| Continuously Variable Transmission (CVT) can change ratio continuously, it's the ideal transmission for vehicles. Control system is one of the key technologies of CVT, which still has many problems currently. This is the reason why performances of CVT equipped vehicles such as power performance, fuel economy and driveability haven't reach the expected level. In combination with the industrial development of CVT in our country, a series of researches on CVT control system was carried out based on a passenger car equipped with CVT, the main researches and conclusions are as flow:①Key components of the CVT powertrain such as engine, torque converter and CVT were put into test to obtain their performance characteristic. The test data was used to establish the numerical model of performance and efficiency for each part, which were used in system optimization and simulation subsequently.②Optimize of the shift schedule for fuel economy and power performance during starting up and drive conditions with integrated consideration of engine operation condition, efficiency of the torque converter and CVT efficiency. During the starting up condition, with consideration of the coupling relations between engine operating point, efficiency of the torque converter and CVT efficiency, the target CVT ratio was optimized to obtain maximum drive power, and the optimal shift schedule for maximum power performance during starting up was obtained; After the start up is finished, with consideration of engine characteristic and CVT efficiency, target CVT ratio was optimized to obtain maximum drive power and minimal fuel consumption respectively, and the optimal shift schedule for maximum power performance and minimal fuel consumption during driving condition were obtained.③CVT equipped vehicles have poor driving performance during transient conditions, this is one of the main drawbacks of CVT. To deal with this problem, a control strategy of engine torque compensation together with shift speed restriction during hard acceleration maneuvers was proposed, which can eliminate the drop of acceleration during accelerate effectively. At the same time, a control strategy to tune the steady operating line of engine based on statistic features of driving parameters was proposed, which uses the historic data of driving to determine the operating point of engine reasonably. This control strategy can tune the engine to operating on points with more backup torque before a transient condition began, which can improve the response speed for transients efficiently. The combine of the two strategies can improve the CVT vehicle's response characters for transient maneuvers efficiently, and the driving performance of CVT equipped vehicle was enhanced.④Systemic research on the design method of performance parameters for CVT hydraulic system was carried out. Methods to design performance parameters based on the need of vehicle performance for various subsystems such as clamping force and ratio control system, clutch control system and cooling and lubricating system was proposed, method to design the displacement of the oil pump was also proposed. The performance parameters for hydraulic system designed by the proposed methods were close to the ones used in the production system, which indicate that the proposed design methods for hydraulic performance parameters were correct and effective.⑤A hardware-in-the-loop test bench for CVT powertrains was developed based on the simulation tool of Matlab/Simulink and the real time controlling and measuring system of dSPACE, which can be used for control strategies evaluation and the developing and testing of control software and TCU. The control strategies and optimal shift schedules proposed in this dissertation were put into test on the test bench, test results indicate that the proposed control strategies and optimal shift schedules were effective.Researches aim at many key issues of CVT control system was carried out in this dissertation, simulation and test results indicated that outcomes of the researches can improve the performance of CVT equipped vehicle effectively, which provides theoretic support for the industrial development of CVT control system.
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