1. Field of the Invention
The present invention relates to an electric compressor having a compression mechanism for sucking, compressing and discharging fluid, an electric motor for driving the compression mechanism, and a housing for containing the compression mechanism and the motor, in which the electric motor is driven by an inverter.
2. Description of the Related Art
In the electric compressor of this kind, an inverter, and a compression mechanism and an electric motor are installed separately from one another (refer to, for example, Japanese Patent Laid-Open Publication Nos. 2000-291557 (patent document 1), 2002-070743 (patent document 2), 2002-174178 (patent document 3), 2002-180984 (patent document 4), 2002-188574 (patent document 5), 2002-285981 (patent document 6)). Electric compressors disclosed in the patent documents 1 to 5, except for an electric compressor shown in FIG. 3 of the patent document 3, are provided with a partition for dividing a housing into a compressor chamber and an inverter chamber in an axial direction. The compressor chamber contains a compression mechanism and an electric motor, and the inverter chamber contains an inverter. The compression mechanism sucks a returned refrigerant from space outside of the housing between the partition and the compression mechanism to compress it, and discharges the compressed refrigerant out of the housing, wherein the electric motor side is defined as a suction side, and the other side is defined as a discharge side. The inverter faces the suction side across the partition to exchange heat with the refrigerant sucked into the compression mechanism, so that the inverter is prevented from being heated by heating parts. In the electric compressor shown in FIG. 3 of the patent document 3, an inverter is externally provided around the middle of the housing on the suction side, in order to exchange heat with the refrigerant to be sucked. In an electric compressor disclosed in the patent document 6, an inverter is externally provided in the middle of a housing, which contains a compression mechanism and an electric motor, over a compression mechanism installation area and a part of an electric motor installation area. The high heating portion of the inverter is thermally combined with the inlet of the refrigerant sucked into the compression mechanism, so that the inverter is cooled.
A housing of an electric compressor with an inverter installed therein needs an exclusive part, as compared with an electric compressor an electric motor of which is not driven by an inverter, because the structure of them are partly different. Such an exclusive part increases manufacturing cost due to increase in the types of parts of the housing. Even if the inverter is externally provided around the middle of the housing, an inverter attachment portion is so formed in the housing as to flatly protrude on one side of a radial direction. Therefore, the electric compressors with and without the inverter need respective exclusive part, so that cost increases after all.
In the electric compressor with the inverter externally provided in the housing, the attachment portion makes the housing large on one side of the radial direction aside from the inverter itself. Thus, the electric compressor becomes large and heavy. Especially in FIG. 3 of the patent document 3, many fins, which extend to the vicinity of a cylindrical surface formed by a stator of the electric motor, are formed on the flat inner surface of the attachment portion, so that the electric compressor becomes heavier. In the inverter of the patent document 6, a switching device as a high heating portion is divided from a capacitor the heating value of which is lower. Only the switching device is thermally combined with the returned refrigerant, and hence the protrusion area of the attachment portion is smaller than the whole inverter. When both the switching device and the capacitor are thermally combined with the returned refrigerant, however, the protrusion area becomes as large as that shown in FIG. 3 of the patent document 3.
In the patent documents 1 to 6, the refrigerant is discharged outside from the compression mechanism without passing through an electric motor side. Consequently, it is difficult to isolate lubricating oil from the discharged refrigerant for the purpose of improving the performance of a refrigerating cycle, because the lubricating oil has to be isolated during the process of discharge to the outside. Thus, a full and large-scale isolation apparatus as disclosed in the patent document 6 is necessary, whereby the housing becomes large and heavy.
The electric compressor according to the patent documents 1 to 6 is hard to be installed in a small engine room. When the electric compressor is installed in an electric vehicle or a gasoline-electric hybrid vehicle, drive power obtained from batteries is not as high as that of a gasoline vehicle. Thus, miniaturization and weight reduction are the most important challenges for the electric compressor, but the ordinary one is hard to achieve them.
In the patent documents 1 to 5, the returned refrigerant sucked on the electric motor side is used for cooling the electric motor before being sucked to the compression mechanism. The returned refrigerant, however, hardly contains the lubricating oil, so that lubrication tends to be insufficient in portions, in which the lubricating oil is not mechanically supplied, such as the bearing of the end of a drive shaft on the electric motor side which is far from the compression mechanism. In the patent document 6, the midpoint of a passage for sucking the returned refrigerant into the compression mechanism is connected to the electric motor side. To cool the electric motor, used are a part of the sucked refrigerant stagnating in the electric motor side, and heat and refrigerant moving forward and backward in accordance with difference in pressure and temperature between the suction passage of the returned refrigerant and the electric motor side. The performance of cooling the electric motor is inferior, in addition to the insufficiency of lubrication as with the patent documents 1 to 5. These problems adversely affect the lifetime and performance of the electric compressor.