JPH0886218A - Combustion chamber for whirl-chamber diesel engine - Google Patents

Abstract

PURPOSE: To improve an air adoption ratio of a main combustion chamber by providing a diffusion cavity which is recessed in respect to the top surface of a piston independently on a large cavity, and gradually deepend from the center of the piston to an area immediately below injection ports. CONSTITUTION: A main combustion chamber 9 is determined between a cylinder head 2 and a piston 3, while a whirl chamber 5 is determined on the side of the cylinder head 2. Injection ports 6, 7 are opened around the main combustion chamber 9 so as to direct injected flow to the center of the main combustion chamber 9. A pair of cavities, each having an opposed wall 17A substantially circularly formed across a center line of injected flow from the whirl chamber 5 and a guide wall 17B, are recessed on a top surface of the piston 3. A diffusion cavity 11 are recessed independently thereon, which cavity 11 is gradually deepened from the center of the piston 3 to an area immediately below the injection ports 6, 7. It is thus possible to sufficiently improve an air adoption ratio of the main combustion chamber 9 and also improve fuel consumption, output, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a combustion chamber of a swirl chamber type diesel engine.

[0002]

2. Description of the Related Art As a main combustion chamber shape of a conventional swirl chamber type diesel engine, for example, one shown in FIG. 4 is known (see Japanese Patent Application Laid-Open No. 200012/1989).

To explain this, an injection port 6 for ejecting a jet containing fuel from the swirl chamber 5 of the cylinder head 4 opens in the peripheral portion of the main combustion chamber 9 above the piston 3, and the main combustion is seen in the plan view. A dispersion table 13 is formed on the top surface 8 of the piston 3 at a position close to the injection port 6 on the jet center line L toward the center of the chamber 9.

A pair of large cavities 12 are defined by an arc-shaped outer shell 17 symmetrically arranged with the center line L of the jet stream sandwiched in front of the dispersion base 13 which is formed in a substantially diamond shape. .

A part of the outer shell 17 is formed with an opposed wall portion 17A located on the jet center line L and protruding in a substantially V shape.

A side cavity portion 14 is also formed in front of the dispersion table 13 so as to communicate with each other on the left and right, and the side cavity portion 14 also communicates with the large cavity portion 12 on both side surfaces of the dispersion table 13.

An outer shell 18 which defines the lateral cavity portion 14.
Is formed in a circular arc shape along the outer circumference of the piston 3 on the back side of the injection port 6, and on the connection side with the large cavity section 12, a curved guide section 18A is formed so that its curvature is gradually reduced. , The jet gas flowing from the side cavity portion 14 into the large cavity portion 12 is guided toward the tip of the dispersion base 13 so as to join from the tangential direction of the swirling flow generated in the large cavity portion 12. There is.

The large cavity bottom surface 22 is continuous with the large cavity portion 12 and the side cavity portion 14 without a step, and is formed in a plane parallel to the top surface 8 of the piston 3.

The flame jet containing unburned fuel ejected from the swirl chamber 5 to the main combustion chamber 9 through the nozzle 6 as the compression top dead center shifts to the expansion stroke is formed immediately before the jet. When it collides with the dispersion table 13 located at, the swirling flow is generated in the large cavity portions 12 on the left and right with the substantially V-shaped facing wall portion 17A on the jet center line L as a boundary, as shown by an arrow c.

Further, the jet flow branched from the front side of the dispersion base 13 to the lateral cavity portion 14 as shown by an arrow b is guided by the guide portion 18A continuous from the arcuate outer shell 18 to the dispersion base 1
3 is directed inward toward the jet center line L ahead of 3,
The swirl flow of the large cavity portion 12 joins from the tangential direction.

In this way, the jet flow containing the unburned fuel component diffuses combustion to the outside while taking in air while causing a lateral swirling flow in the large cavity portion 12.

[0012]

However, in the shape of the main combustion chamber in which the side cavity portion 14 spreads out at a constant depth in front of the dispersion table 13, the piston 3 has a combustion stroke near the top dead center. In the first half, the jet flow ejected from the injection port 6 into the main combustion chamber 9 is narrowed by the bottom surface of the side cavity portion 14 and resistance is imparted at the outlet portion of the injection port 6, so that gas containing much fuel from the swirl chamber 5 is generated. There is a possibility that the outflow is delayed, the combustion is performed in the swirl chamber 5 in a state where the oxygen concentration is low, and the amount of smoke generated is increased by thermal decomposition.

In particular, in the main combustion chamber shape in which the dispersion table 13 rises between the large cavity portion 12 and the side cavity portion 14, the periphery of the main combustion chamber is arranged so that the jet flow from the swirl chamber is directed toward the center of the main combustion chamber. If a structure with a main injection port that opens to the main part and a sub injection port that is located closer to the center of the piston than the main injection port and connects the main combustion chamber and the swirl chamber is applied, the main injection port passes through the sub injection port before the main injection port in the combustion process. The jet containing a large amount of unburned fuel flowing into the combustion chamber 9 collides with the dispersion table 13 and stays in the side cavity 14, and is subsequently entrained in a flame jet having a low oxygen concentration and a high temperature. As a result of increased combustion, unburned fuel and smoke emissions may increase.

Further, the jet flow ejected from the injection port 6 to the main combustion chamber 9 is narrowed by the bottom surface of the side cavity portion 14, so that the force of the gas flow swirling in the large cavity portion 12 as shown by the arrow c is sufficient. Difficult to strengthen. For this reason, the air utilization ratio cannot be sufficiently increased, which causes a problem of increasing the concentration of unburned fuel components in the exhaust during low load operation or increasing the smoke concentration during high load operation.

It is an object of the present invention to solve the above problems and provide a combustion chamber of a swirl chamber type diesel engine having a high air utilization rate.

[0016]

A combustion chamber of a swirl chamber type diesel engine according to claim 1, wherein a main combustion chamber defined between a cylinder head and a piston and a swirl chamber defined on the cylinder head side. The jet from the swirl chamber opens toward the center of the main combustion chamber, and the jet port opens in the peripheral part of the main combustion chamber, and it is concavely recessed with respect to the top surface of the piston, sandwiching the centerline of the jet from the swirl chamber. With a pair of large cavities that spread in a substantially circular shape,
And a diffusion cavity portion that is recessed into the top surface of the piston independently of the large cavity portion and gradually deepens from the piston center direction to the region directly below the injection port.

According to a second aspect of the present invention, the combustion chamber of the swirl chamber type diesel engine in the first aspect of the present invention constitutes an outer shell that defines a large cavity portion, and its apex faces the jet flow from the swirl chamber. A projecting facing wall portion and a guide wall portion that constitutes an outer shell that defines the large cavity portion and that has its apex projecting facing the facing wall portion are provided.

The combustion chamber of the swirl chamber type diesel engine according to claim 3 includes a main combustion chamber defined between the cylinder head and the piston, and a swirl chamber defined on the cylinder head side.
A main injection port that opens in the peripheral part of the main combustion chamber so that the jet from the swirl chamber goes to the center of the main combustion chamber, and a sub injection port that is located closer to the piston center than the main injection port and connects the main combustion chamber and the swirl chamber. , A pair of large cavities that are concavely recessed with respect to the top surface of the piston and spread out in a substantially circular shape with the center line of the jet flow from the swirl chamber sandwiched between them, and are recessed independently of the large cavity with respect to the top surface of the piston. The recess includes a diffusion cavity portion that is gradually deepened from the center of the piston to a region directly below the main injection port, and a trench portion that is recessed in a concave shape with respect to the top surface of the piston and communicates with the large cavity portion from a region directly below the sub injection port.

A combustion chamber of a swirl chamber type diesel engine according to a fourth aspect is the combustion chamber according to any one of the first to third aspects, in which the diffusion cavity portion is directed from the region directly below the main injection port to each large cavity portion. To form a V-shaped branched portion.

[0020]

In the combustion chamber of the swirl chamber type diesel engine according to the present invention, the combustion is started by injecting and supplying the fuel when the position of the piston is near the top dead center.
Along with the start of combustion in the swirl chamber, a flame jet containing expanded gas and a part of the injected fuel is ejected into the main combustion chamber through the injection port.

In the first half of the combustion stroke in which the piston is in the vicinity of the compression top dead center, the flame jet ejected from the swirl chamber to the main combustion chamber through the injection port is a large cavity on the left and right in the main combustion chamber via diffusion cavities. And is guided to the outer shell to generate a lateral swirling flow in the large cavity.

Since the diffusion cavity is recessed so as to become gradually deeper from the center of the piston to the region directly below the injection port, when the piston is near the compression top dead center and the volume of the main combustion chamber is small. A flow path having a sufficient cross-sectional area is defined between the piston and the main combustion chamber side opening of the injection port. As a result, the jet flow ejected from the injection port into the main combustion chamber is not greatly throttled through the diffusion cavity, so the resistance applied at the outlet of the injection port is suppressed to a low level, and the gas containing a large amount of fuel from the swirl chamber is suppressed. Quickly flow out into the main combustion chamber. As a result, it is possible to suppress combustion in the swirl chamber in a state where the oxygen concentration is low, and reduce the amount of smoke generated.

Since the diffusion cavity portion is recessed so as to become gradually shallower from the region directly below the injection port toward the center of the piston, the jet flow ejected from the injection port to the main combustion chamber is in the process of passing through the diffusion cavity portion. A vertical swirl component is imparted to the upper part and is diffused while taking in air such as a valve recess recessed in the upper surface of the cylinder head.

Since the diffusion cavity has a structure in which it is dented on the top surface of the piston independently of the large cavity, the degree of freedom in setting the depth is high, and the piston descends from the compression top dead center from the first half to the second half of the combustion stroke. However, the jet flow ejected from the injection port to the main combustion chamber hits the diffusion cavity portion and can be diffused through the diffusion cavity portion.

In this way, from the first half to the second half of the combustion stroke, the jet flow containing the unburned fuel component propagates and diffuses in a wide area of the main combustion chamber while generating a strong swirling flow in the large cavity. The air utilization rate in the combustion chamber can be increased. Smoke generated in the swirl chamber is re-combusted in the main combustion chamber, and the smoke emission amount under high load can be significantly reduced.

Since the diffusion cavity portion ensures a sufficient flow passage cross-sectional area for the flame jet from the nozzle, the degree of freedom in setting the depth of the large cavity portion is increased, and the volume ratio of the large cavity portion to the swirl chamber is increased. , The compression ratio can be set to an appropriate value.

In the combustion chamber of the swirl chamber type diesel engine according to the second aspect, the jet flow that diffuses to the central portion of the main combustion chamber through the diffusion cavity portion hits the facing wall portion that opposes this and projects its apex. A swirling component that splits the flow is given to each large cavity, and its apex is guided by a guide wall that protrudes facing the facing wall to generate a strong swirling flow in each large cavity while taking in air. Combustion spreads to the outside.

In this way, the jet containing the unburned fuel component ejected from the swirl chamber to the main combustion chamber propagates and diffuses in a wide area of the main combustion chamber while generating a strong swirling flow in the large cavity. , The air utilization rate in the main combustion chamber can be increased. Smoke generated in the swirl chamber is re-combusted in the main combustion chamber, and the smoke emission amount under high load can be significantly reduced.

In a combustion chamber of a swirl chamber type diesel engine according to claim 3, a flame jet which is ejected from the swirl chamber to the main combustion chamber through the auxiliary jet port in the first half of the combustion stroke in which the piston is in the vicinity of the compression top dead center. In the main combustion chamber, diffuses into each large cavity through the diffusion cavity, and the flame jet ejected from the swirl chamber through the main injection port into the main combustion chamber is It diffuses into the large cavity and is guided by the outer shell to generate a lateral swirling flow in the large cavity.

Since the jet gas containing a large amount of fuel, which is jetted from the auxiliary jet port to the main combustion chamber prior to the main jet port, is guided to the trench portion and rapidly diffuses to each large cavity portion, the oxygen jetted from the main jet port is generated. Smoke is suppressed from being generated by thermal decomposition without being caught in a high-temperature flame with low concentration.

Since the diffusion cavity portion is recessed so as to become gradually deeper from the center of the piston to the region immediately below the main injection port, when the piston is near the compression top dead center and the volume of the main combustion chamber is small. In addition, a flow path having a sufficient cross-sectional area is defined between the opening of the main injection port on the main combustion chamber side and the piston. As a result, the jet flow ejected from the main injection port into the main combustion chamber is not greatly throttled through the diffusion cavity, so the resistance applied at the outlet of the main injection port is suppressed to a small amount, and a large amount of fuel is discharged from the swirl chamber. The contained gas quickly flows out to the main combustion chamber. As a result, it is possible to suppress combustion in the swirl chamber in a state where the oxygen concentration is low, and reduce the amount of smoke generated.

Since the diffusion cavity portion is recessed so as to gradually become shallower from the region directly below the main injection port toward the center of the piston, the jet flow ejected from the main injection port into the main combustion chamber is the main combustion in the process of passing through the diffusion cavity portion. A vertical swirl component is imparted to the upper part of the chamber and diffuses while taking in air such as a valve recess recessed in the upper surface of the cylinder head.

In this way, from the first half to the latter half of the combustion stroke, the jet flow containing the unburned fuel component propagates and diffuses in a wide area of the main combustion chamber while generating a strong swirl flow in the large cavity. The air utilization rate in the combustion chamber can be increased. Smoke generated in the swirl chamber is re-combusted in the main combustion chamber, and the smoke emission amount under high load can be significantly reduced.

In the combustion chamber of the swirl chamber type diesel engine according to claim 4, the jet flow that diffuses through the diffusion cavity portion to the central portion of the main combustion chamber is bent toward each large cavity portion through the diffusion cavity portion. As a result, a strong swirl flow is generated in each large cavity portion, and the jet force force that goes straight from the main injection port, goes over the outer shell of the large cavity portion and collides with the cylinder bore can be reduced, and quench of combustion flame can be reduced. .

[0035]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

In FIG. 2, 1 is a cylinder block, 2
Is a cylinder head, and 3 is a piston. A main combustion chamber 9 is defined between the lower surface 10 of the cylinder head 2 and the top surface 8 of the piston 3. The lower surface 10 of the cylinder head 2 and the top surface 8 of the piston 3, which define the main combustion chamber 9, are each formed in a plane shape orthogonal to the piston center line (cylinder axis) C.

On the lower surface 10 of the cylinder head, not shown, 2
The two valve recesses are recessed, and an intake valve and an exhaust valve are provided in each valve recess.

A substantially spherical swirl chamber 5 is defined between the cylinder head 2 and the hot plug 31 fitted from the lower surface 10 thereof. The swirl chamber 5 includes a fuel injection valve 32 and a glow plug 3
3 is arranged so as to face the upper part thereof.

The main combustion chamber 9 and the swirl chamber 5 communicate with each other through the main injection port 6 and the sub injection port 7 having a relatively small diameter.

As shown in FIG. 1, the main injection port 6 has a main combustion chamber 9
The auxiliary injection port 7 is located closer to the center of the piston than the main injection port 6 and is open to the peripheral portion of the communication port with the swirl chamber 5. The main injection port 6 and the sub injection port 7 are arranged on the jet center line L intersecting the center of the piston in the plan view.

The main injection port 6 has a flat cross-sectional shape in a direction orthogonal to the jet flow center line L, and the sub injection port 7 has a circular cross-sectional shape.

The main injection port 6 is formed so as to be inclined with respect to the center line C of the piston at a predetermined angle. The main injection port 6 opens in the tangential direction to the substantially spherical swirl chamber 5, and most of the air compressed in the main combustion chamber 9 in the compression stroke in which the piston 3 rises is swirled through the main injection port 6. Pushed into chamber 5, swirl chamber 5
A vortex flow (longitudinal swirl flow) is generated.

A part of the air compressed in the main combustion chamber 9 in the compression stroke in which the piston 3 rises is pushed into the swirl chamber 5 through the auxiliary injection port 7 and is generated in the swirl chamber 5 through the main injection port 6. Facing the vortex flow.

Combustion is started when the position of the piston 3 is near the top dead center and fuel is injected and supplied from the fuel injection valve 32. With the start of combustion in the swirl chamber 5, the expanded gas and a part of the unburned fuel are ejected into the main combustion chamber 9 through the auxiliary injection port 7 and the main injection port 6 and mixed with the air in the main combustion chamber 9. While burning. The opening of the auxiliary injection port 7 on the side of the swirl chamber 5 is open at a portion of the inner wall of the swirl chamber 5 that faces the fuel injection direction of the fuel injection valve 32. The auxiliary injection port 7 communicates with the stagnation region 19 that is recessed in a concave shape with respect to the substantially spherical swirl chamber 5, and is arranged in the fuel injection direction of the fuel injection valve 32. As a result, a large amount of unburned fuel is ejected into the main combustion chamber 9 through the auxiliary injection port 7 in the combustion process.

Concavely recessed with respect to the top surface 8 of the piston 3,
A pair of large cavities 12 are formed from the swirl chamber 5 so as to spread in a substantially circular shape across the center line L of the jet flow.

Each of the large cavities 12 is defined by a bottom surface 22 formed in a plane orthogonal to the piston center line C and an arc-shaped outer shell 17 symmetrically arranged with the jet center line L interposed therebetween. To be done.

Since a jet flow from the swirl chamber 5 causes a lateral swirling flow in each large cavity portion 12, a part of the outer shell 17 is located on the jet center line L and protrudes in a substantially V shape. The facing wall portion 17A is formed.

A guide wall portion 17B is formed in a part of the outer shell 17 so that its apex faces the facing wall portion 17A on the jet flow center line L and projects in a substantially V shape.

In order to quickly diffuse the jet flow from the swirl chamber 5 into the main combustion chamber 9, a diffusion cavity portion is formed on the top surface 8 of the piston 3 and is concave in the extension direction of the main injection port 6 and the sub injection port 7. 11 is formed.

The diffusion cavity portion 11 is recessed in the top surface 8 of the piston 3 independently of each large cavity portion 12 and spreads from the region directly below the main combustion chamber side opening of the main injection port 6 toward the center of the piston. .

An opening edge portion of the diffusion cavity portion 11 with respect to the top surface 8 of the piston 3 is located on the piston center side and an opening edge portion 14A curved in an arc along the main combustion chamber side opening portion of the main injection port 6. And has an opening edge portion 14B extending linearly.

The bottom of the diffusion cavity portion 11 is recessed with a cross section curved in an arc shape, and the maximum depth thereof is larger than the depth of the large cavity portion 12.

The bottom of the diffusion cavity 11 has a main injection port 6
It has an upstream-side inclined portion 16A that inclines along with, and a downstream-side inclined portion 16B that becomes gradually deeper from the piston center direction to the region directly below the main injection port 6. The downstream side inclined portion 16B is
It serves to reflect the jet flow ejected from the main injection port 6 to the main combustion chamber 9 to the upper part of the main combustion chamber 9.

With the above construction, the operation will be described below.

Most of the air compressed in the main combustion chamber 9 in the compression stroke in which the piston 3 rises is pushed into the swirl chamber 5 through the main injection port 6 and a swirl flow is generated in the swirl chamber 5. The air flow pushed through the sub injection port 7 has a force that tends to swirl in the opposite direction to the vortex flow generated in the vortex chamber 5. The sub-injection port 7 communicates with the stagnation region 19 that is recessed with respect to the substantially spherical swirl chamber 5, and is arranged in the fuel injection direction of the fuel injection valve 32. Therefore, a large amount of unburned fuel is generated in the combustion stroke. It is ejected to the main combustion chamber 9 through the sub injection port 7.

Combustion is started when fuel is injected and supplied from the fuel injection valve 32 when the position of the piston 3 is near the top dead center. Along with the start of combustion in the swirl chamber 5, a flame jet containing expanded gas and a part of the injected fuel is ejected to the main combustion chamber 9 through the sub injection port 7 and the main injection port 6 and mixed with the air in the main combustion chamber 9. While burning.

In the first half of the combustion stroke in which the piston 3 is in the vicinity of the compression top dead center, the flame jet ejected from the swirl chamber 5 to the main combustion chamber 9 through the main injection port 6 and the sub injection port 7 is in the main combustion chamber 9. It diffuses to the left and right large cavity portions 12 via the diffusion cavity portion 11 and is guided by the outer shell 17 to generate a swirling flow in the large cavity portion 12.

Since the diffusion cavity portion 11 is recessed so as to become deepest in the region directly below the main injection port 6 and the sub injection port 7, the piston 3 is located near the compression top dead center and the main combustion chamber 9 is located.
When the volume is small, a flow path having a sufficient cross-sectional area with the main combustion chamber 9 side openings of the main injection port 6 and the sub injection port 7 is defined. Thereby, the main injection port 6 and the sub injection port 7
The jet flow ejected from the main combustion chamber 9 from the diffusion cavity portion 1
1, the resistance imparted at the outlets of the main injection port 6 and the sub injection port 7 is suppressed to a low level, and the jet gas containing a large amount of fuel from the swirl chamber 5 quickly enters the main combustion chamber 9. leak. As a result, it is possible to suppress combustion in the swirl chamber 5 in a state where the oxygen concentration is low, and reduce the amount of smoke generated.

Further, the jet flow ejected from the main injection port 6 and the sub injection port 7 into the main combustion chamber 9 is not greatly narrowed through the diffusion cavity portion 11, and the speed of ejection from the main injection port 6 and the sub injection port 7 is increased. Thus, the air flow in the main combustion chamber 9 is strengthened.

In the process of passing through the diffusion cavity portion 11, the jet flow ejected from the main injection port 6 and the sub injection port 7 is diffused along the upstream side inclined portion 16A and then reflected on the downstream side inclined portion 16B. Then, it is directed to the upper part of the main combustion chamber 9.
As a result, a vertical swirling component is imparted and diffuses while taking in air such as a valve recess recessed in the upper surface of the cylinder head 2.

The jet flow diffusing into the central portion of the main combustion chamber 9 through the diffusion cavity portion 11 hits the facing wall portion 17A protruding in a substantially V shape on the jet center line L, and is branched into the left and right large cavity portions 12. The swirl component is imparted, and the combustion is diffused outward while taking in air while generating a strong swirl flow in each large cavity portion 12 by being guided by the substantially V-shaped guide wall portion 17B.

Since the diffusion cavity portion 11 is recessed in the top surface 8 of the piston 3, the degree of freedom in setting the depth is high, and even if the piston 3 descends from the compression top dead center during the first half and the second half of the combustion stroke. The jet flow ejected from the main injection port 6 and the sub injection port 7 into the main combustion chamber 9 hits the diffusion cavity portion 11 and can be diffused through the diffusion cavity portion 11.

In this way, from the first half to the latter half of the combustion stroke, the jet flow containing the unburned fuel component is the large cavity portion 1
In 2, the strong swirl flow is generated and propagated and diffused in a wide area of the main combustion chamber 9, and the air utilization rate in the main combustion chamber 9 can be increased. Smoke generated in the swirl chamber 5 is re-combusted in the main combustion chamber 9, and the smoke discharge amount under high load can be significantly reduced.

Since the diffusion cavity portion 11 ensures a sufficient flow passage cross-sectional area for the flame jets from the main injection port 6 and the sub injection port 7, the degree of freedom in setting the depth of the large cavity portion 12 is increased, and the large cavity is increased. It is possible to set the volume ratio of the portion 12 to the swirl chamber 5 and the compression ratio to appropriate values.

Next, another embodiment shown in FIG. 3 will be described. It should be noted that the same reference numerals are used for the portions corresponding to those in FIGS. 1 and 2.

Concavely recessed with respect to the top surface 8 of the piston 3,
A trench portion 25 that communicates with the large cavity portion 12 from a region directly below the sub injection port 7 is formed.

The outer shell 26 defining the trench portion 25 is curved along the opening of the auxiliary injection port 7 on the main combustion chamber 9 side and is curved in an arc shape with respect to the outer shell 17 defining the large cavity portion 12. While continuing.

A branch portion 27 is formed in the diffusion cavity portion 11 so as to extend in a V-shape from a region directly below the main injection port 6 toward each large cavity portion 12. Each branch portion 27 is a trench portion 2
5 is extended to each large cavity part 12 so as to bypass.

With the above arrangement, the operation will be described.

In the first half of the combustion stroke, the jet gas containing a large amount of fuel, which is ejected from the sub-injection port 7 into the main combustion chamber 9 prior to the main injection port 6, is guided to the trench portion 25 and quickly flows into the left and right large cavity portions 12. Therefore, the smoke is prevented from being caught in the high-temperature flame jet having a low oxygen concentration and ejected from the main injection port 6, and the generation of smoke due to thermal decomposition can be suppressed.

From the first half to the latter half of the combustion process, the jet flow ejected from the main injection port 6 to the main combustion chamber 9 is bent toward the left and right large cavity portions 12 while bypassing the trench portion 25 via the diffusion cavity portion 11. Therefore, the force of the swirl flow generated in each large cavity portion 12 is strengthened, and the jet force force that goes straight from the main injection port 6 and goes over the outer wall of the large cavity portion to collide with the cylinder bore is weakened to quench the combustion flame. Can be reduced.

[0072]

As described above, the combustion chamber of the swirl chamber type diesel engine according to claim 1 is defined on the cylinder head side and the main combustion chamber defined between the cylinder head and the piston. The swirl chamber, the jet port that opens toward the center of the main combustion chamber so that the jet from the swirl chamber opens in the peripheral portion of the main combustion chamber, and the center line of the jet from the swirl chamber that is recessed in a concave shape with respect to the top surface of the piston. It has a pair of large cavities that spread out in a substantially circular shape with the gap between them, and a diffusion cavity that is recessed into the top surface of the piston independently of the large cavity and gradually deepens from the center of the piston to the region directly below the injection port. As a result, the jet gas containing a large amount of fuel is swiftly discharged from the swirl chamber into the main combustion chamber, and the swirl flow generated in the main combustion chamber via the diffusion cavity is strengthened to ensure a sufficient air utilization rate in the main combustion chamber. Raise to With to improve the fuel efficiency and output,
It is possible to reduce the concentration of unburned fuel components in the exhaust during low load operation, and reduce the smoke concentration during high load operation.

The combustion chamber of the swirl chamber type diesel engine according to a second aspect of the present invention is, in the invention according to the first aspect, an outer shell that defines a large cavity portion, and its apex faces a jet flow from the swirl chamber. Ejecting from the swirl chamber to the main combustion chamber during the combustion process because it has a protruding opposing wall portion and an outer shell that defines the large cavity portion, and the apex of the guide wall portion protrudes facing the opposing wall portion. The jet flow containing the unburned fuel component that is generated propagates and spreads in a wide area of the main combustion chamber while generating a strong swirl flow in the large cavity through the opposing wall portion and the guide wall portion. The air utilization rate can be increased. Smoke generated in the swirl chamber is re-combusted in the main combustion chamber, and the smoke emission amount under high load can be significantly reduced.

The combustion chamber of the swirl chamber type diesel engine according to claim 3 comprises a main combustion chamber defined between the cylinder head and the piston, and a swirl chamber defined on the cylinder head side.
A main injection port that opens in the peripheral part of the main combustion chamber so that the jet from the swirl chamber goes to the center of the main combustion chamber, and a sub injection port that is located closer to the piston center than the main injection port and connects the main combustion chamber and the swirl chamber. , A pair of large cavities that are concavely recessed with respect to the top surface of the piston and spread out in a substantially circular shape with the center line of the jet flow from the swirl chamber sandwiched between them, and are recessed independently of the large cavity with respect to the top surface of the piston. The depression, a diffusion cavity portion that gradually becomes deeper from the piston center direction to the region directly below the main injection port, and a concave portion that is recessed with respect to the top surface of the piston and has a trench portion that communicates with the large cavity portion from the region immediately below the sub injection port, In the first half of the combustion process, the jet gas containing a large amount of fuel ejected from the sub-injection into the main combustion chamber prior to the main injection is guided to the trench and rapidly diffuses into each large cavity,
It is possible to prevent smoke from being generated due to thermal decomposition without being caught in a high-temperature flame with a low oxygen concentration ejected from the main injection port.

A combustion chamber of a swirl chamber type diesel engine according to a fourth aspect of the present invention is the combustion chamber according to any one of the first to third aspects, in which the diffusion cavity portion is directed from the region directly below the main injection port to each large cavity portion. Since a branch portion extending in a V-shape is formed, the jet flow that diffuses into the main combustion chamber through the diffusion cavity portion in the combustion process is bent toward each large cavity portion through the diffusion cavity portion, and thus each large cavity portion It is possible to reduce the quench of combustion flame by generating a strong swirl flow in the section, weakening the jet force that goes straight from the main injection port, goes over the outline of the large cavity section, and collides with the cylinder bore.

[Brief description of drawings]

FIG. 1 is a plan view of a piston showing an embodiment of the present invention.

FIG. 2 is a sectional view of the same engine.

FIG. 3 is a plan view of a piston showing another embodiment.

FIG. 4 is a plan view of a piston showing a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cylinder block 2 Cylinder head 3 Piston 5 Vortex chamber 6 Main injection port 7 Sub injection port 8 Piston top surface 9 Main combustion chamber 11 Diffusion cavity part 16A Upstream sloped part 16B Downstream sloped part 17 Large cavity outer shell 17A Opposed wall part 17B Guide Wall part 25 Trench part 26 Trench part outer shell 27 Branch part

Claims (4)

[Claims] 1. A main combustion chamber defined between a cylinder head and a piston, a swirl chamber defined on the cylinder head side, and a main combustion chamber in which a jet flow from the swirl chamber is directed toward the center of the main combustion chamber. A jet port that opens in the peripheral part of the chamber, a pair of large cavities that are concavely recessed with respect to the top surface of the piston, and spread in a roughly circular shape with the centerline of the jet from the swirl chamber sandwiched, and the top surface of the piston A combustion chamber of a swirl chamber type diesel engine, comprising: a diffusion cavity portion that is recessed independently of the large cavity portion and gradually deepens from the direction of the center of the piston to the region directly below the injection port. 2. An outer shell defining a large cavity portion,
An abutting wall portion whose apex protrudes in opposition to the jet flow from the swirl chamber, and a guide wall portion which forms an outer shell defining a large cavity and whose apex protrudes in opposition to the abutting wall portion. The combustion chamber of the swirl chamber type diesel engine according to claim 1. 3. A main combustion chamber defined between a cylinder head and a piston, a swirl chamber defined on the cylinder head side, and a main combustion chamber in which a jet flow from the swirl chamber is directed toward the center of the main combustion chamber. Main jet port that opens to the periphery of the chamber, a sub jet port that is located closer to the center of the piston than the main jet port, and that connects the main combustion chamber and the swirl chamber, and a jet recess from the swirl chamber that is recessed in the top surface of the piston. A pair of large cavities that spread out in a roughly circular shape across the center line of the piston and a diffusion cavity that is recessed in a concave shape independent of the large cavity with respect to the top surface of the piston and gradually deepens from the piston center direction to the area immediately below the main injection port. A combustion chamber of a swirl chamber type diesel engine, comprising: a portion, and a trench portion that is recessed in a concave shape with respect to the top surface of the piston and communicates with a large cavity portion from a region directly below the auxiliary injection port. 4. The diffusion cavity portion is formed with a branch portion extending in a V-shape from a region directly below the main injection port toward each large cavity portion, according to any one of claims 1 to 3. Vortex chamber type diesel engine combustion chamber.