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Suspension design for off-road construction machines
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Construction machines, also referred to as engineering vehicles or earth movers, are used in a variety of tasks related to infrastructure development and material handling. While modern construction machines represent a high level of sophistication in several areas, their suspension systems are generally rudimentary or even nonexistent. This leads to unacceptably high vibration levels for the operator, particularly when considering front loaders and dump trucks, which regularly traverse longer distances at reasonably high velocities. To meet future demands on operator comfort and high speed capacity, more refined wheel suspensions will have to be developed. The aim of this thesis is therefore to investigate which factors need to be considered in the fundamental design of suspension systems for wheeled construction machines.

The ride dynamics of wheeled construction machines are affected by a number of particular properties specific to this type of vehicle. The pitch inertia is typically high in relation to the mass and wheelbase, which leads to pronounced pitching. The axle loads differ considerably between the loaded and the unloaded condition, necessitating ride height control, and hence the suspension properties may be altered as the vehicle is loaded. Furthermore, the low vertical stiffness of off-road tyres means that changes in the tyre properties will have a large impact on the dynamics of the suspended mass. The impact of these factors has been investigated using analytical models and parameters for a typical wheel loader. Multibody dynamic simulations have also been used to study the effects of suspended axles on the vehicle ride vibrations in more detail. The simulation model has also been compared to measurements performed on a prototype wheel loader with suspended axles.

For reasons of manoeuvrability and robustness, many construction machines use articulated frame steering. The dynamic behaviour of articulated vehicles has therefore been examined here, focusing on lateral instabilities in the form of “snaking” and “folding”. A multibody dynamics model has been used to investigate how suspended axles influence the snaking stability of an articulated wheel loader. A remote-controlled, articulated test vehicle in model-scale has also been developed to enable safe and inexpensive practical experiments. The test vehicle is used to study the influence of several vehicle parameters on snaking stability, including suspension, drive configuration and mass distribution. Comparisons are also made with predictions using a simplified linear model.

Off-road tyres represent a further complication of construction machine dynamics, since the tyres’ behaviour is typically highly nonlinear and difficult to evaluate in testing due to the size of the tyres. A rolling test rig for large tyres has here been evaluated, showing that the test rig is capable of producing useful data for validating tyre simulation models of varying complexity.

The theoretical and experimental studies presented in this thesis contribute to the deeper understanding of a number of aspects of the dynamic behaviour of construction machines. This work therefore provides a basis for the continued development of wheel suspensions for such vehicles.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology , 2011. , ix, 80 p.
Series
Trita-AVE, ISSN 1651-7660 ; 2011:39
Keyword [en]
construction machine, engineering vehicle, earth mover, wheel loader, vehicle dynamics, vehicle engineering, whole body vibrations, off-road vehicle
Keyword [sv]
anläggningsmaskin, entreprenadmaskin, hjullastare, fordonsdynamik, fordonsteknik, helkroppsvibrationer, terrängfordon
National Category
Vehicle Engineering
Identifiers
URN: urn:nbn:se:kth:diva-33883ISBN: 978-91-7501-040-3OAI: oai:DiVA.org:kth-33883DiVA: diva2:418343
Public defence
2011-06-14, D2, Lindstedtsvägen 5, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
TrenOp, Transport Research Environment with Novel Perspectives
Note
QC 20110531Available from: 2011-05-31 Created: 2011-05-22 Last updated: 2012-06-12Bibliographically approved
List of papers
1. Ride comfort simulation of a wheel loader with suspended axles
Open this publication in new window or tab >>Ride comfort simulation of a wheel loader with suspended axles
2008 (English)In: International Journal of Vehicle Systems Modelling and Testing, ISSN 1745-6436, Vol. 3, no 3, 168-188 p.Article in journal (Refereed) Published
Abstract [en]

Wheel loaders are used in a variety of tasks. The traditional design of the vehicle is unfavourable from a ride comfort standpoint, as the unsuspended axles lead to high vibration levels. This study investigates the possibility to reduce driver vibrations by introducing suspended wheel axles. A multibody simulation model is used to study vibration levels with and without suspension. Results show that vertical and longitudinal vibrations are reduced significantly when comparing with the unsuspended vehicle. Less reduction is attained in the lateral direction, mainly because of high roll stiffness and the high placement of the driver seat.

Keyword
Front end loader, Hydropneumatic suspension, MBS, Multibody simulations, Off-road vehicle, Ride comfort, Wheel loader
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-8130 (URN)10.1504/IJVSMT.2008.023836 (DOI)2-s2.0-63149139074 (ScopusID)
Note
QC 20101119 Uppdaterad från submitted till published (20101119).Available from: 2008-03-19 Created: 2008-03-19 Last updated: 2011-05-31Bibliographically approved
2. Pitch comfort optimisation of a front end loader using a hydropneumatic suspension
Open this publication in new window or tab >>Pitch comfort optimisation of a front end loader using a hydropneumatic suspension
2007 (English)In: SAE technical paper series, ISSN 0148-7191, no 2146, 67-76 p.Article in journal (Refereed) Published
Abstract [en]

Front end loader vehicles are prone to excessive pitching when travelling at high speed, partly due to the absence of axle suspension. This paper studies the fundamental design of a hydropneumatic suspension for a medium wheel loader. The vehicle is analysed using an analytical frequency response model as well as multibody simulations. Results show that favourable pitching response can be achieved by increasing the rear axle stiffness, but also that a similar effect is achieved with higher front axle stiffness. For the loaded vehicle, it is also found that the benefits of an optimal stiffness distribution are offset to some extent by the reduction in relative damping as the vehicle mass and inertia increases. Thus, it is desirable to increase suspension damping under load to maintain a suitable level of relative damping.

Keyword
Analytical frequencies, Front end, Fundamental design, Hydro-pneumatic suspension, Multibody simulations, Optimisations, Response model, Stiffness distributions, Suspension damping, Vehicle mass, Wheel loaders
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-8131 (URN)10.4271/2007-01-4269 (DOI)2-s2.0-77952330972 (ScopusID)
Conference
Commercial Vehicle Engineering Congress and Exhibition; Rosemont, IL; United States; 30 October 2007 through 1 November 2007
Note

QC 20101119

Available from: 2008-03-19 Created: 2008-03-19 Last updated: 2014-11-24Bibliographically approved
3. Influence of tyre properties on the ride dynamics of heavy off-road vehicles
Open this publication in new window or tab >>Influence of tyre properties on the ride dynamics of heavy off-road vehicles
2011 (English)Conference paper (Other academic)
Abstract [en]

Wheeled earthmoving machines are a class of off-road vehicles that are typically equipped withlarge and soft tyres to obtain sufficient traction and flotation on unpaved surfaces. Theunsuspended mass is typically larger than for road vehicles. This indicates that the tyreproperties will affect not only the dynamics of the wheels and axles, but may also have asubstantial effect on the ride dynamics of the vehicle. This paper investigates how the tyrecharacteristics influence the optimal design of a wheel suspension for an off-road constructionmachine. Frequency domain analysis of a pitch and bounce model show that overallacceleration levels are significantly affected by tyre stiffness and damping, but that the tradeoffbetween pitch and bounce is unaffected by tyre properties although the main ride frequenciesare offset. Also, optimal suspension damping is fairly independent of the tyres. It is alsoinvestigated if a locked front axle suspension may be used in the loaded case, to simplifysuspension system design by using tyres as sole suspension elements. It is found that thisconfiguration leads to decreased ride quality, mainly due to the increased suspension stiffnessand lack of damping.

National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-33884 (URN)
Conference
Joint 9th Asia-Pacific ISTVS Conference and Annual Meeting of Japanese Society for Terramechanics
Note
QC 20110531Available from: 2011-05-22 Created: 2011-05-22 Last updated: 2011-05-31Bibliographically approved
4. Snaking stability of articulated frame steer vehicles with axle suspension
Open this publication in new window or tab >>Snaking stability of articulated frame steer vehicles with axle suspension
2010 (English)In: International Journal of Heavy Vehicle Systems, ISSN 1744-232X, Vol. 17, no 2, 119-138 p.Article in journal (Refereed) Published
Abstract [en]

A known problem of articulated vehicles is that snaking oscillations may occur at high speed. For ride comfort reasons, it is desirable to introduce suspended axles on articulated vehicles such as wheel loaders which are traditionally built without wheel suspension. This paper investigates how this may affect the snaking stability, by studying the vehicle dynamic behaviour of a multibody simulation model with and without suspension. Results show that an axle suspension may have a slightly destabilising effect, although the difference is small and can be offset by a stiffer or more damped steering system.

Keyword
articulated vehicles, snaking stability, lateral stability, MBS, multibody simulations
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-8132 (URN)10.1504/IJHVS.2010.033178 (DOI)000278964400002 ()2-s2.0-77952414229 (ScopusID)
Note
QC 20101119 Uppdaterad från submitted till published (20101119).Available from: 2008-03-19 Created: 2008-03-19 Last updated: 2011-05-31Bibliographically approved
5. Scale model investigation of the snaking and folding stability of an articulated frame steer vehicle
Open this publication in new window or tab >>Scale model investigation of the snaking and folding stability of an articulated frame steer vehicle
Show others...
2011 (English)In: International Journal of Vehicle Systems Modelling and Testing, ISSN 1745-6436, Vol. 6, no 2, 126-144 p.Article in journal (Refereed) Published
Abstract [en]

This paper describes the development and evaluation of an articulated frame steer testvehicle on a model-scale. Vehicles with articulated steering are known to exhibit unstable behaviour in the form of snaking or folding instabilities when operated at high speed, as previously studied using analytical models, simulations and full vehicle tests. The aim ofthis study is to design a scaled test vehicle that is able to reproduce unstable modes found in articulated vehicles. The model vehicle may provide greater insight than simulations, while avoiding the costs and hazards associated with full vehicle tests. The objective is also to investigate how well a linearised planar model and eigenvalue analysis can predict vehicle stability properties. Experimental and theoretical results have been critically analysed, and found to exhibit typical full vehicle behaviour. The linear mathematical model exhibited similar trends when compared to the scale model test results.

Place, publisher, year, edition, pages
InderScience Publishers, 2011
Keyword
articulated frame steer, snaking, folding, jack-knifing, scale model, wheel loader, remote control
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-33885 (URN)10.1504/IJVSMT.2011.042392 (DOI)2-s2.0-80052782080 (ScopusID)
Funder
TrenOp, Transport Research Environment with Novel Perspectives
Note

QC 20110531

Available from: 2011-05-22 Created: 2011-05-22 Last updated: 2016-04-28Bibliographically approved

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