Hi Kirk,
Jake Brakes work because the mechanicals are a bit different between
diesel and gasoline engines. A gasoline engine has a butterfly valve
that limits air intake when the throttle isn't depressed, so there
isn't much pressure built up on the compression stroke. Diesel
engines don't have these, and continue to build up pressure even when
no throttle is active, and causes a bit of acceleration due to the
pressure build up which forces the piston back down. So Jake Brakes
are extra mechanicals that release the pressure from the compression
strokes, and that extra pressure getting released causes the "machine
gun" sounds when the Jake Brake is activated and helps to slow the
forward momentum of the vehicle.
Greg Gowins
Driftwood, TX
On Fri, Mar 25, 2011 at 9:48 PM, Kirk Hargreaves <khargreaves2 at gmail.com>
wrote:
> I have had this question in my head for a while and thought I would throw
it
> out to the list.
>
> How does a Jake brake work? I understand that it shuts off or controls
the
> output of the exhaust which causes back up pressure to slow the engine for
> engine braking?
>
> The engine would need to be firing in order for their to be exhaust to
cause
> back pressure?
>
> Just something that has bothered me. . and I could not seem to find
> anything on line that would give a good breakdown of the process.
>
> Certainly there are those on the list who have a good understanding as to
> how this braking process works in big diesel rigs.
>
> Thanks,
>
> Kirk
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