Download Reducing CO Output through Demand

D e ve l op m ent
Energy Management
Reducing CO2 Output
through Demand-based
Performance Control
Reducing the quantity of CO2 emitted by automobiles is becoming an increas­
ingly important concern – one that will cause automobile development and
manufacturing costs to rise. High CO2 emissions will also create additional
costs for car buyers, as policymakers begin taxing CO2 and auto makers pass
on to consumers the costs of CO2 trading certificates and CO2 penalties. In
this article, Infineon shows how a realistic and commercially viable reduction
in CO2 output of around 20g per kilometer can be achieved by incorporating
demand-based control into a small number of automotive applications.
1 Introduction
Authors
Dr.-Ing. Alfons Graf,
is the Director of
Automotive Power
Innovations at Infineon
Technologies AG in
Neubiberg, Germany.
Benno Köppl
is Principle Engineer
in the Competence
Center Drives, Automotive Power at Infineon
Technologies AG in
Neubiberg, Germany.
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ATZelektronik 01I2008 Volume 3
Since it became known that European
automakers would fail to meet their
self-imposed CO 2 reduction target of
140 g/km in 2008 by around 20 g/km,
pressure on them from consumers and
policymakers to lower fuel consumption has been mounting. The EU Commission left no doubt that it would not
back down on the introduction of upper limits for automobile CO 2 emissions and that plans to limit the fleet
average to 140 g/km in 2008 and to 130
g/km (including biodiesel) by 2012
would remain in place. It is likely that
automakers failing to meet these targets will be penalized. Fleets with a
high CO2 output will create disadvantages with a quantifiable financial impact for car makers, and how much effort will need to go into successfully
reducing CO2 output can be seen from
cost-benefit analyses. This article puts
forward a number of ideas that highlight the potential for CO2 reduction
and focuses specifically on those electric loads and items of auxiliary equipment in today’s motor vehicles that are
not controlled on a demand-driven basis. The same subject matter is addressed more extensively and in great­
er detail in [1].
2 CO2 Cost-Benefit Assessment
Equipping automobiles with the capability to control equipment on a demanddriven basis in order to reduce CO2 emissions generally entails higher costs. In
the past, the only real benefit to be
gained from doing this was a reduction
in fuel consumption, but the situation
today is somewhat different. Customers
stand to gain from fuel savings and from
lower CO2 taxation (pending), while car
makers will benefit by ensuring compliance with fleet consumption requirements, thus avoiding penalty fines (pending), and from not having to offer their
less attractive models at as heavily discounted prices. Taking these factors into
account, how much would a reduction
in CO2 output of 1g/km benefit car buyers and car makers? The much discussed
connection between fuel consumption
and electric power consumption or addi-
tional payload provides the basis for an
answer.
Figure 1 shows that a 100 W electric
load or carrying an additional payload of
50 kg causes a car’s fuel consumption to
increase by 0.1 liters over a distance of
100 km. Thus, emissions of 1g of CO2 per
kilometer equate to a continuous electric
load of roughly 40 W or a payload of
around 20 kg.
Figure 2 shows the benefit that can be
achieved by reducing CO2. It assumes that
that, in future, an automobile with higher CO2 emissions will be more difficult to
sell than a competing automobile with
better CO2 performance. In order to sell a
vehicle with additional emissions of 50 g
of CO2 per kilometer and a price tag of
Euro 20,000, an auto maker might have to
offer a discount of 5 percent or Euro 1,000.
This is equivalent to Euro 20 per vehicle
and gram of CO2 per kilometer of additional emissions. Expressed another way,
the auto maker (the OEM) could invest
Euro 20 in reducing CO2 output by 1 g/km
without diminishing his profit. The picture is similar when it comes to penalties and fines paid by the manufacturer
for non-compliance with fleet consumption requirements. These penalties can be
estimated approximately.
In January 2007, for example, Ferdinand Dudenhöffer put forward a proposal [2] according to which the use of smaller cars like the Smart should be encouraged with a payment of Euro 720 and
larger cars like the Porsche Cayenne Turbo S should be penalized with a charge
of Euro 7,100. Given CO2 emissions of 116
g/km for the Smart and 378 g/km for the
Porsche Cayenne, OEMs could save Euro
29.80 per gram of CO2 per kilometer that
they eliminate.
The advantage for OEMs in financial
terms – through better vehicle sales and
lower penalties – adds up to a total of
Euro 49.80 per vehicle and gram of CO2
per kilometer. This is a remarkably high
figure and shows that it can be worth going to considerable lengths to reduce
cars’ CO2 emissions, even from a commercial perspective.
A similar calculation can be carried
out for car buyers. Assuming a gasoline
price of Euro 1.40/l and an annual distance traveled of 15,000 km, the potential saving works out at Euro 8.90 per
year and gram of CO2 per kilometer, not
taking into account future additional
taxation based on CO2 emissions. Details
of tax plans were not available as of this
writing, but the German government
has indicated that automobile taxation
could remain at the same level overall as
today but would be CO2-based rather
than engine capacity-based as at present.
The mean engine capacity-based tax
(gasoline and diesel) for a 2-liter vehicle
in the category D4 is currently Euro 233
per year. Assuming that a vehicle in this
category emits 175 g CO2/km, the potential saving is Euro 1.33 per year and gram
of CO2/km that can be eliminated.
Figure 3 summarizes the total potential
saving for a car buyer – Euro 10.23 per
year and gram of CO2/km eliminated. Applied to the number of kilometers traveled
(15,000 km a year), a CO2 saving of 1 g /km
amounts to a saving of 6.8 Euro cents for
every 100 km for the car buyer. The potential saving or cost advantage, both for the
manufacturer and for the buyer, justify
putting a certain amount of additional effort into manufacturing a vehicle with
improved CO2 performance. This is something that automobile manufacturers
have evidently understood [3].
3 Reducing CO2 through Demandbased Performance Control
3.1 Demand-based Control in General
Body Applications
Based on the energy savings and benefits
for manufacturers and buyers addressed
in the previous section, we can examine
a number of different applications and
assess whether the additional expense
involved in creating CO2 savings is worthwhile commercially and how soon the
investment would pay for itself over time
and in terms of mileage. The calculations
are based on manufacturing costs. The
extent to which other expenses might be
charged to the end user is up to the OEM.
In addition, the calculations are conservative, only taking into account the potential savings for the car buyer on fuel on
CO2 tax.
Figure 1: CO2
emissions in
relation to the
consumption of
electric power
and the carry­
ing of additio­
nal payload
Figure 2: The
potential com­
mercial benefit
per gram of
CO2 saved per
kilometer
ATZelektronik 01I2008 Volume 3
17
D e ve l op m ent
Energy Management
Figure 3: Cost
b­ enefit/savings
­potential for auto
makers and auto
buyers of eliminat­
ing 1g of CO2 per
­kilometer
Table 1: Overview of examples
would likely need 100 W at the most. Again
assuming a day-to-night ratio of 1:1, this
would translate into a mean saving of 50
W, which would allow a reduction of
around 1.2 g/km in CO2 emissions or 0.05
l/100km in fuel consumption.
Fitting LED lighting technology to a
car is still relatively costly and is estimated conservatively as adding Euro 45 to
the cost of a vehicle. LED controller components available today include the
TLE8366 and TLD5045 DC-/DC converters. In the circumstances described, LED
lighting would pay for itself after 56,000
kilometers or 3.7 operating years.
3.1.3 Reducing the Operating Current
of Control Units
3.1.1 Demand-based PWM Control
of Lamps
Incandescent lamps have been used in
automobiles for a long time now and
generally operate at the battery voltage.
These lamps are designed for 12 V operation but for the most part they are actually operated at a higher charging voltage of, say, 14.4 V. This causes a higher
current and shortens a lamp’s operating
life. Pulse width modulation (PWM) control units are widely used with lamps in
production automobiles, primarily to
avoid shortening the operating life at
higher voltages and to avoid fluctuations
in light intensity. If lamps are operated
at 14.4 V, the power consumed by all of
the car’s lighting increases substantially
– typically from 200 W to 270 W. This
means that PWM control units can save
around 70 W when the lighting is in use.
Assuming a day-to-night ratio of 1:1, the
mean power saving is 35 W, which reduces CO2 output by 0.8 g/km or fuel consumption by 0.03 l/100km. This kind of
system is easy to fit to cars, has already
been implemented in a variety of produc18
ATZelektronik 01I2008 Volume 3
tion vehicles using protected MOSFETs
like Infineon’s extensive PROFET and
SPOC families, and would involve estimated additional costs of around Euro 7
per vehicle. Thus, it would pay for itself
after just 13,000 kilometers or a period
of 0.8 years, while at the same time increasing lamp durability and delivering
more constant light.
3.1.2 Reducing Power Consumption
by Using LEDs instead of Incandescent
Lamps
Auto makers have been fitting LED lamps
to the rear of vehicles for a number of
years. Besides offering greater latitude in
terms of design, LEDs offer a number of advantages from an engineering perspective.
The key benefit in connection with the CO2
debate is their greatly improved luminous
efficiency. The luminous flux of tomorrow’s LEDs will be well in excess of 50 lm/
W, in other words roughly twice that of
halogen lamps. Compared to today’s lighting consisting of incandescent lamps,
which, as already noted, consumes around
200 W of electric power, LED lighting
Reducing the quiescent current of control units has been the focus of development initiatives for some time now,
whereas the actual operating current of
control units has been paid less attention
to date. It is hardly surprising, therefore,
that today’s control units like those used
in infotainment systems commonly draw
a continuous current of around 8 A, even
though there are ways to operate this
kind of system with a mean continuous
current of 4 A. Using DC/DC voltage controllers like the TLE6389 or TLE8366 is
just one option for lowering the power
requirements. Cutting the operating
power of an infotainment system by 4 A
equates to a saving of 50 W of electric
power, which translates into a reduction
of 1.2 g/km in CO2 or 0.05 l/100km in fuel.
System improvements of this kind can be
implemented relatively inexpensively
and with readily available technologies.
The estimated costs of around Euro 5 per
control unit could be recouped quickly
– after just 7,000 kilometers or 0.4 operating years.
3.2 Demand-based Control
of Drives and Powertrain Systems
3.2.1 Fuel Pump with PWM Control
In the field of electric drives, there are
numerous examples of ways to cut CO2
output substantially. Fuel pumps are a
case in point. Today’s automobiles are
commonly fitted with an electric fuel
pump that is switched on directly and
statically by a relay or by a MOSFET. Using PWM to control the fuel pump on a
demand-driven basis could reduce the
Figure 4:
Overview of pro­
posed measures
to reduce CO2
power consumption by as much as 40
percent. Assuming that an additional
control unit comprising an XC866 8-bit
microcontroller, a TLE7259 LIN transceiver, a BTS7970 half bridge, and a voltage
controller is installed directly on the fuel
pump, a car would produce 1.9 g/km less
CO2 at a cost of around Euro 20. The investment would pay for itself after just a
year or 15,000 kilometers.
3.2.2 Air-conditioning Fan
with PWM Control
The air-conditioning fans in many vehicles are already fitted as standard with a
PWM control unit. However a substantial
proportion of fans on the market still
use a linearly driven MOSFET as an external resistance between fan and motor,
turning between 80 W and 130 W of power into waste heat. The example here assumes a mean reduction in heat loss of
around 80 W or 1.9 g CO2/km. The additional expense of installing a PWM fan
would amount to less than Euro 10, regardless of whether MOSFETs like the
Optimos-T or protected solutions like the
NovalithIC are used. This investment
would pay for itself in just 0.5 years or
8,000 kilometers.
3.2.3 Alternator with Active,
Low-loss Power Rectification
The alternator is an example of a component that involves substantially higher
costs. In contrast to the prior examples,
the focus here is not on reducing the
electric power consumption but on increasing the efficiency of power generation. Standard alternators use diodes to
rectify the voltage, but replacing the diodes with switching MOSFETs reduces
diode on-state power loss and increases
alternator efficiency by around 10 percent. This 10 percent efficiency gain cre-
ates a fuel saving equivalent to an electrical power saving of 150 W and lowers the
CO2 output by 3.5 g/km. The expense of
Euro 180 would be offset after roughly
75,000 kilometers or five years.
investment of around Euro 55, the costs
would be covered after 0.8 years or 12,000
kilometers.
3.3 Cumulative Potential CO2 Savings
through Demand-based Control
Table 1 contains an overview of all the potential savings described in this article. If
all of these savings were implemented in
a vehicle, the overall outcome would be as
shown in Figure 4. Given that many of the
improvements addressed here are taken
into account in the official driving cycles
used to determine a vehicle’s CO2 emissions, these measures would help OEMs
to come a great deal closer to achieving
the set target of 130 g/km of CO2.
3.2.4 Electric Power-assisted Steering
(EPS)
4 Conclusion
In conventional, hydraulic power steering systems, the hydraulic pump is driven directly by the car engine via the Vbelt. Hydraulic power steering consumes
the equivalent of 300 W of electric power.
If the steering assistance is delivered directly by an electric motor, the average
power consumption drops to well below
50 W, a saving of 250 W. Assuming additional costs of around Euro 60 for electric power steering based on two XC2200
microcontrollers, a TLE7189F bridge driver, six IPB180N04S3-02 MOSFETs and one
custom system IC, the investment in EPS
would pay for itself in just a year or after
15,000 kilometers. At 5.9 g/km, EPS delivers an exceptional reduction in CO2 output, exceeded only by what can be
achieved with an electric main water
pump.
In summary, improvements to a few key
applications would enable auto makers to
cut automobile CO2 emissions from
around 160 g/km at present to close to 140
g/km. All of the semiconductor components needed to implement the demandbased control of applications are already
available. The additional expense of incorporating this technology into automobiles would pay for itself in a period of
between one and five years through lower
fuel consumption and savings on future
CO2 tax alone. OEMs would also benefit
financially by incurring lower CO2 penalties. Improvements made to applications
in order to reduce CO2 have additional advantages not addressed here that would
also benefit customers. Given such factors
as rising fuel prices and policymakers’
plans to introduce CO2-based automobile
taxation, a cost-benefit analysis now clearly shows that it pays to take steps to reduce CO2, both from an auto maker’s and
a consumer’s perspective.
3.2.5 Electric-powered Main Water
Pump with Demand-based Control
If you compare a conventional water
pump driven by the engine with an electric-powered solution, two key advantages emerge: First, pump operation can be
demand-based (the pump can be switched
off completely during the cold running
phase, for example). Second, heat management can be improved, enhancing
the car engine’s efficiency. Calculations
show a possible fuel efficiency improvement of around 0.3 l/100km. This translates into 7.1 g/km CO2 reduction – the
greatest among all of the examples presented here. Given the relatively minor
References
[1] Graf, A., Köppl, B.: “CO2-Reduktion durch bedarfsgerechte Leistungssteuerung”, 13th International
Conference on Electronics in Automobiles, BadenBaden, October 10-11, 2007
[2] Dudenhöffer, F.: “Experte fordert Emissionshandel
auch für Autos”, Die Welt - by Helmut Weinand,
January 24, 2007; http://www.welt.de/motor/­
article711232/Experte_fordert_Emissionshandel_
auch_fuer_Autos.html
[3]Michael, U.: “Mehr Elektronik im Porsche”,
­Elek­tronik automotive 3/2007
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