Measuring and testing – Engine detonation – Specific type of detonation sensor
Reexamination Certificate
2000-08-10
2002-03-26
Moller, Richard A. (Department: 2856)
Measuring and testing
Engine detonation
Specific type of detonation sensor
C073S035060
Reexamination Certificate
active
06360587
ABSTRACT:
BACKGROUND OF THE INVENTION
1. FIELD OF THE INVENTION
The present invention relates generally to a system for detecting a condition in an internal combustion engine, and more particularly, to a system configured to detect a pre-ignition condition within a combustion chamber of the engine.
2. DESCRIPTION OF THE RELATED ART
A condition called “pre-ignition” combustion is known for internal combustion engines when spontaneous combustion of the air/fuel mixture occurs before a spark is generated by the ignition system. Pre-ignition may occur when the engine is running at high output or wide-open throttle, because of the corresponding increase in temperature, especially of the spark plug itself. Pre-ignition is a serious condition, since it may cause an engine failure due to overheating of the piston dome and cylinder head.
One approach taken in the art to address this problem involves the development of a heat range for spark plugs having a sequence of steps. A particular step in the heat range refers to how much heat a spark plug is capable of removing from the combustion chamber. Each step “colder” corresponds to an increased ability to remove an additional amount of heat (e.g., 70-100° C.). However, a shortcoming with this approach lies in selecting the correct step in the heat range. If a “colder” plug than needed is chosen, it may prevent pre-ignition, but may also result in plug fouling, due to a spark plug tip temperature that is too low. Fouling is the lesser problem, compared to pre-ignition. Accordingly, it is a frequent occurrence to err on the side of caution, and choose a “colder” plug in the heat range. This result is generally undesirable.
It is also known to sense a combustion condition (e.g., misfire) using a so-called ion sense system. It is known that the combustion of an air/fuel mixture in an engine results in molecules in the cylinder being ionized. It is further known to apply a relatively high voltage across, for example, the electrodes of a spark plug after the ignition operation to produce a current across the electrodes. Such current is known as an ion current. The ion current that flows is proportional to the number of combustion ions present in the area of, for example, the spark plug gap referred to above, and is consequently indicative of the ionization throughout the entire cylinder as combustion occurs. The level or amount of ion current is indicative of the quality of the combustion event, or whether in fact combustion has occurred at all (e.g., a misfire condition).
Conventional ion current sensing systems generally include a capacitor or the like configured to store a voltage as seen by reference to U.S. Pat. No. 5,866,808 issued to Ooyabu et al. Ooyabu et al. disclose an ion sense system that includes a capacitor that is charged during ignition. The stored voltage is thereafter used as a “bias” voltage which is applied to the spark plug to generate the ion current. However, since Ooyabu et al. senses the ion current after the spark, the system cannot distinguish between combustion that occurs due to pre-ignition and combustion that occurs because of the spark. Thus, known ion sense systems, as presently used, offers little to solving the above problems.
There is therefore a need to provide an apparatus for detecting a pre-ignition combustion condition that minimizes or eliminates one or more of the shortcomings as set forth above.
SUMMARY OF THE INVENTION
This invention provides for accurate and reliable detection of a pre-ignition combustion condition by detecting an ion current before the spark event, when there should be no combustion (and therefore no ion current) unless pre-ignition has occurred.
The inventive pre-ignition detector has the advantage of allowing the use of “hotter” spark plugs (“hotter” in the plug's heat range), which reduces the incidence of cold temperature plug fouling. An additional advantage is that it prevents pre-ignition engine related failures, since fuel can be cut off to the cylinder where pre-ignition has been detected.
An apparatus is provided for detecting a pre-ignition condition in a combustion chamber of an internal combustion engine of the type having an ignition coil associated therewith. The coil has a primary winding, and a secondary winding that is connected to a spark plug. The apparatus includes a control circuit, and an ion sense circuit. The control circuit is configured to generate an ignition control signal for controlling a switch connected to the primary winding to thereby cause a primary current to flow through the primary winding. The control circuit is further configured to discontinue the ignition control signal for interrupting the primary current to thereby produce a spark. The ion sense circuit is configured to apply a bias voltage to the spark plug to generate an ion sense signal representative of an ion current through the spark plug. According to the invention, the ion sense circuit is operable to generate the ion sense signal prior to the control circuit discontinuing the ignition control signal to generate the spark.
In one embodiment, the ion sense circuit is configured to sense and generate the ion sense signal during a dwell interval.
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NGK Spark Plugs—computer printout Mar. 8, 2000—2 pages.
Delphi Technologies Inc.
Dobrowitsky Margaret A.
Moller Richard A.
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