Abstract: The design and optimization method for the key parameters of proportional solenoid valve used for automatic transmissions are explored. The operating principle of valve is investigated based on the structural analysis. The proportional solenoid valve is divided into 3 components, including electro-magnet, mechanical component, and hydraulic component. The mathematical models for the three components are built separately, and the key factors which influence its response time and pressure dynamic output are analyzed. The optimization design of electro-mechanical converter is performed. The relationship between electromagnetic force and input current is determined, and the genetic algorithm is used to optimize and analyze the proportional solenoid valve by taking the valve mass, spring stiffness, initial compression of spring and viscous damping coefficient as optimized parameters, and the response time and overshoot of output pressure as optimized object. Several structure schemes of proportional solenoid valve are obtained by changing the scope of population, the number of the generation, the crossing-over rate and the mutation rate. The research results show that the dynamic response of output is improved by 12.5%，and the overshoot of output pressure is decreased by 50% after optimization.

Key words: control science and technology, automatic transmission, proportional solenoid valve, optimal design, genetic algorithm