Vehicle Dynamics Control by Active
Steering
The
development of active steering control for automatic steering and the
individual vehicle's safety improvement has been a topic of research and
development in the institute for about 15 years. In the meantime, by
various industrial cooperations the practical relevance and efficiency
were demonstrated. Active steering control concepts will be addressed in
detail below.
Along the way, work has also been spent on mechatronic hardware
components suitable for active steering. The institutes's mechatronic
linear actuator with positioning and force sensors can be used as a
steering motor.
It has its origins in the gripper for the world-wide first space robot
ROTEX and is based on the patented
DLR Planetary Roller Spindle Drive (PRSD). Due to its high power
density and programmable dynamics the mechatronic linear actuator still
offers multifaceted potential for use in vehicles, for example for active
suspension. A European patent covers the use of the PRSD for an active
steering actuator.
Simulation of vehicle dynamics is an indispensable tool for the
development and virtual testing of vehicle dynamics control. Therefore,
effort has been contributed to the development of vehicle dynamics models
using MODELICA standard (Andreasson, Möller, Otter 2000), (Heller, Bünte
2003).
Yaw stabilisation and skidding
avoidance
The driving safety, comfort, and handling can be significantly improved
by using the steering input channel to vehicle dynamics in terms of
control. Various concepts have been investigated and developed to
stabilize the yaw motion (i.e. yaw disturbance rejection and skidding
avoidance). By robust unilateral decoupling of the yaw motion from the
lateral motion, the driver is supported by the controller regarding yaw
stabilization. Therefore, he can concentrate on the task of path
following. In the period under review this concept has been profoundly
developed further (Ackermann, Bünte 1997CEP), (Ackermann, Bünte
1997Kybernetika), (Ackermann, Bünte 1998Amiens), (Bünte 1998Diss.) and
partly patented (Ackermann 1996patent), (Ackermann 2002patent). During
experimental assessment of the robust decoupling active steering control,
oscillatory instability occurred due to actuator rate saturation. In the
context of specific investigations, a remedy against limit cycles for
active steering was developed (Ackermann, Bünte 1997IEEEMed), (Ackermann,
Bünte 1999Kybernetika). As well, a method for mapping limit cycle
boundaries into parameter space was elaborated. This laid the foundations
for a more generic parameter space analysis of a class of nonlinear
systems using loci stability criteria (see " -stability" in the
methodological results chapter).
More recent results were obtained by the application of the Disturbance
Observer control structure. It turned out to be eminently qualified for
the task of yaw stabilization of vehicles (Aksun-Güvenc et. al. 2001),
(Bünte et. al. 2002), (Güvenc et. al. 2004) and therefore, as well applied
for as patent (Güvenc et. al. 2000patent). The following figure shows
exemplary simulation results for a safety critical maneuver. Recent
experiments with an industrial partner proved good performance and
suitability for series production.
Other conceptual investigations for yaw dynamics control covered
Disturbance Decoupling (Aneke et . al. 1999), PID control (Wang, Ackermann
1997DLR-IB), Positivity (Wang, Ackermann 1999), and estimation of the tire
cornering stiffness (Sienel 1997).
Roll stabilisation and rollover
avoidance
Vehicles with an unfavourably high ratio of center of gravity level
over track width are specifically vulnerable concerning rollover.
Investigations offered that the roll motion of a vehicle with a can be
efficiently affected and stabilized by active steering. Therefore, a
control concept was developed (Ackermann, Odenthal 1998), (Odenthal et.
al. 1999), (Odenthal 2002Diss.) and patented (Odenthal, Bünte 1999patent)
aiming at roll damping improvement and rollover prevention. For achieving
the latter also active emergency braking is considered.
The active steering part of rollover control concept was developed
mainly based on frequency magnitude specifications. Therefore, the mapping
of respective criteria into parameter space was established, (see
"B-stability" in the methodological results chapter).
Automatic car steering
Actually, the institute's active steering activities had evolved from
an early occupation with automatic steering control. Though not
continuously, automatic steering has still kept being a subject of
research and development (Guldner et. al. 1999), (Guldner et. al.
1997ECC).
Recently, automatic steering based on robust unilateral decoupling was
investigated (Ackermann, Walter, Bünte 2004).