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Practice English Speaking&Listening with: F1 Braking Systems

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Formula 1 cars can come to a stop from 100 km/h in about 15 metres, which is almost a

quarter of the braking distance of your average road car. They can go from 300 km/h to a complete

stop in under four seconds, pulling up to 6G of deceleration force.

With such high speeds and tough corners, F1 cars need to be able to produce massive braking

forcesnot just for performance but for safety as well. A driver needs to know the

car will respond when they press the brake pedal, and not cream into a wall or the back

of a competitor. Lets look at the braking system of an F1

car as a whole before we dive into the individual components.

When the driver hits the brake pedal, it transmits a force to two master cylinders. One cylinder

controls rear braking and the other front braking. Lets focus on the front braking

to start with as its much simpler. The master cylinder acts on brake callipers

which squeeze brake pads onto the brake discsthis hard friction between the brake pads

and the discs slows the car down. Lets take a closer look at those components

then. These master cylinders are filled with brake

fluidjust a couple of hundred milliletres worth. The fluid fills brake lines that run

from these cylinders to the brake callipers, acting as arteries of the braking system.

Fluid is incompressible, so when the pedal is pressed and the plunger is pushed into

the cylinder the fluid immediately puts forces on the other ends of the brake line. This

is how hydraulic systems work. The brake callipers are like clamshells around

the brake discs and house brake pads within each side of the shell.

The hydraulics feed into pistonsno more than sixwithin the callipers; these pistons

push the brake pads into the brake discs. As the brake discs are attached to and spin

with the wheels, when the pads clamp on the wheels, the frictional force between them

will slow the spinning of the wheel and ultimately the speed of the car.

The callipers themselves are often mounted low on the discs to keep centre of mass low,

but tend to be placed closer to the 5 or 7 oclock position rather than lowest 6 o

clock position. This is partly because the bleed nipple needs to be fairly high.

A bleed nipple?’ you asked with horror in your eyes. Well, remember when I said fluid

was incompressible and that was what allowed pedal force to instantly translate to the

brakes? Well sometimes air bubbles can get into the hydraulics and gas is compressible.

So when the brake pedal is pushed, the gas in the hydraulic system can deform, reducing

the braking force at the other end. To flush this gas out, you can open the nipple

andas its placed high up, the gas will rise more readily to the top and be flushed

out when you force fluid into the system. Youll often bleed the system between sessions

to be on the safe side. Onto the actual brake pad and discs, then.

The brake discs cannot be larger than 278 mm (11 inches) in diameter [USE SCHOOL RULER]

or 32 mm thick. A larger diameter means greater stopping power as its easier to stop a spinning

disc by grabbing it further from the pivot point than closer to the centre. The restriction

of the rules in this area is to limit the braking power of the car so braking zones

can remain somewhat competitive. Unlike the steel-type brakes on modern road

cars, F1 brakes are made of a special carbon composite called, hilariously, carbon-carbon.

Its called this because its two types of carbon composited togethera carbon

lattice like graphite reinforced with carbon fibres.

Carbon-carbon is strong, can withstand very high temperatures and has a very high coefficient

of friction. The coefficient of friction of a material just tells you how well a material

grips when rubbing against another materialice, being slidey has a low coefficient

of friction; rubber, being not slidey as all,has a high coefficient of friction.

Carbon-carbon also has a very low thermal expansion and low thermal shockmeaning

it wont deform or crack suddenly under high temperatures. This ability to stay robust

under high temperatures is incredibly important. The way brakes slow tyres down is by converting

energy. The kineticor moving energyof the spinning wheels is converted by the braked

into heat energy. As the brake pads grip the discs, the high

frictional forces turns the energy of the wheel into tremendous amounts of heat.

A cold brake can heat up by as much as 100°C every tenth of a second in the initial phase

of braking. Carbon brakes work optimally between 400°C

and 800°C, though heavy braking can often push brakes to 1000°C or 1200°C.

Brakes being overly hot causes two real problems: Oneif the brake is already hot it has

less ability to absorb heat and therefore take energy from the wheels. If, under braking,

the brake disc rises from 300 to 1000°C its acting as much more of an energy pump than

if it could only move from 800 to 1000°C. Twothe main driver of brake wear is thermal

degradationwear due to temperature. At high temperature, the carbon will readily

oxidise, which is essentially burning at its surface layers.

In excessive wear or prolonged overheating, carbon deeper within the brakes can oxidise

and weaken the structural integrity of the brakes which is why worn out brakes start

to disintegrate to dust. In worst cases, the brakes can simply explode.

So, the temperatures of brakes need to be carefully managed if they are going to late

a race distance and as fluid cooling is banned, the engineers use good old air cooling to

solve this problem. The premise of air cooling is simple and exactly

the same as using a fan to cool yourself off on a hot day: By using a stream of fast flowing

airheat will transfer from a hot surface to the air molecules passing by, which will

carry this heat away from the hot body. As a car moves quickly through the air, brake

ducts channel some of the cooler air stream into the brakes to do this job.

To further improve air cooling, the brake discs themselves are ventilated. Narrow channels

run through the brake disc from the centre to its circumference.

As the brake disc spins, cool air is force from the centre out through the brakes and

away from the system, carrying brake heat away downstream.

Over the years these channels have reduced in size but increased in number, providing

greater overall volume for channelling air. Now larger drake ducts can be more of an aerodynamic

drag but the difference in top speeds between using larger brake ducts and smaller version

are only a couple of km/h. A greater reason from adjusting the size of

the ducts is more to do with the braking nature of the circuit. If youre having to brake

a frequently and/or heavily, the brakes will need more intensive cooling as you arent

coming off the brakes as often and giving them enough time to lose their temperature.

You dont want to keep heading into braking zones will the brakes at 800°C.

So larger brake ducts will more intensively cool the brakes in the periods between braking

zones. On the other hand, the brakes dont actually

work very well when they are cold. You ideally want them at at least 400°C when you hit

the brakes. If youre not braking very often on a circuit, so there are long periods of

time between braking zones for the brake temps to come back down, youll probably opt for

smaller brake ducts so they dont lose too much temperature.

When you hit the brakes at cold temperature, the brakes can take a few hundredths or even

tenths of a second to kick in properly, which isnt ideal.

The other interesting problem to manage is that of feeding the thermal degradation problem.

As I said, at high temperatures, the carbon oxidises. This means the carbon atoms bond

with oxygen atoms in the air, forming carbon monoxide or carbon dioxide.

Now, the brakes take a while to cool down and all the time they are at a high temperature,

they are still ripe of oxidation. And all this while the brake ducts are feeding the

carbon more and more air, including oxygen, which can accelerate the process. A tricky

problem. Youll often see engineers blanking off

brake ducts withaptlyduct tape if the ducts seem to be feeding too much air

into the brakes either temperature or degradation-wise. So thats the simple end of the braking

systemthe front brakes are powered by a straightforward hydraulic system.

The rear endthats more complicated. Since the hybrid power unit was introduced,

the MGUK is a significant part of the system that slows down the rear wheels. This duty

is now shared between the brakes and the MGUK. To manage this effectively, the rear brakes

are not operated by a simple hydraulic system but by brake-by-wire.

A brake-by-wire system (sometimes obliviously referred to as BBW) means the physical action

of the brake pedal is not directly attached to the physical action of the brake callipers.

Instead, theres a computer in between telling the brakes what to do.

The MGUK can take up to 2 mega joules of energy from the rear wheels per lap. How much energy

the MGUK harvests under braking at any given time is decided by things like brake pedal

pressure, harvesting settings and battery level. The rest of the deceleration is performed

by the actual brakes. The Electronic Control Unit (or ECU) is fed

live info constantly, calculating and delivering exactly how much work the physical brakes

and MGUK perform in decelerating the car when the brake pedal is pushed.

Any excess hydraulic pressure not used to brake the car is automatically fed back into

the system via a release value. This all happens on the fly and is incredibly

sophisticated and, while all this is going on, it has to feel like real braking to the

driver. Now, because the rear brakes dont have

to do as much work as they are sharing the load with the MGUK, the brake discs themselves

are a lot smaller than they previously were. But if theres a failure of the MGUK and

brake by wire system, the rear brakes will have to do all the work and this is suddenly

a massive problem. Larger discs can manage and dissipate heat much more efficiently than

small discs which overheat very quickly. This happened to Ricciardo in Monaco after

his MGUK failure so he had to move the brake bias forwards to take the load off the rear

brakes. Brake bias (or brake balance) sets how the

braking force is shared between the front and rear of brakes when the pedal is pushed.

Ideally you want each brake doing the exact amount of work necessary for the weight load

its managing. At rest an F1 cars weight is distributed roughly 45:55i.e. 55%

of the weight is supported by the rear tyres. But under heavy braking, the weight shifts

forward to as much as 55:45, so youll tend to end up setting a brake bias to about 55%

frontwards. Too much front brake bias and the fronts will

grip too tightly and lock the wheels, causing heavy understeer.

Too much rear bias and the back wheels can lock and cause the car to become unstable

and spin. Ideally, you want all of you brakes to each

deliver their maximum force and, if you pushed slightly too hard, all wheels should lock

in unison. But erring on the side of front bias is wise as a lock up of the front at

least keeps the car stable, not throwing it into a spin.

Drivers can adjust brake bias between corners from within their cockpit but this is only

allowed while the car is off the brakes. F1 brakes are a complicated technology with

the potential for phenomenal stopping power. With such state-of-the-art materials and design,

half the battle continues to be managing brake temperature and bias throughout each session

to keep degradation at bay and try to ensure the brakes are in the perfect temperature

region into every braking zone.

The Description of F1 Braking Systems