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On modally distributed damping in heavy vehicles
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
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.
Series
Trita-AVE, ISSN 1651-7660 ; 2006:78
Keyword [en]
damping, modal damping, chassis suspension, heavy vehicle, attachment compliance
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-4163OAI: oai:DiVA.org:kth-4163DiVA: diva2:11003
Public defence
2006-11-16, F3, Lindstedtsvägen 26, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100830Available from: 2006-11-01 Created: 2006-11-01 Last updated: 2010-08-30Bibliographically approved
List of papers
1. Aspects on roll and bounce damping for heavy vehicles
Open this publication in new window or tab >>Aspects on roll and bounce damping for heavy vehicles
2002 (English)In: SAE Technical paper, no 2002-01-3060Article in journal (Refereed) Published
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-6316 (URN)
Note
QC 20100830Available from: 2006-11-01 Created: 2006-11-01 Last updated: 2010-08-30Bibliographically approved
2. Possibilities and limitations with distributed damping in heavy vehicles
Open this publication in new window or tab >>Possibilities and limitations with distributed damping in heavy vehicles
2004 (English)In: Vehicle System Dynamics, ISSN 0042-3114, E-ISSN 1744-5159, Supplement to Vehicle System Dynamics, Vol. 41, 172-181 p.Article in journal (Refereed) Published
Abstract [en]

This paper investigates passive damping performance in heavy vehicles. The objective is comparison of conventional individual dampers and system with modally distributed damping. An analytical model with 7 DOF is first used to derive theoretical damping expressions. Considered degrees of freedom are for sprung mass; bounce, pitch, roll and for unsprung mass; bounce and roll. Vehicle simulations are then performed with a 4x2-tractor semitrailer combination. Load cases of both ride and handling character are used for damping system evaluation and comparison. The vehicle model with conventional individual dampers is validated against measurement data.

Keyword
Aerodynamics; Damping; Maneuverability; Reliability; Roads and streets; Surface roughness; Trucks; Vehicle suspensions
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-6317 (URN)000225095100018 ()
Note
QC 20100830Available from: 2006-11-01 Created: 2006-11-01 Last updated: 2017-12-14Bibliographically approved
3. Load case characterization and modal coordinate estimates from damper displacements
Open this publication in new window or tab >>Load case characterization and modal coordinate estimates from damper displacements
2004 (English)In: SAE technical paper series, ISSN 0148-7191, no 2004-01-2713Article in journal (Refereed) Published
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-6318 (URN)2-s2.0-84877217716 (Scopus ID)
Note

QC 20100830

Available from: 2006-11-01 Created: 2006-11-01 Last updated: 2017-12-14Bibliographically approved
4. Estimating modal coordinates from damper displacements – A system identification approach
Open this publication in new window or tab >>Estimating modal coordinates from damper displacements – A system identification approach
2006 (English)In: Vehicle System Dynamics, ISSN 0042-3114, E-ISSN 1744-5159, 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.

Keyword
Damping, Heavy vehicle, Modal coordinate estimation, System identification
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-6319 (URN)10.1080/00423110600886713 (DOI)000244729300077 ()
Note
QC 20100830Available from: 2006-11-01 Created: 2006-11-01 Last updated: 2017-12-14Bibliographically approved
5. Experimental evaluation of modally distributed damping in heavy vehicles
Open this publication in new window or tab >>Experimental evaluation of modally distributed damping in heavy vehicles
2008 (English)In: Vehicle System Dynamics, ISSN 0042-3114, E-ISSN 1744-5159, 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.

Keyword
modal damping, heavy vehicles, experimental evaluation
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-6320 (URN)10.1080/00423110701496461 (DOI)000256805100005 ()2-s2.0-46149123726 (Scopus ID)
Note
QC 20100830Available from: 2006-11-01 Created: 2006-11-01 Last updated: 2017-12-14Bibliographically approved
6. Aspects on damper-attachment compliance
Open this publication in new window or tab >>Aspects on damper-attachment compliance
2006 (English)In: Int. J. of Vehicle Design, ISSN 0143-3369, Vol. 40, no 1/2/3, 77-92 p.Article in journal (Refereed) Published
Abstract [en]

This paper investigates how attachment compliance coming from mounting bushings or brackets affects damper efficiency. Analyses with a simple mass-spring-damper system show that compliance in damper-attachment points reduces the damper efficiency. If however vibration isolation of the mass is considered, it may be seen that compliance increases low frequency vibrations but reduces high frequency vibrations. Through analyses of this system, the relative damping ratio is studied as a function of excitation frequency and attachment stiffness. furthermore obtained from both static finite element (FE) analysis of the chassis frame and from dynamic FE analysis of a tractor. The effect damper-attachment compliance has on vehicle behaviour is finally quantified with MBS simulations of a tractor semi trailer combination. It is found that attachment stiffness should be considered when simulating load cases containing high frequency inputs.

Keyword
attachment compliance; heavy vehicle; hydraulic dampers; parameter extraction; relative darriping; suspension systems
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-6321 (URN)10.1504/IJVD.2006.008454 (DOI)000234901300006 ()2-s2.0-31044437181 (Scopus ID)
Note
QC 20100830Available from: 2006-11-01 Created: 2006-11-01 Last updated: 2010-12-06Bibliographically approved

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