JP2004179034A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system capable of exhausting residual moisture even when remaining pressure of hydrogen is low by making a volume of hydrogen exhausted from an exhaust valve constant while preventing wasteful consumption of air for dilution. <P>SOLUTION: The fuel cell system S is provided with a circulation flow path 24 sending hydrogen exhausted from a fuel cell FC back to the fuel cell FC, and a purge valve 25 for hydrogen for exhausting hydrogen in the circulation flow path 24 outside. The fuel cell system S is further provided with a pressure sensor 4 detecting remaining pressure of the hydrogen in the circulation flow path 24 at generation stoppage of the fuel cell FC, and an ECU 3 setting an opening time of the purge valve for hydrogen 25 according to a signals output from the pressure sensor 4 and controlling it so as to exhaust a given volume of hydrogen outward by opening the purge valve 25 during the opening time. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
TECHNICAL FIELD The present invention relates to a fuel cell system that effectively discharges water remaining therein when power generation is stopped in order to smoothly start a fuel cell in a low-temperature environment.
[0002]
[Prior art]
Conventionally, in a fuel cell system, when a power generation is stopped, a purge valve for discharging hydrogen provided in a hydrogen electrode side flow path of the fuel cell is opened, so that condensed water remaining inside the fuel cell during power generation is reduced to a residual pressure of hydrogen. The method of draining using such as was taken. In this method, the residual water is discharged by opening the purge valve for a certain time immediately after the power generation is stopped. Incidentally, as another method, there is a method in which the output current of the fuel cell is controlled based on the amount of remaining water in the fuel cell to improve the evaporation rate and efficiently remove the remaining water (for example, And Patent Document 1).
[0003]
[Patent Document 1]
JP-A-2002-246053 (Page 2, FIG. 1)
[0004]
[Problems to be solved by the invention]
By the way, in the above-mentioned method of draining residual moisture by using the residual pressure of hydrogen, the purge valve is opened for a certain time immediately after the power generation is stopped, so that the amount of hydrogen discharged from the purge valve depends on the residual pressure at that time. Varies depending on Therefore, the amount of air for diluting the hydrogen discharged from the purge valve and releasing it to the atmosphere is set to the maximum value of the estimated amount of discharged hydrogen in order to keep the hydrogen concentration after the dilution below a certain value. It was necessary to set according to. If the amount of air is set in accordance with the maximum value of the amount of discharged hydrogen in this manner, a large amount of air is sent even when a small amount of hydrogen is discharged, and energy is wasted by that amount. Was.
[0005]
Further, when the opening time of the purge valve is set short to keep the maximum value of the discharged hydrogen amount low so as not to waste energy as described above, when the residual pressure of hydrogen is low, the residual moisture is reduced. There was a risk that the water could not be drained sufficiently.
[0006]
Accordingly, an object of the present invention is to prevent the wasteful consumption of air for dilution by making the amount of hydrogen discharged from the purge valve constant, and to ensure the residual water content even when the residual pressure of hydrogen is low. It is an object of the present invention to provide a fuel cell system capable of discharging fuel to a fuel cell.
[0007]
[Means for Solving the Problems]
According to a first aspect of the present invention that solves the above-mentioned problems, a circulation flow path for returning hydrogen discharged from the fuel cell to the fuel cell again, and a purge for discharging hydrogen in the circulation flow path to the outside A fuel cell system comprising: a valve; a detection unit configured to detect a residual pressure of hydrogen in the fuel cell or the circulation channel when power generation of the fuel cell is stopped; and a signal output from the detection unit. And a control device for controlling the discharge of hydrogen to the outside by setting the open time of the purge valve based on the above, and opening the purge valve during the open time.
[0008]
According to the first aspect of the invention, when the power generation of the fuel cell is stopped, the detecting means detects the residual pressure of hydrogen in the fuel cell or the circulation flow path and outputs a signal to the control device. The control device sets the opening time of the purge valve based on a signal from the detection means, for example, using a predetermined map, and opens the purge valve during this opening time to discharge hydrogen to the outside.
[0009]
According to a second aspect of the present invention, in the configuration of the first aspect, the control device prohibits the opening of the purge valve when the residual pressure of the hydrogen detected by the detection unit is equal to or less than a predetermined value. The purge valve is controlled so as to perform the operation.
[0010]
According to the second aspect of the present invention, in addition to the operation of the first aspect of the present invention, when the detecting means detects that the residual pressure of hydrogen is equal to or lower than a predetermined value when the power generation of the fuel cell is stopped, Prohibits the opening of the purge valve based on the signal from this detecting means.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the fuel cell system according to the present invention will be described in detail with reference to the drawings. In the drawings to be referred to, FIG. 1 is a configuration diagram showing a fuel cell system according to the present invention, and FIG. 2 is a diagram showing a map referred to by the ECU in FIG. FIG. 3 is a flowchart showing the operation of the ECU shown in FIG. 1, and FIG. 4 is a graph (a) showing the relationship between the residual pressure in the circulation flow path and time shown in FIG. 1 and the time shown in FIG. FIG. 5B is a sequence diagram illustrating a power generation state of the fuel cell corresponding to the axis, and FIG. 4C is a sequence diagram illustrating an operation state of the hydrogen purge valve corresponding to the time axis of FIG.
[0012]
As shown in FIG. 1, the fuel cell system S includes a fuel cell FC that supplies current to the traveling motor M, an air supply system 1 that supplies air to the fuel cell FC, and a hydrogen cell that supplies hydrogen to the fuel cell FC. It mainly includes a supply system 2 and an ECU (control device) 3 that controls various devices. The air supply system 1 includes a supercharger S / C that compresses and supplies air, and air for guiding air from the supercharger S / C to the fuel cell FC and guiding air discharged from the fuel cell FC to the outside. The apparatus mainly includes a flow path 11 and an air purge valve 12 that is appropriately opened and closed to discharge air in the air flow path 11.
[0013]
The hydrogen supply system 2 mainly includes a hydrogen tank T, a hydrogen supply flow path 21, a shutoff valve 22, an ejector 23, a pressure sensor (detection means) 4, a circulation flow path 24, a circulation pump P, and a hydrogen purge valve 25. ing. The hydrogen tank T is filled with hydrogen as a fuel gas, and this hydrogen is discharged to the fuel cell FC by opening the shut-off valve 22 and an electromagnetic valve (not shown) provided in the hydrogen tank T. It is supposed to be. The ejector 23 mixes the hydrogen from the hydrogen tank T with the hydrogen returned from the fuel cell FC, and re-supplies this to the fuel cell FC to circulate the hydrogen.
[0014]
The circulation flow path 24 is a flow path for returning the hydrogen discharged from the fuel cell FC to the fuel cell FC via the ejector 23 again. The pressure sensor 4 is attached to a portion near the inlet of the fuel cell FC to which hydrogen is supplied, and a circulation pump P and a purge valve 25 for hydrogen are attached to a portion near the outlet of the fuel cell FC. Have been. The flow path connecting the inlet of the fuel cell FC and the ejector 23 functions as a hydrogen supply flow path 21 for guiding the hydrogen from the hydrogen tank T to the fuel cell FC, and also re-uses the hydrogen discharged from the fuel cell FC. It also functions as a circulation channel 24 returning to the fuel cell FC.
[0015]
The pressure sensor 4 detects the remaining pressure of hydrogen in the circulation channel 24 when the power generation of the fuel cell FC is stopped. The circulation pump P circulates hydrogen in a predetermined direction (counterclockwise in the figure) in the circulation channel 24. The hydrogen purge valve 25 appropriately discharges hydrogen and residual moisture in the fuel cell FC and the circulation flow path 24 to the outside. Further, the hydrogen purge valve 25 is disposed at a lower position in consideration of the water discharging property of the fuel cell system S, that is, at a position where residual water in the fuel cell FC and the circulation flow path 24 is likely to accumulate. .
[0016]
The ECU 3 controls the components of the fuel cell system S, mainly the supercharger S / C, the air purge valve 12, the shutoff valve 22, the circulation pump P, and the hydrogen purge valve 25. In particular, the ECU 3 sets the opening time of the hydrogen purge valve 25 based on a signal output from the pressure sensor 4 when the power generation of the fuel cell FC is stopped, and opens the hydrogen purge valve 25 during this opening time. This controls a certain amount of hydrogen to the outside. Specifically, the ECU 3 sets the opening time such that the higher the pressure, the shorter the opening time, based on the signal (pressure) output from the pressure sensor 4 using the map shown in FIG.
[0017]
The ECU 3 constantly monitors the pressure in the circulation channel 24 via the pressure sensor 4 after the power generation of the fuel cell FC is stopped. When the residual pressure of hydrogen detected by the pressure sensor 4 is equal to or lower than a predetermined value, the hydrogen purge valve 25 is controlled so that the opening of the hydrogen purge valve 25 is prohibited. The threshold value for inhibiting the opening of the hydrogen purge valve 25, that is, the predetermined value may be set to any number. However, in the present embodiment, the inside of the hydrogen supply system 2 is appropriately sealed with hydrogen ( For this reason, the value will be described as a value slightly higher than 140 kPa.
[0018]
Next, a method of draining residual moisture by the fuel cell system S will be described mainly with reference to FIGS.
As shown in FIG. 3, when the power generation of the fuel cell FC stops (IG OFF), first, a control signal is output from the ECU 3 to the shut-off valve 22, and the shut-off valve 22 is closed based on the control signal (see FIG. 1). . Next, when the ECU 3 reads a signal (residual pressure of hydrogen) output from the pressure sensor 4, the ECU 3 sets an opening time of the hydrogen purge valve 25 based on the signal with reference to a map shown in FIG. Then, the hydrogen purge valve 25 is opened during this opening time (step S2).
[0019]
Thereafter, the ECU 3 determines whether the residual pressure of hydrogen in the circulation flow path 24 is equal to or lower than a predetermined value (step S3). If it is determined in step S3 that the remaining pressure is higher than the predetermined value (No), the ECU 3 determines whether the opening time set in step S1 has elapsed (step S4). If it is determined in step S4 that the release time has not elapsed (No), the process returns to step S3 again.
[0020]
If it is determined in step S3 that the remaining pressure is equal to or lower than the predetermined value (Yes), or if it is determined in step S4 that the open time has elapsed (Yes), the hydrogen purge valve 25 is closed by the ECU 3 ( Step S5), the drainage operation in the fuel cell system S ends.
[0021]
The control method by the ECU 3 will be described in more detail. As shown in FIGS. 4B and 4C, when the power generation of the fuel cell FC is stopped (IG OFF) and the hydrogen purge valve 25 is opened, As shown in the graph of FIG. 4A, the residual pressure in the circulation channel 24 gradually decreases. If the remaining pressure becomes equal to or less than a predetermined value before the opening time (map value) set in the map shown in FIG. 2 elapses, it is indicated by a dotted line in FIG. Thus, the purge valve 25 for hydrogen is closed, and the residual pressure in the circulation flow path 24 is maintained at a predetermined value not lower than 140 kPa.
[0022]
As described above, the following effects can be obtained in the present embodiment.
Since the hydrogen purge valve 25 is opened for an opening time appropriately set based on the value of the residual pressure in the circulation flow path 24, a fixed amount of hydrogen can be discharged from the hydrogen purge valve 25. Therefore, it is not necessary to set the dilution air more than necessary, so that the wasteful consumption is prevented, and the residual moisture can be reliably discharged even when the residual pressure of hydrogen is low.
When the residual pressure of hydrogen in the circulation flow path 24 becomes equal to or lower than a predetermined value, the hydrogen purge valve 25 is closed, so that the pressure in the circulation flow path 24 does not drop more than necessary. It is possible to reliably prevent air or the like from being sucked into the inside.
[0023]
As described above, the present invention is not limited to the above embodiment, but may be embodied in various forms.
In the present embodiment, the opening time is set using the map. However, the present invention is not limited to this. For example, the opening time is determined based on the pressure value output from the pressure sensor 4 under various conditions (the purge valve for hydrogen). 25 may be set so as to be calculated each time. Further, even when the hydrogen supply system 2 is not used for a while, the inside of the hydrogen supply system 2 is appropriately sealed (filled) with hydrogen, so that it is easy to restart.
[0024]
【The invention's effect】
According to the first aspect of the present invention, since a fixed amount of hydrogen is discharged from the purge valve regardless of the residual pressure of hydrogen, wasteful consumption of air for dilution is prevented, and the residual pressure of hydrogen is reduced. Even when it is low, residual water can be reliably discharged.
[0025]
According to the second aspect of the invention, in addition to the effect of the first aspect, when the residual pressure of hydrogen in the fuel cell or the circulation flow path is equal to or lower than a predetermined value, the purge valve does not open. The pressure in the fuel cell or the circulation channel will not be reduced more than necessary, and it is possible to reliably prevent air or the like from being sucked into the circulation channel or the like due to the negative pressure.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing a fuel cell system according to the present invention.
FIG. 2 is a view showing a map referred to by an ECU of FIG. 1;
FIG. 3 is a flowchart showing an operation of the ECU of FIG. 1;
4 is a graph (a) showing the relationship between the residual pressure in the circulation flow path and time in FIG. 1 and a sequence diagram (b) showing a power generation state of the fuel cell corresponding to the time axis in FIG. 4 (a). FIG. 5C is a sequence diagram (c) illustrating an operation state of the hydrogen purge valve corresponding to the time axis of FIG.
[Explanation of symbols]
S Fuel cell system M Running motor FC Fuel cell T Hydrogen tank P Circulation pump 1 Air supply system 2 Hydrogen supply system 21 Hydrogen supply flow path 22 Shutoff valve 23 Ejector 24 Circulation flow path 25 Hydrogen purge valve 3 ECU (control device)
4 Pressure sensor (detection means)

Claims (2)

A circulation flow path for returning hydrogen discharged from the fuel cell to the fuel cell again;
A purge valve for discharging hydrogen in the circulation flow path to the outside,
When power generation of the fuel cell is stopped, a detecting unit that detects a residual pressure of hydrogen in the fuel cell or the circulation flow path,
A control device is provided for setting an open time of the purge valve based on a signal output from the detection means, and controlling to discharge hydrogen to the outside by opening the purge valve during the open time. A fuel cell system, characterized in that: 2. The control device according to claim 1, wherein the control device controls the purge valve so as to prohibit the opening of the purge valve when the residual pressure of the hydrogen detected by the detection unit is equal to or less than a predetermined value. Fuel cell system.

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