Fachgebiet Fahrzeugtechnik

Prof. Dr. rer. nat. Hermann Winner

Vehicle dynamics, stabilty and brake

performance of motorcycles

Dipl.-Ing. Patrick Seiniger

MYMOSA Training Course on PTW

Accident Research and Reconstruction,

Neumünster, 23.1.2008

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Introduction and Overview

Vehicle dynamics

› Stability for steady-stade situations,

› Instabilities,

› Transient situations,

Brake performance of Motorcycles

› Physical limitations,

› Limitations due to rider abilities,

› ABS-Systems.

Typical motorcycle accidents

3/70

PART ONE – VEHICLE

DYNAMICS

Vortragstitel

Vortragender, Ort, Datum

4/70

Vehicle dynamics

Steady-state cornering

Stabilization mechanisms

• Steering control

• Gyroscopic effects

Instabilities

• Wobble

• Weave

• Kick-back

Transient cornering

5/70

STEADY-STATE CORNERING

AND STABILIZATION

Vortragstitel

Vortragender, Ort, Datum

6/70

Steady-state cornering

Passenger car Motorcycle

FF

G

G

FF

Fres

λ

Quelle:BMW Group

7/70

Roll equilibrium of forces and

momentum

8/70

Stabilization mechanisms

V = 0 kph V < 40 kph

V < 40 kph V > 40 kphSource:ARD

9/70

Geometric properties

Castor angle

Trail of front wheel

wheel base

10/70

Stabilization by steering control

Wheel contact patch

axis is moved by

steering angle control

Steering system

Frame system

Wheel contact patch

axis

trail

Wheelb

ase

Weight force arm is

controlled

Top view Rear view

Up to 30 kph

12/70

Gyroscopic effect:

Right-hand-rule

above 30 kph

Right-hand rule for gyroscopic effect:

R = Spinning axis

S = Input Axis

A = Output Axis

Output Spinning Spinning InputT

13/70

X =Input axis: Roll velocity

Y = Spinning axis

Z = Output

axis: Steering

torque

y

z

x

Wheel,Rot

Gyroscope: Reaction on roll

velocity

14/70

Stabilization by gyroscopic effect

Banking to the right

induces steering angle

to the right

Steering angle to the right

generates side force to the

right

Upside-down pendulum

is an unstable system –

will be destabilized for

any pertubation

Side force to the right results in

lateral acceleration to the left and

thus roll momentum to the left

• Capsize is fully damped by this

mechanism above approx. 30 kph

15/70

INSTABILITIES

Vortragstitel

Vortragender, Ort, Datum

16/70

Instabilities

Kickback

17/70

Wobble mode

• natural mode of steering system

• natural mode demands

• angle steering angle

• angle-dependant moment front

tire self-alingment moment

• inertia moment of inertia with

respect to steering axis

• excitation uneven roads, … .

• frequency approx 10 Hz, velocity

approx. 50…60 kph

Quelle:Uni Padua

18/70

Weave mode

• natural frequency of the whole vehicle

(over-compensated stabilization effect)

• Speed approx. 160 kph … vmax

• Freqency approx. 2…4 hz

• Very dangerous instability

Quelle:Uni Padua

19/70Quelle: Bayer, B.: Das Pendeln und Flattern von Krafträdern. Diss. THD 1985

Typical weave data

Steering

torque

Steering

angle

Lateral

acceleration

Vehicle

velocity

20/70

Attenuation Factor as function of

vehicle velocity and rider‘s posture

0,300,250,200,150,100,050

Dämpfungsra

te D

100 120 140 160 180[km/h]Fahrgeschwindigkeit v

Füße des Fahrers aufFahrerfußrastenFüße des Fahrers aufhinteren Fußrasten

Att

en

uati

on

Facto

rD

Vehicle velocity in kph

Rider‘s feet on Riders‘s

footpegs

Rider‘s feet on rear

footpegs

21/70

Weave damping with certain

vehicle modifications

Rid

er‘

sfe

et

on

Rid

ers

‘sfo

otp

eg

s

Mo

torc

ycle

tra

vell

ing

wit

hp

ass

en

ger

…w

ith

2 c

as

es

, in

to

tal 20

kg

Bag

gag

e5 k

g f

ixed

tofo

rk

Wit

hste

eri

ng

win

dsh

ield

Incre

as

ed

fork

sti

ffn

ess

Ste

eri

ng

dam

per Ste

er

beari

ng

wit

h

tom

uch

fric

tio

n

Ste

er

beari

ng

wit

h

tom

uch

fric

tio

n

Un

bala

nced

fro

nt

wh

eel

Un

pro

per

tire

s

Base: Motorcycle

without any

modifications at 130

kph

22/70

Measure Weave Handling Wobble

Longer wheel base + - o

Longer castor + - -

Roll higher + - o

Steer higher - - +

Baggage (without own damping) - - -

weight distribution changed to front + -* +

Higher tire damping + o +

Higher torsional and lateral stiffness of

tires

+ o -

+ improvement o neutral - worsening

* no negative influence on front if achieved by aerodynamic measures

Constructive measures

23/70

Kick-back

• parametric excited vibration of steering

system

• Demands:

• wheel load variation on front wheel

• side force on front wheel

• Initiation:

• Front wheel runs with low load and

large side-slip angle

• wheel load increases immedeatly

• side force also increases

immedeatly inducing a high steering

torque

• dangerous with uneven roads

Quelle:ARD, Eurosport

24/70

Experiment to

provoke kick-backParameter variations:

-One or two steps,

-Engine torque and gear,

-Cornering, riding straight ahead

-Rider posture

-Additional off-center mass

25/70

Positionen der überfahrenen Stufen

zu den Rädern beim Lenkerschlagen

/ t = ca. 300 grd/s

26/70

Kick back

27/70

TRANSIENT CORNERING

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28/70

Initiation of a bend

iiizis kkFF ,,,,

, ,( ) sin

cos

Roll s v s h s

s

F F h

m g h

Couter-steering to

increase roll angle

29/70

Transient cornering, trajectory

for motorcycle

Counter-steering to

increase roll angle

• Motorcycles initiate a

bend with counter-

steering

• Space demand is higher

than for cars

30/70

Lateral µ demand for transient

cornering

0

0zF m g

yF m ylateral

cos ²z sF m g m h

sin ²y sF m y m h lateral

cos ² sinz s sF m g m h m h

sin ² cosy s sF m y m h m h lateral

31/70

Lateral µ demand: corner braking

32/70

Summary: vehicle dynamics

Steady-state situations

• Roll angle is a function of lateral acceleration

Stability is achieved by

• Steer angle control by rider (up to 30 kph)

• Gyroscopic effects above 30 kph (beginning at 20 kph)

Instabilities

• Wobble is harmless

• Weave is often dangerous, induced by wrong loading and speeding

• Kick back is dangerous and induced by uneven roads

Transient cornering

• Motorcycles counter-steer

33/70

PART TWO – BRAKE

PERFORMANCE

Vortragstitel

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34/70

Brake performance

• µ-s-plots for motorcycle tires

• Ideal brake force distribution

• Real (rider-controlled) brake force distribution

• Brake pitch movement

• Front wheel lock and ABS

• Corner braking

35/70

TIRE PROPERTIES

Vortragstitel

Vortragender, Ort, Datum

36/70

Front tire type influence on µ-sL

ate

ral fr

icto

nco

effic

ient

µl

Dry asphalt

Slip value s

37/70

Tire pressure on µ-s

Kra

ftsch

lussb

eiw

ert

µl

Schlupf s

Dry asphalt

Late

ral fr

icto

nco

effic

ient

µl

Slip value s

38/70

Vehicle velocity on µ-s

Schlupf s

Late

ral fr

icto

nco

effic

ient

µl

Wet asphalt

Slip value s

39/70

BRAKE FORCE DISTRIBUTION

Vortragstitel

Vortragender, Ort, Datum

40/70

Center of Gravity Mot - Car

lv,Krad

lv,PKW

lPKW

lKrad

SPKW

SKrad

CG height approx. equal

Wheel base approx. half Rear wheel lift-off possible

due to relatively high CG

41/70

Equations ideal brake force

distribution

,

,

!

, , ,

,

h s

z v

v s

z h

B i z i z i

B v h

Dynamic wheel load

l hF m g m x

l l

l hF m g m x

l l

and brake force at constant friction

xF F F

g

shows brake forces for equal friction coefficient on both wheels

F lx

m g g l

,

²

²

²

²

s

B h v s

hx

g l

F l hx x

m g g l g l

0 :x accelerating

42/70

Ideal brake force distribution

0 0.2 0.4 0.6 0.8 1 1.20

0.05

0.1

0.15

0.2

0.25

1 2 3 4 5 6 7 8 9 10 11

FB,front

/ (m g)

FB

,rea

r / (

mg

)

lines o

f consta

nt d

ecelle

ratio

n

ideal BFD with pitching movement neglected

Car Opel Astra HMotorcycle BMW R1150RT

43/70

Real BFD of an unexperienced

rider

44/70

Brake pitch: effects on vehicle

geometry

Konstanter

Nachlauf

Eintauchweg

Case 1: compression for constant velocity (a = 0)

Case 2: braking

trailis shortened due to pitch movement

Brake pitch shortens the vehicle

trail, vehicle gets more unstable

45/70

FRONT WHEEL LOCKING

Vortragstitel

Vortragender, Ort, Datum

46/70

Brake pitch: wheel load change

Zeit t

Gv,stat

Gv,dyn

Annahme:µ = 1

FB,v

µ

µ

gleit

0

0

t a t s t v

Vo

rde

rra

db

rem

skra

ft F

B,v

dyn

am

ische

Vo

rde

rrad

last

Gv,d

yn

Dynam

ic w

hee

llo

ad

Fro

nt w

he

elbra

ke

forc

e

47/70

Experiment: dynamic front wheel

lock

Fo

rce

in

N

Velo

city

in k

ph

Time in N

Brake force

Wheel load

Wheel speed

48/70

Instability due to front wheel lock

λth

Rear wheel contact patch

Fz

G

Rear wheel contact patch

Rear view Top view

Y component ofbrake force

Vehicle side-slip angle = 0

Vehicle side-slip angle > 0

Front wheel contact patchfor S-S angle > 0

System CG

FB

max

Front wheel contact patch

49/70

Evolution of ABS

System Manufacturer Integral comments

ABS 1 (1988) FTE no 2 brake pressure modulators, one for each wheel

ABS 2 (1993) FTE no First system with combined modulator

IABS 1 (2001) FTE yes, hydraulic First and only motorcycle system with brake force

boost

IABS 2 (2006) Conti yes, electric Half ESP hydraulic control unit (HCU)

CBS-ABS (1992) Honda yes, hydraulic Hydraulic brake force distribution

Magnetventil

(1994)

Bosch no low cost system

ABS 8M (2006) Bosch yes Half ESP HCU

50/70

CORNER BRAKING

Vortragstitel

Vortragender, Ort, Datum

51/70

Corner braking

52/70

Potential of corner braking

Ideal corner braking:

100%

160%Brake distance

from 30 m/s

(calculation)

Front wheel lock leads to capsize [no ABS]

Pulsating steering torque destabiles

vehicle [ABS]

y

-x

max

Friction circle

53/70

Today‘s ABS and corner

detection

State of technology for ABS

› Control frequency approx. 5 Hz

› Adaptive brake force distribution

› Systems are considered „corner approved“ with limitations [BMW

Motorrad: Das neue Integral ABS, ATZ 103(2001)3]

› No brake system has corner detecion

› Adaption of BFD to corner situation is not possible

54/70

Corner braking

Experiment

Corner braking

› Friction µmax > 1

› Mean decceleration 7,7 m/s²

› ABS control at λ = 20

Bild: Google Earth / GeoContent

Contidrom, Jeversen

100 km/h

R = 100

55/70

Corner braking (2)

-1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 30

20

40

60

80

100

120G

eschw

indig

keit [

km

/h]

Radgeschwindigkeit vorneRadgeschwindigkeit hinten

Wheel speed

decrease, front

Wheel speed

decrease, rear

56/70

Corner braking (3)

-1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 3-40

-35

-30

-25

-20

-15

-10

-5

0

5

10W

inkel [°

]

LenkerdrehwinkelRollwinkel

Vehicle raises fast

Steer angle oscillation

Steering angle

Roll angle

57/70

Summery brake performance

µ-s-plots of motorcycle tires

• Slightly higher friction values than cars

Ideal brake force distribution

• Rear wheel lift-off is possible

Real brake force disrtibution

• Riders do not reach the real BFD

Brake pitch

• Brake pitch changes geometry

• Slow pitch movements and high brake force gradients can result in early front

wheel locks

Front wheel lock

• Motorcycles are instable for front wheel lock and will capsize very fast

Corner braking

• Today, no corner braking systems available, but will be on the marked in 5 to 10 years

58/70

PART THREE – ACCIDENTS

Vortragstitel

Vortragender, Ort, Datum

59/70

Consequences for typical

accidents

Examples

• Wrong brake force distribution

• Front wheel lock

Potential for ABS

60/70

Example 1: accident scene

Quelle: Sporner, A.: Das Zusammenspiel von aktiver und passiver Sicherheit

beim Motorrad am Beispiel ABS. Fahrzeugtechnisches Seminar TU Darmstadt 2000

61/70

Example 1: Sketch

Fall

vF=85 km/hvK=35 km/h

Theoretical demand ofbrake distance 30,5 mFinal pos.

brake initiationscratches

Skid marks FW 12m

Skid marks RW 23,8m

Without fall, the motorcycle would have stopped approx. 4 m in front of the car – the rider would have

survived.

Quelle: Sporner, A. und T. Kramlich: Zusammenspiel von aktiver und passiver Sicher-

heit bei Motorradkollisionen. 3. Internationale Motorradkonferenz, München 2000

62/70

Example 1: simulation

Quelle: Sporner, A.: Das Zusammenspiel von aktiver und passiver Sicherheit beim Motorrad am Beispiel ABS. Fahrzeugtechnisches Seminar TU Darmstadt 2000

63/70

Example 1 with ABS

Quelle: Sporner, A.: Das Zusammenspiel von aktiver und passiver Sicherheit beim Motorrad am Beispiel ABS. Fahrzeugtechnisches Seminar TU Darmstadt 2000

64/70

Exanple 2: scene

Overview

Final pos

Quelle: Sporner, A.: Das Zusammenspiel von aktiver und passiver Sicherheit

beim Motorrad am Beispiel ABS. Fahrzeugtechnisches Seminar TU Darmstadt 2000

65/70

Example 2

scratches

In this position, the motorcycle

crashed

Quelle: Sporner, A.: Das Zusammenspiel von aktiver und passiver Sicherheit

beim Motorrad am Beispiel ABS. Fahrzeugtechnisches Seminar TU Darmstadt 2000

66/70

theoretical demand

of brake distance

Skid marks RW: 10,4 m

Skid marks FW: 7 m

Fall

v=88 km/h

Final pos

vk 74 km/h

vABS = 64 km/h

Example 2: Sketch

Quelle: Sporner, A. und T. Kramlich: Zusammenspiel von aktiver und passiver Sicher-

heit bei Motorradkollisionen. 3. Internationale Motorradkonferenz, München 2000

67/70

MAIS for Car-Motorcycle Collisions

0,3

11,2

28,0

43,3

5,2 4,07,9

88,4

17,1

2,4

19,0

42,9

9,5 9,5

16,7

97,6

35,7

0

10

20

30

40

50

60

70

80

90

100

MAIS 0 MAIS 1 MAIS 2 MAIS 3 MAIS 4 MAIS 5 MAIS 6 MAIS 2+ MAIS 4+

%

all accidents (n=596)

Accidents with a fall event

When a Fall occurs, the risk of having injuries MAIS 4+ is doubled

Leichte

Verletzungen

Schwere bis tödl.

VerletzungenQuelle: Sporner, A.: Das Zusammenspiel von aktiver und passiver Sicherheit

beim Motorrad am Beispiel ABS. Fahrzeugtechnisches Seminar TU Darmstadt 2000

68/70

Potential for Motorcycle ABS

Quelle: Pressemitteilungen des Gesamtverbands der Deutschen Versicherungswirtschaft, München 2000

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

In 6

5 %

alle

r K

ollis

ionen

zw

ischen P

kw

und

Moto

rrad k

ann d

er

Moto

rradfa

hre

r ein

eB

rem

sung

ein

leiten

In 2

0 %

die

ser

Fä

llekom

mt es z

um

Stu

rz

In 9

3 %

die

ser

Fä

llew

äre

der

Moto

rrad-

fahre

r m

it A

BS

nic

ht

gestü

rzt

Moto

rcycle

rid

er

bra

ke

d

the v

ehic

lein

65%

ofall

car-

moto

rcycle

colli

sio

ns

In 2

0%

ofall

these

situations

a fall

occure

d

In 9

3%

ofall

these

situations

AB

S c

ould

have

pre

ven

ted

the fall

event

8-10%

69/70

Summary

Typical accidents

Examples

• Wrong BFD

• Front Wheel lock

Expectations for ABS

• Experts say 8…10% less killed motorcycle riders with 100% ABS

70/70

Thank you for your attention.

Any questions left ?

71/70

Bremskraftverteilung

Honda CBR 1000 F

72/70

Funktionsschema Honda Dual CBS

73/70

Radumfangsgeschwindigkeit

Rad

um

fan

gsg

esch

win

dig

keit

Bre

msd

ruck a

m S

att

el

Zeit

Bremsdruck am Sattel

Prinzip einer ABV-Regelung

74/70

1 vom Hauptbremszylinder

2 zum Radbremszylinder

3 Kolben

4 Umlenkung

5 Kern

6 Elektromagnet

1

23

45

6

ABS Druckmodulator

75/70

Schaltplan des BMW

Magnetventil-ABS

76/70

Schaltplan des BMW Integral-ABS

77/70

ABS-Bremsung auf einer Fahrbahn

mit hohem Reibwert

78/70

ABS-Bremsung auf poliertem,

nassem Kiesel

79/70

Indirekte Rückschlüsse auf ein

abhebendes Hinterrad