In particular on heavy duty commercial vehicles, the continuous braking systems “engine braking system” and “retarder”, which are independent of the service braking system, are installed to handle the continuous braking load on downhill stretches. These systems are also used to reduce lining wear and thermal loads of the service braking system.
Exhaust braking systems are the most widely used form of engine braking systems. The current state-of-the-art in retarders is represented by two basic concepts, the electrodynamic retarder and the hydrodynamic retarder. A performance comparison of the different systems shows that low mountain descending speeds are the domain of engine braking systems, whereas retarders are more effective for medium and high descending speeds. The electrodynamic retarder is more favourable for lower road speeds, while the hydrodynamic retarder develops its effectiveness during higher downhill speeds.
The additional braking forces at the rear axle of the towing vehicle of a tractor-/trailer-combination, which are caused by these continuous braking systems, tend to alter the braking force distribution of the vehicles to instable conditions. The braking efficiency of the continuous braking systems together with the service braking system should therefore be controlled by a central “Braking management system”, which will lead to a significant increase in safety and economy.