JP2021095874A - Method of manufacturing internal combustion engine and internal combustion engine - Google Patents

Abstract

To easily form a heat insulating layer which is excellent in quality, specifically is free from peeling and the like, on a piston crown surface of an internal combustion chamber.SOLUTION: A method of manufacturing an internal combustion engine includes: an application step of applying a coating material as a material for a heat insulating layer to the crown surface of a piston; an assembly step of assembling the piston etc. while the coating material is unhardened; and a firing step of heating and hardening the coating material by combusting fuel injected from an injector thereby reciprocating the piston. The firing step includes a first firing step of combusting the fuel on the condition that an engine speed becomes a first speed N1, and a second firing step, following the first firing step, of combusting the fuel on the condition that the engine speed becomes a second speed N2 higher than the first speed N1.SELECTED DRAWING: Figure 5

Description

The present invention comprises a cylinder forming member that forms a cylinder inside, a piston that is reciprocally housed in the cylinder, an injector that supplies fuel to a combustion chamber defined by the cylinder and the piston, and an injector that faces the injector. The present invention relates to an internal combustion engine and a method for manufacturing the same, which covers the crown surface of the piston and has a heat insulating layer having a thermal conductivity lower than that of the piston.

It has been proposed to cover the wall surface of the combustion chamber with a heat insulating layer for the purpose of improving the thermal efficiency of the internal combustion engine. For example, Patent Document 1 below discloses an internal combustion engine in which a heat insulating layer having a lower thermal conductivity than that of the base material is formed on the surface of a base material that defines a combustion chamber.

Specifically, in Patent Document 1, as a method of forming the heat insulating layer, a coating material (a mixture of Si-based resin, hollow particles, a diluting solvent, etc.) which is a material of the heat insulating layer is applied to the surface of the base material. , It is proposed to assemble the engine in that state and perform a combustion test (ignition test). When an engine coated with a coating material is subjected to a combustion test, the surface of the coating material is oxidized (hardened) by the combustion heat, whereby the heat insulating layer is formed.

According to the method for forming the heat insulating layer in Patent Document 1, a part of the process for forming the heat insulating layer can be replaced by a combustion test usually performed after the engine is assembled, so that the man-hours required for forming the heat insulating layer can be reduced. There are advantages such as reduction.

Japanese Unexamined Patent Publication No. 2014-1718

However, according to the research by the inventors of the present application, when the heat insulating layer is formed by the method of heating the coating material with the combustion heat of the air-fuel mixture as in Patent Document 1, the quality of the heat insulating layer is not always stable and the heat insulating layer is heat-insulated. It was found that there were cases where peeling occurred in a part of the layer. As a result of investigating the cause, the inventors of the present application have found that a part of the fuel supplied from the injector adheres to the coating material as droplets during the combustion test, which is a probable cause. That is, when the fuel in the droplet state adheres to the coating material, the coating material is diluted or dissolved by the adhered fuel (hereinafter, simply referred to as dilution), and the viscosity of the coating material in this diluted portion (the portion to which the fuel adheres). As a result, it is considered that the coating material of the relevant portion receives the combustion pressure at the time of the combustion test and scatters, causing the above-mentioned peeling.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for manufacturing an internal combustion engine or the like, which can easily form a heat insulating layer of excellent quality without peeling or the like. To do.

To solve the above problems, the present invention comprises a cylinder forming member that forms a cylinder inside, a piston that is reciprocally housed in the cylinder, and a combustion chamber defined by the cylinder and the piston. A method for manufacturing an internal combustion engine having an injector for supplying fuel and a heat insulating layer that covers the crown surface of a piston facing the injector and has a heat conductivity lower than that of the piston, and is a material for the heat insulating layer. A coating step of applying the coating material to the crown surface of the piston, an assembly step of assembling the piston to the cylinder forming member in a state where the coating material is uncured, and a fuel injected from the injector to burn the piston. The firing step includes a firing step of heating and curing the coating material by reciprocating the engine, and the firing step includes a first firing step of burning fuel under the condition that the engine rotation speed becomes the first rotation speed. It is characterized by including a second firing step carried out after the first firing step and burning the fuel under the condition that the engine rotation speed becomes a second rotation speed higher than the first rotation speed (claimed). Item 1).

According to the present invention, the coating material applied to the crown surface of the piston is fired (cured) by utilizing the combustion heat during operation carried out after assembling the main parts including the piston and the cylinder forming member. For example, by combining the operation for firing (firing step) with the test operation (combustion test) normally performed in the manufacturing process of the internal combustion engine, the labor and cost required for firing the coating material, that is, forming the heat insulating layer can be reduced. can do.

Further, in the first firing step, which is the first stage of the firing step, the engine speed is suppressed to be lower than that in the second firing step in the latter stage, so that the fuel adheres as droplets to the coating material applied to the piston crown surface. The possibility of doing so can be reduced. That is, the low engine speed (in other words, the average moving speed of the piston is slow) means that the piston stays far away from the injector (especially near the bottom dead center) for a longer time than at high speed. Means to be. This allows the piston to inject the required amount of fuel within a period of time far from the injector and allows the fuel to be sufficiently vaporized before it reaches the piston crown. As a result, it becomes difficult for the fuel injected from the injector to reach (adhere) to the coating material on the piston crown surface as droplets, so that the adhered fuel (particularly toluene contained in the fuel) dilutes the uncured coating material. The possibility of fuel is reduced. Therefore, even if a large pressure (combustion pressure) due to combustion acts on the coating material, the shape change that occurs in the coating material can be minimized, and the quality of the heat insulating layer made of the coating material after curing is sufficiently ensured. be able to. For example, if the coating material is diluted by the adhesion of fuel, the viscosity of the coating material decreases in this diluted portion (the portion where the fuel adheres), and when a high combustion pressure acts, the coating material becomes There is a risk of scattering. On the other hand, in the present invention, the engine speed is limited to a low value so that the fuel does not easily adhere to the coating material, so that the possibility of scattering of the coating material caused by the above circumstances can be reduced. it can. As a result, the possibility of problems such as peeling of the heat insulating layer can be reduced, and the quality of the heat insulating layer can be ensured satisfactorily.

On the contrary, since the engine speed is increased in the second firing step in the subsequent stage, it is possible to promote the curing (firing) inside the coating material while ensuring the above-mentioned effect of suppressing defects such as peeling, and heat insulation. The man-hours required to form the layer can be reduced. That is, the curing of the coating material proceeds faster on the surface than on the inside. On the other hand, if the surface of the coating material is sufficiently cured (even if the inside is uncured), the coating material will not be diluted due to the adhesion of fuel, and a part of the coating material will be scattered due to the combustion pressure. Is considered to be avoided. In the present invention, the engine speed is increased according to the transition from the first firing step to the second firing step. Therefore, for example, by shifting to the second firing step at the timing when the surface of the coating material is sufficiently cured, the coating film is formed. While avoiding the above-mentioned situation where a part of the material is scattered, the frequency of heating the coating material (frequency of exposure of the coating material to high-temperature combustion gas) can be increased by increasing the engine speed, and it is uncured. The curing speed inside a certain coating material can be increased. As a result, the time required to cure the coating material as a whole can be shortened, and the formation of the heat insulating layer can be made more efficient while ensuring the quality of the heat insulating layer.

Preferably, in the first firing step, the injection amount of fuel from the injector is reduced as compared with that in the second firing step (claim 2).

The possibility that the fuel injected from the injector reaches the coating material on the crown surface of the piston as droplets decreases as the amount of fuel injected decreases. In this aspect, since the fuel injection amount is reduced in the first firing step of the previous stage, the possibility that the injected fuel reaches (adheres) to the coating material as droplets is further reduced due to the above circumstances. Can be done.

On the contrary, since the fuel injection amount is increased in the second firing step in the subsequent stage, the combustion heat (heating capacity) can be increased by increasing the injection amount. This, in combination with the increase in engine speed described above, leads to an increase in the curing speed inside the uncured coating material. As a result, the time required to cure the coating material as a whole can be further shortened, and the formation of the heat insulating layer can be made sufficiently efficient.

Preferably, in the first firing step, the injection period of the fuel from the injector is set to a period including the intake bottom dead center (claim 3).

The possibility that the fuel injected from the injector reaches the coating material as droplets decreases as the piston approaches bottom dead center (in other words, as the piston moves away from the injector). In this aspect, since the fuel is injected over a series of periods including the intake bottom dead center, the injected fuel reaches (adheres) the coating material on the piston crown surface as droplets due to the above circumstances. The possibility can be further reduced.

Preferably, the second firing step is started when the elapsed time from the start of the first firing step reaches a predetermined predetermined time (claim 4).

In this aspect, the transition from the first firing step to the second firing step can be determined by a simple method.

The present manufacturing method may further include a determination step of determining the degree of curing of the surface of the coating material to be fired by the first firing step. In this case, when it is determined in the determination step that the surface of the coating material has been cured, it is preferable to shift from the first firing step to the second firing step (claim 5).

Once the surface of the coating material has been cured, even if the fuel adheres, the coating material will not be diluted. Therefore, the need to suppress the adhesion of the fuel to the coating material by the first firing step is reduced. In this aspect, the timing at which the curing of the surface of the coating material is completed is determined, and the transition from the first firing step to the second firing step is performed at the determined timing, so that the coating material is avoided from scattering due to the combustion pressure. The mode of fuel injection can be appropriately switched while ensuring the above-mentioned effects. The timing at which the curing of the surface of the coating material is completed may be determined by a direct method such as detecting the content of the diluent in the exhaust gas, or a period obtained experimentally in advance has elapsed. It may be judged by an indirect method of confirming that.

The present invention also provides an internal combustion engine manufactured by the above-mentioned manufacturing method (claim 6).

As described above, according to the present invention, it is possible to easily form a heat insulating layer of excellent quality without peeling or the like on the wall surface of the combustion chamber of the internal combustion engine.

It is a system diagram which shows the schematic structure of the internal combustion engine manufactured by the manufacturing method which concerns on one Embodiment of this invention. It is sectional drawing of the main part of the said internal combustion engine. It is a flowchart which shows the specific procedure of the manufacturing method of the said internal combustion engine. It is explanatory drawing explaining the state of applying the coating material to the piston crown surface. It is a time chart which shows the time change of various parameters at the time of operation for firing the said coating material.

[Overall engine configuration]
FIG. 1 is a system diagram showing a schematic configuration of an internal combustion engine manufactured by the manufacturing method according to the embodiment of the present invention, and FIG. 2 is a cross-sectional view of a main part of the internal combustion engine. The internal combustion engine (hereinafter, simply referred to as an engine) shown in this figure is a four-cycle gasoline engine and includes a cylinder block 1, a cylinder head 3, and a piston 5. The cylinder block 1 and the cylinder head 3 are members for forming a cylindrical cylinder 2 inside, and correspond to the "cylinder forming member" in the claim. That is, the cylinder block 1 has a wall surface (cylinder liner) that defines the peripheral surface of the cylinder 2, and the cylinder head 3 is attached to the upper surface of the cylinder block 1 so as to close the cylinder 2 from above. .. The piston 5 is a cylindrical member having an inner peripheral surface (cylinder liner) of the cylinder block 1 and a slidable outer peripheral surface, and is housed inside the cylinder 2 so as to be reciprocating. The engine of this embodiment is an in-vehicle engine mounted as a power source in a vehicle such as an automobile, and is typically a multi-cylinder engine having a plurality of cylinders 2. However, for the sake of simplicity, the engine will be described by focusing on only one cylinder 2.

A crankshaft 7, which is an output shaft of the engine, is provided below the piston 5, and the crankshaft 7 and the piston 5 are connected via a connecting rod 9.

A combustion chamber C is defined above the piston 5. That is, the combustion chamber C has a wall surface defining the peripheral surface of the cylinder 2 (inner peripheral surface of the cylinder block 1), a wall surface defining the upper surface of the cylinder 2 (lower surface of the cylinder head 3), and a crown surface 5a of the piston 5. It is a space defined by (upper surface).

The cylinder head 3 is provided with an injector 11 and a spark plug 12. The injector 11 is an injection valve that injects fuel (fuel containing gasoline as a main component) into the combustion chamber C. The spark plug 12 is a plug that ignites the air-fuel mixture in the combustion chamber C, that is, the air-fuel mixture injected from the injector 11 mixed with air in the combustion chamber C.

When the air-fuel mixture is burned by the ignition of the spark plug 12, the piston 5 reciprocates in the vertical direction in response to the expansion force generated by the combustion. The reciprocating motion of the piston 5 is transmitted to the crankshaft 7 via the connecting rod 9 to rotate the crankshaft 7.

The injector 11 is arranged along the central axis Z of the cylinder 2 so that its tip is located at the center of the ceiling surface C1 of the combustion chamber C (see particularly FIG. 2). The injector 11 has a plurality of injection holes at its tip, and injects fuel radially from the injection holes toward the crown surface 5a of the piston 5. Reference numeral F in FIG. 2 represents spraying of fuel injected from the injector 11.

The spark plug 12 is attached adjacent to the injector 11 in an inclined posture with respect to the central axis Z of the cylinder 2 so that the tip portion thereof is located near the center of the ceiling surface C1 of the combustion chamber C. An electrode for discharging sparks is provided in the combustion chamber C at the tip of the spark plug 12.

As shown in FIG. 1, the cylinder head 3 is formed with an intake port 13 and an exhaust port 14 communicating with the combustion chamber C. The intake port 13 is a port for introducing intake air into the combustion chamber C, and the exhaust port 14 is a port for deriving exhaust gas from the combustion chamber C. The cylinder head 3 is assembled with an intake valve 15 that opens and closes the opening of the intake port 13 on the combustion chamber C side and an exhaust valve 16 that opens and closes the opening of the exhaust port 14 on the combustion chamber C side.

An intake passage 20 and an exhaust passage 21 are connected to the cylinder head 3. The intake passage 20 is a passage through which the intake air introduced into the combustion chamber C flows, and is connected to one side surface of the cylinder head 3 in a state of communicating with the intake port 13. The exhaust passage 21 is a passage through which the exhaust gas derived from the combustion chamber C flows, and is connected to the other side surface of the cylinder head 3 in a state of communicating with the exhaust port 14.

[Structure of piston crown surface]
As shown in FIG. 2, a heat insulating layer 30 is formed on the crown surface 5a of the piston 5 (hereinafter, also simply referred to as the piston crown surface 5a). The heat insulating layer 30 is made of a resin material having a lower thermal conductivity than the piston 5. That is, while the piston 5 is made of a metal material such as an aluminum alloy, the heat insulating layer 30 is made of a resin material having a significantly lower thermal conductivity than the metal material (base material) constituting the piston 5. ing.

Specifically, the heat insulating layer 30 in this embodiment is made of a heat-resistant silicone-based resin. Examples of the silicon-based resin include a silicon resin made of a three-dimensional polymer having a high degree of branching, such as a methyl silicone resin and a methyl phenyl silicone resin. The heat insulating layer 30 may contain hollow particles such as a shirasu balloon. As will be described in detail later, the heat insulating layer 30 is fixed to the piston crown surface 5a by firing a paste-like resin material (coating material 30A described later) applied to the piston crown surface 5a.

Forming the heat insulating layer 30 having the above-mentioned properties on the piston crown surface 5a leads to a reduction in cooling loss and an improvement in fuel efficiency of the engine. That is, since the heat insulating layer 30 suppresses the combustion energy of the air-fuel mixture burned in the combustion chamber C from being released to the outside through the piston crown surface 5a, the loss caused by the release of the thermal energy, that is, the cooling loss is reduced. .. As a result, it is expected that the thermal efficiency, which is the ratio of heat energy converted into work, will be improved, in other words, the fuel efficiency of the engine will be improved.

[Engine manufacturing method]
Next, a method of manufacturing the engine of the present embodiment having the above structure will be described. FIG. 3 is a flowchart showing a specific procedure of the engine manufacturing method of the present embodiment. The manufacturing method shown in this flowchart is mainly related to the formation of the heat insulating layer 30. Therefore, as a premise for implementing the method, it is assumed that the main parts (cylinder block 1, cylinder head 3, piston 5, etc.) constituting the engine have already been prepared.

When the method of FIG. 3 is started, first, the coating material 30A shown in FIG. 4 is applied to the piston crown surface 5a (step S1). The coating material 30A is the material of the heat insulating layer 30 described above, and is a paste-like resin material diluted with a diluent. In the present embodiment, as the coating material 30A, a paste-like silicon resin (methyl silicone resin, methyl phenyl silicone resin, etc.) diluted with toluene to reduce the viscosity is used. When forming a heat insulating layer 30 containing hollow particles (such as a shirasu balloon), the hollow particles are also contained in the coating material 30A. Further, as a curing catalyst for accelerating the curing of the coating material 30A, a trace amount of catalyst such as a platinum ion solution may be contained in the coating material 30A.

As shown in FIG. 4, a spray gun G is used for applying the coating material 30A to the piston crown surface 5a. That is, by spraying the coating material 30A from the spray gun G in the form of a spray, the coating material 30A is evenly sprayed onto the piston crown surface 5a. As a result, a layer of the coating material 30A having a substantially constant thickness is formed on the piston crown surface 5a. When applying the coating material 30A, it is desirable that the piston crown surface 5a is previously subjected to a treatment such as degreasing or sandblasting.

Next, the coating material 30A applied to the piston crown surface 5a is naturally dried (step S2). The drying here is a process for avoiding a situation in which the coating material 30A easily adheres to members other than the piston 5 (cylinder block 1, cylinder head 3, etc.) when assembling the engine, which will be described later, and at least the coating is applied. The viscosity of the surface of the material 30A may be increased to some extent. Therefore, the drying treatment in step S2 may be, for example, a treatment in which the piston 5 after coating the coating material 30A is left at room temperature for a predetermined time.

Next, an assembly is constructed in which the main parts including the cylinder block 1, the cylinder head 3, and the piston 5 are combined with each other (step S3). This assembly is a combination of main parts so that the air-fuel mixture can be burned in the combustion chamber C (hereinafter, this is referred to as a pre-completion engine), and the cylinder block 1, cylinder head 3, and piston described above are used. In addition to 5, parts such as an injector 11, a spark plug 12, an intake valve 15, and an exhaust valve 16 are combined. It should be noted that the diluent contained in the coating material 30A is not completely volatilized only by the natural drying in the previous step S2. Therefore, the coating material 30A is in an uncured state when the pre-completion engine is assembled in step S3.

Next, the operation of actually operating the pre-completion engine is performed (step S4). That is, by injecting fuel from the injector 11 into the combustion chamber C to form an air-fuel mixture and igniting the air-fuel mixture using the spark plug 12, the air-fuel mixture is burned and the piston 5 is reciprocated. Then, the reciprocating movement of the piston 5 (operation of the engine before completion) due to such combustion is continued for a predetermined first period (period T1 in FIG. 5 described later). However, the operation of the pre-completion engine here is performed in a special mode for suppressing fuel from adhering to the coating material 30A covering the piston crown surface 5a. Hereinafter, the mode in which the engine is operated before completion in step S4 is referred to as an adhesion suppression mode. Further, the mode in which the engine is operated before completion in step S6 described later is called a full-scale mode. The operation in the adhesion suppression mode and the full-scale mode also serves as a test operation (combustion test) for confirming that the engine operates without any trouble.

FIG. 5 is a time chart showing details of operation in step S4 (adhesion suppression mode) and step S6 (full-scale mode) described later. Specifically, in FIG. 5, the chart (a) shows the degree of curing of the coating material 30A, the chart (b) shows the engine speed, the chart (c) shows the fuel injection amount, and the chart (d) shows the fuel injection timing. Are shown respectively. Further, the origin of the horizontal axis in each chart is the start time of the operation in the adhesion suppression mode in step S4, and the period T1 thereafter indicates the operation period (that is, the first period) in the adhesion suppression mode. Further, the period T2 following the first period T1 indicates an operation period (second period) in the full-scale mode.

As shown in the waveform of the chart (b) during the first period T1, in the adhesion suppression mode (step S4), the engine speed is set to a predetermined first speed N1. The first rotation speed N1 is, for example, about 1000 rpm, and is set to about half of the rotation speed (second rotation speed N2) set in the later full-scale mode (step S6).

Further, as shown in the charts (c) and (d), in the adhesion suppression mode, the injection amount of the fuel injected from the injector 11 is smaller than in the later full-scale mode, and the fuel injected from the injector 11 is reduced. The injection timing is set near the intake bottom dead center (intake BDC). Specifically, in the adhesion suppression mode, the fuel injection amount is set to about half that in the full-scale mode. Further, the fuel injection timing is set to a timing (period) in which the fuel is injected over a series of periods including the intake bottom dead center. That is, the fuel injection by the injector 11 starts near the advance side of the intake bottom dead center and ends near the retard side of the intake bottom dead center. In other words, the timing of fuel injection by the injector 11 is set so that the injection start time (SOI) is the end of the intake stroke and the injection end time (EOI) is the beginning of the compression stroke. As is well known, the intake stroke is the period from the exhaust top dead center (exhaust TDC) to the intake bottom dead center (intake BDC), and the compression stroke is from the intake bottom dead center (intake BDC). It is the period until the compression top dead center (compression TDC). In this way, injecting a relatively small amount of fuel near the intake bottom dead center where the piston 5 is farthest from the injector 11 causes the fuel to reach (adhere) as droplets to the coating material 30A of the piston crown surface 5a. This will greatly reduce the possibility.

After the operation in the adhesion suppression mode is started as described above, the operation in the adhesion suppression mode is continued until the elapsed time from the start of the operation reaches the above-mentioned first period T1 (step S5). That is, the elapsed time from the start of operation is counted using a timer, it is determined whether or not the count value has reached the first period T1, and the operation in the adhesion suppression mode is continued until the first period T1 is reached. ..

As shown in the chart (a) of FIG. 5, the first period T1, which is the operation period in the adhesion suppression mode, is set to a period in which the curing of the surface of the coating material 30A is almost completed. That is, the coating material 30A is heated by the combustion heat of the air-fuel mixture and gradually hardened, but the surface of the coating material 30A directly exposed to the combustion gas is larger than the inside of the coating material 30A not directly exposed to the combustion gas. Due to the high temperature, the curing rate is faster on the surface of the coating material 30A. During the first period T1 of the chart (a), the slope of the waveform of the broken line indicating the degree of curing of the surface of the coating material 30A is larger than the slope of the waveform of the alternate long and short dash line indicating the degree of curing inside the coating material 30A. This is why it is so big. That is, when the degree of curing of the target coating material 30A is P, the degree of curing reaches the target value P (that is, the curing is completed) on the surface of the coating material 30A than on the inside of the coating material 30A. Will be faster. On the premise of this, the first period T1, which is the operation period in the adhesion suppression mode, is a period in which the surface of the coating material 30A is almost completely cured (the degree of curing almost reaches the target value P) at the end of the operation period. Is set to. Therefore, when the first period T1 elapses (that is, when the operation in the adhesion suppression mode is completed), the curing of the surface of the coating material 30A is almost completed, but the curing of the inside of the coating material 30A is insufficient. There is up to. The first period T1 for obtaining such a state of the coating material 30A can be experimentally obtained in advance.

When the progress of the first period T1 is confirmed in step S5, the operation mode is switched from the adhesion suppression mode to the full-scale mode (step S6), and the operation in this full-scale mode is continued to the first period T1. It continues over the second period T2 (step S7). The full-scale mode is a mode in which the pre-completion engine is operated under the condition that the engine speed is higher than that in the adhesion suppression mode. The engine speed set in this full-scale mode, that is, the second speed N2 is, for example, about 2000 rpm, and the speed set in the previous adhesion suppression mode (step S4) (first speed N1). Is doubled against.

Further, in the full-scale mode, the fuel injection amount is increased and the injection timing is advanced as compared with the previous adhesion suppression mode. Specifically, during operation in the full-scale mode, as shown in FIG. 5, the fuel injection amount is set to about twice that in the adhesion suppression mode. Further, the fuel injection timing is set to a timing (period) in which the fuel is injected over a series of periods included in the intake stroke. In other words, in the fuel injection by the injector 11, both the injection start time (SOI) and the injection end time (EOI) are on the retard side of the exhaust top dead center (exhaust TDC) and on the advance side of the intake bottom dead center. Is controlled to be. The period from the start of injection to the end of injection is made longer than in the adhesion suppression mode in response to the increase in the injection amount described above.

As described above, injecting a relatively large amount of fuel during the intake stroke increases the amount of heat generated by combustion and promotes curing (firing) of the coating material 30A of the piston crown surface 5a. That is, in the full-scale mode in which the amount of heat generated is large, the temperature inside the coating material 30A is higher than in the previous adhesion suppressing mode, so that the curing rate inside the coating material 30A is accelerated. In the chart (a) of FIG. 5, the curing rate inside the coating material 30A in the second period T2 (full-scale mode) is faster than the curing rate in the first period T1 (adhesion suppression mode). Is for this reason. Since the surface of the coating material 30A has already been cured at the end of the adhesion suppression mode (at the start of the full-scale mode), the degree of curing does not change even when the full-scale mode is entered.

As shown in the chart (a), the second period T2, which is the operation period in the full-scale mode, is set to a period in which the curing inside the coating material 30A is almost completed. That is, by continuing the operation in the full-scale mode over the second period T2, the degree of hardening inside the coating material 30A rises to substantially the target value P. As a result, not only the surface of the coating material 30A but also the inside is sufficiently cured, and the firing of the coating material 30A (formation of the heat insulating layer 30) is completed. In other words, almost all of the diluent (toluene) volatilizes from the coating material 30A, so that the coating material 30A is solidified as a whole, and the solidified coating material 30A serves as the heat insulating layer 30 (FIG. 2) and the piston crown surface 5a. Is formed in. The second period T2 for completing the curing of the inside of the coating material 30A in this way can be experimentally obtained in advance.

When the formation of the heat insulating layer 30 is completed as described above, the fuel injection from the injector 11 is stopped, and the operation of the engine by the combustion of the air-fuel mixture is terminated (step S8). After that, parts (accessory parts, etc.) that were not included in the pre-completion engine assembled in step S3 are assembled, and the production of the engine is completed.

In the engine manufacturing method as described above, step S1 corresponds to the "coating step" in the claim, step S3 corresponds to the "assembly step" in the claim, and step S4 corresponds to the "assembly step" in the claim. Corresponding to the "first firing step", step S5 corresponds to the "determination step" in the claim, and step S6 corresponds to the "second firing step" in the claim.

[Action effect]
As described above, in the present embodiment, the step (S1) of applying the paste-like coating material 30A to the piston crown surface 5a and the main parts including the piston 5 after application are assembled to each other to construct the pre-completion engine. The heat insulating layer 30 is formed on the piston crown surface 5a by a method including a step (S3) and a step (S4, S6) of operating the pre-completion engine in two modes in which the engine speed is different. According to such a configuration, there is an advantage that the formation of the heat insulating layer 30 can be facilitated while ensuring good quality.

That is, in the above embodiment, the coating material 30A applied to the crown surface 5a of the piston is fired (cured) by utilizing the combustion heat during operation carried out after assembling the main parts including the piston 5. For example, by combining the operation for firing with the test operation (combustion test) normally performed in the manufacturing process of the engine, it is possible to reduce the labor and cost required for firing the coating material 30A, that is, forming the heat insulating layer 30. .. For example, when the coating material 30A applied to the piston crown surface 5a is fired by heating using a heating furnace or the like, the man-hours for the firing and the man-hours for the test operation are separately required and the heating is performed. It is necessary to newly install equipment such as a furnace. On the other hand, when the coating material 30A is fired by the combustion heat of the air-fuel mixture as in the above embodiment, it is not necessary to newly provide equipment for the firing, and the heat insulating layer 30 is provided. Since a part of the process for forming can be substituted by the test operation of the engine, it becomes possible to manufacture an engine having a heat insulating layer 30 and having excellent thermal efficiency at low cost and in a short time.

Further, as the operation for firing the coating material 30A, the operation in the adhesion suppression mode (S4) and the operation in the full-scale mode (S6) are carried out in this order, and the engine speed during the operation in the adhesion suppression mode in the previous stage. Is set to a relatively low first rotation speed N1, so that the possibility that the fuel adheres as droplets to the coating material 30A applied to the piston crown surface 5a can be reduced.

That is, the low engine speed (in other words, the average moving speed of the piston 5 is slow) means that the piston 5 is far away from the injector 11 (particularly near the bottom dead center) when the engine speed is high. Means to be longer than. This allows the piston 5 to inject the required amount of fuel within a period of time far from the injector 11 and allows the fuel to be sufficiently vaporized before it reaches the piston crown 5a. To do. As a result, it becomes difficult for the fuel injected from the injector 11 to reach (adhere) to the coating material 30A of the piston crown surface 5a as droplets, so that the coating material uncured by the adhered fuel (particularly toluene contained in the fuel). The possibility that 30A will be diluted is reduced. Therefore, even if a large pressure (combustion pressure) due to combustion of the air-fuel mixture acts on the coating material 30A, the shape change that occurs in the coating material 30A can be minimized, and the heat insulating layer 30 made of the coating material 30A after curing can be minimized. The quality of the product can be ensured well. For example, if the coating material 30A is diluted by the adhesion of fuel, the viscosity of the coating material 30A decreases in the diluted portion (the portion to which the fuel adheres), and when a high combustion pressure acts, the coating material 30A is coated. Material 30A may scatter. On the other hand, in the above embodiment, the possibility of fuel adhesion is reduced by the adhesion suppression mode in which the engine speed is limited to be low, so that the scattering of the coating material 30A caused by the above circumstances is effectively suppressed. be able to. As a result, the possibility of problems such as peeling of the heat insulating layer 30 can be reduced, and the quality of the heat insulating layer 30 can be ensured satisfactorily.

On the contrary, in the full-scale mode following the adhesion suppression mode, the engine speed is increased (set to the second rotation speed N2 higher than the first rotation speed N1), so that the above-mentioned effect of suppressing defects such as peeling is guaranteed. At the same time, the curing (firing) inside the coating material 30A can be promoted, and the man-hours required for forming the heat insulating layer 30 can be reduced. That is, the curing of the coating material 30A proceeds faster on the surface than on the inside. On the other hand, if the surface of the coating material 30A is sufficiently cured (even if the inside is uncured), the coating material 30A will not be diluted due to the adhesion of fuel, and a part of the coating material 30A will be scattered by the combustion pressure. Such a situation is considered to be avoided. In the above embodiment, the engine speed is increased according to the transition from the adhesion suppression mode to the full-scale mode. Therefore, by shifting to the full-scale mode at the timing when the surface of the coating material 30A is sufficiently cured, one of the coating materials 30A The frequency of heating the coating material 30A (frequency of exposure of the coating material 30A to high-temperature combustion gas) can be increased by increasing the engine speed while avoiding the above-mentioned situation in which the parts are scattered, and the coating material 30A is uncured. The curing speed inside the coating material 30A can be increased. As a result, the time required to cure the coating material 30A as a whole can be shortened, and the formation of the heat insulating layer 30 can be made more efficient while ensuring the quality.

In particular, in the above embodiment, since a smaller amount of fuel is injected near the intake bottom dead center during operation in the adhesion suppression mode than in the later full-scale mode, the injected fuel remains as droplets on the piston crown surface 5a. The possibility of reaching (adhering) to the coating material 30A of the above can be significantly reduced. That is, the possibility that the injected fuel from the injector 11 reaches the coating material 30A as droplets decreases as the distance from the injector 11 to the piston 5 increases, and decreases as the fuel injection amount decreases. This is because the fuel vaporizes sufficiently before the fuel reaches the piston crown surface 5a. In the above embodiment, in the above adhesion suppression mode, the injection amount is reduced as compared with the later full-scale mode, and in a series of periods including the intake bottom dead center where the distance from the injector 11 to the piston 5 is the largest. Since the fuel is injected over the entire range, the injected fuel may reach (adhere) to the coating material 30A of the piston crown surface 5a as droplets in combination with the effect of limiting the engine speed described above. It can be significantly reduced. As a result, it is possible to prevent a part of the coating material 30A from being scattered during firing, and it is possible to ensure good quality of the heat insulating layer 30.

On the contrary, in the full-scale mode following the adhesion suppression mode, the fuel injection amount is increased, so that the combustion heat (heating capacity) can be increased by increasing the injection amount. This, in combination with the increase in the engine speed described above, leads to an increase in the curing speed inside the uncured coating material 30A. As a result, the time required to cure the coating material 30A as a whole can be further shortened, and the formation of the heat insulating layer 30 can be made sufficiently efficient.

Furthermore, in the full-scale mode in which the amount of fuel is increased, the fuel injection timing is advanced compared to in the adhesion suppression mode (both the injection start timing and the injection end timing are set during the intake stroke). The increased amount of fuel can be sufficiently mixed with air to form a uniform air-fuel mixture in the combustion chamber C, and sufficient combustion stability can be ensured while generating high combustion heat for promoting curing. ..

[Modification example]
In the above embodiment, the operation in the adhesion suppression mode is continued for the predetermined first period T1, and then the operation is shifted to the full-scale mode, but the method for determining the mode switching timing is limited to this. I can't. For example, if the content of toluene (diluent) contained in the exhaust gas discharged during the operation for firing the coating material 30A (test operation) is detected by a sensor, which is the curing (firing) of the coating material 30A? It is considered that it can be determined whether or not the progress has been made. Therefore, the content of toluene in the exhaust gas is monitored using the above sensor, and when the content drops to a predetermined threshold value (a value at which the surface of the coating material 30A can be considered to be sufficiently hardened), the operation mode is used. May be shifted from the adhesion suppression mode to the full-scale mode. This makes it possible to accurately determine the timing suitable for the transition to the full-scale mode, that is, the timing when the surface of the coating material 30A is sufficiently cured. However, the period required to sufficiently cure the surface of the coating material 30A can be experimentally determined with a certain degree of accuracy. In the above embodiment, utilizing this fact, the adhesion suppression mode and the full-scale mode are simply separated by time. This makes it possible to appropriately perform the firing operation of the coating material 30A using the heat of combustion without providing special additional equipment (sensor or the like).

In the above embodiment, the engine speed (first speed N1) in the adhesion suppression mode is set to about 1000 rpm, while the engine speed (second speed N2) in the full-scale mode is set to about 2000 rpm. However, specific examples of the first rotation speed N1 and the second rotation speed N2 are not limited to this. The first rotation speed N1 can be appropriately changed within a range in which the purpose of reducing the possibility of fuel adhesion to the coating material 30A of the piston crown surface 5a can be achieved, and the second rotation speed N2 is from the first rotation speed N1. Can be changed as appropriate within a high range. For example, the second rotation speed N2 may be set to a value higher than 2000 rpm for the purpose of further promoting the curing inside the coating material 30A. However, when the engine speed increases to some extent, the temperature fluctuation range of the combustion chamber C during one combustion cycle tends to decrease, and the peak temperature of the combustion chamber C (maximum temperature during one combustion cycle) tends to decrease. Therefore, even if the engine speed is increased unnecessarily, it may not necessarily lead to the acceleration of curing of the coating material 30A. In addition, operating the pre-completion engine at an extremely high speed may adversely affect any of the engine parts. Therefore, in the above embodiment, by keeping the second rotation speed N2 at about twice the first rotation speed N1, damage to engine parts and the like is surely prevented and a sufficient curing promoting effect is obtained.

In the above embodiment, the fuel is injected over a series of periods including the intake bottom dead center in the adhesion suppression mode, but the fuel injection timing is such that the fuel adhesion to the coating material 30A can be suppressed. It suffices if the time is set, that is, the time when the piston is separated from the top dead center to some extent, and it can be changed as appropriate as long as the desired purpose can be achieved. For example, considering that the piston 5 starts to rise after the intake bottom dead center, the fuel may be injected at a timing such that the fuel injection ends immediately before the intake bottom dead center.

In the above embodiment, in order to advance the fuel injection timing in the full-scale mode as compared with that in the adhesion suppression mode, both the fuel injection start timing (SOI) and the injection end timing (EOI) are in the intake stroke. The angle was advanced to the time included in, but the mode of advance is not limited to this. For example, in the full-scale mode, the injection amount increases, so that the injection period from SOI to EOI becomes long. Therefore, the SOI may be advanced while fixing the EOI.

In the above embodiment, in the adhesion suppression mode, both the fuel injection amount and the injection timing are adjusted in a direction in which fuel adhesion is less likely to occur (that is, the injection amount is reduced and the injection timing is closer to the bottom dead center). However, only one of the injection amount and the injection timing may be adjusted in a direction in which fuel adhesion is less likely to occur. Further, it is possible to adjust the fuel injection pressure in addition to or in place of the injection amount and injection timing. For example, it is considered that if the injection pressure is lowered, the penetration (penetration force) of the fuel is weakened, and the possibility that the fuel reaches the coating material 30A is reduced. Therefore, the fuel injection pressure may be lowered in the adhesion suppression mode as compared with the full-scale mode.

In the above embodiment, the heat insulating layer 30 is formed only on the piston crown surface 5a that defines the bottom surface of the combustion chamber C, but the same heat insulating layer can be applied to the wall surface of the combustion chamber C other than the piston crown surface 5a. It is possible. For example, in addition to the piston crown surface 5a, a heat insulating layer is also provided on the ceiling surface C1 (lower surface of the cylinder head 3) of the combustion chamber C, the lower surface of the umbrella portion of the intake / exhaust valve, and the peripheral surface (cylinder liner) of the cylinder 2. Is possible to form. Similar to the heat insulating layer 30 of the above embodiment, the heat insulating layer formed on any surface can be formed by a method of firing a paste-like coating material which is a material of the heat insulating layer by the combustion heat of the air-fuel mixture. it can.

In the above embodiment, the tip end portion of the injector 11 is arranged in the center of the ceiling surface C1 of the combustion chamber C (hereinafter, simply referred to as the combustion chamber ceiling surface C1), and fuel is supplied downward from the tip end portion toward the piston crown surface 5a. Although the injection is performed, the injector may be any as long as it injects fuel into the combustion chamber C from a position facing the piston crown surface 5a, and the injector can be arranged at various positions as long as the injector is used. For example, the tip of the injector may be arranged at the edge of the combustion chamber ceiling surface C1 on the intake side, and fuel may be injected diagonally downward from the tip.

Although the description is omitted in the above embodiment, the vaporization property (easiness of vaporization) of the fuel varies depending on the temperature condition of the combustion chamber C. For example, the higher the temperature of the combustion chamber C immediately before injecting the fuel, the easier it is for the fuel to vaporize. Further, the fact that the fuel is easily vaporized reduces the possibility that the fuel adheres to the coating material 30A. Therefore, for example, when the intake air temperature (or outside air temperature) is high, or when the engine water temperature is high, the engine speed set during operation in the adhesion suppression mode is increased, or fuel injection is performed, as compared with when the engine water temperature is not high. You may increase the amount.

In the above embodiment, an example in which the present invention is applied to a gasoline engine that injects gasoline fuel from the injector 11 into the combustion chamber C has been described, but the engine to which the present invention can be applied is not limited to this, and for example, the present invention is also applied to a diesel engine. The invention is applicable.

In the case of a diesel engine, that is, an engine that burns light oil fuel by compression ignition, in the adhesion suppression mode, for example, the engine speed is set low and at least a part of the fuel is injected relatively early in the compression stroke. If the fuel is burned in the premix mode, the possibility of the fuel adhering to the coating material on the crown surface of the piston can be reduced.

1: Cylinder block (cylinder forming member)
2: Cylinder 3: Cylinder head (cylinder forming member)
5: Piston 5a: Crown surface (of piston) 11: Injector 30: Insulation layer 30A: Coating material C: Combustion chamber N1: First rotation speed N2: Second rotation speed

Claims (6)

A cylinder forming member that forms a cylinder inside, a piston that is reciprocally housed in the cylinder, an injector that supplies fuel to a combustion chamber defined by the cylinder and the piston, and a crown of a piston that faces the injector. A method of manufacturing an internal combustion engine that covers a surface and has a heat insulating layer having a thermal conductivity lower than that of the piston.
A coating step of applying a coating material, which is a material of the heat insulating layer, to the crown surface of the piston, and
Assembling step of assembling the piston to the cylinder forming member in a state where the coating material is uncured,
It includes a firing step of heating and curing the coating material by burning the fuel injected from the injector and reciprocating the piston.
The firing step is a first firing step in which fuel is burned under the condition that the engine speed becomes the first speed, and a second firing step that is performed after the first firing step and the engine speed is higher than the first speed. A method for manufacturing an internal combustion engine, which comprises a second firing step of burning fuel under a condition of two rotation speeds. In the method for manufacturing an internal combustion engine according to claim 1.
A method for manufacturing an internal combustion engine, characterized in that, in the first firing step, the amount of fuel injected from the injector is reduced as compared with that in the second firing step. In the method for manufacturing an internal combustion engine according to claim 1 or 2.
The method for manufacturing an internal combustion engine, characterized in that, in the first firing step, the injection period of fuel from the injector is set to a period including the intake bottom dead center. In the method for manufacturing an internal combustion engine according to any one of claims 1 to 3.
A method for manufacturing an internal combustion engine, wherein the second firing step is started when the elapsed time from the start of the first firing step reaches a predetermined predetermined time. In the method for manufacturing an internal combustion engine according to any one of claims 1 to 3.
Further including a determination step for determining the degree of curing of the surface of the coating material to be fired by the first firing step.
A method for manufacturing an internal combustion engine, which comprises shifting from the first firing step to the second firing step when it is determined in the determination step that the surface of the coating material has been cured. An internal combustion engine manufactured by the manufacturing method according to any one of claims 1 to 5.

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