Implementation and Testing of a Semi-Active Damping System

Abstract: The purpose of this thesis is to implement and test a semi-active damping system based on a concept from an earlier thesis. The project includes implementation of mechanical, hydraulic and electronic hardware, aswell as controller software. The idea is to measure the movements of the vehicle chassis and based on these measurements set the damping torque using hydraulics. To be able to develop, test and evaluate the system, realistic input data must be available. To acquire such data, driving trials have been conducted on a variety of tracks. The first part of the system is the sensors that measure chassis movements. Both accelerometers and a gyro has been used. To remove drift and high frequency vibrations, the signals are filtered. The suggested controller from the earlier thesis requests damping torque based on the dampers vertical velocity. When accelerometer signals are integrated, measurement and rounding errors causes drift in the velocity. To compensate for this, a floating average is calculated and used. The main hydraulic component is a pressure reduction valve that controls the pressure inside the damper. Higher pressure will give higher damping torque. The reaction speed of the system is mostly depending on the hydraulic components. It is important to know the time delay from a change in the valve control signal, to when the actual pressure in the damper has been reached. Tests have shown that a large step, going from 10 Bar to 60 Bar takes approximately 46ms, and that a small step from 1 Bar to 20 Bar takes 63ms. The valve is faster when higher pressure levels are requested. In addition to the hydraulic response time the delay through the signal filters, measured to about 14ms, must be added. The sensors are affected by vibrations. If these can be reduced, the digital filters can be made less sharp with a lower filter delay as result. It is also important to have a good control computer so that large rounding errors in the filter calculations can be avoided. This would greatly decrease drift in the integrated velocity.