Abstract
Research has been conducted on an extended expansion engine, using a multiple linkage system to increase the thermal efficiency of general-purpose engines. In this research, first, the test engine was subjected to an engine acoustics measurement to clarify its noise characteristics. Then, based on the analysis results of the noise characteristics, we propose the direction to reduce the noise of the multiple linkage system engine.
When the test engine was operated under a no-load firing condition, rattle noise was observed. Also it was found that the timing of the occurrence of the rattle noise was near after top dead center (ATDC) 90 degrees in crank angle (degCA).
Focusing on the gear for linkage drive as a cause of the rattle noise, the authors formulated the torque acting on the gear. Entering the cylinder pressure and angular velocity of crankshaft, which were derived from the condition that the rattle noise was occurring, in this formula, we found that the major factor of the noise was the collisions between the gears teeth resulted from the reversal of torque transmission direction, which occurred at ATDC 90 degCA.
As a result of analysis, it is effective to reduce piston acceleration during the process of expansion stroke to lower the rattle noise. Here, we have designed a new multiple linkage system of low noise specifications. The noise of it was measured -13.1 dB(A) in comparison with that of the test engine; thus, its effect has been confirmed.