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Nowadays, most automatic transmissions of passenger car adopt an electronically controlled shifting mechanism to enhance the driveability and fuel economy. As the performance requirement, especially on shift quality, of automatic transmission become rigorous in recent years, power train engineers have made an great effort to improve ride comfort during shift. EF-automatic transmissions for FWD passenger car, installed in Hyundai's EF-sonata model, are originally developed by Mitsubishi Motor Company and equipped with full electronic control system. Its major design features are that clutch-to-clutch shifting mechanism is employed for simplified construction and lighter weight and four independently operated PWM solenoid valves control the applying pressure on the friction elements during shift.

Since 1980s, the electronic control units of automatic transmissions have been greatly advanced to make smooth gear shifting and improve fuel economy. Along with it, the solenoid valves as electro-hydraulic actuators have been rapidly developed which have high pressure and large flow capacity. In these days, it is not an expensive solution to adopt more electro-hydraulic actuators to get the better performance of the automatic transmission. This paper introduces a new scheme of full electronic control system, direct active shift control, using the proportional control solenoid valves to control the pressure of each friction element independently and without any passive hydraulic or mechanical component. At first, it reviews the structures of widely used control systems from the old-fashioned to the modern. Next, the concept of the direct active shift control scheme is introduced and the performance of the actuators discussed.

Generally, the widely used hydraulic control system in automatic transmissions is pulse width modulation (PWM) type. It consists in a PWM solenoid valve and a reducing type second stage valve, so called pressure control valve (PCV), to amplify pressure or flow rate. In this study, the mathematical models of the PWM solenoid valve and the PCV with moderate complexity are proposed. Then, their behavior is analyzed from the steady state characteristics. Finally, we find that there are good matches between the dynamic simulation results and the experimental data.

As most of today's automatic transmissions adopt a electro-hydraulic control system, the role of electronically controlled solenoid valves occupies an important position. This paper presents a dynamic modelling technique of a proportional control solenoid valve(PCSV) for automatic transmissions in terms of the system identification theory, and analyzes the dynamic characteristics of the PCSV in frequency domain. Also we find that there are good matches between the nonlinear dynamic simulation results and the experimental data.