JPH0217151Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Field of Application) The present invention relates to the structure of a subchamber in a diesel engine, etc., and particularly relates to an improvement of a structure in which the subchamber wall is formed of ceramic.

(Prior Art) Various engines have been known that are equipped with an auxiliary chamber that communicates with the main combustion chamber. For example, in a diesel engine, air flows from the main combustion chamber into the auxiliary chamber through a nozzle to create a vortex flow in the auxiliary chamber. A vortex chamber type is widely used in which fuel is injected into a subchamber in the generated state and ignited. In this type of engine, preventing the dissipation of heat from the pre-chamber and keeping the pre-chamber temperature high is effective in improving ignition performance at low temperatures and preventing half-misfires. When made of highly conductive aluminum alloy, it is strongly desired to prevent heat dissipation from the subchamber. For this reason, a device has been developed in which the inner wall of the sub-chamber is made of a ceramic material with excellent heat insulation properties.

In addition, when the sub-chamber wall is formed of a ceramic material, as shown in Japanese Unexamined Patent Publication No. 57-10723, the ceramic material is attached to the nozzle for the purpose of facilitating processing of the ceramic material and preventing damage during processing. A ceramic member is molded separately into a cavity part and a cavity part, and a metal sleeve is fitted around the outer periphery of both parts by shrink fitting, etc., to integrate these parts and apply compressive stress to the ceramic member. It is known what has been done. By applying compressive stress to the ceramic member in advance in this manner, it is also possible to prevent the occurrence of cracks due to thermal stress during engine operation. In other words, since ceramic has lower tensile strength than metal, cracks occur when tensile stress is applied to the outer periphery of the ceramic member due to the temperature difference between the inside and outside of the ceramic member when the temperature inside the subchamber rises. Although this is likely to occur, if compressive stress is applied in advance, the above-mentioned tensile stress can be suppressed. In addition, in the above publication, only the nozzle part and the lower peripheral wall of the sub-chamber wall are made of ceramic material, but in order to further enhance the heat insulation effect, a structure in which the entire sub-chamber wall is made of ceramic material has also been proposed. In this case as well, the ceramic member is divided into a plurality of parts in advance, and the parts are integrated while applying compressive stress using a metal sleeve or the like.

Incidentally, in such a structure, the coefficient of thermal expansion of the metal sleeve is higher than that of the ceramic member, and when the ceramic member is divided into parts, the parts that require particularly high thermal shock resistance and the other parts are made of different types. In the case of a ceramic member, the coefficients of thermal expansion of these parts are different, so that as the temperature of the ceramic member and sleeve changes, the above-mentioned compressive stress also changes. Therefore, there has been a desire for a means that can absorb the above-mentioned difference in coefficient of thermal expansion and always apply uniform compressive stress to the ceramic member.

(Purpose of the invention) In view of these circumstances, the present invention applies uniform compressive stress to the ceramic member forming the inner wall of the subchamber, and prevents stress from being applied to the ceramic member even if the holding member covering the outer periphery of the ceramic member expands thermally. An object of the present invention is to provide an engine pre-chamber structure that can more reliably prevent the occurrence of cracks in ceramic members by preventing the compressive stress caused by the ceramic member from decreasing.

(Structure of the invention) The present invention includes an auxiliary chamber that communicates with the main combustion chamber, an inner wall of the auxiliary chamber is formed of a ceramic member, and a support member that covers the outer periphery of the ceramic member has a coefficient of thermal expansion larger than that of the ceramic member. In the subchamber structure of an engine made of material, a mat-like thermal expansion member that expands in the thickness direction as the temperature rises is interposed between the ceramic member and a support member that covers the outer periphery of the ceramic member. The structure is such that uniform compressive stress is applied from the support member to the ceramic member via the thermal expansion member. According to this structure, compressive stress is applied in advance to the ceramic member from the support member via the thermal expansion member, and even when the temperature rises, the thermal expansion member that thermally expands in the thickness direction applies compressive stress to the ceramic member. The support member effectively exhibits the effect of increasing the compressive force, thereby compensating for the decrease in compressive force caused by the thermal expansion of the support member.

(Embodiment) FIG. 1 shows an embodiment of a pre-chamber structure applied to a swirl chamber type diesel engine. In these figures, 1 is a cylinder block and 2 is a cylinder head, both of which are molded from aluminum alloy or the like.
A piston 4 is inserted into the cylinder hole 3 of the cylinder block 1, and a main combustion chamber 5 is formed above the piston 4. On the other hand, a main combustion chamber 5 is provided in the vicinity of the side of the cylinder head 2 through a nozzle 7.
A subchamber (vortex chamber) 6 communicating with the vortex chamber is provided.
Furthermore, a fuel injection valve 8 that injects fuel toward a predetermined position within the auxiliary chamber 6, and a globe lug 9 whose tip extends into the auxiliary chamber 6 for preheating during startup are attached to the cylinder head 2. There is. As the piston 4 operates, air flows from the main combustion chamber 5 through the nozzle 7 into the auxiliary chamber 6, and the air is highly compressed in the auxiliary chamber 6, and fuel is injected from the fuel injection valve 8 in a state where a vortex is generated. is injected and self-ignited, and the flame is sent out from the nozzle 7 to the main combustion chamber 5. 10 is a seal member installed at the tip of the fuel injection valve 8.

The entire inner wall of the auxiliary chamber 6 is formed of a ceramic member 11. This ceramic member 11
It is desirable to form the ceramic material by combining a part made of silicon nitride, which has excellent thermal shock resistance, and a part made of partially stabilized zirconia, which has inferior thermal shock resistance but excellent heat insulation properties. . For example, a lower end wall 11a having a spout 7,
The lower peripheral wall 11b, the through hole 12 through which the fuel injection valve 8 is exposed, and the through hole 1 through which the globe lug 9 is inserted.
The ceramic member 11 is divided in advance into three parts: an upper dome-shaped wall 11c having a diameter of 3, the lower end wall 11a receiving a large thermal shock near the nozzle 7 is made of silicon nitride, and the lower peripheral wall 11b is made of partially stabilized zirconia;
The upper dome wall 11c is formed of silicon nitride or partially stabilized zirconia, and these three are bonded together to form a predetermined shape. Alternatively, the ceramic member may be preliminarily divided into two parts, a lower part and an upper part from the middle part of the peripheral wall, the lower part being molded with silicon nitride, and the upper part being molded with partially stabilized zirconia.

The ceramic member 11 is held within a shell (supporting member) 14 made of metal or the like, and a thermal expansion member 15 is interposed between the inner peripheral surface of the shell 14 and the outer peripheral surface of the ceramic member 11. . The shell 14 is formed to cover the entire member except the lower end surface of the ceramic member 11, and the through holes 12, 13 of the ceramic member 11 are formed near the upper end of the shell 14.
Corresponding through holes 16 and 17 are provided.
The thermal expansion member 15 is formed into a mat shape by mixing a heat-resistant fiber material such as ceramic fiber or glass fiber with a thermal expansion substance such as vermiculite or vermiculite, and the thickness changes depending on the temperature rise. It has the property of expanding in one direction and has both elasticity and heat resistance. This thermal expansion member 15 is installed so as to surround the lower peripheral wall 11b of the ceramic member 11 and the outer periphery of the range excluding the upper end of the upper wall 11c, and the shell 14 is fitted onto the ceramic member 11 from the outside. As a result, the thermal expansion member 15 is in a compressed state,
Compressive stress is applied from the shell 15 to the ceramic member 11 via the thermal expansion member 15.

Ceramic member 1 integrated in this way
1, the shell 14, and the thermal expansion member 15 constitute a sub-chamber insert 18, and this insert 18 includes:
For the recessed hole 19 formed in the cylinder head 2,
The lower edge 14a of the shell 14 and the cylinder head 2
A small hole 20 for positioning provided in each of the
21 and a pin 22 connected thereto, the cylinder head 2 is fitted into the cylinder head 2 while being positioned in the circumferential direction, and the lower end edge 14a is fitted into the inner surface of the lower end of the recessed hole 19, thereby being fixed to the cylinder head 2. There is.

In this auxiliary chamber structure, when ignition and combustion are repeated in the auxiliary chamber 6 and the temperature inside the auxiliary chamber 6 rises, the inner wall of the auxiliary chamber 6 is formed of the ceramic member 11 to maintain heat. Sexuality is enhanced. Also,
Since compressive stress is applied to the ceramic member 11 from the shell 14 via the thermal expansion member 15, tensile stress caused by the temperature difference between the inside and outside of the ceramic member 11 is suppressed, and the ceramic member 11 is prevented from occurring.

Since the shell 14 has a higher coefficient of thermal expansion than the ceramic member 11, if the shell 14 is in direct pressure contact with the outer peripheral surface of the ceramic member 11, the compressive force on the ceramic member 11 will be reduced when the shell 14 thermally expands. However, if the thermal expansion member 15 is interposed as described above, this thermal expansion member 15 will cause the ceramic member 1 to decrease as the temperature rises.
Shell 14 to increase the compressive force on 1
The decrease in compressive force due to thermal expansion is compensated for. Further, as described above, the ceramic member 11 has a plurality of parts 11a, 11b, 11c using different types of ceramic materials.
Therefore, even if these parts have different coefficients of thermal expansion, a uniform compressive force is applied to the ceramic member 11 via the highly elastic thermal expansion member 15. Therefore, the ceramic member 11 and the shell 1
Even if the temperature of the ceramic member 11 changes, this difference in thermal expansion will prevent the holding force from decreasing and the ceramic member 11 will come off, and the occurrence of cracks will be more reliably prevented. .

FIG. 2 shows another embodiment of the invention. In this embodiment, the shell 24 is formed into a cylindrical shape that covers the outer periphery of the ceramic member 11 except for the lower end surface and the upper dome-shaped portion, and an annular heat insulating space 2 is formed on the outer periphery.
6 is provided. This heat insulating space 26 is formed by making a predetermined range of the inner peripheral surface of the recessed hole 19 of the cylinder head 2 larger in diameter than the shell 24. Further, the thermal expansion member 25 interposed between the ceramic member 11 and the shell 24 has an upper end extending upward from the shell 24, and this upper end portion 25a is interposed between the inner surface of the recessed hole 19 and the ceramic member 11. ing.

With this structure, heat radiation from the outer periphery of the ceramic member 11 is suppressed by the heat insulating space 26, so that the heat retention of the subchamber 6 is enhanced and the temperature difference between the inside and outside of the ceramic member 11 is reduced. This is more effective in preventing cracks. In this case, the thermal expansion member 25 has the same function as the thermal expansion member 15 of the first embodiment, and also has an upper end 25a that connects the inner surface of the recess 19 and the ceramic member 1.
1 and also exerts a sealing effect to prevent gas flow. Therefore, gas in the auxiliary chamber 6 is prevented from leaking into the heat insulating space 26 from the through holes 12 and 13, and the heat insulating space 26 is prevented from becoming a dead volume.

(Effect of the invention) The present invention as described above has a mat-like thermal expansion that expands in the thickness direction as the temperature rises between the ceramic member forming the inner wall of the subchamber and the retaining member covering the outer periphery of the ceramic member. Since the structure has a structure in which a uniform compressive stress is applied from the support member to the ceramic member through the thermal expansion member, the heat between the ceramic member and the holding member when the temperature rises is reduced. The decrease in compressive stress caused by the difference in expansion coefficients is compensated for by the thermal expansion member, making it possible to securely hold the ceramic member and more reliably prevent the occurrence of cracks. Furthermore, the thermal expansion member can improve the heat insulation and sealing properties around the ceramic member.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing one embodiment of the present invention;
The figure is a sectional view showing another embodiment. 1...Cylinder block, 2...Cylinder head,
5... Main combustion chamber, 6... Sub-chamber, 11... Ceramic member, 14, 24... Shell (holding member), 15, 2
5...Thermal expansion member.

Claims (1)

[Scope of utility model registration request] A sub-chamber that communicates with the main combustion chamber, an inner wall of the sub-chamber is made of a ceramic member, and a support member that covers the outer periphery of the ceramic member is made of a material with a higher coefficient of thermal expansion than the ceramic member. In the chamber structure, a mat-shaped thermal expansion member that expands in the thickness direction as the temperature rises is interposed between the ceramic member and a support member that covers the outer periphery of the ceramic member, and the support member is expanded through the thermal expansion member. A pre-chamber structure for an engine, characterized in that a uniform compressive stress is applied to the ceramic member.