Hydraulic control system for automatic transmission

摘要

A hydraulic control system for an automatic transmission to establish a predetermined gear stage by applying a first frictional engagement element (B-2) and releasing a second frictional engagement element (B-3), comprising: a first hydraulic servo (29) for actuating the first frictional engagement element (B-2); a second hydraulic servo (28) for actuating the second frictional engagement element (B-3); change-over means for switching the feed of an oil pressure to the first hydraulic servo; signal pressure generating means (SLU;...) for generating a signal pressure; and a pressure regulator valve for regulating the pressure to be fed to the second hydraulic servo. The pressure regulator valve includes: a first valve member (251) having a first pressure receiving area (A1) to be fed with the signal pressure in one direction; a second valve member (252) arranged coaxially with the first valve member (251) and adapted to come into abutment against the first valve member (251) in the other direction, the second valve member (252) having a second pressure receiving area (A3) to be fed with the oil pressure to the first hydraulic servo (29) in the other direction, when the oil pressure is fed by the change-over means; and bias means (259) so disposed at the side of the second valve member (251) axially opposed to the first valve member as to bias the second valve member (252) into abutment against the first valve member (251).