Vehicle Chassis Integrated System Coordinated Control Based On Function Allocation And Stability Analysis

Vehicle is one of the important means of transport, which is most closely related topeople’s production and life. The chassis as one of the important vehicle assembly, playsan important role in improving vehicle ride comfort, handling and security performance.The chassis is composed of suspension, steering and braking subsystems. Applying theactive control to them can improve vehicle certain aspects of performance. Due to thecoupling relation among the subsystems, the optimal control to chassis integratedsystem is difficult. The designed control system can improve the chassis system controlperformance from some aspects. But how to consider the function difference of differentsubsystems, carry out the function allocation to the chassis integrated system’ssubsystems and design coordinated control system to guarantee the chassis with thewhole-region optimal control performance, is the difficulty of the current research.In this thesis, the coupled dynamics among the chassis’ three subsystems ofsuspension, steering and braking is considered. The research is on system modeling,subsystems’ controller design and order reduction for high-order suspension controller,integrated system corordinated control and optimization based on function allocation,and stability analysis. And the hardware-in-loop simulation is carried out to verify thedesigned control method. The details are illustrateed as follows.1) To solve the problems of high-order and hard to engineering realization offull-vehicle suspension controller, the7degree-of-freedom full-vehicle activesuspension model is built. Based on the minimal information loss method, theorder-reduction of active suspension controller is studied. Through thefrequency-domain simulation and ride-comfort analysis to the full-order andreduced-order active suspension control systems, the research results demonstrate thatthe20th-order of active suspension controller can be significantly reduced, and systemstate controllability and observability information loss is less.2) Based on building the vehicle syspension and steering system coupled dynamicmodel, the deviation and deviation derivative are chosen as the characteristic quantities,and the extension set is established. The three measure modes of the classical domain,extension domain and non-domain are divided according to the correlation function.The control functions are allocated in different extension sets, and the correspondingcontrol algorithms are separately designed to form the function allocation based extension controller (FAEC). The simulation research results demonstrate that the FAECcan further improve the control performance of the suspension and steering integratedsystem.3) For the system with parameters uncertainty and time-delay, the sufficient conditionof system stability is given. And then the stability is analyzed for the suspension andsteering system. The integrated control system stability is analyzed when utilizing thesuspension and steering system parameters as the variables by different control methods.The analysis results show that adopting the FAEC, the control system is with betterstability. When increasing suspension damping, vehicle velocity and the front-wheelsteering angle to certain values, vehicle time-domain responses’ instability degreeincreases. And when changing the FAEC error weighted coefficients, it brings differentdegrees of influences to the integrated control system performance. If constantlyincreasing the extension controller function control coefficient, it leads the vehiclecontrol system to instability.4) For suspension and steering nonlinear integrated system, the bilinear control basedon deviation separation(BCDS),H∞control and sliding mode variable structurecontrol (SMVSC) are utilized to design the nonlinear controllers. The human-vehiclefunction allocation module(HVFAM) based on fuzzy rules is adopted to coordinate thesyspension and steering system control weights. The simulation results demonstrate thatthe BCDS can better improve vehicle ride comfort and handling performance thanH∞control and SMVSC. And the HVFAM can futher improve integrated system controlperformance.5) Considering the coupled dynamics among suspension, steering and brakingsub-systems in vehicle chassis, the sub-optimal controllers of nonlinearH∞control,direct yaw moment PID control and sliding mode control are separately designed for thesuspension, steering and braking subsystems. The subsystems’ control functions areallocated based on the function allocation principle, and the subsystem’s controlfunction indices are utilized for competing by game theory. The fuzzy rules are utilizedto adaptively adjust the subsystems’ control output in order to follow the whole-regioncontrol object. The considerable simulations are carried out for full-vehicle coordinatedcontrol system. The results demonstrate that the full-vehicle coordinated control systembased on game theory can obtain the best control performances than the uncoordinatedcontrol system and uncontrolled system.6) The hardware-in-loop simulation test(HILST) platform is designed based on NI Compact-cRIO. The HILST for vehicle suspension subsystem, steering subsystem andintegrated system are carried out, to varify that the designed extension controller andbilinear controller can futher improve vehicle ride comfort and handling. Then thevehicle test based on rapid prototyping is carried out by adopting Compact-cRIO9025under three different conditions. And the test results also demonstrate the designedbilinear controller can obtain the best vehicle ride comfort and handling performance.