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Research Papers

Advanced Signal Processing Tools for the Vibratory Surveillance of Assembly Faults in Diesel Engine Cold Tests

[+] Author and Article Information
Simone Delvecchio1

Department of Engineering, University of Ferrara, Via Saragat 1, 44100 Ferrara, Italysimone.delvecchio@unife.it

Gianluca D’Elia

Department of Engineering, University of Ferrara, Via Saragat 1, 44100 Ferrara, Italygianluca.delia@unife.it

Emiliano Mucchi

Department of Engineering, University of Ferrara, Via Saragat 1, 44100 Ferrara, Italyemiliano.mucchi@unife.it

Giorgio Dalpiaz

Department of Engineering, University of Ferrara, Via Saragat 1, 44100 Ferrara, Italygiorgio.dalpiaz@unife.it

1

Corresponding author.

J. Vib. Acoust 132(2), 021008 (Mar 17, 2010) (10 pages) doi:10.1115/1.4000807 History: Received June 22, 2009; Revised November 25, 2009; Published March 17, 2010; Online March 17, 2010

This paper addresses the use of several signal processing tools for monitoring and diagnosis of assembly faults in diesel engines through the cold test technology. One specific fault is considered here as an example: connecting rod with incorrectly tightened screws. First, the experimental apparatus concerning the vibration tests is introduced. Subsequently, the dynamic analysis of the engine has been carried out in order to calculate the connecting rod forces against the crankpin for predicting the position where mechanical impacts are expected. Then, a vibration signal model for this type of faults is introduced. It deals with the cyclostationary model in which the signal is subdivided into two main parts: deterministic and nondeterministic. Finally, the acceleration signals acquired from the engine block during a cold test cycle at the end of the assembly line are analyzed. For quality control purposes in order to obtain reliable thresholds for the pass/fail decision, a method based on the image correlation of symmetrized dot patterns is proposed. This method visualizes vibration signals in a diagrammatic representation in order to quickly detect the faulty engines in cold tests. Moreover, the fault identification is discussed on the basis of the cyclostationary model of the signals. The first-order cyclostationarity is exploited by the analysis of the time synchronous average (TSA). In addition, the residual signal is evaluated by subtracting the TSA from the raw synchronized signal, and thus, the second-order cyclostationarity analysis is developed by means of the Wigner–Ville distribution (WVD), Wigner–Ville spectrum (WVS), and mean instantaneous power. Moreover, continuous wavelet transform is presented and compared with the WVD and WVS.

Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 2

Dynamic model of a single-cylinder engine: global coordinate system x-y

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Figure 3

Theoretical air pressure within the combustion chamber

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Figure 4

Local coordinate system (z-w) integral with the connecting rod

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Figure 5

Polar graph of the Rzw force transmitted by the rod against the crankpin during two crankshaft revolutions: first crankshaft revolution (solid line) and second crankshaft revolution (dashed line)

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Figure 6

Zoom of the polar graph depicted in Fig. 5

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Figure 7

SDP method: (a) time input waveform, (b) symmetrized dot polar graph, and (c) image obtained after the edge detection algorithm application

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Figure 8

Symmetrized dot polar graphs: (a) healthy engine (reference pattern) and (b and c) faulty engines

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Figure 9

Model of IC engine acceleration signal, considering only pressurization, inertial forces, and an impulsive component

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Figure 10

Model of IC engine acceleration signal, considering only pressurization, inertial forces and an impulsive component: (a) deterministic part; (b) cyclostationary part; (c) mean instantaneous power of the cyclostationary

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Figure 11

WVS of the cyclostationary part, represented in Fig. 1

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Figure 12

Healthy engine: (a) time synchronous average, and (b) residual signal

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Figure 13

Incorrectly tightened rod screws: (a) time synchronous average, (b) residual signal, and (c) mean instantaneous power of the residual signal

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Figure 14

Incorrectly tightened rod screws: (a) WVD of the TSA; (b) WVD of the residual signal; (c) CWT of the TSA; (d) CWT of the residual signal

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Figure 15

Incorrectly tightened rod screws: WVS of the residual signal

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