1. Field of the Invention
The present invention relates to a portable generator having an engine and a generator body driven by the engine and accommodated within a sound insulating case together with the engine.
2. Description of the Prior Art
In general, portable generators include a generator body driven by an engine. Most of the portable generators have a sound insulating case within which the engine and its peripheral components are accommodated to reduce noise resulting from operation of the engine. The engine and a muffler heated by engine exhaust gases constitute a heat generating component. In order to accommodate such heat generating component within the sound insulating case, appropriate measures should be taken to cool the heat generating component.
One example of such portable generators is known from Japanese Utility Model Publication No. SHO 64-3777. The known portable generator includes a sound insulating case composed of a base, a main cover secured to the base along opposite longitudinal edges, and two side covers closing opposite ends of the main cover. Within the sound insulating case, an engine, a generator body and a muffler are accommodated. The engine has a cooling fan. The engine and the cooling fan are covered by an engine cover. The engine cover is covered by a shroud. The generator body and the muffler are covered by a duct. The duct is connected to the shroud, and the shroud is connected to the engine cover. The respective internal spaces of the engine cover, shroud and duct communicate with each other. Thus, by the engine cover, shroud and duct is formed a ventilating duct extending from an intake hole formed in the engine cover to an exhaust hole formed in the sound insulating case.
In the known portable generator of the foregoing construction, outside air is introduced into the sound insulating case from a plurality of air intake holes formed in the base. A part of the outside air is drawn into a cylinder of the engine for combustion, and exhaust gases are discharged from the muffler to the outside of the generator. By the cooling fan driven by the engine, another part of the outside air is drawn into the engine cover, then forced to flow downstream through the shroud and the duct to cool the engine and the muffler, and finally exhausted from vent holes formed in the side cover.
In the aforesaid forced air-cooling system where the outside air is forced against the outside surface of the engine to cool the same, increase of the cooling efficiency requires either enlargement of the surface area (cooling area) of the engine, or increase of the quantity of outside air forced against the engine. In general, there is a limit to which extent the engine surface area can be enlarged. Accordingly, the second alternative (i.e., increase of the outside air quantity) is usually chosen. However, in order to increase the quantity of outside air, a larger cooling fan is needed and, hence, upsizing of the portable generator is not avoidable.