Rotary machine

1. A rotary machine comprising:

a shaft that rotates;

a disc that has a substantially cylindrical hub fitted into the shaft and is provided so as to widen outward in a radial direction from a front end to a rear end of the substantially cylindrical hub; and

an impeller having a plurality of blades provided on a surface of the disc,

wherein the substantially cylindrical hub comprises:

a tight fit section having an internal radius that is smaller than a radius of the shaft; and

a loose fit section having an internal radius that is greater than the internal radius of the tight fit section,

wherein the loose fit section is provided on a front end side of the substantially cylindrical hub with respect to the tight fit section, and

wherein a tapered portion having an external radius gradually increasing toward the front end of the substantially cylindrical hub is provided in the rear end of the substantially cylindrical hub.

2. The rotary machine according to claim 1 , wherein a groove portion dented so as to surround the substantially cylindrical hub is provided on a rear surface of the surface of the disc.

3. The rotary machine according to claim 1 , further comprising:

a sleeve that is fitted into the shaft so as to come into contact with the front end of the substantially cylindrical hub, and guides air flow to the disc.

4. The rotary machine according to claim 3 , wherein the impeller is one of a plurality of impellers provided in series in the shaft,

wherein a sleeve that guides the air flow to the disc of another one of the plurality of impellers is further included between the substantially cylindrical hub of the one of the plurality of impellers and the substantially cylindrical hub of the other one of the plurality of impellers, which are adjacent to each other,

wherein the tapered portion is a first tapered portion, and

wherein a second tapered portion having an internal radius gradually decreasing toward a rear end of the sleeve so as to be matched with a shape of the first tapered portion provided in the rear end of the substantially cylindrical hub is provided in a front end of the sleeve.

5. The rotary machine according to claim 3 , wherein a concave portion is provided in one of a rear end of the sleeve and the front end of the substantially cylindrical hub, and a convex portion matched with a shape of the concave portion is provided in another one of the rear end of the sleeve and the front end of the substantially cylindrical hub.

6. The rotary machine according to claim 3 , wherein a third tapered portion having an internal radius gradually decreasing toward a front end of the sleeve is provided in a rear end of the sleeve, and

wherein a fourth tapered portion having an external radius gradually reducing toward the front end of the substantially cylindrical hub so as to be matched with a shape of the third tapered portion is provided in the front end of the substantially cylindrical hub.

7. The rotary machine according to claim 1 , wherein the tight fit section is provided over the front end side of the substantially cylindrical hub with respect to a rear surface of the disc from the rear end of the substantially cylindrical hub.

8. The rotary machine according to claim 1 , wherein the substantially cylindrical hub further comprises an intermediate section that connects the tight fit section with the loose fit section and a tightening allowance of the intermediate section is approximately equal to a tightening allowance of the tight fit section, or slightly smaller than the tightening allowance of the tight fit section.