Comparison of brake-based and drive torque-based electronic stability control systems on 4x4 vehicles with independent suspension systems

1. COMPARISON OF BRAKE-BASED AND DRIVE
TORQUE-BASED ELECTRONIC STABILITY
CONTROL SYSTEMS ON 4X4 VEHICLES WITH
INDEPENDENT SUSPENSION SYSTEMS
Ragnar Ledesma
2007

2. Abstract
• A TruckSim model of a 4x4 vehicle was developed in order to compare the
performance of brake-based and drive torque-based electronic stability
control systems. The brake-based stability control system utilizes
independent braking of each of the 4 wheels to control the vehicle side
slip angle when the vehicle is subject to high lateral accelerations. The
drive torque-based stability system utilizes independent drive torques on
each of the 4 wheels to control the vehicle side slip angle. Both control
systems utilize the β-phase plane approach to control the directional
stability of the vehicle. Two scenarios were considered in the performance
comparison: 1) double lane change maneuver at 100 km/hr on a road
surface with friction coefficient m = 0.5, and 2) sinusoidal steer maneuver
at 100 km/hr on a road surface with friction coefficient m = 0.5. Both
scenarios show that either system is capable of maintaining vehicle
stability even at high levels of lateral acceleration on moderately slippery
roads. The drive torque-based ESC system, however, has the advantage of
not interfering with the longitudinal dynamics of the vehicle.

3. Vehicle Model in TruckSim

4. Vehicle Model Description
• The TruckSim model represents a 4x4 JLTV vehicle
loaded at 12,000 lbs per axle. The TruckSim
model consists of rigid bodies for the sprung
mass and unsprung masses, and includes
independent suspension compliance and
kinematics, and Pacejka tire models for vehicle
handling performance prediction. The model of
the drive train system consists of a static engine
torque map and torque balance equations for the
transmission, transfer case and differentials.

5. Brake-Based ESC System
• Brake-based stability system utilizes independent
braking of each of the 4 wheels to control the
vehicle side slip angle when the vehicle is subject
to high lateral accelerations
• Utilize the β-phase plane approach to control the
directional stability of the vehicle
• Brake-Based Stability Control Logic:
– Oversteer condition: apply brake at the outer wheel of
the front axle.
– Understeer condition: apply brake at the inner wheel
of the rear axle.

6. Drive Torque-Based ESC System
• Drive torque-based stability system utilizes
independent drive torques on each of the 4
wheels to control the vehicle side slip angle
• Utilize the β-phase plane approach to control the
directional stability of the vehicle
• Drive Torque-Based Stability Control Logic:
– Oversteer condition: apply drive torque at the inner
wheel of the front axle.
– Understeer condition: apply drive torque at the outer
wheel of the rear axle.

7. Test 1: Double-Lane Change Maneuver
• Double lane change maneuver at 100 km/hr on a
road surface with friction coefficient μ = 0.5
• The lane width is set at 3.5 meters, the transition
length is set at 25 meters, and the length of the
second lane is also set at 25 meters.
• Three vehicle configurations were simulated:
– a baseline vehicle without active stability control
– the same vehicle with brake-based ESC
– the same vehicle with drive torque-based ESC.

8. Test 1: Double-Lane Change Maneuver
Vehicle trajectory, double lane change at 100 km/hr

9. Test 1: Double-Lane Change Maneuver
Vehicle speed, double lane change at 100 km/hr

10. Test 1: Double-Lane Change Maneuver
Vehicle CG lateral acceleration, double lane change at 100 km/hr

11. Test 1: Double-Lane Change Maneuver
Vehicle yaw rate, double lane change at 100 km/hr

12. Test 1: Double-Lane Change Maneuver
Vehicle side slip angle, double lane change at 100 km/hr

13. Test 1: Double-Lane Change Maneuver
Steering wheel angle, double lane change at 100 km/hr

14. Test 1: Double-Lane Change Maneuver
Stability plot (phase plane plot), double lane change at 100 km/hr

15. Test 2: Sinusoidal Steer Inputs
• Sinusoidal steer inputs at 100 km/hr on a road
surface with friction coefficient μ = 0.5
• 0.2 Hz sinusoidal steer input (90 degree
steering wheel angle)
• Three vehicle configurations were simulated:
– a baseline vehicle without active stability control
– the same vehicle with brake-based ESC
– the same vehicle with drive torque-based ESC.

16. Test 2: Sinusoidal Steer Inputs
Vehicle trajectory, 0.2 Hz sinusoidal steer input at 100 km/hr

17. Test 2: Sinusoidal Steer Inputs
Vehicle speed, 0.2 Hz sinusoidal steer input at 100 km/hr

18. Test 2: Sinusoidal Steer Inputs
Vehicle CG lateral acceleration, 0.2 Hz sinusoidal steer input at 100 km/hr

19. Test 2: Sinusoidal Steer Inputs
Vehicle yaw rate, 0.2 Hz sinusoidal steer input at 100 km/hr

20. Test 2: Sinusoidal Steer Inputs
Vehicle side slip angle, 0.2 Hz sinusoidal steer input at 100 km/hr

21. Test 2: Sinusoidal Steer Inputs
Stability plot (phase plane plot), 0.2 Hz sinusoidal steer input at 100 km/hr

22. Conclusions
• Either brake-based or drive torque-based ESC system is
capable of maintaining vehicle stability even at high levels of
lateral acceleration on moderately slippery roads.
• The drive torque-based ESC system has the advantage of not
interfering with the longitudinal dynamics of the vehicle.
• Analysis of the control logic leads one to infer that in
situations involving very high lateral acceleration and
significant transfer of vertical load from the inner wheel to the
outer wheel, the control yaw moment due to drive torque-
based ESC systems can be limited by the amount of traction
capacity at the lightly loaded inner wheel.
• In this extreme case, the brake-based stability control system
can be expected to provide a better performance.

23. Conclusions (continued)
• A combination of brake-based and drive torque-based stability
control system can provide an even better performance compared
to the stand-alone systems.
• With a combined system, the stability control can be provided by
the drive torques when the magnitude of the required corrective
yaw moment is relatively small.
• If the required corrective yaw moment is relatively large, a part of
the corrective yaw moment will be provided by the drive torque,
and the remainder will be produced by the appropriately braked
wheel.
• In this manner, the longitudinal dynamics of the vehicle will be
minimally affected by the stability control system at moderate
levels of lateral acceleration and vehicle stability is assured at
extreme levels of lateral acceleration.