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).
Page from The Autocar magazine discussing and illustrating various designs of automobile silencers.
| Identifier | ExFiles\Box 152\3\ scan0015 | |
| Date | 13th July 1912 | |
| THE AUTOCAR, July 13th, 1912. 73 Silencers. care should be taken to prevent the plug from coming loose, which it is quite liable to do under the combined effects of pressure, water vapour, heat and vibration. Fig. 12 shows a simple type of perforated tube silencer such as is fitted to the standard car. The arrangement of the whole affair is made quite clear in the sketch. Here it will be seen a single plugged pipe is used. On the Vauxhall car two of these silencers, each being quite small, are arranged in tandem with a considerable length of piping between them; in many ways this plan is to be recommended, as if the boxes are small they can be made of cast iron, and so made a very tight and rattle-proof job. A glance at fig. 12 will show that with perforations arranged in this manner the gas has a good chance of being forced on to the walls of the shell. Variations of the above are found, amongst others, on the Bell and Ariel chassis (fig. 13). The course of the gases is in this case the same except that between one set of perforations and the other they are passed through a perforated baffle-plate. The effect of this is practically to turn one compartment into an expansion chamber and the other into a cooling box. Another variation is shown in fig. 14, and represents the type used on the Crossley and Maudslay cars. Practically it is two of the silencers shown in fig. 12 in tandem. In this case the difficulty of cleaning the middle section of the pipe is pretty obvious. It is the sole disadvantage of an otherwise thorough system. It may be noted that when a series of perforations of this kind are used, the sets of holes in number or size, or both, should bear some fairly definite ratio, so as to provide as far as possible a uniform retardation to the gas. The Wolseley silencer (fig. 15) belongs in some respects to the same class, from which, however, it differs in a very radical manner, inasmuch as it is provided with a properly muffled cut-out, or perhaps it would be more correct to say that one can take one's choice of two degrees of sound without in any way falling foul of the authorities. Provided the main silencer be well designed, we cannot see that much increase of power is likely to be obtainable by opening the mushroom valve which allows the gases another path of exit. On the other hand there is this aspect of the matter: that many drivers—to the number of which we belong—prefer the soft mutter that suggests power to the sometimes woolly breathing which indicates a species of partial suffocation. Perhaps we shall be best understood if we say that we like the sound of an exhaust, but not the noise of one, between which there is a deep gulf of difference. A proprietary silencer, known under the name of the “Universal Victoria,” has several points of interest, chief amongst which is the desirable feature that air-cooling ribs are provided on the walls of the expansion chambers, which are globular in shape so as to offer as much surface as possible to the path of the gas, and which can be added to indefinitely in number, being joined up by flanges. (Fig. 16.) The next class of silencer is that in which a combination of perforations and deflectors is used, and this is also a numerous class. Amongst them are to be found the R.M.C. (fig. 17), wherein an internal perforated tube discharges through an eccentric intermediate tube into an outer shell, from which the gas reaches the atmosphere through a taper nozzle. A rather peculiar device is the Sheffield-Simplex, a section of which is given in fig. 18. The sketch is quite self-explanatory, but it should be pointed out that by reason of the trumpet-shaped expansion chamber abutting against the end plate a metallic noise can easily be set up unless this latter part is of good thickness. In practice this silencer seems to work well, but it is in almost direct opposition to the theory communicated previously, viz., that the gas should be allowed to occupy a smaller and smaller volume as is its natural tendency when cooled. In this particular case the progression is from small volume to large, and then again from small to large. Fig. 16.—The air-cooled Universal-Victoria. Fig. 17.—The R.M.C. silencer. Fig. 18.—The Sheffield-Simplex device. Fig. 19.—The parallel pipes of the Sunbeam silencer. Fig. 20.—The Dennis silencer. Fig. 21.—The silencer used on Lanchester cars | ||