JP2007100612A - Auxiliary chamber type internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an auxiliary chamber type internal combustion engine of a compact constitution capable of expanding a limit of an operation area up to a higher load area by further surely avoiding early ignition of an air-fuel mixture even in a high load of easily rising in the auxiliary chamber temperature by restraining a temperature rise in an auxiliary chamber tip part of being conventionally difficult for cooling while avoiding an excessive increase in a cooling loss and an increase in a generation quantity of unburnt HC. <P>SOLUTION: This auxiliary chamber type internal combustion engine has a main chamber 2 being a main combustion chamber, an auxiliary chamber 4 communicating with the main chamber 2 via a communicating passage 12 and having the volume smaller than the main chamber 2, and a spark plug 30 for igniting the air-fuel mixture in the auxiliary chamber 4. A cavity-like volume part 32 is formed in a wall of the auxiliary chamber 4, and a heat transfer medium 34 is sealed in the volume part 32. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a sub-chamber internal combustion engine, and more particularly to a technique for preventing abnormal combustion due to overheating of a sub-chamber wall.

As a sub-chamber internal combustion engine that solves the destabilization of lean combustion, those disclosed in Patent Documents 1 and 2 have a sub-combustion chamber that communicates with the main combustion chamber. A strong torch is ejected from the communication path between the sub-combustion chamber and the main combustion chamber, and stable lean combustion is realized in the main combustion chamber. As a result, it is possible to improve thermal efficiency and reduce exhaust gas, and improve ignitability under a lean air-fuel mixture.
JP 2002-81321 A JP 2004-308656 A

In the sub-chamber internal combustion engine, when the sub-combustion chamber is on the cylinder head side, the torch is ejected from the communication passage along with the combustion in the sub-combustion chamber due to the structure of the internal combustion engine. And the communication path becomes hot.
However, in Patent Document 1, there is no particular description regarding the cooling of the inside of the auxiliary combustion chamber and the communication passage. If some cooling is not performed, a part of the air-fuel mixture will be generated if the engine load is shifted to a higher load. There is a risk of early ignition (hot surface ignition in the compression stroke) due to high temperature, and there is a problem that combustion noise is generated if early ignition (hot surface ignition) is performed.

Further, in Patent Document 2, the thermal conductivity of the partition (subchamber wall) between the main combustion chamber and the subcombustion chamber is increased to lower the temperature of the subchamber (subchamber wall), and early ignition of the air-fuel mixture is performed. However, since the entire sub chamber is constantly cooled, there is a concern that the cooling loss increases and the high load is limited.
Furthermore, in Patent Document 2, the fuel spray is directly applied to the tip of the sub chamber, and the temperature of the sub chamber wall is lowered by the heat of vaporization. This increases the amount of unburned HC generated during cold start. There are concerns.

  The present invention has been made in view of the conventional problems as described above, and avoids an excessive increase in cooling loss and an increase in the amount of unburned HC, while the sub-chamber has conventionally been difficult to cool. By suppressing the temperature rise at the tip, it is possible to more reliably avoid early ignition of the air-fuel mixture even at high loads, where the subchamber temperature tends to rise, and to expand the operating range limit to a higher load range. It is an object of the present invention to provide a sub-chamber internal combustion engine having a configuration.

  For this reason, the present invention provides a main chamber that is a main combustion chamber, a sub chamber that communicates with the main chamber via a communication passage, and has a smaller volume than the main chamber, and an ignition plug that ignites an air-fuel mixture in the sub chamber. In the sub-chamber internal combustion engine including the above, a hollow volume portion is formed in the sub-chamber wall, and a heat transfer medium is sealed in the volume portion.

With the above configuration, heat exchange is performed between the sub chamber wall heated by the combustion and the heat transfer medium sealed in the volume portion.
Therefore, the compact configuration effectively suppresses the temperature increase around the sub chamber wall, and can reliably avoid early ignition of the air-fuel mixture around the sub chamber wall even at high loads, thereby limiting the operating range. Is expanded to a higher load range.

  In addition, in order to reduce the temperature of the sub chamber wall, it is not necessary to increase the thermal conductivity of the sub chamber wall or to apply fuel spray to the tip of the sub chamber, and an excessive increase in cooling loss can be achieved. The concern about an increase in the amount of unburned HC is also eliminated.

Below, 1st Embodiment in this invention is described.
In the present embodiment, as shown in FIG. 1, the combustion chamber is composed of a main chamber 2 (main combustion chamber) and a sub chamber 4.
The main chamber 2 is composed of a cylinder head 6, a cylinder block 8, and a piston 10.

The sub chamber 4 has a smaller volume than the main chamber 2 and extends in a substantially vertical direction above the main chamber 2 (on the cylinder head 6 side) in a substantially vertical direction, and a tip portion 4a on the main chamber 2 side is formed in a hemispherical shape. The main chamber 2 communicates with the main chamber 2 through a plurality of communication passages 12 opened at the distal end portion 4a of the sub chamber wall, thereby enabling gas exchange.
The intake port 14 introduces fresh air into the main chamber 2 via the intake valve 16, and the exhaust port 18 discharges exhaust from the main chamber 2 via the exhaust valve 20.

The intake valve 16 and the exhaust valve 20 are driven by an intake valve drive cam 22 and an exhaust valve drive cam 24, respectively. The intake valve 16 and the exhaust valve 20 include an intake valve spring 26 and an exhaust valve spring 28, respectively.
A fuel injection valve (not shown) is arranged to inject fuel spray into at least one of the intake port 14, the main chamber 2, and the sub chamber 4.

The spark plug 30 is disposed with the electrode facing the sub chamber 4 so that the center axis thereof substantially coincides with the center axis of the sub chamber 4, and ignites the air-fuel mixture in the sub chamber 4.
A hollow volume portion 32 that branches from the tip portion 4a into a plurality of portions and passes between adjacent communication passages 12 so as to avoid the communication passage 12 and reaches the opposite side (upper peripheral wall 4b of the sub chamber wall). Is formed.

A heat transfer medium 34 is enclosed inside the volume portion 32.
As the heat transfer medium 34, a substance that causes a phase change from a solid phase to a liquid phase at about 600K to 1000K in a temperature range higher than the boiling point of water may be used, but a substance that is liquid at room temperature may also be used. As such a substance, for example, sodium is known, but with a single metal, thallium, magnesium and the like have similar properties. In addition, tellurium, sodium peroxide, and the like can be used as the heat transfer medium 34. Further, the heat transfer medium 34 may be either a simple substance or a composite material.

  If the heat transfer medium 34 is a substance having a boiling point equivalent to that of water, the heat transfer medium 34 boils easily by combustion in the main chamber 2 and the sub chamber 4, and heat transfer medium is generated by generating bubbles (vaporization). There is a concern that the heat transfer coefficient of 34 may decrease, or the sub chamber wall may be damaged due to a significant increase in pressure in the volume 32. For this reason, the heat transfer medium 34 is a substance that causes a phase change at a temperature higher than the boiling point of water.

A cooling water passage 36 is disposed so as to be close to the portion of the peripheral wall 4b where the volume portion 32 is formed and to surround the peripheral wall 4b.
In the compression stroke having the above-described configuration, the air-fuel mixture flows from the main chamber 2 toward the sub chamber 4 through the communication passage 12. On the other hand, in the combustion expansion stroke, with combustion in the sub chamber 4, a torch-like flame jet is ejected from the sub chamber 4 toward the main chamber 2 through the communication passage 12, and the air-fuel mixture in the main chamber 2 is combusted. Let me. Note that the pressure in the sub chamber 4 varies as shown in FIG.

Due to the combustion in the sub chamber, the sub chamber wall, particularly the front end portion 4a on the main chamber side, becomes high temperature, and cooling is difficult even by gas exchange in the intake and exhaust. There is a problem that the operating range in which the combustion is possible is limited.
Therefore, in the present embodiment, the above-mentioned problem is solved by cooling a portion of the sub chamber 4 that is difficult to cool by promoting heat exchange (heat radiation) of the sub chamber 4 by the heat transfer medium 34.

That is, as shown in FIG. 5, in the compression stroke to the combustion stroke in which the temperature in the sub chamber 4 rises, the heat transfer medium 34 has a phase from a solid to a liquid from the point of time when the temperature of the phase change (melting point) is reached. The latent heat of change further absorbs heat from the tip portion 4a and effectively suppresses a rapid temperature rise of the tip portion 4a.
On the other hand, from the combustion period (late combustion stage) to before the intake stroke of the next cycle, the heat transfer medium 34 near the peripheral wall 4b is cooled by the cooling water flowing through the cooling water passage 36, and the heat transfer medium 34 near the tip 4a In addition, a temperature difference occurs between them, and vibration due to pressure fluctuation accompanying combustion in the main chamber 2 propagates to the melted heat transfer medium 34 via the tip 4a. Thereby, the convection of the heat transfer medium 34 is promoted between the vicinity of the tip portion 4a of the volume portion 32 and the opposite side (upper portion of the peripheral wall 4b), and the peripheral wall 4b having a relatively low temperature from the higher temperature tip portion 4a. Heat is transferred to the upper part, and heat exchange that cools the tip 4a is activated.

As described above, since the heat transfer medium 34 filled in the volume portion 32 can more effectively avoid the rapid temperature rise of the tip portion 4a and can cool the tip portion 4a more effectively, the tip portion 4a It is possible to prevent early ignition of the air-fuel mixture in a high load range where the temperature of the fuel is likely to rise. Therefore, it is possible to expand a high load (high output) region.
In the low load region, the temperature near the electrode of the spark plug 30 can be increased by moving heat from the tip portion 4a to the upper portion of the peripheral wall 4b, and the ignitability can be improved.

  Here, the central axis of the sub chamber 4 extends in the vertical direction of the engine, and the tip end portion 4a protrudes toward the main chamber 2 vertically downward of the engine. Further, the heat transfer medium 34 that has changed into a liquid due to the phase change is reduced in specific gravity by being heated in the vicinity of the front end portion 4a, while the specific gravity remains large in the vicinity of the upper portion of the peripheral wall 4b due to a relatively low temperature. Thereby, the vertical convection of the heat transfer medium 34 is further promoted.

Further, by arranging the cooling water passage 36 so as to surround the peripheral wall 4b, an effect equivalent to increasing the heat capacity of the peripheral portion of the sub chamber 4 is obtained, and an abnormality in the peripheral portion of the sub chamber 4 in a high load region. Temperature rise can be avoided more effectively. Thereby, also in the main chamber 2, since early ignition of the air-fuel mixture can be reliably avoided in the high load region, the limit of the operation region is expanded to the higher load region.
Further, since the cooling water passage 36 is arranged close to the volume portion 32, heat exchange by the heat transfer medium 34 can be further promoted, and at the same time, most of the heat radiation to the cooling water passage 36 is transferred from the tip portion 4a to the heat transfer medium. The amount of heat transferred from the air-fuel mixture in the sub chamber 4 is suppressed. In addition, since the heat transfer medium 34 is in a liquid phase even in a temperature range higher than the boiling point of the cooling water flowing through the cooling water passage 36, the sub chamber 4 (the peripheral wall 4b) is kept at a higher temperature than when cooled by the cooling water. Be drunk. For this reason, it becomes possible to suppress the cooling loss in the sub chamber 4, and it becomes possible to perform stable operation with higher thermal efficiency in the high load region.

As a method for forming the volume portion 32, for example, a lost wax manufacturing method may be used. Thereby, it becomes possible to manufacture easily and at low cost regardless of the shape inside the volume portion 32.
Below, 2nd Embodiment in this invention is described.
As shown in FIGS. 6 and 7, the present embodiment is different from the first embodiment in that the cross-sectional area of the volume portion 32 is enlarged as the position is closer to the upper part of the peripheral wall 4b.

Accordingly, convection of the heat transfer medium 34 is easily generated in the volume portion 32, heat exchange around the sub chamber 4 is further promoted, and the capacity of the heat transfer medium 34 cooled by the cooling water is increased. By increasing compared with the case of 1 embodiment, it becomes possible to improve the cooling performance of the front-end | tip part 4a.
Below, 3rd Embodiment in this invention is described.

In the present embodiment, as shown in FIGS. 8 and 9, the volume portion 32 that forms a plurality of passages extending in a substantially vertical direction between adjacent communication passages 12 is formed by connecting these plurality of passages to the upper part of the peripheral wall 4 b. This is different from the first and second embodiments in that the cooling water passage 36 is arranged so as to be gathered and joined to the gathering portion 32a of the place and to be close to the gathering portion 32a.
Thereby, since the location where the upper part of the peripheral wall 4b and the heat transfer medium 34 exchange heat is limited to the vicinity of the gathering part 32a, excessive cooling of the upper part of the peripheral wall 4b can be avoided. Therefore, the cooling loss of the sub chamber 4 can be suppressed and the ignitability of the air-fuel mixture is ensured.

On the other hand, since the cooling water passage 36 is disposed so as to be close to the collecting portion 32a, the cooling effect of the tip portion 4a is also ensured.
Below, 4th Embodiment in this invention is described.
In this embodiment, as shown in FIGS. 10 and 11, a plurality of fins 38 extending in a substantially vertical direction are formed in a portion formed on the peripheral wall 4 b of the surface (inner wall 32 b) forming the volume portion 32. This is different from the first to third embodiments.

  By arranging a plurality of fins 38 extending in the vertical direction at an appropriate number and interval with respect to the portion formed on the peripheral wall 4b of the inner wall 32b (that is, forming a large number of irregularities on the inner wall 32b), The contact area with the heat transfer medium 34 is increased. Thereby, the heat transfer amount of the inner wall 32b increases, and it becomes possible to promote the heat exchange between the heat transfer medium 34 and the peripheral wall 4b more effectively. In this way, the responsiveness of cooling to the operating state is improved, and stable operation is possible in a high rotation or high load range.

At the same time, the flow (convection) of the relatively high-temperature heat transfer medium 34 heading from the tip portion 4a to the upper part of the peripheral wall 4b and the relatively low-temperature heat transfer medium 34 heading in the opposite direction is made into a plurality of flows. It is possible to rectify by the passages defined by the fins 38, increase the cooling rate, and further improve the cooling performance of the tip portion 4a.
In addition to the above embodiment, as the simplest configuration, the heat transfer medium 34 that changes in phase at the temperature of the tip portion 4a in the high load region can be enclosed only in the tip portion 4a. In this configuration, the heat dissipation effect from the tip portion 4a due to the convection of the melted heat transfer medium 34 cannot be obtained, but abnormal combustion due to early ignition is prevented only by suppressing the temperature rise of the tip portion 4a due to latent heat at the time of phase change. effective.

Structure diagram of the first embodiment of the present invention AA sectional view in FIG. BB sectional view and CC sectional view in FIG. The figure of the pressure change of the sub chamber in a 1st embodiment of the present invention Explanatory drawing of the heat exchange in 1st Embodiment of this invention The cross-sectional view of the sub chamber wall in the second embodiment of the present invention AA sectional view and BB sectional view in FIG. The cross-sectional view of the sub chamber wall and the cooling water passage in the third embodiment of the present invention AA sectional view in FIG. The cross-sectional view of the sub chamber wall in 4th Embodiment of this invention AA sectional view and BB sectional view in FIG.

Explanation of symbols

2 Main chamber 4 Sub chamber 4a Tip (sub chamber tip)
6 Cylinder head 8 Cylinder block 12 Communication passage 30 Spark plug 32 Volume portion 34 Heat transfer medium 36 Cooling water passage 38 Fin

Claims (9)

A sub chamber provided with a main chamber which is a main combustion chamber, a sub chamber which communicates with the main chamber via a communication passage and has a volume smaller than that of the main chamber, and an ignition plug which ignites an air-fuel mixture in the sub chamber. In the internal combustion engine,
A sub-chamber internal combustion engine, wherein a hollow volume portion is formed in the sub-chamber wall, and a heat transfer medium is sealed in the volume portion.   The sub-chamber internal combustion engine according to claim 1, wherein the heat transfer medium is a substance that causes a phase change between a solid and a liquid in a temperature range higher than a boiling point of cooling water of the engine. A central axis of the sub chamber extends in a substantially vertical direction of the engine,
3. The sub-chamber internal combustion engine according to claim 1, wherein the tip portion of the sub-chamber protrudes toward the main chamber substantially vertically downward of the engine.   The sub-chamber internal combustion engine according to any one of claims 1 to 3, wherein a cooling water passage of the engine is disposed so as to surround a part of the sub-chamber.   The sub-chamber internal combustion engine according to claim 4, wherein the cooling water passage is disposed at a position close to the volume portion.   The sub chamber according to any one of claims 1 to 5, wherein the volume portion is disposed so as to reach the opposite side from the tip portion of the sub chamber, avoiding the communication path. Internal combustion engine.   The sub-chamber internal combustion engine according to claim 6, wherein the cross-sectional area of the volume portion gradually increases from the tip end portion of the sub-chamber toward the opposite side.   The sub-chamber internal combustion engine according to any one of claims 1 to 7, wherein unevenness is provided on a surface forming the volume portion to increase a contact area with the heat transfer medium.   9. The sub-chamber internal combustion engine according to claim 8, wherein the unevenness is formed by a plurality of fins extending in a substantially vertical direction.

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