| 摘要 |
PURPOSE:To reduce a speed change shock, by controlling the pressure of oil by an electronic control unit with a 1-2 shift valve as left being held in a 2-speed side and gradually releasing a kickdown brake, in the case of an automatic transmission equipped with a gear transmission function. CONSTITUTION:If a speed change command from a 2-speed to a 1-speed is generated from an electronic control unit 54, a device, holding a 1-2 shift valve 37 as left in a 2-speed position, increases duty ratio of a solenoid valve 55 in a predetermined changing speed. In short, the device, decreasing a control pressure of oil in an oil path 51, reduces a line pressure, supplied to the 1-2 shift valve 37 from an oil path 41 while to a kickdown servo 36 through an oil path 38, in a predetermined changing speed. Accordingly the device, gradually releasing the engagement of a kickdown brake 23 and starting a kickdown drum 34 to rotate, starts an effective speed change. Then the device, gradually decreasing the duty ratio of the solenoid value 55 in a predetermined changing speed to gradually increase the line pressure supplied to the kickdown servo 36, gradually increases a rotary speed of the drum 34. |
