JPH0646001B2 - Ceramic rotor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a ceramic turbo rotor constituting an exhaust turbocharger to be mounted on an internal combustion engine or the like equipped with a ceramic rotating body.

[Conventional technology]

For internal combustion engines used for various purposes, in addition to improving output and reducing fuel consumption, in order to further improve thermal efficiency and improve rotational response, the rotating body exposed to high temperatures must have mechanical strength and heat resistance. , A metal having excellent wear resistance and a small specific gravity, especially a sintered rotor such as silicon nitride sialon, silicon carbide, etc., that constitutes a turbo rotor, and has a rotating shaft on which a high load acts and high strength and excellent workability. It has been researched and proposed to use these as materials and combine them into ceramic turbo rotors.

In the ceramic turbo rotor of the type as described above, Kovar, Invar, Amber, iron-nickel alloy and the like, the thermal expansion coefficient of 1.3 × 10 ^-6 / ° C to 5.5 × 10 ^-6 / ° C. A metal member for joining having a recess for receiving a connecting shaft integrally projecting on the shaft core of a rotating body made of metal, and after joining the connecting shaft by brazing or interference fitting, the metal member is used for mechanical structure It has been performed to join metal rotary shafts made of carbon steel or the like by means such as pressure welding or welding.

However, the strength of the joining metal member is low at high temperatures, and the recess of the joining metal member that receives and joins the connecting shaft has an enlarged opening end of the recess during high-temperature and high-speed rotation. There was a great risk that the joint with the joining metal member would be separated. Therefore, in order to solve the above-mentioned drawbacks, as shown in FIG. 2, it has been proposed to use a heat-resistant alloy such as Inconel or Hastelloy having a high strength at high temperature as the joining metal member 3.

However, the coefficient of thermal expansion of Inconel, Hastelloy, etc.
11.3 × 10 ^-6 / ℃ to 16.0 × 10 ^-6 / ℃, silicon nitride 3.2 × 10 ^-6 / ℃, Sialon 3.0 × 10 ^-6 / ℃
℃, silicon carbide is 4.2 × 10 ^-6 / ℃ and metal member for bonding 3
Since the difference in thermal expansion between the connecting shaft 2 and the connecting shaft 2 integrally provided on the shaft core of the ceramic rotating body 1 is large, the connecting shaft 2 and the joining metal member 3 are not easily connected during brazing or interference fitting. The stress generated due to the difference in heat shrinkage was concentrated on the connecting shaft 2 which was a brittle material rather than the joining metal member 3 having high toughness, and could not withstand the stress, and the connecting shaft 2 was broken.

Further, in order to eliminate the above-mentioned drawback, as shown in FIG. 3, the length of the ceramic connecting shaft 2 is set to be at least three times the maximum outer diameter, and as shown in FIG. Recess 5 formed on metal rotary shaft 4 and ceramic connecting shaft 2
It has been proposed to provide the tight fitting area L with the location where it is not easily affected by the heat of the exhaust gas flowing in the bearing housing.

[Problems to be solved by the invention]

However, the above proposal focuses only on the required heat resistance characteristics of the joint portion between the ceramic member and the metal member, and increases the cost for grinding the ceramic coupling shaft and the long axis and the entire fitting region of the coupling shaft. Since it is difficult to perform uniform tight fitting over a wide range of temperatures from room temperature to high temperature, extremely large eccentric stress generated by high-speed rotation that changes rapidly is concentrated on the uneven fitting portion of the connecting shaft. As a result, it is unavoidable that the connecting shaft 2 is broken in the low speed rotation range, and the ceramic turbo rotor is not sufficiently satisfactory.

[Means for solving problems]

As a result of earnest research in view of the above-mentioned present situation, the present invention has revealed that the maximum outer diameter of a ceramic rotating body, the outer diameter of a ceramic connecting shaft, the outer diameter of a ceramic connecting shaft, and a shaft portion of a metal bearing based on various physical properties of a metal rotating shaft. Finding a correlation with the outer diameter, satisfying this correlation, in particular, the length of the connecting shaft is the maximum outer diameter of the connecting shaft.
In the recess of the metal rotary shaft that is less than 3 times and has a groove for mounting the seal ring, the connecting shaft is not in contact and the length is sufficient to fit in the recess of the bearing shaft cooled by oil. It is characterized by doing.

〔Example〕

 Hereinafter, the present invention will be described in detail with reference to Examples.

In FIG. 1, reference numeral 11 denotes a ceramic rotating body,
A connecting shaft 12 is integrally formed with the shaft core of 11. The connecting shaft 12 of the rotating body 11 is fitted into the recess 15 of the metal rotating shaft 13. In this case, the connecting shaft 12 and the metal rotary shaft 13 are not in contact with each other at the corresponding portion of the recess 15 having the annular groove 16 for mounting the seal ring, but at the corresponding portion of the bearing shaft portion 14 of the recess 15. They are joined by means such as shrink fitting, brazing, or the like.

In this example, the test piece cut out from the ceramic rotor 11 had a JIS three-point bending strength of 69.0 Kg / mm ² on average, and a silicon nitride rotor having a coefficient of thermal expansion larger than that of Kovar, Invar, etc. Even if the metal member fitted to the ceramic member is thinned in order to relieve the tightening stress caused by shrinkage, it has physical properties that can withstand high temperature and high speed rotation with an ambient temperature of 500 to 800 ° C and a peripheral speed of up to 600 m / sec. As
Coefficient of thermal expansion is 5.0 × 10 in the temperature range from room temperature to 600 ℃
^-6 / ℃ ~ 14.0 × 10 ^-6 / ℃, which is lower than Inconel and Hastelloy of the conventional example, 0.2% proof stress in the temperature range from room temperature to 650 ° C is 90 Kg / mm ² or more, which is higher than Inconel and Hastelloy of the conventional example. The dimensions of each part shown in Table 1 were machined and the connecting shaft 12 and the metal rotating shaft 13 were machined under the same conditions.
At the corresponding portion of the bearing shaft portion 14 of the recess 15 of the
Four ceramic turbo rotors were manufactured.

A comparative example using the SCM435 for the metal rotating shaft 13 was also used, and the same Inconel was used, as shown in FIGS. 2, 3, and 4.
The one prepared as shown in the figure is a conventional example. However, a comparative example,
In all the conventional examples, the joint between the connecting shaft and the metal rotary shaft is brazed.

In addition, in the conventional example of FIG. 2, a metal member for bonding Inconel is used.
After brazing the connecting shaft 2 to 3 and joining carbon steel SCM435 for machine structure to the metal member 3 for joining by electron beam welding
Joined at S.

The ceramic turbo rotor manufactured as described above was adjusted to an unbalance amount of less than 0.02 gcm using a balance tester, and subjected to a high temperature and high speed rotation endurance test at a supply gas temperature of 950 ° C.
The results in the table were obtained. It should be noted that those that have rotated up to a predetermined number of revolutions without abnormality are indicated by a circle, and those that have been damaged while rising to a predetermined number of revolutions are indicated by a cross. Fig. 5 shows the relationship between the maximum outer diameter of the ceramic rotor and the outer diameter of the ceramic rotor connecting shaft based on the results in Table 2, and the results of the high-temperature high-speed rotation durability test.

[Evaluation] As is clear from Tables 1 and 2, when the ratio of the outer diameter of the connecting shaft of the ceramic rotor to the outer diameter of the bearing shaft of the metal rotating shaft is less than 80% (Sample No. 1, 9,17,25,33) is
Even if the unbalance amount is less than 0.02 g · cm, it cannot withstand the eccentric stress generated by high-speed rotation, breaks from the connecting shaft at a peripheral speed of 500 m / s, and the above ratio exceeds 90% (Sample No. 5 , 13, 21, 29, 37), the thickness of the bearing shaft portion that receives and joins the connecting shaft becomes thin, undergoes repeated deformation due to the eccentric stress, and fractures from the innermost corner of the recess. Also has a problem with durability.

If the ratio of the length of the ceramic rotating body to the maximum diameter of the connecting shaft is 3 times or more (Sample No. 7,15,31,3
In the case of 9), fracture occurred from the connecting shaft at a peripheral speed of 600 m / sec or less, and it is considered that the eccentric stress was concentrated on the non-uniform tightening fitting part.

On the other hand, in the comparative example (Sample Nos. 8,16,24,32,40) using carbon steel SCM435 for machine structure on the metal rotating shaft, the innermost part of the recess that receives and joins the connecting shaft at the peripheral speed of about 500 m / s. A conventional example in which Inconel was used for the metal rotating shaft due to repeated deformation due to the eccentric stress from the corners, and it was fractured (Sample No. 4
1,42,43), in the case of sample No. 41, it was destroyed from the connecting shaft at a peripheral speed of 400 m / s, and the connecting shaft had a maximum diameter of 3 mm.
Specimen No. 42, which is more than doubled to reduce the required heat resistance of the joint
In the case of, the sample is broken at the peripheral speed of 500 m / s from the opening of the concave part of the metal rotary shaft that receives the connecting shaft. It was destroyed from the side edge of the rotating body. On the other hand, in the case of the present invention (sample numbers 2, 3, 4, 10, 11, 12, 18, 18, 19, 20, 26, 27, 2
(8,34,35,36) all endure high temperature and high speed rotation endurance tests of 600 m / sec at peripheral speed, and are destroyed from the ceramic rotating body, and the connecting shaft of the ceramic rotating body for joining and the metal rotating No abnormality was found in the bearing shaft of the shaft.

From Fig. 5 showing the relationship between the maximum outer diameter of the ceramic rotating body and the outer diameter of the connecting shaft of the ceramic rotating body (outer diameter of the connecting shaft: mm) ≥ 0.07 x (maximum outer diameter of the rotating body of ceramic : m
m) + 4.2 [however, 40 mm ≤ (maximum outer diameter of the ceramic rotating body) ≤ 150 mm] on the boundary line of "breakage from ceramic rotating body" and "breakage from ceramic connecting shaft" It is clearly divided into regions, and the results of the high-temperature high-speed rotation endurance test in Table 2 show that the region of "breakage rather than ceramic rotors" is desirable.

〔The invention's effect〕

As described above, according to the present invention, the maximum outer diameter of the ceramic rotating body based on the physical properties of the metal rotating shaft and the correlation between the ceramic connecting shaft outer diameter and the metal bearing shaft outer diameter are satisfied, Especially, the length of the connecting shaft is less than 3 times the maximum diameter of the connecting shaft, and the connecting shaft is not in contact with the concave part of the metal rotary shaft part having the groove for mounting the seal ring. By fitting in the recess of the shaft part, the required heat resistance of the joint between the ceramic member and the metal member is reduced, and the large eccentric stress caused by high-temperature high-speed rotation causes the metal-made rotating shaft to receive and join the ceramic connecting shaft. It is possible to obtain a ceramic turbo rotor excellent in durability and reliability, which does not cause breakage of the concave portion and does not break the connecting shaft of the ceramic rotating body.

[Brief description of drawings]

FIG. 1 is a partial sectional view showing a ceramic turbo rotor according to an embodiment of the present invention, FIGS. 2, 3, and 4 are partial sectional views showing a conventional example of a ceramic turbo rotor, and FIG.
The figure is a diagram showing the relationship between the maximum outer diameter of the ceramic rotor and the outer diameter of the ceramic rotor connecting shaft. 11: Ceramic rotor 12: Connecting shaft 13: Metal rotating shaft 14: Bearing shaft 15: Recess 16: Groove 17: Arc starting point of base L ₁ : Maximum outer diameter of ceramic rotor L ₂ : Connecting shaft length l ₁ : Coupling shaft outer diameter l ₂ : Bearing shaft outer diameter

Claims (2)

[Claims] 1. A ceramic turbo rotor comprising a ceramic rotating body and a metal rotating shaft joined together, wherein the metal rotating shaft has a coefficient of thermal expansion of 5.0 × 10 ⁻⁶ / ° C. to 14.0 × 10 ⁻⁶ / ° C. , Young's modulus of 15,000 to 20,000 Kg / mm ² and 90 Kg / mm
A connecting shaft made of a heat-resistant alloy having a 0.2% proof stress of ² or more and integrally protruding from the shaft core of the ceramic rotating body is used for bearing shafts other than the seal ring mounting groove of the metal rotating shaft. While fitting in the recess, the outer diameter of the connecting shaft of the ceramic rotating body is larger than the maximum outer diameter of the ceramic rotating body (outer diameter of the connecting shaft: mm) ≥ 0.07 × (of the ceramic rotating body Maximum outer diameter: mm) + 4.2 [however, 40 mm ≤ (maximum outer diameter of ceramic rotating body) ≤ 150 mm] is satisfied, and it is 80 to 90% of the outer diameter of the bearing shaft of the metal rotating shaft. A ceramic turbo rotor characterized in that. 2. The connecting shaft of the ceramic rotating body, wherein the length from the starting point of the base arc of the connecting shaft is less than 3 times the maximum outer diameter of the connecting shaft. Ceramic turbo rotor.