Abstract:
An internal combustion engine includes a piston ( 2 ) and a crankshaft ( 33 ). The crankshaft ( 33 ) includes: a journal ( 33 A) as a rotation center; a crank pin ( 33 B) that is located eccentrically with respect to the journal ( 33 A) and rotates integrally with the journal ( 33 A), the crank pin ( 33   b ) connecting the piston ( 2 ) to the crankshaft ( 33 ); and a counter weight ( 33 C) that is located eccentrically with respect to the journal ( 33 A) in a direction opposite to the crank pin ( 33 ) and rotates uniformly with the journal ( 33 A). A cutout ( 11 ) through which the counter weight ( 33 C) passes is formed in a wall ( 1 ) of a cylinder bore that accommodates the piston ( 2 ) so as to be free to move reciprocally along the wall ( 1 ). As a result, the bottom dead center position of the piston can be lowered, and the overall height of the engine can be decreased.

Description:
FIELD OF THE INVENTION 
   This invention relates to reduction of the height of an internal combustion engine. 
   BACKGROUND OF THE INVENTION 
   JP 11-343802 A, published by the Japan Patent Office in 1999, discloses an internal combustion engine in which crankshaft counter weights are disposed on an outer side of a cylinder bore. By disposing the counter weights in this manner, the counter weights will not interfere with a piston. It is thus possible to shorten the distance between a piston pin and the crankshaft, and to reduce the height of the internal combustion engine. 
   SUMMARY OF THE INVENTION 
   In order to dispose counter weights on an outer side of a cylinder bore, the axial distance from a connecting rod connecting part of a crankshaft to the counter weight must be set larger than the radius of the cylinder bore. However, when the distance from the connecting rod connection part to the counter weight becomes large, a bending force acting on the crankshaft increases when an engine rotates at high speed. This is not a structurally preferable operating environment. 
   It is therefore an object of this invention to reduce the height of an internal combustion engine without increasing the distance from a connecting rod connection part to a counter weight. 
   In order to achieve the above object, this invention provides an internal combustion engine which comprises a piston, a crankshaft connected to the piston and comprising a journal as a rotation center, a crank pin located eccentrically with respect to the journal and rotating together with the journal, the piston being connected to the crankshaft via the crank pin, and a counter weight located eccentrically with respect to the journal in a direction opposite to the crank pin and rotating together with the journal, and a cylinder bore accommodating the piston such that the piston is free to reciprocate along a wall of the cylinder bore, the wall of the cylinder bore having a first cutout that allows a part of the counter weight to pass-through when the piston reciprocates in the cylinder bore. 
   The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a front elevation of a piston and related members at top dead center of a multiple link internal combustion engine to which this invention is applied. 
       FIG. 2  is a side elevation of the piston and the related members as viewed from the right side of  FIG. 1 . 
       FIG. 3  is similar to  FIG. 1 , but shows a state after the piston has passed through the top dead center. 
       FIG. 4  is similar to  FIG. 1 , but shows a state where the piston is at bottom dead center. 
       FIG. 5  is a side elevation of main part of a cylinder liner according to this invention as viewed from the left side of  FIG. 1 . 
       FIG. 6  is a front elevation of main part of the cylinder liner as viewed from the same direction as in  FIG. 1 . 
       FIG. 7  is a side elevation of main part of the cylinder liner as viewed from the right side of  FIG. 1 . 
       FIG. 8  is a side elevation of the piston as viewed from the left side of  FIG. 1 . 
       FIG. 9  is a front elevation of the piston as viewed from the same direction as in  FIG. 1 . 
       FIG. 10  is a side elevation of the piston as viewed from the right side of  FIG. 1 . 
       FIG. 11  is a side elevation of the piston and the related members as seen from the left side of  FIG. 3 . 
       FIG. 12  is a side elevation of the piston and the related members as seen from the left side of  FIG. 4 . 
       FIG. 13  is a side elevation of the piston and the related members as seen from the right side of  FIG. 4 . 
       FIG. 14  is similar to  FIG. 5 , but shows a second embodiment of this invention. 
       FIG. 15  is similar to  FIG. 6 , but shows the second embodiment of this invention. 
       FIG. 16  is similar to  FIG. 7 , but shows the second embodiment of this invention. 
       FIG. 17  is a diagram corresponding to  FIG. 16 , for explaining a relationship between a cylinder liner and a lower link at top dead center of a piston according to the second embodiment of this invention. 
       FIG. 18  is a diagram corresponding to  FIG. 16 , for explaining a relationship between the cylinder liner and the lower link at bottom dead center of the piston according to the second embodiment of this invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to  FIG. 1  of the drawings, an internal combustion engine  10  is a multiple link engine in which a piston  2  and a crankshaft  33  are connected by two links, an upper link  41  and a lower link  42 . The structure of a multiple link engine is known in U.S. Pat. No. 6,505,582 B, and is explained simply below. 
   Under a combustion pressure, the piston  2  moves reciprocally within a cylinder liner  1  inserted into a cylinder block. The cylinder liner  1  corresponds to a wall of a cylinder bore in the Claims. 
   An upper end of the upper link  41  connects to the piston  2  through a piston pin  31 , and a lower end of the upper link  41  connects to a lower link  42  through a first connecting pin  32 . 
   The lower link  42  includes a first member  42 A and a second member  42 B. The first member  42 A and the second member  42 B are tightened securely together by bolts  42 C. A crank pin  33 B of the crankshaft  33  is disposed in a center connection hole formed by the first member  42 A and the second member  42 B. The lower link  42  rotates about the crank pin  33 B. 
   Referring to  FIG. 2 , an outer end of the first member  42 A is divided into two branches, forming a U-shape, and connects on an inner side thereof to the upper link  41 . A first connecting pin  32  thus passes through the upper link  41  and latches onto the two branches of the first member  42 A. The first member  42 A corresponds to a two-branch member in the Claims. An outer end of the second member  42 B is divided into two branches, forming a U-shape, and connects on an inner side thereof to a control link  43 . A second connecting pin  34  thus passes through the control link  43  and latches the control link  43  onto the two branches of the second member  42 B. 
   Referring to  FIG. 2 , the crankshaft  33  includes one pair of journals  33 A, the crank pin  33 B, and one pair of counter weights  33 C for one cylinder liner  1 . The crankshaft  33  rotates about the journals  33 A. Referring to  FIG. 1 , the rotation center of the crankshaft  33  is disposed on a side opposite to the first connecting pin  32 , sandwiching a cylinder center axis L 1 . Referring to  FIG. 4 , the positions of the journals  33 A are determined in advance so that the rotating counter weights  33 C do not collide with a left side wall of the cylinder liner  1 . The crank pin  33 B joins the one pair of counter weights  33 C together. Again referring to  FIG. 1 , the crank pin  33 B is decentered from the journals  33 A by a fixed amount. The piston  2  moves reciprocally in an inner part of the cylinder liner  1 , through the lower link  42 , when the crankshaft  33  rotates. 
   The control link  43  is connected to a control shaft  35  so as to be free to rock. Further, the control link  43  is connected to the second member  42 B of the lower link  42  by the second connecting pin  34  so as to be free to rotate. The control link  43  functions to regulate the movement of the lower link  42  and to control the top dead center position of the piston  2 . 
   The piston  2  and the crankshaft  33  are connected through two links, the upper link  41  and the lower link  42 , in the multiple link engines  10 . Accordingly, the distance from the piston  2  to the crankshaft  33  increases, and thus the engine height tends to become large. Shortening the distance from the piston  2  to the crankshaft  33  by shortening the upper link  41  may be conceived of in order to reduce the engine height. However, the bottom dead center position of the piston  2  moves downward when the upper link  41  is shortened, and there is a fear that the counter weights  33 C will interfere with the piston  2 . Furthermore, it is also necessary to extend the wall of the cylinder liner  1  downward to be capable of guiding the movement of the piston  2 , whose bottom dead center position has moved downward. However, there is a fear that the counter weights  33 C or the lower link  42  will interfere with the extended cylinder liner  1 . 
   Description will be given below on this point. 
   In the multiple link engine  10 , the piston  2  moves from the top dead center position shown in  FIG. 1  to the state of  FIG. 3  when the crankshaft  33  rotates in the direction of an arrow r, and once again returns to the top dead center position shown in  FIG. 1  after passing through the bottom dead center position shown in  FIG. 4 . 
   When the cylinder liner  1  is extended downward and the piston  2  is in the top dead center position, there is a fear that the lower link  42  will interfere with the cylinder liner  1  in a part enclosed by a circle I in  FIG. 1 . 
   Further, when the piston  2  is in a position slightly below top dead center, there is a fear that the lower link  42  will interfere with the cylinder liner  1  in a part surrounded by a circle II in  FIG. 3 . 
   In addition, when the piston  2  is in the bottom dead center position, there is a fear that the counter weights  33 C will interfere with the cylinder liner  1  in a part surrounded by a circle III in  FIG. 4 . 
   Referring to  FIGS. 6 and 7 , a part of the right side wall of the cylinder liner  1  of  FIG. 1  is cutout in the present invention, forming counter weight pass-through parts  11 . The counter weight pass-through part  11  corresponds to a first cutout in the Claims. By thus forming the counter weight pass-through parts  11 , the counter weights  33 C will pass-through the counter weight pass-through parts  11  as shown in  FIG. 13  and not interfere with the cylinder liner  1 , even when the piston  2  is at bottom dead center. 
   Referring to  FIGS. 6 and 7 , a part of the right side wall of the cylinder liner  1  is further cutout, forming a lower link pass-through parts  12 . The lower link pass-through part  12  corresponds to a second cutout in the Claims. By thus forming the lower link pass-through parts  12 , the lower link  42  will pass-through the lower link pass-through parts  12  as shown in  FIG. 2  and not interfere with the cylinder liner  1 , even when the piston  2  is in the top dead center position. 
   Referring to  FIGS. 5 and 6 , a part of the left side wall of the cylinder liner  1  of  FIG. 1  is cutout, forming a lower link pass-through part  13 . The lower link pass-through part  13  corresponds to a third cutout in the Claims. By forming the lower link pass-through part  13 , the lower link  42  will pass-through the lower link pass-through part  13  as shown in  FIG. 11  and not interfere with the cylinder liner  1 , even when the piston  2  is in a position slightly lower than top dead center. 
   It should be noted that the rotation center of the crankshaft  33  is positioned on the right side of  FIG. 1  with respect to the cylinder center axis L 1 , and the counter weights  33 C will not collide with the left side wall of the cylinder liner  1  of  FIG. 1 , as described above. It is therefore not necessary to form a cutout in order to avoid collisions with the counter weights  33 C in the vicinity of the lower link pass-through part  13  as shown in  FIG. 5 . 
   Further, with the multiple link engine  10 , an angle θ 1  formed by the cylinder center axis L 1  and a center axis L 2  of the upper link  41  at top dead center as shown in  FIG. 1  can be made smaller than an angle θ 2  formed by the cylinder center axis L 1  and the center axis L 2  of the upper link  41  at the piston bottom dead center shown in  FIG. 4 . Provided that the angle θ 1  can thus be made smaller than the angle θ 2 , a thrust force acting on the piston  2  in the vicinity of top dead center where pressure in the cylinder is large can be made smaller, and a piston skirt of the piston  2  can be made smaller. 
   Referring to  FIGS. 8 to 10 , the piston  2  includes a piston skirt  21  and a piston skirt  22  in a front and back thereof. A piston skirt is not formed, however, on an extension of the piston pin  31 . The counter weights  33 C can pass-through both sides of the piston skirt  21 , and do not interfere with the piston  2 , when the piston  2  is in the vicinity of bottom dead center as shown in  FIG. 13  because a piston skirt is not formed on the extension of the piston pin  31 . 
   Furthermore, referring to  FIGS. 6 and 7 , a piston guide  14  that is an extension of the wall of the cylinder liner  1  is formed in the cylinder liner  1  between the lower link pass-through parts  12 . The piston skirt  21  of the piston  2  slides on the piston guide  14  in the vicinity of bottom dead center as shown in  FIG. 13 . The piston  2  can move reciprocally with a stable posture in the vicinity of bottom dead center about the piston pin  31 , without rocking, because the piston skirt  21  slides on the piston guide  14 . 
   Referring to  FIG. 7 , the cutouts of the cylinder liner  1  are formed so as to become deeper from the piston guide  14  toward outer sides. By thus forming the cutouts so as to become deeper from the piston guide  14  toward the outer sides, lubricating oil flowing from above along the wall of the cylinder liner  1  collects in the piston guide  14 , thus forming an oil film. The durability of the piston skirt  21 , which slides on the piston guide  14 , thus increases. 
   In this embodiment, the counter weight pass-through parts  11  and the lower link pass-through parts  12  are separated by a step, but desirable results in which an oil film is formed on the piston guide  14  may also be achieved by changing the height between the counter weight pass-through parts  11  and the lower link pass-through parts  12  using an incline instead of forming a step. 
   Referring to  FIG. 3  and  FIG. 11 , the lower link  42 , through which the first connecting pin  32  passes, travels through the lower link pass-through part  13 . Accordingly, a piston guide like that of the right side wall of the cylinder liner  1  cannot be formed in the center of the lower link pass-through part  13 . 
   Referring to  FIG. 8 , the circumference of the piston skirt  22  of the piston  2  is lengthened to be longer than the cutout length of the lower link pass-through part  13 . Referring to  FIG. 12 , the piston skirt  22  of the piston  2  slides on the wall of the cylinder liner  1  on an outer side of the lower link pass-through part  13  when in the vicinity of bottom dead center. Accordingly, the piston  2  moves reciprocally with a stable posture, without rocking, about the piston pin  31 . 
   According to this embodiment, a part of the right side wall of the cylinder liner  1  shown in  FIG. 1  is cutout, forming the counter weight pass-through parts  11  and the lower link pass-through parts  12 , and a part of the left side wall of the cylinder liner  1  shown in  FIG. 1  is cutout, forming the lower link pass-through part  13 . In addition, although the piston skirt  21  and the piston skirt  22  are formed in the front and the back of the piston  2 , a piston skirt is not formed on an extension of the piston pin  31 . Accordingly, the lower link  42  and the counter weights  33 C do not interfere with the cylinder liner  1  or the piston  2 , and the overall height of the engine can be reduced. 
   Furthermore, the cutouts formed in the cylinder liner  1  are formed so as to become deeper from the piston guide  14  toward outer sides. Accordingly, lubricating oil flowing from above collects in the piston guide  14 . An oil film is formed by the lubricating oil thus collected, increasing the durability of the piston skirt  21 . 
   Referring to  FIGS. 14 to 18 , a second embodiment of this invention will be explained next. 
     FIGS. 14 to 16  correspond to  FIGS. 5 to 7  of the first embodiment. 
   The second embodiment differs from the first embodiment in the shape of the cutouts of the cylinder liner  1 , as shown in the figures. Other structures and configurations of the second embodiment are identical to those of the first embodiment. 
   Referring to  FIG. 17 , a forward end of the upper link  41  is formed having two branches. The lower link  42  is connected to the two branches through the first connecting pin  32 . 
   Referring to  FIG. 16 , the cylinder liner  1  includes the lower link pass-through part  12  where a rectangular shape is cutout from a center part of a lower end of the cylinder liner  1 . Further, the counter weight pass-through parts  11  is also formed, similar to the first embodiment. Accordingly, referring to  FIG. 17 , the lower link  42  passes through the lower link pass-through part  12 , and does not interfere with the cylinder liner  1 , when the piston  2  is in the vicinity of top dead center. 
   Furthermore, referring to  FIG. 18 , the counter weights  33 C pass through the counter weight pass-through parts  11 , and do not interfere with the cylinder liner  1 , when the piston  2  is in the vicinity of bottom dead center. 
   The piston guides  14  are formed between the lower link pass-through part  12  and the counter weight pass-through parts  11  on both sides of the lower link pass through part  12 . Referring to  FIG. 18 , in the vicinity of bottom dead center of the piston  2 , the piston skirt  21  slides on the piston guide  14 . Accordingly, in the vicinity of bottom dead center, the piston  2  moves reciprocally with a stable posture, without rocking, about the piston pin  31 . 
   The overall height of the engine can be reduced according to this embodiment, similar to the first embodiment. 
   Although the invention has been described above by reference to certain embodiments of the invention, the invention is not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art, within the scope of the Claims. 
   For example, although an engine type in which the cylinder liner  1  is inserted into a cylinder block is explained in the embodiments described above, it is also possible to apply the present invention to an engine that does not possess the cylinder liner  1 . The counter weight pass-through part  11  and the lower link pass-through part  12  may be formed by directly cutting out a wall of a cylinder bore when the engine does not possess the cylinder liner  1 . 
   Furthermore, although a multiple link engine in which the piston  2  is connected to the crankshaft  33  through the upper link  41  and the lower link  42  is explained in the embodiments described above, this invention may also be applied to a normal engine in which a piston is connected to a crankshaft through a connecting rod. Similar effects can be obtained provided that a part of a cylinder bore is cutout, forming a counter weight pass-through part. However, the overall height of the multiple link engines described above tends to increase due to its structure. A larger effect can therefore be obtained when applying the present invention to a multiple link engine compared to a normal engine. 
   The contents of Tokugan 2004-379447 with a filing date of Dec. 28, 2004 in Japan are hereby incorporated by reference. 
   The embodiments of this invention in which an exclusive property or privilege is claimed are defined as follows: