Computer Simulation Based Computation of Natural Frequencies and Mode Shapes of Loose Transmission Gearbox Casing

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Computer Simulation Based Computation of Natural Frequencies and Mode Shapes of Loose Transmission Gearbox Casing
* Ashwani Kumar, Himanshu Jaiswal,  Pravin P Patil
Abstract. The main objective of this research work is to compute the dynamic response in
terms of natural frequencies and mode shapes of the heavy vehicle truck transmission gearbox
loose mounted casing. The results of this analysis are compared with the zero displacement
constraint condition when casing is full tightly mounted on chassis frame using 37 bolts. The
loose mounted transmission causes torsional vibration that produce rattling and clattering noise.
Reciprocity Principle has used to determine the frequencies and mode shape for loose mounted
transmission casing. The first 20-vibration mode shape and natural frequencies were calculated
using ANSYS 14.5. The study has theoretical and practical reference for the structure
optimization of truck transmission casing. ANSYS 14.5 has good analysis features suited for
analysis of complex objects like transmission casing. The natural frequency for zero
displacement condition varies from 1669 Hz to 3576 Hz and for loose transmission, casing
frequency varies from 1165 Hz to 3467 Hz. This frequency difference is in range of (3-30) %
frequency reduction by changing boundary condition.
Keywords: Simulation, Torsional Vibration, Zero Displacement, Constraint, Bolt, Loose
Transmission Casing.
Conclusion
Loose transmission cause excessive vibration and resonance. The natural frequency
for zero displacement condition when all 37 bolts are constraint varies from 1669 Hz
to 3576 Hz. The back part of heavy vehicle truck transmission casing is connected by
9 bolts to the truck chassis frame and other mountings of truck. When all 9 bolts are
loosened the natural frequency varies from 1165 Hz to 3467 Hz. The looseness of the
casing cause reduction in natural frequency and these lower order frequencies are the
main reason for the excitation, which causes resonance. In resonance the transmission
casing were subjected to heavy vibration leads to failure of transmission For the first
order frequency (f1), there is a difference of 504 Hz (30%) for the zero displacement
and loosened condition and for the 20-order frequency, the difference is 109 Hz (3%).
The simulation shows that the transmission casing is subjected to axial bending
vibration, torsional vibration and axial bending with torsional vibration. Torsional
vibration causes rattling and clattering noise. Reciprocity Principle was used to
evaluate the 20 natural frequencies and corresponding mode shapes using ANSYS
14.5. In conclusion, the numerical simulation of casing has confirmed that bolts
loosening condition leads failure of the transmission system. The frequencies (f17, f18,
f19, f20) of loose casing (series 2 , figure 6) are overlapped by the same frequency of
zero displacement condition (series 1 figure 6). The mechanical properties of grey
cast iron HT 200 was consider for the realistic approach analysis. The FEA simulation
based analysis provides satisfactory results. This research work deals with only one
position loose condition in future this study can be extended to others position and
bolts loose conditions.
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