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In recent years, internal-combustion engines have been required to satisfy various performance standards against emission regulations and fuel-efficiency targets. To this end, accurate measurement of piston temperature under various engine operating conditions is important. Some studies reported the use of wireless methods to confirm the reliability of the measurement system at the highest engine speed and create a piston temperature map under all operating conditions. However, previous case studies only considered relatively large displacement engines, and the advantage of wireless methods—a high degree of freedom for design—was not used. In terms of engine operating conditions, few cases focus on the piston to cylinder wall clearance during engine warm-up conditions. Thus, wireless methods are still space to use their features.

Lead-added free-cutting steel has been used by many parts which need high machinability because lead improves chip friability and drill life. However, the demand of lead reduction increases in recent years, because of environmental impact substance reduction. Therefore, we developed lead-free crankshaft for motorcycle. Until now, crankshaft for motorcycle has been manufactured with lead-added free-cutting steel by a following process; Hot-Forging - Quenching and Tempering (QT) - Prior Machining - Nitrocarburizing - Finishing process because of strength and machinability. When we tried to change steel to lead-free, we examined to change to sulfur-added free-cutting steel. However, chip friability of sulfur-added free-cutting steel is inferior to lead one. Thus, we concerned about increase in machining expense. Then, heat-treatment after forging was examined to change from QT to normalizing for reducing the heat-treatment expense.

The automobile industry presently focuses on improving fuel economy and reducing the weight of vehicles. One part of these efforts is to develop high-performance engines for improved combustion efficiency and lower emissions. Against this background, many high-performance motorcycle engines use forged pistons made of extruded or continuously cast aluminum alloy for high reliability and material properties. The cost of forged pistons is higher than that of gravity die cast pistons. To replace these expensive forged pistons, a low-cost, high-performance piston with increased endurance and thermal resistance has been developed using a newly developed aluminum alloy and a high-quality die casting technology using an oxygen supply system and additional pressure.