Electromagnetic Suspension

Savitribai Phule Pune University
ABSTRACT
Today’s vehicle suspensions use hydraulic dampers (shock absorbers) and springs that
are charged with the tasks of absorbing bumps, minimizing the car's body motions
while accelerating, braking and turning and keeping the tires in contact with the road
surface. Typically, these goals are somewhat at odds with each other. Luxury cars are
great at swallowing bumps and providing a plush ride, but handling usually suffers as
the car is prone to pitch and dive under acceleration and braking, as well as body lean
under cornering .On the other end of the spectrum, stiffly sprung sports cars exhibit
minimal body motion as the car is driven aggressively, as cornering is flat, but the
ride quality generally suffers.
In an ongoing research project that has spanned over 24 years Bose has created a
unique electromagnetic suspension system for automobiles that is close to commercial
release and is set to replace traditional shocks and springs with electronic actuators.
"This is the first time a suspension system is the same for a sports car and for a luxury
car", said its creator, Dr Amar Bose, chairman and head of technical design. The
result is a ride that is level and bump free over incredibly rough terrain and when the
vehicle turns in to corners.
Government College Of Engineering And Research, Awasari, Mechanical Engineering
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2. BACKGROUND
2.1 Suspension
2.1.1 Every automotive suspension has two goals
1] Passenger comfort
2] Vehicle control.
Comfort is provided by isolating the vehicle’s passengers from road disturbances.
Control is achieved by keeping the car body from rolling and pitching excessively,
and maintaining good contact between the tire and the road. Unfortunately, these
goals are in conflict. In a luxury sedan the suspension is usually designed with an
emphasis on comfort, but the result is a vehicle that rolls and pitches while driving
and during turning and braking. In sports cars, where the emphasis is on control, the
suspension is designed to reduce roll and pitch, but comfort is sacrificed.
2.1.2 Main Objectives Of The Suspension
1] To prevent the road shocks from being transmitted to the vehicle parts, thereby
providing suitable riding and cushioning effect to the occupants.
2] To keep the vehicle stable while in motion by providing good road holding during
driving cornering and braking.
3] Provides safe vehicle control and free of irritating vibrations and reduce wear and
tear.
3. SIGNIFICANT ADVANCEMENT
The Bose suspension required significant advancements in four key disciplines:
1] Linear electromagnetic motors.
2] Power amplifiers.
3] Control algorithms.
4] Research vehicles.
Bose took on the challenge of the first three disciplines, and bet on developments that
industry would make on the fourth item. Prototypes of the Bose suspension have been
installed in standard production vehicles. These research vehicles have been tested on.
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Fig 3.1: parts of suspension system
3.1 Linear Electromagnetic Motor
A linear electromagnetic motor is installed at each wheel of a Bose equipped vehicle.
Inside the linear electromagnetic motor are magnets and coils of wire. When electrical
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power is applied to the coils, the motor retracts and extends, creating motion between
the wheel and car body. One of the key advantages of an electromagnetic approach is
speed.
The linear electromagnetic motor responds quickly enough to counter the effects of
bumps and potholes, maintaining a comfortable ride. Additionally, the motor has been
designed for maximum strength in a small package, allowing it to put out enough
force to prevent the car from rolling and pitching during aggressive driving
maneuvers.
3.2 Power Amplifier
The power amplifier delivers electrical power to the motor in response to signals from
the control algorithms. The amplifiers are based on switching amplification
technologies pioneered by Dr. Bose at MIT in the early 1960s – technologies that led
to the founding of Bose Corporation in 1964.
The regenerative power amplifiers allow power to flow into the linear electromagnetic
motor and also allow power to be returned from the motor. For example, when the
Bose suspension encounters a pothole, power is used to extend the motor and isolate
the vehicle’s occupants from the disturbance. On the far side of the pothole, the motor
operates as a generator and returns power back through the amplifier. In so doing, the
Bose suspension requires less than a third of the power of a typical vehicle’s air
conditioning system.
3.3 Control Algorithms
The Bose suspension system is controlled by a set of mathematical algorithms
developed over the 24 years of research. These control algorithms operate by
observing sensor measurements taken from around the car and sending commands to
the power amplifiers installed in each corner of the vehicle.
The goal of the control algorithms is to allow the car to glide smoothly over roads and
to eliminate roll and pitch during driving.
3.4 Research Vehicle
In many of today’s production vehicles, the suspension system is comprised of front
and rear suspension modules that bolt to the underside of the vehicle. The Bose
suspension takes advantage of this configuration by creating replacement front and
rear suspension modules.
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Using this approach, the research team has been able to retrofit the Bose suspension
into existing production vehicles with minimal modifications. Bose’s front suspension
modules use a modified McPherson strut layout and the rear suspension modules use
a double-wishbone linkage to attach a linear electromagnetic motor between the
vehicle body and each wheel. Torsion springs are used to support the weight of the
vehicle. In addition, the Bose suspension includes a wheel damper at each wheel to
keep the tire from bouncing as it rolls down the road.
Unlike conventional dampers, which transmit vibrations to the vehicle occupants and
sacrifice comfort, the wheel damper in the Bose suspension system operates without
pushing against the car body, maintaining passenger comfort.
3.5 Challenges
Every automotive suspension has two goals: passenger comfort and vehicle control.
Isolating the vehicle’s passengers from road disturbances like bumps or potholes
provides comfort. Control is achieved by keeping the car body from rolling and
pitching excessively, and maintaining good contact between the tire and the
road.Unfortunately, these goals are in conflict.
In a luxury sedan the suspension is usually designed with an emphasis on comfort, but
the result is a vehicle that rolls and pitches while driving and during turning and
braking. In sports cars, where the emphasis is on control, the suspension is designed
to reduce roll and pitch, but comfort is sacrificed. Bose engineers took a unique
approach to solving this problem, and the result is an entirely new approach to
suspension design.
3.6 Solution
In 1980, Bose founder and CEO Dr. Amar Bose conducted a mathematical study to
determine the optimum possible performance of an automotive suspension, ignoring
the limitations of any existing suspension hardware. The result of this 5-year study
indicated that it was possible to achieve performance that was a large step above
anything available.
After evaluating conventional and variable spring/damper systems as well as
hydraulic approaches, it was determined that none had the combination of speed,
strength, and efficiency that is necessary to provide the desired results.
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The study led to electromagnetics as the one approach that could realize the desired
suspension characteristics.
Fig 3.2: Car with installed Bose electromagnetic suspension.
4. WORKING
The Bose system uses a linear electromagnetic motor (L.E.M.) at each wheel, in lieu
of a conventional shock and spring setup. The L.E.M. has the ability to extend (as if
into a pothole) and retract (as if over a bump) with much greater speed than a fluid
damper (taking just milliseconds). These lightning-fast reflexes and precise movement
allow the wheel's motion to be so finely controlled that the body of the car remains
level, regardless of the goings-on at the wheel level. The L.E.M. can also counteract
the body motion of a car while accelerating, braking and cornering, giving the driver a
greater sense of control and passengers less of a need for Dramamine. To further the
smooth ride goal, wheel dampers inside each wheel hub smooth out small road
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imperfections, isolating even those nuances from the passenger compartment. Torsion
bars take care of supporting the vehicle, allowing the Bose system to concentrate on
optimizing handling and ride dynamics.
A power amplifier supplies the juice to the L.E.M.s. The amplifier is a regenerative
design that uses the compression force to send power back through the amplifier.
Thanks to this efficient layout, the Bose suspension uses only about a third of the
power of a vehicle’s air conditioning system. There are a few other key components
in the system, such as control algorithms that Bose and his fellow brainiacs
developed. .
Fig 4.1: Installed suspension unit in car
The different types of suspension system which are available are mentioned below:
4.1 Front Suspension
Solid I-Beam
It’s a Non-independent design .These is used on trucks and other large vehicles. Its
economical and simple .It has low maintenance but poor handling.
Twin I-Beam
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Found on many Ford trucks. Its Forged, cast, or stamped axles. Has excellent load
capacity. It requires special equipment for alignment adjustments.
Mac Pherson Strut
One of the most popular systems .It has one Control Arm. Ideal for front wheel drive.
Light weight and economical. Good ride quality and handling characteristics. It’s used
for both front and rear suspensions.
Short-Long Arm
Independent design uses an upper and a lower control arm uses either torsion bars or
coil springs Good ride quality and handling characteristics Heavy and complex design
requires a lot of space.
4.2 Rear Suspension
Non Independent Rear Leaf Springs:
It’s a non-independent design Similar to front solid I-beam axle. Used for large load
carrying capacity.
Non Independent Rear Coil Springs:
It’s a non-independent design .Uses coils and control arms instead of leaf springs. Has
good load carrying capacity.
Trailing Arm:
It’s an Independent Design Uses individual lower control arms. Uses coil springs and
shocks for good ride quality.
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Fig 4.2: suspension in front wheel
The Bose suspension system installs easily into the front of the vehicle. A new engine
cradle connects the front suspension to the car body using the original factory
mounting hardware, creating a drop-in replacement module. Bose's front suspension
modules use a modified Mac Pherson strut layout and the rear suspension modules
use a double-wishbone linkage to attach a linear electromagnetic motor between the
vehicle body and each wheel. Torsion springs are used to support the weight of the
vehicle.
In addition, the Bose suspension includes a wheel damper at each wheel to keep the
tire from bouncing as it rolls down the road. Unlike conventional dampers, which
transmit vibrations to the vehicle occupants and sacrifice comfort, the wheel damper
in the Bose system operates without pushing against the car body, maintaining
passenger comfort.
4.3 Linear Motor
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Fig 4.3: linear motor
Linear motor is essentially a multi-phase alternating current (AC) electric motor that
has had its stator "unrolled" so that instead of producing a torque (rotation) it
produces a linear force along its length. The most common mode of operation is as a
Lorentz-type actuator, in which the applied force is linearly proportional to the current
and the magnetic field (F = qv × B).
Many designs have been put forward for linear motors, falling into two major
categories, low-acceleration and high-acceleration linear motors. Low-acceleration
linear motors are suitable for maglev trains and other ground-based transportation
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applications. High-acceleration linear motors are normally quite short, and are
designed to accelerate an object up to a very high speed and then release the object,
like roller coaster.
They are usually used for studies of hypervelocity collisions, as weapons, or as mass
drivers for spacecraft propulsion. The high-acceleration motors are usually of the
linear induction design (LIM) with an active three-phase winding on one side of the
air-gap and a passive conductor plate on the other side.
The low-acceleration, high speed and high power motors are usually of the linear
synchronous design (LSM), with an active winding on one side of the air-gap and an
array of alternate-pole magnets on the other side. These magnets can be permanent
magnets or energized magnets. The Transrapid Shanghai motor is an LSM.
Fig 4.4: Bose suspension system
5. COMPARISON
5.1 On A Bumpy Surface
Two vehicles of the same make and model are driven over a bump course at night.The
vehicle on the top has the original factory installed suspension and the vehicle on the
bottom has a BOSE suspension system.
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Fig 5.1: A Lexus with a standard suspension
Joggles as it coasts along a bumpy surface, while another Lexus with the BOSE
suspension system (below) sails along the same road unperturbed.
Fig 5.2: A Lexus with a BOSE suspension
5.2 Body Roll While Cornering
Two vehicles of the same make and model are shown performing an aggressive
cornering maneuver.
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Fig 5.3: A Lexus with a standard suspension
Fig 5.4: A Lexus with the BOSE suspension
In the photo, the Lexus car without the BOSE system leans as it turns a corner, while
the car with the Bose system remains stable.
Body Pitch on braking & accelerating: The front end of the car dips when the driver
of a Lexus fitted with the standard factory fitted suspension system slams brakes. In a
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Lexus with the BOSE suspension system; drivers quickly notice the elimination of
body pitch during hard braking and acceleration. Professional test drivers have
reported an increased sense of control and confidence resulting from these behaviors.
Fig 5.5: Comparison at cornering.
6. VEHICLE PERFORMANCE
Vehicles equipped with the Bose suspension have been tested on a variety of roads
and under many different conditions, demonstrating the comfort and control benefits
drivers will encounter during day to-day driving. In addition, the vehicles have
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undergone handling and durability testing at independent proving grounds. When test
drivers execute aggressive cornering maneuvers like a lane change, the elimination of
body roll is appreciated immediately. Similarly, drivers quickly notice the elimination
of body pitch during hard braking and acceleration.
Professional test drivers have reported an increased sense of control and confidence
resulting from these behaviors. When test drivers take the Boss suspension over
bumpy roads, they report that the reduction in overall body motion and jarring
vibrations results in increased comfort and control.
7. FEATURES
1] The system draws about two horsepower or one-third the load of a typical air
conditioner. While it can exert 50 kilowatts (67 horsepower) of energy to leap a
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2x6(plank) covers 49 kilowatts cushioning the landing, with the shocks working like
generators.
2] Torsion bars and shock units weigh about what two conventional springs and
shocks. The controllers and upsized alternator also add some weight, but the total
should be less than that of a hydraulic active suspension.
3] The system lets a vehicle ride lower at highway speeds to produce less drag and
improve handling.
4] To save power the system is regenerative. When the far side of a pothole helps to
push the wheel up almost all the power is recovered. The motors momentarily become
generators, shunting the recovered energy to storage, either in the engine battery or in
some other device. The system ends up consuming one-third of the energy used by a
cars air-conditioner.
8. DISADVANTAGES
Every system has some disadvantages attached to it.Some of the drawbacks can be
grouped as below.
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The main drawback of the system is the cost.As it uses nyodinium magnets which are
costly to manufacture. Thus this makes this suspension system costlier than any other
suspension available.Thus this system can be seen in only high end cars.
1] The second drawback is ,when this system breakdowns its very difficult and costly
affair to repair it .The other system available can be easily be repaired.
2] The system is very complex and requires high precision machinery and skilled
workers to manufacture.
9. FUTURE PROSPECTS
Dr. Bose stated that within five years the company hopes to have the Bose suspension
offered on one or more high-end luxury cars, and thanks to the system's modular
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design, it shouldn't be much of a problem to install at the factory. A manufacturer will
be chosen to co-develop a production application for sale after three or four years.
GM is expected to be the first development partner, given the long relationship
between the companies. The biggest setback would be the cost as it is going to cost
more than any suspension does now. The neodymium iron in the magnets is the most
expensive part. Expect to see electromagnetic suspensions only on very expensive
cars first, and probably never on cheap ones, though we imagine that the cost would
come down as production goes up.
10. CONCLUSION
For the first time, the Bose suspension demonstrates the ability to combine in one
automobile a much smoother ride than any luxury sedan, and less roll and pitch than
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any sports car. This performance results from a proprietary combination of suspension
hardware and control algorithms.
11. REFERENCE
1]“ElectromagneticSuspensionSystems”,http://www.bose.com/learning/project_sound
/bose_suspension.jsp.
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2]“Bose Redefines Automobile Suspension System”, S.R.Gupta, Penguin metro
reads.
3]“Electronic Suspension” , U.V.Bakshi.
4]“Future of Car Suspensions”, J.K.Thomson.
5]“Motorcycle dynamics” by Cossalter.
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