Abstract: The shifting process of automatic transmission is an alternating process of two actuators filling and draining the hydraulic oil. The improper oil filling and draining of two shifting actuators may cause power interruption or too much overlap, power lose, impact of shifting and aggravated wear of shift actuator. Lagrange equation is used to establish the dynamic equation of the shifting process by taking Allison automatic transmission (HD4070PR) as the study subject. The timing method of two shifting actuators filling and draining hydraulic oil during shifting process is analyzed on the basis of the equation, and verified by real vehicle test. The research results show that, for the upshifting process, the power shifting can be realized, and the impact of shifting can be reduced through the rational power lap;and for the downshift process, since the emergence of power interruption is inevitable, only the loss of the power should be reduced as far as possible.

Key words: control science and technology, hydraulic mechanical automatic transmission, shifting actuator, timing method