design and vehicle implementation of an adaptive abs
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Design and Vehicle Implementation of an Adaptive ABS. J. Tigelaar 13 May 2011. 1. Design and Vehicle Implementation of an Adaptive ABS. Design and Vehicle Implementation of an Adaptive ABS. Goal. … Taking the research one step further …. - PowerPoint PPT PresentationTRANSCRIPT
1Challenge the future
Design and Vehicle Implementation of an Adaptive ABSJ. Tigelaar 13 May 2011
1Design and Vehicle Implementation of an Adaptive ABS
2Challenge the future
Design and Vehicle Implementation of an Adaptive ABS
3Challenge the future
Goal
• Research on ABS is part of a larger research objective
• Load based vehicle dynamics control• Decrease in system complexity• Decrease in development cost• Increase in performance
Novel ABS algorithm evaluated on testbench.Limitations: no changing load on tyre
no changing friction coefficient
…Taking the research one step further…
Goal: Evaluate ABS robustness (Fz, µ) and implement in test vehicle
Design and Vehicle Implementation of an Adaptive ABS
4Challenge the future
Contents
• Why do we need ABS?• How does it work?
• PART 1 -> Algorithm Design: increase its robustness• Simulation evaluation
• PART 2 -> Vehicle Implementation: implement in test vehicle• Track testing
• Does Load Based Sensing offer improvements in performance?
The next ~25 min
Design and Vehicle Implementation of an Adaptive ABS
5Challenge the future
Why does one need ABS?ABS video
Introduction to ABS
This video contains shocking
images and is therefore not suitable for BMW fans.
6Challenge the future
Why does one need ABS?ABS video
Introduction to ABS
This video contains shocking
images and is therefore not suitable for BMW fans.
To prevent wheel-lock
What happens at wheel-lock?
7Challenge the future
BrakingForces are generated at tyre-road contact patch
• Many different models of tyre-road interaction
Introduction to ABS
[Jazar, Reza N. (2008): Vehicle dynamics. Theory and application. New York, NY: Springer.]
8Challenge the future
Braking (Fx)Longitudinal Tyre Forces
( )x zF F
1x
x x
v r rv v
0 0.2 0.4 0.6 0.8 10
0.2
0.4
0.6
0.8
1
1.2
slip
fric
coef
f
()
dry asphaltwet asphaltdry cobblestonesnow
Introduction to ABS
max Fx -> BD
F x/F
z
Slip λ
9Challenge the future
Braking (Fy)Lateral Tyre Forces
( , )F Fy z
Steerability -> front
Stability -> rear
Introduction to ABS
[Tanelli, M.; Corno, M.; Boniolo, I.; Savaresi, S.M. (2009): Active braking control of two-wheeled vehicles on curves.]
Slip λ
F Y/F
Z
10Challenge the future
Re-capTrade-off between Fx and Fy
Many different control strategies
to achieve this
Ideal operating range
Prevent wheel-lock in order to:• Maintain
steerability• Maintain stability• Decrease braking
distance
Introduction to ABS
Slip λ
Norm
alize
d fo
rce
11Challenge the future
How does ABS work?Sensor
Control
Actuator
How does ABS cycle?
Hold/Decrease/Increase pressure
ValvesWheel speed sensor
Control
5 Phase : hybrid wheel deceleration based logic
Introduction to ABS
12Challenge the future
A 2-Phase exampleA hybrid wheel deceleration based logic
Continuous and discrete states
Algorithm Design
Slip λ
Norm
alize
d fo
rce
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ABS 5-Phase algorithm (x1 and x2)A hybrid wheel deceleration based logic
*1x *
2 xx r a
* *1 2 1
1 ( ( ) )xx
x x x av
* *2 1 2 1'( )( ( ) )x
x
bx x x x a uv
2
zRb FJ
Ru TJ
Set of dynamic equations
Algorithm Design
X1 : Wheel slip offsetX2 : Wheel acceleration offset
14Challenge the future
5-Phase algorithmA hybrid wheel deceleration based logic
Stating that
• Brake torque will either be kept constant or change rapidly
• Switching between torques is triggered by thresholds
• Thresholds are wheel deceleration based
Regulation logic chosen as such to keep unmeasured x1 small
close to 0
Algorithm Design
15Challenge the future
5-Phase Automaton
*1x
*2 xx r a
The hybrid automatonState transistions governed by guard conditions.Evolution of continuous states is determined by dynamic system.
Algorithm Design
[Pasillas-Lépine, W. (2006): Hybrid modeling and limit cycle analysis for a class of five-phase anti-lock brake algorithms.]
16Challenge the future
5-Phase 1st Integrals
For constant brake torque
For large torque variations,Approximate first integral is
Approximation error with
2
1 2 1( )ZRI x F xJ
* * * 22 1 2 1
0
1ln(1 ) ( ( ) )2 xI x x x au
Phase-plane (x1-x2) trajectories
22 * * 2 *
2 1 1( ( ) ) ( ( ) )x z xRerror x x a F x aJ
0
1u
Algorithm Design
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5-Phase CriteriaThe criteria
2
zRb FJ
Satisfying all 5criteria
Algorithm Design
Stability guarantee
d
Criterion 1 :
Criterion 2 :
Criterion 3 :
Criterion 4 :
Criterion 5 :
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Load transferStatic and Dynamic stati
cdynami
c
1
22 cogZ x
hlF mg maL L
,
2,11 ( )2F R
cogZ x
hlF mg ma
L L
2
12 cogZ x
hlF mg maL L
Algorithm Design
[Jazar, Reza N. (2008): Vehicle dynamics. Theory and application. New York, NY: Springer.]
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Fz and StabilityThe fifth criteria
• [B] Maintain stability at lower loads -> retune (ε5) thresholds (limited)
• [C] Maintain stability at lower µ’s -> T rate increase in phase 5
,
2,11 ( )2F R
cogZ x
hlF mg ma
L L
static
dynamic
Z
ZF
cog
F Lmgh
Algorithm Design
Friction coefficient µ
Load
tran
sfer
[N]
20Challenge the future
5-Phase SimulationSimulation results
• 4 wheel car model. Algorithm runs separately on each wheel.
• Straight line braking starting from 150 km/h
• Cost functions are defined as:• Maximum slip
• Braking distance
max( )J
1
0
( ) ( )t
tJ s v t dt
Fy
Fx
Algorithm Design
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5-Phase Simulation at high µSimulation results (FL wheel)
• Observed that as µ increases, the algorithm cycles within stable zone.
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.40
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000Long tire force FL vs Slip
Slip
Long
tyre
forc
e [N
]
= 0.4 = 0.65 = 0.9
Algorithm Design
Larger force dropoccurs duringcycling
Long
itudi
nal T
yre
Forc
e [N
]
Slip λ
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-40 -35 -30 -25 -20 -15 -10 -5 0 5 10 15-120
-100
-80
-60
-40
-20
0
20
40
60
80
Slip offset x1 [%]
Whe
el a
ccel
erat
ion
offs
et x 2 [m
/s2 ]
ABS Phase-plane evolution (1st initial cycle 1:1900)
Phase 2Phase 3
Phase 1
Phase 2
Phase 5
Phase 2
Phase 4
ABSInitialization
Phase 3
5
4
3
1
2
5-Phase Simulation Limit CycleSimulation results
• 5th thresholddeterminesthe slip levelreached in theunstable zone
Algorithm Design
Wheel slip offset x1 [%]
Whe
el a
ccel
erat
ion
offse
t [m
/s2 ]
23Challenge the future
5-Phase Simulation at low µSimulation results
• An increased ε5 would be beneficial for higher µ, but adverse for low µ
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.40
500
1000
1500
2000
2500
3000
3500Longitudinal tire forces FL RR vs Slip
slip
LF Fx
LF Fx
RR Fx
RR Fx
A dynamic threshold
ε5 = 50
ε5 = 50
ε5 = 30
ε5 = 30
Algorithm Design
Slip λ
Long
itudi
nal T
yre
Forc
e [N
]
24Challenge the future
5-Phase Dynamic ThresholdDynamic fifth threshold
• Fifth threshold can be freely defined
• Friction coefficient cannot be measured directly
5, 5 28.527 max 14.218xDynamic
z
FF
( ) X
Z
FF
Algorithm Design
FX/FZ
ε 5
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Adaptive 5-Phase ResultsResults - improvements
0.3 0.4 0.5 0.6 0.7 0.8 0.9 160
80
100
120
140
160
180
200
220
240
260
Friction coefficient road
Bra
king
dis
tanc
e [m
]
Braking distance for different threshold e5
e5=30e5=50e5=e5dynTheoretical
0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
0.05
0.1
0.15
0.2
Friction coefficient road
Slip
Maximum slip for different threshold e5
e5=30e5=50e5=de5
0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
0.05
0.1
0.15
0.2
Friction coefficient road
Slip
e5=30e5=50e5=de5
• 20 % decrease in braking distance• Maximum slip level is maintained
front
rear
ε5=30
ε5=50
Theoretical
ε5=d ε5
Algorithm Design
Friction coefficient
Friction coefficient
Friction coefficient
Brak
ing
dist
ance
[m]
26Challenge the future
Adaptive 5-Phase VideoResults - improvements
• VIDEOS – steering manoeuvre (2m to the left)
• White car : No ABS• Red car : ABS with standard 5-Phase• Blue car : ABS with adaptive 5-Phase
Lane change during braking from 150km/h
Algorithm Design
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Vehicle modifications (VM)BMW 530 (E60)
Vehicle Implementation
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VM PrincipleBasic principle
• Original ABS serves as a benchmark, driver can switch
• ECU (sensor input and required control decisions)• Power stage (amplify the control signal)• Hydraulic unit (actuate the solenoid valves)
ABS module
DummyABS
module
Vehicle Implementation
How?
Individual wheel control
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VM dSpaceBasic principle
dSpace Autobox enables receiving and sending signalsIN: wheel speed (tapped)
brake pressure (installed)OUT: control action valves
control action pump
Vehicle Implementation
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VM Brake circuitBrake pressure sensors
Intake Valve (#6) Exhaust Valve (#7) Modeopen closed Pressure build-up
closed closed Hold pressureclosed open Pressure decrease
6
7
4
8
12
3 1 Brake pedal 2 Master cylinder 3 Brake booster4 Brake calliper 5 Return pump6 Intake valve 7 Exhaust valve 8 Pressure sensor
5
Vehicle Implementation
[Robert Bosch GmbH (2007): Automotive Electrics Automotive Electronics. 5th: Wiley.]
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VM T-splitBrake pressure sensors
Vehicle Implementation
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VM dSpaceBasic principle
dSpace Autobox enables receiving and sending signalsIN: wheel speed (tapped)
brake pressure (installed)OUT: control action for valves (hold and decrease
presssure)control action for pump (increase pressure)
Vehicle Implementation
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VM ECUThe ABS Module
The ECU
Still beingreverse engineered.
Vehicle Implementation
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VM ConventionalSystem overview - conventional
Vehicle Implementation
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VM NovelSystem overview - novel
Vehicle Implementation
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VM Track testing
Vehicle Implementation
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ConclusionsAn overview
PART 1• Through the use of load sensing:
Dynamic thresholds can significantly improve ABS
performanceDecreased braking distance by 20%Maintained lateral stability and steerability
PART 2• Vehicle modification allow performance evaluation
Conclusion
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?Conclusion
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BrakingThe braking process
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Is ABS improvement worthwhile?
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Further researchTU Delft
• ABS Activation Logic• Different than slip based (e.g. brake pedal)
• Coupling of all 4 wheels• Synchronization on front• A-Synchronization on rear
• Modeling of brake efficiency• Thermal effects
Extra Slides
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Future of ABSPossible outcomes
• From motion based to force based control systems
• Electro-Mechanical Brakes• Force modulation is continous (not discrete)• No vibrations to brake pedal (safety)• No toxic brake fluid (leakage)
• From threshold based control rules (wheel deceleration)
move to slip control (multi-applications, ABS, ESP, TCS, …)
• ABS simplificationExtra Slides
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ABS Synchronization
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0 0.05 0.1 0.15 0.2 0.25 0.3 0.350
10
20
30
40
50
60
70
Time interval occurence
Time steps
Occ
uran
ce
occurencemean time interval
Controller Area Network (CAN)Tests show a deviation in time interval reception, thus large jumps in value
Average time interval over all 4 wheel signals = 60 msec
Whe
el sp
eed
[km
/h]
Occu
rrenc
e
Time [s]
Time steps
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Wheel speedActive Inductance Sensors
• Sense change in magnetic field due to incremental ring
• Contains 3 Hall sensors• 1 and 3 serve for velocity estimation• 2 serves for direction of rotation
• Derive wheel deceleration is challenging. Two main methods• Lines-Per-Period• Fixed-position
Extra Slides
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Bosch ABS
• Based on:
Heuristics•Requires extensive tuning per vehicle model
Rule-of-Thumb• System is unclear -> contains many control rules
System complexity ever increasing
• Also uses (amongst others) wheel deceleration values
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VM PWMBasic principle
• Pulse-Width Modulatedsignal for valve hold controland pump increase control
• Additional I/O signalfor valve release control
50% duty cycle