JP2000073768A - Engine and engine ignition method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an engine and an engine ignition method which can ignite a fuel accurately and securely at a desired ingnition time, in a simple structure without adding a new device to an existing engine. SOLUTION: While a recess 2b is formed to the upper part of a piston 3 and one side of a cylinder head 2a, a projection 3b is formed to the other side of the piston 3, and an auxiliary combustion chamber 6 having a compressive ratio larger than a main combustion chamber 4 is formed by the recess 2b and the projection 3b. As a result, the fuel is ignited earler in the auxiliary combustion chamber 6 having the compressive ratio larger than the main combustion chamber 4, and the fuel in the mixing gas in the main combustion chamber 4 is ignited accurately and securely at a desired ingnition timing, by the ignited mixing gas flowing out to the main combustion chamber 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine such as a diesel engine which supplies air and fuel to a combustion chamber of an engine, compresses a mixture of the air and fuel, ignites the fuel at a desired time, and performs combustion. More particularly, the present invention relates to an engine structure and an ignition method for causing ignition at a desired ignition timing in a combustion chamber of the engine.

[0002]

2. Description of the Related Art Diesel engines have advantages such as higher thermal efficiency than gasoline engines and durability under severe conditions (high-load continuous operation). On the other hand, however, there are disadvantages that the exhaust gas is not clean and environmentally unfavorable, such as emission of nitrogen oxides NOx about two to three times that of a gasoline engine and emission of soot (particulate emissions). is there.

Therefore, the present inventors have been studying a method of purifying exhaust gas while maintaining thermal efficiency.

[0004] Here, conventional diesel engine combustion involves burning fuel by injecting fuel into high-temperature air compressed by a piston (conventional combustion method). However, if this conventional combustion method is adopted, the combustion temperature locally rises in the cylinder, and as described above, NOx
Occurs in large quantities. Further, as described above, a large amount of soot is generated due to a local shortage of air in the cylinder. Here, conventionally, these problems have been dealt with by increasing the fuel injection pressure. However, it has become clear that there is a limit to the method of using high pressure fuel injection.

Therefore, the following combustion method has recently been considered.

That is, a predetermined amount of fuel is added to the cylinder during compression by the piston (while the piston is located near bottom dead center). Thereafter, as the process of compressing the premixed gas by the piston proceeds, the temperature in the cylinder increases. When the mixture exceeds the ignition critical condition determined by each parameter such as temperature, the fuel self-ignites over the entire combustion chamber (combustion chamber) in the cylinder. Here, the fuel has sufficiently vaporized by the time of self-ignition, and the fuel and the air have been mixed. This combustion method is referred to herein as a "lean premixed auto-ignition method".

When the lean premixed self-ignition system is employed, air and fuel can be uniformly mixed in advance before self-ignition, so that the fuel can be uniformly distributed over the entire combustion chamber (combustion chamber) in the cylinder. Burns. Therefore, it is possible to avoid that the air-fuel ratio burns only at a stoichiometric mixture ratio or a condition close to the stoichiometric mixture ratio, and to suppress the generation of NOx. Therefore, the amount of NOx discharged can be reduced. Further, since the fuel is uniformly burned, the amount of soot discharged can be reduced.

In this lean premixed self-ignition method, it is necessary to ignite a gas mixture of fuel and air (premixed gas) at a predetermined timing θd near the piston top dead center as shown in FIG. If the ignition timing is not appropriate and ignition is delayed, abnormal combustion such as afterburning may occur, which may cause a problem such as a decrease in thermal efficiency. Here, in the lean premixed self-ignition system, there is a demand that the mixture be sufficiently diluted (the ratio of fuel to air be extremely small). As the air-fuel mixture becomes thinner, the pre-air-fuel mixture becomes more difficult to ignite.

Therefore, in the lean premixed self-ignition method, it is necessary to eliminate the difficulty of igniting the premixed gas in order to increase the leanness and to ignite the ignition at an appropriate ignition timing without delay.

Therefore, it is conceivable to apply a conventional method for assisting self-ignition to a premixed gas which is difficult to self-ignite.
A conventional method considered as the ignition assist is as follows.

(1) A spark discharge type spark plug (spark plug) is used.

(2) Use a glow plug.

(3) Inject fuel into the premixed gas near the piston top dead center.

[0014]

The method of the above (1) is as follows.
A proven method for gasoline engines.

In this method, a very high voltage is applied between the two electrodes placed in the combustion chamber, and the fuel is locally ignited by spark discharge generated between the electrodes. Then, starting from local ignition by spark discharge, the flame is propagated to the entire air-fuel mixture to burn the entire air-fuel mixture.

However, in the above method (1), it is necessary to provide an ignition system to ignite the ignition plug.
The device configuration around the engine becomes complicated. A method of burning the entire air-fuel mixture by propagating a flame caused by local ignition generated between the electrodes (a method using one-point ignition)
Therefore, it takes time for the flame to propagate throughout the mixture and ignite the entire mixture. For this reason, the isocapacity is reduced, and the thermal efficiency is reduced. Another problem is that end gas knock is likely to occur.

The method (2) has been used for preheating the combustion chamber of a diesel engine by the conventional combustion method, and is a proven method. But this (2)
Similarly, in the method (1), it is necessary to provide a device such as a preheating circuit in order to operate the glow plug, and the device configuration around the engine becomes complicated. Also, the glow plug needs to be energized at all times to raise the surface temperature, and it is difficult to control the ignition timing to an appropriate timing.

Similarly, the method (3) requires a separate fuel injection control device for further injecting fuel into the premixed gas near the piston top dead center, which complicates the structure of the device around the engine. In addition, since the method of directly injecting fuel into the premixture of the combustion chamber is employed, N
Ox is generated, and the original purpose of reducing NOx cannot be achieved.

Further, as recently disclosed in Japanese Patent Application Laid-Open No. 9-195772, an ignition combustion chamber is provided separately from an original combustion chamber consisting of a piston and a cylinder, and an air-fuel mixture ignited by the ignition combustion chamber is supplied to a nozzle. A technology has been proposed in which the fuel is injected into a combustion chamber via a gas to ignite an air-fuel mixture in the combustion chamber.

However, according to the technology described in this publication, it is necessary to prepare an ignition piston separately from the original piston to constitute the ignition combustion chamber. In addition, a cam drive mechanism and the like for driving the ignition piston are separately required. Further, a nozzle for injecting the ignition air-fuel mixture into the original combustion chamber remote from the ignition combustion chamber is required.

As described above, according to the technique described in Japanese Patent Application Laid-Open No. 9-195772, it is necessary to add a complicated mechanism or the like to an existing engine, and the device configuration around the engine is similarly complicated. become.

In any case, according to the conventional method, the configuration of the device around the engine must be complicated.

The present invention has been made in view of the above circumstances, and it is possible to accurately and reliably ignite fuel at a desired ignition timing with a simple structure without adding a new device to an existing engine. An object of the present invention is to provide an engine and an ignition method.

[0024]

In order to achieve the above object, the first invention of the present invention supplies air and fuel to a main combustion chamber formed by a cylinder head and a piston upper surface of an engine. In an engine that compresses a mixture of air and fuel and ignites the fuel at a desired time, a concave portion is formed on one of the upper portion of the piston and the cylinder head, and a convex portion is formed on the other. A sub-combustion chamber having a compression ratio greater than that of the main combustion chamber is formed by the section, the fuel is ignited in the sub-combustion chamber, and the ignited combustion mixture is discharged into the main combustion chamber, thereby mixing the fuel in the main combustion chamber. I try to ignite fuel in the air.

According to a second aspect of the present invention, in the first aspect, a fuel supply means for further supplying fuel to the air-fuel mixture in the sub-combustion chamber is provided.

In a third aspect based on the first aspect, the sub-combustion chamber is formed at an outer edge of the upper surface of the cylinder head and the piston.

According to a fourth aspect, in the first aspect, the concave portions and the convex portions have substantially the same thermal expansion coefficient.

According to a fifth aspect of the present invention, in the first aspect, the surfaces of the concave portions and the convex portions facing each other have a curved surface shape. According to the sixth aspect of the present invention, there is provided an engine for supplying air and fuel to a main combustion chamber formed by a cylinder head and a piston upper surface of an engine and compressing a mixture of the air and fuel to ignite the fuel at a desired time. A step of igniting the fuel in the sub-combustion chamber after forming a sub-combustion chamber having a compression ratio larger than that of the main combustion chamber by the cylinder head and the upper surface of the piston; Discharging the burned air-fuel mixture into the main combustion chamber to ignite the fuel in the air-fuel mixture in the main combustion chamber.

According to the present invention, the auxiliary combustion chamber having a higher compression ratio than the main combustion chamber is formed by the cylinder head and the upper surface of the piston, so that the fuel can be supplied to the existing engine with a simple structure without adding a new device. It is characterized in that accurate and reliable ignition is performed at a desired ignition timing.

According to the first invention, as shown in FIG. 1, the recess 2b is formed in the upper part of the piston 3 and one of the cylinder heads 2a.
Is formed, and a convex portion 3b is formed on the other side. The concave portion 2b and the convex portion 3b form a sub-combustion chamber 6 having a higher compression ratio than the main combustion chamber 4. As a result, the fuel is ignited early in the sub-combustion chamber 6 having a large compression ratio, and the ignited combustion mixture flows out to the main combustion chamber 6, so that the fuel in the mixture in the main combustion chamber 6 reaches a desired ignition timing. Accurate and reliable ignition.

That is, the upper part of the piston 3 and the cylinder head 2 can be added to the existing engine 1 without adding a new device.
a, a concave portion 2b is formed on one side and a convex portion 3b is formed on the other side.
Is formed, the mixture in the main combustion chamber 4 is accurately and reliably ignited at a desired ignition timing.

According to the second invention, as shown in FIG. 3, fuel is further supplied to the air-fuel mixture in the sub-combustion chamber 6 by the fuel supply means 7, and The ignitability is further improved. For this reason, the certainty of ignition of the air-fuel mixture in the main combustion chamber 4 is further improved, and the ignition timing of the air-fuel mixture in the main combustion chamber 4 can be made closer to the top dead center (TDC) side. It becomes possible.

According to the third invention, as shown in FIG. 4, the sub-combustion chamber 6 is formed at the outer edge of the upper surface of the cylinder head 2a and the piston 3. The ignited air-fuel mixture flows out of the sub-combustion chamber 6 at the outer edge to the outer edge of the main combustion chamber 4, so that the air-fuel mixture at the outer edge of the main combustion chamber 4 (near the inner wall surface of the cylinder 2), which is originally difficult to combust, is discharged. Combustion is promoted.

According to the fourth aspect, the concave portion 2b and the convex portion 3
b has substantially the same thermal expansion coefficient. As a result, unnecessary contact between the metal surfaces of the concave portion 2b and the convex portion 3b due to thermal expansion can be prevented, and serious damage such as scuffing and seizure can be avoided.

According to the fifth aspect, as shown in FIG. 6, the surfaces where the concave portions 2b and the convex portions 3b face each other have a curved surface shape. This prevents a heat spot from being generated in the sub-combustion chamber 6.

In a sixth aspect of the present invention, the first aspect of the apparatus is invented by a method.

As shown in FIG. 1, a sub-combustion chamber 6 may be formed by forming a convex portion 3b on the top of the piston 3 and forming a concave portion 2b on the cylinder head 2a, as shown in FIG. Then, a concave portion 3c is formed in the upper part of the piston 3,
The auxiliary combustion chamber 6 may be configured by forming the convex portion 2c on the cylinder head 2a.

The engine to which the present invention is applied is not limited to a diesel engine which uses fuel having a low self-ignition temperature and ignites fuel by compression heat, and ignites fuel by using a fuel having a high self-ignition temperature and spark ignition. The present invention is also applicable to a gasoline engine to be used.

[0039]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an engine and an engine ignition method according to the present invention will be described below with reference to the drawings.

In this embodiment, a diesel engine is assumed, but the present invention can be applied to a gasoline engine. That is, any engine such as an in-cylinder injection gasoline engine that supplies air and fuel into the combustion chamber of the engine, compresses a mixture of the air and fuel, ignites the fuel at a desired timing, and performs combustion. Applicable.

Embodiment 1 FIG. 1 shows the structure of the engine of Embodiment 1.

That is, as shown in FIG. 1, the engine 1 is roughly composed of a cylinder 2, a piston 3 slidably disposed in the cylinder 2, and reciprocating up and down in the cylinder 2; 3 includes a connecting rod 5 for transmitting the reciprocating motion of the motor 3 to a crankshaft (not shown) as a rotational motion. The cylinder chamber above the piston 3 constitutes the main combustion chamber 4. The main combustion chamber 4 is a chamber in which fuel in the air-fuel mixture is burned and also a compression chamber in which the air-fuel mixture is compressed by the piston 3.

In the drawing, a fuel supply device for supplying fuel to the main combustion chamber 4 of the engine 1 and a main combustion chamber 4 of the engine 1 are shown.
The intake pipe for supplying air to the air supply is omitted. A fixed amount of fuel is discharged from the fuel injection pump of the fuel supply device at predetermined pulse intervals, and the fuel is injected and supplied into the cylinder 2 of the engine 1 through the injection nozzle. The exhaust gas burned in the cylinder 2 is discharged to the outside air via an exhaust pipe (not shown).

The engine 1 is supplied with air into the main combustion chamber 4 via an intake pipe. And from the fuel supply device,
The fuel is supplied to the main combustion chamber 4 at a predetermined ratio with respect to the air.
Supplied within. In this way, a relatively thin mixture is formed in the main combustion chamber 4. As for the fuel, the piston 3 has a bottom dead center (B.
D. C), and is injected and supplied at a predetermined timing during the compression stroke from when the top dead center (TDC) is reached.

In this embodiment, air and fuel are supplied into the cylinder 2 through different supply pipes to form a mixture in the cylinder 2. However, the air and fuel are mixed before being introduced into the cylinder 2. After the mixture is formed, the mixture may be sucked into the cylinder 2. In short, as long as combustion is performed by the above-mentioned lean premixed auto-ignition method, the method of supplying fuel and air is arbitrary.

A piston projection (projection) 3b is formed on the upper part of the piston 3 and the cylinder 2
The cylinder head 2a is formed with a cylinder head recess 2b. Then, the concave portion 2b and the convex portion 3b
Thereby, the sub-combustion chamber 6 having a higher compression ratio than the main combustion chamber 4 is formed.

FIG. 7 shows the dimensions of each part of the engine 1 of FIG.
It is a table shown for each of Example 1, Example 2, and Example 3. The bore diameter D is the diameter of the piston 3 (cylinder 2), the stroke S is the reciprocating distance of the piston 3, and the main chamber volume V is the concave portion 3a formed on the upper part of the piston 3. And the volume of the main combustion chamber 4 when the piston 3 reaches the top dead center (TDC). The projection height h is the height of the piston projection 3b, the sub-chamber depth g is the depth of the cylinder head recess 2b, and the sub-chamber diameter d is It is the diameter of the cylinder head recess 2b. The unit of the table in FIG. 7 is mm.

In FIG. 8, the horizontal axis represents the crankshaft angle (crank angle) θ, and the vertical axis represents the compression ratio ε of the engine 1.
It is a graph that takes The range in which the crank angle θ is changed from 120 ° to 180 ° which is the top dead center (TDC) is shown. The compression ratio is generally defined as piston 3
VT of the main combustion chamber 4 at the top dead center (TDC)
Means the value V0 / VT obtained by dividing the volume V0 of the main combustion chamber 4 at the bottom dead center (BDC), and the “compression ratio ε” in this specification is Compression ratio ε
1. It means the larger value of the compression ratio ε2 of the sub-combustion chamber. Here, the compression ratio ε1 of the main combustion chamber 4 is defined as the main combustion chamber 4 at an arbitrary stroke position S1 of the piston 3.
Means the value V0 / V1 obtained by dividing the volume V0 of the main combustion chamber 4 at the bottom dead center (BDC) by the volume V1. The compression ratio ε2 of the sub-combustion chamber 6 is obtained by dividing the volume v0 of the sub-combustion chamber 6 at the bottom dead center (BDC) by the volume v1 of the sub-combustion chamber 6 at an arbitrary stroke position S1 of the piston 3. Means the value v0 / v1. However, since the sub-combustion chamber 6 functions to ignite a small portion of the air-fuel mixture in the main combustion chamber 4, V
1 >> v1.

As shown in FIG. 8, if the conditions of the parameters other than the compression ratio ε such as the rotation speed of the engine 1, the fuel injection amount, the cooling water temperature, the intake air temperature, and the intake air pressure are fixed, a predetermined The air-fuel mixture in the cylinder 2 self-ignites in the compression ratio range A equal to or higher than the compression ratio threshold value εc (= 14). FIG. 8 shows the ignitable range A in which the air-fuel mixture in the cylinder 2 is self-ignited by hatching.

Hereinafter, with reference to FIG.
The process of igniting and burning the air-fuel mixture (fuel in the air-fuel mixture) in the combustion chamber of the engine 1 for every two or three will be described.

As the piston 3 rises in the compression stroke and the crank angle θ increases, the compression ratio ε of the main combustion chamber 4 increases.
1 rises gradually. In the case of the engine 1 of the first embodiment, when the crank angle θ becomes the angle θ1, the piston protrusion 3b
Begins to be inserted into the piston head recess 2b, and thereafter the compression ratio ε2 of the sub-combustion chamber 6 becomes larger than the compression ratio ε1 of the main combustion chamber 4. When the crank angle θ reaches the angle θ1d, the compression ratio ε2 of the sub-combustion chamber 6 reaches the ignitable range A and the sub-combustion chamber 6
The mixture will self-ignite. At this crank angle θ1d, the compression ratio ε1 of the main combustion chamber 4 does not reach the ignitable range A.

Similarly, in the case of the engine 1 of the second embodiment,
When the crank angle θ becomes the angle θ2 later than in the first embodiment, the piston convex portion 3b starts to be inserted into the piston head concave portion 2b, and thereafter the compression ratio ε2 of the sub-combustion chamber 6 becomes
Is larger than the compression ratio ε1. When the crank angle θ reaches the angle θ2d later than in the first embodiment, the compression ratio ε2 of the sub-combustion chamber 6 reaches the ignitable range A and the sub-combustion chamber 6
The mixture will self-ignite.

Similarly, in the case of the engine 1 of the third embodiment,
Even later than in the case of Embodiment 2, the crank angle θ becomes the angle θ
When it becomes 3, the piston convex part 3b becomes the piston head concave part 2b.
After that, the compression ratio ε2 of the sub-combustion chamber 6 becomes larger than the compression ratio ε1 of the main combustion chamber 4. When the crank angle θ reaches the angle θ3d further later than in the case of the second embodiment, the compression ratio ε2 of the sub-combustion chamber 6 reaches the ignitable range A, and the air-fuel mixture self-ignites in the sub-combustion chamber 6.

When the piston 3 descends during the expansion stroke,
The piston convex portion 3b escapes from the piston head concave portion 2b. At this time, the combustion gas ignited in the sub-combustion chamber 6 is injected into the main combustion chamber 4. Then, the unignited premixed gas is ignited by the jetted combustion gas at each location in the main combustion chamber 4, and the entire air / fuel mixture is ignited not in the local area of the main combustion chamber 4 but in the entire area of the main combustion chamber 4. Will be.

FIG. 9 is a graph in which the horizontal axis represents the crank angle θ and the vertical axis represents the volume V of the main combustion chamber 4. As described above, the combustion gas ignited in the sub-combustion chamber 6 flows out to the main combustion chamber 4, so that the air-fuel mixture is ignited in the main combustion chamber 4 at an angle θd near the top dead center (TDC) of the expansion stroke. The main combustion proceeds.

Here, a comparison will be made with the case of a conventional engine in which the auxiliary combustion chamber 4 does not exist. In the case of the conventional engine, since the compression ratio ε1 is smaller than the compression ratio ε2 of the first embodiment (Examples 1 to 3) (see FIG. 8), the ignitable range A is considerably delayed from the case of the first embodiment. Will be reached. For this reason, the air-fuel mixture in the main combustion chamber 4 is to be ignited at an ignition timing θ ′ which is considerably delayed from the ignition timing θd of the first embodiment (see FIG. 9).

On the other hand, in the case of the first embodiment,
The fuel is ignited early in the combustion chamber 6 having a compression ratio larger than that of the main combustion chamber 4, and the ignited combustion air-fuel mixture flows out to the main combustion chamber 6. The ignition is reliably started early at the ignition timing θd.

That is, according to the first embodiment, the concave portion 2b is formed in the upper portion of the piston 3 and one of the cylinder head 2a without adding a new device (for example, an ignition system device of a spark plug) to the existing engine 1. In addition, with the simple structure of forming the convex portion 3b on the other side, the air-fuel mixture in the main combustion chamber 4 can be accurately and reliably ignited at the desired ignition timing θd.

Various modifications can be made to the embodiment shown in FIG.

Embodiment 2 In the case of the engine 1 of Embodiment 1 shown in FIG. 1, the skirt portion of the convex portion 3b formed on the upper part of the piston 3 is made upright, and the corresponding portion of the cylinder head recess portion 2b is made upright. However, as shown in FIG. 2, the skirt portion of the piston convex portion 3b may have a mountain-like shape, and the corresponding portion of the cylinder head concave portion 2b may have the same mountain-like shape.

In short, the compression ratio ε2 of the sub-combustion chamber 6 (= v0
/ v1) is larger than the compression ratio ε1 (= V0 / V1) of the main combustion chamber 4 and the concave portion 2b and the convex portion 3b may have any shape as long as the condition of V1 >> v1 is satisfied.

Third Embodiment As shown in FIG. 3, apart from a fuel supply device for supplying fuel to the main combustion chamber 4, a sub-fuel supply device for further supplying fuel to an air-fuel mixture in the sub-combustion chamber 6 is provided. A fuel supply device 7 for the combustion chamber may be provided. The fuel supply device 7 for the sub combustion chamber is specifically composed of a fuel pump, a fuel injection pump, and the like. The fuel is further injected into the sub-combustion chamber 6 from the fuel supply device 7 for the sub-combustion chamber, so that the concentration of the air-fuel mixture in the sub-combustion chamber 6 (the ratio of fuel to air) is reduced. Greater than the concentration. Therefore, the ignitability of the air-fuel mixture in the sub-combustion chamber 6 is further improved. Specifically, as shown by the one-dot chain line in FIG. 8, the compression ratio threshold εc at which the air-fuel mixture can be ignited can be made smaller, and the ignition timing in the sub-combustion chamber 6 can be advanced. As a result, the reliability of the ignition of the air-fuel mixture in the main combustion chamber 4 is further improved, and the ignition timing θd of the air-fuel mixture in the main combustion chamber 4 is made closer to the top dead center (TDDC) side. It becomes possible.

Embodiment 4 In the embodiment 1 shown in FIG. 1, the auxiliary combustion chamber 6 is formed at the center of the upper surface of the cylinder head 2a and the piston 3, but as shown in FIG. 6 may be formed on the outer edges of the upper surfaces of the cylinder head 2 a and the piston 3.

FIG. 4A is a front view, and FIG.
FIG. 4C is a top view of the cylinder head 2a shown in FIG.
5 is a top view of the piston 3 shown in FIG.

As shown in FIGS. 4 (a), 4 (b) and 4 (c), a ring-shaped auxiliary combustion chamber 6 is formed at the outer edge of the upper surface of the cylinder head 2a and the piston 3 as viewed from the upper surface.

In the expansion stroke, the ignited air-fuel mixture flows out of the sub-combustion chamber 6 at the outer edge toward the outer edge of the main combustion chamber 4. For this reason, the combustion of the air-fuel mixture at the outer edge portion (near the inner wall surface of the cylinder 2) of the main combustion chamber 4, which is originally difficult to burn, is promoted.

Embodiment 5 Further, the thermal expansion coefficients of the cylinder head concave portion 2b and the piston convex portion 3b may be the same. Specifically, the cylinder head concave portion 2b and the piston convex portion 3b are formed of the same material metal (for example, cast iron). As a result, unnecessary contact between the metal surfaces of the concave portion 2b and the convex portion 3b due to thermal expansion is prevented, and serious damage such as scuffing and seizure can be avoided.

Embodiment 6 As shown in FIG. 6, the surfaces of the cylinder head concave portion 2b and the piston convex portion 3b facing each other may be curved surfaces. Specifically, the upper surface of the piston convex portion 3b is formed in a hemispherical shape, and the corresponding surface of the cylinder head concave portion 2b is formed in the same hemispherical shape. In this way, by forming the surfaces of the cylinder head concave portion 2b and the piston convex portion 3b that face each other into a curved surface, it is possible to prevent generation of a heat spot in the sub-combustion chamber 6.

Embodiment 7 In the above-described Embodiments 1 to 6, the auxiliary combustion chamber 6 is formed by forming the convex portion 3b on the upper part of the piston 3 and forming the concave portion 2b on the cylinder head 2a. Conversely, as shown in FIG. 5, the auxiliary combustion chamber 6 may be formed by forming a concave portion 3c on the upper part of the piston 3 and forming a convex portion 2c on the cylinder head 2a. FIG. 5 shows a case where the sub-combustion chamber 6 is formed at the center of the cylinder head 2a and the upper surface of the piston 3, but as shown in FIG. Is similarly applicable to the case where is formed.

The above-described embodiments 1 to 7 can be appropriately combined with each other as long as they can be combined in terms of the structure of the engine.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a structure of an engine according to a first embodiment.

FIG. 2 is a diagram illustrating a structure of an engine according to a second embodiment.

FIG. 3 is a diagram illustrating a structure of an engine according to a third embodiment.

FIG. 4 is a diagram illustrating a structure of an engine according to a fourth embodiment.

FIG. 5 is a diagram showing a structure of an engine according to a seventh embodiment.

FIG. 6 is a diagram illustrating a structure of an engine according to a sixth embodiment.

FIG. 7 is a table showing dimensions of each part of the engine of FIG. 1 for each of Examples 1, 2, and 3;

FIG. 8 is a graph showing an ignition range of an air-fuel mixture in which air-fuel mixture in a cylinder is ignited in relation to a compression ratio.
It is a graph which shows the ignition timing of the air-fuel mixture of a subcombustion chamber every two or three.

FIG. 9 is a graph showing how the volume of the main combustion chamber changes with respect to the crank angle. FIG. 9 shows the ignition timing of the air-fuel mixture in the main combustion chamber of the embodiment and the ignition of the air-fuel mixture in the conventional main combustion chamber. It is a graph shown in comparison with time.

[Description of Signs] 1 engine 2 cylinder 2a cylinder head 2b cylinder head recess 2c cylinder head protrusion 3 piston 3b piston protrusion 3c piston recess 4 main combustion chamber 6 sub combustion chamber 7 fuel supply device

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Taisuke Muroya 1200 Manda, Hiratsuka-shi, Kanagawa F-term in the Komatsu Ltd. Research Laboratory 3G023 AA01 AB01 AB05 AC04 AD02 AD14 AD23 AD26 AG02 3G092 AA01 AA02 AA06 AA09 AB02 AB03 BA08 DD09 DE03Y FA00 HA04Z HA05Z HB01Z HE01Z HE08Z

Claims (6)

[Claims] An engine that supplies air and fuel to a main combustion chamber formed by a cylinder head and a piston upper surface of an engine, compresses a mixture of the air and fuel, and ignites the fuel at a desired time. A concave portion is formed in one of the upper portion of the piston and the cylinder head and a convex portion is formed in the other, and a sub-combustion chamber having a compression ratio larger than that of the main combustion chamber is formed by the concave portion and the convex portion; An engine that ignites the fuel in the mixture in the main combustion chamber by igniting the fuel and causing the ignited combustion mixture to flow into the main combustion chamber. 2. The engine according to claim 1, further comprising fuel supply means for further supplying fuel to the air-fuel mixture in the sub-combustion chamber. 3. The engine according to claim 1, wherein the sub-combustion chamber is formed at an outer edge of the upper surface of the cylinder head and the piston. 4. The engine according to claim 1, wherein said concave portion and said convex portion have substantially the same thermal expansion coefficient. 5. The engine according to claim 1, wherein surfaces of the concave portion and the convex portion facing each other have a curved shape. 6. An ignition of an engine that supplies air and fuel into a main combustion chamber formed by a cylinder head and a piston upper surface of an engine, compresses a mixture of the air and fuel, and ignites the fuel at a desired time. A method of igniting the fuel in the sub-combustion chamber after forming a sub-combustion chamber having a higher compression ratio than the main combustion chamber by the cylinder head and the piston upper surface; and igniting in the sub-combustion chamber. Igniting the fuel in the air-fuel mixture in the main combustion chamber by causing the combustion air-fuel mixture to flow into the main combustion chamber.