ROTARY BODY

Abstract

The rotary body according to the present invention is made of resin and attached to a crankshaft. The rotary body has an outside plate element and an inside plate element which are attached to an outside surface and an inside surface of an arm portion of the crankshaft, respectively, and a pair of filler elements disposed between the outside plate element and the inside plate element and on both sides of the arm portion. 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.

Claims

1. A rotary body 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.

2. The rotary body according to claim 1, wherein 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.

3. The rotary body according to claim 2, wherein the outside plate element has an engagement feature to be positioned to the crankpin portion.

4. The rotary body according to claim 1, wherein each of the pair of the filler elements has an interior space sealed by the outside plate element and the inside plate element.

5. The rotary body according to claim 1, wherein each of the pair of the filler elements is solid.

6. The rotary body according to claim 4 or 5, wherein 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.

7. The rotary body according to claim 5, wherein 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 onto the pin, and the pin and the through aperture are coupled together.

8. The rotary body according to claim 7, wherein the pin and the through aperture are disposed at a position of a center of gravity of the filler element.

9. The rotary body according to claim 1, wherein 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.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG. 1 is a partial cross-sectional front view of an engine having a rotary body according to the present invention.

[0028] FIG. 2 is a partial perspective view of a crankshaft.

[0029] FIG. 3 is a cross-sectional view of the crankshaft viewing from its left side.

[0030] FIG. 4 is an exploded perspective view of the rotary body.

[0031] FIG. 5 is an exploded cross-sectional front view of the rotary body.

[0032] FIG. 6 is a left-side view of an outside part.

[0033] FIG. 7 is a perspective view of an inside plate element.

[0034] FIG. 8 is a right-side view of the inside plate element.

[0035] FIG. 9 is a perspective view of the outside part assembled into the crankshaft.

[0036] FIG. 10 is an exploded perspective view of the rotary body of a second embodiment.

DESCRIPTION OF EMBODIMENTS

[0037] Now, referring to the drawings, a first embodiment of a rotary body according to the present invention will be explained.

[0038] 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).

[0039] As shown in FIGS. 1 and 2, the crankshaft 20 is rotatable about a rotational axis A1, and has a pair of shaft portions 22 which are disposed on the rotational axis A1, 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 A1, and a crankpin portion 28 which extends from one of the pair of the arm portions 24 parallel to the rotational axis A1 to the other of the pair of the arm portions 24, and is offset from the rotational axis A1. 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).

[0040] As shown in FIG. 3, viewing in a direction of the rotational axis A1 (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 A1. Thus, spaces 29a 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.

[0041] As shown in FIG. 2, the arm portion 24 has an outside surface 24a and an inside surface 24b. Further, the counterweight portion 26 has an outside surface 26a located in the same plane as the outside surface 24a of the arm portion 24, and an inside surface 26b located inside of the inside surface 24b 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.

[0042] 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 24a of the arm portion 24 (and the outside surface 26a of the counterweight portion 26), a pair of filler elements 34 which are to be disposed in the spaces 29a on the opposite sides of the arm portion 24, and an inside plate element 36 which is to be attached to the inside surface 24b 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.

[0043] 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 A1. The first engagement feature 38 includes, for example, a portion of the shaft portion 22 and an aperture 38a formed in the outside plate element 32 to fit onto the portion of the shaft portion 22.

[0044] 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 40a formed in the crankpin portion 28 (see FIG. 1) and a pin 40b formed on the outside plate element 32 to fit into the aperture 40a.

[0045] 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 17a and an inner lace 17b of the bearing 17.

[0046] 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 34a 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.

[0047] 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 36a 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.

[0048] 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 42a provided in the inside surface 24b of the arm portion 24 and on the rotational axis A1 (see FIG. 9), and a pin 42b formed on the inside plate element 36. In this way, the third engagement feature 42 and the aperture 38a of the outside plate element 32 are arranged coaxially with the rotational axis A1.

[0049] 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 44a formed on the filler elements 34, and pins 44b formed on the inside plate element 36. A thickness of the inside plate element 36 including the pin 42b and the pins 44b is preferably less than a distance between the pair of the counterweight portions 26.

[0050] Next, an assembling procedure of the rotary body 30 will be explained.

[0051] 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 42b and the pins 44b 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.

[0052] 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 A1 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 34a of the filler elements 34 are sealed. The welding is, for example, vibration welding.

[0053] 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 34a, 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 17a and the inner lace 17b of the bearing 17 allows a strength of the outside plate element 32 to increase.

[0054] 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 17a and the inner lace 17b of the bearing 17 further allows the empty space in the crank chamber 12 to be reduced.

[0055] Next, a second embodiment of the rotary body will be explained.

[0056] 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.

[0057] 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 54a formed in the filler elements 54 and the outside plate element 32, and pins 44b disposed on the inside plate element 36. A thickness of the inside plate element 36 including the pin 42b and the pins 44b is preferably less than a distance between the pair of the counterweight portions 26.

[0058] Next, an assembling procedure of the rotary body 50 will be explained.

[0059] 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 44b and the through apertures 54a are bonded or welded. The welding is, for example, vibration welding.

[0060] 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 44b can be bonded or welded to the through aperture 54a by accessing from an outside area of the through aperture 54a. 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 44b and the through aperture 54a at a position of center of gravity of each of the pair of the filler elements 54.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 17: bearing

[0065] 20: crankshaft

[0066] 22: shaft portion

[0067] 24: arm portion

[0068] 24a: outside surface

[0069] 24b: inside surface

[0070] 26: counterweight portion

[0071] 28: crankpin portion

[0072] 30, 50: rotary body

[0073] 31, 51: outside part

[0074] 32: outside plate element

[0075] 34, 54: filler element

[0076] 34a: interior space

[0077] 36: inside plate element

[0078] 38a: aperture (first engagement feature)

[0079] 40: second engagement feature

[0080] 41: annular convex portion

[0081] 44b: pin

[0082] 54a: through aperture

[0083] A1: rotational axis