Exhaust gas recirculation valve

An exhaust gas recirculation valve comprising a back pressure control chamber connected with the exhaust pipe of an internal combustion engine via a throttling means, a membrane which constitutes a part of the wall defining said back pressure control chamber, the outside surface of said membrane being exposed to the atmospheric pressure while the inside surface of said membrane being closely opposed by an open end of a gas outlet tube so that said membrane and said open end constitute a valve structure for controlling the exhaust gas flow through the exhaust gas recirculation valve.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to the exhaust gas recirculation system (EGR 
System) for an internal combustion engine and, more particularly, an 
exhaust gas recirculation valve (EGR Valve) for controlling the amount of 
exhaust gas recirculated through the exhaust gas recirculation system. 
2. Description of the Prior Art 
It is known to be effective for reducing the emission of nitrogen oxide 
(NOx) from internal combustion engines that a part of the exhaust gas is 
recirculated to the intake air. In order to obtain the optimum effect of 
the exhaust gas recirculation in view of the overall performance of an 
internal combustion engine, it is considered favorable that the ratio of 
the amount of exhaust gas recirculated to the total amount of exhaust gas, 
i.e., the exhaust gas recirculation ratio, is constantly maintained at a 
predetermined value. In order to accomplish a constant exhaust gas 
recirculation ratio, a region is provided in the route of the exhaust gas 
recirculation extending from the exhaust pipe of an engine to the intake 
tube thereof, said region being constantly maintained at atmospheric 
pressure, wherein a throttling means of a predetermined throttling ratio 
is provided at the entrance of said particular region. Several examples of 
an exhaust gas recirculation valve based upon the abovementioned principle 
so as to accomplish a constant exhaust gas recirculation ratio are 
disclosed, for example, in Japanese Patent Application 35241/72, U.S. Pat. 
No. 3,799,131 and U.S. Pat. No. 3,802,402. However these conventional 
exhaust gas recirculation valves have relatively complicated structures 
and, furthermore, since in these valves the exhaust gas flow is controlled 
by a conventional valve element-valve seat structure, there is a drawback 
in that the tight contact between the valve element and the valve seat is 
obstructed by small particles contained in the exhaust gas, thereby 
resulting in an inaccurate control of the exhaust gas flow. Furthermore, 
since the valve element is movably supported by a valve stem which in turn 
is slidably supported by a guide means, the small particles contained in 
the exhaust gas also enter into the space between the valve stem and the 
guide means thereby obstructing smooth operation of the valve element. 
SUMMARY OF THE INVENTION 
It is the object of the present invention to remove the abovementioned 
drawbacks by providing an exhaust gas recirculation valve of a very simple 
structure wherein, however, a constant exhaust gas recirculation ratio is 
positively maintained based upon the aforementioned principle. 
Other objects and further scope of applicability of the present invention 
will become apparent from the detailed description given hereinafter; it 
should be understood, however, that the detailed description and specific 
examples, while indicating preferred embodiments of the invention, are 
given by way of illustration only, since various changes and modifications 
within the spirit and scope of the invention will become apparent to those 
skilled in the art from this detailed description. 
According to the present invention, the abovementioned object is 
accomplished by an exhaust gas recirculation valve comprising a back 
pressure control chamber connected with the exhaust pipe of an internal 
combustion engine via a throttling means, a membrane which constitutes a 
part of the wall defining said back pressure control chamber, the outer 
surface of said membrane facing opposite to the inside of said chamber and 
being exposed to atmospheric pressure, and a gas outlet tube having an 
open end positioned to closely oppose the inside surface of said membrane 
facing the inside of said chamber, the opening of said open end being 
controlled by said membrane, wherein the ratio of the opening area of said 
open end to effective pressure response area of said membrane is 
substantially smaller than 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the drawing, an internal combustion engine 1 diagrammatically 
shown in FIG. 1 takes in air or a fuel-air mixture through an intake tube 
2 and discharges exhaust gases through an exhaust pipe 3. An exhaust gas 
branch pipe 4 is branched from the exhaust pipe 3 and is connected to the 
exhaust gas recirculation valve of the present invention generally 
designated by 5. A gas outlet tube 6 having one end thereof incorporated 
within the exhaust gas recirculation valve extends from the valve and is 
connected to the intake tube 2 at the other end thereof. Thus, an exhaust 
gas recirculation system including the exhaust gas branch pipe 4, the 
exhaust gas recirculation valve 5 and the exhaust gas outlet tube 6 is 
established. 
The exhaust gas recirculation valve 5 comprises a vessel-like housing 7 and 
a membrane 8 which closes the open end of said housing thereby defining a 
back pressure control chamber 9. The chamber 9 is provided with an exhaust 
gas inlet port 10 which is connected with the exhaust gas branch pipe 4 
though a throttling means like an orifice 11 so as to be supplied with the 
exhaust gas separated from the exhaust gas flow in the exhaust pipe 3. A 
protective housing 12 is provided to cover the membrane 8. However, the 
protective housing has an opening or openings 13 so that the outer surface 
of the membrane 8 facing opposite to the inside of said back pressure 
control chamber 9 is constantly exposed to the atmospheric pressure. 
Within the back pressure control chamber 9 an open end 14 of the exhaust 
gas outlet tube 6 is positioned to closely oppose a central portion of 
said inside surface of the membrane 8. The open end of the tube 6 has a 
flat end face positioned substantially parallel to the flat central 
portion of the membrane 8 so that when the central portion of the membrane 
contacts the open end 14 of the exhaust gas outlet tube, the open end is 
closed. In this manner, the opening of the open end 14 of the exhaust gas 
outlet tube is controlled by the membrane 8. As explained in detail 
hereinunder, the central portion of the membrane 8 is applied with a light 
downward spring force as seen in the figure by a compression coil spring 
15. In other words, the central portion of the membrane 8 is applied with 
a resilient force which removes the central portion from the open end 14 
of the gas outlet tube 6. Element 16 designates a retainer for the 
compression coil spring 15. 
In the following, the operation of the exhaust gas recirculation valve 5 is 
explained. 
Denoting the exhaust gas flow by G.sub.E and substituting the throttling 
action effected by a muffler, etc. provided at an outlet portion of the 
exhaust pipe by that of an equivalent orifice 17 having flow coefficient 
C.sub.1 and flow area A, the relation between the exhaust gas pressure 
P.sub.E and the atmospheric pressure P.sub.O is given by the following 
equation: 
EQU G.sub.E = C.sub.1 A .sqroot.P.sub.E - P.sub.O (1) 
the amount of exhaust gas g.sub.E recirculated through the branch pipe 4 is 
determined from the pressure P in the back pressure control chamber 9, 
flow coefficient C.sub.2 of the orifice 11 and flow area a of said 
orifice: 
EQU g.sub.E = C.sub.2 a .sqroot.P.sub.E - P (2) 
therefore, if P is constantly maintained at P.sub.O, the condition of 
g.sub.E /G.sub.E = C.sub.2 a/C.sub.1 A = constant is maintained regartless 
of the operating condition of the engine, thus maintaining a constant 
exhaust gas recirculation ratio. 
Referring now to the exhaust gas recirculation valve 5, assuming that the 
central portion of the membrane 8 is positioned very close to the open end 
14 of the gas outlet tube 6, by denoting the suction pressure in the 
intake tube 2 by P.sub.S, effective pressure responsive area of the 
membrane 8 by a.sub.1, effective sectional area of said open end 14 by 
a.sub.2 and the spring force which the compression coil spring 15 applies 
to the membrane 8 in this condition by F, the following equation is 
established: 
EQU a.sub.1 P.sub.O = (a.sub.1 - a.sub.2) P + a.sub.2 P.sub.S + F = a.sub.1 P - 
a.sub.2 (P - P.sub.S) + F (3) 
in this case, the restoring force of the membrane 8 is assumed to be very 
small and negligible. All pressures are expressed by the absolute scale. 
The suction pressure P.sub.S generally fluctuates within the range 1-0.2 
atmospheric pressure in an ordinary internal combustion engine. With 
respect to areas a.sub.1 and a.sub.2, if, for example, the diameter of the 
effective sectional area of the open end 14 of the gas outlet tube 6 is 
one seventh of the diameter of the effective pressure responsive surface 
of the membrane 8, a.sub.2 is one forty-ninth of a.sub.1. Therefore, the 
magnitude of term a.sub.2 .times. (P - P.sub.S) is so small when compared 
with term a.sub.1 P that it can be disregarded. As mentioned above, since 
the spring force of the compression coil spring 15 is designed to be weak, 
term F can be disregarded when compared with term a.sub.1 P. Therefore, 
the equation (3) can be approximately reduced to: 
EQU a.sub.1 P.sub.O .apprxeq. a.sub.1 P (4) 
EQU P .apprxeq. P.sub.o (5) 
This means that the pressure P in the back pressure control chamber 9 is 
constantly maintained at the atmospheric pressure. Based upon this 
condition, the equation (2) can be rewritten as follows: 
EQU g.sub.E .apprxeq.C.sub.2 a .sqroot.P.sub.E - P.sub.o (2)' 
Thus, the ratio of the recirculation gas flow g.sub.E to the exhaust gas 
flow G.sub.E is maintained to be substantially constant. 
In a qualitative manner, the operation of the exhaust gas recirculation 
valve 5 is explained as follows. Assuming that the gas existing in the 
back pressure control chamber 9 is inhaled by the vacuum in the intake 
tube 2 thereby lowering the pressure P below the atmospheric pressure 
P.sub.o, the membrane 8 is urged upward as seen in FIG. 1 due to a 
relatively larger force applied to its lower surface when compared with 
the force applied to its upper surface. Therefore, the central portion of 
the membrane approaches to the open end 14 and reduces the cross sectional 
area of the annular passage which connects the inside space of the back 
pressure control chamber 9 and the passage defined in the gas outlet tube 
6. Therefore, the exhaust gas flow passing through the annular passage is 
correspondingly reduced. If the exhaust gas flow from the back pressure 
control chamber 9 to the exhaust gas outlet tube 6 reduces, an 
accumulation occurs with respect to the exhaust gas flowing into the back 
pressure control chamber 9 through the orifice 11, whereby the pressure P 
in the back pressure control chamber 9 increases to be restored toward the 
atmospheric pressure P.sub.O. On the other hand, if the pressure P in the 
back pressure control chamber 9 has increased beyond the atmospheric 
pressure P.sub.O due to a larger amount of exhaust gas inflow, the 
membrane 8 is urged downward due to a relatively larger force applied to 
its upper surface when compared with that applied to its lower surface, 
whereby the central portion of the membrane is removed from the open end 
14 and increases the cross sectional area of the annular passage 
connecting the back pressure control chamber 9 to the gas outlet tube 6. 
Therefore, the gas flow from the back pressure control chamber 9 to the 
exhaust gas outlet tube 6 increases thereby reducing the accumulation of 
exhaust gas within the back pressure control chamber 9. Thus, the pressure 
P in the back pressure control chamber 9 lowers toward the atmospheric 
pressure P.sub.O. In this manner, the pressure P in the back pressure 
control chamber 9 is automatically controlled toward the target value of 
atmospheric pressure P.sub.O. 
It will be appreciated that since the exhaust gas recirculation valve of 
the present invention employs co-operation of the membrane 8 and the open 
end 14 of the gas outlet tube for controlling the flow of exhaust gas and 
does not include the valve stem and valve guide as in the conventional EGR 
valve, it is free from the trouble that the small particles contained in 
the exhaust gas attach to the valve stem and cause a dull sliding action 
or sticking of the valve stem. Furthermore, since the clearance between 
the membrane 8 and the open end 14 of the gas outlet tube is very narrow 
and the membrane 8 reciprocates very quickly in a manner of almost 
vibrating to open or close the open end 14, the exhaust gas flow traverses 
said clearance very quickly thereby blowing off small particles which 
intend to attach to said open end. Therefore, the danger that the membrane 
sticks to the open end 14 or the control of the recirculating gas flow 
becomes inaccurate is positively avoided. 
FIGS. 2-4 show an embodiment of the exhaust gas recirculation valve 
according to the present invention in more detail. FIG. 2 is a view 
similar to FIG. 1 showing a longitudinal section of the exhaust gas 
recirculation valve 5. In FIG. 2, the portions corresponding to those 
shown in FIG. 1 are designated by the same reference numerals. 
In the embodiment shown in FIG. 2, the membrane 8 comprises a central 
portion 8' made of a thin sheet of stainless steel and an annular 
peripheral portion 8" made of heat resistive rubber, these two portions 
being joined by, for example, baking. By forming the peripheral portion of 
the membrane by a soft material like the heat resistive rubber, the spring 
coefficient of the membrane 8 is made substantially zero, whereby the 
aforementioned equation (3) is more correctly established. In relation to 
the structure of forming the peripheral portion of the membrane 8 by the 
heat resistive rubber material, the embodiment shown in FIG. 2 comprises a 
funnel-like guide means 18 which operates to guide relatively hot exhaust 
gas flow introduced into the back pressure control chamber 9 from the port 
10 directly toward the open end 14 of the gas outlet tube 6 without 
causing direct contact between the hot gas and the annular peripheral 
portion 8" made of rubber. Similarly, the retainer 16 for the compression 
coil spring 15 is made of a cylindrical element which prevents direct 
contact between the hot exhaust gas and the compression coil spring 15 so 
that the spring performance of the coil spring is not thermally effected. 
As shown in FIG. 3, radiation fins 19 may be provided at the outside of the 
housing 7 so that heating up of the exhaust gas recirculation valve up to 
an unfavorable temperature is avoided. 
As shown in FIG. 4, the membrane protecting housing 12 may preferably be 
provided with a plurality of openings 13 so that a large opening area is 
available. This structure having a plurality of openings provides for a 
good ventilation and cooling of the membrane 8 without losing the function 
of protecting the membrane. 
From the foregoing, it will be appreciated that the present invention 
provides a gas recirculation valve which has a very simple structure and 
yet is able to constantly maintain a predetermined constant exhaust gas 
recirculation ratio.