Power train battery assembly of an electric, fuel-cell or hybrid vehicle

A power train battery assembly of an electric, fuel-cell or hybrid vehicle, said assembly having a plurality of battery cells (16), each encased in an individual and externally-closed cell housing (18), that are combined into a cell stack and moreover having at least one pipe (36) conducting cooling fluid for the removal of heat energy from the battery cells (16). At least one heat-conducting fin (42) that originates from the pipe (36) flatly abuts, at least in sections, at least one cell housing (18).

RELATED APPLICATIONS

This application claims priority to and all the advantages of German Patent Application No. DE 10 2007 021 309.5, filed on May 7, 2007.

The invention relates to a power train battery assembly of an electric, fuel-cell or hybrid vehicle, said assembly having a plurality of battery cells, each encased in an externally-closed cell housing, that are combined into a cell stack and moreover having at least one pipe conducting cooling fluid for the removal of heat energy from the battery cells.

Because pure internal combustion engines adversely affect the environment owing to CO2pollution, electric power trains for vehicles transporting passengers or goods are being increasingly developed and are at least partially replacing internal combustion engines. The present invention concerns such power train battery assemblies for electric, fuel-cell or hybrid vehicles. In such power train battery assemblies, prefabricated, externally-closed battery cells are joined with a high-voltage battery (customary voltages of 130 volts for the so-called “mild” hybrids and 360 volts for a “full” hybrid) and combined in a joint outer housing. The battery cells are manufactured separately from each other, each possess an individual metal outer housing whose exterior is coated in plastic to ensure electrical insulation. The battery cells are conventionally NiMh- or Li-ion battery cells that generate heat during the charging and discharging process. However, these battery cells should not exceed their maximal cell temperature of 55° C. to 80° C. which could limit the lifetime of the battery. An inhomogeneous temperature distribution between the cells can also reduce battery cell life and thus the life of the entire assembly. It is therefore important to ensure that the temperatures between the cells does not differ by more than ±2 to 5 K, preferably by only ±2 to 3 K. Since the cells are electrically connected in series, one defective cell can lead to the complete failure of the entire battery assembly. Considerations have already been made regarding how to maintain the battery assembly at a constant temperature by means of an active fluid cooling system. Examples of this are DE 195 36 115 A1, whose subject matter is a heat exchanger designed in the form of a plate stack; JP 2006 185 788 A2, which shows a very complicated air-cooling system having controlled air-flow diversion vanes; and JP 30 93 172 A2, which envisions a plurality of heat exchangers between individual cells that nevertheless could lead to space concerns.

The invention presents a simple, space-saving, actively-cooled power train battery assembly that can be manufactured at a reasonable cost. The invention guarantees a battery-assembly life span of ten years or more.

The invention furthermore is intended to ensure that the energy amounts, which accumulate to some extent, are to be carried away, and range from 300 to 1,500 watts, are effectively removed without the volume of the power train battery assembly being thereby increased.

This is achieved in the power train battery assembly of the initially-mentioned type by means of at least one heat-conducting fin originating from the pipe that at least in portions lies flat against at least one cell housing. The invention moreover describes thin fins that originate from the pipe and that provide a solid thermal bridge between the individual battery cells and the one pipe or plurality thereof. Such fins are very thin and therefore conserve space, permit a rapid heat transfer, and are easy to manufacture. Moreover, because the fins have a minimal wall thickness, they can easily be adjusted to the external geometry of the cell housing in such a manner that they are extensively flatly applied there against.

The fin is thus at least in portions brought into line with the outer housing of the battery cell in order to rapidly transport heat away therefrom and toward the pipe.

An additional advantage of the invention is that without altering the concept, the assembly can operate with different cooling media. For example, a water/glycol mixture, R134a, CO2or another cooling agent can be used. The weight of the power train battery assembly according to the invention is less than that disclosed in the prior art in which, inter alia, numerous heat exchangers are embedded in the battery assembly. The fins can also be conducted around the individual cells ensuring heat transfer from locations difficult to access and having space issues. There is also a plurality of possibilities for guiding the arrangement of the pipe through the assembly. The pipe sections or the plurality of pipe lines need not be arranged immediately next to the individual battery cells to ensure a uniform heat distribution across the battery pack.

With regard to piping, metal pipes having a thermal conductivity of >40 W/m/K, aluminum pipes in particular, are customarily used.

The pipes customarily have an outer diameter of only 4 to 10 mm.

The pipe wall thickness is customarily between 0.3 and 2 mm. As mentioned, it is of course possible to provide a plurality of pipes that can be connected in series or parallel. The pipes can be connected to an inlet collector and an outlet collector from which the pipes originate or into which they lead.

As fins, thin sheet metals, in particular composed of aluminum, copper or another very heat-conductive material, are used that, according to the preferred embodiment, exhibit a thermal conductivity of 60 W/m/K to 400 W/m/K.

The thickness of the fins is between 0.1 and 2.5 mm, preferably between 0.5 and 1.5 mm.

As has been determined, the optimal inner diameter of the pipes is between 3 to 6 mm with a wall thickness of 0.3 to 1 mm when water or R134 is used as a cooling agent, and 1.5 to 4 mm with a wall thickness of 1 to 2 mm when CO2is used as a cooling agent.

Customarily, a plurality of fins are provided on one pipe, said fins being distributed about the circumference of the pipe and partially enclosing one or more battery cells in order to cool them. Up to ten battery cells are sufficiently cooled by means of one pipe, and one fin is assigned to up to three battery cells.

It is possible for one fin to originate from a plurality of pipes, that is, for example, with its two opposing edges being attached to different pipes.

According to the preferred embodiment, the fin presses against the cell housing. It should therefore be impossible for an air gap to form between the fin and the outer housing and the heat exchange to be reduced. An additional advantage of the prestressing consists in making it possible to collect the allowable variations of the outer housing of the battery cells. The outer housings do not all have technically the exact same outer diameter but rather variations within a tolerance that is captured by a precise prestressing of the fins. To this end, the position and geometry of the fin is coordinated to the minutest dimensions of a battery cell. This ensures that even in the instance of a battery cell on the lower limit of the allowable variation, the fin is always securely applied against the cell housing.

In this connection, it is advantageous if the fin hugs the shape of at least one cell housing by means of a press fit on the outer diameter of said cell housing, that is to say it substantially adopts the shape of the outer housing. The thin-walled fin is also particularly suited for this purpose.

Should the fin run so extensively around the battery cell so as to be fixed thereto in a self-locking manner, a form-fitting positioning of the fin to the associated battery cell or cells is possible without additional means.

The heat exchange between the fin and the pipe is also important. The solution provides for the fin to enclose or encompass the pipe in sections in order for an extensive heat exchange to be possible at that location.

The fastening of the fin to the pipe can be effected by means of adhesive bonding, welding, soldering or a mechanical fastening means, the fin preferably being affixed directly to the pipe to create immediate heat exchange.

Similar to the battery cell, in order for the fin to be fastened to the pipe, it can encompass the pipe partially by forming a press fit or it can completely encompass the pipe.

The battery cells are customarily elongate bodies, in particular cylindrical bodies such as circularly cylindrical bodies or a rectangular parallelepiped, that is to say bodies with a longitudinal axis. From the perspective from the direction of the longitudinal axis, the fin should contact more than 90° of the circumference when abutting the battery housing in order to ensure a sufficiently large heat-exchange surface.

At least 40% of the surface of the outer circumference of the cell housing should abut the fin, as is provided for in the embodiment.

The battery cell or cells can be clamped between a plurality of fins that engage opposed sections of the outer circumference of the cell housing, said fins also possibly being allocated to a plurality of pipes or pipe sections. The previously mentioned complete contact surfaces can accordingly be made up of a plurality of individual contact surfaces of different fins on the same battery cell.

In precisely the design of the cell housing having a cylindrical or circular cylindrical form, the fins can be fitted in a space-saving manner if they extend through the cell stack in a concertina arrangement or, in rectangular parallelepiped cell housings in a crenellation arrangement on cells in differing rows.

It is advantageous if fin sections or fins of adjacent cells do not come into contact with each other in order to provide the fins with sufficient latitude as this is important to the tolerance compensation.

The invention moreover develops a battery assembly with a plurality of battery cells, of which each is externally closed by its own cell housing, as well as at least one pipe which conducts cooling fluid and is laterally flattened in the region of an adjacent cell. This makes it possible to place the pipe in the space between the adjacent battery cells without cross-sectional restrictions, while flattening critical installation-space regions in order to reduce the overall dimensions of the power train battery assembly.

The pipe is preferably provided upstream and downstream of the flattened regions and has a circularly cylindrical cross section.

As already mentioned, the pipe runs especially in concertina or crenellation arrangement through the cell stack. For this purpose, the pipe has at least one section that runs alongside the longitudinal axis of the cells and at least one section that runs transversely to the longitudinal axis of the cells, the transversely-running section preferably comprising the partially flattened section.

In circularly cylindrical cell housings, the pipe extends at least partially into the envelopes of adjacent cells, the flattened and transversely-running section being positioned outside the envelopes. The envelope is a theoretically geometrical structure that is wrapped around the cell stack like tightly stretched fabric.

The area of the pipe to which the cells are attached can be located on the outer edge of the cell stack or within the cell stack in the empty space between the adjacent battery cells. The arrangement outside the pipe is advantageous because it permits simple installation of the cells, pipes, and fins. The arrangement inside the cell stack results in shorter heat-exchange pathways making it possible for interior cells to also be cooled quickly.

The pipe should extend alternately upwards and downwards in the longitudinal direction of the cells, and thus provide more sections running lengthwise on which the fins can be arranged.

Since there are different distances between the battery cells and the allocated pipe section on which the fin of the battery cell is attached, the cells are cooled at different intensities. The fins positioned farther from the pipe are at a disadvantage in this instance because the difference in temperature between the adjacent fin portion and the outer side of the cell housing is less than with the battery cells whose fins or fin sections are positioned closer to the cooled pipe. However, since a minimal temperature difference between the battery cells during charging and discharging is, as previously mentioned, vital to the life span of the batteries, the invention provides for those battery cells that are more distant from the allocated pipe or pipes to contact the fin or fins by means of a greater contact surface, that is to say a greater heat-exchange surface is provided than is found with battery cells arranged more closely to the allocated pipe.

The differing contact surfaces can, for example, be realized in that the fins or the fin sections for the more-closely-positioned battery cells have at least one recess or depression by means of which the contact surface is decreased.

A particular difficulty results with the use of so-called zeotropic coolants. They are mixtures of different liquids with different saturation temperatures. When boiling or vaporizing, the composition of the liquid changes resulting in a change the total saturation temperature of the remaining liquid.

The present invention also makes it possible for zeotropic coolants to be used to cool power train batteries. As previously mentioned, all batteries used to have to be kept at the same temperature if at all possible. The use of a zeotropic coolant runs counter to this aim since the coolant changes its saturation temperature while traveling through the battery assembly and therefore exhibits an increasingly diminished cooling effect.

For this purpose, the invention provides for a power train battery assembly having a plurality of battery cells, each encased in an externally-closed cell housing, that are combined into a cell stack and moreover having at least one pipe conducting a zeotropic coolant for the removal of heat energy from the battery cells. The pipe section positioned within the battery assembly is designed so that the coolant undergoes a decrease in pressure in such a manner that the saturation temperature of the coolant in the pipe section substantially remains constant. The invention compensates for the temperature change in saturation temperature arising for and because of itself by a purposive pressure reduction within the pipe section.

Slight fluctuations of temperature of ±1 K are tolerable and within the range of production fluctuations.

According to the preferred embodiment, the conceived decrease in pressure lies within the range of 0.25 to 0.75 bar.

Possible methods for obtaining a decrease in pressure are, for example, a narrowing, in particular a continuous narrowing, of the cross section of the pipe up to the outlet by means of a reduction of diameter or a flattening of the pipe, for example. In pipe sections connected in series, the number of pipe sections can also achieve a decrease in pressure.

Another solution the invention provides for the use of zeotropic coolants is the use of a plurality of pipe sections conducting a zeotropic coolant within the battery that are in direct thermal contact and are flowed through in a counter-current manner. The temperatures in the pipe sections average themselves out through the counter-current flow in such a manner that a uniform cooling effect is achieved overall.

The pipe sections should preferably run parallel to each other within the battery and should be arranged as close as possible to each other.

A particularly effective temperature compensation results when one or more fins issue from both pipe sections together since it is in the fins themselves that the temperature becomes more uniform.

FIG. 1shows a power train battery assembly of an electric, fuel-cell or hybrid vehicle that is equipped with an active cooling. The outer housing10consists of a basin-shaped base body open on one side and a cover that closes base body12, both base body and cover being manufactured of plastic (PP, PA, PPS or PPA) by means of injection molding. Numerous battery cells16are housed in the outer housing10and are connected in series in such a manner that a high-voltage battery, more precisely a high-voltage storage battery, is created. The individual battery cells16are NiMH- or Li-ion batteries and are self-contained units that are externally closed by an individual cell housing18. The battery cells are either grouped into a pack in the outer housing10prior to assembly or become a pack only upon insertion into the outer housing10.

The battery cells16become positioned in the outer housing by means of the outer housing10having interior, integrally formed positioning projections20. The cells16have a cylindrical, in particular a circularly cylindrical, external geometry, it being noted that the positioning projections20project into the spaces between adjacent battery cells16as is shown inFIGS. 1 to 3. The battery cells16are positioned precisely above the positioning projections, which are preferably primarily integrally formed on the floor22and on the lid14, in all directions, that is to say in the direction of the longitudinal axis A of the battery cells16and in a radial direction. To achieve this positioning, the positioning projections20engage the end faces24of the battery cells16and the axial edges of the peripheral faces26. The engagement surface is very minimal in its entirety, with the positioning projections20extending only 2 to 20% in the longitudinal direction beyond the entire length of the associated battery cell16adjacent thereto. The corresponding length L in the axial direction is represented inFIGS. 2 and 3.

The battery cells16have tolerance with respect to the cell housing18that should not be disregarded. To ensure that the battery cells16are stably fastening in the outer housing10without free travel, the positioning projections20have sections of differing elasticity. This is shown, for example, inFIG. 2. A first section28projects until under the end face24and consists of the same material as the portion visible from the outside of the outer housing10. This first section28is relatively hard and stabile and has a receptacle for a cross-sectionally T-shaped second section30composed of a rubber-like plastic of minimal elasticity that then abuts the end faces24and the peripheral faces26of the cell housing18. Given that the second section30is very soft, it contributes to a prestressed, tolerance-equalizing mounting of the battery cells16. The manufacture of the outer housing10with the sections28,30having differing degrees of hardness or differing degrees of elasticity is the result of the so-called two-component injection molding method. For ease of inserting batteries individually or inserting them between a plurality of positioning projections20, said positioning projections have insertion chamfers that are recognizable inFIG. 3.

FIG. 5shows that the positioning projections20in part completely encompass the battery cells on the peripheral edges. However, for lateral securing, the peripheries should provide for at least a three-point mounting. In the alternative shown inFIG. 5, the softer, second section30runs closed around the adjacent battery cells16. Additional positioning projections20in the form of ribs or star-shaped ridges laterally hold the battery cells16from the outside. The outer battery cells in particular abut the rib-shaped positioning projections20. Star-shaped positioning projections project into the space between adjacent battery cells in such a manner that one positioning projection20contributes to holding a plurality of battery cells16. The positioning projections represented inFIG. 5in rib- or star-shaped form extend in part over the axial edge of the peripheral faces26into the middle sections of the peripheral faces26or even extend from the floor22to near the lid14or, conversely, from the base of the lid14to near the base body12. In oversized battery cells16, the positioning projections20deform as well as the cell housings18if need be.

It can also be seen inFIG. 3that ribs32in the region of the floor22are integrally formed and thus are intended to increase the stability of the outer housing10. A thermal insulating layer34can be applied, through two-component injection molding or through foaming, between the ribs22or, very generally, in certain sections of the outer housing10.

As previously mentioned, the battery assembly according to the invention possesses an active cooling device, more precisely a cooling circuit. The cooling device consists of one or more pipes36that conduct cooling fluid, extend through the outer housing10, and are connected to a coolant circuit or refrigerant circuit outside the outer housing10. The cooling fluid can be a water/glycol mixture, R-134a, CO2or an alternative coolant that passes through the cooling circuit in the corresponding phase stage. The pipe or pipes36do not run linearly through the outer housing10, bur rather in concertina arrangement or in the broadest sense in crenellation arrangement. This means that the pipe36has sections38running longitudinally to the cell longitudinal axis A (seeFIG. 1) and sections40running transversely thereto. This course is intended to maximize the pipe length running inside the outer housing10.

Numerous, thin fins42are fastened to pipe36. The fins42, which have a wall thickness of only 0.1 to 2.5 mm, preferably 0.5 to 1.5 mm and consist of aluminum, copper or corresponding materials exhibiting high thermal conductivity, conform to the outer shape of the cell housing18and lie flat and abut by means of a press fit the peripheral faces26, that is to say they “hug” said faces. In the manufacture of the fins42, consideration is given to the fact that their position and geometry are coordinated with battery cells16having outer dimensions of the lower limit. This ensures that the fins42can always conform to the allocated battery cell16and flatly abut it in a prestressed manner if the cell16is slid into the corresponding receiving chamber defined by the fin42or the plurality of fins42. The numerous fins are directly affixed to a pipe36in order to ensure a favorable heat exchange. The corresponding fins are affixed to their pipe section through adhesive bonding, welding, soldering or a mechanical fastening means. It can be seen inFIGS. 4 and 5that fins42in the area of the pipe36are shaped into half shells46that abut opposite ends of the pipe36and enclose it in a clamp-like manner. This permits the fins42to be pressed against the pipe36by means of simple bolted or riveted connections48.

The fins42contact at least 40% of the outer peripheral surface, that is to say the peripheral faces26of the cell housing18, in such a manner that the corresponding portion of the peripheral face26of the cell housing18is covered by one or more fins42in order to carry heat away from the battery cells16in the direction of the pipes36.

In the embodiments shown inFIGS. 4 and 5, the individual fins32encase over 180° of the circumference of the cell housing18(see angle α), when viewed from the direction cell longitudinal axis A, meaning that the fins32are affixed to the cell housing18in a self-adhering manner. The previously mentioned ribs and ridge-shaped positioning projections20also likewise partially abut the fins42and additionally support them (seeFIG. 5). It is also easily recognizable from the figures that the battery cells16are in part clamped between a plurality of fins42engaging opposite outer peripheral sections of the cell housing18. The fins42extend in a concertina arrangement along the battery cells16in order to contact more battery cells16.

The fin sections adjacent battery cells16may indeed come into contact with each other, as is shown between the lower, two left battery cells16inFIG. 4, however it is preferable that a minimal amount of clearance be provided by means of which the tolerances in the outer periphery of the cell housing can be captured. The fins42represented there each have a W-shaped area that bulges outward that is spatially distanced from the battery cells16(seeFIGS. 7 to 9). The corresponding clearance has reference sign50. The W-shaped section forms a form-fitting retaining section52into whose exterior cavity a rib32or a positioning projection20projects. The flexibility of the fins42is retained by means of the gap50.

FIG. 8shows that the star-shaped positioning projection20simultaneously positions three adjacent fin sections by means of corresponding retaining sections52.

The retaining sections52need not also extend over the entire axial length of the fins42, but rather can position only a small edge or section of the fins42, as can be seen on the lower edge of the fin42shown inFIG. 9.

The pipes36can be arranged entirely outside the cell stack or, should there be sufficient space between the battery cells16, they can run partially or entirely within the corresponding spaces. In the embodiment according toFIGS. 4 to 6, the longitudinally running pipe sections38partially project into the cell stack that is defined externally by the so-called “envelope” of the cells. InFIG. 5, the envelope would ostensibly be a “line” that, as a tangent, abuts the sides of the outer battery cells16like fabric tightly stretched around the battery pack.

After the longitudinally-running section38partially extends into the cell stack and the transversely-running section40should not run beneath the lower end face24or above the upper end face24of the battery cells but rather should laterally bypass them, the pipe36, otherwise circularly cylindrically designed, is flattened on the one side of the section40that runs transversely and is turned towards the corresponding cell16. The flattened or indented section is designated with reference sign51. The section40that runs transversely thus lies outside the envelope, remains spatially distanced from the battery cells16, and has a very minimal lateral structure. In this manner, the installation space gained from the sections38partially extending into the pack is also not increased in the transversely-running section40.

FIGS. 10 and 11show that pipe36or pipe sections can also run entirely within the cell stack. The continuous section of each pipe36should make it clear that a section40running above the upper end face24is concerned, whereas the sections40represented by a broken line represent a section40running beneath the lower end face24. The pipes36themselves run parallel, for example, and begin at an inlet collector54and end at an outlet collector56. The fins36affixed to the pipes36, or more precisely on the longitudinally-running sections, are represented by thicker lines. InFIGS. 10 and 11, the fins42are undulatory and grasp a row of battery cells16either on their outer or on their inner surface. The battery cells16are thus gripped from opposite surfaces and are extensively contacted in total by the fins42.

FIGS. 12 to 16disclose different designs of the fins42as well as cell stacks of varying thicknesses.FIGS. 12 and 15show, for example, a three-rowed cell stack with rows offset from each other, whileFIGS. 13 and 14show a two-rowed cell stack with one external pipe according toFIG. 14and two external pipes according toFIG. 13, and finallyFIG. 16shows a four-rowed cell stack.

FIGS. 17 to 19represent different embodiments of how the fins42can be designed in the area of connection to the pipe36.

According toFIG. 17, the middle-section of a fin42is substantially shaped to have an Q shape and encloses the pipe36, from a longitudinal direction, by almost 270°. A press fit is formed between fin42and pipe36, said press fit also ensuring that the fin42is well positioned on the pipe36. Prior to being clipped onto the pipe36, the fin42can already be correspondingly shaped or can be correspondingly crimped around the pipe36.

FIG. 18shows a pipe-receiving groove in the mid-section of the fin42upon insertion of the pipe36.

To achieve a press fit between the pipe36and the fin42, the lateral lobes of the pipe-receiving groove are, during a second procedure step, pressed inward toward each other in such a manner that the pipe36is held over 270° in a form-fitting manner. In addition to press fitting, soldering or adhering can of course be considered, it being noted that heat-conducting particles such as aluminum preferably be integrated in the adhesive.

The pipes36are metal pipes with favorable thermal conductivity of greater than 180 W/m/K and customarily have an outer diameter of 4 to 10 mm, the thickness of the pipe walls being 0.3 to 2 mm depending on the cooling fluid used. The thickness of the walls of the pipes36for a water/glycol mixture and for R134a is approximately 0.3 to 1 mm, and 1 to 2 mm for CO2. The inner diameter of the pipes for the for water/glycol mixture and for R134a is 3 to 6 mm, and 1.5 to 4 mm for CO2. One pipe36supplies about 1 to 10 battery cells16, and one fin is assigned to approximately 1 to 3 battery cells16and is in contact with them.

FIG. 20shows a larger representation than already shown inFIG. 4of the affixing of two fins42to a pipe section by means of a mechanical fastening48.

Altogether, the execution of the cooling devices permits a modular design for battery assemblies of differing sizes.

The positioning of the pipes36themselves can also be very easily effected by means of corresponding positioning projections20in the outer housing10. This can be understood, for example, from looking at the right pipe section36represented inFIG. 5, said pipe section between mounted between a positioning projection20and the insulating layer34.

In the embodiment according toFIG. 21, the battery cells16are not only arranged adjacent to each other and connected in series by means of contact wires64as shown inFIG. 4, but two packs of battery cells, one atop the other, are also combined into one complete pack. The longitudinal axis A of the battery cells16align here so that shared spaces aligning with each other exist between the battery cells16and provide space for the pipes36and the fins32(see alsoFIG. 22).

FIG. 23represents an example of how a cooling device can be entirely preassembled. The sections38that run longitudinally in this instance, do not each have two fins42, for example, that are fastened to the corresponding section38and that each abut one side of a row of three adjacent battery cells16.

Comments on how the assembly is assembled follow. First, the battery cells16are placed individually or in groups in the base body12and are positioned between positioning projections20and ribs32. The cooling device is mounted parallel thereto, although in a separate assembly tool, the fins42having been previously fastened to the already bent pipes36. In the assembly tool, the fins42are bent around so-called “dummies” that simulate the battery cells16, the dummies having a corresponding minus allowance in order to ensure the subsequent press-fitting of the fins42. The fins may be entirely pre-shaped in an upstream roll tool or blanking tool so that the fins in the assembly tool are held corresponding only to the basic battery grid dimension, or the shaping of the fins occurs partially or entirely in the assembly tool. The dummies are fitted with a skirting that conically broadens toward the bottom. The skirting receives the upper ends of the battery cells when they are placed on the pre-assembled pack comprising base body12and battery cells16from above and the skirting precisely centers the battery cells16. Since the skirting is wider than the battery cells16, the complete cooling device with the shaped fins32facing downward, regardless of the tolerance of the cell housing, can be inserted into the base body12during which process the fins42are stuck to the cells16.

To ensure that during charging and discharging the individual battery cells16all have approximately the same temperature and are uniformly cooled, the battery cells16are contacted, depending on their distance from the allocated pipe36, to a different extent by the allocated fin or fins42. The cells16arranged closer to the pipe36have the advantage that the adjacent fin section, owing to its close proximity to the pipe36, is cooler than the fin sections more distant from the pipe36. The contact surfaces of differing sizes is intended to achieve a uniform cooling effect for all battery cells16so that their temperatures vary only in the range between ±2 to 3 K.

The differing contact surfaces and thus heat-exchange surfaces are easily and simply realized by means of openings58in those fin sections that are positioned closer to the pipe36(FIG. 24), by means of cavities60for forming an air gap that is intended to be greater than 0.1 mm, preferably greater than 0.5 mm, or by means of fins42spatially distanced one from another (seeFIG. 26).

FIG. 27shows that the cavity60can also run alongside the longitudinal axis of the battery and not only alongside the periphery of the battery as shown inFIG. 25. The cavity60can also be designed only in a specific location and need not traverse the entire circumference.

Customarily, all of the battery cells16that are combined into a battery pack as a finished, preassembled unit are encompassed from their housing outward by an insulating plastic wrapping. This plastic wrapping is fastened onto metal outer housings by means of shrinking. This step naturally requires time and leads to more costly battery cells.

FIGS. 28 and 29represent a method that reduces the costs for the individual battery cells16in an assembly according to the invention.

Namely the battery cells16are preferably constructed with only one metal outer housing18and have no insulating wrapping composed of plastic. The electrical insulation of the battery cells with regard to each other is effected by the fins42that are covered with an insulating layer, also called insulation70, in the contact area with the metal cell housing18.

The fin42preferably has an insulating layer70on both sides, a one-sided insulating layer70also being sufficient if need be.

To produce the sheet metal from which fins42are cut, the coiled sheet metal coil72is uncoiled after production. During the uncoiling process, plastic sheeting coiled on cylinders74is simultaneously uncoiled and partially rolled onto one or both sides of the sheet metal. A lined sandwich construction results. The cylinders74, however, do not have the width of the sheet metal, thereby resulting in a residual non-insulated strip76. The individual fins42are separated from the resulting sandwich strips transverse to the direction of uncoiling (see the dot-and-dash line inFIG. 29). The resulting fins are then fastened to the pipe36on the non-insulated strips, while the insulated section78serves to contact the battery cells16and insulate them.

FIG. 30shows a section, in concertina arrangement, of the pipe36, said section being arranged within the battery group and conducting a zeotropic coolant. A thermostatic expansion valve80is arranged in the inlet region of the pipe36in the battery assembly. In the power train assembly, the pipe36has a greater cross-section closer to the inlet (see cross-section A-A) than it does in the outlet region (see cross-section B-B). The difference in diameters is selected in order bring about a drop in pressure in the coolant in the area of the shown pipe section. This fall in pressure is so great that the saturation temperature of the coolant in the pipe section remains substantially constant.

FIG. 31shows a pipe38that is encompassed by a fin42. The pipe cross-section in the region of cross-section B-B is represented by a broken line. The pipe cross-section can preferably continuously taper in order to maintain a constant saturation temperature truly across the entire length of the pipe section active in the assembly.

The tapering of the cross section shown inFIG. 31can be difficult to manufacture; therefore, an alternative, as represented inFIG. 32, has been considered in which the flow diameter of the pipe38is changed by altering the pipe by flattening it, for example. By means of just such a flattening, the flow diameter can be particularly easily reduced.

This construction permits a consistent saturation temperature across the entire pipe section.

A similar effect can be achieved by interposing valves such as additional thermostatic expansion valves, for example.

In the embodiment according toFIG. 33, two pipe sections82,84are parallel, are arranged in close proximity to each other, and are formed in a concertina arrangement. The pipe sections82(represented with a solid line) and84(represented with broken lines) are two directly successive sections of a single pipe36. At the inlet in the region of the vale80, the zeotropic coolant flows through the pipe section82along the battery cells16up to a reversal point86, from which it flows through the pipe section84parallel to and in the opposite direction of the pipe section82until it reaches the outlet and flows out of the assembly.

FIG. 34shows that both pipe sections82,84are arranged in the immediate proximity of each other and thus are in thermal contact with each other. Both pipe sections82,84may also touch each other. Fins42encompass both pipe sections82,84in such a manner that the mean of the temperature of the fins results in the area of the battery cells16although the saturation temperature of the coolant in the pipe sections82,84differs.

In the embodiments according toFIGS. 30 to 34, the pipes36are part of a coolant circuit that is reproduced only in sections.

Instead of two pipe sections82,84of a pipe36, it is of course also possible for two pipes to be provided which are separate from each other and through which the flow traverses in opposite directions.