Abstract:
A heated air horn is provided in which heat is applied to the base of the bell by a cylindrical heating element incorporated into the base of the bell in a manner which does not harm the acoustics of the horn.

Description:
TECHNICAL FIELD  
       [0001]     The invention relates to the field of pneumatic or air horns, an in particular pneumatic or air horns which are heated for winter use.  
       BACKGROUND  
       [0002]     Air horns are widely used on locomotives, to duplicate the sound of traditional steam locomotive whistles, as well as on commercial marine vessels, trucks, for industrial uses and wide area warning. Such horns are generally exposed to the elements, and a build-up of snow or ice in winter conditions is detrimental to the performance of the horn. Consequently modifications have been made to provide electrical heating coils on the horn to melt snow or ice. For example, Pearson U.S. Pat. No. 2,409,954 discloses an air horn in which a heating grid extends across the mouth of the horn, or a heating coil extends around the inner periphery of the mouth of the horn. Eveanowsky, Jr. et al. U.S. Pat. No. 5,022,341 discloses an air horn in which three heating cartridges are provided, extending into channels in the diaphragm housing. It remains that such designs can be less effective for preventing ice buildup at the base of the horn trumpet, and effect the audible performance of the horn.  
         [0003]     The foregoing examples of the related art and limitations related thereto are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.  
       SUMMARY  
       [0004]     The following embodiments and aspects thereof are described and illustrated in conjunction with systems, tools and methods which are meant to be exemplary and illustrative, not limiting in scope. In various embodiments, one or more of the above-described problems have been reduced or eliminated, while other embodiments are directed to other improvements.  
         [0005]     The present invention provides a heated air horn in which heat is applied to the base of the trumpet in a manner which does not harm the acoustics of the horn. More particularly the invention provides a heated air horn comprising a bell having an open end and a base end secured to a housing containing a sound-generating diaphragm, the bell having an inner surface surrounding a resonating chamber, further comprising a heating assembly mounted in the base end of the bell between the bell and the resonating chamber, the heating assembly comprising a retaining sleeve and a heating element. According to one aspect of the invention the heater assembly fits in a recess in said inner surface of the bell so that the heating element is held between the retaining sleeve and the bell, in direct contact with the bell.  
         [0006]     In addition to the exemplary aspects and embodiments described above, further aspects and embodiments will become apparent by reference to the drawings and by study of the following detailed descriptions.  
       BRIEF DESCRIPTION OF DRAWINGS  
       [0007]     Exemplary embodiments are illustrated in referenced figures of the drawings. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than restrictive.  
         [0008]      FIG. 1  is a perspective view of an air horn incorporating the invention;  
         [0009]      FIG. 2  is a lengthwise cross-section view of the air horn in  FIG. 1 ;  
         [0010]      FIG. 3  is a detail exploded cross-section of the air horn shown in  FIG. 1 ;  
         [0011]      FIG. 4  is a longitudinal cross-section of the air horn shown in  FIG. 1 ; and  
         [0012]      FIG. 5  is an exploded view of the air horn shown in  FIG. 1 . 
     
    
     DESCRIPTION  
       [0013]     Throughout the following description specific details are set forth in order to provide a more thorough understanding to persons skilled in the art. However, well known elements may not have been shown or described in detail to avoid unnecessarily obscuring the disclosure. Accordingly, the description and drawings are to be regarded in an illustrative, rather than a restrictive, sense.  
         [0014]     With reference to  FIG. 1 , air horn  10  has a flared metal trumpet horn or bell  12  made of a suitable metal such as cast aluminum and having a flared open end  22  covered by protective screen  24  held in place by adjustable ring  26  having clamp assembly  27 . With reference to  FIG. 2 , diaphragm cap  14  is secured to diaphragm head  16  of bell  12  by bolts  18 . Circular, flexible flat metal diaphragm assembly  20  is held between diaphragm cap  14  and diaphragm head  16  and is formed of two parallel circular stainless steel discs  30 ,  32  between which is sandwiched an annular cushion ring  34  made of silicone rubber.  
         [0015]     Air horn  10  is mounted on base  38  by fasteners  37  and base  38  is in turn mounted on a vehicle by fasteners extending through holes  36  in base  38 . Compressed air is introduced through passage  40  in base  38  or the like. The compressed air flows through restricted aperture  42 , into passage  44  and into annular chamber  46 . The air flows around annular diffuser  48 , which is secured to diaphragm head  16  by bolts  49  ( FIG. 5 ), and into chamber  50 , causing diaphragm assembly  20  to move off seat  51  and allowing air to escape out central chamber  52  of bell  12 . Once pressure is reduced in chamber  50 , diaphragm assembly  20  returns to its original position and the cycle repeats causing in the usual way a vibration of diaphragm assembly  20  and a sound wave in chamber  52  at a frequency which depends on the length of the bell  12 . Holes  54  in diaphragm cap  14  relieve air pressure behind diaphragm assembly  20 . Servicing access hole  56  permits access to the device for service.  
         [0016]     Heater assembly  80  fits in cylindrical recess  62  in the base of bell  12 . Heater assembly  80  comprises a heat-conducting cylindrical stainless steel retaining sleeve  72  which has a flared end  74  and a cylindrical heating element  60 . Heating element  60  is constructed of a resistance conductor made from an alloy such as nichrome embedded in a fiberglass and vulcanized silicone rubber sleeve. Conductor  66  provides electric current to heating element  60  through protective cable  68  and threaded connector  70 . Heating element  60  is retained in contact with bell  12  by the cylindrical retaining sleeve  72  and flared end  74 . Retaining sleeve  72  and flared end  74  fit integrally in recess  62  with a friction fit and are further tightly held in place and prevented from backing out of the bell  12  by screw  82 . In this way the heating element  60  is brought into direct contact with the bell  12  without altering the acoustic features of the bell.  
         [0017]     While a number of exemplary aspects and embodiments have been discussed above, those of skill in the art will recognize certain modifications, permutations, additions and sub-combinations thereof. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions and sub-combinations as are within their true spirit and scope.