U.S. patent application number 12/671042 was filed with the patent office on 2010-07-29 for exhaust state control device for fuel cell for mobile unit.
This patent application is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. Invention is credited to Takahide Izutani, Keigo Suematsu, Hiromi Tanaka.
Application Number | 20100190069 12/671042 |
Document ID | / |
Family ID | 40304980 |
Filed Date | 2010-07-29 |
United States Patent
Application |
20100190069 |
Kind Code |
A1 |
Tanaka; Hiromi ; et
al. |
July 29, 2010 |
EXHAUST STATE CONTROL DEVICE FOR FUEL CELL FOR MOBILE UNIT
Abstract
An exhaust state control device for a fuel cell for a mobile
unit includes an exhaust gas temperature sensor (17) that measures
the temperature of exhaust gas in a discharge passage that
discharges the exhaust gas from the main body of the fuel cell, and
an ambient temperature sensor (19A) that measures the temperature
of ambient air to which exhaust gas is to be discharged. If, based
on the difference between the exhaust gas temperature and the
ambient temperature, it is determined that white smoke is
generated, it is determined whether a condition to reduce white
smoke is satisfied. When a first condition is satisfied, a process
to reduce white smoke is activated. When a second condition, which
requires further reduction of white smoke than under the first
condition, is satisfied, a process to suppress the generation of
white smoke is activated.
Inventors: |
Tanaka; Hiromi; (Aichi-ken,
JP) ; Suematsu; Keigo; (Aichi-ken, JP) ;
Izutani; Takahide; (Shizuoka-ken, JP) |
Correspondence
Address: |
FINNEGAN, HENDERSON, FARABOW, GARRETT & DUNNER;LLP
901 NEW YORK AVENUE, NW
WASHINGTON
DC
20001-4413
US
|
Assignee: |
TOYOTA JIDOSHA KABUSHIKI
KAISHA
Toyota-shi, Achi-ken
JP
|
Family ID: |
40304980 |
Appl. No.: |
12/671042 |
Filed: |
July 31, 2008 |
PCT Filed: |
July 31, 2008 |
PCT NO: |
PCT/IB2008/002012 |
371 Date: |
January 28, 2010 |
Current U.S.
Class: |
429/428 ;
429/444 |
Current CPC
Class: |
H01M 8/04007 20130101;
B60L 58/30 20190201; Y02E 60/50 20130101; H01M 8/0662 20130101;
H01M 2250/20 20130101; H01M 8/04156 20130101; Y02T 90/40
20130101 |
Class at
Publication: |
429/428 ;
429/444 |
International
Class: |
H01M 8/04 20060101
H01M008/04 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 1, 2007 |
JP |
2007-201241 |
Claims
1. An exhaust state control device for a fuel cell for a mobile
unit that detects a state of exhaust gas from a fuel cell mounted
on a mobile unit, comprising: an exhaust gas temperature sensor
that measures, as a state of the exhaust gas, a temperature of the
exhaust gas in a discharge passage that discharges the exhaust gas
from a main body of the fuel cell; an ambient temperature sensor
that measures, as a state of the ambient air, a temperature of the
ambient air to which the exhaust gas is to be discharged; a motion
sensor that detects movement of the mobile unit; a white smoke
generation determination section that determines whether white
smoke is generated based on a relationship between the state of
exhaust gas and the state of ambient air; a condition determination
section that determines whether a predetermined condition to reduce
white smoke is satisfied based on a detection signal from the
motion sensor when the white smoke generation determination section
determines that white smoke is generated; and a control section
that activates a process to reduce white smoke if the condition
determination section determines that the predetermined condition
is satisfied.
2. The exhaust state control device for a fuel cell according to
claim 1, further comprising: an operation state sensor that detects
an operating state of an operating section that operates the mobile
unit; and a sensor that senses a surrounding environmental state of
the mobile unit, wherein the condition determination section
determines whether the predetermined condition to reduce white
smoke is satisfied based on at least one of the detected moving
state of the mobile unit, the detected operating state of the
operating section that operates the mobile unit, and the detected
surrounding environmental state of the mobile unit.
3. The exhaust state control device for a fuel cell according to
claim 1, wherein the control section activates a process to reduce
white smoke when the condition determination section determines
that a first predetermined condition is satisfied, and activates a
process to further reduce generation of white smoke than when the
first predetermined condition is determined to be satisfied, if the
condition determination section determines that a second
predetermined condition is satisfied.
4. The exhaust state control device for a fuel cell according to
claim 2, wherein the control section activates a process to reduce
white smoke when the condition determination section determines
that a first predetermined condition is satisfied, and activates a
process to further reduce generation of white smoke than when the
first predetermined condition is determined to be satisfied, if the
condition determination section determines that a second
predetermined condition is satisfied.
5. The exhaust state control device for a fuel cell according to
claim 4, wherein the white smoke generation determination section
determines whether white smoke is generated according to the
difference between the exhaust gas temperature and the ambient air
temperature.
6. The exhaust state control device for a fuel cell according to
claim 4, further comprising an ambient humidity sensor that
measures a humidity of the ambient air to which the exhaust gas is
to be discharged, wherein the white smoke generation determination
section determines whether white smoke is generated according to
the difference between the exhaust gas temperature and the ambient
air temperature, and the ambient air humidity.
7. The exhaust state control device for a fuel cell according to
claim 4, wherein: the first predetermined condition is satisfied if
either one of the conditions, where a moving speed of the mobile
unit is determined to be at or below a predetermined value and
where a visibility of white smoke around the mobile unit is
determined to be higher than that in a reference environment, is
satisfied; and the second predetermined condition is satisfied if
both the conditions, where the moving speed of the mobile unit is
determined to be at or below the predetermined value and where the
visibility of white smoke around the mobile unit is determined to
be higher than that in the reference environment, are
satisfied.
8. The exhaust state control device for a fuel cell according to
claim 7, wherein the condition where the moving speed of the mobile
unit is determined to be at or below the predetermined value
includes a state where the mobile unit is stationary.
9. The exhaust state control device for a fuel cell according to
claim 7, wherein the moving speed of the mobile unit is an absolute
speed of the mobile unit or a relative speed between the mobile
unit and the ambient air around the mobile unit.
10. The exhaust state control device for a fuel cell according to
claim 4, wherein: the mobile unit is a vehicle; the first
predetermined condition is satisfied if either one of conditions,
where a shift lever is determined to be in a parking position and
where a visibility of white smoke around the mobile unit is
determined to be higher than that in a reference environment, is
satisfied; and the second predetermined condition is satisfied if
both the conditions, where the shift lever is determined to be in
the parking position and where the visibility of white smoke around
the mobile unit can be determined to be higher than that in the
reference environment, are satisfied.
11. The exhaust state control device for a fuel cell according to
claim 4, wherein: the first predetermined condition is satisfied if
either one of conditions, a condition where the white smoke
generation determination section determines that white smoke is
generated, or a condition where a moving speed of the mobile unit
is at or below a predetermined value and where a visibility of
white smoke around the mobile unit is determined to be lower than
that in a reference environment, is satisfied; and the second
predetermined condition is satisfied if both the conditions, where
the moving speed of the mobile unit is determined to be at or below
the predetermined value and where the visibility of white smoke
around the mobile unit is determined to be higher than that in the
reference environment, are satisfied.
12. The exhaust state control device for a fuel cell according to
claim 11, wherein if the conditions, where the white smoke
generation determination section determines that white smoke is
generated, and where the moving speed of the mobile unit is at or
below the predetermined value and the visibility of white smoke
around the mobile unit is determined to be lower than that in the
reference environment, are satisfied, the process to reduce white
smoke, which is performed when the condition determination section
determined that the first predetermined condition has been
satisfied, is performed in different level.
13. The exhaust state control device for a fuel cell according to
claim 4, wherein: the first predetermined condition is satisfied if
either one of conditions, where a vision of an operator who
operates the mobile unit is determined to be affected by white
smoke and where a visibility of white smoke around the mobile unit
is higher than that in a reference environment, is satisfied; and
the second predetermined condition is satisfied if both the
condition, where the vision of the operator who operates the mobile
unit is determined to be affected by white smoke and where the
visibility of white smoke around the mobile unit is higher than
that in the reference environment, are satisfied.
14. The exhaust state control device for a fuel cell according to
claim 7, wherein the reference environment includes at least one of
a daytime environment and a non-rainy environment.
15. The exhaust state control device for a fuel cell according to
claim 14, wherein: the mobile unit is a vehicle; the operating
state of the operating section is determined based on whether a
headlight is on; the surrounding environmental state is determined
based on at least one of: whether a darkness detection signal for
an automatic light is on; whether a current time is after a sunset
and before a sunrise; whether a signal from a global positioning
system cannot be received; whether a wiper is on; whether a rain
sensing signal is on; and whether a detection value of the ambient
humidity sensor exceeds a predetermined value; and the condition
determination section determines that the reference environment is
the daytime or non-rainy environment if at least one of the
determined states above is satisfied.
16. The exhaust state control device for a fuel cell according to
claim 13, wherein the vision of the operator is determined to be
affected by white smoke if the mobile unit advances in a
discharging direction of the exhaust gas.
17. The exhaust state control device for a fuel cell according to
claim 13, wherein: the mobile unit is a vehicle; and it is
determined that the condition where the white smoke interferes with
vision of the operator of the mobile unit is satisfied when at
least one of the shift lever is in a reverse position and the
parking brake is off.
18. The exhaust state control device for a fuel cell according to
claim 4, wherein the process to reduce white smoke is at least one
of a process to control the exhaust gas temperature and a process
to control a flow rate of the exhaust gas at an air electrode side
of the fuel cell.
19. The exhaust state control device for a fuel cell according to
claim 18, wherein discharge of the exhaust gas at the air electrode
side is controlled such that a limit of the flow rate of the
exhaust gas decreases as the moving speed of the mobile unit
decreases.
20. The exhaust state control device for a fuel cell according to
claim 18, wherein a pressure or the flow rate of the exhaust gas at
the air electrode side is controlled such that the limit of the
flow rate of the exhaust gas increases as the pressure of the
exhaust gas increases.
21. The exhaust state control device for a fuel cell according to
claim 4, wherein the process to reduce the generation of white
smoke, which is performed when the condition determination section
determines that the second predetermined condition is satisfied,
includes at least one of stopping scavenging air and shutting off a
hydrogen supply pressure to the fuel cell.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a technique to control the
exhaust state for a fuel cell for a mobile unit.
[0003] 2. Description of the Related Art
[0004] In fuel cells, a reaction generates electricity and
discharges a corresponding amount of generated water. Especially in
fuel cells for automobiles, a larger amount of water is generated
as the vehicle travels a longer distance. Most fuel cells for
automobiles are of a solid polymer type, which basically operates
at low temperatures. A common problem with the fuel cells is the
treatment of the generated water, that is, preventing the generated
water from freezing on the road in cold regions or from splashing
toward any following vehicles.
[0005] Depending on the ambient air conditions and the driving
conditions, however, it is also necessary to suppress the
generation of white smoke from the exhaust port of a discharge
passage for off gas. Generation of the white smoke is not desirable
from the standpoint of the merchantability of the automobiles. In
some instances, the impact of the automobiles on the surroundings
due to the white smoke should be taken into account. In view of the
above, proposals have been made to suppress the white smoke in fuel
cells for vehicles in Japanese Patent Application Publication No.
7-169498 (JP-A-7-169498) and Japanese Patent Application
Publication No. 2001-185199 (JP-A-2001-185199).
[0006] To reduce the white smoke, in general, the fuel cells for
vehicles have adopted means for cooling or heating the off gas
beyond the temperature range where white smoke is easily generated,
means for suppressing the amount of scavenged air, and so forth.
Therefore, energy is required to reduce the white smoke, which
contradicts the requirement to improve the power generation
efficiency.
[0007] That is, the fuel cells described in the above documents
estimate the generation of white smoke mainly based on the
difference between the exhaust air temperature and the ambient
temperature. Then, a white smoke reduction process is executed
according to the estimation results. If the white smoke reduction
process is executed frequently, the fuel efficiency is reduced due
to the heating, the energy efficiency is reduced, the output is
reduced due to the suppressed amount of scavenged air, etc., to a
larger degree.
[0008] As a result of a more detailed examination of the
circumstances where the white smoke is generated, the following may
be pointed out. The white smoke generated is not noticeable while
the vehicle is in motion because of the diffusion effect of the
head wind, but is noticeable while the vehicle is stationary or
traveling at low speeds. The visibility of the white smoke varies
in accordance with the environmental conditions around the vehicle,
such as whether it is daytime or nighttime and whether it is sunny
or rainy. The white smoke generated affects the vision of the
operator when backing the vehicle.
SUMMARY OF THE INVENTION
[0009] The present invention provides an exhaust state control
device for a fuel cell for a mobile unit, such as a vehicle,
powered by a fuel cell, that determines the necessity for white
smoke reduction based on the traveling conditions of the mobile
unit, the operating state of the mobile unit, or the environmental
conditions to efficiently suppress the white smoke.
[0010] An aspect of the present invention is directed to an exhaust
state control device for a fuel cell for a mobile unit that detects
a state of exhaust gas from a fuel cell provided in the mobile
unit. The exhaust state control device for the fuel cell includes:
a white smoke generation determination section that determines
whether white smoke is generated based on relationship between a
state of the exhaust gas and a state of the ambient air; a motion
sensor that detects movement of the mobile unit; a condition
determination section that determines whether a condition to reduce
white smoke is satisfied based on a detection signal from the
motion sensor when the white smoke generation determination section
determines that white smoke is generated; and a control section
that activates a process to reduce white smoke if the condition
determination section determines that a predetermined condition is
satisfied.
[0011] The exhaust state control device for a fuel cell for a
mobile unit may further include: an operation state sensor that
detects an operating state of an operating section that operates
the mobile unit; and a sensor that senses a surrounding
environmental state of the mobile unit, and the condition
determination section may determine whether the condition to reduce
white smoke is satisfied based on at least one of the detected
moving state of the mobile unit, the detected operating state of
the operating section that operates the mobile unit, and the
detected surrounding environmental state of the mobile unit.
[0012] In the exhaust state control device for a fuel cell for a
mobile unit, the control section may activate a process to reduce
white smoke when the condition determination section determines
that a first predetermined condition is satisfied, and activate a
process to further reduce generation of white smoke than when the
first predetermined condition is determined to be satisfied, if the
condition determination section determines that a second
predetermined condition is satisfied.
[0013] The exhaust state control device for a fuel cell for a
mobile unit according to the above aspect may further include: an
exhaust gas temperature sensor that measures a temperature of the
exhaust gas in a discharge passage that discharges the exhaust gas
from a main body of the fuel cell; and an ambient temperature
sensor that measures a temperature of the ambient air to which the
exhaust gas is to be discharged, and the white smoke generation
determination section may determine whether white smoke is
generated according to the difference between the exhaust gas
temperature and the ambient temperature.
[0014] The exhaust state control device for a fuel cell for a
mobile unit according to the above aspect may further include: an
exhaust gas temperature sensor that measures a temperature of the
exhaust gas in a discharge passage that discharges the exhaust gas
from a main body of the fuel cell; an ambient temperature sensor
that measures a temperature of the ambient air to which the exhaust
gas is to be discharged; and an ambient humidity sensor that
measures a humidity of the ambient air to which the exhaust gas is
to be discharged, and the white smoke generation determination
section may determine whether white smoke will be generated
according to the difference between the exhaust gas temperature and
the ambient temperature and the ambient humidity.
[0015] According to the above aspect, if it is determined that
white smoke will be generated, white smoke reduction can be
performed in different levels by determining whether the first
condition is satisfied or the second condition, which requires
greater reduction of white smoke than the first condition does, is
satisfied. In general, the process to further reduce white smoke
lowers the efficiency of the fuel cell for a mobile unit more than
the process to reduce white smoke does. Thus, the exhaust state
control device for a fuel cell for a mobile unit can improve the
efficiency of the fuel cell for a mobile unit by determining in
detail the conditions under which white smoke is generated to
perform the white smoke reduction process in different levels.
[0016] In the above aspect, the first condition may be satisfied if
either one of the conditions, where a moving speed of the mobile
unit is determined to be at or below a predetermined value and
where a visibility of white smoke around the mobile unit is
determined to be higher than that in a reference environment, is
satisfied; and the second condition may be satisfied if both the
conditions, where the moving speed of the mobile unit is determined
to be at or below the predetermined value and where the visibility
of white smoke around the mobile unit is determined to be higher
than that in the reference environment, are satisfied. According to
the above aspect, the exhaust state control device for a fuel cell
for a mobile unit can determine in detail the circumstances where
white smoke is generated by defining the first condition and the
second condition which requires greater reduction of white smoke
than the first condition does.
[0017] In the above aspect, the condition, where the moving speed
of the mobile unit is determined to be at or below the
predetermined value may include a state where the mobile unit is
stationary. Greater reduction of white smoke is occasionally
required when the vehicle is stationary than when it is moving. In
the above aspect, the moving speed of the mobile unit may be an
absolute speed of the mobile unit or a relative speed between the
mobile unit and the ambient air around the mobile unit. The
generation and the visibility of white smoke are affected by the
relative speed between the mobile unit and the ambient air.
[0018] In the above aspect, the mobile unit may be a vehicle; the
first condition may be satisfied if either one of conditions, where
a shift lever is determined to be in a parking position and where a
visibility of white smoke around the mobile unit is determined to
be higher than that in a reference environment, is satisfied; and
the second condition the second condition may be satisfied if both
the conditions, where the shift lever is determined to be in the
parking position and where the visibility of white smoke around the
mobile unit can be determined to be higher than that in the
reference environment, are satisfied.
[0019] In the above aspect; the first condition may be satisfied if
either one of conditions, where the white smoke generation
determination section determines that white smoke is generated or a
condition where a moving speed of the mobile unit is at or below a
predetermined value and where a visibility of white smoke around
the mobile unit is determined to be lower than that in a reference
environment, is satisfied; and the second condition may be
satisfied if both the conditions, where the moving speed of the
mobile unit is determined to be at or below the predetermined value
and where the visibility of white smoke around the mobile unit is
determined to be higher than that in the reference environment, are
satisfied.
[0020] In the above aspect, if the conditions, where the white
smoke generation determination section determines that white smoke
is generated, and where the moving speed of the mobile unit is at
or below the predetermined value and the visibility of white smoke
around the mobile unit is determined to be lower than that in the
reference environment, are satisfied, the condition determination
section may perform the process to reduce white smoke, in the case
the condition determination section determined that the first
predetermined condition has been satisfied, in different level.
[0021] In the above aspect, the first condition may be satisfied if
either one of conditions, where a vision of an operator who
operates the mobile unit is determined to be affected by white
smoke and where a visibility of white smoke around the mobile unit
is higher than that in a reference environment, is satisfied; and
the second condition maybe satisfied if both the condition, where
the vision of the operator who operates the mobile unit is
determined to be affected by white smoke and where the visibility
of white smoke around the mobile unit is higher than that in the
reference environment, are satisfied. According to the above
aspect, the exhaust state control device for a fuel cell for a
mobile unit can determine in detail the circumstances where white
smoke is generated by defining the first condition and the second
condition which requires greater reduction of white smoke than the
first condition does.
[0022] In the above aspect, the reference environment may include
at least one of a daytime environment and a non-rainy environment.
The visibility of white smoke is considered to be lowest in daytime
or non-rainy environments.
[0023] In the above aspect, the mobile unit may be a vehicle; the
operating state of the operating section may be determined based on
whether a headlight is on; the surrounding environmental state may
be determined based on at least one of: whether a darkness
detection signal for an automatic light is on; whether a current
time is after a sunset and before a sunrise; whether a signal from
a global positioning system cannot be received; whether a wiper is
on; whether a rain sensing signal is on; and whether a detection
value of the ambient humidity sensor exceeds a predetermined value;
and the condition determination section may determine that the
reference environment is the daytime or non-rainy environment if at
least one of the determined states above is satisfied.
[0024] In the above aspect, it may be determined that the white
smoke interferes with the vision of the operator when the mobile
unit advances in a discharging direction of the exhaust gas. The
possibility that the white smoke will interfere with the vision of
the operation increases if the white smoke is at the advance
direction and the operator is looking in the advance direction of
the mobile unit.
[0025] In the above aspect, the mobile unit may be a vehicle; and
it may be determined that the condition where the white smoke
interferes with vision of the operator of the mobile unit is
satisfied when at least one of the shift lever is in a reverse
position and the parking brake is off.
[0026] In the above aspect, the process to reduce white smoke may
be at least one of a process to control the exhaust gas temperature
and a process to control a flow rate of the exhaust gas at an air
electrode side of the fuel cell. The generation of white smoke can
be controlled by the exhaust gas temperature and the flow rate of
the exhaust gas at the air electrode side.
[0027] In the above aspect, discharge of the exhaust gas at the air
electrode side may be controlled such that a limit of the flow rate
of the exhaust gas decreases as the moving speed of the mobile unit
decreases. The generation of white smoke is reduced and the
visibility of white smoke is lowered when the moving speed of the
mobile unit is at or above a predetermined value.
[0028] In the above aspect, a pressure or the flow rate of the
exhaust gas at the air electrode side may be controlled such that
the limit of the flow rate of the exhaust gas increases as the
pressure of the exhaust gas increases. To discharge the same amount
in mass of exhaust gas, the volumetric flow rate of the gas is
decreased as the pressure of the gas is increased. Therefore, to
discharge the same amount in mass of exhaust gas, the amount of
water vapor to be discharged is reduced as the pressure of the
exhaust gas is higher. To maintain approximately the same amount of
water vapor to be discharged, a larger amount in mass of exhaust
gas can be discharged when the pressure of the exhaust gas is
increased than when the pressure is not increased.
[0029] In the above aspect, the process to reduce the generation of
white smoke, which is performed when the condition determination
section determines that the second predetermined condition is
satisfied, includes at least one of stopping scavenging air and
shutting off a hydrogen supply pressure to the fuel cell.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] The foregoing and further features and advantages of the
invention will become apparent from the following description of
example embodiments with reference to the accompanying drawings,
wherein like numerals are used to represent like elements and
wherein:
[0031] FIG. 1 shows an example configuration of a fuel cell
system;
[0032] FIG. 2 is a flowchart illustrating the operation of the fuel
cell system;
[0033] FIG. 3 shows an example process of the white smoke reduction
control;
[0034] FIG. 4 shows the classification of the white smoke reduction
process;
[0035] FIG. 5 shows an example process of the white smoke reduction
control;
[0036] FIG. 6 shows an example process of the white smoke reduction
control;
[0037] FIG. 7 is a flowchart illustrating the operation of the fuel
cell system;
[0038] FIG. 8 shows an example of the map showing white smoke
reduction regions;
[0039] FIG. 9 is a configuration diagram of the fuel cell
system;
[0040] FIG. 10 shows the concept of a vehicle equipped with the
fuel cell system; and
[0041] FIG. 11 shows an example process of the white smoke
reduction control.
DETAILED DESCRIPTION OF EMBODIMENTS
[0042] A fuel cell system according to a first embodiment of the
present invention is described below with reference to FIGS. 1 to
3.
[0043] FIG. 1 shows an example configuration of a fuel cell system
in accordance with an embodiment of the present invention. As shown
in FIG. 1, the fuel cell system includes a fuel cell stack 1. The
fuel cell system also includes, a hydrogen tank 7, which serves as
its hydrogen system that supplies hydrogen to the fuel cell stack
1; a pressure regulator 10, an anode gas passage 2, an anode off
gas passage 3, a hydrogen pump 8, an anode off gas circulation
passage 4, a gas-liquid separator 12, which separates water from
anode off gas; a drain tank 13, and an exhaust/drain valve 14. The
fuel cell system additionally includes, as its air system that
supplies air to the fuel cell stack 1, an air filter 11, a pump 9,
a cathode gas passage 5, and a cathode off gas passage 6. The fuel
cell system further includes, as its control system and measurement
system, an electronic control unit (ECU, equivalent to the exhaust
state control device for a fuel cell for a mobile unit) 15, a
discharge gas temperature sensor 17, an ambient temperature sensor
19A, an ambient humidity sensor 19B, and a stack temperature sensor
20. As shown schematically in FIG. 1, the fuel cell system is
mounted on a mobile unit such as a vehicle to function as a power
source for the mobile unit.
[0044] The fuel cell stack 1 is composed of a plurality of cells
stacked over each other. Each cell is composed of an electrolyte
membrane, an anode (fuel electrode), a cathode (air electrode), and
a separator. Flow paths for hydrogen and air are formed between the
anode and the cathode.
[0045] The hydrogen tank 7 supplies anode gas to the anode gas
passage 2. The anode gas supplied from the hydrogen tank 7 is
adjusted to a predetermined pressure by the pressure regulator 10.
Then, the anode gas is supplied from the anode gas passage 2 to the
anode of the fuel cell stack 1.
[0046] Air drawn via the air filter 11 is supplied through the
cathode gas passage 5 to the cathode of the fuel cell stack 1 from
outside the fuel cell system by the pump 9 (which may be an air
compressor).
[0047] When the anode gas is supplied to the anode of the fuel cell
stack 1, hydrogen ions are generated from hydrogen contained in the
anode gas. Oxygen contained in the air is supplied to the cathode
of the fuel cell stack 1. Then, in the fuel cell stack 1, an
electrochemical reaction occurs between the hydrogen and the oxygen
that generates electrical energy. In addition, at the cathode of
the fuel cell stack 1, the hydrogen ions, generated from hydrogen,
and oxygen are combined that generates water.
[0048] Gas containing unreacted hydrogen and nitrogen and so forth
permeated from the cathode (hereafter referred to as "anode off
gas") is discharged from the fuel cell stack 1 to the anode off gas
passage 3.
[0049] The anode off gas discharged from the anode of the fuel cell
stack 1 passes through the anode off gas passage 3 and the anode
off gas circulation passage 4, and again is supplied to the anode
of the fuel cell stack 1 along with anode gas from the hydrogen
tank 7. The anode off gas passage 3 supplies the anode off gas to
the gas-liquid separator 12. This allows the anode off gas to be
supplied to the anode off gas circulation passage 4 after water is
separated from the anode off gas.
[0050] Unreacted cathode gas (hereinafter referred to as "cathode
off gas") is discharged from the fuel cell stack 1 to the cathode
off gas passage 6. The cathode off gas contains the water generated
by the fuel cell stack 1 in the form of water vapor. The cathode
off gas discharged from the cathode is discharged through the
cathode off gas passage 6 to the ambient air.
[0051] The ECU 15 is electrically connected to the pump 9, a
driving motor (not shown) that drives the pressure regulator 10,
the discharge gas temperature sensor 17, the ambient temperature
sensor 19A, the ambient humidity sensor 19B (equivalent to one of
the sensors), and the stack temperature sensor 20. The ECU 15
controls supply of the pump 9 and the driving motor (not shown) for
the pressure regulator 10. The ECU 15 acquires the temperature of
the cathode off gas detected by the discharge gas temperature
sensor 17. The ECU 15 acquires the ambient temperature detected by
the ambient temperature sensor 19A and the ambient humidity
detected by the ambient humidity sensor 19B. The ECU 15 acquires
the operating temperature of the fuel cell stack 1 measured by the
stack temperature sensor 20. The ECU 15 includes a CPU, a ROM, and
so forth inside. The CPU executes various processes according to a
control program stored in the ROM.
[0052] The discharge gas temperature sensor 17 detects the
temperature of the cathode off gas that is discharged via the
cathode off gas passage 6 to the ambient air. The discharge gas
temperature sensor 17 may be provided at any position in the
cathode off gas passage 6. For example, the discharge gas
temperature sensor 17 may be provided in the vicinity of an exhaust
exit (tail end) of the cathode off gas passage 6 so as to measure
the temperature of the cathode off gas immediately before being
discharged to the ambient air.
[0053] The ambient temperature sensor 19A measures the temperature
outside the fuel cell system, that is, the ambient temperature.
Meanwhile, the ambient humidity sensor 19B measures the ambient
humidity. The stack temperature sensor 20 measures the operating
temperature of the fuel cell stack 1. The stack temperature sensor
20 may be directly attached to the fuel cell stack 1, or may
measure the temperature of the coolant of the fuel cell stack
1.
[0054] The vehicle is provided with a vehicle speed sensor 22
(equivalent to one of the sensors) that detects the moving speed of
the vehicle, and various levers, operating buttons, knobs, pedals,
and so forth that allow a driver to operate the mobile unit.
Examples of the various levers, operating buttons, knobs, pedals,
and so forth include a shift lever that designates the ratio
between the rotational speed of a motor driven by a power source
and that of a driving part (for example, a wheel), a wiper lever
that turns on and off a wiper, a knob of an in-vehicle device that
receives a signal from a global positioning system (GPS) to provide
an indication of the present location and time, guidance to a
destination, and so forth, and a parking brake lever. The vehicle
in accordance with this embodiment has respective sensors that
sense operations of the various levers, operating buttons, knobs,
pedals, and so forth by the driver (each equivalent to the sensor
of the present invention), and executes control according to the
operations. During this control, the ECU 15 monitors the operations
of the various sensors and so forth to recognize their operating
states.
[0055] FIG. 2 is a flowchart of an exhaust state control process
that is executed by the ECU 15. The process is implemented by a
control program executed by the CPU. This process is executed
periodically at predetermined time intervals.
[0056] In the process, the ECU 15 first acquires the gas
temperature at the exhaust exit, detected by the discharge gas
temperature sensor 17 and the temperature detected by the ambient
temperature sensor 19A. Then, the ECU 15 determines whether the
difference between the gas temperature at the exhaust exit and the
ambient temperature exceeds a predetermined value T1 (S1). If the
difference between the gas temperature at the exhaust exit and the
ambient temperature does not exceed the predetermined value T1 (NO
in S1), the ECU 15 returns the process to S1. In this case, the ECU
15 may execute S1 and the subsequent steps after a predetermined
amount of time has elapsed. Here, the predetermined value T1 and
the predetermined time may be set as factory default, or set by the
dealer or the user of the vehicle, for example. Incidentally, the
ECU 15 which executes the process in S1 may be equivalent to the
white smoke generation determination section of the present
invention.
[0057] On the other hand, if the difference between the gas
temperature at the exhaust exit and the ambient temperature exceeds
the predetermined value T1 (YES in S1), the ECU 15 reads the
traveling speed of the vehicle from the vehicle speed sensor 22 and
reads the position of the shift lever (S2).
[0058] Then, the ECU 15 determines whether the vehicle speed is 0,
or determines whether the shift lever is in the parking position (P
position) (S3). At this time, the ECU 15 may determine whether the
vehicle speed is 0 and whether the shift lever is in the P
position. The conditions in S3 may be equivalent to the first
condition of the present invention.
[0059] Then, if the vehicle speed is not 0, or if the shift lever
is not in the P position (NO in S3), the ECU 15 returns the process
to S1. On the other hand, if the vehicle speed is 0, or if the
shift lever is in the P position (YES in S3), the ECU 15 determines
the surrounding environmental conditions (S4). The surrounding
environmental conditions include the following, for example. (1) A
headlight is on (which may be equivalent to the operating state of
the operating section of the present invention). (2) A darkness
detection signal for an automatic light is on (which may be
equivalent to the environmental state of the present invention).
Here, the "automatic light" refers to a headlight that is turned on
and off automatically. That is, the automatic light generates a
darkness detection signal to turn on the headlight when its
controller senses that the brightness in its environment has fallen
below a predetermined threshold. (3) It is after a sunset and
before a sunrise (which may be equivalent to the environmental
state of the present invention). (4) A signal from the GPS cannot
be received (which may be equivalent to the environmental state of
the present invention). (5) The wiper is on (which may be
equivalent to the operating state of the operating section of the
present invention). (6) For a vehicle provided with an automatic
wiper, a rain sensing signal is on (which may be equivalent to the
environmental state of the present invention). (7) A detected
ambient humidity h of the ambient humidity sensor 19B exceeds a
predetermined value A (which may be equivalent to the environmental
state of the present invention). Here, the predetermined value A
may be set as factory default, or set by the dealer or the user of
the vehicle, for example.
[0060] Then, the ECU 15 determines whether the surrounding
environment determined in S4 satisfies a predetermined condition
(S5). Here, the predetermined condition may be set as factory
default, or set by the dealer or the user of the vehicle, for
example. If none of these conditions is satisfied (NO in S5), the
ECU 15 executes the white smoke reduction control (S6). In this
case, the surrounding environmental condition is determined that it
is daytime, that it is not rainy, and that the ambient humidity is
less than a predetermined value. Thus, it is determined that the
visibility of the white smoke is low, and therefore the process to
reduce the generated white smoke is executed.
[0061] Here, the white smoke reduction control is a process that
reduces the amount of scavenging air at the air electrode. For
example, the ECU 15 reduces the amount of scavenging air from the
pump 9 by a predetermined proportion. Alternatively, the cathode
off gas may be heated by a heater (not shown) provided in the
cathode off gas passage 6, for example. Conversely, the cathode off
gas may be cooled by a heat exchanger (not shown) to a temperature
close to the ambient temperature.
[0062] The cathode off gas may be heated or cooled based on
conditions for white smoke that is generated, which are obtained
from the relationship between the ambient temperature and the gas
temperature at the exhaust exit, for example. This is made possible
by experimentally or empirically preparing a map of the
relationship that "the differential between the ambient temperature
and the gas temperature at the exhaust exit is .DELTA.T or less at
a humidity of h," and storing the map in a storage device of the
ECU 15. Then, the ECU 15 can perform control so as to heat or cool
the cathode off gas such that the differential between the ambient
temperature and the gas temperature at the exhaust exit is .DELTA.T
or less at the ambient humidity.
[0063] On the other hand, if any of the above conditions is
satisfied (YES in S5), the ECU 15 executes the white smoke
suppression control (S7). In this case, the surrounding
environmental condition is determined that it is nighttime, that
the headlight is used, that it is rainy, or that the ambient
humidity exceeds the predetermined value. Thus, the visibility of
the white smoke is high, and therefore the process to reduce the
generated white smoke is not enough and the white smoke suppression
process is executed. Incidentally, the white smoke suppression
control in the present invention may be equivalent to the process
to further reduce generation of white smoke.
[0064] Here, the white smoke suppression control may include, for
example, stopping the operation of the pump 9 (that is, stopping
scavenging air), and suspending the operation of the fuel cell
system by shutting off the hydrogen supply pressure with the
pressure regulator 10.
[0065] As discussed above, the fuel cell system in accordance with
this embodiment can precisely determine whether white smoke
reduction is required by determining the visibility of white smoke
based on the traveling conditions of the vehicle, the operating
state of the vehicle, and the surrounding environmental conditions
when the generation of white smoke is highly possible in
consideration of the relationship between the temperature of
cathode off gas to be discharged to the ambient air and the ambient
temperature. Then, the fuel cell system in accordance with this
embodiment executes a white smoke reduction process when the
visibility of the white smoke is estimated to be not particularly
high, and executes a white smoke suppression process when it is
estimated to be high. That is, white smoke reduction is switched
according to the driving conditions of the vehicle and the
surrounding environmental conditions. This contributes to precisely
determining whether white smoke reduction is required, and to
reducing wasteful energy consumption and a decrease in the power
generation efficiency.
[0066] In the first embodiment, as described in relation to S4 and
S5 of FIG. 2, the ECU 15 executes the white smoke reduction control
if none of the above conditions (1) to (7) is satisfied, and
executes the white smoke suppression process if any of the above
conditions (1) to (7) is satisfied. Alternatively, the ECU 15 may
execute the white smoke suppression process (S7) if a specific
combination of the above conditions (1) to (7) are satisfied. For
example, the ECU 15 may execute the white smoke suppression process
if the headlight is on and it is nighttime. Further, the ECU 15 may
execute the white smoke suppression process if the wiper is on and
the detected ambient humidity exceeds the predetermined value A.
Then, the ECU 15 may execute the white smoke reduction process (S6)
if the specific combination of the above conditions (1) to (7) are
satisfied.
[0067] In the first embodiment, if it is determined in S3 of FIG. 2
that the vehicle speed is not 0, or that the shift lever is not in
the P position, the process returns to S1. That is, in this case,
neither of the white smoke reduction control and the white smoke
suppression control is executed. Alternatively, the ECU 15 may
first perform the determination in S5 of FIG. 2, that is, determine
whether the surrounding environmental conditions are satisfied.
Then, in the case where none of the above conditions (1) to (7) is
satisfied, the ECU 15 may return the process to S1. That is, the
ECU 15 may execute neither of the white smoke reduction control and
the white smoke suppression control. Conversely, if any of the
above conditions (1) to (7) is satisfied, the ECU 15 may determine
whether the vehicle speed is 0, or whether the shift lever is in
the P position, and execute either the white smoke reduction
control or the white smoke suppression control according to the
determination results.
[0068] In the above first embodiment, the necessity for white smoke
reduction is determined, and either the white smoke reduction
control or the white smoke suppression control is executed,
depending mainly on whether white smoke is highly visible from
outside the vehicle. Alternatively, the ECU 15 may determine the
necessity for white smoke reduction, and execute either the white
smoke reduction control or the white smoke suppression control,
depending on whether the vision of the driver of the vehicle is
affected. FIG. 3 shows an example of such a process.
[0069] In this process, the ECU 15 first acquires the gas
temperature at the exhaust exit detected by the discharge gas
temperature sensor 17 and the temperature detected by the ambient
temperature sensor 19A. Then, the ECU 15 determines whether the
difference between the gas temperature at the exhaust exit and the
ambient temperature exceeds a predetermined value T1 (S1). If the
difference between the gas temperature at the exhaust exit and the
ambient temperature does not exceed the predetermined value T1 (NO
in S1), the ECU 15 returns the process to S1. On the other hand, if
the difference between the gas temperature at the exhaust exit and
the ambient temperature exceeds the predetermined value T1 (YES in
S1), the ECU 15 determines the surrounding environmental conditions
(S4). These conditions are the same as in the first embodiment, and
therefore their descriptions are omitted.
[0070] Then, the ECU 15 determines whether the surrounding
environment determined in S4 satisfies a predetermined condition
(S5). If none of the surrounding environmental conditions (the
above conditions (1) to (7)) is satisfied (NO in S5), the ECU 15
returns the process to S1. On the other hand, if any of the
surrounding environmental conditions (the above conditions (1) to
(7)) are satisfied (YES in S5), the ECU 15 reads the position of
the shift lever and a switch signal of the parking brake (S8).
[0071] In S9 that follows, the ECU 15 determines whether the shift
lever is in the R position (reverse position), or whether the
parking brake signal is off. At this time, the ECU 15 may determine
whether the shift lever is in the R position and whether the
parking brake signal is off.
[0072] Then, if the shift lever is not in the R position, or if the
parking brake signal is on (NO in S9), the ECU 15 executes the
white smoke reduction control (S10). In this case, the vehicle does
not move in the direction in which gas is discharged from the
exhaust exit, and therefore the ECU 15 determines that the
possibility that the vision of the driver is affected is low, even
under conditions where white smoke is generated and its visibility
is relatively high. In this case, the ECU 15 determines that the
white smoke reduction process is sufficient.
[0073] Alternatively, if the shift lever is in the R position, or
if the parking brake signal is off (YES in S9), the ECU 15
determines that the possibility that the vehicle is moving in the
direction in which gas is discharged from the exhaust exit is high.
In this case, the ECU 15 determines not only that the white smoke
is easily viewable from outside the vehicle, but also that the
white smoke can affect the vision of the driver, and thus executes
the white smoke suppression control (S11).
[0074] As discussed above, in this modification, the ECU 15
estimates the influence of white smoke on the driver by determining
whether the advancing direction of the vehicle coincides with the
discharging direction of gas. Then, the ECU 15 executes the white
smoke suppression control in the case where the advancing direction
of the vehicle coincides with the discharging direction of gas.
[0075] In the white smoke suppression control, the ECU 15 stops
scavenging air, suspends the operation of the fuel cell system,
and/or the like. On the other hand, in the white smoke reduction
control, the ECU 15 restricts scavenging air, heats the cathode off
gas with a heater, and/or the like.
[0076] According to such control, the ECU 15 executes the white
smoke reduction control when the visibility of the white smoke is
high, and executes the white smoke suppression process when the
white smoke affects the vision of the driver, allowing efficient
utilization of the fuel cell system. For example, it is possible to
very precisely determine whether to stop scavenging air for the
fuel cell stack 1 or to suspend the operation of the fuel cell
system.
[0077] In the above embodiment, the ECU 15 determines in S3 of FIG.
2 whether the vehicle speed is 0, or whether the shift lever is in
the P position. However, the white smoke reduction process or the
white smoke suppression process may be executed when the vehicle
speed is at or below a predetermined speed, from the standpoint of
the merchantability or upon user request. In this case, the
predetermined speed may be set as factory default, adjusted by the
dealer, or set by the user. If the vehicle speed is at or below (or
below) the predetermined speed, the ECU 15 executes the processes
in S4 to S7 of FIG. 2.
[0078] Referring to FIGS. 4 and 5, a fuel cell system in accordance
with a second embodiment of the present invention will be
described. In the above first embodiment, the ECU 15 does not
execute white smoke reduction in the case where the vehicle speed
is not 0, or in the case where the shift lever is not in the P
position. Further, in the case where the vehicle speed is 0, or in
the case where the shift lever is in the P position, the ECU 15
selectively executes the white smoke reduction control or the white
smoke suppression control depending on the status of whether the
surrounding environmental conditions (1) to (7) are satisfied.
Alternatively, the fuel cell system in accordance with the second
embodiment of the present invention executes white smoke reduction
in more diversified levels. In the description below, white smoke
reduction is executed in white smoke reduction control 1, white
smoke reduction control 2, and white smoke reduction control 3
(white smoke suppression control). The other configuration and
function of this embodiment are the same as those of the first
embodiment. Thus, like processes are denoted by like reference
numerals to omit their descriptions. The system configuration is
the same as that shown in FIG. 1.
[0079] FIG. 4 shows the classification of the white smoke reduction
process by the fuel cell system in accordance with this embodiment.
In the white smoke reduction control 1, the scavenging air is
reduced by 30%, and the power for heating the cathode off gas is
set to 300 watts, for example. Reducing the scavenging air by 30%
means reducing by 30% the driving power for the pump 9 at the air
electrode side. In the white smoke reduction control 2, the
scavenging air is reduced by 60%, and the power for heating the
cathode off gas is set to 600 watts, for example. In the white
smoke reduction control 3, the scavenging air is reduced by 100%,
and the power for heating the cathode off gas is set to 1000 watts,
for example. That is, in the white smoke reduction control 3, the
pump 9 is stopped to stop the scavenging air. In this case, the
operation of the fuel cell system itself may be stopped by shutting
off the hydrogen pressure with the pressure regulator 10, for
example. In this way, the ECU 15 compulsorily suppresses the
generation of white smoke.
[0080] FIG. 5 shows the control by the ECU 15 in the fuel cell
system. The steps S1, S2, and S3 in this process are the same as
those in the first embodiment, and therefore their descriptions are
omitted.
[0081] If the determination in S3 is NO, the ECU 15 executes the
white smoke reduction control 1 (S6A). On the other hand, if the
determination in S3 is YES, the ECU 15 determines the surrounding
environmental conditions (S4). The surrounding environmental
conditions determined in S4 are identical to the conditions (1) to
(7) described in relation to the first embodiment.
[0082] Then, if none of the conditions (1) to (7) is satisfied, the
ECU 15 executes the white smoke reduction control 2 (S6B). However,
if any of the conditions (1) to (7) is satisfied, the ECU 15
executes the white smoke reduction control 3 (S6C). That is, the
scavenging air for the fuel cell stack 1 is stopped, or the fuel
cell system is suspended to suppress the generation of white
smoke.
[0083] As discussed above, according to the fuel cell system in
accordance with this embodiment, white smoke reduction can be
executed in more diversified levels than in the first
embodiment.
[0084] As described in relation to the modification of the first
embodiment, the ECU 15 may execute the white smoke suppression
process (S7) when a specific combination of the above conditions
(1) to (7) are satisfied. For example, the ECU 15 may execute the
white smoke suppression process if the headlight is on and it is
nighttime. Further, the ECU 15 may execute the white smoke
suppression process if the wiper is on and the detected ambient
humidity exceeds the predetermined value A.
[0085] In addition, as described in relation to FIG. 3, the ECU 15
may determine the necessity for white smoke reduction, and execute
either the white smoke reduction control or the white smoke
suppression control, depending on whether the vision of the driver
of the vehicle is affected. FIG. 6 shows an example of such a
process.
[0086] In this process, when the surrounding environment satisfies
none of the conditions (1) to (7)) (NO in S5), the ECU 15 executes
the white smoke reduction control 1 (S10A). On the other hand, if
any of the surrounding environmental conditions (the above
conditions (1) to (7)) are satisfied (YES in S5), the ECU 15 reads
the position of the shift lever and a switch signal of the parking
brake (S8). Subsequently, the ECU 15 determines whether the shift
lever is in the R position, or whether the parking brake signal is
off.
[0087] Then, if the shift lever is not in the R position, or if the
parking brake signal is on (NO in S9), the ECU 15 executes the
white smoke reduction control 2 (S10B). On the other hand, if the
shift lever is in the R position, or if the parking brake signal is
off (YES in S9), the ECU 15 determines that the possibility that
the vehicle moves in the direction in which gas is discharged from
the exhaust exit is high. In this case, the ECU 15 determines not
only that the white smoke is easily viewable from outside the
vehicle, but also that the white smoke can affect the vision of the
driver, and executes the white smoke suppression control (S11).
[0088] Referring to FIGS. 7 to 9, a third embodiment of the present
invention will be described. In the first and second embodiments,
the ECU 15 determines whether white smoke reduction is necessary
based on the difference between the gas temperature at the exhaust
exit and the ambient temperature (see the process in S1 of FIGS. 2,
3, 5, and 6). Alternatively, the ECU 15 may determine whether white
smoke reduction is necessary based on the surrounding environmental
conditions of the vehicle, which include the ambient temperature
and the ambient humidity, and the gas temperature at the exhaust
exit. The other configuration and function of this embodiment are
the same as those of the first and second embodiments. Like
components are denoted by like reference numerals to omit their
descriptions.
[0089] FIG. 7 is a flowchart illustrating the operation of the fuel
cell system in accordance with the embodiment of the present
invention.
[0090] The ECU 15 first acquires the temperature of the cathode off
gas detected by the discharge gas temperature sensor 17 (S1A). The
ECU 15 also acquires the ambient temperature detected by the
ambient temperature sensor 19A (S1A). The ECU 15 further acquires
the ambient humidity detected by the ambient humidity sensor 19B
(S1A). In this embodiment, the ambient humidity measured by the
ambient humidity sensor 19B is referred to as "detected ambient
humidity."
[0091] Next, the ECU 15 makes a determination as to a white smoke
reduction region based on the temperature of the cathode off gas,
the detected ambient temperature, and the detected ambient humidity
(S1B).
[0092] In S1B, the term "white smoke reduction region" refers to
the state where water vapor contained in the cathode off gas
discharged to the ambient air is white and visible. The
relationship between the white smoke reduction region and the
temperature of the cathode off gas, the ambient temperature, and
the ambient humidity may be obtained in advance by experiment or by
simulation. For example, a map (table) as shown in FIG. 8 is
prepared in advance by experiment or by simulation. Then, the ECU
15 may make a determination as to the white smoke reduction region
using the map.
[0093] The symbol .DELTA.T indicated in FIG. 8 represents the
difference between the temperature of the cathode off gas and the
ambient temperature. The term "humidity" indicated in FIG. 8 refers
to the ambient humidity. The circular marks in FIG. 8 indicate that
.DELTA.T1 and the ambient humidity are in the white smoke reduction
region. The X marks in FIG. 8 indicate that .DELTA.T1 and the
ambient humidity are not in the white smoke reduction region. If
the map in FIG. 8 is used to determine whether .DELTA.T1 and the
ambient humidity are in the white smoke reduction region, the ECU
15 calculates .DELTA.T1, the difference between the temperature of
the cathode off gas and the ambient temperature. Then, the ECU 15
references the map shown in FIG. 8 to determine whether .DELTA.T1
and the ambient humidity are in the white smoke reduction region
(S1B).
[0094] If .DELTA.T1 and the ambient humidity are determined to be
in the white smoke reduction region (YES in S1B), the ECU 15
executes the processes in and after S2. The processes in and after
S2 are the same as those in the first embodiment and the second
embodiment, and therefore their descriptions are omitted. On the
other hand, if the ECU 15 determines that .DELTA.T1 and the ambient
humidity are not in the white smoke reduction region (NO in S1B),
the process is returned to S1A.
[0095] According to this embodiment, it is possible to determine at
an initial stage whether white smoke reduction is required in
consideration of the ambient humidity as well:
[0096] In addition, in and after S2 of FIG. 7, the same processes
as those in and after S2 of FIG. 2 are executed. Alternatively, in
and after S2 of FIG. 7, the same processes as those in and after S4
of FIG. 3 may be executed. As a further alternative, the same
processes as those in and after S2 of FIG. 5, or those in and after
S4 of FIG. 6, of the second embodiment may be executed in and after
S2 of FIG. 7.
[0097] Referring to FIGS. 9 to 11, a fuel cell system in accordance
with a fourth embodiment of the present invention will be
described. In the first to third embodiments, when white smoke
reduction is determined to be necessary, then the ECU 15 executes
the white smoke reduction control or the white smoke suppression
control depending on whether white smoke is highly visible from
outside the vehicle, or whether white smoke affects the vision of
the driver.
[0098] In this embodiment, the fuel cell system dilutes the cathode
off gas containing water vapor and having passed through the fuel
cell stack 1 with air that has not passed through the fuel cell
stack 1. In this case, the dilution ratio with air containing water
vapor as the target of control is determined using an evaluation
expression reflecting the speed of the vehicle. The other
configuration and function are the same as those of the first to
third embodiments. Like components are denoted by like reference
numerals to omit their descriptions.
[0099] FIG. 9 is a configuration diagram of a fuel cell system in
accordance with this embodiment. In FIG. 9, compared to the
configuration of FIG. 1, an air back pressure regulator 31 and a
diluter 32 are added at the cathode side. The cathode off gas
passage 6 is connected to the diluter 32 from the cathode side.
[0100] At the anode side, an anode off gas branch passage 37 is
connected to the anode off gas passage 3 via an exhaust valve 36.
The anode off gas branch passage 37 is also connected to the
diluter 32. Furthermore, in FIG. 9, a shut valve 30 is provided
upstream of the pressure regulator 10 for hydrogen.
[0101] The ECU 15 controls the air backpressure regulator 31, the
exhaust valve 36, and the pump 9 to control the dilution ratio of
the anode off gas and the cathode off gas.
[0102] FIG. 10 shows the concept of a vehicle equipped with the
fuel cell system. In FIG. 10, the vehicle advances in the direction
of the arrow at a speed v. The flow rate of the cathode off gas
discharged from the cathode off gas passage 6 to the diluter 32 at
this time is defined as Qairex.
[0103] In this case, the dilution ratio Dr of the cathode off gas
at the vehicle speed v, which reflects the effect that the cathode
off gas is diffused by the ambient air, is defined by Expression 1
below.
Dilution ratio : Dr = P H 2 O @ FC P H 2 O @ atm .times. Q air ex Q
air ex + k v [ Expression 1 ] ##EQU00001##
Where,
[0104] k: Conversion factor to obtain dilution air amount
Qair.sub.ex: Amount of exhaust air P.sub.H2O@FC: Saturated water
vapor pressure at operating temperature of FC P.sub.H2O@atm:
Saturated water vapor pressure at ambient temperature
[0105] In the expression, k represents a conversion factor for
calculating the amount of air with which the cathode off gas is
diluted at the vehicle speed v, P.sub.H2O@FC is a saturated vapor
pressure at the operating temperature of the fuel cell stack 1, and
P.sub.H2O@atm is a saturated vapor pressure at the ambient
temperature.
[0106] In the physical sense, Expression 1 means that the
concentration of the cathode off gas is lowered by dilution as the
vehicle speed v is higher. That is, if the saturated vapor pressure
at the operating temperature of the fuel cell stack 1 is higher
than the saturated vapor pressure at the ambient temperature,
P.sub.H2O@FC/P.sub.H2O@atm is more than 1, which satisfies the
condition under which white smoke is generated. Here,
P.sub.H2O@FC/P.sub.H2O@atm represents the proportion of the cathode
off gas that is condensed into water droplets when the gas is
released to the ambient air. In addition,
(P.sub.H2O@FC/P.sub.H2O@atm).times.Qairex represents the amount of
the cathode off gas that is condensed into water droplets when the
gas is released to the ambient air.
[0107] When the vehicle speed v is sufficiently high, however,
white smoke is not noticeable due to the same effect as when the
cathode off gas is diluted. The dilution ratio Dr indicates the
degree of such effect.
[0108] Thus, P.sub.H2O@FC/P.sub.H2O@atm is set to a plurality of
values, and for each value, the degree of the generation of white
smoke is observed while varying the cathode off gas flow rate
Qairex and the vehicle speed v. Based on the values obtained from
such experiments, the relationship between P.sub.H2O@FC,
P.sub.H2O@atm, Qairex, and the vehicle speed v and the degree of
the generation (visibility) of white smoke may be obtained. From
the values obtained from the experiments, the value to be fulfilled
by the dilution ratio Dr (hereinafter referred to as "reference
value Dr0") is determined. Then, with the reference value Dr0 set
in a memory (not shown) of the ECU 15, the operating state of the
fuel cell may be controlled such that the dilution ratio Dr is at
the reference value Dr0 or less.
[0109] FIG. 11 is a flowchart showing the control executed by the
ECU 15 in that case. In this process, the ECU 15 first reads the
operating temperature of the fuel cell stack 1 from the stack
temperature sensor 20 to calculate the saturated vapor pressure
P.sub.H2O@FC of the cathode off gas (S21). However, the exhaust gas
temperature sensor 17 of FIG. 1 may be used in place of the stack
temperature sensor 20 to detect the temperature of the cathode off
gas.
[0110] Next, the ECU 15 reads the ambient temperature from the
ambient temperature sensor 19A to calculate the saturated vapor
pressure of the ambient air P.sub.H2O@atm (S22). Further, the ECU
15 reads the vehicle speed v from a vehicle speed sensor (not
shown) (S23). Then, the ECU 15 determines the cathode off gas flow
rate Qairex such that the dilution ratio Dr is at the reference
value Dr0 or less according to Expression 1 (S24). Then, the ECU 15
controls the rotational speed of the pump 9 such that the cathode
off gas flow rate is at Qairex or less (S25).
[0111] As discussed above, according to the fuel cell system in
accordance with the fourth embodiment, the ECU 15 controls the
discharge amount of the cathode off gas, that is, the rotational
speed of the pump 9, such that the dilution ratio is at the
reference value Dr0 or less based on the saturated vapor pressure
of the cathode off gas, the saturated vapor pressure of the ambient
air, and the vehicle speed. According to such control, white smoke
due to the cathode off gas may be controlled so as not to be
noticeable by controlling the discharge amount, that is, the
dilution ratio, of the cathode off gas according to the vehicle
speed v.
[0112] In the fourth embodiment, the ECU 15 controls the discharge
amount, that is, the dilution ratio, of the cathode off gas
according to the vehicle speed v to suppress white smoke. In such
control, the ECU 15 may further control the backpressure at the
cathode side. The backpressure at the cathode side is controlled by
the opening of the backpressure regulator 31 at the exit of the
flow path of the fuel cell stack 1 at the cathode side.
[0113] In the fuel cell system, the ECU 15 calculates the amount in
mass of the cathode off gas that is discharged. For example, it is
assumed that power is generated while the cathode off gas is
required that is discharged in an amount of M gram. As the
backpressure at the cathode side is higher, the volume of the off
gas that is discharged is smaller for the same mass. For example,
when the back pressure doubles, the required flow rate of the off
gas that is discharged is halved.
[0114] On the other hand, the saturated vapor pressure relies upon
the temperature, rather than the backpressure, of the off gas, and
therefore a generally constant amount of water vapor is contained
in the off gas of the same volume, regardless of the backpressure.
Thus, when the back pressure doubles, the required volumetric flow
rate of the off gas that is discharged is halved. Thus, at this
time, the amount of water vapor to be discharged together with the
off gas is also halved.
[0115] With the influence of the backpressure reflected in the
dilution ratio given by Expression 1, Expression 2 below can be
obtained.
Dr = P H 2 O @ FC P H 2 O @ atm .times. ( Q air ex .times. P atm P
back ) Q air ex + k v Q air ex .times. P atm P back : [ Expression
2 ] ##EQU00002##
Changes in volumetric flow rate brought about by increasing
backpressure
[0116] In the expression, Patm represents the atmospheric pressure,
Pback represents the backpressure at the cathode side, and
Qair.times.(Patm/Pback) represents changes in volumetric flow rate
brought about by increasing the backpressure. Thus, for the same
amount (in mass) of the off gas to be discharged, the dilution
ratio may be reduced by the changes in volumetric flow rate.
Conversely, during operation when the backpressure is reduced, the
generation of white smoke may be reduced by reducing the amount in
mass of the off gas to be discharged.
[0117] As described in the above modification 1, the ECU 15 may
reduce the generation of white smoke by further controlling the
back pressure in addition to performing the process of FIG. 11. If
the control of the backpressure is given priority, the ECU 15 may
increase and reduce the amount in mass of the off gas to be
discharged according to changes in back pressure.
[0118] In the fourth embodiment, the ECU 15 controls the discharge
amount, that is, the dilution ratio, of the cathode off gas
according to the vehicle speed v to suppress the generation of
white smoke. In this case, the influence of winds around the
vehicle may be reflected in the vehicle speed v. For example, wind
pressure sensor may be disposed at four positions around the
vehicle, namely, at the front, rear, left, and right sides of the
vehicle, to calculate the relative speed V between the vehicle and
the ambient air based on the wind pressures, irrespective of
whether the vehicle is stationary or traveling. As the relative
speed V between the vehicle and the ambient air, the larger one of
the relative speed V1 in the longitudinal direction, which is based
on the wind pressure in the longitudinal direction of the vehicle,
and the relative speed V2 in the lateral direction, which is based
on and the lateral direction of the vehicle, may be used.
[0119] Then, the ECU 15 may calculate the dilution ratio of
Expression 1 based on the relative speed V between the vehicle and
the ambient air in place of the vehicle speed v. In this way, while
the fuel cell system suppresses the generation of white smoke, the
limit amount of the cathode off gas can be discharged is increased,
even when the vehicle is traveling at a low speed or stationary, by
calculating the dilution ratio with the relative speed between the
vehicle and the ambient air taken into account.
[0120] While the invention has been described with reference to
example embodiments thereof, it is to be understood that the
invention is not limited to the described embodiments or
constructions. To the contrary, the invention is intended to cover
various modifications and equivalent arrangements. In addition,
while the various elements of the example embodiments are shown in
various combinations and configurations, other combinations and
configurations, including more, less or only a single element, are
also within the spirit and scope of the invention.
* * * * *