 Engine brake
kfz-tech.de/PDB13
The air brake of a truck, especially when loaded and with a trailer, can hardly cope with a long downhill pass. Even if vehicles today are equipped with disc brakes, these would get too hot, except perhaps when driving at
slow speeds.
A continuous brake is required for trucks. The engine brake and retarder often work together here, usually even used carefully from the driver's seat. Now you might think that the engine brake consists mainly of a
pneumatically operated flap in the exhaust (picture below), just before or usually after the turbocharger.
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It may be that this is sufficient for a smaller vehicle, for example in distribution transport, but definitely not for heavy goods vehicles. Next step is a type of decompression that prevents the power stroke from accelerating the
piston unnecessarily.
This second step of the engine brake therefore utilizes the congestion caused by the exhaust gases that are difficult to dissipate and additionally that due to compression. This is done either by a small additional valve in the
combustion chamber or by hydraulics in the valve train of the exhaust valve. The key is to somehow permanently open the combustion chamber to the closed exhaust tract.
kfz-tech.de/PDB15
Just like with an engine, we talk about performance that is somehow destroyed, or, pardon, converted into heat. With the light vehicle's single-stage engine brake, that's perhaps only 50 kW. In this way, up to 300 kW of
braking power can be achieved in heavy-duty trucks. Together with the retarder, that's up to 735 kW (1000 hp). Mind you, the service brake would also be added.
Gone are usually the days of a button in the footwell. It is often operated using hand levers on the steering wheel. Used much more often and more variably than before, the engine brake can noticeably reduce pad and disc
wear. This fits in with the much longer maintenance intervals, even more so in the truck sector than in the car sector.
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