Immersion-cooled battery pack thermal management system for inhibiting condensation and humidity detection

Abstract

A thermal management system for a battery pack that is immersion-cooled in dielectric fluid includes a control subsystem to inhibit condensation of water vapor in a reservoir that stores a portion of the dielectric fluid. The control subsystem may heat the dielectric fluid, turn off a pump that drives flow of the dielectric fluid, or output a warning based on a temperature of the dielectric fluid in the reservoir, and the temperature and humidity of air in the reservoir. The control subsystem may notify a user to service a vehicle based on humidity and temperature of air in the reservoir at different times. The control subsystem may control an actuator to move a closure member to permit fluid communication via a reservoir vent between the reservoir and the ambient environment, based on a fluid pressure in the thermal management system or the battery pack.

Description

IMMERSION-COOLED BATTERY PACK THERMAL MANAGEMENT SYSTEM FOR INHIBITING CONDENSATION AND HUMIDITY DETECTIONCROSS-REFERENCES TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Patent Application 63 / 600,915, filed November 20, 2023, and titled "CONDENSATION PREVENTION ALGORITHM AND SENSORS", the contents of which are incorporated herein by reference in their entirety.FIELD OF THE DISCLOSURE

[0002] This disclosure relates to thermal management systems for battery packs that inhibit condensation of water vapor and detect humidity in reservoirs storing dielectric fluid for immersion-cooled battery packs.BACKGROUND

[0003] A liquid immersion-cooled battery pack is a battery pack in which constituent battery cells are submerged in and in direct contact with a dielectric fluid (e.g., a synthetic dielectric oil) that flows through a housing of the battery pack to carry heat away from the battery cells. The dielectric fluid is circulated by a pump between the battery pack and a fluidically connected reservoir. The reservoir is oversized with respect to the volume of dielectric fluid contained therein, to have an air space to accommodate volumetric changes to the dielectric fluid within the operating temperature ranges (e.g., -40 °C to 70 °C) and operating pressure ranges (e.g., 70 kPa to 180 kPa) of the battery pack. The reservoir has a vent to allow for expulsion of air (e.g., due to volumetric changes to the dielectric fluid) or other gases (e.g., that may be generated by the battery pack) to the surrounding ambient environment, and thus limit pressure in the battery pack.

[0004] The vent, however, allows air including water vapor to enter into the reservoir. If the temperature of the reservoir falls to the dew point temperature, then the water vaporwill condense into liquid water and mix with the dielectric fluid. This compromises the desired dielectric nature of the dielectric fluid. Further, when the liquid water is pumped into the battery pack module, the liquid water may hydrolyze into hydrogen and oxygen and corrode the battery cells, render the battery pack inoperative and create a safety hazard.SUMMARY OF THE DISCLOSURE

[0005] There remains a need in the art for inhibiting condensation and detecting humidity in a reservoir containing dielectric fluid of an immersion-cooled battery pack.

[0006] In one aspect, the disclosure relates to a thermal management system for a battery pack. The thermal management system includes a conduit subsystem, a pump, a reservoir and a control subsystem. The conduit subsystem is arranged to transport a dielectric fluid to and from the battery pack. The battery pack includes a plurality of cells which are positioned for immersion in the dielectric fluid. The pump is for driving a flow of the dielectric fluid into and out of the battery pack and through the conduit subsystem. The reservoir is positioned for storage of a portion of the dielectric fluid and for containing a volume of air. The reservoir is fluidically connected to the conduit subsystem. The reservoir includes a vent that permits fluid communication between the volume of air contained in the reservoir and an ambient environment outside of the reservoir. The control subsystem includes a processor and a memory. The memory contains instructions that are executable by the processor to:

[0007] a) determine a temperature of the portion of the dielectric fluid;

[0008] b) determine a temperature and a humidity of the volume of air contained in the reservoir; and

[0009] c) carry out at least one corrective action based at least in part on the temperature of the portion of the dielectric fluid, the temperature of the volume of air contained in the reservoir, and the humidity of the volume of air contained in the reservoir, wherein the at least one corrective action is selected from the group of corrective actionsconsisting of: heating the portion of the dielectric fluid; turning off the pump so as to stop the flow of the dielectric fluid; and outputting a warning.

[0010] In another aspect, the disclosure relates to a thermal management system for a battery pack for a vehicle. The thermal management system includes a conduit subsystem, a pump, a reservoir and a control subsystem. The conduit subsystem is arranged to transport a dielectric fluid to and from the battery pack. The battery pack includes a plurality of cells which are positioned for immersion in the dielectric fluid. The pump is for driving a flow of the dielectric fluid into and out of the battery pack and through the conduit subsystem . The reservoir is positioned for storage of a portion of the dielectric fluid and for containing a volume of air. The reservoir is fluidically connected to the conduit subsystem. The reservoir includes a vent that permits fluid communication between the volume of air contained in the reservoir and an ambient environment outside of the reservoir. The control subsystem includes a processor and a memory. The memory contains instructions that are executable by the processor to:

[0011] a) determine, at a first point in time, a first humidity of the volume of air contained in the reservoir;

[0012] b) determine, at a second point in time, a second humidity of the volume of air contained in the reservoir; and

[0013] c) notify a user of the vehicle to service the vehicle based at least in part on the first humidity and the second humidity.

[0014] In another aspect, the disclosure relates to a thermal management system for a battery pack for a vehicle. The thermal management system includes a conduit subsystem, a pump, a reservoir, a closure member, an actuator and a control subsystem. The conduit subsystem arranged to transport a dielectric fluid to and from the battery pack, wherein the battery pack includes a plurality of cells which are positioned for immersion in the dielectric fluid. The pump is for driving a flow of the dielectric fluid into and out of the battery pack and through the conduit subsystem. The reservoir is positioned for storage of a portion of the dielectric fluid and for containing a volume of air. The reservoir is fluidically connected to the conduit subsystem. The reservoir includes a vent thatpermits fluid communication between the volume of air contained in the reservoir and an ambient environment outside of the reservoir. The closure member is moveable between a closed position and an open position. The closure member in the closed position prevents fluid communication via the vent between the reservoir and the ambient environment, wherein the closure member in the open position permits fluid communication via the vent between the reservoir and the ambient environment. The actuator is to drive the closure member between the closed position and the open position. The control subsystem includes a processor and a memory, wherein the memory contains instructions that are executable by the processor to:

[0015] a) determine at least one fluid pressure selected from the group of fluid pressures consisting of: a pressure of the dielectric fluid; and a pressure of the volume of air contained in the reservoir; and

[0016] b) control the actuator to drive the closure member from the closed position to the open position based at least in part on the determined fluid pressure.BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The foregoing and other aspects of the invention will be better appreciated with reference to the attached drawings, as follows:

[0018] Figure 1 is a schematic depiction of an embodiment of a thermal management system of the present disclosure for an immersion-cooled battery pack.

[0019] Figure 2 shows a schematic depiction of part of the thermal management system of Figure 1 .

[0020] Figure 3 is a flowchart showing an embodiment of a method for taking a corrective action based on air conditions and dielectric fluid temperature in a reservoir of the thermal management system of Figure 1.

[0021] Figure 4 is a psychrometric chart showing a relationship between air temperature, air humidity and dew point temperature used in implementing the method of Figure 3.

[0022] Figure 5 is a flowchart showing an embodiment of a method for notifying a user to service an electric vehicle based on air conditions in a reservoir of the thermal management system of Figure 1 .

[0023] Figure 6 is a flowchart showing an embodiment of a method for controlling a closure member of a reservoir of the thermal management system of Figure 1 , based on fluid pressure in the thermal management system or the battery pack.

[0024] Figure 7 is a side view of an electric vehicle incorporating the thermal management system of Figure 1 .DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0025] INTERPRETATION

[0026] For simplicity and clarity of illustration, where considered appropriate, reference numerals may be repeated among the Figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiment or embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein may be practiced without these specific details. In other instances, well-known methods, procedures and components have not been described in detail so as not to obscure the embodiments described herein. It should be understood at the outset that, although exemplary embodiments are illustrated in the figures and described below, the principles of the present disclosure may be implemented using any number of techniques, whether currently known or not. The present disclosure should in no way be limited to the exemplary implementations and techniques illustrated in the drawings and described below.

[0027] Various terms used throughout the present description may be read and understood as follows, unless the context indicates otherwise: "or" as used throughout is inclusive, as though written "and / or"; singular articles and pronouns as used throughout include their plural forms, and vice versa; similarly, gendered pronouns include their counterpart pronouns so that pronouns should not be understood as limiting anythingdescribed herein to use, implementation, performance, etc. by a single gender; "exemplary" should be understood as "illustrative" or "exemplifying" and not necessarily as "preferred" over other embodiments. Further definitions for terms may be set out herein; these may apply to prior and subsequent instances of those terms, as will be understood from a reading of the present description.

[0028] Modifications, additions, or omissions may be made to the systems, apparatuses, and methods described herein without departing from the scope of the disclosure. For example, the components of the systems and apparatuses may be integrated or separated. Moreover, the operations of the systems and apparatuses disclosed herein may be performed by more, fewer, or other components and the methods described may include more, fewer, or other steps. Additionally, steps may be performed in any suitable order. As used in this document, "each" refers to each member of a set or each member of a subset of a set.

[0029] The indefinite article "a" is not intended to be limited to mean "one" of an element. It is intended to mean "one or more" of an element, where applicable, (i.e. unless in the context it would be obvious that only one of the element would be suitable).

[0030] Any reference to upper, lower, top, bottom or the like is intended to refer to an orientation of a particular element during use of the claimed subject matter and not necessarily to its orientation during shipping or manufacture. The upper surface of an element, for example, can still be considered its upper surface even when the element is lying on its side.

[0031] COMPUTER IMPLEMENTATION

[0032] The term "processor", as used herein, refers to one or more electronic hardware devices that is / are capable of reading and executing instructions stored on a memory to perform operations on data, which may be stored on a memory or provided in a data signal. The term "processor" includes a single device or a plurality of physically discrete, operatively connected devices despite use of the term in the singular. The plurality of processors may be arrayed or distributed. Non-limiting examples of processors include integrated circuit semiconductor devices and / or processing circuit devicesreferred to as computers, servers or terminals having single or multi-processor architectures, microprocessors, microcontrollers, microcontroller units (MCU), central processing units (CPU), field-programmable gate arrays (FPGA), application specific circuits (ASIC), digital signal processors, and combinations of the foregoing

[0033] The term "memory", as used herein, refers to a non-transitory tangible computer-readable medium for storing information (e.g., data or data structures) in a format readable by a processor, and / or instructions (e.g., computer code or software programs or modules) that are readable and executable by a processor to implement an algorithm. The term "memory" includes a single device or a plurality of physically discrete, operatively connected devices despite use of the term in the singular. Non-limiting types of memory include solid-state semiconductor, optical, magnetic, and magneto-optical computer readable media. Examples of memory technologies include optical discs such as compact discs (CD-ROMs) and digital versatile (or video) discs (DVDs), magnetic media such as floppy disks, magnetic tapes or cassettes, and solid-state semiconductor random access memory (RAM) devices, read-only memory (ROM) devices, electrically erasable programmable read-only memory (EEPROM) devices, flash memory devices, memory chips and combinations of the foregoing. Memory may be non-volatile or volatile. Memory may be physically attached to a processor, or remote from a processor. Memory may be removable or non-removable from a system including a processor. Memory may be operatively connected to a processor in such a way as to be accessible by a processor. Instructions stored by a memory may be based on a plurality of programming and / or markup languages known in the art, with non-limiting examples including the C, C++, C#, Python ™, MATLAB ™, Java ™, JavaScript ™, Perl ™, PHP ™, SQL ™, Visual Basic ™, Hypertext Markup Language (HTML), Extensible Markup Language (XML), and combinations of the foregoing programming languages. Instructions stored by a memory may also be implemented by configuration settings for a fixed-function device, gate array or programmable logic device.

[0034] Any method, application or module herein described may be implemented using computer readable / executable instructions that may be stored or otherwise held by a memory and executed by a processor. Aspects of the present invention may bedescribed with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor, such that the processor, and a memory storing the instructions, which execute via the processor, collectively constitute a machine for implementing the functions / acts specified in the flowchart and / or block diagram block or blocks.

[0035] The flowcharts and functional block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present disclosure. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and / or flowchart illustration, and combinations of blocks in the block diagrams and / or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.

[0036] OVERVIEW

[0037] Figures 1 and 2 show aspects of a thermal management system for a battery pack. Figures 3, 5 and 6 show methods implemented by the thermal management system.

[0038] The thermal management system is not limited by the application of the battery pack, which may include non-vehicular applications (e.g., a power bank of a building) and vehicular applications. As shown in Figure 7, the thermal management system 10 andbattery pack 30 may be applied in an electric vehicle 120 to supply power to an electric motor 122 for driving one or more wheels 124, and may include additional elements in the thermal management system 10, other than what is shown in the accompanying figures, for use in managing the battery pack 30 and / or for managing other elements of the electric vehicle 120 such as a passenger cabin 126 and the electric motor 122.

[0039] THERMAL MANAGEMENT SYSTEM IN GENERAL

[0040] As shown in Figures 1 and 2, in one aspect, the thermal management system 10 includes a conduit subsystem 20, a pump 22, a reservoir 24 and a control subsystem 26. The conduit subsystem 20 is arranged to transport a dielectric fluid 28 to and from the battery pack 30. The battery pack 30 includes a plurality of cells 32. Only a few cells 32 are shown in the schematic views shown in Figure 1 , however it will be understood that there may be hundreds or even thousands of cells in the battery pack 30. The battery pack 30 is configured such that the cells 32 are positioned for immersion in the dielectric fluid 28. The cells 32 may be any suitable type of cells such as cylindrical cells, rectangular cells, pouch cells or any other suitable type of cell. The battery pack 30 may be arranged with the cells 32 grouped together in modules, or with the cells 32 all together in a single large chamber, or the battery pack 30 may have any other suitable arrangement of the cells 32.

[0041] PUMP

[0042] The pump 22 is positioned for driving a flow of the dielectric fluid 28 into and out of the battery pack 30 and through the conduit subsystem 20. The pump 22 may be positioned anywhere suitable in the conduit subsystem 20 for this purpose. The pump 22 may be any suitable type of pump.

[0043] RESERVOIR AND ASSOCIATED PARTS

[0044] Referring to Figure 2, the reservoir 24 is positioned for storage of a portion 34 of the dielectric fluid 28 and for containing a volume of air 36. The reservoir 24 is fluidically connected to the conduit subsystem 20. The reservoir 24 includes a vent 38 that permitsfluid communication between the volume of air 36 contained in the reservoir 24 and an ambient environment 40 outside of the reservoir 24.

[0045] In some embodiments such as shown in Figure 2, a filter member 56 may optionally be positioned in the vent 38, and is positioned to inhibit ingress of liquid water into the reservoir 24 (e.g., in the event that it is raining or that there is liquid water otherwise in the ambient environment 40 outside of the reservoir 24). The filter member 56 may be any suitable type of filter member, such as a (polytetrafluoroethylene) PTFE filter member. The filter member 56 may, for example, be made from a material such as Go re tex™ .

[0046] In some embodiments such as shown in Figure 2, a quantity of desiccant 58 may be positioned in fluid communication with the volume of air 36 contained in the reservoir 24, so as to remove water from the volume of air 36 contained in the reservoir 24. The desiccant 58 may be any suitable type of desiccant, such as a silica gel, activated carbon or any other suitable type of desiccant. The desiccant 58 may be effective in controlling the relative humidity of the volume of air 36 contained in the reservoir 24 (e.g., by decreasing the relative humidity from 70% without the desiccant to 30% with the desiccant). Nevertheless, the humidity of the volume of air 36 contained in the reservoir 24 may still be sufficient to condense into liquid water if the temperature of the portion 34 of the dielectric fluid 28 is sufficiently low. Moreover, the desiccant 58 may become saturated with water during the life of the battery pack 30 rendering ineffective in removing further water vapor in the volume of air 36. The timing of such saturation will depend on the environmental conditions in which the battery pack 30 is used and may therefore be difficult to predict. Replacement of the desiccant 58 may be required to ensure the efficacy of this mitigation approach, but this may be undesirable or impractical in some applications such as when installed in an electric vehicle, such as the electric vehicle 120 shown in Figure 7. Alternatively, in some embodiments, the electric vehicle 120 may nonetheless be provided with an arrangement to permit easy access to the desiccant 58 for replacement of the desiccant 58 at a suitable time.

[0047] In some embodiments such as shown in Figure 1 and 2, the thermal management system 10 may include an optional closure member 66 that is movablebetween an open position (as shown in dashed line in Figure 2) which permits fluid communication via the vent 38 between the reservoir 24 and the ambient environment 40, and a closed position (as shown in solid line in Figure 2) which prevents fluid communication via the vent 38 between the reservoir 24 and the ambient environment 40. In some embodiments, the closure member 66 may be biased to the closed position by a spring. In Figure 2, the closure member 66 is shown as a flap that pivots between the open position to expose the vent 38 and the closed position to occlude the vent 38. In other embodiments, the closure member 66 may be a single contiguous element or alternatively it may itself be made up of a plurality of closure member portions that are movable in other ways relative to an opening of the reservoir 24 to alternately permit or prevent communication between the reservoir 24 and ambient environment. The opening may be the vent 38 or another opening of the reservoir 24 (i.e. , a second vent). As nonlimiting examples, the closure member 66 may be provided as a valve element in a valve known in the art such as a ball valve, butterfly valve, diaphragm valve, gate valve, needle valve, piston valve, a spool valve, and so forth. An actuator 68 controlled by the control subsystem 26 is provided to drive the closure member 66 between the open and closed positions. The actuator 68 may be implemented by a variety of means suitable for moving the one or more member portions of the closure member 66 between the open position and the closed position. As non-limiting examples, the actuator 68 may be an electromechanical actuator such (e.g., a motor or a solenoid), a hydraulic actuator, or a pneumatic actuator.

[0048] CONDUIT SUBSYSTEM COMPONENTS

[0049] In some embodiments such as shown in Figure 1 , an optional heater 59a may be provided at a suitable place in the conduit subsystem 20. Alternatively, or additionally, an optional heater 59b may be provided right in the reservoir 24, thus permitting heating of the portion 34 of the dielectric fluid 28 without the need to turn on the pump 22. As a non-limiting example, the heater 59a and / or heater 59b may be implemented by an electrically-powered heater such as an electrical resistance heater (e.g., a positive temperature coefficient (PTC) heater), an induction heater (e.g., an induction coil), an infrared heater, a microwave heater, or any other kind of heater.

[0050] In some embodiments such as shown in Figure 1 , an optional heat exchanger 62 may be provided in the conduit subsystem 20, to permit heat exchange between the dielectric fluid 28 in the conduit subsystem 20 with fluid from another system in the electric vehicle 120 (Figure 7), such as, for example, a refrigerant system, a radiator, or a cold plate of the vehicle 120. Embodiments of heat exchangers with electrically-powered heaters suitable for use in the conduit subsystem 20 are disclosed in International Patent Application Publications no. WO 2023 / 060352 A1 ("Coolant-Refrigerant Heat Exchanger and Thermal Management System" to Litens Automotive Partnership, published April 20, 2023) and no. WO 2024 / 092359 A1 ("Coolant-Refrigerant Heat exchanger 20 with Induction Heater and Thermal Management System" to Litens Automotive Partnership, published May 10, 2024), the entire contents of which are incorporated by reference herein. As noted in the foregoing publications, the electrically-powered heater may be an electrical resistance heater (e.g., a positive temperature coefficient (PTC) heater), an induction heater (e.g., an induction coil), an infrared heater, a microwave heater, or any other kind of heater.

[0051] While Figure 1 shows the heat exchanger 62 downstream from the heater 59a, it will be understood that it is alternatively possible for the heat exchanger 62 to be positioned upstream from the heater 59a (e.g. for their positions shown in Figure 1 to be switched relative to one another).

[0052] In some embodiments such as shown in Figure 1 , an optional dielectric fluid filter 60 may be provided for use in filtering the dielectric fluid 28 upstream from the battery pack 30 so as to inhibit ingress of particulate matter that may become entrained in the dielectric fluid 28 into the battery pack 30.

[0053] SENSORS

[0054] In some embodiments such as shown in Figure 2, one or more of the following optional sensors may be provided.

[0055] An optional dielectric fluid temperature sensor 50 may be provided for use by the control subsystem 26 to determine a temperature of the portion 34 of the dielectric fluid 28. The dielectric fluid temperature sensor 50 may be any suitable temperaturesensor known in the art, and optionally includes a temperature transducer, or any other suitable structure for generating a signal based on the temperature of the dielectric fluid.

[0056] An optional air temperature sensor 52 and / or an air humidity sensor 54 may be provided for use by the control subsystem 26 to determine a temperature and a humidity, respectively, of the volume of air 36 contained in the reservoir 24. The air temperature sensor 52 and the air humidity sensor54 may be any suitable air temperature sensor and any suitable air humidity sensor known in the art. For example, the air temperature sensor 52 and the air humidity sensor 54 may include a suitable temperature transducer and a suitable humidity transducer respectively, or any other suitable structure for generating signals based on the temperature and humidity respectively, of the volume of air 36. The air temperature sensor 52 and / or the air humidity sensor 54 may be included as part of the thermal management system 10, or may be preexisting sensors that are already present in the vehicle 120, or may be preexisting sensors that are present outside of the vehicle 120 such that the vehicle 120 draws data therefrom by any suitable means such as by a wireless internet connection.

[0057] One or more optional fluid pressure sensors 55a, 55b, 55c (generally 55) may be provided for use by the control subsystem to determine a fluid pressure (e.g., a pressure of air and / or dielectric fluid) in one or more locations such as the battery pack 30 (see fluid pressure sensor 55a in Figure 1), the conduit subsystem 20 (see fluid pressure sensor 55b in Figure 1), the reservoir 24 (see fluid pressure sensor 55c in Figure 2) or any other suitable location of the thermal management system 10. The fluid pressure sensor 55 may be any fluid pressure sensor known in the art.

[0058] VISUAL OUTPUT DEVICE

[0059] In some embodiments such as shown in Figure 1 , one or more visual output devices 70a, 70b, 70c (generally 70) may be provided. The visual output device 70 may be any suitable electronic device known in the art that can be interfaced with the control subsystem 26 to provide an indicator that is visible to a user of the thermal management system 10, such as for the purpose of providing a warning or a notification to the user. As a non-limiting example, as shown in Figure 1 , the visual output device 70a may be adisplay screen such as provided in a dashboard or an infotainment system in the passenger cabin 126 of an electric vehicle 120 (Figure 7) containing the battery pack 30. As another non-limiting example, the visual output device 70b may be a display screen of a portable smartphone, tablet computer or other computer device that may be located remotely from the battery pack 30. As another non-limiting example, the visual output device 70c may be a light source such as a light-emitting diode (LED) or an incandescent light bulb in a dashboard of an electric vehicle 120 or a control panel.

[0060] CONTROL SUBSYSTEM

[0061] Referring to Figures 1 and 2, the control subsystem 26 includes a processor 26a and a memory 26b. The processor 26a is programmed by instructions stored in the memory 26b to implement methods as described below. For this purpose, the control subsystem 26 may be operatively connected to a pump 22, a dielectric fluid temperature sensor 50, an air temperature sensor 52, an air humidity sensor 54, a fluid pressure sensor 55, a heater 59, an actuator 68 and / or a visual output device 70, in embodiments of the thermal management system 10 where one or more such other components are present. In Figures 1 and 2, operative connections between the control subsystem 26 and such other components are shown by dashed lines, which in embodiments may be implemented by wired connections and / or wireless connections known in the art.

[0062] METHOD FOR TAKING CORRECTIVE ACTION BASED ON AIR CONDITIONS AND DIELECTRIC FLUID TEMPERATURE IN THE RESERVOIR

[0063] Figure 3 is a flowchart showing an embodiment of a method 80 for taking a corrective action based on conditions of the volume of air 36 and the temperature of the portion 34 of dielectric fluid 28 in the reservoir 24, which method is implemented by processor 26a implementing the instructions stored in some embodiments of the memory 26b.

[0064] At step 82, the control subsystem 26 determines a temperature, T(df), of the portion 34 of the dielectric fluid 24 in the reservoir 24. In some embodiments, the control subsystem 26 may do so using a dielectric fluid temperature sensor 50, if provided. Alternatively, the temperature, T(df), of the portion 34 of the dielectric fluid 28 in thereservoir 24 may be determined any other suitable way, without a dielectric fluid temperature sensor 50.

[0065] At step 84, the control subsystem 26 determines a temperature, T(a), and a humidity, H(a) of the volume of air 36 contained in the reservoir 36. In some embodiments, the control subsystem 26 may do so using an air temperature sensor 52 and an air humidity sensor 54, if provided. Alternatively, these values may be determined any other suitable way, without one or more of the sensors 52 and 54.

[0066] Stated broadly, at step 88, the control subsystem 26 carries out at least one corrective action. The carrying out of the corrective action at step 88 is based on (e.g., conditional on or determined by) the temperature, T(df), of the portion 34 of the dielectric fluid 28, and on the temperature, T(a), and the humidity, H(a), of the volume of air 36 contained in the reservoir 24.

[0067] Steps 84 and 86 are a non-limiting example of how carrying out of the at least one corrective action at step 88 may be based on these values. At step 84, the control subsystem 26 determines the dew point temperature, T(dp), for the temperature, T(a), and the humidity, H(a), of the volume of air 36 contained in the reservoir. In Figure 3, this determination is shown generically by expressing T(dp) as a computational function of T(a) and H(a). For example, Figure 4 is a psychrometric chart showing the relationship between dew point temperature, temperature of air and relative humidity of air. The computational function may be implemented using a lookup table based on datapoints in the relationship shown in Figure 4. For instance, Figure 4 indicates that when T(a) = 25 °C and H(a) = 50%, T(dp) = ~14 °C. Alternatively, the computational function may be implemented by the following mathematical relationship,Equation [1]The relationship is approximately accurate when H(a) is expressed as a relative humidity in percent and is greater than 50% and T(dp), and T(a) are expressed in degrees Celsius. At step 86, the temperature, T(df) of the portion 34 of dielectric fluid 28 in the reservoir 24 is compared to the determined dew point temperature, T(dp). If T(df) is greater than T(dp),then water vapor in the volume of air 36 in the reservoir 24 is not at risk of condensing. A ‘safety factor1temperature T(sf) may further be employed, to further reduce the risk of condensation of water vapor in the volume of air 36 in the reservoir 24. The buffer temperature T(sf) may be a selected number of degrees of ‘safety factor1that are added to the determined value for T(dp) when comparing it to the temperature T(df). Thus, if T(df) is greater than T(dp) + T(sf) then the control subsystem 26 may consider there to be no risk of condensation of water vapor in the reservoir 24. The value of T(sf) may be any suitable value, such as, for example, 3 degrees Celsius, or 5 degrees Celsius, or even 0 degrees Celsius, depending on the risk tolerance in the particular application. The value of T(dp) + T(sf) may be referred to as a threshold temperature T(t), keeping in mind that the value of T(sf) may be 0 degrees Celsius in which case the threshold temperature T(t) is the same as T(dp), or may be greater than 0 degrees Celsius in which case the threshold temperature T(t) is greater than T(dp). Thus, it may be said that if T(df) is greater than T(t) then the control subsystem 26 may consider there to be no risk of condensation of water vapor in the reservoir 24. Accordingly, the method 80 returns to step 82 and the method 80 may repeat. Alternatively, if T(df) is less than or equal to T(t), then the control subsystem 26 may consider the water vapor in the volume of air 36 in the reservoir 24 to be at risk of condensing. Accordingly, the method proceeds to step 88.

[0068] At step 88, the control subsystem 26 controls the thermal management system 10 to take at least one corrective action. By carrying out the at least one corrective action, there is a lower likelihood of liquid water reaching the cells 32 in the battery pack 30 where the liquid water may corrode the cells 32 or otherwise damage the battery pack 30 or create a safety hazard.

[0069] In embodiments, the at least one corrective action may include heating the portion 34 of the dielectric fluid 28. Heating the portion 34 of the dielectric fluid 28 raises the temperature of the dielectric fluid 28 such that the dielectric fluid 28 does not cool the volume of air 36 contained in the reservoir 28 to the dew point temperature, thereby reducing the likelihood of liquid water from being collected in the portion 34 of the dielectric fluid 28 in the reservoir 24. In one embodiment as shown in step 88a, and with reference to Figure 1 , this may be carried out by controlling the heater 59a provided inthe conduit subsystem 20 and / or the heater 59b provided in the reservoir 24 to turn “on” or to increase the power of its heat output.

[0070] In embodiments, as shown in step 88b with reference to Figure 1 , the at least one corrective action may additionally or alternatively include turning off the pump 22. Turning off the pump 22 inhibits the flow of any water that may have collected in the portion 34 of the dielectric fluid 28 in the reservoir 24 from being transported to the battery pack 30.

[0071] In embodiments, as shown in step 88c, the at least one corrective action may additionally or alternatively include outputting a warning. In embodiments, outputting the warning may involve controlling the visual output device 70 (Figure 1) to display a visible warning indicator (e.g., a display of text and / or graphics on a display screen of visual output device or an illumination of a light source such as an LED or an incandescent bulb). As non-limiting examples, the warning that may be outputted may include any one or more of the following warnings: a warning to instruct a user of the electric vehicle 120 to stop operation of the electric vehicle 120, in order to inhibit a flow of any liquid water that may collect in the portion 34 of the dielectric fluid 28 in the reservoir 24 from being transported to the battery pack 30; a warning to instruct a user of the electric vehicle 120 to not operate the electric vehicle 120; a warning to instruct a user of the electric vehicle 120 to turn off the pump 22; and a warning to instruct a user of the electric vehicle 120 to bring the electric vehicle 120 into a service center for service.

[0072] METHOD FOR NOTIFYING A USER TO SERVICE AN ELECTRIC VEHICLE BASED ON AIR CONDITIONS IN THE RESERVOIR AT DIFFERENT TIMES

[0073] Figure 5 is a flowchart showing an embodiment of a method 90 for notifying a user to service an electric vehicle 120 (Figure 7) based on humidity and optionally temperature of the volume of air 36 in the reservoir 24 at different times. The method 90 may be implemented by processor 26a implementing the instructions stored in some embodiments of the memory 26b.

[0074] At steps 92 and 96, the control subsystem 26 determines, at a first point in time (t1) and a second point in time (t2), respectively, a first humidity, H(a1), and a secondhumidity, H(a2), respectively, of the volume of air 36 contained in the reservoir 24. In some embodiments, the control subsystem 26 may do so using an air humidity sensor 54, if provided. Alternatively, the values may be determined any other suitable way, without the air humidity sensor 54.

[0075] At optional steps 94 and 98, the control subsystem 26 determines, at the first point in time (t1) and a second point in time (t2), respectively, a first temperature (Ta1) and a second temperature (Ta2), respectively, of the volume of air 36 contained in the reservoir 24. In some embodiments, the control subsystem 26 may do so using an air temperature sensor 52, if provided. Alternatively, the values may be determined any other suitable way, without the air temperature sensor 52.

[0076] The elapsed time interval from the first point in time (t1 ) to the second point in time (t2) may be arbitrarily selected. As non-limiting examples, the elapsed time may be less than or equal to 1 second, 5 seconds, 10 seconds, 30 seconds, 1 minute, 5 minutes or 10 minutes, so as to be less than a typical duration in which the electric vehicle 120 is continuously operated.

[0077] Stated broadly, at step 102, the control subsystem 26 notifies a user of the electric vehicle 120 to service the electric vehicle 120 based at least in part on the first humidity, H(a1), and the second humidity, H(a2) and, optionally, further based on the first temperature (Ta1) and the second temperature (Ta2), if determined. In some embodiments, the notification may involve causing the visual output device 70a, 70b (Figure 1 ) to display a visible warning indicator (e.g., a display of text and / or graphics on a display screen of visual output device or an illumination of a light source such as an LED or an incandescent bulb).

[0078] Step 100 is a non-limiting example of how notifying the user of the electric vehicle 120 to service the electric vehicle 120 at step 102 may be based on such value(s). For example, the control subsystem 26 may determine a change in humidity from the value of H(a1) to the value of H(a2), or a time-based rate of change thereof based further on the elapsed time between t1 and t2. As another example, the control subsystem 26 may determine a change from a first dew point temperature, T (dpi ), based on T(a1 ) andH(a1) at the first point in time, (t1), to a second dew point, T(dp2), based on T(a2) and H(a2) at the second point in time, (t2). The dew point temperatures may be determined using the relationship shown in Figure 4 or Equation [1], If the change in humidity exceeds a predetermined maximum permissible change in humidity, AH(a)max, and / or the change in dew point temperature exceeds a predetermined maximum permissible change in dew point temperature, AT(dp)max, then the control subsystem 26 may generate the notification in accordance with step 102. The predetermined values of AH(a)max and / or AT (dp)max may be selected to provide warning of an abnormal operating condition of the electric vehicle 120 such as the desiccant 58 (Figure 2) nearing saturation and needing replacement, or the thermal management system 10 being compromised to allow for ingress of unacceptable amounts moisture. Alternatively, if such value(s) are not exceeded, then the control subsystem 26 returns to step 92 so that the method 90 may repeat during operation of the electric vehicle 120.

[0079] In other embodiments, step 100 may not involve determining a change between the humidity values H(a1) and H(a2) or a change between the dew point temperatures T(dp1 ) and T(dp2) at the two points in time. Instead, the value at the second point in time may be used as confirmation of the value at the first point in time. For example, if both the humidity values H(a1) and H(a2) exceed a predetermined maximum humidity value, Hmax, or if both the dew point temperature values T(dp1) and T(dp2) exceed a predetermined maximum dew point temperature, T(dp)max, then the control subsystem 26 may generate the notification in accordance with step 102. This approach may help to avoid generating notifications in accordance with step 102 based on transient abnormal conditions, or based on false positive detection of abnormal conditions.

[0080] METHOD FOR CONTROLLING A CLOSURE MEMBER OF RESERVOIR BASED ON FLUID PRESSURE

[0081] Figure 6 is a flowchart showing an embodiment of a method 110 for controlling a closure member 66 (Figure 2) of the reservoir 24 based on fluid pressure in the thermal management system 10.

[0082] At step 112, the closure member 66 is in the closed position, or if the closure member 66 is in the open position, then control subsystem 26 may control the actuator 68 to move the closure member 66 to the closed position.

[0083] At step 114, the control subsystem 26 determines a fluid pressure, P, of the thermal management system 10 or the battery pack 30. In some embodiments, the determined fluid pressure may be a pressure of the dielectric fluid 28 in the battery pack 30, which may be determined using pressure sensor 55a (Figure 1). In some embodiments, the determined fluid pressure may additionally or alternatively be a pressure of the dielectric fluid 28 in the conduit subsystem 20, which may be determined using pressure sensor 55b (Figure 1). In some embodiments, the determined fluid pressure may additionally or alternatively be a pressure of the portion 34 of the dielectric fluid 28 in the reservoir, or of the volume of air 36 in the reservoir 24, which may be determined using pressure sensor 55c (Figure 2). Alternatively, the determined pressure may be determined in any other suitable way, without use of a pressure sensor 55.

[0084] At step 116, the determined fluid pressure, P, is compared to a predetermined pressure range. In some embodiments, the predetermined pressure range may be defined by a prescribed minimum fluid pressure, Pmin, or a maximum fluid pressure, Pmax, or both Pmin and Pmax. The values of Pmin or Pmax may be or be based on a pressure of the ambient environment 40 (Figures 1 and 2) that is either expected or measured during operation of the thermal management system 10. For example, in embodiments where the determined fluid pressure is a pressure in the volume of air 36 in the reservoir 24, the values of Pmin and Pmax may be set to values that are below and above, respectively, the air pressure in the ambient environment 40 by a tolerance value.

[0085] If the determined fluid pressure, P, is within the predetermined pressure range then the method 110 returns to step 114 so that the method 110 may repeat during operation of the thermal management system 10. Alternatively, if the determined fluid pressure, P, is not within the predetermined pressure range, then the method 110 proceeds to step 118, at which the control subsystem 26 controls the actuator 68 to move the closure member 66 to the open position. In some embodiments, the actuator 68 may retain the closure member 66 in the open position for a set period of time (e.g. a fractionof a second, or one or more seconds) to permit equalization of the fluid pressure in the thermal management system 10 with pressure in the ambient environment 40. In other embodiments, the control subsystem 26 continues to determine the fluid pressure in the thermal management system 10 while the closure member 66 is in the open position, and the control subsystem 26 controls the actuator 68 to retain the closure member 66 in the open position until the determined fluid pressure in the thermal management system 10 is within the predetermined pressure range. At the conclusion of step 118, the method 110 returns to step 112 so that the method 110 may repeat during operation of the thermal management system 10.

[0086] By providing the closure member 66 and keeping it in the closed position except for brief periods in which it is in the open position as described above, a smaller overall amount of water vapor may be taken into the reservoir 24 over time, which reduces the risk of condensation from occurring and which reduces the load on the desiccant 58 if desiccant is provided.

[0087] While the description contained herein constitutes a plurality of embodiments of the present invention, it will be appreciated that the present invention is susceptible to further modification and change without departing from the fair meaning of the accompanying claims.

[0088] LIST OF ITEMS

Claims

CLAIMSWhat is claimed is:1 . A thermal management system for a battery pack, the thermal management system comprising: a conduit subsystem arranged to transport a dielectric fluid to and from the battery pack, wherein the battery pack includes a plurality of cells which are positioned for immersion in the dielectric fluid; a pump for driving a flow of the dielectric fluid into and out of the battery pack and through the conduit subsystem; a reservoir positioned for storage of a portion of the dielectric fluid and for containing a volume of air, wherein the reservoir is fluidically connected to the conduit subsystem, wherein the reservoir includes a vent that permits fluid communication between the volume of air contained in the reservoir and an ambient environment outside of the reservoir; and a control subsystem that includes a processor and a memory, wherein the memory contains instructions that are executable by the processor to: a) determine a temperature of the portion of the dielectric fluid; b) determine a temperature and a humidity of the volume of air contained in the reservoir; and c) carry out at least one corrective action based at least in part on the temperature of the portion of the dielectric fluid, the temperature of the volume of air contained in the reservoir, and the humidity of the volume of air contained in the reservoir, wherein the at least one corrective action is selected from the group of corrective actions consisting of: heating the portion of the dielectric fluid; turning off the pump so as to stop the flow of the dielectric fluid; and outputting a warning.

2. The thermal management system as claimed in claim 1 , wherein the at least one corrective action comprises heating the portion of the dielectric fluid.

3. The thermal management system as claimed in any one of claims 1 to 2, wherein the at least one corrective action comprises turning off the pump so as to stop the flow of the dielectric fluid.

4. The thermal management system as claimed in any one of claims 1 to 3, wherein the at least one corrective action comprises outputting the warning.

5. The thermal management system as claimed in any one of claims 1 to 4, further comprising a dielectric fluid temperature sensor for use by the control subsystem in carrying out step a), and a reservoir air temperature sensor and a reservoir air humidity sensor for use by the control subsystem in carrying out step b).

6. The thermal management system as claimed in any one of claims 1 to 5, further comprising a quantity of desiccant that is in fluid communication with the volume of air contained in the reservoir, so as to remove water from the volume of air contained in the reservoir.

7. The thermal management system as claimed in any one of claims 1 to 6, further comprising a filter member in the vent that is positioned to inhibit ingress of liquid water into the reservoir.

8. A thermal management system for a battery pack for a vehicle, the thermal management system comprising: a conduit subsystem arranged to transport a dielectric fluid to and from the battery pack, wherein the battery pack includes a plurality of cells which are positioned for immersion in the dielectric fluid; a pump for driving a flow of the dielectric fluid into and out of the battery pack and through the conduit subsystem; a reservoir positioned for storage of a portion of the dielectric fluid and for containing a volume of air, wherein the reservoir is fluidically connected to the conduit subsystem, wherein the reservoir includes a vent that permits fluidcommunication between the volume of air contained in the reservoir and an ambient environment outside of the reservoir; and a control subsystem that includes a processor and a memory, wherein the memory contains instructions that are executable by the processor to: a) determine, at a first point in time, a first humidity of the volume of air contained in the reservoir; b) determine, at a second point in time, a second humidity of the volume of air contained in the reservoir; and c) notify a user of the vehicle to service the vehicle based at least in part on the first humidity and the second humidity.

9. The thermal management system as claimed in claim 8, further comprising an air humidity sensor for use by the control subsystem in carrying out steps a) and b).

10. The thermal management system as claimed in any one of claims 8 to 9, wherein the processor is further programmed by the instructions stored in the memory to: d) determine, at the first point in time, a first temperature of the volume of air contained in the reservoir; and e) determine, at the second point in time, a second temperature of the volume of air contained in the reservoir, and wherein the processor is further programmed to notify the user of the vehicle in step c) to service the vehicle further based at least in part on the first temperature and the second temperature.11 . The thermal management system as claimed in claim 10, further comprising an air temperature sensor for use by the control subsystem in carrying out steps d) and e).

12. The thermal management system as claimed in any one of claims 8 to 11 , further comprising a quantity of desiccant that is in fluid communication with the volume of air contained in the reservoir, so as to remove water from the volume of air contained in the reservoir.

13. The thermal management system as claimed in any one of claims 8 to 12, further comprising a filter member in the vent that is positioned to inhibit ingress of liquid water into the reservoir.

14. A thermal management system for a battery pack for a vehicle, the thermal management system comprising: a conduit subsystem arranged to transport a dielectric fluid to and from the battery pack, wherein the battery pack includes a plurality of cells which are positioned for immersion in the dielectric fluid; a pump for driving a flow of the dielectric fluid into and out of the battery pack and through the conduit subsystem; a reservoir positioned for storage of a portion of the dielectric fluid and for containing a volume of air, wherein the reservoir is fluidically connected to the conduit subsystem, wherein the reservoir includes a vent that permits fluid communication between the volume of air contained in the reservoir and an ambient environment outside of the reservoir; and a closure member moveable between a closed position and an open position, wherein the closure member in the closed position prevents fluid communication via the vent between the reservoir and the ambient environment, wherein the closure member in the open position permits fluid communication via the vent between the reservoir and the ambient environment; and an actuator to drive the closure member between the closed position and the open position, a control subsystem that includes a processor and a memory, wherein the memory contains instructions that are executable by the processor to:a) determine at least one fluid pressure selected from the group of fluid pressures consisting of: a pressure of the dielectric fluid; and a pressure of the volume of air contained in the reservoir; and b) control the actuator to drive the closure member from the closed position to the open position based at least in part on the determined fluid pressure.

15. The thermal management system as claimed in claim 14, wherein the fluid pressure comprises the pressure of the dielectric fluid.

16. The thermal management system as claimed in any one of claims 14 to 15, wherein the fluid pressure comprises the pressure of the volume of air contained in the reservoir.

17. The thermal management system as claimed in any one of claims 14 to 16, wherein in step b), the actuator retains the closure member in the open position for a set period of time.

18. The thermal management system as claimed in any one of claims 14 to 16, wherein in step b), the actuator retains the closure member in the open position until the fluid pressure equalizes with a pressure of the ambient environment or is within a predetermined pressure range.

19. The thermal management system as claimed in any one of claims 14 to 18, further comprising a fluid pressure sensor for use by the control subsystem in carrying out step a).

20. The thermal management system as claimed in any one of claims 14 to 19, further comprising a quantity of desiccant that is in fluid communication with the volume of air contained in the reservoir, so as to remove water from the volume of air contained in the reservoir.

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