Study on Dynamic Stiffness of CV Mountings and Frame Structure

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					     Study on Dynamic Stiffness of CV Mountings and Frame Structure

                            M. Natarajan                                     B.Sandeep Reddy
                         Deputy Manager                                     Research Engineer
                Hyundai Motor India Engg. Pvt. Ltd.                 Hyundai Motor India Engg. Pvt.Ltd.
                 Izzat nagar, Hyderabad 500084                       Izzat nagar, Hyderabad 500084

Keywords: Chassis frame, NVH, IPI, Modal analysis etc...


This paper presents the study on vibration characteristics of chassis frame and mountings that include mode shapes, natural
frequencies and dynamic stiffness of mountings. The study primarily utilizes the modal and point inertance analysis results. The FE
modeling is done using HyperMesh and the solution is obtained by solving it in Radioss solver.


The vibration analyses on chassis frame as well as improving the dynamic stiffness of mountings are
important as they have huge influence in the NVH characteristics of vehicle. The mounting we chose in this
paper is cab mounting. The cab is connected to the chassis through cab mounting. As the loads from the
chassis are transferred to the cab through cab mounting, it is necessary to have a stiffer mounting. In this
paper, two cab mountings are studied and the methodologies to improve the dynamic stiffness using
Radioss are discussed.

                 Frame -A                                                                       Frame-B

Process Methodology (details with figures)

1. The finite element model (shell/solid) of frames are modeled using HyperMesh and modal analysis is
   performed to extract the natural frequencies and their corresponding mode shapes.

2. The input point inertance analysis (using AMSES) is carried out to determine the dynamic stiffness at
   the cab mountings. The use of AMSES card enhances the solving speed to a great extent.

3. The weak regions can be identified by performing operation deflection shape analysis using frequency
   response analysis( direct ) method for the cab mounting at particular frequencies.

Simulation Driven Innovation                                                                                                   1
Results & Discussions

Modal Analysis

The modal analysis results shows that due to the design changes in the chassis frame, there is an
improvement in torsional frequency.

                      Torsion Mode

Point Inertance Analysis (IPI)

The dynamic stiffness at the cab mounting is calculated by performing input point inertance analysis at cab
mount locations. The unit load is excited in all three directions (X,Y,Z). The results are plotted and from the
graph, the dynamic stiffness of the mount is calculated. It is easy to identify from the graph, the frequencies
(encircled peak) at which the stiffness of the mount is very less.

ODS Analysis

By performing the ODS analysis, the weak regions can be identified for the particular excitation. The cab
mount is excited at the corresponding frequencies (at which stiffness is low) and the results are analyzed for
further improvement of cab mount.

           IPI Graph of Cab mounting (X-dir)                           ODS Contour of Cab mounting (X-dir)

Red curve- A model, Green curve-B model and Blue curve - 1000Kgf/mm reference curve.

Simulation Driven Innovation                                                                                 2
Future Plans

The paper just deals with the study on dynamic stiffness of cab mount. In the next stage, we are planning to
do acoustic analysis on cab using Radioss acoustic capabilities to determine the noise level in the cabin.


The study has given a vast insight into the methodology of improving the dynamic stiffness of mountings
using the Radioss tool. The various ideas generated during the course of this study will surely help us in
solving the similar issues in the future.


We would like to thank our Managing Director Mr. Y.S.Roh and Mr. Lee Wong Sang, CAE –Head of the
Department and our team for their continued support and for encouraging throughout the development of
this paper.

Simulation Driven Innovation                                                                             3

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