Dynamic Analysis of Diesel V8 Cranktrain Václav Píštěk, Pavel Novotný Abstract At the present time the requirements of numeric simulations increase. Modern powertrains are required to have high reliability and power, low consumption, emissions and vibration level. The internal combustion engine development process requires CAE models which deliver results for the concept phase at the very early stage. The vibratory and acoustic behavior of the cranktrain is a highly complex one that greatly affects global engine noise emissions. In the case of this paper the Diesel V8 engine analysis is presented. The aim of this dynamic analysis of the powertrain is the reduction of the vibrations. A major problem for powertrain designers when optimizing the vibration and noise characteristics of the powertrain is the crankshaft and the engine block interaction. Non-contact measurements enable to verify the complex calculation models. Souhrn V současné době vzrůstá potřeba využití numerických simulací různých fyzikálních dějů. Na současné pohonné jednotky jsou kladené vysoké nároky na spolehlivost a výkon a zároveň na nízkou spotřebu, emise i úroveň hluku. Při vývoji nových pohonných jednotek je účelné aplikovat soudobé výpočtové modely již v prvních fázích návrhu. Na vibrace a s nimi související akustické emise motoru mají významný vliv parametry klikového mechanismu. Cílem tohoto článku je presentovat způsob, jakým lze pomoci konstruktérům pohonné jednotky tyto nežádoucí jevy snížit. Virtuální motor, jehož centrální modul řeší interakci klikového mechanismu a bloku motoru, je vyvíjen na bázi prostředí ANSYS a ADAMS. Pro verifikaci výpočtových modelů je aplikována laserová měřicí technika.

12. ANSYS Users’ Meeting, 30.září – 1.října 2004 na Hrubé Skále

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1. Introduction In the powertrain development process several numerical simulation techniques have continuously gained importance. The main target is the design support which means help for design decisions. With the increasing power of computers accurate pre-calculations become possible with consideration of large number of effects and backward influences. In the case of dynamic structural calculations the Finite Element Method (FEM) is state of the art. The ANSYS system is used for all FE solutions. The calculation of the structural transfer behavior of single components is efficiently possible in frequency domain, considering a large number of degrees of freedom. 2. FE models For dynamic analyses in MBS a uniform FE mesh is used for all FE models. This is fully sufficient for dynamic behavior of main engine parts. In case of stress-strain analysis more complex models must be created. Fig. 1 illustrates FE model of a Diesel V8 engine block and Fig. 2 illustrates FE model of a Diesel V8 engine crankshaft.

Fig. 1 FE model of V8 engine block

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Fig. 2 FE model of V8 crankshaft 3. Reduction of FE models The FE models of crankshafts or engine blocks are created in ANSYS. Modal analyses can be performed in ANSYS and they are not time-consuming, but for solution in time domain these models are very large and they require a reduction. The discretization of a flexible component into a finite element model represents the infinite number of degree of freedom (DOF) with a finite, but very large number of finite DOF. The FE model of the engine block is reduced to the number of boundary nodes selected by the user. Their number is selected according to the application of constrains of the model. Loads are applied on these nodes only. The reduction of FE models from ANSYS into ADAMS is executed from ANSYS. The parameters which influence the accuracy of the reduction are the number and location of the boundary nodes and the number of first modes considered during the reduction. 3. Interaction between reduced FE models In the case of Diesel V8 engine roller bearings are used. The creation of a nonlinear FE model of roller bearing is a first step, however, MBS using the simpler model have to be created. The nonlinear radial and bending stiffness is computed by using a complex FE model which is then used at MBS dynamic model. The FE and MBS bearing models are presented in Fig. 3.

Fig. 3 FE and MBS models of Diesel V8 roller bearings 12. ANSYS Users’ Meeting, 30.září – 1.října 2004 na Hrubé Skále

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4. Solution in ADAMS The solution of the complex model in time domain runs in ADAMS. A complex model of the V8 Diesel engine is presented in Fig. 4. The V8 Diesel engine model includes flexible FE models of the crankshaft and the engine block. Pistons, piston pins and connecting rods are solved as rigid. The virtual engine includes a model of a viscous torsional vibration damper. The viscous torsional vibration damper consists of two parts a ring part, and a hub part which are connected together by a revolute joint. The hub part is constrained with a fixed joint at the attachment part. The force (torque) is transmitted from the one part to another through of a high viscosity liquid (silicon oil). The viscous torsional vibration damper model consists of spring-damper system.

Fig. 4 Cranktrain model – major part of virtual engine Gas forces on pistons are applied in ADAMS as well. Some temperature elements for dependency on temperature are defined.

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6. Results A flexible crankshaft is a major part of an engine model. Some results, for example torsional vibrations or axial vibrations of a crankshaft, are not too sensitive in using a flexible behavior of engine block. However, the flexible block has a decisive effect on bending vibrations of a crankshaft. Torsional vibrations of the crankshaft are one of the major problems. First the modal analysis of an engine model without a torsional-vibration damper can be computed. The engine speeds that respond modal torsion eigenfrequency in combination with κ−harmonic component can be found. After that a dynamic simulation in time domain is computed. Torsional vibrations from the dynamic simulation are analyzed and the using of a viscous torsional vibration damper is considered. The torsional vibration order analysis of the crankshaft front without a damper is presented in Fig. 5.

Fig. 5 Torsional vibration order analysis of crankshaft front without damper It is evident that dominant orders with resonances in an engine speed range are 8th and 12th.

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Torsinal vibration problems can be solved by using torsional vibration damper. In Fig. 6 the torsional vibration order analysis of the crankshaft front with damper is presented.

Fig. 6 Torsional vibration order analysis of crankshaft front with damper The viscous torsional vibration damper causes a reduction of relevant orders in resonances. Other results from cranktrain model as a major part of virtual engine can be axial vibrations of the crankshaft, flexible body stress analyses or acoustic analyses. 8. Conclusion The internal combustion engine simulation is a very complex problem consisting of many partial issues. The combination of ANSYS and ADAMS provides a powerful implement for virtual engine design. The simulation of the cranktrain dynamics is a central module of the virtual engine. The Diesel V8 engine analyses help designers make decision before a prototype phase.

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Acknowledgement The problems mentioned above are being solved within the framework of the project No 101/01/0027 which has been given by the Grant Agency of the Czech Republic. The authors would like to thank GA CR for the rendered assistance. References [1] PÍŠTĚK, V. Crank mechanism simulation – a module of the virtual engine. [CDROM]. In Engineering mechanics 2001. National conference with international participation, Svratka, Czech Republic, May 14.-17., 2001. ISBN 80-85918-64-1. [2] NOVOTNÝ, P., PÍŠTĚK, V. The conversion of FE models between ANSYS and ADAMS systems. [CD-ROM]. In 10. Ansys User’s Meeting. 2002. Čejkovice, Czech Republic, September 26.-27., 2002. pages 1-6. ISBN 80-238-9394-7. [3] NOVOTNÝ, P., PÍŠTĚK, V. ANSYS and ADAMS - A Tool For Design of Diesel Engines. [CD-ROM]. In 11. Ansys User’s Meeting. 2003. Znojmo, Czech Republic, September 25.-26, 2003. pages 1-6. [4] XIE, M. Flexible Multi-Body System Dynamic – Theory and Applications, Taylor & Francis, Washington DC, USA, 1994. ISBN 1-56032-300-0 [5] WILLIAMS, J., A. Engineering Tribology. Oxford science publication. Midsoner Norton, Avon, 1994. ISBN 63 19 856343 4

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