It seems than at Thu, 13 Dec 2007 13:33:36 -0800, Alex wrote: > On Dec 13, 2007 1:17 PM, Fmiser <[EMAIL PROTECTED]> wrote: > > > What you referred to as "compression braking" has practically nothing > > to do with compression. The braking effort of the engine is caused by > > it's inefficiency as an air pump. Any energy used to compress the air > > is regained when the piston travels down. > > That makes sense, although I've never heard it called anything but. > Clearly the term should really be reserved for Jake brakes. I was > taught by an older generation of drivers for whom the practice was > commonplace when driving a stick shift, and I used to be baffled by > road signs saying "Compression braking prohibited"---how else am I > supposed to slow down?
"Engine braking" could be used for the generic effect. "Compression brake" is the proper term for what Jacobs first marketed, but now in the US universally called a "Jake brake". It is a mechanism that open the exhaust valve at the top of the compression stroke. Thus all the energy used to compress the air is _not_ regained. There are other kind of "engine retarders" - electric, hydraulic, and (like the little Cummins uses), a butterfly valve in the intake to make the engine-as-an-air-pump even less efficient. Any of these can be dangerous on low traction road surfaces - but so can a car with an automatic transmission that's not in neutral, especially as the road speed decreases toward zero. -- Philip, with a few million miles in a big truck. _______________________________________ http://www.okiebenz.com For new parts see official list sponsor: http://www.buymbparts.com/ For used parts email [EMAIL PROTECTED] To Unsubscribe or change delivery options go to: http://okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
