A Study of Triple Skyhook Control for Semi-Active Suspension System 2019-01-0168

The research described in this paper focused on improving occupant ride comfort and road holding by suppressing sprung and unsprung vibration using a semi-active suspension system. It has been reported that occupants tend to perceive vertical vibrations in a frequency range between 4 and 8 Hz as uncomfortable (described below as the “mid-frequency range”). Previous research into semi-active suspension system has focused on reducing vibration in this mid-frequency range, as well as close to the sprung resonance frequency of between 1 and 2 Hz. Skyhook damper (SH) control is a typical ride comfort control used to damp vibration close to the sprung resonance frequency. However, since SH control is not capable of damping vibration in the mid-frequency range, the shock absorbers are configured with a lower damping factor. This helps to achieve a good balance between reducing vibration close to the sprung mass resonance and in the mid-frequency range. In contrast, it has the trade-off effect of increasing unsprung vibration. The triple skyhook (tSH) control, which suspends the vehicle using three virtual elements (i.e., springs, dampers, and inerters), has been proposed to help resolve these issues. This control is capable of reducing sprung vibration over a wide range without altering the suspension characteristics. Furthermore, this control only uses information from sprung mass sensors, and can be configured using simple control laws. The purpose of this research is to simultaneously satisfy requirements for both ride comfort and road holding by applying tSH control to a vehicle with a semi-active suspension system. This was accomplished by driving a test vehicle over an irregular road surface, and analyzing the vehicle roll, pitch, and heave, as well as the unsprung vibration frequency. As a result, this research confirmed that the proposed control improves ride comfort by reducing sprung vibration over a wide frequency range. In addition, by suppressing deterioration in unsprung vibration, the control improves the road-holding performance compared to the conventional SH control.