Bose Redefines Automobile Suspension Systems
By Mike Hanlon
September 30, 2004
Bose Corporation is best known for creating high quality audio products, and if asked to piece together your ideal car, its 11-speaker sound system would certainly be a contender to feature within. But the suggestion that Bose's new suspension systems would feature without begs an explanation.
In an ongoing research project that has spanned over twenty-four 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.
The computer-controlled suspension system originated from a research assignment established by Dr Bosch in 1980. Back then, he 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 much better than 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 was necessary to provide the desired results.
The study led to electro-magnetics as the one approach that could realise the desired suspension characteristics. The Bose suspension concept required significant advancements in four key disciplines: linear electromagnetic motors, power amplifiers, control algorithms, and computation speed. Bose took on the challenge of the first three factors and hedged its bets on Moore's law providing assistance for the necessary developments needed in computation speeds.
The purpose of an automobile's suspension system is two-fold: passenger comfort and 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.
Dr. Bose, set out to prove these goals were in conflict and so began the long road that has led to the revolutionary new system. 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.
Today, prototypes of the Bose suspension have been installed in standard production vehicles. These research vehicles have been tested on a wide variety of roads, on tracks, and on durability courses with amazing results.
Automobilemag.com experienced the system first hand in a Lexus LS400 on a ride simulator and likened it to sailing along with only the slightest of cradle rock. All the while via adjacent mirrors the spectacle of bouncing tyres beneath could be witnessed.
The heart of the system is based upon a linear electromagnetic motor which is installed at each wheel. Inside the linear electromagnetic motor are magnets and coils of wire. When electrical 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.
A 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.
The whole system is controlled by a set of mathematical algorithms developed over the twenty-four 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.
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 so that a vehicle may be retrofitted with minimal modifications.
Bose's front suspension modules use a modified MacPherson 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. The suspension also includes a wheel damper at each wheel to keep the tire from bouncing as it rolls. 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.
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. When test drivers execute aggressive cornering maneuvers like a lane change, the elimination of body roll is felt immediately. When test drivers take the Bose suspension over bumpy roads, they report that the reduction in overall body motion and jarring vibrations results in increased comfort and control.
In bringing the product to market Dr Bose expects that the company will choose one automaker that is dedicated to performance. When exactly this will be is laughed off by Dr Bose as he points out the long past the project already has. It is speculated however that the system will be commercially available within the next two years.