FR2727247A1 - COOLING DEVICE FOR A BATTERY CONSISTING OF SEVERAL ELEMENTS - Google Patents

Abstract

In this cooling device for a battery, the elements of which are arranged in a battery box and are surrounded by a circulating cooling liquid (4.1), the boiling temperature of this liquid is within an admissible range of operating temperatures cells (3), the battery box (2) is filled to a level (4) by the coolant (4.1) and a vapor (4.2) of the coolant accumulates above this level and is sent to cooling and recondensation means (9), then is returned to the battery box (2), the means (9) being arranged above the level (4). Application in particular to traction batteries of electric vehicles.

Description

The invention relates to a cooling device for a battery with

  high temperature, consisting of several elements and in which the elements are arranged inside a common box of thermally insulating battery, and a coolant circulates directly around the elements. One field of application of the invention relates to the cooling of traction batteries of all types for electric vehicles. These high power batteries require efficient cooling to be able to dissipate the dissipated heat which appears in the case of intense currents, since too much heating would destroy the battery. This is more valid for high temperature batteries, such as for example sodium (Na) / sulfur (S) batteries or sodium (Na) / nickel chloride (NiCl2) (ZEBRA) batteries, which should preferably operate at a temperature of 270 C to 350 C. To be able to

  keep the batteries in this operating temperature range -

  In addition, the batteries must have, apart from a heating device, also good thermal insulation. With better insulation, the dissipated heat is lower and the efficiency in terms of energy drawn from the sector is better, since the battery has less need to be heated. This is why priority should be given to having good insulation. However, it also has the disadvantage that the dissipated heat, which appears inside the battery during operation, cannot be dissipated and that, consequently, the

  battery temperature may rise above the allowable value

  corn. This is why thermally insulated batteries require,

  a particular degree, an effective cooling device.

  According to German patent application DE 26 38 862 A1, a cooling device of the type indicated is known for cooling a battery made up of several elements. Inside a common housing, the elements are arranged so that between the walls of this housing and the elements on the one hand as well as between the walls of neighboring elements on the other hand are formed channels , in which a coolant can be circulated. The coolant, for example a coolant, is sent to the battery pack via a supply line and is again removed therefrom via a collection line, in order to dissipate heat. The coolant is heated and cooled in a heat exchanger which returns, on the outlet side, via the supply line, the cooled coolant to the battery pack. To drive the coolant circuit, a pump is inserted in one

suitable location.

  According to German patent application DE 74 39 582.7 U1, a cooling device is known for a lead or steel accumulator made up of several elements and in which

  cooling plates are arranged between the individual elements.

  To obtain better cooling power, the cooling sheets located between the individual elements can be arranged in the form of flat evaporators. In these evaporators is placed a liquid which boils at a temperature below the maximum admissible temperature of approximately 50 C. The evaporator is connected to a condenser by means of a system of hermetically closed tubes. Due to the use of the heat of evaporation of the coolant, such a system is particularly efficient and reliable since it has no moving parts. It can be considered that a drawback resides in the fact that the cooling of the elements takes place in a non-uniform manner, that is to say only at the level of the surface which is in thermal contact with a cooling sheet. On the other hand we do not know how we can use such a process for the

  high temperature battery cooling.

  All the cooling devices studied so far, which use air or a liquid as cooling fluid, do not provide satisfactory results. The solutions presented do not provide the necessary cooling power or else introduce a non-uniform distribution of the temperature inside the battery or also inside the different elements, in their vertical direction. As a result, individual elements or individual parts of elements operate at the upper limit of the allowable temperature range and others operate at the lower limit of this allowable range of temperatures. This affects the internal resistance of the battery and durably reduces the service life and potential capacity of the battery. In addition, because of the insufficient cooling power, cooling must be started very early as a precaution, to avoid an inadmissible rise in temperature, in the event of an intense power demand, lasting quite a long time. This, on the other hand, introduces unnecessary energy losses, when, due to only a low power demand, the critical temperature (upper temperature limit) is not even reached and that by

  therefore cooling would start too early.

  The object of the invention is to indicate a cooling device of the type indicated in the preamble, for a high temperature battery made up of several elements, which allows a

  efficient and uniform cooling of the battery.

  This problem is solved in accordance with the invention with the aid of a cooling device of the type indicated, characterized in that - the boiling point of the coolant is situated within the admissible range of temperatures of service of the elements, - the battery box is filled with coolant only to a certain level and coolant vapor collects above the level, - coolant vapor is sent, from the battery box, to cooling and recondensation means and the recondensed coolant is returned to the battery box, and - the cooling and recondensation means are

  arranged, from the geodesic point of view, above the level.

  According to a preferred embodiment of the invention, the cooling and recondensation means are connected, on the input side, by means of a collection pipe to at least one outlet opening of the battery box and, output side, via a supply line, to at least one inlet opening of the battery box, the collection line and the supply line being produced so as to be

thermally insulating.

  Then, preferably, a pressure compensation tube, not thermally insulated, extends in bypass from the collection pipe. By choosing a liquid, the boiling temperature of which is within the admissible range of operating temperatures of the battery, for example near the maximum permissible operating temperature, cooling is obtained, which is based mainly on the

  evaporative cooling and has some advantages.

  A first advantage is due to the fact that a specific cooling action is obtained which occurs at the place of heating, by the fact that where the local temperature at the level of the surface of the elements reaches the boiling point of the coolant, the coolant evaporates. The vapor phase rises in the form of small bubbles in the coolant, which causes rapid heat dissipation. Therefore, local cooling is always obtained only where there is a

  corresponding need for cooling.

  Evaporative cooling has the additional advantage that with changing the state of the unit, when absorbing heat for the coolant and when vapor bubbles are formed, produces comparatively intense heat absorption. Since the amount of heat to be removed is largely absorbed as heat of evaporation, it is absorbed without increasing the temperature of the coolant. This contributes to a very uniform temperature distribution at

  inside the entire battery.

  Overall, thanks to the solution according to the invention, a limitation of the temperature inside the battery is obtained in a very simple but effective manner, at a maximum temperature.

  set by the boiling temperature.

  In conventional cooling devices, the heat is removed only by transfer of the heated cooling medium (convection) so that the cooling power depends on the total flow of the coolant and therefore on the power of a circulation pump, which drives in the coolant circuit. On the contrary, the cooling device according to the invention has the additional advantage that, by means of a corresponding arrangement, no circulation pump is necessary. The cooling circuit is maintained and switched on only by excess dissipated heat, which would otherwise heat the battery beyond

  the boiling point of the coolant.

  Other features and advantages of this

  invention will emerge from the description given below taken into account

  reference to the attached drawing, the Unique Figure of which shows a form

  preferred embodiment of the invention.

  a The Single Figure shows the cooling device according to the invention for a battery 1 which is made up of several elements 3 arranged inside a battery case 2. In the case of a high temperature battery, the case 2 has a thermal insulator, which is not shown on

  the drawing, as well as a heater also required.

  The battery case 2 is hermetically closed to the outside, the coolant 4.1 filling the battery case 2 only to a determined level 4. Above this level 4, the battery case 2 is filled with 4.2 air or coolant vapor. Level 4 is chosen so that the elements 3 are largely immersed in the coolant 4.1, so that their uniform cooling is guaranteed. The elements 3 are arranged so that between the walls of the battery case 2 and the elements 3 on the one hand as well as between the walls of neighboring elements 3 on the other hand there appear channels, which

  allow free circulation of the coolant 4.1.

  For the same reason, the elements 3 are arranged on a support bottom 6, at a distance from the bottom of the battery case 2, the support bottom having, in a manner analogous to a grid, a multiplicity of passage openings. for coolant 4.1. In the Figure, the elements 3 are shown connected in series to the

  by means of a connector between poles from one element to the next.

  The battery box 2 has an outlet opening 7, to which a collection pipe 8 is connected, by means of which the vapor 4.2 of the coolant can be evacuated from the battery box 2. The other end of the collection pipe 8 is connected to cooling and recondensation means, here a cooler 9. In the latter, there is a cooling of the vapor 4.2 of the coolant, which by delivering the heat of evaporation returns to the phase liquid and therefore recondenses with the coolant 4.3. To assist the cooling power of the cooler 9, a fan 10 can be provided, which if necessary, is activated automatically. The coolant 4.3, which is recondensed in the cooler 9, is returned to the battery 1 via a supply pipe 11 and an inlet opening 12. The return supply takes place preferably via an upstream chamber 13, which communicates only in the bottom part, with the part, which houses the elements 3, of the battery case 2. This guarantees that the

  4.3 recondensed coolant is always introduced

  below level 4 and added to coolant 4.1

  already present and does not react with the vapor phase 4.2.

  In the case of a high-temperature battery to be cooled, the collection pipe 8 can be arranged so as to be thermally insulated so that no vapor 4.2 of the coolant is deposited in this pipe and is condensed by a uncontrolled way. Likewise, the supply pipe 11 must be thermally insulated so that the returned coolant 4.3 is not cooled too strongly. Too intense cooling would eventually lead to the appearance of an undesirable temperature gradient of the coolant 4.1 inside

of the battery case 3.

  In addition, above the cooler 9, there is provided a pressure compensation tube 14 which extends vertically in bypass from the collection pipe 8. This tube is open upwards and is not thermally insulated unlike the collection pipe 8. In the case where cooling is carried out, the air discharged by the vapor, which forms, of the coolant

  can be evacuated through this pressure compensation tube 14.

  Conversely, air can re-enter the cooling device via this tube, when the cooling stops again and a vacuum is established. Evacuation of the vapor 4.2 from the coolant is prevented by the fact that this vapor is deposited on the interior walls of the pressure compensation tube 14 which is not thermally insulated and is sent to the cooler 9 in the form of

recondensed drops of liquid.

  To replace the coolant 4.1, there is provided, in the supply line 11, successively in the direction of flow, an inlet 15 for the compressed air, which can be blocked, a shut-off valve 16 and, finally, a liquid outlet 17, which can be blocked. In normal operation, as shown in the Figure, the compressed air inlet 15 and the outlet of

  liquid 17 are blocked and the stop valve 16 is open.

  Hereinafter, the operation of the cooling device according to the invention will be described: under the effect of the complete filling of the battery case 2 with the coolant 4.1, the cooling circuit, which certainly does not include any circulation, is not in operation until coolant 4.1 has evaporated. It is only when locally the boiling temperature of the coolant 4.1 is exceeded in an element 3, that it is established cooling by natural circulation: when the heat to be removed increases, the vapor pressure, which s 'established under the effect of the bubbles of vapor which rise in the upper part of the battery case 2, increases. The vapor 4.2 of the coolant is evacuated from the battery case 2 via the collection pipe 8 provided for this purpose and is condensed in the cooler 9, while delivering the heat of evaporation to the environment . Then, the recondensed liquid 4.3 returns to the battery case 2 via the upstream chamber 13, under the influence of gravity. A necessary condition for the desired operation of the natural recirculating cooling system is that the cooler is located, geodetically, at a level higher than level 4 in the battery box 2. Otherwise, it would be necessary to use a pump to draw the condensed coolant back into the battery. Likewise, in this case, it would be necessary to prevent, through appropriate provisions,

  coolant from the battery in the cooler.

  When selecting an appropriate coolant, apart from a tuning of the boiling temperature to the maximum permissible operating temperature of the battery, other points of view must also be taken into account . For optimal cooling action, the coolant should also have heat of evaporation

  as high as possible and good thermal storage capacity.

  In addition, the coolant should be electrically neutral and not chemically vary across the range of operating temperatures, in the case of high temperature batteries this is the range of - 20 C to 350 C, even in the case of the presence of an electric field. Near the lower limit of the operating temperature range, the coolant should still be liquid. For reasons of operational safety and compatibility with the environment, the coolant must be non-corrosive,

  non-toxic, non-combustible and insoluble in water.

  As the coolant, which is suitable in particular for cooling Na / NiCl2 batteries and meets the requirements indicated above, the substance may be indicated: dibutyl ortophthalate (C16H2204). This dibutyl ortophthalic acid ester does not contain fluorine and chlorine and is known as a transformer coolant, used in

  industrial scale. The boiling point of this liquid is 335 C.

Claims (3)

  1. Cooling device for a high temperature battery, consisting of several elements and in which the elements are arranged inside a common thermally insulating battery case, and a cooling liquid circulates directly around the elements, characterized in that at the boiling point of the coolant (4.1) is located within the allowable range of service temperatures of the elements (3), * the battery case (2) is filled with coolant (4.1) only up to a certain level (4) and the coolant vapor (4.2) accumulates above the level (4), * the coolant vapor (4.2) is sent from the battery box (2), to cooling and recondensation means (9) and the recondensed coolant (4.3) is returned to the battery box (2), and * the means of cooling and d e recondensation (9)   are arranged, from a geodesic point of view, above level (4).   2. Cooling device according to claim 1, characterized in that the cooling and recondensation means (9) are connected, on the inlet side, by means of a collection pipe (8), to at least one opening of outlet (7) of the battery case (2) and, on the outlet side, via a supply pipe (11), to at least one inlet opening (12) of the battery case (2 ), the collection pipe (8) and the supply pipe (11) being produced so as to be thermally insulating. 3. Cooling device according to claim 2, characterized in that a pressure compensation tube (14), not thermally insulated, extends in bypass from the pipe collection (8).