Swellable adsorbent diagnostic for fuel vapor handling system

An apparatus and method for use in diagnosing an evaporative emission canister collection and purge system. An EVAP system of a vehicle can be diagnosed through the use of a swellable adsorbent disposed in the system's canister. The swellable adsorbent is expandable upon adsorption of fuel vapors and contractible upon desorption. By sensing the expansion and contraction response, a diagnostic mechanism can determine whether the vapor collection and purge functions are operating properly.

BACKGROUND OF THE INVENTION 
This invention relates to a fuel vapor handling system. More particularly, 
the invention is directed to an apparatus and method for use in diagnosing 
the system. The subject of this application is related to the following 
copending patent application: Ser. No. 08/236,071, filed May 2, 1994, 
entitled Conductivity Sensor Diagnostic for Fuel Vapor Handling System, 
filed concurrently with this specification and assigned to the assignee of 
this invention. 
Automobiles conventionally include a system directed to controlling the 
emission of fuel vapors generated by fuel carried in the vehicle's fuel 
system. These evaporative emission control systems, known as "EVAP" 
systems, are implemented as a collateral system to the fuel system. The 
diurnal and running loss vapors the EVAP system collects result primarily 
from ambient temperature excursions and from the cyclic operation and 
parking of a vehicle that results from the operator's use of the vehicle 
as transportation. 
An EVAP system typically includes a vapor collection system with an 
adsorption mechanism to capture and store vapors generated by the fuel 
system. The EVAP system also includes a purge system to transfer the 
stored vapors from the adsorbent to the vehicle's engine for consumption 
in the normal combustion process. The purge system generally includes a 
purge valve that selectively opens a passage between the EVAP system and 
the vehicle's engine to effect a controllable rate of purge. 
Conventionally, effective diagnosis of an EVAP system is generally provided 
through manual inspection of the system in response to noticeable engine 
performance degradation or noticeable fuel or vapor leakage. Periodic 
manual vacuum testing for leaks and purge valve functional checking 
provides additional effectiveness in diagnosing system operation. 
Research has been conducted into developing on-board means for 
automatically diagnosing EVAP systems, capable of automatically detecting 
leaks in the system and determining whether the purge system is operating 
properly. Development of on-board automatic diagnostic systems has 
generally resulted in proposed systems related to mechanisms that close 
the EVAP system off from the atmosphere and then generate a positive or 
negative internal system pressure. By then measuring changes in the system 
pressure, the diagnostic mechanisms attempt to discern whether the 
evaporative control system is functioning properly. 
Generally, sensitive diagnostic systems are proposed with precision 
pressure detection devices to work on small pressure differentials. To 
avoid unacceptable erroneous fault reporting, a pressure based diagnostic 
system must be able to discern that unexpected pressure gradients are a 
result of system malfunctions and not changing ambient conditions or other 
normal collateral effects. This tends to complicate and drive up the cost 
of a diagnostic mechanism. Accordingly, automatic EVAP diagnostic systems 
have proven difficult to implement. 
Adsorption canister collection and storage system use in on-board refueling 
vapor recovery (ORVR) systems is known. ORVR systems are vehicle based 
systems directed to capturing fuel vapors generated by the transfer of 
fuel from a pump to a vehicle. ORVR systems have been proposed that are 
configured in a manner similar to an EVAP system including a storage 
canister and a purge system. 
SUMMARY OF THE INVENTION 
This invention is directed to a fuel vapor handling system and generally 
includes a fuel vapor storage canister containing a swellable adsorbent 
material expandable and contractible in response to changes in fuel vapor 
concentration. A sensor to detect expansion and contraction of the 
adsorbent is provided for use in assisting automatic diagnosis of the 
system. A diagnostic system is preferably provided as part of a vehicle's 
conventional electronic controller, capable of utilizing expansion and 
contraction data generated from the adsorbent in diagnosing the system. 
The swellable adsorbent system is directed to a device that provides for 
automatically assisting in diagnosis of the vapor collection and purge 
systems, functions without closing the fuel vapor control system off from 
the atmosphere and can be implemented with minor changes to existing fuel 
vapor control system components.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENT 
FIG. 1 illustrates an EVAP system of a vehicle's fuel system employing 
principles of the present invention. The system includes a vapor storage 
canister 10. Canister 10 preferably includes a chambered arrangement 
created by the exterior wall 12 and the interior wall 11. Chambers 14 and 
15 result from this arrangement. Interior wall 11 does not completely 
separate chamber 14 from chamber 15, rather a passage 17 is established 
between the chambers. 
Wall 12 establishes a substantially closed container by providing a surface 
on all sides of the canister 10. In the preferred arrangement, wall 12 
creates a canister 10, that is substantially rectangular parallelepiped in 
shape, although the shape is not a critical feature. Selected openings are 
provided in canister 10 through wall 12. Opening 21 between chamber 14 and 
the atmosphere functions as a vent. Opening 22, between chamber 15 and 
conduit 34, functions as a threshold to conduit 34 permitting selected 
flow out of canister 10. Opening 23, between chamber 15 and conduit 35, 
functions as a threshold for chamber 15 to conduit 35 permitting flow 
therebetween. 
Conduit 35 establishes a closed flow path between canister 10 and the top 
of fuel tank 50 that carries a supply of fuel 60. Conduit 34 establishes a 
closed flow path between canister 10 and an engine 40. Conduit 34 includes 
normally closed purge valve 70 that functions to selectively control the 
fluid flow rate through conduit 34. Vent opening 21 allows the flow of air 
into and out of canister 10, thereby facilitating the transfer of fluid 
into and out of the canister through openings 23 and 22. 
Chamber 14 principally contains activated carbon particles 80. Activated 
carbon is a conventional adsorbent used in EVAP systems. It is preferable 
to include an amount of activated carbon 80 in the present arrangement to 
optimize the adsorptive characteristics of the mechanism, although the 
activated carbon 80 may be excluded from the device. Chamber 14 preferably 
contains a screen 18 to prevent the passage of particles from chamber 14 
to opening 21 and to aid in distributing air flow passing through the vent 
and into chamber 14. A conventional material used for screen 18 is a 
polymeric foam, although alternate materials can readily be substituted. 
Another filter 19, is preferably, similarly positioned between chamber 15 
and openings 22 and 23. 
Chamber 15 contains an organic polymer compound as expandable and 
contractible adsorbent 90. Adsorbent 90 is a material such as highly cross 
linked polystyrene that functions as an adsorbent and also expands upon 
adsorption of fuel vapors and contracts upon desorption of the vapors. An 
example of a suitable material is DOW XU-43546.01 which is supplied as 
nominal 1.5 millimeter diameter spherical beads. This material has a pore 
volume of approximately 1.24 cubic centimeters per gram and a surface area 
of approximately 1400 square meters per gram. 
Other polymeric compounds that expand upon adsorption of fuel vapors and 
contract upon desorption, such as polypropylene and polyisoprene, are 
known in the art. Another material with a known property to expand in 
relation to the concentration of fuel vapor is silicone rubber. Therefore, 
alternative materials can be configured to provide the expanding and 
contracting function of the invention. A device using an alternative 
material includes a canister primarily filled with activated carbon and 
includes the expandable and contractible material disposed adjacent to a 
sensor to detect the expansion and contraction. 
A moveable partition 101 is preferably disposed at the bottom of canister 
10. Although partition 101 is disposed substantially about the entire 
bottom of canister 10, it could function sufficiently if limited to within 
chamber 15 for coaction with the expandable and contractible adsorbent 90. 
Partition 101 is biased against the adsorbent materials by springs 105 and 
106. The springs urge partition 101 against the adsorbent thereby 
maintaining the individual particles in close proximity to one another. 
Although the biasing agent shown comprises springs 105 and 106, 
alternative devices such as a volume of resilient material may be used. 
Partition 101 coordinatedly moves with the expansion and contraction of 
adsorbent 90 in relation to the concentration of fuel vapor in the 
adsorbent. 
Sensor 107 is disposed between partition 101 and canister wall 12. The 
sensor illustrated represents a contact that is closed in response to 
expansion of adsorbent 90 and is opened in response to contraction of 
adsorbent 90. Other sensing devices are readily applicable to serving this 
function. Known devices such as a load cell can be used to sense force 
when adsorbent expansion compresses partition 101 against wall 12. A 
sensor such as a linear motion potentiometer can be used to sense movement 
of partition 101. Any of numerous similar devices can be used as sensor 
107 to generate signals indicative of expansion and contraction of 
adsorbent 90. With some conventional sensors partition 101 would not be 
required and therefore the device could be positioned directly in contact 
with adsorbent 90. 
Referring to FIGS. 2 and 3 alternative embodiments of the canister are 
illustrated. In FIG. 2, canister 110 is arranged with chambers 115 and 
114, separated by horizontal partition 111. Horizontal partition 111 
includes a plurality of openings that facilitate fluid communication 
between chambers 114 and 115. Chamber 115 includes expandable and 
contractible adsorbent 190 and chamber 114 contains activated carbon as 
adsorbent 180. 
The canister 110 includes openings 121-123. Opening 121 serves as a vent. 
Openings 122 and 123 provide fluid paths for connection to conduits (not 
shown) permitting fluid to be transferred into and out of canister 110. 
Sensor 207 is disposed between moveable wall 201 and canister wall 112. 
Sensor 207 is responsive to expansion and contraction of adsorbent 190 in 
relation to the concentration of fuel vapors in canister 110. Resilient 
foam 118 demonstrates compressibility upon expansion of adsorbent 190 and 
expandability upon contraction of adsorbent 190 biasing wall 201 against 
adsorbent 190. 
FIG. 3 illustrates a canister substantially identical to that shown in FIG. 
2 except that the activated carbon and partition are absent. In this 
embodiment canister 210 is substantially filled with expandable and 
contractible adsorbent 290. Sensor 307 provides a device to detect 
expansion and contraction of the adsorbent. 
FIG. 4 illustrates performance characteristics of a swellable polymeric 
adsorbent. The data represents the movement possible with this type of 
adsorbent arranged in a 570 cubic centimeter bed of 18 centimeters height. 
The solid curve represents the expansion of the adsorbent bed in response 
to increasing concentrations of gasoline vapor. The dashed curve 
represents the contraction of the adsorbent bed in response to decreasing 
concentrations of gasoline vapor. The resultant movement can be taken up 
by the springs 105 and 106 (as shown in FIG. 1) when an appropriate amount 
of adsorbent is contained in a closed canister arrangement. 
Referring once again to FIG. 1 the adsorption process will be described. 
Under certain conditions vehicle fuel 60 has the capacity to give off 
vapor, particularly in response to changing temperatures and pressures, 
thereby creating a vapor constituent in the air contained in head space 61 
in fuel tank 50. When the vapors cause the pressure inside tank 50 to rise 
above atmospheric, a flow is generated through conduit 35. Vapors 
entrained in the head space 61 flow through conduit 35 and enter canister 
10 through opening 23. The fuel vapors are taken up by adsorbents 90 and 
80 and the air is allowed to pass to the atmosphere through opening 21. 
As the concentration of vapor in adsorbent 90 increases the adsorbent 90 
responds with a physical increase in size, (reference is directed to FIG. 
4). The increase in size creates a force against partition 101 and acts to 
compress springs 105 and 106. The movement of partition 101 reaches a 
point where the contacts of sensor 107 are closed. This indicates that the 
EVAP system is working correctly to collect the vapors generated in tank 
50. 
When the engine 40 is operated, the normally closed purge valve 70 is 
selectively opened to purge fuel vapors from canister 10. When purge valve 
70 is open, flow is induced through conduit 34 by engine 40. Air is drawn 
through vent opening 21 into canister 10 desorbing vapors from adsorbent 
80 and 90. The purge system operates by entraining the vapors in flow 
through opening 22, conduit 34 and into engine 40 for consumption. 
As the concentration of vapors in adsorbent 90 decreases, there is a 
resulting physical decrease in the size of adsorbent 90, (reference is 
again directed to FIG. 4). As the size is reduced the biasing force 
applied by springs 105 and 106 causes partition 101 to move to maintain a 
particulate packed relationship in the adsorbent 90. The movement of 
partition 101 reaches a point where the contacts of sensor 107 are opened. 
This indicates that the EVAP system is working correctly to purge fuel 
vapors from canister 10. 
The information available from sensor 107 is usable in a diagnostic program 
to evaluate the performance of the EVAP system. Illustrated in FIG. 1, the 
electronic controls or engine control module (ECM) 41 of a vehicle 
conventionally receives engine operational data and controls the operation 
of purge valve 70 accordingly. The ECM takes the form of a digital 
computer that can be programmed to coordinatedly run a diagnostic test to 
evaluate the performance of the EVAP system. 
The diagnostic test occurs during the initial start up routine of the 
engine. Referring to FIG. 5, the diagnostic routine is entered at point 
300 and proceeds to step 301 where a reading is taken from sensor 107. 
From step 301 the program proceeds to step 303 where it determines whether 
or not the adsorbent bed is loaded with fuel vapor and whether or not the 
purge system is operating. 
To determine if the purge system is operating the program conducts a memory 
check of engine operational data, particularly fuel flow calculations 
which indicate whether collateral fuel vapor flow entered the engine from 
the EVAP system. A determination that no collateral fuel vapors have been 
received from the EVAP system is indeterminate and the program continues 
to step 305. A determination that collateral fuel vapors have been 
received from the EVAP system is indicative of a correctly operating purge 
system and a determination of adsorbent bed expansion or contraction is 
then made. 
If the reading from sensor 107 indicates an expanded bed condition, step 
303 determines that the adsorbent bed is loaded which indicates a 
correctly operating vapor collection system and the test is complete. If 
the reading from sensor 107 indicates a contracted bed condition, step 303 
determines that the adsorbent bed is not loaded and the program proceeds 
to step 305 where a signal is generated to initiate disabling purge valve 
70 from opening. When purge valve 70 is disabled, normal purging of 
canister 10 is prevented. 
From step 305 the program proceeds to step 307 where it waits for a 
specified time t. During time t, the engine 40 must continue to run for 
the program to proceed. While the engine is running, fuel is being 
supplied to engine 40 from tank 50 through fuel line 36 and warmed fuel is 
being returned from the engine 40 to tank 50 through fuel return line 37. 
This fuel exchange results in an increase in temperature of fuel 60 in 
tank 50. In addition, fuel temperature increase occurs due to underbody 
air flow heated by the engine and exhaust system and other collateral 
sources. The increase in temperature results in running loss vapor 
generation by fuel 60. The generated vapor, if collected in canister 10, 
as is expected, causes adsorbent bed 90 to expand. 
When specified time t is reached, the program continues from step 307 to 
step 309. In step 309 a reading is again taken from sensing means 107 and 
the program proceeds to step 311 where it determines whether the adsorbent 
bed is expanding or contracting. Since the purge valve has been closed and 
the engine running it can be predicted when vapor generation will occur. 
The generated vapor will be collected in canister 10 unless a leak in the 
EVAP or fuel system is allowing it to be emitted to the atmosphere or 
conditions are not such that vapor generation is predicted. 
At step 311, a determination that the adsorbent bed is expanding, 
corresponds to a correctly functioning vapor collection system of the EVAP 
system and the program proceeds to step 313 where a signal is generated to 
initiate starting the purge system. At this point a conventional purge 
controller operates to selectively open the normally closed purge valve 
according to engine operational criteria in order to purge fuel vapors 
from the canister 10. 
From step 313, after allowing time for the canister purge function of the 
EVAP system to take effect, the program proceeds to step 315 where a 
reading is again taken from sensor 107. From step 315, the program 
proceeds to step 317 for a determination of whether the adsorbent bed is 
contracting. If the purge system of the EVAP system is operating correctly 
the adsorbent bed should be contracting. If, in step 317 it is determined 
that the reading from sensor 107 indicates the adsorbent bed is 
contracting, the test is complete. If it is determined that the adsorbent 
bed is not contracting, the program proceeds to step 324 and a fault 
report is generated, completing the test. 
From the generation of the fault report, a mechanism such as a warning 
light on the vehicle's instrument panel can be used to indicate to the 
operator that EVAP system servicing is required. Alternatively, a 
confirmation test can be run at a later time or the next time the vehicle 
is started before the operator is notified of a diagnostic test failure. 
Returning to step 311, if a determination is made from the reading of 
sensor 107 that the adsorbent bed is not expanding, the program proceeds 
to step 319. At step 319, a reading is taken from three sensors (not 
shown), for values indicative of the ambient temperature, the temperature 
change that has occurred in the fuel tank as a result of engine operation 
and the fuel level in the fuel tank. For a determination of the fuel 
temperature change a comparison value corresponding to the fuel 
temperature when the engine was started is required and therefore, must be 
available in memory. The comparison value is obtained from a fuel 
temperature reading preferably taken when the engine is started. 
Criterion values can be established for the three readings taken at step 
319 that represent conditions indicative of whether or not vapor 
generation should be occurring at a level to load the canister. Preferred 
values for the conditions suitable for use as criteria are: an ambient 
temperature greater than approximately 50 degrees Fahrenheit, an in-tank 
fuel temperature increase of greater than approximately 20 degrees 
Fahrenheit and a fuel tank level of less than approximately 60 percent 
full. When these criteria are met, vapor generation sufficient to be 
indicated by the canister sensor 107 can be predicted. 
From step 319, the program proceeds to step 321 for an evaluation of 
whether the three criteria are met. If all of the three criteria are not 
met, the program proceeds to step 323 and the test is discarded as 
indeterminate and complete. If all three of the criteria are met, the 
program proceeds to step 324 where a fault report is generated and the 
test is complete. 
In the foregoing manner, the vapor collection system and purge system are 
diagnosed. The mechanism used in the preferred embodiment may readily be 
adapted for use in other fuel vapor handling systems that include systems 
to collect and purge fuel vapor.