Swirl chamber-type diesel engine

A swirl chamber-type diesel engine includes a secondary combustion chamber assembly coupled to a cylinder head to define a secondary combustion chamber having, on an inner wall surface thereof, a curved swirl induction part, and a connecting passage formed at a lower end of the swirl induction part, and a piston defining a primary combustion chamber and including a trench part being in communication with the connecting passage, and clover parts formed at both sides of the trench part, in which a guide structure is provided in the connecting passage, and the guide structure divides combustion gas, discharged from the secondary combustion chamber to the primary combustion chamber, into three portions and guides the combustion gas.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a National Stage of International Application No. PCT/KR2018/009235 filed on Aug. 13, 2018, which claims the benefit of Korean Patent Application No. 10-2017-0110082 filed on Aug. 30, 2017 and Korean Patent Application No. 10-2017-0122005 filed on Sep. 21, 2017 with the Korean Intellectual Property Office, the entire contents of each hereby incorporated by reference.

FIELD OF TECHNOLOGY

The present invention relates to a swirl chamber-type diesel engine and, more specifically, to a swirl chamber-type diesel engine provided with a guide structure in a connecting passage for connecting a secondary combustion chamber and a primary combustion chamber in the swirl chamber-type diesel engine, the guide structure being capable of dividing combustion gas, discharged from the secondary combustion chamber to the primary combustion chamber, into three portions and guiding the combustion gas, thereby facilitating diffusion combustion in the diesel engine and inhibiting harmful gas, such as smog, from being produced.

BACKGROUND

There is no great intrinsic difference between diesel engines and gasoline engines in terms of main structures (cylinder heads, cylinder blocks, piston connecting assemblies, crank shafts, cam shafts, and valve mechanisms) that convert thermal energy into mechanical energy.

However, there is a difference between the gasoline engine and the diesel engine in terms of processes of combusting fuel. While the gasoline engine compresses a gas mixture of air and fuel and then ignites the fuel by producing an electrical flame, the diesel engine ignites fuel by means of autoignition (compression ignition) by drawing only air, compressing the air at a high compression ratio so that a temperature of air is raised to 500 to 600° C. or higher, pressing the fuel with an injection pump, and then injecting the fuel into a cylinder from an injection nozzle.

A combustion chamber of the diesel engine needs to meet the following requirements. That is, the injected fuel needs to be completely combusted within a short period of time as quickly as possible, an average effective pressure needs to be high, and a fuel consumption rate needs to be low. In addition, a combustion state needs to be good even at a high rotational speed, the diesel engine needs to operate easily, and diesel knock needs to be less generated.

The injection nozzle is installed in the cylinder head and provided above the combustion chamber. The injection nozzle is a device configured to inject into the combustion chamber the finely atomized high-pressure fuel supplied from the injection pump. The fuel spray injected from the injection nozzle needs to be excellent in atomization and penetration properties and needs to be evenly injected and to have an appropriate injection degree and rate. A flow coefficient of the nozzle also needs to be accurate.

Based on the type of combustion chamber, diesel engines are classified as a direct-injection chamber-type diesel engine, which is a single chamber-type diesel engine; a pre-combustion chamber-type diesel engine, which is a double chamber-type diesel engine; and a swirl chamber-type diesel engine. The direct-injection chamber-type diesel engine has a structure in which a combustion chamber is defined by a cylinder head and a concave-convex portion provided on a piston head, and fuel is injected directly into the combustion chamber. The direct-injection chamber-type diesel engine is called a single chamber-type diesel engine because the direct-injection chamber-type diesel engine has only a primary combustion chamber. The combustion chamber has a heart shape, a spherical shape, a hemispheric shape, or the like.

The pre-combustion chamber-type diesel engine has a structure in which a combustion chamber is provided above a primary combustion chamber formed between a piston and a cylinder head; part of injected fuel is combusted in the pre-combustion chamber to produce high-temperature, high-pressure gas; and the remaining part of the fuel is injected into the primary combustion chamber and then completely combusted by the high-temperature, high-pressure gas.

The swirl chamber-type diesel engine has a swirl chamber provided in a cylinder or a cylinder head, such that a swirl is generated in the swirl chamber in a compression stroke. When fuel is injected into the swirl chamber, the injected fuel is ignited and combusted by being mixed with swirling air and then discharged into a primary combustion chamber. Further, in the primary combustion chamber, noncombusted fuel is combusted by being mixed with new air.

FIG. 1is a view illustrating an internal structure of a combustion chamber of a swirl chamber-type diesel engine in the related art.FIG. 1mainly illustrates a structure of a secondary combustion chamber (swirl chamber)2a.

Referring toFIG. 1, the secondary combustion chamber2ais provided as a secondary combustion chamber assembly2is separately assembled in a cylinder head1. A primary combustion chamber3ais formed in an upper surface of a piston3. In the cylinder head1, an injection nozzle4is provided at a center upper end of the secondary combustion chamber2aso as to eccentrically inject fuel into the secondary combustion chamber2a. A glowplug5is mounted at an upper end of the secondary combustion chamber2a. The glowplug5is installed because a temperature in the combustion chamber is low when the engine starts or operates at a low speed. A connecting passage2bis inclinedly provided at a lower end of the secondary combustion chamber2a, and the air is introduced from the primary combustion chamber3athrough the connecting passage2b. The connecting passage2bis mainly provided in a direction tangential to the secondary combustion chamber2a. Further, a coolant passage1ais formed at the periphery of the secondary combustion chamber2a.

In the compression stroke in the swirl chamber-type combustion chamber configured as described above, a strong swirl is generated, as indicated by the arrows (A inFIG. 1), when compressed air introduced from the primary combustion chamber3aflows into the secondary combustion chamber2athrough the connecting passage2b. At this time, the fuel is injected from the injection nozzle4, and the fuel is mostly combusted in the secondary combustion chamber2a.

The swirl chamber-type combustion chamber in the related art is a Comet Vb type invented by Ricardo. In particular, as illustrated inFIG. 2, the shape of the secondary combustion chamber assembly2may include a fuel collision part2chaving a straight cross-sectional shape with which the fuel injected from the injection nozzle4collides and a swirl induction part2dhaving a curved shape. In this case, the connecting passage2bis structured to be tangential to the swirl induction part2d. In particular, as illustrated inFIG. 2, the shape of the connecting passage2bhas a one-piece cross-sectional shape defining an arc tangential to two circles.

Because of the shape of the connecting passage2bstructured as described above, diffusion of the combusted gas mixture is concentrated in a straight direction when the gas mixture combusted in the secondary combustion chamber2ais discharged into the primary combustion chamber3a. For this reason, swirls cannot be appropriately formed in the left and right clover parts, which causes a deterioration in diffusion combustion and an increase in emission of harmful substances in exhaust gas, particularly smog.

The present invention has been made in an effort to solve the aforementioned problems, and an object of the present invention is to provide a swirl chamber-type diesel engine that divides a gas mixture, discharged from a secondary combustion chamber2ato a primary combustion chamber3a, into three portions and guides and discharges the gas mixture, thereby facilitating diffusion in a straight direction and promoting swirls in left and right clover parts, and thus effectively inhibiting the production of harmful substances, such as smog, included in exhaust gas.

The detailed objects of the present invention will be apparently identified and understood by experts or researchers in this technical field through the specific description disclosed below.

SUMMARY

In order to achieve the aforementioned object, a swirl chamber-type diesel engine according to an exemplary embodiment of the present invention includes a secondary combustion chamber assembly2coupled to a cylinder head1to define a secondary combustion chamber2ahaving, on an inner wall surface thereof, a curved swirl induction part2d, a connecting passage2bformed at a lower end of the swirl induction part2d, a piston3defining a primary combustion chamber3aand including a trench part3cbeing in communication with the connecting passage2b, and clover parts3bformed at both sides of the trench part3c, in which a guide structure2eis provided in the connecting passage2b, and the guide structure2edivides combustion gas, discharged from the secondary combustion chamber2ato the primary combustion chamber3a, into three portions and guides the combustion gas.

In this case, the three portions of the combustion gas, which are divided and guided by the guide structure2e, may be guided to be introduced into the trench part3cin a straight direction or introduced into the clover parts3bat both sides of the trench part3c.

In addition, the guide structure2emay include three curved shapes provided on an upper surface of the connecting passage2band disposed adjacent to one another.

In this case, the three curved shapes provided on the upper surface of the connecting passage2bmay have the same shape throughout the connecting passage2b.

In this case, the three curved shapes provided on the upper surface of the connecting passage2bmay have the same radius.

In addition, the guide structure2emay include a first guide groove21epositioned at a center thereof and second and third guide grooves22eand23epositioned at both sides of the first guide groove21e, and a center of the first guide groove21emay be positioned at a higher position than a straight line that connects a center of the second guide groove22eand a center of the third guide groove23e.

In addition, the guide structure2emay include a first guide groove21epositioned at a center thereof and second and third guide grooves22eand23epositioned at both sides of the first guide groove21e, and a distance D between the second guide groove22eand the third guide groove23emay be three times a radius r of the first guide groove21e(D=3r).

Further, the guide structure2emay include a first guide groove21epositioned at a center thereof and second and third guide grooves22eand23epositioned at both sides of the first guide groove21e, and the first guide groove21emay be positioned at a higher position than the second guide groove22eand the third guide groove23e.

Here, the first guide groove21e, the second guide groove22e, and the third guide groove23emay approximately uniformly divide the combustion gas and guide the combustion gas.

In this case, the first guide groove21e, the second guide groove22e, and the third guide groove23emay have the same cross-sectional area.

Further, a bottom surface of the clover part3bmay have a stereoscopic structure in which a height of a bottom surface in a second region, which is distant in a direction of a flow of the combustion gas at a predetermined distance from a first region into which the combustion gas is introduced from the trench part3c, is greater than a height of a bottom surface in the first region.

In this case, the bottom surface of the clover part3bmay have a stereoscopic structure in which the height of the bottom surface is gradually increased in the direction of the flow of the combustion gas so that the introduced combustion gas flows while being gradually raised.

In addition, the clover parts3bmay have cylindrical structures disposed adjacent to both sides of the trench part3c, and each may include a spiral structure in which the height of the bottom surface is gradually increased in the direction of the flow of the combustion gas.

Further, the clover part3bmay have a structure in which the height of the bottom surface is gradually increased toward an outer periphery thereof.

In addition, the bottom surface of the trench part3cmay have a predetermined gradient so that the combustion gas to be introduced into the clover part3bis introduced while being raised.

The swirl chamber-type diesel engine according to the exemplary embodiment of the present invention is provided with the guide structure in the connecting passage for connecting the secondary combustion chamber and the primary combustion chamber in the swirl chamber-type diesel engine, and the guide structure may divide combustion gas into three portions and guide the combustion gas. Since the combustion gas discharged from the secondary combustion chamber to the primary combustion chamber is divided, guided, and discharged, it is possible to facilitate diffusion combustion in the diesel engine and to inhibit the production of harmful gas, such as smog.

Further, in the swirl chamber-type diesel engine according to the exemplary embodiment of the present invention, each of the bottom surfaces of the clover parts positioned at the periphery of the trench part in the primary combustion chamber of the swirl chamber-type diesel engine is implemented to have a helical stereoscopic structure, as a result of which it is possible to improve the oxidation capability of the diesel engine and to effectively inhibit the production of harmful substances such as particulate matters (PM) included in exhaust gas.

DETAILED DESCRIPTION

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. First, in assigning reference numerals to constituent elements of the respective drawings, it should be noted that the same constituent elements will be designated by the same reference numerals, if possible, even though the constituent elements are illustrated in different drawings. In addition, in the description of the present invention, the specific descriptions of publicly known related configurations or functions will be omitted when it is determined that the specific descriptions may obscure the subject matter of the present invention. Further, the exemplary embodiments of the present invention will be described below, but the technical spirit of the present invention is not limited thereto and may of course be carried out by those skilled in the art.

First, a configuration and an operation of a general swirl chamber-type diesel engine will be schematically described with reference toFIGS. 3A and 3Band then technical features of the present invention will be described.

More specifically, there is enough time to form a gas mixture in medium and large diesel engines, and thus the contact between fuel and air may be sufficiently achieved only by injecting the fuel. However, in a small or high-speed diesel engine, it is difficult to complete combustion in a short period of time without the aid of a swirl of air. In order to solve this problem, various types of combustion chamber structures, such as a swirl chamber-type combustion chamber structure, are used. In particular, a swirl chamber-type diesel engine is structured to combust fuel by injecting the fuel into a swirl formed in a secondary combustion chamber2ain a compression stroke.

As illustrated inFIG. 3A, the swirl chamber-type diesel engine may generally include a primary combustion chamber3aand the secondary combustion chamber2a. In this case, the secondary combustion chamber2amay be formed as a secondary combustion chamber assembly2is provided in a cylinder head1.

In addition, the primary combustion chamber3amay be formed in an upper surface of a piston3.

An injection nozzle4is provided at an upper end of a center of the secondary combustion chamber2a, and the injection nozzle4may eccentrically inject the fuel toward a fuel collision part2cformed on one side wall surface of the secondary combustion chamber2aand having a straight cross-sectional shape. In addition, a swirl induction part2dhaving a curved shape is provided on the other side wall surface of the secondary combustion chamber2aand forms a swirl when compressed air introduced from the primary combustion chamber3aflows to the secondary combustion chamber2avia a connecting passage2b.

In addition, the connecting passage2bmay be inclinedly formed at a lower end of the secondary combustion chamber2a, and the connecting passage2bconnects the secondary combustion chamber2aand the primary combustion chamber3aand provides a passageway through which air is introduced from the primary combustion chamber3ato the secondary combustion chamber2a. The connecting passage2bmay be provided mainly in a direction tangential to the swirl induction part2dof the secondary combustion chamber2a.

Further, a glowplug5is provided in the secondary combustion chamber2ato prevent a temperature in the combustion chamber from being lowered when the engine starts or operates at a low speed. Further, a coolant passage1amay be formed at the periphery of the secondary combustion chamber2a.

When combustion gas formed in the secondary combustion chamber2ais discharged to the primary combustion chamber3ain the general swirl chamber-type diesel engine, diffusion of the combustion gas flowing to a trench part3cinFIG. 3Bis concentrated in a straight direction. For this reason, swirls cannot be appropriately formed in clover parts3bpositioned at both sides of the trench part3c, which may cause a deterioration in diffusion combustion and a problem of an increase in emission of harmful substances in exhaust gas, particularly smog.

More specifically, referring toFIGS. 3A, 3B, 4A, and 4B, in the typical swirl chamber-type diesel engine in the related art, the secondary combustion chamber2amay be formed as the secondary combustion chamber assembly2is provided in the cylinder head1. The secondary combustion chamber2ais connected to the primary combustion chamber3avia the connecting passage2b, such that the combustion gas formed in the secondary combustion chamber2ais discharged into the primary combustion chamber3a.

FIG. 4Aillustrates a shape of the secondary combustion chamber assembly2, which defines the secondary combustion chamber2a, and a shape of the connecting passage2bwhen viewed from an upper side (a1), a lower side (a2), and a lateral side (a3). In addition,FIG. 4Bis a cross-sectional view illustrating the shape of the secondary combustion chamber assembly2, which defines the secondary combustion chamber2aand the shape of the connecting passage2b. More specifically,FIG. 4B(b3) concretely illustrates a cross-sectional shape of the connecting passage2b.

In particular, as illustrated inFIG. 4B(b3), the connecting passage2bfor connecting the primary combustion chamber3aand the secondary combustion chamber2aof the swirl chamber-type diesel engine in the related art has a one-piece cross-sectional shape defining an arc tangential to two circles. In this case, when the gas mixture combusted in the secondary combustion chamber2ais discharged to the primary combustion chamber3a, diffusion of the combustion gas introduced into the trench part (3cinFIG. 3B) is concentrated in a straight direction. For this reason, swirls cannot be appropriately formed in the clover parts (3binFIG. 3B) positioned at both sides of the trench part3c, which may cause a deterioration in diffusion combustion and a problem of an increase in emission of harmful substances in exhaust gas, particularly smog.

In contrast,FIGS. 5A and 5Bspecifically illustrate features of the swirl chamber-type diesel engine provided with the connecting passage2baccording to the exemplary embodiment of the present invention.

FIG. 5Aillustrates a shape of the secondary combustion chamber assembly2, which defines the secondary combustion chamber2a, and a shape of the connecting passage2bwhen viewed from an upper side (a1), a lower side (a2), and a lateral side (a3) in the swirl chamber-type diesel engine provided with the connecting passage2baccording to the exemplary embodiment of the present invention.

In addition,FIG. 5Bis a cross-sectional view illustrating the shape of the secondary combustion chamber assembly2, which defines the secondary combustion chamber2aand the shape of the connecting passage2bin the swirl chamber-type diesel engine provided with the connecting passage2baccording to the exemplary embodiment of the present invention. More specifically,FIG. 5B(b3) concretely illustrates a cross-sectional shape of the connecting passage2b.

In particular, as illustrated inFIG. 5A(a2) andFIG. 5B(b3), a guide structure2emay be provided in the connecting passage2bfor connecting the primary combustion chamber3aand the secondary combustion chamber2aof the swirl chamber-type diesel engine according to the exemplary embodiment of the present invention, and the guide structure2emay divide the combustion gas, discharged from the secondary combustion chamber2ato the primary combustion chamber3a, into three portions and guide the combustion gas.

Further,FIG. 6is a cross-sectional view illustrating the guide structure2eformed in the connecting passage2bin order to explain the connecting passage2baccording to the exemplary embodiment of the present invention.

As illustrated inFIG. 6, the guide structure2emay include three curved shapes provided on an upper surface of the connecting passage2b. With the shape of the guide structure2e, the combustion gas may be divided into the three portions and then guided.

In this case, the guide structure2emay have the three curved shapes provided on the upper surface of the connecting passage2band have the same radius.

More specifically, the three portions of the combustion gas, which are divided and guided by the guide structure2e, may be introduced into the trench part3cin the straight direction or introduced into the clover parts3bpositioned at both sides of the trench part3c. Therefore, in the present invention, with the use of the guide structure2econfigured to guide the combustion gas while dividing the combustion gas into the three portions and provided in the connecting passage2bfor connecting the secondary combustion chamber2aand the primary combustion chamber3a, the combustion gas, discharged from the secondary combustion chamber2ato the primary combustion chamber3a, may be divided into the three portions and then discharged. In contrast to the related art in which the combustion gas is concentrated into the trench part3cin the straight direction and swirls cannot be appropriately formed in the left and right clover parts3b, the diffusion combustion in the diesel engine may be facilitated and the production of harmful gas, such as smog, may be effectively inhibited as the proportion of the combustion gas to be discharged into the trench part3cand the clover parts3bis adjusted by the guide structure2e.

Further, the guide structure2ehas the three curved shapes adjacent to one another on the upper surface of the connecting passage2b, and the guide structure2emay have a first guide groove21epositioned at a center, and second and third guide grooves22eand23epositioned at both sides of the first guide groove21e.

In this case, a center of the first guide groove21emay be positioned at a higher position than a straight line that connects a center of the second guide groove22eand a center of the third guide groove23e. That is, as illustrated inFIG. 6, based on a centerline (C inFIG. 5B) of the connecting passage2b, the first guide groove21emay be positioned at a higher position than the second guide groove22eand the third guide groove23e. Therefore, as illustrated inFIG. 5B(b3), based on the centerline (C inFIG. 5B) of the connecting passage2b, the first guide groove21eprotrudes most outward so as to be positioned at the high position.

Further, the first guide groove21eis positioned at the center between the second guide groove22eand the third guide groove23e, and the first guide groove21ehas the same cross-sectional area as the second guide groove22eand the third guide groove23e, such that the first guide groove21e, the second guide groove22e, and the third guide groove23emay divide and guide the combustion gas.

Further, the first guide groove21e, the second guide groove22e, and the third guide groove23emay have the same radius or the same cross-sectional area, such that the combustion gas may be approximately uniformly divided and guided, thereby uniformly discharging the combustion gas, which was concentrated into the trench part3c, to the trench part3cand the clover parts3bpositioned at both ends of the trench part3c.

That is, in the present invention, the configuration in which the first guide groove21e, the second guide groove22e, and the third guide groove23eapproximately uniformly divide the combustion gas and guide the combustion gas means that the first guide groove21e, the second guide groove22e, and the third guide groove23ehave the same radius or the same cross-sectional area such that the amount of combustion gas to be discharged into the clover parts3bpositioned at both sides of the trench part3cmay be increased to be equal to the amount of the combustion gas to be discharged into the trench part3c, in contrast to the related art in which the combustion gas is mostly concentrated and discharged into the trench part3cfrom the connecting passage2b.

In particular, a distance (D inFIG. 6) between the second guide groove22eand the third guide groove23eis three times a radius (r inFIG. 6) of the first guide groove21e(D=3r), and the proportion of the combustion gas to be discharged into the trench part3cand the clover parts3bis optimized, such that swirls may be efficiently formed in the clover parts3b, diffusion combustion may be facilitated, and the production of harmful substances, such as smog, in exhaust gas may be effectively inhibited.

Further, the proportion of the combustion gas to be guided by the first guide groove21emay be adjusted by adjusting the cross-sectional area of the first guide groove21eby adjusting the height of the first guide groove21e. Furthermore, it is possible to appropriately adjust the proportion of the combustion gas to be introduced into the trench part3cin the straight direction and the combustion gas introduced into the clover parts3bpositioned at both sides of the trench part3c.

Further,FIGS. 7A, 7B, and 7Cillustrate the internal structure of the connecting passage2bin order to explain the connecting passage2baccording to the exemplary embodiment of the present invention.

As illustrated inFIG. 7A, the connecting passage2bhas a shape constant from a start point S to an end point E. All cross sections a1, a2, and a3parallel to a lower surface (surface B inFIG. 7C) of the secondary combustion chamber assembly2have the same shape.

Further, as illustrated inFIG. 7B, all cross sections b1, b2, and b3perpendicular to a central axis (D-D inFIG. 7C) in a running direction of the connecting passage2balso have the same shape.

FIGS. 8A and 8Billustrate the improvement of a flow of combustion gas in the swirl chamber-type diesel engine provided with the connecting passage2baccording to the exemplary embodiment of the present invention. First, as illustrated inFIG. 8A, when combustion gas formed in the secondary combustion chamber2ais discharged to the primary combustion chamber3ain the typical swirl chamber-type diesel engine in the related art (A0inFIG. 8A), diffusion of the combustion gas introduced to the trench part3cis concentrated in the straight direction (A2inFIG. 8A). For this reason, swirls cannot be appropriately formed in the clover parts3bpositioned at both sides of the trench part3c(A1and A3inFIG. 8A), which may cause a deterioration in diffusion combustion and a problem of an increase in emission of harmful substances in exhaust gas, particularly smog.

In contrast, in the swirl chamber-type diesel engine according to the exemplary embodiment of the present invention, with the use of the guide structure2econfigured to guide the combustion gas while dividing the combustion gas into the three portions and provided in the connecting passage2bfor connecting the secondary combustion chamber2aand the primary combustion chamber3a, the combustion gas, discharged from the secondary combustion chamber2ato the primary combustion chamber3a, may be divided into the three portions and then discharged (B0inFIG. 8B), such that the combustion gas may be divided and discharged in accordance with the appropriate proportion of the combustion gas (B2inFIG. 8B) to be introduced into the trench part3cin the straight direction and the combustion gas (B1and B3inFIG. 8B) to be introduced into the clover parts3bpositioned at both sides of the trench part3c.

Therefore, in the swirl chamber-type diesel engine according to the exemplary embodiment of the present invention, the swirls are more strongly formed in the clover parts3bpositioned at both sides of the trench part3c, as a result of which it is possible to facilitate diffusion combustion in the diesel engine and to effectively inhibit the production of harmful gas, such as smog.

In addition, in the swirl chamber-type diesel engine according to the exemplary embodiment of the present invention, each of the bottom surfaces of the clover parts3bpositioned at the periphery of the trench part3cin the primary combustion chamber3aof the swirl chamber-type diesel engine is implemented to have a helical stereoscopic structure, as a result of which it is possible to improve the oxidation capability of the diesel engine and to effectively inhibit the production of harmful substances, such as PM, included in exhaust gas.

That is, in the swirl chamber-type diesel engine in the related art, when the combustion gas produced in the secondary combustion chamber2ais discharged to the primary combustion chamber3a, the swirls cannot be appropriately formed in the clover parts3b, and complicated flows cannot be activated, which may cause a deterioration in oxidation capability and thus a problem of an increase in emission of harmful substances, particularly PM, in exhaust gas.

More specifically, referring toFIG. 9A, in the typical swirl chamber-type diesel engine in the related art, the clover parts3bof the primary combustion chamber3amay be disposed adjacent to left and right sides of the trench part3c. In particular, as illustrated inFIGS. 9B and 9C, a bottom surface of the clover part3bhas a flat surface structure having a constant depth. For this reason, a swirl of the combustion gas cannot be effectively formed in the clover part3b, and complete combustion cannot be achieved, and as a result, exhaust gas, including harmful substances such as PM, is produced.

In contrast, as illustrated inFIGS. 10A, 10B, and 10C, in the primary combustion chamber3aof the swirl chamber-type diesel engine according to the exemplary embodiment of the present invention, a bottom surface of the clover part3bhas a stereoscopic structure in which a height of a bottom surface of a second region (C inFIG. 10A), which is distant in a direction (indicated by the arrow B inFIG. 10A) of the flow of the combustion gas at a predetermined distance from a first region (A inFIG. 10A) into which the combustion gas is introduced from the trench part3cis greater than a height of a bottom surface of the first region. As a result, a strong swirl may be formed in the clover part3b, complicated flows may be activated, and the oxidation capability may be improved, the result of which it is possible to effectively inhibit emission of harmful substances, particularly PM, in exhaust gas.

That is, the swirl chamber-type diesel engine according to the exemplary embodiment of the present invention is the swirl chamber-type diesel engine including: the secondary combustion chamber assembly2coupled to the cylinder head1to define the secondary combustion chamber2ahaving, on the inner wall surface thereof, the curved swirl induction part2d, and the connecting passage2bformed at the lower end of the swirl induction part2d; the piston3defining the primary combustion chamber3aand including the trench part3cbeing in communication with the connecting passage2b; and the clover parts3bformed at the left and right sides of the trench part3c, in which the bottom surface of the clover part3bhas the stereoscopic structure in which the height of the bottom surface of the second region (C inFIG. 10A), which is distant in the direction (indicated by the arrow B inFIG. 10A) of the flow of the combustion gas at the predetermined distance from the first region (A inFIG. 10A) into which the combustion gas is introduced from the trench part3cis greater than the height of the bottom surface of the first region.

Further, referring toFIGS. 10B and 10C, in the primary combustion chamber3aof the swirl chamber-type diesel engine according to the exemplary embodiment of the present invention, the bottom surface of the clover part3bdoes not have the flat surface structure but has the stereoscopic structure in which the height of the bottom surface is gradually increased in the direction of the flow of the combustion gas.

Therefore, the combustion gas introduced into the clover part3bflows while being raised along the shape of the bottom surface of the clover part3b, thereby forming a stronger swirl.

More specifically, the features of the primary combustion chamber3aof the swirl chamber-type diesel engine according to the exemplary embodiment of the present invention in comparison with the general swirl chamber-type diesel engine will be described in detail with reference toFIGS. 11A, 11B, 11C, 12A, 12B, and 12C.

First,FIG. 11Ais a top plan view,FIG. 11Bis a cross-sectional side view, andFIG. 11Cis a perspective view illustrating the shape of the primary combustion chamber3aformed in the upper surface of the piston3of the general swirl chamber-type diesel engine.

In particular, as illustrated inFIGS. 11B and 11C, the clover part3bof the primary combustion chamber3aof the general swirl chamber-type diesel engine has the flat surface structure in which the bottom surface of the clover part3bhas the constant depth. As a result, when the gas mixture combusted in the secondary combustion chamber2ais discharged to the primary combustion chamber3a, a swirl of the combustion gas cannot be effectively formed in the clover part3b, and complete combustion cannot be achieved, which causes a problem of production of exhaust gas, including harmful substances such as PM.

In contrast,FIGS. 12A, 12B, and 12Cspecifically illustrate features of the swirl chamber-type diesel engine according to the exemplary embodiment of the present invention.

More specifically,FIG. 12Ais a top plan view,FIG. 12Bis a cross-sectional side view, andFIG. 12Cis a perspective view illustrating the shape of the primary combustion chamber3aformed in the upper surface of the piston3of the swirl chamber-type diesel engine according to the exemplary embodiment of the present invention.

In particular, as illustrated inFIGS. 12B and 12C, the bottom surface of the clover part3bof the primary combustion chamber3aof the swirl chamber-type diesel engine according to the exemplary embodiment of the present invention has the stereoscopic structure in which the height of the bottom surface of the second region, which is distant in the direction of the flow of the combustion gas at the predetermined distance from the first region into which the combustion gas is introduced from the trench part3c, is greater than the height of the bottom surface of the first region. As a result, a strong swirl of the combustion gas introduced into the clover part3bmay be formed, complicated flows may be activated, and the oxidation capability may be improved, the result of which it is possible to effectively inhibit emission of harmful substances, particularly PM, in exhaust gas.

Furthermore, the bottom surface of the clover part3bmay have the stereoscopic structure in which the height of the bottom surface is gradually increased in the direction of the flow of the combustion gas so that the introduced combustion gas may flow while being gradually raised. In particular, the clover parts3bhave cylindrical structures disposed adjacent to the left and right sides of the trench part3c, and each of the clover parts3bhas the stereoscopic structure, including a spiral structure in which the height of the bottom surface is gradually increased in the direction of the flow of the combustion gas. As a result, the combustion gas introduced into the clover part3bflows while being raised along the shape of the bottom surface of the clover part3b, thereby forming a strong swirl.

In addition, as illustrated inFIG. 12C, the clover part3bmay include a structure in which the height of the bottom surface is gradually increased toward an outer periphery thereof. Further, the bottom surface of the trench part3cmay have a predetermined gradient, such that the combustion gas may be introduced into the clover part3bwhile being raised along the gradient of the bottom surface of the trench part3c.

FIGS. 13A and 13Billustrate the improvement of the flow of the combustion gas in accordance with the stereoscopic structure of the bottom surface of the clover part3bin the swirl chamber-type diesel engine according to the exemplary embodiment of the present invention. First, as illustrated inFIG. 13A, when the combustion gas produced in the secondary combustion chamber2ais discharged to the primary combustion chamber3ain the typical swirl chamber-type diesel engine in the related art (A0inFIG. 13A), a swirl cannot be appropriately formed because the combustion gas introduced into the clover part3bflows along the flat bottom surface having a constant depth (A1and A3inFIG. 13A). As a result, there may occur problems in that complicated flows cannot be activated, the oxidation capability may deteriorate, and emission of harmful substances, particularly PM, in exhaust gas may be increased.

In contrast, as illustrated inFIG. 13B, in the swirl chamber-type diesel engine according to the exemplary embodiment of the present invention, the bottom surface of the clover part3bof the primary combustion chamber3ahas the stereoscopic structure in which the height of the bottom surface is gradually increased in the direction of the flow of the combustion gas so that the introduced combustion gas may flow while being raised gradually. As a result, the combustion gas introduced into the clover part3bflows while being raised along the shape of the bottom surface of the clover part3b, thereby forming a stronger swirl.

More specifically, since the bottom surface of the clover part3bof the primary combustion chamber3ahas the stereoscopic structure in which the height of the bottom surface is gradually increased in the direction of the flow of the combustion gas, a swirl is strongly formed in the clover part3bwhen the combustion gas produced in the secondary combustion chamber2ais discharged to the primary combustion chamber3ain the swirl chamber-type diesel engine according to the exemplary embodiment of the present invention (B0inFIG. 13B). As a result, complicated flows may be activated, the oxidation capability may be improved, and emission of harmful substances, particularly PM, in exhaust gas may be effectively inhibited.

The above description is simply given for illustratively describing the technical spirit of the present invention, and those skilled in the art to which the present invention pertains will appreciate that various modifications, changes, and substitutions are possible without departing from the essential characteristic of the present invention. Accordingly, the exemplary embodiments disclosed in the present invention and the accompanying drawings are intended not to limit but to describe the technical spirit of the present invention, and the scope of the technical spirit of the present invention is not limited by the exemplary embodiments and the accompanying drawings. The protective scope of the present invention should be construed based on the following claims, and all the technical spirit in the equivalent scope thereto should be construed as falling within the scope of the present invention.