Internal-combustion engines – High tension ignition system – Safety device
Reexamination Certificate
2000-07-03
2002-09-17
Wong, Don (Department: 2821)
Internal-combustion engines
High tension ignition system
Safety device
C123S632000, C315S2090SC
Reexamination Certificate
active
06450157
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to automotive ignition systems, and more specifically to systems for minimizing ignition coil ringing effects resulting from coil activation.
BACKGROUND OF THE INVENTION
Modern inductive-type automotive ignition systems commonly utilize power switching devices to control the flow of current through an ignition coil. Such devices are typically controlled so as to switch from an “off” state to a fully saturated “on” state within a short time period, wherein such switching results in the voltage across the ignition coil changing rapidly from substantially zero volts to near battery voltage. The inductive nature of the ignition coil reflects and steps up this voltage across the primary coil to the secondary coil connected to an ignition plug, wherein the initial response of the secondary coil to this process may result in ringing. This ringing may, in some cases, create sufficient voltage across the spark gap of the ignition plug to cause a spark event. Such a mistimed spark event is undesirable and potentially damaging to the engine.
Referring to
FIG. 1
, one known example of an ignition system
10
of the type just described is illustrated in
FIG. 1
, wherein system
10
includes an ignition control circuit
12
having an electronic spark timing (EST) buffer circuit
14
receiving an EST control signal from a control circuit
16
via signal path
18
. The EST buffer circuit
14
buffers the EST control signal and provides a buffered EST control signal ESTBF to a gate drive circuit
20
. The gate drive circuit
20
is responsive to the ES TBF signal to supply a gate drive signal GD to a gate
22
of an insulated gate bipolar (IGBT) transistor
24
or other coil switching device via signal path
26
. A collector
28
of IGBT
24
is connected to one end of a primary coil
30
forming part of an automotive ignition coil having an opposite end connected to battery voltage V
BATT
. An emitter
32
of IGBT
24
is connected to one end of a sense resistor R
S
having an opposite end connected to ground potential, and to a noninverting input of a comparator
36
via signal path
38
. An inverting input of comparator
36
is connected to a reference voltage VR, and an output of comparator
36
supplies a trip voltage V
TRIP
to gate drive circuit
20
. A secondary coil
40
is coupled to the primary coil
30
and is connected to an ignition plug
44
defining a spark gap
42
as is known in the art.
In the operation of system
10
, gate drive circuit
20
is responsive to a rising edge of an ESTBF signal to supply a gate drive signal GD to the gate
26
of IGBT
24
as shown by the GD waveform
45
in FIG.
2
A. As IGBT
24
rapidly begins to conduct in response to the gate drive signal GD, a coil current I
C
begins to flow through primary coil
30
, as shown by the coil current (I
C
) waveform
47
in
FIG. 2B
, thereby establishing a “sense voltage” V
S
across resistor R
S
. Due to the rapid turn on of IGBT
24
and subsequent rapid increase in voltage across the primary coil
30
to near battery voltage V
BATT
, ringing effects may result in the initial portion of the V
SC
waveform
49
as shown in
FIG. 2C
due to known LRC effects of the ignition coil. This ringing, as described hereinabove, may be sufficient to undesirably create a spark event across the gap
44
of ignition plug
42
.
As the coil current I
C
increases due to the inductive nature of the ignition coil, the sense voltage V
S
across R
S
likewise increases until it reaches the comparator reference voltage VR. At this point, the comparator
36
switches state and the corresponding change in state of the trip voltage V
TRIP
causes the gate drive circuit
20
to turn off or deactivate the gate drive voltage GD so as to inhibit the flow of coil current I
C
through the primary coil
30
and coil current switching device
24
. This interruption in the flow of coil current I
C
through primary coil
30
causes primary coil
30
to induce a current in the secondary coil
40
, wherein the secondary coil
40
is responsive to this induced current to generate desired arc across the spark gap
42
of ignition plug
44
.
To minimize, or at least reduce, ringing effects associated with the activation of coil current switching devices, a technique commonly referred to as “phased turn-on”, or PTO, has been developed. PTO reduces the ringing voltage illustrated in
FIG. 2C
by initiating the coil charging period with a carefully timed initial drive pulse to the coil current switching device (e.g., IGBT
24
of FIG.
1
). Details relating to the foregoing PTO technique are described in U.S. Pat. No. 5,392,754 which is assigned to the assignee of the present invention, and the disclosure of which is incorporated herein by reference. In accordance with the concepts described in the '754 patent, the coil current switching device is initially turned on for a short time period (e.g., 2-7 microseconds), turned off for a similar time period, and then turned on again for the duration of the coil charging dwell period. The durations of the initial “on” and “off” periods are dependent upon the characteristics of the ignition coil being driven and are chosen such that the ringing created by the second turn-on is 180 degrees out of phase with the ringing produced by the initial turn-on. If the pulse timing is selected properly, this “phasing” of the coil response effectively damps the overall voltage response at the terminals of the secondary coil
40
and reduces the peak ringing voltage by as much as 50%. The use of this ring suppression technique can eliminate the need for an additional blocking diode in the coil assembly.
Another advancement in modern ignition systems is the use of multiple coil charging and spark events for a single combustion cycle. By generating multiple sparks in a rapid sequence, more spark energy can be delivered to the combustion cylinder than with a single spark event, thereby enhancing ignition of the air/fuel mixture. In accordance with this known technique, the coil current switching device (e.g., IGBT
24
) is switched back on before all of the coil energy has been depleted, thereby recharging the primary coil
30
to its peak value from some intermediate coil current level as shown by the GD waveform
43
and I
C
waveform
46
in
FIGS. 3A and 3B
respectively. While only one recharging cycle is illustrated in
FIGS. 3A-3C
, it is known to use any desired number of recharge cycles, wherein systems of this type will be referred to hereinafter as multiple pulse ignition systems. One drawback to such a system, however, is that the unused energy within the ignition coil when the switching device is turned back on changes the coil's response to the voltage transitions resulting from the switching of the coil current switching device. Referring to
FIGS. 3A and 3C
, for example, not only does the abrupt rising edge of the initial GD signal
43
result in a corresponding ringing of the secondary voltage V
SC
, as shown by waveform
48
, but every rising edge thereafter of the GD signal
43
results in similar V
SC
ringing which may result in an unwanted spark event. The peak level of this ringing can be 50% higher than the baseline “make” voltage (e.g., V
BATT
*coil turns ratio “N”), and may therefore cause mistimed spark events. Addition of a diode in series with the secondary coil
40
can also prevent a “spark-on-make” for a negative voltage system, although such a diode would interfere with potential ion current detection in an “ion sense” ignition system, and a PTO technique is therefore critical for such applications.
What is therefore needed is an improved phased turn-on strategy. Such a modified PTO strategy should ideally be readily adaptable to any number of coil charging events to thereby minimize or at least reduce the resulting ringing events associated with the secondary coil voltage V
SC
in a multiple pulse ignition system. The strategy should further include provisions for adjusting the pulse widths of the PTO pulses to compens
Boyer John W.
Kesler Scott B.
Delphi Technologies Inc.
Funke Jimmy L.
Tran Chuc
Wong Don
LandOfFree
Automotive ignition system with adaptable start-of-dwell... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Automotive ignition system with adaptable start-of-dwell..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Automotive ignition system with adaptable start-of-dwell... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2845767