Fuel cell system

Abstract

Fuel cell system comprising: a fuel cell (10); a tank (20) adapted to store a fuel gas; a supply channel (30) designed to supply the fuel gas from the tank (20) to the fuel cell (10) through the supply channel (30); a first valve (32) configured to open and close the supply channel (30); a second valve (34) configured to open and close the supply channel (30), wherein the first valve (32) and the second valve (34) are provided in the order of first valve (32), second valve (34) in a direction from an upstream side to a downstream side; a pressure sensor (42) configured to detect a pressure in a detection target region (30a), which is a region of the supply channel (30) between the first valve (32) and the second valve (34); a heating unit (42h) designed to heat the pressure sensor (42); and a controller configured to cause the heating unit (42h) to heat the pressure sensor (42) in a state in which a detection value of the pressure sensor (42) is not greater than a predetermined threshold value, characterized by a bypass channel (60) having a forwarding region (60a) in which a pressure can be detected by the pressure sensor (42) and providing connection between the detection target region (30a) and the outside air; and a switching mechanism (62, 63) configured to switch between a first state in which the relaying area (60a) is in communication with the detection target area (30a) while being separated from the outside air, and a second state in which the relaying area (60a) is in communication with the detection target area (30a) while being in communication with the outside air, wherein the pressure sensor (42) is designed to detect the pressure in the detection target area (30a) through the forwarding area (60a), and the controller is configured to cause the heating unit (42h) to heat the pressure sensor (42) in a state in which the detection value is not greater than the predetermined threshold value and the fuel cell system is in the second state.

Description

BACKGROUND OF THE INVENTION 1. Field of the invention

[0001] The present invention relates to a fuel cell system. 2. Description of related technology

[0002] A fuel cell system in which a fuel gas is supplied from the interior of a tank to a fuel cell through a supply channel is known. In some cases, two valves are provided in this supply channel, on an upstream side and a downstream side relative to each other, and a pressure sensor is provided in the supply channel between the two valves (see, for example, JP 2013 - 177 910 A). JP 2011 - 2393 A discloses a fuel cell system according to the preamble of the independent claims. Further prior art relating to fuel cell systems can be found in JP 2009 - 59 573 A and JP 2011 - 204 411 A. BRIEF DESCRIPTION OF THE INVENTION

[0003] The pressure in the supply channel between the two valves tends to reach a relatively high pressure. This means that if the upstream valve opens while the downstream valve is closed, the fuel gas stored at high pressure in the tank will fill the supply channel between the two valves, building up pressure in the supply channel. Therefore, a pressure sensor that detects the pressure in such a valve is exposed to the high-pressure fuel gas. One possible result is that components of the fuel gas are firmly dissolved in the pressure sensor, reducing the detection accuracy of the pressure sensor.

[0004] The present invention provides a fuel cell system that can restore the detection accuracy of a pressure sensor.

[0005] A fuel cell system according to the present invention includes: a fuel cell; a tank configured to store a fuel gas; a supply channel configured to supply the fuel gas from the tank to the fuel cell through the supply channel; a first valve configured to open and close the supply channel; a second valve configured to open and close the supply channel, the first and second valves being provided in the order of first valve, second valve in a direction from an upstream side to a downstream side; a pressure sensor configured to detect a pressure in a detection target region, which is a region of the supply channel between the first valve and the second valve; a heating unit configured to heat the pressure sensor;and a controller configured to cause the heating unit to heat the pressure sensor in a state where a detection value of the pressure sensor is not greater than a predetermined threshold;

[0006] In a first embodiment of the invention, the fuel cell system may further comprise: a bypass channel having a relay region in which a pressure is detectable by the pressure sensor and providing communication between the detection target region and the outside air; and a switching mechanism configured to switch between a first state in which the relay region communicates with the detection target region while being separated from the outside air, and a second state in which the relay region is separated from the detection target region while being in communication with the outside air.The pressure sensor may be configured to detect the pressure in the detection target range via the relay range, and the controller may be configured to cause the heating unit to heat the pressure sensor in a state where the detection value is not greater than the predetermined threshold and the fuel cell system is in the second state.

[0007] In a second aspect of the invention, the fuel cell system may further comprise: a bypass channel having a relay region in which a pressure is detectable by the pressure sensor and providing communication between the detection target region and a downstream region of the supply channel located further downstream than the second valve; and a switching mechanism configured to switch between a first state in which the relay region communicates with the detection target region while being disconnected from the downstream region, and a second state in which the relay region is disconnected from the detection target region while being connected to the downstream region.The pressure sensor may be configured to be capable of detecting the pressure in the detection target range via the relay range, and the controller may be configured to cause the heating unit to heat the pressure sensor in a state where the detection value is not greater than the predetermined threshold and the fuel cell system is in the second state.

[0008] Heating the pressure sensor in a low-pressure environment where the pressure sensor's detection value is not greater than the predetermined threshold can promote the release of components of the fuel gas that are solidly dissolved in the pressure sensor from the pressure sensor. Thus, the reduced detection accuracy of the pressure sensor can be restored.

[0009] The controller may be configured to cause the heating unit to heat the pressure sensor in a state where the detection value is not greater than the predetermined threshold and the first valve is closed.

[0010] The fuel cell system may further include an injection valve provided in the supply channel further downstream than the second valve and configured to inject the fuel gas on the downstream side. The controller may be configured to control the detection value so that it is not greater than the predetermined threshold by causing the injection valve to inject the fuel gas in a state where the first valve is closed and the second valve is open.

[0011] The fuel cell system may further include an injection valve provided in the bypass passage further downstream than the switching mechanism and configured to inject the fuel gas on the downstream side. The controller may be configured to control the detection value so that it is not greater than the predetermined threshold by causing the injection valve to inject the fuel gas in the second state.

[0012] The present invention can provide a fuel cell system that can restore the detection accuracy of a pressure sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Features, advantages and technical and industrial significance of exemplary embodiments of the invention are described below with reference to the accompanying drawings, in which like reference numerals designate like elements and wherein: Fig. 1 is a view illustrating a fuel gas supply line of a fuel cell system in an embodiment; Fig. 2 is a schematic sectional view of a pressure sensor; Fig. 3A is a graph showing changes over time in the error of a detection value of the pressure sensor; Fig. 3B is a graph showing a failure recovery speed of four samples of the pressure sensor; Fig. 4 is an example of a flowchart of controlling recovery in the embodiment; Fig. 5 is an example of a timing chart showing control of recovery in the embodiment; Fig. 6 is a view illustrating a fuel gas supply line of a fuel cell system in a first modified example; Fig. 7 is an example of a flowchart showing the control of recovery in the first modified example; Fig. 8 is an example of a timing chart showing the control of recovery in the first modified example; Fig. 9 is a view illustrating a fuel gas supply line of a fuel cell system in a second modified example; Fig. 10 is an example of a flowchart showing the control of recovery in the second modified example; Fig. 11 is an example of a timing chart showing the control of recovery in the second modified example; Fig. 12A is a view illustrating a fuel gas supply line of a fuel cell system in a third modified example; Fig. 12B is a view illustrating a fuel gas supply line of a fuel cell system in a fourth modified example; and Fig. 12C is a view illustrating a fuel gas supply line of a fuel cell system in a fifth modified example. DETAILED DESCRIPTION OF EMBODIMENTS

[0014] Fig. 1 is a view illustrating a fuel gas supply line of a fuel cell system 1 in one embodiment. The fuel cell system 1 includes a fuel cell 10, a tank 20, a supply channel 30, a main shutoff valve 32, a pressure reducing valve 34, an injection valve 36, pressure sensors 42, 44, and so on. The fuel cell 10 has a stacked structure in which a plurality of individual cells are stacked, and is supplied with a fuel gas and an oxidizing gas to generate electric power through electrochemical reactions between the fuel gas and the oxidizing gas. Hydrogen gas, which is the fuel gas supplied to the fuel cell 10, is stored under high pressure in the tank 20. The supply channel 30 connects the fuel cell 10 and the tank 20, and the fuel gas is supplied from the tank 20 to the fuel cell 10 via the supply channel 30.The fuel gas and the oxidizing gas are supplied to the fuel cell 10 when a control unit 100 controls the operations of the relevant devices.

[0015] The fuel cell system 1 is provided with an exhaust passage through which the fuel gas is discharged into the outside air, a coolant supply passage through which a coolant is supplied to the fuel cell 10, and various components such as auxiliary devices. In this embodiment, the fuel cell system 1 is installed in a vehicle, and the fuel cell 10 supplies electric power to a drive motor of the vehicle.

[0016] The main shutoff valve 32, the pressure reducing valve 34, and the injection valve 36 are provided in the supply passage 30 in the order of the main shutoff valve 32, the pressure reducing valve 34, and the injection valve 36 in a direction from an upstream side to a downstream side. The main shutoff valve 32 controls the inflow of the fuel gas from the tank 20 to the upstream side of the supply passage 30. The pressure reducing valve 34 is a pressure reducing valve that adjusts the pressure of the fuel gas on the upstream side of the supply passage 30 to a set low pressure. In this embodiment, the main shutoff valve 32 and the pressure reducing valve 34 are examples of the "first valve" and the "second valve," respectively, and are provided in the order of "first valve" and "second valve" in the direction from the upstream side to the downstream side. The main shutoff valve 32 opens and closes the supply passage 30.The pressure reducing valve 34 opens halfway when the ambient pressure is high and opens fully when the ambient pressure is low. The injection valve 36 is an electromagnetically controlled injection valve that injects the fuel gas to the downstream side of the supply passage 30. The area of ​​the supply passage 30 between the main shutoff valve 32 and the pressure reducing valve 34 is referred to as a detection target area 30a.

[0017] The pressure sensor 42 is provided in the detection target area 30a and detects the gas pressure of the fuel gas discharged from the main shutoff valve 32. The pressure sensor 42 is provided with a heating element 42h, as described in detail later. The pressure sensor 44 is provided in the supply passage 30 between the pressure reducing valve 34 and the injection valve 36 and detects the pressure of the fuel gas reduced by the pressure reducing valve 34.

[0018] The control unit 100 is constituted by a computer including a central processing unit (CPU), a random access memory (RAM), a read-only memory (ROM), a storage device, etc. The control unit 100 corresponds to the "controller" that executes various processes and control operations by controlling the main shutoff valve 32, the pressure reducing valve 34, the injection valve 36, and the heater 42h based on the detection values ​​of the pressure sensors 42, 44, etc.

[0019] The Fig. 2 is a schematic sectional view of the pressure sensor 42. The pressure sensor 42 includes a body 42b, a diaphragm 42d, a strain gauge 42g, and the heating element 42h. The body 42b is made of metal and has a substantially cylindrical shape, and accommodates the diaphragm 42d, the strain gauge 42g, and the heating element 42h. An open end 42b1 of the body 42b on the leading end side is inserted into an outer wall in the detection target area 30a. The diaphragm 42d is made of metal, such as stainless steel, and includes a cylindrical part 42d1 and a thin-walled pressure-receiving part 42d3, which is integrated in the cylindrical part 42d1 and one end of the cylindrical part 42d1 on the upper side in the Fig. 2. The pressure-receiving part 42d3 undergoes distortion due to the pressure of the fuel gas introduced into the cylindrical part 42d1.

[0020] Four strain gauges 42g are provided on an outer surface of the pressure-sensing part 42d3. A stress applied to each strain gauge 42g changes according to the deflection of the pressure-sensing part 42d3, and the resistance of the strain gauge 42g changes accordingly. With this change in resistance value used as a differential output of a bridge circuit, an output proportional to the pressure of the fuel gas can be obtained. The heating element 42h is provided near the diaphragm 42d and the strain gauges 42g. The energization of the heating element 42h is controlled by the control unit 100, and the diaphragm 42d is heated when the heating element 42h is energized.

[0021] Here, a metal material is used for the diaphragm 42d. Therefore, when the diaphragm 42d is exposed to the fuel gas at high pressure, hydrogen, a component of the fuel gas, may be solidly dissolved in this metal material. As a result, the error in the detection value of the pressure sensor 42 may increase, and the detection accuracy may be reduced.

[0022] The Fig. Figure 3A is a graph showing changes over time in the error of the detection value of the pressure sensor 42. This graph shows changes in the error of the detection value of the pressure sensor 42 for the case where first a high-pressure fuel gas environment and then a low-pressure fuel gas environment are created around the pressure sensor 42. As shown in the Fig. As shown in Figure 3A, the error in the high-pressure fuel gas environment gradually increases over time. In contrast, in the subsequent low-pressure fuel gas environment, the error gradually decreases. One possible explanation for this result is that the high-pressure environment promotes the solid dissolution of hydrogen in the metal material of the pressure sensor 42 more than the low-pressure environment, and that the low-pressure environment causes the release of the hydrogen solidly dissolved in the metal material of the pressure sensor 42.

[0023] The Fig. 3B is a graph showing the error recovery speed of four samples A to D of the pressure sensor 42. These samples A to D were previously placed in a high-pressure fuel gas environment so that the error increased. The error increased in the order of the samples A to D. Samples A, C, and D were placed in a low-pressure fuel gas environment. Sample B was heated while placed in a low-pressure fuel gas environment. As a result, the fastest recovery speed was recorded for sample B heated in a low-pressure fuel gas environment. In this embodiment, the control unit 100 controls the recovery of the detection accuracy of the pressure sensor 42 by having the heating element 42h heat the pressure sensor 42 in a low-pressure environment.

[0024] The Fig. 4 is an example of a flowchart of the recovery control in this embodiment. The control unit 100 repeatedly executes this control in predetermined cycles. First, it is determined whether it is time to recover the detection accuracy of the pressure sensor 42 (step S1). If the determination is negative, the current control is terminated. This negative determination is made when a recovery request flag is on and the vehicle ignition switch-off is detected. The ignition switch-off is detected based on an output signal of an ignition switch. The recovery request flag is switched from off to on when a travel distance of the vehicle reaches or exceeds a predetermined threshold, or when an elapsed time since the last execution of the recovery control reaches or exceeds a predetermined threshold.

[0025] These predetermined threshold values ​​can be corrected to become smaller as the period during which the outside air temperature is at or above a predetermined value while the vehicle is traveling is longer, or as the period during which the detection value of the pressure sensor 42 is at or above a predetermined value is longer. This is because the solid solution is further conveyed as the outside air temperature is higher while the vehicle is traveling and the period during which the pressure sensor 42 is exposed to the high-pressure fuel gas is longer. In this case, the period during which the detection value of an outside air temperature sensor is at or above a predetermined value is stored in a memory of the control unit 100, or the period during which the detection value of the pressure sensor 42 is at or above the predetermined value is stored in the memory of the control unit 100.

[0026] If the determination in step S1 is affirmative, the interior of the detection target area 30a is depressurized (step S3). Specifically, the fuel gas is injected through the injection valve 36 in a state where the main shutoff valve 32 is closed and the pressure reducing valve 34 is open, and thus the interior of the detection target area 30a is depressurized. As a result, the pressure around the pressure sensor 42 decreases. Meanwhile, the fuel gas and the oxidizing gas inside the system are discharged to the outside, so that the fuel cell 10 stops generating electric power.

[0027] Next, it is determined whether the detection value of the pressure sensor 42 has decreased to or below a threshold value P (step S5). If the determination is negative, the pressure relief continues. If the determination is positive, the pressure relief is stopped (step S7). Specifically, the injection of the fuel gas by the injection valve 36 is also stopped. Thus, the interior of the detection target area 30a is maintained in a predetermined pressure-relieved state.

[0028] Next, the pressure sensor 42 is heated (step S9). Specifically, the heating element 42h is energized to heat the diaphragm 42d and the strain gauges 42g. Thus, the diaphragm 42d and these strain gauges 42g are heated while the periphery of the pressure sensor 42 is in a depressurized state. In this way, it is possible to promote the release of hydrogen solidly dissolved in the metal material of the pressure sensor 42 and quickly restore the detection accuracy of the pressure sensor 42.

[0029] Next, it is determined whether the magnitude of change in the detection value of the pressure sensor 42 has decreased to or below a predetermined threshold ΔP over a predetermined time (step S11). The detection value of the pressure sensor 42 does not stabilize while the hydrogen solid-dissolved in the metal material of the pressure sensor 42 is released to the surrounding area because the pressure sensor 42 is heated. Therefore, if the magnitude of change in the detection value of the pressure sensor 42 has decreased to or below the predetermined threshold ΔP, it is determined that the hydrogen solid-dissolved in the metal material has been sufficiently released. If the determination is negative, heating of the pressure sensor 42 is continued.Since this determination is made with the main shutoff valve 32 closed, factors other than hydrogen release can be prevented from influencing the detection value of the pressure sensor 42, and thus the determination can be made accurately. Alternatively, in step S11, it can be determined whether the rate of change of the detection value of the pressure sensor 42 has decreased to or below a predetermined threshold.

[0030] If the determination in step S11 is affirmative, heating of the pressure sensor 42 is stopped based on the assumption that the solid solute has been removed and that the detection accuracy of the pressure sensor 42 has been restored (step S13). The above-described restoration request flag is switched from on to off.

[0031] Next, it is determined whether it is time to return to the original state (step S15). Specifically, it is determined whether the vehicle's ignition switch has been detected. The ignition switch is detected based on an output signal from the ignition switch. If the determination is negative, the process in step S15 is executed again.

[0032] If the determination in step S15 is affirmative, the main shutoff valve 32 is opened to return the state of the interior of the detection target area 30a to the high-pressure state before the pressure release (step S17). Thus, the fuel gas can be supplied to the fuel cell 10 through the pressure reducing valve 34 and the injection valve 36, and the fuel cell 10 can generate electric power.

[0033] The Fig. 5 is an example of a timing chart showing the recovery control in the embodiment. When the recovery request flag is on and ignition off is detected, at time t1, the main cut valve 32 is closed, and the fuel gas is injected through the injection valve 36 to start depressurization. When the detection value of the pressure sensor 42 decreases to or below the threshold value P at time t2, injection by the injection valve 36 is stopped, and heating of the pressure sensor 42 is started. Thus, at time t3, the change magnitude of the detection value of the pressure sensor 42 fluctuates and becomes unstable. When the change magnitude of the detection value of the pressure sensor 42 decreases to or below the threshold value ΔP at time t4, heating of the pressure sensor 42 is stopped.When ignition turn-on is detected at time t5, the main shutoff valve 32 opens, and the detection target area 30a returns to the original high-pressure state. The detection value of the pressure sensor 42 after time t5 is smaller than that before time t1. This is because before time t1, the detection value of the main shutoff valve 32 is larger than the actual pressure value due to the error, while after time t4, the error is eliminated, and the detection value is almost equal to the actual pressure value. Fig. 5 illustrates the case where the injection valve 36 also injects the fuel gas before the time t1 and the injection valve 36 injects the fuel gas immediately after the time t5, but the present invention is not limited to this example.

[0034] As described above, when the ignition shutdown is detected, the recovery control of the pressure sensor 42 is performed by closing the main shutoff valve 32. As long as the main shutoff valve 32 is closed, no additional fuel gas is supplied from the tank 20 to the fuel cell 10. Here, when the ignition shutdown is detected, the fuel cell 10 stops generating electric power after a lapse of at least a predetermined period. Therefore, performing the recovery control by closing the main shutoff valve 32 and starting the pressure relief when the fuel cell 10 is expected to stop generating electric power can restore the detection accuracy of the pressure sensor 42 without affecting the electric power generation by the fuel cell 10.

[0035] The present invention is not necessarily limited to the example in which the recovery control is performed when the ignition switch-off is detected. For example, when the vehicle is in an operating state where the amount of electric power stored in a secondary battery installed in the vehicle is at or above a predetermined value and the required amount of electric power generation by the fuel cell 10 is low, the opening and closing of the main shutoff valve 32, etc., can be controlled, and the depressurization of the interior of the detection target area 30a can be started.In other words, under the condition that the vehicle is in an operating state in which the depressurization of the interior of the detection target area 30a does not significantly affect the electric power generation by the fuel cell 10, the depressurization can be started and the control of the recovery of the pressure sensor 42 can be executed.

[0036] Next, fuel cell systems in modified examples will be described. Components and processes of the fuel cell systems in the modified examples, which are the same as those in the above-mentioned embodiment, are denoted by the same reference numerals to avoid overlapping descriptions.

[0037] Fig. 6 is a view illustrating a fuel gas supply line of a fuel cell system 1a in a first modified example. The fuel cell system 1a includes an exhaust passage 50, a bypass passage 60, an upstream shutoff valve 62, a downstream shutoff valve 63, and a pressure reducing valve 64. The exhaust passage 50 is a passage through which a fuel-off gas discharged from the fuel cell 10 is discharged to the outside air, and although not shown, the exhaust passage 50 is also provided in the fuel cell system 1. The bypass passage 60 communicates with the detection target area 30a at one end and with the exhaust passage 50 at the other end. Accordingly, the bypass passage 60 communicates with the outside air via the exhaust passage 50.The upstream shutoff valve 62, the downstream shutoff valve 63, and the pressure reducing valve 64 are provided in the bypass passage 60 in the order of upstream shutoff valve 62, downstream shutoff valve 63, and pressure reducing valve 64 in the direction from the upstream side to the downstream side. The upstream shutoff valve 62, the downstream shutoff valve 63, and the pressure reducing valve 64 are controlled by a control unit 100a. The pressure sensor 42 is provided in the bypass passage 60 between the upstream shutoff valve 62 and the downstream shutoff valve 63. In the first modified example, the area of ​​the bypass passage 60 between the upstream shutoff valve 62 and the downstream shutoff valve 63 is referred to as a relay area 60a, in which the pressure is detectable by the pressure sensor 42.

[0038] The upstream shutoff valve 62 and the downstream shutoff valve 63 are an example of the "switching mechanism" that switches between a first state in which the relay section 60a communicates with the detection target section 30a while being cut off from the outside air, and a second state in which the relay section 60a is cut off from the detection target section 30a while being connected to the outside air. Specifically, the first state is implemented when the upstream shutoff valve 62 is open and the downstream shutoff valve 63 is closed. The second state is implemented when the upstream shutoff valve 62 is closed and the downstream shutoff valve 63 is open. The pressure reducing valve 64 fully opens at a low pressure and half opens at a high pressure, and is thus open in both the first and second states.

[0039] In the first modified example, the fuel cell system is controlled to the first state when the recovery control is not executed. Therefore, the pressure in the relay region 60a is equal to the pressure in the detection target region 30a, and the pressure sensor 42 can detect the pressure in the detection target region 30a via the relay region 60a. Since the downstream shutoff valve 63 is closed, the fuel-off gas is prevented from flowing back through the outlet channel 50 into the bypass channel 60 and into the supply channel 30.

[0040] The Fig. 7 is an example of a flowchart showing the recovery control in the first modified example. The control unit 100a repeatedly executes this control in predetermined cycles. First, it is determined whether it is time to recover the detection accuracy of the pressure sensor 42 (step S1a). If the determination is negative, the current control is terminated. Unlike the above-mentioned embodiment, this determination is positive when no ignition shutdown is detected and the pressure sensor 42 recovery request flag is on.

[0041] If the determination in step S1a is affirmative, the interior of the relay section 60a is depressurized (step S3a). Specifically, the fuel cell system is switched to the second state, and the fuel gas in the relay section 60a is discharged into the outside air. Thus, the pressure in the relay section 60a decreases to substantially the same as the outside air pressure, and the periphery of the pressure sensor 42 is depressurized. Since the upstream shutoff valve 62 is closed, a part of the bypass channel 60 on the downstream side of the upstream shutoff valve 62 and the detection target section 30a are separated from each other. Thus, even when depressurization is performed, fuel gas can be continuously supplied from the tank 20 to the fuel cell 10 through the supply channel 30.

[0042] Next, if the determination in step S5 is affirmative, the pressure relief is stopped (step S7a), as in the above-mentioned embodiment. Specifically, the pressure reducing valve 64 is fully opened. Next, the processes in steps S9 to S13 are executed as in the above-mentioned embodiment. When the process in step S13 is executed, the fuel cell system is switched to the first state so that the pressure in the relay region 60a becomes equal to the pressure in the detection target region 30a, and the pressure in the relay region 60a is returned to the high pressure before the pressure relief (step S17a).

[0043] Thus, control of the recovery of the pressure sensor 42 can be performed even while the fuel gas is continuously supplied from the tank 20 to the fuel cell 10. Therefore, for example, it is possible to quickly recover the pressure sensor 42 from a reduction in detection accuracy even while the vehicle is traveling, and appropriately control the fuel cell system 1a based on the detection value of the pressure sensor 42 with the recovered accuracy.

[0044] The Fig. 8 is an example of a timing chart showing the recovery control in the first modified example. When the recovery request flag is turned on at time t1, the upstream shutoff valve 62 is closed and the downstream shutoff valve 63 is opened, and pressure relief is started by the pressure reducing valve 64. When the detection value of the pressure sensor 42 decreases to or below the threshold value P at time t2, heating of the pressure sensor 42 is started. Thus, at time t3, the change magnitude of the detection value of the pressure sensor 42 fluctuates and becomes unstable. When the change magnitude of the detection value of the pressure sensor 42 decreases to or below the threshold value ΔP at time t4, heating of the pressure sensor 42 is stopped.Then, at time t5, the upstream shutoff valve 62 is opened and the downstream shutoff valve 63 is closed, so that the pressure in the relay area 60a returns to the high pressure equal to the pressure in the detection target area 30a.

[0045] In the first modified example, the pressure reducing valve 64 may be omitted. This is because, when the recovery control is not performed, opening the upstream shutoff valve 62 and closing the downstream shutoff valve 63 can allow the pressure sensor 42 to detect the pressure in the detection target area 30a, and during the recovery control, closing the upstream shutoff valve 62 and opening the downstream shutoff valve 63 can depressurize the inside of the relay area 60a.

[0046] In the first modified example, the downstream shutoff valve 63 remains open during heating of the pressure sensor 42, however, the downstream shutoff valve 63 may instead remain closed.

[0047] The Fig. 9 is a view illustrating a fuel gas supply line of a fuel cell system 1b in a second modified example. In the second modified example, the area of ​​the supply passage 30 between the injection valve 36 and the fuel cell 10 is referred to as a downstream area 30b. The fuel cell system 1b includes a bypass passage 70, an upstream shutoff valve 72, a downstream shutoff valve 73, a pressure reducing valve 74, and an injection valve 76. The bypass passage 70 communicates with the detection target area 30a at one end and with the downstream area 30b at the other end.The upstream shutoff valve 72, the downstream shutoff valve 73, the pressure reducing valve 74, and the injection valve 76 are provided in the bypass passage 70 in the order of upstream shutoff valve 72, downstream shutoff valve 73, pressure reducing valve 74, and injection valve 76 in the direction from the upstream side to the downstream side. The pressure sensor 42 is provided in the bypass passage 70 between the upstream shutoff valve 72 and the downstream shutoff valve 73. In the second modified example, the area of ​​the bypass passage 70 between the upstream shutoff valve 72 and the downstream shutoff valve 73 is referred to as a relay area 70a, in which the pressure is detectable by the pressure sensor 42.

[0048] The upstream shutoff valve 72 and the downstream shutoff valve 73 are an example of the "switching mechanism" that switches between a first state in which the relaying section 70a communicates with the detection target section 30a while being disconnected from the downstream section 30b, and a second state in which the relaying section 70a is disconnected from the detection target section 30a while communicating with the downstream section 30b. Specifically, the first state is implemented when the upstream shutoff valve 72 is open and the downstream shutoff valve 73 is closed. The second state is implemented when the upstream shutoff valve 72 is closed and the downstream shutoff valve 73 is open. The pressure reducing valve 74 fully opens at a low pressure and half opens at a high pressure, and is thus open in both the first and second states.

[0049] In the second modified example, the fuel cell system is controlled to the first state when the recovery control is not executed. Therefore, the pressure in the relay region 70a is equal to the pressure in the detection target region 30a, and the pressure sensor 42 can detect the pressure in the detection target region 30a via the relay region 70a. When the recovery control is not executed, the downstream shutoff valve 73 is closed, and the injection valve 76 does not operate. Thus, the fuel gas injected from the injection valve 36 is prevented from flowing back through the bypass channel 70.

[0050] The Fig. 10 is an example of a flowchart showing the recovery control in the second modified example. A control unit 100b repeatedly executes this control in predetermined cycles. When step S1a is executed and the determination in step S1a is affirmative, the interior of the relay section 70a is depressurized (step S3b). Specifically, the upstream shutoff valve 72 is closed, the downstream shutoff valve 73 is opened, and the fuel gas is injected through the injection valve 76. Thus, the fuel gas in the relay section 70a is supplied to the fuel cell 10, and the periphery of the pressure sensor 42 is depressurized, while the fuel gas discharged from the relay section 70a can be effectively used by the fuel cell 10 for electric power generation.In addition, since the upstream shut-off valve 72 is closed, the fuel gas can be continuously supplied from the tank 20 to the fuel cell 10 through the supply channel 30.

[0051] Next, if the determination in step S5 is affirmative, the pressure relief is stopped (step S7b), as in the above-mentioned embodiment. Specifically, the pressure reducing valve 74 is fully opened. Next, the processes in steps S9 to S13 are executed as in the above-mentioned embodiment. When the process in step S13 is executed, the fuel cell system is switched to the first state so that the pressure in the relay region 70a becomes equal to the pressure in the detection target region 30a, and the pressure in the relay region 70a is returned to the high pressure before the pressure relief (step S17b).

[0052] The Fig. 11 is an example of a timing chart showing the recovery control in the second modified example. When the recovery request flag is turned on at time t1, the upstream shutoff valve 72 is closed and the downstream shutoff valve 73 is opened, and the fuel gas is injected through the injection valve 76 through the pressure reducing valve 74 to start depressurization. When the detection value of the pressure sensor 42 decreases to or below the threshold value P at time t2, depressurization is stopped and heating of the pressure sensor 42 is started. Thus, at time t3, the change magnitude of the detection value of the pressure sensor 42 fluctuates and becomes unstable. When the change magnitude of the detection value of the pressure sensor 42 decreases to or below the threshold value ΔP at time t4, heating of the pressure sensor 42 is stopped.Then, at time t5, the upstream shutoff valve 72 is opened and the downstream shutoff valve 73 is closed, so that the pressure in the relay area 70a returns to the high pressure equal to the pressure in the detection target area 30a.

[0053] Thus, in the second modified example, it is possible to effectively use the fuel gas by being able to carry out the control of the recovery of the pressure sensor 42 even while the fuel gas is continuously supplied from the tank 20 to the fuel cell 10.

[0054] The Fig. 12A is a view illustrating a fuel gas supply line of a fuel cell system 1' in a third modified example. The configuration of the third modified example is similar to that of the above-mentioned embodiment, except that the supply passage 30' is provided instead of the supply passage 30. The supply passage 30' includes a main passage 30m through which the fuel gas is supplied from the tank 20 to the fuel cell 10 and in which the main shutoff valve 32, the pressure reducing valve 34, and the injection valve 36 are arranged as described above, and a branch passage 30A branching from the main passage 30m and having one end closed. The pressure sensor 42 is provided in the branch passage 30A, not in the detection target area 30a. In this configuration, the pressure sensor 42 can also detect the pressure in the detection target area 30a through the branch passage 30A.The detection accuracy of the pressure sensor 42 can be restored by the same technique as in the above-mentioned embodiment.

[0055] The Fig. 12B is a view illustrating a fuel gas supply line of a fuel cell system 1a' in a fourth modified example. The configuration of the fourth modified example is similar to that of the first modified example described above, except that a three-way valve 62a is provided instead of the upstream shutoff valve 62 and the downstream shutoff valve 63, and a bypass passage 60' is provided instead of the bypass passage 60. The bypass passage 60' includes a main passage 60m that provides communication between the detection target area 30a and the outside air and in which the pressure reducing valve 64 is disposed as described above, and a branch passage 60A that branches off at a point in the main passage 60m that is further upstream than the pressure reducing valve 64 and whose other end is closed.The pressure sensor 42 is provided in the branch channel 60A and detects the pressure in the branch channel 60A. The three-way valve 62a is provided at the point where the branch channel 60A branches off from the main channel 60m. The three-way valve 62a is controlled by the control unit 100a'.

[0056] The three-way valve 62a is an example of the "switching mechanism" that switches between a first state in which the branch duct 60A communicates with the detection target area 30a while being cut off from the outside air, and a second state in which the branch duct 60A is cut off from the detection target area 30a while being cut off from the outside air. Specifically, the first state is implemented when the three-way valve 62a provides communication only between the branch duct 60A and the area of ​​the main duct 60m on the upstream side of the three-way valve 62a, and cuts off the area of ​​the main duct 60m on the downstream side of the three-way valve 62a from this upstream area and the branch duct 60A.The second state is implemented when the three-way valve 62a provides the connection only between the branch channel 60A and the area of ​​the main channel 60m on the downstream side of the three-way valve 62a and separates the area of ​​the main channel 60m on the upstream side of the three-way valve 62a from this area on the downstream side and the branch channel 60A.

[0057] In the fourth modified example, the fuel cell system is also controlled to the first state when the recovery control is not executed. In the first state, the branch channel 60A and the detection target area 30a communicate with each other through the area of ​​the main channel 60m upstream of the three-way valve 62a, so that the pressure in the branch channel 60A is equal to the pressure in the detection target area 30a. Thus, the pressure sensor 42 can detect the pressure in the detection target area 30a through the branch channel 60A, and so on.

[0058] During recovery control, the fuel cell system is switched to the second state. Therefore, the fuel gas in the branch duct 60A is discharged into the outside air through the main duct 60m in a state where the detection target area 30a and the branch duct 60A are separated from each other. Thus, the interior of the branch duct 60A is depressurized. In this configuration, the periphery of the pressure sensor 42 can also be depressurized.

[0059] The Fig.12C is a view illustrating a fuel gas supply line of a fuel cell system 1b' in a fifth modified example. The configuration of the fifth modified example is similar to that of the second modified example described above, but differs in that a three-way valve 72a is provided instead of the upstream shutoff valve 72 and the downstream shutoff valve 73, and that a bypass passage 70' is provided instead of the bypass passage 70. The bypass passage 70' includes a main passage 70m that provides communication between the detection target region 30a and the downstream region 30b and in which the pressure reducing valve 74 and the injection valve 76 are provided as described above, and a branch passage 70A that branches off at a point in the main passage 70m that is further upstream than the pressure reducing valve 74 and whose other end is closed.The pressure sensor 42 is provided in the branch channel 70A and detects the pressure in the branch channel 70A. The three-way valve 72a is provided at the point where the branch channel 70A branches off from the main channel 70m. The three-way valve 72a is controlled by the control unit 100b'.

[0060] The three-way valve 72a is an example of the "switching mechanism" that switches between a first state in which the branch channel 70A communicates with the detection target area 30a while being disconnected from the downstream area 30b, and a second state in which the branch channel 70A is disconnected from the detection target area 30a while communicating with the downstream area 30b. Specifically, the first state is implemented when the three-way valve 72a provides communication only between the branch channel 70A and the upstream area of ​​the main channel 70m from the three-way valve 72a, and disconnects the downstream area of ​​the main channel 70m from the upstream area and the branch channel 70A from the three-way valve 72a.The second state is implemented when the three-way valve 72a provides the connection only between the branch channel 70A and the area of ​​the main channel 70m on the downstream side of the three-way valve 72a and separates the area of ​​the main channel 70m on the upstream side of the three-way valve 72a from this area on the downstream side and the branch channel 70A.

[0061] In the fifth modified example, the fuel cell system is also controlled to the first state when the recovery control is not executed. In the first state, the branch channel 70A and the detection target area 30a communicate with each other through the area of ​​the main channel 70m upstream of the three-way valve 72a, so that the pressure in the branch channel 70A is equal to the pressure in the detection target area 30a. Thus, the pressure sensor 42 can detect the pressure in the detection target area 30a through the branch channel 70A, and so on.

[0062] When controlling the recovery, the fuel cell system is switched to the second state, and fuel is injected from the injection valve 76. Therefore, the fuel gas in the branch channel 70A is supplied to the fuel cell 10 in a state where the detection target area 30a and the branch channel 70A are separated from each other. Thus, the interior of the branch channel 70A is depressurized. In this configuration, the periphery of the pressure sensor 42 can also be depressurized.

[0063] Although the embodiment of the present invention has been described in detail above, the present invention is not limited to this specific embodiment, and various modifications and changes may be made thereto within the scope of the gist of the invention described in the claims.

[0064] The pressure sensor 42 is not limited to the strain gauge resistance-based pressure sensor described above, and may be any pressure sensor made of a metal material in which fuel gas components can be solidly dissolved, and which has an increasing detection error due to the solid solution. For example, the pressure sensor 42 may be any of the following: a piezoresistive semiconductor pressure sensor, an electric capacitance pressure sensor, and a resonant silicon pressure sensor.

[0065] In the above-mentioned embodiment and modified examples, the heating element 42h is provided inside the pressure sensor 42, but the present invention is not limited to this configuration. For example, a heating unit may be arranged on an outer surface of the pressure sensor 42, and the metal material of the pressure sensor 42 may be heated from the outer surface of the pressure sensor 42.

Claims

[1] Fuel cell system comprising: a fuel cell (10); a tank (20) adapted to store a fuel gas; a supply channel (30) designed to supply the fuel gas from the tank (20) to the fuel cell (10) through the supply channel (30); a first valve (32) configured to open and close the supply channel (30); a second valve (34) configured to open and close the supply channel (30), wherein the first valve (32) and the second valve (34) are provided in the order of first valve (32), second valve (34) in a direction from an upstream side to a downstream side; a pressure sensor (42) configured to detect a pressure in a detection target region (30a), which is a region of the supply channel (30) between the first valve (32) and the second valve (34); a heating unit (42h) designed to heat the pressure sensor (42); and a controller configured to cause the heating unit (42h) to heat the pressure sensor (42) in a state in which a detection value of the pressure sensor (42) is not greater than a predetermined threshold value, characterized by a bypass channel (60) having a forwarding region (60a) in which a pressure can be detected by the pressure sensor (42) and providing connection between the detection target region (30a) and the outside air; and a switching mechanism (62, 63) configured to switch between a first state in which the relaying area (60a) is in communication with the detection target area (30a) while being separated from the outside air, and a second state in which the relaying area (60a) is in communication with the detection target area (30a) while being in communication with the outside air, wherein the pressure sensor (42) is designed to detect the pressure in the detection target area (30a) through the forwarding area (60a), and the controller is configured to cause the heating unit (42h) to heat the pressure sensor (42) in a state in which the detection value is not greater than the predetermined threshold value and the fuel cell system is in the second state. [2] Fuel cell system comprising: a fuel cell (10); a tank (20) adapted to store a fuel gas; a supply channel (30) designed to supply the fuel gas from the tank (20) to the fuel cell (10) through the supply channel (30); a first valve (32) configured to open and close the supply channel (30); a second valve (34) configured to open and close the supply channel (30), wherein the first valve (32) and the second valve (34) are provided in the order of first valve (32), second valve (34) in a direction from an upstream side to a downstream side; a pressure sensor (42) configured to detect a pressure in a detection target region (30a), which is a region of the supply channel (30) between the first valve (32) and the second valve (34); a heating unit (42h) designed to heat the pressure sensor (42); and a controller configured to cause the heating unit (42h) to heat the pressure sensor (42) in a state in which a detection value of the pressure sensor (42) is not greater than a predetermined threshold value, characterized by a bypass channel (70) having a forwarding region (70a) in which a pressure can be detected by the pressure sensor (42) and providing communication between the detection target region (30a) and a downstream region (30b) of the supply channel (30) located further downstream than the second valve (34); and a switching mechanism (72, 73) configured to switch between a first state in which the relay region (70a) is in communication with the detection target region (30a) while being separated from the downstream region (30b), and a second state in which the relay region (70a) is separated from the detection target region (30a) while being in communication with the downstream region (30b), wherein the pressure sensor (42) is designed to detect the pressure in the detection target area (30a) through the forwarding area (70a), and the controller is configured to cause the heating unit (42h) to heat the pressure sensor (42) in a state in which the detection value is not greater than the predetermined threshold value and the fuel cell system is in the second state. [3] The fuel cell system according to claim 1 or 2, wherein the controller is configured to cause the heating unit (42h) to heat the pressure sensor (42) in a state where the detection value is not greater than the predetermined threshold and the first valve (32) is closed. [4] The fuel cell system according to claim 3, further comprising an injection valve (36) provided in the supply passage (30) further downstream than the second valve (34) and configured to inject the fuel gas to the downstream side, wherein the controller is configured to control the detection value so as not to be greater than the predetermined threshold value by causing the injection valve (36) to inject the fuel gas in a state where the first valve (32) is closed and the second valve (34) is open. [5] The fuel cell system according to claim 2, further comprising an injection valve (76) provided in the supply passage (70) further downstream than the switching mechanism (72, 73) and configured to inject the fuel gas to the downstream side, wherein the controller is configured to control the detection value so as not to be greater than the predetermined threshold value by causing the injection valve (76) to inject the fuel gas in the second state.

Images