Bring on the Potholes

April 4, 2005

7 Min Read
Bring on the Potholes

Two Lexus models negotiate Bose's body motion and bump course. The vehicle on the left has the original factory-installed suspension, and the one on the right is equipped with the Bose active suspension.

When you hear the name Bose, most people immediately think of sound: home theater systems, custom power amplifiers in cars, and the omnipresent wave radio/CD player.

In recent months, however, the Framingham, MA, technology company has grabbed attention for something entirely different: a revolutionary active suspension system that promises to deliver a unique blend of rider comfort and vehicle control.

That's a tall order. Not only must Bose perfect the design, but it must also find an automotive OEM willing to roll the dice and prepare the new system for a production vehicle.

Meanwhile, companies with many years of experience in the suspension business are pushing ahead with their own semi-active systems—arguing that their approaches offer marked improvements for drivers at a far lower cost than active systems.

Clean Sheet of Paper

Those who know company founder Amar Bose fully understand this new foray into suspensions is by no means a whim. Yes, the former MIT engineering professor became personally fascinated with suspensions after owning both a 1958 Pontiac Bonneville and a Citroën equipped with novel air suspensions. But Dr. Bose wasn't about to tackle a whole new venture unless he could make a significant difference in performance.

"Many companies would start such a project with a piece of hardware," notes Neal Lackritz, a Bose research engineer. "Dr. Bose started with mathematics."

A five-year mathematical study on optimal suspensions performance, launched in 1980, showed that major improvements were possible. However, the Bose researchers determined that conventional spring/damper and hydraulic approaches could not deliver the combination of speed, strength, and efficiency needed for a great leap forward.

Instead, the new Bose system—24 years in the making—relies on advances in four key areas: linear electromagnetic motors, power amplifiers, control algorithms, and computational speed.

In the Bose front corner module, the linear electromagnetic motor serves as a telescoping suspension strut along with a two-piece control arm. A torsion bar connected to one end of the lower arm supports the weight of the vehicle, while the wheel damper keeps the car from bouncing and losing contact with the road.

In the prototype system, applied to a Lexus LS400 sedan, Bose researchers installed a linear electromagnetic motor on each wheel. Inside these motors are magnets and coils of wire. When the system applies electrical power to the coils, the motor retracts and extends, creating motion between the wheel and the car body.

"This is the key difference between our active system and conventional springs and shock absorbers," Lackritz explains. "Our electromagnetic system can actually create forces quickly enough to counter the effects of bumps and potholes."

To deliver the electrical power to the wheel motors, Bose relies on power amplifiers derived from basic switching amplification technologies developed by Dr. Bose at MIT in the early 1960s. The new suspension system features regenerative amplifiers that allow power to flow into the linear electromagnetic motor, as well as allow power to be returned from the motor. So when the suspension first hits a pothole, the power is used to extend the motor and isolate passengers from the jolt. On the far side of the pothole, the motor operates as a generator and returns power back through the amplifier.

The system relies on a set of control algorithms developed over the long history of the project. These algorithms operate by observing sensor measurements taken from around the car and sending commands to the power amplifiers on each corner of the vehicle. The objective: Allow the car to glide smoothly over roads and to eliminate roll and pitch during driving.

Raves and Challenges

At Bose headquarters, the press and other visitors have watched test drivers negotiate a conventional Lexus 400 and one equipped with the Bose suspension through bump tests and maneuvers like cornering, slalom, and lane changing. The overall consensus: rave reviews, as the Bose vehicle delivered a flat, smooth ride with no pitch or roll. "To say that this technology is the biggest advance in automobile suspensions since all-independent design is an understatement," crows auto writer John Dippier in Edmunds' Inside Line.

Popular Science was so impressed that it gave Bose its Grand Award for 2004 in the auto technology category, triggering a long litany of praises from readers on the magazine's website. One reader writes: "I've seen the product demonstrated. It's fantastic. No roll. No bumps. No dips."

Praise from the press and public, however, is no guaranty of success. Researcher Lackritz observes that design challenges still remain. For example, engineers need to buggerize the hardware and insure that it can survive crash tests, as well as tests for temperature extremes, salt, and fog. Bose also needs to make further progress in shaving weight from the system, which has a weight target of 200 lbs.

Perhaps even more daunting is the business challenge of finding an auto OEM willing to join hands in development. "This is a long-term project, and many CEOs at publicly held companies are reluctant to take on the extra costs and risks," Lackritz says.

Even so, Bose is hoping to develop a relationship with a partner company within the next six to 12 months. Because of the added costs associated with a leading-edge active system, Dr. Bose has noted that the logical first application of the technology will be in a luxury car.

A linear electromagnetic motor is installed at each wheel of a Bose-equipped vehicle. Contorl algorithms operate by observing sensor measures taken from around the car and sending commands to the motors.

View from the Trenches

How do companies that are veterans in suspension design view the Bose innovation? "It is wonderful to see new developments like this," says Aly Badawy, VP of Steering & Suspension Engineering for TRW, a major worldwide suspension supplier. "But if this system adds another $4,000 or $5000 to vehicle costs, it will be difficult to implement."

Badawy notes that tests his company has done with ordinary drivers show that many people have a difficult time distinguishing the difference in ride between expensive active suspension systems and more traditional designs.

Currently, TRW has development contracts with four automotive OEMs for its new Active Dynamic Control system, which is based on active stabilizer bars. In this semi-active design, a hydraulic roll control actuator replaces the rigid drop link at one end of the sway bar. An electrohydraulic control unit regulates the actuator pressure and oil flow direction, based on driving conditions monitored through sensor data.

Badawy observes that this design, which TRW hopes to have in production cars by 2008, offers cost advantages to OEMs and consumers because it leverages other systems already in place. For example, the ADC system uses existing antilock brake and stability control system signals provided by the communication bus to reduce sensor costs. The design, which can reduce the roll acceleration of a vehicle by as much as 50 percent, gives the option of putting actuators on two axles for both lateral dynamic control and roll control. TRW estimates that ADC would boost a car's sales price by as little as $1,000.

Another major suspension supplier, Delphi, is looking to add more platforms for its MagneRide™ semi-active suspension control system, now found on the Corvette.

Web Resources

»For details on Bose suspension system, including quick time film clips of car tests

»TRW suspension systems

»Delphi MagneRide system

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