I have heard that exhaust brakes are obligatory in Germany
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on some types of vehicle. Is this correct? If so, what are the classes of vehicle involved?
AAccording to the German regulations,
public service vehicles with a g.v.w. of more than 51 tons and goods vehicles weighing more than 9 tons must be fitted with an independent braking system. in addition to the serviceand parking-brake systems, that will prevent the vehicle accelerating when descending a 7 per cent gradient at 30 km/h (18.6 m.p.h.) over a length of 6 km (3.72 miles).
This order of braking force is obtainable from a well matched exhaust brake, but other types of independent brake are also suitable, including, for example, eddy-current and hydrodynamic retarders.
Incidentally, the German Voith hydrodynamic retarder is claimed to offer the advantage of instant release which is of particular merit in a skid.
A retarder of this type is somewhat similar in design to a torque converter and braking force is applied by feeding fluid into the casing, the braking force provided in proportion to the maximum being a function of the filling percentage. The brake is released by exhausting the fluid from the casing and because the Voith system is based on a small unit with a step-up drive, the time taken completely to release the brake is minimal.