Cycle News is a weekly magazine that covers all aspects of motorcycling including Supercross, Motocross and MotoGP as well as new motorcycles
Issue link: https://magazine.cyclenews.com/i/126894
(Above) Chris Meyers tests the BMW Anti Skid System on simulated wet ice at the FAG test track. (Right) The self-contained ASBS modulator with the piston assembly on the right and the li near motor in t he middle. The rea r wheel unit as it appears on a BMW K1 00; the unit was t ested in various road conditions w ith favorable reviews . BMW takes aim at anti-lock brakes By Chris Myers It's impressive: I tried a BMW Kl 00 with the two-wh eel Anti Sk id Bra ke System (ASBS) on a wide variety of tricky surfaces, including simulated wet ice, and stopped safel y each tim e. Brakin g was unca nn il y smoo th a n d acc ura te a n d full co n tro l wa s a lways maintained . A . d ' F C' S .we a r r r ve a ~ A. s test 20 track It s ta rted sn o w rng light lv r ight o n time 10 prove a real test o f ASIBS. ed th e ASBS o n di ffer ent sur' tri faces: sand o n tarmac, co b bles, ta rmac. was h board co ncre te, deep grave l a nd a p las tic su rface tha t w hen flood ed with water has a coefficien t of Iricli on o f slig h tly less th an smooth wet ice. On th e wa shbo a rd - a ser ies o f 10ng sh allowramps -the KlOO lOok a lo ng lime to stop from 60-70 m p h , hUI thi s was a severe res t since th e whee l was u p in the a ir most o f the time . Howev er , wit hou t AS BS th is would hav e p resent ed a serious problem , esp ecia ll y with a softly- sprung bik e li ke th e KI 00 . Brakin g ha rd o n wet tarma c a nd cha rg ing into dry sa nd was a sever e test : th e ASBS p rovided hard braking ·u nt il th e fr ont -wheel- hit th e sa nd, th en ra p id ly let th e pressure o ff a nd I stopped safe ly with full fo rce 01 1 the bra ke lever. Brak in g fro m we t ta rm ac to wet co b bles a nd ba ck o n 10 wet tarmac aga in present ed no probl ems even from speed s a s hi gh as 50 -fiO mph . For th~ e i test I swu c h ed . fro m a ' o r t e Ice co n ,:en tlona l bike 10 o ne whi ch had outrigger w!leel s 01.1 l.o n ~ d:!llIped a rms - bu t I wa~ stil l imposs ibl e 10 .t fa ll o ff. Braki ng dis tan ces were much I ng er, but ASBS a lways brought th e bike .to a co n tro lla ble SlOp. As m y co n fi d e nce ~~ew, I . d e l ibc ra te l y swerved from Side 10. Side as I braked a! ld a lmost uncannil y I stayed uprigh t .. . a lm o st. T he sensation wa s unique - th ere wa s enoug h braking force 10 throw th e bik e upri gh t as it rried 10 rees tablish it s normal path. On th e solo bike bra king in a be nd. th e sensation wa s sim i la r whet her you used fro nt or rear brakes. BUI the main th in g is th e bike sto p ped saf el y ea ch time. ASBS wi ll be fitted on prod uction BMWs in 1987 . . . thai co u ld we ll m ak e it the worl d 's fi rst p ro d uc tion a mi -lo ck system o n a m ot o rcycle. But FAG wi ll onl y le t Bi\I\V have it excl us ive ly for a limit ed period ; po ssibly two yea rs, then rh ev'Il o ffer i t 10 a ll co mers. AI the mome nt it lo ok s as if th e FAG I BMW syst em will be in producti on a nd o n bik es a head o f the riva l a ll-mecha n ira l Hrirish Lucas-G irl ing Stop Control System (SC5). BUI is it bet ter? H av ing rried bo th sys tems . it 's diffi cu lt fo r me to choose. Wha t is ce rt a in is that both - wh en test ed in ad va nced prototype form - worked effecti ve lv. FAG savs AS BS has severa l advantag es o ver'SCS: fir stl y, th ai sinc e th e un i ts are m ou nt ed o n the c hassis th e un sp r un g wei gh I is no t increased app reciably, a nd seco ndly. that th eirs has a m o re so p h is tica ted warn ing sys re ru in th e eve n t o f a m alfunct ion . But my feeling is thai th e u nspru ng weight argum ent is ra th er acad em ic. ce rta in ly o n a hik e like the Bi\I\\' K I 00 . And it's impo rtant io p oint OUI th at a safety devi ce has been paten ted for the SCS - the sp eed o drive is tak en o ff th e driven Ilvwheel so it will g ive an instant warning - if th e fl ywh eel SlOpS . .. so does th e speedo. And prod uc tion SCS versions co u ld he in corporated into a wh eel h ub . so reduci ng th e th ree-pou nd weight of each unit by u p 10 40%. The IWOsvst ems mav not be riva ls. bu t that 's riot im porta n t: wha t we want is c hea p , effe ct ive a n ti -lock braki ng syste ms av a ilable for all bi kes as SOO Il as po ssi ble. How it works B:\I\"'s new a nt i-lock brake system is ror a ll y unlike th e se t-u p us~ o n Bi\I\' '"s ca rs . .. o r o n a nv ca r fo r tha: m atter. FAG. th e hydraul ic specia lists who developed the system for BMW 's bikes. say th at th eir ASBS system is a pass ive d evi ce as opposed to the actin' systems in use o n a ll GIl'S. All ca r sys tems respond 10 wheel locking b y si m p ly dumping flu id o u t o f th e lin e a nd th en activel y pumping it back to reservo ir. In co ntrast, no fluid is lo st in the FAG svste m .. . it responds to anti -loc k req u ire m ents by reduci ng th e pressure (a nd so releasi n g th e bra ke ) a nd th en rea p p lies the brake by increasi ng the p ressure aga in .. . a nd so o n . The active ca r system eve nt ua lly SlOp S worki ng when th ev run o u t of fluid. Th en th ey revert to normal , no a nti -lock braking . T hat situat io n GIII- nOI arise wi th ASBS. H ere's how th e AS BS works: Each w heel's speed a n d accelera tio n is m oni tored by a sensor - a radi o frequ en cy emi tter/ receive r that picks up sig na ls from the wheel driven toothed cog. T h is signa l is then fed 10 a n electori ng box wh ich co m pa res it with that from a signa l genera tor. The idea is 10 co m pa re rhe decelerarion o f th e wh eel with kno wn ide a l values. As soon as th e s to p p ing exc eed s a ce rt a in level , th en a regulator acts to releas e t h e b r a ke pres sure . T he m ech anical device- th e m odulalor thai does this is the key to th e AS BS system. II's basica lly a sp ri ng loa d ed pis ton in th e bra ke line th ai 's co n trolled by a li nea r motor. a so p h is t ica red fo rm o f so leno id . T he p is to n is m ech anicall y linked to a valve in t he line [rom th e m ast er cvlinde r a nd the in st ant it mo ves down to lei the brake off, the press u re from th e m aster cv Iin der is a u to rn a rica ll y isolated. ' On ce th e w heel dcce lera rio n is wi th in arrcp m ble limi ts - o r skid ding ha s cea sed - th en th e linear m ot o r is de -ac tiv a ted a nd the spring acts to res lore n orm al brak ing. FAG claims that the br a kes ca n be released wi thin 50 mi ll iseconds . On ce th e system has started a n a nti-loc k cycle, th en th e brak es ca n he rel eased a nd reappli ed within 100 mill iseconds. An addit ional so p h is tica tion is a co m pa ra tor tha t checks rea r wheel deceleratio n with that o f the front wheel. FAG S:IY tha i since th e rear w heel is eng ine bra ked . then it need s a differe nt sens ing sys tem . T here is a n in evit abl e mi cro comp ut er in th e system. but th is docs nOI co n tro l the a nti -loc k fu nctio n . Ir' s there 10 m onitor the w hol e se t- u p and flash a warning liglu if a nyt hi ng goes w ro ng . T here is fai l-safe in th e set- up so that n ormal braking is possib le in the eve n t o f th e ASBS fo u li ng up . II 's th e spring, which is powerful eno u g h - o ver 300 pounds - not to a llow any sig n ifica nt p ist on mo vem ent a ga inst no rm a l brak in g pressures (a bo u t 1000 psi ) from the master cy li nder. T he cu rrent ASBS svstern is st ill in p rot ot ype fo rm . T he fin ear m OlOr sril l a to p-secre t devi ce that' s a lready covered by a number o f parent appli ca tio n s - a nd p istrm assem bly is h eavy. But FAG says th ai as d evelopm ent co nti nues it ca n o n ly ge r li ghter. th o ugh si nce it in corporal es h eav y winding s it's unlikel y to ever g et very much lig h ter th an th e present 6.6 pounds. _