Internal-combustion engines – High tension ignition system – Electronic cylinder sequencing
Reexamination Certificate
1999-02-10
2001-02-20
Yuen, Henry C. (Department: 3747)
Internal-combustion engines
High tension ignition system
Electronic cylinder sequencing
C123S651000, C310S07000A, C310S07000A
Reexamination Certificate
active
06189522
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to waste-spark ignition of an internal combustion engine (the term “waste-spark” is herein used to indicate a technique of firing two spark plugs at the same time by means of one ignition coil). More particularly, the present invention relates to a method of and apparatus for producing spark for such waste-spark ignition, which is capable of preventing or suppressing occurrence of a difference in the spark plug discharge characteristic between the cylinders due to wear of the electrodes of the spark plugs.
2. Description of the Related Art
In recent multi-cylinder engines is used an electronic ignition system which provides sparks to cylinders without use of a distributor. Enumerated as such an electronic ignition system are (1) first one wherein cylinders which differ in operating cycle phase by 360 degrees are and when one of the paired cylinders is on compression stroke (thus, the other cylinder is on exhaust stroke) two spark plug provided to the respective cylinders are fired at the same time, i.e., a so-called simultaneous ignition or waste-spark type, and (2) another one wherein the spark plugs are fired independently when the respective cylinders are on compression stroke. The first mentioned, waste-spark type of the above mentioned two ignition systems can provide sparks to two cylinders by means of one ignition transformer or coil and therefore superior in cost to the second mentioned type.
FIG. 6
shows a prior art waste-spark or double ended distributorless ignition system
100
wherein a primary winding
2
of an ignition coil or transformer
1
is connected at an end thereof to a direct current source E by way of a key switch or ignition switch K and at another end thereof to a collector of a transistor
4
. A secondary winding
3
is connected at opposite ends thereof to spark plugs P
1
and P
2
provided to rective cylinders N
1
and N
2
of an engine N, which differ in operating cycle phase by 360 degrees.
Although the actual number of cylinders of the engine N is not always two but six for instance, explanation for other cylinders is omitted for brevity.
With this circuit, an ignition operation is carried out at a predetermined ignition angle in response to the output of a crank angle sensor or the like. Specifically, when the ignition switch K is turned on to connect the direct current source E to the primary winding
2
, the voltage at the ignition signal line Sig of the ECU (engine control unit)
5
rises up to turn on the transistor
4
, thus allowing current to flow from the direct current source E to the primary winding
2
. Thereafter, the voltage at the ignition signal line Sig is lowered at a predetermined ignition timing (e.g., on compression stroke of the cylinder N
1
) by means of the ECU
5
, a high voltage is induced in the secondary winding
3
to cause the first and second spark plugs P
1
and P
2
to produce sparks, thus igniting the air-fuel mixture in one of the cylinders (e.g., cylinder N
1
) on compression stroke while producing waste-spark in the other cylinder (e.g., cylinder N
2
) on exhaust stroke.
However, in case the circuit shown in
FIG. 6
is used, the polarity of the high voltage induced in the secondary winding
3
is constant. Thus, negative polarity spark is always produced by the first spark plug P
1
in which the more negative potential is caused in the center electrode P
1
i
than in the ground electrode P
1
o
which is grounded, whereas positive polarity spark is always produced by the second spark plug P
2
in which the more positive potential exists in the center electrode P
2
i
than in the ground electrode P
2
o.
For this reason, the two spark plugs P
1
and P
2
differ in the negative potential electrode which is more liable to wear away than the positive potential electrode since it is impacted by positive ions caused by the sparks. Thus, wear of the center electrode P
1
i
is mainly caused in the first spark plug P
1
, whereas wear of the ground electrode P
2
o
is mainly caused in the second spark plug P
2
.
In the meantime, in case ignition is carried out with the above described waste-spark method, sparks are provided to both of the cylinders N
1
and N
2
on both of their compression and exhaust strokes, but most wear of the electrodes is caused by spark on compression stroke. It is assumed that the electrodes are liable to wear away on compression stroke since on compression stroke the electrodes are subjected to a high pressure and exposed to a high temperature by being surrounded by the flames during spark discharge.
Further, more marked wear results in case natural gas or the like fuel that burns at high temperature is used or high voltage is used to produce the spark for lean-burn.
In this instance, increase of the spark gap due to wear of the electrodes is largely influenced by the wear of the center electrode P
1
i
which is smaller in volume. In contrast to this, the ground electrode P
2
o
is larger in volume so its wear can increase the spark gap at only a small rate. For this reason, more increase of the spark gap is caused in the first spark plug P
1
as eared with the second spark plug P
2
, thus increasing the voltage necessitated for producing the spark.
However, in case the spark plugs are used in an engine of the type in which the ground electrodes are liable to have a high temperature to be oxidized, there may occur such a case in which the wear of the ground electrodes is accelerated by the oxidization. In such a case, increase of the spark gap is largely influenced by the wear of the ground electrodes.
In any event, the difference in the wear of the spark plug electrode occurs between the cylinders to cause a difference in the spark plug discharge characteristic between the cylinders N
1
and N
2
. Further, such difference in wear causes one of the spark plugs to increase in spark gap excessively, thus causing the life of one of the spark plugs to expire faster than the other, e.g., the life of the first spark plug P
1
expires faster than the second plug P
2
.
In this connection, it is considered to use spark plugs of different part number for the spark plugs P
1
and P
2
to be put to the engine N, i.e., to use a spark plug with a wear-resistant center electrode P
1
i
for the first spark plug P
1
and a spark plug with a wear-resistant ground electrode P
2
o
for the second spark plug P
2
. However, this is not desirable since this will cause the part numbers of spark plugs to be controlled, to be doubled and furthermore will induce erroneous installation of spark plugs.
Thus, in order to prevent the wear of the electrodes, it has been practiced to use such spark plugs P
1
and P
2
in which all of the center electrodes P
1
i
and P
2
i
and the ground electrodes P
1
o
and P
2
o
have welded thereto wear-resistant electrode chips. However, one of the wear-resistant electrode chips which are made of an expensive metal such as platinum, iridium, rhodium and rhenium, e.g., the wear-resistant electrode chip attached to the ground electrode P
1
o
of the spark plug P
1
remains unchanged without having almost any wear even when the chip of the center electrode P
1
i
has worn away to cause expiration of the life of the spark plug P
1
, so one of the wear-resistant electrode chips is wasted.
SUMMARY OF THE INVENTION
With the prior art ignition method and ignition system of the kind in which one ignition coil fires two spark plugs at the same time, a difference in wear between the spark plugs is inevitably caused. Such a difference in wear will lead to a difference in the spark plug discharge characteristic between the cylinders. Furthermore, such a difference in wear will shorten the life of the spark plug and waste costly wear-resistant electrode chips in case the spark plug has such chips provided to the electrodes thereof.
It is an object of the present invention to provide an ignition method for an internal combustion engine which can prevent or suppress occurrence of a difference in the discharge charact
Foley & Lardner
NGK Spark Plug Co. Ltd.
Vo Hieu T.
Yuen Henry C.
LandOfFree
Waste-spark engine ignition does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Waste-spark engine ignition, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Waste-spark engine ignition will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2580758