JP5678779B2 - Cylinder liner and cylinder block including the same - Google Patents

Description

  The present invention relates to a cylinder liner that has a cylindrical shape and is provided with a plurality of annular grooves that are continuous in the circumferential direction on the outer peripheral surface thereof in the axial direction and is cast by a cylinder block body, and a cylinder block including the cylinder liner. The present invention relates to a cylinder liner suitable when the block body is made of a magnesium-based material.

  In an internal combustion engine such as an automobile, a cylinder block having a cylinder bore serving as a sliding surface of a piston is provided. The cylinder block is manufactured by casting the outer peripheral surface of a cylindrical cast iron cylinder liner by casting with a cylinder block body made of a die-cast material (cast metal). In the old days, the cylinder block main body was also made of cast iron. However, in recent years, there has been a demand for weight reduction in order to improve fuel efficiency and reduce exhaust gas, and the cylinder block main body is often made of aluminum.

  However, when the cylinder block body is made of cast iron, the cylinder liner and the cylinder block body are made of the same metal, so no major problems have occurred. However, as in recent years, cast iron cylinder liners are made of aluminum cylinder block bodies. When casting, the adhesion of the interface (joint surface) between the cylinder liner and the cylinder block body becomes a problem. That is, when casting the cylinder block, the molten die-cast material solidifies while shrinking, but the cast iron constituting the cylinder liner and the aluminum constituting the cylinder block body have different thermal expansion coefficients (thermal expansion coefficients). There arises a problem that residual strain caused by residual stress and a gap is generated between the cylinder liner and the cylinder block body. This causes a decrease in the thermal conductivity and the like of the cylinder block and a defect.

  Therefore, as a technique for solving such a problem, for example, the following Patent Document 1 has been proposed. In Patent Document 1, a plurality of annular grooves that are continuous in the circumferential direction are provided on the outer peripheral surface of a cylindrical cast iron cylinder liner in the axial direction, and these are cast by an aluminum cylinder block body. Here, the shape of each groove is improved, and in the axial cross-sectional shape, the diameter gradually decreases as it moves from the outer peripheral edge continuous to the flat surface on the one axial end side to the one axial end side. A first inclined surface that is undercut with respect to the surface, a first curved surface that gradually decreases in diameter from the inner peripheral end of the first inclined surface, and from the inner peripheral end of the first curved surface to the other axial end side The first circumferential groove formed in a J-shaped cross section in which the diameter of the first inclined surface and the second inclined surface opposed to the first inclined surface are sequentially continuous and the outer peripheral end of the second inclined surface and the other A third inclined surface that gradually decreases in diameter as it moves toward the axial direction end side, a second curved surface that gradually increases in diameter from the inner peripheral end of the third inclined surface, and the one of the first curved surface from the outer peripheral end of the second curved surface. Axial direction adjacent to the third inclined surface while gradually increasing in diameter as it moves toward the end in the axial direction A second circumferential groove formed in a J-shaped cross section in which a fourth inclined surface undercut with respect to the flat surface, the outer peripheral edge of which is continuous with the edge of the flat surface on the end side, is successively formed Each groove is formed. That is, each groove has a laterally widening shape with its side surface extending at an inclination angle exceeding 90 ° with respect to the outer peripheral surface, and is formed in an inverted heart shape in section. As a result, when casting the cylinder liner with the cylinder block body made of an aluminum alloy, the movement of the molten aluminum alloy is suppressed by each groove to prevent cracking of the cylinder block body, and between the cylinder liner and the cylinder block body. Interfacial adhesion and bond strength are ensured.

JP 2010-59909 A

  By the way, recently, in order to further reduce the weight of automobiles, the cylinder block body tends to be made of magnesium instead of conventional aluminum. This is because magnesium is a metal belonging to the lowest specific gravity among practical metals. However, magnesium has a larger difference in thermal expansion coefficient from cast iron than aluminum. For this reason, the concept of adhesion is different from the case of casting with an aluminum cylinder block body. Specifically, when casting with an aluminum cylinder block body, the higher the adhesion between the cylinder liner and the cylinder block body, the better. However, when casting with a cylinder block body made of magnesium, the difference in thermal expansion coefficient from cast iron is large, so if the adhesiveness is too high, the residual strain will be increased. It is known that when a cylinder liner is cast with a magnesium cylinder block body, three times as much residual strain is generated as compared with a case where the cylinder liner is cast with an aluminum cylinder block body. Therefore, when casting with a cylinder block body made of magnesium, it is necessary to secure a certain degree of freedom during shrinkage solidification in order to reduce residual strain while ensuring adhesion.

  On the other hand, in patent document 1, each groove | channel provided in the outer peripheral surface of a cylinder liner is made into a special shape, The movement of a molten metal is suppressed at the time of casting, and adhesiveness is ensured. In this case, when casting with the magnesium cylinder block main body, the movement of the molten magnesium is excessively suppressed, so that the residual strain due to the residual stress increases. Conventionally, there is a technique for improving the adhesion by roughening the outer peripheral surface of the cylinder liner. However, Patent Document 1 does not pay particular attention to the surface roughness of the cylinder liner. In Patent Document 1, when the surface roughness of the outer peripheral surface of the cylinder liner is large, the movement of the molten metal is further suppressed.

  Therefore, the present inventors have found that it is possible to reduce the residual stress by providing a certain degree of freedom of molten metal while ensuring adhesion to such an extent that the cylinder liner can be prevented from coming off from the cylinder block body, The present invention has been completed. That is, this invention solves the said subject, and provides a cylinder liner which can reduce the residual distortion resulting from the residual stress at the time of casting by the cylinder block main body made from magnesium, and a cylinder block provided with the same. Objective.

  As a means for this, the present invention has a cylindrical shape, and a plurality of annular grooves that are continuous in the circumferential direction are provided on the outer circumferential surface at a predetermined pitch in the axial direction, and are cast by a cylinder block body made of a magnesium-based material. A cylinder liner, wherein a surface roughness (Rz) in at least the groove of the outer peripheral surface of the cylinder liner is 20 μm or less. In the present invention, the magnesium-based material is a concept including pure magnesium and a magnesium alloy. The surface roughness “Rz” indicates “ten-point average roughness” defined in JIS B 0601.

  According to this, since the movement of an axial direction is suppressed because a molten magnesium enters in each groove | channel formed in the axial direction, the minimum adhesiveness is ensured. Further, the anchor effect can surely prevent the cylinder liner from coming off from the cylinder block body. On the other hand, each groove is annularly provided continuously in the circumferential direction, and at least the surface roughness (Rz) in each groove is 20 μm or less, so there is no restriction in the circumferential direction. High degree. Thereby, the residual stress generated with the solidification shrinkage of the molten metal when casting the cylinder block main body can be dispersed in the circumferential direction, and when using a magnesium-based material for the cylinder block main body, the residual strain is reduced. be able to.

  In addition, it is preferable that the inclination | tilt angle of the side wall of the said groove | channel with respect to the said outer peripheral surface (its flat surface) shall be 45 degrees-90 degrees. As in Patent Document 1, when the inclination angle of the side wall of each groove is formed at a large inclination angle exceeding 90 ° with respect to the outer peripheral surface, the molten metal stays in the deep part of the groove and stress is concentrated. This is because the movement in the circumferential direction is restricted. If the side wall of each groove is 45 ° to 90 °, it will not be restrained in the circumferential direction while ensuring the adhesion in the axial direction and preventing it from coming off. Distortion can be reduced.

  Moreover, according to this invention, the cylinder block by which the cylinder liner of the said structure was cast-in can also be provided. The cylinder block is preferably heat treated at 150 to 250 ° C. after casting the cylinder liner. Residual strain can be reduced more positively by heat treatment at a predetermined temperature after casting.

  According to the present invention, when a cylindrical cylinder liner is cast with a magnesium cylinder block body, residual strain due to residual stress can be reliably reduced.

It is a perspective view of a cylinder liner. It is sectional drawing of a groove | channel. It is sectional drawing of a cylinder block. It is sectional drawing which shows the modification of a groove | channel. It is sectional drawing which shows the modification of a groove | channel. It is sectional drawing which shows the modification of a groove | channel. It is sectional drawing which shows the modification of a groove | channel. It is sectional drawing which shows the modification of a groove | channel. It is sectional drawing which shows the modification of a groove | channel. It is a residual-strain measurement test result.

  The embodiment of the present invention will be specifically described below. As shown in FIGS. 1 and 3, the cylinder liner 10 is a cast iron cylindrical member, and a plurality of grooves 11 arranged at a predetermined pitch in the axial direction are formed on the outer peripheral surface S thereof. The cast iron is not particularly limited as long as it is conventionally used for a cylinder liner. For example, carbon is about 3.2 to 4.4 wt%, silicon is about 0.8 to 2.6 wt%, manganese is about 0.1 to 2.4 wt%, sulfur is about 0.001 to 0.2 wt%, Cast iron having a composition containing about 0.01 to 0.6 wt% phosphorus and the balance being iron and inevitable impurities can be used. Furthermore, chromium is about 0.01 to 0.6 wt%, copper is about 0.01 to 1.0 wt%, aluminum is about 0.05 to 1.0 wt%, tin is about 0.001 to 0.3 wt%, It may contain about 0.001 to 0.2 wt% of antimony or about 0.01 to 2.0 wt% of boron. The inner peripheral surface of the cylinder liner 10 finally becomes a cylinder bore of the cylinder block 30.

  Each groove 11 is formed in an annular shape that is continuous in the circumferential direction over the entire circumference of the outer peripheral surface S. Each groove 11 may be provided by forming one groove spirally, or may be an independent groove formed separately. Even when one groove is formed in a spiral shape, each groove 11 is substantially parallel to the circumferential direction by forming a large number of small pitches. Each groove 11 restrains the movement (sliding) of the molten metal in the axial direction when it is cast by casting, thereby ensuring the close contact between the cylinder liner 10 and the cylinder block main body 31, and from the cylinder block main body 31 by the anchor effect. The cylinder liner 10 is provided to prevent the cylinder liner 10 from coming off. Therefore, it is preferable to provide as many grooves 11 as possible (densely). However, when the number of the grooves 11 is excessively large, the strength of the outer peripheral surface S is reduced, and the outer peripheral surface of the cylinder liner 10 may be lost during casting or the like. Therefore, as shown in FIG. 2, the center-to-center distance l between the grooves 11 is preferably about 2.0 to 5.0 mm. If it is this range, the said function can be exhibited reliably, ensuring the intensity | strength of the outer peripheral surface S. The center distance l between the grooves 11 is more preferably about 2.5 to 4.0 mm.

  Moreover, it is preferable that the depth d of each groove | channel 11 shall be about 0.5-2.5 mm. When the depth d of each groove 11 is less than 0.5 mm, it is difficult to sufficiently exhibit the above-described function. On the other hand, if the depth d of each groove 11 exceeds 2.5 mm, stress concentration may occur during casting and the cylinder liner 10 may be lost. The depth d of each groove 11 is more preferably about 1.0 to 2.0 mm.

  Further, the side wall W of each groove 11 is formed such that the inclination angle θ with the flat surface of the outer peripheral surface S is 45 ° to 90 °. If the inclination angle θ of the side wall W is less than 45 °, the axial movement of the molten metal cannot be sufficiently restricted during casting, and the anchor effect is also reduced. On the other hand, when the inclination angle θ of the side wall W exceeds 90 °, the molten metal stays in the inner part of each groove 11 and the movement in the circumferential direction is restricted, and the residual strain can be reduced accurately. Disappear. Preferably, the inclination angle θ of the side wall W in each groove 11 is about 50 ° to 85 °. FIG. 2 illustrates a V-shaped groove in which the inclination angle θ of the side wall W is about 60 °.

  In addition, the shape of each groove | channel 11 can also be made into the shape as shown in FIGS. 4-9 other than the V shape shown in FIG. Specifically, as shown in FIG. 4, it may be V-shaped with the apex in an eccentric position. In this case, as shown in FIG. 5, the eccentric direction of each groove | channel 11 does not need to correspond. Alternatively, as shown in FIGS. 6 and 7, it can be formed as a groove having a bottom wall B. The groove 11 shown in FIG. 6 has a flat bottom wall B, and the groove 11 shown in FIG. 7 has a curved bottom wall B. Further, as shown in FIGS. 8 and 9, the side wall W may be a groove having a right angle with respect to the outer peripheral surface S (inclination angle θ is 90 °).

  In addition, the surface roughness Rz in each groove 11 is set to 20 μm or less. When the surface roughness Rz in each groove 11 exceeds 20 μm, the slipperiness of the molten metal in the circumferential direction is reduced, so that the residual strain cannot be reduced accurately. Preferably, the surface roughness Rz in each groove 11 is 15 μm or less, more preferably 10 μm or less. The lower limit of the surface roughness Rz is not particularly limited, but may be about 5 μm from the viewpoint of productivity. The surface roughness of the outer peripheral surface S of the cylinder liner 10 is not particularly limited. However, considering the time for surface treatment separately from each groove 11, it may be equal to the surface roughness in each groove 11. If the surface roughness Rz of the outer peripheral surface S of the cylinder liner 10 is also 20 μm or less, the movement in the circumferential direction becomes smoother.

  On the other hand, as shown in FIG. 3, the cylinder block 30 includes the cylinder liner 10 having the above-described configuration and a cylinder block main body 31 that is cast so as to enclose it. Specifically, the cylinder block 30 is manufactured by casting the cylinder block body 31 made of a magnesium-based material outside the cylinder liner 10. Reference numeral 32 denotes a water jacket. As the magnesium-based material, any known magnesium-based die casting material that has been conventionally used for a cylinder block body can be used without particular limitation. Specific examples include MDC1B, MDC1D, MDC2B, MDC3B, MDC4, MDC5, and MDC6 defined in JIS H5303 and JIS H2222. Pure magnesium may be used.

  Next, a method for manufacturing the cylinder liner 10 and the cylinder block 30 including the cylinder liner 10 will be described. First, a plurality of grooves 11 are formed on the entire outer peripheral surface of a cylinder liner 10 that has been previously formed into a cylindrical shape by casting. For example, the cylinder liner 10 may be cut with a cutting edge having a predetermined-shaped cutting edge while rotating the cylinder liner 10 about the central axis C. At this time, it is preferable to form a plurality of grooves 11 arranged in parallel in the axial direction by forming a single groove in a spiral shape, but it is preferable for productivity to be high. it can. Next, the entire surface is processed as needed, including at least the inside of each groove 11, preferably the outer peripheral surface S. Specifically, if the surface roughness is large, the surface is smoothed by polishing or the like. If the original surface roughness is sufficiently small, the surface may be roughened by shot blasting or the like to improve adhesion, but at least the surface roughness Rz is kept to 20 μm or less.

The cylinder block 10 in which the cylinder liner 10 is cast can be obtained by casting the cylinder block body 31 made of a magnesium-based material on the outer side of the cylinder liner 10 thus obtained. The casting is preferably a high pressure casting method. Specifically, after the cylinder liner 10 is preliminarily disposed in the die casting mold, a magnesium-based material melt of 5000 to 10000 kgf / cm ² is placed in the cavity formed between the die casting mold and the cylinder liner 10. Cast at high pressure and solidify by cooling.

  At this time, the molten metal enters the grooves 11 so that the movement (sliding) in the axial direction is restricted, and adhesion is ensured. On the other hand, there is a difference in thermal expansion coefficient between the cast iron cylinder liner 10 and the magnesium-based material, so that residual stress can be generated. However, since each groove 11 is formed in the circumferential direction and the surface roughness Rz is small, movement in the circumferential direction is not restricted. Thereby, the residual stress can be dispersed in the circumferential direction, so that the residual strain is reduced.

  Even if it remains as it is, it can be a product, but it is preferable that the cylinder block 30 be further heat-treated (aging treatment). Thereby, the residual strain after casting is further dispersed, so that the residual strain can be further reduced. The heat treatment temperature at this time is preferably 150 to 250 ° C. If it is less than 150 ° C., it is difficult to obtain a further effect of reducing residual strain. On the other hand, if it exceeds 250 ° C., there is a risk that the residual strain and the like will rise. The heat treatment temperature is preferably about 160 to 230 ° C, more preferably about 170 to 200 ° C. The heat treatment may be performed for about 4 to 24 hours.

  Specific examples of the present invention will be described below. A plurality of V-shaped grooves were formed in the axial direction on the outer peripheral surface of a cylindrical cast iron cylinder liner having an inner diameter of 81 mm, an outer diameter of 93 mm, and a height of 137 mm. The depth of each groove was 1 mm, the inclination angle of the side wall with respect to the outer peripheral surface was 60 °, and the center-to-center distance was 25 mm. As a result of measuring the surface roughness Rz in each groove 11 at this time with a Vickers hardness tester, Rz was 7 μm.

  Next, after placing the cylinder liner of the structure into the casting mold, Al 3 to 15 wt%, Ca 0.2 to 5 wt%, Mn 0 to 0.5%, Sr 0 to 1% are contained, and the balance is Mg and inevitable impurities A pseudo cylinder block obtained by casting the magnesium-based die casting material into a cylindrical shape having a thickness of 5 mm was taken as Example 1.

  Further, a pseudo cylinder block manufactured in the same manner as in Example 1 was further subjected to aging treatment at 175 ° C. for 4 hours as Example 2. Furthermore, a pseudo cylinder block manufactured under the same conditions as in Example 1 using a spiny liner manufactured by Teikoku Piston Ring Co., Ltd., which is most commonly distributed as a cylinder liner, was used as Comparative Example 1.

  The obtained samples (Examples and Comparative Examples) were cut in the axial direction, and strain gauges were attached to two places on the left and right sides 1 cm away from the cutting line. -23), the amount of strain was measured. The result is shown in FIG. Each sample had the same amount of strain at the two left and right locations.

  From the results of FIG. 10, the residual strain was high in Comparative Example 1 using the conventional product, but in Example 1 in which a plurality of circumferential grooves having a low surface roughness Rz were provided, the residual strain was compared to Comparative Example 1. Was reduced by about 35%. Further, in Example 2 subjected to aging treatment, the residual strain could be reduced by about 60% compared to Comparative Example 1.

10 Cylinder liner 11 Groove 30 Cylinder block 31 Cylinder block body B Groove bottom wall S Cylinder liner outer peripheral surface W Groove side wall

Claims (4)

A cylinder liner that has a cylindrical shape and is provided with a plurality of axially continuous annular grooves on its outer peripheral surface in the axial direction, and is cast by a cylinder block body made of a magnesium-based material,
A cylinder liner having a surface roughness (Rz) in at least the groove of the outer peripheral surface of the cylinder liner of 20 μm or less.   The cylinder liner according to claim 1, wherein an inclination angle of a side wall of the groove with respect to the outer peripheral surface is 45 ° to 90 °.   A cylinder block in which the cylinder liner according to claim 1 or 2 is cast. The cylinder block according to claim 3, wherein the cylinder block is heat-treated at 150 to 250 ° C. after casting the cylinder liner.

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