A frac­tion too much fric­tion . . .

Whangarei Report - - DRIVEN.CO.NZ -

There’s lots of physics in­volved in a mov­ing car . . . weight, mass, speed, fric­tion, en­ergy and some other techie stuff.

Ge­om­e­try is there as well with pitch, roll and yaw — and you thought you’d never need maths.

All those forces and ac­tions are ap­plied to just four smart­phone­sized patches of rub­ber between you and the road and as the driver, you have the most con­trol over just one of them with your right foot.

Too much speed, brak­ing at the wrong time, sharp turns or slip­pery road con­di­tions are just some rea­sons that can cause those small patches of rub­ber not to cope.

Then came the en­gi­neers who in­vented anti-lock brak­ing sys­tems (ABS), which does what its name sug­gests by pre­vent­ing the wheels from lock­ing when you brake and al­low­ing you to steer the ve­hi­cle while safely bring­ing it to a stop.

Elec­tronic Brake­force

Dis­tri­bu­tion (EBD) goes a lit­tle fur­ther than ABS with a col­lec­tion of sen­sors that de­tect what im­pact all the var­i­ous forces have on the car and then con­trol the level of brak­ing on each wheel.

Typ­i­cally, the front end of a ve­hi­cle will carry the most weight so the EBD ap­plies less pres­sure to the rear brakes, stop­ping them lock­ing and caus­ing the car to skid.

EBD in con­junc­tion with ABS

Un­der heavy brak­ing with­out ABS and EBD, the wheels will typ­i­cally lock and the fric­tion cre­ated between the road sur­face and the tyre will slow the car to a stop.

This usu­ally isn’t a prob­lem on a straight dry road, but add in a bit of rain or a slip­pery sur­face like gravel, ice or snow, and the stop­ping dis­tance has to in­crease.

If the wheels lock up on a cor­ner, the an­gle that the front wheels are turned be­comes ir­rel­e­vant as the car’s mass opts for a straight line, which could mean cross­ing the white line into on­com­ing traf­fic, find­ing a ditch or meet­ing a tree.

When you bring ABS into the pic­ture, the sit­u­a­tion im­proves sig­nif­i­cantly by pre­vent­ing the wheels from lock­ing and bring­ing the ve­hi­cle to a stop in a more con­trolled way.

Con­trol of the car re­lies on its wheels con­tin­u­ing to turn and this is where EBD helps.

Un­der heavy brak­ing, sen­sors mon­i­tor wheel speed and re­lease pres­sure on in­di­vid­ual wheels. Mod­ern sys­tems have in­di­vid­ual brake lines to each wheel and can com­pen­sate for fric­tion changes on dif­fer­ent road sur­faces. Less brake pres­sure is needed to lock a wheel on icy or gravel roads, com­pared to tarsealed sur­faces.

EBD in con­junc­tion with elec­tronic sta­bil­ity con­trol (ESC)

EBD can also work with ESC to ma­nip­u­late the speed of ac­cel­er­a­tion when cor­ner­ing.

In most cases, taking a cor­ner at speed will lead to un­der­steer­ing, when the nose doesn’t swing around as much as you ex­pect, or over­steer­ing, when the car turns quicker than in­tended, po­ten­tially forc­ing the back end to slide out.

To avoid this sce­nario, ESC em­ploys some­thing called a yaw rate sen­sor to de­tect the an­gle of the steer­ing wheel and the di­rec­tion the ve­hi­cle is turn­ing.

If the yaw sen­sor de­tects over­steer or un­der­steer from dif­fer­ent an­gles between the steer­ing wheel and the tyres, ESC will ac­ti­vate one of the front or rear brakes to ro­tate the car back on to its in­tended course.

ABS brak­ing helps pre­vent wheels from lock­ing and EBD ap­plies the ap­pro­pri­ate brake force to al­low ESC to work.

Com­bined with safe driv­ing, these safety as­sist tech­nolo­gies are help­ing to pre­vent crashes and man­u­fac­tur­ers con­tinue to them.

Al­though this tech­nol­ogy is re­li­able, it is only as good as the sen­sors that en­able it to work. If you see a warn­ing light on your dash­board, get your car in­spected as soon as pos­si­ble.

Photo / Sup­plied

Safety as­sist tech­nolo­gies are con­tin­u­ally be­ing im­proved.

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