DOC AIRBUS | AMM A320FTHRUST REVERSER SYSTEM COMPONENTS - DESCRIPTION AND OPERATION
** ON A/C NOT FOR ALL
1. Description
The thrust reverser actuation system includes:
** ON A/C NOT FOR ALL The thrust reverser actuation system includes:
Thrust Reverser-Component Location- two double switches for the deploy position
- four door position switches for the stow and locked position
- four door latches (primary lock)
- four actuators with inner latch (secondary lock)
- hydraulic control unit (HCU) including:
a pressurizing valve
a directional valve
a flow limiter
a bleed valve
a pressure switch
a filter and clogging indicator
a check valve restrictor
a mechanical inhibition - hydraulic hoses
- electrical harnesses and junction box
- a SOV and associated filter
2. Component Description
A. Deployed Doors Switch
(1) General
The deployed position of the doors is sensed by two thrust reverser double switches : one for the two right side doors and one for the two left side doors.
They are located between the corresponding doors in 3 and 9 o'clock beams. One single switch includes 2 cells one for each ECU channel.
Junction wires inside the switch are bedded in grease to avoid friction wear problems.
A screw enables lever position rigging. The cells are hermetically sealed and include a compensatory system enabling their use in over-pressure (up to 2 bars).
The switches are connected to the ECU via the electrical junction box.
For each door, one cell is connected to ECU channel A, the other one to channel B. All doors are electrically connected in series.
Each time a door reaches 95% of its travel, the circuit closes.
Electrical characteristics :
The deployed position of the doors is sensed by two thrust reverser double switches : one for the two right side doors and one for the two left side doors.
They are located between the corresponding doors in 3 and 9 o'clock beams. One single switch includes 2 cells one for each ECU channel.
Junction wires inside the switch are bedded in grease to avoid friction wear problems.
A screw enables lever position rigging. The cells are hermetically sealed and include a compensatory system enabling their use in over-pressure (up to 2 bars).
The switches are connected to the ECU via the electrical junction box.
For each door, one cell is connected to ECU channel A, the other one to channel B. All doors are electrically connected in series.
Each time a door reaches 95% of its travel, the circuit closes.
Electrical characteristics :
- Open voltage : 5 to 50VDC
- Min. open circuit resistance : 0.1 Megohm
- Current : 2 to 10mA
- Max. closed circuit resistance : 5 ohms
(2) Operation
Initially, lever (1) is held in a neutral position under spring (3) force. Lever (2) transmits lever (1) motion to a plate (5), which controls cells A and B together. The doors in the deploying sequence come into contact with the lever 1 which is caused to rotate, (the force exerted by the actuator being greater than the spring (3) force). At 95% of the deployed position, the switch is closed. The switches are connected in series so that only when all the switch contacts are closed, the ECU will receive the information "all doors deployed".
Initially, lever (1) is held in a neutral position under spring (3) force. Lever (2) transmits lever (1) motion to a plate (5), which controls cells A and B together. The doors in the deploying sequence come into contact with the lever 1 which is caused to rotate, (the force exerted by the actuator being greater than the spring (3) force). At 95% of the deployed position, the switch is closed. The switches are connected in series so that only when all the switch contacts are closed, the ECU will receive the information "all doors deployed".
B. Stow Door Switch
(1) General
The stowed position of the doors is sensed by four thrust reverser single switches, one per door, located onto the forward frame rear side next to the latches.
The switches are dual, i.e. they include 2 cells one dedicated to each channel of the ECU. Junction wires, connection section are bedded in grease to avoid friction wear. A screw enables lever position rigging.
Cells are hermetically sealed and include a compensatory system enabling their use in over-pressure (up to 2 bars).
The switches are connected to the ECU via the electrical junction box.
All stow switches are connected in parallel.
At 0.9% of blocker doors flush position , the cells are closed .
Electrical characteristics :
The stowed position of the doors is sensed by four thrust reverser single switches, one per door, located onto the forward frame rear side next to the latches.
The switches are dual, i.e. they include 2 cells one dedicated to each channel of the ECU. Junction wires, connection section are bedded in grease to avoid friction wear. A screw enables lever position rigging.
Cells are hermetically sealed and include a compensatory system enabling their use in over-pressure (up to 2 bars).
The switches are connected to the ECU via the electrical junction box.
All stow switches are connected in parallel.
At 0.9% of blocker doors flush position , the cells are closed .
Electrical characteristics :
- Open voltage : 5 to 50VDC
- Min. open circuit resistance : 0.1 Megohm
- Current : 2 to 10mA
- Max. closed circuit resistance : 5 ohms
(2) Operation
Initially under spring (2) force, the lever (3) (linked in rotation with the lever (1)) holds the two cells (5) by the plate (4) and screw (6), in position (circuit 1 open, circuit 2 closed). When the door during its stowing sequence comes to 1.1% of its flush position, a spigot fixed onto the door makes contact with the lever (1) causing it to rotate (the force exerted by actuator being greater than the spring force). Lever (1) makes lever (3) rotate.
At 0.9% of flush position, lever (3) position is such that the contacts are : circuit 1 closed, circuit 2 open.
The ECU receives the information one "stowed door". The contacts are connected in parallel.
The signal combination and their complements enable to give the following information :
Initially under spring (2) force, the lever (3) (linked in rotation with the lever (1)) holds the two cells (5) by the plate (4) and screw (6), in position (circuit 1 open, circuit 2 closed). When the door during its stowing sequence comes to 1.1% of its flush position, a spigot fixed onto the door makes contact with the lever (1) causing it to rotate (the force exerted by actuator being greater than the spring force). Lever (1) makes lever (3) rotate.
At 0.9% of flush position, lever (3) position is such that the contacts are : circuit 1 closed, circuit 2 open.
The ECU receives the information one "stowed door". The contacts are connected in parallel.
The signal combination and their complements enable to give the following information :
- all the doors are stowed
- 1, 2 or 3 unstowed doors
- none stowed door.
(1) General
There are four latches, one per blocker door. The latches hold the doors in the stowed position and are located beside the actuators on the thrust reverser forward frame. The latches are connected in series. They are hydraulically supplied by the HCU (Hydraulic Control Unit).
One latch includes :
There are four latches, one per blocker door. The latches hold the doors in the stowed position and are located beside the actuators on the thrust reverser forward frame. The latches are connected in series. They are hydraulically supplied by the HCU (Hydraulic Control Unit).
One latch includes :
- a hook maintained in the unlocked position by two springs
- a lever enabling under the action of two springs to maintain the hook in its locked position
- a hydraulic actuator
- a hydraulic valve
(2) Operation
(a) Door unlocking sequence (deployment)
Under high pressure action, the latch actuator actuates the lever. At the end of the latch actuator stroke, the piston ports hydraulic fluid through a hole which enables the following latch actuator high pressure supply. The lever is then in a position which does not interfere with the hook rotative movement.
As soon as the door leaves the stowed position, because of the door actuator force and aerodynamic loads, the hook is held by the two levers in the unlocked position and releases the olive shaped button.
Under high pressure action, the latch actuator actuates the lever. At the end of the latch actuator stroke, the piston ports hydraulic fluid through a hole which enables the following latch actuator high pressure supply. The lever is then in a position which does not interfere with the hook rotative movement.
As soon as the door leaves the stowed position, because of the door actuator force and aerodynamic loads, the hook is held by the two levers in the unlocked position and releases the olive shaped button.
(b) Door locking sequence (stowage)
At the end of deployment the latch hydraulic actuator is connected to return. The latch actuator ports fluid out under spring action. Fluid output of the next latch is made possible by a hole in the chamber of the valve.
The door hook olive shaped button makes contact with the hook which makes it rotate untill the lever moved by spring action achieves its locked position. As long as the door actuators are under pressure the door remains on its latch inner stop (door over stowing of 2 mm maxi (0.08 in. maxi).
As soon as the door actuators are connected to return, the doors move to the flush position under seal action and aerodynamic loads. The olive-shaped button is then displaced to the upper part of the latch hook which has taken up the play.
There is a manual unlocking pin which permits the unlocking sequence without hydraulic pressure.
At the end of deployment the latch hydraulic actuator is connected to return. The latch actuator ports fluid out under spring action. Fluid output of the next latch is made possible by a hole in the chamber of the valve.
The door hook olive shaped button makes contact with the hook which makes it rotate untill the lever moved by spring action achieves its locked position. As long as the door actuators are under pressure the door remains on its latch inner stop (door over stowing of 2 mm maxi (0.08 in. maxi).
As soon as the door actuators are connected to return, the doors move to the flush position under seal action and aerodynamic loads. The olive-shaped button is then displaced to the upper part of the latch hook which has taken up the play.
There is a manual unlocking pin which permits the unlocking sequence without hydraulic pressure.
(3) Removal/installation
The latch is secured by four bolts on the thrust reverser forward frame.
The latch is secured by four bolts on the thrust reverser forward frame.
(4) Adjustment
The adjustment of the flush position of the door is made by sliding the latch fitting.
The adjustment of the flush position of the door is made by sliding the latch fitting.
(1) General
There are four hydraulic actuators, mounted on the forward frame by a ball joint assembly support.
They constitute a differential double-acting unit.
They are supplied by the HCU.
These hydraulic actuators have four different functions :
There are four hydraulic actuators, mounted on the forward frame by a ball joint assembly support.
They constitute a differential double-acting unit.
They are supplied by the HCU.
These hydraulic actuators have four different functions :
- to deploy doors
- to stow doors
- to ensure a secondary lock in stowed position by a system of claws
- to ensure that doors rotation speed slows down at the end of the deploy phase.
(a) Deploy sequence
The actuator is initially in position of direct flow, locked. On the deploy command the hydraulic pressure is supplied to the rod side of the actuator (chamber B). The hoses are located on the head of the actuator, then the pressure is supplied (to chamber B) by the means of a central hose and an interior chamber which communicate with the chamber B through port (T).
After the unlocked sequence of the door latches, the head actuator chamber (A) is supplied by the HCU.
The pressures in chambers (A) and (B) are equal but the difference of surfaces between the piston, the head side and the rod side enables the movement of the piston and thus opening of the door.
The actuator limits the speed of the deployment.
Load required to deploy is about 684 daN (15.38 lbf) with a pressure of 206 bar (2987 psi).
The actuators have a stroke of 260 mm (10.24 in.).
The actuator is initially in position of direct flow, locked. On the deploy command the hydraulic pressure is supplied to the rod side of the actuator (chamber B). The hoses are located on the head of the actuator, then the pressure is supplied (to chamber B) by the means of a central hose and an interior chamber which communicate with the chamber B through port (T).
After the unlocked sequence of the door latches, the head actuator chamber (A) is supplied by the HCU.
The pressures in chambers (A) and (B) are equal but the difference of surfaces between the piston, the head side and the rod side enables the movement of the piston and thus opening of the door.
The actuator limits the speed of the deployment.
Load required to deploy is about 684 daN (15.38 lbf) with a pressure of 206 bar (2987 psi).
The actuators have a stroke of 260 mm (10.24 in.).
(b) Unlocking sequence
At the beginning of the deploy sequence, the hydraulic pressure is applied to the differential section locking sleeve (1). Then the sleeve moves away and the claws (4) which maintain the actuator rod, are free.
Under the action of the nut (3) the claws open and the actuator rod becomes free.
The minimum hydraulic pressure for which the locking sleeve moves away and the claws become free is 40 bars (580 psi). 3.5 cc (0.12 USOZ) are necessary to release the claws.
At the beginning of the deploy sequence, the hydraulic pressure is applied to the differential section locking sleeve (1). Then the sleeve moves away and the claws (4) which maintain the actuator rod, are free.
Under the action of the nut (3) the claws open and the actuator rod becomes free.
The minimum hydraulic pressure for which the locking sleeve moves away and the claws become free is 40 bars (580 psi). 3.5 cc (0.12 USOZ) are necessary to release the claws.
(c) Speed slowing down system
At 95% of the deploy stroke, the hole (T), which permits the communication between the central hose and the rod actuator chamber, is closed by the piston shoulder. Then the fluid must pass through the restrictor (R), the pressure pushes the cup on its seat, and the fluid passes through a calibrated hole which causes speed reduction (speed less than or equal to 50 mm/s or 1.97 in./s).
At 95% of the deploy stroke, the hole (T), which permits the communication between the central hose and the rod actuator chamber, is closed by the piston shoulder. Then the fluid must pass through the restrictor (R), the pressure pushes the cup on its seat, and the fluid passes through a calibrated hole which causes speed reduction (speed less than or equal to 50 mm/s or 1.97 in./s).
(d) Stow sequence
The actuator is initially in reverse flow position. As soon as the stow order is given, high pressure is ported into chamber (B), while chamber (A), is connected to return.
Inside the restrictor, the pressure moves the sliding cup, then the fluid passage is free allowing a high speed at the beginning of stowing.
The return pressure is 15 bars (217.5 psi).
The nominal pressure in chamber (B) is 206 bars (2987 psi).
The stowing strength obtained is about 2305 daN (51.82 lbf).
The actuator is initially in reverse flow position. As soon as the stow order is given, high pressure is ported into chamber (B), while chamber (A), is connected to return.
Inside the restrictor, the pressure moves the sliding cup, then the fluid passage is free allowing a high speed at the beginning of stowing.
The return pressure is 15 bars (217.5 psi).
The nominal pressure in chamber (B) is 206 bars (2987 psi).
The stowing strength obtained is about 2305 daN (51.82 lbf).
(e) Locking sequence
The nut (3) which is linked with the piston, arrives against the claws.
As the shape of the claws is bevelled, the nut can displace the claws.
While the actuator is not locked, the locking sleeve is maintained in unlocked position by the spring (5) and in the locking sequence by the open claws.
When the nut is passed, the claws return to their initial position, and over the action of the spring (7), the locking ring fixes the claws.
When the actuator is locked, the nut arrives in abutment against the actuator body, which permits a small over flushing of the doors. When the doors are locked, the chamber (B) is connected to return, the actuator takes a rest position.
In this position the rod has a locking clearance of 3 mm (0.118 in.).
The nut (3) which is linked with the piston, arrives against the claws.
As the shape of the claws is bevelled, the nut can displace the claws.
While the actuator is not locked, the locking sleeve is maintained in unlocked position by the spring (5) and in the locking sequence by the open claws.
When the nut is passed, the claws return to their initial position, and over the action of the spring (7), the locking ring fixes the claws.
When the actuator is locked, the nut arrives in abutment against the actuator body, which permits a small over flushing of the doors. When the doors are locked, the chamber (B) is connected to return, the actuator takes a rest position.
In this position the rod has a locking clearance of 3 mm (0.118 in.).
(f) Door latch failure
If a door latch breakes, the nut comes against the claws which are fixed, and that prevents the door from moving more than 1/2 in. from the stowed position. This movement is sufficient to actuate the UNSTOW switch to provide cockpit indication of the failure. The ECU logic will also evaluate the unstow signal. If reverser deployment has not been selected, the HCU pressurizing valve will be commanded to open thus supplying stow pressure to the actuator.
If a door latch breakes, the nut comes against the claws which are fixed, and that prevents the door from moving more than 1/2 in. from the stowed position. This movement is sufficient to actuate the UNSTOW switch to provide cockpit indication of the failure. The ECU logic will also evaluate the unstow signal. If reverser deployment has not been selected, the HCU pressurizing valve will be commanded to open thus supplying stow pressure to the actuator.
E. Hydraulic Control Unit
(1) General
The hydraulic control unit controls hydraulic fluid flow to the thrust reverser latches and blocker door actuator. Control and feedback signals are exchanged with the engine ECU. The HCU is mounted on the upper forward face of the right hand thrust reverser forward frame. The HCU incorporates the following items :
Flow rate supply from aircraft does not exceed 34.45 l/min by thrust reverser.
Flow rate return to hydraulic reservoir does not exceed 45.8 l/min (12.1 US gal/min).
Temperature :
Pressurizing valve solenoid and directional valve solenoid :
Each ECU channel interfaces with the thrust reverser valve solenoids.
Each solenoid contains two electrically independent coils, one dedicated to channel A and the other to channel B. Each of these windings conforms to the following characteristics :
The resistance of the wiring in series with each winding as measured at the connection to the ECU will be less than 55 ohms.
The hydraulic control unit controls hydraulic fluid flow to the thrust reverser latches and blocker door actuator. Control and feedback signals are exchanged with the engine ECU. The HCU is mounted on the upper forward face of the right hand thrust reverser forward frame. The HCU incorporates the following items :
- a pressurizing valve and a mechanical inhibition
- a directional valve
- a flow limiter
- a bleed valve
- a pressure switch
- a filter and clogging indicator
- a check valve restrictor
- a thermal blanket
Flow rate supply from aircraft does not exceed 34.45 l/min by thrust reverser.
Flow rate return to hydraulic reservoir does not exceed 45.8 l/min (12.1 US gal/min).
Temperature :
- Fluid temperature during use is between -40 deg.C to +107 deg.C (-40 deg.F to 224.6 deg.F)
- The temperature of equipment is between -54 deg.C to +121 deg.C (-65.2 deg.F to +249.8 deg.F) during the operating phase.
- supply pressure to the hydraulic system (pressurizing valve)
- regulate blocker doors stow speed (flow limiter)
- supply latches (directional valve solenoid)
- supply actuators (directional valve).
Pressurizing valve solenoid and directional valve solenoid :
Each ECU channel interfaces with the thrust reverser valve solenoids.
Each solenoid contains two electrically independent coils, one dedicated to channel A and the other to channel B. Each of these windings conforms to the following characteristics :
- actuation current : 300 mA min from ECU
- actuation voltage : 16VDC max at 300 mA
- max steady state voltage 31.5VDC
- DC resistance : 18 ohms min.
- reactance (below 300 Hz) 500 millihenries nominal
- update time capability 50 milliseconds min.
The resistance of the wiring in series with each winding as measured at the connection to the ECU will be less than 55 ohms.
NOTE: Pressurizing valve solenoid :
- energized: pressurizing valve open
- deenergized: pressurizing valve closed
Directional valve solenoid : - energized: thrust reverser deploy
- deenergized: thrust reverser stow
(2) Component description
(a) Pressurizing valve and mechanical inhibition
The pressurizing valve is a two position valve which is solenoid actuated to the open position. The valve is spring loaded to the closed position (solenoid de-energized).
The pressurizing valve can also be manually closed and pinned (inhibited) to prevent inadvertent actuation of the thrust reverser during maintenance work.
Energizing the valve solenoid opens a port (B) allowing the displacement of the piston valve (2). Then the hydraulic pressure (A) is supplied to the stow side of the actuators and to the directional valve (in C).
The pressurizing valve is a two position valve which is solenoid actuated to the open position. The valve is spring loaded to the closed position (solenoid de-energized).
The pressurizing valve can also be manually closed and pinned (inhibited) to prevent inadvertent actuation of the thrust reverser during maintenance work.
Energizing the valve solenoid opens a port (B) allowing the displacement of the piston valve (2). Then the hydraulic pressure (A) is supplied to the stow side of the actuators and to the directional valve (in C).
(b) Directional valve
The directional valve is a three port, two position, valve.
Energizing the valve solenoid opens a port (B) allowing hydraulic pressure for the door latches (the HCU pressurizing valve must be open).
When the last latch is supplied the hydraulic pressure return (C') moves a piston valve (13) to the deploy position.
Then hydraulic pressure is ported to the deploy side of the actuator piston (B').
De-energizing the solenoid closes a port and allows spring (12) and hydraulic pressure to move the piston valve to the stow position. In normal operation, the hydraulic pressure will move the piston valve to the stow position if the spring breaks.
The directional valve is a three port, two position, valve.
Energizing the valve solenoid opens a port (B) allowing hydraulic pressure for the door latches (the HCU pressurizing valve must be open).
When the last latch is supplied the hydraulic pressure return (C') moves a piston valve (13) to the deploy position.
Then hydraulic pressure is ported to the deploy side of the actuator piston (B').
De-energizing the solenoid closes a port and allows spring (12) and hydraulic pressure to move the piston valve to the stow position. In normal operation, the hydraulic pressure will move the piston valve to the stow position if the spring breaks.
(c) Flow limiter
The flow limiter regulates the hydraulic fluid flow returning to the HCU from the actuator piston head in order to control/limit the blocker door stowing rate under varying conditions. Flow entering the flow limiter from the actuators goes through an orifice which creates a pressure drop. The pressure in the flow limiter chamber then acts on a spring loaded piston. As pressure is increased, the piston (1) moves down and compresses the spring (2). As the piston moves down, it begins closing the chamber exit (F), therefore restricting the flow rate from the actuator.
The maximum flow obtained is 40 l/min (10.57 US gal/min).
The flow limiter regulates the hydraulic fluid flow returning to the HCU from the actuator piston head in order to control/limit the blocker door stowing rate under varying conditions. Flow entering the flow limiter from the actuators goes through an orifice which creates a pressure drop. The pressure in the flow limiter chamber then acts on a spring loaded piston. As pressure is increased, the piston (1) moves down and compresses the spring (2). As the piston moves down, it begins closing the chamber exit (F), therefore restricting the flow rate from the actuator.
The maximum flow obtained is 40 l/min (10.57 US gal/min).
(d) Bleed valve
The bleed valve is provided as a means to ensure air is purged from the thrust reverser actuation system. While the system is self-purging by means of cycling the doors prescribed the thrust reverser actuation system is connected to hydraulic supply, the application of a procedure using the HCU bleed valve following removal/replacement of hydraulic components will assist removal of trapped air that could affect proper operation of clogging indicator.
The bleed valve is provided as a means to ensure air is purged from the thrust reverser actuation system. While the system is self-purging by means of cycling the doors prescribed the thrust reverser actuation system is connected to hydraulic supply, the application of a procedure using the HCU bleed valve following removal/replacement of hydraulic components will assist removal of trapped air that could affect proper operation of clogging indicator.
(e) Pressure switch
The pressure switch indicates to the ECU that hydraulic circuit is pressurized or not.
Pressure switch signal is available to the ECU and can be used for maintenance purpose.
Electrical characteristics :
The pressure switch indicates to the ECU that hydraulic circuit is pressurized or not.
Pressure switch signal is available to the ECU and can be used for maintenance purpose.
Electrical characteristics :
- open voltage : 5 to 50VDC
- min open circuit resistance : 0.1 Megohm
- max closed circuit resistance : 5 ohms
- current : 2 to 10 mA
(f) Check valve restrictor
A check valve restrictor is installed in the HCU block, adjacent to the flow limiter. This component protects against the possibility of a blockage in the main hydraulic return line leading to an unsafe pressure build-up within the system. A hydraulic line between the check valve restrictor discharge port and the case drain line provides an additional line to the reservoir. If the main return line is clogged, leading to subsequent increase of pressure within the system (as a result of normal leakage at the pressurizing valve) the check valve restrictor will open (at a differential pressure at 200 psid/13.8 bar) and vent the system to the case drain line, thus maintaining the internal system pressure well below the unlock range.
A check valve restrictor is installed in the HCU block, adjacent to the flow limiter. This component protects against the possibility of a blockage in the main hydraulic return line leading to an unsafe pressure build-up within the system. A hydraulic line between the check valve restrictor discharge port and the case drain line provides an additional line to the reservoir. If the main return line is clogged, leading to subsequent increase of pressure within the system (as a result of normal leakage at the pressurizing valve) the check valve restrictor will open (at a differential pressure at 200 psid/13.8 bar) and vent the system to the case drain line, thus maintaining the internal system pressure well below the unlock range.
(3) Filter and Clogging Indicator
(a) Filter
- General
A filter at the HCU inlet is used to filter the fluid supply from the hydraulic system. The filter is a flow through cartridge type filter. - Description/operation
The unfiltered fluid arrives through A port which communicates with the internal body filter. The fluid passes through the cartridge and gets out through B port. - Removal
When removing the cartridge, the shutoff diaphragm (2) is pushed against its lower seat by the spring (3), preventing fluid leakage.
(b) Clogging indicator
- General
The clogging indicator monitors the pressure loss through the filter cartridge and features a pop-out indicator to signal when it is necessary to replace the filter element. - Description/operation
The clogging indicator incorporates two spring loaded magnetic pistons (1 and 4) whose magnetic attraction keep the pop-out indicator (5) in the retracted position. The lower magnetic piston (1) monitors the differential pressure between the filtered and unfiltered fluid across the filter element. As the differential pressure increases, the piston compresses the spring (2) and moves away from the upper magnetic piston (4) at a threshold of 11 bar (159.5 psi).
At a preset displacement of approximately 2mm, the upper magnetic piston spring overcomes the magnetic face and drives the pop-out indicator from its retracted position.
(4) Operation
Selection of either stow or deploy from the cockpit sends a signal to the engine ECU which, in turn, supplies two independent signals to the thrust reverser HCU pressurizing and directional control valves.
These signals to the HCU are only provided if the ECU has received correct signals e.g. reverser position engine power setting.
Solenoid conditions are as follows :
Selection of either stow or deploy from the cockpit sends a signal to the engine ECU which, in turn, supplies two independent signals to the thrust reverser HCU pressurizing and directional control valves.
These signals to the HCU are only provided if the ECU has received correct signals e.g. reverser position engine power setting.
Solenoid conditions are as follows :
| ------------------------------------------------------------------------------- |
| Conditions Pressurizing valve Directional |
| solenoid valve solenoid |
| ------------------------------------------------------------------------------- |
| Forward thrust 0 0 |
| Deploying 1 1 |
| Reverse thrust 0 1 |
| Stowing 1 0 |
| ------------------------------------------------------------------------------- |
NOTE: 1 = solenoid energized
0 = solenoid de-energized
0 = solenoid de-energized
(a) Initial stowed position
In the initial stowed position with the reverse stow control selected in the cockpit, the hydraulic pressure is applied to the input of the HCU. All reverser hydraulic systems are connected to the return line as long as the aircraft is in flight and, no signal is sent to open the pressurizing valve solenoid.
In the initial stowed position with the reverse stow control selected in the cockpit, the hydraulic pressure is applied to the input of the HCU. All reverser hydraulic systems are connected to the return line as long as the aircraft is in flight and, no signal is sent to open the pressurizing valve solenoid.
(b) Deploy sequence
1 When reverse thrust is selected in the cockpit, the ECU controls that deploying conditions are achieved.
In that case, the electrical power (28VDC) is sent to the pressurizing valve solenoid and to the directional valve solenoid.
The SEC and the static relay open the SOV.
In that case, the electrical power (28VDC) is sent to the pressurizing valve solenoid and to the directional valve solenoid.
The SEC and the static relay open the SOV.
2 When the pressurizing valve is opened and the directional solenoid energized, high pressure (HP about 3000 psi) is routed to the hydraulic actuator rod side. Actuators overstow, relieving loads on hydraulic door latches. Pressure signal is sent to the EIU. Pressure from directional valve causes door primary latches to unlock in sequence.
3 When the last latch is opened, the pressure drives the directional valve which enables to supply hydraulic actuator heads with pressure. Actuator secondary locks release.
4 As soon as one blocker door is at more than one percent of angular travel, its stow switch changes over and sends a "1 or 2 or 3 unstowed doors" signal to the ECU. In the cockpit an amber REV indication is displayed in the middle of the N1 dial.
The "unstowed doors" signal will not be send to the ECU until all blockers doors are at more than one percent of their angular travel.
The "unstowed doors" signal will not be send to the ECU until all blockers doors are at more than one percent of their angular travel.
5 Each blocker door arriving at 95 percent of its travel is slowed down until completely deployed through hydraulic actuator inner restriction: at this moment the switch is also activated. When the four blocker doors are deployed the ECU receives the "deployed doors" information and stops pressurizing valve solenoid supply.
REV indication changes to green.
Latches remain in door stowed position.
REV indication changes to green.
Latches remain in door stowed position.
1 When blocker doors stowage is selected, the ECU controls that stowing conditions are achieved. In this case, the ECU reverses the electrical power supplies of the end of deploy sequence. Pressurizing valve solenoid is energized, directional valve solenoid de-energized. When one door is at less than 95% of his travel, REV indication changes to amber color.
2 Pressurizing valve opens and hydraulic actuators rod are supplied.
Hydraulic actuator heads are connected to return.
A flow limiter controls hydraulic actuator retraction speed.
Hydraulic actuator heads are connected to return.
A flow limiter controls hydraulic actuator retraction speed.
3 When all blocker doors are at one percent from their stowed position they activate the switches which send the "stowed door" information to the ECU. The REV indication disappears.
4 The ECU maintains pressurizing valve solenoid in energized conditions for one second after receipt of "doors stowed" signal from stow switches. This permits hydraulic pressure supply to actuators to ensure full retraction of doors and re-engagement of the latches.
5 HCU in de-energized condition connects all circuits to return. The pressure switch transmits a "without pressure" signal to the ECU.