Hydraulic circuit for automatic transmission

A hydraulic circuit for an automatic transmission that is adapted to supply hydraulic pressure to a plurality of friction members provided in the automatic transmission so as to realize a plurality of shift speeds, the hydraulic circuit comprising:

• a plurality of proportional control solenoid valves controlling the hydraulic pressure such that an operating hydraulic pressure required by the friction members is supplied to the friction members;
• a plurality of supply hydraulic paths each connecting a corresponding one of the proportional control solenoid valves with a corresponding one of the friction members, and adapted to supply the operating hydraulic pressure controlled by the corresponding proportional control solenoid valve to the corresponding friction member;
• a plurality of switch valves each disposed in a corresponding one of the supply hydraulic paths so as to selectively open or close the corresponding supply hydraulic path;
• an on/off solenoid valve operating at least two of the switch valves;
• and
• an elastic member provided to each of the at least two switch valves for returning the switch valves to an original position,
• wherein foreign materials having flowed into the proportional control solenoid valves which are connected with the friction members are simultaneously removed in a case in which the plurality of switch valves are connected with the one on/off solenoid valve by stopping the switch valves and operating the one on/off solenoid valve in a full stroke.