______________________________________________________________________________________2000 International ADAMS User Conference 1

International ADAMS User Meeting19.06.2000 bis 21.06.2000Orlando

Thema: "Dynamic Crankshaft Stress Calculation using a combination of MSS and FEA"

Vortragender:/Autoren: M. Rebbert, Rainer Lach and Philipp KleyFEV Motorentechnik GmbH, Aachen, Germany

(Vortrags- / Veröffentlichungsanmeldung liegt vor!)

To save time and expenses in engine development processes, an increasing amount of CAE support isdemanded. 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 tasksby simulation. However, it is still necessary to evaluate the efficiency of the different CAE tools and to checkcarefully which kind of simulation matches the targets best.

Often combinations of different simulation techniques show the best results. A good example is the combinationof nonlinear Multibody System Simulation (MSS) with linear Finite Element Analysis (FEA). The dynamics ofcontinuous structures, represented by a large number of degrees of freedom are calculated and reduced, usingFEA. 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 deformationbehavior, 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 bythe rotation of crankshaft and flywheel is considered, combining FEA and MSS. The highly nonlinearhydrodynamics of the plain bearings may be taken into consideration using specific subroutines, called by theMSS 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 hydrodynamicjournals and the piston-rod assembly has to be predicted accurately. Experiences from applications have beenused for enhancements, which provide higher accuracy.

Secondly the broad operating envelope of the engine has to be considered. This means, that a large number ofsimulations has to be executed. New integration and simulation methods reduce elapsed CPU-time and offersignificantly improved usability of the simulation method. However, simplified calculation tools are necessary fora predefinition of the engine working conditions that have to be investigated in detail, using nonlinear MSS. Thismeans 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 thetarget 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 MSSsimulations the ADAMS product line has been used. The general working scope and the hydrodynamic couplingof the plain bearings were developed by FEV Motorentechnik GmbH, Aachen, Germany in cooperation with theRWTH Aachen.

6/7/00 - Rebbert 1

Dynamic Crankshaft Stress Calculationusing a combination of MSS and FEA

Martin RebbertRainer LachPhilipp Kley

FEV Motorentechnik GmbH

International ADAMS Users’ Conference, Orlando, Florida, U.S.A. June 20th, 2000

6/7/00 - Rebbert 2

Dynamic Crankshaft Stress Calculation using a combination of MSS and FEAIntroduction: General simulation strategy

Solution Post-Proc.

ModelSetup

SolutionModelSetup

MSSModelMSS

Model Noise & VibrationsNoise & Vibrations

Friction & WearoutFriction & Wearout

Component Stresses& Durability

Component Stresses& Durability

Iterations

GlobalDynamicsResults

Detailed Results

for Design

Decisions

Global Refined

6/7/00 - Rebbert 3

Dynamic Crankshaft Stress Calculation using a combination of MSS and FEATraditional Procedure: Angular Displacement at Crankshaft Free End Side

6/7/00 - Rebbert 4

Dynamic Crankshaft Stress Calculation using a combination of MSS and FEATraditional Procedure: Nominal Torsional Stress referred to the Crank Pin

6/7/00 - Rebbert 5

Dynamic Crankshaft Stress Calculation using a combination of MSS and FEATraditional Procedure:

Nominal Bending Stress referred to the Crank Web Area

6/7/00 - Rebbert 6

Dynamic Crankshaft Stress Calculation using a combination of MSS and FEATraditional 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 FEATraditional Procedure: Equivalent Stress at the Crank Pin Fillet Radius

6/7/00 - Rebbert 8

Dynamic Crankshaft Stress Calculation using a combination of MSS and FEAMSS Simulation: Calculation Path of Crank Train Dynamics

Implementation of- Rigid Bodies

- Constraint Connections- Gas Pressure Data

In the MSS-Preprocessor

MSS - SOLVERTime 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

6/7/00 - Rebbert 9

Dynamic Crankshaft Stress Calculation using a combination of MSS and FEAMSS Simulation: Crank Train Model

Crankshaftflexible structure

Engine Block flexible structure

Piston, rigid body

Read Out: αααα

Apply: FZ p(α)α)α)α)===

=- Table

Read Out: Bearing Condition

Hydrodynamic calculation

Apply: reaction Forces

Con Rod, rigid body

Tors. Vibr.Damper

Spring-Damper Coupling

Flywheel

ωωωω = const

6/7/00 - Rebbert 10

Dynamic Crankshaft Stress Calculation using a combination of MSS and FEARecoupling of MSS Results to the FE-Analysis: Refined Crankshaft Model

6/7/00 - Rebbert 11

Dynamic Crankshaft Stress Calculation using a combination of MSS and FEARecoupling 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

6/7/00 - Rebbert 12

Dynamic Crankshaft Stress Calculation using a combination of MSS and FEARecoupling of MSS Results to the FE-Analysis:

Deformed Shape of the Crankshaft at 6000 rpm

6/7/00 - Rebbert 13

Dynamic Crankshaft Stress Calculation using a combination of MSS and FEAComparison between traditional and new calculation method

The additional safety margin detected by the new, more realistic method isabout 12% at 6000 rpm, full load.

6/7/00 - Rebbert 14

Dynamic Crankshaft Stress Calculation using a combination of MSS and FEASummary

• 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 forfurther investigations, not only for stress issues, but also for questionsconcerning 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.