The present invention relates to a portable power working machine such as a chain saw, a power cutter, a hedge trimmer, etc., which is provided with an internal combustion engine as a driving power source for driving the working components thereof, and in particular, to a portable power working machine which is designed to prevent as much as possible an air cleaner attached to an air intake system of an internal combustion engine from being clogged with dust.
A conventional portable power working machine, such as a chain saw, is generally constructed such that a small air-cooled internal combustion engine acting as a driving power source for driving the working components, such as a saw chain, is mounted in a main housing, that a cooling fan driven by the internal combustion engine is disposed on one side of the main housing, and that a carburetor chamber housing therein an air cleaner and a carburetor is disposed on an upper rear side of the internal combustion engine.
In the operation of the portable power working machine as described above, dust that includes Sawdust of relatively large size, powder of cut material and sand-like dust is inevitably generated. When dust of those kinds is allowed to enter together with air into the air intake system of the internal combustion engine, and to collect on the filter element of the air cleaner, the clogging of the filter results, thus giving rise to an irregularity of the engine as well as a deterioration of performance of the engine due to an insufficiency in the flow rate of intake air. Accordingly, it is required in the operation of the portable power working machine to frequently clean the air cleaner, etc., which is a task that is quite troublesome for the operator.
The present invention has been made to solve the aforementioned problems. In particular, it is an object of the present invention to provide a portable power working machine which is capable of preventing as much as possible an air cleaner of the air intake system of a small air-cooled internal combustion engine acting as a driving power source for working components from being clogged with dust, thereby relieving an operator from the task of frequently cleaning the air cleaner.
With a view to attaining the aforementioned object, there is provided, in accordance with the present invention, a portable power working machine comprising a small air-cooled internal combustion engine received in a main housing, a cooling fan which is adapted to be driven by the internal combustion engine and disposed on one side of the main housing, and an air cleaner disposed in the air-intake system of the internal combustion engine; wherein the power working machine is featured in that part of air introduced into the main housing by means of the cooling fan is allowed to be sucked again by the cooling fan so as to be recirculated.
In a preferred embodiment, a carburetor chamber housing therein the air cleaner and a carburetor is placed in the air-intake system of the internal combustion engine, wherein part of air introduced into the main housing by means of the cooling fan is allowed to be sucked again by the cooling fan, thereby enabling it to be recirculated through the carburetor chamber and a circulating air duct disposed outside the carburetor chamber, and at the same time, part of air introduced into the carburetor chamber is allowed to be introduced from the air cleaner into the internal combustion engine.
In this case, preferably, the circulating air duct may be disposed in such a manner that the open end on the upstream side thereof is positioned lower than the air cleaner housed in the carburetor chamber, while the open end on the downstream side thereof may be positioned in the vicinity of the air-intake port of the cooling fan.
In a more preferred embodiment, the circulating air duct may be constructed such that the upstream region of the passageway has a larger cross-sectional area than that of the downstream region of the passageway, and that a flange-like guiding member is placed in the vicinity of the aforementioned downstream side open end of the circulating air duct, thereby effectively enhancing the air intake power of the cooling fan.
A typical example of a portable power working machine in which the present invention is especially advantageous is a chain saw, which includes a saw chain set composed of a saw chain and a guide bar that is located on the side of the main housing opposite from the cooling fan and the carburetor chamber housing. Because chain saws produce large quantities of dust, including relatively large particles, reducing the rate of accumulation of dust on the air cleaner offers important improvements in the chain saw.
According to the aforementioned preferred embodiment of the portable power working machine, when the power working machine is operated, the air (cooling air) that has been introduced from one side of the main housing by the suction of the cooling fan and hence accelerated and pressurized is transmitted so as to cool the internal combustion engine and then discharged through a discharge port formed in the main housing toward the external atmosphere, part of air thus introduced into the main housing being sucked again by the cooling fan after passing through the carburetor and the circulating air duct so as to be recirculated, whereas part of the air introduced into the carburetor chamber is sucked into the internal combustion engine through the air cleaner and carburetor during the intake stroke of the engine.
In this case, since the circulating air duct is disposed in such a manner that the open end on the upstream side thereof is positioned lower than the air cleaner housed in the carburetor chamber, and the open end on the downstream side thereof is positioned in the vicinity of the air-intake port of the cooling fan, most of the dust existing in the air that has been introduced into the carburetor chamber is caused, due to the gravity thereof, to be sucked by the Cooling fan after passing through the carburetor chamber and the circulating air duct, thus preventing most of the dust from reaching the air cleaner.
As a result, it is now possible to minimize the clogging of the air cleaner, thus making frequent cleaning of the air cleaner unnecessary and improving the efficiency of work.
In another preferred embodiment of the portable power working machine according to the present invention, the air cleaner and carburetor are placed in the air-intake system of the internal combustion engine, wherein part of external air that has been pressurized and accelerated due to the sucking power of the cooling fan is caused to be sucked again by the cooling fan after passing through a discharge port formed at the outer periphery of a volute case and through the circulating air duct, thereby enabling part of external air to be recirculated, and at the same time, part of air flowing through the circulating air duct is caused to be separated from an intermediate portion of the circulating air duct and allowed to flow in a direction which is approximately orthogonal to the direction of the intermediate portion of the circulating air duct, thereby enabling the air to be introduced into the internal combustion engine through the air cleaner and the carburetor.
In this case, preferably, the circulating air duct is constituted by an upstream side passageway extending from the discharge port toward the air cleaner, the aforementioned intermediate passageway being disposed below the filter element of the air cleaner and communicating with the upstream side passageway, and a downstream side passageway communicating with the intermediate passageway and having an open distal end which is positioned in the vicinity of the intake port of the cooling fan.
In another preferred embodiment, a carburetor chamber housing a carburetor is placed in the air-intake system of the internal combustion engine, and the aforementioned air cleaner having a sheet-like filter element as a partitioning wall is disposed in the carburetor chamber.
According to the aforementioned preferred embodiment of the portable power working machine, when the power working machine is operated, the air (cooling air) that has been-introduced from one side of the main housing by the suction of the cooling fan and hence accelerated and pressurized is transmitted so as to cool the internal combustion engine and then, discharged through a discharge port formed in the main housing toward the external atmosphere. Part of air thus introduced into the main housing is sucked again by the cooling fan after passing through a discharge port formed at the outer periphery of a volute case and through the circulating air duct, thereby enabling part of the air to be recirculated. At the same time, part of air flowing through the circulating air duct is caused to be separated from an intermediate portion of the circulating air duct and allowed to flow in a direction which is approximately orthogonal to the direction of the intermediate portion of the circulating air duct, thereby enabling the air to be introduced into the internal combustion engine through the air cleaner and the carburetor.
In this case, since most of the dust present in the air being introduced from the discharge port into the circulating air duct is caused, due to the gravity and inertia thereof, to be sucked by the cooling fan after passing through the circulating air duct. The air which is separated from an intermediate portion (an intermediate passageway) disposed lower than the air cleaner in the circulating air duct and directed to flow in a direction orthogonal to the intermediate passageway can be substantially prevented from being contaminated by the dust.
As a result, it is now possible to minimize the clogging of the air cleaner, thus making frequent cleaning of the air cleaner unnecessary and improving the efficiency of work.
Further, although the quantity of air introduced into the internal combustion engine may be sharply reduced at the moment when the throttle valve of the carburetor is turned from a relatively wide-opened state back to a minimum opening (opening at idling of the engine), since the cooling fan can keep rotating at a high speed for a while due to the inertia, the sucking action by the cooling fan to the dust in the air cleaner chamber can be maintained, thereby making it possible to minimize the clogging of the air cleaner by this action of the cooling fan.
For a better understanding of the present invention and further advantages thereof, reference may be made to the following description of an exemplary embodiment, taken in conjunction with the accompanying drawings.