Fuel cell system

Details Fuel cell system Fuel cell system

2000-05-19

2004-08-10

Chaney, Carol (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

Having magnetic field feature

C429S006000, C429S006000

Reexamination Certificate

active

06773837

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a fuel cell system preventing damage to fuel cell at reducing electromotive force, e.g., a case in which a fuel cell at operating is stopped suddenly.
BACKGROUND OF THE INVENTION
Conventionally, as for an art in this field, there is, e.g., Japanese Publication Patent Laid-Open No. 7-78624.
FIG. 2
is a schematic block diagram showing a conventional fuel cell system described in Japanese Patent Publication Laid-Open No. 7-78624.
The fuel cell system has a motor
1
generating driving torque S
1
. A compressor
2
is connected to the motor
1
. The compressor
2
has a function taking in and compressing cathode active material A (e.g., oxygen, air or the like) and supplying cathode active material S
2
whose amount depends on the number of revolutions of the motor
1
. The cathode active material S
2
is taken in to a fuel cell
3
. A fuel blower
4
is provided in the fuel cell system and takes in anode active material F (e.g., fuel of hydrogen gas easy to undergo oxidation) and sends out anode active material S
4
. The anode active material S
4
is taken in to the fuel cell
3
. The fuel cell
3
has a cathode side gas chamber
3
a
, a cathode
3
b
, an anode side gas chamber
3
c
, an anode
3
d
and an electrolyte layer
3
e
between the cathode
3
b
and the anode
3
d
. The fuel cell
3
takes in the cathode active material S
2
to the cathode side gas chamber
3
a
and takes in the anode active material S
4
to the anode side gas chamber
3
c
. Moreover, the fuel cell
3
discharges reaction product S
3
a
, S
3
c
and S
3
e
from the cathode side gas chamber
3
a
, the anode side gas chamber
3
c
and the electrolyte layer
3
e
, respectively, and generates electromotive force S
3
between the cathode
3
b
and the anode
3
d
. Load L is connected to the cathode
3
b
and the anode
3
d
. The reaction product S
3
a
is discharged via a turbine
5
. The reaction product S
3
c
is discharged by controlling pressure by a control valve
6
.
Next, operation of
FIG. 2
will now described.
The cathode active material A is taken in to the compressor
2
and compressed, and the cathode active material S
2
whose amount depends on the number of revolutions of the motor
1
is sent out from the compressor
2
. The cathode active material S
2
is taken in to the fuel cell
3
. The anode active material F is taken in to the fuel blower
4
and the anode active material S
4
is sent out to the fuel cell
3
. The fuel cell
3
takes in the cathode active material S
2
the cathode side gas chamber
3
a
and takes in the anode active material S
4
to the anode side gas chamber
3
c
. Moreover, the fuel cell
3
discharges the reaction product S
3
a
, S
3
c
and S
3
e
from the cathode side gas chamber
3
a
, the anode side gas chamber
3
c
and the electrolyte layer
3
e
, respectively, and generates electromotive force S
3
between the cathode
3
b
and the anode
3
d.
The electromotive force S
3
is controlled on the basis of the number of revolutions of the motor
1
and opening of the control valve
6
and supplied to the load L. The reaction product S
3
a
is discharged via the turbine
5
and the reaction product S
3
c
is discharged by controlling pressure by the control valve
6
.
However, the conventional fuel cell system in
FIG. 2
has a following problem.
FIG. 3
is a characteristic view showing a generation state of overshoot in pressure of the cathode active material S
2
and the reaction product S
3
a
in the cathode side gas chamber
3
a
in
FIG. 2. A
vertical axis is pressure and a horizontal axis is time.
In the fuel cell system in
FIG. 2
, when a command for changing the electromotive force S
3
is input, the time required for reducing the number of revolutions of the motor
1
, from 8000 rpm to 0 rpm of a target value is 1 second and the time required for reducing the opening of the control valve
6
, e.g., from 80° to 0° of a target value is 0.01 second. Specifically, before the motor
1
is stopped the control valve
6
is closed. Therefore, as shown in a characteristic curve C
1
in
FIG. 3
, pressure of the cathode active material S
2
and the reaction product S
3
a
in the cathode side gas chamber
3
a
is P
1
kPa at operating. After a lapse of T
1
second since an operation stopping command (i.e., 0 second), the pressure is P
2
kPa and overshoot is generated. The pressure is reduced gradually and becomes P
3
kPa (where P
2
>>P
3
). When overshoot is generated, cathode-anode differential pressure between the cathode side gas chamber
3
a
and the anode side gas chamber
3
c
is wider than a permissible value and there is a case in which the fuel cell
3
is damaged and destroyed. To solve this problem, Japanese Patent Publication Laid-Open No. 7-78624 proposes a fuel cell system as shown in FIG.
4
.
FIG. 4
is a schematic block diagram showing another conventional fuel cell system described in Japanese Patent Laid-Open No. 7-78624.
The fuel cell system has a cathode-anode differential pressure gage
7
added to the fuel cell system in FIG.
2
. Reaction product S
3
a
and S
3
c
are taken in to the cathode-anode differential pressure gage
7
and differential pressure between the cathode side gas chamber
3
a
and the anode side gas chamber
3
c
is measured to output measured result S
7
. A control portion
8
is connected to an output side of the cathode-anode differential pressure gage
7
. The measured result S
7
is input to the control portion
8
and a control signal S
8
at a level proportional to the measured result S
7
is output from the control portion
8
. A cathode-anode differential pressure valve
9
is connected to an output side of the control portion
8
. The control signal S
8
is input to the cathode-anode differential pressure valve
9
and the S
3
c
is discharged from the cathode-anode differential pressure valve
9
at an opening proportional to the control signal S
8
. Therefore, differential pressure between the cathode side gas chamber
3
a
and the anode side gas chamber
3
c
is kept within a permissible value and the fuel cell
3
is prevented from being damaged and destroyed. However, the fuel cell system has a problem that the fuel cell system has a cathode-anode differential pressure gage
7
, the control portion
8
and the cathode-anode differential pressure valve
9
added to the fuel cell system in
FIG. 2
therefore the number of parts is large and structure is complex.
SUMMARY OF THE INVENTION
To solve the above-described problem the present invention provides a fuel cell system comprising:
a supply means taking in cathode active material, supplying the cathode active material proportional to a level of a first control signal and detecting a flow rate of the cathode active material to generate a flow rate detecting signal;
a fuel cell having a cathode side gas chamber, a cathode, an anode side gas chamber, an anode and an electrolyte layer between the cathode and the anode, taking in the cathode active material supplied by the supplying means to the cathode side gas chamber, taking in given anode active material to the anode side gas chamber, discharging first and second reaction product from the cathode side gas chamber and the anode side gas chamber, respectively, and generating electromotive force between the cathode and the anode
a pressure regulating means having a pressure regulating valve regulating pressure at discharging the first reaction product on the basis of a level of a second control signal and detecting an opening of the pressure regulating valve to generate an opening detecting signal.
The input signal indicating the target electric power of the fuel cell inputs the control means and the control means decides the target value of a flow rate of the cathode active material and the target value of the opening of the pressure regulating valve in accordance with the input signal. The first control signal in accordance with the flow rate of the cathode active material and the second control signal in accordance with the target value of the op

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