Electricity: measuring and testing – Internal-combustion engine ignition system or device – Electronic ignition system
Reexamination Certificate
2001-01-25
2003-04-08
Oda, Christine (Department: 2858)
Electricity: measuring and testing
Internal-combustion engine ignition system or device
Electronic ignition system
C123S644000, C361S257000
Reexamination Certificate
active
06545478
ABSTRACT:
TECHNICAL FIELD
The present invention regards an electronic ignition device with limitation of the voltage at an ignition coil primary winding terminal.
BACKGROUND OF THE INVENTION
As is known, one of the problems present in electronic ignition devices for inductive loads is to limit the voltage at the primary winding terminal of the ignition coil, in the event of a malfunctioning of the device being detected, so as to prevent an ignition spark from being generated on the secondary winding terminal of the same coil.
In this connection,
FIG. 1
shows a schematic circuit diagram of an electronic ignition device
1
comprising an ignition coil
2
and a power element
3
, for example an IGBT or a bipolar power transistor. In greater detail, the ignition coil
2
includes a primary winding
2
a
and a secondary winding
2
b
; a first terminal
2
c
of the primary and secondary windings
2
a
,
2
b
is connected to a supply line
4
, set at a battery voltage V
B
, a second terminal
5
of the primary winding
2
a
is connected to a collector terminal of the power element
3
, and a second terminal
6
of the secondary winding
2
b
is connected to a spark plug (not shown in
FIG. 1
) which generates the ignition spark. The power element
3
has an emitter terminal
7
connected to ground GND and a control terminal
8
connected to a microprocessor
9
, shown only schematically in
FIG. 1
, through a resistor
10
. A high voltage Zener diode
25
has its cathode connected to the second terminal
5
of the primary winding
2
a
and its anode connected to the control terminal
8
of the power element
3
. The high voltage Zener diode
25
limits the maximum voltage applied to the second terminal
5
of the primary winding
2
a
to prevent the latter from exceeding the breakdown voltage of the power device
1
.
The microprocessor
9
controls turning on of the power element
3
by supplying, to the control terminal
8
of the latter, a trigger signal at a high logic level (FIG.
2
). Upon turning on of the power element
3
, across the primary winding
2
a
a voltage is applied that is close to the battery voltage V
B
. Consequently, a primary current I
out
starts flowing in the terminal of the primary winding
5
(FIG.
2
).
Once an appropriate time has elapsed during which the primary current I
out
reaches a preset value I
o
(charging time of the ignition coil
2
), the microprocessor
9
controls turning off of the power device
3
by sending the trigger signal to a low logic level. In this condition, a voltage pulse V
0
, is generated at the second terminal
5
of the primary winding
2
a
(FIG.
2
); the voltage pulse, transferred onto the second terminal of the secondary winding
2
b
multiplied by the turn ratio of the ignition coil
2
, gives rise to a spark.
In an electronic ignition device of the type described above, it is necessary that the spark is generated only when the microprocessor
9
turns off the power element
3
by sending the trigger signal to the low logic level. However, in the event of malfunctioning of the device, it may be necessary to turn off the power element
3
independently of the logic level of the trigger signal and without a spark being produced on the second terminal
6
of the secondary winding
2
b.
As shown in
FIG. 3
, to meet this requirement, the electronic ignition device
1
is provided with a protection circuit
11
, shown only schematically in
FIG. 3
, for detecting anomalous operating conditions of the electronic ignition device
1
, such as overheating of the power element
3
or exceeding the preset current value I
o
, and supplying, at an output terminal
16
, a logic signal EN used as enable signal for a voltage limiting circuit
12
.
In greater detail, the voltage limiting circuit
12
has a first input terminal
13
, a second input terminal
14
, and an output terminal
15
. The first input terminal
13
of the voltage limiting circuit
12
is connected to the second terminal
5
of the primary winding
2
a
; the second input terminal
14
of the voltage limiting circuit
12
is connected to the output terminal
16
of the protection circuit
11
through an inverter
17
; and the output terminal
15
of the voltage limiting circuit
12
is connected to the control terminal
8
of the power element
3
.
The voltage limiting circuit
12
comprises an enable transistor
18
of the NPN type, having a collector terminal connected to the first input terminal
13
of the voltage limiting circuit
12
through a high voltage resistor
19
, an emitter terminal connected to ground GND, and a control terminal connected to the second input terminal
14
of the voltage limiting circuit
12
.
The voltage limiting circuit
12
further comprises a first high voltage vertical transistor
20
a
and a second high voltage vertical transistor
20
b
, both of the NPN type and coupled in Darlington configuration. In particular, the first high voltage vertical transistor
20
a
has a collector terminal connected to the first input terminal
13
of the voltage limiting circuit
12
, a control terminal connected to the collector terminal of the enable transistor
18
through a first circuit node
30
, and an emitter terminal. The second high voltage vertical transistor
20
b
has a collector terminal connected to the first input terminal
13
of the voltage limiting circuit
12
, a control terminal connected to the emitter terminal of the first transistor
20
a
, and an emitter terminal connected to the output terminal
15
of the voltage limiting circuit
12
through a Zener diode
22
. The Zener diode
22
has its cathode connected to the emitter terminal of the second transistor
20
b
and its anode connected to the output terminal
15
of the voltage limiting circuit
12
. A resistive element
21
is connected between the control terminal and the emitter terminal of the second high voltage vertical transistor
20
b.
The electronic ignition device
1
further comprises a protection transistor
23
having a collector terminal connected to the control terminal
8
of the power element
3
via a second circuit node
31
, an emitter terminal connected to ground GND, and a control terminal connected to the output terminal
16
of the protection circuit
11
.
A biasing resistor
24
is coupled between the second circuit node
31
and the output terminal
15
of the voltage limiting circuit
12
.
After detecting a malfunctioning of the electronic ignition device
1
, the protection circuit
11
generates, on the control terminal of the protection transistor
23
, a high logic level of the logic signal EN. Consequently, the protection transistor
23
saturates, generating on the second circuit node
31
a voltage V
cesat
equal to its own saturation voltage (voltage present between the collector and the emitter terminal of the protection transistor
23
in saturation) and determining turning off of the power element
3
, with consequent increase in the voltage on the second terminal
5
of the primary winding
2
a.
At the same time, the inverter
17
generates, on the control terminal of the enable transistor
18
, a logic signal, correlated to the logic signal EN, at a low logic level. Consequently, the enable transistor
18
turns off, generating on the first circuit node
30
a voltage that turns on the high voltage vertical transistors
20
a
and
2
b
. These transistors supply the Zener diode
22
and the biasing resistor
24
with a current that causes a biasing voltage VP across the biasing resistor
24
. The biasing voltage VP causes turning on again of the power element
3
, which maintains the voltage on the second terminal
5
of the primary winding
2
a
at a value VL that maintain the high voltage vertical transistors
20
a
,
20
b
on, so that the latter continue to supply current until complete exhaustion of the energy stored in the primary winding
2
a
of the ignition coil
2
. In particular, the value V
L
is
V
L
=V
R
+V
be1
+V
be2
+V
Z
+V
P
+V
ceat
(1)
wherein V
R
is the voltage across t
Kerveros James
Oda Christine
LandOfFree
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