Information
-
Patent Grant
-
6761058
-
Patent Number
6,761,058
-
Date Filed
Wednesday, June 6, 200123 years ago
-
Date Issued
Tuesday, July 13, 200420 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Williams; Hezron
- Garber; Charles D.
Agents
-
CPC
-
US Classifications
Field of Search
US
- 073 40
- 073 405 R
- 073 497
- 073 481
- 123 520
- 702 51
-
International Classifications
-
Abstract
There is provided a leakage determination system for an evaporative fuel processing system, which, even when pressure within the evaporative fuel processing system is temporarily increased e.g. due to an increase in the amount of generation of evaporative fuel in a fuel tank, is capable of performing an accurate leakage determination by eliminating the influence of the temporary rise in the pressure within the evaporative fuel processing system on the leakage determination. A pressure sensor detects pressure within the evaporative fuel processing system. Negative pressure is introduced from the intake system into the evaporative fuel processing system, whereby the pressure within the evaporative fuel processing system is reduced until the detected pressure becomes equal to a predetermined negative pressure. After the pressure reduction, the negative pressure is introduced from the intake system into the evaporative fuel processing system under predetermined conditions. Whether or not there is a leak in the evaporative fuel processing system is determined based on a state of the pressure within the evaporative fuel processing system, which has been detected during the introduction of the negative pressure from the intake system.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a leakage determination system for an evaporative fuel processing system of an internal combustion engine, for determining whether or not there is a leak in the evaporative fuel processing system which causes a canister to temporarily store evaporative fuel generated from a fuel tank, and supplies the same to an intake system of the engine with proper timing.
2. Description of the Prior Art
Conventionally, a leakage determination system of the above-mentioned kind was proposed e.g. in Japanese Laid-Open Patent Publication (Kokai) No. 9-291854. The evaporative fuel processing system includes a canister, a fuel tank, a charge passage, and a purge passage. The canister is connected to the fuel tank via the charge passage. The charge passage is provided with a pressure sensor that detects pressure within the charge passage (hereinafter referred to as “the tank internal pressure” because the pressure within the charge passage is approximately equal to pressure within the fuel tank in a steady state of the system). In a bypass passage bypassing the charge passage, there is arranged a bypass valve for opening and closing the bypass passage. Further, the canister is connected to an atmosphere passage which is open to the atmosphere, and in the atmosphere passage, there is arranged a vent shut valve for opening and closing the same. In the purge passage, there is arranged a purge control valve for opening and closing the same.
The leakage determination system determines whether or not there is a leak in the evaporative fuel processing system, by carrying out a pressure-reducing mode process and a leakage-checking mode process sequentially as described below. First, in the pressure-reducing mode process, the bypass valve and the purge control valve are opened, and the vent shut valve is closed, whereby the pressure within the evaporative fuel processing system is reduced until the tank internal pressure is lowered to a predetermined negative pressure.
Then, in the leakage-checking mode process, the bypass valve, the purge control valve and the vent shut valve are all closed to maintain the evaporative fuel processing system in a sealed state over a predetermined time period, and in this state, changes in the tank internal pressure are monitored. Through this monitoring, if a change in the tank internal pressure becomes equal to or larger than a predetermined value, it is determined that there is a leak in the system, whereas if the changes in the tank internal pressure are held below the predetermined value, it is determined that there is no leak.
In the above conventional leakage determination system, however, e.g. when the vehicle is jolted with only a small amount of fuel remaining in the fuel tank or when the outside temperature is high, the amount of evaporative fuel within the fuel tank can be increased to raise the tank internal pressure in a short time, which makes it impossible to effect an accurate leakage determination. In short, the leakage-checking mode process is only executed for checking changes in the tank internal pressure within the predetermined time period, and hence if the tank internal pressure is temporarily increased for some reason as mentioned above, it can be erroneously determined that there is a leak, even though there is no leak.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a leakage determination system for an evaporative fuel processing system, which, even when pressure within the evaporative fuel processing system is temporarily increased e.g. due to an increase in the amount of evaporative fuel in a fuel tank, is capable of performing an accurate leakage determination by eliminating the influence of the temporary rise in the pressure within the evaporative fuel processing system.
To attain the above object, according to a first aspect of the invention, there is provided a leakage determination system for an evaporative fuel processing system that causes a canister to absorb evaporative fuel generated from a fuel tank and supplies the evaporative fuel absorbed in the canister to an intake system of an internal combustion engine,
the leakage determination system comprising:
pressure detection means for detecting pressure within the evaporative fuel processing system;
pressure reduction means for reducing the pressure within the evaporative fuel processing system until the detected pressure within the evaporative fuel processing system becomes equal to a predetermined negative pressure, by introducing negative pressure from the intake system;
negative pressure introduction means for introducing the negative pressure from the intake system into the evaporative fuel processing system under predetermined conditions after the pressure reduction by the pressure reduction means; and
leakage determination means for determining whether or not there is a leak in the evaporative fuel processing system, based on a state of the pressure within the evaporative fuel processing system, which has been detected during the introduction of the negative pressure from the intake system by the negative pressure introduction means.
Preferably, the negative pressure introduction means introduces the negative pressure from the intake system at a predetermined constant negative pressure introduction flow rate.
According to this leakage determination system for an evaporative fuel processing system, in a leakage determination process, first, negative pressure is introduced from the intake system into the evaporative fuel processing system, whereby the pressure within the evaporative fuel processing system is reduced to the predetermined negative pressure. Then, after the pressure reduction is terminated, negative pressure is introduced again from the intake system into the evaporative fuel processing system at the predetermined constant negative pressure introduction flow rate, and whether or not there is a leak in the evaporative fuel processing system is determined based on a pressure within the evaporative fuel processing system, which has been detected during the introduction of the negative pressure at the constant flow rate. According to the first aspect of the invention, since the pressure within the evaporative fuel processing system is detected while introducing the negative pressure as described above, the detected pressure represents an offset between an increment of a pressure increased by leakage and a decrement of the same reduced by the introduction of the negative pressure. Therefore, leakage determination for the evaporative fuel processing system can be carried out based on the pressure within the evaporative fuel processing system.
Further, since the pressure within the evaporative fuel processing system is detected while continuously introducing the negative pressure, even when the pressure within the evaporative fuel processing system is temporarily increased e.g. due to an increase in the amount of evaporative fuel generated in the fuel tank, it is possible to carry out leakage determination while reducing the temporary rise in the pressure. Consequently, the influence of the temporary rise in the pressure caused by other factors than leakage on the leakage determination can be eliminated, which enables accurate determination of whether or not there is a leak in the evaporative fuel processing system.
More preferably, the negative pressure introduction means includes pressure re-reduction means for holding the evaporative fuel processing system in a closed state and introducing the negative pressure from the intake system whenever the pressure within the evaporative fuel processing system rises to a predetermined pressure higher than the predetermined negative pressure, to thereby repeatedly reduce the pressure within the evaporative fuel processing system to a second predetermined negative pressure lower than the predetermined pressure,
the leakage determination system further comprising pressure reduction cycle detection means for detecting a pressure reduction cycle of the pressure reduction performed by the pressure re-reduction means, and
the leakage determination means determining whether or not there is a leak in the evaporative fuel processing system, based on a plurality of pressure reduction cycles detected by the pressure reduction cycle detection means.
According to this preferred embodiment, in the leakage determination process, first, negative pressure is introduced from the intake system, whereby the pressure within the evaporative fuel processing system is reduced to the predetermined negative pressure. After the reduction of the pressure within the evaporative fuel processing system, negative pressure is introduced from the intake system while holding the evaporative fuel processing system in the closed state, whenever the pressure within the evaporative fuel processing system rises to reach the predetermined pressure higher than the predetermined negative pressure, to thereby repeatedly reduce the pressure within the evaporative fuel processing system to the second negative pressure. Then, whether or not there is a leak in the evaporative fuel processing system is determined based on the plurality of pressure reduction cycles detected during the repetition of pressure reduction. If there is a leak in the evaporative fuel processing system, an atmospheric pressure enters the evaporative fuel processing system via the leak. As a result, the rate of increase in the pressure within the evaporative fuel processing system after termination of the pressure reduction becomes faster, and hence the pressure reduction cycle becomes shorter than when there is no leak, so that it is possible to determine from the pressure reduction cycle whether or not there is a leak in the evaporative fuel processing system.
Further, since the pressure within the evaporative fuel processing system is repeatedly reduced, even when the pressure within the evaporative fuel processing system is temporarily increased e.g. due to an increase in the amount of generation of evaporative fuel in the fuel tank, it is possible to reduce the temporary rise in the pressure whenever it occurs, and detect a pressure reduction cycle subsequent thereto. Moreover, since whether or not there is a leak in the evaporative fuel processing system is determined based on the plurality of pressure reduction cycles detected during the repetition of pressure re-reduction, even when a temporary rise in the pressure has caused a variation in the pressure reduction cycle, it is possible to assess the plurality of pressure reduction cycles as a whole, thereby compensating for the variation in the pressure reduction cycle. Thus, the influence of the temporary rise in the pressure caused by other factors than leakage on the leakage determination can be eliminated, which enables accurate determination of whether or not there is a leak in the evaporative fuel processing system.
To attain the above object, according to a second aspect of the invention, there is provided a leakage determination method for an evaporative fuel processing system that causes a canister to absorb evaporative fuel generated from a fuel tank and supplies the evaporative fuel absorbed in the canister to an intake system of an internal combustion engine,
the leakage determination method comprising:
a pressure detection step of detecting pressure within the evaporative fuel processing system;
a pressure reduction step of reducing the pressure within the evaporative fuel processing system until the detected pressure within the evaporative fuel processing system becomes equal to a predetermined negative pressure, by introducing negative pressure from the intake system;
a negative pressure introduction step of introducing the negative pressure from the intake system into the evaporative fuel processing system under predetermined conditions after the pressure reduction at the pressure reduction step; and
a leakage determination step of determining whether or not there is a leak in the evaporative fuel processing system, based on a state of the pressure within the evaporative fuel processing system, which has been detected during the introduction of the negative pressure from the intake system.
Preferably, at the negative pressure introduction step, the negative pressure from the intake system is introduced at a predetermined constant negative pressure introduction flow rate.
More preferably, in the leakage determination method according to the second aspect of the invention, at the negative pressure introduction step, the negative pressure is introduced from the intake system while holding the evaporative fuel processing system in a closed state whenever the pressure within the evaporative fuel processing system rises to a predetermined pressure higher than the predetermined negative pressure, whereby the pressure within the evaporative fuel processing system is repeatedly reduced to a second predetermined negative pressure lower than the predetermined pressure,
the leakage determination method further comprising a pressure reduction cycle detection step of detecting a pressure reduction cycle of the pressure reduction at the negative pressure introduction step, and
the leakage determination step includes determining whether or not there is a leak in the evaporative fuel processing system based on a plurality of detected pressure reduction cycles.
To attain the above object, according to a third aspect of the invention, there is provided a recording medium storing a leakage determination control program for causing a computer to carry out leakage determination for an evaporative fuel processing system that causes a canister to absorb evaporative fuel generated from a fuel tank and supplies the evaporative fuel absorbed in the canister to an intake system of an internal combustion engine.
The recording medium is characterized in that the leakage determination control program causes the computer to detect pressure within the evaporative fuel processing system, reduce the pressure within the evaporative fuel processing system until the detected pressure within the evaporative fuel processing system becomes equal to a predetermined negative pressure, by introducing negative pressure from the intake system, introduce the negative pressure from the intake system into the evaporative fuel processing system under predetermined conditions after the pressure reduction to the predetermined negative pressure, and determine whether or not there is a leak in the evaporative fuel processing system, based on a state of the pressure within the evaporative fuel processing system, which has been detected during the introduction of the negative pressure from the intake system.
Preferably, the leakage determination control program causes the negative pressure to be introduced from the intake system at a predetermined constant negative pressure introduction flow rate, after the pressure reduction to the predetermined negative pressure.
Also preferably, the leakage determination control program causes the negative pressure to be introduced while causing the evaporative fuel processing system to be held in a closed state, after the pressure reduction to the predetermined negative pressure, whenever the pressure within the evaporative fuel processing system rises to a predetermined pressure higher than the predetermined negative pressure, thereby repeatedly reducing the pressure within the evaporative fuel processing system to a second predetermined negative pressure lower than the predetermined pressure, detecting a cycle of the pressure reduction, and determining whether or not there is a leak in the evaporative fuel processing system, based on a plurality of detected pressure reduction cycles.
The above and other objects, features, and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a block diagram schematically showing the arrangement of an evaporative fuel processing system for an internal combustion engine incorporating a leakage determination system according to first and second embodiments of the invention;
FIG. 2
is a flowchart of a routine for a leakage determination process executed by the
FIG. 1
leakage determination system according to the first embodiment;
FIG. 3
is a continuation of the
FIG. 2
flowchart;
FIG. 4
is a timing chart showing an example of changes in a tank internal pressure PTANK detected through execution of pressure re-reduction when there is no leak in the evaporative fuel processing system;
FIG. 5
is a timing chart showing an example of changes in the tank internal pressure PTANK detected through execution of pressure re-reduction when there is a leak in the evaporative fuel processing system;
FIG. 6
is a flowchart of a routine for a leakage determination process executed by the
FIG. 1
leakage determination system according to the second embodiment of the invention; and
FIG. 7
is a timing chart showing examples of changes in the tank internal pressure PTANK detected through execution of the
FIG. 6
leakage determination process.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The invention will now be described in detail with reference to the drawings showing embodiments thereof. Referring first to
FIG. 1
, there is schematically shown the arrangement of an evaporative fuel processing system for an internal combustion engine incorporating a leakage determination system according to a first or second embodiment of the present invention. The leakage determination system
1
carries out determination whether or not there is a leak in the evaporative fuel processing system
20
for the internal combustion engine
3
(hereinafter simply referred to as “the engine
3
”) and includes an ECU
2
(pressure reduction means, pressure re-reduction means, pressure reduction cycle detection means, negative pressure introduction means, leakage determination means). The evaporative fuel processing system
20
and the ECU
2
will be described in detail hereinafter.
The engine
3
is a gasoline engine which is installed on an automotive vehicle, not shown. The engine
3
has an engine rotational speed sensor
12
mounted thereto for detecting a rotational speed NE of the engine and delivering a signal indicative of the sensed engine rotational speed NE to the ECU
2
.
Further, the engine
3
has an intake system
4
including an intake pipe
5
and a throttle valve
6
arranged in an intermediate portion of the intake pipe
5
. At a location downstream of the throttle valve
6
, there is mounted an intake pipe absolute pressure sensor
13
in a manner inserted into the intake pipe
5
. The intake pipe absolute pressure sensor
13
senses an intake pipe absolute pressure PBA within the intake pipe
5
, and delivers a signal indicative of the sensed absolute pressure PBA to the ECU
2
.
Further, injectors (fuel injection valves)
7
(only one of which is shown) are inserted into the intake pipe
5
at locations downstream of the intake pipe absolute pressure sensor
13
in a manner facing respective intake ports, not shown, of the engine
3
. A fuel injection time period TOUT over which each injector
7
is opened is controlled by the ECU
2
. The injector
7
is connected to a fuel tank
21
via a fuel supply pipe
8
. In an intermediate portion of the fuel supply pipe
8
, there is arranged a fuel pump
9
for delivering fuel to the injector
7
by pressure.
On the other hand, in an exhaust pipe
10
at a location upstream of a catalyst device
11
, there is mounted an O2 sensor
14
. The O2 sensor
14
detects the concentration of oxygen contained in exhaust gases and delivers a signal indicative of the sensed oxygen concentration to the ECU
2
. Based on the signal from the O2 sensor
14
, the ECU
2
calculates an air-fuel ratio correction coefficient KO2 for use in calculation of the fuel injection time period TOUT.
Further, the automotive vehicle is equipped with a vehicle speed sensor
15
. The vehicle speed sensor
15
detects a vehicle speed VP and delivers a signal indicative of the sensed vehicle speed VP to the ECU
2
.
Next, the aforementioned evaporative fuel processing system
20
will be described in detail. The evaporative fuel processing system
20
temporarily stores evaporative fuel generated from the fuel tank
21
, in a canister
24
, and delivers the same into the intake pipe
5
as required. The evaporative fuel processing system
20
includes the fuel tank
21
, a charge passage
22
, a refueling-time charge passage
23
for use during refueling, the canister
24
, and a purge passage
25
.
The fuel tank
21
is connected to the canister
24
via the charge passage
22
and the refueling-time charge passage
23
. Fuel generated in the fuel tank
21
is sent to the canister
24
through the charge passage
22
. A pressure sensor
26
(pressure detection means) is arranged in the charge passage
22
at a location close to the fuel tank
21
. The pressure sensor
26
formed e.g. by a piezoelectric element detects pressure within the charge passage
22
and delivers a signal indicative of the sensed pressure to the ECU
2
. Normally, the pressure within the charge passage
22
is approximately equal to pressure within the fuel tank
21
, and hence hereinafter referred to as the tank internal pressure PTANK.
Further, the charge passage
22
has a two-way valve
27
arranged therein at a location between the pressure sensor
26
and the canister
24
. The two-way valve
27
is formed by a mechanical valve comprised of a diaphragm-type positive pressure valve and a diaphragm-type negative pressure valve. The positive pressure valve opens when the tank internal pressure PTANK exceeds the atmospheric pressure by a predetermined value. This opening operation of the positive pressure valve allows delivery of evaporative fuel from the fuel tank
21
to the canister
24
. On the other hand, the negative pressure valve opens when the tank internal pressure PTANK becomes lower than pressure within the canister
24
by a predetermined value, whereby evaporative fuel stored in the canister
24
is returned to the fuel tank
21
.
Further, in an intermediate portion of the charge passage
22
, there is provided a charge bypass passage
28
bypassing the two-way valve
27
and connecting between a canister-side portion of the charge passage
22
downstream of the two-way valve
27
and a pressure sensor-side portion of the same upstream of the two-way valve
27
. In an intermediate portion of the charge bypass passage
28
, there is arranged a charge bypass valve
31
(pressure reduction means, pressure re-reduction means, negative pressure introduction means). The charge bypass valve
31
formed by a normally-closed solenoid valve is normally held closed to maintain the charge bypass passage
28
in a closed state, and opens when it is driven by the ECU
2
, to open the charge bypass passage
28
.
The aforementioned refueling-time charge passage
23
(only a portion thereof is shown) is for use in sending a large amount of evaporative fuel generated in the fuel tank
21
particularly during refueling to the canister
24
. The refueling-time charge passage
23
has a larger diameter than that of the charge passage
22
. In an intermediate portion of the refueling-time charge passage
23
, there is arranged a diaphragm valve
23
a
for opening and closing the refueling-time charge passage
23
. The diaphragm valve
23
a
is held closed except during refueling. When refueling, the diaphragm valve
23
a
opens, whereby evaporative fuel is delivered to the canister
24
via the refueling-time charge passage
23
.
The fuel tank
21
is provided with float valves
21
a
,
21
b
. The float valves
21
a
,
21
b
open and close respective fuel tank-side openings of the charge passage
22
and the refueling-time charge passage
23
. Normally, the valves
21
a
,
21
b
hold the two passages
22
,
23
open, respectively, whereas e.g. when the fuel tank
21
jolts or becomes full, the valves
21
a
,
21
b
close the respective openings of the passages
22
,
23
to thereby prevent fuel from flowing into the two passages
22
,
23
.
The canister
24
contains activated carbon for absorbing evaporative fuel. Further, the canister
24
is connected to an atmosphere passage
29
open to the atmosphere. The atmosphere passage
29
is provided with a vent shut valve
32
for opening and closing the same. The vent shut valve
32
formed by a normally-open solenoid valve is normally held open to maintain the atmosphere passage
29
in an open state, and closes when it is driven by the ECU
2
, to close the atmosphere passage
29
.
In an intermediate portion of the purge passage
25
, there is arranged a purge control valve
33
(pressure reduction means) for opening and closing the purge passage
25
. The purge control valve
33
is formed by a solenoid valve whose degree of opening continuously changes according to the duty ratio of a drive signal from the ECU
2
. By opening the purge control valve
33
when the vent shut valve
32
is open, evaporative fuel absorbed by the canister
24
is delivered into the intake pipe
5
by negative pressure within the intake pipe
5
. The ECU
2
performs duty control of the degree of opening of the purge control valve
33
during purge control to thereby control the flow rate, or purge rate, of the evaporative fuel delivered from the canister
24
into the intake pipe
5
.
Further, connected to the purge passage
25
is a purge bypass passage
30
similar to the charge bypass passage
28
. The purge bypass passage
30
which bypasses the purge control valve
33
connects between a portion of the purge passage
25
at a location between the purge control valve
33
and the canister
24
and a portion of the same at a location downstream of the purge control valve
33
. In an intermediate portion of the purge bypass passage
30
, there are mounted a purge bypass valve
34
and a jet
35
in the mentioned order from the canister side.
The purge bypass valve
34
(pressure re-reduction means, negative pressure introduction means) formed by a normally-closed solenoid valve is normally closed to maintain the purge bypass passage
30
in a closed state, and opens when it is driven by the ECU
2
, to open the purge bypass passage
30
. When the purge bypass valve
34
opens, the negative pressure within the intake pipe
5
is introduced into the evaporative fuel processing system
20
, whereby the pressure within the evaporative fuel processing system
20
is reduced. The jet
35
(negative pressure introduction means) is formed by an orifice having a predetermined diameter, for limiting the flow rate of evaporative fuel flowing through the purge bypass passage
30
to a predetermined flow rate and limiting the flow rate (of a gas containing evaporative fuel) for introduction of the negative pressure to a predetermined constant flow rate.
The ECU
2
is formed by a microcomputer including an I/O interface, a CPU, a RAM and a ROM, none of which are shown. The signals input to the ECU
2
from the sensors
12
to
15
,
26
are subjected to A/D conversion and waveform shaping by the I/O interface and then input to the CPU. The CPU determines operating conditions of the engine
3
based on the signals and carries out a leakage determination process, described in detail hereinafter, while driving the valves
31
to
34
, based on control programs stored in the ROM in advance and data stored in the RAM.
In the following, a leakage determination process for the evaporative fuel processing system
20
, according to the first embodiment, which is executed by the ECU
2
, will be described with reference to
FIGS. 2 and 3
showing flowcharts of a program for carrying out the leakage determination process. The process or program is carried out by an interrupt handling routine at predetermined time intervals (e.g. every 80 msec.) set by a timer, but not carried out after execution of leakage determination at a step S
21
, referred to hereinafter. That is, the leakage determination by the present process is carried out only once during a time period from the start of operation of the engine
3
to the end thereof.
First, it is determined at a step S
1
whether or not a monitoring condition is satisfied. The determination as to the monitoring condition is carried out so as to determine whether or not conditions for executing the leakage determination process are satisfied, and only when the following conditions (1) to (4) are all satisfied, it is determined that the monitoring condition is satisfied.
(1) Purge control is being executed with the purge control valve
33
in the open state.
(2) The engine
3
is in a predetermined steady operating condition (which is determined e.g. based on the intake pipe absolute pressure PBA and the engine rotational speed NE).
(3) The vehicle is cruising with a small change in the vehicle speed VP.
(4) The air-fuel ratio correction coefficient KO2 is equal to or larger than a predetermined value, and hence the influence of purged fuel upon the air-fuel ratio A/F is small.
If the answer to the question of the step S
1
is negative (NO), i.e. if at least one of the conditions (1) to (4) is not satisfied, the program is immediately terminated.
On the other hand, if the answer to the question is affirmative (YES), i.e. if the conditions (1) to (4) are all satisfied, the program proceeds to a step S
2
, wherein it is determined whether or not an initial pressure reduction termination flag FPOK assumes “1”. The initial pressure reduction termination flag FPOK is set to “1” at a step S
7
upon termination of initial pressure reduction carried out at steps S
3
to S
6
described below.
Immediately after the present process is started, the flag FPOK assumes “0”, so that the answer to the question of the step S
2
is negative (NO). Therefore, the program proceeds to the step S
3
, wherein the initial pressure reduction for reducing the pressure within the evaporative fuel processing system
20
is started. More specifically, in a state of the purge bypass valve
34
being held closed, the vent shut valve
32
is closed, and the charge bypass valve
31
is opened. At the same time, the duty ratio of the purge control valve
33
is controlled based on the tank internal pressure PTANK detected by the pressure sensor
26
, such that the tank internal pressure PTANK becomes equal to a predetermined negative pressure POBJ (predetermined negative pressure, second predetermined negative pressure (e.g. −20 hPa)). As a result, the evaporative fuel processing system
20
communicates with the intake pipe
5
, and negative pressure is introduced from the intake pipe
5
into the evaporative fuel processing system
20
, whereby the tank internal pressure PTANK is reduced to the predetermined negative pressure POBJ. In this case, since the charge bypass valve
31
is open, the tank internal pressure PTANK represents the pressure within the evaporative fuel processing system
20
.
Then, the program proceeds to the step S
4
, wherein it is determined whether or not a pressure reduction time period has elapsed. The pressure reduction time period is set to a value (e.g. 15 sec.) within which the tank internal pressure PTANK is expected to be positively lowered by the initial pressure reduction to the predetermined negative pressure POBJ so long as there is no large amount of leakage from the evaporative fuel processing system
20
and the valves
31
to
34
and the pressure sensor
26
are normally operating. If the answer to the question of the step S
4
is negative (NO), i.e. if the pressure reduction time period has not elapsed, the program is immediately terminated.
On the other hand, if the answer to the question of the step S
4
is affirmative (YES), i.e. if the pressure reduction time period has elapsed, the program proceeds to the step S
5
, wherein it is determined whether or not the tank internal pressure PTANK is equal to or lower than the predetermined negative pressure POBJ.
If the answer to the question is negative (NO), i.e. if PTANK≦POBJ holds, it is judged that there is a large amount of leakage within the evaporative fuel processing system
20
or one or more of the valves
31
to
34
and the pressure sensor
26
are not normally operating, and hence that the leakage determination for the system
20
cannot be normally performed, so that a leakage determination termination flag FDONE is set to “1” at a step S
9
, followed by terminating the program. By setting the leakage determination termination flag FDONE to “1”, the present program or the leakage determination by the present process is prevented from being executed from this time on.
If the answer to the question of the step S
5
is affirmative (YES), i.e. if PTANK≦POBJ holds, the program proceeds to the step S
6
, wherein the initial pressure reduction is terminated. More specifically, in a state of the vent shut valve
32
and the purge bypass valve
34
being held closed and the charge bypass valve
31
being held open, the purge control valve
33
is closed to close the evaporative fuel processing system
20
.
Then, the program proceeds to the step S
7
, wherein the initial pressure reduction termination flag FPOK is set to “1”. Further, at the following step S
8
, the count of a pressure reduction timer formed by a programmable countup timer is reset to “0”, and then counting by the timer is started, followed by the program proceeding to a step S
10
in FIG.
3
. Once the initial pressure reduction termination flag FPOK is set to “1” at the step S
7
, the answer to the question of the step S
2
becomes affirmative (YES) in the following loops. Therefore, the steps S
3
to S
8
are skipped, and the program jumps to the step S
10
.
At the step S
10
, it is determined whether or not a leakage check time period has elapsed. The leakage check time period is set to a value (e.g. 60 sec.) which positively allows pressure re-reduction, described in detail hereinafter, to be repeatedly carried out a plurality of times irrespective of whether or not there is a leak in the evaporative fuel processing system
20
.
If the answer to the question of the step S
10
is negative (NO), i.e. if the leakage check time period has not elapsed, the program proceeds to a step S
11
, wherein it is determined whether or not a pressure re-reduction-in process flag FPON assumes “1”. The pressure re-reduction-in process flag FPON indicates whether or not pressure re-reduction is being executed, and hence, as described hereinbelow, it is set to “1” when the pressure re-reduction is being executed, whereas it is set to “0” when the pressure re-reduction is not being executed.
If the answer to the question of the step S
11
is negative (NO), i.e. if the pressure re-reduction is not being executed, the program proceeds to a step S
12
, wherein it is determined whether or not the tank internal pressure PTANK is equal to or higher than a predetermined pressure PREF (e.g. −17 hPa) which is higher than the predetermined negative pressure POBJ. If the answer to this question is negative (NO), i.e. if PTANK<PREF holds, the program is immediately terminated.
On the other hand, if the answer to the question of the step S
12
is affirmative (YES), i.e. if the tank internal pressure PTANK has risen to a level equal to or higher than the predetermined pressure PREF (PTANK≧PREF), the program proceeds to a step S
13
, wherein the pressure re-reduction is started. More specifically, in a state of the charge bypass valve
31
being held open and the vent shut valve
32
and the purge control valve being held closed, the purge bypass valve
34
is opened. As a result, the evaporative fuel processing system
20
communicates with the intake pipe
5
, whereby the pressure within the evaporative fuel processing system
20
is reduced by the negative pressure within the intake pipe
5
, and this pressure reduction is carried out by introducing the negative pressure into the evaporative fuel processing system
20
via the jet
35
, so that the pressure re-reduction is executed at a constant pressure reduction rate.
Then, the program proceeds to a step S
14
, wherein a count of the pressure reduction timer at the present time point is obtained (sampled) as a present pressure reduction cycle TCY and stored in the RAM. Thus, the pressure reduction cycle TCY is calculated as a time period between the immediately preceding pressure reduction termination timing and the present pressure reduction start timing.
Then, at the following step S
15
, the pressure re-reduction-in process flag FPON is set to “1”, followed by the program proceeding to a step S
16
. As a result, in the following loops, the answer to the question of the step S
11
becomes affirmative (YES), so that the steps S
12
to S
15
are skipped, and the program jumps to the step S
16
.
At the step S
16
, similarly to the step S
5
, it is determined whether or not the tank internal pressure PTANK is equal to or lower than the predetermined negative pressure POBJ. If the answer to the question is negative (NO), i.e. if the tank internal pressure PTANK has not been reduced to the predetermined negative pressure POBJ, the program is immediately terminated.
On the other hand, if the answer to the question of the step S
16
is affirmative (YES), i.e. if PTANK≦POBJ holds, the pressure re-reduction is terminated at a step S
17
, and then the flag FPON is set to “0” at a step S
18
so as to indicate the termination of the pressure re-reduction. Subsequently, similarly to the step S
8
, the count of the pressure reduction timer is reset to “0”, and the counting by the timer is started at a step S
19
, followed by terminating the program. More specifically, the pressure re-reduction is terminated by closing the purge bypass valve
34
with the charge bypass valve
31
held open and the vent shut valve
32
and the purge control valve
33
held closed, whereby the evaporative fuel processing system
20
is closed.
From this time on, the steps S
11
to S
19
are repeatedly executed until the leakage check time period has elapsed, and whenever the tank internal pressure PTANK rises to the predetermined pressure PREF, the re-reduction of the pressure PTANK to the predetermined negative pressure POBJ and calculation of the pressure reduction cycle TCY are repeatedly carried out.
On the other hand, if the answer to the question of the step S
10
is affirmative (YES), i.e. if the leakage check time period has elapsed, the program proceeds to a step S
20
, wherein the plurality of pressure reduction cycles TCY are averaged to thereby calculate an averaged pressure reduction cycle TCYAVE.
Then, the program proceeds to a step S
21
, wherein it is determined whether or not the averaged pressure reduction cycle TCYAVE is larger than a predetermined value TCYREF. The predetermined value TCYREF is set as a threshold value for determining whether or not there is a leak in the evaporative fuel processing system
20
. If the answer to the question is affirmative (YES), i.e. if TCYAVE>TCYREF holds, it is judged that there is no leak in the evaporative fuel processing system
20
, and the program proceeds to a step S
22
, wherein a leakage determination flag FLEAK is set to “0” so as to indicate that there is no leak in the system
20
.
Then, at the following step S
23
, the initial pressure reduction termination flag FPOK and the pressure re-reduction-in process flag FPON are each set to “0”, and the leakage determination flag FDONE is set to “1”, followed by terminating the program. Similarly to the step S
9
, since the leakage determination termination flag FDONE is set to “1”, the present program will not be executed from this time on. That is, the leakage determination by the present process is performed only once during a time period from the start of operation of the engine
3
to the end thereof.
On the other hand, if the answer to the question of the step S
21
is negative (NO), i.e. if TCYAVE≦TCYREF holds, it is judged that there is a leak in the evaporative fuel processing system
20
, and the program proceeds to a step S
24
, wherein the leakage determination flag FLEAK is set to “1” so as to indicate that there is a leak in the evaporative fuel processing system
20
. Then, the step S
23
is executed, followed by terminating the program.
Next, examples of changes in the tank internal pressure PTANK exhibited by execution of the above leakage determination process will be described with reference to timing charts shown in
FIGS. 4 and 5
. These figures show changes in the tank internal pressure PTANK obtained when there is no leak in the evaporative fuel processing system
20
and when there is a leak in the same, respectively.
As shown in each of the figures, first, when the initial pressure reduction is started (time t0, t10), the tank internal pressure PTANK falls. Thereafter, at a time point (time t1, t11) the tank internal pressure PTANK has fallen to the predetermined negative pressure POBJ and the pressure reduction time period has elapsed, the purge control valve
33
is closed in synchronism with the lapse of the pressure reduction time period, whereby the evaporative fuel processing system
20
is closed. Then, at a time point (time t2, t12) the tank internal pressure PTANK has slowly risen to reach the predetermined pressure PREF higher than the predetermined negative pressure POBJ, the pressure re-reduction is started, and at a time point (time t3, t13) the tank internal pressure PTANK has been reduced to the predetermined negative pressure POBJ, the evaporative fuel processing system
20
is closed again. After the time t3 or t13, whenever the tank internal pressure PTANK reaches the predetermined pressure PREF (e.g. time t4, t14), the pressure re-reduction is repeatedly carried out a plurality of times.
When the pressure re-reduction is repeatedly carried out as described above, the pressure reduction cycle TCY is longer in the
FIG. 4
case where there is no leak, due to a slow rate of increase in the tank internal pressure PTANK, than in the
FIG. 5
case where there is a leak.
As described above, according to the leakage determination system
1
of the present embodiment, since the re-reduction of the pressure within the evaporative fuel processing system
20
is repeatedly carried out, even if the tank internal pressure PTANK is temporarily increased e.g. due to an increase in the amount of generation of evaporative fuel in the fuel tank
21
, it is possible to reduce the temporary rise in the tank internal pressure PTANK whenever it occurs, and detect the pressure reduction cycle TCY. Whether or not there is a leak in the evaporative fuel processing system
20
is determined based on the averaged pressure reduction cycle TCYAVE as an averaged value of a plurality of pressure reduction cycles TCY detected during the repetition of pressure re-reduction. Therefore, even when a temporary rise in the tank internal pressure PTANK has caused a variation in the pressure reduction cycle TCY, the leakage determination carried out by the use of the averaged pressure reduction cycle TCYAVE described above makes it possible to assess the plurality of pressure reduction cycles TCY as a whole while compensating for the variation in the pressure reduction cycles TCY. Thus, the influence of the temporary rise in the tank internal pressure PTANK on the leakage determination can be reduced, which enables accurate determination of whether or not there is a leak in the evaporative fuel processing system
20
.
Although in the above embodiment, the jet
35
and the purge bypass valve
34
are used for pressure re-reduction, the pressure re-reduction may be carried out by introducing negative pressure from the intake system
4
at a low flow rate (of a gas containing evaporative fuel) by using the purge control valve
33
in place of the jet
35
and the purge bypass valve
34
. Further, although in the above embodiment, the reference value for control of the initial pressure reduction and the threshold value for termination of the pressure re-reduction are set to an identical value (predetermined negative pressure POBJ), they may be set, respectively, to two values different from each other. Moreover, although in the present embodiment, the pressure reduction cycles TCY are detected by operation of the ECU
2
, this is not limitative, but any suitable method capable of determining the pressure reduction cycles TCY may be employed. In addition, the start of counting of each pressure reduction cycle TCY may be delayed to prevent erroneous determination due to noise generated by the pressure sensor
26
. Further, although in the above embodiment, whether or not there is a leak is determined based on the pressure reduction cycles TCY, the determination may be made based on the number of pressure re-reductions executed during a leakage check time period.
Furthermore, although in the above embodiment, the leakage check (leakage determination) is performed on the whole evaporative fuel processing system
20
, a leakage check may be executed only on the fuel tank
23
side by holding the charge bypass valve
31
closed during the leakage check and open during pressure re-reduction. This makes it possible to determine which of the canister
24
side and the fuel tank
23
side has a leak.
Next, a leakage determination process for the evaporative fuel processing system
20
, according to the second embodiment, will be described with reference to
FIGS. 6 and 7
. Similarly to the first embodiment, the leakage determination process of the present embodiment is executed by the ECU
2
.
FIG. 6
is a flowchart showing a program for carrying out the leakage determination process. Similarly to that of the first embodiment, the process is carried out by an interrupt handling routine at predetermined time intervals (e.g. every 80 msec.) set by a timer, but not carried out after execution of leakage determination at a step S
114
, referred to hereinafter. That is, in the present process, the leakage determination is carried out only once during a time period from the start of operation of the engine
3
to the end thereof.
First, it is determined at a step S
101
whether or not a monitoring condition is satisfied. The monitoring condition is identical to that for the leakage determination of the first embodiment.
If the answer to the question of the step S
101
is negative (NO), i.e. if the monitoring condition is not satisfied, the program is immediately terminated.
On the other hand, if the answer to the question is affirmative (YES), i.e. if the monitoring condition is satisfied, the program proceeds to a step S
102
, wherein it is determined whether or not a primary pressure reduction termination flag FPOK
1
assumes “1”. The flag FPOK
1
is set to “1” at a step S
107
upon termination of the primary pressure reduction carried out at steps S
103
to S
106
described below.
Immediately after the program is started, the flag FPOK
1
assumes “0”, so that the answer to the question of the step S
102
is negative (NO). Therefore, the program proceeds to the step S
103
, wherein the primary pressure reduction for reducing pressure within the evaporative fuel processing system
20
is started. More specifically, in a state of the purge bypass valve
34
being held closed, the vent shut valve
32
is closed, and the charge bypass valve
31
is opened. At the same time, the duty ratio of the purge control valve
33
is controlled based on the tank internal pressure PTANK detected by the pressure sensor
26
, such that the tank internal pressure PTANK becomes equal to a predetermined negative pressure POBJ (e.g. −20 hPa)). As a result, negative pressure is introduced from the intake pipe
5
into the evaporative fuel processing system
20
, whereby the tank internal pressure PTANK is reduced to the predetermined negative pressure POBJ. In this case, since the charge bypass valve
31
is open, the tank internal pressure PTANK represents the pressure within the evaporative fuel processing system
20
.
Then, the program proceeds to the step S
104
, wherein it is determined whether or not a pressure reduction time period has elapsed. The pressure reduction time period is set to a value (e.g. 15 sec.) within which the tank internal pressure PTANK is expected to be positively lowered by the primary pressure reduction to the predetermined negative pressure POBJ so long as the valves
31
to
34
and the pressure sensor
26
are normally operating and there is no large amount of leakage from the evaporative fuel processing system
20
. If the answer to the question of the step S
104
is negative (NO), i.e. if the pressure reduction time period has not elapsed, the program is immediately terminated.
On the other hand, if the answer to the question of the step S
104
is affirmative (YES), i.e. if the pressure reduction time period has elapsed, the program proceeds to the step S
105
, wherein it is determined whether or not the tank internal pressure PTANK is equal to or lower than the predetermined negative pressure POBJ.
If the answer to the question is negative (NO), i.e. if PTANK>POBJ holds, it is judged that one or more of the valves
31
to
34
and the pressure sensor
26
are not normally operating or there is a large amount of leakage from the evaporative fuel processing system
20
, and hence that the leakage determination for the system
20
cannot be normally performed, so that a leakage determination termination flag FDONE is set to “1” at a step S
108
, followed by terminating the program. By setting the leakage determination termination flag FDONE to “1”, the present program or the leakage determination by the present process is prevented from being executed from this time on.
If the answer to the question of the step S
105
is affirmative (YES), i.e. if PTANK≦POBJ holds, the program proceeds to the step S
106
, wherein the primary pressure reduction is terminated and a secondary pressure reduction is started in succession thereto. More specifically, in a state of the vent shut valve
32
being held closed and the charge bypass valve
31
being held open, the purge control valve
33
is closed and the purge bypass valve
34
is opened, whereby the evaporative fuel processing system
20
communicates with the intake pipe
5
only via the purge bypass passage
30
, and negative pressure is introduced from the intake pipe
5
into the evaporative fuel processing system
20
at a constant flow rate Q (of a gas containing evaporative fuel) via the jet
35
. The flow rate Q is set to a value (e.g. 3 liters per second) which will cause the tank internal pressure PTANK to slowly decrease during the secondary pressure reduction when there is no leak in the evaporative fuel processing system
20
.
Then, at the following step S
107
, the primary pressure reduction termination flag FPOK
1
is set to “1”, followed by the program proceeding to a step S
109
. After the flag FPOK
1
having been set to “1” at the step S
107
, the answer to the question of the step S
102
becomes affirmative (YES) in the following loops. Therefore, in the following loops, the steps S
103
to S
108
are skipped, and the program jumps to the step S
109
.
At the step S
109
, it is determined whether or not a leakage check time period has elapsed. The leakage check time period is set to a time period (e.g. 30 sec.) e.g. after the start of the secondary pressure reduction, which is long enough to positively reveal the tendency of a change in the tank internal pressure PTANK dependent on whether or not there is a leak. If the answer to the question is negative (NO), i.e. if the leakage check time period has not elapsed, the program is immediately terminated.
On the other hand, if the answer to the question of the step S
109
is affirmative (YES), i.e. if the leakage check time period has elapsed, the program proceeds to a step S
110
, wherein the secondary pressure reduction is terminated, and at the same time a variation amount ΔP of the tank internal pressure PTANK is calculated. The secondary pressure reduction is terminated by closing the charge bypass valve
31
and the purge bypass valve
34
and opening the vent shut valve
32
with the purge control valve
33
held closed.
The variation amount ΔP of the tank internal pressure PTANK is calculated as a differential pressure between a final tank internal pressure PTANK
2
detected e.g. at the end of the counting of the leakage check time period, i.e. at a time point (time t22 in
FIG. 7
) the secondary pressure reduction is terminated and an initial tank internal pressure PTANK
1
detected e.g. at the start of the counting of the leakage check time period, i.e. at a time point (time t21 in
FIG. 7
) the secondary pressure reduction is started (ΔP=PTANK
2
−PTANK
1
). It should be noted that PTANK
1
=POBJ is normally maintained by duty ratio control of the purge control valve
33
.
Then, the program proceeds to a step S
111
, wherein it is determined whether or not the variation amount ΔP calculated at the step S
110
is smaller than a predetermined leakage reference value ΔPREF (e.g. 5 hPa). If the answer to the question is affirmative (YES), i.e. if ΔP<ΔPREF holds, it is determined that the tank internal pressure PTANK is falling slowly or that the rate of increase in the tank internal pressure PTANK is small and hence that there is no leak in the evaporative fuel processing system
20
. Then, a leakage determination flag FLEAK is set to “0” at a step S
112
so as to indicate that there is no leak in the system
20
, and the primary pressure reduction termination flag FPOK
1
and the leakage determination termination flag FDONE are set to “0” and “1”, respectively, at a step S
114
, followed by terminating the program.
On the other hand, if the answer to the question of the step S
111
is negative (NO), i.e. if ΔP≧ΔPREF holds, it is judged that the rate of increase in the tank internal pressure PTANK is large and hence that there is a leak in the evaporative fuel processing system
20
, so that the program proceeds to a step S
113
, wherein the leakage determination flag FLEAK is set to “1” so as to indicate that there is a leak in the system
20
. Thereafter, the step S
114
is executed, followed by terminating the program.
Next, examples of changes in the tank internal pressure PTANK detected through execution of the above leakage determination process will be described with reference to a timing chart shown in FIG.
7
. In the figure, a solid line indicates a change in the tank internal pressure PTANK detected when there is no leak in the evaporative fuel processing system
20
, while a broken line indicates a change in the tank internal pressure PTANK detected when there is a leak in the evaporative fuel processing system
20
.
First, when the primary pressure reduction is started (time t20), the tank internal pressure PTANK falls. Thereafter, at a time point (time t21) the tank internal pressure PTANK has fallen to the predetermined negative pressure POBJ and the pressure reduction time period has elapsed, the purge control valve
33
is closed, and the charge bypass valve
34
is opened in synchronism with the lapse of the pressure reduction time period, whereby the primary pressure reduction is terminated, and the secondary pressure reduction is started. Then, at a time point (time t22) the leakage check time period has elapsed, the secondary pressure reduction is terminated, and the variation amount ΔP is calculated as a differential pressure between the final tank internal pressure PTANK
2
and the initial tank internal pressure PTANK
1
. Further, the leakage determination is performed by comparing the variation amount ΔP with the leakage reference value ΔPREF.
If there is no leak in the evaporative fuel processing system
20
, the tank internal pressure PTANK slowly falls during the secondary pressure reduction as indicated by the solid line in
FIG. 7
, so that the variation amount ΔP assumes a negative value, and hence the answer to the question of the step S
111
becomes affirmative (YES)(ΔP<ΔPREF). From this, it is determined that there is no leak in the evaporative fuel processing system
20
. On the other hand, if there is a leak in the evaporative fuel processing system
20
, the tank internal pressure PTANK slowly rises as indicated by the broken line in the figure, and the variation amount ΔP becomes equal to or larger than the leakage reference value ΔPREF (ΔP≧ΔPREF). From this, it is determined that there is a leak in the evaporative fuel processing system
20
.
As described above, according to the leakage determination system
1
of the present embodiment, during the secondary pressure reduction, the tank internal pressure PTANK is detected while introducing negative pressure from the intake system
4
into the evaporative fuel processing system
20
, and the variation amount ΔP is calculated as a differential pressure between the final tank internal pressure PTANK
2
and the initial tank internal pressure PTANK
1
. The calculated variation amount ΔP represents a final pressure value obtained as an offset between an increment of the initial tank internal pressure PTANK caused by a leak, if any, and a decrement of the same caused by introduction of the negative pressure. Therefore, it is possible to determine whether or not there is a leak in the evaporative fuel processing system
20
by comparing the variation amount ΔP with the predetermined reference value ΔPREF.
Further, since the tank internal pressure PTANK is detected while continuing the secondary pressure reduction, even if the tank internal pressure PTANK is temporarily increased e.g. due to an increase in the amount of generation of evaporative fuel in the fuel tank
21
, it is possible to reduce the temporary rise in the tank internal pressure PTANK whenever it occurs, and carry out the leakage determination. Consequently, the influence of the temporary rise in the tank internal pressure PTANK caused by other factors than leakage on the leakage determination can be eliminated, which enables accurate determination of whether or not there is a leak in the evaporative fuel processing system
20
.
Although in the above embodiment, the variation amount ΔP is calculated as a differential pressure between the final tank internal pressure PTANK
2
and the initial tank internal pressure PTANK
1
each detected during the secondary pressure reduction, it is possible to use a proper parameter other than the variation amount AP as one indicative of a change in the tank internal pressure PTANK during the secondary pressure reduction. For example, the variation amount ΔP may be calculated as a cumulative value of differences between a plurality of respective tank internal pressures PTANK detected at different time points during the secondary pressure reduction, and the initial tank internal pressure PTANK
1
, or alternatively as an integral value of the tank internal pressure PTANK calculated during the secondary pressure reduction, with respect to the initial tank internal pressure PTANK
1
.
Further, a flow rate adjustment valve may be used in place of the purge bypass valve
34
and the jet
35
, for limiting the flow rate in the purge bypass passage
30
to a flow rate Q identical to that in the jet
35
. Alternatively, the purge bypass passage
30
, the purge bypass valve
34
and the jet
35
may be all omitted, and in place of the purge control valve
33
, a control valve which is capable of accurately controlling the flow rate in the purge passage
25
within a range from the same flow rate Q as provided by the jet
35
to the same flow rate as provided by the purge control valve
33
may be used to carry out the purge control and the secondary pressure reduction. Further, alternatively, the purge bypass passage
30
may be formed separately from the purge passage
25
, for communicating between the intake pipe
5
and the canister
24
during the secondary pressure reduction.
It is further understood by those skilled in the art that the foregoing are preferred embodiments of the invention, and that various changes and modifications may be made without departing from the spirit and scope thereof.
Claims
- 1. A leakage determination system for an evaporative fuel processing system that causes a canister to absorb evaporative fuel generated from a fuel tank and supplies the evaporative fuel absorbed in the canister to an intake system of an internal combustion engine,the leakage determination system comprising: pressure detection means for detecting pressure within the evaporative fuel processing system; primary pressure reduction means for primarily reducing the pressure within the evaporative fuel processing system until the detected pressure becomes equal to a predetermined negative pressure, by introducing negative pressure from the intake system; secondary pressure reduction means for secondarily reducing the pressure within the evaporative fuel processing system by introducing the negative pressure from the intake system successively after the primary pressure reduction by said primary pressure reduction means under predetermined conditions; and leakage determination means for determining that there is a leak in the evaporative fuel processing system when a variation amount of the detected pressure detected during the secondary pressure reduction by said secondary pressure reduction is higher than a predetermined leakage reference value.
- 2. A leakage determination system according to claim 1, wherein said secondary pressure reduction means introduces the negative pressure from the intake system at a predetermined constant negative pressure introduction flow rate.
- 3. A leakage determination method for an evaporative fuel processing system that causes a canister to absorb evaporative fuel generated from a fuel tank and supplies the evaporative fuel absorbed in the canister to an intake system of an internal combustion engine,the leakage determination method comprising: a pressure detection step of detecting pressure within the evaporative fuel processing system; a primary pressure reduction step of primarily reducing the pressure within the evaporative fuel processing system until the detected pressure becomes equal to a predetermined negative pressure, by introducing negative pressure from the intake system; a secondary pressure reduction step of secondarily reducing the pressure within the evaporative fuel processing system by introducing the negative pressure from the intake system successively after the primary pressure reduction at the primary pressure reduction step under predetermined conditions; and a leakage determination step of determining that there is a leak in the evaporative fuel processing system when a variation amount of the detected pressure detected during the secondary pressure reduction is higher than a predetermined leakage reference value.
- 4. A leakage determination method according to claim 3, wherein at said secondary pressure reduction step, the negative pressure from the intake system is introduced at a predetermined constant negative pressure introduction flow rate.
Priority Claims (2)
Number |
Date |
Country |
Kind |
2000-171837 |
Jun 2000 |
JP |
|
2000-171838 |
Jun 2000 |
JP |
|
US Referenced Citations (9)