PURPOSE: To prevent the generation of the judder caused by the pulsation of line pressure by changing the drive frequency of a solenoid valve in the higher side when a friction clutch, by which hydraulic fluid is supplied and discharged through an oil passage not provided with a hydraulic pressure damping means, is engaged.
CONSTITUTION: An automatic transmission has a hydraulic mechanism FS to control the supply and discharge of hydraulic fluid to and from a variety of friction clutches, which is provided with a manual valve and shift valve as well as a line pressure controlling means L. In addition, it is provided with a pressure reducing valve 54, modulator valve 55, solenoid valve 57, etc., to form the pilot pressure supplied to the line pressure controlling means L, and the solenoid valve 57 is controlled in duty by a control unit 32. In controlling this valve 57, when the automatic transmission changes speed to a speed stage at which a coast clutch is engaged by manual operation, the solenoid valve 57 is driven at a relatively high frequency to reduce the pulsation of line pressure, which prevents the generation of the judder caused by the coast clutch.
YOSHIMURA HIROSHI
KITADA MASAHITO
OKAMOTO KENJI
