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Experimental evaluation of modally distributed damping in heavy vehicles
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
2008 (English)In: Vehicle System Dynamics, ISSN 0042-3114, Vol. 46, no 6, 523-541 p.Article in journal (Refereed) Published
Abstract [en]

This work presents theory as well as implementation of a modally distributed damping system with electronically controlled variable dampers. The presented approach follows from estimation of vehicle modal motions, through calculation of desirable modal damping forces to distribution of forces on the Utilised dampers. The response time of the damping system is first evaluated in a damper test rig. The damping system is then implemented on a 4 x 2 tractor that is connected to a semi-trailer. Several road tests are performed to investigate how the system work under real driving conditions on a real vehicle, that includes nonlinearities and chassis frame flexibility that are theoretically unaccounted for, together with the limitations that comes with the control algorithm implementation. It is shown that the approach works and that it results in a considerable improvement for both the bounce and pitch modes, i.e. the system enables selecting damping for the sprung mass modes separately.

Place, publisher, year, edition, pages
2008. Vol. 46, no 6, 523-541 p.
Keyword [en]
modal damping, heavy vehicles, experimental evaluation
National Category
Mechanical Engineering
URN: urn:nbn:se:kth:diva-6320DOI: 10.1080/00423110701496461ISI: 000256805100005ScopusID: 2-s2.0-46149123726OAI: diva2:11001
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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