AN AIR-DRIVEN LOW FREQUENCY SOUND GENERATOR AND A METHOD FOR REGULATING THE PISTON IN SUCH A GENERATOR

Description

[0001] The invention relates to an air-driven low frequency sound generator, as is described in the preamble of patent claim 1. The invention also relates to a method for regulating the stand-still position of a piston included in a low frequency sound generator, as described in the preamble of patent claim 6.

[0002] In particular, the present invention relates to a low frequency sound generator of the type described in WO-A1-8807894, in which a feeder unit comprising a movable piston is used to generate a standing gas-borne sound wave in a resonator. The piston performs a reciprocating movement inside a cylinder, which is surrounded by a surge tank connected to a pressure gas source. The piston regulates a connection opening between the cylinder and the surge tank. Since this connection opening of the cylinder is located close to an open end of the cylinder, which is facing and in communication with an open end of the resonator tube, the resonator tube is also in communication with the interior of the surge tank.

[0003] The dimensions of the resonator are chosen in such a way that a standing sound wave may be generated in the resonator by the pressure gas supplied via the surge tank. Preferably, the resonator is a quarter wave resonator, in most cases a quarter wave resonator tube. When a standing sound wave has been generated in the resonator, this standing sound wave has its maximum sound pressure amplitude where the feeder unit is situated. This sound pressure works on the end surface of the piston, resulting in a reciprocating movement of the piston. The other end of the piston is spring-loaded, and the piston can move in phase with the variations in sound pressure of the standing wave under the condition that the resonance frequency of the oscillating mechanical system is higher than the frequency of the standing sound wave in the resonator. US4359962 discloses a second generator with a resonator tube and a slide which is located in the cylinder.

[0004] Sound generators of this type are, for example, used for cleaning big boilers, heat exchangers and other apparatus where it is difficult to get access to the surfaces that need to be cleaned.

[0005] In many of their applications, these sound generators are used intermittently. When the sound generator is to be shut off for a certain period of time, this has, according to prior art, been achieved by shutting off the supply of pressure gas to the surge tank of the feeder unit. In such a stand-still position, the piston will normally be located such that the connection opening between the surge tank and the inside of the cylinder is not completely blocked by the piston and thereby gas will be flowing back from the resonator tube into the cylinder and further into the surge tank. This gas flow has the disadvantage that it may cause corrosion on the sliding surfaces for the piston inside the cylinder when the gas flows from the resonator tube via the cylinder and into the surge tank. Since there is only a very small gap between the external sides of the piston and the inside of the cylinder, the build-up of corrosion on the inside of the cylinder could be quite detrimental to the functioning of the feeder unit. If there is too much corrosion, there is even a risk that the movement of the piston is inhibited.

[0006] Another disadvantage with this prior art sound generator is that the start-up of the feeder unit does not result in that the piston immediately starts moving with its working displacement amplitude. Instead there is a progressive start of the movement of the piston that will take up to approximately one half of a second before it has reached its working displacement amplitude.

[0007] The object of the present invention is primarily to solve the problems discussed above. This is achieved, according to the present invention, by means of an air-driven low frequency sound generator provided with the new features as defined in the characterizing portion of patent claim 1, and by a method as defined in the characterizing portion of claim 6.

[0008] Accordingly, by providing a method and means for bringing said piston to a stand-still position, in which said connection opening is blocked by the piston, by exerting an additional pressure on said first spring-loaded end of said piston, the important advantage is achieved that corrosion is avoided on the inner surfaces of the cylinder, due to the fact that any gas flow back from the resonator tube into the surge tank is effectively prevented.

[0009] Another important advantage that is achieved by the present invention is that a much speedier start-up of the movement of the piston is obtained. In accordance with the present invention, an additional pressure is exerted on the spring-loaded end of the piston, which result in the connection opening between the surge tank and the cylinder being blocked completely, thereby shutting off the pressure gas supply to the feeder unit. When, later on, said additional pressure is made to cease, said connection opening is instantly opened completely, a powerful gas pulse rushes into the resonator and the generator will start immediately. Tests have shown that the operating sound pressure amplitude can be reached in as short a time as within 1/10 of a second.

[0010] In most cases, the present invention will result in a stand-still position where the second lower end of the piston will be located in the vicinity of the open end of the cylinder, next to the resonator.

[0011] Further features and advantages of the present invention will be apparent from the remaining dependent claims.

[0012] It should be understood that by the expression "low frequency sound" is intended sound of a frequency below approximately 38 Hz. A suitable operating sound frequency would be between approximately 15-35 Hz.

[0013] The present invention will now be described by means of a preferred embodiment, given as an example only, and with reference to the enclosed schematic drawings, in which:

Fig. 1 is a schematic illustration of a sound generator according to the present invention, during operation, with the piston located at its upper dead centre,

Fig. 2 is a schematic illustration of a sound generator, according to the present invention, during operation, with the piston located at its lower dead centre, and

Fig. 3 is a schematic illustration of a sound generator, according to the present invention, when it is at an intermittent stand-still.

[0014] Reference is initially made to Figs. 1 and 2. The illustrated sound generator comprises a feeder unit 1 mounted on a resonator, which in the illustrated case is a quarter wave resonance tube 2. The feeder unit includes a piston 4 that is arranged to perform a reciprocating movement inside a cylinder 5, between an upper dead centre 3, shown in Fig. 1, and a lower dead centre 8, shown in Fig. 2. The piston is spring-loaded by means of a spring 6, which is attached to the closed end of the cylinder. The cylinder and the piston are mounted in a surge tank or casing 7. A first pressure gas source 9, providing a constant gas pressure p_c1, preferably by compressed air, is connected to the surge tank 7. The cylinder has an open end 11 facing the resonance tube and communicating therewith. The cylinder is also provided with one or several connection openings or ports 10 in the cylinder wall by means of which the pressure gas supplied to the surge tank can also enter into the cylinder and continue down into the resonance tube. At the upper closed end of the cylinder, above the piston, there is a connection opening 18 used for pressure equalisation and it provides a communication either to atmospheric pressure or to a space at the open end of the resonator tube.

[0015] When the sound generator is in operation, the gas pressure p_g at the rear end of the resonance tube, i.e. that end of the resonance tube that is communicating with the cylinder and the feeder unit, below the piston, varies according to

[0016] Where

p₁ = constant air pressure at the rear end of the resonance tube

p̂₀ = amplitude of the sound pressure at the rear end of the resonance tube

f = frequency of the standing sound wave

t = time

[0017] If the constant air pressure above the piston, p₂, is equal to the constant pressure at the rear end of the resonance tube, p₁, the differential pressure over the piston is p̂₀ sin 2π·f·t.

[0018] When the differential pressure has its maximum value (+p̂₀), the piston is pressed to the upper dead centre, which is illustrated in Fig. 1. At that position, the ports 10 in the cylinder 5 are open and an air pulse 12 is fed into the cylinder.

[0019] When the differential pressure has its minimum value (-p̂₀), the piston is suctioned to its lower dead centre, as illustrated in Fig. 2, and the ports are closed.

[0020] According to the present invention, at the opposite end of the cylinder, i.e. that end which is not facing the resonance tube and at which end the spring of the piston is fitted, there is a second pressure gas source 14 connected to the cylinder. This second pressure source 14 supplies a constant gas pressure, p_c2, preferably compressed air, which is regulated by a regulating valve 15. This compressed air pressure, p_c2, is much higher than the gas pressure p_g. As long as the regulating valve 15 is at the position shown in Figs. 1 and 2, i.e. the supply from the pressure gas source 14 is shut off, the piston will move between the upper and lower dead centres with the frequency f of the standing wave in the resonance tube.

[0021] When the valve 15 is switched into the open position shown in Fig. 3, the high compressed air pressure, p_c2, generated by the second pressure gas source 14, will act upon the upper end of the piston and serve to press down the piston. This gas pressure p_c2 should be so high, as compared to the gas pressure pg, that the piston is pressed down to a position such that its upper dead centre will be located below the ports 10. Thereby said ports will be blocked by the piston and the gas pressure p_c1 from the first pressure gas source 9 will be shut off. In this position, the sound generator will come to a stand-still since the movement of the piston will stop when the compressed air from the first pressure gas source 9 cannot enter into the resonance tube 2. In the advantageous embodiment illustrated in Fig. 3, the piston will be pressed down to a seat 16 arranged at the lower end of the cylinder 5.

[0022] When it is desired that the sound generator should enter into operation again, the position of the valve 15 is changed back from the position illustrated in Fig. 3, to the position illustrated in Fig. 1. The spring will then move the piston to a position above the ports, and the piston will be free to move again between its upper and lower dead centres. The pressure gas from the first pressure gas source 9 will then be allowed again to enter into the cylinder and further down into the resonance tube.

[0023] In order to control the operation of the regulating valve 15, some type of control means are preferably provided. These control means may be manual means or some kind of automatic control means, known per se.

[0024] The inventive concept, according to the present invention, should not be limited to the embodiment illustrated here, by way of example only, but may be modified and varied within the scope of the invention as defined in the appended patent claims.

Claims

1. An air-driven, low frequency sound generator comprising an open resonator working as a sound emitter and also comprising a feeder unit (1), for the generation of standing, gas-borne sound waves, which sound waves produce a varying sound pressure inside said resonator, said feeder unit (1) including a cylinder (5) with one open end (11) facing said open resonator and communicating therewith, further including a piston (4) performing a reciprocating movement inside said cylinder (5) and having a first spring loaded end and a second opposite end facing said resonator, and also including a surge tank (7), at least partly surrounding said cylinder (5) and connected to a first pressure gas source (3), for feeding pressure gas into the surge tank (7) and further into said cylinder (5) via at least one connection opening (10) arranged in a wall of said cylinder, and said piston (4) functioning as a valve for regulating said connection opening, characterized in that it comprises means (14) for bringing said piston (4) to a stand-still position, in which said connection opening (10) is blocked by the piston (4), by exerting an additional pressure on said first spring-loaded end of said piston.

2. A low frequency sound generator according to claim 1, characterized in that it comprises a second pressure gas source connected to said cylinder for feeding pressure gas to a space inside said cylinder and behind said piston in order to exert said pressure on the spring-loaded end of the piston.

3. A low frequency sound generator according to claim 2, characterized in that it comprises a regulating valve for regulating the connection of said second pressure gas source.

4. A low frequency sound generator according to claim 3, characterized in that it comprises control means for opening said regulating valve when the sound generator is to be brought to an intermittent stand-still and for closing said valve when the sound generator is intended to enter into operation again.

5. A low frequency sound generator according to any one of claims 2-4, characterized in that a seat is arranged at the open end of said cylinder and that said second end of said piston is brought to abutment against said seat in its stand-still position.

6. A method for regulating the stand-still position of a piston (4) included in a low frequency sound generator comprising an open resonator working as a sound emitter and also comprising a feeder unit (1), for the generation of standing, gas-borne sound waves, which sound waves produce a varying sound pressure inside said resonator, said feeder unit (1) including a cylinder (5) with one open end facing said resonator and communicating therewith, further including said piston (4) performing a reciprocating movement inside said cylinder (5), said piston (4) having a first spring-loaded end and a second opposite end facing said resonator, and also including a surge tank (7), at least partly surrounding said cylinder (5) and connected to a first pressure gas source (9), for feeding pressure gas into the surge tank (7) and further into said cylinder (5) via at least one connection opening (10) arranged in a wall of said cylinder (5) and said piston (4) functioning as a valve for regulating said connection opening (10), characterized in that said piston (4) is brought to a stand-still position in which said connection opening (10) is being blocked by the piston (4), by means (14) of exerting an additional pressure on said first spring-loaded end of said piston (4).

7. A method according to claim 6, characterized in that said additional pressure is exerted in the form of a gas pressure, which gas pressure is fed into said cylinder from a second pressure gas source connected to said cylinder.

8. A method according to claim 7, characterized in that the connection of said pressure gas source is regulated by a regulating valve.

9. A method according to claim 8, characterized in that said regulating valve is opened when the low frequency sound generator is to be brought to an intermittent stand-still and in that it is closed when the sound generator is intended to enter into operation again.

10. A method according to any one of claims 6-9, characterized in that said second end of said piston is brought to abutment against a seat located at the open end of said cylinder by means of exerting said additional pressure.

Ansprüche

1. Luftbetriebener Niederfrequenz-Schallgenerator mit einem offenen Resonator, der als Schallquelle wirkt, sowie mit einer Speiseeinheit (1), zur Erzeugung stehender Schallwellen in Gas, welche Schallwellen im Innern des Resonators einen wechselnden Schalldruck bewirken, wobei die Speiseeinheit (1) einen Zylinder (5) mit einem offenen Ende (11) beinhaltet, das dem offenen Resonator zugewandt und mit demselben verbunden ist, weiter beinhaltend einen Kolben (4), der sich im Zylinder (5) hin- und herbewegt und ein erstes, federbelastetes Ende und ein gegenüberliegendes zweites, dem Resonator zugewandtes Ende aufweist, sowie einen Ausgleichsbehälter (7), der den Zylinder (5) zumindest teilweise umgibt und mit einer ersten Druckgasquelle (9) verbunden ist, um über mindestens eine in einer Wand des Zylinders angeordnete Verbindungsöffnung (10) Druckgas in den Ausgleichsbehälter (7) und weiter in den Zylinder (5) zu leiten, und wobei der Kolben (4) als Ventil zur Regelung der Verbindungsöffnung wirkt, dadurch gekennzeichnet, dass er Mittel (14) beinhaltet, um den Kolben (4) in eine Stillstandsstellung zu bringen, in welcher die Verbindungsöffnung (10) durch den Kolben (4) verschlossen ist, indem auf das erste, federbelastete Ende des Kolbens ein zusätzlicher Druck ausgeübt wird.

2. Niederfrequenz-Schallgenerator nach Anspruch 1, dadurch gekennzeichnet, dass er eine zweite Druckgasquelle aufweist, welche mit dem Zylinder verbunden ist, um Druckgas zu einem Zwischenraum im Innern des Zylinders und hinter dem Kolben zuzuführen, um den Druck auf das federbelastete Ende des Kolbens auszuüben.

3. Niederfrequenz-Schallgenerator nach Anspruch 2, dadurch gekennzeichnet, dass er ein Regelventil zur Regelung der Zuleitung der zweiten Druckgasquelle aufweist.

4. Niederfrequenz-Schallgenerator nach Anspruch 3, dadurch gekennzeichnet, dass er Steuermittel zum Öffnen des Regelventils aufweist, wenn der Schallgenerator vorübergehend zum Stillstand gebracht werden soll, und zum Schliessen des Ventils, wenn der Schallgenerator wieder in Betrieb genommen werden soll.

5. Niederfrequenz-Schallgenerator nach einem der Ansprüche 2-4, dadurch gekennzeichnet, dass am offenen Ende des Zylinders eine Auflage angeordnet ist, und dass das zweite Ende des Kolbens in dessen Stillstandsstellung an diese Auflage anstösst.

6. Verfahren zur Regelung der Stillstandsstellung eines Kolbens (4) eines Niederfrequenz-Schallgenerators mit einem offenen Resonator, der als Schallquelle wirkt, sowie mit einer Speiseeinheit (1), zur Erzeugung stehender Schallwellen in Gas, welche Schallwellen im Innern des Resonators einen wechselnden Schalldruck bewirken, wobei die Speiseeinheit (1) einen Zylinder (5) mit einem offenen Ende beinhaltet, das dem Resonator zugewandt und mit demselben verbunden ist, weiter beinhaltend den Kolben (4), der sich im Zylinder (5) hin- und her bewegt, wobei der Kolben (4) ein erstes, federbelastetes Ende und ein gegenüberliegendes zweites, dem Resonator zugewandtes Ende aufweist, sowie einen Ausgleichsbehälter (7), der den Zylinder (5) zumindest teilweise umgibt und mit einer ersten Druckgasquelle (9) verbunden ist, um über mindestens eine in einer Wand des Zylinders (5) angeordnete Verbindungsöffnung (10) Druckgas in den Ausgleichsbehälter (7) und weiter in den Zylinder (5) zu leiten, und wobei der Kolben (4) als Ventil zur Regelung der Verbindungsöffnung (10) wirkt, dadurch gekennzeichnet, dass der Kolben (4) in eine Stillstandsstellung gebracht wird, in welcher die Verbindungsöffnung (10) durch den Kolben (4) verschlossen ist, indem (14) auf das erste, federbelastete Ende des Kolbens (4) ein zusätzlicher Druck ausgeübt wird.

7. Verfahren nach Anspruch 6, dadurch gekennzeichnet, dass der zusätzliche Druck in Form eines Gasdrucks ausgeübt wird, welcher Gasdruck aus einer zweiten mit dem Zylinder verbundenen Druckgasquelle in den Zylinder geleitet wird.

8. Verfahren nach Anspruch 7, dadurch gekennzeichnet, dass die Zuleitung dieser Druckgasquelle durch ein Regelventil geregelt wird.

9. Verfahren nach Anspruch 8, dadurch gekennzeichnet, dass das Regelventil geöffnet wird, wenn der Niederfrequenz-Schallgenerator vorübergehend zum Stillstand gebracht werden soll, und dass es geschlossen wird, wenn der Schallgenerator wieder in Betrieb genommen werden soll.

10. Verfahren nach einem der Ansprüche 6-9, dadurch gekennzeichnet, dass das zweite Ende des Kolbens an eine Auflage am offenen Ende des Zylinders angedrückt wird, indem der genannte zusätzliche Druck ausgeübt wird.

Revendications

1. Générateur de sons basse fréquence à entraînement pneumatique comprenant un résonateur ouvert agissant comme émetteur sonore et comprenant également une unité d'alimentation (1), pour la formation d'ondes sonores stationnaires transmises par gaz, lesquelles ondes sonores produisent une pression sonore variable à l'intérieur dudit résonateur, ladite unité d'alimentation (1) incluant un cylindre (5) ayant une extrémité ouverte (11) en regard dudit résonateur ouvert et communiquant avec celui-ci, incluant en outre un piston (4) qui effectue un mouvement alternatif à l'intérieur dudit cylindre (5) et ayant une première extrémité soumise à l'action d'un ressort et une deuxième extrémité opposée en regard dudit résonateur, et incluant également un réservoir d'égalisation (7) entourant au moins partiellement ledit cylindre (5) et relié à une première source de gaz sous pression (9), afin d'alimenter un gaz sous pression au réservoir d'égalisation (7) et de celui-ci audit cylindre (5) par l'intermédiaire d'au moins une ouverture de liaison (10) agencée dans une paroi dudit cylindre, et ledit piston (9) ayant la fonction d'une soupape pour régler ladite ouverture de liaison, caractérisé en ce qu'il comprend des moyens (14) permettant d'amener ledit piston (4) à une position d'arrêt dans laquelle ladite ouverture de liaison (10) est bloquée par le piston (4), en exerçant une pression additionnelle sur ladite première extrémité à ressort dudit piston.

2. Générateur de sons basse fréquence selon la revendication 1, caractérisé en ce qu'il comprend une deuxième source de gaz sous pression reliée audit cylindre pour alimenter un gaz sous pression à un espace à l'intérieur dudit cylindre et à l'arrière dudit piston afin d'exercer ladite pression sur l'extrémité à ressort du piston.

3. Générateur de sons basse fréquence selon la revendication 2, caractérisé en ce qu'il comprend une soupape de régulation pour régler le branchement de ladite deuxième source de gaz sous pression.

4. Générateur de sons basse fréquence selon la revendication 3, caractérisé en ce qu'il comprend des moyens de commande pour ouvrir ladite soupape de régulation lorsque le générateur de sons doit être mis à l'arrêt temporairement et pour fermer ladite soupape lorsque le générateur de sons doit à nouveau être mis en service.

5. Générateur de sons basse fréquence selon l'une quelconque des revendications 2-4, caractérisé en ce qu'un siège est agencé à l'extrémité ouverte dudit cylindre, et que ladite deuxième extrémité dudit piston est appuyée contre ledit siège dans sa position d'arrêt.

6. Procédé pour régler la position d'arrêt d'un piston (4) compris dans un générateur de sons basse fréquence comprenant un résonateur ouvert agissant comme émetteur sonore et comprenant également une unité d'alimentation (1), pour la formation d'ondes sonores stationnaires transmises par gaz, lesquelles ondes sonores produisent une pression sonore variable à l'intérieur dudit résonateur, ladite unité d'alimentation (1) comprenant un cylindre (5) ayant une extrémité ouverte en regard dudit résonateur et communiquant avec celui-ci, incluant en outre ledit piston (4) qui effectue un mouvement alternatif dans ledit cylindre (5), ledit piston (4) ayant une première extrémité soumise à l'action d'un ressort et une deuxième extrémité opposée en regard dudit résonateur, et incluant également un réservoir d'égalisation (7) entourant au moins partiellement ledit cylindre (5) et relié à une première source de gaz sous pression (9), afin d'alimenter un gaz sous pression au réservoir d'égalisation (7) et de celui-ci audit cylindre (5) par l'intermédiaire d'au moins une ouverture de liaison (10) agencée dans une paroi dudit cylindre (5), et ledit piston (4) ayant la fonction d'une soupape pour régler ladite ouverture de liaison (10), caractérisé en ce que ledit piston (4) est amené à une position d'arrêt dans laquelle ladite ouverture de liaison (10) est bloquée par le piston (4), au moyen (14) d'une pression additionnelle exercée sur ladite première extrémité à ressort dudit piston (4).

7. Procédé selon la revendication 6, caractérisé en ce que ladite pression additionnelle est exercée sous forme d'une pression gazeuse, laquelle pression gazeuse est alimentée audit cylindre à partir d'une deuxième source de gaz sous pression reliée audit cylindre.

8. Procédé selon la revendication 7, caractérisé en ce que le branchement de ladite source de gaz sous pression est réglé par une soupape de réglage.

9. Procédé selon la revendication 8, caractérisé en ce que ladite soupape de régulation est ouverte lorsque le générateur de sons basse fréquence doit être mis à l'arrêt temporairement, et en ce qu'elle est fermée lorsque le générateur de sons doit à nouveau être mis en service.

10. Procédé selon l'une quelconque des revendications 6-9, caractérisé en ce que ladite deuxième extrémité dudit piston est appuyée contre un siège situé à l'extrémité ouverte dudit cylindre en exerçant ladite pression additionnelle.

Drawing