Delphi was first to market with an Active Stabiliser Bar System in 1999 and has subsequently developed both linear and rotary systems for a range of applications. In 2005, Delphi's second generation system was launched on the Range Rover Sport, contributing to its world-class combination of handling, comfort and off-road ability. The unique ball screw rotary actuator technology provides the highest angular articulation of any system currently in production and is also the most efficient, converting around 95 percent of pump energy into hydraulic pressure compared with around 65 - 85 percent for competitor systems.
"The new system keeps Delphi comfortably ahead of the competition," comments development manager Olivier Raynauld. "Generation 3 ASBS provides best-in-class performance by any measure and has helped us win some very exciting development programmes across a range of vehicle types."
A traditional stabiliser bar improves vehicle stability through corners by reducing roll angle and managing the tyre to road interface. High performance vehicles and heavy vehicles with a high centre of gravity typically require stiff, large diameter stabiliser bars but these will substantially reduce ride comfort and refinement and can also reduce traction in some conditions. Traditional stabiliser bars also restrict wheel travel, decreasing off-road performance for SUVs, and can create an effect known as 'head toss' that can be particularly uncomfortable in vehicles where the occupants are seated high.
Delphi's ASBS technology splits the stabiliser bar in the middle, allowing a computer-controlled actuator to apply a variable level of torque to each end. When the vehicle is travelling in a straight line, the system effectively de-couples the stabiliser bars from the vehicle, substantially improving ride comfort and allowing up to 88 degrees of free stabiliser bar rotation for greater wheel articulation. In a corner, anti roll torque is instantly applied and can be optimised for any driving condition in just 20ms.
The key innovation that gives the third generation technology its additional dynamic and refinement benefits is a new hydraulic control system. Contemporary systems use a directional control valve to reverse the hydraulic pressure and hence the force applied to the roll bars. This gives poor steering feel around centre, with limited control authority when travelling in a straight line and can also generate significant noise.
Delphi's patented continuous pressure control system solves these issues by eliminating the need to switch the direction in which pressure is applied and by maintaining a constant small on-centre pressure to improve steering feel and response. Switching noise is eliminated and two channel control allows component sharing front-to-rear and the integration of different control calibrations for comfort and sport modes. Because it is truly active (i.e., it can apply force to the suspension), the system can also be used to tune roll damping. The high efficiency of the system further reduces noise and allows a proven pump to be used with a small reservoir and low-cost, easily routed hoses.
"With Generation 3, we can tune the steering feel and dynamic behaviour via the roll-control system and change the response as vehicle speed increases," adds Raynauld. "For example, we can provide oversteer at low speeds to give sharp, agile handling in towns, with subtle levels of understeer at high speeds to increase safety and provide a feeling of sure-footed security for the driver."
"No one else is offering on-centre pressure control," continues Raynauld. "It's a significant breakthrough that we are very proud of. Customers who have analysed the Delphi system tell us that it is clearly the best available."
Other innovations throughout the system, including new techniques for attaching the roll bars to the actuators, substantially reduce size and mass and mean that Delphi is able to deliver the system at an extremely competitive price. Delphi expects to enter production with a linear actuator system in 2011 and with a rotary actuator system in 2012, both for European customers.
Delphi's portfolio of ASBS technologies includes systems suitable for most classes of vehicle. The company also supplies a wide range of other chassis control technologies including electronic stability systems, variable damping control systems and antilock braking systems.