Device for gradually increasing hydraulic pressure

A device for gradually increasing hydraulic pressure in a hydraulic fluid supply control circuit of a transmission in which a plurality of clutch means, each having a hyraulically operated cylinder-piston assembly, and a source of hydraulic pressure, said device including an inlet connected to said source of hydraulic pressure;

• an outlet connected to said cylinder-piston assembly;
• a first passage formed therethrough for permitting said inlet and outlet to communicate with each other;
• means for gradually increasing hydraulic pressure having a pressure chamber and slidably provided within a box of the device by the side of said inlet while intersecting said first passage;
• a second passage formed therewithin for permitting said first passage and the pressure chamber of said means to communicate with each other;
• a back pressure chamber formed therewithin at the back of said means;
• a third passage formed therewithin for permitting said second passage, said back pressure chamber and a drain to communicate with one another;
• and a quick return valve slidably provided with the device by the side of said outlet while intersecting said first, second and third passages for controlling said means so that hydraulic fluid in said first passage is supplied through said second passage to said pressure chamber of said means to control the gradual increase of hydraulic pressure in said first passage, said quick return valve having first, second, third and fourth annular land portions formed, in turn, on its outer periphery along its longitudinal axis;
• first, second and third annular recess portions formed between the respective land portions;
• and a cavity formed therein along its longitudinal axis, one end of said cavity being opened to said first passage and the other opposite end thereof being formed with an orifice so as to permit said cavity and said back pressure chamber to communicate therethrough with each other, the improvement characterized in that said quick return valve comprises:
• a. another annular land portion formed between said first and second annular land portions so that, when said quick return valve is located at a first position for shutting off said first passage through said first annular land portion and at a second position for opening said first passage, said quick return valve shuts off said second passage through said another annular land portion and said second annular land portion, respectively, and while said quick return valve is slidingly moving from said first position to said second position, said second passage is opened,
• b. another orifice formed between said first passage and said second passage so as to permit said first passage and said second passage to communicate with each other when said quick return valve is located at said first position, and
• c. a hole formed in said means for permitting said second passage and said pressure chamber of said means to immediately communicate with each other,
• whereby the responsibility of said means to gradually increase hydraulic pressure in said first passage is improved at the time when the gradual increasae of hydraulic pressure is started without producing peak pressure immediately before the start of the gradual increase of hydraulic pressure, thereby providing fast shifting of said transmission.