Centrifugal compressor, turbocharger provided with the centrifugal compressor, and method for producing the centrifugal compressor

1. A centrifugal compressor, comprising:

a housing;

an impeller disposed rotatably inside the housing and comprising a hub with an attachment hole and a plurality of blades integrally provided with the hub;

a drive shaft comprising a shaft section extending inside the attachment hole of the impeller, a stepped section separated from the impeller, and a middle section disposed between the shaft section and the stepped section;

a fastening member screwed to a distal end side of the shaft section;

at least one flange portion fitted onto the middle section;

a thrust member fixedly disposed relative to the housing and comprising a through hole through which the drive shaft is inserted and a thrust section which is disposed around the through hole and which contacts the flange portion; and

a sleeve section fitted onto the middle section and disposed between the flange portion and the impeller,

wherein an inner peripheral surface of the attachment hole comprises a clamp surface which is in close contact with the shaft section by shrink fitting, and a diameter-widening surface with an inner diameter which increases with a distance from the clamp surface in an axial direction of the attachment hole,

wherein an outer peripheral surface of the sleeve section comprises a diameter-reducing surface with an outer diameter which reduces toward the clamp surface in the axial direction of the attachment hole,

wherein the diameter-widening surface and the diameter-reducing surface respectively comprise an impeller-side contacting portion and a sleeve-side contacting portion which contact each other, and

wherein a relationship represented by an expression θs<atan (d/L) is satisfied, where

d is a length from an axis of the attachment hole to the sleeve-side contacting portion in a radial direction of the attachment hole,

L is a length from the sleeve-side contacting portion to the clamp surface in the axial direction of the attachment hole, and

θs is a sleeve inclination angle formed by an intersection of an axis of the sleeve section and a generatrix of a virtual cone which contacts the diameter-reducing surface at the sleeve-side contacting portion.

2. The centrifugal compressor according to claim 1 ,

wherein the impeller comprises a first position-determining surface which is substantially orthogonal to the axis of the attachment hole, and

wherein one of the sleeve section or the drive shaft comprises a second position-determining surface which is substantially orthogonal to the axis of the attachment hole and which is contactable with the first position-determining surface during the shrink fitting.

3. The centrifugal compressor according to claim 1 ,

wherein the sleeve inclination angle θs is 30° or more.

4. The centrifugal compressor according to claim 1 ,

wherein a difference between the atan (d/L) and the sleeve inclination angle θs is 20° or less.

5. The centrifugal compressor according to claim 1 ,

wherein the diameter-widening surface comprises a female tapered surface having constant inclination with respect to the axis of the attachment hole, and

wherein the diameter-reducing surface comprises a male tapered surface having constant inclination with respect to the axis of the attachment hole.

6. The centrifugal compressor according to claim 1 ,

wherein the diameter-widening surface comprises a female tapered surface having constant inclination with respect to the axis of the attachment hole, and

wherein the diameter-reducing surface comprises a curved surface having varying inclination with respect to the axis of the attachment hole.

7. The centrifugal compressor according to claim 1 ,

wherein the diameter-widening surface comprises a curved surface having varying inclination with respect to the axis of the attachment hole, and

wherein the diameter-reducing surface comprises a male tapered surface having constant inclination with respect to the axis of the attachment hole.

8. A turbocharger, comprising:

the centrifugal compressor according to claim 1 ; and

a turbine comprising a turbine blade fixed to the drive shaft.

9. A method of producing a centrifugal compressor which comprises:

a housing;

an impeller disposed rotatably inside the housing and comprising a hub with an attachment hole and a plurality of blades integrally provided with the hub;

a drive shaft comprising a shaft section extending inside the attachment hole of the impeller, a stepped section separated from the impeller, and a middle section disposed between the shaft section and the stepped section;

a fastening member screwed to a distal end side of the shaft section;

at least one flange portion fitted onto the middle section;

a thrust member fixedly disposed relative to the housing and comprising a through hole through which the drive shaft is inserted and a thrust section which is disposed around the through hole and which contacts the flange portion; and

a sleeve section fitted onto the middle section and disposed between the flange portion and the impeller,

wherein an inner peripheral surface of the attachment hole comprises a clamp surface which is in close contact with the shaft section by shrink fitting, and a diameter-widening surface with an inner diameter which increases with a distance from the clamp surface in an axial direction of the attachment hole,

wherein an outer peripheral surface of the sleeve section comprises a diameter-reducing surface with an outer diameter which reduces toward the clamp surface in the axial direction of the attachment hole,

wherein the diameter-widening surface and the diameter-reducing surface respectively comprise an impeller-side contacting portion and a sleeve-side contacting portion which contact each other, and

wherein a relationship represented by an expression θs<atan (d/L) is satisfied, where

d is a length from an axis of the attachment hole to the sleeve-side contacting portion in a radial direction of the attachment hole,

L is a length from the sleeve-side contacting portion to the clamp surface in the axial direction of the attachment hole, and

θs is a sleeve inclination angle formed by an intersection of an axis of the sleeve section and a generatrix of a virtual cone which contacts the diameter-reducing surface at the sleeve-side contacting portion, the method comprising:

a first inserting step of inserting the drive shaft into the through hole of the thrust member, the flange portion, and the sleeve section;

a heating step of heating the impeller;

a second inserting step of inserting the shaft section into the attachment hole of the impeller heated in the heating step, after the first inserting step; and

a fastening step of screwing a fastening member to a distal end side of the shaft section, after the second inserting step.

10. The method of producing a centrifugal compressor according to claim 9 ,

wherein the impeller comprises a first position-determining surface which is substantially orthogonal to the axis of the attachment hole,

wherein one of the sleeve section or the drive shaft comprises a second position-determining surface which is substantially orthogonal to an axis of the drive shaft, and

wherein the second inserting step comprises making the second position-determining surface contact the first position-determining surface.

11. The method of producing a centrifugal compressor according to claim 9 ,

wherein the fastening step is performed after the heating step and before a temperature of the impeller decreases to an ambient temperature.