Thermal runaway detection of automotive traction batteries using force sensing resistor (FSR) pressure sensors

Abstract

A detection device (32) for detecting a thermal runaway condition in a rechargeable automotive traction battery, the rechargeable automotive traction battery comprising a closed traction battery housing (10) for accommodating at least a plurality of rechargeable electrochemical energy cells and provided with a safety relief valve (22). The detection device (32) comprises a force sensing resistor (34). The force sensing resistor (34) comprises: a flexible substrate (38) separated by a spacer member (40) and defining a force sensitive region (36); and a vent tube (42) connecting an exhaust outlet (44) and a space between the two substrates (38). At least the force sensitive region (36) of the force sensing resistor (34) is positionable inside the traction battery housing (10), and the exhaust outlet (44) is fluidly connectable to a detection zone (24) of an interior space (18) of the traction battery housing (10), the detection zone (24) being located near the safety relief valve (22).

Description

Technical Field

[0001] The present invention relates to a detection device for detecting a thermal runaway condition in a rechargeable automotive traction battery and a closed automotive traction battery housing including such a detection device. Background Art

[0002] In the field of motor vehicle technology, it is known that a motor vehicle comprises a drive comprising an electric drive train with an electric motor which can be operated by an electric current generated by an electrical energy source. The electrical energy source can be designed as an electrochemical energy storage device, for example as at least one rechargeable battery, which is often, somewhat inaccurately, referred to as a traction battery.

[0003] Such automotive vehicles may be designed as battery electric vehicles (BEVs) that employ an electric motor exclusively for propulsion, hybrid electric vehicles (HEVs) that include an internal combustion engine and an electric propulsion system, or plug-in hybrid electric vehicles (PHEVs) that include an internal combustion engine and a traction battery that can be recharged by connecting a plug to the electrical grid. A common feature of these automotive vehicles is a rechargeable traction battery with a capacity (ampere hours) that allows an acceptable range of vehicles.

[0004] Due to the amount of energy that can be stored in a rechargeable battery, there are increased safety requirements to prevent the amount of stored energy from being suddenly released. Therefore, it is critical to be able to detect if thermal runaway has begun inside the battery pack before any smoke or fire reaches the interior of the vehicle cabin.

[0005] Thermal runaway is known to be one of the most serious failure modes of rechargeable traction batteries. Details are described, for example, in "Fast Thermal Runaway Detection for Lithium-Ion Cells in LargeScale Traction Batteries." by Koch, Sascha et al. (Batteries 2018, 4(2), 16; DOI: 10.3390 / batteries4020016). Thermal runaway of single cells in large-scale lithium-ion batteries is a well-known risk that can lead to critical situations if measures are not taken in today's lithium-ion traction batteries used in battery electric vehicles (BEVs), plug-in hybrid electric vehicles (PHEVs) and hybrid electric vehicles (HEVs). The United Nations has published a draft global technical regulation on electric vehicle safety (GTR EVS), which describes safety features that warn passengers in the event of thermal runaway. Therefore, fast and reliable detection of faulty cells experiencing thermal runaway in lithium-ion batteries is a key factor in battery design for comprehensive passenger safety.

[0006] A set of various possible sensors was selected based on the determined impact of thermal runaway on the battery cell. These sensors have been tested in battery installations of different sizes and compared with respect to their ability to detect thermal runaway quickly and reliably and their feasibility for use in traction batteries. The sensors selected are: voltage sensors, gas sensors, smoke detectors, creep distance sensors (which are sensitive to contamination of pads arranged on their surface), temperature sensors, pressure sensors (placed on the battery cell and measuring 2kPa ≤ p sens ≤304 kPa absolute pressure in the range to determine the increase in internal pressure of the battery due to gas generation in the single battery cell); and sens Single point thin film piezoresistive force sensor with a range of ≤445N for measuring the forces between a thermal runaway cell and adjacent components / cells due to cell expansion. Summary of the invention

[0007] Purpose of the invention

[0008] It is therefore an object of the present invention to provide a low complexity detection device which is able to reliably detect a thermal runaway condition in a rechargeable traction battery of an automotive vehicle, preferably at the earliest possible stage, for example before there is a noticeable fire or smoke outbreak in the vehicle interior.

[0009] General Description of the Invention

[0010] In one aspect of the invention, the object is achieved by a detection device for detecting a thermal runaway condition in a rechargeable automotive traction battery. The automotive traction battery comprises a closed traction battery housing for housing at least a plurality of rechargeable electrochemical energy cells. The detection device comprises a force sensing resistor comprising: at least two flexible substrates separated by a spacer member and defining a force sensitive region; and an exhaust pipe connecting an exhaust outlet of the force sensing resistor and a space between the two substrates. At least the force sensitive region of the force sensing resistor can be placed inside the traction battery housing. The exhaust outlet can be fluidly connected to a detection zone of the interior space of the traction battery housing, the detection zone being located near a safety pressure relief valve.

[0011] The term "automobile" as used in this patent application is to be understood in particular as applying to vehicles including passenger cars, trucks, semi-trucks and buses. The term "enclosed traction battery housing" as used in this patent application is to be understood in particular as a housing whose fluid leakage to the space outside the housing is sufficiently low to allow a pressure increase in the interior space of the housing for the gas generation rate expected in a thermal runaway condition.

[0012] In a typical FSR, as contemplated in the present application, a paste-like sensing film may be sandwiched between two conductive electrodes covered by a polymer film. When a predetermined force is applied to the sensing film, the resistance between the electrodes may drop dramatically. This change or drop in resistance may be detected and / or measured by a control circuit or resistance detection circuit operatively coupled to the FSR sensor.

[0013] During normal operation of the electrochemical energy cell, the safety relief valve is in a closed state and there is an equilibrium pressure in the interior space of the traction battery housing, which is also applied to the force-sensitive area of ​​the FSR and the vent tube between the two flexible substrates of the FSR.

[0014] The balanced pressure condition persists even when the pressure inside the traction battery housing increases to a value below the predetermined pressure limit of the safety pressure relief valve during a thermal runaway condition of at least one electrochemical energy cell. When the pressure in the interior space of the traction battery housing exceeds the predetermined pressure limit, the safety pressure relief valve is turned to an open state and an air flow is generated through the detection zone and out of the traction battery housing at the safety pressure relief valve.

[0015] The insight of the invention is that when the generated air flow passes through the detection zone, the static pressure decreases according to the Bernoulli principle (Venturi effect), and by fluidly connecting the exhaust outlet and the ventilation duct in the detection zone, the reduction in static pressure is transmitted to the ventilation duct. As a result, the pressure applied to the outer surface of the force-sensitive area of ​​the FSR dominates and induces a mechanical force on the force-sensitive area, which causes a sharp drop in the resistance of the FSR at a predetermined pressure difference.

[0016] Thereby a low complexity detection device for detecting a thermal runaway condition in a rechargeable automotive traction battery at an early stage can be provided. Furthermore, relatively simple electronics can be used to evaluate the signal from the FSR, which can keep the hardware effort low.

[0017] In a preferred embodiment of the detection device, one of the flexible substrates of the force sensing resistor is configured to be able to be arranged in contact with a portion of the inner wall of the traction battery housing. The phrase "configured to" as used in the present application should be understood in particular as being specifically arranged, disposed or arranged. In this way, the inner wall of the traction battery housing can be used as a support for the FSR and produce a confined and directed effect of an increased pressure on the FSR inside the traction battery housing in the event of a thermal runaway situation, which increased pressure exceeds the pressure in the FSR ventilation duct. Furthermore, the FSR can be placed inside the traction battery housing in a most space-saving manner. The control circuit or the resistance detection circuit operatively coupled to the FSR sensor can preferably be arranged outside the battery housing and coupled to the FSR sensor by appropriate connecting lines.

[0018] In a preferred embodiment, the detection device further comprises a fluid connection member having two ends. One of the ends is fluidly connected to the exhaust outlet, and the other of the ends is configured to fluidly connect the exhaust outlet to the detection zone. By using the fluid connection member, the FSR can be positioned according to a specific application and appropriately perform its intended function in a variety of locations, and thereby enabling a large degree of design freedom.

[0019] Preferably, the ventilation duct is defined by a spacer member.By using a spacer member having a dual function, the design of the FSR can be kept simple.

[0020] In another aspect of the present invention, a closed automotive traction battery housing is provided, defining an interior space configured to accommodate at least a plurality of rechargeable electrochemical energy cells. The traction battery housing is provided with a safety pressure relief valve and includes an embodiment of a detection device disclosed herein. At least a force sensitive region of a force sensing resistor is disposed within the interior of the traction battery housing. An exhaust outlet of the FSR is fluidly connected to a detection zone of the interior space of the traction battery housing, the detection zone being located proximate to the safety pressure relief valve.

[0021] The benefits described in conjunction with the detection device according to the invention fully apply to the proposed vehicle traction battery housing.

[0022] In a preferred embodiment, the automotive traction battery housing further comprises a socket having two ends. One of the ends is fluidically connected to the inner space of the traction battery housing and a safety pressure relief valve is arranged at the other end of the socket. In this way, in the event of a thermal runaway condition of at least one electrochemical energy cell, the reduction of the static pressure in the detection zone according to the Bernoulli principle can be enhanced. The socket can have an elliptical, in particular circular, cross-sectional area, but can also have a cross-sectional area defined by a polygon with or without rounded edges.

[0023] Preferably, at least one transverse dimension of the opening of the safety relief valve and the tube seat is adapted to each other so that the cross-sectional area of ​​the opening of the safety relief valve overlaps the cross-sectional area of ​​the tube seat to cover the main part of either cross-sectional area. The term "main part" as used in the present application should be understood in particular as being equal to or greater than 50% of the cross-sectional area, more preferably greater than 60%, and most preferably greater than 70%, and should include a portion with 100% coverage. In this way, in the event of a thermal runaway condition of at least one electrochemical energy cell, the reduction of the static pressure in the detection zone according to the Bernoulli principle can be optimized without affecting the safety function of the safety relief valve.

[0024] In a preferred embodiment of an automotive traction battery housing having a detection device comprising a fluid connection member as described above, the other end of the fluid connection member is attached to the side wall of the socket. In this way, a particularly reliable and durable positioning of the fluid connection member can be achieved, thereby ensuring a reliable and well-defined detection of thermal runaway conditions.

[0025] Preferably, the other end of the fluid connection member comprises an opening, the normal of which is aligned in a direction substantially lying in a plane arranged perpendicularly to the center line of the tube seat. In this way, the adverse effect of the dynamic pressure of the generated gas flowing through the detection zone on the function of the detection device under thermal runaway conditions can be avoided at least to a large extent.

[0026] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0027] It should be pointed out that the features and measures described individually in the preceding description can be combined with one another in any technically meaningful manner and represent further embodiments of the invention. The description characterizes and explains the invention in detail, particularly in conjunction with the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Further details and advantages of the present invention will become apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings, in which:

[0029] Figure 1 schematically shows a closed automotive traction battery housing with an embodiment of a detection device according to the invention in a sectional side view in an installed state; and

[0030] Figure 2 Shown according to Figure 1 Schematic detailed front view and cross-sectional side view of a force sensing resistor (FSR) of a detection device.

[0031] In the different figures, identical parts are always provided with the same reference symbols or numbers, respectively. Therefore, they are usually described only once. DETAILED DESCRIPTION

[0032] Figure 1 A closed automotive traction battery housing 10 is schematically shown with a possible embodiment of a detection device according to the invention in a sectional side view in the installed state.

[0033] The traction battery housing 10 defines an interior space 18 that is configured to accommodate a battery that is not in the Figure 11 and 2. The traction battery housing 10 is a housing for a plurality of rechargeable electrochemical energy cells shown in FIG. The electrochemical energy cells may form a lithium-ion battery (accumulator). The traction battery housing 10 is closed in the sense that at the gas generation rate expected in a thermal runaway condition of at least one electrochemical energy cell, fluid leakage from the traction battery housing 10 to the exterior space 20 is sufficiently low to allow a pressure increase in the interior space 18 of the traction battery housing 10.

[0034] The traction battery housing 10 may be made at least in part from sheet metal (e.g., injected aluminum side walls), from fiber reinforced plastic (e.g., glass fiber reinforced plastic), or from a combination of those materials. The traction battery housing 10 includes side walls 12 , a cover plate 14 , and a bottom plate 16 .

[0035] The traction battery housing 10 is provided with a safety pressure relief valve 22 as a fail-safe. When the pressure in the interior space 18 of the traction battery housing 10 exceeds a predetermined pressure limit, the safety pressure relief valve 22 provides a fluid connection for the gas inside the interior space 18 of the traction battery housing 10 to be discharged to the exterior space 20 of the traction battery housing 10. The safety pressure relief valve 22 may be designed as a spring-loaded valve. In other embodiments of the traction battery housing, the safety pressure relief valve 22 may be designed as a bursting disk. In general, any other type of safety pressure relief valve suitable to a person skilled in the art may be used. The traction battery housing 10 includes a detection zone 24, which forms part of the interior space 18 and is located near the safety pressure relief valve 22.

[0036] The traction battery housing 10 may further include a pipe socket 26 having two ends and a center line 30 virtually connecting the two ends. One of the ends is fluidly connected to the internal space 18 of the traction battery housing 10. The safety relief valve 22 is arranged at the other end of the pipe socket 26. The cross-sectional area of ​​the pipe socket 26 arranged perpendicular to the center line 30 has a circular shape, and the area size of the circular shape varies along the center line 30. The opening of the safety relief valve 22 and the transverse dimensions of the pipe socket 26 are adapted to each other, so that the cross-sectional area of ​​the opening of the safety relief valve 22 and the cross-sectional area of ​​the pipe socket 26 near the safety relief valve 22 overlap to cover the main part of the two cross-sectional areas.

[0037] The traction battery housing 10 is provided with a detection device 32 for detecting a thermal runaway condition in a rechargeable automotive traction battery. The detection device 32 includes a force sensing resistor (FSR) 34 located inside the traction battery housing 10. The FSR 34 may include two flexible substrates 38 separated by a spacer member 40 and defining a force sensitive area 36 ( Figure 2). The component may encapsulate a conductive ink layer. The FSR 34 may include two sets of conductive wires that are electrically insulated from each other and attached to at least one of the two flexible substrates 38. When a sufficiently large force is applied to the outside of the FSR 34 or a sufficiently large force is caused by negative pressure to the inside of the force sensing area according to the Bernoulli principle (Venturi effect), the conductive ink layer establishes a conductive path between the two sets of conductive wires, resulting in a reduction in resistance.

[0038] The FSR 34 also includes a vent duct 42 defined by the spacer member 40. The vent duct 42 connects an exhaust outlet 44 of the FSR 34 and the space between the two flexible substrates 38.

[0039] The flexible substrate 38 can be made of a plastic material selected from a group of plastic materials, which includes but is not limited to the following materials: polyester (PE), polyethylene terephthalate (PET), polyimide (PI), polyetherimide (PEI), polyethylene naphthalate (PEN), and a combination of at least two of these plastic materials.

[0040] Suitable FSRs are commercially available in a variety of variations, covering a wide range of applications.

[0041] Reference again Figure 1 , the FSR 34 is placed inside the traction battery housing 10 such that one of the flexible substrates 38 of the FSR 34 is arranged in contact with a portion of the inner wall of the traction battery housing 10. The FSR 34 may be attached to the inner wall by using an adhesive.

[0042] The detection device 32 further comprises a fluid connection member 46. The fluid connection member 46 comprises a pipe having two ends. One of the ends of the fluid connection member 46 is fluidly connected to the exhaust outlet 44 of the FSR 34. The other of the ends is arranged in the detection zone 24 and thus fluidly connects the exhaust outlet 44 to the detection zone 24. The end facing the FSR 34 is attached to a portion of the inner wall of the traction battery housing 10 that partially defines the detection zone 24 and the side wall 28 of the tube seat 26. The end facing away from the FSR 34 is attached to the side wall 28 of the tube seat 26. The end comprises an opening 48 in the shape of an ellipse having a virtual normal line. The normal line is aligned in a direction substantially lying in a plane arranged perpendicularly to the center line 30 of the tube seat 26 (i.e., a plane corresponding to the cross-sectional plane).

[0043] During normal operation of the electrochemical energy cell, the safety relief valve 22 is in a closed state and the pressure in the interior space 18 of the traction battery housing 10 (which is also applied to the force sensitive area 36 of the FSR 34) and the pressure in the vent tube 42 between the two flexible substrates 38 of the FSR 34 and at the exhaust outlet 44 are balanced.

[0044] The condition of balanced pressure persists even when the pressure inside the traction battery housing 10 increases to a value below the predetermined pressure limit of the safety relief valve 22 in the case of thermal runaway of at least one electrochemical energy cell. When the pressure in the interior space 18 of the traction battery housing 10 exceeds the predetermined pressure limit, the safety relief valve 22 is switched to an open state and an air flow is generated through the detection zone 24 and out of the traction battery housing 10 at the safety relief valve 22. As a result, a reduction in static pressure is generated in the detection zone 24 and is transmitted to the vent 42 of the FSR 34. The pressure in the interior space 18 of the traction battery housing 10 and in the vent 42 between the two flexible substrates 38 of the FSR 34 is no longer balanced and the pressure in the interior space 18 exceeds the pressure in the vent 42. When the predetermined threshold of the air flow is exceeded, the sharp drop in the resistance of the FSR 34 can be easily detected by a control circuit or a resistance detection circuit operatively coupled to the FSR sensor.

[0045] It should be understood that the detection device may also include an optional liquid detection sensor, which is implemented to detect any liquid leakage inside the battery pack. The liquid detection sensor can be advantageously placed inside the battery pack and preferably close to the FSR sensor, so that both the FSR sensor and the liquid detection sensor can be connected to the corresponding control circuit or the common control circuit via corresponding connection lines.

[0046] It is pointed out that the drawings in the present application are not to be regarded as drawings drawn to scale. In particular, the ratios of the longitudinal and transverse dimensions are chosen for illustrative reasons and do not necessarily correspond to actual conditions.

[0047] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments.

[0048] Other variations of the embodiments to be disclosed may be understood and implemented by those skilled in the art in practicing the claimed invention by studying the drawings, the disclosure and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude the plural, which is intended to express a quantity of at least two. The fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

[0049] Reference Symbols List

[0050] 10 Traction battery housing

[0051] 12 Sidewall

[0052] 14 Cover

[0053] 16 Bottom Plate

[0054] 18. Interior Space

[0055] 20 External Space

[0056] 22 Safety relief valve

[0057] 24 Detection Area

[0058] 26 Tube socket

[0059] 28 Sidewall

[0060] 30 Centerline

[0061] 32 Detection device

[0062] 34 Force Sensing Resistors

[0063] 36 Force sensitive areas

[0064] 38 Flexible Substrate

[0065] 40 Spacer member

[0066] 42 Ventilation pipe

[0067] 44 Exhaust outlet

[0068] 46 Fluid connection components

[0069] 48 Opening

[0070] 50 Fluid detection sensor

Claims

1. A detection device (32) for detecting a thermal runaway condition in a rechargeable automotive traction battery, the rechargeable automotive traction battery comprising a closed traction battery housing (10) for housing at least a plurality of rechargeable electrochemical energy cells and provided with a safety pressure relief valve (22), the detection device (32) comprising a force sensing resistor (34), the force sensing resistor (34) comprising: - at least two flexible substrates (38) separated by a spacer member (40) and defining a force sensitive area (36); as well as - a ventilation tube (42) connecting the exhaust outlet (44) of the force sensing resistor (34) and the space between the two substrates (38), wherein at least the force sensitive region (36) of the force sensing resistor (34) can be placed inside the traction battery housing (10), and the exhaust outlet (44) can be fluidly connected to a detection zone (24) of the interior space (18) of the traction battery housing (10), the detection zone (24) being located near the safety relief valve (22).

2. The detection device (32) according to claim 1, wherein: One of the flexible substrates (38) of the force sensing resistor (34) is configured to be arrangeable in contact with a portion of an inner wall of the traction battery housing (10).

3. The detection device (32) according to claim 1 or 2, further comprising a fluid connection member (46) having two ends, wherein: One of the ends is fluidly connected to the exhaust outlet (44), and the other of the ends is configured to fluidly connect the exhaust outlet (44) to the detection zone (24).

4. The detection device (32) according to claim 1 or 2, wherein: The ventilation duct (42) is defined by the spacer member (40).

5. A closed automotive traction battery housing (10) defining an interior space (18) configured to accommodate at least a plurality of rechargeable electrochemical energy cells and provided with a safety pressure relief valve (22), the traction battery housing (10) comprising a detection device (32) as claimed in any one of the preceding claims, wherein: At least the force sensitive area (36) of the force sensing resistor (34) is placed inside the traction battery housing (10), and the exhaust outlet (44) is fluidly connected to a detection zone (24) of the interior space (18) of the traction battery housing (10), the detection zone (24) being located near the safety relief valve (22).

6. The enclosed traction battery housing (10) of claim 5, further comprising a tube base (26) having two ends, wherein: One of the ends is fluidly connected to the interior space (18) of the traction battery housing (10), and wherein the safety relief valve (22) is arranged at the other end of the pipe socket (26).

7. The closed traction battery housing (10) according to claim 6, wherein: At least one transverse dimension of the opening of the safety relief valve (22) and the pipe seat (26) are adapted to each other so that the cross-sectional area of ​​the opening of the safety relief valve (22) and the cross-sectional area of ​​the pipe seat (26) overlap to cover a major portion of either of the cross-sectional areas.

8. A closed traction battery housing (10) according to claim 6 or 7, comprising a detection device (32) according to any one of claims 3 or 4, wherein: The other of the ends of the fluid connection member (46) is attached to the side wall (28) of the tube seat (26).

9. The closed traction battery housing (10) according to claim 8, wherein: The other of the ends of the fluid connection member (46) includes an opening (48) having a normal line aligned in a direction substantially within a plane arranged perpendicular to a centerline (30) of the header (26).

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