Dynamic Crankshaft Stress Calculation using a combination of MSS

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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- / Veröffentlichungsanmeldung 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 results
on 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 between limitation of computer resources and results accuracy is the main exercise.

This paper describes the above defined engineering process based on an example of a real engine. For the MSS
simulations the ADAMS product line has been used. The general working scope and the hydrodynamic coupling
of the plain bearings were developed by FEV Motorentechnik GmbH, Aachen, Germany in cooperation with the
RWTH Aachen.




______________________________________________________________________________________
2000 International ADAMS User Conference                                            1
                   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
6/7/00 - Rebbert                                   1
Dynamic Crankshaft Stress Calculation using a combination of MSS and FEA
Introduction: General simulation strategy

                           Iterations          Refined
      Global


   Model Solution                       Model Solution Post-
   Setup                                Setup          Proc.
                                        Friction & Wearout
                                        Friction & Wearout     Detailed
       MSS                  Global                             Results
        MSS
       Model               Dynamics     Noise & Vibrations
                                        Noise & Vibrations       for
       Model
                            Results                             Design
                                        Component Stresses
                                        Component Stresses     Decisions
                                        & Durability
                                        & Durability


        6/7/00 - Rebbert                       2
Dynamic Crankshaft Stress Calculation using a combination of MSS and FEA
Traditional Procedure: Angular Displacement at Crankshaft Free End Side




        6/7/00 - Rebbert                   3
Dynamic Crankshaft Stress Calculation using a combination of MSS and FEA
Traditional Procedure: Nominal Torsional Stress referred to the Crank Pin




        6/7/00 - Rebbert                   4
Dynamic Crankshaft Stress Calculation using a combination of MSS and FEA
Traditional Procedure:
             Nominal Bending Stress referred to the Crank Web Area




        6/7/00 - Rebbert                   5
Dynamic Crankshaft Stress Calculation using a combination of MSS and FEA
Traditional Procedure: FE-Analysis of Stress Concentration Factor




                           MISES
                                   -INFINITY
                                   + 1.00E-10
                                   + 3.50E-01
                                   + 7.00E-01
                                   + 1.05E+00
                                   + 1.40E+00
                                   + 1.75E+00
                                   + 2.10E+00
                                   + 2.26E+00




        6/7/00 - Rebbert                        6
Dynamic Crankshaft Stress Calculation using a combination of MSS and FEA
Traditional Procedure: Equivalent Stress at the Crank Pin Fillet Radius




        6/7/00 - Rebbert                   7
Dynamic Crankshaft Stress Calculation using a combination of MSS and FEA
MSS Simulation: Calculation Path of Crank Train Dynamics

                                   Linear FEA                                     Nonlinear
                                   Calculation                                  Hydrodynamic
                                                                                 Simulation



      Modal Description of                  Modal Description of             Hydrodynamic Reaction
           Engine Block                           Crankshaft                    Force Databases
        Structural Stiffness                  Structural Stiffness

                                                                             Implementation of
                                   MSS - SOLVER                                - Rigid Bodies
                                    Time Domain                          - Constraint Connections
                                                                            - Gas Pressure Data
                                                                         In the MSS-Preprocessor


                           Dynamic Solution:
                           Displacements, Velocities,
                              Accelerations, Forces
        6/7/00 - Rebbert                                             8
Dynamic Crankshaft Stress Calculation using a combination of MSS and FEA
MSS Simulation: Crank Train Model


     Piston,
     rigid body
                                                                              Apply: FZ     p(α)=- Table

     Con Rod,                                                                Read Out: α
     rigid body

   Spring-Damper
   Coupling

   Tors. Vibr.
   Damper                                                                                  ω = const

           Read Out: Bearing Condition
                                                       Crankshaft
                                                       flexible structure
     Hydrodynamic calculation                                                  Flywheel
                                                        Engine Block
                              Apply: reaction Forces    flexible structure




           6/7/00 - Rebbert                                           9
Dynamic Crankshaft Stress Calculation using a combination of MSS and FEA
Recoupling of MSS Results to the FE-Analysis: Refined Crankshaft Model




        6/7/00 - Rebbert                  10
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


                                                  MISES
                                                          + 2.07E-03
                                                          + 6.00E+01
                                                          + 8.59E+01
                                                          + 1.11E+02
                                                          + 1.34E+02
                                                          + 1.63E+02
                                                          + 1.89E+02
                                                          + 2.15E+02
                                                          + 2.41E+02
                                                          + 2.67E+02



        6/7/00 - Rebbert                     11
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




        6/7/00 - Rebbert                  12
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 is
               about 12% at 6000 rpm, full load.



        6/7/00 - Rebbert                               13
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.


         6/7/00 - Rebbert                            14

				
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posted:10/28/2011
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