Method and system for controlling ignition spark timing of an internal combustion engine of the multiple plugs type

A method and system for controlling ignition spark timing of an internal combustion engine of the multiple plugs type, in which a plurality of spark plugs are energized at different timings with a predetermined phase in dependence on the flow of air-fuel mixture in a combustion chamber, whereby air-fuel mixture is ignited at timings optimum for rapid combustion.

BACKGROUND OF THE INVENTION 
This invention relates in general to internal combustion engines of the 
multi-spark plug type and, more particularly, to a method and apparatus 
for controlling ignition spark timing for such engines. 
As is well known in the art, it has heretofore been proposed to have an 
internal combustion engine equipped with a plurality of spark plugs 
adapted to provide a plurality of flames which propagate from a 
circumference of a wall of a combustion chamber toward a center portion 
thereof. In this type of engine, the flame propagation distance is less 
than that of a prior art internal combustion engine of the type having a 
single spark plug and, therefore, it is possible to effect rapid 
combustion of air-fuel mixture in the combustion chamber. Accordingly, it 
makes it possible to increase the exhaust gas recirculation rate up to 40% 
without sacrificing the performance efficiency of the engine. Another 
advantage is that the concentration of nitrogen oxides in engine exhaust 
gases can be remarkably decreased. In a known internal combustion engine 
of the multi-spark plug type, it has been a usual practice to energize the 
spark plugs at the same ignition timing. Since, however, the combustion 
state in the combustion chamber varies in dependence on the state of 
air-fuel mixture supplied into the combustion chamber and operating 
conditions of the engine etc. Thus, it is desired that the spark plugs be 
energized at various ignition timings in dependence on the various 
factors. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a method for 
controlling ignition spark timing of an internal combustion engine of the 
type having a plurality of spark plugs in a combustion chamber. 
It is another object of the present invention to provide a method for 
controlling ignition spark timing of an internal combustion engine of the 
multiple plugs type by which exhaust gas recirculation rate can be 
increased and the concentration of nitrogen oxides in engine exhaust gases 
can be remarkably decreased. 
It is still another object of the present invention to provide a method for 
controlling ignition spark timing of an internal combustion engine of the 
multiple plugs type so as to effect optimum flame propagation in a 
combustion chamber. 
It is a further object of the present invention to provide an ignition 
spark timing control system for an internal combustion engine of the 
multiple plugs type in which a plurality of spark plugs are energized at 
predetermined ignition timings to promote flame propagation in a 
combustion chamber to reduce noxious compounds in engine exhaust gases. 
It is a still further object of the present invention to provide an 
ignition spark timing control system for an internal combustion engine of 
the multiple plugs type, which system is simple in construction and highly 
reliable in operation. 
It is a still further object of the present invention to provide an 
ignition spark timing control system for an internal combustion engine, 
which system is arranged to control ignition spark timing at different 
phases thereby to effect combustion of air-fuel mixture in a combustion 
chamber in the most efficient manner. 
It is a still further object of the present invention to provide an 
ignition spark timing control system for an internal combustion engine of 
the multiple plugs type in which a phase control in ignition spark timing 
is highly reliably made with a simplified construction and arrangement.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to FIGS. 1 and 2, there is schematically shown an internal 
combustion engine of the multiple plugs type to which the present 
invention is directed. The internal combustion engine has a cylinder 10 
and a cylinder head 12 mounted thereon. A combustion chamber 14 is formed 
by the cylinder 10 and the cylinder head 12. The combustion chamber 14 has 
an intake port 16 and an exhaust port 18, and has two spark plugs 20 and 
22 which are directed toward a center portion of the combustion chamber 
14. With this construction, air-fuel mixture containing recirculated 
exhaust gases is supplied through the intake port 16 and flows in a curved 
direction as shown by arrows A in FIGS. 1 and 2. In this condition, the 
air-fuel mixture prevailing around the spark plug 20 is at relatively low 
temperature while the air-fuel mixture prevailing around the spark plug 22 
is at relatively high temperature because it is warmed by the cylinder 
wall. Due to this temperature difference in the air-fuel mixture, the 
gasified condition of the air-fuel mixture is not homogeneous and, thus, 
optimum ignition timings for the spark plugs 20 and 22 are not necessarily 
consistent with one another. Accordingly, if the spark plugs 20 and 22 are 
ignited at the same ignition timing, a satisfactory combustion effect can 
not be obtained resulting in the sacrifice in the stability and 
performance efficiency of the internal combustion engine. 
The present invention contemplates the provision of a new method for 
controlling ignition spark timing of an internal combustion engine of the 
multi-spark plug type. According to an essential feature of the present 
invention, a plurality of spark plugs are ignited at different spark 
timings, i.e., at predetermined phases optimum for respective spark plugs 
thereby effecting improved combustion of air-fuel mixture in the 
combustion chamber. This makes it possible to reduce combustion period in 
the combustion chamber. Thus, the flame propagation speed in the 
combustion chamber will be maintained at high level even when a larger 
quantity of recirculated engine exhaust gases is contained in the air-fuel 
mixture, and, therefore, the concentration of nitrogen oxides in the 
engine exhaust gases can be remarkably reduced without sacrificing the 
engine performance efficiency. 
In order to achieve this concept, the present invention features to 
determine the phase difference in ignition spark timing for the plurality 
of spark plugs by experimental practice in accordance with the state of 
air-fuel mixture in the combustion chamber. Since the temperature 
distribution in the air-fuel mixture has an influence on the optimum 
ignition spark timings for the respective spark plugs, the ignition spark 
timings may be determined by experimentally measuring the flow of air-fuel 
mixture in the combustion chamber during intake and compression strokes 
and the temperature distribution of the air-fuel mixture prevailing around 
the spark plugs. As already mentioned, since the air-fuel mixture 
prevailing around the spark plug 20 is lower in temperature than that 
prevailing around the spark plug 22, it is desirable to ignite the spark 
plug 20 at a timing prior to the ignition of the second spark plug 22 
thereby causing the flame near the first spark plug 20 to propagate at the 
same speed as that of air-fuel mixture prevailing around the second spark 
plug 22, whereby total combustion time intervals can be significantly 
reduced. 
It should be noted that since the phase difference in ignition spark timing 
has a relation with a flow of air-fuel mixture in the combustion chamber 
during intake stroke and other factors such as squishing action of the 
air-fuel mixture during a compression stroke and it is difficult to obtain 
optimum phase difference in accordance with limited factors, it is 
preferable to determine the optimum phase difference in ignition spark 
timing through various experiments in view of inherent characteristics of 
respective internal combustion engines. The experiments have revealed that 
in an internal combustion engine which is constructed and arranged as 
shown in FIGS. 1 and 2, the combustion time intervals are remarkably 
decreased by igniting the spark plugs 20 and 22 at the phase difference 
ranging from 0 to 15 degrees of crankangle. 
FIG. 3 illustrates an example of an ignition spark timing control circuit 
to carry out the method of the present invention. In this illustrated 
example, the electric circuitry comprises a signal generator of the magnet 
type. The signal generator, which is generally designated by 24, has a 
shaft 26 which is connected to a distributor (not shown) and a rotor 28 
having cam lobes or projections at its outer periphery corresponding in 
number of the engine cylinders and fixedly connected to the shaft 26. The 
signal generator 24 also comprises a casing 30 provided with a pick-up 
device 32 having a projection 32a adapted to generate an ignition signal 
when one of the projections of the rotor 28 comes to the closest position. 
The pick-up device 32 of the signal generator 24 is electrically connected 
to an amplifying circuit 34 comprising transistors arranged to amplify the 
ignition signal so that the spark plugs 20 and 22 readily ignite the 
air-fuel mixture supplied into the combustion chamber. 
Ignition coils 36 and 38 are electrically connected to the output of the 
amplifying circuit 34 in parallel. With this arrangement, the high voltage 
produced by the amplifying circuit 34 is directly applied to the first 
spark plug 20, while the high voltage is applied to the second spark plug 
22 through a delay circuit 40 so that the second spark plug 22 is 
energized at a timing delayed from the energization of the first spark 
plug 20. 
With the arrangement mentioned hereinabove, the ignition signal from the 
signal generator 24 is directly supplied to the ignition coil 36 via the 
amplifying circuit 34 thereby energizing the first spark plug 20, while 
the second spark plug 22 is supplied with the ignition signal through the 
delay circuit 40 so that the second spark plug 22 is energized at a timing 
posterior to the energization of the first spark plug 20. In this manner, 
the first and second spark plugs 20 and 22 are consecutively ignited at 
predetermined phases. 
A modified form of the electric circuitry is shown in FIG. 4, in which like 
or corresponding component parts are designated by the same reference 
numerals as those used in FIG. 3. In this illustrated embodiment, the 
signal generator 24 also has an additional pick-up device 32' having its 
projection 32'a located at an angle corresponding to a predetermined phase 
with respect to the projection 32a of the first pick-up device 32 by which 
ignition signals are generated at predetermined phases. The ignition 
signals thus generated are applied through amplifying circuits 34 and 34' 
to the ignition coils 36 and 38 for thereby energizing the first and 
second spark plugs 20 and 22 at predetermined phases. 
It will now be appreciated that in accordance with the present invention a 
plurality of spark plugs are ignited at a predetermined phase whereby 
air-fuel mixture prevailing various parts in a combustion chamber can be 
ignited at optimum timings resulting in a quick combustion to permit a 
large proportion of exhaust gas recirculation to reduce nitrogen oxide 
concentration in engine exhaust gases. 
Referring now to FIG. 5, there is schematically shown an ignition spark 
timing control system according to the present invention. As shown, the 
ignition spark timing control system comprises first and second signal 
generators 50 and 52 each comprising a breaker arm, a cam adapted to 
actuate the breaker arm and breaker points. The first and second signal 
generators 50 and 52 are arranged to generate ignition signals at a 
predetermined phase, which are applied through first and second ignition 
coils 54 and 56 to first and second distributors 58 and 60, respectively. 
The first distributor 58 is connected to first spark plugs 62a, 62b, 62c 
and 62d provided in combustion chambers 64a, 64b, 64c and 64d, 
respectively. Likewise, the second distributor 60 is connected to second 
spark plugs 66a, 66b, 66c and 66d mounted in respective combustion 
chambers. With the arrangement mentioned above, ignition signals are 
generated at a timing with a predetermined phase difference by the signal 
generator 50 and 52. These signals are applied through the ignition coils 
54 and 56 and through the distributors 58 and 60 to the first and second 
spark plugs, which are consequently energized at timings optimum for 
burning air-fuel mixture in the most efficient manner. The ignition coils 
and spark plugs may be of any known construction and, therefore, a 
detailed description of the same is herein omitted. 
FIGS. 6A and 6B show one example of a phase control device to be used for 
the ignition spark timing control system shown in FIG. 5. In general, the 
first and second signal generators 50 and 52 are incorporated in a casing 
70 and arranged to cooperate with a vacuum advance control device 
responsive to suction prevailing in an induction passage upstream of a 
throttle valve to provide ignition signals at different timings with a 
predetermined phase in accordance with varying degrees of the suction 
prevailing in an induction passage upstream of a throttle valve. As shown, 
the first signal generator 50 comprises a breaker arm 50a and a breaker 
point 50b, which are mounted on a first rotatable breaker plate 72. The 
first breaker plate 72 is urged in a counterclockwise direction as viewed 
in FIG. 6A by a biasing means such as a tension spring 74. Similarly, the 
second signal generator 52 comprises a breaker arm 52a and a breaker point 
52b, which are mounted on a second breaker plate 76. The second breaker 
plate 76 is urged in a counterclockwise direction by a biasing means such 
as a tension spring 78 connected to the first breaker plate 72. As best 
shown in FIG. 6B, the second breaker plate 76 is disposed over the first 
breaker plate 72, between which a breaker cam 80 is rotatably mounted. The 
second breaker plate 76 thus arranged is connected by a linkage or 
actuating rod 82 to an actuating device 86. The actuating device 86 
comprises a casing 86a in which a flexible diaphragm 86b divides the 
casing into vacuum chamber 86c and an atmospheric chamber 86d. The vacuum 
chamber 86c is connected to a suction prevailing in an induction passage 
upstream of a throttle valve, while the atmospheric chamber 86d is vented 
to the atmosphere. The flexible diaphragm 86b is connected to the 
actuating rod 82 which in turn is connected to the second breaker plate 76 
as previously described. Indicated at 86e is a biasing means such as a 
compression spring which urges the flexible diaphragm 86b rightward as 
viewed in FIG. 6A. 
While, in FIGS. 6A and 6B, the supporting means for the first and second 
breaker plates 72 and 76 are not shown, it should be noted that these 
breaker plates are rotatably mounted on a stationary plate by bearings in 
a known manner. The breaker cam 80 is arranged to rotate at a speed 
proportional to the engine speed in a known manner to actuate breaker arms 
50a and 52a thereby generating ignition signals. It should be understood 
that the breaker cam 80 has four projections because the engine E shown in 
FIG. 5 is of the type having four cylinders. 
When, in operation, the suction prevailing in an induction passage upstream 
of a throttle valve is applied to the vacuum chamber 86c of the actuating 
device 86, it acts on the diaphragm 86b thereby moving the same leftward 
as viewed in FIG. 6A until the force developed by the suction prevailing 
in an induction passage upstream of a throttle valve acting on the 
diaphragm balances with the force of the compression spring 86e and the 
atmospheric pressure acting on the diaphragm 86b. In this instance, the 
actuating rod 82 is moved leftward with the movement of the diaphragm 86b, 
rotating the second breaker plate 76 clockwise as viewed in FIG. 6A. 
Rotation of the second breaker plate 76 causes rotation of the first 
breaker plate 72 via the tension spring 78. It should be noted that it is 
possible to provide a difference in rotational angle between the first and 
second breaker plates by arbitrarily selecting the preloads of the tension 
springs 74 and 78 and the spring constant of each tension spring. Since 
the rotation of the first breaker plate 72 will cause change in the 
breaking point or timing of the first signal generator 50 and the rotation 
of the second breaker plate 76 will cause change in the breaking point or 
timing of the second signal generator 52, it is possible to cause the 
first and second signal generators 50 and 52 to generate ignition signals 
at different timings with a predetermined phase by varying the rotational 
angles of the respective breaker plates 72 and 76 through the use of the 
tension springs 74 and 78. It should also be understood that a 
predetermined phase for an ignition advance may also be provided by 
positioning the first and second breaker plates at predetermined 
locations. 
As previously noted, the actuating rod 82 of the actuating device 86 is 
moved to varying degrees in dependence on the instantaneous value of the 
suction prevailing in an induction passage upstream of the throttle valve, 
thereby rotating the second breaker plate 76. This causes rotation of the 
first breaker plate 72 by the tension spring 78 connected between the 
first and second breaker plates 72 and 76. Under these circumstances, 
difference will exist in rotational angle between the first and second 
breaker plates 72 and 76 due to the difference in spring constant between 
the first and second tension springs 74 and 78. Therefore, ignition 
signals are generated at different timings with a predetermined phase by 
the first and second signal generators 50 and 52. Accordingly, the first 
and second spark plugs in each combustion chamber will be energized at 
different spark timings thereby effecting rapid combustion of air-fuel 
mixture in the combustion chamber. It is to be noted that the phase 
control device mentioned above is arranged to control the ignition spark 
timing in dependence on the variations in the engine intake manifold 
vacuum and, thus, a conventional vacuum advance mechanism may be employed 
in that device. 
FIG. 7 shows a modified form of the phase control device shown in FIGS. 6A 
and 6B, and corresponding or like component parts are designated by the 
same reference numerals as those used in FIGS. 6A and 6B. As shown in FIG. 
7, the phase control device has a single rotary breaker plate 90 on which 
first and second signal generators 50 and 52 are operatively mounted. The 
breaker plate 90 is connected through the actuating rod 82 to the 
diaphragm 86b of the actuating device 86 in a manner as previously 
described. In this illustrated form, the breaker cam 80 and the rotary 
breaker plate 90 are arranged such that the center G80 of rotation of the 
breaker cam 80 and the center G90 of rotation of the breaker plate 90 are 
eccentric with respect to each other. Further, the first and second signal 
generators 50 and 52 are located on the breaker plate 90 at symmetric 
positions with respect to an axis passing through the centers G80 and G90 
of the breaker cam 80 and the breaker plate 90. With this arrangement, 
when the suction prevailing in an induction passage upstream of the 
throttle valve changes in level, the breaker plate 90 is rotated to a 
degree in dependence on the variations in the suction prevailing in an 
induction passage upstream of the throttle valve. As a result, the 
engaging positions of the breaker arms 50a and 52a of the first and second 
signal generators with respect to the breaker cam 80 are changed by a 
degree corresponding to a difference between rotational radii r1 and r2 of 
the breaker arms 50a and 52a, so that ignition signals will be generated 
at different timings with a predetermined phase. Other operation of the 
phase control device of FIG. 7 is similar to that of the device shown in 
FIGS. 6A and 6B and accordingly a detailed description of the same is 
herein omitted. 
FIGS. 8A, 8B, 8C, 8D and 8E show a still modified form of the phase control 
device according to the present invention. In this illustrated form, the 
signal generators 50 and 52 are mounted on first and second breaker plates 
92 and 94, respectively, which are partially disposed in layers. The first 
and second breaker plates 92 and 94 are pivotally mounted on a plate 96 by 
pins 98 shown in FIG. 8E. As best shown in FIG. 8E, the plates 92, 94 and 
96 are formed with bores 92a, 94a and 96a, respectively, through which a 
cam plate 97 extends. The cam plate 98 is rotatably mounted on a shaft 100 
connected to the casing 70. An end of the cam plate 98 is connected to an 
actuating rod 82 which in turn is connected to a diaphragm 86b of an 
actuating device 86 in a manner as shown in FIG. 8A. As shown in FIGS. 8B 
and 8C, the cam plate 98 is eccentrically mounted on the shaft 100 and 
disposed in the bores 92a and 94a of the first and second breaker plates 
92 and 94 such that one end of the cam plate 98 engages with the bore 92a 
of the first breaker plate 92 and the other end of the cam plate 98 
engages with the bore 94a of the second breaker plate 94. The cam plate 98 
thus arranged is actuated by the actuating device 86 through the actuating 
rod 82 to move the first and second breaker plates 92 and 94 toward and 
away from each other so that the breaker arms 50a and 52a engages with the 
breaker cam 80 at different timings to generate ignition signals. 
Accordingly, if the first and second signal generators 50 and 52 are 
disposed on opposed positions at 180 degrees with respect to each other 
while the cam plate 98 assumes a position as shown in FIG. 8B, the first 
and second signal generators 50 and 52 will generate ignition signals at 
the same time. If, on the other hand, the cam plate 98 assumes a position 
as shown in FIG. 8C, the first and second breaker plates 92 and 94 are 
displaced from each other at a maximum degree so that a maximum phase 
difference will exist between the ignition signals generated by the first 
and second signal generators 50 and 52. The rotational angle of the first 
and second breaker plates 92 and 94 may be selectively changed by varying 
ratio of distance l.sub.1 and l.sub.2 between the end of the cam plate 98 
and the central axis of the shaft 100 and another end of the cam plate 98 
and the central axis of the shaft 100, respectively. The phase control 
device thus arranged will operate in a manner similar to that as 
previously described and, therefore, a detailed description of the same is 
herein omitted. 
Another modified form of the phase control device is shown in FIGS. 9A and 
9B. In this illustrated form, the phase control device comprises first and 
second contoured breaker plates 102 and 104 having curved faces 102a and 
104a, respectively. These breaker plates 102 and 104 are partially 
superposed by one another and rotatably supported by a shaft (no numeral) 
on which the breaker cam 80 is mounted. A biasing means such as a tension 
spring 106 is connected between the first and second breaker plates 102 
and 104 so that the curved faces 102a and 104a are urged toward each other 
to engage with an eccentric cam 108 rotatably mounted a shaft 108a. The 
shaft 108a is connected to a stationary plate 110 on which bearings 112 
and 114 to support the first and second breaker plates 102 and 104 are 
mounted. The eccentric cam 108 is connected to an actuating rod 82, which 
in turn is connected to a diaphragm of an actuating device in a manner 
already described hereinabove. 
When the vacuum advance mechanism is actuated, the actuating rod 82 is 
moved upward as shown by an arrow in FIG. 9A so that the eccentric cam 108 
will rotate around the shaft 108a. In this instance, the distance l.sub.3 
between the central axis of the shaft 108a and the curved face 102a and 
l.sub.4 between the central axis of the shaft 108a and the curved face 
104a will be varied so that the first and second breaker plates 102 and 
104 are rotated at different rotational angles. The phase control device 
thus arranged will operate in a manner as previously mentioned and, 
therefore, a detailed description of the same is herein omitted. 
It will now be appreciated from the foregoing description that in 
accordance with the present invention a plurality of spark plugs in each 
combustion chamber of an internal combustion engine are energized at 
different timings with a predetermined phase whereby air-fuel mixture can 
be combusted in the most efficient manner. 
It will also be understood that in accordance with the present invention a 
plurality of spark plugs in each combustion chamber of an internal 
combustion engine are adapted to be energized by independent ignition 
circuits which are arranged to generate ignition signals at different 
timings with a predetermined phase and, accordingly, one of the spark 
plugs in the combustion chamber can be reliably energized even when 
failure occurs in one of the ignition circuits. It should also be noted 
that a phase control device for use in an ignition spark timing control 
system has signal generators which are accommodated in a single casing so 
as to generate ignition signals whereby the phase control device is simple 
and compact in construction and low in manufacturing cost. 
While the present invention has been shown and described with reference to 
particular embodiments, it should be noted that various other changes or 
modifications may be made without departing from the scope of the present 
invention. For example, more than two spark plugs may be provided in each 
combustion chamber and, in this case, the ignition spark timing control 
system may be modified to generate ignition signals at respective timings 
optimum for each spark plug. Further, while the signal generators have 
been shown and described as being comprised of breakers, it should be 
understood that the signal generators may be of the type having 
transistors.