| With the development and popularization of new energy vehicles in China,the technology used in new energy vehicles is also constantly innovate and progress.At the same time,new energy vehicles is developing towards a more intelligent,energy-saving direction,meeting the performance of traditional vehicles.EHB electronic hydraulic braking system of the TOYOTA Prius have a very wide range of applications in new energy vehicles.First of all,on the new energy vehicles with electro-hydraulic brake system,EHB system can meet the requirements of braking system for braking energy recovery,at the same time,it can provide good braking feedback to driver.Secondly,in the aspect of Advanced Driver Assistant Systems,EHB braking system can build the brake pressure based on the needs of the algorithm automatically,for example ACC,AEB and other ADAS algorithm.Thus,the research on the EHB hydraulic braking system of the TOYOTA Prius,is very useful for the development and application of new energy automobile braking system.The EHB consists of 10 solenoid valves,including 8 linear solenoid valve.The flow of the Linear solenoid valve can be adjusted linearly,to realize the precise adjustment of the wheel cylinder pressure.However,the domestic research on the modeling and control strategy of EHB linear solenoid valve is relatively new field and there is few study on it.The present control algorithm canot bring into play the linear regulating role of linear solenoid valve,but it is used as on-off valve.After reading and collecting a large number of domestic and foreign literature,this paper will select electronic hydraulic actuator as the research object,find a simple method to establish the accurate model of linear solenoid valve,at the same time,and develop the control strategy of braking pressure,so that the braking pressure can follow the target pressure accurately.Firstly,the hardware and software environment of experiment should be constructed,beacause the model and control algorithm of linear solenoid valve needs to be carried out on the experimental bench.Designing and building the EHB hydraulic braking bench to restore the original EHB braking system.Desiging the drive plate to achive power amplifier.And using the Micro Auto Box II 1401/1501 of d SPACE company as the controller to finish signal acquisition from pressure sensor and output control signal after calculating.In the respect of software tool,Matlab/Simulink and Control Desk are used mainly to establish the model of linear solenoid valve,develop the control strategy of braking pressure and download the automatic code generation file to Micro Auto Box II 1401/1501 to carry out rapid prototyping.Secondly,the HCU is disassembled,the structural characteristics of the solenoid valve are analyzed,and the physical model of the solenoid valve is established.At the same time,a large number of experimental data are used to identify the parameters,and the unknown parameters are solved.Compared with the actual experimental conditions,the linear valve is modeled.Thirdly,the characteristics of the HCU motor and the hydraulic characteristics of the solenoid valve were tested on the EHB hydraulic brake experiment bench,including that the calibration of the EHB internal sensor,the selection of PWM control frequency,the pressurization characteristics of high pressure accumulator,the pressurization characteristics and the current of linear solenoid valve in different duty ratio.Finally,the EHB braking pressure following control algorithm is developed.At first,the pressure closed loop PID control strategy is established and the typical working condition of pressure following control is tested,but the control effect is not ideal,and the linear range of linear valve is not well utilized.And then the pressure-current double closed loop control strstegy with the feedforward is developed according that the basic adjustment factors of opening is current.At last the rapid prototype experiment is carried out on the EHB hydraulic brake test-bed to verify the correctness of the algorithm.It can be seen from the experimental results that the control effect has been greatly improved,and the linear interval of linear valve is fully utilized.At the same time,the upper ESP control strategy of the EHB and the bottom pressure control algorithm are fused,and the fused algorithm is downloaded to the controller for hardware in the loop experiment.The improved control algorithm can follow the pressure of the upper layer,and achieve the expected control of the ESP control strategy.In this paper,the control algorithm is developed based on a thorough understanding of the characteristics of linear solenoid valve.It can make full use of the advantages of linear pressure regulation,reduce the pulsation and impact of hydraulic system.This paper provides a research method for the accurate pressure of the braking energy recovery system and the further research of ADAS intelligent auxiliary braking. |
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