Electricity: measuring and testing – Internal-combustion engine ignition system or device – In situ testing of spark plug
Patent
1992-11-09
1997-09-30
Regan, Maura K.
Electricity: measuring and testing
Internal-combustion engine ignition system or device
In situ testing of spark plug
123605, 324388, 324391, F02P 5145, F02P 1700
Patent
active
056729723
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates generally to a diagnostic system for an internal combustion engine and, more particularly, to a system for detecting electrical faults in a capacitor discharge ignition system.
BACKGROUND ART
Capacitor discharge ignitions (CDI's) are well known in the art. Typically, CDI's include a charge storage mechanism, such as a capacitor, and a step-up transformer with a secondary coil connected to a spark ignition device, such as a spark plug. A mechanism is provided to discharge the capacitor through the transformer primary coil in timed relationship with a desired engine ignition sequence. Discharge of the capacitor through the transformer primary coil induces a high voltage signal in the transformer secondary coil, which, if sufficiently high, causes a spark to arc across the spark plug gap. More specifically, the voltage applied across a spark ignition device must be greater than or equal to a predetermined characteristic "spark ionization potential" (voltage) V.sub.SP in order to initiate the spark. Such ionization potentials are typically on the order of 10 Kv or more. The ionization potential V.sub.SP is dependent on factors such as spark plug gap, cylinder pressure, engine load, and air/fuel ratio.
Typically, a CDI includes a separate transformer for each engine cylinder. As such it is possible for electrical faults, such as an electrical short in a transformer secondary circuit, to occur in any one of the engine cylinders. Such a fault will result in a deterioration of the overall engine operation and, therefore, it is desirable to be able to detect such faults. However, to date little work has been done in providing detection and diagnostics of electrical faults in the transformer secondary circuit.
Currently, when a fault is suspected, the first step typically is to replace or regap all the spark plugs in the engine. If this does not correct the problem, it is common to systematically replace individual transformers until proper engine performance resumes. Such methods result in substantial delays in downtime and lost productivity from the engine. Therefore, it is desirable to provide a means for detecting electrical faults in the secondary circuits of individual engine cylinders and to provide an indication of the particular type of fault that is detected.
The subject invention is directed toward addressing one or more of the problems as set forth above by providing a diagnostic system for a capacitor discharge ignition system which can detect a variety of electrical faults in individual cylinders. Furthermore, the subject invention is capable of providing an indication of when individual spark plugs need to be replaced or regapped.
DISCLOSURE OF THE INVENTION
In one aspect of the present invention, an apparatus is provided for monitoring ignition in individual cylinders of a multicylinder engine of the type having an ignition system which includes separate transformers for each cylinder. Each transformer has primary and secondary coils. The secondary coils are electrically connected in series with spark gaps in associated engine cylinders. The ignition system further includes a switching circuit for receiving cylinder select signals and responsively connecting respective transformer primary coils to a power source to induce current flow through a respective primary coil. The current flow through the primary coil results in a voltage potential across an associated spark gap which normally increases to a magnitude sufficient to cause a spark across the spark gap. A first circuit receives the cylinder select signals, senses a time delay between the reception of a cylinder select signal and sparking in a respective cylinder and responsively produces a delay signal indicative of the sensed time delay. A diagnostic controller receives the delay signal, compares the delay signal to a plurality of preselected thresholds and responsively produces a status signal indicating the status of ignition in a respective cylinder.
In a second aspect of the present invention,
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patent: 4413508 (1983-11-01), Kamamura et al.
patent: 5019779 (1991-05-01), Ookawa
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patent: 5208540 (1993-05-01), Hoeflich
patent: 5216369 (1993-06-01), Toyama
patent: 5237279 (1993-08-01), Shimasaki et al.
McCoy Steven R.
Scheel Horst
Caterpillar Inc.
Regan Maura K.
Vander Leest Kirk A.
Wilbur R. Carl
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