GB460148A - Improvements relating to exhaust gas mufflers - Google Patents

Abstract

460,148. Silencing and cooling exhaust. WILMAN, Z. July 18, 1935, Nos. 20493/35 and 5661 /36. Convention dates, July 19, 1934 and July 5, 1935. [Class 7 (ii)] The exhaust gases are silenced by a resonator chamber 3 surrounding the exhaust pipe 1 and partitioned by a helical strip 2 of variable pitch, the pipe being perforated at 4. The pitch of the helix 2 decreases towards the ends, but the number of perforations increases. The perforations are provided particularly at the nodal points of two successive odd harmonics, for example the third and fifth. In a modification, both the pipe 1 and chamber 3 are tapered, and the helix 2 does not extend to the inlet end 6 of the chamber. Again, a Venturi constriction may be provided in the tube 1 at about the middle of the chamber, the constriction being controlled by a valve actuated either manually, or opened by the exhaust gases against spring action. Fig. 3 shows another form, in which the exit pipe 7 of the silencer extends at 9 into the pipe 1 and is surrounded by another helix ; a series of such helices may be provided in the pipe 1 ; or a single helix may be provided near the middle of the pipe 1 around a perforated tube' which is closed toward the inlet 6 and open toward the exit 7. Again, the pipe 1 may be of double-conical form within the chamber and be surrounded by a spirally-wound strip. Fig. 12 shows similar spirally-wound strips 18 arranged around a central tubular formation 17 within the pipe 1 ; or the spiral windings may be replaced by a sound-absorbing filling. In these forms, the low-frequency waves are damped by the helical chamber 20, and the high-frequency waves by the spiral chambers 18 or the filling ; also the length of the chamber 20 is designed to give an interference effect. Fig. 14 shows another form in which the principal sound wave is damped by interference caused by passing back some of the gases through conduits 28, a helical resonator 24 damping the third and fifth harmonics, and a further helical resonator 27 the upper harmonics ; the conduits 28 also serve to cool the gases. The helical partition may be made of iron shavings enclosed by metallic gauze, or of flax or other soundproof material. The silencers may be cooled by air passing through hollow radial fins on the outside of the casing, and such fins may be staggered along the casing. Fig. 16 shows another form in which cooling-air entering at 33 passes through a tubular helix 32 and discharges through a Venturi 34, while the exhaust from a conduit 35 passes between the coils of the helix 32, and then through a silencer 39 similar to those described above. Some exhaust also escapes through holes 36 opening into the hollow cooling-fins 37, 40. Some of the cooled gases will be returned by a pipe 41 to the spaces between the coils 32. The gases may enter tangentially into these spaces from the conduit 35. In a modification, the tubular helix 32 is omitted, and the cooling- air passes only through the central passage 47 ; or several air tubes may pass through the exhaust chamber. Also, where the tubular helix is employed, the exhaust may be divided into two branches leading tangentially to two points along the helix separated by a distance sufficient to cause interference of the sound waves. Fig. 26 shows a crosssection of another modification, in which the exhaust enters tangentially into an expansion chamber 58 through pipes 57, and is discharged through a series of tubes 59 entering tangentially between different coils of the tubular air helix 60 ; or the gases may enter a chamber 61, Fig. 25, axially and pass through tangential tubes 62 into the coils of a helical conduit of varying pitch such as that shown at 2, Fig. 1. In another form, the exhaust passes from a central tube outwards through spiral coils, from which it escapes through orifices in the walls of the coils to air spaces between the coils. Fig. 32 shows another cooling-device in which the exhaust pipe 1 opens into the manifold 2 opposite an expansion chamber 81, into which the gases are directed by a tapered tube 82. The Specification as open to inspection under Sect. 91 describes also a machine for constructing silencers with the helical strips, which forms the subject matter of Specification 460, 166, [Group XXII]; also the exhaust pipe may be provided with cooling-fins of aluminium, and at such points may be lined with sheet steel, and a cast aluminium member, formed with several passages for the gases and with external fins, may be inserted between the exhaust pipe and silencer; further, tubes conveying cooling-air may extend through the exhaust conduit. This subject-matter does not appear in the Specification as accepted.