To provide an automatic transmission in which oil is prevented from jetting through a breather hole by stabilizing the pressure in a case.
In this automatic transmission, the breather hole allowing the inside of the case to communicate with the atmosphere to supply and discharge air according to the difference between the pressure in the case and the atmosphere is formed at the upper part of the case in which a shift mechanism is installed. The automatic transmission comprises a control part U having a heavy-load operation determination means 36 for determining the presence or absence of heavy-load operation information and a line-pressure control means 30 for so outputting a command signal to a hydraulic control device 17 that a regulator valve 18 can hold a line pressure at a predetermined high pressure when the heavy-load operation determination means 36 determines that the heavy-load operation information is present. Since the pressure in the case can be held constant by holding the line pressure at a constant pressure, the oil is prevented from jetting through the breather hole.
NAKAMURA ATSUSHI
HAYASHI TAKAYUKI
ITATSU NAOKI
TOYOTA MOTOR CORP