Suction silencer

A suction silencer for suppressing generation of noise caused by gas or air sucked by a machine such as a compressor, internal combustion engine or the like. The suction silencer has amounting seat by which it is mounted on the suction side of a machine such as an internal combustion engine. The mounting seat has an opening leading to the suction port of the machine. An inversed conical surface protrudes from the peripheral edge of the opening. A lid member is attached to cover the inversed conical surface such that a small gap is left between the inner surface of the lid member and the large-diameter end of the inversed conical surface. The lid member has an inversed conical member which projects into the space defined by the conical surface so that an annular passage is formed between the inversed conical surface and the peripheral surface of the inversed conical member.

BACKGROUND OF THE INVENTION 
The present invention relates to a suction silencer for use in machines 
such as air compressors, internal combustion engines or the like. 
Machines which suck gas or air, such as air compressors, internal 
combustion engines and so forth employ a suction silencer for suppressing 
the generation of noise by the sucked gas or air. It is well known that a 
silencing effect is achieveable by making the gas or air expand and 
contract repeatedly. 
BRIEF SUMMARY OF THE INVENTION 
The invention aims as its principal object at providing a suction silencer 
which relies upon the principle explained above. 
More specifically, it is a primary object of the invention to provide a 
suction silencer in which the sucked gas or air is made to pass through an 
annular passage defined by two conical surfaces thereby to reduce the 
level of the noise. 
Another object of the invention is to provide a suction silencer which, 
when mounted on the intake opening of a carburetor of an internal 
combustion engine, effectively serves also as a plate for preventing 
so-called blowing back of air-fuel mixture. 
To this end, according to the invention, there is provided a suction 
silencer comprising a mounting seat at which the suction silencer is 
mounted on the suction side of a machine adapted to suck gas or air, the 
mounting seat having therein an opening communicating with the suction 
port of the machine; a member defining an inversed conical surface 
continuous with the peripheral edge of the opening; and a lid member 
covering the larger-diameter end of the inversed conical surface with a 
predetermined gap left therebetween, the lid member having an inversed 
conical member projcting into the space defined by the inversed conical 
surface. 
Preferably, the member defining the inversed conical surface is surrounded 
by a region which constitutes a filter for filtrating the gas or air to be 
sucked through the suction silencer. 
There and other objects, features and advantages of the invention will 
become clear from the following description of the preferred embodiment 
taken in conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The invention will be fully described hereinunder with reference to the 
accompanying drawings. 
The attached drawings in combination show a suction silencer in accordance 
with a first embodiment of the invention which is suitable for use in 
combination with a carburetor 3 for the engine of a portable machine such 
as chain saw 1. The suction silencer of the invention, generally 
designated at a reference numeral 5, is assembled as a unit with an air 
filter and this unit is attached through an elbow 4 to the intake opening 
of the carburetor 3 which is accomodated by a carburetor chamber 2 
provided in the machine 1. The suction silencer 5 has a box-like body of a 
substantially square shape, composed of an upper housing part and a lower 
housing part 6 and 12 coupled to each other to define therein a cavity 23. 
A substantially circular lid plate 8 is provided on the upper surface of 
the upper housing part 6. The like plate 8 is connected to the peripheral 
portion of the upper housing part 6 through ribs 28. Each region defined 
by adjacent ribs 28 is covered by a gauze wire 7 of fine mesh constituting 
a filter which permits the internal cavity 23 to communicate with the 
exterior. Preferably, the gauze wire 7 is formed as a unit with the upper 
housing part 6. The lid plate 8 is recessed at its central portion as at 9 
so that the central portion of the lid plate 8 as a whole presents an 
inversed conical body 20 whose apex 18 is directed towards the internal 
cavity 23. Mounting screw holes 10 formed in the base portion of the 
conical body 20 are adapted to receive screws by means of which the lid 
plate 8 is mounted on the body of the machine 1. A substantially circular 
mounting seat 14 is provided on the lower surface of the lower housing 
part 12 at a portion of the latter corresponding to the aforementioned lid 
plate 8. As in the case of the upper housing part 6, the mounting seat 14 
is connected to the peripheral portion through ribs 26. Each region 
defined by adjacent ribs 26 is covered with a gauze wire 13 of fine mesh 
which consitutes a filter through which the internal cavity 23 is 
communicated with the exterior. The mounting seat 14 is provided with an 
opening 19 whose center substantially aligns with the apex 18 of the 
inversed conical body 20. The internal cavity 23 is communicated with the 
suction port of the carburetor 3 through the opening 19. An inversed 
frusto-conical surface 21 is protruded from the peripheral edge of the 
opening 19 towards the internal cavity 23. The peripheral edge 25 of the 
large-diameter end of the frusto-conical surface 21 is rounded and 
positioned to oppose to the inner surface of the lid plate 8 with a small 
gap 22 left therebetween. Holes 16 are formed in the portions of the 
mounting seat 14 corresponding to the mounting screw holes 10 of the upper 
housing part 6. 
In order to obtain an airtight seal in the juncture 24 between the upper 
housing part 6 and the lower housing part 12, a ridge is formed on the 
juncture surface of one of these housing parts while a mating grove is 
formed in the mating surface of the other. Reference numerals 11 and 17 
denote tool engaging portions into which a screw driver or the like tool 
is inserted to forcibly separate the upper and lower housing parts 6 and 
12. 
By assembling these two housing parts 6 and 12 together, the inversed 
conical body 20 is projected into the space 27 defined by the 
frusto-conical portion 21 so that a substantially annular passage is 
formed between two conical surfaces. 
As shown in FIG. 5, the suction silencer 5 of the invention having the 
described construction is attached through the elbow 4 to the carburetor 
3. As the engine is started, the ambient air is sucked through the upper 
and lower filter gauze wires 7, 13 and the filtrated air is introduced 
into the internal cavity 23 which has a considerably large volumn. The air 
then flows through the annular gap 22 while being guided by the inner 
surface of the lid plate 8 (preferably provided with a guide protrusion 
15) and rounded peripheral edge 25 so as to be deflected substantially by 
180.degree.. The air is then made to flow through the annular passage 
between two conical surfaces and sucked ito the carburetor 3 through the 
opening 19. In consequence, the air is first introduced into the internal 
cavity 23 of a comparatively large volume and then guided through the 
restricted annular gap 22 where the air is subjected to an abrupt 
contraction and turning of flowing direction. Thereafter, the flow of air 
is settled as it passes the annular passage and is then introduced to the 
opening 19 which has a comparatively large cross-sectional area. In 
consequence, the noise produced by the sucked air is suppressed 
effectively by the repetitional expansion and contraction. 
Assuming here that there is a blowing back of air-fuel mixture from the 
carburetor 3, the droplets of fuel are returned to the carburetor 3 
without fail while being guided by the conical surface. In consequence, 
various problems attributable to the blowing back of air-fuel mixture, 
e.g. contamination or clogging of the filter gauze wires 7 and 13, are 
avoided advantageously. 
A series of tests was conducted to confirm the effect of the suction 
silencer of the invention, by employing an air-cooled 2-cycle engine 
having a displacement of 66 cc, for various combinations of the size of 
the annular gap 22 and the shape of the annular passage defined between 
two conical surfaces. The best combination provided about 5 db reduction 
in the noise level while suppressing the reduction of output power of the 
engine to a low level of about 3%. 
Although the invention has been described through specific terms, it is to 
be noted here that the described embodiment is not exclusive and various 
changes and modifications may be imparted thereto wihtout departing from 
the scope of the invention which is limited solely by the attached claims.