CDC SAFE, SUREFOOTED CORNERING

ZF was the first supplier to bring an adaptive, electronic damping system for cars to market, in the form of Continuous Damping Control (CDC). Today, the system is fitted as standard to a broad range of cars, trucks, buses, farm vehicles and even motorcycles.

As any economist will tell you, the difference between a new idea and a genuine innovation is simple: it all depends on the product’s success in the marketplace. This can be measured most clearly in terms of the volume of units produced and purchased each year. By this yardstick, ZF has every reason to be delighted with CDC. Since becoming the first company to put a continuously adjustable chassis control system for cars into volume production back in 1994, more than 18 million units have left ZF’s production line. What was once an optional extra for luxury and premium vehicles has become a standard product enjoying wide-ranging market success across all passenger-car classes, commercial vehicles, farm machinery and motorcycles.

When a team of designers and research engineers started developing CDC toward the end of the 1980s, Mannesmann Sachs AG – subsequently acquired by ZF – already had around a decade’s worth of experience with electronically controlled damping systems. However, these were simple, manually activated systems, where simple adaptive governors known as threshold controllers were capable of choosing between two or three different damper characteristics depending on ambient driving conditions - the comfort was left more or less literally by the roadside. At the same time, the early system’s production process was very complex and as a result the manufacturing costs disproportionately high. “As the 1980s drew to a close, we started looking for some way to reduce the electronic damping system’s production costs while at the same time improving ride comfort – without making any compromises in terms of safety,” explains Heinrich Schürr, Head of Active Damper Development. “It soon became clear that we needed a damping system based on a stepless or continuously variable valve, rather than a stepped valve.”

From paper to product

This epiphany cleared the way for an in-house predevelopment project: While designers considered the architecture of the new valve, research engineers worked on perfecting the interplay between the individual damper components and developing the necessary control systems. This close collaboration produced CDC solutions for cars and commercial vehicles in parallel. "At this point, we were the first supplier to take a holistic, systemic approach to suspension design; all of the other suppliers were still working at the level of individual components”, adds Schürr. The team was effectively anticipating something that would soon become a major trend in the automotive industry – the shift of systems expertise from manufacturers to suppliers.

The key element in a CDC damper is the proportional valve. The valve’s position reduces or increases the flow of oil through the aperture, adjusting the hardness of the suspension precisely and steplessly. The process operates independently for each wheel.

In 1997, South Korean carmaker Ssang Yong was the first to seize the opportunity to differentiate
its flagship Chairman model from the competition by installing CDC. Other premium cars and sportscars soon followed suit, including the BMW 7 Series, Ferrari 360 Modena, VW Phaeton, Maserati 3200 Coupé and Audi A8. But the technology’s performance soon impressed manufacturers enough for CDC to make a big leap forward, becoming standard equipment in top-of-the-range executive limos built by BMW and Audi. Of course this meant production volumes went up, setting the stage for further expansion into the mid-range segment,” explains Dr. Andreas Fink, who is responsible for the Active Dampers product line. The breakthrough into standard equipment came in 2004, when BMW fitted CDC to all 7 Series models and Opel equipped its high-volume Astra, Vectra and Zafira models with the adaptive damping system. CDC production figures rocketed as a result. But the full potential of this innovative technology was far from exhausted. They also regularly upgraded both hardware and software, as well as the control unit’s functional algorithms.

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Continuous improvement

Even so, for a long time CDC was simply too costly to be considered for the price-sensitive subcompact car segment. The response by ZF’s engineers came in the form of CDC 1XL (pronounced “one axle”), an adapted version of the system that first went into production in 2014, in he Honda Civic Tourer. This modified system uses the same damper technology and system architecture as the full-size system, albeit at reduced cost.

CDC has offered similar advantages to motorcycle riders since 2012 – driving, braking or accelerating under different loading conditions, with or without passengers.Top-of-the-range models from Aprilia, BMW and Ducati now take uneven road surfaces in their stride thanks to CDC. CDC is also helping keep passengers comfortable in buses and protecting fragile loads in trucks. Other developments are ongoing – and benefiting from the synergies available when several divisions work together. “We’re currently transferring the knowledge we’ve gained from developing full systems for cars to cab damping for farm machines and trucks,” adds Heinrich Schürr.

Damping by default

This steady expansion of the range of applications for the CDC system is the reason why a total of some 18 million CDC dampers have been manufactured to date.“If we look at installation levels worldwide, our CDC technology is still only in single figures,” sums up Dr. Fink. “In terms of the technology’s theoretical growth potential – well, the sky’s the limit!”

And that brings us back to the definition of innovation we explored at the start. These high production volumes are both a blessing and a curse. They’re a visible sign of the system’s success – but because it has been so successful in penetrating so many different market segments, few people now think of CDC as an innovative technology. The adaptive damping system is becoming a standard item – to the considerable benefit of vehicle occupants.

Pictures: Corbis

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