3 research outputs found
Comparison of classical and optimal active suspension control systems
British Rail has been designing active suspensions for some 16 years,
starting with tilt systems for the Advanced Passenger train. These
have been designed using classical control techniques requiring a
combination of experience, intuition and frequency response stability
techniques, such as Nichols' plots. In order to see if a more
systematic approach to control system design could produce
improvements in performance and implementation the current
investigation was instigated in which controllers designed using
classical techniques are compared with controllers designed using
linear optimal control theory.
The active suspension used for the investigation was an Electro
Magnetic active vertical suspension fitted to a service MkIII coach.
Design of the actuators is described in the thesis along with the
design of analogue and digital control systems.
Two classical control systems were designed. a simple "Sky Hook"
damper control system and a more sophisticated position control system
developed from British Rail’s experience with Maglev suspensions. A
regulator designed using linear optimal control theory was found to
give very good results in theory. However to implement the regulator
it was necessary to design a system observer. In order to achieve a
practically realisable observer considerable rationalisation of the
vehicle model was required, which drew heavily on experience gained
designing classical control systems.
The classical control systems proved to be much easier to commission
than the optimal controllers as they were designed with implementation
in mind. During track testing problems of interaction between
vehicles were encountered, as a result the biggest improvements in
ride were obtained with the simple Sky Hook damper, as it was less
specific to the vehicle than the other configurations.
With further development one of the optimal control systems considered
will probably turn out to be the most effective as it draws on the
attributes of both classical and optimal design techniques
A comparison of braking and differential control of road vehicle yaw-sideslip dynamics
Two actuation mechanisms are considered for the comparison of performance capabilities
in improving the yaw–sideslip handling characteristics of a road vehicle. Yaw moments are generated
either by the use of single-wheel braking or via driveline torque distribution using an overdriven active
rear differential. For consistency, a fixed reference vehicle system is used, and the two controllers are
synthesized via a single design methodology. Performance measures relate to both open-loop and
closed-loop driving demands, and include both on-centre and limit handling manoeuvres
Yaw motion control via active differentials
The majority of vehicle dynamics control systems currently in production utilize some form of brake or throttle intervention to generate a yaw moment and control wheel slip. Such control systems can be both intrusive and inefficient. The use of active driveline technology is therefore an attractive alternative and recent advances in controlled differential technology have served to make it a potentially viable one. Using simulation results, this paper will demonstrate the power of these devices to influence vehicle dynamics by first proposing a suitable control strategy. This is then used to illustrate how, with perfect actuation, a vehicle's handling characteristics may be modified. The actuator limitations imposed by the two main classes of contemporary controlled differentials are then discussed and imposed on the simulation model. Using the ideal results as a benchmark, the relative merits of each type are then assessed