During engine durability tests (peak power, constant engine speed) conducted in the development process, it has been the case that excessive wear has occurred to the upper surfaces of the piston top ring grooves, despite the fact that contact pressure due to combustion pressure has been low. This has resulted in considerable increases in development man-hours. The research discussed in this paper therefore set out to conduct a factor analysis of wear on the upper surfaces of piston top ring grooves in order to elucidate the wear mechanism in petrol engine for passenger car. This paper will discuss the test method employed in the factor analysis and the mechanism of wear demonstrated by the analysis. First, the form of the wear was analyzed, and rig test methods able to reproduce wear were developed. With regard to the form of wear, both sliding and impact modes were observed. Sensitivity analyses for each form of wear were conducted using rig tests. Quality engineering was employed in the tests, and sensitivity was analyzed based on the design of experimental method. Following this, an engine motoring test method was developed that was closer to the operating state of an actual engine, and that allowed tests to be simply conducted. This motoring test was able to reproduce a compound form of wear produced by sliding and impact, equivalent to that observed in an actual engine, and verified the accuracy of the factor sensitivity demonstrated in the rig tests. In addition, the motoring test was able to reproduce asymmetrical wear in the direction of the circumference of the grooves, which could not be reproduced in the rig test, and made it possible to elucidate the causes of this wear. Finally, an actual engine test was conducted combining the highest and lowest of the determined sensitivities, confirming the validity of the identified wear factors.
