Optimization and control of semi-active suspension system for off-road vehicles

Abstract

This study evaluates the dynamic response of three semi-active control policies as analyzed on a several off-road models. Two-axle 7DOF, three-axle 9DOF and four-axle 11DOF full vehicle system was developed to evaluate skyhook, groundhook, and hybrid controls. As well as exploring the relative benefits of each of these controllers, the performance of each semi-active controller was compared to the performance of conventional passive system. Each control policy is evaluated for its control performance under three different base excitations: step, bump and random. Corresponding to the bump and random inputs, peak-to-peak, RMS and frequency responses are considered for each control policy along with passive system. Specifically, sprung mass (heavy, pitch and roll acceleration), suspension and tire deflection. A comparison between different suspension systems were examined using half vehicle model and step input used to generate the time domain values of settling time and PTP acceleration for hybrid control policy and compared to fully active and passive systems using two-axle half vehicle model. Furthermore, Due to the importance of ride comfort for off-road vehicles, minimizing the peak-to-peak of the vertical, pitch and roll acceleration and reducing the settling time would lead to better ride comfort. In solving this problem, the step input was used for the optimization of a two-axle full vehicle's semi-active suspension system parameters with respect to ride comfort and handling. Genetic algorithm optimization technique is developed and used. Step input also used to generate the time domain and frequency domain responses of the four-axle full vehicle model. Reponses of sprung mass, suspension and tired deflection are obtained. Results of this study show that semi-active control offers benefits beyond those of conventional passive system. Further, traditional skyhook control is shown to be better in improving the vehicle body acceleration PTP, RMS and PSD responses. The groundhook control is shown to be better in controlling the tire deflection. Hybrid as a combination of both control policies skyhook and groundhook, shows to be better compromise in improving ride comfort and handling of the vehicle compared to passive system in all cases. Result shows also, that GA has consistently found near-optimal solutions within specified parameters ranges for several independent runs. Ride comfort improved without reducing the handling of the vehicle.