| Continuously Variable Transmission is a type of ideal automatic transmission technology, has become one of the main research of 21st century automotive technology. Metal V-Belt CVT, as the outstanding representative of CVT, compared with other automatic transmissions, has many advantages such as simple in structure, easy to operate, low cost, high performance and efficiency, low noise, energy-saving, and so on. As the world's most potential developing automotive market, China has increasing emphasis and demand on continuously variable transmission technology, and continuously variable transmission has a bright market prospects in our country. More importantly, R&D of CVT with our own intellectual property rights has important economic and social significance to our automotive industry.Metal V-Belt CVT is a high-tech product with mechanical, hydraulic, electronic and computer control technology, which is an ideal transmission method for vehicles. The integrated hydraulic control system one of the core technologies to achieve the ideal CVT performance, whose R&D level and product realization is one of the keys to improve capacity of automatic transmission independent development for China-made passenger cars, and is of great realistic significance to achieve shorten the technological gap with the developed countries.In view of the existence of unresolved key technical issues of CVT, research of this article is as follows:1. On the basis of referring to a large number of domestic and foreign professional literature, this dissertation systemic introduced CVT's develop history and status of domestic and foreign R&D and it's application. The CVT's structure characteristic and working principle are also introduced in detail, and transmission characteristic of steady state, transient state and power loss are analyzed in-depth, which provided the theoretical basis for development of high-performance electro-hydraulic control system.2. The digital control hydraulic system model for dual-state CVT was established based on AMESim software, and the controller models aiming at special requirements of electro-hydraulic control system was also constructed based on Simulink software. After data exchange was realized by AMESim and MATLAB/Simulink S-function interface module, the co-simulation platform was constructed. Through typical working conditions simulation, it was validated that the co-simulation platform could simulate kinetics characteristic of whole vehicle with dual-state CVT and dynamic characteristic of electro-hydraulic, and was effective and practicable for R&D of dual state CVT. The simulation results also showed that: the co-simulation platform could improve the efficiency of modeling and control system can be directed to the special requirements of different control algorithms designed to meet different requirements of the accuracy of the model controller. 3. Considering the non-linear time-varying characteristic and the coupling features between input and output, aiming at the special requirements of CVT ratio control and based on the comparison of control effects of PID control and fuzzy control, mixed-type self-adapting ratio tracking controller was designed combining the advantages of both PID and fuzzy control. The simulation results showed that the real ratio could track the target ratio effectively, and the controller has strong capacity of robust and decoupling and good dynamic response and high accuracy control of steady state, and good dynamic stability under the resistance of outside environment.4. Utilizing hydraulic resistance networks theory, digital design and control technology research was carried out on CVT digital control hydraulic system. Aiming at the dynamic design requirement of electro-hydraulic valve-control system, the key components of the system were dynamic analyzed and designed, and model of pressure relief valve of pilot-operated type based on stepper motor control, digital pressure reducing valve of pilot-operated type based on high-speed on-off valve control, were constructed. Static and dynamic characteristic analysis of the control valve mentioned above was carried out. According to the dynamic response demand of hydraulic actuating system, optimization design based on genetic algorithm (GA) was processed on the key system parameters.5. Aiming at the control demand of integrated hydraulic control system, the electronic control unit for CVT was independent designed based on micro-controller of Infineon XC164CS, which could provide high performance digital electronic control circuit and power amplifier for digital electro-hydraulic valve-control system;6. The dissertation designed digital pressure relief valve of pilot-operated type based on stepper motor control, digital pressure reducing valve control valve of pilot-operated type based on high-speed on-off valve control, and carried out the characteristic test of electro-hydraulic system on hydraulic test rig, studyed the regulations of the influence of the key parameters and static and dynamic features of electro-hydraulic digital control valve on system control pressure, flow rate and control performance. Test results show that the performance of the electro-hydraulic digital valve-control system could meet the requirements of the vehicle working conditions, and improved the performance of driving comfort and shift smooth, and also driving and economy performance, which had laid a solid foundation for further independent development of high-performance product of hydraulic control unit and CVT.The innovations in this article are as follows:(1) It's the first time to establish of a simulink-AMESim co-simulation platform for digital control hydraulic system of dual-state CVT, and design mixed-type ratio tracking controller. The simulation results under typical working conditions showed that co-simulation platform has good practibility for analyzing CVT transmission characteristic and controller development.(2) Through the application of digital control technology, the dissertation carried out the digital design and control technology research on digital control hydraulic system, and optimization design based on genetic algorithm on the key parameters, which improved the dynamic response performance and reliability, and reduced product development costs. At the same time, the application of digital technology made development of control software easier.(3) The dissertation designed and developed the key components of digital control hydraulic system, namely pressure relief valve of pilot-operated type based on stepper motor control, digital pressure reducing valve control valve of pilot-operated type based on high-speed on-off valve control. The bench test results showed that the system had reasonable design, the integrated digital hydraulic control system has high repeat accuracy and good reliability, which fully met the CVT performance requirements in clamping force, Ratio Control, as well as control of the torque converter, and provided a better solution to low repeat accuracy, large size, slow response caused by the use of electro-hydraulic proportional control valve.
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