51a intersect the circumferential direction Dc of the turbine impeller 6.

From a face, on the turbine side, of the bearing housing 13, a pin 53 extends towards the turbine side in the axial direction Ds. The pin 53 and the U-notch 51 are arranged at the same circumferential position. The pin 53 is a round rod-like member, whose diameter is nearly equal to a gap between the inner wall faces 51a (width of the U-notch 51). Alternatively, the diameter of the pin 53 is slightly larger than the gap between the inner wall faces 51a. The pin 53 may be a solid pin 53A having a solid circular cross section as illustrated in FIG. 5A. The pin 53 may alternatively be a spring pin 53B having a C-shaped cross section lacking a part of the ring as illustrated in FIG. 5B. The pin 53 may alternatively be a coiled pin 53C formed of a member coiled in multiple turns as illustrated in FIG. 5C.

A base end of the pin 53 is press-fitted into the bearing housing 13. A distal end 53p of the pin 53 is inserted into the U-notch 51, and held between the inner wall faces 51a in the circumferential direction Dc. With this structure, the variable nozzle unit 20 is positioned in the circumferential direction Dc with respect to the bearing housing 13, with the aid of the pin 53. There is a clearance in the radial direction Dr, between the pin 53 and the bottom of the U-notch 51. Contact points of the pin 53 with the inner wall faces 51a, 51a reside at middle parts, in the radial direction Dr, of the inner wall faces 51a, 51a. That is, the inner wall faces 51a, 51a, which are parallel to each other, extend from a position on the inner circumferential side relative to the contact points with the pin 53 to a position on the outer circumferential side (outer circumferential end face 49a).

The distal end 53p of the pin 53 is press-fitted into the U-notch 51. That is, the pin 53 is tightly fitted without clearance between the inner wall faces 51a in the circumferential direction Dc, and is therefore fixed to the U-notch 51 under the surface pressure applied in the circumferential direction Dc from the inner wall faces 51a, 51a. Since there is a gap between the pin 53 and the bottom of the U-notch 51 in the radial direction Dr as described previously, the pin 53 can shift in the radial direction Dr in the U-notch 51, against the frictional force from the inner wall faces 51a, 51a ascribed to the surface pressure.

As illustrated in FIGS. 2 and 3, the turbocharger 1 has two pairs of the pin 53 and the U-notch 51. The turbocharger 1 has the engagement parts 50, where the pin 53 and the U-notch 51 are engaged, at two places as described previously. The turbocharger 1 may have a single engagement part 50, or multiple engagement parts 50.

Paragraphs below will describe operations of the turbocharger 1 equipped with the aforementioned U-notch 51 and the pin 53. In the turbocharger 1 illustrated in FIG. 3, the circumferential shift of the variable nozzle unit 20 (the rotational position of the variable nozzle assembly 20) is restricted, by insertion of the pin 53 that extends from the bearing housing 13 into the U-notch 51 of the variable nozzle unit 20. The distal end 53p of the pin 53 is press-fitted into the U-notch 51 as described previously, whereby the pin 53 is fixed under the surface pressure applied in the circumferential direction Dc from the inner wall faces 51a, 51a. Therefore, there is no circumferential clearance between the pin 53 and the U-notch 51, so that the variable nozzle unit 20 may not cause the circumferential shift ascribed to the clearance. Hence, the variable nozzle unit 20 during operation is suppressed from shifting in the circumferential direction Dc, so that the turbocharger 1 may suppress change in the flow rate of exhaust gas in the nozzle flow passage 19.

Assuming a case where a circle hole into which the pin 53 is press-fitted were provided in place of the U-notch 51, the variable nozzle unit 20 would be restricted also in the radial direction Dr by the pin 53. Accordingly, difference in thermal expansion between the variable nozzle unit 20 and the bearing housing 13, if occurred, would cause thermal deformation of the variable nozzle unit 20 centered round the engagement part 50. In contrast, in the U-notch 51 illustrated in FIG. 3 or 4, the pin 53 becomes able to move in the U-notch 51 in the radial direction Dr, against the frictional force with the inner wall faces 51a, 51a. The aforementioned difference in thermal expansion is therefore absorbed, and this successfully suppresses change in the flow rate of exhaust gas in the nozzle flow passage 19 during operation.

Moreover, when a solid pin 53A (FIG. 5A) is used as the pin 53, it may have higher strength of the pin 53 compared to a spring pin 53B (FIG. 5B) or a coil pin 53C (FIG. 5C).

Now, a press-fitting load of the pin 53 into the U-notch 51 will be considered. The press-fitting load, if large, means that the frictional force between the pin 53 and the inner wall faces 51a, 51a is large, and this tends to promote wear of the pin 53 or the inner wall faces 51a, 51a, when the pin 53 moves in the U-notch 51 against the frictional force. Wear of the pin 53 or the inner wall faces 51a, 51a may produce a circumferential gap between the pin 53 and the inner wall faces 51a, 51a.

The spring pin 53B illustrated in FIG. 5A or the coiled pin 53C illustrated in FIG. 5B is given as a member whose dimension (e.g., width) Dm in the direction the inner wall faces 51a, 51a are opposed (circumferential direction Dc) is elastically variable. The coiled pin 53C is a member whose outer diameter is elastically variable. Hence, the spring pin 53B or the coiled pin 53C may require the press-fitting load for press-fitting into the U-notch 51, relatively smaller than that required by the solid pin 53A. Hence, the frictional force between the pin 53B or 53C and the inner wall faces 51a relatively smaller than the frictional force between the pin 53A and the inner wall faces 51a. Accordingly, the pin 53B or 53C may suppress the aforementioned wear of the pin 53B, 53C or the inner wall faces 51a compare to the pin 53A. Moreover, even if the pin 53B, 53C or the inner wall faces 51a