Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
2000-12-21
2003-12-02
Ryan, Patrick (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S006000, C429S010000, C429S010000
Reexamination Certificate
active
06656618
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a fuel cells system that enables fuel cells to be activated with a high efficiency of energy conversion, as well as to a method of controlling such fuel cells.
DISCUSSION OF THE BACKGROUND
As shown in an example of
FIG. 5
, in a background art fuel cells system mounted on an electric vehicle, a reformer unit
128
receives supplies of fuel
124
, for example methanol and water, fed via a pump
126
and produces a hydrogen-containing gaseous fuel from the fuel
124
through a steam reforming reaction of methanol. Fuel cells
136
receive a flow of the produced gaseous fuel and the air
130
and generate an electromotive force through electrochemical reactions of the gaseous fuel and the air
130
. The electric power generated by the fuel cells
136
and the electric power output from a battery
140
, which is connected in parallel with the fuel cells
136
, are supplied to an inverter
144
to drive a motor
146
and obtain a driving force of the electric vehicle.
A control unit
120
calculates a required output (required electric power) of the inverter
144
from an accelerator travel of the electric vehicle measured by an accelerator pedal position sensor
122
, and regulates the inverter
144
based on the calculated required output. Such regulation causes electric power corresponding to the required output to be supplied to the motor
146
via the inverter
144
.
The fuel cells
136
output the electric power to cover the required output of the inverter
144
. When the electric power output from the fuel cells
136
is insufficient for the required output, the battery
140
outputs the electric power to the inverter
144
to compensate for the insufficiency. The output electric power of the fuel cells
136
accordingly depends upon the required output of the inverter
144
.
In response to a requirement of the output of electric power from the inverter
144
, the fuel cells
136
can not output the required electric power in the case in which the gaseous fuel supplied from the reformer unit
128
to the fuel cells
136
is not sufficient for the output of the required electric power. That is, the output electric power of the fuel cells
136
also depends upon the quantity of the gaseous fuel (that is, the gas flow rate) fed to the fuel cells
136
.
The control unit
120
drives the pump
126
based on the required output of the inverter
144
, and regulates the quantities of the fuel
124
fed to the reformer unit
128
, in order to regulate the quantity of the gaseous fuel supplied to the fuel cells
136
according to the required output of the inverter
144
.
The quantity of the gaseous fuel produced by the reformer unit
128
does not immediately increase (or decrease) with an increase (or a decrease) in supplied quantities of the fuel
124
, but increases or decreases after a time lag of 2 to 20 seconds. The quantity of the gaseous fuel required for the fuel cells
136
is thus not always identical with the actual supply of the gaseous fuel (the gas flow rate) to the fuel cells
136
.
As described above, in the background art fuel cells system, the output electric power of the fuel cells
136
depends upon the required output of the inverter
144
and upon the quantity of the gaseous fuel (the gas flow rate) supplied to the fuel cells
136
. The working point of the fuel cells
136
is thus varied with variations in required output of the inverter
144
and in gas flow rate.
FIG. 6
is a characteristic chart showing variations in power generation efficiency versus the output electric power in general fuel cells with a variation in quantity of the gaseous fuel (the gas flow rate) supplied to the fuel cells as a parameter.
FIG. 7
is a characteristic chart showing a variation in output electric power versus the required quantity of the gaseous fuel in general fuel cells.
In the background art fuel cells system described above, as shown in
FIG. 6
, although the fuel cells are capable of being activated at a working point “a” of high power generation efficiency, the fuel cells may be activated, for example, at a working point “b” of low power generation efficiency since the actual working point is varied with a variation in gas flow rate.
In the background art fuel cells system described above, as shown in
FIG. 7
, even when a sufficient quantity Qc of the gaseous fuel is supplied from the reformer unit to the fuel cells to generate an output electric power Wc, the fuel cells may be activated, for example, at a working point “d” to generate only an output electric power Wd since the actual working point is varied with a variation in required output of the inverter. In this case, the quantity of the gaseous fuel required to generate the output electric power Wd is equal to only Qd, and the wasteful quantity of the gaseous fuel is (Qc−Qd). This lowers the utilization factor of the gaseous fuel.
As described above, in the background art fuel cells system, the working point of the fuel cells is varied with variations in required output of the inverter and in gas flow rate. The fuel cells are thus not always activated at the working point of high power generation efficiency or at the working point of high gas utilization factor.
The power generation efficiency and the gas utilization factor have a tradeoff relationship, so that it is difficult to enhance both the power generation efficiency and the gas utilization factor. Maximizing the product of the power generation efficiency and the gas utilization factor enhances both the power generation efficiency and the gas utilization factor as much as possible. The product of the power generation efficiency and the gas utilization factor is expressed as an energy conversion efficiency of the fuel cells.
SUMMARY OF THE INVENTION
An object of the present invention is thus to solve the problems of the background art and to provide a fuel cells system that enables fuel cells to have an enhanced energy conversion efficiency.
At least part of the above and the other related objects is attained by a first fuel cells system that has fuel cells, which receive a supply of a gas and generate electric power, and which supply the generated electric power to a load. The first fuel cells system includes: a gas flow rate-relating quantity measurement unit that measures a gas flow rate-relating quantity, which relates to a flow rate of the gas supplied to the fuel cells; and a control unit that specifies a working point associated with an output electric current-output voltage characteristic of the fuel cells corresponding to the observed gas flow rate-relating quantity, and regulates electric power to be taken out of the fuel cells, so as to cause the fuel cells to be activated at the specified working point.
The present invention is also directed to a first method of controlling fuel cells that receive a supply of a gas and generate electric power. The first method includes the steps of: (a) measuring a gas flow rate-relating quantity, which relates to a flow rate of the gas supplied to the fuel cells; (b) specifying a working point associated with an output electric current-output voltage characteristic of the fuel cells corresponding to the observed gas flow rate-relating quantity; and (c) regulating electric power to be taken out of the fuel cells, so as to cause the fuel cells to be activated at the specified working point.
The operation of the first fuel cells system and the corresponding first method of the present invention measures the gas flow rate-relating quantity, which relates to the flow rate of the gas supplied to the fuel cells, and specifies a working point associated with the output electric current-output voltage characteristic of the fuel cells corresponding to the observed gas flow rate-relating quantity. The operation then regulates the electric power to be taken out of the fuel cells, so as to cause the fuel cells to be activated at the specified working point.
In the first fuel cells system and the corresponding first method of the present invention, the worki
Martin Angela J
Toyota Jidosha & Kabushiki Kaisha
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