Investigating Functional Redundancies in the Context of Vehicle Automation – A Trajectory Tracking Perspective

Abstract

Level 3+ automated driving implies highest safety demands for the entire vehicle automation functionality. For the part of trajectory tracking, functional redundancies among all available actuators provide an opportunity to reduce safety requirements for single actuators. Yet, the exploitation of functional redundancies must be well argued if employed in a safety concept as physical limits can be reached. In this paper, we want to examine from a trajectory tracking perspective whether such a concept can be used. For this, we present a model predictive fault-tolerant trajectory tracking approach for over-actuated vehicles featuring wheel individual all-wheel drive, brakes, and steering. Applying this approach exemplarily demonstrates for a selected reference trajectory that degradations such as missing or undesired wheel torques as well as reduced steering dynamics can be compensated. Degradations at the physical actuator limits lead to significant deviations from the reference trajectory while small constant steering angles are partially critical.

Actuator Fault-Tolerant Vehicle Motion Control: A Survey

“…With respect to brake and drive degradations, most publications -namely 66 -consider zero torque [29, 45, 48-50, 54, 55, 57, 58, 65, 66, 68, 70, 74, 76-80, 83-86, 88-93, 95, 97, 98, 101-110, 116, 122, 126, 128, 133-137, 141-143, 145, 147, 150, 155, 159-163, 167, 175, 177] followed by a reduced torque range with 54 publications [30-33, 38, 40, 43, 45, 51, 52, 64, 66-68, 74, 82, 94, 109, 114, 115, 117, 120, 121, 123, 124, 126, 127, 129-131, 138-142, 144-146, 149, 150, 152, 159, 162, 163, 165-168, 170, 172-176]. 15 publications assume a constant torque [39,42,67,69,70,119,126,127,142,144,146,150,156,157,176], whereas only six consider locking or spinning wheels [58, 103-105, 126, 158]. Last but not least, a sole publication addresses malfunctioning anti-lock and anti-spin control systems [126], which is not displayed in Table I.…”

Sensitivity Analysis for Vehicle Dynamics Models -- An Approach to Model Quality Assessment for Automated Vehicles

“…2). As the x-by-wire system provides no mechanical fall backs in case of actuator failures, the architecture has been designed to include fault tolerant trajectory planning and tracking modules [20,21]. The fault tolerant control modules are designed to exploit the over-actuated actuator topology, e.g.…”

“…Fig. 2), are based on Model Predictive Control approaches [20,21]. The trajectory generation layer generates trajectories for a horizon of several seconds, using a dynamic single-track model.…”

“…For the following simulations, we used a similar double track model as formulated in [20] with added roll and pitch…”

“…locked steering for one of δ ij , free-running, or locking wheels) induced after a given time. The fault-tolerant controller is used to try to compensate the introduced faults, as discussed in [20]. The states and the sensitivities for the states with respect to the model parameters have been computed for each of those simulations.…”