JP2022191869A - Battery cooling device - Google Patents

Abstract

To accurately perform leakage determination of a refrigerant.SOLUTION: A battery cooling device is mounted on a vehicle and includes: a thermosiphon type battery cooling circuit in which a refrigerant is sealed; and a processor for executing leakage determination processing for determining refrigerant leakage from the battery cooling circuit. The battery cooling circuit includes: a cooler for cooling one or a plurality of battery cells by absorbing the heat generated by one or the plurality of battery cells and evaporating a liquid phase refrigerant; a condenser arranged further upward in the vertical direction than the cooler, and for condensing a gaseous phase refrigerant evaporated in the cooler; and a steam passage and a liquid passage. In the leakage determination processing, after the vehicle stops and a predetermined time has elapsed, the processor executes gaseous phase overheat control. After the gaseous phase refrigerant has come into an overheat state by the gaseous phase overheat control, the leakage of the refrigerant is determined based on a comparison result between a pressure detection value by a refrigerant pressure sensor and a pressure estimation value of the refrigerant in the battery cooling circuit under a sealing amount of the refrigerant at the initial sealing time.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a battery cooling device that includes a thermosiphon battery cooling circuit.

Patent Literature 1 discloses a thermosyphon type temperature control device. This temperature control device includes a fluid circulation circuit having an equipment heat exchanger, a condenser, a vapor-phase side pipe, and a liquid-phase side pipe. A vapor-phase refrigerant temperature sensor is arranged in the heat exchange section of the equipment heat exchanger above the proper liquid level position corresponding to the proper amount of refrigerant to be enclosed. The temperature adjustment device includes a fluid amount estimator that estimates the current amount of refrigerant charged by comparing the surface temperature detected by the vapor-phase refrigerant temperature sensor with a reference surface temperature corresponding to the appropriate amount of refrigerant charged.

JP 2019-086214 A

In the technique described in Patent Document 1, as described above, the surface of the heat exchange portion detected by the gas-phase refrigerant temperature sensor arranged in the heat exchange portion above the appropriate liquid level position corresponding to the appropriate amount of encapsulation The amount of refrigerant charge is estimated based on the result of comparison between the temperature and the reference surface temperature corresponding to the appropriate amount of charge. Here, when a thermosiphon type battery cooling device is mounted on a vehicle, the proper liquid surface position in the heat exchange section of the equipment heat exchanger (cooler) changes depending on the inclination of the vehicle. For this reason, in the method using the temperature difference as described in Patent Document 1, a situation may arise in which it is difficult to accurately capture and estimate the liquid level change in the heat exchange part due to the change in the amount of refrigerant charged. . Therefore, the technique described in Patent Document 1 has room for improvement in terms of accurately estimating the refrigerant charge amount.

The present disclosure has been made in view of the problems described above, and an object of the present disclosure is to enable accurate coolant leakage determination in a battery cooling device that includes a thermosiphon type battery cooling circuit.

A battery cooling device according to an aspect of the present disclosure includes a thermosiphon battery cooling circuit mounted on a vehicle and containing a refrigerant, and a processor. The processor executes leakage determination processing for determining refrigerant leakage from the battery cooling circuit.
The battery cooling circuit includes a cooler that cools the one or more battery cells by absorbing heat generated by the one or more battery cells and evaporating a liquid-phase refrigerant, and is arranged vertically above the cooler. is connected between the condenser for condensing the vapor phase refrigerant vaporized in the cooler and between the condenser and the condenser, and the vapor passage for circulating the vapor phase refrigerant to the condenser is connected between the condenser and the condenser, a liquid passage for communicating liquid refrigerant to the cooler.
The battery cooling device further includes a refrigerant pressure sensor attached to the battery cooling circuit to detect the pressure of the refrigerant in the battery cooling circuit, and a superheater for superheating the vapor phase refrigerant.
In the leak determination process, the processor executes vapor-phase superheating control for controlling the superheater so that the vapor-phase refrigerant is superheated after a predetermined time has elapsed since the vehicle stopped. After the phase refrigerant is overheated, refrigerant leakage is determined based on the result of comparison between the pressure detection value by the refrigerant pressure sensor and the pressure estimation value. The estimated pressure value is the estimated pressure value of the refrigerant in the battery cooling circuit under the amount of refrigerant charged at the time of initial charging, and is the product of the pressure of the liquid-phase refrigerant, which is the saturated vapor pressure, and the volume of the liquid-phase refrigerant. and the product of the gas-phase refrigerant pressure and the gas-phase refrigerant volume based on the gas equation of state, divided by the volume of the battery cooling circuit.

A battery cooling device according to another aspect of the present disclosure includes a thermosiphon battery cooling circuit mounted on a vehicle and containing a refrigerant, and a processor. The processor executes leakage determination processing for determining refrigerant leakage from the battery cooling circuit.
The battery cooling circuit includes a cooler that cools the one or more battery cells by absorbing heat generated by the one or more battery cells and evaporating a liquid-phase refrigerant, and is arranged vertically above the cooler. is connected between the condenser for condensing the vapor phase refrigerant vaporized in the cooler and between the condenser and the condenser, and the vapor passage for circulating the vapor phase refrigerant to the condenser is connected between the condenser and the condenser, a liquid passage for communicating liquid refrigerant to the cooler.
The battery cooling device is attached to the battery cooling circuit, and includes a refrigerant pressure sensor that detects the pressure of the refrigerant in the battery cooling circuit, a refrigerant temperature sensor that detects the temperature of the gaseous refrigerant, and a superheater that superheats the gaseous refrigerant. , is further provided.
In the leak determination process, the processor executes vapor-phase superheating control for controlling the superheater so that the vapor-phase refrigerant is superheated after a predetermined time has elapsed since the vehicle stopped. The temperature change rate of the gas-phase refrigerant and the pressure change rate of the refrigerant in the battery cooling circuit obtained using the refrigerant pressure sensor and the refrigerant temperature sensor for a predetermined period after the phase refrigerant becomes overheated are measured at the time of initial charging. Refrigerant leakage is determined by comparing the relationship between the temperature change rate and the pressure change rate under the charged amount of refrigerant.

According to the battery cooling device according to one aspect of the present disclosure, when the temperature of the refrigerant is stabilized after a predetermined time has elapsed since the vehicle stopped, the overheated state on the gas phase side that deviates from the saturated state is the gas phase. Formed using superheat control. Refrigerant leakage is determined based on the result of comparison between the pressure value detected by the refrigerant pressure sensor and the pressure estimated value assuming the amount of refrigerant charged at the time of initial charging. According to this determination method, if the gas phase is overheated, the refrigerant pressure (pressure detection value) will be affected by the decrease in the gas phase volume due to the decrease in the amount of refrigerant charged. can be detected. According to this determination method, it is not necessary to accurately detect changes in the liquid level of the cooler (heat exchange section) due to changes in the amount of refrigerant charged. can be done accurately.

Further, according to the battery cooling device according to another aspect of the present disclosure, after the gas phase overheating state is formed in the same manner as in the above aspect, the refrigerant pressure sensor and The rate of change in temperature of the gas-phase coolant and the rate of change in pressure of the coolant in the battery cooling circuit, which are obtained using a coolant temperature sensor, are calculated as the rate of change in temperature and the rate of change in pressure under the amount of coolant initially charged. Refrigerant leakage is determined by comparing the relationship with velocity. According to such a determination method, the relationship between the pressure change speed (that is, the amount of change in the pressure detection value with respect to time) and the temperature change speed, rather than the pressure detection value itself, which may cause variations due to individual differences in refrigerant pressure sensors. Leak determination is performed using the Therefore, more accurate determination can be performed compared to the above aspect.

1 is a diagram showing a schematic configuration of a battery cooling device according to Embodiment 1; FIG. FIG. 10 is a diagram showing the battery cooling circuit when refrigerant leakage occurs relative to the initial charging state; 4 is a graph showing a saturated vapor pressure curve of a refrigerant; FIG. 4 is a diagram showing the relationship between the volume ratio of the gas phase and liquid phase in the battery cooling circuit and the amount of refrigerant charged when the gas phase refrigerant is in a superheated state. 4 is a flow chart showing the flow of leakage determination processing according to Embodiment 1; 9 is a flow chart showing the flow of leakage determination processing according to the second embodiment; 9 is a graph for explaining an overview of leak determination processing according to Embodiment 2;

Embodiments of the present disclosure will be described below with reference to the accompanying drawings. However, elements common to each figure are given the same reference numerals, and overlapping descriptions are omitted or simplified. When referring to numbers such as the number, quantity, amount, range, etc. of each element in the embodiments shown below, unless otherwise specified or clearly specified in principle, the number referred to However, the technical idea according to the present disclosure is not limited to this. In addition, structures, steps, and the like described in the embodiments shown below are not necessarily essential to the technical concept of the present disclosure, unless otherwise specified or clearly specified in principle.

1-1. Configuration of Battery Cooling Device FIG. 1 is a diagram showing a schematic configuration of a battery cooling device 10 according to Embodiment 1. As shown in FIG. A battery cooling device 10 is mounted on a vehicle. More specifically, the vehicle is equipped with a battery pack 1 . For example, the battery pack 1 contains a plurality of stacked battery cells. However, the number of battery cells accommodated in the battery pack 1 is not particularly limited, and may be one. The battery pack 1 stores electric power to be supplied to the motor for driving the vehicle.

When the battery pack 1 is discharged and charged, each battery cell generates heat as it is energized. Battery cooling device 10 is configured to cool each battery cell in battery pack 1 . FIG. 1 shows, as an example, four battery stacks 2, which are stacks of a plurality of battery cells stacked in the depth direction of the paper.

The battery cooling device 10 transports the heat of the battery cells of each battery stack 2 and radiates the heat. Specifically, the battery cooling device 10 includes a thermosiphon-type battery cooling circuit 12 in which a refrigerant (working fluid) is sealed. Battery cooling circuit 12 includes cooler 14 , condenser 16 , vapor passage 18 and liquid passage 20 .

A steam path 18 connects between each cooler 14 and the condenser 16 . Liquid passages 20 connect between the condenser 16 and each cooler 14 . That is, the steam passage 18 and the liquid passage 20 are formed in an annular shape as refrigerant passages. The battery cooling circuit 12 is a heat pipe that transfers heat by evaporating and condensing a refrigerant. It is configured to be a loop-shaped thermosiphon separated from the passage 20 .

As the refrigerant circulating in the battery cooling circuit 12, for example, a Freon-based refrigerant (eg, R134a or R1234yf) used in a vapor compression refrigeration cycle can be used. Alternatively, other refrigerant such as carbon dioxide or antifreeze may be used as the refrigerant.

As shown in FIG. 1, the cooler 14 is arranged between a pair of battery stacks 2, as an example. Since two pairs of cell stacks 2 are illustrated in FIG. 1, the number of coolers 14 in this example is two. Each cooler 14 is in contact with each side surface of two adjacent cell stacks 2 via, for example, a thermally conductive material 22 . More specifically, the cooler 14 extends in the stacking direction of the battery cells (the depth direction of the paper surface) and is formed to contact each battery cell included in each battery stack 2 via the heat conductive material 22 . ing.

Inside the cooler 14 , a coolant passage that functions as a part of the coolant passage of the battery cooling circuit 12 is formed. A liquid-phase refrigerant is supplied to the cooler 14 from a liquid passage 20 . The cooler 14 cools each battery cell by absorbing heat generated by the battery stack 2 (a plurality of battery cells) and evaporating the liquid-phase coolant.

As shown in FIG. 1, a liquid-phase refrigerant inlet (liquid inlet) 14a to the cooler 14 is provided vertically downward. An outlet (vapor outlet) 14b for the vapor-phase refrigerant from the cooler 14 is provided vertically upward. The liquid inlet 14a and the vapor outlet 14b are arranged opposite to each other in the direction perpendicular to the vertical direction (the depth direction of the paper surface). As a result, the liquid-phase refrigerant supplied to the cooler 14 receives the heat of each battery cell and evaporates (boiling) (boiling cooling). The gas-phase refrigerant (vapor) vaporized inside the cooler 14 moves upward in the vertical direction and flows out from the vapor outlet 14b into the vapor passage 18 .

The vapor passage 18 is a refrigerant passage through which the vaporized refrigerant (vapor-phase refrigerant) in the cooler 14 flows to the condenser 16 . That is, the heat generated in each battery cell is transported to the capacitor 16 by the gas-phase refrigerant. More specifically, the vapor passage 18 is connected to the vapor inlet 16 a of the condenser 16 after the vapor passage 18 is extended vertically upward after the vapor phase refrigerant from each cooler 14 merges.

Inside the capacitor 16, a refrigerant passage that functions as a part of the refrigerant passage of the battery cooling circuit 12 is formed. The condenser 16 cools and condenses the vapor-phase refrigerant vaporized in the cooler 14 . That is, the heat transported from cooler 14 is radiated in condenser 16 .

The condenser 16 is arranged vertically above the cooler 14 . A specific configuration of the condenser 16 for condensing the gas-phase refrigerant is not particularly limited. For example, the condenser 16 may be configured to heat-exchange a low-pressure refrigerant flowing through a refrigeration cycle device used in a vehicle interior air conditioning system with a vapor-phase refrigerant. Furthermore, for example, the condenser 16 may be configured to heat-exchange a fluid (eg, long-life coolant (LLC)) cooled by the low-pressure refrigerant flowing through the refrigeration cycle device with the vapor-phase refrigerant. Further, for example, the condenser 16 may be configured as an air-cooled radiator configured to heat-exchange ambient air with a vapor-phase refrigerant. In the following description, as an example, the condenser 16 is assumed to have a configuration for exchanging heat between the LLC and the gas-phase refrigerant.

Additionally, according to the two examples of using the refrigeration cycle device described above, by controlling the temperature of the fluid (the low-pressure refrigerant or LLC) that exchanges heat with the refrigerant in the condenser 16 by controlling the refrigeration cycle device, It is possible to perform temperature control (temperature control) of the gas-phase refrigerant including not only cooling of the gas-phase refrigerant but also superheating of the gas-phase refrigerant (vapor).

A liquid passage 20 is connected to the liquid outlet 16 b of the condenser 16 . The liquid passage 20 is a refrigerant passage through which the liquid-phase refrigerant liquefied by the condenser 16 flows to the cooler 14 . The liquid passage 20 is connected to the liquid inlet 14a of each cooler 14 after extending downward along the vertical direction. As a result, the liquid-phase refrigerant that has flowed out of the condenser 16 moves downward in the vertical direction due to the weight of the liquid-phase refrigerant.

According to the battery cooling circuit 12 described above, when the temperature of the battery cells of each battery stack 2 becomes high in a state where the gas-phase refrigerant can be cooled by the condenser 16, the refrigerant naturally circulates, thereby continuously cooling the battery cells. It can be carried out.

The battery cooling device 10 also includes an electronic control unit (ECU) 30 . The ECU 30 is a computer that executes various processes related to the battery cooling device 10 . Specifically, the processing executed by the ECU 30 includes processing related to temperature control of the capacitor 16 and "leak determination processing", which will be described later. The ECU 30 has a processor 30a and a storage device 30b. The processor 30a reads and executes a program stored in the storage device 30b. As a result, various processes are realized by the processor 30a.

The ECU 30 takes in sensor signals from various sensors used for the various processes described above. The various sensors referred to here include, for example, the refrigerant pressure sensor 32, the refrigerant temperature sensor 34, and the battery temperature sensor 36. A refrigerant pressure sensor 32 is attached to the battery cooling circuit 12 and detects the pressure of the refrigerant in the battery cooling circuit 12 . Although the refrigerant pressure sensor 32 is attached to the steam passage 18 as an example, it may be attached to a portion other than the steam passage 18 on the battery cooling circuit 12 . A refrigerant temperature sensor 34 is mounted, for example, in the steam passage 18 to detect the temperature of the vapor phase refrigerant (vapor phase temperature) _TVP . The battery temperature sensor 36 detects the temperature of the battery cell (hereinafter also simply referred to as "battery temperature T _B "). As an example, the battery temperature sensors 36 are provided for a predetermined number of battery cells among the battery cells included in each of the battery stacks 2 . A warning light 38 installed in the vehicle is also connected to the ECU 30 .

1-2. Refrigerant Leak Judgment Processing Since the thermosiphon type battery cooling circuit 12 uses natural circulation as described above, the circulation flow rate of the refrigerant is smaller than in a method in which the refrigerant is circulated by a pump. Therefore, it is necessary to fill the battery cooling circuit 12 with a large amount of coolant. In the battery cooling device 10 of such a system, the amount of refrigerant charged has a great effect on the cooling performance of the battery cooling device 10 when the vehicle is tilted and when the vehicle is subjected to gravitational acceleration. Therefore, it is important to manage the amount of refrigerant charged, and accurate detection of refrigerant leakage is required.

The "liquid level L1" described in FIG. 1 above corresponds to the liquid level of the coolant (liquid phase coolant) in the initial charging state in which a predetermined appropriate amount of coolant is sealed in the battery cooling circuit 12. do. On the other hand, FIG. 2 is a diagram showing the battery cooling circuit 12 when refrigerant leakage occurs in the initial charging state. That is, the "liquid level L2" shown in FIG. 2 shows an example of the liquid level when the refrigerant is leaking from the initial charging state.

In the present embodiment, the ECU 30 executes the following "leak determination process" in order to detect refrigerant leakage in the initial charging state.

Here, the inside of the battery cooling circuit 12 is basically in a saturated state where the liquid-phase refrigerant and the gas-phase refrigerant coexist. In a saturated state, the pressure of both the liquid-phase refrigerant and the gas-phase refrigerant becomes the saturated vapor pressure. FIG. 3 is a graph showing saturated vapor pressure curves of refrigerants. In the saturated state, as shown in FIG. 3, the pressure of the refrigerant in the battery cooling circuit 12 can be obtained by obtaining the saturated vapor pressure corresponding to the temperature of the refrigerant. That is, the refrigerant pressure in the battery cooling circuit 12 is not affected by the amount of refrigerant charged. In other words, the effect of refrigerant leakage does not appear on the refrigerant pressure at saturation.

On the other hand, when the gas-phase refrigerant is in a superheated state, it becomes possible to apply the equation of state of gas represented by the equation (1) to the gas-phase refrigerant. Equation (1) can be converted to a pressure equation as in Equation (2). In equations (1) and (2), P is pressure, V is volume, n is mass, R is gas constant, and T is temperature.
PV = n R T (1)
P=(n/V)・R・T (2)

FIG. 4 is a diagram showing the relationship between the volume ratio of the gas phase and liquid phase in the battery cooling circuit 12 and the amount of refrigerant charged when the gas phase refrigerant is in a superheated state. More specifically, FIG. 4 compares and expresses the volume ratio between the refrigerant charge amount A and the refrigerant charge amount B, which is larger than the refrigerant charge amount A. As shown in FIG. As shown in FIG. 4 as an example, the volume (volume ratio) of the gas phase becomes smaller (lower) as the amount of refrigerant charged increases. Therefore, when the gas-phase refrigerant is in a superheated state, the pressure of the gas-phase refrigerant can be said to increase as the amount of refrigerant charged increases according to the equation (2). The pressure value of the refrigerant in the battery cooling circuit 12 detected by the refrigerant pressure sensor 32 (hereinafter also referred to as “sensor value P _S ”) is affected by the pressure of the gas-phase refrigerant in the superheated state. Therefore, when the amount of refrigerant charged decreases due to the occurrence of refrigerant _leakage , the sensor value PS becomes lower than the amount of refrigerant charged at the time of initial charging.

Therefore, in the leak determination process according to the present embodiment, the ECU 30 (processor 30a) first determines that the gas phase side is "Vapor-phase superheating control" is performed so that (that is, the gas-phase refrigerant) becomes superheated. Then, after the gas phase side is overheated by the gas phase overheating control, the ECU 30 determines refrigerant leakage based on the result of comparison between the sensor value _{PS and the estimated pressure value PAVE .}

The estimated pressure value P _AVE referred to here is calculated according to the following equation (3). In equation (3), the function f(T _LQ ) corresponds to the pressure of the liquid-phase refrigerant, which is the saturated vapor pressure determined by the function of the liquid-phase temperature T _LQ . _VLQ is the liquid phase volume. (n/V _VP )×RT _VP corresponds to the gas phase refrigerant pressure based on equation (2). More specifically, n is the mass of the gas phase refrigerant, _VVP is the gas phase volume, R is the gas constant, and _TVP is the gas phase temperature. _TTOT is the volume of the battery cooling circuit 12, which is the sum of the liquid phase volume _VLQ and the vapor phase volume _VVP as shown in equation (4).
_PAVE =(f( _TLQ )* _VLQ +(n/ _VVP )* _RTVP * _VVP )/ _VTOT (3)
_VTOT = _VLQ + _VVP (4)

Sensor value P _S detects the overall coolant pressure in battery cooling circuit 12 . In other words, according to the sensor value _PS , the refrigerant pressure obtained by averaging the pressure difference between the gas phase and the liquid phase can be obtained. Therefore, in equation (3), the estimated pressure value P _AVE used for comparison with the sensor value P _s is the value in the battery cooling circuit 12 under the amount of refrigerant charged at the time of initial charging (that is, in a state where there is no refrigerant leakage). is the estimated pressure value of the refrigerant, which is the pressure of the liquid-phase refrigerant expressed by the saturated vapor pressure (f(T _LQ )) and the pressure of the gas-phase refrigerant expressed by the gas state equation of equation (2) (( n/V _VP )×RT _VP ) are expressed as values obtained by weighted averaging the respective volume ratios.

FIG. 5 is a flow chart showing the flow of leakage determination processing according to the first embodiment. ECU 30 (processor 30a) first determines in step S100 whether or not the vehicle has stopped. Whether or not the vehicle has stopped can be determined, for example, based on whether or not an IG-OFF signal has been input from the ignition switch of the vehicle. The process of step S100 is performed to determine that the current in each battery cell of the battery pack 1 has become zero (that is, that each battery cell is in a state of no heat generation).

In step S100, if the vehicle is not stopped, the ECU 30 terminates the current processing cycle. On the other hand, when the vehicle has stopped, the process proceeds to step S102.

In step S102, the ECU 30 determines whether or not the soak time of the vehicle is sufficient. Specifically, it is determined whether or not a predetermined time has passed since the vehicle stopped. This predetermined time is set in advance as a time corresponding to a sufficient soak time, such as a time necessary for establishing a temperature condition in which the difference between the temperature of each battery cell and the ambient temperature in the battery pack 1 becomes sufficiently small. ing. As a result, when the soak time is sufficient, the process proceeds to step S104.

In step S104, the ECU 30 executes gas-phase superheating control. Vapor-phase superheating control can be performed using temperature control of the capacitor 16, for example. More specifically, for example, the vapor-phase refrigerant can be superheated by controlling the refrigeration cycle device described above to raise the temperature of the LLC. In this example, the refrigeration cycle device corresponds to an example of the "superheater" according to the present disclosure. Alternatively, the superheater may be, for example, a heater located on the gas phase side (eg, steam path 18) within the cell cooling circuit 12. The heater is not limited to the vapor passage 18 as long as the portion where the gas phase refrigerant exists, the condenser 16, the upper part of the cooler 14, or the upper part of the liquid passage 20 (condenser 16 site).

In step S106 following step S104, the ECU 30 determines whether or not the gas phase side (gas phase refrigerant) has become overheated. This determination can be made, for example, based on whether or not the difference between the gas phase temperature T _VP and the battery temperature T _B (liquid phase temperature T _LQ ) is equal to or greater than a predetermined threshold. The vapor phase temperature _TVP can be detected by the coolant temperature sensor 34 . The battery temperature T _B (liquid phase temperature T _LQ ) can be detected by the battery temperature sensor 36 . More specifically, the battery temperature T _B used in this determination may be, for example, the average value of the detection values of all the battery temperature sensors 36 provided in the battery cooling device 10, or alternatively, a specific battery temperature sensor 36 detection values may be used.

In step S106, while the gas phase side is not overheated, the gas phase superheating control is continued. On the other hand, if the gas phase side is overheated, the process proceeds to step S108.

In step S108, the ECU 30 compares the sensor value P _S with the pressure estimate value P _AVE that assumes the amount of refrigerant charged at the time of initial charging. Regarding the calculation of the estimated pressure value P _AVE using the equation (3), the liquid phase temperature T _LQ can be obtained using the detection value of the battery temperature sensor 36, for example, in the same manner as in the process of step S106. Instead of such an example, the battery cooling circuit 12 may include a refrigerant temperature sensor for directly detecting the liquidus temperature _TLQ . Also, since the volume V _TOT of the battery cooling circuit 12 is known, the liquid phase volume V _LQ and the gas phase volume V _VP are, for example, the liquid phase volume V _LQ and the gas phase volume V _VP respectively and the gas phase temperature T _VP can be calculated from the vapor phase temperature _TVP detected by the coolant temperature sensor 34 by obtaining the relationship between the . Also, the mass n of the gas-phase refrigerant in the equation (3) can be calculated, for example, by subtracting the mass of the liquid-phase refrigerant from the refrigerant charging amount (known value) at the time of initial charging. The mass of the liquid phase refrigerant can be calculated, for example, from the liquid phase volume V _LQ and the density of the liquid phase refrigerant according to the liquid phase temperature T _LQ (battery temperature T _B ).

Then, in step S108, refrigerant leakage from the battery cooling circuit 12 is determined based on the result of comparison between the sensor value P _S and the estimated pressure value P _AVE . Specifically, for example, when the amount of decrease in the sensor value P _S with respect to the estimated pressure value P _AVE is less than a predetermined threshold, the ECU 30 determines that there is no refrigerant leakage, and the amount of decrease is equal to or greater than the threshold. If so, it is determined that refrigerant leakage has occurred. Further, the ECU 30 may determine that the larger the amount of decrease, the larger the leakage amount of the refrigerant.

In step S110 following step S108, the ECU 30 proceeds to step S112 if there is leakage based on the determination result of step S108, and terminates the current processing cycle if there is no leakage.

A decrease in the amount of coolant charged leads to poor cooling of the battery pack 1 . Therefore, in step S112, the ECU 30 executes processing for warning the user of the vehicle of refrigerant leakage. Specifically, for example, the ECU 30 turns on the warning light 38 . Note that the refrigerant leakage warning may be performed using any other method such as sound instead of using the warning light 38 or in addition thereto. The ECU 30 ends the current processing cycle after performing the processing of step S112.

It should be noted that the sensor value PS obtained by the refrigerant pressure sensor ₃₂ has individual differences. Therefore, when the determination result of step S110 is negative (when there is no leakage), the ECU 30 controls the liquid phase temperature T _LQ (battery temperature T _B ), the vapor phase temperature _TVP , and the coolant pressure (sensor value P _S ) may be stored as the initial learning value of the sensor value P _s in the absence of leakage. It is desirable that such an initial learning value is acquired at a time when it can be determined that refrigerant leakage has not occurred, such as shortly after the vehicle is manufactured. Then, when the process of step S108 is performed after that, the following determination process may be performed supplementarily. That is, the comparison between the sensor value P _S obtained by the process of step S108 and the initial learning value may be performed supplementarily. Then, for example, even if the amount of decrease in step S108 is less than the threshold, if the difference between the sensor value _PS and the initial learning value is greater than or equal to the predetermined threshold, it is determined that refrigerant leakage has occurred. may

1-3. Effect According to the leak determination process according to the first embodiment described above, in a situation where the temperature of the refrigerant is stabilized after a predetermined time has passed since the vehicle stopped, the overheated state of the gas phase that deviates from the saturated state is formed using gas phase superheat control. Refrigerant leakage is determined based on the result of comparison between the sensor value _{PS and the estimated pressure value PAVE ,} which assumes the amount of refrigerant charged at the time of initial charging. According to such a determination method, if the gas phase is in a superheated state, the refrigerant pressure (sensor value P _S ) is affected by the decrease in the gas phase volume _VVP due to the decrease in the amount of refrigerant charged. leaks can be detected. According to this determination method, since it is not necessary to accurately capture changes in the liquid level of the cooler 14 (heat exchange section) due to changes in the amount of refrigerant charged, refrigerant leakage can be determined even if the vehicle is tilted. can be performed accurately.

In addition, since the presence or absence of leakage is determined after the vehicle has stopped and the coolant temperature has stabilized after a predetermined period of time has passed, the determination must be performed in a state in which the influence of heat generated by each battery cell is eliminated. can be done. In addition, by heating the gas phase side, compared with the case of heating the liquid phase side instead of the gas phase side or the case of warming the liquid phase side together with the gas phase side, the change in the liquid phase temperature _TLQ is small ( More specifically, it is possible to change the pressure of the liquid-phase refrigerant (saturated vapor pressure) with a change in the liquid-phase temperature _TLQ . This makes it possible to more reliably capture changes in the gas phase volume _VVP caused by a decrease in the amount of charged refrigerant using the sensor value _PS .

2. Embodiment 2
The second embodiment differs from the above-described first embodiment in the contents of the "leak determination process".

FIG. 6 is a flow chart showing the flow of leakage determination processing according to the second embodiment. The processing of the flowchart shown in FIG. 6 will be described below, focusing on differences from the flowchart shown in FIG. 5 of the first embodiment.

In FIG. 6, after it is determined in step S106 that the gas phase side is in an overheated state, the process proceeds to step S200. In step S<b>200 , the ECU 30 determines refrigerant leakage based on the temperature change rate ΔT _VP of the vapor-phase refrigerant and the pressure change rate ΔP of the refrigerant in the battery cooling circuit 12 .

FIG. 7 is a graph for explaining an outline of leakage determination processing according to the second embodiment. The relationship shown in FIG. 7 is for when the gas phase side is in a superheated state. Specifically, the _curve indicated by the solid line in FIG. showing relationships. This criterion curve C can be obtained, for example, by performing an experiment or the like in advance. On the other hand, the dashed curve in the figure shows an example of the relationship between the temperature change speed _ΔTVP and the pressure change speed ΔP when refrigerant leakage occurs.

As described in the first embodiment, if the gas phase is in a superheated state, the refrigerant pressure (sensor value P _S ) is affected by a decrease in the gas phase volume V _VP due to a decrease in the charged amount of refrigerant. Therefore, when refrigerant leakage occurs, the pressure change speed ΔP under the same temperature change speed _ΔTVP becomes lower than the value on the criterion curve C, as shown in FIG.

Therefore, in step S200, the ECU 30 uses the refrigerant temperature sensor 34 and the refrigerant pressure sensor 32 to obtain the temperature change rate _ΔTVP and the pressure change rate ΔP during a predetermined period after the gas phase side becomes overheated. Then, the ECU 30 compares the obtained temperature change rate _ΔTVP and pressure change rate ΔP with the relationship between the temperature change rate _ΔTVP and the pressure change rate ΔP at the amount of refrigerant charged at the time of initial charging (that is, the determination reference curve C). compare.

Specifically, for example, the ECU 30 determines if the difference between the pressure change rate ΔP on the determination reference curve C corresponding to the temperature change rate _ΔTVP acquired this time and the pressure change rate ΔP acquired this time is equal to or greater than a predetermined threshold value. Determine whether or not there is If the difference is less than the threshold, the ECU 30 determines that there is no refrigerant leakage, and if the difference is greater than or equal to the threshold, the ECU 30 determines that there is refrigerant leakage. Further, the ECU 30 may determine that the larger the difference, the larger the leakage amount of the refrigerant.

In addition, the data of the temperature change rate _ΔTVP and the pressure change rate ΔP for specifying the criterion curve C may be acquired (learned) on the actual machine. For such learning, for example, when the determination result of step S110 is negative (no leakage), the temperature change rate ΔT _VP and the pressure change rate ΔP data acquired for the process of step S200 are stored. It may be done by Further, such learning is not limited to the case where an overheated state on the gas phase side is formed in the leak determination process, but is performed under conditions where the atmospheric temperature and gas phase temperature _TVP in the battery pack 1 change greatly (for example, during rapid charging). ) by storing the temperature change rate ΔT _VP and pressure change rate ΔP data obtained in .

According to the leak determination process according to the second embodiment described above, after the gas phase overheating state is formed in the same manner as in the first embodiment, the temperature change rate ΔT _VP and the pressure change rate ΔP is compared with the relationship between the temperature change rate ΔT _VP and the pressure change rate ΔP at the amount of refrigerant charged at the time of initial charging (that is, the judgment reference curve C) to determine refrigerant leakage. . According to such a determination method, the pressure change speed _ΔP (that is, the amount of change in the sensor value _PS with respect to time) and the temperature change speed are measured instead of the sensor value PS itself, which may vary due to individual differences in the refrigerant pressure sensor 32. A leak determination is made using the relationship with ΔT _VP . For this reason, it is possible to perform a more accurate determination than the leak determination process according to the first embodiment.

1 Battery pack 2 Battery stack 10 Battery cooler 12 Battery cooling circuit 14 Cooler 14a Cooler liquid inlet 14b Cooler vapor outlet 16 Condenser 16a Condenser vapor inlet 16b Condenser liquid outlet 18 Vapor passage 20 Liquid passage 22 Heat conduction Material 30 Electronic control unit (ECU)
30a Processor 32 Refrigerant pressure sensor 34 Refrigerant temperature sensor 36 Battery temperature sensor 38 Warning light

Claims (2)

A battery cooling device mounted on a vehicle,
a thermosiphon-type battery cooling circuit in which a refrigerant is enclosed;
a processor that executes leakage determination processing that determines leakage of the refrigerant from the battery cooling circuit;
with
The battery cooling circuit,
a cooler that cools the one or more battery cells by absorbing heat generated by the one or more battery cells and evaporating a liquid-phase refrigerant;
a condenser arranged above the cooler in the vertical direction for condensing the vapor-phase refrigerant vaporized by the cooler;
a vapor passage connecting between the cooler and the condenser and allowing the vapor-phase refrigerant to flow through the condenser;
a liquid passage connecting between the condenser and the cooler and allowing the liquid-phase refrigerant to flow through the cooler;
including
The battery cooling device
a refrigerant pressure sensor attached to the battery cooling circuit for detecting the pressure of the refrigerant in the battery cooling circuit;
a superheating device for superheating the gas-phase refrigerant;
further comprising
The processor, in the leak determination process,
After a predetermined time has passed since the vehicle stopped, performing gas phase superheating control for controlling the superheating device so that the gas phase refrigerant is in a superheated state,
After the gas-phase refrigerant has been superheated by the gas-phase overheating control, judging leakage of the refrigerant based on a comparison result between a pressure detection value by the refrigerant pressure sensor and an estimated pressure value,
The estimated pressure value is an estimated pressure value of the refrigerant in the battery cooling circuit under the amount of the refrigerant charged at the time of initial charging, and the pressure of the liquid phase refrigerant which is the saturated vapor pressure and the liquid phase It is a value obtained by dividing the sum of the product with the volume of the refrigerant and the product of the pressure of the gas phase refrigerant based on the gas equation of state and the volume of the gas phase refrigerant by the volume of the battery cooling circuit. A battery cooling device characterized by: A battery cooling device mounted on a vehicle,
a thermosiphon-type battery cooling circuit in which a refrigerant is enclosed;
a processor that executes leakage determination processing that determines leakage of the refrigerant from the battery cooling circuit;
with
The battery cooling circuit,
a cooler that cools the one or more battery cells by absorbing heat generated by the one or more battery cells and evaporating a liquid-phase coolant;
a condenser arranged above the cooler in the vertical direction for condensing the vapor-phase refrigerant vaporized by the cooler;
a vapor passage connecting between the cooler and the condenser and allowing the vapor-phase refrigerant to flow through the condenser;
a liquid passage connecting between the condenser and the cooler and allowing the liquid-phase refrigerant to flow through the cooler;
including
The battery cooling device
a refrigerant pressure sensor attached to the battery cooling circuit for detecting the pressure of the refrigerant in the battery cooling circuit;
a refrigerant temperature sensor that detects the temperature of the vapor-phase refrigerant;
a superheating device for superheating the gas-phase refrigerant;
further comprising
The processor, in the leak determination process,
After a predetermined time has passed since the vehicle stopped, performing gas phase superheating control for controlling the superheating device so that the gas phase refrigerant is in a superheated state,
A temperature change rate of the gas-phase refrigerant and the battery cooling circuit obtained using the refrigerant pressure sensor and the refrigerant temperature sensor in a predetermined period after the gas-phase refrigerant is overheated by the gas-phase overheating control. determining the leakage of the refrigerant by comparing the pressure change rate of the refrigerant in the A battery cooling device characterized by:

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