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AN I NVESTI GATI ON OF MOTORCYCLEBRAKI NG CONTROL GAI NS

R.G J uni per

MC. Good

Depar t ment of Mechani caland I ndus t r i al Engi neer i ngUni ver s i t y of Mel bour ne

August 1983

Pr epar ed f or

Of f i ce of Road Saf et yDepar t ment of T r anspor t , Aus t r a l i a

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Repor t No. I SSNs ma wsat eCR 30 0 642 51003 239 + v i i i983 CR = 0810- 77OX

Ll t l e and Subti t l e

AN I NVESTI GATI ON OF MOTORCYCLE BRAKI NG CONTROL GAI NS

i utbor ( S)R. G. J UNI PERM C. GOOD

' er f orm ng Organi sat i on ( N mand Mck es s )UNI VERSI TY OF MEL BOURNE,DEPARTMENT OF MECHANI CAL AND I NDUSTRI AL ENGI NEERI NG,PARKVI LLF: , VI C, 3052.

ms o r man=and -ss)Of f i ce of Road Saf et y,Depar t ment of Tr anspor t ,P. O. BOX 594,Ci vi c Squar e, ACT, 2608.

Wai l abl e f run mare and Fddress) Pr i ce/ Avai l abi l i t y/ ' FmOf f i ce of Road Saf et y

mA pi l ot experi ment al i nvest i gat i on was madef t he ef f ec t o f mot or cycl ebr ake cont r ol gai ns on r i der subj ect i ve opi ni on and obj ect i veper f or mance i n emer gency s t oppi ng manoeuvr es. var i abl e br aki ngcont r ol gradi ent ( VBCG) mot or cycl e was devel oped f or t he exper i ment ,whi ch al l owed i ndependent var i at i onf t he f or ce and di spl acementcont r ol gai ns of t he f r ont and r ear wheel br akes. Devel opment of t heVBCG sys t em was pr eceeded bycompr ehensi ve i nvest i gat i onof t hebr aki ng per f or mance char act er i st i cs of t hr ee pr oduct i on mot or cycl es.

KEywRDs: Motor cycl es, Br aki ngSyst ems, Vehi c l eDynam cs I l odel l i ng, Pedal Force,Pedal Tr avel .

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ACKNOWLEDGEMENTS

The aut hors wi sh t o expr ess appr eci at i on t o al l t hose peopl e whof ol l owi ng ar e acknowl edged:as s i s t ed wi t h t hi s r es ear c h pr o j ec t . I n par t i cul ar , t he

Of f i ce of Road Saf et y, Depar t ment f Transpor tf or s pons o r s h i n of t he stud: JSwi nbur ne I nst i t ut eo f Technol ogy f or grant i ng l eaveo M.J uni per coul d be engaged n t hi s pr oj ectMr. Rodney Howar d, an engi neer empl oyedon t hi s pro j ec t , orhi s weal t h of knowl edge of el ect r oni cs, engi neer i ng

ever yt hi ng wor k; and f or hi s ser vi ces s an exper tand mot or cycl es whi ch gr eat l y assi st ed i nxk i ngr i der i n al l t he experi ment al phases of t hr pr oj ectMr. Br endan Gl eeson f or hi s s er vi cess an exper t t est r i derThe Depar t ment of Def ence f or t hese of t he t e s t trackf ac i l i t i es at Monegeet t aThe Aust r al i an Road Resear ch Boar d, or use of t he t estt r ack and gar age f aci l i t i es at t hei r Ver montompl exHonda hl l str al i a Pt v Lt d and Kawasnki Not or sPty L td f orpr ovi di ng t he mot orcycl es used n t he exper i ment s

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CONTENTS

V

CONTENTS vi

0. EXECUTI VE S W R Y 11. I l l T?.ODUCTI ON

1. 1 BACKGROUND TO THI S STUDY1. 2 OUTLI NE OF STUDY

2. CHARACTERI ZATI ON OF MOTORCYCLE BRAKE RESPONSE PROPERTI ES21 I NTRODUCTI ON22 ON- BOARD DATA ACQUI SI TI ON2.3 QUANTI TI ES MEASURED TO DETERMI NE BRAKI NG BEHAVI OUR2.4 TESTSI TE2. 5 PI LOT STUDY OF MOTORCYCLE BRAKE DYNAMI CS

2. 5. 1 Response Char act er i st i cs Met hodol ogy2. 5. 2 I nt er pr et at i on Of St ep Di spl acement Dat a2.5.3 Di spl acement Modul at ed Dat a2. 5. 4 Swept Si ne Wave Dat a2. 5. 5 St at i c Test s

2. 6 MATHEMATI CAL MODEL OF AN HYDRAULI C DI SC BRAKE SYSTEM2.6.1 For ce- di spl acement Behavi our2.6.2 Tr ansf er Funct i ons2. 6. 3 St ep Responses

2. 7 MI NI MUM TEST REQUI REMENTS FOR CHARACTERI ZATI ON OFAMOTORCYCLE HYDRAULI C DI SC BRAKE SYSTEM

2. 8 DATA COLLECTI ON W TH250 m1AND 750 m1 MOTORCYCLES

1313131717182022222225252935353540414849

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2.9 RESULTS OF MOTORCYCLE BRAKE EXPERI MENTS2.9.1 250 m1 Mot or cycl e2.9.2 750 m1 Mot orcycl e293 Compar i son Of 250m , 400 m , and 750 m1 Br akeSyst em Per f ormance

2.10 SUMMARY AND CONCLUSI ONS

3. DESI GN AND CONSTRUCTI ONOF A MOTORCYCLE W TH VARI ABLE BRAKECONTROL GRADI ENTS3.1 I NTRODUCTI ON3.2 VBCG SYSTEM DESI GN

321 Def i ni t i on o f VBCG Syst em Per f or manceSpec i f i cat i ons

3.2.2 Real i zat i on of Per f or mance Speci f i cat i ons3.3 CALI BRATI ON OF VBCG SYSTEM

3.3.1 Exper i ment al Pr ocedure3. 3. 2 Anal ysi s and I nt er pr et at i on of Dat a3.3.3 Cal i br at i on Resul t s

4 I NVESTI GATI ON I NTO ERGONOMI C ASPECTSOF MOTORCYCLEDECELERATI ON CONTROL4.1 I NTRODUCTI ON4. 2 EXPERI MENTALOBJ ECTI VE4.3 EXPERI MENTALDESI CN4. 4 SELECTI ON OF RANGE FOR VARI ABLES I NVESTI GATED4.5 CALI BRATI ON OF VBCG

4.5.1 Sel ec t i on of Conf i gur at i ons f or Cal i br at i on4. 5. 2 Descr i pt i on of Cal i br at i on Exper i ment s

( a) I nst r ument at i on(b) Test s i t e( c) Test i ng pr ocedur e( d) Dat a anal ysi s and resul t s of cal i br at i on

exper i ment s46 DESI GN OF RSM EXPERI MENTAL BRAKI NG TASK

4.6.1 The St oppi ng Task4. 6. 2 I nst r ument ati on

505052

5371

757575757780898186

8989a9909293539393969696104104107

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4.7 EXPERI MENTAL PROCEDURE4. 7. 1 Test Si t e4. 7. 2 Subj ect s4. 7. 3 Test Super v i s i on4. 7. 4 Test Logi s t i cs

4. 8 BRAKI NG PERFORMANCE MEASURES4. 8. 1 Subj ect i ve Measur es4. 8. 2 Obj ect i ve Measur es

4. 9 RESULTS AND. DI SCUSSI ON4. 9. 1 Subj ect i ve Measur es4. 9. 2 Obj ect i ve Measur es

4. 10 SUMMARY AND CONCLUSI ONS

REFERENCESAPPENDI CES :

A. TRANSDUCER DESI GN AND CALI BRATI ONB. RECOVERY RATE GRADI ENTC. MATHEMATI CAL MODEL OF AN HYDRAULI C DI SC BRAKE SYSTEMD. VBCG MOTORCYCLE HARDWARE DESI GN DETAI LSE. VBCG RSM EXPERI MENTAL RESULTSF. OPTI KUM PROPORTI ONI NG OF WHEEL DECELERATI ON

108108108108109109109113114115128145

150153153181185193207237

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0. EXECUTI VE UMMARY

I NTRODUCTI ONThi s r epor t document s wor k per f or med i n t he second phase of at wo- phase r esear ch pr oj ect concer ned wi t h br aki ng, st abi l i t y andhandl i ng of mot or cycl es. Phase I of t he pr oj ec t , a l i t er at ur eand r esearch r evi ew*, was di r ect ed at sur veyi ng t he st at e ofknowl edge, i sol at i ng pr obl em areas and r ecommendi ng pr i or i t i esf orur t heresear ch. As a r esul tfhi sevi ew,ni nvest i gat i on of some er gonom c aspect s of mot or cycl e br aki ngcont r ol was i ni t i at ed as Phase1 of t he proj ect .

The physi cal perf or mance of mot or cyc l e braki ng syst ems hasbeen he ubj ect of bot h sc i ent i f i c t udy andgover nmentr egul ati on i n r ecent years. The t ask of appl yi ng t he br akes on amot or cycl e dur i ng an emergency s t op i s qui t e demandi ng, r equi r i ngas i t does t he i ndependent modul at i on of f r ont and rear br aki nge f f o r t s o as t o avoi d wheel l ock- up and consequent l os s ofdi r ect i onalont r ol .owever ,er yi t t l enf or mat i onsavai l abl e n he i t er at ur eas o how t hedi f f i cul t y, OKot herwi se, of t he br aki ng t ask i s r el at ed t o the br aki ng syst emchar act er i st i cs. The mot or cycl e acci dent l i t er at ur e shows t hatr i der s typi cal l y do notmake f ul l use of t he braki ng capaci t y oft hei r machi nes, t he f r ont br ake bei ng especi al l y under - ut i l i zed.I n vi ew of t hi s, and t he r el at i vel y hi gh f r equency and sever i t yof mot orcycl e acci dent s, i t was concl uded i n Phase I of t hi sst udyhat t he r el at i onshi pet weenrakeyst emf eel "pr oper t i esand i der l cyc l ebr aki ngperf or mance i sa mat t err equi r i ng nvest i gat i onat a hi gh pr i or i t y. Accor di ngl y, i n

* J uni per , R.G and Good, MC. , Br aki ng, St abi l i t y and Handl i ngof Mot or cycl es. Aust r al i an Depar t ment of Tr anspor t , Of f i ce ofRoad Saf et y, Repor t CR 29 ( 1983) .

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Phase 11, an xper i ment al t udy was nder t aken, i med ati dent i f y i ng the most i mpor t ant vehi c l e paramet er s a f f ec t i ng the4, br aki ng qual i t y" of motor cyc l es and quant i f y i ng t he e f f ect oft hesepar amet er son bot h obj ect i vemeasur es of r i de r l cyc l ebr aki ng per f ormance and r i ders ' subj ect i ve r at i ngs of br aki ngqual i t y.

To enabl e t he exper i ment at i on t o be per f or med e f f i c i ent l y , avar i abl e br ake cont r ol gradi ent ( VBCG) mot or cycl e was devel oped.The i nves t i gat i onsof he esponse haract er i s t i cs of someproduct i on mot or cycl es, and t he means by whi ch t he mai n f eat ur esof t hese r esponses wer e made var i abl e n t he VBCG mot or cycl e, ar edes c r i bed i n t hi s r e por t . A si mpl e mat hemat i cal model of t hebrake syst em whi ch accounts or t he mai n r esponse char acter i s t i csi s l s o devel oped. Fi nal l y. a pi l ot s t udy, i nwhi ch t woexper i enced r i ders per f or med a number of braki ng t asks wi t h t heVBCG mot or cycl e i s descr i bed.

I NVESTI GATI ON OF BRAKE RESPONSE PROPERTI ES

To al l ow t he des i gn of a VBCG mot or cyc l e to pr oceed, i nf or mat i onon t he dynam c r esponse proper t i es of pr oduct i on mot or cycl e br akesys t ems was r equi r ed so t hat t he mport ant f eat ur es of t heser esponses coul d be r epr oduced and var i ed i ndependent l y. Al t houghusef ul dat a on br aki ng sys t emcomponent s have been r epor t edpr evi ousl y, i t was necessar y t o under t ake an exper i ment al andana l y t i c al i nv es t i gat i on i n o r der o ga i n a n u nder s t andi ngof t hecompl et e s yst em dynam c r esponses. I t shoul d be noted t hat , t or educe t he s cope and hazards of t hi s st udy, br aki ng under dr yweat her condi t i ons onl y was consi der ed. Al t hough wet weat herbr a ki ngso ns i der a bl yor ei f f i c ul t , i t s eems t hatc ompar i t i vel y l i t t l e r i di ng i s i n f ac t done i n t heet .

Thr ee mot orcyc l es , of 250, 400 and 750 m1 eng i ne capac i t y ,were se l ect ed f or i nvest i gat i on. Al l t he machi nes were equi pped

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wi t h hydr aul i cal l y- oper at ed, s i ngl e, s t ai nl ess s teeli sc br akes,except f or t he r ear wheel of t he 400 m1 mot or cycl e, whi ch wasf i t t ed wi t h a si ngl e l eadi ng- shoe, l ever - oper at ed dr um br ake.The di sc pads on t he 250 m1 machi ne wer e of t he s i nt er ed met al" al l weat her" t ype; al l t he remai ni ng pads were t he convent i onalorgani c t ype. I t was t hought t hat t he var i at i ons i n machi ne s i zeand br ake t ype coul d yi el d some i nt erest i ng cont r ast s i n dynam cbehavi our .

The mot or cycl es wer e i nst r ument ed t o measure f or war d speed,hand nd oot r ake ever nput or ce nd i spl acement ,mai n- f r ameecel era t i onndi t c hat e,nduspensi ondef l ec t i ons . Si gnal s r omup to ei ght r ansducer scoul dbesi mul t aneousl yondi t i oned,ncoded andecor dedi t h al i ght - wei ght dat a acqui si t i on syst em whi ch r epl aced t he nor malf uel t ank on t he mot orcycl es.

The dat a acqui si t i on syst em was devel oped f or t hi s and acompani on DOT st udy*. I n t he syst em t he ei ght channel s of dat awere encoded i nt o a ser i al st r eamof cl ock- synchr oni zed pul ses,usi ng a t i me- di vi si on mul t i pl exi ng scheme, f or r ecor di ng on ahi gh- qual i t y, port abl e audi o casset t e t ape r ecor der . Decodi ngci r cui t r y al l owed subsequent r econst r uct i on of t he c l ock pul sesand the ei ght par al l el channel s of dat a, wi t h a bandwi dt h f r omd.c. o 20 Hz. These dat a were t r ansf err ed t o a l aborat orycomput er syst em f or pr ocessi ng and anal ysi s.

The br ake syst em on a mot orcycl e pr oduces decel erat i on i nr esponse t o t he r i der appl yi ng a f orce t o, and t he consequentdi spl acement of , t her ake cont r ol ever .Manual ont r olr esear ch as hown hat uman per at or s r e apabl e ofcont r ol l i ng ei t her l i mb pos i t i on or f or ce, t he choi ce dependi ngon t he appr opr i at eness t o t he dynam cs of t he syst emunder

* " Motor cycl e Ri der Ski l l Assessment ", DOT Or der No. H 40598.

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cont r ol . Re l i abl e f eedback of one of t hes e quant i t i e s c an a l s oenhance cont r o l o f t he ot her . t s t hought t hat aut omobi l edr i ver s cont r ol t hei r f o rce out put t o t he b rake peda l i n or der t oachi eve des i r ed decel er at i ons . Mot orcyc l e br akes , however , ares ubj ec t t o f ai r l y l ar ge hys t e r et i c ef f ec t s i n t he dec el er at i onr esponse t o f o rces appl i ed t o t he cont r ol l ever . I t has beensuggest ed t hat , becauseheys t er e si s i nhedecel er a t i on/ l ever - di spl acement r el at i on i s l es s mar k ed, a vi abl es t r at egy woul d be t o use l ever di spl acement t o cont r o l f o r ceout put .

Exper i ence i n aut omobi l e handl i ng r esearch has shown t hat af r ui t f ul way of char ac te r i z i ng t he vehi cl e' s r esponse pr oper t i esi s i n t erms of t he st eady- st ate cont r ol gai ns and measur es of t her api di t y and s t abi l i t y o f t he r es pons e t o c ont r ol i nput s whi c hare epr esent a t i veof dr i ver i nput s n ypi ca l manoeuvres .Accor di ngl y ,a er i eso f t e s t swas per f or med on t he hr eepr oduct i on mot or cycl es whi ch, i t was hoped, woul d y i e l d usef ulpar amet er sor char act er i z i ng "s teady- s tate ' ' f o rce anddi spl acement gai ns ( and t hei r var i a t i on wi t h f or war d speed) , t hehys t er es i s ev el saf f ect i ngmodul at ed or ceand di spl acementi nput s, and t he r esponse t i mes and over shoot s associ at ed wi t hr api d br ake appl i cat i ons . The t es t s , per f or med separ ate l y f ort he f r ont and r ear br akes, were:

( a) St ep l ever - di spl acement i nput t es t .A c har ac t er i s t i c f eat ur e of t he brake f or ce r esponse t o a r api ds t ep- l i ke i nput of l ever di spl acement f o r a l l t he hydr aul i c br akesyst ems was an ni t i a l peak, or "over shoot " , f o l l owed by agr adual dec l i ne i n t he f or c e l evel equi r ed t omai nt a i n aconst ant l ever di spl acement . Thus t he br ake syst em pr esent s at i me- var yi ng " s t i f f ness " to t he r i der . For t he moto r cyc l es wi t hor gani c di sc pads , and f or t he dr um br ake, t he " f orce gai n" GF( m s 2 of dec el er at i on per N of f o rce appl i ed to t he br ake l ever )was essent i al l y const ant t hr oughout t he s top. W t h t he s i nt ered

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met al pads on t he 250 m1 machi ne, however , bot h t he f r ont andreargai nsusual l y ncr eased as t he peeddecr eased.Thedecel erat i on r esponse of t he motor cycl es was qui t e r api d, t hedi f f er ence bet ween t he 63% r i se t i mes of decel erat i on and l everdi spl acement bei ng of t he or der of 25 as.( b) Si nusoi dal l ever i nput t est .W t h a l i t t l e pr act i ce, t he t est r i der was abl e t o pr oduce ar easonabl y smoot h, const ant ampl i t ude si nusoi dal i nput of br akel ever di spl acement , wi t h a f r equency of about 2 Hz. Thi s t esti nput was chosen as epr esent at i ve of cont r ol l ed r aki ngsi t uat i ons i n whi ch t he braki ng ef f or t i s modul at ed f or f i necont r ol of decel er at i on. Ther e was ver y l i t t l e hyst er esi s i n t her el at i onshi p bet ween decel erat i on and l ever di spl acement f or anyof hebr akes est ed.The ever- f or cecharact er i s t i cswer ehowever subj ect t o subst ant i al hyst er esi s, whi ch woul d m t i gat eagai nst f i ne adj ust ment of decel er at i on by f orce cont r ol . Thesensi t i v i t y of t he mot or cycl e decel er at i on ( a) t o l ever cont r oli nput s of f or ce (F) and di spl acement ( S) was char act er i zed by t he"f or ce gr adi ent " dF/ da and t he "di spl acement gr adi ent " dcj da,measur ed as t he sl opes of t he respect i ve char act er i st i c cur vesdur i ng t he br ake appl i cat i on phase of t he si nusoi dal l ever i nput .Ot her br ake "f eel " paramet ers measured were t he "br ake st i f f ness"dF/ dG and t he "f or ce hyster esi s" . Ther e was a r oughl y t wo- f ol dvar i at i on bet ween machi nes i n al l t he par amet er s, except f or hef r ont di spl acement gr adi ent , whi ch was r emarkabl y consi st ent atabout 2.6 nrm per m/ s 2 f or al l t hr ee machi nes.

(c) Swept - si ne l ever i nput t est .Al t hough mot orcycl e br ake syst ems cl ear l y exhi bi t some nonl i nearr esponseharact er i s t i c s, a l i near i z edr equency- domai nr epr esent at i on of t he dynam cs may pr ovi de some i nsi ght s i nt or i dercont r ols t ra tegi es i n c l osed- l oop,cont ro l l edbr aki ngt asks. Fr equencyr esponse unct i onsr el at i ngdecel er at i ont ol ever or ce nd i spl acement nput s, nd ever f or ce t o

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di spl acement ( "dynam c st i f f ness") , wer e obt ai ned as f o l l ows:When t r ave l l i ng at 100 k m h t he t es t r i der appl i ed a s i nus oi dall ever i nput whi ch s t ar t ed l owl y , but whi ch ncr eased nf r equency up t o t he l i m t of hi s capabi l i t y ( about 7 Hz) dur i ngt he t es t . The r es ul t i ngec el er at i on, l ever - f or c e andl ever - di spl acement t r aces wereprocessed b y di gi t a lFour i erAnal ys i s t echni ques t o yi el d t her equi r ed f r equency r esponsef unct i ons . For a l l t he hydraul i c br ake systems t est ed i t wasf ound t hat, wher eas t he f orce gai n was r el at i vel y const ant overt he r ange of appl i ed f r equenci es, t he di spl acement gai n and t hebr ake dynam c s t i f f ness wer e const ant at l ow f r equenc i es , butdi spl ayed a r oughl y t hr ee- f ol d i ncr ease over t he f r equency r ange0.5 - 1.5 Hz. The hi gher gai n l evel s wer emai nt ai ned f orf r equenc i es up t o n ear t he l i m t of t he i nput bandwi dt h ( 7 Hz).The phase di f f er ence bet ween t he decel er at i on and t he l everdi spl acement was qui t e smal l at a l l f r equenc i es . By cont r ast ,t he dece l erat i on i ncr eas i ngl y agged he ever f o r ce as t hef r equency i ncr eased.

MATHEMATI CAL MODELOF BRAKE SYSTEMA r el at i vel y s i mpl e mat hemat i ca l model of a hydr aul i c br akesys t em was devel oped, i n whi ch t he mai n sour ces of e l as t i c i t y,dr y f r i c t i on, v i s c ous r es i s t anc e and l os t mot i on wer e i dent i f i ed.The model was successf ul i n account i ng f or t he mai n f eat ur es oft he experi ment al r esponses, i nc l udi ng:( a ) t h edynam c f o rcemagni f i c at i on and l ong- t er m s t i f f nes s

var i a t i on e f f ects obser ved i n t he s t ep l ever - di spl acementt e s t s ;( b) t he hys t er es i s l oops obser ved i n t he s i nuso i dal l ever i nputt e s t s ;

( c) t he f or ms of t he f r equency r esponse f unct i ons measur ed n t heswept - s i ne l ever i nput t es t s .

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VARI ABLE BRAKE CONTROL GRADI ENT MOTORCYCLE

The st eady- st at e gr adi ent s f l ever f or ce and di spl acement wi t hdecel er at i on ( as deter m ned by t he si nusoi dal l ever i nput test)wer e sel ect ed as t he pri mar y br ake syst empar amet er s t o bemani pul at ed wi t h t he VBCG mot or cycl e. For t he ot her possi bl yr el evant f eel pr oper t i es, t he desi gn obj ect i ve was t o mai nt ai nver y shor t r esponse t i mes, and r epr esent at i ve l evel s of f or cehyst er esi s .

The means by whi ch t he f or ce and di spl acement gradi ent s oft he YBCG mot or cycl e wer e made i ndependent l y var i abl e, usi ng anai r - assi st ed hydr aul i c br ake system ar e descr i bed i n t he r epor t .Cal i br ati on t est s showed t hat t he cont r ol gr adi ent sf pr oduct i onmot or cycl es measur ed i n t he pr esent st udy, and i n a pr evi ousi nvest i gat i on, gener al l y f el l wi t hi n t he range achi evabl e wi t ht he var i abl e br ake system The l evel of f or ce hyst er esi s wassomewhat hi gher t han measur ed on t he pr oduct i on machi nes i n t hepr esent st udy, but st i l l wi t hi n t he r ange measur ed i n t he ear l i erst udy .

Exper i enced test r i der s r epor t ed that t he VBCG mot or cycl ebehaved and f el t nor mal . The onl y qual i f i cat i ons t o t hi s wer et hat some r i ders comment ed on the r el at i vel y hi gh l evel of f or cehyst er esi s or her ear brake, and t he noi semade by hedi schar ge of ai r when t he br akes wer e r el eased. Ri ders r api dl ybecame accust omed t o t he l at t er i di osyncracy of t he BCG systemt he f ormer coul d be cor r ect ed by r educi ng t he f r i ct i on i n t hebr ake l ever f ul crum

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PI LOT STUDY OF ERGONOMI C ASPECTS OF BRAKI NG CONTROL

An exper i ment was desi gned t odet er m ne t he e f f ec t of t h edi spl acement and f or ce cont r o l gr adi ent s on mot or cyc l e br ak i ngqual i t y. The r el at i ve i mpor t anceoi der s f hese t wogr adi ent s , and t he i nt er act i ons bet ween t hei r val ues f or t he handand f oot br akes , wer e of i nt er est . I t was i nt ended t hat t heexper i ment woul d be per f or med usi ng a gr oup of about t hi r t yr i der s of var y i ng ev el s of e xper i enc e and s ki l l . Bef or eunder t aki ng a f ul l - scal e s t udy i t was cons i dered prudent t o car r yout a pi l ot s t udy , wi t h t wo s ki l l ed r i der s onl y, t o ev al uat e t hepr oposed exper i ment al pr ocedur es and per f or mance measur es. I twas a l so t hought t hat t he r esul t s of a pi l ot s t udy i nvol vi ng awi de r ange of br ake syst em char act er i s t i cs m ght show t hat somecombi na t i ons of cha rac t e r i s t i c s were c l ear l y unaccept abl e. Thesecoul d t hen be el i m nat ed f r omt he f ul l - s cal e s t udy , t her ebyr educi ng bot h t he magni t ude and t he hazar ds of t hat t ask. I n t heevent , t h er e was i ns uf f i c i ent t i me avai l abl e i n t hi s pr o j ec t t odo more t han car r y out t he pi l ot st udy.

The xper i ment al desi gn was based on Response Sur f aceMet hodol ogy ( RSM) , whi ch prov i des an exper i ment a l l y ef f i c i entmea ns f or i nv es t i gat i ng t he ef f ec t s of a l ar genumber ofi ndependent ar i abl es , nd t hei r i nt er act i ons . Second- or derr esponse sur f aces wer e t obe f i t t ed t o t he dat a t o a l l ow opt i mumbr ake conf i gur at i ons t o be def i ned. The RSM des i gn r equi r ed f i vel evel s f or each of t he i ndependent var i abl es and t he VBCG syst emwas set up and cal i br ated accordi ngl y . The r anges of cont r olgr adi ent s expl ored i n t hi s s t udy wer e:

Fr ont di spl acement gr adi ent ( FBD) : 10 - 5.7 mm per m s2Front or cegradi ent ( FBP) : 17.5 - 76.7 N per m s 2Rear di spl acement gr adi ent ( RBD) : 1.6 - 12.9 mm per m s 2Rear orce r adi ent (FBF): 25. 8 - 84. 6 N per m s 2

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The exper i ment al br ak i ng task i nvol ved the r i der t r avel l i ngi n a s t r a i ght l i ne at0 km h ( chosen l ow f or saf ety r easons) andmoni t or i ng a t r af f i c s i gnal l i ght ahead. On r ecei pt of a r edsi gnal , t he r i der s t ask was t o br i ng t he motor cycl e to a st opbef ore r eachi ng a l i ne marked acr oss t he r oadway. The t i m ng oft he s i gnal l i ght was adj ust ed to r equi r e ei t her a s l ow st op(0. 2g nom nal decel er at i on) , a medi um st op (0. 3g) or a qui ckst op (0.5g). Because of t he r i der s r eact i on t i me, t he act ualdecel erat i on r equi r ed exceeded t hese nom nal val ues. To pr eventant i c i pat i on of a qui ck st op, no st op r uns wer e random yi nt ers pers ed t hr ough t he t est sequence.

Two exper t r i der s wer e used as subj ect s i n t he pi l ot st udy,i n t he hope t hat t hey woul d exhi bi t more consi st ent braki ngbehavi our andpr ovi demor emeani ngf ul subj ec t i verat i ngsofvar i ous aspect s of t he br ak i ng qual i t y than woul d l ess- sk i l l edr i der s. Rat i ngs of t he br ake f orce and di spl acement r equi r ement sand over al l i mpress i ons f t he br aki ng qual i t y wer e obt ai ned r omt he r i ders ; obj ect i ve measures of t he decel erat i on perf ormance,t he cont r i but i ons t o t hi s f r om t he f r ont and r ear br akes , t heover al l st oppi ng di st ance and t he r i der s r eact i on t i me wer ederi ved f r om t he r ecor ded dat a. SPSS Mul t i pl e regr essi on wasused t o obt ai n the coef f i c i ent s def i ni ng the r esponse sur f acesand s t ati st i cal measur es of t he s t r engt h and si gni f i cance of t heobser ved r el at i onshi ps.

The mai n f i ndi ngs f r om t he dat a anal ysi s were:( a) The t wo expert r i der s wer e abl e t o modi f y t hei r cont r ol

i nput s s o as to ( on aver age) achi eve r oughl y t he same br aki ngper f or mance over t he whol e r angef br ake conf i gur ati ons.

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( b) On aver age, bo th i der sdi s t r i but ed hebr aki nge f f o r tbet ween t he f r ont and r ear wheel s i n an opt i mal manner , agai ndespi t e t he wi de r anges and combi nat i ons of f r ont and r earbr ake sensi t i v i t i es wi t h whi ch hey were pr esent ed.

( c) Al l t he da ta , however , exhi bi t ed l ar ge er r or var i ance whi chgener al l yr ec l udedheef i ni t i on of s i gni f i cantr e l at i ons hi pset weenesponsemeas ur esndherakec onf i gur at i on var i abl es .

(d) Per f ormance i n t he qui ck s t op taskwas pr i mar i l y af f ec t ed byt he f r ont br ake di spl acement gr adi ent . However , onl y smal land cont r adi ct ory t r ends were obt a i ned f r om t he t wo r i der s :f or one, average dece l e rat i on i ncr eased marg i na l l y wi t h amore di spl acement sens i t i ve f r ont br ake; f o r t he ot her i tdecreased s l i ght l y .

( e) Subj ect i ve at i ngs of t he br ake yst emwer epr i mar i l yi nf l uenced by t he rear br ake di sp l acement gr adi ent . Agai n,however, qui t e Cont Kadi ct OKy r esul t s were obt ai ned f r om t het WO r i der s.

CONCLUSI ONS

Usef ul nf or mat i onhasbeenobt a i nedabout heper f or mancecharact er i s t i cs of convent i onal mot orcyc l e br aki ng syst ems. Themaj or f eat ur es of t he exper i ment al r esponses have been account edf or wi t h a r e l at i vel y s i mpl e mathemat i ca l model . A var i abl ebr ak i ng c ont r ol ai nmot or cycl e , and ai ght - wei ght da taacqui si t i on syst em have been devel oped and have pr oved t hemsel vesasel i abl eool sorar r y i ng out mot or cyc l e br aki ngexper i ment s. The r e sul t s of api l ot s t udy of t heef f ec t ofbr aki ng cont r o l ai ns on br aki ngual i t yt t e s t t oheadapt abi l i t y of exper ti der s t o changes i n vehi c l echaract er i s t i cs and t o t he i ndi v i dual di f f e rences between human

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subj ect s.hear i abi l i t ynhei l o tt udyat awasdi sappoi nt i ng and suggest s t hat modi f i cat i ons i n experi ment alt echni que ar e r equi r ed, Fut ur e st udi es shoul d al l ow t he r i der sl onger t i me i n whi ch t o become f am l i ar wi t h each new br aki ngconf i gur ati on and br aki ng f r o m hi gher s peed shoul dbe at t empt ed.A pai r ed- compar i son exper i ment al desi gn shoul d ead t o moreconsi st ent subj ect i ve r at i ngs t han wer e obt ai ned i n t he pr esentstudy. Exper i ment s wi t h l ess ski l l ed r i der s woul d al so pr obabl yyi el d per f or mance measur es t hat wer e mor e st r ongl y af f ect ed byt he br ake syst em var i abl es.

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1. I NTRODUCTI ON1.1 BACKGROUND TO THI S STUDYI n i t s r epor t on mot orcycl e and bi cycl e saf et y, t he House ofRepr esent at i ves St andi ng Comm t t ee on Road Saf et y ( HoR, 1978,Para. El ) r ecommended t hat :

" A l i t er at ur e and r esear ch r evi ewf exi s t i ngand pot ent i al pr obl ems r el at i ng t o mot or cycl est abi l i t y and handl i ng be undert aken by t heAdvi soryComm t t ee on Saf et y nVehi c l eDesi gn. ' '

Fur t her mor e, t he comm t t ee r ecommended exper i ment al apprai sal ofant i l ock and l i nked br ake syst ems. They express ed concer n aboutpossi bl e mot or cyc l e i nst abi l i t i es ar i s i ng t hr ough t he f i t ment off ai r i ngs and t he car r yi ng of l uggage. I n addi t i on, they sai dt hat t he saf ety aspect s of t he mat chi ng of t yres t o machi nesshoul d be i nvest i gated.

On t he basi s of t hese recommendat i ons t he Of f i ce of RoadSaf et y of t he Aust r al i an Depar t ment of Tr anspor t comm ss i oned at wo- phase esear chpr oj ectent i t l ed Br aki ng,St abi l i t yandHandl i ng of Mot or cycl es". Phase I , a l i t er at ur e and r esear chr evi ew, has been report ed separat el y ( J uni per and Good, 1983).Thi sepor tocument s t he Phase I 1 i nvest i gat i onf ahi gh- pr i ori t y pr obl em area r eveal ed by t he r evi ew, namel y t heef f ect of mot orcycl e br ake cont r ol gai nsn br aki ng per f ormance.

1.2 OUTLI NE OF STUDY

The t opi cs cover ed i n t he l i t er at ur e r evi ew ( J uni per and Good,1983) i nc l uded br aki ng pr obl ems, and st abi l i t y and handl i ngaspect s of mot orcycl es.hecci dentt udi esevi ewedhi ghl i ght ed many probl em ar eas wi t h mot or cycl es. I n par t i cul ar ,i n- dept h acci dent st udi es suggest ed t hat many r i ders do notut i l i ze t he f ul l decel er at i on capabi l i t yof t hei r mot or cycl e when

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br ak i ng t o avoi d col l i s i on. Hence many acc i dent s wer e mor esever e t han t hey woul d have been i fhe r i der s had used bot hf r ont and r ear br ak es up o t he avai l abl e l i m t s of f r i c t i onbet ween t he t yres and t he r oad sur f ace. Thi s suggest s a possi bl em s- mat ch bet ween t he char act er i s t i cs of mot or cyc l e br akes andthe r i der cont r ol capabi l i t i es .

I mpo r t a nt aspec t s of t he des i gn o f a ny dyna m c sys t emi nc or por at i ng a h uma n c ont r ol l er ar e t he s ens i t i v i t y o f t hes y s t e m r e s p on s e t o c o nt r o l i n pu t s and t he c ont r ol ' f eel 'a va i l abl e f r omt he ma ni pul a to r used t o exer c i se cont r ol . Thel i t er at ur e r evi ew r eveal ed no account s of sci ent i f i c s tudi es ofthe ef f ect of mot or cycl e br ake cont r ol gai ns or f eel pr oper t i eson hr aki ng per f o r mance , a l t houghhe need f o r such s t udi es wasnot ed ( Er vi n, McAdam and I , J at anabe, 1977; I r vi ng, 1978; Zel l ner ,1980; Taguchi and Sunayama, 1973).

Af t er consul t at i on wi t h t he Of f i ce of Road Saf et y, Phase I 1was i ni t i at ed as an exper i ment al . st udy of t he er gonom c aspect sof mot or cycl e br aki ng cont r ol . The st udy compr i sed t hr ee mai nparts.

F i r s t , t he dy nam c r es p ons e t o br ak i ng i nput s of t h r e emotor cyc l es was t o be i nvest i ga t ed i n some det ai l . Thei nf o r mat i on ga i ned her e was h i t her t o unavai l abl e and wasnecessar y t o al l ow char act eri sat i on of t he r esponse pr oper t i es,s o t hat t hese coul de ma ni pul a t ed i n expe r i ment s wi t hi der s .Thi s par t of t he st udy i s descr i bed n Chapt er 2

Havi ng det er m ned t hat t he pr i mar y r esponse par amet er s of t hebr ake sys t em ar ehe f o rce a nd di sp l a cement cont r o l gr adi ent s( r espect i vel y. t he br ake l ever f or ce and di spl acement i ncr ement sr equi r ed to i ncr ease theecel er at i on by I m s2), a var i abl e br akecont r ol gr adi ent ( VBCG) mot or cycl e was desi gned and const r uct ed

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t o a l l ow r api d and i ndependentxper i ment al cont r ol over t hesepar amet er s. The devel opment f t he VBCG sys t ems det a i l ed i nChapt er 3.

T he t hi r d pa r t c ompr i s e s a pi l ot s t udy of t he ef f ec t s ofbr ake cont r ol gr adi ent s on mot orcycl e/ r i der braki ng perf ormanceus i ng t he VBCG mot or cyc1. e. Thi s exper i ment i s r epor t ed i nChapt er 4.

I t shoul d he not ed t hat t hi s wor k i s c onc er ned wi t h dr yweat her br aki ng onl y. Al t hough c onsi der abl e pr obl ems exi st nbr aki ng of mot or cycl es wi t h wet br akes and on wet sur f aces, t heres t r i c t i on t o dr y braki ngas made because:

( a) t he gr e at maj o r i t yof r i di ng i s done i n dr y weat her ;Hur t , Ouel l et , nd Tho m, ( 1981) put t he f i g ur e a t mor et han 97% f or Cal i f or ni a,USA;

(b) t he r esour ces of t he s t udy we r e no t s uf f i c i ent t oenc omp as s t he addi t i ona l expe r i ment a l v ar i abl esandmet hodol ogi ca l pr obl ems i n t r oduced wi t h wet weat herbr aki ng.

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2. CHARACTERI ZATI ON OF MOTORCYCLE BRAKE RESPONSE PROPERTI ES

2.1 I NTRODUCTI ON

The r evi ew by J uni per and Good ( 1983) f oundno publ i shed st udy oft he ef f ect s on mot or cyc l ej r i derbr aki ngper f or mance of t her esponse pr oper t i es of t he motor cycl e br aki ng syst em Even f oraut omobi l es her e ar e f ew st udi es vai l abl e.Mor t i mer tal . 1970) charact eri zedaut omobi l ebrakes i n t er msof hest eady- st at e decel er at i onj pedal f or ce gai nnd st udi ed t he ef f ectof var i ous l evel s of thi s gai n on braki ng per f or mance. The weakopt i ma f ound f or t he f or ce gai n depended somewhat on t he ski dnumber of t he pavement , but per f or mance was i ndependent of t heamount of pedal di spl acement requi r ed t o achi eve a gi ven f orcel evel . It was concl uded t hat t he br ake i s modul at ed l argel y byf orce f eedback r at her t hany di spl acement .

Mot orcycl ebr akes, however , aresubj ect t o f ai r l y ar gehyst er et i c ef f ect s i n t he decel er at i on r esponseo f or ces appl i edt o hebr ake ever . It hasbeensuggest ed Zel l ner, 1980;Zel l ner and Kl aber , 1981) t hat , because t he hyst eresi s i n t hedece~er at i onj ~ever i spl acement el at i on s essmar ked, avi abl e st r at egy woul d be t o use l ever di spl acement to cont r olf or ce out put .

Manual cont r ol r esear ch has shown t hat human oper at or s ar ecapabl e of cont r ol l i ng ei t her l i mb pos i t i on r f or ce, the choi cedependi ng on t he appr opr i at eness t o t he dynam cs of t he syst emunder cont r ol ( see, f or exampl e, Good, 1979). Rel i abl e f eedbackof one of t hese quant i t i es can al so enhance cont r ol of t he ot her .Exper i ence i n aut omobi l e handl i ng r esear ch ( Good, 1977; 1979)has shown t hat a f r ui t f ul way of char ac ter i z i ng t he vehi c l e sr esponse pr oper t i es i s i n t er ms of st eady- st at e cont r ol gai ns orgr adi ent s and measur es of t he rapi di t y and st abi l i t y of t her esponse t o cont r ol i nput s whi ch ar e r epr esent at i ve of dr i veri nput s i n t ypi cal manoeuvr es.

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Be f o r e a ppr opr i a t e pa r a me t er s c o ul d be s e l e c t e d f o rexper i ment al i nvest i gat i on of t hei r ef f ec tsn mot orcycl e br aki ngper f ormance, i t was necessary to i nvest i gat e i n some det ai l t hequest i on: ' What act ual l y happens when t he br akes of a mot or cycl ear e appl i ed? '

T hr e e mo t o r c y c l e s we r e s e l e c t e d f o r t h e pu r p os e sofi nvest i gat i ng br ake dynam c behavi our . One of t he machi nes ' wasof 250 m1 engi ne capaci t y , and had s i ngl e d i s c b r a kes o n bot hwheel s . I t was f i t t ed wi t h 'al l weat her ' di sc pads of s i nt er edmet al const r uct i on. The manuf act ur er cl ai med t hese br akes gi vegood r e spo nse cha ra c t e r i s t i c s i n we t condi t i ons . The secondmot or cycl e was of 400 m1 capaci t y and conf i gur ed i t h a st ai nl esss t eel di s c br ak en t he f r o nt whee l , nd a s i ngl e l eadi ng- shoe,l e ve r - o pe r a t e d d r u m b r a k e o n t h e r e ar wheel . T he t hi r dmot orcycl e, of 750 m1 engi ne capaci t y , had st ai nl ess st eel s i ngl edi s c b r a k es o n t he f r ont and r e ar whe el s , wi t h c onv ent i o nalor gani c mat er i al br ake pads. I t was expect ed t hat t hi s var i at i oni n br ake conf i gur at i ons and machi ne s i ze coul d yi el d i nt er est i ngcont r ast s i n dynam cbehavi our .

22 ON- BOARD DATA ACQUI SI TI ON

A l i ght - wei ght dat a acqui si t i on syst emas devel oped i n order tomeasur e r i der i nput s and mot orc ycl e r esponses whi l sthe machi newas bei ng r i dden i n a nor mal manner . An i mpor t ant cr i t er i on wast hat i t s houl d not s i gni f i c ant l y al t er t he mot or c y cl e mas sdi s t r i but i on, s o as not t o i nf l uence t he dynam c behavi our ofhemachi ne. The maj or par t of t he har dwar ewas ar r anged t o r epl acet he f uel t ankn any o f t he machi nes . A sma l l one l i t r e vesse lwas used f or f uel suppl y dur i ngest i ng.

The syst em pr ovi ded f or ei ght anal ogue i nput channel s whi chcoul d be r ecor ded f orup to 45 m nut es cont i nuousl y. I t empl oyeda hi gh qual i t y por t abl e casset t e t ape r ecor der . The dat a f or t he8 channel s was encoded i nt oa s i ngl e channel of i nf or mat i on us i ng

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Dat a acqui si t i on system( r epl aces pet r ol t ank)

\

Fi gur e 2. 1 Dat a accpi si t i on syst em mount edon250 m1 mot or zyc l e

P9

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a t i me di vi s i on mul t i pl exi ng scheme, whi ch resul t ed i n a squar ewave of f r equency var yi ng bet ween . 75 kHz and 75 kHz. Decodi ngc i r c ui t r y , bac k i n t h e l abor at or y, r ec ons t r uc t ed t he anal oguei nput s i gnal s f r om t he casset t e t ape. The l evel of t he anal oguei nput s i gna l s was equi r ed to be bet ween 0 and 10 vol t s . Thesys t em bandwi dt h was f oundo be f r om d.c. t o 20Hz perhannel .Thi s was c onsi der ed adequat e f or t he mot or cycl e exper i ment s, asr i der i nput s andmot or cvcl ey nam c s a r e gener al l y of f r equenc yl ess t han 10Hz.

F i gur e 21 shows t he dat a acqui si t i on syst em mount ed on t he250 m1 machi ne. Al t hough i t i seen t o be some cent i met r es hi ghert han t he ori gi nal f uel t ank, hi s pr oved t o be not not i ceabl e t ot he r i der , as hi si . s i on i s gener al l y concent r at ed aheadf t hemotorcycl e.

2. 3 QUANTI TI ES MEASURED TO DETERM NE BRAKI NG BEHAVI OUR

I n order t o r educe t he speed of amotor cycl e, t he r i der pr ovi desa f or ceand di spl acement at t he f r ont brake hand l ever and/ orher ear brake f oot pedal . I n r esponse t o t hes e i nput s , t hemot or cycl e decel erat esand t he mai n f r ame of t he machi ne pi t chesf orward.

The quant i t i es measur ed t o i nvest i gat e br ake dynam cs wer ef r ont br ake l ever f or ce and di spl acement , r ear br ake l ever f or cea nd di s p l a c eme nt , mo t o r c y c l e f o r wa r d s pe ed , ma i n f r a medecel er at i on and pi t ch r at e, and suspensi on def l ect i ons.

The det a i l s of t he des i gn and cal i br at i on of t he var i oust r ansducer s may be f ound i n Append i x A Tabl e 21 shows t hesensi t i v i t i es of he t r ansducer s as usedn t hr ee motorcycl es.

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TABLE 2.1TRANSDUCER SENSI TI VI TI ES

Moto r cyc l er ont Br ake(1) Rearr ake Fr ont Br ake(2) Rear Brake Speed F r ontuspensi on Rear Suspensi onForceo rcei spl acementi spl acementf l ec t i ononN/ v N/ v mm v mm v [mmsYv mm v mml v

250 m1 25. 7 25. 5 4. 47 9. 8 4. 71 15. 027. 8(3)

400 m1 62. 6 30. 18( 4) 4. 47 7.2 5 . 1 5 15.0750 m1 38. 1 36. 7 4. 47. 43. 00 15. 0

10. 1

10.1

101

Not es: ( 1) Measured when f or ce appl i ed 115 mm f r o m l ev er f ul c r u m( 2) Lever di spl acement measur ed 115 mm f r o m f u l c r um( 3) Appl i es t o gauges adher ed t o brake ac tua t i ng a rm( 4 ) Appl i es t o gauges adhered t o rear brake l ever

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2.4 TEST SI TE

The exper i ment al wor k n t hi s phase of t he pr ogr amas per f or medat t he Aust r al i an Depart ment of Def ence Tr i al snd Pr ovi ng W ng,l ocat ed at Monegeet t a, 55 k m NNW of Mel bour ne.

Two ar eas wer e used,hese bei ng t he st r ai ght away and t heb i t umen pads . The s t r a i ght away i s smoot h , s t r a i ght nd ver ynear l y l evel s t r et c hf concr et e r oadway of20 m l engt h, wi t hdi s t ance mar kers pl aced t 200 m i nt er v al s . T he bi t ume npadsmeas ur e 60 m by 60 m each and ar e i n t er connec t ed a t t he i rcorner s, t hereby pr ovi di ng appr oxi matel y 70 m of cl ear r oadway.The pad sur f aces ar e verysmoot h, f i rs t - qual i t y hot - m x bi t umen,and wer e f ound t o be of s u f f i c i ent l engt h f o r mos t t es tpr ocedur es. Smoot h r oad sur f aceswer e necessary to m ni m se dat adr opout s due t o t ape r ecor der i br at i on

2. 5 PI LOT STUDY OF MOTORCYCLE BRAKE DYNAMI CS

One of t he t hr ee mot or cyc l es was f ul l y i ns t r ument ed. Manyexpl orat ory experi ment swer e t hen per f or med s o as t o i dent i f y t hem ni mum r equi r ement s f or char acter i zat i onf t he dynam c r esponseof a mot or cycl e brake syst em Exper i ment s wer e t hen per f or medwi t h t he o t her t wo machi neso obt a i n t he r equi r ed par amet er swhi ch woul d al l ow compar i son of t hei r br aki ng behavi our . The 400m1 machi ne was chosen f or t he f i r st ser i es of experi ment s, wi t ht he ma j o r e f f o r t be i ng devo t edo i t s f r ont br ak e, as t he r earwheel was f i t t ed wi t h a mechani cal l y oper at ed drumrake.

2.5.1 Response Char act er i st i cs Met hodol ogyThe br ake syst em ona mot orcycl e pr oduces decel erat i on n r eponset o the r i der appl yi ng f or ce and di spl acement athe br ake cont r oll ever . T o i nv es t i ga t e t he behavi ourf a dynam c s ys t e m i t i scommon t o obser ve i t s r esponse t o c er t ai n s t andar di zed i nput s ,

. whi ch may be of st ep, r amp, i mpul se or si ne wave f orm

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Wei r , Ze l l ne r a nd Teper 1978) used a br ake l i ne pr essur el i m t er to r egul at e appl i ed br ake f or ce dur i ng cor ner i ngf br ak i ngexper i ment s . The t es t r i de r a ppl i edl ar ge pedal orand gr i pf or ce, and a cont r ol syst em l i m t ed t he br akel i ne pr essur e t o aconst ant , pr eset val ue. Thi s, t hen, pr ovi ded a st ep f or ce i nput ,but t he br ake mast er cyl i nder dynam cs wer e el i m nat ed f r om t hesystem s o t hat onl y wheel cyl i nder dynam cs woul d bebservabl e.

To pr ovi de a st ep i nput r esponsen t he pr esent exper i ment s,a mechani cal di spl acement l i m t er was f i t t ed o t he f r ont br akel ev er o n t he 400 m1 machi ne. Thi s i s shown i n F i gur e. 2, anda l l o we d t he r i der t o appl y r api d s t ep i nputf di sp l acement .Adj ust ment was pr ovi ded s o t hat di f f er ent l evel s of i nputdi spl acement coul d beappl i ed. The st r ai n gauges used t o measur ef orce i nput wer e ' downst r eam of t he di spl acement l i m t er . Thust hey cont i nued t o measur e f or ce behavi our af t er t he di spl acementl i m t had been r eached.

The r ear br ake on t he 400 m1 mot or cycl e was a mechani cal l y-operat ed dr um type. When t he r ear suspensi on def l ect s dur i ng abr a ki ng ma no euv r e , t he a mo unt o f b ra k i ng e f f o r t i s l t er ed.T ak i ng ac c ount of t hi s ,rea r brakedi s pl ac ement l i m t er wasdesi gned whi ch woul dbe i ndependent of suspens i on de f l ec t i onef f ec t s , andyet s t i l l al l ow moni t or i ng of br akeor ce. Thi s wasac c ompl i s hed by l i m t i ng t he di s p l a c eme nt of t he r e arrakeact uati ng ar m and adher i ng t he sensi ng st r ai n gauges al ong t hi sar m ( see Appendi x A.

W t h a l i t t l e pr act i ce, the tes t r i der was abl e t o provi de ar easonabl y s moot h, const ant ampl i t ude si ne wave i nput of br akedi spl acement . For t hi s pr ocedur e, t he i ni t i al speedwas about 60km h, and t he f r equency of appl i cat i on anpr oxi mat el y. 0 Hz.

As a f ur t her at t empt to i nvest i gat e t he f r equency r esponseft he s ys t em, a ' swept s i ne wave' t echni que was empl oyed. Thi s

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( a) Top vi ew ' str ai n gauges

( b ) Under s i de v i ew ' t r a i n gaugesF i gur e 2. 2 F ro nt br ak e di s pl ac ement l i m t er .

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t est commenced at about 100 km h. The r i der appl i ed a si ne wavedi spl acement i nput whi ch st art ed ver y sl owl y but t he f r equency ofwhi ch ncreased up t o t he i m t of t he r i der ' s capabi l i t i es( about 7 Hz) dur i ng t he t est .2.5.2 I nt erpr et at i on Of St ep Di spl acement Dat aF i gur e 2. 3 shows t r aces of f r ont br ake f orce and di s pkW311ent ,and speed f ol l owi ng a st ep i nput of br ake di spl acement f r om20km h. These dat a al l ow t he var i at i on of t he decel er at i on/ f or cegai n, GF ( m s 2 per N) , wi t h speed, V, t o be obser ved.

Appendi x B shows t hat t he r at e of changef GF wi t h V can bei nt erpr et ed as t he Recover y Rat e Gr adi ent ( RRG) i nvest i gat ed byZel l ner and Kl aber ( 1981). F i gur e 2. 4 shows t hat f or t he 400 m1machi ne t here was essent i al l y no var i at i on of f or ce gai n GF wi t hspeed, so t hat t he f r ont br ake f or t hi s motor cycl e has a zer oRRG.

Ref er r i ng agai n t o Fi gur e 2. 3, i t can be seen t hat whi l e t hebr ake l ever di spl acement was hel d const ant , t he requi r ed br akef or ce var i ed wi t h t i me, r eachi ng a peak ear l y i n t he t est andsl owl y dec l i ni ng af t er war ds. Thi s ' dynam c f or ce magni f i cat i onef f ect' means t hat t he f or ce gai n and st i f f ness' t he br akesystem pr esent s t o t he r i der wi l l var y.

2.5.3 Di spl acement Modul at ed Dat a

Fi gur es 2.5 and 2.6 show t hedecel er at i on- di spl acementanddecel er at i on- f or ce char ac ter i s t i cs f or a 2 Hz si nusoi dal i nput fbrakeeveri spl acement .i gure 25 demonst r at eshatdecel er at i on ol l ows t he modul at eddi spl acement nputqui t ec l osel y, wi t h l i t t l e hysteres i s . However i n Fi gur e 2. 6 t here i sa subst ant i alhyst er esi s i n r esponse o f or ce i nput s.Themagni t ude of t he f or ce hyster esi s i s about 0 N.

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ti me, SScal es :i sp 4. 47 mm di v

f or ce 62. 6 N/ di vdecel 1. 96 ms / d i vspeed 5. 15 rns / di v

- 2- 1

F i gur e 2. 3 Fo rce and decel e ra t i on r esponse t o a r api dl yappl i ed di spl acement l i m t ed ramp, ront brake400 m1 mot orcycl e.

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b

r

0)U0F

- 1Speed 1. 03 mn / di vi ni t i al s peed = 5. 41

t i c i nt er v al = 0. 125 S

F i gur e 2. 4 For ce gai n ver sus s peed, 400 m1 mot or cycl e.

m s

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- 1 1

0. 00 0. 05Fr ont Br ake Di sp. ( m>F i gur e 2. 5 Decel er at i on vs . di spl acement , 400 m1 mot or cycl e

10. 00

A01001a

0. 00 0. 0 200. 0F r ont Br ak e F or c e ( N>F i gur e 2.6 Decel er at i on vs. f or c e, 400 m1 mot or cycl e.

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As poi nt ed out by Zel l ner and Kl aher ( 1981) , t he presence o fhys te res i s r esul t s i n t he os s of f i ne cont r ol and i ncreases t hephase l a? bet ween sma l l a mp l i t ude co nt r o l i npu t snd machi ner eponses . Hys t er es i s t he re f o re degr ades t he qua l i t y o f t hebr ak i ng sys t em espec i al l y or f orce i nput s.

These data can al so be used to ext r act t he f or ce gai n GF andt he d i s p l a c eme nt p ai n G par a met e r s . The s l opes of t hedecel er at i on- di spl acement and t he decel er at i on- f or ce gr aphsdur i ng t he brake app l i ca t i on phase o f t he modul a t ed i nputr epr esent c and GF, r es pec t i vel y . A co mput e r p ro gr a m wa swr i t t en t o ext r ac t he dat a f or t he appl i cat i on phase and t henof i t a ' l east- squar es' str ai ght l i ne t o t he poi nt s. Thi s yi el dedan aver age di spl acement gai nG and f or ce gai n GF f or t he usabl er ange of t he br ake cont r ol .

8

E

6

2.5.4 Swept Si ne Wave Dat aT he s e da t a we r e us e d t o de t e r m ne de c el e r a t i o n/ f o r c e ,de ce l er a t i o n/ d i s p l a ce me nt and f o rce / di sp l a cement f r equencyr es p ons e f unc t i o ns , whi c h ar e s hown i n Fi gur e s7 and 2.8 and29 f or t he 400 m1 machi ne. For t he 400 m1 mot or cycl e, t he f or cegai n i s appr oxi mat el y const ant over t he r ange of r i der cont r olf r equenc i es , wher eas t he d i sp l acement gai n i s r equencydependent , i nc r eas i ng by a f ac t o r o f 3 bet ween 0.5 and 1. 5 Hz.The magni t ude o f t he ' dynam c s t i f f nes s' F/ 6 i s s i m l ar l yf r equency dependent : however , t her e i s a h i gh f r equency phasel ead f or t hi s f r equency r esponse f unct i on.

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1.

0.

?l

200. 0

Am(IIW"

F i gur e 2. 7 Decel e ra t i on- di spl acement t r ans f er f unc t i on,400 m1 mot or cvcl e.

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I '

F i gur e 2. 8 nec el er at i on- f or c e t r ans f er f unc t i on,400 m1 mot or cvc l e .

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F i gur e 2. 9 For ce- di snl acement t r ans f e r f unc t i on,400 m1 mot or cycl e.

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Scal es : di sp 4. 47 rmn/ di vf o r c e 31. 3 N/ di v

F i gur e 2. 10 Dynam c f or c e magni f i c at i on ef f ec t , f r ont br ak e400 m1 mot or cycl e.

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0 2 4 6 8 10 12 14 16 18 20t i me, S

Scal es :i sp 4. 47 mm di vf o r c e 62. 6 N/ di v

F i gur e 2. 11 Long t er m f r ont br ak e f or c e behavi our af t er ast ep i nput of di spl acement , 400 m1 mot orcycl e.

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2. 5. 5 St at i c Test s

Labor at or y t est s wi t h t he j nst r ument ed br ake syst emon t he 400 m1machi ne suppl i ed f ur t her i nf ormat i on. For exampl e, Fi gur e 2. 10c l ear l y demonst r a t es t he dy nam c f or c e magni f i c at i on ef f ec t( di scussed i n sect i on .5.2) i n r esponse t o a api d appl i cat i onof br ake l ever di spl acement . Fi gur e 2.11 shows f r ont br ake f or ceand di spl acement agai n, but over a much l onger t i me per i od. Her ei t c anbe seen t hat he f orce r equi r ed t o mai nt a i n a const antdi spl acement r educes onsi derabl y over t he f i r st f i ve seconds.Thi s i s t hought t o be due t o i nt e rnal l eakage wi t hi n t hehydr aul i c mast er cyl i nder . The brake syst em t hus pr esent s a t i mevar y i ng st i f f ness t o the r i der .26 MATHEPi ATI CAL MODEL OF AN HYDRAULI C DI SC BRAKE SYSTEM

A mat hemat i cal model of a t ypi cal mot orc- ycl e di sc br ake syst emwas devel oped t o account f or t he mai n f eat ur es of t he behavi ourobserved i n Sect i on 25 The det ai l s of t he model deri vat i on canbe f ound i n Appendi x.

Fi gur e 2.12 shows schemat i cal l y t hephysi cal ar r anpement of amot o r cyc l e hydr aul i c di sc br ake sys t em nd Fi gur e 2. 13 i s asymbo l i c r epr esent a t i on of t he i dent i f i abl e s t i f f ness. dampi ngand coul omb f r i ct i on ef f ect s.

261 For ce- di spl acement Behavi our

Fi gur e 2.14 i s a sket ch of t he expect ed f orce r esponse f or a verysl ow d i sp l acement i nput . Thi s pr edi ct ed r el at i onshi p compar esf avour abl y wi t h t he f or m obt ai ned n a l abor at or y t est of t he00m1 mot or cycl e f r ont brake, as hown i n Fi gur e 2.15.

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F

F i gur e 2. 14 Expect ed f or ce- di spl acement r esponse of brake model .

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Di spl acement , 4. 47 mm di v

F i gur e 2. 15 Fr ont brake f or ce- di spl acement behavi our whenbr ake i s s l owl y appl i ed, 400 m1 mot or cyc l e .

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2.6.2 Tr ansf er Funct i ons

The sys t em r epr esent ed i n F i gur e 2.13 i s non- l i near due t oc oul omb f r i c t i on ef f ec t s F c ~ , F c ~nd F c 3 , and due t odi s p l a c ement s t e ps d l , d2, d 3 and d4. F or t he pur poses ofaccount i ng f or t he ai n f eat ur es of t he swept si ne wave and st epdi s pl ac ement r es ul t s , a l i near dy nam c model i s uf f i c i ent .I gnori ng t he coul omb f or ces and ass um ng t he di spl acement st epst o be ' t aken up' , r esul t s i n t he si mpl i f i ed spr i ng- damper . modelshown i n Fi gur e 2.16,

I n Appendi x C i t i s shown t hat , f or t he model f Fi gur e 2.16,t he t r ans f er f unc t i on r e l at i ng br ak e l ev er f or c e F a nddi spl acement 6 i s of t he gener al f or mF 1 ( 1 +s/al )(l + s/a,)6 l /k , + l / k 3 + l /k, ( 1 +s / b l ) ( l + s/ b2)- = [ + - - - - - - - - - - - - - - - - - - _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ .2. 1)

The di sk c l a mp i ng f o r ce F i n r esponse t o br ake l everdi spl acement a nd f or c e i nput s i s det er m ned by t h e t r ans f erf unct i ons

C

1 1 ( 1 + s/a,)""""""""" """"""""""6 L l / k , + 1/ k3 + l /k, ( 1 + s/ bl ) ( l + s/ b2) ( 2. 2)

F 1 3c = [ """""""""""~ "-1 + s/ a3) . (2. 3)F 1 + kl / k2+kl / k3i k l / k 4 ( 1 +s/al )(l + s/a,)I f I t i . s a ssumed t hat t he mo t or cyc l e decel er a t i on i spr opor t i onal t o t he di s k c l ampi ng f or c e, equat i ons 2. 2) and

( 2. 3) c a nb eu s e d t o p r e d i c t h e o r m o f t h ede c el e r a t i o nl d i s p l a ce me nt and dec el er at i onf f or c e f r equenc yr esponse f unct i ons measur ed n t he swept si ne wave t ests.

By compar i ng t he t r ansf er f unct i on f or ms i n equat i ons (2.1)t o (2.3) wi t h t he co r r espond i ng dat a f o rhe 400 m1 mot or cycl e

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F i gur e 2. 16 Si mpl i f i ed spr i ng- damper model of b rake s y s t e m

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l eO- r -

- 1e0 . L . -0. l 0

FREQUENCY

l

1 . ~ - ~II1l

l .1. 00FREQUENCY

-

LI

F i gur e 2. 17 Pr edi ct ed f orce- di spl acement f r equencv r esponsef unc t i on.' I 2

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10.FREQUENCY

- 1B0. L -0. 1 0 I . 00 10.FREQUENCY (Hlz>

F i gur e 2. 18 pr edi c t ed decel erat i on- di spl acement f r equencyr esponse f unc t i on.43

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2QvH0l-

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01L00U-L01>01dY01Lom

F i gur e 2. 20 Pr edi c t ed br ake l ever f or ce r esponse af t er a s tepof l ever di spl acement .

0. 000 Ti me ( e> 1. 000

' 7i gure 2. 21 Predi c t ed mot orcyc l e dece l erat i on r esponse a f t er as t e p of l ever di spl acement .45

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2

0

000

a.PI- 0m40amPLL

0000. 000 Ti me

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( shown i n Fi gur es 2.9, 2. 7 and 2. 8) i t i s shown i n Appendi x Ct hat r easonabl e est i mat es of t he t r ansf er f unct i on par amet er sare:

a1/ 2n = 0.8 Hza2/ 2n = 6.0 Hza3/ 2n = 0.6 Hzb1/ 2n = 18 Hzb2/ 2n = 8.0 Hz

Bode pl ots of t he f r equency r esponse f unct i ons pr edi ct ed byequat i ons (2. 1) t o (2. 3) f or t hese par amet er val ues ar e shown nFi gur es 2. 17, 2. 18 and 2. 19. The ampl i t ude r at i os i n t hese pl ot shave been nor mal i sed y t he st eady- st at e val ues.

Det ai l ed compar i son of t he pr edi ct ed and measur ed Bode pl ot sshows t hat t he pr oposedmat hemat i cal model s abl e t o account f ort he mai n f eat ur es o f t he measur ed f r ont br ake r esponses, i npar t i cul ar t he r el at i vel yc ons t ant dec el er at i onl f or c e gai n andt he m d- f r equenc y ' pl at eau' i n de c el e r a t i o nl d i s p l a c eme nt andbr ake st i f f ness gai ns. The di f f erences bet ween t he phase cur vesar e al so wel l account ed f or .2. 6. 3 St ep Responses

Usi ng t he paramet er val ues est abl i shed i n t he l ast Sect i on, t het r ansf er f unct i ons n equat i on (2. 1) and (2.2) may a l s o be usedt o pr edi ct t he l ever f orce and mot orcycl e decel erat i on r esponsest o a st ep i nput of l ever di spl acement . These comput ed t r ansi entr esponses ( no rma l i sedby t he s t eady s t a t e val ues) a rehown i nFi gur es 2.20 and 2.21. The ' dynam c f orce magni f i cat i on' ef f ect ,not ed f o r t he 400 m1 mot or cycl e i n Fi gur es 2.3 and 2. 10, i scl ear l y evi dent i n t he pr edi ct ed br ake l ever f or ce.

The pr edi ct ed decel erat i on r esponse ( assumed pr oport i onal t ot he di s c c l ampi ng or c e) exhi bi t s a s i m l ar i ni t i al peak. Th eexpe r i ment a l decel e ra t i o n t r ace i n F i gur e 2. 3 al so sho ws an

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i ni t i al peak, f ol l owed hy s ome osci l l at i ons. An i ni t i al peak i nt he dece l e ra t i on r esponse o s t ep i nput sof hr ake cont r o l hasbeen not ed pr evi ous l y by Wei r , Ze l l ner and Teper (1978) andZel l ner and Kl aber (1981). Zel l ner (1980) at t r i but es t he peak t ot he t r ans i ent we i ght t r ans f er t o t he f r ont whe el whi c hmoment ar i l y j . ncreases t he hr aki ng f or ce avai l abl e. I twoul d seemt hat l ongi t udi nal t vr e dynam cs coul d pl ay a par t al so. Fi gur e23 i ndi cat es a r at her l i ght l y damped osci l l at ory dynam c mode.Suc h dy na m c e f f e ct s a r e not c ons i der ed i n t h e s i mpl emat hemat i cal model of Appendi x C

Tak i ng i t t ha t t hi s os ci l l at or y behavi our i sa r es ul t ofdynam c ef f ec t s not di r ec t l y r el at ed t ohe br ake mec hani s msmodel l ed i n Appendi x C, t hen t he f o r m pr edi c t ed f o r t hedecel er at i on t r ace appear s i n r easonabl e accor d wi t h t heexper i ment .

On t he whol e, i t may he conc l uded t ha t t he mat hemat i calmodel pr esent ed i n Appendi x C account s f or t he i mpor t ant aspect sof t he t r ansi ent and st eady- st at e r esponses of t he br ake syst emI t i s of s ome i nt er es t , t her ef or e,o use t he model t o pr edi c tt he mot or cyc l e r esponseo an i nput wh i ch oul d not be appl i ede xpe r i me nt a l l y wi t h anyccuracy: a s t ep i nput o f br ake l eve rf or c e. The r e s ul t , s hown i n F i gur e. 22, sugges t s t hat t he00m1 mot or cycl e woul d r espond ver y r api dl y and accur at el yo such af orce i nput .27 MI NI MUM TEST REQUI REMENTS FOR CHARACTERI ZATI ON OF A

MOTORCYCLE HYDRAULI C DI SCRAKE SYSTEMFr om t he exper i ~ment s onduct ed wi t h t he 400 m1 machi ne i t wasconcl uded t hat t he ol l owi ng t est pr ogr am shoul d be suf f i c i ent t oi dent i f y t he behavi our o f a mot orcycl e di sc brake:

( I ) St at i c abor a t or y es t s , t o r e vea l o r c e-d i s p l a c eme nt c ha r ac t e r i s t i c s , quant i f y i ng

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s t i f f ness , hys te res i s , dynam c f or ce magni f i cat i onand l eakage ef f ect s.

( 11) Di spl acement modul at i on t est s, car r i ed out i n t hef i el d, yi el di ng di s pl a cement l dec el er at i on gr adi ent ,f orcel decel erat i on gr adi ent and di spl acement - decel -er at i on and f or ce- decel er at i on hysteres i soops.

( 111) St ep di spl acement t est s t o al l ow obser vat i on ofr ecover y r at e gr adi ent ( RRG) and t he dynam c f or cemagni f i cat i on ef f ec t .

( I V) Swepti nei spl acementest i ng.hi sl l owsquant i f i cat i on of di spl acement l f or ce,ecel -er at i on/ di spl acement and decel er at i on/ f or cet r ansf er f unct i ons, and hence t he magni t ude andphase f r equency r esponse of he syst em

2. 8 DATA COLL ECTI ON W TH250 m1 AND 750 m1 MOTORCYCLES

The 250 m1 and 750 m1 machi nes wer e i nst r ument ed as descr i bed i nSect i on 2.3,., and Appendi x A

The t est pr ogr am out l i ned i n Sect i on2.7 was compl et ed wi t ht he 250 m1 and 750 m1 mot or cyc l es. Al l exper i ment swer econduct ed at t he Aust r al i an Ar my Tr i al s and Provi ng W ng atMonegeet t a. One t est r i der was used f or al l experi ment s.

The swept si ne di spl acement t est was not per f ormed wi t h t he750 m1 mot or cycl e due to l ack of t i me and i ncl ement weatherdur i ng t he dat a col l ect i on phase. However t hi s mot orc ycl e wasf i t t ed wi t h or gani c pads f t he same const r uct i on as t hosen t he400 m1 mot or cyc l e, and coul d be expect ed to behave i n a si m l armanner .

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2.9 RESULTS OF NOTORCYCL E BRAKE EXPERI MENTS2. 9. 1 250 m1 Mot or cyc l e

The s t a t i c l abo r a t o r y t es t s wer e per f o r medo st udy t he f o rce-di s pl ac ement c har ac t er i s t i c s of t he br ak e s y s t em on t hi smot orcycl e. Fi gur e 2.23(a) s hows f r ont brake f or ce as a f unct i onof t i me f or a st ep i nput of l ever di spl acement . A f o r c emagni f i cat i on of 0.5 s econds dur at i on i s evi dent i n t he i ni t i alr esponse t o t he r api d br ake appl i cat i on. Thi s ef f ect i s st r ongl ydependent o n t he r a t e at whi c h t he br a ke i s a ppl i e d;he r a t eus ed i n t hes e e xpe r i me nt s wo ul d be s i m l a r t o t ha t i n a nemer gency stop. The peak ampl i f i cat i on of t he st eady st at e f orcei n t hi s case i s appr oxi mat el y 30% The same f orce magni f i cat i onef f ect was observed wi t h the 400 m1 mot or cycl e. Fi gur e 2.23(b)shows t he f o r ce magni f i c a t i on f o rhe r ear brake on t he 250 m1mot orcycl e, and t he peak ampl i cat i on i s smal l er at about 12%

Leakage of hydr aul i c f l ui d past i l l - f i t t i ng mast er cyl i nderc ups wi l l r es ul t i n a de cr eas i ng f or c e l ev el at c o ns t antdi spl acement , and consequent l y educed decel er at i on wi t hi me.Fi gur e 2. 24(a) s hows no l eakage pr obl ems wi t h t he50 m1 f r ontbrake. Fi gur e 2.24(b) on t heot her hand, ndi cat es s omer el ax at i o n of f or c e l ev el ov er per i od of about 7 seconds f o rt he 250 m1 r ear brake.

Di spl acement cycl i ng of t he br akesn t he l abor at or ywas usedt o quant i f y hyst er esi s ef f ect s. F i gur es 2.25(a) and (b) showpl ot s o f br ake l ever f o r ce ver sus di spl acement f orhe 250 m1f r ont and r ear r akes. I n each ase yst eresi s oopi s cl ear l y evi dent . The upper par t of each cur ve cor r esponds tobr ake appl i cat i on. Dur i ng br ake r e l ease , t he br ake f o r cedecr eas es unt i l c o ul o mb f r i c t i o n f o r c e s i n t he s y s t e m a r eover come and t hen t he di s pl acement decr eases. As can he seenf rom Fi gure 2.25 t he hyst er esi s f or ce as about 25N f or t he f r ontbr ake and 60N f or t he r ear brake.

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T he f o r c e - d ec e l e r a t i o n a nd di s pl ac ement - dec el er at i ongr adi ent s wer e obt ai ned f r om t he dynam c di spl acement modul at i ont est procedur e out l i ned i n Sect i on 2.5.3. The br ake di spl acementand f orce gr adi ent swer e deter m ned by di gi t i z i ng and st or i ng t hedat a t hus obt ai ned onaPDP 11/ 23 comput er syst em A pr ogr am waswr i t t en whi ch accessed t he f orce, di spl acement and decel er at i ondat a dur i nF t he br ake onset phase, nd used l i near r egr ess i onanal ys i s t o f i t a s t r ai ght l i ne whi c h y i el ded t he r equi r edg r a di e nt s . F i g ur e s 2. 26( a) a nd ( h ) s h o w dec el e r a t i on-di spl acement and decel er at i on- f or ce dat a r espect i vel y f or t he 250m1 f r ont bra ke. The r egr ess i on l i nes ar e i nc l uded o n t hesegr aphs. The f r ont br aked i sp l acement gr adi ent wa s 2. 62 mms 2 / mand t he f o rce gr adi ent was 16. 8 Ns / m These f r ont br aker esul t s , and t hose f or t he r ear br ake, ar e set outn Tabl e 22

2

The st ep di spl acement dat awere al so di gi t i zed and st or edont he PDP 11/ 23 comput er ys tem Thi s enabl ed t he r ecover y r a t egr adi ent ( RRG - s ee Sect i on 2.5.2) t o be st udi ed. The RRG hasbe en i n t e r p r e t e d i n t h i s wo r k a s t he r at e o f change o fdecel er at i on f or ce Rai n i t h speed. The f or ce gai ns pl ot t edanai nst speed i n Fi gur es . 27(a) and ( h) f or t he f r o nt and r earbr akes r espect i vel y. The f orce gai n i s obser ved t o i ncr ease wi t hdecr eas i ng speed or bot h t he f r ont and r ear br ak es i t h t hi smot or c yc l e. Thi s mac hi ne i s f i t t ed wi t h met al s i nt er edads,wh i ch Ze l l ner nd Kl aber ( 1981) f o und ma y y i e l d pos i t i ve RRGunder dr y c ondi t i ons . T hi s di d i n f ac t oc c urn most occas i onswi t h t hi s mot or cycl e, and Fi gur es 2.27(a) and (b) ar e i ndi cat i veof t vpi cal per f or mance. The RRG f or t hese r uns was measur ed t ohe 1. 0 X w 3 - l 5- l on aver age, f or bot h f r ont and r ear br akes.These re su l t s a re pr esent ed i n T abl e 2.2. However , RRG wasobser ved t o change f r omr un t o r u n, and a l so dur i ng a r un, s ot hat pos i t i ve, zer o and negaci veRRGs wer e al l obser ved at somet i me wi t h t hi s mot or cyc l e. Thi s so mewha t e r r a t i c beha vi o urc a n no t h e expl . ai ned a t t hi s s t a ge , and wa r r a nt s f ur t heri nvest i gat i on.

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The swept - si ne di spl acement t est was al so per f or med, and t heda t a pr oc es s ed wi t h t he l abor at or y c omput er s y s t e m t o obt ai nf o rce / di sp l acement , decel erat i on/ di sp l acement and decel -er at i onl f or c e t r ans f er f unc t i ons . T he us e f ul f r eque nc y r a nge i sf r om zer o to about 7 Hz, whi ch was t he maxi mummodul at i onf r equency t he r i der coul d pr oduce. The r esul t s f o r t he f r ont andr ear br akes ar e shown i n Fi gur es 2. 28 (a), ( b) and (c) , and 2.29(a) , ( b) and ( c ) r espec t i vel y. As was not ed wi t h t he 400 m1mot or cyc l e ( see Sect i on 2. 5. 4). t he f o rce ga i n i s appr oxi mat el ycons t ant over t he r ange of r i der cont r o l f r equenc i es , and t hedi spl acement gai n and dynam c st i f f ness are f r equency dependenti n the r ange 0 t o 1.5 Hz.2.9.2 750 m1 Mot or cycl e

The s t at i c s t ep di spl acement t es t s f or th i s mot o rcyc l e r eveal eddynam c f or ce magni f i cat i on f o r t he f r ont br ake of 134, and 6%f or t he r ear br ake ( Fi gur es 2. 30 ( a) and (b)). Obser vat i on oft he s t ep di spl acement t r aces over a l onger t i me per i od i ndi cat edhydr aul i c f l ui d l eakage wi t h t he f r ont brake. The l ever f o rcedecr eased by 40 N i n 8.4 seconds. Negl i gi bl e l eakage, however,was obser ved wi t h t he r ear br ake.

The dynam c i spl acement modul at i on dat a wer e used t oi nves t i gat e f or c e hys t er es i sf f ec t s ( a s t het at i c dat aco l l ec t ed f or t hi s pur pose were unaccept abl y noi sy) . P l o t s ofbr ake f orce ver sus di spl acement f or t he f r ont and r ear br akes ar es hown i n Fi gur es 2. 31(a) and ( b) r espec t i vel y. For ce hys t er es i swas meas ur ed t o be 20 N wi t h t he f r ont br ake and 35 N wi t h t her ear br ake.

The f or c el dec el er at i on and di s pl a cement f de cel er a t i o ngr adi ent s wer e obt ai ned by a s i m l ar p rocedur e t o t hat used f ort he 250 m1 machi ne. The r esul t s , t oget her wi t h t hose obt ai nedf o r t h e 250 m1 and 400 m1 mot or cycl es, ar e shown i n Tabl e 2. 2.

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The dynam c st ep di spl acement dat a wer e used t o obt ai n t heRRG f or t he 750 m1 machi ne. The r esul t s ar e shown i n Fi gur e2.32(a) and (b). The RRG i s seen to be al most zer o, as was t hecase wi t h the 00 m1 mot orcycl e.2. 9. 3 Compar i son of 250 m , 400 m , and 750 m1 Br ake Syst em

Per f or manceThe f or ce magni f i cat i on phenomenon was obser ved wi t h al l t hehydr aul i c di sc br akes t est ed. The maxi mum ampl i f i cat i on obser vedwas appr oxi mat el y 30% fo r the 250 m1 f r ont br ake.

Leakage ef f ect s wer e not i ced wi t h t hree br ake syst ems. The750 m1 f r ont br ake f or ce dropped by 40 N i n 8. 4 seconds atconst ant di spl acement . Si m l ar pr obl ems were encount ered, to al esser ext ent , wi t h t he 400 m1 f r ont br ake and t he 250 m1 r earbrake.

For ce hyst er esi swas i nvest i gat ed, and a wi de r angeof val ueswasobser ved, ascanbeseen r om Tabl e 2. 2. The ar gesthyst er esi s f or ce was 70 N wi t h t he 400 m1 f r ont br ake, and t hesmal l est was 20 N wi t h t he 750 m1 f r ont br ake. Thi s r epr esent s a35 t i mesvar i at i on i n magni t ude.The ar gest earbrakehyst er esi s f or ce was 0 N wi t h the 250 m1 mot or cycl e.

A compar i son of f r ont br ake di spl acement gr adi ent s showedthat the 250 m1 machi ne had t he l ar gest val ue2. 62 mm s / m, andt he 750 m1 t he smal l est ( 2. 53 mm s2/ m . Thi s r epr esent s onl yabout 5% di f f er ence bet ween t he l ar gest and smal l est val ues off r ont br ake di spl acement gr adi ent . For t he r ear br akes, t he250 m1 machi nehad he ar gest di spl acement gr adi ent ( 4. 42mms / m, whi ch was 2.2 t i mes l arger t han t he m ni mum val ue1. 72mm s / m f ound wi t h t he 400 m1 r ear br ake. The l at t er has amechani cal l i nkage rat her t hann hydr aul i c syst em

2

22

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0. 05

4I IL0

LL- 0. 05

4- 44-0. 00 5. 00Ti me (8)

200. 0 r""" ' "I0- a JLLL04c0LLL

- 200.F i gur e 2. 23 ( a) Dynam c f or c e magni f i c at i on ef f ec t , f r ont br ak e

250 m1 mot or cycl e.54

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0. 05

- 0. 050. 00 Ti me ( S) 5. 00

200a. r -' 'ynz -W -.010L0

---LL -

a JY0m -1 --L0alK ---

- 200. 0.0. 00 5. 00Ti me ( S)

F i gur e 2. 23 ( b) Dynam c f or c e magni f i c at i on e f f e c t , rea r b rake250 m1 mot or cycl e.

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200.nZWa,0L0LL

c

- 200.

0 ~" ' " " " " " " " " " " 'di spl acement

--

F i gur e 2. 24 ( a) Fr ont br ake f orce behavi our over 9 S , 250 m1 mot or cyc l e

200.nzvar0L0LL

- 200.

0

di spl acement

00. 00Ti me ( S) 00F i gur e 2. 24 ( b) Rear br ake f orce behavi our over 7 S , 250 m1 mot or cyc l e

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100. 0 r

0. 00.0 Fr ont Br ake Di sp. ( m>F i gur e 2. 25 ( a) F ro nt br ak e f or c e- di s pl ac ement c har ac t er i s t i c s

200. 0

0. 0

250 m1 mot or cycl e.

1

0. 00 0. 05Rear Br ake Di sp. ( m>F i gur e 2. 25 ( b) Rear br ake f o rce - di spl acement char ac te r i s t i c s ,

250 m1 mot or cycl e.51

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10. 00

0. 00

r

0.0 0. 05Fr ont Br ake Di sp. ( m>F i gur e 2. 26 ( a ) F r ont br ake decel er at i on- di spl acement

c har a ct er i s t i c s, 250 m1 mot or cyc l e.

10. 00G**0\E\ i /

0. 00 0. 0 200. 0F r ont Br ake For ce ( NIF i gur e 2. 26 ( b) F ro nt br ak e dec el er at i on- f or c e

c har a ct er i s t i c s, 250 m1 mot or cyc l e.58

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0. 1Ela(a )Front brake

I

0. 000. -0. 00

0. 050

0. 000

10.mSpeed ( m/ s>

( b) Rear br ake 1

0. 00 10. 00Speed ( m s >F i gur e 2. 27 Force gai n ver sus speed, 250 m1 mot or cycl e.

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nE\Ec\]**\WE

rl

UW

260

E

( a) Decel er at i on/ di spl acement .

"

-200. 0 L 10-05 Fr eq ( Hz> 50. 00

F i gur e 2. 28 Fr equencv r esponse f unct i ons , 250 m1 mot or cycl e,f r ont hrake.

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nN**\0EU"LL\0

t i

0. 001"" ' i l.0. 05 F r eq ( HA 50. 00

tli

F i gur e 2. 28 cont 3

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( C ) For ce/ d i sp l acement .

200. 0 1 1 "lt

I "Ld50. 007

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(a) Decel erat i onl di spl acement .2. 000 7 - r - r 8 3 I -

200. 0

- 200. 00. 05 F r eq (Hz) 50. 00

F i gur e 2. 29 Pr equencv r esnonse f unc t i ons , 250 m1 mot or cyc l e ,r ear br ake.63

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( h) Dec el er at i on/ f or c e.

Z\ ,

0. I I .LA50. 00

0. 05 Fr eq Wz > 50. 00

F i gur e 2. 29 ( cont . )

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L

.

"7

L 50. 00

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0. 050nEW

- 0. 0500. 000 5. 000Ti me ( S)

500. 0 -nW -

-z 4

. a ,0LLL0

Y(UDL

-

/m- c,f0 -LLL

-- -- 500. 0 L0. 000 5. 000Ti me ( S)

F i gur e 2. 30 ( a) Dy nam c f or c e magni f i c at i on ef f ec t , f r ont br ak e750 m1 mot or cycl e.66

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0. 050

200.AZWa,0L

LLYQ5Lm

- 200.

1

*

0. 000 5. 000Ti me ( S)F i eur e 2. 30 ( b) Dy nam c f or c e magni f i c at i on ef f ec t , r ear b ra k e

750 m1 mot or cycl e.67

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200.nZWa0L0LL(UY0Lm

-clI I0LLL

0.

0

0

l

~ 0. 000 0. 05Fr ont Br ake Di sp. ( m>F i gur e 2. 31 ( a) F ro nt br ak e f or c e- di s pl ac ement c har ac t er i s t i c s

750 m1 mot or cycl e.

InW

0. 000 0. 05Rear Br ake Di sp. ( m>F i gur e 2. 31 ( b) Rear b rake f or ce- di spl acement char ac t er i s t i c s

750 m1 mot or cycl e.68

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0.

0.

0. 050( h) Rear brake

a0L0LL0. 000 '0. 00 20. 00Speed ( m/ s)

F i gur e 2. 32 Force ga i n ver sus speed, 750 m mo t o r c y cl e .

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TABLE 2.2.PRODUCTI ON MOTORCYCL E BRAKE RESPONSE PARAMETERS.

Machi ne Di spl acement Force Br ake Force Recover y Rat eCapaci t y Gr adi ent Gr a di ent St i f f ness Hy s t e r es i s Gr adi ent

Brakem ) ( m s / m ( N. s2/ m ( N / d 0-0 ( l / Ns )Front 250 2.626. 8. 4 25 1.0 X 10- 3

400 2.606. 54. 0 70 007 50 2.535. 1. 9 20 0.0

Rear 250 4. 429.01. 2 60 10 X 1 0 - ~400 2.008.39. 2 " 0.0750 3.255.5.9 35 00

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The ar gest al ue of f r ont r ake or ce r adi entwas36. 5 N. s2/ m f or t he 400 m1 mot or cycl e, and t he smal l est val ue16. 8 N. s2/ m f o r t he 250 m1 machi ne. Of t he r ear brake f orcegr adi ent s , t he 250 m1 had t he l argest val ue of 49. 0 Ns / m andt he 750 m1 t he smal l est at25 . 5 Ns / m

22

Thus, f or di spl acement gr adi ent s, t here was consi derabl y morevar i at i on bet ween t he r ear br akes of t hese machi nes t han f or t hef r ont br akes. The var i at i on i n f or ce gr adi ent s was si m l ar f ort he f r ont and rear br akes.

Br ake st i f f ness was al so assessed. The 250 m1 f r ont br akehad t he l owest st i f f ness of 6.4 N/ mm wi t h t he 400 m1 havi ng t he' st i f f est ' f r ont brake wi t h 14 N/ m. The owest r ear br akest i f f ness occur r ed wi t h the 750 m1 machi ne, bei ng 7. 9 N/ mm andt he maxi mum val ue was f or t he00 m1 mot or cycl e wi t h 19. 2 N/ mmThere was a l arge var i ati on i n st i f f ness, wi t h a maxi mum t om ni mum r at i o of 2. 2 f or t he f r ont br akes, and 2.4 f or t he r earbrakes.

The mot orcycl es wi t h or gani c di sc pads ( 400 m1 and 750 m )exhi bi t ed zer o RRG. The 250 m1 mot or cycl e wi t h met al si nt er edpads had a s i gni f i c ant pos i t i ve RRG ( f r ont br ake and r ear br ake10 X 10- 3 Nls-'). These r esul t s conf i r m t hose of Zel l ner andKl aber ( 1981) whi ch suggest s i m l ar di f f er ences bet ween or gani cand s i nt er ed met al f r i c t i on char acter i s t i cs .

The swept si ne di spl acement modul at i on dat a r eveal ed nodi f f er ences i n the f or m of t he f or cel di spl acement , decel er at i on/di spl acement and decel er at i on/ f or ce t r ansf er f unct i ons bet weenmot or cycl es.

2. 10 SUMMARY AND CONCLUSI ONS

A t est pr ogr amwas desi gned f or dynam c charact eri zat i on ofmot or cycl e di sc brake per f or mance. The m ni mum r equi r ement s wer ef ound t o be as f ol l ows:

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* St at i c t e st s( a) St ep i nput of d i spl acement . By moni t or i ng br ake f or ce

dur i ng t hi s pr ocedur e, t wo phenomena can be obser ved.F i r s t l y, f or c e magni f i c at i on s evi dent dur i ng t hei n i t i a lppl i c at i on phas e; s ec ondl y , l ong t e rmobs er v at i onwi l l eveal eakagepr obl ems ( i f t heyexi s t ) .

( b) Di spl acement cyc l i ng,whi ch al l ows ssess ment off or ce- di spl acement hysteres i s .

* Dynam c Test s( a) St ep i nput of di spl acement . The change of f orce gai n,

GF, wi t h speed, V, can be comput ed f r om t hese dat a,y i e l di ng t he Recover y Rate Gr adi ent (RRG) .

( b) Low f r equency (

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The over al l r ange f or t he di spl acement gr adi ent was f ound t obe 2. 0 mm s / m t o 4.4 mm s / m whi ch i s a 2. 2 t i mes var i at i on.The f orce/ decel erat i on gr adi ent s were f ound to be i n t he r ange16. 8 N. s2/ m to 49.0 N. s2/ m whi ch i s a t hr ee- f ol d var i at i on. Ther ear brakes wer e a gr eat er sour ce of var i abi l i t y than t he f r ontbr akes f or bot h t hese cont r ol gr adi ent s. Br ake st i f f ness wasmeasur ed and f ound t o var y bet ween9. 2 N/ mm t o 6.4 N/ mm f o r t hemot or cycl es t est ed. Thi s r ange r epr esent s a r at i o of 3: l . Whent hi s compar i son i s made excl udi ng t he mechani cal r ear br ake ont he 400 m1 machi ne, t he r ange i s 14.0 N/ mm t o 6. 4 Nj mm a r at i oof 2. 2: l .

2 2

The dat a obt ai ned f r omhe dynam c l ow- f r equency di spl acementcycl i ng show t he decel er at i on- di spl acement and decel er at i on- f or cechar acter i s t i cs. I t was seen t hat wher eas decel er at i on f ol l owedt hemodul at eddi spl acement nputqui t e l osel y, her ewassubst ant i al hyst er esi s i n t he r esponse t o f or ce nput s. Theef f ectofhyst er esi s s l os s of pr ec i s i on i n f i ne br aki ngcont r ol . The t ypi cal f or ce hyst er esi s was measur ed t o be about40 N. The maxi mum val ue obs er ved was 70 N f or t he 400 m1 f r ontbrake.

The f r equency r esponse f unct i ons comput edr om t he swept si nedi spl acement dat a r eveal t hat t he f orce gai n was appr oxi mat el yconst ant over t he r ange f r i der cont r ol f r equenci es, wher eas t hedynam cs t i f f nes sand hedi spl acementgai nwer e r equencydependent . The l at t er i ncr eased by a f act or of about t wo f r om0. 5 t o 1 Hz and t hen r emai ned r el at i vel y const ant at hi gherf r equenci es. Thi s char act er i st i c was i ndependent of t he t ype ofdi sc br ake pad mat er i al used,

The var i at i on of f or ce gai n wi t h speed was i nt erpr et ed asRRG. Thi s par amet er was f ound t o be zer o f or t he mot or cycl eswi t h or gani c di sc pads. The 250 m1 mot or cycl e had met al si nt er ed

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' al l weat her ' di s c pads , whi ch gener al l y exhi bi t ed a pos i t i veRRG, wi t h an aver age val ue of 10 X 10- 3 N- l s - l f o r bot h t hef r ont and r ear br akes.

Leakage of hydraul i c f l u i d past t he master cyl i nder cups wasobser ved wi t h t hr ee of t he f i ve hydr aul i c br akes t es t ed. I t wasmost sever e wi t h t he 750 m1 f r ont br ake, wher e at const antdi spl acement t he br ake f or ce dr opped by 40 N i n 8.4 seconds.Thus , t h e br ake s ys t em wi t h eak age pr es ent s a t i me v ar y i ngs t i f f nes s t o t he r i der .

To f ur t he r desc r i be t he dynam c behav i our of a sys t em i t i susua l t o speci f y a measur e of t he r api di t y of t he syst emr esponset o cont r o l i nput s . The dece l e ra t i on r esponse o f t he moto r cycl eswas ver y r api d , t he d i f f erence bet ween t he 63% r i se t i mes ofdece l er at i on and l ever di spl acement bei ng of t he or der o f 25 ms.I n human oper at or cont r ol t er ms , t her ef or e, t he dece l e ra t i onr esponse t o brake l ever movement can be r egarded as ef f ect i vel yi ns t ant aneous . The pr esence of f o r ce hyst er es i s r esul t s i n somephase l ag f or smal l ampl i t ude modul at i on of t he r i der ' s f o r c ei nput .

The var i ous phenomena descr i bed above have been account ed f orby a mat hemat i cal model of t he br ake syst em dynam cs. The modelaccounted f or t he mai n f eat ur es of t he r esponses, such as:

* dynam c f or ce magni f i cat i on* t i me- var yi ng s t i f f nes s* hy s t e re s i s l oops* f r equency r esponse f unct i ons