Development of Metal Full-Filling Method Joining Ceramic Shaft to Metal Sleeve for High Performance
Toyota Motor Corporation has mass-produced turbochager with sillicon nitride ceramic rotors. A moment of inertia was reduced by 60% using ceramic rotor which improved turbochager response. The ceramic rotor was joined to metal shaft by new method which compensated problems in both shrink fitting and active brazing methods. They are generals for mechanical and chemical techniques, respectively. There still exist the following disadvantages. It is quite severe to controll the clearance of shrink fitting to obtain the reliability of the joint. The shaft may be loosened at high temperature with a small shrink-fit interference. The large shrink-fit interference could result in a failure of ceramic shaft due to large stress. Those may require a machinig accuracy with micron meter order of surface roughness which, leads to high cost.