US2101385A - Air horn - Google Patents

Description

Dec. 7, 1937. o. H. EKMAN AIR HORN 3 Sheets-Sheet l Filed 001;. 51, 1935 Dec. 7, 1937. Q L N 2,101,385

I AIR HORN Filed Oct. 31, 1935 Sheets-Sheet 2 Dec. 7, 1937. Q I, H KMAN 2,101,385

' AIR HORN Filed 001;. 51, 1935 3 Sheets-Sheet 3 Patented Dec. 7, 1937 UNITED STATES PATENT OFFHCE AIR HORN lof Ingemar Harald Ekman, Stockholm,

Sweden 11 Claims.

This invention relates to air horns for producing strong characteristic tones, as for fire alarm purposes, or for use in connection with special cars to be driven at a high speed. More particularly, the invention relates to that kind of horns in which the sound is produced by means of compressed air expelled from a chamber at certain definite intervals. As a rule, the compressed air is generated by means of a blade wheel revolving at a high speed inside a cylindrical wall provided with a series of ports alternately opened and closed during the rotation of the blade wheel. To control the opening and closing of said ports there is provided either a separate slide valve having a corresponding series of openings or a circumferential flange on the blade wheel formed with a similar series of openings. By this means, a successive opening and closing of the ports in the cylindrical wall will be obtained, each port being successively opened to its full extent and immediately thereafter successively closed, so that the progress of the opening and closing of the ports may be represented by a, substantially, sinusoidal curve. In this way, however, it is impos- 5 sible to obtain atone which is sufiiciently sharp for many purposes. In order to obtain such an exceedingly sharp tone, the opening and closing periods should be as short as possible as compared with the entire uncovered period, preferably momentary, so that in a graphical representation, the said sinusoidal curve will be replaced by a rectangular figure. In this case, the area representing the work done will be correspondingly larger than that obtained in connection with a sinusoidal curve.

The present invention has for its object to provide a horn which enables a more rapid opening and closing of the sound ports leading from the chamber containing the compressed air than that obtainable in connection with a horn having a revolving blade wheel.

The invention is characterized, chiefly, by the fact that the outlet port or ports of the chamber containing the compressed air is or are provided with one or more valves controlled, in part, by a magnetic or other retaining power decreasing with increased opening of the valve, which tends to keep the valve or valves in closed position, and in part, by a counter-power alternately brought into and out of action or alternately increasing and decreasing which tends to open the valve or valves, the strength or the highest strength of this counter-power being sufficient to overcome the retaining power. Thus, the counter-power, which hereinafter will be termed the opening power,

will open the valve at a speed which is accelerated accordingly as the. retaining power decreases, for instance, by the square on the distance, and, should the valve during the opening period exceed the working range of the retaining power, said opening power will be further increased due to the fact that the opening power need no longer overcome any retaining power and may, consequently, yield more work. In the said lastmentioned case it is necessary, in order again to bring the opened valve within the reach of the retaining power, when the opening power ceases or is decreased sufficiently, either temporarily to increase the retaining power or to impart an initial movement to the valve by the action of gravity, or by means of springs or the like. The valve is then brought to its closed position under the action of the retaining power, i. e. at a speed accelerating accordingly as the valve approaches its closed position, as for instance, inversely as the square on the distance to the closed position. It is thus evident that the invention allows the attainment in both directions of the same acceleration at least as that appearing in case of the magnetic attraction. Any similar eifect cannot be obtained with the use of a diaphragm or a spring as a counter-power counter-acting a magnetic attraction, because the magnetic attraction would be counteracted by the unavoidable tension of the diaphragm or spring. The opening power may be of different kind; it may, for instance, be produced electromagnetically or pneumatically, or by means of some merely mechanical means.

With the use of a magnet or an electro-magnet for the production of the retaining power, the amount of the opening power required may be varied arbitrarily by varying the strength of field of the magnet or the strength of current of the electro-magnet. and it is thus possible to obtain, in a simple way, an exact adjustment of the working effect to be released in the one instance or the other. By thus varying the retaining power, the frequency of the cutting in and cutting out of the opening power and thus also the frequency of the sound emission may be varied. Another advantage gained by the apparatus according to the invention involves that the apparatus operates in a practically constant magnetic field, so that the movements will not be retarded by the action of such large counter-electromotive forces which act to delay, or suppress, the acceleration of the movements of the armature of an electric frequency apparatus of the hammer type or of some other type, especially at higher frequencies.

In the accompanying drawings, Fig. 1 is a secmatic way. Fig. 2 shows a modified form of the apparatus shown in Fig. 1. Fig. 3 is a section of a horn of a modified design, but still constructed so that the opening power is pneumatic. Fig. 4 is a section of a horn provided with two valves. Fig. 5 is a section on the line V,V of Fig. 1; Fig. 6 is a section on the line VIVI of Fig. 3; Fig. '7 is a section on the line VII-VII of Fig. 4; Fig. 8 is a perspective view of elements of the device of Fig. 3; Fig. 9 is a perspective view of the device of Fig. 4 with the horn and the valves removed.

With reference to Figs. 1 and 5, the numeral I indicates a chamber communicating through an opening 2 with a receptacle 3 containing compressed air. Leading from the chamber I to a horn is an outlet passage 5 controlled by a valve 6. Said valve 6 comprises avery elastic diaphragm, preferably consisting of an elastic steel blade clamped at its one end, as shown at 1, and so arranged as to form an armature of an electromagnet 8 the core of which 9 forms a pole piece against which the free end of the diaphragm B bears when in closed position. The circuit of the electromagnet contains, preferably, a variable resistance I 0 in series with a source of current II. The size of the opening 2 between the chamber I and the receptacle 3 may be varied by means of a screw I2. The operation is as follows:

Let it be assumed that the chamber I contains air of atmospheric pressure and that the valve 6 is closed, as shown in the drawings. Compressed air will enter the chamber I from the receptacle 3 through opening 2, subjecting the diaphragm valve 6 to an increasing pressure which tends to lift the valve away from the pole piece 9.

As soon as this pressure overcomes the suitably adjusted attraction exerted by the magnet 8, the valve 6 will be moved to its open position by a power increasing according as the attraction of the magnet decreases, that is to say, at a rapidly accelerating speed. A quantity of compressed air is now expelled through the horn, reducing the pressure in the chamber I and allowing the valve 6 to be restored to its closed position by the attraction exerted by the magnet 2. As soon as a maximum pressure is attained in chamber I, the operation described will be repeated.

The restoring of the diaphragm 6 to its closed position may be controlled either by controlling the circuit of the electromagnet 8 or by adjusting the size of the opening 2 with a view to obtaining a sufiicientperiod of rest in the emission of the sound. By a regulation of the circuit of the magnet with a view to increasing the strength of field, a higher air pressure must be produced below the diaphragm before the latter starts its opening movement. This results in a more rapid opening movement of the diaphragm 6, that is to say, a more rapid expelling of the air into the horn, as well as an expelling of a larger quantity of air per unit of time during the first part of the expelling period. The expelled air will have a steeper wave front and the air particles producing the sound will have a larger kinetic force, that is to say, I will obtain a tone of a higher intensity than that obtainable as result of the expelling of air of a lower pressure and more successively.

The air contained in the passage 5 above the diaphragm valve 6 is caused to cooperate instantly with the compressed air bel w th diaphragm, inasmuch as the diaphragm, when leaving the pole piece 9, acts on said air to expel same. At the same time a suitable cushioning of the impact of the diaphragm upon the upper most wall of the passage 5 is secured.

If, for instance, the pole of the magnet 8 facing the diaphragm is assumed to be a north pole, the part of the diaphragm bearing against the pole piece 9 will represent a south pole. Of course, I may provide in the upper wall of the passage 5 an auxiliary magnet having its north pole facing the diaphragm and so arrange said auxiliary magnet as to allow it to keep the diaphragm away from the magnet 8 during a longer period of time in case of large deflections of the diaphragm, that is to say, in case of an adjustment for a higher pressure of the air in the chamber I. Said action is due to the fact that the diaphragm as a result of larger deflections will enter a more and more strong field as produced by said auxiliary magnet.

In order that the device may operate in the desired way it is an indispensable condition that the retaining power tending to keep the valve in its closed position, decreases with increasing opening movement of. the valve, as otherwise the diaphragm would adjust itself into an equilibrium or vibrate about an equilibrium between closed and completely open position.

In Fig. 2 is shown a modified form of the outlet passage 25 leading from the pressure chamber M to the horn 24. Herefthe outlet passage 25 is constricted symmetrically from, its top and bottom walls at its mouth opening into the born 24, as shown at 26, thereby allowing the air column in the horn to be acted upon centrally by the blow of pressure as exerted by the outflowing air.

In Figs. 3, 6 and 8 is shown an embodiment, in which the armature of the retaining magnet 38 which forms a valve between the pressure chamber 3| and the horn 34, is shaped as a conical surface 36. The core 39 of the retaining magnet 38 is cup-shaped and surrounds the pressure chamber 3I, openings 32 being provided in the bottom of the cup-shaped core in order to allow communication with the receptacle for the compressed air 33. At its top or mouth the core 39 is formed with a seat 31 to be engaged by the conical valve 36. The horn 34 is connected at its rear end to an annular space 35 surrounding the uppermost part of the valve 36. The operation is similar to that above described. In order to guide the valve 36 to its proper position into engagement with the seat 31, when attracted by the magnet 38, there is provided a spring 40 attached to the apex of the conical valve 36. The conical valve 36 may be provided with apertures or projections, if required, to prevent the valve from being locked against movement.

It is to be noted that the single diaphragm armature of the retaining magnet may be replaced by a plurality of armature elements'or diaphragms acting as valves, this arrangement, however, requires a complete synchronism between the movements of the various armature elements or valves in order to obtain a pure tone and an efficient cooperation,

A solution of this problem requires the satisfaction of the following conditions:

There must be a common pressure chamber to produce the opening movement of the diaphragms or valves in order that the pressures acting on the individual valves shall change synchronously. Each diaphragm or valve must allow individual adjustment once for all by means of resistances inserted in the circuit of the electromagnet or, if desired, by using diaphragm valves of predetermined tension. There must be a device for effecting an automatic control of the various valves with relation to each other, so that any valve when opening may facilitate the opening of the other valves. This efiect may be obtained, for instance, by the use of a common retaining magnet circuit for all valves and magnets, so that a reduction of the attractive force will automatically take place, as soon as air is admitted to the 'iron circuit through any valve. One embodiment of this type is illustrated in Figs. 4, 7 and 9.

With reference to Fig. 4, the core :39 of the magnet 68 constitutes a pressure chamber 4| communicating through apertures, one of which is shown at 42, with a receptacle for compressed air, not shown. The connection between the pressure chamber ll and the horn 44 is controlled'by two diaphragm valves 46. These valves bear in their closed position with their free ends upon a pole piece 50 on opposite sides of a non-magnetic mass 5!, so that in this position a closed magnetic circuit exists which includes the two diaphragm valves 45. If one of the diaphragm valves, say the left one, lifts prior to the other, the air gap thus formed between the pole piece 50 and this diaphragm is introduced into the magnetic circuit, reducing the attractive force, so that the magnet cannot keep the other diaphragm attracted, with the result that also this diaphragm will be released.

What I claim is:

1. A siren having a chamber for receiving a fluid under pressure and an outlet leading from said chamber, a valve for controlling said outlet, electro-magnetic means for producing a retaining power acting upon the valve to keep same in closed position, said retaining power being of such a nature as to become reduced with increasing opening of the valve, said chamber having a restricted inlet to allow the fluid to generate in the chamber, a source of counter-power acting on the valve to open same, said counter-power being of such nature as to be alternately increased and decreased depending on the closing and opening of the valve, the strength, or the highest strength, of said counter-power being sufficient for overcoming the action of the retaining power.

2. A siren having a chamber for receiving a fluid under pressure, said chamber having a restricted inlet and a large outlet, a valve for controlling said outlet, said valve having a large area exposed to the interior of said chamber toallow the fluid pressure therein to produce the counterpower tending to open the valve, and electro magnetic means for producing a retaining power acting upon the valve to keep same in closed position, said retaining power being of such a nature as to become reduced with increasing opening of the valve, the strength, or the highest strength, of said counter-power being sufficient for overcoming the action of the retaining power.

3. A siren having a chamber for receiving a fluid under pressure, said chamber having a restricted inlet and a large outlet, a valve for controlling said outlet, said valve having a large area exposed to the interior of said chamber, an electro-magnet for producing a retaining power ac ing upon the valve to keep same in closed position, and a source of counter-power acting on the valve tending to open said valve, the strength, or the highest strength, of said counter-power being sufficient for overcoming the action of the retaining power, and means to vary the section of pas sage of said inlet.

4. A siren having a chamber for receiving a fluid under pressure, said chamber having a restricted inlet and a large outlet, a diaphragm clamped at its one end for controlling said outlet, an electromagnet cooperating with the free'end of said diaphragm to keep same in closed position, the diaphragm being exposed between its ends to the interior of said chamber so as to be subjected to the pressure of the fluid therein, acting on the diaphragm to open same, the pressure, or the highest pressure, in said chamber being sufficient to overcome the action of the retaining power, as exerted by the electromagnet.

5. A siren having a chamber for receiving a fluid under pressure, said chamber having a restricted inlet and a large outlet passage, means to vary the section of passage of said inlet, an electromagnet arranged in the wall of said chamber near the mouth of said passage, and a diaphragm valve of magnetic material clamped in the wall of the chamber at the end of said outlet passage remote from the electromagnet and cooperating at its free end with said electromagnet so as to extend, substantially, in the longitudinal direction of the outlet passage and being capable of moving under the influence of the fluid pressure in the chamber, with its free end, between said electromagnet and the opposite wall of the outlet passage.

6. A siren having a chamber for receiving a fluid under pressure, said chamber having a restricted inlet opening and a large outlet passage, means to vary the section of passage of said inlet opening, a horn leading from the mouth of said outlet passage, an electromagnet arranged in the wall of said chamber near the mouth of said passage, a diaphragm valve of magnetic material clamped in the wall of the chamber at the end of said passage remote from the electromagnet and cooperating at its free end with said electromagnet so as to extend, substantially, in the longitudinal direction of the outlet passage and being capable of moving under the influence of the fluid pressure in the chamber, with its free end, between said electromagnet and the opposite wall of the outlet passage.

7. A siren having a chamber for receiving fluid under pressure, said chamber having a restricted inlet opening and a large outlet passage, the mouth of said passage being contracted symmetrically from opposite sides. a horn leading from said contracted mouth, an electromagnet arranged in the wall of said chamber near the mouth of said passage, a diaphragm valve of magnetic material clamped in the wall of the chamber at the end of said passage remote from the electromagnet and cooperating at its free end with said electromagnet so as to extend, substantially, in the longitudinal direction of the outlet passage and being capable of moving under the influence of the fluid pressure in the chamber, with its free end, between said electromagnet and the opposite wall of the outlet passage.

8. A siren having a chamber for receiving a fluid under pressure, said chamber having a restricted inlet and a large outlet, a conical valve to control said outlet, an electromagnet for closing said valve, an annular core belonging to said electromagnet, said core having an annular conical seat for said valve, said valve being exposed to the interior of said chamber on its side facing the'electromagnet so as to be opened by the pressure of the fluid in said chamber.

9. A siren comprising a receptacle for a fluid under pressure, an electromagnet, a cup-shaped core belonging to said electromagnet, said core having openings in its bottom for communication with said receptacle, the core forming an annular seat at its open top, a conical valve to be brought into engagement with said seat under the action of the electromagnet and to be lifted therefrom under the action of the fluid contained in the cup-shaped core, said receptacle forming an annular space above said seat, and a horn leading from said annular space.

10. A siren having a chamber for receiving a fluid under pressure and an outlet leading from said chamber, a horn leading from said outlet, a plurality of valves for controlling said outlet, said valves being exposed to the interior of said chamber so as to be opened by the pressure of the fluid in said chamber, an electromagnet to bring said valves to closed position, said valves being so arranged as to form parts of the magnetic circuit of said electromagnet when in their closed or the highest strength, of said fluid pressure being sufficient to overcome the action of the electromagnet, and means to vary the strength of the electromagnet.

OLOF INGEMAR HARALD EKMAN.

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