Patent Publication Number: US-2023151844-A1

Title: Rotary body

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a National Stage Application of International Patent App. No. PCT/JP2021/014595, filed Apr. 6, 2021, which claims the benefit of Japanese Patent Application No. 2020-068836 filed on Apr. 7, 2020, the entire disclosures of both of which are hereby incorporated by reference as if set forth in their entirety herein. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a rotary body attached onto a crankshaft of an engine. 
     BACKGROUND ART 
     A two-stroke engine is used in many small working machines such as a chainsaw, a mower, and a blower. 
     In the two-stroke engine, while a piston is raised, mixed gas of fuel and air in a combustion chamber is compressed and a negative pressure is caused in a crank chamber so that when an intake passage communicates with the crank chamber, the crank chamber is filled with new mixed gas of fuel and air through the intake passage. Then, while the piston is lowered due to explosion in the combustion chamber and when an exhaust passage communicates with the combustion chamber, combustion gas is exhausted through the exhaust passage. Further, the mixed gas in the crank chamber is compressed so that when the crank chamber communicates with the combustion chamber through a scavenging passage, the mixed gas flows from the crank chamber through the scavenging passage into the combustion chamber. 
     In the two-stroke engine, it is known that a compression ratio of the mixed gas in the crank chamber (primary compression ratio) can be increased by reducing a volume or an empty space in the crank chamber, so that output performance, acceleration performance, and reduction of emissions (emission of air pollutants such as hydrocarbons) of the engine can be enhanced. 
     Further, the crankshaft includes a shaft portion disposed on a rotational axis, an arm portion extending from the shaft portion in a radial direction, and a counterweight portion in a substantially semicircular form disposed on an opposite side with respect to the arm portion in the radial direction, wherein the arm portion and the counterweight portion define a substantially 
     T shape. Thus, it is known that a pair of filler elements are attached to the crankshaft, and spaces adjacent to the arm portion and the counterweight portion are filled with the pair of filler elements to reduce the empty space in the crank chamber (for example, see the Patent Publications 1-3). Please note that the filler elements attached to an opposite side with respect to the counterweight portion are lightweight or made of resin, so that the filler elements do not greatly restrict the function of the counterweight portion. 
     PRIOR ART PUBLICATION 
     Patent Publication 1: U.S. Pat. No. 6,062,180. 
     Patent Publication 2: Japanese Patent Laid-open Publication No. 2005-140170. 
     Patent Publication 3: Japanese Patent Laid-open Publication No. 2012-117630. 
     SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
     When the spaces adjacent to the arm portion and the counterweight portion are filled with the resin filler elements, the filler elements may be deformed at a high rotational speed. To reduce such deformation, a metal cup or band surrounding the resin filler elements may have been used (see the Patent Publications 1 and 2). In this case, the function of the counterweight portion may be restricted due to weight of the metal cup or band. 
     Further, in the Patent Publication 3, an S-shaped wire is used for attachment of the resin filler elements. In this case, if an area around the wire is filled with the filler elements, the empty space in the crank chamber can be more reduced. 
     Thus, an object of the present invention is to provide a rotary body that can be attached onto the crankshaft without using metal and can reduce the empty space in the crank chamber. Preferably, an object of the present invention is to provide a rotary body which can be easily attached to the crankshaft. 
     Means for Solving the Problem 
     To achieve the above-stated object, the rotary body according to the present invention is made of resin and attached to a crankshaft which is rotatable about a rotational axis; the crankshaft having a shaft portion which is disposed on the rotational axis and supported by a bearing, an arm portion and a counterweight portion which are connected to an end of the shaft portion perpendicularly with respect to the rotational axis, and a crankpin portion which is offset from the rotational axis and extends from the arm portion parallel to the rotational axis, the arm portion having an outside surface on a side toward the shaft portion, and an inside surface on a side toward the crankpin portion; and, the rotary body including an outside plate element which is attached to the outside surface of the arm portion, an inside plate element which is attached to the inside surface of the arm portion, and a pair of filler elements which are disposed between the outside plate element and the inside plate element and on both sides of the arm portion, wherein the outside plate element and the pair of the filler elements are coupled to each other, and the pair of the filler elements and the inside plate element are coupled to each other. 
     The rotary body configured in this way is made of resin, while the outside plate element attached to the outside surface of the arm portion, the inside plate element attached to the outside surface of the arm portion, and the pair of the filler elements disposed between the outside plate element and the inside plate element on both sides of the arm portion are attached together to the crankshaft to surround the arm portion, namely, no metal is needed to be used. By attaching the rotary body to the crankshaft, the empty space in the crank chamber can be reduced. 
     In an embodiment of the present invention, preferably, the outside plate element has an aperture for fitting onto the shaft portion, and the inside plate element has an engagement feature to be positioned to the arm portion, and more preferably, the outside plate element has an engagement feature to be positioned to the crankpin portion. 
     Since the rotary body configured in this way is positioned on the crankshaft by the aperture and the engagement feature, deformation at a high rotational speed can be restricted. 
     In an embodiment of the present invention, preferably, each of the pair of the filler elements has an interior space sealed by the outside plate element and the inside plate element. 
     In the rotary body configured in this way, since each of the pair of the filler elements has the interior space, the rotary body can be made lighter. 
     In an embodiment of the present invention, each of the pair of the filler elements may be solid. 
     In an embodiment of the present invention, preferably the outside plate element and the pair of the filler elements are integrally preformed as an outside part, and the inside plate element is coupled to the outside part. 
     In the rotary body configured in this way, the rotary body can be attached to the crankshaft even if the distance between the pair of the arm portions is small. Thus, the empty space in the crank chamber can be reduced. 
     In the embodiment of the present invention in which the pair of the filler elements are solid, preferably, the outside plate element and the pair of the filler elements are integrally preformed as an outside part, the inside plate element has a pin, the outside plate element and the pair of the filler elements have a through aperture fitted onto the pin, and the pin and the through aperture are coupled together, and more preferably, the pin and the through aperture are disposed at a position of the center of gravity of the filler elements. 
     In the rotary body configured in this way, when the inside plate element and the outside part are coupled to each other, the pin can be accessed from outside of the through aperture. Thus, the rotary body can be easily attached to the crankshaft. Also, when the pin and the through aperture are formed at the position of the center of gravity of each of the pair of the filler elements, deformation of portions of the inside plate element and the outside part, which are not coupled to each other, is restricted at a high rotational speed. 
     In an embodiments of the present invention, preferably, the outside plate element is disposed adjacent to the bearing supporting the shaft portion and has an annular protrusion extending between an outer lace and an inner lace of the bearing. 
     In the rotary body configured in this way, the empty space in the crank chamber can be further reduced by the annular protrusion extending between the outer lace and the inner lace of the bearings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a partial cross-sectional front view of an engine having a rotary body according to the present invention. 
         FIG.  2    is a partial perspective view of a crankshaft. 
         FIG.  3    is a cross-sectional view of the crankshaft viewing from its left side. 
         FIG.  4    is an exploded perspective view of the rotary body. 
         FIG.  5    is an exploded cross-sectional front view of the rotary body. 
         FIG.  6    is a left-side view of an outside part. 
         FIG.  7    is a perspective view of an inside plate element. 
         FIG.  8    is a right-side view of the inside plate element. 
         FIG.  9    is a perspective view of the outside part assembled into the crankshaft. 
         FIG.  10    is an exploded perspective view of the rotary body of a second embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Now, referring to the drawings, a first embodiment of a rotary body according to the present invention will be explained. 
       FIG.  1    shows a portion of an engine  10  which is a two-stroke engine with a single cylinder used in a small working machine, such as a chainsaw, a mower, and a blower. The engine  10  has a cylinder block  14  which defines a crank chamber  12 , a crankshaft  20 , and a connecting rod  16  for connecting the crankshaft  20  to a piston (not shown). 
     As shown in  FIGS.  1  and  2   , the crankshaft  20  is rotatable about a rotational axis A 1 , and has a pair of shaft portions  22  which are disposed on the rotational axis A 1 , a pair of arm portions  24  and a pair of counterweight portions  26  which portions  24 ,  26  extend from the shaft portion  22  in a direction perpendicularly to the rotational axis A 1 , and a crankpin portion  28  which extends from one of the pair of the arm portions  24  parallel to the rotational axis A 1  to the other of the pair of the arm portions  24 , and is offset from the rotational axis A 1 . Each of the shaft portions  22  is rotatably supported by a bearing  17  and extends toward the outside of the cylinder block  14  via an oil seal  18 . For example, a flywheel (not shown) and a recoil starter (not shown) are attached to one of the shaft portions  22 , while a clutch mechanism (not shown) is attached to the other of the shaft portions  22 . The crankshaft  20  may be made of a metal such as SCM material. Hereinafter, for each of the arm portions  24 , a side toward the other arm portion  24  is referred to as “inside”, while the opposite side of the inside is referred to as “outside” (see  FIG.  2   ). 
     As shown in  FIG.  3   , viewing in a direction of the rotational axis A 1  (or rotational-axis direction), the arm portion  24  and the counterweight portion  26  are arranged in a substantially T shape and are positioned within a virtual circle  29  around the rotational axis A 1 . Thus, spaces  29   a  within the virtual circle  29 , in which neither the arm portion  24  nor the counterweight portion  26  are present, are caused on the opposite sides of the arm portion  24 . 
     As shown in  FIG.  2   , the arm portion  24  has an outside surface  24   a  and an inside surface  24   b.  Further, the counterweight portion  26  has an outside surface  26   a  located in the same plane as the outside surface  24   a  of the arm portion  24 , and an inside surface  26   b  located inside of the inside surface  24   b  of the arm portion  24 . Namely, in the rotational-axis direction, a thickness of the arm portion  24  is less than a thickness of the counterweight portion  26 . 
       FIGS.  4  and  5    are an exploded perspective view and an exploded cross-sectional front view of a rotary body  30  according to the present invention, respectively. The rotary body  30  is positioned within the virtual circle  29 , and includes an outside plate element  32  which is to be attached to the outside surface  24   a  of the arm portion  24  (and the outside surface  26   a  of the counterweight portion  26 ), a pair of filler elements  34  which are to be disposed in the spaces  29   a  on the opposite sides of the arm portion  24 , and an inside plate element  36  which is to be attached to the inside surface  24   b  of the arm portion  24 . The outside plate element  32  and the pair of the filler elements  34  are coupled with each other and, in this embodiment, these elements  32 ,  34  are pre-formed as a single outside part  31 . The pair of the filler elements  34  and the inside plate element  36  are to be coupled with each other after the outside part  31  and the inside plate element  36  are attached to the crankshaft  20 . The rotary body  30  may be made of lightweight resin, which may be lightweight, such as PA6, PA66 and PPS. 
     As shown in  FIG.  1   , the outside plate element  32  is positioned between the arm portion  24  and the bearing  17 . A thickness of the outside plate element  32  in the rotational-axis direction is, for example, within a range of  1 - 2  mm. As shown in  FIGS.  4 - 6   , a first engagement feature  38  is provided for positioning the outside plate element  32  with respect to the rotational axis A 1 . The first engagement feature  38  includes, for example, a portion of the shaft portion  22  and an aperture  38   a  formed in the outside plate element  32  to fit onto the portion of the shaft portion  22 . 
     A second engagement feature  40  is provided for positioning the outside plate element  32  with respect to the arm portion  24  and the crankpin portion  28 . The second engagement feature  40  includes, for example, an aperture  40   a  formed in the crankpin portion  28  (see  FIG.  1   ) and a pin  40   b  formed on the outside plate element  32  to fit into the aperture  40   a.    
     As shown in  FIGS.  1  and  5   , the outside plate element  32  (the reference number is omitted in  FIG.  1   ) preferably has an annular protrusion  41  extending between an outer lace  17   a  and an inner lace  17   b  of the bearing  17 . 
     As can be seen from  FIGS.  3  and  6   , each of the filler elements  34  has a profile to fill the space enclosed by the virtual circle  29 , the arm portion  24 , and the counterweight portion  26 . In this embodiment, each of the filler elements  34  includes an interior space  34   a  and is integrally formed with the outside plate element  32 . A thickness of the filler elements  34  in the rotational-axis direction is preferably equal to the thickness of the arm portion  24  in the rotational-axis direction. 
     As shown in  FIGS.  7  and  8   , the inside plate element  36  includes an edge portion corresponding to the pair of the filler elements  34 , another edge portion corresponding to a border of the counterweight portion  26 , and a cutout  36   a  to avoid interference with the crankpin portion  28 . In the rotational-axis direction, a thickness of the inside plate element  36  is preferably the same as a difference between the thickness of the counterweight portion  26  and the thickness of the arm portion  24 , and, for example, within a range of 1-2 mm. 
     As shown in  FIGS.  7 - 9   , a third engagement feature  42  is provided for positioning the inside plate element  36  with respect to the arm portion  24 . The third engagement feature  42  includes, for example, an aperture  42   a  provided in the inside surface  24   b  of the arm portion  24  and on the rotational axis A 1  (see  FIG.  9   ), and a pin  42   b  formed on the inside plate element  36 . In this way, the third engagement feature  42  and the aperture  38   a  of the outside plate element  32  are arranged coaxially with the rotational axis A 1 . 
     As shown in  FIGS.  6 - 9   , a fourth engagement feature  44  is provided for positioning the inside plate element  36  with respect to the pair of the filler elements  34 . The fourth engagement feature  44  includes, for example, recesses  44   a  formed on the filler elements  34 , and pins  44   b  formed on the inside plate element  36 . A thickness of the inside plate element  36  including the pin  42   b  and the pins  44   b  is preferably less than a distance between the pair of the counterweight portions  26 . 
     Next, an assembling procedure of the rotary body  30  will be explained. 
     After the crankshaft  20  is assembled and adjusted, the inside plate element  36  is attached to the crankshaft  20 . Since the thickness of the inside plate element  36  including the pin  42   b  and the pins  44   b  is less than the distance between the pair of the counterweight portions  26 , the inside plate element  36  can be passed between the pair of the counterweight portions  26 . The inside plate element  36  is positioned with respect to the rotational axis Al by the third engagement feature  42 . 
     Then, the outside part  31  (namely, the outside plate element  32  and the pair of the filler elements  34  which are integrally formed) is attached to the crankshaft  20  (see  FIG.  9    in which the inside plate element  36  is omitted). The outside part  31  is positioned with respect to the rotational axis A 1  and the arm portion  24  by the first and second engagement features  38 ,  40 . Further, the fourth engagement feature  44  allows the outside part  31  (particularly, the pair of the filler elements  34 ) and the inside plate element  36  to be positioned with respect to each other. Then, the inside plate element  36  is bonded or welded to peripheries of the pair of the filler elements  34  so that the interior spaces  34   a  of the filler elements  34  are sealed. The welding is, for example, vibration welding. 
     Since the rotary body  30  configured as explained above is made of resin and attached to the crankshaft  20  to surround the arm portion  24 , metal is not needed to be used. This allows the rotary body  30  to be maintained lightweight. Further, since each of the pair of the filler elements  34  has its interior space  34   a,  the rotary body  30  can be made more lightened. Further, since the rotary body  30  is positioned to the crankshaft  20  by the engagement features  38 ,  40 ,  42 ,  44 , deformation of the rotary body  30  due to its rotation at a high speed can be restricted. Also, the annular protrusion  41  extending between the outer lace  17   a  and the inner lace  17   b  of the bearing  17  allows a strength of the outside plate element  32  to increase. 
     Since each of the filler elements  34  has the profile to fill the space surrounded by the virtual circle  29 , the arm portion  24  and the counterweight portion  26 , an empty space in the crank chamber  12  can be reduced. The combination of the inside plate element  36  and the outside part  31  also allows a distance between the pair of arm portions  24  to be reduced, and allows the empty space in the crank chamber  12  to be further reduced. The annular protrusion  41  extending between the outer lace  17   a  and the inner lace  17   b  of the bearing  17  further allows the empty space in the crank chamber  12  to be reduced. 
     Next, a second embodiment of the rotary body will be explained. 
     A rotary body  50  of the second embodiment has the same structure as that of the rotary body  30  of the first embodiment except that a pair of filler elements  54  are solid. 
     Each of the pair of the filler elements  54  is solid. Further, a fourth engagement feature  44  is provided for positioning the inside plate element  36  with respect to the pair of the filler elements  54 . The fourth engagement feature  44  includes, for example, through apertures  54   a  formed in the filler elements  54  and the outside plate element  32 , and pins  44   b  disposed on the inside plate element  36 . A thickness of the inside plate element  36  including the pin  42   b  and the pins  44   b  is preferably less than a distance between the pair of the counterweight portions  26 . 
     Next, an assembling procedure of the rotary body  50  will be explained. 
     After the crankshaft  20  is assembled and adjusted, the inside plate element  36  is attached to the crankshaft  20  as in the rotary body  30  of the first embodiment. Then, the outside part  51  (the outside plate element  32  and the pair of the filler elements  54  which are integrally formed) are attached to the crankshaft  20  as in the rotary body  30  of the first embodiment. Then, the pins  44   b  and the through apertures  54   a  are bonded or welded. The welding is, for example, vibration welding. 
     In the rotary body  50  configured as explained above, when the inside plate element  36  and the outside part  51  are coupled to each other, the pin  44   b  can be bonded or welded to the through aperture  54   a  by accessing from an outside area of the through aperture  54   a.  This allows the rotary body  50  to be easily attached to the crankshaft  20 . In this case, the inside plate element  36  may not be bonded or welded to the peripheries of the filler elements  54 . Although the inside plate element  36  and/or the filler elements  54  may be deformed due to a high rotational speed, the Applicant confirmed by his analysis that such deformation could be minimized by placing the pin  44   b  and the through aperture  54   a  at a position of center of gravity of each of the pair of the filler elements  54 . 
     Although the embodiments of the present invention have been now described, the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the invention recited in the claims, and it is needless to say that such modifications are also fallen within the scope of the present invention. 
     Although in the above-described embodiments, the rotary body  30 ,  50  is attached to the crankshaft  20  of the two-stroke engine  1 , the rotary body  30 ,  50  may be applied to any crankshafts. 
     Although in the above-described embodiments, the outside plate element  32  and the pair of the filler elements  34 ,  54  are integrally pre-formed, the inside plate element  36  and the filler elements  34 ,  54  may be integrally pre-formed, to which the outside plate element  32  may be assembled later. 
       17 : bearing 
       20 : crankshaft 
       22 : shaft portion 
       24 : arm portion 
       24   a:  outside surface 
       24   b:  inside surface 
       26 : counterweight portion 
       28 : crankpin portion 
       30 ,  50 : rotary body 
       31 ,  51 : outside part 
       32 : outside plate element 
       34 ,  54 : filler element 
       34   a:  interior space 
       36 : inside plate element 
       38   a:  aperture (first engagement feature) 
       40 : second engagement feature 
       41 : annular convex portion 
       44   b:  pin 
       54   a:  through aperture 
     A 1 : rotational axis