Combustion chamber of an internal combustion engine

An internal combustion engine comprising a combustion chamber and an accumulation chamber which are interconnected to each other via a mixture passage. An accumulation valve is arranged in the mixture passage and opened during the compression stroke. The mixture passage is connected to the combustion chamber at an opening formed on the peripheral inner wall of the cylinder head. The opening of the mixture passage is covered by the rear face of the raised portion formed on the top face to the piston when the piston reaches the top dead center.

DESCRIPTION OF THE INVENTION 
The present invention relates to an internal combustion engine. 
At present, in the field of internal combustion engines, an important 
problem is to improve the thermal efficiency while reducing the amount of 
harmful components in exhaust gas. As a method of effectively reducing the 
amount of harmful components in exhaust gas, there has been known a method 
of simultaneously reducing the amount of harmful HC, CO and NO.sub.x 
components in the exhaust gas by using a lean air-fuel mixture, and there 
has also been known a method of reducing the amount of harmful NO.sub.x 
components in the exhaust gas by recirculating the exhaust gas into the 
intake system of an engine. However, in either case wherein a lean 
air-fuel mixture or a mixture containing the recirculated exhaust gas 
therein is used, there occurs a common problem in that, since the flame 
speed of such a mixture is very low and, thus, the burning velocity is 
low, a high termal efficiency cannot be obtained and, as a result, a 
satisfactory high output of an engine cannot be obtained. Consequently, in 
the case wherein a lean air-fuel mixture or a mixture containing the 
recirculated exhaust gas there in is used, in order to improve a thermal 
efficiency, the most important problem is to increase the flame speed. 
With regard to an engine capable of increasing the burning velocity of the 
combustible mixture in the combustion chamber, the present applicant has 
already proposed an engine equipped with an accumulation chamber which is 
connected to the combustion chamber via an accumulation valve, so that a 
part of the suction gas introduced into the combustion chamber from the 
intake system of the engine is temporarily accumulated in the accumulation 
chamber. In this engine, the accumulation valve is opened from the 
beginning of the compression stroke to the end thereof, so that the 
suction gas accumulated under high pressure in the accumulation chamber is 
spouted from the accumulation chamber into the combustion chamber in the 
first half of the compression stroke. The suction gas thus spouted causes 
a strong swirl motion in the combustion chamber and, as a result, the 
burning velocity is increased. 
In order to create a much stronger swirl motion in the combustion chamber 
in the above-mentioned engine, it is necessary to increase the pressure of 
the mixture accumulated in the accumulation chamber. To this end, it is 
necessary to retard the closing time of the accumulation valve as much as 
possible. However, in the case wherein the closing time of the 
accumulation valve is retarded, the flame of the mixture ignited by the 
spark plug in the combustion chamber propagates into the accumulation 
chamber and, thus, the mixture accumulated in the accumulation chamber is 
ignited by the flame. Nevertheless, in this case, since the accumulation 
valve is closed immediately after the mixture in the accumulation chamber 
is ignited, the mixture in the accumulation chamber is merely burned and, 
thus, the combustion of the mixture in the accumulation chamber does not 
contribute to the movement of the piston 2. This results in a problem in 
that the output power of the engine is reduced. Consequently, in the 
above-mentioned engine, in order to prevent the flame in the combustion 
chamber from propagating into the accumulation chamber, the closing time 
of the accumulation valve is set at a time near a time at which the 
ignition is carried out. 
An object of the present invention is to provide an internal combustion 
engine provided with an accumulation chamber, which is capable of 
retarding the closing time of the accumulation valve while preventing the 
flame in the combustion chamber from propagating into the accumulation 
chamber. 
According to the present invention, there is provided an internal 
combustion engine comprising: a cylinder block having an inner wall 
defining a cylinder bore; a cylinder head having an inner wall therein and 
mounted on said cylinder block; a piston reciprocally movable in said 
cylinder bore and having a top face and an upper circumferential wall 
which is aproachable to at least one of a peripheral portion of the inner 
wall of said cylinder head and an upper portion of the inner wall of said 
cylinder bore when said piston reaches the top dead center; a combustion 
chamber formed between the inner wall of said cylinder head and the top 
face of said piston; an intake valve movably mounted on said cylinder head 
for leading a suction gas into said combustion chamber; and exhaust valve 
movably mounted on said cylinder head for discharging an exhaust gas into 
the atmosphere; an accumulation chamber in said inner wall; a gas passage 
communicating said accumulation chamber with said combustion chamber and 
having an opening which is formed on at least one of the peripheral 
portion of the inner wall of said cylinder head and the upper portion of 
the inner wall of said cylinder bore so that said opening is covered by 
the upper circumferential wall of said piston when said piston reaches the 
Top dead center, and; a valve means arranged in said gas passage and 
opened during the compression stroke. 
The present invention may be more fully understood from the following 
description of preferred embodiments of the invention, together with the 
accompanying drawings.

DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring to FIGS. 1 and 2, 1 designates a cylinder block, 2 a piston 
reciprocally movable in the cylinder block 1; 3 designates a cylinder head 
fixed onto the cylinder block 1; 4 designates a combustion chamber formed 
between the top face 2a of the piston 2 and the semi-spherical inner wall 
3a of the cylinder head 3; 5 designates an intake valve, 6 an intake port, 
7 an exhaust balve, 8 an exhaust port, and 9 a spark plug. An accumulation 
chamber 10 and a mixture passage 11 are formed in the cylinder head 3, and 
an accumulation valve 12 is arranged at the bottom end of the accumulation 
chamber 10. As is illustrated in FIG. 1, the accumulation valve 12 is 
actuated by a cam 13 which is driven by the engine. The mixture passage 11 
is connected to the combustion chamber 4 at an opening 14 which is formed 
on the periphery of the semi-spherical inner wall 3a of the cylinder head 
3. Consequently, when the accumulation valve 12 is opened, the 
accumulation chamber 10 is connected to the combustion chamber 4 via the 
accumulation valve 12 and the mixture passage 11. As is illustrated in 
FIG. 1, a raised portion 15 is formed in one piece on the top face 2a of 
the piston 2 so that, when the piston 2 is positioned at the top dead 
center as illustrated in FIG. 1, the spherical rear face 16 of the raised 
portion 15 covers the opening 14 of the mixture passage 11 and, at the 
same time, a squish area A is formed between the rear face 16 of the 
raised portion 15 and the inner wall 3a of the cylinder head 3. 
Referring to FIG. 6, the curved lines B, C and D indicate the opening time 
of the intake valve 5, the exhaust valve 7 and the accumulation valve 12, 
respectively. In FIG. 6, the ordinate L indicates valve lift and the 
abscissa .theta. indicates crank angle. From FIG. 6, it will be understood 
that the accumulation valve 12 is opened at a crank angle near the bottom 
dead center at the beginning of the compression stroke and closed at a 
crank angle near the top dead center at the beginning of the power stroke. 
In operation, at the time of the intake stroke, a lean air-fuel mixture or 
a mixture containing a large amount of the recirculated exhaust gas 
therein is introduced into the combustion chamber 4 via the intake valve 
5. After this, when the piston 2 moves downwards to the bottom dead center 
and then begins to move upwards, the accumulation valve 12 is opened 
immediately before the intake valve 5 is closed. As is hereinafter 
described, a combustible mixture under high pressure, which is introduced 
into the accumulation chamber 10 at the compression stroke in the 
preceding cycle, is accumulated in the accumulation chamber 10 and, on the 
other hand, the pressure in the combustion chamber 4 is lower than the 
atmospheric pressure at the start of the compression stroke. Consequently, 
the pressure difference between the pressure in the combustion chamber 4 
and the accumulation chamber 10 is large and, thus, when the accumulation 
valve 12 is opened, the combustible mixture accumulated in the 
accumulation chamber 10 is spouted from the opening 14 into the combustion 
chamber 4 at a high speed. At this time, since the opening 14 is directed 
tangentially to the circumferential inner wall of the combustion chamber 4 
as illustrated in FIG. 2, a strong swirl motion shown by the arrow W in 
FIG. 2 is created in the combustion chamber 4. Then, if the piston 2 
further moves upwards, since the pressure in the accumulation chamber 10 
is maintained higher than that in the combustion chamber 4 for a while, 
the combustible mixture in the accumulation chamber 10 continues to be 
spouted into the combustion chamber 4. As a result of this, the swirl 
motion created in the combustion chamber 4 is further strengthened. When 
the piston 2 further moves upwards and the pressure in the accumulation 
chamber 10 becomes equal to that in the combustion chamber 4, the spouting 
operation of the combustible mixture in the accumulation chamber 10 is 
stopped. After this, when the piston 2 further moves upwards, since the 
pressure in the combustion chamber 4 becomes higher than that in the 
accumulation chamber 10, the combustible mixture in the combustion chamber 
4 flows into the accumulation chamber 10. As the piston 2 further moves 
upwards, the pressure in the combustion chamber 4 is increased and, 
accordingly, the pressure in the accumulation chamber 10 is also 
increased. After this, when the piston 2 approaches the top dead center, 
the mixture in the combustion chamber 4 is ignited. As a result, the flame 
of the mixture thus ignited spreads within the combustion chamber 4 and 
the pressure in the combustion chamber 4 is increased. At this time, since 
the piston 2 has reached a position near the top dead center, the flame 
spreading towards the opening 14 is extinguished within the squish area A. 
However, at this time, since the pressure in the combination chamber 4 
propagates into the accumulation chamber 10 via the mixture passage 11, 
the pressure in the accumulation chamber 10 is considerably increased. 
After this, when the accumulation valve 12 is closed, the unburned mixture 
under high pressure is accumulated in the accumulation chamber 10. This 
combustible mixture under high pressure is spouted into the combustion 
chamber 4 at the next cycle to create a strong swirl motion in the 
combustion chamber 4. In addition, in the embodiment illustrated in FIG. 
1, since a squish flow is spouted from the squish area A into the 
combustion chamber 4 at the end of the compression stroke, a turbulence is 
further added to the swirling mixture in the combustion chamber 4 and, as 
a result, the burning velocity is considerably increased. 
FIGS. 4 and 5 illustrate a alternative embodiment according to the present 
invention. In this embodiment, an accumulation chamber 20 is formed in the 
cylinder block 1 and connected to the combustion chamber 4 via an 
accumulation valve 21 and a mixture passage 22. As is illustrated in FIG. 
4, the mixture passage 22 is connected to the combustion chamber 4 at an 
opening 23 which is formed on the inner wall of the cylinder bore 1a of 
the cylinder block 1. The opening 23 of the mixture passage 22 is directed 
tangentially to the inner wall of the cylinder bore 1a as illustrated in 
FIG. 5. The accumulation valve 21 is opened by a cam 24 which is driven by 
the engine as illustrated by the curved line D in FIG. 6. Consequently, in 
this embodiment, in the same manner as described with reference to FIG. 1, 
the mixture under high pressure accumulated in the accumulation chamber 20 
is spouted from the opening 23 in the first half of the compression stroke 
and, as a result, a strong swirl motion is created in the combustion 
chamber 4. On the other hand, since the opening 23 is covered by the 
circumferential wall of the piston 2 when the piston 2 approaches the top 
dead center, the flame created in the combustion chamber 4 cannot 
propagate into the accumulation chamber 20. However, since the pressure in 
the combustion chamber 4 propagates into the accumulation chamber 20, the 
unburned mixture under high pressure is accumulated in the accumulation 
chamber 20. 
According to the present invention, since it is possible to retard the 
closing time of the accumulation valve while preventing the flame in the 
combustion chamber from propagating into the accumulation chamber, the 
unburned mixture under high pressure can be accumulated in the 
accumulation chamber. As a result of this, since the velocity of the 
mixture spouted from the accumulation chamber in the first half of the 
compression stroke is increased, a considerably strong swirl motion can be 
created in the combustion chamber. Consequently, if a lean air-fuel 
mixture or a mixture containing recirculated exhaust gas therein is used, 
the burning velocity can be increased and, thus, a stable combustion can 
be ensured even if the engine is operating under a light load. 
While the invention has been described by reference to specific embodiments 
choses for purposes of illustration, it should be apparent that numerous 
modifications could be made thereto by those skilled in the art without 
departing from the spirit and scope of the invention.