Abstract:
A counterbalancing shaft accommodating structure includes: a pair of counterbalancing shafts, provided in an oil pan attached to a lower end portion of an engine; and a housing, adapted to accommodate the counterbalancing shafts in the oil pan. An upper end portion of the housing is provided further upwards than the lower end portion of the engine. An opening is formed continuously to expand over both rotational axes of the pair of counterbalancing shafts in an upper surface of the housing.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to a counterbalancing shaft accommodating structure which is suitable for use in a motor vehicle engine. 
         [0002]    There has been known a technique which uses counterbalancing shafts as one of techniques for absorbing vibrations of a reciprocating engine (hereinafter, referred to simply as an engine). 
         [0003]    In addition, there has also been known a structure in which the counterbalancing shafts are provided within an oil pan which is provided on a lower side of the engine, and a structure like this is disclosed in JP-A-2005-36872 below. 
         [0004]    However, when the counterbalancing shafts are provided within the oil pan, there occurs a situation in which the counterbalancing shafts stir oil within the oil pan. As this occurs, there may appear a situation in which a phenomenon is caused in which air bubbles are generated in oil (so-called aeration) or a loss of drive torque of the engine is caused. 
         [0005]    Incidentally, in the technique in JP-A-2005-36872, as is shown in FIG. 4 of the same document, a structure is disclosed in which balance shafts (counterbalancing shafts) (44, 45) are accommodated within an upper housing (42) and a lower housing (43). 
         [0006]    A plurality of openings (to which no reference numeral is imparted) are formed in the upper and lower housings (42, 43) in the technique of JP-A-2005-36872. Namely, it is not that the upper and lower housing (42, 43) are sealed hermetically. 
         [0007]    Because of this, in the technique of JP-A-2005-36872, even though the balance shafts (44, 45) are accommodated within the upper and lower housings (42, 43), oil flows into the interior of the upper and lower housings (42, 43), and the oil continues to be stirred by the balance shafts (44, 45), leading to a problem that the aeration of the oil or the torque loss is caused. 
         [0008]    In addition, in general, the use of counterbalancing shafts increases the size of an engine. Note that in the technique of JP-A-2005-36872, although the engine is considered to be made small in size to some extent by providing the balance shafts (44, 45) within the oil pan, there are still demands for smaller engines. 
       SUMMARY 
       [0009]    It is therefore an object of the invention to provide a counterbalancing shaft accommodating structure which can contribute to realizing a small engine while suppressing the occurrence of oil aeration and torque loss. 
         [0010]    In order to achieve the object, according to the invention, there is provided a counterbalancing shaft accommodating structure, comprising: 
         [0011]    a pair of counterbalancing shafts, provided in an oil pan attached to a lower end portion of an engine; and 
         [0012]    a housing, adapted to accommodate the counterbalancing shafts in the oil pan, wherein 
         [0013]    an upper end portion of the housing is provided further upwards than the lower end portion of the engine, and 
         [0014]    an opening is formed continuously to expand over both rotational axes of the pair of counterbalancing shafts in an upper surface of the housing. 
         [0015]    Edge portions of the opening may be substantially equal in height to upper ends of outermost rotational loci of the counterbalancing shafts. 
         [0016]    Edge portions of the opening may be offset further inwards towards a center of the housing than side edge portions of the housing, respectively. 
         [0017]    The housing may have side wall portions which are formed curvedly in such a manner as to follow outermost rotational loci of the counterbalancing shafts. 
         [0018]    The counterbalancing shaft accommodating structure may further include a journal portion that extends in a direction, which intersects both the rotational axes of the counterbalancing shafts at right angles, in the housing, and that supports rotatably the counterbalancing shafts. The opening may be partitioned into at least two areas by the journal portion. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is an exemplary perspective view as downwardly viewed which shows an overall configuration of a counterbalancing shaft accommodating structure according to an embodiment of the invention. 
           [0020]      FIG. 2  is an exemplary front view of the counterbalancing shaft accommodating structure according to the embodiment of the invention, as viewed from a direction indicated by an arrow II shown in  FIG. 1 . 
           [0021]      FIG. 3  is an exemplary perspective view as upwardly viewed which shows the overall configuration of the counterbalancing shaft accommodating structure according to the embodiment of the invention. 
           [0022]      FIG. 4  is an exemplary top view which shows the overall configuration of the counterbalancing shaft accommodating structure according to the embodiment of the invention. 
           [0023]      FIG. 5  is an exemplary sectional view of the counterbalancing shaft accommodating structure according to the embodiment of the invention which is sectioned along the line V-V in  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0024]    Hereinafter, a counterbalancing shaft accommodating structure according to an embodiment of the invention will be described based on the drawings. 
         [0025]    As is shown in  FIG. 1 , a motor vehicle engine  10  is configured to have a cylinder head  11  and a cylinder block  12 . An oil pan  14  is, as is shown in  FIG. 2 , provided at a lower end portion  13  of the cylinder block  12 . 
         [0026]    In addition, a counterbalancing unit  15  is provided within the oil pan  14  for reducing the vibration of the engine  10 . 
         [0027]    In addition, as is shown in  FIGS. 3 and 4 , this counterbalancing unit  15  includes a drive-side shaft  1 G, a driven-side shaft  17  and a housing  19 . Note that these drive-side shaft  16  and driven-side shaft  17  are both those called counterbalancing shafts. 
         [0028]    A sprocket, not shown, is provided at a front end portion  25  of the drive-side shaft  16 , and this sprocket is mechanically connected to a crankshaft (whose illustration is omitted) of the engine  10  via a chain, not shown. 
         [0029]    Additionally, a drive gear  26  is provided on the drive-side shaft  16 , and a driven gear  27  is provided on the driven-side shaft  17 . These drive gear  26  and driven gear  27  mesh with each other, so that the rotation of the drive-side shaft  16  is made to be transmitted to the driven-side shaft  17 . 
         [0030]    An A balancer weight  21  and a B balancer weight  22  are provided on the drive-side shaft  16 . 
         [0031]    On the other hand, the driven-side shaft  17  has a length which is shorter than the drive-side shaft  16 , and a C balancer weight  23  and a D balancer weight  24  are provided on the driven-side shaft  17 . 
         [0032]    As is shown in  FIG. 5 , the A balancer weight  21  and the B balancer weight  22  have a substantially semi-circular cross section, and a center of gravity G 21  of the A balancer weight  21  and a center of gravity G 22  of the B balancer weight  22  are provided eccentrically with a rotational axis C 16  of the drive-side shaft  16 . 
         [0033]    Similarly, the C balancer weight  23  and D balancer weight  24  also have a substantially semi-circular cross section, and a center of gravity G 23  of the C balancer weight  23  and a center of gravity G 24  of the D balancer weight  24  are provided eccentrically with a rotational axis C 17  of the driven-side shaft  17 . 
         [0034]    The housing  19  includes an upper housing  28  and a lower housing  29 , and the upper housing  28  and the lower housing  29  are fastened together with fastening bolts  31 . 
         [0035]    In addition, fixing bolt holes  32  are formed in the upper housing  28 , as is shown in  FIG. 4 . 
         [0036]    Then, although not shown, fixing bolts are passed through these fixing bolt holes  32 , whereby the upper housing  28  is fixed to the cylinder block  12  from therebelow with the fixing bolts. 
         [0037]    As is shown in  FIG. 1 , provided on the lower housing  12  are a lower front end drive journal  33 , a lower intermediate drive journal  34  and a lower rear end drive journal  35 , as well as a lower front end driven journal  36  and a lower rear end driven journal  37 . These five journals  33  to  37  all extend in a direction which intersects the rotational axis C 16  of the drive-side shaft  16  and the rotational axis C 17  of the driven-side shaft  17  at right angles. 
         [0038]    The lower front end drive journal  33  is a bearing which supports rotatably an area of the drive-side shaft  16  which lies near the front end portion  25  from therebelow. 
         [0039]    The lower intermediate drive journal  34  is a bearing which supports rotatably an area of the drive-side shaft portion  16  which lies near the A balancer weight  21  between the front end portion  25  and the A balancer weight  21  of the drive-side shaft  16  from therebelow. 
         [0040]    The lower rear end drive journal  35  is a bearing which supports rotatably an area of the drive-side shaft  16  which lies between the A balancer weight  21  and the B balancer weight  22  from therebelow. 
         [0041]    In addition, the lower front end driven journal  36  is a bearing which supports rotatably an area of the driven-side shaft  17  which lies near the C balancer weight  23  between a front end portion  38  and the C balancer weight  23  from therebelow. 
         [0042]    The lower rear end driven journal  37  is a bearing which supports rotatably an area of the driven-side shaft  17  which lies between the C balancer weight  23  and the D balancer weight  24  from therebelow. 
         [0043]    On the other hand, as is shown in  FIG. 4 , provided on the upper housing  28  are an upper front end drive journal  41 , an upper intermediate drive journal  42  and an upper rear end drive journal  43  which each extend in a direction which intersects the rotational axis C 16  of the drive-side shaft  16  at right angles, as well as, an upper front end driven journal  44  and an upper rear-end driven journal  45 . Note that all the five journals  41  to  45  provided on the upper housing  28  extend in the direction which intersects the rotational axis C 16  of the drive-side shaft  16  and the rotational axis C 17  of the driven-side shaft  17  at right angles. 
         [0044]    The upper front end drive journal  41  is a journal which supports rotatably an area of the drive-side shaft  16  which lies near the front end portion  25  from thereabove in a position which confronts the lower front end drive journal  33 . 
         [0045]    The upper intermediate drive journal  42  is a bearing which supports rotatably an area of the drive-side shaft portion  16  which lies near the A balancer weight  21  between the front end portion  25  and the A balancer weight  21  of the drive-side shaft  16  from thereabove in a position which confronts the lower intermediate drive journal  34 . 
         [0046]    The upper rear end drive journal  43  is a bearing which supports rotatably an area of the drive-side shaft  16  which lies between the A balancer weight  21  and the B balancer weight  22  from thereabove in a position which confronts the lower rear end drive journal  35 . 
         [0047]    In addition, the upper front end driven journal  44  is a bearing which supports rotatably an area of the driven-side shaft  17  which lies near the C balancer weight  23  between the front end portion  38  and the C balancer weight  23  from thereabove in a position which confronts the lower front end driven journal  36 . 
         [0048]    The upper rear end driven journal  45  is a bearing which supports rotatably an area of the driven-side shaft  17  which lies between the C balancer weight  23  and the D balancer weight  24  from thereabove in a position which confronts the lower rear end driven journal  37 . 
         [0049]    In addition, as is shown in  FIG. 4 , an opening  53  is formed in an upper surface of the upper housing  28 . 
         [0050]    The opening  53  is an opening which expands continuously over both the rotational axis C 1  of the drive-side shaft  16  and the rotational axis C 17  of the driven-side shaft  17  and is made to discharge oil that has flowed into an interior of the housing  19  for atomization. 
         [0051]    In addition, the opening  53  is partitioned into a first area  51  and a second area  52  by the upper rear end drive journal  43  and the upper rear end driven journal  45 . 
         [0052]    The first area  51  of the opening  53  is formed into a quadrangle above the A balancer weight  21  and the C balancer weight  23 . 
         [0053]    The second area  52  of the opening  53  is formed into a quadrangle above the B balancer weight  22  and the D balancer weight  24 . 
         [0054]    Consequently, oil is discharged from the interior of the housing  19  through the first area  51  of the opening  53  in association with the rotation of the A balancer weight  21  and the C balancer weight  23 , and oil is discharged from the interior of the housing  19  through the second area  52  of the opening  53  in association with the rotation of the B balancer weight  22  and the D balancer weight  24 . 
         [0055]    In addition, as viewed from the top, that is, in a condition shown in  FIG. 4 , one edge portion  54  of the opening  53  is offset further inwards towards a center of the housing  19  by a predetermined distance L than one edge portion  55  of the housing  19 , and the other edge portion  56  of the opening  53  is offset further inwards towards the center of the housing  19  by the predetermined distance L than the other edge portion  57  of the housing  19 . 
         [0056]    In addition, as is shown in  FIG. 5 , both the edge portions  54 ,  56  of the opening  53  are substantially equal in height to an upper end of an outermost rotational locus D 16  of the drive-side shaft  16  and an upper end of an outermost rotational locus D 17  of the driven-side shaft  17 . 
         [0057]    Additionally, the upper surface of the upper surface of the upper housing  28  is formed substantially flat. 
         [0058]    As is shown in  FIG. 5 , the upper housing  28  has side wall portions  46 ,  47  which are each formed curvedly in such a manner as to follow the outermost rotational locus D 16  of the drive-side shaft  16  and the outermost rotational locus D 17  of the driven-side shaft  17 . 
         [0059]    In addition, as is shown in  FIG. 2 , an upper end portion of the upper housing  28  is provided further upwards than the lower end portion  13  of the cylinder block  12 . 
         [0060]    A drive-side shaft working hole  58  and a driven-side shaft working hole  59  are opened in a rear wall portion  48  of the counterbalancing unit  15  which includes a rear wall portion  48 A of the upper housing  28  and a rear wall portion  48 B of the lower housing  29 . These drive-side shaft working hole  58  and driven-side shaft working hole  59  are formed in such a manner as to communicate with each other. 
         [0061]    In addition, by providing the drive-side shaft working hole  58  and the driven-side shaft working hole  59 , the working mechanic is allowed to carry out maintenance work on the drive-side shaft  16  and the driven-side shaft  17  through the drive-side shaft working hole  58  and the driven-side shaft working hole  59  without removing the counterbalancing unit  25  from the engine  10 . 
         [0062]    Note that a rib can be formed on the lower housing  29  in such a manner as to extend in parallel with the rotational axis C 16  of the drive-side shaft and the rotational axis C 17  of the driven-side shaft  17 . By forming the rib in that way, the rigidity of the lower housing  29  can be increased further. 
         [0063]    Since the counterbalancing shaft accommodating structure according to the embodiment of the invention is configured as has been described heretofore, the following functions and advantages will be provided. 
         [0064]    As is shown in  FIG. 2 , since the counterbalancing unit  15  is provided in such a manner that the upper end portion of the upper housing  28  is positioned further upwards than the lower end portion  13  of the engine  10 , a relatively long distance between the opening  53 , the drive-shaft side working hole  58  and the driven-side shaft working hole  59  and oil in the oil pan  14  can be secured, whereby it is made hard for oil to flow into the interior of the housing  19 . In addition, by locating the counterbalancing unit  15  in the upper position which is higher than those in the related-art structures, the height of the engine  10  can be suppressed. 
         [0065]    In addition, as is shown in  FIG. 4 , since the opening  53  which is formed in the upper housing  28  is formed as the opening which expands continuously over both the rotational axes C 16 , C 17  of the counterbalancing shafts  16 ,  17 , oil that has flowed into the interior of the housing  19  can be discharged from the interior of the housing  19  in a promoted fashion, thereby making it possible to prevent the occurrence of a situation in which oil continues to be stirred within the housing  19 . 
         [0066]    Consequently, the counterbalancing shaft accommodating structure of the invention can contribute to the reduction in size of the engine  10  while preventing the aeration of oil and suppressing the torque loss of the engine  10 . 
         [0067]    In addition, by forming the one edge portion  54  of the opening  53  in such a manner as to be substantially equal in height to the upper end of the outermost rotational locus D 16  of the drive-side shaft  16 , the enlargement of the engine  10  can be prevented while allowing the oil in the housing  19  to be discharged with good efficiency. 
         [0068]    In addition, as is shown in  FIG. 4 , since the one edge portion  54  of the opening  53  is formed in such a manner as to be offset further inwards towards the center of the housing  19  by the predetermined distance L than the one edge portion  55  of the housing and the other edge portion  56  of the opening  53  is formed in such a manner as to be offset further inwards towards the center of the housing  19  by the predetermined distance L the other edge portion of the housing  19 , the flow of oil into the interior of the housing  19  from the sides of the housing  19  can be prevented. 
         [0069]    Additionally, as is shown in  FIG. 5 , the side wall portion  46  is provided on the housing  19  which is formed curvedly in such a manner as to follow the outermost rotational locus D 16  of the drive-side shaft  16  and the side wall portion  47  is also formed thereon which is formed curvedly in such a manner as to follow the outermost rotational locus D 17  of the driven-side shaft  17 . Consequently, while preventing the enlargement of the housing  19 , the opening  53  can be prevented from being expanded too largely, so as to prevent the flow of oil into the interior of the housing  19 . 
         [0070]    In addition, since the opening  53  is partitioned into the first area  51  and the second area  52  by the upper rear end drive journal  43  and the upper rear end driven journal  45 , the reduction in rigidity of the housing  19  can be suppressed. 
         [0071]    Additionally, the A balancer weight  21  and the C balancer weight  23  which are provided below the first area  51  and the B balancer weight  22  and the D balancer weight  24  which are provided below the second area  52  are, as is shown in  FIG. 5 , each formed to have the substantially semi-circular cross section, and the oil in the housing  19  can be discharged to the outside of the housing  19  through the first area  51  and the second area  52  by the rotation of the C balancer weight  23  and the D balancer weight  24 . 
         [0072]    Then, with the first area  51  and the second area  52  of the opening  53  which contribute largely to the discharge of oil from the interior of the housing  19  kept open, the rigidity of the housing  19  is attempted to be increased by the upper rear end drive journal  43  and the upper rear end driven journal  45 . 
         [0073]    Namely, the area of the drive-side shaft  16  which is supported by the upper rear end drive journal  43  and the area of the driven-side shaft  17  which is supported by the upper rear end driven journal  45  are each formed into a substantially true circle, the contribution thereof to the discharge of oil in the housing  19  is relatively low. Because of this, even though the portions of the opening  53  which contribute less to the discharge of oil are covered in a restricted fashion, the covering of the areas in question does not interrupt the discharge of oil from the interior of the housing  19 . 
         [0074]    In addition, as is shown in  FIG. 5 , since the upper surface of the upper housing  28  is formed substantially flat, a distance to a bottom portion  14 A of the oil pan  14  can be secured largely when the counterbalancing unit  15  is fixed to the cylinder block  12  of the engine  10 . Consequently, the suppression of an oil flow into the interior of the housing  19  can be enabled. 
         [0075]    Thus, while the embodiment of the invention has been described heretofore, the invention is not such as to be limited to the embodiment and hence, in carrying out the invention, the invention can be changed or modified variously without departing from the spirit and scope thereof.