JP7447576B2 - piston - Google Patents

Description

The present invention relates to a piston equipped with a catalyst for purifying exhaust gas discharged from an internal combustion engine.

2. Description of the Related Art Conventionally, a piston is known in which a catalyst is disposed to purify exhaust gas discharged from an internal combustion engine (for example, see Patent Document 1). The piston of Patent Document 1 includes a first catalyst section and a second catalyst section. In the first catalyst section, a first catalyst (rhodium in the piston of Patent Document 1) having a relatively low catalyst activation temperature is disposed on the surface layer. In the second catalyst section, a second catalyst (palladium in the piston of Patent Document 1) having a relatively high catalyst activation temperature is arranged on the surface layer.

Furthermore, Patent Document 1 discloses a piston with a cavity and a piston without a cavity. In the piston having a cavity disclosed in Patent Document 1, the first catalyst portion is placed by coating on the top surface inside the cavity where the temperature of the combustion chamber is low, and the second catalyst portion is placed on the top surface of the outer periphery of the cavity where the temperature of the combustion chamber is high. Place by applying. Furthermore, in the piston without a cavity disclosed in Patent Document 1, the first catalyst portion is placed by applying it to the center of the flat top surface of the piston. The second catalytic portion is disposed by applying it in an annular manner around the first catalytic portion. In this manner, in the piston of Patent Document 1, gas is efficiently purified by arranging catalysts having different activation temperatures in the surface layer according to the combustion temperature of the combustion chamber.

JP2018-131913

However, in the piston having a cavity disclosed in Patent Document 1, only the first catalyst portion is disposed on the top surface inside the cavity. Therefore, in the piston of Patent Document 1, for example, if the exhaust gas components become uneven inside the cavity, there is a risk that the purification performance of the first catalyst and the second catalyst may not be sufficiently exhibited.

Further, in the piston without a cavity disclosed in Patent Document 1, the outer edge of the first catalyst portion and the inner edge of the second catalyst portion may be arranged on the flat top surface so as to coincide with each other. In such a case, the first catalyst part and the second catalyst part need to be coated after being positioned so that the first catalyst part and the second catalyst part, which have different surface layers, do not overlap. For this reason, the catalyst application process becomes complicated, and there is a possibility that a plurality of catalysts cannot be easily applied.

An object of the present invention is to provide a piston that can purify exhaust gas components in response to uneven distribution of exhaust gas components within a combustion chamber and that can be easily coated with a plurality of catalysts.

A piston according to the present invention is a piston that is provided with a catalyst that purifies exhaust gas discharged from an internal combustion engine. The piston includes a top surface, a lower catalyst layer, and an upper catalyst layer. The top surface is arranged towards the combustion chamber of the internal combustion engine. A catalyst underlayer is provided on the top surface. The catalyst upper layer is provided on the upper surface of the catalyst lower layer. The piston carries a first catalyst, which purifies components contained in exhaust gas, on either the lower catalyst layer or the upper catalyst layer so that the loading density increases from the center side of the piston toward the outer circumferential side. A second catalyst, which is different from the first catalyst and which purifies components contained in exhaust gas, is supported on one of the pistons so that the supporting density decreases from the center side of the piston toward the outer circumferential side.

According to this piston, the catalyst is supported at a position corresponding to the uneven distribution of exhaust gas components within the combustion chamber.

Further, the lower catalyst layer supports either the first catalyst or the second catalyst, and the upper catalyst layer supports the other catalyst. That is, the catalyst supported on the surface layer is one type of first catalyst or second catalyst. Therefore, the catalyst can be easily applied. As a result, it is possible to provide a piston that can purify exhaust gas components in response to uneven distribution of exhaust gas components within the combustion chamber and that can be easily coated with a plurality of catalysts.

The first catalyst may have a high ability to purify hydrocarbons contained in exhaust gas, and the second catalyst may have a high ability to purify nitrogen oxides contained in exhaust gas.

According to this configuration, the first catalyst purifies hydrocarbons contained in the exhaust gas, and the second catalyst purifies nitrogen oxides contained in the exhaust gas. Therefore, the first catalyst can purify hydrocarbons that are unevenly distributed near the outer periphery of the piston in the combustion chamber. Furthermore, the second catalyst can purify nitrogen oxides that are distributed near the center of the piston.

The first catalyst may be palladium and the second catalyst may be rhodium.

According to this configuration, palladium can purify hydrocarbons contained in exhaust gas, and rhodium can purify nitrogen oxides contained in exhaust gas components.

The piston may have a base layer comprising zeolite between the top surface and the lower catalyst layer. The base layer may support zeolite in such a manner that the supporting density increases from the center side to the outer peripheral side of the piston.

According to this configuration, zeolite with a high heat insulation coefficient is supported on the base layer. As a result, the zeolite suppresses heat in the combustion chamber from being transmitted to the main body of the piston, making it easier to keep the lower catalyst layer and the upper catalyst layer warm. As a result, the purification efficiency of the first catalyst and the second catalyst is increased. Furthermore, the zeolite is supported on the base layer such that the supporting density increases from the center side to the outer peripheral side of the piston. Zeolite is a catalyst that purifies hydrocarbons by adsorbing them. This allows the piston to easily adsorb and purify hydrocarbons that are distributed in the combustion chamber near the outer periphery of the piston.

Further, the piston may have a plurality of grooves formed on the top surface.

According to this configuration, the surface area of the top surface of the piston can be increased. This increases the area in which the catalyst lower layer contacts the top surface of the piston. As a result, it is possible to suppress the catalyst lower layer from peeling off from the top surface of the piston.

Further, the first catalyst may have a supporting density that increases toward the outer circumferential side from a position facing the ignition device of the internal combustion engine. The region where the second catalyst is highly supported may be located at a position facing the ignition device.

According to this configuration, the second catalyst supported on the upper catalyst layer has a high supporting density at a position facing the ignition device, where the temperature tends to be higher. This makes it possible to efficiently purify nitrogen oxides that are unevenly distributed near the ignition device.

Furthermore, the first catalyst supported in the lower catalyst layer has a supporting density that increases from a position facing the ignition device of the internal combustion engine toward the outer circumference of the piston. That is, the first catalyst has a high loading density near the outer periphery of the piston where the temperature is lower than the position facing the ignition device. As a result, deterioration of the portion of the first catalyst having a high loading density can be suppressed. As a result, hydrocarbons contained in exhaust gas components can be efficiently purified.

According to the present invention, it is possible to provide a piston for an internal combustion engine that can purify exhaust gas components in response to uneven distribution of exhaust gas components within a combustion chamber and that can be easily coated with a plurality of catalysts.

1 is a schematic diagram showing a combustion chamber of an engine incorporating a piston according to an embodiment of the present invention. 1 is a schematic diagram of a piston according to an embodiment of the invention. FIG. FIG. 3 is a sectional view taken along the line AA in FIG. 2;

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic diagram of an internal combustion engine E including a piston 6 in one embodiment of the present invention. Arrows T and B in FIG. 1 indicate the axial direction of the cylinder 4 formed in the internal combustion engine E, with the arrow T indicating the upper side of the internal combustion engine E, and the arrow B indicating the lower side of the internal combustion engine E. Therefore, arrow T and arrow B change depending on the attitude of internal combustion engine E, and do not necessarily coincide with the direction of gravity.

As shown in FIG. 1, the internal combustion engine E includes a combustion chamber 2, a cylinder 4, a piston 6, an intake passage 8, an intake valve 10, an exhaust passage 12, an exhaust valve 14, an ignition device 16, It has a fuel injection device 18. In this embodiment, the internal combustion engine E is a gasoline engine that starts combustion by igniting a mixture of fuel injected by a fuel injection device 18 and air taken in from an intake passage 8 by an ignition device 16. be. Further, in this embodiment, the internal combustion engine E is a gasoline engine that repeats four cycles consisting of an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke.

The combustion chamber 2 is a space surrounded by a top surface 22 of the piston 6, an inner circumferential surface 42 of the cylinder 4, and an upper surface 44 of the cylinder 4, which will be described later, and combustion in the internal combustion engine E takes place. The cylinder 4 is provided in a cylinder block 4a. The upper surface 44 of the cylinder 4 is provided on a cylinder head 44a. In this embodiment, the upper surface 44 has a pent roof shape.

The piston 6 is housed inside the cylinder 4 and slides within the cylinder 4 in the directions of arrows T and B. The piston 6 is arranged facing the combustion chamber 2, and as the piston 6 slides, four cycles of the internal combustion engine E are performed. As shown in FIGS. 1 and 3, the piston 6 includes a top surface 22, an outer periphery 26, a groove 28, a lower catalyst layer 30, an upper catalyst layer 32, and a base layer 34. As shown in FIG. 1, the top surface 22 is disposed toward the combustion chamber 2 and receives gas expanded by a combustion reaction occurring in the combustion chamber 2 during the expansion stroke. The top surface 22 also pushes out the exhaust gas after combustion during the exhaust stroke. An outer periphery 26 forms the perimeter of the top surface 22 . That is, the outer periphery 26 is a boundary line between the side surface 6a and the top surface 22 of the piston 6. Details of the grooves 28, the lower catalyst layer 30, the upper catalyst layer 32, and the base layer 34 will be described later. In this embodiment, the center portion 24 is the intersection of the center axis Cx of the ignition device 16, which will be described later, and the top surface 22.

As shown in FIG. 1, the intake passage 8 is connected to the combustion chamber 2, and an intake valve 10 is disposed at an outlet 8a of the intake passage 8. In this embodiment, a fuel injection device 18 is arranged in the intake passage 8 .

The intake valve 10 is moved up and down by an intake cam (not shown). The intake valve 10 switches between an open state in which the intake passage 8 and the combustion chamber 2 communicate with each other, and a closed state in which the intake passage 8 and the combustion chamber 2 are partitioned. When the intake valve 10 moves downward B, the intake passage 8 and the combustion chamber 2 communicate with each other to be in an open state, and the gas inside the intake passage 8 flows into the combustion chamber 2. On the other hand, when the intake valve 10 moves upward T, the intake passage 8 and the combustion chamber 2 are separated into a closed state, and the gas inside the intake passage 8 remains in the intake passage 8.

The exhaust passage 12 is connected to the combustion chamber 2, and an exhaust valve 14 is disposed at an entrance 12a of the exhaust passage 12.

The exhaust valve 14, like the intake valve 10, is moved up and down by an exhaust cam (not shown). The exhaust valve 14 switches between an open state in which the combustion chamber 2 and the exhaust passage 12 communicate with each other, and a closed state in which the combustion chamber 2 and the exhaust passage 12 are partitioned. When the exhaust valve 14 moves downward B, the combustion chamber 2 and the exhaust passage 12 communicate with each other to be in an open state, and the gas inside the combustion chamber 2 flows into the exhaust passage 12. On the other hand, when the exhaust valve 14 moves upward T, the combustion chamber 2 and the exhaust passage 12 are separated into a closed state, and the gas inside the combustion chamber 2 remains within the combustion chamber 2.

The ignition device 16 is arranged above the combustion chamber 2 . In this embodiment, the ignition device 16 is disposed facing the top surface 22 of the piston 6 from the top of the pent roof shape of the upper surface 44 toward the downward direction B. More specifically, the ignition part 16a disposed at the tip of the ignition device 16 is disposed facing the top surface 22 of the piston 6 from the top of the pent roof. That is, in the axial direction of the cylinder 4, the center portion 24 of the top surface 22 of the piston 6 and the ignition portion 16a of the ignition device 16 are arranged to face each other. In this embodiment, the central axis Cx of the ignition device 16 is arranged to coincide with the axial direction of the cylinder 4.

The fuel injection device 18 supplies fuel to the combustion chamber 2 by injecting combustion. In this embodiment, the fuel injection device 18 is disposed in the intake passage 8 and injects fuel into the intake passage 8 by being driven by an actuator (not shown). However, the fuel injection device 18 may be a direct injection type fuel injection device 18 that injects fuel directly into the combustion chamber 2.

Next, details of the groove 28, the lower catalyst layer 30, the upper catalyst layer 32, and the base layer 34 of the piston 6 in this embodiment will be explained.

As shown by broken lines in FIG. 2, the grooves 28 are formed in the top surface 22 of the piston 6 in the form of a plurality of thin lines. In this embodiment, the groove 28 is formed in the top surface 22 of the piston 6 as a plurality of linear and circular recesses having different diameters. Further, the grooves 28 are arranged concentrically from the center portion 24 to the outer periphery 26. The groove 28 is provided to increase the surface area of the top surface 22 of the piston 6. As the surface area of the top surface 22 increases, the contact area between the top surface 22 and the catalyst lower layer 30 increases. This makes it difficult for the catalyst lower layer 30 to peel off from the top surface 22. As a result, the durability of the catalyst lower layer 30 is improved.

As shown in FIG. 3, the catalyst lower layer 30 is arranged on the combustion chamber 2 side of the top surface 22. The catalyst lower layer 30 supports palladium 33 (an example of the first catalyst). Palladium 33 is a noble metal catalyst that has a high ability to purify hydrocarbons by oxidizing hydrocarbons (first exhaust gas component) into water and carbon dioxide through a catalytic reaction. In the catalyst lower layer 30, the density of palladium 33 supported increases from the center 24 side of the piston 6 toward the outer periphery 26 side. Support density is the amount of catalyst components supported per unit area. Therefore, the hydrocarbon purification performance of the catalyst lower layer 30 improves as it moves toward the outer periphery 26 of the piston 6. In this embodiment, the palladium 33 is arranged in three layers: a high loading density palladium layer 30a, a middle loading density palladium layer 30b, and a low loading density palladium layer 30c in order from the outer periphery 26. The catalyst lower layer 30 is formed by applying a catalyst material containing palladium 33 at a supporting density corresponding to each palladium layer from a high supporting density palladium layer 30a to a low supporting density palladium layer 30c to a base layer 34, which will be described later. It is formed by aligning. At this time, for example, the inner edge of the high loading density palladium layer 30a and the outer edge of the middle loading density palladium layer 30b may be coated so as to overlap. However, although the high supported density palladium layer 30a and the medium supported density palladium layer 30b have different supported densities of palladium 33, the components of the catalyst material are the same. Therefore, the purification performance of the catalyst lower layer 30 is not affected. In other words, when forming the catalyst lower layer 30, it is not necessary to precisely position the high-support density palladium layer 30a to the low-support density palladium layer 30c on the base layer 34.

The catalyst upper layer 32 is arranged on the combustion chamber 2 side of the catalyst lower layer 30. In this embodiment, the catalyst upper layer 32 is arranged above the catalyst lower layer 30. Further, in this embodiment, the catalyst upper layer 32 supports rhodium (an example of a second catalyst) 37 that purifies nitrogen oxides (a second exhaust gas component). Rhodium-37 is a noble metal catalyst that purifies nitrogen oxides by reducing them to nitrogen and oxygen, and has a high ability to purify nitrogen oxides. In the catalyst upper layer 32, the density of rhodium 37 supported decreases toward the outer periphery 26 of the piston 6.

Further, the catalyst upper layer 32 has a constant thickness, and the supporting density of rhodium 37 decreases from the center 24 side of the piston 6 toward the outer circumference 26 side. Therefore, the catalyst upper layer 32 improves the purification performance of the central portion 24 of the piston 6 and nitrogen oxides. In this embodiment, the rhodium 37 of the catalyst upper layer 32 is formed into three layers, which are a high-support density rhodium layer 32c, a medium-support density rhodium layer 32b, and a low-support density rhodium layer 32a, in order from the center 24 side to the outer periphery 26 side. It is arranged separately. Similarly to the catalyst lower layer 30, the catalyst upper layer 32 is coated with a catalyst material containing rhodium 37 at a loading density corresponding to each rhodium layer from the low loading density rhodium layer 32a to the high loading density rhodium layer 32c. It is later formed by aligning it to a constant thickness. Similarly to the catalyst lower layer 30, in the catalyst upper layer 32, when forming the catalyst upper layer 32, it is not necessary to precisely position the lower catalyst layer 30 from the low loading density rhodium layer 32a to the high loading density rhodium layer 32c.

Base layer 34 is disposed between catalyst lower layer 30 and top surface 22 . Base layer 34 supports zeolite 35. Zeolite 35 has a higher thermal insulation coefficient than rhodium 37 and palladium 33. Thereby, heat due to the combustion reaction of the air-fuel mixture can be prevented from being transmitted from the combustion chamber 2 to the top surface 22 of the piston 6. As a result, the catalyst upper layer 32 and the catalyst lower layer 30 are easily kept warm. As a result, rhodium 37 contained in the catalyst upper layer 32 and palladium 33 and rhodium 37 in the catalyst lower layer 30 are likely to undergo a catalytic reaction. As a result, exhaust gas can be efficiently purified.

Moreover, the zeolite 35 is a catalyst that purifies hydrocarbons by adsorbing them. The base layer 34 has a higher supporting density of zeolite 35 from the center 24 side of the piston 6 toward the outer periphery 26 side. Therefore, the hydrocarbon purification performance of the base layer 34 improves from the center 24 side of the piston 6 toward the outer circumference 26 side. Further, in this embodiment, the zeolite 35 is formed into three layers, which are a low-support density zeolite layer 34c, a medium-support density zeolite layer 34b, and a high-support density zeolite layer 34a, in order from the center 24 side to the outer periphery 26 side. placed separately. The base layer 34 is formed by coating the top surface 22 with a catalytic material containing zeolite 35 having a supporting density corresponding to each zeolite layer from the high-supporting density zeolite layer 34a to the low-supporting density zeolite layer 34c. It is formed by making the thickness uniform. Therefore, similarly to the catalyst lower layer 30, when forming the base layer 34, it is not necessary to precisely position the high-support density zeolite layer 34a to the low-support density zeolite layer 34c on the top surface 22. As a result, the base layer 34 can be easily coated with a catalytic material.

Next, the combustion state in the internal combustion engine E and the exhaust gas purification functions of the lower catalyst layer 30, the upper catalyst layer 32, and the base layer 34 will be described using FIG.

During the intake stroke, the intake valve 10 moves downward B, and the intake passage 8 and combustion chamber 2 are in an open state. At this time, gas inside the intake passage 8 flows into the combustion chamber 2. Inside the intake passage 8, an air-fuel mixture is generated in advance, in which air taken in from outside the internal combustion engine E and fuel injected by the fuel injection device 18 are mixed at a predetermined ratio. During the intake stroke, the air-fuel mixture generated inside the intake passage 8 flows into the combustion chamber 2.

Next, in the compression stroke, the piston 6 moves upward T, and the volume of the combustion chamber 2 becomes smaller. At this time, the intake valve 10 moves upward T, and the intake passage 8 and the combustion chamber 2 are in a closed state. Also, in the combustion chamber 2, components contained in the exhaust gas generated in the previous combustion reaction and remaining near the inner circumferential surface 42 of the cylinder 4, or components contained in the fuel and oil adhering to the inner circumferential surface 42. is scraped upward T by the movement of the piston 6 upward T. Therefore, the concentration of these components inside the combustion chamber 2, particularly near the outer periphery 26 of the piston 6, is higher than the concentration at other locations within the combustion chamber 2. In this embodiment, hydrocarbons, which are components of the fuel adhering to the inner circumferential surface 42, are distributed more in the combustion chamber 2, particularly near the outer circumference 26 of the piston 6, than in other locations in the combustion chamber 2.

Next, in the expansion stroke, a spark is generated in the ignition part 16a of the ignition device 16, and in the intake stroke, the air-fuel mixture that has flowed into the combustion chamber 2 is ignited to cause a combustion reaction. The piston 6 is pushed by the gas expanded by this combustion reaction and moves downward B. At this time, the top surface 22 receives the expanded gas. The flame generated by the combustion reaction of the air-fuel mixture starts near the top surface 44 of the cylinder 4 where the ignition part 16a is arranged, that is, near the center 24 of the top surface 22 of the piston 6, and moves toward the outer circumference 26 of the piston 6. Propagates radially. Therefore, the temperature distribution in the combustion chamber 2 is such that the temperature is highest at the location where the ignition part 16a of the ignition device 16 is arranged, and the temperature decreases toward the vicinity of the outer circumference 26 of the piston 6. Further, as the combustion reaction of the air-fuel mixture progresses, exhaust gas is generated within the combustion chamber 2. Different components of the exhaust gas are generated based on the combustion temperature of the mixed gas. Therefore, the distribution of components contained in the exhaust gas generally matches the temperature distribution within the combustion chamber 2. That is, nitrogen oxides (second exhaust gas component), which is one of the components contained in the exhaust gas, are distributed in large quantities in the combustion chamber 2, particularly in areas where the combustion temperature is high. On the other hand, hydrocarbons (first exhaust gas component), which is one of the components contained in the exhaust gas, are largely distributed in locations in the combustion chamber 2 that are different from locations where nitrogen oxides are distributed.

In this embodiment, the top surface 22 of the piston 6 has a concentric temperature distribution in which the temperature decreases from the center 24, which is the intersection of the central axis Cx of the ignition device 16 and the top surface 22 of the piston 6, toward the outer periphery 26. Become. Therefore, the top surface 22 of the piston 6 has the highest temperature near the center portion 24. As a result, on the top surface 22 of the piston 6, the concentration of nitrogen oxides is highest at the center 24, and the concentration decreases toward the outer circumference 26 of the piston 6. On the other hand, due to the influence of the fuel adhering to the inner circumferential surface 42, more hydrocarbons are distributed within the combustion chamber 2, particularly near the outer circumference 26 of the piston 6, than at other locations within the combustion chamber 2. Therefore, even during the expansion stroke, hydrocarbons remain unburned near the outer periphery 26 and are distributed more than in other locations. That is, the hydrocarbons are distributed on the top surface 22 of the piston 6 such that the concentration increases from the center 24 toward the outer periphery 26.

Next, in the exhaust stroke, the exhaust valve 14 moves downward B, and the combustion chamber 2 and exhaust passage 12 are in an open state. At this time, exhaust gas generated by the combustion reaction of the air-fuel mixture flows from the combustion chamber 2 into the exhaust passage 12. Further, in the exhaust stroke, the piston 6 moves upward T. Therefore, inside the combustion chamber 2, components contained in the exhaust gas are scraped up toward the upper direction T by the movement of the piston 6. Therefore, the concentration of components contained in the exhaust gas inside the combustion chamber 2, particularly near the outer periphery 26 of the piston 6, is higher than the concentration at other locations within the combustion chamber 2. In this embodiment, more hydrocarbons contained in the exhaust gas are distributed in the combustion chamber 2, particularly near the outer circumference 26 of the piston 6, than in other locations in the combustion chamber 2. In addition, immediately after the internal combustion engine E is started, the amount of fuel injected is large at the time of startup, and since the internal combustion engine E has not yet warmed up, there is a lot of unburned fuel, and the hydrocarbons that are the components of the fuel are distributed more toward the outer periphery 26. do.

The catalyst lower layer 30 purifies the first exhaust gas component that is mostly distributed around the outer periphery 26 during the exhaust stroke. The catalyst upper layer 32 purifies the second exhaust gas component that is distributed at a different location from the first exhaust gas component. In this embodiment, in the combustion chamber 2 during the exhaust stroke, more hydrocarbons are distributed toward the outer periphery 26. On the other hand, the hydrocarbon purification performance of the catalyst lower layer 30 improves toward the outer periphery 26 of the piston 6. That is, palladium 33, which can purify hydrocarbons, is supported at positions corresponding to the uneven distribution of hydrocarbons in the combustion chamber 2. Thereby, the piston 6 can efficiently purify hydrocarbons.

Further, in the combustion chamber 2 during the exhaust stroke, nitrogen oxides are distributed such that the concentration increases from the center 24 toward the outer periphery 26. On the other hand, the nitrogen oxide purification performance of the catalyst upper layer 32 improves as the distance from the outer periphery 26 of the piston 6 increases. That is, rhodium 37, which can purify nitrogen oxides, is supported at positions corresponding to the uneven distribution of nitrogen oxides in the combustion chamber 2. This allows the piston 6 to efficiently purify nitrogen oxides.

Further, in this embodiment, a layer in which catalysts are supported in the order of rhodium 37, palladium 33, and zeolite 35 is formed on the top surface 22 of the piston 6 from the upper side T toward the lower side B. Therefore, the zeolite 35 is arranged below the rhodium 37 and the palladium 33. Thereby, the zeolite 35 can suppress the heat generated by the combustion reaction within the combustion chamber 2 from being transmitted to the lower part B of the piston 6. Therefore, the temperature of the catalyst supported on the lower catalyst layer 30 and the upper catalyst layer 32 can be prevented from falling below the activation temperature. As a result, the piston 6 can efficiently purify the exhaust gas within the combustion chamber 2.

Furthermore, in this embodiment, rhodium 37 is arranged above palladium 33 and zeolite 35. Therefore, the palladium 33 and zeolite 35 that purify hydrocarbons can be prevented from being directly exposed to the exhaust gas in the combustion chamber 2. This makes it possible to suppress the palladium 33 and the zeolite 35 from being covered and deteriorated by a large amount of hydrocarbons and carbon monoxide contained in the exhaust gas generated immediately after starting the internal combustion engine E, in particular. As a result, the piston 6 can efficiently purify the exhaust gas in the combustion chamber 2 regardless of the operating state of the internal combustion engine E.

As explained above, according to the present embodiment, the piston of the internal combustion engine E can purify exhaust gas components in response to the uneven distribution of exhaust gas components in the combustion chamber 2, and can easily apply a plurality of catalysts. 6 can be provided.

<Other embodiments>
Although the present embodiment has been described above, the present invention is not limited to the above embodiment, and various changes can be made without departing from the gist of the invention. In particular, the plurality of modifications described in this specification can be arbitrarily combined as necessary.

(a) In the above embodiment, the internal combustion engine E is explained using a gasoline engine as an example, but the present invention is not limited to this. That is, the internal combustion engine E may be a diesel engine. In this case, a cavity recessed downward B may be provided in the top surface 22 of the piston 6.

(b) In the above embodiment, the groove 28 is formed by a plurality of linear and circular depressions having different diameters arranged concentrically from the center part 24 to the outer periphery 26 on the top surface 22. However, the present invention is not limited thereto. The groove 28 may be a curved line using a plurality of linear recesses, a straight line, a pattern, or a combination thereof. Further, the groove 28 may be formed on a part or the entire surface of the top surface 22 of the piston 6.

(c) In the above embodiment, palladium 33, zeolite 35, and rhodium 37 were explained as examples, but the present invention is not limited thereto. That is, for example, platinum or platinum may be used instead of rhodium-37. Further, instead of the zeolite 35, for example, alumina, zirconium oxide, cerium oxide, a composite oxide containing zirconium oxide or cerium oxide as a main component, etc. may be used.

(d) In the above embodiment, an example was explained in which palladium 33 is supported on the catalyst lower layer 30 and rhodium 37 is supported on the catalyst upper layer 32, but the present invention is not limited thereto. The lower catalyst layer 30 may support rhodium 37, and the upper catalyst layer 32 may support palladium 33.

E: Internal combustion engine 6: Piston 22: Top surface 26: Outer circumference 16: Ignition device
30: Catalyst lower layer 32: Catalyst upper layer 38: Base layer 33: Palladium (an example of a first catalyst) 37: Rhodium (an example of a second catalyst)
35: Zeolite

Claims (5)

A piston equipped with a catalyst that purifies exhaust gas emitted from an internal combustion engine,
a top surface disposed toward the combustion chamber of the internal combustion engine;
a catalyst lower layer provided on the surface of the top surface;
a catalyst upper layer provided on the upper surface of the catalyst lower layer;
Equipped with
A first layer for purifying components contained in exhaust gas is provided in either the lower catalyst layer or the upper catalyst layer.
The catalyst is supported so that the supporting density increases from the center side to the outer peripheral side of the piston,
A second catalyst different from the first catalyst, which purifies components contained in exhaust gas, is supported on one of the pistons so that the supporting density decreases from the center side toward the outer circumferential side of the piston ,
The first catalyst has a high ability to purify hydrocarbons contained in the exhaust gas,
The second catalyst has a high ability to purify nitrogen oxides contained in the exhaust gas.
piston. A piston equipped with a catalyst that purifies exhaust gas emitted from an internal combustion engine,
a top surface disposed toward the combustion chamber of the internal combustion engine;
a catalyst lower layer provided on the surface of the top surface;
a catalyst upper layer provided on the upper surface of the catalyst lower layer;
Equipped with
A first layer for purifying components contained in exhaust gas is provided in either the lower catalyst layer or the upper catalyst layer.
The catalyst is supported so that the supporting density increases from the center side to the outer peripheral side of the piston,
A second catalyst different from the first catalyst that purifies components contained in exhaust gas is provided on either one of the catalysts.
Supported so that the supported density decreases from the center side to the outer peripheral side of the piston,
The first catalyst is palladium, and the second catalyst is rhodium.
piston. a base layer containing zeolite between the top surface and the catalyst lower layer,
The base layer supports the zeolite so that the supporting density increases from the center side to the outer peripheral side of the piston.
The piston according to claim 1 or 2 . The piston has a plurality of grooves formed on the top surface.
A piston according to any one of claims 1 to 3 . The first catalyst has a supporting density that increases toward the outer circumferential side from a position facing the ignition device of the internal combustion engine,
The region where the second catalyst is supported at a high density is a position facing the ignition device,
A piston according to any one of claims 1 to 4 .