(b) The ball-bearing-type screw and nut assembly consists of a screw, nut, ball-return tube, a clamp attached by 2 screws and washers, and 68 balls. The screw is made of special induction-hardened steel. It has a rolled thread, flat at crest, with a circular radius form at root. A flanged bushing is shrunk on one end of the screw shaft and 2 flats are machined on the cylindrical portion at the other end.
(c) The nut it also made of special alloy steel and its thread is matched to the screw. Two cylindrical pins are machined on the nut sides. The internal thread is nitrided and the external nut surfaces are cadmium plated with the exception of the end faces. Two holes are drilled in the nut body to receive the ball return tube, and another 2 holes are tapped to fasten the tube clamp with 2 screws.
(d) The ballscrew translating nut is held during rotation by 2 pins which slide within 2 slots in the actuator body. The screw is protected by 2 boots made of silicone elastomer.
(e) The travel of the nut is transmitted to the door by 2 links. A lever, integral with the door, is connected to the position sensor. The output motion of the first pair of bevel gears is transferred to the 10 other ballscrew actuators through flexible shafts driven by 2 ends of the output gear of this pair of bevel gears.
F. Bleed-Valve and Ballscrew-Actuator Assembly
(1) General
(a) The bleed-valve and ballscrew-actuator units are attached to the fan frame. They operate in synchronization with the eleventh bleed-valve and master ballscrew-actuator unit.
(b) The bleed-valve and master ballscrew-actuator unit provides the driving input to the other (follower) ballscrew-actuators through a linkage of flexible shafts.
(2) Description
Each bleed-valve and ballscrew-actuator is exactly of the same internal design as the master ballscrew-actuator as far as the ballscrew system is concerned. The only difference lies in the fact that there is only one reduction gear instead of two.
Each bleed-valve and ballscrew-actuator is exactly of the same internal design as the master ballscrew-actuator as far as the ballscrew system is concerned. The only difference lies in the fact that there is only one reduction gear instead of two.
G. Variable-Bleed-Valve (VBV) Position Sensor
(1) General
The VBV position sensor is of the Rotary Variable Differential Transducer (RVDT) type. It is installed on the VBV stop mechanism. It is electrically supplied with 7.07 volts RMS, 300 Hz, provided by the Electronic Control Unit (ECU).
The VBV position sensor is of the Rotary Variable Differential Transducer (RVDT) type. It is installed on the VBV stop mechanism. It is electrically supplied with 7.07 volts RMS, 300 Hz, provided by the Electronic Control Unit (ECU).
(2) Description
The VBV position sensor is composed of:
- one housing assembly,
- one electromagnetic assembly (RVDT).
The VBV position sensor is composed of:
- one housing assembly,
- one electromagnetic assembly (RVDT).
(a) The housing assembly has the following elements:
- two receptacles, each secured by 4 bolts,
- one centering lug,
- three attachment tabs,
- one rear flange secured by 4 bolts,
- one front flange secured by 3 bolts,
- one groove provided with a seal for tightness with the RVDT drive shaft.
- two receptacles, each secured by 4 bolts,
- one centering lug,
- three attachment tabs,
- one rear flange secured by 4 bolts,
- one front flange secured by 3 bolts,
- one groove provided with a seal for tightness with the RVDT drive shaft.
(b) Electromagnetic assembly
This assembly is composed of one fixed part and one rotary part. The fixed part includes the following elements:
- one body
- two stators, each having the following items:
. one fixed armature
. one primary coil
. two secondary coils
- three bolts securing the assembly to the housing.
The rotary part is composed of the following elements:
- one shaft with a splined end on which are installed the following items:
. one spacer
. one control lever secured to the shaft by a bolt, a uniball and an index
- one close-coil spring with its fixed end located in a hole of the housing assembly
- two inner armatures (stacking of plates)
- two ball bearings.
This assembly is composed of one fixed part and one rotary part. The fixed part includes the following elements:
- one body
- two stators, each having the following items:
. one fixed armature
. one primary coil
. two secondary coils
- three bolts securing the assembly to the housing.
The rotary part is composed of the following elements:
- one shaft with a splined end on which are installed the following items:
. one spacer
. one control lever secured to the shaft by a bolt, a uniball and an index
- one close-coil spring with its fixed end located in a hole of the housing assembly
- two inner armatures (stacking of plates)
- two ball bearings.
(3) Operation
(a) Purpose
The purpose of this sensor is to transmit to the ECU, the angular positions of the variable bleed valves by means of 2 dual electrical signals (channels A and B).
The purpose of this sensor is to transmit to the ECU, the angular positions of the variable bleed valves by means of 2 dual electrical signals (channels A and B).
NOTE: The sensor is a dual sensor because it has 2 RVDTs with the two inner armatures installed on the same shaft.
(b) Principle
The following description applies to the two RVDTs.
The position sensor is of the induction type. The primary coil, once energized, creates a magnetic flux, which induces a potential difference in both secondary coils. In the particular case of an RVDT, the lines of force created by the primary coil magnetic field are changed by the metallic contour of the inner armature (core) installed on the shaft. Any rotation of the shaft, and consequently, of the armature contour, changes the pattern of the lines of force of the primary coil and therefore changes the potential differences generated in the secondary coils.
These electrical signals are interpreted by the ECU as a shaft rotation caused by an angular displacement of the master ballscrew-actuator bleed-valve.
The following description applies to the two RVDTs.
The position sensor is of the induction type. The primary coil, once energized, creates a magnetic flux, which induces a potential difference in both secondary coils. In the particular case of an RVDT, the lines of force created by the primary coil magnetic field are changed by the metallic contour of the inner armature (core) installed on the shaft. Any rotation of the shaft, and consequently, of the armature contour, changes the pattern of the lines of force of the primary coil and therefore changes the potential differences generated in the secondary coils.
These electrical signals are interpreted by the ECU as a shaft rotation caused by an angular displacement of the master ballscrew-actuator bleed-valve.