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  • 1.
    Edrén, Johannes
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics.
    Jonasson, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics.
    Nilsson, Andreas
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics.
    Rehnberg, Adam
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics.
    Svahn, Fredrik
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics.
    Stensson Trigell, Annika
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics.
    Modelica and Dymola for education in vehicle dynamics at KTH2009In: Proceedings from 7th Modelica Conference 2009, 2009, p. 775-783Conference paper (Refereed)
    Abstract [en]

    Dymola and Modelica has been used at KTH Vehicle Dynamics (KTHVD) for research work since 2000, see e.g. [1]. With the Vehicle Dynamics Library (VDL) [2], Modelica has become far more accessible for both researchers and students in the field of vehicle dynamics. Therefore a project aiming at introducing it as a tool in education was initiated in order to evaluate the current state of Dymola and Modelica as tools for wider use in education at the division. The work presented in this paper was realized as a part of a PhD course, where one of the tasks were to design dedicated exercises to illustrate fundamentals of vehicle dynamics for students.

  • 2.
    Rehnberg, Adam
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics.
    Suspension design for off-road construction machines2011Doctoral 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.

  • 3.
    Rehnberg, Adam
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics.
    Vehicle dynamic analysis of wheel loaders with suspended axles2008Licentiate 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.

  • 4.
    Rehnberg, Adam
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics.
    Drugge, Lars
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics.
    Influence of tyre properties on the ride dynamics of heavy off-road vehicles2011Conference 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.

  • 5.
    Rehnberg, Adam
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics.
    Drugge, Lars
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics.
    Pitch comfort optimisation of a front end loader using a hydropneumatic suspension2007In: SAE technical paper series, ISSN 0148-7191, no 2146, p. 67-76Article in journal (Refereed)
    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.

  • 6.
    Rehnberg, Adam
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Drugge, Lars
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Ride comfort simulation of a wheel loader with suspended axles2008In: International Journal of Vehicle Systems Modelling and Testing, ISSN 1745-6436, Vol. 3, no 3, p. 168-188Article in journal (Refereed)
    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.

  • 7.
    Rehnberg, Adam
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Drugge, Lars
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Stensson Trigell, Annika
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Snaking stability of articulated frame steer vehicles with axle suspension2010In: International Journal of Heavy Vehicle Systems, ISSN 1744-232X, Vol. 17, no 2, p. 119-138Article in journal (Refereed)
    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.

  • 8.
    Rehnberg, Adam
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Edrén, Johannes
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Eriksson, Magnus
    Drugge, Lars
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Stensson Trigell, Annika
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Scale model investigation of the snaking and folding stability of an articulated frame steer vehicle2011In: International Journal of Vehicle Systems Modelling and Testing, ISSN 1745-6436, Vol. 6, no 2, p. 126-144Article in journal (Refereed)
    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.

1 - 8 of 8
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  • ieee
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