On Jun 24, 12:34*pm, "Arfa Daily" wrote:

I have no idea whether there is a similar system fitted to UK trucks, but I
can't say that I've ever heard anything that sounded out of the ordinary
with a truck engine, so maybe not.

A quick google shows Jacobs brakes are fitted to ERF (Foden) trucks,
which use Cummins diesel engines. I couldn't find anything regarding
Perkins' engines.


I have seen signs here though at the
start of long downhill grades that tell trucks to engage a low gear, and
that was my understanding of what the term "engine braking" meant - taking
advantage of the engine's inherent compression, multiplied by the low gear
ratio, to produce an overun 'drag' to prevent the truck running away

Unlike in a spark ignition engine, apparently, in a Diesel, air is
free to move through the cylinders. (A spark ignition engine's
throttle changes the amount of air, and thus fuel, flowing through the
engine. The Diesel's airflow is constant; the accelerator pedal
changes the amount of fuel flowing only.) Thus the engine's inherent
compression is immediately followed by the engines's inherent
expansion, with only a negligible net slowing effect. The Jake brake
interrupts the flow and changes the engine into an air compressor.


in a
manner that couldn't be readily corrected by use of the brakes, because of
brake fade, which I've also seen mentioned on IRT.

Brake fade is related to heat. When sufficiently hot, the coefficient
of friction of the brake lining of the (in heavy trucks, still drum
shoes) is relatively low. There are other causes of fade, too. Here at
the tops of hills, you will see spots to pull over and let your brakes
cool.


Is this not the same
thing ? What is the difference / advantage of the Jake Brake over what I've
described, given that it is apparently noisy ?


Here's an interesting historical treatment with some description, but
mostly focusing on the inventor:

http://files.asme.org/ASMEORG/Commun...marks/5577.pdf