Internal-combustion engines – High tension ignition system – Power supply – ignition coil primary – and interrupter element...
Reexamination Certificate
2001-12-20
2003-04-01
Mohanty, Bibhu (Department: 3747)
Internal-combustion engines
High tension ignition system
Power supply, ignition coil primary, and interrupter element...
Reexamination Certificate
active
06539930
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ignition apparatus for internal combustion engine. More specifically, this invention relates to the ignition apparatus that has a function to generate a firing voltage (Hereinafter referred to as “a high voltage for firing”) in the ignition coil for generating the spark discharge between electrodes of a spark plug and to supply an ionized current after a spark discharge.
2. Description of the Related Art
In internal combustion engines used in such as vehicle engines, when an air-fuel mixture is ignited by a spark discharge that is generated by a spark plug, ion is generated following this firing. Therefore, after the air-fuel mixture is ignited by the spark discharge of the spark plug, an ionized current flows by supplying a voltage between electrodes of the spark plug. As the amount of the generated ion changes with ignited conditions of the air-fuel mixture, the ionized current generating by the generated ion is detected and analyzed, whereby to carry out a misfire detection or knocking detection.
In the conventional ignition apparatus for internal combustion engine, which has a function for generating the ionized current, the spark plug is electrically connected to one end of a secondary winding while a capacitor is provided in series to the other end thereof;
when the spark discharge generates at the spark plug, the capacitor is charged by a spark discharge current (Hereinafter, referred to as “secondary current”) flowing in the secondary winding of the ignition coil and the spark plug;
the charged capacitor is discharged after stopping the spark discharge, whereby a voltage is supplied between electrodes of the spark plug through the secondary winding (for example, Japanese Patent Publication NO.Hei4-191465 or Japanese Patent Publication NO.Hei10-238446).
In such an ignition apparatus for internal combustion engine, a Zener diode is provided in parallel to the capacitor for preventing the capacitor from destruction, which is caused by an overcharge thereof. Moreover, in the ignition apparatus, a voltage at both ends or the capacitor is limited to be constant voltage. (100 to 300[V])
Thus, the ignition apparatus for internal combustion engine employing the capacitor as an electric power supply for generating the ionized current does not require to particularly provide an electric power supply (such as battery) exclusively used for supplying the ionized current. Therefore, parts of the ignition apparatus are reduced and miniaturization is realized.
However, in the ignition apparatus for internal combustion engine of the structure which discharges the capacitor charged with the secondary current flowing while generating a spark discharge at the spark plug, when turning on electricity in the primary winding for accumulating magnetic flux energy in the ignition coil, a high voltage (several kV) which has a opposed polarity to the high voltage for firing, is generated at the secondary winding, whereby the spark discharge of the spark plug is generated before a normal firing time. Therefore, this may bring about a misfire of the air-fuel mixture.
The above-mentioned ignition apparatus is structured such that a conductive path of the secondary current causes a current to be conductive in both directions, whereby the ignition apparatus makes it possible to charge the capacitor connected in series to the conductive path of the secondary current when generating the spark discharge at the spark plug and to discharge the capacitor when generating the ionized current between the electrodes of the spark plug. The ignition apparatus is structured such that the conductive path of the secondary current causes current to be conductive in both directions. Therefore, in such an ignition apparatus for internal combustion engine which is accompanied with changing of magnetic flux density in the ignition coil at starting conduction to the primary winding, an induced voltage having an opposed polarity thereof at the time to cut off the primary current, is generated at both ends of the secondary winding.
In case the induced voltage generated at the time to cut off the primary current is higher than a voltage value necessary to generate the spark discharge, the spark discharge is generated at the spark plug under a condition where the secondary current flows in a opposed direction to a secondary current flowing at the time of an inherent spark discharge.
Further, under a condition where the conduction of the primary current to the primary winding is constant, the rotation speed of the internal combustion engine is higher, a time of starting the conduction of the primary current to the primary winding is determined at “an earlier period of a crank angle”. Herein, “The earlier period of the crank angle” indicates “a time when an internal pressure within a cylinder is low”.
It is known that the lower the internal pressure in the cylinder is, the lower the discharge voltage at he spark plug. Therefore, When the internal combustion engine operated at high rotation speed, a misfire of the air-fuel mixture is easy to happen, since the high voltage (several kV) of the opposed polarity to the high voltage for firing, which is generated in the secondary winding. at the time to start a conduction to the primary winding. In order to avoid generating the misfire of the air-fuel mixture at the earlier period (“a time when an internal pressure within a cylinder is low”), it is necessary that a conductive direction in the conductive path of the secondary current is determined to be one direction and a so-called diode for preventing reverse current is provided between one end of the secondary winding and one end of the spark plug so that current is allowed to flow only when the time to cut off the primary current.
However, in case the diode for preventing reverse current is provided between one end of the secondary winding and one end of the spark plug so as to allow only the conduction of the secondary current in the secondary winding when the time to cut off the primary current, the ignition apparatus for internal combustion engine having the function generating the ionized current makes it possible to charge the capacitor by the secondary current, and the current by discharging from the capacitor cannot flow, whereby it is difficult to provide the ionized current between electrodes of the spark plug.
Therefore, the ionized current flowing between the electrodes of the spark plug cannot be detected.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an ignition apparatus for internal combustion engine which can restrain a misfire of the air-fuel mixture caused by generating the spark discharge at the spark plug when the time to start a conduction to the primary winding, and can generate and detect the ionized current between electrodes of the spark plug.
According to the first aspect of the invention, an ignition apparatus for an internal combustion engine comprises:
an ignition coil comprising a primary winding and a secondary winding, wherein the secondary winding has a high voltage side and a low voltage side, and the ignition coil generates a firing voltage supplied to the secondary winding by cutting off a primary current flowing in the primary winding;
a switching device for conducting and cutting off the primary current;
a spark plug connected in series to the secondary winding to form a closing loop, wherein a spark discharge is generated in the spark plug when a secondary current generated by the firing voltage flows in the spark plug;
a diode for preventing a reverse current, connected to a conducting path between the spark plug and the high voltage side, wherein the diode conducts the secondary current when a primary current is cut off, the diode cuts off the secondary current when the primary current starts to flow;
a current detecting device connected in series to the secondary winding and the spark plug; and
a supplied voltage limiting device holding a voltage applied to the current
Mohanty Bibhu
Morgan & Lewis & Bockius, LLP
NGK Spark Plug Co. Ltd.
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