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Rear axle steering systems electronically controlled and hydraulically actuated are discussed for commercial vehicles. With these steered axles, the major objective is to improve the manoeuvrability of these vehicles. With the aid of the steering strategy “Rear end Swing-out Compensation” it will be assured, that in two-axle, all-wheel steering trucks dangerous rear end swing-out effects, occuring primarily in low speed ranges, will not take place. In addition, it is possible to enhance the dynamic stability of two-axle trucks while braking on split adhesion road surfaces with the aid of specific control algorithms. Furthermore, the application of a rear axle steering system can suppress dangerous lateral oscillations of centre-axle trailers.

One of the most common and technically interesting handling maneuvers in everyday service is braking in a turn. For this reason the braking performance in a turn is one of the most important points in the vehicle concept, which has to be precisely observed when designing a motor vehicle. The reactions of the vehicle must demonstrate, after the corresponding optimizations on the vehicle have been completed, a most favorable compromise between steerability, directional stability and deceleration.

The tyre, as a link between vehicle and road, is an essential component to which great attention is paid when new vehicle concepts are being developed. The main criteria required of commercial vehicles are economy, safety and comfort- Increasing importance, as far as handling of commercial vehicles is concerned, is attached to the frictional behaviour of tyres. The influence of typical parameters, such as wheel load, road speed, inflation pressures of tyres, tyre tread depth and road surface as well as the effect of the scattering of the coefficient of adhesion of the different tyre makes are shown by means of steady-state and dynamic measurements. The directional control behaviour of a heavy commercial vehicle is analyzed with the aid of a simulation system developed by Mercedes-Benz. This includes computer-controlled test stands for tyres, brakes and axle kinematics as well as programmes for simulating the dynamics of a vehicle making use of the measured characteristics.

In the following essay, vehicle, and test stand related measuring and calculating methods will be introduced which have proven to be a suitable basis for the discussion of the criteria of driving mechanics for commercial vehicles (1 to 23). Because of the progress of electronics development these methods are reliable and quickly performed today. In connection with tire and brake characteristics, which are the basis for measuring driving maneuvers, and with the knowledge of axle and wheel movement, a purposeful and physically correct evaluation of the driving behavior of vehicles is possible. With the aid of complex mathematical vehicle substitution systems it is already possible to accurately estimate tendencies in the pre-development stage of a vehicle.

The first part of this paper contains a description of the assessment criteria (deceleration, steerability, stability), plus an analysis of the most important disturbance factors (engine braking moment, brake-factor variations etc.) which can have a strong influence on the braking performance of a light commercial vehicle. In the second part a description is given of the equipment which is required for the simulation of a braking vehicle on process-computer-controlled test stands. The combination of calculation, brake simulation on test stands and concluding road tests ensures that an optimum commercial vehicle brake design is provided not only for practical operation but also for the safe fulfilment of legal specifications.