Research and applications of viscoelastic vibration damping materials: A review

This paper presents the development of a novel regenerative shock absorber sized for a passenger car suspension system. The shock absorber includes a simple and highly efficient motion converter called a two-leg mechanism , a planetary gearhead, and a brushless three-phase rotary machine. The design and analysis of the regenerative shock absorber are presented by considering the dynamics and efficiency of the electromechanical device. The performance of the regenerative damper is evaluated under sinusoidal excitation inputs for typical amplitudes and frequencies in a vehicular suspension system. Experimental results show that a damping coefficient of $1720$ N $\cdot$ s/m can be achieved by controlling the external loads. Furthermore, a mechanical energy conversion efficiency between 0.71 and 0.84 is achieved, which is considerably higher than other mechanisms reported in the literature, such as ball screw, rack-and-pinion, and linear mechanisms.

Regenerative Shock Absorber Using a Two-Leg Motion Conversion Mechanism

Dynamic stiffness and loss factor measurement of engine rubber mount by impact test

A magnetorheological damper is evaluated under exhaustive experimental scenarios, generating a complete database. The obtained database includes classical tests and new proposals emphasizing the fr...

https://hal.archives-ouvertes.fr/hal-00733253/document

Magnetorheological damper—an experimental study

The linear quarter car model is the most widely used suspension system model. A number of authors expressed doubts about the accuracy of the linear quarter car model in predicting the movement of a complex nonlinear suspension system. In this investigation, a quarter car rig, designed to mimic the popular MacPherson strut suspension system, is subject to narrowband excitation at a range of frequencies using a motor driven cam. Linear and nonlinear quarter car simulations of the rig are developed. Both isolated and operational testing techniques are used to characterise the individual suspension system components. Simulations carried out using the linear and nonlinear models are compared to measured data from the suspension test rig at selected excitation frequencies. Results show that the linear quarter car model provides a reasonable approximation of unsprung mass acceleration but significantly overpredicts sprung mass acceleration magnitude. The nonlinear simulation, featuring a trilinear shock absorber model and nonlinear tyre, produces results which are significantly more accurate than linear simulation results. The effect of tyre damping on the nonlinear model is also investigated for narrowband excitation. It is found to reduce the magnitude of unsprung mass acceleration peaks and contribute to an overall improvement in simulation accuracy.

An insight into linear quarter car model accuracy

This paper deals with the dynamic characterization of an automotive shock absorber, a continuation of an earlier work [1]. The objective of this on-going research is to develop a testing and analysis methodology for obtaining dynamic properties of automotive shock absorbers for use in CAE-NVH low-to-mid frequency chassis models. First, the effects of temperature and nominal length on the stiffness and damping of the shock absorber are studied and their importance in the development of a standard test method discussed. The effects of different types of input excitation on the dynamic properties of the shock absorber are then examined. Stepped sine sweep excitation is currently used in industry to obtain shock absorber parameters along with their frequency and amplitude dependence. Sine-on-sine testing, which involves excitation using two different sine waves has been done in this study to understand the effects of the presence of multiple sine waves on the estimated dynamic properties. In an effort to obtain all frequency dependent parameters simultaneously, different types of broadband random excitations have been studied. Results are compared with stepped sine sweep tests. Additionally, actual road data measured on different road profiles has been used as input excitation to obtain the shock absorber parameters for broad frequency bands under realistic amplitude and frequency conditions. These results are compared with both simulated random excitation and stepped sine sweep test results. INTRODUCTION The shock absorber is one of the most important elements in a vehicle suspension system. It is also one the most non-linear and complex elements to model. The current method of characterizing the dynamic properties of shock absorbers for CAE models involves testing at discrete frequencies, displacements, and preloads using an MTS test machine. The dynamic stiffness (K) and damping (C) are extracted by fitting a linear model of the form F(ω)=K*x(ω)+C*v(ω) to the measured input displacement (x), velocity (v), and output force (F). The excitation technique is a pure sine excitation at the desired frequency and amplitude. These harmonic excitations are then swept through all desired frequency and amplitudes. Parametric and non-parametric models also exist for the shock absorber. A non-parametric model based on a restoring force surface mapping has been developed [2,3,4]. The model considers the force to be a function of displacement and velocity. Although, this model is more applicable to a single frequency excitation, it serves as a useful tool for identifying the non-linearity’s in the system. A comprehensive physical model was developed by Lang [5], later condensed and validated by Morman [6]. Lang’s model has more than 80 parameters, is computationally complex and is not suitable for comprehensive vehicle simulation studies. Morman’s model has been shown to be useful for studying the effects of design changes for a particular shock. Reybrouck [7] has developed a physical model, which has 14 parameters, valid for frequencies up to 20 Hz, but has limited appeal for the analysis of shock absorbers for NVH applications.

The Effects of Different Input Excitation on the Dynamic Characterization of an Automotive Shock Absorber

Different methodologies to test and analyze the dynamic stiffness (K) and damping (C) properties of several silicone and EPDM rubber automotive exhaust hangers were investigated in this research. One test method utilized a standard MTS hydraulic test machine with a single sine excitation at discrete frequencies and amplitude levels, while a second method utilized an electrodynamic shaker with broadband excitation. Analysis techniques for extracting the equivalent stiffness and damping were developed in the shaker tests using data from time domain, frequency domain, as well as force transmissibility. A comparison of all of the shaker testing methods for repeatability and accuracy was done with the goal of determining the appropriate method that generates the most consistent results over the range of testing. The shaker testing in the frequency domain using a frequency response function model produced good results and the set-up is relatively inexpensive. The hydraulic excitation method, however, is more suitable for large displacements and is ideal to study the variations of K and C with frequency, displacement, temperature and pre-load.

Dave Griffiths

Papers

The Effects of Different Input Excitation on the Dynamic Characterization of an Automotive Shock Absorber

Measurement of Dynamic Parameters of Automotive Exhaust Hangers