U.S. patent application number 12/638330 was filed with the patent office on 2010-06-17 for fuel cell system.
This patent application is currently assigned to HONDA MOTOR CO., LTD.. Invention is credited to Kuri Kasuya, Narihiro Takagi.
Application Number | 20100151291 12/638330 |
Document ID | / |
Family ID | 42240924 |
Filed Date | 2010-06-17 |
United States Patent
Application |
20100151291 |
Kind Code |
A1 |
Takagi; Narihiro ; et
al. |
June 17, 2010 |
FUEL CELL SYSTEM
Abstract
A fuel cell system includes: a fuel cell having an anode and a
cathode; an oxidant gas flowpath supplying the oxidant gas to the
fuel cell and discharging the oxidant gas from the fuel cell; a
first shut-off valve disposed upstream from the fuel cell and
having a first valve body; a second shut-off valve disposed
downstream from the fuel cell and having a second valve body; a
cathode control unit for sealing the cathode; and a scavenging unit
for scavenging the anode by supplying the oxidant gas to the anode,
wherein the cathode control unit, before scavenging the anode by
using the scavenging unit, unseals the cathode by opening the first
shut-off valve and the second shut-off valve. The fuel cell system
is capable of preventing the valve bodies pressed against seat
sections from being frozen even below the freezing temperature, and
capable of avoiding a situation unable to restart a turned-off
state of the fuel cell system.
Inventors: |
Takagi; Narihiro; (Saitama,
JP) ; Kasuya; Kuri; (Saitama, JP) |
Correspondence
Address: |
WESTERMAN, HATTORI, DANIELS & ADRIAN, LLP
1250 CONNECTICUT AVENUE, NW, SUITE 700
WASHINGTON
DC
20036
US
|
Assignee: |
HONDA MOTOR CO., LTD.
Tokyo
JP
|
Family ID: |
42240924 |
Appl. No.: |
12/638330 |
Filed: |
December 15, 2009 |
Current U.S.
Class: |
429/429 |
Current CPC
Class: |
H01M 8/04225 20160201;
H01M 8/04303 20160201; H01M 8/04223 20130101; H01M 8/04201
20130101; H01M 8/04089 20130101; H01M 8/04253 20130101; Y02E 60/50
20130101; H01M 8/0271 20130101 |
Class at
Publication: |
429/14 ;
429/24 |
International
Class: |
H01M 8/04 20060101
H01M008/04 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 16, 2008 |
JP |
2008-319419 |
Claims
1. A fuel cell system comprising: a fuel cell having an anode to
which fuel gas is supplied, and a cathode to which oxidant gas is
supplied; a first oxidant gas flowpath through which the oxidant
gas is supplied to the fuel cell; a second oxidant gas flowpath
through which the oxidant gas is discharged from the fuel cell; a
first shut-off valve disposed upstream from the fuel cell and
connected to the fuel cell through the first oxidant gas flowpath,
the first shut-off valve having a first valve body; a second
shut-off valve disposed downstream from the fuel cell and connected
to the fuel cell through the second oxidant gas flowpath, the
second shut-off valve having a second valve body; a cathode control
unit for sealing the cathode by closing the first shut-off valve
and the second shut-off valve after electro-chemical reaction is
stopped from progressing in the fuel cell; and a scavenging unit
for scavenging the anode based on a predetermined condition by
supplying the oxidant gas to the anode while stopping the
electro-chemical reaction from progressing in the fuel cell,
wherein the cathode control unit, before scavenging the anode by
using the scavenging unit, unseals the cathode by opening the first
shut-off valve and the second shut-off valve.
2. The fuel cell system as claimed in claim 1, further comprising a
valve lock unit for locking the first valve body of the first
shut-off valve and the second valve body of the second shut-off
valve in open state after unsealing the cathode.
3. A counter-freeze control method for a fuel cell system, the fuel
cell system comprising: a fuel cell having an anode to which fuel
gas is supplied, and a cathode to which oxidant gas is supplied; a
first shut-off valve connected to and disposed upstream from the
fuel cell, the first shut-off valve having a first valve body; a
second shut-off valve connected to and disposed downstream from the
fuel cell, the second shut-off valve having a second valve body; a
cathode control unit for sealing and unsealing the cathode by using
the first shut-off valve and the second shut-off valve, the method
comprising the steps of: stopping an electro-chemical reaction,
which has been previously under way, from progressing in the fuel
cell; closing the first shut-off valve and the second shut-off
valve to seal the cathode; measuring temperature in the fuel cell;
determining whether the cathode control unit performs a
counter-freeze-scavenging process based on the measured
temperature, residual water remaining in the anode and the cathode
being discharged by supplying oxidant gas to both the anode and the
cathode in the counter-freeze-scavenging process; unsealing the
cathode by opening the first shut-off valve and the second shut-off
valve; maintaining the first valve body and the second valve body
open; and performing the counter-freeze-scavenging process.
4. The method as claimed in claim 3, wherein the fuel cell system
further comprises a valve lock unit which locks the first valve
body and the second valve body in open state after the cathode is
unsealed, and wherein the valve lock system is used in the step of
maintaining the first valve body and the second valve body in open
state.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the foreign priority benefit under
Title 35, United States Code, .sctn.119 (a)-(d), of Japanese Patent
Application No. 2008-319419, filed on Dec. 16, 2008, in the Japan
Patent Office, the disclosure of which is herein incorporated by
reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a fuel cell system capable
of unsealing a cathode of a fuel cell before scavenging flowpaths
in the fuel cell, in which electro-chemical reaction has been
stopped previously by closing a first shut-off valve and a second
shut-off valve.
[0004] 2. Description of the Related Art
[0005] Japanese Patent Laid-open Publication No. 2008-218072
(hereinafter called Patent Document 1) discloses an example of fuel
cell system having fuel cells including an air-inlet shut-off valve
provided at an inlet of a cathode and an air-outlet shut-off valve
provided at an outlet of the cathode and preventing gas cross-leak,
i.e. a short circuit caused by either gas passing from one side to
the other side of the fuel cell through a membrane while no
electro-chemical reaction is under way in the fuel cell, by sealing
the cathode by means of the air-inlet shut-off valve and the
air-outlet shut-off valve after stopping the electro-chemical
reaction from progressing in the fuel cell.
[0006] The fuel cell system disclosed in Patent Document 1 has a
buffer tank for storing air compressed by an air compressor. The
pressure of air stored in the buffer tank is higher than a pressure
of air supplied to the fuel cell. The fuel cell system disclosed in
Patent Document 1 switches the air-inlet shut-off valve and the
air-outlet shut-off valve to open and close by using a pressure
difference between an atmospheric pressure chamber communicating
with ambient air and a pressurized chamber containing the air
supplied from the buffer tank.
[0007] Japanese Patent Laid-open Publication No. 2006-221836
(hereinafter called Patent Document 2) discloses a fuel cell system
including a fuel cell. The fuel cell system disclosed in Patent
Document 2 has two normally-closed electromagnetic valves provided
respectively at an outlet and an inlet of a cathode, and closes the
electromagnetic valves while no electro-chemical reaction is under
way in the fuel cell.
[0008] The fuel cell systems disclosed in Patent Documents 1 and 2
cannot be restarted sometimes if water remaining on seat sections
and on valve bodies pressed against the seat sections freezes in
the shut-off valves when ambient temperature lowers below the
freezing temperature after stopping electro-chemical reaction in
these prior art fuel cells and sealing the cathode by using
shut-off valves.
SUMMARY OF THE INVENTION
[0009] The present invention was conceived in view of the
aforementioned circumstances, and an object thereof is to provide a
fuel cell system capable of preventing valve bodies pressed against
seat sections from freezing even below the freezing temperature,
and capable of avoiding a situation unable to restart a turned-off
state of the fuel cell system.
[0010] In order to achieve the aforementioned object, the present
invention provides a fuel cell system which includes: a fuel cell
having an anode to which fuel gas is supplied, and a cathode to
which oxidant gas is supplied; a first oxidant gas flowpath through
which the oxidant gas is supplied to the fuel cell; a second
oxidant gas flowpath through which the oxidant gas is discharged
from the fuel cell; a first shut-off valve disposed upstream from
the fuel cell and connected to the fuel cell through the first
oxidant gas flowpath, the first shut-off valve having a first valve
body; a second shut-off valve disposed downstream from the fuel
cell and connected to the fuel cell through the second oxidant gas
flowpath, the second shut-off valve having a second valve body; a
cathode control unit for sealing the cathode by closing the first
shut-off valve and the second shut-off valve after electro-chemical
reaction is stopped from progressing in the fuel cell; and a
scavenging unit for scavenging the anode based on a predetermined
condition by supplying the oxidant gas to the anode while stopping
the electro-chemical reaction from progressing in the fuel cell,
wherein the cathode control unit, before scavenging the anode by
using the scavenging unit, unseals the cathode by opening the first
shut-off valve and the second shut-off valve.
[0011] In order to scavenge the anode by using the scavenging unit,
the cathode control unit of the present embodiment is capable of
switching the cathode from sealed state to unsealed state by
opening the first shut-off valve and the second shut-off valve.
[0012] Therefore, even if ambient temperature lowers below the
freezing temperature, the cathode control unit according to the
present embodiment can switch the first shut-off valve and the
second shut-off valve from closed state to open state by lifting
off the first valve body of the first shut-off valve and the second
valve body of the second shut-off valve from the seat sections
easily since residual water and gas can be discharged from the fuel
cell by using the scavenging unit. Accordingly, the fuel cell
system according to the present invention can avoid a situation
unable to restart the fuel cell system once after turning off the
ignition switch since no water exists on seat sections of the first
shut-off valve and the second shut-off valve. In addition, the fuel
cell system may use a fewer number of parts to achieve a simple,
small-size, and light-weight structure since the fuel cell system
according to the present embodiment can eliminate an anti-freezing
mechanism for preventing the seat sections in the first shut-off
valve and the second shut-off valve from freezing.
[0013] The fuel cell system of the present invention may further
include a valve lock unit for locking the first valve body of the
first shut-off valve and the second valve body of the second
shut-off valve in open state after unsealing the cathode. By doing
this, the present invention is capable of maintaining the first
shut-off valve and the second shut-off valve in open state stably
and reliably.
[0014] Even when an ambient temperature lowers below the freezing
temperature, the fuel cell system of the present invention is
capable of moving the shut-off valves smoothly since no water
exists on the valve bodies and on the seat sections.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a schematic diagram of a fuel cell system
according to an embodiment of the present invention.
[0016] FIG. 2 is a longitudinal cross-sectional view showing a
first and a second shut-off valves included in the fuel cell
system.
[0017] FIG. 3 is a block diagram of an electronic control unit used
in the fuel cell system.
[0018] FIG. 4 is a flowchart of a scavenging process conducted in
the fuel cell system.
[0019] FIGS. 5A to 5C show movements of the first shut-off valve
and the second shut-off valve. FIG. 5A is a longitudinal
cross-sectional view showing the shut-off valve in closed state.
FIG. 5B is a longitudinal cross-sectional view showing the shut-off
valve in open state. FIG. 5C is a longitudinal cross-sectional view
showing the shut-off valve locked in open state.
DETAILED DESCRIPTION OF THE INVENTION
[0020] The structure of a fuel cell system according to an
embodiment of the present invention will be explained in detail
with reference to the accompanying drawings.
[0021] The present invention is not limited to fuel cells used in
vehicles and can be applied to any other fuel cells used for
transportation means including ocean vessels and aircrafts, and for
stationary fuel cell systems.
[0022] As shown in FIG. 1, a fuel cell system 10 according to the
present embodiment includes a fuel cell 12; an anode system 14; a
cathode system 16; an anode-scavenging system 18; and a control
system 20.
[0023] The fuel cell 12 is a polymer electrolyte fuel cell (PEFC)
which includes a plurality of stacked single cells each having a
membrane electrode assembly (MEA) disposed between two separators
(not shown in the drawings).
[0024] The MEA includes a cathode; an anode; and an electrolyte
membrane (e.g. polymer membrane) disposed between the anode and the
cathode. Each of the cathode and the anode have an electrode
catalyst layer having a catalyst such as platinum supported on a
catalyst support made of carbon black etc. Each separator has an
anode flowpath 22 and a cathode flowpath 24, both of which are
grooves or through holes.
[0025] The fuel cell 12 starts to generate electricity when
electro-chemical reaction occurs on the catalysts included in the
anode and the cathode with hydrogen supplied to the anode and air
supplied to the cathode.
[0026] The fuel cell 12 generates electricity with an external load
(not shown in the drawings) connected to the fuel cell 12 and
creates electric current from electrons produced in the
electro-chemical reaction. The external load may be a motor for
driving a fuel cell vehicle, a capacitor serving as condenser or
battery, or an air pump 26 which will be explained later.
[0027] The anode system 14 includes a hydrogen tank 28; a shut-off
valve 30; a purge valve 32; and pipes a1 to a5 etc.
[0028] The hydrogen tank 28 stores highly pressurized and very pure
hydrogen, and is connected to the shut-off valve 30 disposed
downstream from the hydrogen tank 28 through the pipe a1. The
shut-off valve 30, which may be an electromagnetic valve, is
connected to the inlet of the anode flowpath 22 of the fuel cell 12
disposed downstream from the shut-off valve 30 through the pipe
a2.
[0029] The purge valve 32, which may be an electromagnetic valve,
is connected to the outlet of the anode flowpath 22 of the fuel
cell 12 disposed upstream from the purge valve 32 through the pipe
a3. Non-reacted hydrogen is discharged from the outlet of the anode
of the fuel cell 12 and returns to the inlet of the anode through
the pipe a4. The pipe a4 is connected with the pipe a2 connected to
the inlet of the anode flowpath 22. The pipe a4 is also connected
with the pipe a3 connected to the outlet of the anode flowpath
22.
[0030] An ejector, which is not shown in the drawing, is provided
at a junction point of the pipe a4 and the pipe a2. The ejector
uses a negative pressure, created by a flow of the hydrogen
supplied from the hydrogen tank 28, to suck gas (hydrogen in this
embodiment) returning through the pipe a4. The purge valve 32 is
connected with a diluting apparatus 34 through the pipe a5 disposed
downstream from the purge valve 32.
[0031] The cathode system 16 includes the air pump 26; a first
shut-off valve 36a; a second shut-off valve 36b; a
back-pressure-regulating valve 38; the diluting apparatus 34; and
pipes c1 to c5 (oxidant gas flowpaths) etc.
[0032] The air pump 26 may be a mechanical supercharger driven by a
motor not shown in the drawings. Air introduced from outside into
the air pump 26 is compressed therein and supplied to the fuel cell
12.
[0033] The first shut-off valve 36a is connected to the air pump 26
through the pipe c1, and is connected to an inlet of the cathode
flowpath 24 through the pipe c2. The second shut-off valve 36b is
connected to the outlet of the cathode flowpath 24 of the fuel cell
12 through pipe c3, and is connected to the
back-pressure-regulating valve 38 through the pipe c4.
[0034] Hereinafter, the structure of the first shut-off valve 36a
will be explained. The explanation of the structure of the second
shut-off valve 36b will be omitted since the first shut-off valve
36a and the second shut-off valve 36b (which may be hereinafter
simply called "shut-off valves" or "each shut-off valve") are
normally-closed valves having an identical structure.
[0035] As shown in FIG. 2, the first shut-off valve 36a includes: a
valve housing 42; a chamber 44; a valve body 46; a seat section 48;
a spring 50; a valve-driving section 52; and a locking section 54.
The valve housing 42 has an inlet port 40a into which gas (i.e. air
in the present embodiment) is supplied; and an outlet port 40b from
which the supplied gas is discharged. The chamber 44 is formed in
the valve housing 42. The valve body 46 turns on and shuts off
communication between the inlet port 40a and the outlet port 40b.
The seat section 48 is formed in the valve housing 42. The spring
50 presses the valve body 46 toward the seat section 48. The
valve-driving section 52 moves the valve body 46 in two directions
i.e. from and toward the seat section 48. The locking section 54
maintains the valve body 46 open.
[0036] As shown in FIG. 1, the pipe c1 is disposed between the air
pump 26 and the inlet port 40a of the valve housing 42 of the first
shut-off valve 36a. The pipe c2 is disposed between the outlet port
40b of the valve housing 42 of the first shut-off valve 36a and the
inlet of the cathode flowpath 24 of the fuel cell 12. The pipe c3
is disposed between the outlet of the cathode flowpath 24 of the
fuel cell 12 and the inlet port 40a of the valve housing 42 of the
second shut-off valve 36b. The pipe c4 is disposed between the
outlet port 40b of the second shut-off valve 36b and an inlet of
the back-pressure-regulating valve 38. In the present embodiment,
the first shut-off valve 36a and the second shut-off valve 36b have
the reverse arrangement of the inlet port 40a and the outlet port
40b (see FIG. 4).
[0037] The valve body 46 has a circular-plate disc section 46a; and
a rod section 46b attached to the center of the disc section 46a. A
valve packing 46c is attached on the bottom surface of the disc
section 46a and is pressed against the seat section 48 of the valve
housing 42 to seal the cathode.
[0038] The valve-driving section 52 may include, for example, a
rotational driving source 56, a pinion 58, and a rack section 60.
The rotational driving source 56 has an electric drive unit such as
a stepper motor etc. and a rotational driving shaft 56a provided
therein. The pinion 58 is attached on the rotational driving shaft
56a. The rack section 60 in mesh with the pinion 58 is formed on an
outer periphery of the rod section 46b and is exposed from the
valve housing 42. The rotational driving source 56 is fixed on the
valve housing 42 via a fixture (not shown in the drawing).
[0039] In this structure, the rotational driving force produced by
the rotational driving source 56 is transmitted to the pinion 58
through the rotational driving shaft 56a and is converted into a
linear (vertical) movement of the valve body 46 through the rack
section 60 being in mesh with the pinion 58. Accordingly, when the
valve body 46 presses against the seat section 48 and closes the
outlet port 40b, communication is shut off between the inlet port
40a and the outlet port 40b; and when the valve body 46 is lifted
off from the seat section 48, the communication is obtained from
the inlet port 40a to the outlet port 40b through the chamber 44 of
the valve housing 42.
[0040] The locking section 54 includes: a solenoid (not shown in
the drawings) made of a wire coil wound in the locking section 54;
a fixed core; a movable core, not shown in the drawings, retracted
toward the fixed core by means of excitation effect obtained by
supplying electricity to the solenoid; a lock pin 62 joined to the
movable core and capable of protruding and retracting in the
horizontal directions X1 and X2 together with the movable core. An
engagement block 64 is joined to an end (e.g. a free end) of the
rod section 46b of the valve body 46. The engagement block 64 moves
together with the valve body 46 and is locked in open state by the
lock pin 62. The valve housing 42 has a support 68 attached thereon
for supporting the locking section 54 having the lock pin 62. The
solenoid, the movable core, and the fixed core are not shown in the
drawings.
[0041] When an electronic control unit (ECU) 100 stops electricity
from being supplied to the solenoid, the lock pin 62 protrudes by a
predetermined length in the direction X1. The protruded lock pin 62
is capable of locking the engagement block 64. When the ECU 100
starts supplying electricity to the solenoid, the lock pin 62
retracts in the direction X2 by means of excitation effect of the
solenoid. The lock pin 62 in this state is disposed apart from the
engagement block 64.
[0042] The fuel cell system 10 according to the present invention
is not limited to use the lock pin 62 which engages with the
engagement block 64 joined to the valve body 46 in the elevated
position to maintain the open state of the shut-off valves 36a and
36b. Alternatively, the present invention may omit the lock pin 62
and may protrude the movable core, not shown in the drawings, to
lock the engagement block 64 directly.
[0043] In the present invention, the fuel cell system 10 has a
high-voltage battery and a low-voltage battery, which are not shown
in the drawings. The ECU 100 drives the rotational driving source
56 of the valve-driving section 52 and the solenoid of the locking
section 54 by using the low-voltage battery. In addition, the
present invention does not limit the first shut-off valve 36a and
the second shut-off valve 36b to the aforementioned normally-closed
shut-off valves. For example, the present invention may use
normally-open shut-off valves, which are opened during
electro-chemical reaction progressing in the fuel cell 12 and are
closed by the aforementioned valve-driving section 52 while
maintaining the cathode in sealed state after stopping
electro-chemical reaction from progressing in the fuel cell 12. In
addition, a fixture (or a locking mechanism) not shown in the
drawings may support the shut-off valves in closed state.
[0044] The back-pressure-regulating valve 38 for controlling the
pressure of oxidant gas in the cathode of the fuel cell 12 may be,
for example, a normally-open butterfly valve whose opening is
variable. The back-pressure-regulating valve 38 is connected with
the diluting apparatus 34 through the pipe c5.
[0045] The un-reacted hydrogen discharged from through the purge
valve 32 is mixed with cathode off-gas discharged from the cathode
in the diluting apparatus 34, and then discharged out of the fuel
cell vehicle. The cathode system 16 has a humidifier, not shown in
the drawings, in the pipe c1 for humidifying air supplied by the
air pump 26.
[0046] The anode-scavenging system 18 includes: an air introduction
pipe 70; an air-introduction valve 72; an air-discharging pipe 74;
and an air-discharging valve 76 etc. In the present embodiment, the
air introduction pipe 70, the air-introduction valve 72, the
air-discharging pipe 74, and the air-discharging valve 76
constitute a scavenging unit.
[0047] The air introduction pipe 70 has an upstream end and a
downstream end. Air (also called scavenging gas or oxidant gas)
supplied by the air pump 26 is introduced into the anode through
the air introduction pipe 70. The upstream end of the air
introduction pipe 70 is connected with the pipe c1, and the
downstream end of the air introduction pipe 70 is connected with
the pipe a2. The air introduction pipe 70 has the air-introduction
valve 72. ECU 100 opens the air-introduction valve 72 prior to
scavenging the anode after stopping the electro-chemical reaction
from progressing in the fuel cell 12.
[0048] The air discharged (i.e. gas purged) from the anode passes
through the air-discharging pipe 74 and returns to the cathode
system 16. The upstream end of the air-discharging pipe 74 is
connected with the pipe a3, and the downstream end of the
air-discharging pipe 74 is connected with the pipe c5. The
air-discharging pipe 74 has the air-discharging valve 76. ECU 100
opens the air-discharging valve 76 prior to scavenging the
anode.
[0049] FIG. 3 is a block diagram of the electronic control unit 100
used in the fuel cell system 10.
[0050] The control system 20 includes: the ECU 100; and a thermo
sensor 102 for measuring the temperature in the fuel cell 12. The
ECU 100 includes a central processing unit (CPU); a read-only
memory (ROM) storing a program for controlling a scavenging
process; and a random access memory (RAM) etc.
[0051] As shown in FIG. 3, the ECU 100 has a fuel cell temperature
measurement section 100a for measuring the temperature in the fuel
cell 12 and a counter-freeze control section 100b. The ECU 100
sends out an instruction signal to the thermo sensor 102 to send
back a signal indicative of a measured temperature at a
predetermined interval. The thermo sensor 102 sends out the signal
indicative of the measured temperature, to the fuel cell
temperature measurement section 100a. The counter-freeze control
section 100b determines whether the ECU 100 scavenges inside the
fuel cell 12 based on the measured temperature in the fuel cell 12
measured by the thermo sensor 102. Hereinafter, this process is
called a counter-freeze-scavenging process.
[0052] The ECU 100 opens and closes the shut-off valve 30, the
purge valve 32, the first shut-off valve 36a, the second shut-off
valve 36b, the air-introduction valve 72, and the air-discharging
valve 76. The ECU 100 also controls the valve-driving section 52
and the locking section 54 of each shut-off valve. The ECU 100
regulates the pressure of air passing through the cathode system 16
by controlling the rotation speed of the motor provided in the air
pump 26 and the opening degree of the back-pressure-regulating
valve 38.
[0053] Hereinafter, operation of the fuel cell system 10 according
to the present embodiment having the aforementioned basic structure
will be explained with reference to the accompanying drawings,
particularly to the flowchart of FIG. 4.
[0054] Firstly, when the fuel cell system 10 starts operation after
the driver turns on an ignition switch of the fuel cell vehicle,
the ECU 100 opens both the first shut-off valve 36a and the second
shut-off valve 36b to unseal the cathode, and opens the shut-off
valve 30 to supply hydrogen from the hydrogen tank 28 to the anode.
The ECU 100 drives the air pump 26 to supply air to the cathode,
and then the electro-chemical reaction starts in the fuel cell
12.
[0055] While the fuel cell system 10 is in operation, the ECU 100
keeps both the air-introduction valve 72 and the air-discharging
valve 76 closed, and the ECU 100 opens the purge valve 32 at a
predetermined interval to discharge impurities, such as nitrogen or
water permeating from the cathode through the electrolyte membrane
to the anode and remaining in an anode circulation system including
the pipes a2 to a4 and the anode flowpath 22.
[0056] Secondly, operation of the fuel cell system 10 according to
the present invention will be explained as follows after turning
off an ignition switch of the fuel cell vehicle and stopping
electro-chemical reaction (see a flowchart starting from "IG-OFF"
as shown in FIG. 4) from progressing in the fuel cell 12.
[0057] When the ECU 100 recognizes that the driver turns off the
ignition switch ("IG-OFF" in the flowchart), the ECU 100 supplies
air to the cathode, for example, for a predetermined duration while
driving the air pump 26. The diluting apparatus 34 dilutes hydrogen
remaining in the diluting apparatus 34 by using the cathode off-gas
discharged from the cathode. The gas containing the diluted
hydrogen and water produced in the cathode is discharged out of the
fuel cell vehicle. The ECU 100 closes the shut-off valve 30 to stop
supplying hydrogen to the anode and stops supplying air to the
cathode to stop electro-chemical reaction from progressing in the
fuel cell 12. The ECU 100 further disconnects the external load
from the fuel cell 12 electrically.
[0058] As shown in FIG. 4, the ECU 100 in step S1 sends out a
control signal to each of the first shut-off valve 36a and the
second shut-off valve 36b to close the valve bodies of the first
shut-off valve 36a and the second shut-off valve 36b to seal the
cathode of the fuel cell 12.
[0059] As shown in FIG. 5A, the first shut-off valve 36a and the
second shut-off valve 36b of the present embodiment are
normally-closed shut-off valves each having the spring 50 pressing
the valve body 46 onto the seat section 48 by means of spring force
to keep the valve body 46 seated on the valve body 46. While the
cathode is kept sealed, the communication is shut off between the
inlet port 40a and the outlet port 40b in each shut-off valve, and
no electricity is supplied from the batteries included in the fuel
cell system 10 to the rotational driving source 56 of the
valve-driving section 52. In addition, the solenoid of the locking
section 54 is unexcited.
[0060] Therefore, the fuel cell system 12 of the present invention
is capable of preventing fresh air from coming into the cathode
flowpath 24 while no electricity is being generated in the fuel
cell 12, and is capable of preventing gas cross-leak which may
reduce power output efficiency of the fuel cell 12, since the ECU
100 controls the normally-closed shut-off valves 36a and 36b to
seal the cathode of the fuel cell 12.
[0061] In step S2, the fuel cell temperature measurement section
100a detects the temperature in the fuel cell 12 measured by the
thermo sensor 102. The fuel cell temperature measurement section
100a sets an interval for the thermo sensor 102 to measure the
temperature of the fuel cell 12. After the fuel cell temperature
measurement section 100a measures the temperature in the fuel cell
12, the flowchart proceeds to step S3.
[0062] In the step S3, the ECU 100 determines whether the
counter-freeze control section 100b conducts a
counter-freeze-scavenging process in the fuel cell 12. In the
present invention, the counter-freeze-scavenging process is defined
as a process of blowing and discharging residual water from the
anode and the cathode etc. by supplying air (scavenging gas) to the
anode and the cathode if the ECU 100 determines that the water
existing in the fuel cell 12 will freeze when the temperature in
the fuel cell 12 lowers below the freezing temperature.
[0063] More specifically, if the temperature in the fuel cell 12
measured by the thermo sensor 102 in the step S3 is higher than the
freezing temperature (0.degree. C.) ("No" in the flowchart of FIG.
4), the fuel cell operation returns to the step S2 since the
residual water remains unfrozen; and if the temperature in the fuel
cell 12 lowers below the freezing temperature ("Yes" in the
flowchart of FIG. 4), the fuel cell operation proceeds to step S4
since the residual water remaining in the fuel cell 12 will
freeze.
[0064] In the step S4, the ECU 100 sends out a control signal to
the first shut-off valve 36a and the second shut-off valve 36b to
switch the valve bodies 46 of the first shut-off valve 36a and the
second shut-off valve 36b from the closed state to open state to
unseal the cathode.
[0065] More specifically, at first, when the ECU 100 supplies
electricity to the solenoid of the locking section 54 of each
shut-off valve, the lock pin 62 moves together with the movable
core (not shown in the drawings) in the retracting direction X2 by
means of the excitation effect of the solenoids as shown in FIG.
5B. After that, when the ECU 100 supplies electricity to the
rotational driving source 56 of the valve-driving section 52 to
rotate the rotational driving shaft 56a. As the pinion 58 coupled
with the rotational driving shaft 56a is rotated counter clockwise
(as indicated by an arrow X3 in the drawing), the rack section 60
in mesh with the pinion 58 exceeds the downward spring force of the
spring 50, and then valve body 46 is elevated through engagement
between the pinion 58 and the rack section 60.
[0066] Accordingly, the valve body 46 in each shut-off valve is
lifted off from the seat section 48 by a predetermined distance
through the rotational movement of the rotational driving source 56
being converted to a linear movement of the rack section 60 in mesh
with the pinion 58. As a result, communication is obtained from the
inlet port 40a to the outlet port 40b through the chamber 44.
[0067] After both the shut-off valves 36a and 36b open, the ECU 100
stops electricity from being supplied to the solenoid of the
locking section 54 of each shut-off valve and the solenoid becomes
unexcited. A return spring, not shown in the drawings, presses the
lock pin 62 together with the movable core in direction X1 as shown
in FIG. 5C. The lock pin 62 locks the engagement block 64 to
maintain each shut-off valve open.
[0068] After the shut-off valves 36a and 36b are locked and become
open, the ECU 100 sends a control signal to the aforementioned
low-voltage battery to stop supplying electricity to the rotational
driving source 56.
[0069] In step S6, the ECU 100 conducts the
counter-freeze-scavenging process in the fuel cell 12. More
specifically, firstly, the ECU 100 sends out a control signal to
the air-introduction valve 72 and the air-discharging valve 76 to
open the valve bodies of the air-introduction valve 72 and the
air-discharging valve. Then, the ECU 100 drives the air pump 26 and
supplies air (scavenging gas) to the anode flowpath 22 of the fuel
cell 12 to blow off residual water remaining in the anode flowpath
22. The gas replaced by the scavenging gas and blown off from the
anode flowpath 22 contains anode off-gas. The water and gas
discharged from the anode flowpath 22 and the cathode flowpath 24
are introduced into the diluting apparatus 34, and then discharged
out of the fuel cell vehicle.
[0070] The fuel cell system 10 of the present invention can
discharge produced water together with residual gas remaining in
the fuel cell 12 by performing the aforementioned
counter-freeze-scavenging process. The fuel cell system 10 of the
present invention is capable of preventing gas cross-leak even if
the valve bodies 46 of the first shut-off valve 36a and the second
shut-off valve 36b are locked in open state since no chemical
reaction occurs between the anode and the cathode after performing
the counter-freeze-scavenging process. Since anode gas (hydrogen)
remaining in the anode flowpath 22 is replaced sufficiently with
scavenging gas (air or oxidant gas), both the anode and the cathode
of the fuel cell 12 fill with air (or oxidant gas). In this state,
the fuel cell 12 will suffer no degradation since no
electro-chemical reaction occurs locally in the fuel cell 12.
Therefore, the ECU 100 after performing the
counter-freeze-scavenging process does not have to seal the cathode
by using the first shut-off valve 36a and the second shut-off valve
36b.
[0071] Hereinafter, an operation of releasing the locked state of
the first and second shut-off valves 36a and 36b will be
explained.
[0072] In order to unlock both the shut-off valves 36a and 36b,
electricity is supplied to the solenoid of each locking section 54.
Then, the lock pin 62 moves together with the movable core in the
direction X2 with the excitation effect of the solenoid. The
engagement block 64 is released from the lock pin 62, and then the
spring 50 presses the valve body 46 onto the seat section 48 with
its spring force. Accordingly, the first shut-off valve 36a and the
second shut-off valve 36b in locked state are switched from open
state to closed state.
[0073] According to the present embodiment, the ECU 100 prior to
performing the counter-freeze-scavenging process is capable of
switching the cathode from sealed state to unsealed state by
opening the first shut-off valve 36a and the second shut-off valve
36b.
[0074] Since water and gas are discharged from the fuel cell in a
counter-freeze-scavenging process, no water exists on the seat
sections 48 of the first shut-off valve 36a and the second shut-off
valve 36b after the counter-freeze-scavenging process. Therefore,
even when the ambient temperature lowers below the freezing
temperature, the ECU 100 according to the present embodiment can
open the first shut-off valve 36a and the second shut-off valve
36b, which are being closed, by lifting off the valve bodies 46 of
the shut-off valves 36a and 36b from the seat sections 48.
Accordingly, the fuel cell system 10 according to the present
embodiment can avoid a situation unable to restart a turned-off
state of the fuel cell system 10. In addition, the fuel cell system
10 may use a fewer number of parts to achieve a small-size and
light-weight valve control unit having a simple structure since the
fuel cell system 10 according to the present embodiment can
eliminate an anti-freezing mechanism for preventing the seat
sections 48 in the first shut-off valve 36a and the second shut-off
valve 36b from freezing.
[0075] As explained above, the fuel cell system 10 of the present
invention is capable of moving the shut-off valves 36a and 36b
smoothly since the valve bodies 46 will not freeze while being
pressed against the seat sections 48 even when an ambient
temperature lowers below the freezing temperature.
[0076] The fuel cell system 10 according to the present embodiment
is capable of maintaining the first shut-off valve 36a and the
second shut-off valve 36b in open state stably and reliably while
avoiding reduced efficiency in terms of electricity output, since
the valve-driving section 52 does not consume electricity while
maintaining the valve body 46 in open state.
[0077] The present invention is capable of preventing damage to the
fuel cell system 10 or system down of the fuel cell system 10 due
to abnormal pressure since the locking section 54 locks and
maintains the valve body 46 in open state. More specifically, the
locking section 54 never switches the valve body 46 from open state
to closed state even if the valve-driving section 52 for driving
the valve body 46 has a defect (e.g. power drop if the
valve-driving section 52 is driven electrically as explained
according to the present embodiment, or abnormal air pressure if
the valve-driving section 52 is a pneumatic unit not shown in the
drawings). In addition, the fuel cell system 10 can save
electricity by stopping electricity from being supplied to the
rotational driving source 56 while the valve body 46 is maintained
open, since the valve-driving section 52 needs no force for
maintaining the valve body 46 in open state. In addition, if the
fuel cell system 10 uses pneumatic valve-driving mechanisms 52, the
present invention can reduce the number of parts used in the
shut-off valves 36a and 36b because a pneumatic valve-driving
section 52 can eliminate a pressure-control mechanism.
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