EP0074220A2

EP0074220A2 - Improvements in or relating to inserts for silencers

Info

Publication number: EP0074220A2
Application number: EP82304500A
Authority: EP
Inventors: Timothy Clokey
Original assignee: Lancaster Glass Fibre Ltd
Current assignee: Lancaster Glass Fibre Ltd
Priority date: 1981-08-26
Filing date: 1982-08-26
Publication date: 1983-03-16
Also published as: GB2106591B; EP0074220A3; GB2106591A

Abstract

An insert for use in an internal combustion engine silencer consisting of a central cylindrical former, an outer portion surrounding the former formed of a fibrous material in which the fibres are heat resistant such as basalt fibres, and an outer covering of sheet or scrim material for retaining the fibrous material of the outer portion in position relatively to the former. The insert is formed by inserting a length of the fibrous material loosely around the former placing the fibrous material and former into a loop of an endless belt, applying tension thereto and rotating the endless belt to roll the fibrous material around the former and an outer covering of sheet or scrim material is wrapped around the rolled insert to retain the shape thereof.

Description

This invention relates to inserts for use in silencers of the type used in silencing the exhaust gases of internal combustion engines.
Known types of silencers comprise a silencer box having a perforated pipe extending therethrough and it is usual to provide a packing of fibrous material in the space between the internal surface of the silencer box and the external surface of the perforated pipe.
_.Although the precise manner in which this packing of fibrous material reduces the noise level of the exhaust gases is not fully understood, it will be appreciated that part of the exhaust gases enter the packing through some of the perforations in the pipe and then re-enters the pipe through other.perforations. During the passage of the exhaust gases through the packing, the speed of flow is reduced and the fibrous nature of the material smoothes out turbulence in the gas flow.
The fibrous material can be packed by hand into the silencer box through an open end thereof to fill the space between the internal surface of the silencer box and the external surface of the perforated pipe. However, such manual packing is a time consuming and therefore expensive operation and it is also difficult to control the density of the fibrous packing. It will be appreciated that the density of the packing has an important effect on the efficiency of the silencer as the packing must not be so tightly compacted that the fibres are unable to move which reduces the sound deadening effect thereof but on the other hand the packing must not be so loose as to allow the fibres to escape through the perforations in the pipe.
It is known to produce the silencer packing as a pre-formed rigid insert in which the fibrous material is formed into a shape which will fit readily into the space in the silencer box surrounding the perforated pipe, and the material is treated with adhesive so as to cause the fibres to adhere together and sustain the preformed shape during the handling required to fit the insert in the silencer box. Although the use of rigid inserts reduces the cost of manufacture of the silencer and makes it easier to ensure that the material is of a suitable and consistent density, the known inserts have been produced from material formed wholly or mainly of glass fibres which is relatively expensive and the object of this invention is to provide a less expensive insert.
According to one aspect of this invention, an insert for a silencer of an internal combustion engine comprises a central portion constituting a former; an outer portion surrounding the former formed of a fibrous material, the fibres of which are heat resistant fibres; and comprises an outer covering of material adapted to retain the fibrous material of the outer portion in position relatively to the former.
Preferably, the former is formed of a high porosity, heat resistant material which is capable of retaining its shape. Preferably, also, the former material glass fibres in whole or in part secured together by adhesive to form a rigid-member, and the glass fibres may be E glass fibres.
"E" glass is a known type of glass manufactured in the United Kingdom by Turner Newall Limited and Fibreglass Limited and the significant characteristic of this glass for the purposes of the present invention is that it will withstand temperatures of up to 750⁰C so that it can be used in silencers of internal combustion engines and can be used to form a heat resistant and highly porous former.
The former is, preferably, of a hollow cylindrical shape and may be arranged to remain in situ when the insert is placed in a silencer box with the former sliding over a perforated pipe secured in the silencer box:

Preferably, the fibrous material from which the outer portion of the insert is formed are mineral fibres such as, for example, basalt fibres. Preferably, also, the outer covering is a sheet or scrim of plastics material.

According to another aspect of this invention, a method of forming an insert to said one aspect of the invention comprises placing a length of fibrous material loosely around the former, placing the fibrous material and the former into a loop of an endless belt which extends over two spaced-apart rollers and depends therebeneath, moving the rollers into close relationship and applying tension to the belt to decrease the length of the loop of the endless belt to apply pressure to the fibrous material disposed around the former, rotating the endless belt to roll and compress the fibrous material around the former,and applying an outer covering to wrap the rolled insert so as to retain the shape thereof.
Preferably, the outer covering is wrapped around the rolled insert during the final stages of the rolling operation by inserting the edge of the covering between the belt and the rolled insert and rotating the insert to wrap the covering completely around the periphery of the insert.
Preferably, also, the length of fibrous material is cut from a mat thereof and the cut length of material is weighed so as to control the density of the fibrous material in the insert.
The insert is, preferably, cut to a desired length according to the length of silencer box into which the insert is to be inserted and a plurality of inserts may be cut from a length of rolled insert where the finished insert is to be of a relatively short length.
The former may be produced by moulding a mixture of glass fibres and adhesive around a mandrel, curing the adhesive and removing the mandrel prior to placing the fibrous material therearound.
Additionally, the fibrous material may be mixed with an adhesive binder prior to placing the fibrous material around the former and after completion of the method according to said other aspect of this invention, the cut lengths of the insert are placed in a mould and cured by applying heat thereto. Preferably, the insert is cut along the centre line thereof to enable the insert to be assembled around the perforated pipe in a silencer box by bringing the two halves of the insert together instead of sliding the insert longitudinally over the perforated pipe.
A method of manufacturing an insert for a silencer of an internal combustion engine will now be described, by way of example only, with reference to the accompanying drawings, in which:-

Figure 1 is a diagrammatic sectional end elevation of an insert;
Figure 2 is a diagrammatic sectional end elevation of an insert of alternative shape;
Figure 3 is a diagrammatic end elevation of a machine for forming an insert.

Referring now to the drawings, an insert indicated generally at 10 of substantially circular cross-section is formed by cutting a length of fibrous material 12, for example mineral fibres such as basalt fibres, from a loose mat of such fibres. Basalt fibres are capable of withstanding heat and are relatively long staple fibres but it has been found to be difficult to manually form a mat of such fibres into a desired shape to constitute an insert suitable for inserting into a silencer box (not shown) of a conventional internal combustion engine exhaust gas silencer.
The loose mat of basalt fibres is ·conveniently some six feet in width and the length of mat which is cut is dependent upon the diameter of insert 10 which is to be formed. The length of mat controls the density of the basalt, fibres in the completed insert 10 and an accurate method of controlling this density is to weigh the cut length of mat. The weight of mat required is determined on an empirical basis according to the diameter of the completed insert and the number of inserts to be formed from the length of the rolled mat.
After the length of mat has been cut, it is loosely wrapped around a former 14. The former 14 can be a cardboard tube or, alternatively, a rigid cylinder of glass fibres. Where the former 14 is to be discarded when the insert 10 is placed in the silencer box, the cardboard tube is arranged to be of substantially the same diameter as the conventional perforated pipe in the silencer box. When the insert 10 is slid longitudinally into the silencer box, the end of the perforated pipe engages the former 14 and ejects it from the insert 10 as the insert is inserted into the silencer box.
However, where the former 13 is to remain in situ within the insert 10, the internal diameter of the former 14 is arranged to be a close sliding fit on the perforated pipe in the silencer box. The former 14 is formed from glass fibres, such as "E" glass fibres, mixed with an adhesive binder such as phenol. The glass fibres and adhesive binder are moulded in conventional manner around a mandrel and the adhesive is cured. After curing the mandrel is removed and the former 14 of a rigid cylindrical shape of heat resistant glass fibres and having a high porosity is ready for use in the method of forming the insert 10.
The mat of basalt fibres wrapped around the former 14 is then placed in a rolling machine 16. The machine 16 comprises two spaced-apart main rollers 18 and 20, the roller 18 being mounted in a fixed position on a frame 22 of the machine and provided with a handle 24 to effect rotation thereof whereas the position of the roller 20 is adjustable to vary the spacing between the two main rollers.
In the operative position, the roller 20 is disposed adjacent to the roller 18 but spaced-apart therefrom and in the inoperative or loading position shown in broken lines, the distance between the rollers 18 and 20 is arranged to be greater than the maximum diameter of the mat of basalt fibres loosely wrapped around the former 14.
Two parallel spaced- apart tension rollers 26 and 28 are mounted on a sub frame 30 which is pivotally connected to the frame 22 for pivotal movement relatively thereto about an axis which is parallel to the rotational axes of the rollers 18, 20, 26 and 28.
An endless belt 32 extends around the rollers 18, 20, 26 and 28 and is of such a length that a loop 34 depends below the rollers 18 and 20 when said rollers are in their operative position. The position of the roller 28 is adjustable in the direction of the arrow A to vary the length of the loop 34 and an additional idler roller 26 is also provided whose position is also adjustable in the direction of the arrow B to provide additional adjustment of the length of the loop 34.
Furthermore, the position of the sub frame 30 in its operative position is adjustable by means of a screw mechanism 38 which carries a spring-loaded manually releasable catch for retaining the sub frame 30 in said operative position and here again this adjustment enables the length of the loop 34 to be varied. These various adjustments of the length of the loop 34 enable various diameters of insert to be rolled on the machine 16.
The upper surface of the frame 22 of the machine 16 has a cutting table mounted thereon which extends parallel to the roller 18 and a sliding carriage assembly 42 carrying a roll 44 of plastics sheet or film 46 such as, for example, self adhering plastics film is also mounted thereon. Alternatively, a scrim of plastics material can be utilised instead of a sheet or film. The carriage assembly 42 is slidable along the length of the machine 16 to enable the plastics film to be applied to the whole length of the insert 10.
The roller 20 is moved to the inoperative or loading position and the sub frame 30 is released and moves under the action of a counter balance weight 46 to an upper loading position indicated in broken lines. The mat of basalt fibres loosely wrapped around the former 14 is placed in the loop 34 of the endless belt 32 and the roller 20 is moved to the operative position.
The sub frame 30 with the rollers 26 and 28 mounted therein is pivoted downwardly to the operative position where it is retained by the spring loaded catch thus applying tension to the loop 34 of the belt 32. The roller 18 is rotated by the handle 24 which causes the basalt fibres to be rolled to the desired diameter around the former 14.
The plastic film 46 is then drawn from the roll 44 and the free edge is placed between the belt 32 and the basalt fibres of the insert 10. The. roller 18 is again rotated until the basalt fibres are completely wrapped therein. whereupon the film is cut by running a knife along the cutting table 40. The excess film is then wrapped around the insert 10 by rotating the roller 18.
The insert 10 is then removed from the machine 16 by releasing the sub frame 30 and moving the roller 20 to its inoperative position and the film retains the basalt fibres around the former 14. The insert 10 is then cut into one or more desired lengths depending upon the type of silencer box into which the insert is to be fitted.
Where a non-circular cross-section insert is to be produced, additional lengths of the mat of basalt fibres are inserted adjacent to the former 14 so that during the rolling operation a cross-section such as the elliptical cross-section insert shown in Figure 2 of the drawings is produced.
In a modification, the basalt fibres are mixed with or have an adhesive binder applied thereto. The mat of basalt fibres and adhesive binder are rolled around the former 14 in the above described manner. After removal of the rolled insert from the machine 16 and cutting it to the desired length or lengths, each insert is placed in a mould and heat is applied to cure the adhesive binder. The insert is then cut along its centre into two mating halves which can then be assembled around the perforated pipe in a silencer box by bringing the two halves of the insert together. This type of insert is suitable for utilisation in a silencer box which is assembled in two halves. It will be appreciated that if a cardboard former is used it will have to be removed from the insert before the insert is installed in the silencer.

Claims

1. An insert for a silencer of an internal combustion engine comprising a central portion constituting a former; and outer portion surrounding the former formed of a fibrous material, the fibres of which are heat resistant fibres; and an outer covering of material adapted to retain the fibrous material of the outer portion in position relatively to the former.

2. An insert according to Claim 1, wherein the former is formed of a high porosity, heat resistant material which is capable of retaining its shape.

3. An insert according to Claim 2, wherein the former material comprises glass fibres in whole or in part secured together by adhesive to form a rigid member.

4. An insert according to Claim 3, wherein the glass fibres are E glass fibres.

5. An insert according to any one of the preceding claims, wherein the former is of hollow cylindrical shape and is adapted to remain in situ when the insert is placed in a silencer box with the former sliding over a perforated pipe secured in the silencer box.

6. An insert according to any one of the preceding claims, wherein the fibrous material from which the outer portion is formed are mineral fibres.

7. An insert according to Claim 6, wherein the mineral fibres are basalt fibres.

8. An insert according to any one of the preceding claims, wherein the outer covering is a sheet or scrim of plastics material.

9.. A method of forming an insert, according to any one of the preceding claims, comprising placing a length of fibrous material loosely around the former, placing the fibrous material and the former into a loop of an endless belt which extends-over two spaced-apart rollers and depends therebeneath, moving the rollers into close relationship and applying tension to the belt to decrease the length of the loop of the endless belt to apply pressure to the fibrous material disposed around the former, rotating the endless belt to roll and compress the fibrous material around the former, and applying an outer covering to wrap the rolled insert so as to retain the shape thereof.

10. A method according to Claim 9, wherein the outer covering is wrapped around the rolled insert during the final stages of the rolling operation by inserting the edge of the covering between the belt and the rolled insert and rotating the insert to wrap the covering completely around the periphery of the insert..

11. A method according to Claim 9 or Claim 10, wherein the length of fibrous material is cut from a mat thereof and the cut length of material is weighed so as to control the density of the fibrous material in the insert.

12. A method according to any one of Claims 9 to 11, wherein the insert is cut to a desired length or into a plurality of desired lengths where the finished insert is to be of a relatively short length.

13. A method according to any one of Claims 9 to 12, wherein the former is produced by moulding a mixture of glass fibres and adhesive around a mandrel, curing the adhesive, and removing the mandrel prior to placing the fibrous material therearound.

14. A method according to Claim 12, wherein the fibrous material is mixed with adhesive prior to placing the fibrous material around the former and after completion of the formation thereof, the cut lengths of insert are placed in a mould and cured by applying heat thereto.

15. A method according to Claim 14, wherein the cured insert is cut along the centre line thereof to enable the insert to be assembled around the perforated pipe in a silencer box by bringing the two halves of the insert together instead of sliding the insert longitudinally over the perforated pipe.

16. A silencer for an internal combustion engine, comprising a silencer box having a perforated pipe secured therein and an insert according to any one of Claims 1 to 8 and/or manufactured by the method of any one of Claims 9 to 15 located therein around the perforated pipe.