U.S. patent number 3,874,355 [Application Number 05/386,549] was granted by the patent office on 1975-04-01 for ignition device for internal combustion engine equipped with protective device.
This patent grant is currently assigned to Hitachi, Ltd.. Invention is credited to Shiro Ida, Yasunori Mori, Seiji Suda.
United States Patent |
3,874,355 |
Suda , et al. |
April 1, 1975 |
IGNITION DEVICE FOR INTERNAL COMBUSTION ENGINE EQUIPPED WITH
PROTECTIVE DEVICE
Abstract
An ignition device for an internal combustion engine provided
with a circuit for protecting the ignition device from thermal
damage due to the current flowing across the ignition coil when the
engine is stopped. The protective device consists of a
charge-discharge circuit having a time constant larger than the
ignition period. The charge-discharge circuit is reset by the
pulses indicative of ignition timing. When the engine is stopped,
the charge-discharge circuit produces an output after the lapse of
time determined by its time constant due to the absence of the
input pulse. By the output of the circuit the current flowing
across the ignition coil is automatically interrupted.
Inventors: |
Suda; Seiji (Mito,
JA), Mori; Yasunori (Hitachi, JA), Ida;
Shiro (Katsuta, JA) |
Assignee: |
Hitachi, Ltd. (Katsuta,
JA)
|
Family
ID: |
13681111 |
Appl.
No.: |
05/386,549 |
Filed: |
August 8, 1973 |
Foreign Application Priority Data
|
|
|
|
|
Aug 9, 1972 [JA] |
|
|
47-79122 |
|
Current U.S.
Class: |
123/632 |
Current CPC
Class: |
F02P
15/12 (20130101); F02P 3/0556 (20130101) |
Current International
Class: |
F02P
3/02 (20060101); F02P 15/00 (20060101); F02P
3/055 (20060101); F02P 15/12 (20060101); F02p
003/02 () |
Field of
Search: |
;123/148R,148E |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Burns; Wendell E.
Attorney, Agent or Firm: Craig & Antonelli
Claims
What we claim is:
1. An ignition device for an internal combustion engine,
comprising:
input means to which pulses indicative of the ignition timing of an
internal combustion engine are applied;
first switching means being switched off at an ignition time in
response to the output of said input means;
an ignition coil comprising the primary coil and the secondary
coil, said primary coil being connected in series with said first
switching means between terminals for supplying a DC voltage, said
secondary coil being connected with a spark plug;
time constant means comprising a charge-discharge circuit
consisting of a capacitor and a resistor, said charge-discharge
circuit having a time constant sufficiently longer than the pulse
interval of said pulses, said time constant means producing an
output the value of which varies with the lapse of time from the
time at which an output of said input means is applied thereto and
which reaches a predetermined value after the lapse of time
determined by the said time constant; and
second switching means for turning said first switching means off
when the value of the output of said time constant means exceeds a
predetermined level, said second switching means comprising a
transistor, the emitter and collector of said transistor being
connected to one terminal of said DC source and the input terminal
of said first switching means, respectively, and the base of said
transistor being connected to the output of said time constant
means; said resistor and capacitor of said time constant means
being connected in series between the base of said second switching
transistor and said DC source, and a junction point of said
resistor and capacitor being electrically connected with said input
means through a first diode, the input terminal of said first
switching means being electrically connected with the output of
said input means through a second diode.
2. An ignition device according to claim 1, in which said input
means comprises at least one switching transistor, the collector of
which is connected to said time constant means and said first
switching means through said first diode and said second diode,
respectively, and when said pulse is applied to said input means,
said switching transistor of said input means discharges said
capacitor of said time constant means through said first diode.
3. An ignition device according to claim 1, in which said input
means comprises a transistor monostable multivibrator, the
collector of the transistor of said monostable multivibrator, which
is normally in the off state and turned on by the application of an
input pulse, is electrically connected with the inputs of said time
constant means and said first switching means through said first
diode and said second diode, respectively, and said capacitor of
said time constant means is discharged through said first diode
when an input pulse is applied to said input means.
Description
The present invention relates to an ignition device for an internal
combustion engine, and more particularly, to an ignition device
provided with a protective device for preventing the ignition coil
of an ignition device in an operation interrupted state from being
kept supplied with an electric current for a long time.
There have been two types of ignition devices. In one type of
ignition device, an electric current is allowed to always flow
through the primary coil of the ignition coil, which is interrupted
at ignition timing of an internal combustion engine, when the
energy stored in the primary coil is discharged at the gap of a
spark-plug connected with the secondary coil.
In a second type of ignition device, an electric current is
normally not allowed to flow through the primary coil of the
ignition coil. The primary current is allowed to flow only at
ignition timing, when the energy thereof is discharged at the gap
of the spark-plug in the secondary coil circuit.
In the former type, when a voltage continues to be applied to the
ignition device of an engine in the state that the engine is
stopped and yet the key switch is set, an electric current
continues to flow through the primary coil of the ignition device.
The ignition coil would become over-heated by this current to be
damaged. The heat generation by a switching circuit for cutting off
the primary current is also so considerable that it would be
damaged if the current continues to flow for a long time.
Recently, it has become required to clean the exhaust gas of the
internal combustion engine. To meet this requirement, the sparking
energy of the spark-plug must be large, which requires a low
internal resistance of the ignition coil. However, the reduction in
the internal resistance of the ignition coil results in an increase
in the trouble due to the overheat of the ignition coil itself.
An object of the present invention is to provide an ignition device
having a protective device capable of automatically cutting off the
electric current flowing across the ignition coil in the state that
the engine is stopped and yet a voltage is applied to the ignition
circuit.
Another object of the present invention is to provide an ignition
device capable of protecting the ignition coil by a very simple and
inexpensive method.
The ignition device according to the present invention has a time
constant circuit which detects the interruption of the engine. When
the engine is stopped, a driving or switching transistor connected
in series with the primary coil of the ignition device is turned
off.
During the operation period of the engine, pulses indicative of the
ignition timing of the engine are supplied to the ignition device
at the intervals determined by the rotational speed of the engine.
When the rotation of the engine is reduced, the pulse intervals
become longer, and when the engine is stopped, the pulse intervals
become infinitely long, or in other words, no pulse is supplied to
the ignition device.
The time constant circuit according to the present invention has a
predetermined time constant, and produces a constant level of
voltage when the time determined by the time constant has elapsed.
Consequently, when the time constant circuit having a time constant
larger than the interval of the pulses is started to operate by the
application of the pulse, the stopping of the engine can be
detected from the output of the time constant circuit. That is,
when the predetermined level of output is produced, the engine can
be regarded as having stopped.
Then, it is sufficient to turn off the driving transistor in
accordance with the output of the time constant circuit.
It is necessary for the time constant circuit according to the
present invention that the starting time thereof is always the time
at which a pulse is applied thereto, or in other words, it is
always reset by the pulse. According to the present invention, this
is achieved very simply by forming a charge-discharge circuit of a
resistor and a capacitor in which the accumulated charge of the
capacitor is discharged by the application of a pulse. When the
pulse applied thereto is no longer present, the capacitor is
charged to its saturation level. By detecting the output of the
capacitor the driving or switching transistor is turned off.
Consequently, when the engine is stopped, the ignition coil is
surely cut off from the power source, and no heat production by the
switching circuit occurs, either.
The above and other objects, features and advantages of the present
invention will become more apparant from the following detailed
description of the preferred embodiment of the present invention,
which is made by way of example only, when taken in conjunction
with the accompanying drawings, in which:
FIG. 1 is a block diagram of an ignition device according to the
present invention; and
FIG. 2 is a detailed circuit diagram of the ignition device of FIG.
1.
The circuit of FIG. 1 is to automatically interrupt the current
flowing across the ignition coil when the engine is stopped.
In motorcars generally used, when the key is set, a voltage is
applied to the ignition device. In the ignition device of the type
that in the above state a high tension is produced at the secondary
coil by cutting the current flowing across the primary coil, a
current is kept flowing across the ignition coil when the engine is
stopped. Consequently, it is necessary to automatically interrupt
the current when the engine is stopped.
In the circuit of FIG. 1, a signal or pulses indicative of the
ignition timing of the engine are produced by a signal generator
10, and supplied to a differentiating circuit 20. The signal
differentiated by the differentiating circuit 20 triggers a
monostable multivibrator circuit 30. The output of the monostable
multivibrator 30 switches off a power switching circuit 50 through
a switching circuit 40. The power switching circuit 50 which is
connected in series between the primary coil of the ignition device
and the power source is normally switched on to supply the primary
coil with a current. Only when the output of the monostable
multivibrator 30 is supplied, the power switching circuit 50 is
switched off to interrupt the primary current of the ignition coil.
A high tension is produced in the secondary coil of the ignition
device by the change in the magnetic flux developed in the ignition
coil at that time and supplied to a predetermined plug through a
distributor.
The output of the monostable multivibrator 30 is also applied to a
time constant circuit 60. The time constant circuit 60 detects the
interruption of the engine by detecting the interruption for a
certain time of the output of the monostable multivibrator 30, and
operates the switching circuit 40 to switch off the power switching
circuit 50.
The signal generator 10 is a device for generating a signal or
pulses indicative of the ignition timing of the engine and is
ordinarily provided in the distributor. The signal generator may be
a pulse generator coupled with the shaft of the engine and
generating a pulse when the shaft reaches a predetermined
rotational angle.
The monostable multivibrator 30 is not important to the primary
purpose of the present invention. In principle, even if the output
of the signal generator 10 is supplied directly to the switching
circuit 40 to actuate the power switching circuit 50, the system
operates properly. In this case, the output of the signal generator
10 is also supplied directly to the time constant circuit 60 to
reset it.
The monostable multivibrator 30 is provided to adjust the "off"
time and "on" time of the power switching circuit 50. If the
rotation of the engine is accelerated, the time period during which
a current is flowing across the ignition coil becomes shorter. At a
high speed rotation, since a current may be interrupted before
sufficient energy is accumulated in the primary coil, the spark
energy may be insufficient. To reduce the difference between the
spark energy at a low and a high rotation it is quite preferable to
provide the monostable multivibrator 30. However, the provision of
the monostable multivibrator 30 has nothing to do with the
prevention of the thermal damage of the ignition coil and the power
switching circuit 50.
FIG. 2 is a materialized circuit diagram of the system of FIG. 1.
The output of the signal generator 10 in FIG. 1 is applied to the
differentiating circuit 20 through an input terminal 222. The
differentiating circuit 20 is composed of a capacitor 224, a
resistor 226, and a diode 228.
The monostable multivibrator 30 is composed of resistors 231, 232,
233, 234 and 235, a capacitor 236, transistors 237 and 238, and a
diode 239. The collector of the transistor 238 is connected
electrically to the power switching circuit 50 through a diode 272
and, at the same time, to the time constant circuit 60 through a
diode 274 and a resistor 276.
The switching circuit 40 is composed of a resistor 242 and a
transistor 244.
The power switching circuit 50 is composed of resistors 252 and
254, an amplifying transistor 256, and a switching transistor 258.
The switching transistor 258 is connected in series with a power
source terminal 290 through the primary side of the ignition coil
270 and a resistor 278. The secondary side of the ignition coil 270
is connected to a spark plug 280.
The time constant circuit 60 consists of a resistor 262 and a
capacitor 264.
When the key switch of the motorcar is set, the battery voltage is
applied to the terminal 290.
The transistor 237 of the monostable multivibrator 30 is in the
"on" state and the transistor 238 thereof is in the "off" state.
The base current of the transistor 244 of the switching circuit 40
which is in the "on" state charges the capacitor 264 through the
resistor 262. The collector current of the transistor 244 flows in
the base of the transistor 256 through the resistor 242 to put the
transistor 256 in the "on" state. Consequently, the transistor 258
is put in the "on" state to enable a current fo flow from the
terminal 290 into the primary side of the ignition coil 270 through
the resistor 278.
Now, if a pulse indicative of ignition timing is applied from the
input terminal 222 to the differentiating circuit 20, the
transistor 238 is turned to the "on" state to reduce the base
potential of the transistor 256 to substantially the ground level
through the diode 272. At the same time, the charge stored in the
capacitor 264 is discharged through the resistor 276 and the diode
274. As a result, the transistor 256 is switched off, hence the
transistor 258. Then, the energy stored in the primary coil of the
ignition coil 270 descharges at the gap of the spark plug 280.
If a pulse is applied to the terminal 222 according to the ignition
sequence of the engine, a spark is produced at the gap of the spark
plug 280.
When the engine stops, the transistor 238 maintained its "off"
state because no pulse is applied to the terminal 22 any more. The
capacitor 264 is charged with the base current of the transistor
244 through the resistor 262. With the increase in the amount of
charge of the capacitor 264, the base current of the transistor 244
decreases to eventually put the transistor 244 in the "off" state.
At the same time, the transistor 256 turns off because no base
current flows any more, and hence the transistor 258 also turns
off. Consequently, the current flowing across the primary coil of
the ignition coil 270 is automatically interrupted.
The pulse interval of the pulses representative of the ignition
timing applied to the terminal 222 varies with the rotating speed
of the engine. This change can be known beforehand. If the time
constant determined by the resistor 262 and the capacitor 264 is
set sufficiently longer than the above pulse interval, the
switching circuit 40 operates only when the engine stops.
The diodes 272 and 274 are provided for preventing back current
current. resistor 276 is to limit the current flowing from the
capacitor 264 into the transistor 238. To discharge the capacitor
238 immediately after the application of a pulse to the terminal
222 to switch on the transistor 238, the time constant of the
resistor 276 and the capacitor 264 is made very small.
The transistor 256 is provided to amplify the base current of the
transistor 258. The collector of the transistor 244 may be
connected directly to the base of the transistor 258 through the
resistor 242. However, since the base current of the transistor 258
is required to high, it is difficult to supply the base current of
the transistor 244 directly to the transistor 258. Consequently, it
is preferable to amplify the base current of the transistor 244 by
the transistor 256.
The switching circuit 40 and the time constant circuit 60 are
connected with the collector of the transistor 238 through the
diodes 272 and 274, respectively. However, even if pulses of
negative polarity are supplied directly to the diodes 272 and 274,
the fundamental purpose of the present invention can be achieved.
That is, the purpose of the present invention can be achieved by
discharging the capacitor 264 of the time constant circuit 60 by
the input pulse and by burning the power switching transistor 258
off.
The monostable multivibrator circuit 30 is provided to adjust the
"off" time of the transistor 258.
The primary coil of the ignition coil 270 operates as an inductance
element. Consequently, if the switching period of the transistor
258 becomes short, the current flowing into the ignition coil 270
becomes low. As the rotation of the engine becomes higher, the
energy stored in the primary coil of the ignition coil 270 becomes
lower. Consequently, there is the difference in the spark energy
discharged at the spark plug 280 between at a high rotation and at
a low rotation. If the designing factors of the ignition are set at
those at a low rotation, the spark energy becomes defficient at a
high rotation. To the contrary, if the designing factors are set at
those at a high rotation, heat generation becomes considerable at a
low rotation. Consequently, it is preferable to make the currents
flowing across the primary coil of the ignition coil 270 at a high
and a low rotation substantially the same.
In order to reduce the difference in the spark energy between at a
high rotation and at a low rotation, it is preferable to decrease
the "off" time period of the transistor at a low rotation. That is,
if the "off" period of the transistor is prolonged at a low
rotation, it becomes equivalent to the situation at a high
rotation. This is effected by the monostable multivibrator circuit
30.
When the transistor 237 is in the "on" state, the transistor 258 is
also in the "on" state, while when the transistor 238 is "on"
state, the transistor 258 is "off" state.
The "on" period of the transistor 238 is determined by the
discharge period of the capacitor 236. Consequently, it is
sufficient to determine the resistance and the capacity such that
the charge on the capacitor 236 at a high rotation is reduced, and
it is increased at a low rotation.
This is done by increasing the current at the resistor 232 and by
reducing the current flowing across the resistor 233 into the
capacitor 236. That is, the time constant of the resistor 233 and
the capacitor 236 is made sufficiently large. As a result, the
capacitor 236 is not saturated by the pulses of the pulse interval
applied to the terminal. Consequently when the pulse interval is
large, the charge stored in the capacitor 236 is increased, while
when the pulse interval is small the charge stored in the capacitor
236 is reduced. Thus, the time period of the "on" state of the
transistor 238 is automatically varied depending on the pulse
interval of the pulses applied to the terminal 222.
The amplifying transistor 256 of the power switching circuit 50 may
be of the inverter type. However, in the case of the inverter type,
either one of the transistors 256 and 258 is necessarily in the
"on" state, i.e., conductive to produce heat. Consequently, the
type shown in FIG. 2 is preferable. A darlington type of amplifying
circuit is also very preferable similarly to the type of FIG.
2.
When the transistor 258 is turned on, a very high current, for
example a current of 3A to 4A flows across the resistor 278 and the
ignition coil 270. Consequently, the heat generated is very large.
Also, the collector current of the transistor 256 which supplies
the base current to the transistor 258 is high. Further, also the
heat generated by the resistor 252 cannot be neglected.
Consequently, it is desirable that the transistors 256 and 258 are
simultaneously turned off when the engine is stopped.
When the engine is stopped, the resistance of the ignition coil 270
due to the reactance component becomes zero, so that a current
flowing across the ignition coil 270 sometimes reaches as high as
ground 6A. Consequently, the heat generation by the ignition coil
270 and the power switching circuit 50 furte increases. During the
operation period of the engine, the current is reduced compared
with that when the engine is stopped by the resistance of the
ignition coil due to its reactance because the "on" and "off"
states of the transistor 258 alternate.
* * * * *