Electricity: measuring and testing – Internal-combustion engine ignition system or device – Electronic ignition system
Reexamination Certificate
2000-02-09
2001-08-14
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Internal-combustion engine ignition system or device
Electronic ignition system
C324S388000, C073S035080
Reexamination Certificate
active
06275041
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a combustion state detecting apparatus for an internal combustion engine, which apparatus is designed for detecting the combustion state of an air-fuel mixture within a cylinder or cylinders of the engine by detecting an ion current making appearance upon combustion of the air-fuel mixture. More particularly, the invention is concerned with a combustion state detecting apparatus for the internal combustion engine, which apparatus is imparted with a function or facility for estimating the causes for non-generation or disappearance of a combustion signal based on the ion current.
2. Description of Related Art
For having better understanding of the concept underlying the present invention, background techniques thereof will first be reviewed in some detail.
FIG. 5A
is a circuit diagram showing schematically an arrangement of a hitherto known or conventional combustion state detecting apparatus for an internal combustion engine (hereinafter also referred to simply as the engine), which apparatus is designed for detecting the combustion state within an engine cylinder or cylinders on the basis of an ion current produced upon combustion of air-fuel mixture. Referring to the figure, reference numeral
1
denotes an ignition coil which includes a primary winding
11
having a high-voltage end connected to a positive electrode of a power supply source
3
such as an onboard battery, while the low-voltage end of the primary winding
11
is connected to a collector electrode of a power transistor
2
which serves as a switching element for turning on/off a primary current flowing through the primary winding
11
. The power transistor has an emitter electrode connected to the ground potential. On the other hand, a secondary winding
12
of the ignition coil
1
has a high-voltage end connected to an electrode of a spark plug
4
disposed within a cylinder of the engine while a low-voltage end of the secondary winding
12
is connected to a bias circuit
5
which is designed to apply a bias voltage of positive polarity to the spark plug
4
through a wiring conductor.
Further, referring to
FIG. 5A
, reference numeral
6
denotes an ion current detecting circuit which is designed for detecting by way of the bias circuit
5
an ion current making appearance upon combustion of the air-fuel mixture and flowing through an inter-electrode gap of the spark plug
4
to thereby convert the ion current into a voltage signal. More specifically, the ion current detecting circuit
6
is implemented in the form of a conventional current mirror circuit constituted by a series connection of transistors Q
1
a
and Q
1
b
and a transistor Q
2
which are connected in parallel between a positive voltage source (i.e., voltage source of plus or positive polarity) +V and the ground potential. A resistor R
1
is inserted between the ground potential and the collector of the transistor Q
2
. A current analogous to the ion current flows through the resistor R
1
to undergo a voltage conversion, whereby an ion current detection voltage signal (hereinafter referred to as the ion current detection signal) X
2
is produced.
The ion current detection signal X
2
is supplied to a decision circuit
7
which is designed for shaping the ion current detection signal X
2
detected by the ion current detecting circuit
6
into a pulse signal, which then undergoes a processing for deciding occurrence of combustion of the air-fuel mixture, as a result of which a pulse-like decision signal X
3
is outputted from the decision circuit
7
to be supplied to an ECU (Electronic Control Unit)
10
.
More specifically, for shaping the ion current detection signal X
2
resulting from the voltage conversion mentioned above into a pulse signal, the decision circuit
7
includes a comparator circuit composed of a comparator CP
1
for comparing the level of the ion current detection signal X
2
with a reference voltage Vth
4
, an integrating circuit composed of a resistor R
2
and a capacitor C
2
for eliminating noise components N
1
and N
2
superposed on the pulse-like ion current outputted from the comparator CP
1
, and a delay circuit composed of a comparator CP
2
. Parenthetically, it should be mentioned that a pull-up resistor R
3
connected to the output terminal of the comparator CP
2
serves for pulling up the output voltage level thereof.
Next, referring to a signal waveform diagram shown in
FIG. 5B
, description will be made of operations of the conventional combustion state detecting apparatus in conjunction with normal combustion, a first type of non-combustion event (e.g. due to absence of fuel supply) and a second type of non-combustion event (e.g. due to failure of generation of high voltage for firing).
1. Normal combustion
Upon rising of the ignition signal X
1
applied to the base of the power transistor
2
under the control of the ECU
10
, the current flowing through the primary winding
11
of the ignition coil
1
is interrupted, as a result of which a high voltage E is induced in the secondary winding
12
of the ignition coil
1
, whereby a spark discharge is caused to take place within the inter-electrode gap of the spark plug
4
.
The ion current generated due to the combustion of the air-fuel mixture within the engine cylinder in which the spark discharge has taken place is inputted to the ion current detecting circuit
6
by way of the bias circuit
5
to undergo the current-to-voltage conversion in the current mirror circuit, whereby the ion current detection signal X
2
is outputted from the ion current detecting circuit
6
.
At this juncture, it should be mentioned that the ion current detection signal X
2
outputted from the circuit
6
contains in addition to the intrinsic ion current component due to the combustion of the air-fuel mixture a noise component N
1
produced upon rising of the ignition signal and the noise component N
2
making appearance upon termination or extinction of the spark discharge. Accordingly, these noise components N
1
and N
2
have to be eliminated before outputting the decision signal X
3
for deciding the combustion event on the basis of the ion current.
Thus, before eliminating the noise components N
1
and N
2
through the medium of the delay circuit, the ion current detection signal X
2
is inputted to the comparator CP
1
constituting the comparator circuit for comparing the levels of the signal components of the ion current detection signal X
2
with the reference voltage Vth
4
. Since each of the noise components N
1
and N
2
is intrinsically in the form of a spike-like signal, these components are shaped into pulses each having an extremely short time duration.
Thus, even when the pulse-like noise components N
1
and N
2
are inputted to the CR integrating circuit constituting a part of the delay circuit to thereby raise the charge voltage of the capacitor C
2
up to or beyond the reference voltage Vth
5
preset at the comparator CP
2
, the pulse-like noise components Ni and N
2
will assume low level before the charge voltage of the capacitor C
2
reaches the reference voltage Vth
5
because the time duration of the noise components is short of the CR time constant. Consequently, no decision signal will be outputted from the comparator CP
2
in response to the noise components N
1
and N
2
.
On the other hand, when the ion current component undergone the pulse-shaping operation is inputted to the integrating circuit, the capacitor C
2
is charged to a level equal to or exceeding the reference voltage Vth
5
after lapse of a predetermined time, because the time duration of the pulse-like ion current component is greater than the CR time constant, as a result of which the output of the comparator CP
2
becomes high, whereby the decision signal X
3
indicating that the combustion has taken place normally, i.e., normal combustion, is outputted.
At this juncture, the time taken for the charge voltage of the capacitor C
2
to exceed the reference voltage Vth
5
will be defined as
Hatazawa Yasuyoshi
Koiwa Mitsuru
Nobe Hisanori
Ohashi Yutaka
Okamura Koichi
Metjahic Safet
Mitsubishi Denki Kabushiki Kiasha
Nguyen Vincent Q.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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