JPH0141841Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to an assembly of a turbine wheel and a compressor wheel of a turbine rotationally driven by fluid.

For example, as shown in FIG. 1, a turbine wheel assembly in a turbocharger of an automobile engine is constructed by inserting a compressor wheel 3 into a small diameter portion 2a at the tip of a turbine shaft 2 integrally formed with a turbine wheel 1, and loosening the compressor wheel 3. It is fixed to the turbine shaft 2 by connecting a nut 5 to the threaded end portion 2b via a spring washer 4 in the form of a disc spring for locking. Turbine wheel 1 and turbine shaft 2
The compressor wheel 3 is precision cast from a nickel or cobalt super heat-resistant alloy, and the compressor wheel 3 is precision cast from an aluminum alloy. The threaded end portion 2b of the turbine shaft 2 formed of such a material has sufficient strength even when tightened with the nut 5.

On the other hand, the progress of ceramics as an industrial material has been remarkable in recent years, and even in such turbochargers, ceramic turbine wheels have appeared for the purpose of improving heat resistance and reducing weight. However, since ceramic is susceptible to local contact stress, a thread is cut in the tip 2b of the turbine shaft 2.
It is not possible to assemble the compressor wheel 3 by connecting the nut 5 to this. Therefore, in the past, this assembly was performed using an adhesive.

The object of this invention is to provide a novel turbine wheel assembly that can securely fix a compressor wheel to a turbine shaft of a ceramic turbine wheel.

The turbine wheel assembly according to this invention includes a turbine wheel 11 made of ceramic, for example, and a small-diameter tip portion 1 of a turbine shaft 12 integrally formed therewith.
A compressor wheel 13 is inserted into 2a, and a stop ring 15 is shrink-fitted onto the turbine shaft 12 via a spring washer 14 in the form of a disc spring to fix the compressor wheel 13.

Shrink fitting of the stopper ring 15 is performed by heating the stopper ring 15, which has an inner diameter slightly smaller than the diameter of the small diameter portion 12a of the turbine shaft, to expand its inner diameter dimension, and then press-fitting the stopper ring 15 into the small diameter portion 12a of the turbine shaft. However, even if the stopper ring 15 is shrink-fitted in this way, when viewed microscopically,
When the stopper ring 15 rotates, the centrifugal force causes the stopper ring 15 to be pulled outward, reducing the interference at the shrink-fit portion with the turbine shaft small diameter portion 12a, and there is a possibility that the stopper ring 15 may not be sufficiently fixed to the turbine shaft small diameter portion 12a.

The tightening allowance Ur in this shrink-fitted portion is approximately rN ² k/ depending on the shape and material of the stopper ring 15.
It changes at the rate of E. Here, r is the density, N is the rotational speed, k is the ratio of the inner diameter to the outer diameter, and E is the Young's modulus. Therefore, in order to minimize the change in the interference margin Ur, since the rotational speed N is the same, it is sufficient to select a material with a small r/E and a shape with a small k. Materials with small r/E are
Ceramics such as SiC or Al ₂ O ₃ are suitable, and a shape with a small k is a thin cylinder.

However, simply constructing the stopper ring 15 with a thin cylinder made of ceramic does not allow the stopper ring 15 to fully exhibit its function. This is because the stopper ring 15 needs to support the axial surface pressure of the compressor wheel 13 loosely fitted to the small diameter portion 12a of the turbine shaft. Therefore, in one embodiment of this invention, as shown in _FIG .
The length L ₁ of a is the thick part 15b at the end of the surface with the outer diameter D ₂ ,
15c is made longer than the length L ₂ , that is, the contact area with the turbine shaft is made larger, so that one thick wall portion 15b supports the axial surface pressure from the compressor wheel 13, and the central thin wall portion 15a This ensures a radial surface pressure between the turbine shaft and the small diameter portion 12a of the turbine shaft having a diameter D ₀ .

As shown in FIG. 4, the surface pressure distribution in the radial direction of the stopper ring 15 is such that when the stopper ring 15 is stopped, as shown by the solid line, and when it is rotating, as shown by the chain line, the thick portions 1 at both ends are
While it greatly decreases in the region of length L ₂ corresponding to 5b and 15c, it does not decrease much in the region of length L ₁ corresponding to the central thin part 15a having a larger area. Therefore, even when the turbine wheel 11 rotates at high speed, the compressor wheel 13 can be securely fixed to the turbine shaft 12.

In FIG. 3, the other thick portion 15c is not necessarily necessary in the sense of supporting the axial surface pressure of the compressor wheel 13, but it provides better balance as a rotating body. Also, both end thick portions 15b,
Annular groove 15d, 1 dredged in the axial direction of the base of 15c
5e is for suppressing the drop in surface pressure at both end thick portions 15b and 15c during rotation; without this, the drop in surface pressure at both end thick portions would be significant, as shown by broken lines in FIG. So it's better to warm it up.

As described above, in the turbine wheel assembly according to this invention, the compressor wheel is fixed by shrink-fitting the ceramic stopper ring onto the turbine shaft of the ceramic turbine wheel, so that the compressor wheel is securely fixed to the turbine shaft. Become something. In addition, the shape of the stopper ring is composed of a thick part on the compressor wheel side in the axial direction and a thin part that has a larger contact area with the turbine shaft than this thick part, so that the centrifugal force generated by the rotation of the stopper ring can be applied to the turbine. This suppresses the drop in contact pressure with the shaft, and ensures the contact pressure in the axial direction against the compressor wheel.
The fixation of the compressor wheel to the turbine shaft becomes even more reliable.

[Brief explanation of the drawing]

FIG. 1 is a partial cross-sectional schematic front view showing an example of a conventional turbine wheel assembly, FIG. 2 is a view similar to FIG. 1 showing an embodiment of this invention, and FIG. FIG. 4, which is a partially enlarged cross-sectional view of one embodiment, is a graph showing the surface pressure distribution during stop and rotation in one embodiment of this invention. 11... Turbine wheel, 12... Turbine shaft, 12a... Small diameter portion, 13... Compressor wheel, 14... Spring washer, 15...
Stopper ring, 15a...thin part, 15b, 1
5c...Thick part.

Claims (1)

[Scope of utility model registration request] A turbine wheel assembly in which a compressor wheel is inserted into a turbine shaft integrally molded with a ceramic turbine wheel, and a stopper ring is shrink-fitted onto the turbine shaft to fix the compressor wheel, the stopper ring being fixed to the turbine shaft in the axial direction. A turbine wheel assembly which is a ceramic stopper ring having a thick wall portion on the compressor wheel side and a thin wall portion that has a larger contact area with the turbine shaft than the thick wall portion.