FR2989323A1 - Battery module for supplying power to electric traction machine of hybrid or electric motor vehicle, has cold source containing fusion material whose melting point is lower than evaporation temperature of fluid in heat pipe - Google Patents

Abstract

The module (30) has parallelepiped electrochemical cells (32) regrouped in a compartment, and a cooling device including flat heat pipes (34), each having coolant subjected to evaporation and condensation cycle. An end of the heat pipe is inserted between the cells to collect calories and to restore the calories with a cold source i.e. die (36), at another end. The cold source contains a fusion material whose melting point is lower than evaporation temperature of fluid in the heat pipe. The pipe includes a woven wick extended along a watertight enclosure for forming a network of capillaries.

Description

TECHNICAL FIELD The present invention relates to a battery module comprising a cooling device, and to a hybrid or electric vehicle equipped with such a battery module. BACKGROUND OF THE INVENTION Hybrid or electric vehicles generally comprise a compartment forming a module containing energy accumulators, which may be electrochemical cells made according to various known technologies, hereinafter referred to as batteries. Depending on the technology, these batteries may require a cooling system to ensure performance, service life and safety. In particular lithium-ion cells having a high energy density relative to the mass, require a significant monitoring of their operating conditions, such as voltage or temperature, and a cooling system to maintain them in a reduced temperature range. Moreover, it is necessary to ensure inside the battery module sufficiently homogeneous cooling of all the cells, in order to avoid a temperature increase of some less well-cooled cells, which would cause premature aging of these cells, and Damage to the complete battery system. A known battery system, presented in particular by the documents US-A1-2011 / 0000241 and US-A1-2011 / 0206965, comprises heat pipes whose one end is inserted between the cells, comprising a fluid which evaporates in contact with these cells by absorbing a latent heat of evaporation, and which then circulates at the other end of the heat pipe to liquefy by restoring this energy by the latent heat of liquefaction. Compact thermal conductors are thus produced capable of transmitting a high thermal power, which is clearly greater than that transmitted by conductive materials remaining in the same state. Heat pipes conduct heat to various active dissipation systems, such as radiators that dissipate calories in the ambient air, or heat exchangers that use these calories for other thermal systems in the vehicle. However, these active dissipation systems are not thermally autonomous, they are linked to external exchangers requiring fluid circulation systems, such as pumps or fans, to dissipate the calories produced. These fluid circulation system require energy to drive that increases the overall consumption of the vehicle, and have a mass and a volume that penalize the vehicle. The present invention is intended to avoid these disadvantages of the prior art. It proposes for this purpose a battery module comprising electrochemical cells grouped in a compartment, and a cooling device comprising heat pipes having a heat transfer fluid undergoing a cycle of evaporation and condensation, which comprise an end inserted between these cells. for collecting calories, and return them to a cold source at the other end, characterized in that the cold source contains a melting material having a melting temperature lower than the evaporation temperature of the heat pipe fluid.

An advantage of this battery module is that it may comprise a matrix integrated in the compartment, containing the melting material having a high latent heat of fusion, to produce a compact assembly capable of internally absorbing different powers. heat dissipated by each of the cells, with good homogeneity of the temperatures thanks to the high heat conduction of the heat pipes.

The battery module according to the invention may further comprise one or more of the following features, which may be combined with each other. According to a first embodiment, the heat pipes comprise a woven wick which extends along a sealed enclosure, forming a network of capillaries. According to a second embodiment, the heat pipes comprise grooves arranged along the axis, which surround an empty axial volume, forming a network of capillaries.

According to a third embodiment, the heat pipes comprise a sintered powder, comprising agglomerated grains, forming a network of capillaries. In particular, the heat pipes may comprise upper portions protruding above the cells, and inserted in the cold source, which form a angle with respect to the main direction of the parts inserted between these cells. Advantageously, the melting material of the cold source comprises paraffin. Advantageously, the melting material of the cold source is integrated in a matrix comprising porosities, which has a high thermal conductivity. Advantageously, the matrix comprises a sintered powder having a material comprising a good thermal conductivity. In particular, the cells having a cylindrical shape of circular section, and being aligned in rows and columns, the heat pipes may comprise a star shape which is inserted between the different adjacent cells. Since the cells are aligned in rows or columns with spacings between them, the heat pipes can form plates which are interposed in these spacings.

The invention also relates to a hybrid or electric motor vehicle comprising battery modules for powering an electric traction machine, having any of the preceding characteristics.

The invention will be better understood and other characteristics and advantages will appear more clearly on reading the following description given by way of example and in a nonlimiting manner, with reference to the appended drawings in which: FIGS. 5 are sectional views of heat pipes made in five different variants; FIG. 6 is a diagram presented in perspective of a battery module according to the invention; FIG. 7 is a diagram presented in perspective of a module according to a variant; FIG. 8 is a diagram presented in front view of this module including an option; - Figures 9 and 10 show two forms of heat pipes adapted for electrochemical cells of circular section; and FIGS. 11 and 12 show two forms of heat pipe adapted for electrochemical cells of rectangular section. FIGS. 1 to 5 show five examples of heat pipes, each comprising a sealed enclosure 4 of shape elongated along an axis, and thermally conductive, comprising an end placed in contact with a hot source, such as the electrochemical cells of a battery, for take calories from this hot spring. The other end of the heat pipes is placed in contact with a cold source, to deliver the calories to this cold source. Each heat pipe comprises a network of capillaries which extends over the entire length of the enclosure 4, allowing the capillary circulation of a coolant, one end of this heat pipe in contact with the hot source, to the other end in contact with the cold source. An axial volume extending over the entire length of the heat pipe, is left free to allow the circulation in the other direction of the gas produced by the evaporation of this fluid in contact with the hot source. The heat transfer fluid comprises an evaporation temperature which is, given the internal pressure in the heat pipe, included in the operating temperature range of the hot source. The heat transfer fluid can be pure or consists of a binary mixture, it is chosen to include a very good wettability of the capillary network. In the case of battery electrochemical cells comprising, according to the technology used, a use temperature of between 20 and 35 ° C., examples of heat transfer fluids available for these applications are water, ammonia, acetone or ethanol. FIG. 1 shows a first type of heat pipe, comprising a woven wick 2 extending along the sealed enclosure 4, which conveys the liquid by capillary action from the cold source to the hot source. An empty axial volume 10 extends along this woven wick 2, so as to pass the return of the circulating gas in the opposite direction. FIG. 2 shows a second type of heat pipe, comprising an enclosure 4 comprising on its inner surface, a succession of grooves of small section disposed along the axis 12, which surround the empty axial volume 10, and form a network of capillaries. FIG. 3 shows a third type of heat pipe similar to the second type, receiving in addition an internal wire 14 forming a sheath which separates the grooves arranged along the axis 12, of the empty axial volume 10.

FIG. 4 shows a fourth type of heat pipe, comprising a network of capillaries constituted by a sintered metal powder, which comprises agglomerated metal grains having empty spaces which are left empty forming the capillary network. An axial volume 10 is left empty in the center of the sintered powder 20, for the passage of gases.

FIG. 5 shows a fifth type of heat pipe comprising a sealed enclosure 4, an inner fabric 14 covering the inner face of this enclosure, and delimiting the empty axial volume 10 which comprises a sintered metal artery 20 extending along this heat pipe. . The capillary network is formed by the inner fabric 14 and the sintered metal artery 20. The principle of operation of the heat pipes is as follows. In contact with the hot source, the calories are transmitted to one end of the conductive enclosure 4 comprising the heat transfer fluid in the liquid state contained in the capillary network. This fluid evaporates, absorbing a latent heat of evaporation that cools this hot source. The vapor pressure of the coolant then conducts these gases by the empty axial volume 10 towards the other end of the heat pipe inserted in the cold source. In contact with the cold source, the vapors condense by releasing a latent heat of condensation which warms the cold source, and creates a pressure drop which allows with the increase of pressure of the evaporation, to circulate the gases.

The condensed heat transfer fluid is then conducted by capillarity in the capillary network to the hot source, which renews this fluid ready to undergo a new cycle. The sealed enclosure 4 of the heat pipe in particular has sufficient mechanical strength to hold the internal pressure, as well as stability to avoid corrosions by the liquid or the gases contained. In particular, copper or aluminum may be used, which have good thermal conductivity. A very efficient passive thermal conduction system is thus obtained which, for a given volume, produces a much greater quantity of heat than that transported by a direct conduction with a material remaining in the same phase. This system can be compact and economical, in relation to the amount of heat energy driven. FIG. 6 shows a battery module 30, comprising a succession of electrochemical cells 32 of parallelepipedal shape, comprising flat heat pipes 34 interposed each between two adjacent cells, so as to simultaneously cover an entire main face of each of these cells. For each heat pipe 34, a large thermal exchange surface with two cells 32 is thus obtained. In addition, a thermally conductive foam can be placed between the cells 32 and the heat pipes 34 to improve the thermal conduction between these components. Most of the volume of each heat pipe 34 is interposed between the cells 32, a small upper portion protruding above the cells, is inserted into a matrix 36 which covers the central cells. The matrix 36 comprises a material comprising a melting temperature lower than the evaporation temperature of the fluid of the heat pipe 34, which is in this case of the order of 30 to 40 ° C, and a high latent heat of fusion. The melting material is advantageously chosen to include a good thermal conductivity, a high specific heat, a small volume variation during the change of phase for the transition to the liquid state, a high stability after a large number of cycles, a flammability , low corrosivity and no toxicity. Advantageously, paraffin is used comprising most of these criteria, but having a low thermal conductivity which is of the order of 0.5 W / mK, which can pose problems of temperature differences within the material. To remedy this, a matrix 36 having a high thermal conductivity is advantageously used, comprising, for example, graphite, a metal or a semi-metal, which may comprise a conductivity of 500 W / mK, which is produced by sintered powder so as to get a rigid set with many porosities. The matrix 36 is then impregnated with paraffin so as to fill all the internal porosities. The operation of the battery module 30 is as follows. In contact with the hottest cells 32 at temperatures of the order of 30 to 40 ° C, the fluid located in the lower part of the heat pipes 34 vaporizes by absorbing the heat released by these cells, corresponding to the latent heat evaporation. The gases produced then rise to the upper part of the heat pipes 34 under the effect of the slight pressure generated by this vaporization. The gases arriving in the upper part of the heat pipes 34 warm the matrix 36, as well as paraffin contained in its pores which was solid at room temperature. The good thermal conductivity of the matrix 36 makes it possible to evenly distribute the heat released by the heat pipes 34 into the paraffin, even if these heat pipes are heated in an inhomogeneous manner. When the paraffin reaches its melting temperature, it melts by absorbing a latent heat of fusion, which stabilizes its temperature on a plateau corresponding to this melting temperature. It is then possible to absorb a large amount of heat depending on the mass of available solid paraffin, until all this paraffin is melted. Then, in the case where the cells 32 continue to release calories, a temperature of the matrix 36 starts to rise again. FIG. 7 alternatively shows a battery module 30 comprising upper portions of heat pipes 34 protruding above the cells 32 and integrated in the matrix 36, which are inclined at an angle to the main direction of the heat pipe portions contiguous to the cells. . We can then obtain a volume of these upper parts of the heat pipes 34, and exchange surfaces of these parts with the matrix 36, which remain equivalent while reducing the height of this matrix. Advantageously, the paraffin mass is calculated to allow the cooling of the cells 32 necessary in the majority of the cycles of use of the battery module 30. This calculation makes it possible to limit the mass, the bulk and the cost of the matrix. , by not taking into account the occasional thermal power peaks. FIG. 8 shows a similar battery module 30, further comprising a heat sink 40 lying flat above the die 36, allowing heat exchange with the ambient air.

Advantageously, the heat sink 40 comprises a metal comprising a high thermal conductivity, such as aluminum, and strongly cut forms with large surfaces, to achieve exchanges with the air that is pulsed by a fan on the exchanger. To absorb the exceptional heat generation peaks of the cells 32, all of the paraffin being then melted, the monitoring system of the battery module 30 measures the temperature of the heat sink 40 by a temperature probe, to start the fan when this temperature becomes too high. We must then size this active cooling system for thermal power peaks that are limited in time, which keeps a compact system, lightweight and economical. Figure 9 shows a top view of the cylindrical cells 32 of a battery module, aligned in rows and columns, the different rows or columns being very close to each other. The heat pipes 34 may be separate elements in the form of a four-pointed star, each of which is in contact with four adjacent cells 32. There is then a high modularity of assembly, all the heat pipes 34 being identical. Alternatively, the cylindrical cells 32 could be staggered, which would provide three-pointed star-shaped heat pipes 34 for remaining in contact with the three adjacent cells. Figure 10 shows a top view of the cylindrical cells 32 also aligned in rows and columns, the rows being spaced apart from each other. It is then possible to form heat pipes 34 in the form of plates 50 arranged between two rows of cells 32, which makes it possible to produce fewer components and to facilitate their assembly by manipulating a reduced number of components.

On the other hand, this arrangement requires plates 50 of different lengths, in the case where the rows do not all have the same number of cells 32. It will be noted for these different variants, that the heat pipes 34 5 still cover a great deal of space. part of the surfaces of the cells 32, which promotes heat exchange. Figure 11 shows in plan view parallelepipedal cells 32, receiving heat pipes 34 of flat shape which cover in one piece, the entire main surface of the adjacent cells.

Figure 12 shows alternatively the same cells 32 receiving between them two identical flat heat pipes 34, which cover a major part of the main surface of the adjacent cells. A greater number of heat pipes 34 are thus used, each having reduced dimensions.

In general, by combining the heat-conducting pipes 34 having a very high thermal conductivity, with the melting material that can absorb a large amount of heat, a compact battery module is obtained, with a good homogeneity of the temperatures and a capacitance. significant heat absorption, which ensures the safety of these batteries is to preserve their life. In particular, it is possible to obtain a temperature gradient of less than 1 ° or 2 ° in the set of cells 32. The battery system according to the invention can advantageously be used with lithium-ion accumulators, but also with all types of electrochemical cells requiring cooling.

Claims (11)

CLAIMS1 - Battery module comprising electrochemical cells (32) grouped in a compartment, and a cooling device comprising heat pipes (34) having a heat transfer fluid undergoing a cycle of evaporation and condensation, which have an inserted end between these cells for collecting calories, and return them to a cold source (36) at the other end, characterized in that the cold source (36) contains a melting material having a melting temperature below the temperature d evaporation of the heat pipe fluid. 2 - battery module according to claim 1, characterized in that the heat pipes (34) comprise a woven wick (2) which extends along a sealed chamber (4), forming a network of capillaries. 3 - battery module according to claim 1 or 2, characterized in that the heat pipes (34) comprise grooves disposed along the axis (12), which surround an empty axial volume (10) forming a network of capillaries. 4 - battery module according to any one of the preceding claims, characterized in that the heat pipes (34) comprise a sintered powder (20), comprising agglomerated grains having empty spaces intermediate, forming a network of capillaries. 5 - Battery module according to any one of the preceding claims, characterized in that the heat pipes (34) comprise upper parts protruding above the cells (32), and inserted in the cold source (36), which form a angle with respect to the main direction of the parts inserted between these cells. 6 - Battery module according to any one of the preceding claims, characterized in that the melting material of the cold source (36) comprises paraffin 30 7 - Battery module according to any one of the preceding claims, characterized in that the melting material of the cold sourceisintegrated in a matrix (36) having porosities, which has a high thermal conductivity. 8 - battery module according to claim 7, characterized in that the matrix (36) comprises a sintered powder having a material comprising a good thermal conductivity. 9 - battery module according to any one of the preceding claims, characterized in that the cells (32) having a cylindrical shape of circular section, and being aligned in rows and columns, the heat pipes (34) comprise a form of star that fits between the different adjacent cells. 10 - Battery module according to any one of the preceding claims, characterized in that the cells being aligned in rows or columns comprising spacings between them, the heat pipes (34) form plates (50) which are interposed in these spacings. . 11 - Hybrid or electric motor vehicle comprising battery modules (30) for powering an electric traction machine, characterized in that these modules are made according to any one of the preceding claims.