Influence of Shock Absorber Friction on Vehicle Ride-Comfort Studied by Numerical Simulation Using Classical Single Wheel Model

Along with the suspension improvement in these two decades, it is well known that the suspension friction force became one of major parameters to affect ride comfort performance. However, it was difficult to carry out quantitative prediction on ride comfort improvement against friction force change with high correlation. It was difficult to analyze correlation between actual vehicle performance and simulation since there were difficulties in controlling damping force and friction individually. On the other hand, magneto-rheological shock absorber (MR Shock) has had several applications and widely spread to passenger vehicles. The large variation and high response of damping force especially in slow piston speed region contributes to achieve an excellent vehicle dynamics performance. However, MR Shock shows the high friction characteristics, due to the unique sliding regime of internal parts. It is said that this high friction characteristic is causing obstacles in ride-comfort. To respond to these demands on ride comfort improvement and its prediction in simulation, we made it possible to purely control damper friction force without changing damping force, by changing fluid, bushing and oil sealing design of MR Shocks. This enabled us to simulate ride comfort characteristics against friction and evaluate the correlation to actual vehicle. To simplify the model, a classical single wheel model with damping and friction force look up table was used for simulation. Experimental or calculated data of damping force and friction force is used to simulate multiple friction cases. The both results of simulation and actual vehicle test showed that friction reduction reduces transfer characteristics especially in cut-off and isolation frequency region. A deviation has been observed between simulation and experimental ride comfort performance in low friction region, possibly oriented to the other suspension parts remained friction. These correlated results proved the possibility of prediction of friction effect on ride comfort.