Conference Session A7
Paper #240
Disclaimer — This paper partially fulfills a writing requirement for first year (freshman) engineering students at the
University of Pittsburgh Swanson School of Engineering. This paper is a student, not a professional, paper. This paper is
based on publicly available information and may not be provide complete analyses of all relevant data. If this paper is used for
any purpose other than these authors’ partial fulfillment of a writing requirement for first year (freshman) engineering students
at the University of Pittsburgh Swanson School of Engineering, the user does so at his or her own risk.
APPLICATION OF REGENERATIVE BRAKING SYSTEMS IN MODERN
AUTOMOBILES
Nicholas Harn, [email protected], Budny 10:00, BryanPatrick Farren, [email protected], Lora 3:00
Abstract—In this paper, we aim to investigate the
origins of a popular type of regenerative braking known as
the Kinetic Energy Recovery System (KERS), analyze the
different ways to implement the system, and determine which
implementation would be most sustainable for the
environment. The KERS converts kinetic energy from a
braking vehicle into usable energy, which is then stored and
accessed later to increase fuel efficiency. Since regenerative
braking was developed by the racing community to increase
speed and efficiency, one may not expect it to be applicable to
the comfort-focused consumer vehicles that populate the
streets. However, KERS is even more useful on the road than
on the racetrack. If automakers can properly implement this
technology into their products, overall vehicle fuel efficiency
will increase beyond 30 percent and enter into an era where
significant reductions in carbon emissions are possible. This
research and development of sustainable technologies by the
automotive industry will benefit the environment and vehicle
owners who are looking to save money on fuel.
In our paper, we research regenerative braking by
investigating its origins, development, and applications,
particularly in the consumer market. We will compare various
methods of storing the energy generated by braking, and
evaluate which system would be most practical for everyday
use.
Key Words—Energy recovery, Fuel efficiency, Fuel sipper,
Hybrid Electric Vehicles, KERS Rechargeable hybrid battery
vehicle, Kinetic Energy Recovery Systems, Regenerative
braking
REGENERATIVE BRAKING: MAXIMIZING
AUTOMOBILE EFFICIENCY
On the road today, the average United States automobile
uses 14 to 30% of the energy found in gasoline to power the
vehicle down the pavement. This allows for efficiency gains
to be made in the automobile sector. Most of the inefficiencies
can be attributed to frictional forces found within the Internal
Combustion Engine (ICE) itself [1]. Moreover, braking
technology is equally inefficient. A paper from the Institute
of Electrical and Electronics Engineers revealed that “in
University of Pittsburgh Swanson School of Engineering 1
2-10-2017
urban driving, about one third to one half of the energy
required for operation of a vehicle is consumed during
braking” [2]. This energy, which is normally dissipated as
heat from the friction between the brake pads and discs, can
be stored and then used to propel the vehicle forward. This is
outstanding news for those looking to help the environment
and save money on gas. Automotive manufacturers decided
to begin implementing energy-saving technologies in their
vehicles to increase their efficiency. This led to the creation
of the modern-day Hybrid Electric Vehicle (HEV), which
uses regenerative braking to recapture energy lost from
braking. The goal of this invention is to reduce the amount of
wasted energy associated with automobile usage and to make
the most out of every gallon of gasoline, thereby increasing
the efficiency and sustainability of the vehicle. By burning
less fuel, the the vehicle will contribute less greenhouse gases
to the environment which can be appreciated by all who live
on this planet.
ENERGY RECOVERY: BRAKING FOR THE
FUTURE
Standard regenerative braking technology was first
implemented in the late 2000s to combat rising gas prices and
reflect a social shift towards sustainable design. During this
time, consumers hoped to minimize the amount of fuel they
consumed so that they could save money, conserve natural
resources for future generations, and reduce the effect of
carbon emissions on the environment [3]. Businesses took
note of this movement as the sales of environmentallyfriendly products increased and altered their practices to
reflect the social transition. Even the government joined the
cause for environmental awareness, passing legislation such
as the Corporate Average Fuel Economy standards to
decrease carbon emissions [5].
BryanPatrick Farren
Nicholas Harn
which converted the braking energy of the car into electrical
energy stored in a supercapacitor. Using technology like that
of the Prius, the racers can press a button that releases the
vehicle’s stored kinetic energy, giving them an additional 80
horsepower for 6.7 seconds per lap [8]. Overall, KERS has
reshaped the world of Formula One racing by increasing the
environmental friendliness of the sport and providing a speed
boost to racers. Like most F1 technologies, iterations of
KERS should slowly make their way to the consumer market.
The Kinetic Energy Recovery System
The Kinetic Energy Recovery System (KERS) is the
most commonly used form of regenerative braking in the
racing realm. Developed by the Formula One racing industry
to increase fuel efficiency and decrease lap times, KERS
stores a vehicle’s kinetic energy during braking instead of
releasing it as heat. This energy can later be used to accelerate
the vehicle, reducing fuel consumption by 10 to 25% [6].
Although KERS was developed for a racing scenario, various
commercial vehicle producers such as Nissan have
implemented KERS in their HEVs to decrease carbon
emissions [7]. All KERS follow the same principles of storing
and releasing energy, though the mechanisms used to
accomplish this task vary from vehicle to vehicle.
Figure 1.0
Chart of recent Hybrid Electric Vehicle sales [4]
However, consumers also desired to maintain their
comfortable lifestyles, and corporations wished to continue
making profits. This increased the sustainability of their
products, or the balancing of environmental, social, and
economic concerns when making decisions to produce the
best possible outcome for the future. Sustainability
manifested itself in various practices, such as reducing waste
without decreasing production, reducing the consumption of
resources without significantly reducing the consumption of
goods, and other forms of decreasing the negative footprint of
human activity.
One of the most common methods for accomplishing
these goals is to increase the efficiency of processes involved
in creating and using products. For example, if a vehicle
manufacturer developed a more efficient vehicle, consumers
would purchase less fuel, thereby saving both money and
natural resources. Demand for such a vehicle would most
likely increase, allowing the manufacturer to profit. This
increased demand for efficient vehicles occurred during the
2007 Recession, when the average fuel cost in the United
States was $3.57 per gallon and the sustainability movement
was in full-swing [5]. Manufacturers quickly responded to
this change in vehicle preference.
Vehicle manufacturers rushed to keep up with the high
demand for fuel efficient vehicles, and funding was pushed
towards the research of energy-saving technologies. One such
development was regenerative braking, which is based on
simple physics: When an electric motor is spun, it produces a
current [6]. Regenerative braking systems, such as those
found in the Toyota Prius and Nissan Leaf, slowly charge a
large battery pack by spinning the wheels’ electric motors in
reverse during braking [7]. Although this system i s the most
common, it is not a perfect design.
Some drawbacks to KERS include the cost, weight, and
complexity which are added to the vehicle. During the green
movement, the Formula One racing industry wanted to better
its public image by it introducing KERS in the 2009 racing
season. This first iteration of KERS was an electrical unit,
Harnessing the Energy of Braking
Variations of KERS use numerous technologies to
collect and store a vehicle’s kinetic energy. For example, a
HEV with a KERS decelerates by reversing its wheels’
motors, generating and storing electricity in the vehicle’s
battery. Similarly, an ICE vehicle connects its wheels to an
auxiliary flywheel through the car’s transmission, slowing the
rotation of its wheels and storing kinetic energy in the
flywheel [2]. Upon acceleration, a KERS releases its stored
energy, giving the vehicle a slight speed boost. This can either
be released by an automated system, like in a HEV, or
manually, as is done in a Formula One racecar [6]. Although
efficient in recapturing energy, no KERS provides the power
necessary to suddenly stop the vehicle during an emergency.
Therefore, all KERS must be supplemented with traditional
friction brakes [6]. This decreases the amount of energy
recovered, but drastically increases the safety of the vehicle
and its surroundings. Also, the practicality of a KERS
depends upon the situation in which it is used.
CONVERTING AND STORING KINETIC ENERGY
As previously mentioned, KERS come in a variety of
forms. These systems can be divided into two categories
based on the type of energy stored: mechanical and electrical
systems. As these classifications suggest, the electrical KERS
converts the vehicle’s kinetic energy into electricity, stores
said electricity within either a battery or a capacitor, and later
converts the energy back into kinetic energy [2]. In contrast,
2
BryanPatrick Farren
Nicholas Harn
a mechanical KERS stores the car’s kinetic energy directly
within a spinning auxiliary flywheel. Mechanical KERS are
usually used in ICE vehicles, such as Formula One racecars
or “Flybrid” busses, while electrical KERS are typically
found in HEVs [7]. Each has its own advantages over the
other in certain circumstances. For instance, Mechanical
KERS’ run the risk of mechanical failure, which can cause
damage to people and property, while Electrical KERS’ can
potentially harm mechanics and engineers via electrical
shock.
Flywheels are the most basic form of Mechanical KERS.
These mechanisms store kinetic energy by spinning a
weighted disk. When braking, a Mechanical KERS connects
an extra flywheel inside of the car to the vehicle’s wheels
through a continuously variable transmission(CVT). A
portion of the wheels’ momentum and kinetic energy is then
transferred to the flywheel, slowing the vehicle [2]. Once the
wheels cannot transfer any more energy to the storage device,
such as when the vehicle stops, the car’s transmission
separates the flywheel from the wheels, storing its kinetic
energy for later use. As long as the flywheel is made of
durable materials and kept in a sealed vacuum chamber, the
system’s friction is minimized and its kinetic energy is
effectively stored [7].
Electrical KERS
Electrical systems are the most common forms of
KERS. Found in various HEVs, such as the Toyota Prius and
Honda Civic Hybrid, Electrical KERS converts kinetic energy
into electricity by reversing the vehicle’s motors. An electric
motor turns by utilizing the relationship between magnetic
torque and electric current. When current travels through a
wire, it forms a magnetic field parallel to the wire’s surface.
This field exerts a force perpendicular to both the current and
the magnetic field. Therefore, if a current and a uniform
magnetic field pass through a wire that is drawn into a loop,
the resulting magnetic force spins the loop. An electric motor
operates by using this motion to spin another object, such as
a wheel. This relationship can also be used to generate
electricity: if a non-charged wire loop spins in a magnetic
field, a current will run through the loop. Similarly, an
electrical KERS recovers energy by using the wheel’s
momentum to spin a motor, generating a current. The
electricity is then either stored as electric potential energy
within a capacitor, or it is converted to chemical potential
energy and stored in a battery [2]. Once needed, the motor
accesses the battery or capacitor like its normal power source,
turning the vehicle’s wheels.
These devices take advantage of electrical components
already present within most HEVs, furthering the Electrical
KERS’ popularity. In fact, some Formula One racecars use
devices known as “ultracapacitors” as lightweight, durable,
and high-capacity energy storage units. An ultracapacitor is a
type of capacitor that utilizes a sheet of one-molecule thick
activated carbon as a dielectric instead of a ceramic or plastic
dielectric [2]. This layer drastically increases the device’s
capacitance, allowing it to store more charge than most other
capacitors. They also contain electrolytes similar to those of a
battery, increasing its energy density [10]. Ultracapacitors
even have longer lifespans than batteries and provide reliable
power at a greater range of temperatures [3]. Furthermore,
capacitors are designed to charge and discharge rapidly,
allowing them to harness the most energy during a sudden
stop. Batteries, although inefficient under such circumstances,
are five times cheaper than ultracapacitors. In contrast,
Mechanical KERS are three times as efficient as batteries and
only twice the cost [2].
Figure 2.0
Diagram of Volvo Mechanical KERS system [9]
When the vehicle accelerates, the flywheel is re-attached
to the wheels via a clutch system, transferring its momentum
and kinetic energy to the wheels. The released energy then
accelerates the car, requiring the ICE to work less and
therefore save fuel. These systems are astoundingly efficient:
a non-drivetrain mechanical KERS can have an efficiency
upwards of 80% [7]. In fact, carbon-fiber flywheels are
sometimes included in Formula One racecars to increase
vehicle efficiency and offer the driver a 10% power boost [8].
These devices are also safe for the environment, although they
are quite hazardous to both driver and bystander in the event
of an accident due to their high rotational velocities [7].
Comparison of KERS Variations
Although both types of KERS recover a vehicle’s
energy, Mechanical systems have multiple advantages over
Electrical systems and vice-versa. For example, flywheels are
lighter, smaller, and more efficient than batteries due to their
component materials and lack of energy conversions. They
offer a consistent power supply over a temperature span of 40 C to 150 C. In contrast, Lithium batteries only offer a stable
voltage from about -30 C to 60 C, and capacitors offer a
Mechanical KERS
3
BryanPatrick Farren
Nicholas Harn
constant voltage on an interval from -40 C to 70 C [2].
However, flywheel-based KERS can be especially dangerous
during an accident, since a KERS’ flywheel can spin at speeds
up to 60,000 rpm. If this disk were to break free from its
housing, it could damage the vehicle’s internal components
and injure anyone in the vicinity [7]. Therefore, the flywheel’s
vacuum chamber must be reinforced with stronger materials,
increasing the system’s overall weight and volume.
Battery and capacitor-based KERS are relatively safe
compared to the Mechanical system’s flywheels, since the
electrical energy is confined to the vehicle’s internal circuitry
[2]. The devices are only a danger to mechanics, machinists,
and others who may accidentally come into contact with the
system without proper protection. This is evident through an
incident in 2009 where a Formula One mechanic was
hospitalized after being shocked by a vehicle’s KERS [8].
Electrical devices also have higher energy densities than the
Mechanical systems, meaning that they store a greater amount
of energy per unit volume [3]. These systems even build off
of components already present in most vehicles, such as
motors and energy storage devices. As a result, they take up
less space in the vehicle. These systems involve far more
energy conversions, though, decreasing their efficiencies. For
instance, batteries must convert kinetic energy into electricity
and then change this electricity into chemical potential
energy. These conversions are often inefficient, allowing
some of the kinetic energy to dissipate as heat. Also, batteries
cannot absorb electrical energy as quickly as capacitors or
flywheels, reducing the amount of kinetic energy recovered
by KERS during rapid braking. As a result, batteries only
account for 5 percent of the total efficiency gains that would
be made by implementing all forms of KERS [2]. They
typically last a maximum of 10 years and contain materials
that are harmful to the environment if disposed of improperly,
making their mass implementation even more problematic.
However, they are the cheapest form of KERS energy storage
and do not require as many additional components as other
KERS, making them the most popular form of storage [2].
Ultracapacitors, on the other hand, are by far the most
expensive and efficient form of KERS. The devices are
lightweight, have long life cycles, and are almost 5 times as
efficient as batteries [2]. As previously mentioned, though,
they cost 5 times as much as a battery, detracting from their
popularity. This problem could be averted by using an electromechanical hybrid KERS.
One way to combine the benefits of multiple KERS
technologies is to combine storage technologies. If paired
with a battery KERS, a capacitor could extend the battery’s
life and increase the system’s overall efficiency [3]. This
system would then have the energy density of a battery, the
efficiency of a capacitor, and an increased influence on the
vehicle’s fuel consumption while being able to hold a charge
if the energy is not used immediately. The Audi R18 e-tron
Quattro Le Mans utilizes another hybrid KERS known as an
electric flywheel accumulator. This device converts the
vehicle’s kinetic energy into electricity, then stores the energy
by powering a motorized carbon-fiber flywheel [11]. This
saves space within the vehicle by replacing the Mechanical
KERS’ specialized, bulky transmission with wires and a
motor, thereby increasing the system’s energy density.
APPLICATIONS OF KERS
KERS and HEVs
In 2012, a survey was conducted regarding consumer
choices in fuel efficient vehicles. Participants were asked to
estimate the timespan required for an HEV’s reduced fuel
consumption to save enough money to balance its additional
cost relative to standard non-hybrid vehicles [12]. It
concluded that the average new car buyer expected a payback
period of about 2.5 years when deciding to spend extra money
on the more efficient hybrid car. This means the buyer
expected a return on his investment to cover the added cost of
purchasing a hybrid or fuel efficient vehicle within a 2.5-year
period [12]. Unfortunately, this is not the usual the case.
Using the US Department of Energy’s hybrid comparison
tool, it would take approximately 5.5 years to pay off the
additional $4,000 expense of purchasing a new 2017 Honda
Accord Hybrid sedan over the standard model, assuming the
price of fuel averages $3.00 per gallon [13]. This information
is crucial to understanding why hybrid vehicle sales
drastically dropped after fuel prices came down [14]. To
buyers, the investment into a hybrid drivetrain currently is not
worth the initial cost of purchasing a hybrid vehicle.
However, KERS can boost these sales by decreasing the cost
of a hybrid vehicle.
Energy recovery systems have already been
implemented in multiple HEVs, such as the aforementioned
Honda Accord and Toyota Prius. These cars are widely
renowned for their high fuel efficiencies and sustainable
technologies. However, the usage of battery-based KERS to
store and release kinetic energy could reduce the energy
consumption of these vehicles by 10 to 25% [6]. This would
increase the fuel savings of the HEV’s even further without
raising their prices significantly, since they would be using
the cheapest form of KERS. As a result, the demand for the
vehicles would most likely rise. This is evident through the
popularity of the Nissan Leaf, which utilizes an electric
KERS.
The Nissan Leaf uses a battery KERS to recover and
store its kinetic energy during braking. According to a
research paper by Alberto Boretti of RMIT University, the
fully-electric vehicle’s energy recovery system is 16 to 26%
efficient at a temperature of 9.7 degrees Celsius and 61 to 71%
efficient at a temperature of 22.2 degrees Celsius [11]. The
deviations with these values are due to the varying initial
temperatures of the KERS during the test. This data reveals
that an electrical KERS becomes more efficient as its
temperature increases. While most HEVs use the safer,
cheaper, and less efficient battery KERS, public
4
BryanPatrick Farren
Nicholas Harn
transportation vehicles tend to utilize the more powerful and
lightweight mechanical versions.
installation of their Flybrid system costs a quarter of the price
to produce a battery-powered hybrid system [18]. This is
wonderful news for thrifty, environmentally-conscious
consumers. When KERS is applied to public transport
vehicles, it allows bussing companies to decrease ticket prices
because of the reduced fuel usage. This has already been done
in Britain with the WrightBus Company, and concluded with
positive results. The WrightBus Company first tested the
durability of the Flybrid system by simulating 1,000,000
kilometers of use in a passenger bus [19]. Both companies
then tested a prototype bus outfitted with a Flybrid system in
March of 2015 and drove a daily route to determine its
benefits. The results proved that the Flybrid was a viable
method for sustainably decreasing carbon dioxide emissions
and fuel consumption. Following this, the bussing company
decided to implement the KERS into their vehicle fleet. One
of the deciding factors for the bussing company was that they
would no longer need to replace each vehicle’s battery pack
at regular service intervals if they utilized the flywheel
system. This decreased the cost of ownership and increased
the returns on the bus company’s investment. In May of 2016,
the company began using the Flybrid-powered busses on the
roads of Great Britain [20]. These advancements were
originally developed for racecars before they became
available on the commercial market.
KERS and Flywheel Vehicles
The automobile manufacturer Volvo, has recently begun
working with the Swedish government and a private company
named Torotrak to test a flywheel variant of KERS in one of
its vehicles. Their design is compact enough to fit in the
vehicle’s trunk, yet powerful enough to give it an 80horsepower boost during optimal conditions [15] [16]. Volvo
plans on focusing this development mainly on city driving,
where the constant acceleration and braking can drain a fuel
tank more quickly than smooth highway driving. The KERS
will assist the ICE during acceleration, which is the most
inefficient part of driving. What this means for consumers is
less stress on their engine during city driving along with
increased power during acceleration. Volvo claims that the
new system can subtract 1.5 seconds from the time taken for
the vehicle to accelerate from 0 to 60 mph and increase its fuel
efficiency by 25% [17]. Moreover, the company has dubbed
the new system a “financially viable and very efficient
solution” [15]. This technology hopes to give consumers the
best of efficient and sustainable travel; a powerful car with
high fuel economy ratings that remains cheaper than a typical
hybrid drivetrain to purchase.
KERS and Formula One Racing
KERS began as a cheap way to decrease lap times in
Formula One racing. According to an article published by the
International Journal of Control, “In the lead up to the 2008–
2017 Formula One engine development freeze, it was
estimated that an average of four milliseconds per lap were
gained for every million dollars spent on engine refinements”
[21]. This low return of investment sparked investigation into
new, cheap methods of increasing a vehicle’s average speed.
The racing teams experimented with various technologies,
including KERS, to gain an advantage over their opponents.
Eventually, KERS was made a common implementation in
the sport, as the technology raised vehicle efficiency,
improved the industry’s environmental credentials, and gave
drivers a speed boost that was necessary when overtaking
competitors [8]. One example of these vehicles is the Audi
R18 e-tron Quattro Le Mans. This vehicle, as previously
stated, utilizes an electric flywheel accumulator in its KERS
instead of the conventional battery or flywheel. More
specifically, it uses the “Williams Hybrid Power (WHP)”
energy system, a highly condensed, non-drivetrain
mechanical KERS. Similar versions of this technology are
theorized to be up to 80% efficient, although no data on this
particular variation has been accumulated as of yet [7]. As a
result of this unique system, the R18 e-tron Quattro can power
all four of its wheels simultaneously while retaining the
benefits of a two-wheel-drive powertrain [7]. Since the
widespread implementation of KERS in 2009, the Formula
One industry has inspired HEV producers, public
Figure 2.1
Volvo KERS system positioned in the trunk of test
vehicle [14.]
Before it began assisting in designing a flywheel system
with Volvo, Torotrak had been developing KERS
applications for years. Torotrak designs and manufactures
flywheel-based KERS for a variety of vehicles, including
those with consumer and commercial uses. The company can
install their ‘Flybrid’ KERS into a variety of vehicles, even if
the vehicle was not initially a hybrid. Also, they claim the
5
BryanPatrick Farren
Nicholas Harn
transportation departments, and even consumers to
investigate this up-and-coming technology. As a matter of
fact, luxury vehicle producers Jaguar and Volvo are currently
working with Flybrid Systems, a company that specializes in
manufacturing and installing flywheel KERS’, to make their
vehicles more fuel efficient [7]. However, every developing
technology comes with its fair share of risks.
be a dangerous addition to a vehicle. If properly implemented,
however, this technology can be quite helpful in the battle for
increased fuel economy and decreased carbon emissions.
Environmental Effects
Adding Kinetic Energy Systems to consumer vehicles
will significantly raise their overall efficiencies. This is
because the technology increases the distance a vehicle can
travel per gallon of gasoline consumed, thereby allowing the
cars to burn less fuel during operation [24]. By consuming
less fuel, vehicles with KERS will emit less carbon dioxide
into the atmosphere, improving air quality and preventing
environmental damage. This fuel-efficiency would also
conserve oil, a quickly depleting natural resource, by
decreasing demand for gasoline. However, KERS can be
quite dangerous to the environment if handled improperly.
For instance, the batteries used in most electric KERS drain
with use, gradually decreasing in efficiency as time passes.
After about 10 years of use, the device becomes so inefficient
that it must be replaced [7]. The dead batteries must then
either be disposed of or recycled by specialized facilities, as
they contain various hazardous chemicals. This requirement
would most likely cause environmental problems if KERS
were implemented on a large scale, since some regions may
lack the facilities needed to process the depleted batteries. The
batteries might then be disposed of improperly, allowing their
toxic contents to contaminate the surrounding water supply
[25]. This danger could easily be avoided by using other
forms of KERS, such as the flywheel or ultracapacitor. These
storage devices last far longer than batteries and do not pose
a hazard to the environment upon disposal [7]. Automakers
and vehicle owners should be aware of both the costs and
benefits of KERS when implementing the technology in the
future.
KERS’ EFFECTS ON THE WORLD
Vehicle Safety
Formula One racing is already dangerous enough.
Extraordinarily lightweight cars traveling at speeds over
100mph can be a recipe for disaster, especially when a crash
occurs. The added weight of the KERS could possibly
decrease the handling of the racing vehicles, which could lead
to more crashes in the sport. Also, with the high-voltage
electronic system on board, mechanics and drivers have an
increased chance of being shocked by the KERS battery. This
occurred during the 2009 racing season, where a BMW
mechanic was hospitalized after receiving an electric shock
from touching a racecar. Luckily the mechanic survived, as
the KERS’ in 2009 had only half the power of the modern
systems [8]. After this incident, the sport required vehicle
maintenance personnel to wear specialized rubber gloves that
block the flow of electricity to the user. Another example of
how an electronic KERS endangered mechanics is when a fire
erupted in the workshop of the Red Bull - Renault team. The
battery-powered system caught fire during development,
causing an evacuation of the testing facility [22]. Other lives
are also at risk with this technology, including the first
responders to accidents. In 2012, the Society of Automotive
Engineers published recommendations for emergency
personnel to follow in the event of a hybrid vehicle crash [23].
The document includes labelling suggestions for vehicle
manufacturers to follow, so that an EMT knows that the
vehicle is an HEV. Properly labelling a vehicle and its parts
could mean the difference between life and death for an owner
trying to save money on repairs, or a first responder trying to
save someone’s life. Although Formula One teams had the
choice to use electrical or mechanical systems during the 2009
season, all chose to use the electrical variation [22]. As a
result, little data exists on what might happen to a mechanical
KERS in the event of a collision.
Mechanical flywheel KERS’ introduce different safety
concerns than their counterparts. If a flywheel were to be
chipped or damaged while operating, it could disintegrate and
shoot pieces of metal or carbon-fiber at a high velocity.
Similar dangers forced Chrysler to cancel its hybrid racecar
project, the “Patriot”, in the 1990’s [7]. Ideally, the device
would be contained within a metal housing to prevent such a
disaster, but the housing must be sturdy enough to block the
shrapnel, adding weight to the vehicle. Also, if a crash were
to occur, the metal housing would likely be launched from the
vehicle, possibly injuring spectators [7]. In the end, KERS can
THE FUTURE OF KERS
Currently, the price of gasoline remains much lower
than it did at the time when KERS was born. This is reflected
in the current sales of hybrid vehicles, which have dropped
over the past few years [6]. However, government initiatives
still require automakers to decrease their carbon emissions in
order to preserve the environment. These initiatives include
the Corporate Average Fuel Economy (CAFE) standards,
which require that the average fuel economy of a vehicle
producer’s fleet reaches an annual minimum value. This
threshold is increased each year in the hopes of reaching an
average fuel efficiency of 50.8 miles per gallon by 2025 [5].
To meet this level of efficiency, automotive manufacturers
must remain keen on increasing their vehicles’ fuel
economies. This will in turn decrease the overall air pollution
produced by vehicles, creating a more sustainable future for
humanity.
Implementing KERS technology into modern vehicles
will be a giant step forward for the automobile. No longer will
6
BryanPatrick Farren
Nicholas Harn
[4] “U.S. HEV Sales by Model”. U.S. Department of Energy
Alternative Fuels Data Center. 1.2016. Accessed 3.31.2017.
http://www.afdc.energy.gov/data/10301
[5] “Vehicle Emissions Standards”. Congressional Digest.
11-2016.
Accessed
3.29.17.
http://web.a.ebscohost.com/ehost/pdfviewer/pdfviewer?vid=
12&sid=00c411a4-df9c-40a4-b56d1b7c3464309f%40sessionmgr4009&hid=4109
[6] C. M. Gonzalez. “What's the Difference Between Friction
and Regenerative Car Brakes? Let's Take a Closer Look at
Conventional Friction Car Brakes and How Electric Vehicles
Regain Energy with Regenerative Brakes”. Machine Design.
03-2016.
Accessed
01.10.2017.
http://go.galegroup.com/ps/i.do?p=AONE&sw=w&u=upitt_
main&v=2.1&id=GALE%7CA458260267&it=r&asid=16a9
84a925c63dedeb8d425ee12f32f7 P.42
[7] C. Sliwinski. “Kinetic Energy Recovery Systems in Motor
Vehicles”. IOPscience. 09.27.2016. Accessed 02.27.2016.
http://iopscience.iop.org/article/10.1088/1757899X/148/1/012056/pdf
[8] “Formula for Success - Kers and DRS”. BBC Sport.
11.26.2012.
Accessed
1.26.2017.
http://www.bbc.com/sport/formula1/20496330
[9] A. Stoklosa. “Volvo Testing KERS Kinetic Energy
Recovery Flywheels for its Lineup”. Car and Driver.
5.26.2011.
Accessed
3.31.2017.
http://blog.caranddriver.com/volvo-testing-kers-kineticenergy-recovery-flywheels-for-its-lineup/
[10] “Baltic Exchange; Manufacturing Ultracapacitors”. The
Economist.
10.15.2016.
Accessed
02.25.2016.
http://rt4rf9qn2y.search.serialssolutions.com/?genre=article
&title=Economist&atitle=Baltic%20exchange.&author=&au
thors=&date=20161015&volume=420&issue=9011&spage=
75&issn=00130613
[11] A. Boretti. “Analysis of the Regenerative Braking
Efficiency of a Latest Electric Vehicle”. SAE International.
11.27.2013. Accessed 03.01.2017 https://pitt-illiad-oclcorg.pitt.idm.oclc.org/illiad/illiad.dll?Action=10&Form=75&
Value=119145
[12] D. L. Greene, D. H. Evans, J. Hiestand. “Survey evidence
on the willingness of U.S. consumers to pay for automotive
fuel
economy”.
10.2016.
Accessed
2.28.2017.
http://www.sciencedirect.com/science/article/pii/S03014215
13003868
[13] “Can a Hybrid Save Me Money?”. US Department of
Energy.
Accessed
02.25.2017.
https://www.fueleconomy.gov/feg/hybridCompare.jsp
[14] B. Tuttle. “Why This Might Be the Beginning of the End
for the Toyota Prius”. Time Magazine. 01.06.2015. Accessed
02.02.2017. http://time.com/money/3654905/toyota-priushybrids-sales-decline/
[15] S. Siler. “Spin Doctors: Volvo Closer to Using FlywheelBased KERS to Boost Fuel Economy of Its Passenger Cars”.
Car and Driver Magazine. 03.26.2014. Accessed 3.1.2017.
http://blog.caranddriver.com/spin-doctors-volvo-closer-to-
the car remain a standard ICE and transmission setup. Now it
will be an even more elaborate device for transporting the
masses. Depending on the continued popularity of HEVs and
other energy-efficient vehicles, KERS’ future could go down
one of two paths. If sustainable vehicles continue to garner
support from the public, KERS may likely be implemented in
more cars. In fact, they may even be added to standard ICE
vehicles in order to increase their fuel efficiencies. According
to the US Department of Energy, 5 to 7% of the energy
produced by a car’s ICE is lost as thermal energy through
braking [1]. This inefficiency, which forces the vehicle to
burn more fuel and generate more carbon dioxide, may be
enough to warrant the implementation of KERS in ICE
vehicles. Flywheels would be perfect for this job, as they are
efficient and do not require additional electrical systems.
Meanwhile, batteries would most likely continue being the
staple of HEV KERS’ due to their relatively low prices, high
energy densities, and utilization of pre-existing components
[2]. However, if the push for sustainability died down, KERS
would most likely be lost to the ages, only existing on the
Formula One racetrack as a “speed boost” button. This would
be most unfortunate for the environment and the world, as
KERS and regenerative braking in general have too much
potential to be wasted as another discarded idea.
ACKNOWLEDGEMENTS
Thank you, staff of the University of Pittsburgh’s
Hillman Library, for providing us with a quiet, comfortable
environment while writing this paper. Next, we would like to
thank Dr. Daniel Budny for keeping us motivated. Finally,
thank you to our parents for raising us, encouraging us, and
providing for us in our academic pursuits.
SOURCES
[1] “Where the Energy Goes: Gasoline Vehicles.” U.S.
Department
of
Energy.
Accessed
1.9.2017.
http://www.fueleconomy.gov/feg/atv.shtml
[2] R. Kapoor, C. Mallika Parveen. “Comparative Study on
Various KERS.” Proceedings of the World Congress on
Engineering 2013 Vol III. 7.3-5.2013. Accessed 1.12.2017.
http://www.iaeng.org/publication/WCE2013/WCE2013_pp1
969-1973.pdf
[3] J. Cowperthwaite. “Ultracapcitors, Batteries Join Forces
for Fuel Efficiency: One Option to Increase Vehicle Fuel
Efficiency is to Make Battery Systems More Efficient”.
Design
News.
06-2013.
Accessed
02.27.2017.
http://rt4rf9qn2y.search.serialssolutions.com/?genre=article
&title=Design%20News&atitle=Ultracapacitors%2C%20Ba
tteries%20Join%20Forces%20for%20Fuel%20Efficiency.&
author=Cowperthwaite%2C%20Jeremy&authors=Cowperth
waite%2C%20Jeremy&date=20130601&volume=68&issue
=6&spage=14&issn=00119407
7
BryanPatrick Farren
Nicholas Harn
J. German. “Hybrid Vehicles: Technology Development
and Cost Reduction.” International Council on Clean
Transportation.
7.2015.
Accessed
2.10.2017.
http://www.theicct.org/sites/default/files/publications/ICCT_
TechBriefNo1_Hybrids_July2015.pdf
using-flywheel-based-kers-to-boost-fuel-economy-of-itspassenger-cars/
[16] B. Wojdyla. “Volvo Builds a Different Kind of Hybrid”.
Popular Mechanics. 7.15.2013. Accessed 3.20.2017.
http://www.popularmechanics.com/cars/hybridelectric/a9234/volvo-demonstrates-kers-system-15682389/
[17] N. Rooke. “Volvo Car group and Flybrid conduct UK
testing of flywheel technology”. Volvo Car UK Ltd.
03.26.2014.
Accessed
03.22.2017.
https://www.media.volvocars.com/uk/engb/media/pressreleases/141626/volvo-car-group-and-flybridconduct-uk-testing-of-flywheel-kers-technology
[18] “Flybrid KERS for Buses & Commercial Vehicles”.
Accessed 3.2.2017. http://www.torotrak.com/productspartners/case-studies/flybrid-kers-for-buses-commercialvehicles/
[19] “Press Release from Partner WrightBus”. 3.16.2015.
Accessed 3.1.2017. http://www.torotrak.com/press-releasefrom-partner-wrightbus/
[20] “Bus KERS – Coming to a bus stop near you”. 5.1.2016.
Accessed
3.1.2017.
http://www.torotrak.com/bus-kerscoming-to-a-bus-stop-near-you/
[21] D.J.N. Limebeer, G. Perantoni, & A.V. Rao. “Optimal
control of Formula One car energy recovery systems.”
International Journal of Control. 2014. Accessed 1.12.2017.
http://www.tandfonline.com/doi/pdf/10.1080/00207179.201
4.900705
[22] D. Simanaitis “KERS are Coming – Again”. Road and
Track.
3.9.2011.
Accessed
3.1.2017.
http://www.roadandtrack.com/motorsports/news/a17117/ker
s-are-comingagain/
[23] B. Stebner. “First responders 'at risk of electrocution
from hybrid and electric cars after serious accidents’”. Daily
Mail.
12.29.2012.
Accessed
3.2.2017.
http://www.dailymail.co.uk/news/article-2254602/Firstresponders-risk-electrocution-hybrid-electric-carsaccidents.html
[24] A. Gabriel-Buenaventura, B. Azzopardi. “Energy
Recovery Systems for Retrofitting in Internal Combustion
Engine Vehicles: A Review of Techniques”. Renewable and
Sustainable Energy Reviews. 9.26.2014. Accessed 3.29.2017.
https://pitt-illiad-oclcorg.pitt.idm.oclc.org/illiad/illiad.dll?Action=10&Form=75&
Value=121999
[25] C. Tagliaferri, S. Evangelisti, F. Acconcia, T. Domenech,
P. Ekins, D. Barletta, P. Lettieri. “Life Cycle Assessment of
Future Electric and Hybrid Vehicles: A Cradle-to-Grave
Systems Engineering Approach”. Chemical Engineering
Research & Design: Transactions of the Institution of
Chemical Engineers Part A. 08-2016. Accessed 3.29.2017.
http://www.sciencedirect.com/science/article/pii/S02638762
16301824
ADDITIONAL SOURCES
8