15-06-2012, 12:12 PM
CONTROLS SYSTEM OF VEHICLE MODEL WITH FOUR
WHEEL STEERING (4WS)
CONTROLS SYSTEM OF VEHICLE MODEL.pdf (Size: 239.35 KB / Downloads: 106)
Abstract:
Four-Wheel Steering – Rear Wheels Control. For parking and low-speed maneuvers, the rear Wheel
steer in the opposite direction of the front wheels, allowing much sharper turns. At higher speeds, the rest wheels
steer in the same direction as the front wheels. The result is more stability and less body lean during fast lane
changes and turns because the front wheels don’t have to drag non-steering rear wheels onto the path.
INTRODUCTION
Mainly in aviation and shipping industry, the scale models belong for many years to common methods of
experiment implementation. For example, in aerodynamics of aviation structures, the aircrafts’ scale parts or entire
aircrafts have been used for experimental determination of aerodynamic characteristics and their optimisation. With
the help of similarity theory, using this method, it is possible to obtain relatively accurate experimental results with
low costs incurred. It is also possible to execute experiments, which would otherwise be entirely infeasible, verify
function of even small-scale variations and modifications of the structure.
SYSTEM 4WS
Contemporary rear axles allows for coincidental steering through the influence of variation of elastokinematic
steering; rear wheels rotate, due to an influence of variation of vertical load of wheels (tilting), in the same direction
as front wheels. Nevertheless, such a turn of rear wheels is very small and driver’s will-independent. A
disadvantage of this so-called passive steering system is that it operates even when driving in straight direction
when single wheel of an axle hits surface irregularity (deterioration of directional stability).
New generation of active steering systems distinguishes a need of steering of rear wheels for the reason of
directional stability from a need of steering of rear wheels for the reason of cornering at slow speed. Therefore, the
active system means that rear wheels are possible to be turned either coincidently or non-coincidently.
TESTING OF CONTROLLABILITY AND STABILITY ON A MODEL OF THE
AUTOMOBILE
As already stated above, experiments are implemented using scaled vehicles. Most of similar experiments in the
world utilise sets of German model manufacturer FG Modellsport, which are design-wise very similar to real
vehicles and are able to meet basic requirement of ability to transfer the data gained experimentally into reality.
Models have been primarily of a hobby nature, but hobby sphere is recently already at a semi-professional level.
The world racetrack championship has been put out for models equipped with combustion engines and fastest
scale models reach maximum speeds of more than 100 km/h.
THE BASIC PHILOSOPHY OF THE ACTIVE SYSTEMS FOR STEERING THE REAR WHEELS
In order to meet these contradictory requirements, it has been necessary to find such a technical solution that may
provide either for concordant or disconcordant steering of the rear wheels, depending upon the intended driving
manoeuvre. From the technical point of view, it is rather difficult to provide for steering the rear wheels: the wheel
suspension must allow for its steering, the design must include actuating elements that will provide for precise
adjustment, but in addition, it is necessary to employ a control system that will issue the necessary instructions to
the actuating elements.
CONCLUSIONS
The aim of 4WS system is a better stability during overtaking manoeuvres, reduction of vehicle oscillation around
its vertical axis, reduced sensibility to lateral wind, neutral behaviour during cornering, etc., i.e. improvement of
active safety.
The model of the vehicle in the scale 1:5 will allow us to follow the behaviour of the 4WS automobile at a much
lower cost, and on a smaller scale than with a real automobile. By means of the control computer in the model, we
will be able to assess several types of the algorithms for steering the rear wheels. These algorithms will be
optimised according to the size and course of the lateral acceleration and the yawing velocity.