Application of PM Materials in Synchronizer Rings  (1,79MB)
Michael Krehl and Günter Rau
Euro PM 2000, München

Manual transmissions are equipped with synchronizer-systems for better and more comfortable gearchange performance. A main component of such a synchro-system ist the synchronizer-ring. The synchronizer or blocker-ring has three main functions:
1. generate friction thus torque for synchronizing 2. hight wear resistance of the blocker-teeth - especially in the case of automated shifting (ASM). 3. high strength and toughness to enable compact design (low weight, reduced rebound space)
Such synchronizer rings are made from different forged brass alloys, forged steel but also powdermetallurgically (P/M) from steel. In case of P/M rings the required high strength, toughness, wear resistance in the teeth region and the stop cog, the dimensional accuracy and the low cost can be met by the following different materials and processes:
•	Fe/Mo/Cu or Cr with low carbon content, high-temperature-sintering, sizing and hardening by plasmanitriding or carburization
•	high performance Fe/Mo/Ni and Cu with high carbon content, warm compacted and sinterhardened
•	Fe/Mo alpha-phase-high-temperature-sintered and carburized.
For superior friction behaviour the synchro-rings can have a friction lining CD-welded into the inner cone. Applications, properties, advantages and disadvantages of these differnet materials as synchronizer-rings and processes are discussed.