Internal combustion gasoline engine

An exhaust gas purification system for internal combustion engines having at least two cylinders of which the port of each exhaust valve communicates with a port passage provided in the cylinder head, and a pair of the adjacent port passages communicate with a common port passage forming a siamese port passage therewith. A secondary air intake passage having a check valve communicates with the port passages for introducing secondary air by exhaust pulsation. In order to enhance the exhaust pulsation effect, the exhaust pipe connected to the opening of the common port passage has a constant cross section of a fixed diameter. Heat insulation is provided along the siamese port passage and a portion of the exhaust pipe for good oxidation of the unburned constituents. The total volume of the exhaust passage through the siamese port passage and the heat insulated exhaust pipe portion is equal to the displacement volume of the corresponding cylinders for introduction of a sufficient amount of the secondary air. The ignition timing is retarded to restrict the combustion temperature to under 2000.degree. C. for reducing the amount of nitrogen oxides.

FIELD OF THE INVENTION 
This invention relates to improvements in an internal combustion gasoline 
engine and more particularly to a new and improved internal combustion 
gasoline engine for reducing pollutants in exhaust gas to a predetermined 
level. 
THE PRIOR ART 
Many exhaust emission control devices have been proposed for meeting the 
strict emission regulations. These conventional devices may generally be 
classified into two categories. One is that an engine body itself is 
modified for clarifying the poisonous exhaust gas. The other features in 
that the exhaust gas is treated for clarification in the exhaust system 
following the engine body. The stratified combustion system in which a 
combustion chamber is further provided with another combustion chamber, 
belongs to the former category. For example, an exhaust emission control 
in which a device for further burning the poisonous exhaust gas is 
provided in the exhaust system, and one in which a catalytic converter 
system for promoting the clarification of the exhaust gas is additionally 
provided in the exhaust system are included in the latter category of the 
conventional exhaust emission control devices. 
The stratified combustion system of the engine is complicated in engine 
structure due to the fact that an additional combustion chamber and an 
intake valve are provided, and is also complicated in the control of the 
mixture ratio because of stratified charging. Thus, this system is 
defective in that it is difficult to keep the necessary reliability during 
operation and control as compared with the conventional systems and 
special maintenance is required. 
The exhaust emission control device of the latter case accompanied by the 
thermal reactor or catalyst device suffers from many disadvantages. That 
is, when the engine misfires, an abnormal temperature rise occurs thus to 
possibly cause a fire in the car. For this, a precise safety apparatus 
must be installed. Further, this system is large and complicated in 
structure and requires heat-resisting material and noble metal for 
constructing it. Therefore, the manufacturing cost thereof is high. 
Additionally, it may give rise to a secondary public nuisance, although it 
is effective when preventing a primary public nuisance. Moreover, it 
requires periodical maintenance and changing of parts. Especially, in the 
case of the catalytic converter system, the special fuel(unleaded 
gasoline) must be used and when the engine is insufficiently warmed, no 
reduction of the pollutants in the exhaust gas is effected and, more 
adversely, the poisonous gases may increase. 
It is well known how the components of exhaust gas are affected by various 
factors controlling the engine operation, for example, the shape of 
combustion chambers, air-fuel ratio ignition timing, timing of valve 
action, or the heat retention of exhaust pipes. Many exhaust emission 
control devices based on any of these factors have been proposed. These 
devices, however, are used just as an auxiliary device to the above 
mentioned systems, and have not yet provided satisfactory results of the 
reduction of the pollutants in exhaust gas. 
SUMMARY OF THE INVENTION 
Accordingly, an object of the present invention is to provide an internal 
combustion gasoline engine capable of reducing carbon monoxides, 
hydrocarbons, and nitrogen oxides in exhaust gases to a predetermined 
level without using any additional reaction chamber and any modification 
of the engine structure. 
Another object of the present invention is to provide an exhaust emission 
control device for internal combustion gasoline engines which is simply 
constructed by just modifying the exhaust system for heat retaining and 
without any re-combustion chamber or catalytic converter. 
To achieve these objects, the internal combustion engine has at least two 
cylinders of which the ports of the exhaust valves communicate with a 
common port passage in the cylinder head to provide a siamese port passage 
which in turn communicates with an exhaust pipe, a secondary air intake 
passage being connected to the siamese port passage for introducing the 
secondary air by exhaust pulsation, and heat insulation means are provided 
along the siamese port passage and the exhaust pipe. 
The siamese port passage has the effect of maintaining the temperature of 
the exhaust gas passing therethrough to be at a high temperature, since 
each branch port passage is heated by the exhaust gases passing through 
the adjacent branch port passage, so that the branch passages are kept at 
a high temperature. Thus, oxidation of unburned harmful constituents may 
effectively occur. The exhaust passage through the insulated siamese port 
passage and the heat insulated exhaust pipe has a volume equal to the 
displacement volume of the corresponding cylinders for effective oxidation 
of the unburned constituents. Further, the ignition timing is retarded to 
restrict the combustion temperature to under 2000.degree. C. for reducing 
the amount of nitrogen oxides. 
Engine control factors, such as the ignition timing, are controlled to 
lower the combustion gas temperature in the cylinder, and the exhaust gas 
temperature in the exhaust passage is maintained at a high temperature, 
whereby the three harmful above-mentioned exhaust gas constituents can be 
decreased by controlling the gas temperatures in the cylinder and in the 
exhaust passage. 
For a clearer understanding of the nature and objects of this invention, 
reference may be had to the following detailed description taken in 
connection with the accompanying drawings, in which:

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The inventors experimentally confirmed the fact that the combustion gas 
temperature and the exhaust gas temperature are indispensable to be taken 
into account in removal of the pollutants of the exhaust gas. For example, 
nitrogen oxides generally are produced at a high temperature and the ratio 
of increasing amount of the products of nitrogen oxides sharply increases 
at about 1,800.degree. C. Carbon monoxide and hydrocarbons tends to 
self-react when the exhaust gas temperature reaches a predetermined level. 
Such self-reaction triggering temperature is about 750.degree. C. 
With these facts in mind, when reading the graph in FIG. 5, it will easily 
be seen that the conventional engine is completely ineffective in reducing 
of the pollutants in exhaust gas. As indicated by the dotted line in FIG. 
5, the combustion gas temperature is by far above 2,000.degree. C. and 
then reduces to be 1,000.degree. C. to 1,200.degree. C., and the 
temperature of the gas exhausted to the exhaust port passage through the 
exhaust valve port further reduces to 350.degree. C. to 800.degree. C. 
That is, the amount of nitrogen oxides generated is very large because of 
a high combustion temperature, and unclean exhaust gas including carbon 
monoxide and hydrocarbons are emitted to the exterior since the 
temperature of the gas exhausted to the exhaust system suddenly falls 
below the self-reaction triggering temperature. 
Another experiment by the inventors confirmed the following facts, as shown 
in FIG. 3. First, carbon monoxide reduces in proportion to the air fuel 
ratio, and its reduction stops in the vicinity of the stoichiometric ratio 
(14.7). The amount of hydrocarbons is reduced with an increase of the 
air-fuel ratio and is increased as the air-fuel ratio increases over the 
stoichiometric ratio. 
Second, nitrogen oxides increase with increase of the A/F ratio and reaches 
the peak near the stoichiometric, and then decreases with an increase of 
the A/F ratio. 
Other experiments by the inventors show that the amount of the nitrogen 
oxides in the exhaust gas was proportionally related to the ratio of the 
piston stroke to the cylinder bore, as shown in FIG. 4, and the exhaust 
gas temperature exhibited a tendency of increase with retardation of the 
ignition timing, as shown in FIG. 6, the details of which will be referred 
to later. Incidentally, the exhaust gas temperature in the FIG. 6 
experiment was measured in accordance with the 10 mode measuring method, 
Japanese Exhaust Emission Test Procedure. 
The present invention is based on all of these experimental facts. In the 
present invention, the port passage in the cylinder head is formed into a 
siamese port passage communicating with the adjacent cylinders. The 
stroke-bore ratio of the engine is small. A heat insulating means is 
provided along the inner wall of the siamese port passage in the cylinder 
head. The exhaust pipe is also provided with a heat insulation structure. 
The ignition timing is so timed that the combustion gas temperature in the 
conbustion chamber is below 2,000.degree. C. With such construction, the 
exhaust gas temperature is maintained above 750.degree. C. over a volume 
of the exhaust passage following the exhaust valve port corresponding in 
amount to the engine displacement volume. In the present invention, these 
features mentioned above are systematically cooperatively combined so that 
the gas temperature distribution from the cylinder to the exhaust valve 
becomes more effective for reduction of the pollutants in exhaust gas, as 
indicated by the solid line in FIG. 5. It is to be noted that the ratio of 
surface area to volume in the combustion chamber may be made large for 
effecting a slower rate of combustion, and the exhaust valve, may set to 
open near the bottom dead center so as to retain the combustion gas in the 
combustion chamber for a long time for promoting oxidation in the 
cylinder. 
Referring now to FIGS. 1 and 2, there is shown an internal combustion 
gasoline engine of the type of a horizontal opposed-piston engine of which 
each bank is provided with two cylinders 15 incorporating the present 
invention, having an air cleaner 1 and a carburetor 2 as conventional, but 
improved so as to supply a relatively lean air fuel mixture (15 to 20 of 
the air-fuel ratio) to the engine. There are provided an intake tube 3 and 
a combustion chamber 4 which is of a flat shaped type with about 4 
cm.sup.-1 ratio of surface area to volume (S/V). Both exhaust valves 5 and 
5 of the cylinders in each bank are arranged adjacent to each other and 
both exhaust valve ports communicate with a common port passage 16 in the 
cylinder head 14, each via a branch port passage 17, to provide a siamese 
port passage 6. The siamese port passage 6 is provided with a liner 13 
extending from the exhaust valve port to the common outlet of the siamese 
port passage 6. Reference numeral 8 designates an exhaust pipe following 
the siamese port passage 6. The exhaust tube 8 is covered with a heat 
insulating pipe 7 over a region thereof. The heat insulated exhaust 
passage "1" comprising the siamese port passage 6 and the heat insulated 
region of the exhaust pipe 8 has a volume equal to the displacement volume 
of the corresponding cylinders. According to our experiments it is 
preferable to design the heat-retaining portion in the exhaust passage to 
physically correspond to the engine displacement volume. By such 
construction of the exhaust passage, the exhaust gas passing therethrough 
is heat-retained over this length of the exhaust passage. Further, as 
shown in FIG. 6 the exhaust system provided with the above liner and the 
heat-retaining means provides by far a higher exhaust gas temperature at 
both the A and B portions shown in FIG. 2, when compared with that in the 
exhaust system without the liner and the heat-insulating means. Moreover, 
in this invention, the ignition timing is adjusted to be retarded somewhat 
(10.degree. to 20.degree. of crank angle) from the minimum advance for 
best torque (MBT). 
As described above, the air fuel mixture supplied is a lean mixture with 
the air fuel ratio (15 to 20) larger than the stoichiometric A/F ratio 
(14.7). The result is that, as seen from FIG. 3, the pollutants of carbon 
monoxide and hydrocarbons are reduced and the oxidation in the exhaust gas 
continues since a relatively large amount of oxygen resides in the exhaust 
gas. For further, improving such a reduction process of the pollutants, 
the ignition timing is delayed by a retarding ignition timing unit 18, 
thereby to raise the exhaust gas temperature, as shown in FIG. 6, and the 
port liner 13 and heat-retaining means are employed. As a result, the 
self-reaction of the pollutants, carbon monoxides and hydrocarbons, 
continues and the oxidation rapidly progresses, resulting in a remarkable 
reduction of carbon monoxide and hydrocarbons. With respect to the shape 
of the combustion chamber, the S/V ratio is designed to be large so that 
the combustion chamber has a flat shaped space with a long flame 
propagation space. Therefore, the combustion in the combustion chamber 
mildly progresses, so that the maximum combustion temperature may be 
lowered, thereby reducing remarkably the amount of the nitrogen oxides in 
the exhaust gas. Such slow rate combustion causes the temperature of the 
combustion gas when exhausted from the exhaust value to rise with the 
result that the oxidation is further promoted in the port passage and the 
exhaust pipe. Moreover, the ignition timing is set to be delayed as 
compared with the conventional engine and thus the maximum combustion 
temperature is restricted low. Accordingly, this, together with the unique 
shape of the combustion chamber, serves to further reduce the amount of 
the nitrogen oxides in the exhaust gase. This also facilitates the 
oxidation of carbon monoxide and hydrocarbons. 
As previously described, the retardation of the ignition timing causes the 
exhaust temperature to rise, as shown in FIG. 5 thereby to provide a good 
condition for the oxidation after the gas is exhausted. The port passage 6 
is wholly lined with the liner 13 which ends near the exhaust valve seat. 
The liner 13 serves to impede the transfer of heat to the cylinder head 14 
and thus the fall of the exhaust temperature may be controlled to a 
minimum. The gas exhausted from the cylinder in response to the opening of 
the exhaust valve is most intensively oxidized in the port passage and is 
continuously oxidized in the exhaust pipe being maintained at a given 
temperature, thereby extremely reducing the pollutants in the exhaust gas. 
This results from the fact that the liner 13 is provided over the inner 
wall of the port passage and the exhaust valve is heat-insulated for heat 
retention so that the exhaust gas temperature may be maintained in the 
temperature range permitting the oxidation, i.e. above 750.degree. C. 
It should be noted that the two exhaust valves 5 and 5 of the adjacent 
cylinders 15 and 15 are arranged adjacent each other and both adjacent 
exhaust valve ports of the respective adjacent exhaust valves 5 and 5 
communicate with the common port passage 16 via branch port passages 17 
and 17, respectively, to form the siamese port passage 6 in the cylinder 
head 14. The siamese port passage has the advantage of reducing carbon 
monoxide and hydrocarbons. More particularly, each branch port passage 17 
is heated by the other adjacent branch port passage 17, since both branch 
port passages 17 and 17 are closely disposed next to each other. 
Therefore, the exhaust gases passing through the branch port passages may 
be maintained at a high temperature, so that oxidation of CO and HC may be 
further enhanced. In addition, since the siamese port passage 6 is 
provided in the cylinder head 14, a high heat maintainance effect may be 
expected and it is not necessary to provide an external, complex exhaust 
manifold, whereby the exhaust passage and exhaust pipe 8 are simplified 
and manufactured easily. 
The following table shows the result of the internal combustion gasoline 
engine according to the present invention in comparison with the 
conventional one. Comparison is made with respect to three poisonous 
components in the exhaust gas and the temperatures at different places in 
the exhaust system. Measurement for this comparison was made according to 
the Japanese Exhaust Emission Test Procedure, 10 mode measuring method. 
__________________________________________________________________________ 
Exhaust Gas 
Temperature (10 M 
Test.) Amount of Exhaust Gas 
A Portion 
B Portion 
CO HC NOX 
__________________________________________________________________________ 
Conventional 
Engine 600.degree. C. 
350.degree. C. 
12 g/Km 
2.2 g/Km 
1.8 g/Km 
Engine of 
This Invention 
800.degree. C. 
750.degree. C. 
1.8 g/Km 
0.15 g/Km 
0.9 g/Km 
'75 Emission Mean Mean Mean 
Standard (20 M) 2.10 0.25 1.20 
Japan) 
Evaluation 
In conventional 
Reduction 
Reduction 
Reduction 
engine, heat 
of about 
of about 
of about 
dispersion is 
large. Engine of 
85% 93% 50% 
this invention has 
a remarkable heat- 
Fulfils 
retaining. '75 emission 
regulations 
__________________________________________________________________________ 
As seen from the above table, the three poisonous components of nirogen 
oxides, carbon monoxide and hydrocarbons are substantially reduced and the 
result of the reduction thereof satisfactorily fulfils the requirements of 
the Japan's strict 1975 emission standards. 
The engine of this invention with the additional known exhaust gas 
recirculation device can meet the more strict emission regulations to be 
enforced after 1975. 
As seen from FIG. 4, the engine with the small ratio of stroke to bore is 
effective in nitrogen oxide reduction because, in this case, the flaming 
distance is large and the combustion of the gas in the cylinder continues 
for a long time (see FIG. 4). 
In case the exhaust value is set so as to open at 50.degree. before the 
bottom dead center to 20.degree. after bottom dead center by mechanism 19 
therefor (although, in the case of the conventional one, it is opened at 
47.degree. to 60.degree. before the bottom dead center) and additionally 
the ignition timing is delayed, the combustion gas at a high temperature 
may remain in the combustion chamber for a long time with the result of 
facilitating oxidation. 
A known air injection system for secondary air supply may partly be used in 
the engine of this invention. The data results from many experiments by 
inventors which showed that there was no need for a secondary air supply 
for the reason that the A/F ratio is large when the car runs at a light 
load, i.e. it runs on a level road at a normal speed. On the other hand, 
when the car runs at a heavy load (on the road of a high grade, for 
example), the A/F ratio of the mixture taken in is small. Thus, in this 
case, the supply of secondary air is necessary for increasing the A/F 
ratio. 
To cope with this problem, the internal combustion gasoline engine is 
provided with an intake passage 11 for secondary air communicating with 
the exhaust port passage 6 with its opening near the exhaust valve 5 and 
also communicating with an air cleaner 10. A check valve 9 is disposed in 
the intake passage 11, and is operated by the pulsation of the exhaust 
gases to open when the inner pressure of the exhaust passage is lowered 
below the atmospheric pressure, and to close when the former rises above 
the latter. The negative pressure given by the pulsation results in 
introduction of secondary air from the air cleaner 10 into the exhaust 
passage. In this case, the check valve 9 may be used in a manner that it 
is interlocked with an accelerator pedal and secondary air is supplied 
immediately after or with some time dleay after operating the pedal. The 
check valve 9 may also be controlled in its opening in response to the 
change of the negative pressure in the intake passage. When the car runs 
at heavy load, the temperature of the exhaust gas is high. In such case, 
the supply of secondary air may be controlled on the basis of the change 
of the exhaust gas temperature. 
Referring now to FIG. 5, the gas temperature of the present invention is 
compared with that of a conventional engine, whereby it may be noted that 
with the present invention the ignition timing is retarded to restrict the 
combustion gas temperature to under 2000.degree. to reduce the amount of 
nitrogen oxides, and the exhaust passage temperature is maintained higher 
than that of the conventional engine to enhance the oxidation therein of 
CO and HC.