Frequency domain engine defect signal analysis

Details Frequency domain engine defect signal analysis Frequency domain engine defect signal analysis

1982-07-06

1984-01-10

Myracle, Jerry W.

Measuring and testing

Vehicle chassis

Steering

73115, 364551, G01M 1500

Patent

active

044247095

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention relates to a method and an apparatus for detecting defects in an internal combustion engine using frequency domain signal analysis.


BACKGROUND ART

In known conventional time domain signal analysis techniques, various engine transducers (e.g. exhaust pressure, intake manifold vacuum, oil pressure, crankcase pressure and engine speed) produce periodic electronic signals which define certain engine operating conditions (e.g. intake/exhaust valve opening and closing, cylinder combustion quality, exhaust cylinder blowdown, etc.). The fundamental frequency of these signals is termed the engine's firing frequency and is defined by the following equation:
As indicated by the above equation, the fundamental frequency of the signals is a function of engine speed and therefore the electronic signals change frequency as engine speed is increased or decreased. Each engine firing includes two crankshaft revolutions (through 720.degree.) and, for a four cylinder engine, four cylinder firings or, for an eight cylinder engine, eight cylinder firings. In time domain signal analysis, time records as a function of engine crank angle are stored in a computer for the various transducers for an engine containing no defects and operated at a constant speed (e.g. 1000 RPM) in order to establish baseline waveforms. A second time record is taken for a defective engine for comparison to the baseline "normal" waveform. Comparing the two time records, a discriminant is extracted from the data to represent the particular defect as shown in FIG. 1. By determining defects by this method (data as a function of crankangle), defects can also be isolated to a particular cylinder. In this manner, a discriminant can be defined for many engine defects by implanting known defects in normal engines and repeating the above tests. This method can require a considerable amount of data storage and manipulation.
In addition to time domain analysis, frequency domain analysis is also known. For example, U.S. Pat. No. 4,083,234 to Aono et al teaches a method and apparatus for detecting a misfire in an internal combustion engine. A cylinder misfiring is detected by initially sensing the exhaust noises and producing a continuous signal wave having an exhaust noise frequency which is variable with the detected exhaust noises. The waveform has a frequency spectrum having peak values at various frequencies. One such peak exists at the fundamental frequency of the wave and represents a normal operating condition. Other peak values occur at certain fractional harmonics of the fundamental frequency component and represent a misfire of an engine cylinder. The system also incorporates an engine speed signal which, in combination with a frequency spectrum analyzer, aids in the evaluation of the misfired cylinder. In operation, the speed signal is used to control the band pass filtering of the exhaust noise waveform. This patent shows a misfire detection technique using band pass filtering and subsequent frequency spectrum analysis of a noise signal representing exhaust noise. This patent does not teach detection of engine faults other than misfire. Further, there is no teaching of using a plurality of different sensors to identify engine operating conditions. These are some of the problems this invention overcomes.


DISCLOSURE OF THE INVENTION

A signal analyzer for identifying engine defects includes sensor means for indicating engine intake manifold vacuum, exhaust pressure, crankcase pressure, oil pressure and engine speed. Such detected signals for normal engines are compared in the frequency domain with detected signals from engines with implanted defects operated at constant speed without external engine loading. By recognizing specific differences, or looking for the "abnormal" frequency components, engine defects can be identified.
Frequency domain signal analysis can utilize the same engine sensors as known conventional time domain signal analysis techniques. Further, frequency domain signal analysis can provide the same

REFERENCES:
patent: 4064747 (1977-12-01), Rackliffe et al.
patent: 4083234 (1978-04-01), Aono et al.
patent: 4108362 (1978-08-01), Trussell et al.
patent: 4128005 (1978-12-01), Arnston et al.
patent: 4398259 (1983-08-01), Levine
patent: 4401949 (1983-08-01), Gold

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