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 ….

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Design and vehicle implementation of an adaptive abs

Design and Vehicle Implementation of an Adaptive ABS

J. Tigelaar 13 May 2011

1

Design and VehicleImplementation of anAdaptive ABS


Design and vehicle implementation of an adaptive abs

Design and VehicleImplementation of anAdaptive ABS


Design and vehicle implementation of an adaptive abs

Goal

…Taking the research one step further…

  • 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

Goal:Evaluate ABS robustness (Fz, µ) and implement in test vehicle

Design and VehicleImplementation of anAdaptive ABS


Contents

Contents

The next ~25 min

  • 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?

Design and VehicleImplementation of anAdaptive ABS


Why does one need abs

Why does one need ABS?

ABS video

This video containsshocking images and is thereforenotsuitablefor BMW fans.

Introduction to ABS


Why does one need abs1

Why does one need ABS?

ABS video

This video containsshocking images and is thereforenotsuitablefor BMW fans.

To prevent wheel-lock

What happens at wheel-lock?

Introduction to ABS


Braking

Braking

Forces are generated at tyre-road contact patch

  • Many different models of tyre-road interaction

[Jazar, Reza N. (2008): Vehicledynamics. Theory and application. New York, NY: Springer.]

Introduction to ABS


Braking f x

Braking (Fx)

LongitudinalTyreForces

Fx/Fz

maxFx -> BD

Slip λ

Introduction to ABS


Braking f y

Braking (Fy)

LateralTyreForces

FY/FZ

Steerability -> front

Stability -> rear

Slip λ

[Tanelli, M.; Corno, M.; Boniolo, I.; Savaresi, S.M. (2009): Active braking control of two-wheeled vehicles on curves.]

Introduction to ABS


Re cap

Re-cap

Prevent wheel-lock in order to:

  • Maintain steerability

  • Maintain stability

  • Decrease braking distance

Trade-offbetweenFx and Fy

Idealoperating range

Normalizedforce

Many different controlstrategies to achievethis

Slip λ

Introduction to ABS


How does abs work

  • Control

How does ABS work?

How does ABS cycle?

Hold/Decrease/Increase pressure

Valves

Wheel speed sensor

5 Phase : hybridwheeldecelerationbasedlogic

Introduction to ABS


A 2 phase example

A 2-Phase example

A hybridwheeldecelerationbasedlogic

Continuous and discrete states

Normalizedforce

Slip λ

Algorithm Design


Abs 5 phase algorithm x 1 and x 2

ABS 5-Phase algorithm (x1 and x2)

A hybridwheeldecelerationbasedlogic

X1 : Wheel slip offset

X2 : Wheel acceleration offset

Set of dynamicequations

Algorithm Design


5 phase algorithm

5-Phase algorithm

A hybridwheeldecelerationbasedlogic

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


5 phase automaton

5-Phase Automaton

The hybridautomaton

State transistionsgovernedbyguardconditions.

Evolution of continuousstates is determinedbydynamic system.

[Pasillas-Lépine, W. (2006): Hybrid modeling and limit cycle analysis for a class of five-phase anti-lock brake algorithms.]

Algorithm Design


5 phase 1 st integrals

5-Phase 1st Integrals

Phase-plane (x1-x2) trajectories

For constant brake torque

For large torque variations,

Approximate first integral is

Approximation error

with

Algorithm Design


5 phase criteria

5-Phase Criteria

The criteria

Satisfying all 5

criteria

Criterion 1 :

Criterion 2 :

Criterion 3 :

Stabilityguaranteed

Criterion 4 :

Criterion 5 :

Algorithm Design


Load transfer

Load transfer

Static and Dynamic

dynamic

static

[Jazar, Reza N. (2008): Vehicledynamics. Theory and application. New York, NY: Springer.]

Algorithm Design


F z and stability

Fz and Stability

dynamic

The fifth criteria

static

  • [B] Maintain stability at lower loads -> retune (ε5) thresholds (limited)

  • [C] Maintain stability at lower µ’s -> T rate increase in phase 5

Load transfer [N]

Frictioncoefficient µ

Algorithm Design


5 phase simulation

5-Phase Simulation

Simulationresults

  • 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

Fy

Fx

Algorithm Design


5 phase simulation at high

5-Phase Simulation at high µ

Simulationresults (FL wheel)

  • Observed that as µ increases, the algorithm cycles within stable zone.

LongitudinalTyreForce [N]

Larger force drop

occurs during

cycling

Slip λ

Algorithm Design


5 phase simulation limit cycle

5-Phase Simulation Limit Cycle

Simulationresults

Wheel acceleration offset [m/s2]

  • 5th threshold

    determines

    the slip level

    reached in the

    unstable zone

Wheel slip offset x1 [%]

Algorithm Design


5 phase simulation at low

5-Phase Simulation at low µ

Simulationresults

  • An increased ε5 would be beneficial for higher µ, but adverse for low µ

LongitudinalTyreForce [N]

ε5 = 30

ε5 = 50

ε5 = 30

ε5 = 50

A dynamicthreshold

Slip λ

Algorithm Design


5 phase dynamic threshold

5-Phase Dynamic Threshold

Dynamicfifththreshold

  • Fifth threshold can be freely defined

  • Friction coefficient cannot be measured directly

ε5

FX/FZ

Algorithm Design


Adaptive 5 phase results

Adaptive 5-Phase Results

Results - improvements

  • 20 % decrease in braking distance

  • Maximum slip level is maintained

Braking distance [m]

Frictioncoefficient

front

ε5=30

ε5=50

rear

Frictioncoefficient

Frictioncoefficient

Theoretical

ε5=d ε5

Algorithm Design


Adaptive 5 phase video

Adaptive 5-Phase Video

Results - 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

Lanechangeduring braking from 150km/h

Algorithm Design


Vehicle modifications vm

Vehicle modifications (VM)

BMW 530 (E60)

VehicleImplementation


Vm principle

VM Principle

Basicprinciple

  • 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

Individualwheelcontrol

Dummy

ABS module

How?

VehicleImplementation


Vm dspace

VM dSpace

Basicprinciple

dSpaceAutobox enables receiving and sending signals

IN: wheel speed (tapped)

brake pressure (installed)

OUT: control action valves

control action pump

VehicleImplementation


Vm brake circuit

VM Brake circuit

Brakepressure sensors

3

2

1

6

5

7

8

4

[Robert Bosch GmbH (2007): Automotive Electrics Automotive Electronics. 5th: Wiley.]

VehicleImplementation


Vm t split

VM T-split

Brakepressure sensors

VehicleImplementation


Vm dspace1

VM dSpace

Basicprinciple

dSpaceAutobox enables receiving and sending signals

IN: wheel speed (tapped)

brake pressure (installed)

OUT: control action for valves (hold and decrease presssure)

control action for pump (increase pressure)

VehicleImplementation


Vm ecu

VM ECU

The ABS Module

The ECU

Still being

reverse engineered.

VehicleImplementation


Vm conventional

VM Conventional

System overview - conventional

VehicleImplementation


Vm novel

VM Novel

System overview - novel

VehicleImplementation


Vm track testing

VM Track testing

VehicleImplementation


Conclusions

Conclusions

Anoverview

PART 1

  • Through the use of load sensing:

    Dynamic thresholds can significantly improve ABS performance

    Decreased braking distance by 20%

    Maintained lateral stability and steerability

    PART 2

  • Vehicle modification allow performance evaluation

Conclusion


Design and vehicle implementation of an adaptive abs

?

Conclusion


Braking1

Braking

The braking process


Is abs improvement worthwhile

Is ABS improvementworthwhile?


Further research

Further research

TU 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


Future of abs

Future of ABS

Possibleoutcomes

  • From motion based to force based control systems

  • Electro-MechanicalBrakes

    • Forcemodulation is continous (not discrete)

    • No vibrations to brakepedal (safety)

    • No toxicbrakefluid (leakage)

  • From threshold based control rules (wheel deceleration)

    move to slip control (multi-applications, ABS, ESP, TCS, …)

  • ABS simplification

Extra Slides


Abs synchronization

ABS Synchronization


Controller area network can

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

Wheel speed [km/h]

Occurrence

Time [s]

Time steps


Wheel speed

Wheel speed

Active Inductance Sensors

  • Sensechange in magnetic field due to incremental ring

  • Contains 3 Hall sensors

    • 1 and 3 serve forvelocityestimation

    • 2 serves fordirection of rotation

  • Derivewheeldeceleration is challenging. Twomainmethods

    • Lines-Per-Period

    • Fixed-position

Extra Slides


Bosch abs

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


Vm pwm

VM PWM

Basicprinciple

  • Pulse-Width Modulated

    signal for valve hold control

    and pump increase control

  • Additional I/O signal

    for valve release control

50% dutycycle


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