Suspension damping force control algorithms using vehicle states with driver and road inputs

Abstract

"The damping force control system of the shock absorber is relatively simply constituted and adopted widely. Skyhook semi-active control logic is representative algorithm which reduces vehicle vibration due to road input and vehicle posture changes such as roll or pitch angle due to driver operation input. However, it is difficult to reduce both of vehicle vibration and vehicle posture change when road input and driver operation input occur simultaneously like a case to run through the corner with road undulation. For this problem, control method considering the frequency range difference between vehicle behavior due to road input and that due to driver operation input is suggested. Also, the effectiveness of changing control constant depending on the vehicle state such as tire contact load is reported. In this paper vehicle behavior due to road input and that of driver operation input is calculated for analysis of skyhook shock absorber control using random wave which simulated actual road surface and driver maneuver.Non-linearity caused by the difference between target damping force and actual damping force increases vehicle behavior due to driver operation input in case of combination with road input. Also amplitude dependency was evaluated by changing the scale of road and driver input. As a result, it was confirmed that the effect of combination input is particularly remarkable when road surface input is large compared to driver input. Countermeasure control logic with additional damping force calculated with vehicle model is proposed to decrease vehicle behavior due to driver operation input. The vehicle model based on 3DOF of roll, lateral and yaw direction estimates vehicle behavior due to driver input. In addition, improvement of the estimation precision was attempted by digitizing suspension properties considering change of the damping force due to shock absorber damping force control in a frequency domain. The estimated state accuracy and the vehicle performance improvement were confirmed in actual vehicle tests."