Automatic Transmission SOLENOID valve (iron) in the application, solenoid valve in the hydraulic system is divided into pilot control and direct drive control, pilot solenoid valve control pressure and flow are relatively low, can not directly drive the actuator, pilot control pressure only. Direct-drive solenoid valve than the pilot valve has more electromagnetic force, control pressure and flow can be directly driven actuator. The hydraulic system using direct drive solenoid valve reduces the number of mechanical valves and simplifies the structure of the system. Another kind of electromagnetic valve product is proportional electromagnet. Compared with other electromagnetic valves, proportional electromagnet only has electromagnetic part, which provides electromagnetic force. The hydraulic part is integrated on the hydraulic valve body. The hydraulic part is designed by the customer according to the needs of the specific system, more flexibility, but at the same time increased the difficulty of hydraulic system integration. Four: The Automobile Gearbox electromagnet, the automobile gearbox electromagnet is through the gearbox electromagnet and the Shift Control Electromagnetism Valve completes the shift control together. The main principles are: 1 shift control rules, to meet the shift conditions; 2 by comparing the driving resistance and traction of the new gear, if the traction force is greater than the driving resistance, to meet the shift conditions; (up 12, up 12, up again). Downshift 1 satisfies the downshift condition by Shifting Control Law; 2 by comparing the driving resistance and traction of the current gear, if the traction force is less than the running resistance, the downshift condition is met (because the engine speed will increase after downshift, so it is necessary to ensure that the engine will not overspeed because of downshift) .