Vapor recovery system with variable delay purge

A vapor recovery system has its purge valve opened with a time delay, following throttle opening, that allows the engine to get up to speed before vapor purging begins. However, the time delay varies, depending on how long the throttle has been closed. Therefore, if the throttle has been closed only a short time, and the engine has thus not decelerated enough that it will need as much time to get back up to speed, the delay in purging will be less.

This application relates to vehicle fuel vapor recovery systems in general, 
and specifically to such a system in which the opening of a canister purge 
valve is delayed after an engine throttle is opened with a time delay that 
varies depending on how long the engine throttle was closed before 
opening. 
BACKGROUND OF THE INVENTION 
A typical vehicle fuel vapor recovery system found in a vehicle with a 
carbureted engine includes a vapor storage canister in which vapors from 
the fuel tank, and often from the carburetor float bowl as well, are 
adsorbed and stored, rather than being released to the atmosphere. These 
vapors are later purged from the canister by engine manifold vacuum and 
fed into a port in the throttle body located downstream of the throttle 
and burned in the engine. The withdrawal and burning of stored fuel vapors 
is generally controlled so as to in turn limit and control the richness of 
the fuel air mixture. For example, it would overly enrich the mixture if 
vapors were to be purged during engine idling. Therefore, it is desirable 
that purging begin only when, or at least be greatest when, the vehicle 
has reached a sufficient speed. Accordingly, the control system shown in 
U.S. Pat. No. 4,527,532 uses a speed sensor and a solenoid valve to 
increase the purging rate when that sufficient speed has been reached. 
While such an approach is obvious and is directly tailored to vehicle 
speed, it is expensive and somewhat complex, due to the electronics 
involved. 
The more common approach is to control air fuel ratio with a strictly 
mechanical purge valve that is closed during engine idling, but which 
opens when the throttle opens, even though it takes some time after 
throttle opening for the vehicle to get up to speed. A typical example of 
a fuel vapor recovery system with such a control is illustrated in FIG. 7. 
A fuel tank 10 continuously feeds excess vapors to a storage canister 12. 
A throttle body 14 supports a carburetor bowl 16, and houses a throttle 
18, with a manifold vacuum port 20 located downstream from throttle 18 and 
with a control vacuum port 22 located upstream from throttle 18. When 
throttle 18 is closed, as shown, the control vacuum port 22 is exposed to 
atmospheric pressure, but is exposed to manifold vacuum when throttle 18 
is opened. A canister control valve, designated generally at 24, contains 
a purge valve, and also controls the vapor venting from carburetor bowl 
16. Canister control valve 24 has a generally hollow body, and is ported 
to four lines, a canister line 26 that runs to canister 12, a carburetor 
bowl line 28 that runs to carburetor bowl 16, a manifold vacuum line 30 
that runs to manifold vacuum port 20, and a control vacuum line 32 that 
runs to control vacuum port 22. Two internal spring and diaphragm valves, 
a vapor vent valve 34 and a purge valve 36, operate as follows. When the 
engine is off, there is no vacuum through line 30 or line 32, and both 
valves 34 and 36 are in the down position shown, meaning that vapor vent 
valve 34 is open, while purge valve 36 is closed. This allows fuel vapors 
to vent from carburetor bowl 16, through line 28 to line 26 and ultimately 
to canister 12, but blocks vapors from flowing from canister 12, through 
line 26 to line 30. When the engine has been started, but is only idling, 
throttle 18 will still be in the closed position shown, but there will be 
enough manifold vacuum through line 30 to close valve 34, and block vapors 
from venting from bowl 16. However, line 32 will still not be exposed to 
manifold vacuum, so purge valve 36 will remain closed, and there will be 
no vapor purging from canister 12. When throttle 18 opens, control vacuum 
port 22 becomes exposed to manifold vacuum, pulling up and opening purge 
valve 36. This allows vapors to purge from canister 12, through lines 26 
and 30 and into throttle body 14 to be burned. As soon as throttle 18 
recloses, port 22 becomes exposed to atmospheric pressure again, and purge 
valve 36 closes almost immediately, stopping the purging from canister 12. 
An optional thermal switch 38 in control vacuum line 32 prevents purging 
at all when the engine is cold. 
The rapid closing of purge valve 36 upon the closing of throttle 18 is 
needed in order to prevent the fuel air mixture from becoming too rich 
during deceleration. However, the other side of the coin, the rapid 
opening of purge valve 36 upon the reopening of throttle 18, can cause a 
temporary over richness of the mixture. This is because, as noted, it 
takes some time after throttle opening for the vehicle and engine to get 
up to speed, and for the carburetor to develop sufficient airflow to be 
able to easily handle the increased fuel vapors from the canister. A 
partial solution is to put a one way air flow delay valve into the control 
vacuum line 32, between switch 38 and purge valve 36. Then, there will be 
a time delay between the opening of throttle 18 and the opening of purge 
valve 36, which will give the engine time to speed up before vapor purging 
begins. A shortcoming of this approach, however, is that in order to get 
sufficient delay, a fairly restrictive delay valve must be used. The purge 
valve 36 closes almost immediately when the throttle 18 closes, but that 
closing may be very short, with the vehicle and engine staying at 
substantially at the same speed, and thus more than capable of burning 
purged fuel vapors upon the reopening of throttle 18. However, the same, 
relatively long time delay in the reopening of purge valve 36 will occur 
as when it was initially opened, as the system has no way of 
distinguishing between the initial throttle opening and the reopening 
after only a short throttle closing. Delaying the reopening of purge valve 
36 under these conditions, that is, when the engine is still more than 
capable of burning purged vapors, would undesirably reduce the degree of 
purging. 
SUMMARY OF THE INVENTION 
The invention solves the above noted shortcoming with a control means for 
the purge valve that provides a time delay that varies, depending on the 
amount of time that the throttle has been closed. The mechanism that 
provides the variable time delay is entirely mechanical and, therefore, 
relatively inexpensive. 
The preferred embodiment of the invention disclosed is combined with a 
conventional vapor recovery system that has the type of canister control 
valve described above. A first delay valve is located in the control 
vacuum line, between the canister purge valve and the control vacuum port 
in the throttle body. The first delay valve faces so as to restrict the 
flow of air from the canister purge valve to the control vacuum port, but 
does not restrict air flow in the other direction. Between the first delay 
valve and the canister purge valve, a side line branches from the control 
vacuum line, and runs to an air accumulator. A second delay valve, similar 
to the first but facing in the opposite direction, is located in the side 
line, between the control vacuum line and the air accumulator. The second 
delay valve acts to restrict the flow of air from the control vacuum line 
to the accumulator, but does not restrict the flow of air from the 
accumulator to the control vacuum line. 
In operation, when the throttle initially opens, after having been closed 
for a relatively long time, the control vacuum line will first draw air 
from the accumulator. The air so drawn from the accumulator flows freely 
through the side line and second delay valve and restrictively through the 
control vacuum line and first delay valve. The opening of the canister 
purge valve is thereby delayed for a period of time, until sufficient air 
has been drawn from the accumulator to in turn allow sufficient vacuum to 
be applied to the purge valve to open it. The delay gives the vehicle and 
engine time to get up to sufficient speed to efficiently burn the purged 
fuel vapors. Although the second delay valve does not contribute to the 
initial delay in the opening of the purge valve, the combined action of 
the accumulator and the first delay valve gives a substantially longer 
delay than could be achieved with the first delay valve alone. When the 
throttle is allowed to close, exposing the control vacuum port to 
atmospheric pressure, air will flow back freely through the control vacuum 
line and the first delay valve to the purge valve, thereby closing the 
purge valve almost immediately. Simultaneously, air will flow from the 
control vacuum line and restrictively through the side line and the second 
delay valve back to the accumulator. The restrictiveness of the second 
delay valve can be chosen to substantially delay the refilling of the 
accumulator since, as mentioned, it has no effect on the delay in the 
initial opening of the purge valve. Thus, if the throttle is closed only 
shortly, then the accumulator will refill only a small amount, and the 
amount that it does refill will depend on how long the throttle remains 
closed. Consequently, the delay in reopening the purge valve that occurs 
when the throttle is reopened will be significantly shorter than the 
initial delay involved at cold start, and the length of that delay will 
vary depending on how long the throttle has been closed. 
It is, therefore, an object of the invention to provide a purge valve 
control means for a vehicle fuel vapor recovery system that delays the 
opening of the purge valve after the throttle has been opened by an amount 
that varies, depending on how long the throttle has been closed before 
being opened, so as to better control the richness of the air fuel 
mixture, but without decreasing the degree of stored fuel vapor purging. 
It is another object of the invention to provide such a control means that 
is strictly mechanical, and which can be easily combined with an existing 
fuel vapor recovery system. 
It is yet another object of the invention to provide such a control means 
that combines two oppositely facing one way air flow delay valves and a 
closed air accumulator which cooperate so as to delay the initial opening 
of the purge valve until the accumulator has been sufficiently emptied, 
giving a delay time sufficient for the engine to reach a desired speed, 
but which allows the purge valve to reclose almost immediately upon 
throttle closing, while delaying the reopening of the purge valve not by 
the same amount, but with a delay that varies depending on how long the 
accumulator has had to refill.

Referring first to FIG. 1, the conventional fuel vapor recovery system 
described above by reference to FIG. 7 is shown in combination with the 
variable delay control means of the invention, designated generally at 40. 
The variable delay control means of the invention 40 includes three basic 
components in combination, a first one way air flow delay valve, 
designated generally at 42, a second delay valve 44, and an air 
accumulator 46. Delay valve 42 is located in the control vacuum line 32, 
between the control vacuum port 22 and the purge valve 36, specifically 
between switch 38 and purge valve 36. Delay valve 42 is a commercially 
available sintered metal type, with a central internal umbrella 48 that 
covers non-restrictive flow passages 50, and which is surrounded by 
restrictive flow passages 52. Given the direction that first delay valve 
42 faces, it will be understood that it acts to restrict the flow of air 
from the canister purge valve 36 toward the control vacuum port 22, but 
does not restrict air flow in the other direction. Second delay valve 44 
is located in a side line 54, which branches from control vacuum line 32 
between first delay valve 42 and purge valve 36, and which runs to the 
accumulator 46. Delay valve 44 is similar to first delay valve 42, with 
the same umbrella 48 and passages 50 and 52, but faces oppositely. 
Therefore, it will be understood that the second delay valve 44 acts to 
restrict the flow of air from the control vacuum line 32 to the 
accumulator 46, but does not restrict the flow of air from the accumulator 
46 to the control vacuum line 32. Delay valves like 42 and 44 have an 
inherent delay or "bleed down" time that can be specifically chosen. Here, 
first delay valve 42 has a delay time of approximately a second, while 
second delay valve 44 has a delay time that is significantly longer, in 
the range of ten to fifteen seconds. The accumulator 46 is also a 
commercially available type, which is an aluminum bulb, closed except for 
its opening into side line 54. Accumulator 46 is at its fullest in FIG. 1, 
as indicated by the density of the stippling. The valves 42 and 44 and the 
accumulator 46 do not operate independently, but cooperate in a fashion 
that will be next described. 
The operation of the control means 40 will be illustrated by following the 
operation of the entire system from the starting of the engine, through 
idling, accelerating, momentary closing of the throttle 18 and, finally, 
reopening of the momentarily closed throttle 18. 
Referring first to FIG. 2, after the engine has been cold started, vacuum 
from port 20, acting through manifold vacuum line 30, closes vapor vent 
valve 34, stopping the venting of carburetor bowl 16 through carburetor 
bowl line 30 to canister 12. Vent valve 34 remains closed so long as there 
is manifold vacuum through line 30, that is, until the engine stops. 
Because throttle 18 is still closed, no manifold vacuum has yet been 
applied to control vacuum port 22, which remains exposed to atmosphere. 
Consequently, purge valve 36 remains down, which is its closed position, 
and there is no vapor purging yet from canister 12. The accumulator 46 is 
still at its fullest, as in FIG. 1. 
Referring next to FIG. 3, when the throttle 18 is initially opened from 
idle, the control vacuum port 22 is exposed to manifold vacuum, and, 
assuming that the engine is warm enough for switch 38 to be open, air is 
drawn through control vacuum line 32 and slowly through first delay valve 
42 to port 22. The air so drawn through control vacuum line 32 must first 
be drawn down from accumulator 46 before sufficient vacuum is presented to 
purge valve 36 to pull it up and open it. The flow of air from accumulator 
46, shown by arrows, proceeds freely through second delay valve 44 and 
through side line 54 to control vacuum line 32. Accumulator 46 is shown 
about half filled, as indicated by the less dense stippling. The volume of 
accumulator 46, and the inherent delay characteristics of first delay 
valve 42, will determine the amount of time delay before purge valve 36 
can be opened. In the embodiment disclosed here, the first delay valve 42 
and accumulator 46 cooperate to give a predetermined time delay in the 
range of five to ten seconds, while the first valve 42 acting alone would 
give a much shorter delay of about a second. That predetermined time 
delay, in turn, would be tailored to the particular acceleration 
characteristics of the engine involved so as to assure that the vehicle 
and engine will generally have reached a speed sufficient to handle purged 
fuel vapors with optimum efficiency, before purge valve 36 opens. 
Next, FIG. 4 shows the system after the engine has accelerated long enough 
to have reached the desired speed, with the accumulator 46 having 
substantially emptied. Enough manifold vacuum will then be applied to 
purge valve 36, through control vacuum line 32, to pull it up and open. 
Then, adsorbed fuel vapors are purged from canister 12, through canister 
line 26, through the body of canister control valve 24, and then through 
manifold vacuum line 30 to manifold vacuum port 20 to be burned. Enough 
air is then flowing through throttle body 14 that the air fuel mixture 
will not become overly enriched. While purging valve 36 is open, which 
will continue so long as throttle 18 is not allowed to close, there is no 
air flow through line 32. 
Next, FIG. 5, shows the system after throttle 18 has been allowed to close 
momentarily. Vacuum control port 22 is then immediately re-exposed to 
atmosphere, and air consequently flows immediately back through control 
vacuum line 32, in the non-restricted direction through first delay valve 
42. The vacuum at purge valve 36 is quickly relieved, which allows valve 
36 to quickly close, stopping the purge of vapors from canister 12. 
Concurrently, air begins to flow up side line 54, slowly through second 
delay valve 44, and back into accumulator 46, as shown by the arrows. How 
much air will flow back into accumulator 46 will depend on how long the 
throttle 18 remains closed, and on the time delay character of second 
delay valve 44. Since second valve 44 is chosen to be more restrictive 
than first valve 42, as noted above, very little air will refill 
accumulator 46 during a short closing of the throttle. And, the shorter 
the time that throttle 18 is closed, the lesser the volume of air that 
will flow back in. Accumulator 46 is illustrated as being about one-third 
refilled in FIG. 5. 
Referring finally to FIG. 6, the situation is shown after throttle 18 has 
been quickly reopened, before the vehicle has had time to decelerate a 
great deal. The same sequence of events that began when throttle 18 was 
first opened from idle begins again, with air flowing out of accumulator 
46, freely through valve 44 and slowly through valve 42, with the air flow 
in the same direction as was shown in FIG. 3. However, since the 
accumulator 46 started out less full than it was when the throttle 18 was 
first opened, (FIG. 2) the delay in reopening the purge valve 36 is 
proportionally less. If the throttle 18 is closed a very short time, then 
the delay in reopening of purge valve 36 is almost none, since very little 
air will have refilled accumulator 46. This is just what is desired, since 
the vehicle will need less time to re-accelerate to the same speed. This 
is to be contrasted with the case of a single delay valve 42, where the 
delay in reopening purge valve 36 would be invariant, undesirably delaying 
purge when the vehicle engine was more than capable of efficiently 
accepting purged fuel vapors almost immediately. Thus, the delay valves 42 
and 44, and the accumulator 46, although they are, by themselves, 
relatively simple mechanical parts, cooperate in the configuration of the 
invention to give a combination of significant advantages. 
The embodiment 40 of the invention disclosed is particularly advantageous, 
because it may be easily retrofitted to the conventional vapor recovery 
system illustrated in FIG. 7. However, it may be incorporated in any vapor 
recovery system with a purge valve that is activated by control vacuum. 
The invention could also be incorporated in control systems that do not 
have an on-off purge valve as such, but which have a purge valve that 
provides a continuously variable rate of purging. Such a variable rate 
valve could still be activated with the variable time delay of the 
invention, just as the purge valve 36 here is turned completely on and 
off. An air valve means other than the two delay valves 42 and 44 
disclosed could be substituted, so long as, when throttle 18 was first 
opened, it provided for freely draining the accumulator 46, but 
restricting the flow of air through control vacuum line 32, and so long as 
it also provided for refilling accumulator 46 restrictively when the 
throttle 18 was closed, but still allowed for the free flow of atmospheric 
air back through line 32 to quickly close purge valve 36. Different 
combinations of inherent delay characteristics of valves 42 and 44 and 
volumes of accumulator 46 can be chosen to give any combination of initial 
purge valve opening delay and purge valve reopening delay desired, 
depending on the particular engine involved. Therefore, it will be 
understood that the invention could be embodied in structures other than 
the preferred embodiment disclosed here, and is not intended to be so 
limited.