| Nowadays, hub motor driving technology mainly focused on hub motor design andsuspension design worldwide, but researches involved with matches between hub motorsand EV (electric vehicle), driving and braking control of hub motors were rarely presented,which is also an obstacle in applications of hub motors. Dedicated to the research onenergy-saving and New-energy Vehicle with so many years, Professor WANG.Qingnian,led his team-the innovation research team of EV&HEV Key Technology, carried outanti-skid driving technology, adaptive differential control and blend braking control of hubmotor drive electric vehicles, also some scientific achievement: road adhesion recognizing,diferential steering and regenerative braking. As X-by-wire and chassis integrated controltechnology develop, conventional hydraulic brake system and parking brake systembecome outdated and will be eliminated in one day, therefore, a new brake system for hubmotor drive electric vehicle, which combined service brake and parking brake functionsafely, should be developed. In the thesis, electric brake characteristics of hub motor driveEV are studied, also the service brake chararcteristics and parking brake characteristics.First of all, advantages of hub motor driving technology are discussed. Applicationbackground of hub motor driving system and scientific research background areintroduced briefly.Secondly, conventional hydraulic brake system model with disc actuator is built inAMESim, including pneumatic vacuum booster model, master cylinder model and brakecaliper model. Then, a hub motor control model based on Permanent Magnet SynchronousMotor (PMSM) Hysteresis Comparison Control method is built. With off-line simulation,transient state response characteristics under step input and steady state responsecharacteristics of hydraulic brake system and electric brake system.action are compared.The simulation results indicate: electric brake exerted by hub motor torque not onlyenhances the response speed of the system, but also makes the torque of each wheelcontrollable independently, which inproves the brake performance of EV, and proves theelectric brake scheme feasible.Thirdly, according to the transient state response characteristics of hub motors, in thepaper, with electric brake utilized, an anti-lock brake control strategy is designed for the EV driven by hub motors. Besides, based on15dimensions of freedom chassis model inAMESim, we add hub motor model, suspension model-spring, damper, end stop, antirollbar, aerodynamic model, tire and road model, sensors model and steering system model tothe multibody chassis model to form hub motor drive EV model. Also, an anti-lock brakecontrol model is established, referred to logical threshold algorithm. With AMESimCo-simulation with MATLAB/Simulink, simulation of electric brake anti-brake control iscarried out. The simulation result indicate: the anti-brake control strategy designed forelectric brake not only improves the brake performance in emergency brake mission, butalso perfectly fits for hub motor drive EVs and enhances the active safety.Fourthly, parking brake system trend is discussed, and the hypothesis applying hubmotor torque to parking brake control is presented. Therefore, compared to the CaliperIntegrated Electric Parking Brake System, the feasibility is analyzed. To investigate thefeasiblilty of electric brake replaceing the EPB system, the EPB actuator model is built inAMESim, including screw-nut transmission model, gear redactor model and servo-motormodel. Also compared to PMSM hysteresis comparison control model, transient andsteady state performance of EPB system and parking brake system with hub motor areanalyzed through the simulation, and the simulation result shows: the non-linar motion ofscrew-nut transmission structure restricts the EPB system response performance andcauses the delay. As the load of brake pad increase, the force on nut fluctuates a lot,affecting the braking stability. However, when taking the hub motor as parking brakeactuator, the stability of braking is enhanced, besides, the energy consumption of hubmotor during parking is relatively small, making no difference to daily use.Fifthly, functional requirements of intelligent parking brake system are analysed,based on these requirements, ultilizing the hub motor torque, electric parking brake systemis design for hub motor drive EVs. Except the basic parking brake function, otherextended intelligent functions are developed. To deal with insufficient driving experienceand complex road conditions, dynamic drive-off assistant function is designed to helpdriver to drive the EV along the slope smoothly and allows the vehicle to be driven offwithout jolts or backroll. To tackle the emergency situation: the brake pedal loses itsfunction or becomes blocked, dynamic emergency stop function is designed to ensure thevehicle can be braked heavily by means of hub motor torque. To handle with the trafficjam or slow moving traffic or drive-off on steep slope, the AUTOHOLD function isdesigned to assist automatic brake of EV. The AUTOHOLD function assures an automaticand controlled hold over the vehicle when stationary, irrespective of the way the vehiclewas brought to a halt.Since the driver no longer has to hold the vehicle on the brake pedal all the time, driving is made easier. At last, the control strategies to fulfill these functionsare simulated off-line.Finally, software-in-the-loop simulation is carried out to verify the electric brakecontrol strategies, in the way of downloading the control model into the dSPACEprocessor board. The real-time simulation provides real environment interaction to controlmodel, and adjusts control strategy in time according to the simulation result. Byconnecting the hub motor and other sensors to I/O interface, Dspace hub motor electricbrake simulation platform is created. Besides, taking TTC200as the vehicle controller, thehardware-in-the-loop simulation is performed to testify the functionality of hub motorelectric brak control strategy. The simulation results demonstrates that the regular parkingbrake function, the dynamic drive-off assistant function, the dynamic emergence brakefunction are all valid and reliable, also the hub motor drive EV brake performance andsafety are improved by applying anti-lock brake control strategy. |
PDF Full Text Request