Friction plate and wet multiple-plate clutch with friction plate

A friction plate comprising:

• a plurality of friction material segments fixed to a surface of a substantially annular core plate in a circular arrangement, each friction material segment being elongated radially so that its length, disposed in a radial direction, is greater than its width in a circumferential direction,
• wherein a through groove that penetrates from an inside diameter side to an outside diameter side of the core plate is formed between each of adjacent friction material segments, and each of the friction material segments has circumferential groove that is spaced radially from opposite ends of the friction material segment, that opens to the through groove, that extends in the circumferential direction and that terminates in the friction material segment,
• wherein a circumferential length of each circumferential groove is greater than a radial width of the circumferential groove, and the radial width of each circumferential groove is substantially the same along the circumferential length of the circumferential groove from an open end to a closed end of the circumferential groove,
• wherein the circumferential grooves are formed at both of end portions of the friction material segments in the circumferential direction,
• wherein the circumferential grooves at both end portions are disposed at different positions in the radial direction and
• such that oil passes through the through grooves and rotation movement of the oil entering the circumferential grooves and rotating in the circumferential grooves accelerates the flow rate of the oil passing through the through grooves, and the rotating oil rides onto a friction surface of the friction material segments.