Abstract:
A number of embodiments of acoustical devices for improving either or both the intake and exhaust sounds emanated from an internal combustion engine. This is achieved by employing acoustical devices which are configured so as to discharge the desired sound waves to the atmosphere rather than by attempting to dampen the undesired sound waves generated in the system.

Description:
BACKGROUND OF INVENTION  
         [0001]    This invention relates to an acoustical device for an internal combustion engine and more particularly to an improved device for generating the desired sounds from either or both of the engine induction system and the engine exhaust system.  
           [0002]    Various devices have been proposed for use in conjunction with internal combustion engines so as to provide the desired sound in either or both of the induction system and the exhaust system. Generally, the desired sound has been achieved by providing acoustical devices that will tune or minimize the frequencies which are not desired so as to retain the desired frequencies. The problem with these systems is that they require multiple devices to tune out multiple frequencies other than the frequency or frequencies desired. Various types of silencing devices have been employed for attempting to cancel out or reduce the objectionable or undesirable frequencies and these include such things as side branch, resonators and Helmholtz resonators.  
           [0003]    It is, therefore, a principal object to this invention to provide an improved acoustical device for an engine that will be capable of rather than tuning out undesired frequencies, amplifying the desired frequencies so as to simply the system.  
           [0004]    It is a further object to this invention to provide such an acoustical device for either or both of the engine induction and exhaust systems.  
         SUMMARY OF INVENTION  
         [0005]    This invention is adapted to be embodied in an internal combustion engine comprised of an engine body forming at least one combustion chamber. An induction system is provided having an atmospheric communication opening for introducing at least an air charge to the combustion chamber. An exhaust system is also provided for discharging exhaust gasses from the combustion chamber through an atmospheric communicating opening. An acoustical device for amplifying sounds of a predetermined frequency is provided in at least one of the induction and exhaust systems and has an opening facing the atmospheric communicating opening of the system. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0006]    [0006]FIG. 1 is a partially schematic, cross-sectional view taken through an internal combustion engine having an acoustical device in its induction system constructed in accordance with a first embodiment of the invention.  
         [0007]    [0007]FIG. 2 is a partial cross-sectional view, in part similar to FIG. 1, showing another embodiment of the invention.  
         [0008]    [0008]FIG. 3 is a partial schematic view, in part similar to FIGS. 1 and 2, showing a third embodiment of the invention.  
         [0009]    [0009]FIG. 4 is a partial schematic cross-sectional view, in part similar to FIGS. 1 through 3, showing a fourth embodiment of the invention.  
         [0010]    [0010]FIG. 5 is a partial cross-sectional view, in part similar to FIG. 4, and shows a fifth embodiment of the invention.  
         [0011]    [0011]FIG. 6 is a partial cross-sectional view, in part similar to FIGS. 4 and 5, showing a sixth embodiment of the invention.  
         [0012]    [0012]FIG. 7 is a partial cross-sectional view, in part similar to FIGS. 4, 5 and  6  showing a seventh embodiment of the invention.  
         [0013]    [0013]FIG. 8 is a partial schematic view of a portion of an internal combustion engine showing the application of an acoustical device to an exhaust system for the engine.  
         [0014]    [0014]FIG. 9 is a partial schematic view, in part similar to FIG. 8, and shows an eighth embodiment of the invention.  
         [0015]    [0015]FIG. 10 is a partial schematic cross-sectional view, in part similar to FIG. 9, and shows a tenth embodiment of the invention.  
         [0016]    [0016]FIG. 11 is a partial schematic cross-sectional view, in part similar to FIGS. 9 and 10, and shows an eleventh embodiment of the invention.  
         [0017]    [0017]FIGS. 12 and 13 are graphical views showing how the system shown in FIG. 11 could be modified to change respectively the diameter of the orifices in the opening and the length thereof in response to changes in engine speed to improve the performance.  
         [0018]    [0018]FIGS. 14 and 15 show how the sound waves in the system in accordance with the invention compare with those in the prior art.  
         [0019]    [0019]FIG. 16 is a graphical view also showing a comparison of the sound waves and frequencies in connection with the prior art and the invention. 
     
    
     DETAILED DESCRIPTION  
       [0020]    Before proceeding with a detailed description of the several embodiments of the invention, it is believed advantageous to describe the theory by which the invention operates and contrast it with the prior art. In conventional systems, as noted in the Background portion of this application, devices such as side branch tubes or Helmholtz resonators have been employed for attenuating certain frequencies which are not desired in the sound of either or both of the induction and exhaust systems. These devices are positioned so that they intersect or extend generally perpendicularly to the flow path through either or both the induction or exhaust systems to interfere with and dampen undesired frequencies. Side branch resonators consist of tubes having a predetermined length and cross sectional area. These devices provide silencing in accordance with the following equation: 
         Side Branch Frequency Effect  f=C /4 L ×(2 n −1) 
         [0021]    Where:  
         [0022]    C=Sound Velocity  
         [0023]    L=Tube Length  
         [0024]    n=constant (integer)  
         [0025]    Thus, it will be seen that the frequency dampened is related to the length and cross sectional area of the side branch tube. However, this is because the side branch tube generates a blocking frequency. In accordance with the invention, the side branch tube is directed so that its opening faces to the atmosphere and hence, this frequency will be amplified rather than dampened. The Helmholtz frequency effect is set forth in the following formula: 
         Helmholtz Frequency Effect  f=[C /2 n ]{square root}[1 /V×Sp/Lp]   
         [0026]    Where:  
         [0027]    V=Volume of the resonator chamber  
         [0028]    C=Sound Velocity  
         [0029]    n=constant (integer)  
         [0030]    Sp=Connecting tube cross sectional area  
         [0031]    Lp=Connecting tube length  
         [0032]    Thus, by using these Helmholtz resonators as a side branch device extending perpendicularly to the direction of flow, the frequency f is silenced by blocking it. However, in accordance with the invention, the connecting tube has its opening facing the atmosphere and hence, the desired frequency will be amplified rather than damping other frequencies.  
         [0033]    The various embodiments will now be described by reference to the drawings and referring first to the embodiment of FIG. 1, the invention is described in conjunction with an internal combustion engine, indicated generally by the reference numeral  21  and more particularly with the induction system  22  thereof.  
         [0034]    The engine  21  is comprised of an engine body  23  which, in the illustrated embodiment, is of the four cylinder inline type having four combustion chambers which are served by the induction system  22 . Since the construction of the basic engine may be of any desired type, little of the details thereof are believed necessary to permit those skilled in the art to practice the invention.  
         [0035]    The induction system  22  has an air cleaner  24  having an angularly disposed inlet pipe  25  with an atmospheric inlet opening  26  for communicating the induction system  22  and specifically the air cleaner  24  with the atmosphere.  
         [0036]    The induction system  22  further includes a delivery tube  27  that communicates the downstream side of the air cleaner  24  with a throttle body  28  in which a flow controlling throttle valve  29  is positioned. As is well known, the throttle valve  29  is controlled by the demand of an operator of the engine  21 .  
         [0037]    The throttle body  28  communicates the atmospheric air with a plenum chamber  31  of an intake manifold, indicated generally by the reference numeral  32 . The intake manifold  31  has runner sections  33  each of which communicates with an intake port of the engine body  23 . The construction as thus far described may be considered to be conventional.  
         [0038]    In accordance with the invention, a side branch tube  34  is provided in the inlet section  25  of the air cleaner  24  and has an opening  35  which faces the atmospheric opening  26  of the inlet device  25 . A throttle valve  36  is provided at the mouth of the tube  24  to selectively close or open the communication of the tube  34  with the intake device  25 .  
         [0039]    When the engine is running at a specified engine speed or range, the valve  36  is opened to permit communication and thus, provide an amplified sound at such desired frequency in the range determined by the aforenoted equation. In addition to this sound amplifying device in the induction system, a device of a similar nature or devices shown in any of FIGS. 8 through 11 may be provided in the exhaust system for providing the same degree of amplification to provide the desired exhaust note.  
         [0040]    [0040]FIG. 2 shows another embodiment of the invention which differs only in the positioning of the sound amplifying device in the inlet pipe  25 . Therefore, this embodiment is shown only partially in connection with this part of the engine.  
         [0041]    The inlet pipe  25  is, in accordance with this embodiment, provided with an enlarged opening  41  at one side of the normal opening  26  thereof to define a further opening  42  of a side branch tube  43  which is formed integrally with the inlet pipe  25  at one side thereof. The opening formed by the walls  41  and  42  faces the atmosphere as with the previously described embodiment and thus functions as aforenoted. If desired, a control valve such as the valve  36  of FIG. 1 may be placed in the opening.  
         [0042]    In this embodiment, it is also possible to have the intake portion  41  that forms the chamber  43  transversely moveable so as to increase the effective diameter of the side branch tube and thus provide tuning for amplification of variable frequencies.  
         [0043]    [0043]FIG. 3 shows an embodiment that can be utilized in conjunction with a V-type engine such as a V-Twin or V-multiple cylinder engine, indicated generally by the reference numeral  51 . Each bank of the engine is provided with an induction manifold  32  as previously described including the plenum chamber  31 . Each plenum chamber is served by a respective air filter  24  and inlet pipe  27 . Throttle valves may be positioned at the inlet pipes or at the main inlet to the system.  
         [0044]    In connection with this embodiment, each air filter has a respective inlet section  52  which inlet sections are coextensive with each other and served by a perpendicularly extending atmospheric inlet opening  53 . A side branch device  34  having a control valve  36  is positioned so that its opening  35  extends in facing relationship to the inlet opening  53  and thus amplified the sound for both banks of the engine, in accordance with the aforenoted principal.  
         [0045]    [0045]FIG. 4 shows another embodiment, having a construction generally like the embodiment of FIG. 1 but in this embodiment the side branch device, indicated here by the reference numeral  61 , has an effective length that can be varied. This includes a fixed tube portion  62  which is cylindrical and has its opening  63  facing the inlet opening  26  of the inlet device  25 .  
         [0046]    A closed end cylindrical member  64  is slideably supported on the outer portion of the tube  62  and is actuated by a servo motor  65  through a rack  66  and pinion  67  so as to vary the length indicated by the arrow L and thus, provide tuning for amplifying varying frequencies. The frequency can be changed in accordance with engine speed or any other desired parameter.  
         [0047]    Generally, the concept would be that the length or volume is increased as the engine speed decreases and decreased as the engine speed increases. Of course, variations can be made depending upon what effect is desired.  
         [0048]    [0048]FIG. 5 is another embodiment utilizing a sound amplifying device, indicated generally by the reference numeral  71  which, has its effective length variable. This includes a closed ended tubular section  72  having an opening  73  that faces the opening  26  of the inlet device  25 .  
         [0049]    A feed screw  74  passes through the end wall  75  of the tube  74  and carries a cylindrical member  76  having a cross sectional area equal to that of the tube. A servo motor  77  operates a drive nut  78  so as to cause the member  76  to be moved in the direction of the arrow L to change the effective length of the device  71 . Typically the length will be decreased as the engine speed is increased.  
         [0050]    [0050]FIG. 6 is a partial view, in part similar to FIGS. 4 and 5, and shows another embodiment of side branch type amplifying devices, indicated generally by the reference numeral  81 . Again, this includes a closed ended tube  82  having an opening  83  that faces the inlet opening  26  of the air inlet device  25  of the engine.  
         [0051]    A moveable wall  84  is positioned within the tube  82  and is urged by a spring  84  in a direction to decrease the effective length of the tube  82 . A servo motor  86  drives a flexible transmitter  87  that extends through an end wall  88  of the tube  81  so as to position the wall  84  in position along the length L so as to vary the effective length of the device. Again, the position can be varied in response to engine speed so as to provide the desired sound amplification in the induction system.  
         [0052]    All of the embodiments as thus far described utilize side branch type tubes. FIG. 7 is a partial view in part similar to FIGS. 2 and 4 through  6 , and shows an adjustable Helmholtz device, indicated generally by the reference numeral  91 . This Helmholtz device includes a tube section  92  having an opening  93  which faces the opening  26  of the inlet pipe  25  and the atmosphere. The tube  92  has an enlarged portion  93  over which a cylindrical member  94  is slideably positioned. A servo motor  95  drives the cylindrical member  94  through a rack  96  and pinion  95  so as to vary the volume of the resonating chamber  98  and thus, change the amplified frequencies in accordance with the aforenoted equation.  
         [0053]    It should be understood also that the length of the tube  92  can be adjusted by utilizing mechanisms of the types shown in FIG. 4 except that in this instance the closed end wall  64  will not be provided. That is, both the length of the tube  92  and volume of the chamber  98  may be adjusted to provide a wider range of sound amplifying effects.  
         [0054]    [0054]FIG. 8 is a schematic view of another embodiment of the invention that is utilized with a four cylinder inline engine having an engine body  23  as shown in FIG. 1. However, in this instance, the sound amplifying acoustical system is provided in the engine exhaust system, indicated generally by the reference numeral  101 .  
         [0055]    The engine exhaust system  101  includes an exhaust manifold  102  having pipe sections  103  each of which communicates with a respective one of the exhaust ports of the engine. The exhaust gases then may flow through a catalytic converter  104  of any known type to a sub-silencer  105  positioned in an exhaust pipe  106 .  
         [0056]    At the end of the exhaust pipe  106  is provided a main muffler  107  that is provided with any desired type of internal baffling and silencing system. The muffler  107  has an outlet pipe  108  having an outlet opening  109  which communicates with and faces the atmosphere.  
         [0057]    Positioned in this outlet pipe  108  is a side branch tube  111  which has a closed end wall  112  and an atmospheric facing opening  113  which is positioned coaxially within the outlet tube  108  and faces its atmospheric opening  109 .  
         [0058]    [0058]FIG. 9 shows another embodiment of the invention which is generally similar to the embodiment of FIG. 8 and thus, this is shown in only a partial figure. In this embodiment, components which are the same as those previously described have been identified by the same reference numerals.  
         [0059]    The side branch tube,  121  in this embodiment, extends into the interior of the main muffler  101  and has a closed end wall  122  positioned therein. Its atmospheric facing opening  123  faces the atmospheric opening  109  of the outlet tube  108  and thus functions in the manner as thus previously described.  
         [0060]    [0060]FIG. 10 shows another embodiment of the invention which is generally similar to FIGS. 8 and 9 but which embodies a Helmholtz resonator  131  which is positioned within the rear portion of the main muffler  107 . The Helmholtz resonator  131  has a chamber  132  which communicates with the atmosphere through a tube section  134 . The tube section  134  has, in this embodiment, an L shape so that its atmospheric opening  135  will face the atmospheric opening  109  of the exhaust outlet tube  108 .  
         [0061]    [0061]FIG. 11 shows a further arrangement for positioning in the outlet tube  108  of the main muffler which is not shown in this figure, but which has its outlet opening  109  as afore described. In this embodiment, there are provided a pair of side branch tubes  141  and  142  each of which has a closed end adjacent the muffler  107  and a respective atmospheric opening  143  and  144  facing the exhaust outlet pipe atmospheric opening  109 .  
         [0062]    It should be understood that the afore described arrangements for varying the length of the side branch tubes and either the tube or volume of the Helmholtz resonator as previously described may be employed in the exhaust side of the system.  
         [0063]    If desired, the diameter of inlet opening of the branch tube can be adjusted so as to change the sound effect and this can be done in the embodiment of FIG. 11 as shown in FIG. 12 wherein the diameter of the tubes  143  and  144  are changed in response to engine speed changes.  
         [0064]    In addition, the lengths can be changed as shown in FIG. 13 also in response to changes in speed to obtain the desired effect. The effect of this type of arrangement relative to the prior art can be understood by a comparison of FIG. 14, which shows the invention, with FIG. 15, which shows the prior art type of arrangement. It is desired in this specific embodiment to obtain amplification in the range of about 260 Hz. As may be seen in FIG. 14 as compared with FIG. 15, the sound in this range is maintained fairly constant at all engine speeds while in the prior art type of construction, there is little concentration of the sound at this particular range except at extremely high engine speed. Of course, this can be done to improve the sound at other frequencies than those in the range of about 260 Hz.  
         [0065]    [0065]FIG. 16 shows how the inventive arrangement as shown in the curve A can provide significant increases in various speed ranges over the conventional system as indicated by the curve B. Again, the peaks occur at the desired frequencies and are considerably higher than those in the prior art.  
         [0066]    Therefore, in accordance with the described embodiments it is possible to obtain the desired sounds in either or both of the intake and exhaust systems by amplifying the desired frequencies, rather than by attempting to dampen all of the other or undesired frequencies. This provides a significant simplification and permits the obtainment of a result over a wider range of engine operating conditions. Of course, the foregoing description is that of preferred embodiments of the invention and various changes and modifications may be made without departing from the spirit and scope of the invention, as defined by the appended claims.