Bose Knows Shocks?

One of the world's foremost audio innovators has its eye on the suspension business.

It started with a '58 Pontiac's air-suspension system, recalls Massachusetts Institute of Technology Prof. Amar G. Bose. “I owned the car 10 years and got to know its suspension,” he says. “I spent as much time under the car as in the driver's seat.”

That triggered a life-long fascination with the dynamics of vehicle ride and handling that culminated recently with Bose Corp.'s unveiling a radical electromagnetic suspension system at the audio company's headquarters in Framingham, MA.

The semi-active suspension results from Bose's 24-year research to combine the best ride-and-handling attributes of luxury sedans and sports cars. The Bose suspension smooths out the bumpiest roads and minimizes roll and pitch in aggressive driving.

Bose says his company has yet to approach any vehicle manufacturer to adopt the system. However, Bose engineers have logged thousands of miles in prototype vehicles fitted with the proprietary setup.

In recent demos, the new suspension imparts impressive body control and isolation. Using two identical Lexus LS 400s, one with an OEM suspension and the other with a retrofitted Bose suspension, engineers demonstrate a remarkable contrast in performance and handling.

Journalists sat in a test car mounted on a chassis dynamometer in front of a large mirror. A ride over a bumpy road was simulated. Although the wheels could be seen in the mirror bouncing crazily, the vehicle's body was kept fairly stable. The bumps couldn't be felt. The same test in a car with a standard production suspension offered a marked degree of discomfort.

The two cars also are put through high-speed lane-changes and other handling maneuvers. The production-suspension Lexus leans radically from side to side. The Lexus with the prototype suspension stays virtually flat through all the tests.

Bose is the latest player to propose advanced technologies to adapt more readily to changes in the road surface for a smoother ride. Other suppliers developing similar packages include ZF Friedrichshafen AG, Delphi Corp., Robert Bosch GmbH, TRW Automotive and Continental Teves Inc.

The Bose setup consists of four bulky shocks at each corner. Inside each of the towers is a linear electromagnetic motor acting on the strut connected to the wheel hub.

When power is applied to the coils, the motor retracts and extends the shock's strut, absorbing or generating motion between the wheel and car body. The motor responds in milliseconds to control the strut, negating bumps. Apart from absorbing bumps and other road irregularities, energy can be applied to the strut to keep the vehicle from rolling or pitching when cornering, accelerating and braking.

Power amplifiers, using switching technologies invented by Bose, magnify and deliver electrical power to the motor as instructed by an electronic control unit.

This contemporary version uses regenerative power amplifiers that not only deliver energy to the motor but also store energy when road forces act on the strut.

When a wheel drops into a pothole, the motors extend the struts to isolate the vehicle body from the bump. On the “far” side of the pothole — as the strut must retract to allow the wheel to absorb the rising impact — the motor works as a generator and sends power back through the amplifier.

Helped by its innovative energy-capturing capability, engineers say Bose's semi-active suspension uses less than one-third the power required by a conventional vehicle air conditioner. The system's responses are generated from mathematical algorithms created during the research project.

Using input from sensors around the vehicle, the control unit sends signals to the amplifiers and motor-actuated struts at each corner of the vehicle. The result is a smooth glide over all types of roads.

Bose engineers also say the bulky suspension hardware eventually will be reduced to half the current size. An advantage of the Bose suspension is that it can easily be retrofitted into existing production cars with little modification, Bose says.

Bose front-suspension modules use a modified MacPherson strut layout, while the rear modules have a double-wishbone linkage, or strut, connecting the linear electromagnetic motors and each wheel. Torsion springs are used to support the vehicle's weight. Also installed is a passive damper at each corner to aid wheel control.

Growing out of a research program called “Project Sound,” even though it is not an acoustics product, the suspension is founded on the mathematics of sound. Suspensions such as that of the '58 Pontiac have what car engineers call a bounce rate and electrical engineers call fundamental resonance. When a vehicle's bumper is pushed down and released, the vehicle will exhibit its fundamental bounce rate.

In air-suspension vehicles, Bose says, there is a higher-frequency bounce rate when more occupants are in the vehicle. The reverse happens with conventional passive suspensions.

These discoveries persuaded Bose that vehicle owners didn't have to choose between ride comfort and handling. With a keen focus on R&D, Bose was able to assemble a team that worked for 24 years to develop the suspension. Bose spent the first five years of the project forming the mathematical models needed to solve the conflicts between ride and comfort.

The research led him to the high-efficiency, high-power motors and amplifiers to drive the linear motors and sophisticated control algorithms to govern suspension performance and stability. The requisite compact, high-speed computer power to control it all didn't exist when the project began in 1980.

Bose gambled computing technology would accelerate in time to complete the project. It did. Whether the investment of time and money, which Bose declines to reveal, will pay off in profits for the company won't be determined until auto makers decide whether to make their own bets on Bose's new suspension technology.

Still, he is pleased to have solved a problem that has intrigued him since his first exposure to the air-ride Pontiac.