Study of modeling method for shock absorbers

Abstract

The pace of globalization of vehicles has increased in recent years, along with new requirements for steering stability and durability in rough road conditions that had not been anticipated in Japan. Accordingly, the range of physical quantities such as acceleration and force needs more in-depth examination. The shock absorber is a component that particularly determines ride comfort. A shock absorber is composed of a piston and a cylinder. In general, when the piston speed is low, the damping force is generated by fluid passing through a fixed orifice. When the speed is higher, a valve opens in addition to the fixed orifice. This suppresses the damping force of the fluid flow, thus maintaining stability and improving ride comfort. Therefore, the damping characteristics of the shock absorber have a large non linearity. In addition, when the excitation frequency increases, hysteresis appears between the piston speed and the damping force. The parameters such as the loss factor and dynamic stiffness in the frequency domain can be used for steady-state response analysis. However for transient response analysis of bumps and rough road conditions that affect the ride comfort, those characteristics must be expressed in the time domain. Therefore, in this study, measurement results are used to build a physical model composed of frequency-independent elements as simple as possible. This allows a time domain analysis to be done for a shock absorber with non-linearities of complex structure and frequency dependence. The Maxwell model is used to take into account the non-linearity of damping force and represents the hysteresis and frequency dependence that can be found in the actual measurement results. Our model can provide a non-linearity in the damping characteristics of the dashpot of the Maxwell model. In addition, the effectiveness of the proposed method is verified by experimental analysis of the shock absorber only and the whole vehicle.