Hydraulic control system for automatic transmission

Claim 1

In an automatic transmission driven by an engine having a throttle valve and including an input shaft, an output shaft and hydraulic servo means for actuating brake means and clutch means to provide a plurality of gear ratios between said input and output shafts in accordance with the actuation of said brake means and clutch means, a hydraulic control system comprising: a hydraulic pressure source for supplying pressure oil to said hydraulic servo means through oil passage means; shift valves connected in said oil passage means and adapted to be actuated by signals corresponding to driving conditions to establish a higher forward gear ratio by connecting an oil passage to said oil passage means leading to a hydraulic servo in said hydraulic servo means with said hydraulic pressure source for establishing a higher forward gear ratio, said shift valves draining said oil passage to establish a lower forward gear ratio; and a pressure regulator means connected to said hydraulic pressure source for controlling pressure oil from said hydraulic pressure source, said pressure regulator valve means including: a valve spool, a spring acting on said valve spool, a first coil chamber communicating with said hydraulic pressure source to apply a force to said valve spool against a biasing force of said spring, a second oil chamber communicating with said hydraulic pressure source, a third oil chamber communicating with an exhaust passage for discharging a portion of pressure oil from said hydraulic pressure source when said valve spool is shifted in a direction to compress said spring and said second oil chamber thereby communicates with said third oil chamber, diaphragm means responsive to intake manifold vacuum of said engine induced by said throttle valve for producing a force corresponding to said intake manifold vacuum, a member having one end thereof in contact with said diaphragm means and having the other end thereof in contact with said valve spool to apply the force produced by said diaphragm means to said valve spool in the same direction as the biasing force of said spring, the said other end of said member being disposed in oil-tight sliding contact with an inner wall of a hole provided in one end of said valve spool, a fourth oil chamber adapteD, when supplied with pressurized oil, to apply a force to an end face of the other end of said valve spool against the biasing force of said spring and, simultaneously, to apply hydraulic pressure to an end face of said other end of said member by way of an oil passage, which axially penetrates said valve spool, in a direction opposite to the force applied by said member to said valve spool, a fifth oil chamber defined by the inner wall of the hole provided in one end of said valve spool and said other end of said member, and, when supplied with pressurized oil, adapted to apply a force to said valve spool in a direction opposite to the force applied to the end face of the other end of said valve spool by said fourth oil chamber, and a conduit connecting said fourth chamber and said oil passage whereby said fourth chamber is supplied with oil in the higher forward gear ratio position and is drained in the lower forward gear ratio position so that in the higher forward gear position but not in the lower forward gear ratio, said force applied by said diaphragm means to said valve spool corresponding to said intake manifold vacuum may be counteracted.