Abstract
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.
In this paper, EF-automatic transmission was redesigned with proportional control solenoid valves of which control pressures are directly applied to control elements and modified transmission was tested on transmission-dynamometer to prove the shifting performance of proposed electrohydraulic control system. We established a dynamic model of EF-automatic transmission power train to investigate the shifting characteristics and proposed a open-loop pressure control strategy during torque phase in terms of power train static torque analysis and designed a closed-loop controller that is based on the linearized turbine dynamics model during inertia phase. From the experimental results conducted with modified EF-automatic transmission in which proportional control solenoid valves are employed, we verified the validity of the proposed shifting control algorithm and concluded that shifting quality could be improved with the use of proportional control solenoids.