| After more than a century of development,the automotive industry has gradually developed from the mechanical physical system to cyber physical system,a new type of chassis system with high integration,simple structure and easy to be realized is needed in the trend of automotive electricization and intelligence.The automotive braking system is gradually evolving to Brake-By-Wire.Compared with the mechanical brake-by-wire system,the hydraulic brake-by-wire system has become one of the international research focuses due to its advantages in electronics,hardware and production cost,and its performance of "active pressure build fast,accurate pressure control" determines whether the vehicle can follow the driver's intention to produce braking force quickly and accurately.High speed switched solenoid valve(HSV)is a key part in the pressure control of the automotive braking system,the analysis,evaluation and optimization of its nonlinear flow controllability are the key to improve the pressure control effect of the automotive braking system.Better wheel cylinder pressure control strategy and estimation method is an important cornerstone to ensure the braking performance of the whole vehicle.From the point of view of improving the performance of the hydraulic brake-by-wire system,this paper has carried out in-depth research on the nonlinear flow controllability of HSV,wheel cylinder pressure control strategy and estimation method,respectively.The main contents of this paper are as follows:Firstly,a new hydraulic brake-by-wire system is propsed,and the dynamic model for dynamic analysis of the system is established.Taking a traditional chassis system passenger car as the design object,a new type of hydraulic brake-by-wire system with valve control and pressure regulation is developed.The high pressure accumulator is used as the brake pressure source,and the pedal-sensing simulator is introduced to realize the complete decoupling of brake hydraulic regulation and brake pedal sensation.The working mechanism of the hydraulic brake-by-wire system under different working modes is analyzed.The possibility of realizing the performance index of "active pressure build fast,accurate pressure control" of the hydraulic brake-by-wire system is also discussed.The modular dynamic model of the hydraulic brake-by-wire system is constructed by mathematical analysis method,and used to analyze the system performance.Secondly,the mechanism of expansion of nonlinear flow control interval of HSV is revealed,and a new type of Normally Closed High speed Linear solenoid Valve(NNCHLV)is presented.HSV is the key component to adjust brake hydraulic pressure,and its nonlinear flow controllability is the core to realize the rapid pressure change and accurate pressure control of braking system.The flow characteristics of Normally Open High Speed switch solenoid Valve(NOHSV)and Normally Closed High Speed switch solenoid Valve(NCHSV)are studied by simulation,and the reason why the two solenoid valves have a smaller flow controllable interval is analyzed.The mechanism that HSV is easy to open and close completely is revealed.The "flow controllability factor" is proposed to evaluate the nonlinear flow controllability of HSV,and a New type of Normally Closed High speed Linear solenoid Valve(NNCHLV)is presented.An adaptive weighted particle swarm(APSO)optimization method is used to optimize the structure parameters of the NOHSV and the NNCHLV.Thirdly,aiming at the key problem of "active pressure build fast,accurate pressure control",which is urgently needed to be solved in hydraulic brake-by-wire system,an improved hydraulic brake-by-wire system and pressure control strategy based on the NNCHLV is proposed.The solenoid valve controller based on RBF neural network and fuzzy Bang-Bang is studied.Two kinds of wheel cylinder pressure control strategies are proposed,which are suitable for the initial proposed hydraulic brake-by-wire system and the improved hydraulic brake-by-wire system.The dynamic response characteristics of cylinder pressure in two kinds of hydraulic brake-by-wire system under various signal excitation are analyzed.The simulation results show that both the initial and improved hydraulic brake-by-wire system with two control strategies have better performance of fast booster and accurate pressure control,and the improved hydraulic brake-by-wire system and its control strategy have better performance.Fourthly,aiming at the problem that single sensor and single model can not solve the problem of sensor signal distortion easily caused by high frequency transient motion characteristics and complex driving conditions,which leads to lower or even wrong estimation accuracy of wheel cylinder pressure.An Interacting Multiple-model Probabilistic Data Association(IMMPDA)filtering algorithm for cylinder pressure estimation is proposed.Two pressure models,including constant pressure and constant pressure change rate,are established.Based on the two cylinder pressure measurements information of nonlinear characteristics of actuators and vehicle dynamics,the accurate estimation of cylinder pressure is obtained by using multi-sensor data fusion filtering algorithm to improve the accuracy and adaptability of cylinder pressure estimation in clutter environment.Finally,the hardware-in-the-loop test bench of the hydraulic brake-by-wire system is built,the actuator dynamic characteristic tests and the wheel cylinder pressure dynamic characteristic tests were carried out.The model simulation is in good agreement with the test results.the pressure holding experiment of the NOHSV and the opening experiment of the NCHSV are completed.The P-V characteristics of high pressure accumulator and the wheel cylinder are tested,a series of experiments of continuous control of wheel cylinder pressure under various virtual target pressures are carried out.The experimental results show that the actuator controller and wheel cylinder pressure control strategies proposed in this paper can effectively meet the dynamic response requirements of the hydraulic brake-by-wire system,which has a good capability of quick pressurization and accurate pressure control. |
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