Patent ID: 6055879
Filing Date: 2000-05-02
Classification: F16H,Y10T

Abstract:
A hydraulic control system for an automatic transmission having at least two power transmission shafts, and clutches which are engageable in response to application of a hydraulic pressure thereto to selectively connect one of the power transmission shafts to a power transmission path, comprising:a first switchover valve connected to supply hydraulic fluid to one of said clutches, said first switchover valve having a spool positioned in a hydraulic fluid supply position for supplying the hydraulic fluid to the one of the clutches and movable to a hydraulic fluid cutoff position;a second switchover valve connected to supply hydraulic fluid to another of said clutches, said second switchover valve having a spool positioned in a hydraulic fluid supply position for supplying the hydraulic fluid to the another of the clutches and movable to a hydraulic fluid cutoff position;a first duty controlled solenoid valve controllable to selectively supply the hydraulic fluid supplied to said one of said clutches to said first switchover valve;a second duty controlled solenoid valve controllable to selectively supply the hydraulic fluid supplied to said another of said clutches to said second switchover valve; andmeans for moving the spool of the second switchover valve to the hydraulic fluid cutoff position when said first duty controlled solenoid valve selectively supplies the hydraulic fluid supplied to said one of said clutches to said first switchover valve, and for moving the spool of the first switchover valve to the hydraulic fluid cutoff position when said second duty controlled solenoid valve selectively supplies the hydraulic fluid supplied to said another of said clutches to said second switchover valve, so that a malfunction of one of said solenoid valves will not cause a simultaneous engagement of the one and the another of the clutches.