JPS60145445A - Cylinder head structure for engine - Google Patents

Abstract

PURPOSE:To prevent any crack from occurring, by covering an outer surface of a ceranics cylindrical body with a metallic ring. CONSTITUTION:An upper part of a concave part 35 is formed into a semispherical concave part 36, while a ceramics cylindrical body 38 is inserted into the concave part 35, and a concave part formed in this cylindrical body 38 and the semispherical concave part 36 constitute a sub-chamber 34. A metallic ring 48 is fitted on an output surface of the cylindrical body 38 by means of press fit or shrinkage fit, and this metallic ring 48 performs such action as transmitting high heating temperature from a main chamber 42 to the cylindrical body 38. With this constitution, the occurrence of any crack attributable to a temperature differential is preventable.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a cylinder head structure for an engine, and particularly to a cylinder head structure for an engine provided with a sub-combustion chamber.

[Background Art] In general, diesel engine combustion methods include a direct injection method in which high-pressure fuel is injected into a single combustion chamber formed between a piston and a cylinder head for combustion, and a main combustion chamber (hereinafter referred to as the main combustion chamber). In addition to the pre-combustion chamber, a sub-combustion chamber (hereinafter referred to as sub-chamber) such as a pre-combustion chamber or a vortex chamber is installed, and combustion is performed in advance in the sub-chamber type. Among these, the pre-chamber type utilizes the intense flow and turbulence of air that occurs when it goes in and out of the communication hole when fuel and air are mixed, so it has the advantage of good combustion at a high air-fuel ratio. Additionally, in order to eliminate the difficulty of starting at low temperatures, which is a drawback of the subchamber type, a heater is installed above the subchamber.

However, in the subchamber type, the cooling area by the radiator is large, resulting in greater heat loss than in the direct injection type.

For this reason, recently, a structure has been developed in which the cylindrical body occupying the lower part of the subchamber is made of ceramics with excellent heat resistance to facilitate fuel ignition and to suppress heat loss. For example, in the cylinder head 10 shown in FIG.
2 is formed of a cylindrical body 14 made of ceramics,
Air is introduced from the main chamber 16 of the cylinder 20 through an inclined communication hole 18 provided between the cylinder 20 and the main chamber 16 . Next, in a state where the piston in the main chamber 16 compresses air and the temperature becomes high, fuel is injected into the sub chamber 12 from the injection nozzle 22 to perform compression ignition. The reference numeral 24 in the figure is a glow plug for a heater.

In such a ceramic cylindrical body 14, the inner circumferential surface through which high-temperature combustion gas passes and the bottom surface facing the main chamber 16 become extremely hot. On the other hand, the cylinder head 10 is cooled, and the outer peripheral surface and upper end surface of the cylindrical body 14 that are in contact with the cylinder head 10 are cooled.

Although ceramics have superior heat resistance and oxidation resistance compared to conventional metals, they lack tensile strength, so the temperature imbalance Φ causes thermal stress in the cylindrical body 14, which can lead to cracking. Cause.

For this reason, a structure in which the periphery of the cylindrical body is covered with a metal ring has been proposed (see Utility Model Application No. 112905/1983).

However, even in this type of structure, the outer surface of the cylindrical body is cooled through the cylinder head, and the inner surface is exposed to combustion gas, so there is always a considerable temperature difference. As a result, thermal stress is generated, which may cause cracks in the cylindrical body.

[Object of the Invention] The present invention has been made in view of the above circumstances, and its purpose is to provide an engine cylinder head structure that can prevent cracks in a ceramic cylindrical body caused by temperature differences. be.

[Structure of the Invention] In the present invention, the cylinder head is provided with four parts facing the main combustion chamber to form the auxiliary combustion chamber, and a cylindrical body made of ceramic is inserted into a part of the four parts to separate the main combustion chamber and the auxiliary combustion chamber. A cylinder head structure that is interposed between the cylinder head and the combustion chamber, in which the outer surface of a ceramic cylindrical body is covered with a metal ring, and a gap communicating with the main combustion chamber is provided on the outer periphery of the metal ring or on the axial side surface, and The outer periphery of the cylindrical body is communicated with the gap directly or via the metal ring, and high-temperature gas in the main combustion chamber is introduced into the gap, and the outer periphery of the cylindrical body is heated by the high-temperature gas directly or via the metal ring. It has become. Furthermore, the metal ring is made of a material with excellent thermal conductivity, so that the high heat of the combustion gas can be quickly transferred to the cylindrical body. This brings the temperature of the outer circumferential surface of the ceramic cylindrical body closer to the temperature of the combustion gas in the pre-chamber over the entire operating range of the diesel engine, from low speeds to high speeds, reduces the temperature difference between the inner and outer surfaces of the cylindrical body, and reduces thermal stress. 11- Prevents the occurrence of cracks.

In a preferred embodiment of the present invention, the metal ring annularly covers one of the outer surfaces of the cylindrical body, and an annular gap is formed below the outer surface of the cylindrical body.6 Therefore, the lower outer surface of the cylindrical body The high heat of the combustion gas is directly transmitted through the air gap, and the high heat is transmitted to the upper outer surface of the cylindrical body through a metal ring.

In another specific aspect of the present invention, the height or thickness of the annular gap is made larger as the portion farther from the main combustion chamber is disposed, so that the high heat of the combustion gas is more uniformly transmitted to the cylindrical body.

Furthermore, in another specific embodiment of the present invention, a second metal ring is provided below the metal ring, and a gap for introducing combustion gas is formed between the metal ring and the cylindrical body.

In this manner, the present invention attempts to transmit high heat to the cylindrical body as quickly and uniformly as possible by using both the good thermal conductivity of the metal ring and the gap for introducing combustion gas.

[Embodiment of the Invention] FIGS. 2(A) and 2(B) show a first embodiment of a cylinder head structure according to the present invention. cylinder head 3
0 of the cylinder block 32 via the gasket 31.
It is installed on one side. This cylinder head 30 has a main chamber 4 formed in the lower part, that is, in the cylinder block 32.
A cylindrical four part 35 is formed facing 2, and the upper part of this four part M is a hemispherical four part 36. A cylindrical body 38 made of ceramics is inserted into the fourth part 35 , and the four parts formed in this cylindrical body 38 and the hemispherical fourth part 36 constitute a subchamber 34 , and this subchamber 34 is a part of the cylindrical body 38 . It communicates with the main chamber 42 via an inclined communication hole 40 drilled into the bottom surface. Further, an injection nozzle 44 for fuel injection and a glow plug 46 for a heater are arranged in the cylinder head 30 facing the hemispherical four portions 36. In addition, although not shown, the cylinder head 30 includes:
Intake and exhaust valves, etc. are provided.

Therefore, when a piston (not shown) in the cylinder block 32 descends, a predetermined amount of air is sucked into the main chamber 42 from the intake valve. Next, this air is compressed to a high temperature by the rising of the piston, and this high temperature air is sent into the subchamber 34 through the communication hole 40. When a predetermined amount of fuel is injected from the injection nozzle 44, combustion occurs in the auxiliary chamber 34 and then in the main chamber 42, and the piston in the cylinder block 32 descends to rotate the crankshaft (not shown). .

A metal ring 48 is fitted onto the outer surface of the cylindrical body 38 by press fit or shrink fit. This metal ring 48 functions to transfer high heat from the main chamber 42 to the cylindrical body 38.

Furthermore, as can be seen from FIG. 2(B), a substantially semi-cylindrical cavity 50 is formed around the cylindrical body 38, and the lower part of the cavity 50 communicates with the main chamber 42. Further, a notch 48A is formed in a part of the lower end of the metal ring 48, so that the gap 50 also extends to the side surface of the metal ring 48 in the axial direction. Therefore, the high-temperature combustion gas burned in the auxiliary chamber 34 flows into the main chamber 42 through the communication hole 40, but a portion of the combustion gas also enters the gap 50, and this combustion gas flows into the metal ring 42 with good thermal conductivity. The outer surface of the cylindrical body 38 is quickly heated through the notch 48A or directly at the notch 48A. Further, heat from the notch gap of the metal ring 48 can also be transferred to the outer surface of the cylindrical body 38 . Since the heating action of the cylindrical body 38 by the combustion gas is performed repeatedly during operation of the engine, the temperature difference between the inside and outside of the cylindrical body 38 becomes small, thus preventing the occurrence of cracks due to thermal stress. That will happen.

It is desirable that the metal ring 48 be fitted to such an extent that it is in constant contact with the outer surface of the cylindrical body 38 during engine operation. Generally, ceramics have a small coefficient of thermal expansion and metals have a large coefficient of thermal expansion, so a gap may occur between the metal ring 48 and the cylindrical body 38 depending on the degree of temperature rise. Therefore, the materials and dimensions of both members need to be set in consideration of the coefficient of thermal expansion and thermal conductivity. Furthermore, since the metal ring 48 is exposed to combustion gas, it is desirable to use a material that also has heat resistance, such as heat-resistant steel such as iron-based, iron-nickel-based, nickel-based, or chromium-based steel. Since these metals have better thermal conductivity than ceramics, the cylindrical body 38 can be heated quickly.

Next, FIG. 3 shows a second embodiment of the present invention, in which, unlike the previous embodiment, a notch is not provided at the lower end of the metal ring 48, and the outer periphery of the cylindrical body 38 is It comes into contact with the cavity 50 only through 48.

If the wall thickness t of the metal ring 48 is too small, the contact between the metal ring 48 and the cylindrical body 38 will deteriorate due to thermal deterioration.
Heat conduction from the combustion gas becomes uneven, and conversely, if the wall thickness t is too large, the responsiveness of heat conduction may deteriorate. Therefore, if all conditions are considered, the wall thickness of the metal ring 48 It is desirable to set t in the range of 0.5 to 5 mm.

It is desirable that the height h of the void 50 is set to 1/2 or more of the dimension a of the cylindrical body 38. This is because, although the state of thermal stress differs depending on the lower shape of the cylindrical body 38, if the shape is as shown in the figure, large thermal stress is likely to occur in the lower outer circumference. Furthermore, the axial height h of the cavity 50 is
It is desirable to form the height smaller than the height H of . Therefore,
The height h of the void 50 is 1/10 to 9 of the height H of the cylindrical body 38.
/10 is good. Further, if a means such as positioning that can reliably attach the cylindrical body 38 to the cylinder head 30 is used, it is possible to provide the gap 50 to a height equivalent to the height of the cylindrical body 38 without any problem.

The thickness C of the gap 50 is set to about 0.1 to 2 mm. If it is smaller than this, the introduction of combustion gas will be poor, and if it is too large, the volume ratio of the combustion chamber will also increase, and the ignitability will be impaired due to a reduction in the compression ratio. Although it is best to form the void 50 around the entire outer periphery of the metal ring 48, a semicircular shape can also provide a considerable effect. However, when viewed from above, the void 5
0 is preferably equal to or larger than the outer periphery of the main chamber 42 (that is, the gap 50 is made to extend to the right side of the inner circumferential arc of the cylinder block 32 in FIG. 3(B)). This makes it possible to protect the part facing the main chamber 42 where cracks are most likely to occur.

Therefore, various modifications other than those shown in FIGS. 2 and 3 are conceivable as long as the above-mentioned conditions are satisfied.

A third embodiment of the present invention is shown in FIGS. 4(A) and CB). In this embodiment, the metal ring 48 is connected to the cylindrical body 3.
8, and a gap 50 is also formed around the entire circumference of the metal ring 48.
The lower inner periphery of the metal ring 5 connected to the main chamber 42 is cut out in a ring shape, and the axial height of the gap 50 is the same as that of the metal ring 4.
8 is about half the height of 3. The metal ring 48 has a wall thickness of 1
mm nickel-base heat-resistant steel is used, and the gap 50 is 0.2 m.
It has a uniform thickness of m. Therefore, the high heat of the combustion gas introduced into the cavity 50 is transferred to the cylindrical body 3 through the metal ring 48.
This will be communicated to 8.

When this structure was used in a 4-cylinder diesel engine with a displacement of 2400 cc and operated under severe conditions, cracks appeared below the cylindrical body 38 in the conventional structure, but no cracks occurred in this structure. There wasn't.

A fourth embodiment of the present invention is shown in FIGS. 5A and 5B. In this embodiment, the lower outer periphery of the metal ring 48 is cut out in a ring shape to form an annular gap 50.

The metal ring 48 is made of iron-nickel base heat-resistant steel with an upper wall thickness of 2 mm and a lower wall thickness of 1 mm. Therefore, the void 5
The thickness of 0 is 1 mm. Further, the axial height of the gap 50 is the same as in the previous embodiment.

When this structure was operated using a diesel engine similar to the previous example, a larger amount of combustion gas was introduced into the gap 50 than in the third example, and the temperature of the metal ring 48 could be further raised. Also in this structure, high heat is transmitted to the cylindrical body 38 via the metal ring 48. As a result, no cracks were generated in the cylindrical body 38.

A fifth embodiment of the present invention is shown in FIGS. 6(A) and 6(B). The material, dimensions, etc. of the metal ring 48 are almost the same as those in the third embodiment, but the axial height of the gap 50 is approximately the same as the portion closed by the cylinder block 32 on the side where combustion gas is difficult to enter (the right side in the figure). It has a large shape. In addition, the air gap 50
The height dimension is from 1/2 to 9/10 of the height of the cylindrical body 38.
It changes continuously until

When this structure was tested under the same conditions as in the previous example, it was possible to raise the temperature almost uniformly even in the portion of the cylindrical body 38 away from the main chamber 42. Along with this, the outer surface temperature of the cylindrical body 38 can also be raised more uniformly than in the third embodiment,
Cracks in the cylindrical body 38 could be completely prevented.

A sixth embodiment of the present invention is shown in FIGS. 7(A) and 7(B). The material, dimensions, and attachment of the metal ring 48 are the same as in FIG. As a result, the outer surface temperature of the cylindrical body 38 was raised more uniformly than in the case of FIG. 4, and no adverse effects were caused to the cylindrical body 38.

A seventh embodiment of the present invention is shown in FIGS. 8(A) and 8(B). The metal ring 48 is made of iron-based heat-resistant steel with a wall thickness twice that of that shown in FIG.
It is formed by cutting the inner circumference of the However, in this embodiment, as can be seen from FIG. 8(B), the center is shifted to the right and the thickness is increased on the side where combustion gas is difficult to enter. Further, the height of the gap 50 is 2/3 of the height of the cylindrical body 38, and the gap dimension (gap thickness) with the metal ring 48 is continuously changed in the range of 0.2 to 1.8 mm. .

As a result, a large amount of combustion gas could be introduced to the right side of the gap 50, and the temperature of the outer surface of the metal ring 48 could be uniformly raised by 5 R. Furthermore, by increasing the thickness of the metal ring 48, thermal deterioration did not occur even when the metal ring was made of an iron-based metal whose heat resistance was somewhat inferior. Moreover, no cracks were generated in the cylindrical body 38 at all.

An eighth embodiment of the present invention is shown in FIGS. 9(A) and 9(CB). The metal ring 48 is made of iron-nickel base heat-resistant steel with a wall thickness of 0.7 mm, and its height is approximately half the height of the cylindrical body 38, and is fitted onto the -1 part of the outer periphery of the cylindrical body 38. . As a result, a gap 50 is formed below the metal ring 48, that is, on the axial side surface over the entire circumference.

As a result, the high heat of the combustion gas is directly transmitted to the cylindrical body 38 through the gap 50, resulting in a higher temperature, and the temperature difference between the inner circumferential surface and the outer circumferential surface of the cylindrical body 38 is further reduced. On the other hand, the temperature in the cylindrical body portion covered by the metal ring 48 was slightly lower, and the temperature distribution was wider than in the other examples.

However, in this structure, as in the previous embodiment, the cylindrical body 38
Not only did no cracks occur in the metal ring 48, but no deterioration was observed in the metal ring 48 at all. In addition, the structure 7 6 is easy to draw, and the cylinder head 30 and metal ring 48
Since it is easy to process, it is considered to be suitable for practical use.

10(A) and 10(B) show a ninth embodiment of the present invention, in which the height of the metal ring 48 is made shorter than the cylindrical body 38 as in the previous embodiment, and the cylindrical shape is It is attached to the upper outer periphery of the body 38. The thickness, material, etc. of the metal ring 48 are the same as in the third embodiment, but the thickness of the gap 50 is 1 mm,
Its axial height is in the range of 174 to 2/3 of the height of the cylindrical body 38, and is formed so that the side farther from the main chamber 42 is continuously larger.

As a result, the combustion gas is distributed throughout the void 50 and high heat is transferred to the cylindrical body 38 either directly or via the metal ring 48. In particular, by increasing the height of the gap 50 on the right side of the drawing, the temperature of the entire outer surface of the cylindrical body 38 increased uniformly.

Moreover, no cracks in the cylindrical body 38 and no deterioration of the metal ring 48 occurred.

11(A) and 11(B) show a 108th embodiment of the present invention. In this embodiment, the fourth part 35 has a stepped hole shape, and a second metal is further inserted below the metal ring 48. A ring 52 is fitted. In addition, the second metal ring 5
The inner periphery of the −1 end of 2 is in contact with a tapered portion 48A provided on the outer periphery of the lower surface of the metal ring 48. As a result, a thin gap 5o is formed between the second metal ring 48 and the cylindrical body 38 below the metal ring 48, that is, on the axial side surface thereof, and communicates with the main chamber 42.

Martensitic silicon-chromium base heat-resistant steel is used for the metal ring 48, and the gap 5o has an axial height equal to that of the cylindrical body 3.
The thickness can be reduced by inserting the second metal ring 52, and was set to 0.1 mm in the experiment. Further, the metal ring 48 could be made as large as 2 mm in thickness even though the thickness of the cavity 50 was small. The second metal ring 52 has a wall thickness of 6 mm and is made of the same material as the cylinder head 3o, and is used to protect the metal ring 48 from deterioration caused by combustion gas.

As a result, in this embodiment, the lower outer periphery of the cylindrical body 38 receives heat directly from the combustion ant gas, and the upper outer periphery receives heat through the metal ring 48, thereby increasing the temperature uniformly.

When an experiment similar to the above example was conducted with this structure,
Cracks in the cylindrical body 38 and deterioration of the metal ring 48 could be completely prevented. Further, since the metal ring 48 can be fixed by the second metal ring 52, the cylinder head 3
0 is easier to assemble than other embodiments, and a metal ring 48 with a large wall thickness can be used.

From the above experimental results, the results showed that the present invention was most effective.
This is the structure shown in Example 8.9.10. However, since no cracks occur in the cylindrical body 38 in other embodiments, it is considered that the structure is considerably more effective than the conventional structure.

[Effects of the Invention] As described in Section 2, in the cylinder head structure of the present invention, the outer surface of the ceramic cylindrical body is covered with a metal ring, and a gap communicating with the main combustion chamber is formed on the outer periphery or axial side surface of the metal ring. Since the outer periphery of the cylindrical body is directly connected to this gap through the metal ring, the high heat of the combustion gas is transmitted to the outer periphery of the cylindrical body directly or through the metal ring with good heat conduction. This has the effect of preventing cracks from occurring due to temperature differences between the inside and outside of the body.

[Brief explanation of the drawing]

FIG. 1 is a sectional view taken along the axis of an injection nozzle showing a conventional cylinder head structure, and FIG. 2(A) is a longitudinal sectional view showing a first embodiment of the cylinder head structure according to the present invention.
FIG. 2(B) is a sectional view taken along line BB in FIG. 2(A),
3(A), (B) to FIG. 11(A), (B) respectively show the second to tenth embodiments of the present invention.
), (B) is a sectional view corresponding to FIG. 3011...Cylinder head, 34φ...Sub chamber, 3811・φ Ceramic cylindrical body, 40...Communication hole, No. 42--Main chamber, 44...Injection nozzle, 1 48...Metal ring, 50...φ gap, 52 Kaiken/second metal ring. Agent Patent Attorney Jun Nakajima 2 Figure 4 (A) Figure 4 (B) ＼ 32゛4 Figure 5 (A) 0! - Figure 7 (A) Figure 7 (B) Figure 8 (A) Figure 8 CB) Figure 10 (A) Figure 10 (B) Figure 11 (A) Figure 11 (B) ) 3n. 'X, -to/゛

Claims (12)

[Claims] (1) A sub-combustion chamber is formed by providing four parts facing the main combustion chamber in the cylinder head, and a ceramic cylindrical body is inserted into a part of the four parts to create a space between the main combustion chamber and the sub-combustion chamber. In the cylinder head structure, the outer peripheral surface of the cylindrical body is covered with a metal ring, and a gap communicating with the main combustion chamber is provided on the outer periphery or axial side of the metal ring, so that the outer periphery of the cylindrical body is directly covered with a metal ring. A cylinder head structure for an engine, characterized in that the cylinder head communicates with the gap through the metal ring or the metal ring. (2) The engine cylinder head structure according to claim (1), wherein the gap is formed in a semicircular shape on the main combustion chamber side of the outer surface of the cylindrical body. (3) The engine cylinder head structure according to claim (1), wherein the gap is formed in an annular shape over the entire circumference of the outer surface of the cylindrical body. (4) Claims (1) to (3), wherein the metal ring covers the entire outer peripheral surface of the ceramic cylindrical body.
) The cylinder head structure for an engine as described in any of the above items. (5) The cylinder head structure for an engine according to claim (1), wherein the gap is formed by cutting out a part of the outer surface of a metal ring, and the gap communicates with the main combustion chamber. (6) The cylinder head structure for an engine according to claim (1), wherein the axial height of the gap is formed to be larger at a portion farther from the main combustion chamber. (7) The axial height of the gap is 1 of the height of the cylindrical body.
The cylinder head structure for an engine according to claim 1, wherein the engine cylinder head structure is from /10 to 9/10. (8) The engine cylinder head structure according to claim (1), wherein the gap has a thickness of 0.1 mm to 2 mm. (9) The cylinder head structure for an engine according to claim (1), wherein the thickness of the gap increases as the distance from the main combustion chamber increases. (10) The metal ring is 1/10 to 9/of the height of the cylindrical body.
10. The engine cylinder head structure according to claim 1, wherein the remaining gap not covered by the metal ring on the outer surface of the cylindrical body is formed in an annular shape. (11) The height of the gap in the axial direction is larger at a portion farther from the main combustion chamber, and the gap directly communicates with the outer surface of the cylindrical body. Engine cylinder head structure. (12) The engine according to claim (1), wherein a second metal ring is installed below the metal ring, and the gap is formed between the second metal ring and the cylindrical body. Cylinder head structure for.