Base oil for cooling of device, device-cooling oil containing the base oil, device to be cooled by the cooling oil, and device cooling method using the cooling oil

Abstract

A device-cooling base oil includes 30 mass % of at least one of an oleyl ester (e.g., oleate and oleyl alcohol ester) and oleyl ether. The oleyl ester and the oleyl ether each have 23 or more of a total number of a terminal methyl group, a methylene group and an ether group in a main chain and 1 or less of a total number of a methyl branch and an ethyl branch. The base oil has a kinematic viscosity at 40 degrees C. in a range of 4 mm2 / s to 30 mm2 / s. A device-cooling oil provided by blending the base oil is excellent in electrical insulation properties and thermal conductivity, and thus is favorably usable for cooling a motor, a battery, an inverter, an engine, an electric cell or the like in an electric vehicle, a hybrid vehicle or the like.

Description

TECHNICAL FIELD[0001]The present invention relates to a base oil for cooling a device, a device-cooling oil using the base oil, a device to be cooled by the device-cooling oil, and a device cooling method using the device-cooling oil.BACKGROUND ART[0002]An improvement in the performance of electric vehicles and hybrid vehicles results in an increase in the power density and, consequently, the heat generation of a motor. Accordingly, coil, magnet and the like have been improved in heat resistance and, further, a variety of modifications in motor design have been made for, for instance, reducing the increased heat generation resulting from the improved performance of a motor.[0003]For cooling a motor, there have been suggested three types of methods, i.e., an air-cooling method, a water-cooling method and an oil-cooling method. Among the above, the air-cooling method advantageously does not require any specific coolant to be prepared, but is unlikely to provide a large cooling capacit...

AI Technical Summary

Benefits of technology

[0012]For increasing heat transfer coefficient by modifications in terms of a fluid, it should be noted that since heat transfer coefficient is variable in relation to Nusselt number, Reynolds number and Prandtl number, the cooling properties of a fluid are affected by the physical properties of the fluid such as kinematic viscosity, thermal conductivity, specific heat and density. Specifically, a fluid having smaller kinematic viscosity but larger thermal conductivity, specific heat and density exhibits better cooling properties. Accordingly, it has been considered to lower the viscosity of a fluid (e.g., a lubricating oil) for improving the cooling properties thereof. However, when the viscosity of a lubricating oil is lowered, the cooling properties are improved but a sufficient film thickness of the lubricating oil cannot be provided, thereby causing lubrication failure. In view of the above, the minimum viscosity is determined depending on conditions regarding a portion to be lubricated in a transmission or the like. Thus, among lubricating oils having the same kinematic viscosity, one having larger thermal conductivity, specific heat and density has better cooling properties. For instance, a heat transfer coefficient during forced convection of a plate having a uniform temperature is proportional to the thermal conductivity to the power of two thirds, the specific heat to the power of one third and the density to the power of one third, so that the heat transfer coefficient is the most affected by the thermal conductivity.

[0014]As a result of concentrated studies in terms of molecular design, the inventor has found that a compound having a predetermined molecular structure is excellent in cooling properties, electrical insulation properties and lubricity.

[0016]A device-cooling oil provided by blending a base oil for cooling a device according to the invention is excellent in electrical insulation properties and thermal conductivity, and thus is favorably usable for cooling a motor, a battery, an inverter, an engine, an electric cell or the like in an electric vehicle, a hybrid vehicle or the like.

Problems solved by technology

Among the above, the air-cooling method advantageously does not require any specific coolant to be prepared, but is unlikely to provide a large cooling capacity.

However, since a motor coil cannot be directly cooled because of the electrical conductivity of water, a cooling pipe has to be laid out, which, disadvantageously, increases the size of a cooling device.