Hydraulic controlling apparatus for automatic transmission for vehicle

A hydraulic controlling apparatus for an automatic transmission for vehicle, comprising:

• a hydraulic pump that outputs an operation oil pressure;
• a manual valve that generates a hydraulic pressure for forward running based on the operation oil pressure, when a valve position of the manual valve is switched in accordance with a shifting operation to a forward running position;
• a solenoid valve device, that, when the first solenoid valve is in a normal state, selectively supplies an output hydraulic pressure to plural hydraulic type frictionally engaging devices to establish plural speed-change steps of the automatic transmission;
• and
• a fail-safe gear step switching valve that (i) upon a failure state of the solenoid valve, switches to a first position to establish a low-speed side fail-safe gear step or to a second position to establish a high-speed side fail-fail gear step, of plural speed-change steps of the automatic transmission, both the first position and the second position being set in advance based on the output hydraulic pressure from the solenoid valve device just before failure thereof occurs, so that the low-speed side fail-safe gear step or the high-speed side fail-safe gear step is selected in an alternative way, and (ii) is held at the second position based on a base pressure which is based on the operation oil pressure from the hydraulic pump and which does not fluctuate regardless of the valve position of the manual valve,
• wherein the fail-safe gear step switching valve is held at the first position based on a decreased base pressure and biasing force of a bias member,
• the solenoid valve device includes a first solenoid pressure regulation valve that supplies the output hydraulic pressure to a first hydraulic type frictionally engaging device for establishing the low-speed side gear step including a lowest-speed gear step and the fail-safe gear step switching valve, and a second solenoid pressure regulation valve that supplies the output hydraulic pressure to a second hydraulic type frictionally engaging device for establishing the high-speed side gear step including a highest-speed gear step and the fail-safe gear step switching valve, and
• the fail-safe gear step switching valve is switched to the first position based on the output hydraulic pressure from the first solenoid pressure regulation valve, and switched to the second position based on the output hydraulic pressure from the second solenoid pressure regulation valve.