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Tires of modern commercial vehicles must meet a specific requirement profile, containing the economic aspects, ride comfort and driving safety, as well. These three primary criteria are discussed in this paper, whereby emphasis is placed on the force transmission behavior of commercial vehicle tires regarded as a variable directly associated to driving safety. At the same time, the influence of distinct parameters such as wheel load, road speed, tire inflation pressure, tread depth and coefficient of adhesion between tire and road on the lateral and braking force behavior is illustrated using steady state and dynamic measurements. They were carried out on real roads using a specially prepared mobile tire dynamometer, but on an indoor drum-type tire test stand, as well. In addition to the above mentioned parameter variations the differences of the results on account of the test method are analysed.

During recent years there has been a continuing increase in the demands for higher braking performance of commercial vehicle engines. Mercedes-Benz had introduced the engine brake with continuously open decompression valve (‘Konstantdrossel’) into series production in 1989 as an option (1). A further increase of braking power was to be achieved while retaining the additional decompression valve in the cylinder head. For this, the decompression valve was no longer kept open during the whole working cycle (continuously open decompression valve), but only for a short period from just before compression TDC to about 90...120° crank angle after compression TDC (pulsed decompression valve). The hydraulic actuating system which opens and closes the decompression valves was developed in cooperation with Mannesmann-Rexroth GmbH, Lohr, Germany. The engine braking performance attainable with this system is shown in comparison to other known engine braking systems.

Modern commercial vehicle engines are equipped with turbocharging and intercooling. This results in low emissions and fuel consumption. In the lower speed and load range and under transient conditions, these engines have disadvantages, as the fuel injection rate has to be limited to avoid excessive smoke emission. Also, the engine braking performance of highly charged, small displacement engines is also lower than that of large displacement engines. Mercedes-Benz decided to develop a combination of turbocharger and mechanical supercharger. In the lower speed range higher torque levels are possible and maximum torque is available without any lag especially in the transient mode with low smoke emission and fuel consumption. Vehicle performance during acceleration can be improved by up to 30%. During engine braking operation, the mechanical supercharger is activated throughout the whole engine speed range which results in a distinctive increase in braking power.

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.

In January 1996 Mercedes-Benz has introduced a new 4-cylinder engine OM 904 LA of the new engine family for light commercial vehicles. The power range of the OM 904 LA comprises ratings from 90 kW up to 125 kW at 2300 rpm. From the beginning of the design of this engine, a noise emission output as low as possible was strived for, aside from the high targets as far as durability, maintenace and fuel consumption are concerned. The basis is the development of noise regulations for commercial vehicles. The noise reduction measures have to be concentrated on the engine since up to now it still is one of the main noise emission sources at the vehicle. Already at the lay-out of the engine the prerequisits for a low-noise engine behaviour have been taken into consideration. The engine is equipped with a fuel injection system featuring particular unit injector pumps for each cylinder which is superior to the conventional in-line injection pump as far as acoustics are concerned.