JPH06100087B2 - Secondary combustion chamber of engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention mainly relates to a sub-combustion chamber provided in a diesel engine, particularly a sub-combustion in which a metal cylinder is fitted around the outer periphery of a ceramic sub-chamber constituting member. Regarding the room.

(Prior Art) In a diesel engine, auxiliary combustion chambers such as a swirl chamber and a pre-combustion chamber are provided in the cylinder head in addition to the main combustion chamber, but this auxiliary combustion chamber is exposed to combustion gas of extremely high temperature, In order to obtain good combustion properties, it is necessary to keep the temperature inside the chamber high. Therefore, it has been attempted to form the auxiliary combustion chamber with a ceramic material having excellent heat resistance and heat insulation. In that case, the ceramic material lacks strength and mountability to the cylinder head.
As disclosed in Japanese Patent No. 18, it is customary to fit and hold a pair of vertically divided ceramic sub-chamber constituent members in a metallic cylinder.

However, as the material of the metal cylinder, a material having a required heat resistance and good workability, and a low coefficient of thermal expansion so as to maintain the ceramic material even when the temperature rises during engine operation. Therefore, it has been considered to use a martensitic heat resistant steel such as SUH3 or SUS403 as a material satisfying such a condition (according to Japanese Utility Model Publication No. 58-51371). SUS43
The use of 0 is indicated).

However, it is not enough that the thermal expansion coefficient is small as described above in order for this cylindrical body to securely hold the ceramic material with sufficient restraining force even at high temperature and to maintain the holding property for a long period of time. , Shrink-fitting property is excellent, that is, shrink-fitting can obtain sufficient tensile stress corresponding to the tightening force on the ceramic material, and the tubular body itself has sufficient hot strength. And the like, and it is also necessary to have excellent oxidation resistance so as not to be oxidized by combustion gas. However, the above materials such as SUH3 and SUS403 are not necessarily satisfactory in these points.
According to the experiment, a gap is created between the cylinder and the ceramic material during engine operation, which causes problems such as damage to the mating surfaces of the pair of upper and lower ceramic materials and leakage of combustion gas from the mating surfaces. In addition, defects such as cracks were found in the cylinder itself.

(Object of the Invention) The present invention addresses the above-described situation regarding an auxiliary combustion chamber of an engine in which a ceramic sub-chamber constituent member is fitted and held in a metal cylinder, and as a material of the cylinder, Not only does it have a small coefficient of thermal expansion and excellent heat resistance and workability, but it also has a material that is excellent in shrink fit, hot strength, and oxidation resistance. Maintaining good retainability of the cylindrical body with respect to the ceramic material to prevent damage to the ceramic material, leakage of combustion gas, and the like, and also to prevent cracks and damages in the cylindrical body itself. With the goal.

(Structure of the invention) That is, in the present invention, in a sub-combustion chamber of an engine formed by shrink-fitting a metal cylinder on the outer periphery of a ceramic sub-chamber constituting member, the composition of the material of the cylinder is expressed by weight ratio, 0.13 to 0.20%
C (carbon), 0.30-0.70% Si (silicon), 0.50
~ 1.00% Mn (manganese), 10.50 ~ 12.50% Cr (chromium), 0.60 ~ 1.00% Mo (molybdenum), 0.10 ~
It is composed of 0.30% V (vanadium), 0.15 to 0.35% Nb (niobium), 0.02 to 0.05% B (boron), and Fe (iron) that substantially occupies the balance, and It is characterized in that the structure is made into a sorbite structure by quenching and tempering.

The above composition basically constitutes a martensitic heat-resistant steel, and the components in the respective ratios have the following functions.

That is, 0.13 to 0.20% of C is a necessary and sufficient amount to form a uniform austenite phase by quenching at a temperature of 1000 to 1250 ° C. in the coexistence with Mo as an alloying element, and more than this amount. If so, the precipitation of carbides becomes remarkable and the creep strength is lowered.

0.30 to 0.70% Si and 0.50 to 1.00% Mn are necessary and sufficient amounts as a deoxidizing agent.

10.50 to 12.50% of Cr improves heat resistance. If it is less than this, the heat resistance becomes insufficient, and if it is too much, it becomes 10
The austenite region near 00 to 1300 ° C becomes narrow and the creep strength decreases.

0.60 to 1.00% Mo strengthens the secondary effect phenomenon by annealing and increases the creep strength during hot working.

And 0.10-0.30% added to these basic compositions
V and 0.15 to 0.35% of Nb enhance the secondary effect phenomenon by annealing like the above-mentioned Mo to improve the creep strength during hot work, and especially V makes the crystal grains fine and heat-resistant. Property is further improved, and Nb improves oxidation resistance.

Further, 0.02 to 0.05% of B remarkably improves the hot strength, especially the creep strength.

Then, the structure is changed from a martensite structure to a sorbite structure by quenching and tempering treatment before shrink fitting and fitting a cylindrical body made of a material having the above composition into a ceramic sub chamber constituent member, The tensile strength and toughness of the metal cylinder are improved.

(Effects of the Invention) As described above, according to the present invention, as a material of a metal tubular body that is shrink-fitted to the outer periphery of a ceramic sub-chamber constituent member, it has a low thermal expansion coefficient and heat resistance and In addition to being excellent in workability, a material that is excellent in shrink fit and maintains the required tightening force for the sub-chamber constituent members, and that is excellent in hot strength and oxidation resistance as the cylinder itself Will be realized. As a result, the ceramic sub-chamber component can be held well even during long-term use as an engine sub-combustion chamber in which a metal cylinder is fitted around the outer periphery of the ceramic sub-chamber component. It is possible to obtain a sub-combustion chamber in which there is no breakage of the member or leakage of combustion gas from the mating surfaces, and there is no occurrence of cracks in the cylindrical body or deterioration due to oxidation.

(Example) Hereinafter, the Example of this invention is described based on drawing.

As shown in FIG. 1, a secondary combustion chamber 1 of a diesel engine
Is provided eccentrically with respect to the main combustion chamber 2 in the cylinder head 3 forming the upper surface of the main combustion chamber 2. The sub-combustion chamber 1 is composed of an upper member 4 and a lower member 5, each of which is made of a ceramic material such as Si ₃ N ₄ (silicon nitride), and a sub-chamber 6 having a substantially spherical interior. The sub-chamber forming member 7 and the metal cylinder 8 fitted around the outer periphery of the member 7 are fitted in the mounting recess 3a provided in the cylinder head 3 in a state where the both are integrated. Have been combined. The lower member 5 of the auxiliary chamber constituent member 7 is formed with an injection port 5a for communicating the auxiliary chamber 6 with the main combustion chamber 2, and the upper member 4 is provided with a glow plug insertion hole 4a and a fuel injection hole 4b. The tip of the glow plug 9 attached to the cylinder head 3 is projected into the sub chamber 6 through the insertion hole 4a, and the tip of the fuel injection nozzle 10 also attached to the cylinder head 3 is inserted through the injection hole 4b. It faces the sub-chamber 6. Further, a flange 8a is formed at the lower end of the metal tubular body 8, the flange 8a is press-fitted into the lower end of the mounting recess 3a, and the outer peripheral surface of the tubular body 8 and the recessed portion above the flange 8a are depressed. A heat insulating space 11 is formed between the inner peripheral surface of 3a.

However, the metal tubular body 8 is fitted to the outer periphery of the ceramic sub chamber constituent member 7 by shrink fitting, but the sub chamber 6 and the cylinder head 3 are in a high temperature state during engine operation. Also in this case, it is necessary that the shrink-fitting effect is maintained, good holding property for the sub chamber constituent member 7 is obtained, and this holding property is maintained for a long period of time.

Therefore, in this embodiment, a material having the following composition is used as the material of the cylindrical body 8 that satisfies the above requirements.

That is, the material of the cylindrical body 8 is 0.14% by weight of C,
0.43% Si, 0.66% Mn, 0.024% P, 0.002%
S, 11.03% Cr, 0.64% Mo, and 0.17% V, 0.18% Nb, 0.022% B, in addition to this,
The composition is Fe and substantially occupies the rest (see Table 1).

This composition is basically that of a martensitic heat-resistant steel, which has a low coefficient of thermal expansion and excellent heat resistance and workability, but it also contains 0.17% V to form crystals. The grains are refined to improve the heat resistance, the oxidation resistance is improved by containing 0.18% of Nb, and the hot strength is improved by containing 0.022% of B.

Then, the cylindrical body 8 is heated at 1100 ° C. for 60 minutes, then subjected to a quenching treatment for oil cooling, then heated at 690 ° C. for 3 hours, and then tempered for cooling by air, so that the structure is martensite. Change from system organization to solvite organization, then 600-8
It is heat-fitted at 50 ° C. and fitted onto the outer periphery of the sub chamber constituent member 7 by shrink fitting. As a result, the cylindrical body 8 contracts, and a required restraining force for the sub chamber forming member 7 is obtained.

As described above, it is possible to prevent deterioration due to oxidation due to long-term use of the metal tubular body 8 during hot use, generation of cracks and damage due to insufficient hot strength, and a ceramic sub-chamber constituent member. 7 is reliably held, and problems such as damage at the mating surface of the upper member 4 and the lower member 5 and leakage of combustion gas from the mating surface are eliminated.

In addition, the thermal expansion coefficient, hot strength and oxidation resistance of the material having the above composition according to this example were confirmed together with other martensitic heat resistant steels SUH3 (Comparative Example I) and SUS403 (Comparative Example II). The engine was actually equipped with a sub-combustion chamber consisting of a cylindrical body made of these materials and a ceramic sub-chamber constituent member, and a test for confirming the shrink fit and the condition of the sub-combustion chamber was conducted. Therefore, these results will be described below.

Here, the compositions of the above Examples and Comparative Examples I and II are as shown in Table 1, and the conditions for quenching and tempering are as shown in Table 2 (Examples are as described above).

First, FIG. 2 shows the coefficient of thermal expansion at each temperature of the materials (test pieces) having the compositions of the example of the present invention and the comparative examples I and II, both of which are 14.0 × 10 even at high temperature during engine operation. It was found that the thermal expansion coefficient was ^-6 / ℃ or less and had a sufficiently low coefficient of thermal expansion as a shrink fit material of this kind.

Next, FIG. 3 shows 0.2% proof stress (yield point) in the hot state. In both cases, the proof stress decreases remarkably from around 500 ° C., but in Examples, Comparative Examples I and II It was confirmed that the value was larger than that.

Further, FIG. 4 shows the 1000-hour creep rupture strength in the hot state, and this strength also decreases as the temperature rises, but the Example showed a larger value than Comparative Examples I and II in the entire temperature range. .

The 0.2% proof stress and the 1000-hour creep rupture strength in the hot state show the hot strength of the material.
The hot strength is superior to I and II.

Further, FIG. 5 shows the resistance to hot oxidation by increasing the amount of oxidation by leaving it in the air for 100 hours. The example and the comparative example I showed less increase in the amount of oxidation than the comparative example II and were excellent in the oxidation resistance. Was confirmed.

Further, FIG. 6 shows the values of shrink fit values of the tensile stress on the surface of the cylindrical body when the cylindrical body formed of the material having each composition shown in Table 1 is shrink fitted to the ceramic sub chamber constituent member. The higher the tensile stress, the greater the tightening force with respect to the sub chamber constituent member, and the better the shrink fit. In addition, this tensile stress was measured by a durability test of an engine equipped with the auxiliary combustion chamber (12,000 cycles of a new thermal endurance test in which the engine was operated at 4650 rpm at full load for 2 minutes and then at idle at 650 rpm for 1 minute. What to do)
I went before and after.

Here, the temperature difference between the cylindrical body and the sub chamber constituent member (Si ₃ N ₄ ) at room temperature and during operation is Δt ₁ , Δt ₂ , the thermal expansion coefficients are α ₁ and α ₂ , and the diameter of the fitting surface is d ₁ , d ₂ , the minimum shrinkage allowance δ for preventing a gap between the two during operation is δ = (Δt ₁ × α ₁ × d ₁ ) − (Δt ₂ × α ₂ × d ₂ ), and by substituting concrete numerical values into it, δ = (480 × 12.5 × 10 ^-6 × 30) − (680 × 3.5 × 10 ^-6 × 3
0) = 0.1086 (mm). Therefore, considering shrinkage of the cylinder due to long-term use, a shrink fit of about 150 μm is required.

And, the tensile stress on the surface of the cylinder at this shrink fit is
EXAMPLE about 70 Kg / mm ² (endurance experiment before), that a 55 Kg / mm ² (after durability experiment) showed a large value compared Comparative Example I, the II, it has excellent ocular shrink Was confirmed.

Finally, the conditions of the auxiliary combustion chamber in the above-mentioned actual durability test are summarized in Table 3, and the damages of the ceramic auxiliary chamber constituent members and the metal cylinders recognized in Comparative Examples I and II are shown in the examples. Moreover, it was confirmed that the leakage of the combustion gas from the mating surfaces of the sub-chamber constituent members, which was observed due to the adhesion of carbon, was smaller in the examples than in the comparative examples I and II.

Incidentally, as the material of the cylindrical body, the above-mentioned Examples and Comparative Examples I and II
In addition to martensitic heat resistant steel, SUS304 as austenitic heat resistant steel, Nimonic8 as Ni based super heat resistant alloy
0A (trade name), Incoloy 90 as a Fe-Ni based low expansion alloy
I also confirmed 3,904 (trade name), but SUS304 and Nim
The thermal expansion coefficient of onic80A is too large, and Incoloy 903,904
It was confirmed that is not suitable for use as this type of cylinder because of poor workability and oxidation resistance.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the constitution of the auxiliary combustion chamber and its periphery according to the present invention, and FIGS. 2 to 6 are the thermal expansion coefficient, 0.2% proof stress, creep rupture strength and oxidation of the material according to the embodiment of the present invention. Increase,
3 is a graph showing tensile stress on the surface of a cylinder and a comparative example together with a comparative example. 1 ... Sub combustion chamber, 7 ... Ceramic sub chamber constituent member, 8
...... Metal cylinder

Claims (1)

[Claims] 1. A sub-combustion chamber of an engine, which is obtained by shrink-fitting a metal cylinder around an outer periphery of a ceramic sub-chamber constituting member,
The material of the metal cylinder is 0.13 to 0.20% C by weight.
And 0.30-0.70% Si, 0.50-1.00% Mn, 10.50
~ 12.50% Cr, 0.60-1.00% Mo, 0.10-0.30%
V, 0.15 to 0.35% Nb, 0.02 to 0.05% B, and Fe that substantially occupies the balance, and the structure of the cylindrical body is a sorbite structure. Characteristic engine secondary combustion chamber.