| 1. | Low frequency sound generator, preferably for use with infrasound grills or any other infrasound or low frequency sound supported combustion characteriz in that air pulses are being generated by a diaphragm (14, 35) which is imparted a reciprocating movement by means of an electro magnet (18, 38). |
| 2. | Low frequency sound generator according to claim 1 characterized in t the diaphragm (14, 35) is located inside a housing consisting of a front plate (9, 30 rear cover plate (11 , 32) and a sweep (10, 31 ); that said plates are connected to th sweep (10,31); and that inside the sweep (10, 31 ) an air proof cloth is mounted (1 34). |
| 3. | Low frequency sound generator according to claim 2 characterized in t the front plate (9, 30) preferably has the shape of a truncated cone and that at the truncated end of the front plate a flange (8, 29) is located connecting the low frequency sound generator with a grill and through which said flange (8, 29) air pulses generated by the diaphragm (14, 35) are propagated with a low frequency, preferably lower than 20 Hz. |
| 4. | Low frequency sound generator according to any of the preceding claims characterized in that the diaphragm (14, 35) is being connected to a plung (19, 39) of the electro magnet (18, 38) via a link mechanism (20, 40). |
| 5. | Low frequency sound generator according to any of the preceding claims characterized in that the diaphragm (14, 35) is supported in the housing b means of mechanical springs (15, 16, 36, 37). |
| 6. | Low frequency sound generator according to claim 5 characterized in t the springs together with a mass, consisting mainly of the mass of the diaphragm, constitute an oscillating massspring system which is characterized by a certain natural frequency. |
| 7. | Low frequency sound generator according to claim 6 characterized in t the plunge (19, 39) of the electro magnet (18, 38) is driven by a frequency approximately equal to the natural frequency of the massspring system. |
| 8. | Low frequency sound generator according to claim 7 characterized in t the operation of the plunge (19, 39) is being controlled by an electronic control uni. |
| 9. | Low frequency sound generator according to any of the claims 28 characterized in that the rear cover plate (11 , 32) is provided with holes (1 33) for letting air out during the reciprocating movement of the diaphragm (14, 35). |
This invention relates to a low frequency sound generator especially suited for the use in infrasound barbecue grills, open fire stoves or other infrasound supported combustion.
Through i.a. SE, B, 412 635, WO 85/02452 and US, A, 1 173 708 it is previously known to use low frequency sound in order to achieve improved combustion of sol • fuel lying on a grate. In the mentioned WO publication a method and an apparatus described where low frequency sound is produced with the help of a Helmholtz-resonator placed beneath the grate carrying the fuel (e.g. charcoal or c on for instance an outdoor barbecue grill, an open fire stove or a restaurant grill. Sound of a certain frequency is produced by a loudspeaker element placed inside resonator. In another embodiment, air pulses are produced by means of a flexible bellows mounted on one side of the resonator and which is given a reciprocating movement by means of a crank mechanism connected to the outside of the bellow In the mentioned publication it is also described how the bellows can be replaced a diaphragm in order to achieve a relatively high amplitude in the same way as wh using a bellows.
The apparatus according to the present invention relates to an improved design of low frequency sound generator for grills as described above. The heavy and spac demanding box consisting of the Helmholtz resonator can be excluded due to the f that the new sound generator is very powerful. The new generator comprises a dri unit including an electro magnet, which is being allowed to influence a diaphragm suspended with springs, and where said diaphragm and springs together form an oscillating mass-spring system having a certain, predetermined natural frequency. The apparatus provides a more effective combustion which results in lesser quanti of soot and smoke contaminating the food to be grilled and also results in quicker
lighting of the fuel.
The invention, with embodiments, will now be explained in detail with reference to enclosed drawings, of which
Fig 1 shows an explanatory sketch of an infrasound grill Fig 2 is an exploded view showing the design of one embodiment of the infrasound generator
Fig 3 shows a cross-section of a second embodiment of the infrasound generator.
Fig 1 shows an infrasound barbecue grill with a container 1. In the lower part of t container 1 a grate 2 is situated, on which fuel, such as preferably charcoal, is pl Above the grate 2 a gridiron 3 is situated at a suitable height, preferably changea on which the foodstuffs to be grilled are placed. At the bottom of the container 1 t is an opening which through a pipe 4 leads down to an ash box 5. At the side of s pipe 4 there is an opening which connects the pipe with another horisontal pipe 6 which, in its turn, the infrasound generator 7 itself is connected The grill may also equipped with a hole or connection at the bottom of the container for attachment . LP-gas container or equivalent which will be used when lighting the grill. The infrasound generator itself is run by electricity, for outdoor grills preferably with th help of batteries.
Fig 2 and Fig 3 shows two different embodiment of the infrasound generator. On infrasound generator there is a flange 8, 29 through which the infrasound genera connected to the horisontal pipe 6 of the infrasound grill. The flange 8, 29 and th pipe 6 may in some cases be constructed as one part. On the flange 8, 29 there front plate 9, 30 which preferably has the shape of a truncated cone. Due to this design the air resistance is decreased when air eventually is to pass through the flange 8, 29. The front plate 9, 30 is connected to a rear cover plate 11 , 32 throu sweep 10, 31. Together, the front plate 9, 30, the sweep 10, 31 and the rear cov plate 11 , 32 form a housing. The cover plate 11 , as in the embodiment accordin Fig 2, may also have the shape of a truncated cone or be almost flat with a sligh
bellying surface turned away from the sweep. Fig 3 shows an embodiment with a completely flat rear cover plate 32. The rear cover plate 11 , 32 is equipped with h 12, 33 to allow air to pass. Inside the sweep 10, 31 there is an airproof cloth 13, 3 installed. This cloth is at one end fastened to the housing and at its other end fastened to a diaphragm 14, 35 mounted inside the housing. According to Fig 2, t cloth 13 is fastened to that end of the front plate 9 which is turned towards the sw 10 and said diaphragm 14 is being mounted at that side of the sweep which is turn towards the rear cover plate 11. On the other hand, as shown in Fig 3, the cloth 3 may also be fastened to the rear cover plate 32 while the diaphragm 35 is mounte by means of springs 36, 37 to that end of the sweep 31 which is facing the front pl 30, or even to the front plate. According to both embodiments, between the diaphr 14, 35 and the housing there are located several mechanical springs 15,16, 36, 3 In the embodiment of Fig 2 two crossed plate springs are used. In Fig 3, helical springs 36, 37 are used with a radially located fixing point and in this embodiment springs also functions as suspension for the diaphragm in addition to the function described below. Other types of springs and spring arrangements may of course b used as well. These springs are especially selected in order to give the mass-spri system a certain natural frequency.
According to the embodiment of Fig 2, as a fastener for the springs, a spacer ring may be used which is placed inside the rear cover plate 11. The springs may be secured into this spacer ringl 7 or into any of the parts 9, 10, 11 forming the housi and into the diaphragm 14. In the embodiment according to Fig 3 no spacer ring is needed.
At the far end of the truncated cone or in the centre of the bellying surface or flat surface constituting the rear cover plate 11 , 32 there is an electro magnet 18, 38 installed with a plunge 19, 39 connected to the diaphragm 14, 35. Via a special electronic control unit the plunge 19, 39 in the electro magnet can be driven back forth with a frequency approximately equal to the natural frequency of the mass-s system. It is desirable that these two frequencies correspond as much as possible the system to use as little power as possible. Extending from the plunge 19, 39 of electro magnet there is a link mechanism 20, ' 40 which is fastened to the diaphrag
14, 35. When the electro magnet 18, 38 is switched on and the plunge 19, 39 start reciprocating movement, the diaphragm is imparted a reciprocating movement via link mechanism 20, 40. The link mechanism 20, 40 may have a certain flexibility in order to absorb irregularities in the reciprocating movements of the diaphragm, if 5 and thus preventing them from propagating to the plunge 19, 39. In the embodime according to Fig 2 the link mechanism 20 may be made of rubber or other suitable material.
The infrasound generator functions as follows. At rest, i.e. when the electro magn 0 not switched on, the plunge is partly drawn out of the magnet centre with the help the spring power in the springs 15,16, 36, 37. When the magnet is switched on, it strives to draw the plunge into the centre of the magnet and by means of the link mechanism 20, 40 the springs and the diaphragm 14, 35 are consequently move from their rest position towards the magnet. A condition for the springs and diaph
15 to move is that air can pass through the holes 12, 33 located in the rear cover pla 11 , 32. When the power to the electric magnet is switched off again, the plunge is drawn out of the centre of the magnet with the help af the spring power and the springs and the diaphragm spring back and past their rest position. The air contai between the diaphragm and the flange 8, 29 is thereby squeezed out through the
20. flange and into the horisontal pipe 6 of the grill. This motion sequence is repeated due to the fact that the movement of the electro magnet and the plunge are contr by the electronic control unit. In this way, a reciprocating movement is achieved i diaphragm 14, 35 and repeated air pulses are produced with a certain low freque preferably less than 20 Hz. This influences the combustion of the charcoal on the
25 grate 2 in such a way that a pulsating combution is achieved and the temperatur increases. The oscillation of the diaphragm 14, 35 is increased by the springs 15 36, 37 oscillating along. To be more exact, the mass of this oscillating mass-spri system does not only include the mass of the diaphragm but includes also the m of the springs, the fastening device for the springs etc, the link mechanism, the
30 plunge, the cloth and the air contained in the housing.
The apparatus according to the invention is not only restricted to use with barbe grills, open fire stoves and restaurant grill as described here, but may also be us
other apparatuses where a small and less space demanding low frequency sound generator is required.