Evaluation of Wear in an Automotive Transmission Using Powder Metal (PM) Gears

Abstract

In 2008, Höganäs together with KBE+ redesigned the transmission for the smart fortwo car. The ambition was to create a PM friendly, reduced weight transmission that could be built into the original transmission housing whilst maintaining reliability. The reverse engineering analysis showed that this could be done without sacrificing service life, and with an accumulated weight reduction on the gears of 1 kg. In 2010, this transmission was built into a smart fortwo, driven to the PM World Congress in Florence and exhibited there. Since the congress, the smart car has been used as an everyday driver for eight years and accumulated 200 000 km.

In this paper, an evaluation of the PM gears will be presented. The gears are visually inspected after 200 000 km of real driving. The wear, as well as any other damage to gears and synchronizers will be investigated and discussed. Topography measurements before and after 200 000 km will be shown for quantification of wear, and pictures of the gear flanks will be shown to establish the general condition of the gears. From the design work the stress conditions are known, and from the logging system in the car, information on cycles and load can be estimated to further understand the load history of the gears.