Hydraulic control apparatus for hydraulically operated vehicular transmission

A hydraulic control apparatus for a hydraulically operated vehicular transmission in which an oil supply pressure to a hydraulic engaging element provided therein is controlled by an output pressure of a duty-controlled solenoid valve, said apparatus having a hydraulic oil pressure changeover means which can switch an input pressure to said solenoid valve between at least two stages of a high pressure and a lows pressure,

• wherein said hydraulic oil pressure changeover means comprises:
• a pressure reduction valve which can be switched between an operating condition for outputting a low hydraulic oil pressure and a non-operating condition for outputting a high hydraulic oil pressure;
• a changeover valve which can be switched between a low-pressure position for inputting an output pressure from said pressure reduction valve to said solenoid valve and a high-pressure position for inputting a hydraulic oil pressure to be supplied without passing through said pressure reduction valve to said solenoid valve;
• and
• a control valve which can be switched between a first position for outputting a first signal pressure to switch said pressure reduction valve from the operating condition to the non-operating condition and a second position for outputting a second signal pressure which operates in a direction to switch said changeover valve from said high-pressure position to said low-pressure position, such that when said control valve is in said first position and said changeover valve remains in said low-pressure position, as a result of said second signal pressure failing to switch said changeover valve to said high-pressure position, said high hydraulic oil pressure is supplied by said pressure reduction valve through said changeover valve to said solenoid valve.