Torsional vibration absorbers in heavy-duty truck powertrains

The heavy-duty vehicle manufacturers face large challenges when it comes to reducing CO2 emissions from vehicles. The ongoing development of more efficient combustion engines leads to an increase in torsional vibrations. Experience within the industry indicates that the conventional single mass flywheel (SMF) and clutch will not be enough to protect the gearbox and rear driveline from engine induced vibrations in the future; more advanced technology will be needed.The work presented in this thesis focuses on simulation and analysis of torsional vibration absorbers for heavy-duty truck applications. Different multiple-mass flywheels are analysed, including dual mass flywheels (DMFs), power split vibration absorbers (PSVAs) and DMFs combined with tuned vibration absorbers (TVAs). DMFs have been used in smaller vehicles for many years, but the use in heavy-duty commercial applications is to date very limited. The other two vibration absorbers studied in this work have not yet been industrialised.The vibrations absorbers are analysed by means of simulations. Methodologies for efficient simulations in time- and frequency-domain have been developed and are presented in the thesis. The frequency-domain methods used include the harmonic response and a harmonic balance method, combined with an arc-length continuation scheme. For models with many gap-activated springs, a time-domain approach is proposed, where the dynamics problem is reformulated as a linear complementary problem (LCP).A detailed DMF model, including internal parts, friction and clearances, is presented for time-domain studies requiring high accuracy. The model is correlated based on test rig measurements.The torsional vibrations in typical heavy-duty truck powertrains with the different multiple-mass flywheels are simulated in a large engine load and speed range. The results are analysed and compared to corresponding conventional powertrains. It is evaluated how different design parameters affect the torsional vibrations and the feasibility of the concepts for heavy-duty use is studied. The simulations show that the torsional vibration amplitudes are generally significantly lower with a DMF than with an SMF, but under some conditions significant resonance excitation can occur. The PSVA and DMF equipped with a TVA can reduce vibrations further than a corresponding DMF within limited speed ranges, but lead to higher vibration amplitudes outside these ranges

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

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

Vibration dynamics in non-linear dual mass flywheels for heavy-duty trucks

A non-linear model for simulations of a dual mass flywheel (DMF) for heavy-duty applications is proposed. The model includes internal clearances and friction. LuGre friction model is used, which depends on normal force, relative velocity between the two surfaces and an internal deflection variable. Measurements on the DMF are performed in a test rig and the test rig properties are analysed. The correlation shows that the general behaviour of the DMF is reproduced by the proposed simulation model. The viscous part of the friction is dominant for the analysed cases with zero mean torque, and a conventional Coulomb friction model would not suffice for this application. Near resonances, the model also shows a high sensitivity to internal clearances and spring stiffness. This indicates that correlation could be improved further if the static stiffness was measured with good accuracy for the relevant range of deflection angles

Torsional vibrations in truck powertrains with dual mass flywheel having piecewise linear stiffness

The vehicle industry faces big challenges when it comes to reducing the emissions of heavy vehicles. In order to cope with the increasing demand for efficient, low emission vehicles, the trend within the industry is to down-size and down-speed the engines. These measures lead to higher torsional vibrations in the powertrain and therefore there is also an increasing need for efficient reduction of torsional vibrations. One way to reduce the vibration is to use a dual mass flywheel. A dual mass flywheel consists of two flywheels connected by a torsional spring package.\ua0 The spring package should have low stiffness but must also cope with very high torques. Therefore the dual mass flywheels are often designed so that they have a piecewise linear relationship between torque and wind-up angle. A full powertrain model has been used with realistic engine load in order to evaluate how the piecewise linear design affects the vibrations in the powertrain. Simulations have been performed in frequency domain and time domain and evaluation is done both with respect to mode shapes and frequencies and computed steady-state vibration amplitudes. In the linear region, there is a frequency shift for a problematic resonance mode that leads to significant decrease in vibration amplitude at low engine speeds. In non-linear regions, a resonance mode corresponding to half the main exciting frequency from the engine can be excited, leading to high vibration amplitudes. The frequency of this mode and the extent to which it is excited depends on the engine torque and highest amplitudes are not always obtained at the highest load

Dual-mass flywheels with tuned vibration absorbers for application in heavy-duty truck powertrains

As the heavy-duty combustion engine development goes towards lower rotational speeds and higher cylinder pressures, the torsional vibrations increase. There is therefore a need to identify and study new types of vibration absorbers that can reduce the level of torsional vibrations transmitted from the engine to the gearbox. In this work, the concept of a dual-mass flywheel combined with a tuned vibration absorber is analysed. The tuned vibration absorber efficiently reduces the vibration amplitudes for engine load frequencies near the tuning frequency, but it also introduces an additional resonance into the system. By placing the tuned vibration absorber on an intermediate flange between the two dual-mass flywheels, the introduced resonance frequency will be lower than the tuning frequency and a resonance in operating engine speed range can be avoided. Numerical simulations are used to show how the torsional vibration amplitudes in a heavy-duty truck powertrain are affected by the tuned vibration absorber and how the different parameters of the tuned vibration absorber and the dual-mass flywheel affect the torsional vibrations and the resonance frequencies

Analysis of power split vibration absorber performance in heavy-duty truck powertrains

The current development of more efficient combustion engines leads to an increase in engine torsional vibrations; therefore, new technology is needed for reducing the vibrations transmitted from the engine to the driveline. In this article, the concept of power split vibration absorber is evaluated. A mathematical model of the power split vibration absorber is presented, and an analytical study shows how different design parameters affect the power split vibration absorber performance. Numerical simulations with models representing typical heavy-duty truck powertrains are used in the evaluations. It is concluded that for a low level of damping, the power split vibration absorber can provide significantly lower vibration amplitudes than a corresponding dual mass flywheel within a limited speed range. If the power split vibration absorber is optimised for the critical low engine speeds, an overall decrease in the level of vibration can be obtained, but a larger installation space than with a conventional dual mass flywheel would probably be required

Numerical Algorithms for Simulation of One-Dimensional Mechanical Systems With Clearance-Type Nonlinearities

In many mechanical systems there are nonlinearities of clearance type. This type of nonlinearity often causes problems with convergence and accuracy in simulations, due to the discontinuities at impact. For systems with gap-activated springs connected to ground, it has been proposed in previous work to reformulate the problem as a linear complementary problem (LCP), which can be solved in a very efficient way. In this paper, a generalization of the LCP approach is proposed for systems with gap-activated springs connecting different bodies. The generalizations enable the LCP approach to be used for an arbitrary number of gap-activated springs connecting either different bodies or connecting bodies to ground. The springs can be activated in either compression or expansion or both and a gear ratio can be included between the bodies. The efficiency of the algorithm is demonstrated with an application example of a dual mass flywheel (DMF)