Research On Monitoring And Control Methods For Hydraulic Braking Status Of RBS Applied To Electric Car

National automotive industry plan clearly emphasized to accelerate the development of new-energy automotive industry to help relieve pressure on energy and the environment.Brake energy recovery is one effective means for new energy vehicles to achieve energy saving.It uses the regenerative braking of motor to recycle the kinetic energy loss while vehicle braking,which can reduce vehicle energy consumption and extend the driving range.As a kind of new energy vehicles,electric cars have a relatively large proportion of electric drive,and its powerful motor and battery capacity increases the potential to make a significant upgrade of regenerative braking.Therefore,on the premise of safety and no worse effect on braking traditional brake feel,improving the energy recovery level becomes the major goal of high quality brake energy recovery system.Energy recovery systems for electric cars ussually adopt motor and hydraulic composite brake mode.To achieve these above goals,the software needs to solute three key technical problems,such as hydraulic brake force coordination with regenerative braking force,identification of the driver's braking intent and exact implementation of the braking force.Related researches are conducted by auto companies and research institutes around the world widely.Foreign study started earlier with significant advantage of hardware resources.There are already many products apllied to electric cars on the market,which make a remarkable performance on energy recovery.Due to limitations of hardware resources,domestic research stay in the new configuration prototype development and theoretical simulation stage,where are many technical problems to be solved.Relying on the national 863 program,combined with results of national 973 program and international science and technology cooperation project,investigations of new related technology home and abroad,a brake energy recovery system will be developed for the'Besturn' electric cars.This paper focuses on issues related to hydraulic brake controlto carry out the following research work:1.Energy recovery system solutions analysis.System level analysis derives control objectives of hydraulic brake.Through hardware analysis and regenerative brake component performance testing,figure out restrictions for hydraulic brake control.Software analysis based on RBS and ABS control process to get clear requirements of execution status.System performance will be alse analyzed to clear effects and requirements of the hydraulic brake pressure control.2.Analysis structural principle of the new hydraulic brake component-brake pedal stroke simulator,and bench test will be carried out to make sure its influnce to the traditional hydraulic braking.Structure theoretical analysis of the key hydraulic executioncomponents-hydraulic control unit.Further study of the working mechanism of its main components,such as proportional solenoid valves,on-off solenoid valves and hydraulic pump,with necessary simulation analysis.According to the working mechanism of components to determine their drive method,and bench test about hydraulic characteristics will be carried out to verify the accuracy of mechanism analysis,meanwhile to provide theoretical and experimental basis for exploring pressure control methods.3.Research on status monitoring methods for hydraulic brake systems.A stable and observable hydraulic braking system is a prerequisite for the implementation pressure closed-loop control.The new components-the pressure sensor and pedal stroke simulator is the weak link of syatem.According to the working mechanism,drive and signal acquisition method of pressure sensor,sensor failure mode analysis will be conducted.Potential failure states will be analized for new component-pedal stroke simulator based on its structure and working mechanism.Research on wheel cylinder pressure estimation methods based pressure sensor signal and vehicle dynamics.Combined signal of pressure sensors,signal of pedal stroke simulator sensor and estimated pressure of wheel cylinder,develop failure recognition algorithm and sensor signal fault tolerant algorithms,to improve reliability of braking system.Based on system solution,conduct research of driver braking intent identification.4.Research on brake pressure control methods.On level of controller software,analysis pressure response requirement from RBS and ABS control algorithm.Based on working mechanism and control features of hydraulic components,respectively typical pressure control method will be studied,including step pressure control,linear pressure control and active pressurization control.Through mechanism analysis and experimental research,make sure the influence factors and critical control parameters which affect the accuracy of pressure control,and find simple and feasible methods for parameter calibration.Strengths and weaknesses of such pressure control methods will be summarized,and pressure control methods will be applied pressure increase or decrease process of RBS or ABS based on finite state machine theroty.5.Verify the effectiveness of the hydraulic condition monitoring and control methods developed in this paper by bench test.Based on real car test conditions,hydraulic monitoring and control method will be intagrated with system software,and system performnce test about typical RBS and ABS braking process will be carried out.The following conclusions can be derived from these above studies:1.By associating the master cylinder pressure,wheel cylinder pressure and pedal displacement information,system working status can be monitored.Driver braking requirement,which is derived mainly from the master cylinder pressue with brake pedal situation considered,can well attenuate the invalid perturbations mixed in the sensor signals,and improve the accuracy of brake input recognition.2.Based on working mechanism derivation and characteristics test research of hydraulic components,combined with pressure control requirement of control software,specially develop pressure control method what proved effective.3.On the basis of understanding the key factors and control parameters that influence pressure control precision,develop simple pressure control and parameter calibration methods to improve the portability of the control algorithm,which makes significant practical sense.Calibration methods for pressure control parameters,from the application level,propose valid requirement for key parameters match and prototype production of the system components.4.Results of bench and real car test show that,the hydraulic brake status monitoring and control methods described herein has a good adaptability while integrated in the energy recovery system,which receives a more accurate identification of the driver's braking demand,high precision of pressure control and small fluctuations of vehicle braking strength in the electrical and hydraulic brake force adjustment process.During emergency braking,the actual pressure of wheel cylinder can follow the target working pressure well,which makes wheel slip be controlled within the stable range.