Multi-body Dynamics Simulation on Flexible Crankshaft ... - IFToMM

12th IFToMM World Congress, Besançon (France), June18-21, 2007
<strong>Multi</strong>-<strong>body</strong> <strong>Dynamics</strong> <strong>Simulation</strong> on Flexible Crankshaft System
Ma Xingguo 1 You Xiaomei 2 Wen Bangchun 3
Northeastern University 1 Shenyang LiGong University Northeastern University
Shenyang LiGong University 2 Shenyang ,China Shenyang ,China
Shenyang ,China
Abstract—A virtual prototype of flexible multi-<strong>body</strong>
crankshaft system of engine is used to do the dynamics
simulation. The theory of flexible multi-<strong>body</strong> systems dynamics is
combined with FEA method to study the crankshaft, the dynamic
boundary loads on the joints in a working cycle are determined
by the simulation on the crankshaft system. The real-time
dynamics response of the crankshaft in a cycle is achieved. It
provides an important foundation for the crankshaft optimum
design.
Keywords: crankshaft, engine, dynamics, multi-<strong>body</strong>
I. Foreword
Crankshaft-mechanism of engine works in HTHP
environment. Crankshaft acted by the alternating loads
endures different loads such as compress, stretch, bent and
torsion, so its intensity and rigidity must be guaranteed in
design. Crankshaft is a key part of engine, its mechanical
property directly influence on the reliability and longevity
of engine. At present, simplified models are mostly used
in methods of the stress analysis of the crankshaft. The
method are limited to one moment, does not deal with the
whole working process, and cannot be used to accurately
determine the stress state on the real working process of
crankshaft. In recent years, the development of the virtual
prototype technology and the flexible multi-<strong>body</strong>
dynamics theory make it come true to know the real-time
dynamics response of the crankshaft.
II. The Method of <strong>Multi</strong>-<strong>body</strong> <strong>Dynamics</strong> <strong>Simulation</strong>
Analysis on Flexible Crankshaft System
The modelling of a virtual prototype of crankshaft system,
constituted by crankshaft, link, piston and so on, has three
steps. First, the three-dimensional model of these parts are
built in modeling software. Second, they are transferred to
ADAMS, the multi-<strong>body</strong> dynamics analysis software.
Finally, the kinematical pairs are simplified to the ideal
constraint used in the dynamics simulation. The flexibility
action of the crankshaft has very important influence on
the dynamics characteristic of the whole engine. In order
to consider the elastic deformation of crankshaft, a
relative description method is adopted to create the
1 mxg@mail.edu.cn
2 prime_queen@163.com
3 bcwen1930@sina.com
flexible model of crankshaft, then the motion of
crankshaft can be disassembled as implication movement
of rigid crankshaft and deformation of flexible crankshaft
relative to the moving reference frame. The deformation is
described by modal vector and modal coordinates, that
is [1] :
u f
= φ ⋅ q η
φ= [φ1 φ2 … ф N ], φ is matrix of modal vector,q η =
q η ,t,, q η is modal coordinates, N is the number of modal
vector.
Modal analysis is achieved by ANSYS, and a modal
neutral file (.MNF) can be gotten. Then the file can be
input directly into ADAMS to create the flexible model.
Furthermore, the model of multi-<strong>body</strong> dynamics system
including the flexible crankshaft can be used to do
dynamics simulation. The analysis flow is shown in Fig.1
.
Fig.1 The flow of simulation on multi-<strong>body</strong> dynamics system with
flexible crankshaft
III. The Example of <strong>Multi</strong>-<strong>body</strong> System <strong>Simulation</strong> of
Crankshaft
A. The Model of <strong>Multi</strong>-rigid Body <strong>Dynamics</strong>
The model of multi-rigid <strong>body</strong> system of the crankshaft of
some V8 engine is created in ADAMS. The model is
shown in Fig3. The movement discipline of every part can
be determined by simulating. Interaction forces between
parts, centralized forces of the nodes, can be determined
also. The model can be also used to do analysis for
balance of engine.

12th IFToMM World Congress, Besançon (France), June18-21, 2007
Fig.2 the multi-rigid <strong>body</strong> dynamics model of crankshaft system
C. Results of Flexible <strong>Multi</strong>-<strong>body</strong> <strong>Dynamics</strong> <strong>Simulation</strong> of
The Crankshaft System
Distribution of stress on real time of the crankshaft system
in a cycle, as shown in Fig.5, can be determined by the
simulation. According to the ignition order of engine and
by putting a rotation, whose rev is equal to rated speed of
engine, on the crankshaft. The simulation is achieved by
applying burst gas pressure on the pistons and transferring
the pressure to flexible crankshaft. The dangerous area of
crankshaft in a working cycle can be estimated.
B. The <strong>Multi</strong>-<strong>body</strong> System Model of Crankshaft System
with Flexible Crankshaft
Modal analysis of the crankshaft is done on crankshaft
finite element model, and a modal neutral file (.MNF) is
created when Craig-Bampton modal is orthogonalized on
free modal. The flexible crankshaft is created by
transferring the MNF to ADAMS. The finite element
model of the crankshaft created in ANSYS is shown in
Fig.3.
Fig.5 distribution of stress of the crankshaft
Fig.3 finite element model of the crankshaft
The other parts in crankshaft system just transfer the burst
gas pressures and inertia forces in work, so multi-<strong>body</strong>
system model can be built as multi-rigid <strong>body</strong> system
model at first, that means all parts can be built as rigid
<strong>body</strong>. The flexible multi-<strong>body</strong> system model, as shown in
Fig.4, can be built by replacing the rigid crankshaft with
flexible crankshaft.
The dynamic boundary load (.lod file) on the joints of
crankshaft system in a working cycle can be determined
by the simulation of flexible multi-<strong>body</strong> dynamics. The
concentrated load, determined by the multi-rigid <strong>body</strong>
dynamics simulation, can be dispersed on the finite
element nodes of the joint surface. The dispersible loads
express the real load boundary conditions. Then, an
accurate transient dynamics response analysis on the
crankshaft can be achieved.
D. Transient <strong>Dynamics</strong> Response Analysis of The
Crankshaft
After the multi-<strong>body</strong> dynamics simulation in ADAMS,
accurate dynamics response on real time in a cycle of the
crankshaft is achieved in ANSYS. The dynamic boundary
loads of crankshaft system is considered as boundary
condition in ANSYS, the dynamic loads are applied on the
crankshaft to do a transient dynamic response analysis.
Moreover, the precise real time stress distribution of the
crankshaft can be determined, as shown in Fig.6.
The stress value and its distribution of the crankshaft
determined by simulation analysis are close to test results,
which can infer that the results of simulation are reliable.
Fig.4 the multi-<strong>body</strong> dynamics model of crankshaft system with flexible
crankshaft

12th IFToMM World Congress, Besançon (France), June18-21, 2007
1
Ma Xingguo is a doctor of mechanical design and theory of
Northeastern University , a professor of Shenyang LiGong University, a
visiting scholar in the University of Tampere Polytechnic, owner of
Chinese government special allowance, winner of the “Famous Teacher”
of Liaoning Province, in charge of the research project of multi-<strong>body</strong>
dynamics simulation and engine.
2 You Xiaomei, lectuer of Shenyang LiGong University, engage in
multi-<strong>body</strong> dynamics simulation and mechanical vibration.
3
Wen Bangchun , academician of the Chinese Academy of Sciences.
Professor of mechanical engineering and automation of Northeastern
University, honorary chairman of the Chinese Vibration Engineering
Society.
Fig.6 the distribution at the maximum stress moment of crankshaft
IV. Conclusion
(1) The flexible multi-<strong>body</strong> dynamics simulation is based
on the crankshaft system or a virtual prototype, it can
simulate mechanical behaviour of crankshaft of engine in
real working condition. Comparing to the common
analysis method about individual crankshaft, this method
has three obvious advantages. Firstly, the system model is
more approach to the physical prototype. Secondly, it
need less hypothesis. Thirdly, it faces to process rather
than moment, thus this method has higher analysis
precision.
(2) The centralized force of joint can be dispersed to the
joint’nodes of finite element model by the flexible multi<strong>body</strong>
dynamic analysis. This method can determine the
real-time dynamic loads exactly and provide the real load
boundary condition for the analysis in ANSYS.
(3) The transient dynamics response can be achieved in
ANSYS with dynamic loads, which can be used to
determine the dangerous area of the crankshaft in a
working cycle and to evaluate the mechanical property of
the crankshaft quantificationally.
In conclusion, the method, combined FEA with flexible
multi-<strong>body</strong> dynamics analysis, is of great significance for
predicting dynamic characteristics of engine structure and
for optimization of key parts in design stage.
References
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