Exhaust Brake "Jakebrake" device for eng with deco

[andrewaust]

Thinking exhaust brakes! I had an idea that should work on engines with decompression levers.

The device I'm thinking is a small electronic solenoid to strike the lever at TDC of the compression stroke using a pickup off the flywheel (that will strike every stroke). Running off the cam would be better as you would get an exact hit per 2nd revolution, but is harder to setup.

Holding the lever down simply won't work you need to use the compression to stop the engine before the compressed air pushes the piston down.

Sensing the pulse of the injector I'm thinking about, but remember when throttle is closed no fuel should be getting delivered meaning no pulse - but does that mean no pulse at all? Using a delayed circuit should get you on top dead center!

The other device is a simple butterfly valve in the exhaust, but wouldn't the clatter of a compression release brake sound better = cowboy stopping style.

Its and idea that I'm now going to work on. I'm also hopefully erecting a work-shed/garage, so lathe and mill will follow allowing me to work on compact blowers for engines "HOPEFULLY".

Just remember "Problem / Solution"

Please give me feedback as it is very welcomed. It gets very quiet here on prison island = Australia


PS: Drawing will be posted when I get something solid drawn up.



!!!!!

[Nanko]

deleted

[andrewaust]

Hi Nanco


Yes you must have a hole in the butterfly valve or a slight flat or curved space to let air slowly go through. Your spot on, some trucks do use a pneumatic setup to move the butterfly in exhaust braking devices.

Have you seen how jakebrakes work? The system I'm mainly referring to is this type of device, you'll certainly know which truck is using jakes compared to pneumatic exhaust breaks. If you hear a truck make a clatter clatter sound when braking, that's jakes, the others sound like a hiss, that's a inline pneumatic exhaust brake.

Because of the amount of noise jake compression release brakes make, I think they are trying to stop them being used in some countries.

To me its not to complex as I understand the system, plus I'd like to see how a compression release brake would sound like on a bike .

Here's a link to the Jacobs Brake website: http://www.jakebrake.com/technology/engine.php



Cheers


Andrew

[Nanko]

Have you seen how jakebrakes work?

Hi Andrew

Just visited the page you mentioned.
I should have done that earlyer...
Will remove my nonsense posting

Good luck Nanko

[pietenpol2002]

I would quite agree that it's hard to top the sound of the Jake, but the expense, complexity and weight is prohibitive. I've often thought that the example below would make an inexpensive yet effective engine brake for our smaller diesel purposes. The diameter in this case is a bit small, but you get the idea.

http://tinyurl.com/59bjkn

Ron

[Diesel Dave]

Compression release brake sounds good but be careful you don't drop the pushrod out of its's cup by holding the valve open!

I'm wodering why compression release works better than stopping fuel injection?

If you have a Tiny Tach it will show that small direct injection units stop injecting on overrun - the rpm reading dissapears and it revert's to a time display.

I'll admit to hardly using the brakes when I ride the diesel around country lanes - it's kind of a challenge to do it.

Dave

[andrewaust]

Hi Dave

I've also noticed that with the tiny tach mate, coasting down the hill and no fuel being delivered for a while . That made me think having another sensor on the fuel line to time the valve release would be no good as this is when you want some pulse = bugger

The reason compression release brakes work so well is by releasing the compressed charge of air close to TDC, then the valve shuts so you have two things, no compressed air to push the piston down and a vacuum on the downward stroke giving you two braking forces - compression then vacuum.

Great point regarding the pushrod jumping out, you only want to move the valve off its seat, pushing the valve down to far will also result in a piston strike something you don't want, a few of them and the engine will stop permanently.


A;)

[smokyjoe]

Hi y'all,

I think that a butterfly to stop up the exhaust pipe and a spring loaded poppet valve between the butterfly and the exhaust port will suffice. When the exhaust pressure gets high enough, the poppet releases, making that brrrrrrrr sound we dieselheads all love. This is the way some of the older brakes I've worked on functioned. A offset butterfly can be made with the shaft on the side and a squared off butterfly flap choking the exhaust, that way the shaft and plate isn't in the exhaust stream to be constantly cooked and eventually burnt. Wish I could draw a picture, but don't have a way. I am going to try a Jake when I eventually can get my bike together.

[UAofE]

Compression release brake sounds good but be careful you don't drop the pushrod out of its's cup by holding the valve open!

Cummins prevents this by limiting exhaust valve lift of the jake brake system to 2mm, vs around 69mm normal exhaust valve stroke.
On these small engines, even 0.5mm valve lift would be enough to produce the same function.

The problem is actuation. Trucks do it by either using a master-slave hydraulic piston and operated by the injector rocket lever, or by a dedicated cam lobe on engines without rocker lever actuated injectors.