US Patent 7264085 Hydraulic passage structure of automatic transmission friction element

A hydraulic passage structure of an automatic transmission having at least one friction element for gearshift, the friction element being comprised of a drum. The hydraulic passage structure includes a housing formed integrally with a midway wall protruding inwardly from the housing, a sleeve, a center member joined integrally with the drum of the friction element, a radial passage in the midway wall, a sleeve passage in the sleeve, and a center member passage in the center member. The sleeve is fitted into an inner circumference of the housing, and the center member is inserted in an inner circumference of the sleeve. The sleeve passage connects with the radial passage of the housing, and the center member connects the sleeve passage and the friction element. Line pressure is supplied to the friction element via and in order of the radial passage, the sleeve passage, and the center member passage.