Information
-
Patent Grant
-
6289880
-
Patent Number
6,289,880
-
Date Filed
Monday, May 22, 200024 years ago
-
Date Issued
Tuesday, September 18, 200123 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
-
CPC
-
US Classifications
Field of Search
US
- 123 516
- 123 510
- 123 519
- 123 520
-
International Classifications
-
Abstract
A fuel vapor purge system has an apparatus for detecting leakage. The apparatus detects leakage based on a detected pressure in the tank. A remaining amount of fuel indicating a capacity of air in the tank and an introducing time of a negative pressure indicating an evaporated amount of fuel are taken into consideration of a detecting process. Therefore, the leakage detection is carried out accurately by compensating influences on the detected pressure by the remaining amount of fuel and an evaporated amount of fuel.
Description
CROSS REFERENCE TO RELATED APPLICATION
This application is based on Japanese Patent Application No.Hei 11-140942 filed on May 21, 1999 and No.2000-55981 filed on Feb. 28, 2000, the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for diagnosing a fuel vapor purge system for an internal combustion engine of a vehicle. The apparatus diagnoses and detects leakage of the system.
2. Description of Related Art
JP-A-05-125997 discloses an apparatus for detecting leakage of a fuel vapor purge system. In this apparatus, a remaining amount of fuel in a tank is taken into consideration of a detection of leakage, because a pressure change in the tank is influenced by a capacity of air in the tank indicated by the remaining amount of fuel in the tank.
However, the pressure in the tank is also changed according to an evaporated amount of fuel after the purge system is hermetically closed.
SUMMARY OF THE INVENTION
The present invention addresses these drawbacks by providing an improved apparatus for detecting leakage of a purge system.
It is therefore an object of this invention to provide an apparatus having improved reliability of a detection of leakage of the purge system.
It is a further object of this invention to provide an apparatus accurately detects leakage of the purge system.
According to a first aspect of the present invention, a requirement for detecting leakage is corrected on the basis of both of an introducing speed of anegative pressure and a capacity of air in a tank. The introducing speed is represented by an introducing time of the negative pressure, a pressure change in a predetermined period of time or a changing rate of pressure. The capacity of air in the tank is represented by a remaining amount of fuel in the tank. The introducing speed indicates an evaporated amount of fuel. Therefore, it is possible to improve a detecting accuracy of leakage.
BRIEF DESCRIPTION OF THE DRAWINGS
Other features and advantages of the present invention will be appreciated, as well as methods of operation and the function of the related parts, from a study of the following detailed description, the appended claims, and the drawings, all of which form a part of this application. In the drawings:
FIG. 1
is a schematic diagram of a fuel supply system for vehicle having a vapor purge system and a diagnosis apparatus of a embodiment of the present invention;
FIG.
2
and
FIG. 3
are flow charts of a program for detecting leakage of the vapor purge system of a first embodiment of the present invention;
FIG. 4
is a graph showing conditions of components during a leakage detection;
FIG. 5
is a graph showing a relationship between an evaporated amount of fuel and an introducing time;
FIG. 6
is a graph showing a map for calculating a correction value based on the introducing time and a remaining fuel;
FIG. 7
is a graph showing another measuring method of the introducing time of a second embodiment of the present invention;
FIG. 8
is a graph showing still another measuring method of the introducing time of a third embodiment of the present invention;
FIG. 9
is a graph showing another measuring method of the remaining amount of fuel of a fourth embodiment of the present invention;
FIG. 10
is a flow chart of a program for detecting leakage of the vapor purge system of a fifth embodiment of the present invention;
FIG. 11
is a graph showing a correcting method according to a pressure difference between the pressure in the tank and an intake pressure; and
FIG. 12
is a flow chart of a program for detecting leakage of the vapor purge system of a sixth embodiment of the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Referring to
FIG. 1
to
FIG. 6
, a first embodiment of the present invention will be described.
FIG. 1
shows an engine control system of a vehicle of the embodiment of the present invention. An air cleaner
13
is provided uppermost stream end of an intake pipe
12
of the engine
11
. A throttle valve
14
is disposed in the intake pipe
12
for adjusting an amount of air introducing into the engine
11
. The throttle valve
14
is connected with an accelerator pedal
15
. Injectors
16
for injecting fuel are disposed in branch passages of the intake pipe
12
respectively. Fuel (gasoline) in the tank
17
is pressurized by a pump
18
and is supplied to the injectors
16
through a pipe
19
. A pressure sensor
20
such as a semiconductor type is disposed in the tank
17
for detecting a pressure in the tank
17
. A level sensor
54
for detecting a level of fuel is disposed in the tank
17
as a remaining amount detector for detecting a remaining amount of fuel in the tank
17
.
A purge system
21
having a canister
23
is disposed between the tank
17
and the intake pipe
12
. A connection pipe
22
is disposed to provide a connection between the tank
17
and the canister
23
. The canister
23
contains an absorbent
24
such as an activated charcoal for absorbing a vapor of fuel. A pipe
25
for providing a communication to an atmosphere is disposed on a bottom of the canister
23
. A canister valve
26
for controlling a communication of the pipe
25
is disposed in the pipe
25
. The canister valve
26
is an electromagnetic valve, which is operated to close or open the pipe
25
in response to the signal. The canister valve
26
closes the pipe
25
when the signal is applied. Purge pipes
30
a
and
30
b
are disposed between the canister
23
and the intake pipe
12
to provide a passage for purging the vapor absorbed on the absorbent
24
to the intake pipe
12
. A purge valve
31
such as an electromagnetic valve is disposed between the purge pipes
30
a
and
30
b.
The purge valve
31
is operated by a duty controlled pulse signal so that the purge valve
31
opens the passage in response to a duty ratio of the pulse signal. The purge valve controls a flow amount of the vapor from the canister
23
to the intake pipe
12
. A fuel tank
17
has a filler neck
17
a
and a relief valve
38
integrated with a filler cap. The relief valve
38
regulates a pressure in the tank
17
within −40 mmHg to 150 mmHg. Therefore, the pressure in a section from the tank
17
to the canister
23
is maintained within the predetermined range.
Next, a control system is described. A control circuit
39
has a common bus
44
for connecting units of a microcomputer such as a CPU
40
, a ROM
41
, a RAM
42
and an I/O
43
. The I/O
43
is connected to a plurality of sensors
45
to
51
for detecting operating conditions of the engine. A throttle sensor
45
detects an opening degree of the throttle valve
14
. An idle switch
46
detects an idle position of the throttle valve
14
indicating an idle operation of the engine
11
. A speed sensor
47
detects a speed of the vehicle. An atmospheric pressure sensor
48
detects an atmospheric pressure. An intake pressure sensor
49
detects a pressure in the intake pipe
12
. A water temperature sensor
50
detects a temperature of a coolant of the engine. An intake temperature sensor
51
detects a temperature of an intake air. The ROM
41
and the RAM
42
store programs and data. The control circuit
39
outputs driving signals from the I/O
43
to actuators such as the injectors
16
, an ignition system having spark plugs
52
, the canister valve
26
and the purge valve
31
. The control circuit
39
activates a warning means such as a lamp
53
when the malfunction is detected. The control circuit
39
executes engine controls such as an injection control, an ignition control, a vapor purge control and a diagnosis of the system
21
based on input signals and stored programs and data.
Referring to FIG.
2
and
FIG. 3
, a diagnosis program will be described. The program repeatedly runs every predetermined time intervals (for instance, every 256 (ms)) during an ignition switch of a vehicle is turned on, and acts as a leak detecting means.
At step
101
, whether it is at least one of the idle operation and a stable operation or not is discriminated. In a case that it is not the idle or the stable condition, that is, it is a transient operation, the diagnosis is prohibited to prevent an incorrect result of the diagnosis by making no progress of the program.
In contrast, if the idle operation is detected at step
101
, the program proceeds to steps
102
to
104
. The program branches from these steps
102
to
104
according to a stage of a process of the program. The process includes four stages, which are indicated by three flags F
1
to F
3
. When all the flags F
1
to F
3
indicate ‘0’, it is a first stage, the program proceeds to step
105
.
In the first stage, first at step
105
, the purge valve
31
is closed. For instance, as shown in
FIG. 4
, the purge valve
31
is closed at T
1
even the canister valve
26
is opened. Therefore, pressure in the purge system
21
is maintained at the atmospheric pressure via the pipe
25
. After that, at step
106
, the canister valve
26
is closed to shut up the purge system
21
. For instance, the canister valve
26
is closed at T
2
. Therefore, the closed purge system maintained at the atmospheric pressure is provided. Then, at step
107
, the control circuit
39
reads and memorizes the detected pressure by the pressure sensor
20
as a pressure P
1
a,
and initialize and starts a timer T at T
2
of FIG.
4
. Whether the timer T reaches a predetermined time, for instance 10 seconds, or not is discriminated at step
108
. The first flag F
1
is taken as ‘1’ at step
109
before the timer T reaches 10 seconds.
After step
109
, the program proceeds to the second stage. In the second stage, the program branches from step
102
. In the second stage (T
2
to T
3
), a detected pressure of the pressure sensor
20
rises from P
1
a
(P
1
a
is approximately 0 mmHg) according to an amount of the vapor and an amount of the remaining fuel. If the timer T reaches 10 seconds at step
108
, then the process proceeds to step
110
. At step
110
, the control circuit
39
reads the detected pressure of the pressure sensor
20
and memorizes it as a pressure P
1
b.
A pressure difference ΔP
1
in a first measuring period (T
2
to T
3
) is calculated by ΔP
1
=P
1
b
−P
1
a
at step
111
. At step
112
, the first flag F
1
is taken as ‘0’, the second stage is finished.
In the third stage, first at step
121
of
FIG. 3
, a negative pressure control is started. The purge valve
31
is operated into a full-open condition. Simultaneously, at step
122
, a timer T is initialized and started. From this time (T
3
in FIG.
4
), a negative pressure in the intake pipe
12
is introduced into the purge system
21
. Therefore, the detected value of the pressure sensor
20
is decreased, if the purge system
21
has no leakage. At step
123
, whether the detected pressure in the tank
17
reaches a predetermined negative pressure, for instance −20 mmHg, or not is discriminated. In a case that the pressure reaches −20 mmHg, the process proceeds to step
136
, whether it is elapsed a predetermined time, for instance 5 seconds, or not is discriminated by the timer T. The second flag F
2
is taken as ‘1’ at step
142
before the timer reaches 5 seconds, and the program is circulated through steep
103
,
123
and
136
. If the timer reaches 5 seconds, a flag Fclose is taken as ‘1’, which indicates that the purge system
21
is blocked somewhere. At step
138
, the control circuit
39
turns on the warning lamp
53
to warn a malfunction of the system
21
for a driver. On the other hand, in a case that the pressure decreases under −20 mmHg before the timer T reaches 5 seconds, the process proceeds to a branch of steps
124
to
127
. In this branch, the control circuit
39
reads and memorizes a counted value of the timer T as an introducing time Tx. The above-mentioned steps
121
to
124
act as means for measuring an introducing rate of negative pressure. The memorized time Tx indicates an amount of the vapor evaporated during the negative pressure is introduced into the purge system
21
. The second flag F
2
is taken as ‘0’ at step
125
. At step
126
, the purge valve
31
is closed at T
4
of FIG.
4
. At step
127
, just after the step
126
, the control circuit
39
reads and memorizes the detected pressure by the pressure sensor
20
as a pressure P
2
a,
and initializes and starts the timer T. Thereby, the process moves from the third stage to the fourth stage.
After the steps
125
to
127
, the pressure in the purge system
21
rises during T
4
to T
5
. The pressure rises from
31
20 mmHg by a rate corresponding to a generated amount of the vapor and the remaining amount of fuel. At step
128
, whether the timer T reaches a predetermined time, for instance 10 seconds, or not is discriminated. The third flag F
3
is taken as ‘1’ at step
139
before the timer T reaches 10 seconds. Therefore, the process jumps from step
104
to step
128
. The control circuit
39
reads and memorizes the detected pressure at T
5
of the pressure sensor
20
as a pressure P
2
b
at step
129
after the timer T reaches 10 seconds. A pressure difference ΔP
2
in a second measuring period (T
4
to T
5
) is calculated by ΔP
2
=P
2
b
−P
2
a
at step
130
. At step
131
, the control circuit
39
reads the remaining amount of fuel detected by the level sensor
54
as a remaining amount Fu. A map memorized in the control circuit
39
as shown in
FIG. 6
is searched for determining a correction value γ based on parameters such as the introducing time Tx and the remaining amount Fu. Therefore, the correction value γ reflecting the introducing time Tx and the remaining amount Fu is obtained. Here, the map shown in
FIG. 6
is designed to optimize a detection of leakage. The correction value γ increases as the introducing time Tx becomes long, and increases as the remaining amount Fu increases (a space in the tank
17
decreased). Instead of the map in
FIG. 6
, a functional equation designed on the basis of experimentations and simulations can be used for calculating the correction value γ.
At step
133
, an existence of leakage in the purge system
21
is discriminated by a requirement such as ΔP
2
>α·ΔP
1
+β+γ. In this requirement, α is a coefficient for correcting a difference between the generated amount of the vapor in the atmospheric pressure and the negative pressure, β is a coefficient for correcting a detecting accuracy of the pressure sensor
20
, leakage of the canister valve
26
or the like. The ΔP
1
is a changed amount of pressure under atmospheric pressure and indicates a difference between a generated volume of vapor in the tank
17
and a lost volume passing through a leakage path. The ΔP
2
is a changed amount of pressure under negative pressure and indicates a sum of a generated volume of vapor in the tank
17
and a volume flowing through the leakage path in the tank
17
. Therefore, if there is the leakage path, the ΔP
2
must be greater than the ΔP
1
.
In a case that the requirement in step
133
is not established, steps
134
and
135
are executed. At step
134
, the flags F
1
, F
2
and F
3
are initialized. At step
135
, the canister valve
26
is fully opened and the purge valve
31
is operated by normal control method.
In a case that the requirement in step
133
is established, steps
140
and
141
are executed. At step
140
, a leakage flag Fleak is taken as ‘1’ indicating an existence of leakage. At step
141
, the control circuit turns on the warning lamp
53
.
In this embodiment, the correction value γ is determined on the basis of the introducing time Tx and the remaining amount Fu. Therefore, it is possible to carry out the leakage diagnosis accurately.
In this embodiment, the generated amount of vapor is reflected on the detection of leakage at step
133
through the introducing time Tx used as a substitution of that. Therefore, a fuel temperature sensor and process for fuel temperature information are not necessary for detecting leakage. It is possible to prevent an influence by a difference of abilities of the evaporation depending on fuel can be suppressed.
In this embodiment, the detection of leakage is carried out when it is in the idle operation or the stable operation. Therefore, the introducing time Tx can be detected accurately by suppressing an influence of a change of the intake pressure.
Further, an influence of moving of a fuel level can be suppressed, when the detection of leakage is carried out only in the idle operation.
As shown in
FIG. 7
, the response delays from a start signal are different from each of the valves. The delays reflect on the introducing time Tx as an erroneous component. In the second embodiment, the introducing time Tx is measured from a point where a predetermined pressure response is detected. For instance, the measurement of the introducing time Tx is started at a point where the detected pressure is decreased a predetermined value α from the pressure P
1
b.
Therefore, the difference of the delays depending on the valves is removed from the measured introducing time Tx.
As shown in
FIG. 8
, in a third embodiment of the present invention, the measurement of the introducing time Tx is started at a point where a predetermined value Psta. Therefore, the difference of the delays depending on the valves is removed from the measured introducing time Tx.
As shown in
FIG. 9
, in a fourth embodiment of the present invention, a remaining fuel amount is presumed on the basis of an inclination of the pressure in the purge system
21
after the atmospheric pressure is introduced into the vacuumed purge system. The inclination of the pressure is substantially in proportion to an air capacity in the tank
17
. For instance, the purge valve
31
is again opened for introducing the negative pressure at T
5
in
FIG. 9
after the pressure difference ΔP
2
is detected. The purge valve
31
is closed at T
6
. The canister valve
26
is opened at T
7
to introduce the atmospheric pressure into the purge system,
21
. After that, the pressure change Pc/Tc is measured and the remaining amount of fuel is presumed from the pressure change Pc/Tc. This presumption process acts as the remaining fuel detecting means. It is possible to eliminate the level sensor
54
, further to suppress an error depending on an inclination of the vehicle.
In a fifth embodiment of the present invention, an influence by the intake pressure will be compensated. As shown in
FIG. 11
, the intake pressures at the idle operation and the stable running operation are different, and the difference influences on the introducing time Tx. Therefore, in the fifth embodiment, steps
131
a
and
132
a
are added on the program as shown in FIG.
10
. in this embodiment, the correction value γ is determined on the basis of different functions f or g according to the decision at step
131
a.
In a case that it is in the idle operation, the correction value γ is determined on the basis of function f. On the other hand, it is in the stable operation, the correction value γ is determined on the basis of function g. Therefore, the intake pressure reflects on the leakage detection through the correction value γ according to the operating condition of the vehicle. Further, the calculation of the correction value γ may be changed according to the intake pressure directly. Further, an additional correction value F
1
may be used for correcting the correction value γ. In a case that the correction is carried out by γ=f(Tx, Fu)×F
1
, the value F
1
is decreased as the intake pressure is increased.
Further, a pressure difference Pd between the pressure in the tank
17
and the intake pressure may be taken into consideration of the determination of value γ. For instance, a map or a function may be defined as γ=f(Tx, Fu, Pd). Further, the value γ may be corrected by an additional correction value F
2
according to the pressure difference Pd and γ=f(Tx, Fu)×F
2
. In this case, the value F
2
is increased as the pressure difference Pd is increased. Therefore, an inclination of the introducing time Tx is compensated.
Further, the introducing time Tx may be corrected by an average value of the pressure difference Pd. In a sixth embodiment, steps
123
a
and
124
a
are added. At step
123
a,
an average value of the pressure difference Pd is calculated. At step
124
a,
the introducing time Tx is corrected by the average value. In this case, the correction coefficient K
3
and Tx=Tx×K
3
are used for correcting the introducing time Tx. As shown in
FIG. 11
, the coefficient K
3
is increased as the pressure difference Pd is increased. Incidentally, the average value Pda can be calculated by a plurality of processes. For instance, the average value Pda may be calculated by Pda=Σ(δPi)/N. In this formula, δP is a pressure difference measured at a sampling timing, i is a subscript of a sampling timing and takes 1 to N and N is a total number of samplings. The average value Pda may be calculated by Pda=(Pdsta+Pdend)/2. In this formula, Pdsta is a pressure difference measured at a start of the measurement of the introducing time and Pdend is a pressure difference measured at an end of the measurement of the introducing time. The average value Pda may be calculated by Pda=Pta−Pia. In this formula, Pta is an average value of the pressure in the tank
17
and Pia is an average value of the pressure in the intake pipe
12
.
Further, the average value Pda may be replaced by a pressure difference measured at an intermediate of the measurement of the introducing time Tx. For instance, a pressure difference may be measured when the pressure in the tank decreases half to a final value or a predetermined time has elapsed. Further, a pressure difference measured at a start or an end of the measurement of the introducing time Tx may be used.
Further, the introducing time Tx may be corrected by the intake pressure or a pressure difference between the intake pressure and the atmospheric pressure during the negative pressure is introduced.
Further, the introducing time Tx may be replaced by another parameter corresponding to an introducing speed of the negative pressure. For instance, a detected value or a decreased value of the pressure detected at a predetermined time has elapsed from a start of the negative pressure introduction may be used.
Further, a requirement for detecting leakage can be modified. For instance, leakage may be detected by whether a variable VA=ΔP
2
−α·ΔP
1
is greater than a predetermined threshold value or not. In this case, the variable VA or the threshold value may be corrected by the introducing speed of the negative pressure and the remaining amount of fuel. Further, the variable VA or the threshold value may be corrected by the intake pressure or the pressure difference Pd.
Although the present invention has been described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications will be apparent to those skilled in the art. Such changes and modifications are to be understood as being included within the scope of the present invention as defined in the appended claims.
Claims
- 1. An apparatus for detecting leakage of a vapor purge system having a canister for absorbing a vapor of fuel from a tank, a purge valve for controlling an amount of the vapor purged to an intake pipe of an engine and means for discriminating an existence of leakage based on a pressure change in the purge system when the purge system is hermetically closed after a predetermined pressure is introduced, comprising:means for measuring a parameter corresponding to an introducing speed of a predetermined pressure into the purge system; and means for detecting an amount of remaining fuel in the tank, wherein said leakage detecting means corrects a requirement for discriminating the existence of leakage based on both of said parameter of said introducing speed and said amount of remaining fuel.
- 2. An apparatus for detecting leakage of a vapor purge system according to claim 1, wherein said parameter of said introducing speed is an introducing time of a negative pressure to control a pressure in said purge system to a predetermined pressure or a changed amount of said pressure in said purge system or a changing rate of said pressure in said purge system when said negative pressure is introduced.
- 3. An apparatus for detecting leakage of a vapor purge system according to claim 1, wherein said parameter is measured on the basis of a measurement started from said pressure in said purge system is decreased a predetermined pressure from a pressure at a start of an introducing of a negative pressure.
- 4. An apparatus for detecting leakage of a vapor purge system according to claim 1, wherein said parameter is measured on the basis of a measurement started from said pressure in said purge system is decreased to a predetermined pressure after a negative pressure is introduced.
- 5. An apparatus for detecting leakage of a vapor purge system according to claim 1, wherein said parameter is measured at a stable operating condition of said engine or an idle operating condition of said engine.
- 6. An apparatus for detecting leakage of a vapor purge system according to claim 1, wherein said leakage detecting means includes means for correcting or modifying said requirement for discriminating the existence of leakage based on a pressure in said intake pipe when a negative pressure is introduced.
- 7. An apparatus for detecting leakage of a vapor purge system according to claim 1, wherein said leakage detecting means includes means for correcting or modifying said requirement for discriminating the existence of leakage based on a pressure in said intake pipe and a pressure in said tank when a negative pressure is introduced.
- 8. An apparatus for detecting leakage of a vapor purge system according to claim 1, wherein said leakage detecting means includes means for correcting or modifying said requirement for discriminating the existence of leakage according to a stable operating condition or an idle operating condition of said engine.
- 9. An apparatus for detecting leakage of a vapor purge system according to claim 1, wherein said leakage detecting means includes means for correcting a measured value of said parameter based on a pressure in said intake pipe when a negative pressure is introduced.
- 10. An apparatus for detecting leakage of a vapor purge system according to claim 1, wherein said leakage detecting means includes means for correcting a measured value of said parameter based on a pressure in said intake pipe and a pressure in said tank when a negative pressure is introduced.
- 11. An apparatus for detecting leakage of a vapor purge system having a canister for absorbing a vapor of fuel from a tank and a purge valve for controlling an amount of the vapor purged to an intake pipe of an engine, comprising:means for controlling a pressure in said purge system to a predetermined pressure by introducing a negative pressure into said purge system and closing said purge system hermetically after said predetermined pressure is provided; means for measuring a response of said pressure when said controlling means introduces said negative pressure; means for detecting an amount of remaining fuel in the tank; means for discriminating an existence of leakage based on a pressure change in said purge system when said purge system is hermetically closed; and means for correcting a parameter used at said discriminating means according to said response of said pressure and said remaining amount of fuel to compensate a difference of an evaporated amount of fuel and a difference of a capacity of air in the tank.
Priority Claims (2)
Number |
Date |
Country |
Kind |
11-140942 |
May 1999 |
JP |
|
12-055981 |
Feb 2000 |
JP |
|
US Referenced Citations (4)
Foreign Referenced Citations (1)
Number |
Date |
Country |
7-12014 |
Jan 1995 |
JP |