Patent ID: 6846259
Filing Date: 2005-01-25
Classification: F16H

Abstract:
1. A hydraulic control system for an automatic transmission, the hydraulic control system comprising: a plurality of hydraulic servos for engaging and disengaging a plurality of friction engagement elements; a control device that supplies engagement pressure to the plurality of hydraulic servos; a first shift valve having a first port to which a source pressure is supplied from an oil pressure source and a second port, the first shift valve being selectively positioned in one of the first and second positions, said first position having said first port and said second port in communication in a first shift speed that is lower than a predetermined shift speed so that the source pressure is output from the second port, said second position blocking communication between the first port and the second port in a second shift speed that is different from the first shift speed, so that the source pressure is not output from the second port; a second shift valve having a third port in communication with said second port, a fourth port to which the source pressure is input without passage through the first shift valve, and a fifth port, the second shift valve being selectively positioned in one of third and fourth positions, said third position providing communication between the third port and the fifth port in a first speed and in the predetermined shift speed so that the source pressure supplied from the first shift valve is output from the fifth port, and the fourth position providing communication between the fourth port and the fifth port in a shift speed that is different from the predetermined shift speed so that the source pressure is output from the fifth port, wherein the control device includes a sixth port in communication with the fifth port, and a seventh port that outputs the source pressure received at the sixth port to one of the plurality of hydraulic servos as the engagement pressure.