Turbocharger having a connector for connecting an impeller to a shaft

Abstract

A connector for connecting an impeller to a shaft is provided. The impeller has a shaft-side hub extension with a central recess. The impeller is formed of a material having a greater coefficient of thermal expansion than the material of the shaft. The connector is inserted into the recess to frictionally connect an outwardly facing surface of the connector with a radially inner surface of the hub extension. The connector has a threaded portion carrying a thread which screws onto a corresponding threaded portion of the shaft, such that the connector provides a rotationally fixed connection between the impeller and the shaft. The connector is formed of a material having a coefficient of thermal expansion which is greater than the coefficient of thermal expansion of the material of the shaft.

1 . A connected impeller and shaft, the impeller having a shaft-side hub extension with a central blind hole recess, the impeller being fitted with a connector which connects the impeller to the shaft, and the impeller being formed of a material having a greater coefficient of thermal expansion than the material of the shaft, wherein: the connector is inserted into the recess to frictionally connect an outwardly facing surface of the connector with a radially inner surface of the hub extension, the frictional connection between the outwardly facing surface of the connector and the radially inner surface of the hub extension transmitting, in use, substantially all of the torque between the shaft and the impeller; and
 the connector has a threaded portion carrying a thread which screws onto a corresponding threaded portion of the shaft, such that the connector provides a rotationally fixed connection between the impeller and the shaft;   charaterised in that:
 the connector is formed of a material having a coefficient of thermal expansion which is greater than the coefficient of thermal expansion of the material of the shaft, the value of (α c −α s )/(α i −α s ) being greater than 0.2 and less than 0.9, where α c  is the coefficient of thermal expansion of the connection, α i  is the coefficient of thermal expansion of the impeller, α s  is the coefficient of thermal expansion of the shaft . 
   
     
     
         2 . (canceled) 
     
     
         3 . (canceled) 
     
     
         4 . (Canceled) 
     
     
         5 . A connected impeller and shaft according to  claim 1 , wherein the connector is formed of a material having a greater strength than the material of the impeller. 
     
     
         6 . (canceled) 
     
     
         7 . A connected impeller and shaft according to  claim 1 , wherein the threaded portion of the connector is within the central recess. 
     
     
         8 . A connected impeller and shaft according to  claim 1 , wherein the connector and/or the impeller has one or more centring portions having respective engagement surfaces which engage with one or more corresponding centring portions of the shaft, the threaded portion of the connector and the centring portions of the connector and/or the impeller being distributed along the impeller axis. 
     
     
         9 . A connected impeller and shaft according to  claim 1 , wherein the impeller has a casing and the connector and/or the hub extension forms a seal with a section of the casing. 
     
     
         10 . A connected impeller and shaft according to  claim 1 , wherein the connector is formed with or carries a circumferential oil thrower formation at its radially outer surface. 
     
     
         11 . (canceled) 
     
     
         12 . (canceled) 
     
     
         13 . A turbocharger having the connected impeller and shaft of  claim 1 .