Field of Invention

The invention relates to a method of prevention of fire development of traction accumulator systems in electric cars and hybrid cars which is carried out for the purpose of the subsequent extinguishing without the risk of their secondary re-ignition and an apparatus for carrying out this method.

Background of the Invention

Currently, in the portfolios of leading world vehicle producers, there are one or more types of electric cam, i.e. cars with purely electric drive when the electric energy is supplied solely by their own accumulators recharged from distribution or other networks distributing the electric energy, wherein the number of such produced vehicles shows a continuously increasing trend for all these manufacturers. In general, an electric car is provided with a drive system consisting of one or more electric motors, a charging system, a regutation/regeneration system and a battery or an accumulator system consisting of a system with serial/parallel connections of other subaccumulators or directly individual cells. So-far, Ni-MH, Li-Po or similar cells are concerned. The whole accumulator system is provided with high-voltage collector clips with the total voltage which is nominal for the car concerned and supplies energy for the required performance of the electric car. The connection of the accumulator system is commonly performed in a closed box usually made of metal

A known and today still expanding issue with electric cars is their flaring-up with a possible fire. A fire of electric cars can occur e.g. due to an operating failure, which originates either during driving or in a stationary vehicle when the failure of electric or electronic circuits results in a short circuit in affected low-voltage or high-voltage circuits which are not fitted with safety elements, or safety elements are not present in circuits concerned, and the short-circuit current heats-up both the flammable cable insulation and the surrounding flammable materials up to the temperature of their ignition. This all happens in a short circuit created by an electric arc or the electric arc is formed on a transition resistor due to a failure within the operating current of the circuit concerned. Another reason for the occurrence of fire may also be, for example, an accident when the above described incendiary phenomenons occur due to a partial or complete destruction of the vehicle parts or its accumulator system, or arson, when the vehicle concerned is intentionally set on fire and the above described initiating sources occur due to the spread of fire to the electric circuits concerned. The tire can also occur during vehicle charging when high charging currents may not go through a proper charging cycle in all parts of the accumulator system, and when accumulation of flammable gases and vapours in the accumulator cell concerned which with its later explosion will cause ignition of the rest of the accumulator system of the vehicle may occur.

The fire brigades all over the world then uniformly state the impossibility of extinguishing such already burning electric cars since in case of a fire, it is a system in which transferring the capacity of the accumulator system to firefighting water (e.g. 600 Vss, 90 Kwh) presumably occurs which means that the fire brigade intervention using water or foam poses a life-threatening situation for intervening firemen or the person using a hydrant. Even after the possible initial extinguishing of flames, their new flaming almost always occurs with the continuing development, of hazardous combustion products and radiant heat, until the capacity of the accumulator ceil is not exhausted during the fire, which in practice can last approximately 30 minutes and more.

Other fire-extinguishing substances have various limitations, e.g. the extinguishing powder is not always available in the amount necessary, the portable Ore extinguishers are sufficient for fire extinguishing only in the initial stage of its free development, the use of the powder fire extinguisher from a powder vehicle is not only expensive but such intervention requires arrival of the powder tire engine to the fire scene which is not possible especially in row, collective or stacker garages. This also applies to inert gases where it is necessary to add that after the drop of the inert gas concentration, there is a directly proportional decrease in the extinguishing effect. Halon fire extinguishers are also unsuitable for extinguishing such fires with respect to their emerging negatively catalytic reaction.

One of the options is also transferring the burning electric car using a lifting technology into a container half filled with water and its complete submersion under the water level in the tank, which is not possible in e.g. closed garages, in tunnels or under bridges or high-voltage wires. At the same time, this extinguishing method requires a considerable water consumption since the water gets heated and evaporates, wherein also after the initial fire extinguishing, it must be observed for several days to check if it flare up again. A similar rather unrealistic possibility is represented by covering the burning vehicle by a large amount of sand or to locate it into a hermetically sealed container, and use water or inert gas for extinguishing.

From patent documents from this field, e.g. the solution according to US 2019/0118013 disclosing an outer vehicle cover which is pulled over the vehicle body in case of fire and is filled with water at least above the level of its batteries is known.

Other fire prevention measures for electric cars or hybrid cars are known from patent documents WO 2020/099397 or MS 2017/0135313 where extinguishing agents are integrated directly into sealed blocks where individual traction accumulator cells in the vehicle are located. The document EP 3569291 discloses a fire extinguishing system consisting of extinguishing agents in the form of sprinklers located close to accumulator cells which are connected to the fire extinguisher inlet. The document US 2920/0222735 discloses a system and a method for fire extinguishing of car accumulators preventing complete vehicle burning residing, in its first stage when the accumulator flares, in immediate injecting the cooling water on the accumulator using a water cooling system integrated in the vehicle, and if the tire is not extinguished in this early stage, in subsequent cooling by other cooling water supplied from the area outside the vehicle.

The document US 2022009519 discloses an electric car fire prevention system which comprises an accumulator status detector which detects the information about the accumulator status in order to monitor the accumulator fire in the vehicle as well as a controller which issues a control signal to remove the battery after detecting that an accumulator fire is about to break out and equipment for the accumulator removal in the vehicle configured to release the accumulator from the vehicle body in response to the control signal of the controller., in case a fire is detected, the prevention system will separate the accumulator from the vehicle which prevents fire spreading ail over the whole vehicle.

The task of the presented invention is ©specialty to enable more efficient fire extinguishing and shortening the intervention time to a common extinguishing time as in other vehicles with combustion engines without endangering the safety of the intervening firemen with respect to the high risk of electric shock during an acceptable time after the arrival of the fire brigade to the scene of an electric car fire.

This task is to a large extent resolved by the method of prevention of fire development of traction accumulator systems in electric cars and hybrid cars and the apparatus for carrying out this method.

The summary of the method according to this invention is In the fact that after the formation of fire, the area around the burning electric car is ventilated, as appropriate, and at least a partial fire smothering and the surroundings cooling is performed to enable the closer approach of the responding firefighters to the electric car. Then, the residual capacity of the traction accumulator system is removed as quick as possible and water is used for complete extinguishing of the electric car. The basic principle of the solution is electrical discharging of the traction accumulator system of the vehicle which prevents further action of the initiation source.

The ventilation of the area around a burning electric car is carried out especially during interventions in closed areas, e.g. garages, etc., and at least partial fire smothering and surroundings cooling is usually carried out by a fragmented stream of water. The complete extinguishing is carried out standardly by combat water jets or by means of a water-stable extinguishing device. The assumption of a successful performance of the whole intervention including the removal of the residual capacity from the traction accumulator system is that this intervention must be carried out by a fire brigade.

With respect to current highest-perfomnance electric cars, it is now fully sufficient to remove the residual capacity from the traction accumulator system with the speed of up to 3,240 kW/hours using the current with up to 900 A for max. 10 minutes. It can be assumed that with the further technology development in this field, the parameters of the electric discharging of the traction accumulator system can increase as well.

The summary of the apparatus for carrying out this method according to the invention then is in the fact that is comprises a resistive load with the input power of at least 540 kW with a discharging circuit adjusted for connection to the traction accumulator system of the electric car by means of connecting wires.

The summary of the apparatus according to the invention is further in the fact that the discharging circuit includes an external electric appliance with a resistance module and with its fan cooling, wherein it is further provided with a safety switch for starting the removal of the residual capacity from the traction accumulator system after its connection to the discharging circuit of the resistive load as well as an evaluative element with an indicator of the progress of the residual capacity decrease up to its zero value.

The fan cooling of the external electric appliance conducts away the heat which is formed by converting the electrical energy of the traction accumulator system to the ambient surrounding of the whole equipment. The heat gain in the closed area will thus be performed in a predictable location and space, wherein the temperature of this heat gain will not exceed the temperature of vehicle combustion products.

This equipment can be either mobile located on a chassis with its own drive unit or can be used otherwise, e.g. as stationary equipment of charging stations for electric cars.

Preferably, this equipment is provided with a reel for connecting wires. At the same time, it can be assumed that with the further development of electric cars and depending on e.g. the size of electric cars or hybrid cars, the apparatus for carrying out the method according to the invention or its resistive load with the discharging circuit of the traction accumulator system of the vehicle can be integrated directly into the structure of these vehicles, already during their manufacturing. In this case, if a fire originates, this equipment can be activated even before the arrival of the fire brigade either directly by the car driver in the car or automatically in case the driver is absent.

The summary of the electric car modification for carrying out the method according to the invention then lies in the fact that the electric car is provided with at least one connecting connector accessible from the exterior to remove the residual capacity from its traction accumulator system. Preferably, the electric car is provided with two connecting connectors out of which one is accessible from the front part of the electric car and the ether one from its rear part in case of fire. This is important for enabling the free access to at least one of these connecting wires especially in garages, depending on how the car is parked, or if its front or rear part is accessible.

Of course, it Is desirable, due to the number of different car manufacturers and the large number of already manufactured types of electric cars, that the connecting connectors were unified and enabled their easy connection to the equipment according to the invention.

Except for enabling a more efficient fire brigade intervention during fire extinguishing, shortening the intervention time to a common extinguishing time as for other vehicles, the advantage of the solution according to the invention is in achieving higher security, protection of health and lives of intervening firemen who are of course equipped with appropriate protective intervention clothes enabling a short-term approach to a burning vehicle, or an approach under the protective water curtain flow. Other advantages are represented by the high level of fire extinguishing, substantial decrease of water consumption and prevention of its possible contamination as well as the minimization of the damage to the environment by combustion emissions from the burning vehicle, Last but not least, the advantage of the solution according to the invention is in prevention of the complete burning of the vehicle and simultaneous significant decrease of insurance technical risks of insurance products in vehicle insurance in the area of liability for damages caused by fire as well as in the area of consequential damages and damages caused by interruption of operation.

The solution according to the invention is independent of any other electronics of the electric car itself since the electronics is potentially malfunctioning during fire extinguishing, and its safety lies in the fact that the equipment with the safety switch is connected to the circuit of the traction accumulator system at the time of their mutual Interconnection by connecting wires, i.e. after withdrawal of all intervening firemen from them burning electric car to a safe distance. Description of the Drawings

The invention is disclosed in more details by drawings of its exemplary embodiments, where

Fig. 1 - shows a schematic view of the equipment and its connection with the electric car;

Fig. 2 - shows the electric circuit diagram.

Exemplary Embodiments of the Invention When carrying out the method to prevent the fire development of traction accumulator systems of electric cars according to the invention as shown in the depicted exemplary embodiment after the fire occurrence and the arrival of the fire brigade, the residual capacity is removed from the outer area of the electric car 1 from its traction accumulator system 2 whereupon complete fire extinguishing Is carried out after the residual capacity decreases to the limit zero value. The removal of the residual capacity from this traction accumulator system 2 of the electric car 1 is carried out with the speed of 3,240 kW/hour by withdrawing the current with the amperage of 900 A for 10 minutes.

The apparatus for carrying out this method, as can be seen in Fig. 1, comprises a resistive load 10 with the input power of 600 kW with a discharging circuit 12 adjusted for connection to the traction accumulator system 2 of the electric car 1 by means of connecting wires 4.

The discharging circuit 12 of the resistive load 10 includes an external electric appliance 3 with a resistance module 6 and with its fan cooling 6a, and is further provided with a safety switch 7 for starting the removal of the residual capacity from the traction accumulator system 2 only after its safe connection to the discharging circuit 12 of the resistive load 10, as well as an evaluative element 9 of the progress of the residual capacity decrease up to its zero value, and an indicator 8 of this decrease. In this case for a better orientation of the intervening fireman, the indicator 8 is optical, consisting of three multi-colored LED diodes, wherein the lighting of the green LED diode means a capacity decrease of the traction accumulator system 2 to the zero value and the possibility to safely extinguish the vehicle.

The equipment in this exemplary embodiment is designed as mobile, transported to the fire scene in the intervening fire engine, wherein it is located on an unmarked chassis for its closer approach to the affected vehicle, and the chassis is provided with its own drive unit 11. consisting of a 5-kW combustion petrol engine and a reel 4a with connecting wires 4.

With respect to the electric car 1, this car is provided with an externally accessible connecting connector 5 located here in the rear part of the electric car 1 for connecting the connecting wires 4 to its traction accumulator system 2.

As can bee seen in Fig. 2, the resistance module 6 comprises a series/parallel connection of power resistors which gives the resulting resistance of 0.66 Ω, and the fan cooling 6a is provided with an unmarked voltage selector. Industrial Applicability

The invention is widely applicable not only in electric cars but generally in the fields of electrical engineering, electronics and energy, or photovolfeics, in relation with accumulator or battery systems and the issue of their power capacity in case of fire or in other emergency situations. Reference Signs List

1- electric car

2- traction accumulator system

3- external electric appliance

4- connection wires

4a- reel

5- connecting connector

6- resistance module

6a- fan cooling

7- safety switch

8- indicator

9- evaluative component

10- resistive load

11- drive unit

12- discharging circuit