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Getting active suspension devices into standard C-segment vehicles would improve safety, but suppliers must first solve the cost equation. By Richard Aucock

Active suspension is already on the market at the top end. BMW has its Adaptive Drive package; Mercedes-Benz has active body control. But they are prohibitively expensive.

Just as we’ll never see a V12 in a C-segment passenger car, they are equally unlikely to be fitted with suspension systems like these. Simplicity is essential.

Active chassis systems operate depending on road load data and try to reduce body roll and pitch by using a combination of adaptive damping and active roll control. Ride height can be equalised with uneven loads in the car. The outside dampers can be made firmer during fast cornering.

Ensuring the vehicle always drives optimally creates a lot of benefits for safety. Dr Veight Held, General Motors Europe’s chassis control system manager, says that by 2015 all cars will have some form of integrated active suspension safety system.

“A decade ago, air conditioning was an expensive option: today, there are only a few that don’t have it as standard,” he says.
Fortunately, there is no shortage of options for OEMs. Tenneco, TRW and ArvinMeritor are among the suppliers with systems ready. TRW offers Active Dynamic Control, in which a hydraulic actuator replaces the roll-bar drop link to neutralise body roll.

Accelerometers control increases in hydraulic pressure.
Active systems need not just be for sharper handling – ride comfort can benefit. Because you can vary the roll bar stiffness, you can have softer coil springs, because they don’t have to contribute to roll-resistance in corners.

ArvinMeritor is preparing to put active suspension into a C-segment model. “We’re working on a sedan platform that, if all goes well, could be in production with an OEM in 2010,” says Bob Carlstedt, vice-president of the firm’s modular suspension systems division.

Tenneco is more cautious about its active suspension system. “We don’t forsee car manufacturers extending it into the C-segment before 2015,” says the firm. Semi-active systems, such as the continuous controlled damping system developed for the Ford Mondeo, are much more likely.

Opel already offers a form of active suspension in the C-segment. Astras can have the Interactive Driving Plus System fitted as an option. This incorporates continuous damping control based on twin-tube ZF Sachs units with an electromagnetically controlled proportional valve, three body acceleration sensors and two wheel acceleration sensors.

It is not cheap, but it is a sign of progress. The option costs about €600, only slightly more than metallic paint. Some 15 per cent of regular Astras opt for the system. For the sporty VXR version, 30 per cent of buyers choose it.

Audi offers the TT with Delphi’s MagneRide dampers. Nearly 20 per cent of roadster buyers are prepared to pay about €1,700 for the system. Uptake of a €600 sports suspension package is just two per cent. Audi is likely to also use the same technology on future versions of its A3 Sportback compact saloon, scheduled for production in 2009.

Ford was able to reduce the cost of Tenneco’s semi-active suspension system in the Mondeo by spreading the cost across its Premier Automotive Group companies. If the Mondeo alone were to use it, costs and economies of scale would be unjustifiable. Add in Volvo, Land Rover and Mazda, and a case can be argued. But Marcus Rothoff, a product planning manager for Volvo says the step that takes active suspension into the C-segment might still take some years.

There’s a compelling driver in achieving this, however. Manufacturers such as Ford are seeking to share chassis technologies on more models, but also need to differentiate their individual brands. The necessary differences could be created by having active systems, saving in physical development costs. With changes in the control software, it would be relatively cheap to achieve a firmer damper rebound or tauter roll profile on different models.

The expansion in applications could partially offset the cost, but buyers will still have to be willing to contribute. “The on-cost for the consumer would be up to the vehicle manufacturer,” says Aly Badawy, TRW’s vice-president of steering and suspension engineering. “But high-volume production of a system for the C-segment could be done for as little as $250, depending on the system.”

Mass-market take-up won’t come without canny cost control. “Adaptive damping is a fully internal and fully electronically variable valve, which is modular in design,” says Carlstedt of ArvinMeritor. “You don’t have to retool production for other components to support an adaptive damper.”

ArvinMeritor’s active roll control system also has three different levels, depending on the required pricing point. It can either be purely “on-off’ or can induce roll damping with additional sensors. Add more sensors still and it can be a fully active one or two-channel system.

TRW’s system is scaleable too. By adding one or two separate hydraulic circuits, it can go from simple roll control to an increasingly active setup. “This can be done in single-channel systems on just one axle at one end of the stabiliser-bar, or it can be used on both axles and at both ends,” says Badawy. “Of course the cost increases the more actuators and control algorithms you add to the electro-hydraulic control unit – but not to the extent of the more complex systems we’ve seen in the past.” The firm also has a semi-active roll control system.

The suppliers agree that cost reductions will come from integrating the whole system with existing electronic devices. Tenneco is also trying to integrate sensors into the dampers.”

Marcus Rothoff, Volvo’s active safety product planning manager, agrees: “Future sensor technologies will reduce the cost of different vehicle control systems,” he says. If ESC and active suspension can be integrated, why not draw all the suspension input data from the ESC sensors already in place?

Engineers at the suppliers are already thinking even further ahead. TRW is developing short and long-range radar and steer-by-wire. If you could integrate them all using the ESC system to control the dynamics, it would be possible to adapt all systems constantly to changing road conditions.

Add in car-to-car communications and road profile scanning from the GPS navigation system and safety could become predictive, not merely reactive. Suspension could firm up when twisty roads are ahead or soften slightly if it knows wet roads are coming.

It will all come down to cost. Such a vehicle is far beyond what anybody could justify today. But if vehicles with active suspension can be mass-produced for the C-segement, the industry will be a lot closer to making it a reality.