Apparatus for controlling hydraulic pressure for clutch

An apparatus for controlling hydraulic pressure adapted for use with a clutch comprising:

• (a) a plurality of clutch pressure control valves corresponding to a plurality of piston cylinders of a plurality of speed-changing clutches, each clutch pressure control valve including:
• a pressure control valve having a first spool provided with a solenoid on one end thereof and provided with a first spring on the other end thereof, said pressure control valve switching over an output port thereof to one of a drain port and a pump port connected to a pump in accordance with an instruction current applied to said solenoid and variably changing hydraulic pressure of said output port;
• a flow rate detecting valve having a second spool provided on one end thereof with a second spring and an orifice for supplying oil flow through an input port leading to said output port of said pressure control valve and said pump port to a clutch port leading to said piston cylinder of said speed-changing clutch, said one end of said second spool being effected by hydraulic pressure of said clutch port, the other end of said second spool being effected by hydraulic pressure of said input port, said flow rate detecting valve, when opened by a pressure differential across said orifice, effecting hydraulic pressure of said pump port leading to said input port to act directly on said clutch port and, when the oil is filled into said piston cylinder of said speed-changing clutch, closing said pump port and said clutch port;
• and
• (b) control means for controlling, at the time of speed changing, one of said plurality of piston cylinders of said speed-changing clutches connected with one of said plurality of pressure control valves required for said speed change by outputting said instruction current to said solenoid for said required pressure control valve.