Patent Publication Number: US-7219646-B2

Title: In-line multicylinder combustion engine

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention generally relates to an in-line multicylinder combustion engine for use primarily in motorcycles and, more particularly, to provide the in-line multicylinder combustion engine of a kind that is assembled compact in size with its center of gravity lowered and that a relatively large banking angle can be obtained when such combustion engine is mounted on a motorcycle. 
   2. Description of the Prior Art 
   An in-line multicylinder internal combustion engine of a large engine displacement that is mounted on motorcycles has a substantial weight and, accordingly, efforts have been made to render the motorcycle as a whole to have a lower center of gravity by installing a crankshaft at a relatively low position such that the combustion engine has a lower center of gravity. In the in-line multicylinder combustion engine of the type referred to above, the combustion engine has a relatively large width because multiple engine cylinders are arranged in-line, that is, because the multiple engine cylinders are laid transverse relative to a motorcycle frame structure, and, accordingly, where an electric generator, generally known as dynamo, is disposed on one end of the crankshaft that is positioned in a lower region of the combustion engine, the lower region of the combustion engine tends to exhibit an increased width. 
   Also, it is well known that if a cylinder bore is designed to be large in size and a piston stroke is also designed to be short, the combustion engine can provide a high rotational speed, hence a large drive output. However, the larger the cylinder bore, the greater the total width of the combustion engine. Accordingly, considering also that the electric generator is disposed on one end of the crankshaft as discussed above, it is difficult to obtain a relatively large banking angle of the motorcycle frame structure. As a result thereof, increase of the size of the cylinder bores is difficult to achieve. 
   On the other hand, the Japanese Laid-open Publication No. 58-065936, for example, discloses an in-line multicylinder combustion engine of a design in which an electric generator is disposed not on one end of the crankshaft but at a rear side of an engine cylinder. According to this known design, the total width of the combustion engine can advantageously be reduced as compared with that of the engine design in which the electric generator is disposed on one end of the crankshaft and, accordingly, a relatively large banking angle of the motorcycle can be obtained. 
   However, where the crankshaft is arranged in line with input and output shafts as shown in  FIG. 1  of the above discussed patent publication, it has been found that not only does the front-to-rear length or the longitudinal dimension of the combustion engine become great along with increase in weight thereof, but a wheelbase of the motorcycle also increases, resulting in an undesirable increase of the size and weight of the motorcycle. 
   Also, where the crankshaft and the output shaft are arranged level relative to each other with the input shaft positioned below them, the length of the combustion engine can be reduced, but the positioning of the crankshaft above the input shaft requires the electric generator, drivingly coupled with the crankshaft by means of a generally endless belt, to be positioned above the input shaft, shifting the center of gravity of the combustion engine to a higher position. With this design, setteing the center of gravity of the combustion engine at a lower position is difficult to achieve. 
   SUMMARY OF THE INVENTION 
   In view of the foregoing, the present invention is intended to provide an in-line multicylinder combustion engine of a type, in which when such a combustion engine is mounted on a motorcycle, a relatively large banking angle can be secured; and the length and the width of the combustion engine are reduced. The engine can be assembled compact in size with its center of gravity lowered; and in which mass centering occurs in the vicinity of the center of gravity of the combustion engine. 
   In order to accomplish the foregoing object of the present invention, there is provided an in-line multicylinder combustion engine which includes a crankshaft, an input shaft drivingly connected with the crankshaft through a clutch gear, an output shaft drivingly connected with the input shaft, and an electric generator. 
   The output shaft has an axis positioned above an imaginary plane containing respective axes of the crankshaft and the input shaft. Preferably, the imaginary plane containing the respective axes of the crankshaft and the input shaft lies substantially horizontally. 
   The electric generator has a drive gear and is positioned between the crankshaft and the output shaft with its axis positioned above an imaginary inclined plane containing the respective axes of the crankshaft and the output shaft. The drive gear of the electric generator is meshed with a coupling gear that is mounted on the input shaft and is constantly drivingly connected with the crankshaft. 
   Hence, according to the above structure, the positioning of the electric generator within a space defined above the plane containing the respective axes of the crankshaft and the output shaft is effective to reduce the total width of a lower region of the combustion engine as compared with the conventional layout in which the electric generator is arranged around one end of the crankshaft and, accordingly, when the combustion engine of the present invention is mounted on a motorcycle, a relatively large banking angle θ of the motorcycle relative to the road surface can be obtained. 
   Also, the input shaft, the output shaft and the crankshaft are arranged in a generally triangular layout with the crankshaft and the input shaft positioned below the level of the output shaft and, therefore, the center of gravity of the combustion engine can advantageously be lowered. Yet, not only because the total width of the combustion engine E is reduced, but also because the generally triangular layout assumed by the crankshaft, the input shaft and the output shaft affords reduction of the length of the combustion engine, the combustion engine as a whole can advantageously be assembled compact in size. In other words, comparing the combustion engine of the present invention with the conventional combustion engine for a given size of the combustion engine, the cylinder bores can have an increased diameter along with reduction in piston stroke so that a large output can be easily obtained from the combustion engine of the present invention. 
   Furthermore, since the electric generator is positioned above the plane containing the respective axes of the crankshaft and the output shaft, that is, in the vicinity of the rear surface of the cylinder block, centering of the mass, or an approach of a mass point of the generator to a mass point of the whole engine including the generator, can advantageously be accomplished, allowing the motorcycle with the combustion engine of the present invention mounted thereon to exhibit an increased overall performance. 
   Moreover, since the electric generator is of a design in which the drive gear is directly meshed with the coupling gear provided on the input shaft and is not of a type driven by a chain through sprockets, an undesirable increase of the number of component parts employed and that of the weight can advantageously be suppressed. 
   With this arrangement, both the crankshaft and the input shaft can occupy the lowest position thereby to further lower the center of gravity of the combustion engine. 
   In a preferred embodiment of the present invention, the in-line multicylinder combustion engine may also include a clutch mechanism having a clutch axis and disposed around the input shaft and positioned laterally of the combustion engine, and a starter motor having a motor axis. In this case, the electric generator and the starter motor are positioned closer to an intermediate portion of the combustion engine than the clutch mechanism, with the motor and starter longitudinal axes held radially close to each other. 
   According to this preferred design feature, not only the electric generator, but also the starter motor is positioned in the vicinity of the center of gravity of the combustion engine and, accordingly, mass centering in the combustion engine can advantageously be enhanced. 
   In another preferred embodiment of the present invention, the in-line multicylinder combustion engine may additionally include an engine casing including a cylinder block and a crankcase and made up of an upper casing component and a lower casing component, in which the crankshaft and the output shaft are positioned on a plane of joint interface between the upper and lower casing components. 
   The use of the engine casing made up of the upper and lower casing components defines a plane of joint interface between the upper and lower casing, with the crankshaft and the output shaft positioned on such plane. Accordingly, bearing holes for the crankshaft and the output shaft can easily be formed in the engine casing. 
   In a further preferred embodiment of the present invention, the coupling gear referred to above may be the clutch gear. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In any event, the present invention will become more clearly understood from the following description of preferred embodiments thereof, when taken in conjunction with the accompanying drawings. However, the embodiments and the drawings are given only for the purpose of illustration and explanation, and are not to be taken as limiting the scope of the present invention in any way whatsoever, which scope is to be determined by the appended claims. In the accompanying drawings, like reference numerals are used to denote like parts throughout the several views, and: 
       FIG. 1  is a side view of an in-line multicylinder internal combustion engine mounted on a motorcycle in accordance with a preferred embodiment of the present invention; 
       FIG. 2  is a front elevational view of the in-line multicylinder internal combustion engine; 
       FIG. 3  is a schematic side view of the in-line multicylinder internal combustion engine, showing the relationship of a crankshaft, an input shaft and an output shaft employed therein; 
       FIG. 4  is a cross-sectional view taken along the line IV—IV in  FIG. 3 ; and 
       FIG. 5  is a fragmentary sectional view of a portion of the in-line multicylinder internal combustion engine, showing the relation between an electric generator and a clutch employed therein. 
   

   DETAILED DESCRIPTION OF THE EMBODIMENTS 
   Hereinafter, a preferred embodiment of an in-line multicylinder internal combustion engine for a motorcycle in accordance with the present invention will be described in detail with reference to the accompanying drawings. Referring to  FIG. 1  showing a side view of the in-line multicylinder internal combustion engine E for the motorcycle in accordance with one preferred embodiment of the present invention, the combustion engine E is an in-line four-cylinder, four-cycle engine and is mounted on a front lower portion of a motorcycle frame structure F. This motorcycle combustion engine E includes an engine body  1 . The engine body  1  includes an engine casing EC made up of a crankcase CR, a cylinder block CY and a gear case GE. The engine casing EC is of a two-piece construction including an upper casing component C 1  and a lower casing component C 2 . The cylinder block CY, an upper half portion of the crankcase CR and an upper half portion of the gear case GE are integrally formed in the upper casing component C 1  while a lower half portion of the crankcase CR and an lower half portion of the gear case GE are integrally formed in the lower casing component C 2 . 
   A cylinder head  11  is fixedly mounted atop the cylinder block CY, and a cylinder head cover  12 , with a valve chamber defined therein, is in turn mounted fixedly on a top surface of the cylinder head  11 . An oil reservoir or oil pan  13  is secured to an undersurface of the lower casing component C 2 . As indicated above, the engine casing EC, the cylinder head  11 , the cylinder head cover  12  and the oil pan  13  altogether constitute the engine body  1 . 
   Referring particularly to  FIG. 2 , the cylinder head  11  has four exhaust ports  14  fluidly connected with respective exhaust pipes  15 . An electric generator or dynamo  30  and a starter motor  31  shown in  FIG. 1  are disposed rearward of or at the rear side of the cylinder block CY, and an oil filter/cooler unit  16  made up of an oil filter  3  and an oil cooler  4  is mounted on a lower front surface of the combustion engine E through a mounting bracket  5 . 
   The motorcycle combustion engine E also includes a crankshaft  17 , an input shaft  18  drivingly engageable with the crankshaft  17  through a clutch gear  40  as will be described later and an output shaft  19  drivingly engageable with the input shaft  18 . The input shaft  18  is a drive input shaft of a motorcycle transmission while the output shaft  19  is a drive output shaft of the motorcycle transmission. The crankshaft  17 , the input shaft  18  and the output shaft  19  are geometrically arranged in a manner as shown in  FIG. 3  when viewed from laterally of the motorcycle. Specifically, an imaginary plane H containing an axis  70  of the crankshaft  17  and an axis  80  of the input shaft  18  lies substantially horizontally with respect to a road surface R ( FIG. 2 ) while an axis  90  of the output shaft  19  is positioned at a level above the imaginary plane H. In other words, the three shafts including the input shaft  18 , the output shaft  19  and the crankshaft  17  are so arranged as to represent a generally triangular geometry, in which the imaginary plane M containing the respective axes  70  and  90  of the crankshaft  17  and the output shaft  19  is inclined forwardly downwardly with respect to the forward direction of run of the motorcycle while the input shaft  18  is positioned below the forwardly inclined imaginary plane M. 
   With the triangular geometry as described above, the crankshaft  17  is disposed at a lower level, resulting in the center of gravity G of the combustion engine E lowered. It is to be noted that the electric generator  30  is disposed at a location where it does not interfere with a reduction gear train  42  having an input gear  18   a  fixedly mounted on the input shaft  18  and an output gear  19   a  fixedly mounted on the output shaft  19 . 
   As shown in  FIG. 1 , the forwardly inclined imaginary plane M coincides with an interface at which the upper casing component C 1  and the lower casing component C 2  of the engine casing EC are jointed together, with the longitudinal axes  70  and  90  of the shafts  17  and  19  positioned on the imaginary plane M, while the electric generator  30  and the input shaft  18  are positioned in the upper casing component C 1  and the lower casing component C 2 , respectively. As shown in  FIG. 3 , a center axis of the cylinder block CY, that is, the longitudinal axis C of the cylinder block CY lies substantially perpendicular to the plane M of the joint between the upper and lower casing components C 1  and C 2 , and accordingly, cylinder bores in the cylinder block CY can advantageously easily be machined. 
     FIG. 4  illustrates a cross-sectional view taken along the line IV—IV shown in  FIG. 3 , which is depicted as extending, through the longitudinal center axis C of the cylinder block CY, along an imaginary plane H containing the respective axes  70  and  80  of the shafts  17  and  18  and also along the imaginary plane L containing the respective longitudinal axes  80  and  90  of the input and output shafts  18  and  19 . As shown in  FIG. 4 , the engine casing EC positioned below the cylinder head  11  has four cylinders  2 A,  2 B,  2 C and  2 D defining respective cylinder bores  2   a ,  2   b ,  2   c  and  2   d  and also has a crankcase CR defining four crank chambers  3   a ,  3   b ,  3   c  and  3   d , which cylinder bores  2   a  to  2   d  and crank chambers  3   a  to  3   d  are partitioned by associated partition walls  10  such that the crank chambers  3   a  to  3   d  are in communication with the cylinder bores  2   a  to  2   d.    
   Reciprocating piston  3 A,  3 B,  3 C and  3 D are reciprocatingly movably accommodated within the cylinder bores  2   a  to  2   d  of the cylinders  2 A to  2 D, respectively. A crankshaft bearing  35  is provided on a lower portion of each of the partition walls  10 . The reciprocating pistons  3 A to  3 D are drivingly connected with the crankshaft  17  through respective connecting rods  32 . 
   A starter gear  22  is mounted on one of opposite ends of the crankshaft  17 , for example, a left end thereof as viewed in  FIG. 4 , through a one-way clutch  21  and is drivingly meshed with an idle gear  23  that is positioned adjacent such starter gear  22 . The one-way clutch  21  and the starter and idle gears  22  and  23  are covered by a generally bowl-shaped cover  24 . 
   Adjacent the other end (a right end) of the crankshaft  17  there is provided a drive gear  26  that is drivingly meshed with the clutch gear  40 . A clutch mechanism  20  including the clutch gear  40  is mounted on one end of the input shaft  18  and positioned laterally of the combustion engine E. This clutch mechanism  20  is operable to selectively engage and disengage the clutch gear  40  with and from the input shaft  18 , respectively. In parallel with the input shaft  18 , the output shaft  19  engageable therewith through the reduction gear train  42  is disposed. The starter motor  31  is disposed at a location laterally of the combustion engine E at the rear of the cylinder block CY and has a drive gear  27  formed on the starter motor  31  and protruding laterally outwardly from the starter motor  31 . The drive gear  27  is drivingly connected with the crankshaft  17  through the idle gear  23 , the starter gear  22  and the one-way clutch  21 . The clutch mechanism  20  is covered by a clutch cover  28  and an output chain sprocket  29  is fixedly mounted on one end of the output shaft  19  remote from the clutch mechanism  20 . 
   Referring now to  FIG. 5 , the electric generator  30  is of a structure including a stationary shaft  50 , a drive gear  52  mounted on a tip end of the stationary shaft  50  through a bearing  51 , a base  54  for supporting a left or base end of the stationary shaft  50 , an annular coil assembly  55  fixed to the base  54  by means of a plurality of set bolts (not shown), a rotor  56  rotatably mounted around the coil assembly  55  and a casing  57  enclosing those component parts of the electric generator  30 , with the drive gear  52  and the rotor  56  coupled with each other through a coupling damper  58 . 
   The electric generator  30  is positioned closer to a widthwise intermediate portion of the combustion engine E than the clutch mechanism  20  and at the rear of the cylinder block CY The drive gear  52  of the electric generator  30  is meshed with the clutch gear  40  or a coupling gear so that the electric generator  30  can be driven at all times during revolution of the crankshaft  17 . It is to be noted that the clutch gear  40  is fixedly mounted on the input shaft  18  and is drivingly associated with the crankshaft  17  at all times. In this embodiment, the clutch gear  40  mounted on the input shaft  18  is employed as the coupling gear that transmits the rotation of the crankshaft  17  to the electric generator  30 . However, instead of the clutch gear  40 , any other gear on the input shaft  18  can be used as a coupling gear. 
   The starter motor  31  is positioned on one side of the electric generator  30  and opposite the clutch mechanism  20  in the widthwise direction of the combustion engine E. Also, the electric generator  30  and the starter motor  31  have their respective axes  30 C and  31 C so arranged radially close to each other that, when viewed from the lateral side of the combustion engine E, the electric generator  30  may overlap partly with the starter motor  31 . 
   With the combustion engine E so constructed as hereinbefore described, positioning of the electric generator  30  within a space defined above the plane M containing the respective axes  70  and  90  of the shafts  17  and  19  and between these shafts  17  and  19  is effective to reduce the total width of a lower region of the combustion engine E as compared with the conventional layout in which the electric generator  30 A is arranged around one end of the crankshaft as shown by the phantom line in  FIG. 2 . Accordingly, when the combustion engine E is mounted on a motorcycle, the relatively large banking angle θ of the motorcycle, which represents the angle of lateral tilt of the motorcycle relative to the road surface R, can be obtained as compared with the banking angle θ 1  that is obtained by the motorcycle employing such conventional layout. 
   Considering that, as shown in and described with reference to  FIG. 3 , the crankshaft  17 , the input shaft  18  and the output shaft  19  are so arranged as to occupy respective vertexes of the triangular shape, when viewed laterally of the combustion engine E, with the crankshaft  17  and the input shaft  18  positioned below the output shaft  19 , it can readily be understood that the combustion engine E can have a lowered center of gravity G. 
   Also, not only because of the reduction in the total width of the combustion engine E, but also because of reduction in length of the combustion engine E accomplished as a result of the generally triangular disposition of the shafts  17 ,  18  and  19  as discussed hereinabove, the combustion engine E as a whole can advantageously be assembled compact in size. In other words, comparing the combustion engine E with the conventional combustion engine for a given engine size, the present invention makes it possible that the cylinder bores can have an increased diameter along with reduction in piston stroke so that a large output can be easily obtained from the combustion engine E. 
   While the center of gravity G ( FIG. 1 ) of the combustion engine E is generally positioned in the vicinity of the rear surface of the cylinder block CY, the electric generator  30  is positioned above the plane M containing the respective axes  70  and  90  of the crankshaft  17  and the output shaft  19 , that is, in the vicinity of the rear surface of the cylinder block CY and is hence positioned in the vicinity of the center of gravity G of the combustion engine E. Accordingly, the mass centering in the combustion engine E can advantageously be accomplished, allowing the motorcycle with the combustion engine E to exhibit an increased performance. Also, since the electric generator  30  is of the design in which the drive gear  52  is directly meshed with the clutch gear  40  as shown in  FIG. 5  and is not of a type driven by a chain through the sprocket such as in the Japanese Laid-open Publication No. 58-065936, an undesirable increase of the number of component parts employed and that of the weight can advantageously be suppressed. 
   As shown in  FIGS. 4 and 5 , the clutch mechanism  20  including the clutch gear  40  mounted thereon is disposed laterally of the combustion engine E, the electric generator  30  and the starter motor  31  are disposed nearer a widthwise intermediate portion of the combustion engine E than the clutch gear  40 , and the electric generator  30  and the starter motor  31  have their respective axes  30 C and  31 C positioned radially close to each other in parallel with the axis  70  of the crankshaft  17 . Accordingly, not only the electric generator  30  but also the starter motor  31  is positioned in the vicinity of the center of gravity G of the combustion engine E and, therefore, the centering of the mass on and in the vicinity of the center of gravity G of the motorcycle combustion engine E can be facilitated, resulting in increase of the performance of the motorcycle employing the combustion engine E. 
   Also, considering that the engine casing EC including the engine cylinder CY and the crankcase CR is of a two-piece structure made up of the upper and lower casing components C 1  and C 2 , and the crank shaft  17  and the output shaft  19  are positioned on the plane M of the joint interface between the upper and lower casing components-C 1  and C 2 , bearing holes for the crankshaft  17  and the output shaft  19  can easily be formed in the engine casing EC. 
   Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings which are used only for the purpose of illustration, those skilled in the art will readily conceive numerous changes and modifications within the framework of obviousness upon the reading of the specification herein presented of the present invention. By way of example, considering that the drive gear  52  of the electric generator  30  shown in  FIG. 5  may be engaged with any coupling gear mounted on the input shaft  18  and constantly drivingly associated with the crankshaft  17 , this coupling gear may not be always the clutch gear  40 , but may be either formed integrally with the clutch gear  40  or any other gear separate from the clutch gear  40 . Also, although the imaginary plane H containing the respective axes  70  and  80  of the crankshaft  17  and the input shaft  18  lies substantially horizontally in the foregoing embodiment, in some cases, the imaginary plane H may be inclined relative to a horizontal plane or the road surface R. 
   Accordingly, such changes and modifications are, unless they depart from the scope of the present invention as delivered from the claims annexed hereto, to be construed as included therein.