Hydraulic control system for automatic transmission having torque converter with lock-up mechanism

摘要

A lock-up valve includes a spool movable between a clutch engagement position wherein the lock-up clutch is engaged and a clutch release position wherein the engagement of the lock-up clutch is released. A spring biases the spool toward the clutch release position. The spool has a first pressure acting area and a second pressure acting area. A fluid pressure is applied to the first pressure acting area during operation in the m+th speed ratio (where: m is an integer) and the m+1th speed ratio to urge the spool against the spring toward the clutch engagement position. A lock-up timing valve is provided which allows the application of another fluid pressure to the second pressure acting area during shifting between the m th speed ratio and the m+1th speed ratio to urge said spool toward the clutch release position.