Everyone wants it, thought these might be of some small assistance, maybe.

Naturally some sort of "brake heat convective and radation" cooling model would also be needed. This should just be a fairly straight adaptation from the tyre model though.

There are two things the cooling model requires.

The rate at which the brakes cool down with various levels air speed (this varies depending on vented or solid discs, vented discs cool twice as fast(says this text book)). The second rate is the radiation of excessive heat from cooked rotors. (when they get massively hot they radiate heat at a rate that needs modeling).

^

Describes it all.

Quote from The Very End :

U speak my mind.

Looks very interesting, and would work quite well given a few constants added to a car data file (if they are not already). But I'm sure there are simpler ways of doing it. Brake torque is easy to calculate, and the temperature increase due to braking is easy to calculate. How far does brake simulation really need to go?

What text book is that?

I can't remember the title exactly, I was digging around in the library for stuff on karts, and came accross it. It's for designing brakes. I'll have a look when i'm back there tomorrow.

I thought that was the simplified way of doing it, the complicated method in the book had sections for each strip of the brake disc in increasing radii, and the pad divided into 8 sections!

I'm guessing the constants you are referring to are disc mass etc, seeing as those don't change with every brake heat calculation?

Yarr, indeedy.

For the varying radii, the radius could be integrated between min/max values to find the instananeous heat build up over the whole disc, couldn't it? Or you could just model the brake disc as having uniform temperature, and compare that temperature to a graph/equation for pad/disc wear and friction.

I didn't understand that section on pad wear in the least. It seems very obsessed with the vehicle in general and relies heavily on the assumption that the brakes don't lock.

I have written a simplified version of the first attachment which would probably be much more useful from a development perspective, have a peek at the attachment if you would care to.
Of course, in regards to Tristan's last comment, this is on the premise the brake is assumed to be a point contact, as I don't think heat conductivity within the metal of the disc will be modelled in the near future.


edit: This has been bugging me; assuming that the braking torque is proportional to the radius the section of pad is from the axis of rotation, then it increases proportionally to the area that the torque is spread across. ie. twice as far from the axis, twice as much braking force but also twice as much material for the heat energy to be dispersed over. So the brake disc should increase in temperature proportionally. As heat is conducted well within metal, I don't think that the greater air cooling for the outer regions of the disc is a major concern, I could be wrong. I also don't know if the temperature of the pad itself is of importance, as the section of the pad furthest from the axis would get hotter than the rest.
I don't know about leading-edge and trailing-edges of brake pads, though, if that's what you meant by the sections discussed in the book.

Quote from tristancliffe :

Yarr, indeedy.

For the varying radii, the radius could be integrated between min/max values to find the instananeous heat build up over the whole disc, couldn't it? Or you could just model the brake disc as having uniform temperature, and compare that temperature to a graph/equation for pad/disc wear and friction.

Yes, but surely you'd want to model the surface temperature seperately from the bulk rotor temperature, just like LFS does currently with the tyres?

I would imagine that it's the rotor surface temperatures which determine braking performance, not the overall rotor temperature.

Quote from Live for Sideways :

I didn't understand that section on pad wear in the least. It seems very obsessed with the vehicle in general and relies heavily on the assumption that the brakes don't lock.

How much wear does a locked brake experience?

Quote from StewartFisher :

How much wear does a locked brake experience?

Erm none?

Quote from StewartFisher :

Yes, but surely you'd want to model the surface temperature seperately from the bulk rotor temperature, just like LFS does currently with the tyres?

I would imagine that it's the rotor surface temperatures which determine braking performance, not the overall rotor temperature.

True, hadn't thought of that.

Haha, touche.
But seriously, that modelling equation is dependant on the deceleration of the vehicle as opposed to the rotational velocity of the disc. So that would be applying wear to a locked disc (and as a bonus it is rather hard to tell what that equation is doing.)

Quote from StewartFisher :

Yes, but surely you'd want to model the surface temperature seperately from the bulk rotor temperature, just like LFS does currently with the tyres?

I would've thought such a dense material would conduct heat rather well, and have a pretty even temperature throughout.

The Rotor may be an excellent conductor of heat, and have a roughly even temperature through out, but green fade (i think this is the right term, the one where little bits of pad get vapourised from the compound and make a gas which stops the pad contacting the rotor so much) would require modelling the pad surface, pad body, and rotor temps at the very least.

If the pad is too hot for too long that would impart heat to the caliper, and in turn boil the brake fluid, resulting in another kind of brake fade.


So you'd need atleast fluid, pad body, pad surface, rotor temp, and a cooling rate for each of those (dependant on the speed of the vehicle). You would also need pad wear, and disc wear.

The second section of the attatchment points out that if the pad experiences too much braking force on the disc without locking up, then it wears VERY rapidly. Concequently it should be possible to overheat the brakes making them very hot, but brake amazingly for a while, before the pad wears down super fast.

I wonder how far they're going to go with the simulation.

In the future, will your rear brakes seize if you leave the handbrake on after a hotlap?

In cars with rear disc brakes, the handbrake is usually a set of drums inside the hats of the brake discs. Speaking from experience, if you cork about with it partly on, or, do a lot of yanking while its running,

The shoes just wear down to nothing, and dismount from their assemblies.

Then you buy new pads and discs at the rears, and a new rear brake innards kit (to replace the mangles assembly), and some new brake shoes.

Then you stop being a complete tonk, and realise, no, you are not the stig, and that yes, this car has to get you to unversity every day!

/offtopic

on topic : I can't find any figures for the thermodynamics of drum brakes, no any rates at which heat dissipates. Guess the UF1 and the XFG will have to go in the bin - nevermind, they're both wrong wheel drive.

Quote from z3r0c00l :

The Rotor may be an excellent conductor of heat, and have a roughly even temperature through out, but green fade (i think this is the right term, the one where little bits of pad get vapourised from the compound and make a gas which stops the pad contacting the rotor so much) would require modelling the pad surface, pad body, and rotor temps at the very least.

If the pad is too hot for too long that would impart heat to the caliper, and in turn boil the brake fluid, resulting in another kind of brake fade.


So you'd need atleast fluid, pad body, pad surface, rotor temp, and a cooling rate for each of those (dependant on the speed of the vehicle). You would also need pad wear, and disc wear.

The second section of the attatchment points out that if the pad experiences too much braking force on the disc without locking up, then it wears VERY rapidly. Concequently it should be possible to overheat the brakes making them very hot, but brake amazingly for a while, before the pad wears down super fast.

Green fade is when the 'fluids' in the pad, from the manufacturing process, boil out of the pad when first used hard. It's quite scary - I had it happen earlier this year bedding in brakes in practice. But once it's done, it's usually done, and I think we can assume that LFS pads have been bedded in properly.

Pad Fade - where the temperature goes out of the operating range of the pad - is easily modelled by comparing the pad temp to a graph of FC vs heat.

Fluid Fade - where the boiling point of the brake fluid is reached - is also reasonably easily modelled based on cooling ducts, rates of dissipation (which may vary with speed) etc etc. But 99% of race cars won't suffer from fluid fade. Road cars can though, but pretty much only on a track (or a mountain pass, going down).

Ah right, thank you for that clarification

I've started buying pre-bedded pads, little bit more money, but it saves the guesswork trying to settle them in right, and it means you can get bedded pads for the rear, something you can't do without a brake bias adjustor valve in a "normal car".

I've been in the car with my cousin (he does the odd rally stage) coming down Box Hill, and he cooked his brakes, we slowed down off the 60 at the bottom to the rounderbout, and they promptly caught fire. That was a Mk2 Golf though... not even the GTI, think that counts as a road car!

I've been keeping up with your reynard site btw, looks to be the best fun I never had!

Pre-bedded pads? Is that wise? I thought bedding in was two fold:

1. To ensure the pad material is in optimum condition for braking
2. To ensure the surface of the pad follows the contours of the disc.

But then, I suppose you fit a pre-bedded pad, and the contours get worn in quickly anyway.

I also recently saw (possibly on an Exige site, I can't remember) someone say that bedding in also 'fixes' some pad material onto the disc. But I don't believe it myself.

I like this discussion, so I thought I would throw some of my own experiences onto the fire.

Bedding processes and results will vary from brand to brand. Recently, I switched over to Carbotech pads for track usage, and they provide specific directions for bedding them properly. This process includes both the pads and the rotors.

In these particular pads, there was certainly a 'green fade' that caused quite a large amount of smoke to come out after getting them up to temperature. Following the requisite cool-down, they performed flawlessly on track, hauling the car down for a long sweeper and hairpin over and over.

As far as the rotor half of the equation, they do mention in the literature that there is an amount of material transferred from the pad to the surface during the bed in. To maximize your benefit, they recommend either brand new rotors, freshly turned (if you used a different brand prior) to expose a new working surface or simply use a rotor that has already had the same brand of pad bedded in to it.

Following the bedding, the rotor had picked up a grayish tinge, which is the same colour as the pad.

Does anyone else here have experience with other brands that can shed some light?

I change pads and rotors over at the same time.