Abstract:
An engine cover mounted to an internal combustion engine of an automobile etc. includes a rigid cover body made of a resin or metal and covering an engine, a foamed member fixed to an inner face of the cover body and including at least a part spaced from the engine, and a plurality of corrugations formed on the part of the foamed member spaced from the engine.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates generally to an engine cover mounted on internal combustion engines of automobiles or the like, and more particularly to such an engine cover including a rigid cover body made from a resin or metal and covering an engine, and a foamed member fixed to an inner face of the cover body.  
           [0003]    2. Description of the Related Art  
           [0004]    JP-A-2002-28934 discloses one of conventional engine covers of the above-described type. The disclosed engine cover comprises a cover body made of a resin or metal and a foamed member fixed to a back side or inner face of the cover body. The foamed member has a configuration conforming to an outer surface of the engine and is pressed onto the outer surface of the engine. However, the above-described conventional engine cover cannot achieve a sufficient sound reduction.  
         SUMMARY OF THE INVENTION  
         [0005]    Therefore, an object of the present invention is to provide an engine cover which can effectively reduce sound produced by the engine.  
           [0006]    The present invention provides an engine cover comprising a rigid cover body made of a resin or metal and covering an engine, a foamed member fixed to an inner face of the cover body and including at least a part thereof spaced from the engine, and a plurality of corrugations formed on the part of the foamed member spaced from the engine.  
           [0007]    A sound-absorbing area of the engine cover is increased with increase in a surface area of the foamed member since the foamed member is formed with a plurality of corrugations. Consequently, sound produced by the engine can effectively be reduced. Further, since a part of the foamed member is spaced from the engine, a space is defined between the foamed member and the engine. Consequently, sound produced by the engine can be damped by air in the space.  
           [0008]    In a preferred form, the corrugations are disposed on an inner face of the expanded portion so that the space is defined between the foamed member and the engine.  
           [0009]    In another preferred form, a difference between a ridge of each protrusion and a trough between said each protrusion and the adjacent protrusion is set at a quarter of a wavelength of the predetermined sound, the quarter being multiplied by any integer. The predetermined sound interferes with sound reflected on the corrugations thereby to deny each other. Consequently, the predetermined sound can effectively be reduced.  
           [0010]    In further another preferred form, the engine cover includes a wall standing from an edge of the foamed member so as to extend toward the engine. Since the sound-leakage preventing wall restrains sound produced by the engine from leaking outside the foamed member, the sound produced by the engine can effectively be reduced.  
           [0011]    Additionally, in further another preferred form, the cover body includes a rib projecting toward the engine from a peripheral edge of the expanded portion on an inner face thereof. The rib can improve the rigidity of the cover body. The improvement in the rigidity of the cover body can restrain the engine cover from vibrating due to vibration produced by the engine. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    Other objects, features and advantages of the present invention will become clear upon reviewing the following description of embodiments, made with reference to the accompanying drawings, in which:  
         [0013]    [0013]FIG. 1 is a plan view of an engine cover in accordance with one embodiment of the present invention;  
         [0014]    [0014]FIG. 2 is a sectional view of the engine cover;  
         [0015]    [0015]FIG. 3 is a rear view of the engine cover;  
         [0016]    [0016]FIG. 4 is a side view of the engine cover;  
         [0017]    [0017]FIG. 5 is a sectional view of the engine cover;  
         [0018]    [0018]FIG. 6 is a sectional view of a corrugated portion of the engine cover;  
         [0019]    [0019]FIG. 7 is a perspective view of a foamed member A;  
         [0020]    [0020]FIG. 8 is a perspective view of a foamed member B;  
         [0021]    [0021]FIG. 9 is a graph showing results of experiment 1;  
         [0022]    [0022]FIG. 10 illustrates a concept of a sound insulation evaluating apparatus;  
         [0023]    [0023]FIG. 11 is a graph showing results of experiment 2;  
         [0024]    [0024]FIG. 12 is a perspective view of a foamed member used in experiment 3; and  
         [0025]    [0025]FIG. 13 is a graph showing results of experiment 3. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0026]    One embodiment of the invention will be described with reference to FIGS.  1  to  13 . Referring to FIG. 1, an engine cover  10  in accordance with one embodiment of the present invention is shown. The shown engine cover  10  comprises a rigid cover body  11  having an inner face  12  to which a foamed member  20  made of, for example, an urethane resin is attached. The engine cover  10  is mounted to an engine  90  so as to cover an upper end of the engine. The urethane resin made into the foamed member  20  includes polyethylene terephthalate, nylon or polypropylene resin. The cover body  11  of the engine cover  10  is made of a metal such as aluminum. The cover body  11  is transversely elongated so as to conform to the engine  90  and has a front edge (a right-hand edge as viewed in FIG. 2) curved downward as shown in FIG. 2.  
         [0027]    The cover body  11  is formed with an expanded portion  14  expanded toward the side away from the engine  90 . The expanded portion  14  has a generally elliptic shape and is elongated in a lengthwise direction of the cover body  11 . The cover body  11  includes a rib  16  projecting toward the engine  90  from a peripheral edge of the expanded portion  14  on an inner face thereof. An improvement in the rigidity of the cover body  11  can restrain the engine cover  10  from vibrating due to vibration produced by the engine  90 . The cover body  11  has a pair of mounting holes  17  formed through a portion thereof in front of the expanded portion  14  for the purpose of mounting the engine cover to the engine  90 . The cover body  11  further has an oil feeding hole  18  formed therethrough so as to be located near one of the mounting holes  17 .  
         [0028]    A fixing wall  13  extends downward from a rear edge of the cover body  11  (a right-hand edge as viewed in FIG. 2) as shown in FIG. 2. The fixing wall  13  extends longer than the expanded portion  14 , and a foamed member  20  is fixed to the cover body  11  so as to extend from a front face of the fixing wall  13  to a front edge of the inner face  12  of the cover body.  
         [0029]    The foamed member  20  includes engine abutments  20 A formed on the front and rear ends (left-hand and right-end ends as viewed in FIG. 2) thereof respectively. The foamed member  20  has a configuration conforming to an outer surface of the engine  90  and is pressed against the outer surface of the engine. A middle portion of the foamed member  20  is curved toward the side opposed to the engine  90  so as to conform to the expanded portion  14  of the cover body  11 . As a result, when the engine cover  10  is mounted to the engine  90 , the middle portion of the foamed member  20  is spaced from the engine such that a space  80  is defined between the engine and the foamed member  20 .  
         [0030]    A sound-leakage preventing wall  21  protrudes from a side edge of the foamed member  20  as shown in FIG. 5. The wall  21  has a lower end abutted against the outer surface of the engine  90  so that sound produced by the engine  90  is restrained from leaking outside the foamed member  20 . The foamed member  20  includes a portion extending along the fixing wall  13  and formed with a plurality of conical holes  22  as shown in FIG. 3.  
         [0031]    The foamed member  20  includes a portion covering the expanded portion  14  of the cover body  11  and formed with a plurality of corrugations  30  curved toward the side opposed to the engine  90  so as to conform to the expanded portion  14  of the cover body  11 , as shown in FIGS. 2 and 3. The corrugations  30  include a row of triangular protrusions extending crosswise relative to the elongation of the expanded portion  14  and tapered toward a ridge line. The protrusions are arranged lengthwise with respect to the expanded portion  14  such that concave and convex portions or ridges and troughs are formed alternately lengthwise with respect to the expanded portion.  
         [0032]    A difference H between the ridge of each corrugation  30  and the trough between each corrugation  30  and the adjacent one as shown in FIG. 6 is determined on the basis of a range of sound produced by the engine  90  and targeted for noise reduction. More specifically, when reference symbol “f” designates a frequency of predetermined sound produced by the engine  90 , the difference H is a quarter of a wavelength λ of the predetermined sound obtained from the following equation:  
         λ( mm )=3.4×10 /f.    
         [0033]    In the embodiment, the difference H becomes 21 mm in order that noise reduction is directed to sound whose frequency is 4 kHz.  
         [0034]    According to the foregoing embodiment, a sound-absorbing surface area of the engine cover  10  is increased since the foamed member  20  is formed with a plurality of corrugations  30 . Consequently, sound produced by the engine  90  can effectively be reduced. Furthermore, the space  80  is defined between the corrugations  30  and the engine  90 , and the corrugations are disposed inside the expanded portion  14 . Consequently, the space  80  is increased such that sound produced by the engine  90  can be damped by air in the space  80 , whereupon sound can be reduced further effectively. Additionally, since the predetermined sound interferes with sound reflected on the corrugations thereby to deny each other, the predetermined sound can effectively be reduced.  
         [0035]    Experiment 1:  
         [0036]    The inventors conducted experiments to examine an amount of sound absorbed by the foamed member with the corrugations  30 .  
         [0037]    (1) Method of Experiment:  
         [0038]    1) The frequency of sound to be absorbed was set at 1.6 kHz and the wavelength λ was obtained from the foregoing equation;  
         [0039]    2) The difference H of the corrugations  30  was 53 mm on the basis of the obtained wavelength λ. An amount of absorbed sound was measured at every frequency regarding the foamed members A to D. The foamed member A had the corrugations  30  including a plurality of ridges and troughs formed alternately and extending in one direction as shown in FIG. 7. The corrugations  30  of the foamed member B included longitudinal corrugations and transverse corrugations formed alternately. The foamed member C had the corrugations  30  formed into a plurality of quadrangular pyramids. The foamed member D served as a blank and had no corrugations but a flat face.  
         [0040]    3) An amount of sound absorbed per frequency was graphed.  
         [0041]    (2) Experimental Results:  
         [0042]    The amounts of sound absorbed regarding the foamed members A to C are compared with reference to FIG. 9. Approximately the same amount of sound absorbed was obtained at every frequency in each foamed member. Further, when compared with the foamed member D with no corrugations, each of the foamed members A to C achieved a larger amount of sound absorbed than the foamed member D remarkably in the frequency range of 1.25 to 1.6 kHz. Thus, when the difference H is set at a quarter of the wavelength of the predetermined sound, the absorbed sound amount can particularly be increased at the frequency values of the predetermined sound and at frequency values near the frequency value of the predetermined sound.  
         [0043]    Experiment 2:  
         [0044]    The engine cover  10  of the foregoing embodiment was compared with an engine cover serving as a compared product. The foamed member of the compared product included a flat face covering the expanded portion. The compared product was the same as the engine cover  10  of the foregoing embodiment in the other respects.  
         [0045]    (1) Method of Experiment:  
         [0046]    A soundproof evaluation apparatus  40  as shown in FIG. 10 was used to measure a sound pressure level in the experiment. The apparatus  40  included a plaster container  70  in which a space S was defined by seven non-parallel sides and had an upper open end. A loud speaker  71  was disposed in the space S so as to be directed toward an opening  72  which was covered with an alloy cover  73  made from the same magnesium alloy as the upper end of the engine  90  was made from. A microphone  74  was disposed at a predetermined position above the alloy cover  73 . The following is an experimental procedure:  
         [0047]    1) Each engine cover was placed opposite the loud speaker  71  with the alloy cover  73  interposed therebetween.  
         [0048]    2) The loud speaker  71  was energized to produce sound, and a sound pressure level was measured at every frequency by a microphone  74  set at a position 300 mm above each engine cover set on the alloy cover  73 .  
         [0049]    3) The measured sound pressure levels of the compared product and the embodiment were graphed.  
         [0050]    (2) Experimental Results:  
         [0051]    When the engine cover  10  of the embodiment is compared with the compared product on the basis of the graph of FIG. 11, the sound pressure level in the embodiment is lower than or equal to that in the compared product in the overall frequency range. This reveals that the provision of the corrugations  30  on the foamed member  20  can improve the soundproof performance of the engine cover  10 . Furthermore, the difference H is set at 21 mm in the engine cover  10  of the embodiment. The sound pressure level is lower in the frequency range of 3 to 6 kHz in the engine cover  10  of the embodiment than in the compared product. This reveals that the soundproof effect can sufficiently be improved on the sound produced by the engine and having the frequency of about 4 kHz.  
         [0052]    Experiment 3:  
         [0053]    Only the shape of the corrugations  30  in experiment 2 was changed and the experimental contents were the same as those in experiment 2. More specifically, the corrugations  30  of the foamed member  20  were formed into a plurality of conical protrusions  51  as shown in FIG. 12. The difference H′ was set at 21 mm. The experiment was carried out in the same manner as in the second experiment. Consequently, as shown in FIG. 13, the soundproof effect was improved on the sound whose frequency was about 4 kHz.  
         [0054]    Each corrugation of the engine cover  10  is conical in shape in the foregoing embodiment. However, each corrugation may be formed into the shape of a pyramid such as a triangular pyramid or the shape of a hemisphere.  
         [0055]    The difference H should not be limited to the value of 21 mm. The difference H may be set at a desired value so that sound having a frequency according to the set difference H is absorbed.  
         [0056]    The foregoing description and drawings are merely illustrative of the principles of the present invention and are not to be construed-in a limiting sense. Various changes and modifications will become apparent to those of ordinary skill in the art. All such changes and modifications are seen to fall within the scope of the invention as defined by the appended claims.