JP2017001235A - Thermal insulation structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal insulation structure that can suppress the occurrence of pumping loss due to overheat of a suction gas or the like even in a high rotation region in an internal combustion engine having improved in thermal efficiency by cooling loss reduction by providing a thermal insulation layer in a portion facing a combustion chamber of an internal combustion engine.SOLUTION: A thermal insulation structure A comprises an intermediate layer 2 and a thermal barrier layer 1 formed on the surface of a base material 3 being an aluminum alloy. The intermediate layer 2 is a layer formed by cold-spraying copper particles onto the base material 3 and the thermal barrier layer 1 is a layer formed by thermal-spraying oxide particles composed mainly of at least one kind selected from the group consisting of zirconia and silica onto the intermediate layer 2. The intermediate layer 2 has a thickness of 20 to 150 μm and the thermal barrier layer 1 has a thickness of 10 to 250 μm. The thermal conductivity λ1 of the thermal barrier layer 1 is smaller than the thermal conductivity λ3 of the base material 3 and the thermal conductivity λ2 of the intermediate layer 2 is larger than the thermal conductivity λ3 of the base material 3.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a heat insulating structure.

  In order to increase the thermal efficiency of an internal combustion engine, it is known that a portion facing the combustion chamber is a heat shield film. An example thereof is described in Patent Document 1, and the thermal barrier film described therein includes a first oxide layer including zirconia particles sprayed on a piston base material and pores, and the first oxide. Oxide particles mainly composed of one selected from the group consisting of alumina, silica, and zirconia, having an average particle size smaller than the average particle size of the zirconia particles of the first oxide layer sprayed onto the layer In addition, in order to improve the adhesion between the piston base material and the first oxide layer, an Ni-20Cr alloy is used as an undercoat layer. Plasma sprayed on the substrate surface.

JP 2013-185202 A

  In an internal combustion engine provided with a heat shield film having a structure described in Patent Document 1 in a combustion chamber, the presence of the heat shield film (heat insulating layer) can reduce cooling loss, which is energy taken away as heat to the outside. It can be expected to improve thermal efficiency. In addition, since the pores included in the first oxide layer are sealed by the second oxide layer, it is possible to prevent the fuel and the like from entering the heat insulating structure.

  However, when operating in a high speed range, the combustion interval is shortened, the surface temperature of the heat shield film cannot be lowered sufficiently until the next combustion, and the surface temperature (base wall temperature) of the heat shield film increases. A phenomenon occurs. FIG. 8 is a diagram for explaining the state, in which the horizontal axis indicates the crank angle (°), and the vertical axis indicates the surface temperature (° C.) of the thermal barrier film. When a high rotation speed region is reached and the combustion interval is shortened, the temperature drop is insufficient as shown in FIG. 4A, and the base wall temperature gradually rises as shown by the broken line (b) in the figure. When the base wall temperature rises, the intake gas receives heat during the intake stroke and expands, so the charging efficiency decreases.In addition, the working gas receives heat during the compression stroke and the pressure in the cylinder rises to increase the compression stroke. The pump loss increases due to an increase in negative work. The effect of the increase in pump loss that occurs in the high engine speed range cancels out the cooling loss reduction effect that is originally expected for the internal combustion engine, resulting in an overall improvement in fuel consumption.

  An object of the present invention is to solve the above-described problems. Specifically, an internal combustion engine in which a heat insulating layer is provided at a portion facing the combustion chamber of the internal combustion engine so as to improve thermal efficiency by reducing cooling loss. Therefore, it is an object of the present invention to provide a heat insulating structure capable of suppressing the occurrence of pump loss due to overheating of the intake gas even in a high rotation range.

  A heat insulating structure according to the present invention is a heat insulating structure including an intermediate layer and a heat shielding layer formed on a surface of a base material that is an aluminum alloy, and the intermediate layer is formed with respect to the aluminum alloy base material that is the base material. The heat shielding layer was formed by spraying oxide particles mainly composed of at least one selected from the group consisting of zirconia and silica on the intermediate layer. The intermediate layer has a thickness of 20 to 150 μm, the thermal barrier layer has a thickness of 10 to 250 μm, the thermal barrier layer has a thermal conductivity smaller than that of the substrate, and The thermal conductivity of the intermediate layer is larger than the thermal conductivity of the substrate.

  The heat insulating structure according to the present invention is selected from the group consisting of a base material made of an aluminum alloy, an intermediate layer made of copper particles cold sprayed on the surface of the base material, and zirconia and silica sprayed on the intermediate layer. It is comprised with the thermal insulation layer which consists of an oxide particle which has at least 1 sort (s) as a main component. When the thermal conductivity of the thermal barrier layer is λ1, the thermal conductivity of the intermediate layer is λ2, and the thermal conductivity of the substrate is λ3, each thermal conductivity λ is λ1 <λ3 <λ2. There is a relationship. Accordingly, the heat possessed by the heat shield layer is more easily transferred to the intermediate layer than when the heat shield layer is directly sprayed onto the base material, compared with the case where heat is transferred from the heat shield layer to the base material. . Further, since λ3 <λ2, the heat transfer from the intermediate layer to the base material is suppressed.

  For this reason, when the heat insulating structure according to the present invention is provided at the portion facing the combustion chamber, it is possible to reduce the cooling loss, which is the energy taken away as heat in the low rotation range. Even when the combustion interval is shortened in the high rotation range, the heat in the combustion chamber is easily transferred from the heat shield layer constituting the heat insulation structure to the intermediate layer, so that the heat shield layer that is the base wall temperature is used. It is possible to avoid an excessive rise in the surface temperature of the air and it is difficult for air overheating to occur. For this reason, it is possible to avoid an increase in pump loss due to intake air overheating in the high rotation range, and the cooling loss reduction effect originally expected for the internal combustion engine can be maintained as it is in the high rotation range. .

  In particular, as shown in the following examples, the intermediate layer has a thickness of 20 to 150 μm, and the heat shield layer has a thickness of 10 to 250 μm.

  By providing the thermal insulation structure according to the present invention in the portion facing the combustion chamber, the internal combustion engine is less likely to cause overheating of the intake air in a high rotation range, and pump loss due to intake air heating is suppressed, and cooling is performed. The fuel efficiency improvement effect is increased without offsetting the loss reduction effect.

The figure which shows typically an example of the heat insulation structure by this invention. The figure which shows typically the internal combustion engine provided with the heat insulation structure by this invention. The figure explaining the heat insulation structure used by the effect verification by simulation. The figure which shows the heat input conditions in simulation. The figure which shows a simulation result. The graph which shows the film thickness of an intermediate | middle layer, and wall temperature rise width (swing width: (DELTA) T). The graph which shows the relationship between the film thickness of a thermal-insulation layer, and a fuel consumption improvement rate. The figure for demonstrating a raise of base wall temperature.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram schematically showing an embodiment of a heat insulation structure according to the present invention, and FIG. 2 is a diagram schematically showing an internal combustion engine provided with the heat insulation structure according to the present invention.

  As FIG. 1 shows, the heat insulation structure A by this invention is equipped with the heat insulation layer 1, the intermediate | middle layer 2, and the base material 3 as basic composition. The base material 3 is a layer made of an aluminum alloy, the intermediate layer 2 is a layer in which copper particles are cold sprayed on the aluminum alloy base material which is the base material 3, and the heat shielding layer 1 is formed on the intermediate layer 2. On the other hand, it is a layer formed by thermal spraying oxide particles mainly composed of at least one selected from the group consisting of zirconia and silica. Although the heat insulation structure A can be used in any place requiring heat insulation, it is preferably used in a portion facing the combustion chamber in the internal combustion engine B as shown in FIG.

  In FIG. 2, 11 is a cylinder block and 12 is a cylinder head. A piston 14 reciprocates in a cylinder bore 13 of the cylinder block 11. The cylinder head 12 is provided with an intake port 15, an exhaust port 16, and the like, and an intake valve 17 and an exhaust valve 18 are attached thereto. In such an internal combustion engine B, a region surrounded by the cylinder bore 13, the cylinder head 12, and the piston 14 is generally called a combustion chamber, and faces the combustion chamber for the purpose of improving the thermal efficiency of the internal combustion engine as described above. A thermal barrier film 19 is formed on the portion. Specifically, the inner surface of the cylinder bore 13, the surface of the cylinder head 12 facing the cylinder bore 13, the surface of the intake port 15 or the exhaust port 16 facing the cylinder bore 13, the top surface of the piston 14, etc. 19 is formed.

  When the heat insulation structure A according to the present invention shown in FIG. 1 is applied to the portion facing the combustion chamber, the base material 3 corresponds to the cylinder block 11 or the cylinder head 12, and they are Since it is almost an aluminum alloy, in the heat insulation structure A by this invention, the base material 3 is made into the base material which is an aluminum alloy. The intermediate layer 2 and the heat shield layer 1 are formed on the side facing the combustion chamber, such as the cylinder block 11 or the cylinder head 12.

  In the heat insulating structure A, the intermediate layer 2 is a layer in which copper particles are cold sprayed on an aluminum alloy base material which is the base material 3 (cylinder block 11 or cylinder head 12 or the like). The conductivity λ2 is larger than the thermal conductivity λ3 (usually about 96 W / mK) of the aluminum alloy constituting the cylinder block 11 or the cylinder head 12 as the base material 3. Further, the intermediate layer 2 is a cold spray coating, and the cold spray coating is hardly oxidized as compared with the thermal spray coating, can maintain the characteristics of the material particles, and has a low porosity.

  The thermal barrier layer 1 is a layer formed by spraying oxide particles mainly containing at least one selected from the group consisting of zirconia and silica on the intermediate layer 2. The conductivity λ1 is usually about 2 W / mK or less, and is smaller than the thermal conductivity λ3 of the aluminum alloy constituting the cylinder block 11 or the cylinder head 12 as the base material 3. That is, in the heat insulating structure A according to the present invention, the thermal conductivity λ1 of the heat shielding layer 1 <the thermal conductivity λ3 of the base material 3 <the thermal conductivity λ2 of the intermediate layer 2 is satisfied. Moreover, the thickness of the said intermediate | middle layer 2 is 20-150 micrometers, and the thickness of the said heat insulation layer 1 is 10-250 micrometers.

Next, the analysis result by the simulation model performed by the present inventors will be described.
FIG. 3 shows a simulation model. An aluminum alloy AC4D having a thickness t = 8 mm was assumed for the base material 3. Aluminum alloy AC4D has a thermal conductivity λ3 of 96.2 W / mK and a volume specific heat of 2638 kJ / m ³ K. A zirconia sprayed film (ZrO ₂ −33 wt% SiO ₂ ) having a thickness t = 80 μm was assumed for the heat shield layer 1. The thermal conductivity λ1 of this zirconia sprayed film is 0.95 W / mK, and the volume specific heat is 1850 kJ / m ³ K.

The intermediate layer 2 is equivalent to the present invention, when copper particles are formed by cold spraying, and as equivalent to the prior art, a Ni-20Cr plasma sprayed coating (Patent Document 1: above-mentioned patent) It was set to two levels when assuming an undercoat layer in a heat insulating structure described in Kai 2013-185202. In all cases, the thickness t was assumed to be 50 μm. The thermal conductivity λ3 of the intermediate layer 2 (corresponding to the present invention) in which copper particles are formed by cold spray is 389 W / mK, the volume specific heat is 3440 kJ / m ³ K, and a plasma sprayed coating of Ni-20Cr The intermediate layer 2 (corresponding to the prior art) has a thermal conductivity λ3 of 12.6 W / mK and a volume specific heat of 3660 kJ / m ³ K.

In the simulation, it is assumed that the surface of the heat shield layer 1 is the heat input side and heat is radiated from the outer surface of the substrate 3. As shown in FIG. 4, the heat input conditions were assumed to be two levels: 800 rpm (FIG. 4 (a)) which is a low rotation region and 2400 rpm (FIG. 4 (b)) which is a high rotation region. In FIG. 4, the horizontal axis represents time (sec), and the vertical axis represents heat transfer coefficient (W / m ² K). In addition, the heat radiation condition was that heat was constantly radiated to 95 degree cooling water with a heat transfer coefficient of 5000 W / m ² K.

  For the calculation, calculation software ANSYS Professional was used, and transient (unsteady) heat transfer analysis by a finite element method was used. Then, a change in the surface temperature T1 of the heat shield layer 1 and a change in the surface temperature T2 of the intermediate layer 2 in a steady state were obtained. Further, the change width (swing width) ΔT of the heat shield layer 1 surface temperature was determined from the change in the surface temperature T1 of the heat shield layer 1. The results are shown in FIG. In FIG. 5, the horizontal axis is the crank angle (°), and the vertical axis is the temperature (° C.).

  As shown in FIG. 5, at 800 rpm, which is a low rotation range, the swing width ΔT is 219 ° C. for the prior art and 216 ° C. for the present invention, which is substantially equal, but in the high rotation range. At 2400 rpm, 243 ° C. is equivalent to the prior art and 290 ° C. is equivalent to the present invention, and the swing width ΔT corresponding to the present invention is larger than that corresponding to the prior art. This is because even in the high rotation range (2400 rpm), the maximum temperature is 460 to 470 ° C., but as shown in FIG. 4B, in the high rotation range, the combustion interval is shortened. In contrast to the present invention, the surface temperature of the heat shield layer 1 increases to 223 ° C. at the start of intake, whereas the surface temperature of the heat shield layer 1 becomes insufficient and increases to 279 ° C. at the start of intake. It can be seen that the difference is the difference in the swing width ΔT.

  In the present invention, the surface temperature of the heat shielding layer 1 is lowered in the high rotation range (2400 rpm) as compared with the conventional technique. The intermediate layer 2 has a thermal conductivity λ2 of zirconia and silica. It is larger than the thermal conductivity λ1 of the thermal barrier layer 1 formed by thermal spraying oxide particles mainly composed of at least one selected from the group, and larger than the thermal conductivity λ3 of the base material 3 made of an aluminum alloy. This is the result of forming a layer of copper particles.

  Next, the thickness of the intermediate layer 2 and the heat shielding layer 1 was verified. For the intermediate layer 2, the above-described simulation at 2400 rpm was performed by changing the thickness of the intermediate layer 2, and the relationship between the film thickness (μm) and the swing width ΔT (° C.) was obtained. The results are shown in FIG. In FIG. 6, the horizontal axis represents the film thickness (μm) of the intermediate layer 2, and the vertical axis represents the swing width ΔT (° C.). As shown in FIG. 6, when the film thickness is less than 20 μm, the significant difference between the equivalent to the prior art and the swing width ΔT is insufficient, and when the film thickness exceeds 150 μm, the increase in the swing width ΔT is not observed. From this, in the equivalent of the present invention, the film thickness of the intermediate layer 2 is in the range of 20 to 150 μm.

  For the heat shield layer 1, the effect of the film thickness of the heat shield layer 1 and the fuel efficiency improvement rate (BSFC) is calculated by refining the fuel efficiency by refining the temperature results obtained in the above simulation into an internal combustion engine model (GTPpower). Analyzed. FIG. 7 shows the analysis result. In FIG. 7, the horizontal axis represents the film thickness (μm) of the thermal barrier layer 1, and the vertical axis represents the BSFC improvement rate (%).

As described above, when the portion facing the combustion chamber in the internal combustion engine is shielded, the energy (cooling loss) escaped to the head side is reduced, and the force by which the gas pushes the piston is increased (that is, the net output is improved). ) Fuel economy is small (good). In the calculation, if the required conditions are put into the internal combustion engine model, the fuel efficiency at that time is calculated. Therefore, when the temperature of the head is only the base material made of an aluminum alloy (equivalent to the prior art), Two calculations were performed when the intermediate layer 2 and the heat shielding layer 1 were formed according to the present invention, and the “BSFC improvement rate (%)” was expressed as the difference. However, the thickness t of the intermediate layer 2 on which the copper particles are formed by cold spray is constant at 50 μm, and the thickness of the thermal barrier layer 1 which is a zirconia sprayed film (ZrO ₂ −33 wt% SiO ₂ ) is between 3 μm and 300 μm. It was changed with.

  As shown in FIG. 7, the improvement rate is improved as the film thickness of the heat shield layer 1 is increased. However, the improvement rate is maximum at around 50 to 60 μm, and the improvement rate is gradually decreased as the thickness is further increased. Since an improvement rate of 0.15% or more can be regarded as a significant improvement rate, the film thickness of the thermal barrier layer 1 is significant in the range of 10 to 250 μm from the graph of FIG. It can be considered a range.

  As described above, in the internal combustion engine equivalent to the present invention, by providing the heat insulating structure according to the present invention at the portion facing the combustion chamber, the swing width ΔT (° C.) is higher than that of the prior art in the high rotation range. ) Is increased (indicated by (A) in FIG. 5), thereby improving the cooling loss reduction effect, and also due to a decrease in the surface temperature of the thermal barrier film during intake (indicated by (B) in FIG. 5) It can be seen that intake air overheating hardly occurs and pump loss due to intake air heating is reduced. As a result, the fuel consumption improvement effect is increased without the cooling loss reduction effect being offset.

  Next, an example in which the heat insulating structure according to the present invention is actually formed in a portion facing the combustion chamber of the internal combustion engine will be described.

Masking was attached to the lower surface of the E / G head made of aluminum alloy AC4D for casting, and copper particles were formed at 50 μm by cold spray using Dymet 413 made by OCPS. The conditions of the cold spray are as follows: nozzle diameter 5 mmφ, projection distance 10 mm, gas temperature 500 ° C., gas pressure 4.7 bar, gas flow rate 300 l / min, gas type Air, N ₂ or He, copper particle powder (manufactured by Fukuda Metal Foil Industry) Cu-At-G-100, average particle size 52 μm, distribution 150 μm), and supply amount of copper particle powder 40 g · min.

After the above cold spraying, ceramics (ZrO ₂ −33 wt% SiO ₂ , average particle size 28 μm, distribution −10 + 45 μm) was formed to about 150 μm by plasma spraying using SinplexPro manufactured by Oerlikon Metco. The film formation conditions were an output of 40 kW, an Ar gas flow rate of 60 l / min, an H ₂ gas flow rate of 10 l / min, a spraying distance of 100 mm, and a powder supply amount of 60 g / min.

  After film formation, the masking was removed, the film was ground to a predetermined film thickness (80 μm), and then the powder that had entered the inside was washed. Thereby, the member provided with the heat insulation structure by this invention on the E / G head lower surface was obtained.

A ... heat insulating structure according to the present invention,
1 ... a thermal barrier layer formed by thermal spraying oxide particles mainly composed of at least one selected from the group consisting of zirconia and silica;
2 ... intermediate layer in which copper particles are cold sprayed,
3. A base material that is an aluminum alloy.

Claims (1)

A heat insulating structure comprising an intermediate layer and a heat shielding layer formed on the surface of a base material that is an aluminum alloy,
The intermediate layer is a layer in which copper particles are cold sprayed with respect to the aluminum alloy substrate as the substrate,
The thermal barrier layer is a layer formed by spraying oxide particles mainly containing at least one selected from the group consisting of zirconia and silica on the intermediate layer,
The thickness of the intermediate layer is 20 to 150 μm, the thickness of the heat shield layer is 10 to 250 μm,
The thermal conductivity of the thermal barrier layer is smaller than the thermal conductivity of the substrate, and the thermal conductivity of the intermediate layer is larger than the thermal conductivity of the substrate.
A heat insulating structure characterized by that.

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