Motor vehicle with traction battery, protective structure and detection device

Abstract

A motor vehicle has a body (1) comprising a floor assembly in which a traction battery (4) is housed, wherein a protective structure (7) forming an underside of the body (1) is arranged below the traction battery (4), and a detection device for detecting deformation of the protective structure (7). The detection device comprises a first detection device (8) having a plurality of contact measuring devices (13), each comprising a first contact element (14) and a second contact element (15), wherein the contact elements (14, 15) are spaced apart from each other in an unloaded state of the respective contact measuring device (13), and wherein the contact measuring devices (13) are electrically connected to an evaluation device (18) of the detection device such that an electrical circuit is closed by each contact of the contact elements (14, 15).The detection device further comprises a second detection device (9) which has at least one strain gauge (21). Both the first detection device (8) and the second detection device (9) are assigned to a monitoring area (24) of the protective structure (7).

Description

The invention relates to a motor vehicle with a body comprising a floor assembly in which a traction battery is received, wherein a protective structure forming an underside of the body is arranged below the traction battery. Damage to a motor vehicle battery poses a safety risk because, in extreme cases, it can lead to thermal runaway of the battery, which in turn can cause the vehicle to catch fire. This is particularly true for a vehicle's traction battery, which is designed to provide electrical power to the vehicle's electric traction motor for propulsion. Such a traction battery typically comprises a large number of battery cells, and a thermally runaway battery cell can cause a domino effect, leading to thermal runaway in the other battery cells as well (so-called "thermal propagation"). Due to its considerable size and weight, the traction battery of an electric vehicle is typically integrated into an intermediate floor within the vehicle's body structure, located between two axles. This installation location minimizes the vehicle's interior space and results in a relatively low center of gravity, which can improve handling. Furthermore, the surrounding body structure provides relatively good protection against damage for the traction battery in this location. Regarding damage from below, the body of an electric vehicle typically includes a protective structure, often referred to as an underride guard, which, located in the area of ​​the traction battery, forms the underside of the vehicle. Since such an underride guard should be large enough to completely cover the traction battery and adequately protect it from damage, particularly from contact with an obstacle (which occurs when driving over an obstacle and consequently with considerable force), and is therefore dimensioned to withstand the stresses, an underride guard often has a relatively large mass. This correspondingly increases the overall mass of the vehicle, which is already comparatively high in an electric vehicle, especially due to the enclosed traction battery.In addition, providing a sufficiently robust underride protection system is associated with relatively high costs. The design of an underride guard therefore represents a compromise between adequate protection on the one hand and an acceptably low weight and sufficiently low manufacturing costs on the other. It is generally possible that, when driving over an obstacle, the underride guard will be damaged to such an extent that the traction battery it is intended to protect will also be at least slightly damaged. Such relatively minor damage may go unnoticed by the vehicle's user or at least not be perceived as particularly relevant, because it may not have an immediate impact on the vehicle's functionality. Nevertheless, even such minor damage to a traction battery can lead to consequential damage, including potentially hazardous situations. It is therefore advisable to detect potential damage to a vehicle's traction battery, particularly damage caused by driving over an obstacle, in order to determine whether the traction battery needs to be inspected and, if necessary, repaired. The likelihood of damage to the traction battery depends primarily on the depth of deformation of the protective structure, as contact between the deformed section of the protective structure and the traction battery often only occurs after a certain depth of deformation. Furthermore, the likelihood of damage to the traction battery depends on the extent to which the protective structure deforms or penetrates the traction battery. DE 10 2022 202 614 A1 discloses a method for evaluating an impact against a vehicle battery using an elastic hollow tube between the battery and the vehicle's outer skin, and using at least one pressure sensor at one end of the hollow tube to detect the pressure change occurring inside the hollow tube during an impact. A further impact sensor, for example an acceleration sensor, is provided, and the temporal profile of the pressure sensor signal is evaluated relative to a time point derived from the impact sensor signal. Preferably, the time difference between the start times of these signals is determined, and the position and width of the impact zone are derived from this in more detail. US Patent 2020 / 0161717A1 describes a battery safety device comprising an underbody component for a vehicle, multiple sensors, and an evaluation unit. Each sensor is configured to generate a sensor signal in response to deformation of the underbody component and transmit this signal to the evaluation unit. The evaluation unit is configured to derive from the sensor signals both initial information about the location of the deformation and subsequent information about the magnitude of the deformation. Examples of sensor types include: piezoelectric films, accelerometers for detecting structure-borne sound, pressure hoses with pressure sensors, air pressure sensors, and accelerometers for measuring the acceleration of the safety device. The invention is based on the objective of demonstrating a way to advantageously determine the depth of a deformation of a protective structure located below a traction battery in a motor vehicle. This problem is solved in a motor vehicle according to claim 1 by a method as claimed in claim 10. Advantageous embodiments of the motor vehicle and preferred embodiments of the method are the subject of further claims and will become apparent from the following description of the invention. An (electric) motor vehicle according to the invention comprises a body which has a floor assembly in which a traction battery is received, wherein a protective structure serving as underride protection is arranged below the traction battery, which (also or at least in a section) forms an underside of the body. The vehicle further includes a detection device for identifying deformations of the protective structure. The detection device comprises a first detection device and a second detection device, both of which are assigned to the same monitoring area of ​​the protective structure, so that each can independently detect a deformation of the protective structure within that monitoring area. The first detection device comprises a plurality of contact measuring devices, each including a first contact element and a second contact element. In an unloaded state of the measuring device, the contact elements are spaced apart from one another. The contact measuring devices are electrically connected to an evaluation device of the detection unit such that each contact of the contact elements closes an electrical circuit. The closing of such a circuit can then be interpreted by the evaluation device as a deformation of the protective structure in the area of ​​the corresponding contact measuring device that caused contact between the contact elements. This design of the first detection device is relatively simple in construction and therefore cost-effective to implement. Furthermore, it is characterized by a relatively small installation space requirement, particularly in the vertical direction of the vehicle.This represents a significant advantage in a motor vehicle according to the invention, in which the traction battery is integrated into the underbody, since in such a vehicle, particularly with regard to the vertical direction, as little installation space as possible can be available for the integration of a corresponding detection device. Furthermore, the design of the first detection device with the plurality of contact measuring devices enables spatial localization of a deformation by means of the evaluation device detecting which of the several contact measuring devices the corresponding contact elements are making contact with. On the other hand, it is not possible, or not possible with sufficiently little effort, to determine the depth of a deformation using only the first detection device. Therefore, a motor vehicle according to the invention further comprises a second detection device, which includes at least one strain gauge. The operation of such a strain gauge, often also referred to as a strain gauge, is known to be based on the fact that deformation of the strain gauge leads to a change in its electrical resistance. By integrating such a strain gauge into a circuit that also includes the evaluation device, such a change in electrical resistance can be detected by the evaluation device. The magnitude of the change in electrical resistance can depend directly on the magnitude of the deformation of the strain gauge. This makes it possible to determine the (overall) extent of a deformation of the protective structure.The extent of deformation of the protective structure, as determined by the second detection device, is also nonspecific with regard to depth, since the area or spatial extent of the deformation cannot be determined, or not with an acceptably low level of effort, based on an evaluation of a measurement from the second detection device. Rather, the determined extent of deformation can result from both a relatively large-area deformation with a relatively shallow depth and a relatively small-area deformation with a relatively large depth. However, since the spatial extent of the deformation can be determined using the first detection device, the depth of a deformation of the protective structure that accounts for these two measurements can be determined by combining a measurement from the first detection device with a measurement from the second detection device. This is done by relating the extent and the spatial extent of the deformation to each other. The depth to be determined can depend on the ratio of the extent of the deformation to its spatial extent, so that for a given extent of deformation, the smaller the spatial extent of this deformation, the greater the depth will be. Accordingly, the invention also relates to a method for determining the depth of a deformation of the protective structure of a motor vehicle according to the invention, wherein a (total) extent of a deformation of the protective structure is determined from a measured value of the second detection device, and a spatial extent of the deformation of the protective structure is determined from an evaluation of the positions of those contact measuring devices of the first detection device that were activated by contact between their first and second contact elements. The depth of the deformation is then determined by relating the extent and the spatial extent of the deformation to each other accordingly. The term "floor assembly" is generally understood to refer to the area of ​​the vehicle body that forms the floor, particularly in the case of a unibody construction. The floor assembly, as a load-bearing structure, connects the components of a chassis with a vehicle body, which may include, in particular, a body shell and components arranged within the body shell, such as seats, traction motor, etc. The floor assembly may, in particular, include longitudinal members, cross members, wheel arches, and floor panels. According to the invention, an "electric motor vehicle" is a motor vehicle that comprises at least one electric traction motor capable of propelling the motor vehicle on its own. The motor vehicle may consist solely of the at least one electric traction motor as its drive motor ("electric vehicle"), or the at least one electric traction motor may be provided in addition to another drive device, in particular an internal combustion engine ("hybrid vehicle"). The motor vehicle may, in particular, be a wheeled and not rail-bound motor vehicle (preferably a passenger car or a truck). According to the invention, a "battery" is defined as an electrochemical storage device for electrical energy, in which stored chemical energy is converted into electrical energy by an electrochemical redox reaction during discharge. A battery can comprise one or, more commonly, several battery elements, which, to form a battery cell, are arranged within a casing, usually in the form of a foil casing often referred to as a "pouch" or a housing. Each battery element can comprise two electrodes, a separator arranged between the electrodes for electrical separation of the electrodes, and an electrolyte serving as an ion conductor. A "traction battery" is a battery designed to provide the electrical power required to propel the vehicle by means of the traction motor of an electric motor vehicle. The traction battery of an electric vehicle is typically a relatively large assembly that often occupies a significant portion of the installation space provided by the vehicle's underbody between the two axles. Against this background, the detection device of a vehicle according to the invention should preferably be designed such that it can detect a deformation of the protective structure over a relatively large area, preferably the entire surface of the underside of the traction battery facing the underside of the vehicle. Accordingly, it is preferably provided that the monitoring area extends along the entire underside of the traction battery. To advantageously determine the spatial extent of a deformation using the first detection device, it is preferably possible to arrange the contact measuring devices in a distributed manner along the underside of the traction battery. Furthermore, it can be advantageous if each subset of the multiple contact measuring devices is assigned its own individual electrical circuit (which is thus not assigned to the other subset(s)). A subset of the contact measuring devices can comprise a single contact measuring device or multiple contact measuring devices. According to one embodiment of a motor vehicle according to the invention, the contact measuring devices and / or the at least one strain gauge are arranged on the outer side of the protective structure facing the traction battery. This results in both a functionally advantageous arrangement of these measuring devices and good protection of them from damage caused by contact with an external obstacle. Preferably, the contact measuring devices are integrated into a planar mounting structure. A mounting structure is understood to be a structural unit that positions the contact measuring devices firmly and, in particular, immovably. Such a protective structure is considered planar if its maximum length (extent in the longitudinal direction of the vehicle) and maximum width (extent in the transverse direction of the vehicle) are many times, preferably at least ten or one hundred times, greater than its maximum height (extent in the vertical direction of the vehicle). According to a preferred embodiment, the holding structure may include a support element, which may in particular be or comprise a film, on which (i.e., on at least one of its outer surfaces) the contact measuring devices are arranged. This may result in an advantageous design of the holding structure, which may be characterized in particular by the lowest possible height. According to the invention, a film is defined as a flexible and therefore easily deformable body whose length and width (which define the large areas of the film) are many times greater than its height (i.e., film thickness), wherein the height preferably corresponds to a maximum of 1 / 100, 1 / 500, 1 / 1000, 1 / 10000, or 1 / 100000 of the length and / or width of the film. In particular, a film can be dimensioned with such a small thickness that it would visibly deform under its own weight without support. According to one embodiment of a motor vehicle according to the invention, it can be provided that the at least one strain gauge is also integrated into the planar holding structure, which can result in a structurally simple and therefore cost-effective design for the motor vehicle according to the invention. According to another embodiment of a motor vehicle according to the invention, it can be provided that the strain gauge is integrated into the protective structure and, in particular, is embedded at least partially in a material forming the protective structure. Particularly for such a configuration of a motor vehicle according to the invention, it can be advantageous if the protective structure is at least partially made of plastic, in particular of at least one fiber-reinforced plastic (especially with carbon and / or glass fibers). A protective structure that is at least partially made of plastic can also be characterized by a relatively low mass. According to a preferred embodiment of a motor vehicle according to the invention, the traction battery and the protective structure can be arranged at a distance from each other in at least one section, preferably with respect to the entire underside of the traction battery. The resulting gap can then be configured, at least partially, as a free space filled exclusively with a fluid, in particular air. This prevents a relatively minor deformation of the protective structure from leading to contact between it and the traction battery, which could result in damage to the traction battery. If a deformation of the protective structure is detected that is so deep as to suggest damage to the traction battery, it may be possible to put the traction battery into a safe state. For this purpose, an electrical connection between the traction battery and at least one other electrical component, preferably the integration of the traction battery into the vehicle's overall electrical network, can be disconnected or interrupted. The invention is explained in more detail below with reference to embodiments illustrated in the drawings. The drawings show, in simplified representations: Fig. 1: a motor vehicle according to the invention in a side view, Fig. 2: a section of a motor vehicle according to the invention, Fig. 3: a contact measuring device with a section of a holding structure of a motor vehicle according to the invention, Fig. 4: a first exemplary deformation of a protective structure of a motor vehicle according to the invention, Fig. 5: a second exemplary deformation of a protective structure of a motor vehicle according to the invention, and Fig. 6: a strain gauge of a motor vehicle according to the invention. The motor vehicle shown in Fig. 1 comprises a body 1, which may be of a self-supporting construction. The body 1 can therefore have a so-called floor assembly, which provides mounting points for components of a chassis and a drivetrain of the motor vehicle and may include longitudinal and transverse members as well as floor surfaces and wheel arches. In the section between two axles 2 of the motor vehicle, there is an intermediate floor 3 of the body 1. This forms a battery housing essentially over its entire horizontal extent (extension along a longitudinal axis 10 and a transverse axis 11 of the motor vehicle), within which a traction battery 4 of the motor vehicle is arranged. The traction battery 4 can, as required, supply a traction motor 5 of the motor vehicle with electrical energy for propelling the motor vehicle. The traction battery 4 comprises a plurality of battery cells 6 (see Fig. 2), which may be housed in a battery casing (not shown). The battery cells 6 are firmly integrated into the intermediate floor 3 of the body 1, for example by bolting the battery casing to longitudinal and / or transverse members of the body 1. Below the traction battery 4, the floor assembly of the body 1 forms a protective structure 7 serving as underride protection, which is arranged at a defined distance from the traction battery 4. By integrating the traction battery 4 into the intermediate floor 3 of the body 1, the vehicle's usable space, which is primarily comprised of a passenger compartment and a luggage compartment, is restricted as little as possible. Furthermore, this arrangement provides relatively good protection for the traction battery 4 in the event of a vehicle accident. Nevertheless, a significant risk of damage to the traction battery 4 remains. Such damage can occur, for example, if the vehicle runs over an obstacle 25 and this obstacle 25 deforms the protective structure 7 to such an extent that it makes substantial contact with the traction battery 4. In order to be able to detect such a deformation of the protective structure 7, a motor vehicle according to the invention comprises a detection device with a first detection device 8 and a second detection device 9. The first detection device 8 comprises a plurality of contact measuring devices 13, which are arranged (immovably fixed) on the outside of the protective structure 7 facing the traction battery 4. The basic structure and general operation of such a contact measuring device 13 are shown in Fig. 3. Accordingly, it comprises a first contact element 14 and a second contact element 15, which are spaced apart from each other in an unloaded state of the contact measuring device 13. This space is maintained when the contact measuring device 13 is integrated along a vertical axis 13 of the vehicle. According to Fig. 3, the first contact element 14 can consist of two separately arranged sub-elements 16, which are integrated into the same circuit 17. Due to the separate arrangement of the sub-elements 16 of the first contact element 14, this circuit 17 is open or interrupted in the unloaded state of the contact measuring device 13.If, on the other hand, a relevant force is applied to the contact measuring device 13 with at least one force component in the direction of the distance between the first contact element 14 and the second contact element 15, these contact elements 14 and 15 make contact with each other and the circuit 17 is closed. The resulting current flow in the circuit 17 can be determined by means of an evaluation device 18. From this, it can then be deduced by means of the evaluation device 18 that a relevant force is acting, or at least has acted, on the contact measuring device 13, whereby this force may be due, in particular, to a force acting on the protective structure 7 of the motor vehicle and a resulting deformation of the protective structure 7. As an alternative to the design of the first contact element 14 with two separately arranged sub-elements 16, each of which is integrated into the circuit 17, it is also possible to provide a single first contact element 14, wherein both the first contact element 14 and the second contact element 15 are integrated into the circuit 17. To ensure that the respective contact elements 14, 15 are spaced apart from each other in the unloaded state of the individual contact measuring devices 13, they are integrated into a holding structure 19 which comprises two spaced-apart support elements 20, on which one of the contact elements 14, 15 of the individual contact measuring devices 13 is attached in a mutually facing, spaced-apart arrangement. The multiple contact measuring devices 13 are arranged in a uniform pattern across the surface along the underside of the traction battery 4 in order to detect any force acting on the protective structure 7, which has led to a deformation of the protective structure 7 and thus can potentially lead to damage to the traction battery 4, as far as possible at any point on the protective structure 7 where it covers the traction battery 4.By a suitable, in particular parallel, electrical connection of the contact measuring devices 13 such that they are individually or at least in several subsets electrically connected to the evaluation device 18 independently of one another, such that a contact of the contact elements 14, 15 of these individual contact measuring devices 13 or at least one of the contact measuring devices 13 of each subset closes an associated electrical circuit 17, a spatial localization including a spatial extent of a deformation of the protective structure 7 can also be determined. For this purpose, it is analyzed which or which of the various circuits 17 have been closed. This is illustrated in Figs. 4 and 5. These show a deformation of the protective structure 7 caused, on the one hand, by a relatively large obstacle 25 (see Fig. 4) and, on the other hand, by a relatively small obstacle 25 (see Fig. 5).The area fill represents those contact measuring devices 13 that were activated as a result of the respective deformation, i.e., whose contact elements 14, 15 contact each other or at least have contacted each other. The second detection device 9 comprises at least one strain gauge 21, the basic structure of which is shown in Fig. 6. The strain gauge 21 thus comprises a wire 22 made of an electrically conductive and sufficiently ductile material, for example, a suitable metal (alternatively, an electrically conductive foil), which is applied to a flexible carrier layer 23 and may optionally be covered by an additional cover layer, so that the wire 22 (or the metal foil) is protected between the carrier layer 23 and the cover layer. A meandering shape of the wire 22 ensures that it covers the largest possible area. This also results in a relatively long length of the wire 22, which is advantageous with regard to the measuring function of the strain gauge 21.This measuring function is known to be based on the fact that the wire 22 is integrated into an electrical circuit, whereby a change in the length of the wire 22 also changes the electrical resistance it causes in the circuit. This change in electrical resistance can be determined and evaluated by means of the evaluation device 18 of the motor vehicle. In the motor vehicle according to the invention, the change in length of the wire 22 of the at least one strain gauge 21 occurs only in certain areas due to a local deformation of the protective structure 7 into which the at least one strain gauge 21 is integrated (generally immovably over its entire surface), as shown in Fig. 2. Fig. 2 also shows that both the first detection device 8, i.e. at least its contact measuring devices 13, and the second detection device 9, i.e. at least the wire 22 (or the metal foil) are arranged within the same (monitoring) area 24 of the protective structure 7, so that in principle a deformation of the protective structure 7 can be detected in isolation with each of these detection devices 8, 9.A combined evaluation of corresponding measured values ​​from both detection devices 8, 9 also makes it possible to determine the depth of any deformation of the protective structure 7, which is of particular importance for determining the probability of damage to the traction battery 4, because such damage to the traction battery 4 is to be expected in particular if the protective structure 7 has been deformed so extensively or to such a great depth that it contacts at least one adjacent battery cell 6 of the traction battery 4 in the deformed area and may damage it in the process. Determining the depth of a deformation in the protective structure 7 is based on the fact that the spatial extent of the deformation can be determined using the first detection device 8, as already described, while the (overall) extent of this deformation can be determined using the second detection device 9. By relating the extent and the spatial extent of a deformation, its depth can be determined. For example, if the same (overall) extent is determined for the two deformations according to Figs. 4 and 5 using the second detection device 9, then the deformation according to Fig. 4 has a smaller depth than the deformation according to Fig. 5, which has a smaller spatial extent, due to its larger spatial extent. Instead of integrating the at least one strain gauge 21 into the protective structure 7 according to Fig. 2, it can also be provided that it is arranged on the outer side of the protective structure 7 facing the traction battery 4, as is also provided for the contact measuring devices 13 of the first detection device 8. In particular, it can then also be provided that the at least one strain gauge 21 or the wire 22 (or the metal foil) thereof is integrated into the retaining structure 18 and is preferably attached to one of the support elements 20 on the outside. Reference symbol list 1 Body 2 Axle 3 Intermediate floor 4 Traction battery 5 Traction motor 6 Battery cell 7 Protective structure 8 First detection device 9 Second detection device 10 Longitudinal axis of the vehicle 11 Transverse axis of the vehicle 12 Vertical axis of the vehicle 13 Contact measuring device 14 First contact element 15 Second contact element 16 Sub-element of the first contact element 17 Circuit 18 Evaluation device 19 Mounting structure 20 Support element 21 Strain gauge 22 Wire 23 Carrier layer 24 Monitoring area 25 Obstacle

Claims

Motor vehicle with a body (1) comprising a floor assembly in which a traction battery (4) is received, wherein a protective structure (7) forming an underside of the body (1) is arranged below the traction battery (4), and with a detection device for detecting a deformation of the protective structure (7), characterized in that the detection device comprises a first detection device (8) having a plurality of contact measuring devices (13), each comprising a first contact element (14) and a second contact element (15), wherein the contact elements (14, 15) are spaced apart from each other in an unloaded state of the respective contact measuring device (13), and wherein the contact measuring devices (13) are electrically connected to an evaluation device (18) of the detection device such that an electrical circuit is closed by each contact of the contact elements (14, 15).and • a second detection device (9) comprising at least one strain gauge (21), wherein both the first detection device (8) and the second detection device (9) are assigned to a monitoring area (24) of the protective structure (7). Motor vehicle according to claim 1, characterized in that the monitoring area (24) extends along the entire underside of the traction battery (4). Motor vehicle according to claim 1 or 2, characterized in that several subsets of the contact measuring devices (13) are each assigned an individual electrical circuit (17). Motor vehicle according to one of the preceding claims, characterized in that the contact measuring devices (13) and / or the at least one strain measuring device (21) is / are arranged on an outer side of the protective structure (7) facing the traction battery (4). Motor vehicle according to one of the preceding claims, characterized in that the contact measuring devices (13) are integrated into a planar holding structure (19). Motor vehicle according to claim 5, characterized in that the strain gauge (21) is also integrated into the planar holding structure (19). Motor vehicle according to one of claims 1 to 5, characterized in that the strain gauge (21) is integrated into the protective structure (7). Motor vehicle according to one of the preceding claims, characterized in that the protective structure (7) is at least partially made of plastic. Motor vehicle according to one of the preceding claims, characterized in that the traction battery (4) and the protective structure (7) are arranged spaced apart from each other in at least one section. Method for determining the depth of a deformation of the protective structure (7) of a motor vehicle according to one of the preceding claims, characterized in that an extent of a deformation of the protective structure (7) is determined from a measured value of the second detection device (9) and a spatial extent of the deformation of the protective structure (7) is determined from an evaluation of the positions of those contact measuring devices (13) that were activated by contact of their first and second contact elements (14, 15) and the depth of the deformation is determined by relating the extent and the spatial extent of the deformation to each other.

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