Modelling of bushes and hydro mounts in vehicles using a multi body simulation environment

Abstract

Engine mounts and suspension bushes are crucial for ride comfort and handling, durability loads and vehicle dynamics. To ensure good ride comfort and vehicle handling the various mounts must be tuned carefully for an optimal setup. This tuning work is very time consuming and expensive because prototypes and expert test drivers are needed. Computer based tuning is very beneficial for manufacturers but there is a need for improved elastomer and hydro mount numerical models.

In the established development process, multi body simulations (MBS) based on rigid bodies are used in combination with simple spring-damper models for the rubber mounts. Such linear models enable good forecasts in the time domain within a limited frequency and displacement range, only.

To improve the accuracy of full-vehicle simulations, a practical non-linear model for mounts and bushes has been identified, that takes into account the amplitude dependent behaviour of elastomers. The model has been improved and implemented into a full vehicle simulation environment and numerical issues and principal drawbacks have been solved.

In the past a number of model concepts have been suggested for hydraulically damped mounts, but most of them neglect the amplitude dependence of the underlying rubber parts. This simplification leads to less accuracy. Some hydro mount models need experimental data for parameterization that is not available. Other models are rough estimations for certain types of hydro mounts or they lack a stable and easy-to use parameter identification process. The newly developed elastomer model has therefore been incorporated in a numerical model for hydro mounts, leading to higher accuracy and flexibility for different sorts of hydro mounts and bushes. The suggested model uses physically based model parameters that allow a detailed study of underlying hydro mount phenomena.

Beside the main models, a user-friendly, fast and stable process for parameter identification is needed. Programs for a virtual mount test rig, the import and further processing of measurement data, parameter identification and export of model parameter files for an MBS environment within a graphical user interface (GUI) have been developed to ensure usability and practicality for different areas of use.

The presented models and methods are designed for use in an early phase of development to predict the overall behaviour of vehicles. The mount’s behaviour is simulated within an MBS environment based on parametric data from a few standard experiments. The focus is to predict the transient behaviour based on simple tests from data obtained during sinusoidal excitation.
The models have been implemented into a commonly used MBS environment and validated within full-vehicle models for ride comfort analyses and durability load calculation. For model evaluation, frequencies up to 50 Hz with excitation amplitudes up to +/ 3 mm were of main interest. The accuracy of full-vehicle simulations can be significantly improved, using the new models for all bushes and hydro mounts.

This thesis outlines existing literature relating to the modelling of elastomeric mounts, the model develop process and validation. This is supported by a number of journal publications written by the author that provide additional data and discussion.

Date of Award	29 May 2019
Original language	English
Supervisor	Jos Darling (Supervisor) & Andrew Hillis (Supervisor)