Integrated Path Tracking and Lateral Stability Control with Four-Wheel Independent Steering for Autonomous Electric Vehicles on Low Friction Roads

Abstract

This paper presents a method to design an integrated path tracking and lateral stability controller for an autonomous electric vehicle with four-wheel independent steering (4WIS) on low friction roads. Recent advances in autonomous driving have led to extensive studies on path tracking control. However, path tracking is difficult on low friction roads. In this paper, path tracking control was converted to the yaw rate tracking one to cope with problems caused by low friction roads. To generate a reference yaw rate for path tracking, we present several methods using a driver model and a target path. For yaw rate tracking, we designed a controller with a two-layer control hierarchy, i.e., upper and lower layers. The control yaw moment was calculated using a direct yaw moment controller in the upper layer. In the low layer, a control allocation method was adopted to allocate the control yaw moment into steering angles of 4WIS. To verify the performance of the proposed controller, we conducted a simulation on vehicle simulation software. From the simulation results, it is shown that the proposed controller is effective for path tracking and lateral stability on low friction roads. To analyze path tracking and lateral stability performance of the proposed controller on low friction roads, the effects of the steady-state yaw rate gain are investigated from the simulation results.

Path Tracking Control with Constraint on Tire Slip Angles under Low-Friction Road Conditions

“…In the context of PTC, a 2-DOF bicycle model has been widely employed to represent yaw and lateral behaviors of a vehicle, as discussed in the literature [25,[30][31][32][33][34][35]39,40]. Figure 2 shows the coordinates, geometry, and variables of the bicycle model.…”

“…By expanding Equation (22) from the first to N-th time instant, new vectors and matrices are defined as Equation (23). With these definitions, the state-space equation and LQCF from the first to N-th time instant are calculated as Equation (24) and Equation (25), respectively. By replacing X of Equation (25) with Equation ( 24), the LQCF, Equation (25), is obtained by Equation (26).…”

“…With these definitions, the state-space equation and LQCF from the first to N-th time instant are calculated as Equation (24) and Equation (25), respectively. By replacing X of Equation (25) with Equation ( 24), the LQCF, Equation (25), is obtained by Equation (26). In Equation (27), the bound on steering angle, δ max , is imposed on the control input U.…”

“…Figure 4 illustrates the tire forces at each wheel and ∆M z when ∆M z is positive [25,[30][31][32]35,39,40]. In Figure 4, four wheels are numbered as 1, 2, 3 and 4 in the order of the front left, front right, rear left and rear right wheels, respectively.…”

“…Within Equation ( 31), ζ i is the product of µ and F zi at the wheel i, i.e., µF zi , which represents the friction circle radius. The vector of virtual weights, denoted as κ, is introduced in Equation ( 31) for the purpose of selecting the combination of actuators [25,[30][31][32]35,39]. The quadratic cost function, J EC in Equation (32), is obtained from the constraint Equation (29).…”