Abstract: Seal rings are set in oil grooves which are situated at both sides of two oil passages communicating two hydraulic actuators which operate oppositely. First and second seal rings oil-tightly seal between the first oil passage and sleeve, while third and fourth seal rings oil-tightly seal between the second oil passage and the sleeve. Accordingly even if oil flows oppositely in each of two oil passages due to the opposing motions of the two contiguous hydraulic actuators, not oil leakage occurs. Furthermore, a draining groove is situated between the oil grooves in which the second and third seal rings are installed.

Abstract: Thrust force generated by a hydraulic actuator is absorbed in a attachment device for a four speed automatic transmission mechanism. When hydraulic pressure is applied to the hydraulic actuator to engage a third and a fourth clutches, pressing force from a piston works on a strut member situated between the third and fourth clutches as a compression force, while a force working on a drum member as a tension force, so that these forces are counterbalanced and absorbed in the attachment device. Consequently, one directional move of the attachment device is supported by a little force such as contacting a snap ring and a thrust washer to a clutch drum, on the other hand, another move of the attachment device is supported by a little force such as connecting the drum member and a big ring gear by a snap ring.

Abstract: A pressure regulating device for use in a hydraulic control system for an automatic transmission having a torque convertor, a gear transmission and an hydraulic control system provides a first pressure regulating valve for regulating the pressurized fluid output from a pump to a line pressure level, and applying the line pressure to the hydraulic control system. A second pressure regulating valve regulates the pressure of an excess portion of fluid supplied to the hydraulic control system from the first pressure regulating valve, and supplies the excess fluid to the torque convertor and regions requiring lubrication. Overheating of fluid in the torque convertor is prevented at low pressures by a bypass passage which assures at least a minimum fluid flow through the torque convertor at all times.