BATTERY PACK FOR ELECTRIC VEHICLE WITH GAS EXHAUST PIPE

Abstract

The invention relates to a battery pack (2) for a motor vehicle, comprising a plurality of electrochemical cells and a casing (4) delimiting an internal space (7) of the battery pack in which the plurality of electrochemical cells are located. The battery pack comprises at least one gas venting duct (1), configured to transfer gas from the internal space (7) to an external environment in the event of overpressure occurring in the internal space of the battery pack. The gas venting duct comprises an auxiliary Venturi-effect gas suction device that helps to draw in fresh air and thus lower the temperature of the gas mixture being vented to the outside. Figure 2

Description

Title of the invention: BATTERY PACK FOR ELECTRIC VEHICLE WITH GAS EVACUATION DUCT

[0001] The invention relates to a battery pack for a vehicle. The vehicle may be a 100% electric vehicle (i.e. without a thermal engine) or a hybrid vehicle, for example a plug-in hybrid vehicle. The battery pack is equipped with a gas evacuation duct which can be used in the event of excess pressure occurring inside the battery pack.

[0002] In an electrically powered / tracted motor vehicle, there is a traction battery which is designed to store a significant amount of electrical energy in electrochemical form.

[0003] In practice, we are talking about several tens of kWh. A 100% electric vehicle battery has an energy storage capacity typically between 50 kWh and 120 kWh, depending on the target range, weight and consumption of the vehicle. On hybrid vehicles, the electrical storage capacity may be less, but still represents considerable energy.

[0004] The most common traction batteries on electric vehicles are batteries based on Lithium-Ion type electrochemistry.

[0005] Among these, there are two most widespread types, namely NMC (Nickel Manganese Cobalt) and LFP (Lithium Iron Phosphate / LifePo4).

[0006] In an electric vehicle, the battery is protected from mechanical attack by structural elements of the vehicle, of which the floor of the vehicle is generally a part. The battery is also generally protected from the physicochemical environment, for example humidity, fog, liquid flow, etc.

[0007] Batteries are usually composed of a juxtaposition of unitary electrochemical cells, grouped into modules or not.

[0008] Furthermore, a battery monitoring system, referred to in the art as a 'BMS' (Battery Management System), is provided with the battery, the monitoring system being configured to acquire various information about the battery and its operating parameters: voltage, current, temperature, degassing, etc.

[0009] It turns out that in practice, for lithium-ion batteries, the risk of a phenomenon called "thermal runaway" cannot be completely eliminated.

[0010] This phenomenon of thermal runaway, also commonly called in practice "thermal runaway", occurs when an electrochemical cell reaches too high a temperature and begins to burn while communicating to the neighboring cells enough heat energy to increase the temperature of neighboring cells so that they too will start to burn, which gradually leads to the destruction of the battery.

[0011] On motor vehicles, all precautionary measures are taken to avoid at all costs an unwanted inflammatory or incandescent event for the entire vehicle, including the battery.

[0012] To this end, electric motor vehicles are equipped with high-performance cooling systems to cool the electrochemical cells of their battery. Regarding the battery, it is also planned to limit the stress applied to the battery if the temperature approaches a predefined threshold (this is called voluntary performance derating, also called 'derating').

[0013] Despite all the appropriate precautions taken, the risk of local heating or even a thermal runaway type phenomenon cannot be completely excluded, even if the probability is extremely low.

[0014] Should such an event occur, the battery monitoring system ('BMS') is configured to detect it in order to alert the occupants of the vehicle in question in time, so that they can take all relevant and appropriate actions in view of the situation.

[0015] But despite all the precautions taken for the design and implementation of such electric batteries, the case of thermal runaway on an electrochemical cell cannot be totally excluded, and if such an event occurs, then a gas evacuation conduit is provided which allows overpressure gases to escape inside the battery pack, in particular to avoid any explosion. In the event that such an event occurs, the gases which leave the battery pack are very hot or even burning and they may even self-ignite when they are expelled into the ambient air.

[0016] The inventors sought to minimize the impact and danger of the evacuation of very hot gases from the interior of the battery pack to the environment in the event of the occurrence of such a thermal runaway event.

[0017] To this end, the invention proposes a battery pack for a motor vehicle, comprising a plurality of electrochemical cells and an envelope delimiting an interior space of the battery pack in which the plurality of electrochemical cells are located, the battery pack comprising at least one gas evacuation conduit, configured to transfer gas from the interior space to an external environment in the event of overpressure occurring in the interior space of the battery pack, characterized in that the gas evacuation conduit comprises an auxiliary gas suction device with Venturi effect.

[0018] The auxiliary gas suction device is configured to inject, by virtue of the effect Venturi, gas from the outside of the duct to the inside of the duct, solely due to geometry, passively, without using a pump or equivalent.

[0019] It is noted that the auxiliary gas can simply be outside air, without excluding the additional supply of a particular auxiliary gas as will be seen later.

[0020] With such an arrangement, the Venturi effect is used to draw in cold air so that it mixes with the hot gases coming out of the battery pack in order to cool them.

[0021] Thus the gases which exit at the free end (mouth) of the exhaust duct have a lower temperature and the risk of self-ignition and damage by burning is reduced.

[0022] According to one embodiment, the auxiliary gas suction device with Venturi effect comprises a passage cross-section reduction of at least 15% and at least one orifice connecting the inside to the outside of the gas discharge duct. When gas flows in the duct at the passage cross-section restriction, there is a pressure difference between the inside and the outside, which causes admission through the suction orifice of gas located on the outside. The suction effect is sufficient for a wide range of flow speeds of the hot gases which circulate at this location from the interior volume of the battery pack, the suction of the outside air operates over the entire range of flow speeds of the hot gases.

[0023] According to one embodiment, the reduction in passage section can be at least 20%. It is even possible to have a reduction in passage section of at least 25%. This maximizes the suction effect without, however, causing too great an airflow loss due to the presence of the section restriction.

[0024] According to one embodiment, the gas evacuation conduit may comprise at least one baffle system downstream of the auxiliary gas suction device.

[0025] This prevents incandescent particles from exiting directly from the exhaust duct, the baffle elements stopping said particles in their path.

[0026] According to one embodiment, the baffle system may be configured to produce a whistle similar to a siren whistle. One or more slots may be arranged on the wall of the conduit, for example in an area close to the mouth;

[0027] By means of which, an audible signal is formed for the occupants of the vehicle to encourage them to leave the vehicle quickly.

[0028] According to one embodiment, the gas evacuation conduit may comprise an inlet sleeve delimiting a buffer space for the auxiliary gas suction device with Venturi effect.

[0029] This intake sleeve forms a buffer space or intake chamber to accommodate gas which will be sucked by the Venturi effect into the section restriction.

[0030] Preferably the intake sleeve surrounds the section restriction zone. The buffer space is annular in shape. There can be only one tapping on the inlet sleeve and the injection into the duct is well distributed circumferentially due to the annular shape of the buffer space.

[0031] According to one embodiment, the gas discharge conduit may comprise a first part with a proximal end coupled, directly or indirectly to the casing, and a distal end in the form of a first cone narrowing in the direction of gas flow, a second part with a proximal end, in the form of a second cone, at least partially surrounding the first cone and narrowing in the direction of gas flow, and a distal end forming an outlet mouth, with an interstitial gap between the first cone and the second cone, this interstitial gap forming a Venturi orifice. This two-part configuration makes it possible to form a flow section restriction in a clever manner with the possibility of mounting one part on the other, with or without the inlet sleeve. In this case, the orifice for the Venturi function may be formed as an annular interstitial slot.

[0032] Expressed more concisely, the gas exhaust conduit comprises a double cone configuration converging in the direction of flow.

[0033] According to one embodiment, the gas discharge conduit may comprise an inlet for a catalyst product. The catalyst product supplements the outside air. Thus the auxiliary gas is a combination of outside air and catalyst product.

[0034] The catalyst product may contribute to reducing the temperature and / or toxicity of gases resulting from thermal runaway.

[0035] According to one embodiment, the battery pack may further comprise a discharge valve. Whereby, the interior space of the battery pack is only put into communication with the discharge conduit if the pressure inside the battery pack exceeds a predetermined threshold, for example a relative pressure of 0.5 bar.

[0036] According to one embodiment, the battery pack may further comprise a breathing valve coupled to the gas evacuation conduit.

[0037] This breathing valve allows a low pressure differential to be maintained between the pressure inside the battery pack and the pressure outside the battery pack. It can open in either direction to alleviate a too large pressure difference. Pressure differences can be due to temperature differences or vehicle routes with an increase in altitude or a descent.

[0038] The breathing valve is cleverly connected to the exhaust duct, and is thus protected from direct ingestion of dust or small foreign bodies.

[0039] According to one embodiment, the electrochemical cells are grouped into modules, all of the modules forming the battery pack. According to this configuration, a module comprises a plurality of electrochemical cells and a battery pack comprises a plurality of modules.

[0040] The present invention also relates to a motor vehicle comprising a main floor, at least one battery pack for storing electrical energy arranged under the main floor, the battery pack being as described previously.

[0041] The invention will be further detailed by the description of non-limiting embodiments, and on the basis of the appended figures illustrating variants of the invention, in which: [Fig.l] is a schematic representation in side view of a motor vehicle with an electrical energy storage battery pack and a gas exhaust duct, in accordance with the present invention; [Fig.2] is a schematic representation in longitudinal section of a rear portion of a vehicle battery pack, with a generic example of a gas evacuation duct and Venturi effect section restriction; [Fig.3] represents a top view of an example of the construction of a battery pack; [Fig.4] is a schematic view in partial longitudinal section of another example of a gas exhaust and restriction conduit with Venturi effect; [Fig.5] is an exploded perspective schematic representation of a rear portion of a vehicle battery pack; [Fig.6] is a partial cross-sectional schematic representation of a variant of an example of gas evacuation and its interface with the battery pack casing, [Fig.7] is analogous to [Fig.6] with an exploded view representation, [Fig.8] is a schematic representation of a catalyst product injection system in the configuration of Figures 6 and 7; [Fig.9] is a schematic cross-sectional representation of a baffle system.

[0042] In the various figures, the same references designate identical or similar elements. For reasons of clarity of the description, certain elements are not necessarily represented to scale.

[0043] We are interested in electric or hybrid motor vehicles. The motor vehicle 9 considered here may be a 100% electric vehicle (i.e. without an internal combustion engine) or a hybrid vehicle, for example a plug-in hybrid vehicle. Such a vehicle is illustrated in Figures 1 and 2.

[0044] The motor vehicle 9 has a reference frame in space comprising a longitudinal axis X along a direction of movement of said motor vehicle, a lateral axis Y perpendicular to the longitudinal axis X, and a vertical axis Z perpendicular to the longitudinal axis X and to the lateral axis Y, the vertical axis being directed from bottom to top. The motor vehicle comprises a main floor 3. The main floor 3 generally extends in a plane parallel to XY.

[0045] The electric or hybrid vehicle 9 comprises a battery block 2 (also called a battery pack) whose function is to store electrical energy. This type of battery has a storage capacity of between 20 kWh and 150 kWh. For an all-electric zero-emission vehicle, the storage capacity is most often between 50 kWh and 120 kWh, which represents a considerable amount of energy. The battery pack is arranged under the main floor 3, and in this case, the battery 2 occupies a significant area under the floor of the vehicle as illustrated in [Fig. 1].

[0046] As visible in [Fig.3], the battery pack 2 comprises a plurality of modules 21, each module comprising a plurality of electrochemical cells 22.

[0047] According to a variant, there is not necessarily the equivalent of modules and the battery pack 2 comprises a plurality of electrochemical cells 22.

[0048] The number of electrochemical cells can range from 100 to 1000. In typical application examples, the number of electrochemical cells is between 400 and 700.

[0049] The battery pack 2 comprises an envelope 4 delimiting an interior space 7 of the battery pack in which the plurality of electrochemical cells 22 are located. The battery pack 2 is supported by a rigid metal frame 20.

[0050] In [Fig.2], the battery pack 2 is shown schematically, the region illustrated is that of the rear end of the battery block.

[0051] As explained in the introductory part of this document, although the probability of this event is extremely low, it could happen that an electrochemical cell is subject to thermal runaway and releases hot gases in quantity. In such a case, a gas evacuation conduit system is provided, generally identified by the reference 1.

[0052] Very hot gases can pass through this gas evacuation duct from the internal volume 7 of the battery pack to the external environment.

[0053] Depending on the vehicle configuration and its battery, there may be a single gas discharge duct or several gas discharge ducts. Furthermore, the gas discharge duct 1 may be located in the rear area of ​​the battery pack, but it is not excluded to have a gas discharge duct on the lateral edges of the battery pack or even on the front portion of the battery pack.

[0054] In the example illustrated in [Fig.5], two gas evacuation conduits 1 are provided on the rear part of the battery pack.

[0055] Note the presence of a discharge valve 24 which is normally closed and which can open to release gases contained inside the casing 4. The opening of the discharge valve 24 can occur when a pressure difference between the interior volume and the exterior is greater than a predetermined threshold. for example 0.5 bar or 0.8 bar. The effective setting of this relief valve 24 can be determined after thermal runaway tests.

[0056] Advantageously, each gas evacuation conduit 1 comprises an auxiliary gas suction device with Venturi effect.

[0057] The auxiliary gas suction device with Venturi effect comprises a reduction in passage section marked 13. According to an exemplary embodiment, the reduction in passage section is at least 15%.

[0058] The auxiliary gas suction device with Venturi effect comprises at least one orifice 31 connecting the inside to the outside of the gas discharge conduit.

[0059] The orifice 31 is connected to a tapping 15 which allows outside air to be taken from a little distance.

[0060] The evacuation conduit 1 opens outwards at an opening marked 17.

[0061] A lower cover 72 may be provided, arranged under the battery pack 2.

[0062] In more particular embodiments shown in Figures 4 to 8, the gas evacuation conduit 1 comprises a first tubular part 11 and a second tubular part 12.

[0063] The first tubular part 11 comprises a proximal end 11a coupled, directly or indirectly to the casing 4, and a distal end 11b in the form of a first cone narrowing in the direction of flow of the gas FL.

[0064] The second tubular part 12 comprises a proximal end 12a, in the form of a second cone, at least partially surrounding the first cone and narrowing in the direction of flow of the gas F1, and a distal end 12b where the outlet mouth 17 is located.

[0065] It is noted that there is an interstitial gap 18 between the first cone and the second cone.

[0066] In the variant illustrated in [Fig.6], the Venturi orifice function is formed by this interstitial gap 18.

[0067] In the variant illustrated in [Fig.4], holes 32 are provided at the location of the section restriction 13, these holes 32 forming orifices of the Venturi, the interstitial gap 18 being bordered by a mounting collar 19 provided on the free edge of the proximal portion 12a of the second tumular part.

[0068] The gas discharge conduit 1 has an internal diameter DI. More particularly, the diameter DI corresponds to the diameter of the first tubular part 11.

[0069] At the level of section restriction 13, the diameter is noted D2 which is less than the diameter DI. D2 is between 80% of DI and 92% of DI.

[0070] The internal diameter of the second tubular part 12 is noted D3 point, and preferably, D3 is substantially equivalent to the diameter DI of the first part tubular 11.

[0071] The section restriction to obtain the Venturi effect can also be formulated as a passage section restriction. Preferably the restriction can be at least 15% which corresponds substantially to a diameter ratio D2 / D1 of 92%. According to other embodiments, the passage section can be reduced by at least 20%, or up to 25%.

[0072] It is also not excluded to operate with a smaller section restriction, i.e. between 5% and 15%.

[0073] As regards the orifices necessary to obtain the Venturi effect, these may simply be simple holes 31, 32, with or without a tapping pipe, in particular when the auxiliary gas admitted by the device is simply outside air. It should be noted that the quantity of air sucked in by the Venturi device is substantially proportional to the flow rate of hot gas which passes through the exhaust duct. It is a completely passive, rustic and robust system.

[0074] In advantageous embodiments, the gas discharge conduit comprises an inlet sleeve 5 forming a buffer space for the auxiliary gas suction device with Venturi effect. This buffer space can be called a primary buffer chamber or primary inlet chamber.

[0075] In [Fig.4] centered on the suction device, the distal portion 11b of the first part is tubular with axis Al. Similarly, the proximal portion 12a of the second part is tubular with axis Al. The intake sleeve 5 is a part generally of revolution around the axis AL

[0076] The intake sleeve 5 comprises a main cylindrical portion 50 of axis AL. From this main cylindrical portion on either side of its axial ends, there extend in the direction of the axis: a first radial annular portion 51 and a second radial annular portion 52.

[0077] The intake sleeve 5 covers the distal portion 11b of the first tubular part and the proximal portion 12a of the second tubular part.

[0078] The main cylindrical portion 50 comprises holes 33, 56 forming channels for admitting external air or a mixture which will be discussed later. The intake sleeve may be provided with one or more orifice(s) 33.

[0079] The intake sleeve 5 thus defines a generally closed intake chamber, the contents of which are sucked into the evacuation duct through the orifices 32 or through the interstitial gap 18, this content being replaced by the arrival of an auxiliary gas (outside air or a mixture) via the holes 33, 56.

[0080] An annular bead 16 may be provided for clip-mounting the intake sleeve 5 onto the first tubular part. Another annular bead 36 may be provided for clip-mounting the second tubular part onto the first tubular part.

[0081] The auxiliary gas sucked in by the suction device follows the flow path marked F2 in [Fig.6].

[0082] The gas discharge conduit 1 comprises an inlet for a catalyst product 6. To do this, a product cartridge may be provided, for example a fire-fighting product connected directly to one of the holes 33 of the inlet sleeve 5. This cartridge may be provided with a valve which opens passively when a depression is present or which is opened by means of a controlled member.

[0083] According to a variant, shown in [Fig.8], an injector 60 may be provided, for example controlled by the BMS battery manager.

[0084] The catalyst product 6 may be in the form of a liquid product, where appropriate under pressure, without excluding a powder form.

[0085] As illustrated in Figures 6 and 8, an injection ring 8 may also be provided. This injection ring 8 delimits an annular secondary intake chamber around the intake sleeve 5.

[0086] The volume of the secondary intake chamber is smaller than the volume of the primary intake chamber delimited by the intake sleeve. A hole 58 is provided for housing the outlet of the injector 60. The catalyst product 6 enters through this external hole 58 and after transiting through the secondary intake chamber passes through the plurality of holes 56 regularly distributed on the circumference around the intake sleeve 5 to reach the primary intake chamber.

[0087] The path of the catalyst product follows the flow F2 and enters the discharge pipe through the interstitial space 18 between the first cone and the second cone.

[0088] At the interface between the first tubular part 11 and the casing 4 of the battery pack, a bell 10 is optionally provided, on which fasteners 28 are provided on the one hand and in which the discharge valve 24 is housed. The bell 10 forms a hermetic connection between the casing 4 and the first tubular part 11.

[0089]

[0090] According to an advantageous option, the gas evacuation duct 1 comprises at least one baffle system downstream of the auxiliary gas suction device. The baffle system comprises baffle elements 54, illustrated in Figures 6 and 9.

[0091] The alternation of the baffle elements prevents a direct path in the downstream conduit so as to prevent any solid particles from exiting directly to the outside.

[0092] Optionally, the baffle system is configured to produce a whistle similar to a siren whistle. This provides an intuitive auditory indication to encourage vehicle occupants to leave the vehicle without delay.

[0093] One or more slots 55 may be provided on the wall of the conduit to produce the siren whistle when hot gases travel through the gas exhaust duct.

[0094] In addition, a breathing valve 26 is provided. The breathing valve 26 allows a low pressure differential to be maintained between the pressure inside the battery pack and the pressure outside the battery pack. It can open in either direction to alleviate too great a pressure difference.

[0095] The breathing valve 26 coupled to the gas discharge duct. This configuration makes it possible to protect the breathing valve which is not exposed directly to the external environment but through the gas discharge duct which, except in the very particular case of thermal runaway, is not subjected to a flow of hot gases.

[0096] Advantageously, the bell 10 is provided for the function of evacuating hot gases and can also accommodate the breathing valve 26, which allows it to be protected from the ingestion of dust and direct foreign bodies.

Claims

Claims

1. Battery pack (2) for a motor vehicle (9), comprising a plurality of electrochemical cells (22) and an envelope (4) delimiting an interior space (7) of the battery pack in which the plurality of electrochemical cells are located, the battery pack comprising at least one gas discharge conduit (1), configured to transfer gas from the interior space (7) to an external environment in the event of overpressure occurring in the interior space of the battery pack, characterized in that the gas discharge conduit (1) comprises an auxiliary gas suction device with Venturi effect.

2. Battery pack according to claim 1, characterized in that the auxiliary gas suction device with Venturi effect comprises a reduction in passage section (13) of at least 15% and at least one orifice connecting the inside to the outside of the gas evacuation conduit.

3. Battery pack according to one of claims 1 to 2, characterized in that the gas evacuation duct (1) comprises at least one baffle system downstream of the auxiliary gas suction device.

4. Battery pack according to claim 3, characterized in that the baffle system is configured to produce a whistling sound similar to a siren whistle.

5. Battery pack according to one of claims 1 to 4, characterized in that the gas evacuation conduit comprises an inlet sleeve (5) delimiting a buffer space for the auxiliary gas suction device with Venturi effect.

6. Battery pack according to one of claims 1 to 5, characterized in that the gas evacuation conduit comprises a first tubular part (11) with a proximal end (11a) coupled, directly or indirectly to the casing, and a distal end (11b) in the form of a first cone narrowing in the direction of gas flow, a second tubular part (12) with a proximal end (12a), in the form of a second cone, at least partially surrounding the first cone and narrowing in the direction of gas flow, and a distal end (12b) forming an outlet mouth, with an interstitial gap (18) between the first cone and the second cone, this interstitial gap forming a Venturi orifice.

7. Battery pack according to one of claims 1 to 6, characterized in that the gas discharge conduit comprises an inlet for a product catalyst (6).

8. Battery pack according to one of claims 1 to 7, characterized in that it further comprises a discharge valve (24).

9. Battery pack according to one of claims 1 to 8, characterized in that a breathing valve (26) is provided coupled to the gas discharge conduit.

10. Motor vehicle (9) comprising a main floor (3), at least one battery pack (2) for storing electrical energy arranged under the main floor, the battery pack being in accordance with one of claims 1 to 9.

Images