System and method for self diagnosing an engine control system
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United States of America Patent
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Aug 25, 1992
Grant Date -
N/A
app pub date -
Jan 11, 1991
filing date -
Jan 12, 1990
priority date (Note) -
Expired
status (Latency Note)
Importance
Abstract
A system and method for self diagnosing an engine controlling system such as an ignition system, fuel injection system, and an EGR (Exhaust Gas Recirculation) system are disclosed in which a periodic pseudo random signal is superposed on a control signal such as an ignition signal, fuel injection signal, or EGR rate controlled value indicating signal during an engine steady state condition, a cross-correlation function is calculated from both the superposed periodic random signal and output signal related to deterioration of the engine controlling system, and a value related to the cross-correlation function is compared with a reference value over which a performance of the engine controlling system cannot be maintained. If the value related to the cross-correlation function exceeds the reference value, the diagnostic system determines the occurrence of deterioration in the engine controlling system. The output related to the deteroration of the engine controlling system is, for example, a number of occurrences of misfiring determined according to change in engine revolutional speed. The periodic pseudo random signal is, for example, an M-series sequence signal. In the case of a diagnostic system for an EGR system the value related to the cross-correlation function may be, for example, a step response.
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