Patent GB-425515-A (GB)
Title: Improvements in sirens
IPC: G10K7/00
Filed: 1934-06-25
Abstract: 425,515. Sirens. EKMAN, O. I. H., 64, Malmskillnadsgatan, Stockholm. June 25, 1934, No. 18677. [Class 13] [See also Group XXVI] A siren, Fig. 1, comprises a rotor 3 carried by the motor shaft 2 and surrounded by a wall 5 having a plurality of openings 6 therein and carrying an end wall 7 covering the inlet end of the rotor 3 with the exception of a small sector-shaped inlet opening 8. The rigid wall 7 may be replaced by a rotatable cover so that the inlet 8 can be brought into register with any desired opening 6 or the wall 5 together with the cover 7 may be made rotatable. The openings may also be provided with horns or a separate casing carrying such horns may be mounted around the wall 5. The rotor comprises a wheel having hollow or solid sectorshaped blades 4 which form sector-shaped spaces between them. Figs. 4 and 5 show a modification in which a compressor wheel 11 is carried by the shaft 2 so as to leave a storage chamber 12 for the compressed air above the blade wheel 10. The whole is surrounded by a stationary or rotatable casing 14 carrying a horn 15 leading from two sound openings 16, 17 in the casing. A partition 13 between the chamber 12 and wheel 10 has a sector-shaped preferably adjustable opening 18 arranged with respect to the opening 16, as shown in Fig. 5, whilst the horn 15 is formed with a baffle 21 shaped and arranged so as to cause the air expelled through opening 16 to produce a suction in the passage leading from opening 17. In order to reduce friction between the compressed air in chamber 12 and the casing 14, the chamber is surrounded by a wall 19 rigidly connected to periphery of wheel 11, a packing 20 being provided between the wall and the casing 14. Instead of a single horn, a number of horns may be employed, each leading from one or more openings in co-operation with an inlet 18 for each horn. In order to evacuate the parts of the blade wheel which are out of operation for the time being, the portion of the casing not occupied by the horn 15 may be surrounded by a jacket which leads to the space above the compressor wheel; Figs. 7 and 8, (not shown). According to a further modification, Fig. 9, a compressor wheel 40 of radial flow type is employed leading to a diffusor-shaped annular channel 41 arranged above partition 45 having a restricted opening 46 leading to the blade wheel 47, opening 49 and horn 50. A baffle 51 shaped as shown in Fig. 11, is provided on the partition 45 and within the channel 41 at a certain distance from the opening 46 so that the air entering the channel at this point is divided, part flowing back towards the opening 46 whilst the remainder continues its rotation with the walls 42, 43 of the channel. Fig. 12 shows an arrangement similar to that described with reference to Figs. 4 and 5, but in which means are provided to evacuate the horn 15 alternately with the emission of air therethrough. To this end, the horn is formed with an enlarged chamber 52 which opens both towards the blade wheel 53 and a rotary slide valve 54, the wheel and valve being separated by a partition 58. The valve has an upstanding peripheral flange 55 having an aperture directly below each blade of the wheel 53 whilst the partition 58 is unapertured directly below the opening 59 in partition 56, but has an opening 61 positioned as shown in Fig. 14. In operation, when a space of the wheel 53 is in communication with chamber 60 air is forced out into chamber 52 to produce sound, communication between the chamber and the interior of valve 54 being interrupted by an unapertured portion of flange 55. When the chamber 52 is out of communication with any space of wheel 53, an aperture of flange 55 places the chamber in communication with the interior of the valve 54 and by way of opening 61 and the inoperative spaces of wheel 53 with the jacket 63 so that the chamber is subjected to a suction. The wall surrounding the storage chamber or both this wall and the compressor wheel may widen conically downwards.