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Research Papers: Internal Combustion Engines

# Instantaneous Engine Speed Time-Frequency Analysis for Onboard Misfire Detection and Cylinder Isolation in a V12 High-Performance Engine

[+] Author and Article Information
Fabrizio Ponti

DIEM, University of Bologna, Bologna 40136, Italy

J. Eng. Gas Turbines Power 130(1), 012805 (Jan 09, 2008) (9 pages) doi:10.1115/1.2436563 History: Received June 19, 2006; Revised August 11, 2006; Published January 09, 2008

## Abstract

The diagnosis of a misfire event and the isolation of the cylinder in which the misfire took place is enforced by the onboard diagnostics (OBD) requirements over the whole operating range for all the vehicles, whatever the configuration of the engine they mount. This task is particularly challenging for engines with a high number of cylinders and for engine operating conditions that are characterized by high engine speed and low load. This is why much research has been devoted to this topic in recent years, developing different detection methodologies based on signals such as instantaneous engine speed, exhaust pressure, etc., both in time and frequency domains. This paper presents the development and the validation of a methodology for misfire detection based on the time-frequency analysis of the instantaneous engine speed signal. This signal contains information related to the misfire event, since a misfire occurrence is characterized by a sudden engine speed decrease and a subsequent damped torsional vibration. The identification of a specific pattern in the instantaneous engine speed frequency content, characteristic of the system under study, allows performing the desired misfire detection and cylinder isolation. Particular attention has been devoted to designing the methodology in order to avoid the possibility of false alarms caused by the excitation of this frequency pattern independently from a misfire occurrence. Although the time-frequency analysis is usually considered a time-consuming operation and not associated to onboard application, the methodology proposed here has been properly modified and simplified in order to obtain the quickness required for its use directly onboard a vehicle. Experimental tests have been performed on a $5.7l$ V12 spark-ignited engine run onboard a vehicle. The frequency characteristic of the engine-vehicle system is not the same that could be observed when running the engine on a test bench, because of the different inertia and stiffness that the connection between the engine and the load presents in the two cases. This makes it impossible to test and validate the methodology proposed here only on a test bench, without running tests on the vehicle. Nevertheless, the knowledge of the mechanical design of the engine and driveline gives the possibility of determining the resonance frequencies of the system (the lowest one is always the most important for this work) before running tests on the vehicle. This allows saving time and reducing costs in developing the proposed approach.

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Topics: Engines , Cylinders , Gears , Cycles

## Figures

Figure 7

Amplitude of the harmonic at f* for the steady-state test at 5000rpm in fifth gear at 230km∕hr (one induced misfire every 30 cycles in cylinder 10)

Figure 8

Amplitude of the harmonic at f* for the transient test in third gear (one induced misfire every 50 cycles in cylinder 1)

Figure 3

Engine speed trend for a V12 engine with cylinder 1 misfiring at 0deg crankshaft angle in fifth gear at 230km∕hr

Figure 4

Waterfall representation of the engine speed STFT analysis at 5000rpm in fifth gear at 230km∕hr (one induced misfire in cylinder 10 every 30 cycles)

Figure 5

Engine speed variation for the transient test in third gear (one induced misfire every 50 cycles in cylinder 1)

Figure 6

Engine speed STFT analysis for the transient test in third gear (one induced misfire every 50 cycles in cylinder 1)

Figure 1

Indicated torque mean value evaluation over 60deg intervals, for a V12 engine with cylinder 1 misfiring at the beginning of the engine cycle

Figure 2

Difference between the indicated torque production in case of misfire in cylinder 1 and during normal operating conditions

Figure 9

Engine speed waveform for a test conducted in second gear from 6400rpm to 7600rpm (from 135km∕hr to 160km∕hr)

Figure 10

St(2πf*) evaluation for the test shown in Fig. 9

Figure 11

LUi evaluation for the test shown in Fig. 9

Figure 12

Engine speed waveform for a test conducted in third gear at 4850rpm(140km∕hr)

Figure 13

St(2πf*) evaluation for the test shown in Fig. 1

Figure 14

LUi evaluation for the test shown in Fig. 1

Figure 15

St(2πf*) evaluation for a test conducted at 2500rpm in fifth gear

Figure 16

LUi evaluation for a test conducted at 2500rpm in fifth gear

Figure 17

St(2πf*) evaluation for a test conducted at 2500rpm in fifth gear

Figure 18

LUi evaluation for a test conducted at 2500rpm in fifth gear

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