JP 2007-064268 A describes an exemplary automatic transmission mounted on a vehicle. In this automatic transmission, an engine rotation-driven oil pump supplies hydraulic pressure to a hydraulic control circuit. A hydraulic valve and a manual valve are provided in the hydraulic control circuit to switch a hydraulic circuit and to control a hydraulic pressure. Here, the hydraulic pressure is applied to friction engagement elements (e.g., a brake or a clutch) of a transmission mechanism. As a result, gear shifting, or range shifting, is performed.
This kind of automatic transmission includes a hydraulic supply system equipped with a variable-capacity type oil pump. A discharge amount of the oil pump is adjusted by a solenoid valve. When a rotational speed of the engine increases and, as a result, the rotational speed input to the oil pump exceeds a predetermined value, the solenoid valve switches the oil pump to a low discharge mode (i.e., a mode in which the discharge amount per revolution is low). As a result, excess discharge during high rotational speeds may be prevented, and wasteful energy consumption may be suppressed, thereby improving fuel consumption.