Peter Hill wrote:

On Sun, 24 Jun 2012 16:00:41 -0400, Phil Hobbs
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. 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 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. 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 ?

Arfa

It doesn't heat up and boil the brake fluid when you're coming down a
mountain pass with a full load. (Here in NA we have real mountains.)


Neither does overrun engine braking without compression release.

snip
Piston engines are about 80% efficient as compressors, iirc. So the
amount of braking from overrun with a shut throttle is small. Also,
diesels don't have throttles!

Cheers

Phil Hobbs

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Dr Philip C D Hobbs
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