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Inclusion of assumed bending and torsion modes for prediction of engine block vibrations
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.). Scania CV AB.
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).ORCID iD: 0000-0001-8068-2360
Scania CV AB.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

For existing engine types, measured vibrations are commonly used as input to computations and shake rig tests. Accelerations are possible to compute in positions that have not been measured by fitting measured accelerometer data to a discretised engine block motion description. The computed accelerations can be used in fatigue risk estimation for engine components, mounted in new positions. In addition to the rigid body motion, engine block twist has previously successfully been included to better describe the engine block vibration. In the current paper, three additional deformation modes, of bending type, are suggested in order to describe engine block motions even better. The motion description is validated with an engine vibration measurement on a Scania inline six cylinder, heavy-duty diesel engine. An error measure for RMS vibration, summed for all sensors, is used to rank the studied deformation modes. In the studied frequency range, the most important deformation mode is the engine block twist. Including bending deformation increases the accuracy of the engine block vibration description but it also increases the demands on instrumentation.

Keywords [en]
engine, engine block vibrations, engine block twist, engine block bending, rigid body vibrations, vibration measurement, vibration estimation, assumed modes, bending modes, torsion modes
National Category
Other Mechanical Engineering
Research subject
Solid Mechanics
Identifiers
URN: urn:nbn:se:kth:diva-220537OAI: oai:DiVA.org:kth-220537DiVA, id: diva2:1169277
Note

QC 20171229

Available from: 2017-12-22 Created: 2017-12-22 Last updated: 2017-12-29Bibliographically approved
In thesis
1. Prediction of engine component loads using previous measurements
Open this publication in new window or tab >>Prediction of engine component loads using previous measurements
2017 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Internal combustion engines are used in many applications. The same engine type may have different components mounted to it depending upon its use. These engine mounted components need to be designed against fatigue in order to withstand the engine vibrations. Measured engine vibrations are commonly used as input data for fatigue estimation. The focus in this thesis is set on heavy-duty diesel engines, typically used in trucks, buses and industrial applications. All of the appended papers use engine vibration measurements to evaluate the proposed methods.

In Paper A, the engine block motion is described with a seven degree of freedom kinematic model. These degrees of freedom consist of six rigid body modes and one assumed twisting degree of freedom. With this description, measured engine block vibrations can be used to accurately predict the vibration in positions that have not been measured. Relating the measured vibrations of an engine mounted component with the projected motion of the engine block at that same position, makes it possible to identify local dynamic phenomena.

In Paper B, the kinematic model of Paper A is extended with three assumed bending deformation mode shapes. For the current engine type, all of the assumed deformation modes are ranked within the 10-300 Hz frequency range. The deformation mode of highest importance is the engine block twist. Including bending deformation increases the accuracy of the engine block vibration description but it also increases the demands on instrumentation.

In Paper C, the possibility to modify measured engine vibration signals, for addition or removal of engine mounted components, is investigated. For this purpose, engine vibration measurements were performed with and without a 29 kg brake air compressor mounted to the engine. For the task of removing the effect that this engine mounted component has on the engine block, the two cases of knowing, and not knowing the vibration of the component are both considered. The proposed methodology successfully predicts the changes in engine vibration due to system modification. The proposed method can also be used to estimate the time response of a component's centre of gravity. In this study the component's dynamic properties are derived from measurements but they could also be produced using finite element analysis. This can be useful early in the design process to find critically stressed areas due to base excitation.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2017. p. 16
Series
TRITA-HFL. Report / Royal Institute of Technology, Solid Mechanics, ISSN 1654-1472 ; 0616
Keywords
engine, engine block vibration, engine block twist, engine block bending, vibration measurement, vibration estimation, rigid body vibrations, assumed modes, bending modes, torsion modes, system modification
National Category
Other Mechanical Engineering
Research subject
Solid Mechanics
Identifiers
urn:nbn:se:kth:diva-220532 (URN)978-91-7729-605-8 (ISBN)
Presentation
2017-12-18, Solid mechanics seminar room, Teknikringen 8D, Stockholm, 10:15 (English)
Opponent
Supervisors
Note

QC 20171222

Available from: 2017-12-22 Created: 2017-12-22 Last updated: 2017-12-29Bibliographically approved

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Mikaelsson Elmén, PärOlsson, Mårten

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