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Estimating modal coordinates from damper displacements – A system identification approach
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
KTH, School of Electrical Engineering (EES), Automatic Control.
2006 (English)In: Vehicle System Dynamics, ISSN 0042-3114, Supplement to Vehicle system dynamics, Vol. 44, 805-813 p.Article in journal (Refereed) Published
Abstract [en]

For modal damping systems, estimations of the modal coordinates are crucial. This article shows how the identification of time-domain system can be used to obtain better estimations of the modal coordinates in bounce, pitch and roll for a heavy vehicle. Low-order multiple-input-single-output models used for modal coordinate estimation are identified on data both from multi-body systems' simulations and from vehicle measurements. The identified models show considerable improvements in accuracy when compared with the previously used geometric calculations. Although good models are obtainable for all tested load cases, their validity is somewhat limited to load cases of similar excitation type because driver-induced manoeuvres such as braking and steering wheel action provide different vehicle excitation in comparison to road bumps. A compromise would be to identify an estimation data containing all relevant load cases.

Place, publisher, year, edition, pages
2006. Vol. 44, 805-813 p.
Keyword [en]
Damping, Heavy vehicle, Modal coordinate estimation, System identification
National Category
Mechanical Engineering
URN: urn:nbn:se:kth:diva-6319DOI: 10.1080/00423110600886713ISI: 000244729300077OAI: diva2:11000
QC 20100830Available from: 2006-11-01 Created: 2006-11-01 Last updated: 2010-12-06Bibliographically approved
In thesis
1. On modally distributed damping in heavy vehicles
Open this publication in new window or tab >>On modally distributed damping in heavy vehicles
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This thesis investigates passive damping system performance in heavy vehicles through analytical expressions, simulations with different vehicle models as well as through experimental evaluation in a tractor semi trailer combination. The objective is to study what levels of chassis suspension damping that are desirable for different vehicle modes and how this may be achieved with passive damping systems.

To investigate the influence on performance from damper positioning, analytical expressions for a 2D - suspension model are derived. Geometric key parameters controlling roll and bounce damping are found to be damper vertical aligning and perpendicular distance between damper and suspension roll centre respectively. These parameters are often not easily altered within an already existing vehicle. To investigate performance possibilities from damping not restricted by packaging requirements, the concept with distributed damping is furthermore studied. Theoretical expressions for modally distributed damping are first derived from an analytical tractor model with 7 DOF. Considered motions for which damping is prescribed are bounce, pitch and roll of sprung mass, and axle crossing. These equations are evaluated through various simulations with a 4x2-tractor semi trailer model. Results from simulations show that the conflict in damping demands with passive independent dampers for a single lane change and a one-sided pot hole may be significantly reduced with amplitude dependent modal damping.

Vehicle damping performance is not only affected by the dampers positioning and their individual setting, but also by the damper attachment structure. The influence from compliance in e.g. brackets and mounting bushings at damper attachment points is therefore studied. Linear analysis with a simple spring mass damper model shows that damper attachment compliance reduces the damper efficiency. Finite element analyses of both the chassis frame and the tractor are furthermore performed to obtain numerical values of front-axle damper-attachment stiffness. The effect from damper-attachment stiffness is quantified though simulations with a tractor semi trailer model. Simulation results show that it is important to consider the attachment stiffness during vehicle manoeuvres containing high frequency inputs such as the passage over a plank.

A methodology and equations for prescribing chassis suspension damping as function of general vehicle modes by using electronically controlled variable dampers is presented. A critical input for such implemented modal damping systems are the real time estimation of modal motions necessary for force calculation. From performed simulations it is shown that geometric calculations of modal velocities based solely on relative damper displacements contain significant discrepancies to actual motion for transient road inputs. To overcome this, a time-domain system identification approach is presented, where models that estimate modal coordinate velocities with considerably higher accuracy are identified.

The proposed modal damping approach is implemented on a 4x2 tractor and experimentally evaluated through various road tests. It is shown that the system has the desired ability to control sprung mass bounce and pitch modes separately and that it improves vehicle performance on all tested load cases.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. vii, 53 p.
Trita-AVE, ISSN 1651-7660 ; 2006:78
damping, modal damping, chassis suspension, heavy vehicle, attachment compliance
National Category
Physical Sciences
urn:nbn:se:kth:diva-4163 (URN)
Public defence
2006-11-16, F3, Lindstedtsvägen 26, Stockholm, 10:00
QC 20100830Available from: 2006-11-01 Created: 2006-11-01 Last updated: 2010-08-30Bibliographically approved

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