|BWI’s new roll control actuator (bottom) is substantially more compact than the current generation actuator (top) and contributes to a total system weight reduction of around 30%. Click to enlarge.|
Global braking and chassis systems specialist BWI Group has developed a new ultra-compact version of its Active Stabilizer Bar System (ASBS) that improves handling and comfort while also reducing system weight by around 30%.
A traditional stabiliser bar (anti-roll bar) improves vehicle stability through corners by reducing roll angle and managing the tire-to-road interface. Heavy vehicles with a high center of gravity, such as SUVs (Sport Utility Vehicles), typically require stiff, large diameter stabilizer bars but these will substantially reduce ride comfort and refinement and can also reduce traction in some conditions.
Conventional stabilizer bars also restrict wheel travel, potentially compromising off-road behaviour, and can create an effect known as ‘head toss’ that can be particularly uncomfortable in vehicles where the occupants are seated high.
|BWI’s new Twin Channel Active Stabilizer Bar System uses a new valve block to provide very high levels of real-time control. Click to enlarge.|
BWI’s ASBS technology minimizes all of these issues by splitting the conventional stabilizer bar in the middle. At the intersection of the two roll-bar sections, a computer-controlled actuator applies a variable level of torque. When the vehicle is travelling in a straight line, the system effectively de-couples the stabilizer bars from the vehicle, improving ride comfort and allowing large wheel articulation to increase off-road ability.
In a corner, roll-stiffness is instantly increased by applying torque to each end of the bar. For the new generation system, BWI has developed a Twin Channel architecture that links the control of front and rear roll stiffness to give real-time control of the vehicle’s tendency to understeer or oversteer.
Our system allows vehicle manufacturers to adjust the front-rear balance in real time so that the understeer or oversteer characteristics are continuously optimized for the demands of each driving situation. This means that the same vehicle can be agile in the city at low speeds, stable on the highway at higher speeds and provide improved stability during lane changing by adapting to help initiate the turn then resisting overshoot afterwards.
—Olivier Raynauld, BWI’s Manager, Forward Engineering Controlled Suspensions
BWI has also eliminated the tendency of pressurized actuators to exhibit a dead band (known as a discontinuity) around their center position; an issue that otherwise necessitates complex management.
Existing systems control the flow of fluid between two sides of an actuator. We control the pressure difference between the two sides and that means we avoid a discontinuity at the central position.
BWI claims that the improvements are so significant that the new system can deal with all the vehicle roll angle and roll velocity inputs, leaving the springs and dampers to deal with just vertical inputs and eliminating a major source of compromise in the ride and handling balance. The twin channel approach is suitable for both linear and rotary actuators and will improve the comfort and stability of most vehicle types including sports cars, luxury cars and SUVs. The first production application of new generation roll control system is scheduled for 2012.
BWI currently supplies roll control systems for the Land Rover Discovery and the Range Rover Sport. BWI also supplies a wide range of other chassis control technologies to various vehicle manufacturers worldwide including electronic stability systems, variable damping systems and antilock braking systems.