Why must brake pads and rotors wear out?

[FreeForAll]

I understand their job is to convert motion into heat, but can it not be done without causing wear on a regular passenger vehicle? Even if price is of no concern?

Is it just we didn't find/create the ideal materials yet, or is there a scientific reason why they MUST wear out eventually? Bonus question: If we ignore brake pads and rotors (and cost), what would be the ideal method of slowing down a passenger vehicle without the need to replace brake components for the life of the vehicle? Is an electric motor the best solution we have today?

 

[anorlunda]

Have you heard of eddy current brakes? https://en.wikipedia.org/wiki/Eddy_current_brake

They are different, and they would not wear out in the conventional sense.

But for various reasons, they are not used in many applications, so I must conclude that they are not best for those applications.

 

[AZFIREBALL]

How about magnetic fluid turbos on each wheel?

 

[DaveC426913]

I understand their job is to convert motion into heat, but can it not be done without causing wear on a regular passenger vehicle?

If you brake by having moving surfaces in physical contact with each other, you're going to get wear.
You can avoid wear by using breaking methods that do not make physical contact, as others have exemplified.

 

[CWatters]

Bonus question: If we ignore brake pads and rotors (and cost), what would be the ideal method of slowing down a passenger vehicle without the need to replace brake components for the life of the vehicle? Is an electric motor the best solution we have today?

Yes Ideally some form of regenerative braking. Put the energy back in the "tank".

However there are complicated issues... Such as what if the tank is a battery which just happens to be too full or too hot/cold to take any more energy?

 

[sandy stone]

And of course, batteries wear out.

 

[FreeForAll]

If you brake by having moving surfaces in physical contact with each other, you're going to get wear.

Is this only in the context of my example (slowing down a vehicle), or is this a general rule that any time 2 surfaces rub each other to generate heat there must be wear?

I understand how shearing off microscopic particles generates heat, I was just wondering if the same heat could be generated by having the particles vibrating, but not actually breaking off.
I'm sure if it were that simple it would be in use now, I just don't know if it's a technical reason we haven't surmounted yet, or if it's a "law" that says there must be wear.

 

[FreeForAll]

I took these answers and did a bit of research - seems like electricity is the way to go. I found out an electrical system (eddy current or electric motor) becomes less effective as the road speed drops. So if you're crawling in traffic they may not be effective. I guess this could be resolved by adding energy to the system (such as trying to turn the motor backwards). It might not make economical sense to do that, but I guess it does answer my original question. Being able to use the energy generated is a big bonus.

Magnetic fluid seems like it has no problem working at slow or even zero speeds, however I don't know what happens to this fluid as it heats up or how to make use of the energy.

 

[russ_watters]

Is this only in the context of my example (slowing down a vehicle), or is this a general rule that any time 2 surfaces rub each other to generate heat there must be wear?

Ye, my understanding (though I am having trouble finding a specific reference) is that kinetic friction and wear are two parts of the same thing. You can't have one without the other.

 

[cjl]

One nice thing about the system as it exists right now is that the majority of the heat gets dumped into the rotor, which has a very high temperature capability and is directly exposed to the air, making it very good at shedding heat. In addition, as a braking system is a key safety system for the vehicle, the simplicity is a large benefit (a backdriven electrical motor has substantially more failure modes than a hydraulic cylinder pushing pads onto a disk). Because of that, I'm inclined to say the best system for a lot of cars today is how hybrids and electrical cars do it - have regenerative braking for normal use, but still have disk brakes for emergency or maximum effort stops. Many modern hybrids and electric cars can go well over 100k miles on one set of brake pads, and over a quarter million on one set of rotors, so they've very nearly made them lifetime components already.