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Vehicle dynamic analysis of wheel loaders with suspended axles
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics.
2008 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

The wheel loader is a type of engineering vehicle used primarily to move crude material over shorter distances. As the vehicle is designed without wheel suspension, wheel loader drivers are exposed to high levels of whole body vibration which influences ride comfort negatively. The work presented in this thesis has the aim to investigate the potential in adding an axle suspension to a wheel loader in order to reduce vibrations and increase handling quality. While suspended axles have great potential for improving ride comfort and performance, they will also necessarily affect the vehicle dynamic behaviour which is different in many aspects from that of passenger cars or other road vehicles: the wheel loader has a large pitch inertia compared to its mass, the axle loads vary considerably with loading condition, and the vehicle uses an articulated frame steering system rather than wheel steering. These issues must all be considered in the design process for a wheel loader suspension.

The effects of suspended axles on ride vibrations are analysed by simulating a multibody wheel loader model with and without axle suspension. Results from the simulations show that longitudinal and vertical acceleration levels are greatly reduced with axle suspension, but that the decrease in lateral acceleration is smaller. By reducing the roll stiffness lateral accelerations can be further reduced, although this may not be feasible because of requirements on handling stability. The pitching oscillation of the vehicle has also been studied as this is known to have a large influence on ride comfort. An analytical model is used to study the effect of front and rear suspension characteristics on the pitching response of the wheel loader, showing that a stiffer rear suspension is favourable for reducing pitching but also that a similar effect is attainable with a stiffer front suspension. Results are compared to multibody simulations which show the same trend as analytical predictions. By including a linearised representation of a hydropneumatic suspension in the models, it is also shown that favourable dynamic behaviour can be maintained when the vehicle is loaded by utilising the fact that suspension stiffness is increasing with axle load.

Articulated vehicles may exhibit lateral oscillations known as "snaking" when driven at high speed. The effect of suspended axles on these oscillations are analysed using a multibody simulation model of a wheel loader with an equivalent roll stiffness suspension model. It is found that the roll motion of the sprung mass has a slightly destabilising effect on the snaking oscillations. This effect is more pronounced if the body roll frequency is close to the frequency of the snaking motion, although this loss in stability can be compensated for by increasing the equivalent stiffness or damping of the steering system.

Together with existing vehicle dynamic theory and design rules, the studies reported in this work provide an insight into the specific issues related to suspension design for wheel loaders.

Place, publisher, year, edition, pages
Stockholm: KTH , 2008. , vii, 54 p.
Series
Trita-AVE, ISSN 1651-7660 ; 2008:15
Keyword [sv]
hjullastare, arbetsmaskin, fordonsdynamik, fordonsteknik
National Category
Vehicle Engineering
Identifiers
URN: urn:nbn:se:kth:diva-4677ISBN: 978-91-7178-908-2 (print)OAI: oai:DiVA.org:kth-4677DiVA: diva2:13374
Presentation
2008-04-03, D3, Lindstedsvägen 5, Stockholm, 10:15
Opponent
Supervisors
Note
QC 20101119Available from: 2008-03-19 Created: 2008-03-19 Last updated: 2010-11-19Bibliographically 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 (Scopus ID)
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 (Scopus ID)
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. 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 (Scopus ID)
Note
QC 20101119 Uppdaterad från submitted till published (20101119).Available from: 2008-03-19 Created: 2008-03-19 Last updated: 2011-05-31Bibliographically approved

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