Abstract
Ever growing engine size and power have renewed such crankshaft trouble as axial or coupled torsional-axial vibration. For the former mode some empirical methods have been proposed to calculate its natural frequencies, but are not so reliable as ones for torsional vibration. For the latter it seems to have been dealt with nothing but an experimental, scale-model method.
In this paper, (1) a new equivalent system of crankshaft is supposed ro as to tolerate 4 degrees of freedom : axial, torsional and two kinds of lateral vibration. (2) Theoretical, not empirical equations for calculating stiffness values of the shafting are derived, so that a design-stage forcast of the modes of shaft vibration is possible. (3) Equations of motion are written in matrices, transformed into eigen value problems and solved with the Jacobi-rotation method on a digital computer, not iteratively but directly. (4) The solution gives every mode and frequency on one chart, including coupled torsional-axial modes which have never been correctly explained before.
Two kinds of shafting were investigated, and their solutions showed fairly good agreements with the measured data on board.
The authors recommend to apply this new matrix method not only to coupled systems as above, but also to simple systems without coupling—pure torsional or pure axial—in place of Holzer method for convenience in digital computation.
