\chapter{LITERATURE REVIEW}
\label{ch:exp}

\section{CHAPTER OVERVIEW }
\label{sec:overview}
In this Chapter, an overview on the state-of-the-art of mechatronic suspension systems is presented in Section \ref{sec:22}. 

\section{MECHATRONIC SUSPENSION SYSTEMS}
\label{sec:22}
Mechatronic suspension systems are classified based on the types of their actuators such as the actuator bandwidth, the power demand of the actuators, and their controllability range \citep{Savaresi10}, that is, the restrictions that are imposed by the forces the actuators produce. Thus, according to \cite{Savaresi10} and \cite{Fijalkowski11} there are five groups of mechatronic suspension systems as follow:


Important criteria for the achievable performance of semi-active suspensions are the spread of the damper, which denotes the range $d_{c,min}\leq d_c\leq d_{c,max} $ in which the damping coefficient can be varied, and the dynamics of the damper, which are determined by its electrical and fluid dynamical components. Due to their comparatively low energy consumption (only for the positioning of the electromagnetical valves or the generation of electrical or magnetic fields respectively energy is required), their low costs and their simple structure, semi active damping systems are significantly more prominent in modern mechatronic vehicle suspensions than active systems. However, the semi active suspension systems are not within the scope of the analysis in this Thesis.

\subsection{Active Suspension Systems}

lic active suspension system. \citet{Alleyne95} used formerly constructed nonlinear sliding control law in regard with the hydraulic active suspension system.

 hydraulic actuator employed in a quarter-car hydraulic active suspension system.


The system actively damps the translator movement of the chassis mass as well as the roll and pitch motions and can also operate as a level control system \citep{Pyper03}. A passive damper, however, realizes the damping of the unsprung mass.



\begin{figure}[hbt]
\centering
 \includegraphics[width=0.7\textwidth]{Chapter2/fig.ch.2/22a.png}    % subfigure a
 \subcaption{Assembly of front linear electromagnetic motor (left) and its quarter car model (right)}
 \includegraphics[width=0.8\textwidth]{Chapter2/fig.ch.2/22b.png}    % subfigure b
 \subcaption{Full Assembly of Linear electromagnetic motor.}
 \caption{High bandwidth active suspension concepts by BOSE.} Source: \cite{bose2010,Jones05,Lei08}  % This is the MAIN caption of this figure
 \label{fig:22}
 \end{figure}

%\begin{figure}
%\centering
%\subfigure [Assembly of front linear electromagnetic motor (left) and its quarter car model (right) ]{%
%\includegraphics [width=0.8\textwidth]{Chapter2/fig.ch.2/22a.png}
%\label{fig:subfigure1}}
%\quad
%%\subfigure[Blush Smiley]{%
%%\includegraphics...
%%\label{fig:subfigure2}}
%\subfigure[Full Assembly of Linear electromagnetic motor]{%
%\includegraphics[width=0.8\textwidth]{Chapter2/fig.ch.2/22b.png}
%\label{fig:subfigure3}}
%\quad
%%\subfigure[Angry Smiley]{%
%%\includegraphics...
%%\label{fig:subfigure4}}
%%
%\caption{High bandwidth active suspension concepts by BOSE.} Source: ~\cite{bose2010,Jones05,Lei08}
%\label{fig:22}
%\end{figure}
Furthermore,  performance effected when the crucial parameters, such as spring stiffness and actuator force, were changed.
Moreover, there are many researches were studied the energy requirements for low bandwidth suspension actuators and semi-active dampers and they were searched to find the solutions for energy recuperation concept. They were succeeded to reduce the energy required for these suspension systems to less than half of previous results by using suitable electronics. References \citep{Graves00,Stribrsky07,Efatpenah00} presented rich study about concepts for energy management and recuperation in suspension systems.

\subsection{Suspensions with Variable Stiffness and Damping}
Slow adaptive suspension systems are also able to adjust the stiffness of their primary springs in order to adapt the s presented to approximate a suspension system with variable stiffness and damping by a double suspension, which is a series connection of two suspensions including a spring and a semi-active damper, respectively. By assuming a high spread of the damper, i.e. a large interval in which the damping coefficient can be varied, the spring stiffness resulting from the series 

\section {CONTROL OF ACTIVE SUSPENSION;STATE OF THE ART}\label{sec:23}
Various concepts concerning suspension control can be located in literature intended for active and semi-active vehicle  bandwidth and energy limits are discussed e.g. in \citep{Karnopp83,Karnopp86}.

For the simultaneous increase of passenger comfort and safe drivability, suspension control is considered today in a global 

The controller structure of the Mercedes Benz ABC slow active suspension system consists of four primary parts \citep{Heiring11}: Skyhook control, 

The controller  in \citep{Akbari09,Kim02,Ryu11}.

In recent years,  Moreover, \citet{Alleyne95} presented a skyhook control approach for an active suspension system that involves online estimation of parameters of the hydraulic actuator in order to account for nonlinear and time-varying actuator dynamics.

\section{SUSPENSION ROBUST CONTROL}
\label{sec:24}
model of the shock absorber, which would be time consuming to derive, was presented in \citep{Kaleemullah11}. They then performed a comparison of the controller performance under $H_\infty$, Fuzzy and LQR schemes.

Also, \citet{Zhang05} considered  is discussed.

Multiobjective  $H_\infty$ or mixed $H_2/H_\infty$   control approaches are. Further linear matrix inequality based control approaches for active suspension systems are presented in \citep{Abdalla08,Hao10,Leite05}.



\section{ADAPTIVE CONTROL; BRIEF LITERATURE REVIEW}
\label{sec:25}
Adaptive control is a general control, and flexible space structures control \citep{Chaudhuri04,Schiller97,Tjahyadi04}.

 according to the output error, $e(t)$, so as to follow the reference model output \citep{Bodson94,Ioannou96}.


\section{Summary}
\label{sec:26}
In addition, the performance of this technique was compared with that of new optimal control system as well as a new robust  $\mu$-synthesis control techniques.





