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Abstract. This paper is concerned with the needs and possibilities of implementing the active and semi-active suspensions for wheeled vehicles of the Army of the Czech Republic (ACR) -for drivetrain configuration 4x4 to 8x8. The computer technology is currently on a very high level, the amount of data computed per second is on steep rise and various processes have a capability to be driven almost real-time. The active suspension is nowadays fully implemented in the highest classes of civil cars, therefore, it is time for the implementation into the demands for modernisation of the wheeled vehicles of ACR. The land relief of central Europe is significantly mountainous, thus the demands for the wheeled vehicles, in terms of overcoming obstacles, are very high. After the application of the active suspension, the mobility and driving comfort of the vehicle are greatly enhanced. Unfortunately, at the cost of increased energy consumption. Therefore, the amount of energy available for the drivetrain is significantly lowered. On the other hand, the amount of energy required by the semi-active suspension is remarkably lower. The mobility and driving comfort are better than a passive suspension. Thus, it is recommendable to use scanning of the land relief in front of the vehicle subsequently controlling the chosen elements of the suspension by suitable algorithms. The aim of this study is to create an analysis of accessible information about the applications and control methods of active and semi-active suspensions. Evaluation of the wide range of possibilities was done with regard to the crew of the vehicle. The crew is facing problems from the fatigue and incidence of motion sickness to the worst case scenario, failure of organs.

The main differences between tracked and wheeled vehicles are the cross-country capability, dependability, comfort, travel speed for the paved surfaces (roads) and last but not least -the amount of resistance which needs to be overcome in order to move the vehicle or its energy efficiency. In the past decade, these differences are growing thinner in favour of wheeled vehicles, due to clever design and modern technologies that enabled torque vectoring and suspension types that are far beyond the coil springs and ordinary dampers. The developments are so quick that somehow some designs are skipped and replaced by others, even before we reached its maximal potential. One such example are the leaf springs, the very old design which has its powerful benefits for the heavy trucks. Currently the researchers are focused on the enhancements for the material point of view, spring steel is being replaced by various composite materials, so it weighs less, its behaviour is more controllable and the unsprung mass is lower.But the power of the leaf spring lies elsewhereit is its utilization for the tandem suspensions, often called the tandem bogie, or walking beam -the leaf spring as the beam or equalizing suspension. For the driven axles, this layout greatly enhances the cross-country capability of wheeled vehicle, since it is able to equally distribute the normal forces, therefore the driving forces are higher and the vehicle can better move. This system works really well in real life muddy conditions, however, it is very complex for the simulations and modelling. Firstly, the leaf spring as it is and its dynamic nonlinear hysteretic behaviour is extremely complex, secondly, its implementation to the dynamic simulation is rather challenging. This paper will provide the insight to the differences between the independent suspension and the tandem one, from the perspective of the state-space models with 8 and 9 degrees of freedom.

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The utilization of independent suspension is rising. For a very specific conditions, the dependent suspension types are still preferred, mainly in case of heavier trucks. Ordinary leaf spring material-steel is being replaced by a variety of composite materials. For the dynamic simulation of the vehicle, the greater importance than a material type, lies in the layout of the suspension. The tandem bogie layout of the multileaf spring suspension has many differences in its behaviour in comparison with ordinary layout-set of two separated multileaf springs allocated to one axle. In the first part of the paper, these differences are listed and explained-mainly the ability of load sharing between the axles. The second part deals with specific aspects of the FEM model, along with the necessary analytical background. The third part consists of various simulation cases with different initial conditions-different constrains, pretension and spring as tyre stiffness. In the last part, the effect of the aforementioned conditions are evaluated and commented. The variations of the hysteresis loops, in force-displacements characteristics, along with derived linear stiffness's and its behaviour are recommended to be understood for additional application. Therefore, the conclusions are drawn for further utilization of gathered data for the full vehicle simulation.