JPH0134661Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to the structure of an engine subchamber, particularly the subchamber whose inner wall is made of ceramic material.

(Prior Art) In engines such as automobiles, the combustion chamber is composed of a main combustion chamber and an auxiliary chamber that communicates with the main combustion chamber through a nozzle hole, and fuel is injected from a fuel injection nozzle into the auxiliary chamber. A so-called sub-chamber combustion method is sometimes adopted in which ignition is performed and semi-combusted gas is ejected into the main combustion chamber for diffusion combustion.

In this combustion method, it is important to maintain the interior of the pre-chamber at a high temperature in order to suppress the emission of unburned gas such as hydrocarbons. As if
Attempts have been made to form the lower chamber constituting the subchamber from a ceramic material with excellent heat insulation properties. Further, the above publication discloses a configuration in which a gap C is provided between the outer periphery of the lower chamber A and the inner surface of the recess of the cylinder head B into which the chamber A is fitted, as shown in FIG. According to such a configuration, the gap C acts as a heat insulating space, and the heat insulating effect on the subchamber D is further improved.

By the way, when the sub-chamber is made of ceramic material as described above, the ceramic material has its own heat insulating properties so that the inner surface is hot and the outer surface is cold.
Tensile stress is generated on the outer surface due to the difference in thermal expansion due to the temperature difference, but since ceramic materials are generally vulnerable to tensile stress, this tensile stress can easily cause cracks or breakage. I do things. To deal with this, a ring made of metal or the like is fitted around the outer periphery of the ceramic material by shrink fitting, etc., and compressive stress is applied to the ceramic material in advance. It is possible to prevent stress from occurring. However, when a gap is provided around the outer periphery of the ceramic material in order to improve the heat retention effect for the subchamber as shown in the configuration shown in Figure 1, compressive stress cannot be applied to the ceramic material, resulting in cracks and cracks. Failure to effectively prevent damage.

(Purpose of the invention) The present invention deals with the above-mentioned problems when the inner wall surface of the auxiliary chamber is made of ceramic material.
Furthermore, it is possible to apply compressive stress to the ceramic material, thereby realizing a subchamber structure that has excellent heat insulation effects on the subchamber and prevents cracks and damage due to temperature differences between the inner and outer surfaces of the ceramic material. The purpose is to

(Structure of the invention) That is, the subchamber structure of the engine according to the present invention is such that the inner wall of the subchamber that communicates with the main combustion chamber through the nozzle hole is made of a ceramic material, and compressive stress is applied to the outer periphery of the ceramic material. In the structure in which a ring-shaped support member is fitted in the added state, a large number of tapered protrusions are formed on the outer periphery of the ceramic material, and the tips of the protrusions are brought into pressure contact with the inner surface of the support member.

According to such a configuration, a heat insulating space is formed between each protrusion between the outer periphery of the ceramic material and the support member, and compressive force is applied from the support member to the ceramic material via each protrusion. ,
The above objectives are achieved. In this case, each protrusion has a tapered cross section, that is, the wall thickness is thicker toward the peripheral wall of the ceramic material, and the wall thickness is thinner toward the tip, so that the compressive force acting from the tip is applied to the ceramic material. It will be applied evenly to the surrounding wall,
Further, thermal deformation of the outer peripheral portion of the ceramic material is absorbed.

(Example) Hereinafter, an example of the present invention will be described based on the drawings.

This embodiment is applied to a diesel engine, and as shown in FIG.
The combustion chamber includes a main combustion chamber 5 formed by the cylinder block 2, cylinder head 3, and piston 4, and a main combustion chamber 5 provided within the cylinder head 3 and communicated with the main combustion chamber 5 through a nozzle hole 6. It has an auxiliary chamber 7. The auxiliary chamber 7 is provided by fitting a pre-assembled and integrated hollow auxiliary chamber structure 8 into a recess 3a provided in the cylinder head 3, as shown in FIG. 8 is composed of a metal ring-shaped support member 9 and a hollow ceramic material 10 fitted inside the support member 9, and the inside of the ceramic material 10 is used as the subchamber 7. Further, the cylinder head 3 is equipped with a fuel injection nozzle 11 for injecting fuel into the auxiliary chamber 7, and a glow plug 12 for preheating the inside of the auxiliary chamber 7 when the engine 1 is started. Through holes 13 and 14 are formed in the upper part of the ceramic material 10 in order to introduce the jet stream into the subchamber 7 and to allow the tip of the glow plug 12 to enter the subchamber 7.

In this embodiment, the ceramic material 10 has a lower part 15 in which the injection hole 6 is formed, an upper part 16 in which the through holes 13 and 14 are formed, and an intermediate part 17 sandwiched between the two. Furthermore, the intermediate portion 17 is divided into upper and lower halves for manufacturing reasons. The materials of each part include a lower part 15 in which a nozzle hole 6 is formed through which high-temperature combustion gas and low-temperature air pass alternately, and an upper part 16 in which a crack is likely to occur due to the through holes 13 and 14.
Silicon nitride, which has excellent thermal strength, is used, and zirconia (partially stabilized zirconia), which has particularly excellent heat insulation properties, is used for the intermediate part 17, which requires a particularly good heat insulation effect between it and the cylinder head 3. . Further, the sub-chamber structure 8 is held in the cylinder head 3 by press-fitting the outer circumferential surface of a flange 9a provided at the lower end of the support member 9 into the entrance of the recess 3a.

However, the ceramic material 10 in this subchamber structure 8 is fitted to the support member 9 by shrink fitting or the like in a state where compressive force is applied from the surroundings, and as shown in FIGS. 3 and 4. The ceramic material 10
A vertical protrusion 1 is provided on the outer circumferential surface of the intermediate portion 17 in
8...18 are formed in large numbers at a constant pitch. These protrusions 18...18 are formed by cutting the outer circumferential surface of the ceramic intermediate portion 17 into a semicircular shape.
The ceramic intermediate portion 17 has a tapered protrusion in cross section that is continuous with the peripheral wall, and its tip surfaces 18a...18a are pressed against the inner surface of the support member 9, so that a half cross section is formed between each of the protrusions 18...18. A large number of circular spaces 19...19 are formed.

According to the above configuration, when the engine 1 is operating, air is forced into the auxiliary chamber 7 from the main combustion chamber 5 through the nozzle holes 6 during the compression stroke, forming a vortex flow, and from the compression stroke to the expansion stroke. Fuel is injected from the fuel injection nozzle 11 into the auxiliary chamber 7 at a predetermined time during the transition. This fuel is immediately ignited in the auxiliary chamber 7, becomes semi-combusted gas, and is injected from the nozzle hole 6 into the main combustion chamber 5, where it is further combusted and pushes down the piston 4.

However, the auxiliary chamber 7 is covered almost all around with the ceramic material 10, and there are many spaces between the sub chamber 7 and the support member 9 on the outside of the intermediate section 17 where heat is easily dissipated, especially toward the cylinder head 3 side. 19...19 are formed, the inside of the pre-chamber 7 is maintained at a high temperature due to the heat insulating properties of the ceramic material itself and the heat insulating effect of the spaces 19...19, and as a result, the ignition of the fuel in the pre-chamber 7, This results in good combustion.

On the other hand, the inner surface of the ceramic material 10 is at a high temperature and the outer surface is at a low temperature due to its own heat insulating properties, and the temperature difference causes the ceramic material 10 to thermally deform so as to generate tensile stress on the outer surface. However, the ceramic material 1
The lower part 15 and upper part 16 of 0 are directly compressed by the supporting member 9 from the surroundings, and the intermediate part 17, which has spaces 19...19 on the outside, is compressed by the supporting member 9 via the protrusions 18...18. Compressive force is applied by Therefore, no tensile stress is generated even by the thermal deformation described above, thereby preventing the occurrence of cracks or damage in the ceramic material 10. In particular, zirconia, which has excellent heat insulation properties and is used for the intermediate portion 17 of the ceramic material 10 in this embodiment, has a property that is particularly weak against the above-mentioned tensile stress.
The compressive force applied through the ... 18 reliably prevents the generation of tensile stress or cracks.

Further, since the projections 18...18 have a tapered shape, the tip surfaces 18a...
The compressive force applied from 18a is evenly distributed and acts on the peripheral wall of the ceramic material 10 (intermediate portion 17) as shown by the arrows in FIG. As a result, thermal deformation at the outer circumferential portion of the ceramic material 10 is absorbed, thereby more effectively preventing the generation of the above-mentioned tensile stress.

Furthermore, in this embodiment, as shown in FIG. 2, the circumferential wall of the ceramic intermediate portion 17 has approximately the same wall thickness in the vertical direction to prevent temperature differences in the vertical direction as much as possible. It is also designed to reduce the occurrence of thermal stress.

Note that the cut formed on the outer periphery of the ceramic intermediate portion 17 is not limited to a semicircular cross section, but may be a parabola or the like, as long as it forms a tapered protrusion.

Further, the lower part 15 and the upper part 16 made of ceramic material, which particularly require strength, may be formed of a heat-resistant metal.

(Effect of the invention) As described above, according to the present invention, the sub-chamber structure has an inner wall of the sub-chamber made of ceramic material, and the ceramic material is supported by a ring-shaped support member covering the outer periphery of the ceramic material. In this method, a heat insulating space is formed between the outer periphery of the ceramic material and the support member, and compressive force can be applied to the ceramic material by the support member. This improves the heat insulation effect on the auxiliary chamber, and prevents cracks and damage in the ceramic material.

[Brief explanation of the drawing]

Figure 1 is a sectional view showing a conventional example of subchamber structure;
Figures 5 to 5 show an example of the subchamber structure of the present invention.
Figure 2 is a longitudinal sectional view of the area around the pre-chamber in the engine.
Fig. 3 is a partially cutaway perspective view of the subchamber structure, Fig. 4 is a cross-sectional plan view of the sub-chamber structure cut along the line of Fig. 2, and Fig. 5 is an enlarged cross-sectional plan view of the main parts showing the operation. be. DESCRIPTION OF SYMBOLS 1...Engine, 5...Main combustion chamber, 6...Nozzle hole, 7...Subchamber, 9...Supporting member, 10...Ceramic material, 18...Protrusion, 19...Insulating space.

Claims (1)

[Scope of utility model registration request] In a configuration in which the inner wall of the auxiliary chamber that communicates with the main combustion chamber through the nozzle hole is made of a ceramic material, and the ceramic material is supported under compressive stress by a support member that covers the outer periphery of the ceramic material, the ceramic material is A large number of tapered protrusions are formed on the outer periphery, and the tips of the protrusions are brought into pressure contact with the inner surface of the support member to form a heat insulating space between the support member and the ceramic material. Engine pre-chamber structure.