1 Brake-by-Steer Concept Challenge the future Delft University of Technology Brake-by-Steer Concept Steer-by-wire application with independently actuated wheels used for stopping a vehicle Bas Jansen Master Thesis Presentation Department of Precision and Microsystems Engineering

2 Brake-by-Steer Concept Challenge the future Delft University of Technology Content 1.Introduction -SKF -Drive-by-wire -Brake-by-steer concept 2.Modeling the Brake-by-Steer system -Tire model -Vehicle model -Brake-by-steer cases 3.Implementation on a Go-Kart -Go-kart introduction -Design Implementations 4.Test Results -Braking performance -Lateral behavior 5.Conclusion & Recommendations

3 Brake-by-Steer Concept Challenge the future Delft University of Technology 1. Introduction

4 Brake-by-Steer Concept Challenge the future Delft University of Technology Introduction SKF - Svenska Kullagerfabriken AB

5 Brake-by-Steer Concept Challenge the future Delft University of Technology Introduction SKF European Research Centre Nieuwegein SKF - Svenska Kullagerfabriken AB

6 Brake-by-Steer Concept Challenge the future Delft University of Technology Introduction Conventional steering system Steer-by-wire with independently actuated wheels What is Steer-by-Wire Steering wheel Steering shaft Rack & Pinion Steering Controller Sensor & actuator Data transport

7 Brake-by-Steer Concept Challenge the future Delft University of Technology Introduction Replace hydraulic brake system with an individually electrically actuated brake system What is Brake-by-Wire Electro mechanical braking actuators Braking controller Brake pedal & sensor Data transport

8 Brake-by-Steer Concept Challenge the future Delft University of Technology Introduction Why By-Wire Modular design provides design freedom, reduces weight and requires less space Personalized and adaptive driving experience by varying control settings Increased safety potential in combination with intelligent vehicle safety systems

9 Brake-by-Steer Concept Challenge the future Delft University of Technology Introduction Safety challenge for By-Wire Increase safety level: Implemented redundant components Assign secondary function to initial primary function of a sub system Steer by uneven distributed brake force Brake-by-steer concept Primary systems with redundant back-up systems

10 Brake-by-Steer Concept Challenge the future Delft University of Technology Introduction Research Question: Is it possible to stop a vehicle with the brake-by-steer concept and how does this influence the steering controllability? Brake-by-Steer concept Position the front wheels such that they generate a braking force

11 Brake-by-Steer Concept Challenge the future Delft University of Technology 2. Modeling the Brake-by-Steer system

12 Brake-by-Steer Concept Challenge the future Delft University of Technology Brake-by-Steer Modeling Model build-up: Tire model Vehicle (kart) model Brake-by-Steer cases Model construction Width Length m, I

13 Brake-by-Steer Concept Challenge the future Delft University of Technology Brake-by-Steer Modeling Tire behavior: No resistance force in longitudinal direction (x) Resistance force in lateral direction (y) Slip angle: The angle between tire’s direction of travel (V) and the direction towards which it is pointing (x) Tire modeling

14 Brake-by-Steer Concept Challenge the future Delft University of Technology Brake-by-Steer Modeling Tire modeling Slip angle Lateral Tire Force C

15 Brake-by-Steer Concept Challenge the future Delft University of Technology Brake-by-Steer Modeling Vehicle Model Vehicle equations of motion m, I Tricycle model

16 Brake-by-Steer Concept Challenge the future Delft University of Technology Brake-by-Steer Modeling Brake-by-Steer cases Symmetric Asymmetric Toe-in Toe-out Steering angle Left Steering angle Right Toe-out Toe-in Toe-out Toe-in Steady state straight line driving brake force Brake force [N]

17 Brake-by-Steer Concept Challenge the future Delft University of Technology Brake-by-Steer Modeling Steering to the right results in vehicle moment to the left Steering to the right results in vehicle moment to the right Toe-in steer to the rightToe-out steer to the right Effect of longitudinal vehicle force for vehicle heading

18 Brake-by-Steer Concept Challenge the future Delft University of Technology Brake-by-Steer Modeling Steering to the right results in lateral vehicle force to the left Toe-in steer to the rightToe-out steer to the right Effect of lateral vehicle force for vehicle heading

19 Brake-by-Steer Concept Challenge the future Delft University of Technology Brake-by-Steer Modeling Theoretical Results – Lateral Behavior Steering angle Left Steering angle Right Summation Lateral Vehicle Force [N] Symmetric toe equilibrium Asymmetric toe equilibrium Toe-out Toe-in There is no asymmetric toe-out equilibrium line

20 Brake-by-Steer Concept Challenge the future Delft University of Technology 3. Implementation on a Go-Kart

21 Brake-by-Steer Concept Challenge the future Delft University of Technology Implementation on a Go-Kart Go-Kart Introduction Kart specific features: No individual wheel suspension Flexible tube frame acts as suspension Fixed rear axle Caster angle and kingpin inclination Caster angle Kingpin inclination Caster angle Left tire side view Rotational path Remove mechanical linkage

22 Brake-by-Steer Concept Challenge the future Delft University of Technology Implementation on a Go-Kart Steering Wheel Electromechanical Modifications Steering wheel actuator Steering wheel angle sensor Steering shaft Toe handle Absolute magnetic encoder measures steering angle DC motor provides force feedback sense Toe levers measure toe angle setpoints

23 Brake-by-Steer Concept Challenge the future Delft University of Technology Implementation on a Go-Kart Electromechanical Modifications Wheels Extension brackets Motor + gear Absolute angle sensor Encoders DC motor positions the wheels Encoder used as control position signal Absolute angle sensor used homing during initialization Stub axle

24 Brake-by-Steer Concept Challenge the future Delft University of Technology Implementation on a Go-Kart Control algorithm C Controller +/- K Feedback position control for wheel positions Force feedback to steering wheel Toe mode selection Motor currentsForce

25 Brake-by-Steer Concept Challenge the future Delft University of Technology Implementation on a Go-Kart Control algorithm C Controller K 0 +/- Mimic steering torque with speed dependent return to center torque Feedback position control for wheel positions Toe mode selection

26 Brake-by-Steer Concept Challenge the future Delft University of Technology Implementation on a Go-Kart Implemented design Electronics Batteries Left wheel actuation Steering wheel actuation Velocity sensor

27 Brake-by-Steer Concept Challenge the future Delft University of Technology 4. Test Cases and Results

28 Brake-by-Steer Concept Challenge the future Delft University of Technology Test cases & Results Braking performance of the brake-by-steer concept Lateral vehicle behavior during brake-by-steer maneuver Test cases Test track at SKF ERC Nieuwegein

29 Brake-by-Steer Concept Challenge the future Delft University of Technology Test cases & Results Results – Braking Performance Theoretical maximum: 1.5 kN

30 Brake-by-Steer Concept Challenge the future Delft University of Technology Test cases & Results Results – Lateral behavior Calculated driven path for symmetric toe-in (30º) with steering offset of 2, 4, 6, 8 degrees to the right Slip angles Velocities

31 Brake-by-Steer Concept Challenge the future Delft University of Technology Test cases & Results Results – Lateral behavior Calculated driven path for symmetric toe-out (60º) with steering offset of 2, 4, 6, 8 degrees to the right Slip angles Velocities

32 Brake-by-Steer Concept Challenge the future Delft University of Technology 5. Conclusions & Recommendations

33 Brake-by-Steer Concept Challenge the future Delft University of Technology Conclusions & Recommendations Brake-by-steer concept can back-up failing brakes with a reduced braking performance (~50%). Lateral behavior changes drastically and ranges of inverted steering occur. These make the vehicle uncontrollable for the driver. Conclusions Brake-by-Steer Concept

34 Brake-by-Steer Concept Challenge the future Delft University of Technology Brake-by-Steer Modeling Symmetric Asymmetric Toe-in Good braking capability Good steering capability (although inverted) Not effective braking Good steering capability Toe-out Good braking capability Good steering capability (although partly inverted) Not effective braking Impossible to drive straight Conclusions Toe-modes Theory and practice differ on effectiveness of toe modes due to due to caster angle and kingpin inclination induced roll motion. The kart tire that is turned out the most gains vertical axle load and dictates the lateral behavior of the vehicle.

35 Brake-by-Steer Concept Challenge the future Delft University of Technology Conclusions & Recommendations Recommendations Brake-by-Steer Concept Before the brake-by-steer concept can be applied in cars, the relation between steering angle and vehicle heading must be restored. Calculate how to position the wheels to generate a brake force and follow expected steering input according toe strategy. Controller Wheel actuators Steering angle Brake pedal To create this model the presented conceptual model needs to be extended and validated on a car in stead of a go-kart

36 Brake-by-Steer Concept Challenge the future Delft University of Technology Thank you for your attention Questions?

37 Brake-by-Steer Concept Challenge the future Delft University of Technology

38 Brake-by-Steer Concept Challenge the future Delft University of Technology

39 Brake-by-Steer Concept Challenge the future Delft University of Technology Implementation on a Go-Kart Steering system design requirements Strain gages Angle sensor Velocity sensor Performance requirements: Wheel steering rate typical 80 º/s Steering frequency typical 1 Hz (amp = ~10 deg) Steering torque at wheels Nominal 8 Nm Peak 50 Nm Measured braking performance Braking Force1,2 kN

40 Brake-by-Steer Concept Challenge the future Delft University of Technology Brake-by-Steer Modeling A0 A1 B0 B1 Lateral Vehicle Force [N] Slip angle Inverted steering occurs at symmetric toe mode for > A1 Brake-by-Steer cases – Vehicle controllability

41 Brake-by-Steer Concept Challenge the future Delft University of Technology The hub motor (2) is located inside the wheel rim (1). The electronic wedge brake (3) uses pads driven by electric motors. An active suspension (4) and electronic steering (5) replace conventional hydraulic systems. Siemens VDO eCorner BACKUP

42 Brake-by-Steer Concept Challenge the future Delft University of Technology BACKUP