This invention relates to a container for accommodating a small control device such as an inverter device, and particularly to the construction for radiating heat generated in the box for the protection thereof. The following description will deal with the case of an inverter device. In an inverter device, in general, large amounts of heat are generated by diodes and a transistor module which form a main circuit among other electric circuit parts constituting the inverter device. In an inverter device of small capacity, the box is die cast from an aluminum alloy, and the generated heat is emitted from radiator fins and the surfaces of the box, so that the diodes and transistor elements will work properly and that the electronic parts for a control circuit mounted on a printed wiring board will not be affected by the temperature, in order to maintain improved reliability.
FIGS. 1 and 2 show a conventional container for accommodating an inverter device of the completely sealed type, wherein reference numeral 1 denotes an inverter device of the completely sealed type, and reference numeral 2 denotes a box which is a die cast of an aluminum alloy and which constitutes a container for the inverter device 1. Radiator fins 2a are provided on the back surface of the box and a cooling fan 3 is mounted on the lower side thereof. Electric parts 4 for a main circuit such as diodes and a transistor module are mounted on the side of the front surface of the box 2 in an intimately adhered manner, and a printed wiring board 5 on which are mounted electronic parts for a control circuit is detachably mounted on the box 2. Reference numeral 6 denotes a cover plate made of a plastic material which will be secured to the box by screws 7 to completely seal the inverter device which is assembled and wired in the box 2.
The conventional container has been constructed as mentioned above. Described below is the function of the container. When the inverter device 1 is in operation, electric parts 4 for a main circuit generate heat that is transmitted through contact surface of the box 2 to raise the temperature of the radiator fins 2a. Here, the cooling fan 3 is rotating to upwardly blow air through the radiator fins 2a. Therefore, the heat in the radiator fins is dissipated, and the diodes and transistor elements are allowed to operate at temperatures lower than a specified temperature. Further, the air temperature rises in a portion surrounded by the box 2 and the cover plate 6 due to the heat generated by the electric parts 4 for the main circuit and by the parts on a printed wiring board 5. The volume and the outer size of the inverter device, however, have been so determined so that the heat radiates from the side surfaces of the box and from the cover surface at a rate whereby the air temperature therein is maintained at a value lower than a temperature specified for the electronic parts.
The conventional container for accommodating the inverter device of the completely sealed type is constructed as described above. To keep the electronic parts from being affected by the air temperature, therefore, it is a tendency to increase the outer size of the device. Further, even in a place where a good environment is present and the device need not be completely sealed or protected, the device of the completely sealed type having a larger outer size must be used because to produce products of the same type in a shielded construction for which air tightness is not required as strictly as for the devices of the completely sealed type, it is necessary to employ a different plastic cover plate for the box made of die cast aluminum. For this purpose, however, an expensive metal mold is required, resulting in increased manufacturing costs.