Brake-by-Steer Concept

1. Brake-by-Steer Concept Steer-by-wire application with independently actuated wheels used for stopping a vehicle Master Thesis Presentation Department of Precision and Microsystems Engineering Bas Jansen 25-03-2010

2. Content Introduction SKF Drive-by-wire Brake-by-steer concept Modeling the Brake-by-Steer system Tire model Vehicle model Brake-by-steer cases Implementation on a Go-Kart Go-kart introduction Design Implementations Test Results Braking performance Lateral behavior Conclusion & Recommendations

3. 1. Introduction

4. Introduction SKF - Svenska Kullagerfabriken AB

5. Introduction SKF - Svenska Kullagerfabriken AB SKF European Research Centre Nieuwegein

6. Introduction Conventional steering system Steer-by-wire with independently actuated wheels Steering wheel What is Steer-by-Wire Steering shaft Rack & Pinion Data transport Steering Controller Sensor & actuator Sensor & actuator

7. Introduction Replace hydraulic brake system with an individually electrically actuated brake system What is Brake-by-Wire Electro mechanical brakingactuators Data transport Brakingcontroller Brake pedal & sensor

8. 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. Introduction Safety challenge for By-Wire Primary systems with redundant back-up systems 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

10. 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. 2. Modeling the Brake-by-Steer system

12. Brake-by-Steer Modeling Model build-up: Tire model Vehicle (kart) model Brake-by-Steer cases Model construction m, I Length Width

13. 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 Modeling Tire modeling Lateral Tire Force C Slip angle

15. Brake-by-Steer Modeling Vehicle Model Vehicle equations of motion m, I Tricycle model

16. Brake-by-Steer Modeling Brake-by-Steer cases Steady state straight line driving brake force Toe-out Toe-out Steering angle Right Brake force [N] Toe-in Toe-in Steering angle Left

17. Brake-by-Steer Modeling Effect of longitudinal vehicle force for vehicle heading Toe-in steer to the right Toe-out steer to the right Steering to the right results in vehicle moment to the left Steering to the right results in vehicle moment to the right

18. Brake-by-Steer Modeling Effect of lateral vehicle force for vehicle heading Toe-in steer to the right Toe-out steer to the right Steering to the right results in lateral vehicle force to the left Steering to the right results in lateral vehicle force to the left

19. Brake-by-Steer Modeling Theoretical Results – Lateral Behavior Toe-out Symmetric toe equilibrium Asymmetric toe equilibrium There is no asymmetric toe-out equilibrium line Steering angle Right Summation Lateral Vehicle Force [N] Toe-in Steering angle Left

20. 3. Implementation on a Go-Kart

21. Implementation on a Go-Kart Go-Kart Introduction Caster angle Kingpin inclination Remove mechanical linkage Caster angle • Kart specific features: • No individual wheel suspension • Flexible tube frame acts as suspension • Fixed rear axle • Caster angle and kingpin inclination Rotational path Left tire side view

22. Implementation on a Go-Kart Electromechanical Modifications Steering Wheel Toe handle • Absolute magnetic encoder measures steering angle • DC motor provides force feedback sense • Toe levers measure toe angle setpoints Steering wheel actuator Steering wheel angle sensor Steering shaft

23. Implementation on a Go-Kart Electromechanical Modifications Wheels Extension brackets • DC motor positions the wheels • Encoder used as control position signal • Absolute angle sensor used homing during initialization Motor + gear Encoders Absolute angle sensor Stub axle

24. Implementation on a Go-Kart Control algorithm Toe mode selection +/- C Controller Force Motor currents K Force feedback to steering wheel Feedback position control for wheel positions

25. Implementation on a Go-Kart Control algorithm Toe mode selection K 0 +/- C Controller Mimic steering torque with speed dependent return to center torque Feedback position control for wheel positions

26. Implementation on a Go-Kart Implemented design Steering wheel actuation Electronics Velocity sensor Batteries Left wheel actuation

27. 4. Test Cases and Results

28. 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. Test cases & Results Results – Braking Performance Theoretical maximum: 1.5 kN

30. Test cases & Results Slip angles Results – Lateral behavior Calculated driven path for symmetric toe-in (30º) with steering offset of 2, 4, 6, 8 degrees to the right Velocities

31. Test cases & Results Slip angles Results – Lateral behavior Calculated driven path for symmetric toe-out (60º) with steering offset of 2, 4, 6, 8 degrees to the right Velocities

32. 5. Conclusions & Recommendations

33. 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 Modeling 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. 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. Steering angle Brake pedal Controller Wheel actuators To create this model the presented conceptual model needs to be extended and validated on a car in stead of a go-kart

36. Thank you for your attention Questions?

39. Implementation on a Go-Kart Steering system design requirements Angle sensor Straingages • 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 Force 1,2 kN Velocity sensor

40. Brake-by-Steer Modeling Brake-by-Steer cases – Vehicle controllability A0 A1 A1 Lateral Vehicle Force [N] B0 B1 Slip angle Inverted steering occurs at symmetric toe mode for >

41. BACKUP Siemens VDO eCorner 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.

42. BACKUP