Twin Channel Active Stabilizer Bar System Explained

When developing a new car, the automotive world has always had to make a compromise between a vehicle suspension’s ability to tackle a corner and the comfort offered to the occupants.

Fortunately, sometime in the 80s, the active suspension technology started to be used for certain vehicles, with the technology evolving and spreading to more and more models ever since. However, the active suspension concept only targeted the shock absorbers. It took some years before the first active stabilizer bar for a production model was developed, allowing the engineers to fully play with a vehicle’s suspension.

But let’s start with the beginning: a stabilizer bar, a.k.a. anti-sway bar or anti-roll bar, is the part of the suspension that connects the opposite (right/left) wheels through short lever arms, joined by a torsion spring. Its purpose is to increase the suspension’s stiffness, offering it a greater roll resistance through corners, independent of the spring rate in the vertical direction. This allows the reduction of a vehicle’s body roll without stiffening the suspension’s springs, offering better body control and a comfortable ride at the same time.

Anti-roll bars have a key role, as the are used to tune a car’s handling balance, bringing it closer to the understeer or oversteer zone. This can be tweaked by varying the proportion of the total roll stiffeners for the front and rear axles.

But the anti-sway bars have their limitations. Due to the fact that they connect the opposite wheels of an axle, they transmit the force of one wheel bumps to the opposite wheel. When a vehicles travels over a rough surface, the anti-roll bars can produce jarring and side to side body motions, causing the occupants’ heads to be tossed alternately left and right across the vehicle. These negative effects grow with the diameter and stiffenes of the anti-sway bar and can be a real problem in heavier cars, which require stronger anti-sway bars to control their movement. An extremely stiff anti-sway bar also restricts wheel travel, potentially compromising the off-road behavior of a vehicle.

This is where the active stabilizer bars come into play, as these allow an automatic control, allowing a dedicated suspension ECU to decide when extra stiffness is required to reduce body roll during a corner, or when the wheels should be allowed to make more ample moves, in order to handle the road’s imperfections. These are usually achieved by using an actuator that connects the sides of the anti-roll bar.

The latest development in the area of active stabilizer bars is the ultra-compact version of the Active Stabilizer Bar System (ASBS), which provides comfort benefits and improves the dynamic abilities of a vehicle while using a special architecture that also reduces its weight by 30 percent.

Developed by the BWI Group, the new system allows the stabilizer bars to be decoupled when the vehicle is traveling in a straight line, improving ride quality and allowing large wheel articulations installed on certain vehicles such as SUVs to offer proper off-road abilities. When the car negotiates a bend, the roll stiffenes is instantly increased by applying torque at each end on the bar.

The system’s innovation consists of a Twin Channel architecture that links the control of the front and rear roll stiffness, offering real-time control over the vehicle’s tendency to understeer or oversteer. This means that the same car can be nimble at low city speeds, stable on the highway at higher speeds and offer a good control during lane change maneuvers by adapting to help initiate the turn and then resisting the overshoot.

In addition to that, the ASBS eliminates the tendency of common pressurized actuators to exhibit a dead band (also referred to as a discontinuity) around their center position, an issue that otherwise requires complex management. While other applications control the fluid flow between the two sides of an actuator, the ASBS controls the pressure difference between the two sides, avoiding discontinuity at the central position.

The Twin Channel Active Stabilizer Bar System is able to handle a vehicle’s roll angle and roll velocity inputs, reducing the stress on the springs and dampers, which can better cope with vertical inputs. The twin channel solution is suitable for both linear and rotary actuators, which means that it can be used for multiple vehicles types, such as performance cars, luxury cars and SUVs.
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About the author: Andrei Tutu
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In his quest to bring you the most impressive automotive creations, Andrei relies on learning as a superpower. There's quite a bit of room in the garage that is this aficionado's heart, so factory-condition classics and widebody contraptions with turbos poking through the hood can peacefully coexist.
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