Structure and method for joining nozzle vane and lever, and variable geometry turbocharger

A joint structure of a nozzle vane and a lever, comprising:

• a nozzle vane to be disposed in an exhaust passage for guiding exhaust gas to a turbine wheel of a variable geometry turbocharger, the nozzle vane including a shaft portion;
• and
• a lever including a fitting surface to be fitted with a peripheral surface on one end side of the shaft portion, for transmitting torque to the shaft portion to adjust a vane angle of the nozzle vane,
• wherein the nozzle vane is composed of nickel-based alloy,
• wherein the lever is composed of stainless steel, and
• wherein the lever and the one end side of the shaft portion are welded to each other, and a radiation-center position radiated by heat for welding is disposed outside a position of the fitting surface with respect to a radial direction of the shaft portion, and
• wherein an expression of D/S≥0.25 is satisfied, where D is a distance between the radiation-center position and the position of the fitting surface with respect to the radial direction of the shaft portion and S is a width of weld metal with respect to the radial direction of the shaft portion.

A method of joining a nozzle vane and a lever by welding, comprising:

• providing
• a nozzle vane to be disposed in an exhaust passage for guiding exhaust gas to a turbine wheel of a variable geometry turbocharger, the nozzle vane including a shaft portion and being composed of nickel-based alloy, and
• a lever including a fitting surface to be fitted with a peripheral surface on one end side of the shaft portion, for transmitting torque to the shaft portion to adjust a vane angle of the nozzle vane, the lever being composed of stainless steel;
• and
• welding the lever and the one end side of the shaft portion by radiating heat to the lever and the one end side of the shaft portion so that a radiation-center position is disposed outside a position of the fitting surface with respect to a radial direction of the shaft portion, and
• wherein heat is radiated so that an expression of D/S≥0.25 is satisfied, where D is a distance between the radiation-center position and the position of the fitting surface with respect to the radial direction of the shaft portion and S is a width of weld metal with respect to the radial direction of the shaft portion.