JP2000008858A - Direct injection engine and its piston - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress discharging of emission of HC or the like, in a direct injection engine performing fuel injection executing pilot injection prior to main injection. SOLUTION: Six ceramic films 33 are formed in a peripheral direction at almost equal intervals in a position hit by fuel injected from six nozzles of an injector 8, in a lip part of a top land 3b in a piston 3 of a direct injection diesel engine. The ceramic film 33 has vaporization promoting action, pilot injection is executed to be directed to the ceramic film 33. The injection timing thereof is set to the timing moving vaporized fuel in the vicinity of the nozzle of the injector self ignited in this spot by a squish flow strengthened when the piston 3 approaches the top dead center. Vaporized fuel (including also liquid drop) existing in the vicinity of a surface of the top land 3b flows into a cavity 3a by a squish flow, to generate concentric combustion in the cavity 3a. Consequently, a high temperature is generated in an injection region of main injection.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct injection engine in which fuel injection, such as pilot injection, which injects a small amount of fuel prior to main injection, is directed toward a top land of a piston, and a piston thereof. It is.

[0002]

2. Description of the Related Art In recent years, research on pilot injection in which a small amount of fuel is injected before a main injection in a diesel engine has been actively conducted. The pilot injection injects a small amount of fuel prior to the main injection, suspends the fuel injection once, and performs full-scale fuel injection (main injection) when the fuel is ignited. The decrease in fuel injection amount during the ignition delay period reduces premixed combustion, which is effective in reducing NOx and noise.

At the same time, combustion by pilot injection
The ambient temperature of the combustion chamber increases. Thereby, the vaporization of the fuel injected by the main injection is promoted, and the emission of HC and the like is suppressed.

[0004]

However, the pilot injection timing is generally before the top dead center and the ambient temperature is not high. For this reason, as shown in FIG. 12A, the fuel injected by the pilot injection injected from the injector 51 hardly vaporizes, reaches the wall surface of the combustion chamber 25, for example, the wall surface of the piston 53, and easily attaches. there were. Therefore, as shown in FIG. 12 (b), there is a problem that the fuel adhered to the wall surface of the piston 53 during combustion becomes incomplete combustion and causes emission.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a direct injection engine and a piston thereof which can suppress emission of HC and the like.

[0006]

According to the first aspect of the present invention, a direct injection engine has a cavity on an upper surface, and a fuel injected from at least an injector in a top land is applied to the top land. A piston having a vaporization promoting film formed at a position thereof, and fuel injected from the injector toward the vaporization promoting film is subjected to the squish flow generated when the piston approaches the top dead center before the top is burned. There is provided a fuel injection control device for executing fuel injection from the injector directed to the vaporization promoting film at a timing at which the fuel can be pushed out from the land to the cavity side.

According to a second aspect of the present invention, in the first aspect of the invention, the fuel injection executed in a direction directed to the vaporization promoting film is a pilot injection for injecting a small amount of fuel prior to the main injection. The gist of the invention is that the fuel injection control device executes the main injection of the fuel at a timing at which the injection direction of the injector can be directed in the cavity after at least the fuel of the pilot injection starts burning. .

According to a third aspect of the present invention, in the first or second aspect of the invention, the vaporization promoting film is formed on a lip portion of a top land of the piston. According to the invention described in claim 4, according to claim 2 or claim 3,
In the invention described in the above, the direct injection engine is a diesel engine, and the pilot injection is performed at a timing when the injected fuel can flow into the cavity by squish flow from the vicinity of the top land and then self-ignite. The gist is that it is done.

In the invention described in claim 5, in the invention described in any one of claims 2 to 4, the injector is configured such that the main injection, which is executed substantially at a top dead center, forms a side wall of the cavity. It is set to an injection directional angle that can be directed,
The gist of the invention is that the pilot injection is executed at a timing at which fuel injected from the injector at a pre-injection directivity angle can be directed to the vaporization promoting film on the top land of the piston.

According to a sixth aspect of the present invention, in the first aspect of the invention, the gist is that the vaporization promoting film is a ceramic film.
In the invention according to claim 7, in the invention according to claim 6, the injector has a plurality of injection holes, and the same number of the ceramic films as the injection holes are provided on the top land. It is scattered at substantially equal intervals in the circumferential direction at the position where the fuel injected from the injection hole hits.

According to the invention described in claim 8, in the invention described in claim 6 or claim 7, the ceramic film is
Zirconia or a thermal spray coating containing zirconia as a main component.

According to a ninth aspect of the present invention, in the invention according to any one of the sixth to eighth aspects, the ceramic film is formed in a region of the top land of the piston less than the injection angle of the injector. Is formed.

According to a tenth aspect of the present invention, the piston has the structure according to any one of the first to ninth aspects. (Operation) Therefore, according to the first aspect of the invention, when the fuel injection control device reaches the injection timing, the fuel is injected from the injector. Fuel is injected toward the vaporization enhancing film on the top land of the piston. Even if a part of the fuel adheres to the vaporization promoting film, the fuel is quickly vaporized by the vaporization promoting action. The injected fuel is carried to the cavity side by the squish flow generated when the piston approaches the top dead center, and burns intensively in the cavity.

According to the second aspect of the present invention, the pilot injection is executed from the injector toward the vaporization promoting film on the top land of the piston. Even if fuel adheres to the vaporization promoting film, it is vaporized quickly. When the piston approaches the top dead center and the squish flow becomes stronger on the topland surface,
Fuel near the surface of the topland (vaporized fuel or spray droplets)
Is extruded from the top land to the cavity side. When the fuel self-ignites or ignites, the fuel burns intensively in the cavity. Therefore, the inside of the cavity which is the injection region of the main injection is locally heated. afterwards,
The main injection of the fuel is executed by the fuel injection control device toward the high temperature region in the cavity, and the vaporization and combustion of the fuel of the main injection progresses at a stretch.

According to the third aspect of the invention, a strong squish flow is generated at the lip portion of the top land. The fuel injected from the injector toward the vaporization promoting film is sent from the top land into the cavity at once by a strong squish flow at the lip portion. Further, the vaporization of the fuel is promoted by the strong squish flow.

According to the fourth aspect of the invention, the pilot injected fuel flows into the cavity from the vicinity of the top land by the squish flow and then self-ignites. For this reason, the temperature of the injection region of the main injection becomes high. For example, if the engine is designed to ensure low temperature startability, it is necessary to delay the timing of pilot injection to the top dead center side in order to self-ignite the fuel after the fuel is pushed out to the cavity side by the squish flow. In this case, the distance between the injector and the piston at the time of the pilot injection is shortened, so that the fuel easily adheres to the top land.However, the vaporization of the adhered fuel is promoted by the vaporization promoting film. There is not much worry about sticking.

According to the fifth aspect of the present invention, the fuel is vaporized on the top land from the injector whose injection angle is set such that the main injection executed substantially at the top dead center is directed to the side wall of the cavity. The execution timing of the pilot injection is set to the timing at which the injection can be directed toward the film. The fuel injected by the pilot flows into the cavity from the top land by the squish flow and self-ignites.

According to the sixth aspect of the present invention, since the vaporization promoting film is a ceramic film, even if heat is taken away when the fuel is vaporized, it is difficult to cool as compared with a metal, so that a high fuel vaporization promoting effect is obtained. Is obtained.

According to the present invention, the fuel injected from the plurality of injection holes of the injector impinges on the respective vaporization promoting films scattered on the top land in the same number as the injection holes. Even if the vaporization accelerating film is a ceramic film, it is scattered in a necessary portion, so that the area thereof is almost required to be a minimum, and the reduction of the intake air amount due to the thermal expansion due to the heat insulating effect of the ceramic is suppressed as much as possible.

According to the eighth aspect of the present invention, since the ceramic film contains zirconia or zirconia as a main component, the temperature at which film boiling (Leidenfrost phenomenon) occurs can be shifted to a higher temperature due to the characteristics of the material. In addition, a high fuel vaporization promoting effect can be obtained, for example, by suppressing the phenomenon of fuel floating from the ceramic surface due to film boiling. Further, since the thermal spray coating is used, the surface roughness is large, and the contact area between the fuel droplet and the liquid film, that is, the heat transfer area is widened, so that a high fuel vaporization promoting action can be obtained. In addition, there is little spray that scatters after the collision.

According to the ninth aspect of the present invention, since the ceramic film is formed in a region less than the injection angle of the injector on the top land of the piston, the area for forming the ceramic film is limited as small as possible. Reduction of the amount of intake air due to thermal expansion caused by the heat insulating effect of the membrane is suppressed as much as possible.

According to the tenth aspect of the present invention, a direct-injection diesel engine has the piston according to any one of the first to ninth aspects. The same effect as the invention described in one aspect is obtained.

[0023]

(First Embodiment) A first embodiment of the present invention will be described below with reference to FIGS.

As shown in FIG. 8, a diesel engine (hereinafter simply referred to as an engine) 1 as a direct injection type engine is provided.
A piston 3 is accommodated in a cylinder 2 constituting each cylinder. A piston 3 for each cylinder is connected to a crankshaft 5 by a connecting rod 4. The cylinder head 6 is provided with an injector 8 having a distal end projecting into a combustion chamber 7 formed by the cylinder 2, the piston 3 and the cylinder head 6.

The injector 8 is a multi-hole nozzle, and in this embodiment, is a six-hole type having six nozzles. An injector 8 is connected to a common rail 10 (shown in FIG.
It is connected to the. The engine 1 has an intake passage 11.
And the exhaust passage 12 are connected. An intake valve 13 is provided at a portion where the intake passage 11 is connected to the combustion chamber 7, and an exhaust valve 14 is provided at a portion where the exhaust passage 12 is connected to the combustion chamber 7.

FIG. 7 shows a common rail type fuel injection control device 17 employed in this embodiment. The fuel injection control device 17 includes an injector 8, a common rail 10 for storing fuel at high pressure, a high-pressure supply pump 18 for pumping fuel to the common rail 10, and an ECU (Electric Control Unit) 19.

The fuel pumped by the feed pump 20 from the fuel tank 21 is pumped to the high-pressure supply pump 18. The high-pressure supply pump 18 includes a cam 22 that rotates by the output of the engine 1, and a piston 23 that contacts the cam 22, and the piston 23 moves up and down during operation of the engine to feed fuel to the common rail 10 under pressure. The common rail 10 is provided with a pressure sensor 24 for detecting the pressure of fuel stored inside (hereinafter referred to as fuel pressure). ECU 19 is pressure sensor 2
By controlling the solenoid valve 25 provided in the high-pressure supply pump 18 based on the detection value detected by the step 4, the fuel pressure in the common rail 10 is adjusted to a predetermined set pressure.

The injector 8 includes a three-way solenoid valve 26 that is controlled to be demagnetized by the ECU 19. When the three-way solenoid valve 26 is arranged at the position where it was demagnetized, the hydraulic piston 27 is pushed down by the fuel pressure in the common rail 10 and held at the lowered position, and the spool valve 28 is arranged at the closed position. Fuel injection from each nozzle hole of the nozzle 8a is stopped. When the three-way solenoid valve 26 is located at the position where it was excited, the fuel pressure in the common rail 10 no longer acts on the hydraulic piston 27 and the hydraulic piston 2
7 returns to the raised position, the spool valve 28 is arranged at the valve open position, and fuel from the common rail 10 is injected from each injection hole of the nozzle 8a through the oil passage 29.

The ECU 19 is connected to a cylinder discriminating sensor 30, an engine speed sensor 31, an accelerator sensor 32, and the like. Detection values (cylinder discriminating, engine speed, cam angle, Based on the engine load, the cylinder to be subjected to fuel injection in the next cycle is determined, and the fuel injection timing and fuel injection time for the injector 8 of the cylinder are calculated. In the present embodiment, fuel injection control for executing a pilot injection for injecting a small amount of fuel is performed prior to the main injection, and the fuel injection timing and the fuel injection time are calculated for each of the pilot injection and the main injection. The fuel injection amount is determined by the fuel injection time.

In this embodiment, the fuel injected by the pilot injection is self-ignited before the main injection is performed after the piston 3 approaches the top dead center and a squish flow is generated, and before the main injection is performed. Compared to conventional engines,
The timing of the pilot injection is delayed to a crank angle closer to the top dead center. When the pilot injection timing is delayed in this way, the injection destination of a small amount of fuel injected from each injection hole of the injector 8 is directed to the top land 3b formed around the cavity 3a of the piston 3 (FIGS. 1, 2 and the like). (See FIG. 5A) so that the injection directional angle of each injection hole of the injector 8 is set so as to form a lip portion. Here, the lip portion refers to a peripheral portion of the cavity 3a on the top land 3b, and particularly in this example refers to a region where a squish flow having a certain strength occurs when the piston is raised. For example, it indicates a half area closer to the inner circumference with respect to the width of the top land 3b.

The timing of the main injection is set so as to be executed at a crank angle when the piston 3 is located substantially at the top dead center. When the injection directional angle of each injection hole of the injector 8 is set so as to satisfy the above condition, the injection directional direction of the fuel by the main injection is directed to the inside of the cavity, in particular, to the side wall of the cavity 3a in this example. (See FIG. 6B). The ECU 19 calculates an appropriate injection timing according to the engine speed at each time so that the injection timings of the pilot injection and the main injection set as described above are realized.

FIG. 1 is a plan view of the piston 3, and FIG. As shown in FIGS. 1 and 2, a cavity 3 a is formed at the center of the upper surface (top surface) of the piston 3. The top land 3a forming the upper surface around the cavity 3a of the piston 3 has six fuel injection holes formed in the nozzle 8a of the injector 8 at positions corresponding to the respective fuels pilot-injected from the six injection holes. Each of the ceramic films 33 is formed. In the present embodiment, the same number (six) of the ceramic films 33 as the number of the injection holes of the injector 8 are formed on the lip portion of the top land 3b of the piston 3 so as to be scattered at substantially equal intervals in the circumferential direction. .

The ceramic film 33 is a sprayed film of zirconia (ZrO ₂ ) in this embodiment, and is formed on the base material (for example, aluminum alloy) of the piston 3 via an intermediate layer (not shown). The intermediate layer is made of a material having a thermal expansion coefficient intermediate between that of the zirconia sprayed film and the base material, and is used to increase the adhesion between the zirconia sprayed film and the base material. The ceramic film 33 is not limited to being made of zirconia (including those stabilized and partially stabilized), and may be a mixture or a compound containing zirconia as a main component (for example, 50 wt% or more).

The use of zirconia shifts the temperature at which fuel (droplets) undergoes film boiling to a higher temperature, as described in, for example, JP-A-9-88740 and JP-A-9-88794. This is because it has a property of promoting the vaporization among the ceramic materials. Further, since the ceramic film 33 is a sprayed film formed by a thermal spraying method (for example, a plasma spraying method), there are many fine voids in its bulk, and its surface roughness has fine irregularities of, for example, 10 to 50 μm. It is rough.

In the present embodiment, as shown in FIG. 3, the ceramic film 33 has an area smaller than the injection angle θ substantially at the center of the area of the injection angle θ of the fuel that is pilot-injected from each injection hole of the injector 8. Is formed. Ceramic membrane 3
The area of 3 is set to such a size that almost all of the fuel liquid film FL formed by a large number of spray droplets on the upper surface of the piston 3 upon pilot injection can be formed only on the ceramic film 33. More specifically, in this example, the area of the ceramic film 33 is about の of the area corresponding to the region of the injection angle θ. The reason why the area of the ceramic film 33 is limited to a necessary minimum is that the temperature of the combustion chamber 7 is increased due to the heat insulating effect of the ceramic film 33, so that the amount of intake air is reduced due to thermal expansion and the output of the engine 1 is reduced. It is to prevent.

The reason why the ceramic film 33 can be made so small is that it has a vaporization promoting action. 4A and 4B are diagrams showing a method of growing a fuel liquid film. FIG. 4A shows a case where the ceramic film 33 of the present embodiment is formed, and FIG. 4B shows a case where the fuel liquid film is formed on a metal base material (aluminum alloy). This is the case where a film is formed. As shown in FIG. 4 (b), when a liquid film of the fuel is formed on the metal base material, a liquid film FL starts to be formed from the center of the area of the injection angle θ at the beginning of the fuel injection, and the subsequent injection continues. The liquid film FL grows so that the liquid droplets are successively absorbed by the liquid film FL and spread from the center. Therefore, the maximum liquid film size (area) becomes considerably large.

On the other hand, as shown in FIG. 4A, when the ceramic film 33 is formed, the liquid film FL is similarly formed at the center of the injection angle θ region at the beginning of the fuel injection, and the fuel film FL is formed. As the liquid film FL continues to grow, the fuel attached to the ceramic film 33 is further vaporized and the growth rate of the liquid film FL becomes slower than in the case of FIG. 4B. For this reason, the maximum liquid film size (area) is considerably smaller than when a liquid film is formed directly on the base material without the ceramic film 33. From this, the necessary ceramic film 33
Can be reduced due to the effect of suppressing the growth of the liquid film due to its vaporization promoting characteristics. For this reason, making the area of the ceramic film 33 approximately １ ／ of the area corresponding to the region of the injection angle θ means that the conventional piston without the ceramic film 33 has a maximum fuel liquid film directly formed on its base material. The area is smaller than the area. Note that the area of the ceramic film 33 is not limited to about の of the area corresponding to the area of the injection angle θ.

Next, the operation of the engine 1 will be described. FIG.
As shown in (a), the pilot injection Jp changes its top land 3b at a predetermined time when the piston 3 approaches the top dead center.
The process is performed with the upper ceramic film 33 directed. Among the fuel injected by the pilot, droplets that adhere to the wall surface of the piston 3 to form a liquid film are all formed on the top land 3b.
It adheres to the upper ceramic film 33.

The ceramic film 33 is made of (a) zirconia, the wall temperature at which film boiling of fuel droplets (Leidenfrost phenomenon) occurs shifts to a high temperature side, and the temperature of the combustion chamber 7 of the direct injection diesel engine 1 is usually increased. About 3 which is called wall temperature
The film does not boil at about 00 ° C. (B) Ceramic film 3
(3) The contact area with the liquid film formed by adhering droplets or a large number of droplets, because of the rough surface roughness of (3) and the good wettability with fuel because it is an oxide That is, a large heat transfer area is secured. Therefore, the vaporization of the fuel droplets and the liquid film attached to the ceramic film 33 is promoted.

The pilot injection timing is set so that the fuel injected from each injection hole of the same injector 8 set so that the main injection is directed to the side wall of the cavity 3a is directed to the lip portion of the top land 3b of the piston 3. It is set at the time when it became.

Therefore, the vaporized fuel (including the spray droplets) FG that is pilot-injected and stays (resides) near the surface of the top land 3b is a squish flow (arrow in FIG. 5) as shown in FIG. By S, it flows into the cavity 3a from near the surface of the top land 3b. Further, the vaporization of the fuel attached to the ceramic film 33 is also promoted by the squish flow S.

After the vaporized fuel FG flows into the cavity 3a, it self-ignites near the nozzle of the injector 8 in the cavity 3a. As a result, most of the pilot-injected fuel burns intensively inside the cavity 3a as shown in FIG. 6A. Conventional engines are designed to ensure low-temperature startability (designed to have a compression ratio that causes self-ignition before squish flow occurs). Due to the self-ignition, a wide range of combustion occurred in the radial direction of the cylinder, and heat was easily taken away from the cylinder wall surface. In addition, the heat was dispersed over a wide range, making it difficult to raise the temperature of the injection region of the main injection. On the other hand, in this embodiment, even if a design that ensures low-temperature startability is made, combustion concentrates inside the cavity 3a, so that the injection region of the main injection, that is, the vicinity of the nozzle 8a of the injector 8 is conventionally used. An even higher temperature zone is created.

At this time, the vaporized fuel FG is well mixed with the air by the gas flow when it flows into the cavity 3a by the squish flow S. Therefore, the self-ignited fuel burns almost completely.

Then, as shown in FIG. 6B, when the piston 3 is located at a crank angle substantially at the top dead center, the fuel 8 is injected from the injector 8 into the high-temperature region where the temperature is increased.
m is executed. The main-injected fuel (spray droplets) is vaporized at a stretch, and its combustion proceeds at a burst at a substantially central portion (near the axis) in the cylinder. For this reason, a large explosive power is obtained instantaneously, and a large output is obtained from the crankshaft 5 of the engine 1, so that fuel efficiency is improved.

As described in detail above, according to the present embodiment,
The following effects can be obtained. (1) Pilot injection is performed by directing the ceramic film 33 formed on the lip portion of the top land 3b of the piston 3 and the timing of the pilot injection is determined such that the injected fuel becomes self-ignited after the squish flow becomes strong. It was made to become. Therefore, the fuel adhering to the ceramic film 33 is immediately vaporized and the fuel of the pilot injection is flown into the cavity 3a by the squish flow without increasing the emission caused by the combustion remaining on the wall surface of the fuel, and then is injected into the cavity 3a. Can be intensively burned. As a result, the temperature in the vicinity of the injector 8, which is the injection region of the main injection, can be further increased as compared with the conventional engine. Therefore, the main injected fuel can be burned at once in the central portion of the cylinder, and heat is hardly taken off from the wall surface of the cylinder 2, so that fuel efficiency can be improved.

(2) The ceramic film 33 is placed on the top land 3
Since b is formed at the lip portion where the squish flow is strongly generated, more fuel injected toward the ceramic film 33 can flow into the cavity 3a, and the vicinity of the injector 8 which is the injection region of the main injection Can be heated to a higher temperature.

(3) The fuel adhering due to the vaporization promoting action of the ceramic film 33 is immediately vaporized, and the fuel and the air are well mixed in the cavity 3a by the squish flow, so that the emission of HC and the like does not increase.

(4) Since the ceramic film 33 is a zirconia sprayed film, the liquid is used for a plurality of reasons such as a high temperature at which film boiling occurs, surface roughness, and good wettability with fuel. A large heat transfer area between the droplet and the liquid film can be secured, and the effect of promoting vaporization can be significantly increased.

(5) Since the formation area of the ceramic film 33 is limited to a substantially necessary minimum range smaller than the injection angle of the injection hole of the injector 8, the heat insulation effect of the ceramic film 33 is suppressed and the intake air amount due to thermal expansion is reduced. The decrease can be minimized. In particular, in this example, the area of the ceramic film 33 is set to about の of the area corresponding to the injection angle θ of the fuel injected from the injection hole of the injector 8, so that the reduction in the intake air amount can be more easily suppressed. Therefore, it is possible to avoid a decrease in the output of the engine 1 due to a decrease in the amount of intake air due to thermal expansion.

(Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIGS. This embodiment is an example in which pilot control for injecting a small amount of fuel prior to main injection is performed in a direct injection (in-cylinder injection) gasoline engine.

As shown in FIG. 9, in a direct injection type gasoline engine (hereinafter simply referred to as an engine) 41 as a direct injection type engine, a piston 43 is housed in a cylinder 42 constituting each cylinder. A combustion chamber 45 is formed by the cylinder 42, the piston 43, and the cylinder head 44. An intake valve 47 is provided at a portion where the intake passage 46 is connected to the combustion chamber 45, and the exhaust passage 48 is connected to the combustion chamber 4.
An exhaust valve 49 (shown in FIG. 10) is provided in a portion connected to 5.

As shown in FIG. 9 and FIG.
A cavity (depression) 43a is formed in the crown surface of the top land 43 so as to be slightly displaced from the center toward the exhaust side.
b is wider on the intake side. Topland 43
b shows a ceramic film 5 on the lip portion on the intake side.
0 is formed.

The injector 51 is mounted on the cylinder head 44 at the center of the cylinder. In the present embodiment, the injection of the fuel from the injector 51 includes a main injection,
Prior to the main injection, it is performed twice with a pilot injection that injects a small amount of fuel. The timing of the main injection is determined from the operating state of the engine at each time, and is executed at a crank angle substantially near the top dead center.

On the other hand, the timing of the pilot injection is set earlier than the crank angle at which the piston 43 reaches the top dead center, and more specifically, the generation of a squish flow generated when the piston 43 approaches the top dead center. The timing is set to a timing or a timing slightly earlier than this occurrence timing.
Therefore, the pilot injection is completed in principle before the piston 43 reaches the top dead center.

The direction of fuel injection from the injection hole of the injector 51 is determined by the position of the pilot injection timing (FIG. 9).
The position is set so that the ceramic film 50 on the top land 43b is directed to the piston 43 when the piston 43 is at the position indicated by the solid line in FIG. That is, the injection directivity angle of the injection hole of the injector 51 is set to a predetermined angle (for example, 20 degrees) with respect to the axis of the cylinder 42 as shown in FIG.
(.About.50 °) to the intake side.

The fuel of the pilot injection, which is injected toward the ceramic film 50 and exists near the surface of the top land 43b, is pushed out by the squish flow generated when the piston 43 approaches the top dead center. It is attached to the cylinder head 44 in a state where the ignition portion at the tip thereof is located on the downstream side in the direction in which the ignition is performed. Spark plug 5
2 is ignited once for each main injection and pilot injection. The ignition timing at the time of the pilot injection is such that the fuel Fg pushed out by the squish flow
Is set at the timing of reaching the ignition section. The timing of the pilot injection is determined based on the timing of the main injection so that the main injection is performed after the ignition of the fuel for the pilot injection.

As shown in FIG. 9 and FIG. 10, the ceramic film 50 is formed at a position where the fuel injected from the injector 51 hits, substantially at the center of the region of the injection angle θ, with an area smaller than the injection angle θ. ing. The ceramic film 50 is made of a sprayed zirconia film as in the first and second embodiments. However, the material may be a mixture or a compound containing zirconia as a main component.

The area of the ceramic film 50 is set to about 面積 of the area corresponding to the area of the injection angle θ (the surface area where the injection area of the injection angle θ intersects with the top land 43b). By limiting the area of the ceramic film 50 to a necessary minimum, the temperature of the combustion chamber is increased by the heat insulating effect of the ceramic, and the amount of air taken in due to thermal expansion is prevented from being reduced.

In the direct-injection gasoline engine 41 configured as described above, before the piston 43 reaches the top dead center, at a predetermined timing at the position shown by the solid line in FIG. The operation is performed with the film 50 facing. At this time, a liquid film of the fuel may be formed at the center of the fuel injection angle θ, but such a liquid film is formed on the ceramic film 50, so that the ceramic film 5
It is quickly vaporized by the vaporization promoting action of 0.

The fuel of the pilot injection executed toward the ceramic film 50 exists near the surface of the top land 43b (especially near the lip). When the piston 43 rises to the position shown by the dashed line in FIG. 9, the fuel Fg existing near the surface of the top land 43b is pushed out toward the ignition portion (that is, the cavity 43a) of the ignition plug 52 by the squish flow. When the fuel Fg reaches the ignition portion of the ignition plug 52, the ignition plug 52 is ignited, and
g burns in the cavity 43a.

The main injection is performed in the cavity 43a having a high temperature. Therefore, vaporization of the main injected fuel is promoted. Then, when the ignition plug 52 is ignited, the fuel burns in a state almost close to complete combustion.

Almost all of the fuel near the lip of the top land 43b injected toward the ceramic film 50 is pushed out by air (squish flow) pushed out from the peripheral side of the cylinder, and the surface of the top land 43b Almost no remains near. Further, since the width of the top land 43b is wide on the injection direction destination side and the amount of gas pushed out near the ceramic film 50 is large, and the fuel Fg exists near the lip where the squish flow is strong, the fuel Fg is The strong squish flow ensures that the spark plug 52
To the ignition section.

According to this embodiment, the following effects can be obtained. (6) In the direct injection type gasoline engine 41, the ceramic film 50 is formed on the top land 43b of the piston 43, and the fuel of the pilot injection directed to the ceramic film 50 is applied to the ignition portion of the ignition plug 52 by using the squish flow. The temperature of the cavity 43a, which is the injection region of the main injection, can be effectively raised by the combustion.
Therefore, the vaporization of the main injected fuel can be promoted, and the emission can be reduced and the fuel efficiency can be improved.

In addition, the provision of the ceramic film 36 at the directing point of the pilot injection executed at the stage where the ambient temperature is low enables the vaporization of the fuel for the pilot injection to be promoted. (2)-(5)
The same effect can be obtained.

The embodiment is not limited to the above, but may be modified as follows. In the above embodiment, the ceramic film 33 is formed so as to be scattered at the position where the fuel of the pilot injection is applied. However, for example, as shown in FIG.
A ceramic film 35 may be formed in a strip shape over the entire lip portion. According to this configuration, the effects (1) to (4) described in the above embodiment can be obtained in the same manner, and even if a positional displacement in the circumferential direction occurs due to an assembly error between the piston 3 and the injector 8. Therefore, the fuel of the pilot injection can be securely attached to the ceramic film 35. Also,
Since the area of the ceramic film 35 is small only in the lip portion, the decrease in the engine output due to the reduction in the intake air amount is relatively small. In addition, in consideration of a circumferential displacement due to an assembling error between the piston 3 and the injector 8, the ceramic film may be formed in a shape that is long in the circumferential direction (an ellipse or the like).

A direct injection type engine employing a fuel injection control method in which only pilot injection is performed during idling or the like may be used. ○ The position of the ceramic membrane is sufficient if it is within the area where the squish flow occurs. On the top land 3b, the squish flow becomes weaker toward the outer periphery, but if the ceramic film is located on the top land 3b, the squish flow is weak, but the fuel flows toward the cavity 3a, so that the temperature of the injection region of the main injection increases. Can be planned. Therefore, the position of the ceramic film can be changed to any position on the top land 3b of the piston 3. If the ceramic film is located on the top land 3b, (1),
The effects (3) to (5) can be obtained similarly.

When the ceramic film is scattered at the position where the fuel is applied, the shape is not limited to the substantially circular shape as in the above embodiment. A change in the position of the piston 3 during the fuel injection period causes a change in the position where the fuel strikes, and a change in the fuel injection timing due to the engine speed and the like causes a change in the position where the fuel strikes. The shape of the ceramic film may be determined. For example, an elliptical shape extending in the radial direction of the top land 3b may be used.

The material of the ceramic film 33 is not limited to zirconia or zirconia as a main component. For example, alumina (Al ₂ O ₃ ), silica (Si
O ₂ ), magnesia (MgO), yttria (Y
₂ O ₃ ) or a compound containing these as a main component may be used. Even if other ceramic materials are used, a vaporization promoting effect can be obtained as long as the material is a sprayed film or an oxide. Further, even when a ceramic material other than an oxide, such as a carbide, a nitride, or a boride, has a higher heat capacity than a metal, a vaporization promoting effect can be obtained as compared with the case where the metal surface of the base material is not changed. Further, by forming a sprayed film made of the same material as the base material or a metal material different from the base material and making the surface roughness of the area where the fuel adheres rough, the effect of promoting the vaporization of the fuel can be achieved.

The method for forming the ceramic film 33 is not limited to the thermal spraying method. The ceramic film 33 may be formed by other physical vapor deposition (PVD) or chemical vapor deposition (CVD). For example, a dense film may be formed and the roughness may be small as compared with the thermal spraying method. Further, the ceramic film may be formed by bonding a ceramic plate to a base material of the piston.

A ceramic film may be formed on the position of the main injection fuel, that is, on the side wall of the cavity 3a, if necessary. ○ The number of injection holes of the injector 8 can be changed as appropriate. For example, a five-hole type may be used. Further, the present invention can be implemented in a direct injection diesel engine using a single injection hole type injector.

The fuel injection control device is not limited to the common rail type. A distributed fuel injection pump with an electromagnetic spill valve can also be used. In short, any combustion injection control device that can perform pilot injection is sufficient.

The present invention is not limited to a fuel injection type direct injection engine employing pilot injection. For example, in the direct injection gasoline engine 41 according to the second embodiment, only one injection is performed, and the fuel is injected from the injector 51 to the ceramic film 50. The injection timing is set so that the injected fuel is pushed out of the top land 43b toward the cavity 43a by the squish flow, and is ignited at the pushed-out timing. According to this configuration, since the fuel is less likely to remain on the wall surface of the piston 43 due to the vaporization promoting action of the ceramic film 50, a combustion system in which the injected fuel is carried to the ignition portion of the ignition plug 52 using a squish flow can be realized. .

The fuel is not limited to light oil. For example, the present invention can be implemented in a direct injection diesel engine using a vegetable fuel. That is, the present invention can be applied to any engine that employs fuel injection control that executes pilot injection for injecting a small amount of fuel prior to main injection.

Next, regarding technical ideas other than the invention described in the claims that can be understood from the above embodiments and other examples,
These effects are described below. (1) In claim 1 or 2, the position of the vaporization promoting film is in a region of the top land where a squish flow is generated in a compression stroke. According to this configuration, the fuel of the pilot injection injected toward the top land can be poured into the cavity by the squish flow.

(2) In any one of claims 2 to 5,
The injector is set at an injection directional angle at which the main injection executed substantially at the top dead center can point toward the side wall of the cavity, and the timing of the pilot injection is determined based on the fuel injected from the injector at the injection directional angle. Is set at a time pointed toward the lip portion of the top land of the piston. According to this configuration, the same effect as the invention of claim 5 can be obtained, and more fuel near the top land, which has been pilot-injected by the strong squish flow, can flow into the cavity more. Therefore, the injection range of the main injection can be made higher. (3) The direct-injection engine according to any one of claims 1 to 3, wherein the direct-injection engine is a direct-injection gasoline engine; Fuel that is injected from the injector toward the vaporization promoting film and is present near the surface of the top land is ignited downstream in the direction in which the fuel is carried by the squish flow generated when the piston approaches TDC. The ignition plug is provided so as to be located. Note that the vaporization promoting film is constituted by the ceramic film 50. According to this configuration, the fuel can be sent to the ignition portion of the ignition plug using the squish flow. In addition, the same effect as any one of the first to third aspects of the invention can be obtained.

(4) The cavity is formed so as to be deviated from the axis of the piston, and the top land is wider on the side where the vaporization promoting film is formed. According to this configuration, since the amount of gas pushed out by the wide portion of the top land when approaching the top dead center is relatively large, a strong squish flow is generated near the vaporization promoting film,
The fuel can be reliably transported to the ignition portion of the ignition plug.

(5) Claims 1-5 and (1)-
In any one of (4) and (4), the vaporization promoting film is formed in an annular band shape on a lip portion of a top land of the piston. According to this configuration, even if the direction of the injection hole of the injector varies due to an assembly error between the injector and the piston, the fuel (pilot injection fuel) can be reliably adhered to the vaporization promoting film (ceramic film).

(6) Claims 1 to 10 and (1) to
In any one of (4) and (4), the vaporization promoting film (ceramic film) may have a radius of the piston in consideration of a change in the position of the piston during the pilot injection period and a change in the pilot injection timing according to the engine speed and the like. It is formed in an elongated shape extending in the direction. According to this configuration, even if there is a change in the position of the piston during the pilot injection period, or a change in the pilot injection timing according to the engine speed, etc., the injected fuel can be reliably attached to the ceramic film. .

(7) Claims 1 to 10 and (1),
In any one of (2), (5) and (6), the direct-injection engine is a direct-injection diesel engine, and is designed to ensure low-temperature startability.

(8) In the above (7), the direct-injection diesel engine is designed to have a compression ratio such that the piston approaches self-ignition before approaching the top dead center and generating a squish flow.

(9) Claims 1-7 and (1)-
In any one of the constitutions (8), the vaporization promoting film is a sprayed film. According to this configuration, since the vaporization promoting film is a thermal sprayed film, a large heat transfer area can be secured from the rough surface roughness, and a high vaporization promoting effect can be obtained.

(10) In any one of the sixth, seventh, ninth and tenth aspects, the ceramic film is made of an oxide. According to this configuration, the ceramic film made of an oxide has better wettability with fuel than a non-oxide and can secure a wide heat transfer area, so that a high vaporization promoting effect can be obtained.

(11) In claim 6 or 7, the ceramic film contains zirconia or zirconia as a main component. Since the ceramic film contains zirconia or zirconia as a main component, a high vaporization promoting effect such as suppression of film boiling (Leidenfrost phenomenon) can be obtained from the characteristics of the material.

[0084]

As described above in detail, according to the first and tenth aspects of the present invention, a vaporization promoting film is provided at least at a fuel injection destination position on the top land, and the fuel is heated before combustion. Since the fuel is burned at the timing of being transported from the top land to the cavity side by the squish flow, more fuel is intensively burned in the cavity, and emission of emissions can be suppressed.

According to the second and tenth aspects of the present invention, the pilot injection is executed by pointing the vaporization promoting film on the top land of the piston, and the fuel by the pilot injection is carried to the cavity side by the squish flow. Since the fuel is intensively burned in the cavity, the injection region of the main injection can be heated to a higher temperature, thereby suppressing emission of the emission and improving fuel efficiency.

According to the third and tenth aspects of the present invention, since the vaporization promoting film is formed on the lip portion of the top land where a strong squish flow is generated, the top sprayed with the vaporization promoting film directed toward the lip portion. More fuel near the land can be sent into the cavity, which further contributes to suppressing emissions and improving fuel efficiency.

According to the fourth and tenth aspects of the present invention, the fuel of the pilot injection flows into the cavity from the vicinity of the top land by the squish flow and then self-ignites and burns. A certain cavity can be heated to a high temperature, and in a direct-injection diesel engine, emission of emissions can be suppressed and fuel efficiency can be improved.

According to the fifth and tenth aspects of the present invention, the timing of the pilot injection by the injector having an injection directing angle at which the main injection executed substantially at the top dead center can point to the side wall of the cavity is determined by the top land. Since the timing is set so as to direct the vaporization promoting film, it is possible to set the timing for self-ignition after the fuel flows into the cavity by the squish flow.

According to the sixth and tenth aspects of the present invention, since the vaporization promoting film is a ceramic film, a higher vaporization promoting effect can be obtained as compared with a metal. According to the seventh and tenth aspects of the present invention, the same number of vaporization promoting films as the injection holes are interspersed at positions where the fuel injected from the plurality of injection holes of the injector hits, so that the area thereof is substantially Since it is kept to the minimum necessary, it is possible to minimize the reduction in the amount of intake air due to thermal expansion due to the heat insulating effect of ceramic.

According to the eighth and tenth aspects of the present invention, since the ceramic film is a sprayed film containing zirconia or zirconia as a main component, film boiling (Leidenfrost phenomenon) is suppressed due to the characteristics of the material. And a large heat transfer area can be secured from the rough surface roughness.
A high vaporization promoting effect can be obtained.

According to the ninth and tenth aspects of the present invention, since the ceramic film is formed in a region smaller than the injection angle of the injector, a reduction in the amount of intake air due to thermal expansion due to the heat insulating effect of the ceramic is prevented. It is possible to reduce emissions and improve fuel efficiency while minimizing emissions.

[Brief description of the drawings]

FIG. 1 is a plan sectional view of a piston according to a first embodiment.

FIG. 2 is a side sectional view of a piston.

FIG. 3 is a partial side view showing a relationship between a ceramic film and an injection angle.

4A and 4B are partial side views showing a process of forming a fuel liquid film at the time of pilot injection, wherein FIG.
(B) No ceramic film.

FIG. 5 is a schematic side sectional view of a combustion chamber for explaining fuel injection control.

FIG. 6 is a schematic side sectional view of the combustion chamber.

FIG. 7 is a schematic diagram of a fuel injection control device.

FIG. 8 is a schematic side sectional view of a diesel engine.

FIG. 9 is a partial side sectional view of a gasoline engine according to a second embodiment.

FIG. 10 is a plan view of a piston.

FIG. 11 is a plan view of another example of a piston.

FIG. 12 is a schematic side sectional view of a combustion chamber illustrating a pilot injection according to the related art.

[Explanation of symbols]

1. Diesel engine as direct injection type engine 2.
Cylinder, 3 ... piston, 3a ... cavity, 3b ... top land, 5 ... crankshaft, 7 ... combustion chamber, 8 ... injector, 8a ... nozzle, 10 ... common rail, 17 ... high pressure supply pump, 17 ... fuel injection control device, 19 ... E
CU, 33, 35, 50: ceramic film as vaporization promoting film, 41: direct injection gasoline engine as direct injection engine, 43: piston, 43a: cavity, 43b
… Top land, Jp… Pilot injection, Jm… Main injection, S
... Squish flow, θ ... Injection angle.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 41/02 380 F02D 41/02 380A 41/38 41/38 B F02F 3/14 F02F 3/14 (72 ) Inventor Akira Ito 2-1-1 Toyota-cho, Kariya-shi, Aichi Prefecture Inside Toyota Industries Corporation (72) Inventor Hiroyuki Kusano 2-1-1 Toyota-cho, Kariya City, Aichi Prefecture Inside Toyota Industries Corporation ( 72) Inventor Hiroyuki Sami 2-12-1, Kugakata, Tempaku-ku, Nagoya City, Aichi Prefecture Inside Toyota Institute of Technology (72) Inventor Takayoshi Takano 2-12-1, Kugagata, Tempaku-ku Nagoya City, Aichi Prefecture F-term (Reference) 3G023 AA02 AA04 AB01 AB05 AC05 AD02 AD08 AD09 AD11 AE04 3G060 AA03 AB00 CA01 CA02 CA03 CB06 DA00 GA00 GA02 GA03 GA14 3G301 HA01 HA02 HA06 JA02 JA26 LB13 MA11 M A18 MA23 MA27 PA17Z PB03A PB03Z PB05A PB05Z PB08Z PE01Z PE03Z PE05Z

Claims (10)

[Claims] Claims: 1. A piston having a cavity on an upper surface and having a vaporization promoting film formed at least on a top land at a position where fuel injected from an injector hits, and the injector directing and injecting the vaporization promoting film from the injector. At a timing at which fuel can be pushed out from the top land to the cavity side before combustion by a squish flow generated when the piston approaches the top dead center, fuel is injected from the injector pointing to the vaporization promoting film. A direct injection engine comprising: a fuel injection control device for performing injection. 2. The fuel injection executed in a direction directed to the vaporization promoting film is a pilot injection for injecting a small amount of fuel prior to a main injection. 2. The direct injection engine according to claim 1, wherein the main injection of the fuel is performed at least at a timing after the start of combustion at which the injection direction of the injector can be directed in the cavity. 3. The direct injection engine according to claim 1, wherein the vaporization promoting film is formed on a lip portion of a top land of the piston. 4. The direct injection engine is a diesel engine, and the pilot injection is executed at a timing when the injected fuel can self-ignite after flowing into the cavity by squish flow from near the top land. A direct injection engine according to claim 2 or claim 3. 5. An injector according to claim 1, wherein said injector is set at an injection directing angle at which said main injection executed substantially at a top dead center is directed to a side wall of said cavity. The direct injection engine according to any one of claims 2 to 4, wherein the injection is performed at a timing at which the injected fuel can be directed to the vaporization promoting film on the top land of the piston. 6. The direct injection engine according to claim 1, wherein the vaporization promoting film is a ceramic film. 7. The injector has a plurality of injection holes, and the same number of the ceramic films as the injection holes are provided on the top land in a circumferential direction at a position where the fuel injected from each of the injection holes hits. 7. The direct-injection engine according to claim 6, wherein the direct-injection engine is dotted at substantially equal intervals. 8. The direct injection engine according to claim 6, wherein the ceramic film is zirconia or a thermal sprayed film containing zirconia as a main component. 9. The direct injection engine according to claim 6, wherein the ceramic film is formed in a region of the top land of the piston that is smaller than an injection angle of the injector. 10. A piston according to any one of claims 1 to 9.