Intake valve mechanism for preventing back flow of exhaust gas

The intake valve mechanism employs a back-flow valve to prevent undesirable back-flow of gases from a combustion chamber of an internal combustion engine out an intake port of the chamber during a period of time in which a poppet valve for the intake port of the chamber is open. The back-flow valve is positioned between an intake port valve seat and the intake port poppet valve for blocking the intake port in response to pressure in the combustion chamber. To minimize air-fuel resistance through the intake port, a spring is employed for continuously biasing the back-flow valve to track the movement of the poppet valve, the spring having sufficient strength to prevent the back-flow valve from blocking the intake port when the poppet valve is open until the pressure in the combustion chamber reaches a predetermined value.

BACKGROUND OF THE INVENTION 
This invention is directed to an improved intake valve mechanism for an 
internal combustion engine and particularly to a back-flow valve designed 
to prevent gases in a combustion chamber from being blown back into an 
air-fuel intake port of the chamber and yet not impede the normal flow of 
air-fuel mixture passing into the chamber through the intake port. 
In some four cycle internal combustion engines, intake and exhaust valves 
to the combustion chamber are both kept open simultaneously for a certain 
period in order to increase exhaust efficiency of the engine. However, as 
a consequence of both valves being open simultaneously, part of the 
exhaust gases burnt in the combustion chamber are blown past the open 
intake valve and back into the intake passage of the engine where the 
exhaust gases are mingled with the air-fuel mixture flowing through the 
intake passage during the next engine cycle. The exhaust gases impair 
ignition of the air-fuel mixture and therefore act to make the entire 
combustion operation of the engine unstable. The instability and 
accompanying inefficiency are particularly acute in the medium to low 
speed operational ranges of the engine and during idling of the engine. 
In addition, modern internal combustion engines which are adapted to burn 
lean air-fuel mixtures in order to decrease the amount of toxic substances 
usually present in the engine exhaust gas, demand strict control of the 
air-fuel ratio. In this type of engine, the mingling of exhaust gas with 
the air-fuel mixture in the intake passage of the engine creates an even 
more acute operational deficiency. 
The undesirable back-flow of gases from the combustion chamber to the 
intake passage is not limited to only the overlap period when both intake 
and exhaust valves are open. Back-flow can also occur when the intake 
valve is phased to close slightly behind the time at which the piston 
reaches bottom dead center of its cycle in order to raise the intake 
efficiency of the engine in its high speed operational range. In the 
medium to low speed range, fresh air-fuel mixture which enters the 
combustion chamber before the piston reaches the bottom dead center is 
forced back through the intake passage during the time when the piston 
passes bottom dead center and the intake valve remains open. The result is 
that in the medium to low speed range the intake efficiency of the engine 
is lowered instead of being improved. 
The problem of gas back-flow is not limited to four cycle internal 
combustion engines. Even in a two cycle internal combustion engine, 
exhaust gases may blow back into the combustion chamber through the 
scavenging port due to pressure differentials set up by the operational 
cycle of the intake port. 
In order to improve the output performance of such internal combustion 
engines, it is desirable to provide some means to prevent gas back-flow. 
The prior art has, to date, dealt with the problem of gas-back flow by 
employing an auxiliary intake or back-flow prevention valve slidably 
carried on a conventional intake poppet valve. For example, U.S. Pat. No. 
3,903,855 discloses a back-flow intake valve normally spring-biased into 
closed position upstream of the intake poppet valve. The back-flow 
prevention valve is opened by pressure in the intake passage exceeding the 
pressure in the combustion chamber during the time interval when the 
intake poppet valve is open. By biasing the back-flow prevention valve in 
a normally closed position, the mass of the back-flow prevention valve 
functions as additional resistance against the intake flow of air-fuel 
mixture from the intake passage during the intake stroke and therefore 
lowers the intake efficiency of the engine. In the German Pat. No. 460,151 
a back-flow prevention valve is disclosed with no biasing mechanism 
whatsoever and thus the intake flow of air-fuel mixture from the intake 
passage to the combustion chamber is once again faced with resistance from 
the mass of the back-flow prevention valve. 
The present invention improves upon the intake valves of the prior art 
designed to prevent back-flow of gases in internal combustion engines. The 
present invention effectively combines a back-flow prevention valve with a 
biasing arrangement to result in a commercially-acceptable intake valve 
which not only effectively prevents back flow of gases into the intake 
passage of an internal combustion engine but also minimizes resistance 
against the intake flow of air-fuel mixture during the intake stroke of 
the engine and therefore maximizes the intake efficiency of the engine. 
Accordingly, it is a prime object of this invention to provide a new and 
improved intake valve mechanism for preventing the back-flow of gases from 
the combustion chamber out the intake port. 
It is a further object of this invention to provide an intake valve 
mechanism for preventing back-flow of gases that is simple in construction 
and easy to manufacture. 
Another object of this invention is to provide an intake valve mechanism 
for preventing back-flow of gases that is designed to maximize the intake 
efficiency of the engine. 
Still another object of this invention is to provide an intake valve 
mechanism for preventing back flow of gases that is designed to minimize 
the volume of back flow. 
Additional objects and advantages of the invention will be set forth in 
part in the description which follows, and in part will be obvious from 
the description, or may be learned by practice of the invention. The 
objects and advantages of the invention may be realized and attained by 
means of the instrumentalities and combinations particularly pointed out 
in the appended claims. 
SUMMARY OF THE INVENTION 
To achieve the foregoing objects and in accordance with the purpose of the 
invention, as embodied and broadly described herein, the intake valve 
mechanism for preventing the back-flow of gases from a combustion chamber 
of an internal combustion engine out an intake port of the chamber 
comprises poppet-valve means for alternately opening and blocking the 
intake port; back-flow valve means positioned between the poppet-valve 
means and the intake port for blocking the intake port in response to 
pressure in the combustion chamber; and means for continuously biasing the 
back-flow valve means to track the movement of the poppet valve, the 
biasing means having sufficient strength to prevent the back-flow valve 
means from blocking the intake port when the poppet valve is open until 
the pressure in the combustion chamber reaches a predetermined value. 
Preferably, the poppet valve means includes an intake valve having a stem 
and further having a disc portion mounted on one end of the stem, the 
poppet valve means further including a valve guide for reciprocatingly 
supporting the stem to allow the disc portion to selectively open and 
block the intake port of the combustion chamber; the back-flow valve means 
includes a back-flow prevention valve having a hollow base and further 
having an expanded portion mounted on one end of the base, the hollow base 
being reciprocatingly mounted concentric to the stem to allow the expanded 
portion to slide back and forth between the intake port and the disc 
portion; and the biasing means includes a spring positioned concentric to 
the hollow base of the back-flow prevention valve to bias the expanded 
portion against the disc portion until the gases in the combustion chamber 
reach the predetermined pressure sufficient to overcome the spring and 
force the expanded portion away from the disc portion to block the intake 
port. 
It is also preferred that the expanded portion of the back-flow prevention 
valve extends beyond the disc portion of the intake valve. 
It is also preferred, in an alternative embodiment, that the disc portion 
of the intake valve extends beyond the expanded portion of the back-flow 
valve. 
It is also preferred that the disc portion of the intake valve includes 
notches along the periphery of the disc portion and in the alternative, 
the disc portion of the intake valve includes openings penetrating through 
the disc portion, in either case to allow the gases in the combustion 
chamber to continuously exert pressure on the extended portion of the 
back-flow prevention valve. 
the accompanying drawings, which are incorporated in and constitute a part 
of this specification, illustrate embodiments of the invention and, 
together with the description, serve to explain the principles of the 
invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Reference will now be made in detail to the present preferred embodiment of 
the invention, an example of which is illustrated in the accompanying 
drawings. 
Referring now to FIG. 1, a cylinder head 1 is provided with an intake 
passage 2 to carry a flow of air-fuel mixture into combustion chamber 3 of 
an internal combustion engine. A valve seat 4 is fitted at intake port 5 
of intake passage 2 to form an opening into combustion chamber 3 through 
which the air-fuel mixture passes. 
In accordance with the invention, there is a poppet valve means for 
alternately opening and blocking intake port 5. As embodied herein, the 
poppet-valve means includes an intake valve 6 having a stem 8 and further 
having a disc portion 7 mounted on one end of stem 8. The poppet-valve 
means further includes a valve guide 9, for reciprocatingly supporting 
stem 8 to allow disc portion 7 to selectively open and block intake port 5 
of the internal combustion engine. 
In accordance with the invention, there is a back-flow valve means 
positioned between the poppet-valve means and the intake port for blocking 
the intake port in response to pressure in the combustion chamber. As 
embodied herein, this back-flow valve means includes a back-flow 
prevention valve 10 having a hollow base 12 and further having an expanded 
portion 11 mounted on one end of base 12. The hollow base 12 is 
reciprocally mounted concentric to stem 8 to allow the expanded portion 11 
to slide back and forth between intake port 5 and disc portion 7. 
In accordance with the invention, there is means for continuously biasing 
the back-flow valve means to track the movement of the poppet valve means, 
this biasing means having sufficient strength to prevent the back-flow 
valve means from blocking the intake port when the poppet valve means is 
open until pressure in the combustion chamber reaches a predetermined 
value. As embodied herein, this biasing means includes a spring 13 
positioned concentric to hollow base 12 of back-flow prevention valve 10 
to bias the expanded portion 11 against the disc portion 7 until the 
pressure in the combustion chamber 3 is sufficient to overcome the 
combined strength of spring 13 and the pressure in intake passage 2. Upon 
reaching this predetermined pressure, the gases in combustion chamber 3 
force the expanded portion 11 away from disc portion 7 and against valve 
seat 4 to block intake port 5. 
Expanded portion 11 extends to an edge 14 that in the preferred embodiment 
shown in FIG. 1 projects beyond the edge of disc portion 7 to receive the 
pressure gases back-flowing from combustion chamber 3 into intake passage 
2 at an initial stage of such back-flow. The expanded portion 11 is 
interposed between the disc portion 7 and the intake port 5 so that intake 
port 5 is closed when intake valve 6 is operated to pull expanded portion 
11 and disc portion 7 against valve seat 4. 
Preferably, spring 13 is positioned between valve guide 9 at one end and 
back flow prevention valve 10 at the other end to press the expanded 
portion 11 against disc portion 7 of intake valve 6. 
In operation of the present invention, reference is made to FIG. 2 (a) 
which illustrates the position of intake valve 6 while the engine is on an 
exhaust stroke. During this time, the combustion chamber 3 is filled with 
burnt exhaust gas, and an exhaust gas valve, not shown, is opened to 
enable the exhaust gases to escape from combustion chamber 3. In the 
ordinary engine, the intake valve 6 starts to open when the exhaust valve 
has not been perfectly closed creating a phenomenon known as the overlap 
period wherein both intake and exhaust valves are simultaneously opened. 
During this overlap period, if the pressure of the exhaust gas in 
combustion chamber 3 is higher than the pressure of the air-fuel mixture 
in intake passage 2, back-flow of exhaust gas would occur out intake port 
5. However, in accordance with the present invention, as intake valve 6 is 
lowered as shown in FIG. 2 (b) by valve actuating means not shown, the 
pressure of the exhaust gas in combustion chamber 3 is received at edge 14 
of expanded portion 11 of intake valve 6 to hold prevention valve 10 in 
its seated position against valve seat 4 and close off intake port 5. In 
this state, spring 13 is compressed and exerts a force which attempts to 
push the back-flow prevention valve 10 away from valve seat 4 to open 
intake port 5. Accordingly, when the pressure in combustion chamber 3 
decreases below the sum of the pressure of spring 13 and the pressure of 
the air-fuel mixture in intake passage 2, the back flow prevention valve 
10 is forced by spring 13 to depart from seat 4 of intake valve 5, and 
expanded portion 11 becomes pressed against disc portion 7 to open intake 
port 5 as illustrated in FIG. 2 (c). 
As the pressure of the exhaust gases in combustion chamber 3 becomes 
greater than the combined pressure of spring 13 and the pressure of the 
air-fuel mixture in intake passage 2 while both intake valves 6 and back 
flow prevention valve 10 are open, the operation of the intake valve 
mechanism proceeds from the condition of FIG. 2 (c) back to that of FIG. 2 
(b) and intake port 5 is once again blocked by back-flow prevention valve 
10. 
As will be understood in the above description, the intake valve mechanism 
of the present invention offers a back-flow prevention valve that is 
simple in construction and exact in operation. Also, since the back-flow 
prevention valve is used to close the intake port, the volume of exhaust 
gas back flow into the intake port 5 is much decreased as compared with a 
conventional engine in which there is no back-flow prevention valve or 
only a lead valve is fitted into the intake passage. Only a very slight 
amount of gas that is blown back as a result of the delay in response of 
the back-flow prevention valve 10 enters into the intake passage 2. 
Consequently, distrubance of the air-fuel ratio that might otherwise be 
caused by the back-flow exhaust gas is significantly minimized. In 
addition, the fact that the back-flow prevention valve 10 is continuously 
urged by spring 13 away from intake port 5 removes the resistance the mass 
of back flow prevention valve 10 creates against the intake flow of the 
air-fuel mixture. Accordingly, the intake valve mechanism of the present 
invention holds the lowering of intake efficiency to an absolute minimum. 
The teachings of the present invention are in no means limited to the 
particular embodiment shown in FIG. 1, but instead can be practiced in 
various other forms of preferred embodiments as described below. 
Thus, FIG. 3 discloses an intake valve mechanism constructed in accordance 
with the teachings of the invention in which the expanded portion 11 of 
the back-flow prevention valve 10 extends beyond the disc portion 7 of 
intake valve 6. In particular, edge 14' of the expanded portion 11 of the 
back-flow prevention valve is projected a considerable distance beyond the 
edge of disc portion 7 of the intake valve 6. As a consequence, the 
pressure of the gases in combustion chamber 3 may be received by such over 
extended edge 14' with greater ease. 
In accordance with the invention, an embodiment of the intake valve 
mechanism disclosed in FIG. 4 includes an annular space 15 formed in base 
portion 12 of back-flow prevention valve 10 and spring 13' is positioned 
in annular space 15 with one end attached to base portion 12 and one end 
attached to disc portion 7 to bias the back-flow prevention valve 10 
against the disc portion 7 of intake valve 6 until the gas in the 
combustion chamber reached a predetermined pressure sufficient to overcome 
the spring 13' and force the extended portion 11 of back-flow prevention 
valve 10 away from the disc portion 7 to block intake port 5. 
In accordance with the invention, the embodiment shown in FIG. 5(a) 
discloses an intake valve mechanism wherein the disc portion 7 of intake 
valve 6 extends beyond the expanded portion 11 of back-flow prevention 
valve 10. Spring 13 is proportioned to result in expanded portion 11 being 
held away from disc portion 7 of intake valve 6 when intake valve 6 is 
opened as shown in FIG. 5(b). The space between expanded portion 11 and 
disc portion 7 allows the pressure of the gases in combustion chamber 3 to 
act on expanded portion 11 and hold expanded portion 11 against recessed 
seat 5' of intake port 5 whenever the pressure in combustion chamber 3 
exceeds the sum of the pressure of spring 13 and the pressure of the 
air-fuel mixture in intake passage 2. When intake valve 6 closes as shown 
in FIG. 5(c), a gap 17 of width H is momentarily created between expanded 
portion 11 and disc portion 7. However, as the pressure in gap 17 leaks 
off, expanded portion 11 is quickly forced against disc portion 7 by 
spring 13 to resume the position shown in FIG. 5(a ). 
Accordingly, this embodiment dispenses with extended edges 14 that are 
provided in the embodiments of FIGS. 1 and 3 to receive the pressure of 
gases in chamber 3 because this embodiment is designed to receive such gas 
pressure directly on expanded portion 11. 
In accordance with the invention, an embodiment is shown in FIGS. 6 and 7 
wherein the disc portion 7 of the intake valve 6 includes notches 16 along 
the periphery of the disc portion 7 for allowing gases in the combustion 
chamber 3 to continuously exert pressure on the expanded portion 11 of 
back-flow prevention valve 10. Accordingly, the pressure of the gases in 
combustion chamber 3 is introduced through notches 16 to gap 17 between 
the expanded portion 11 and the intake valve 6. This embodiment also makes 
it unnecessary to provide an edge 14 to receive the pressure of the gas 
back-flow as is done in the embodiments of FIGS. 1 and 3. 
In accordance with the invention, an additional embodiment is shown in 
FIGS. 8 and 9 wherein the disc portion 7 of said intake valve 6 includes 
openings 18 penetrating through disc portion 7 to allow gases in the 
combustion chamber 3 to continuously exert pressure on expanded portion 
11. This design permits the gas in combustion chamber 3 to pass through 
openings 18 into gap 17 between the extended portion 11 and intake valve 6 
accordingly making it unnecessary to provide the edges 14 to receive the 
pressure of the gas back flow as was done in the embodiments in FIGS. 1 
and 3. 
As was explained above with respect to FIGS. 1 and 2, the embodiments in 
FIGS. 3 through 9 also reliably prevent gases in the combustion chamber 3 
from being blown back into intake passage 2, thereby eliminating lowering 
of operational performance due to the poor ignition and irregular rotation 
of gases inherent in the medium to low speed ranges of the conventional 
internal combustion engine. In addition, the increased efficiency results 
in higher engine output and fuel economy. Finally, by utilizing a means 
for continuously biasing the back-flow prevention valve to track the 
movement of the intake valve, the resistance that the mass of back flow 
prevention valve 10 creates against the intake flow of the air-fuel 
mixture is eliminated and accordingly the intake efficiency of the engine 
is maximized. 
It will be apparent to those skilled in the art that various modifications 
and variations could be made in the intake valve mechanism of the 
invention without departing from the scope or spirit of the invention.