Dual mass flywheels in truck powertrains, Modelling, simulations and validation

Licentiate thesis, 2018

The heavy-duty vehicle manufacturers face large challenges when it comes to reducing CO2 emissions from vehicles. The on-going development of more efficient combustion engines leads to an increase in torsional vibrations. In the future, the conventional flywheel and clutch will probably not be enough to protect the gearbox and rear driveline from engine induced vibrations. More advanced technology will be needed.

Dual mass flywheels (DMFs) have been used in smaller vehicles for many years and have shown to reduce the torsional vibrations transmitted to the gearbox. The use in heavy-duty commercial applications is to date very limited.

The work presented in this thesis focuses on DMFs for heavy-duty applications. It comprises modelling, measurements, correlation, development of numerical algorithms and complete powertrain simulations.

Two different DMF simulation models are used. The first one is a piecewise linear model, without the internal DMF parts explicitly modelled. It is used together with the harmonic balance method to evaluate resonances. The simulated results show that with piecewise linear DMF design, sub-harmonic resonance excitation can occur in operating speed range.

The second model includes the DMF internal parts. A simulation method where the dynamics problem is reformulated as a linear complementary problem (LCP) is proposed. The model is correlated based on test rig measurements on a DMF for heavy-duty applications. It is shown that the general DMF behaviour, as observed in the measurements, can be reproduced in the simulations for the speed and torque ranges studied.

The torsional vibrations in a heavy-duty truck powertrain with a single mass flywheel model and with the second DMF model are evaluated with simulations. The effects on resonance modes and frequencies when changing different powertrain parameters are presented. The simulations show that the vibration amplitudes are generally lower with a DMF. Resonance excitation can occur in operating speed range with the DMF and the DMF and clutch properties need to be adapted to the powertrain in order to obtain good vibration isolation in the complete operating speed and torque range.