JPH05141211A - Ceramic valve - Google Patents

Abstract

PURPOSE:To prevent temperature rise in an exhaust valve and a suction valve by using ceramic material with the heat conductivity of specific values or higher at room temperature and 600 deg.C, respectively, for a ceramic valve as the exhaust valve and the suction valve for a gasoline engine. CONSTITUTION:A ceramic valve 1 with the shade 1a, the stem 1b and the axial end 1c is made of ceramic such as composite ceramic material for which monolithic simple substance of silicon nitride, silicon carbide, aluminum nitride, sialon, etc. or one or more of these is used as matrix. The heat conductivity is set to be 40W/(m.k) or more at room temperature and 20W/(m.k) at 600 deg.C. When the ceramic valve is applied to an exhaust valve, no temperature rise occurs in the valve, no hot spot appears in the valve area and no knocking source exists. When applied to a suction valve, the suction efficiency is improved to realize higher torque.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic valve, for example, a ceramic valve suitable for use as an exhaust valve or an intake valve for a gasoline engine.

[0002]

2. Description of the Related Art At present, heat-resistant chrome / nickel steel is often used as a material for exhaust valves for gasoline engines. This chrome / nickel steel has a thermal conductivity of 15 W / (m. Since it is as low as K), a so-called hot spot with the highest temperature is likely to be generated in the combustion chamber of the engine, which may cause knocking in the gasoline engine. There is also a problem that the fatigue strength and the creep strength of the heat-resistant steel may decrease due to the rise of the valve temperature.

In order to improve such a problem, FIG.
As shown in FIG. 1, the umbrella portion 11 a, the stem portion 11 b, and the shaft end portion 1
In the valve 11 having 1c, a sodium-filled hollow metal valve 11 in which the stem portion 11b is hollowed and the metallic sodium 12 is filled in the hollow portion 11d has been put into practical use.

However, the valve temperature tends to rise with the increase in the compression ratio and lean burn of the gasoline engine, and there is an increasing need to lower the temperature of the exhaust valve more efficiently. Then, in order to increase the cooling efficiency in the sodium-filled hollow metal valve 11,
It is necessary to increase the diameter of the hollow portion 11d and increase the amount of the metallic sodium 12 to be enclosed, but the stem portion 11b
At present, the valve cooling performance of the sodium-filled hollow metal valve 11 has almost reached its limit due to the strength of the above.

On the other hand, when a nickel-base or cobalt-base heat-resistant alloy is applied as a valve for a gasoline engine instead of heat-resistant steel in order to improve heat resistance, the high temperature strength is improved, but the thermal conductivity is improved. Is smaller than heat-resistant steel, the valve temperature tends to rise more. Further, since these materials also have a large specific gravity, there is a problem that the friction loss of the entire valve train also increases.

Therefore, it has been a problem to solve the above various problems.

[0007]

SUMMARY OF THE INVENTION The present invention has been conceived in view of the above-mentioned conventional problems, and it is possible to further lower the temperature of the exhaust valve and the intake valve as compared with the conventional one, and the temperature of the exhaust valve. It prevents the temperature rise of the intake valve to prevent hot spots from being formed, and also prevents the temperature rise of the intake valve to improve intake efficiency. It is an object of the present invention to provide a ceramic valve that can cope with an increase in engine rotation speed due to a reduction in engine speed.

[0008]

The ceramic valve according to the present invention has a thermal conductivity of 40 W / (m · K) at room temperature.
It is characterized in that it is made of a ceramic material having a temperature of 20 W / (m · K) or more at 600 ° C., and in the embodiment, the ceramic material is monolithic silicon nitride, silicon carbide, or aluminum nitride. , Sialon alone or composed of a composite ceramic material with one or more of them as a matrix, the thermal conductivity of which is 40 (W / mK) or more at room temperature and 20 (W at 600 ° C).
/ M · K) or more.

Further, in the same manner, at least the umbrella portion of the valve or the stem portion located in the valve guide may be made of a ceramic material. In the same manner, the strength of the ceramic material may be increased. , 4-point bending room temperature strength defined by JIS R1601 is 400 MPa or more.

The present inventors investigated the thermal conductivity of chromium / nickel steel (SUH36), which is one of the exhaust valve materials, and various ceramic materials, and obtained the results shown in FIG.

As shown in FIG. 2, the thermal conductivity of high-strength and high-toughness silicon nitride (Si ₃ N ₄ (A)), which has been generally used as a material for ceramic valves up to now, has a thermal conductivity of chromium-nickel steel (SUH36). ) Is slightly higher than that of silicon carbide (SiC (A),
SiC (B)) and aluminum nitride (AlN (A), AlN
(B)) has a significantly higher thermal conductivity than chromium-nickel steel (SUH36), and also has high thermal conductivity in silicon nitride (Si ₃ N ₄ (B)) than chromium-nickel steel (SUH36). It has been confirmed that the thermal conductivity of thermal conductivity is more than twice as high, and it is possible to lower the valve temperature by utilizing the characteristics of the ceramic material having such high thermal conductivity. The conductivity is
40W / (mK) or more at room temperature and 20W at 600 ° C
By using a ceramic material of (m · K) or more as the material of the valve, improvement of knock resistance when used as the material of the exhaust valve of a gasoline engine and improvement of intake efficiency when used as the material of the intake valve. The present invention has been completed after confirming that the above can be realized.

As the ceramic material, not only a single material such as silicon nitride, silicon carbide, aluminum nitride, sialon, etc., but also a composite ceramic material composed of one or more of them can be used. ..

The present invention is not limited to the case where the entire valve is made of the above-mentioned ceramic material having high thermal conductivity, and at least the umbrella portion of the valve or at least the stem portion located in the valve guide has the above thermal conductivity. Good results can also be obtained by using a ceramic material having a high temperature.

Considering the stress generated in the valve during the operation of the gasoline engine, the strength of the valve ceramic material is JIS R1601.
It was desirable that the four-point bending room temperature strength defined by the above standard be 400 MPa or more.

[0015]

The ceramic valve according to the present invention has a thermal conductivity of 40 W / (m · K) or more at room temperature and 600
Since it is made of a ceramic material with a temperature of 20 W / (mK) or higher at ℃, the temperature of the valve is hard to rise, and when applied to an exhaust valve, the temperature rise is prevented to prevent the valve from becoming hot. Spots are hard to form, which makes it hard to become a source of knocking, and when applied to an intake valve, intake efficiency is improved by preventing temperature rise, and torque is improved. Becomes

[0016]

EXAMPLE In this example, as shown in Table 1, as shown in FIG.
In the hollow portion 11d formed in 1b, metallic sodium 12
Hollow metal valve 11 made of SUH36 in which is encapsulated, solid metal valve made of SUH36 in which metal sodium is not encapsulated as Comparative Example 2, and high-strength / high-toughness silicon nitride conventionally used as a ceramic valve as Comparative Example 3. The present invention is carried out on a ceramic valve made of (Si ₃ N ₄ (A)), and an embodiment of the present invention is applied to a ceramic valve 1 having a cap portion 1a, a stem portion 1b and a shaft end portion 1c as shown in FIG. A ceramic valve made of high thermal conductivity silicon nitride (Si ₃ N ₄ (B)) as No. 1 and Example 2
As an example, a ceramic valve made of aluminum nitride (AlN (B)) is used, and as a third example, a B, C auxiliary silicon carbide (SiC) is used.
(A)) Ceramic valve and BeO as Example 4
It carried out with the ceramic valve made from an auxiliary agent silicon carbide (SiC (B)), respectively.

In evaluating each of these valves, first, a comparative temperature measurement experiment was carried out between various ceramic valves and metal valves by a motoring test on a table using a cylinder head.

In the experiment, as shown in FIG. 3, the camshaft of the engine 2 was driven by the motor 3 and the temperature of the water tank 4 was changed to 8%.
While setting the cooling water temperature to be 0 ° C. and the cooling temperature to be simulated, and the temperature of the oil tank 5 to be 80 ° C. to be the engine oil temperature to be simulated and constant, while reciprocating the valve incorporated in the engine 2, As shown in FIG. 4, the front portion (temperature measuring portion) of the umbrella portions 1a and 11a of each valve 1 and 11 is heated by the burner 6, and the thermocouple 7 provided at the temperature measuring point P is used.
The temperature measurement experiment was performed by.

In this case, the relative comparison experiment between the valves was carried out by the following procedure. That is, Comparative Example 1 serving as a reference
The umbrella surface of the valve 11 is heated by the burner 6 to adjust the burner heat amount to a predetermined temperature, and the burner heat amount is kept constant when the reference valve 11 temperature reaches a predetermined value. The relative comparison experiment between the valves was carried out by heating the umbrella surface of the valve (1) to be compared with this and then measuring the temperature of each part of the valve.

In this relative comparison experiment, temperature measurement was performed at least twice each, and the average value was used as data. The experimental conditions were cam rotation speed: 300 rpm, cooling water temperature: 80 ° C., cooling water amount: 80 l / min, lubricating oil temperature: 80 ° C. The experimental results thus obtained are shown in Table 1 and FIG.

[0021]

[Table 1]

As shown in Table 1 and FIG. 5, the sodium-filled hollow metal valve 11 of Comparative Example 1 exhibits a considerably larger valve temperature cooling effect than the solid metal valve of Comparative Example 2. Further, in Comparative Example 3 (high-strength / high-toughness silicon nitride (A)), the thermal conductivity is slightly better than that of heat-resistant steel (SUH36), so the temperature is almost the same as that of the sodium-filled hollow metal valve 11. There is.

On the other hand, in the ceramic valve 1 of the example of the present invention, considering the sodium-filled hollow metal valve 11 of the comparative example 1 as a reference, the high thermal conductivity silicon nitride (Si ₃ N ₄ (B)) of the example 1 is considered. ) Around -50 ° C, Example 2
The aluminum nitride (AlN (B)) and the silicon carbide (SiC (A), SiC (B)) of Examples 3 and 4 are observed to have a temperature decrease of −150 ° C. or more. From this result, it is understood that the ceramic valve 1 according to the present invention having both light weight and high thermal conductivity can be applied as an exhaust valve having excellent knock resistance.

FIG. 6 shows Example 1 (silicon nitride Si ₃ N ₄
(B)) and Example 3 (silicon carbide SiC (A)) were actually incorporated into a gasoline engine, and the power performance (torque curve) of the engine was measured.

In comparison with the torque curve of the engine using the sodium-filled hollow metal valve 11 of Comparative Example 1, in the case of Example 1 using the ceramic valve 1 made of silicon nitride having a high thermal conductivity, 4000 rpm or less. A torque increase of about 0.2 to 0.5 kgf · m is recognized in the rotation range of No. 3, and a ceramic valve 1 made of silicon carbide (A) having a higher thermal conductivity is used in Example 3 In the case of 1, the torque is improved by 0.5 to 0.8 kgf · m at the rotation speed of 4000 rpm or less, and about 0.2 kgf · m at the rotation speed of more than 4000 rpm.

Such an increase in torque improves knocking resistance due to a decrease in valve temperature, resulting in 1500 to 4000.
The ignition advance angle is about 2 to 6 de in the low and middle rpm range.
This is because it is possible to proceed. Therefore, the torque in the low to medium rotation range, which is the practical range of the engine, is the same as in Comparative Example 1 and Comparative Example 3, in which a conventional sodium-filled hollow metal valve or a ceramic using normal high-strength / high-toughness silicon nitride is used. Compared to valves, etc., it has improved 10-mode fuel consumption and LA10 that are urban driving modes.
It was found that it can have a positive effect on mode fuel economy.

FIG. 7 shows a method of calculating the surface temperature of each ceramic valve by finite element analysis (FEM). The temperature dependence of thermal conductivity is shown in FIG.
As shown in (A) of FIG.
It was approximated to be 0%, and the thermal conductivity between them was linearly supplemented. This approximation applies relatively well for many materials. Also, FIG. 7B shows a mesh division diagram.

FIG. 8 shows the results calculated by the finite element analysis, and shows the temperature difference with respect to the data of the sodium-filled hollow metal valve of Comparative Example 1 obtained from the experiment. From these results, if the thermal conductivity of the ceramic is 40 W / (m · K) or more at room temperature and 20 W / (m · K) or more at 600 ° C., at least a valve temperature lowering effect comparable to that of a sodium-filled hollow metal valve is obtained. It can be seen that

In the engine valve, heat is radiated from the valve seat through the face surface of the valve head portion and from the valve guide through the valve stem portion. Therefore, in order to exert the effect of the present invention, it can be said that at least the stem portion of the engine valve or the stem portion located in the valve guide is made of the above-mentioned ceramic material.

In addition, considering the stress generated in the valve during operation of the gasoline engine, it can be said that the strength of the ceramic valve material is preferably 400 MPa or more in the four-point bending room temperature strength defined by JIS R1601.

FIG. 9 shows the result of calculation of the relationship between the strength of the ceramic material and the yield rate after the guarantee test with the Weibull coefficient m = 10. As is clear from FIG. 9, when considering a guarantee test to secure the minimum strength required for a valve for a gasoline engine, 4
When a ceramic material having a bending strength smaller than 00 MPa is applied to a valve for a gasoline engine, the yield in the proof test is remarkably low at about 50%, so that it can be said that the average strength is 400 MPa or more.

[0032]

As described above, according to the ceramic valve according to the present invention, a sodium-filled hollow metal valve which has been partially put into practical use at present and a high strength / high toughness nitriding material which is a conventional ceramic valve material are used. Instead of applying silicon, monolithic silicon nitride, silicon carbide,
Aluminum nitride, sialon, etc. alone or one of them
It is composed of a ceramic such as a composite ceramic material having at least one kind of matrix, and its thermal conductivity is 40 W / room temperature at room temperature.
20W / (m · K) above (m · K) and 600 ° C
With the above configuration, it is possible to prevent the temperature of the valve from rising, and when this ceramic valve is applied to an exhaust valve of an engine, the temperature of the valve can be prevented from rising, so that Since hot spots are hard to be formed, the anti-knock performance is greatly improved, and the effect of being able to significantly improve the torque of the engine particularly in the low and middle speed range is obtained.

Also, when this ceramic valve is applied to an intake valve of an engine, it is possible to prevent the temperature of the intake valve from rising, thereby improving the intake efficiency and torque.

[Brief description of drawings]

FIG. 1 is a front explanatory view of a ceramic valve according to an embodiment of the present invention.

FIG. 2 is a graph showing temperature dependence of heat conductivity of heat-resistant steel (SUH36), which is an exhaust valve material that is often used at present, and various ceramic materials.

FIG. 3 is an explanatory view showing an outline of an experimental apparatus used when conducting a confirmation experiment of the present invention.

FIG. 4 is an explanatory diagram showing a procedure of performing a temperature measurement experiment with a thermocouple by heating with a burner in the confirmation experiment of the present invention.

FIG. 5 shows a sodium-filled hollow metal valve of Comparative Example 1, a solid metal valve of Comparative Example 2, and a high-strength / high-toughness silicon nitride valve of Comparative Example 3 according to the experimental procedure shown in FIGS. 3 and 4. It is a graph which put together the experimental result of the high thermal conductivity silicon nitride valve of Example 1 which is an invention example, the aluminum nitride valve of Example 2, and the silicon carbide valve of Examples 3 and 4.

FIG. 6 is a graph showing a torque curve when each of the ceramic valves of Examples 1 and 3 was actually installed in a gasoline engine and an experiment was performed in comparison with the sodium-filled hollow metal valve of Comparative Example 1.

7A and 7B show a heat conduction analysis simulation method by a finite element method (FEM), FIG. 7A is a graph showing temperature dependence of heat conductivity, and FIG. 7B is a mesh division diagram.

FIG. 8 is a graph showing a result obtained by estimating the correlation between the thermal conductivity of ceramics by FEM and the valve surface temperature.

FIG. 9 is a graph showing a result of calculating a yield rate of a ceramic valve after a guarantee test based on Weibull statistics.

FIG. 10 is a front half broken front explanatory view of a conventional sodium-filled hollow metal valve.

[Explanation of symbols]

 1 Ceramic Valve 1a Ceramic Valve Head 1b Ceramic Valve Stem 1c Ceramic Valve Shaft End

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toba Toba 2 Takara-cho, Kanagawa-ku, Yokohama, Kanagawa Nissan Motor Co., Ltd. (72) Inventor Satoshi Asano 2958, Ishikawa, Fujisawa, Kanagawa Fuji Valve Co., Ltd. (72) ) Inventor Yasushi Katase Toru Ishikawa 2958 Fujisawa, Kanagawa Fuji Valve Stock Company

Claims (4)

[Claims] 1. The thermal conductivity is 40 W / (m · K) at room temperature.
A ceramic valve, which is made of a ceramic material having a temperature of 20 W / (m · K) or more at 600 ° C. or above. 2. The ceramic valve according to claim 1, wherein the ceramic material is a single material of silicon nitride, silicon carbide, aluminum nitride, sialon, or a composite ceramic material having one or more of them as a matrix. 3. The ceramic valve according to claim 1, wherein at least the stem of the valve or the stem located in the valve guide is made of ceramic. 4. The ceramic valve according to claim 1, wherein the strength of the ceramic is 400 MPa or more in 4-point bending room temperature strength.