Method of manufacturing turbine frame for VGS turbocharger, turbine frame manufactured by the method, exhaust gas guide assembly for VGS turbocharger using the turbine frame, and VGS turbocharger in which the exhaust gas guide assembly is incorporated

Abstract

A novel method of manufacturing a turbine frame for rotatably holding adjustable blades in a VGS turbocharger is provided, which method is capable of manufacturing the turbine frame while almost eliminating a time-consuming cutting operation, whereby mass production of the turbine frame and the like can be realized. The method includes: a blank which is punched out from a metal material having a substantially constant thickness in such a manner as to integrally include a boss forming portion ( 24 a ) and a flange forming portion ( 23 a ) is used as a shaped material (W) serving as an original member for the turbine frame; when the shaped material (W) is processed, the boss forming portion ( 24 a ) is formed into a projecting state by a press forging tool; receiving holes for rotatably holding the respective adjustable blades are formed in the flange forming portion ( 23 a ) by punching; and when the shaped material (W) is processed, some or all of the manufacturing processes are carried out in a warm condition.

1 . A turbine frame for a VGS turbocharger, the turbine frame to be incorporated in the VGS turbocharger and disposed at an outside of an outer periphery of an exhaust turbine wheel for rotatably holding a plurality of adjustable blades,
 wherein exhaust gas discharged from an engine at a flow rate is to be throttled by the adjustable blades so as to increase a velocity of the exhaust gas such that the exhaust gas turbine wheel is rotated by energy of the exhaust gas and a compressor directly coupled to the exhaust turbine wheel feeds more air into the engine than that of natural suction, whereby a high output power of the engine is obtained at low rotational speeds,   the turbine frame comprising:   a frame segment including a flange portion having receiving holes formed thereon for rotatably holding the plurality of adjustable blades, and a boss portion for being fitted therearound with a blade adjusting mechanism,   wherein the flange portion and the boss portion are integrally formed of a metal material by press forging a blank of the metal material having a substantially constant thickness,   wherein the boss portion is axially protruded from a center part of the flange portion,   and wherein the receiving holes are formed in the flange portion by punching.   
   
   
       2 . An exhaust gas guide assembly for a VGS turbocharger, comprising:
 adjustable blades for adjusting a flow rate of exhaust gas discharged from an engine so as to rotate an exhaust turbine wheel;   the turbine frame as defined in  claim 1  rotatably supporting the adjustable blades at an outside of an outer periphery of the exhaust turbine wheel; and   an adjusting mechanism for rotating the adjustable blades so as to adjust the flow rate of the exhaust gas,   wherein the exhaust gas at a low flow rate is throttled by the adjustable blades so as to increase a velocity of the exhaust gas so that a high output power is obtained at low rotational speeds.   
   
   
       3 . A VGS turbocharger constructed such that an exhaust turbine is driven by exhaust energy of an engine so as to rotate a compressor coupled to the exhaust turbine with the power of the exhaust turbine, whereby the engine is supercharged to have more air fed into the engine than is fed into the engine by natural suction, comprising:
 the exhaust gas guide assembly as defined in  claim 2 ,   wherein flow of the exhaust gas at a low flow rate is throttled so as to increase a velocity of the exhaust gas so that a high output power is obtained when the engine is running at low rotational speeds.   
   
   
       4 . The VGS turbocharger according to  claim 3 , wherein the metal material comprises an austenitic heat resisting material. 
   
   
       5 . The VGS turbocharger according to  claim 4 , wherein the austenitic heat resisting material is austenitic stainless steel. 
   
   
       6 . The exhaust gas guide assembly according to  claim 2 , wherein the metal material comprises an austenitic heat resisting material. 
   
   
       7 . The exhaust gas guide assembly according to  claim 6 , wherein the austenitic heat resisting material is austenitic stainless steel. 
   
   
       8 . The turbine frame according to  claim 1 , wherein at least one of the press forging and the punching are carried out in a warm condition. 
   
   
       9 . The turbine frame according to  claim 1 , wherein the metal material comprises an austenitic heat resisting material. 
   
   
       10 . The turbine frame according to  claim 9 , wherein at least one of the blank and a processing device are heated depending on an Md 30  value during processing of the blank of the metal material, the Md 30  value being a strain induced martensitic transformation index of the metal material. 
   
   
       11 . The turbine frame according to  claim 9 , wherein the austenitic heat resisting material is austenitic stainless steel. 
   
   
       12 . The turbine frame according to  claim 1 , wherein the press forging is carried out in a state in which a temperature gradient is imparted to the blank of the metal material. 
   
   
       13 . The turbine frame according to  claim 1 , wherein the press forging is carried out in a state in which a water-soluble heat-resistant lubricant is interposedly disposed at a contact portion between the blank and a press forging tool. 
   
   
       14 . The turbine frame according to  claim 1 , wherein the press forging is carried out by a punch and a blank holder, the punch being subjected to at least one of low-speed control and inching control in the vicinity of a bottom dead point.