Measuring and testing – Engine detonation – Specific type of detonation sensor
Reexamination Certificate
2000-03-20
2002-07-16
McCall, Eric S. (Department: 2855)
Measuring and testing
Engine detonation
Specific type of detonation sensor
C073S117020
Reexamination Certificate
active
06418785
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a combustion/misfire detecting apparatus for an internal combustion engine for detecting combustion and misfire events taking place within a cylinder of the engine on the basis of an ion current making appearance upon combustion of an air/fuel mixture within the cylinder.
2. Description of Related Art
In general, it is known that ions are produced when the air/fuel mixture is burned within a cylinder of an internal combustion engine (hereinafter also referred to simply as the engine). Such ions can be detected in the form of an ion current by means of a probe which is disposed within the cylinder and to which a high voltage is applied as a bias voltage. Thus, by detecting presence or absence of the ion current, it is possible to detect occurrence of combustion or misfire event within all the engine cylinders discriminatively from one another.
For having better understanding of the concept underlying the present invention, background techniques thereof will first be reviewed in some detail.
FIG. 11
is a block diagram showing a structure of a conventional misfire detecting apparatus for an internal combustion engine. In the figure, reference numeral
1
denotes an ignition circuit comprised of an ignition coil IG whose primary winding
11
has a high-voltage end applied with a voltage V
B
of positive or plus polarity while a low voltage end of the primary winding
11
is connected to a switching element
13
for turning on/off a primary current flowing through the primary winding
11
. More specifically, the switching element is constituted by a power transistor having a collector electrode connected to the primary winding
11
as mentioned above and an emitter electrode connected to the ground potential. The base of the switching element
13
is connected to an input terminal of the ignition circuit
1
to which an ignition pulse signal I
B
issued by an electronic control unit or ECU (not shown) which is known per se is applied. On the other hand, the secondary winding
12
of the ignition coil IG has a high-voltage end connected to a spark plug
14
while the low-voltage end of the secondary winding
12
is connected to an ion current detecting unit
15
by a wiring conductor.
The ion current detecting unit
15
in turn is comprised of a bias circuit
16
for applying a vias voltage V
B
of plus polarity to the spark plug
14
, a mask circuit
17
for cutting off or eliminating noises generated upon ignition and firing of the air/fuel mixture from the ion current as detected and a waveform shaper circuit
18
which is designed for shaping the ion current from which the noise component has been eliminated, to thereby output a combustion pulse signal. Incidentally, the noise generated upon firing of the air/fuel mixture as mentioned above will hereinafter be referred to as the ignition noise only for convenience of the description.
Next, description will be directed to the operation of the conventional misfire detecting apparatus. For making it possible to detect the ion current, the bias circuit
16
applies a high voltage of positive or plus polarity (also referred to as the bias voltage) to the spark plug
14
designed to serve also as an ion current detecting probe by making use of the secondary voltage of the ignition coil IG.
Upon application of an ignition pulse I
B
to the switching element
13
, the primary current flowing through the primary winding
11
of the ignition coil IG is interrupted at a falling edge of the ignition pulse I
B
, as a result of which a high voltage of negative or minus polarity is applied to the spark plug
14
connected electrically to the secondary winding
12
of the ignition coil IG, whereby a spark discharge is caused to occur between the electrodes of the spark plug
14
. Thus, the air/fuel mixture is fired to undergo explosive combustion, which results in generation of ions within the engine cylinder due to the effect of the ionization.
In that case, the spark plug
14
will continue to remain in the state applied with the bias voltage of plus polarity from the bias circuit
16
which is charged with the secondary voltage of the ignition coil, even after extinction of the spark discharge. Consequently, the ions produced due to the ionization are caused to migrate under the action of the bias voltage. This migration of ions is detected as an ion current.
In this conjunction, it is however noted that before the ion current is detected, a steep pulse P
1
makes appearance in response to rising of the ignition pulse I
B
and additionally a steep pulse P
3
is produced before generation of the ion current at the time point when the air/fuel mixture is fired by the spark discharge occurring at the spark plug
14
, as is illustrated in
FIG. 12
at (a) and (b). These pulses P
1
and P
3
are detected as the ignition noises as well.
In general, the peak value of the ion current changes in dependence on the operation state of the engine. More specifically, there exists such a trend that the peak value of the ion current becomes smaller as the rotation number or speed (rpm) of the engine decreases while the former becomes larger as the latter increases. Usually, the peak value of the ion current lies within a range of several microamperes (&mgr;A) to several hundred microamperes. Under the circumstances, the threshold value used for detecting the ion current is set on the order of several microamperes with a view to detecting occurrence of the misfire event on the basis of the presence/absence of the ion current over the whole operation range of the engine.
However, when the threshold value is set on the order of several microamperes in practical applications as mentioned above, there may arise such unwanted situation that the ignition noises P
1
and P
3
produced upon rising of the ignition pulse I
B
as well as upon occurrence of the spark discharge at the spark plug
14
will be detected erroneously as the combustion pulse (i.e., the pulse indicating the combustion of the air/fuel mixture). For this reason, the steep noise pulses P
1
and P
3
each of a very short duration are eliminated by the mask circuit
17
so that only the ion current component is shaped into a pulse signal by the waveform shaper circuit
18
to be thereby outputted as the combustion pulse signal. Thus, so long as the combustion of the air/fuel mixture occurs normally, the combustion pulse signal indicative of the ion current can be outputted from the bias circuit
16
after lapse of the masking period from the start of the spark discharge, as can be seen in
FIG. 12
at (c).
Referring to
FIG. 12
at (d), there is illustrated a waveform of the ion current signal outputted upon occurrence of a misfire event. As can be seen from this figure, the noise pulse P
1
generated upon rising of the ignition pulse as well as the noise pulse P
3
generated upon occurrence of the spark discharge make appearance as the ignition noises. However, these ignition noise pulses P
1
and P
3
are eliminated by the mask circuit
17
. Of course, no combustion pulse originating in the ion current is outputted from the waveform shaper circuit
18
either, because no combustion/explosion has taken place within the cylinder (i.e., because of occurrence of the misfire event), as is illustrated in
FIG. 12
at (e).
So long as the normal combustion of the air/fuel mixture takes place, it is thus possible to make decision as to occurrence of the combustion/misfire events on the basis of presence/absence of the combustion pulse which can be derived by shaping the ion current with reference to a fixed threshold value. In this conjunction, it is however to be noted that soot may be deposited on the electrodes of the spark plug
14
as well as the inter-electrode gap thereof due to repetitive combustion of the air/fuel mixture although it depends on the operation state of the internal combustion engine. Such deposition of soot gives rise to a problem that a leak current takes place.
In more concrete, it is assumed
Hatazawa Yasuyoshi
Koiwa Mitsuru
Nobe Hisanori
Ohashi Yutaka
Okamura Koichi
McCall Eric S.
Mitsubishi Denki & Kabushiki Kaisha
Sughrue & Mion, PLLC
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