33 replies to this topic

[jvl]

what is engine braking and the principles behind it?

[gunner]

Engine braking is using the compression of the engine while not under power while down shifting to help slow the car down.

Gunner

[Ray Bell]

This is largely correct, however there is a little more to it. Just as there is one power stroke in the four strokes (two up, two down) of each cycle in the operation of a four-stroke (or four-cycle in some places) engine, and this drives the car, there is a compression stroke, wherein the piston has to travel up within the cylinder and compress the mixture that has been drawn in.
This compression stroke is certainly going to slow the car down, and without power coming from the power stroke, as when the throttle is closed, it will aid braking considerably. In addition to this, the power stroke becomes another help under these conditions, and to a lesser degree the inlet stroke does too.
First, the inlet stroke is sucking mixture from a manifold and port that is closed off by the butterfly that controls the flow, so the piston's downward progress is ******** by that vaccuum. Then, in the firing stroke, it is ******** in the same way, but in a more confined space.

[Wolf]

Engine braking is also a technique used for truck and bus diesel engines (although it could be used in petrol engines as well). It is quite simple method of increasing exhaust pressure by means similar to regulating the air flow through carburetor (butterfly). This is usulaly done before the muffler. This increases the amount of work spent through intake and exhaust cycles significantly decreasing torque and power output.

[gunner]

Wolf.

You are talking about a Jacobson engine Brake. My son drives a truck and told me that they are told to only use them when necessary as they put a heavy load on the engine. Some towns have signs that say (don't use Jake Brakes) as the loud cracking sound disturbes people.

Gunner[p][Edited by gunner on 06-25-2000]

[Wolf]

Where I come from they're just called engine brakes, although Oetiker-brake is more accurate (he invented them in 1938- although only on on/off priciple, I just checked it in my 'Bible'). I have never noticed any increase in noise (don't see why should there be any). Anyway, bus drivers around here use it whenewer posible (just flick the lever few nods up and then back- fiddle with the damn thing almost all the time).
Gunner, here's a tricky one I asked in 'Nostalgia Forum'/superchargers. Did BRM P56 have it's exhaust pipes so nicley sticking up to get opposite effects of Jacobson/Oetiker brake (increasing power through decreasing exhaust pressure)? [p][Edited by Wolf on 06-25-2000]

[gunner]

Wolfe.

There is an old boy that goes by my house and uses the Jake brake to get his girl friends attention. Loud isn't the word for it It sounds like a high speed anti aircraft gun.

Gunner

[gunner]

Wolf.

I don't know about the BRM but what little I remember about the Jake that my son said that it limits the opening of the valves? And builds up a very high pressure in the cylinders. So if it was used on an F1 engine I would think it would tare it to pieces??

Gunner[p][Edited by gunner on 06-25-2000]

[gunner]

Wolfe.

Let me re do this I would say that BRM's exhaust would be the opposite of an engine brake. It might of been a tuned exhaust system which would suck out the exhaust and pull in the intake charge quicker with the help of valve overlap. But if it was Supercharged it wouldn't make any difference.

Gunner

[p][Edited by gunner on 06-25-2000]

[Ray Bell]

In a diesel engine the throttle is always wide open, the only alteration made by using the accelerator pedal is to vary the fuel injected. They are therefore better - especially with their 20+:1 compression ratios - subjects for engine braking.
The Jake brakes then come into play, and as Art says, they are quite loud. We used to live on the highway at the bottom of a very long and steep hill (the Gov spent $3mil doing it up because of the steepness and length, the house in which we lived had been hit previously, while another nearby house had a hole made straight through the middle!) and each night we were certain that each truck was coming in to see us... because of the ever increasing noise of the Jake brakes.
Brake smells always lingered in the air around the place, too.

[Wolf]

If Jake has something to do with valves, it should be something like Saurer brake (it used camshaft that was slided to change valving parameters, such concept was also used in thirties). The one I talked 'bout is only a butterfy (that can be locked in several positions, thus regulating increase in exhaust pressure) stuck up in exhaust pipe. That's all. If you try to picture it on engine diagram (pV), it changes only height (and area) of inversely running part of diagram (the one subtracted from area determined by compression and expansion cycles). Thus engine produces less torque/power at same revs. No additional noise should be result of this. So, Jake is not Oetiker as we presumed.[p][Edited by Wolf on 06-25-2000]

[Ray Bell]

I think the Jake is in the exhaust system... the signs here say "Exhaust Brakes must not be used in town..."

[gunner]

The Jake Brake works hydroliclly by opening the exhaust valve when the pressure reaches about 500psi on the compression stroke driven by the rear wheels venting the power to the exhaust getting retardation from the compression stroke and returning no power to the wheels on the power stroke. And it is called the Jacobs Brake not the Jacobson Brake. http://www.jakebrake...gine/theory.htm

Gunner[p][Edited by gunner on 06-26-2000]

[Ray Bell]

Altavista to the rescue, Art?

[gunner]

There is a lot of informatiom on the net if people would just look around. It saved me the time of waiting untill Steve called.

Gunner[p][Edited by gunner on 06-26-2000]

[Ursus]

If you look around on that site gunner dug up you'll also find the exhaust brake Wolf is talking about. http://www.jakebrake...ts/products.htm

[Wolf]

I visited the site, quite nice. I suppose it works on on/off principle. The one I described has usually quite a few regulating positions. You should try to see to it they use them instead of Jakes, at least they're quiter.

[gunner]

Another very crude but efective emergency brake was used on logging trucks in California where they have very steep mountain grades. They had a reinforced concrete slab mounted with chains in front of the rear wheels. If things got out of hand a valve would release the latches dropping the slab and the rear wheels would climb up on it and friction would stop the truck. It worked but tore the hell out of the tarmack. They later went to some kind of a turbo retarding system but I don't know how it worked.

Gunner

[Wolf]

Gunner.
The simplest things oft turn to be most effective. I like that brake.

[Ray Bell]

That one reminds me of the days when I first had a bicycle. My brother 'borrowed' it and was going down a steep hill. He braked to slow down a bit, but the centrepull brake cable (they were mongrel things!) pulled out and he had nothing.
Remembering everyone at school had said to put your shoe up against the tyre, he promptly put his foot on the front wheel.
Pretty hard on the teeth!
Later he learned that they meant the rear wheel... that was after Dad showed him how to straighten bent front forks!

[Wolf]

Bikes do have strange brakes! A friend of mine used a similar brake, but in less intelligent manner- he has stuck his foot in spokes!!! He got off the bike allright, was a sight to see. Didn't hurt himself though. Fools have all the luck.

[Nathan]

Does using this method put extra wear and tear on the cars engine and tranny? I npoticed a huge difference in braking when I tried this. Will it reck or shorten the life of my car???

[Ray Bell]

Depends on the car. If it's an auto, it will make a huge difference to pad wear... everything's a trade-off..
I just wouldn't drive any other way, myself.

[Hoffy]

My dad always toold me when I was learning to drive, Gears are for going, brakes are for slowing.

Yes it does make a difference to engine brake for large loads, as in a truck, but a modern day car is designed generally for an auto trans, where engine braking becomes less of an effect. So therefore the brakes are generally more then enough to pull the car up.

[gunner]

The most likely thing to fail on a street machine with continual engine braking is the clutch. Each time you use the clutch you have a little slippage and ware. Normal use will get you many more miles out of the clutch. Unless you want to go to a $6,000.00 Jerraco gear box.

Gunner[p][Edited by gunner on 06-29-2000]

[Ray Bell]

My cars never suffer undue clutch wear, Art... brakes, that's a different story.

[gunner]

Yes I know you drive on roads that are straight for a hundred + miles?

Gunner[p][Edited by gunner on 06-30-2000]

[Ray Bell]

Then why do I wear out brakes? The roads that are straigh for that distance are around, I've been on two of them, one hitch-hiking the other in a bus, and both on the same trip, incidentally.
The eastern seaboard, where most of us live, is full of curvy mountain roads, and then in the cities we have intersections, traffic lights, pedestrian crossings, all the sorts of things you enjoy when you go to the big smoke in Maryland... and probably more.

[gunner]

Ray.

Big Savage is nuthing more than an extended hill 2700ft high. The real mountains are the Rocky Mountains out west. I use to set in my living room in San Bernadino Cal. and look at San Gergonia mountain 14,000 ft high. Once you leave Maryland and get to northern Ohio it is flat as a board untill you hit the Rockies. If the weather doesn't get better in 10 years you could put a big red rock in southern Indiana and you would sware you were in the outback.I guess we are kind of Hillbillies we live in a board shack a mile off of the main road with news paper stuffed in the holes in the wall and a wood stove for cooking and heating. We also have a pig pen next to the house that gets a little testy in warm weather. Also a few Chickens in the yard. Maybe someday we will get the modern conveniences you have down under? The worst thing is the outhouse in the winter time man that is a rough trip in three feet of snow.

Gunner[p][Edited by gunner on 06-30-2000]

[Ray Bell]

I believe I'm about to move to similar conditions, Art, but without the warmth and comfort of the nurse... and without the pigs, but there is a couple of sheep in the yard, which my border collie will lo-o-o-o-ove.
Snow won't be as deep... what's it like where my son is, Bloomington, Indiana? I haven't seen him in seven years and he's not much on writing.

[gunner]

Ray.

Bloomington Im not sure but Indiana is about like ohio both are a little hilly in the southern part and when I say hilly I mean more or less rolling land but mostly flat. They get some pretty harsh weather in the winter. I don't really live that bad but it sounded good at the time. As far as the Sheep if I would of had any when the boys were growing up they would of been getting in practice for there future lives. And by the way I got a Hewlett Packard Scan Jet 3400C Scanner as an aniversary present today 22 beautiful years yesterday. When I learn to use it I will scan a picture of Gunner and the wife and I hope they don't consider it obscene.

Gunner[p][Edited by gunner on 06-30-2000]

[Ray Bell]

I just had my eleventh anniversary on April 25, which is the day we celebrate what we call Anzac day, roughly equivalent to your Memorial day, I guess.. the anniversary of the Australian & NZ troops going into action in Turkey to commence their operations in WW1.
Just for interest's sake, Art, I'll tell you about this. I was divorced from my first wife on 11th Nov, Armistice Day, you might recall, and at 11 o'clock, what's more.
Is that good stuff, or what?
Looks like there won't be a twelfth, however, the war is still on, lasted nearly three times as long as WW1!
I sent the above notes to my son, the stuff about ohio, snow and outhouses, might jolt him into writing to me.
He works in Indy, but doesn't go to the race. Works with computers.. which brings me to something else... your scanner.
Don't make the mistake of scanning at high resolutions. For use on the net, or emailing, scan at about 70dpi. Sure, for printing out you might go higher, especially if you have a really good colour printer and good paper for copying pictures, but the files get too big and it's no use anyway. When I scan for the quality mag I write for, I use about 350dpi, that's all that's necessary. Also, always save as jpg files (you'll find there are options like BMP, TIF etc) because they are only tiny compared to the others. I got a pic via email the other week and it was 519k as a jpeg (which took long enough to download!), but I had to use it in a program which didn't recognise jpegs and converted to a Bitmap (BMP - you can do that in Paint in your Windows accessories) and it blew out to 25.6 megs... MEGS!
Enjoy yourself learning to use it...

[gunner]

Speaking of numbers my wifes first husbands birthday is January 18 and so is mine. It will take me a while with the Scanner thanks for the information I will print it out.

Gunner

[Darren]

Ah, and there's the connection to the topic - jpegs and engine brakes are all about compression. You wouldn't want your Jake Brake to be too lossy though. And returning to another thread entirely, jpegs are all about algorithms, too.