HYDRAULIC CONTROL UNIT FOR AUTOMATIC TRANSMISSION

摘要

PURPOSE:To prevent the occurrence of a shock and a rise in an engine in time of selection to shift steps, by making a passage sectional area smaller till hydraulic pressure in a high-speed frictional engaging device reaches to the reference one. CONSTITUTION:A solenoid valve 102 is installed in a discharge oil passage 94, then a hydraulic sensor 44 is installed in a high-speed step clutch 24, and output out of the hydraulic sensor 44 is inputted into a central processing unit 48, while a solenoid valve 70 is controlled so as to make a passage sectional area of the discharge oil passage 94 smaller till hydraulic pressure in the high-speed step clutch 24 reaches to the reference one as well as to make the passage sectional area of the discharge oil passage 94 larger after the hydraulic pressure reaches the reference one. With this constitution, an overlap period comes to the length corresponding to the high-speed step of main transmission so that a shift shock and a rise in an engine in time of selection of an auxiliary transmission from the lowspeed step to high-speed one are preventable irrespective of a shift step of the main transmission.