The damper levels influence on vehicle roll, pitch, bounce and cornering behaviour of passenger vehicles - A study in cooperation with Volvo Car Corporation

The competition within the automotive industry is increasing. It is therefore important to reduce the resources and time spent on developing new vehicles. A significant part of the development is the chassis tuning which consumes a lot of time and resources. Dampers have a key role in chassis tuning and a better understanding of how the level of damping affects the vehicle behaviour could reduce both the number of prototypes built and the time spent on chassis tuning. This thesis investigates the possibility to develop a tool which captures the vehicle behaviour accurately enough to be used for choosing damper levels in the concept phase and as an aid in the tuning of dampers. A Simulink model was developed together with a graphical user interface allowing the user to easily change the level of damping and run simulations. In order to validate the model and see how changes to the level of damping affect the vehicle behaviour, both subjective and objective tests were performed for different damper configurations. It was found that the changes in vehicle behaviour for the various damper levels had a good correlation between the simulation model and the results from the physical tests. However in absolute numbers differences were found between simulations and objective tests. In order to verify the simulation model a limited number of objective tests are required. The tested vehicle should also be measured properly in order to receive better input data to the simulation model.The study found that the pitch balance in the vehicle is mostly affected by the difference in compression and rebound damping between the front and rear dampers. Lower damping at low vertical wheel velocities has a negative impact on roll control. This can to a limited extent be compensated with higher roll stiffness. A good balance between the front and rear damping is also required in order to have good connection to the road and make the vehicle feel more comfortable. The subjective and objective evaluation showed that it might be the time lag between lateral acceleration and steering wheel angle is a good indication of the vehicles turn-in capabilities and that the roll angle time lag determines the response. However more objective and subjective tests are required in order to confirm this connection. A better understanding of how to define good vehicle behaviour objectively is also required if the tool should be used in the concept phase