Fuel cell and associated control method

Abstract

The invention relates to a fuel cell (20) comprising a plurality of unit cells stacked along a main axis (A30) so as to form a stack (30) of cells, the stack being housed in a casing (22) with a sleeve (24) closed by a first cover (26B) and a second cover (26A) opposite the first cover along the main axis. When the fuel cell is in an operating configuration, the main axis is substantially horizontal, and the housing has a top side and a bottom side. The first cover comprises a main ventilation inlet (434) that opens into the housing at a highest point of the first cover, while the second cover comprises a first main ventilation outlet (442) that opens into the housing at a highest point of the second cover, and a second main outlet (444) that opens into the housing at a lowest point of the second cover.

Description

[0001] DESCRIPTION

[0002] TITLE: Fuel cell and associated control method

[0003] The present invention relates to a fuel cell, as well as a method for controlling such a fuel cell.

[0004] A fuel cell is a device for generating electricity by electrochemical reaction between a fuel, for example dihydrogen, and an oxidizer, for example oxygen contained in the air. We are interested here in fuel cells of the solid electrolyte proton exchange membrane type - also called PEMFC in English -, which usually comprise a stack - called in English - of several unit cells each constituting an electrochemical generator.

[0005] Schematically, each unit cell comprises two separators, also called polar plates, between which is inserted a solid electrolyte in the form of a proton exchange membrane. The membrane is made, for example, of a sulfonated perfluorinated polymer material. Within each cell, each separator delimits, with the corresponding membrane, a reactive compartment. One of the two reactive compartments, called the cathodic compartment, houses a cathodic element, formed by a cathodic catalytic layer located on the surface of the membrane, while the other reactive compartment, called the anodic compartment, houses an anodic element, formed by an anodic catalytic layer located on the surface of the membrane. The assembly of the membrane and the anodic and cathodic catalytic layers forms a membrane-electrode assembly, generally known by the acronym AME in French, or MEA in English.

[0006] For two neighboring cells, a separator from one of the two cells is placed back to back with a separator from the other cell. These two separators together form a bipolar separator, also called a bipolar plate. A cooling compartment, in which a cooling fluid such as glycolated water circulates, is generally arranged between the two separators of the bipolar separator.

[0007] Hydrogen, air and coolant are so-called "operating" fluids, which are supplied to the fuel cell during its operation. Hydrogen and air are reactants while the coolant is not involved in the electrochemical reaction. Depending on the operating phases of the fuel cell, the supply of one or more of the operating fluids is continuous, intermittent or even interrupted. The fuel cell provides openings to supply fluids to each of the reactant compartments and the fluids between two neighboring cells. In a widely used design, each bipolar separator ensures, on one side, the fuel supply to the cell adjacent to this side and, on the other side, the oxidant supply to the cell adjacent to this other side, the supplies provided by the bipolar separators being in parallel.

[0008] Generally, in a unit cell, the cathode compartment is supplied with oxidant, for example oxygen, most often in the form of an air supply containing oxygen, and the anode compartment is supplied with fuel, for example dihydrogen. When the stack is formed, the cathode compartments of the unit cells communicate with each other, step by step, forming a cathode circuit of the stack. Similarly, the anode compartments of the unit cells communicate with each other, step by step, forming an anode circuit of the stack.During operation of the cell, the anode circuit of the stack is supplied with hydrogen by a cell anode supply circuit, while the cathode circuit of the stack is supplied with air - and therefore oxygen - by a cell cathode supply circuit, and the stack is supplied with coolant by a cooling circuit.

[0009] Each reactive compartment also generally includes a gas diffusion layer, located between the bipolar separator and the catalytic layer, allowing good circulation of the fuel or oxidizer from the separator to the catalytic layer.

[0010] When the fuel cell is in operation, the electrochemical reaction creates an electrical potential difference between the two separators of each unit cell. The fuel cell thus comprises an electrical insulation device, designed to prevent any electrical contact between two neighboring bipolar separators and between each cell and the external environment, as well as a sealing device to prevent leaks of operating fluids, in particular to prevent the fluid circulating in a reactive compartment from contaminating a neighboring reactive compartment.

[0011] The electrical potential difference between the two separators of each unit cell creates a voltage across each unit cell, referred to as the "cell voltage." All cells in the fuel cell are electrically connected together in series, so that the voltage delivered across the stack is equal to the sum of the cell voltage of all the unit cells. The stack is housed in a housing, which is generally sealed and in which several openings are provided, intended to supply the stack with operating fluids, for electrical connections, for connections to sensors, etc. During operation of the cell, hydrogen may leak from the stack and accumulate in the housing around the stack, which leads to a risk of explosion.

[0012] In particular, when the fuel cell is completely shut down and depolarized, the anode supply circuit is cut off, and gases other than hydrogen, including air, containing oxygen, nitrogen, etc., tend to enter the anode circuit of the stack. When the cell is restarted, the anode supply circuit is reopened, accompanied by the opening of the anode purge solenoid valve, so as to purge the anode circuit until the anode circuit essentially contains only hydrogen. During this step, the cathode supply circuit is kept closed, preventing repolarization of the cell. Hydrogen circulates in the stack without being consumed by an electrochemical reaction, and possible micro-leaks may occur, releasing hydrogen within the casing.

[0013] To prevent hydrogen from accumulating within the casing, which could lead to a risk of explosion, it is known to ventilate the casing, around the stack, with ventilation air. On the other hand, due to the thermal cycles of the fuel cell, the humidity contained in the air in the casing can condense, forming liquid water, which risks impairing the proper functioning of the cell. It is therefore advisable to evacuate the humidity from the casing.

[0014] US20220190362 describes, for example, a fuel cell comprising a ventilation inlet and a ventilation outlet arranged in the upper part of the housing, so as to promote the evacuation of any hydrogen present in the housing. This document, however, remains silent on the evacuation of moisture.

[0015] It is these problems that the invention aims to address more specifically by proposing a fuel cell comprising an improved ventilation circuit.

[0016] For this purpose, the invention relates to a fuel cell, comprising:

[0017] - several unit cells, which are stacked along a main axis so as to form a stack of cells, a case, which provides an internal housing receiving the stack, and which comprises:

[0018] • a jacket, which includes two end openings aligned along the main axis,

[0019] • a first cover and a second cover, different from the first cover, the two covers sealingly closing the two openings of the jacket and delimiting, with the jacket, the internal housing of the case, in which: when the fuel cell is in a usage configuration:

[0020] • the main axis is substantially horizontal,

[0021] • the box has a top side and a bottom side,

[0022] - the first cover comprises a main ventilation inlet, through which ventilation air is introduced into the internal housing, the main inlet opening into the internal housing at a highest point of the first cover, the second cover comprises a first main ventilation outlet, through which the ventilation air introduced into the internal housing is evacuated, the first main outlet opening into the internal housing at a highest point of the second cover, so that the ventilation air introduced through the main inlet exits through the first main outlet by sweeping an upper part of the internal housing, entraining fluids lighter than air, in particular hydrogen,

[0023] - the second cover also includes a second main outlet, which opens into the internal housing at a lowest point of the second cover, so that the ventilation air introduced through the main inlet tends to carry fluids heavier than air, in particular water.

[0024] Thanks to the invention, the second main ventilation outlet is arranged at a lowest point of the housing, which facilitates the evacuation of any liquid water present, which tends to accumulate by gravity in the lower part of the internal housing of the housing. Jointly, the first main inlet and the first main outlet are each arranged in the upper part of the housing, where hydrogen, being lighter than air, tends to accumulate. The overall efficiency of the ventilation of the housing is thus improved.

[0025] According to advantageous but not mandatory aspects of the invention, such a fuel cell may incorporate one or more of the following features taken in isolation or in any technically admissible combination:

[0026] The fuel cell also comprises a switching unit, which is integral with the housing and which is configured to open or close a power circuit of the stack, the switching unit comprises an envelope, which provides an internal volume and which comprises: • a first side and a second side, which is opposite the first side and which is oriented towards the first cover,

[0027] • a high side and a low side, which are different from the first and second sides, the high side and the low side of the switching unit being respectively located on the same side as the high and low sides of the housing when the fuel cell is in the use configuration, the switching unit comprises:

[0028] • an auxiliary ventilation inlet, which is located on the first side and through which ventilation air is introduced into an internal volume of the switching unit,

[0029] • a first auxiliary ventilation outlet, which is located on the second side and through which the ventilation air introduced by the auxiliary inlet is evacuated, the auxiliary inlet and the first auxiliary outlet each open onto one of the respective highest points of the internal volume and are configured so that when the ventilation air is introduced by the auxiliary inlet and exits by the first auxiliary outlet, the ventilation air entrains the fluids lighter than air contained in the internal volume, in particular hydrogen,

[0030] - the first auxiliary output is connected to the first main input, so that the ventilation air used for the box is previously used as ventilation air for the switching unit.

[0031] The switching unit comprises a second auxiliary outlet, which is located on the second side of the switching unit and which opens into the internal volume at a lowest point of the internal volume, so that when ventilation air is introduced through the auxiliary inlet, the ventilation air exiting through the second auxiliary outlet tends to entrain fluids heavier than air, in particular water, the first cover comprises, in addition to the main inlet, a second main inlet, which opens into the internal housing at a lowest point,

[0032] - the second auxiliary output is connected to the second main input.

[0033] The fuel cell includes:

[0034] • an air supply circuit, which is configured to supply air to a cathode circuit of the stack, and

[0035] • a branch circuit, which includes an inlet, through which the branch circuit is connected to the air supply circuit, and an outlet, through which the branch circuit is configured to supply the housing with ventilation air.

[0036] The branch circuit outlet is connected to the main ventilation inlet.

[0037] The air supply circuit includes a compressor, which is configured to compress air supplying the cathode circuit, while the inlet of the bypass circuit is connected downstream of the compressor.

[0038] The fuel cell also includes a calibrated orifice, which is arranged on the bypass circuit, the calibrated orifice 436 having a reduced passage section compared to the rest of the bypass circuit and being configured to limit an air flow through the bypass circuit.

[0039] The air supply circuit includes:

[0040] • an inlet pipe, which connects the compressor to an inlet of the cathode circuit, and an outlet pipe, which connects an outlet of the cathode circuit of the stack,

[0041] • an exhaust, configured to allow the air leaving the cathode circuit to escape and passing through the outlet pipe to the outside environment, while the first main outlet is connected to the exhaust.

[0042] The second main outlet is connected to the exhaust.

[0043] The fuel cell comprises an air supply circuit, which is configured to supply air to a cathode circuit of the stack, the supply circuit comprising:

[0044] • a compressor, configured to compress air,

[0045] • an inlet pipe, which connects the compressor to an inlet of the cathode circuit, and an outlet pipe, which connects an outlet of the cathode circuit of the stack,

[0046] • an exhaust, configured to allow the air leaving the cathode circuit to escape and passing through the outlet pipe to the external environment,

[0047] • a first isolation valve, which is configured to close the inlet pipe and which is arranged between the compressor and the stack,

[0048] • a second isolation valve, which is configured to close the outlet pipe and which is arranged between the stack and the exhaust,

[0049] • a humidifier, which comprises a regulation portion, which is crossed by the inlet pipe, which is located between the first isolation valve and the stack and which is configured to regulate a humidity level in the air passing through the inlet pipe, and a recovery portion, which is crossed by the outlet pipe, which is located between the second isolation valve and the stack and which is configured to recover humidity from the air passing through the outlet pipe, in which the fuel cell also comprises:

[0050] - a bypass circuit, which comprises an inlet, by which the bypass circuit is connected to the inlet pipe, and an outlet, by which the bypass circuit is configured to supply the housing with ventilation air, the inlet of the bypass circuit being connected to the inlet pipe between the compressor and the first isolation valve, a calibrated orifice, which is arranged on the bypass circuit, the calibrated orifice having a reduced passage section compared to the rest of the bypass circuit and being configured to limit an air flow through the bypass circuit.

[0051] The fuel cell also includes:

[0052] • a cooling circuit, configured to supply the stack of unit cells with a cooling fluid, for example glycolated water, and

[0053] • a heat exchanger, configured to exchange thermal energy between the air passing through the inlet pipe and the cooling fluid, the heat exchanger being located, along the inlet pipe, between the compressor and the inlet of the bypass circuit.

[0054] The air supply circuit includes:

[0055] • a pressure sensor, which is arranged between the heat exchanger and the humidifier and which is configured to measure a pressure at the inlet of the bypass circuit,

[0056] • a bypass valve, which is arranged between the inlet of the bypass circuit and the exhaust, the bypass valve being configured to regulate an air pressure at the inlet of the bypass circuit, so as to regulate an air flow passing through the calibrated orifice.

[0057] According to another aspect, the invention also relates to a method for controlling a fuel cell as defined above, in which:

[0058] - we adjust a compressor power, then we measure a pressure in the inlet of the bypass circuit using a pressure sensor,

[0059] - then, depending on the measured pressure, an opening of the bypass valve is adjusted so as to regulate the pressure in the inlet of the bypass circuit and to regulate the air flow passing through the calibrated orifice, the adjustment of the opening of the bypass valve being chosen using a law, previously recorded in a fuel cell computer, which links the air flow through the calibrated orifice and a pressure differential on either side of the calibrated orifice.

[0060] According to advantageous but non-mandatory aspects of the invention, such a control method may incorporate one or more of the following characteristics taken in isolation or in any technically admissible combination: the fuel cell being initially stopped, the first isolation valve and the second isolation valve are closed, so as to isolate the cathode circuit,

[0061] - then, a compressor power is adjusted to a maximum operating value, while the bypass valve is closed, so as to maximize an air flow passing through the bypass circuit, then, hydrogen is supplied to an anode circuit of the stack, so as to purge the anode circuit of gases other than hydrogen.

[0062] Initially, the fuel cell is in a production mode, in which:

[0063] • the compressor operates at a first non-zero power level,

[0064] • the first isolation valve is fully open,

[0065] • the bypass valve is completely closed, then the compressor power is increased to a second power level, higher than the first level, while the first isolation valve is partially closed, while keeping the bypass valve completely closed.

[0066] This control method induces the same advantages as those mentioned above regarding the fuel cell of the invention.

[0067] The invention will be better understood, and other advantages thereof will appear more clearly in the light of the following description of several embodiments of a fuel cell and a control method, in accordance with its principle, given solely by way of example and with reference to the appended drawings, in which:

[0068] - [Fig 1] Figure 1 schematically represents, on an insert a), a vehicle, in accordance with a first embodiment of the invention, the vehicle comprising a fuel cell, also in accordance with the invention, on an insert b), a housing of the fuel cell of the insert a), and on an insert c), a stack of the fuel cell of the insert a), the stack being received in the housing of the insert b);

[0069] - [Fig 2] Figure 2 is a schematic representation of the fuel cell of Figure 1, and - [Fig 3] Figure 3 is a figure similar to Figure 2, representing a fuel cell according to a second embodiment of the invention.

[0070] A vehicle 10 is shown in Figure 1. The vehicle 10 is here a road vehicle, such as a car, a truck or a non-road vehicle, such as for example a forklift. Alternatively, the vehicle 10 is a railway vehicle such as a train or a subway, or an aircraft or even a ship.

[0071] The vehicle 10 here comprises wheels 12, by means of which the vehicle 10 rests on a ground 14. The ground 14 is assumed to be substantially horizontal, the following description being given in relation to the orientation of the various elements of the vehicle 10 as shown in the figures, knowing that it may be otherwise in reality.

[0072] The vehicle 10 comprises a fuel cell 20. The fuel cell 20, also simply called cell 20 in the present description, moves with the vehicle 10 and is a fuel cell mounted on a chassis of the vehicle, called "on-board", as opposed to so-called stationary fuel cells which are fixed, placed on the ground or in a building. The fuel cell 20 is supplied with fuel, here hydrogen, which reacts with the oxygen in the air to generate electricity for the operation of the vehicle 10, part of the energy of the fuel being dissipated in the form of heat. In particular, the vehicle 10 comprises, for its movement, an electric motor, which is powered, directly or indirectly (via batteries for example), by the electrical energy generated by the fuel cell 20. The electric motor is not shown.

[0073] With reference to Figure 1 a), the fuel cell 20 comprises a housing 22, also called a casing in English, the housing 22 comprising a jacket 24. The jacket 24 has the shape of a hollow cylinder, which extends along a main axis A20 and which here has a substantially rectangular section. By cylindrical, we therefore mean here any hollow shape, that is to say an envelope defining a volume inside it. As can be seen in Figure 1 b, the jacket 24 here has a substantially parallelepiped shape, that is to say it defines a hollow block. The jacket 24 provides an internal housing V24 with two opposite end openings, the end openings being respectively closed in a sealed manner by two covers 26A and 26B. The two covers 26A and 26B and the sleeve 24 thus delimit the internal housing V24, which is also, by extension, an internal housing of the housing 22.The openings of the internal housing V24 are thus aligned along the main axis A20, while the covers 26A and 26B each extend along planes orthogonal to the main axis A20. The jacket 24 and the covers 26A and 26B are preferably made of electrically insulating material, such as a polymer material, possibly reinforced with fibers. Alternatively, the covers 26A and 26B are covered, at least on one internal face, with an electrically insulating material.

[0074] Fluid conduits are provided through the housing 22 to allow the passage of operating fluids of the cell 20. The operating fluids here comprise three fluids, including two gaseous fluids, here air - containing dioxygen - and dihydrogen, and a dielectric heat transfer fluid, for example liquid, here glycolated water. The fluid conduits are materialized by fluid connectors 28, which are provided here on the cover 26A, located on the right of FIG. 1 b). Preferably, all or part of the fluid connectors are provided on the cover 26B. Alternatively, all or part of the fluid connectors are located on the jacket 24.

[0075] In the illustrated example, the stack 20 comprises three pairs of fluid connections 28, each pair being intended for the circulation of a clean operating fluid. The three pairs of fluid connections 28 include a first pair of connections 28A, a second pair of connections 28B and a third pair of connections 28C. For each pair of connections, one of the connections called the “inlet connection” is intended for the admission of the corresponding operating fluid, while the other connection called the “outlet connection” is intended for the extraction of the corresponding operating fluid. In the figures, the direction of circulation of the operating fluids is represented schematically by arbitrarily oriented arrows, knowing that it may be otherwise in reality.For example, the connectors 28A are used to supply and evacuate the cell 20 with oxygen, the connectors 28B to supply and evacuate the cell with hydrogen and the connectors 28C to supply and evacuate the cell with coolant. The size and arrangement of the fluid connectors 28 are not limiting. As illustrated in FIG. 1b, all of the connectors 28A, 28B, 28C are advantageously located on the same cover 26A, 26B, preferably the second cover 26A.

[0076] The stack 30 of the fuel cell 20 is shown schematically in partially exploded perspective in insert c) of FIG. 1.

[0077] The stack 30 is held between two end plates 31 A and 31 B, which are shown schematically in Figure 1 a) and in Figures 2 and 3. The end plates 31 A and 31 B make it possible in particular to hold the stack 30 in the housing 22, and to supply the stack 30 with fuel, in the example dihydrogen in gaseous form, and with oxidant, in the example air in gaseous form, and, where appropriate, the circulation of a heat transfer fluid for a cooling circuit.

[0078] The invention will be more particularly described in the context of a common construction in which the stack 30 is formed of several unit cells 32, which each comprise a membrane-electrode assembly 34 and two bipolar plates 36, arranged on either side of the membrane-electrode assembly 34. The membrane-electrode assembly 36 is also called MEA 36 in the context of the present description. However, the invention is also applicable in the context of fuel cells of another type, in particular of the solid electrolyte ion exchange membrane type. The membrane-electrode assemblies 34 and the bipolar plates 36 are each substantially planar and are stacked along a stacking axis A30, which is considered to coincide with the main axis A20 when the stack 30 is received in the housing 24.

[0079] When the fuel cell 20 is installed in the vehicle 10, in a normal operating configuration, the cell 20 is stationary relative to the vehicle 10. Thus, the main axis A20 is considered to be substantially horizontal, while the housing 22 has a top side 21A and a bottom side 21B, which is opposite the top side 21A and which is located between the top side 21A and the ground 14. In the example illustrated, it is considered that the covers 26A and 26B extend along substantially vertical planes.

[0080] It is considered that, for a given fuel cell 20, all the unit cells 32, also simply called cells 32, are identical to each other, therefore having identical characteristics. In practice, each bipolar plate 36 is arranged between two consecutive cells 32 and is common to these two consecutive cells 32. Each bipolar plate 36 comprises a first face 16A, called the anode side face, which supplies one of the two cells 32 with hydrogen, and a second face 16B, which is opposite the first face 16A and which is called the cathode side face, which supplies the other of the two cells 32 with air. In other words, a cell 32 is supplied with hydrogen by a first bipolar plate 36 and is supplied with air by a second bipolar plate. Since the air contains oxygen, the cell 32 is thus supplied with oxygen.

[0081] In the remainder of the description, the terms oxygen and dioxygen, as well as the terms hydrogen and dihydrogen, are used interchangeably.

[0082] In the example, each bipolar plate 36 is formed by assembling two half-plates, which form between them channels for circulation of heat transfer fluid. The circulation of this heat transfer fluid does not play any role in the electrochemical reactions of the fuel cell 10, but makes it possible to control the temperature of the cells 32. In normal operation of the cell 20, the cell 20 generates electricity while releasing heat, which is evacuated by circulating the heat transfer fluid. The heat transfer fluid is then a cooling fluid. In certain particular phases, in particular in the case of a cold start of the fuel cell, the heat transfer fluid is used to heat the cell.However, by misuse of language, the heat transfer fluid is generally called "cooling fluid", and the circuit in which the heat transfer fluid circulates is called "cooling circuit", the term "cooling" not prejudging the operation.

[0083] In each cell 32, there is an anode compartment, formed between the bipolar plate 36 supplying the cell with hydrogen and the membrane 34, and a cathode compartment, formed between the bipolar plate 36 supplying the cell with air and the membrane. Generally, in each unit cell 32, the cathode compartment is supplied with oxidant, for example oxygen, here in the form of a supply of air containing oxygen, and the anode compartment is supplied with fuel, for example hydrogen. When the stack 30 is formed, the cathode compartments of the unit cells 32 communicate with each other, step by step, forming a cathode circuit 38A of the stack. Similarly, the anode compartments of the unit cells communicate with each other, step by step, forming an anode circuit 38B of the stack.Similarly, the cooling compartments of the unit cells 32 communicate with each other, step by step, forming a cooling circuit 38C of the stack 30.

[0084] During operation of the cell, the cathode circuit 38A of the stack 30 is supplied with air - and therefore with oxygen - by a cathode supply circuit 40 of the cell 20, while the anode circuit 38B of the stack 30 is supplied with hydrogen by an anode supply circuit 50 of the cell 20, and the cooling circuit 38C of the stack 30 is supplied with cooling fluid by a cooling supply circuit 60 of the cell. The cathode 40, anode 50 and cooling 60 supply circuits are partially shown in FIG. 2.

[0085] The cathode 38A, anode 38B and cooling 38C circuits are located within the stack 30, received in the housing 24, and are collectively called internal circuits 38 of the fuel cell 20. In contrast, the cathode 40, anode 50 and cooling 60 supply circuits are external circuits of the fuel cell 20. Each internal circuit 38 is associated with one of the pairs of fluid connections 28A, 28B or 28C, via which this internal circuit 30 is connected to the corresponding external circuit. The cathode supply circuit 40 is also called the “air supply circuit”, or simply the “air circuit”.Similarly, the anode supply circuit 50 is also called the “hydrogen supply circuit” 50, or even simply the “hydrogen circuit” 50, while the cooling supply circuit 60 is also called the “external cooling circuit” 60, as opposed to the cooling circuit 38C which is internal to the stack 30.

[0086] The cathode power supply circuit 40 is now described.

[0087] The cathode supply circuit 40, also called the air supply circuit or simply the air circuit, is configured to supply air to the cathode circuit 38A of the stack 30 of unit cells 32. The air supply circuit 40 comprises an air inlet 402, through which the fresh air is supplied.

[0088] The air circuit 40 also advantageously comprises a compressor 404, which is configured to compress the air supplied by the air inlet 402. The air circuit 40 also comprises an inlet pipe 406, which connects the compressor 404 to an inlet of the cathode circuit 38A of the stack 30. The air circuit 40 also comprises an outlet pipe 408, which connects an outlet of the cathode circuit 38A of the stack 30. The air circuit 40 also comprises an exhaust 410, configured to allow the air to escape, to the external environment, the air leaving the cathode circuit 38A and passing through the outlet pipe 408.In normal operation of the fuel cell 20, fresh air enters the cathode circuit 38A through the inlet pipe 406, the oxygen contained in this fresh air is combined with the protons during the electrochemical reaction occurring in each of the unit cells 32, producing water, and the oxygen-depleted and water-enriched air leaves the cathode circuit 38A through the exhaust 410.

[0089] Preferably, the air circuit 40 also comprises a first isolation valve 412, which is configured to close the inlet pipe 406 and which is arranged between the compressor 404 and the stack, more precisely between the compressor 404 and the inlet of the cathode circuit 38A. Preferably, the first isolation valve 412 is a proportional valve, which makes it possible to completely or partially close the inlet pipe 406. Generally speaking, a so-called “closed” valve does not allow any fluid to pass through. A valve which is not closed is an open valve, that is to say one which allows fluid to pass through this valve, whether this valve is “partially open” or “completely open”. By extension, a “partially open” valve is therefore also “partially closed”.

[0090] Preferably, the air circuit 40 also comprises a second isolation valve 414, which is configured to close the outlet pipe 410 and which is arranged between the stack 30 and the exhaust 410, more precisely between the outlet of the cathode circuit 38A and the exhaust 410. Preferably, the second isolation valve 414 is a proportional valve, which makes it possible to completely or partially close the outlet pipe 408. The air circuit 40 advantageously comprises a first pressure sensor 415, which is here arranged at the inlet of the cathode circuit 38A, between the first isolation valve 412 and the stack 30. The first pressure sensor 415 is configured to measure an air pressure at the inlet of the cathode circuit 38A.

[0091] The air circuit 40 advantageously comprises a humidifier 420, which comprises: a regulation portion 422, which is crossed by the inlet pipe 408, which is located between the first isolation valve 412 and the stack 30, more precisely between the first isolation valve 412 and the inlet of the cathode circuit 38A, and which is configured to regulate a humidity level in the air passing through the inlet pipe 408, and

[0092] - a recovery portion 424, which is crossed by the outlet pipe 410, which is located between the second isolation valve 414 and the stack 30, more precisely between the second isolation valve 414 and the outlet of the cathode circuit 38A, and which is configured to recover humidity from the air passing through the outlet pipe 410.

[0093] In simplified terms, the humidifier recovers all or part of the humidity transported by the air leaving the cathode duct 38A, and regulates the humidity of the air entering the cathode circuit 38A.

[0094] The air circuit 40 advantageously comprises a bypass circuit 416, which connects the outlet of the cathode circuit 38A to the outlet pipe 410, without passing through the recovery portion 424. The bypass circuit 416 allows the humidifier 420 to be bypassed, for example when it is not necessary to recover the humidity from the air leaving the cathode circuit 38A. The bypass circuit 416 is connected to the outlet pipe 410 by a junction point 417, which is located between downstream of the second isolation valve 414, between the second isolation valve 414 and the exhaust 410. Throughout the present description, the notions of “upstream” and “downstream” are made in relation to the normal flow direction of the fluids, liquid or gaseous, during normal operation of the fuel cell. The air circuit 40 also includes a third isolation valve 418, which is located on the bypass circuit 416.Preferably, the third isolation valve 418 is a proportional valve, which makes it possible to completely or partially close the bypass circuit 416. It is understood that the coordinated control of the second and third isolation valves 414 and 418 makes it possible to pass all or part of the air flow leaving the cathode circuit 38A through the bypass circuit 416 or through the recovery portion 424, depending on the needs for recovering the moisture contained in the air leaving the cathode circuit 38A. The hydrogen supply circuit 50 is partially shown. The hydrogen circuit 50 comprises an anode inlet pipe 52, which is connected to the inlet of the anode circuit 38B and through which a flow of hydrogen is introduced into the stack 30. The hydrogen circuit 50 comprises an anode outlet pipe 54, which connects an outlet of the anode circuit 38B to the exhaust 410.The hydrogen not consumed in the stack 30 is thus diluted, in the exhaust 410, with the air leaving the outlet pipe 408, before being released into the external environment.

[0095] When the fuel cell 20 is supplied with both hydrogen and air to produce electricity, the fuel cell 20 is in a so-called "production" operating mode, or the cell 20 is simply said to be "in production". In the example illustrated, when the fuel cell 20 is in production mode, the quantity of electricity generated by the fuel cell 20 is regulated by the impedance imposed on its terminals. The quantity of hydrogen injected by the hydrogen circuit 50 into the anode circuit 38B is directly induced by the consumption of the molecules in the stack at iso anode pressure, while the oxygen in the air injected by the air circuit 40 is injected in a super-stoichiometric manner with active control, that is to say in excess, so as to never run out.For example, the quantity of oxygen injected into the cathode circuit 38A is substantially double the quantity required for the electrochemical reaction with the hydrogen injected into the anode circuit 38B.

[0096] According to examples of control of the fuel cell 20, in production mode, a power of the compressor 404 is adjusted to a nominal production value, so as to inject fresh air into the inlet pipe 406 with a nominal production flow rate, while the first isolation valve 412 is left open, preferably fully open, and the second and third isolation valves 414 and 418 are controlled in a coordinated manner, so as to control an air pressure within the cathode circuit 38A. The air pressure within the cathode circuit 38A is measured by means of the first pressure sensor 415. The second and third isolation valves 414 and 418, taken together, are outlet valves 414 and 418 of the cathode circuit 38A, which make it possible to regulate the air pressure in the cathode circuit 38A.

[0097] The external cooling circuit 60 is configured to supply the stack 30 of cells 32 with a cooling fluid, for example glycolated water. The external cooling circuit 60 generally comprises a pump, provided to circulate the cooling fluid in the cooling circuit, and at least one radiator, provided to evacuate into the external environment the heat captured by the cooling fluid during its passage in the cooling circuit 38C. The pump and the radiator of the external cooling circuit 60 are not shown. Depending on the case, the pump and the radiator are not exclusively part of the cooling circuit, but are elements common to the vehicle 10. This aspect is not detailed further.

[0098] In the example illustrated, the air circuit 40 advantageously comprises a heat exchanger 428, also simply called exchanger 428, which is configured to exchange thermal energy between the air passing through the inlet pipe 406 and the cooling fluid, the heat exchanger 428 being located, along the inlet pipe 406, between the compressor 404 and the first isolation valve 412.

[0099] According to one aspect of the invention, the air from the supply circuit 40 is used to ventilate the interior of the housing 22. The fuel cell 20 thus comprises a bypass circuit 430, which comprises an inlet 432, by which the bypass circuit 430 is connected to the inlet pipe 406, and an outlet 434, by which the bypass circuit 430 is configured to supply the housing 22 with ventilation air. The inlet 432 of the bypass circuit 430 is advantageously located between the compressor 404 and the first isolation valve 412. In other words, the inlet 432 of the bypass circuit 430 is connected downstream of the compressor 404. The inlet 432 of the bypass circuit 430 is located upstream of the fluid connection 28 associated with the cathode circuit 38A. In particular, input 432 of branch circuit 430 is located outside of housing 22.In the illustrated example, the inlet 432 of the bypass circuit 430 is connected to the air circuit 40 between the heat exchanger 428 and the first isolation valve 412.

[0100] The fuel cell 20 also comprises a calibrated orifice 436, which is arranged on the bypass circuit 430, the calibrated orifice 436 having a reduced passage section compared to the rest of the bypass circuit 430 and being configured to limit an air flow through the bypass circuit 430.

[0101] The fuel cell 20 also comprises a second pressure sensor 438, which is configured to measure an air pressure at the inlet of the bypass circuit 430. The second pressure sensor 438 is here arranged on the inlet pipe 406, between the first isolation valve 412 and the heat exchanger 428.

[0102] According to another aspect of the invention, a first cover among the two covers 26A and 26B, here the cover 26B, comprises a main ventilation inlet 440, through which ventilation air is introduced into the internal housing V24, the main inlet 440 opening, in the internal housing V24, at a highest point of the first cover 26B. With reference to FIG. 2, the outlet 434 of the bypass duct 430 is connected to the main ventilation inlet 440, the outlet 434 of the bypass duct 430 being here merged with the main ventilation inlet 440. Thus the main ventilation inlet 440 is supplied by the bypass circuit 430. As can be seen in Figure 1 b or in Figure 3 in particular, the main ventilation inlet 440 is distinct and different from the fluid conduits 28, and the connectors 28A, 28b, 28C, and is preferably located opposite the latter.

[0103] A second cover among the two covers 26A and 26B, here the cover 26A, comprises a first main ventilation outlet 442, through which the ventilation air introduced into the internal housing V24 via the main inlet 440 is evacuated. The first main ventilation outlet 442 is distinct and different from the fluid conduits 28 and the connectors 28A, 28B, 28C and is preferably located on the same cover as the latter. The first main outlet 442 is here connected to the exhaust 410 via a first evacuation pipe 443. The first main outlet 442 is thus located on a cover opposite the cover on which the main inlet 440 is arranged. In the example illustrated, the main inlet 440 is arranged on the first cover 26B, while the first main outlet 442 is arranged on the second cover 26A.

[0104] The first main outlet 442 opens into the internal housing V24 at a highest point of the second cover 26A, so that the ventilation air introduced by the first main inlet 440 exits through the first main outlet 442 by sweeping an upper part of the internal housing V24, entraining any fluids that are lighter than air that may be present in the internal housing V24. In particular, any hydrogen leaks tend to accumulate in the upper part of the internal housing V24 and are thus entrained by the ventilation air.

[0105] The second cover 26A also comprises a second main outlet 444, which opens into the internal housing V24, at a lowest point of the second cover 26A, so that the ventilation air introduced by the first main inlet 440 tends to entrain any fluids heavier than air that may be present in the internal housing V24, in particular water. The second main outlet 444 is here connected to the exhaust 410 via a second discharge pipe 445.

[0106] The particular arrangement of the first main ventilation inlet 440, the first main ventilation outlet 442 and the second main ventilation outlet 444 allows efficient ventilation of the internal housing V24, contributing to the proper operation and longevity of the fuel cell 20.

[0107] When ventilation air is introduced into the internal housing V24 through the first main inlet 440, all of this ventilation air finally arrives at the exhaust 410, passing, on the one hand, through the first main outlet 442 then the first exhaust pipe 443 and, on the other hand, through the second main outlet 444 then the second exhaust pipe 445. In simplified terms, by applying Bernoulli's theorem, an air flow Q passing through the calibrated orifice 436 is proportional to the square root of a pressure differential AP on either side of this calibrated orifice 436. In other words: Q = kx VÂP, where k is a constant depending on the geometry of the calibrated orifice, this constant taking into account the pressure losses. Since the exhaust 410 is connected to the external environment, the pressure downstream of the calibrated orifice is close to atmospheric pressure and therefore relatively constant.As a result, as a first approximation, the flow rate passing through the calibrated orifice 436 is proportional to the square root of the pressure measured by the second sensor 438. Thus, the calibrated orifice 436 makes it possible to sample a portion of the air flow circulating in the air supply circuit 40, and to use this sampled air for the ventilation of the housing 24. This avoids the installation of a complete ventilation circuit, comprising a second air intake, a second compressor in addition to the compressor 404, etc. As a corollary, adjusting the inlet pressure of the bypass circuit 430 makes it possible to adjust the flow rate of the ventilation air circulating through the calibrated orifice 436.

[0108] A first way to adjust the inlet pressure of the bypass circuit 430 is to adjust the power of the compressor 404 and the opening of the first isolation valve 412. Advantageously, the fuel cell also comprises a bypass valve 450, which is arranged between the inlet 432 of the bypass circuit 430 and the exhaust 410, the bypass valve 450 being configured to regulate an air pressure at the inlet of the bypass circuit 430, so as to regulate an air flow passing through the calibrated orifice 436. The bypass valve 450 is preferably a propositional valve.

[0109] It is understood that when the bypass valve 450 is fully open, most of the air injected by the compressor 404 into the inlet pipe 406 tends to pass directly to the exhaust 410. When the bypass valve is fully closed, the air injected by the compressor 404 is shared between the bypass circuit and the cathode circuit 38A - if of course the first isolation valve 412 is not closed, and if the second and third isolation valves 414 and 418 are not both closed -.When the bypass valve 450 is partially open - or partially closed, which is equivalent -, the air flow injected into the air circuit 406 by the compressor 404 is shared between a first portion which passes directly through the bypass valve 450 to the exhaust 410, a second portion which passes through the calibrated orifice 436 and serves as ventilation air for the housing 22, and a possible third portion, depending on the opening of the first, second and third isolation valves 412, 414 and 418. The fuel cell 20 comprises a computer, which is configured to receive the measurements from the first and second pressure sensors 415 and 418, to adjust a power of the compressor 404, and to adjust a closing or an opening, total or partial, of each of the isolation valves 412, 414 and 418 and of the bypass valve 450. The calculator is not shown.

[0110] The invention also relates to a method for controlling the fuel cell 20. In general, the method for controlling the fuel cell 20 comprises the following steps:

[0111] - a compressor power 404 is adjusted, then a pressure is measured in the inlet 432 of the bypass circuit 430, here by means of the second pressure sensor 438, then, depending on the pressure measured in the inlet 432 of the bypass circuit 430, an opening of the bypass valve 450 is adjusted, so as to regulate the pressure in the inlet 432 of the bypass circuit 430 and to regulate the air flow passing through the calibrated orifice 436.

[0112] The adjustment of the opening of the bypass valve 450 is chosen using a previously recorded law which links the air flow through the calibrated orifice 436 and a pressure differential AP on either side of the calibrated orifice 436. A first example of a previously recorded law is the law deriving from Bernoulli's theorem, described previously. According to another alternative example, a multidimensional chart is previously recorded in the computer, the chart linking in particular the pressures measured by the first and second pressure sensors 415 and 438 and the opening positions of the isolation valves and the bypass valve 450.

[0113] According to a first particular example of a control method, it is considered that the fuel cell 20 is initially in production mode, in stabilized mode. Thus the compressor 404 operates at a given and non-zero power level, called the first level, the first isolation valve 412 is fully open, while the second and third isolation valves 414 and 418 are each open to an adequate level, on the one hand to ensure sufficient air pressure in the cathode circuit 38A, and on the other hand to ensure the recovery of humidity at the desired level in the humidifier 420. The bypass valve 450 is in a closed position.If, for any reason, it is necessary to urgently increase the ventilation flow rate in the housing 22, for example if a hydrogen sensor detects an increase in the hydrogen concentration in the housing 22, then the power of the compressor 404 is adjusted to a second level, higher than the first level, while the first isolation valve 412 is partially closed so as to prevent an increase in the air flow rate in the cathode circuit 38A, while keeping the bypass valve 450 completely closed. Thus, the pressure increase at the inlet of the bypass circuit 430 is forced, which results in an increase in the air flow passing through the bypass circuit 430.

[0114] As a variant of this first particular example, when it is necessary to increase the ventilation flow rate in the housing 22, then the power of the compressor 404 is adjusted to a power greater than the first level, preferably to a maximum power, while the first isolation valve 412 is partially closed so as to prevent an increase in the air flow rate in the cathode circuit 38A, and the bypass valve 450 is partially open, so as to regulate the air pressure at the inlet of the bypass circuit 430. The air flow rate through the calibrated orifice 436 is thus regulated.

[0115] According to another particular example of a control method, the fuel cell 20 is initially stopped, the first isolation valve 412 and the second isolation valve 414 are closed, so as to isolate the cathode circuit 38A. When the bypass circuit 416 is present, the third isolation valve 418 is also closed. The hydrogen supply circuit 50 is also closed. The bypass valve 450 is normally open at rest. Next, a power of the compressor 404 is adjusted to a maximum operating value, maximizing exhaust ventilation, while the three isolation valves 412, 414 and 418 are kept closed, and the bypass valve 450 is closed, so as to maximize an air flow injected into the bypass circuit 430. Next, the anode circuit 38B of the stack 30 is supplied with hydrogen, so as to purge the anode circuit 38B of gases other than hydrogen.The flow of ventilation air through the housing 22 is thus maximized, reducing the risks associated with possible hydrogen leaks. If the quantity of air injected into the bypass circuit 430 is too large, then it is sufficient to open the bypass valve 450 to the desired level to lower the pressure at the inlet of the bypass circuit 430. Alternatively or in addition, it is also possible to reduce the power of the compressor 404.

[0116] A fuel cell 20', according to a second embodiment of the invention, is shown in Figure 3. In the second embodiment, elements similar to those of the first embodiment bear the same references and operate in the same way. In the following, the differences between the first and second embodiments of the invention are mainly described.

[0117] One of the main differences of the second embodiment with the first embodiment is that the fuel cell 20' of the second embodiment comprises a switching unit 80. The switching unit 80, also called HVSU, acronym for High Voltage Switch Unit in English, is electrically connected to the stack 30 through the housing 22, for example through the first cover 26B, and is arranged electrically in series between the stack 30 and the rest of the fuel cell 20'. The electrical connections are not shown. In particular, the switching unit 80 is generally arranged electrically in series between the stack 30 and a direct current / direct current converter, also called DC / DC converter in English. The converter is not shown.

[0118] The switching unit 80 is configured to open or close a power circuit of the stack 30, so as to electrically isolate the stack 30 from the rest of the fuel cell 20'. The switching unit 80 is secured to the housing 22, generally fixed to the first cover 26B. In the illustrated example, the switching unit 80 is also connected to the external cooling circuit 60, so as to regulate a temperature of the switching unit 80.

[0119] The switching unit 80 comprises a casing 82, which provides an internal volume V82 and which comprises a first side 84A and a second side 84B, which is opposite the first side 84A and which is oriented towards the first cover 26B. The casing 82 also comprises a high side 86A and a low side 86B, which are different from the first and second sides 84A and 84B, the high side 86A and the low side 86B of the switching unit 80 being respectively located on the same side as the high 21A and low 21B sides of the housing 22. When the switching unit 80 is fixed to the first cover 26B, the internal volume V82 communicates with the internal housing V24, and it happens that hydrogen, resulting from leaks from the stack 30 and located in the internal housing V24, is also found in the internal volume V82. It is therefore necessary to ventilate the internal volume V82 to evacuate this hydrogen.

[0120] For this purpose, the switching unit 80 comprises:

[0121] - a first auxiliary ventilation inlet 88, which is located on the first side 84A of the casing 82 and through which ventilation air is introduced into the internal volume V82 of the switching unit 80,

[0122] - a first auxiliary ventilation outlet 90, which is located on the second side 84B of the casing 82 and through which the ventilation air introduced by the first auxiliary inlet 88 is evacuated.

[0123] The first auxiliary outlet 90 is connected to the first main inlet 434, so that the ventilation air used for the housing 22 is previously used as ventilation air for the switching unit 80. In other words, the switching unit 80 is interposed, on the bypass circuit 430, between the calibrated orifice 436 and the first main inlet 434 of the housing 22. Advantageously, the first auxiliary inlet 88 and the first auxiliary outlet 90 each open onto a highest point of the internal volume V82 and are arranged so that, when the ventilation air is introduced through the first auxiliary inlet 88 and exits through the first auxiliary outlet 90, the ventilation air entrains the fluids lighter than air contained in the internal volume V82, in particular hydrogen.

[0124] It also happens that the humidity contained in the air condenses in the internal volume V82. It is also appropriate to evacuate this humidity and this liquid water. Advantageously, the switching unit 80 also comprises a second auxiliary outlet 92, which is located on the same side as the first auxiliary outlet 90 and which opens into the internal volume V82 via a lowest point of the internal volume 82, so that the ventilation air introduced via the first auxiliary inlet 88 tends to entrain fluids heavier than air, in particular water. The first end plate 26B comprises a second main inlet 446, which opens into the internal housing V24 via a lowest point, the second auxiliary outlet 92 being connected to the second main inlet 446.

[0125] Advantageously, when the vehicle 10 is located on horizontal ground 14, the second auxiliary outlet 92 is located at least as high as the second main inlet 446, so as to promote the gravitational flow of the liquid water.

[0126] According to an alternative aspect of the invention, the method for controlling the fuel cell 20 / 20' can be implemented even if the air circuit does not open into the upper part of the internal housing V24 of the casing 24 or into the upper part of the internal volume V82 of the switching unit 80. In particular, the control method can be implemented as soon as the bypass circuit 430 comprises a calibrated orifice 436 and, where appropriate, the bypass valve 450 is installed between the inlet 406 and outlet 408 pipes, making it possible to regulate the air pressure in the inlet of the bypass circuit 430.The control method can be implemented independently of the orientation of the fuel cell in the usage configuration, in particular when the main axis A30 is not horizontal, and / or the top or bottom sides of the housing are not fixed, and / or the ventilation inlets or outlets do not open at the highest or lowest points of the enclosures concerned.

[0127] Thus, according to an example of an alternative piloting method, the piloting method includes the following steps, during which:

[0128] - a compressor power 404 is adjusted, a pressure is measured in the inlet 432 of the bypass circuit 430 using the pressure sensor 438, - then, depending on the measured pressure, an opening of the bypass valve 450 is adjusted so as to regulate the pressure in the inlet of the bypass circuit 430 and to regulate the air flow passing through the calibrated orifice 436, the adjustment of the opening of the bypass valve 450 being chosen using a law, which is previously recorded in a computer of the fuel cell and which connects the air flow through the calibrated orifice and a pressure differential on either side of the calibrated orifice.

[0129] Advantageously: the fuel cell being initially stopped, the first isolation valve 412 and the second isolation valve 414 are closed, so as to isolate the cathode circuit 38A,

[0130] - then, a power of the compressor 404 is adjusted to a maximum operating value, while the bypass valve 450 is closed, so as to maximize an air flow passing through the bypass circuit 430, then, an anode circuit (38B) of the stack 30 is supplied with hydrogen, so as to purge the anode circuit (38B) of gases other than hydrogen.

[0131] Advantageously:

[0132] - initially, the fuel cell is in a production mode, in which:

[0133] • the compressor 404 operates at a first non-zero power level,

[0134] • the first isolation valve 412 is fully open, and

[0135] • the bypass valve 450 is completely closed, then the power of the compressor 404 is increased to a second power level, higher than the first level, while the first isolation valve 412 is partially closed, while keeping the bypass valve 450 completely closed.

[0136] The embodiments and variations mentioned above can be combined with each other to generate new embodiments of the invention.

Claims

CLAIMS 1. Fuel cell (20; 20'), comprising: several unit cells (32), which are stacked along a main axis (A30) so as to form a stack (30) of cells, a housing (22), which provides an internal housing (V24) receiving the stack (30), and which comprises: • a jacket (24), which comprises two end openings aligned along the main axis (A30), • a first cover (26B) and a second cover (26A), different from the first cover (26B), the two covers sealingly closing the two openings of the jacket (24) and delimiting, with the jacket (24), the internal housing (V24) of the casing (22), in which: when the fuel cell (20; 20') is in a usage configuration: • the main axis (A30) is substantially horizontal, • the housing (22) has a top side and a bottom side, the first cover (26B) comprises a main ventilation inlet (434), through which ventilation air is introduced into the internal housing (V24), the main inlet (434) opening into the internal housing (V24) at a highest point of the first cover (26B), the second cover (26A) comprises a first main ventilation outlet (442), through which the ventilation air introduced into the internal housing (V24) is evacuated, the first main outlet (442) opening into the internal housing (V24) at a highest point of the second cover (26A), so that the ventilation air introduced through the main inlet (434) exits through the first main outlet (442) by sweeping an upper part of the internal housing (V24), entraining fluids lighter than air, in particular hydrogen, the second cover (26A) comprises also a second main exit (444), which opens,in the internal housing (V24), at a lowest point of the second cover (26A), so that the ventilation air introduced through the main inlet (434) tends to entrain fluids heavier than air, in particular water., 2. Fuel cell (20') according to claim 1, in which: the fuel cell also comprises a switching unit (80), which is integral with the housing (22) and which is configured to open or close a power circuit of the stack (30), the switching unit (80) comprises an envelope (82), which provides an internal volume (V82) and which comprises: • a first side (84A) and a second side (84B), which is opposite the first side and which is oriented towards the first cover (26B), • a high side (86A) and a low side (86B), which are different from the first and second sides, the high side (86A) and the low side (86B) of the switching unit (80) being respectively located on the same side as the high (21 A) and low (21 B) sides of the housing (22) when the fuel cell (20') is in the use configuration, the switching unit (80) comprises: • an auxiliary ventilation inlet (88), which is located on the first side (84A) and through which ventilation air is introduced into an internal volume (V82) of the switching unit, • a first auxiliary ventilation outlet (90), which is located on the second side (84B) and through which the ventilation air introduced by the auxiliary inlet (88) is evacuated, the auxiliary inlet (88) and the first auxiliary outlet (90) each open onto respective highest points of the internal volume (V82) and are configured so that when the ventilation air is introduced by the auxiliary inlet (88) and exits by the first auxiliary outlet (90), the ventilation air entrains the fluids lighter than air contained in the internal volume (V88), in particular hydrogen, the first auxiliary outlet (90) is connected to the first main inlet (434), so that the ventilation air used for the housing (22) is previously used as ventilation air for the switching unit (80).

3. Fuel cell (20') according to claim 2, wherein: the switching unit (80) comprises a second auxiliary outlet (92), which is located on the second side (84B) of the switching unit (80) and which opens into the internal volume (V82) through a lowest point of the internal volume (V82), so that when the ventilation air is introduced through the inlet auxiliary (88), the ventilation air exiting through the second auxiliary outlet (92) tends to entrain fluids heavier than air, in particular water, the first cover (26B) comprises, in addition to the main inlet (440), a second main inlet (446), which opens into the internal housing (V24) through a lowest point, the second auxiliary outlet (92) is connected to the second main inlet (446).

4. Fuel cell (20; 20') according to any one of claims 1 to 3, wherein the fuel cell comprises: an air supply circuit (40), which is configured to supply air to a cathode circuit (38A) of the stack (30), and a bypass circuit (430), which comprises an inlet (432), by which the bypass circuit (430) is connected to the air supply circuit (40), and an outlet (434), by which the bypass circuit (430) is configured to supply the housing (22) with ventilation air.

5. Fuel cell (20; 20') according to claim 4, wherein: the outlet (434) of the bypass circuit (430) is connected to the main ventilation inlet (440).

6. Fuel cell (20; 20') according to any one of claims 4 or 5, wherein: the air supply circuit (40) comprises a compressor (404), which is configured to compress air supplying the cathode circuit (38A), the inlet (432) of the bypass circuit (430) is connected downstream of the compressor (404).

7. Fuel cell (20; 20') according to any one of claims 4 to 6, wherein: the fuel cell also comprises a calibrated orifice (436), which is arranged on the bypass circuit (430), the calibrated orifice 436 having a reduced passage section compared to the rest of the bypass circuit (430) and being configured to limit an air flow through the bypass circuit (430).

8. Fuel cell (20; 20') according to any one of claims 4 to 7, wherein: the air supply circuit (40) comprises: • an inlet pipe (406), which connects the compressor (404) to an inlet of the cathode circuit (38A), and an outlet pipe (408), which connects an outlet of the cathode circuit (38A) of the stack (30), • an exhaust (410), configured to allow the air leaving the cathode circuit (38A) to escape and passing through the outlet pipe (408) to the external environment, the first main outlet (442) is connected to the exhaust (410).

9. Fuel cell (20; 20') according to claim 8, wherein: the second main outlet (444) is connected to the exhaust (410).

10. Fuel cell (20; 20') according to any one of claims 4 to 9, wherein: the air supply circuit (40) comprises: • a pressure sensor (438), which is arranged between the heat exchanger and the humidifier (420) and which is configured to measure a pressure at the inlet of the bypass circuit (430), • a bypass valve (450), which is arranged between the inlet (432) of the bypass circuit (430) and the exhaust (410), the bypass valve (450) being configured to regulate an air pressure at the inlet of the bypass circuit (430), so as to regulate an air flow passing through the calibrated orifice (436).

11. Method for controlling a fuel cell (20; 20'), the fuel cell being in accordance with claim 4 to 10 taken in combination, in which: a compressor power (404) is adjusted, then a pressure in the inlet (432) of the bypass circuit (430) is measured using a pressure sensor (438), then, depending on the measured pressure, an opening of the bypass valve (450) is adjusted so as to regulate the pressure in the inlet of the bypass circuit (430) and to regulate the air flow passing through the calibrated orifice (436), the adjustment of the opening of the bypass valve (450) being chosen using a law, previously recorded in a computer of the fuel cell, which connects the air flow through the calibrated orifice and a pressure differential on either side of the calibrated orifice.

12. Control method according to claim 11, wherein: the fuel cell (20; 20') being initially stopped, the first isolation valve (412) and the second isolation valve (414) are closed, so as to isolate the cathode circuit (38A), then, a power of the compressor (404) is adjusted to a maximum operating value, while the bypass valve (450) is closed, so as to maximize an air flow passing through the bypass circuit (430), then, an anode circuit (38B) of the stack (30) is supplied with hydrogen, so as to purge the anode circuit (38B) of gases other than hydrogen.

13. Control method according to claim 11, in which: initially, the fuel cell (20; 20') is in a production mode, in which: • the compressor (404) operates at a first non-zero power level, • the first isolation valve (412) is fully open, • the bypass valve (450) is completely closed, then the power of the compressor (404) is increased to a second power level, higher than the first level, while the first isolation valve (412) is partially closed, while keeping the bypass valve (450) completely closed.

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