What Is Engine Braking? What Is A Jake Brake?

[@chrisfix]

Awesome explanation as always! It is amazing how much energy an engine uses when there is no combustion!

[@charleschoo9398]

Nice !

[@Nameless_rat]

+ChrisFix Haha should've know you watch EE :D

[@EngineeringExplained]

+ChrisFix Thanks Chris!

[@davidgruen7423]

Engineering Explained Thanks for explaining this, never thought that it was the vacuum not the compression in gas cars. Just one question tho, when you put a car in gear to hold the vehicle on an inclination when engine is off, is it the compression that holds the car instead of vacuum in this case since pistons aren’t moving.

[@davidgruen7423]

Engineering Explained actually i think it’s both the compression and power stroke in two different cylinders that created the force to hold the vehicle, since the cylinders at intake and exhaust stroke has open valves which would not create any pressure in this case to counteract the force.

[@RobWhittlestone]

BRILLIANT! I always wondered what was going on! I think we call that a compression release brake *retarder* here in Europe. You can hear the engine sound change (older diesels). I always learn something new with you, thank you so much! All the best, Rob

[@MintyGT]

+RobWhittlestone Man, that name is a mouth full.

[@nd318865]

"Compression release" is a whole different thing. Long ago they were on engines to reduce "compression (ratio each revolution) while less effective starters tried starting cold engine (when oil was cold& difficult to pump by starter as well. Todays 12 volt gear reduction starters are FAR MORE EFECTIVE so compression release no longer are used cept maybe in extremely cold climates? Haven't seen one in decades. (did help start my tractor after leaving driving lights on one night in Weed, CA as I recall)

[@RobWhittlestone]

+James Tennier No, I mean the whole term "compression release retarder". I know what you mean: I have compression release on my Yamaha SR500 motorcycle - it's a little lever to open a valve so I can position at TDC to kickstart the 500cc single cylinder engine. Old diesels (eg cement mixers) had this too. All the best, Rob

[@davidrounds9524]

Nice informative video. 2 stroke compression release is much simpler. I have a lever on my 4 stroke 1970 Ducati 450 Scrambler that opens the exhaust valve for starting. I also put one on my 2 stroke 1972 Bultaco 250 Alpina that used the crankcase compression to brake the rear wheel for muddy downhills or when the brakes were wet.

[@kousinkoolaid]

I just recently learned of A technique used in F1 this year using a "pre-ignition chamber", which reminded me of a swirl chamber used in diesel engines. (which is something else I just recently learned about.) Maybe you could find some correlation there, and explain it to us? I know they're not the exact same tech used, but they reminded me of each other. love the channel! keep it up!

[@gmupps]

Many contemporary emissions controlled diesel engines will actually have a throttle valve in the intake path, and sometimes in the exhaust as well. These are used to facilitate EGR flow, however they will also provide some engine braking under certain conditions. It is also worth noting that these throttle valves are controlled exclusively by the ECU. I do not know if they will be closed by default when coasting in gear; someone who knows more than I do about diesel engine ECU strategies would be better able to answer that. (Anecdotally, my 2011 diesel car engine brakes well enough when down shifting.)

[@paulman79]

Besides the jake's breaking, I think the other 2 engine breaking methods relay on the energy needed for the compression step of either cycle, which is big when fuel not injected. There is no vacuum anywhere! Please think about the thermodynamic view of the breaking method.

[@Vielden]

+Paul Malnol There is no vacuum in the sense that there is a complete lack of air in the piston, the vacuum in the gasoline case is the piston needing to forcibly pull air into the cylinder because the throttle body is restricting it.

[@orrin2002]

I fine it interesting that sound and emissions are not mentions. Both systems are heavy on both.

[@TreatmentFreeBeekeeping]

Why emissions? No fuel is being used.

[@Aaronx3Sally]

when engine braking in a petrol/gas engine, do the injectors still inject fuel into the cylinders? If so - why? and what would happen if they didn't?

[@willbergger812]

+Aaronx3Sally Unless there is a computer program to cut the fuel when braking, the idle amount of fuel would still be injected. Some cars cut the fuel to the engine when coasting in gear or braking for the sake of fuel economy.

[@frankeggers4024]

Traditionally engine braking has been called compression braking. Obviously that was wrong, but many people still think that engine braking is compression braking. Regardless of how carefully it is explained, some people insist that engine braking is is caused by compression. This can be tested easily by having an engine on a dynamometer which can motor the engine as well as absorb power from the engine. With the ignition shut off, it takes more power to motor the engine with the throttle closed than with the throttle open thereby proving that the power wasted to suck air in against the vacuum created by the throttle valve is an important source of engine braking. Interestingly enough, it takes more power to motor the engine when the spark plugs are removed.

[@ziggy1ful]

Yes it could be tested on a dyno that powers the engine, but what dynos do this and have you done it? I would say not. All that has to be done to understand that the closed throttle theory causes the braking is to get in a real car and try it. Do it in a manual car with a hard wired throttle. Switch off spark and fuel and see what happens when you operate the throttle under engine braking, there is no runaway effect when the throttle is fully depressed, in fact the braking effect will increase. For those that can only switch off spark, don't suggest you do this as the exhaust can build up with unburnt fuel and cause a nasty bang when you switch the spark back on again(possibly damaging some part of the exhaust. As I posted six months ago, the closed throttle explanation defies the laws of thermodynamics, the energy that the engine is removing has to go somewhere, in the closed throttle theory it apparently "disappears into a vacuum"...not

[@descent8275]

hm... I have to check that "vacuum braking effect" on my car. I use the engine brake every day on every slow down move. but I always thought that the brake effect comes from the friction/compression inside the engine. lower gear is more agressive because: 1. higher rpm = more friciton 2. gearing gives the engine more "torque" to slow the car down. not because a stronger vacuum effect... (read that in a comment somwhere down there) well I check that out on my next run. cut igniton and open the trottle wide open. If your Vacuum theorie is right: my car should not slow down (as fast) My guess: its the same

[@Shikadi297]

+DESCENT The reason why higher RPMs would slow you down more is because you would need to move much more air to travel the same distance. Friction plays a roll as well, though not nearly as much as you would think.

[@MrRexquando]

+DESCENT It's not vacuum. In the old days we called this "compression braking" This is why engine braking works on a diesel without an exhaust restriction valve or a jake brake.

[@descent8275]

I just tested it today. 70km/h third gear 60km/h second gear ignition off Nothing changed while wide open the throttle or a closed one. the only difference was the intake sucking sound. thats all. (K11 CG10DE 40KW) (yes a tiny engine)

[@melroks3]

Yes you are right.. I do this with my scooter as well.. switch ignition off.with wot. engine braking effect doesnt decrease. +engineeringexplained

[@descent8275]

+BeanerMan3k dude I'm a car mechanic. :D yes, its an Old school throttlebody. also I described the Open Intake noise. shouldn't that be clear? :D

[@ackas4576]

Maybe you can do a video the noiseless j brake.

[@drifter.11]

did you talk about specific output in any of your videos. is it a good way to compare engines?

[@EngineeringExplained]

+Patrol 2012 I was planning to make a video on it but never did. Specific output alone doesn't tell much of a story, so not all that useful for direct comparisons. Perhaps I'll make that video!

[@drifter.11]

+Engineering Explained thank you and looking forward to it

[@AndrewRox22]

does downshifting and engine braking down a steep hill cause any excess wear to the engine or transmission through heat in comparison to just braking?

[@sermerlin1]

+AndrewRox22 Unless you have a bad coolant nope. Engine is spinning anyway and you'd want to use that force for braking and saving some fuel and lots of brakes.

[@EngineeringExplained]

Nope, your engine has a dedicated cooling system. So long as it's not overheating, it can handle it just fine.

[@thomasdavis4253]

Diesel engines can utilize engine braking without any kind of valves or Jake brake by doing the same as a gas engine, simply letting off the gas / downshifting... and as you stated they have no throttle body to create vacuum... so...

[@creedence1819]

Can you explain why the jake brakes on 2 stroke diesels have such weak braking?

[@KBS117]

Shorter stroke..

[@Violetcrime]

"Ultimately what you're doing is putting heat into the engine [instead of the brakes]". In the case of a gasoline engine, why would this be the case? I figured that since the engine is creating a vacuum, the expansion would cause the charge to cool fairly drastically, allowing the charge to absorb some of the engine's latent heat before being expelled out of the exhaust valve(s). My only guess is the extra heat comes from the increased friction caused by the heightened engine rpm vs. idle? Is that more than the heat induced by the normal idle charges being detonated?

[@EngineeringExplained]

+Kyle Smith You slow the vehicle by turning kinetic energy into heat. That's what disc brakes do. If you use your engine instead of your disc brakes to slow the vehicle, that wasted energy (used to pull a vacuum) puts heat in the engine.

[@Violetcrime]

+Engineering Explained Ahh, I hadn't considered that wonderfully simple perspective- makes complete sense. Thanks for the response!

[@HPRGarage]

+Engineering Explained What are the disadvantages? and will it cause any damage to clutch plate?

[@SidewaysGts]

+P.R. Hariharan Why would it cause damage to the clutch plate?

[@HPRGarage]

+SidewaysGts I used to reduce speed by down shifting, which is also engine braking isn't it? as I do engine revs a lot because, the wheel speed will be higher than engine speed. So clutch plate will undergo on stress. that's why I questioned.

[@SidewaysGts]

***** If youre talking about intentionally slipping the clutch as you downshift to slow the vehicle down- Then no, thats not "engine braking"- Though it is often erroneously attributed as such. And if you _are_ talking about slipping the clutch to slow down the vehicle during downshifts, then yes- that *can* wear down your clutch. Quite a bit actually. As a mechanic- I can tell you right now people often freak over the silliest and benign of things. But dont intentionally slip the clutch while downshifting. If letting off the throttle wont slow you down at an adequate rate, use the brakes. Thats what theyre there for. Your brakes are far easier, and far *cheaper* to replace than your clutch is :)

[@HPRGarage]

Oh thank you so much! I drive a Fiat Palio which doesn't have ABS,EBD and I kept it as a stock. So if I had to slow down my car from say 150kmph I had to reduce the gear. Brake at that speed ain't working and the stopping distance is too long. That's why I intentionally do Downshifts.. Once again thanks for giving me a clear picture..

[@sridevikulkarni8574]

What is Jake brake activation in mixed mode

[@MUSTASCH1O]

So in either case the car slows because the engine is doing work compressing and expanding the air trapped in the piston chamber?

[@rolandojrcantores7553]

Diesel has a valve in the intake and exhaust that closes at the same.

[@kiwidiesel5071]

No only an extra rocker to open the exhaust valve at the top of he compression stroke, all other valve sequences remain unchanged and continue to operate as normal. All engines have there inlet and exhaust valves closed at the same time during the firing phase to contain the force of the combustion transferring it to the piston.

[@srbicelis]

I listen to you in order to practise my English. You speak very nice ! Thanks

[@brandonshafer1220]

*very well

[@oggie6907]

+Brandon Shafer, or 'very nicely'

[@StanceGarage]

Sprieken sie duetsch ?

[@srbicelis]

hablo español

[@zhengyangsong]

+Gofrin Bicelis 我也是！

[@ernmanke]

So, a jake brake is when a semi truck goes down a hill and makes that loud HHHHHHHHHFAHFILUHAUIEGFBAJKGBALIUHV sound right?

[@bigflood2009]

Best explanation ever!

[@fathead22146]

Hahaha yes indeed!

[@spencerphilippinedream3706]

thats not the sound it makes

[@RushinTruckin]

🤣

[@rebel4446]

nice joke with a jake brake

[@Primer2toneGarage]

That's pretty close to how I explain how a Jake brake works. You flip the switch, witchcraft happens and then the truck sounds like a boss.

[@PolarArctica]

Would trucks be burned at the stake for witchcraft? If so, I feel it would be a punishment for both the truck, and the people watching since watching a perfectly good truck go to waste hurts my soul.

[@scottmonfort]

Wait. There is no switch mentioned in any of this ... just let off the gas (diesel) and the Jake system uses the compressed air to slow it down. NO SWICH RIGHT?

[@asha893]

@@scottmonfort no, the jacobs brake has a switch to activate it.

[@markflierl1624]

I like your explanation better! WITCHCRAFT HAPPENS!

[@KBS117]

@@markflierl1624 yeah. Its witchcraft alright, she is sucking you to a stop..

[@nosoliciting024]

On our heavy haul trucks (pulling two mountain doubles), we had compression brakes (not a Jacob brake) and we had brake savers. The brake saver consisted of an extra compartment filled with engine oil. It was part of the engine and set at the back of the engine at the output shaft. When applied by switch or an extra "Johnny Bar", it would air activate a paddle that would drop down into the extra 3 gallons of engine oil. It slowed the truck down quite a bit in combination with the compression brake. We were hauling 500,000 lbs. gross on private roads. Just thought I'd share.

[@svviftey]

As a Truck Driver, thankyou, I can now explain HOW it turns my motor into a giant 14.5 litre 6 cyl air compressor.

[@luca7069]

+Adrian Foekens 14.5 litre on 6 cyl? That's insane...

[@EngineeringExplained]

14.5 liters of beast, that's awesome, glad you enjoyed the video!

[@Primer2toneGarage]

Whenever I engage the Jake brake on my Peterbilt, country girls throw their panties at my windshield.

[@Yakeru35]

+Adrian Foekens Is this why some trucks are doing such a huge noise when decelerating ?

[@svviftey]

+Yak Eru Yes, That's typically the performance muffler or even straight piped crowd. A Jake Brake sounds fantastic through 10" straight stacks Alot of cities, well, pretty much all of them, technically have bylaws against the uses of engine brakes within city limits because of them lol. thats one of the perks of the silly aerodynamic eco friendly truck I drive, Jake brake is so quiet i can use it everywhere and no one knows. Also driving a straight piped truck 11 hours a day (13 in canada) gets pretty old after the first week. its alot of noise.

[@YouScroob]

The "Jacobs" brake was invented by Clessie Cummins after he retired from Cummins Engine Co. He originally approached Cummins to use it, but they were not interested. So he went to Jacobs Manufacturing (The people that make Jacobs drill chucks) and they built the brake. The logo on the Jacobs brake is the same logo as on the drill chucks.

[@CodyCombat]

I'm glad it became the Jake brake instead of cum brake xD

[@scottmonfort]

Really? I had to read the comments to understand where the term "jake" came from? Thanks to the Wizz. But tell me this ... it is not a switch right? .... just let off the gas, and the system does it (jakes) right?

[@02091992able]

@@scottmonfort You have to usually flick a switch on the dash to engage the Jake Brake then let off the accelerator then it does it's thing. Some have 3 settings off on or standby for the Jake brake the standby mode works when you take your foot off the accelerator pedal and disengages when you put your foot back on the accelerator. The on setting you have to flick the switch off before you can move forward. I may of got some of that wrong but that is how I understand how it works by riding with my father who use to drive trucks as part of his excavation company job well until the state of Vermont took his CDL away for his epilepsy even though at that time I was in my teens and never had I seen him have a seizure but they felt the need to take it away. They even tried to take his drivers license away but after my father said he was going to go on disability because of it they sent the drivers license back he was intending to drop his CDL but what pissed him off was having it taken.

[@tracylemme1375]

Mr. Cummins gave his patent to his daughter and son in-law as a wedding gift. The son in-law was of the Jacobs family.

[@nickwhite6717]

@@02091992able mostly right, except they all have an on/off switch, when on, the jakes will usually only activate when APP is read as 0%, which is when the process wxplained in the video is carried out. Some systems are optioned with a 2 or 3 positon switch, 2 position switches activate either half or all cylinders (3 or 6 in the case of an inline 6) and 3 pos switches activate 2, 4 or 6 cylinders. Gives greater control over braking effect and with prolonged use oil temps can increase, so can be used to prevent that on long downhill runs with brake modulation

[@PolarArctica]

False: a Jake brake is using your friend (Preferably Jake) as a brake by throwing him in front of the car :D It's simple physics, and is easy to do! The only problem is the maintenance cost :/

[@ManuLeach]

Dammit! I wanted to make a very similar comment

[@Primer2toneGarage]

Yes, this is the exact reason why I no longer have any friends names "Jake". But since I do most of my trucking along the Texas/Mexico boarder, I've adapted to using the "Juan brake" it's quite effective and there is an abundance supply down here. 😂😂😂

[@EngineeringExplained]

+Dunkaccino25 Trump makes THE BEST brakes.

[@RaZeRx09]

+Engineering Explained I guess you can say, it Trumps all other brakes.

[@MultiMustafa7]

+Engineering Explained Donald Trump Owns Brembo Braking Systems?

[@Ricardo_C]

Thanks to Jake brakes I can drive in the Rocky mountains without catching my brakes on fire with my 80000 pound semi

[@jimmesc]

Very good point

[@DOWDFILMS1]

Blinker fluid leak. Please help

[@tujiongyhrd]

what car do you own?

[@EngineeringExplained]

+Colin Dowd Sell it immediately, I foresee big problems down the road.

[@_Mario_PL_]

+The Channel of Stuff if it's a BMW, there is no fix for that.

[@lexmaximaguy8788]

***** yeah there is..its called a trade in!

[@_Mario_PL_]

+The Channel of Stuff omg! You just killed me 😂😂😂

[@waydigga1982]

I wish more drivers wouod understand the concept of engine braking. On a flat surface, physics and engine braking constantly want the vehicle to slow down. Normal braking isnt always needed to slow a vehicle (and engine braking helps preserve your brake pads). When approaching a stop sign or red light, you can simply let off the gas and the vehicle will gradually slow down (this can also help gas mileage as the fuel injectors shut down under deceleration when throttle is closed). Using your regular brakes unnecessarily doesnt allow the injectors as long as idle period bc the engine revs drop faster vs engine braking. The injectors will turn on sooner as you approach engine idle speed. Being able to proactively downshift magnifies engine braking as youre able to reduce vehicle speed more aggressively thru gearing and youre allowing the injectors more idle time as the engine revs slowly come down from a higher rpm (from the lower gear you just downshifted too). The lower gear puts the engine at a higher rpm increasing that vacuum which in turn slows the vehicle down more quickly.

[@EngineeringExplained]

+wayde philpot Agree 100%!

[@briana5444]

I've nursed my worn brakes like this for awhile while I'm saving for a brembo upgrade 😂

[@Nameless_rat]

+wayde philpot I wish people on the freeway understood this concept. For some odd reason people think brake lights= I need to slam on my brakes, when in reality you can simply let off the throttle and let physics slow you down. Saves traffic, time, and money (from brake wear)

[@nrdesign1991]

+wayde philpot They even teach this in driving schools over here, arguing that you save some fuel and prolong the life of your brakes in the long run.

[@n1elkyfan]

+MrElpajita The weight of the vehicle keeps it rotating along with the mass of the flywheel. Most engines won't completely shut the injectors off but will open them for a much shorter time so that there is less fuel going in to the cylinders. As the car slows to idle or once you press on the gas to start going the computer sees the increased load and will start to turn on the fuel injectors for longer periods.

[@jameslooker4791]

The story of the Jake Brake is actually quite fascinating. It was not invented by Jacobs. The Jake Brake was independently invented by Clessy Cummins of the Cummins Engine Company and exclusively licensed to Jacobs. He was retired at the time, and he designed the valve system on paper at home, there by proving his brilliance as an engineer beyond any doubt. He wouldn't sell the patent to Cummins because of long standing bitterness about his pension and patent royalties.

[@XecVid]

This is why im awake at 4am, when i actually should of went to sleep 23pm. Useful videos on your channel :)

[@dieselmutt8865]

Very good explanation of this. One thing to add though is with modern electronic diesel engines the 'control' solenoid is no longer needed as the engine computer is able to simply control an electric over oil solenoid to the exhaust valve to activate the system which gives much more precise control than the old master/slave type system of days past. Some modern engines even use the VG valve in the turbo to compound the engine braking using both back-pressure and compression combined together to often give the engine as much or more braking power than it has propulsion power depending on the engine spec for HP.

[@Sens23Bruins]

Cool you should make more diesel videos!

[@Leofred2000]

In Europe, when I took my truck license, I was told there was also another engine brake system called "the retarder" which is a oil turbine based braking system connected to the engine output shaft or driveshaft

[@alanmaier]

+Leofred A company I worked for (US) had Hino brand trucks (Toyota's large truck and bus division) that had a retarder type of engine brake. Key feature user-wise is that it was not loud, so it could be used in areas that normally prohibit Jake brakes due to noise issues. They were actually pretty good trucks - virtually trouble free.

[@nd318865]

+Leofred I knew someone would mention these... Imagine a garden hose, water on... Engine is just moseying along. Now try to bend the hose to minimize water flow; really tightly now... Engine brake on. The difference is the "retarder" uses engine oil and directs it through a smaller orifice within an appendage to the engine/ transmission "connection" Decrease the flow and "braking action" occurs though it also heats the engine oil. Another aside: there are electrical retarders too but that is another story. Imagine a Prius "regenerating electricity to it's battery when throttle is released or brakes are applied...

[@dresdensvo]

the Jacobs engine brake was invented Clessie Cummins {Cummins Diesel} the rights were sold to Jacobs { the inventor of the Vice Grip}

[@joecrumpler]

You are absolutely correct!

[@bobtaylor5196]

Jacobs invented vise grips?? I did not know that, thank you. very interesting

[@NarwahlGaming]

I'm going to stroke my beard - invented by Herbert Beard in the late 1800s.

[@davilathegreat]

If you bore your beard, you might get more torque out of it.

[@jaydunbar7538]

Cummins had Jacobs make them because the board of his company said no, he wanted engine brakes so he could go faster on downgrades and break the coast to coast record.

[@XxCORNFEDxX]

Was going to suggest you cover this topic, was interested to hear you explain it and you did not disappoint! Mint job

[@EngineeringExplained]

+XxCORNFEDxX Happy to hear it!

[@walterk1221]

Very good explanation, as usual. Minor history correction: the Jacobs Engine Brake was actually invented by Clessie Cummins. It is manufactured by the very same Jacobs that makes drill chucks.

[@dinohudson1432]

Thanks for the info, btw... I'm a subscriber w/ notifications. So...... What I win?

[@EngineeringExplained]

You win love!

[@nd318865]

Gas engine; higher compression ratio+/- more "engine braking with throttle closed. 2) Diesel engine "exhaust brake" lets higher, (17.1 18.1) compression exhaust stroke, slam into a closed exhaust pipe gate valve or butterfly (type) valve depending on manufacturer... About the same on a long downgrade at less than "speed limit" as continual 8-10# of air pressure to properly adjusted brakes. 3) Jacobs brake was developed by an engineer at Cummins Engines many years ago. It works just as described. It has been mandated in many European countries as a "safety necessity" for many years. In the U.S. most every manufacturer includes them and has for several decades. (Old saying among us old truckers; "No Jake is no joke!" An aside: Several years of no engine brake on an Allis Chalmers powered Freightliner in the '70s. The Grapevine was my nemesis! Finally installed an exhaust brake as no Jakes were made for the AC and no longer smoked all the way to Bakersfield. True story.

[@nosoliciting024]

James Tennier. That is interesting. I had never looked up the history of Jacobs Brakes. We had a 76' 4300 series International that came out of the factory with a 318 Detroit and true Jacobs brake. Had a lot of problems with them from what I can remember as a kid, so we had them removed. The truck was a flat lander and didn't really need them. When I first drove for CFI in the 90's, none of the fleet had compression brakes. We ran 48 states and Canada. Old school mountain method for downhill was one gear lower than the last gear you topped the hill in.

[@kengamble8595]

James Tennier The grapevine was a nemesis for many, be it semi or pickup and trailer driver ! 😊 Too many times did I get to the bottom with a STRONG amount of suction on the seat ! 😫 If you know what I mean !

[@roadrunner681]

cummins himself invented it after almost hitting a train testing a truck, Jacobs drill and chuck just made the ting cause the had the mills to do it.

[@yo6488]

Clessie cummins designed it after he retired

[@SmartestShark]

Dude, I had a pretty good idea of how automobiles worked before I found your videos, but you've given me a whole new level of understanding. Thanks for what you do man.

[@mantavyaagarwal7345]

plz make a video on trailing and semi-trailing arm suspension plz

[@westerntruckandtractorrepa1353]

Clessie Cummins invented the jake brake and sold the rights to jacobs manufacturing.

[@shobud7943]

oooo thats y trucks make them noises

[@nd318865]

+Sho Bud Actually the noise is a by-product of the driver using engines compression to reduce brake heat buildup. Smoking brakes are a sign that the truck may well be under less control than the driver might wish!

[@richdelgado3405]

Thanks for this video! I never realized that "Jake Braking" was an actual thing. I thought it was just a term, rather than an actual mechanism.

[@ClipSwitchFlashlights]

Good explanation of engine braking! Technically "Jake Brake" is a brand name for a compression brake. Much like Kleenex (for tissues), Band-Aid (for sticking plasters), or Advil (for ibuprofen). Also, in modern diesels there is no combustion mixture during the compression stroke while "Jaking". Since the injectors are electronically controlled, the ECM does not send a signal for fuel injection during use of the compression brake.

[@KeithFox]

I'm actually more confused now having watched this

[@EngineeringExplained]

+Keith Fox Feel free to ask questions! :)

[@danieldeaseweitzelwalker]

You have to know what's surrounding the explanation given here in the video to fully understand. I drive a semi tractor trailer truck so let me just give you an overview on more what it's doing. With some exceptions, on a diesel engine, you do not have a natural vacuum by design (in the video's first example) like a gas engine does that slows the engine down when you take your foot off the accelerator. Instead, air will continue uncontrolled into the engine when you take your foot off the accelerator, which transfers air pressure to the engine similar to both air and fuel but with less power because fuel is not being injected and ignited. Large trucks oftentimes have a compression release brake that is added to the engine called a Jake Brake in reference of Jacob's patented system. The Jake Brake opens the exhaust valves at a time when they would normally be closed - the time when air and fuel are usually being compressed in the engine and are about to ignite. When you take your foot off the accelerator, you are no longer adding diesel fuel into the engine but it's still getting uncontrolled air. As the air is nearly completely compressed, the Jake Brake opens the exhaust valve, letting out the compressed air so that the air pressure doesn't drive the engine. Instead, the friction of the engine and other sources of friction in the drivetrain slows it down because it's not being propelled by air compression. It can be oftentimes used in differently levels (anywhere from 1-4 levels) that determines how much engine braking is used. Whenever you hear a large truck - usually on the highway - make a loud "bop-bop-bop-bop" noise while it's slowing down, that noise caused by the Jake Brake and is the air pressure exiting the exhaust. The higher the level of Jake being used, the louder the noise. The reason it's so loud is because the action of the compressed air suddenly escaping the engine is similar to a gunshot. I hope this helps you to understand what this system is actually doing in the real world with reference to the video.

[@KBS117]

@@danieldeaseweitzelwalker well trained idiots, they have made of us...they have you believing all that crap... Once the compression is vented, (and a diesel is always compressing air), there is no air in that cylinder, and the piston starts down.. it has to pull a vacuum, until the valves are sucked open... That's the popping you hear, is the exhaust valves being sucked open.. Jake not working right? Replace the worn out valve springs, and it will work great again. A Jake shortens engine life.

[@ryans413]

Simple instead of using your brakes just let you foot off the gas and the car will slow.

[@spencer6874]

Im confused about if you the throttle body closed and it created a vacuum wouldnt that mean the car would stop firing and you would here no noise from the engine when you took your foot off your petal? I feel like im missing something obvious.

[@TeamWhos]

i drive an automatic is300 but i only use the manual mode. im constantly downshifting to help my brakes slow the car down. my question is, does this create any extra wear on the engine or transmission? my car obviously wouldnt let me shift into a gear that would harm it but it would create more wear wouldnt it?

[@TreatmentFreeBeekeeping]

Some on the clutch. There is very little wear on engine and transmission components while driving.

[@tigersharma1443]

I am big fan of yours channel, nice clean explanation as always, Respect and Salute to engineering explained channel, God bless

[@EngineeringExplained]

+Tiger Sharma Thanks Tiger! :)

[@LavenderSystem69]

Worth noting that simply downshifting a couple times and releasing both the accelerator and the clutch will also serve a similar purpose to the Jake brake, and is actually the method we're taught to use when road conditions get too slippery... unfortunately, early iterations of the Jake brake had a tendency to exacerbate the risk of slides on wet, snowy and icy roads, so a bit of conventional wisdom got written the blood of drivers: safest way to descend a slick, steep hill, aside from just not descending it at all until conditions improve, is to pick a less efficient gear ratio that favors more torque as opposed to more power

[@navasotatxvault]

The roar of engine braking is outlawed in some municipalities. How can that be mitigated to not create adversity for local businesses and neighbors?

[@Stewie81693]

Older trucks sometimes were ordered without mufflers and that is why the engine brakes were so loud. No mufflers is a cool factor to some drivers, other trucks just had crap mufflers. Newer trucks are mandated to have a DPF, a special type of filter that takes the place of the muffler and makes the soot from the engine go away and the gasses from the engine safer. Think Volkswagen and their recent scandal, it involved the DPF and the software in them. Anyway a truck with a DPF is very quiet and so are the engine brakes on the truck. I normally cant hear the engine brake on mine over the radio. I always use the engine brake even if the sign says no to, police dont care as long as you have a DPF or an older truck with a good muffler. Just unmuffled is a problem because it sounds like a gatling gun going off. For the record I am a licensed truck driver who also has a degree in criminal justice. Many cop friends have told me their views on engine brakes and they are all positive.

[@navasotatxvault]

Delightfully interesting!

[@TreatmentFreeBeekeeping]

In addition to what Stewie said, compression brakes are much quieter than Jake brakes. And there is also the option of a retarder which is mostly silent.

[@milosrog]

Many diesel engines doesn't have throttle body or other valves that create a vacuum. Also vacuum is not so important with gasoline ... Compression and gear ratio play a greater role than vacuum, this is a fact! Just think about it, it's logical! TRY THIS SIMPLE TEST: 1. Turn the engine OFF 2. Put your vehicle in neutral and try to push it, it will go easy 3. Put your vehicle in 1st or 2nd gear and try to push it, you will NOT move it a inch... 4. Put your vehicle in 5th or 6th gear... you will push it almost as easily as in neutral

[@Bebedarkness]

I really don't think that creating a vacuum is enough to slow down a car. It's more likely that compressing the air to 10+ bars without fuel injection is going to act as the engine breaking. So there is no need for exhaust valve to do that on a diesel. Simply when your foot is not on the accelerator the ECU will cut fuel. So the momentum of the car will drive the motor to compress just the air. That's why diesel engine have more engine breaking thant gasoline ones, juste because the compression is much higher in diesel engines.

[@EngineeringExplained]

This is not true at all. The vast majority of the energy used to compress the air will go right back into the engine during the power stroke, making the energy loss very minimal (even without fuel). It's critical to either create a vacuum, build backpressure, or release the potential energy stored at TDC for the compression stroke. There's a reason these devices exist.

[@NimishNadgere]

+Brice Eychenne That's a good explanation. But obviously, there must be a flaw in that system for them to facilitate the exhaust valve mechanism. I think the reason why your explanation isn't actually put to practice is that the engine might not be able to compress that air to such high pressure due to the momentum and therefore stop the engine suddenly causing a 'stall'-like situation which is pretty dangerous.

[@davidrobert2007]

+Engineering Explained Just explain then, why it's so hard to turn an engine over with a spanner? Is it the vacuum in the intake? No it's the compression.

[@NimishNadgere]

Oh now that EE has explained it, I feel quite silly trying to hypothesize a solution. My page didn't load when EE answered it here.

[@NimishNadgere]

davidrobert2007 True, but once you turn it over, it follows through effortlessly right? It's because the pent up energy during compression is released after reaching TDC, right Engineering Explained ?

[@stevethackery9853]

I think your explanation of engine braking in a gasoline engine is wrong, or at least incomplete. As you say, on the intake stroke with a closed throttle the piston will have to pull a partial vacuum, so the force required to pull the piston downwards will act to slow the crankshaft. HOWEVER, the vacuum is still present after BDC, at which point - by trying to pull the piston upwards - it is acting to SPEED UP the crankshaft. The two should basically cancel each other out, much like compressing and releasing a spring: no nett energy is gained or lost. The same argument would apply to those people who claim it is the compression in a diesel engine that slows the crankshaft: no, it cannot be because the energy stored in the compressed air is released again as the piston travels downwards. That's how the Jacob brake works - it removes the stored energy before it can be returned to the crankshaft. But there is no equivalent mechanism in a gasoline engine. Therefore it CANNOT be the vacuum acting above the piston that slows the engine - it must be some other mechanism. I don't know the true answer. I'm assuming a combination of mechanical friction and pumping losses, and maybe some minor heat loss to the coolant due to the not-quite-adiabatic cycle?

[@edyflak]

So there's no combustion when you let go of the gas pedal? The engine keeps moving because the wheels are moving? And the sound of the engine is purely mechanical?

[@EngineeringExplained]

With many modern engines, yes. Though it's possible to still burn a very small amount, depending on the setup. Ideally you would burn no fuel since it's completely wasted. The inertia of the car passes through the wheels/transmission to keep the engine running without fuel.

[@sermerlin1]

+edguiterrez yep.

[@endoftheroad10090]

+Engineering Explained you actually still burn fuel on overrun because of tip-out driveability filters which act on brake torque to give it a smooth deceleration feel (this is done by injecting ever decreasing quantities of fuel to generate a bit of indicated torque). These filters are used pretty much throughout the industry because driveability has become one of the most important customer requirements.

[@CactusJones7]

+Engineering Explained does engine braking wear down your car at all? The compression doesn't seem like it would be good for those small parts

[@sermerlin1]

Ethan Arpin you're compressing either way.... Think of it like this instead of fuel making explosions in your engine to make it move road is turning it. I'd say you're getting even less wear then when you're on throttle.

[@ianirizarry30]

can you do a video on a Miller cycle engine please?

[@KRAUSER0130]

I already knew this, but i have question unrelated to this video, and i can hardly find someone as trusted as you to answer it.. So, VW cars usually have TDI badge at their backs, but why do some have I or DI in that TDI logo colored red? I heard its some color-code for VW's engine power recognition or is it just cosmetic? Also i was told, more red letters in it, more powerful the engine. Thanks in advance!

[@ziggy1ful]

Sorry, once I read that engine braking is due to creating a vacuum in the inlet I stopped listening. It simply is nonsense as it disobeys a fundamental law of nature/physics: the law of conservation of energy. On a long descent if we just used the brakes get very hot as we are converting gravitational potential energy(GPE) into friction/heat energy. If instead we use engine braking to maintain a steady speed during the descent the GPE still has to be disappated, last time I looked I didn't see any red hot inlet manifolds or throttle plates, the theory falls over right there. Where does the energy go, from the engine compressing air and transferring that heat to the engine block and out the exhaust. No, the energy used in compression is not 100% returned in the power stroke, the internal combustion energy is very inefficient - perhaps look up the carnot cycle. Also worthy of mentioning, a vacuum at best only applies 15psi of resistance to the pistons on the intake stroke, but as you all know, on the compression stroke, we can have from 100-200psi depending on rpm and cam profile........that is where the braking effect comes from. As some others have mentioned, try WOT when engine braking with the ignition switched off, it will actually cause a small increase in engine braking(reason as to why we test for engine compression at WOT), if the vacuum theory were the braking would disappear when this occurs, it doesn't........please desist in spreading these myths.

[@ckarsenal]

So to fully utilize engine braking when slowing down in an automatic transmission car you should keep the car in gear? and in a manual transmission car you should downshift as you brake?

[@mbardos]

+ckarsenal yep...

[@buca9696]

+ckarsenal No need to downshift when you brake, unless you want to practise heel-toe or rev matching.

[@tinyman392]

Yup. In an automatic, don't put it in neutral. Some allow you to choose gears now and also rev match automatically. In a manual, you can stay in gear until you don't have enough torque and the engine begins struggling and put it into neutral. Another option is to downshift every gear. The last option is to block shift. The latter two options require you to know how to rev match.

[@buca9696]

***** No you don't have to downshift while you brake. You can downshift after you brake, unless you like doing heel-toe rev matching. As long as the rpm is above idle and the throttle pedal is not depressed, even in 6th gear @1500 rpm the engine will not use fuel.

[@ckarsenal]

+xXxMartin96xXx I tend to downshift to third and then brake to a stop. I find if I simply brake from 5th to a stop, I am using my brakes too much and missing out on the effects of engine braking.

[@ecsolha]

We break for nobody !!

[@LasseHuhtala]

+Ola Håkansson I can't breathe in this thing!

[@iant720]

You really didn't explain the common automotive form of engine braking and downshifting well... Look at all the comments.

[@Widestone001]

+Ian Thompson Hm, I am guessing here (gasoline engine): Downshifting results in a higher RPM. Also, the vacuum gets built over time, until it's strong and actually causes a noticable breaking effect. So, only a small percentage of that vacuum-time is actually effecting breaking-time. I hope I am making sense here - Accountant and Author :-) Now, the higher the RPM, the greater the breaking time per minute - and that's why downshifting causes a greater engine breaking effect. Was that halfay right? :-)

[@pjbadgersuw26]

+Christian Breitenstein Downshifting will also put you in a lower gear, meaning more braking torque will be applied to the wheels.

[@yosefmacgruber1920]

+Christian Breitenstein In lower gears, the amount of air being moved and restricted, is a greater amount of air per mile traveled, thus the kinetic energy or speed of the vehicle, is more efficiently converted into heat which the engine can handle far better than can the easily-overheated brakes. Thus the braking effect is increased in lower gears. That is why automatic transmissions have those low numbers, 3, 2, 1, as those set a limit of the maximum gear that the automatic transmission should engage. Those selections are mainly for engine braking, but perhaps a slightly lower gear should also be selected for towing? Otherwise, just ever leave it in Drive or Overdrive if there is an Overdrive selection, for best fuel economy.

[@danburch9989]

It is vacuum that causes engine braking in a gasoline engine, not compression. The piston is trying to draw air through a restricted port (intake). Connect a vacuum gauge to the intake manifold and you'll see 22"+ of vacuum with the throttle closed during deceleration. Since there is less than normal air pressure in the cylinder during the intake stroke, there's less than normal air pressure for the compression stroke, there is little compression to resist the piston to cause "compression braking". You can't compress a vacuum (even though it isn't a perfect vacuum).

[@KBS117]

Vacuum....sucks you to a stop

[@ianlyne4417]

So in short, this engine braking doesnt apply to automatic transmission cars? Got it. Thank you for the video.

[@1960JCRAY]

The Jake Brake was invented by “Jake” from State Farm.

[@dougcrawford8975]

Really! He did that, I like that! I always figured it was someone in khakis but I figured they were green I think Jake wears Khaki colored khaki's so I think you may have the wrong Jake!

[@PANTYEATR1]

I used to work on Detroit diesel 8V92 engines and I don't remember if the Jake brake was fully electronic or not on that engine using solenoids to open the exhaust valves. it has been a long while. I do remember, with a switch you could have one bank of the engine Jake Braking or both banks. a nice addition to this lecture would have been the exhaust brake, but great video as usual

[@MultiTerpen]

Can you explain compression? What does the numbers mean? What is a high compressions and what is a low compression? Please make a video on this :)

[@EngineeringExplained]

+MultiTerpen kzbin.info/www/bejne/pKfIonaDg7mnnpI

[@MultiTerpen]

Engineering Explained So for example.. I know that the compression ratio for my 69 mustang 351w is 9.5:1 But what does that actually mean? I did not really understand by watching the video. Is it like it becomes 9,5 times as small before it ignights? But what is really a high compression and what specifies a low one? Also what is the difference between NA and forced induction like a turbo?

[@sijankhan7796]

+MultiTerpen The compression ratio isn't necessarily how small the cylinder can get before it ignites, but rather, how small the cylinder is designed to get in a regular cycle. In most gasoline engines, they use a spark to ignite the fuel when the cylinder is in its compressed state. However, in many diesels engines, they rely on autoignition, so the compression ratio in diesels *could* give an indication of how much compression you can get before ignition. Because in diesels, you rely on autoignition, you typically have higher compression ratios than on gasoline engines. When you add a turbo, however, some of the air that enters the cylinder is pressurized, so the autoignition point is at a lower ratio of compression. So to prevent premature ignition, turbo powered gasoline engines typically run have a lower compression ratio. Say for instance, you decide to add a turbo system to your inline 4 or straight V6 engine, which has a compression ratio of 10:1 but may experience knocking if the compression ratio was set to, say 15:1. Due to the turbo, the pressure of the inlet air will be higher. If the pressures increase 100%, then you can only compress the air 7.5 times before ignition. So the 10:1 compression ratio needs to be adjusted, or you should select a different turbo to prevent knocking.

[@nd318865]

+MultiTerpen Compression "ratio" is the factor by which air is compressed from the bottom of a cylinder to the top of the cylinder, during each "compression cycle." Example: assume your tachometer displays 6000 revs per minute. This would equal 3000 compression strokes (up). 3000 power strokes, (down), 3000 exhaust strokes (up) and 3000 intake strokes (down). Where both valves have or are closed at that moment. Near the end of compression stroke, 14 to 30or32 degrees of rotation before the piston actually reaches top dead center (of the crankshaft rotating the (rod) up & in turn pushing "up" the piston, either fuel is injected or (in a carbureted engine, fuel/air is "ignited" by the spark plug. There is a formula (Google, Summit Racing etc) that takes cylinder bore, piston (crown) stroke, head-gasket thickness and cylinder-head combustion chamber capacity in grams usually to determine the total difference between the amount of air in a sealed cylinder with the piston DOWN and the compression ratio in turn is referenced by the number arrived at when the piston crown is UP, at the very other end of it's travel. Octane of gasoline, propane, natural gas all have different numbers, depending on their propensity to be ignited by the spark plug. Diesels on the other hand, compress air to a greater degree, hence much higher compression ratio, and that air heats quickly;y when compressed and fuel under "high" pressure is litterly squirted into combustion chamber and explodes, driving piston down and rotating crankshaft... rather than burns (out in a flame front from the spark plug.) Sorry you asked?

[@MultiTerpen]

James Tennier Thanks :D, but when it is like 9.5:1... Is the space inside the sylinder getting smaller by 9,5 times from when it is at the bottom to when it is at the top then? Is there a difference between saying compression and compression ratio?

[@Emslander]

Very professional and unhesitating presentation. Seems like he knows his stuff.

[@nickamarit]

What about in BMW's Valvetronic and other similar applications - how is engine braking done in those no-throttle-body designs?

[@hyster16t]

Insert Jake brake noise here = BOSS MODE.

[@shawn5773-q4z]

they sound pretty cool on big trucks

[@jackallen6261]

No No!! Engine breaking is when a rod goes through the block! Then the engine is breaking! ROFL Sorry I couldn't resist.

[@BlueCollarExCalifornian]

My old Ford Explorer, with the 4.0 V6 pushrod, always slowed itself down going down grades on the highway. I loved it!

[@ml48963]

+James Dean Youngs That's not a good thing actually. The Ford Explorer isn't equipped with an engine brake, so that 'braking' you experienced was due to internal friction of driveline components (like your transmission), which kills your fuel economy during normal use.

[@BlueCollarExCalifornian]

Mark LaPointe Oh well. Sold it two years ago for 300 bucks.

[@Cristi10077]

why are cars so cheap in the US?

[@CalebJKerns]

CRGamingHD if it was sold for $300 it was a pos.

[@wolfgang7689]

Mark LaPointe "comes with an engine brake"? Have you watched the video...?

[@leosalomao]

But if the piston creates a vacuum on the admission, it is just going to store energy, and then reuse it back on compression, where the vacuum will "pull" back the piston... Right? Where is this energy dissipated?

[@Redtooth75]

It pulls the piston up somewhat, but not enough to make up the difference. It is referred to as pumping loss. The engine has to do work to pump air into and out of the cylinder. Closing a valve on the exhaust or intake will increase pumping loss.

[@fronj]

Can you explain muffler bearings? The ones on my sailboat are making strange noises

[@davidsummerlin1069]

That was about the lamest explanation possible, not to mention incorrect.

[@the8jrfan]

The brakes went out on my engine once 😝

[@TravisMeeks6]

thank God for this video. i've always wondered what's up with jake braking!

[@mohamedzakariachorfi5541]

Is engine brake more effective in a gasoline car than in diesel? In my diesel car, down a hill, when i lift my foot of the throttle and the car is in gear the revs start increasing and the car picks up speed. And i'm obliged to use disc brakes to reduce the speed.

[@Redtooth75]

Diesels dont provide a lot of engine braking without some sort of auxillary device like a jake brake or exhaust brake. Gasoline engines have throttle bodies, when the throttle is closed the pistons pull a vacuum on the intake stroke which provides engine braking.

[@tomasprado8947]

So, is it good to engine break or not?

[@matsurigorekun8975]

+Tomas Prado engine braking uses no fuel, conserves brakes(puts less pressure on air brakes in semis and lorries) and slows you down. does that answer your question?

[@tschmi3856]

No. It's not good to break your engine. Using it to brake can be useful though.

[@tomasprado8947]

+Andrew Barcomb yes, thanks

[@tomasprado8947]

+timpaul paintballisbetterthanairsoft why is it not good?

[@matsurigorekun8975]

to engine brake in a bigger vehicle yes, but not really needed to in a smaller one like a coupe/ suv. the other guy just said that because you misspelled break instead of brake.

[@MrRexquando]

Petrol engine braking is NOT from the vacuum. You prove this by going down hill in gear with the ignition shut off and open the throttle. This used to be called "compression braking" back in the day. You are using the engine as a giant air compressor. Standard diesel cars and trucks do not have a jake or exhaust valve system yet they still can engine brake by this same process.

[@crowmagg1]

+MrRexQuando diesel engines have no throttle plate it's always wide open

[@MrRexquando]

crowmagg1 Agreed! This is proof it isn't the "vacuum" that causes the braking. Its using the engine as a compressor.

[@crowmagg1]

+MrRexQuando i have driven 18 wheelers (diesel) and gas v8's the disesl had almost no engine breaking effect (there is some but not that much) without a jake we had to engage the cooling fan clutch that is because the air that is getting compressed only rebounds during the power stroke then it is pushed out the exaust while on the gasoline engine the intake stroke is pulling from a manafold with a closed throttle butterfly if you put a vacum gauge there you will measure about 30" of mercury the piston is using energy at that part of the stroke because of the differencial between the top (near vacum ) and the bottom (at crankcase pressure (near atmospheric) that energy is returned during the compression stroke but then again lost on the power stroke during the exaust stroke the valve opens and the vacum is lost by a inrush of exaust gasses and almost at once pushed back out during the exaust stroke now with the exaust valve closed the process repeats when the intake valve opens so there is more engine braking effect in gasoline engines than a diesel without additional equippment installed to provide this the engineer here is wrong about the heating effect with a gasoline engine it's more of a cooling effect but both take energy

[@MrRexquando]

crowmagg1 nope- again you can test this yourself with a gas-er. drive down a hill in gear with the ignition off. Opening the throttle increases the engines resistance. The vacuum effect is rubbish.

[@crowmagg1]

+MrRexQuando i do it every day when i ride my mtorcycle on some engines the effect is so strong they make slipper clutches to keep inexperienced riders from crashing both effects we discuss have braking effect but chopping the throttle is stronger and is enough to cause rear wheel lock-up and cause a low side crash experienced riders know to keep some throttle applied when in a turn to prevent this and yes i can cut the ignition any time there a switch for that right next to the throttle but when i do that i notice np extra braking effect with the throttle open i do notice there’s a little less

[@senterpoint]

Good video, I do think the second example is called exhaust braking, because the plugged exhaust is actuating the brake effect. The third example, using the valves, is a true engine brake. Just a minor point, very informative video!

[@hommie789]

Jacobs Engine Brake is just the best known and the most widely used engine brake in north america but they did no invent the engine brake just designed a better mousetrap so to speak.

[@MoonishB]

@engineering explained; in engine braking, the gear ratios also play a role, right? I mean it's not only due to the vacuum in case of gasoline.

[@ATMA_STUDIO]

Correct ! it's a combination between the compression in cylinders, the the lack of explosion (because of no fuel), and the gear ration who stop the car, not the throttle body vacuum !

[@6Twisted]

I just thought engine braking was caused by friction in the engine/gears. And a common argument for doing it is to save your brake pads, but on the flip side this puts more wear on the engine and not using your brake lights can cause you to get rear ended. But on the plus side, it does sound cool and it's fun to see how long you can avoid using the brakes.

[@ZspotMotorsport]

+6Twisted The resistance/friction on the bearings and weight of the rotating assembly surely aid in engine braking, but I think he didn't mention it because its rather obvious and most people probably don't know about the vacuum effect caused by the throttle body. Engine braking isn't inherently hard on parts IMO, but engine braking from a high rpm or coasting down from near redline is asking a lot of the crankshaft and rods, especially in low gears (first and second). I often see people do this in parking lots or on side streets, accelerate hard in first gear and let off near redline and coast at 6500rpm trying to sound cool... seems like that would be hard on equipment!

[@alex90802]

The engine braking on the gasoline one is not correct. As it creates vaccum in the cylinder it gives back power back at the next stage, working as a kind of spring.

[@santerisaari2782]

Oh yeah? So the exhaust valve stops opening magically and the vacuum just stays in the cylinder? You are a genius.

[@alex90802]

@@santerisaari2782 You have a really high IQ. Congratulations.

[@Redtooth75]

incorrect, the vacuum is exactly what creates engine braking. Restricting the intake makes the engine work harder to suck air in, thus creating engine braking. It is a similar concept to an exhaust brake but in reverse

[@alex90802]

@@Redtooth75 if you are so sure of it explain me this process in the 4 stages.

[@Redtooth75]

@@alex90802 the piston moves down and because the throttle is closed it generates a vacuum. Creating a vacuum requires energy. The piston moves back up and then moves back down and then back up again. There is no net energy gain or loss in the past three strokes. Im on mobile right now and cannot provide a source. If you still doubt it I can provide one later

[@moose354]

Back in the 1970s when I was a college student in Los Angeles, I drove Crown school buses. These two and three-axle buses were powered by either Cummins or Detroit Diesel inline 6-cylinder engines with a five or ten-speed Fuller non-synchro transmission. I sometimes used the Jake Brake going uphill to catch an upshift especially first to second or second to third gears. The Jake brake would help decelerate the engine to catch the upshift. I was king of the road with that Detroit 6-71 when I hit that Jake brake.

[@nikosliras8102]

EE you should do a video on "braking in" new engines or rebuilt engines. The do's and don't 's and the reason behind the different methods and why it should be done. BTW excellent work on the videos. KEEP IT UP!!!

[@Pertamax7-HD]

nice sir

[@iseslc]

Cool! Will you make a video explaining in detail how to do it (i.e. pedals, down-shifting, etc.)?

[@spacejaga]

+iseslc there is nothing to explain. if you are on a manual gearbox - just put engine in gear 2 lower than it would be at that speed cruising and release the clutch. you can do rev matching to avoid sudden engagement or just release clutch slowly. during all this you don't apply any braking or accelerator (unless you are doing rev matching, then after putting car into lower gear just press accelerator till revs get to about 3-3.5k and then release the clutch). I drive in a city a lot and use it all the time. average fuel consumption (when used properly and safely) goes down by about 10-15% (my engine uses 0 fuel while in engine braking and ~1.5 liters/h on idle).

[@iseslc]

Senpai Nooberinho Oh cool thx.

[@animal16365]

the Jake brake/ compression brake was actually invented by Cecil Cummins. but he didn't have the money to build the prototype. he went to Jacobson mining equipment manufacturer. they gave him the money. but in the end. Stole his patent

[@buckhorncortez]

+animal16365 Not true. Clessie not "Cecil" had fully operating engine brakes in a number of trucks and a diesel powered boat. The meeting between Clessie and Jacobs was facilitated by his nephew who married the daughter of the President of Jacobs. Clessie was a full partner with Jacobs who manufactured the engine brake in their "Clessie Cummins Division." Nothing was stolen from Clessie Cummins as the broad patent was filed in his name and licensed to Jacobs. If you can't post correct facts - don't bother to post.

[@rookie__pilot]

Can you explain a locked up motor? and how it happens?

[@rookie__pilot]

+Adam Harrington thank you so much! it helped alot!

[@glennso47]

Angel Robles if an engine loses oil it eventually seizes up and won't run anymore.

[@angelsandoval6493]

Excellent video my friend... Congratulations from Venezuela.

[@TransistorBased]

So this, plus threshold braking and transmission retarders equals European truck stopping distances.

[@0RichBoy0]

I wrote a 3 page essay using what I learned from this video, thank you!

[@KBS117]

Hahaha. Too bad it's wrong

[@martinstent5339]

The Jake brake obviously works because it is compressing the input air, which heats it up, thus transferring energy into the air, and then pushing that hot air to the outside. In order to slow down a car, you have to do work. Kinetic energy has to be taken out of the vehicle and moved somewhere. Having a (partial) vacuum on the inlet manifold will exert a force on the engine, but there is no energy entering or leaving the manifold. Not so the cylinders. With a compression ratio of (say) 10, the air being sucked into the cylinder will be compressed around 10 times. Assuming an adiabatic compression, that would put up the air temperature from 300K to around 3000K. The heat transfer from the hot air to the cylinder head will be very good because the air molecules are hitting the cylinder head faster and faster and more and more often as the space above the cylinder contracts. As this air cools down during the expansion cycle the transfer of thermal energy from the cylinder head is not so good because the air molecules are hitting the surface less and less often and moving slower. You can do the same experiment with a bicycle pump. Just close off the outlet and pump away vigorously for a minute. You will notice that the pump warms up quite a lot (as will the pumper!), because the compression and expansion cycles differ in the way that the heat is transferred to and from the pump walls. The theory about the inlet manifold pressure slowing the engine is confusing force and energy. My chair is exerting a force on my backside to stop me falling to the floor, but there is no energy transfer. To move (kinetic) energy out of the car (braking) you have to do work.

[@Redtooth75]

You have a few misconceptions. Fist compression does not play a significant role in engine braking. There is actually not a significant amount of heat loss during the compression stroke because there is simply not enough time. Engines are also designed to absorb as little heat as possible from the cylinder. The compressed air pushes the piston down with almost the same amount of force that was originally used to compress it. Secondly, a closed throttle does in fact provide engine braking. You said that to remove kinetic energy from the car you have to do work. The part your missing is that the engine is doing work on the intake and exhaust stroke. It is moving air from one place to another, that requires work. Closing a throttle on the intake makes it harder for the engine to draw air in, likewise closing a throttle on the exhaust will make it harder for the engine to expel air from the cylinder. The work required for the engine to draw air in and expel it out is referred to as pumping loss.

[@martinstent5339]

@@Redtooth75 I have noticed that many car "experts" share your opinion. We will therefore probably not be able to agree on this issue. You say “It is moving air from one place to another, that requires work”, yes, but not much work. The outside of the car is moving much more air from one place to another, but that doesn’t slow the car down very much. BTW, engine braking also works very well in cars with a carburettor, where there is no significant force on the inlet manifold. How to explain that? It’s also the cylinders compressing air and warming it up that brakes them.

[@Redtooth75]

@@martinstent5339 so you are aware that experts and people who know what they are talking about agree with me, but you just think that you know more or something? Are you an engineer? Cause im pretty sure your just ignorant and refuse to accept evidence that proves you wrong.

[@etteiperdnaxela]

What about a retarder? Is that just a brake on the flywheel itself?

[@shi01]

+etteiperdnaxela No, retarder are in general maintenance-free or low maintenance. There are basically 2 types of retarder. The majority uses oil or water and it's very similar to a torque converter in the working. It's basically a torque converter where one side is locked up, to keep it simple. The other retarder type is also called a "disk eddy current brake" or "induction brake" and works by...well, electromagnetic induction. But this type is more common on trains.

[@ATMA_STUDIO]

So... you tell us that only the vacuum created by the throttle body closing will slow a car when you skip from 4'th to 3'rd gear on 100 km/h (for example)??? Man, i like your videos, full respect for this, but as an automotive engineer myself, i will NEVER EVER buy this explanation. Sorry but i have to disagree this time with you !

[@KBS117]

Its compressing the air that slows the gas engine when decel occurs.. The vacuum aids a little, but is only a restriction of air flow.. The jake brake is different.. It bleeds all the compressed air off of the piston, at top dead center of the compression stroke.. Now the the piston pulls towards absolute zero vacuum, until the valves suck open.. Research the power needed to pull absolute zero vacuum.. Its crazy, how much power it takes to do that.

[@ATMA_STUDIO]

@@KBS117 I know this :) That's why i didnt agree with the explanation in the video

[@Redtooth75]

The compression does not contribute to engine braking. The compressed air acts as spring, any energy used to compress it is returned on the next stroke. The engine braking comes from manifold vacuum. The engine has to pull a vacuum on every intake stroke, this is what creates the engine braking. Most diesels do not have throttle bodies so instead they use a jake brake.

[@BoonBreyne]

Very good video, quick and clear explanation, really shows how good you know your stuff. 1 question: so for the jake brake these particular components are installed only for engine braking?

[@Sturmgeschutz2]

There is a pass about an hour from where it is illegal for truck drivers to use air brakes, so must they be in correct gear before decent and use engine braking, they quite often crawl down this road at 20kmh.

[@Sturmgeschutz2]

*where i live*

[@johncrosk3448]

In California I have seen a couple of signs where it is illegal to use engine brakes. Seems to be in residential-type main roads. I have no idea why that is though.

[@jerryreding7369]

Where is this at, and can you provide any further information? This doesn't make any sense, if we're talking about tractor trailer combinations, since they all operate with air brakes. Not only that, but not all trucks have engine brakes, so this would essentially make it illegal for those trucks to operate on that pass.

[@Muskar2]

Imagine you're approaching a red light at 50 mph, in a manual gasoline car. Is it more wear-efficient to use engine braking, and downshifting every gear until you're in 1st gear and then apply brakes at the end? Back when I had an ICE, I used to run into this discussion often. The counter-argument was usually that you'd wear out the clutch etc. more, but spare the brakes - so essentially a near-worthless trade-off. By this logic, it would be optimal to engine brake until revs were very low in the current gear, and then apply clutch (or put it neutral) and brakes until a full stop. Regardless, what is the difference (in terms of wear) between engine braking at high revs and mid/low revs? Lastly, I've heard an anecdote of a gasoline engine imploding from engine braking down a steep mountain (essentially, pressure become too high). How would a gasoline engine optimally brake down a long steep mountain road?

[@EngineeringExplained]

Probably the most wear efficient to leave it in a gear and then use the brakes at the end. If you rev-match *perfectly* (near impossible) for each gear, you wouldn't have wear on the clutch, just the synchros (unless you double clutched perfectly for each downshift, then no wear, but that's far over-complicated braking haha). Using engine braking shouldn't wear your engine, it's just using the cooling system to reject the heat, rather than the brakes. I don't follow the logic of why a long decent can't use engine braking (gasoline or not). Certainly better than roasting your brakes and not being able to stop.

[@sergeantspeed5941]

What I do, is downshift one gear, assist lightly with the brakes, then coast and use the brake pads for the rest of the stop. pads are cheaper then a clutch.

[@radius50]

Pads are cheaper than a clutch, but the wear and tear from leaving it in gear and engine braking are almost immeasurable. The wear comes from slipping the clutch. When the clutch is fully engaged, it does not really wear.

[@Blair62]

The problem is wearing out your synchros and having to repair the transmission. Brakes are cheap and easy.

[@94sn95gt]

You lost me when you said gasoline engines use vacuum to slow you down. When in fact its the compression of the cylinders. Vehicle speed is faster than engine RPM in a given gear.

[@EngineeringExplained]

The compression of the cylinder forces the piston back down once it reaches top dead center, with little energy lost, so it doesn't end up causing much engine braking. The majority (for gasoline engines) is by pulling a vacuum, which requires energy, and doesn't return that energy into rotating the engine.

[@ziggy1ful]

So explain where the kinetic energy of the vehicle goes when creating a vacuum? you can't!!!!! The answer is of course is that during the compression stroke the gas/air heats up and some of this heat is transferred to the surroundings via the engine block etc, so not all the energy used in compressing is returned in the power stroke...the exhaust air is also hotter, some of the energy is still retained as heat here, this accounts for where the energy goes and hence why it is the compression that slows the car, treating the compression/power stroke like it is just a 100% efficient mechanical spring is a nonsense. This is just basic thermodynamics 101, suggest if you are really an engineer your revise basics such as the carnot cycle.

[@KBS117]

It's the vacuum that sucks you to a stop.. think about that piston at top dead center, starting down, with the valves closed, and no air in the cylinder.. what's going to happen? It will suck a hard vacuum, until the valve springs allow the valves to be sucked open, causing the pop pop pop in the exhaust and intake.

[@JulieAV]

Thank you for explaining this. It is the first time I got even a basic understanding of the Jake Brake even though I have looked for an explanation in other places in the past.