Active Control of Vehicle Dynamics

Michael Fodor
Research Staff, Ford Research Laboratories
Dearborn, MI 48124

Motor vehicles behave well when operated under typical conditions such as uniform, high friction roadways, moderate speeds, and well behaved driver inputs. However, when operated outside of the typical condition range, vehicles can become difficult to control, especially for non-professional drivers under extreme emergency conditions, such as can occur while trying to avoid an unexpected obstacle on a slippery road. By providing a vehicle with a means of monitoring and controlling its response to inputs, it can be made to operate more robustly, providing safer and more enjoyable driving over a wider range of operating conditions and inputs. Several means of actively controlling vehicle behavior have emerged from the automotive industry. These include antilock braking systems, traction control, yaw control through active braking, four-wheel steering, active and semi-active suspensions, and others.

This presentation focuses on several of these systems, including traction control, advanced suspensions, yaw control using active braking, and related. Traction control is presented by introducing the force-producing capability of a tire, showing how tire slip is targeted to produce a desired vehicle response to driver inputs, discussing control methods including actuator and control system partitioning, and showing the tradeoffs between choices of actuation and overall system performance. Advanced suspension systems are presented by discussing the fundamental tradeoff between ride comfort and vehicle handling, and presenting controls and actuation methods. Yaw control using active braking is presented by showing how vehicle body yaw moment is manipulated through active differential braking and by presenting a control methodology for accomplishing closed-loop yaw control.

In addition to presenting vehicle dynamic control subsystems, methods and tools for developing these systems are also discussed. Different development stages are presented including developing an understanding of desired vehicle response, desktop modeling of the system hardware and controls, man-in-the-loop simulations, and open and closed loop in-vehicle testing. The tools used in each stage are also discussed. The presentation ends with a discussion of future possible directions for advanced vehicle controls and related development and testing methodologies.