B777 Logic Speed Controll Unit P/N 2119804-4 - Hydraulic system

[per ulv]

I'm trying in vain to locate some info about the function of this component on the net without success. Does not have access to AMM for B777.

Does this unit control and govern speed of electric hyd pumps?

Thanks for any advice.

[Fargoo]

They control the ADP (Air Driven Pump) of which there are 2.

They control the pump speed and provide overspeed protection using variable inlet guide vanes for speed control.

If an overspeed is detected there's an overspeed latch in the card which can only be reset using the MAT (Maintenance Access Terminal).

The cards are located next to the pumps in the wing/body fairing.

[Fargoo]

Extract from the AMM

General

The ADP assembly gets pressurized air from the airplane pneumatic system.
Air flows through the modulating shutoff valve (MSOV) to the turbine gearbox assembly (TGA).
The TGA turns the ADP hydraulic pump. The LSCU supplies primary speed control and overspeed protection.

The MSOV has these components:
* Butterfly valve
* Dual coil solenoid (auto and continuous run coils)
* Pneumatic actuator.

The TGA has these components:
* Variable inlet guide vanes (VIGVs)
* Unison ring
* Pneumatic actuator
* Electro-pneumatic servo-valve
* LVDT
* Turbine wheel
* Gearbox
* Monopole speed sensor (2)
* Pneumatic speed sensor
* Primary reserve solenoid
* Secondary speed control fluidic circuit.

Normal Operation
The signal to operate the ADP assembly comes from the HYDIM cards when the selector is in the AUTO position or from the ADP selector when the selector is in the ON position. These signals go to the LSCU.

The LSCU energizes either the auto run or continuous run coil in the MSOV. This permits air to go to the MSOV pneumatic actuator.
The actuator opens the butterfly valve and air goes through the open VIGVs to turn the turbine.

Speed Control
The ADP assembly has primary and secondary speed control circuits.
The LSCU contains the primary speed control. A monopole speed sensor on the gearbox sends ADP speed signals to the LSCU. The primary speed control circuits control the pneumatic actuator for the VIGVs. The actuator moves the VIGVs through the unison ring. This keeps the turbine within 2.5 percent of thenormal operating speed.

Normal turbine speed is approximately 32,000 RPM. Normal pump speed is 4315 RPM.
An LVDT supplies actuator position feedback to the LSCU.

The secondary speed control controls the position of the MSOV butterfly valve. The pneumatic speed sensor on the TGA sends a pulsed pneumatic signal in proportion to turbine speed.
This signal goes to the secondary speed control fluidic circuit. This pneumatic circuit controls the MSOV pneumatic actuator.
The secondary speed control tries to keep the pump speed approximately 700 RPM higher than the primary speed control.
When the system operates on the primary speed control, the secondary speed control gets an underspeed input and keeps the MSOV fully open.
If the primary speed control fails and the speed starts to increase, the MSOV starts to close to keep the pump speed at approximately 5000 RPM.

Reserve Mode
A reserve mode lets the turbine turn at a higher speed to operate the pump at 5160 RPM. This increases pump output for autoslat operation when only one ADP can operate. The HYDIM card commands reserve mode operation for 8 seconds.
For reserve mode operation, the LSCU resets the primary speed control circuit to operate the turbine at the higher RPM. The primary speed control uses the monopole speed sensor input to control the VIGVs. To operate at this higher speed, the secondary speed control must be stopped. The LSCU sends a signal to energize the solenoid in the primary reserve solenoid
valve.
The valve closes and blocks the pulsed pneumatic signal from the pneumatic speed sensor. Without a speed input, the secondary speed control fluidic circuit does not operate and the butterfly valve in the MSOV fully opens.

Overspeed Protection

Overspeed protection keeps the ADP assembly from turning too fast.
A second monopole speed sensor on the gearbox supplies a speed signal to the LSCU. If the pump speed is more than 6590 RPM, the LSCU opens the control circuits through the overspeed latch. This removes the power from the solenoid in the MSOV and closes the butterfly valve.[/SIZE]

:ok:

[per ulv]

Hi Fargoo, thanks for valuable info. Not easy to decipher techlogs for a type you are unfamiliar with and do not have access to AMM.

Follow up question, the ADP has a heater element. I assume this is to handle excess cooling due to bleed air expanding in the turbine?

[gas path]

The heater assy's are there to stop ice formation on the MSOV and (turbine) gearbox due to cold soak.