What IS engine braking anyway?

[meekal]

i always wondered what it means when i head to Ginnie Springs

 

[Max Depth]

Its when trucks use an exhaust valve on the engine to slow down. Its loud, you would have heard it before.

 

[wettek]

Engine braking is slowing the engine (and hence vehicle speed) by restricting the exhaust flow. The exhaust can't get away as quickly, so the engine is slowed by the increased back pressure. It is restricted in many places (hence the sign), as it makes the vehicle a hell of a lot louder. It can be "turned on or off" from the driving position, via a restrictor in the exhaust.

 

[PfcAJ]

In addition to the above post, engine braking is when a driver downshifts into a lower gear than the optimum gear for a given speed, whithout pressing the accelerator. The difference in gear ratios actually slows the vehicle down. The driver will see a spike in RPMs (maybe loud), but it quickly falls as the speed of the vehicle is reduced.

 

[Divin'Papaw]

Is this also called "jake breaking"? I've seen signs that say "Jake Breaking Prohibited." Is it the same thing?

 

[karstdvr]

Don't you wish they'd put a grim reeper sign up,that would have people asking questions.

 

[GONEHAWKN]

Another braking feature of semi-trucks is the engine brake, or "Jacobs brake" (usually shortened to "Jake brake"). This feature controls hydraulic actuators on the exhaust valves of the truck's diesel engine. When activated, the actuators hold the valves slightly open, virtually turning the engine into a giant compressor. However, it produces a loud and distinctive exhaust note, and owing to noise concerns, some locales have prohibited or restricted the use of engine brake systems inside their jurisdictions, particularly in residential areas. The advantage to using this instead of conventional brakes is that a truck can travel down a long grade without overheating its wheel brakes.

 

[BabyDuck]

thank you so much for asking. i had always wondered!

 

[Meng_Tze]

In addition to the above post, engine braking is when a driver downshifts into a lower gear than the optimum gear for a given speed, whithout pressing the accelerator. The difference in gear ratios actually slows the vehicle down. The driver will see a spike in RPMs (maybe loud), but it quickly falls as the speed of the vehicle is reduced.

BINGO! It is nicely done in real races (rally), where you 'set up the car' before entering the bend..... Break, downshift (to be in the right gear for the exit, sometimes takes 3 gears down), turn in, accelerate in the corner and speed uptake going out..... Doing this in a 4W drive car, you can usually take a corner that is graded as '35MPH' at about 70-80mph..............as long as you keep the car flat and 'driving'

But the big trucks do it to slow down while being in control.

 

[Gil57usa]

Is this also called "jake breaking"? I've seen signs that say "Jake Breaking Prohibited." Is it the same thing?

Yep, same thing.