Abstract:
An electropneumatic acoustic horn is disclosed, comprising an electric compressor unit for generating compressed air and a sound wave generator comprising at least an acoustic chamber associated to at least a volute wound acoustic duct adapted to propagate the produced sound to the outside. Air channelling means put the compressor unit in communication with each acoustic chamber. The compressor unit and the sound wave generator are mechanically connected in a removable way by fitting slidingly a collar.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to an electropneumatic horn particularly adapted to equip two- and four-wheeled motor vehicles. 
   The electropneumatic horns of the prior art comprise a generator of sound waves including one or more acoustic units, connected to an electric compressor by ducts for air passage to generate a mono, bi o tri tonal tuned sound according to the number of acoustic units. 
   More particularly the acoustic units consist of a straight exponential duct of a length proportional to the frequency to be reproduced, inserted in an acoustic chamber in which a membrane free to move with a reciprocating motion is arranged. 
   The straight duct comprises a first stretch with generally constant section, provided with an inlet mouth for the sound signal generated by the oscillating membrane and a second stretch having a section varying with a generally conic exponential law ending with an outlet mouth for the amplified sound signal. 
   The membrane is properly stretched in a calibration phase by deformation against said membrane of a metal member referred to as bottom and applied to the shape of chamber body, in such a way to generate a sound with predetermined acoustic pressure. 
   In a different constructional version of the prior art the acoustic units are two and the corresponding ducts are volute wound and juxtaposed to limit the overall dimensions of the horn. 
   As already stated said acoustic horns and more particularly those with a straight acoustic units, equip motor vehicles and are generally installed in the engine compartments. 
   Acoustic horns with different features are available on the market, mainly classified according to the number of acoustic units, generally one to maximum three for the tuned sound, and according to the frequency that each unit should reproduce. 
   The need to optimise space and reduce dimensions of every element of the motor vehicle, led to reduce as much as possible the dimensions of the acoustic horns by miniaturization of the compressor assembly and the assembly comprising the acoustic units. 
   The solutions proposed up to now did not lead to great results, mainly in view of the correlation existing between the required sound frequency and required duct lengths, as well as the number of acoustic units anyway indispensable to reproduce simultaneously more frequencies. 
   With regard to installation of said acoustic horns, the compressor and the acoustic units are individually anchored to opposite supports through corresponding fastening members. 
   The compressor is then connected to each acoustic unit through a rubber duct provided with deviations allowing to convey compressed air in each acoustic chamber of the acoustic units. 
   A first drawback of such horns consists of the assembling complexity in the installation phase because bracketing of two or more components corresponding to the compressor and the acoustic units is required. 
   Another drawback consists in that the connection between each acoustic unit and the compressor is difficult and time consuming and does not warrant when improperly effected, instantaneousness and contemporaneousness of sound of the acoustic units. 
   As a matter of fact it is often impossible to carry out a correct assembly, more particularly with regard to the air connection between compressor and sound wave generator, thus making impossible to mount in limited space several components divided from each other but at the same time requiring to be installed close to each other to obtain sound instantaneousness and with the acoustic ducts being equidistant from the compressor to warrant contemporaneousness of sound. 
   In order to remove this drawback electromagnetic horns are widely used, warranting a good response to actuation and having a compact structure as well. 
   However, the assembling phase of said electromagnetic horns requires the use of special brackets, which are essential for their operation and have the drawback of increasing the overall dimensions of the assembly. 
   SUMMARY OF THE INVENTION 
   Object of the present invention is to overcome the above mentioned drawbacks. 
   More particularly a first object of the invention is to provide an electropneumatic horn of a more compact structure relative to the electropneumatic horns of the prior art. 
   Another object of the invention is to provide an electropneumatic horn reducing the assembling complexity relative to equivalent electropneumatic horns of the prior art. 
   A further object of the invention is to provide an electropneumatic horn allowing quick disassemble operations in case of mainteinance work. 
   It is then another object of the invention to provide an acoustic horn that in view of its features may be a valid alternative but with greater acoustic power to the electromagnetic horns. 
   A further object of the invention is to provide an acoustic horn having better features of sound instantaneousness and contemporaneousness relative to known electropneumatic horns, said the features being comparable to those of the electromagnetic horns. 
   A last but not least object of the invention is to provide an electropneumatic horn that may be a valid alternative to the electromagnetic horns in view of its greater reliability, more particularly as to resistance to an uninterrupted sound emission and reliability in the sense of product useful life. 
   Said objects are attained by an electropneumatic horn that according to the wording of the main claim comprises:
         at least a compressor unit provided with at least an air suction inlet from outside ambient and at least an outlet of compressed air;   a sound wave generator comprising at least an acoustic chamber provided with at least an inlet for entry of pressurised air in which there is an elastic membrane for sound generation and at least a volute wound acoustic duct defined between an outer shell and a diaphragm, said acoustic duct communicating with said acoustic chamber and being adapted to propagate to the outside the sound generated by said membrane;   air channelling means adapted to put said outlet of the compressor unit in communication with said inlet of the acoustic chamber;
 
and wherein said at least a compressor unit and said sound wave generator are mechanically connected in a removable way by fitting slidingly a collar.
       

   According to a preferred embodiment the sound wave generator comprises two acoustic ducts defined between two opposite shells between which a diaphragm is interposed, a collar portion being made integral with each shell. 
   Said collar is also provided with a labyrinth suction duct putting the compressor suction inlet in communication with the outside. 
   The channelling means comprise an injector being part of the compressor and arranged after the outlet and coupled to a duct made in the diaphragm by snapping. 
   Said duct is in communication with two intermediate chambers defined in the sound wave generator, the opening communicating with the corresponding acoustic chamber being defined in each intermediate chamber. 
   In a different embodiment the sound wave generator comprises a single acoustic duct defined between a shell and a diaphragm while a portion of the collar is made integral with the shell and another portion with the diaphragm. 
   In both embodiments the acoustic horn comprises fastening means consisting of a single projecting element made in the compressor body for connection to the support structure. 
   Advantageously the acoustic horn of the invention may be supplied as a kit comprising a compressor unit and a sound wave generator that are coupled through the collar and therefore may be used to equip two and four wheeled vehicles with a simple assembling operation of the two main parts by snapping, namely generator and compressor, by the user. 
   Still advantageously, the compact structure of the acoustic horn minimizes the paths of the compressed air flows from the compressor to the acoustic chambers thus increasing the performance as to sound instantaneousness and contemporaneousness when more acoustic ducts are provided. 
   Also advantageously the compact structure of the acoustic horn allows more favourable installations for sound propagation from the vehicles, still respecting the minimum values for the type approval, more particularly in comparison with the electromagnetic horn of substantially less acoustic power. 

   
     BRIEF DESCRIPTION OF THE INVENTION 
     The foregoing objects will be better understood by reading the following description of preferred embodiments given as an illustrative but not limiting example, having reference to the accompanying sheets of drawing in which: 
       FIG. 1  is partially sectioned side view of the acoustic horn of the invention; 
       FIG. 2  is an enlarged view of a detail of the channelling means of  FIG. 1 ; 
       FIG. 3  is a sectional view of the detail of  FIG. 2  taken along line II—II; 
       FIG. 4  is a sectional view of the acoustic horn of  FIG. 1  taken along line I—I; 
       FIG. 5  is a side view of the diaphragm of the acoustic horn of  FIG. 1 ; 
       FIG. 6  is a side view of the diaphragm of  FIG. 5 ; 
       FIG. 7  is a top view of the diaphragm of  FIG. 5 ; 
       FIG. 8  is a sectional view of the detail of  FIG. 4 ; 
       FIG. 9  is a sectional side view taken along line VIII—VIII of  FIG. 8 ; 
       FIG. 10  is a sectional view taken along line I—I of a constructional variation of  FIG. 1 ; 
       FIG. 11  is a sectional view taken along line I—I of another constructional variation of  FIG. 1 ; 
       FIG. 12  is a side view of the diaphragm of  FIG. 11 ; 
       FIG. 13  is a top view of the diaphragm of  FIG. 12 ; and 
       FIG. 14  is a side view of the diaphragm of  FIG. 12 ; 
       FIG. 15  is a sectional view taken along line I—I of a further constructional variation of  FIG. 1 ; 
       FIG. 16  is a lateral view of the diaphragm of  FIG. 15 ; 
       FIG. 17  is a top view of  FIG. 16 ; 
       FIG. 18  is a lateral view of  FIG. 16 . 
   

   DESCRIPTION OF THE INVENTION 
   The acoustic horn of the invention is shown in  FIG. 1  where it is generally indicated with numeral  1 . 
   The horn comprises a compressor unit  2 , a sound wave generator  3  and air channelling means  4  adapted to put the compressor  2  in communication with the sound wave generator  3 . 
   More particularly the compressor unit  2  is provided with a suction inlet  5  from which air from outside is sucked, and an outlet  6  for the compressed air. 
   Proper elements of connection to the power supply, not shown in the drawings for sake of simplicity, are provided in the body of the compressor  2  and are generally arranged in its lower part. 
   With regard now to the sound wave generator  3 , it comprises two acoustic chambers indicated with numerals  7  and  8  in  FIG. 4  respectively, each chamber being provided with an opening  9 ,  10 , for introduction of pressurised air. 
   In each acoustic chamber  7 ,  8 , there is an elastic membrane  11 ,  12 , for sound generation when the membrane is being vibrated by the compressed air coming from the compressor  2 . 
   A volute wound acoustic duct  13 ,  14  is associated to each acoustic chamber  7 ,  8  and defined between an outer shell  15 ,  16  and a diaphragm  17  common to both acoustic duct  13 ,  14  and interposed between said shells  15 ,  16 . 
   Each acoustic duct  13 ,  14  has a first stretch with generally constant section  19 ,  20  provided with an inlet  21 ,  22  communicating with the acoustic chamber  7 ,  8 . 
   The first constant section stretch  19 ,  20  of the acoustic duct  13 ,  14  is connected to a second stretch  23 ,  24  at the point indicated with numerals  25 ,  26  in  FIG. 1  and has a section varying with a generally conic exponential law ending with an outlet  27 ,  28  for sound propagation to the outside. 
   It is known that the configuration of each acoustic duct  13 ,  14  is consistent with the frequency to be obtained and in this case to obtain a tuned bi-tonal sound. 
   With regard now to the channelling means  4 , they put the outlet  6  of the compressor  2  in communication with openings  9 ,  10  for introduction of pressurized air into the acoustic chambers  7 ,  8 . 
   Said channelling means  4 , comprise:
         an injector  29  belonging to the compressor  2  and arranged after the compressor outlet  6 ;   two intermediate chambers  31 ,  32  defined in the sound wave generator  3  where each intermediate chamber  31 ,  32  defines the opening  9 ,  10  of connection with the corresponding acoustic chamber  7 ,  8 ;   a duct  33  made in the diaphragm  17  communicating with the intermediate chambers  31 ,  32  and coupled to the injector  29  as shown in the details of  FIGS. 2 and 3 .       

   More particularly from illustration of  FIG. 3  it is clear that such coupling allows to generate two flows of compressed air in each intermediate chamber  31 ,  32  starting from the single flow coming from the outlet  6  and generated by the compressor  2 . 
   In this way a short and symmetric channel of air connection between compressor  2  and acoustic chambers  7 ,  8  is obtained, warranting optimal sound instantaneousness and in the bi-tonal case of the drawings contemporaneousness. 
   According to the invention the compressor unit  2  and the sound wave generator unit  3  are mechanically connected through a collar generally indicated with numeral  34 . 
   Said flange  34  as better shown in  FIG. 4 , is made as an integral extension of the two shells  15 ,  16  like two portions  34   a  and  34   b  having a generally semicircular shape adapted to receive the body of compressor  2  that has generally a cylindrical shape. 
   Obviously the shape of the two portions  34   a  and  34   b  may be different in other embodiments and fit to the shape of the body of compressor  2 . 
   On collar  34 , and more particularly on the portion  34   b  on the side where the suction inlet  5  is arranged, there is a suction duct  35 , having a labyrinth configuration and putting the suction inlet  5  in communication with the outside. 
   In said suction duct  35  there is also a projecting tubular member  36  which is received inside the suction inlet  5  and is provided with elastically expanding means  37  interfering with said the suction inlet  5  to make the connection of the collar  34  and particularly of its portion  34   b  to the body of compressor  2  warranting a better adhesion of the suction duct  35  of said compressor  2 . 
   As shown in  FIG. 4  each acoustic chamber  7 ,  8  is defined by a shaped body  7   a ,  8   a  applied to the corresponding outer shell  15 ,  16 . 
   The elastic membrane  11 ,  12  is constrained to the shaped body  7   a ,  8   a  through a metal bottom  38 ,  39  superimposed externally and fixed by flanging to the shaped body  7   a ,  8   a  in order to tension the membrane during the calibration phase as a function of the level of sound pressure to be propagated. 
   A cap  40 ,  41  coupled to the shaped body  7   a ,  8   a  by mechanical fit is arranged as a cover and protection of bottom  38 ,  39 . 
   As shown in  FIG. 1  on the body of the compressor  2  there are also fastening means  42  consisting of a shaped projecting member adapted to receive screw elements for connection of the acoustic horn  1  to a support structure S. 
   It is clear that such fastening means  42  in other embodiments may be different to match shape and position of the support structure S. 
   Finally and as shown in  FIG. 5 , the diaphragm  17  is provided with hooking snap means  17   a  adapted to constrain said diaphragm  17  to the compressor unit  2  and to warrant the pneumatic seal when the compressor  2  and the sound wave generator  3  are mutually joined by collar  34  and the injector  29  is fully inserted into the duct  33  made on said diaphragm  17 . 
   Indeed, the acoustic horn  1  may be advantageously supplied as a kit with the parts consisting of the compressor unit  2  and the sound wave generator  3  divided, that can be easily assembled by the user before installation by snapping. 
   The assembling operation is carried out by inserting the injector  29  of the compressor unit  2  into the duct  33  of the diaphragm  17  for such a length as to allow the snap means  17   a  to constrain the diaphragm  17  to the body of the compressor unit  2  warranting the pneumatic seal as well. 
   At the same time the collar  34  through its portions  34   a  and  34   b  is coupled by mechanical fit with the outer surface of the compressor unit  2 . 
   Finally insertion of the tubular projecting member  36  into the suction inlet  5  through the expanding means  37  warrants a further fastening of collar  34  to the compressor. 
   The labyrinth suction duct  35  allows protection of the air suction inlet  5  from possible foreign matter and water splash that instead may enter directly inside the compressor unit  2 . 
   A first embodiment of the acoustic horn is shown in  FIG. 10  and is generally indicated with numeral  100 . 
   This modification differs from the first embodiment in that the shaped body  107   a ,  108   a  of each chamber  107 ,  108  is integral with the corresponding outer shell  115 ,  116 , the whole being made by moulding. 
   In this embodiment each intermediate chamber  131 ,  132  will obviously have a different shape relative to the first embodiment of  FIG. 4 . 
   Another embodiment of the invention is shown in  FIG. 11  and is generally indicated with numeral  200 . 
   This modification relates more particularly to a mono-tonal acoustic horn obviously having a single acoustic duct  213  as a single sound wave should be propagated. 
   In this case, since there is a single outer shell  215 , the connection collar  234  is made in two parts, a first part as extension integral with the outer shell  215  and a second part integral with the diaphragm  217  as shown in detail in  FIGS. 12 and 13 . 
   A further embodiment of the invention is shown in  FIG. 15  and is indicated as a whole with  300 . 
   It relates to a bi-tonal acoustic horn provided with two acoustic ducts  313 ,  314  which, as in the realization of  FIG. 1 , are defined between the two opposed shells  315 ,  316  and the diaphragm  317 . 
   However, in this case the collar  334  is made integral with the diaphragm  317 . Said diaphragm also presents the walls of the acoustic ducts  313 ,  314 , as it can be seen in  FIGS. 16 and 18 . 
   The two shells  315  and  316  are preferably, but not necessarily, connected to the diaphragm  317  through glueing or ultrasound welding. 
   The bi-tonal horns of the invention can be associated to sound modulation systems, which are not shown in the figures, allowing sounds production with different melodies. 
   In particular, it is possible to alternate the duration and the intensity of the air flow in the ducts, in order to obtain different acoustic effects. 
   This can be obtained, according to the known techniques, through the interposition of controlled valve means allowing the control and the convey of the air flow from the compressor unit towards the two acoustic ducts. 
   A first of such known techniques relates to the use of an electrovalve connected to an electronic control unit that determines the position of the electrovalve in order to convey and to modulate the air flow in the ducts. 
   According to another known technique, the distribution of the air flow towards the acoustic ducts is obtained through a gear mechanic system which controls the valve according to the desired flow. Said gear mechanic system is connected to the driving shaft associated to the compressor unit by reducing means. 
   From the foregoing it is clear that the acoustic horn of the invention attains the intended objects and advantages. 
   Other constructional modifications may be made to the acoustic horn in the execution phase. 
   More particularly the configuration of the labyrinth suction duct and the intermediate chambers, shape and extension of the collar, shape and position of the support fastening means or of the diaphragm snap hooking means may be different. 
   It is however to be understood that such variations as well as further modifications neither described nor illustrated in the drawings, whenever falling within the inventive scope indicated in the appended claims, are to be considered covered by the present patent.