GB2143275A - Silencer for exhaust gases - Google Patents

Abstract

A casing 10 has inlet and outlet openings 11 and 12 which communicate with the ends respectively of a gas passage member 15 disposed within the casing 10. The member 15 is composed of two parts 29 and 30 which are secured together and which include respective recesses co-operating to define perforated tubular portions 16, 17 in the member 15. Both the casing 10 and the member 15 are made of plastics material, which may or may not have a fibre or particulate re-inforcement. <IMAGE>

Description

SPECIFICATION Silencer for exhaust gases This invention relates to a silencer for exhaust gases, such as is normally fitted to a motor vehicle.

Such silencers are conventionally made of metal, and are prone to corrosion by exhaust products (such as sulphuric acid and hydrochloric acid), as well as by external influences, for example salt-laden water. Corrosion could be avoided if plastics materials were to be employed in the production of the silencer, and it is an object of the invention to provide a silencer construction which lends itself to production from such materials.

According to the present invention, a silencer for exhaust gases includes a casing made of plastics material and having inlet and outlet openings therein, and a gas passage member disposed within the casing and having passageway means therein which communicates at its ends with the inlet and outlet openings respectively, the passageway means including at least one perforated tubular portion, the gas passage member being composed of two parts which are made of plastics material and which are secured together, said parts including respective recesses which co-operate to define said tubular portion when the parts are secured together.

A number of plastics materials can be used for the casing and the gas passage member: however, it is preferred that the casing at least is made of a material, such as polyester resin, vinyl ester resin or furane resin, which is reinforced by long fibres.

To facilitate the production of the parts of the gas passage member by moulding, the perforations advantageously extend through the thickness of the side walls of the or each tubular portion perpendicularly to a plane defined by the join line between the recesses which define the tubular portion. In one particular embodiment, the or each tubular portion is diamond-shaped in cross-section, with the recess in each part of the gas passage member defining two respective sides of the tubular portion.

In a preferred construction of the silencer, the passageway means is composed of two such perforated tubular portions which are laterally offset from one another and which overlap along their main axes, the overlapping portions being provided respectively with mutually facing openings, substantially larger than the perforations, whereby gases flowing through the passageway means in use can pass from one tubular portion to the other.

The gas passage member can include two mutually spaced ribs which extend across the interior of the casing and which conform in shape to the internal cross-section of the latter, in which case the openings are disposed between these ribs.

Each part of the gas passage member can have a generally planar securement portion by means of which the two parts are secured together in face-to-face relation, the recess or recesses which define the tubular portion or portions being formed integrally with the securement portion. These securement portions desirably have location elements thereon which interengage to prevent relative movement of the parts of the gas passage member in a direction parallel to the plane of each securement portion.

Conveniently, the inlet and outlet openings in the casing are formed by respective tubular spigots, and the tubular portion or portions of the gas passage member terminate in similar tubular spigots which locate inside the spigots on the casing. These spigots are desirably circular in cross-section.

Each of the inlet and outlet openings may have a metal pipe integrally incorporated therein; for example by moulding a metal stub pipe in situ in the casing.

Desirably, the casing is elongate and is formed in two parts which are joined together along a line extending transversely to the longitudinal axis of the casing. The invention will now be further described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a plan view, partly in section, of a silencer according to the present invention; Figure 2 is a side view, also partly in section, of the silencer shown in Figure 1; Figure 3 is a perspective view of a gas passage member which forms part of the silencer shown in Figures 1 and 2; Figure 4 is a section taken alon the line IV IV in Figure 2; Figure 4A is a scrap perspective view showing an alternative form of gas passage member; Figure 5 is an end view of the gas passage member; Figure 6 is an underneath plan view of one of two parts which together form the gas passage member;; Figure 7 is a sectional view showing afirst modification to the silencer shown in Figure 1 to 6; and Figures 8,9 and 10 are sectional views showing further modifications to the silencer.

Referring first to Figures 1 and 2, the silencer shown therein comprises a hollow casing 10 which is generally oval in crosssection and which has an inlet opening 11 and an outlet opening 1 2 at its opposite ends.

The casing 10 is formed from plastics material and is composed of two parts 1 3 and 14 which are secured together along a line extending transversely to the length thereof.

More especially, the part 1 3 forms a main body of the casing and has the outlet opening 1 2 formed therein, while the part 14 has the form of a cap and is provided with the inlet opening 11. Each of the inlet and outlet openings is constituted by a tubular spigot having an axially stepped internal surface, the purpose of which will be explained later.

Disposed within the casing 10 is a gas passage member 15, shown in detail in Figures 3 to 5, which defines a passageway extending between the inlet opening 11 and the outlet opening 1 2 in the casing 10. This passageway is formed by two tubular portions 1 6 and 1 7 which extend longitudinally of the casing and which are offset from one another transversely of their main axes. The tubular portion 1 6 terminates in a spigot 1 8 of circular crosssection which is received within the inlet opening 11, with the end of the spigot abutting against a shoulder 1 9 defined by the aforementioned axial step in the interior of the inlet opening.The tubular portion 1 7 similarly terminates in a spigot 20 which locates within the outlet opening 1 2 and whose end abuts a shoulder 21 on the interior of the latter. The side walls of both tubular portions 1 6 and 1 7 are punctured by perforations 22: for convenience, these perforations are illustrated in Figures 3 and 4 only.

As can be appreciated most readily from Figures 1 and 3, the tubular portions 1 6 and 1 7 overlap in the direction of their main axes.

In the region of such overlap, the gas passage member 1 5 is provided with two mutually spaced ribs 23 and 24 which extend across the interior of the casing 10 and which conform in shape to the internal cross-section of the latter. These ribs abut against respective shouiders 25 and 26 formed on the main body part 1 3 of the casing. In the space defined between the ribs 23 and 24, the overlapping parts of the tubular portions 1 6 and 1 7 are provided with respective openings 27 and 28 which are substantially larger than the perforations 22. These openings face one another, and permit exhaust gases flowing through the tubular portion 1 6 to pass readily into the tubular portion 1 7.

The gas passage member 1 5 is assembled from two parts 29 and 30 made of plastics material, each of these parts having recesses which define half of the tubular portions 16 and 1 7 respectively,and projections which define half of the ribs 23 and 24 respectively.

The part 30 is shown in detail in Figure 6.

Each of the parts 29 and 30 has a generally planar securement portion 31, by means of which the two parts are joined together along a median plane. The securement portions 31 have integrally formed dimples 32 and recesses 33 which interengage to prevent the two parts 29 and 30 from moving relative to one another in directions parallel to the said median plane, at least while these parts are initially secured together. To facilitate location of the member 1 5 within the casing 10, the latter is provided with a groove (not shown) in its internal wall, into which the planar securement portions 31 fit upon assembly.

Although not illustrated in the drawings, the spaces between the internal wall of the casing 10 and the exterior of the gas passage member 1 5 are filled with a sound-absorbing material.

As mentioned above, the parts 1 3 and 14 of the casing 10 and the parts 29 and 30 of the gas passage member 1 5 are all made of plastics material. The particular plastics material employed must be resistant to corrosion by exhaust products and to engine and hydraulic oil, must be capable of withstanding vibration and thermal shock, must not be affected by variations in humidity, and must have the ability to maintain its physical properties at elevated temperatures. The plastics material of which the casing 10 is made must also be resistant to impact (for example by stones) and to corrosion by salt-laden water.

At the same time, the plastics material chosen should enable the silencer to be produced economically and at a reasonable cycle time.

The applicants have investigated the suitability of various plastics materials for this purpose, and have found that fibre-reinforced plastics materials are the most suitable. Long fibre reinforced materials are preferred for the casing 10 since their strength tends to be greater than short fibre reinforced materials, although the latter can be used for the production of the gas passage member 1 5 if desired. The most preferred types of material are long fibre reinforced polyester resin, long fibre reinforced vinylester resin and long fibre reinforced furane resin, since these give the best combination of physical properties and cost.The following materials have however also been found to be suitable: glassfilled P.E.E.K., glass filled P.E.S., epoxy moulding compound, glass filled phenolic, glass filled polyiamide, polyphenylene sulphide, glass filled phenyl arakyl, glass reinforced polyester, glass reinforced phenolic, polyester d.m.c., glass reinforced epoxy, glass reinforced furfuryl alcohol and glass reinforced vinyl ester.

The various component parts of the silencer can be manufactured by injection moulding, compression moulding or resin injection techniques. To facilitate the production of the parts 29 and 30 of the gas passage member 15, the perforations 22 are designed so that they extend through the thickness of the side walls of the tubular portions 1 6 and 1 7 perpendicularly to the median plane over which the two parts are ultimately secured together, as can be seen to particular advantage in Figure 4. In addition, to simplify the mould construction, each of the tubular portions 1 6 and 17 is made diamond-shaped in cross-section, with each part 29, 30 of the gas passage member 1 5 defining two respective sides thereof. It is however possible to form the tubular portions 1 6 and 1 7 with other cross-sectional shapes; for example, they can be of generally circular cross-section but with flat steps extending parallel to the aforesaid median plane, the perforations 22 being provided in these steps. As indicated in Figure 4A, the diamond section portions 1 6 and 1 7 can also be provided with similar flat steps to facilitate moulding.

From the above description, it will be manifest that the silencer has only four major components, and can thereffore be manufactured and assembled very economically and using the minimum of tools.

In the silencer shown in Figures 1 and 2, the cap part 14 of the casing 10 locates inside the main body part 1 3 thereof. As a modification, the cap part may be designed so that it fits externally of the main body part, in the manner indicated in Figure 7. As an alternative or additional modification, one or both of the inlet and outlet openings 11 and 1 2 in the casing 10 can be provided with a metal bush 34 on its internal surface, for engagement with external pipework, for example as illustrated in Figure 8, or can be provided with a flanged metal connector bush 35 moulded in situ as shown in Figure 9, to which existing pipework can be connected by welding.

In the above described construction of silencer, the component (i.e. the gas passage member 15) which is subject to the highest temperatures in use carries negligible mechanical loading. The main stresses are carried by way of the inlet and outlet openings 11 and 1 2 to the casing 10. If desired, the member 1 5 and the internal surface of the casing 10 can be sprayed with a fire resistant material (such as polyester), which will also act as an adhesive for the member 1 5.

In the construction described above, the openings 27 and 28 in the gas passage member 1 5 communicate with a space defined between the ribs 23 and 24, this space being bounded in part by the outer casing 10.

This means that the casing 10 in the region of this space is subject to the effects of the hot exhaust gases as they pass from the opening 27 to the opening 28, requiring the casing 10 to be made of a plastics material which is resistant to high temperatures. If however the gas passage member 1 5 is constructed as indicated in cross-section in Figure 10, i.e. so that it includes shield elements 36 (only one shown) bridging the gap between the ribs 23 and 24 in the region of the oepnings 27 and 28, then the casing 10 can be protected from the worst effects of the hot exhaust gases by the shield elements 36. (The position of one of the shield elements is also indicated by broken lines in Figure 3). Accordingly, only the gas passage member 1 5 needs to be made of high-temperature plastics, and the casing 10 can now be made of a cheaper plastics material which will still of course have impact-resistant properties. Internal baffles 37 can also be provided in the region between the two openings 27 and 28 to suit requirements.

The silencer of the invention is primarily intended for use with internal combustion engines, and is applicable in particular to motor vehicles, as previously noted. It is to be appreciated, however, that the silencer has many other applications, and for example can be used on the exhaust or outlet of a compressor.

Claims (12)

1. A silencer for exhaust gases, comprising a casing having inlet and outlet openings therein, and a gas passage member disposed within the casing and having passageway means therein which communicates at its ends with the inlet openings respectively, the passageway means including at least one perforated tubular portion, the gas passage member being composed of two parts which are secured together and which include respective recesses co-operating to define the tubular portion when the parts are secured together, both the casing and the gas passage member being made of plastics material, either with or without fibre or particulate re-inforcement.

2. A silencer according to claim 1, wherein the casing is made of a plastics material such as polyester resin, vinyl ester resin or furane resin.

3. A silencer according to claim 1 or 2, wherein the perforations in the or each tubular portion extend through the thickness of the side walls of said tubular portion perpendicularly to a plane defined by the join line between the recesses which define the tubular portion.

4. A silencer according to claim 3, wherein the external surface of the or each tubular portion is stepped, and the perforations are formed in these steps.

5. A silencer acccrding to any preceding claim, wherein the or each tubular portion is diamond-shaped in cross-section, with the respective recess in each part of the gas passage member defining two respective sides of the tubular portion.

6. A silencer according to any preceding claim, wherein the gas passage member includes two mutually spaced ribs which extend across the interior of the casing and which conform in shape to the internal cross-section of the latter, and the passageway means is composed of two such perforated tubular portions which are laterally offset from one another and which overlap along their main axes, the overlapping portions being provided respectively with mutually facing openings, substantially larger than the perforations, which communicate with each other by way of a space defined between said ribs.

7. A silencer according to claim 6, wherein shield elements are disposed between the ribs in the region of said openings to shield the casing from the effects of hot exhaust gases passing from one opening to the other.

8. A silencer according to any preceding claim, wherein each part of the gas passage member has a generally planar securement portion by means of which the two parts are secured together in face-to-face relation, the recess or recesses which define the tubular portion or portions being formed integrally with the securement portions, and the securement portions have location elements thereon which interengage to prevent relative movement of the parts in a direction parallel to the plane of the securement portion.

9. A silencer according to any preceding claim, wherein the inlet and outlet openings are each formed by a tubular spigot on the casing having an axially stepped internal bore, and the tubular portion or portions of the gas passage member terminate in spigots which locate respectively inside the spigots of the casing and which abut against shoulders defined by the axial steps in the latter.

10. A silencer according to any preceding claim, wherein the inlet and outlet pipes each have a metal pipe incorporated therein.

11. A silencer according to claim 10, wherein the metal pipe is in the form of a stub pipe moulded in situ in the casing.

12. A silencer for exhaust gases substantially as herein described with reference to and as illustrated in any of the accompanying drawings.