US2174125A - Siren - Google Patents

Description

0. I. H. EKMAN SIREN Sept. 26, 1939.

2 sheets-sheet 1 Filed Nov. 3, 1936 Sept. 26, 1939. o, EKMAN 2,174,125

SIREN Filed Nov. 5, 1936 2 she'ets sheet 2 -25 as circular plates.

Patented Sept. 26, 1939 UNITED STATES PATENT OFFICE Application November 3, 1936, Serial No. 109,012 In Sweden October 29, 1935 6 Claims.

In sirens of the type in which a diaphragm is used as the sound producing member, for instance, selective horns, it is necessary under certain conditions, in order to promote the acoustic effect, to increase the operative surface of the diaphragm. This increase, however, cannot be extended unlimitedly, for the reason, amongst others, that, as the surface of the diaphragm is increased it may become too large to respond to the frequency, the driving power tends to impart to it. In order to overcome this difficulty, to a certain extent at least, the driving power may be distributed over the diaphragm, for instance, by the use of compressed air or the like 5 for effecting the vibrations of the diaphragm instead of, as in the usual magnetic signalling horns, allowing the driving power to act on a small area of the diaphragm only. This limitation of the size of diaphragm is due, substantially, to the increased inertia of the larger diaphragm and the increased effective resistance of the masses of air to be caused to vibrate by the vibrations of the diaphragm.

As a rule, the diaphragms of sirens are formed Such diaphragms, especially those of larger area, present, in addition, the difficulty, that their principal tone is not fully clear, as a superposing may easily occur as a result of natural vibrations of different frequencies. Great difficulties are, therefore, experienced in attempting to obtain a diaphragm of this type which presents a clear tone and is capable of easily getting into resonance with the impulse producing source of power.

For the generation of tones of a higher frequency by the aid of a sound emitting horn of usual design, it is impossible to use too large a diaphragm, as sound waves emitted from the peripheral portions of the diaphragm, will interfere disadvantageously with waves of a later phase emitted from the central portion of the diaphragm.

The present invention has for its object to provide a diaphragm, by which the difiiculties above stated will be overcome. The invention is characterized, chiefly, by a circular set of diaphragms and means for alternately loading and relieving those diaphragms, either in groups or all at the same time, in order to cause them to vibrate.

In the accompanying drawings various embodiments of the invention are illustrated. Fig. 1 is an axial section taken on the broken line l-| of Fig. 2 of an embodiment having radially arranged diaphragms. Fig. 2 is a cross section of said embodiment, taken on the line 2--2 of Fig. I. Fig. 3 is a development of a vertical section as taken centrally through the valve disc and the diaphragms of the embodiment of Fig. 1. Fig. 4 shows part of an axial section of the embodiment 5 of Fig. 1, as taken between a pair of diaphragms, with the horn removed. Fig. 5 is a side elevation, and Fig. 6 is a plan view of a diaphragm clamping device. Fig. 7 is a plan view of part of a diaphragm and valve mechanism according to a 10 modified embodiment of the invention. Fig. 8

is a developed cross section through the centre of the annular portion shown in Fig. 7. Fig. 9

is a vertical section of another modification of the diaphragm and valve mechanism. Fig. 10 15 is an axial section of a horn of a modified embodiment.

In the embodiment shown in Figs. 1 and 2, the numeral I indicates a receptacle, adapted to receive a compressed fluid, as compressed air, 2 which may be either supplied thereto from some external source or produced within the receptacle by means of a compressor disposed therein.

At its top the receptacle carries a ring 2 which presents a cylindrical inner surface 3 at its upper 25 mouth. Said surface is adapted to act as the slide face for a rotary valve in the shape of a disc 4 keyed to a control driving shaft 5. The valve disc 4 presents an undivided, central portion by which it is attached to said shaft and an 30 annular peripheral portion having a set of radially extending ports 6 leading through the disc from its lower to its upper surface, as shown to the right of Fig. 1, and alternately therewith, a set of radial grooves 1 formed in the up- .35 per surface of the disc which lead to the periphery of the disc, right in front of the slide face 3, as shown to the left of Fig. 1. Formed in the ring 2 is a series of ports 8 adapted to communicate with the grooves I of the valve disc when 40 these grooves pass right below the diaphragms, that is to say, the ports are situated each outside its respective diaphragm. The diaphragms 9 are located above the annular portion of the valve 'dis'c. They extend radially and their form and 45 position correspond to those of the openings or grooves of the valve disc. The spacing of the diaphragms is equal to that of the opening 6 or grooves l of the valve disc.

The distance between each two adjacent open- 50 ings 6 or grooves l of the valve disc at the inner circumference of the annular disc portion is equal to the width of a diaphragm. The distance between each two adjacent diaphragms 9 of this embodiment will, as a result, be three times the 55 distance between each two adjacent openings or grooves.

The diaphragms 9 are made from elastic sheet metal of great strength, preferably by cutting off suitable lengths from a band of special steel. Each diaphragm extends between the ring 2 and a centra1 clamping disc l0, situated above the central portion of the valve disc 4 and carrying, if desired, a bearing H for the shaft 5. As shown, each diaphragm is rigidly secured to the inner clamping disc and is further attached to a flange I2 of the ring 2 by means of a pair of cross pieces l3, H, see Figs. 5 and 6, between which the upwardly bent outer end of the diaphragm is clamped by means of a pair of screws l5, the cross pieces with the clamped end of the diaphragm being then attached to the-flange I2 by means of a central screw I6 while exerting a pressure that can be varied by the edge of a nut I1. Inthis attachment the diaphragm bears'on edges i8, #9 of the members 18 and 2, respectively, in order to determine the operative length of the diaphragm. By this means, each diaphragm may be adjusted to produce its individual, practically clear tone in the same way as in the case of an instrumental chord, the natural frequency of the diaphragm being easily adjustable. After all of the diaphragms have been adjusted so as to produce the same tone, the diaphragms as a whole will represent a unitary diaphragm having a clear tone, all portions of which will always simultaneously vibrate in resonance with the vibrating power acting on the individual diaphragms.

The ring 2 and the central clamping member it for the diaphragms are connected together by means of beams or spokes 20 extending between said ring and member alternately with the individual diaphragms. It is thus seen that the said inner portion I0 is carried by the ring 2 by means of said beams or spokes, at the same time that the latter divide the space above the diaphragms into separate sound passages extending from the various diaphragms. The beams or spokes 20 are so formed as to conform at their under side with the smallest clearance possible with relation to the upper side of the annular portion of the valve disc 4, said upper side being shaped in conformity with a downwardly curved surface corresponding to the maximal downward bending of the diaphragms, see Fig. 4. Furthermore, the beams 20 fit with the smallest clearance possible to the lateral edges of the diaphragms 9 in order to prevent leakage of air at the sides of the diaphragms. Placed over the central clamping member ID and the beams 25 is a cover comprising, in the embodiment shown, an inner wall 2! covering the central clamping member l0, and an outer wall 22, supported by the ring 2, so that there will be an annular chamber between said two walls into which the beams 20 project, causing said chamber to branch at its lower end into the separate sound passages leading from the diaphragms. The inner wall 2| may be held in place by being forced down between the cylindrically turned inner ends of the beams 20. At its top the outer wall 22 is connected to a central horn which may be rotatable for the spreading of the sound in various directions. The beams 20 are preferably wedge-shaped with the edge directed upwardly, as shown in Fig. 3, and, furthermore, they grow thicker and higher towards their outer periphery, in order that the individual sound passages may present substantially the same cross section area at the outer periphery as they do at the inner periphery. The operation is as follows:

During the rotation of the valve disc, the vertically through-extending openings 6, that is to say, the loading openings, and the grooves I, that is to say the relief channels, will alternately pass below the diaphragms. When the openings 6 pass below the diaphragms, compressed air contained in the receptacle l is allowed to act on the under side of the diaphragms, forcing them upwardly so as to cause them to produce a pressure wave in the horn, resulting in the emission of a tone. When, thereupon, the grooves 1 pass below the diaphragms, the compressed air contained between the upwardly bent diaphragms and the valve disc will be allowed to escape through the ports 8 of the ring 2, allowing the diaphragms to swing down again by their elasticity. As will appear from Figs. 2 and 3, a groove 1 will not enter the space below a diaphragm before the preceding opening 6 has completely left the range of this diaphragm. In other words, at any time only the openings 6 or the grooves I are in position below the diaphragms.

The frequency depends on the number of revolutions of the valve disc as well as on the number of diaphragms. An increased frequency may thus be obtained by increasing the number of revolutions of the valve disc or by increasing the number of diaphragms, or by these two measurements in conjunction.

In order to be able to increase the number of diaphragms I may, for instance, as shown in Figs. 7 and 8, make the openings 6 and the grooves "I of the valve disc 4 of less width than the diaphragm, as, for instance, equal to a third of the width of the diaphragm, as shown in said figures. In this case it is thus possible to reduce the spacing of the diaphragms to half that of the above described embodiment. As will appear from Fig. 8, in this embodiment a loading opening 6 and a relief passage 1 will simultaneously pass below different portions of one and the same diaphragm, so that said opening will enter below the diaphragm when said passage leaves the diaphragm, and vice versa. As a result, there will be a successively progressing increase of pressure and a likewise successive relieving of the pressure on the diaphragms during each cycle of operation. In this embodiment the pressure will at any moment be applied to part of each diaphragm only, but as there is a certain clearance between the valve disc and the diaphragm, that cannot be avoided, practically the whole diaphragm will be under pressure during the passage of a loading opening therebelow.

Another embodiment is illustrated in Fig. 9, in which openings or passages and diaphragms are .of the same width, though the diaphragm is shielded off at both of its sides by means of projections 30 of the beams 25!, thereby only exposing the central portion of the diaphragm to the action of the pressure.

In order that the horn may act in the most eflicient way care should be taken that the vi.bra tions are led out symmetrically from various radii of the diaphragms. To this end the two walls 2| and 22 of the base portion of the horn may be symmetrical, as shown in Fig. 10.

In the constructions above described, the pressure prevailing in the receptacle I is also always existing in the openings and is thereby allowed to immediately act upon the diaphragms as soon as they are uncovered by said openings, without the necessity of filling any larger space prior to each operation of a diaphragm. Due to the positioning of the valve disc in close proximity of the diaphragms, the loading and the relief of the dia phragms will take place at a minimum loss of time. By the use of separate openings for the loading and the relief, a difference of the direction of flow in the individual openings need never be taken into consideration, whereby the occurrence of undesired flows will be avoided, and losses of energy and time reduced.

In the embodiments described, the diaphragms are disposed in a substantially plane surface, in which they extend radially with respect to a centre representing the axis of rotation of the rotary valve controlling the admission and discharge of the driving fluid acting on the diaphragms. Said embodiments are particularly well adapted for sirens of small and moderate sizes.

If instead of compressed air or another compressed fluid of normal temperature there is used, for instance, hot combustion gases to act upon the diaphragms, the latter due to their heating will be subjected to a certain extension which in case of the diaphragms being rigidly clamped will reduce the stress thereof to such an extent as to result in an undesired tone. To avoid this drawback, the diaphragms may be held stretched by means of springs, preferably long coiled springs of such an initial stress, that the extension the spring may undergo owing to the extension of the diaphragm, will produce a neglectable change of the stress only.

Instead of compressed air or another pressure fluid to effect the operation of the diaphragm, I may use some other power, as electromagnetic force.

What I claim is:

1. A siren having, in combination, a receptacle to receive a fluid under pressure, said receptacle having an end wall and an annular set of openings therein, diaphragms in said openings, a rotary disc in the receptacle in close proximity to the diaphragms, a set of axially through-extending openings in said disc and a set of grooves in the surface of the disc facing the diaphragms, said grooves being arranged alternately with said openings and ending at the outer periphery of the disc.

2. A siren having, in combination, a receptacle to receive a fluid under pressure, said receptacle having an end wall comprising a central portion, an annular peripheral portion and radial connecting members therebetween, said connecting members forming apertures between themselves, diaphragms inserted in said apertures, means to adjust the mechanical stress on the diaphragms, edges on said portions to be engaged by the diaphragms to fix the operative length thereof, a rotary disc in said receptacle in close proximity to the diaphragms to alternately subject the diaphragms to the action of the fluid in the receptacle and relieve them therefrom,

3. A siren having, in combination, a receptacle to receive a fluid under pressure, said receptacle having an end wall formed with an annular set of openings, diaphragms in said openings, a rotary valve disc provided in said receptacle in close proximity to the diaphragms, said valve disc having passages to alternately expose the diaphragms to the action of the compressed fluid and relieve them therefrom, and a horn having an annular base chamber mounted on said end wall of the receptacle outside the diaphragms,

said end wall comprising an undivided central portion, an annular peripheral portion concentric to said central portion and spaced radial connecting members between said portions, said connecting members projecting into the annular base chamber of the horn so as to form partitions between sound passages leading from the various diaphragms to the horn.

4. A siren having, in combination, a receptacle to receive a fluid under pressure, said receptacle having an end wall formed with an annular set of openings, diaphragms in said openings, a rotary valve disc provided in said receptacle in close proximity to the diaphragms, said valve disc having passages to alternately expose the diaphragms to the action of the compressed fluid and relieve them therefrom, and a horn having an annular base chamber mounted on said end wall of the receptacle outside the diaphragms, said end wall comprising a central portion, a concentric peripheral portion, and a set of spaced radial connecting members between said portions, said connecting members projecting into the annular base chamber of the horn and tapering upwardly and inwardly so as to present a uniform transition from the sound passages to the horn.

5. A siren having, in combination, a receptacle to receive a fluid under pressure, said receptacle having an end wall formed with an annular set of openings, diaphragms in said openings, a rotary valve disc provided in said receptacle in close proximity to the diaphragms, said valve having passages to alternately expose the diaphragms to the action of the compressed fluid and relieve them therefrom, and a horn having an annular base chamber mounted on said end wall of the receptacle outside the diaphragms, said end wall comprising a central portion, a concentric peripheral portion, and a set of spaced radial connecting members between said portions, said connecting members projecting into the annular base chamber of the horn and tapering upwardly and inwardly so as to present a uniform transition from the sound passages to the horn, the surface of valve facing the diaphragms being shaped in conformity with the maximum deflection of the diaphragms and the surface of said partitions facing the valve being formed in conformity with said surface of the valve in order to secure maximum sealing effect between the partitions and the valve.

6. A siren having, in combination, a receptacle to receive a fluid under pressure, said receptacle having an end wall comprising a disc-shaped central portion, an annular peripheral portion concentric therewith, and a set of spaced connecting members between said portions, diaphragms inserted in the spaces between said connecting members, a rotary valve disc arranged in the receptacle in close proximity to said end wall, said diaphragms comprising radial tapes extending from said central portion to said peripheral portion, separate means including clamping devices to connect the individual diaphragms to one of said portions so as to permit adjustment of the diaphragms for the same tone, the clamping devices for the outer ends of the diaphragms comprising each a pair of clamping members for the end of the diaphragm and a central bolt to connect said clamping members to the annular peripheral portion of said end wall.

OLOF INGEMAR HARALD EKMAN.

Images