Internal-combustion engines – High tension ignition system – Having specific trigger circuitry
Reexamination Certificate
2001-10-30
2003-10-07
Gimie, Mahmoud (Department: 3747)
Internal-combustion engines
High tension ignition system
Having specific trigger circuitry
C123S652000
Reexamination Certificate
active
06629520
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ignition apparatus for an internal combustion engine in which a spark plug receives high voltage for ignition generated from a secondary winding of an ignition coil upon intermittent supply of primary current to a primary winding thereof, such that the spark plug produces spark discharge in order to burn a fuel-air mixture.
2. Description of the Related Art
Spark energy which an internal combustion engine requires for proper burning of a fuel-air mixture has been known to change depending not only on the type of internal combustion engine, but also on operation conditions such as engine speed and engine load. Spark energy can be represented by the product of the magnitude of discharge current flowing as a result of spark discharge and the duration of the spark discharge.
For example, during low-speed, light-load operation such as idling operation, the amount of fuel-air mixture charged into a combustion chamber is small, and the speed of turbulent flow (swirl flow or tumble flow) of the fuel-air mixture is low. Consequently, combustion of the fuel-air mixture proceeds very slowly. Accordingly, in order to attain stable combustion during low-speed, light-load operation, spark energy must be increased to thereby promote combustion of the fuel-air mixture. Meanwhile, during high-speed, heavy-load operation, the density of the fuel-air mixture charged into the combustion chamber increases, and the speed of turbulent flow of the fuel-air mixture is high, so that the fuel is uniformly agitated. Therefore, sufficient combustion can be attained by means of relatively low spark energy.
In addition, the requisite spark energy varies depending on the air-fuel ratio of the fuel-air mixture. For example, when an internal combustion engine is operated with a lean fuel-air mixture having an air-fuel ratio of 20 or more as in the case of a lean burn engine, the density of fuel is low, and consequently the fuel-air mixture has low ignitability. Therefore, the spark energy must be increased.
In view of the foregoing, a conventional ignition apparatus for an internal combustion engine is designed such that insufficient spark energy does not arise; i.e., the ignition apparatus supplies the maximum spark energy required under various operation conditions of the internal combustion engine.
3. Problems Solved by the Invention
However, the above-described conventional ignition apparatus has the following drawbacks. In a state in which an internal combustion engine can be operated by spark energy lower than the maximum spark energy (e.g., during high-speed, heavy-load operation), supply of spark energy becomes excessive, and the excessive spark energy does not improve the ignitability but accelerates consumption of the spark plug electrodes. In addition, when the internal combustion engine is operated at higher speed or under a heavier load, or at high air-fuel ratio, the speed of turbulent flow of fuel-air mixture increases, and thus, a so-called multiple discharge phenomenon occurs easily. That is, in such a state, spark is caused to flow toward the downstream side during a second half of the spark discharge in which spark energy decreases, the spark discharge is then interrupted, and another spark discharge is generated again. In this manner, multiple discharge occurs. When such a phenomenon occurs, spark concentrates at a downstream point, and electrode temperature increases sharply, thereby accelerating sputtering or melting of electrodes of the spark plug, and only downstream portions of the electrodes are consumed; i.e., so-called local consumption occurs, resulting in shortened service life of the spark plug.
Meanwhile, in recent years, a so-called full-transistor igniter has been widely used for an internal combustion engine. In the full-transistor igniter, a semiconductor device such as a power transistor is used as a switching element for intermittently supplying electricity to a primary winding of an ignition coil in order to apply high voltage for ignition to a spark plug. In such a full-transistor igniter, since the duration of supply of electricity to the primary winding before spark discharge (ignition timing) is controlled (i.e., the drive duration of the switching element is controlled) in accordance with operation conditions of the internal combustion engine, the amount of magnetic flux energy which is accumulated in the ignition coil to be used as spark discharge can be controlled to a level required for combustion of the fuel-air mixture.
However, when the duration of supply of electricity to the primary winding before spark discharge is shortened, the amount of magnetic flux energy which is accumulated in the ignition coil decreases, and consequently the high voltage for ignition generated at the secondary winding through intermittent supply of primary current decreases accordingly. As a result, when electricity-supply duration is controlled in the above-described manner, and the internal combustion engine is operated under conditions, such as high-speed, heavy-load conditions, in which high voltage is required for generation of spark discharge although only a relatively small amount of spark energy is required, the high voltage for ignition generated at the secondary winding decreases and misfire may occur.
In view of the foregoing, as shown in Japanese Patent Application Laid-Open (kokai) No. 11-41717, the present inventors proposed an ignition apparatus for an internal combustion engine which, instead of controlling the duration of supply of electricity to the primary winding of an ignition coil before spark discharge, resumes supply of electricity to the primary winding during spark discharge by use of spark-discharge interruption switching means, to thereby stop spark discharge. When this ignition apparatus for an internal combustion engine is used, it becomes possible to interrupt spark discharge after elapse of a spark discharge duration suitable for operation conditions of the internal combustion engine, while maintaining high voltage for ignition generated at the secondary winding through intermittent supply of electricity to the primary winding. In this manner, the amount of spark energy can be controlled to a proper level.
If the primary current flows continuously after supply of the primary current is resumed for the purpose of interrupting spark discharge, the amount of heat generated by the spark-discharge interruption switching means increases, and power is needlessly consumed. Therefore, the supply of electricity is desirably stopped at a proper timing. However, if the primary current flowing after resumption of electricity supply is stopped abruptly, spark discharge is generated again, thereby impairing operation of the internal combustion engine.
In view of the foregoing, in the ignition apparatus disclosed in Japanese Patent Application Laid-Open No. 11-41717, a capacitive element such as a capacitor is connected in series to the spark-discharge interruption switching means as current adjustment means for decreasing the primary current before stopping the primary current flowing through the primary winding after electricity supply is resumed. Thus, unnecessary generation of spark discharge and needless consumption of power can be suppressed.
In general, in an ignition apparatus for an internal combustion engine, the power source voltage output from a power source unit varies at the time of startup of the internal combustion engine or due to improper operation of a generator, resulting in variations in the amount of magnetic-flux energy accumulated in the ignition coil. That is, when the power source voltage output from the power source unit of the internal combustion engine exceeds its rated value, a larger current flows through the primary winding than in an ordinary state, with the result that an excessive amount of magnetic-flux energy is accumulated in the ignition coil.
Therefore, in the ignition apparatus disclosed in Japanese Patent Application Laid-Open No. 11-417
Inagaki Hiroshi
Nakano Daisuke
Gimie Mahmoud
NGK Spark Plug Co. Ltd.
Sughrue & Mion, PLLC
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