U.S. patent application number 09/838184 was filed with the patent office on 2001-10-25 for fuel gas feeding system.
This patent application is currently assigned to Honda Giken Kogyo Kabushiki Kaisha. Invention is credited to Akazaki, Shusuke, Goto, Hiroyuki, Sakurai, Yoshihito, Yamazaki, Hideharu.
Application Number | 20010032628 09/838184 |
Document ID | / |
Family ID | 18630437 |
Filed Date | 2001-10-25 |
United States Patent
Application |
20010032628 |
Kind Code |
A1 |
Goto, Hiroyuki ; et
al. |
October 25, 2001 |
Fuel gas feeding system
Abstract
A first cutoff valve 24 and a second cutoff valve 41 are closed
in a state in which an internal combustion engine 1 is stopped, and
a reducing amount of a pressure P0 in a high pressure passageway 11
after the passage of a predetermined decision time T0 and a
reducing amount of a pressure P2 in a low pressure passageway 12
after the passage of a predetermined decision time T2 are measured.
When the reducing amount of the first pressure P0 is equal to or
larger than a predetermined reducing amount .DELTA.P0, it is
decided that a leakage is generated in the high pressure passageway
11. When the reducing amount of the second pressure P2 is equal to
or larger than a predetermined reducing amount .DELTA.P2, it is
decided that a leakage is generated in the low pressure passageway
12.
Inventors: |
Goto, Hiroyuki; (Saitama,
JP) ; Akazaki, Shusuke; (Saitama, JP) ;
Yamazaki, Hideharu; (Saitama, JP) ; Sakurai,
Yoshihito; (Saitama, JP) |
Correspondence
Address: |
ARENT FOX KINTNER
PLOTKIN & KAHN, PLLC
Suite 600
1050 Connecticut Avenue, N.W.
Washington
DC
20036-5339
US
|
Assignee: |
Honda Giken Kogyo Kabushiki
Kaisha
|
Family ID: |
18630437 |
Appl. No.: |
09/838184 |
Filed: |
April 20, 2001 |
Current U.S.
Class: |
123/529 ;
123/198D |
Current CPC
Class: |
Y02T 10/32 20130101;
F02D 2041/226 20130101; F02D 19/027 20130101; F02M 21/0278
20130101; F02M 21/0242 20130101; F02D 41/0027 20130101; F02D 19/022
20130101; F02D 19/025 20130101; F02B 43/00 20130101; F02M 21/0215
20130101; Y02T 10/30 20130101 |
Class at
Publication: |
123/529 ;
123/198.00D |
International
Class: |
F02B 043/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 20, 2000 |
JP |
P. 2000-119465 |
Claims
What is claims is:
1. A fuel gas feeding system comprising: a fuel gas feeding
passageway for feeding a fuel gas to an internal combustion engine;
a plurality of cutoff valves provided in the middle of the fuel gas
feeding passageway; a pressure sensor for detecting a pressure in a
portion partitioned by adjacent two of the cutoff valves in the
fuel gas feeding passageway; an engine stop detecting unit
detecting stop of the engine; and a failure detecting unit closing
the two adjacent cutoff valves when the stop of the engine is
detected, measuring a reducing amount of a pressure detected by the
pressure sensor after a predetermined decision time passes, and
deciding that a leakage is generated between the two adjacent
cutoff valves when the reducing amount thus measured is equal to or
larger than a predetermined reducing amount.
2. The fuel gas feeding system according to claim 1, wherein the
fuel gas feeding passageway includes a high pressure passageway
partitioned by a first cutoff valve and a second cutoff valve and
having a comparatively high pressure of a fuel gas, and a low
pressure passageway partitioned by the second cutoff valve and a
third cutoff valve and having a comparatively low pressure of the
fuel gas, a pressure regulator is provided between the low pressure
passageway and the second cutoff valve, and the failure detecting
unit sets the predetermined decision time required for deciding
presence of a leakage in the low pressure passageway depending on a
pressure in the high pressure passageway and a temperature of the
fuel gas in the low pressure passageway.
3. The fuel gas feeding system according to claim 2, wherein the
third cutoff valve is a fuel injection valve.
4. The fuel gas feeding system according to claim 1, further
comprising: an engine coolant temperature sensor detecting a cool
ant temperature of the engine, wherein, when the coolant
temperature is lower than a predetermined coolant temperature, the
processing of the failure detecting unit is stopped.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a fuel gas feeding system
for feeding a fuel gas to an internal combustion engine for burning
a fuel gas such as a compressed natural gas.
[0003] 2. Description of the Related Art
[0004] In recent years, a natural gas has been employed as one of
alternate fuels for gasoline or gas oil. In the case in which the
natural gas is to be used as a fuel of an internal combustion
engine for vehicles, a fuel gas feeding system as described in
JP-A-7-189731 is used, for example, in which a high pressure
cylinder filled with a natural gas compressed to have a pressure of
approximately 200 kg/cm.sup.2 is mounted on a vehicle and the
natural gas is fed from the high pressure cylinder to a combustion
chamber of the internal combustion engine through a fuel gas
feeding passageway, a pressure regulator and a fuel injection
valve.
[0005] In such a fuel gas feeding system, it is necessary to
rapidly detect a situation in which a hole is formed in the fuel
gas feeding passageway and a fuel leaks out, thereby taking a
countermeasure in an early stage.
SUMMARY OF THE INVENTION
[0006] In view of this respect, it is an object of the invention to
provide a fuel gas feeding system having a failure diagnosing
function capable of rapidly detecting that a leakage is generated
in the fuel gas feeding passageway for feeding a fuel gas to an
internal combustion engine.
[0007] In order to achieve the object, a first aspect of the
invention is directed to a fuel gas feeding system having a fuel
gas feeding passageway (11, 12) for feeding a fuel gas to an
internal combustion engine and a plurality of cutoff valves (24,
41, 7) provided in the middle of the fuel gas feeding passageway,
the system comprising a pressure sensor (32, 33) for detecting a
pressure in a portion partitioned by adjacent two of the cutoff
valves in the fuel gas feeding passageway, an engine stop detecting
unit detecting stop of the engine, and a failure detecting unit for
closing the two adjacent cutoff valves when the stop of the engine
is detected, measuring a reducing amount of a pressure detected by
the pressure sensor after a predetermined decision time (T0, T2)
passes, and deciding that a leakage is generated between the two
adjacent cutoff valves when the reducing amount thus measured is
equal to or larger than a predetermined reducing amount (.DELTA.P0,
.DELTA.P2).
[0008] The "predetermined decision time (T0, T2)" and the
"predetermined reducing amount(.DELTA.P0, .DELTA.P2)" are set
according to a leakage amount (volume/time) per unit time to be
decided as a failure and the volume of the passageway to be
decided.
[0009] According to such a structure, the adjacent two of the
cutoff valves provided in the middle of the fuel gas feeding
passageway are closed. Consequently, the reducing amount of the
pressure in the closed passageway is measured after the
predetermined decision time passes. When the reducing amount thus
measured is larger than the predetermined reducing amount, it is
decided that a leakage is generated between the two adjacent cutoff
valves. Therefore, in the case in which the leakage is generated in
the fuel gas feeding passageway, it is possible to rapidly decide
which portion partitioned by the cutoff valves provided in the
passageway generates the leakage.
[0010] A second aspect of the invention is directed to the fuel gas
feeding system according to the first aspect of the invention,
wherein the fuel gas feeding passageway includes a high pressure
passageway (11) partitioned by a first cutoff valve (24) and a
second cutoff valve (41) and having a comparatively high pressure
of a fuel gas and a low pressure passageway (12) partitioned by the
second cutoff valve (41) and a third cutoff valve (7) and having a
comparatively low pressure of the fuel gas, a pressure regulator
(51, 61) is provided between the low pressure passageway (12) and
the second cutoff valve (41), and the failure detecting unit sets
the predetermined decision time (T2) required for deciding presence
of a leakage in the low pressure passageway (12) depending on a
pressure (P0) in the high pressure passageway and a temperature
(TG2) of the fuel gas in the low pressure passageway.
[0011] According to such a structure, the predetermined decision
time required for deciding presence of a leakage in the low
pressure passageway is set depending on the pressure in the high
pressure passageway and the temperature of the fuel gas in the low
pressure passageway. It is considered that a reducing speed of the
pressure in the low pressure passageway is reduced due to the
leakage if the pressure in the high pressure passageway is high and
the temperature of the fuel gas in the low pressure passageway is
low. The predetermined decision time is set to be longer when the
pressure in the high pressure passageway is increased and the
temperature of the fuel gas in the low pressure passageway is
dropped. Consequently, the decision can be carried out
accurately.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a view showing the structure of a fuel gas feeding
system according to an embodiment of the invention,
[0013] FIG. 2 is atypical view showing the structure of a pressure
control unit illustrated in FIG. 1,
[0014] FIG. 3 is a flow chart showing a failure diagnosis
processing for a high pressure passageway,
[0015] FIG. 4 is a flow chart showing the failure diagnosis
processing for the high pressure passageway,
[0016] FIG. 5 is a flow chart showing a failure diagnosis
processing for a low pressure passageway,
[0017] FIG. 6 is a flow chart showing the failure diagnosis
processing for the low pressure passageway,
[0018] FIG. 7 is a chart showing a map to be used for the
processing of FIG. 5, and
[0019] FIGS. 8(a) to 8(h) are time charts illustrating the failure
diagnosis processing shown in FIGS. 3 to 6.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] An embodiment of the invention will be described below with
reference to the drawings.
[0021] FIG. 1 is a view showing the structure of a fuel gas feeding
system according to the embodiment of the invention. The system is
mounted on a rear part of a vehicle, and a compressed natural gas
(CNG) is fed as a fuel gas from a CNG tank 8 filled with the
compressed natural gas to an intake port 2 of an internal
combustion engine (hereinafter referred to as an "engine") 1
mounted on a front part of the vehicle.
[0022] A filling passageway 22 and a high pressure passageway 11
having a comparatively high gas pressure are connected to the CNG
tank 8 through a connecting unit 9, and a filling port 21 is
provided in the filling passageway 22. The connecting unit 9
includes a check valve 23 provided between the filling passageway
22 and the CNG tank 8 and a first cutoff valve 24 provided between
the high pressure passageway 11 and the CNG tank 8.
[0023] The check valve 23 is provided to prevent the natural gas
from reversely flowing from the CNG tank 8 to the filling
passageway 22. Moreover, the first cutoff valve 24 is an
electromagnetic valve which is connected to an electronic control
unit (hereinafter referred to as an "ECU") 5 and of which opening
operation is controlled by the ECU 5.
[0024] The high pressure passageway 11 is provided with a joint box
25, a manual ON-OFF valve 26 and a filter 27 from the upstream side
in order and is connected to a low pressure passageway 12 having a
comparatively low gas pressure through a pressure control unit 28.
The low pressure passageway 12 is connected to a fuel injection
valve 7 for injecting a fuel gas into the intake port 2. The fuel
injection valve (injector) 7 is connected to an injector driver 6,
the injector driver 6 is connected to the ECU 5, and the ECU 5
controls a period required for fuel injection and a time for fuel
injection through the fuel injection valve 7. The fuel injection
valve 7 is provided on the intake port for each cylinder of the
engine 1.
[0025] The joint box 25 is provided with a first pressure sensor 31
for detecting a pressure P0 (hereinafter referred to as a "first
pressure P0") in the high pressure passageway 11 and a first gas
temperature sensor 32 for detecting a fuel gas temperature TG0 in
the high pressure passageway 11. The detection signals of the
sensors 31, 32 are input to the ECU 5.
[0026] The manual ON-OFF valve 26 can be opened manually, and is
usually held in an open state. Moreover, the filter 27 is provided
for removing dust contained in a fuel gas.
[0027] A second pressure sensor 33 for detecting a pressure P2
(hereinafter referred to as a "second pressure P2") in the low
pressure passageway 12 is provided in the vicinity of the outlet of
the pressure control unit 28, and furthermore, a second gas
temperature sensor 34 for detecting a fuel gas temperature TG2 in
the low pressure passageway 12 is provided in the fuel injection
valve 7.
[0028] FIG. 2 is a typical view illustrating the structure of the
pressure control unit 28. The pressure control unit 28 includes a
second cutoff valve 41, a primary pressure reducing valve 51, a
safety valve 56, and a secondary pressure reducing valve 61. The
second cutoff valve 41 is an electromagnetic valve in which a valve
element 44 is urged in a closing direction through a spring 43 and
is conducted to a solenoid 42 so as to open the valve, and the
solenoid 42 is connected to the ECU 5. Accordingly, the second
cutoff valve 41 is opened or closed under control of the ECU 5.
When the second cutoff valve 41 is opened, a fuel gas flows into a
pressure chamber 13 as shown in an arrow F.
[0029] The primary pressure reducing valve 51 includes a diaphragm
52 having a valve element 55 fixed thereto, a pressure regulating
spring 53 and a back pressure chamber 54. The back pressure chamber
54 communicates with an intermediate pressure chamber 14. A
pressure P1 in the intermediate pressure chamber 14 (hereinafter
referred to as an "intermediate pressure P1") is an intermediate
pressure between the first pressure P0 and the second pressure P2
(P0<P1<P2). The primary pressure reducing valve 51 is opened
(an opening is increased) when the intermediate pressure P1 is
lower than a set pressure, while the primary pressure reducing
valve 51 is closed (the opening is decreased) when the intermediate
pressure P1 is higher than the set pressure. Consequently, the
intermediate pressure P1 is held to be almost equal to the set
pressure. In the embodiment, the first pressure P0 is 10 to 260
kg/cm.sup.2, and the set pressure of the intermediate pressure P1
is approximately 6 kg/cm.sup.2.
[0030] The safety valve 56 is opened when the intermediate pressure
P1 is too raised. Thus, the secondary pressure reducing valve 61
and the low pressure passageway 12 are protected.
[0031] The secondary pressure reducing valve 61 is constituted in
the same manner as the primary pressure reducing valve 51, and
includes a diaphragm 62 having a valve element 65 fixed thereto, a
pressure regulating spring 63 and a back pressure chamber 64. A
pressure in the low pressure passageway, that is, the second
pressure P2 is fed to the back pressure chamber 64. The second
pressure P2 is held to be a set pressure (for example, 2.6
kg/cm.sup.2) through the secondary pressure reducing valve 61.
[0032] Returning to FIG. 1, an engine coolant temperature sensor
for detecting a coolant temperature (hereinafter referred to as an
"engine coolant temperature") TW of the engine 1 is connected to
the ECU 5, and a detection signal thereof is supplied to the ECU 5.
Moreover, an ignition switch 36 is connected to the ECU 5, and a
signal indicative of ON/OFF of the ignition switch 36 is supplied
to the ECU 5.
[0033] The ECU 5 serves to control a period required for fuel
injection and a time for fuel injection through the fuel injection
valve 7 in response to signals output from various sensors shown in
FIG. 1 and other sensors which are not shown, and to carry out a
failure diagnosis which will be described below, that is, to decide
the presence of a leakage in the high pressure passageway 11 and
the low pressure passageway 12.
[0034] FIGS. 3 and 4 are flow charts showing a processing for
deciding the presence of the leakage in the high pressure
passageway 11 partitioned by the first cutoff valve 24 and the
second cutoff valve 41. The processing is executed every constant
time in the ECU 5.
[0035] At a step S11, it is decided whether the ignition switch 36
is turned OFF or not. When the ignition switch 36 is not turned
OFF, the processing is ended immediately. When the ignition switch
36 is turned OFF, the first cutoff valve 24 and the second cutoff
valve 41 are closed (step S12) and it is decided whether or not the
engine coolant temperature TW is equal to or higher than a
predetermined coolant temperature TWO (for example, 85.degree. C.)
(step S13). When the warming up of the engine is not completed with
TW<TW0, the temperatures of the fuel gas passageways 11 and 12
and other fuel feeding system parts are indefinite. Therefore,
there is a possibility that precision in the decision might be
deteriorated. Consequently, the processing is ended immediately.
When TW>TW0 is obtained, it is decided whether or not the first
pressure P0 is equal to or lower than the second pressure P2 (step
S14). Usually, since the answer is "NO", a pressure sensor
abnormality flag FLPS indicating the abnormality of the pressure
sensor as "1" is set to "0" (step S16) and the processing proceeds
to a step S17. On the other hand, when the answer of the step S14
is "YES", it is decided that the first pressure sensor 31 or the
second pressure sensor 33 is abnormal and the pressure sensor
abnormality flag FLPS is set to "1" (step S15) and the processing
proceeds to the step S17.
[0036] At the step S17, it is decided whether the pressure sensor
abnormality flag FLPS is "1" or not. When FLPS=1 is obtained,
pressure sensor abnormality display is performed at the time of the
next start of the engine (step S18) and the processing is ended
immediately. The pressure sensor abnormality display is performed
by turning ON an alarm lamp, for example.
[0037] When the pressure sensor is not abnormal with FLPS=0 at the
step S17, the detection value of the first pressure sensor 31 is
fetched and is stored as a first detection value P0(1) (step S19).
Next, the value of a diagnosing timer Tf0 being an up count timer
is reset to "0" (step S20) and steps S21 to S23 are executed. More
specifically, the first pressure sensor output P0 is sampled (step
S21) and it is decided whether or not the ignition switch 36 is
turned ON (step S22). When the ignition switch is continuously set
in the OFF state, it is decided whether or not the value of the
diagnosing timer Tf0 is equal to or greater than a first
predetermined decision time T0 (step S23). If Tf0<T0 is
obtained, the processing returns to the step S21. When the ignition
switch 36 is turned ON before Tf0.gtoreq.T0 is obtained, the
processing is ended immediately (step S22).
[0038] When the answer of the step S23 is "YES", the processing
proceeds to a step S31 (FIG. 4) where the newest sampling value is
stored as a second detection value P0(2), and it is decided whether
or not a differential pressure (=P0(1)-P0(2)) between the first
detection value P0(1) and the second detection value P0(2), that
is, the reducing amount of the first pressure P0 after the first
predetermined decision time T0 passes since the first cutoff valve
24 and the second cutoff valve 41 have been closed, is equal to or
larger than a predetermined reducing amount .DELTA.P0 (step S32).
As a result, when P0(1)-P0(2)<.DELTA.P0 is obtained, it is
decided that there is no failure and the processing immediately
proceeds to a step S34. When P0(1)-P0(2).gtoreq..DELTA.P0 is
obtained, it is decided that there is a leakage in the high
pressure passageway 11 and the first failure detecting flag
FL.DELTA.P0 indicating the presence of the leakage as "1" is set to
"1" (step S33) and the processing proceeds to a step S34.
[0039] At the step S34, it is decided whether the first failure
detecting flag FL.DELTA.P0 is "1" or not. When FL.DELTA.P0=1 is
obtained, high pressure passageway abnormality display indicating
that the high pressure passageway 11 has an abnormality is
performed at the time of the next start of the engine (step S35)
Moreover, when FL.DELTA.P0=0 is obtained, the processing
immediately proceeds to a step S36. The high pressure passageway
abnormality display is performed by turning ON the alarm lamp, for
example.
[0040] At the step S36, it is decided whether or not the first
predetermined decision time T0 is equal to or greater than a second
predetermined decision time T2 to be used for the failure diagnosis
of the low pressure passageway 12 which will be described below.
When T0-T2 is obtained, the power source of the ECU 5 is turned OFF
(step S37). When T0<T2 is obtained, the processing is
immediately ended.
[0041] When T0.gtoreq.T2 is obtained at the steps S36 and S37, the
failure diagnosis of the low pressure passageway 12 has already
been ended or is ended at the same time. Therefore, it is not
necessary to turn ON the power source of the ECU 5. For this
reason, the steps S36 and S37 are provided to be ended by turning
OFF the power source.
[0042] FIGS. 5 and 6 are flow charts showing a processing for
deciding the presence of a leakage in the low pressure passageway
12 partitioned by the second cutoff valve 41 and the fuel injection
valve 7. This processing is executed every constant time in the ECU
5. In the embodiment, the fuel injection valve 7 corresponds to a
third cutoff valve and the fuel injection valve 7 is maintained in
a closing state during the stop of the engine.
[0043] The processings of steps S41 to S48 in FIG. 5 are identical
to the processings of the steps S11 to S18 in FIG. 3. At a step S49
in FIG. 5, the detection value of the second pressure sensor 33 is
fetched and stored as a first detection value P2(1). Next, a T2 map
shown in FIG. 7 is retrieved according to the first pressure P0 and
a second fuel gas temperature TG2, and the second predetermined
decision time T2 is calculated (step S50). In FIG. 7, straight
lines L1, L2 and L3 show the relationship between the first
pressure P0 and the second predetermined decision time T2 at the
second fuel gas temperature TG2=TG20, TG21 and TG22, which have the
relationship of TG20<TG21<TG22. More specifically, the T2 map
is set such that the second predetermined decision time T2 is
prolonged if the first pressure P0 is high and the second fuel gas
temperature T2 is low.
[0044] Even if the second cutoff valve 41 is closed, a fuel gas
having a high pressure remains in pressure chambers 13 and 14 of
the pressure control unit 28. Therefore, the pressure P2 in the low
pressure passageway 12 is not dropped in a short time even if there
is a leakage. If the first pressure P0 is high, it is necessary to
take a longer time for dropping the second pressure P2 by a
predetermined reducing amount of A P2 as a threshold for a decision
(see a step S62 which will be described below). Moreover, if the
fuel gas temperature TG2 is low, the value of the second pressure
P2 is reduced (because of a constant volume). Therefore, the
reducing amount per unit time of the second pressure P2 is also
reduced. By setting the second predetermined decision time T2 using
the T2 map shown in FIG. 7, therefore, the presence of a leakage
can be decided accurately.
[0045] At a step S51 in FIG. 5, the value of a diagnosing timer Tf2
to be an up count timer is reset to "0" and steps S52 to S54 are
executed. More specifically, the second pressure sensor output P2
is sampled (step S52) and it is decided whether or not the ignition
switch 36 is turned ON (step S53). When the ignition switch is
continuously maintained in the OFF state, it is decided whether or
not the value of the diagnosing timer Tf2 is equal to or greater
than the second predetermined decision time T2 (step S54). If
Tf2<T2 is obtained, the processing returns to the step S52. When
the ignition switch 36 is turned ON before Tf2.gtoreq.T2 is
obtained, the processing is ended immediately (step S53).
[0046] When the answer of the step S54 is "YES", the processing
proceeds to a step S61 (FIG. 6) where the newest sampling value is
stored as a second detection value P2(2), and it is decided whether
or not a differential pressure (=P2(1)-P2(2)) between the first
detection value P2(1) and the second detection value P2(2), that
is, the reducing amount of the second pressure P2 after the second
predetermined decision time T2 passes since the second cutoff valve
has been closed, is equal to or larger than a predetermined
reducing amount .DELTA.P2 (step S62). As a result, when
P2(1)-P2(2)<.DELTA.P2 is obtained, it is decided that there is
no failure and the processing immediately proceeds to a step S64.
When P2(1)-P2(2).gtoreq..DELTA.P2 is obtained, it is decided that
there is a leakage in the low pressure passageway 12 and the second
failure detecting flag FL.DELTA.P2 indicating the presence of the
leakage as "1" is set to "1" (step S63) and the processing proceeds
to a step S64.
[0047] At the step S64, it is decided whether or not the second
failure detecting flag FL.DELTA.P2 is "1". When FL.DELTA.P2=1 is
obtained, a low pressure passageway abnormality display indicating
that the low pressure passageway 12 has an abnormality is performed
at the time of the next start of the engine (step S65). Moreover,
when FL.DELTA.P2 =0 is obtained, the processing immediately
proceeds to a step S66. The low pressure passageway abnormality
display is performed by turning ON the alarm lamp, for example.
[0048] At the step S66, it is decided whether or not the second
predetermined decision time T2 is equal to or greater than the
first predetermined decision time T0. When T2.gtoreq.T0 is
obtained, the power source of the ECU 5 is turned OFF (step S67).
When T2<T0 is obtained, the processing is immediately ended.
[0049] FIGS. 8(a) to 8(f) are time charts illustrating a failure
diagnosing method through the processings of FIGS. 3 to 6. When the
ignition switch 36 is turned OFF at a time t0 (FIG. 8(a)), the
first cutoff valve 24 and the second cutoff valve 41 are closed and
the operations of the diagnosing timers Tf0 and Tf2 are started
(FIGS. 8(c), (d), (f) and (g)).
[0050] The first pressure P0 and the second pressure P2 which are
detected by the pressure sensor are dropped little by little with
the passage of a time as shown in a solid line of FIGS. 8(e) and
(h) also in a normal state. However, if there is a leakage, the
pressures are greatly dropped as shown in a broken line in FIGS.
8(e) and (h). FIGS. 8(a) to 8(h) show an example of T0>T2. When
the second predetermined decision time T2 passes to reach the time
t1, the decision of leakage is performed by comparing the reducing
amount (=P2(1)-P2(2)) with the predetermined reducing amount
.DELTA.P2 and the operation of the diagnosing timer Tf2 is stopped.
When the reducing amount is equal to or larger than the
predetermined reducing amount .DELTA.P2, it is decided that there
is a leakage in the low pressure passageway 12.
[0051] When the first predetermined decision time T0 passes from
the time t0 and reaches a time t2, the decision is performed by
comparing the reducing amount (=P0(1)-P0(2)) with the predetermined
reducing amount .DELTA.P0 and the operation of the diagnosing timer
Tf0 is stopped. When the reducing amount is equal to or larger than
the predetermined reducing amount A P0, it is decided that there is
a leakage in the high pressure passageway 11.
[0052] In the embodiment, as described above, in the state in which
the ignition switch 36 is turned OFF and the engine 1 is stopped,
the first cutoff valve 24 and the second cutoff valve 41 are
closed, and the reducing amount of the pressure P0 in the high
pressure passageway 11 after the passage of the predetermined
decision time T0 and the reducing amount of the pressure P2 in the
low pressure passageway 12 after the passage of the predetermined
decision time T2 are measured. When the reducing amount of the
first pressure P0 is equal to or larger than the predetermined
reducing amount .DELTA.P0, it is decided that there is a leakage in
the high pressure passageway 11. When the reducing amount of the
second pressure P2 is equal to or larger than the predetermined
reducing amount .DELTA.P2, it is decided that there is a leakage in
the low pressure passageway 12. Therefore, in the case in which the
leakage is generated in the fuel gas feeding passageway for feeding
a fuel gas from the CNG tank 8 to the engine 1, it is possible to
rapidly decide which portion partitioned by the first and second
cutoff valves 24 and 41 and the fuel injection valve 7 to be the
third cutoff valve generates the leakage.
[0053] Moreover, the predetermined decision time T2 to be used for
the failure diagnosis on the low pressure passageway 12 side is set
to be longer if the pressure P0 in the high pressure passageway 11
is high, or if the fuel gas temperature TG2 in the low pressure
passageway 12 is dropped. Therefore, the decision can be performed
accurately except for the influence of a high pressure fuel gas
remaining in the pressure control unit 28 and the influence of the
fuel gas temperature TG2 also after the second cutoff valve 41 is
closed.
[0054] In the embodiment, the ECU 5 constitutes the engine stop
detecting unit and the failure detecting unit. More specifically,
the step S11 in FIG. 3 or the step S41 in FIG. 5 corresponds to the
engine stop detecting unit and the steps S12 to S23 in FIG. 3 and
the steps S31 to S33 in FIG. 4 or the steps S42 to S54 in FIG. 5
and the steps S61 to S63 in FIG. 6 correspond to the failure
detecting unit. Moreover, the high pressure passageway 11 and the
low pressure passageway 12 correspond to the "fuel gas feeding
passageway". Further, the first cutoff valve 24 and second cutoff
valve 41, and the second cutoff valve 41 and fuel injection valve 7
correspond to the "two adjacent cutoff valves", respectively.
Furthermore, the primary pressure reducing valve 51 and the second
pressure reducing valve 61 correspond to the "pressure
regulators".
[0055] The invention is not restricted to the embodiment but
various modifications can be made. For example, while the example
in which the fuel injection valve 7 acts as the third cutoff valve
and three cutoff valves are therefore provided has been described
in the embodiment, the number of the cutoff valves is not limited
to three but may be two or four or more. In that case, the number
of the pressure sensors may be smaller than that of the cutoff
valves by one.
[0056] While the example in which the fuel gas is a natural gas has
been described in the embodiment, a hydrogen gas or a coal gas may
be used.
[0057] While the decision of the leakage in the high pressure
passageway 11 and that of the leakage in the low pressure
passageway 12 do not always need to be performed at the same time,
it is preferable that they should be executed simultaneously
because a time required for the failure diagnosis can be wholly
shortened.
[0058] According to the first aspect of the invention, as described
above in detail, the adjacent two of the cutoff valves provided in
the middle of the fuel gas feeding passageway are closed.
Consequently, the reducing amount of the pressure in the closed
passageway is measured after the predetermined decision time
passes. When the reducing amount thus measured is larger than a
predetermined reducing amount, it is decided that a leakage is
generated between the two adjacent cutoff valves. Therefore, in the
case in which the leakage is generated in the fuel gas feeding
passageway, it is possible to rapidly decide which portion
partitioned by the cutoff valves provided in the passageway
generates the leakage.
[0059] According to the second aspect of the invention, the
predetermined decision time required for deciding presence of a
leakage in the low pressure passageway is set depending on the
pressure in the high pressure passageway and the temperature of the
fuel gas in the low pressure passageway. It is considered that a
reducing speed of the pressure in the low pressure passageway is
reduced due to the leakage if the pressure in the high pressure
passageway is high and the temperature of the fuel gas in the low
pressure passageway is low. The predetermined decision time is set
to be longer when the pressure in the high pressure passageway is
increased or the temperature of the fuel gas in the low pressure
passageway is dropped. Consequently, the decision can be carried
out accurately.
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