JPS61169164A - Joint structure of rotary shaft - Google Patents

Abstract

PURPOSE:To eliminate the breakage of disc wheel due to differential thermal expansion by making the construction that the inner periphery near the opening of a rotary shaft sleeve part is virtually not joined with the shaft-end part of the disc wheel in case of brazing the disc wheel made of ceramics to the rotary shaft made of metal. CONSTITUTION:A rotary shart 21 is integrally formed on the disc wheel 11 made of ceramics and brazed with engaging to the sleeve part 32 of the rotary shaft 12 made of metal. In this case a metalized layer 41 is formed on the outer periphery of the rotary shaft 21, joined to the inner periphery of the sleeve part 32 via brazing material 51 and no brazing material 51 is made to be adhered to on the inner periphery 33 near the opening of the sleeve part 32. The breakage of disc wheel due to the differential thermal expansion between the ceramics and metal is thus eliminated and the joint structure of high reliability is obtainable.

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD The present invention relates to a rotary shaft joining structure that is applied to joining a ceramic rotary impeller, such as a turbocharger, and a metal shaft.

"Prior art and its problems" In recent years, new ceramics have improved their heat resistance and abrasion resistance,
Ceramic rotor wheels are being adopted in fields such as turbochargers, for example, due to their characteristics such as a lower weight ratio compared to heat-resistant alloys.

Normally, when joining a metal shaft to a ceramic rotor, there are two methods: (1) a structure in which the metal shaft is joined at a high temperature area near the rotor, and (2) the shaft is integrally formed with the rotor, and this shaft is connected to two bearings. Two types of structures are adopted: one in which the joint is joined at a relatively low-temperature region in the middle or on the side of the compressor blade.

However, in the structure of ``--'', a large rotational torque is applied to the rotating shaft of the relatively long ceramic impeller, so there is a problem that the rotating shaft is easily damaged.

On the other hand, as shown in FIG. 2, for example, as shown in FIG. This sleeve part 32 is fitted onto the shaft end of the ceramic rotary shaft 21, and the outer periphery of the shaft end and the inner periphery of the sleeve part 32 are joined by brazing. . That is, a metallized layer 41 made of iron group metals such as Fe, Ni, and Go is formed on the outer periphery of the rotating shaft 21 made of ceramic such as silicon nitride by electroless plating or electrolytic plating. The inner periphery of the sleeve portion 32 of the metal rotating shaft 12 is joined with a brazing material 51 via the metal rotating shaft 12. in this case,
The inner periphery of the sleeve portion 32 is filled with the brazing material 51 up to the opening.
It was firmly joined to the ceramic rotary shaft 21 by.

However, in general, metals and ceramics have significantly different coefficients of thermal expansion, and due to this large difference in expansion, considerable strain remains in the joints during brazing. For example, silicon nitride is used as the ceramic, and copal or Incoloy 903, which has a relatively similar coefficient of thermal expansion as the metal, is used.
, 907, 901, etc., residual I exists near the joint. Therefore, if the sleeve portion 32 of the metal rotating shaft 12 is firmly joined to the ceramic rotating shaft 21 by the brazing material 51 up to the opening as shown in -1-, the vicinity of the opening of the sleeve portion 32 Stress concentration of residual strain occurs at . In addition, in the design of turbochargers, etc., since they are built into automobiles, they are subject to restrictions such as their size, shape, and main star, and are designed to the minimum size that maintains the necessary performance. In general, the design is done to the limit, with a safety factor multiplied by the strength required to ensure safety. For this reason, if strain remains due to the difference in thermal expansion, as shown in ``-'', fracture is more likely to occur at the stress concentration area, and if the joint strength is strong, the stress due to residual strain will be greater in the brittle ceramic part than in the tough metal. Unable to withstand this, the product is destroyed and becomes unusable.

``Object of the Invention'' An object of the present invention is to solve the above-mentioned problems of the prior art. The ceramic shape, metallized portion, and brazing at the joint are designed to reduce the residual strain at the joint, thereby providing a highly reliable joint structure for rotating shafts with increased resistance to rotation.

"Structure of the Invention" The joining structure of a rotating shaft according to the present invention is such that a sleeve part of a metal rotating shaft is fitted to a shaft end of a ceramic rotating shaft, and the outer periphery of the shaft end and the inner periphery of the sleeve part are connected to each other. In this structure, the inner circumference of the sleeve part near the opening is not substantially joined to the shaft end part.

Here, the "inner periphery of the sleeve portion" refers to a straight portion located inside in a cross-sectional view passing through the axis of the sleeve portion 32. In addition, ``the inner periphery of the sleeve portion closer to the opening is not substantially joined to the shaft end'' means that there is no brazing material intervening in the inner periphery of the sleeve portion closer to the opening, or This refers to a state in which the brazing material and the ceramic rotating shaft are not joined even if a material is present.

As described above, in the present invention, since the inner periphery of the sleeve portion near the opening is not substantially joined to the shaft end, residual strain at the joint where strain due to the difference in thermal expansion is concentrated is reduced, thereby reducing the amount of strain at the joint. This increases the bending strength of the rotary shaft, and therefore it can withstand high bending stress that is applied to the joint of the rotating shaft during high-speed rotation due to slight unbalance of the rotating shaft or shaft runout, thereby preventing damage to the joint. can.

The reason will be specifically explained below.

In other words, the cause of the aforementioned residual strain at the joint is due to the difference in thermal expansion coefficient between ceramics and metal, but specifically,
The residual strain can be divided into two types: residual strain due to the force of the metal sleeve portion tightening in the radial direction, and residual strain due to the force causing the metal sleeve portion to contract in the axial direction. In the conventional bonding structure, since both of them occur at the same location, they combine to produce high residual strain, which causes a decrease in the strength of the ceramic.

The present invention reduces or eliminates the residual strain caused by the above two causes, or separates the two.
This reduces locally generated high residual strain.

In other words, if there is no brazing material on the inner periphery of the sleeve near the opening and the inner periphery of the sleeve is not joined, the joining length will be shortened due to the absence of brazing material, and the shaft The force by which the sleeve portion contracts in this direction can be reduced. In addition, if there is a brazing material on the inner periphery of the sleeve near the opening but the brazing material is not bonded to the shaft end, the brazing material on the inner periphery of the sleeve near the opening will Since the sleeve portion is not joined to the sleeve portion, the force that causes the sleeve portion to contract in the axial direction cannot be transmitted, and the residual strain generated due to the above two causes can be separated. Furthermore, if an annular recess is formed at the shaft end opposite to the inner periphery of the sleeve near the opening, and the inner periphery near the opening is not joined to the shaft end, the sleeve may radially The residual strain generated by the tightening force can be eliminated, or rather, compressive residual strain can be used, and the value can be reduced by offsetting the residual strain caused by the force that causes the sleeve portion to contract in the axial direction.

In the present invention, the length of the unjoined portion of the inner periphery of the sleeve portion closer to the opening depends on the length of the inner periphery of the sleeve portion, but is usually from the end of the inner periphery of the sleeve portion closer to the opening. Preferably, it continues from 1 to 41 m. This is because, as described above, it is possible to reduce the residual strain at the joint and also to easily ensure the required joint strength.

Further, in the present invention, the end of the sleeve portion closer to the opening may have a rectangular cross section, or may have a rounded portion as shown in FIG. 1 and FIGS. 3 to 6. When a radiused portion is formed, it is preferable that this radiused portion is not included in the ``inner periphery of the path sleeve portion'' in the present invention, and that no brazing material is present in this radiused portion.

"Embodiment of the Invention" FIG. 7 shows an embodiment in which the present invention is applied to a rotating shaft of a turbocharger. That is, the ceramic rotary shaft 21 is integrally formed with the ceramic impeller 11 made of silicon nitride, for example, and the sleeve portion 32 of the metal rotary shaft 12 is fitted into the shaft end of the ceramic rotary shaft 21. It is soldered.

FIG. 1 shows the main parts of the joining structure between the ceramic rotary shaft 21 and the sleeve portion 32. As shown in FIG. That is, a metallized layer 41 formed by electroless plating and electrolytic plating of iron group elements is formed on the outer periphery of the ceramic rotating shaft 21, and this metallized layer 41 is bonded to the inner periphery of the sleeve portion 32 via a brazing material 51. are doing. In this case, the metallized layer 41 is formed to have a predetermined width from the tip of the ceramic rotating shaft 21, and is formed on the inner periphery 33 of the sleeve portion 32 near the opening.
The brazing material 51 is not attached to the inner periphery 33 near the opening, and the inner periphery 33 is not joined to the ceramic rotary shaft 21.

FIG. 3 shows the main parts of a joining structure in another embodiment of the present invention. In this embodiment, an annular groove 22 is formed on the outer periphery of the ceramic rotating shaft 21, and a metallized layer 41
is formed only at the bottom of the annular groove 22, and this metallized layer 41 portion is joined to the inner periphery of the sleeve portion 32 by a brazing material 51. In this case as well, the inner periphery 33 portion near the opening is separated from the ceramic rotating shaft 21. In this embodiment, since the brazing material 51 is fitted into the annular groove 22, it is strong against forces acting in the axial direction. Note that if a spline-shaped groove is used instead of the annular groove 22, it can be made stronger against rotational torque.

FIG. 4 shows the main parts of a joining structure in still another embodiment of the present invention. In this embodiment, a metallized layer 41 is formed with a predetermined width from the tip of the ceramic rotary shaft 21, and a portion of this metallized layer 41 is joined to the inner periphery of the sleeve portion 32 by a brazing material 51. In this case, the portion of the inner periphery 33 near the opening is also filled with the brazing material 51;
Ceramic rotating shaft 2 facing inner periphery 33 near the opening
Since the metallized layer 41 is not formed on the base of the rotor 1, the brazing filler metal 51 in this portion is not bonded to the ceramic rotating shaft 21. In this way, even if the inner periphery 33 near the opening is filled with the brazing filler metal 51, if the brazing filler metal 51 in that area is not bonded to the ceramic rotating shaft 21, stress concentration due to strain caused by the difference in coefficient of thermal expansion can be prevented. By avoiding this, damage to the ceramic rotating shaft 2I can be prevented.

FIG. 5 shows the main parts of a joining structure in still another embodiment of the present invention. In this embodiment, an annular groove 22 is formed on the outer periphery of a ceramic rotating shaft 21, and a metallized layer 41 is formed to have a predetermined width from the tip of the ceramic rotating shaft 21 to the bottom of the annular groove 22. It is joined to the inner periphery of the sleeve portion 32 by a brazing material 51. In this case as well, the inner periphery 33 near the opening is filled with the brazing material 51;
Since the metallized layer 41 is not formed on the base of the ceramic rotating shaft 21 facing the ceramic rotating shaft 21, the brazing material 51 in this part is not bonded to the ceramic rotating shaft 21.

FIG. 6 shows the main parts of a joining structure in still another embodiment of the present invention. In this embodiment, a metallized layer 41 is formed with a predetermined width from the tip of the ceramic rotary shaft 21, and this metallized layer 41 portion is joined to the inner circumference of the sleeve portion 32 with solder 4451, and the inner circumference near the opening is
An annular recess 23 is formed at the base of the ceramic rotating shaft 21 that faces the three parts. Therefore, opening 11
An annular recess 23 prevents the inner periphery 33 from being joined to the ceramic rotating shaft 21 .

The embodiments shown in FIG. 1, FIG. 5, and FIG. 6 according to the present invention and the conventional example shown in FIG. A sample like this was prepared and a three-point bending test was conducted.

In FIG. 8, 15 is a ceramic shaft body, and 16 is a metal sleeve body. The span is 48+s and the load point is the joint end 17. As a result of the test, the maximum three-point bending load is
The one in Figure 1 is 280 kgF, and the one in Figure 5 is 31
5 kgf, 350 kgf for the one shown in FIG. 6, and 75 kgf for the one shown in FIG. 2, indicating that the strength of the present invention was several times higher than that of the conventional joint structure.

"Effects of the Invention" As explained above, according to the present invention, the inner periphery of the sleeve portion of the metal rotating shaft near the opening is not brazed to the ceramic rotating shaft or is filled with a brazing material. However, since the structure is such that it is not joined to the ceramic rotating shaft, it is possible to avoid stress concentration due to strain due to the difference in coefficient of thermal expansion and prevent damage to the ceramic rotating shaft. Therefore, it is possible to provide a highly reliable joint structure in a turbocharger or the like having a ceramic rotor blade.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a main part showing an example of a joint structure for a rotating shaft according to the present invention, FIG. 2 is a cross-sectional view of a main part showing an example of a conventional joint structure for a rotating shaft, FIGS. , Figures 5 and 6
The figures are cross-sectional views of essential parts showing other embodiments of the joint structure for a rotating shaft according to the present invention, FIG. 7 is a partial cross-sectional view showing an example of applying the joint structure according to the present invention to a turbocharger, and FIG. 8 is a diagram showing strength. FIG. 3 is a cross-sectional view showing the shape of a test sample. In the figure, 11 is a ceramic impeller, 21 is a ceramic rotating shaft, 12 is a metal rotating shaft, 32 is a sleeve portion,
33 is an inner periphery near the opening, 41 is a metallized layer, and 51 is a brazing material. Figure 7 ∆ Procedural amendment (voluntary) 1. Indication of the case Patent Application No. 9496 of 1985 2) Name of the invention Joint structure of rotating shaft 3. Person making the amendment Relationship with the case Patent applicant address Tokyo 2-1-2 Marunouchi, Chiyoda-ku Name (
004) Asahi Glass Co., Ltd. Representative Takeo Sakabe 4, Agent 5, Column 6 for detailed explanation of the invention in the specification subject to amendment, Description r901J on page 4, line 3 of the specification of the contents of the amendment rl10
Correct it to 9 J. From now on

Claims (4)

[Claims] (1) A rotating shaft formed by fitting a sleeve portion of a metal rotating shaft onto the shaft end of a ceramic rotating shaft, and joining the outer periphery of the shaft end and the inner periphery of the sleeve with a brazing material. A joint structure for a rotary shaft, characterized in that an inner periphery of the sleeve portion near the opening is not substantially joined to the shaft end. (2) The joint structure of the rotating shaft according to claim 1, in which the brazing material is not interposed on the inner periphery of the sleeve portion near the opening. (3) The joint structure of the rotating shaft according to claim 1, in which the brazing material interposed on the inner periphery of the sleeve portion near the opening is not joined to the shaft end portion. (4) The joint structure for a rotary shaft according to claim 1, wherein an annular recess is formed in the shaft end facing the inner periphery near the opening of the sleeve portion.