Within the framework of this project, the dynamic behaviour of a sub frame sup- porting the rear differential of vehicles is investigated. The original structure, consisting of sub frame and assembled gear, used hard plastic bushings. This setup caused noise inside the passenger cabin, which was not tolerated by customers. In order to obtain a better understanding of the noise’s source, an experimental modal analysis of the structure is performed. After draping a point cloud over the structure, the frequency response functions between these points are measured. The complex exponential method, including Prony’s method, provides algorithms which are used to extract the structure’s modes. Within the frequency range of approx. 50 to 550 Hz seven eigenmodes are extracted. Two of them show strong interaction between sub frame and differential, while the residual modes are dominated by the frame’s mode shapes.
Table of Contents
1 Introduction
2 Laboratory setup
3 Signal analysis
4 Mode extraction
5 Results
6 Appendix
Project Goals and Scope
This project investigates the dynamic behavior of an automotive subframe provided by GKN Driveline, focusing on understanding how the implementation of soft elastomer bushings influences the structure's noise characteristics and overall vibration profile compared to previously used hard bushings.
- Experimental modal analysis of the subframe and differential assembly.
- Evaluation of structure-borne noise reduction through elastomer decoupling.
- Development of a custom MATLAB GUI for interactive modal animation.
- Systematic identification of seven eigenmodes within the 50 to 550 Hz frequency range.
Excerpt from the Book
1 Introduction
Within the framework of this project, it is the aim to investigate the dynamic properties of an automotive sub-structure provided by GKN Driveline. The modal parameters are extracted experimentally and these results are used to animate the structure’s eigenmodes and to hereby get a better understanding of its dynamic behaviour.
This section shall give a short introduction to the test object and the given problem. It is followed by a listing of the laboratory setup. Section 3 will present an explanation of the signal analysis and hereafter the principal theory behind mode extraction from the obtained frequency response functions (FRFs) is given. In the end, we will present our gathered results and use a self-designed MATLAB program to animate the eigenmodes of the structure. In our last section, we will discuss our findings, prove consistency and try to explain particularities.
Summary of Chapters
1 Introduction: This chapter defines the project scope, introduces the automotive subframe as the test object, and outlines the methodology for experimental modal analysis.
2 Laboratory setup: This chapter details the physical suspension, the measurement grid design, sensor placement, and the excitation method using a hammer.
3 Signal analysis: This chapter explains the signal processing chain, including filtering, FFT application, and the estimation of frequency response functions.
4 Mode extraction: This chapter covers the theoretical framework and the application of Prony’s method to extract system poles, eigenfrequencies, and modal damping from measured FRFs.
5 Results: This chapter presents the identified eigenmodes, discusses the interaction between the gear box and frame, and introduces the MATLAB GUI for visualization.
6 Appendix: This chapter provides supporting technical data, including detailed sensor specifications and comprehensive triangulation tables for the measurement grid.
Keywords
Experimental modal analysis, frequency response functions, GKN Driveline, elastomer bushings, subframe, eigenmodes, MATLAB, Prony’s method, signal processing, structural dynamics, vibration, FFT, damping, resonance, impact hammer.
Frequently Asked Questions
What is the core focus of this project?
The project investigates the dynamic properties of an automotive subframe and analyzes how the use of soft elastomer bushings instead of hard bushings affects noise and vibration characteristics.
What are the central thematic fields?
The work combines structural dynamics, experimental vibration testing, signal analysis, and numerical mode extraction techniques.
What is the primary objective?
The main goal is to understand how the new soft bushings modified the dynamic behavior of the subframe and whether they effectively reduced noise transmission into the passenger cabin.
Which scientific method is applied?
The authors employ experimental modal analysis, utilizing hammer excitation to capture frequency response functions (FRFs) and applying Prony's method in the z-domain for mode extraction.
What is covered in the main section?
The main section covers the experimental setup, the signal processing workflow, the mathematical derivation of modal parameters, and the final identification of resonance modes.
Which keywords characterize this work?
Key terms include experimental modal analysis, frequency response functions, elastomer bushings, structural dynamics, and Prony's method.
Why was Prony's method chosen for this study?
Prony's method was selected because it operates efficiently in the z-domain and is robust for curve fitting FRF data to extract modal parameters from noisy experimental signals.
How was the visualization of the modes handled?
The authors developed a custom MATLAB GUI that allows the user to load modal data and interactively animate the eigenmodes of the structure.
What conclusions were drawn regarding the soft bushings?
The study found that the soft bushings provide good isolation between the subframe and the gear box above a certain frequency, although they also introduce specific tilting modes at lower frequencies.
Are the measurement results considered conclusive?
The results are considered consistent, though the authors suggest future studies should include measurements in x and y directions and different boundary conditions to better simulate real vehicle installation.
- Quote paper
- Martin Rakowitsch (Author), Maximilian Scheid (Author), 2016, Experimental modal analysis of an automotive drivetrain subframe, Munich, GRIN Verlag, https://www.grin.com/document/342046
