Oil pressure control system of automatic transmission

An oil pressure control system of a six speed automatic transmission with first through sixth forward speeds and a reverse speed which comprises first and second clutches, first, second, and third brakes, and first, second, and third planetary gear sets, the system comprising:

• a first clutch and second brake controller, allowing the first clutch to receive a first clutch fastening pressure in said fourth, fifth, and sixth speeds, allowing a second brake to receive a second brake fastening pressure in said first and reverse speeds, and allowing an operation state of the first clutch by the first clutch fastening pressure to be sustained upon operation of the first clutch;
• a second clutch controller allowing the second clutch to receive a second clutch fastening pressure in said third, fifth, and reverse speeds;
• a first brake controller allowing the first brake to receive a first brake fastening pressure in said second and sixth speeds;
• and
• a third brake controller allowing the third brake to receive a third brake fastening pressure in said first, second, third, and fourth speeds;
• wherein the first clutch and second brake controller comprises:
• a first pressure control valve controlling the first clutch fastening pressure with a control pressure of a first proportional control valve;
• a pressure switching valve feeding back the first clutch fastening pressure controlled in the first pressure control valve to the first pressure control valve;
• a first switch valve allowing the first clutch fastening pressure to be supplied to the first clutch or the second brake and allowing the first clutch fastening pressure to be unconditionally supplied to the first clutch when the first clutch is fastened, depending on an output pressure of a first valve;
• a second switch valve allowing the first clutch to selectively receive the first clutch fastening pressure depending on the second clutch fastening pressure, the third brake fastening pressure, the first brake fastening pressure, and a line pressure;
• and
• a third switch valve allowing the second brake to selectively receive the first clutch fastening pressure or a reverse range pressure, depending on the second clutch fastening pressure, the first brake fastening pressure, and the reverse range pressure.