Cylinder head variable swirl siamese type intake port structure including biasing means diverting mixture flow towards diverting means which bypasses straight intake passage control valve

A variable swirl siamese type intake port structure for an internal combustion engine cylinder head includes a first generally straight intake passage which leads to a first intake port and a second generally helical intake passage which leads to a second intake port which is formed with a helical end vortex portion. A control valve is fitted in the first generally straight intake passage at an upstream portion thereof so as to control its flow resistance. A means is provided to the generally straight intake passage on the side thereof towards the generally helical intake passage, for, when the control valve is in its position to maximize the flow resistance of the generally straight intake passage, diverting a relatively minor proportion of air-fuel mixture sucked into the intake port structure from a point upstream of the control valve to a point near the downstream end of the first generally straight intake passage, thus bypassing the control valve. Further, there is provided a means for biasing flow of air-fuel mixture sucked into the intake port structure towards the diverting means. This diverting means may include an auxiliary passage formed from upstream of the control valve to a portion of the generally straight intake passage near the downstream end thereof, or alternatively a notch portion formed in said control valve, preferably in the edge thereof which is on the side thereof towards said generally helical intake passage.

BACKGROUND OF THE INVENTION 
The present invention relates to a variable swirl siamese type intake port 
structure for an internal combustion engine cylinder head, and more 
particularly relates to such a siamesed type variable swirl intake port 
structure for an internal combustion engine cylinder head, which 
incorporates two intake valves (and thus is of the three valve type or the 
four valve type) and a switchover valve construction for selectively 
supplying intake air-fuel mixture to said two intake valves in varying 
proportions, and which is improved as regards air-fuel mixture swirling 
characteristics and volumetric efficiency in various operational 
conditions. 
The present invention has been described in Japanese Patent Application 
Ser. No. 60-187726 (1985), filed by an applicant the same as the entity 
assigned or owed duty of assignment of the present patent application; and 
the present patent application hereby incorporates into itself by 
reference the text of said Japanese Patent Application and the claims and 
the drawings thereof; a copy is appended to the present application. 
Further, the present applicant wishes to attract the attention of the 
examining authorities to the existence of a copending U.S. patent 
application Ser. No. 887,658, which may be considered as relevant to the 
examination of the present patent application. 
In the prior art, there are various types of intake port structures for 
internal combustion engine cylinder heads, and in particular for so called 
siamese type cylinder heads. Such intake port structures typically are of 
the variable swirl siamese type, in which the siamesed intake port 
comprises a generally straight intake passage and a generally helical 
intake passage arranged in parallel with said generally straight intake 
passage, so that both said generally straight intake passage and also said 
generally helical intake passage receive supply of intake air-fuel mixture 
from the engine intake manifold, with a control valve selectively at least 
partially interrupting the flow of air-fuel mixture through said straight 
intake passage, so as selectively to provide extra swirl for the intake 
air-fuel mixture being sucked into the combustion chamber of the engine, 
so as to improve combustibility, flame front propagation speed, and firing 
efficiency and thereby militate against engine knocking, thereby to allow 
the engine to be operated with a weaker intake air-fuel mixture than would 
otherwise be practicable. Such a construction typically includes a 
separating wall which divides between said generally straight intake 
passage and said generally helical intake passage. And a prior air to the 
present patent application, Japanese Patent Application Ser. No. 56-143215 
(1981) which has been laid open as Japanese Patent Laying Open Publication 
Ser. No. 58-48715 (1983) and which was filed by an applicant the same as 
the applicant of the Japanese patent application of which the priority is 
being claimed in the present application and to whom either the present 
application is assigned or is owed a duty of assignment of the present 
application, discloses an improved siamesed type intake port structure for 
an internal combustion engine cylinder head which is provided with a 
bypass air passage through said separating wall, connecting a point on the 
generally straight intake passage downstream of said control valve 
provided therein to a vortex and wall of the generally helical intake 
passage. 
With such an intake port structure for an internal combustion engine 
cylinder head, when the control valve is controlled to be in the closed 
state by a control system therefor, substantially all of the air-fuel 
mixture sucked in by the combustion chamber of the engine is inhaled 
through the generally helical intake passage, and is accordingly imparted 
with strong swirling; this mode of operation is appropriate for when the 
engine is operating at low load, as during the idling engine operating 
condition. In this condition, because of this swirling motion, the limit 
to which the air-fuel mixture being supplied to the engine can be weakened 
without engendering deleterious effects is extended. However, at this time 
the resistance presented to flow of air-fuel mixture by the generally 
helical intake passage by itself alone is high. On the other hand, when 
the control valve is controlled to be in the open state by the control 
system therefor, most of the air-fuel mixture sucked in by the combustion 
chamber of the engine is inhaled through the generally straight intake 
passage with only a minor proportion thereof being inhaled through the 
generally helical intake passage, and accordingly the inhaled air-fuel 
mixture as a whole is imparted with relatively weak swirling, thus 
accordingly causing the volumetric efficiency of the engine to be high so 
as to develop good engine power; this mode of operation is appropriate for 
when the engine is operating at high load, such as full load. At this time 
the resistance presented to flow of air-fuel mixture by the combination of 
the generally straight intake passage and the generally helical intake 
passage is relatively low. 
There is however a problem with such an intake port structure for an 
internal combustion engine cylinder head, in that, when the control valve 
is thus controlled to be in the closed state by its control system and 
substantially all of the air-fuel mixture sucked in by the combustion 
chamber of the engine is being inhaled through the generally helical 
intake passage and is accordingly being imparted with strong swirling, 
although the apparent flame propagation speed is improved and the weak 
mixture limit is extended, nevertheless because of the swirling of the 
air-fuel mixture in the combustion chamber the fuel therein is 
preferentially thrown towards the periphery of the combustion chamber by 
centrifugal force, and so in the radial direction of the combustion 
chamber there is created an air/fuel ratio gradient, with the air-fuel 
mixture at the center portion of the combustion chamber being weaker than 
the air-fuel mixture at the edge portion thereof. Accordingly, if the 
air/fuel ratio of the overall air-fuel mixture being supplied to the 
combustion chamber is near the limit in the weakness direction, then the 
air/fuel ratio at the center portion of the combustion chamber may become 
too low for good ignition, and, since in such a three valve type or four 
valve type internal combustion engine it is convenient and usual to locate 
the spark plug at the center or approximate center of the combustion 
chamber, this means that the air/fuel ratio of the air-fuel mixture near 
and around the ignition portion of said spark plug may become too low for 
proper ignition. For this reason, according to the conventional art, it is 
not practicable to push the weakening of the intake air-fuel mixture to 
the limit, even although good combustion chamber swirling is being 
provided by such a siamese type intake port structure as detailed above. 
Also, as a subsidiary desideratum for such a siamese type intake port 
structure for such an internal combustion engine cylinder head, it is 
important that, especially during transient driving conditions, the fuel 
supply responsiveness of the engine should be as good as possible. 
In order to cope with the problems outlined above, the assignee or entity 
owed duty of assignment of the present patent application has already 
proposed, in copending Japanese Patent Application Ser. Nos. 60-1613149 
(1985) and 60-163150 (1985) neither of which is it intended hereby to 
admit as prior art to the present patent application except to the extent 
otherwise required by applicable law, an intake port structure for an 
internal combustion engine of the general above described variable swirl 
siamese type, in which the siamesed intake port comprises a generally 
straight intake passage and a generally helical intake passage arranged in 
parallel with said generally straight intake passage so that both said 
generally straight intake passage and also said generally helical intake 
passage receive supply of intake air-fuel mixture from the engine intake 
manifold, and with a control valve provided so as selectively at least 
partially to interrupt the flow of air-fuel mixture through said straight 
intake passage so as selectively to provide extra swirl for the intake 
air-fuel mixture being sucked into the combustion chamber of the engine, 
characterized in that an auxiliary passage system, such as for example a 
substantially straight auxiliary passage, is provided for the above 
described generally straight intake passage which, even if the control 
valve is closed, maintains a certain degree of connection of said 
generally straight intake passage on its side towards said generally 
helical intake passage. In this variable swirl siamese type intake port 
structure, when the control valve fitted in the generally straight intake 
passage is closed, a relatively minor but still effective stream of 
air-fuel mixture flowing into said generally straight intake passage via 
the auxiliary passage system squirts into the combustion chamber, cuts 
across the vortex flow of air-fuel mixture set up in the combustion 
chamber by the generally helical intake passage and said second intake 
port, and impinges generally on the ignition point of the spark plug, also 
further entraining some of said swirling vortex flow in it, and thus 
ensures that the air/fuel ratio of the air-fuel mixture in the vicinity of 
said spark plug is not weakened by centrifugal effects or the like. 
Accordingly, even if the average air/fuel ratio for the engine is set 
relatively very weak, there is no risk engendered of misfiring, since the 
air/fuel ratio around the ignition point of the spark plug is ensured of 
being adequate; thus, the limit for weakening the air/fuel ratio for the 
engine is significantly extended. Further, considerable microturbulence is 
generated in the air-fuel mixture in the combustion chamber by the above 
described collision of this relatively minor but nevertheless effective 
straight flow from the generally straight intake passage and the vortex 
flow from the generally helical intake passage and the intake port 
connected thereto, and accordingly good combustion is further promoted and 
the air/fuel ratio weakening limit is further extended. On the other hand, 
when the control valve fitted in the generally straight intake passage is 
open, the stream of air-fuel mixture flowing through the auxiliary passage 
system squirts into the combustion chamber to be added to the quantities 
of air-fuel mixture supplied into the combustion chamber by the generally 
straight intake passage and the intake port connected thereto as well as 
the generally helical intake passage and its intake port, and thereby the 
engine volumetric efficiency is increased and its output power level is 
enhanced. Also, because these air-fuel mixture streams collide in the 
combustion chamber, again good microturbulence is engendered, and high 
speed combustion is made available. Thus, even if the spark plug is 
located in the generally central region of the combustion chamber as is 
typical with such three valve or four valve engine designs, no problem 
arises with the ignition of the mixture, and compact combustion is 
enabled, which increases the mechanical octane value for the engine as 
well as extending the limit for air-fuel ratio weakening. According to a 
particular specialization of the above concept, the auxiliary passage 
system may point through the intake port for the straight passage, when 
open, into the combustion chamber in a direction somewhat to tend to 
cancel large scale turbulence induced in said combustion chamber by flow 
through said generally helical intake passage and the intake port 
therefor; and further said auxiliary passage system may thus in fact point 
through said straight intake passage intake port, when open, into said 
combustion chamber in a direction somewhat to that side of the ignition 
point of the spark plug in the direction to tend to cancel large scale 
turbulence induced in said combustion chamber by flow through the 
generally helical intake passage and the intake port therefor. According 
to such a structure, the deleterious centrifugal effects in the combustion 
chamber are further remedied, and good microturbulence in the combustion 
chamber is further encouraged. 
This above described intake port structure for an internal combustion 
engine of the variable swirl siamese type is successful in meeting the 
objects above, but however there still remain some problems in the 
operation of the internal combustion engine, associated with the degree of 
responsiveness obtainable at a time of acceleration operation, in 
particular at a time of accelerating away from a low load condition such 
as the idling operational condition. 
SUMMARY OF THE INVENTION 
Accordingly, it is the primary object of the present invention to provide a 
variable swirl siamese type intake port structure for an internal 
combustion engine cylinder head, which is improved over the prior art and 
avoids the problems detailed above. 
It is a further object of the present invention to provide such a variable 
swirl siamese type intake port structure for an internal combustion engine 
cylinder head, which has good characteristics with regard to transient 
responsiveness of the engine, especially responsiveness in accelerating 
away from a low load condition such as the idling condition. 
It is a further object of the present invention to provide such a variable 
swirl siamese type intake port structure for an internal combustion engine 
cylinder head, which allows engine output power to be enhanced. 
It is a further object of the present invention to provide such a variable 
swirl siamese type intake port structure for an internal combustion engine 
cylinder head, which allows engine mechanical octane value to be enhanced. 
It is a further object of the present invention to provide such a variable 
swirl siamese type intake port structure for an internal combustion engine 
cylinder head, which provides good ignition characteristics for the 
engine. 
It is a further object of the present invention to provide such a variable 
swirl siamese type intake port structure for an internal combustion engine 
cylinder head, which allows the engine to be operated with a very weak 
mixture. 
It is a further object of the present invention to provide such a variable 
swirl siamese type intake port structure for an internal combustion engine 
cylinder head, which allows for reduction of the flame propagation 
distance in the engine combustion chambers. 
It is a further object of the present invention to provide such a variable 
swirl siamese type intake port structure for an internal combustion engine 
cylinder head, which has good characteristics with regard to engine 
volumetric efficiency. 
It is a further object of the present invention to provide such a variable 
swirl siamese type intake port structure for an internal combustion engine 
cylinder head, which provides good microturbulence in the combustion 
chambers of the engine. 
It is a further object of the present invention to provide such a variable 
swirl siamese type intake port structure for an internal combustion engine 
cylinder head, which provides supply of air-fuel mixture of relatively 
uniform air/fuel ratio to the combustion chambers of the engine. 
It is a further object of the present invention to provide such a variable 
swirl siamese type intake port structure for an internal combustion engine 
cylinder head, which provides for good combustibility of said air-fuel 
mixture being supplied to the combustion chambers of the engine. 
It is a further object of the present invention to provide such a variable 
swirl siamese type intake port structure for an internal combustion engine 
cylinder head, which provides stratified combustion in the combustion 
chambers of the engine. 
According to the most general aspect of the present invention, these and 
other objects are attained by a variable swirl siamese type intake port 
structure for an internal combustion engine cylinder head formed with a 
combustion chamber to which a spark plug having an ignition point is 
provided, comprising: a first generally straight intake passage which 
leads to a first intake port opening to said combustion chamber; a second 
generally helical intake passage which leads to a second intake port, also 
opening to said combustion chamber, formed with a helical end vortex 
portion; a control valve fitted in said first generally straight intake 
passage at an upstream portion thereof so as to control its flow 
resistance; a means, provided to said generally straight intake passage on 
the side thereof towards said generally helical intake passage, for, when 
said control valve is in its position to maximize the flow resistance of 
said generally straight intake passage, diverting a relatively minor 
proportion of air-fuel mixture sucked into said intake port structure from 
a point upstream of said control valve to a point near the downstream end 
of said first generally straight intake passage, bypassing said control 
valve; and: a means for biasing flow of air-fuel mixture sucked into said 
intake port structure towards said diverting means. 
According to such a structure as specified above, the liquid fuel which 
inevitably accumulates on the surface of the intake port structure is 
guided towards the diverting means by the biasing means, and further the 
amount of fuel passing through the intake passage structure as a whole is 
increased, as a result of which the responsiveness of the engine is 
improved during acceleration operation. Further, an appropriately 
saturated and stable air-fuel mixture with superior ignition 
characteristics is provided in the region of the igniting tip portion of 
the spark plug, i.e. in the central portion of the engine combustion 
chamber, and this provides a tendency towards stratified combustion, which 
allows the limit in the lean direction for weakening the air-fuel mixture 
to be yet further extended, without any danger that any ignitability 
problem should be generated in the central region of the combustion 
chamber where said igniting tip portion of the spark plug is typically 
located. The flame propagation distance in the combustion chamber is 
shortened, in comparison to the case in which the spark plug is located at 
one side of the combustion chamber, and therefore so called compact 
combustion becomes possible of attainment, and extension in the lean 
direction of the limit for air-fuel mixture combustion and improvement in 
the mechanical octane value of the engine are made available. 
Further, according to one particular specialization of the present 
invention, the diverting means may comprise a notch portion formed in said 
control valve, which should preferably be formed in the edge of said 
control valve which is on the side thereof towards said generally helical 
intake passage, and/or is that edge of said control valve which is its 
downstream edge when said control valve is in its position to maximize the 
flow resistance of said generally straight intake passage. Alternatively, 
according to another alternative particular specialization of the present 
invention, said diverting means may comprise an auxiliary passage formed 
from upstream of said control valve to a portion of said generally 
straight intake passage near the downstream end thereof. Either of these 
particular specializations may be applied in any individual case, 
according to conditions.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will now be described with reference to the preferred 
embodiments thereof, and with reference to the figures. 
The First Preferred Embodiment 
Construction 
In the first preferred embodiment of the cylinder head intake port 
structure of the present invention, shown in longitudinal sectional view 
in FIG. 1 and in transverse sectional view in FIG. 2, the reference 
numeral 1 denotes the cylinder block of the engine, while on this cylinder 
block 1 there is fitted a cylinder head, which is the first preferred 
embodiment of the cylinder head intake port structure of the present 
invention, denoted by the reference numeral 2. The cylinder block 1 is 
formed with a plurality of cylinder bores 3 of which only one is shown in 
FIG. 1 because the section of FIG. 1 is taken in a plane including the 
central longitudinal axis of said shown cylinder bore 3 and substantially 
perpendicular to the plane including the central longitudinal axes of all 
said cylinder bores 3. In this cylinder bore 3 there reciprocates a piston 
4, and between said piston 4, said cylinder head 2, and the upper portion 
of said cylinder bore 3 there is defined a combustion chamber 5 for this 
piston and cylinder. And the fitting of the cylinder head 2 to the 
cylinder block 1 is done by the use of cylinder head bolts, not 
particularly shown, fitted through cylinder head bolt holes formed in 
bosses, not particularly shown, formed in the cylinder head 2 between each 
pair of adjacent cylinders and at the ends of the row of cylinders. 
For each cylinder, the cylinder head 2 is formed with two intake ports 6 
and 7 and two exhaust ports 8a and 8b, all four of which which open via 
respective valve seats to the combustion chamber 5, with the centers of 
said four valve seats approximately at the corners of a square, as 
generally shown in FIG. 2. Thus, this internal combustion engine is of the 
four valve per cylinder type. And the intake ports 6 and 7 for each of the 
cylinders of this engine are arranged on the one side of the cylinder 
block 1 and the cylinder head 2, in the longitudinal direction of said 
cylinder head 2 along the row of cylinders thereof (which corresponds to 
the direction perpendicular to the drawing paper in FIG. 1 and to the 
horizontal direction in FIG. 2); and, similarly, the exhaust ports 8a and 
8b for each of the various cylinders are arranged on the other side to 
said one side of the cylinder block 1 and of the cylinder head 2. Poppet 
valves 9 and 10 (of which only the poppet valve 9 can be seen in the 
sectional view of FIG. 1) of a per se known type, mounted in per se known 
valve guides fitted in the cylinder head 2, are provided for cooperating 
with intake valve seats inset around the edges of each of the intake ports 
6 and 7 where they open to the combustion chamber 5, so as to provide 
open/close control of communication between said intake ports 6 and 7 and 
the combustion chamber 5; and two other poppet valves 11a and 11b, also 
per se known and mounted in per se known valve guides fitted in the 
cylinder head 2, and again only one of which can be seen in FIG. 1, are 
provided for similarly cooperating with exhaust valve seats inset around 
the edges of the exhaust ports 8a and 8b where they open to the combustion 
chamber 5, so as similarly to provide open/close control of communication 
between the communication between said exhaust ports 8a and 8b and said 
combustion chamber 5. And by actuation of these intake poppet valves 9 and 
10 and exhaust poppet valves 11a and 11b by a per se known type of valve 
gear not particularly shown, the internal combustion engine is caused to 
operate according to an Otto cycle so as to generate rotational power, as 
is per se conventional. And, as best seen in FIG. 2, substantially in the 
middle of the portion of the cylinder head 2 defining the roof of the 
combustion chamber 5 there is formed a screwed hole 12 for fitting a spark 
plug 13 thereinto. 
In more detail, the cylinder head is formed with an intake plenum 19 
opening at its outside left side as seen in the figures, and this intake 
plenum branches into the two intake ports 6 and 7. The intake port 6 is 
formed as a generally straight intake passage, while the other intake port 
7 is formed as a generally helical intake passage. A flow of air-fuel 
mixture is sucked into the combustion chamber 5 of the engine from a 
carburetor, not particularly shown, fitted to an intake manifold 17 which 
is fitted to this cylinder head 2 and is formed with an intake passage 20 
abutted against the intake plenum 19 so as to be communicated therewith. 
This flow of air-fuel mixture first enters the cylinder head 2 into the 
intake plenum 19 upstream of the two intake ports 6 and 7, and then is 
divided by impinging upon the upstream edge of a dividing wall 30 which 
separates said two intake ports 6 and 7, so that part of said air-fuel 
mixture flow enters into the upstream end of the generally straight intake 
port 6 while the remainder of said air-fuel mixture flow enters into the 
upstream end of the generally helical intake port 7. The generally 
straight intake port 6 debouches into the combustion chamber 5 through the 
valve seat controlled by the intake poppet valve 9, while the generally 
helical intake port 7 debouches into the combustion chamber 5 through the 
valve seat controlled by the other intake poppet valve 10. Thus, the lower 
side as seen in the view of FIG. 2 of the downstream portion of the 
air-fuel mixture intake system defines the generally helical intake port 
7, so that air-fuel mixture flowing through this generally helical intake 
port 7, when the intake poppet valve 10 is opened of course, impinges 
against a vortex portion 31 formed around the stem of said intake poppet 
valve 10 in said helical port 7 and is imparted with substantial swirling 
motion. 
In the upstream end or intake end of the generally straight intake port 6, 
just downstream of where said generally straight intake port 6 branches 
off from the intake plenum 19, there is provided a butterfly type air-fuel 
mixture intake control valve 14, which is fixedly mounted on a shaft not 
particularly shown and is selectively positioned via said shaft by an 
actuating device of a per se well known sort, likewise not particularly 
shown, to either one of a closed position as shown in FIGS. 2 and 3 in 
which said air-fuel mixture intake control valve 14 substantially closes 
said upstream end of said generally straight intake port 6 while of course 
leaving uninterfered--with said generally helical intake port 7, or an 
open position, angularly spaced approximately 90 from said shown closed 
position, in which said air-fuel mixture intake control valve 14 
substantially leaves said upstream end of said generally straight intake 
port 6 open and uninterfered with. For example, this air-fuel mixture 
intake control valve 14 may be controlled by said actuating device so as 
substantially to close said generally straight intake port 6, when and 
only when engine load is below a certain determinate value. 
Particularly according to the inventive concept of the present invention, 
the intake control valve 14 is formed with a cutaway portion 15 on its 
side towards the generally helical intake port 7, i.e. on its side towards 
the center of the intake port structure, so that the direction looking 
through said cutaway portion 15 down the generally straight intake port 6 
in the direction of air-fuel mixture flow towards the combustion chamber 5 
aims generally at or near the spark plug 13. This cutaway portion or notch 
portion 15 is preferably formed with a relatively small dimension, the 
cross sectional area thereof being more preferably about 15% or less of 
the cross sectional area of the portion of the generally straight intake 
port 6 at which the intake control valve 14 is fitted. And, as shown in 
FIG. 2, when the intake control valve 14 is selectively positioned via its 
shaft by the actuating device therefor to its closed position in which 
said valve 14 substantially closes said upstream end of said generally 
straight intake port 6, then the cutaway portion 15 thereof is positioned 
at its most downstream side, i.e. the edge of said air-fuel mixture intake 
control valve 14 in which said cutaway notch portion 15 is cut is the 
downstream edge of said valve 14 when said valve 14 is in the closed 
position, while the edge opposite to said notched edge is in such 
circumstances the upstream edge thereof. 
Further, according to a particular specialization of the inventive concept 
of the present invention, the side of the intake manifold 17, just where 
the downstream end of said intake manifold 17 is abutted to the side of 
the cylinder head 2 against the intake plenum 19, is formed with a bulge 
18, configured in this example as defined by a gradually inwardly sloping 
wall 18a on its upstream side and a sharply outwardly extending wall 18b 
on its downstream side. Thus, when air-fuel mixture is being sucked in 
through the intake manifold 17 into the intake plenum 19 by the operation 
of the internal combustion engine, said air-fuel mixture is preferentially 
deflected towards the central portion of the intake plenum 19 by this 
bulge 18, thus being preferentially directed towards the central portion 
of the control valve 14 which is on the side of the generally helical 
intake passage 9, i.e. towards the side of said control valve 14 which is 
formed with the notched portion 15. 
Operation 
This first preferred embodiment of the intake port structure of the present 
invention operates as follows. 
When the air-fuel mixture intake control valve 14 is in the closed 
operational condition--typically as mentioned above when engine load is 
lower than a determinate value--then flow of air-fuel mixture through the 
generally straight intake port 6 is interrupted, and most of the air-fuel 
mixture flow inhaled by the engine from the carburetor (not shown) through 
the intake manifold 17 enters into the upstream end of the generally 
helical intake port 7, and passes through the intake valve port controlled 
by the intake poppet valve 10 into the combustion chamber 5 with a 
substantial amount of swirling being imparted to said sucked in air-fuel 
mixture as it enters said combustion chamber 5 by the vortex portion 31 
formed around the stem of said intake poppet valve 10; this swirling is, 
as shown by the arrow A in FIG. 2, in the counterclockwise direction as 
seen from the point of view of that figure around the central axis of the 
cylinder bore 3. However, a certain relatively small amount of air-fuel 
mixture is also sucked, from the intake plenum 19 through the notched 
portion 15 of the closed control valve 14, along down through the 
generally straight intake port 6 as shown by the arrow "B" in FIG. 2 on 
the side thereof towards the generally helical intake port 7, and comes 
squirting out the downstream end of said generally straight intake port 6 
into the combustion chamber 5 substantially straight at the ignition point 
of the spark plug 13 in a direct stream as shown by the arrow "C" in FIG. 
2, cutting substantially radially across the aforementioned 
counterclockwise swirling flow "A" of the main flow of sucked in air-fuel 
mixture. Thereby, the initially centrifugally dispersed air-fuel mixture 
in said counterclockwise swirling flow "A" is entrained into said direct 
flow "C" and is sucked towards the ignition point of the spark plug 13 as 
a combined flow "D", thus ensuring that the air-fuel mixture in the center 
area of the combustion chamber 5 is not particularly weaker than the 
air-fuel mixture at the edge area thereof--in contrast to what was the 
case with the prior art as described earlier in this specification. 
Therefore, even if the overall air/fuel ratio as supplied by the 
carburetor (not particularly shown) is set to be relatively weak, thus 
taking advantage of an extension in the lean direction of the air/fuel 
ratio of the air-fuel mixture for the engine, nevertheless a relative 
plenitude of fuel is available near the ignition point of the spark plug 
13, and accordingly good ignition performance becomes available, and 
engine misfiring is not liable to occur. Further, since the collision of 
the counterclockwise swirling flow "A" with the direct flow "C" engenders 
microturbulence in the mixed flow, the ignition characteristics of the 
resulting mixture flow are further improved, and thereby the limit for 
weakening the air-fuel mixture is further extended. And, since the direct 
flow "C" collides with the counterclockwise swirling flow "A" near the 
final point of said counterclockwise swirling flow "A", said direct flow 
"C" does not greatly attenuate said counterclockwise swirling flow "A". 
Yet further, since the direct flow "C" spurting out of the downstream end 
of the generally straight intake port 6 in fact is aimed slightly to the 
upper side as seen in the FIG. 2 view of the igniting portion of the spark 
plug 13, i.e. slightly on the side of said spark plug 13 against the 
direction of the swirling air-fuel flow "A" in the combustion chamber 5 
induced by the generally helical intake port 7, thereby the 
macroturbulence or large scale swirling of the mixture in the combustion 
chamber 5 in the collision area between the direct flow "C" and the 
counterclockwise swirling flow "A" is partially cancelled, thereby again 
improving ignition performance, militating against engine misfiring, 
improving ignition characteristics, and further extending the limit for 
weakening the air-fuel mixture. 
On the other hand, when the air-fuel mixture intake control valve 14 is in 
the open operational condition--typically when engine load is greater than 
the previously mentioned determinate value--then most of the air-fuel 
mixture flow inhaled by the engine from the carburetor (not shown) through 
the intake manifold 17 enters into the combustion chamber 5 through the 
generally straight intake port 6, with only a minor amount passing through 
the generally helical intake port 7. Accordingly, only a relatively low 
amount of swirling as a whole is imparted to said sucked in air-fuel 
mixture as it enters said combustion chamber 5 by the vortex portion 31 
formed around the stem of the intake poppet valve 10. Thus, good 
volumetric efficiency for the engine is obtained. 
The fact that, when the intake control valve 14 is positioned to its closed 
position in which said valve 14 substantially closes said upstream end of 
the generally straight intake port 6, then the notched edge of said valve 
14 containing the cutaway portion 15 thereof is positioned at the most 
downstream side of said air-fuel mixture intake control valve 14, while 
the edge opposite to said notched edge is in such circumstances the 
upstream edge thereof, is an important feature of this first preferred 
embodiment of the present invention. According to this, liquid fuel which 
has accumulated on the walls of the intake manifold 17 which define the 
intake passage 20, and on the intake control valve 14 itself, is able to 
trickle past said control valve 14, across the surface thereof which acts 
as a guide panel, through said cutaway portion 15 and thence to flow 
through the generally straight intake port 6 to flow out thereof 
substantially directly above the intake poppet valve 9, thereby to enter 
virtually directly into the combustion chamber 5. Thereby, speed of fuel 
supply response is improved. This guiding of the liquid fuel accumulated 
on the walls of the intake manifold 17 is substantially aided by the bulge 
18 formed on the side wall of said intake manifold 17, and further the 
atomization of at least a portion of said liquid fuel is appropriately 
encouraged by the particular configuration of this bulge 18 as being 
defined by the gradually inwardly sloping wall 18a on its upstream side 
and the sharply outwardly extending wall 18b on its downstream side, since 
this configuration aids with the shearing away of the liquid fuel as it 
trickles past the summit of the bulge 18. 
The Second Preferred Embodiment 
The second preferred embodiment of the cylinder head intake port structure 
of the present invention is shown in FIGS. 4 and 5, in a similar manner to 
FIGS. 1 and 2 respectively relating to the first preferred embodiment; 
and, in FIGS. 4 and 5, like reference numerals to those in FIGS. 1 and 2 
denote like parts. This second preferred embodiment differs from the first 
preferred embodiment described above, in that the control valve 14 for the 
generally straight intake port 6 is not formed with any notched or cutaway 
portion such as the portion 15 of the first preferred embodiment, but on 
the other hand, in addition to the other structures described with 
relation to said first preferred embodiment, a substantially straight 
auxiliary passage 20 is provided as extending from an inlet portion 21 
upstream of the air-fuel mixture intake control valve 14, along 
substantially parallel to, as seen in plan view, and slightly below the 
generally straight intake port 6, on the side thereof towards the 
generally helical intake port 7, to an outlet portion 22 located proximate 
to the valve seat at the downstream end of said generally straight intake 
port 6, i.e. to the valve seat controlled by the one 9 of the intake 
poppet valves. This auxiliary passage 20 is as shown in the figures 
substantially straight and slopes relatively gently downwards, considering 
the engine in the orientation shown in FIG. 4 which is a typical operating 
orientation therefor. Thus, said substantially straight auxiliary passage 
20 bypasses the air-fuel mixture intake control valve 14, performing this 
function instead of the gap 15 that was formed therein in the case of the 
first preferred embodiment described above, and leads a certain quantity 
of the air-fuel mixture supplied by the carburetor (not particularly 
shown) to the intake passage formed in the intake manifold 17, directly to 
just upstream of the intake poppet valve 9. Particularly according to a 
specialization of the concept of this second preferred embodiment of the 
present invention, this substantially straight auxiliary passage 20, when 
said poppet valve 9 is open, points generally at the igniting portion of 
the spark plug 13; although, more exactly, according to a particular 
subfeature of said shown second preferred embodiment of the present 
invention, said substantially straight auxiliary passage 20 in fact points 
slightly to the upper side as seen in the FIG. 5 view of said igniting 
portion of the spark plug 13, i.e. slightly on the side thereof against 
the direction of the swirl induced by the generally helical intake port 7. 
Also, according to a particular distinguishing subfeature of this second 
preferred embodiment of the cylinder head intake port structure of the 
present invention, the upstream end portion 21 of this substantially 
straight auxiliary passage 20 opens to the floor of the intake plenum 19. 
The cross sectional area of the substantially straight auxiliary passage 
20 is substantially less than the cross sectional areas of the generally 
straight intake port 6 and the generally helical intake port 7, being 
about one fifth thereof in a typical constructional implementation. And 
the bulge 18 is formed as defined by the walls 18a and 18b, just as in the 
first preferred embodiment described above, and functions substantially as 
in said first preferred embodiment. 
In this second preferred embodiment, in an analogous fashion to what 
occurred with the first preferred embodiment, when the control valve 14 is 
positioned by the actuating means (not shown) therefor to the closed 
position, a certain relatively small amount of air-fuel mixture is also 
sucked from the intake passage 20 of the intake manifold 17 through the 
substantially straight auxiliary passage 20 sloping relatively gently 
downwards, and comes squirting out of the downstream end of said 
substantially straight auxiliary passage 20 substantially straight at the 
ignition point of the spark plug 13 in a direct stream as shown by the 
arrow "B" in FIG. 5, cutting substantially radially across the 
counterclockwise swirling flow "A" of the main flow of sucked in air-fuel 
mixture, induced by the generally helical intake port 7. Thereby, the 
initially centrifugally dispersed air-fuel mixture in said 
counterclockwise swirling flow "A" is entrained into said direct flow "B" 
and is sucked towards the ignition point of the spark plug 13 along with 
said direct flow "B", thus, as in the case of the first preferred 
embodiment, ensuring that the air-fuel mixture in the center area of the 
combustion chamber 5 is not particularly weaker than the air-fuel mixture 
at the edge area thereof. Therefore, even if the overall air/fuel ratio as 
supplied by the carburetor (not particularly shown) is set to be 
relatively weak, a relative plenitude of fuel is available near the 
ignition point of the spark plug 13, and accordingly good ignition 
performance becomes available, and engine misfiring is not liable to 
occur; and, further, since the collision of the counterclockwise swirling 
flow "A" with the direct flow "B" engenders microturbulence in the mixed 
flow, the ignition characteristics of the resulting mixture flow are 
further improved, and thereby the limit for weakening the air-fuel mixture 
is further extended. As before, since the direct flow "B" collides with 
the counterclockwise swirling flow "A" near the final point of said 
counterclockwise swirling flow "A", said direct flow "B" does not greatly 
attenuate said counterclockwise swirling flow "A". Yet further, since, 
according to the previously mentioned particular feature of the shown 
second preferred embodiment of the present invention, the direct flow "B" 
spurting out of the substantially straight auxiliary passage 20 in fact is 
aimed slightly to the upper side as seen in the FIG. 5 view of the 
igniting portion of the spark plug 13, i.e. slightly on the side of said 
spark plug 13 against the direction of the swirling air-fuel flow "A" in 
the combustion chamber 5 induced by the generally helical intake port 7, 
thereby the macroturbulence or large scale swirling of the mixture in the 
combustion chamber 5 in the collision area between the direct flow "B" and 
the counterclockwise swirling flow "A" is partially cancelled, thereby 
again improving ignition performance, militating against engine misfiring, 
improving ignition characteristics, and further extending the limit for 
weakening the air-fuel mixture. 
On the other hand, when the air-fuel mixture intake control valve 14 is in 
the open operational condition--typically when engine load is greater than 
the previously mentioned determinate value--then most of the air-fuel 
mixture flow inhaled by the engine from the carburetor (not shown) through 
the intake manifold 17 enters into the combustion chamber 5 through the 
generally straight intake port 6, with only a minor amount passing through 
the generally helical intake port 7. Accordingly, only a relatively low 
amount of swirling as a whole is imparted to said sucked in air-fuel 
mixture as it enters said combustion chamber 5 by the vortex portion 31 
formed around the stem of the intake poppet valve 10. Thus, good 
volumetric efficiency for the engine is obtained. Since a certain 
relatively small amount of air-fuel mixture is also, in this operational 
condition as well, sucked through the substantially straight auxiliary 
passage 20 into the center area of the combustion chamber 5, thereby 
engine volumetric efficiency is increased even further. 
Further, according to an important feature of this second preferred 
embodiment of the present invention, liquid fuel which has accumulated on 
the walls of the intake manifold 17 which define the intake passage 20 is 
able to trickle down into the upstream end portion 21 of the auxiliary 
passage 20 and is able to be transferred through said auxiliary passage 20 
to flow out thereof substantially directly above the intake poppet valve 
9, thereby to enter virtually directly into the combustion chamber 5. 
Thereby, again, speed of fuel supply response is furthermore improved. 
A further beneficial effect of this second preferred embodiment is that, in 
all operational circumstances, some of the air-fuel mixture supplied to 
the intake plenum 19 from the intake manifold 17 is supplied into the 
straight intake port 6, and inevitably, when said air-fuel mixture intake 
control valve 14 is in the closed operational condition as shown in FIG. 
5, some of the fuel in this air-fuel mixture will condense out in liquid 
form on said air-fuel mixture intake control valve 14 and on the defining 
surfaces of the straight intake port 6 immediately above said valve 14. 
This condensed out liquid fuel, according to the shown second preferred 
embodiment type construction, reliably trickles downwards and enters into 
the upstream end portion 21 of the substantially straight auxiliary 
passage 20, to pass down said auxiliary passage 20 and to then exit 
through the exit portion 22 thereof, to be deposited near the intake 
poppet valve 9 for entering into the combustion chamber 5 of the engine. 
Thus, worsening of the fuel supply response during transient engine 
operational conditions is militated against, and a relatively rich mixture 
is supplied to the combustion chamber from the straight intake port 6, 
thus providing a stable rich mixture good for ignition purposes in the 
ignition region of the spark plug 13, and thus extending even further the 
weak mixture limit of combustibility. 
Although the present invention has been shown and described in terms of the 
preferred embodiments thereof, and with reference to the appended 
drawings, it should not be considered as being particularly limited 
thereby, since the details of any particular embodiment, or of the 
drawings, could be varied without, in many cases, departing from the ambit 
of the present invention. Accordingly, the scope of the present invention 
is to be considered as being delimited, not by any particular perhaps 
entirely fortuitous details of the disclosed preferred embodiments, or of 
the drawings, but solely by the scope of the accompanying claims, which 
follow.