Friday, November 27

How Modern F1 Cars Cope With Brake Busting

MONTREAL, Canada–Ask any junior formulae driver who gets to test an F1 car for the first time what the most impressive thing is, and most of the time they will say it’s the brakes.  Considering the F1 car’s near 1000hp and +4g cornering performance, it’s the +5g braking performance that gets all the attention.  Achieving this incredible feat, stopping the car from 200mph in just a seconds, is a complex mix of down-force, mechanics, and electronics.

Performance

A current F1 car’s braking system is made up of the brake discs, calipers, pedal and master cylinder – all linked by pipework and with a brake-by-wire unit controlling the rear brakes.  Despite the deceleration available, the brakes are heavily regulated to limit their ability to deliver even greater performance.

Slowing the car from 210mph approaching the 13th turn around the Montreal’s Circuit Gilles Villeneuve, the driver will brake for just 2.09 seconds slowing to 83mph in a mere 122 meters, which is about 20 car lengths!  In order to achieve this amazing feat, more is required than just the brakes, it needs the wide Pirelli slick tyres for the traction, plus huge amounts of down-force and powerful leg muscles.

It’s only possible to get this 5G performance because the car has so much grip at the tyre contact patch. To make the best of the braking potential available, most effort is required at the start of the braking event, when down-force is the highest. The braking effort from the driver is not quite on/off, as they will need to ease back on the pedal as the down-force decreases with speed, in order to balance the retardation with the grip available.

This blend of down-force, tyres and braking system makes F1 cars the most efficient decelerating race machines in motorsport.

Discs and Calipers

Everything depends on the bite of the brakes on the discs, so F1 cars run carbon discs and pads with aluminium six pot calipers.  Carbon fibre is used for two main reasons and it’s not the myth about steel brakes being less powerful.  Fundamentally, carbon fibre is lighter than a steel disc, but it also copes with running at high temperature better than steel.  Having first appeared on aircraft, with the technology being introduced to F1 by Gordon Murray at Brabham in the early eighties, the compromise with carbon discs is the cost.  Anything lighter on an F1 car is worth the cost, so carbon disc brakes have been the de facto choice since the early teething problems were worked out in the eighties.

Over this time, the disc and pad pairing has been rapidly developed. They are both made from the same friction material and thus both wear out at similar rates.  Maintaining a working temperature has been the challenge with these brakes – too cool (<300c) and the brakes don’t bite as hard, too hot (>1000c) then the material oxidizes and wear increases.  Keeping heat in the brakes is achieved with the careful sizing of the brake ducts, and this is less of a problem.  However, overheating is a much greater issue. If the brakes are run white hot for too long, the oxidization will wear the disc too thin and the disc can fail catastrophically. Initially, radial cooling holes similar to steel discs were run.  As teams were able to exploit the brake materials even more, they needed more cooling, so the number of cooling holes increased commensurately.  From 100 in 2005 to some 1500 in 2019, the cooling holes are at the point where any more would structurally weaken the disc too much.   This limitation is based on the rules that the disc must only be 32mm thick and capped at 278mm.  These rules work to prevent even more powerful and expensive brakes, while also allowing them to be fitted inside the regulation sized 13” wheel rim.  At this size, the brake disc weighs just 1200 grammes!

In first practice, a new pair of discs/pads will be bedded in, then removed and reused as the qualifying\race brakes.  Meanwhile, a used set will be fitted for the rest of free practice which gives the parts a life of just 500 miles!  Brake material is supplied to the team by two key suppliers; Brembo and Carbone Industrie.

The disc mounts the axle via an intermediate ring, known as a disc bell.  This is a precision-machined part that matches the inner splines on the disc and the corresponding splines on the axle.  The splines do the majority of transferring the torque from disc to axle, although bolts are also used.  These are limited as the hole for the bolt invites stress into the assembly.  Teams may manufacture their own disc bells or the brake manufacturer may do so. Either way, the precision is crucial to prevent stress occurring which may see the disc or the bell fail.

Cooling for the disc is routed around the upright in carbon fibre ducting and into the cooling hole son the inside of the disc.  Every team has their own method of achieving this, either ducting direct to the disc or routing air through channels in the disc bell then into the disc.

Gripping the disc is the caliper, again a heavily regulated part, to limit its potential performance.  Current F1 calipers are limited to one per corner, six pistons, two mountings and made from aluminum based alloys.

Despite these limitations, iterative design sees the caliper as stiff for ever decreasing weights, the use of Finite Element Analysis (FEA) software packages being critical to the caliper body design.  Equally, the thermal stress on the caliper is researched with simulation tools. Heat builds up in the caliper body as the disc runs through the central channel, making the caliper hottest near the last of the opposing piston pairs.

Luckily, the need to cool and lighten the caliper sees the body skeletonized, with drillings and openings around the piston bores to save weight and reject heat.  Even the pistons have a ring of radial drillings to cool the piston and brake fluid behind it from the heat of the carbon friction material at work.  Likewise, the carbon brake pads can have drillings to try to insulate the caliper from the heat.

Made from aluminum lithium alloy, or other aluminum alloys with a stiffness limit of 80Gpa, the caliper body is machined from solid.  Brembo is currently the dominant manufacturer and AP racing are also a common supplier, while 920e supply Racing Point and Akebono supply McLaren.

Although six piston calipers are demanded by the rules, teams can run smaller numbers of pistons.  Since the 2014 rules exploited more braking from the ERS-K, the rear brakes are hardly required at some circuits, only when initial braking is high is the caliper used to brake – the rest of the braking effort coming from the regenerative braking effect.  So, teams can run four piston rear calipers to save some weight, and balance the effort and cooling required from them.

Source: MotorSport–To read more, go to this link.

 

 

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David Kiley is Chief of Content for The BRAKE Report. Kiley is an award-winning business journalist and author, having covered the auto industry for USA Today, Businessweek, AOL/Huffington Post, as well as written articles for Automobile and Popular Mechanics.