43 fev crankshaft stress
TRANSCRIPT
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International ADAMS User Meeting
19.06.2000 bis 21.06.2000
Orlando
Thema: "Dynamic Crankshaft Stress Calculation using a combination of MSS and FEA"
Vortragender:/Autoren: M. Rebbert, Rainer Lach and Philipp Kley
FEV Motorentechnik GmbH, Aachen, Germany
(Vortrags- / Verffentlichungsanmeldung liegt vor!)
To save time and expenses in engine development processes, an increasing amount of CAE support is
demanded. To achieve this target, the calculations have to be quick on one hand and must deliver reliable resultson the other hand.
The increasing power of modern computers leads to the possibility, to support more and more development tasks
by simulation. However, it is still necessary to evaluate the efficiency of the different CAE tools and to check
carefully which kind of simulation matches the targets best.
Often combinations of different simulation techniques show the best results. A good example is the combination
of nonlinear Multibody System Simulation (MSS) with linear Finite Element Analysis (FEA). The dynamics of
continuous structures, represented by a large number of degrees of freedom are calculated and reduced, using
FEA. The global dynamics of several parts, interacting with each other may be then calculated by MSS,
considering all nonlinearities in the coupling locations between the parts and the structural deformation
behavior, as eigenvectors from the FEA calculation.
A typical example for this simulation procedure is the interaction between rotating crankshaft and engine block.
Beneath the structural deformations of crankshaft and block the influence of the gyroscopic effects, caused by
the rotation of crankshaft and flywheel is considered, combining FEA and MSS. The highly nonlinear
hydrodynamics of the plain bearings may be taken into consideration using specific subroutines, called by the
MSS solver.
For realistic crankshaft stress calculations three main working steps are necessary in general:
First the dynamics of rotating flexible crankshaft and flexible engine block, that are coupled by hydrodynamic
journals and the piston-rod assembly has to be predicted accurately. Experiences from applications have been
used for enhancements, which provide higher accuracy.
Secondly the broad operating envelope of the engine has to be considered. This means, that a large number of
simulations has to be executed. New integration and simulation methods reduce elapsed CPU-time and offer
significantly improved usability of the simulation method. However, simplified calculation tools are necessary for
a predefinition of the engine working conditions that have to be investigated in detail, using nonlinear MSS. This
means that maximum efficiency can only be achieved, combining tools with different degrees of refinement.
Finally the problem of finding stresses and the locations of their concentrations has to be solved. Again the
target conflict bet een limitation of comp ter reso rces and res lts acc rac is the main e ercise
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Dynamic Crankshaft Stress Calculation
using a combination of MSS and FEA
Martin Rebbert
Rainer Lach
Philipp Kley
FEV Motorentechnik GmbH
International ADAMS Users Conference, Orlando, Florida, U.S.A.
June 20th, 2000
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Dynamic Crankshaft Stress Calculation using a combination of MSS and FEA
Introduction: General simulation strategy
Solution Post-
Proc.
Model
Setup
SolutionModel
Setup
MSS
Model
MSS
Model Noise & Vibrations
Noise & Vibrations
Friction & Wearout
Friction & Wearout
Component Stresses& Durability
Component Stresses& Durability
Iterations
Global
Dynamics
Results
DetailedResults
for
Design
Decisions
Global Refined
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Dynamic Crankshaft Stress Calculation using a combination of MSS and FEA
Traditional Procedure: Angular Displacement at Crankshaft Free End Side
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Dynamic Crankshaft Stress Calculation using a combination of MSS and FEA
Traditional Procedure: Nominal Torsional Stress referred to the Crank Pin
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Dynamic Crankshaft Stress Calculation using a combination of MSS and FEA
Traditional Procedure:Nominal Bending Stress referred to the Crank Web Area
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Dynamic Crankshaft Stress Calculation using a combination of MSS and FEA
Traditional Procedure: FE-Analysis of Stress Concentration Factor
+ 1.00E-10
-INFINITY
+ 3.50E-01
+ 7.00E-01
+ 1.05E+00
+ 1.40E+00
+ 1.75E+00
+ 2.10E+00
+ 2.26E+00
MISES
+ 1.00E-10
-INFINITY
+ 3.50E-01
+ 7.00E-01
+ 1.05E+00
+ 1.40E+00
+ 1.75E+00
+ 2.10E+00
+ 2.26E+00
+ 1.00E-10
-INFINITY
+ 3.50E-01
+ 7.00E-01
+ 1.05E+00
+ 1.40E+00
+ 1.75E+00
+ 2.10E+00
+ 2.26E+00
MISESMISES
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Dynamic Crankshaft Stress Calculation using a combination of MSS and FEA
Traditional Procedure: Equivalent Stress at the Crank Pin Fillet Radius
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Dynamic Crankshaft Stress Calculation using a combination of MSS and FEA
MSS Simulation: Calculation Path of Crank Train Dynamics
Implementation of
- Rigid Bodies
- Constraint Connections
- Gas Pressure Data
In the MSS-Preprocessor
MSS - SOLVER
Time Domain
Dynamic Solution:
Displacements, Velocities,
Accelerations, Forces
Modal Description of
Engine Block
Structural Stiffness
Modal Description of
Crankshaft
Structural Stiffness
Hydrodynamic Reaction
Force Databases
Nonlinear
Hydrodynamic
Simulation
Linear FEA
Calculation
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Dynamic Crankshaft Stress Calculation using a combination of MSS and FEA
MSS Simulation: Crank Train Model
Crankshaft
flexible structure
Engine Block
flexible structure
Piston,
rigid body
Read Out:
Apply: FZ p())))- Table
Read Out: Bearing Condition
Hydrodynamic calculation
Apply: reaction Forces
Con Rod,
rigid body
Tors. Vibr.Damper
Spring-Damper
Coupling
Flywheel
= const
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Dynamic Crankshaft Stress Calculation using a combination of MSS and FEA
Recoupling of MSS Results to the FE-Analysis: Refined Crankshaft Model
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Dynamic Crankshaft Stress Calculation using a combination of MSS and FEA
Recoupling of MSS Results to the FE-Analysis:
Local Stress at the Fillet Radii at 6000 rpm
+ 2.67E+02
+ 2.07E-03
+ 6.00E+01
+ 8.59E+01
+ 1.11E+02
+ 1.34E+02
+ 1.63E+02
+ 2.15E+02
+ 2.41E+02
+ 1.89E+02
MISES
+ 2.67E+02
+ 2.07E-03
+ 6.00E+01
+ 8.59E+01
+ 1.11E+02
+ 1.34E+02
+ 1.63E+02
+ 2.15E+02
+ 2.41E+02
+ 1.89E+02
MISES
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Dynamic Crankshaft Stress Calculation using a combination of MSS and FEA
Recoupling of MSS Results to the FE-Analysis:
Deformed Shape of the Crankshaft at 6000 rpm
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Dynamic Crankshaft Stress Calculation using a combination of MSS and FEA
Comparison between traditional and new calculation method
The additional safety margin detected by the new, more realistic method isabout 12% at 6000 rpm, full load.
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Dynamic Crankshaft Stress Calculation using a combination of MSS and FEA
Summary
For crankshaft stress calculations traditional methods based on simple
superposition of torsional and bending stresses are state of the art.
New calculation methods are necessary to achieve more accurate results,
that allow a design that is nearer to the mechanical limit.
The combination of MSS and FEA methods is the most efficient way of
calculating crank train dynamics. The results are boundary conditions for
further investigations, not only for stress issues, but also for questions
concerning friction and wearout and for NVH.
With the increasing power of modern computers the new techniques will
replace the traditional methods.
Further studies are necessary to optimize the interaction of the CAE
programs and to validate the new technology.