| China’s vehicle population has increased every year with the economic development,huge economic losses and casualties have been made because of traffic accidents each year,people take more and more attention to safety performance of vehicle. Accompanied byadvances in vehicle electronic technology, vehicle chassis control system have beendeveloping rapidly and is widely used, which improve the driving safety of vehicle. Whenmultiple control systems installed on the vehicle, which will lead to the vehicle structure isvery complex, the number of sensors and actuators is excessive, part of the system functionsis overlapped or exists control target conflict. Without coordinated control to these systems,the overall performance of the vehicle decreased. The degree of automation is graduallyincreased in recent years, X-by-wire system gradually been applied in the vehicle. Thistechnology reduces the complexity of the mechanical system, which makes arrangement ofthe vehicle more flexible, the most important thing is easier to achieve integrated chassiscontrol for the steering systems, suspension systems, braking systems. Accordingly,coordinated control of by-wire system has become a focus in vehicle chassis control research.The integrated control effect factors of by-wire systems have two aspects: one is thealgorithm of coordinated control subsystems in software, the other is the precision of by-wiresystem actuators control in hardware.In response to these problems, this paper is combined with Ministry of educationHenry Fok funded project “Vehicle intelligent integrated electric control system research”,NFSC project“Research on vehicle dynamics control based on brake-by-wire”,“The keyscientific issues and key technologies of vehicle electronic control timeshare brake pressure regulating device”. Based on the summery of domestic and foreign research results, thispaper takes a light vehicle as the research object and conducts steering/braking controlsystem research base on accurate regulation of by-wire actuators. Based on theoreticalanalysis and simulation experiment on by-wire actuators, accurate regulation method ofby-wire actuators is proposed. Centralized control structure framework of active steering andactive braking system is established, it uses nonlinear model predictive control methoddesigned active steering/braking control algorithm, it uses fuzzy control theory designedsteer-by-wire and brake-by-wire controller. Vehicle dynamics model includes steer-by-wireand brake-by-wire systems is established, steer-by-wire and brake-by-wire coordinatedcontrol offline simulation platform and hardware in the loop test platform of target vehicle isindependently designed and built, off-line simulation and hardware in the loop test werecarried out to verify the steering/braking control algorithm which has been designed.The main contents include:1. Establishing the vehicle dynamics model based on by-wire systemAccording to the requirements of integrated control system strategy, a fifteen degree offreedom nonlinear vehicle dynamics model has been established. Vehicle model includes sixdegrees of freedom for sprung mass (longitudinal, lateral, vertical, roll, pitch and yawmotion), the four vertical vibration degrees of freedom for the unsprung mass, the frontwheel steering and the rotation of four wheels, and an auxiliary calculation module, tiremodel, the driver model and by-wire system models, which provided the foundations forbuilding of the steering/braking offline simulation platform and hardware in the loop testplatform.2. By-wire actuators accurate regulation methodThe precision of by-wire actuators is a key factor to influence the control effect ofintegrated chassis control.Mathematical model of by-wire actuators--brushless DC motorwas built in this paper, and established a brushless DC motor model in MATLAB/SIMLINK. The simulation analysis results indicate when pulse width modulation (PWM)method is used to control the brushless DC motor, phase current fluctuations exists at commutation and non-commutation time, leading to fluctuations in torque. Then analyzedusing different PWM modulation control brushless DC motor, Non-commutation existsphase current fluctuations during commutation period and the conduction phase currentexists phase current fluctuations during non-commutation period. Finally, the dynamicperformance of brushless DC motor when used pwm-on-pwm modulation has been analyzed.30°electrical angle digital implementation method was raised. Finally, comparing thesimulation result verified control effect. Using the proposed30°electrical angle digitalimplementation method obtained30°electrical angle moment at no additional cost.Pwm-on-pwm modulation without increasing switching losses effectively inhibited torquefluctuations, achieved accurate regulation of by-wire actuators--brushless DC motor torque,which provided the foundations for building of the steering/braking by-wire systemsuperior controller development.3. Steering/braking by-wire system coordinated controlThe overall structure of steering/braking by-wire stability control algorithm wasdesigned in this paper. Nonlinear model control algorithm was raised which applied to theinitial balanced point and non-balanced point. Nonlinear model predictive control algorithmwas designed by using nonlinear four wheel three degrees of freedom vehicle model as areference model. The algorithm used longitudinal speed, yaw angle, yaw rate and lateraldisplacement as the control target to solve optimized control input for active front corner andactive four braking force. This paper achieved regulation of active front steering and activebraking force in execution layer by using fuzzy control, and completed a comprehensivecoordinated control algorithm of active steering and active braking.4. Constructing offline simulation platformAccording to the vehicle dynamics model and active steering and active brakingstability control algorithm, this paper built up offline simulation platform by using Matlabsoftware. Simulation platform including vehicle dynamics simulation software, controlalgorithms Simulink module and simulation platform graphical interface. The platformcombined the off-line simulation control and parameter adjustment and data post-processing well, which made the control algorithm parameter adjustment more convenient. Offlinesimulation of step steering, sine steering and square wave incremental steering were carriedout on offline simulation platform.The results showed that: the designed steering/braking coordinated control system caneffectively eliminate active steering and active braking system interference, which cansignificantly improve the vehicle steering stability.5. Building hardware in the loop test platform and experiment researchIn order to verify the effectiveness of the designed steering/braking by-wire controlsystem, the by-wire control system hardware in the loop test platform program wasdesigned, a steering/braking control hardware in the loop test platform was built based ondSPACE real-time simulation platform. This paper simulated the vehicle actual operatingenvironment under the test conditionsand, which reduced the dependent on road tests insteering/braking by-wire control system development, which reduced costs and shorten thedevelopment cycle. Test platform including real-time platform, hardware and softwarecomponents, this paper selected and designed various parts of a hardware system. Typicalconditions were performed on the hardware in the loop test platform.The results showed that: the software and hardware of by-wire system hardware in theloop test platform matched reasonable. The designed steering/braking by-wire systemachieved accurate regulation of by-wire actuators, which has good control effect, it caneffectively improve the vehicle handling stability. |
PDF Full Text Request