Underrun protection with thermally optimized reinforcement, underrun protection battery module and motor vehicle with improved underbody protection device

Abstract

The present invention relates to an underrun protection device (1) for mounting underneath a high-voltage battery (3) of a motor vehicle, which battery module (2) is the ideal embodiment, comprising a main body (4) which can be constructed or is constructed in a sandwich-like manner, wherein a thermal reinforcement (6) is arranged on or at the upper side (5) of the main body (4) facing the battery module, wherein the thermal reinforcement (6) comprises carbon, just like an underrun protection battery module (7) and a motor vehicle / BEV.

Description

[0001] The present invention relates, inter alia, to a thermally optimized reinforcement of an underbody protection device / an underbody protection / an underrun protection, ergo an underbody protection device / an underbody protection / an underrun protection battery module and a preferably land-based motor vehicle, such as a passenger car or a commercial vehicle, with an improved underbody protection device / an improved underrun protection.

[0002] Such motor vehicles are usually battery electric vehicles (BEVs), which use (high-voltage) batteries / traction batteries as the sole or additional energy source.

[0003] To protect traction batteries arranged on the underbody of electrically powered motor vehicles, reinforcement structures are generally used today to absorb impacts or stone chips and the like in order to prevent deformation of battery cells placed on the underbody of a motor vehicle (the traction battery / high-voltage battery) and a resulting externally triggered short circuit.

[0004] Such reinforcement structures are known, for example, from documents DE 10 2021 119 168 A1, JP 2014-192 052 A, KR 10 2018 006 150 A, US 2013 / 0 059 175A1, WO 2022 006 894 A1, and DE 10 2021 204 370 A1. Generic prior art is also known from DE 10 2014 004 853 A1 and DE 10 2022 105 511 B3.

[0005] Furthermore, DE 10 2022 118 977 B3 discloses an underbody protection device for arrangement below a traction battery on the underbody of an at least partially electrically driven motor vehicle, comprising an underbody protection plate for protecting the underbody of the motor vehicle, a gas guide structure which can be arranged between the traction battery and the underbody protection plate and is arranged on the underbody protection plate for guiding a gas escaping from the traction battery along the underbody protection plate, wherein the gas guide structure can be arranged on the traction battery in such a way that a gas can be introduced into the gas guide structure via a degassing outlet of the traction battery, wherein the gas guide structure has a plurality of branching points for the branched guidance of the gas escaping from the traction battery along the underbody protection plate,wherein the gas guide structure has at least one gas outlet opening for discharging the gas escaping from the traction battery and guided along the underbody protection plate.,

[0006] Furthermore, DE 10 2022 118 978 B3 discloses an underrun protection device and a method for producing an underrun protection device.

[0007] The reinforcement structures essentially serve to protect the battery systems from corrosion damage caused by splashing water or road salt. In addition to effectively preventing externally triggered short circuits, increasing driving safety in electric vehicles also requires preventing internally triggered short circuits and minimizing the resulting damage. It has proven effective to quickly and effectively vent the hot battery gases escaping from internal short circuits in motor vehicle battery systems from a battery module or battery system in order to prevent a resulting chain reaction that could lead to fire or explosion of the entire battery module or battery system.

[0008] For this purpose, it is known to equip traction battery systems of motor vehicles with a gas discharge system for discharging hot battery gases into the ambient atmosphere. These gas discharge systems are guided through the reinforcement structures arranged on the underbody of a motor vehicle. These reinforcement structures can be designed in such a way that they have gas channels with a large number of branching points in order to force the gas flow into a long guide path to a defined gas outlet opening located at the end of the path, thereby cooling the gas flowing past. Due to the centrifugal forces acting on the gas flow, corner regions in the gas guide structure assume the function of particle traps for the hot or glowing combustion products from the battery cells that are carried along with them, which are thus filtered out of the gas flow.

[0009] In this way, the risk of explosion when the gases escape into the ambient air at the end of the gas guide structure is minimized, since the flammable gas mixed with oxygen has ideally cooled to a temperature below the auto-ignition point and the risk of externally triggered ignition by ejected glowing particles is greatly reduced.

[0010] The gas outlet openings are preferably located at the end of a gas guide structure and dimensioned to handle the sudden gas flow in the event of a thermal runaway and ensure its reliable discharge. The entry of oxygen-containing air from the ambient atmosphere due to pressure differences must be avoided, as otherwise an explosive gas mixture could form and ignite within the gas channels. It has proven advantageous to hermetically seal the gas outlet opening with a membrane and / or a valve, whereby the membrane and / or valve is preferably only permeable to the battery gas above a certain overpressure.

[0011] Due to the effort to equip vehicles with ever larger traction batteries without shifting the vehicle type-specific floor interface downwards, the available height of the underbody protection plate and thus the height of the effective gas duct cross-section is limited and is essentially restricted to the necessary minimum heights resulting from the mechanical load cases. The height of the gas ducts is usually in a range of more than approximately 5 mm but less than approximately 30 mm. The usable gas duct volume is further reduced by the support structures required to support the underbody protection plate on the battery housing above it, which can be rib-like, trapezoidal, columnar or flat in order to be aligned with the load-bearing zones of the battery housing. These support structures, in turn, consume volume in the degassing chamber, even though they sometimes provide an open channel for the gas discharge system orin turn form the gas conducting structure.

[0012] The adverse consequence of a gas channel cross-section that is too small is that high internal pressures build up in the event of thermal runaway, preventing rapid heat dissipation. This effect can be exacerbated by increasing channel constriction as combustion products from the battery cells deposit on the surfaces and particle traps of the gas discharge system. A backflow of hot gases into the cell casings of the traction battery can promote chain reactions within the battery system and / or cause functional failure of seals, interfaces, adhesives, or structural failure of the battery enclosure or gas discharge system, thus leading to fires and explosions.

[0013] In the event of a thermal runaway of the high-voltage battery / HV battery, it is important to prevent the underrun protection from burning through due to the escaping abrasive gases and to ensure their safe dissipation so that the occupants can leave the vehicle safely.

[0014] High-voltage batteries for BEVs are often mounted on the vehicle's underbody and therefore require protection from external influences such as dirt, water, and mechanical damage from below during normal operation. The underride guard also performs load-bearing functions during structural load cases such as fatigue strength over service life, overall vehicle rigidity, and crash load cases.

[0015] In the event of a fire underneath the vehicle, the underrun protection must protect the HV technology above it so that it does not pose a danger to the occupants.

[0016] As a technical solution for the requirements mentioned, suitable systems have been established on the market. These systems are often designed as panel-shaped sandwich constructions using continuous fiber-reinforced cover layers, thus creating a maximum level of shock absorption capacity and functional reliability while at the same time forming a good compromise in terms of weight and cost-effectiveness.

[0017] However, the known designs have so far only inadequately taken into account the case of “thermal runaway” and are often not robust enough to meet the increasingly stringent legislative, regulatory and safety requirements.

[0018] Thermal runaway is particularly critical in battery architectures with downward-facing battery burst vents, as the underrun protection is exposed to the concentrated escaping gas jet at a few exposed points over a short distance and must withstand this for several minutes in the event of thermal propagation (i.e., temperature transfer from one cell of the high-voltage battery to another cell of the high-voltage battery). Particularly with lithium batteries, temperatures of up to approximately 1200°C can occur in a highly exothermic reaction (caused by cell combustion or cell combustion products). This, combined with projectile-like particle discharge, has a destructive thermal and abrasive effect on the underrun protection.

[0019] Even under these conditions, the affected area must still have sufficient tightness and structural strength to prevent the hot flammable gases (mainly methane, ethane, ethylene or hydrogen) and the glowing particles from escaping into the surrounding atmosphere, which would otherwise lead to immediate ignition under the influence of atmospheric oxygen, which is to be avoided.

[0020] The thermally robust solutions currently used, made of steel and / or mica, also have significant disadvantages. Such common solutions are often heavy, complex, and expensive. Examples include the sheet steel option, with its poor weight performance, and the mica option, with its questionable mining and manufacturing conditions, which, in light of new legislation, make its use increasingly risky and uneconomical.

[0021] It is the object of the present invention to avoid or at least mitigate the disadvantages of the prior art.

[0022] This object is achieved by the subject matter of claim 1, namely by an underrun protection device for mounting beneath a high-voltage battery / traction battery, preferably comprising a battery module, for a preferably (exclusively) battery-powered (land-based) motor vehicle, comprising a main body that can be constructed or is constructed in a sandwich-like manner, wherein a thermal reinforcement is arranged on or at the upper side of the main body facing the battery module, wherein the thermal reinforcement comprises carbon. The thermal reinforcement is constructed as a graphite foil.

[0023] This provides a thermally robust solution that is lightweight, easy to install, inexpensive and cost-optimized.

[0024] The result is a material that offers such high temperature resistance that it does not lose structural strength prematurely, while simultaneously possessing sufficient mechanical resistance to the effects of particle impact / thermal runway. To determine the performance of various material alternatives, their barrier effect against hole penetration is classified in a suitable surrogate test using stage fountains.

[0025] Advantageous embodiments are the subject of the subclaims and are explained in more detail below.

[0026] Thus, an advantageous embodiment is characterized in that the main body has a sand core and a cover layer laminate (constructed from one layer or several layers) is arranged on the battery side.

[0027] The thermal reinforcement is arranged between the cover layer laminate and outgassing openings in a battery module / battery.

[0028] Furthermore, it is advantageous if the thermal reinforcement is designed as a local reinforcement or as a layer.

[0029] It has proven to be effective if the thermal reinforcement runs essentially / partially completely in one (straight / flat) plane.

[0030] If the thermal reinforcement consists of pure carbon or at least comprises carbon, particularly good protection against burn-off is achieved.

[0031] It is advisable for the thermal reinforcement to cover the main body completely or in sections.

[0032] A further advantageous embodiment is characterized in that the thermal reinforcement is designed as a preferably doubled (thin) layer of graphite foil.

[0033] The invention also relates to an underrun protection battery module, with an underrun protection according to one of the preceding claims, which is arranged under a battery module / fastened to it.

[0034] It is advantageous if the battery module has a housing for accommodating battery cells of the (high-voltage) battery, and at least one outgassing opening is present in the housing, wherein the thermal reinforcement is arranged and designed as a barrier that stops, diverts or at least conducts the gases in the direction of ejection of hot gases in the event of a "thermal runaway" of the (high-voltage) battery from the housing.

[0035] The invention also relates to a motor vehicle with an underrun protection battery module of the type according to the invention.

[0036] It was found that the task is best solved by using materials made of pure carbon, with its advantageous properties such as high temperature resistance and low density. High-purity carbon is readily available in the form of graphite foil made from expanded natural graphite, for example, for sealing applications. It was demonstrated that the use of graphite foil and carbon fiber laminates in the above-mentioned test method significantly exceeds the resistance of conventional materials such as steel and mica for the same weight. This means that these materials offer a superior combination of thermal and mechanical resistance.

[0037] In a preferred embodiment, the underrun protection is designed as a GRP fiber composite component with a PU sandwich core.

[0038] The underrun protection can also be made monolithically from another material such as SMC (Sheet Molding Compound) or metal.

[0039] In the example shown, the battery above has vents located in the center of the vehicle, sealed with rupture discs. In the event of a thermal runaway, these vents rupture due to the resulting high internal pressure, allowing the battery to vent downward onto the underbody protection.

[0040] The most heavily stressed area (First Impact Zone) is now additionally reinforced with a thermal barrier made of one of the carbon materials presented above to prevent the underrun protection from burning through.

[0041] The reinforcement can be implemented as a doubled, thin layer of graphite foil. The invention is explained in more detail below with the aid of a drawing. The following illustrates the use of the invention in an exemplary vehicle architecture with a high-voltage automotive battery and (as viewed in the direction of gravity) an underrun protection system underneath.

[0042] They show: Fig. 1 is a perspective exploded view of an underrun protection device according to the invention with a thermal reinforcement according to a first preferred embodiment, Fig. 2 a cross-section through the three components Fig. 1, and Fig. 3 an enlargement of area III from Fig. 2.

[0043] The figures are merely schematic and serve only to facilitate understanding of the invention. The same elements are designated by the same reference numerals.

[0044] Features of individual embodiments can be interchanged or complement each other.

[0045] Fig. 1 shows an underrun protection 1 for attachment below a high-voltage battery 3 of a motor vehicle, which preferably has a battery module 2, with a main body 4 which can be constructed or is constructed in a sandwich-like manner, wherein a thermal reinforcement 6 is arranged on or at the upper side 5 of the main body 4 facing the battery module 2, wherein the thermal reinforcement 6 comprises carbon.

[0046] An underrun protection battery module 7 comprises a housing 8 of the battery module 3, the main body 4, and the thermal reinforcement 6. The housing 8 is prepared to accommodate battery cells 9.

[0047] There are (see Fig. 3) in the housing 8 a plurality of outgassing openings 10, which can be closed (each) with a bursting disc (not shown).

[0048] A fastener, such as a rivet, a screw or a crimp element, is in Fig. 2 is referenced with the reference number 11.

Claims

[1] Underrun protection (1) for mounting underneath a high-voltage battery (3) of a motor vehicle, which battery module (2) is the case, with a main body (4) which can be constructed or is constructed in a sandwich-like manner, wherein a thermal reinforcement (6) is arranged on or at the upper side (5) of the main body (4) facing the battery module, wherein the thermal reinforcement (6) is constructed as a graphite foil. [2] Underrun protection (1) according to claim 1, wherein the thermal reinforcement (6) is formed as a local reinforcement or as a layer. [3] Underrun protection (1) according to one of the preceding claims, wherein the thermal reinforcement runs completely in a (straight / flat) plane. [4] Underrun protection (1) according to one of the preceding claims, wherein the thermal reinforcement (6) consists of / is constructed of or at least comprises pure carbon. [5] Underrun protection (1) according to one of the preceding claims, wherein the thermal reinforcement (6) covers the main body (4) completely or in sections. [6] Underrun protection (1) according to one of the preceding claims, wherein the thermal reinforcement (6) is designed as a doubled layer of graphite foil. [7] Underrun protection battery module (7), with an underrun protection (1) according to one of the preceding claims, which is arranged under a battery module (2). [8] Underrun protection battery module (7) according to claim 7, wherein the battery module (7) has a housing (8) for receiving battery cells (9) of a battery, and at least one outgassing opening (10) is present in the housing (8), wherein the thermal reinforcement (6) is arranged and designed as a barrier that stops, diverts or at least conducts the gases in the direction of expulsion of hot gases in the event of a "thermal runaway" of the battery from the housing (8). [9] Motor vehicle with an underrun protection battery module according to claim 7 or 8.

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