From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Article from 'The Autocar' magazine discussing and comparing various designs of automobile silencers.
| Identifier | ExFiles\Box 152\3\ scan0014 | |
| Date | 13th July 1912 | |
| 72 THE AUTOCAR, July 13th, 1912. Silencers. The Ford silencer is shown in fig. 5. It consists of three concentric chambers, through which the gas flows successively via large exit holes (a single one in each chamber), these holes being placed so as to cause the maximum of deflection. A fault in this device is that the outer shell is not used quite as much as it might be as a cooling surface. A similar idea is more elaborately carried out in the Cadillac silencer (fig. 6). It will be noticed that, in one respect, this is the direct opposite of the Ford, since the gases are cooled suddenly by the outer shell instead of progressively. It is an open question as to which principle is the better. The Cadillac silencer is simply a number of concentric tubes so arranged that they do not “bottom” on both cap ends. As the gas becomes reduced in volume the cross-section of its passage becomes smaller and smaller. Silencers of this direct type are especially good in that their large passages are not easily blocked up by oily precipitations. Fig. 11.—The Clair silencer. In fig. 7—the Star device—is shown a silencer of considerable ingenuity. A plain box is divided by a baffle plate into two compartments, in each of which is a sort of helical spring made of stiff steel strip. The exhaust gases in their course are deflected by the edges of these helices against the wall of the shell, and all sound waves are likewise thoroughly broken up by them. Fig. 12.—The simple perforated tube device used on the Vauxhall cars. The Binks silencer, of which a section is given in fig. 8, is of the multiple cone type, one of the desirable features of which is that the cones in themselves are stiff enough to withstand vibration. They serve to deflect the gases against the outer wall of the box, whence they return to the centre of the following cone. After passing through successive cones in this manner they make exit to the atmosphere through a conical funnel. Another device—the perforated plate—is used in a considerable number of silencers, either by itself or in conjunction with plain baffles, perforated tubes, and deflecting cones. The Panhard silencer, fig. 9, shows one of the simplest forms in which it can figure. There being two plates in this case. The purpose of the perforated baffle or pipe is simply to act as a brake, or perhaps it would be more correct to say a dashpot, on the gas. Owing to the great resistance of plates perforated with small holes to high speed fluids it is necessary to have the total aggregate area of the holes considerably greater than the area of the pipe in order to prevent serious back pressure, though, as previously mentioned, this is a matter largely decided by the position of the silencer box relative to the engine. The Rolls-Royce silencer is particularly interesting, as this car was one of the first to show that almost absolute silence, so far as the exhaust is concerned, was obtainable. The silencer, fig. 10, consists essentially of two portions—a forward one providing expansion chambers to each of the three-cylinder units, and a terminal one introducing two baffle plates with perforations and a constricted exit nozzle. One of the particular features of this device is the fact that, relatively speaking, the deflection of the gases is small, whilst the cooling area available is very large indeed. The possibility of back-pressure existing is very remote, and in general this silencer approximates perhaps more closely than any others of a standard type to the plain tube which has been already discussed. Fig. 14.—The type fitted to Crossley and Maudslay cars. A well-known and popular proprietary silencer—the Clair—is illustrated in section in fig. 11. It consists of a number of cups with perforations arranged so that the gases to pass through one set of holes to the next have to pass over the whole surface of each cup successively. Before meeting the baffles the gases are taken to a semi-spherical expansion chamber. Both from the manufacturing point of view and for the thorough manner in which it traps direct sound waves, the Clair silencer has much to commend it, but it is not entirely free from the trait that to operate really efficiently it requires to be at the end of a long exhaust pipe, through which the gases may be cooled as the radiating surface of the silencer itself is relatively small. Fig. 15.—The Wolseley silencer with muffled cut out. The next type to be considered is that in which perforated tubes are used as disintegrators. This is a very numerous class indeed, due, no doubt, to manufacturing facilities and to the fact that it enjoys a great immunity from the possibility of harmonic vibrations being set up. It is likewise quite simple, the parts in most cases being few, whilst it is also possible to provide a fairly large cooling area. One disadvantage is, however, the likelihood which small holes in a pipe have of becoming choked with soot and burnt oil. In many cases the most obvious way to clean out these holes would be to poke a wire through them from the outside, but this pushes the soot inside, where it remains ready to fill up the perforations again. Where pipes are intermediately plugged great Fig. 13.—The type of silencer used on Ariel and Bell cars. | ||