Technical Field
[0001] The present teaching relates to an engine, a cylinder body member, and a vehicle.
Background Art
[0002] Recently, for the purpose of reducing the weight of an engine, alloying a cylinder
body part with Al is becoming more popular. The cylinder body part needs to have a
high strength and a high wear resistance. This is why an Al alloy with a high Si content,
which means a hypereutectic Al-Si based alloy, can be one option among Al alloys for
making the cylinder body part.
[0003] Patent Literature 1 (PTL1) discloses the following technique which relates to an
engine including a cylinder block made of an Al alloy with a relatively high Si content.
[0004] The cylinder block has a sliding surface on which a piston ring is slidable, and
Si crystal grains and an Al alloy base material are exposed on the sliding surface.
The sliding surface is mechanically processed such that the Si crystal grains emerge
thereat. An exposed surface of each Si crystal grain exists more inward of the cylinder
than an exposed surface of the Al alloy base material does. Thus, the piston ring
comes into contact with the Si crystal grains. Contact of the piston ring with the
Al alloy base material is avoided. The cylinder block, which is made of the Al alloy
with a relatively high Si content, is manufactured by a high-pressure die casting
process. This enables Si primary crystal grains each having an appropriate size to
be distributed appropriately over the sliding surface. That is, each Si primary crystal
grain receives a reduced load during an engine operation, and therefore breakdown
of the Si primary crystal grain is suppressed. In addition, since each Si primary
crystal grain has an appropriate size, fall-off of the Si primary crystal grains from
the sliding surface is suppressed. Accordingly, contact of the piston ring with the
Al alloy base material is effectively avoided. This can suppress generation of scuffs
which may be caused by contact between the Al alloy base material and the piston ring.
Moreover, a lubricant is retained between the Si crystal grains which emerge at the
sliding surface, and recesses each formed between the Si crystal grains function as
oil reservoirs. This provides an improved lubricity to the piston sliding in the cylinder,
so that a scuff resistance of the cylinder body part is improved.
[0005] In the cylinder block of Patent Literature 1, as described above, the Si primary
crystal grains each having an appropriate size are exposed in the form of floating
islands on the sliding surface while being distributed with an appropriate density.
Accordingly, contact between the Al alloy base material and the piston ring is avoided,
and the recesses each formed between the Si crystal grains function as oil reservoirs.
As a result, generation of scuffs is suppressed.
[0006] Patent Literatures 2 and 3 (PTLs 2 and 3) as well as Patent Literature 1 relate to
an engine including a cylinder block made of an Al alloy with a relatively high Si
content.
[0007] In the cylinder block of Patent Literature 2, a sliding surface is etched such that
Si crystal grains emerge thereat. Since the etching is given, a surface of an Al alloy
base material is textured in its portion located in each recess between the Si crystal
grains. This enables the recess between the Si crystal grains to retain a larger amount
of lubricant, as compared with the cylinder block of Patent Literature 1. Accordingly,
generation of scuffs is suppressed more effectively.
[0008] In the cylinder block of Patent Literature 3, a sliding surface is etched such that
a surface of an Al alloy base material is textured more deeply in its portion located
in each recess between Si crystal grains at or near the top dead center. This can
increase the amount of lubricant retained in each recess between the Si crystal grains
at or near the top dead center. Generation of scuffs at or near the top dead center
is suppressed more effectively.
[0009] At or near the top dead center, a lubrication between a sliding surface and a piston
part is mostly a boundary lubrication. The top dead center is close to a combustion
chamber of an engine. Lubrication conditions are therefore severe at or near the top
dead center. Scuffs tend to be generated at or near the top dead center. This is why
the technique for suppressing generation of scuffs at or near the top dead center
is proposed, as in Patent Literature 3.
[0010] Conventionally, a cylinder block made of an Al alloy with a relatively high Si content
and manufactured by a high-pressure die casting process has been upgraded under the
presupposition that Si crystal grains are exposed in the form of floating islands.
In other words, the technique relating to a cylinder block made of an Al alloy with
a relatively high Si content and manufactured by a high-pressure die casting process
involves an underlying presupposition that generation of scuffs can be suppressed
by achieving the following two conditions:
suppressing contact between a piston ring and an Al alloy base material; and
making a recess between Si crystal grains function as an oil reservoir.
Citation List
Patent Literature
[0011]
PTL 1 : Japanese Patent Application Laid-Open No. 2005-273654
PTL 2 : Japanese Patent Application Laid-Open No. 2008-180218
PTL 3 : Japanese Patent Application Laid-Open No. 2010-31840
Summary of the Invention
Technical Problem
[0012] An object of the present teaching is to provide an engine, a cylinder body member,
and a vehicle that are able to suppress generation of scuffs at or near the top dead
center more effectively.
Solution to Problem
[0013] The present teaching can adopt the following configurations.
- (1) An engine including a piston part and a cylinder body part with a sliding surface
on which the piston part is slidable,
the cylinder body part being made of an Al alloy with an Si content of 16% by mass
or more, the cylinder body part including Si primary crystal grains, Si eutectic crystal
grains, and an Al alloy base material, the Si primary crystal grains having an average
crystal grain diameter of 8 µm or more and 50 µm or less, the Si eutectic crystal
grains having an average crystal grain diameter less than the average crystal grain
diameter of the Si primary crystal grains,
the sliding surface being configured such that, at least in an upper quarter region
of the sliding surface, the Si primary crystal grains and the Al alloy base material
are exposed so as to be contactable with the piston part, and a plurality of substantially
parallel linear grooves are formed at a pitch greater than the average crystal grain
diameter of the Si primary crystal grains so that the plurality of substantially parallel
linear grooves have a portion that exists between adjacent ones of the Si primary
crystal grains, the plurality of substantially parallel linear grooves having a depth
equal to or more than one-third of an upper limit value of a diameter range of the
Si eutectic crystal grains in a grain size distribution of Si crystal grains in the
cylinder body part.
In the configuration of (1), the cylinder body part is made of an Al alloy with an
Si content of 16% by mass or more. The average crystal grain diameter of the Si primary
crystal grains exposed on the upper quarter region of the sliding surface is 8 µm
or more and 50 µm or less. In consideration of receiving a load from the piston part,
the Si primary crystal grains are given appropriate sizes and distributed appropriately
over the sliding surface. Under such conditions, the Si primary crystal grains and
the Al alloy base material are exposed so as to be contactable with the piston part,
and a plurality of substantially parallel linear grooves are formed at a pitch greater
than the average crystal grain diameter of the Si primary crystal grains, the plurality
of substantially parallel linear grooves having a depth equal to or more than one-third
of an upper limit value of a diameter range of the Si eutectic crystal grains in a
grain size distribution of Si crystal grains in the cylinder body part. Since the
plurality of substantially parallel linear grooves are formed at a pitch greater than
the average crystal grain diameter of the Si primary crystal grains, uniformity of
dispersion of a lubricant on the sliding surface can be improved. As a result, uniformity
of an oil film formed on the sliding surface can be enhanced. In addition, a sufficient
amount of lubricant can be retained in the grooves, because the plurality of linear
grooves have a depth equal to or more than one-third of an upper limit value of a
diameter range of the Si eutectic crystal grains in a grain size distribution of Si
crystal grains in the cylinder body part. Accordingly, discontinuity of the oil film
on the sliding surface can be suppressed. Furthermore, the plurality of linear grooves
have a portion that extends between adjacent ones of the Si primary crystal grains.
Since a load of the piston part is received by the Si primary crystal grains, wear
of the sliding surface (the Al alloy base material) is suppressed in its regions near
both sides of the groove, so that the retention of the lubricant in the groove is
facilitated.
The A1 alloy base material is exposed on the sliding surface so as to be contactable
with the piston part. Contact of the Al alloy base material with the piston part has
conventionally been considered to be undesirable from the viewpoint of suppression
of generation of scuffs. In the configuration of (1), however, the Al alloy base material
as well as the Si primary crystal grains, which have appropriate sizes and are distributed
appropriately over the sliding surface, is exposed on the sliding surface. In the
configuration of (1), as described above, the uniformity of the oil film formed on
the sliding surface is enhanced while a sufficient amount of lubricant is retained.
An influence of contact of the Al alloy base material with the piston part is accordingly
reduced to an acceptable level, and the improved uniformity of the oil film exerts
an anti-scuff effect. In this manner, generation of scuffs can be suppressed more
effectively.
- (2) An engine including a piston part and a cylinder body part with a sliding surface
on which the piston part is slidable,
the cylinder body part being made of an Al alloy with an Si content of 16% by mass
or more and formed by a high-pressure die casting process, the cylinder body part
including Si primary crystal grains, Si eutectic crystal grains, and an Al alloy base
material, the Si eutectic crystal grains having an average crystal grain diameter
less than the average crystal grain diameter of the Si primary crystal grains,
the sliding surface being configured such that, at least in an upper quarter region
of the sliding surface, the Si primary crystal grains and the Al alloy base material
are exposed so as to be contactable with the piston part, and a plurality of substantially
parallel linear grooves are formed at a pitch greater than the average crystal grain
diameter of the Si primary crystal grains so that the plurality of substantially parallel
linear grooves have a portion that exists between adjacent ones of the Si primary
crystal grains, the plurality of substantially parallel linear grooves having a depth
equal to or more than one-third of an upper limit value of a diameter range of the
Si eutectic crystal grains in a grain size distribution of Si crystal grains in the
cylinder body part.
In the configuration of (2), the cylinder body part is made of an Al alloy with an
Si content of 16% by mass or more and formed by a high-pressure die casting process.
In consideration of receiving a load from the piston part, the Si primary crystal
grains are given appropriate sizes and distributed appropriately over the sliding
surface. Under such conditions, the Si primary crystal grains and the Al alloy base
material are exposed so as to be contactable with the piston part, and a plurality
of substantially parallel linear grooves are formed at a pitch greater than the average
crystal grain diameter of the Si primary crystal grains, the plurality of substantially
parallel linear grooves having a depth equal to or more than one-third of an upper
limit value of a diameter range of the Si eutectic crystal grains in a grain size
distribution of Si crystal grains in the cylinder body part. Since the plurality of
substantially parallel linear grooves are formed at a pitch greater than the average
crystal grain diameter of the Si primary crystal grains, uniformity of dispersion
of a lubricant on the sliding surface can be improved. As a result, uniformity of
an oil film formed on the sliding surface can be enhanced. In addition, a sufficient
amount of lubricant can be retained in the grooves, because the plurality of linear
grooves have a depth equal to or more than one-third of an upper limit value of a
diameter range of the Si eutectic crystal grains in a grain size distribution of Si
crystal grains in the cylinder body part. Accordingly, discontinuity of the oil film
on the sliding surface can be suppressed. Furthermore, the plurality of linear grooves
have a portion that extends between adjacent ones of the Si primary crystal grains.
Since a load of the piston part is received by the Si primary crystal grains, wear
of the sliding surface (the Al alloy base material) is suppressed in its regions near
both sides of the groove, so that the retention of the lubricant in the groove is
facilitated.
The Al alloy base material is exposed on the sliding surface so as to be contactable
with the piston part. Contact of the Al alloy base material with the piston part has
conventionally been considered to be undesirable from the viewpoint of suppression
of generation of scuffs. In the configuration of (2), however, the Al alloy base material
as well as the Si primary crystal grains, which have appropriate sizes and are distributed
appropriately over the sliding surface, is exposed on the sliding surface. In the
configuration of (2), as described above, the uniformity of the oil film formed on
the sliding surface is enhanced while a sufficient amount of lubricant is retained.
An influence of contact of the Al alloy base material with the piston part is accordingly
reduced to an acceptable level, and the improved uniformity of the oil film exerts
an anti-scuff effect. In this manner, generation of scuffs can be suppressed more
effectively.
- (3) The engine of (1) or (2), in which
the plurality of linear grooves have a depth equal to or more than one-third of an
upper limit value of a diameter range of the Si eutectic crystal grains and less than
the upper limit value of the diameter range of the Si eutectic crystal grains, in
a grain size distribution of Si crystal grains in the cylinder body part.
The configuration of (3) enables a sufficient and appropriate amount of lubricant
to be retained in the plurality of linear grooves. Thus, the anti-scuff effect exerted
by the improved uniformity of the oil film is enhanced. Accordingly, generation of
scuffs can be suppressed further effectively.
- (4) The engine of any one of (1) to (3), in which
the plurality of linear grooves have a depth of 2.0 µm or more and 6.0 µm or less.
The configuration of (4) enables a sufficient and appropriate amount of lubricant
to be retained in the plurality of linear grooves. Thus, the anti-scuff effect exerted
by the improved uniformity of the oil film is enhanced. Accordingly, generation of
scuffs can be suppressed further effectively.
- (5) The engine of any one of (1) to (4), in which
in a region between adjacent ones of the linear grooves, both the Si primary crystal
grain and the Al alloy base material are exposed on the sliding surface so as to be
contactable with the piston part.
In the configuration of (5), the Al alloy base material as well as the Si primary
crystal grains is exposed between adjacent linear grooves on the sliding surface so
as to be contactable with the piston part. Thus, wear of the sliding surface (Al alloy
base material) is suppressed more effectively. The retention of the lubricant in the
grooves is further facilitated. Accordingly, generation of scuffs can be suppressed
further effectively.
- (6) The engine of any one of (1) to (5), in which
the piston part includes a piston main body and a piston ring part, the piston ring
part including a plurality of piston rings arranged on an outer periphery of the piston
main body, and
the plurality of linear grooves are formed at a pitch that is greater than the average
crystal grain diameter of the Si primary crystal grains and less than the distance
from a lower end of the piston ring part to an upper end of the piston ring part with
respect to a reciprocating direction of the piston part.
The configuration of (6) enables a sufficient and appropriate amount of lubricant
to be retained in the plurality of linear grooves. Thus, the anti-scuff effect exerted
by the improved uniformity of the oil film is enhanced. Accordingly, generation of
scuffs can be suppressed further effectively.
- (7) The engine of any one of (1) to (6), in which
the piston part includes a piston main body and a piston ring arranged on an outer
periphery of the piston main body, and
the plurality of linear grooves have a width that is less than the thickness of the
piston ring.
In the configuration of (7), it is less likely that the piston ring is clipped or
caught on the groove while the piston ring is sliding on the sliding surface. This
allows the piston part to reciprocate more smoothly, and thus generation of scuffs
can be suppressed further effectively.
- (8) The engine of any one of (1) to (7), in which
the Si primary crystal grains exposed on the sliding surface are at least partially
broken down, and a surface appearing on the Si primary crystal grain as a result of
the breakdown is exposed on the sliding surface.
In the configuration of (8), a surface (hereinafter referred to as a fracture surface)
appearing on the Si primary crystal grain as a result of the breakdown functions as
an oil reservoir. Since the fracture surface of the Si primary crystal grain is textured,
the oil reservoir is capable of retaining a large amount of lubricant. The open area
of the oil reservoir is, for example, comparable with the cross-sectional area of
the Si primary crystal grain. The depth of the oil reservoir is, for example, less
than the diameter of the Si primary crystal grain. Not only the plurality of substantially
parallel linear grooves but also the oil reservoirs including the fracture surfaces
of the Si primary crystal grains are formed in the sliding surface. This enables an
increased amount of lubricant to be retained while maintaining the uniformity of dispersion
of the lubricant. Generation of scuffs can be suppressed more effectively.
- (9) A cylinder body member provided with the cylinder body part included in the engine
of any one of (1) to (8).
The configuration of (9) achieves a cylinder body member that is able to suppress
generation of scuffs at or near the top dead center more effectively.
- (10) A vehicle including the engine of any one of (1) to (8).
[0014] The configuration of (10) achieves a vehicle including an engine that is able to
suppress generation of scuffs at or near the top dead center more effectively.
Advantageous Effects of the Invention
[0015] The present teaching achieves more effective suppression of generation of scuffs
at or near the top dead center.
Brief Description of the Drawings
[0016]
[Fig. 1] A cross-sectional view schematically showing an engine 150 according to an
embodiment of the present teaching.
[Fig. 2] A side view schematically showing a piston part 122 included in the engine
150 shown in Fig. 1.
[Fig. 3] A perspective view schematically showing a cylinder body part 100 included
in the engine 150 shown in Fig. 1.
[Fig. 4] A cross-sectional view schematically showing the cylinder body part 100 shown
in Fig. 3.
[Fig. 5] A plan view schematically showing, on an enlarged scale, a portion of a sliding
surface 101 of the cylinder body part 100 shown in Fig. 3.
[Fig. 6] (a) and (b) are cross-sectional views each schematically showing, on an enlarged
scale, a portion of the sliding surface 101 of the cylinder body part 100 shown in
Fig. 3.
[Fig. 7] A graph showing a preferred example of a grain size distribution of Si crystal
grains.
[Fig. 8] A side view schematically showing a motorcycle including the engine 150 shown
in Fig. 1.
Description of Embodiments
[0017] Conventionally, a cylinder body part made of an Al alloy with a relatively high Si
content and manufactured by a high-pressure die casting process has a sliding surface
processed such that Si primary crystal grains are exposed in the form of floating
islands. On the sliding surface, contact between a piston ring and an Al alloy base
material is suppressed, and recesses each formed between the Si crystal grains function
as oil reservoirs. This is how generation of scuffs is suppressed.
[0018] Against such a conventional design concept, the inventors of the present teaching
have conducted intensive studies for achieving more effective suppression of generation
of scuffs at or near the top dead center, to reach the following findings.
[0019] In a cylinder body part made of an Al alloy with a relatively high Si content and
manufactured by a high-pressure die casting process, Si primary crystal grains are
given appropriate sizes and distributed appropriately over a sliding surface, in consideration
of receiving a load from a piston part. This leads to balanced retention of a sufficient
amount of lubricant between the Si primary crystal grains at or near the top dead
center, thus improving uniformity of an oil film formed on the sliding surface, which
makes generation of scuffs less likely to occur even though an Al alloy base material
is contacted by the piston part. That is, contact between the Al alloy base material
and the piston part is allowable. Owing to advantages of the improved uniformity of
the oil film, generation of scuffs at or near the top dead center can be suppressed
more effectively.
[0020] The present teaching is an teaching accomplished based on the above-described findings
which are contradictory to the conventional design concept. Embodiments of the present
teaching are described below with reference to the drawings.
<Engine>
[0021] Fig. 1 is a cross-sectional view schematically showing an engine 150 according to
an embodiment of the present teaching. In this embodiment, R represents the reciprocating
direction of a piston part 122. U represents the upward direction, which means the
direction away from a cylinder body part 100 and toward a cylinder head 130. L represents
the downward direction, which means the direction away from the cylinder body part
100 and toward a crank case 110. Although the following description illustrates a
water-cooled type engine as an example, the present teaching is not limited thereto
and also applicable to air-cooled type engines. In the present teaching, no particular
limitation is put on the number of cylinders of an engine, though this embodiment
describes a single-cylinder engine. The engine of this embodiment is a four-stroke
engine, but instead it may be a two-stroke engine.
[0022] The engine 150 includes the crank case 110, the cylinder body part 100, and the cylinder
head 130. Although this embodiment illustrates the cylinder body part 100 and the
crank case 110 configured as separate bodies, the cylinder body part 100 and the crank
case 110 of the present teaching may be integrated as a single body.
[0023] The crank case 110 has a crankshaft 111 arranged therein. The crankshaft 111 includes
a crank pin 112 and a crank web 113.
[0024] The cylinder body part 100 is provided above the crank case 110. The cylinder body
part 100 includes a cylinder wall 103 and an outer wall 104. The cylinder wall 103
has a generally cylindrical shape. The cylinder wall 103 is formed so as to define
a cylinder bore 102. The outer wall 104, which encloses the cylinder wall 103, forms
an outer contour of the cylinder body part 100. A water jacket 105 is provided between
the cylinder wall 103 and the outer wall 104.
[0025] The piston part 122 is received in the cylinder bore 102 of the cylinder body part
100. The piston part 122 is configured to slide within the cylinder bore 102 while
being in contact with a sliding surface 101 of the cylinder body part 100 (see Fig.
2). The piston part 122 is made of, for example, an Al alloy (typically, an Si-containing
Al alloy). The piston part 122 is formed by, for example, forging as disclosed in
the specification of United States Patent No.
6205836. A process for manufacturing the piston part 122 is not particularly limited. For
example, the piston part 122 may be formed by casting.
[0026] No cylinder sleeve is provided in the cylinder bore 102. No plating is applied to
an inner surface of the cylinder wall 103 of the cylinder body part 100. This embodiment,
which requires no cylinder sleeve, can simplify a process for manufacturing the engine
150, reduce the weight of the engine 150, and improve cooling performance. In addition,
since no plating need be applied to the inner surface of the cylinder wall 103, manufacturing
costs can be reduced. The present teaching is not limited to this embodiment, and
it may also be acceptable that, for example, a cylinder sleeve including the cylinder
body part 100 of this embodiment is provided in the cylinder bore 102. No particular
limitation is put on how the cylinder sleeve is provided, examples of which include
fitting into the cylinder bore 102, casting around, or the like. In such a case, the
cylinder sleeve includes the sliding surface 101 of this embodiment. No plating is
applied to an inner surface of the cylinder body part 100 included in the cylinder
sleeve.
[0027] The cylinder head 130 is provided on the cylinder body part 100. The cylinder head
130, in combination with the piston part 122 of the cylinder body part 100, defines
a combustion chamber 131. The cylinder head 130 includes an intake port 132 and an
exhaust port 133. In the intake port 132, an intake valve 134 is arranged for supply
of a mixed gas into the combustion chamber 131. In the exhaust port 133, an exhaust
valve 135 is arranged for exhaust in the combustion chamber 131.
[0028] The piston part 122 and the crankshaft 111 are coupled to each other via a connecting
rod 140. More specifically, a piston pin 123 of the piston part 122 is inserted through
a through hole provided in a small-end portion 142 of the connecting rod 140, and
a crank pin 112 of the crankshaft 111 is inserted through a through hole provided
in a large-end portion 144 of the connecting rod 140, thereby coupling the piston
part 122 to the crankshaft 111. A roller bearing (rolling-element bearing) 114 is
provided between the crank pin 112 and an inner peripheral surface of the through
hole of the large-end portion 144. Although the engine 150 is not provided with an
oil pump configured to forcibly feed a lubricant, the engine of the present teaching
may be provided with an oil pump.
[0029] Fig. 2 is a side view schematically showing the piston part 122 included in the engine
150 shown in Fig. 1.
[0030] The piston part 122 is arranged in the cylinder bore 102. The piston part 122 includes
a piston main body 122a and a piston ring part 122b. The piston main body 122a includes
the piston pin 123 for insertion into the through hole of the connecting rod 140.
The piston ring part 122b includes three (a plurality of) piston rings 122c, 122d,
and 122e which are arranged on the outer periphery of the piston main body 122a.
[0031] The piston ring 122c, which is also referred to as a top ring, is fitted in a top
ring groove 122f formed in the outer periphery of the piston main body 122a. The piston
ring 122d, which is also referred to as a second ring, is fitted in a second ring
groove 122g formed in the outer periphery of the piston main body 122a. The piston
ring 122e, which is also referred to as an oil ring, is fitted in an oil ring groove
122h formed in the outer periphery of the piston main body 122a. The top ring 122c,
the second ring 122d, and the oil ring 122e are arranged at intervals and in this
sequence from top to down with respect to the reciprocating direction R of the piston
part 122. In this embodiment, therefore, an upper end 122m of the piston ring part
122b with respect to the reciprocating direction R of the piston part 122 corresponds
to an upper surface of the top ring 122c. A lower end 122n of the piston ring part
122b corresponds to a lower surface of the oil ring 122e. Of the piston part 122,
in particular, the piston ring part 122b (the piston rings 122c, 122d, 122e) is in
contact with the sliding surface 101 of the cylinder wall 103. Although this embodiment
illustrates the piston ring part 122b including three piston rings, the number of
piston rings included in the piston ring part 122b is not particularly limited.
[0032] Fig. 3 is a perspective view schematically showing the cylinder body part 100 included
in the engine 150 shown in Fig. 1. Fig. 4 is a cross-sectional view schematically
showing the cylinder body part 100 shown in Fig. 3.
[0033] The cylinder body part 100, which includes the sliding surface 101, is made of an
Si-containing Al alloy. It more specifically is made of an Al alloy with an Si content
of 16% by mass or more. Preferably, the Al alloy has an Al content of 73.4% by mass
or more and 79.6% by mass or less, an Si content of 16% by mass or more and 24% by
mass or less, and a copper content of 2.0% by mass or more and 5.0% by mass or less.
The wear resistance and strength of the cylinder body part 100 can be increased. It
is also preferable that the Si content is 18% by mass or more. It is also preferable
that the Si content is 22% by mass or less. It is preferable that the Al alloy has
a phosphorus content of 50 ppm by mass or more and 200 ppm by mass or less, and a
calcium content of 0.01% by mass or less. The Al alloy having a phosphorus content
of 50 ppm by mass or more and 200 ppm by mass or less can suppress coarsening of Si
crystal grains, thus allowing the Si crystal grains to be uniformly dispersed in the
alloy. In addition, the Al alloy having a calcium content of 0.01% by mass or less
can ensure that an effect of refining the Si crystal grains be exerted by phosphorus,
so that a metallographic structure with an excellent wear resistance is obtained.
[0034] As shown in Figs. 3 and 4, the cylinder body part 100 includes the cylinder wall
103 provided with the sliding surface 101, and the outer wall 104 provided with an
exposed surface on the outer periphery thereof. The water jacket 105 is provided between
the cylinder wall 103 and the outer wall 104. The water jacket 105 is configured to
hold a cooling liquid.
[0035] The cylinder body part 100 includes the sliding surface 101 to be contacted by the
piston part 122 (see Fig. 1). The sliding surface 101 is a surface (an inner peripheral
surface) of the cylinder wall 103 on the cylinder bore 102 side. In other words, the
sliding surface 101 is the innermost surface of the inner peripheral surface of the
cylinder wall 103 with respect to the radial direction of the cylinder body part 100.
In the present teaching, contact of the sliding surface 101 with the piston part 122
includes contact of the sliding surface 101 with the piston part 122 with interposition
of an oil film formed by the lubricant.
[0036] In this specification, the "upper side" of the sliding surface 101 means the cylinder
head side (the top-dead-center side). The "lower side" of the sliding surface 101
means the crank case side (the bottom-dead-center side). An upper quarter region 101a
of the sliding surface 101 means a region closest to the cylinder head among four
regions obtained by equally dividing the entire sliding surface 101 into four with
respect to the piston sliding direction (the central axis direction of the cylinder
bore 102). A lower quarter region 101b of the sliding surface 101 means a region closest
to the crank case.
[0037] In this embodiment, below-described linear grooves 8 (see Fig. 5) are formed throughout
the sliding surface 101. The present teaching, however, is not limited to this example.
In the present teaching, it suffices that a portion where the linear grooves 8 are
formed is at least the upper quarter region 101a of the sliding surface 101. The portion
where the linear grooves 8 are formed may be only the upper quarter region 101a of
the sliding surface 101, or alternatively may be the upper quarter region 101a and
the lower quarter region 101b of the sliding surface 101.
[0038] Fig. 5 is a plan view schematically showing, on an enlarged scale, the sliding surface
of the cylinder body part 100 shown in Fig. 3. R represents the reciprocating direction
of the piston part 122. Figs. 6(a) and 6(b) are cross-sectional views each schematically
showing, on an enlarged scale, the sliding surface of the cylinder body part 100 shown
in Fig. 3. The cross-sections shown in Figs. 6(a) and 6(b) are along the direction
R. In Figs. 6(a) and 6(b), for illustrative convenience, only first linear grooves
8a of the linear grooves 8 are shown.
[0039] On the sliding surface 101, a plurality of Si primary crystal grains 1, a plurality
of Si eutectic crystal grains 2, and an Al alloy base material 3 are exposed. Si crystal
grains that are first deposited upon cooling of a molten Al-Si based alloy having
a hypereutectic composition are called "Si primary crystal grains". Si crystal grains
that are subsequently deposited are called "Si eutectic crystal grains". The Si primary
crystal grain 1 is relatively large, and has a granular shape for example. The Si
eutectic crystal grain 2 is relatively small, and has an acicular shape for example.
Not all of the Si eutectic crystal grains 2 have acicular shape. Some of the Si eutectic
crystal grains 2 may have granular shapes. In such a case, acicular Si eutectic crystal
grains 2 among the plurality of Si eutectic crystal grains 2 serve as main crystal
grains. The Al alloy base material 3 is a solid solution matrix containing Al. The
cylinder body part 100 includes the plurality of Si primary crystal grains 1, the
plurality of Si eutectic crystal grains 2, and the Al alloy base material 3. The plurality
of Si primary crystal grains 1 and the plurality of Si eutectic crystal grains 2 are
dispersed in the Al alloy base material 3.
[0040] The average crystal grain diameter of the Si primary crystal grains 1 is, for example,
8 µm or more and 50 µm or less. A sufficient number of Si primary crystal grains 1
exist per unit area of the sliding surface 101. Each of the Si primary crystal grains
1, therefore, receives a relatively low load during operation of the engine 150. Breakdown
of the Si primary crystal grains 1 during operation of the engine 150 is suppressed.
A portion of each Si primary crystal grain 1 embedded in the Al alloy base material
3 is large enough to make the Si primary crystal grain 1 less likely to fall off.
This leads to reduction of wear of the sliding surface 101, which may be caused by
fallen Si primary crystal grains 1. If the average crystal grain diameter of the Si
primary crystal grains 1 is less than 8 µm, a portion of the Si primary crystal grain
1 embedded in the Al alloy base material 3 is small. The Si primary crystal grain
1 is therefore likely to fall off during operation of the engine 150. Since fallen
Si primary crystal grains 1 act as abrasive particles, much wear of the sliding surface
101 may occur. If the average crystal grain diameter of the Si primary crystal grains
1 is more than 50 µm, the number of Si primary crystal grains 1 existing per unit
area of the sliding surface 101 is small. Each of the Si primary crystal grains 1,
therefore, receives a high load during operation of the engine 150, which may cause
breakdown of the Si primary crystal grains 1. Since fragments of broken-down Si primary
crystal grains 1 act as abrasive particles, much wear of the sliding surface 101 may
occur. It is preferable that the average crystal grain diameter of the Si primary
crystal grains 1 is 12 µm or more.
[0041] In this embodiment, the cylinder body part 100 is made of an Al alloy with an Si
content of 16% by mass or more and formed by a high-pressure die casting process (HPDC).
The high-pressure die casting process is a casting process in which a pressure is
applied to a molten so that the molten is supplied into a die under a pressure greater
than atmospheric pressure. In the high-pressure die casting process, a portion to
be the sliding surface 101 can be cooled at a high cooling speed (e.g., 4°C/sec or
more and 50°C/sec or less). This makes it possible that, for example, the average
crystal grain diameter of the Si primary crystal grains 1 is controlled to be 8 µm
or more and 50 µm or less.
[0042] The average crystal grain diameter of the Si eutectic crystal grains 2 is less than
the average crystal grain diameter of the Si primary crystal grains 1. Preferably,
the average crystal grain diameter of the Si eutectic crystal grains 2 is 7.5 µm or
less. The Si eutectic crystal grains 2 serve to reinforce the Al alloy base material
3. Refining the Si eutectic crystal grains 2 leads to improvement in the wear resistance
and strength of the cylinder body part 100.
[0043] Here, a grain size distribution of the Si crystal grains in the cylinder body part
100 is described.
[0044] Fig. 7 is a graph showing a preferred example of the grain size distribution of the
Si crystal grains.
[0045] In the graph of Fig. 7, an Si crystal grain having a crystal grain diameter of 1
µm to 7.5 µm is an Si eutectic crystal grain 2, and an Si crystal grain having a crystal
grain diameter of 8 µm to 50 µm is an Si primary crystal grain 1. Preferably, the
Si crystal grains 1, 2 of the cylinder body part 100 have a grain size distribution
in which peaks appear where the crystal grain diameter is in a range of 1 µm to 7.5
µm and in a range of 8 µm to 50 µm. The wear resistance and strength of the cylinder
body part 100 can be highly improved.
[0046] From the viewpoint of reinforcing the Al alloy base material 3 with the Si eutectic
crystal grains 2, as shown in Fig. 7, it is preferable that the frequency at a first
peak (a peak due to the Si eutectic crystal grains 2) in the crystal grain diameter
range of 1 µm to 7.5 µm is five times greater than the frequency at a second peak
(a peak due to the Si primary crystal grains 1) in the crystal grain diameter range
of 8 µm to 50 µm.
[0047] As a way to control the average crystal grain diameters of the Si primary crystal
grains 1 and the Si eutectic crystal grains 2, it is conceivable to adjust the speed
of cooling a portion to be the sliding surface 101 in the step of forming a molded
body by casting (below-described step S1c). In one specific example, casting is performed
such that a portion to be the sliding surface 101 is cooled at a cooling speed of,
for example, 4°C/sec or more and 50°C/sec or less, thus enabling the Si crystal grains
1 and 2 to be deposited with the Si primary crystal grains 1 having an average crystal
grain diameter of 8 µm or more and 50 µm or less and the Si eutectic crystal grains
2 having an average crystal grain diameter of 7.5 µm or less.
[0048] Next, the linear grooves 8 formed in the sliding surface 101 are described.
[0049] As shown in Figs. 5, 6(a), and 6(b), a plurality of linear grooves 8 are formed in
the sliding surface 101. In this embodiment, the plurality of linear grooves 8 include
a plurality of first linear grooves 8a and a plurality of second linear grooves 8b.
The plurality of first linear grooves 8a, which are shaped so as to extend from the
upper left to the lower right in Fig. 5, are substantially in parallel with one another.
The plurality of first linear grooves 8a form a striped pattern on the sliding surface
101. The plurality of second linear grooves 8b, which are shaped so as to extend from
the upper right to the lower left in Fig. 5, are substantially in parallel with one
another. The plurality of second linear grooves 8b form a striped pattern on the sliding
surface 101. The plurality of first linear grooves 8a and the plurality of second
linear grooves 8b are not in parallel but intersect with each other. Thus, the plurality
of linear grooves 8 form a lattice pattern on the sliding surface 101. In Fig. 5,
portions where the Si primary crystal grains 1 and/or the Si eutectic crystal grains
2 overlap the linear grooves 8 indicate portions where the linear grooves 8 are formed
so as to pass over exposed surfaces of the Si primary crystal grains 1 and/or the
Si eutectic crystal grains 2. At least a part of these portions has a fracture surface
5a as shown in Fig. 6(b).
[0050] At least two linear grooves 8 of the plurality of linear grooves 8 are substantially
in parallel with each other. Some linear grooves 8 (the first linear grooves 8a) and
the other linear grooves 8 (the second linear grooves 8b) of the plurality of linear
grooves 8 may intersect with each other. It may also be acceptable that the plurality
of linear grooves 8 are formed such that none of them intersect but all of them are
substantially in parallel with one another. Here, being "substantially in parallel"
means a state where adjacent linear grooves 8 extend without crossing each other.
The meaning of being "substantially in parallel" can therefore be interpreted as follows.
For example, even though adjacent linear grooves 8 are, in a strict sense, not in
parallel with each other because of errors, misalignments, etc., caused during formation
of the linear grooves 8; in the present teaching, the adjacent linear grooves 8 can
be considered to be substantially in parallel with each other. Although a set of first
linear grooves 8a and a set of second linear grooves 8b are provided as sets of parallel
linear grooves in the sliding surface 101, the number of sets of parallel linear grooves
is not particularly limited in the present teaching. Grooves belonging to different
sets intersect with each other. A pattern formed by the plurality of linear grooves
8 provided in the sliding surface 101 is not limited to a square lattice pattern as
shown in Fig. 5. A pattern formed by the plurality of linear grooves 8 may be a striped
pattern as formed by the first linear grooves 8a or the second linear grooves 8b,
or may be a polygonal lattice pattern such as a triangular lattice pattern. The square
lattice pattern is an example of the polygonal lattice pattern. In the striped pattern
and the lattice pattern, the pitch of grooves may not necessarily be constant.
[0051] In this embodiment, the plurality of linear grooves 8 form a regular pattern (a striped
pattern, a polygonal lattice pattern, etc.). In this embodiment, the Al alloy base
material 3 as well as the Si primary crystal grains 1 included in the regular pattern
is exposed on the sliding surface 101 such that it is contactable with the piston
ring part 122b (the piston part 122). The sliding surface 101 having the linear grooves
8 formed therein in the regular pattern enables a lubricant to be dispersed with an
improved uniformity, as compared with a conventional irregular sliding surface (a
sliding surface on which Si crystal grains are exposed in the form of floating islands).
As a consequence, in this embodiment, an oil film formed on the sliding surface 101
has a high uniformity. In the following, descriptions of the linear grooves 8 apply
to both the first linear grooves 8a and the second linear grooves 8b, except where
the first linear grooves 8a and the second linear grooves 8b are distinguished from
each other.
[0052] As for the shapes of the linear grooves 8 in a plan view, the linear grooves 8 have
straight-line shapes in a plan view, as shown in Fig. 5. In the present teaching,
however, the shapes of the linear grooves 8 in a plan view are not limited to straight-line
shapes, and it suffices that they are line-like shapes extending substantially in
parallel with one another such that adjacent linear grooves 8 do not intersect. To
be specific, it may be acceptable that the linear grooves 8 have curved-line shapes.
The linear groove 8 may include a portion with a curved-line shape and a portion with
a straight-line shape. The linear groove 8 may include a flexed portion. The plurality
of linear grooves 8 may have different shapes in a plan view. All of the linear grooves
8 may have identical or substantially identical shapes in a plan view. It is not always
necessary that each of the plurality of linear grooves 8 is formed continuous throughout
the entire sliding surface 101. It is not always necessary that each of the plurality
of linear grooves 8 extends to an end edge of the sliding surface 101. It may be acceptable
that each of the plurality of linear grooves 8 includes a discontinuous portion on
the sliding surface 101.
[0053] As for the width of the linear groove 8, no particular limitation is put on the width
of the linear groove 8. Preferably, the width of the linear groove 8 is less than
the thickness of the thinnest one of the piston rings 122c, 122d, and 122e. Preferably,
the width of the linear groove 8 is equal to or more than the average crystal grain
diameter of the Si primary crystal grains 1. Preferably, the width of the linear groove
8 is equal to or more than a maximum value of the grain diameter range of the Si primary
crystal grains 1 in the grain size distribution in the cylinder body part 100. Although
Fig. 5 illustrates the linear grooves 8 having a fixed width, this example does not
limit the present teaching. It may be acceptable that the width of the linear groove
8 varies depending on its location. It may also be acceptable that the plurality of
linear grooves 8 have different widths. It may also be acceptable that all of the
linear grooves 8 have the same width or substantially the same width.
[0054] As for the depth of the linear groove 8, the linear groove 8 of this embodiment has
a depth equal to or more than one-third of the upper limit value of the grain diameter
range of the Si eutectic crystal grains 2 in the grain size distribution of the Si
crystal grains in the cylinder body part 100. Here, the significance of the depth
of the linear groove 8 is described. Patent Literature 3 discloses a technique for
suppressing generation of scuffs at or near the top dead center more effectively.
In Patent Literature 3, a sliding surface is etched, and an Al alloy base material
is removed in the depth direction substantially uniformly over the entire sliding
surface except its regions having Si crystal grains which exist in the form of floating
islands. In the technique of Patent Literature 3, therefore, it is preferable to perform
the etching process so as to make the Si crystal grains less likely or unlikely to
fall off from the sliding surface, which means that forming deep recesses or grooves
is disadvantageous. In this embodiment, on the other hand, the linear grooves 8 are
formed at a pitch greater than the average crystal grain diameter of the Si primary
crystal grains, and thus a limited amount of the Al alloy base material is removed.
It is therefore possible to form the linear grooves 8 having a relatively large depth.
To be specific, the linear grooves 8 of this embodiment have a depth equal to or more
than one-third of the upper limit value of the grain diameter range of the Si eutectic
crystal grains 2 which generally have acicular shapes, but fall-off of the Si eutectic
crystal grains 2 is prevented or suppressed. Since the average crystal grain diameter
of the Si primary crystal grains 1 is larger than the average crystal grain diameter
of the Si eutectic crystal grains 2, fall-off of the Si primary crystal grains 1 is
also prevented or suppressed. Since the plurality of substantially parallel linear
grooves with a relatively large depth are formed in the sliding surface, a large amount
of lubricant can be retained, so that the uniformity of dispersion of the lubricant
is improved. Accordingly, this embodiment is able to prevent or suppress fall-off
of the Si crystal grains with enhancement of the uniformity of the oil film. Preferably,
the linear groove 8 has a depth of 2.0 µm or more. It may be acceptable that the linear
groove 8 has a depth of 40% or more of the upper limit value of the grain diameter
range of the Si eutectic crystal grains 2 in the grain size distribution of the Si
crystal grains in the cylinder body part 100. It may also have a depth equal to or
more than one-half of the upper limit value of the grain diameter range of the Si
eutectic crystal grains 2 in the grain size distribution of the Si crystal grains
in the cylinder body part 100.
[0055] Furthermore, it is preferable that the linear grooves 8 have a depth less than the
upper limit value of the grain diameter range of the Si eutectic crystal grains 2.
This allows the lubricant retained in the linear grooves 8 to be appropriately and
efficiently supplied to the sliding surface 101. It is preferable that the linear
grooves 8 have a depth of 6.0 µm or less. In the present teaching, in a case where
the upper limit value and the lower limit value of the depth of the linear groove
8 are defined, a groove having a depth less than the lower limit value of the depth
of the linear groove 8 and/or a groove having a depth more than the upper limit value
of the depth of the linear groove 8 may be formed in the sliding surface 101. In other
words, in the present teaching, it may be acceptable that a groove other than the
linear groove defined in the present teaching is formed in the sliding surface.
[0056] The linear groove 8 has such a cross-sectional shape that the width of the linear
groove 8 decreases as the depth of the linear groove 8 increases. The cross-sectional
shape of the linear groove 8 means the shape of a cross-section of the linear groove
8 in a plane perpendicular to the direction in which the linear groove 8 extends.
In the present teaching, the cross-sectional shape of the linear groove 8 is not particularly
limited. The cross-sectional shape of the linear groove 8 may be, for example, generally
U-shaped or generally V-shaped as shown in Fig. 6(a). It is not necessary that all
the cross-sections of the linear grooves 8 have identical shapes. Different portions
of the linear groove 8 may have different cross-sectional shapes, or different linear
grooves 8 may have different cross-sectional shapes. A portion (ridge) between linear
grooves 8 may not necessarily have a flat surface as shown in Figs. 5, 6(a), and 6(b).
The portion between linear grooves 8 may have an inclined surface or may form a ridge
line. One or more grooves having a depth less than the depth of the linear groove
8 may be formed.
[0057] As for the pitch of the first linear grooves 8, the plurality of first linear grooves
8a that are substantially in parallel are formed at a pitch greater than the average
crystal grain diameter of the Si primary crystal grains 1. As a result, at least a
part of the plurality of Si primary crystal grains 1 exists between adjacent first
linear grooves 8a. In this embodiment, both the Si primary crystal grain 1 and the
Al alloy base material 3 are exposed on the sliding surface 101 in a region between
adjacent first linear grooves 8a such that both the Si primary crystal grain 1 and
the Al alloy base material 3 are contactable with the piston part 122. Since the portion
of the sliding surface 101 contactable with the piston part 122 is adjacent to the
first linear grooves 8a in a plan view, a lubricant can be smoothly supplied to the
sliding surface 101. Although the Al alloy base material 3 is exposed on the sliding
surface 101 so as to be contactable with the piston part 122, the Si primary crystal
grains 1 are also exposed on the sliding surface 101 so as to be contactable with
the piston part 122, and therefore wear of the sliding surface 101 (the Al alloy base
material 3) is suppressed more effectively. Although Fig. 5 illustrates a case where
a pair of adjacent first linear grooves 8a extend at a constant pitch irrespective
of location, this example does not limit the present teaching. The pitch of the pair
of adjacent first linear grooves 8a may not necessarily be constant. For example,
it may be acceptable that each of adjacent first linear grooves 8a is formed in a
meandering shape so that the pitch of the first linear grooves 8a varies depending
on location. While the above descriptions are for the first linear grooves 8a, the
same descriptions as those of the first linear grooves 8a apply to the second linear
grooves 8b, and therefore descriptions of the second linear grooves 8b are omitted
herein.
[0058] In this embodiment, as shown in Fig. 5, at least one of the linear grooves 8 passes
through an Si primary crystal grain 1 while breaking down the Si primary crystal grain
1. That is, at least one of the linear grooves 8 is formed so as to pass over an exposed
surface of an Si primary crystal grain 1. This provides a further enhanced uniformity
of dispersion of the lubricant on the sliding surface 101. The present teaching is
not limited to this example.
[0059] In this embodiment, as shown in Fig. 6(b), the Si primary crystal grain 1 having
the fracture surface 5a is exposed on the sliding surface 101. That is, in this embodiment,
the Si primary crystal grain 1 exposed on the sliding surface 101 is at least partially
broken down, and a surface (which means the fracture surface 5a) that appears on the
Si primary crystal grain 1 as a result of the breakdown is exposed on the sliding
surface 101. In this manner, an oil reservoir 5b is formed in the sliding surface
101. Since the fracture surface of the Si primary crystal grain 1 is textured, the
oil reservoir 5b is capable of retaining a large amount of lubricant. The open area
of the oil reservoir 5b is comparable with the cross-sectional area of the Si primary
crystal grain 1 (the area of a portion exposed on the sliding surface 101). The depth
of the oil reservoir 5b is less than the diameter of the Si primary crystal grain
1. Not only the plurality of first linear grooves 8a that are substantially in parallel
with one another but also the oil reservoirs 5b including the fracture surfaces 5a
of the Si primary crystal grains 1 are formed in the sliding surface 101. This enables
an increased amount of lubricant to be retained while maintaining the uniformity of
dispersion of the lubricant. Generation of scuffs can be suppressed more effectively.
The fracture surfaces 5a are formed during a surface treatment performed on the cylinder
body part 100, the surface treatment being performed after the cylinder body part
100 is formed by the casting process. More specifically, for example, the fracture
surfaces 5a are formed while the Si primary crystal grains 1 are honed with a grinding
stone.
[0060] In this embodiment, the cylinder body part 100 is made of an Al alloy with an Si
content of 16% by mass or more. The average crystal grain diameter of the Si primary
crystal grains 1 exposed on the upper quarter region 101a of the sliding surface 101
is 8 µm or more and 50 µm or less. In consideration of receiving a load from the piston
part 122, the Si primary crystal grains 1 are given appropriate sizes and distributed
appropriately over the sliding surface. Under such conditions, the Si primary crystal
grains 1 and the Al alloy base material 3 are exposed so as to be contactable with
the piston part 122, and moreover the plurality of substantially parallel linear grooves
8 (the first linear grooves 8a and the second linear grooves 8b) having a depth equal
to or more than one-third of the upper limit value of the grain diameter range of
the Si eutectic crystal grains 2 in the grain size distribution of the Si crystal
grains in the cylinder body part 100 are formed at a pitch greater than the average
crystal grain diameter of the Si primary crystal grains 1. Since the plurality of
substantially parallel linear grooves 8 are formed at a pitch greater than the average
crystal grain diameter of the Si primary crystal grains 1, the uniformity of dispersion
of the lubricant on the sliding surface 101 can be improved. As a result, the uniformity
of the oil film formed on the sliding surface can be enhanced. In addition, a sufficient
amount of lubricant can be retained in the linear grooves 8, because the plurality
of linear grooves 8 have a depth equal to or more than one-third of the upper limit
value of the grain diameter range of the Si eutectic crystal grains 2 in the grain
size distribution of the Si crystal grains in the cylinder body part 100. Accordingly,
discontinuity of the oil film on the sliding surface can be suppressed. Furthermore,
the plurality of linear grooves 8 have portions that extend between adjacent Si primary
crystal grains 1. Since a load of the piston part 122 is received by the Si primary
crystal grains 1, wear of the sliding surface 101 (the Al alloy base material 3) is
suppressed in its regions near both sides of the linear groove 8, so that the retention
of the lubricant in the linear groove 8 is facilitated.
[0061] The Al alloy base material 3 is exposed on the sliding surface 101 so as to be contactable
with the piston part 122. Contact of the Al alloy base material 3 with the piston
part 122 has conventionally been considered to be undesirable from the viewpoint of
suppression of generation of scuffs. In this embodiment, however, the Al alloy base
material 3 as well as the Si primary crystal grains 1, which have appropriate sizes
and are distributed appropriately over the sliding surface 101, is exposed on the
sliding surface 101. The uniformity of the oil film formed on the sliding surface
101 is enhanced while a sufficient amount of lubricant is retained, as described above.
An influence of contact of the Al alloy base material 3 with the piston part 122 is
accordingly reduced to an acceptable level, and the improved uniformity of the oil
film exerts an anti-scuff effect. In this manner, generation of scuffs can be suppressed
more effectively.
<Manufacturing Process>
[0062] A process for manufacturing the cylinder body part 100 of this embodiment is described.
[0063] The cylinder body part 100 is manufactured by, for example, performing the following
steps S1 to S4 in order:
step S1 of preparing a molded body;
step S2 of performing a fine boring;
step S3 of performing a rough honing; and
step S4 of performing a finishing honing.
[0064] In the process for manufacturing the cylinder body part 100, firstly, a molded body
made of an Si-containing Al alloy is prepared (step S1). The molded body includes,
near a surface thereof, Si primary crystal grains and Si eutectic crystal grains.
The step S1 of preparing the molded body includes, for example, steps S1a to S1e:
step S1a of preparing a silicon-containing Al alloy;
step S1b of producing a molten;
step S1c of performing a high-pressure die casting process;
step S1d of performing a heat treatment; and
step S1e of performing a machining.
[0065] Firstly, an Si-containing Al alloy is prepared (step S1a). To ensure that the wear
resistance and strength of the cylinder body part 100 be sufficiently high, it is
preferable to adopt an Al alloy having an Al content of 73.4% by mass or more and
79.6% by mass or less, an Si content of 16% by mass or more and 24% by mass or less,
and a copper content of 2.0% by mass or more and 5.0% by mass or less.
[0066] Then, the Al alloy thus prepared is heated and melted in a melting furnace, to form
a molten (step S1b). It is preferable that about 100 ppm by mass of phosphorus is
added to an unmelted Al alloy beforehand or to the molten. The Al alloy having a phosphorus
content of 50 ppm by mass or more and 200 ppm by mass or less can suppress coarsening
of Si crystal grains, thus allowing the Si crystal grains to be uniformly dispersed
in the alloy. In addition, the Al alloy having a calcium content of 0.01% by mass
or less can ensure that an effect of refining the Si crystal grains be exerted by
phosphorus, so that a metallographic structure with an excellent wear resistance is
obtained. For these reasons, it is preferable that the Al alloy has a phosphorus content
of 50 ppm by mass or more and 200 ppm by mass or less and a calcium content of 0.01%
by mass or less.
[0067] Then, a high-pressure die casting process is performed to cast the molten Al alloy
(step S1c). To be specific, the molten is cooled in a casting mold, to form a molded
body. At this time, a portion of the cylinder wall 103 to be the sliding surface 101
is cooled at a high cooling speed (e.g., 4°C/sec or more and 50°C/sec or less), so
that a molded body including, near its surface, Si crystal grains which contribute
to the wear resistance is obtained. For this casting step S1c, a casting apparatus
disclosed in the
WO2004/002658 pamphlet can be used, for example.
[0068] Then, the molded body removed from the casting mold is subjected to any of heat treatments
called "T5", "T6", and "T7" (step S1d). T5 treatment is a treatment in which a molded
body is quenched by water-cooling, etc. immediately after removed from a casting mold,
then subjected to artificial aging at a predetermined temperature for a predetermined
period for the purpose of improving mechanical properties and obtaining dimensional
stabilization, and then air-cooled. T6 treatment is a treatment in which a molded
body is subjected to a solution treatment at a predetermined temperature for a predetermined
period after removed from a casting mold, then water-cooled, then subjected to an
artificial aging treatment at a predetermined temperature for a predetermined period,
and then air-cooled. T7 treatment, which is a treatment in which overaging is made
as compared with T6 treatment, is able to provide more dimensional stabilization than
T6 treatment is, but can provide less hardness than T6 treatment can.
[0069] Subsequently, a predetermined machining process is performed on the molded body (step
S1e). More specifically, a mating surface for mating with a cylinder head and a mating
surface for mating with a crank case are ground, for example.
[0070] After the molded body is prepared in the above-described manner, a fine boring process
is performed on a surface of the molded body, and more specifically on an inner peripheral
surface (that is, a surface to be the sliding surface 101) of the cylinder wall 103,
for the purpose of adjusting dimensional accuracy (step S2).
[0071] Then, the surface having the fine boring process performed thereon is subjected to
a rough honing treatment (step S3). To be specific, the surface to be the sliding
surface 101 is polished with a grinding stone of relatively low count (a grinding
stone having large abrasive particles). In this embodiment, the rough honing treatment
is performed throughout a region of the molded body to be the sliding surface 101,
but the present teaching is not limited to this example. In the present teaching,
it suffices that the rough honing treatment is performed at least on the upper quarter
region of the sliding surface 101.
[0072] Then, a finishing honing treatment is performed (step S4). To be specific, of the
surface of the molded body, a region to be the sliding surface 101 is polished with
a grinding stone of relatively high count (a grinding stone having small abrasive
particles). The rough honing treatment and the finishing honing treatment can be implemented
by using, for example, a honing apparatus disclosed in Japanese Patent Application
Laid-Open No.
2004-268179. Specifications (e.g., the type of the abrasive particles, the count (abrasive particle
diameter), the type of a bonding agent, etc.) of the grinding stones used in the rough
honing treatment and the finishing honing treatment can be set according to specifications
of the linear grooves 8 to be formed in the sliding surface 101.
[0073] The sliding surface 101 of this embodiment is formed through the above-described
steps. The plurality of Si primary crystal grains 1 and the Al alloy base material
3 are exposed on the sliding surface 101. While the piston part 122 is reciprocating
in the cylinder bore 102, the plurality of Si primary crystal grains 1 and the Al
alloy base material 3 are contacted by the piston part 122. The sliding surface 101
has the plurality of linear grooves 8 that are formed at least in the upper quarter
region of the sliding surface 101. The plurality of linear grooves 8 include the plurality
of substantially parallel first linear grooves 8a and the plurality of substantially
parallel second linear grooves 8b. In this embodiment, the linear grooves 8 are formed
by using a grinding stone, but the present teaching is not limited to this example.
The linear grooves 8 may be formed by using laser, for example. The number of times
the rough honing treatment and the finishing honing treatment are performed is not
limited to one, and they can be performed twice or more.
<Cylinder Body Member>
[0074] The cylinder body member of this embodiment is itself the above-described cylinder
body part 100 (see Fig. 1, etc.). The cylinder body part 100 is a part including the
sliding surface 101. The cylinder body member of the present teaching, however, is
not limited to this example. It suffices that the cylinder body member is provided
with the cylinder body part 100 including the sliding surface 101. The cylinder body
member of the present teaching may be a member (a so-called cylinder block) constituted
of the cylinder body part 100 and the crank case 110 formed integrally with each other.
The cylinder body member of the present teaching may be a cylinder sleeve that is
installed in the cylinder bore 102 when used. Since the cylinder body member includes
the above-described sliding surface 101, application of the cylinder body member to
an engine enables more effective suppression of generation of scuffs (particularly
at or near the top dead center) in the engine.
<Vehicle>
[0075] The vehicle of the present teaching includes various types of vehicles such as automobiles,
motorcycles, snowcats as exemplified by snowmobiles, and the like. The number of wheels
is not particularly limited to, for example, four, three, or two. The vehicle of the
present teaching may be a box-type vehicle in which an engine is arranged in a place,
such as an engine room, distant from a seat, or may be a straddled vehicle in which
an engine is at least partially arranged below a seat straddled by a driver. The straddled
vehicle includes a scooter-type vehicle that a driver can ride with feet together.
[0076] As an example of the vehicle, a motorcycle is illustrated below.
[0077] Fig. 8 is a side view schematically showing a motorcycle including the engine 150
shown in Fig. 1.
[0078] In the motorcycle shown in Fig. 8, a head pipe 302 is arranged at the front end of
a main body frame 301. A front fork 303 is attached to the head pipe 302, so as to
be swingable in the lateral direction of the vehicle. A front wheel 304 is rotatably
supported at the lower ends of the front fork 303. A handlebar 305 is provided at
the upper end of the front fork 303.
[0079] A rear frame 306 is provided so as to extend rearward from the upper side of a rear
end portion of the main body frame 301. A fuel tank 307 is provided above the main
body frame 301, and a main seat 308a and a tandem seat 308b are provided above the
rear frame 306.
[0080] A rear arm 309 extending rearward is attached to the rear end portion of the main
body frame 301. A rear wheel 310 is rotatably supported at the rear end of the rear
arm 309.
[0081] The engine 150 shown in Fig. 1 is held in a middle portion of the main body frame
301. The engine 150 adopts the cylinder body part 100 of this embodiment. A radiator
311 is provided on the front side of the engine 150. An exhaust tube 312 is connected
to the exhaust port of the engine 150. A muffler 313 is attached to the rear end of
the exhaust tube 312.
[0082] The engine 150 is coupled with a transmission 315. The transmission 315 has an output
shaft 316 to which a drive sprocket 317 is attached. The drive sprocket 317 is coupled
to a rear-wheel sprocket 319 of the rear wheel 310 via a chain 318. The transmission
315 and the chain 318 function as a transmission mechanism for transmitting power
generated by the engine 150 to a drive wheel.
[0083] The motorcycle (vehicle) of this embodiment, which is mounted with the engine 150
including the cylinder body part 100 with the sliding surface 101, is able to suppress
generation of scuffs, particularly at or near the top dead center, more effectively.
[0084] The average crystal grain diameters of the Si primary crystal grains and the Si eutectic
crystal grains are measured by applying image processing to a portion of the cylinder
body part to be the sliding surface. Based on the area of each Si crystal grain in
an image obtained by the image processing, the diameter (equivalent diameter) of the
Si crystal grain is calculated, assuming that the Si crystal grain in the image is
in the shape of a true circle. A fine crystal having a diameter of less than 1 µm
is not counted as the Si crystal grain (neither the Si primary crystal grain nor the
Si eutectic crystal grain). In this manner, the number (frequency) and the diameters
of the Si crystal grains are identified. Based on them, a grain size distribution
of the Si crystal grains in the cylinder body part is obtained. The grain size distribution
is, for example, a histogram as shown in Fig. 7. The grain size distribution has two
peaks. The grain size distribution is divided into two regions, the threshold for
the division being the diameter value corresponding to a valley portion between the
two peaks. A region corresponding to a larger diameter is defined as a grain size
distribution of the Si primary crystal grains. A region corresponding to a smaller
diameter is defined as a grain size distribution of the Si eutectic crystal grains.
The average crystal grain diameter of the Si primary crystal grains and the average
crystal grain diameter of the Si eutectic crystal grains are calculated based on the
grain size distributions, respectively.
[0085] The width of the linear groove is the distance between a pair of adjacent ridge lines
in a cross-section (profile curve) across the linear groove. The cross-section is
in parallel with the direction in which the piston part slides relative to the sliding
surface (the reciprocating direction R of the piston part). The cross-section is also
in parallel with the radial direction of the cylinder body part. The depth of the
linear groove is the depth from the higher one of a pair of ridge lines that are adjacent
to a linear groove to the lowest point of the linear groove. The pitch of the linear
grooves is the distance between the lowest points of a pair of adjacent grooves in
the cross-section (profile curve). In a configuration in which portions of the sliding
surface adjacent to a linear groove have substantially flat surfaces, the width of
the linear groove is the distance between edges of a pair of such portions (flat surfaces)
of the sliding surface.
[0086] In the present teaching, for the width, depth, and pitch of the linear grooves, respective
values averaged over linear grooves included in a profile curve within 3 to 5 mm are
adopted. In the present teaching, a groove other than the linear groove having the
depth specified in the present teaching may be formed in the sliding surface. In such
a case, the linear grooves having the depth specified in the present teaching are
used to identify the width and pitch of the linear grooves.
[0087] It should be understood that the terms and expressions used herein are for descriptions
and not to be construed in a limited manner, do not eliminate any equivalents of features
shown and mentioned herein, and allow various modifications falling within the claimed
scope of the present teaching.
[0088] The present teaching may be embodied in many different forms. The present disclosure
is to be considered as providing examples of the principles of the teaching. A number
of illustrative embodiments are described herein with the understanding that such
examples are not intended to limit the teaching to preferred embodiments described
herein and/or illustrated herein.
[0089] While some illustrative embodiments of the teaching have been described herein, the
present teaching is not limited to the various preferred embodiments described herein.
The present teaching includes any and all embodiments having equivalent elements,
modifications, omissions, combinations (e.g., of aspects across various embodiments),
adaptations and/or alterations as would be appreciated by those in the art based on
the present disclosure. The limitations in the claims are to be interpreted broadly
based on the language employed in the claims and not limited to examples described
in the present specification or during the prosecution of the application, which examples
are to be construed as non-exclusive. For example, in the present disclosure, the
term "preferably" is non-exclusive and means "preferably, but not limited to".
Reference Signs List
[0090]
- 1
- Si primary crystal grain
- 2
- Si eutectic crystal grain
- 3
- Al alloy base material
- 5a
- fracture surface
- 5b
- oil reservoir
- 8
- linear groove
8a first linear groove
8b second linear groove
- 100
- cylinder body part (cylinder body member)
- 101
- sliding surface
- 101a
- upper quarter region of sliding surface
- 101b
- lower quarter region of sliding surface
- 102
- cylinder bore
- 103
- cylinder wall
- 104
- outer wall
- 105
- water jacket
- 122
- piston part
122a piston main body
122b piston ring part
122c top ring (piston ring)
122d second ring (piston ring)
122e oil ring (piston ring)
122f top ring groove
122g second ring groove
122h oil ring groove
122m upper end (of piston ring part 122b)
122n lower end (of piston ring part 122b)
- 123
- piston pin
- 140
- connecting rod
- 150
- engine