Coolant composition and cooling system for electric vehicle

Abstract

To provide a coolant composition capable of readily grasping a state of deterioration due to use.SOLUTION: The present embodiment is a coolant composition used in a cooling system of an electric vehicle, the coolant composition comprising: water; at least one alcohols selected from the group consisting of monohydric alcohols, dihydric alcohols, trihydric alcohols and alkylene glycol monoalkyl ethers; and an absorbance changeable dye whose absorbance is easily changed by the presence of potassium fluoro-aluminate, in which the absorbance changeable dye is a dye by which the absorbance at a maximum absorption wavelength in a visible light region of a solution containing 0.0005 pt.mass to 0.0050 pt.mass of the absorbance changeable dye and 0.5 pt.mass of potassium fluoro-aluminate in 100 pts.mass of an ethylene glycol 50 mass% aqueous solution becomes 50% or less relative to the absorbance at the maximum wavelength in a visible light region of a solution containing the same amount of absorbance changeable dye in 100 pts.mass of the ethylene glycol 50 mass% aqueous solution.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present embodiment relates to a coolant composition and a cooling system for an electric vehicle using the coolant composition. [Background technology]

[0002] Electric vehicles equipped with a driving motor, such as hybrid vehicles and electric vehicles, are equipped with a power control unit (PCU) for appropriately controlling electric power. The PCU includes an inverter that drives the motor, a boost converter that controls voltage, a DC-DC converter that steps down high voltage, and the like. The inverter or converter has a power card that is a card-type power module with a built-in semiconductor element, and the power card generates heat as a result of switching operations. Therefore, the inverter and converter are devices that can generate heat to a high temperature. In addition to the inverter and converter, other heat-generating devices in electric vehicles include, for example, batteries. Therefore, electric vehicles are equipped with a cooling system for cooling the inverter, converter, battery, and the like.

[0003] A cooling system includes a coolant that circulates inside the system and serves as a medium for transporting heat. A water-based coolant (e.g., a mixture of ethylene glycol and water) that contains water is generally used as the coolant. Water-based coolants that contain water are generally used because they have excellent cooling properties. However, when used in a cooling system, materials contained in the radiator (e.g., flux), metal ions (e.g., aluminum ions) from metal parts such as piping, and sulfate ions from rubber products such as packings may dissolve into the coolant, increasing its electrical conductivity. If the electrical conductivity of the coolant increases due to the dissolution of ionic substances (decreasing insulation resistance), the power generation system may not be able to start up because it is determined that the electrical conductivity is too high.

[0004] Therefore, Patent Document 1 discloses a fuel cell system including a fuel cell, a circulation path through which a coolant for cooling the fuel cell circulates, a pump provided in the circulation path to circulate the coolant, a radiator provided in the circulation path to radiate heat from the coolant, an ion exchanger provided in the circulation path to recover the insulation resistance of the coolant, a detector provided in the circulation path downstream of the radiator in the direction of circulation of the coolant and detecting the conductivity of the coolant, and a control unit electrically connected to the detector and the pump and controlling the operation of at least the pump, and the control unit starts the operation of the pump so that the coolant passes through the ion exchanger when the pump is stopped and the insulation resistance of the coolant calculated from the conductivity of the coolant detected by the detector becomes equal to or less than a specific value. That is, Patent Document 1 discloses a fuel cell cooling system including a detector for measuring the conductivity of the coolant. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2020-053170 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, the installation of a detector for measuring the conductivity of the coolant as in Patent Document 1 leads to a complicated configuration of the cooling system and increased costs. Therefore, there has been a demand for a simpler method for grasping the deterioration state of the coolant.

[0007] Therefore, an object of the present embodiment is to provide a coolant composition that allows easy understanding of the state of deterioration caused by use. [Means for solving the problem]

[0008] An example of this embodiment is as follows.

[0009] (1) A coolant composition for use in a cooling system of an electric vehicle, comprising: Water, at least one alcohol selected from the group consisting of monohydric alcohols, dihydric alcohols, trihydric alcohols, and alkylene glycol monoalkyl ethers; an absorbance-variable dye whose absorbance is easily changed by the presence of potassium fluoroaluminate; Including, The coolant composition is such that the absorbance-variable dye is a dye such that the absorbance at the maximum absorption wavelength in the visible light region of a solution containing 0.0005 to 0.0050 parts by mass of the absorbance-variable dye and 0.5 parts by mass of potassium fluoroaluminate in 100 parts by mass of a 50% by mass aqueous solution of ethylene glycol is 50% or less of the absorbance at the maximum absorption wavelength in the visible light region of a solution containing the same amount of the absorbance-variable dye in 100 parts by mass of a 50% by mass aqueous solution of ethylene glycol. (2) further comprising an absorbance-resistant dye whose absorbance is unlikely to change in the presence of potassium fluoroaluminate; The coolant composition according to (1), wherein the absorbance-resistant dye is a dye such that the absorbance at the maximum absorption wavelength in the visible light region of a solution containing 0.0005 to 0.0050 parts by mass of the absorbance-resistant dye and 0.5 parts by mass of potassium fluoroaluminate in 100 parts by mass of a 50% by mass aqueous solution of ethylene glycol is 60% or more of the absorbance at the maximum absorption wavelength in the visible light region of a solution containing the same amount of the absorbance-resistant dye in 100 parts by mass of a 50% by mass aqueous solution of ethylene glycol. (3) The coolant composition according to (2), wherein the color of the absorbance-changing dye and the color of the absorbance-slow-changing dye are not adjacent to each other on a hue wheel chart of the 20 colors of the Munsell color system. (4) The coolant composition according to (2) or (3), wherein the color of the absorbance-changing dye and the color of the absorbance-slow-changing dye are separated by two or more colors on a hue wheel chart of the 20 colors of the Munsell color system. (5) The coolant composition according to any one of (1) to (4), wherein the content of the dye in the coolant composition is 0.0001% by mass to 0.01% by mass. (6) The coolant composition according to any one of (1) to (5), wherein the alcohol comprises ethylene glycol. (7) A cooling system for an electric vehicle, comprising the coolant composition according to any one of (1) to (6), a refrigerant pipe through which the coolant composition flows, and a heat-generating device as an object to be cooled. (8) The cooling system for an electric vehicle according to (7), wherein the heat-generating device is at least one selected from an inverter, a converter, a generator, a motor, and a battery. Effect of the Invention

[0010] According to this embodiment, it is possible to provide a coolant composition whose deterioration state due to use can be easily grasped. [Brief description of the drawings]

[0011] [Figure 1] 1 is a schematic perspective view showing a configuration example of a semiconductor device used in an inverter of a drive system of an electric automobile; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The present embodiment is a coolant composition used in the cooling system of an electric vehicle, comprising water, at least one alcohol selected from the group consisting of monohydric alcohols, dihydric alcohols, trihydric alcohols, and alkylene glycol monoalkyl ethers, and an absorbance-variable dye whose absorbance is likely to change in the presence of potassium fluoroaluminate, wherein the absorbance-variable dye is a dye such that the absorbance at the maximum absorption wavelength in the visible light region of a solution containing 0.0005 parts by mass to 0.0050 parts by mass of the absorbance-variable dye and 0.5 parts by mass of potassium fluoroaluminate in 100 parts by mass of a 50% by mass aqueous solution of ethylene glycol is 50% or less of the absorbance at the maximum absorption wavelength in the visible light region of a solution containing the same amount of the absorbance-variable dye in 100 parts by mass of a 50% by mass aqueous solution of ethylene glycol.

[0013] The coolant composition according to the present embodiment contains water and alcohols as base materials. The use of water and alcohols as base materials can improve the cooling performance of the coolant composition. On the other hand, in an aqueous coolant containing water and alcohols, there is a tendency for ionic substances such as flux (potassium fluoroaluminate) to be eluted from the components used in the cooling system. Therefore, in the coolant composition according to the present embodiment, the deterioration state of the coolant composition can be easily grasped by blending an absorbance-variable dye. As described above, in the coolant composition, ionic substances such as flux are eluted from the components used in the cooling system during use, and the conductivity of the coolant composition increases. When the conductivity of the coolant composition increases, that is, when the coolant composition deteriorates, when an attempt is made to start the power generation system, the conductivity may be determined to be high and the system may not be able to start. Therefore, in order to easily grasp the deterioration state of the coolant composition, an absorbance-variable dye whose absorbance is easily changed by the presence of potassium fluoroaluminate is contained in the coolant composition. The absorbance-changing dye is a dye in which the absorbance at the maximum absorption wavelength in the visible light region of a solution containing 0.0005 to 0.0050 parts by mass of the absorbance-changing dye and 0.5 parts by mass of potassium fluoroaluminate in 100 parts by mass of a 50% by mass aqueous solution of ethylene glycol is 50% or less than the absorbance at the maximum absorption wavelength in the visible light region of a solution containing the same amount of the absorbance-changing dye in 100 parts by mass of a 50% by mass aqueous solution of ethylene glycol. Potassium fluoroaluminate is a reducing substance, and the dye is reduced by potassium fluoroaluminate. That is, the absorbance-changing dye in this embodiment can be understood as a material whose absorbance change is relatively large when reduced by potassium fluoroaluminate. In the coolant composition according to this embodiment, the absorbance-changing dye is reduced by potassium fluoroaluminate dissolved in the coolant composition. The absorbance of the dye with easily variable absorbance decreases due to reduction, and as a result, the absorbance of the coolant composition also decreases and changes color. That is, when the amount of potassium fluoroaluminate in the coolant composition increases and deterioration progresses, the color of the coolant composition changes, and by observing this color change, the deterioration state of the coolant composition can be easily grasped.For example, when the concentration of potassium fluoroaluminate dissolved in the coolant composition increases and the absorbance of the absorbance-variable dye decreases, the light absorption of the coolant composition decreases, causing the color to become lighter (closer to transparent). By observing this color change, the deterioration state of the coolant composition can be grasped. In other words, this embodiment can provide a coolant composition that has excellent cooling performance and allows the deterioration state to be easily grasped.

[0014] This embodiment will be described in detail below.

[0015] 1. Coolant composition The coolant composition according to the present embodiment contains water and an alcohol as a base. The alcohol is at least one type of alcohol selected from the group consisting of monohydric alcohols, dihydric alcohols, trihydric alcohols, and alkylene glycol monoalkyl ethers. By including water and an alcohol as a base, it is possible to impart excellent cooling performance to the coolant composition.

[0016] The alcohols are selected from the group consisting of monohydric alcohols, dihydric alcohols, trihydric alcohols, and alkylene glycol monoalkyl ethers. These alcohols have a freezing point depressing effect. The alcohols may be used alone or in combination of two or more.

[0017] Examples of the monohydric alcohol include methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, and octanol. The monohydric alcohol may be used alone or in combination of two or more.

[0018] Examples of the dihydric alcohol include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, hexylene glycol, etc. The dihydric alcohol may be used alone or in combination of two or more.

[0019] Examples of trihydric alcohols include glycerin, trimethylolethane, trimethylolpropane, 5-methyl-1,2,4-heptanetriol, 1,2,6-hexanetriol, etc. The trihydric alcohols may be used alone or in combination of two or more.

[0020] Examples of alkylene glycol monoalkyl ethers include ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, tetraethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monobutyl ether, etc. The alkylene glycol monoalkyl ethers may be used alone or in combination of two or more.

[0021] As the alcohols, ethylene glycol, propylene glycol and 1,3-propanediol are preferred from the viewpoints of ease of handling, cost and availability. Therefore, the alcohols preferably contain at least one selected from the group consisting of ethylene glycol, propylene glycol and 1,3-propanediol, and more preferably contain ethylene glycol.

[0022] The water is preferably ion-exchanged water.

[0023] The content of the base, i.e., the total content of water and alcohols, is preferably 50 parts by mass or more, preferably 60 parts by mass or more, preferably 70 parts by mass or more, preferably 80 parts by mass or more, preferably 90 parts by mass or more, and preferably 95 parts by mass or more, relative to 100 parts by mass of the coolant composition, from the viewpoint of functioning as a coolant. In addition, the content of the base is preferably 99 parts by mass or less, preferably 95 parts by mass or less, preferably 94 parts by mass or less, and preferably 93 parts by mass or less, from the viewpoint of blending other components other than the base material. These lower and upper limits can be combined arbitrarily.

[0024] The blending ratio of water and alcohols can be adjusted as desired, taking into consideration, for example, antifreeze and flammability. The mass ratio of water to alcohols in the base is preferably 20:80 to 90:10 (water:alcohols), and more preferably 40:60 to 75:25, from the viewpoint of avoiding the occurrence of a flash point. These upper and lower limits can be combined as desired.

[0025] The pour point of the coolant composition according to this embodiment is preferably less than -30°C, and more preferably -35°C or lower, from the viewpoint of ensuring fluidity at low temperatures.

[0026] The coolant composition according to the present embodiment includes an absorbance-variable dye whose absorbance is easily changed by the presence of potassium fluoroaluminate. The absorbance-variable dye is a dye in which the absorbance at the maximum absorption wavelength in the visible light region of a solution containing 0.0005 to 0.0050 parts by mass of the absorbance-variable dye and 0.5 parts by mass of potassium fluoroaluminate in 100 parts by mass of a 50% by mass aqueous solution of ethylene glycol (i.e., an aqueous solution containing ethylene glycol at a concentration of 50% by mass) is 50% or less of the absorbance at the maximum absorption wavelength in the visible light region of a solution containing the same amount of the absorbance-variable dye in 100 parts by mass of a 50% by mass aqueous solution of ethylene glycol.

[0027] For measuring the absorbance of the absorbance-varying dye, a solution is prepared by adding 0.0005 to 0.0050 parts by mass of the absorbance-varying dye and 0.5 parts by mass of potassium fluoroaluminate to 100 parts by mass of 50% by mass ethylene glycol aqueous solution, and a control solution is prepared by adding 0.0005 to 0.0050 parts by mass of the same amount of the absorbance-varying dye to 100 parts by mass of 50% by mass ethylene glycol aqueous solution (not including potassium fluoroaluminate). These solutions may be stored at a predetermined temperature in some cases to accelerate the reaction and bring them into equilibrium. Specifically, these solutions can be left standing at 90°C for 1000 hours to accelerate the reaction. Then, the absorbance of each solution at the maximum absorption wavelength in the visible light region is measured. The dye with easily variable absorbance in this embodiment is a dye whose absorbance in an aqueous solution containing potassium fluoroaluminate is 50% or less of the absorbance in an aqueous solution of the dye not containing potassium fluoroaluminate as a control. The absorption wavelength is within the visible light region (300 nm to 800 nm). The CAS number of potassium fluoroaluminate is 60304-36-1.

[0028] As described above, the coolant composition is used over time, and ionic substances such as potassium fluoroaluminate are eluted from the components used in the cooling system, increasing the conductivity of the coolant composition. If the conductivity of the coolant composition increases, there is a possibility that the power generation system will not be able to start because the conductivity is determined to be high when it is attempted to start. The main cause of the increase in conductivity is the flux (potassium fluoroaluminate) used in the manufacturing process of cooling devices such as radiators. Therefore, in this embodiment, in order to easily grasp the deterioration state of the coolant composition, an absorbance-varying dye whose absorbance is easily changed by the presence of potassium fluoroaluminate is contained in the coolant composition. When the amount of potassium fluoroaluminate in the coolant composition increases, the absorbance of the absorbance-varying dye decreases, and the color of the coolant composition changes. That is, in this embodiment, the degree of elution of potassium fluoroaluminate in the coolant composition can be visualized by the change in color of the coolant composition. Therefore, the deterioration state of the coolant composition can be easily grasped. For example, when the concentration of potassium fluoroaluminate in the coolant composition increases and the absorbance of the absorbance-variable dye decreases, the color of the coolant composition becomes lighter (becomes nearly colorless) due to the decreased light absorption. By observing this color change, the deterioration state of the coolant composition can be grasped.

[0029] As described above, in this specification, the absorbance-variable dye is a dye for which the absorbance at the maximum absorption wavelength in the visible light region of a solution containing 0.0005 parts by mass to 0.0050 parts by mass of a readily absorbance-variable dye and 0.5 parts by mass of potassium fluoroaluminate in 100 parts by mass of a 50% by mass aqueous solution of ethylene glycol is 50% or less, preferably 40% or less, more preferably 30% or less, even more preferably 20% or less, and particularly preferably 10% or less, of the absorbance at the maximum absorption wavelength in the visible light region of a solution containing the same amount of 0.0005 parts by mass to 0.0050 parts by mass of a readily absorbance-variable dye in 100 parts by mass of a 50% by mass aqueous solution of ethylene glycol.

[0030] Examples of the dyes with easily variable absorbance include azo dyes with a color index (CI) of 11000 to 37625, anthraquinone dyes with a color index (CI) of 58000 to 72999, and thiazine dyes with a color index (CI) of 52000 to 52999, and more specifically, tartrazine (Cas: 1934-21-0), acid green 25 (Cas: 4403-90-01), methylene blue (Cas: 61-73-4), etc. The dyes with easily variable absorbance may be used alone or in combination of two or more kinds.

[0031] The content of the absorbance-varying dye in the coolant composition is not particularly limited and can be adjusted appropriately. The content of the absorbance-varying dye in the coolant composition is, for example, 0.0001 mass% to 0.01 mass%. The content of the absorbance-varying dye is, for example, 0.0001 mass parts to 0.01 mass parts per 100 mass parts of the substrate.

[0032] The coolant composition according to the present embodiment preferably further contains an absorbance-resistant dye whose absorbance is unlikely to change due to the presence of potassium fluoroaluminate. The absorbance-resistant dye is a dye in which the absorbance at the maximum absorption wavelength in the visible light region of a solution containing 0.0005 to 0.0050 parts by mass of the absorbance-resistant dye and 0.5 parts by mass of potassium fluoroaluminate in 100 parts by mass of a 50% by mass aqueous solution of ethylene glycol is 60% or more of the absorbance at the maximum absorption wavelength in the visible light region of a solution containing the same amount of the absorbance-resistant dye in 100 parts by mass of a 50% by mass aqueous solution of ethylene glycol.

[0033] By combining a dye with a readily changeable absorbance and a dye with a long-lasting absorbance change, it becomes easier to grasp the degree of dissolution of potassium fluoroaluminate into the coolant composition. In other words, when a dye with a readily changeable absorbance is used alone, the pH change can be grasped by the change in color brightness (brightness) or intensity due to a decrease in absorbance, or by the change to colorlessness, but by combining a dye with a readily changeable absorbance and a dye with a long-lasting absorbance change, it becomes possible to grasp the pH change by the change in hue or chromaticity. The change in hue or chromaticity can be grasped more easily and accurately by visual inspection.

[0034] The absorbance of the dye with low absorbance change can be measured in the same manner as described for the dye with high absorbance change. Specifically, a solution is prepared by adding 0.0005 to 0.0050 parts by mass of the dye with low absorbance change and 0.5 parts by mass of potassium fluoroaluminate to 100 parts by mass of 50% by mass ethylene glycol aqueous solution, and a control solution is prepared by adding 0.0005 to 0.0050 parts by mass of the same amount of the dye with low absorbance change to 100 parts by mass of 50% by mass ethylene glycol aqueous solution (not including potassium fluoroaluminate). These solutions may be stored at a predetermined temperature in some cases to accelerate the reaction and bring them into equilibrium. Specifically, the reaction can be accelerated by leaving these solutions at rest at 90°C for 1000 hours. Then, the absorbance of each solution at the maximum absorption wavelength in the visible light region is measured. The dye with low absorbance change in this embodiment is a dye whose absorbance in an aqueous solution containing potassium fluoroaluminate is 60% or more of the absorbance in an aqueous solution of the dye not containing potassium fluoroaluminate as a control. The visible light region is specifically within the range of 300 nm to 800 nm.

[0035] The absorbance-resistant dye is preferably one whose absorbance does not change as much as possible due to the presence of potassium fluoroaluminate. Therefore, the absorbance-resistant dye is preferably one whose absorbance at the maximum absorption wavelength in the visible light region of a solution containing 0.0005 to 0.0050 parts by mass of the absorbance-resistant dye and 0.5 parts by mass of potassium fluoroaluminate in a 50% by mass aqueous solution of ethylene glycol is 70% or more, more preferably 80% or more, and even more preferably 90% or more, of the absorbance at the maximum absorption wavelength in the visible light region of a solution containing the same amount of the absorbance-resistant dye in 100 parts by mass of a 50% by mass aqueous solution of ethylene glycol.

[0036] Examples of the dyes having a low change in absorbance include xanthene dyes having a CI of 45000 to 45999 and triarylmethane dyes having a CI of 42000 to 44999, and more specifically, Acid Red 52 (Cas: 3520-42-1), Phenol Red (Cas. 143-74-8), Acid Blue 1 (Cas. 116-95-0), etc. The dyes having a low change in absorbance may be used alone or in combination of two or more kinds.

[0037] The color of the absorbance-changing dye and the color of the absorbance-slow-changing dye are preferably as dissimilar as possible in terms of hue or chromaticity. Therefore, it is preferable that the color of the absorbance-changing dye and the color of the absorbance-slow-changing dye are not adjacent to each other in the 20-color hue wheel chart of the Munsell color system. In other words, not adjacent to each other in the 20-color hue wheel chart of the Munsell color system means that the color of the absorbance-changing dye and the color of the absorbance-slow-changing dye are one or more colors apart in the 20-color hue wheel chart of the Munsell color system. For example, in the 20-color hue wheel chart of the Munsell color system, the color that is one or more colors apart from 10YR is 10Y to 10R. It is more preferable that the color of the absorbance-changing dye and the color of the absorbance-slow-changing dye are two or more colors apart in the 20-color hue wheel chart of the Munsell color system, and it is even more preferable that they are three or more colors apart. For example, in the 20-color hue wheel chart of the Munsell color system, the colors that are two or more colors away from 10YR are 5GY to 5R.

[0038] The content of the absorbance-resistant dye in the coolant composition is not particularly limited and can be adjusted appropriately. The content of the absorbance-resistant dye in the coolant composition is, for example, 0.0001% by mass to 0.01% by mass. The content of the absorbance-resistant dye is, for example, 0.0001 parts by mass to 0.01 parts by mass with respect to 100 parts by mass of the substrate.

[0039] The coolant composition according to the present embodiment may contain other additives, as necessary, in addition to the above-mentioned components, within a range that does not impair the effects of the present embodiment. Examples of other additives include antioxidants, rust inhibitors, friction modifiers, anticorrosive agents, viscosity index improvers, pour point depressants, dispersants / surfactants, antiwear agents, bittering agents, and solid lubricants. These may be used alone or in combination of two or more.

[0040] For example, the coolant composition may contain at least one rust inhibitor to effectively inhibit corrosion of metals used in engine coolant paths, etc. Examples of the rust inhibitor include phosphoric acid and / or its salt, aliphatic carboxylic acid and / or its salt, aromatic carboxylic acid and / or its salt, triazoles, thiazoles, silicates, nitrates, nitrites, borates, molybdates, and amine salts. One rust inhibitor may be used alone, or two or more rust inhibitors may be used in combination.

[0041] For example, the coolant composition may contain at least one pH adjuster as the anticorrosive agent to prevent metal corrosion. Examples of the pH adjuster include sodium hydroxide, potassium hydroxide, and lithium hydroxide. The pH adjuster may be used alone or in combination of two or more.

[0042] The pH of the coolant composition at 25° C. is preferably 6 or more, more preferably 7 or more, and preferably 10 or less, more preferably 9 or less.

[0043] The total amount of the other additives is usually 10 parts by mass or less, and preferably 5 parts by mass or less, per 100 parts by mass of the coolant composition.

[0044] The method for producing the coolant composition is not particularly limited, and a method for producing a normal coolant composition can be used. For example, the coolant composition can be produced by uniformly stirring the mixture at an appropriate temperature.

[0045] The coolant composition according to the present embodiment can be used as a coolant for use in the cooling system of an electric vehicle. In this specification, the term "electric vehicle" refers to a vehicle equipped with an electric motor for driving, and includes not only electric vehicles that do not have an engine and have only an electric motor as a power source, but also hybrid vehicles that have both an electric motor and an engine as power sources. In addition, fuel cell vehicles are also included in the term "electric vehicle".

[0046] 2. Cooling system The coolant composition according to the present embodiment is used in a cooling system provided in an electric vehicle. That is, one aspect of the present embodiment is a cooling system for an electric vehicle that uses the coolant composition according to the present embodiment as a refrigerant. Another aspect of the present embodiment is a cooling system for cooling a heat-generating device mounted on the electric vehicle. Another aspect of the present embodiment is an electric vehicle having the cooling system according to the present embodiment and a heat-generating device cooled by the cooling system.

[0047] As one of the measures to address environmental issues, electric vehicles, such as hybrid vehicles, fuel cell vehicles, and electric vehicles, that run on the driving force of a motor, are attracting attention. In such electric vehicles, heat generating devices such as motors, generators, inverters, converters, and batteries generate heat at high temperatures, so these heat generating devices need to be cooled. As described above, the coolant composition according to the present embodiment has excellent cooling properties and is excellent in cooling ability. Therefore, it can be preferably used in the cooling system of electric vehicles.

[0048] The cooling system includes, for example, a refrigerant pipe through which the coolant composition flows, a reserve tank for storing the coolant composition, a circulation device for circulating the coolant composition in a circulation path, or a cooling device for lowering the temperature of the coolant composition. An example of the circulation device is an electric pump. An example of the cooling device is a radiator, a chiller, or an oil cooler. The object to be cooled by the cooling system is a heat-generating device such as an inverter, a converter, a generator, a motor, or a battery.

[0049] The configuration of the cooling system is not particularly limited. The cooling system includes, for example, a refrigerant pipe, a reserve tank, an electric pump, a radiator, and a cooling unit provided in the heat generating device. The cooling unit is a part that receives heat from the heat generating device. For example, the coolant composition is pumped up from the reserve tank by the electric pump, and then the heat generating device is cooled by the cooling unit, and then the coolant composition returns to the reserve tank via the downstream radiator. The temperature of the coolant composition that has cooled the cooling unit increases, so the temperature of the coolant composition that has increased in temperature is lowered by the radiator. In addition, a configuration in which an oil cooler is placed in the middle of the refrigerant pipe and the motor is cooled by this oil cooler can also be adopted.

[0050] For example, FIG. 1 is a schematic diagram for explaining the configuration of a semiconductor device used in an inverter of a drive system of an electric vehicle. The semiconductor device 2 in FIG. 1 is a unit in which a plurality of power cards 10 and a plurality of coolers 3 (cooling units) are stacked. In FIG. 1, only one power card is given the reference number 10, and the reference numbers of the other power cards are omitted. In addition, a case 31 that houses the semiconductor device 2 is drawn with a dotted line so that the entire semiconductor device 2 can be seen. One power card 10 is sandwiched between two coolers 3. An insulating plate 6a is sandwiched between the power card 10 and one of the coolers 3, and an insulating plate 6b is sandwiched between the power card 10 and the other cooler 3. Grease is applied between the power card 10 and the insulating plates 6a and 6b. Grease is also applied between the insulating plates 6a and 6b and the cooler 3. In FIG. 1, one power card 10 and the insulating plates 6a and 6b are extracted from the semiconductor device 2 for easy understanding. The power card 10 houses a semiconductor device. The power card 10 is cooled by a refrigerant passing through a cooler 3 serving as a cooling unit. The refrigerant is liquid, typically water. The power cards 10 and the coolers 3 are alternately stacked, with the coolers 3 located at both ends of the stacking direction of the unit. The multiple coolers 3 are connected by connecting pipes 5a and 5b. The cooler 3 located at one end of the stacking direction of the unit is connected to a refrigerant supply pipe 4a and a refrigerant discharge pipe 4b. The refrigerant supplied through the refrigerant supply pipe 4a is distributed to all the coolers 3 through the connecting pipe 5a. The refrigerant absorbs heat from the adjacent power cards 10 while passing through each cooler 3. The refrigerant that has passed through each cooler 3 passes through the connecting pipe 5b and is discharged from the refrigerant discharge pipe 4b.

[0051] One aspect of this embodiment is a cooling system for an electric vehicle, including the coolant composition according to this embodiment, a refrigerant pipe through which the coolant composition flows, and a heat-generating device to be cooled. The heat-generating device may be at least one selected from an inverter, a converter, a generator, a motor, and a battery. In the cooling system for an electric vehicle according to this embodiment, the deterioration state of the coolant composition can be easily grasped by visually checking the color change of the coolant composition. EXAMPLES

[0052] The present embodiment will be described in more detail below using examples, but the present embodiment is not limited to the following examples.

[0053] [Example 1] (Preparation of Coolant Composition) To 100 parts by mass of a 50% by mass aqueous solution of ethylene glycol (water:ethylene glycol = 50:50 (mass ratio)), 0.0005 parts by mass of a dye with low absorbance change (Acid Red 52, Cas: 3520-42-1), 0.0005 parts by mass of a dye with easy absorbance change (Tartrazine, Cas: 1934-21-0), and an appropriate amount of rust inhibitor were added to obtain coolant composition E1.

[0054] The electrical conductivity of the coolant composition E1 immediately after production was 33 μS / cm. Also, the color of the coolant composition E1 immediately after production was orange.

[0055] (evaluation) The coolant composition E1 was circulated in a cooling system, and the deterioration state was observed. The cooling system used included a refrigerant pipe through which the coolant composition flows, an electric pump for circulating the coolant composition in the circulation path, a radiator, and a battery.

[0056] Coolant composition E1 was circulated in a cooling system, and the change in the coolant composition over time was observed. The evaluation items were electrical conductivity [μS / cm], yellow absorbance rate [%], and color. The yellow absorbance rate [%] was calculated from the absorbance ratio (absorbance at the time of measurement / absorbance immediately after production) at the yellow maximum absorption wavelength.

[0057] In the first measurement, the conductivity increased to 313 μS / cm, the yellow absorbance rate [%] decreased to 15.5%, and the color changed to pink. This is thought to be because the absorbance of tartrazine, which was used as a dye with a high absorbance change rate, decreased with increasing pH, while the absorbance of Acid Red 52, which was used as a dye with a low absorbance change rate, did not change as much as tartrazine with increasing pH, causing the yellow color to decrease and change to pink.

[0058] In the second measurement, the conductivity had increased further to 393 μS / cm, the yellow absorbance rate [%] had decreased to 2.1%, and the color had changed to a brighter pink.

[0059] If the conductivity of the coolant composition is 400μS / cm or higher, it is advisable to replace it with a new coolant composition, so if the bright pink color observed in the second measurement is observed during inspection, replacing the coolant composition is recommended.

[0060] From the above, it was confirmed that this embodiment can provide a coolant composition whose deterioration state due to use can be easily grasped visually.

[0061] It should be understood that the terms used herein are used in the sense commonly used in the art unless otherwise specified. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention belongs. In case of conflict, the present specification (including definitions) shall prevail.

[0062] The upper limit and / or lower limit of the numerical ranges described in this specification can be arbitrarily combined to define a preferred range. For example, the upper limit and lower limit of the numerical range can be arbitrarily combined to define a preferred range, the upper limit of the numerical range can be arbitrarily combined to define a preferred range, and the lower limit of the numerical range can be arbitrarily combined to define a preferred range.

[0063] Although the present embodiment has been described in detail above, the specific configuration of the present disclosure is not limited to this embodiment, and even if there are design changes within the scope that does not deviate from the gist of the present disclosure, they are included in the present disclosure. [Explanation of symbols]

[0064] 2: Semiconductor device 3:Cooler 4a: Refrigerant supply pipe 4b: Refrigerant discharge pipe 5a, 5b: Connecting pipe 6a, 6b: Insulating plate 10: Power Card 31: Case

Claims

1. A coolant composition for use in a cooling system of an electric vehicle, comprising: Water, at least one alcohol selected from the group consisting of monohydric alcohols, dihydric alcohols, trihydric alcohols, and alkylene glycol monoalkyl ethers; an absorbance-variable dye whose absorbance is easily changed by the presence of potassium fluoroaluminate; Including, The coolant composition is such that the absorbance-variable dye is a dye such that the absorbance at the maximum absorption wavelength in the visible light region of a solution containing 0.0005 to 0.0050 parts by mass of the absorbance-variable dye and 0.5 parts by mass of potassium fluoroaluminate in 100 parts by mass of a 50% by mass aqueous solution of ethylene glycol is 50% or less of the absorbance at the maximum absorption wavelength in the visible light region of a solution containing the same amount of the absorbance-variable dye in 100 parts by mass of a 50% by mass aqueous solution of ethylene glycol.

2. The dye further includes a dye whose absorbance is unlikely to change in the presence of potassium fluoroaluminate, 2. The coolant composition according to claim 1, wherein the absorbance-resistant dye is a dye such that the absorbance at the maximum absorption wavelength in the visible light region of a solution containing 0.0005 to 0.0050 parts by mass of the absorbance-resistant dye and 0.5 parts by mass of potassium fluoroaluminate in 100 parts by mass of a 50% by mass aqueous solution of ethylene glycol is 60% or more of the absorbance at the maximum absorption wavelength in the visible light region of a solution containing the same amount of the absorbance-resistant dye in 100 parts by mass of a 50% by mass aqueous solution of ethylene glycol.

3. 3. The coolant composition according to claim 2, wherein the color of the absorbance-changing dye and the color of the absorbance-resistant dye are not adjacent to each other on a color wheel chart of the 20 colors of the Munsell color system.

4. 4. The coolant composition according to claim 2, wherein the color of the absorbance-easily-changeable dye and the color of the absorbance-hardly-changeable dye are separated by two or more colors on a hue wheel chart of 20 colors of the Munsell color system.

5. The coolant composition according to any one of claims 1 to 4, wherein the content of the dye in the coolant composition is 0.0001% by mass to 0.01% by mass.

6. The coolant composition according to any one of claims 1 to 5, wherein the alcohol comprises ethylene glycol.

7. A cooling system for an electric vehicle, comprising the coolant composition according to any one of claims 1 to 6, a refrigerant pipe through which the coolant composition flows, and a heat-generating device as an object to be cooled.

8. 8. The cooling system for an electric vehicle according to claim 7, wherein the heat-generating device is at least one selected from the group consisting of an inverter, a converter, a generator, a motor, and a battery.

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