Tank venting and vapor recovery system

An apparatus is provided for controlling discharge of fuel vapors from a vehicle fuel tank having a filler neck. The apparatus comprises a housing defining an interior region, the housing being formed to include first and second inlet ports, a signal port, and an outlet port. The apparatus further comprises a first valve assembly movable between a blocking position preventing fuel vapor received from the first inlet port from flowing through the interior region during vehicle refueling and a venting position allowing fuel vapor received from the first inlet port to flow through the interior region to the outlet port during vehicle operation. A signal passageway extends between the filler neck and the signal port to expose the first valve assembly to fuel vapor pressure from the filler neck to move the first valve assembly toward its venting position during vehicle operation. The apparatus further comprises second valve assembly movable between a blocking position preventing fuel vapor received from the second inlet port from flowing through the interior region when the first valve assembly is positioned in its venting position during vehicle operation and a venting position allowing fuel vapor received from the second inlet port to flow through the interior region to the outlet port when the first valve assembly is positioned in its blocking position during the vehicle refueling.

BACKGROUND AND SUMMARY OF THE INVENTION 
The present invention relates to systems for controlling venting of fuel 
vapors from a vehicle fuel tank. More particularly, the present invention 
relates to systems including control valve assemblies for venting fuel 
vapor from the fuel tank via a first vent path during vehicle operation 
and for venting fuel vapor from the fuel tank via a second vent path 
during vehicle refueling. 
It is well understood that significant quantities of fuel vapor can escape 
from a fuel tank through the filler neck to the atmosphere during the 
refueling of motor vehicles. Early attempts to control the vapor escape 
focused upon control devices fitted to the fuel dispensing nozzle. Later, 
control devices mounted directly on-board the vehicle (and thus referred 
to as "on-board vapor recovery" systems or "OBVR" systems) were developed. 
See, for example, U.S. Pat. No. 4,836,835, relating to a vacuum-actuated 
vapor recovery system mounted on the fuel tank filler neck. OBVR systems 
which mount to the fuel tank have also been developed. 
In addition to controlling vapor escape, well-designed OBVR systems also 
assist in controlling the amount of liquid fuel which can be pumped into 
the fuel tank during refueling. For safety reasons, fuel systems are 
designed so that the fuel tank is never completely filled with liquid 
fuel. Rather, at least a predetermined portion of the fuel tank is left 
for liquid fuel and fuel vapor expansion. Although fuel pump nozzles 
typically include sensors for shutting off the flow of liquid fuel into 
the fuel tank when the fuel tank is nearly filled, fuel pump users may 
manually override the sensors by continuing to pump fuel after the sensors 
have automatically shut the pump nozzle off. To assist in preventing tank 
overfill under such conditions, the OBVR system is usually provided with a 
fill-limit valve which prevents the escape of vapor through the OBVR 
system, and thus assists in triggering the nozzle shut-off mechanism, when 
the level of liquid fuel in the fuel tank has risen to a predetermined 
level. 
It has also long been recognized that fuel vapor is generated in the fuel 
tank during operation of the vehicle, for example, by evaporation or by 
sloshing of the liquid fuel against the walls of the tank. Excessive 
pressure can build up in the fuel tank as a result of the newly-formed 
fuel vapor unless control devices are provided to vent the fuel vapor from 
the fuel tank during vehicle operation. Such valves have been referred to 
as "run-loss" valves or tank venting rollover valves because they handle 
fuel vapor loss during vehicle run and are capable of preventing liquid 
fuel carry over during vehicle rollover. 
Coincident with developing OBVR systems to handle venting of fuel vapor 
during refueling, fuel systems engineers pursued advancements in tank 
pressure control systems, particularly run-loss valves for venting the 
fuel tank during vehicle operation. One driving force behind such 
advancements was the need to provide run-loss valves having very large 
flow capacities. For example, prior valves typically had flow orifices in 
the range of 0.050 inch diameter or smaller. Current valves might have 
flow orifice diameters as large as 0.290 inch. 
Presumably, one might wish to use a high flow capacity run-loss valve with, 
for example, a tank-mounted OBVR system including fill limit control to 
provide a comprehensive vapor recovery and pressure control system. But it 
is contemplated that a parallel arrangement of the run-loss valve with the 
OBVR system would prove unacceptable because the two tend to work at odds 
with one another in controlling overfill of the fuel tank. 
During refueling of a fuel tank provided with a parallel arrangement of a 
run-loss valve and an OBVR system, the fill-limit control valve in the 
OBVR system will close off the OBVR system, preventing further escape of 
fuel vapor, when a predetermined amount of liquid fuel has been pumped 
into the tank. However, the high-flow capacity run-loss valve will tend to 
remain open, continuing to allow escape of fuel vapor and thus allowing 
additional liquid fuel to be pumped into the fuel tank. It would thus be 
desirable to provide a tank venting and vapor recovery system capable of 
selectively providing venting through either a run-loss valve or an OBVR 
valve while properly preventing tank overfill. 
According to the present invention, an apparatus is provided for 
controlling discharge of fuel vapors from a vehicle fuel tank having a 
filler neck. The apparatus is particularly suited for controlling venting 
of fuel vapor from a first vent valve (for example, a run-loss valve) and 
a second vent valve (for example, an OBVR system). 
In particular, the controlling apparatus comprises a housing defining an 
interior region. The housing is formed to include first and second inlet 
ports connecting the interior region in fluid communication with the fuel 
tank. The housing is also formed to include a signal port connecting the 
interior region in fluid communication with the filler neck, and an outlet 
port. 
The controlling apparatus further includes a first valve assembly movable 
between a blocking position and a venting position. When moved to its 
blocking position, the first valve assembly prevents fuel vapor received 
from the first inlet port from flowing through the interior region during 
vehicle refueling. When positioned in the venting position, the first 
valve assembly allows fuel vapor received from the first inlet port to 
flow through the interior region to the outlet port during vehicle 
operation. 
The controlling apparatus further includes a signal passageway extending 
between the filler neck and the signal port to expose the first valve 
assembly to fuel vapor pressure from the filler neck. Filler neck pressure 
thus moves the first valve assembly toward its venting position during 
vehicle operation. 
The controlling apparatus further includes a second valve assembly also 
movable between a blocking position and a venting position. When moved to 
its blocking position, the second valve assembly prevents fuel vapor 
received from the second inlet port from flowing through the interior 
region. Advantageously, the second valve assembly is maintained when the 
first valve assembly is moved to its venting position during vehicle 
operation. When the second valve assembly is positioned in its venting 
position, fuel vapor received from the second inlet port is able to flow 
through the interior region to the outlet port. Also advantageously, the 
first valve assembly is maintained in its blocking position when the 
second valve assembly moves to its venting position during vehicle 
refueling. 
Further advantageously, the first valve assembly is initially actuated to 
move away from its blocking position by fuel vapor pressure received from 
the filler neck, but then is further depressed by fuel vapor pressure 
received from the fuel tank. This helps ensure that the first valve 
assembly maintains the second valve assembly in its blocking position 
during vehicle operation. 
In accordance with one aspect of the invention, the controlling apparatus 
further includes a flow tube extending between the first inlet port and 
the first valve assembly. The flow tube includes a valve seat and the 
first valve assembly includes a rigid valve body sized to sealingly engage 
the valve seat. The first valve assembly further includes a flexible 
member linked to the rigid valve body and deformable under a predetermined 
amount of fuel vapor pressure received from the signal port to move the 
rigid valve body out of engagement with the valve seat to place the first 
valve assembly in its venting position. 
Additional objects, features, and advantages of the invention will become 
apparent to those skilled in the art upon consideration of the following 
detailed description of preferred embodiments exemplifying the best mode 
of carrying out the invention as presently perceived.

DETAILED DESCRIPTION OF THE DRAWINGS 
A preferred embodiment of a fuel tank venting and vapor recovery system in 
accordance with the present invention is illustrated in FIG. 1. The system 
is operable to control venting and vapor recovery from a vehicle fuel tank 
10 having a filler neck 12. A fuel cap 14 sealingly engages the upper end 
of filler neck 12 during normal vehicle operation. 
The tank venting and vapor recovery system includes a run-loss valve 16, a 
fill-limit valve 18, and a control valve 20 for controlling venting from 
the run-loss valve 16 and the fill-limit valve 18 respectively. Control 
valve 20 is connected to a fuel vapor recovery device 22, which may be a 
carbon canister or other art recognized device. 
Run-loss valve 16 is typically a valve of the type shown, for example, U.S. 
Pat. No. 5,028,244 issued to Szlaga or U.S. Pat. No. 5,065,782 to Szlaga, 
relevant portions of which are incorporated by reference herein. Run-loss 
valve 16 functions to vent substantial volumes of fuel vapor from the fuel 
tank during vehicle operation to maintain appropriate operating pressure 
in the fuel tank. As those of ordinary skill in the art will appreciate, 
run-loss valve 16 may be one of a variety of commercially available 
run-loss valves. 
Fill-limit valve 18 may be of the variety shown in detail in FIG. 3 and 
described hereinbelow. As noted above, fill limit valve 18 rises on rising 
liquid fuel and closes at a predetermined liquid fuel level, preventing 
additional fuel vapor from venting through control valve 20. This creates 
a vapor blanket or pressure head above the liquid fuel in fuel tank 10 
which acts to force fuel up filler neck 12 at the proper point during 
vehicle refueling to trigger a fuel nozzle shut-off device. 
Control valve 20 includes a housing 24 which defines an interior region 26. 
Housing 24 is formed to include a first inlet port 28, a second inlet port 
30, a signal port 32, and an outlet port 34. A vapor inlet passageway 36 
extends between run-loss valve 16 and first inlet port 28 and cooperates 
with first inlet port 28 to connect interior region 26 in fluid 
communication with fuel tank 10. Vapor inlet passageway 36 and first inlet 
port 28 thus serve as first means for conducting fuel vapor from fuel tank 
10 to interior region 26. 
Likewise, a vapor inlet passageway 38 extends between fill-limit valve 18 
and second inlet port 30 and cooperates with second inlet port 30 to 
connect interior region 26 in fluid communication with fuel tank 10. Vapor 
inlet passageway 38 and second inlet port 30 thus serve as second means 
for conducting fuel vapor from fuel tank 10 to interior region 26. 
Signal port 32 connects interior region 26 to filler neck 12 by way of a 
signal passageway 40. Signal passageway 40 and signal port 32 together 
provide third means for conducting fuel vapor from the filler neck to 
interior region 26 to assist in actuating control valve 20 as described 
below. 
A vapor outlet passageway 42 extends between outlet port 34 and vapor 
recovery device 22. Because vapor recovery device 22 is exposed to 
atmospheric pressure, vapor outlet passageway 42, and any portion of 
interior region 26 connected via outlet port 34 in fluid communication 
therewith, is also exposed to atmospheric pressure. 
A first valve assembly 44 is disposed in interior region 26. First valve 
assembly 44 is movable between a blocking position preventing fuel vapor 
received from first inlet port 28 from flowing through interior region 26 
to outlet port 34 and a venting position allowing fuel vapor received from 
first inlet port 28 to flow through interior region 26 to outlet port 34, 
and subsequently through outlet passageway 42 to vapor recovery device 22. 
Thus, first valve assembly 44 serves as first valve means for selectively 
blocking flow of fuel vapors from first vapor inlet passageway 36 and 
first vapor inlet port 28 through interior region 26. 
First valve assembly 44 includes a flexible diaphragm 46 and a backing 
plate 48 appended to diaphragm 46 for movement therewith. Backing plate 48 
includes an extension or stop 50. First valve assembly 44 also includes a 
central portion 52 corresponding to the central portion of diaphragm 46, 
an intermediate annular portion 54 concentric with central portion 52 and 
corresponding with the intermediate portion of diaphragm 46, and an outer 
circumferential portion 56 corresponding with the outer circumferential 
portion of diaphragm 46. Diaphragm 46 is mounted in interior region 26 by 
its peripheral edge 58 which is sandwiched between portions of an interior 
wall 60 of housing 24 and an exterior wall 62 thereof. 
One important advantage of the embodiment of the invention illustrated in 
FIG. 1 is that it provides a concentric venting flow path for venting of 
fuel vapor received at first inlet port 28 from fuel tank 10 by way of 
run-loss valve 16. In the concentric venting flow path, central portion 52 
is exposed to fuel vapor pressure from fuel tank 10 via first inlet port 
28, outer circumferential portion 56 is exposed to fuel vapor pressure 
from filler neck 12 via signal port 32, and intermediate portion 54 is 
exposed to atmospheric pressure via outlet port 34. The concentric flow 
path is effected by cooperation between a flow tube 64, an annular 
partition 66, walls 60 and 62 of housing 24, and diaphragm 46 itself. 
In particular, flow tube 64 connects first inlet port 28 with central 
portion 52 to expose central portion 52 to fuel vapor pressure exhausted 
from fuel tank 10 and passing thereafter through run-loss valve 16 and 
first vapor inlet passageway 36 to reach first inlet port 28. Flow tube 64 
is preferably of relatively large diameter (for example, 0.290 inch) to 
handle the large volumes of fuel vapor exhausted from fuel tank 10 through 
run-loss valve 16. Flow tube 64 terminates in a first valve seat 68 
against which diaphragm 46 seats when first valve assembly 44 is in its 
blocking position as illustrated in FIG. 1. For purposes of describing 
this embodiment of the invention, first valve seat 68 defines the border 
between central portion 52 and intermediate portion 54. 
Annular partition 66 lies in spaced-apart relationship with flow tube 64 
and surrounds it so as to define an intermediate annular chamber 70. 
Annular partition terminates in a second valve seat 72 defining the border 
between intermediate portion 54 and outer circumferential portion 56. 
Annular partition 66 also is formed to include an opening 74 placing 
intermediate annular chamber 70 in fluid communication with an outlet tube 
76 which in turn is linked to outlet port 34. Because intermediate annular 
chamber 70 is thus open to outlet port 34, chamber 70 and, 
correspondingly, intermediate portion 54, are exposed to atmospheric 
pressure. 
Annular partition 66 also cooperates with housing 24 to define an outer 
circumferential chamber 78. Outer circumferential chamber 78 is bordered 
by walls 60, 62 of housing 24, and a top wall 80 thereof, as well as by 
annular partition 66 and outer circumferential portion 56 of diaphragm 46. 
Chamber 78 is open to signal port 32 so that chamber 78, and portion 56 of 
diaphragm 46, are exposed to fuel vapor pressure from filler neck 12. As 
described below, this fuel vapor pressure signal from filler neck 12 acts 
upon outer circumferential portion 56 to move diaphragm 46 from its 
blocking position toward its venting position, allowing venting to occur 
during vehicle operation to properly regulate pressure in fuel tank 10. 
A second valve assembly 82 is positioned in interior region 26 to provide 
an on-board vapor recovery function during vehicle refueling. Second valve 
assembly 82, which may be a standard valve plate or poppet valve, is 
positioned for sealing engagement with a valve seat 84. Second valve 
assembly 82 is movable between a blocking position (illustrated in FIG. 1) 
preventing fuel vapor received from second inlet port 30 from flowing 
through interior region 26 and a venting position (not shown) allowing 
fuel vapor received from second inlet port 30 to flow through interior 
region 26 to outlet port 34. Second valve assembly 82 thus serves as 
second valve means for selectively blocking flow of fuel vapor from second 
inlet passageway 38 and second inlet port 30 to interior region 26. 
Advantageously, a spring 86 extends between valve assembly 82 and backing 
plate 48 to serve as means for biasing second valve assembly 82 in 
opposition to first valve assembly 44. The outer edges 88 of backing plate 
48 and valve assembly 82 may be curved to better retain spring 86 in its 
proper position. Spring 86 assists in maintaining second valve assembly 82 
in its blocking position when first valve assembly 44 moves to its venting 
position, thus allowing control valve 20 to properly select between 
venting through first valve assembly 44 during vehicle operation and 
through second valve assembly 82 during vehicle refueling. 
In operation, the embodiment the invention illustrated in FIG. 1 provides 
selective venting to vapor treatment site 22 through either the run-loss 
valve 16 or the fill-limit valve 18 by venting fuel vapor through either 
first valve assembly 44 or second valve assembly 82. In FIG. 1, control 
valve 20 is shown in a static configuration in which both first valve 
assembly 44 and second valve assembly 82 are in their respective blocking 
positions. It will be appreciated that during vehicle operation, first 
valve assembly 44 is positioned in its venting position, holding second 
valve assembly 82 in its blocking position. During vehicle refueling, the 
opposite configuration is reached; that is, second valve assembly 82 is 
moved to its venting position, assisting in holding first valve assembly 
44 in its blocking position. 
Specifically, during vehicle operation with fuel cap 14 securely mounted on 
filler neck 12, fuel vapor from fuel tank 10 can pass through run-loss 
valve 16 and through vapor inlet passageway 36 to reach first inlet port 
28, from which it passes through flow tube 64 to impinge upon relatively 
small central portion 52 of diaphragm 46. At the same time, fuel vapor 
pressure from the upper portion of filler neck 12 travels through signal 
passageway 40, passing through signal port 32 to reach outer 
circumferential chamber 56. Although the fuel vapor from filler neck 12 is 
likely to be at a pressure slightly less than tank pressure, the fuel 
vapor acts across the relatively large outer circumferential portion 56 of 
diaphragm 46. It is thought that the filler neck pressure is likely to be 
less than tank pressure, at least when the fuel tank is filled with liquid 
fuel, because some pressure is lost when liquid fuel is lifted up filler 
neck 12. 
Additionally, the underside of diaphragm 46 is exposed to atmospheric 
pressure received from outlet port 34. Thus, the combined force of tank 
pressure on central portion 52 and filler neck pressure on outer 
circumferential portion 56 is sufficient to depress or deform diaphragm 46 
in opposition to spring 86, moving first valve assembly 44 away from its 
blocking position toward its venting position. This increases the pressure 
on spring 86, assisting in holding second valve assembly 82 in its 
blocking position. 
Diaphragm 46, when depressed in this fashion, simultaneously unseats from 
both first valve seat 68 and second valve seat 72. This allows fuel vapor 
in flow tube 66 to flow into intermediate annular chamber 54 and to pass 
to opening 74, from which the fuel vapor can flow through outlet tube 76 
and through outlet port 34 to ultimately reach outlet passageway 42. 
Some fuel vapor from flow tube 64 will tend to flow through intermediate 
annular chamber 70 to reach outer circumferential chamber 78, bringing the 
pressure in outer circumferential chamber 78 up from neck pressure to tank 
pressure. This is advantageous because it ensures that diaphragm 46 is 
fully depressed, so that stop 50 contacts valve assembly 82, assisting in 
preventing valve assembly 82 from moving out of sealing engagement with 
valve seat 84. Thus, second valve assembly 82 is held in its blocking 
position preventing fuel vapor received from second inlet 30 from reaching 
interior region 26. Thus, while neck pressure initially actuates diaphragm 
46 to unseat diaphragm 46 from valve seats 68, 72, it is tank pressure 
which thereafter sets to depress diaphragm 46 and therefore to move first 
valve assembly 44 to its venting position. 
During vehicle refueling, fuel cap 14 is removed from filler neck 12 so 
that pressure in filler neck 12, and hence in signal passageway 40, is 
atmospheric. The pressure in outer circumferential chamber 78, and 
correspondingly at outer circumferential portion 56 of diaphragm 46, is 
thus also atmospheric. Likewise, the pressure at the underside of 
diaphragm 46 is atmospheric. First valve assembly 44 therefore remains in 
its blocking position. 
When fuel vapor pressure in fuel tank 10 increases to a predetermined 
amount (for example, about 1 kPa), second valve assembly 82 is moved away 
from valve seat 84 against the bias of spring 86 to its venting position 
allowing fuel vapor received from second inlet 30 to vent through interior 
region 26 to outlet port 34. Thus, advantageously, in this configuration, 
control valve 20 connects fill limit valve 18 in fluid communication with 
vapor outlet 34 while blocking fuel vapor from run-loss valve 16 from 
venting to outlet port 34. That is, in this configuration, control valve 
20 properly performs the OBVR and fill limit functions without 
interference from run-loss valve 16. 
It is contemplated that the ratio of the diameter of flow tube 64 to the 
diameter of diaphragm 46 will be kept relatively low. Of course, the 
diameter of flow tube 64 must be sufficient to handle the relatively large 
flow of fuel vapor exhausted through run-loss valve 16. However, because 
flow tube 64 conducts tank pressure to central portion 52 of diaphragm 46, 
as the flow tube diameter (and hence the central portion diameter) 
increases, there is a greater likelihood that the action of tank pressure 
on central portion 52 alone will move diaphragm 46 away from valve seats 
68, 72 during refueling. By keeping the diameter ratio as low as possible, 
this potential problem can be avoided. 
Another embodiment of the invention is illustrated in FIG. 2, in which 
features having reference numbers similar to those in FIG. 1 perform the 
same or similar function as they perform in FIG. 1. In the embodiment of 
FIG. 2, a first valve assembly 144 includes a diaphragm 146. First valve 
assembly 144 includes a central portion 152 corresponding to the central 
portion of diaphragm 146, an intermediate portion 154, and an outer 
circumferential portion 156. 
However, in contrast to the embodiment of FIG. 1, central portion 152 is 
exposed to atmospheric pressure and intermediate portion 154 is exposed to 
fuel vapor pressure from fuel tank 10. In particular, flow tube 164 
extends between first inlet port 128 and an intermediate annular chamber 
174 defined between the walls of flow tube 164 and between partitions 166 
and 168. Outer circumferential chamber 178 is similar to that in the 
embodiment of FIG. 1. 
In FIG. 2a, a partial sectional view of control valve 120 is provided. As 
shown, central portion 152 of diaphragm 146 is exposed to atmospheric 
pressure received from outlet port 134 through opening 176. Flow tube 164 
communicates with intermediate chamber 174. Wall 168 defines the border 
between outer circumferential chamber 178 and intermediate chamber 174. 
Thus, in operation of the embodiment of FIG. 2 during operation of the 
vehicle, outer circumferential chamber is once again exposed to fuel vapor 
pressure from filler neck 112, received via signal port 132. Intermediate 
annular chamber 174 is exposed to fuel vapor pressure from fuel tank 
received via first inlet port 128. The underside of diaphragm 146 is 
exposed to atmospheric pressure as in the embodiment of FIG. 1. The 
combined force of neck pressure on the outer circumferential portion 156 
and tank pressure on intermediate portion 154 causes first valve assembly 
144 to move away from its blocking position toward its venting position, 
unseating from valve seats 170, 172. 
Advantageously, the shifting of flow tube 164 to extend to intermediate 
annular chamber 154 may be important to prevent diaphragm 146 from 
unseating improperly from valve seats 170, 172. Specifically, it is 
thought that fuel vapor will reach that part of outer circumferential 
portion 156 which is closest to signal port 132 and may act on that part 
of portion 156 disproportionately, causing diaphragm 146 to tip by moving 
away from one of valve seats 170, 172 prior to moving away from the other. 
It is thought that shifting flow tube 164 to an offset position as shown 
in FIG. 2 can assist in preventing this tipping problem. 
The embodiment of FIG. 2 also includes a second valve assembly 182 provided 
with a vacuum relief valve 196. An opening 194 is formed in valve assembly 
182. A backing plate 186 appended to valve assembly 182 is also formed to 
include such an opening. 
Vacuum relief valve 196 is a "T"-shaped member having a horizontal portion 
configured to sealingly engage backing plate 186 to prevent leakage of 
fuel vapor through opening 194. A spring 198 extends between horizontal 
portion 168 and a spring seat 199 formed in passageway 138. Spring 199 
biases valve 196 into sealing engagement with plate 186. 
Under vacuum conditions in fuel tank 10, valve 196 moves against the bias 
of spring 198 out of engagement with backing plate 186, allowing vacuum 
relief. As those of ordinary skill in the art will appreciate, any 
standard vacuum relief valves can be used in place of valve 196. For 
example, an umbrella-type valve as will be further described in reference 
to FIGS. 3-7. 
Another embodiment of the claimed invention is illustrated in FIGS. 3-7 in 
which features having reference numbers similar to those in FIG. 1 perform 
the same or similar function as they perform in FIG. 1. As shown, e.g., in 
FIG. 3, this embodiment of the invention includes a valve assembly 244 
which includes a diaphragm 246. The peripheral edge 254 of diaphragm 246 
is sandwiched between walls 256 and 258 of housing 224. Diaphragm 246 
includes a central portion 247 and an outer circumferential portion 249. 
A pair of plates 260, 262 is appended to diaphragm 246 for movement 
therewith. Plates 260, 262 cooperate to define a central chamber 250 
corresponding to central portion of diaphragm 247. Plate 260 includes a 
projection or stop 264. Plate 262 is formed to include an opening 268. 
Valve assembly 244 also includes a rigid valve body 270. Valve body 270 
includes a head 272 sized to sealingly engage a valve seat 276 to block 
flow of fuel vapor through flow tube 227. A spring 278 extending between 
an interior partition 279 and head 272 biases valve body 270 into 
engagement with valve seat 276. Valve body 270 also includes a post 274 
extending through opening 268 into central chamber 250. 
At the end of post 274 opposite head 272 is a projection or flange 280 
which is larger in diameter at its uppermost portion than is opening 268. 
Post 274 extends a predetermined distance into central chamber 250 when 
valve assembly 244 is positioned in its blocking position as shown in FIG. 
3. 
Outer circumferential portion 249 of diaphragm 246 cooperates with an 
interior wall 256 and interior partition 279 to define an outer 
circumferential chamber 282. Outer circumferential chamber is open to 
signal port 232 to expose outer circumferential portion 249 to fuel vapor 
pressure from filler neck 212. 
Second valve assembly 289 is similar to second valve assembly 182 shown in 
FIG. 2. Second valve assembly 289 includes valve plates 286, 288. Valve 
plate 288 sealingly engages a valve seat 290 when second valve assembly 
289 is positioned in its blocking position. Valve plate 286 is formed to 
include an opening 292. An umbrella-type vacuum relief valve 294 mounted 
to valve plate 286 is movable relative to the opening in response to tank 
vacuum conditions. 
Like the embodiments of FIGS. 1 and 2, the embodiment of FIG. 3 includes a 
spring 296 nested between second valve assembly 289 and first valve 
assembly 244. Spring 296 provides means for biasing second valve assembly 
289 in opposition to first valve assembly 244. 
Detailed construction of a fill-limit valve 218 is also shown in FIG. 3. 
Fill-limit valve 218 includes a housing 298 in which a fill-limit valve 
member 300 is movably received. The illustrated valve member 300 is 
similar to those described in U.S. Pat. Nos. 5,044,397 and 4,991,615 to 
Szlaga et al., relevant portions of which are hereby incorporated by 
reference. Valve member 300 is sized to engage a valve seat 302 formed in 
housing 298. It will be appreciated by those of ordinary skill in the art 
that a wide variety of fill-limit valves may be used in accordance with 
the invention described herein. 
Housing 298 extends through an opening 291 in a top wall 293 of fuel tank 
210. Housing 298 includes a circular flange 295 mateable with a similar 
flange 297 on control valve 220. A gasket 299 is sandwiched between 
flanges 295, 297 and extends to top wall 293 of fuel tank 210 to assist in 
preventing unwanted leakage of fuel vapor between housing 298 and the 
edges of top wall 293 defining opening 291. Additionally, an 0-ring gasket 
301 may be provided to further assist in preventing such leakage. 
Operation of the embodiment of FIG. 3 during operation of the vehicle under 
low tank pressure conditions is illustrated in FIG. 4. Because the vehicle 
is in operation, fuel cap 214 is securely mounted on filler neck 212. Fuel 
vapor pressure in the filler neck is transmitted via signal passageway 240 
to outer circumferential chamber 282. Thus, outer circumferential portion 
249 of diaphragm 246 is exposed to fuel vapor pressure on one side as 
indicated by flow arrows 304 and atmospheric pressure on the other side. 
Diaphragm 246 therefore begins to move relative to rigid valve body 270 
over a predetermined distance as shown in FIG. 3. 
If tank pressure is relatively low (for example, less than 0.25 kPa) 
diaphragm 246 will not depress far enough for plate 260 to come into 
engagement with plate 286. Thus, rigid valve body 270 will remain seated 
against valve seat 276, blocking the flow of fuel vapor from flow tube 227 
to outlet tube 284. 
Preferably, the predetermined distance is calibrated so that diaphragm 246 
moves at least 50% of its total movement distance before plate 260 engages 
plate 286. Advantageously, this provides a delay between the time of 
initial depression of diaphragm 246 and the movement of valve assembly 244 
to its venting position by way of the unseating of rigid valve body 270 
from valve seat 276. This allows for a buildup of tank pressure in outer 
circumferential chamber 282 to act against outer circumferential portion 
249. When the tank pressure becomes high enough, as shown in FIG. 5, 
diaphragm 246 is fully depressed prior to venting fuel vapor past valve 
seat 276 to outlet tube 284, ensuring that second valve assembly 289 
remains in its blocking position preventing unwanted sloshing of liquid 
fuel through second inlet port 230. 
Particularly in FIG. 5, as diaphragm 246 has continued to depress due to 
fuel vapor pressure buildup in outer circumferential chamber 282, rigid 
valve body 270 unseats from valve seat 276, moving against the bias of 
spring 278 to place valve assembly 244 in its venting position allowing 
flow of fuel vapor through flow tube 227 to outlet tube 284 and ultimately 
to vapor outlet 234 as indicated by flow arrows 306. 
In addition, valve assembly 289 is retained in its blocking position when 
valve assembly 244 is moved to its venting position. Plate 260 engages 
plate 286, and stop 264 may engage a portion of vacuum relief valve 294, 
preventing second valve assembly 289 from unseating from valve seat 290. 
Thus, during vehicle operation at high tank pressure conditions, all 
venting from fuel tank 210 occurs via flow tube 227, which receives fuel 
vapor output from run-loss valve 216; no venting occurs through second 
valve assembly 289. 
Operation of the embodiment of FIG. 3 during tank vacuum conditions is 
shown in FIG. 6. There, both first valve assembly 244 and second valve 
assembly 289 are shown in their respective blocking positions. Vacuum 
relief valve 294 is shown moved away from opening 283 in response to tank 
vacuum conditions. Atmosphere can enter the fuel tank through opening 283 
as illustrated by arrows 308 to relieve the vacuum condition. 
Operation of the embodiment of FIG. 3 during vehicle refueling is 
illustrated in FIG. 7. Effectively, FIG. 7 shows control valve 220 
performing its OBVR function. There, a liquid fuel 314 is introduced into 
fuel tank 210, fuel vapor pressure builds up in fuel tank 210 and acts 
against second valve assembly 289. However, because the upper filler neck 
is at atmospheric pressure, the pressure in outer circumferential chamber 
282 is likewise atmospheric. Although tank pressure is received in central 
chamber 250 by way of first inlet port 228 and flow tube 227, it is 
insignificant since it acts only across relatively small central portion 
247 of diaphragm 246. 
Thus, second valve assembly 289 is moved against the bias of spring 288 
away from its blocking position, unseating from valve seat 290. Fuel vapor 
received through second inlet port 230 can vent to outlet port 234 as 
indicated by arrows 310. Advantageously, when second valve assembly is 
moved to its venting position as illustrated in FIG. 7, the force on 
spring 288 is increased such that first valve assembly is prevented from 
moving away from its blocking position. Thus, fuel vapor exhausted through 
run-loss valve 216 cannot vent to outlet port 234. 
When the level of liquid fuel in fuel tank 210 reaches a predetermined 
level, fill limit valve 218 (shown in FIG. 3) rises and seats against 
valve seat 302. This prevents further venting through second valve 
assembly 289. 
Yet another embodiment of the invention is illustrated in FIG. 8. As the 
embodiment of FIG. 8 shows, a control valve in accordance with the present 
invention need not be mounted directly atop the fill-limit valve. Rather, 
control valve 220 may be provided with a passageway extension 336 to mate 
with a similar extension 338 on fill-limit valve 318. In other respects, 
this embodiment of the invention is identical in structure and function to 
the embodiment of FIGS. 3-7. 
Although the invention has been described in detail with reference to 
certain preferred embodiments, variations and modifications exist within 
the scope and spirit of the invention as described and defined in the 
following claims.