SE2251289A1 - A fire suppressing apparatus and related system and method - Google Patents

Abstract

A fire suppressing apparatus for a battery unit is provided, the apparatus comprising an aerosol generator (2) and a sensor (3) arranged to detect measurable characteristics and/or effects resulting from battery thermal runaway and to trigger the aerosol generator (2) when said characteristics and/or effects are detected.

Description

TECHNICAL FIELD The present invention relates to a fire suppressing apparatus for a battery unit, a system comprising a fire suppressing apparatus and a battery unit, and a method for suppressing a fire in a battery unit.

BACKGROUND Batteries, usually lithium ion batteries, are increasingly common in e.g. vehicles. This type of battery is also used in stationary installations of e.g., energy production systems. A safety risk connected to these batteries is the risk of thermal runaway, which may lead to fire and explosion. ln order to avoid and/or limit the impact if any of these would occur, a fire extinguishing or suppressing unit can be mounted in connection with the battery. For safety reasons, the fire extinguishing or suppressing unit should be automatically triggered in the event of fire. lt is of high importance that the automatic triggering is reliable.

SUMMARY The invention is defined by the appended independent claims. Additional features and advantages of the concepts disclosed herein are set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the described technologies. The features and advantages of the concepts may be realized and obtained by means of the instruments and combinations partic- ularly pointed out in the appended claims. These and other features of the described technologies Will become more fully apparent from the following description and ap- pended claims, or may be learned by the practice of the disclosed concepts as set forth herein. ln a first aspect, a fire suppressing apparatus for a battery unit is provided, the ap- paratus comprising an aerosol generator, a sensor arranged to detect measurable characteristics and/or effects resulting from battery thermal runaway and to trigger the aerosol generator when said characteristics and/or effects are detected.

This fire suppressing apparatus is advantageous in that it is configured to sup- press a fire when the fire is detected by the sensor, which is beneficial in a battery unit. ln one embodiment, the sensor is a mechanical pressure sensor. This is advanta- geous in that to electronics is required for detecting the fire, making the apparatus more robust and reliable. ln one embodiment, the sensor is mechanically connected to the aerosol genera- tor for triggering the aerosol generator. This is advantageous in that to electronics is required in order to transmit a signal, in this case a mechanical signal, to the aerosol generator when a fire has been detected, making the apparatus more robust and re- liable. ln one embodiment, the sensor includes a membrane configured to detect a pressure increase due to the thermal runaway. The use of a membrane is beneficial in that it is a mechanical sensor, not being dependent on electric signals. lt is a ro- bust and reliable sensor. ln one embodiment, the membrane is arranged in mechanical connection with a power transmission unit connected to a trigger mechanism of the aerosol generator. The membrane is configured to apply a force on the power transmission unit in re- sponse to said pressure increase in order to trigger the aerosol generator by means of the trigger mechanism. The use of a mechanical power transmission unit is bene- ficial in that it is not dependent on electric signals. lt is a robust and reliable power transmission means. ln one embodiment, the pressure sensor is configured to trigger the aerosol gen- erator at a detected differential pressure of approximately 0.2 - 0.8 bar, more pre- ferred 0.4 - 0.6 bar and most preferred 0.5 bar compared to an reference pressure. This is beneficial in that it provides a fast fire suppression, but a threshold value as low as to risk false triggering. ln one embodiment, the aerosol generator and the battery unit share a common continuous volume when the fire suppressing apparatus is mounted to a battery unit.

This is beneficial in that no valve or similar is required to open in order for the aero- sol to spread throughout the battery unit when released. This reduces the risk of fail- ure of spreading the aerosol. ln one embodiment, the battery unit comprises at least one battery cell, and the membrane is configured to deform in response to a pressure increase in the com- mon continuous volume due to thermal runway of one of the at least one battery cell.

The deformation of the membrane is configured to apply a force on a power trans- mission unit connected to a trigger mechanism of the aerosol generator. A pressure change in the battery unit is detectable also in the area of the membrane thanks to the common continuous volume. ln one embodiment, the battery unit comprises a housing, and the fire suppress- ing apparatus is mountable to an outer surface of the housing or enclosed within the housing of the battery unit. lt is advantageous to mount the fire suppressing appa- ratus within the battery housing at manufacturing. lt is advantageous to mount the fire suppressing apparatus to an outer surface of the battery housing when retro fit- ting the fire suppressing apparatus to an existing battery unit. ln one embodiment, the aeroso| generator comprises a solid compound, and the solid compound preferably is potassium nitrate. A solid compound is compact, sta- ble and not pressurized. ln one embodiment, the fire suppressing apparatus further comprises a pressure relief valve configured to release gas from the common continuous volume to an ambient when pressure in the common continuous volume exceeds a predeter- mined differential pressure threshold value. lt is advantageous to release the pres- sure inside the common continuous volume since more aerosol is required if the pressure continues to rise. By relieving the pressure, the amount of aeroso| required can be kept down. ln one embodiment, the pressure relief valve is configured to open when a pres- sure difference between the common continuous volume and the ambient volume is 0.1-0.5 bar above a threshold value for triggering the aeroso| generator. ln one embodiment, when the pressure relief valve is open, the pressure relief valve is configured to re-close when pressure in the common continuous volume falls below a predetermined threshold value, which pressure preferably is approxi- mately 0.2 - 0.8 bar, more preferred 0.4 - 0.6 bar and most preferred 0.5 bar com- pared to the ambient. ln one embodiment, the pressure relief valve comprises a non-flammable mate- rial. This is advantageous in that the valve is not damaged by hot fire gases, and thus may be re-closed when the fire gases have passed through the valve. ln a second aspect, a system comprising a fire suppressing apparatus and a bat- tery unit is provided. The fire suppressing apparatus is mounted to the battery unit such that the aeroso| generator and the battery unit share a common continuous vol- ume. The system is advantageous in that no valves are necessary to provide fire suppressing aeroso| to the battery unit. ln a third aspect, a method for suppressing a fire in a battery unit provided with a fire suppressing apparatus is provided. The method comprises the steps of detect- ing measurable characteristics and/or effects resulting from battery thermal runaway and triggering the aeroso| generator. By this method, a fire may be efficiently sup- pressed when a characteristic indicative of fire is detected. ln one embodiment, the step of detecting measurable Characteristics and/or ef- fects resulting from battery thermal runaway comprises detecting an increase in pressure due to the thermal runaway. Pressure change is a reliable characteristic to measure in order to determine whether there is thermal runaway or fire in a battery unit. ln one embodiment, the method further comprising a step of opening a pressure relief valve when a pressure difference between the common continuous volume and the ambient volume exceeds a predetermined threshold value, and a step of at least partially closing the opened pressure relief valve when the pressure difference between the common continuous volume and the ambient volume is reduced, pref- erably when the pressure difference is 0.2 - 0.8 bar, more preferred 0.4 - 0.6 bar and most preferred 0.5 bar.

BRIEF DESCRIPTION OF THE DRAWINGS ln order to best describe the manner in which the above-described embodiments are implemented, as well as define other advantages and features of the disclosure, a more particular description is provided below and is illustrated in the appended drawings. Understanding that these drawings depict only exemplary embodiments of the invention and are not therefore to be considered to be limiting in scope, the ex- amples will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: Fig. 1 is a perspective view of a fire suppressing apparatus, Fig. 2 is a side section view of a fire suppressing apparatus according to one embodiment, Fig. 3 is a side section view of a sensor unit of the fire suppressing apparatus in Fig. 2 in an idle state, Fig. 4 is a side section view of the sensor unit in Fig. 3 in a pressure affected state, Fig. 5 is a side section view of a fire suppressing apparatus according to one embodiment, Fig. 6 is a side section view of a fire suppressing apparatus according to one embodiment, Fig. 7 is a perspective front view of a pressure relief valve according to one embodiment, Fig. 8 is an exploded view of the pressure relief valve in Fig. 7, Fig. 9a is a side section view of the pressure relief valve in Figs 7-8 in a closed position, Fig. 9b is a side section view of the pressure relief valve in Figs 7-9 in an open position, Fig. 9c is a side section view of the pressure relief valve in Figs 7-10 in a re- closed position, Fig. 10 is a side section view of a sensor unit of a fire suppressing apparatus according to one embodiment in an idle state, and Fig. 11 is a side section view of the sensor unit in Fig .10 in a pressure affected state.

Further, in the figures like reference characters designate like or corresponding parts throughout the several figures.

DETAILED DESCRIPTION Various embodiments of the disclosed methods and arrangements are discussed in detail below. While specific implementations are discussed, it should be under- stood that this is done for illustration purposes only. A person skilled in the relevant art will recognize that other components, configurations, and steps may be used without parting from the spirit and scope of the disclosure. ln the description and claims the word "comprise" and variations of the word, such as “comprising” and “comprises”, does not exclude other elements or steps.

Hereinafter, certain embodiments will be described more fully with reference to the accompanying drawings. lt will be apparent to those skilled in the art that various modifications and variations can be made without departing from the inventive con- cept. Other embodiments will be apparent to those skilled in the art from considera- tion of the specification and practice disclosed herein. The embodiments herein are provided by way of example so that this disclosure will be thorough and complete and will fully convey the scope of the inventive concept, and that the claims be con- strued as encompassing all equivalents of the present inventive concept which are apparent to those skilled in the art to which the inventive concept pertains. lf nothing else is stated, different embodiments may be combined with each other.

A lithium ion battery, typically used in electric vehicles or energy storage in en- ergy production systems, comprises a number of battery cells arranged in a hous- ing. lf one or more of the cells in the battery pack malfunctions, there is a risk of thermal runaway, meaning a positive feedback process where an increase in tem- perature in one cell releases energy that causes a further increase in temperature. lf this process is not brought to a stop, nearby cells are at risk of malfunctioning as well, contributing to the positive feedback of the thermal runaway. The process ac- celerates logarithmically, resulting in a risk of explosion. There is also a risk of arc discharges, meaning that a cell is short circuited, resulting in the air becoming ionized and electrically conductive, causing further battery cells to become short cir- cuited.

Therefore, it is desirable to bring the process of thermal runaway to a stop before it has spread to nearby battery cells, or to suppress it enough to prevent it from spreading.

When a battery cell is subject to thermal runaway, it causes a pressure increase within the battery housing. ln order to prevent the battery housing from bursting, it is desirable to prevent the pressure from reaching too high, compared to the strength of the battery housing.

The thermal runaway process is fast, and therefore it is desirable that any coun- teractions are equally fast or faster. lt is known in the art to use aerosol fire suppressors to suppress a fire in Li-ion batteries. An aerosol fire suppressor is a partic-le-tvased form of fire extinction. it uti- iizes a fire-extinguishing agent eensistihg ef very fine soiiri eartieies as weil as gase- eus matter. The cendensed aeresei rhiereparticies and effiuent gases are generated by an exotherntic reaction; the particiee rernain in vapor state untii the process of being diseharged frem the device. Then, it is "cendensed" and cooied Within the de- viee and diseharged as seiid particies.

Condensed aeresois are defined as soiids of iess than 10 rnierenteters in diame- ter.

The seiid particuiates have a eensiderahiy srnaiier rnass rnedian aeredynarnic di- ameter (Mt/EAC) than these ef dry chernieai suppressieit agents. The partieulates aise rernain airborne signifieantiy tenger and ieave ntueh iess residue vvithin the pre- tected area.

Cendensed aeresois are fioeriing agents. They are effective regarriiess of tne ie- eatien and height ef the fire.

The current fire suppressing apparatus is an aerosol fire suppressor utilizing a solid compound of an which transforms into an aerosol of nanoparticles when heated. The nano particles of the gas bind to free radicals such as oxygen. Thereby, with no free oxygen, a fire cannot pursue and is suppressed.

When a battery cell is under thermal runaway, large quantities of harmful gases are produced. The nano particles of the aerosol combines also with the harmful gas particles, which neutralizes them. By neutralizing the harmful combustion gases, and not using harmful extinguishing agents, this is an environmentally friendly as Well as unharmful fire extinguishing or suppressing method.

Referring to Figs 1 and 2, a battery unit 5 is shown. The battery unit 5 comprises a housing 9 enclosing an inner volume 14. A number of battery cells or battery mod- ules 10 are arranged in the inner volume 14 enclosed by the housing 9. The battery cells 10 may be arranged in rows and/or columns and may be arranged in an upright position or in a sideways position. ln Fig. 2, the battery cells 10 are arranged in horizontal rows, with a vertical air gap between each row. The housing 9 is further provided with a pressure relief valve 6. ln other embodiments, the housing 9 may comprise several pressure relief valves 6.

A fire suppressing apparatus 1 is arranged in connection with the battery housing 9. The fire suppressing apparatus 1 comprises a casing 12 enclosing an inner vol- ume 13. An aerosol generator 2 is arranged in the inner volume 13 enclosed by the casing 12. The aerosol generator 2 is connected to a sensor 3. The sensor 3 is con- figured to detect characteristics of a battery thermal runway, and when such charac- teristics have been detected, the sensor 3 is configured to trigger the aerosol gener- ator 2. The sensor 3 may be different types of sensors, which will be explained fur- ther below.

The casing 12 of the fire suppressing apparatus 1 is connected to the housing 9 of the battery unit 5 such that the inner volume 14 of the battery housing 9 and the inner volume 13 of the casing 12 of the fire suppressing apparatus 1 form a continu- ous common volume 8. A continuous common volume is here defined to mean that the volume 8 is not cut of or parted by e.g., a valve, shutter or similar. Within the common continuous volume 8 air, particles etc., are allowed and able to move freely in both directions between the inner volume 13 of the fire suppressing apparatus casing 12 and the inner volume 14 of the battery housing 9. The common continu- ous volume 8, not comprising any blocking obstacles provides for a uniform and even air pressure throughout the common continuous volume 8. ln one embodiment, shown in Fig. 2, and in detail in Figs 3-4, the sensor 3 is a mechanical pressure sensor. The pressure sensor 3 comprises a membrane 4 ar- ranged in the common continuous volume 8. The pressure sensor 3 is configured to react to a pressure change in the common continuous volume 8. ln a working state, or normal state, of the battery, there is a certain pressure in the common continuous volume 8. This pressure acts on the pressure sensor. This may be referred to as initial state pressure, first pressure, normal pressure, or refer- ence pressure. ln the case the pressure sensor is a membrane 4, this pressure acts on both side of the membrane 4, resulting in the membrane being in equilibrium.

However, the membrane is not necessarily in equilibrium in the working state, or normal state, of the battery. This pressure of this state is however still referred to as initial pressure state, first pressure state, normal pressure state, or reference pres- sure state. These terms are used interchangeably throughout this application.

The pressure sensor 3 is configured to interact with a power transmission ar- rangement. The power transmission arrangement is in the shown embodiment formed by a spring 16 and a rod 15. A first end of the rod 15 is connected to the membrane 3 and a second end of the rod 15 is connected to a trigger mechanism 18 of the aerosol generator, here shown as a pin 22. The rod 15 is connected to the spring 16 in a spring-suspended manner such that the membrane 4 and the rod 15 are in balance in an idle state of the pressure sensor 3. The pressure sensor 3, the power transmission arrangement, and the trigger mechanism 18 will be further ex- plained below.

The aeroso| generator 2 is in several aspects formed as a conventional aeroso| generator, comprising a container 17 comprising the following components: oxidant, fuel binder, additional fuel, coolant, catalysts, and various processing aids.

The oxidant is a solid compound, which preferably is lithium nitrate, sodium ni- trate or potassium nitrate, most preferred potassium nitrate. The oxide being a solid compound is advantageous in that it is compact, stable and not pressurized.

Referring to Figs 2-4 , when a battery cell 10a is subject to thermal runaway, gas is generated in the battery cell 10a. The battery cell 10a is prone to break, spreading the gas into the common continuous volume 8 of the battery housing 9. Fire gases are spread from the cell 10a as indicated by dashed arrows in Fig. 2. This results in a pressure increase in the common continuous volume 8 of the battery housing. The pressure increase propagates and spreads uniformly and momentarily within the common continuous volume 8 of the battery housing volume 14 and the fire sup- pressing apparatus casing volume 13. Marked by dashed arrows in Fig. 4, the pres- sure propagates to the membrane 4 of the pressure sensor 3. The pressure-in- crease acts on the membrane 4 and causes it to deform as shown in Fig. 4.

When subjected to pressure, he membrane 4 deforms, and as it is attached to the rod 15, the rod 15 is brought in an upwards direction as shown in Fig. 4, according to the solid line arrow. When the rod 15 is shifted in the direction of the solid line ar- row, it releases the trigger mechanism 18 of the aeroso| generator 2, which triggers the aeroso| generator 2 to release the aeroso|.

Now referring to Fig. 2, when the aeroso| generator 2 has been triggered, the solid compound is transformed into nano particles. The compound particles, prefera- bly potassium nitrate, transitions into an aeroso| of nano particles which are distrib- uted throughout the entire common continuous volume 8, as schematically shown by solid arrows in Fig. 2. As the solid compound still is in a solid state when trans- formed into nano particles, the triggering of the aeroso| generator does not contrib- ute to a pressure increase in the common continuous volume 8.

The nano particles react, or combines, with the oxygen being present in the com- mon continuous volume 8, as described above, in order to suppress any fire possi- bly started by the thermal runaway. The aeroso| does not contribute to any further pressure increase, as the nano particles fill out the space between air molecules, without affecting them.

At the same time, caused by the pressure increase in the common continuous volume 8 due to the thermal runaway in cell 10a, the pressure relief valve 6 opens in order to relieve the pressure. When the pressure in the common continuous volume 8 of the battery unit 5, caused by the thermal runaway, reaches a certain predeter- mined threshold level, the pressure relief valve 6 is configured to open. The prede- termined threshold pressure value is preferably set in relation to the pressure at which the sensor 3 is configured to trigger the release of aerosol. Preferably, the threshold pressure value for opening the pressure relief valve 6 is slightly higher than the threshold pressure for the pressure sensor 3 to trigger the release of aero- sol.

Aerosol particles, shown as solid arrow, combined with combustion gas particles and oxygen, respectively, as well as uncombined with anything, shown as dashed ar- row, flows out through the pressure relief valve 6. As described above, the combus- tion gases released through the valve 6 have become neutralized by the aerosol par- ticles, and are thus harmless when entering the ambient air 7.

When the pressure of the common continuous volume 8 has decreased to a pre- determined extend, or below a predetermined threshold, the pressure relief valve 6 is designed to be at least partly re-closed. The pressure relief valve 6, and the fea- tures will be further described below.

By reclosing the pressure relief valve 6, the main part of the released aerosol is kept within the common continuous volume 8. lf the pressure relief valve 6 would stay open, all, or a large share of, the aerosol would be vented out of the common continuous volume 8. Since the cell 10a subject to thermal runaway is hot, adjacent cells could be heated enough to ignite. lf this would happen, there would be no fire suppressing system to suppress that fire, as all/main share of aerosol particles would have been vented out from the common continuous volume 8.

Therefore, by re-closing the pressure relief valve 6, the main share of the aerosol particles is kept within the common continuous volume 8. lf any further battery cell 10 ignites, the aerosol particles are still present and may suppress that fire. ln another embodiment, shown in Fig. 5, the sensor is an electrical sensor 19. This sensor 19 may be an electrical pressure sensor, a heat sensor, or a gas or smoke sensor. When detecting a pressure change, heat, gas or smoke, the sensor 19 is configured to transmit an electrical signal to a control unit 20 included in the fire suppression apparatus 1. The control unit 20 is configured to trigger the aerosol generator to release the aerosol, in the same manner as described above. The rest of the fire suppressing process of this embodiment corresponds to what has been described above in connection with the mechanical pressure sensor. ln another embodiment, shown in Fig. 6, the sensor is a heat sensor 21 config- ured to react on the heat produced by the thermal runaway of a battery cell 10a, represented as dashed arrows, and when heated to a certain temperature, trigger the aerosol generator 2 to release the aerosol. The rest of the fire suppressing pro- cess of this embodiment corresponds to what has been described above in connec- tion with the mechanical pressure sensor.

Pressure relief valve Hereafter, the pressure relief valve 6 will be described in more detail. The pres- sure relief valve is shown in perspective view in Fig. 7, and in an exploded view in Fig. 8. The pressure relief valve 6 comprises a base plate 23, a spring 24, a sealing 25, a disc 26, and a spring retainer 27. The spring retainer 27 comprises an abut- ment surface 30, configured to abut the spring 24 in a mounted state of the valve 6.

The base plate 23 comprises one or more through openings 28. The base plate 23 further comprises a through hole 29 configured to receive the spring retainer 27.

The disc 26 is of a size adapted to cover the openings 28 in the base plate 23 in a mounted state of the valve 6. ln Fig. 8 a construction 31 to be pressure relieved is schematically shown by dashed lines. ln the mounted state, on an inside (left hand side in Fig. 8) of the construction 31 to be pressure relived, the spring 24 is arranged on the spring retainer 27. The spring retainer 27 is in turn passed through the through hole 29 of the base plate 23 such that the spring 24 abuts the abutment surface 30 of the spring retainer 27, and an inner side of the construction 31.

On an outer side (right hand side in Fig. 8) of the construction 31 to be pressure relived, the base plate 23 is arranged to fit with through openings in the construction 31 to be pressure relieved. The baseplate 23 may be glued, bolted, attached with rivets or screws, or any other suitable fastening method to said construction 31.

The disc 26 is arranged to match up with the through openings in the construc- tion 31 and the through openings 28 in the base plate 23, such that said openings 28 are covered. This is done e.g., by passing the spring retainer 27 through an opening in the disc 26. The opening may be a through opening, as shown in Fig. 8. Then, the disc 26 is retained by a fastening means 32 such as e.g., a screw, or a rivet, pro- vided to interact with the spring retainer 27. ln another embodiment, the opening in the disc 26 is a blind opening designed to interact with the spring retainer 27 in a locking manner.

The sealing 25 is sandwiched between the base plate 23 and the disc 26. The sealing 25 may be attached to either the base plate 23 or the disc 26 by means of e.g., glue.

The base plate 23, spring 24, disc 26 and spring retainer 27 of the pressure relief valve 6 are made from a fire resistant or non-flammable material. This material may be e.g., metal, ceramics, composite, or a combination thereof.

The sealing 25 may be made of any suitable sealing material.

The pressure relief valve 6 is advantageously used in fire suppressing or fire ex- tinguishing applications, or other applications where the pressure relief valve 6 is ex- posed to high temperature gases or fluids. 11 The functionality of the pressure relief valve 6 will now be explained with refer- ence to Figs 9a-c. ln Fig. 9a, the pressure relief valve 6 is shown in a closed state. When the pres- sure increases on the inside of the construction 31 to be pressure relieved (to the left hand side in Fig. 9a), the pressure acts on the disc 26, which is retained by the spring 24. When the pressure exceeds a certain calibrated threshold level, the disc 26 is lifted from the base plate 23 such that a passage, indicated by arrows in Fig. 9b, is opened between the sealing 25 and the base plate 23. Fluid may pass through the passage and into an ambient volume, relieving the pressure on the inside of the construction 31.

When hot gases/fluids flow through the pressure relief valve 6, the sealing 25 may burn, if it is made of a material not resistant to the current temperature. The other parts of the pressure relief valve 6 however, are made of a fire resistant or non-flam- mable material and are thus not damaged by the temperature.

Thus, when the hot gases/fluids originating from inside the construction 31 to be pressure relieved have passed through the pressure relief valve 6 to such an extent that the pressure in the construction 31 has been lowered below the threshold value, the spring 24 returns the disc 26 towards the base plate 23, as shown in Fig. 9c. Since the sealing 25 may have been damaged or burnt away, the disc 26 will not close completely or tightly against the base plate 23. However, it will close the pas- sage enough to limit the flow to a leak.

This is especially advantageous when the construction 31 is associated with a fire extinguishing or fire suppressing apparatus utilizing an aerosol. When the pressure is built up in the construction 31 due to a fire or thermal runaway, the fire suppress- ing/extinguishing apparatus connected to the construction 31 will release aerosol particles. Once the pressure relief valve 6 opens, as described above, the aerosol will pass through the pressure relief valve 6 together with the hot gases/fluids to a certain extent. When the pressure relief valve 6 re-closes, the remaining aerosol par- ticles will remain inside the construction 31. Thus, if the fire re-ignites or recurs, or another fire starts in the construction 31, there are enough aerosol remaining in the construction 31 to extinguish or suppress that fire.

The various embodiments described above are provided by way of illustration only and should not be construed to limit the invention. For example, the principles herein may be applied to any suitable sensor of the fire suppressing apparatus. Those skilled in the art will readily recognize various modifications and changes that may be made to the present invention without following the example embodiments and applications illustrated and described herein, and without departing from the scope of the present disclosure.

The trigger mechanism may e.g., be a pin, as shown in Fig. 4. ln the shown em- bodiment, the pin 18 is configured to move to the left in Fig. 4, thereby triggering the 12 aerosol generator to release the aerosol. ln other embodiments, the pin 18 may be configured to be pulled out of the aerosol generator, thereby triggering the release of the aerosol.

Alternatively, and/or additionally, the trigger mechanism may be an electric trig- ger mechanism configured to heat a heat resistance in order to start the process of transforming the solid compound into gas, a heat trigger mechanism, or any other suitable trigger mechanism. ln the embodiment shown in Figs 1-4, the rod 15 is arranged perpendicular to the pin, but may in other embodiments be arranged parallel to the pin, as shown in Figs 10-11. ln yet another embodiment, not shown, the membrane is directly connected to the pin (or other trigger mechanism).

Claims (1)

1. CLAIMS A fire suppressing apparatus (1) for a battery unit, comprising: an aerosol generator (2) - a sensor (3) arranged to detect measurable Characteristics and/or effects resulting from battery thermal runaway and to trigger the aerosol genera- tor (2) when said characteristics and/or effects are detected. The fire suppressing apparatus (1) according to claim 1, wherein the sensor (3) is a mechanical pressure sensor. The fire suppressing apparatus (1) according to claim 2, wherein the sensor (3) is mechanically connected to the aerosol generator (2) for triggering the aerosol generator (2). The fire suppressing apparatus (1) according to claims 2 or 3, wherein the sensor (3) includes a membrane (4) configured to detect a pressure increase due to the thermal runaway. The fire suppressing apparatus (1) according to claim 4, wherein the mem- brane (4) is arranged in mechanical connection with a power transmission unit (15) connected to a trigger mechanism (18) of the aerosol generator (2), wherein the membrane (2) is configured to apply a force on the power trans- mission unit (15) in response to said pressure increase in order to trigger the aerosol generator (2) by means of the trigger mechanism (18). The fire suppressing apparatus (1) according to any one of claims 2-5, wherein the pressure sensor (3) is configured to trigger the aerosol genera- tor (2) at a detected differential pressure of approximately 0.2 - 0.8 bar, more preferred 0.4 - 0.6 bar and most preferred 0.5 bar compared to a reference pressure. The fire suppressing apparatus (1) according to any one of the preceding claims, wherein the aerosol generator (2) and the battery unit (5) share a common continuous volume (8) when the fire suppressing apparatus (1) is mounted to a battery unit (5). The fire suppressing apparatus (1) according to claim 7, wherein the battery unit (5) comprises at least one battery cell (10), wherein the membrane (4) isconfigured to deform in response to a pressure increase in the common con- tinuous volume (8) due to thermal runway of one of the at least one battery cell (10), and wherein the deformation of the membrane (8) is configured to apply a force on a power transmission unit (15) connected to a trigger mech- anism (18) of the aeroso| generator (2). The fire suppressing apparatus (1) according to c|aims 7 or 8, wherein the battery unit (5) comprises a housing (9), and wherein the fire suppressing ap- paratus (1) is mountable to an outer surface of the housing (9) or enc|osed within the housing (9) of the battery unit (5). The fire suppressing apparatus (1) according to any one of the preceding c|aims, wherein the aeroso| generator (2) comprises a solid compound, wherein the solid compound preferably is potassium nitrate. The fire suppressing apparatus (1) according to any one of the preceding c|aims, further comprising a pressure relief valve (6) configured to open and release gas from the common continuous volume (8) to an ambient (7) when pressure in the common continuous volume (8) exceeds a predetermined differential pressure threshold value. The fire suppressing apparatus (1) according to claim 11, wherein the pres- sure relief valve (6) is configured to open at a differential pressure compared to ambient being 0.1-0.5 bar above a threshold value for triggering the aero- so| generator (2). The fire suppressing apparatus (1) according to c|aims 11-12, wherein when the pressure relief valve (6) is open, the pressure relief valve (6) is config- ured to close when pressure in the common continuous volume (8) falls be- low a predetermined threshold value, which pressure difference preferably is approximately 0.2 - 0.8 bar, more preferred 0.4 - 0.6 bar and most preferred 0.5 bar compared to the ambient (7). The fire suppressing apparatus (1) according to c|aims 11-13, wherein the pressure relief valve (6) comprises a non-flammable material. A system comprising a fire suppressing apparatus (1) according to any one of the preceding c|aims and a battery unit (5), wherein the fire suppressing apparatus (1) is mounted to the battery unit (5) such that the aerosol genera- tor (2) and the battery unit (5) share a common continuous volume (8). A method for suppressing a fire in a battery unit (5) provided With a fire sup- pressing apparatus (1) according to any one of the c|aims 1-14, the method comprising the steps of - detecting measurable characteristics and/or effects resulting from battery therma| runaway; - triggering the aerosol generator (2). The method for suppressing a fire according to c|aim 16, wherein the step of detecting measurable characteristics and/or effects resulting from battery therma| runaway comprises detecting an increase in pressure due to the therma| runaway. The method for suppressing a fire according to c|aims 16-17, further com- prising a step of opening a pressure relief valve (6) when a pressure differ- ence between the common continuous volume (8) and the ambient volume (7) exceeds a predetermined threshold value, and a step of at least partially closing the opened pressure relief valve (6) when the pressure difference be- tween the common continuous volume and the ambient volume (7) is re- duced, preferably when the pressure difference is 0.2 - 0.8 bar, more pre- ferred 0.4 - 0.6 bar and most preferred 0.5 bar.