Characteristics of Bending Stress with Whirling at the Rear End of a Crankshaft in an Inline 4-Cylinder High Speed Diesel Engine 2019-01-1592

This paper describes characteristics of the bending stress with a severe sharp peak measured on the rearmost crank-pin fillet portion of a crankshaft. The measurements are carried out with two different specification flywheels with different weights, and the influence of the flywheel weight on the characteristics is also studied. First, from the order tracking analysis of the measured bending stress, it is found that the resonance frequencies of the bending vibration at the crankshaft rear end are present around four different straight lines which increase or decrease as resonant engine speed increases. And it is shown that the resonance frequencies presenting around the four straight lines can occur when the crankshaft rear end is whirling. It is also described how the weight of a flywheel influences the resonance frequencies. Next, from examining the relationship between the bending stress amplitude and the radial force acting on the crank-pin which is the exciting force of the bending vibration of the crankshaft rear end, it is revealed to have almost proportional relationships. And the ratios of the stress amplitude to the radial force for forward-whirl which takes place in the same direction as the rotation of the crank-journal are larger than those for reverse-whirl which takes place in the opposite direction as the rotation of the crank-journal, and those increase further as the flywheel weight is heavier. Furthermore, from examining the relationship between the bending stress amplitude and the engine speed which is closely related to the force and the gyroscopic moment acting on the crankshaft rear end due to whirl, it is found the engine speed influence the bending stress amplitude. Finally, It is discussed that the reason why the ratios of the stress amplitude to the radial force are larger when forward-whirl occurring.