Internal-combustion engines – High tension ignition system – Safety device
Reexamination Certificate
2002-11-27
2004-08-24
Gimie, Mahmoud (Department: 3747)
Internal-combustion engines
High tension ignition system
Safety device
C123S655000
Reexamination Certificate
active
06779517
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an ignition device for internal combustion engine, having a function of generating a spark discharge between electrodes of a spark plug by applying an igniting high voltage generated in an ignition coil between the electrodes of the spark plug, and a function of generating an ionic current after completion of the spark discharge.
BACKGROUND OF THE INVENTION
In an internal combustion engine used as a car engine or the like, when an air-fuel mixture is burned by a spark discharge in a spark plug, ions are produced with the combustion of the air-fuel mixture. Therefore, if a voltage is applied between electrodes of the spark plug after the air-fuel mixture is burned by the spark discharge of the spark plug, an ionic current flows. Because the amount of produced ions varies in accordance with the state of combustion of the air-fuel mixture, ignition failure, knocking or the like can be detected if the ionic current is detected and analyzed.
As an example of a related-art ignition device for internal combustion engine having a function of generating such an ionic current, there is a device in which a center electrode
61
of a spark plug
13
is electrically connected to one end of a secondary winding
34
of an ignition coil
15
while a capacitor
45
is series-connected to the other end of the secondary winding
34
as shown in FIG.
4
. The ignition device
101
for internal combustion engine is configured so that the capacitor
45
is charged by a discharge current
22
(secondary current
22
) flowing in the secondary winding
34
of the ignition coil
15
and the spark plug
13
at the time of generation of a spark discharge in the spark plug
13
, and so that the charged capacitor
45
is discharged after completion of the spark discharge to thereby apply a voltage between electrodes of the spark plug
13
through the secondary winding
34
to generate an ionic current
42
. Further, a detection resistor
47
is provided at the other end of the capacitor
45
opposite to the secondary winding
34
so that the ionic current is detected on the basis of the voltage between opposite ends of the detection resistor
47
.
Incidentally, in the ignition device
101
for internal combustion engine, a Zener diode
111
is provided in parallel to the capacitor
45
to prevent the capacitor
45
from being broken by overcharge and to limit the voltage between the opposite ends of the capacitor
45
to a constant value (100 to 300 V).
As described above, in the ignition device for internal combustion engine using the capacitor
45
as a power supply for detecting an ionic current, it is unnecessary to provide any special power supply unit (such as a battery) exclusively used for detecting an ionic current. Hence, there is an advantage that a relatively small number of parts can be used while the size of the ignition device can be reduced.
SUMMARY OF THE INVENTION
In the ignition device
101
for internal combustion engine, however, magnetic flux energy is stored in the ignition coil
15
. For this reason, a voltage (several kV) reversed in polarity to an igniting high voltage is generated in the secondary winding
34
when current conduction to a primary winding
33
is started. Hence, there is fear that the spark plug
13
may generate a spark discharge before normal ignition timing to thereby cause wrong ignition of an air-fuel mixture.
FIG. 6
is a time chart showing states of a first command signal and the voltage between the opposite ends of the secondary winding in the ignition device
101
for internal combustion engine shown in FIG.
4
. Incidentally, when the level of the first command signal is low, an igniter
17
is open-circuited so that there is no current flowing in the primary winding
33
. On the other hand, when the level of the first command signal is high, the igniter
17
is short-circuited so that a current flows in the primary winding
33
. In
FIG. 6
, the waveform of the voltage between the opposite ends of the secondary winding
34
is shown with the igniting high voltage as a negative-polarity voltage. Hence, points of time t12 and t15 show igniting high voltage generation timing (ignition timing).
In
FIG. 6
, points of time t11 and t14 show start timing for conduction of the primary current. It is found that a voltage (several kV) reversed in polarity to the igniting high voltage is generated between the opposite ends of the secondary winding
34
in this timing. There is fear that wrong ignition may be caused by this voltage.
To prevent the generation of such wrong ignition, in the ignition device
101
for internal combustion engine shown in
FIG. 4
, for example, a so-called reverse current prevention diode may be provided in a current-conduction path formed between one end of the secondary winding
34
and the spark plug
13
so that a current is allowed to flow in the current-conduction path of the secondary current
22
only at the time of conduction of the primary current
21
.
If the reverse current prevention diode is provided in the ignition device
101
for internal combustion engine shown in
FIG. 4
, it is however impossible to detect an ionic current flowing in between the electrodes of the spark plug
13
because the capacitor
45
can be charged by the secondary current
22
but cannot be discharged due to the reverse current prevention diode.
An ignition device
103
for internal combustion engine shown in
FIG. 5
is configured in consideration of this problem. In the ignition device
103
, a reverse current prevention diode
31
is provided and an ionic current detection circuit
113
for applying an ionic current-detecting voltage to the spark plug
13
through a current-conduction path different from the secondary winding
34
is provided so that an ionic current can be detected. The ionic current detection circuit
113
is configured as follows. An ionic current-detecting voltage is applied to the spark plug
13
by an internal power supply
115
. An ionic current is detected on the basis of the voltage between the opposite ends of the detection resistor
47
. A discrimination circuit
55
outputs an ionic current detection result signal
24
to an electronic control unit. Incidentally, an applied voltage-limiting Zener diode
53
prevents a signal of an excessive voltage higher than the allowable maximum input voltage value from being input to the discrimination circuit
55
. Hence, the discrimination circuit
55
is prevented from being broken.
In the ignition device
103
for internal combustion engine configured as described above, an inflow prevention diode
117
for preventing the secondary current
22
from flowing into the ionic current detection circuit
113
at the time of generation of the igniting high voltage is provided in order to prevent the ionic current detection circuit
113
from being broken by application of the igniting high voltage. In addition, the inflow prevention diode
117
prevents the secondary current
22
from leaking to the ionic current detection circuit
113
. Hence, the inflow prevention diode
117
is also effective in preventing energy supplied to the spark plug
13
from being reduced at the time of generation of the igniting high voltage.
In the ignition device
103
for internal combustion engine shown in
FIG. 5
, it is however necessary to make the inflow prevention diode
117
from a high-voltage-proof diode of an allowable withstand voltage not lower than the igniting high voltage (about 40 kV) because the inflow prevention diode
117
is connected on the secondary high potential side. At the existing time, it is impossible to obtain such a diode constituted by one high-voltage-proof element.
Therefore, when a plurality of diodes series-connected in order to obtain an allowable withstand voltage not lower than the igniting high voltage as a whole are provided as the inflow prevention diode
117
, the ignition device
103
for internal combustion engine shown in
FIG. 5
can be achieved.
When such a plurality of diodes series-connected a
Gimie Mahmoud
Morgan & Lewis & Bockius, LLP
NGK Spark Plug Co. Ltd.
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