Patent Description:
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 <NUM>-<NUM>). 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.

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 <NUM> and <NUM>). 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 <NUM>, 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.

In addition, <CIT> discloses a rotary body attached to a crankshaft according to the preamble of claim <NUM> with a filler member to be installed in a crankshaft including a crank web includes: an arm member, extending in a diametrical direction of a crank journal, and a weight member extending in a radial direction of the crank journal. The filler member includes: a fitting member, a connecting member mounted on the bodies. The fitting member is fixed to an outer side face of the crank web. The connecting member is mounted on the bodies to stride the arm member on inner side face of the crank web.

Furthermore, <CIT> shows a crankshaft with which a crank cotter pin and a crank journal are connected by the arm at which the balance weight was provided wherein a shape correction member which covers this from the radial direction of said crank journal is attached to said arm. In this attachment state, said arm exhibits the shape of a disk shape.

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.

To achieve the above-stated object, the rotary body according to the present invention is made of resin and configured to be 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.

According to the invention, the outside plate element is disposed adjacent to the bearing supporting the shaft portion and has an annular protrusion extending between an outer ring and an inner ring 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 ring and the inner ring of the bearings.

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

<FIG> shows a portion of an engine <NUM> 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 <NUM> has a cylinder block <NUM> which defines a crank chamber <NUM>, a crankshaft <NUM>, and a connecting rod <NUM> for connecting the crankshaft <NUM> to a piston (not shown).

As shown in <FIG>, the crankshaft <NUM> is rotatable about a rotational axis A1, and has a pair of shaft portions <NUM> which are disposed on the rotational axis A1, a pair of arm portions <NUM> and a pair of counterweight portions <NUM> which portions <NUM>, <NUM> extend from the shaft portion <NUM> in a direction perpendicularly to the rotational axis A1, and a crankpin portion <NUM> which extends from one of the pair of the arm portions <NUM> parallel to the rotational axis A1 to the other of the pair of the arm portions <NUM>, and is offset from the rotational axis A1. Each of the shaft portions <NUM> is rotatably supported by a bearing <NUM> and extends toward the outside of the cylinder block <NUM> via an oil seal <NUM>. For example, a flywheel (not shown) and a recoil starter (not shown) are attached to one of the shaft portions <NUM>, while a clutch mechanism (not shown) is attached to the other of the shaft portions <NUM>. The crankshaft <NUM> may be made of a metal such as SCM material. Hereinafter, for each of the arm portions <NUM>, a side toward the other arm portion <NUM> is referred to as "inside", while the opposite side of the inside is referred to as "outside" (see <FIG>).

As shown in <FIG>, viewing in a direction of the rotational axis A1 (or rotational-axis direction), the arm portion <NUM> and the counterweight portion <NUM> are arranged in a substantially T shape and are positioned within a virtual circle <NUM> around the rotational axis A1. Thus, spaces 29a within the virtual circle <NUM>, in which neither the arm portion <NUM> nor the counterweight portion <NUM> are present, are caused on the opposite sides of the arm portion <NUM>.

As shown in <FIG>, the arm portion <NUM> has an outside surface 24a and an inside surface 24b. Further, the counterweight portion <NUM> has an outside surface 26a located in the same plane as the outside surface 24a of the arm portion <NUM>, and an inside surface 26b located inside of the inside surface 24b of the arm portion <NUM>. Namely, in the rotational-axis direction, a thickness of the arm portion <NUM> is less than a thickness of the counterweight portion <NUM>.

<FIG> and <FIG> are an exploded perspective view and an exploded cross-sectional front view of a rotary body <NUM> according to the present invention, respectively. The rotary body <NUM> is positioned within the virtual circle <NUM>, and includes an outside plate element <NUM> which is to be attached to the outside surface 24a of the arm portion <NUM> (and the outside surface 26a of the counterweight portion <NUM>), a pair of filler elements <NUM> which are to be disposed in the spaces 29a on the opposite sides of the arm portion <NUM>, and an inside plate element <NUM> which is to be attached to the inside surface 24b of the arm portion <NUM>. The outside plate element <NUM> and the pair of the filler elements <NUM> are coupled with each other and, in this embodiment, these elements <NUM>, <NUM> are pre-formed as a single outside part <NUM>. The pair of the filler elements <NUM> and the inside plate element <NUM> are to be coupled with each other after the outside part <NUM> and the inside plate element <NUM> are attached to the crankshaft <NUM>. The rotary body <NUM> may be made of lightweight resin, which may be lightweight, such as PA6, PA66 and PPS.

As shown in <FIG>, the outside plate element <NUM> is positioned between the arm portion <NUM> and the bearing <NUM>. A thickness of the outside plate element <NUM> in the rotational-axis direction is, for example, within a range of <NUM>-<NUM>. As shown in <FIG>, a first engagement feature <NUM> is provided for positioning the outside plate element <NUM> with respect to the rotational axis A1. The first engagement feature <NUM> includes, for example, a portion of the shaft portion <NUM> and an aperture 38a formed in the outside plate element <NUM> to fit onto the portion of the shaft portion <NUM>.

A second engagement feature <NUM> is provided for positioning the outside plate element <NUM> with respect to the arm portion <NUM> and the crankpin portion <NUM>. The second engagement feature <NUM> includes, for example, an aperture 40a formed in the crankpin portion <NUM> (see <FIG>) and a pin 40b formed on the outside plate element <NUM> to fit into the aperture 40a.

As shown in <FIG> and <FIG>, the outside plate element <NUM> (the reference number is omitted in <FIG>) has an annular protrusion <NUM> extending between an outer ring 17a and an inner ring 17b of the bearing <NUM>.

As can be seen from <FIG> and <FIG>, each of the filler elements <NUM> has a profile to fill the space enclosed by the virtual circle <NUM>, the arm portion <NUM>, and the counterweight portion <NUM>. In this embodiment, each of the filler elements <NUM> includes an interior space 34a and is integrally formed with the outside plate element <NUM>. A thickness of the filler elements <NUM> in the rotational-axis direction is preferably equal to the thickness of the arm portion <NUM> in the rotational-axis direction.

As shown in <FIG>, the inside plate element <NUM> includes an edge portion corresponding to the pair of the filler elements <NUM>, another edge portion corresponding to a border of the counterweight portion <NUM>, and a cutout 36a to avoid interference with the crankpin portion <NUM>. In the rotational-axis direction, a thickness of the inside plate element <NUM> is preferably the same as a difference between the thickness of the counterweight portion <NUM> and the thickness of the arm portion <NUM>, and, for example, within a range of <NUM>-<NUM>.

As shown in <FIG>, a third engagement feature <NUM> is provided for positioning the inside plate element <NUM> with respect to the arm portion <NUM>. The third engagement feature <NUM> includes, for example, an aperture 42a provided in the inside surface 24b of the arm portion <NUM> and on the rotational axis A1 (see <FIG>), and a pin 42b formed on the inside plate element <NUM>. In this way, the third engagement feature <NUM> and the aperture 38a of the outside plate element <NUM> are arranged coaxially with the rotational axis A1.

As shown in <FIG>, a fourth engagement feature <NUM> is provided for positioning the inside plate element <NUM> with respect to the pair of the filler elements <NUM>. The fourth engagement feature <NUM> includes, for example, recesses 44a formed on the filler elements <NUM>, and pins 44b formed on the inside plate element <NUM>. A thickness of the inside plate element <NUM> including the pin 42b and the pins 44b is preferably less than a distance between the pair of the counterweight portions <NUM>.

Next, an assembling procedure of the rotary body <NUM> will be explained.

After the crankshaft <NUM> is assembled and adjusted, the inside plate element <NUM> is attached to the crankshaft <NUM>. Since the thickness of the inside plate element <NUM> including the pin 42b and the pins 44b is less than the distance between the pair of the counterweight portions <NUM>, the inside plate element <NUM> can be passed between the pair of the counterweight portions <NUM>. The inside plate element <NUM> is positioned with respect to the rotational axis A1 by the third engagement feature <NUM>.

Then, the outside part <NUM> (namely, the outside plate element <NUM> and the pair of the filler elements <NUM> which are integrally formed) is attached to the crankshaft <NUM> (see <FIG> in which the inside plate element <NUM> is omitted). The outside part <NUM> is positioned with respect to the rotational axis A1 and the arm portion <NUM> by the first and second engagement features <NUM>, <NUM>. Further, the fourth engagement feature <NUM> allows the outside part <NUM> (particularly, the pair of the filler elements <NUM>) and the inside plate element <NUM> to be positioned with respect to each other. Then, the inside plate element <NUM> is bonded or welded to peripheries of the pair of the filler elements <NUM> so that the interior spaces 34a of the filler elements <NUM> are sealed. The welding is, for example, vibration welding.

Since the rotary body <NUM> configured as explained above is made of resin and attached to the crankshaft <NUM> to surround the arm portion <NUM>, metal is not needed to be used. This allows the rotary body <NUM> to be maintained lightweight. Further, since each of the pair of the filler elements <NUM> has its interior space 34a, the rotary body <NUM> can be made more lightened. Further, since the rotary body <NUM> is positioned to the crankshaft <NUM> by the engagement features <NUM>, <NUM>, <NUM>, <NUM>, deformation of the rotary body <NUM> due to its rotation at a high speed can be restricted. Also, the annular protrusion <NUM> extending between the outer ring 17a the inner ring 17b of the bearing <NUM> allows a strength of the outside plate element <NUM> to increase.

Since each of the filler elements <NUM> has the profile to fill the space surrounded by the virtual circle <NUM>, the arm portion <NUM> and the counterweight portion <NUM>, an empty space in the crank chamber <NUM> can be reduced. The combination of the inside plate element <NUM> and the outside part <NUM> also allows a distance between the pair of arm portions <NUM> to be reduced, and allows the empty space in the crank chamber <NUM> to be further reduced. The annular protrusion <NUM> extending between the outer ring 17a and the inner ring 17b of the bearing <NUM> further allows the empty space in the crank chamber <NUM> to be reduced.

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

A rotary body <NUM> of the second embodiment has the same structure as that of the rotary body <NUM> of the first embodiment except that a pair of filler elements <NUM> are solid.

Each of the pair of the filler elements <NUM> is solid. Further, a fourth engagement feature <NUM> is provided for positioning the inside plate element <NUM> with respect to the pair of the filler elements <NUM>. The fourth engagement feature <NUM> includes, for example, through apertures 54a formed in the filler elements <NUM> and the outside plate element <NUM>, and pins 44b disposed on the inside plate element <NUM>. A thickness of the inside plate element <NUM> including the pin 42b and the pins 44b is preferably less than a distance between the pair of the counterweight portions <NUM>.

After the crankshaft <NUM> is assembled and adjusted, the inside plate element <NUM> is attached to the crankshaft <NUM> as in the rotary body <NUM> of the first embodiment. Then, the outside part <NUM> (the outside plate element <NUM> and the pair of the filler elements <NUM> which are integrally formed) are attached to the crankshaft <NUM> as in the rotary body <NUM> of the first embodiment. Then, the pins 44b and the through apertures 54a are bonded or welded. The welding is, for example, vibration welding.

In the rotary body <NUM> configured as explained above, when the inside plate element <NUM> and the outside part <NUM> 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 <NUM> to be easily attached to the crankshaft <NUM>. In this case, the inside plate element <NUM> may not be bonded or welded to the peripheries of the filler elements <NUM>. Although the inside plate element <NUM> and/or the filler elements <NUM> 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 <NUM>.

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 <NUM>, <NUM> is attached to the crankshaft <NUM> of the two-stroke engine <NUM>, the rotary body <NUM>, <NUM> may be applied to any crankshafts.

Claim 1:
A rotary body (<NUM>, <NUM>) made of resin and configured to be attached to a crankshaft (<NUM>) which is rotatable about a rotational axis (A1),
the crankshaft (<NUM>) having a shaft portion (<NUM>) which is disposed on the rotational axis (A1) and supported by a bearing (<NUM>), an arm portion (<NUM>) and a counterweight portion (<NUM>) which are connected to an end of the shaft portion (<NUM>) perpendicularly with respect to the rotational axis (A1), and a crankpin portion (<NUM>) which is offset from the rotational axis (A1) and extends from the arm portion (<NUM>) parallel to the rotational axis (A1), the arm portion (<NUM>) having an outside surface (24a) on a side toward the shaft portion (<NUM>), and an inside surface (24b) on a side toward the crankpin portion (<NUM>),
the rotary body (<NUM>) including an outside plate element (<NUM>) which is attached to the outside surface (24a) of the arm portion (<NUM>), an inside plate element (<NUM>) which is attached to the inside surface (24b) of the arm portion (<NUM>), and a pair of filler elements (<NUM>) which are disposed between the outside plate element (<NUM>) and the inside plate element (<NUM>) and on both sides of the arm portion (<NUM>),
wherein the outside plate element (<NUM>) and the pair of filler elements (<NUM>) are coupled to each other, and the pair of filler elements (<NUM>) and the inside plate element (<NUM>) are coupled to each other, and
characterised in that
the outside plate element (<NUM>) is disposed adjacent to the bearing (<NUM>) supporting the shaft portion (<NUM>) and has an annular protrusion (<NUM>) extending between an outer ring (17a) and an inner ring (17b) of the bearing (<NUM>) .