| 摘要 |
PURPOSE:To prevent shocks upon shift operation of an automatic speed change gear unit, by controlling a servo device such that one rotating member in the timing of stopping of a planetary gear mechanism is substantially coincident with the timing of stroke completion of a piston in the servo device upon shift operation from a high speed shift stage to a low speed shift stage. CONSTITUTION:When an electronic control device 19 issues a shift signal from the third shift stage to the second shift stage upon running of a vehicle, hydrau lic pressure in a passage 20 is discharged by a shift control valve which is not shown, and therefore, a 2-3 shift valve 10 is moved to the second shift stage side. Then, the timing of initiation of lowering hydraulic pressure for a servo device 2b in a kick-down brake 2a is compared with the output of a detector device 22 for detecting the position of a piston 5 in the servo device 2b. If the piston 5 passes the hydraulic pressure lowering position, a solenoid valve 18 is opened at a predetermined rate, and thereafter, when the rotational speed of a kick-down drum 3 exceeds a predetermined value, a band 4 fastens the drum 3 to complete the shift operation of the second shift stage. |
