ABSTRACT
The advanced ISAD system for internal combustion engines & hybrid
electric vehicle applications to reduce emissions, fuel consumption and enhance
energy efficiency. The new starter-alternator combination provides a more
efficient and higher output platform, which will provide the vehicle designer
unique ways to reengineer many functions under the hood. Virtually any
accessory, which is presently belted driven, may be converted to an
electrically powered counterpart with the ready availability of more electrical
power from the larger alternator component of the system. Hydraulic power
steering units, belt driven air conditioning compressors, various fluid pumps
and their components could be replaced with more efficient electric
motor-driven system powered by the ISAD. Starting motor advents of the new ISAD
system include a quite start feature because the gears and whine of the
traditional starter will be eliminated. This system will be able to increase
the starting speed and it also supports the acceleration phase. The total
system weight is nearly the same. The ISAD system provides all the functions of
the engines starter motor and alternator in one electric system installed
between the engine and gearbox without significantly increasingly weight and
volume of the vehicle. The system has been demonstrated for passenger’s cars
and it can be used in commercial vehicles as well.
During starting, the induction machine cranks the engine
with high starting torque. In the generation mode, the power is input to the
ISA from automotive engine, which is emulated using permanent magnet DC motor,
while the DC bus voltage is maintained at 42V.
This paper includes the comparison between conventional
starter, ISG, and ISA. Also this paper contains the principle of ISA mild
hybridization and one case study of Valeo and Ricardo for 42V diesel vehicle.
At last we conclude that, the ISAD
system is the first step to HEV (Hybrid electric vehicle) technology.
1. INTRODUCTION
1.1
NEED OF ELECTRIFICATION
In last years, the automotive electrical load has
increased, by replacing of different mechanical equipments with servomotors, by
using electrical equipments that improve the internal combustion engine (ICE)
performances, in parallel with the comfort and safety (e.g. positioning and
regulation systems, navigation and control systems). Today, the average
electrical power load on the automotive alternator is between 750 W and 1 kW.
It is expected to increase to 4 – 6 kW, in the next decade. Since, the present
automotive 12V System didn’t cover this power. It is likely to adopt the 42 V
systems for the new-generation auto vehicles. The changing of this voltage
level will be a good opportunity for substituting the automotive starter and
alternator, by a single equipment, the integrated starter-alternator (ISA). The
conventional Lund ell (claw-pole) alternator is coupled to ICE, by a
transmission belt (typically 3:1 ratio), and the starter, a DC brushed motor,
accelerates the ICE to cranking speed, due to a large mechanical gear
(typically 10:1)
1.2 DEVELOPMENT TARGETS
1. Achieve fuel economy twice as good as or better than
that of gasoline-powered vehicle in the same class.
2. Secure driving performance equivalent to that of gasoline-powered
vehicles in the same class.
3. Achieve a 10%
exhaust emission levels of current Japanese standard
4. Achieve other performance characteristics comparable to
those of conventional models.
1.3 FEATURES
1. “Start-Stop” is a fuel saving function that
automatically cuts off the engine when the vehicle comes to a
stop and restarts it when the driver engages a gear or releases the brake (automatic
transmissions).
2. “Green-Boost” is the alternator motor mode ability to
deliver up to 10 kW more mechanical power to the transmission.
3. Regenerative braking is a feature that makes it
possible to regenerate the energy of braking phases into useful
electric energy.
4. High electrical output: up to 12 kW at 42 Volt.
5. Noiseless and rapid engine starting.
6. Compatible with future 42 Volt electrical networks.
1.4 HYBRID ELECTRIC VEHICLE
A type of vehicle that may address many of the problems
associated with electric vehicles is a hybrid electric vehicle (HEV). HEVs
combine an electric motor and battery pack with an internal combustion engine
to improve efficiency. In some HEVs, the batteries are recharged during
operation, eliminating the need for an external charger. In other cases, the
vehicle must still be plugged in at the end of the day. Either way, range and
performance can be significantly improved over electric vehicles.
The combustion and electric systems of HEVs are combined
in various configurations. In one configuration (series hybrid), the electric
motor supplies power to move the wheels, while the combustion engine is
connected to a generator which powers the motor and recharges the batteries. In
another configuration(parallel hybrid), the combustion engine provides primary
power, while the electric motor adds extra power for acceleration and climbing,
or the electric motor is the primary power source, with extra power provided by
the engine. In some parallel hybrid systems, the engine and electric motor work
in tandem, with either system providing primary or secondary power depending on
driving conditions.
The hybrid drive train allows the combustion engine to
operate at or near peak efficiency most of the time. This can lead to
significantly higher levels of overall vehicle system efficiency. The higher
efficiency of these vehicles allows them to achieve very high fuel economy and
lower emissions. For example, the hybrid Honda Insight is rated at 61 miles per
gallon (mpg) in the city, and 70 mpg on the highway. A gasoline-fueled Honda
Civic Hatchback, by comparison, achieves a rating of 32 mpg city and 37 mpg
highway.24 Fuel economy improvements can help cut demand for foreign petroleum,
and the higher efficiency enables hybrid vehicles to attain, and even surpass,
the range of conventional vehicles, even with a smaller fuel tank. Furthermore,
since these vehicles utilize conventional fuel, the fueling infrastructure problems
associated with electric vehicles can be eliminated.
The only hybrid vehicles currently available in the U.S. market are
the Honda Insight, the Honda Civic Hybrid, and the Toyota Prius. Over the next
few years, however, most major manufacturers plan to introduce hybrid passenger
vehicles. Further, while the currently available hybrids are smaller cars,
manufacturers are also developing larger hybrids such as mini-vans and sport
utility vehicles.25
Until recently, HEVs were treated as conventional vehicles
because they run on gasoline or diesel fuel. However, the Internal Revenue
Service announced on May21, 2002, that it will allow taxpayers to claim a
clean-burning fuel vehicle tax deduction of $2,000.26
2. ELECTRIC MOTOR TECHNOLOGIES
In
this section, the three most common electric motor technologies and the power
electronic devices with control circuits in vehicle applications are discussed.
The three motors are the permanent magnet (brushed and brushless type) motors,
induction motors, and switched reluctance motors. Among those three motor
configurations, the permanent magnet motor type is more widely applied in the
vehicles because of its merits. An electric motor is a well-known device that
converts electrical energy to mechanical energy using magnetic field linkage.
An electric motor consists of two major elements: (1) a fixed stator with
current-carrying windings or permanent magnets, (2) a rotating rotor which
provides a magnetic field produced by additional current carrying windings or
attached permanent magnets between the rotor and stator magnetic fields. Modern
electric motor advances have resulted from developments and refinements in
magnetic materials, integrated circuits, power electronic switching devices, computer
modeling and simulation, and manufacturing technology, rather than by
fundamental changes in operating and control principles. The dramatic
improvements in permanent magnet materials and power electronic devices over
the last two decades have led to the development of brushless permanent magnet
motors that offer significant improvements in power density, efficiency, and
noise/vibration reduction. Also, because there is no electrical Sparks, there is less
radiated noise.
2.1
PERMANENT MAGNET MOTORS
The
permanent magnet machine is highly coveted for its high power density and high
efficiency. This is mainly due to the
high energy density NdFeB and SmCo magnets, which are commercially available
today. In other words, advancements in high-energy permanent magnet materials
and magnet manufacturing technologies enabled the manufacturing of high power
density and high efficiency permanent magnet motors at a reasonable cost. Also,
the availability of fast switching high power semiconductor devices with low on-state
voltage drop such as MOSFETs and IGBTs. Ever increasing high-speed
microprocessors/digital signal processors have contributed to permanent magnet
electric motors. While the cost for semiconductors and the permanent magnets is
still high at the present time, trends for cost reduction are continuing and
encouraging.
2.1.1
BRUSH TYPE PERMANENT MAGNETIC MOTOR
There
are two types of permanent magnet motors: brush and brushless. Today’s vehicle
applications almost exclusively use brush type permanent magnet motors.
The
brush permanent magnet motors have four general characteristics that cause them
to be useful for vehicle application:
1)
Desirable torque versus speed,
2)
Simple control of torque and speed,
3)
High electromagnetic power density, and
4)
Inverters are not required.
Nevertheless,
there are six general characteristics that detract from more wide applications in
the automotive industry:
1)
friction between the brushes and the commutator,
2)
brushes and commutators require maintenance,
3)
current is supplied to the armature through the brushes
and commutator,
4)
brushes and commutators are open and produce sparking,
5)
cooling of a DC motor is difficult, and
6)
Switching of large currents is required for control of
DC motors.
The brushless motors are becoming stronger
candidates over traditional brush type motors for the following reasons: higher
efficiency, higher power density, better heat dissipation, and increased motor
life. In addition, brushless motors experience no losses due to brush friction
and they deliver higher torque compared to a brushed type motor of equal size
and weight.
2.1.2
BRUSHLESS TYPE PERMANENT MAGNET MOTOR
Electronically
commutated, brushless permanent magnet motors are however, becoming prime
movers in vehicle propulsion, industrial drives, and actuators as a result of
improvements in permanent magnet materials, advances in the power electronic
devices, and power integrated circuits in the last two decades. Not only have
there been gradual improvements in Alnico and Ferrite (ceramic) alloys, but the
rapid development of rare-earth magnets, such as samarium-cobalt (Sm -Co) and
neodymium-boron-iron (Nd B Fe) around 1980, have provided designers with a
significant increase in available field strength. This new high density,
brushless, permanent magnet motor system provides a very high torque to inertia
ratio.
2.1.3
PERMANENT MAGNET MATERIAL
Figure
4 summarizes the four most common permanent magnet materials used today by
motor manufacturers. In most cases, the higher remanence with higher coercivity
in a permanent magnet is desired by motor designers. The alnico magnet provides
a fairly high remanence flux density but a low coercive force. When the
coercive force is low and two opposing magnetic poles are in proximity of each
other, the magnetic poles can weaken each other and there is a possibility of
permanent demagnetization by the opposing field.
Unlike
an alnico magnet, the ferrite magnet has a low flux density, but a high
coercive force. It is possible to magnetize the ferrite magnet across its width
as a result of this high coercive force. Ferrite magnets are most widely used
in electric motors because their material and production costs are low. The
cost of a typical ferrite magnet material at this time is about 6-8 times lower
than the Nd B Fe. Nonetheless, output power to weight ratio is 1.22, ferrite,
vs. 1.36, Nd B Fe. This means that the ferrite magnet motor will be about 20%
heavier for the same output compared with the Nd B Fe magnet motor. Another
measurement is an output power per unit cost of active material. It is
predicted that the output power per unit cost is about 4 times lower for
ferrite magnet motor compared to the Nd B Fe magnet motor. Delco Remy uses the
ferrite and Nd B Fe magnets for different starter motor applications. Rare-earth
magnets have both high magnetic remanence, and high coercive force. Since the
initial cost is high, these permanent magnets are used in applications such as
high performance and high-energy density motor applications. For a given
volume, the flux density is twice that of the ferrite, leading to a larger
torque production. Nd B Fe magnetic materials are superior to any other
magnetic material now on the market. The only disadvantage of using an Nd B Fe
magnet, as opposed to an Sm Co magnet, is that the high-energy density Nd B Fe
permanent magnet has a maximum operating temperature of 100 to 150 degrees C,
as compared to 200-300 degrees C for Sm Co, alnico, and ferrite.
2.2 INDUCTION
MOTORS
Alternating
current (AC) induction motors are the most common of all types of electric
motors manufactured for the general use in household applications, industrial
drives, and electric propulsion. These motors are rugged, relatively
inexpensive, and require very little maintenance. They range in size from a few
watts to about 15,000 hp. The induction motors have certain inherent
disadvantages including speed which, is not easily controlled, plus it runs at
low lagging power factors when lightly loaded, and the starting current is
usually five to seven times full-loaded current.
Induction
motors have relatively low manufacturing cost and are mechanically rugged
because they can be built without slip rings or brush and commutators.
Consequently much attention has been given to induction motors for automotive
applications in the areas of vehicle propulsion, engine starting, braking,
electricity generating, speed reversal, speed change, etc. In spite of many
interests in vehicle applications, the costs of the power electronic components
are still relatively high, especially in the low power region. Furthermore, in
many automotive applications it is either not possible or not desirable to use
a mechanical sensor for speed or angle, etc. This means, a simple and
affordable control system, using only the voltage and the current of the
induction motor as measured quantities, is necessary. A sensor less controller
technology has been demonstrated using a switched reluctance motor by many
academia and industrial teams.
3. CONVENTIONAL
STARTER, ISG & ISA.
3.1 STARTER AND GENERATOR: -
Fig3.1: - Delco
self starter generator unit
The automotive starter (sometimes called a cranking motor)
dates back to the early part of the automotive industry. In 1912 the Cadillac
Motor Car Company introduced the electric self- starter to replace the hand
crank. Frank and Perry Remy of the Remy Electric Company were also early
innovators in the automotive industry. Remy Electric also developed and
introduced starting motors in the same time period. This innovation in essence
broadened the accessibility of the automobile from those strong enough to hand
crank to virtually everyone. There have been many developments and refinements
in the starting motor since its introduction in 1912 (see Figure 7). The
primary innovations focused on the engagement method, changing from six to 12
volts, and gear reduction. From the 1980s to today the industry has focused on
size and weight reduction as well as reliability and durability improvement.
3.2 INTEGRATED
STARTER GENERATOR
An
integrated starter-generator can be used in conventional vehicles to reduce
fuel consumption and improve acceleration. As with a hybrid vehicle, using the
high-torque device allows the engine to shut off when the vehicle is stopped. When
power is applied, the engine can restart in less than one second.45 It is
believed that the integrated starter-generator could improve fuel economy of
conventional vehicles by as much as 20%. However, because the integrated
starter-generator requires considerable amount of electrical power, it is being
developed concurrently with 42-volt electrical systems.
3.3
ISA SYSTEM DISCRIPTION
A
block diagram of the overall system is illustrated in the figure. As indicated
in the figure, the system is based on an induction machine mechanically coupled
to an engine, and it is fed by a 36V battery through a three phase IGBT
inverter. The controller has been implemented using dSACE 1104 control card.
The control algorithm derives PWM signals for the three phase inverter by
taking speed, IM line currents and DC voltage as inputs.
1.1kW/22V
Induction machine has been used for the prototype hardware. The induction
machine line to line voltage of 22V is chosen because of the 42V DC bus voltage
and to ensure that the inverter operates in boost mode, so that motor current is
in continuous conduction at all times.
3.4 SPECIFICATIONS
In practice, the available 30-36V
battery voltage at motoring and required 30-36V charging voltage at generating
is the main problem during electric machine design. Besides the dilemma from voltage specifications, the requirement
of a wide speed range and the high temperature of cooling media in the ISA
system. The ambient temperature range from -40°C to 125°C, which is a typical
for an air cooled ISA machine. If the machine cooled by liquid, the available
engine coolant temperature will be up to 135-140°C, unless a separate liquid
cooling loop is introduced. The speed of electric cool machine runs from 0-6000
r/min for the crankshaft mounted ISA system, which is the same as engine speed.
The maximum operating speed electric machine run as high as 13,800-19,200 r/min
for the belt driven ISA system with the belt transfer ratio of 2.3-3.2.
In the 42V DC electric system, the motoring performance
specifications should met over at lower voltage level of 30-33V dc, although
the maximum available battery voltage is 36V at the dc input of the electric
machine drive. If the 14V electric system is used for the ISA system onboard
vehicle, the motoring operations of the machine have to be fully functional at 10-11V
dc voltage in spite of the battery voltage of 12V. the low available voltage is
caused by a low battery charge state and internal resistance as well as ambient
temperature. If a three phase induction machine is used for ISA machine and the
space vector control is introduced for its control, it needs to meet all
motoring specifications at the minimum available line to line voltage of 21-23V
ac and 7-8V ac in rms value for the 42V dc and the 14V dc systems,
respectively.
2. Automotive direct-drive integrated
starter-alternator requirements and selection
The proposed solution is represented by a direct-drive,
where the electrical machine of ISA is coaxial with the shaft of the ICE and
the transmission (clutch and gear box).
(Figure 2)
The integration of the starter and alternator in just one
electrical machine will make more efficient the use of electrical equipment,
and eliminate the space and weight problems, improving in the same time the
performances and reducing the generator and starting noises. Another advantage
is that ISA eliminates mechanical elements, such as transmission belt, pulleys
and flywheel.
ISA allows at start the operation in motor regime, as a
starter, and after that, will work in generator regime, providing electrical
energy as an alternator. In motor regime, the ISA system should reach 500 rpm
in maximum 3-5 s, overcoming a load torque of 80 – 150 Nm. In generator regime,
the ISA system transforms the mechanical energy in a.c. electrical energy,
which after rectification recharges the
automotive battery. Table 1
Table:-Automotive starter/alternator
performance requirement
Summarizes the automotive starter and alternator
performance requirements, for both, conventional and integrated system. The
interior permanent-magnet synchronous machine (IPMSM) has been selected to
fulfill the above-stated performance requirements for an automotive ISA (Figure
3).
The associated electronic power
converter is considered of bi-directional AC-DC three-phase bridge type in IGBT
technology (Fig. 4).
The control of ISA
system means the current control by hysteresis regulators, in function of the
motor speed error. The main challenge in the selection of an ISA direct-drive
is the fulfillment of performance at the lowest possible system cost.
The main data and parameters of the IPMSM designed for
automotive direct-drive ISA are the
following:
- Rated voltage: U = 42 V;
- Output power: P = 6 KW;
- Stator phase resistance: Rs = 0,0103;
- d – axis inductance: Ld = 0,06497 * 10-3 H;
- q – axis inductance: Lq = 0,30505 * 10-3 H;
=0,063 Wb;
- Permanent magnet excitation flux: PM
- Number of poles pairs: p = 12;
4. PRINCIPLE OF ISA MILD
HYBRIDIZATION
Vehicle speed is controlled by the driver through either
the accelerator pedal or the brake pedal. Depending on the driving mode, either
a positive or a negative torque is requested from the engine; however, in case
of braking, if the negative torque provided by the engine is insufficient,
friction torque in the wheels provides an additional braking torque which
results in energy loss. The engine speed is determined by the transmission and
the gear ratio between the engine crankshaft and the wheel. Consequently, the
engine torque is the only available variable that can be adjusted in order to
operate the engine in efficient BSFC regimes. For a parallel hybrid
configuration, power can be provided for propulsion by both the thermal and
electrical paths. The ISA is mechanically coupled to the engine, as depicted in
Figure.
Figure 4.1: Schematic diagram of the HMMWV
power train incorporating the ISA
(T-Turbine, C-Compressor, D-F- Front
Differential, D-Rear Differential, EM- Exhaust Manifold, IM- Intake Manifold,
ISA-Integrated Starter Alternator, T/C- Torque Coupler, Trans-Transmission)
Hence, the ISA speed is determined by the engine speed by
means of a constant ratio. As a consequence, the additional power available by
the ISA can only be regulated by adjusting the ISA torque. The latter can be
either positive or negative contingent upon the mode in which the ISA is
operating, as designated by the power management algorithm. In the motor mode,
the ISA contributes power to the driveline by drawing electrical energy from
the battery. In the generator mode, the ISA absorbs power from the driveline
and charges the battery.
In cruising, the power requested from the power train by
the driver is expressed by positive amount of torque, TDRIVER, given a
fixed engine speed:
Tdriver = TISA + TEngine
The
power management algorithm comes to a decision regarding the ISA torque, TISA, based on the current SOC, in order to
utilize the most proper engine operating point as far as fuel consumption is concerned.
Conversely, when braking is demanded by the driver, the power is expressed by a
negative torque TDRIVER:
T Driver= T Engine+ T ISA+ T Brake
A
fraction of this torque is absorbed by the engine, ENGINE, whereas the
ISA absorbs the maximum absolute amount within the constraints imposed by the battery
and the ISA. If a residual amount remains, this must be handled by the friction
brakes, TBRAKE. Consequently, the ISA can recover the energy that
otherwise would be lost by means of friction brakes so as to charge the battery.
5. CASE
STUDY
Valeo and Ricardo team for 42-V diesel vehicle
Valeo's high-efficiency integrated starter-alternator system,
which will be mounted on the crankshaft between the engine and the
transmission, performs a number of key functions. The integrated unit uses
electronic control to crank the engine, providing stop-and-go capability. When
a driver stops at a traffic light, for example, the engine is automatically
cut, both saving fuel and reducing emissions. As soon as the driver engages a
gear again, the engine automatically and quietly restarts. NVH improvements are
inherent when at standstill because of the absence of engine noise. The quiet
starting is realized through the use of the integrated starter-alternator in
motor mode. Since this unit is fully integrated into the powertrain and
replaces the traditional starter motor, engaging the starter's gear on the ring
gear is no longer. The starting time is 0.3 s as opposed to 1 s with a
conventional starter motor, leading to further reduction in emissions.
.
The special design of the Valeo
integrated starter-alternator means it can provide additional torque into the
powertrain over the full range of engine speeds. During acceleration, the
starter-alternator is used as an electric motor to give an extra boost to the
engine; despite the smaller engine size, the i-MoGen powertrain can supply
similar torque to the much larger and heavier 2.0-L diesel engine.
In a conventional vehicle, the
kinetic energy of a vehicle is lost as heat when the driver applies the brakes.
With the high-output starter-alternator, a part of this energy can be saved,
using the alternator to generate electric energy. As soon as the driver presses
the brake pedal, an electronic communication is sent to the integrated
starter-alternator that immediately converts kinetic energy from the vehicle to
electrical energy that can be stored in the battery. It is then possible to
re-use this energy, which is the basic principle behind regenerative braking.
The maximum electrical output power
from the Valeo integrated starter-alternator unit—when running in alternator
mode—is 6 kW, which is three times higher than conventional alternators. This
high output is necessary to allow the operation of high- power electrical
components such as the electrical HVAC compressor or the electrically heated
diesel particulate filter, a Ricardo solution that efficiently destroys harmful
diesel particulate.
As part of the
integrated starter-alternator system, Valeo will integrate a dc/dc converter to
supply 14 V to the low-power electrical components that are not converted to 42
V. Such a high capacity dc/dc converter is expected to be a requirement in
future 42-V vehicles where specific components will require lower voltage.
A key requirement
for 42-V systems is the reliability of available power. Valeo is collaborating
with a battery expert to develop and integrate fault-tolerant batteries with a
battery state-of-charge function to guarantee the reliability of all its 42-V
systems.
6. ADVANTAGES, DISADVANTAGES &
APPLICATIONS
6.1 ADVANTAGES
- Reduce
fuel consumption.
- Reduce
emission.
- Enhance
energy efficiency.
- Weight
is less
- High
power generation.
- Quick
start & stop.
- Well
engine performance.
- Big
cities getting more advantage.
6.2 DISVANTAGES
1.
Requirement of mass production.
2.
Audible normally associated with engine cranking.
3.
Battery required is of
high voltage.
6.3 APPLICATIONS
1. Vehicle magnetic air conditioner
2.
Camless electromagnetic valve System.
3.
Turbocharger generator
4.
Permanent magnet traction wheel
motor
5.
Electric variable transmission
7. CONCLUSION
The
automotive industry trends and prediction of the future electrical system was
presented. Today’s 2 kw platforms need to be replace with 20 kw or even 50 kw
platforms on which host of electrically generated functions will be enabled
-some of which we have not even conceived .The three major motor configuration
and enabling technologies that support more electrical system to vehicle
application were presented. Some devices on the vehicle that are now driven
mechanically could be driven electrically, since the needed power will be
availed by ISA system. Component such as air conditioner compressor, the water
pump and the power steering system can then be operated only on demand, instead
of remaining a continuous parasitic load on the engine when they are in the
“off” part of their operating cycle. This will further reduce fuel consumption
and emission. The ISA system is the first step to HEV technology.
8. REFERENCES
- www.indiacar.com
- www.automotiveengineering.com
- www.automobile.com
- www.google.com
- IEEE
industry applications magazine.
- Automotive Research Center,
The University of Michigan() SAE technical paper series-by Andreas Malikopoulos, Zoran Filipi and
Dennis Assanis)
