Most of us use the exhaust brake - but can anyone explain the physics and the mechanism involved?
Regular brakes are easy enough - moving disc/drum brought into contact with brake pads/linings, resulting in friction which directly converts the rotational energy into heat, which is in turn dissipated to the air. But what are the Physics and mechanics of an exhaust brake?
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Basically a guillotine in the exhaust pipe after the turbo creates back pressure, useless in my opinion best removed before they stick with carbon .ive removed them on both my lorries and put a jake on instead .
Exhaust brake as above slows engine slows vehicle, engine brake creates back pressure by closing exhaust valves in engine.
I think a lot of trucks now have three stages on one lever/button 1. Exhaust 2. valves on three pistons 3. valves on all pistons.
Punchy Dan:
Basically a guillotine in the exhaust pipe after the turbo creates back pressure, useless in my opinion
Clearly not driven anything with hill descent speed control. On the DAFs I drive they’ll hold you at whatever speed you set going down Windy Hill fully loaded, no need to use the brakes.
They shouldn’t be sticking with carbon, we had no issues with them with the 100+ lorries in the fleet even at over a million km.
They work by pressing a little button on the floor (in some cases) and they slow you down instead of the possibility of ending up with brake fade. 
Some do work better than others but they all help if used correctly. 
I agree with punchy-up your exhaust would be a great place to push jakey 
Beau Nydel:
I agree with punchy-up your exhaust would be a great place to push jakey
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how wide would it need to be to accommodate his head,never mind his ego??
That’s a blast from the past; an exhaust brake button on the floor! Must admit I preferred them there but can’t honestly remember the last lorry I drove that wasn’t controlled by a stalk on the steering column. Probably my Sed Ak Strato I reckon.
Conor:
Punchy Dan:
Basically a guillotine in the exhaust pipe after the turbo creates back pressure, useless in my opinionClearly not driven anything with hill descent speed control. On the DAFs I drive they’ll hold you at whatever speed you set going down Windy Hill fully loaded, no need to use the brakes.
They shouldn’t be sticking with carbon, we had no issues with them with the 100+ lorries in the fleet even at over a million km.
He didn’t say that he hadn’t driven anything with proper hill descent control, just exhaust brakes aren’t very effective, and I thought DAF’s had Retarders or Engine Brakes?
the maoster:
That’s a blast from the past; an exhaust brake button on the floor! Must admit I preferred them there but can’t honestly remember the last lorry I drove that wasn’t controlled by a stalk on the steering column. Probably my Sed Ak Strato I reckon.
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leyland marathon.
all it was good for was playing tunes when letting it run away with you down hills.
Some didn’t used to turn off the engine with the key and you had to use the exhaust brake pedal on the floor.
The butterfly valve in the exhaust style are ok when they’re new but do lose a lot of efficiency as they age. Think a lot will now still use the exhaust brake automatically anyway regardless what you do with the switch but never used to understand the drivers who would turn it off. Would always find it switched off when I came back off hols - can understand why you wouldn’t want the exhaust brake when you lift off the gas settting but don’t see the logic of why you wouldn’t want the additional benefit under actual braking.
muckles:
Conor:
Punchy Dan:
Basically a guillotine in the exhaust pipe after the turbo creates back pressure, useless in my opinionClearly not driven anything with hill descent speed control. On the DAFs I drive they’ll hold you at whatever speed you set going down Windy Hill fully loaded, no need to use the brakes.
They shouldn’t be sticking with carbon, we had no issues with them with the 100+ lorries in the fleet even at over a million km.
He didn’t say that he hadn’t driven anything with proper hill descent control, just exhaust brakes aren’t very effective, and I thought DAF’s had Retarders or Engine Brakes?
Yes I think my 65 reg Daf has a 3 stage engine brake by Clessy ■■■■■■■ aka Jacobs ,I’ll check with Conor though 
Own Account Driver:
Some didn’t used to turn off the engine with the key and you had to use the exhaust brake pedal on the floor.The butterfly valve in the exhaust style are ok when they’re new but do lose a lot of efficiency as they age. Think a lot will now still use the exhaust brake automatically anyway regardless what you do with the switch but never used to understand the drivers who would turn it off. Would always find it switched off when I came back off hols - can understand why you wouldn’t want the exhaust brake when you lift off the gas settting but don’t see the logic of why you wouldn’t want the additional benefit under actual braking.
The old MANs that I used to drive were a nightmare. You’d put a little pressure on the brakes and a fraction later the exhaust brake would kick in, throwing you forward in your seat. Worst of all, the telematics system would record a harsh brake for it!
I’m not a fan of these auto gadgets in my lorry and would turn most of them off if I could.
Own Account Driver:
Some didn’t used to turn off the engine with the key and you had to use the exhaust brake pedal on the floor.The butterfly valve in the exhaust style are ok when they’re new but do lose a lot of efficiency as they age. Think a lot will now still use the exhaust brake automatically anyway regardless what you do with the switch but never used to understand the drivers who would turn it off. Would always find it switched off when I came back off hols - can understand why you wouldn’t want the exhaust brake when you lift off the gas settting but don’t see the logic of why you wouldn’t want the additional benefit under actual braking.
Yes the old DAF 2800s and such used to be switched off by using the exhaust brake.
In regard to switching off the auto switch for the exhaust brake; this is good to do in icy conditions as it can lead to jack knifing. This is especially the case when running empty.
Roymondo:
Most of us use the exhaust brake - but can anyone explain the physics and the mechanism involved?Regular brakes are easy enough - moving disc/drum brought into contact with brake pads/linings, resulting in friction which directly converts the rotational energy into heat, which is in turn dissipated to the air. But what are the Physics and mechanics of an exhaust brake?
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Disambiguation needed.
Do you really mean an exhaust brake? A simple block on the exhaust pipe to increase back pressure a little and give slightly more engine braking.
Or a form of engine braking? Valves are used to turn the engine into an air compressor.
Or a retarder? A fluid brake on the rear of the gearbox, that turns rotational energy into heat.
Or even (unlikely today on trucks) an electrical retarder?
Conor:
Punchy Dan:
Basically a guillotine in the exhaust pipe after the turbo creates back pressure, useless in my opinionClearly not driven anything with hill descent speed control. On the DAFs I drive they’ll hold you at whatever speed you set going down Windy Hill fully loaded, no need to use the brakes.
They shouldn’t be sticking with carbon, we had no issues with them with the 100+ lorries in the fleet even at over a million km.
Exhaust brake is a pretty crude device, which, as Dan says, is just a guillotine across the exhaust pipe, south of the turbo.
Some are more effective than others, but none are much good really.
Many heavy trucks now are fitted with an auxiliary braking system, and there are two main types.
Hydraulic retarders, which operate on a gearbox shaft, and work on a similar principle to a hydraulic pump with variable flow.
The other common type is the engine compression brake, a system, as Dan points out, which has been in use for many years, but until more recent times was more often found on American engines. Volvo, and now Daf (I think) fit them now.
There is an element of sorcery in how they work, and the following is my understanding of it.
By a combination of electrics and hydraulics, the engine valve timing is altered, so that with every upstroke of the piston, a valve is opened at top dead centre, and the air compressed by the upward stroke of the piston is released to the atmosphere. This effectively turns the engine into a compressor, and a two stroke at that, meaning that it does work on every upstroke, not every second one, as in a four cycle engine. This in turn, via the transmission of the vehicle, provides powerful retardation.
I think that many vehicles also have a degree of brake blending, which combines whatever system is in use, (be it gearbox retarder or engine brake) with the exhaust brake if fitted, and the wheel brakes. This is what permits some of our correspondents to go down Windy Hill wherever that is, ( it’ll be a mere pimple compared to some of our big bollock Scottish hills) without a care in the world.
All of the above may be a complete load of manure, but I think it sound real, so fire away if you think you’re hard enough.
In some cases that valve in the exhaust also gets used to assist in the dpf regen cycle, one time mine seized up it didn’t take long before it was failing to regen the dpf properly.
the maoster:
That’s a blast from the past; an exhaust brake button on the floor! Must admit I preferred them there but can’t honestly remember the last lorry I drove that wasn’t controlled by a stalk on the steering column. Probably my Sed Ak Strato I reckon.
in regards to the button on the floor I still think the floor operated hi/lo beam was a better system… I know showing my age but I preferred it…
Its a simple butterfly valve like a carburettor choke that slows the air getting past, its just back pressure that slows the vehicle or in the case of a DAF stops the engine.
It is not linked to the gearbox, axle cooling system or anything else, it sits in the exhaust manifold, the higher the engine revs the more efficient it is.
Franglais:
Roymondo:
Most of us use the exhaust brake - but can anyone explain the physics and the mechanism involved?Regular brakes are easy enough - moving disc/drum brought into contact with brake pads/linings, resulting in friction which directly converts the rotational energy into heat, which is in turn dissipated to the air. But what are the Physics and mechanics of an exhaust brake?
Sent from my VOG-L09 using Tapatalk
Disambiguation needed.
Do you really mean an exhaust brake? A simple block on the exhaust pipe to increase back pressure a little and give slightly more engine braking.
Butterfly Valve in Pipe
Or a form of engine braking? Valves are used to turn the engine into an air compressor.
Jacobs Brake. ■■■■■■■ / Volvo
Or a retarder? A fluid brake on the rear of the gearbox, that turns rotational energy into heat.
ZF Intarder type
Or even (unlikely today on trucks) an electrical retarder?
Telma type