Cooling circuit for a fuel cell installed in a motor vehicle

Abstract

The invention relates to a cooling circuit (0) for a fuel cell installed in a motor vehicle comprising: - a first branch comprising the cell assembly (1) and a pump (9), - a second branch comprising at least one liquid / air type radiator (2), - a third branch comprising a heat exchanger (3a), - a fourth branch (4) providing a possible bypass of the radiator(s) (2) by the coolant coming from the cell assembly (1) via the pump (9), - a three-way valve (15) capable of directing the flow entering it via an inlet (15a): - in the open position, towards a first outlet (15b) in fluid communication with an inlet of the cell assembly (1), - in the closed position, towards a second outlet (15c) in fluid communication with a suction of the pump (9) so as to bypass the cell assembly (1). Figure 1

Description

Title of the invention: Cooling circuit for a fuel cell installed in a motor vehicle

[0001] The present invention relates to a cooling circuit for a fuel cell installed in a motor vehicle.

[0002] Engine braking is a braking method by which a vehicle is slowed down by the resistance its engine opposes to its operation. This technique is linked to piston engines, which then produce significant losses by pumping (the fuel injection being then cut off) and by the friction of the mechanical parts of the traction chain. The term is also used for vehicles powered by electric motors when these operate as generators and recharge, for example, a battery of accumulators by regenerative braking.

[0003] Engine braking is an important feature for vehicles that tow and / or transport heavy loads on steeply sloping roads because it considerably reduces the braking work of the vehicle when going downhill. Intensive use of the friction braking system on long, steep descents quickly (within a few minutes) leads to their limit of effectiveness, due to excessive heating, or even to their destruction. Under the effect of temperature, the pads and drum linings can melt, while the brake circuit fluid can vaporize. Very long descents are therefore common sites of accidents.

[0004] A Diesel powertrain generates significant braking power: for a given engine, up to 160kW at 3500 rpm, approximately 100kW at 2500 rpm and up to 50kW at 1500 rpm. A spark-ignition powertrain of equivalent engine power has, at 5500 rpm, approximately 100kW less, and less than 20kW at 2500 rpm.

[0005] The braking power of electric vehicles is significantly lower than that of vehicles with internal combustion engines. Electric vehicles, however, have highly efficient regenerative braking systems that can generate high braking performance, provided that the state of charge of the electrochemical traction storage device is low enough, at the top of a descent, to store all the energy accumulated during braking.

[0006] Over long distances downhill and even more so on steep gradients, the state of charge of the electrochemical traction storage device can quickly reach 100%, inhibiting any opportunity for additional energy storage. In this case, the vehicle's friction braking system must dissipate the energy needed to brake the vehicle. At the maximum permissible rolling weight (MPTRA), if the trailer brakes are limited, the vehicle's friction braking system quickly overheats, leading to its destruction and therefore the loss of the vehicle's braking function.

[0007] The fuel cell of an electrified vehicle does not have any intrinsic braking power. The fuel cell vehicle thus has a significant deficit compared to a vehicle with self-ignition or even controlled ignition engines, and can then only rely on regenerative braking and the storage of the recovered energy in the electrochemical traction storage unit that it incorporates, itself of much smaller size, power, capacity and energy than the electrochemical traction storage unit of an equivalent electric vehicle.

[0008] All the subsystems and components of the vehicle and its powertrain are used to dissipate the excess electrical power: electric heaters (electrochemical traction storage, fuel cell, passenger compartment), motor-fan units of the vehicle's thermal systems (including the one or ones dedicated to cooling the fuel cell), electric air conditioning compressor, electric air compressor of the fuel cell, deliberate degradation of the efficiency of the electric motor(s) and its (or their) inverter(s), etc. as well as a system dedicated to the thermal management of the fuel cell.

[0009] The thermal management system of the fuel cell is also used to then dissipate a portion of the excess electrical power in the form of thermal power, for example by activating at least one electric heater of one of the fluid loops of the vehicle and putting said fluid loop in thermal contact, via a heat exchanger between their two heat transfer fluids, with the cooling circuit of the fuel cell. It is then essential, whether the fuel cell is operational (then idling) or deactivated, not to degrade the durability of the cell in the short or medium term by: - excessively high (or even too low) coolant temperature conditions at the inlet and / or outlet of the stack, - and / or too great a temperature gradient between the inlet and outlet of the coolant from the battery, - and / or an excessively high flow rate of coolant within the battery, - and / or an internal humidity level of the battery outside the permissible limits, leading to deterioration and / or irreversible degradation, by excessive drying or humidification, of the assembly formed by the membrane and the electrodes of each cell of the battery.

[0010] These conditions reduce the availability of the thermal management system of the fuel cell. fuel to dissipate part of the excess electrical power. In addition, state-of-the-art systems do not offer optimal functionality for dissipating part of the excess electrical power into thermal power.

[0011] In order to effectively overcome these drawbacks, the cooling circuit of the fuel cell according to the invention is splittable and makes it possible to isolate the cell from any passage of heat transfer fluid internally. The cooling circuit of the fuel cell comprises additional devices in order to increase the cooling potential of the cell.

[0012] When it is necessary to dissipate, by the thermal management system of the fuel cell, the excess electrical power into thermal power, the cooling circuit of the cell takes a configuration such that the heat transfer fluid used therein bypasses the cell without passing through it. Under these conditions, the cell, deactivated and dissociated from its cooling circuit, no longer poses constraints on the evacuation of very high thermal power through its thermal management system, which is then entirely mobilized to dissipate the excess electrical power into thermal power. In a complementary manner, additional devices are implemented within the cooling circuit of the fuel cell in order to increase its cooling potential.

[0013] A pressure-controlled valve is arranged on a radiator bypass duct. Its implementation makes it possible, in certain operating modes, to increase the flow rate of coolant from the fuel cell through a second liquid / liquid heat exchanger, in order to increase the dissipation of calories in the cooling circuit of the cell to accelerate its heating or to promote the evacuation of calories from excess electrical power.

[0014] A valve, advantageously of the on / off type (or possibly a proportional control valve) is arranged on the branch carrying this liquid / liquid type heat exchanger, upstream or downstream of the latter, to maximize the flow rate of coolant from the fuel cell through its cooling radiator and to secure the cooling circuit of the fuel cell as well as the cell itself in the event of failure and excessive dissipation of thermal power from the excess electrical power.

[0015] A bypass valve, judiciously arranged within the cooling circuit of the fuel cell, allows the heat transfer fluid, implemented in the circuit by the associated pump, to bypass the cell without passing through it. The thermal management system of the fuel cell thus overcomes the constraints posed by the latter and can dissipate to the environment outside the vehicle a thermal power resulting from much greater excess electrical power.

[0016] Thus, any safety risk of overheating, degradation, inflammation, boiling of the The vehicle's conventional friction braking system and the risk of accidents are eliminated. This allows the vehicle to travel long distances or downhill without risk.

[0017] More specifically, the invention relates to a cooling circuit for a fuel cell installed in a motor vehicle, said fuel cell comprising an assembly of cells, said cooling circuit comprising four branches in parallel with each other constituted by: - a first branch comprising the assembly of cells and a coolant circulation pump, - a second branch comprising at least one liquid / air type radiator with which at least one motor-fan unit is associated to ensure dissipation to the outside air of calories from a coolant circulating in the cooling circuit, - a third branch comprising a liquid / liquid type heat exchanger between the coolant of the cell assembly and another coolant of at least one other fluid loop of the motor vehicle chosen from: a fluid loop providing heating of a passenger compartment and a fluid loop providing heating or cooling of an electrochemical motor storage device, a valve being arranged on this third branch upstream or downstream of the liquid / liquid type heat exchanger, - a fourth branch providing a possible bypass of the radiator(s) by the coolant from the cell assembly via the pump, a valve being arranged at the inlet of the fourth branch in fluid communication with a discharge of the pump, and at the outlet of the second, third and fourth branches and upstream of the first branch of the circuit is arranged a three-way valve capable of directing the flow entering it via an inlet: - in the open position, towards a first outlet in fluid communication with an inlet of the cell assembly, - in the closed position, to a second outlet in fluid communication with a suction of the pump within a pipeline also connecting an outlet of the cell assembly to the suction of the pump, so as to bypass the cell assembly.

[0018] According to one embodiment of the invention, the first branch further comprises a particle filter.

[0019] According to one embodiment of the invention, at the interface between the second and fourth branches of the circuit is arranged a three-way valve capable of ensuring thermoregulation of the cell assembly by distributing via its internal valve a flow admitted at the inlet of the cell assembly between a portion of flow of re liquid cooling from the fourth branch without having undergone heat exchange with an external environment and a portion of coolant flow from the second branch after having undergone heat exchange with the external environment through the radiator(s).

[0020] According to one embodiment of the invention, the three-way valve is of the proportional type.

[0021] According to one embodiment of the invention, said cooling circuit comprises a reservoir of cooling liquid for the assembly of cells ensuring the functions of degassing the circuit, thermal expansion of the liquid and pressurization of the circuit at the inlet of the pump.

[0022] According to one embodiment of the invention, the tank comprises a coolant inlet opening into the air into the tank from an auxiliary coolant outlet of the cell assembly via an auxiliary branch comprising an ion exchanger or deionizer.

[0023] According to one embodiment of the invention, the tank comprises a coolant inlet opening underwater into the tank from an auxiliary coolant outlet of the radiator so that this portion of the liquid flow which comes from it has not exchanged calories through the radiator with outside air.

[0024] According to one embodiment of the invention, the reservoir comprises a coolant outlet opening towards a suction inlet of the pump.

[0025] The invention also relates to a motor vehicle comprising a cooling circuit as previously defined.

[0026] According to one embodiment of the invention, said motor vehicle comprises a fuel cell.

[0027] The invention will be better understood upon reading the following description and examining the accompanying figures. These figures are given only for illustrative purposes but in no way limit the invention.

[0028] [Fig. 1] [Fig. 1] is a schematic representation of a cooling circuit for a fuel cell installed in a motor vehicle according to the invention;

[0029] [Fig.2] [Fig.2] is a schematic representation illustrating in bold the circulation of the coolant of the circuit of [Fig.l] when the ambient temperature is lower than a cold start temperature of the fuel cell or when the fuel cell is active under low load in the temperature rise phase or in established thermal regime;

[0030] [Fig.3] [Fig.3] is a schematic representation illustrating in bold the circulation of the coolant of the circuit of [Fig.l] when the battery is stressed under a load greater than that of the operating case of [Fig.2];

[0031] [Fig.4] [Fig.4] is a schematic representation illustrating in bold the circulation of the coolant of the circuit of [Fig.l] during thermal regulation of the fuel cell;

[0032] [Fig.5] [Fig.5] is a schematic representation illustrating in bold the circulation of the coolant of the circuit of [Fig.l] during a high cooling requirement of the fuel cell;

[0033] [Fig.6] [Fig.6] is a schematic representation illustrating in bold the circulation of the coolant of the circuit of [Fig.l] during an exceptional need for cooling of the fuel cell;

[0034] [Fig.7a] [Fig.7a] is a schematic representation illustrating in bold the cir circulation of the coolant from the circuit of [Fig.l] when it is necessary to dissipate part of the excess electrical power of the vehicle in thermal form within the cooling circuit while the fuel cell is inactive or deactivated;

[0035] [Fig.7b] [Fig.7b] is a schematic representation illustrating in bold the cir culation of the coolant of the circuit of [Fig.l] when it is necessary to store more thermal energy than in the case of operation of [Fig.7a]

[0036] [Fig.7c] [Fig.7c] is a schematic representation illustrating in bold the cir culation of the coolant from the circuit of [Fig.l] when the coolant dissipates calories in the radiator following the progressive opening of the valve located at the interface between the second and fourth branches.

[0037] Identical, similar, or analogous elements retain the same reference from one figure to another.

[0038] [Fig.l] details the cooling architecture implemented to ensure the thermal management of the fuel cell consisting of an assembly of cells (1) called "stack" according to English terminology and other components necessary for its operation not shown here. The coolant is moved within the cooling circuit (0) of the assembly of cells (1) by a pump (9) preferably driven electrically. Immediately upstream of the assembly of cells (1) is arranged within the cooling circuit (0) a particle filter (11) in order to protect the constituent parts of the pack (1).

[0039] The cooling circuit (0) comprises four branches in parallel. A first branch comprises the cell assembly (1), the particle filter (11) and the pump (9).

[0040] A second branch comprises at least one radiator (2) to which is fixed at least one motor-fan unit or GMV (2a), the assembly ensuring the dissipation to the outside air of the calories by the cooling liquid in the entire circuit (0).

[0041] A third branch comprises a heat exchanger (3a) of the liquid / liquid, between the (specific) coolant of the cell assembly (1) and the coolant of at least one other fluid loop (3) of the vehicle chosen from: a fluid loop ensuring the heating of the passenger compartment and comprising at least one electric heater (3d) and a heat exchanger (3b) of the liquid / air type between this coolant and the air entering the passenger compartment and a pump (3c), and a fluid loop ensuring the heating and cooling of the electrochemical traction storage device. The fluid loop associated with the electrochemical storage device comprises an electric heater (3d'), a heat exchanger (3b1) between this coolant and components of the electrochemical traction storage device (in particular electrochemical cells) and a pump (3c1). The passenger compartment heating loop and the loop of the electrochemical storage device may be provided in parallel with each other.Thus, the heat exchanger (3a) allows an exchange of calories between the coolant of the cell assembly (1) circulating in the cooling circuit (0), and the coolant of one of the at least two other fluid loops (3). A valve (16) advantageously of the on / off type is arranged on this third branch, upstream or downstream of the heat exchanger (3a). The use of a proportional control valve is also possible.

[0042] A fourth branch (4) provides a possible bypass of the radiator(s) (2) by the coolant coming from the cell assembly (1) via the pump (9). At the inlet of the fourth branch in fluid communication with the discharge of the pump (9) is arranged a pressure-activated valve (5), for example moved against a return spring by the pressure exerted by the pump (9) in operation.

[0043] At the interface between the second and fourth branches of the circuit (0) is arranged a first three-way valve (10), of proportional type, ensuring the thermoregulation of the assembly of cells (1) by distributing via its internal valve (10a) the flow admitted at the inlet of the assembly of cells (1) between a portion of flow of coolant coming from the branch (4) without having undergone heat exchange with the external environment and a portion of flow of coolant coming from the second branch after having undergone heat exchange with the external environment through the radiator(s) (2).

[0044] The closed position of the valve (5) essentially makes it possible to force the passage of the coolant coming from the cell assembly (1) through the third branch of the circuit (0) when the valve (10) is closed, that is to say in a configuration such that its internal valve (10a) produces a composition of the flow which leaves the valve (10) at 100% from the flow of coolant coming from the branch (4).

[0045] At the outlet of the second, third and fourth branches and upstream of the first branch of the circuit (0) is arranged a second three-way valve (15), advantageously of the on / off type. A proportional control valve could be admitted. The valve (15) makes it possible to direct the flow entering it via the inlet (15a): - in the open position, towards the 1st outlet (15b) in fluid communication with the inlet of the cell assembly (1) via the particle filter (11); - in the closed position, towards the second outlet (15c) in fluid communication with the suction of the pump (9) within a pipe (8) also connecting the outlet of the cell assembly (1) to the suction of the pump (9).

[0046] The cooling circuit (0) also comprises a reservoir (14) for cooling liquid for the cell assembly (1) providing the functions of degassing the circuit (0), thermal expansion of the liquid and pressurization of the circuit (0) at the inlet of the pump (9). The reservoir (14) comprises two inlets for the cooling liquid: - one opening into the air in the tank (14) (above the maximum liquid level in the tank (14)), coming from an auxiliary coolant outlet of the cell assembly (1) by an auxiliary branch (12) of the circuit (0) carrying an ion exchanger or deionizer (13) in order to preserve a very low electrical conductivity of the coolant within the circuit (0) and passing through the cell assembly (1); - the other opening underwater into the tank (14) (below the minimum liquid level in the tank (14)), coming from an auxiliary coolant outlet of the radiator (2) arranged within the radiator (2) so that this portion of liquid flow which comes from it has not exchanged calories through the radiator (2) with the outside air moved through the radiator (2) by the movement of the vehicle and / or the activation of the GMV(s) (2a).

[0047] The reservoir (14) comprises a coolant outlet opening towards a suction inlet of the pump (9), in particular within the pipe (8), immediately upstream of the pump (9) and downstream of the fluid connection of the outlet (15c) of the second three-way valve (15) on the pipe (8).

[0048] [Fig.2] illustrates the configuration taken by the circuit (0) while: either the fuel cell is inactive, the ambient temperature (T°amb) is negative and lower than the cold start temperature of the cell (T°fcs for "freeze cold start" according to English terminology), therefore T°amb < T°fcs such that it is therefore necessary to heat the cell and in particular the cell assembly (1) by an external source, namely the heater (3d); either the fuel cell is active under low load, in the temperature rise phase or in established thermal regime, such that the heat transfer fluid pump (9) is under low load (need for a low coolant flow rate at within the cell assembly (1)).

[0049] In these two cases, the pump (9) is activated with a coolant flow rate setpoint within the cell assembly (1) so as to optimize heat exchanges: on the one hand, within the liquid / liquid exchanger (3a) from on the one hand the liquid of the fluidic loop (3) heated by the electric heater (3d) to raise the temperature of the passenger compartment and / or of the electrochemical motor storage device and of the cell assembly (1), to on the other hand the cooling liquid of the cell assembly (1) or, within the liquid / liquid exchanger (3a) from the cooling liquid of the cell assembly (1) to the liquid of the fluid loop (3) to at least contribute to raising the temperature of the passenger compartment and / or of the electrochemical motor storage device, the electric heater (3d) being inactive or only slightly used in order to reduce its electrical consumption; and on the other hand, within the cell assembly (1), between the coolant of the cell assembly heated through the exchanger (3a) and the constituent elements of the cell assembly (1).

[0050] The setting pressure of the valve (5) (for example of its spring) is defined and adjusted so that in this configuration (in particular, once the set flow rate of coolant has been established within the cell assembly (1)) the pressure exerted at the outlet of the pump (9) upstream of the valve (5) is insufficient to cause it to open even partially, so that the valve (5) is closed and blocks the access of the coolant from the cell assembly (1) through the branch (4). The setting pressure of the valve (5) is also chosen so as to protect the heat exchanger (3a) from any excessive flow rate through it and / or from any excessive pressure at its inlet, generated according to the operating point of the pump (9): this case is taken care of by the configuration described by [Fig.3].

[0051] Furthermore, in this configuration, the first three-way valve (10) is closed and blocks the passage of the coolant from the cell assembly (1) through the second branch and in particular through the radiator (2): thus, all the flow of coolant from the cell assembly (1) and, through the pipe (8), from the pump (9), passes exclusively through the third branch of the circuit carrying the heat exchanger (3a) of the liquid / liquid type and whose valve (16) is here in the open position. At its outlet, the second three-way valve (15) open, so that its inlet (15a) is then in fluid communication with the first outlet (15b), directs the coolant from the third branch through the valve (16) at the inlet of the cell assembly (1) via the particle filter (11). Finally, a small part of the flow of coolant passing through the cell assembly (1) exits through branch (12) and accesses the tank (14).

[0052] The circuit (0) occupies the configuration described by [Fig.3], if the cell is stressed under a higher load requiring a higher flow rate of coolant within the cell assembly (1). The pump (9) is then activated with a higher setpoint causing the valve (5) to open and releasing access to the coolant from the cell assembly (1) through the branch (4). In doing so, the flow rate of coolant through and the liquid pressure at the inlet of the heat exchanger (3a) are reduced, protecting the latter from any degradation and any risk of internal or external leakage.As a result, the second three-way valve (15) opened, so that its inlet (15a) is then in fluid communication with the first outlet (15b), directs the coolant from the third branch through the valve (16) and from the bypass branch (4) of the radiator (2) via the first three-way valve (10) closed, into the cell assembly (1) via the particulate filter (11).

[0053] [Fig.4] describes the configuration taken by the circuit (0) when it is necessary to regulate at a given temperature setpoint (for a low or medium load applied to the fuel cell) the temperatures of the coolant at the inlet and outlet of the cell assembly (1) as well as the temperature difference across the cell assembly (1), so that then the full cooling requirement, provided by the radiator(s) (2) and assisted or not by the GMV(s) (2a), is not necessary. In this case, the flap (10a) of the valve (10) occupies a half-open position, intermediate between complete closure (as seen in figures 2 or 3) and full opening (see [Fig.5] or 6). Even partial opening of the valve (10) allows the entry (2b) of coolant, coming from the radiator(s) (2) without having exchanged calories with the outside air, underwater in the tank (14).The coolant flow rate at the outlet of the valve (10) is then a mixture between a portion of coolant flow rate from the branch (4), modulo the position of the valve (5), without having undergone heat exchange with the external environment and a portion of coolant flow rate from the second branch after having undergone heat exchange with the external environment through the radiator(s) (2). Thus, the value of the coolant flow rate leaving the valve (10), for a given position of the valve (5), is independent of the position of the valve (10a) internal to the valve (10): the position of the valve (10a) only changes its composition (distribution between the portions of flow rate from the branch (4), without having undergone heat exchange, and flow rate from the radiator(s) (2)) and therefore the temperature.Thus, the flap (10a) of the valve (10) occupies a position that is all the more open (or even 100% open as illustrated in figures 5 or 6) as the temperatures of the coolant at the inlet and outlet of . the cell assembly (1) are high and increase. Conversely, the valve (10a) of the valve (10) occupies a position that is all the more closed (or even 100% closed as illustrated in figures 2 or 3) as the temperatures of the coolant at the inlet and outlet of the cell assembly (1) are low and decrease. Furthermore, the temperature difference across the cell assembly (1), between the inlet and outlet of the cell assembly (1), directly influences the coolant flow setpoint through the cell assembly (1) applied to the pump (9).In this configuration, the third branch remains active (for example if it is necessary to heat the passenger compartment from the calories dissipated in its coolant by the cell assembly (1)) and the valve (16) is open, so that the coolant flow admitted at the inlet (15a) of the second three-way valve (15) (and therefore at the inlet of the cell assembly (1) via the outlet (15b) of the open valve (15) and the filter (11)) is the sum of the flow rates from the valve (10) (from which comes a mixture of flow rates between the portion from the branch (4) modulo the position of the valve (5), with the portion from the radiator(s) (2)) and from the third branch via the valve (16).

[0054] In the event of a significant cooling requirement, the circuit (0) adopts the configuration described in [Fig.5] where the valve (10) occupies a fully open position, such that its flap (10a) closes off any passage of coolant flow via the branch (4) bypassing the radiator(s) (2) through the valve (10) and such that the flow of coolant passing through and leaving the valve (10) is 100% from the radiator(s) (2).The branch (4) then being closed by the valve (10a) but the third branch remaining active (for example if it is necessary to heat the passenger compartment from the calories dissipated in its coolant by the assembly of cells (1)) and the valve (16) being open, the flow of coolant admitted at the inlet (15a) of the second open three-way valve (15) (and therefore at the inlet of the assembly of cells (1) via the outlet (15b) of the valve (15) and the filter (11)) is the sum of the flow coming from the valve (10) (itself coming entirely from the radiator(s) (2)) and the flow coming via the valve (16) of the third branch carrying the exchanger (3a).

[0055] In the event of a very high or exceptional cooling requirement, the circuit (0) adopts the configuration described in [Fig.6] where the valve (10) occupies the same fully open position, described in [Fig.5], and where the third branch is deactivated by closing the valve (16), for example if it is no longer necessary to heat the passenger compartment by the calories dissipated in its coolant by the assembly of cells (1), for example by an ambient temperature higher than a predetermined threshold, and / or if it is no longer necessary to heat the electrochemical motor storage device by the same means, for example in the case where its temperature has reached and exceeded a threshold predetermined. In this configuration, the flow of coolant admitted at the inlet (15a) of the second open three-way valve (15) (and therefore at the inlet of the cell assembly (1) via the outlet (15b) of the valve (15) and the filter (11)) is entirely and solely the flow coming from the valve (10), itself coming entirely from the radiator(s) (2).

[0056] In the case where it is necessary to dissipate at least a part of the excess electrical power of the vehicle by dissipating it in the form of thermal power within the thermal management system of the fuel cell and while the cell is inactive or deactivated, [Fig.7a] shows the configuration then taken by the circuit (0). In this state, the excess electrical power is dissipated in the form of heat by the heater (3d) in the coolant of the fluid loop (3) driven by the pump (3c), and the associated heat is transferred through the liquid / liquid heat exchanger (3a) to the coolant of the fuel cell, driven within the circuit (0) by the activation of the pump (9) and the open position of the valve (16). However, in this mode of operation, while the cell is inactive or deactivated, it is advisable that this coolant does not pass through the cell assembly (1) of the cell,in order not to degrade the constituents or harm their durability, or that of the cell, in the short or medium term, by conditions of coolant temperature that are too high or too low at the inlet and / or outlet of the cell and the cell assembly (1) and / or of temperature gradients that are too high between the inlet and outlet of the coolant of the cell assembly (1) and / or of coolant flow rate that is too high within the cell assembly (1) and / or of humidity outside the permissible limits internally of the cell assembly (1), these conditions leading to deterioration and / or irreversible degradation, by excessive drying or humidification, of the assembly formed by the membrane and the electrodes of each cell of the cell assembly (1) of the fuel cell. Consequently,the valve (15) is closed: the blocking of its first outlet (15b) and the fluid communication of its inlet (15a) with its second outlet (15c) allows the coolant of the circuit (0) to bypass the assembly of cells (1) and to go directly to the suction of the pump (9) within the pipe (8). Thus in this configuration, the thermal power coming via the heater (3d) from the excess electrical power is transferred via the exchanger (3a) in the form of heat in the coolant of the circuit (0) whose configuration taken in this operating mode allows this heat to be stored in the circuit (0), via the heat capacity of the coolant of the assembly of cells (1) and the volume of liquid then used in the circuit (0), until a predetermined temperature threshold is reached in the coolant of the circuit (0) at the outlet of , the exchanger (3a), in order to maximize the evacuation of heat through the radiator(s) (2) when the valve (10) opens, by maximizing, at the coolant flow rate given by the pump control instruction (9), the temperature difference between the temperature of the coolant in the circuit (0) at the inlet of the radiator(s) (2) and the temperature of the outside air passing through the radiator(s) (2) by the advancement of the assisted vehicle and / or the activation of the GMV(s) (2a).

[0057] As shown in [Fig.7b], it is possible to store more thermal energy or heat within the circuit (0) by controlling the pump (9) with a higher flow rate setpoint chosen so as to optimize the flow rate of coolant from the circuit (0) through the exchanger (3a), despite the at least partial opening of the valve (5) which in this configuration increases the volume of coolant used in the circuit (0) by the connection to the circuit (0) of the branch (4) despite the bypassing of the exchanger (3a) which it provides to the coolant by the opening of the valve (5). The control setpoint of the pump (9) is then chosen so that the configuration then taken by the circuit (0) in accordance with [Fig.7b] provides an advantage of thermal energy stored in the circuit (0) compared to the configuration taken by the circuit (0) in accordance with [Fig.7a].

[0058] As soon as the predetermined temperature threshold in the coolant of the circuit (0) at the outlet of the exchanger (3a) is reached, the valve (10) gradually adopts a fully open position as illustrated in [Fig.7c], separating the branch (4) from the circuit (0) and forcing the passage of the coolant of the circuit (0) through the radiator(s) (2). In this configuration, by the position of the valves (10) and (16), the pump (9) sucks through the second and third branches of the circuit (0) the coolant respectively through the exchanger (3a) and the radiator(s) (2) and delivers this mixture to the inlet of these two same exchangers then arranged in parallel with each other, while bypassing the assembly of cells (1) with the coolant of the circuit (0) via the valve (15).Thus, a large amount of heat and thermal power can be dissipated through the exchanger (3a) in the circuit (0) and therefore a large amount of electrical power can thus be dissipated, since the configuration of the circuit (0) taken in figures 7a, 7b and 7c makes it possible to overcome the constraints posed by the cell assembly (1) of the stack, which the coolant of the circuit (0) bypasses without passing through it. The thermal management system of the fuel cell can thus dissipate to the environment outside the vehicle a thermal power resulting from very significant excess electrical power, since this thermal management system has been dimensioned (pump (9), radiators (2), GMV (2a)) to dissipate, taking into account the efficiency of the fuel cell subsystem, a thermal power greater than the maximum electrical power delivered by the stack. (e.g., 180 to 200kW of thermal power under severe ambient conditions, for 150kW of electrical power provided by the fuel cell subsystem).

[0059] In the case similar to that explained in Figures 7a-7c, where it is necessary to dissipate at least a portion of the excess electrical power of the vehicle by dissipating it in the form of thermal power within the thermal management system of the fuel cell and while the cell is active at idle (in order not to deactivate it so as not to have to reactivate it quickly, the deactivation / activation cycles damaging the internal components of the cell assembly (1)), it is then imperative that the cell assembly (1) is crossed by the coolant of the circuit (0). It is then no longer possible for the coolant of the circuit (0) to bypass the cell assembly (1) by the configuration taken in Figures 7a-7c by the valve (15) and the circuit (0) then adopts a configuration similar to that described in [Fig.5].In this operating mode where, in a manner similar to that presented in the context of figures 7a-7c, at least part of the excess electrical power of the vehicle is dissipated in the form of thermal power through the exchanger (3a) within the thermal management system of the fuel cell and more particularly to the coolant of the circuit (0), the hot coolant having passed through the third branch and loaded with calories dissipated by the fluid loop (3) through the exchanger (3a) is mixed, upstream of the inlet (15a) of the valve (15), with the cold coolant coming from the radiator(s) (2).The opening instruction of the valve (10a) of the valve (10) and the coolant flow instruction of the pump (9), defined by criteria of coolant temperature at the inlet of the cell assembly (1) and of the coolant temperature difference between the outlet and inlet of the cell assembly (1), are then higher than those that would have been required by the sole thermal management of the fuel cell and in particular the cell assembly (1), so that: a coolant at an already mixed temperature, resulting from the mixing of the hot coolant from the exchanger (3a) with the cold coolant from the radiator(s) (2), is introduced at the inlet of the cell assembly (1). to take into account the additional heat dissipation that constitutes, via the exchanger (3a), the fluid loop (3) of the vehicle. In this case, the assembly of cells (1) is not the only source of calories that must be evacuated to the external environment via the radiator(s) (2) and the GMV(s) (2a).

[0060] Conversely, if the cooling provided to the cooling liquid of the circuit (0) by the implementation of the radiator(s) (2) and / or the GMV(s) (2a), is greater (in absolute value) than the heat dissipation in this liquid by the assembly of cells (1) and by the fluidic loop (3) through the exchanger (3a), the instructions for opening the valve (10a) of the valve (10) and the liquid flow rate of the pump (9) will be adapted (and in particular reduced) so as to respect the criteria of liquid temperature at the inlet of the cell assembly (1) and of the liquid temperature difference between the outlet and inlet of the cell assembly (1).

[0061] Thus, it is possible to dissipate significant thermal power in the circuit (0) without disconnecting the fuel cell then active at idle.

Claims

Claims

1. Cooling circuit (0) for a fuel cell installed in a motor vehicle, said fuel cell comprising an assembly of cells (1), characterized in that said cooling circuit (0) comprises four branches in parallel with each other constituted by: - a first branch comprising the assembly of cells (1) and a pump (9) for circulating coolant, - a second branch comprising at least one liquid / air type radiator (2) with which at least one motor-fan unit (2a) is associated to ensure dissipation to the outside air of calories from a coolant circulating in the cooling circuit (0), - a third branch comprising a liquid / liquid type heat exchanger (3a) between the coolant of the cell assembly (1) and another coolant of at least one other fluid loop (3) of the motor vehicle chosen from: a fluid loop ensuring the heating of a passenger compartment and a fluid loop ensuring the heating or cooling of an electrochemical motor storage device, a valve (16) being arranged on this third branch upstream or downstream of the liquid / liquid type heat exchanger (3a), - a fourth branch (4) providing a possible bypass of the radiator(s) (2) by the coolant from the cell assembly (1) via the pump (9), a valve (5) being arranged at the inlet of the fourth branch in fluid communication with a discharge of the pump (9), and in that at the outlet of the second, third and fourth branches and upstream of the first branch of the circuit (0) is arranged a three-way valve (15) capable of directing the flow entering it via an inlet (15a): - in the open position, towards a first outlet (15b) in fluid communication with an inlet of the cell assembly (1), - in the closed position, to a second outlet (15c) in fluid communication with a suction of the pump (9) within a pipe (8) also connecting an outlet of the cell assembly (1) to the suction of the pump (9), so as to bypass the cell assembly (1).

2. Cooling circuit according to claim 1, characterized in that the first branch further comprises a particle filter (11).

3. Cooling circuit according to claim 1 or 2, characterized in that, at the interface between the second and fourth branches of the circuit (0) is arranged a three-way valve (10) capable of ensuring thermoregulation of the cell assembly (1) by distributing via its internal valve (10a) a flow admitted at the inlet of the cell assembly (1) between a portion of coolant flow coming from the fourth branch (4) without having undergone heat exchange with an external environment and a portion of coolant flow coming from the second branch after having undergone heat exchange with the external environment through the radiator(s) (2).

4. Cooling circuit according to claim 3, characterized in that the three-way valve (10) is of the proportional type.

5. Cooling circuit according to any one of claims 1 to 4, characterized in that it comprises a reservoir (14) of cooling liquid for the assembly of cells (1) ensuring the functions of degassing the circuit (0), thermal expansion of the liquid and pressurization of the circuit (0) at the inlet of the pump (9).

6. Cooling circuit according to claim 5, characterized in that the reservoir (14) comprises a coolant inlet opening into the air into the reservoir (14) from an auxiliary coolant outlet of the cell assembly (1) via an auxiliary branch (12) comprising an ion exchanger or deionizer (13).

7. Cooling circuit according to claim 5 or 6, characterized in that the tank (14) comprises a coolant inlet opening underwater into the tank (14) from an auxiliary coolant outlet of the radiator (2) so that this portion of the liquid flow which comes from it has not exchanged calories through the radiator (2) with outside air.

8. Cooling circuit according to any one of claims 5 to 7, characterized in that the reservoir (14) comprises a coolant outlet opening towards a suction inlet of the pump (9).

9. Motor vehicle comprising a cooling circuit as defined according to any one of the preceding claims.

10. Motor vehicle according to claim 9, characterized in that it comprises a fuel cell.

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