JP2972083B2 - Bearing structure of two-stroke internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bearing structure for a two-stroke internal combustion engine, and more particularly, to at least one of a crankshaft rotating in a crank chamber of a two-stroke internal combustion engine and a piston reciprocating in a cylinder of the internal combustion engine. The present invention relates to a bearing structure used for connecting one to a connecting rod.

[0002]

2. Description of the Related Art FIG. 6 shows a connection structure between a connecting rod and a crankshaft or piston of a conventional two-stroke internal combustion engine. The two-stroke engine 100 includes a cylinder 50 and a crank chamber 60.
The crankshaft 1 rotates within the crank chamber 60. The piston 2 reciprocates in the cylinder 50. Crankshaft 1
The piston 2 is connected to the piston 2 by a connecting rod 3. In the connection structure between the connecting rod 3 and the crank pin 4 and between the connecting rod 3 and the piston pin 5, a rolling bearing structure is adopted for the purpose of high-speed rotation.

Specifically, the crank pin 4 is used as an inner ring,
A needle roller bearing structure 8 is mounted so that the large end 6 of the connecting rod 3 is an outer ring. Further, a needle roller bearing structure 9 is mounted so that the piston pin 5 is an inner ring and the inner surface of the small end 7 of the connecting rod 3 is an outer ring.

[0004] The needle roller bearing structures 8 and 9 comprise a needle roller 10 and a retainer 11 as shown in FIG. A plurality of pockets 11a are formed at equal intervals on the circumference of the retainer 11 so that the needle rollers 10 are not rotatable inward and outward and are rotatably held.

Usually, the needle roller 10, the retainer 11, the connecting rod 3, the crankpin 4, and the piston pin 5 are manufactured using a metal material. For example, the needle rollers 10 are made of bearing steel, the cage 11 is made of case hardened steel, and the connecting rod 3, the crankpin 4 and the piston pin 5 are made of Cr-Mo steel.

[0006] Also, WO 89/12760 bread
Fret (1989) discloses that the needle rollers of the needle roller bearing structure used for the large end of the connecting rod are formed from a ceramic mainly composed of silicon nitride.

[0007] The lubricating action of the contact sliding portion in the bearing structure of the two-cycle engine as described above is extremely severe because it is performed by a mixture of vaporized fuel and lubricating oil. Therefore, the lubricating film is not sufficiently formed on the sliding portion of the bearing structure, and there is a concern that the connecting rod portion may be abnormally worn during use and seizure may occur. In particular, under conditions of high-speed rotation of 7000 to 10,000 thousands rpm, the temperature of the bearing portion rises. Therefore, if the member constituting the sliding surface of the bearing portion is made of steel, a mechanism may be considered in which the material is tempered and softened, resulting in seizure.

Further, the cage type cage 11 as shown in FIG. 7 is broken from the corner portion or the side surface, particularly at the time of high speed rotation, due to the attack by the needle rollers 10 as the rolling elements, and holds the rolling elements. There is a concern that it cannot be obtained and cannot be used.

On the other hand, WO 89/12760 bread
In the fret (1989) , the use of needle rollers made of ceramics mainly composed of silicon nitride has been proposed to prolong the life of the rolling elements in a corrosive environment due to an air-fuel mixture. However, the life of the bearing in the connecting rod is improved due to causes other than damage to the rolling elements, and the engine speed is reduced by 7
The above publication does not sufficiently consider the reliability of the silicon nitride sintered body with respect to breakage of the silicon nitride rolling element under high-speed rotation of 000 rpm or more.

Therefore, an object of the present invention is to provide a high-speed rotation
Durability that does not cause seizure and abnormal wear on bearing structures where the components that make up the sliding surface may be softened by tempering and the cage type cage may be damaged due to insufficient lubrication oil supply during high temperature operation. An object of the present invention is to provide a bearing structure excellent in reliability and reliability, particularly a bearing structure for a two-cycle internal combustion engine.

[0011]

A bearing structure according to the present invention comprises at least a crankshaft rotating in a crank chamber of a two-cycle internal combustion engine or a piston reciprocating in a cylinder of the internal combustion engine. Used to connect either one to the connecting rod. The rolling elements constituting the bearing structure are formed of a silicon nitride based sintered body. The sintered body has a two-phase mixed structure including an α phase and a β phase. The α phase has at least one of α-Si ₃ N _{4 and} α ′ sialon. β phase is β-Si ₃ N
_It has at least one of ₄ or β 'sialon. The composition ratio of the α phase and the β phase represented by the relative intensity ratio of the diffraction intensity by the X-ray diffraction method is 0 <α / (α + β) ≦ 0.3
It is. The crystal grain diameter of the α phase represented by the major axis diameter approximated to the ellipse on the projection plane is 0.5 μm or less, and the crystal grain diameter of the β phase is 5 μm or less.

It is known that rotation of a shaft in a mechanical element generates heat in a bearing portion such as a fastening portion between the crank pin 4 or the piston pin 5 and the connecting rod 3 in FIG. Due to this heat generation, especially in a machine element rotating at a high speed, the temperature of the rolling surface increases, and as a result, the seizure resistance may be reduced due to the tempering softening of the steel material.

Further, the cage type cage does not hold the rolling element by the cage itself, so that the mechanical loss due to rotation is low, but the rolling element attacks the cage at the time of rolling. There is a concern that the damage will be severe and the life of the bearing will be shortened.

The inventors of the present application have conducted intensive studies from the viewpoint of the mechanical action of the bearing structure, and as a result, have found that heat generation in the bearing portion can be suppressed by increasing the rigidity of the entire bearing structure. According to this study, for example,
When eccentricity occurs in the shaft to which the bearing is fastened, torsional deformation occurs in the bearing constituent member. Torsional deformation is caused by sliding contact with the rolling element due to direct contact between the cage type cage and the raceway surface of the inner and outer races of the bearing, and uneven deformation of the rolling raceway and local deformation of the rolling surface due to uneven load. cause. For this reason,
A friction loss greater than a normal rolling state occurs. Since the friction loss is converted into heat, abnormal heat is generated near the surface of the rolling surface,
The contact surface undergoes tempering. It is considered that this causes the rolling surface to soften, causing "galling" or the like by the end portion of the rolling element, resulting in seizure. Therefore, by reducing the amount of deformation of the components with respect to the load, that is, by increasing the rigidity of the bearing structure, it is possible to prevent seizure due to heat generation of the bearing portion.

As described above, methods for increasing the rigidity of the bearing structure include improving the rigidity of the end ring of the connecting rod, which is the housing, and improving the rigidity of the rolling elements. In particular, it is preferable to increase the rigidity of the rolling elements. The reason for this is that the rigidity of the end ring of the connecting rod is increased by increasing its thickness, so that the inertial mass of the connecting rod increases, and the followability in the high-speed rotation range decreases.

Therefore, as a result of examining the material of the rolling element having high rigidity, it was found that a ceramic material having higher rigidity and lower specific gravity than the conventional steel material was effective.

Ceramic materials are non-metallic materials, and have poor reactivity with iron-based materials used as bearing structural materials. Therefore, adhesion, which is a seizure phenomenon due to a chemical action between the sliding members, is unlikely to occur. As a result, the seizure limit becomes higher as compared with conventional steel materials. Therefore, it is possible to provide a connecting rod end bearing that does not cause adhesion up to a high-speed rotation region in which the sliding surfaces are activated by heat generation. This makes it possible to design a two-cycle engine with high speed and high reliability.

However, if a ceramic-based material, which is a brittle material, is applied to the connecting rod end bearing structure, reliability against immediate destruction becomes a problem. Therefore, when the crushing load of the rolling element was examined for silicon nitride ceramics having heat resistance and high strength, the three-point bending test strength based on JIS R1601, which is a conventional silicon nitride material, was 100 kgf / mm ² level. In the material, 0.
The unreliability of 03% was 80 kgf / mm ^2, which was insufficient for an actual applied load, and a 15% cut-off was required for the current bearing steel level.

In order to solve this problem, the present inventors diligently studied the reliability of silicon nitride-based materials against compression fracture. As a result, the matrix of the silicon nitride-based sintered body has an α phase (including at least one of α-Si ₃ N _{4 and} α ′ sialon) and a β phase (at least one of β-Si ₃ N _{4 and} β ′ sialon). And α / (α + β) is 0 <α as a relative intensity ratio of the diffraction intensity by the X-ray diffraction method.
/(Α+β)≦0.3, the crystal grain size of which is 0.5 μm in the α-phase with the major axis diameter obtained by approximating the crystal grain to the ellipse on the projection plane.
Hereinafter, it was found that a sintered body having a β phase of 5 μm or less has excellent reliability against compression fracture.

The structure of the sintered body has a two-phase structure of α phase and β phase. The α-phase crystal particles are equiaxed, and the β-phase crystal particles are acicular. The sintered compact of the present invention exhibits excellent crushing load characteristics because it has fine and equiaxed α-phase crystals and β-columnarized β-phase crystals.
By combining phase crystals, conventional columnar β '
This is because Young's modulus and hardness are improved as compared with a sintered body composed of only the sialon crystal phase. These are physical property values indicating the deformation resistance of the material. For a brittle material such as a ceramic material, improving these values leads to an improvement in the strength of the material in a broad sense.

Further, the basic concept of fracture of brittle material is
According to Griffith's theory, the fracture strength σf of the sintered body is given by the following equation.

[0022]

(Equation 1)

Here, since γs is considered to be proportional to the composition and thickness of the grain boundary phase, compounding of crystal grains, which improves the density of crystal grains in terms of thickness, is particularly advantageous in improving the fracture strength σf. It is. According to the above equation, to improve the crushing load, that is, to improve the fracture stress, E
Needs to be increased and a must be decreased. Since a depends on the crystal grain size if unavoidable defects are eliminated in the manufacturing process, the structure of the sintered body of the present invention, in which the filling property is improved by fine crystal grains, has an improved fracture stress in terms of E and γs. Is advantageous. From this, it is considered that the resistance to the compressive fracture of the rolling element made of the silicon nitride sintered body of the present invention increases, and as a result, its reliability increases.

In actually applying a ceramic material to a bearing member, there is a problem of reliability with respect to the life of the material. It is generally known that the life of a bearing is governed by the peeling of a rolling surface in current metallic materials. As a result of examining the rigidity, life, and damage mode of various materials, it was found that a silicon nitride-based sintered body having the structure of the present invention exhibits excellent life characteristics as a bearing material having a rolling surface.

The first reason that the silicon nitride-based sintered body having this structure has excellent peeling life characteristics is that the structure is finer than that of a conventional silicon nitride-based sintered body. is there.

The fracture of a silicon nitride-based sintered body is generally caused by a crack growth rate v = A × X ⁿ (K: stress intensity factor, A: constant)
It has been clarified that the crack growth rule shown in Fig. 1 is obeyed. Therefore, it is considered effective to suppress the peeling failure due to the repeated stress of the silicon nitride based sintered body by increasing the crack propagation resistance. When considering the crack growth from an internal crack, it is said that when the elastic strain energy at the internal crack tip reaches a certain upper limit, the crack propagates from the internal crack tip. In a brittle polycrystalline material such as a ceramic sintered body, the cracks grow one crystal grain at a time and stop at the grain boundary triple point.
It is thought that the crack propagated again in the same process. From this, making the crystal grains constituting the sintered body finer means that the amount of crack propagation in the minute region, that is, the length of the crack extending from the end of the intrinsic crack is reduced, which is macroscopic. It is believed that the energy required to propagate a unit length crack increases. Therefore, resistance to destruction due to repetitive stress such as rolling separation increases, and it is considered that application to members involving rolling is effective.

The second reason is that the structure of the silicon nitride sintered body of the present invention has a two-phase structure of α phase and β phase.
The α-phase crystal particles are equiaxed, and the β-phase crystal particles are acicular. It is known that crack growth in solids grows perpendicular to the maximum principal stress. In the case of a ceramic sintered body, two types of crack propagation paths can be considered, a grain boundary and an intragranular. However, since the α phase and β phase constituting the sintered body of the present invention have high strength, they have lower strength. There is a characteristic that cracks easily propagate through the grain boundary phase. From this, since the silicon nitride-based sintered body of the present invention has a structure in which the α phase and the β phase are intertwined in a complicated manner, the growth of the cracks is easily dispersed in the direction in which the acicular crystals extend, and the tip of the crack is the largest. It is considered that the resistance to the crack growth increases as a result of the deviation from the stress direction.

On the other hand, the bearing life due to wear is also an important consideration when applying a ceramic material to a bearing member. The present inventors have found that a silicon nitride-based material as a rolling element material has excellent wear resistance and low aggressiveness to a counterpart material. In particular, as described above, the matrix of the silicon nitride sintered body has a two-phase mixed structure of α phase and β phase, and the composition ratio of α phase and β phase is α / α as the relative intensity ratio of the diffraction intensity by the X-ray diffraction method. (Α + β) is 0 <α / (α
+ Β) ≦ 0.3, and their crystal grain diameter is a major axis diameter obtained by approximating the crystal grain to an ellipse on the projection plane, the α phase is 0.5 μm or less,
It was found that the above characteristics were particularly excellent when the sintered body had a β phase of 5 μm or less.

Conventionally, in sliding or rolling between metal and silicon nitride, generally, wear particles fall off from the silicon nitride sintered body, the hard particles bite between the contact surfaces, and the mating steel becomes large. It is considered to be worn.

On the other hand, the silicon nitride-based sintered body of the present invention has a complexly entangled structure because the structure of the sintered body is composed of two phases, α phase and β phase. further,
In the structure of the sintered body, the crystal grain size constituting the α phase is 0.
Since the crystal grain size constituting the β phase is controlled to 5 μm or less, the silicon nitride sintered body of the present invention exhibits remarkably excellent wear resistance and anti-attack property. this is,
By making the crystal grains finer, the entanglement of the two-phase crystal particles becomes denser, and the wear particles fall off due to the tensile stress on the surface caused by the Hertz stress (elastic contact stress) during rolling and the impact contact. Is not easily generated and does not cause excessive wear of the sintered body itself and the mating material.

For such a silicon nitride sintered body,
When a three-point bending test according to IS R1601 was performed, the average strength was 140 to 170 kgf / mm ² and the Weibull coefficient was 14 to 21 (however, the number of n was 2
0). Further, the fracture toughness according to the SEPB method is 5.5-6.
It was 2 MPa. Accordingly, the silicon nitride-based sintered body having a microstructure of the present invention has high strength and high toughness, and is a bearing structure material of a two-cycle internal combustion engine which is subjected to an impact load due to an explosion of a mixture of fuel and air. It is considered to be suitable.

As another failure factor, there is a problem that the cage-type cage is broken at the corners and side surfaces during use. On the other hand, by combining the cage-type cage with the rolling element of the silicon nitride-based sintered body of the present invention, the damage life of the cage-type cage can be greatly extended. This is because the weight reduction of the rolling elements reduces the impact load on the cage and reduces the damage. Furthermore, the microstructure and toughness make the cage-type cage have an abrasive effect on the cage type cage. Since the generation of abrasion powder on the rolling element of the silicon-based sintered body is greatly improved, it is considered that this is due to a synergistic effect of these two actions.

Further, as a cause of breakage of the side portion of the cage type cage, the contact of the rolling element end face with the side surface of the cage due to the falling of the connecting rod in the thrust direction can be cited. On the other hand, in the bearing structure of the present invention, by performing the crowning process on the end of the rolling element, it is possible to mitigate an attack on the cage-type cage due to the end face edge of the rolling element, and the life of the cage-type cage is reduced. Can be improved.

As described above, according to the present invention, by increasing the rigidity of the bearing portion in the bearing structure of the connecting rod (connecting rod) of the two-cycle engine, it is possible to prevent seizure at high speed rotation. . In particular, by forming the rolling elements constituting the bearing structure from a silicon nitride based sintered body having a specific structure, it becomes possible to greatly improve the seizure property, the life, and the reliability thereof. Thereby, it is possible to provide a bearing structure excellent in reliability with respect to seizure and life especially at high speed rotation.

If the rigidity of the connecting rod ring is the same, the rolling element is formed from the silicon nitride sintered body having the specific structure according to the present invention, whereby the inertial weight of the connecting rod is reduced as compared with the conventional steel. Since it can be reduced, it is possible to provide a connecting rod having excellent followability at higher rotation speed.

[0036]

【Example】

 Example 1 Average particle size 0.4 μm, α crystallization ratio 96%, oxygen content 1.4
Weight% silicon nitride raw material powder, average particle size 0.8 μm,
0.4 μm, 0.5 μm, Y_TwoO _Three, Al
_TwoO_Three, AlN, and MgO powders in ethanol for 10
For 0 hour, wet mixing was performed using a nylon ball mill.
Then, the mixed powder obtained by drying was 3,000 kgf /
cm^TwoCIP molding was performed under the following pressure. This molded body is
N_Two6 hours at 1500 ° C in gas, 1650 ° C in gas
For 3 hours. The obtained sintered body was heated to a temperature of 160.
0 ° C, 1000 atm N_TwoSecondary sintering in a gas atmosphere
Was.

The ratio of the crystal phase in the silicon nitride sintered body thus obtained is determined from the peak height of the diffraction intensity (I) of each crystal phase obtained by the X-ray diffraction method shown in FIG. Was calculated using the following equation.

[0038]

(Equation 2)

The crystal grain size was calculated by observing the structure of the sintered body using a transmission electron microscope. Table 1 shows the crystal phase ratio, crystal grain size, three-point bending strength, and fracture toughness of the obtained sintered body.

The three-point bending strength is in accordance with JIS R1601.
Table 1 shows the average breaking strength measured in accordance with
At the same time, the Weibull coefficient m, which is an index of reliability against fracture
(N is 20) is also shown. The fracture toughness is SE
It is a mode I fracture toughness value KIc by the PB method.

[0041]

[Table 1]

The crushing load of the needle rolling element made of the silicon nitride sintered body obtained as described above was changed according to JIS B
It was measured according to 1501. Needle shape is diameter φ
The size was 3 mm × 12 mm. The surface of the needle was finished by grinding using a # 800 diamond grindstone. The crushing test was carried out for 15 pieces of each material.
The results are shown in Table 2. It can be seen that the crushing load and the Weibull coefficient of the needle rolling element made of the silicon nitride sintered body of the present invention are improved as compared with the comparative example.

[0043]

[Table 2]

These needle rolling elements were incorporated into the large end of a connecting rod of a two-cycle engine. As shown in FIG. 2, a needle rolling element 12 is incorporated in the large end 6 of the connecting rod 3. A tensile load was applied in the direction indicated by the arrow, and the strain on the outer peripheral surface of the large end 6 at that time was measured via the strain gauge 13. The result is shown in FIG.
Is shown in As is clear from FIG. 3, it is recognized that the use of the silicon nitride-based sintered body of the present invention for the needle rolling element reduces the amount of strain with respect to load and improves the rigidity of the large end.

Example 2 The materials 1 to 16 evaluated in Example 1 were subjected to a wear test and a rolling life test. In the test, as shown in FIG. 4, the rolling elements 14 are arranged in the lubricating oil 18 so as to roll on the thrust plate 15, the bearing race 17 is placed thereon, and the rotating shaft 16 is moved. This was done by placing it further on it. A thrust load was applied in the direction of arrow 19, and the rotating shaft 16 was rotated in the direction of arrow 20. Three rolling elements 14 are arranged on the thrust plate 15.

The test conditions were that the thrust load was 500 kgf,
The number of revolutions was 1200 rpm. First, each material 1-1
From No. 6, the amount of wear per unit time when a rolling element was formed was measured. At this time, the thrust plate 15 was formed from bearing steel, and the amount of wear of the rolling elements 14 and the thrust plate 15 was measured. The results are shown in Table 3.

As is clear from Table 3, in the present invention,
It can be seen that the wear of the silicon nitride-based sintered body itself and the bearing steel as the mating material is sufficiently suppressed. Further, when the sliding surface after the test was observed, in the comparative example, many scratches were observed on the bearing steel side, and many drops of crystal grains which did not exist before the test were observed on the silicon nitride side. On the other hand, in the example of the present invention, the number of scratches on the bearing steel side was reduced, and the surface was dense on the silicon nitride side, and no dropout marks were observed.

[0048]

[Table 3]

Next, a life test of each of the materials 1 to 16 was performed. The life test was performed by forming the thrust plate 15 from each material and forming the rolling elements 14 from bearing steel. The test piece life was evaluated by 10% cumulative damage time (L10) estimated from Weibull statistical theory. The life test was terminated at 1 × 10 ⁸ times.

The results are shown in Table 3. As is clear from Table 3, the life of the silicon nitride-based sintered body of the present invention was uniformly improved, and it was found that the reliability of the bearing structure could be improved.

Example 3 A two-cycle engine incorporating a connecting rod in which the silicon nitride-based sintered body of the present invention was applied to a rolling element of a bearing portion was subjected to an engine bench endurance test at 1,000 rpm for an engine speed of 8,000 rpm. The materials used for the rolling elements were a silicon nitride-based sintered body and bearing steel shown in Table 1. The results are shown in Table 4.

The bearing steel and the comparative example No. In the rolling elements made of silicon nitride sintered bodies Nos. 1 to 11, seizure and damage to the rolling elements occurred during the test. In particular, those marked with * in Table 4 were caused by seizure due to the breakage of the rolling elements, and in others, seizure was caused by peeling of the rolling elements.

On the other hand, in the example of the present invention, the durability test of 1000 hours was cleared. Furthermore, in order to confirm the reliability of the bearing structure under high-speed rotation, the engine speed was set to 15,000 rpm.
m, a durability test was performed. As a result, the α phase is 100%,
In the case of using a conventional silicon nitride sintered body having a microstructure having a β phase of 100%, the rolling element was destroyed at the beginning of the test, resulting in seizure. On the other hand, the one using the silicon nitride sintered body of the present invention exhibited a life of 100 hours or more, and exhibited high reliability even under high-speed rotation.

Therefore, by applying a sintered body having a two-phase structure and a fine structure like the silicon nitride sintered body of the present invention to a rolling element having a connecting rod bearing structure, a high impact load can be obtained. It was found that it works repeatedly and shows high reliability under severe lubrication conditions.

[0055]

[Table 4]

Example 4 The silicon nitride-based sintered body of the present invention shown in Table 1 and a conventional rolling element of bearing steel were assembled in a connecting rod of a two-cycle engine, and the same engine bench test as in Example 3 was carried out.
= 15 and a life test was performed. The evaluation result is shown in FIG.

FIG. 5 is a Weibull plot of the life of the bearing. According to FIG. 5, the regression curve of the one using the rolling element of the bearing steel is inflected, and the stratified analysis by the failure mode was performed. However, on the short life side, it was due to breakage of the cage type cage. On the other hand, in the case of using the rolling element of the silicon nitride-based sintered body, the rolling was discontinued at 100 hours, and no damage of the cage type cage made of the bearing steel was observed. Therefore, it has been found that the combination of the cage-type cage made of bearing steel and the rolling element made of the silicon nitride-based sintered body of the present invention provides a highly reliable bearing.

[Brief description of the drawings]

FIG. 1 is a view showing a peak height of diffraction intensity of each crystal phase for obtaining a ratio of crystal phases of a silicon nitride sintered body in Example 1.

FIG. 2 is a diagram conceptually illustrating a method for measuring the rigidity of a large end of a connecting rod of a two-cycle engine.

FIG. 3 is a diagram showing a measurement result of rigidity of a large end of a connecting rod measured in Example 1.

FIG. 4 is a view conceptually showing a wear test apparatus used in Example 2.

FIG. 5 is a diagram showing a failure factor analysis result obtained in Example 4.

FIG. 6 is a cross-sectional view showing a connection structure in a conventional two-stroke engine to which the present invention is applied.

FIG. 7 is a cross-sectional view showing a cage and roller type needle roller bearing structure.

[Explanation of symbols]

 8, 9: Needle roller bearing structure 10: Needle roller 11: Cage

Continued on the front page (72) Inventor Kaoru Murabe 1-1-1, Koyokita, Itami-shi, Itami-shi, Hyogo Sumitomo Electric Industries, Ltd. Itami Works (72) Inventor Masaya Miyake 1-1-1, Konokita, Itami-shi, Hyogo No. 1 Sumitomo Electric Industries, Ltd. Itami Works (56) References WO 89/12760 (WO, A1) (58) Fields investigated (Int. Cl. ⁶ , DB name) F16C 9/04 F16C 33/34

Claims (1)

(57) [Claims] 1. A two-stroke internal combustion engine used to connect a connecting rod to at least one of a crankshaft rotating in a crank chamber of a two-stroke internal combustion engine and a piston reciprocating in a cylinder of the internal combustion engine. In the bearing structure of (1), the rolling elements constituting the bearing structure are formed of a silicon nitride-based sintered body, and the sintered body includes an α-phase having at least one of α-Si ₃ N _{4 and} α ′ sialon. , Β
And a β phase having at least one of —Si ₃ N _{4 and} β ′ sialon, and the α phase and the β phase represented by the relative intensity ratio of diffraction intensity by X-ray diffraction. The phase composition ratio is 0 <α / (α + β) ≦ 0.
3. The two-cycle internal combustion engine according to claim 2, wherein the α-phase has a crystal grain diameter of 0.5 μm or less and the β-phase has a crystal grain diameter of 5 μm or less, expressed by a major axis diameter approximated to an ellipse on a projection plane. Engine bearing structure.