JPH0218243Y2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a ceramic turbine wheel that is used in a turbocharger for an internal combustion engine, a gas turbine, etc. and is exposed to high-temperature gas.

Conventional technology Although ceramics have a low specific gravity,
It has superior heat resistance compared to metals and strength comparable to that of metals. For example, silicon nitride (Si ₂ N ₅ ) ceramics, which have been attracting attention recently, have a bending strength of 90 kgf/mm ² at room temperature. However, even at 1000°C, it still has a bending strength of 80 Kgf/mm ² .

Ceramics, which have such excellent heat resistance, are being adopted in place of metal parts for various mechanical parts that are subject to harsh operating conditions.One example is the turbine blade wheel used in the turbocharger of an internal combustion engine. can be mentioned.

A turbocharger is a device that precompresses intake air or a mixture by rotating an exhaust turbine using engine exhaust energy and driving a compressor with that power. Since it is a member that is exposed to heat and rotates at high speed, it is effective to form it from ceramics that have excellent heat resistance and low specific gravity.

However, it is extremely difficult to form a turbine wheel and the rotary shaft that supports it with high machining precision into one piece, and in order to solve this problem, the turbine wheel, which has a high heat load, is made of ceramic. , a ceramic turbine wheel with a metal rotating shaft with high machining accuracy was introduced.

For this type of turbine blade wheel, Japanese Patent Application Laid-Open No. 1983-
As shown in Publication No. 42520, in order to connect a ceramic turbine wheel to a metal rotating shaft, the boss part of the turbine wheel was fitted integrally into the hollow cylindrical part of the rotating shaft. When the state changes from a stopped state to a high-temperature operating state, the hollow cylindrical part of the metal rotary shaft, which has a high coefficient of thermal expansion, expands more than the boss part of the ceramic turbine wheel, which has a lower coefficient of thermal expansion. There is a risk that the turbine impeller boss portion may slip out of the rotary shaft hollow cylinder portion, and as a measure to prevent this, the axial length of the boss portion is made to be at least three times its diameter. For this reason, in this turbine wheel, the diameter of the rotating shaft becomes thick over the entire length, making it difficult to reduce the weight.

In addition, in the turbine wheel described in Japanese Utility Model Publication No. 56-150801, a hollow cylindrical portion of the metal rotary shaft is connected to the boss portion of the ceramic turbine wheel through a metal sleeve having approximately the same coefficient of thermal expansion. Although it was a tight fit, the outer diameter of the shaft had increased, making it difficult to reduce the weight.

As a product that overcomes these difficulties, the
There are those described in JP-A-5701 and JP-A-59-103902.

Problems that the invention attempts to solve The problem described in Utility Model Application Publication No. 56-5701 is as follows:
As shown in FIG. 1, the length of the boss part 02 of the ceramic impeller 01 is set to be approximately equal to its diameter, and the boss part 02 is made of a metal whose coefficient of thermal expansion is close to that of the ceramic. Shrink fit sleeve 03,
Since the metal sleeve 03 and the metal shaft 04 were connected by welding, the metal shaft 0
However, on the other hand, residual stress exists near the welding due to the welding strain that occurs when welding the sleeve 03 and the shaft 04, and the bottom corner of the sleeve 03 Part 03a and axis 0
Since stress tends to be concentrated at the corner 04a of 4, cracks are likely to occur along the line 05 connecting both corners 03a and 04a. Moreover, if a large shrink fit allowance is taken to prevent the boss part 02 from slipping out from the sleeve 03, a large stress will be generated at the base of the boss part 02, making it easy to break.

Furthermore, in the method described in Japanese Patent Application Laid-Open No. 59-103902, as shown in FIG. Cylindrical sleeve with 06
and the end surface 06a of the cylindrical sleeve 06 was fixed to the metal shaft 04 by welding, so that under heat load, the coefficient of thermal expansion of the cylindrical sleeve 06 and the thermal expansion of the metal shaft 04 Cracks 07 are likely to occur along the joint surfaces of the two due to the difference in ratio, and furthermore, the outer circumferential portion 04b of the shaft end of the metal shaft 04 adjacent to the end surface 06a of the cylindrical sleeve 06 is
It becomes difficult to follow the thermal deformation of the shaft portion 04c of the metal shaft 04 due to the influence of residual strain due to welding between the metal shaft 04 and the sleeve 06, and the difference in the thermal expansion coefficients of the two.
Cracks 08 are likely to occur along the line connecting the shaft corner 04a and the metal shaft end surface 04d that is not in contact with the cylindrical sleeve end surface 06a.

Means and Effects for Solving the Problems The present invention relates to an improvement of a ceramic turbine impeller that eliminates the above-mentioned drawbacks. A metal sleeve having a thermal expansion coefficient close to that of ceramic is fitted onto the ceramic impeller boss portion, and the ceramic impeller is integrally joined to the metal rotating shaft via the metal sleeve. In the ceramic turbine impeller, the metal rotating shaft is made of a material having a coefficient of thermal expansion larger than that of the ceramic impeller, and the end surface of the metal rotating shaft on the impeller side is heated to a high temperature. When the impeller boss fits therein, a recess with a size such that the boss fits tightly is formed due to the difference in coefficient of thermal expansion between the boss and the rotating shaft under normal operating conditions lower than the high temperature, and the ceramic The metal sleeve and each end of the metal rotating shaft are integrally joined by welding at a location located closer to the blade wheel than the tip of the blade wheel boss and the bottom of the metal rotating shaft recess. That is.

In the present invention, a material having a coefficient of thermal expansion larger than that of the ceramic impeller is used for the metal rotating shaft, and the end surface of the metal rotating shaft on the impeller side is provided with a material that has a coefficient of thermal expansion larger than that of the ceramic impeller. Since the recess is formed with a size such that the boss part is tightened and fitted due to the difference in coefficient of thermal expansion between the boss part and the rotating shaft in the normal operating state where the impeller boss part is fitted and the temperature is lower than the above-mentioned high temperature, the above-mentioned When the impeller boss is fitted into the rotary shaft recess and cooled to a low temperature, the tightening stress applied to the circumferential surface of the boss toward the center can be gradually increased from the base toward the tip.

Further, in the present invention, the metal sleeve and each end of the metal rotating shaft are welded together at a location located on the blade wheel body from the tip of the ceramic blade wheel boss and the bottom of the metal rotating shaft recess. Therefore, the corners of the rotary shaft recess are not strongly affected by residual strain that occurs due to welding.

Embodiments Hereinafter, the embodiments shown in FIGS. 3 to 7 will be described in which the present invention is applied to a turbocharger attached to an automobile gasoline engine.

The turbocharger rotor consists of a turbine impeller 1 made of silicon nitride ceramic and Koval (Ni23 to
30wt%, Co17~30wt%, Mn0.6~0.8wt%, balance
It consists of a sleeve 10 made of Fe) (trade name), a rotating shaft 20 made of Cr-Mo steel (JIS SCM 435), and a compressor impeller (not shown) that is integrally assembled to the rotating shaft 20 made of Cr-Mo steel. There is.

In addition, the inner peripheral surface 11 of the sleeve 10 made of Koval
is formed in such a size and shape that it can be fitted to the boss portion 3 of the silicon nitride ceramic turbine impeller 1 with a short, substantially constant distance from the boss base circumferential surface 5 to the boss tip circumferential surface 7. There is.

Furthermore, the shaft end 21 of the Cr-Mo steel rotating shaft 20
has a larger diameter than the central portion 27, and like the inner circumferential surface 11 of the Koval sleeve 10, the coaxial end portion 2
1 includes the silicon nitride ceramic turbine wheel 1.
A cylindrical recess 22 is formed in the boss tip 6 of the cylindrical recess 22 such that it can be fitted with a short and substantially fixed period of time, and the end surface 24 of the cylindrical recess 22 is connected to the planar sleeve end surface of the Kobal sleeve 10. It is formed flat so that it can collide flush with 14.

Furthermore, the bottom part 23 and the central part 27 of the cylindrical recess 22
It communicates with the outer circumferential surface of through a communication hole 28.

Furthermore, the small diameter portion 2 of the Cr-Mo steel rotating shaft 20
A compressor impeller (not shown) is fitted to 9.
The compressor wheel is integrally assembled to the small diameter portion 29 by a nut (not shown) that is screwed onto the male thread 30 of the small diameter portion 29.

The silicon nitride ceramic turbine wheel 1, Koval sleeve 10, and Cr-Mo steel rotating shaft 20
are assembled together with each other in accordance with the following sequence:

First, the sleeve end surface 14 of the sleeve 10 made of Koval and the tip surface 24 of the shaft end 21 of the Cr-Mo steel rotating shaft 20 are integrally joined by friction welding, and then the recess of the Cr-Mo steel rotating shaft 20 is bottom 23
A brazing material 31 is charged in advance into the communication hole 28, and the boss portion 3 of the silicon nitride ceramic turbine wheel 1 is connected to the inner circumferential surface 11 of the Koval sleeve 10 and the Cr-
When the Mo steel rotating shaft 20 is fitted into the cylindrical recess 22 and heated to a temperature higher than the welding temperature of the solder material 31 (approximately 700°C), the Cr-Mo steel rotating shaft 20 thermally expands. Since the coefficient of thermal expansion is larger than that of the silicon nitride ceramic turbine wheel 1 and the Koval sleeve 10, as shown in FIG.
Inner peripheral surface 11 of Koval sleeve 10 and Cr
The diameter of the circumferential surface of the cylindrical recess 22 of the -Mo steel rotary shaft 20 gradually increases as it approaches the recess bottom 23, during which time the bottom portion 32 is filled with the solder material 31.

and silicon nitride ceramic turbine impeller 1,
The temperature of the assembly of Koval sleeve 10 and Cr-Mo steel rotating shaft 20 is set to the welding temperature of the brazing material 31 (approximately
When the temperature is gradually lowered to below 700°C, the solder material 31 begins to solidify before the solder material 32 returns to the uniform thickness distribution as shown in FIG. 7, and the temperature decreases to atmospheric temperature. Cr, which has a large coefficient of thermal expansion,
- The Mo steel rotary shaft 20 shrinks more than the silicon nitride ceramic turbine wheel 1 and the Koval sleeve 10, and the thicker part of the brazing material 31
To resist the contraction of the rotating shaft 20 made of Cr-Mo steel, the boss portion 3 of the turbine wheel 1 made of silicon nitride ceramic has a
As shown in FIG. 7, a gradually larger tightening force is applied as one approaches the boss tip 6 from the boss base 4.

The boss portion 3 of the turbine impeller 1 made of silicon nitride ceramic is not only held by the sleeve 10 made of Koval which is integrated with the shaft end portion 21 of the rotating shaft 20 made of Cr-Mo steel, but also made of Cr-Mo steel. The rotating shaft 20 made of Cr-Mo steel is gripped by the cylindrical recess 22, and the tightening force against the boss 3 gradually increases as it approaches the boss tip 6 of the silicon nitride ceramic turbine wheel 1. It is possible to reliably prevent the silicon nitride ceramic turbine wheel 1 from slipping off from the shaft 20.

Furthermore, the tightening force on the boss portion 3 of the silicon nitride ceramic turbine impeller 1 gradually increases from the boss base 4 near the impeller main body 2 toward the boss tip 6, so that a large stress is applied to the circumferential surface 5 of the boss base. did not occur,
The boss portion 3 will not break and separate from the blade wheel body 2.

Furthermore, since the boss base circumferential surface 5 is formed into a curved surface with a gentle radius of curvature, stress is unlikely to concentrate near the boss base circumferential surface 5.

Furthermore, in the shaft end 21 of the Cr-Mo steel rotating shaft 20, the shaft end corner 25 and the shaft end corner 26 are formed into gently curved surfaces, so stress is not concentrated on these parts. , cracks are less likely to occur between the corner of the cylindrical recess 22 and the shaft end corner 25 or shaft end corner 26.

In the embodiment shown in FIGS. 3 to 7, the boss 3 of the silicon nitride ceramic turbine wheel 1 is attached to the Koval sleeve 10 and the cylindrical recess 22 of the Cr-Mo steel rotating shaft 20 by brazing. However, the boss portion 3 may be integrally joined to the Koval sleeve 10 and the cylindrical recess 22 by shrink fitting as shown in FIG. The shape of the inner circumferential surface 11 and the cylindrical recess 22 of the Cr-Mo steel rotating shaft 20 may be formed to be slightly tapered toward the bottom 23 of the recess.

Effects of the Invention As described above, the present invention can gradually increase the tightening stress applied to the circumferential surface of the boss portion toward the center from the base toward the tip, so that large stress can be applied to the base of the boss portion. It is possible to suppress the occurrence of cracks in this part without causing cracks, and to prevent the boss part of the ceramic impeller from slipping out of the metal sleeve and the metal rotary shaft recess, thereby preventing the boss part of the impeller blade from slipping out. It can be firmly and integrally coupled to the metal shaft.

Further, in the present invention, since the corners of the rotary shaft recess are not strongly affected by residual strain generated during welding, cracks are less likely to occur from the corners toward the surface of the rotary shaft.

[Brief explanation of the drawing]

1 and 2 are partially longitudinal side views of a conventional ceramic rotating body, FIG. 3 is a partially longitudinal side view illustrating an embodiment of the ceramic rotating body according to the present invention, and FIG. 4 is a partially longitudinal side view of a conventional ceramic rotating body. FIG. 3 is a view taken along the - arrow in FIG. 3, FIG. 5 is an exploded longitudinal cross-sectional view of the same embodiment, and FIGS.
The figure shows the heated expanded state for brazing, FIG. 7 shows the cooled contracted state after brazing, and FIG. 8 is a longitudinal sectional side view of the main part of another embodiment. 1...Silicon nitride ceramic turbine wheel, 2
...Blade wheel body, 3...Boss part, 4...Boss base,
5...Boss base circumferential surface, 6...Boss tip, 7...
Boss tip circumferential surface, 10... Kobal sleeve,
11... Inner circumferential surface, 12... Inner circumferential surface on the impeller body side, 1
3... Rotating shaft side inner peripheral surface, 14... Sleeve end surface,
20... Cr-Mo steel rotating shaft, 21... Shaft end,
22... Cylindrical recess, 23... Bottom of the recess, 24...
... Tip surface, 25 ... Shaft end corner, 26 ... Shaft end corner, 27 ... Center part, 28 ... Communication hole, 29 ...
Small diameter part, 30... male thread, 31... brazing material, 32...
...Between.

Claims (1)

[Scope of utility model registration request] The length and diameter of the boss of the ceramic impeller are approximately equal, and a metal sleeve having a thermal expansion coefficient close to that of the ceramic is fitted onto the ceramic impeller boss. In a ceramic turbine impeller in which the ceramic impeller is integrally joined to a metal rotating shaft through a metal sleeve, the metal rotating shaft has a coefficient of thermal expansion larger than that of the ceramic impeller. The impeller boss fits into the metal rotary shaft end face on the impeller side in a high temperature state, and the difference in thermal expansion coefficient between the boss and the rotary shaft in a normal operating state lower than the high temperature. A recess with a size that allows the boss to be tightened is formed, and the metal sleeve and A ceramic turbine blade wheel characterized in that each end of a metal rotating shaft is integrally joined by welding.