Vehicle dynamics, stabilty and brake performance of ... dynamics, stabilty and brake performance of...
Transcript of Vehicle dynamics, stabilty and brake performance of ... dynamics, stabilty and brake performance of...
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
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PART ONE – VEHICLE
DYNAMICS
Vortragstitel
Vortragender, Ort, Datum
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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
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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
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X =Input axis: Roll velocity
Y = Spinning axis
Z = Output
axis: Steering
torque
y
z
x
Wheel,Rot
Gyroscope: Reaction on roll
velocity
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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
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INSTABILITIES
Vortragstitel
Vortragender, Ort, Datum
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Instabilities
Kickback
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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
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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
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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
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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
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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
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Positionen der überfahrenen Stufen
zu den Rädern beim Lenkerschlagen
/ t = ca. 300 grd/s
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Kick back
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TRANSIENT CORNERING
Vortragstitel
Vortragender, Ort, Datum
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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
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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
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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
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Lateral µ demand: corner braking
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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
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PART TWO – BRAKE
PERFORMANCE
Vortragstitel
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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
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TIRE PROPERTIES
Vortragstitel
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Front tire type influence on µ-sL
ate
ral fr
icto
nco
effic
ient
µl
Dry asphalt
Slip value s
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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
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Vehicle velocity on µ-s
Schlupf s
Late
ral fr
icto
nco
effic
ient
µl
Wet asphalt
Slip value s
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BRAKE FORCE DISTRIBUTION
Vortragstitel
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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
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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
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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
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FRONT WHEEL LOCKING
Vortragstitel
Vortragender, Ort, Datum
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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
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Experiment: dynamic front wheel
lock
Fo
rce
in
N
Velo
city
in k
ph
Time in N
Brake force
Wheel load
Wheel speed
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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
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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
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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
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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
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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
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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