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29 Νοε 2013 (πριν από 4 χρόνια και 4 μήνες)

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John R. Wilson


Farmington Hills, MI



Introduction and Overview

Recently, the U.S. has proposed an increase in the fleet average mpg for passenger
cars to 54.5 miles per U.S gallon by 2025. That is the equivalent of 64.5
miles per
imperial gallon; a figure achieved by very few vehicles currently available in fuel
conscious Europe other than the 2
cylinder “twin air” Fiat 500, the minute Kia
Picanto (not available in the U.S.) and a few diesel versions of the BMW mi
and the Ford Ka and Fiesta

(also not available here). Of course, any all
electric vehicle
and even some hybrids (driven on a carefully
chosen and tightly controlled test cycle)
can beat these figures but very few of these are available in the U.
S; if they are battery
powered only, none have the driving range to attract most American buyers. Population
centers are both more compact and also closer together in Europe. Furthermore, very
few drivers will be able to achieve the test mileages obtaine
d either in the U.S. or

To provide a measure of the challenge involved, the mpg of the average car has
increased by just 10mpg over the past
years to the current fleet average of 27.3
mpg. That figure has substantially depended on the compa
ratively ‘low
hanging fruit’ of
direct injection, double overhead camshafts, variable cam timing and a general switch to
port fuel injection from carburetors (notwithstanding NASCAR’s continued interest
in the latter) and, in a very few cases, substa
ntial weight or size reduction. The
challenges that must be met in the years between 2011and 2025 are likely to be
considerably more difficult.

We should note that there is time for many political changes between now and 2025
and that any new administrat
ion may choose to relax the new standards, especially if
electric vehicles are not widely accepted by the public.

Even in 2025, there will be many vehicles that fail to meet the mileage targets.
Presumably, those that do not do so by wide enough margins
will have pay some sort of
consumption tax or be offset by sufficient more economical vehicles in the
manufacturer’s fleet.

Just some of the areas that past experience has shown must be addressed to reach the
2025 targets are:

Substantial weight reducti
on while maintaining acceptable internal passenger
and luggage space; novel lightweight materials that also permit low
manufacture will be required in some cases;


Energy source or power plant type changes/reductions in size while maintaining

acceptance, especially with respect to performance;

Improved aerodynamics while maintaining low
cost manufacturability; rolling
resistance of tires, wheel bearings, etc. (including brake drag);

Changes in engine management
while maintaining

existing improvements such
as automatic engine stop
start (at, for example, traffic lights) and variable
camshaft drive on both intake and exhaust cams;

Increasing the number of gears in the transmission, perhaps to as many as 10 (8
are now becoming comm
on) to keep conventional engines in their optimal
operating rpm range; CVTs have generally not been widely accepted, despite
Honda’s best efforts;

Maintaining a full complement of passenger needs or preferences such as air
conditioning, heating (including
rear window and mirror heating), stereo systems,
windshield wipers and so on; all of these consume power and decrease range as
well as adding weight.

Whether CO

emissions reduction or a reduction in the use of imported
petroleum is the primary target of
the mileage increases, the use of bio
fuels should be allowed to offset
both CO
fuel consumption requirements.
are now becoming available in the form of hydrogen

based aviation fuel (renewable kerosene or HDRK
) and sh
uld soon be available
as bio
based “drop
in” HDRD diesel and even hydrogen
derived renewable
gasoline (HDRG). The technology for these exists but lower costs are urgently
needed (see
our separate paper on fuels

There is a popular but, we believe, incor
rect view that the required weight reduction can
be achieved exclusively by the use of carbon fiber composites. This is not true. To
reduce fuel consumption by 37.2 mpg (US) by 2025 through weight reduction alone
would require a reduction of mass of about

4 times that of the average 2011 vehicle

clearly not a practical proposition. Thus weight reduction must be combined with other
means of fuel economy improvement such as engine size reduction, credits for “drop
based fuels and electrification (
hybrids and EVs).

In addition, Carbon fiber
composites have so far been far too costly for low to mid
range vehicles although they
find some use in vehicles priced at $100K and above.

The greatest single issue may be overcoming the public’s preferences
for very different
vehicles than those that will result from all of the changes that will be necessary to meet
the mandated 2025 requirements, even regardless of price. The 2025 vehicle will be

smaller than today’s product and will depend, at least i
n part, on electric power,
probably combined with a small gasoline or diesel engine, as in
a mini
version of
today’s Toyota Prius or Chevrolet Volt. However, substantial weight reduction will still

be needed in most vehicle components and there are major
questions regarding the
ability to achieve these, even with

carbon fiber composites. As more vehicles
become available with high fuel economy but significant trade
offs in user comfort and
convenience, the public will keep their old vehicles for
longer periods and will depend
much more on the used car market and the repair shops that will keep their older
conventional vehicles running.

All of these important factors

and many more

are discussed in the pages that follow

or in our separate paper
s on energy sources and technologies

that can contribute to
improved fuel mileage.

The New Café Standards

It was only two years ago that the Obama administration boosted the Corporate
Average Fuel Economy (CAFE) standard to 34.1 mpg in 1916 from 25.3 in
2010. This
was already an enormous challenge for the auto industry but now the administration has
proposed pushing the standards even higher. The administration is proposing 54.5 mpg
by 2025

a 59% increase over the 2016 target and 99% higher than the c
urrent (2011)
standard of 27.3 mpg.

The new standards are very complex, just as they were for 2016 and are size based.
This means that the standard for each car will be determined by a formula that relates
the standard to the vehicle’s “footprint”, the p
roduct of its wheelbase and track
dimensions. In 2011 for example the CAFE standard for the smallest car

exceed 31.2 while the largest car was assigned 24 mpg. For 2025, these targets go up
to 61.6 and 45.6 respectively.

Truck mpg will be measu
red in the same way but will use a different formula. For 2011
the figures were 21.1 to 27.1 mpg. For the 2025 proposal, the targets will increase to
30.2 and 50.4 mpg respectively. Note that the low end of the spectrum rises less than
the high end to
accommodate large trucks.

In both cases, each car company ends up with a different CAFE requirement depending
on the mix of car and truck sizes that it plans to sell. For every model year, each
manufacturer must determine what it can sell or has sold and

determine its sales
weighted average for its actual mix sold. Companies such as GM and Ford which sell a
lot of heavy pickups and SUVs will have a lower CAFÉ requirement than a company
that concentrates on small vehicles. Note, too that the EPA mileage
data on the
window sticker are determined quite differently than the CAFE mileages and will usually
be about 20% lower than the CAFE requirement.


As we will discuss below, the nominal 54.5 mpg target represents an easily

emissions requireme
nt. The actual mpg requirement will be lower at about 49.6
mpg with the additional CO

requirement coming from higher
efficiency air conditioning
systems that use a more environmentally friendly refrigerant. The manufacturers will
also get credits for ado
pting more efficient technologies that will include stop
systems such as those already in use by several manufacturers, active radiator
shutters, electric heat pumps, high
efficiency lights and even solar roof panels (if they
can be protected from ca
r washes). The manufacturer may have to provide data to
justify the additional credits. Additional credits will also be given for electric vehicles
(which will be counted at 2X actual sales in 2017, phasing down to 1.5X by 2021) and
in hybrids (whic
h will be factored in at 1.6X in 2017, phasing down to 1.3X in
2021). Other credits will be provided for hybrid trucks, natural gas powered vehicles
(matching their reduction in greenhouse gases). However, diesels will not be penalized
for the additional

carbon content of the fuel since the higher efficiency of diesels more
than offsets that. Ethanol fuels like E85 rightly continue to lose support because of their
poor mileage, which more than offsets any of the very questionable benefits of working

high ethanol content fuels.

The program will be re
evaluated at the mid
term point (about 2018) to determine
whether the 2022
2025 objectives are actually technically feasible and the vehicles cost
effective and acceptable to buyers. We anticipate that
considerable adjustments will be
necessary, perhaps even before that. The results of the re
evaluation will depend
somewhat on the price of gasoline by that time, but it seems unlikely to fall. As we note
below, the targets beyond about 2016 will be extr
emely difficult for automakers to meet,
especially for the luxury car manufacturers. Only hybrids seem likely, at this point, to be
able to meet the CAFE standards in 2017 and beyond, even allowing for the breaks for
electric vehicles and the like offered

by the program.


Vehicle Body Weight Reduction

Over the past few years,
and despite considerable effort, on average very little net
reduction in weight has been achieved in auto bodies. The weight reductions that have
been achieved through the
use of high
strength steels of reduced thickness and
extensive use of aluminum and its alloys in body and suspension parts have been more
than offset by the increases in weight due to safety design

especially crash resistance
and control

and also by in
terior hardware sought by the customers. While these have
all been necessary, it is difficult to see how, in mixed traffic, the same level of protection
of those in the passenger compartment can be achieved in an ultra
lightweight car such
as is currently

being proposed. A great deal of progress has been achieved in current
vehicles with high strength low alloy (HSLA) steel and now with ultra
high strength alloy

, also called boron steels

(especially for the passenger cell) but the crash

of these materials cannot yet be equaled by composite materials despite
major improvements in the energy
absorption capacity of the latter since about 1980.
They also bring added difficulties for res cue personnel.

Steel, in particular (and some

alloys) absorb large amounts of energy by progressively collapsing while
composite materials are built so strong that they either protect the occupants like an ice
breaker or absorb energy by fragmentation, leading to a loss of protection.

Based on racecar experience using the latest monocoque construction methods, it
requires about 600 lb. of body shell per occupant to provide adequate protection, even
with honeycomb core construction. The 1,000 lb. required for a small 2
person body
sts a total vehicle weight (including interior appointments, engine and running
gear) of at least 2,000lb depending on the engine and transmission selected

far higher
than can meet the 2025 mileage target with a gasoline or diesel engine. This probabl
implies the use an electric power source and battery pack, both of which must of much
lighter design than at present (see below) or heavy use of renewable fuels. Notably,
however, Gordon Murray Design of the UK has just partnered with Toray Industries o
Japan to produce a very attractive but small two
seater carbon fiber vehicle with
aluminum suspension hardware that weighs only 850 kg (1,900
), 225 kg of which is
accounted for by the battery. This Murray car, like his other minicar efforts, offers r
poor performance (0
60 mph in around 10 sec).

This puts the electric vehicle in a situation where range per charge, rather than mpg or
acceleration, becomes the primary objective. The Tesla, with its massive battery pack,
achieves high performance
but at the expense of weight and range. Most of the other
EVs proposed to date are designed to be city vehicles where range is
thought to be
important. Greater range will have to wait for the development of a battery of higher
energy density (see
r paper on energy sources

Carbon Fiber Composites

Almost all carbon fiber used in the U.S. is made by carbonizing polyacrylonitrile (PAN)
fiber at high temperature in a furnace. The resulting fiber has a very high tensile
modulus and is very strong. A

proven alternative source of carbon fiber is petroleum or
tar pitch. This can make a fiber of even higher modulus but of lower strength. The
U.S. no longer has a manufacturer of pitch
based carbon fiber. Various attempts are
being made to develop
alternative precursors such as polyolefin fiber or lignin but these
have yet to result in a commercial product

of the right price

carbon fiber composites such as those used in the aerospace industry start (once
the C fiber has been made) as rolls or

strips of prepreg


fiber held together by “green” or uncured epoxy resin. These strips are then laid up,
usually by a highly automated tape
laying machine, to form parts such as helicopter
blades or body parts. Construction
techniques used by high
end vehicles may be the
same but the carbon fiber used for aerospace application is typically too expensive and
too difficult to process (e.g., cure) for mass
produced vehicles. Another barrier is resin
(typically epoxy) cost and i
ts slow rate of curing. Resin producers like BASF and Dow
are working to reduce part cost by reducing resin cost and increasing cure rates, thus
shortening the part production cycle. Even at the cure rates that we have seen
proposed recently, cycle times

are likely to be far too long for the cost
conscious high
volume auto industry. For cars costing above $100,000 in 2011, the additional cost may
not be a major factor but for cars in the price range that most people can afford
$25,000 in 2011 do
llars) it will be prohibitive. High
end manufacturers like
BMW, Mercedes and, of course, Lamborghini and Ferrari have a lot more leeway but it
is hard to see a Mini
sized vehicle being acceptable at anything above $25,000.

As mentioned above, carbon fibe
r used in composite materials for high
end applications
(aerospace, for example) are made from polyacrylonitrile (PAN) fiber precursor which
when carbonized produces a high
modulus, high
strength fiber, albeit with a substantial
(and costly) loss of mass.

For automotive use, other precursors may make more sense
from a cost standpoint

pitch from coal or petroleum sources, for example, or polyolefin
fibers such as polyethylene or polypropylene. Significant industry efforts are also being
made (for example

by Zoltek with Weyerhauser ) to develop a “green” carbon fiber
based on lignin derived from trees used for paper production. Lignin, a natural material,
is inherently variable in its properties and is relatively costly when purified and

An interesting recent development in carbon composites is the use of carefully
prepreg chips (of either PAN or pitch origin) to make a small
particle material suitable
for compression molding. The prepreg is chopped into pieces that are typically a
3mm wide by 5mm long (the optimum size distribution is not yet known) and then used
as a feed for a high
temperature compression molding operation. The process is
sometimes called “forging”. The resulting cured parts have very high strength and
fness and are being used in prototype suspension parts for the new $3 million
Lamborghini Sesto Elemento, unveiled at the 2011 Paris Auto Show. The car also uses
carbon fiber composites for the passenger compartment, the front and rear end
structures alon
g with the interior and all exterior panels. Even the car’s tailpipes are
made from a carbon and glass

ceramic composite. Of course, all of this is currently
possible only with a very high
end car of very high price.


An alternative compression
technique uses the same fiber with thermoplastic
resins, usually of the high
performance kind such a polyimides and PEEK (polyether
ether ketone). Because of their high heat resistance, these materials, which can also
be compression
molded but require no
curing, can be used for moderate
applications. They are however difficult to mold, especially with long fiber reinforcement
and are also relatively expensive.

For some applications, lower
cost thermoplastics
such as Nylon 6/6 resin (polyamid)
, reinforced with carbon or a hybrid fiber system (see
below) may be more cost

A major question is whether carbon fiber made from any source can meet the realistic
cost requirements of the auto industry even if precursors of sufficiently low co
st are
available. At present, this seems unlikely. The auto industry has made a habit
since1975 or so of encouraging manufacturers to produce low cost carbon fiber, only to
ask for impossibly low prices once the material becomes available. In 1980, thei
r target
was $2/lb., well below the production cost of the fiber, regardless of the precursor. Now
the figure being discussed is $5
$7/lb. for high
volume vehicle production but the auto
industry will probably want it to drop to $3 or so by the time actua
l use is possible.
Currently, the cost of pan

carbon fiber is about $ 30/lb.
grade fiber is significantly more expensive. As usual, most of the talk about
using carbon fiber in high
volume vehicle production is unrealistic hype, apparently used
to make the auto companies appear more enviro
nmentally responsible.

The best low
cost precursor for carbon fiber is probably pitch, all production of which
has moved to Japan (Nippon, Toray) and to China (where there are many sources,
often secondary processors who offer only short fiber). For au
to parts, pitch
based fiber
makes a lot of sense since it makes use of what would otherwise be a residue of
petroleum (or less often, coal) processing that otherwise presents disposal problems.
based fiber has higher tensile elastic modulus that PAN

fiber but a lower strength.
It is therefore best used in applications where stiffness, rather than strength, is at a
premium. It is also much less costly than PAN fiber. Despite the large potential market
for pitch fiber for automotive applications, it

is seldom used in the U.S.

Lignin seems unlikely as a precursor, both on cost grounds as well as predictability of
performance and availability in the necessary high grade. Polyolefin fibers may also be
candidates provided that precursor costs can be
low enough although a sufficiently
stable molecular orientation is difficult to achieve, especially in polypropylene. Once
again, perhaps it is time to revisit pitch fiber (which offers good

, although it is doubtful that anyone
in the U.S. could now be persuaded
to produce it in volume given current and historical market uncertainties.

Another way in which part costs can be reduced is through the use of

systems. In principle, these can be blends of two or more diff
erent fibers in tows but
that is practically difficult. More often components are made that consist of faces
reinforced with the higher
performing fiber combined with cores of a lower
fiber. Sometimes, as in some honeycomb structures, the core

may contain no fiber at
all. Prepreg “chips” of two different fibers can easily be blended to make a high
performance but lower cost compression
part. This would lead more precisely
to a hybrid fiber part. One of the problems with hybrid compo
sites is the differential
thermal expansion of the fibers. In a rigid matrix such as a fully
cured epoxy this can
lead to problems with cracking but works better in a more flexible matrix, especially if
use does not involved such wide temperature variatio
ns as it does in combat aircraft
that fly above the speed of sound.

Ultimately, it is
cost rather than materials cost that determines the acceptability of
automotive parts. Here, materials like aluminum or steel that can be stamped from
sheet, fo
r example, have the edge because productivity is high

the production cycle is
very short, typically multiple parts/minute for small items. Small injection
molded plastic
parts can also be produced very quickly using multi
cavity molds. Even filled plas
parts (e.g., those using calcium carbonate or carbon particles as a filler, often for
coloring purposes), can be injection molded in a short
cycle process but larger or fiber
reinforced parts generally cannot be produced quickly and therefore cheaply,
years of development efforts. There is considerable doubt whether carbon
reinforced parts using a heat
curable resin such as epoxy or vinyl ester can ever be
produced quickly enough to make the low
cost parts that are called for in mass
uced vehicles. Processes such as resin transfer molding simply take too long and
are often accompanied by a long oven
curing process. The rapid
cycle requirements
for building an automobile are very different than the needs of aircraft or wind turbine
ade manufacturers.

Materials for Engine and Transmission Weight Reduction

A major contributor to the total weight of the vehicle is the engine and transmission.
Major reductions have already been made through the use of aluminum alloy in engine
and, in most cases, cylinder heads. The old cast iron engines have largely been
replaced in gasoline
powered cars and in some small diesels. Aluminum or sometimes
magnesium alloy is commonly used for transmission housings. Further reductions in


Liu, Chang, “Mesophase Pitch
Based Carbon Fiber and its Composites: Preparation and Characterization”,
Master’s Thesis, University of Tennessee at K
noxville, December, 2010


mass are

probably achievable only through further engine downsizing, perhaps assisted
by turbocharging, which adds little weight but a lot of power and especially torque. The
latter is a major factor in vehicle drivability to the extent that turbocharging or even

supercharging (which adds more weight) is likely to become more and more common as
engine sizes diminish. This trend is already evident in Ford’s new 3
cylinder 1,000cc
engine with ”Ecoboost” (their trade name for turbocharging) which is intended for the

future Ford Focus and probably Fiesta
. It has an intentionally unbalanced flywheel (but
no countershaft) to compensate for the inherently very unbalanced nature of a three
cylinder engine.

Recently, efforts have been renewed

this time with some succe

to develop a
“carbon engine”

one of near
net shape built from carbon
polymer (usually carbon

epoxy) composites. This was attempted first for race cars in the early 1980s as the
“Polymotor”, but reliability was a problem, especially if carbon was u
sed for moving
parts as well as for the block and head. The latest engines

use a short (~6mm)
graphite fiber
reinforced block based on the Ford 4
cyl. Duratec engine with an
aluminum head. Eventually a composite head will also be used. Main bearings
metal inserts and the bores will, at least initially, have plasma spray coated aluminum
silicon liners to minimize friction losses. It is less clear when pistons and connecting
rods will become carbon fiber parts. At least connecting rods have been t
ried previously
and found to be reliable, but pistons would require something like composite “forging”,
referred to earlier, to produce reliable, precisely dimensioned parts.

The new “Polymotor” will be used for race purposes only and initially will be fa
r too
expensive for consideration for road cars. However, further development is possible
and should lead to a viable road
going engine that offers about a 40% reduction in
weight over an all
aluminum engine.



See for example,
Racecar Engineering, August 2011