Optimization Of Shift Schedule Based On The Best Performance Operation Line Of Engine

Shift schedule is the rule gear-shift timing between two adjacent gears varies according to the control parameters( usually velocity and throttle opening), which is the main line of a stepped automatic transmission for it has a great effect on the power performance, fuel economy and emission of a vehicle. Using the engine test data, this paper proposed a multi-performance optimization of shift schedule based on the curve of overall performance, and tested the proposed shift schedule in the model of a small car equipped with a five-speed automatic transmission. The main contents are as follows.(1) The types and operational principle of automatic transmission are introduced; the research situation and development trends of shift schedule are summarized.(2) Based on the curve of power performance or fuel economy, the power performance shift schedule and the fuel economy shift schedule are calculated. When the throttle opening is set to a definite value, the value of power varies with the engine speed. The engine speed corresponding to the maximum value of the power is regarded as the optimal engine speed. In this way, couples of data of throttle openings and engine speeds are obtained, with which the curve of power performance is established. The optimization of shift schedule is based on the total difference of the engine speed between the two engine working points at the moments before and after gear-shifting and the curve of power performance: the velocity corresponding to the smallest difference is the shift speed.(3) Based on the overall performance, the power performance dominated shift schedule and the fuel economy dominated shift schedule are calculated. By considering together the power performance, fuel economy and emission, the synthetic function is founded. The engine speed corresponding to the maximum value of the synthetic function is regarded as the optimal engine speed. In this way,couples of data of throttle openings and engine speeds are obtained,with which the power performance dominated curve and the fuel economy dominated curve are established. The optimization of shift schedule is based on the total difference of the engine speed between the two engine working points at the moments before and after gear-shifting and the curve of overall performance: the smaller the difference is, the better. The velocity corresponding to the smallest difference is the shift speed.To test how the shift schedules perform in a specific car, the shift schedules are applied to the simulation model developed by MATLAB/Simulink. Simulation includes the power performance simulation and the drive cycle simulation. Results show that, compared with traditional method, the proposed method can improve the overall performance of a car equipped with stepped automatic transmission.