Evaluation of dynamic absorber to suppress subharmonic nonlinear vibration in car powertrain

This paper analyzed the suppression method of the nonlinear vibration called subharmonic vibration of order 1/2 in the car powertrain by using a dynamic absorber. In the car powertrain, the torsional forced vibration caused by engine explosions leads to inhibition of the ride quality. Thus, in the torque converter of an automatic transmission car, a piecewise-linear spring called damper is used to reduce the transmission of the forced vibration. However, the subharmonic vibration occurred in the actual vehicle, when the spring restoring characteristics is around the switching point. The fundamental vibration frequency of the subharmonic vibration is half to the engine forced vibration frequency. Although the design of the dynamic absorber to suppress the forced vibration has been established for the linear systems, the optimum design to suppress the subharmonic vibration of order 1/2 has not yet been investigated. The powertrain is modeled by multi degree-of-freedom system as an actual vehicle, including engine, torque converter, transmission gears and wheels. Equation of motion is developed with also considering spring restoring force of piecewise-linear spring. The numerical result shows subharmonic vibration occurs when the engine excitation frequency is almost twice of the second mode of natural frequency, and the result shows a good agreement with the experimental data. Then, the dynamic absorber is introduced to suppress the occurrence of subharmonic vibration theoretically. In this paper, the optimum design of the dynamic absorber to suppress the subharmonic vibration is discussed. The numerical result shows the optimally designed dynamic absorber in the natural frequency and the damping ratio is capable of suppressing the occurrence of the subharmonic vibration.