Adaptive Damper Control
The results of parameter variation on damper stiffness suggested that body acceleration as well as wheel load variations can be minimized for a wide frequency range, if a relatively high level of damping is available in the areas of body and wheel resonance while a softer damping is available in the range outside the points of resonance.
A clear improvement of conventional suspension systems can hence theoretically also be achieved by a damping system which depends on the excitation frequency of the system, see figure.
The potential for improvement which can be achieved by damper control is limited by the fact that the selection of a definite frequency is not possible as a result of the randomness of road irregularities. Apart from that, the improvement potential also depends on the achievable range of variation of damper characteristics and to what extent the system life can be reduced.
The EDC system (Electronic Damper Control) of BMW was developed in cooperation with Boge and VDO. Here, the damper characteristics are adjusted in three steps using control electronics. The EDC system identifies the road excitation over an acceleration sensor mounted on the body.
The sensor signals are processed by the ECU in a manner allowing the determination of separate characteristics for excitations with respect to body and axle natural frequencies. Depending on vehicle load and the intensity of instantaneous vibration excitation, different threshold values will result in a stepped damper adjustment.
The effectiveness of the system is illustrated with the help of a conflict diagram between comfort and driving safety, see figure.