JP2018021537A - Cylinder block of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a heat insulation film on an internal peripheral face of a cylinder bore while suppressing a mechanical loss, related to a cylinder block.SOLUTION: A cylinder block 12 comprises a cylinder bore 12a in which a piston 16 reciprocates. The cylinder block 12 comprises a first heat insulation film 20 which is formed in a region 28a at an upper side of a cylinder axial line direction D at an internal peripheral face 28 of the cylinder bore 12a (cylinder liner 12b). Furthermore, the cylinder block 12 comprises a second heat insulation film 22 which is formed at the internal peripheral face 28 in a region 28b located at a lower side of the cylinder axial line direction D compared with the region 28a in which the first heat insulation film 20 is formed, and has thermal conductivity lower than the thermal conductivity of the first heat insulation film 20.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a cylinder block of an internal combustion engine.

  For example, Patent Document 1 discloses a piston for an internal combustion engine. A heat shield film is formed on the top surface of the piston to reduce cooling loss.

JP 2014-105619 A Japanese Patent Laid-Open No. 2001-200751 JP 2005-330873 A JP 2007-016735 A

  In order to further reduce heat loss (cooling loss, mechanical loss, etc.), it is conceivable to provide a heat shielding film on the inner peripheral surface of the cylinder bore of the cylinder block. In addition, there is a difference in temperature rise caused by combustion between an upper portion in the cylinder axial direction (mainly a portion constituting the combustion chamber) and a lower portion thereof on the inner peripheral surface of the cylinder bore. In the structure around the cylinder block, one of the problems is the presence of mechanical loss due to non-uniform thermal expansion due to this difference.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a cylinder block in which a thermal barrier film is provided on the inner peripheral surface of a cylinder bore while reducing mechanical loss. .

  The cylinder block which concerns on this invention is a cylinder block provided with the cylinder bore which a piston reciprocates inside, Comprising: A 1st heat insulation film | membrane and a 2nd heat insulation film | membrane are provided. The first heat shield film is formed on a portion of the inner peripheral surface of the cylinder bore on the upper side in the cylinder axial direction. The second thermal barrier film is formed on the inner peripheral surface at a portion located on the lower side in the cylinder axial direction as compared with the portion where the first thermal barrier film is formed. The thermal conductivity is smaller than the thermal conductivity.

  According to the present invention, the thermal conductivity of the second thermal barrier film on the lower side in the cylinder axis direction is configured to be lower than the thermal conductivity of the first thermal barrier film in the same direction. For this reason, about the site | part below the cylinder bore with the small temperature rise by combustion, it can make it difficult for heat to escape to the periphery. And, in the upper part of the cylinder bore where the temperature rise due to combustion is large, heat can easily escape to the periphery as compared with the lower part. For this reason, the temperature difference between these parts can be made small. Thereby, the difference of a thermal expansion coefficient between these parts becomes small. Therefore, according to the present invention, a thermal barrier film can be provided on the inner peripheral surface of the cylinder bore while reducing mechanical loss.

It is the figure which represented typically the structure of the principal part of the cylinder block with which the internal combustion engine which concerns on embodiment of this invention is provided. It is a figure which expands and shows a part of internal combustion engine shown in FIG.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a diagram schematically showing a configuration of a main part of a cylinder block 12 included in an internal combustion engine 10 according to an embodiment of the present invention. A configuration around a cylinder cut along a plane passing through a cylinder axis L is shown. Show.

  As shown in FIG. 1, the internal combustion engine 10 includes a cylinder block 12 and a cylinder head 14 attached to the cylinder block 12 via a gasket (not shown). Each cylinder of the internal combustion engine 10 includes a piston 16 that reciprocates within the cylinder block 12. In FIG. 1, for convenience of explanation, each of the piston 16 when located at the top dead center (TDC) and the piston 16 when located at the bottom dead center (BDC) is illustrated.

  The cylinder block 12 includes a cylindrical cylinder liner 12b as a part constituting the cylinder bore 12a. In the cylinder block 12, a water jacket 18 through which cooling water for cooling the internal combustion engine 10 flows is formed on the outer peripheral side of the cylinder liner 12b.

  Further, in the internal combustion engine 10 of the present embodiment, the first heat shield film 20 and the inner peripheral surface 28 of the cylinder liner 12b (that is, the inner peripheral surface of the cylinder bore 12a), which is a portion facing the piston 16 in the cylinder block 12, are provided. A second thermal barrier film 22 is formed. Next, with reference to FIG. 2 together with FIG. 1, detailed arrangement portions and heat shielding characteristics of the heat shielding films 20 and 22 will be described.

  FIG. 2 is an enlarged view showing a part of the internal combustion engine 10 shown in FIG. As shown in FIG. 2, the piston 16 includes a top ring 24 attached to the top ring groove 16 a on the side thereof. A second ring groove 16b for attaching a second ring (not shown), which is a compression ring for maintaining airtightness, as well as the top ring 24, and an oil ring (not shown) are attached to the side of the piston 16. For this purpose, an oil ring groove 16c is formed. In the cylinder axial direction D, the top ring groove 16a is provided at a position closest to the combustion chamber 26 among these grooves 16a to 16c. The combustion chamber 26 is a space surrounded by the cylinder head 14, the cylinder liner 12 b, and the piston 16. Further, as shown in FIG. 1, the sliding range of the piston 16 is from the upper end position of the top ring 24 when the piston 16 is located at the top dead center to the piston 16 when the piston 16 is located at the bottom dead center. It can be defined as a range up to the lower end position of the skirt 16d.

(Location of the first and second thermal barrier films in the cylinder axis direction)
The first thermal barrier film 20 is formed on a portion 28a on the upper side in the cylinder axial direction D on the inner peripheral surface 28 of the cylinder liner 12b (that is, the inner peripheral surface of the cylinder bore 12a). More specifically, in the present embodiment, as an example of the first heat shield film 20 formed in such a manner, as shown in FIG. 2, the first heat shield film 20 includes a top ring 24 at the time of combustion. Is formed in a portion 28a of the inner peripheral surface 28 located on the upper side (that is, on the combustion chamber 26 side) with respect to the lower end position of the inner peripheral surface.

  On the other hand, the second heat shield film 22 is formed on the inner peripheral surface 28 at a portion 28b located on the lower side in the cylinder axial direction D as compared with the portion 28a where the first heat shield film 20 is formed. Moreover, regarding the circumferential direction of the cylinder bore 12a, the first heat shield film 20 and the second heat shield film 22 are formed over the entire circumferential direction.

(Thermal barrier properties of the first and second thermal barrier films)
The first thermal barrier film 20 is configured to have a low thermal conductivity. The “low thermal conductivity” for the first thermal barrier film 20 here means a thermal conductivity of 2 W / mK or less. Here, the site | part 28a of the internal peripheral surface 28 of the cylinder liner 12b in which the 1st thermal insulation film | membrane 20 is arrange | positioned is a site | part which receives the influence of combustion gas directly. More specifically, the heat of the combustion gas is directly transmitted to the portion 28a as in the heat flow A indicated by arrows in FIG. There is also a heat flow B that is transferred from the combustion gas through the top ring 24 to the site 28a. In addition, since the piston 16 of this embodiment is provided with the heat insulation film | membrane 16e in the top part as an example, as shown in FIG. Flow C is suppressed.

  Further, the second heat shield film 22 is configured to have a lower thermal conductivity (that is, less than 2 W / mK) than the thermal conductivity of the first heat shield film 20. Since the part 28b where the second thermal barrier film 22 is disposed (that is, the part below the lower end position of the top ring 24 during combustion) is not directly affected by the combustion gas, the heat source of the part 28b is the main heat source. The heat generated by the sliding of the piston.

  According to the above configuration in which the thermal conductivity of the lower second thermal barrier film 22 in the cylinder axis direction D is lower than the thermal conductivity of the upper first thermal barrier film 20 in the same direction D, the temperature due to combustion As for the lower portion 28b in the cylinder axis direction D where the rise is small, it is possible to make it difficult for heat to escape to the water jacket 18 side particularly during warm-up. And in the site | part 28a of the upper side of the cylinder liner 12b with a large temperature rise by combustion, compared with the site | part 28b, heat can escape easily to the water jacket 18 side. For this reason, the temperature difference between the part 28a and the part 28b (that is, the temperature difference between the upper and lower sides of the cylinder liner 12b) can be reduced. Thereby, the difference in coefficient of thermal expansion between the part 28a and the part 28b is reduced. For this reason, the mechanical loss can be reduced particularly during warm-up.

  In addition, according to the above-described configuration relating to the thermal conductivity, it is possible to prevent the temperature of the upper portion 28a in the cylinder axis direction D from rising intensively, particularly during warm-up. As a result, the clearance between the piston 16 and the cylinder wall (the surface of the first heat shield film 20) at the portion 28a, and the clearance between the cylinder wall of the piston 16 (the surface of the second heat shield film 22) at the portion 28b. An increase in the difference can be suppressed. For this reason, it becomes possible to suppress an increase in piston hitting sound during warm-up.

  In addition, by providing the first thermal barrier film 20 with low thermal conductivity characteristics, the so-called swing width (the fluctuation range of the cylinder bore wall surface temperature during one cycle) can be increased, thereby reducing the cooling loss. You can also plan.

Furthermore, the first thermal barrier film 20 of the present embodiment is configured to obtain a low heat capacity (low volume specific heat) characteristic. The “low volume specific heat” for the first thermal barrier film 20 here means a volume specific heat of 2200 kJ / m ³ K or less. By imparting such a low heat capacity characteristic to the first heat shield film 20, it is possible to suppress heating of the intake air flowing into the cylinder. For this reason, knocking can be suppressed. As described above, the lower portion 28b where the second thermal barrier film 22 is disposed is not directly affected by the combustion gas and has little influence on intake air heating (knock). For this reason, in the present embodiment, the above-described low heat capacity characteristic is not imparted to the second heat shield film 22.

(Configuration example of first and second thermal barrier films)
Next, a configuration example of the heat shield characteristics of the first and second heat shield films 20 and 22 used in the present embodiment will be described. In the present embodiment, an alloy having a quasicrystalline structure (as an example, an alloy mainly composed of aluminum, iron, chromium, and cobalt) is used as the material of the first and second thermal barrier films 20 and 22. Such an alloy can be formed using a spherical atomized powder of 100 μm or less.

  The main characteristics of the quasicrystal are as follows. That is, the electron diffraction pattern of the quasicrystal exhibits symmetry of 5, 8, 10, or 12 times. In addition, a sharp diffraction spot appears in the diffraction pattern of the quasicrystal, and the structure of the quasicrystal is not a random structure such as amorphous, but has a high degree of order. In addition, since the first and second heat shield films 20 and 22 are provided on the sliding portion with the piston 16, the material of the first and second heat shield films 20 and 22 is a low friction material (specifically, It is desirable to use a material having a friction coefficient μ of 0.5 or less. By using an alloy having a quasicrystalline structure having the above-mentioned characteristics as a heat shielding material, low thermal conductivity, low heat capacity, and a low friction coefficient can be preferably achieved.

  In the present embodiment, quasicrystalline films having a quasicrystalline structure are used as the first and second thermal barrier films 20 and 22. As shown in FIGS. 1 and 2, the first thermal barrier film 20 is a relatively thin film, while the second thermal barrier film 22 is a relatively thick film. Thus, in order to provide a difference in film thickness, the inner peripheral surface 28 of the cylinder liner 12b is formed so that the diameter of the part 28b is larger than the diameter of the part 28a. According to the configuration example of the first and second thermal barrier films 20 and 22, by appropriately setting the ratio of the film thickness between the first thermal barrier film 20 and the second thermal barrier film 22. In addition to imparting low thermal conductivity characteristics to the first thermal barrier film 20, the thermal conductivity of the second thermal barrier film 22 is lower than that of the first thermal barrier film 20. Can do. In addition, the above-described low heat capacity (low volume specific heat) characteristics can be imparted to the first thermal barrier film 20.

  By the way, in Embodiment 1, the example in which the boundary between the first heat shield film 20 and the second heat shield film 22 is the lower end position of the top ring 24 during combustion has been described. However, the first and second heat shielding films to be disposed in the present invention are arranged such that the first heat shielding film is formed on the inner peripheral surface of the cylinder bore on the upper side in the cylinder axial direction D, and the first In the first embodiment, if the second heat shielding film is formed on the inner peripheral surface located on the lower side in the cylinder axial direction D as compared with the part where the heat shielding film is formed, It may be determined in a mode other than the mode described. Therefore, instead of the above-described example, for example, a first heat shield film is formed on the upper side of the boundary with the upper end position (approximately 10 to 20 ATDC) of the top ring at the time of combustion as a boundary, and the lower side of the boundary. A second thermal barrier film may be formed.

  In the first embodiment, the example in which the inner peripheral surface 28 of the cylinder liner 12b functions as the inner peripheral surface of the cylinder bore 12a has been described. However, the cylinder block that is the subject of the present invention does not necessarily include a cylinder liner. That is, the first and second thermal barrier films may be formed on the inner peripheral surface of the cylinder bore formed on the base material of the cylinder block that does not include the cylinder liner.

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 12 Cylinder block 12a Cylinder bore 12b Cylinder liner 14 Cylinder head 16 Piston 16a Top ring groove 18 Water jacket 20 First heat insulation film 22 Second heat insulation film 24 Top ring 26 Combustion chamber 28 Inside of cylinder liner (cylinder bore) Peripheral surfaces 28a, 28b Internal peripheral surface parts

Claims (1)

A cylinder block having a cylinder bore in which a piston reciprocates,
A first heat-shielding film formed on an upper portion of the inner peripheral surface of the cylinder bore in the cylinder axial direction;
Heat conduction smaller than the thermal conductivity of the first thermal barrier film, formed on the inner peripheral surface at a site located on the lower side in the cylinder axis direction compared to the site where the first thermal barrier film is formed. A second thermal barrier film having a rate;
A cylinder block comprising:

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