Abstract
Developing active safety systems for road vehicles, e. g. vehicle dynamic control (VDC), active front steering (AFS), will significantly reduce the number of crashes and severe injuries of road occupants. Electric vehicles with electrified chassis systems e.g. brakes, steering have an increased safety potential because of the reduced response time and the ability to apply continuous control. The main subject of the present paper is the development of an integrated chassis control scheme using all feasible actuators such as steering, braking in an optimal coordination towards regulating the vehicle dynamics.
During critical driving situations, in which some of the tires reach their limits, the vehicle dynamics are nonlinear and complex. The State Dependent Riccati Equation (SDRE) technique is a reconfigurable nonlinear optimal controller. In SDRE the nonlinear dynamics of the system is factorized into the state vector and the product of a matrix valued function that depends on the state itself. In doing so, the nonlinearities of the system are fully captured bringing the nonlinear system to a linear like structure having state-dependent coefficient (SDC) matrices. The nonlinear regulator is derived by minimizing an objective function which is formulated as a weighted integral of the system response and the actuators effort.
The proposed optimized integrated control is based on a 3 DOF vehicle model with a nonlinear combined slip Pacejka tire model and the SDRE technique. An extended linearization scheme of the system’s state space equations on the basis of the Pacejka tire model is developed and a suboptimal controller is computed at each time increment by solving efficiently an Algebraic Riccati Equation. The proposed control strategy has been evaluated experimentally by implementing the control system on a real time dSpace platform on a prototype vehicle. Experimental results show the effectiveness of the proposed IVDC in stabilizing the vehicle during limit handling manoeuvres.
A limitation of the current study is using the limited fault diagnosis and fault tolerant module. For the first time the application of SDRE using different vehicle actuators is presented and proven to be effective. Furthermore, the benefit of the proposed approach for obstacle avoidance maneuvers is shown through comparison with other methods found in the literature.
The problem of designing an optimal integrated chassis control system based on the SDRE technique has been presented. The proposed system has been tested experimentally and has been proven capable to stabilize the vehicle with an optimized tire force distribution.
KEYWORDS – State dependent Riccati equation, Integrated control, Nonlinear optimal control, Extended Kalman filter, State Dependent Coefficient