An investigation of multibody system modelling and
control analysis techniques for the development of
advanced suspension systems in passenger cars
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Abstract
The subject of this thesis is the investigation of multibody system modelling
and control analysis techniques for the development of advanced suspension
systems in passenger cars. A review of the application of automatic control to
all areas of automotive vehicles illustrated the important factors in such
developments, including motivating influences, constraints and methodologies
used. A further review of specific applications for advanced suspension systems
highlighted a major discrepancy between the significant claims of theoretical
performance benefits and the scarcity of successful practical implementations.
This discrepancy was the result of idealistic analytical studies producing
unrealistic solutions with little regard for practical constraints. The
predominant application of prototype testing methods in implementation studies
also resulted in reduced potential performance improvements.
This work addressed this gap by the application of realistic modelling and
control design techniques to practical realistic suspension systems. Multibody
system modelling techniques were used to develop vehicle models incorporating
realistic representations of the suspension system itself, with the ability to
include models of the controllers, and facilitate control analysis tasks. These
models were first used to address ride control for fully active suspension
systems. Both state space techniques, including linear quadratic regulator and
pole placement and frequency domain design methods were applied. For the
multivariable frequency domain study, dyadic expansion techniques were used
to decouple the system into single input single output systems representing
each of the sprung mass modes. Both discretely and continuously variable
damping systems were then addressed with a range of control strategies,
including analytical solutions based on the active results and heuristic rule-based
approaches. The controllers based on active solutions were reduced to
satisfy realistic practical limitations of the achievable damping force. The
heuristic techniques included standard rule-based controllers using Boolean
logic for the discretely variable case, and fuzzy logic controllers for the
continuously variable case