Höganäs puts PM automotive transmission gears to the ultimate test
One of the main attractions in the PM2010 World Congress exhibition hall was a Smart Fortwo car, fitted with seven powder metallurgy transmission gears that had been driven from Höganäs AB’s headquarters in southern Sweden to Florence, Italy. The aim of the trip was to demonstrate that PM technology is more than capable of producing the high performance gears that are used in automotive gearboxes.
The demonstration car’s Getrag gearbox has seen PM power transmission gears replacing 7 out of 13 conventional machined gears. The gears are copies of the original design and gear pairs 3, 4, 5 and the reverse idler gear were pressed, sintered and machined before being case hardened and ground to final tolerances. Final density was reported as 7.25 g/cm³ and the material was a standard powder alloyed with 0.85% Mo and 0.25% C (Astaloy 85 Mo).
Höganäs’ gear expert Dr Anders Flodin, who drove the car from Sweden, believes the general opinion regarding PM technology is about to change. “A few years ago people laughed as we spoke of PM gears. By going on this journey, we now have the opportunity to show that the technology is real and here to stay”.
Anders began his journey across Europe with the intention of proving the concept of load-carrying gears on Friday, 1st of October. The first stop on Anders’ journey was Garching, a small town outside Munich, Germany, where an international conference on gears was held from 4th-6th of October. Anders then travelled in to RWTH Aachen before arriving at the World PM 2010 conference in Florence.
The Smart car, with its PM gearbox parts and striking iron powder graphics, had been used extensively in Sweden before the drive to Italy, having been made available as a “loan car” for Höganäs AB staff in order quickly to build up “real-life” mileage. So far the gearbox has achieved 60,000 km and no sign of damage or measurable wear has been detected. There is confidence that the PM gears will comfortably achieve in excess of 200,000KM.
A paper that looks in greater detail at this project, and design aspects relating to powder metal gears was presented at the International Conference on Gears 2010. The paper concluded that specific design aspects need to be considered when developing PM power transmission gears, however PM offers the advantages of light weight design possibilities and improved performance.
Inertia losses in the gear box can easily be reduced by 6-7%, with the possibility to reduce costs at the same time.
It was also shown that the damping is clearly affected by the density of the material, a feature that can be used in order to reduce noise emission from the gears. PM gears also appear to be as fault tolerant as conventional gears, and suffer less from variations in manufacturing quality.
