Automobile evaporative emission control device

In combination with an internal combustion engine having a throttle valve disposed in an intake manifold, an evaporative emission control device for controlling the emission to the atmosphere of fuel vapors from an internal combustion engine fuel system which comprises an air cleaner housing having a primary air intake conduit, a gating valve operatively disposed in the primary air intake conduit for selectively opening and closing the primary air intake conduit, a diaphragm valve assembly for bringing the gating valve means in position to open the primary air intake duct when a negative pressure developed in the intake manifold is induced in a working chamber, a fluid passage extending between the working chamber and the intake manifold, and a delay unit operable, when the negative pressure in the intake manifold decreases, for delaying a corresponding decrease of the once-induced negative pressure in the working chamber for a predetermined time to maintain the gating valve in the opened position.

BACKGROUND OF THE INVENTION 
The present invention relates to an automobile evaporative emission control 
device for controlling the emission to the atmosphere of fuel vapors from 
an internal combustion engine fuel system wherein the emission arises from 
the evaporation of the fuel. 
It has generally been recognized by those skilled in the art that a major 
cause of air pollution so far as automobiles are concerned arises not only 
from the emission of combustion products through the exhaust system, but 
also from the fuel vapors emitted due to evaporation of the fuel. The U.S. 
Pat. No. 3,540,423 to Edward D. Tolles III, patented on Nov. 17, 1970, 
describes the possibility of air pollution resulting from the emission of 
the fuel vapors in automobiles and the importance of prevention of such 
fuel vapor emission. To this end, the E. D. Tolles' patent discloses an 
automobile evaporative emission control device which comprises an air 
filter or cleaner housing mounted on an intake manifold, leading to an 
engine combustion chamber or chambers through a carburetor; a gating valve 
operatively disposed in a primary air intake passage communicated to the 
atmosphere on one hand and, on the other hand, to the intake manifold 
through an annular adsorbent bed housed in the air cleaner housing, the 
gating valve being normally urged to a closed position by a biasing 
spring, but capable of being brought to an opened position in response to 
the negative pressure developed in the intake manifold at a position 
proximate to the throttle valve in the carburetor, the annular adsorbent 
bed defining a secondary air intake passage which extends through the 
central hollow of the annular adsorbent bed and is in communication with 
the intake manifold upstream of the carburetor and downstream of the 
adsorbent bed; and a pressure responsive two-way valve assembly so 
designed as to operate in such a manner that, when the engine is not 
operating or is operating at a low air consumption with no primary air 
introduced through the gating valve, a fluid circuit between the 
carburetor fuel bowl to the upstream side of the adsorbent bed can be 
established and, when increased engine air consumption is attained with 
the primary air introduced through the gating valve together with the 
secondary air, an alternative fluid circuit can be established between the 
carburetor fuel bowl and the intake manifold upstream of the throttle 
valve. 
The pressure responsive two-way valve assembly employed in the Tolles' 
patent is comprised of a pressure responsive diaphragm valve and a two-way 
valve operatively coupled therewith while the gating valve is employed in 
the form of a butterfly valve. 
The Tolles' patent also discloses the communication between the fuel tank 
and the first mentioned fluid circuit downstream of the pressure 
responsive two-way valve assembly, that is, between the fuel tank and a 
portion of the first mentioned fluid circuit which is between the pressure 
responsive two-way valve assembly and the annular adsorbent bed for 
withdrawing fuel vapors from the fuel tank to the adsorbent bed together 
with fuel vapors from the carburetor fuel bowl when the pressure 
responsive two-way valve assembly is held in position to establish the 
first mentioned fluid circuit. 
The Japanese Utility Model Publication No. 47-10003 published on Apr. 14, 
1972, discloses a similar automobile evaporative emission control device 
which comprises an air cleaner housing mounted on an intake manifold 
leading to an engine combustion chamber or chambers through a carburetor, 
the air cleaner housing having an air intake duct outwardly extending 
therefrom, said air intake duct including a gating valve, in the form of a 
butterfly valve, disposed therein for rotation between closed and opened 
positions and operatively coupled to a diaphragm valve. The diaphragm 
valve has a diaphragm member coupled to the gating valve through a 
connecting rod and being displaceable between a first position, in which 
the gating valve is held in the closed position, and a second position in 
which the gating valve is held in the opened position. This diaphragm 
valve is operatively associated with the intake manifold in such a manner 
that, when the engine is not operating or is operating at a low air 
consumption, the diaphragm is displaced to the first position with the 
gating valve consequently held in the closed position and, when the engine 
is operating at an increased air consumption, the diaphragm is displaced 
to the second position with the gating valve consequently held in the 
opened position for the introduction of air into the intake manifold 
through the air cleaner housing. For recovering fuel vapors from both of 
the intake manifold and the fuel tank, the emission control device 
disclosed in this Japanese Utility Model Publication further comprises a 
filter housing having two inlet ports, respectively communicated to the 
fuel tank and a portion of the air duct between the air cleaner housing 
and the gating valve whereby, while fuel vapors within the fuel tank are 
always introduced into the filter housing prior to the discharge thereof 
to the atmosphere irrespective of the engine operating condition, fuel 
vapors occurring in the intake manifold are introduced into the filter 
housing when and so long as the gating valve is held in the closed 
position. For operating the diaphragm valve, the negative pressure is 
drawn from the intake manifold from a position corresponding to a venturi 
section of the carburetor. 
In the arrangement disclosed in the above mentioned Japanese Utility Model 
Publication, since the absolute value of the negative pressure developed 
in the venturi section of the carburetor is relatively small, the gating 
valve cannot be accurately and precisely operated between the closed and 
opened position and, more particularly, the gating valve can not readily 
be brought to the opened position during the engine idling condition. 
However, the Japanese Utility Model Laid-open Publication No. 52-10211, 
laid open to public inspection on Jan. 24, 1977, discloses the use of an 
electromagnetic valve, instead of the butterfly valve employed in the 
above mentioned Japanese Utility Model Publication, for opening the air 
duct when and so long as the automobile ignition switch is turned on. 
However, it has been found that the use of the electromagnetic valve 
requires consumption of an electric power, but also the electromagnetic 
valve itself is expensive. 
Although less pertinent to the present invention than the prior art 
references hereinbefore discussed, the U.S. Pat. No. 3,683,878 to Joe E. 
Rogers, patented on Aug. 15, 1972, discloses the use of a gating valve of 
a type normally biased by a leaf spring to allow the passage of the 
primary air into the filter housing and then into the intake manifold 
while blocking the flow of air or fuel vapor in the opposite direction 
from the filter housing to the atmosphere. This type of gating valve may 
be considered a reed valve. 
In any event, the conventional evaporative emission control devices 
particularly disclosed in the Tolles' patent and the Japanese Utility 
Model Publication involve a common disadvantage. As is well known to those 
skilled in the art, when the engine, which has been decelerated or has 
been operated at a relatively low velocity starts its acceleration to 
attain a relatively high velocity, the throttle valve is generally fully 
opened temporarily and the rate of flow of the primary air into the intake 
manifold by way of the air cleaner housing is consequently increased with 
the negative pressure present in the intake manifold at a position 
proximate to the throttle valve being reduced. In view of this, in the 
conventional evaporative emission control devices referred to above, the 
gating valve appears to be substantially closed during this transit period 
in which the engine is accelerated, to such an extent that the amount of 
the primary air to be introduced into the intake manifold tends to become 
short of the amount required during the substantially full opening of the 
throttle valve, the consequence of which is that the response of the 
engine to the acceleration is adversely affected. 
SUMMARY OF THE INVENTION 
Accordingly, the present invention has for its essential object to provide 
an improved evaporative emission control device for an automobile for 
controlling the emission to the atmosphere of fuel vapors not only from 
the intake manifold, but also from the fuel tank, which are free from the 
above described disadvantages and inconveniences inherent in the prior art 
devices of similar kind. 
Another important object of the present invention is to provide an improved 
evaporative emission control device of the type referred to above, which 
is simple in construction and reliable in operation and which can readily 
be installed in operative connection with any existing internal combustion 
engine without inviting any possible reduction in performance of the 
engine. 
A further important object of the present invention is to provide an 
improved evaporative emission control device wherein the gating valve can 
accurately and effectively be maintained at the full opening required 
during the transit period in which the engine is accelerated. 
To this end, according to the present invention, there is provided an 
improved evaporative emission control device for an internal combustion 
engine having a fuel tank and an intake manifold including a carburetor 
for combining fuel from the fuel tank with primary air to form a 
combustible mixture, said carburetor having a throttle valve for 
controlling the rate of delivery of the combustible mixture to at least 
one combustion chamber of the engine through the intake manifold. The 
evaporative emission control device comprises an air cleaner housing 
communicated to one end of the intake manifold remote from the combustion 
chamber and upstream of the carburetor and having a primary air intake 
duct extending outwardly therefrom for the introduction of the primary air 
from the atmosphere into the intake manifold, a gating valve means 
disposed in the primary air intake duct and operable to allow the passage 
of the primary air from the atmosphere into the intake manifold through 
the air cleaner housing, but to block the flow of air or fuel vapors in 
the opposite direction from the intake manifold back towards the 
atmosphere, a first diaphragm valve assembly having a working chamber and 
a diaphragm member operatively coupled to the gating valve means and 
displaceable between a first position, in which the gating valve means is 
brought in a closed position, and a second position in which the gating 
valve means is brought in an opened position, a first fluid conduit means 
having one end communicated to the working chamber of the first diaphragm 
valve assembly and the other end opening towards the intake manifold at a 
position downstream of the throttle valve, and a fluid delay means 
disposed on said first fluid conduit means and operable to allow the 
pressure within the working chamber to become equal to the negative 
pressure within the intake manifold to displace the diaphragm member to 
the second position when the negative pressure within the intake manifold 
is high and to delay the rate of decrease of the once-created negative 
pressure within the working chamber for a predetermined time even when and 
after the negative pressure within the intake manifold is subsequently 
decreased. 
For collecting fuel vapors arising from and drifting in the intake manifold 
and the air cleaner housing during the closure of the gating valve means 
and, hence, during an inoperative condition of the engine, the evaporative 
emission control device acccording to the present invention further 
comprises a second fluid conduit having a purifying unit through which the 
fuel vapors are vented. In addition, for periodically regenerating the 
filtering or adsorbent material in the purifying unit thereby avoiding the 
use of a purifying unit of a prohibitively large size and/or the 
replacement thereof at frequent intervals, there is also provided in the 
evaporative emission control device of the present invention a third fluid 
conduit means extending between the purifying unit and a portion of the 
intake manifold downstream of the throttle valve. This third fluid conduit 
means is opened only when the negative pressure is developed in the intake 
manifold to allow the passage of fuel vapors which have previously been 
deposited on the purifying or adsorbent material without being discharged 
to the atmosphere and which are removed or desorbed therefrom as a fresh 
air is drawn from the atmosphere into the third fluid conduit means 
through the purifying unit. A second diaphragm valve assembly operable by 
the effect of the negative pressure in the intake manifold and a switching 
valve are employed for selectively closing and opening the third fluid 
conduit means. The fuel tank may be communicated to the third fluid 
conduit means for the prevention of emission of fuel vapors from the fuel 
tank. 
According to the present invention, the gating valve means may be of any 
known type, for example, a butterfly valve. However, the use is preferred 
of a type having an eccentrically rotatably supported valve member so 
that, so long as the flow of the primary air from the atmosphere through 
the primary air intake duct occurs and during the loaded drive of the 
engine, for example, acceleration, the reduction in negative pressure 
within the working chamber of the first diaphragm valve assembly can 
advantageously be retarded in cooperation with the fluid delay means by 
the reason which will become clear from the detailed description.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to FIG. 1, there is shown an intake manifold 10 having an air 
cleaner housing 11 mounted on one end thereof, the other end of said 
intake manifold 10 being communicated to at least one combustion chamber 
of an internal combustion engine (not shown). The intake manifold 10 
includes a carburetor 12 positioned between the air cleaner housing 11 and 
the engine combustion chamber and has a fuel bowl 13, an air vent tube 14, 
a choke valve 5, a venturi section 16 and a throttle valve 17, the 
detailed construction and operation of said carburetor 12 being well known 
to those skilled in the art and, therefore, omitted herein for the sake of 
brevity. 
The air cleaner housing 11 is of a shape substantially similar to a closed 
circular box and includes an annular filtering bed 18 installed therein in 
coaxial relation to the open end of the intake manifold 10 opening towards 
the interior of the air cleaner housing 11. This air cleaner housing 11 
has a primary air intake duct 19 extending radially outwardly from the 
periphery of the air cleaner housing 11 and opening towards the atmosphere 
so that a primary air can be introduced from the atmosphere into the 
intake manifold 10 after having past through the filtering bed 18. 
A gating valve, generally designated by 20, is installed within the primary 
air intake duct 19 and comprises a valve member 21 rigidly mounted for 
eccentric rotation between closed and opened positions on a shaft 22 
having one end rotataly journalled to a portion of the wall forming the 
primary air intake duct 19 and the other end rotataly extending through 
the opposite portion of the wall forming the primary air intake duct 19. 
This shaft 22 extends at right angles to and in laterally offset relation 
to the longitudinal axis of the primary air intake duct 19. Said other end 
of the shaft 22 situated outside of the primary air intake duct 19 has a 
motion translating lever 23 rigidly mounted thereon for rotation together 
with said shaft 22, which motion translating lever 23 is operatively 
coupled to a first diaphragm valve assembly 24 in a manner as will be 
described later. 
The first diaphragm valve assembly 24 comprises a valve housing 25, the 
interior of which is divided into first and second chambers 25a and 25b by 
a diaphragm member 25c, the first chamber 25a being communicated to the 
intake manifold 10 in a manner as will be described later and the second 
chamber 25b communicated to the atmosphere, and a connecting rod 26 having 
one end rigidly connected to the diaphragm member 25c and the other end 
pivotally connected to the motion translating lever 23. The first 
diaphragm valve assembly 24 further comprises a biasing spring 27 
accommodated within the first chamber 25a for urging the diaphragm member 
25c to a first operative position thereby maintaining the gating valve 20 
in the closed position as shown, said diaphragm member 25c being 
displaceable to a second operative position against the biasing spring 27 
to bring the gating valve 20 to the opened position when a negative 
pressure is developed in the first chamber 25a. However, it is to be noted 
that the biasing spring 27 may be omitted if the diaphragm member 25c has 
a sufficient elasticity by which the diaphragm member 25c itself can be 
displaced to and maintained at the first operative position when no 
negative pressure is developed in the first chamber 25a. 
The first chamber 25a of the first diaphragm valve assembly 24 is 
communicated to a portion of the intake manifold 10 downstream of the 
throttle valve 17 through a first conduit means constituted by fluid 
conduits 28a and 28b and including a fluid delay unit 29 disposed between 
the fluid conduits 28a and 28b. So far illustrated, the fluid delay unit 
29 comprises first and second passages 30 and 31 extending in parallel 
relation to each other between the fluid conduits 28a and 28b, the first 
passage 30 including a check valve 32 so designed as to allow the passage 
of a fluid medium from the conduit 28a to the conduit 28b, but to block 
the passage of the fluid medium in the opposite direction from the conduit 
28b to the conduit 28a while the second passage 31 includes a constricted 
area 33 such as constituted by an orifice. It is to be noted that the 
check valve 32 is shown as constituted by a casing 32a having a pair of 
opposed ports 32b and 32c, respectively communicated to the conduits 28a 
and 28b, a ball 32d and a biasing spring 32e normally urging the ball 32d 
to close the port 32b. 
In the construction so far described, it will readily be seen that, when 
the negative pressure is developed in the intake manifold 10 downstream of 
the throttle valve 17, the ball 32d is displaced against the biasing 
spring 32e to open the port 32b with a major amount of fluid medium 
present within the first chamber 25a and the conduit 28a flowing into the 
conduit 28b while, when the negative pressure within the intake manifold 
10 is subsequently decreased due, for example, to the subsequent full 
opening of the throttle valve 17, the ball 32d is held by the spring 32d 
in position to close the port 32b and, consequently, the fluid medium 
present in the conduit 28b is allowed to pass through the passage 31 by 
way of the constricted area 33 on to the conduit 28a. 
For collecting fuel vapors resulting from evaporation of fuel in the intake 
manifold 10 and drifting in the intake manifold and the air cleaner 
housing 11 during the closure of the gating valve 20 in the manner as 
shown in FIG. 1, a purifying unit 34 is employed. This purifying unit 34 
comprises a canister 35 having first and second inlet ports 35a and 35b 
and a vent port 35c and including a purifying bed 35d which may be 
composed of any known filtering material or any known adsorbent material 
such as activated carbon particles. This purifying unit 34 is fluid 
connected to the air cleaner housing 11 by means of a second conduit 36 
having one end, extending through the first inlet port 35a into the 
purifying bed 35d, and the other end held in communication with the air 
cleaner housing 11 at a position downstream of the filtering bed 18 with 
respect to the direction of flow of the primary air from the primary air 
intake duct 19 into the intake manifold 10. 
For periodically regenerating the purifying bed 35d within the canister 35 
by the removal of fuel vapors deposited on the purifying bed 35d, there is 
employed a third conduit means which comprises a third conduit 37 having 
one end communicated to the second inlet port 35b of the purifying unit 34 
and the other end communicated to the intake manifold 10 at a position 
downstream of the carburetor throttle valve 17, a substantially 
intermediate portion of said third conduit 37 having a switching valve 38 
installed thereon for selectively opening and closing the third fluid 
conduit 37. This switching valve 38 includes a valving member 38a held in 
position to selectively close and open the third fluid conduit 37 
according to the magnitude of the negative pressure developed in the 
intake manifold 10. For this purpose, there is employed a second diaphragm 
valve assembly 39 which comprises a valve housing 40, the interior of 
which is divided into first and second chambers 40a and 40b by a diaphragm 
member 40c. The first chamber 40a is communicated by a conduit 41 to a 
portion of the intake manifold 10 proximate to the throttle valve 17 and, 
more particularly, slightly upstream of the throttle valve 17 when the 
latter is held in a substantially closed position and downstream of the 
throttle valve 17 when the latter is rotated a small angle to open from 
the substantially closed position, whereas the second chamber 40b is 
communicated to the atmosphere. The diaphragm member 40c is displaceable 
between first and second positions, but is normally biased to the first 
position by a biasing spring 40d accommodated within the first chamber 
40a. This diaphragm member 40c is operatively connected to the valving 
member 38 a of the switching valve 38 so that, when the diaphragm member 
40c is displaced towards the second position against the biasing spring 
40d, the valving member 38a can be brought in position to open the third 
fluid conduit 37. The displacement of the diaphragm member 40c from the 
first position towards the second position against the biasing spring 40d 
takes place when the negative pressure is induced in the first chamber 40a 
through the conduit 41. 
A fuel tank 43 is shown to be fluid connected to a portion of the third 
fluid conduit 37 between the purifying unit 34 and the switching valve 38 
by means of a fluid conduit 44 so that fuel vapors drifting within the 
fuel tank 43 and above the top level of the fuel within such tank 43 can 
be introduced into that portion of the third fluid conduit 37 and/or 
canister and, when the valving member 38a is held in position to open the 
third fluid conduit 37, into the intake manifold 10. 
While the evaporative emission control device of the present invention is 
constructed as hereinbefore described, it operates in the following 
manner. It is, however, to be noted that, for better understanding of the 
present invention, the operation of the evaporative emission control 
device will now be described according to its different operative 
conditions. 
Inoperative Condition 
When the automobile engine which has been operated is brought to an 
inoperative condition with an ignition switch (not shown) turned off, a 
so-called "hot soak" period commences and fuel droplets wetting to the 
inner surface of the intake manifold 10 and fuel within the carburetor 
bowl 13 evaporate under the influence of the ambient temperature, thereby 
tending to escape to the atmosphere through the air cleaner housing 11. 
However, since the pressure within the intake manifold 10 becomes equal to 
the atmospheric pressure as soon as the engine is shut off, the pressure 
within the intake manifold 10 is introduced into the first chamber 25a of 
the first diaphragm valve assembly 24 through the conduit 28b, then the 
constricted area 33 on the passage 31 and finally through the conduit 28a, 
whereby the diaphragm member 25c which has been displaced to the second 
position against the spring 27 is urged back to the first position by the 
action of the spring 27. This displacement of the diaphragm member 25c 
back to the first position causes the gating valve 20 to assume the closed 
position as shown and, therefore, the fuel vapors arising from the intake 
manifold 10 and subsequently drifting in the air cleaner housing 11 will 
not escape to the atmosphere through the primary air intake duct 19, but 
flow through the conduit 36 into the purifying unit 34 whereat the fuel 
vapors are deposited on or adsorbed by the purifying bed 35d prior to 
being discharged to the atmosphere through the vent or outlet port 35c of 
the purifying unit 34. 
It is to be noted that not only the fuel vapors so introduced into the 
purifying unit 34 in the manner described above, but also fuel vapors 
within the fuel tank 43 will not be circulated into the intake manifold 10 
through the third fluid conduit 37 during the inoperative condition of the 
engine. This is because the pressure within the intake manifold 10, which 
is equalized to the atmospheric pressure as hereinbefore described, is 
also introduced into the first chamber 40a of the second diaphragm valve 
assembly 39 through the conduit 41 with the diaphragm member 40c displaced 
to the first position by the action of the spring 40d and, therefore, the 
valving member 38a of the switching valve 38 is held in position to close 
the third fluid conduit 37. 
Operative Condition 
(I) Engine Start and Idling 
When and after the ignition switch is turned on to start the engine, a 
starter (not shown) is operated to rotate the engine. As the engine is so 
rotated by the starter, a negative pressure is developed in the intake 
manifold 10 downstream of the throttle valve 17 and, accordingly, this 
negative pressure is induced in the first chamber 25a of the first 
diaphragm valve assembly 24 through the check valve 32 then opened. More 
specifically, as the negative pressure is developed in the intake manifold 
10 downstream of the throttle valve 17 in the manner described above, air 
present within the first chamber 25a is drawn into the intake manifold 10 
forcing the ball 32d to displace against the spring 32e to open the port 
32d and, consequently, a negative pressure of a value substantially equal 
to the negative pressure within the intake manifold 10 downstream of the 
throttle valve 17 is developed in the first working chamber 25a with the 
diaphragm member 25c displaced towards the second position against the 
spring 27. Therefore, the gating valve 20 is opened to such an extent as 
to allow the passage of the primary air therethrough into the intake 
manifold 10 via the air cleaner housing 11 in an amount required to start 
the engine. 
As the engine starts its operation, an increased negative pressure is 
developed in the intake manifold 10 at a position downstream of the 
throttle valve 17, which is in turn induced in the first chamber 25a to 
displace the diaphragm member 25c to the second position with the gating 
valve 20 consequently fully opened. Accordingly, even when the engine is 
subsequently driven at an idling speed, the gating valve 20 can be 
maintained at the full open position. 
It is to be noted that the throttle valve 17 is substantially closed during 
the start and idling of the engine and, therefore, the pressure introduced 
in the duct 41 is still equal to or slightly higher than the atmospheric 
pressure because the end of the duct 41 remote from the first chamber 40a 
of the second diaphragm valve assembly 39 opens towards the intake 
manifold 10 at a position upstream of the throttle valve 17 in the 
substantially closed position. Therefore, the diaphragm member 40c of the 
second diaphragm valve assembly 39 is maintained at the first position as 
biased by the spring 40d as shown and the switching valve 38 is held in 
position to close the fluid conduit 37. 
(II) Loaded Drive of the Engine 
When the engine is subsequently driven under load with the throttle valve 
17 opened, the negative pressure which has been developed in the intake 
manifold 10 at a position downstream of the throttle valve 17 decreases. 
When this decrease takes place, the check valve 32 is immediately brought 
in a position to interrupt the communication between the ducts 28a and 28b 
by way of the passage 30 with the ball 32d held in position to close the 
port 32d as biased by the spring 32e. Accordingly, the negative pressure, 
which has been induced in the first chamber 25a of the first diaphragm 
valve assembly 24 during the idling operation of the engine, is 
substantially maintained in the first chamber 25a, thereby preventing the 
closure of the gating valve 20 during the loaded drive of the engine. 
On the other hand, the pressure within the first chamber 25a tends to 
become equal to the pressure in the duct 28b and, hence, the pressure in 
the intake manifold 10 downstream of the throttle valve 17, since the 
ducts 28a and 28b are communicated to each other through the constricted 
area 33 on the passage 31 even when the check valve 32 is in position to 
close the passage 30. However, because of the design of the constricted 
area 33, the time required for the pressure in the conduit 28a and, hence, 
that in the first chamber 25a, to become equal to the pressure in the 
conduit 28b can be prolonged. By way of example, if the system is so 
designed that the gating valve 20 can be fully opened when the negative 
pressure of about -20 mmHg is introduced in the first chamber 25a, there 
is no possibility that the gating valve 20 will be closed since the 
negative pressure developed in the intake manifold 10 during the loaded 
drive of the engine is usually about -30 mmHg. On the other hand, it is 
admitted that the negative pressure of about -20 mmHg will be developed in 
the intake manifold 10 during a low speed, high load drive of the engine 
which often continues for a relatively short period of time, in which case 
the premature closure of the gating valve 20 can be avoided by suitably 
selecting the effective cross sectional area of the constricted area 33. 
On the other hand, during the loaded drive of the engine, the throttle 
valve 17 is opened and, therefore, the opening of the end of the duct 41 
remote from the first chamber 40a of the second diaphragm valve assembly 
39 is positioned downstream of the throttle valve. Accordingly, the 
negative pressure developed in the intake manifold 10 downstream of the 
throttle valve 17 is induced in the first working chamber 40a with the 
diaphragm member 40c consequently displaced towards the second position 
against the spring 40d. The displacement of the diaphragm member 40c 
towards the second position so effected causes the switching valve 38 to 
open the third fluid conduit 37 to allow the fuel vapors, which have been 
deposited on the purifying bed 35d in the purifying unit 34 and are 
subsequently removed or desorbed therefrom, to flow through the third 
fluid conduit 37 into the intake manifold 10 and then into the engine 
combustion chamber. The removal or desorption of the fuel vapors from the 
purifying bed 35d takes place as a fresh air from the atmosphere passes 
into the conduit 37 through the purifying bed 35d by way of the port 35c 
by the effect of a pressure differential between the atmosphere and the 
intake manifold 10 and, consequently, the purifying bed 35d can 
effectively be regenerated. Simultaneously therewith, fuel vapors arising 
from the fuel tank 43 are also introduced into the intake manifold 10 by 
means of the conduit 44 and then the conduit 37. 
It is to be noted that the use of the eccentrically rotatably supported 
valve member 21 for the gating valve 20 is advantageous in that, even when 
the first diaphragm valve assembly 24 fails to operate properly during, 
for example, a high load drive of the engine or is malfunctioned, the 
gating valve 20 can be opened by the effect of the flow of the primary air 
being sucked into the intake manifold 10 under the influence of the 
negative pressure then developed in the intake manifold 10. 
It is also to be noted that the system for collecting the fuel vapors from 
the intake manifold 10 and the air cleaner housing 11 during the closure 
of the gating valve 20 and for subsequently regenerating the purifying bed 
35d may not be limited to that described with reference to and shown in 
FIG. 1, but may be of any known type. By way of example, depending upon 
the type of the purifying material forming the purifying bed 35d, the 
third fluid conduit 37 and its associated arrangement including the second 
diaphragm valve assembly 39 may not be omitted with the conduit 44 fluid 
connected to the duct 36. Alternatively, the system for collecting the 
fuel vapors from the intake manifold and for regenerating the purifying 
bed disclosed in the Tolles' patent referred to above may be employed with 
no substantial modification. 
In practice, the fluid delay unit 29 is constructed in a manner as shown in 
FIG. 2, reference to which will now be made. It is, however, to be noted 
that this does not means that the combined arrangement of the check valve 
32 and the constricted area 33 shown in FIG. 1 cannot be practically 
employed. 
Referring now to FIG. 2, the delay unit 29 comprises a substantially hollow 
cylindrical casing 50 having its opposed ends communicated to the conduits 
28a and 28b, respectively, and a tube 51 rigidly supported within the 
casing 50 by means of an annular partition wall 52 which protrudes 
radially outwardly from the inner peripheral surface of the casing 50 and 
terminating in integral contact with the outer peripheral surface of the 
tube 51. The annular partition wall 52 is formed with at least one 
aperture 53 extending completely through the thickness of the partition 
wall 53, which aperture 53 has one open end adjacent the conduit 28b 
adapted to be selectively closed and opened by a valve member 54, the 
valve member 54 being so designed as to allow the passage of the fluid 
medium from the conduit 28a towards the conduit 28b through the aperture 
53, but block the flow of the fluid medium in the opposite direction from 
the conduit 28b towards the conduit 28a through the aperture 53. It will, 
therefore, readily be seen that the fluid passage including the aperture 
53 and the valve member 54 possibly corresponds in function to the passage 
30 including the check valve 32 shown in FIG. 1. 
Within the hollow of the tube 51 which corresponds to the passage 31 shown 
in FIG. 1, there is filled a porous barrier 55, made of an open-celled 
porous metallic material such as a sintered alloy, which functionally 
corresponds to the constricted area 33 shown in FIG. 1. The term "porous" 
employed hereinabove and in the appended claims in connection with the 
barrier 55 is to be understood as meaning that the material for the 
barrier 55 has a plurality of voids or pockets which are interconnected in 
such a manner that gas may pass from one to another. In this sense, the 
porous material may be referred to as an open-celled material. 
Reference numerals 56 and 57 represent respectively filtering material 
positioned adjacent the openings at the opposite ends of the casing 50. 
Although the present invention has fully been described in connection with 
the preferred embodiment thereof, it is to be noted that various changes 
and modifications are apparent to those skilled in the art. By way of 
example, in addition to the changes and modifications such as described 
above, the conduit 28b may be fluid connected to a portion of the conduit 
37 between the intake manifold 10 and the switching valve 38 or that 
portion of the conduit 37 may be fluid connected to the conduit 28b. 
Accordingly, such changes and modifications are to be understood as 
included within the true scope of the present invention unless they depart 
therefrom.