Hydraulic control apparatus for automatic transmission

A hydraulic control apparatus for an automatic transmission, comprising:

• a control valve for outputting a control pressure in accordance with a throttle opening;
• a first pressure regulating valve to regulate a line pressure in accordance with the control pressure;
• a second pressure regulating valve to regulate a secondary pressure, which is lower than the line pressure, in accordance with the control pressure, the secondary pressure being supplied to a hydraulic transmission apparatus having a lock-up clutch and a torque converter, the second pressure regulating valve comprising:
• a spool formed having a large diameter portion formed with a large diameter land portion on a first axial side thereof, and a small diameter portion formed with a land portion having a smaller diameter than the large diameter land portion on a second axial side thereof;
• a pressure regulating portion to regulate the secondary pressure such that the secondary pressure increases as the spool moves to the first axial side;
• a first oil chamber operated by the control pressure on an end portion of the second axial side of the spool;
• a second oil chamber operated by a feedback pressure of the secondary pressure on an end portion of the first axial side of the spool;
• and
• a third oil chamber formed between the large diameter portion and the small diameter portion, and
• a gain increasing pressure input device which is capable of inputting a pressure to increase a gain of the second pressure regulating valve in relation to the control pressure beyond 1 into the third oil chamber.