Date of Award

12-2008

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Mechanical Engineering

Advisor

Ayalew, Beshah

Committee Member

Law , Harry

Committee Member

Pisu , Pierluigi

Abstract

Vehicle Dynamics Control (VDC) systems, also called Electronic Stability Control (ESC) systems, are active on-board safety systems intended to stabilize the dynamics of vehicle lateral motion. In so doing, these systems reduce the possibility of the driver's loss of control of the vehicle in some critical or aggressive maneuvers. One approach to vehicle dynamics control is the use of appropriate drive torque distribution to the wheels of the vehicle. This thesis focuses on particular torque distribution management systems suitable for vehicles with independently driven wheels.
In conducting this study, a non-linear seven degree-of-freedom vehicle model incorporating a non-linear tire model was adopted and simulated in the MATLAB/SIMULINK environment. Using this model, various VDC torque management architectures as well as choices of feedback controllers were studied. For the purposes of upper level yaw stability control design, the desired or reference performance of the vehicle was obtained from the steady state bicycle model of the vehicle.
To achieve the corrective yaw moment required for directional control, four torque distribution strategies were devised and evaluated. For each strategy, the following feedback control variables were considered turn by turn: 1) yaw rate 2) lateral acceleration 3) both yaw rate and lateral acceleration. Standard test maneuvers such as fish hook maneuver, the FMVSS 126 ESC test and the J-turn were simulated to evaluate the effectiveness of the proposed torque distribution strategies. Effects of road friction conditions, yaw-controller gains, and a driver emulation speed controller were also studied. The simulation results indicated that all VDC torque management strategies were generally very effective in tracking the reference yaw rate and lateral acceleration of the vehicle on both dry and slippery surface conditions. Under the VDC strategies employed, the sideslip angle of the vehicle remained very small and always below the steady-state values computed from reference bicycle model. This rendered separate side slip angle control unnecessary, for the test conditions and test vehicle considered.
The study of the various proposed independent torque control strategies presented in this thesis is an essential first step in the design and selection of actuators for vehicle dynamics control with independent wheel drives. This is true for certain powertrain architectures currently being considered for pure Electric or Hybrid Electric and Hydraulic Hybrid Vehicles.

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