Practical Development of Control Technology
for the More Electric Engine
MORIOKA Noriko : Manager, Control Systems Engineering Department, Research &
Engineering Division, Aero-Engine & Space Operations
KAKIUCHI Daiki : Control Systems Engineering Department, Research & Engineering
Division, Aero-Engine & Space Operations
OZAWA Kanji : Manager, Engine Technology Department, Research & Engineering
Division, Aero-Engine & Space Operations
SEKI Naoki : Engine Technology Department, Research & Engineering Division,
Aero-Engine & Space Operations
OYORI Hitoshi : Manager, Electrical Technologies Office, Technologies Development
Department, IHI AEROSPACE Co., Ltd.
The More Electric Engine (MEE) is a next generation turbofan engine that will lead engine control for MEA
(More Electric Aircraft) in the 21st century. Recently, IHI has started investigations and studies in order to meet
the challenge of creating “an ECO-friendly engine for the future.” This paper overviews the IHI MEE and reveals
details of IHI’s “Green Innovations.”
1. Introduction
In the aviation industry, improving the eff iciency of
aircraft and their engines has become an important issue
from the standpoint of the environment, specif ically
the prevention of global warming. MEE (More Electric
Engine) is a technology that will bring about reductions
in engine weight and improvements in engine efficiency
in conjunction with the elimination of engine bleed from
engines and the electrification of flight control systems,
which are introduced by MEA (More Electric Aircraft).
IHI MEE is aimed at developing control systems to
improve fuel system efficiency and reducing the size and
weight of components with high voltage electrification
technology. Electrif ication of engine control systems
improves fuel consumption and reduces CO 2 emissions
from aircraft, making it possible to achieve flight operating
cost reduction, which is a customer requirement.
2. Overview of MEE development
2.1 Background of development
This study is aimed at the practical application of MEE
control technology, which focuses on fuel systems, power
systems, and other engine control systems, to improve
fuel consumption and reduce CO 2 emissions. Aircraft
manufacturers have already introduced high voltage electric
power systems for practical application of MEA and
employed a starter generator, which combines an electric
engine starter and generator, electric actuator, and electric
ECS (Environment Control System) in their Boeing 787
(The Boeing Company, U.S.) or Airbus A380 (Airbus
S.A.S., France).
Key concepts of MEA are the integration of electric
power management and the elimination of engine bleed. It
provides ① improved fuel consumption, ② improved ontime departure rate, ③ improved passenger satisfaction
with cleaner cabin air, and ④ easier maintenance and
inspection.(1) MEE is a technology that improves engine
efficiency and reduces engine weight in conjunction with
MEA.
2.2 Benefits of MEE
(1) Improvement of engine efficiency
To reduce the circulation of excess fuel, the
rotational speed of the fuel pump driven by an electric
motor is directly controlled to adjust the fuel flow.
This provides improved engine efficiency with less
engine power being consumed by the fuel pump.
(2) Elimination of accessory gearboxes, hydraulic
systems, and pneumatic systems
In the present system, components such as pumps
and generators are driven by engine power, which
is mechanically extracted from the engine via an
accessory gearbox. In addition, the engine is started by
a pneumatic engine starter installed in the accessory
gearbox. Electrification of these components enables
the reduction of mechanical power transmission
mechanisms such as accessory gearboxes as well as
the reduction of hydraulic and pneumatic lines.
(3) Reduction of air resistance on aircraft
In addition to the elimination of the accessory
gearbox, a starter generator is installed inside the
engine. It reduces air resistance on aircraft with a
reduced frontal projected area.
V o l . 4 5 N o . 1 2 0 12
21
(4) Optimization of idle engine rotational speed on the
ground
During an engine run-up or while an aircraft is
taxiing on the ground, a large portion of the engine
output power is consumed by the aircraft system.
To absorb this fluctuation in the load demand by the
aircraft system, the engine rotational speed must be set
high. If the load fluctuation can be compensated for
by electric power management, the engine rotational
speed on the ground can be set lower.
(5) Facilitation of accessory maintenance work
Electrification reduces the installation and removal
work of hydraulic pipes, making it possible to replace
accessories in a shorter time. In addition, electrification
reduces the amount of oil drained, enabling
environmentally friendly, clean maintenance work.
2.3 IHI MEE development steps (Fig. 1)(2)
(1) Step 1: Electric fuel system
An electric motor-driven fuel pump is introduced,
and a generator is installed in the accessory gearbox,
which was conventionally used to drive the fuel pump.
The electric power from the generator is used to drive
the electric fuel pump. In addition, the hydraulic
actuators used to drive variable geometries, such as
variable stator vanes, are electrified (Fig. 1-(a)).
(2) Step 2: Starter generator and full electrification
Full electrification eliminates the need for the
accessory gearbox, so the engine output shaft is
connected to the generator without the accessory
gearbox. The generator is used as a starter generator to
① start the engine, ② generate electric power for the
aircraft, and ③ generate electric power for the engine
accessories (Fig. 1-(b)).
(3) Step 3: Embedded starter generator
The starter generator is embedded inside the engine.
The engine components are distributed, providing the
highest engine efficiency with the smallest projected
engine area (Fig. 1-(c)).
(a) Step 1
3. Concepts of IHI MEE
3.1 Fuel system
Figure 2 shows a comparison between the IHI MEE
fuel system and a conventional fuel system. The fuel
system using a fixed displacement fuel pump driven by
an accessory gearbox is used mainly for commercial
aircraft engines. The accessory gearbox-driven fuel pump
discharges fuel in proportion to the engine rotational
speed and when the pump discharge flow excesses the
engine required fuel flow, the system bypasses and
circulates excess fuel to the pump inlet. Such recirculation
unnecessarily consumes engine horsepower, causing the
fuel temperature to increase due to the consumed energy.
As the fuel temperature increases, it causes a decrease
in the cooling performance of the fuel-cooled oil cooler,
which uses fuel as coolant. To compensate for the decrease
in performance, an air-cooled oil cooler, which uses fan
discharge air as its cooling medium, is needed. However,
the air-cooled oil cooler exhausts the fan discharge air into
the atmosphere, resulting in deteriorated fuel consumption
(SFC) with reduced engine fan efficiency.
The IHI MEE fuel system uses an electric motor to drive
a gear pump type fuel pump and controls the fuel flow
based on the motor rotational speed. This can reduce engine
power extraction as shown in Fig. 3.(3) In addition, the fuel
temperature can be prevented from increasing, and the
cooling performance of the fuel-cooled oil cooler increases,
eliminating the extraction of fan discharge air by the aircooled oil cooler. Figure 4 shows a heat management
analysis model. The above enables the provision of a highefficiency engine system.(3) In comparison with other pump
systems for which efforts are being made to improve the
efficiency, as shown in Fig. 5, the IHI MEE fuel system has
higher efficiency than other fuel systems with a variable
displacement pump(4) and a centrifugal pump.(5) In other
words, the IHI MEE fuel system is the most efficient fuel
system with optimized heat management. In addition, the
(b) Step 2
(c) Step 3
Alternator
Starter
generator
ECU
Aircraft generator
Hydraulic pump
Starter
Ignition
Lube and scavenge
pump
ECU
Ignition
Lube and scavenge
pump
Fuel pump
Actuator
Accessory gearbox
Starter
generator
Engine
accessories
Fuel pump
Actuator
Generator
Aircraft electric
power bus
Electric power distributor
Aircraft electric
power bus
(Note)
Electric power distributor
: Mechanical system
: Electric power system
: Components developed
ECU : Engine Control Unit
Fig. 1 Steps in development of IHI MEE
22
V o l . 4 5 N o . 1 2 0 12
(a) Conventional fuel system
(b) IHI MEE fuel system
Circulation of excess fuel
From airframe
High-pressure
pump
Low-pressure pump
Accessory
gearbox
Oil pump
Electric
motor
Fuel control
Air-cooled
oil cooler
Fuel-cooled
oil cooler
Oil pump
Tank
Tank
Scavenge pump
Scavenge pump
Fuel-cooled
oil cooler
Waste of fan discharge
air for cooling
Fig. 2 Schematic of the proposed IHI MEE system
: Conventional accessory gearbox-driven system
: IHI MEE electric motor-driven system
Engine power extraction*1 (%)
120
100
80
60
40
20
0
Ground
Takeoff
Climb
Cruise
Descent
Ground
Flight mission
(Note) *1 : The engine power extraction when an aircraft with
an accessory gearbox taking off is taken to be 100%.
Fig. 3 Reduction in power extracted from engine
IHI MEE fuel system, unlike conventional systems with
a fuel metering mechanism, does not require complicated
mechanisms involving metering valves and pressure control
valves, and therefore has a simple construction, which
contributes to improved reliability and maintainability with
fewer components and hydraulic lines.
We calculated the improvement effect of the improved
fuel system efficiency on the fuel consumption with a
typical small engine,(5) and found that the fuel consumption
decreased by about 0.4% through the reduction of engine
power extraction with an optimized fuel pump drive, and by
about 0.6% through the reduction of fan discharge air loss by
the elimination of the air-cooled oil cooler, which means that
the total fuel consumption reduction is about 1%.(3) Figure 6
shows the SFC improvement effect in IHI MEE step 1.
3.2 Effects on engine performance
3.2.1 Effects of the elimination of the fuel metering
mechanism on engine response
The conventional system, which uses a metering valve
and pressure control valve in the fuel metering mechanism
to measure the fuel flow, responds extremely quickly to
change the fuel flow as compared to the required response
time of the engine rotational speed. However, the IHI MEE
system controls the fuel flow based on the motor rotational
speed, which drives the pump, and therefore, the fuel
flow response time is affected by the motor acceleration/
deceleration time response. Because electric motors have a
greater moment of inertia than the moving parts of valves,
electric motors are considered inferior in terms of quick
response. Figure 7 shows the results of analysis of the time
response of fuel flow rate carried out for this evaluation.
The analysis results show that the control with a motor
responds as quickly to changes in the fuel flow as the
control with a conventional fuel metering mechanism,
and has an adequate response for engine control. In other
words, the IHI MEE system is believed to have the same
engine control response as conventional systems.
3.2.2 Effects of increases in the required electric power
on engine performance
It is estimated that MEA and MEE increase the electric
power required by aircraft, which significantly increases the
engine power extraction for power generation. A generator
with increased capacity has been employed to deal with
increases in the required electric power, and as shown in
Fig. 8, the larger generator can work as an engine starter,
instead of a conventional pneumatic starter.
However, increased engine power extraction could
make engine control unstable. Figure 9 shows the effect
of increased engine power extraction. As suggested by
the analysis result in Fig. 9-(a), if the engine power is
extracted from the high-pressure shaft as in conventional
engines, as the power extraction increases, the low-pressure
compressor operating line moves up and closer to the surge
line (boundary line of the area where the balance between
the flow of air flowing into the compressor and the pressure
ratio becomes unstable and the compressor malfunctions),
causing the surge margin to decrease. As a solution to this,
the authors are studying a method by which the power is
V o l . 4 5 N o . 1 2 0 12
23
(a) Comparison of fuel temperature rise
Accessory
gearbox-driven
system
(c) Heat management model
T f Ei
∆T f _ MEE − ∆T f _ con
HPf p
Fuel pump
∆Tf
IHI MEE electric
motor-driven
system
0.0
0.5
Fuel temperature rise ratio
QACOC
1.0
Air-cooled
oil cooler
(Note) When the fuel temperature rise of the accessory
gearbox-driven system is 1.0
T f Fi
ToFi
QFCOC
Fuel-cooled
oil cooler
h
ToFo
T f Fo
ToAi
MCpo
Engine
(b) Calculation formula
- Fuel temperature ∆T f =
rise
(Note)
HPf p_
Cpf ⋅
Pressure = p
Qeng
- Increase of heat h ⋅ MCpo ⋅ ( ∆Tf _ MEE − ∆T f _ con )
exchange
= QFCOC_MEE − QFCOC_con
Flow =
Wf
r
MEE
Wf
r
∆T f
Tf
T f Fi
T f Fo
T f Ei
∆T f _MEE
: Fuel temperature rise (K)
: Fuel temperature (K)
: Fuel-cooled oil cooler inlet fuel temperature (K)
: Fuel-cooled oil cooler outlet fuel temperature (K)
: Engine inlet fuel temperature (K)
: Fuel temperature rise in the IHI MEE electric
motor-driven system (K)
∆T f _con : Fuel temperature rise in the accessory
gearbox-driven system (K)
To
: Oil temperature (K)
ToAi
: Air-cooled oil cooler inlet oil temperature (K)
ToFi
: Fuel-cooled oil cooler inlet oil temperature (K)
ToFo
: Fuel-cooled oil cooler outlet oil temperature (K)
HPf p
: Pump horsepower (W)
HPf p_MEE : Electric motor-driven pump horsepower (W)
: Mass specific heat (J/kg·K)
Cp
: Fuel mass specific heat (J/kg·K)
Cp f
: Mass specific heat capacity (J/K·s)
MCpo
: Engine heat generation (W)
Qeng
: Air-cooled oil cooler heat exchange (W)
QACOC
: Fuel-cooled oil cooler heat exchange (W)
QFCOC
QFCOC_MEE : Fuel-cooled oil cooler heat exchange in the
IHI MEE electric motor-driven system (W)
QFCOC_con : Fuel-cooled oil cooler heat exchange in the
accessory gearbox-driven system (W)
: Fuel pressure (Pa)
p
: Engine fuel flow (kg/s)
Wf
: Heat exchange efficiency (–)
h
: Specific gravity (kg/m3)
r
Fig. 4 Heat-management analysis model
(a) Analytical conditions*1
(b) Comparison of fuel pump efficiency*2
: When the aircraft is cruising
: When the aircraft is taking off
IHI MEE
system
: When the aircraft is cruising
: When the aircraft is taking off
Variable
displacement
pump system
20%
Fuel flow
Centrifugal
pump system
3-gear pump
system
90%
Rotational
speed of engine
high-pressure
shaft
Conventional
system
0
25
50
75
100
0.0
0.5
1.0
1.5
Fuel pump efficiency (–)
Ratio of fuel flow and rotational speed
of engine high-pressure shaft (%)
(Notes)
*1 : When the takeoff value is 100%
*2 : When the fuel pump efficiency of the IHI MEE system is 1.0
Fig. 5 Calculated efficiency of various fuel systems
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V o l . 4 5 N o . 1 2 0 12
Type
Current
system
Fuel pump
(Power extraction)
Total thrust
Fgcon = f ( Fg j − Fex, Was
− ∆Wacoc, Wap )
Air-cooled oil cooler
(Air flow, fan discharge air flow)
Engine power extraction
: Fex
With air-cooled oil cooler
∆Wacoc
1%
Was
Reduced power extraction
: ∆ Ff p
Without air-cooled oil cooler
∆Wacoc = 0
IHI MEE
system
FgMEE = f ( Fg j − Fex +
∆ Ff p, Was, Wap )
IHI MEE SFC
Improvement*1 (%)
2
0
−2
−4
−6
Ground Takeoff
Climb
Cruise Descent Ground
Flight mission
*1 : ∆ SFC =
Fgcon − Dr
FgMEE − Dr
−1
(Note) Fgcon : Current system total thrust
FgMEE : IHI MEE total thrust
Dr
: Drag
∆ Ff p : Power extraction reduction
Fg j
: Core total thrust
: Core air flow
Wap
: Bypass air flow
Was
∆Wacoc : ACOC (air-cooled oil cooler) fan discharge air flow
Fig. 6 SFC reduction accomplished by using IHI MEE step 1
(a) High-pressure shaft
Power extraction
: Command value
: Actual fuel flow
0.2
0.4
0.6
0.8
1.0
Time (s)
Fig. 7 Engine transient simulation of the IHI MEE metering system
: Starter characteristic
: Power generation characteristic of conventional generator
: Power generation characteristic when the generator output is doubled
: Electrical performance of conventional generator
: Electrical performance of generator when the generator output is
doubled
Surging area
The operating
line moves
up
Surge margin
Large
Small
Air flow
Low-pressure compressor
Pressure ratio
Large
Small
0
Low-pressure compressor
Pressure ratio
Large
5
Large
: Surge line
: Low-pressure compressor
operating line
(Before the low-pressure shaft
power extraction increases)
: Low-voltage compressor
operating line
(After the low-pressure shaft
power extraction increases)
: Surge line
: Low-pressure compressor
operating line
(Before the high-pressure
shaft power extraction increases)
: Low-pressure compressor
operating line
(After the high-pressure shaft
power extraction increases)
10
0
(b) Low-pressure shaft
Power extraction
Small
Fuel flow (%)
15
Surging area
Surge
margin
The operating
line moves down
Large
Small
Air flow
Small
Starter generator Torque
Fig. 9 Analysis of effect of increase in power extraction from
engine
0
5 000
10 000
15 000
Rotational speed of engine (rpm)
Fig. 8 Torque-speed characteristics of engine starter and aircraft
generator
extracted from the low-pressure shaft.
As a result of analysis with a typical small engine, it was
found that when the engine power extracted from the lowpressure shaft is increased, the operating line moves in a
direction such that the surge margin increases (Fig. 9-(b)),
but the efficiency has a reverse characteristic, which
means that power extraction from the low-pressure shaft
is not necessarily the best solution. Selecting which shaft
to extract engine power from for the generator will be
an important design issue for MEA and MEE to address
increases in the required electric power.
V o l . 4 5 N o . 1 2 0 12
25
4. Advanced technologies and future tasks
for IHI MEE
Our future task for IHI MEE is to improve efficiency,
reduce size and weight, and further improve reliability
and safety of the aircraft engines. To accomplish this task,
we are developing technologies to make higher voltage
available and simplify fuel metering systems and power
generation systems.
4.1 Introduction of high-voltage active-active control
The technology to increase the voltage to 270 VDC, which
has been applied to MEA to improve the efficiency, is an
essential technology for IHI MEE as well. In the 1990s,
the IHI Group developed and put to practical use a highvoltage (270 VDC) electric control system for ELVs
(Expendable Launch Vehicles).(6) For IHI MEE, in order to
apply this technology to aircraft engines, redundant system
design is required for increased safety.
IHI MEE employs active-active control to increase safety
and minimize weight increment.(2) Active-active control,
unlike active-standby control, instantaneously avoids a loss
of control when a failure occurs and allows all redundant
systems to operate in a normal state so as to distribute
loads, reduce current loss, and contribute to improving the
efficiency and reducing the weight of the entire system.
The following describes key technologies being studied for
practical use.
(1) Current control of multi-wound motors(7)
This uses the servo theory and is an electric current
control technology that uses active-active control with
a redundant configuration where two windings are
used such that if one of them fails, the current flowing
in the other is doubled. The sum of the current flowing
in the two windings is fed back to the current servo to
instantaneously compensate for the current decrease
and reduce the fail-over time (Fig. 10).
(2) Current phase control of a faulty motor (7)
IHI MEE employs digital technology for current
phase control of three-phase motors to increase the
motor safety and provide a fail-safe system where,
if one phase fails, control is provided by the other
two phases. Three-phase motors have an oval-shape
current vector when one phase fails, but digital control
is provided so that they have a circular current vector,
which enables smooth motor rotational speed control
(Fig. 11).
(3) Speed summing actuator (8)
Electromechanical actuators have a simple structure
without hydraulic devices, but require handling of
a jamming failure, which is typically seizure of the
reduction gears. Typically, the clutch is disengaged if
a gear gets seized, but the reliability and weight of the
clutch mechanism itself become issues. In addition,
when active-active control is configured, if two output
motor shafts are directly connected to each other, each
servo system has an error and the calculated output
torque of one system contradicts that of the other
system, which causes the two forces to fight with each
other, resulting in vibration.
To solve this problem, IHI MEE employs a technology
that connects the motor output shafts not based on
the force, but based on the speed. A speed summing
(a) When the motors operate normally
Current
command
Ic = 1
(b) When motor 2 fails
Current
command
Ic = 1
Inverter
Ki
Motor 1
Inverter
Ki
Motor 1
Im1 = 0.5
Im1 = 1
I f1 = 1
I f1 = 1
If 2=1
If 2=1
Im2 = 0.5
Inverter
Inverter
Motor 2
Ki
Im2 = 0
Motor 2
Ki
(c) Current waveform before and after the motor fails
Current
(+)
0
(−)
Motor 1
Current command
Motor 2
Motor 1
(Note)
Ki
Motor 2
When the motors
operate normally
Motor 2 fails
Time
: Current controller gain
: Motor 1 and Motor 2 current
(when the motors operate normally)
: Motor 1 current (when Motor 2 fails)
: Motor 2 current (when Motor 2 fails)
: Motor 1 current
: Motor 2 current
Fig. 10 Schematics of redundant motor current control system
26
V o l . 4 5 N o . 1 2 0 12
Operating
condition
Three-phase motor current
(+)
Magnet
Winding
Current
Normal
: u-phase current
: v-phase current
: w-phase current
Positions of stator (winding) and rotor (magnet)
Current vector
a
u-phase
w
N
b
0
S
w-phase
(−)
v-phase
Time
(+)
a
: u-phase current
: v-phase current
: w-phase current
Current
w
Faulty
(−)
Current
(+)
Phase
compensation
Magnet
0
Winding
N
w-phase
S
v-phase
a : Electric angle rotating
coordinate system a axis
b : Electric angle rotating
coordinate system b axis
w : Current vector rotating
angle velocity
a
w
b
Faulty winding
0
(−)
b
u-phase
Time
: u-phase current
: v-phase current
: w-phase current
a : Electric angle rotating
coordinate system a axis
b : Electric angle rotating
coordinate system b axis
w : Current vector rotating
angle velocity
Time
a : Electric angle rotating
coordinate system a axis
b : Electric angle rotating
coordinate system b axis
w : Current vector rotating
angle velocity
Fig. 11 Phase control for faulty motors
mechanism (the sum of the input speeds is equal to
the output speed) is configured with a ball screw
mechanism. One of the motor output shafts is attached
to a screw lead, and the other is attached to a ball nut.
The result is that the total output speed from the actuator
is equal to the sum of the speed of the two output shafts,
which allows for weight reduction (Fig. 12).
4.2 Development of a new fuel metering system(3)
IHI MEE uses an electric motor to drive a fuel pump and
controls fuel flow by changing the motor rotational speed.
Conventional systems use a hydraulic mechanism with a
metering valve and pressure regulating valve to control the
fuel flow, providing high response and accuracy. In the IHI
MEE system, the fuel flow response and metering accuracy
depend on the motor response characteristics and fuel
flow feedback accuracy, respectively (Fig. 13). To improve
motor response, a direct-drive motor is used to drive the
fuel pump, and in addition, the motor-driven pump is
designed to have improved reliability.
In order to accurately measure the fuel flow with an
electric motor-driven fixed displacement fuel pump, there is
a need to compensate for changes in the pump volumetric
efficiency due to changes in the fuel temperature or long
operation times. The most reliable method is feed-back
control of the fuel flow to the motor rotational speed
control. One way to measure the fuel flow is using a highaccuracy flow sensor to directly measure fuel flow, but in
this case, there is a need to prevent pressure loss caused
by installing a flow sensor in the fuel passage, which
means that the sensor must be a non-contact sensor. At the
present time, however, there are many issues in terms of
measurement accuracy and installability regarding the noncontact sensors.
In order to simplify the fuel system configuration to
the maximum extent possible, IHI MEE places a valve
mechanism downstream of the pump and measures the
pressure difference between the upstream and downstream
of the valve mechanism to reflect the measured data in
the fuel flow control. In this measuring system, the valve
mechanism is designed so that the differential pressure
can be measured accurately in all ranges from the low flow
range to the high flow range. In the low flow range, the
valve mechanism produces sufficient differential pressure
so as to ensure high measurement accuracy by a differential
pressure sensor. In the high flow range, the valve mechanism
maintains the pump outlet pressure so that it does not get
too high, meaning that both measurement accuracy and
high efficiency of the pump system can be achieved. This is
a new fuel control system that eliminates complicated fuel
metering units, which is to say, it is a simple, reliable fuel
system, which is one of the key concepts of IHI MEE.
4.3 Application of permanent magnet generator
technology (7)
For IHI MEE, in order to develop a small, lightweight
generator that can deal with increases in the required
electric power output, the authors are studying permanent
V o l . 4 5 N o . 1 2 0 12
27
(a) Principle of speed summing active-active control mechanism
(b) Operation test result of speed summing active-active control
Normal : Stable and smooth control
Electric motor 2
①
Extension
① By speed summing active-active control,
two motors control one actuator at the same
time.
Neutral
Electric motor 1
Contraction
Nut speed
w2
Lead speed
w1
When a failure occurs : Operation continues and restoration is made based on the
diagnostic result.
Extension
②
Extension
Actuator
stroke
Ball screw
1s
③
② A jamming failure occurred in one motor.
③ The faulty motor slows down the actuator
Neutral
Contraction
Contraction
but continues to stroke.
1s
④
④ The controller determines that the motor is
faulty and changes the gain of the other
motor to restore the control characteristics
to normal.
When one motor is faulty : Control characteristics have been restored.
Extension
⑤ With one faulty motor, the control
characteristics are restored to normal with
the other motor, so it remains in control.
Neutral
Contraction
1s
Fig. 12 Speed summing actuator
(a) Conventional system
Aircraft tank
Servo valve command
Servo valve
feedback
: Low pressure
Fuel metering mechanism
: High pressure
Pressure
: Regulated pressure
regulating valve
: Metering valve outlet pressure
: Pressurizing valve inlet pressure
: Fuel nozzle inlet pressure
: Electric signal
Differential
pressure
control valve
Fuel flow
servo valve
High
Low
-pressure
Metering
-pressure
gear
valve
pump
pump
Metering valve
feedback
Digital engine control
Fuel nozzle
Minimum
pressurizing
valve
Pressurizing
valve
Accessory gearbox-driven pump
(b) IHI MEE system
Command
Motor
controller
Aircraft tank
Low
-pressure
pump
Digital engine control
Feedback
Flow sensor
High
-pressure
gear
pump
: Low pressure
: Pressurizing valve inlet pressure
: Fuel nozzle inlet pressure
: Electric signal
Fuel nozzle
Pressurizing
valve
Electric motor-driven pump
Fig. 13 Schematics of IHI MEE fuel metering system
28
V o l . 4 5 N o . 1 2 0 12
magnet generators, which are expected to be lighter than
conventional generators by 20%.
Conventional aircraft generators consist of ① an exciter
generator, ② a generator that transfers the exciter power
from the stator to the rotor via the generator controller, and
③ a main generator that uses the exciter power, and they
have a function to cut off power if a short circuit failure
occurs on the load side or inside the generator. The output
current of each generator is monitored by the generator
controller, and when an error occurs, the exciter power
is cut off. When a permanent magnet generator is used,
an alternative method for this cutoff function must be
provided, which proved to be an issue.
In order to equip a permanent magnet generator with the
cutoff function, we are studying the neutral point breaker
system, which has a function equivalent to the power
generation stop function. Using the configuration shown in
Fig. 14, it becomes possible to cut off current when a short
circuit failure occurs inside the generator, although it is not
possible with conventional permanent magnet generators.(7)
4.4 Issues for larger systems(9)
It is estimated that application of IHI MEE to a typical
small engine will not cause the weight to increase
significantly, considering elimination of components and
parts.(1) However, it is believed that application to medium
and large engines requires further weight reduction. Based
on the current technology, as shown in Fig. 15, the weight
of the electric fuel pump alone calculated for large engines
is larger than the weight of the current accessory gearboxdriven pump. Methods are necessary to reduce the weight
of the electric fuel pump system by increasing the motor
rotational speed, to reduce the size of the controller, and at
the same time, apply advanced power devices.(9)
5. Conclusion
This paper describes an overview of the development of
IHI MEE, technical features, and efforts for introduction
of advanced technologies. IHI MEE is expected to meet
the environmental and economical requirements, which are
global requirements, and represents the next generation of
aircraft engine systems. IHI MEE will continue to make
great contributions to the world with our technologies,
focusing on the more electric engine control system
architecture.
Acknowledgements
We would like to sincerely thank SINFONIA TECHNOLOGY
CO., LTD. for providing valuable information and all the
people involved in this study on IHI MEE for their great
contributions.
Generator output voltage
An error occurs
Vu
Vv
Failure diagnosis
Vw
iu
Load
ON/OFF
iw
Generator
ON/OFF
iv
Vu
Power circuit breaker
ON/OFF
iu
Time
Thyristor
iv
Thyristor
iw
Thyristor
Power circuit breaker
Power circuit breaker
Vw
Vv
Generator output current
An error occurs
iu
iv
iw
(Note)
Time
Vu, Vv, Vw : Output voltage
iu, iv, iw : Output current
Fig. 14 Schematic of generator shutdown mechanism using permanent magnets
V o l . 4 5 N o . 1 2 0 12
29
200
: Motor controller
: Electric motor
: Fuel pump
Mass (kg)
150
100
50
0
Conventional
accessory
gearbox-driven
gear pump
Electric pump with
a rated speed of
7 000 rpm
Electric pump with
a rated speed of
15 000 rpm
Large engine
Conventional
accessory
gearbox-driven
gear pump
Electric pump with
a rated speed of
7 000 rpm
Medium engine
Electric pump with
a rated speed of
15 000 rpm
Electric pump
Small engine
Fig. 15 Weight of fuel pump for medium and large engines
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