GB2392954A

GB2392954A - I.c. engine exhaust silencer for portable power tool

Info

Publication number: GB2392954A
Application number: GB0317984A
Authority: GB
Inventors: Robert B Wirtz
Original assignee: Andreas Stihl AG and Co KG
Current assignee: Andreas Stihl AG and Co KG
Priority date: 2002-08-02
Filing date: 2003-07-31
Publication date: 2004-03-17
Anticipated expiration: 2023-07-31
Also published as: CN1478994A; GB2392954B; US20050155818A1; GB0317984D0; CN100559018C; DE10235408A1; GB2392954A8

Abstract

An exhaust silencer for an engine in a handheld, portable power tool such as a motor-driven chain saw, a disc grinder or similar, has silencer housing 2 enclosing at least one damping chamber 5. The silencer housing 2 has an inlet 3 for exhaust gases from the motor and an outlet 4. In order improve the noise-absorbing properties of the exhaust silencer 1, it has a resonator chamber 6 sealed off from the damping chamber 5 so as to be substantially fluid-tight. A resonance pipe 7 carrying exhaust gas runs through the resonator chamber 6, an acoustic link existing between the resonance pipe 7 and the resonator chamber 6. The acoustic link may be provided in the form of orifices 8 in the resonance pipe 7, for example.

Description

Exhaust silencer The invention relates to an exhaust silencer for an

internal combustion engine of a handheld, portable power tool such as a chain saw, a disc grinder or similar.

An exhaust silencer for an engine of a handheld power tool is known from patent specification DT 25 39 516 Al. The exhaust silencer has a damping chamber in a housing.

An inlet opens into the damping chamber and an outlet leads out of the damping chamber.

The present invention seeks to provide an exhaust silencer which has good sound absorption properties.

According to the present invention there is provided an exhaust silencer for an engine for a handheld, portable power tool, with a silencer housing enclosing at least one damping chamber, having an inlet for exhaust gases from the engine and an outlet, wherein the exhaust silencer has a resonator chamber sealed off from the damping chamber so as to be substantially fluid-tight, through which a resonance pipe carrying exhaust gas runs, an acoustic link existing between the resonance pipe and the resonator chamber. The fact that the resonator chamber is acoustically linked to the resonance pipe secures an additional silencing effect. At the same time, there is essentially no flow of fluid from the resonance pipe into the resonator chamber. The resonator chamber absorbs particularly high frequencies in the range of from 1000 Hz to approximately 2500 Hz.

The resonance pipe is expediently disposed in between the damping chamber and the outlet in the flow direction of the exhaust gases. The exhaust gas temperature in the resonator chamber is therefore relatively low, which means that the resonator chamber can be packed with glass wool. for example. For practical purposes, the acoustic link is provided in the form of orifices in the resonance pipe. In order obtain effective noise absorption, the total surface area of the orifices is approximately 200 mm2 to 500 mm2, in particular from 350 mm2 to 400 mm2. To make manufacturing easier, the orifices are circular in shape. The diameter of the orifices is expediently between 1 mm and 4 mm, in

particular approximately 2 mm. Good noise-absorbing properties are obtained if the resonance pipe has 100 to 150, in particular approximately 120 orifices leading to the resonator chamber.

For practical purposes, the resonance pipe in the resonator chamber runs in a bent arrangement. In particular, the end of the resonance pipe remote from the damping chamber forms the outlet. The exhaust gases therefore leave the silencer after flowing through the resonance pipe. The resonator chamber constitutes the last stage of noise absorption. Good noise absorption is achieved as a result. This is also a simple way of providing the outlet. The inlet and outlet are arranged more or less opposite one another.

For practical purposes, the silencer housing is made from two half-shells, namely a bottom shell incorporating the inlet and a top shell. The exhaust silencer can be easily manufactured with few parts due to the fact that the resonator chamber is provided in the form of a resonator chamber shell which has a flow connection to a half-shell of the silencer housing, in particular the top shell. The connection is expediently brazed to render it fluid-tight.

The end of the resonance pipe directed towards the damping chamber is disposed at a distance from the resonator chamber. Before reaching the resonator chamber, the exhaust gases therefore have to pass along a specific path in the resonance pipe. This further improves the noiseabsorption properties. In practical terms, the distance is at least 30% of the height of the silencer housing, so that the height constitutes the greater part of the silencer housing extension in the joining plane of the two half-shells. Having an approximately rectangular cross section in the joining plane, the height is therefore the longer side of the rectangle. The length of resonance pipe projecting into the damping chamber advantageously extends substantially parallel with the joining plane of the two half-shells, the longitudinal mid-axis of the resonance pipe specifically extending substantially in the direction of the height of the exhaust silencer. Exhaust gases are therefore unable to flow into the resonance pipe until they have passed through the damping chamber. Furthermore, the flow must change direction before flowing into the resonance pipe. For practical purposes, the resonator chamber is disposed inside the silencer housing. The mounting space needed for an exhaust silencer with resonator chamber is therefore no different from the mounting space needed for an exhaust silencer with no resonator chamber. Incorporating the resonator chamber improves noise

absorption whilst requiring no extra mounting space. To obtain efficient noise-absorption properties, the resonator chamber is also packed with glass fibre, in particular glass wool.

The silencer advantageously has two damping chambers, which are separated from one another by a dividing wall, a catalyst being provided in the dividing wall. The resonator chamber is advantageously disposed in the damping chamber downstream in the flow direction of the exhaust gases.

An embodiment of the invention will be described by way of example below with reference to the appended drawings in which: Figs. l - 3 are perspective views of an exhaust silencer, Fig. 4 is an exploded diagram of the exhaust silencer illustrated in Figs. l to 3, Fig. 5 is a side view of the exhaust silencer illustrated in Figs. l to 3, Fig. 6 is a section along line VI-VI indicated in Fig. 5, Fig. 7 is a section along line VII-VII indicated in Fig. 5, Fig. 8 is a section along line V111- VIII indicated in Fig. 6, Fig. 9 is a side view of the resonance pipe of the silencer illustrated in Figs. l to 8 in the direction of arrow IX indicated in Fig. l O. Fig. lo is a side view of the resonance pipe of the exhaust silencer illustrated in Figs. l to 8, Fig. l l is a side view of the resonance pipe in the direction of arrow Xl indicated in Fig. l O. The exhaust silencer l illustrated in the perspective diagrams of Figs. l to 3 has a silencer housing 2 into which an inlet 3 leads. The inlet 3 is provided in the form of a

substantially rectangular orifice and opens into the damping chamber 5 illustrated in Fig. 6. Fixing orifices 28 are provided on either side of the inlet 3, by which the exhaust silencer 1 is attached to an engine, in particular an engine of a handheld portable power tool such as a motordriven chain saw or a disc grinder. A tubular outlet 4 leads out of the exhaust silencer 1. The silencer housing 2 is essentially made from two half-shells. The bottom shell 10 directed towards the motor and incorporating the inlet 3 has two reinforcing beads 24 extending substantially parallel. The top shell 9 remote from the motor has a cruciform reinforcing bead 25 which lies more or less opposite the two parallel reinforcing beads 24. The two half-shells 9, 10 are joined to one another at their rims 14, 13, the rim 13 of the bottom shell 10 being turned over in a bead to engage around the rim 14 of the top shell 9.

As may be seen from the exploded diagram shown in Fig. 4, a peripheral gasket 12 is provided between the rims 13, 14. Disposed inside the silencer housing 2 is a resonator chamber shell 11, through which a resonance pipe 7 leads. Bushes 15 are inserted through the silencer housing 2 at either end of the resonance pipe 7 and have a widened rim 29 at their end directed towards the top shell 9. Both the top shell 9 and the bottom shell 10 have lateral raised areas 30 extending substantially perpendicular to the rims 13, 14 of the half-shells, increasing their strength. The resonator chamber shell 11 has a peripheral rim 31, by which it is secured to the top shell 9. The resonator chamber shell 11 has an orifice 32, the contour of which matches the external contour of the resonance pipe 7.

As may be seen more particularly from the section illustrated in Fig. 6, a part of the longitudinal extension of the resonance pipe 7 is disposed inside the resonator chamber 6 formed in the resonator chamber shell 11. The resonator chamber shell 11 is sealed off from the damping chamber 5 formed in the silencer housing 2 so as to be fluid-tight. The resonator chamber shell is closed off by the top shell 9. To this end, the rim 31 of the resonator chamber shell 11 is joined to the top shell by brazing. For practical purposes, however, other types of joints could be used. In the region of the resonator chamber 6, the resonance pipe 7 has a plurality of orifices 8 providing an acoustic link between the interior of the resonance pipe 7 and the resonator chamber 6. The volume of the resonator chamber 6 is smaller, in particular significantly smaller, than that of the damping chamber 5. The volume of the resonator chamber 6 is advantageously a fraction of the volume of the damping chamber 5.

The resonance pipe 7 projects out of the resonator chamber 6 into the damping chamber 5. The end 18 of the resonance pipe 7 disposed in the damping chamber 5 therefore sits at a distance a from the resonator chamber shell 11. In practical terms, the distance a is at least 30% of the height h indicated in Fig. 5. The height h is the bigger extension of the exhaust silencer tin the joining plane 23 of the half-shells 9 and 10. In terms of the substantially rectangular cross section of the silencer housing 2 in the joining plane 23, the height h constitutes the long side of a rectangle delineating the cross section.

The run 22 of the resonance pipe 7 lying in the damping chamber 5 outside of the resonator chamber 6 is fixed by means of the web 17 spot-welded onto the top shell 9. The web 17 is brazed onto the end 18 of the resonance pipe 7 projecting into the interior of the silencer housing 2. The longitudinal mid-axis 21 in the run 22 extends substantially parallel with the joining plane 23, in particular substantially in the direction of the height h. The resonance pipe 7 constitutes the outlet 4 from the exhaust silencer 1. The resonance pipe 7 extends in a bent arrangement inside the resonator chamber 6. A pull-through piece 16 is formed in the top shell 9, through which the resonance pipe 7 leads. Relative to a line perpendicular 33 to the joining plane 23, the longitudinal mid-axis 21 of the resonance pipe 7 at the outlet 4 is inclined at an angle it, which in practical terms is in the range of between 5 and approximately 20 . However, it may also be expedient to provide a different angle of inclination. The longitudinal mid-axis 21 intersects with the top shell 9 in the region of the outlet 4 at a distance e from the longitudinal midaxis 34 of the bushes 15, simultaneously constituting the mid-axis of the inlet 3, which in practical terms is in the range of from 20 mm to 40 mm.

As illustrated in Fig. 5, a tab 19 is provided at the rims 13, 14 of the half-shells 9, 10 and has a central fixing orifice 20. The width b of the exhaust silencer 1 as measured in the joining plane 23 is smaller than the height h. When a power tool is disposed in the normal operating position, the height h extends in the vertical direction in the standard assembled position.

As may be seen from the section illustrated in Fig. 7, the longitudinal mid-axis 34 of the bushes 15 subtends an angle cr with the line perpendicular 33 to the joining plane 23 which may be between 5 and 40 , in particular approximately between 20 and 30 . The reinforcing beads 24 are provided in the form of raised areas and the reinforcing bead 25 as a recess. The inlet 3 as well as the orifices 28 disposed on either side of the inlet 3 is at

a distance c from the joining plane 23 which for practical purposes is in the range of between 30 mm and 60 mm. As may also be seen from the section illustrated in Fig. 8, the bushes 15 are pushed from the top shell 9 out through pull-through pieces 27 in the top shell 9. At their end directed towards the bottom shell 10, the bushes 15 have a shoulder 35, which sits on a reinforcing element 26. The reinforcing element 26 is therefore disposed between the bottom shell 10 and the shoulder 35 of the bush 15. The reinforcing element 26 prevents the bottom shell 10 from being torn out in the region of the fixing. In order to secure the exhaust silencer I to a motor, it is screwed to the motor by means of screws, pushed through the bushes 15, which project through the orifices into the reinforcing elements 26. In the region of the top shell 9, the bushes 15 have a rim 29, which abuts with the pull-through piece 27 and retains the bush 15. For practical purposes, the bush 15 is secured to the top shell 9 by additional means.

Figs. 9 to 11 illustrate the resonance pipe 7, The resonance pipe 7 has lateral rims 36, which lie substantially diametrically opposite one another. The rims 36 extend from the end 18 of the resonance pipe 7 disposed in the damping chamber 5 as far as the point at which the resonance pipe 7 leaves the resonator chamber 6. The terminal edges 37 of the rims 36 sit against the internal face of the top shell 9. The position of the resonance pipe 7 is fixed as a result. The rims 36 have a half width f, which may be in the range of from 0.3 mm to 1.5 mm. In the region of the resonator chamber 6, the resonance pipe 7 has a plurality of orifices 8. The orifices 8 are circular in shape and have a diameter d in the range of from I mm to 4 mm and in particular approximately 2 mm. The resonance pipe 7 advantageously has approximately 100 to 150, in particular 120 orifices 8. In practical terms, the total surface area of the orifices 8 is 200 mm2 to 500 mm2, in particular 350 mm2 to 400 mm2. The orifices 8 provide an acoustic link between the resonance pipe 7 and the resonator chamber 6. In order to obtain efficient absorption, the resonator chamber 6 is completely filled with glass fibres, in particular glass wool, or with some other sound-absorbing material.

It may be of advantage to split the damping chamber 5 into two damping chambers. To this end, a dividing wall extends in particular in the joining plane 23. A catalyst may be provided in the dividing wall. Instead of the circular orifices, it would also be possible to provide other acoustic links between the interior of the resonance pipe and the resonator chamber. The resonator chamber may also be arranged externally to the

silencer housing 2. It might be of advantage to arrange the resonator chamber in the region of the outlet, although it may also be expedient to arrange the resonator chamber in the region of the inlet to the exhaust silencer.

The invention may advantageously be used in conjunction with low capacity internal combustion engines in the range of approximately 20 cm3 to approximately 250 cm3 piston displacement.

Claims

1. An exhaust silencer for an engine for a handheld, portable power tool, with a silencer housing enclosing at least one damping chamber, having an inlet for exhaust gases from the engine and an outlet, wherein the exhaust silencer has a resonator chamber sealed off from the damping chamber so as to be substantially fluid-tight, through which a resonance pipe carrying exhaust gas runs, an acoustic link existing between the resonance pipe and the resonator chamber.

2. An exhaust silencer as claimed in claim 1, wherein the resonance pipe is disposed between the damping chamber and the outlet in the flow direction of the exhaust gases.

3. An exhaust silencer as claimed in claim I or 2, wherein the resonance pipe has orifices constituting the acoustic link to the resonator chamber.

4. An exhaust silencer as claimed in claim 3, wherein the total surface area of the orifices is from 200 mm2 to 500 mm2.

5. An exhaust silencer as claimed in claim 4, wherein the total surface area of the orifices is from 350 mm2 to 400 mm2.

6. An exhaust silencer as claimed in claim 3, 4 or 5, wherein the orifices are circular in shape and have a diameter d of from I mm to 4 mm.

7. An exhaust silencer as claimed in claim 6, wherein the orifices are circular in shape and have a diameter d of substantially 2 mm.

8. An exhaust silencer as claimed in any one of claims 3 to 7, wherein the resonance pipe has 100 to 150 orifices opening into the resonator chamber.

9. An exhaust silencer as claimed in any one of claims 3 to 8, wherein the resonance pipe has 120 orifices opening into the resonator chamber.

10. An exhaust silencer as claimed in any one of claims 1 to 9, wherein the resonance pipe extends in the resonator chamber in a bent arrangement.

1 1. An exhaust silencer as claimed in any one of claims 1 to 1 O. wherein the end of the resonance pipe remote from the damping chamber forms the outlet.

12. An exhaust silencer as claimed in any one of claims 1 to 11, wherein the inlet and the outlet lie substantially opposite one another.

13. An exhaust silencer as claimed in any one of claims 1 to 12, wherein the silencer housing comprises two half-shells, namely a bottom shell incorporating the inlet and a top shell.

14. An exhaust silencer as claimed in claim 13, wherein the resonator chamber is provided in the form of a resonator chamber shell, which is joined to a half-shell of the silencer housing in a fluid-tight arrangement.

15. An exhaust silencer as claimed in claim 14, wherein the resonator chamber shell is joined to the top shell.

16. An exhaust silencer as claimed in claim 14 or 15, wherein the resonator chamber shell is joined to the half-shell by brazing.

17. An exhaust silencer as claimed in any one of claims 1 to 16, wherein the end of the resonance pipe directed towards the damping chamber is disposed at a distance a from the resonator chamber.

18. An exhaust silencer as claimed in claim 17,

wherein the distance a is at least 30% of the height h of the silencer housing, the height h constituting the larger extension of the silencer housing in the joining plane of the two half-shells.

19. An exhaust silencer as claimed in claim 17 or 18, wherein the run of the resonance pipe projecting out of the resonator chamber into the damping chamber extends substantially parallel with the joining plane of the two half-shells, the longitudinal mid-axis of the resonance pipe extending substantially in the direction of the height h of the exhaust silencer.

20. An exhaust silencer as claimed in any one of claims I to 19, wherein the resonator chamber is disposed inside the silencer housing.

21. An exhaust silencer as claimed in any one of claims 1 to 20, wherein the resonator chamber is filled with glass fibres.

22. An exhaust silencer as claimed in any one of claims 1 to 21, wherein the exhaust silencer has two damping chambers separated from one another by a dividing wall, a catalyst being disposed in the dividing wall.

23. An exhaust silencer as claimed in claim 22, wherein the resonator chamber is disposed in the damping chamber lying downstream in the flow direction of the exhaust gases.

24. An exhaust silencer for an engine for a handheld, portable power tool, substantially as described herein with reference to and as illustrated in the accompanying drawings.