1. Field of the Invention
This invention relates to an inverter device having in one casing a main circuit section which is a source of heat, a logical section and components of low heat resistance such as smoothing capacitors. More particularly, the present invention relates to an actual mounting structure suitable for improvement of reliability having a device of closed or totally enclosed structure.
2. Description of the Prior Art
An inverter device is generally composed of a main circuit section and a logical section. In a conventional inverter device, the main circuit section and the logical section are contained in, one casing as disclosed in Laid-Open Japanese Utility Model Registration No. 61-153499. The main circuit section which produces a large amount of heat is directly mounted to cooling fins for air cooling. The logical section, although producing little heat, has low resistance to heat and accordingly requires a lowering of ambient air temperature. Where the logical section and the main circuit section are housed in one casing, the air around the logical section is heated by the large amount of heat produced from the main circuit section, resulting in an increased logical section temperature. To prevent a temperature rise in the logical section in excess of its permissible temperature, large-sized cooling fins are provided for the main circuit section, or a cooling fan is installed, thus increasing the cooling capacity in order to lower the heat of the main circuit section. The main circuit section, having a switching function, is likely to become a noise source to the logical section. In order to prevent this electromagnetic noise, a space is provided between the main circuit section and the logical section, and an electromagnetic shield plate is also provided, thereby preventing misoperation of the logical section due to electromagnetic noise.
Due to the fact no shield is used particularly for thermal separation between the main circuit section and the logical section, the air heated by the main circuit section elements, which produces a large amount of heat, flows into the logical section between the electromagnetic shield plate disposed between the main circuit section and the logical section, and the inner wall of the casing, resulting in an increased air temperature around the logical section. The air thus heated by the main circuit section will heat the electromagnetic shield plate. The electromagnetic shield plate made of iron sheet for the purpose of improving the magnetic shield effect is a good heat conductor, which is likely to raise the air temperature on the logical section side. In the inverter device containing the main circuit section and the logical section in one casing as described above, there is the problem that an air temperature rise occurs around the logical section less resistant to heat from the main circuit section. Furthermore, it is necessary to provide sufficient space to dispose an electromagnetic shield plate for electromagnetic noise prevention between the main circuit section and the logical section. This is disadvantageous from the standpoint of reducing the size of the device.
Furthermore, the conventional device, as stated in Japanese Utility Model Registration No. 60-151186, includes heat-generating parts, such as switching elements, and a smoothing capacitor both contained in one casing, above the terminal of the smoothing capacitor is located a printed circuit board mounted with a control circuit of the switching element. No means is provided for cooling the smoothing capacitor and no protective means is provided for protection of a control circuit in the event of a rupture of the smoothing capacitor caused by overcurrent. A smoothing capacitor cooling structure has been disclosed in Japanese Utility Model Registrations No. 61-47699 and 61-67994.