Abstract
This paper investigates the front-wheel differential steering system (DSS) for a four-wheel independent-drive (4WID) electric vehicle (EV) with a steer-by-wire (SBW) system in case of the steering failure. The nonlinear dynamic model of differential steering vehicle (DSV) is established and the stability regions at different adhesion coefficients are determined based on the theory of phase plane. The traditional front-wheel steering vehicle is selected as the reference model. The direct yaw moment control (DYC) aiming to restore the vehicle to the stability region, and the DSS control aiming to achieve the normal steering function based on the theory of model reference sliding mode control, are researched and applied to the nonlinear dynamic model successively. The direct yaw moment and differential driving torque of the front-wheel needed for the vehicle stability and DSS are obtained respectively. The simulation results show that the proposed integrated control can simultaneously ensure the differential steering and vehicle stability of the nonlinear vehicle on different adhesion coefficient roads.
Highlights
The appearance of four-wheel independent-drive (4WID) electric vehicles (EV), whose driving motors are mounted into the wheels, enables the independent control of motors, eases the process of vehicle yaw control, and opens up the possibility of differential steering system (DSS) [1]–[5]
This paper mainly studies the feasibility of differential steering after the failure of SBW system, so two kinds of normal working conditions are selected to simulate
Assuming that the steering motor cannot turn properly and the driver’s instructions cannot be responded to, the integrated control of the nonlinear vehicle is studied: 1) Simulation results indicate that the integrated control can ensure the nonlinear vehicle to achieve the normal steering on both high and low μ road while the steering motor fails
Summary
The appearance of four-wheel independent-drive (4WID) electric vehicles (EV), whose driving motors are mounted into the wheels, enables the independent control of motors, eases the process of vehicle yaw control, and opens up the possibility of differential steering system (DSS) [1]–[5]. The DSS refers to the way of realizing steering by controlling the driving moments of the left and right front wheels so that the front steering wheels can rotate around their kingpins at different angles respectively. It differs from the traditional steering system in that the cause of wheel steering is the differential driving moment between the left and right front wheels, rather than the steering wheel. For the vehicles equipped with the SBW system, the steering of vehicles is driven by the steering motors, but the steering motor may be
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