Are the anti-roll bar’s days numbered? The answer is probably “yes” — at least for premium-model cars and light trucks, as advanced active ride control systems that use the vehicle's sensor array become more widely adopted. Tenneco, through its Monroe subsidiary, is currently developing a fully active suspension system with significant advances over incumbent semi-active systems.
Current production suspension systems typically rely on electronic actuation of the damper valves to improve damping response. In the case of the Monroe CVSA2 system, the dampers are equipped with two electronically activated valves to control both the rebound and compression strokes of the dampers. The aim is to improve ride and handling particularly for luxury models, SUVs and sports cars.
A further development of the system, called CVSA2/Kinetic, can already eliminate the need for anti-roll bars by providing a hydraulic connection between the CVSA2 dampers on each axle. This provides improved ride comfort by providing control over vehicle roll. This system enables vehicle weight to be reduced by removing the anti-roll bars, but the level of ride control is still limited by the reliance on wheel movement to generate the damping forces.
Tenneco's latest ride-control system, ACOCAR, eliminates the need for anti-roll bars. There are two variants of the system under evaluation, as Automotive Industries was shown during a recent demonstration in Europe. One has no interconnection between suspension dampers on the same axle. In this case, each damper is equipped with an integrated electrically powered pump, which continuously circulates oil through the shock absorber, with damping valves that can be controlled independently to control vehicle body movement.
The other ACOCAR system uses a single pump for each axle, providing pressure to each damper as required. The result is a suspension that can react very rapidly to changes in surface quality. Our demonstration vehicle was a Range Rover equipped with ACOCAR. Part of the demo included driving with two wheels on smooth tarmac and the other two on a broken surface. Despite the significantly different surfaces the vehicle showed little deterioration in ride quality.
Cornering at speed also demonstrated the system’s ability to contain roll. Roll angles were limited to a few degrees by the calibration, but the controlled wheel movements ensured tire/road contact to improve vehicle handling.
A production version of the ACOCAR system is expected in the 2021-2 timeframe, according to Esteban Mendez, Tenneco Senior Research Engineer.
“The ACOCAR system has a much bigger impact on the total vehicle than the CVSA2 system," Mendez said. "The ACOCAR system requires much more from the OEM from an integration point of view. It requires a power source for the hydraulic pumps and it also requires full integration with the vehicle’s ECU and everything around it.”
The basic ACOCAR system is still a reactive set-up, able to respond much more quickly to changes in surface and to control roll angles. Further improvements could be offered if the system incorporated other sensors. For example, a camera scanning the road surface ahead of the vehicle would enable the system to anticipate factors affecting ride quality and prepare the damping system for them. Signals from such a camera system could be combined with existing cameras responsible for road sign recognition as well as scanning road markings and traffic lights.
If road scanning is added to the primary ride control, "you would be really able to pre-set the suspension at events like a speed bump, or pothole to minimize the body motion even further, compared with what we are doing today,” comments Gunther Bismans, Monroe’s Technical Team Leader for Vehicle Dynamics.
“Even in the case of potholes, if you know that they are coming, you can keep the wheel up and prevent it from falling into the pothole to minimize the resulting impact," he explained, adding "I would expect a big improvement from such a system.”
Other sensors, such as radar and laser based systems are also under evaluation. Camera-based systems would obviously not work effectively in low light conditions.
Tenneco engineers would not proscribe the sensor technology it is using, but would leave that choice to OEMs to decide which system they would prefer to offer. Testing with a range of sensors is being carried out to ensure that the system would work effectively regardless of the sensor system chosen.