GB2613184A

GB2613184A - Battery fault detection

Info

Publication number: GB2613184A
Application number: GB2117064.2A
Authority: GB
Inventors: Fai Yu Tung
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2021-11-26
Filing date: 2021-11-26
Publication date: 2023-05-31
Also published as: GB202117064D0

Abstract

A vehicle battery pack 122 comprises a battery module 120, vent system 136 and light sensor 144, preferably a photo transistor. The module comprises first and second ends 152,154 between which an array of cells 126 are provided in a cell volume 124. The cell volume is in fluid communication with the vent system, which receives fluid vented from any one or more of the cells during a failure of the cell(s) and delivers the fluid via fluid flow passaging of the vent system to an exterior of the battery pack. The light sensor detects light levels in a portion of the vent system and outputs a signal to a vehicle occupant warning system when required. The light sensor may be located outside the fluid flow passaging of the vent system, preferably inside a sealed housing (146, Fig 3) of a cell supervisory circuit 142 which monitors the cells. Preferably, multiple modules are provided, with light sensors for each adjacent module being located at opposite ends. Fluid may be vented into a module vent volume 132 extending over the surface of the module, and may pass into a common vent volume 156,158 located at each end of the modules.

Description

BATTERY FAULT DETECTION

TECHNICAL FIELD

The present disclosure relates to a battery fault detection and particularly, but not exclusively, to a vehicle battery pack, a vehicle, a method of detecting a vehicle battery pack fault and a vehicle occupant warning system controller.

BACKGROUND

There has recently been increased interest in providing battery-powered vehicles, which has led to developments in vehicle battery, in particular vehicle traction battery, technology. It is important to ensure that occupant safety is not compromised in the event of a vehicle battery being damaged. One potential failure mechanism is 'hard vent' associated with a fire. Such a failure can in principle arise as a result of various circumstances overcharging when rapid charging, a vehicle accident, over temperature and exceeding an overcurrent limit. Some regulatory tests require that occupants of a vehicle are given a warning to vacate the vehicle well prior (e.g. 5 minutes) to fire, resulting from a battery cell undergoing a hard vent failure, entering the vehicle cabin.

It desirable to be able to accurately, reliably and promptly detect a hard vent failure of a battery cell, in order that a warning can be issued as soon as possible. Existing detection schemes such as pressure sensing, temperature sensing and gas detection have various potential disadvantages in terms of accuracy, rate of detection, durability and design freedom.

It is an object of embodiments of the invention to at least mitigate one or more of the problems of the prior art.

SUMMARY OF THE INVENTION

Aspects and embodiments of the invention provide a vehicle battery pack, a vehicle, a method of detecting a vehicle battery pack fault and a vehicle occupant warning system controller as claimed in the appended claims.

According to an aspect of the invention a vehicle battery pack is provided comprising a battery module, a vent system and a light sensor, the module comprising an array of cells provided in a cell volume, the cell volume being in fluid communication with the vent system and the light sensor being arranged to detect light levels in a portion of the vent system.

According to a further aspect of the invention a vehicle battery pack is provided comprising a battery module, a vent system and a light sensor, the module comprising a first end and a second end between which an array of cells are provided in a cell volume, the cell volume being in fluid communication with the vent system, the vent system thereby being arranged to receive fluid vented from any one or more of the cells during a failure of said one or more of those cells and deliver said fluid via fluid flow passaging of the vent system to an exterior of the battery pack and wherein the light sensor is arranged to detect light levels in a portion of the vent system and output a signal to a vehicle occupant warning system, said signal being dependent on said detected light level.

Monitoring the light levels may allow detection of the occurrence of a 'hard vent' (i.e. a thermal runaway that cannot be stopped, leading to fire) in view of the detection of the light emitted from the associated fire. Detecting a hard vent in this way may have several advantages by comparison with alternatives which might be contemplated such as pressure monitoring, temperature monitoring and gas detection (e.g. carbon monoxide monitoring). For instance, monitoring light levels may allow for a more rapid detection upon initiation of the fire and/or more reliable detection of a comparatively small fire. Specifically, light from flames may be detected substantially instantaneously and/or regardless of the size of the fire, whereas temperature, pressure and/or gas changes may take longer to manifest and/or be detected. Monitoring of light levels may also allow discrimination between a hazardous (hard vent) failure and a non-hazardous ('soft vent'), the latter not giving rise to fire and so increased light levels and yet potentially giving rise to pressure changes and/or detectable emissions of gas. Such soft venting may for instance occur where a cell vents gas but without associated fire.

Soft venting might for instance occur where a cell is charged rapidly or is over charged, causing gas generation, rupture and venting, without substantive damage to a separator in the cell (which might otherwise cause a short-circuit). Further, the failure may cause disconnection of the positive terminal, preventing further charging/discharging.

Additionally, monitoring of light levels may be less likely (than for instance temperature monitoring) to give rise to false detection events based on the heat of electrical components (which may for instance operate within tolerance at temperatures between 60°C and 200°C). Additionally, greater design freedom may be offered. It may be for instance that where pressure monitoring is used to detect a hard vent, that the enclosed volume must be limited in order to achieve detection within a desired timeframe. Such internal volume restrictions may need not apply in the case of light level based detection. Additionally, light level monitoring may allow detection at a greater distance from potential sources and/or the path of fire, potentially allowing the sensor to be located so as to be better protected from the effects of the failure and therefore to provide better resilience and/or reliability. A thermistor by comparison may need to be located relatively nearer to the expected source and/or passage of the fire in order to give acceptable detection performance and may therefore be damaged and/or destroyed more quickly.

In some embodiments the light sensor is a photo transistor.

In some embodiments the light sensor is located outside of the fluid flow passaging. This may serve to better protect it from the effects of hot gases and/or flames passing through the fluid flow passaging in the event of a hard vent failure.

In some embodiments the module comprises a cell supervisory circuit arranged to monitor the cells, the cell supervisory circuit being provided in a substantially sealed housing. The cell supervisory circuit may for instance be used in combination with corresponding sensors to monitor parameters such as the voltage across the cells and/or their temperature.

In some embodiments the light sensor is located inside the substantially sealed housing of the cell supervisory circuit. The housing may thereby protect the light sensor (e.g. from fluids, heat and/or fire) and/or may provide supporting circuitry to run the light sensor. The light sensor may for instance be provided on a printed circuit board of the cell supervisory circuit and/or may be connected to the printed circuit of the printed circuit board. The printed circuit board may for instance supply power to the light sensor and/or a communication circuit for transmission of the signal to the vehicle occupant warning system. One or more windows may be provided in the housing arranged to give the sensor a field of view of part of the fluid flow passaging.

In some embodiments the cell supervisory circuit is located at one of the first and second ends of the module.

In some embodiments each of the cells has a first end and a second end and the cells are disposed within the cell volume in a common orientation and such that the first ends of each of the cells are substantially coplanar with each other and the second ends of each of the cells are substantially coplanar with each other.

In some embodiments the module comprises a module vent volume running for substantially the length and width of the cell array, the module vent volume forming part of the fluid flow passaging and being located to the side of the cell volume and so as to face the first ends of the cells. The module vent volume may provide a route for fluid discharged from any of the cells of the module to leave the cell volume and be ported for ultimate venting to atmosphere.

In some embodiments the light sensor is located outside of the module vent volume.

In the event of a failure, the module vent volume may contain fluids and/or fire and/or may be at a high temperature. The light sensor may therefore be less susceptible to damage and/or destruction if it is away from the module vent volume. The use of a light sensor may facilitate this because, with an appropriate field of view, it may be capable of detecting radiated light from within the fluid flow passaging (e.g. within the module vent volume) without needing to be in the fluid flow passaging itself.

In some embodiments a wall of the module separating the cell volume and module vent volume has vent passages therethrough disposed substantially throughout its extent, thereby allowing fluid communication between each of the cells and the module vent volume locally to each respective cell. This may reduce the likelihood of a cell which is experiencing a failure negatively impacting (and potentially inducing failure in e.g. a cascade of thermal runaway reactions) other nearby cells, by allowing fluid to be vented locally to the failing cell rather than forcing fluid to travel a significant distance through the cell volume.

In some embodiments the fluid flow passaging further comprises a first common vent volume at the first end of the module, the first common vent volume being in fluid communication with and running substantially perpendicularly to the module vent volume. The common vent volume may provide a route for fluid discharged from the module vent volume to be ported for ultimate venting to atmosphere.

In some embodiments the fluid flow passaging further comprises a second common vent volume at the second end of the module, the second common vent volume being in fluid communication with and running substantially perpendicularly to the module vent volume. The use of two vent volumes may provide increased venting capacity and in at least some circumstances, a shorter path for hazardous gas to escape.

In some embodiments the light sensor is arranged such that its field of view comprises at least part of the module vent volume. Since fire resulting from a cell failure will need to travel through the module vent volume before reaching other parts of the fluid flow passaging, a field of view into the module vent volume may give rise to earlier detection of elevated light levels associated with a cell fire.

In some embodiments the light sensor is arranged such that its field of view comprises at least part of the first or second common vent volume. Especially where (as discussed further below) more than one module vent volume each associated with a different module vents into the relevant common vent volume, a field of view comprising the relevant common vent volume may provide redundancy and/or corroborative data from multiple light sensors. Specifically, the light sensor may be capable of earlier detection of elevated light levels resulting from a cell fire in any one of multiple different modules.

In some embodiments the battery pack comprises a plurality of said battery modules.

In some embodiments the modules are arranged side by side in the battery pack in a common orientation and such that the first ends of each module are substantially coplanar with each other and the second ends of each module are substantially coplanar with each other.

In some embodiments the module vent volume of each module is in fluid communication with the first common vent volume, wherein the first common vent volume runs substantially perpendicularly to each of the module vent volumes at the first ends of the modules. The common use of the first common vent volume may be efficient in that it may consequently be unnecessary to provide similar but dedicated vent volumes for each module.

In some embodiments the module vent volume of each module is in fluid communication with the second common vent volume, wherein the second common vent volume runs substantially perpendicularly to each of the module vent volumes at the second ends of the modules.

In some embodiments one light sensor is provided per module. This may increase reliability and rate of detection of a cell fault as well as increasing redundancy because in the event of failure a light sensor associated with a particular module, one or more other light sensors associated with other modules may still detect elevated light levels resulting from a cell failure in the module associated with the failed light sensor.

In some embodiments one light sensor is located in or adjacent to a corresponding respective module.

In some embodiments the positioning of the light sensors varies from one module to the next in an alternating manner between being located at the first end of the module and being located at the second end of the next module. In this manner, the effectiveness of the light sensors serving as back-ups for each other may be increased in that one or more additional light sensors are provided relatively nearby to each other. Thus, if a light sensor fails, other light sensors may be relatively nearby, allowing for timely detection of elevated light levels associated with a failure in a cell of the module having a failed light sensor associated therewith.

In some embodiments the battery pack comprises a first dedicated communication channel arranged to deliver the signals from the light sensors at the first ends of the modules to the vehicle occupant warning system and a second dedicated communication channel arranged to deliver the signals from the light sensors at the second ends of the modules to the vehicle occupant warning system. This may improve detection redundancy in the event of failure of a communication channel.

In some embodiments the battery comprises a housing arranged to substantially occlude the interior of the battery pack from exterior light. In this way light generated by a fire associated with a failure of a cell may create a larger and therefore more easily detected light level differential.

In some embodiments the interior surfaces of the fluid flow passages are at least in part reflective. Such reflective surfaces may aid in terms of light generated by a fire reaching one or more of the light sensors and may mean that light level variation is more readily detected even where there is no direct line of sight between the relevant light sensor and the fire. It is noted that mirrored surfaces are not necessarily required. It may be for instance that the relevant surface is partially reflective and could for instance be untreated steel or aluminium.

According to a still further aspect of the invention a vehicle is provided comprising the vehicle battery pack of the previous aspect.

In some embodiments the vehicle comprises a vehicle occupant warning system arranged to receive the signals from the modules, determine whether to output a warning in dependence on the signals received and deliver the warning as determined using a warning delivery means. It may be for instance that a warning is issued if at least one of the light sensors detects light levels above a threshold.

According to another aspect of the invention there is provided a method of detecting a vehicle battery pack fault in a battery pack comprising a battery module and a vent system, the module comprising an array of cells in a cell volume, the cell volume being in fluid communication with the vent system, the vent system thereby being arranged to receive fluid vented from any one or more of the cells during a failure of one or more of those cells and deliver it via fluid flow passaging of the vent system to the exterior of the battery pack, the method comprising detecting light levels in a portion of the vent system and outputting a signal, the signal being dependent on said detected light level and said signal being indicative of a fault in the battery pack.

According to still another aspect of the invention there is provided a vehicle occupant warning system controller arranged to warn of a fault in a vehicle battery pack, the battery pack comprising a battery module, a vent system and a light sensor, the module comprising an array of cells in a cell volume, the cell volume being in fluid communication with the vent system, the vent system thereby being arranged to receive fluid vented from any one or more of the cells during a failure of one or more of those cells and deliver it via fluid flow passaging of the vent system to the exterior of the battery pack and where further the light sensor is arranged to detect light levels in a portion of the vent system and output a signal, said signal being dependent on said detected light level, the controller comprising: an input means arranged to receive the signal; a processing means arranged to make a determination in dependence on said signal as to whether a fault has occurred; and an output means arranged to output a signal for controlling the issue of a fault warning via a warning delivery means.

The making of the determination in dependence on said signal may comprise making the determination in dependence on the light levels.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described by way of example only, with reference to the accompanying figures, in which: Figures 1A-C show different views of a cylindrical cell that may be used in a vehicle

battery module (PRIOR ART);

Figure 2 is a cut-away perspective view of part of a battery module according to an embodiment of the invention; Figure 3 is a perspective view of part of a battery module according to an embodiment of the invention; Figure 4 is a top section view of a vehicle battery pack according to an embodiment of the invention; Figure 5 is a top section view of a vehicle battery pack according to an embodiment of the invention; Figure 6 is a perspective view of a vehicle according to an embodiment of the invention; Figure 7 is a schematic representation of a vehicle occupant warning system controller according to an embodiment of the invention; and Figure 8 is a schematic representation of a method according to an embodiment of the invention.

DETAILED DESCRIPTION

Figures 1A-C show different views of a conventional cylindrical cell 100. Cylindrical cells 100 are widely available in a variety of different sizes. For example, in traction batteries for vehicles cells having a diameter D of 21mm and a length L of 70mm are often used. Such cells are typically referred to as 21700 cells (the first two numbers referring to the diameter D, in mm, and the last three numbers referring to the length L. in tenths of mm). However, it will be understood that other sizes of cell may also be used in embodiments of the present invention.

As will be well understood by the skilled person, the cell 100 comprises a positive terminal 100P, a negative terminal 100N, and vent means 100V. The positive terminal is provided by a steel end cap 106 in a central region of the first end 104 of the cell, and the negative terminal is provided by a steel cylindrical case 108. The steel cylindrical case 108 covers the second end 102, the entire cylindrical surface between the first and second ends, and a peripheral region 100S of the first end surface. The peripheral region of the first end surface may also be referred to as a "shoulder" region 100S of the first end surface 104. In commercially-available cells, it is sometimes the case that the end cap that defines the positive terminal 100P on the first end surface 104 protrudes beyond the shoulder region of the first end surface, although this is not the case in the cell shown in figure 1. This allows a substantially planar connector to be connected to the positive terminal and not the negative terminal. As will be well understood by the skilled person, it is important to avoid direct electrical connections between the positive and negative terminals, as such connections create a short circuit which may damage the cell.

As shown in figure 1, the cell 100 comprises three vent means 100V in the first end surface 104, between the steel end cap 106 that defines the positive terminal 100P and the shoulder region 100S of the steel cylindrical case 108. The vent means 100V are gaps that are covered by a material that will rupture to allow hot gases to escape through the gaps between the end cap 106 and steel cylindrical case 108 in the event of excessive pressure occurring inside the cell, thereby mitigate against the risk of the cell exploding.

Cells 100 may be grouped together within an enclosure and electrically connected together by a busbar assembly to create a battery module.

As will be well understood by the skilled person, abnormal operation of cells in a battery module can lead to the cell undergoing "thermal runaway", which is a self-sustaining exothermal reaction which emits a large volume of gas, and that will typically continue until all of the available fuel within the cell has been consumed by the reaction. Thermal runaway event associated with fire (i.e. 'hard venting') is potentially hazardous and may therefore require some mitigating action such as warning the occupants of the vehicle. However, venting without fire (i.e. 'soft venting') need not trigger such warnings to occupants. Cell venting means are typically designed to allow hot gases to escape when the temperature and pressure has reached a level which is not necessarily sufficient to initiate thermal runaway. Venting when the conditions within the cell are not yet sufficiently extreme to cause thermal runaway can prevent an abnormal operating condition from progressing into thermal runaway. Accordingly, abnormal operating conditions within cells that lead to venting events may be categorised into those that do and do not ultimately lead to thermal runaway.

Referring now to Figures 2 and 3, a battery module is generally shown at 120. The battery module 120 forms part of a vehicle battery pack 122 discussed further below with respect to Figures 4 and 5. The battery module 120 has a cell volume 124 in which are provided an array of cells 126. The cells 126 may be similar to those described above with respect to Figure 1. Each of the cells 126 has a first end 128 and a second end 130. The cells are oriented similarly. Additionally, the first ends 128 of each of the cells 126 are substantially coplanar with each other and the second ends 130 of each of the cells 126 are substantially coplanar with each other. At one of the first 128 and second 130 ends of the cells 126 are positive terminals of the cells 126 and at the other are negative terminals of the cells 126. The positive terminals are connected by a positive busbar of the battery module and the negative terminals are connected by a negative busbar.

The battery module 120 has fluid flow passaging in the form of a module vent volume 132 running for substantially the length and width of the cell array, located to the side of the cell volume 124 and so as to face the first ends 128 of the cells 126. The module vent volume 132 forms part of a vent system 136 of the battery pack 122 providing for fluid communication between the cell volume 124 and an exterior of the battery pack 122 (though prior to a failure creating a sufficient pressure build-up, fluid communication may be prevented by a burst disc or similar). A wall 138 (best seen in Figure 3) separating the cell volume 124 and module vent volume 132, has vent passages 140 therethrough disposed substantially throughout its extent. The vent passages 140 provide fluid communication between the cell volume 124 and the module vent volume 132. The fluid which would, in the event of a failure, be vented via the vent system 136 (and indeed its constituent parts such as the module vent volume 132) might for instance be hot gas and flames. Other materials may be contained in/carried by the fluid flow e.g. burning particles.

The battery module 120 also has a cell supervisory circuit 142. The cell supervisory circuit 142 has a printed circuit board on which are mounted or to which are connected one or more electrical components arranged to receive and process signals from sensors for monitoring the voltage and temperature of the cells 126 of the battery module 120. Also mounted on or connected to the printed circuit board is a light sensor 144 On this case a photo transistor) arranged to monitor light levels in a portion of the vent system 136. Also mounted on or connected to the printed circuit board are one or more components for transmitting, via a communication channel, signals indicative of the sensed parameters to a vehicle monitoring and control processor which forms part of a vehicle occupant warning system. The cell supervisory circuit 142 also has a sealed housing 146 which encloses the printed circuit board and the light sensor 144. The sealed housing may be fire and/or heat resistant or proof (for instance having a fire and/or heat rating). The cell supervisory circuit 142 is located at an end 147 of the battery module 120. A window 148 is provided in the housing 146 giving the light sensor 144 a field of view of part of the fluid flow passaging 134. Figure 2 shows various possible fields of view 150 of the light sensor 144 when located and oriented correspondingly. More specifically, the light sensor 144 and window 148 may be arranged such that the field of view is of at least part of the module vent volume 132 or alternatively is of at least part of a common vent volume (discussed further below).

Referring now to Figure 4 the battery module 120 is one of several similar battery modules 120 of the battery pack 122. The battery modules 120 are arranged side by side in the battery pack 122 in a common orientation and such that first ends 152 of each module are substantially coplanar with each other and second ends 154 of each module are substantially coplanar with each other.

The vent system 13601 the battery pack 122 also has a first common vent volume 156 provided in fluid communication with all of the module vent volumes 132. The length of the first common vent volume 156 runs substantially perpendicularly to the lengths of the module vent volumes 132 and it is provided adjacent the first ends 152 of the battery modules 120. Similarly, the vent system 136 of the battery pack 122 has a second common vent volume 158 provided in fluid communication with all of the module vent volumes 132. The length of the second common vent volume 158 runs substantially perpendicularly to the lengths of the module vent volumes 132 and it is provided adjacent the second ends 154 of the battery modules 120. Thus, where for instance the battery pack 122 is provided in a vehicle, the battery modules 120 and their module vent volumes 132 may be considered to run transversely across the vehicle, while the first 156 and second 158 common vent volumes may be considered to run in a longitudinal direction (i.e. in the direction of the length of the vehicle).

As best seen in Figure 5, each battery module 120 has its cell supervisory circuit 142, and therefore light sensor 144, mounted at its opposite end to its immediate neighbouring battery module or modules 120. Thus, whilst a first of the battery modules 120 has its cell supervisory circuit 142 located at its first end 152, the next will have its cell supervisory circuit 142 located at its second end 154 and the one after that its first end 152 and so on.

In this embodiment the field of view for each of the light sensors 144 is a portion of the first common vent volume 156 or second common vent volume 158 to which it is adjacent, the portion being in the locale of the battery module 120 of which the light sensor 144 forms part. In other embodiments one or more of the battery modules 120 may instead have a field of view of part of the module vent volume 132 of the battery module of which it forms part.

A first dedicated communication channel is used to deliver the signals from the light sensors 144 at the first ends 152 of the battery modules 120, whilst a different second dedicated communication channel is used to deliver the signals from the light sensors 144 at the second ends 154 of the battery modules. The first and/or second dedicated communication channels may for instance be electric, electronic and/or electromagnetic based communication channels.

The battery pack 122 has a housing around the battery modules 120 and vent system 136 which occludes the interior of the battery pack 122 from exterior light. Further, the interior surfaces of the fluid flow passages are reflective.

The battery pack 122 as described is installed in a vehicle 160 (see Figure 6). The battery pack 122 is used, at least in part, for delivery of propulsion for the vehicle 160.

In use, the light sensors 144 are used to detect light associated with flames in the event of a hard vent failure of one or more of the cells 126. Specifically, in the event of a hard vent failure 162 of one of the cells 126, fluid and flames are vented from the relevant cell volume 124 into the relevant module vent volume 132 via the vent passages 140 in the vicinity of the cell 126. Fluid and flames are then vented 164 into the first 156 and second 158 common vent volumes and thereafter through one or more ports in the housing around the battery pack 122 and ultimately, via further fluid flow passaging, to atmosphere outside of the vehicle 160.

For those of the light sensors 144 for which sufficient illumination in its field of view (i.e. sufficient to exceed a threshold set for the respective light sensor 144 or all light sensors 144) is caused by detection of light from the fire, the relevant light sensor 144 will send a signal indicative of the light level sensed to an input 170 of a vehicle occupant warning system controller 172 of the vehicle 160. A processor 174 of the vehicle occupant warning system controller 172 makes a determination in dependence on said signal as to whether a hard vent fault has occurred. In the event that the determination is that a hard vent fault has occurred, the processor 174 sends a signal via an output 176 to an occupant warning delivery means instructing issuance of a warning. The occupant warning delivery means may for instance be a display arranged to provide a visual warning and/or a speaker arranged to provide an audio warning and/or a movement generator arranged to provide a haptic warning and/or a vehicle systems interface arranged to activate and/or deactivate one or more vehicle systems (e.g. hazard lights, door locks, seat position and vehicle drive). The warning may at least in part advise/instruct occupants of the vehicle 160 to leave the vehicle 160.

Normally, the first sensor to detect elevated light levels associated with the fire would be the light sensor 144 associated with the battery module 120 containing the cell 126 or cells which have failed. However, not least because the fire will spread, it is likely that other of the light sensors 144 will also sense the elevated light levels. Such 'secondary' detection may occur more rapidly where, as here, the light sensors 144 have their fields of view directed at respective parts of the first 156 and second 158 common vent volumes, since fluid and fire originating from any of the module vent volumes 132 will pass along these common vent volumes and will tend to do so before entering other of the module vent volumes 132.

Because light from a fire is radiated to areas where there is not yet fire itself, and in further view of the interior surfaces of the fluid flow passaging being reflective, it is likely that light sensors 144 will detect elevated light levels well in advance of fire itself being present in the field of view of the relevant light sensor 144. The removal of noise that would otherwise be caused by light from the external environment (given the housing around the battery pack 122) may also assist in accurately detecting light levels associated with a fire.

The arrangement of the light sensors 144 of neighbouring battery modules 120 (i.e. alternating between being located at the first 152 and second 154 ends of their respective battery modules, with corresponding fields of view) may enhance the rate at which elevated light levels associated with a cell fire are detected. Specifically and by way of example, even if a cell failure occurs proximate the second end 154 of a battery module 120 having its light sensor at its first end 152, the neighbouring battery module 120 or modules will have their light sensors 144 at their second ends 154 and will therefore be nearby to the cell 126 experiencing the failure. Additionally, in the event of a failure of a light sensor 144, for instance the light sensor 144 of the battery module 120 in which the cell failure has occurred, the arrangement of the light sensors 144 of neighbouring battery modules 120 may also reduce the distance between a failing cell and the nearest functioning light sensor 144.

It is further noted that there is no need for the light sensors 144 to be in the path of fire, but rather simply that they have a field of view capable of observing elevated light levels. This allows freedom in terms of the positioning of the light sensors 144, and allows for positioning so as to reduce the likelihood of the sensors being damaged by fire and heat. In particular, the light sensors 144 can, as here, be positioned inside the protective sealed housing 146 of the cell supervisory circuit 142. Redundancy is also provided by the use of the distinct communication channels for the light sensors 144 on opposite sides of the battery modules 120 and the distribution of the light sensors 144 of neighbouring modules as discussed above.

Whilst not shown here, in other embodiments, the light sensors 144 might be arranged so as to instead have fields of view of their respective module vent volumes. This might tend to still further increase initial rate of detection under ideal conditions (the module vent volumes tending to be nearer in terms of fluid flow path to the source of the failure than the first 156 and second 158 common vent volumes) but may somewhat reduce secondary' detection rate (discussed above) in the event of a relevant light sensor 144 failure.

Figure 8 shows a method 200 according to an embodiment of the present invention.

The method 200 provides detection of a vehicle battery pack fault in a battery pack comprising features of the battery pack as hereinbefore described. At 202 the method comprises detecting light levels in a portion of the vent system. At 204 the method comprises outputting a signal. The signal is dependent on the detected light level and is indicative of a fault in the battery pack.

It will be appreciated that embodiments of the present invention can be realised in the form of hardware, software or a combination of hardware and software. Any such software may be stored in the form of volatile or non-volatile storage such as, for example, a storage device like a ROM, whether erasable or rewritable or not, or in the form of memory such as, for example, RAM, memory chips, device or integrated circuits or on an optically or magnetically readable medium such as, for example, a CD, DVD, magnetic disk or magnetic tape. It will be appreciated that the storage devices and storage media are embodiments of machine-readable storage that are suitable for storing a program or programs that, when executed, implement embodiments of the present invention. Accordingly, embodiments provide a program comprising code for implementing a system or method as claimed in any preceding claim and a machine readable storage storing such a program. Still further, embodiments of the present invention may be conveyed electronically via any medium such as a communication signal carried over a wired or wireless connection and embodiments suitably encompass the same.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed. The claims should not be construed to cover merely the foregoing embodiments, but also any embodiments which fall within the scope of the claims.

Claims

CLAIMS1. A vehicle battery pack comprising a battery module, a vent system and a light sensor, the module comprising a first end and a second end between which an array of cells are provided in a cell volume, the cell volume being in fluid communication with the vent system, the vent system thereby being arranged to receive fluid vented from any one or more of the cells during a failure of said one or more of those cells and deliver said fluid via fluid flow passaging of the vent system to an exterior of the battery pack and wherein the light sensor is arranged to detect light levels in a portion of the vent system and output a signal to a vehicle occupant warning system, said signal being dependent on said detected light level.
2. A battery pack according to claim 1 where the light sensor is located outside of the fluid flow passaging.
3. A battery pack according to claim 1 or claim 2 where the module comprises a cell supervisory circuit arranged to monitor the cells, the cell supervisory circuit being provided in a substantially sealed housing.
4. A battery pack according to claim 3 where the light sensor is located inside the substantially sealed housing of the cell supervisory circuit.
5. A battery pack according to any preceding claim where each of the cells has a first end and a second end and the cells are disposed within the cell volume in a common orientation and such that the first ends of each of the cells are substantially coplanar with each other and the second ends of each of the cells are substantially coplanar with each other.
6. A battery pack according to claim 5 where the module comprises a module vent volume running for substantially the length and width of the cell array, the module vent volume forming part of the fluid flow passaging and being located to the side of the cell volume and so as to face the first ends of the cells. 7. 8. 9. 10. 11. 12. 13. 14.
A battery pack according to claim 6 where the light sensor is located outside of the module vent volume.
A battery pack according to claim 6 or claim 7 where a wall of the module separating the cell volume and module vent volume has vent passages therethrough disposed substantially throughout its extent, thereby allowing fluid communication between each of the cells and the module vent volume locally to each respective cell.
A battery pack according to any of claims 6 to 8 wherein the fluid flow passaging further comprises a first common vent volume at the first end of the module, the first common vent volume being in fluid communication with and running substantially perpendicularly to the module vent volume.
A battery pack according to claim 9 wherein the fluid flow passaging further comprises a second common vent volume at the second end of the module, the second common vent volume being in fluid communication with and running substantially perpendicularly to the module vent volume.
A battery pack according to any of claims 6 to 10 where the light sensor is arranged such that its field of view comprises at least part of the module vent volume.
A battery pack according to claim 9 or claim 10 where the light sensor is arranged such that its field of view comprises at least part of the first or second common vent volume.
A battery pack according to any preceding claim where the battery pack comprises a plurality of said battery modules.
A battery pack according to claim 13 when dependent through to 9 or claim 10 where the module vent volume of each module is in fluid communication with the first common vent volume, wherein the first common vent volume runs substantially perpendicularly to each of the module vent volumes at the first ends of the modules.
15. A battery pack according to claim 14 when dependent on claim 10 where the module vent volume of each module is in fluid communication with the second common vent volume, wherein the second common vent volume runs substantially perpendicularly to each of the module vent volumes at the second ends of the modules.
16. A battery pack according to any of claims 13 to 15 where one light sensor is provided per module.
17. A battery pack according to claim 16 wherein said one light sensor is located in or adjacent to a corresponding respective module.
18. A battery pack according to any of claims 13 to 17 where the positioning of the light sensors varies from one module to the next in an alternating manner between being located at the first end of the module and being located at the second end of the next module.
19. A battery pack according to claim 18 comprising a first dedicated communication channel arranged to deliver the signals from the light sensors at the first ends of the modules to the vehicle occupant warning system and a second dedicated communication channel arranged to deliver the signals from the light sensors at the second ends of the modules to the vehicle occupant warning system.
20. A battery pack according to any preceding claim comprising a housing arranged to substantially occlude the interior of the battery pack from exterior light.
21. A battery pack according to any preceding claim where the interior surfaces of the fluid flow passages are reflective.
22. A vehicle comprising the vehicle battery pack according to any preceding claims.
23. A vehicle according to claim 22 comprising a vehicle occupant warning system arranged to receive the signals from the modules, determine whether to output a warning in dependence on the signals received and deliver the warning as determined using a warning delivery means.
24. A method of detecting a vehicle battery pack fault in a battery pack comprising a battery module and a vent system, the module comprising an array of cells in a cell volume, the cell volume being in fluid communication with the vent system, the vent system thereby being arranged to receive fluid vented from any one or more of the cells during a failure of one or more of those cells and deliver it via fluid flow passaging of the vent system to the exterior of the battery pack, the method comprising detecting light levels in a portion of the vent system and outputting a signal, said signal being dependent on said detected light level and said signal being indicative of a fault in the battery pack.
25. A vehicle occupant warning system controller arranged to warn of a fault in a vehicle battery pack, the battery pack comprising a battery module, a vent system and a light sensor, the module comprising an array of cells in a cell volume, the cell volume being in fluid communication with the vent system, the vent system thereby being arranged to receive fluid vented from any one or more of the cells during a failure of one or more of those cells and deliver it via fluid flow passaging of the vent system to the exterior of the battery pack and where further the light sensor is arranged to detect light levels in a portion of the vent system and output a signal, said signal being dependent on said detected light level, the controller comprising: an input means arranged to receive the signal; a processing means arranged to make a determination in dependence on said signal as to whether a fault has occurred; and an output means arranged to output a signal for controlling the issue of a fault warning via a warning delivery means.