The answer to the question, who needs an engine brake? is, of course everyone, in a truck. However, the way technology is developing is likely to make the famous Jake Brake just a little less important in the scheme of the things, in truck development of the future.
Recent developments have seen the increased use of transmission retarders in truck design, as demonstrated in this video. The Intarder from ZF has started appearing in many European truck designs. Truck brands like Scania, MAN, DAF and Isuzu include retarders in their top-end prime movers as a matter of course.
Including a retarder doesn’t preclude including a compression engine brake. Many have both and use the brake blending techniques of exhaust brake, then engine brake, then retarder and finally service brake as a cascading method of bringing each technology in as the foot on the brake pedal gets more insistent.
There are plusses and minuses for the retarder. The plus is the retarder will pull the truck up much more than the compression engine brake. Its retardation effort is stronger and and can be used to hold a fully loaded truck at a preset speed down a steep descent.
The minus is the fact the retarder does have a limit, fluid temperature. The sheer effort by the stator to slow the liquid flow in the retarder, is taking a lot of energy out of the driveline. This energy has to go somewhere and heats up the medium used in the retarder putting a strain on the cooling capacity of the truck.
As the temperature rises it can reach a critical level, at which point the liquid no longer slows the truck as effectively. A retarder can run out of retardation if pushed too far.
In most practical applications retarders will not reach these critical temperature levels, but the fact remains that the possibility of failure is there. The high temperatures also mean the maintenance on these items can be expensive.
A system which has been in use in other parts of the world, but which hasn’t gained much traction in Australia, is the Telma. This uses electricity to slow the driveshaft and can be effective, it is widely used on buses in Europe.
With the rise of electric trucks and hybrids in the future, the chances are this kind of technology will find it’s way into new truck designs. If there is going to be an electric motor/generator on board anyway, it might as well be used as an engine brake as well?