FLY-BY-WIRE BRAKES

F1 Racing - - INSIDER - Pat Sy­monds ex­plains

We’ve heard the ex­pres­sions ‘fly by wire’, ‘drive by wire’ and now ‘brake by wire’. Gener­i­cally, what do they mean?

The use of the term ‘by wire’ gen­er­ally means that an ac­tu­a­tor, be it on the ailerons of an air­craft, the throt­tle of a car, or, in this case, the brakes, is ac­tu­ated by a de­vice that is un­der the con­trol of a com­puter.

Drive-by-wire throt­tles have been with us for many years and are an easy way of ex­plain­ing the tech­nol­ogy. In this ex­am­ple, a po­ten­tiome­ter is con­nected to the throt­tle pedal. The po­ten­tiome­ter is a sim­ple elec­tri­cal sen­sor that mea­sures the ex­act po­si­tion of the pedal. This po­si­tion is fed to the com­puter in the ECU, which cal­cu­lates what torque the driver is de­mand­ing with the pedal and pro­vides it in the best pos­si­ble way. Of course, the pri­mary means will be to open the en­gine throt­tles, and this is done by an ac­tu­a­tor, which may be elec­tri­cally or elec­tro-hy­drauli­cally driven. The elec­tri­cal wiring con­nec­tion be­tween the pedal and the ECU and that be­tween the ECU and the ac­tu­a­tor gives rise to the ex­pres­sion ‘drive by wire’.

Aren’t elec­tronic sys­tems in­her­ently more un­re­li­able than me­chan­i­cal sys­tems?

No. They may be more com­plex and there­fore have more po­ten­tial points of fail­ure, but they are ac­tu­ally more re­li­able in the long term.

They also al­low for smarter con­trol. With an old-fash­ioned throt­tle ca­ble, the po­si­tion of the throt­tle was de­ter­mined by the po­si­tion of the driver’s foot. With mod­ern sys­tems this can be over­rid­den dur­ing, for ex­am­ple, a gear shift. In terms of re­li­a­bil­ity, if a ca­ble broke, the car stopped. With elec­tronic sys­tems, an el­e­ment of re­dun­dancy can be eas­ily built in by hav­ing two tracks on the po­ten­tiome­ter. Soft­ware then au­to­mat­i­cally de­tects if one fails and switches to the sec­ond with no loss of per­for­mance.

Why has ‘brake by wire’ come in for 2014?

The 2014 pow­er­trains’ com­plex hy­brid sys­tems rely heav­ily on en­ergy re­cov­ery through brak­ing. Es­sen­tially, an elec­tric mo­tor and an elec­tric gen­er­a­tor are the same thing. If the ar­ma­ture of an elec­tric mo­tor is turned, it pro­duces elec­tric­ity; if elec­tric­ity is ap­plied to the ar­ma­ture, it will ro­tate. This prin­ci­ple is what the en­ergy re­cov­ery and en­ergy re­lease of a hy­brid ve­hi­cle is all about. How­ever, the re­cov­ery of ki­netic en­ergy and con­ver­sion to elec­tri­cal en­ergy doesn’t come for free. As a gen­er­a­tor pro­duces elec­tric­ity it pro­duces a drag that acts like the brakes on the car. If this drag were con­stant then there would be no prob­lem, but the elec­tric­ity pro­duced by the gen­er­a­tor is stored in a bat­tery.

This bat­tery must not be over­charged, so as the bat­tery reaches full charge, the gen­er­a­tor is shut down. Since this is in­di­rectly con­nected to the rear wheels it has a ma­jor ef­fect on the brak­ing ca­pa­bil­ity of the rear axle. In ad­di­tion, there is a hard limit as to how much en­ergy can be re­cov­ered by the sys­tem and when this limit is reached then the re­cov­ery is also switched off.

The brake-by-wire sys­tem is de­signed to en­sure that, as the elec­tri­cal en­ergy re­cov­ery is switched in and out, the ap­por­tion­ing of brak­ing en­ergy be­tween the elec­tri­cal ‘brake’ and the hy­draulic brake is man­aged in a way that does not dis­turb the car or driver.

Why wasn’t this nec­es­sary with last year’s ki­netic re­cov­ery sys­tem (KERS)?

It would have helped last year, but since the 2013 KERS was only 60kW it was not pow­er­ful enough to cause ma­jor prob­lems. For 2014 this power was in­creased to 120kW, which rep­re­sents a signicant amount of brak­ing power.

So how does the new sys­tem work?

It is a com­plex sys­tem but, in essence, the pres­sure in the front brakes is con­trolled en­tirely hy­drauli­cally in re­sponse to the driver’s pres­sure on the brake pedal, while the rear brake pres­sure can be modied by the con­trol sys­tem to achieve a con­stant brake bal­ance ir­re­spec­tive of the state of the rear-axle en­ergy re­cov­ery sys­tem. Safety is al­ways para­mount, and even though the rear brakes are sub­ject to elec­tronic con­trol, they al­ways have a di­rect hy­draulic con­nec­tion so they will al­ways slow the car even in the event of a fail­ure of the elec­tron­ics.

As the en­ergy re­cov­ery sys­tem switches on to re­cover en­ergy, the brake-by-wire sys­tem will de­crease the pres­sure in the rear brakes and, as the re­cov­ery sys­tem switches off, the brake-by­wire will al­low the full hy­draulic pres­sure to be ap­plied to the rear wheels.

Are there changes to the brake sys­tem it­self?

Yes. Since the en­ergy re­cov­ery sys­tem is do­ing so much more of the work of brak­ing, it has been pos­si­ble to t smaller rear brakes. The large six-pis­ton rear cal­lipers that were ubiq­ui­tous in pre­vi­ous years have now been re­placed by small four-pis­ton cal­lipers. In ad­di­tion, the com­plex me­chan­i­cal sys­tems that used to be em­ployed to shape the brake bal­ance curve as a func­tion of brake pres­sure have now been re­placed with much more sim­ple elec­tronic map­ping.

How does the brake-by-wire sys­tem af­fect the feel of the brakes?

The sim­ple an­swer is that if it is work­ing per­fectly, the driver should feel noth­ing as the con­trol switches in and out. In fact, the sys­tem should im­prove sta­bil­ity un­der brak­ing and a pleas­ant by-prod­uct of the lay­out is that the brake pedal now has much greater stiff­ness, be­cause it is not ex­posed to the com­pli­ance of the rear brake lines.

Brake-by-wire man­ages the brake ef­fort of the rear wheels and com­pen­sates for ex­tra drag caused by the re­cov­ery sys­tems as they har­vest en­ergy. Some driv­ers, such as Kimi Räikkö­nen (pic­tured) are re­port­edly strug­gling to get to grips with it

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