WO2023112125A1 - Internal combustion engine and transportation device - Google Patents

Abstract

An internal combustion engine (100) comprises a piston (40) formed of aluminum alloy and a cylinder block (10) having a cylinder wall 12 including a sliding surface (12a) on which the piston slides. The cylinder block is formed of an aluminum alloy containing silicon and has a plurality of primary crystal silicon grains (2) on the sliding surface. The ten-point average roughness Rz_JIS of the sliding surface is 0.5 μm or less, and the crushing rate of the plurality of primary crystal silicon grains on the sliding surface is 20% or less.

Description

Internal combustion engines and transportation equipment

The present disclosure relates to internal combustion engines, and more particularly to internal combustion engines having a cylinder block formed from an aluminum alloy containing silicon. The present disclosure also relates to vehicles equipped with such internal combustion engines.

In recent years, the use of aluminum alloys for cylinder blocks has been progressing for the purpose of reducing the weight of internal combustion engines. Since cylinder blocks are required to have high wear resistance, aluminum alloys containing a large amount of silicon, that is, hypereutectic aluminum-silicon alloys, are expected to be used as aluminum alloys for cylinder blocks. In a cylinder block made of an aluminum-silicon alloy, silicon crystal grains located on the sliding surface contribute to an improvement in wear resistance. A cylinder block formed from an aluminum-silicon based alloy is disclosed, for example, in US Pat.

In addition, in order to improve the wear resistance and seizure resistance of the cylinder block, mesh-like grooves called crosshatch are generally formed on the surface of the cylinder wall that defines the cylinder bore. By accumulating oil (lubricating oil) in the crosshatch, it is possible to maintain lubricity between the cylinder wall and the piston skirt and piston ring, thereby suppressing wear and seizure.

WO2004/002658

However, the unevenness of the cylinder wall surface generated in the process of forming the crosshatch prevents the formation of a uniform oil film, so partial breakage of the oil film causes an increase in frictional resistance. In addition, the oil accumulated in the crosshatch remains on the surface of the cylinder wall without being scraped off by the piston rings, and is exposed to high-temperature combustion gas, evaporates or burns and is discharged as exhaust gas, reducing oil consumption. increases, which accelerates the deterioration of catalyst performance.

The embodiments of the present invention have been made in view of the above problems, and an object of the present invention is to provide an internal combustion engine having a cylinder block made of an aluminum alloy containing silicon, while ensuring seizure resistance, while maintaining the cylinder wall. to reduce frictional resistance and oil consumption.

This specification discloses the internal combustion engine and transportation equipment described in the following items.

[Item 1]
a piston formed from an aluminum alloy;
a cylinder block having a cylinder wall including a sliding surface on which the piston slides;
with
The cylinder block is made of an aluminum alloy containing silicon, and has a plurality of primary crystal silicon grains on the sliding surface,
The ten-point average roughness Rz _JIS of the sliding surface is 0.5 μm or less,
The internal combustion engine, wherein the crushing rate of the plurality of primary crystal silicon grains on the sliding surface is 20% or less.

In the internal combustion engine according to the embodiment of the present invention, the ten-point average roughness Rz _JIS of the sliding surface of the cylinder wall is 0.5 μm or less. In other words, the unevenness of the sliding surface is so small that it can be said that the sliding surface is mirror-finished. Therefore, a uniform oil film is formed on the sliding surface, and frictional resistance can be reduced. Therefore, sliding loss can be reduced and fuel efficiency can be improved. In addition, since the amount of oil (lubricating oil) left behind on the piston rings and remaining on the surface of the cylinder wall is reduced, oil consumption is reduced and deterioration of catalyst performance is suppressed. Furthermore, since the unevenness of the sliding surface is small, the aggressiveness of the cylinder wall (aggressiveness to piston rings and piston skirts) is also reduced.

It should be noted that if the surface roughness of the sliding surface is reduced, there is concern that the amount of oil retained on the sliding surface will be reduced and the seizure resistance will be reduced. However, in the internal combustion engine according to the embodiment of the present invention, the primary crystal silicon grains of high hardness are present on the sliding surface, so the surface pressure applied to the aluminum alloy base material (matrix) is reduced, and the seizure resistance is improved. can be sufficiently secured. Furthermore, since a groove such as a crosshatch is not required and the oil can be prevented from escaping into the groove, the oil film pressure is increased and a fluid lubrication state can be suitably realized. This also ensures the seizure resistance.

Further, in the internal combustion engine according to the embodiment of the present invention, since the crushing rate of the primary crystal silicon grains on the sliding surface of the cylinder wall is 20% or less, the uncrushed (so to speak sound) primary crystal silicon grains slide. Exposed on the surface. This also reduces opponent aggression. Furthermore, the contact load with the piston skirt and the piston ring is distributed to the exposed healthy primary crystal silicon grains, thereby improving the seizure resistance and wear resistance of the cylinder wall.

[Item 2]
The internal combustion engine according to item 1, wherein the sliding surface has an arithmetic average roughness Ra of less than 0.05 μm.

When the arithmetic mean roughness Ra of the sliding surface of the cylinder wall is less than 0.05 μm, the unevenness of the sliding surface is small, so that a uniform oil film is formed on the sliding surface and the frictional resistance can be reduced. Therefore, sliding loss can be reduced and fuel efficiency can be improved. In addition, since the amount of oil left behind on the piston ring and remaining on the surface of the cylinder wall is reduced, the amount of oil consumed is reduced and the deterioration of catalyst performance is suppressed. Furthermore, since the unevenness of the sliding surface is small, the aggressiveness of the cylinder wall (aggressiveness to piston rings and piston skirts) is also reduced.

[Item 3]
3. The internal combustion engine according to item 1 or 2, wherein the ratio of the area occupied by the plurality of primary crystal silicon grains on the sliding surface is 8% or more.

When the ratio of the area occupied by the primary crystal silicon grains on the sliding surface is 8% or more, the surface pressure applied to the alloy base material is reduced, so the seizure resistance and wear resistance are improved.

[Item 4]
When the sliding surface is divided into a plurality of squares of 0.1 mm x 0.1 mm, and the ratio of the number of squares in which primary crystal silicon grains are not present to the total number of squares is called a blank ratio,
4. The internal combustion engine according to any one of items 1 to 3, wherein the blank rate is 55.5% or less.

"Blank ratio" is an index of the degree of dispersion of primary crystal silicon grains. The lower the void ratio, the better the primary crystal silicon grains are dispersed. When the blank ratio of the sliding surface is 55.5% or less, the surface pressure applied to the alloy substrate is sufficiently reduced, so that the seizure resistance and wear resistance are improved.

[Item 5]
5. The internal combustion engine according to any one of items 1 to 4, wherein the cylinder block is made of an aluminum alloy containing 15% by mass or more and 25% by mass or less of silicon.

From the viewpoint of sufficiently increasing the wear resistance and strength of the cylinder block, the silicon content of the aluminum alloy, which is the material of the cylinder block, is preferably 15% by mass or more and 25% by mass or less. When the silicon content is 15% by mass or more, a sufficiently large amount of primary crystal silicon grains can be crystallized, and the wear resistance of the cylinder block can be sufficiently improved. When the silicon content is 25% by mass or less, the strength of the cylinder block can be maintained sufficiently high.

[Item 6]
6. The internal combustion engine according to any one of items 1 to 5, wherein the average grain size of the plurality of primary crystal silicon grains is 8 μm or more and 50 μm or less.

By setting the average crystal grain size of the primary crystal silicon grains within the range of 8 μm or more and 50 μm or less, the wear resistance of the cylinder block can be further improved.

When the average crystal grain size of the primary crystal silicon grains exceeds 50 μm, the number of primary crystal silicon grains per unit area of the sliding surface is small. Therefore, a large load is applied to each of the primary crystal silicon grains during operation of the internal combustion engine, and the primary crystal silicon grains may be crushed. Fragments of the crushed primary-crystal silicon grains act as abrasive particles, which may significantly wear the sliding surface.

Also, when the average crystal grain size of the primary crystal silicon grains is less than 8 μm, the portion of the primary crystal silicon grains buried in the matrix is small. Therefore, during operation of the internal combustion engine, the primary crystal silicon grains are likely to fall off. Since the fallen primary crystal silicon grains act as abrasive particles, there is a possibility that the sliding surface is greatly worn.

On the other hand, when the average crystal grain size of the primary crystal silicon grains is 8 μm or more and 50 μm or less, a sufficient number of primary crystal silicon grains exist per unit area of the sliding surface. Therefore, the load applied to each primary-crystal silicon grain during operation of the internal combustion engine is relatively small, so crushing of the primary-crystal silicon grains is suppressed. In addition, since the portion of the primary-crystal silicon grains embedded in the matrix is sufficiently large, the falling-off of the primary-crystal silicon grains is reduced, and wear of the sliding surface due to the falling-off primary-crystal silicon grains is also suppressed.

[Item 7]
The piston has a piston body and a plurality of piston rings attached to the outer periphery of the piston body,
7. The internal combustion engine according to any one of items 1 to 6, wherein each of the plurality of piston rings has a diamond-like carbon layer on its outer peripheral portion.

When each piston ring has a diamond-like carbon layer on the outer peripheral portion, scuffing of the cylinder wall by the piston ring can be prevented more reliably.

[Item 8]
The piston has a piston head and a piston skirt extending from the outer circumference of the piston head,
8. The internal combustion engine according to any one of items 1 to 7, wherein the piston skirt has a resin layer or a plating layer formed on at least part of the outer peripheral surface.

When the piston skirt has a resin layer or a plating layer formed on at least part of the outer peripheral surface, the wear resistance and seizure resistance of the piston can be improved.

[Item 9]
Transportation equipment provided with the internal combustion engine according to any one of items 1 to 8.

　The internal combustion engine according to the embodiment of the present invention is suitable for use in various types of transportation equipment.

According to the embodiment of the present invention, in an internal combustion engine having a cylinder block made of an aluminum alloy containing silicon, it is possible to reduce frictional resistance and oil consumption of the cylinder wall while ensuring seizure resistance.

1 is a cross-sectional view schematically showing an engine (internal combustion engine) 100 according to an embodiment of the present invention; FIG. FIG. 2 is a side view schematically showing a piston 40 included in engine 100. FIG. 1 is a perspective view schematically showing a cylinder block 10 included in engine 100. FIG. 2 is a cross-sectional view schematically showing the vicinity of a sliding surface 12a of a cylinder wall 12; FIG. It is an example of the image of the sliding surface 12a. It is a figure for demonstrating the definition of the blank ratio of the sliding surface 12a. 4 is a cross-sectional view schematically showing a piston ring 42 of the piston 40. FIG. 4 is a cross-sectional view schematically showing a piston skirt 44 of the piston 40; FIG. 4 is a flow chart showing a manufacturing process of the cylinder block 10. FIG. 4 is a flow chart showing a manufacturing process of the cylinder block 10. FIG. It is a graph which shows the relationship between the grade of a grindstone, and the crushing rate of a primary-crystal silicon grain. 4 is a graph showing the roughness curve of the sliding surface of Comparative Example 1. FIG. 4 is a graph showing a roughness curve of the sliding surface 12a of Example 1. FIG. 5 is a graph showing oil consumption measured by a sampling method for Comparative Example 1 and Example 1. FIG. FIG. 4 is a diagram schematically showing how oil OL is scraped off by a piston ring 42 on a sliding surface 12a' of a cylinder wall 12' of the engine of Comparative Example 1; 4 is a diagram schematically showing how oil OL is scraped off by a piston ring 42 on a sliding surface 12a of a cylinder wall 12 of the engine 100 of the first embodiment; FIG. 5 is a graph showing measurement results of frictional mean effective pressure (FMEP) for Examples 2 to 5. FIG. 4 is a graph showing FMEP reduction ratios for Examples 2 and 3 at engine speeds of 4400 rpm, 4800 rpm and 5200 rpm. 10 is a graph showing the results of repeated FMEP measurements for Example 6. FIG. 7 is a graph showing the results of repeated measurements of FMEP for Comparative Example 2. FIG. 10 is a graph showing changes over time in wear height of barrel-shaped test pieces in an SRV test for Example 7 and Comparative Example 3. FIG. FIG. 10 is a graph showing changes over time in the wear height of cylinder test pieces in an SRV test for Example 7 and Comparative Example 3. FIG. 10 is a graph showing the time from the start of engine operation until seizure of the piston and cylinder occurs in Example 7 and Comparative Example 3. FIG. 1 is a side view schematically showing a motorcycle 300 equipped with an engine 100; FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. Although a water-cooled engine will be described below as an example, the engine according to the embodiment of the present invention is not limited to a water-cooled engine, and may be an air-cooled engine. In addition, although a single-cylinder engine will be described below as an example, the number of cylinders of the engine is not particularly limited.

[Engine configuration]
FIG. 1 shows an engine (internal combustion engine) 100 according to an embodiment of the invention. FIG. 1 is a cross-sectional view schematically showing engine 100. As shown in FIG.

The engine 100 includes a cylinder block 10, a cylinder head 20, and a crankcase 30, as shown in FIG. Engine 100 further includes a piston 40 , a crankshaft 50 and a connecting rod (connecting rod) 60 . Hereinafter, the direction from the cylinder block 10 to the cylinder head 20 is defined as the upward direction, and the direction from the cylinder block 10 to the crankcase 30 is defined as the downward direction.

A cylinder block (sometimes called a "cylinder body") 10 has a cylinder wall 12 and an outer wall 13. Cylinder wall 12 is formed to define cylinder bore 11 . The outer wall 13 surrounds the cylinder wall 12 and constitutes the outer shell of the cylinder block 10 . A water jacket 14 that retains coolant is provided between the cylinder wall 12 and the outer wall 13 .

The cylinder head 20 is provided on the cylinder block 10. Cylinder head 20 defines combustion chamber 70 with cylinder wall 12 and piston 40 . The cylinder head 20 has an intake port 21 for introducing fuel into the combustion chamber 70 and an exhaust port 22 for discharging exhaust gas from the combustion chamber 70 . An intake valve 23 is provided in the intake port 21 and an exhaust valve 24 is provided in the exhaust port 22 .

The crankcase 30 is provided under the cylinder block 10. That is, the crankcase 30 is provided so as to be located on the side opposite to the cylinder head 20 with respect to the cylinder block 10 . Crankcase 30 may be separate from cylinder block 10 or may be formed integrally with cylinder block 10 .

The piston 40 is housed inside the cylinder bore 11 . In this embodiment, no cylinder sleeve is fitted in the cylinder bore 11 . Therefore, the piston 40 reciprocates up and down in the cylinder bore 11 while being in contact with the inner peripheral surface 12a of the cylinder wall 12 (the surface on the cylinder bore 11 side). That is, the inner peripheral surface 12a of the cylinder wall 12 is a sliding surface on which the piston 40 slides.

The crankshaft 50 is housed inside the crankcase 30 . The crankshaft 50 has a crankpin 51 and a crank arm 52 .

The connecting rod 60 has a rod-shaped rod main body 61 , a small end 62 provided at one end of the rod main body 61 , and a large end 63 provided at the other end of the rod main body 61 . The connecting rod 60 connects the piston 40 and the crankshaft 50 . Specifically, the piston pin 48 of the piston 40 is inserted into the through hole (piston pin hole) of the small end 62 , and the crank pin of the crankshaft 50 is inserted into the through hole (crank pin hole) of the large end 63 . 51 is inserted, thereby connecting the piston 40 and the crankshaft 50 . A bearing 66 is provided between the inner peripheral surface of the big end 63 and the crank pin 51 .

FIG. 2 is a side view schematically showing the piston 40 of the engine 100. FIG. In this embodiment, the piston 40 (more specifically, a piston body 41 described later) is made of an aluminum alloy. The piston 40 may be formed by forging or by casting. The piston 40 has a piston body 41 and a plurality of piston rings 42, as shown in FIG. Piston body 41 includes a piston head 43 and a piston skirt 44 .

The piston head 43 is located at the upper end of the piston 40. A ring groove for holding the piston ring 42 is formed in the outer peripheral portion of the piston head 43 . A piston skirt 44 extends downwardly from the outer periphery of the piston head 43 .

The piston ring 42 is attached to the outer peripheral portion of the piston body 41 , more specifically to the outer peripheral portion of the piston head 41 . Here, a configuration in which the piston 40 has three piston rings 42 is illustrated, but the number of piston rings 42 is not limited to three. Of the three piston rings 42, for example, the upper and middle piston rings (top ring and second ring) 42a and 42b are compression rings for keeping the combustion chamber 70 airtight, and the lower piston ring (third 42 c is an oil ring for scraping off excess oil adhering to the cylinder wall 12 . The piston ring 42 is made of a metallic material (eg steel).

FIG. 3 is a perspective view schematically showing the cylinder block 10 of the engine 100. FIG. As already explained, the cylinder block 10 has the cylinder wall 12 including the sliding surface 12a and the outer wall 13, and the water jacket 14 is provided between the cylinder wall 12 and the outer wall 13. . In this embodiment, the cylinder block 10 is made of an aluminum alloy containing silicon. More specifically, the cylinder block 10 is made of a hypereutectic aluminum-silicon alloy.

FIG. 4 is a cross-sectional view schematically showing the vicinity of the sliding surface 12a of the cylinder wall 12. As shown in FIG. The cylinder wall 12 of the cylinder block 10 includes, as shown in FIG. Some of the primary crystal silicon grains 2 are exposed on the sliding surface 12a. That is, the cylinder block 10 has the primary crystal silicon grains 2 on the sliding surface 12a.

Although not shown here, the cylinder wall 12 further includes a plurality of eutectic silicon grains dispersed in the matrix 1. Therefore, the cylinder block 10 may further have eutectic silicon grains on the sliding surface 12a. When a molten aluminum-silicon alloy with a hypereutectic composition is cooled, the relatively large silicon crystal grains that first precipitate are "primary silicon grains", and the relatively small silicon crystal grains that precipitate next are "co-crystalline". crystalline silicon grains”.

In this embodiment, the cylinder block 10 is formed so that the ten-point average roughness Rz _JIS of the sliding surface 12a is within a predetermined range. Specifically, the ten-point average roughness Rz _JIS of the sliding surface 12a is 0.5 μm or less over substantially the entire sliding surface 12a.

Ten-point average roughness Rz _JIS , as represented by the following formula, is the altitude of the highest to fifth peaks R1, R3, R5, R7 and R9 and the average values of the elevations R2, R4, R6, R8 and R10 of the five deepest valleys. The ten-point average roughness Rz _JIS can be measured using a surface roughness measuring machine (for example, Surfcom 1400D manufactured by Tokyo Seimitsu Co., Ltd.).

In addition, in this embodiment, the cylinder block 10 is formed so that the crushing rate of the primary crystal silicon grains 2 on the sliding surface 12a is within a predetermined range. Specifically, the crushing rate of the primary crystal silicon grains 2 on the sliding surface 12a is 20% or less over substantially the entire sliding surface 12a. The crushing rate of the primary-crystal silicon grains 2 is the ratio of the area of the crushed portion of the primary-crystal silicon grains 2 to the area occupied by the primary-crystal silicon grains 2 on the sliding surface 12a, expressed as a percentage. A specific method for measuring the crushing rate will be described later.

As described above, in the engine 100 of the present embodiment, the ten-point average roughness Rz _JIS of the sliding surface 12a of the cylinder wall 12 is 0.5 μm or less. That is, the unevenness of the sliding surface 12a is so small that it can be said that the sliding surface 12a is mirror-finished. Therefore, a uniform oil film is formed on the sliding surface 12a, and frictional resistance can be reduced. Therefore, sliding loss can be reduced and fuel efficiency can be improved. In addition, since the amount of oil (lubricating oil) left behind on the piston ring 42 and remaining on the surface of the cylinder wall 12 is reduced, the amount of oil consumed is reduced and the deterioration of catalyst performance is suppressed. Furthermore, since the unevenness of the sliding surface 12a is small, the aggressiveness of the cylinder wall 12 (aggressiveness to the piston ring 42 and the piston skirt 44) is also reduced. From the viewpoint of further enhancing the effects described above, the ten-point average roughness Rz _JIS of the sliding surface 12a is more preferably 0.3 μm or less.

It should be noted that if the surface roughness of the sliding surface 12a is reduced, there is concern that the amount of oil retained on the sliding surface 12a will be reduced and the seizure resistance will be reduced. However, in the engine 100 of the present embodiment, since the high-hardness primary crystal silicon grains 2 are present on the sliding surface 12a, the surface pressure applied to the alloy base material (matrix) 1 is reduced, and the seizure resistance is improved. can be sufficiently secured. Furthermore, since a groove such as a crosshatch is not required and the oil can be prevented from escaping into the groove, the oil film pressure is increased and a fluid lubrication state can be suitably realized. This also ensures the seizure resistance.

In addition, in the engine 100 of the present embodiment, since the crushing rate of the primary crystal silicon grains 2 on the sliding surface 12a of the cylinder wall 12 is 20% or less, the uncrushed (so to speak sound) primary crystal silicon grains 2 are Many are exposed on the sliding surface 12a. This also reduces opponent aggression. Furthermore, the contact load with the piston skirt 44 and the piston ring 42 is distributed to the exposed healthy primary crystal silicon grains 2, so that the seizure resistance and wear resistance of the cylinder wall 12 are improved.

The crushing rate of the primary crystal silicon grains 2 can be measured, for example, as follows.

First, an image of the sliding surface 12a is taken using a borescope. FIG. 5 is an example of an image of the sliding surface 12a. As shown in FIG. 5, the sliding surface 12a has a crushed portion 2a of the primary crystal silicon grains 2 and a non-crushed portion 2b. Next, the area S1 of the crushed portion 2a of the primary crystal silicon grain 2 is determined by binarization using image analysis software. Since the crushed portion 2a has a black appearance, it can be distinguished from the non-crushed portion 2b and the alloy substrate 1 by binarization. Subsequently, by binarization using image analysis software, the area S2 of the primary crystal silicon grains 2 (including both the crushed portion 2a and the uncrushed portion 2b) is obtained. After that, from the obtained areas S1 and S2, the crushing rate of the primary crystal silicon grains 2 is calculated based on the following formula.
Crushing rate of primary crystal silicon grains [%] = (S1/S2) x 100

The surface roughness of the sliding surface 12a of the cylinder wall 12 can also be represented by, for example, the arithmetic mean roughness Ra. In this embodiment, the arithmetic mean roughness Ra of the sliding surface 12a is less than 0.05 μm, for example.

From the viewpoint of seizure resistance and wear resistance, the ratio of the area occupied by the primary crystal silicon grains 2 on the sliding surface 12a is preferably 8% or more. When the ratio of the area occupied by the primary crystal silicon grains 2 in the sliding surface 12a is 8% or more, the surface pressure applied to the alloy base material 1 is reduced, thereby improving the seizure resistance and wear resistance.

The ratio of the area occupied by the primary crystal silicon grains 2 on the sliding surface 12a can be measured, for example, as follows. First, an image of the sliding surface 12a is taken using a borescope. Next, the area S2 of the primary crystal silicon grain 2 is determined by binarization using image analysis software. After that, the ratio of the area occupied by the primary crystal silicon grains 2 can be calculated based on the following formula from the obtained area S2 and the area S3 of the entire measurement field.
Ratio of area occupied by primary crystal silicon grains on sliding surface [%]=(S2/S3)×100

In addition, the sliding surface 12a can also be evaluated by the "blank rate". FIG. 6 is a diagram for explaining the definition of "blank rate". As shown in FIG. 6, if the sliding surface 12a is divided into a plurality of squares Sq of 0.1 mm×0.1 mm, these squares Sq are, of course, divided into squares Sq1 where the primary crystal silicon grains 2 are present and A cell Sq2 in which no crystalline silicon grain 2 exists. The "blank ratio" is the ratio (percentage) of the number of cells Sq2 in which the primary crystal silicon grains 2 do not exist with respect to the total number of cells Sq.

It can be said that the "blank ratio" is an index of how the primary crystal silicon grains 2 are dispersed. The lower the void ratio, the better the primary crystal silicon grains 2 are dispersed. When the blank ratio of the sliding surface 12a is 55.5% or less, the surface pressure applied to the alloy base material 1 is sufficiently reduced, thereby improving the seizure resistance and wear resistance.

From the viewpoint of sufficiently increasing the wear resistance and strength of the cylinder block 10, the silicon content of the aluminum alloy, which is the material of the cylinder block 10, is preferably 15% by mass or more and 25% by mass or less. When the silicon content is 15% by mass or more, a sufficiently large amount of primary crystal silicon grains 2 can be crystallized, and the wear resistance of the cylinder block 10 can be sufficiently improved. When the silicon content is 25% by mass or less, the strength of the cylinder block 10 can be maintained sufficiently high.

The wear resistance of the cylinder block 10 can be further improved by setting the average crystal grain size of the primary crystal silicon grains 2 within the range of 8 μm or more and 50 μm or less. When the average crystal grain size of the primary crystal silicon grains 2 exceeds 50 μm, the number of primary crystal silicon grains 2 per unit area of the sliding surface 12a is small. Therefore, a large load is applied to each of the primary crystal silicon grains 2 during operation of the engine 100, and the primary crystal silicon grains 2 may be crushed. Fragments of the crushed primary-crystal silicon grains 2 act as abrasive particles, so there is a risk that the sliding surface 12a will be greatly worn. Further, when the average crystal grain size of the primary-crystal silicon grains 2 is less than 8 μm, the portion of the primary-crystal silicon grains 2 buried in the matrix 1 is small. Therefore, during operation of the engine 100, the primary crystal silicon grains 2 are likely to fall off. Since the dropped primary-crystal silicon grains 2 act as abrasive particles, the sliding surface 12a may be greatly worn.

On the other hand, when the average crystal grain size of the primary crystal silicon grains 2 is 8 μm or more and 50 μm or less (more preferably 12 μm or more and 50 μm or less), a sufficient number of primary crystal silicon grains 2 per unit area of the sliding surface 12a. exist. Therefore, the load applied to each primary-crystal silicon grain 2 during operation of the engine 100 is relatively small, so crushing of the primary-crystal silicon grains 2 is suppressed. In addition, since the portion of the primary-crystal silicon grains 2 embedded in the matrix 1 is sufficiently large, the drop-off of the primary-crystal silicon grains 2 is reduced, and wear of the sliding surface 12a due to the dropped-off primary-crystal silicon grains 2 is also suppressed. be done.

The average crystal grain size of the eutectic silicon grains is smaller than the average crystal grain size of the primary crystal silicon grains 2 . The average crystal grain size of the eutectic silicon grains is, for example, 7.5 μm or less.

The average crystal grain size of the primary crystal silicon grains 2 and the eutectic silicon grains can be measured as follows by performing image processing on the image of the sliding surface 12a. First, based on the area of the silicon crystal grain obtained by image processing, the diameter (equivalent diameter) of each silicon crystal grain is calculated assuming that the silicon crystal grain is a perfect circle. Specify the number (degrees) and diameter. Fine crystals with a diameter of less than 1 μm are not counted as silicon crystal grains. Based on the calculated number (frequency) and diameter of the silicon crystal grains, the grain size distribution of the silicon crystal grains is obtained. The resulting particle size distribution (histogram) contains two peaks. The grain size distribution is divided into two regions with the diameter of the portion forming the valley between the two peaks as the threshold, the region corresponding to the large diameter being the grain size distribution of the primary crystal silicon grains, and the region corresponding to the small diameter being the eutectic. Suppose it is the particle size distribution of silicon particles. Then, based on each particle size distribution, the average crystal grain size of the primary crystal silicon grains and the average crystal grain size of the eutectic silicon grains can be calculated.

FIG. 7 is a cross-sectional view showing an example configuration of the piston ring 42 of the piston 40. As shown in FIG. In the example shown in FIG. 7 , a diamond-like carbon layer (hereinafter referred to as “DLC layer”) 42D is formed on the outer peripheral portion (outer peripheral surface) of the piston ring 42 . An outer peripheral portion of the piston ring 42 is a portion that contacts the cylinder wall 12 . Although the piston rings 42 do not have to have the DLC layer 42D, each piston ring 42 has the DLC layer 42D on the outer peripheral portion, thereby more reliably preventing the piston rings 42 from scuffing the cylinder wall 12. can do.

The DLC layer 42D is preferably formed by a vapor deposition method (for example, CDV method or PVD method). There are no particular restrictions on the composition or thickness of the DLC layer 42D. The thickness of the DLC layer 42D is preferably 2 μm or more in order to more reliably prevent scuffing. In terms of adhesion, the thickness of the DLC layer 42D is preferably 20 μm or less.

FIG. 8 is a cross-sectional view showing an example of the configuration of the piston skirt 44 of the piston 40. As shown in FIG. In the example shown in FIG. 8, the piston skirt 44 has a resin layer rl formed on at least part of the outer peripheral surface. The resin layer rl is provided on the base material bl made of an aluminum alloy.

The resin layer rl includes, for example, a polymer matrix and solid lubricant particles dispersed in the polymer matrix. As a material for the polymer matrix, for example, thermosetting polyamideimide can be suitably used, but the material is of course not limited to this. As the solid lubricant particles, various known solid lubricant particles can be used, and for example, graphite particles and molybdenum particles can be preferably used. The resin layer rl can be formed, for example, by applying a liquid resin material to the piston skirt 44 by a spray method or various printing methods (screen printing, pad printing, etc.).

When the piston skirt 44 has the resin layer rl formed on at least a part of the outer peripheral surface, the wear resistance and seizure resistance of the piston 40 can be improved.

Also, the piston skirt 44 may have a plating layer (for example, an iron plating layer) instead of the resin layer rl. The wear resistance and seizure resistance of the piston 40 can also be improved by having the plating layer formed on at least a portion of the outer peripheral surface of the piston skirt 44 . It should be noted that the piston skirt 44 may have neither the resin layer rl nor the plating layer.

[Manufacturing method of cylinder block]
A method of manufacturing the cylinder block 10 included in the engine 100 of this embodiment will be described with reference to FIGS. 9 and 10. FIG. 9 and 10 are flow charts showing the manufacturing process of the cylinder block 10. FIG.

First, a compact made of an aluminum alloy containing silicon is prepared (step ST1). This compact contains primary crystal silicon grains and eutectic silicon grains in the vicinity of the surface. The step ST1 of preparing the compact includes steps ST1a to ST1e shown in FIG. 10, for example.

First, an aluminum alloy containing silicon is prepared (step ST1a). For the reason already explained, the silicon content of the aluminum alloy is preferably 15% by mass or more and 25% by mass or less. The aluminum content of the aluminum alloy is, for example, 73.4% by mass or more and 79.6% by mass or less. Moreover, the aluminum alloy may contain copper, and in that case, the copper content is, for example, 2.0% by mass or more and 5.0% by mass or less.

Next, a molten metal is formed by heating and melting the prepared aluminum alloy in a melting furnace (step ST1b). About 100 ppm by mass of phosphorus may be added to the aluminum alloy or molten metal before melting. When the aluminum alloy contains 50 mass ppm or more and 200 mass ppm or less of phosphorus, it is possible to suppress the coarsening of the silicon crystal grains, so that the silicon crystal grains can be uniformly dispersed in the alloy. Also, by setting the calcium content of the aluminum alloy to 0.01% by mass or less, the effect of refining silicon crystal grains by phosphorus can be ensured, and a metal structure with excellent wear resistance can be obtained. In other words, the aluminum alloy preferably contains 50 mass ppm or more and 200 mass ppm or less of phosphorus and 0.01 mass% or less of calcium.

Subsequently, casting (specifically, high-pressure die casting) is performed using molten aluminum alloy (step ST1c). That is, the molten metal is cooled in the mold to form the compact. At this time, by cooling the portion of the cylinder wall 12 that will become the sliding surface 12a at a high cooling rate (for example, 4° C./sec or more and 50° C./sec or less), the silicon crystal grains that contribute to wear resistance are moved to the vicinity of the surface. A molded body having This casting step ST1c can be performed, for example, using the casting apparatus disclosed in International Publication No. 2004/002658 pamphlet.

Next, any one of the heat treatments called "T5", "T6" and "T7" is performed on the compact taken out from the mold (step ST1d). The T5 treatment is a treatment in which the compact is rapidly cooled by water cooling or the like immediately after it is removed from the mold, then artificially aged at a specified temperature for a specified time in order to improve mechanical properties and stabilize dimensions, and then air-cooled. . The T6 treatment is a treatment in which the compact is removed from the mold, solution-treated at a predetermined temperature for a predetermined time, then water-cooled, then artificially aged at a predetermined temperature for a predetermined time, and then air-cooled. The T7 treatment is a treatment for overaging compared to the T6 treatment, and can achieve more dimensional stabilization than the T6 treatment, but the hardness is lower than that of the T6 treatment.

Subsequently, the molded body is subjected to predetermined machining (step ST1e). Specifically, the mating surface with the cylinder head 20 and the mating surface with the crankcase 30 are ground.

After preparing the molded body as described above, the first honing process (referred to as "rough honing process") is performed on the inner peripheral surface of the portion of the molded body that will become the cylinder wall (step ST2). Specifically, the inner peripheral surface is polished using a grindstone with a relatively small number (for example, a diamond grindstone with a number of #600).

After that, a second honing process (referred to as "finish honing process") is performed on the inner peripheral surface (step ST3). Specifically, the inner peripheral surface is polished using a grindstone with a grit larger than that for rough honing (for example, diamond whetstone with grit #3000). Rough honing and finish honing can be performed using a honing apparatus as disclosed in Japanese Patent Application Laid-Open No. 2004-268179, for example.

Thus, the cylinder block 10 can be obtained. In addition, the number of times of the honing process is not limited to 2 illustrated here. By adjusting the number of the grindstone used in the honing process, the ten-point average roughness Rz _JIS of the sliding surface 12a can be controlled, and in the last honing process among the honing processes performed multiple times, the number is relatively large. By using a grindstone, the ten-point average roughness Rz _JIS can be made 0.5 μm or less. Further, according to the study of the inventor of the present application, it was found that the crushing rate of the primary crystal silicon grains 2 on the sliding surface 12a can be reduced to 20% or less by using a grindstone with a count of #3000 or more in the final honing process. .

FIG. 11 is a graph showing the verification results of the relationship between the number of grindstone and the crushing rate of primary crystal silicon grains. This verification was performed by performing the first honing process using a #600 diamond whetstone, and then performing the second honing process using a diamond whetstone with a predetermined grit so that the polishing depth was 4 μm or more. It was carried out by measuring the crushing rate of the primary crystal silicon grains 2 at that time. In FIG. 11, the abscissa indicates the grain size of the grindstone used in the second honing treatment, and the ordinate indicates the crush rate of the primary crystal silicon grains. It can be seen from FIG. 11 that the crushing rate of the primary crystal silicon grains can be reduced to 20% or less by using a grindstone with a count of #3000 or higher.

[Effect verification results]
First, an engine 100 according to an embodiment of the present invention was produced as a prototype (Example 1), and the results of verification of the oil consumption reduction effect in comparison with the engine of Comparative Example 1 will be described. The cylinder block 10 of the engine 100 of Example 1 was manufactured by the manufacturing method described above. When manufacturing the cylinder block of the engine of Comparative Example 1, two honing treatments were performed: rough honing for the purpose of forming oil grooves, and finish honing for the purpose of forming plateau portions between oil grooves. It was honed twice.

12 shows the roughness curve of the sliding surface of Comparative Example 1, and FIG. 13 shows the roughness curve of the sliding surface 12a of Example 1. As shown in FIG. 12 and 13, it can be seen that the surface roughness of the sliding surface 12a of Example 1 is smaller than the surface roughness of the sliding surface of Comparative Example 1. FIG. The ten-point average roughness Rz _JIS of the sliding surface of Comparative Example 1 was 3.05 μm, while the ten-point average roughness Rz _JIS of the sliding surface 12a of Example 1 was 0.25 μm. The crushing rate of the primary crystal silicon grains 2 on the sliding surface 12a of Example 1 was 20% or less.

Fig. 14 shows the oil consumption measured by the sampling method for Comparative Example 1 and Example 1. As can be seen from FIG. 14, in Example 1, the oil consumption was reduced by 21% as compared to Comparative Example 1.

FIG. 15A is a diagram schematically showing how the oil OL is scraped off by the piston ring 42 on the sliding surface 12a' of the cylinder wall 12' of the engine of Comparative Example 1. FIG. In Comparative Example 1, since the surface roughness (ten-point average roughness Rz _JIS ) of the sliding surface 12a′ is relatively large, much oil OL remains on the sliding surface 12a′ without being scraped off by the piston ring 42 . Since the remaining oil OL is exposed to the flame FL to evaporate or burn, a large amount of the remaining oil OL results in a large amount of oil consumption.

FIG. 15B is a diagram schematically showing how the oil OL is scraped off by the piston ring 42 on the sliding surface 12a of the cylinder wall 12 of the engine 100 of the first embodiment. In Example 1, since the ten-point average roughness Rz _JIS of the sliding surface 12a is as small as 0.25 μm, it is considered that the amount of oil OL remaining on the sliding surface 12a is reduced, thereby reducing the oil consumption.

Next, the result of verifying the effect of reducing friction resistance (friction loss) will be described. For Examples 2, 3, 4 and 5 in which the ten-point average roughness Rz _JIS of the sliding surface 12a is 0.224 μm, 0.334 μm, 0.403 μm and 0.496 μm, the friction average effective pressure (FMEP: Friction Mean Effective Pressure) was measured by the floating liner method. The crushing ratios of the primary crystal silicon grains 2 of Examples 2, 3, 4 and 5 were all 6 to 7%. FMEP is a value obtained by dividing the frictional work per cycle by the stroke volume, and the larger the value, the greater the frictional force. FIG. 16 shows the measurement results of FMEP. Note that FIG. 16 shows the average values of the FMEP values when the engine speed is 4400 rpm, 4800 rpm and 5200 rpm. Further, in FIG. 16, the FMEP value (120.1 kPa) of the engine of Comparative Example 1 is indicated by a dashed line.

From FIG. ₁₆ , it can be seen that the smaller the ten-point average roughness Rz _JIS , the more the FMEP is reduced. It can be seen that the FMEP values of Example 1 are below.

FIG. 17 shows the FMEP reduction rate for Examples 2 and 3 at engine speeds of 4400 rpm, 4800 rpm and 5200 rpm. It can be seen from FIG. 17 that the effect of reducing FMEP tends to be high on the low rotational speed side.

Next, the results of verifying the durability of the effect of reducing friction loss will be described. FIG. 18 shows the results of repeated FMEP measurements for Example 6 in which the sliding surface 12a has a ten-point average roughness Rz _JIS of 0.214 μm and a crushing rate of the primary crystal silicon grains 2 is 20% or less. . FIG. 19 shows the results of repeated FMEP measurements for Comparative Example 2 in which the ten-point average roughness Rz _JIS (after nine measurements) of the sliding surface is 0.563 μm.

As can be seen from FIGS. 18 and 19, when comparing at the same timing (the same number of measurements), in Example 6, FMEP was reduced by 10% or more than in Comparative Example 2 at all timings. For example, the FMEP of Example 6 was reduced by 17% compared to Comparative Example 2 in the first measurement. Moreover, even in the tenth measurement, in which the FMEP reduction effect was the smallest, a reduction effect of 10% or more (specifically, 10.3%) was obtained.

Next, the result of verifying the aggressiveness and wear resistance of the cylinder wall will be described. This verification was performed by a vibration friction wear test (SRV test) using a barrel-shaped test piece simulating a piston skirt and a cylinder test piece cut from a cylinder wall. The SRV test was performed with Example 7 in which the ten-point average roughness Rz _JIS of the sliding surface 12a was 0.124 to 0.237 (0.162 on average) μm, and the crushing rate of the primary crystal silicon grains 2 was 15%. , and Comparative Example 3 in which the ten-point average roughness Rz _JIS of the sliding surface was 1.6 to 3.2 μm. The SRV test was performed by sliding the barrel test piece under a constant load at an oil temperature of 130° C. (immersion), and the wear height of the barrel test piece and the cylinder test piece was measured.

　Fig. 20 shows the time change of the wear height of the barrel-shaped test piece. 20 that in Example 7, the wear height of the barrel-shaped test piece is smaller than in Comparative Example 3. FIG. Comparing the wear height after 60 minutes from the start of the test, in Example 7, the wear height could be reduced by 69% compared to Comparative Example 3. Thus, in Example 7, it was confirmed that the aggressiveness of the cylinder wall 12 against the opponent was reduced.

Fig. 21 shows the time change of the wear height of the cylinder test piece. 21 that in Example 7, the wear height of the cylinder test piece is smaller than in Comparative Example 3. FIG. Thus, in Example 7, it was confirmed that the wear resistance of the cylinder wall 12 was improved.

For Example 7 and Comparative Example 3, the operation was performed under conditions that promote seizure of the cylinder and piston, and the time from the start of operation to the occurrence of seizure was measured. FIG. 22 shows the measurement results of the time from the start of operation to the occurrence of seizure.

As shown in FIG. 22, in Example 7, the time until seizure occurred was about 6.5 times longer than in Comparative Example 3. Therefore, in Example 7, the seizure resistance of the cylinder wall 12 was improved. confirmed.

[Transport equipment]
The engine 100 according to the embodiment of the present invention is suitable for use in various transportation equipment. FIG. 23 shows an example of a motorcycle equipped with an engine 100 according to an embodiment of the invention.

A motorcycle 300 shown in FIG. 23 is provided with a head pipe 302 at the front end of a body frame 301 . A front fork 303 is attached to the head pipe 302 so as to swing in the lateral direction of the vehicle. A front wheel 304 is rotatably supported at the lower end of the front fork 303 .

A seat rail 306 is attached so as to extend rearward from the upper part of the rear end of the body frame 301 . A fuel tank 307 is provided on the body frame 301, and a main seat 308a and a tandem seat 308b are provided on the seat rails 306. As shown in FIG.

A rear arm 309 extending rearward is attached to the rear end of the body frame 301 . A rear wheel 310 is rotatably supported at the rear end of the rear arm 309 .

The engine 100 is held in the central portion of the body frame 301 . A radiator 311 is provided in front of the engine 100 . An exhaust pipe 312 is connected to an exhaust port of the engine 100 and a muffler 313 is attached to the rear end of the exhaust pipe 312 .

A transmission 315 is connected to the engine 100 . A drive sprocket 317 is attached to the output shaft 316 of the transmission 315 . Drive sprocket 317 is connected to rear wheel sprocket 319 of rear wheel 310 via chain 318 . Transmission 315 and chain 318 function as a transmission mechanism that transmits the power generated by engine 100 to the drive wheels.

Since the motorcycle 300 includes the engine 100 according to the embodiment of the present invention, effects such as improved fuel efficiency, reduced oil consumption, and suppressed catalyst performance deterioration can be obtained.

Although a motorcycle is illustrated here as an example of transportation equipment, the engine according to the embodiment of the present invention is not limited to motorcycles, and is also suitable for other transportation equipment such as four-wheeled motor vehicles, three-wheeled motor vehicles, and ships. used for

As described above, the internal combustion engine 100 according to the embodiment of the present invention includes the piston 40 made of aluminum alloy and the cylinder block 10 having the cylinder wall 12 including the sliding surface 12a on which the piston 40 slides. The cylinder block 10 is made of an aluminum alloy containing silicon, and has a plurality of primary crystal silicon grains 2 on a sliding surface 12a. The ten-point average roughness Rz _JIS of the sliding surface 12a is 0.5 μm or less, and the crushing rate of the plurality of primary crystal silicon grains 2 on the sliding surface 12a is 20% or less.

In the internal combustion engine 100 according to the embodiment of the present invention, the ten-point average roughness Rz _JIS of the sliding surface 12a of the cylinder wall 12 is 0.5 μm or less. That is, the unevenness of the sliding surface 12a is so small that it can be said that the sliding surface 12a is mirror-finished. Therefore, a uniform oil film is formed on the sliding surface 12a, and frictional resistance can be reduced. Therefore, sliding loss can be reduced and fuel efficiency can be improved. In addition, since the amount of oil (lubricating oil) left behind on the piston ring 42 and remaining on the surface of the cylinder wall 12 is reduced, the amount of oil consumed is reduced and the deterioration of catalyst performance is suppressed. Furthermore, since the unevenness of the sliding surface 12a is small, the aggressiveness of the cylinder wall 12 (aggressiveness to the piston ring 42 and the piston skirt 44) is also reduced.

It should be noted that if the surface roughness of the sliding surface 12a is reduced, there is concern that the amount of oil retained on the sliding surface 12a will be reduced and the seizure resistance will be reduced. However, in the internal combustion engine 100 according to the embodiment of the present invention, since the primary crystal silicon grains 2 with high hardness are present on the sliding surface 12a, the surface pressure applied to the aluminum alloy base material (matrix) 1 is reduced, Sufficient seizure resistance can be ensured. Furthermore, since a groove such as a crosshatch is not required and the oil can be prevented from escaping into the groove, the oil film pressure is increased and a fluid lubrication state can be suitably realized. This also ensures the seizure resistance.

Further, in the internal combustion engine 100 according to the embodiment of the present invention, since the crushing rate of the primary crystal silicon grains 2 on the sliding surface 12a of the cylinder wall 12 is 20% or less, Many grains 2 are exposed on the sliding surface 12a. This also reduces opponent aggression. Furthermore, the contact load with the piston skirt 44 and the piston ring 42 is distributed to the exposed healthy primary crystal silicon grains 2, so that the seizure resistance and wear resistance of the cylinder wall 12 are improved.

In one embodiment, the arithmetic mean roughness Ra of the sliding surface 12a is less than 0.05 μm.

When the arithmetic mean roughness Ra of the sliding surface 12a of the cylinder wall 12 is less than 0.05 μm, the unevenness of the sliding surface 12a is small, so that a uniform oil film is formed on the sliding surface 12a to reduce the frictional resistance. be able to. Therefore, sliding loss can be reduced and fuel efficiency can be improved. In addition, since the amount of oil left behind on the piston ring 42 and remaining on the surface of the cylinder wall 12 is reduced, the amount of oil consumed is reduced and the deterioration of catalyst performance is suppressed. Furthermore, since the unevenness of the sliding surface 12a is small, the aggressiveness of the cylinder wall 12 (aggressiveness to the piston ring 42 and the piston skirt 44) is also reduced.

In one embodiment, the ratio of the area occupied by the plurality of primary crystal silicon grains 2 on the sliding surface 12a is 8% or more.

When the ratio of the area occupied by the primary crystal silicon grains 2 in the sliding surface 12a is 8% or more, the surface pressure applied to the alloy base material 1 is reduced, so the seizure resistance and wear resistance are improved.

In one embodiment, the sliding surface 12a is divided into a plurality of squares Sq of 0.1 mm×0.1 mm, and the ratio of the number of squares Sq2 in which the primary crystal silicon grains 2 are not present to the total number of squares Sq is defined as the blank ratio. When called, the blank rate is 55.5% or less.

"Blank ratio" is an index of how the primary crystal silicon grains 2 are dispersed. The lower the void ratio, the better the primary crystal silicon grains 2 are dispersed. When the blank ratio of the sliding surface 12a is 55.5% or less, the surface pressure applied to the alloy base material 1 is sufficiently reduced, thereby improving the seizure resistance and wear resistance.

In one embodiment, the cylinder block 10 is made of an aluminum alloy containing 15% by mass or more and 25% by mass or less of silicon.

From the viewpoint of sufficiently increasing the wear resistance and strength of the cylinder block 10, the silicon content of the aluminum alloy, which is the material of the cylinder block 10, is preferably 15% by mass or more and 25% by mass or less. When the silicon content is 15% by mass or more, a sufficiently large amount of primary crystal silicon grains 2 can be crystallized, and the wear resistance of the cylinder block 10 can be sufficiently improved. When the silicon content is 25% by mass or less, the strength of the cylinder block 10 can be maintained sufficiently high.

In one embodiment, the average crystal grain size of the plurality of primary crystal silicon grains 2 is 8 μm or more and 50 μm or less.

The wear resistance of the cylinder block 10 can be further improved by setting the average crystal grain size of the primary crystal silicon grains 2 within the range of 8 μm or more and 50 μm or less.

When the average crystal grain size of the primary crystal silicon grains 2 exceeds 50 μm, the number of primary crystal silicon grains 2 per unit area of the sliding surface 12a is small. Therefore, a large load is applied to each of the primary crystal silicon grains 2 during operation of the internal combustion engine 100, and the primary crystal silicon grains 2 may be crushed. Fragments of the crushed primary-crystal silicon grains 2 act as abrasive particles, so there is a risk that the sliding surface 12a will be greatly worn.

Further, when the average crystal grain size of the primary-crystal silicon grains 2 is less than 8 μm, the portion of the primary-crystal silicon grains 2 buried in the matrix 1 is small. Therefore, during operation of the internal combustion engine 100, the primary crystal silicon grains 2 are likely to fall off. Since the dropped primary-crystal silicon grains 2 act as abrasive particles, the sliding surface 12a may be greatly worn.

On the other hand, when the average crystal grain size of the primary crystal silicon grains 2 is 8 μm or more and 50 μm or less, a sufficient number of primary crystal silicon grains 2 are present per unit area of the sliding surface 12a. Therefore, since the load applied to each primary-crystal silicon grain 2 during operation of the internal combustion engine 100 is relatively small, crushing of the primary-crystal silicon grain 2 is suppressed. In addition, since the portion of the primary-crystal silicon grains 2 embedded in the matrix 1 is sufficiently large, the drop-off of the primary-crystal silicon grains 2 is reduced, and wear of the sliding surface 12a due to the dropped-off primary-crystal silicon grains 2 is also suppressed. be done.

In one embodiment, the piston 40 has a piston body 41 and a plurality of piston rings 42 attached to the outer periphery of the piston body 41, each of the plurality of piston rings 42 having a diamond-like carbon layer on the outer periphery. 42D.

If each piston ring 42 has a diamond-like carbon layer 42D on the outer peripheral portion, scuffing of the cylinder wall 12 by the piston ring 42 can be prevented more reliably.

In one embodiment, the piston 40 has a piston head 43 and a piston skirt 44 extending from the outer peripheral portion of the piston head 43, and the piston skirt 44 is a resin layer rl or a plating layer formed on at least a portion of the outer peripheral surface. have layers.

When the piston skirt 44 has a resin layer rl or a plating layer formed on at least a portion of the outer peripheral surface, the wear resistance and seizure resistance of the piston 40 can be improved.

A transportation device according to an embodiment of the present invention includes an internal combustion engine 100 having any of the configurations described above.

The internal combustion engine 100 according to the embodiment of the present invention is suitable for use in various types of transportation equipment.

According to the embodiment of the present invention, in an internal combustion engine having a cylinder block made of an aluminum alloy containing silicon, it is possible to reduce frictional resistance and oil consumption of the cylinder wall while ensuring seizure resistance. INDUSTRIAL APPLICABILITY An internal combustion engine according to an embodiment of the present invention is suitable for use in various types of transportation equipment including motorcycles.

1: matrix (alloy base material), 2: primary crystal silicon grains, 2a: crushed portion of primary crystal silicon grains, 2b: uncrushed portion of primary crystal silicon grains, 10: cylinder block, 11: cylinder bore, 12 : Cylinder wall 12a: Sliding surface (inner peripheral surface of cylinder wall) 13: Outer wall 14: Water jacket 20: Cylinder head 21: Intake port 22: Exhaust port 23: Intake valve 24: Exhaust valve, 30: crankcase, 40: piston, 41: piston body, 42: piston ring, 42a: top ring, 42b: second ring, 42c: third ring, 42D: diamond-like carbon layer, 43: piston head, 44: Piston skirt 48: Piston pin 50: Crankshaft 51: Crank pin 52: Crank arm 60: Connecting rod 61: Rod main body 62: Small end 63: Large end 70: Combustion chamber 100: engine (internal combustion engine), 300: motorcycle, Sq: square, Sq1: square in which primary crystal silicon particles are present, Sq2: square in which primary crystal silicon particles are not present, bl: base material, rl: resin layer

Claims (9)

a piston formed from an aluminum alloy;
a cylinder block having a cylinder wall including a sliding surface on which the piston slides;
with
The cylinder block is made of an aluminum alloy containing silicon, and has a plurality of primary crystal silicon grains on the sliding surface,
The ten-point average roughness Rz _JIS of the sliding surface is 0.5 μm or less,
The internal combustion engine, wherein the crushing rate of the plurality of primary crystal silicon grains on the sliding surface is 20% or less. The internal combustion engine according to claim 1, wherein the sliding surface has an arithmetic mean roughness Ra of less than 0.05 µm. The internal combustion engine according to claim 1 or 2, wherein the ratio of the area occupied by the plurality of primary crystal silicon grains on the sliding surface is 8% or more. When the sliding surface is divided into a plurality of squares of 0.1 mm x 0.1 mm, and the ratio of the number of squares in which primary crystal silicon grains are not present to the total number of squares is called a blank ratio,
4. The internal combustion engine according to any one of claims 1 to 3, wherein said blank ratio is 55.5% or less. The internal combustion engine according to any one of claims 1 to 4, wherein said cylinder block is made of an aluminum alloy containing 15% by mass or more and 25% by mass or less of silicon. The internal combustion engine according to any one of claims 1 to 5, wherein the average crystal grain size of the plurality of primary crystal silicon grains is 8 µm or more and 50 µm or less. The piston has a piston body and a plurality of piston rings attached to the outer periphery of the piston body,
7. The internal combustion engine according to any one of claims 1 to 6, wherein each of said plurality of piston rings has a diamond-like carbon layer on its outer peripheral portion. The piston has a piston head and a piston skirt extending from the outer circumference of the piston head,
8. The internal combustion engine according to any one of claims 1 to 7, wherein said piston skirt has a resin layer or a plating layer formed on at least part of its outer peripheral surface. A transportation device equipped with the internal combustion engine according to any one of claims 1 to 8.

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