Issue: Sep 2009


Networked Chassis in the New Opel Astra



Intelligent dampers react in milliseconds to the latest driving situation

by Nick Palmen

New generation Astra drivers are enjoying a high-tech chassis. The the electronic CDC (Continuous Damping Control) by ZF not only enhances comfort, driving dynamics and safety; in the “FlexRide" option, the intelligent system is also networked to the electronic driving aids and the transmission, as well as to the economical electric power steering system by ZF Steering Systems.

With the new Opel Astra, "FlexRide" - previously an exclusive option for the mid-range model Insignia - is available for the first time in the compact car class. The CDC by ZF Sachs is the technical basis of the intelligent chassis control system. ZF Sachs engineers cooperated closely with Opel to integrate the system in the new Astra. Thus, the automobile manufacturer from Ruesselsheim, Germany, is continuing its success story. The previous Astra generation was already the first compact car with electronic damper control.

Optimally damped in every driving situation 

The intelligent CDC system is made up of special dampers as well as control electronics that detect the current driving situation: Sensors record data concerning the road conditions, vehicle speed, and vehicle reactions that are forwarded to the electronic control unit. Furthermore, the electronics record the damping force necessary for the respective driving situation every five milliseconds. A proportional valve in the damper adjusts this damping individually to each wheel. This adjustment is made according to what is called the "Advanced Skyhook” strategy. Its goal is to keep the vehicle body as stable as possible regardless of driving and road conditions, as if the vehicle were suspended on a track parallel to the sky.

Individual damping force - depending on the driving style
In the new Astra, FlexRide also allows the driver to set the electronic damping system to his or her individual driving style. At the push of a button, the driver can select from two modes with different damping characteristic curves: in the comfortable Tour mode, the dampers react softer, while in the firm Sports mode, the CDC adjusts to a stiffer configuration in milliseconds.

Versatile networking possibilities 

However, because a sporty or comfortable driving feel is not generated solely by the respective chassis setting, CDC is networked to the other necessary components, such as driving stability programmes, steering, accelerator pedal calibration, and transmission. This is possible thanks to the damping system's electronic control unit: it collects the data calculated by the CDC sensors concerning the current driving situation and uses the data not only for damper setting but also provides said data to the other systems. At the same time, the control unit processes the information transmitted to it by the other components and systems in the network. For example, from the Servolectric electric power steering system by ZF Steering Systems, a joint venture between Robert Bosch GmbH and ZF Friedrichshafen AG. In the FlexRide chassis, the CDC is - strategically-compatible - fully networked with the intelligent steering system.

Strategic networking for greater safety 

The core of the intelligent steering is the precise electronic control unit. It processes and permanently saves all relevant data, such as information about the vehicle, engine status, driving and steering speed. It can be networked to the adaptive CDC dampers using CAN bus without any problems. As a result, an uninterrupted data interchange is possible, which not only ensures optimal steering force and therefore a comfortable driving feel, but also ensures considerably more safety at the same time: the perfectly fine-tuned interplay between steering and damping significantly improves handling in sudden dangerous situations.

Not only smart, but also economical: the Servolectric 

Apart from its networking possibilities, the Servolectric provides for additional advantages. In contrast to conventional hydraulic power steering systems, it only consumes energy when the driver is actually steering. An electric motor replaces the usual hydraulic system, as a result of which permanent oil pressure is no longer required. This Power-on-Demand principle consumes less energy: Compared to hydraulic steering systems, this steering system saves about 0.4 litres of fuel in the NEDC (New European Driving Cycle) and up to 0.8 litres per 100 kilometers in city driving.

Benefiting from all the steering technology provided by one system partner
With the installation of a steering column and intermediate steering shaft, Opel is benefiting from the system expertise of ZF Steering Systems and is purchasing the entire "wheel-to-wheel" steering system with coordinated individual components from a single source.

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