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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electromagnetic suspension

Engineering

car body

automotive suspension

vehicle parts

bose equipped vehicle

safe vehicle control

vehicle stable

parts of suspension

years bose