Patent ID: 7264085

Claim:
A hydraulic passage structure of an automatic transmission having at least one friction element for gearshift, the friction element comprising a drum, the hydraulic passage structure comprising: a housing; a sleeve which is fitted into an inner circumference portion of the housing; a center member joined integrally with the drum of the friction element, the center member being inserted in an inner circumference of the sleeve; a radial passage formed in the housing; a sleeve passage formed in the sleeve, the sleeve passage connecting with the radial passage of the housing; and a center member passage formed within the center member, the center member passage connecting the friction element and the sleeve passage, line pressure being supplied to the friction element via and in order of the radial passage, the sleeve passage, and the center member passage, wherein the sleeve passage comprises a plurality of axial grooves which connects with the radial passage of the housing, each axial groove having an opening formed therein which connects to the center member passage.