The CDC (continuous damping control) shock absorbers, similar to those used on the luxury Q7 SUV with air suspension, are twin-tube hydraulic units with an additional external valve and connecting pipe. Their operation can be continuously varied: an electromagnetically energised proportional-action valve opens against the force exerted by a spring and regulates the flow of hydraulic fluid between the inner and outer shock-absorber tubes. A smaller flow cross-section makes the damping characteristic firmer, a larger one makes it softer.
Within the mode that the driver has chosen via Audi drive select, the control unit employs adaptive characteristics. It modifies its command signals to match the driving style and road conditions. Even in the ‘comfort’ mode the shock absorbers can be switched in an instant to a firm setting if required, though not to the absolute limit. They are installed in conjunction with sports suspension springs, which have the effect of lowering the body by 20 millimetres, but still provide a good standard of ride comfort
The control unit selects the optimal damping force for the actual driving situation, for instance firmer damping to prevent body roll when cornering fast or braking, lower damping force if the surface under the wheels is extremely rough or average settings on poorly-surfaced country roads.Published 9 February 2008