Rotary kinetic fluid motors or pumps – Working fluid passage or distributing means associated with... – Plural distributing means immediately upstream of runner
Reexamination Certificate
2001-02-26
2003-01-28
Verdier, Christopher (Department: 3745)
Rotary kinetic fluid motors or pumps
Working fluid passage or distributing means associated with...
Plural distributing means immediately upstream of runner
C415S119000, C415S185000, C415S121200, C415S208200, C415S210100, C416S24700A, C015S326000
Reexamination Certificate
active
06511286
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a portable power working machine having a centrifugal blower, such as a backpack blower apparatus or power duster; and, more particularly, is concerned with a technique for reducing the noise of a centrifugal blower.
2. Related Background Art
Known as a portable power working machine is one equipped with a centrifugal blower, such as a backpack blower apparatus or power duster. In general, the centrifugal blower used in such a portable power working machine has an intake port provided with a port cover in order to prevent foreign matters from being drawn into the centrifugal blower or hands, clothes, and the like of users from carelessly or accidentally entering the blower.
A typical conventional cover has a net structure in which a plurality of rod-shaped members are combined like a web or lattice (see FIG.
4
).
FIG. 16
is a sectional view partly showing a conventional port cover
1
. As shown, each of rod-shaped members
2
,
3
has a substantially rectangular cross-sectional form, whereas their longer sides are arranged substantially in parallel with the air passing direction in the state where the cover
1
is attached to the centrifugal blower. Consequently, the leading and trailing edge portions
4
of rod-shaped members
2
,
3
, i.e., the shorter sides
4
of their cross sections, are arranged substantially perpendicular to the air passing direction.
FIG. 17
is a sectional view partly showing another conventional port cover
5
. In the port cover
5
of
FIG. 17
, trailing edge portions
8
of rod-shaped members
6
,
7
are rounded into a semispherical form.
In a portable power working machine provided with the port cover
1
or
5
mentioned above, noise is generated from parts surrounding the port cover
1
or
5
when driving the centrifugal blower.
Therefore, it is an object of the present invention to provide a centrifugal blower yielding low noise, and a portable power working machine equipped with such a centrifugal blower.
SUMMARY OF THE INVENTION
The inventors have carried out various studies in order to achieve the above-mentioned object and, as a result, have found that, due to the presence of a port cover, a large turbulent flow or swirl occurs on the downstream side of the port cover, i.e., in the center part within the centrifugal blower, thereby causing noise. Also, the inventors have found that a flow of air having flowed into the centrifugal blower from the intake port along the axis of rotation of an impeller is deflected radially outward within the blower, thus becoming one of causes for generating the swirl.
Hence, the present invention provides a centrifugal blower comprising an impeller having a plurality of blades arranged in a circumferential direction and an air inlet portion surrounded by the blades; a casing for accommodating the impeller, the casing having an intake port disposed at a region opposing the air inlet portion of the impeller; and a port cover, disposed in the casing, for covering the intake port, the port cover comprising a plurality of rod-shaped members arranged in a net structure; wherein at least one of the plurality of rod-shaped members is configured such that an airflow passing through the port cover so as to flow into the air inlet portion is deflected away from an axis of rotation of the impeller.
The air drawn into the centrifugal blower changes the direction of its flow away from a direction extending along the axis of rotation of the impeller, i.e., into a radially outward direction. Since the rod-shaped members function so as to assist in this deflection, the air smoothly changes the direction of its flow after passing through the port cover, so that swirls or turbulences are restrained from occurring on the downstream side of the port cover, whereby noise is reduced.
The port cover may be constituted by a combination of a plurality of concentrically arranged annular rod-shaped members with a radially extending rod-shaped member.
In this case, it will be effective if a trailing edge portion of the annular rod-shaped member has an inner face which forms a slanted surface inclining outward as it advances in the air passing direction. This slanted surface exhibits the deflecting effect.
It will similarly be effective if both sides of the trailing edge portion of the radially extending rod-shaped member form a slanted surface such that the trailing edge portion becomes thinner as it advances in the air passing direction.
If a trailing edge portion of one of the plurality of annular rod-shaped members is projected downstream the trailing edge portion of the rest of the plurality of annular rod-shaped members in the air passing direction, then the airflow in the air inlet portion can be held stably, whereby swirls can be restrained from occurring.
The amount of downstream projection in the trailing edge portion of the rod-shaped member in the air passing direction may vary in a direction in which the rod-shaped member extends. In this configuration, the leading edge of the rod-shaped member becomes irregular, for example, so that the positions or times at which swirls occur may vary, whereby the swirls are kept from growing.
The present invention is also directed to a portable power working machine having the centrifugal blower mentioned above. The portable power working machine includes a backpack blower apparatus.
These and other features and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described illustrative embodiments of the invention.
REFERENCES:
patent: 2305136 (1942-12-01), Campbell
patent: 2950859 (1960-08-01), Kirk
patent: 4325163 (1982-04-01), Mattson et al.
patent: 4756668 (1988-07-01), Gassen et al.
patent: 4913112 (1990-04-01), Iida
patent: 5131352 (1992-07-01), Hoshino et al.
patent: 5259726 (1993-11-01), Bacria
patent: 5460485 (1995-10-01), Sugiyama et al.
patent: 6017191 (2000-01-01), Harmsen
patent: 1-159498 (1989-06-01), None
Maruyama Mfg. Co. Inc.
Rosenthal & Osha L.L.P.
Verdier Christopher
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