Regulator valve

A regulator valve which constitutes a portion of a hydraulic control apparatus of an automatic transmission, comprising:

• a valve body having a valve chamber and a plurality of ports;
• a valve spool which is axially displaceably housed in the valve chamber;
• a coil spring which is housed in the valve chamber in such a manner as to be interposed between the valve body and the valve spool;
• and
• a plunger which is displaceably housed in the valve body, a first end side of the plunger defining a spring chamber that houses the coil spring between the plunger and the valve spool, and a second end side of the plunger receiving a range signal pressure through one of the plurality of ports,
• wherein the hydraulic pressure discharged from one of the plurality of ports is regulated according to the displacement of the valve spool being urged to a first side in the axial direction by hydraulic pressure to be regulated that is received through another of the plurality of ports, and being urged to a second side in the axial direction by a combination of i) throttle pressure from one of the ports that is connected to the spring chamber, ii) spring force from the coil spring corresponding to the displacement of the valve spool, and iii) operating force of the plunger corresponding to the throttle pressure and the range signal pressure, and
• wherein the plunger has a small diameter portion and a large diameter portion which has a diameter larger than a diameter of the small diameter portion, both of which are axially displaceably retained in the valve body, the small diameter portion is urged to the first side in the axial direction at a first end side which faces the valve spool, and the large diameter portion is urged to the second side in the axial direction by the range signal pressure at a second end side which is isolated from the small diameter portion located in the spring chamber.