Intake Silencer For An Internal Combustion Engine

Abstract

An intake silencer for an internal combustion engine disposed on the intake side of a carburetor has an expansion chamber formed by a base board and a cover which are shaped like a pan, and in which there are disposed air horns connected to the carburetor and silencer tubes introducing the external air into the chamber. The base board and silencer tubes are integrally molded with synthetic resin.

Description

BACKGROUND OF THE INVENTION

This invention relates to an intake silencer and more particularly to an intake silencer for a small capacity internal combustion engine.

In a small capacity internal combustion engine mounted on, for example, a small snow vehicle or cultivator, the intake side of a carburetor is provided with a device for preventing those portions of such vehicles which are located near the engine from being stained by the so-called blow back of a sucked air-fuel mixture from the engine and also for reducing engine suction noises. However, the conventional type of such device is accompanied with various drawbacks, failing fully to meet user's demand. A typical type among such devices of the prior art capable of fully attaining the desired effect of silencing engine suction noises and preventing the above-mentioned blow back has the shortcomings that it is not only of complicated structure resulting in high production cost, subject to frequent failures, and difficult to handle, but also has such a great weight that its fitting applies excess stresses to the carburetor and its joint with the engine, often leading to the damage thereof.

SUMMARY OF THE INVENTION

It is accordingly an object of this invention to provide an intake silencer of simple construction and small weight for an internal combustion engine which fully silences engine suction noises and prevents stains resulting from the blow back of an air-fuel mixture.

Another object of the invention is to provide an intake silencer which, when fitted to an internal combustion engine, saves itself and the carburetor from undue stresses caused by the shaking of the engine during its operation.

Still another object of the invention is to provide an intake silencer which facilitates the replacement of an air horn undertaken to change engine characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view, partly in section, of an intake silencer embodying this invention and fitted to a carburetor;

FIG. 2 is a cross sectional view along line 2--2 of FIG. 1;

FIG. 3 is an enlarged cross sectional view of the joint of the fitting plate and base board of the intake silencer;

FIG. 4 is a perspective view of a packing used in the joint of FIG. 3; and

FIG. 5 is an enlarged cross sectional view of the joint of the base board and its cover of the intake silencer.

DESCRIPTION OF THE INVENTION

There will now be described by reference to the appended drawings an intake silencer embodying this invention.

Throughout the figures, a referential numeral 11 shows a carburetor connected at one end to the internal combustion engine (not shown) of, for example, a snow vehicle and at the other end provided with an intake port 12. Coaxially to said intake port 12 is detachably fitted a flared air horn or funnel 13 by the later described means. To the flange 11a of the carburetor 11 constituting the peripheral portion of the intake port 12 is attached one side of a rectangular fitting plate 15 made of sheet metal. Against the opposite side of said fitting plate 15 abuts the rear end of the air horn 13. The flange 11a of the intake port 12, the fitting plate 15 and the air horn 13 are fixed in place by screws 14 inserted therethrough from the side of the air horn 13. The fitting plate 15 is bored with two openings 15a corresponding to the intake ports 12 of two carburators 11, said openings enabling the intake ports 12 to communicate with the air horns 13.

To the fitting plate 15 is fixed a base board 16 shaped like a shallow pan with a continuous rim 16a and provided at the bottom with a rectangular through hole or an opening 17 into which the air horns 13 are inserted. Said base board 16 is fixed to the fitting plate 15 on the peripheral edge of the through hole 17 by screws 18 and nuts 19. Between the fitting plate 15 and base board 16 is interposed an elastic packing 21, for example, a rubber packing shown in FIG. 4. This packing 21 consists of a rectangular rim member 21a whose dimensions are large enough to surround the through hole 17, smaller ring members 21b provided in the same number as the screws 18 (in this embodiment there are used six smaller diameter ring members 21b arranged at nearly equal peripheral distance apart) and cylindrical members 21c (similarly six in this embodiment) which are coaxially inserted into holes 16b so as to connect the rim member 21a to the smaller ring members 21b. Into the cylindrical members 21c are coaxially fitted collars 20 through which the screws 18 project beyond the fitting plate 15 with the projecting portions tightened by nuts 19. As the result, the fitting plate 15 and base board 16 are connected by the elastic packing 21 in airtight and elastic relationship.

The base board 16 is provided with a large number of the later described silencer tubes 22 disposed parallel with the air horns 13 and projecting into a later described expansion chamber 24 at right angles to said base board 16. The base board 16 and silencer tubes 22 are integrally molded from synthetic resin. To the peripheral edge of the rim 16a of the base board 16 is detachably fitted a cover 23 shaped like a pot with a continuous side wall 23a and made of synthetic resin. The base board 16 and cover 23 define an expansion chamber 24. Between the inner wall of the expansion chamber 24 and the projecting end of each silencer tube 22 is allowed a proper space, for example, equal to half or one-third of the inner diameter of the silencer tube 22. The air horns 13 also project into the expansion chamber 24 with a considerable space allowed, as apparent from FIG. 1, between the inner wall of the expansion chamber 24 and the projecting end of each air horn 13.

The cover 23 is detachably fitted to the base board 16, for example, in the following manner. In the outer wall of the rim 16a of the base board 16 are linearly formed a pair of engagement grooves 31 (FIG. 5). On that side of the rim 16a of the base board 16 which is disposed opposite to said engagement grooves 31 is provided an outwardly extending fixing projection 25. Into the end face of the projection 25 is forcefully inserted a metal collar 26, in the inner wall of which there is cut out a female screw. On those parts of the inner wall of the side wall 23a of the cover 23 which closely face the aforementioned engagement grooves 31 of the base board 16 are formed a pair of engagement projections 28 engageable with said grooves 31. On the opposite side of the side wall 23a of the cover 23 to said paired engagement projections 28 is provided an outwardly extending projection 29 bored with a hole into which there is inserted a male screw 30 engageable with the female screw of the collar 26. Accordingly, the cover 23 can be easily fixed to the base board 16 by fitting the engagement projections 28 of the cover 23 into the engagement grooves 31 of the base board 16, and connecting the projection 29 of the cover 23 to the fixing projection 25 of the base board 16. Thus the peripheral edge of the side wall 23a is detachably fitted with the peripheral edge of the rim 16a.

There will now be described the operation of the intake silencer of the above-mentioned arrangement. Where an internal combustion engine is operated under the condition in which the air horns 13, base board 16 made of synthetic resin and cover 23 are set in place as illustrated in FIG. 1, external air is conducted in the directions of the arrows indicated in FIG. 1 into the expansion chamber 24 through a large number of silencer tubes 22 molded from synthetic resin integrally with the base board 16. The air conducted in said chamber 24 is expanded and is introduced into the carburetor 11 through the air horns 13. Where the blow back takes place in the engine, then a fuel, for example, gasoline, contained in an air-fuel mixture ejects backward from the carburator 11 into the expansion chamber 24. However, the fuel is obstructed in the passage by the cover 23 and attaches itself to the inner walls thereof. In the normal operation of the engine, therefore, said blow backed air-fuel mixture is prevented from discharging outside and forced backward into the carburetor 11 by the succeeding influx of external air. Suction noises occurring in the engine, particularly in the carburetor 11, are eliminated by resonance and interference taking place in the expansion chamber 24 and silencer tubes 22.

According to the above-mentioned embodiment, the base board 16 and silencer tubes 22 are integrally molded from synthetic resin. Therefore, this assembly is of simple structure and sufficiently small weight to prevent the other parts of the engine from being subjected to a heavy load and in consequence causes little damage thereto.

For the object of this invention, not only the base board 16, but also the cover 23 may be formed of synthetic resin. In this case, it is advised to mold silencer tubes from synthetic resin integrally with the base board 16 or cover 23. When not molded with the silencer tubes 22, the base board 16 or cover 23 may consist of a suitable material, for example, metal or synthetic resin.

Further according to this invention, the base board 16 and fitting plate 15 are joined together through the elastic packing 21, namely, do not directly abut against each other. Therefore, the vibrations of the engine occurring during its operation are transmitted to these members in an appreciably attenuated state. The fixing or removal of the cover 23 to or from the base board 16 is effected simply by fitting or withdrawing bolts, considerably facilitating the replacement of the air horns 13 to change the engine characteristics.

Claims

What is claimed is:

1. An intake silencer for an internal combustion engine disposed on the side of an intake port of a carburetor, comprising a base board fixed to the peripheral portion of said intake port of the carburetor; a cover, the peripheral edge of said cover being detachably fitted with the peripheral edge of said base board; an expansion chamber defined by said base board and cover; and a plurality of silencer tubes fixed to at least one of said base board and cover and having openings at each end thereof, the openings at one end being open in said expansion chamber, the openings at the other end being open in the external air, said plurality of silencer tubes and said one of said base board and cover being integrally molded from synthetic resin, whereby the external air conducted into said expansion chamber is sucked in said intake port of the carburetor during the operation of the engine.

2. An intake silencer as claimed in claim 1, wherein said base board is shaped like a shallow pan with a continuous rim along the periphery thereof, said cover is shaped like a pot with a continuous side wall and the peripheral edge of said side wall of said cover is detachably fitted along the whole periphery thereof with the peripheral edge of the rim of said base board by engagement means.

3. An intake silencer according to claim 2, wherein the engagement means comprises a groove and projection assembly formed on the mutually facing walls of the base board and cover which is disposed on one side of the peripheral edge of said base board and cover and a screw provided on the opposite side of said assembly to join the base board and cover.

4. An intake silencer as claimed in claim 3, further comprising a tubular air horn replaceably fixed to the peripheral portion of said intake port of the carburetor coaxially therewith, said air horn projecting into said expansion chamber.

5. An intake silencer as claimed in claim 1, wherein said plurality of silencer tubes are projecting from said one of said base board and cover into said expansion chamber at right angles to said one of said base board and cover.

6. An intake silencer as claimed in claim 2, wherein said plurality of silencer tubes are integrally molded with said base board and projecting into said expansion chamber at right angles to said base board.

7. An intake silencer according to claim 2, further comprising a fitting plate fixed to the peripheral portion of said intake port of the carburetor, said plate being bored with an opening corresponding to said intake port of the carburetor, the base board being also bored with an opening closed by said fitting plate, and the base board being apartly joined with an elastic packing interposed therebetween.

8. An intake silencer as claimed in claim 7, wherein the edge of said opening of said base board and the peripheral portion of said fitting plate are spatially screwed together with said elastic packing interposed therebetween.

9. An intake silencer comprising a fitting plate disposed on that side of a carburetor body on which there is formed an intake port, through which an air horn is pressed at one end against the body; screws for joining together the air horn, fitting plate and carburetor body; a base board shaped like a shallow pan, bored with an opening for receiving the air horn and provided with a plurality of silencer tubes molded from synthetic resin integrally with said base board; an elastic packing having a rim member interposed between the peripheral edge of the opening of the base board and the peripheral edge of the fitting plate; screws for joining together the elastic packing, fitting plate and base board; a pot-shaped cover having a peripheral edge matching along the whole peripheral length thereof a peripheral edge of the pan-shaped base board and defining an expansion chamber with the fitting plate and base board; and means for detachably fitting the peripheral edge of the cover to that of the base board.