Hydraulic control apparatus for automatic transmission

A hydraulic control apparatus for an automatic transmission, comprising:

• a main shaft connected to an output shaft of an internal combustion engine via any one of a first clutch and a second clutch both actuated under hydraulic pressure;
• a gear train transmitting rotation of the main shaft to a transmission output shaft;
• and
• a hydraulic circuit adapted to transmit pressure of a working fluid to the first clutch and the second clutch is provided for each of the first and second clutches individually, the hydraulic circuit including:
• a manual valve;
• a linear solenoid valve connected to an outlet of the manual valve;
• an emergency valve connected to an outlet of the manual valve and the linear solenoid valve;
• and
• a changeover valve connected to the emergency valve,
• wherein the working fluid from the manual valve is fed to the changeover valve via the linear solenoid valve and the emergency valve when the linear solenoid is operational, and the working fluid from the manual valve is fed to the changeover valve via the emergency valve, bypassing the linear solenoid valve when the linear solenoid has failed, and
• wherein a speed ratio is determined by engagement and disengagement of the first and second clutches and engagement and disengagement of a dog clutch in the gear train.

A hydraulic control apparatus for an automatic transmission, the automatic transmission including a main shaft connected to an output shaft of an internal combustion engine via any one of a first clutch and a second clutch both actuated under hydraulic pressure, and a gear train transmitting rotation of the main shaft to a transmission output shaft, said hydraulic control apparatus comprising:

• a first oil passage adapted to supply a working fluid to the first clutch;
• a second oil passage adapted to supply the working fluid to the second clutch;
• a changeover valve adapted to connect the pressure of the working fluid to any one of the first oil passage and the second oil passage;
• and
• an orifice control valve provided at a guiding branch formed on each of midways of the first oil passage and the second oil passage.