Information
-
Patent Grant
-
6202478
-
Patent Number
6,202,478
-
Date Filed
Tuesday, August 17, 199925 years ago
-
Date Issued
Tuesday, March 20, 200123 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Williams; Hezron
- Cygan; Michael
Agents
-
CPC
-
US Classifications
Field of Search
US
- 073 40
- 073 405 R
- 073 405 T
- 073 497
- 073 1181
- 073 115
- 073 116
- 701 31
- 123 198 D
- 123 520
-
International Classifications
-
Abstract
A method is provided for testing an evaporative emission control system for a missing or loose fuel cap comprising detecting a refueling event and running a leak detection test of the evaporative emission control system to determine if a large leak is present. If a large leak is detected, the methodology sets a fault code and activates a driver warning lamp indicating a potential cap sealing problem. The leak detection test is repeatedly re-executed after the large leak is detected to determine when the large leak condition ceases. When the large leak condition ceases, the previously set fault code is removed and the driver warning lamp is deactivated. If the large leak does not cease and is detected again after the next refueling event when an opportunity for resealing the cap existed, a new fault code is set indicating that the potential cap sealing problem is a persistent problem so that the integrity of the evaporative system may need to be tested. After setting the new fault code, fuel cap specific leak detection testing is suspended until the condition is serviced and the fault code is cleared or a normal leak detection test determines that there is no longer a problem. If no large leak is detected, the fuel cap is assumed to be properly sealed.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to evaporative emission control systems for automotive vehicles and, more particularly, to a leak detection assembly and method for determining if a fuel cap sealing problem is present in an evaporative emission control system for an automotive vehicle.
2. Description of the Related Art
Modern automotive vehicles typically include a fuel tank and an evaporative emission control system that collects volatile fuel vapors generated in the fuel tank. The evaporative emission control system includes a vapor collection canister, usually containing an activated charcoal mixture, to collect and store volatile fuel vapors. Normally, the canister collects volatile fuel vapors which accumulate during refueling of the automotive vehicle or from increases in fuel temperature. The evaporative emission control system also includes a purge valve placed between an intake manifold of an engine of the automotive vehicle and the canister. The purge valve is opened by an engine control unit an amount determined by the engine control unit to purge the canister, i.e., the collected volatile fuel vapors are drawn into the intake manifold from the canister for ultimate combustion within a combustion chamber of the engine.
Recently, governmental regulations have required that certain automotive vehicles powered by volatile fuels such as gasoline have their evaporative emission control systems checked to determine if a leak exists in the system. As a result, on board vehicle diagnostic systems have been developed to determine if a leak is present in a portion of the evaporative emission control system. One such diagnostic system utilizes a vacuum regulator/sensor unit to draw a vacuum on the evaporative emission control system and sense whether a loss of vacuum occurs within a specified period of time.
Diagnostic systems also exist for determining the presence of a leak in an evaporative emission control system which utilizes positive pressurization rather than negative pressurization, i.e., vacuum. In positive pressurization systems, the evaporative emission control system is pressurized to a set pressure, typically through the use of an electric air pump. A sensor determines whether the pressure remains constant over a certain amount of time.
At times, a leak will exist in the system due to a fuel cap sealing problem. That is, the fuel cap is either missing, loose, or is not properly sized to the fuel tank fill tube. Present diagnostic systems do not specifically perform a test to identify this type of leak condition. As such, the sealing problem is not detected until operation of the standard diagnostic test. Further, conventional diagnostic systems treat such a leak condition the same as other types of leaks thereby activating the warning signals and/or setting fault codes. Such warning signals and fault codes are typically not cleared until after three cold starts, i.e., three days. As such, vehicle operators are taking their vehicles to dealerships for repair when a simple check and resealing of the fuel cap may resolve the situation.
In view of the foregoing, it would be desirable to provide a leak detection system for specifically determining if a fuel cap sealing problem is present in the evaporative emission control system of the automotive vehicle and informing the operator or service technician of the same.
SUMMARY OF THE INVENTION
It is, therefore, one object of the present invention to provide a leak detection system for use in testing the integrity of an evaporative emission control system for an automotive vehicle.
It is another object of the present invention to provide a leak detection system for use in testing the integrity of the fuel cap sealing in an evaporative emission control system after each refueling event.
It is yet another object of the present invention to provide a leak detection system for notifying the vehicle operator and/or service technician of a potential fuel cap sealing problem.
To achieve the foregoing objects, the present invention is a method of testing an evaporative emission control system for a missing or loose fuel cap comprising detecting a refueling event and running a leak detection test of the evaporative emission control system to determine if a large leak is present. If a large leak is detected, the methodology sets a fault code and activates a driver warning lamp indicating a potential cap sealing problem. The leak detection test is repeatedly re-executed after the large leak is detected to determine when the large leak condition ceases. When the large leak condition ceases, the previously set fault code is removed and the driver warning lamp is deactivated. If the large leak continues to be detected and is then detected again after the next refueling event (when an opportunity for resealing the cap existed), a new fault code is set indicating that the potential cap sealing problem is a persistent problem so that the integrity of the evaporative system may need to be tested. After setting the new fault code, fuel cap specific leak detection testing is suspended until the condition is serviced and the fault code is cleared or the standard leak detection test determines that the leak has been corrected. When no large leak is detected, the fuel cap is assumed to be properly sealed.
One advantage of the present invention is that a leak detection system is provided for an evaporative emission control system of an automotive vehicle. Another advantage of the present invention is that a potential fuel cap sealing problem is quickly identified after each refueling event. Yet another advantage of the present invention is that the potential fuel cap sealing problem is identified separately from other non-cap related leak conditions. Still yet another advantage of the present invention is that the indicator lamp and fault codes are immediately removed after the fuel cap sealing problem condition is corrected.
Other objects, features, and advantages of the present invention will be readily appreciated as the same becomes better understood after reading the subsequent description taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a schematic diagram of an evaporative emission control system according to the present invention.
FIG. 2
is a cross-sectional view of a leak detection pump and valve assembly of the evaporative emission control system of FIG.
1
.
FIGS. 3A and 3B
are a flow chart of a method of leak detection according to the present invention for the evaporative emission control system of FIG.
1
.
FIG. 4
is a graphic illustration of a series of refueling events depicting the periodic execution of the method of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to
FIG. 1
, an evaporative emission control system
10
is shown for an automotive vehicle (not shown) including a leak detection pump and valve assembly, generally indicated at
12
. The control system
10
also includes a carbon canister
14
connected by a conduit
15
to the leak detection pump and valve assembly
12
. A fuel tank
16
is connected to the carbon canister
14
by a tank rollover and vapor flow control valve
18
and a conduit
17
. This is a representative example of several possible means by which the fuel tank
16
is connected to the carbon canister
14
.
An intake manifold
20
is connected to the carbon canister
14
by a conduit
22
. The control system
10
includes a purge valve
24
mounted on the conduit
22
. The control system
10
also includes an engine control unit
26
connected to and operative to control the leak detection pump and valve assembly
12
and the purge valve
24
. The control system
10
includes a remote filter
27
connected to the leak detection pump and valve assembly
12
and atmosphere.
In operation, a supply of volatile liquid fuel for powering an engine (not shown) of the automotive vehicle is placed in the fuel tank
16
. As fuel is pumped into the fuel tank
16
or as the temperature of the fuel increases, vapors from the fuel pass through the conduit
19
and are received in the canister
14
. The purge valve
24
is normally closed. Under certain vehicle operating conditions conducive to purging, the engine control unit
26
operates the purge valve
24
such that a certain amount of engine intake vacuum is delivered to the canister
14
causing the collected vapors to flow from the canister
14
through the conduit
22
and the purge valve
24
to the intake manifold
20
for combustion in the combustion chambers.
Referring to
FIG. 2
, the leak detection pump and valve assembly
12
includes a vacuum actuated leak detection pump, generally indicated at
28
, and a mechanically actuated canister vent control valve, generally indicated at
32
. An atmospheric vent hose
34
interconnects the leak detection pump
28
and atmosphere. It should be appreciated that the vent control valve
32
seals or closes the conduit
15
between the carbon canister
14
and an atmospheric vent in order to positively pressurize the evaporative emission control system
10
.
In accordance with the present invention, the leak detection pump and valve assembly
12
is used to perform a test of the integrity of the evaporative emission control system
10
. To conduct the test, the engine control unit
26
closes the purge valve
24
and actuates the leak detection pump
28
. The vent control valve
32
is mechanically actuated such that a vacuum drawn to activate the leak detection pump
28
, results in a corresponding mechanical motion which causes the vent control valve
32
to close and seal the canister
14
from the atmospheric vent and remote filter
27
(FIG.
1
). Once the conduit
15
is sealed off, the leak detection pump
28
then positively pressurizes the evaporative emission control system
10
and fuel tank
16
to a predetermined pressure. Once the predetermined pressure is assumed to have been reached, the leak detection pump
28
enters a diagnostic mode to be described. If the control system
10
has a leak, the pressure is reduced and the leak detection pump
28
will sense the reduced pressure and will actuate. The leak detection pump
28
will continue to pump at a rate which will be representative of the flow characteristic as related to the size of the leak. From this information, it can be determined if the leak is larger or smaller than the required detection limit, e.g., a large leak as caused by a missing or loose fuel cap or a small leak as set by applicable governmental standards.
Referring to
FIGS. 3A-3B
, a method of detecting a leak according to the present invention in the evaporative emission control system
10
is illustrated. While a brief description of the large leak test and normal leak test are described herein, it should be appreciated that both tests are conducted in essentially the same manner as described with the large leak test only detecting leaks possibly attributable to a loose or missing fuel cap and the normal leak test looking for large or small leaks down to those limits set by applicable governmental standards. A more thorough description of the diagnostic test utilizing the present invention can be found in U.S. Pat. No. 5,606,121 entitled METHOD OF TESTING AN EVAPORATIVE EMISSION CONTROL SYSTEM to Blomquist, et al. and assigned to the assignee of the present invention which is hereby expressly incorporated by reference herein.
The methodology begins in bubble
100
to perform tasks that are common to each periodic execution of the routine. To perform the common tasks, the methodology advances to diamond
102
. In diamond
102
the methodology determines whether the vehicle has just experienced a refueling event, for example, by looking for an indicator such as a flag. The flag would be set when a large increase of fuel is detected in the fuel tank. If a refueling event has just occurred at diamond
102
, the methodology advances to diamond
106
. However, if no refueling event has just occurred at diamond
102
, the methodology advances through connector A to diamond
115
to determine if it is time to run a normal leak test.
In diamond
106
, the methodology determines if the vehicle is in the appropriate drive mode for large leak testing, for example, by looking for an indicator such as a flag. For instance, for vehicles including an automatic transmission, the flag would be set each time the transmission is transitioned from neutral or park into drive. For vehicles equipped with a manual transmission, the flag would be set each time the vehicle speed changes from zero. If the vehicle is not in the appropriate drive mode at diamond
106
, the methodology advances through connector A to diamond
115
. However, if the vehicle is in the appropriate drive mode at diamond
106
, the methodology advances to diamond
108
.
In diamond
108
, the methodology determines if a large leak fault code is set, for example, by looking for an indicator such as a flag. For instance, the large leak fault code flag would be set if the last execution of the routine prior to the last refueling event resulted in a large leak being detected. The large leak fault code is indicative of a short term correctable fault which could easily be corrected. If the large leak fault code is set at diamond
108
, the methodology advances to block
110
. However, if the large leak fault code is not set at diamond
108
, the methodology advances to diamond
112
. As can be appreciated from the description of decision block
102
, the large leak test of block
110
is only conducted one time after each transition form park or neutral to drive in vehicles equipped with automatic transmissions, or after each change in speed from zero in vehicles with manual transmissions, if the large leak fault code is set at decision block
108
.
In block
110
, the methodology runs a large leak test to determine the integrity of the evaporative emission control system
10
as described above. The size of the leak tolerance for the large leak test is set according to a leak which could be attributable to a fuel cap sealing problem, such as a missing or loose fuel cap rather than by applicable governmental standards. In other words, the large leak test does not test the system for compliance with governmental standards by looking for small leaks but rather only tests for large leaks possibly attributable to a fuel cap sealing problem. It should be noted that no new execution of the routine is started if a test is already under way. Also, testing is conducted regardless of temperature gates or other factors normally used to limit testing. Further, the vehicle's purge system is disabled during the large leak test. If a large leak is detected, the methodology assumes that the leak is due to an open fill tube. Thereafter, an assumption is made that vapor generation and other issues that could cloud the data from the leak detection pump are not present.
From block
110
, the methodology advances to diamond
114
. In diamond
114
, the methodology determines whether a large leak was detected by the large leak test at block
110
. If so, the methodology advances to block
116
and sets a persistent leak fault code. The persistent leak fault code indicates that after two consecutive refueling events, a large leak was detected presumably indicating that the fuel cap was missing or loose, and that an opportunity to correct the problem was afforded, but the problem was not corrected, i.e., the driver could have put the fuel cap back on after the second refueling event. When downloaded, the persistent leak fault code indicates to a service technician that the evaporative emission control system problem may be related to a persistent fuel cap sealing problem. As such, the service technician will know to carefully check the fuel cap for damage, proper make/style, and/or can advise the vehicle operator of the need to carefully reseal the fuel cap. From block
116
, the methodology advances through connector A to diamond
115
. However, if no large leak is detected by the large leak test at decision block
114
, the methodology advances to block
117
. In block
117
, the methodology clears the previously set large leak fault code. From block
117
, the methodology advances to block
119
. In block
119
, the methodology extinguishes any operator warning lamp that may have been lit in conjunction with the large leak fault code. From block
119
, the methodology advances through connector A to diamond
115
.
Referring again to diamond
108
, if the large leak fault code is not set, the methodology advances to diamond
112
. In diamond
112
, the methodology determines whether the persistent leak fault code is set, for example, by looking for an indicator such as a flag. If the persistent leak fault code is set at diamond
112
, the methodology advances through connector A to diamond
115
. However, if the persistent leak fault code is not set at diamond
112
, the methodology advances to diamond
118
.
In diamond
118
, the methodology determines if a normal leak fault code counter is greater than zero. As described in greater detail below, if a standard leak test indicates that a leak is present in the evaporative emission control system
10
, the fuel cap leak specific testing (i.e., the large leak test) is suspended. Therefore, if the normal leak fault code counter is greater than zero at diamond
118
, the methodology advances through connector A to diamond
115
. However, if the normal leak fault code counter is not greater than zero at diamond
118
, the methodology advances to block
120
.
In block
120
, the methodology runs the large leak test to determine if a potential fuel cap sealing problem exists as described above. From block
120
, the methodology advances to diamond
122
to determine if a large leak was detected. If a large leak is detected by the large leak test, the methodology advances from diamond
122
through connector B to block
124
. However, if no large leak is detected at diamond
122
, the methodology advances through connector A to diamond
115
.
In block
124
, the methodology sets the large leak fault code which will, when downloaded, indicate to a service technician that the evaporative emission control system problem may be fuel cap sealing related. As such, the technician will know to carefully inspect the fuel cap for a missing or loose condition. After setting the large leak fault code at block
124
, the methodology advances to block
128
and activates a warning lamp to apprise the vehicle operator of a potential problem with fuel cap sealing. That is, the indicator lamp will apprise the operator that the fuel cap may have been left off or misaligned.
From block
128
, the methodology advances to block
130
. In block
130
, the methodology reruns the large leak test as described above to determine when the fuel cap problem is corrected. From block
130
, the methodology advances to diamond
132
where the methodology determines whether the large leak was re-detected by the large leak test. If the large leak continues to be detected at diamond
132
, the methodology advances to bubble
104
and exits the subroutine pending another drive mode transition at diamond
102
. However, if no large leak is detected at diamond
132
, the methodology advances to block
134
. It should be noted, however, that if the length at which the leak detection pump
28
pumps (i.e., the pump period) indicates that the flow characteristics of the leak represent a smaller leak than that normally attributable to a missing or loose fuel cap, no large leak is present and therefore the large leak fault code is removed and the warning lamp is extinguished. Also, the loop between diamond
132
and block
130
is interrupted at the next refueling event even if the leak continues to be detected. Thereafter, the methodology follows the sequence as described above with respect to diamond
106
et seq.
In block
134
, the methodology removes the large leak fault code since the problem has been corrected. From block
134
, the methodology advances to block
136
and deactivates the warning lamp. From block
136
, the methodology advances to diamond
115
.
Referring again to diamond
122
, if no large leak is detected by the initial large leak test (block
120
), the methodology advances through connector A to diamond
115
. As such, the normal leak test is only run during a drive cycle in which the large leak test eventually indicates that no large leak is present. In diamond
115
, the methodology determines if it is time to run the normal leak test. If so, the methodology advances to block
126
. However, if it is not time to run the normal leak test, the methodology advances to bubble
104
and exits the routine.
In block
126
, the methodology runs the normal leak test as described above. In this test, not only are large leaks detected, but small leaks down to the limits set by applicable government standards are also detected. From block
126
, the methodology advances to diamond
138
. In diamond
138
the methodology determines if a leak was detected by the normal leak test.
If no leak is detected at diamond
138
, the methodology advances to diamond
140
. In diamond
140
, the methodology determines if the normal leak fault code is greater than or equal to two. If so, the methodology advances to block
142
and increments a no leak counter. However, if the normal leak fault code is less than two at diamond
140
, the methodology advances to diamond
144
. Similarly, after incrementing the no leak counter at block
142
, the methodology advances to diamond
144
.
Referring again to diamond
138
, if a leak is detected in the system by the normal leak test, the methodology advances to block
146
and increments the normal leak fault code. From block
146
, the methodology advances to diamond
144
. In diamond
144
, the methodology determines if the normal leak fault code is greater than or equal to two. If not, the methodology advances to bubble
104
and exits the routine.
However, if the normal leak fault code is greater than or equal to two, the methodology advances to diamond
146
. In diamond
146
, the methodology determines if the no leak counter is greater than or equal to three. If not, the methodology advances to block
148
. In block
148
, the methodology activates the operator warning light to indicate that there is a leak in the system. From block
148
, the methodology advances to bubble
104
and exits the routine.
Referring again to diamond
146
, if the no leak counter is greater than or equal to three, the methodology advances to block
150
. In block
150
, the methodology extinguishes the operator warning lamp. From block
150
the methodology advances to block
152
. In block
152
, the methodology sets the normal leak fault code to zero. As such, the normal leak fault code is removed and the operator warning lamp is extinguished after being set by the normal leak test only after three consecutive normal leak tests indicate that no leak is present. From block
152
, the methodology advances to bubble
104
and exits the routine.
Referring now to
FIG. 4
, a graphic depiction of a series of refueling events and a representative sample of the testing according to the present invention is illustrated. Subsequent refueling events are represented by the vertical lines
200
-
206
and subsequent depletion of the fuel in the fuel tank is represented by angled lines
208
-
214
. The hollow triangle represents a large leak test where no large leak is detected, the solid circle represents a normal leak cold start test where no leak is detected, the solid triangles represent a large leak test where a large leak is detected and the solid squares represent the normal cold start leak test where a large or small leak is detected.
Thus, reading the graph from left to right, after the refueling event
200
, the large leak test is conducted at
216
which indicates that no large leak was detected. The assumption is that the fuel cap has been properly replaced. Shortly thereafter at
218
, the methodology conducts the normal leak test. This test also indicates that no leaks are present in the system. Thereafter at
220
, the normal leak test is run again and again detects no leaks.
After the next refueling event
202
, the large leak test is run at
222
and detects a large leak. The assumption is that the fuel cap is not properly sealed. Accordingly, the large leak fault code is set and the operator warning lamp is lit. From
224
through
234
, the large leak test is repeatedly run in an attempt to immediately identify when the fuel cap problem is corrected. After the next refueling event
204
, the large leak test is run once again at
236
. If a large leak is again detected, a persistent leak fault code is set indicating that the vehicle operator had an opportunity to fix the potential fuel cap sealing problem but did not. If no leak is detected at
236
, the large leak fault code is cleared and the operator warning lamp is extinguished.
For the purposes of this discussion, it will now be assumed that a large leak was detected at
236
. Thus, the persistent leak fault code is set and the large leak test is suspended. At
238
, the methodology performs a normal leak cold start test which again detects a leak in the system but also notes that the fuel cap is not the problem since there has been ample opportunity for the fuel cap to be corrected. The methodology then sets the normal leak fault code counter to one. After the refueling event
206
, the large leak test is not run since the normal leak fault code equals one. At
240
and
242
, the normal leak test indicates that a leak is still present. As such, the normal leak fault code counter is incremented and the operator warning lamp remains lit. Thus, at
238
-
242
, the normal leak test continues to confirm that the leak is present. On the other hand, should the normal leak test at each of
238
,
240
and
242
indicate that no leak is present, the normal leak fault code is decremented to zero and the operator warning lamp is extinguished. Thus, the normal leak fault code is removed and the operator warning lamp is extinguished after three consecutive normal leak tests indicate that no leak is present.
Thus, the present invention provides a means for specifically detecting a leak in an evaporative emission control system attributable to a potential fuel cap sealing problem. The methodology does not need to wait until a normal leak detection test is executed for determining the potential fuel cap sealing problem after a refueling event. Further, a diagnostic fault code is set and a warning lamp is lit indicating to a service technician and/or vehicle operator that the leak in the system is possibly due to a loose or missing fuel cap. As soon as the large leak condition is corrected, the fault code is cleared and the warning lamp is extinguished.
The present invention has been described in an illustrative manner. It is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation.
Many modifications and variations of the present invention are possible in light of the above teachings. Therefore, within the scope of the appended claims, the present invention may be practiced otherwise than as specifically described.
Claims
- 1. A method of testing an evaporative emission control system for a fuel cap sealing problem comprising:detecting a refueling event; running a large leak test of said system to determine if a large leak is present; setting a large leak fault code and activating a driver warning lamp indicating a potential cap sealing problem if said large leak is detected; rerunning said large leak test repeatedly after said large leak is detected to determine when said large leak condition ceases; removing said large leak fault code and deactivating said driver warning lamp when said large leak condition ceases; detecting a next refueling event after said large leak is detected if said large leak condition has not ceased; rerunning said large leak test after said next refueling event; setting a persistent leak fault code indicating that said potential cap sealing problem had an opportunity to be corrected but was not if said large leak is again detected; suspending subsequent large leak tests until said persistent leak fault code is cleared; and suspending said large leak test from running after two consecutive normal leak tests indicate a leak is present in said system.
- 2. The method of claim 1 wherein said large leak test is run for an automatic transmission vehicle when said vehicle is in drive.
- 3. The method of claim 1 wherein said large leak test is run for a manual transmission vehicle when said vehicle changes speed from zero.
- 4. The method of claim 1 further comprising running a normal leak test to check said system for any leak if said large leak test does not detect said large leak.
- 5. The method of claim 1 further comprising suspending a running of a normal leak test to check said system for any leak if said large leak test detects said large leak.
- 6. The method of claim 1 further comprising disabling a purge system while said large leak test is running.
- 7. A method of testing an evaporative emission control system for a fuel cap sealing problem comprising:detecting a refueling event; running a large leak test of said system to determine if a large leak is present; setting a large leak fault code, activating a driver warning lamp indicating a potential cap sealing problem, and suspending all normal leak tests to check said system for any leaks if said large leak is detected; rerunning said large leak test repeatedly after said large leak is detected to determine if said large leak condition ceases and removing said large leak fault code and deactivating said driver warning lamp when said large leak condition ceases; running said normal leak tests to check said system for any leaks if said large leak is not detected; suspending further large leak tests from running if two consecutive normal leak tests detect a leak in said system; detecting a next refueling event after said large leak is detected if said large leak condition has not ceased; rerunning said large leak test after said next refueling event; setting a persistent leak fault code indicating that said potential cap sealing problem had an opportunity to be corrected but was not if said large leak is again detected; and suspending subsequent large leak tests until said persistent leak fault code is cleared.
US Referenced Citations (17)