Automotive innovation the science and engineering behind cutting edge automotive technology

Automotive Innovation

http://www.taylorandfrancis.com

Automotive Innovation

The Science and Engineering behind

Cutting-Edge Automotive Technology

Patrick Hossay

CRC Press

Taylor & Francis Group

6000 Broken Sound Parkway NW, Suite 300

Boca Raton, FL 33487-2742

CRC Press is an imprint of Taylor & Francis Group, an Informa business

No claim to original U.S. Government works

Printed on acid-free paper

International Standard Book Number-13: 978-1-138-61176-4 (Hardback)

This book contains information obtained from authentic and highly regarded sources. Reasonable efforts have been

made to publish reliable data and information, but the author and publisher cannot assume responsibility for the

validity of all materials or the consequences of their use. The authors and publishers have attempted to trace the

publish in this form has not been obtained. If any copyright material has not been acknowledged please write and let

us know so we may rectify in any future reprint.

Except as permitted under U.S. Copyright Law, no part of this book may be reprinted, reproduced, transmitted, or

utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including

photocopying, microfilming, and recording, or in any information storage or retrieval system, without written

permission from the publishers.

For permission to photocopy or use material electronically from this work, please access www.copyright.com (http://

www.copyright.com/) or contact the Copyright Clearance Center, Inc. (CCC), 222 Rosewood Drive, Danvers, MA

01923, 978-750-8400. CCC is a not-for-profit organization that provides licenses and registration for a variety of users.

For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been

arranged.

Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for

identification and explanation without intent to infringe.

Library of Congress Cataloging‑in‑Publication Data

Names: Hossay, Patrick, 1964- author.

Title: Automotive innovation : the science and engineering behind

cutting-edge automotive technology / Patrick Hossay.

Description: First edition. | Boca Raton, FL : CRC Press/Taylor & Francis

Group, [2020]

Identifiers: LCCN 2019009155 | ISBN 9781138611764 (hardback)

Subjects: LCSH: Automobiles—Technological innovations—Popular works. |

Automobiles—Design and construction—Popular works.

Classification: LCC TL240 .H655 2020 | DDC 629.2—dc23

LC record available at https://lccn.loc.gov/2019009155

Visit the Taylor & Francis Web site at

http://www.taylorandfrancis.com

and the CRC Press Web site at

http://www.crcpress.com

http://www.copyright.com

https://lccn.loc.gov

http://www.taylorandfrancis.com

http://www.crcpress.com

Contents

Preface ..............................................................................................................................................ix

Author ........................................................................................................................................... xiii

1. Bringing the Fire .....................................................................................................................1

What Is Gasoline? ....................................................................................................................2

The Engine ................................................................................................................................3

The Four Strokes ......................................................................................................................4

The Engine Comes Together ..................................................................................................8

Valve Train .............................................................................................................................. 11

Defining the Combustion Chamber .................................................................................... 13

Pistons ..................................................................................................................................... 16

The Head ................................................................................................................................. 19

Ignition ....................................................................................................................................23

Knocking ................................................................................................................................. 24

Fuel Delivery .......................................................................................................................... 27

Low-Temperature Combustion ............................................................................................34

2. The End of Compromise ..................................................................................................... 39

Advanced Digital Control..................................................................................................... 39

Sensor Technology .................................................................................................................40

Engine Control .......................................................................................................................42

Variable Valve Actuation ......................................................................................................45

Induction ................................................................................................................................. 52

Forced Induction ....................................................................................................................55

Compression Ratio .................................................................................................................58

3. Getting Power to the Pavement .........................................................................................65

What Do We Need a Drivetrain to Do? ..............................................................................65

Manual Transmission Coupler .............................................................................................72

Manual Transmission ............................................................................................................ 74

Automated Manual ................................................................................................................ 76

Automatic Transmission Coupler ........................................................................................80

Automatic Transmissions ..................................................................................................... 82

Transmission Control ............................................................................................................86

Continuously Variable Transmissions ................................................................................88

Differentials, AWD, and Torque Vectoring ........................................................................ 92

Advanced Tires and Control ................................................................................................ 96

4. Electric Machines ..................................................................................................................99

The Principles of the Electric Motor .................................................................................. 100

Making an Electric Machine .............................................................................................. 102

Motor Performance ..............................................................................................................

1.13

Advanced piston manufacturing.

Future piston structures may be defined with 3D printing. IAV Automotive Engineering is developing this pis-

ton with a honeycomb lattice to define the piston’s structure. IAV reports exceptional strength, about 20% less

weight than its conventional counterpart, and reduced thermal expansion.

18 Automotive Innovation

printed with a thin graphite-infused, low-friction patch. A recently developed piston coat-

ing that includes graphite, molybdenum disulfide, and carbon fiber promises a full 10%

friction reduction over an uncoated piston (Image 1.14).6

Even with this increasing sophistication and precision, the aluminum piston is now fac-

ing a challenge from a high-tech version of its old iron rival made of new high-strength

steel alloys for diesel passenger car applications. Because of the greater strength of this

new steel, the piston can be made smaller and lighter. In particular, the distance from

the piston pin to the upper surface of the piston, called the crown, can be shortened. This

allows for less mass and potentially a longer connecting rod and thus a larger displace-

ment in the same overall size engine. Or, with the same displacement, a shorter block

could be used, allowing a significant reduction in engine size and weight. Because steel

offers lower heat conductivity than aluminum, the steel piston must make use of cooling

galleries, which significantly complicates the manufacturing process since the piston must

be made in two parts. Because steel expands less with heat than aluminum, the challenge

of accommodating thermal expansion is eased a bit. Whether gasoline engine applications

of an advanced steel piston could be developed is still to be seen. We’ll look more closely

at advanced steel in Chapter 8.

Another piston option that has been touted by producers of aftermarket performance

parts but not by OEM producers is ceramic-coated piston crowns. The idea is to produce

a strong, insulating coating on the top of pistons. Zirconium ceramic fits the bill well, as

it provides good insulation and thermal expansion behavior that matches the metal and

thus allows for an enduring bond.7 The hope is that this insulation will help maintain the

heat energy in the cylinder, increasing thermal efficiency; and evidence indicates this is

6 M. Ross, “Pumped Up: Piston Evolution.” Engine Technology International.com March, 2015.

7 D. Das, K.R. Sharma and G. Majumdar, Review of emission characteristics of low heat rejection internal com-

bustion engines. International Journal of Environmental Engineering and Management 4 (4), 2013, 309–314.

IMAGE 1.14

Steel piston.

Aluminum pistons are now common in all production automobiles, with cast aluminum common in fleet vehi-

cles and hypereutectic or stronger forged aluminum used in performance applications, but pistons manufac-

tured from new steel alloys such as this are set to change this for diesel engines. This monotherm steel piston

made by Mahle was the first made for light passenger cars.

Source: Mahle

http://International.com

19Bringing the Fire

the case.8 However, the process can be expensive, the gains are modest, and the resulting

increased combustion temperature also tends to produce higher NOx emission, making

this a problematic adoption for production cars.9

As goes the piston, so goes the connecting rod. Like the piston, the rod has been exposed

to increasing pressure and heat. Performance rods are often made of forged steel, though

aluminum alloy rods are not unusual. Titanium offers extremely light and strong per-

formance rods. And because of a rod’s simpler design requirements, it’s easier and more

cost-effective to make rods out of titanium than pistons. Aluminum MMCs also offer some

promise. In fact, because it’s not exposed to the same extreme temperatures as the piston,

the connecting rod offers many promising avenues for weight reduction. Newer research is

examining the use of composite materials for connecting rods, with Lamborghini explor-

ing the possibility of a carbon fiber rod that is half the weight of a conventional steel rod.10

Similarly, the design of piston rings has evolved over time. Rings provide the seal

against the cylinder wall, but in defining that tight fit, they also account for a majority

of the friction in the engine. Classically, an upper ring provided a tight seal, called the

compression ring, and a lower ring ensured that engine oil from the crankcase didn’t

make its way in the combustion chamber, called an oil control ring or scraper. This lower

ring allows excess oil to be cleaned off the cylinder walls and returned to the crankcase

through oil drain holes in the ring groove, leaving only a slight lubricating film, enough

to allow movement of the piston without excessive fouling of the combustion chamber.

There are multiple variations in the number, cross-sectional design, and the placement of

the rings, though generally automobile manufacturers have moved to smaller ring packs

to reduce friction loss, with some recent compression rings less than a millimeter thick,

less than half the thickness of typical rings a decade ago.11 Ceramic coating is also used to

reduce ring friction and wear, and new application technologies are significantly reducing

the cost of this once-expensive option (Images 1.15 and 1.16).12

The Head

The head, and the valves it contains, define the last remaining wall of the combustion

chamber. The head must be engineered precisely enough to define the top end of the com-

bustion chamber, ensure a tight seal with the block, and provide precision-machined valve

seats that are able to maintain an exact fit at high temperatures.

8 K.S. Mahajan and S.H. Deshmukh, Structural and thermal analysis of piston. International Journal of

Current Engineering and Technology 5 (June), 2016, 22–29. Available at http://inpressco.com/category/ijcet;

K.Thiruselvam, Thermal barrier coatings in internal combustion engine. Journal of Chemical and Pharmaceutical

Sciences 7, 2015, 413–18; and A. Sh. Khusainov, A.A. Glushchenko, Theoretical prerequisites for lowering pis-

ton temperature in internal combustion engines. International Conference on Industrial Engineering, ICIE 2016

Procedia Engineering 150, 2016, 1363–1367.

9 D. Das, K.R. Sharma and G. Majumdar, Review of emission characteristics of low heat rejection internal

combustion engines. International Journal of Environmental Engineering and Management 4 (4) 2013, 309–314.

Available at http://www.ripublication.com/ ijeem.htm

10 D. Undercoffler, “Lambo Expands Carbon-fiber Footprint.” Automotive News July 4, 2016.

11 V.W. Wong and S.C. Tung, Overview of automotive engine friction and reduction trends—Effects of surface,

material, and lubricant-additive technologies. Friction 4(1), 2016, 1–28.

12 L. Kamo, P. Saad, W. Bryzik and M. Mekari, Ceramic coated piston rings for internal combustion engines.

Proceedings of WTC2005 World Tribology Congress III September 12–16, 2005, Washington, DC, USA.

http://inpressco.com

http://www.ripublication.com

20 Automotive Innovation

Perhaps the most noticeable variation in the design of the head is how many valves are

integrated into the combustion chamber and in exactly what way. While the classic engine

had one intake and one exhaust valve, by the early 1980s this convention was regularly

challenged in an effort to allow greater flow in and out of the cylinder. In fact, in the

IMAGE 1.16

Piston coatings.

Ceramic coatings can reduce surface friction by a third. This advanced coating by FederalMogul includes solid

lubricants and carbon fibers, offering reduced friction and significantly improved wear.

IMAGE 1.15

Advanced piston.

Pistons have advanced significantly. Ring packs have become much smaller and slipperier than they once were.

And cooling channels, such as the one in this Federal-Mogul Elastothermic piston, can reduce piston crown

temperatures by about

a fifth.

21Bringing the Fire

mid-1980s, an experimental Maserati V6 2.0-liter turbo used six valves per cylinder, defin-

ing a very tight fit. While six-valve heads are decidedly not common, four valves per cylin-

der certainly are. Particularly with the greater demands being placed on smaller engines,

multivalve heads accommodate higher rpm, allowing the engine to breath at a much faster

rate. Because the incoming charge is cooler than the high-heat, high-energy exhaust, a

common variation is to increase the size or number of the intake valves specifically. This

allows more area for the relatively cool, heavy and slower-moving intake charge to enter

the cylinder. There’s reason for caution, however. More valves are not always better and

can complicate the valve train and constrain head design options. Similarly, the common

performance upgrade of installing oversized valves in hopes of producing more horse-

power can be a fool’s errand, as the valve size is frequently not the performance bottleneck.

The larger question is how do we integrate these valves into the head, and what geom-

etry will we use to shape the upper combustion chamber? There are three primary con-

siderations at play in answering this question: First, maintaining the high energy and

full emulsification of the incoming fuel–air mixture, principally by producing an agitated

flow into the chamber that keeps the kinetic energy of the incoming charge high. Second,

intensifying the energy of the vaporized charge in the last stage of compression to prepare

the charge for combustion, we call this squish. And, third, removing the exhausted charge

in the chamber quickly and completely after combustion to allow it to be replaced with a

fresh charge, we call this scavenging. Let’s look at each of these.

A priority is to ensure a highly energized flow into the cylinder as this helps produce a

desirable and fast-moving flame front upon combustion. The placement of the valves and

shape of the piston are vital here. Positioning the valves so that the intake occurs obliquely,

with both an end-over-end rotation, called tumble, and a spiral rotation of the mixture,

called swirl, is the goal. Without this energy, the charge might lose the integrity of its tar-

geted mixture profile, and the resulting flame front from a low energy charge may move

too slowly for a high-speed engine (Image 1.17).

A clean and fast flame front is also encouraged by shaping the piston and head to define

a desired squish pattern. Squish is the final squeezing of the charge in the last bit of the

compression stroke. Ideally this injects a burst of energy into the fuel–air mixture. With

contemporary engines designed to make maximum use of this effect, the area between the

IMAGE 1.17

Swirl and tumble.

Proper swirl and tumble patterns are key variables in the vaporization and emulsification of charge delivery

in a high-performing engine. Producing a high-energy charge promotes a faster flame front that can meet the

needs of high-speed performance.

22 Automotive Innovation

head and piston at TDC, called the clearance volume, is tiny by the standards of past gen-

erations. Modern engine pistons come within a single millimeter of the head. This brings

the charge into an unstable and highly energized state, greatly speeding the rate of com-

bustion and allowing the piston to absorb as much of the combustion energy as possible.

The chamber shape and piston head are designed to make maximum use of this energy.

But there’s a trick to this: you need to avoid preignition and maintain low emission of NOx

which tend to increase with rising ignition temperature. We’ll look at just how that’s done

in the next chapter.

Scavenging is yet another consideration. The shape and dynamics that keep an incom-

ing charge energized and turbulent can also be used the help eject the exhaust out of the

cylinder. One method is allowing for some valve overlap, a short period when the exhaust

valve hasn’t yet completely closed and the intake valve begins to open. This can allow for

cross-flow thru the combustion chamber, with some of the energy of the incoming air

being used to push the remaining exhaust out of the chamber. The effect can be facili-

tated by placing the valves opposed to each other so that flow from one to the other drafts

through the cylinder.

So, how do we shape the head to ensure that we achieve all these aims? As you might

expect, there’s no single answer. Over the years, there have been any number of com-

bustion chamber designs. Early ‘flat heads’, for example, had valves either side by side

(called a T head) or across from each other (L head) that faced upward and were adjacent

to the cylinder. Once common, these configurations are now obsolete, as they can’t offer

the sort of compression and control desired in modern, high-performance automobiles.

More recently, engines have tended toward some variation of three head designs. The first

two utilize a so-called I-head that mounts valves facing the piston directly and can thus

allow the upward facing valve stems to connect with one or two camshafts in the head,

thus called an overhead cam. These can commonly entail either an inverted cup-shaped

chamber that has earned it the name bathtub chamber, or an angled design with one side

higher than the other, forming a wedge chamber.

A heart-shaped chamber is a common variation on the bathtub design that is defined

by two squish regions, typically a large circle at the spark plug and a smaller one on the

opposing end. The result forms a crescent or heart shape. The spark plug in the center of

the head favors a desirable flame front. However, having the valves close to each other

makes heat transfer a problem, limiting octane tolerance of the engine (Image 1.18).

A third common configuration is the hemispherical head. This may be the most well-

known head design, largely thanks to Dodge’s promotion of its ‘hemi’ engine. The rounded

chamber top offers good geometry for turbulence and facilitates the use of opposing valve

placement and so allows excellent cross-flow scavenging. In addition, because the valves

are on opposing sides of the head, they are more thermally isolated. This helps keep the

valves cooler and so helps avoiding knocking. A variant of this design can accommodate

multiple valves and is called a pentroof, or penta, design. Because it must provide multiple

valve seats, it tends to have flatter sides.

New innovations in the material and manufacturing have also helped improve valve

design. Stainless steel valves are now common and available in various alloys that can

improve hardness and heat resistance. Recently developed titanium valves can be 40%

lighter than stainless steel valves. As previously discussed, the weight of oscillating com-

ponents can be definitive to performance. Valve weight in particular can be a limiting

factor on maximum engine speed. Valves that are even just a slight bit lighter can signifi-

cantly reduce the energy needed to operate the valves and so allow for more aggressive

valve lift. This can mean significant rewards in engine response and speed. Sodium-filled

23Bringing the Fire

valves offer another interesting example. As the sodium liquefies with heat, it shifts back

and forth through the stem of the valve, transferring heat away from the head, another

example of shaker cooling.

Ignition

With the combustion chamber defined, and the charge primed and ready for ignition, the

obvious question arises: when do we ‘light ‘er up’? The ignition of the charge has to come

at the right time, not too soon, since this might cause the cylinder pressure to rise too high

before the piston completes the compression stroke; and not too late, since this might mean

we’ll lose some of our ability to absorb the combustion energy before the end of the power

stroke.

IMAGE 1.18

Chamber designs.

Just about every manufacturer has used some version

of a wedge design (upper left). With the valves aligned

side by side on the long wall of an asymmetric wedge, the spark plug is placed on the opposing short side. The

walls of this design allow for advantageous tumble. And the intense push of the charge from the narrow to the

full side of the wedge at the late point of compression offers desirable squish. The heart-shaped head (upper

right) represents a common head design. Note the close proximity of the valves.

The bathtub chamber (lover left) defines a symmetrical head shape that can place valves upright or at slight

opposing angles. The hemispherical head (lower right) may be the most well-known head design, largely

thanks to Dodge’s promotion of its ‘hemi’ engine with excellent cross-flow scavenging and good thermal isola-

tion for the valves, the design deserves some praise.

24 Automotive Innovation

Because ignition timing needs to change while the engine operates, it’s not quite as sim-

ple as the timing of the valve and piston movement. These two parts can move in synch

with no trouble; every turn of the crankshaft needs half a turn of the camshaft, no matter

what engine speed, no matter what driving conditions. But, for ignition timing, the situ-

ation changes. As previously noted, combustion is a process. The flame front initiated by

the spark plug is not instantaneous, it takes time to pass through the combustion chamber,

and that time varies as a result of the energy in the charge and the richness of the mixture.

Leaner air–fuel ratios define a slower-moving flame front. High energy due to intense

compression or high heat can speed the flame front. And, of course, the engine moves

at dramatically different speeds, sometimes rotating at an idle, say about 800 rpm, and

sometimes at as much as 6,000 or more rpm. Because we need the flame front to develop

it’s push at just the right time, this means we need to adjust the ignition event to account

for engine speed and mixture, so that the main push of the flame front occurs when the

piston is early in the downward stroke and can absorb the energy effectively.

Consequently, to ensure proper timing of the flame front, we need to initiate ignition

before the piston reaches the top of the compression stroke, or TDC. This is called igni-

tion advance. If we didn’t have an advance, and the spark plug ignited at TDC, the main

push of combustion would occur late in the power stroke, and the piston would reach the

bottom of the stroke before the combustion force was complete. The faster the engine is

rotating, the worse this effect would get, since the flame front moves at a relatively fixed

rate and won’t speed up to match engine speed. We measure the advance of the ignition in

degrees of crankshaft rotation before TDC, or BTDC, and so talk about advance in number

of degrees.

This means that at low rpm, we might want the spark plug to fire 15° BTDC. But at high

rpm, we might need ignition to be 30° or more BTDC, to allow the expanding combustion

gasses to fill the chamber and provide a maximum amount of power to the piston well

before the piston reaches the end of the power stroke (Image 1.19). Older cars had a simple

mechanism that could allow for two timing settings, one for low rpm and one for high

rpm. New cars allow for much better ignition timing because the engine’s operations are

computer controlled (lots more on this in the next chapter). Ideally, we’d like to advance the

ignition timing as much as we can, to allow us to harvest as much of the energy from the

power stroke as possible (Image 1.20). The problem is, if we advance the timing too much,

we can create or exacerbate engine knocking.

Knocking

In a perfect engine, the arcing of the spark plug will ignite a critical flame kernel that will

in turn begin the propagation of an even flame front and a resulting fast and powerful but

smooth push against the piston head. An abrupt, explosive blow, even though powerful,

won’t do. Think of this like a playground merry-go-round. To keep it moving, you need

even and firm pushes. Imagine trying to get that merry-go-round spinning by slamming

it with a sledgehammer. When this sort of uncontrolled or uneven combustion happens in

an engine, we call it knocking. This is a general term that actually refers to two things that

can go wrong: preignition and detonation.

Preignition, as the name implies, is when the ignition process starts early through

autoignition, before the spark plug fires. To fully understand what causes this, we need

25Bringing the Fire

IMAGE 1.19

Ignition advance.

Ensuring that combustion takes place just after the piston reaches top dead center (TDC) requires having initial

ignition take place well before TDC, and be adjusted to accommodate engine speed. The faster the engine speed,

the greater the ignition advance required.

IMAGE 1.20

Combustion chamber pressure.

Ideally, maximum combustion chamber pressure is reached just after TDC, about 15° or so, allowing for maxi-

mum recovery of combustion energy by the piston. To ensure proper scavenging, the exhaust valve opens

(EVO) before combustion pressure has completely dropped.

26 Automotive Innovation

to recall a key characteristic of gasoline—octane rating. Remember that the octane rating

gives us a sense of the fuel’s tolerance to compression. A high octane rating means the fuel

can be compressed more without fear of triggering autoignition, and a low octane rating

indicates that the fuel is more likely to spontaneously ignite under relatively lower pres-

sure. So, if an engine is run on a fuel with an octane rating that is too low, the heat and

pressure caused by the compression stroke could trigger autoignition before the spark

plug fires. This might be made more likely if the spark plugs or valves get overheated, add-

ing excess heat to the compression stroke. This preignition is clearly not a good thing. If

ignition happens too early, the force of combustion could actually push against the piston

while it’s still in the compression stroke, effectively trying to turn the engine against its

direction of rotation.

A more common form of knocking is detonation. Unlike preignition, detonation does

not begin before the spark plug fires. Instead, the spark-initiated ignition increases the heat

and pressure in the combustion chamber, causing spontaneous autoignition in at least one

other location in the cylinder (Image 1.21). So, combustion in the chamber happens in more

than one location at a time, and instead of having a singular kernel that leads to a unified

and even push, we have multiple points of ignition that lead to a more disorganized com-

bustion and a much less even push against the piston. The resulting violent combustion is

a frequent cause of damage to bearings and pistons.

This threat of detonation is the core challenge of ignition timing. One cause of detona-

tion could be excessive ignition advance. If the spark plug fires too early, the cylinder pres-

sure will increase while the combustion chamber is still relatively large and before the

flame front can travel through the chamber, leading to one or more points of unburned

IMAGE 1.21

Knocking.

Desired ignition is defined by a single ignition point and flame front in the combustion chamber. Knocking

can be caused by preignition, defined by the autoignition of the fuel–air mixture before the spark plug fires, or

detonation, defined by multiple ignition points caused by the increased heat and pressure resulting from spark

ignition.

27Bringing the Fire

fuel igniting on their own as the chamber’s pressure and heat increase beyond the fuel’s

autoignition point. The solution is to back off on the ignition advance, and allow the piston

to travel a bit more before initializing combustion. But, if you back off too much, as dis-

cussed, you’ll lose the ability to harvest some of the energy from combustion. The balance

can be tricky.

A central variable in this effort is how much

we compress the charge. This is defined by

the engine’s compression ratio, defining the amount the air is squeezed prior to combus-

tion. This ratio is defined by the proportion of the volume of the combustion chamber

when it’s at it’s largest (bottom dead center) to the volume at its smallest (top dead center).

We called the smallest volume clearance volume (most often written Vc), the change in

volume caused by piston movement is called displacement volume (Vd), and so the total

volume when the piston is at BDC is the two volumes combined. That means the compres-

sion ratio is (Vc + Vd)/Vc.

Taking what we’ve already discussed into account, we can see that defining an engine’s

compression ratio is a balancing act too. A higher compression ratio can allow us to draw

more power from combustion. This could enable us to gain significant improvements in

fuel economy or power, as we’re able to draw a much greater amount of energy from a

given amount of fuel. But, as the compression ratio goes up, so does the need for higher

octane fuel that can withstand the higher pressure without autoignition; and, if we com-

press the charge too much, we invite preignition and detonation. Preignition is more likely

when the engine is operating at high load since the engine temperature goes up. So, a

high-performance engine might have a compression ratio (CR) 8:1 to avoid knocking at

high engine loads, while an engine targeting high efficiency might be closer to 13:1. With

advanced control discussed in the next chapter and appropriate fuel, compression ratios

as high as 14:1 are possible. By comparison, diesel engines start at 14:1 and go to about 23:1.

This adds complexity to much of what we’ve discussed so far, since how we manage

heat, engine speed, and knocking are all shaped by the compression ratio. For example,

a higher compression ratio will increase engine heat, but cooling the piston temperature

with galleries could reduce the threat of detonation and thus allow a higher compression

ratio. Or a richer mixture can speed the rate of combustion, but it could also cool the com-

bustion chamber and may reduce the possibility of detonation.

Fuel Delivery

Delivering fuel and air to the combustion chamber can be tricky too. To be ready for com-

bustion, the fuel must be atomized (suspended in small bits), emulsified (fully blended with

air), and vaporized (changed into a stable and consistent gas). As we discussed previously,

without adequate access to oxygen, gasoline will not burn. So, the delivery of fuel and the

delivery of air are irrevocably linked. Complicating this somewhat is our desire to avoid

the production of nitrogen oxides. NOx is formed when combustion temperatures are high

enough to break apart the nitrogen in the incoming air supply. As a result, exhaust gas

recirculation (EGR) has been used since the 1970s to return a small portion of the exhaust

gases to the combustion chamber in the next intake stroke as a way of cooling the tempera-

ture of combustion and reducing the formation of these undesirable pollutants.

Early engines did not offer any real opportunity for precise control of the mixture. The

engine that powered the Wright brother’s first flight, for example, simply spilled fuel on a

28 Automotive Innovation

manifold and used the engine’s heat to help vaporize it. And into the 1980s, automobiles

utilized carburetors that channeled the engine’s incoming air through a narrow passage, a

venturi. The resulting vacuum simply sucked up gas from an adjacent small reservoir. The

system worked adequately, but the mixture was imperfect, and would not meet the needs

of today’s engines. Carburetors were replaced by more precisely controlled spray nozzles

for gasoline, fuel injection, by the start of the 1990s. The early systems simply sprayed

fuel through a nozzle into the central throttle that replaced the carburetor, called throttle

body injection (TBI). In the end, TBI was not too different from the carbureted systems

they supplanted.

Both of these systems, the TBI and carburetors, presented an inherent challenge.

Because the air and fuel were mixed at the start of the intake manifold, and had to travel

through the intake manifold channels to get into the chamber, it was always a challenge

to ensurethe mixture remained fully emulsified and atomized as it made its way to the

cylinder. Suspended fuel particles are heavier than the surrounding air, and thus inclined

to settle if the flow calms or slows. So, this was particularly a problem at low engine

speeds when induction flow slowed. To address this, the manifold had to be designed to

ensure continued high-energy turbulent flow to maintain suspension of the fuel particles.

Intuitively, you’d want the path of an intake manifold to be as smooth and large as pos-

sible so that plenty of air can reach the cylinders with minimal resistance. But, a large open

intake would mean low-energy, slow-moving air, which could easily cause the fuel to drop

out of the mixture. Similarly, if you need to ensure the air–fuel mixture remains energized,

smooth walls and wide turns are not your friend. You want sharp edges, rough walls

and sharp corners to stimulate turbulence. However, such a design also meant high flow

resistance, and at higher engine speed this meant a significant power loss. So, the result

was a significant compromise in high-end power to ensure continued emulsification of the

air–fuel mixture at low engine speeds.

Current systems, however, get around this challenge by adding fuel just before the cyl-

inder, in the case of port injection, or in the cylinder itself, with direct injection. This

eliminates an extended run of fuel–air mixture through a manifold, and thus allows for

more precise and independent control of both air and fuel. Manifolds for a port or direct-

injected engine carried only air and so could be made smooth and streamlined. This

reduced pumping losses and so improved efficiency. An open chamber at the start of the

induction system can act as an air reservoir to slow the incoming air and allow a resulting

pressure increase. This air reservoir, or plenum, can dampen pressure fluctuations and

provide higher density air to the inlet channels that feed each cylinder with air, called

intake runners.

The most common fuel system, port injection, sprays the fuel on the backside of the valve

just outside the cylinder. Designing the spray pattern can ensure desirable atomization

and a spray and inlet geometry that promotes a beneficial swirl and tumble pattern. The

result is a fuel flow that is far more precisely defined than previous carburetor or central-

ized injection systems. While older designs sprayed fuel continuously, newer sequential

port fuel injection provides pulses timed with the intake cycle.

More recently, direct injection offers a notable uptick in precision and control. Borrowing

once again from the diesel world, rather than mixing the fuel and air before it enters the

cylinder, gasoline direct injection (GDI) injects a precise spray of fuel in the cylinder itself.

The basic idea has been around for a while, but lack of capable control mechanisms and

the challenge of high-pressure precision injection have made this idea problematic and

expensive until very recently. The resulting control over the amount and pattern of the

fuel delivery offers substantial advantages in fuel economy and performance. Like diesel

29Bringing the Fire

engines, GDI provides a major decrease in pumping loss at low speed by providing a very

lean charge and avoiding the energy loss resulting from drawing intake air through a

narrow throttle. Fuel pulses can be altered for a lean burn when acceleration and torque

demand is low, a stoichiometric burn for moderate driving, or a rich burn for cold starts or

when increased power is demanded.

Direct injection not only allows for precise mixture control, but it can also allow us to

more easily vary the distribution

of the mixture throughout the charge, defining rich and

lean areas of the combustion chamber, though not all GDI systems are capable of this. It

is this characteristic that allows for a very lean operation without jeopardizing ignition

(Image 1.22). A charge with a consistent air–fuel mixture throughout its volume is called

a hom*ogeneous charge, and this is the rough characteristic of a conventional engine’s

intake. The challenge is that a very lean hom*ogeneous charge may not provide enough

fuel to initiate combustion at the spark plug. But the richness required to initiate combus-

tion may be excessively rich at low-load conditions and may invite knocking. So, our desire

to provide a much more lean charge at low loads can be achieved with a stratified charge,

defined by a cloud of rich mixture around the sparkplug tapering to a leaner mixture as

you move through the chamber. The ability to lean the mixture outside of the initial igni-

tion region significantly reduces the threat of knocking, allows for improved efficiency,

and so is a major potential benefit of GDI.

Achieving a precise stratified charge is no easy task. Injection takes place in the later

stage of the compression stroke, allowing a very short amount of time to deliver and vapor-

ize the charge. The required injection speed and pressure to make this happen requires

a high-pressure fuel delivery that can provide fuel at nearly 1,500 psi, some 30 times the

40–70 psi typically present in a port injection fuel manifold. Shaping the distribution of

IMAGE 1.22

Advanced ignition systems.

Very lean operation or extra EGR can improve efficiency, but it can also make achieving a reliable ignition of

the charge challenging. Advanced ignition systems can help address this challenge. For example, BorgWarner’s

EcoFlash system utilizes high-frequency ignition (HFI) to produce an extended corona discharge. The system

can ignite the hydrocarbons throughout the combustion chamber virtually simultaneously, allowing for the

precise and reliable ignition of a very lean charge. Comparing the corona image on the left to a conventional

sparkplug on the right gives a clear sense of the difference.

Image: BorgWarner

30 Automotive Innovation

this high-pressure injection is also a challenge, and has generally been accomplished with

three approaches: a wall-guided process that uses a specifically designed piston head and

the chamber wall to shape the injection spray; an air-guided process that relies on swirl

and tumble pattern; or a spray-guided process, using precisely defined mist from an injec-

tor adjacent to the plug to place a rich cloud directly at the plug location.13 While any

direct-injection system will have some characteristics of each of these approaches, each

system typically adopts one as the primary determinant of chamber dynamics.

A wall-guided, or geometry-guided, approach has the advantage of allowing the great-

est amount of time between injection and ignition, since injection begins much earlier in

the compression stroke. Typically, the injector is located at the side of the chamber near

the intake valves, with the spark plug at the center of the chamber. Proximity to the intake

valves allows the fuel spray to mix with the incoming air more easily, and helps keep the

injector cooler. A specially designed piston head receives the injection spray and shapes

it in the combustion chamber as it moves upward (Image 1.23). Often a deep bowl pis-

ton head is used. The challenge is that this piston geometry can make the attainment of

a hom*ogeneous charge more difficult. And, the spraying of fuel directly on the piston

and cylinder walls can lead to incomplete vaporization, or wetting, and resulting higher

emissions of CO and unburnt hydrocarbons.14 As a result, this approach is not typically

used alone.

An air-guided system is similar, though the swirl of the intake is more definitive in

shaping the charge, so the design of the inlet ducts becomes more critical and the shape of

13 G. Fiengo, A. di Gaeta, A. Palladino, and V. Giglio, Common Rail System for GDI Engines. Springer Briefs in

Electrical and Computer Engineering. Springer, London, 2013.

14 G. Fiengo, A. di Gaeta, A. Palladino, and V. Giglio, Common Rail System for GDI Engines. Springer Briefs in

Electrical and Computer Engineering. Springer, London, 2013.

IMAGE 1.23

Piston crown.

A wall-guided GDI system relies on the interaction of the injector spray pattern and piston head geometry

to shape the incoming fuel charge. The shape of the piston crown in this Buick Enclave engine is designed to

receive the injector spray.

31Bringing the Fire

the piston head less so. The intake ports are specifically designed to develop the targeted

swirl and tumble pattern, often oriented more vertically and using baffles or narrowing

to define a distinct tumble pattern that will help concentrate the fuel mixture at the spark-

plug. In some systems with two intake valves, only one value operates in stratified mode,

to allow for a more defined, high-velocity pattern. The challenge is that while the piston

head geometry is not as vital to defining the charge geometry and so piston wetting is

reduced, a flow-guided system does not fully resolve the performance and efficiency limits

at high load previously mentioned.

These challenges can be largely met with more recently developed spray-guided GDI

systems. This approach locates the injector close to the spark plug in the center of the

chamber and can therefore define more precise spray dynamics (Image 1.24). This allows

for a more reliable and symmetrical fuel distribution and more effective utilization of the

air charge, and so results in the best efficiency and performance at differing engine speeds.

Better injector control can also eliminate wetting and allow for a much higher level of EGR,

as the rich cloud around the sparkplug will avoid the misfire otherwise associated with a

higher level of exhaust gas in the chamber. However, the injector location next to the spark

plug presents some challenges as well. It can cause undesirable heating of the injector and

IMAGE 1.24

Mazda SkyActiv fuel injection.

Mazda uses a notable piston cavity to define a stratified air–fuel mixture around the spark plug. This allows

delayed ignition timing during warm-up to speed emissions system warming and helps avoid the flame front

contacting the piston head too soon.

Image: Mazda

32 Automotive Innovation

lead to plug fouling and soot formation. The soot deposit can also lead to disturbed injec-

tor orifices and thus compromised spray patterns. So, while a spray-defined system can

offer greater efficiency, it also requires not only a robust sparkplug that can accommodate

the thermal stress of repeated cooling and heating, but a very precise control of the fuel

delivery (Image 1.25).

The needed precise control is provided by what is called a piezoelectric injector. This

injection technology utilizes a crystalline material that we will see a lot of in advanced

automotive components. Within the crystalline structure are opposing positive and nega-

tive charges, called dipoles. When the crystal is exposed to an electric charge these dipoles

react, and the material physically expands. In this case, this expansion can be used with a

levering mechanism that amplifies the movement to open and close an injector orifice. The

result is far more precise control of the fuel spray, with pulses as short as a few millisec-

onds. Classic solenoid injectors utilize electromagnets to actuate injection pulses. While

cost-effective, this technology has a longer response time and is not capable of graduated

control, making it difficult to provide the precision spray needed for GDI systems. By con-

trast, varying the voltage applied to piezo injector allows for variation in the extent of the

reaction and regulated control of the injector opening. The result is a highly responsive

very precise delivery of

fuel that can accurately control the volume of fuel injection, from

1 to 150 mg/pulse. This also enables the delivery of multiple pulses per cycle, called split

injection, and can enable very lean operation.15

15 C. Park, S. Kim, H. Kim, S. Lee, C. Kim and Y. Moriyoshi, Effect of a split-injection strategy on the per-

formance of stratified lean combustion for a gasoline direct-injection engine. Proceedings of the Institute of

Mechanical Engineers: Journal of Automotive Engineering 225 (10), 2011, 1415–1426.

IMAGE 1.25

The piezoelectric injector.

This piezo common rail injector by Continental offers an impressive example of a cutting-edge piezoelectric

application. With an ability to handle pressures over 36,000 psi (2,500 bar), a piezo-servo drive, and self- adjusting

servo valve and needle control, this unit can provide extremely precise fuel regulation, variable injection pat-

terns and up to ten injections per cycle. All of this means more precise control, which translates to improved

fuel economy and reduced emissions.

Image: Continental AG

33Bringing the Fire

Split injection can enable a small preinjection during the intake stroke, for example,

which can help cool the combustion chamber. This allows for the exploitation of what is

called the heat of vaporization, defined by the heat absorbed by the fuel as it transitions

from suspended liquid droplets to a vapor. As the atomized fuel in this preinjection pulse

vaporizes it absorbs heat energy, not unlike the heat removed from your body as perspi-

ration evaporates. This cooling increases the density of the air in the cylinder and more

importantly helps avoid knock by cooling the combustion chamber.16 The remaining fuel

is delivered later with a longer pulsation. In some diesel engines, piezoelectric injectors

can provide up to seven injections per cycle.

The use of high-pressure direct injection does not exclude the use of lower pressure port

injection; in fact, the two can be used to compliment each other. So, while direct injec-

tion offers a cooler combustion chamber and so helps avoid knocking, a port injection

system can cool the incoming air and thus allow for its increased density and a resulting

improved air intake efficiency (see the next chapter for volumetric efficiency). This allows

the best of both worlds. The cooling effect of GDI on the combustion chamber can reduce

knocking and potentially allow for a higher compression ratio for greater efficiency. And

by allowing more time for the fuel to vaporize, port injection can reduce some of the chal-

lenges of exclusive direct injection. Direct injection can deliver fuel at high engine loads,

when chamber cooling is important, and a combination can be used at lower loads to help

keep injectors clear and efficiency high.

Combining DI and PI can also avoid some of the challenges of direct injection alone.

The need to deliver some 50 times the fuel pressure required by port injection systems

can result in increased engine noise. In addition, while not universal, there is potential

for more pronounced carbon buildup on some GDI engines. By injecting fuel directly on

the backside (or tulip) of the valves, port injection actually helped keep valves clean. This

effect is lost when the fuel is injected directly in the cylinder. More critically, during rapid

acceleration, a GDI system will be challenged to transition quickly from low-end stratified

charge to a rich hom*ogeneous charge as the engine accelerates. Combining GDI with PI

can help address each of these issues. The combination can also allow for other innova-

tions. For example, the Toyota’s D-4S engine couples this with slits on the side of the injec-

tor that are periodically charged to blow the carbon off the outside of the injector as an

automated self-clearing mechanism.17

Mercedes has been using a cutting-edge form of multiple method fuel delivery, called

Turbulent Jet Injection (TJI) in its F1 cars since 2014; Ferrari is looking to follow suit soon.

TJI replaces the spark plug with a jet injector inside a small ignition chamber (Image 1.26).

While the main combustion chamber is supplied with the majority of the charge, about 3%

of the fuel is injected in this small adjacent chamber, providing an excessively rich mixture

around the plug. Ignition triggers a rapid flame jet streaming through precisely defined noz-

zles into the main combustion chamber. The fuel is ignited simultaneously at several points

in the top chamber, causing more effective combustion, more power, and lower emission

while avoiding knocking. This allows for an ultra-lean burn, with a fuel–air ratio exceeding

29:1 (λ = 2), and theoretically approaching 60:1. Several manufacturers have worked over the

past two decades to define an ultra-lean burning engine that would be highly efficient and

clean. The availability of precision fuel injection has now made that possible.

16 S.P. Chincholkara and Dr. J.G. Suryawanshib, Gasoline direct injection: An efficient technology. 5th

International Conference on Advances in Energy Research, ICAER 2015, December 15–17, 2015, Mumbai, India

Energy Procedia 90 2016, 666–672.

17 C. Schweinsberg, “Toyota Advances D4S with Self-Cleaning Feature on Tacoma.” Wardsauto.com August 27,

2015.

http://Wardsauto.com

34 Automotive Innovation

Low-Temperature Combustion

Similar technology is being explored to pursue the possibility of what is called low-

temperature combustion (LTC). The idea is a gasoline-fueled engine that operates with

compression ignition like a diesel, and so burns at a much lower temperature. The goal

is to reduce the heat of combustion so that we can dramatically reduce the generation

of harmful NOx caused by excessive heat, or PM caused by excessive richness, and reap

higher fuel efficiency. Some of these aims are achieved in current production cars with

EGR, recirculating about 10% of the exhaust gas back into the combustion chamber to cool

the combustion chamber. This is a well-established technology. But a promising route for

significant further improvement is to design a gasoline engine that can capture the sort

of thermal efficiency that has long existed in diesel engines, while avoiding the emissions

challenges of diesel fuel. Because gasoline offers a much lower autoignition temperature

than diesel, this sort of design could only be possible with the precise fuel and combustion

control offered by modern fuel systems.

hom*ogeneous charge compression ignition (HCCI) is being examined as a possible

path to this sort of ultra-efficient combustion. A lean, well-mixed fuel–air charge in the

intake stroke is ignited by the heat of compression rather than a spark plug. Again, the

hope is to achieve the efficiency of a diesel engine with the emission of a gasoline engine.

With rising pressure and even mixture distributed throughout the combustion chamber,

ignition takes place as a spontaneous reaction throughout the cylinder, producing a rapid

IMAGE 1.26

Turbulent jet injection (TJI).

The TJI system replaces the spark plug with a small precombustion ignition chamber that can trigger a rapid

flame jet ignition into the main combustion chamber.

Source: Mahle

35Bringing the Fire

and distributed pressure rise rather than a flame front. The low temperature and fast reac-

tion means very low production of NOx.

A key to making this work is in the fuel. In HCCI, all fuel has to fully vaporize prior to

the reaction, or remaining liquid droplets will lead to undesirable emissions. Even more

importantly, fuel characteristics are critical to ignition timing in HCCI, since the system

relies on spontaneous autoignition, without the timing assistance of either a spark plug or

a timed injector. So, in HCCI fuel chemistry plays a determinant role. Since the charge is

definitively uniform, variations in fuel mixture or vaporization distribution that shaped

spark ignition engines do not exist. As you might guess, typical pump gasoline is generally

not precise enough for such a system. The imprecise autoignition point of pump gas makes

it hard to achieve a predictable ignition, particularly at low load. Instead, a precisely engi-

neered fuel with a well-defined octane rating is needed. All of this means HCCI needs very

accurate control. And HCCI experiments in the laboratory, where control is relatively easy,

have at times lead to more CO and more unburned fuel in the emissions.18 A turbocharger,

which we will discuss in the next chapter, can help produce more complete combustion by

providing more air to the combustion chamber to help ensure that all the fuel is completely

burned. But, ensuring a complete and controlled HCCI burn remains a challenge.19

The challenge is that we need to provide a mixture that is rich enough to support autoig-

nition, but not so rich that it can’t all be efficiently burned once combustion has started. A

solution might come from stratified charge compression ignition (SCCI). At partial loads,

the mixture can be leaned to ensure efficiency. If combined with compression ignition

technology, the result could be highly efficient.

The trick is that we need to be able to ensure a desirable burn under varying engine

conditions and loads. The perfect compression ignition engine really needs a fuel that is

somewhere between gasoline and diesel, and the precise point changes as the engine load

changes. A diesel engine defines a precise ignition point by injecting the fuel late in the

process, timed to generate the targeted ignition sequence. But, this generates plenty of NOx

and soot. Gasoline typically produces less NOx and soot, but ignition through compression

is hard to control. Current research in what’s called Reactively Controlled Compression

Ignition (RCCI) tries to bridge this by providing a primary charge of gasoline through port

injection and a smaller secondary injection of diesel through direct injection. Fuel reactivity

could even potentially be precisely controlled with multiple injections of diesel to produce

a specific gradient of fuel mixtures in the squish region and outward. Or an alternative fuel

with a more defined octane rating might be used to more precisely determine the ignition

point.20 The result is high efficiency and low emissions, possibly the best of both worlds.

18 A.A. Hairuddin, A.P. Wandel and T. Yusaf, An introduction to a hom*ogeneous charge compression igni-

tion engine. Journal of Mechanical Engineering and Sciences 7 (December), 2014, 1042–1052; and P. Kumar and

A.Rehman, hom*ogeneous charge compression ignition (HCCI) combustion engine—A review. IOSR Journal

of Mechanical and Civil Engineering 11 (6) Ver. II, 2014, 47–67.

19 S. Saxena and I.D. Bedoya, Fundamental phenomena affecting low temperature combustion and HCCI

engines, high load limits and strategies for extending these limits. Progress in Energy and Combustion

Science 39, 2013, 457–488; M.M. Hasan and M.M. Rahman, hom*ogeneous charge compression ignition

combustion: Advantages over compression ignition combustion, challenges and solutions. Renewable and

Sustainable Energy Reviews 57 (May), 2016, 282–291; and M. Izadi Najafabadi and N.A. Aziz, hom*ogeneous

charge compression ignition combustion: Challenges and proposed solutions. Journal of Combustion

57(May), 2013, 1–14.

20 S. Saxena and I.D. Bedoya, Fundamental phenomena affecting low temperature combustion and HCCI

engines, high load limits and strategies for extending these limits. Progress in Energy and Combustion Science

39, 2013, 457–488; and S.L. Kokjohn, R.M. Hanson, D.A. Splitter and R.D. Reitz, Fuel reactivity controlled com-

pression ignition (RCCI): A pathway to controlled high-efficiency clean combustion. International Journal of

Engine Research 12 Special issue paper 209.

36 Automotive Innovation

If this sounds like science fiction, it’s not. Ford has looked at an ethanol boost ‘Bobcat’

Engine to possibly replace its 6.7 liter diesel in its super duty truck. The ethanol boosting

system (EBS) runs as a typical port injection gasoline engine at modest loads. But to meet

high-load demands, the engine injects E85 ethanol from a separate tank. With the high

octane and cooling capacity of E85, the engine can accommodate more compression and

produce more power on demand. The engine isn’t ready for prime time, but Ford and

others are looking for ways they can provide all the power and torque of diesel, with-

out all the expensive diesel emissions treatment equipment. Just as impressive, Mazda

is placing a variant of an HCCI engine in its next-generation Mazda 3, defining the first

production car with a form of gasoline compression ignition. Its supercharged SkyActiv-X

engine will offer an ultra-lean burn mode that can decrease emission by nearly a third, the

manufacturer claims (Image 1.27).21

21 A. Stoklosa, “Driving Mazda’s Next Mazda 3 with Its Skyactiv-X Compression-Ignition Gas Engine.” Car and

Driver September, 2017.

IMAGE 1.27

Spark-controlled compression ignition.

Mazda’s SkyActiv-X engine offers what the carmaker is calling a spark-controlled compression ignition (SPCCI)

engine. The aim is to combine the reliability and reduced emissions of spark ignition with the fuel economy of

compression ignition. While the idea of spark-controlled compression ignition may seem oxymoronic, the basic

principle is a sort of hybrid of spark and compression ignition that can offer improved efficiency by enabling a

lean mixture to burn more evenly and reliably. Ignition is initiated by the spark plug, which raises the cylinder

pressure so that the remaining lean charge in the cylinder ignites via compression. Under conditions when

compression ignition is not ideal, the engine can shift back to traditional spark ignition.

Image: Mazda

37Bringing the Fire

None of these innovations would have been possible a generation ago. All of them

require a more sophisticated engine management system that can precisely determine the

vehicle’s driving conditions and engine parameters, and deliver fuel exactly as needed.

Taking into account torque demand, engine speed, and other operating parameters, the

engine management system can alter the fuel and type of charge to suit changing con-

ditions. A hom*ogeneous charge could be used for improved emissions throughout the

range. At a modest torque range, a simple stratified charge can be implemented, adding

EGR at low torque range to improve emissions. When more power is desired, a duel injec-

tion could occur, defining a hom*ogeneous charge in most of the cylinder and a localized

enriched charge near the plug. This sort of control capacity has fundamentally altered the

possibilities for the internal combustion engine, and is the subject of the next chapter.

http://www.taylorandfrancis.com

The End of Compromise

For a century, automotive engine design has been a game of compromise. Designing an

engine for high engine speed meant it would be rough and inefficient at low speed. An

engine designed for low-end torque meant limited high-speed performance. Similarly,

anintake designed for efficient cruising often meant compromised acceleration. Or a high

compression ratio meant for efficient cruising could invite knocking in high-end operation.

However, the enhanced control capacity made possible with more sophisticated micro-

processors and advanced materials and design are quickly making such compromises a

thing of the past. Increasingly, we are able to change the fundamental characteristics of

the engine while it’s running, to effectively remake the engine into what we want when

we want it.

Advanced Digital Control

A fundamental element that has made this possible is the use of increasingly powerful

computer systems that manage and actually modify the basic characteristics of the engine

while it operates. This has allowed for an ever-increasing level of control and innovation.

These dedicated computer systems, or embedded systems, function with an array

actuators, sensors, microprocessors, controllers and instruments to replace and enhance

mechanical functions with more precise and smarter electronics. So, they add considerable

functionality and capacity to today’s automobile, but they also add complexity.

While enhanced digital control has reset the bar for automotive performance and rede-

fined what’s possible, it’s also worth noting a few challenges as we begin. Automotive

digital control technology has developed irregularly, and its evolution is far from com-

plete. Multiple stand-alone control units marked the early adoption of embedded systems,

and soon progressed to an array of microcontrollers, sensors, and associated functions.

Like the broader systems overall, the software has developed incrementally, without a

clear overarching architecture or plan.1 The result is somewhat of a technological patch-

work quilt in the modern car. Each manufacturer defines a distinct control architecture,

with their own priorities, approaches, and functions. A typical automobile manufactured

today may have well over 100 electronic control units (ECUs), with multiple intercon-

necting buses that allow devices to communicate with each other. Because each hardware

component typically includes its unique software, every new function or feature of a car

usually means the introduction of an additional control unit. The result is what can be

called a highly heterogeneous system architecture; and the resulting challenge of software

1 R. Hegde, G. Mishra and K.S. Gurumurthy, Software and hardware design challenges in automotive embed-

ded systems. International Journal of VLSI Design and Communication Systems 2 (3), 2011, 164–174.

40 Automotive Innovation

integration and development has been overwhelming, with tens of millions of lines of

code, and thousands of signals travel between different ECUs.2

As cost, complexity, and redundancy increase and ECUs reach the limit of their pro-

cessing power, interest increases in developing a more integrated control architecture for

vehicles with organized interconnected networks and serial sharing of data and infor-

mation.3 The up-integration of control functions, use of more powerful microcontrollers

that can manage multiple functions, multicore processors that can allow one control unit

to take on a greater number of operations, integration of functions located near each into

single controllers, and other innovations promise to cut the inefficiency, complexity, and

cost of current automotive digital systems significantly.4 In the same vein, an international

effort to develop a universal software architecture for vehicle systems, called Automotive

Open System Architecture Consortium (AUTOSAR), could allow for improvements and

additions of functions to a vehicle without the high initial time and cost investments.5 The

appeal of a standardized modular system with standardized interconnects and scalability

is clear.

Still, while there are some challenges to work out, the digitalization of the automobile

also offers unprecedented opportunity. Just about every aspect of the modern automobile

has become ‘smarter’, including not just the engine, but also the transmission, brakes, sus-

pension, steering, safety features, and the increasing sophisticated infotainment system.

Most notably, the engine control module (ECM) of a modern car receives signals from

dozens of sensors to actively adjust ignition timing, intake parameters, fuel mixture, injec-

tion pulses, and other variables to more ideally tune the engine for enhanced performance,

fuel economy, and emissions reduction. This requires ongoing communication between

a processor capable of running millions of processes a second with an array of sensors

that measure the mass of incoming air, the fuel mixture, engine knocking, system voltage,

engine temperature, oil pressure, atmospheric pressure, vehicle speed, exhaust quality,

crankshaft position, camshaft position, and many other factors. It gets complicated for

sure, but the result is a car that is better, cleaner, and more efficient than ever thought

possible.

Sensor Technology

Understanding the new digital landscape requires that we first understand what infor-

mation we’re working with and what sensors are in place. And there are many. Either

optical or magnetic sensors are used as crankshaft position sensors (CKP) and cam-

shaft position sensors (CMP) to allow tracking of rotation within a very few degrees.

Updated versions of engine coolant temp sensors (ECT), throttle position sensors (TPS),

2 R. Coppola and M. Morisio, Connected car: Technologies, issues, future trends. ACM Computing Surveys 49 (3),

2016, 1-36; and A. Sangiovanni-Vincentelli and M. Di Natale, Embedded system design for automotive applica-

tions. IEEE Computer Society 40 (10), 2007, 42–51.

3 “Automotive Technology: Greener Vehicles, Changing Skills.” Electronics, Software and Controls Report,

Center for Automotive Research (CAR), May 2011.

4 Ibid; and R. Hegde, G. Mishra, and K.S. Gurumurthy, Software and hardware design challenges in automotive

embedded systems. International Journal of VLSI design & Communication Systems 2 (3), 2011, 165–174.

5 J. Schlegel, “Technical foundations for the development of automotive embedded systems.” Available at: hpi.

de/fileadmin/user_upload/fachgebiete/giese/Ausarbeitungen_AUTOSAR0809/Technical_Foundations_

schlegel.pdf

hpi.de/fileadmin/user_upload/fachgebiete/giese/Ausarbeitungen_AUTOSAR0809/Technical_Foundations_schlegel.pdf

41The End of Compromise

vehiclespeed sensors (VSS), fuel pressure sensors (FPS), and others provided a more pre-

cise, responsive, digitized version of the mechanical sensors we once relied on. It is no lon-

ger sufficient to simply measure coolant temperature; modern vehicles now continuously

monitor intake air temperature, outside air temperature, engine coolant temperature, oil

temperature, transmission fluid temperature, and exhaust temperature. Other sensors are

more distinctly new and innovative, measuring manifold air pressure, engine knocking,

and emissions quality.

A key variable in engine control is the mass of incoming air. A manifold air pressure

(MAP) sensor functions like a strain gauge, sensing the slightest deformations of a sensing

element to measure air pressure. Older systems used a combination of MAP and the engine

speed to calculate the approximate amount of air entering the engine. More recently, mass

airflow (MAF) sensors allow for a direct and more accurate measure. Because air changes

its density with temperature, simply measuring the volume of air entering an engine

would not be sufficient. It would miss the thinning of the air with rising temperature or

altitude and so be inexact. An MAF sensor suspends a heated wire in the path of incoming

air. The electrical resistance of the wire changes with temperature, so by precisely measur-

ing the change in resistance of this heated wire, we are able to assess the cooling effect of

the mass of air passing the wire. The integrated circuited converts the resistance reading

to a useful signal and the ECM is able to calculate the mass of incoming air quickly and

with precision. Cool, right? (Image 2.1).

As discussed in the previous chapter, the ability to identify detonation or preignition is

vital to engine control, and accomplished with a knock sensor (KS). Typically located in

the engine block or head, this sensor allows the ECM to adjust engine timing to resolve

knocking. Piezo materials make this possible. You’ll remember from Chapter 1 that piezo-

electric materials alter their shape when exposed to a charge. This also works in reverse,

when the crystal experiences a change in its shape, it generates an electric charge. When

squeezed or shaken (or knocked), the dipoles are disturbed, and rearrange, resulting in a

small electric charge across the crystal. That charge sends a signal to the ECM, which then

knows to adjust timing.

IMAGE 2.1

Measuring air.

This mass airflow sensor (MAF) uses a ‘hot wire’, a heated wire with a resistance that changes predictably with

temperature, to measure the cooling effect of incoming airflow. This then allows us to know the air’s mass.

42 Automotive Innovation

A key in defining a cleaner car, and correctly managing the fuel mixture, is the ability to

assess the emissions from the engine, and thus enable responsive management of the fuel

mixture. The oxygen sensor, also called a lambda sensor, does this by evaluating oxygen

content in the exhaust. The sensor usually consists of a thin, thimble-shaped component

of ceramic zirconium dioxide (ZrO2) coated with platinum on either side. The thimble is

placed in the exhaust pipe, so one side is exposed to the exhaust gas and one side is exposed

to outside air. The difference in exposure to oxygen causes a chemical reaction that pro-

duces charged particles of oxygen (ions) traveling through the ceramic membrane. As the

difference in oxygen levels on the two sides varies, so does the flow of ions. This produces a

voltage difference, not unlike a tiny battery, but in this case called a Nernst cell. You might

also think of this as a difference in the pressure of oxygen on either side of the sensor,

leading to a flow of oxygen particles across the zirconium dioxide. The resulting voltage

difference won’t tell you the actual percentage of oxygen, but it does allow you to identify

changes in oxygen concentration compared to the outside air, and that’s good enough to see

if the engine is burning lean or rich. When the mixture is rich, there is very little oxygen left

in the exhaust and the voltage increases. When the mixture is lean, more oxygen is left in

the exhaust and a lower voltage results. Because the membrane is only conductive at high

temperatures (600°F), a heating element is contained in the sensor housing. The exhaust

would eventually heat the sensor, but a heater allows for reliable readings sooner.

Of course, this description is partial, and highly simplified, highlighting a few charac-

teristics of the ECM architecture and some key sensors. Actual operation includes multiple

ongoing diagnostic routines providing continuous analysis, data, and communications

potential through the on-board diagnostic (OBD) system. It includes multiple modes

of communication between the powertrain, chassis, suspension, differential, and other

vehicle sensors and mechanisms. And, as we’ll see in Chapter 9, automotive control sys-

tems increasingly incorporate rapid expansion in the integration of echo detection sensors

such as radar, lidar, and sonar, as well as navigation and communication technology from

advanced GPS to automated vehicle-to-vehicle coordination, and countless additional fea-

tures. We will explore the possibilities and implications of these innovations later, but for

now, let’s look at how enhanced digital control has redefined the operation of the internal

combustion engine.

Engine Control

The automotive advances made possible through digital control are nowhere more impres-

sive than in the performance of the internal combustion engine. Let’s begin with three

primary aims to digital engine control: managing the fuel mixture, ignition timing, and

exhaust gas recirculation in engines so equipped. (We’ll see in a bit that other functions,

such as varying valve operation, are also in play.) Digital control allows for the identifi-

cation of distinct operational modes, based on driving conditions and driver demands,

with targeted engine parameters within each mode. Once again, this allows us to avoid

the compromises of previous generations, and define distinct targeted priorities and cor-

responding control logic for each mode. While manufactures differ in the precise differ-

entiation, most ECMs include some variation of seven basic modes: engine start, engine

warm-up, normal cruising with both an open-loop and closed-loop variation, high load

(acceleration), deceleration (often with a high and low variant), andidle.

43The End of Compromise

Upon engine initial start, the ECM crank control logic is automatically selected and

delivers the rich mixture required to start the engine, pulsing the fuel injectors to promote

a quick start up. The target air–fuel ratio will be determined by engine temperature, and

may vary anywhere from an extreme rich mixture of 2:1 to a modestly rich 12:1, as defined

by data stored in a programmable read-only memory (PROM). Engine characteristics will

change this greatly, of course; with a GDI engine potentially requiring a much less rich

mixture thanks to more precise fuel metering, for example. The ECM may also check bat-

tery voltage, to determine any needed operating compensation, as fuel injector timing and

response speed can be significantly affected by low voltage.

Once idle rpm is achieved, the ECM switches to idle mode, maintaining an air–fuel

ratio that ensures the lowest stable engine idle while avoiding stall. The thermostat will

ensure that the coolant is automatically recirculated through a short loop that bypasses

the radiator to assist in quick engine warm-up, as has been done for decades, but now an

electrically assisted thermostat can also manage the ideal temperature for optimal engine

operation dependent on initial driving demands. Called a MAP-controlled thermostat

since the Manifold Air Pressure sensor provides an indication of engine load to the ECM,

this feature allows the thermostat to alter warm-up parameters to suit engine load while

addressing combustion and engine temperature, NOx reduction, and fuel economy. While

this is done, the oxygen sensor is warmed, and idle speed, injector pulse duration, and

mixture are progressively adjusted to suit engine temperature.

Once the engine has warmed up, the ECM will enter open-loop operation, meaning that

the ECM will rely on limited sensor data and continue to use PROM fuel ratio data, some-

times called a lookup table, to manage fuel mixture until the O2 sensors can provide useful

information. This is not ideal, as the ECM principally uses engine speed to define igni-

tion timing without compensating for the important impact load has on proper timing.

Once the O2 sensors are warm and providing reliable information, signals from the oxygen

sensors in the exhaust can be used to modify mixture for ideal performance and clean

operation. So, the ECM can move from a feed-forward control to closed-loop operation

and begin to reduce emissions levels quickly. Because virtually every car manufacturer in

the US utilizes a three-way catalyst (TWC) for emissions management, which works best

when combustion is stoichiometric, keeping the fuel mixture at or near the stoichiometric

ratio is a key concern (Image 2.2). Using information from the MAF, the controller is able to

determine the airflow into the combustion chamber to manage the amount of fuel through

the injectors.

Unlike open-loop operation, closed-loop control allows for automatic adaptation to

mechanical conditions. The ECM is managing more than just mixture; it may be defin-

ing fuel injector pulse duration, spark timing, and multiple additional variables based

on engine temperature, MAF, barometric pressure, engine speed, knocking, and other

variables. Again, a key concern in this process is knocking. The ECM will automatically

advance spark timing to achieve improved performance. However, the desirability of spark

advance is limited by the threat of denotation. Once the KS identifies excessive knocking,

spark timing is moved slightly later, or retarded. Different manufactures do this differ-

ently; but generally, the ECM will drop the advance until knocking is eliminated, and then

progressively increase it

until the knock point is identified, allowing high-performance

operation at the cusp of the knock limit. The ECM may even make micro adjustments dur-

ing operation based on learned past knocking events, a practice Subaru called Fine Knock

Learning. Like many ECM functions, managing ignition timing while avoiding knocking

requires precise and fast-processing capacity, as the engine rotates a full 18° in a single

millisecond at 3,000 rpm.

44 Automotive Innovation

The ECM’s monitoring and responsive control is not limited to mixture and spark timing

of course. Multiple variables are monitored and the ECM may initiate additional adjust-

ments at this point. The ECM will initialize EGR, allowing a percentage of exhaust gas to

be cooled and recirculated into the combustion chamber in an effort to cool combustion

temperatures and reduce the production of NOx. The ECM may trigger the delivery of

secondary air to the catalytic converter to ensure complete combustion of remaining emis-

sion pollutants if it has a secondary air injection (SAI) system. System voltage may require

adjustment to fuel injector signals. More generally, a range of powertrain variations may

be initiated. For example, if the vehicle is equipped with a lock-up torque converter (we’ll

look at this in the next chapter), it may signal a solenoid to lock the clutch mechanism

and therefore eliminate efficiency-draining slip. In sum, closed-loop operation allows

for sophisticated control logic that ensures engine performance as operating conditions

change, both in the management of combustion and the vehicle more generally.

During high-load demand, signaled by the TPS or possibly an additional sensor that identi-

fies wide-open throttle, the ECM will again switch modes to provide a rich mixture that can

meet the demand for hard acceleration. This rich mixture will temporarily degrade emissions

control and fuel economy; but engineers and regulators view this as an acceptable compro-

mise to provide demanded acceleration, as acceleration capacity is at times needed for safety.

Upon deceleration, the ECM will lean the fuel mixture to allow for reduced emission

and improved fuel economy. This also helps avoid an exhaust backfire caused by excessive

rich mixture. If the deceleration is severe, the lean-out may be extended to a complete fuel

cut-off, allowing for more effective engine braking and reduced emissions. Signals from

the MAP and TPS will bring the ECM back into closed-loop mode quickly to avoid stall-

ing, or the ECM will return to idle control mode when the vehicle is stopped.

This might seem complicated, but it’s actually a highly simplified rendition of the ECM

operation. We’re not even considering the integration with the transmission operation,

IMAGE 2.2

Three-way catalytic converter operation.

Although NOx emission can be higher at a stoichiometric fuel ratio, the catalytic converter works most effec-

tively to reduce unburned hydrocarbons, carbon monoxide, and NOx at stoichiometry. So, in order to ensure a

clean burning car, the ECM targets stoichiometry in closed-loop operation.

45The End of Compromise

fuel system evaporative emissions control, cabin air conditioning and heating demand,

and a host of other variables and functions. But the principle point is clear: ECMs are

defining a move beyond conventional control practices. These are no longer single-input/

single-output systems (SISO). They define increasingly complex, multivariate operations

with sophisticated algorithms and multiple control strategies.6 Data from disparate sen-

sors are combined to create performance information that exceeds the capacity of any one

sensor, a process called sensor fusion. The resulting control structure moves toward a

form of artificial intelligence, with the ability to monitor, adapt, and modify control logic

by ‘learning’ from past outcomes. Future ECMs may determine what ignition timing, fuel

management, or response to knocking work best for your engine, or even your driving,

and adapt accordingly. We’ll see more on these sorts of systems in Chapter 9.

Variable Valve Actuation

All of this control technology has allowed for a level of management of the engine’s pro-

cesses that was unthinkable a generation ago. We’ve already seen the results of this in mix-

ture and ignition timing management, though it is perhaps even more impressive in the

control of valve movement, a variable that was once mechanically fixed with no possible

variation during operation. More varied and precise control of the valves allows us to once

again make an end run around the compromises that were once unavoidable. Where once

we had to make a tough choice in defining valve movement, now we can have our cake and

eat it too. We can design variable valve events that allow our cars to feel like a sports car at

high revs without sacrificing efficiency when cruising.

As discussed in the previous chapter, in the classic internal combustion engine, the

intake valve opens and closes during the intake stroke; and the exhaust valve opens and

closes during the exhaust stroke. The problem with this scenario is that the velocity of

incoming air does not vary to suit the engine speed. As the engine speeds up, like the

flame front, the speed of the incoming charge often cannot keep up. With a conventional

cam, the valve lifts from its seat pretty slowly, so while the valve may be ‘open’ it takes

some time for air to begin to flow freely through the opening. In fact, flow through an open

valve is significantly restricted for perhaps two-thirds of the total valve opening time.7 The

solution may be to keep the valves open longer, but it’s not that easy. The ideal valve opera-

tion changes with engine speed or load. In a perfect world, the opening and closing of each

valve could be timed to the precise needs of the engine at a given load.

A key variation in the operation of valves at high engine speeds and loads is to open the

intake valve earlier and close the exhaust valve later, defining valve overlap (Image2.3). In

addition to allowing more time for air movement, as discussed previously, it can enhance

scavenging, allowing the incoming charge to help push out the outgoing exhaust. Typically,

the opening of the intake valve (IVO) is timed to begin about 10° BTDC, to allow the valve

to fully open for the intake stroke. And, the resulting aggressive pulsation of pressure

in the exhaust manifold as all cylinders exhibit powerful cross flow can create pressure

waves in the exhaust manifold that can help actively draw the exhaust out of the cylinder.

6 H. Morris, Control systems in automobiles. In J. Haappian-Smith (ed) Modern Vehicle Design. Butterworth-

Heinemann, Oxford, 2001.

7 R. Stone and J.K. Ball, Automotive Engineering Fundamentals. SAE International, Warrendale, PA, 2004.

46 Automotive Innovation

At high engine speeds, this is desirable, but the advantages of a large overlap diminish at

low engine speeds. In fact, at low loads, keeping some of the exhaust in the combustion

chamber is actually a good thing. It means less incoming air is needed when the throttle

is more closed, decreasing pumping losses. And, like the effect of the EGR system, more

exhaust gas in the chamber at low loads can mean lower NOx emissions. In effect, this is a

bit like making the combustion chamber smaller at lower engine speeds.

The advantage of longer valve opening isn’t limited to the benefits of overlap. There is

also an advantage to an early exhaust valve opening. Ideally, we’d want to extract all the

power we can out of the expanding combustion gas before we open the exhaust valve.

However, pushing all the exhaust gas out of the combustion chamber also takes energy.

And, opening the exhaust valve before reaching the end of the power stroke can help us

save some of the energy required to push out the still-pressurized exhaust gas at the start

of the exhaust stroke, called blowdown loss. At high load and

108

Torque and Power ................................................................................................................ 110

Cooling .................................................................................................................................. 112

vi Contents

Induction Motor ................................................................................................................... 113

Permanent-Magnet Machines ............................................................................................ 118

Magnets ................................................................................................................................. 121

BLPM Control ....................................................................................................................... 122

Reluctance Machines ........................................................................................................... 124

Advanced Motor Possibilities ............................................................................................ 126

5. Electrified Powertrains ...................................................................................................... 131

Gas versus Electrons? .......................................................................................................... 131

Hybrid Drive ......................................................................................................................... 133

Baby Steps ............................................................................................................................. 135

Mild Hybrid .......................................................................................................................... 137

Full Hybrid ........................................................................................................................... 141

Adding a Plug ....................................................................................................................... 148

Power ..................................................................................................................................... 148

Electric Vehicle ..................................................................................................................... 151

Electric Car Viability ........................................................................................................... 155

Using Energy Effectively .................................................................................................... 160

6. The Electric Fuel Tank ....................................................................................................... 165

What’s a Battery? .................................................................................................................. 166

Battery Performance ............................................................................................................ 171

Battery Management ........................................................................................................... 172

Cell Balancing ....................................................................................................................... 175

Cooling Systems ................................................................................................................... 176

Battery Chemistry ................................................................................................................ 179

Nickel-Based Batteries ......................................................................................................... 181

Lithium .................................................................................................................................. 184

Future Possibilities............................................................................................................... 190

7. Automotive Architecture .................................................................................................. 195

General Chassis Design ...................................................................................................... 195

Frames ................................................................................................................................... 197

Crashworthiness ..................................................................................................................200

Materials ................................................................................................................................ 203

Alternative Metals ............................................................................................................... 210

Manufacturing Metal .......................................................................................................... 216

Plastics ................................................................................................................................... 218

Suspension ............................................................................................................................ 224

Chassis Control .................................................................................................................... 226

Bringing It All Together ......................................................................................................229

Modularity ............................................................................................................................230

8. The Power of Shape ............................................................................................................233

The Nature of Drag ..............................................................................................................234

The Power of Shape .............................................................................................................235

Boundary Layer .................................................................................................................... 237

The Shape of a Car ...............................................................................................................238

The Front of the Car ............................................................................................................. 240

viiContents

Addressing the Rear Wake ................................................................................................. 243

Three Dimensional Flow .................................................................................................... 247

Vortex Generators ................................................................................................................250

Lift .......................................................................................................................................... 251

The Ground ...........................................................................................................................253

Wheels ................................................................................................................................... 257

Bringing the Body Together ............................................................................................... 259

Active Aerodynamics .......................................................................................................... 261

9. Smarter Cars ........................................................................................................................ 265

Smarter Driving ................................................................................................................... 266

Perception.............................................................................................................................. 272

Radar ......................................................................................................................................

high engine speed, an early

opening of the exhaust valve will allow more time for the pressure inside the chamber to

drop before the piston begins to move up. But, in low-load conditions, the early exhaust

opening means lost energy and torque, since there’s plenty of time for the pressure to drop

before the exhaust stroke.

On the other end of the stroke, we can consider the closing of the intake valve. For great-

est power at high load, we would want to time the closing of the intake valve to ensure the

largest mass of incoming charge. You might expect this to be at the bottom of the stroke;

however, the incoming air through the intake manifold develops a momentum that has

the effect of pushing a wave of air into the cylinder, thus favoring a late closing of the

intake valve at high engine speeds. The intake pressure wave tends to maximize late in the

stroke. So, taking full advantage of this effect, and maximizing the mass of incoming air,

requires we close the intake valve a bit after BDC. At high rpm, this might be significantly

longer than at low power where a late valve closing might be detrimental as it diminishes

the compression stroke.

Similar challenges present themselves with defining valve lift. We might be tempted to

presume that maximum valve lift is always desirable, since this would allow for the least

restrictive flow when the valve is open and so faster intake flow and improved exhaust

exit. This is true at high rpm, but, at low rpm, there is a cost to high valve lift. High valve

IMAGE 2.3

Valve overlap.

Delaying the closing of the exhaust valve and advancing the opening of the intake valve create an overlap that

will allow for more effective scavenging of the combustion chamber by allowing cross flow of incoming air.

47The End of Compromise

lift means air can flow into the chamber slowly and calmly at low rpm, losing turbulence

and risking wetting.8 Additionally, at partial loads, a smaller valve opening reduces the

need for a more restrictive throttle, reducing pumping losses. So, while a smaller valve

opening is severely detrimental to the engine’s high-load performance, a high lift opening

can deteriorate low-load performance.9 In the past, we conventionally identified a lift pat-

tern that defined a compromise, but that’s no longer necessary.

Over the past two decades, control of valve timing and lift has become increasingly

more sophisticated. Systems that allow a basic phase change of the camshaft for discrete

high and low speed cam timing are now common. With a single cam, a valve phase change

can retard valve timing by roughly 10°, allowing for significantly improved high-load

operation with an earlier intake opening. If the engine has separate intake and exhaust

cams, each might be adjusted independently, allowing for greater allowance for engine

load and speed. However, while allowing for two or more discreet valve timing settings is

an improvement, the possibility of a progressive variation in valve timing to suit changing

conditions would be better (Image 2.4).

8 T. Wang, D. Liu, G. Wang, B. Tan and Z. Peng, Effects of variable valve lift on in-cylinder air motion. Energies

8, 2015, 13778–13795.

9 F. Uysal, The effects of a pneumatic-driven variable valve timing mechanism on the performance of an otto

engine. Journal of Mechanical Engineering 61 (11), 2015, 632–640.

IMAGE 2.4

Toyota dynamic force engine.

Toyota’s 2.0-liter, direct-injection, in-line, 4-cylinder engine uses advanced combustion control technology and

variable valve timing to achieve an impressive 40% thermal efficiency.

Image: Toyota Motor Company

48 Automotive Innovation

In fact, greater capacity for variation and control is possible. Cam profile switching

(CPS) typically uses two sets of distinct cam lobes, or otherwise shift between two distinct

cam profiles. As a result, both timing and lift can be changed. But once again, only as a

choice between two options, typically a close-to-conventional cam for normal operation,

and a cam designed for performance operation at high rpm. Manufacturers have defined

multiple sophisticated systems that can allow for control of both lift and timing, and can

offer incremental or continuous variable valve timing (VVT), variable valve lift (VVL),

or both. BMW, for example, uses a sprocket on a helical spline of the camshaft to progres-

sively adjust valve timing; and their Valvetronic variable valve system utilizes an electron-

ically adjusted cam and rocker arm to vary the relationship between the camshaft and the

valve stem allowing variation in valve lift from 0.3 to 9.7 mm (Image 2.5). This means valve

lift variation can be used to control engine speed, and once again eliminate throttling loss

from a conventional throttle.

There are nearly as many ways to accomplish VVT as there are manufacturers. Honda

was an early adopter of variable valve profiles with its VTEC engine. The engine switched

between two cam profiles, allowing smooth operation and efficiency at low rpm, with

greater performance possibilities when the engine switched to the more aggressive cam at

4,500 rpm. Honda’s recent engines include a three-stage VTEC with separate cams for low,

IMAGE 2.5

BMW’s VANOS variable valve timing system.

BMW’s VANOS variable valve timing system places a sprocket on a helical spline at the end of the camshaft.

The sprocket moves in and out with oil pressure, causing a progressive shift in the relative alignment of the

camshaft and thus a change in timing.

Source: BMW

49The End of Compromise

medium, and high engine speeds. GM’s Intake Valve Lift Control uses an adjustable cam

to shift the pivot point of the rocker arms and thus vary valve lift. FIAT’s MultiAir sys-

tem utilizes an electrohydraulic system, using pressurized engine oil to actuate the intake

valves, allowing for control of both lift and timing.

As mentioned, more complete control of valve events can allow for a change in the fun-

damental parameters of the engine’s operation, even redefining the basic four-stroke pro-

cess. Atkinson cycle engine operation offers a great example. The idea of an Atkinson cycle

has long defined a variation from the classic Otto cycle four-stroke engine. Dating back to

the mid-1800s, the basic idea is this: since there is more combustion power to be extracted

at the end of the power stroke, the Atkinson Cycle allows for a longer power stroke rather

than the equal length strokes of the Otto Cycle (Image 2.6). The extra piston travel allows

the engine to usefully extract more energy from combustion. The Toyota Prius was notably

the first to mimic this cycle in a production car by delaying the close of the intake valve.

This allows some of the intake charge to return to the manifold, effectively shortening the

intake stroke, and by relation, making the power stroke comparatively longer. The result

is a significant improvement in efficiency, but a loss of power. Compressing the incoming

air with a super or turbo charger can help compensate for this shorter compression stroke

and recover lost power, defining a variant called the Miller Cycle. Multiple car manufac-

turers now use VVT to produce a variant of this Miller/Atkinson Cycle. So, this isn’t just

about fine tuning engine operation; these systems are basically changing the fundamental

operation of the four-stroke engine on the fly as conditions warrant. Is it just me, or is that

really, really cool?

IMAGE 2.6

Atkinson cycle engine.

The Atkinson cycle originally dates to an idea initiated by John Atkinson in the mid-1800s. His design used a

multilink connection to allow for a significantly longer power stroke and a shorter intake stroke, allowing the

piston to harvest a greater proportion of the combustion energy than is possible when the two strokes are equal.

50 Automotive Innovation

Equally amazing, advanced valve control can effectively change the size of the engine

as needed, on the fly. The ability to effectively shut

down cylinders by closing both valves

Automotive innovation the science and engineering behind cutting edge automotive technology - Engenharia Mecânica (2024)