Kinetic Energy Recovery System
This presentation describes the complete working of flywheel based Kinetic Energy recovery system. It is used in racing cars like F1 and other racing cars.
Published on: Mar 3, 2016
Transcripts - Kinetic Energy Recovery System
Kinetic Energy Recovery System
By- Ankit Singh
• The flywheel
• The flywheel vacuum chamber
• Magnetic bearing
• The Continuously variable transmission (CVT) unit
• Step-up gearing and clutch
• The clutch
Advantages and Disadvantages
• Today, many hybrid electric vehicles have been developed in
order to reduce the consumption of fossil fuels; unfortunately
these vehicles require electrochemical batteries to store
energy, with high costs as well as poor conversion efficiencies.
• By integrating flywheel hybrid systems, these drawbacks can
be overcome and can potentially replace battery powered
hybrid vehicles cost effectively.
• The advantages of this technology over the electric hybrids
will be elucidated carefully. The latest advancements in the
field, the potential future and scope of the flywheel hybrid
will be assessed.
• The Kinetic Energy Recovery System
(KERS) is a type of regenerative
braking system which has the
capability to store and reuse the lost
• Unfortunately the poor conversion
efficiencies cancel out most of the
advantages these battery powered
hybrid vehicles bring with them. The
flywheel-based kinetic energy
recovery system is a possible solution
which could potentially replace the
• The KERS was first designed for
formula one racing cars.
Drawbacks of Electric Hybrid
• The flywheel energy storage is based on the principle of regenerative
braking. Regenerative braking is a mechanism which reduces the vehicle
speed, converting the kinetic energy into another useful form of energy
mechanical energy, electrical energy or the like.
• When the vehicle brakes, the motor rotates in the opposite direction,
acting as a generator and in the process slows down the car. The electricity
produced is then sent to the battery which stores the energy as chemical
• When desired, the battery supplies the stored energy back to the wheels,
giving an additional “boost” of power. Unfortunately the many energy
conversions- from mechanical to electrical energy and from electrical to
chemical energy, reduces the overall efficiency to the system to about
30%. The mechanical hybrid overcomes this drawback.
• The flywheel hybrid primarily consists of a rotating flywheel, a
continuously variable transmission system (CVT), a step up gearing (along
with a clutch) between the flywheel and the CVT and clutch which
connects this system to the primary shaft of the transmission.
• When the brakes are applied or the vehicle decelerates, the clutch
connecting the flywheel system to the driveline/ transmission is engaged,
causing energy to be transferred to the flywheel via the CVT.
• The flywheel stores this energy as rotational energy and can rotate up to a
maximum speed of 60000 rpm. When the vehicle stops, or the flywheel
reaches its maximum speed, the clutch disengages the flywheel unit from
the transmission allowing the flywheel to rotate independently.
• Whenever this stored energy is required, the clutch is engaged and the
flywheel transmits this energy back to the wheels, via the CVT. Generally
the flywheel can deliver up to 60 kW of power or about 80 HP.
Volvo’s flywheel KERS system Layout
• The flywheel is the component which harvests kinetic energy, when the vehicle brakes, by
increasing its rotational speed. The ability of flywheels to store energy is explained by the
relation between the flywheel’s inertia, angular velocity and kinetic energy.
• The equation for the inertia of a flywheel is:
• Therefore energy stored in the flywheel is given by:
• A flywheel's energy is proportional to its mass, and proportional to the square of its
rotational speed or angular velocity. In other words, by doubling the mass, the energy stored
is also doubled, and by doubling the speed, the energy stored is quadrupled. Thus by
increasing the speed of the flywheel it will be possible to reduce the mass and size of it, to a
level where its weight is insignificant while analyzing fuel efficiency.
• The weight of the flywheel is a very important factor in determining the efficiency of the
The Flywheel Vacuum Chamber
• The vacuum chamber is another very essential part of the flywheel hybrid
• The major function of the vacuum chamber is to minimize the air
resistance as the flywheel rotates. Without the vacuum chamber, the
friction caused by air resistance is enough to cause significant energy
losses and heat the carbon fiber rim to its glass transition temperature.
• . Vacuum chambers for KERS systems are frequently made of metals like
aluminum, stainless steel, or the like because these metals can provide
adequate strength to withstand differential pressure between an
evacuated interior and the surrounding atmosphere, as well as to provide
a barrier to the passage of atmospheric gases through the chamber wall
by diffusion or flow through structural defects.
• Magnetic bearings have replaced
mechanical bearings as they greatly
reduce losses due to friction.
• The magnetic bearings support the
flywheel by the principle of magnetic
levitation. It is a method by which an
object is suspended with no support
other than magnetic fields. A
permanent or electro permanent
magnetic bearing system is utilized.
• The best performing bearing is the
(HTS) magnetic bearing, which can
situate the flywheel automatically
without need of electricity or
positioning control system.
Waukesha magnetic bearing
Continuously Variable Transmission (CVT)
• The most important interface that connects the flywheel to the
transmission system is the CVT.
• The speed ratio between the vehicle and the flywheel constantly changes
between acceleration and braking. The reason why a stepped drive unit is
not preferred in this system is because it has only a fixed number of gear
ratios as opposed to the CVT’s which have an infinite number of gear
ratios between the maximum and the minimum value which allows a
seamless transfer of energy without any loss of power.
• The surface contact area is the factor which determines which shaft
rotates faster. When both the rollers have equal contact on the toroidal
surfaces of the input and output shafts, the gear ratio is 1:1. Any change in
the CVT ratio can be viewed as the transfer of kinetic energy between the
flywheel inertia and vehicle.
Step-up Gearing & Clutch
• A step up gearing system consisting of Epicyclic gears is
connected between the CVT and the flywheel unit.
• The reason why this gearing system is used is because
the high speed at which the flywheel rotates (60000
RPM) needs to be reduced to a manageable speed
outside the vacuum chamber, in order for the energy to
be smoothly transferred back to the CVT.
• The clutch disconnects the CVT from the flywheel when it
is not transferring power to reduce free running losses.
• The clutch is used to couple the flywheel hybrid system to the
• It engages the system while the flywheel is accelerating from
rest and disengaging while the flywheel is rotating and the
vehicle is at rest.
• Torque is transferred through clutch between the flywheel
and vehicle. Hence, the power transmitted in the flywheel
system can be controlled by a clutch that could continuously
manipulate the torque.
• High Efficiency.
• Low fuel consumption.
• Low cost compared to electric hybrid.
• Tests have proven that flywheel-based KERS
can recover and store over 70% of the vehicles
• Cars with a flywheel based energy recovery system, though
significantly more expensive than cars without this system, have
more power and better fuel efficiency.
• According to www.thegreencarwebsite.co, “the system could
reduce fuel consumption by as much as 20% and give a four-cylinder
engine acceleration like a six-cylinder unit.” This effectively
means that cars with the Flywheel KERS system have better fuel
efficiency and more power than the cars without the KERS system.
• Better fuel efficiency directly translates to a cleaner, greener
environment. It reduces the negative impact on the environment by
decreasing harmful CO2 emissions.