Engine Brakes, what are they?

[MrCodyWeston]

I always hear about how engine brakes are used with braking and KERS harvesting, but how does it come in to play? For example, if there is a KERS failure the driver worries about how the car will respond to braking, with engine brakes being used. I'm thinking about Jenson Button in Abu Dhabi in 2011 for reference. Thanks guys!

[piast9]

I think you mean engine BRAKING. The effect that you experience in a manual gearbox car when you lift the gas pedal leaving the gear engaged. Car slows down mainly because of the resistance of engine pumping air with closed throttle. If car has KERS then there is significant additional resistance because of the MGU working as a generator. As far as I know there are no additional brakes in the F1 engine.

[richard_leeds]

Engine braking is the friction from the engine slowing the car. You can feel it most on a road car when changing down a gear, the car will suddenly slow down.

[autogyro]

Controlling engine brakeing used to be around half of the skills needed by a top racing driver.
Today it is all masked by aero downforce and results in a struggle to stop the rear tyres wearing out.

[j3st3r]

I read somewhere that the offthrottle engine braking in a F1 car is the same as standing on the brakes in your normal roadcar.

[Cam]

Here's how the big rigs do it. Also, love the 70's retro video and editing - awesome sauce.

[autogyro]

Engine brakes are a special way of slowing the car down at high speed when the normal wheel brakes aren't able to take full advantage of the high aero downforce. A brake disc is placed on the crankshaft, with a set of calipers and pads etc all inside the engine. It acts directly on the crankshaft, which brakes the rear wheels via the gearbox, diff and so-on.

Non of that makes any sense.
The KERS m/g in F1 does this however when recovering energy.
The problem is it unbalances front to rear wheel brake balance, which has to be reset.

[superdread]

Engine brakes are a special way of slowing the car down at high speed when the normal wheel brakes aren't able to take full advantage of the high aero downforce. A brake disc is placed on the crankshaft, with a set of calipers and pads etc all inside the engine. It acts directly on the crankshaft, which brakes the rear wheels via the gearbox, diff and so-on.

That's rubbish. There are no brake discs inside the engine of any race, sports or normal car. Engine brake is just a name for the braking effect an engine can produce (open valve during compression strokes close during expanding strokes).

There are systems with brakes between gearbox and differential (for lorries and tanks).

[Harv]

Engine brakes are a special way of slowing the car down at high speed when the normal wheel brakes aren't able to take full advantage of the high aero downforce. A brake disc is placed on the crankshaft, with a set of calipers and pads etc all inside the engine. It acts directly on the crankshaft, which brakes the rear wheels via the gearbox, diff and so-on.

Definitely not used in any road/sports car, and I've never heard of a commercial road engine using this.

Most engine brakes (which are a separate system) use cylinder compression to slow by valve trickery, which are only on commercial vehicles.

[Lurk]

Definitely not used in any road/sports car, and I've never heard of a commercial road engine using this.

I think mainly because it could be easily replaced by any bigger standard brake system for less cost & better overall efficiency.

BTW i just hope angus response was a joke...

[wrcsti]

Im pretty sure its the force of compression that causes most of engine braking, not friction

[Tommy Cookers]

the F1 car, on throttle closing, is trying to suck air 350 litres/sec past throttle plates (almost) closed to prevent this

that is even a bigger part of 'engine braking' than friction ? (diesels show far less EB for this reason)

[Dragonfly]

My pure empirical experience tells me exactly the opposite about diesels.

[Tommy Cookers]

in everyday driving surely you find that with the diesel you must lift off the accelerator much earlier, or you have to brake more ?
(with a turbo diesel, a N/A diesel is so slow that it's not a true comparison with a petrol/gasoline car, neither is a bicycle)

I was not speaking of enthusiastic driving, changing gears down like the race driver

does anyone else have a view ?
do trucks etc have the engine air throttled on the over-run power-off to help the brakes ?