DE102021001215A1 - Supplementary cooling device - Google Patents

Abstract

The invention relates to a device for additional cooling of a battery module (1) with at least one individual battery cell (2), with cooling via a cooling medium with an additional heat sink (5) and with a thermally acting switching element (7) which, depending on the temperature, produces thermally conductive contact between the battery module (1) and the heat sink (5), wherein the thermally acting switching element (7) comprises at least two materials (7.1, 7.2). The invention is characterized in that the first material (7.1) encloses at least one cavity, the second material (7.2) at least partially filling this at least one cavity or at least some of the cavities.

Description

The invention relates to a device for additional cooling of a battery module with at least one individual battery cell, with cooling via a cooling medium, and with an additional heat sink for additional cooling, according to the type defined in more detail in the preamble of claim 1.

The cooling of individual battery cells or individual battery cells combined to form battery modules is known from the prior art. Cooling via a cooling medium is often used, for example liquid cooling or cooling via the cooling medium of an air conditioning system. In this way, battery modules of this type, which can be designed, for example, as part of a traction battery in an at least partially electrically driven vehicle, can be cooled well during regular operation. In order to ensure adequate cooling of the battery modules even in situations that are difficult with regard to thermal management, provision can be made for the cooling via the cooling medium to be designed for the maximum cooling requirement. For most regular operating conditions, however, the structure of the cooling system is then oversized, so that this strategy ensures reliable operation, but this is associated with relatively high manufacturing costs and a high need for installation space and volume for correspondingly larger cooling lines, feed pumps and the like. In principle, this is undesirable since, particularly in vehicle applications, the cooling should be selected to be as simple, efficient, and cost-effective as possible and as small as possible in terms of weight and the required structural volume.

From the prior art in the form of DE 10 2015 014 034 A1 a battery module with a passive heat sink is known. This passive heat sink can consist, for example, of a material that acts reversibly or also irreversibly, which absorbs additional heat when required. Such a material can, for example, be a phase change material (PWM or in English phase change material PCM). Such a material can absorb a relatively large amount of heat during a phase transition, for example from solid to liquid. Alternative heat sinks could also be heat-conducting ribs surrounded by cooling air or the like. In principle, such materials can be used to increase the cooling capacity. In the case of the document mentioned, this is irreversible in order to intercept a thermal runaway of individual battery cells, but in principle phase change materials are reversible, so that it is also known that they can be used for additional cooling.

the U.S. 2005/0074666 A1 describes the use of a bimetal to additionally cool a battery that is only cooled by the air flowing around it from a certain ambient temperature, in that the bimetal deforms accordingly and a cooling element, for example a surface with cooling fins to improve heat dissipation to the ambient air, is in heat-conducting contact pivoted to the battery module. This structure, which can be interpreted as a thermal switch in the broadest sense, is typically implemented on the basis of bimetals. That's how it shows DE 10 2008 034 887 A1 such a thermal switch made of a bimetal. Here, too, if additional cooling is required, heat-conducting contact is established between a heat sink, here a heat dissipation element with cooling fins positioned on the outer surface of a vehicle, and the actual cooler of the battery module, through which a liquid cooling medium flows. Bimetal elements are also used for this purpose, which press a resilient heat transfer element against the liquid cooler of the battery module when the bimetal moves accordingly. The heat-conducting element connected to the cooling element as a heat sink in another area can then dissipate heat from the cooler in the direction of the cooling element. If the temperature changes accordingly, the element is lifted off the battery module's cooler again, so that it takes over the cooling alone.

In contrast to the US document mentioned, there is no disadvantage here that the entire flow of heat has to go through the bimetal itself. However, the heat-conducting element, which uses the bimetal to create thermal contact between the two parts of the cooling system if necessary, also has the disadvantage of a relatively small available cross-sectional area and a relatively small contact area, so that the cooling here is relatively inhomogeneous in individual areas of the battery module he follows. In addition, there is a risk of mechanical failure in the case of elements which are repeatedly bent in the direction of one or the other partner to be cooled, so that the structure as a whole is relatively unreliable over a long period of operation.

The object of the present invention is now to specify a device for additional cooling of a battery module, which can avoid the disadvantages mentioned at the outset.

According to the invention, this object is achieved by a device having the features in claim 1, here in particular in the characterizing part of claim 1. Advantageous refinements and developments of the invention direction arise from the dependent subclaims.

In the case of the device according to the invention, it is the case that it also uses a thermal switch or thermal switch which, comparable to a bimetal, comprises at least two materials. However, the structure of the device according to the invention is completely different from that when bimetals are used. In the device according to the invention, it is the case that the first material encloses at least one cavity, with the second material at least partially filling this at least one cavity or at least some of the cavities if there are accordingly several. This structure can, for example, be a cavity enclosed by the first material, which preferably has relatively good thermal conductivity. As an alternative to this, a large number of cavities would also be conceivable, for example in that this first material is designed as a porous material, for example in the form of a felt, a knitted fabric or, in particular, a porous sponge. The second material then at least partially fills the at least one cavity or at least some of the cavities. This second material then brings about the actual switching effect of the thermal switch because, like virtually all materials, it expands when heated and contracts when cooled. The battery module itself can now be regularly cooled by means of a cooling medium via a comparatively small cooling system. If a particularly high cooling requirement arises, for example because a vehicle is being driven uphill at high outside temperatures and a correspondingly large amount of electrical power is required, then this cooling system, which is not designed for the maximum cooling capacity, is typically unable to cope with this on its own and the resulting waste heat cannot be sufficiently dissipated. In this situation, an additional heat sink is now used, which is brought into thermally conductive contact with the battery module via the thermal switch in order to absorb additional heat in the area of the heat sink. The heat sink itself can be designed in any way, for example as a passive heat sink, as an additional cooling element for dissipating heat into the environment, or the like. The thermal switch in the embodiment according to the invention now brings this additional heat sink into thermally conductive contact with the battery module. Part of the waste heat from the battery can be dissipated via the heat sink, ideally so much waste heat that the rest can be dissipated via the cooling system, which is designed for a typical operating point. With a simple, compact and cost-effective design, the battery module can be ideally cooled even in situations with a high cooling capacity requirement, despite the comparatively small cooling system.

According to a very favorable embodiment, as has already been explained above, the at least one cavity can be formed as part of a porous material. According to a very advantageous further development of this idea, the first material can be designed in particular as a metal foam. The second material is then introduced into at least some of the interconnected cavities of this metal foam and at least partially fills them. If there is a warming in an area where the dissipation of the waste heat produced by the conventional cooling system is no longer guaranteed, then there is a corresponding thermal expansion of the second material, just like in principle the first material. According to a very advantageous development of the device according to the invention, a suitable selection of the second material can be used to ensure that it expands relatively strongly when heated, for example by a phase transition from the solid to the liquid phase at a temperature critical for the dissipation of waste heat in the order of 40 to 70°C. In this case, due to the expansion of the second material at this corresponding limit temperature, existing cavities are filled and, if necessary, further cavities are flooded, in particular when the first material is designed as a porous metal foam. As a result, this will expand overall and can thus establish the thermally conductive contact between the battery module on the one hand and the heat sink on the other.

An extraordinarily favorable further development of this idea of the invention provides that the second material has or is a paraffin. Paraffins typically have a relatively strong expansion when melting, so that the volume increases by 10%, for example, which leads to a considerable expansion of the second material and thus ultimately also to a thermally induced expansion of the entire structure of the thermal switch caused thereby. This can be brought from a point-and-point contact on one of the elements, i.e. the heat sink or the battery module, through the expansion into a largely flat contact, which improves the heat conduction within the thermal switch and thus for heat transfer from the battery module to the heat sink cares. As a result, excess waste heat that cannot be dissipated by the regular cooling system in operating situations that are critical with regard to heat management and possibly also when a thermal Runaway to be absorbed by the heat sink.

The use of paraffin as the second material mentioned according to a very advantageous development also has the advantage that the paraffin itself can absorb a relatively large amount of heat during the phase change from solid to liquid without the temperature increasing. In addition to the effect of activating the thermal switch by melting the paraffin, there is also heat absorption in the paraffin itself, which, in addition to the actual additional heat sink, then serves as a phase change material as a further heat sink within the thermal switch and already here a part of the can absorb waste heat.

According to a very favorable embodiment, the entire thermal switch can be provided with a casing in order to prevent the second material that becomes liquid from flowing out, for example. In particular, the casing can be made of a material that conducts heat relatively well, in order not to negatively influence the heat transfer through the thermal switch from the battery module to the heat sink.

An alternative configuration of the device can also provide for the at least one cavity to be formed solely by a cover. Such a shell, which according to an advantageous development has in particular high thermal conductivity, can therefore enclose the second material. For example, the shell can be made of a metal, for example a metal foil. The second material located therein, for example paraffin as above, is then arranged in its solid form inside the shell, so that the shell does not touch at least the battery module or the heat sink, or at least not over the entire surface. If it then heats up to the area in which the paraffin melts, and this can be largely freely adjusted by mixing the paraffin in the order of magnitude of 40 to 70°C relevant for battery modules, then the paraffin melts and increases in size volume by about 10%. This leads to an expansion within the shell, which can be designed to be correspondingly elastic or which can have folds, which smooth out accordingly when the second material melts and expands, in order to ensure full-surface contact with the battery module on the one hand and on the heat sink on the other to guarantee. The material of the shell then transfers most of the heat. Some of the heat can in turn pass through the second material, which typically has a lower thermal conductivity than the first material. Here too, when paraffin is used, which is purely exemplary, the benefit of absorbing heat through the phase change of the paraffin can also be utilized.

According to an extraordinarily favorable embodiment of the device according to the invention in one or the other of the described embodiment variants, provision can be made for the thermal switch to be connected to the battery module. This connection to the battery module, which ensures a good thermally conductive connection thereto, enables the thermal switch to react to the temperature of the battery module. Due to the non-existent or only poor heat conduction in the direction of the heat sink, the activation of the thermal switch, largely determined solely by the temperature of the battery, can be activated if necessary, i.e. if more heat is generated in the area of the battery module than can be dissipated by conventional cooling, take place.

According to a very favorable development of the idea, it is provided that a gap is formed between the thermal switch and the heat sink in the non-activated state of the thermal switch, or that only a few punctiform and/or linear contact surfaces occur between the thermal switch and the heat sink . In the activated state, there is then a corresponding expansion of the materials, which is in particular dominated by the expansion of the second material, so that there is full-area or at least large-area contact of the thermal switch with the heat sink. If this is implemented in combination with the thermal switch that is already connected to the battery module over a large area, good contact can be achieved via the thermal switch between the battery module and the heat sink at the limit temperature above which the second material achieves sufficient thermal expansion, so that good additional cooling of the battery module is made possible.

In principle, the device is suitable for all types of battery modules. In particular, however, it is advantageous when the battery module is subjected to a correspondingly high dynamic load and a correspondingly different load depending on the situation. Especially with such structures, it is advantageous if the regular cooling system does not have to be designed for the conceivable maximum load, but if it is designed for a typically occurring load, and potential peaks above this typical load of the cooling system are then intercepted by means of the device according to the invention can become. The structure of the device itself should preferably be designed to be reversible, since its primary goal is not to cushion thermal runaways, but to actively cool the battery module during load or waste heat peaks.

Such a dynamic load combined with strict specifications for the cooling system in terms of costs, weight and construction volume now occur in particular in vehicles in which the battery module serves as a traction battery or forms part of one. The preferred use of the device is therefore in the area of vehicles that are at least partially electrically driven via one or more battery modules. This can be, for example, a purely electric vehicle or a hybrid vehicle, for example with an internal combustion engine or a fuel cell system as an additional energy unit.

Advantageous refinements and developments of the device according to the invention and its use also result from the exemplary embodiments, which are presented in more detail below with reference to the figures.

• 1 eine schematische Schnittdarstellung eines Batteriemoduls mit der erfindungsgemäßen Vorrichtung in einer ersten Ausführungsform im kalten Zustand des Thermoschalters;
• 2 die Darstellung des Batteriemoduls mit der Vorrichtung analog zu der in 1 im warmem Zustand des Thermoschalters;
• 3 eine schematische Schnittdarstellung eines Batteriemoduls mit der erfindungsgemäßen Vorrichtung in einer zweiten Ausführungsform im kalten Zustand des Thermoschalters; und
• 4 die Darstellung des Batteriemoduls mit der Vorrichtung analog zu der in 3 im warmem Zustand des Thermoschalters.

show:

• 1 a schematic sectional view of a battery module with the device according to the invention in a first embodiment in the cold state of the thermal switch;
• 2 the representation of the battery module with the device analogous to that in 1 in the warm state of the thermal switch;
• 3 a schematic sectional view of a battery module with the device according to the invention in a second embodiment in the cold state of the thermal switch; and
• 4 the representation of the battery module with the device analogous to that in 3 when the thermal switch is warm.

In the representation of 1 a battery module 1 with schematic battery cells 2 is shown within a housing 3 in a schematic diagram. The individual battery cells 2 of the battery module 1 are regularly cooled via a heat exchanger labeled 4 . In the representation of 1 A heat sink 5 is located in the housing 3 below the battery module 1 and has optional temperature control connections 6 . This heat sink 5 can contain a phase change material, for example, and/or can have a cooling element that is cooled via a further cooling circuit or, in the case of vehicle use, via the ambient air, for example.

In regular operation, the battery module 1 is cooled via the heat exchanger 4, through which, for example, a cooling liquid or the refrigerant of an air conditioning system flows as a cooling medium. In most typically occurring situations, this heat exchanger 4 is sufficient to dissipate the waste heat generated in the battery module 1 . The cooling system, which is not shown here in its entirety and of which the heat exchanger 4 forms a part, can be optimized for the cooling performance that typically occurs during normal operation. If higher cooling requirements occur, for example because more waste heat is produced due to higher power consumption from the battery module 1, then the additional heat sink 5 can be switched on to dissipate the waste heat produced with the heat exchanger 4 above the capacity of the cooling system.

For this purpose, a thermal switch 7, which can also be referred to as a thermal switch, is installed between the heat sink 5 and the battery module 1. This thermal switch 7 essentially consists of a first material 7.1 and a second material 7.2. The first material 7.1 is shown as a carrier structure, for example, which consists of a metallic foam. Such a metallic foam with an open portion, i.e. essentially a pore portion of 10% of its volume, is represented here by a honeycomb structure in the illustration 1 implied. The free space of this support structure is partially impregnated with a second material 7.2, which is indicated here by irregular cross-hatching. This material can be paraffin, for example. The bearing surface on the heat sink can be structured somewhat, for example, with a rough wave shape or the like, in order to ensure that the structure on the battery module is in good thermally conductive contact on the one hand and accordingly not on the heat sink 5 or only in points or lines, in order to in this area to reduce the heat transfer between the thermal switch 7 and the heat sink 5 accordingly.

The metal foam as the first material 7.1 has a thermal conductivity which is reduced by a factor of approximately 100 compared to a full-volume metal body. For example, instead of 200 W/mK for solid metal, the thermal conductivity is only around 2 W/mK. This is basically comparable to the thermal conductivity of thermally conductive pastes or thermally conductive epoxy resins, which are used as potting materials in batteries, for example to connect a heat exchanger. These have thermal conductivity values in the order of approx. 1 to 3 W/mK. The second material 7.2, which is in the metallic foam of the first material 7.1 is stored, is there in the solid state. If the paraffin melts, it changes its volume by about 10%, ie the volume increases by 10%. As a result, previously unfilled pores in the metal foam of the first material 7.1 are flooded by the second material 7.2 and there is an overall change in the volume of the thermal switch 7, which is thus pressed between the battery module 1 and the heat sink 5 if the design is appropriate, as is shown in FIG presentation of the 2 can be seen. There is now a largely complete connection both to the battery module 1 and to the heat sink 5. The melting temperature of the paraffin can be set in a range of approx the thermal switch 7 in this structure can be switched on at a sensible temperature of, for example, 65° C. for additional dissipation of waste heat produced in the battery module 1 .

The thermal switch 7 is as shown in the illustration 1 can be seen, connected as flatly as possible to the battery module 1 or in principle also to its heat exchanger 4, which would also be conceivable. As a result, the control temperature for melting the second material 7.2, i.e. the paraffin, is the temperature of the battery module 1. As soon as this reaches the limit temperature mentioned, because the conventional cooling system in the heat exchanger 4 can no longer completely dissipate the waste heat produced, the paraffin melts , the composite of paraffin and metal foam of the thermal switch 7 increases its volume and there is a firm contact with the heat sink 5. As a result, heat is now dissipated in the area of the heat sink. In addition to the thermal conductivity of the metal foam, the additional thermal conductivity of the paraffin also comes into play. Although this is relatively low at approx. 0.26 W/mK, it does have a certain effect on improving the heat conduction of the structure.

In addition, the paraffin also acts as a phase change material, since a heat of fusion of the order of 200 to 240 kJ/kg is required to melt the paraffin. Part of the heat, which is generated as additional waste heat in the area of the battery 1, is thus also absorbed in this way by the second material 7.2 of the thermal switch 7 itself and withdrawn from the individual battery cells 2 of the battery module 1. The second material 7.2 also contributes to the cooling of the battery module 1.

The process is reversible. If the temperature of the battery module 1 falls below the melting point again, the paraffin gradually solidifies. This changes its volume again and the composite of the open-pored metal foam as the first material 7.1 with its cavities filled by the paraffin as the second material 7.2 shrinks overall and the in 1 The non-active state of thermal switch 1 shown, i.e. its “cold” state, is restored.

Analogous to the representation in the 1 and 2 is in the 3 and 4 an alternative structure of the thermal switch 7 is shown with components provided with comparable reference numbers. The cavity is not formed here in the form of many cavities within a metal foam as the first material 7.1, but the first material 7.1 here consists of a shell, for example in the form of a thicker metal foil. The shell as the first material 7.1 of the thermal switch 7 is filled with the second material 7.2, for example again a paraffin, as indicated here by the cross-hatching. The process is essentially the same as that already described above.

In the representation of 3 the thermal switch 7 rests flat on the battery module 1 and is largely objected to by the heat sink 5 or has only a punctiform or linear contact with it in a few areas. With a heating above the melting point of the paraffin as the second material 7.2 of the thermal switch 7, this expands and ensures the in 4 State shown, in which the thermal switch 7 is "warm" and thus activated. The cover made of the first material 7.1 is firmly attached to both the battery module 1 and the heat sink 5 and thus ensures good heat conduction from the battery module 1 to the heat sink 5 through the material of the cover from the first material 7.1 almost completely filling the second material 7.2 passed from the battery module 1 to the heat sink 5. In this way, an effect comparable to that of the variant of the thermal switch 7 described above can be achieved.

Here, too, if paraffin is used as the second material 7.2, for example, the heat of fusion, which is necessary to convert the paraffin from the solid to the liquid state, can be used to absorb heat directly in the thermal switch 7 or to store it temporarily. by using the physical properties of the phase transition in a manner known per se.

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• DE 102015014034 A1 [0003]
• US 2005/0074666 A1 [0004]
• DE 102008034887 A1 [0004]

Claims (10)

Device for additional cooling of a battery module (1) with at least one individual battery cell (2), with cooling via a cooling medium with an additional heat sink (5) and with a thermally acting switching element (7) which, depending on the temperature, creates a thermally conductive contact between the Battery module (1) and the heat sink (5), wherein the thermally acting switching element (7) comprises at least two materials (7.1, 7.2), characterized in that the first material (7.1) encloses at least one cavity, the second material ( 7.2) at least partially fills this at least one cavity or at least some of the cavities. device after claim 1 , characterized in that the at least one cavity is formed as part of a porous first material (7.1). device after claim 2 , characterized in that the porous material is designed as an open-pored metal foam. device after claim 1 , 2 or 3 , characterized in that the second material (7.2) increases in volume with increasing heating. Device according to one of Claims 1 until 4 , characterized in that the second material (7.2) comprises paraffin. Device according to one of Claims 1 until 5 , characterized in that the thermal switching element (7) has a sheath. Device according to one of Claims 1 or 4 until 6 , characterized in that the at least one cavity is formed by a shell made of the first material (7.1). device after claim 7 , characterized in that the shell has a higher thermal conductivity than the second material (7.2). Device according to one of Claims 1 until 8th , characterized in that the thermally acting switching element (7) is connected to the battery module (1) in a thermally conductive manner. Device according to one of Claims 1 until 9 , characterized in that the thermally active switch (7) in the non-activated state has a gap or a few punctiform and/or linear contact points between itself and the heat sink (5), the thermally active switching element (7) in the activated state having a full-surface or has large-scale contact with the heat sink (5).

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