43 Fev Crankshaft Stress

8/13/2019 43 Fev Crankshaft Stress

1/15

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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Traditional Procedure: Angular Displacement at Crankshaft Free End Side


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Traditional Procedure: Nominal Torsional Stress referred to the Crank Pin


6/15

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Traditional Procedure:Nominal Bending Stress referred to the Crank Web Area


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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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Traditional Procedure: Equivalent Stress at the Crank Pin Fillet Radius


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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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6/7/00 - Rebbert 9


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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Recoupling of MSS Results to the FE-Analysis: Refined Crankshaft Model


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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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Recoupling of MSS Results to the FE-Analysis:

Deformed Shape of the Crankshaft at 6000 rpm


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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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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.

Documents

43 Fev Crankshaft Stress