Abstract
Turbochargers have been used for high power automobiles which achieve a rapid acceleration. And a higher performance and a compact turbo design are making progress. Floating bush type bearings are applied to most of the turbochargers running around 100,000 rpm. Good seizure resistance is required for the bearings because of a mixing of foreign obstacles such as carbonates into the oil and a poor oil supply at an engine starting period, although the bearings usually operate at a fully hydrodynamic lubricating condition. Also corrosion resistance and wear resistance are required for basic tribology properties of bearings. Current bearing materials are lead bronze or free-cutting lead brass, on which the lead has played an important role for seizure resistance. However the reduction of use of lead, an environmental pollutant, is required today from the view point of environmental problem. For the above reasons, bearing materials containing bismuth has been developed which can replace lead contained materials. And also dispersing intermetallic compounds are added to the bearing materials as hard particles in the brass matrix to improve seizure resistance and wear resistance. Seizure resistance and wear resistance tests were conducted on a ring-on-disk friction and wear test apparatus. Also corrosion test was carried out. The test results proved that the developed material has better tribology properties compared with the lead contained bearing materials for the turbocharger bearings.
Keywords:lead-free, bearing, turbochargers