Electricity: measuring and testing – Internal-combustion engine ignition system or device – In situ testing of spark plug
Reexamination Certificate
1999-01-28
2001-04-24
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Internal-combustion engine ignition system or device
In situ testing of spark plug
Reexamination Certificate
active
06222368
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an ion current detection apparatus for detecting ion current that flows after spark discharge of a spark plug.
Conventionally, in order to detect misfire or knocking of an internal combustion engine, as well as various other operation conditions of the internal combustion engine (e.g., such as air-fuel ratio, lean limit of air-fuel ratio, limit in amount of recirculated exhaust gas), there has been utilized a technique for detecting the ion current which flows due to ions present in the vicinity of electrodes of a spark plug of the engine after spark discharge.
That is to say, within a cylinder of an internal combustion engine, ions are generated when combustion (flame propagation) occurs after spark discharge of a spark plug, and the resistance between the electrodes of the spark plug changes in accordance with the number of ions generated, which in turn changes depending on the combustion state or the operation state of the engine. Therefore, changes in the resistance between electrodes of the spark plug (i.e., the changes in operation state) can be detected by a method in which, after application of high voltage for ignition purpose (i.e., after spark discharge of the spark plug), a voltage is externally applied to the spark plug in order to cause a flow of ion current, which is then detected.
BACKGROUND OF THE INVENTION
An example of such an ion current detection apparatus disclosed in Japanese Patent Application Laid-Open No. 4-191465 will be described.
As shown in
FIG. 6
of the accompanying drawings, an ignition apparatus
2
to which is applied an ion current detection apparatus
100
includes a spark plug
10
provided for each cylinder (only one cylinder is represented in
FIG. 6
) of an internal combustion engine, as well as an ignition coil
12
for applying the spark plug
10
with high voltage for ignition purpose.
A battery voltage Vb is applied to one end of a primary winding L
1
of the ignition coil
12
, while the other end of the primary winding L
1
is grounded via a power transistor
14
, which is turned on and off in accordance with an ignition signal IG. One end of a secondary winding L
2
of the ignition coil
12
is connected to a center electrode of the spark plug
10
, and the other end of the secondary winding L
2
is connected to the ion current detection apparatus
100
. An outer electrode of the spark plug
10
is grounded.
In the ignition apparatus
2
, when the ignition signal IG is at a high level, the power transistor
14
is turned on, so that a current flows through the primary winding L
1
of the ignition coil
12
. When the ignition signal IG subsequently reaches a low level and the power transistor
14
is turned off, a high ignition voltage is generated across the secondary winding L
2
of the ignition coil
12
. This high voltage is applied to the center electrode of the spark plug
10
in order to cause the spark plug
10
to effect spark discharge. The ignition apparatus
2
is designed such that the center electrode of the spark plug
10
attains negative polarity during the spark discharge; therefore, the spark discharge current Isp caused by the spark discharge flows from the spark plug
10
to the secondary winding L
2
.
The ion current detection apparatus
100
includes a resistor
20
, one end of which is grounded; a diode
22
which is connected in parallel to the resistor
20
and whose cathode is grounded; a capacitor
24
connected in series to the ungrounded end of the resistor
20
and to the ungrounded end of the diode
22
; and a Zener diode
26
which is connected in parallel to the circuit comprising the resistor
20
, the diode
22
, and the capacitor
24
. The cathode of the Zener diode
26
is connected to the capacitor
24
, and the anode of the Zener diode
26
is grounded. The connection line between the capacitor
24
and the Zener diode
26
is connected to the secondary winding L
2
of the ignition coil
12
. A voltage generated across the resistor
20
is output as a detection value Vio.
In the ion current detection apparatus
100
having the above-described structure, the spark discharge current Isp stemming from spark discharge of the spark plug
10
flows through a current path including the capacitor
24
and the diode
22
, while causing the Zener diode
26
to produce a Zener voltage Vz. Therefore, due to the spark discharge current Isp, the capacitor
24
is charged by a voltage Vc (=Vz−Vf) which is smaller than the Zener voltage Vz of the Zener diode
26
by the forward voltage Vf of the diode
22
.
When the high ignition voltage induced in the secondary winding L
2
drops to a level lower than the Zener voltage Vz, the capacitor
24
starts discharging, so that a high detection voltage according to the charged voltage Vc is applied to the spark plug
10
via the secondary winding L
2
of the ignition coil
12
. As a result, an ion current Iio flows in accordance with the number of ions generated between the electrodes of the spark plug
10
. Since the ion current Iio flows through the resistor
20
, the ion current detection apparatus
100
outputs a detection value Vio corresponding to the ion current Iio.
However, in the secondary-side circuit of the ignition apparatus
2
, since the inductance of the secondary winding L
2
of the ignition coil
12
and the capacitance between the electrodes of the spark plug
10
form a resonant circuit, voltage damped oscillation is generated after completion of spark discharge of the spark plug.
Depending on the operation conditions of the internal combustion engine, the magnitude of the current that flows during that period may reach a value of several to several tens of times the ion current Iio. In addition, the oscillation continues for a relatively long period of time as long as several milliseconds. Therefore, as shown in
FIG. 7
, the oscillation component is superposed on the ion current Iio, resulting in it being impossible to measure properly the ion current Iio.
In order to overcome the above-described problem, the measurement may be performed at a point in time when the voltage damped oscillation has converged. However, since the charge accumulated in the capacitor
24
is consumed by the voltage damped oscillation, when the voltage damped oscillation converges, a high voltage required for detection of the ion current Iio becomes impossible to obtain, resulting in possible failure to detect the ion current Iio.
This problem can be mitigated through an increase in the capacitance of the capacitor
24
, which allows a larger amount of charge to be accumulated during spark discharge of the spark plug
10
. However, in this case, if only a small amount of charge is consumed due to flow of the ion current Iio, an undesirable voltage is applied to the spark plug
10
due to the charge remaining in the capacitor
24
. In this case, if particles of deposited carbon and liquid fuel are present on the surface of the insulator of the spark plug
10
, particles are easily moved and aligned between the electrodes by an electric field that is produced through the voltage application. As a result, there arises a new problem that so-called contamination of the spark plug
10
, in which the insulating resistance between the electrodes of the spark plug decreases, occurs quickly.
SUMMARY OF THE INVENTION
In view of the forgoing problems, an object of the present invention is to provide an ion current detection apparatus which can detect ion current with a high degree of accuracy regardless of the presence of voltage damped oscillation and which does not cause contamination of a spark plug.
In order to achieve the above object, an ion current detection apparatus according to a first aspect of the invention includes: a capacitor which forms a closed loop together with a spark plug and a secondary winding of an ignition coil; current detection means for detecting current flowing through the closed loop; and charge means for charging the capacitor to a predetermined high voltage for detection, throug
Inagaki Hiroshi
Kondo Noriaki
Miyata Shigeru
Kerveros J
Metjahic Safet
NGK Spark Plug Co. Ltd.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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