ZF Friedrichshafen AG has further optimized and extended its well-established electronic damping portfolio, the Continuous Damping Control (CDC): In the fourth generation, sensors have been integrated into the control unit. For the special requirements of subcompact cars and vans, the supplier has developed a pure rear axle system (CDC 1XL, i.e. "One Axle").
In comparison to both standard dampers and engageable systems on the market, which only permit fixed predefined settings, the CDC offers clear advantages: ZF technology provides uninterrupted adjustment of suspension damping to the respective driving situation in real time—smoothly, accurately and for each individual wheel. Thus, the CDC resolves the conflict of aims between comfortable-soft and dynamic-firm chassis tuning. This adjustment is made according to what is known as the "Advanced Skyhook” strategy. Its aim is to keep the vehicle body as stable as possible irrespective of the driving and road conditions, as if the vehicle were running along a track parallel to the sky.
Damping comfort of the fourth generation
In the CDC, sensors record data regarding road condition, vehicle speed, and driver's actions, and pass them on to the control unit. From this data, the electronics calculate the damping force necessary for the respective driving situation in fractions of a second. An electromagnetically regulated proportional valve in the damper adjusts this damping individually for each wheel. For example, the dampers facing the bend become rigid when cornering in order to minimize the roll; when braking, the front axle damping firms up and reduces undesirable pitching. And the driver can also choose between comfortable or sporty chassis tuning. The optimal damping of the CDC makes driving not only more comfortable and dynamic, but also safer: The extra stability is particularly noticeable when carrying out sudden evasive maneuvers or when the vehicle is fully loaded.
ZF has further enhanced the design of the CDC in its fourth generation: It used to be necessary to fit acceleration sensors to the vehicle chassis to record body movements. ZF has now integrated these directly into the control unit. The simplified system design reduces the number of components, weight, assembly work and installation space requirements of the CDC system. In particular, the wiring effort for the OEM is considerably smaller, and this makes using CDC technology even more cost-effective. Integration of the individual sensors into a cluster is further proof of ZF's electronics expertise in chassis technology.
CDC for all vehicle segments
The ZF CDC was originally predominantly found in upper range vehicle categories, but now it has also become established in passenger cars in the middle and compact car range. Recently, ZF has also been targeting the price-sensitive subcompact car models, as well as vans, as active damping can offer significant advantages here: Passenger cars in this segment have a shorter wheelbase and a high payload compared to the empty weight. As a result, there can sometimes be extreme fluctuations in axle loads: If only the driver is in the vehicle, there is considerably more weight on the front axle. When fully loaded, this distribution in the subcompact car changes significantly and the rear axle carries up to two thirds of the load. Conventional, passive rear axle dampers constantly require compromises because the design is always focused on driving safety (hard damping), which has a negative impact on comfort. This is where ZF's CDC 1XL comes into play: As an active damping system, it minimizes the effects of these strong variations of the rear axle load and, additionally, improves driving dynamics and comfort. It uses ZF's well-known and established damping technology—as well as the system design with an integrated sensor cluster as mentioned previously.
CDC also provides greater safety and driving dynamics for two-wheeled vehicles. For the first time, ZF is equipping motorcycles with the active damper system as well. Top of the range models from several manufacturers—including the Multistrada S models from Ducati — make the ride over uneven road surfaces even smoother. Features like the direct responsiveness of the suspension elements or accurate suspension feedback have been enabled by using CDC. The special tuning provided by the electronics in the CDC control unit balances out the highly dynamic changes in wheel load that are characteristic of motorcycles when braking and accelerating, and thereby ensures comfort at all times when cornering.
Thanks to ZF's systems expertise and its many years of experience in the field of regulated damping systems, the company is able to make use of the synergies between the automotive sector and motorcycle applications. Support from ZF Race Engineering for both segments rounds off ZF's competence and service portfolio in the field of regulated damping systems.
On the road in the millions
ZF's electronic damping has been winning over vehicle manufacturers since its market launch in 1994—and is still doing so with its fourth generation. The continuing increase in CDC production figures illustrates this; 2011 marked the temporary record high with more than 2.2 million dampers produced for Alpina, Audi, Bentley, BMW, Ferrari, Maserati, Opel, Rolls-Royce, Mercedes-Benz, Porsche and Volkswagen. About 16 million CDC systems have already come off the production line at ZF and consistent expansion of the range has played a major role in this success. ZF expects an annual production of more than three million CDC units for passenger car applications by 2016. This does not include ZF systems for buses, trucks, agricultural machines and motorcycles.