Cooling system for secondary battery, and secondary battery system

Abstract

This cooling system for a secondary battery comprises: a liquid flow path for moving a liquid refrigerant downward in the vertical direction, the liquid flow path being formed by a plate-shaped member which has a pair of surfaces and onto the outer surface of which or into which the liquid refrigerant can move, and the secondary battery being in contact with one of the pair of surfaces; a gas flow path for moving a gaseous refrigerant upward in the vertical direction, the gas flow path being adjacent to the other of the pair of surfaces of the liquid flow path, and the refrigerant being capable of moving between the gas flow path and the liquid flow path via the other surface; a cooling unit that is positioned above the liquid flow path and the gas flow path in the vertical direction and that cools the gas refrigerant to be in liquid form; and a heating unit that is positioned below the liquid flow path and the gas flow path in the vertical direction and that heats the liquid refrigerant to be in gas form.

Description

Secondary battery cooling system and secondary battery system

[0001] The present invention relates to a cooling system for a secondary battery and a secondary battery system.

[0002] Secondary batteries used as batteries for electric vehicles and the like are known (see, for example, Patent Document 1). In the secondary battery described in Patent Document 1, multiple battery modules (secondary batteries) are each connected to a heat sink via a heat pipe. A cooling water passage is formed in the heat sink, through which coolant cooled by a radiator flows. Therefore, the secondary battery, which heats up during charging and discharging, is cooled by the heat sink through which coolant flows.

[0003] Japanese Patent Application Publication No. 11-204151

[0004] In the liquid-cooling cooling method described in Patent Document 1, which transfers heat using a liquid, water as a heat medium has a high fluid specific heat and high cooling capacity. However, due to the high sensible heat of water, a large amount of heat is required to cool or heat the water. Air-cooling, which uses a gas as a heat medium, has a low fluid specific heat and low heat transport capacity, unlike liquid-cooling, and has high exhaust heat loss. Vapor heat transport, a cooling method different from liquid-cooling and air-cooling, cools the battery using the latent heat of vaporization of a low-boiling-point medium, which has a boiling point lower than the heat generation temperature of the battery. The vaporized low-boiling-point medium is cooled and liquefied by a cooling unit, and then cools the battery again. However, cooling by vapor heat transport may result in the depletion of the low-boiling-point medium liquid under high battery heat loads, causing dryout. In this case, the mismatch between the battery's heat generation and the supply of low-boiling-point medium liquid results in an increase in battery temperature. In addition to battery cooling, battery temperature drops under low battery loads, and smooth warm-up is desirable.

[0005] The present invention has been made to solve at least part of the above-mentioned problems, and has an object to provide a cooling method that has good robustness against environmental disturbances and input fluctuations to a secondary battery.

[0006] The present invention has been made to solve at least part of the above-mentioned problems, and can be realized in the following forms.

[0007] (1) According to one aspect of the present invention, there is provided a cooling system for a secondary battery, the cooling system including: a liquid flow path for vertically downward movement of a liquid refrigerant, the liquid flow path being formed by a plate-like member having a pair of surfaces and allowing the liquid refrigerant to move on or inside the liquid flow path, with the secondary battery in contact with one of the pair of surfaces; a gas flow path for vertically upward movement of a gas refrigerant, the gas flow path being adjacent to the other of the pair of surfaces of the liquid flow path and allowing refrigerant to move between the gas flow path and the liquid flow path via the other surface; a cooling unit located vertically above the liquid flow path and the gas flow path and configured to cool the gas refrigerant to a liquid; and a heating unit located vertically below the liquid flow path and the gas flow path and configured to heat the liquid refrigerant to a gas.

[0008] With this configuration, the liquid refrigerant moving on the surface or inside of the liquid flow path in contact with the secondary battery vaporizes and flows into the gas flow path due to heat exchange with the secondary battery, which generates heat during charging and discharging. The gas refrigerant that flows into the gas flow path moves vertically upward within the gas flow path and is cooled by the cooling unit. The cooled gas refrigerant condenses and moves vertically downward again through the liquid flow path, cooling the secondary battery. The liquid refrigerant that does not vaporize due to heat exchange with the secondary battery moves vertically downward and is heated by the heating unit. The heated liquid refrigerant vaporizes and moves vertically upward through the liquid flow path. With this configuration, the liquid refrigerant that moves vertically downward is vaporized by the heating unit, so the flow rate of the liquid refrigerant moving on the surface or inside of the liquid flow path increases by the amount of refrigerant vaporized by the heating unit. By increasing the amount of refrigerant flowing through the liquid flow path and the gas flow path, air bubbles that form dry patches due to temperature increases in the secondary battery are removed. Furthermore, in this configuration, the vapor mass ratio (ratio of vapor flow rate to total weight) of the refrigerant that flows vertically downward without vaporizing due to heat exchange with the secondary battery is low, so that dryout occurring in the liquid flow path is suppressed even if the secondary battery generates excessive heat. As a result, the secondary battery is cooled with good robustness even if the secondary battery generates excessive heat due to environmental disturbances or input fluctuations.

[0009] (2) In the cooling system of the above aspect, the boiling point of the refrigerant may be equal to or higher than 20 degrees Celsius and equal to or lower than 40 degrees Celsius. According to this configuration, when the recommended operating temperature of the secondary battery is approximately 5 degrees Celsius to 45 degrees Celsius, the boiling point of the refrigerant is operated within the recommended operating temperature, thereby efficiently cooling the secondary battery to within an appropriate battery temperature range.

[0010] (3) In the cooling system of the above aspect, the liquid flow path may be formed of any one of a porous body, urethane foam, and a metal plate with grooves formed on the other surface. With this configuration, the liquid flow path can slow the speed of the liquid refrigerant moving vertically downward, allowing more of the latent heat of evaporation of the refrigerant condensed by the cooling unit to be used to cool the secondary battery. As a result, the efficiency of the entire cooling system is improved.

[0011] (4) The cooling system of the above aspect may further include a battery temperature acquisition unit that acquires the temperature of the secondary battery, a heating temperature acquisition unit that acquires the temperature of the heating unit, a heat generation amount acquisition unit that acquires the heat generation amount of the secondary battery, and a temperature setting unit that sets the cooling temperature of the cooling unit using the acquired temperature of the secondary battery, the temperature of the heating unit, and the heat generation amount. According to this configuration, the vapor quality, which is the proportion of vapor in the liquid flow path and the gas flow path, is calculated based on the change in the difference between the saturated vapor pressure and the vapor pressure. The change in the difference is determined by the temperature of the secondary battery, the temperature of the heating unit, the heat generation amount of the secondary battery, and the cooling temperature. In this configuration, the cooling temperature of the cooling unit is set to a vapor quality that does not cause dryout. This suppresses excessive heat generation in the secondary battery due to depletion of liquid refrigerant in the vertically lower part of the liquid flow path, where dryout is likely to occur, and maintains a more uniform temperature throughout the secondary battery.

[0012] (5) The cooling system of the above aspect may further include a heat exchange medium circulating between the cooling unit and the heating unit, a compression unit that compresses the heat exchange medium discharged from the cooling unit before being supplied to the heating unit, a heat dissipation unit that dissipates heat from the heat exchange medium discharged from the heating unit, and an expansion unit that expands the heat exchange medium discharged from the heat dissipation unit before being supplied to the cooling unit. This configuration forms a refrigeration cycle in which the pressure level of the heat exchange medium supplied to the cooling unit is adjusted by the expansion unit, and the pressure level of the heat exchange medium supplied to the heating unit is adjusted by the compression unit. Therefore, the pressure difference between the heat exchange medium supplied to the cooling unit and the heat exchange medium supplied to the heating unit is increased or decreased by adjusting the expansion unit. Furthermore, the overall pressure of the heat exchange medium is increased or decreased by adjusting the compression unit. Furthermore, this configuration reduces sensible heat loss from auxiliary equipment, etc., compared to conventional cooling using a circulating water pump, and the temperatures of the heating unit and cooling unit are set with high response. Furthermore, the high heat transfer coefficient of the two-phase flow between the evaporation of the refrigerant in the heating section and the condensation of the refrigerant in the cooling section allows for a large amount of heat exchange with a small temperature difference due to the high heat transfer coefficient. As a result, the power consumption of the cooling system is reduced without increasing the pressure difference in the refrigeration cycle with this configuration.

[0013] (6) The cooling system of the above aspect may further include a heat exchanger arranged in parallel with the cooling unit and performing heat exchange between the heat exchange medium and the atmosphere; a battery temperature acquisition unit that acquires the temperature of the secondary battery; and a supply destination determination unit that sets the supply destination of the heat exchange medium discharged from the expansion unit to the heat exchanger when the acquired temperature of the secondary battery is below a temperature threshold, and sets the supply destination of the heat exchange medium discharged from the expansion unit to the cooling unit when the temperature of the secondary battery is equal to or greater than the temperature threshold. With this configuration, the supply destination of the heat exchange medium is switched based on a constant temperature threshold. Conventional heat pump systems use a four-way valve to switch between high-temperature and low-temperature heat exchange media. This can easily cause the four-way valve to deteriorate and malfunction due to thermal shock during switching. Furthermore, conventional systems reverse the flow direction of the heat exchange medium during switching. In contrast, with this configuration, the temperature of the heat exchange medium when switching the supply destination is near the temperature threshold, resulting in less thermal shock and reduced malfunction. Furthermore, with this configuration, the flow direction of the heat exchange medium does not change before and after switching the heat exchange medium, shortening the response time required for control. This high-response switching allows, for example, when a secondary battery is used as a power source for a vehicle, it can be used for intermittent warm-up, even during short wait times at traffic lights. Furthermore, even when charging or discharging begins during warm-up, the short switching time for the heat exchange medium supply destination prevents the secondary battery from overheating due to resistance heating during the switch, and cooling of the secondary battery begins quickly.

[0014] (7) The cooling system of the above aspect may further include a current acquisition unit that acquires a current of the secondary battery, a vapor pressure acquisition unit that acquires a vapor pressure of the gas flow path, and a bypass flow path arranged in parallel with the heating unit and through which the heat exchange medium can flow. When the temperature of the secondary battery is equal to or higher than the temperature threshold, the supply destination determination unit may select the heating unit as the supply destination of the heat exchange medium discharged from the compression unit if the vapor pressure is equal to or higher than a pressure threshold determined based on the current, and may select the bypass flow path as the supply destination of the heat exchange medium discharged from the compression unit if the vapor pressure is lower than the pressure threshold. According to this configuration, the saturation temperature of the refrigerant is calculated using the acquired current of the secondary battery and a thermal resistance known from components of the liquid flow path. Using the vapor pressure at the saturation temperature as a pressure threshold, if the acquired vapor pressure is high, the liquid refrigerant is insufficient and the vapor pressure temperature is elevated. On the other hand, if the acquired vapor pressure is equal to or lower than the pressure threshold, the flow rate of the liquid refrigerant is sufficient. When the flow rate of the liquid refrigerant is sufficient, the refrigerant is not heated by the heating unit using the heat exchange medium, but is instead passed through the bypass flow path, thereby reducing the power required for heating, and thereby reducing the power consumed for cooling the secondary battery.

[0015] The present invention can be realized in various forms, for example, in the form of a cooling system for a secondary battery, a secondary battery system, an electric vehicle, a cooling method for a secondary battery, a system including these devices, a computer program for executing these devices, a server device for distributing this computer program, a non-transitory storage medium storing the computer program, etc.

[0016] 1 is a block diagram of a secondary battery system according to one embodiment of the present invention; FIG. 2 is an explanatory diagram of changes in liquid refrigerant contained in a liquid flow path; FIG. 3 is an explanatory diagram of temperature changes in a secondary battery when dryout occurs; FIG. 4 is an explanatory diagram of a maximum and minimum temperature difference of a secondary battery according to a C-rate during discharge; FIG. 5 is an explanatory diagram of temperature changes during discharge at a C-rate of 2C; FIG. 6 is an explanatory diagram of temperature changes during discharge at a C-rate of 2C; FIG. 7 is an explanatory diagram of temperature changes in a secondary battery during discharge at a C-rate of 2C; FIG. 8 is a Mollier diagram of a refrigeration cycle in this embodiment; FIG. 9 is a schematic block diagram of a thermal circuit in a secondary battery system; FIG. 10 is a schematic block diagram of a secondary battery system during warm-up in a second embodiment; FIG. 11 is a schematic block diagram of a secondary battery system during cooling in a second embodiment; FIG. 12 is a Mollier diagram of a refrigeration cycle during warm-up in a second embodiment; FIG. 13 is a Mollier diagram of a refrigeration cycle during cooling in a second embodiment; FIG. 14 is a flowchart of a control method for a cooling system in a second embodiment; FIG. 15 is a sub-flowchart of a heating setting process.

[0017] <First Embodiment> Fig. 1 is a block diagram of a secondary battery system 100 according to one embodiment of the present invention. The secondary battery system 100 of this embodiment is used as a power source for a battery-powered vehicle or the like. The secondary battery system 100 includes a plurality of stacked secondary batteries BT and a cooling system 101 that cools the plurality of secondary batteries BT. Fig. 1 shows one secondary battery BT among the plurality of secondary batteries BT and components near the secondary battery BT.

[0018] As shown in FIG. 1 , the secondary battery system 100 includes a secondary battery BT, a storage section 30 that stores the secondary battery BT and a refrigerant 50 that cools the secondary battery BT, a liquid flow path (liquid flow path) 40 that extends vertically within the storage section 30, a cooling section 10 that is disposed vertically above the liquid flow path 40 and in contact with the liquid flow path 40, a heating section 20 that is disposed vertically below the liquid flow path 40 and in contact with the liquid flow path 40, and a heat transfer section 10 that circulates between the cooling section 10 and the heating section 20. The heat exchanger includes a heat exchange medium 80, a compression unit 70 that compresses the heat exchange medium 80, a heat dissipation unit 60 that dissipates heat from the heat exchange medium 80, an expansion unit 65 that expands the heat exchange medium 80, a first temperature sensor (battery temperature acquisition unit) SS1 that detects the battery temperature of the secondary battery BT, a second temperature sensor (heating temperature acquisition unit) SS2 that detects the heating temperature by the heating unit 20, and a control unit (temperature setting unit) 90 that controls the compression of the heat exchange medium 80 by the compression unit 70. In this embodiment, the secondary battery BT is cooled and warmed up by vapor heat transport utilizing the latent heat of evaporation of the refrigerant 50. When the secondary battery BT is cooled under high load (e.g., during discharge at a high C rate), the refrigerant 50 is heated by the heating unit 20, thereby increasing the flow rate of the refrigerant 50 circulating within the accommodation unit 30 and improving the cooling performance of the secondary battery BT.

[0019] In this embodiment, the secondary battery BT is, for example, a lithium ion battery. The housing 30 forms a sealed space containing multiple secondary batteries BT and a refrigerant 50. The multiple secondary batteries BT are housed in the housing 30 at intervals along the X-axis shown in FIG. 1 , which is the stacking direction. The Cartesian coordinate system CS shown in FIG. 1 is composed of an X-axis parallel to the stacking direction, a Z-axis parallel to the vertical direction, and a Y-axis parallel to the depth direction and perpendicular to the X-axis and Z-axis. The Cartesian coordinate system CS shown in FIG. 1 corresponds to the Cartesian coordinate system CS shown in FIG. 2 and subsequent figures. The Cartesian coordinate system CS applies to the positional relationship between the housing 30, the heating unit 20, and the cooling unit 10, and is unrelated to the relative positions of the compression unit 70, the expansion unit 65, the control unit 90, and the like.

[0020] Each of the spaced-apart secondary batteries BT is a battery cell having a rectangular surface parallel to the YZ plane and a thickness parallel to the X axis. A liquid flow path 40 having a surface parallel to the YZ plane is formed on the positive and negative X-axis sides of each secondary battery BT. Note that FIG. 1 illustrates only the liquid flow path 40 located on the positive X-axis side of one secondary battery BT. In this embodiment, the liquid flow path 40 is formed of a porous material. Therefore, the liquid refrigerant 50 is widely distributed within the liquid flow path 40 due to capillary action. In other words, the liquid flow path 40 forms a flow path within itself for the liquid refrigerant 50 to move vertically downward. As shown in FIG. 1 , the liquid flow path 40 is formed of a plate-like member having a pair of surfaces parallel to the YZ plane perpendicular to the X axis. The negative X-axis surface of the pair of surfaces is in contact with the positive X-axis surface of the secondary battery BT.

[0021] 1 , the accommodation unit 30 has a gas flow path 31 adjacent to the surface of the pair of surfaces of the liquid flow path 40 on the positive X-axis side. The gas flow path 31 contacts the cooling unit 10 at an upper vertical position and contacts the heating unit 20 at a lower vertical position. Within the gas flow path 31, the gas refrigerant 50 can move vertically upward. The refrigerant 50 can also move between the gas flow path 31 and the liquid flow path 40.

[0022] As shown in FIG. 1 , the cooling unit 10 is disposed vertically above the housing unit 30. A low-temperature heat exchange medium 80 expanded by the expansion unit 65 flows through the cooling unit 10. The refrigerant 50 is cooled by heat exchange between the low-temperature heat exchange medium 80 in the cooling unit 10 and the refrigerant 50 in the housing unit 30. The heating unit 20 is disposed vertically below the housing unit 30. A high-temperature heat exchange medium 80 compressed by the compression unit 70 flows through the heating unit 20. The refrigerant 50 is heated by heat exchange between the high-temperature heat exchange medium 80 in the heating unit 20 and the refrigerant 50 in the housing unit 30. As shown in FIG. 1 , the secondary battery BT is disposed within the housing unit 30, separated from the heating unit 20 and the cooling unit 10. Therefore, direct heat exchange does not occur between the secondary battery BT and the heating unit 20, or between the secondary battery BT and the cooling unit 10.

[0023] In this embodiment, the refrigerant 50 is a fluorocarbon-based low-boiling-point medium. In this embodiment, the boiling point of the refrigerant 50 is set to 20 degrees Celsius (°C). Therefore, when the secondary battery BT generates heat and its temperature rises above 20°C, the liquid refrigerant 50 in the liquid flow path 40 vaporizes due to the heat of the secondary battery BT. The refrigerant 50 then flows from the liquid flow path 40 to the gas flow path 31 along the direction of the arrow shown in FIG. 1 , rises within the gas flow path 31, and is cooled by the cooling unit 10. The cooled and condensed liquid refrigerant 50 again flows vertically downward within the liquid flow path 40. In this manner, in this embodiment, the secondary battery BT is cooled by vapor heat transport of the refrigerant 50. A portion of the liquid refrigerant 50 does not vaporize but comes into contact with the heating unit 20 located vertically below and vaporizes due to heating by the heating unit 20.

[0024] 2A to 2C are explanatory diagrams illustrating changes in the liquid refrigerant 50 contained in the liquid flow path 40. In FIGS. 2A to 2C, the refrigerant 50 in the liquid flow path 40 when the automobile equipped with the secondary battery system 100 is operated, stopped, and then started again is shown by hatching with diagonal lines. FIG. 2A shows the refrigerant 50 in the liquid flow path 40 during operation. FIG. 2B shows the refrigerant 50 in the liquid flow path 40 when the automobile is stopped after operation. FIG. 2C shows the refrigerant 50 in the liquid flow path 40 when the automobile is started again after being stopped.

[0025] During operation as shown in FIG. 2( a), the cooling unit 10 cools the refrigerant 50 in the housing 30 by circulating the heat exchange medium 80, thereby cooling the secondary battery BT, which generates heat during operation. Due to vapor heat transport, a sufficient amount of liquid refrigerant 50 is contained in the liquid flow path 40. When the vehicle is stopped, the circulation of the heat exchange medium 80 stops. While some of the heat exchange medium 80 is retained in the liquid flow path 40 while the vehicle is stopped, the remaining heat exchange medium 80 does not contribute to vapor heat transport. This repeated operation and stoppage reduces the amount of refrigerant 50 contained in the liquid flow path 40, as shown in FIG. 2( b). If the secondary battery BT is subsequently operated with a reduced amount of refrigerant 50 in the liquid flow path 40, a sufficient amount of refrigerant 50 is not contained in the liquid flow path 40, as shown in FIG. 2( c), which may result in dryout or dry patches occurring below the liquid flow path 40 where the liquid refrigerant 50 is not readily distributed. However, in this embodiment, the liquid refrigerant 50 that falls without vaporizing is heated and vaporized by the heating unit 20. This increases the flow rate of the refrigerant 50 circulating through the liquid flow path 40 and the gas flow path 31, thereby suppressing the occurrence of dry-out and dry patches.

[0026] FIG. 3 is an explanatory diagram of temperature changes in the secondary battery BT when dryout occurs. FIG. 3 shows temperature changes T1 and T2 of the secondary battery BT when the secondary battery BT is subjected to a high thermal load. The temperature change T1 shown by the solid line represents the temperature change in the upper part of the secondary battery BT where dryout does not occur. The temperature change T2 shown by the dashed line represents the temperature change in the lower part of the secondary battery BT where dryout occurs. As shown in FIG. 3, the temperature change T2 at the location where dryout occurs rises sharply after about 15 minutes have passed. As such, when dryout occurs, the temperature of the secondary battery BT rises sharply, which may result in deterioration of the secondary battery BT.

[0027] FIG. 4 is an explanatory diagram of the maximum and minimum temperature differences of the secondary battery BT according to the C-rate during discharge. The maximum and minimum temperature differences shown in FIG. 4 are the difference between the maximum and minimum temperatures measured at 10 locations (50 locations in total) equally spaced along the vertical direction of each secondary battery BT in a secondary battery system 100 in which five secondary batteries BT are stacked in the housing 30. The temperature differences ΔT1_1C, ΔT2_1C, and ΔT3_1C are the temperature differences of the secondary battery system 100 of this embodiment when the C-rate is 1C, 2C, and 3C, respectively. The temperature difference ΔT2_2C is the temperature difference when the heating unit 20 of the secondary battery system 100 is not heating when the C-rate is 2C. The temperature differences ΔT3_1C and ΔT3_2C are the temperature differences during cooling of the secondary battery system of the comparative example when the C-rate is 1C and 2C. In the comparative example, a liquid-cooling system using coolant is used. In the comparative example, 5 mm resin plates are arranged between the five secondary batteries BT, and cooling water flows vertically below the secondary batteries BT in the housing portion 30 of this embodiment.

[0028] The temperature difference ΔT1_2C of the secondary battery system 100 during discharge at a C-rate of 2C was 6.4°C, lower than the temperature difference ΔT2_2C of 8.9°C when the secondary battery system 100 was not heated by the heating unit 20 and the temperature difference ΔT3_2C of 17.4°C in the comparative example. That is, during discharge at a C-rate of 2C, the cooling performance of the secondary battery system 100 of this embodiment is the highest among the three maximum and minimum temperature differences. Similarly, the temperature difference ΔT1_1C of the secondary battery system 100 during discharge at a C-rate of 1C was 3.1°C, lower than the temperature difference ΔT3_1C of 9.2°C in the comparative example. The temperature difference ΔT1_3C of the secondary battery system 100 during discharge at a C-rate of 3C was 12.7°C. Note that in the comparative example during discharge at a C-rate of 3C, the maximum battery temperature exceeded the set upper limit of 45°C, so the maximum and minimum temperature difference was not measured.

[0029] Fig. 5 is an explanatory diagram of temperature changes in the maximum temperature T1max_C2 (dashed line) and minimum temperature T1min_C2 (solid line) of the secondary battery system 100 during discharge at a C rate of 2 C. Fig. 6 is an explanatory diagram of temperature changes in the maximum temperature T3max_C2 (dashed line) and minimum temperature T3min_C2 (solid line) of the comparative example during discharge at a C rate of 2 C. Each of Figs. 5 and 6 shows the time progression of the maximum and minimum temperatures among the temperatures measured at 50 locations.

[0030] The temperature difference between the maximum temperature and the minimum temperature shown in Figures 5 and 6 is the temperature difference when the SOC (State of Charge) decreases from 96% to 13% during discharge. As shown in Figure 5, in this embodiment, the maximum temperature T3max_C2 and the minimum temperature T3min_C2 increase after decreasing between 10 and 20 minutes of elapsed time. The reason for the temporary temperature decrease is that the cooling capacity of the cooling system 101 exceeds the heat generation amount of the secondary battery BT. On the other hand, as shown in Figure 6, the maximum temperature T3max_C2 and the minimum temperature T3min_C2 in the comparative example increase over time, and the maximum-minimum temperature difference ΔT3_2C between the maximum temperature T3max_C2 and the minimum temperature T3min_C2 increases to 17.4°C.

[0031] FIG. 7 is an explanatory diagram of the temperature change of the secondary battery BT during discharge at a C rate of 2C. FIG. 7 shows the time progression of the voltage V1_2C (solid line) of the secondary battery BT in the secondary battery system 100 of this embodiment and the voltage V3_2C (dashed line) of the secondary battery BT of the comparative example. The resistance value of the secondary battery BT decreases as the temperature of the secondary battery BT increases. Therefore, the voltage V3_2C of the comparative example, which has a higher temperature than this embodiment, transitions higher than the voltage V1_2C of this embodiment at the same current. In other words, the fact that the voltage V1_2C of this embodiment transitions lower than the voltage V3_2C of the comparative example at the same current indicates that the cooling system 101 of this embodiment suppresses the temperature rise of the secondary battery BT.

[0032] The compression unit 70 shown in FIG. 1 is a compressor that compresses the heat exchange medium 80 discharged from the cooling unit 10 before being supplied to the heating unit 20. The heat dissipation unit 60 is a radiator that dissipates heat from the heat exchange medium 80 discharged from the heating unit 20. In the radiator, a fan blows outside air through tubes through which the heat exchange medium 80 flows. The expansion unit 65 is an expansion valve that expands the heat exchange medium 80, whose temperature has been reduced by the heat dissipation unit 60, before being supplied to the cooling unit 10. The expansion unit 65 expands the heat exchange medium 80 to a low temperature and low pressure. Therefore, in the cooling system 101 of this embodiment, the cooling unit 10 and the heating unit 20 function as an evaporator and a condenser in a refrigeration cycle, respectively.

[0033] The control unit 90 sets the pressure level of the heat exchange medium 80, which is compressed to a high temperature and high pressure, by controlling the rotation speed of the motor of the compressor, which is the compression unit 70. The control unit 90 also sets the pressure level of the heat exchange medium 80, which is expanded to a low temperature and low pressure, by adjusting the opening degree of the expansion valve, which is the expansion unit 65. Controlling the pressure level by the control unit 90 of this embodiment allows for temperature setting with less sensible heat loss and higher response than conventional methods of controlling the cooling temperature of the cooling unit 10 and the heating temperature of the heating unit 20 using a circulating water pump.

[0034] FIG. 8 is a Mollier diagram (ph(pressure-enT h COP (Coefficient of Performance) of the refrigeration cycle in this embodiment is β, cold energy (β×Wc) and hot energy ((1+β)×Wc) are generated for the work Wc of the compressor. The COP of the refrigeration cycle is high, and the power consumption for generating cold energy to cool the secondary battery BT is small. In this embodiment, the required cold energy (β×Wc) is calculated by multiplying the heat generation amount Q of the secondary battery BT by β. b (= (Y Cap) 2 ×R b (Y: C rate, Cap (A h ): Capacity, R bThe output Pbat (=V×Y·Cap, V: voltage) during charging and discharging of the secondary battery BT is sufficiently large compared to the amount of heat generated by the battery. Therefore, the increase in power required for heating by the heating unit 20 is small compared to the output Pbat of the charging and discharging value of the secondary battery BT. In other words, the cooling capacity of the secondary battery BT is improved by heating by the heating unit 20, which requires only a small amount of power.

[0035] The control unit 90 shown in FIG. 1 detects the battery temperature T b and the heating temperature T h and the heat generation amount Q of the secondary battery BT b The control unit 90 acquires the C rate of the secondary battery BT during charging and discharging and the previously acquired capacity A of the secondary battery BT. h and the battery resistance R of the secondary battery BT b By acquiring the above, the heat generation amount Q of the secondary battery BT is calculated. b The control unit 90 calculates the battery temperature T b and heating temperature T h and the heat generation amount Q b The cooling temperature T of the cooling unit 10 is controlled by controlling the expansion unit 65 using the c In this embodiment, the control unit 90 sets the heat generation amount Q b It also functions as a heat generation amount acquisition unit that acquires the heat generation amount.

[0036] 9 is a schematic block diagram of a thermal circuit in the secondary battery system 100. In FIG. 9, the cooling unit 10, the heating unit 20, and the secondary battery BT, which are heat sources, and the thermal resistances between the components are shown as a modeled thermal circuit. As shown in FIG. 9, the vapor temperature T s and cooling temperature T c The thermal resistance of the cooling part K c is expressed as the following formula (1): b and steam temperature T s Secondary battery thermal resistance K b is expressed by the following formula (2): h and steam temperature T sHeating part thermal resistance K h is expressed as the following formula (3).

[0037] In addition, A shown in formulas (1) to (3) c , A b , A h is the heat transfer area (m 2 ) α c , α b , α h is the heat transfer coefficient (W / (m 2 ・K)).

[0038] Each thermal resistance K c , K b , K h The heat flowing through each c , Q b , Q h (W), and the temperature difference between each thermal resistance is ΔT c , ΔT b , ΔT h Then, from the relationship of the following equation (4), the temperature difference ΔT c , ΔT b , ΔT h The relationship is expressed as the following formula (5).

[0039] Here, for the refrigerant 50 flowing through the gas flow path 31 by vapor heat transport, the flow rate of the refrigerant 50 vaporized in each of the heating unit 20 and the liquid flow path 40 is defined as M h , M b (mol / s), and the flow rate of the refrigerant 50 liquefied in the cooling unit 10 is M c (mol / s), the relationship of the following formula (6) is derived. V in formula (6) is the spatial volume (m 3 ) where R is the gas constant (J / (mol·K)). δP is the vapor pressure P s is the pressure difference obtained by subtracting the saturated vapor pressure from the pressure.

[0040] When the differential pressure δP in the above formula (6) is greater than zero, the vapor pressure P sWhen the differential pressure δP is smaller than zero, excess cooling occurs and liquid refrigerant 50 accumulates on the upper surface of the heating unit 20. When the differential pressure δP is zero, all of the liquid refrigerant 50 is vaporized.

[0041] The preset target temperature of the secondary battery BT is set to the battery temperature T b By setting the above, the relationship of the following formula (7) is established. The heat generation amount Q of the secondary battery BT in the following formula (7) b As described above, the C rate, the capacity Cap, and the battery resistance R b It is calculated from the following.

[0042] In this embodiment, the vapor quality x that does not cause dryout of the refrigerant 50 in the liquid flow path 40 is out is given. Steam quality x out Using the above, the heat ratio (Q b / Q c ) is x out : (1-x out ) and the temperature difference ΔT b is expressed as the following equation (9).

[0043]

[0044] From the relationship of the above formula (5), the cooling temperature T c is expressed as the following formula (10): By using the relationship of the above formula (9) in the following formula (10), the temperature difference ΔT c is expressed by the following formula (11): Using the following formula (11), the cooling temperature T c The set cooling temperature T c is the temperature of the cooling section 10 for preventing dryout from occurring in the liquid flow path 40.

[0045] As described above, in the cooling system 101 for the secondary battery BT of this embodiment, the cooling unit 10 is disposed vertically above the liquid flow path 40 and the gas flow path 31, and the heating unit 20 is disposed vertically below the liquid flow path 40 and the gas flow path 31. The liquid flow path 40 of the plate-shaped member contacts the secondary battery BT on the surface facing the negative X-axis direction and contacts the gas flow path 31 on the surface facing the positive X-axis direction. In this embodiment, the liquid refrigerant 50 moving inside the liquid flow path 40 in contact with the secondary battery BT vaporizes and flows into the gas flow path 31 through heat exchange with the secondary battery BT, which generates heat during charging and discharging. The gas refrigerant 50 flowing into the gas flow path 31 moves vertically upward through the gas flow path 31 and is cooled by the cooling unit 10. The cooled gas refrigerant 50 condenses and moves vertically downward again through the liquid flow path 40 to cool the secondary battery BT. Liquid refrigerant 50 that does not vaporize due to heat exchange with the secondary battery BT moves vertically downward and is heated by the heating unit 20. The heated liquid refrigerant 50 vaporizes and moves vertically upward through the liquid flow path 40. In this embodiment, the liquid refrigerant 50 that moves vertically downward is vaporized by the heating unit 20, so the flow rate of the liquid refrigerant 50 moving inside the liquid flow path 40 increases by the amount of refrigerant 50 vaporized by the heating unit 20. By increasing the amount of refrigerant 50 flowing inside the accommodating unit 30, air bubbles that form dry patches due to a temperature rise in the secondary battery BT are removed. Furthermore, because the vapor mass ratio (the ratio of liquid flow rate to total weight) of the refrigerant 50 that flows vertically downward without vaporizing due to heat exchange with the secondary battery BT is reduced, dryout in the liquid flow path 40 is suppressed even if the heat generated by the secondary battery BT becomes excessively large. As a result, even if the heat generation of the secondary battery BT becomes excessively large due to environmental disturbance or input fluctuation to the secondary battery BT, the secondary battery BT is cooled with good robustness.

[0046] In addition, the boiling point of the refrigerant 50 in this embodiment is set to 20° C. The recommended operating temperature of the secondary battery BT in this embodiment is approximately 5° C. to 45° C. By operating the refrigerant 50 at a boiling point of 20° C., which is within the recommended operating temperature range, the secondary battery BT is efficiently cooled by vapor heat transport using the latent heat of evaporation of the refrigerant 50.

[0047] Furthermore, in this embodiment, the liquid flow paths 40 are formed of a porous material. Therefore, the porous liquid flow paths 40 can slow down the speed of the liquid refrigerant 50 moving vertically downward within the liquid flow paths 40. Therefore, the latent heat of evaporation of the refrigerant 50 condensed by the cooling unit 10 can be used more effectively to cool the secondary battery BT, improving the efficiency of the entire cooling system 101.

[0048] In addition, the control unit 90 of this embodiment detects the battery temperature T b and the heating temperature T h and the heat generation amount Q of the secondary battery BT b The cooling temperature T of the cooling unit 10 is controlled by controlling the expansion unit 65 using the c In this embodiment, the vapor quality x , which is the ratio of vapor of the refrigerant 50 in the liquid flow path 40 and the gas flow path 31, is set. out is calculated from the change in the differential pressure δP obtained by subtracting the vapor pressure from the saturated vapor pressure. The change in the differential pressure δP is calculated based on the battery temperature T b and heating temperature T h and the heat generation amount Q of the secondary battery BT b and the cooling temperature T c In this embodiment, the steam quality x at which dryout does not occur is determined. out The cooling temperature T of the cooling unit 10 c This suppresses excessive heat generation in the secondary battery BT due to depletion of the liquid refrigerant 50 on the vertically lower side of the liquid flow path 40 where dryout is likely to occur, and maintains a more uniform temperature throughout the secondary battery BT.

[0049] In this embodiment, the compression section 70 compresses the heat exchange medium 80 discharged from the cooling section 10 before it is supplied to the heating section 20. The heat dissipation section 60 dissipates heat from the heat exchange medium 80 discharged from the heating section 20. The expansion section 65 expands the heat exchange medium 80, whose temperature has been reduced by the heat dissipation section 60, before it is supplied to the cooling section 10. In this embodiment, a refrigeration cycle is formed in which the pressure level of the heat exchange medium 80 supplied to the cooling section 10 is adjusted by the expansion section 65, and the pressure level of the heat exchange medium 80 supplied to the heating section 20 is adjusted by the compression section 70. Therefore, adjustment of the expansion section 65 increases or decreases the pressure difference between the heat exchange medium 80 supplied to the cooling section 10 and the heat exchange medium 80 supplied to the heating section 20. Adjustment of the compression section 70 increases or decreases the pressure of the entire heat exchange medium 80. Furthermore, in this embodiment, compared to conventional cooling using a circulating water pump, sensible heat loss from auxiliary equipment, etc. is reduced, and the temperatures of the heating unit 20 and the cooling unit 10 are set with high response. Furthermore, because the heat transfer coefficient of the two-phase flow during evaporation of the refrigerant 50 by the heating unit 20 and condensation of the refrigerant 50 by the cooling unit 10 is high, the high overall heat transfer coefficient enables large-volume heat exchange with a small temperature difference. As a result, the power consumption of the cooling system 101 is reduced without excessively increasing the pressure difference in the refrigeration cycle of this embodiment.

[0050] 10 to 12 are schematic block diagrams of a secondary battery system 100a according to a second embodiment. The secondary battery system 100a according to the second embodiment differs from the secondary battery system 100 according to the first embodiment in that it includes a heat exchanger 66 arranged in parallel with the cooling unit 10 and a bypass flow path FP arranged in parallel with the heating unit 20, with respect to the flow path through which the heat exchange medium 80 flows, and in that the supply destination of the heat exchange medium 80 discharged from the expansion unit 65 and the supply destination of the heat exchange medium 80 discharged from the compression unit 70 are switched between warming up and cooling down the secondary battery BT. Therefore, in the second embodiment, only the configuration and control that are different from those of the first embodiment will be described, and a description of the configuration and control that are the same as those of the first embodiment will be omitted.

[0051] As shown in FIGS. 10 to 12, the secondary battery system 100a further includes a heat exchanger 66 arranged in parallel with the cooling unit 10 and exchanging heat between the heat exchange medium 80 and the atmosphere, a bypass flow path FP arranged in parallel with the heating unit 20, and a vapor pressure P s a pressure sensor (vapor pressure acquisition unit) SS3 that detects the current I flowing through the secondary battery BT; b The battery system 100a includes an ammeter (current acquisition unit) SS4 that detects the current flowing through the battery BT and four three-way valves V1 to V4. FIG. 10 shows a schematic block diagram of the secondary battery system 100a in a connected state during warm-up of the secondary battery BT. FIGS. 11 and 12 show schematic block diagrams of the secondary battery system 100a in a connected state during cooling of the secondary battery BT. Of the four three-way valves V1 to V4, the first three-way valve V1 opens and closes the connection between the heat exchanger 66 or the cooling unit 10 and the compression unit 70. The second three-way valve V2 opens and closes the connection between the expansion unit 65 and the heat exchanger 66 or the cooling unit 10. The third three-way valve V3 opens and closes the connection between the compression unit 70 and the heating unit 20 or the bypass flow path FP. The fourth three-way valve V4 opens and closes the connection between the heating unit 20 or the bypass flow path FP and the heat dissipation unit 60.

[0052] The recommended operating temperature for the secondary battery BT in this embodiment is 5°C to 40°C. If charging or discharging is performed when the temperature of the secondary battery BT is too low, the secondary battery BT will deteriorate. For example, when charging or discharging is started in a cold region, or when intermittent discharging occurs due to traffic congestion or the like while the secondary battery BT is not warmed up, the battery temperature T b In such a case, the secondary battery system 100a of the second embodiment does not cool the secondary battery BT using the cooling unit 10, but instead warms up the secondary battery BT by heating the heat exchange medium 80 using the heating unit 20 and the heat exchange unit 66 arranged in parallel to the cooling unit 10.

[0053] The control unit (supply destination setting unit) 90a detects the battery temperature T b The control unit 90a acquires the battery temperature T bWhen the temperature T is less than a preset temperature threshold Ttar (e.g., 5°C), the controller 90a selects the heat exchange medium 80 discharged from the expansion unit 65 to be supplied to the heat exchange unit 66, thereby warming up the secondary battery BT. As shown in Fig. 10 , the controller 90a controls the opening and closing of the first three-way valve V1 to connect the heat exchange unit 66 and the compression unit 70, and the second three-way valve V2 to connect the expansion unit 65 and the heat exchange unit 66. The controller 90a also controls the opening and closing of the third three-way valve V3 to connect the compression unit 70 and the heating unit 20, and the fourth three-way valve V4 to connect the heating unit 20 and the heat dissipation unit 60. During warm-up, the controller 90a stops the first fan FN1 of the heat dissipation unit 60 and activates the second fan FN2 of the heat exchange unit 66.

[0054] Fig. 13 is a Mollier diagram of the refrigeration cycle during warm-up in the second embodiment. Fig. 13 shows the case where the outside air temperature is 0°C. In the second embodiment, the control unit 90a controls the expansion unit 65 to set the temperature of the heat exchange medium 80 supplied from the expansion unit 65 to the heat exchange unit 66 to -15°C and set the pressure of the heat exchange medium 80 to 0.16 MPa during warm-up. The heat exchange unit 66 heats the heat exchange medium 80 by heat exchange with outside air that is hotter than the temperature of the heat exchange medium 80 (e.g., 0°C).

[0055] The control unit 90a controls the compression unit 70 to compress the heat exchange medium 80 supplied from the heat exchange unit 66 to the compression unit 70 to a high temperature and high pressure. The compression unit 70 compresses the heat exchange medium 80 supplied to the heating unit 20 so that the temperature of the heat exchange medium 80 is 40°C and the pressure of the heat exchange medium 80 is 1 MPa. As a result, the heat exchange medium 80 at 40°C supplied to the heating unit 20 warms up the secondary battery BT in the accommodation unit 30 through vapor heat transport of the refrigerant 50.

[0056] The control unit 90a calculates the acquired battery temperature T bis equal to or greater than the temperature threshold value Ttar, the supply destination of the heat exchange medium 80 discharged from the expansion section 65 is set to the cooling section 10, and the secondary battery BT is cooled. The control section 90a controls the opening and closing of the first three-way valve V1 to connect the cooling section 10 and the compression section 70, and controls the opening and closing of the second three-way valve V2 to connect the expansion section 65 and the cooling section 10. When the second fan FN2 is operating, the control section 90a stops the second fan FN2.

[0057] Furthermore, the control unit 90a controls the vapor pressure P s and the current I flowing through the secondary battery BT detected by the ammeter SS4. b The saturation temperature Ts,cal of the refrigerant 50 in the gas flow path 31 is calculated based on the thermal resistance K of the secondary battery expressed by the above formula (2). b and the battery temperature T b Using the above, it is expressed as in the following equation (13).

[0058] In this embodiment, the control unit 90a sets the vapor pressure at the saturation temperature Ts,cal as the pressure threshold Ps,tar. In other words, the pressure threshold Ps,tar is determined by the ratio of the current I b The vapor pressure P obtained when cooling the secondary battery BT is determined according to s is equal to or greater than a preset pressure threshold Ps,tar, the control unit 90a sets the supply destination of the heat exchange medium 80 discharged from the compression unit 70 to the heating unit 20. The control unit 90a controls the opening and closing of the third three-way valve V3 to connect the compression unit 70 and the heating unit 20, and controls the opening and closing of the fourth three-way valve V4 to connect the heating unit 20 and the heat dissipation unit 60. In this case, the control unit 90a also sets the rotation speed of the first fan FN1 to high rotation N_high as shown in FIG. 11 . When the refrigerant 50 is heated by the heating unit 20, the cooling heat quantity Q of the cooling unit 10 is c is the heat generation amount Q of the secondary battery BT b and the heating heat quantity Q of the heating unit 20 h It is the sum of.

[0059] 14 is a Mollier diagram of the refrigeration cycle during cooling in the second embodiment. s14 shows a Mollier diagram of a state in which heating is being performed by the heating unit 20 when the pressure is equal to or greater than the pressure threshold Ps,tar. During cooling while heating is being performed by the heating unit 20 as shown in FIG. 14 , the control unit 90a controls the expansion unit 65 to set the temperature of the heat exchange medium 80 supplied from the expansion unit 65 to the cooling unit 10 to 15°C and the pressure of the heat exchange medium 80 to 0.48 MPa. As a result, the heat exchange medium 80 at 15°C is supplied to the cooling unit 10. The control unit 90a compresses the heat exchange medium 80 supplied from the cooling unit 10 to the compression unit 70 to a high temperature and high pressure. The compression unit 70 compresses the heat exchange medium 80 supplied to the heating unit 20 so that the temperature of the heat exchange medium 80 is 45°C and the pressure of the heat exchange medium 80 is 1.16 MPa. As a result, the 45°C heat exchange medium 80 supplied to the heating unit 20 heats the storage unit 30. The secondary battery BT is cooled by vapor heat transport of the coolant 50 circulating through the liquid flow path 40 and the gas flow path 31, in the same manner as in the first embodiment.

[0060] On the other hand, when cooling, the vapor pressure P s is less than the pressure threshold value Ps,tar, the control unit 90a sets the supply destination of the heat exchange medium 80 discharged from the compression unit 70 to the bypass flow path FP. The control unit 90a controls the opening and closing of the third three-way valve V3 to connect the compression unit 70 and the bypass flow path FP, and controls the opening and closing of the fourth three-way valve V4 to connect the bypass flow path FP and the heat dissipation unit 60. s When the amount of heat generated by the secondary battery BT is low, a large amount of liquid refrigerant 50 is present in the storage section 30. b In this state, the control unit 90a does not heat the inside of the accommodation unit 30 by the heating unit 20. In this case, the control unit 90a sets the rotation speed of the first fan FN1 to low rotation N_low as shown in FIG. 12. When the refrigerant 50 is not heated, the cooling heat quantity Q of the cooling unit 10 c is the heat generation amount Q of the secondary battery BT b is equal to.

[0061] 15 is a flowchart of a control method for the cooling system 101a in the second embodiment. In the control flow shown in FIG. 15, the control unit 90a first calculates the battery temperature T b (Step S1). The control unit 90a acquires the battery temperature T b It is determined whether the battery temperature T is smaller than the temperature threshold value Ttar (step S2). b If it is determined that the temperature T is smaller than the temperature threshold Ttar (step S2: YES), the control unit 90a connects the heat exchange unit 66 and the heating unit 20 so that the heat exchange medium 80 flows through them, and warms up the secondary battery BT (step S3). The control unit 90a controls the opening and closing of the four three-way valves V1 to V4 so as to achieve the connection state shown in FIG.

[0062] The control unit 90a sets the compression of the heat exchange medium 80 by the compression unit 70 and the expansion of the heat exchange medium 80 by the expansion unit 65 to the pressure levels during warm-up (step S4). In this embodiment, the compression unit 70 during warm-up compresses the heat exchange medium 80 so that the temperature of the heat exchange medium 80 is 40°C and the pressure of the heat exchange medium 80 is 1 MPa, as shown in the Mollier diagram of Fig. 13. Furthermore, the expansion unit 65 during warm-up expands the heat exchange medium 80 so that the temperature of the heat exchange medium 80 is -15°C and the pressure of the heat exchange medium 80 is 0.16 MPa.

[0063] The control unit 90a stops the first fan FN1 of the heat dissipation unit 60 and activates the second fan FN2 of the heat exchange unit 66 (step S5). Thereafter, the control unit 90a determines whether or not to end the control flow (step S10). The end determination is made based on the presence or absence of an input such as the stopping of the vehicle in which the secondary battery system 100a is mounted. If it is determined not to end the control flow (step S10: NO), the control unit 90a again measures the battery temperature T b It is determined whether or not the temperature is smaller than the temperature threshold value Ttar (step S2).

[0064] Battery temperature T bis equal to or higher than the temperature threshold value Ttar (step S2: NO), the control unit 90a controls the first three-way valve V1 and the second three-way valve V2 so that the expansion unit 65 and the compression unit 70 are connected to the cooling unit 10 (step S6). If the second fan FN2 of the heat exchange unit 66 is operating at this time, the control unit 90a stops the second fan FN2.

[0065] The control unit 90a sets the compression of the heat exchange medium 80 by the compression unit 70 and the expansion of the heat exchange medium 80 by the expansion unit 65 to pressure levels during cooling (step S7). In this embodiment, the compression unit 70 during cooling compresses the heat exchange medium 80 so that the temperature of the heat exchange medium 80 is 45°C and the pressure of the heat exchange medium 80 is 1.16 MPa, as shown in the Mollier diagram of Fig. 14. Furthermore, the expansion unit 65 during cooling expands the heat exchange medium 80 so that the temperature of the heat exchange medium 80 is 15°C and the pressure of the heat exchange medium 80 is 0.48 MPa. Thereafter, the control unit 90a performs a heating setting process (step S8).

[0066] 16 is a sub-flowchart of the heating setting process. In the heating setting sub-flow shown in FIG. 16, the control unit 90a calculates the steam pressure P s (Step S81). The control unit 90a acquires the acquired steam pressure P s It is determined whether or not the pressure threshold Ps,tar is less than the pressure threshold Ps,tar (step S82). The pressure threshold Ps,tar is determined by the current I b It is determined according to the

[0067] Vapor pressure P sIf it is determined that Ps,tar is less than the pressure threshold value Ps,tar (step S82: YES), the control unit 90a connects the bypass flow path FP so that the heat exchange medium 80 compressed by the compression unit 70 is supplied to the bypass flow path FP (step S83). The control unit 90a controls the third three-way valve V3 to connect the compression unit 70 to the bypass flow path FP, and controls the fourth three-way valve V4 to connect the bypass flow path FP to the heat dissipation unit 60. Next, the control unit 90a sets the rotation speed of the first fan FN1 to high rotation speed N_high and operates the first fan FN1 (step S84). Thereafter, the process of step S9 in FIG. 15, which will be described later, is performed.

[0068] In the process of step S82, the steam pressure P s If it is determined that Ps,tar is equal to or greater than the pressure threshold value Ps,tar (step S82: NO), the control unit 90a connects the heat exchange medium 80 compressed by the compression unit 70 to the heating unit 20 (step S85). The control unit 90a controls the third three-way valve V3 to connect the compression unit 70 and the heating unit 20, and controls the fourth three-way valve V4 to connect the heating unit 20 and the heat dissipation unit 60. Next, the control unit 90a sets the rotation speed of the first fan FN1 to low rotation speed N_low and operates the first fan FN1 (step S86).

[0069] 15 is completed, the control unit 90a starts charging or discharging the secondary battery BT (step S6). If the secondary battery BT is already being charged or discharged, the charging or discharging continues. If it is determined in the processing of step S10 that the control flow should be ended (step S10: YES), the control flow ends.

[0070] As described above, the cooling system 101a for the secondary battery BT of the second embodiment includes the heat exchanger 66 arranged in parallel with the cooling unit 10. The control unit 90a controls the battery temperature T b is less than a preset temperature threshold Ttar (for example, 5° C.), the supply destination of the heat exchange medium 80 discharged from the expansion section 65 is set to the heat exchange section 66, and the secondary battery BT is warmed up. bWhen the temperature of the heat exchange medium 80 is equal to or higher than the temperature threshold Ttar, the supply destination of the heat exchange medium 80 discharged from the expansion section 65 is set to the cooling section 10 to cool the secondary battery BT. In this embodiment, the supply destination of the heat exchange medium 80 is switched based on the temperature threshold Ttar, which is a constant temperature. In conventional heat pump systems, a four-way valve is used to switch between high and low temperature heat exchange medium 80, which can easily deteriorate and malfunction due to thermal shock during switching. Furthermore, in conventional systems, the flow direction of the heat exchange medium 80 is reversed upon switching. In contrast, in this embodiment, the temperature of the heat exchange medium 80 at the time of supply destination switching is near the temperature threshold Ttar, which reduces thermal shock and reduces malfunctions. Furthermore, in this embodiment, the flow direction of the heat exchange medium 80 does not change before and after switching the heat exchange medium 80, thereby shortening the response time required for control. By achieving high-response switching, for example, when the secondary battery BT is used as a power source for an automobile, it can be used for intermittent warm-up even during short wait times at traffic lights. Furthermore, even when charging / discharging is started during warm-up, the time required to switch the supply destination of the heat exchange medium 80 is short, so that the secondary battery BT is prevented from becoming too hot due to resistance heat generation during switching, and cooling of the secondary battery BT begins quickly.

[0071] In addition, the control unit 90a of this embodiment calculates the vapor pressure P s is equal to or greater than a preset pressure threshold Ps,tar, the supply destination of the heat exchange medium 80 discharged from the compression section 70 is set to the heating section 20. s If the pressure is less than the pressure threshold Ps,tar, the supply destination of the heat exchange medium 80 discharged from the compression unit 70 is set to the bypass flow path FP. b and the secondary battery thermal resistance K k ... b The saturation temperature Ts,cal of the refrigerant 50 is calculated using the above formula. The vapor pressure at the saturation temperature Ts,cal is set as the pressure threshold Ps,tar, and the acquired vapor pressure P s When the vapor pressure P sis equal to or less than the pressure threshold Ps,tar, this indicates that the flow rate of the liquid refrigerant 50 is sufficient. When the flow rate of the liquid refrigerant 50 is sufficient, the heat exchange medium 80 is not heated by the heating unit 20 using the heat exchange medium 80, but is instead passed through the bypass flow path FP, thereby reducing the power required for heating. This reduces the power consumed for cooling the secondary battery BT.

[0072] <Modifications of the Embodiments> The present invention is not limited to the above-described embodiments, and can be embodied in various forms without departing from the spirit thereof, including, for example, the following modifications: In the above-described embodiments, part of the configuration realized by hardware may be replaced with software, and conversely, part of the configuration realized by software may be replaced with hardware.

[0073] <Variation 1> In the first and second embodiments, examples of the secondary battery system 100, 100a and the cooling system 101, 101a for the secondary battery BT were described. However, the secondary battery system and the cooling system can be modified as long as a cooling unit is disposed vertically above the liquid flow path 40 and the gas flow path 31, a heating unit is disposed vertically below the liquid flow path 40, and the secondary battery BT is cooled by vapor heat transport using the refrigerant 50. For example, the number of secondary batteries BT disposed in the housing 30 and the shapes and sizes of the liquid flow path 40 and the gas flow path 31 can be modified. While a fluorocarbon-based medium with a boiling point of 20°C is used as the refrigerant 50, a boiling point higher or lower than 20°C may be used, and a heat medium other than a fluorocarbon-based medium may also be used. The boiling point of the refrigerant 50 is preferably 20°C or higher and 40°C or lower.

[0074] In the first embodiment, a porous material is used as the material for forming the liquid flow path 40. However, the liquid flow path 40 can be deformed within the range of a plate-like member on or inside of which the liquid refrigerant 50 can move. For example, the liquid flow path 40 may be formed from urethane foam, or from a metal plate with grooves formed on the surface that contacts the gas flow path 31. The liquid flow path 40 may also be formed from urethane foam or sandblasted onto the surface of the secondary battery BT.

[0075] Although the cooling system 101 of the first embodiment includes the first temperature sensor SS1, the second temperature sensor SS2, and the control unit 90, these may not be included. The cooling system 101 does not need to be controlled using temperatures detected by the temperature sensors SS1 and SS2. The secondary battery system and the cooling system can be modified to the extent that the amount of refrigerant 50 circulating in the accommodation unit 30 is increased by heating using the heating unit 20, thereby improving cooling capacity. In the cooling system 101, the refrigerant is cooled and heated by the heat exchange medium 80 circulating between the heating unit 20 and the cooling unit 10. However, the temperature of the refrigerant 50 may be adjusted by heating using the heating unit, which is a heater, and cooling using circulating coolant using the cooling unit 10. Although a radiator of an automobile equipped with a secondary battery BT is used as the heat dissipation unit 60 of the first embodiment, a device other than a radiator may be used. Furthermore, the expansion unit 65 may be a device other than an expansion valve. The compression unit 70 may be a device other than a compressor.

[0076] <Modification 2> The cooling system 101a of the second embodiment warms up the secondary battery BT using the heat exchange medium 80, but the system may not require warming. The cooling system 101a may not include the heat exchanger 66 and may simply warm up the secondary battery BT using the heater 20 alone. The control unit 90a of the cooling system 101a implemented two cooling methods for the secondary battery BT: one using the heater 20 for heating and one using the bypass flow path FP without heating. However, the cooling methods do not need to be divided into multiple types. The control unit 90a may not include the bypass flow path FP, and the heater 20 may be a heater, and multiple cooling methods may be implemented by switching between using and not using the heater. The control unit 90a may maintain a constant rotation speed of the first fan FN1 of the heat dissipation unit 60 during cooling.

[0077] The control unit 90a of the second embodiment controls the current I flowing through the secondary battery BT. b The pressure threshold Ps,tar may be set without using the temperature and vapor pressure P of the refrigerant 50. sIt may be given as a map function that depends on , or as a single constant threshold.

[0078] This aspect has been described above based on embodiments and modifications. However, the above-described embodiments are intended to facilitate understanding of this aspect and are not intended to limit this aspect. This aspect may be modified or improved without departing from the spirit and scope of the claims, and equivalents thereof are included in this aspect. Furthermore, if a technical feature is not described as essential in this specification, it may be deleted as appropriate.

[0079] The present invention can also be realized in the following aspects. [Application Example 1] A cooling system for a secondary battery, comprising: a liquid flow path for moving a liquid refrigerant downward in the vertical direction, the liquid flow path being formed by a plate-like member having a pair of surfaces and allowing the liquid refrigerant to move on or inside the liquid flow path, with the secondary battery in contact with one of the pair of surfaces; a gas flow path for moving a gas refrigerant upward in the vertical direction, the gas flow path being adjacent to the other of the pair of surfaces of the liquid flow path and allowing refrigerant to move between the liquid flow path and the gas flow path via the other surface; a cooling unit located vertically above the liquid flow path and the gas flow path, which cools the gas refrigerant to a liquid; and a heating unit located vertically below the liquid flow path and the gas flow path, which heats the liquid refrigerant to a gas. [Application Example 2] The cooling system according to Application Example 1, wherein the boiling point of the refrigerant is equal to or higher than 20 degrees Celsius and equal to or lower than 40 degrees Celsius. [Application Example 3] The cooling system according to Application Example 1 or Application Example 2, wherein the liquid flow path is formed of any one of a porous body, a urethane foam, and a metal plate having a groove formed on the other surface. [Application Example 4] The cooling system according to any one of Application Examples 1 to 3, further comprising: a battery temperature acquisition unit that acquires the temperature of the secondary battery, a heating temperature acquisition unit that acquires the temperature of the heating unit, a heat generation amount acquisition unit that acquires the heat generation amount of the secondary battery, and a temperature setting unit that sets the cooling temperature of the cooling unit using the acquired temperature of the secondary battery, the temperature of the heating unit, and the heat generation amount. [Application Example 5] The cooling system according to any one of Application Examples 1 to 4, further comprising: a heat exchange medium circulating between the cooling unit and the heating unit; a compression unit that compresses the heat exchange medium discharged from the cooling unit before being supplied to the heating unit; a heat dissipation unit that dissipates heat from the heat exchange medium discharged from the heating unit; and an expansion unit that expands the heat exchange medium discharged from the heat dissipation unit before being supplied to the cooling unit.[Application Example 6] The cooling system according to any one of Application Examples 1 to 5, further comprising: a heat exchanger arranged in parallel with the cooling unit, exchanging heat between the heat exchange medium and the atmosphere; a battery temperature acquisition unit acquiring the temperature of the secondary battery; and a supply destination determination unit that sets the heat exchanger as the supply destination of the heat exchange medium discharged from the expansion unit when the acquired temperature of the secondary battery is below a temperature threshold, and sets the cooling unit as the supply destination of the heat exchange medium discharged from the expansion unit when the temperature of the secondary battery is equal to or higher than the temperature threshold. Application Example 7 The cooling system according to any one of Application Examples 1 to 6, further comprising: a current acquisition unit that acquires a current of the secondary battery; a vapor pressure acquisition unit that acquires a vapor pressure of the gas flow path; and a bypass flow path that is arranged in parallel with the heating unit and through which the heat exchange medium can flow, wherein the supply destination determination unit sets the supply destination of the heat exchange medium discharged from the compression unit to the heating unit when the temperature of the secondary battery is equal to or higher than the temperature threshold and the vapor pressure is equal to or higher than a pressure threshold determined according to the current, and sets the supply destination of the heat exchange medium discharged from the compression unit to the bypass flow path when the vapor pressure is less than the pressure threshold. Application Example 8 A secondary battery system comprising: a secondary battery; a liquid flow path for moving a liquid refrigerant downward in the vertical direction, the liquid flow path having a pair of surfaces and formed by a plate-like member on or inside of which the liquid refrigerant can move, the liquid flow path being in contact with one of the pair of surfaces; a gas flow path for moving a gas refrigerant upward in the vertical direction, the gas flow path being adjacent to the other of the pair of surfaces of the liquid flow path and allowing refrigerant to move between the gas flow path and the liquid flow path via the other surface; a cooling unit located vertically above the liquid flow path and the gas flow path and cooling the gas refrigerant to liquefy it; and a heating unit located vertically below the liquid flow path and the gas flow path and heating the liquid refrigerant to gas.

[0080] DESCRIPTION OF SYMBOLS 10... Cooling section 20... Heating section 30... Storage section 31... Gas flow path 40... Liquid flow path (liquid flow path) 50... Refrigerant 60... Heat dissipation section 65... Expansion section 66... ​​Heat exchange section 70... Compression section 80... Heat exchange medium 90... Control section (temperature setting section) 90a... Control section (supply destination determination section) 100, 100a... Secondary battery system 101, 101a... Cooling system BT... Secondary battery CS... Cartesian coordinate system Cap... Capacity FN1... First fan FN2... Second fan FP... Bypass flow path P s ...Vapor pressure Ps, tar...Pressure threshold Q b …heat generation amount of secondary battery R b ...Battery resistance SS1...First temperature sensor (battery temperature acquisition unit) SS2...Second temperature sensor (heating unit temperature acquisition unit) SS3...Pressure sensor (vapor pressure acquisition unit) SS4...Ammeter (current acquisition unit) T b ...Battery temperature T c ...Cooling temperature T h ...Heating temperature T s ...Steam temperature Ts, cal...Saturation temperature Ttar...Temperature threshold V1...First three-way valve V2...Second three-way valve V3...Third three-way valve V4...Fourth three-way valve x out …Steam quality

Claims

1. A cooling system for a secondary battery, comprising: a liquid flow path for moving a liquid refrigerant vertically downward, the liquid flow path being formed by a plate-like member having a pair of surfaces and allowing the liquid refrigerant to move on or inside the liquid flow path, with the secondary battery in contact with one of the pair of surfaces; a gas flow path for moving a gas refrigerant vertically upward, the gas flow path being adjacent to the other of the pair of surfaces of the liquid flow path and allowing refrigerant to move between the gas flow path and the liquid flow path via the other surface; a cooling unit located vertically above the liquid flow path and the gas flow path, which cools the gas refrigerant to convert it to a liquid; and a heating unit located vertically below the liquid flow path and the gas flow path, which heats the liquid refrigerant to convert it to a gas.

2. The cooling system according to claim 1, wherein the boiling point of the refrigerant is between 20 and 40 degrees Celsius.

3. A cooling system according to claim 1, wherein the liquid flow path is formed from either a porous material, urethane foam, or a metal plate having grooves formed on the other surface.

4. A cooling system as described in claim 1, further comprising: a battery temperature acquisition unit that acquires the temperature of the secondary battery; a heating temperature acquisition unit that acquires the temperature of the heating unit; a heat generation amount acquisition unit that acquires the amount of heat generated by the secondary battery; and a temperature setting unit that sets the cooling temperature of the cooling unit using the acquired temperature of the secondary battery, the temperature of the heating unit, and the amount of heat generated.

5. A cooling system according to any one of claims 1 to 4, further comprising: a heat exchange medium circulating between the cooling section and the heating section; a compression section that compresses the heat exchange medium discharged from the cooling section before being supplied to the heating section; a heat dissipation section that dissipates heat from the heat exchange medium discharged from the heating section; and an expansion section that expands the heat exchange medium discharged from the heat dissipation section before being supplied to the cooling section.

6. A cooling system as claimed in claim 5, further comprising: a heat exchange unit arranged in parallel with the cooling unit and exchanging heat between the heat exchange medium and the atmosphere; a battery temperature acquisition unit that acquires the temperature of the secondary battery; and a supply destination determination unit that sets the heat exchange unit as the supply destination of the heat exchange medium discharged from the expansion unit when the acquired temperature of the secondary battery is below a temperature threshold, and sets the cooling unit as the supply destination of the heat exchange medium discharged from the expansion unit when the temperature of the secondary battery is equal to or higher than the temperature threshold.

7. A cooling system as defined in claim 6, further comprising: a current acquisition unit that acquires the current of the secondary battery; a vapor pressure acquisition unit that acquires the vapor pressure of the gas flow path; and a bypass flow path that is arranged in parallel with the heating unit and through which the heat exchange medium can flow, wherein the supply destination determination unit sets the supply destination of the heat exchange medium discharged from the compression unit to the heating unit when the temperature of the secondary battery is equal to or higher than the temperature threshold and the vapor pressure is equal to or higher than a pressure threshold determined according to the current, and sets the supply destination of the heat exchange medium discharged from the compression unit to the bypass flow path when the vapor pressure is less than the pressure threshold.

8. A secondary battery system comprising: a secondary battery; a liquid flow path for moving a liquid refrigerant vertically downward, the liquid flow path being formed by a plate-like member having a pair of surfaces and allowing the liquid refrigerant to move on or inside the liquid flow path, with the secondary battery in contact with one of the pair of surfaces; a gas flow path for moving a gas refrigerant vertically upward, the gas flow path being adjacent to the other of the pair of surfaces of the liquid flow path and allowing refrigerant to move between the gas flow path and the liquid flow path via the other surface; a cooling unit located vertically above the liquid flow path and the gas flow path and cooling the gas refrigerant to liquefy it; and a heating unit located vertically below the liquid flow path and the gas flow path and heating the liquid refrigerant to gas.

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