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).
Patent specification for improvements to sound wave attenuating apparatus, specifically for internal combustion engines.
| Identifier | ExFiles\Box 147\1\ scan0075 | |
| Date | 10th April 1933 | |
| Rm.{William Robotham - Chief Engineer} WYMAN MORD Gord x1247 PATENT SPECIFICATION 417,935 Convention Date (United States): Sept. 15, 1932. Application Date (in United Kingdom): April 10, 1933. No. 10,668/33. Complete Accepted: Oct. 10, 1934. COMPLETE SPECIFICATION. Improvements in and relating to Sound Wave Attenuating Apparatus. We, GENERAL MOTORS RESEARCH CORPORATION, a corporation organized and existing under the laws of the State of Delaware, United States of America, located at Detroit, State of Michigan, United States of America, do hereby declare the nature of this invention and in what manner the same is to be performed, to be particularly described and ascertained in and by the following statement:— This invention relates generally to the attenuation of sound waves, and, particularly, to the attenuation of sound waves in the exhaust systems of internal combustion engines. In our prior specification No. 391,180 we have described the attenuation of sound waves of low frequency produced in the intake or exhaust passage of an internal combustion engine by the employment of one or more resonators. In carrying out the present invention as hereafter set forth and claimed we may employ as the attenuating unit a resonance unit or a plurality of resonance units. The term unit is used herein to mean a chamber or a plurality of chambers which communicate with a sound wave passage or with another chamber or chambers. These chambers will hereinafter be referred to as ‘‘resonators.’’ As regards the number and arrangement of the constituent resonators, resonance units may be divided into a number of classes. To facilitate the description of the sound wave attenuating units shown in the drawing and hereinafter described, the principal classes will here be named and defined. A simple resonance unit is one which consists of a single resonator which is adapted to be acoustically connected to a sound wave passage. A multiple-compound resonance unit is one which consists of a plurality of juxtaposed resonators of which each is adapted to be acoustically connected to a sound wave passage independently of the other or the others. A series-compound resonance unit is one which consists of a plurality of acoustically interconnected resonators of which one is adapted to be acoustically connected to a sound wave passage. A complex multiple-compound resonance unit is one which consists of a plurality of juxtaposed simple and/or multiple-compound resonance units and series-compound resonance units of which each is adapted to be acoustically connected to a sound wave passage independently of the other or others. In the attenuation of forced vibrations occurring in a sound wave passage, for example vibrations set up by an internal combustion engine in the exhaust pipe of the engine, attention has in the past been directed to the forced vibrations themselves without any particular reference to the acoustic properties of the sound wave passage. However, since the passage is essentially a pipe, which in the case of the internal combustion engine is open at one end and closed at the other, there will be certain frequencies of vibration to which the passage responds. These are termed ‘‘natural’’ or ‘‘characteristic’’ vibrations of the passage. Because of this property of the passage to respond to particular frequencies, it will tend to reinforce certain of the vibrations set up by the sound wave source, and other frequencies, not themselves occurring in the passage, for example when a characteristic frequency of the passage is a harmonic of a frequency generated at the source. It is the purpose of the invention to take into account these properties of the sound wave passage. The invention is therefore based mainly upon the discovery that the efficiency of sound wave attenuating units is markedly affected by their location along the sound wave passage with respect to the source of the sound waves upon which they operate, and by the relation between the frequencies to which the attenuating units respond and the characteristic frequencies of the passage, that is, its fundamental and harmonics, and upon the further discovery that a sound wave attenuating unit in which there are incorporated both a multiple-compound resonance unit and a series-compound resonance unit has decided advantages [Price 1/-] | ||