Brake power

[tomislavp4]

Guys I wonder in what measure do you measure the brakes stoping power? N or something? And how big is it in an f1 car? If you have some information I´d liuke to hear it, thanks

[Belatti]

How big is it in an f1 car?
Thats a difficult one, I have no info, but lets see:

1- we have got an x pressure [psi, kgf/cm2] in the hidraulic line
2- supposing that hydraulic pressure is effectively transmited to brake pad (6 piston calipers in the middle, I think)
3- pressure transmited to brake pad * brake pad area = force transmited to the disc [N]
4- force transmited to the disc * disc radius = "stopping momentum"

5- this "stopping momentum" is transmited to the tyre (tyre radius) and we have got breaking force, we have to make this = to what the tyre can handle just a fraction before locking (this is maximun when braking at high speed due to downforce)

6- To calculate this maximun we should have some input data like: how much does the car decelerates in the first fraction (the fraction depends on the accuracy of the calculus, the speed first derivate would be ideal data here but who dares to approximate an ecuation there??? , with telemetry speed vs time graphic will be enough for an overall -4 wheel- calculation)

Overall:
stopping momentum / tyre radius = car mass * negative acceleration

individual:
individual tyre stopping momentum / tyre radius = friction coeff * normal load (max downforce)

and max downforce = weight + mass transfer the fraction we have selected + aero downforce

As you see, I need some data I don´t know, maybe can find and some data and we have to suppose some other. Tons of simplifications here (homogeneous load distribution in the piston-caliper-pad and tyre-ground, cog position to calculate mass transfer, etc)

[modbaraban]

And how big is it in an f1 car?

Dimensions

Length: 4545 mm
Width: 1796 mm
Height: 959 mm

[riff_raff]

As the old saying goes: "the brakes only stop the tires; the tires stop the car". You can't brake any harder than the instantaneous traction coefficient of the tires allow. The limit of the braking system itself is generally defined by how efficiently the brakes can absorb and dissipate the heat energy created by friction. The friction heat being a conversion of the kinetic energy of the moving vehicle.

As the brakes are applied, the brake pads and rotor will heat up. The rate at which is a function of the mass of the components, and the component material's specific heat. To keep the components from over-heating and experiencing structural failure, the maximum temperature they see must be kept within acceptable limits thru air cooling. CRC brake pads and rotors have excellent high temperature strength properties, but they still have limits.

[tomislavp4]

Thanks guys, lots of info
I wanted to know because from PML claim their motors with regenerative braking are as good in braking as the brakes in high performance saloon...which I have hard time believing in They have torque at 500Nm at each wheel. Your toughts?

[riff_raff]

tomislavp4,

Brakes absorb power, not torque. So that 500 Nm figure you quote is meaningless, unless you also define the time or rate value associated with it.

Of course, braking systems must also dissipate (or be capable of absorbing without failure) all of that braking energy. Battery/electric regenerative systems have typically very low capture efficiency (ie. <10%), because the chemical battery cannot absorb the electrical power at the same rate as the generator produces it. It will overheat and explode if it does.

The KERS system works because it stores that braking energy as inertia in a flywheel. KERS can absorb (and discharge) braking energy as fast as the CVT drive system can adjust its speed.

[Mikey_s]

Just to add some support to the comments from Riff-Raff,

the purpose of the brake is to convert kinetic energy into heat by friction. It does this by applying a retarding force onto the brake disc, so there is a torque element to it (bigger discs = better retardation, longer lever).

A quick calculation will give you a feel for the numbers and they are really quite extraordinary; F= 1/2 M.V^2
A big 'stop' will dissipate several megajoules in a very short time - I was at Spa last September and I noted that the drivers were not hitting the brakes at La Source hairpin until somwhere between 75 and 50m before the turn... scrubbing off some 200km/h... that's a lot of heat to dump in a very short time

... anyone else like seeing red hot brake discs? (I love it)

[bar555]

Just a small correction
E=1/2 M*V^2
M=mass (matter)
V= Velocity of the vehicle

E=Kinetic energy

ΔΕ= 1/2 Μ*(V2-V1)^2
V2=Velocity after braking
V1=Velocity before braking
So the ΔE is the amount of energy converted into heat by friction . The majority of heat is produced on the brake discs but a signifficant amount on the tyres (front especially ) too . That is why tyres are heated by breaking

[Reca]

A rough idea of the peak power a F1 braking system is capable of comes from knowing basic data about a particular braking, starting speed and peak deceleration plus mass of vehicle. These are enough since the definition of power is force times velocity, hence mass * acceleration * velocity.
That’s the power required to achieve a certain acceleration, or deceleration in our case, that is generated by brakes and aero drag.
The latter is clearly equal to engine power (times transmission efficiency) minus the power required by tyre rolling resistance, and as a first order approximation we can assume it’s around 600-650 hp or thereabout (but we’ll see later that an error of even 100 hp while guessing engine power doesn’t really change by much the end result given we’re looking at a rough estimate). Subtracting this power from the one calculated above we have the power generated by the braking system.

So, to make an example, we can use the braking for last corner in Malaysia, data come from the analysis I did of Massa’s pole lap last year :
viewtopic.php?f=1&t=5307

initial speed / final speed / time / distance / avg acc. / peak acc.
303 km/h / 83 km/h / 2.93 s. / 133 m. / -2.13 g / -4.6 g

Consider mass = 620 kg (it was in q3 with a few laps of fuel)

The power required for that braking is = 620 [kg] * (4.6 * 9.81) [m/s2] * (303 / 3.6) [m/s]= 2355 kW

Assuming engine power devoted only to aero is 650 hp = 485 kW, we have that the power the braking system is generating in that particular case is roughly 2355 – 485 = 1870 kW about 2500 hp.

That’s quite impressive especially if we consider that it isn’t the most demanding braking of the calendar, as the ones usually regarded as such are the hairpin in Montreal and the Monza’s chicanes where speed is in excess of 330-340 km/h and peak deceleration gets closer to 5 g, meaning peak power exerted by braking system is around 3000 hp if not more.

ΔΕ= 1/2 Μ*(V2-V1)^2

surely you mean ΔΕ= 1/2 Μ*(V2^2 – V1^2)

[riff_raff]

This is turning into quite an interesting and informed thread.

The total braking capability of an F1 car does not just involve the brakes. The car is also slowed through engine braking, with the engine essentially acting as a big pneumatic absorber.

Also, as I mentioned, the brakes are only as effective as the traction capability of the tires. The brakes are capable of easily locking up the tires at any speed. Any aero downforce produced during braking will increase the traction capability of the tires, and thus increase the braking rate.

[Mikey_s]

Rif raff,

of course you are correct; in addition to engine braking there is also aerodynamic drag - and, like most things, the more one starts to think about it the more complex it becomes;

At the highest speed the aero drag and engine braking will be significant. The downforce will also be at its highest, permitting the driver to apply maximum braking effort without locking up the tyres. As the speed reduces the downforce also reduces, therefore the braking effort will need to be reduced accordingly.

One of the areas I find interesting is the way in which all the factors interplay. At the end of a long straight the brakes will be at their coolest and therefore the efficiency of the system will be relatively low, Shortly after hitting the brakes the temperature of the disc and pads will skyrocket, efficiency will increase and the speed will reduce; as this happens the cooling ability is falling due to less air being farced through the disc as a result of forward motion. Heat sink issues will be transferring heat to the calliper, which will be heating the brake fluid up to close to boiling range, and this is where a poorly set up car will start to notice the pedal becoming long.

There are a bunch of compromises that the engineers will need to optimise to ensure that the brakes work throughout the race without compromising aero efficiency or safety.

btw; anyone have an idea why we have seen a disc failure at each of the two GPs this season when I am trying hard to think of another one since Trulli blew one spectacularly at Montreal in 2005? - lack of engine braking perhaps?

[checkered]

btw; anyone have an idea why we have seen a disc failure at each of the two GPs this season when I am trying hard to think of another one since Trulli blew one spectacularly at Montreal in 2005? - lack of engine braking perhaps?

That's a good

call, I think you're onto something there. I don't think anything re: the brakes themselves has changed from last season - engine braking is the notable variable. Furthermore the current Bridgestones have prompted all teams to shift the CoG/CoD forward over a longer period already, something that is perhaps exacerbated by the need to rein in an unrulier rear. At Sepang, Hamilton's right front (the one that caused grief) released plumes of fine CF dust, I half expected that one to fail as well. Some drivers have referred to the "window" of performance having gotten very much narrower. Nico has said this on several occasions and reflecting that on your notions (and in the light of Williams' very veried performances over two tracks) I have to wonder whether or not there's an overall increased possibility for a conflict of interest between managing the tyres and managing the brakes?