Patent ID: 6374687
Filing Date: 2002-04-23
Classification: F16H,Y10T

Abstract:
A vehicle automatic transmission comprising:a first speed clutch for establishing a first speed gear shift stage when engaged, a first speed hold clutch for establishing a first speed hold gear shift stage when engaged, a first clutch piston for causing frictional engagement elements of the first speed clutch to be engaged with each other, a first clutch oil chamber for driving the first clutch piston in a direction to make the first speed clutch engaged, a second clutch piston relatively movably positioned inside the first clutch piston, the second clutch piston causing the frictional engagement elements of the first speed hold clutch to be engaged with each other, a second clutch oil chamber for driving the second clutch piston in a direction to make the first speed hold clutch engaged, a clutch housing shared by the first speed clutch and the first speed hold clutch, a check valve on the first clutch piston for discharging hydraulic fluid from the first clutch oil chamber into the inside of the clutch housing when the hydraulic pressure of the first clutch oil chamber is less than a predetermined value and cutting off the connection between the first clutch oil chamber and the inside of the clutch housing when the hydraulic pressure of the first clutch oil chamber is at or above the predetermined level, and wherein when a first speed hold gear shift stage is established, after the first speed clutch has been engaged by supplying hydraulic fluid to the first clutch oil chamber to drive the first clutch piston in the direction of engagement, the first speed hold clutch is engaged by supplying hydraulic fluid to the second clutch oil chamber to drive the second clutch piston relative to the first clutch piston in the direction of engagement.