Fuel cell system

Abstract

To provide a fuel cell system that suppresses a decrease in the accuracy of control of the flow rate of fuel gas supplied to a fuel cell.SOLUTION: A fuel cell system includes a fuel cell, a linear solenoid valve that injects fuel gas to be supplied to the fuel cell, an exhaust valve that exhausts fuel off-gas discharged from the fuel cell, and a control device that opens the exhaust valve when hunting of the opening degree of the linear solenoid valve is detected.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a fuel cell system. [Background technology]

[0002] There is a fuel cell system equipped with a linear solenoid valve that injects fuel gas to be supplied to the fuel cell (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-087520 Summary of the Invention [Problem to be solved by the invention]

[0004] If the opening of the linear solenoid valve fluctuates, there is a risk that the accuracy of controlling the flow rate of the fuel gas supplied to the fuel cell will decrease.

[0005] Therefore, an object of the present invention is to provide a fuel cell system that suppresses a decrease in the accuracy of control of the flow rate of fuel gas supplied to the fuel cell. [Means for solving the problem]

[0006] The above object can be achieved by a fuel cell system comprising a fuel cell, a linear solenoid valve that injects fuel gas to be supplied to the fuel cell, an exhaust valve that exhausts fuel off-gas discharged from the fuel cell, and a control device that opens the exhaust valve when hunting of the opening degree of the linear solenoid valve is detected. [Effects of the Invention]

[0007] It is possible to provide a fuel cell system that suppresses a decrease in the accuracy of control of the flow rate of fuel gas supplied to the fuel cell. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a configuration diagram of a fuel cell system. [Figure 2] 4 is a flowchart illustrating an example of opening hunting suppression control. [Figure 3] 4 is a timing chart illustrating an example of opening hunting suppression control. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Fuel cell system configuration] Fig. 1 is a configuration diagram of a fuel cell system 1. The fuel cell system 1 is mounted on a vehicle and includes an ECU (Electronic Control Unit) 3, a fuel cell (hereinafter referred to as FC) 4, an oxidant gas supply system 10, and a fuel gas supply system 20. The fuel cell system 1 is mounted on the vehicle. Electric power generated by the FC 4 is supplied to a motor that is a drive source for running the vehicle.

[0010] The FC4 is composed of a stack of multiple solid polymer electrolyte unit cells that generate electricity when supplied with oxidant gas and fuel gas. The FC4 contains a cathode flow path 4c through which the oxidant gas flows and an anode flow path 4a through which the fuel gas flows. The unit cell is composed of a membrane electrode assembly and a cathode-side separator and an anode-side separator that sandwich the assembly. The cathode flow path 4c is defined primarily between the membrane electrode assembly and the cathode-side separator, and is a space through which the oxidant gas can flow. The anode flow path 4a is defined between the membrane electrode assembly and the anode-side separator, and is a space through which the fuel gas can flow. The membrane electrode assembly includes an electrolyte membrane and catalyst layers formed on both sides of the electrolyte membrane.

[0011] The oxidant gas supply system 10 supplies air containing oxygen as an oxidant gas to the FC4, and includes a supply pipe 11, a discharge pipe 12, a bypass pipe 13, an air compressor 14, a bypass valve 15, an intercooler 16, and a backpressure valve 17. The supply pipe 11 is connected to the inlet of the cathode flow path 4c of the FC4. The discharge pipe 12 is connected to the outlet of the cathode flow path 4c of the FC4. The bypass pipe 13 connects the supply pipe 11 and the discharge pipe 12. The bypass valve 15 is provided at the connection between the supply pipe 11 and the bypass pipe 13. The bypass valve 15 switches the communication state between the supply pipe 11 and the bypass pipe 13. The air compressor 14, the bypass valve 15, and the intercooler 16 are arranged on the supply pipe 11 in this order from upstream to downstream. The backpressure valve 17 is arranged on the discharge pipe 12, upstream of the connection between the discharge pipe 12 and the bypass pipe 13. The air compressor 14 supplies air containing oxygen as an oxidant gas to the FC4 via a supply pipe 11. The oxidant gas supplied to the FC4 is discharged via a discharge pipe 12. An intercooler 16 cools the oxidant gas supplied to the FC4. A back pressure valve 17 adjusts the back pressure on the cathode side of the FC4. The operation of the air compressor 14, bypass valve 15, and back pressure valve 17 is controlled by an ECU 3. The ECU 3 adjusts the opening of the bypass valve 15 and back pressure valve 17, thereby adjusting the flow rate of the oxidant gas supplied from the air compressor 14 to the FC4.

[0012] The fuel gas supply system 20 supplies hydrogen gas as fuel gas to the FC4, and includes a tank 20T, a supply pipe 21, a circulation pipe 22, a discharge pipe 23, a tank valve 24, a pressure regulating valve 25, an injector (hereinafter referred to as INJ) 26a, a linear solenoid valve (hereinafter referred to as LSV) 26b, a pressure sensor P, a gas-liquid separator 27, a discharge valve 28, and a multi-nozzle ejector (hereinafter referred to as MEJ) 29. The tank 20T and the inlet of the anode flow path 4a of the FC4 are connected by the supply pipe 21. Hydrogen gas, which is fuel gas, is stored in the tank 20T. The tank valve 24, the pressure regulating valve 25, the INJ 26a and the LSV 26b, and the MEJ 29 are arranged in this order from the upstream side of the supply pipe 21. The INJ 26a and the LSV 26b are respectively provided at portions of the supply pipe 21 where they partially branch off from each other. The pressure sensor P detects the pressure in the supply pipe 21 downstream of the INJ 26a and the LSV 26b, in other words, the inlet pressure of the FC4. With the tank valve 24 open, the opening of the pressure regulating valve 25 is adjusted, and at least one of the INJ 26a and the LSV 26b is driven to inject fuel gas. The injected fuel gas passes through the MEJ 29 and is supplied to the FC4.

[0013] The INJ 26a is an on-off valve that can control the opening of its injection port only between fully closed and fully open positions and intermittently injects hydrogen gas. The injection amount of the INJ 26a is set to be smaller than the injection amount of the LSV 26b.

[0014] The LSV 26b is a valve that opens and closes the injection orifice by driving a linear solenoid. The LSV 26b is an injection amount adjustment valve (flow rate adjustment valve) that controls the opening of the injection orifice to maintain a predetermined opening between fully closed opening (opening 100%) and fully open opening (opening 0%), and can adjust the injection amount (flow rate) of fuel gas to a predetermined amount. Note that the "predetermined opening" is a value that changes depending on the operating conditions, and the "predetermined amount" is an amount that corresponds to the required power generation amount.

[0015] The circulation pipe 22 connects the outlet of the anode flow path 4a of the FC4 to the MEJ 29. A gas-liquid separator 27 is provided in the circulation pipe 22. The circulation pipe 22 is a pipe for returning fuel gas to the FC4. When fuel gas injected from at least one of the INJ 26a and the LSV 26b passes through the MEJ 29, negative pressure is generated within the MEJ 29. Due to this negative pressure, fuel off-gas discharged from the FC4 is drawn into the MEJ 29 via the gas-liquid separator 27. As a result, the fuel off-gas discharged from the FC4 is supplied to the FC4.

[0016] A discharge pipe 23 is connected to the gas-liquid separator 27. A discharge valve 28 is provided in the discharge pipe 23. The gas-liquid separator 27 separates and stores water from the fuel off-gas discharged from the FC4. When the discharge valve 28 opens, the water and fuel off-gas stored in the gas-liquid separator 27 are discharged to the outside of the fuel cell system 1 via the discharge pipe 23. The operation of the tank valve 24, the pressure regulating valve 25, the INJ 26a, the LSV 26b, and the discharge valve 28 is controlled by the ECU 3.

[0017] The ECU 3 includes a CPU (Central Processing Unit), ROM (Read Only Memory), and RAM (Random Access Memory). The ECU 3 is electrically connected to the accelerator position sensor 6, the air compressor 14, the bypass valve 15, the back pressure valve 17, the tank valve 24, the pressure regulating valve 25, the INJ 26a, the LSV 26b, and the discharge valve 28. The ECU 3 calculates the required output power for the FC4 based on the detection value of the accelerator position sensor 6 and the driving states of the vehicle accessories and the FC4 accessories. The ECU 3 also calculates a target current value for the FC4 according to the required output power for the FC4, and controls the flow rates of the oxidizer gas and fuel gas supplied to the FC4 by the air compressor 14, the INJ 26a, or the LSV 26b so that the output current value of the FC4 becomes the target current value.

[0018] [LSV opening hunting phenomenon] A hunting phenomenon, in which the opening of the LSV 26b fluctuates, may occur. The hunting phenomenon in opening is caused by the LSV 26b resonating when its natural frequency coincides with the air column resonance frequency in the supply pipe 21, the circulation pipe 22, and the like. The natural frequency of the LSV 26b varies depending on its opening and the pressure it receives. The air column resonance frequency varies depending on the gas composition and temperature in the supply pipe 21, the circulation pipe 22, and the like. This hunting phenomenon in opening may cause fluctuations in the flow rate and pressure of the fuel gas injected from the LSV 26b, which may reduce the control accuracy of the flow rate of the fuel gas supplied to the FC4. Therefore, the ECU 3 executes control to suppress the hunting phenomenon in opening of the LSV 26b as follows.

[0019] [Opening hunting suppression control] FIG. 2 is a flowchart illustrating the opening hunting suppression control. The ECU 3 determines whether or not the occurrence of hunting in the opening of the LSV 26b has been detected (step S1). The occurrence of hunting can be detected, for example, based on the inlet pressure of the FC4 detected by the pressure sensor P. For example, the ECU 3 may detect that hunting has occurred when the inlet pressure of the FC4 is higher than a pressure command value used for control by a predetermined value or more. Alternatively, the ECU 3 may detect that hunting has occurred when the amplitude of the current value corresponding to the opening of the LSV 26b is equal to or greater than a predetermined value. If the determination in step S1 is No, this control ends.

[0020] If the answer to step S1 is Yes, the ECU 3 opens the exhaust valve 28 (step S2). This causes the fuel off-gas to be discharged to the outside through the exhaust valve 28, reducing the pressure in the supply pipe 21 and the circulation pipe 22, and also reducing the pressure received by the LSV 26b. As a result, the natural frequency of the LSV 26b and the above-mentioned air column resonance frequency change, and the resonance of the LSV 26b stops. This also stops the hunting phenomenon of the opening degree of the LSV 26b.

[0021] The ECU 3 determines whether or not the hunting phenomenon has stopped (step S3). The method of detecting the stop of the hunting phenomenon may be, for example, when the pressure value detected by the pressure sensor P changes from a state higher than the pressure command value by a predetermined value or more to a state lower than the pressure command value. Alternatively, the ECU 3 may detect the stop of the hunting phenomenon when, for example, the amplitude of the current value corresponding to the opening degree of the LSV 26b becomes less than a predetermined value. If the answer is No in step S3, step S2 continues. If the answer is Yes in step S3, the ECU 3 closes the discharge valve 28 (step S4).

[0022] Fig. 3 is a timing chart illustrating the aperture hunting suppression control. Fig. 3 shows the transition of the power generation amount of the FC4, the hydrogen concentration in the supply pipe 21 and the circulation pipe 22, the current value of the LSV 26b, the inlet pressure of the FC4, and the open / close state of the discharge valve 28. The current value of the LSV 26b correlates with the aperture of the LSV 26b. If the power generation amount of the FC4 and the aperture of the LSV 26b are constant, the proportion of fuel off-gas in the supply pipe 21 and the circulation pipe 22 gradually increases compared to the proportion of fuel gas over time. As a result, the hydrogen concentration gradually decreases.

[0023] When the current value of LSV 26b fluctuates and a hunting phenomenon occurs in the opening of LSV 26b, the inlet pressure of FC4 also increases (time t1). When ECU 3 detects the hunting phenomenon and opens exhaust valve 28 (time t2), fuel off-gas is discharged to the outside, the inlet pressure of FC4 decreases, and the hydrogen concentration increases. When the hunting phenomenon stops, exhaust valve 28 closes (time t3). In this way, the hunting phenomenon in the opening of LSV 26b stops. This suppresses a decrease in the control accuracy of the flow rate of fuel gas supplied to FC4.

[0024] In the above embodiment, the hunting phenomenon is stopped by opening the exhaust valve 28. For example, the injection of fuel gas through the LSV 26b may be stopped and the injection of fuel gas through the INJ 26a may be started, or the LSV 26b may be opened and closed at a predetermined cycle. This also changes the natural frequency and air column resonance frequency of the LSV 26b, and stops the hunting phenomenon in the opening degree of the LSV 26b.

[0025] Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as described in the claims. [Explanation of symbols]

[0026] 1. Fuel cell system 3 ECU (control unit) 4 fuel cell 26b Linear solenoid valve 28 Discharge valve

Claims

[Claim 1] A fuel cell; a linear solenoid valve that injects fuel gas to be supplied to the fuel cell; an exhaust valve for exhausting fuel off-gas discharged from the fuel cell; a control device that opens the discharge valve when hunting of the opening degree of the linear solenoid valve is detected; A fuel cell system comprising:

Images