JP6973318B2 - Fuel cell system - Google Patents

Description

The present invention relates to a fuel cell system.

Patent Document 1 discloses a power source cooling device in which a heat insulating expansion valve and a heat exchanger are provided in a hydrogen supply pipe that supplies hydrogen gas from a hydrogen cylinder to a fuel cell stack. The adiabatic expansion valve lowers the temperature of the hydrogen gas by adiabatic expansion. In the heat exchanger, heat exchange is performed between the cooling water that cools the fuel cell stack and the low-temperature hydrogen gas.

Japanese Unexamined Patent Publication No. 2006-73404

There is a fuel cell system in which an expander for generating cold heat of hydrogen by adiabatic expansion of hydrogen and obtaining expansion energy as power is provided in a hydrogen supply pipe. In this fuel cell system, hydrogen is introduced into the supply pipe in a high pressure state, so that high pressure hydrogen may leak to the downstream side of the expander after the fuel cell system is started and stopped. When high-pressure hydrogen leaks to the downstream side of the expander, the difference between the pressure on the upstream side of the expander and the pressure on the downstream side of the expander becomes small. Here, when the fuel cell system is restarted, the operation of the expander may become unstable because the pressure difference between the upstream side and the downstream side of the expander is small. In other words, there is room for improvement in order to obtain a fuel cell system that can stably operate the expander when it is restarted.

In consideration of the above facts, an object of the present invention is to obtain a fuel cell system capable of stably operating an expander when restarted.

The fuel cell system according to the present invention according to claim 1 has a supply path in which hydrogen is supplied from a hydrogen tank to the fuel cell and in the supply path, which is in contact with a heat exchanger in contact with a cooling path of the fuel cell. An expander provided on the upstream side of the heat exchanger to insulate and expand hydrogen, an on-off valve provided on the upstream side of the expander in the supply path, and a downstream side of the expander in the supply path. A detection means for detecting the pressure of hydrogen in the supply passage, and a pressure lowering means provided on the downstream side of the expander in the supply passage to reduce the pressure of hydrogen in the supply passage. When the fuel cell is started and the detected pressure detected by the detecting means is equal to or higher than the set pressure, the on-off valve is closed and the pressure drops until the detected pressure becomes lower than the set pressure. It has a control means for controlling the operation of the means and controlling the closing of the on-off valve when the fuel cell is started and stopped.

In the fuel cell system according to the present invention according to claim 1, in the activated state, hydrogen supplied from the hydrogen tank to the supply path is adiabatically expanded in the expander to generate cold heat of hydrogen and as power. Expansion energy is obtained. The cold heat of the generated hydrogen is used to cool the cooling water in the cooling path via the heat exchanger. Further, hydrogen that has passed through the expander is supplied to the fuel cell from the supply path and used for power generation of the fuel cell.

When the fuel cell system is started and stopped, hydrogen may leak to the downstream side of the expander due to the high pressure of hydrogen supplied from the hydrogen tank to the supply path. When hydrogen leaks to the downstream side of the expander, the pressure of hydrogen existing in the supply path on the downstream side of the expander becomes higher than that before the start / stop.

Here, the control means controls to close the on-off valve when the fuel cell system is started and the detection pressure detected by the detection means is equal to or higher than the set pressure. Further, the control means controls to close the on-off valve when the fuel cell is started and stopped. Therefore, it is possible to prevent hydrogen from leaking to the downstream side of the expander. Further, the control means controls to operate the pressure lowering means until the detected pressure becomes lower than the set pressure. Therefore, the pressure of hydrogen on the downstream side of the expander is reduced. In other words, the ratio of the pressure of hydrogen on the outlet side of the expander to the pressure of hydrogen on the inlet side of the expander is larger than the ratio of the pressure before the operation of the pressure reducing means. As a result, when the on-off valve is opened, the pressure ratio required for operating the inflator is secured, so that the inflator can be operated stably when the inflator is restarted.

As described above, the present invention can stably operate the expander when it is restarted.

It is explanatory drawing which shows the whole structure of the fuel cell system which concerns on this embodiment. It is a flowchart which shows the flow of the pressure drop processing in the fuel cell system which concerns on this embodiment. It is a graph which shows the time change of the pressure of hydrogen in the supply path on the downstream side of the expander which concerns on this embodiment.

The fuel cell system 10 as an example of the present embodiment will be described. The fuel cell system 10 is mounted on a vehicle (not shown) as an example.

As an example, the fuel cell system 10 shown in FIG. 1 includes a fuel cell stack 12, a cooling path 14, a heat exchanger 16, a hydrogen tank 18, a supply path 22, an expander 24, an on-off valve 26, a pressure sensor 28, and a first injector. It has 32 and a control unit 34. Further, the fuel cell system 10 includes a main valve 42, a pressure regulating valve 44, a flow rate adjusting unit 46, a sub tank 48, a radiator 52, a temperature sensor 54, a bypass path 56, a second injector 62, a return path 64, a separation unit 66, and a drain valve. It also has 68 and a pump 72.

In the following description, the hydrogen tank 18 side will be described as the upstream side of the hydrogen flow path, and the fuel cell stack 12 side will be described as the downstream side of the hydrogen (hydrogen gas) flow path. Further, the arrow H shown in FIG. 1 represents the flow of hydrogen. The arrow W represents the flow of cooling water.

The fuel cell stack 12 is an example of a fuel cell. Specifically, the fuel cell stack 12 is a unit that generates electricity by an electrochemical reaction between hydrogen and oxygen, and is formed by stacking a plurality of single cells. Oxygen in compressed air is supplied to the fuel cell stack 12 from an air supply device (not shown). Further, hydrogen is supplied to the fuel cell stack 12 from the hydrogen tank 18 via the supply path 22 or the bypass path 56.

The cooling path 14 is composed of a pipe that circulates cooling water from the radiator 52 to the radiator 52 again via the inside of the fuel cell stack 12 and the heat exchanger 16. The circulation of the cooling water in the cooling path 14 is performed by a pump (not shown). Further, the portion of the cooling path 14 that comes into contact with the heat exchanger 16 is, for example, a bent portion 15 that is bent in a U shape. The bent portion 15 has an increased contact area with the heat exchanger 16 as compared with a configuration in which the bent portion 15 is not formed. Further, a temperature sensor 54 is provided near the outlet of the fuel cell stack 12 in the cooling path 14. The fuel cell stack 12 is cooled by the cooling water flowing through the cooling path 14.

As an example, the heat exchanger 16 is in contact with the bent portion 15 of the cooling path 14. Further, the heat exchanger 16 is in contact with a portion of the supply path 22 described later on the downstream side of the expander 24. The heat exchanger 16 is configured to exchange heat between hydrogen cooled by adiabatic expansion by the expander 24 and cooling water circulating in the cooling path 14.

Further, the heat exchanger 16 is also in contact with the supply path 22 on the upstream side of the expander 24, for example. This is when the heat of the high-temperature cooling water flowing from the fuel cell stack 12 through the cooling path 14 is used to raise the temperature of hydrogen in the supply path 22 and then adiabatically expanded by the expander 24. This is because the volume increases and more driving force, which will be described later, can be obtained. Further, since hydrogen has a high rate of temperature decrease when expanded, the heat of the cooling water is given to hydrogen on the upstream side of the expander 24 in order to prevent excessive cooling by the expander 24.

The hydrogen tank 18 is filled with high-pressure (for example, 70 MPa or more) hydrogen for supplying the fuel cell stack 12. Further, the upstream end of the supply path 22 is connected to the hydrogen tank 18.

The supply path 22 is composed of a pipe through which hydrogen flows. Further, the supply path 22 connects the hydrogen tank 18 and the fuel cell stack 12. In other words, in the supply path 22, hydrogen is supplied from the hydrogen tank 18 to the fuel cell stack 12. Further, the supply path 22 is in contact with the heat exchanger 16 as described above. A main valve 42, a pressure regulating valve 44, a flow rate adjusting unit 46, an on-off valve 26, an expander 24, a pressure sensor 28, a sub tank 48, and a first injector 32 are provided in the middle of the supply path 22.

In the following description, regarding the supply path 22, the portion from the hydrogen tank 18 to the expander 24 is referred to as an upstream supply path 22A, and the portion from the expander 24 to the fuel cell stack 12 is referred to as a downstream supply path 22B. May be done. The upstream supply path 22A is provided with a pressure sensor (not shown) that detects the pressure of the supplied hydrogen. The pressure information detected by the pressure sensor is output to the control unit 34, which will be described later.

The expander 24 is provided on the upstream side of the heat exchanger 16 in the supply path 22. Further, the expander 24 is configured to adiabatically expand (decompressed expansion) the hydrogen supplied from the hydrogen tank 18. An energy recovery device 25 is connected to the expander 24. The energy recovery device 25 has a fan 25A as an example, and recovers the expansion energy when the expander 24 adiabatically expands hydrogen by converting it into mechanical energy (driving force for rotating the fan 25A). The fan 25A is arranged to face the radiator 52 and blows air toward the radiator 52.

As an example, the on-off valve 26 is composed of a three-way valve, and is provided in the vicinity of the expander 24 (on the upstream side of the expander 24) in the upstream side supply path 22A. Specifically, the on-off valve 26 has a port Va, a port Vb, and a port Vc. The port Va is connected to the end of the upstream supply path 22A opposite to the hydrogen tank 18 side. The port Vb is connected to one end of the bypass path 56, which will be described later. The port Vc is connected to the downstream side (expansor 24 side) of the port Va in the upstream side supply path 22A. The ports Va, Vb, and Vc are set to either an open state or a closed state under the control of the control unit 34.

Specifically, the on-off valve 26 can be switched to any one of a closed state, a first open state, and a second open state by the control unit 34. The closed state is a state in which the ports Va, Vb, and Vc are closed, or a state in which the ports Va and Vc are closed and the port Vb is opened. The first open state is a state in which only port Vb is closed and port Va and port Vc are open. In the first open state, hydrogen flows from the upstream side supply path 22A to the downstream side supply path 22B via the expander 24. The second open state is a state in which only the port Vc is closed and the port Va and the port Vb are open. In the second open state, hydrogen flows from the upstream supply path 22A to the bypass path 56.

The pressure sensor 28 is an example of the detecting means. Further, the pressure sensor 28 is provided on the downstream side of the expander 24 in the downstream side supply path 22B. Further, the pressure sensor 28 is configured to detect the pressure of hydrogen in the downstream supply path 22B between the expander 24 and the sub tank 48, and output the obtained pressure information to the control unit 34. The detected pressure of hydrogen detected by the pressure sensor 28 is Px [MPa].

The first injector 32 is an example of the pressure reducing means. Further, the first injector 32 is provided on the downstream side of the expander 24 in the downstream supply path 22B and on the downstream side of the sub tank 48. As an example, the first injector 32 has two injectors 32A and 32B including an electromagnetic on-off valve so that the operation or deactivation of the injectors 32A and 32B can be switched according to the pressure of hydrogen to be lowered. It is configured in. The first injector 32 has a function of reducing the pressure of hydrogen in the downstream supply path 22B.

The control unit 34 is an example of control means, and includes an ECU (Electronic Control Unit) (not shown). The ECU is composed of a microcomputer including a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like. A program for controlling the operation of each part of the fuel cell system 10 is set in the control unit 34.

In the control unit 34, a lower limit pressure P0 [MPa] and an upper limit pressure P1 [MPa] are set for the detected pressure Px in the pressure sensor 28. The upper limit pressure P1 is an example of the set pressure. Further, the control unit 34 is set with a reference temperature T0 [° C.] for the detection temperature Tc in the temperature sensor 54 described later. Then, as an example, the control unit 34 is configured to control the opening / closing of the ports Va, Vb, and Vc and the driving of the first injector 32 and the second injector 62 described later based on the detected pressure Px and the detected temperature Tc. Has been done.

As an example of control, the control unit 34 closes the port Vc of the on-off valve 26 and the detected pressure Px is higher than the set pressure when the fuel cell stack 12 is started and the detected pressure Px is the upper limit pressure P1 or more. Control is performed to operate the first injector 32 until the pressure becomes low. Further, the control unit 34 controls to close the port Vc of the on-off valve 26 when the fuel cell stack 12 is started and stopped.

The main valve 42 is composed of a valve body that is in either an open state or a closed state under the control of the control unit 34. Hereinafter, it is assumed that the main valve 42 is in the open state. The pressure regulating valve 44 adjusts the pressure of hydrogen in the supply path 22. The flow rate adjusting unit 46 adjusts the flow rate of hydrogen in the upstream supply path 22A.

The sub tank 48 is configured as an accumulator (accumulator). Further, the sub tank 48 has a function of suppressing the flow rate of hydrogen flowing through the downstream supply path 22B from becoming unstable when the opening / closing frequency of the second injector 62, which will be described later, changes. In the following description, it is assumed that the pressure of hydrogen on the outlet side of the expander 24 is adjusted by the first injector 32, and the description of the sub tank 48 will be omitted.

The radiator 52 cools the cooling water in the cooling path 14 by using the traveling wind of a vehicle (not shown). Further, in the radiator 52, cooling is also performed by blowing air from the fan 25A described above. The temperature sensor 54 is configured to detect the temperature of the cooling water in the cooling path 14 and output the obtained temperature information to the control unit 34. Let Tc be the detected temperature in the temperature sensor 54. Further, the reference temperature of the cooling water is T0. The reference temperature T0 is set to 30 [° C.] as an example.

The bypass path 56 is composed of a pipe through which hydrogen flows. One end of the bypass path 56 is connected to the port Vb, and the other end of the bypass path 56 is a portion downstream of the first injector 32 in the downstream supply path 22B and from the connection portion of the return path 64 described later. Is also connected to the upstream part.

The second injector 62 is provided in the middle of the bypass path 56. As an example, the second injector 62 has two injectors 62A, 62B including an electromagnetic on-off valve, and the operation or operation of the injectors 62A, 62B depends on the amount of hydrogen supplied to the fuel cell stack 12. It is configured so that the stop can be switched. That is, the second injector 62 has a function of supplying hydrogen to the fuel cell stack 12.

One end of the return path 64 is connected to the fuel cell stack 12. The other end of the return path 64 is connected to a portion downstream of the first injector 32 in the downstream supply path 22B. The separation unit 66 separates the hydrogen gas and the reaction gas discharged from the fuel cell stack 12 into a gas component and a liquid component. The drain valve 68 discharges the liquid component separated by the separation unit 66 to the outside. The pump 72 functions as a circulation pump that sends hydrogen contained in the gas component separated by the separation unit 66 to the downstream supply path 22B.

[Action and effect]
Next, the operation and effect of the fuel cell system 10 of the present embodiment will be described with reference to the flowchart shown in FIG. Refer to FIG. 1 for each part of the fuel cell system 10.

In step S10, the port Va is opened or closed based on the start or end request of the fuel cell system 10. Then, the process proceeds to step S12.

In step S12, the control unit 34 determines whether or not the port Va is closed. If the port Va is closed, the process proceeds to step S14. On the other hand, when the port Va is open, the process proceeds to step S16.

In step S14, the on-off valve 26 is operated. Specifically, the port Vb is opened and the port Vc is closed. Then, the program is terminated.

In step S16, the control unit 34 determines whether or not the detected pressure Px in the pressure sensor 28 is equal to or higher than the upper limit pressure P1. If the detected pressure Px is equal to or higher than the upper limit pressure P1, the process proceeds to step S18. On the other hand, when the detected pressure Px is lower than the upper limit pressure P1, the process proceeds to step S20.

In step S18, the port Vb and the port Vc are closed, and the first injector 32 is started to be driven. The first injector 32 is driven until the detected pressure Px becomes lower than the upper limit pressure P1. Then, the process proceeds to step S12.

In step S20, the control unit 34 determines whether or not the detected pressure Px is lower than the lower limit pressure P0. If the detected pressure Px is lower than the lower limit pressure P0, the process proceeds to step S22. On the other hand, when the detected pressure Px is equal to or higher than the lower limit pressure P0, the process proceeds to step S24.

In step S22, the second injector 62 is started to be driven in a state where the port Vb is opened and the port Vc is closed. That is, when the hydrogen pressure in the downstream supply path 22B is too low, the hydrogen on the bypass path 56 side is supplied to the fuel cell stack 12. Then, the process proceeds to step S12.

In step S24, the control unit 34 determines whether or not the detected temperature Tc in the temperature sensor 54 is equal to or lower than the reference temperature T0. If the detected temperature Tc is equal to or lower than the reference temperature T0, the process proceeds to step S26. On the other hand, when the detected temperature Tc is higher than the reference temperature T0, the process proceeds to step S28.

In step S26, the second injector 62 is started to be driven in a state where the port Vb is opened and the port Vc is closed. That is, when the temperature of the cooling water is lower than the reference temperature T0, the hydrogen is cooled more than necessary when the expander 24 is operated. Therefore, the bypass path 56 side is not operated without operating the expander 24. Hydrogen is supplied to the fuel cell stack 12. Then, the process proceeds to step S12.

In step S28, the first injector 32 is started to be driven in a state where the port Vb is closed and the port Vc is opened. That is, when the temperature of the cooling water is higher than the reference temperature T0, the energy recovery efficiency in the expander 24 becomes high, so that hydrogen on the downstream side supply path 22B side is supplied to the fuel cell stack 12. Then, the process proceeds to step S12.

In the fuel cell system 10 described above, in the activated state of the fuel cell stack 12, the hydrogen supplied from the hydrogen tank 18 to the supply path 22 is adiabatically expanded by the expander 24 to generate cold heat of hydrogen. Expansion energy as power is obtained. The cold heat of the generated hydrogen is used for cooling the cooling water of the cooling path 14 via the heat exchanger 16. Further, the hydrogen that has passed through the expander 24 is supplied to the fuel cell stack 12 from the supply path 22 and is used for power generation of the fuel cell stack 12.

When the fuel cell system 10 is started and stopped, the pressure of hydrogen supplied from the hydrogen tank 18 to the supply path 22 is high, so that hydrogen may leak to the downstream side of the expander 24. When hydrogen leaks to the downstream side of the expander 24, the pressure of hydrogen existing in the supply path 22 on the downstream side of the expander 24 becomes higher than that before the start / stop.

Here, the control unit 34 controls to close the port Vc of the on-off valve 26 when the fuel cell stack 12 is activated and the detected pressure Px detected by the pressure sensor 28 is equal to or higher than the upper limit pressure P1. conduct. Further, the control unit 34 controls to close the port Vc of the on-off valve 26 when the fuel cell stack 12 is started and stopped. As a result, hydrogen in a high-pressure state is blocked from flowing into the expander 24, so that it is possible to prevent hydrogen from leaking to the downstream side of the expander 24.

Further, with the port Vc closed, the control to operate the first injector 32 is performed until the detected pressure Px becomes lower than the upper limit pressure P1, so that the pressure of hydrogen on the downstream side of the expander 24 is increased. It is lower than the upper limit pressure P1. In other words, the ratio of the hydrogen pressure on the outlet side of the expander 24 to the hydrogen pressure on the inlet side of the expander 24 is the ratio of the pressure before the operation of the first injector 32 when the on-off valve 26 is opened. It will be larger than. As a result, the pressure ratio required for the operation of the inflator 24 is secured, so that the inflator 24 can be operated stably when the fuel cell system 10 is restarted.

In the fuel cell system 10, the cooling path 14 is in contact with not only the downstream supply path 22B but also the upstream supply path 22A. As a result, the high-temperature cooling water flowing from the fuel cell stack 12 warms the hydrogen before it flows into the expander 24, and the temperature of the hydrogen rises. Therefore, the recovery efficiency of converting the expansion energy into mechanical energy and recovering it. Can be enhanced.

In FIG. 3, as an example, the detected pressures Px at each time point are shown in graphs G1 and G2. Time point t0 is the start time point of the fuel cell system 10 (see FIG. 1). The time point t1 is a time point when the operation of the fuel cell system 10 is stopped (started and stopped). The time point t2 is a time point when the fuel cell system 10 is restarted. The graph G2 shows a preferable state in which the detected pressure Px is between the lower limit pressure P0 and the upper limit pressure P1.

In the graph G1, the detected pressure Px is gradually lowered from the time t0 when the fuel cell system 10 is started to the time t1 when the fuel cell system 10 is started and stopped in a state where the pressure Px is lower than the upper limit pressure P1. This is because hydrogen is consumed in the fuel cell stack 12 (see FIG. 1). Then, when the fuel cell system 10 is started and stopped at the time point t1, the high pressure hydrogen leaked from the port Vc (see FIG. 1) gradually increases the pressure of hydrogen in the downstream supply path 22B, and eventually the upper limit is reached. The pressure exceeds the pressure P1. Here, at time point t2, when the fuel cell system 10 is restarted (restarted), the port Vc is closed and the first injector 32 (see FIG. 1) is operated, so that the detection pressure Px is the upper limit. The pressure is lower than P1. As a result, as described above, the expander 24 (see FIG. 1) is stably operated.

The present invention is not limited to the above embodiment.

The fuel cell system 10 may be configured such that the on-off valve 26 is not a three-way valve but an on-off valve for one flow path and does not use the bypass path 56. Further, in the fuel cell system 10, the heat exchanger 16 may be configured so as not to come into contact with the upstream supply path 22A. Further, the fuel cell system 10 may not be provided with the sub tank 48. In addition, the fuel cell system 10 does not have to be provided with the temperature sensor 54.

It is not preferable that the port Vc remains open from the viewpoint of suppressing hydrogen leakage to the expander 24. Therefore, when the port Va is closed, it is preferable to close the port Vc promptly.

A vehicle (not shown) equipped with the fuel cell system 10 does not run at a constant power consumption (load), and the power consumption increases, for example, on a slope. Here, if hydrogen is supplied via the expander 24, the hydrogen supply cannot catch up and the pressure may drop. In that case, the port Vb may be opened to supply hydrogen from both the supply path 22 and the bypass path 56.

The fuel cell system 10 is not limited to the configuration in which the cooling water cooled by the heat exchanger 16 is flowed to the radiator 52, and the cooling water cooled by the radiator 52 is further cooled by the heat exchanger 16 (implementation). It is also possible to flow the cooling water in the direction opposite to the direction of the form).

10 Fuel cell system 12 Fuel cell stack (an example of a fuel cell)
14 Cooling path 16 Heat exchanger 18 Hydrogen tank 22 Supply path 24 Inflator 26 On-off valve 28 Pressure sensor (example of detection means)
32 First injector (an example of pressure reducing means)
34 Control unit (an example of control means)

Claims (1)

A supply path that is in contact with a heat exchanger that is in contact with the cooling path of the fuel cell and that supplies hydrogen from the hydrogen tank to the fuel cell.
An expander provided on the upstream side of the heat exchanger in the supply path to adiabatically expand hydrogen.
An on-off valve provided on the upstream side of the expander in the supply path,
A detection means provided on the downstream side of the expander in the supply path and detecting the pressure of hydrogen in the supply path.
A pressure reducing means provided on the downstream side of the expander in the supply path and reducing the pressure of hydrogen in the supply path,
When the fuel cell is started and the detected pressure detected by the detecting means is equal to or higher than the set pressure, the on-off valve is closed and the pressure drops until the detected pressure becomes lower than the set pressure. A control means that controls the operation of the means and controls the closing of the on-off valve when the fuel cell is started and stopped.
Has a fuel cell system.

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